Engineering Seminars

Seminar -mech engg- AUTOMATIC TRANSMISSION IN CARS

2014-05-02T10:20:00.002-07:00

AUTOMATIC TRANSMISSION IN CARS

CONTENTS: -

Page No.

1. ABSTRACT…………………………………………………………..03

2. INTRODUCTION……………………………………………………04

3. COMPONENTS OE AUTOMATIC TRANSMISSION…………….05

4. SPOTTING PROBLEMS…………………………………………….10

5. PRECAUTIONS AND MAINTENANCE…………………………...10

6. ADVANTAGES OF AUTOMATIC TRANSMISSION..…...……....10

7. LIMITATIONS OF AUTOMATIC TRANSMISSION ...…………...10

8. CONCLUSIONS……………………………………………………..11

9. REFERENCES……………………………………………………….11

ABSTRACT

The modern automatic transmission is by far, the most complicated mechanical component in today's automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem. This article will help you understand the basic of the transmission, about automatic transmission, differences between manual and automatic transmission, the concepts behind what goes on inside these technological marvels and what goes into repairing them when they fail.

What is a transmission?

The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the engine within that range. It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be going in excess of 70 MPH. In addition to the various forward gears, a transmission also has a neutral position, which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing you to back up.

INTRODUCTION

One of the biggest things that has always separated drivers is whether they prefer an automatic transmission (sometimes known as a "slushbox", because of the characteristic "slushy" feel it creates when shifting between gears) or a standard transmission (often called, for more obvious reasons, a "stick shift").

There are a number of benefits to the standard transmission, but the prevailing reason that most people get them is because they prefer them. Car enthusiasts enjoy the feel of being able to control what gear they're in; it makes them feel closer to the vehicle. People who just want to drive and don't care much about how the car works usually prefer the automatic trannie.

If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and manual transmission:

Ø There is no clutch pedal in an automatic transmission car

Ø There is no gear shift in an automatic transmission car. Once you put the transmission into Drive, everything else is automatic!

The need to shift from manual to automatic transmission

The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission. Driving a manual transmission is especially painful in stop-and-go traffic, where you constantly have to change your gear state. You might also make the case that having to concentrate on shifting your transmission takes some of your attention away from the actual driving, which is dangerous, because you might be concentrating on your tachometer or your gearshift when you really should be focusing on the traffic. An automatic transmission bypasses these problems entirely.

COMPONENTS OF AUTOMATIC TRANSMISSION

When you take apart and look inside an automatic transmission, you find a huge assortment of parts in a fairly small space. Among other things, you see:

Ø Planetary gear sets

The automatic system for current automobiles uses a planetary gear set instead of the traditional manual transmission gear set. The planetary gear set contains four parts: sun gear, planet gears, planet carrier, and ring gear (see Figure 1.) Based on this planetary set design, sun gear, planet carrier, and ring gear spin centrifugally. By locking one of them, the planetary set can generate three different gear ratios, including one reverse gear, without engaging and disengaging the gear set.

Normally an automatic transmission system has two planetary gear sets with different sizes of sun gears with their planet gears inter-meshed (see Figure 2.) Only one planet carrier is used to connect both sets of planet gears. This is called a compound planetary gear set. This design can generate four different gear ratios and one reverse gear.

Figure 1 : Planetary Gear Set Figure 2 : Compound Planetary Gear set

Figure 3 : planetary Gear sets with Band and Clutch

Ø Hydraulic System

It uses a special transmission fluid sent under pressure by an Oil Pump through the Valve Body to control the Clutches and the Bands in order to control the planetary gear sets. Both the band and clutch piston are pressurized by the hydraulic system. The part connecting the band or clutches to the hydraulic system is called the shift valve, while the one connecting the hydraulic system to the output shaft is called the governor (see Figure 4). The governor is a centrifugal sensor with a spring loaded valve. The faster the governor spins, the more the valve opens. The more the valve opens, the more the fluid goes through and the higher the pressure applied on the shift valve. Therefore, each band and clutch can be pushed to lock the gear based on a specific spin speed detected by the governor from the output shaft. To make the hydraulic system work efficiently, a complex maze of passages was designed to replace a large number of tubes (see Figure 5).

Figure 4 Governor

Figure 5 Hydraulic System with maze

Figure 4 :Governor Figure 5 :Hydraulic System with Maze structure

Ø The Torque Converter

Unlike a manual transmission system, automatic transmission doesn’t use a clutch to disconnect power from the engine temporarily when shifting gears. Instead, a device called a torque converter was invented to prevent power from being temporarily disconnected from the engine and also to prevent the vehicle from stalling when the transmission is in gear. Consider two fans facing each other: when one of them is turned on and starts spinning, the other one will also start spinning at a lower speed (see Figure 6). That’s because the first fan moves the air to drive the second fan to spin. This is the same idea as the torque converter of an automatic transmission system, except that it uses fluid instead of air as the transportation media.

A torque converter consists of four parts, a pump (impeller), turbine, stator, and transmission fluid (Figure7). The pump is connected to the engine and transfers engine power to the transmission fluid. The fluid causes the turbine, which is connected to the input shaft, to spin. The stator is used to redirect fluid returning from the turbine before it hits the pump, again to increase the efficiency. In this design, even when the vehicle is in gear but not moving (the turbine is forced to stop), the pump can still keep spinning without causing the engine to stall. When the vehicle speed is slow, the turbine is always spinning more slowly than the pump. However, when the vehicle moves at high speed, the turbine can spin at almost the same speed as the pump. Therefore, for modern cars, a “lock up” will occur between pump and turbine when the vehicle is at high speed in fourth gear, which makes the torque converter work more efficiently.

Figure 6 Figure 7: The Structure of a Torque Converter.

Ø Tiptronic transmission is a special type of automatic transmission with a computer controlled automatic shift. The driver can switch the transmission to manual mode, which lets the driver to shift the gear at his wish sequentially up (+) or down (-) (see Figure 8) without disengaging the clutch. This works just like a manual transmission; however, it still uses a torque converter to transfer power from the engine. Unfortunately, this is less efficient than a manual transmission.

Figure 8 : Tiptronic transmission.

Spotting problems before they get worse

Ø Watch for leaks or stains under the car.

Ø Check fluid for color and odor.

Ø Be sensitive to new noises, vibrations and shift behavior.

Precautions and Maintenance

Ø Transmission fluid should be changed periodically.

Ø According to ‘B & M’, the optimum operating temperature for automatic transmission fluid is 170 degrees. For every 10 degree increase in operating temperature, the useable life of the fluid is reduced by half.

Advantages of automatic transmission

Ø It's a lot less work because you don't have to worry about juggling the gearshift with the clutch.

Ø You don't need to worry about stripping your gears.

Ø Car will never stall during gear shifting.

Limitations of automatic transmission

Ø Indirect contact of the torque converter causes the power loss during transmission.

Ø The ‘killer’ of automatic transmissions is heat. Excessive heat causes the fluid to lose its ability to lubricate, which leads to higher internal-component friction, all resulting in rapid wear-and-tear and premature transmission failure.

Ø Complicated planetary structure makes the transmission heavy and easily broken.

Conclusion

Being able to drive a stick-shift means more than just understanding your gears, however. That's because to shift gears, you usually don't just move the shift lever and be done with it. (You can do this sometimes, but it's not recommended in day-to-day driving, and we'll get to it later.) Instead, you have to press the clutch pedal while you shift. . Keeping the transmission and its fluid cool, and in the correct operating-temperature range is crucial for long life.

Friction stir welding

2010-08-07T05:17:00.001-07:00

ABSTRACT

Friction Stir Welding (FSW) is a solid state joining process that involves joining of metals without fusion or filler materials. The frictional heat is produced from a rapidly rotating non-consumable high strength tool pin that extends from a cylindrical shoulder. The process is particularly applicable for aluminium alloys but can be extended to other products also. Plates, sheets and hollow pipes can be welded by this method. The process is also suitable for automation. The weld produced is of finer microstructure and superior in characteristics to that parent metal. FSW finds application in shipbuilding, aerospace, railway, electrical and automotive industry. The limitations of FSW are reduced by intensive research and development. Its cost effectiveness and ability to weld dissimilar metals makes it a commonly used welding process in recent times.

CONTENTS
1. INTRODUCTION
2. WORKING PRINCIPLE
3. DESCRIPTION OF THE ROTATING TOOL PIN
4. MICROSTRUCTURE CLASSIFICATION
5. FACTORS AFFECTING WELD QUALITY
6. MATERIAL SUITABILITY
7. OTHER MATERIALS
8. JOINT GEOMETRICS
9. FSW OF MILD STEEL
10. FRICTION STIR WELDING MACHINES
11. ADVANTAGES OF FSW
12. APPLICATIONS OF FSW
13. LIMITATIONS OF FSW
14. RETRACTABLE PIN TOOL
15. FSW EQUIPMENT MANUFACTURERS
16. AREAS OF ACTIVE DEVELOPMENT AND RESEARCH
17. CONCLUSION
18. BIBLIOGRAPHY

1. Introduction
In late 1991 a very novel and potentially world beating welding method was conceived at TWI. The process was duly named friction stir welding (FSW), and TWI filed for world-wide patent protection in December of that year. TWI (The Welding Institute) is a world famous institute in the UK that specializes in materials joining technology. Consistent with the more conventional methods of friction welding, which have been practiced since the early 1950s, the weld is made in the solid phase, that is, no melting is involved. Compared to conventional friction welding, FSW uses a rotating tool to generate the necessary heat for the process. Since its invention, the process has received world-wide attention and today two Scandinavian companies are using the technology in production, particularly for joining aluminium alloys. Also, FSW is a process that can be automated. It is also a cleaner and more efficient process compared to conventional techniques.

2. Working principle
In friction stir welding (FSW) a cylindrical, shouldered tool with a profiled probe is rotated and slowly plunged into the joint line between two pieces butted together. The parts have to be clamped onto a backing bar in a manner that prevents the abutting joint faces from being forced apart. Frictional heat is generated between the wear resistant welding tool and the material of the work pieces. This heat causes the latter to soften without reaching the melting point and allows traversing of the tool along the weld line. The maximum temperature reached is of the order of 0.8 of the melting temperature of the material. The plasticized material is transferred from the leading edge of the tool to the trailing edge of the tool probe and is forged by the intimate contact of the tool shoulder and the pin profile. It leaves a solid phase bond between the two pieces. The process can be regarded as a solid phase keyhole welding technique since a hole to accommodate the probe is generated, then filled during the welding sequence

3. Description of the rotating tool pin
The non-consumable tool has a circular section except at the end where there is a threaded probe or more complicated flute; the junction between the cylindrical portion and the probe is known as the shoulder. The probe penetrates the work piece whereas the shoulder rubs with the top surface. The tool has an end tap of 5 in 6 mm diameter and a height of 5 to 6 mm (may vary with the metal thickness). The tool is set in a positive angle of some degree in the welding direction. The design of the pin and shoulder assembly plays a major role on how the material moves during the process.

4. Microstructure Classification
The first attempt at classifying microstructures was made by P L Threadgill (Bulletin, March 1997). This work was based solely on information available from aluminium alloys. However, it has become evident from work on other materials that the behavior of aluminium alloys is not typical of most metallic materials, and therefore the scheme cannot be broadened to encompass all materials. It is therefore proposed that the following revised scheme is used. This has been developed at TWI, but has been discussed with a number of appropriate people in industry and academia, and has also been provisionally accepted by the Friction Stir Welding Licensees Association. The system divides the weld zone into distinct regions as follows:

A. Unaffected material
B. Heat affected zone (HAZ)
C. Thermo-mechanically affected zone (TMAZ)
D. Weld nugget (Part of thermo-mechanically affected zone)
Unaffected material or parent metal: This is material remote from the weld, which has not been deformed, and which although it may have experienced a thermal cycle from the weld is not affected by the heat in terms of microstructure or mechanical properties.
Heat affected zone (HAZ): In this region, which clearly will lie closer to the weld centre, the material has experienced a thermal cycle, which has modified the microstructure and/or the mechanical properties. However, there is no plastic deformation occurring in this area. In the previous system, this was referred to as the "thermally affected zone". The term heat affected zone is now preferred, as this is a direct parallel with the heat affected zone in other thermal processes, and there is little justification for a separate name.
Thermo-mechanically affected zone (TMAZ): In this region, the material has been plastically deformed by the friction stir welding tool, and the heat from the process will also have exerted some influence on the material. In the case of aluminium, it is possible to get significant plastic strain without recrystallisation in this region, and there is generally a distinct boundary between the recrystallised zone and the deformed zones of the TMAZ. In the earlier classification, these two sub-zones were treated as distinct microstructural regions. However, subsequent work on other materials has shown that aluminium behaves in a different manner to most other materials, in that it can be extensively deformed at high temperature without recrystallisation. In other materials, the distinct recrystallised region (the nugget) is absent, and the whole of the TMAZ appears to be recrystallised.
Weld Nugget: The recrystallised area in the TMAZ in aluminium alloys has traditionally been called the nugget. Although this term is descriptive, it is not very scientific. However, its use has become widespread, and as there is no word which is equally simple with greater scientific merit, this term has been adopted. A schematic diagram is shown in the above Figure which clearly identifies the various regions. It has been suggested that the area immediately below the tool shoulder (which is clearly part of the TMAZ) should be given a separate category, as the grain structure is often different here. The microstructure here is determined by rubbing by the rear face of the shoulder, and the material may have cooled below its maximum. It is suggested that this area is treated as a separate sub-zone of the TMAZ.

5. Factors affecting weld quality

• Type of metal
• Angle of tool
• Traversing speed of the tool
• Spinning speed of tool
• Pressure applied by the pin tool
Research is going on to combine the above factors in order to control the process in a better way.

6. Material suitability
TWI has concentrated most of its efforts to optimizing the process for the joining of aluminium and its alloys. Subsequent studies have shown that cast to cast and cast to extruded (wrought) combinations in similar and dissimilar aluminium alloys are equally possible. The following aluminium alloys could be successfully welded to yield reproducible high integrity welds within defined parametric tolerances:

• 2000 series aluminium (Al-Cu)
• 3000 series aluminium (Al-Mn)
• 4000 series aluminium (Al-Si)
• 5000 series aluminium (Al-Mg)
• 6000 series aluminium (Al-Mg-Si)
• 7000 series aluminium (Al-Zn)
• 8000 series aluminium (Al-Li)

7. Other materials

The technology of friction stir welding has been extended to other materials also, on which researches are going on . Some of them are as follows-
• Copper and its alloys
• Lead
• Titanium and its alloys
• Magnesium and its alloys
• Zinc
• Plastics
• Mild steel
Companies practicing and developing FSW are spending a lot of money on improving its use for plastics. It has been demonstrated that FSW is a much more efficient and cleaner process than conventional adhesive bonding in plastics. But it is yet to be made cost and material effective. Ceramics is another field where FSW could be very useful in the future.

8. Joint Geometrics
FSW is independent of gravity. Hence, it can be used to weld in any position- vertical, horizontal and even annular. For this reason FSW has been used to make circumferential annular welds in fuel tanks for spaceships. Besides these FSW can also be utilized for normal fillet and corner welds and also double v-butt joints etc.

9. FSW of Mild Steel

Steel can be friction stir welded, but the essential problem is that tool materials wear rapidly. The sample becomes red hot during welding (as shown in the figure). Since the tool gets red hot it is necessary to protect it against the environment using a shielding gas. So generally FSW is avoided for mild steel. This is not such a great disadvantage since there are more efficient methods to weld mild steel. The weld shown is made by Hitachi of Japan.

10. Friction stir welding machines

10. 1 ESAB SuperStir TM machine FW28
The machine has a vacuum clamping table and can be used for non-linear joint lines.
• Sheet thickness: 1mm-25mm aluminium
• Work envelope: Approx 5 x 8 x 1m
• Maximum down force: Approx 60kN (6t)
• Maximum rotation speed: 5000rev/min :
•
10. 2 Modular machine FW22 to weld large size specimens
A laboratory machine was built in October 1996 to accommodate large sheets and to weld prototype structures. The modular construction of FW22 enables it to be easily enlarged for specimens with even larger dimensions.
• Sheet thickness: 3mm-15mm aluminium
• Maximum welding speed: up to 1.2m/min
• Current maximum sheet size: 3.4m length x 4m width
• Current maximum working height: 1.15m
•
10. 3 Moving gantry machine FW21
The purpose built friction stir welding machine FW21 was built in 1995. This machine uses a moving gantry, with which straight welds up to 2m long can be made. It was used to prove that welding conditions can be achieved which guarantee constant weld quality over the full length of long welds.
• Sheet thickness: 3mm-15mm aluminium
• Maximum welding speed: up to 1.0m/min
• Current maximum sheet size: 2m length x 1.2m width

10. 4 Heavy duty Friction Stir Welding machines FW18 and FW14
Two existing machines within TWI's Friction and Forge Welding Group have been modified exclusively to weld thick sections by FSW. The following thickness range has been experimentally investigated but the machines are not yet at their limits.
• Sheet thickness: 5mm-50mm aluminium from one side
10mm-100mm aluminium from two sides
5mm thick titanium from one side
• Power: up to 22kW
• Welding speed: up to 1m/min

10. 5 High rotation speed machine FW20
For welding thin aluminium sheets TWI equipped one of its existing machines with an air cooled high speed head which allows rotation speeds of up to 15,000rev/min.

• Sheet thickness: 1.2mm-12mm aluminium
• Maximum welding speed: up to 2.6m/min, infinitely variable

10. 6 Friction Stir Welding demonstrator FW16
TWI's small transportable machine produces annular welds with hexagonal aluminium alloy discs. It has been exhibited on fairs in USA, Sweden, Germany, and the United Kingdom in recent years. It is an eye catcher which enables visitors to produce their first friction stir weld themselves. It can be operated with 110V or 220V-240V and has been used by TWI and its member companies to demonstrate the process.

11. Advantages of FSW
• The process is environment friendly since no fumes or spatter is generated and no shielding gas is required.
• A non consumable tool is used
• Since the weld is obtained in solid phase, gravity does not play any part and hence the process can be done in all positions(vertical, horizontal, overhead or orbital)
• No grinding, brushing or pickling is required.
• Since the temperature involved in the process is quite low, shrinkage during solidification is less
• One tool can be typically used for up to 1000 metres of weld length (6000 series aluminium alloy)
• No fusion or filler materials is required
• No oxide removal necessary as in fusion welding.
• The weld obtained is of superior quality with excellent mechanical properties and fine micro structure.
• The process is cost effective since mechanical forming after welding can be avoided
• Dissimilar metals can be welded.
• Automation is possible

12. Applications of FSW
12. 1 Shipbuilding and marine industries
The shipbuilding and marine industries are two of the first industry sectors which have adopted the process for commercial applications. The process is suitable for the following applications:
• Panels for decks, sides, bulkheads and floors
• Aluminium extrusions
• Hulls and superstructures
• Helicopter landing platforms
• Offshore accommodation
• Marine and transport structures
• Masts and booms, e.g. for sailing boats
• Refrigeration plant
12. 2 Aerospace industry
At present the aerospace industry is welding prototype parts by friction stir welding. Opportunities exist to weld skins to spars, ribs, and stringers for use in military and civilian aircraft. This offers significant advantages compared to riveting and machining from solid, such as reduced manufacturing costs and weight savings. Longitudinal butt welds and circumferential lap welds of Al alloy fuel tanks for space vehicles have been friction stir welded and successfully tested. The process could also be used to increase the size of commercially available sheets by welding them before forming. The friction stir welding process can therefore be considered for:
• Wings, fuselages, empennages
• Cryogenic fuel tanks for space vehicles
• Aviation fuel tanks
• External throw away tanks for military aircraft
• Military and scientific rockets
• Repair of faulty MIG welds
12. 3 Railway industry
The commercial production of high speed trains made from aluminium extrusions which may be joined by friction stir welding has been published. Applications include:
• High speed trains
• Rolling stock of railways, underground carriages, trams
• Railway tankers and goods wagons
• Container bodies
12. 4 Land transportation
The friction stir welding process is currently being experimentally assessed by several automotive companies and suppliers to this industrial sector for its commercial application.. Potential applications are:
• Engine and chassis cradles
• Wheel rims
• Attachments to hydro formed tubes
• Tailored blanks, e.g. welding of different sheet thicknesses
• Space frames, e.g. welding extruded tubes to cast nodes
• Truck bodies
• Tail lifts for lorries
• Mobile cranes
• Armour plate vehicles
• Fuel tankers
• Caravans
• Buses and airfield transportation vehicles
• Motorcycle and bicycle frames
• Articulated lifts and personnel bridges
• Skips
• Repair of aluminium cars
• Magnesium and magnesium/aluminium joints
12. 5 Construction industry
The use of portable FSW equipment is possible for:
• Aluminium bridges
• Facade panels made from aluminium, copper or titanium
• Window frames
• Aluminium pipelines
• Aluminium reactors for power plants and the chemical industry
• Heat exchangers and air conditioners
• Pipe fabrication
12. 6 Electrical industry
The electrical industry shows increasing interest in the application of friction stir welding for:
• Electric motor housings
• Busbars
• Electrical connectors
• Encapsulation of electronics
12.7 Other industry sectors
Friction stir welding can also be considered for:
• Refrigeration panels
• Cooking equipment and kitchens and furniture
• Gas tanks and gas cylinders, connecting of aluminium or copper coils in rolling mills

13. Limitations

• Welding speeds are moderately slower
• Work pieces must be rigidly clamped
• Backing bar required
• Keyhole at the end of each weld
• Requirement of different length pin tools when
• welding materials of varying thickness

Hole at the end of FSW

14. Retractable pin tool

Two major drawbacks of FSW is the requirement for different length pin tools when welding materials of varying thickness and a keyhole at the end of the weld may be overcome with the help of a retractable pin tool developed by NASA. The automatic retractable pin tool uses a computer controlled motor to automatically retract the pin into the shoulder of the tool at the end of the weld preventing keyholes. This design allows the pin angle and length to be adjusted for changes in material thickness.

15. FSW equipment manufacturers

Some of the manufacturers of friction stir welding machines are:
• Friction stir welding link, U.S.A
• General tool company, U.S.A
• Hitachi limited, Japan
• Smart technology limited, U.K

16. Areas of active development and research

• Development of new tool design
• Use of process at higher speeds
• Research in the use of other materials
• Investigation of fundamental characteristics of FSW created joints

17. Conclusion
Such has been the interest in FSW, which was patented not so long ago that considerable effort is being made in transferring the technological benefits from aluminium to other materials. Efforts are on to make the process more flexible. In the new millennium there is no doubt that the automotive sector will find an increasing number of uses for this process as its cost effectiveness and ability to weld dissimilar material combinations with minimal distortion is more widely appreciated. The process has been an excellent substitute for alloys that have inherent fusion welding problems.

18. Bibliography

 Friction stir welding
-University of Cambridge, H.K.D.H Bhadesia.
 TWI world centre for materials joining technology -
-Friction stir welding at TWI, Stephan Kallee and Dave Nicholas.
 Friction stir welding
-An improved way to join metals, William Palmer.

FLUID FLOW VISUALIZATION

2010-08-07T05:16:00.001-07:00

FLUID FLOW VISUALIZATION

Abstract

The flow of air cannot be seen by the naked eye. The flow of water can be seen but not its streamlines or velocity distribution. The consolidated science which analyses the behavior of fluid invisible to the eye like this as image information is called ‘flow visualization’, and it is extremely useful for clarifying fluid phenomena. The saying ‘seeing is believing’ most aptly expresses the importance of flow visualization.

This report presents an overview of techniques for visualization of fluid flow data.
The popular techniques Temperature Sensitive Paint, Pressure Sensitive Paint, Tuft Method, Hydrogen Bubble, Optical Methods, and Particle Imaging Velocimetry are explained in details. The figures for various techniques have been presented at the end of this report.

This report mainly concentrated on the experimental fluid flow visualization. Still important computer aided visualization methods have summarized, like the particle imaging Velocimetry. A summary of all the important techniques have been presented at the end of the report. Introduction to the computer graphics flow visualization have been made so that the reader can have a basic idea of the techniques of graphics visualization.

Purposes and Problems of Flow Visualization

Flow visualization probably exists as long as fluid flow researches itself. Until recently,
Experimental flow visualization has been the main visualization aid in fluid flow research. Experimental flow visualization techniques are applied for several reasons:
• To get an impression of fluid flow around a scale model of a real object, without any
Calculations;
• As a source of inspiration for the development of new and better theories of fluid flow;
• To verify a new theory or model.

Though used extensively, these methods suffer from some problems. A fluid flow is often affected by the experimental technique, and not all fluid flow phenomena or relevant parameters can be visualized with experimental techniques. Also, the construction of small scale physical models and experimental equipment such as wind tunnels are expensive, and experiments are time consuming.

Recently a new type of visualization has emerged: computer-aided visualization. The increase of computational power has led to an increasing use of computers for numerical simulations. In the area of fluid dynamics, computers are extensively used to calculate velocity fields and other flow quantities, using numerical techniques to solve the governing Navier-Stokes equations. This has led to the emergence of Computational Fluid Dynamics (CFD) as a new field of research and practice.

To analyze the results of the complex calculations, computer visualization techniques are necessary. Humans are capable of understanding much more information when it is shown visually, rather than numerically. By using the computer not only for calculating the numerical data, but also for visualizing these data in an understandable way, the benefits of the increasing computational power are much greater.

The visualization of fluid flow simulation data may have several different purposes. One purpose is the verification of theoretical models in fundamental research. When a flow phenomenon is described by a model, this flow model should be compared with the ‘real’ fluid flow. The accuracy of the model can be verified by calculation and visualization of a flow with the model, and comparison of the results with experimental results. If the numerical results and the experimental flow are visualized in the same way, a qualitative verification by visual inspection can be very effective. Research in numerical methods for solving the flow equations can be supported. By visualizing the solutions found, but also by visualization of intermediate results during the iterative solution process.

Another purpose of fluid flow visualization is the analysis and evaluation of a design. For the design of a car, an aircraft, a harbor, or any other object that is functionally related with fluid flow, calculation and visualization of the fluid flow phenomena can be a powerful tool in design optimization and evaluation. In this type of applied research, communication of flow analysis results to others, including non-specialists, is important in the decision making process.

In practice, often both experimental and computer-aided visualization will be applied. Fluid flow visualization using computer graphics will be inspired by experimental visualization. Following the development of 3D flow solution techniques, there is especially an urgent need for visualization of 3D flow patterns. This presents many interesting but still unsolved problems to computer graphics research. Flow data are different in many respects from the objects and surfaces traditionally displayed by 3D computer graphics. New techniques are emerging for generating informative images of flow patterns; also, techniques are being developed to transform the flow visualization problem to display of traditional graphics primitives.

Experimental Flow Visualization

1. Pressure Sensitive Paint (psp) And Temperature Sensitive Paint (tsp)
The use of luminescent molecular probes for measuring surface temperature and pressure on wind tunnel models and flight vehicles offers the promise of enhanced spatial resolution and lower costs compared to traditional techniques. These new sensors are called temperature-sensitive paint (TSP) and pressure-sensitive paint (PSP).

Traditionally, arrays of thermocouples and pressure taps have been used to obtain surface temperature and pressure distributions. These techniques can be very labor-intensive and model/flight vehicle preparation costs are high when detailed maps of temperature and pressure are desired. Further, the spatial resolution is limited by the number of instrumentation locations chosen. By comparison, the TSP and PSP techniques provide a way to obtain simple, inexpensive, full-field measurements of temperature and pressure with much higher spatial resolution. Both TSP and PSP incorporate luminescent molecules in a paint which can be applied to any aerodynamic model surface. Figure 1 shows a schematic of a paint layer incorporating a luminescent molecule.

The paint layer is composed of luminescent molecules and a polymer binder material. The resulting ‘paint’ can be applied to a surface using a brush or sprayer. As the paint dries, the solvent evaporates and leaves behind a polymer matrix with luminescent molecules embedded in it. Light of the proper wavelength to excite the luminescent molecules in the paint is directed at the model and luminescent light of a longer wavelength is emitted by the molecules Using the proper filters, the excitation light and luminescent emission light can be separated and the intensity of the luminescent light can be determined using a photo detector. Through the photo-physical processes known as thermal- and oxygen quenching, the luminescent intensity of the paint emission is related to temperature or pressure. Hence, from the detected luminescent intensity, temperature and pressure can be determined. The polymer binder is an important ingredient of a luminescent paint used to adhere the paint to the surface of interest. In some cases, the polymer matrix is a passive anchor. In other cases, however, the polymer may affect significantly the photo physical behavior of the paint through a complicated interaction between the luminescent molecules and the macro-molecules of the polymer. A good polymer binder should be robust enough to sustain skin friction and other forces on the surface of an aerodynamic model. Also, it must be easy to apply and repair to the surface in a smooth, thin film.
For TSP, many commercially available resins and epoxies can be chosen serve as polymer binders if they are not oxygen permeable and do not degrade the activity of the luminophore molecules. In contrast, a good polymer binder for a PSP must have high oxygen permeability besides being robust and easy to apply.

The CCD camera system for luminescent paints is the most commonly used in aerodynamic testing. A schematic of this system is shown in Figure 2. The luminescent
Paint (TSP or PSP) is coated on the surface of the model. The paint is excited to
Luminance by the illumination source, such as a lamp or a laser. The luminescent intensity Image is filtered optically to eliminate the illuminating light and then captured by a CCD
Camera and transferred to a computer with a frame grabber board for image processing.
Both wind-on image (at temperature and pressure to be determined) and wind-off image
(At a known constant temperature and pressure) are obtained. The ratio between the wind on and wind-off images is taken after the dark current level image is subtracted from both
Images, yielding a relative luminescent intensity image. Using the calibration relations, the surface temperature and pressure distributions can be computed from the relative
Luminescent intensity image.
TSP has also been utilized as an approach to flow transition detection since convective heat transfer is much higher in turbulent flow than in laminar flow, TSP can visualize the surface temperature difference between turbulent and laminar regions. In low speed wind tunnel tests, the model is typically heated or cooled to enhance temperature variation across the transition line.
The PSP/TSP technique provides a promising tool for measuring surface pressure
distributions on a high-speed rotating blade at a high spatial resolution. Instrumentation is
Particularly difficult in the rotating environment and the pressure taps weaken the
Structure of the rotating blade. Recently, a test was performed to measure the chord wise pressure distributions on the rotor blades of a high speed axial flow compressor/ TSP (Ru(bpy)-Shellac) and PSP (Ru(ph2-phen) in GE RTV 118) were applied to alternating blades. The TSP provided the temperature distributions on the blades for
temperature correction of the PSP results. A scanning laser system was used for
excitation and detection of luminescence. Both the TSP and PSP were excited with an
Argon laser and luminescence was detected with a Hamamatsu PMT. The same system
was used on an Allied Signal F109 gas turbine engine giving the suction surface
pressure map at 14000 rpm shown in Figure 3

Figure 3: Fan blade pressure distribution at 14,000rpm

Characteristics of PSP:
As mentioned previously, PSP simply consists of a luminescent molecule suspended in some type of oxygen permeable binder. Currently, the majority of these binders are some form of silicone polymer. The vast majority of PSP formulations to date come in a liquid form that is suitable for use with normal
Spray-painting equipment and methods
Typically, in its simplest application, PSP is the topmost layer of a multilayer coating on a model surface. The PSP is usually applied over a white undercoat, which provides two related benefits. The white undercoating reflects a large portion of the light that is incident upon it, which results in the benefits of amplifying not only the excitation illumination, but the emission illumination as well.

Advantages:
As previously mentioned, pressure sensitive paints are used to measure surface pressures. The conventional methods of measuring these pressures are to apply pressure taps or transducers to a model, but these approaches have some significant disadvantages.
First of all, taps and transducers only allow measurements at discrete points on the model surface. The surface pressures at other locations on the model can only be interpolated from the known points. Another disadvantage is that taps and transducers are intrusive to the flow. Measurements cannot be taken downstream of other taps or transducers, since the flow is altered once it passes over the upstream disturbances. Finally, taps and transducers are time-consuming and expensive to use. Typical models used for determining surface loads in aircraft design typically cost $500,000 to $1 million, with approximately 30% of that cost going towards the pressure taps and their installation.

A relatively new method to surface pressure measurement utilizes pressure sensitive paint, or PSP. Pressure sensitive paint has numerous advantages over the more conventional pressure taps and transducers. The most obvious is that PSP is a field measurement, allowing for a surface pressure determination over the entire model, not just at discrete points. Hence, PSP provides a much greater spatial resolution than pressure taps, and disturbances in the flow are immediately observable.

PSP also has the advantage of being a non-intrusive technique. Use of PSP, for the most part, does not affect the flow around the model, allowing its use over the entire model surface. The use of PSP eliminates the need for a large number of pressure taps, which leads to more than one benefit. Since pressure taps do not need to be installed, models can be constructed in less time, and with less money than before. Also, since holes do not need to be drilled in the model for the installation of taps, the model strength is increased, and higher Reynolds numbers can be obtained. Not only does the PSP method reduce the cost of the model construction, but it also reduces the cost of the instrumentation needed for data collection. In addition, the equipment needed for PSP costs less than pressure taps, but it can also be easily reused for numerous models.

In aircraft design, PSP has the potential to save both time and money. The continuous data distribution on the model provided by PSP can easily be integrated over specific components, which can provide detailed surface loads. Since a model for use with the PSP technique is faster to construct, this allows for load data to be known much earlier in the design process.

Disadvantages:

Unfortunately, PSP is not without its undesirable characteristics. One of these characteristics is that the response of the luminescent molecules in the PSP coating degrades with time of exposure to the excitation illumination. This degradation occurs because of a photochemical reaction that occurs when the molecules are excited. Eventually, this degradation of the molecules determines the useful life of the PSP coating. This characteristic becomes more important for larger models, as the cost and time of PSP reapplication becomes a significant factor.
A second undesirable characteristic of PSP is that the emission intensity is affected by the local temperature. This behavior is due to the effect temperature has on the energy state of the luminescent molecules, and the oxygen permeability of the binder. This temperature dependence becomes even more significant in compressible flow tests, where the recovery temperature over the model surface is not uniform.

Experimental Setup
As seen below, the PSP experimental setup is composed of a number of separate elements. The specifications of each element are dependent upon the test conditions, objectives, and budget.

Typical PSP experimental setup
Illumination:
The illumination element ("light source") of the setup is used to excite the luminescent molecules in the PSP coating. Since the intensity of the emitted illumination is proportional to the excitation illumination, the source of illumination must be of sufficient power in the absorption spectrum of the PSP coating, and also have a stable output over time. For complex models with numerous surfaces, multiple illumination elements are often needed to achieve an adequate coverage of the model surface. Some examples of illumination elements are lasers, continuous and flash arc lamps, and simple incandescent lamps.
Imaging:
The imaging element ("camera") used in the experimental setup is heavily dependent upon the required results. In most cases, a good spatial resolution of the pressure distribution is required. Imaging elements that can provide a good spatial resolution include conventional still photography, low-light video cameras, or scientific grade CCD cameras. In most PSP applications, the electronic CCD cameras are the preferred imaging element due to their good spatial resolution and capability to reduce the data they acquire in real time. CCD cameras can be divided into two groups, conventional black and white video cameras and scientific grade CCD digital cameras.
Conventional black and white video cameras are attractive mainly due to their low cost. Typical cameras deliver an 8-bit intensity resolution over a 640 X 480 pixel spatial resolution. Even though conventional black and white video cameras are not precision scientific instruments, when coupled with a PC image processor, the results obtained are more than acceptable for qualitative analysis, and are potentially acceptable for quantitative analysis in certain conditions.
Scientific grade cooled CCD digital cameras, on the other hand, are precision scientific instruments that provide high-precision measurements, at the price of an increased cost. Typical cameras of this type can exhibit 16-bit intensity resolution and spatial resolution up to 2048 X 2048 pixels. For many PSP applications, the high resolution provided by these cameras is mandatory.

Images taken of pressures on an AIM-54 Phoenix missile separating from an F-14 fighter
Optical Filters:
In order to avoid erroneous illumination readings, it is necessary that the illumination element only output in the absorption spectrum, while the imaging element only records the emission spectrum. When lasers are used for excitation purposes, this is not an issue, as a laser only produces light in one wavelength. Most excitation sources, however, produce light in a wide spectrum. In order to prevent the excitation source spectrum from overlapping the emission spectrum, optical filters are placed over both the illumination element and the imaging element. This constraint also makes it necessary to conduct all PSP testing in a darkened test section; otherwise ambient light may contaminate the readings.
Data Acquisition & Post Processing:
The data acquisition and post processing in most PSP applications is done in a modular fashion. Initially the camera and computer acquire images for wind-on and wind-off conditions. These images can then be corrected and processed as necessary, either on the same or different machine. This modular approach provides a benefit in that the processing for small-scale tests can easily be done with common software running on PCs. In larger-scale facilities, however, much more computing power is needed, as runs can easily produce large amounts of data that need to be processed. This leads to the requirement of high power graphics workstations and high capacity storage facilities. It is also important to note that in the false color is typically added to the images in the post-processing phase in order to facilitate flow visualization (PSP is monochromatic).

2.Liquid Films
This method makes use of the contrast obtained on account of the unequal rates of evaporation of a liquid film in the laminar and turbulent regions. A film of some volatile oil is applied on the surface of the model prior to starting of the flow. When the air flow takes place over this surface the evaporation of the oil film is faster in the turbulent than in the laminar region. A clearer contrast is obtained by using black paint on the surface. This method can be easily employed for aerofoil blade surfaces in wind tunnels.

3. Smoke
Dense smoke introduced into a flow filed be the flow by the smoke generator can make stream line pattern visible. Smoke is generally injected into the flow through an array of nozzles or holes.
Kerosene oil can be conveniently used in smoke generator. The oil is heated to its boiling point by an electric coil: the smoke is formed by introducing the vapors into the air stream. Smoke can also be produced by many other methods. For better results smoke should be light, non-poisonous and free of deposits.

4) Hydrogen Bubbles

A very easy and effective method to visualize flow fields is the electrolytic generation of hydrogen bubbles with a platinum cathode (d 50 µm) on the model/ flow field. Typically, depending on cathode size, bubbles are very small, approximately 0.1 mm in diameter and are therefore very responsive such that they can completely trace the flow over a body or a complex flow field. Light sheet illumination produces internal reflection within the bubbles and hence visualization of the flow field. This method has general advantages over other methods because there is no contamination of the working fluid and it is very convenient to use, i.e. on electrical switching on/off. Moreover the cathode can be sized to produce bubbles over as much or as little of the model as necessary.

5. Optical methods
Optical method for studying a flow field is a valuable and widely used technique. The refractive index of the medium (Flow field) and the velocities of light through it are functions of the density field. For a given medium and wavelength of light refractive index is a function of density.

n=f(ρ)

For compressible flows this can be approximately expressed as

n = 1+β (P/ρref)

The basis of all the optical methods of study of compressible flow is the
variation of the density to a lesser or greater degree.

The three optical techniques described here are:
(i) the shadowgraph,
(ii) The interferometer and
(iii) The Schlieren system

Each of these techniques is based on either of the variations shown in the figure.
If the variations of refractive index in the flow field are measured the
Corresponding density variations can be determined from this. Density along
with pressure can yield the values of temperature, velocity of sound, Mach
number etc.
By using these techniques the flow field can either be observed on a screen or its permanent record is obtained on a photographic plate. The great advantage of optical methods over other methods is that the instruments are not inserted into the flow; thus the flow is undisturbed in this method of flow investigation.

Though the working of these methods is described here with reference to a model in the wind tunnel test section, they can no doubt be used in a variety of other situations. The flow direction in the test section is considered perpendicular (x-direction) to the plane of the paper, while the light beam is parallel to the span (z-direction) of the model an aerofoil or a wedge.

6. Shadow Technique
The arrangement adopted in this technique is shown in Fig. and is often referred to as a shadowgraph. The collimating lens provides a collimated beam of light from the source. This beam passes through the transparent walls of the test section. The shadow picture of the flow is directly obtained on a white screen placed on the other side of the test section. The degree of brightness on the screen is proportional to the second derivative of the density, a2P/ax2 the varying degree of brightness is a measure of the variations in the density field.
This technique gives clear pictures of the density variation in flows with shocks and combustion. The method is convenient because the required equipment is inexpensive and easy to operate.

Shadowgraph visualizes the density distribution in the flow around an axisymmetric model in a supersonic flow (Courtesy High-Speed Laboratory, Dept. of Aerospace Engineering, Delft University of Technology)

7. Interferometer Technique
In this technique the variation of density in the flow field is directly determined from the interference pattern obtained on the screen or a photographic plate.
The most widely used apparatus based on this technique is the Mach-Zehnder interferometer which is shown in figure. It consists of two plane half silvered mirrors (splitters) A and C, and two fully reflecting mirrors B and D. A parallel beam of light is obtained from the light source through the lens L and concave
mirror A. The splitter A reflects a part of this beam to the transparent section of the test section; the rays of light from the test section are reflected by the mirror D to a concave mirror M2 through the splitter C.
The part of the beam from Ml which passes through the splitter A is
reflected by the mirror B to the reference section; this has transparent walls
identical to those of the test section. Therefore these walls act as compensating
plates. The rays from the reference section also reach the concave mirror M2 after reflection from the splitter C. Thus the mirror A/2 collects the rays coming separately from the test section and the reference section and directs them on the screen or a photographic plate. After emerging from the splitter G the two parts of the light beam merges into one single coherent beam before reaching the mirror A/2; thus the pattern of illumination reflected on the screen would be uniform when there is no flow in the test section like the reference section. When the flow is established in the test section the beam of light passing through its density field will be out of phase with the beam coming through the reference section; in this case the mirror M2 will reflect an interference pattern on the screen; this represents the variable density pattern in the flow field.
While the interferometer is suitable for quantitative measurement of the density variation in a flow field it requires expensive equipment which is difficult to operate.

8. Schlieren technique

In this technique the density gradient (dp/dx) in the flow field is obtained
in terms of the varying degree of the brightness on the screen; the degree of brightness or intensity of illumination is proportional to the density gradient in the flow field.
The arrangement adopted in the Schlieren technique is shown in Fig.

A beam of light is sent through the test section from the light source by a
properly oriented concave mirror A/t.

The beam coming from the test section is reflected on to the screen or a photographic plate through two suitably located concave mirrors A/2 and A/3.
A sharp knife edge is inserted at the focal point of the mirror M2 to intercept about half the light. Thus in the absence of flow through the test section
the screen is illuminated uniformly by the light escaping the knife edge, But
in the presence of flow the rays of light are differently deflected (as in a prism)
on account of the variable density and the refractive index in the flow field
Therefore greater or lesser part of the light beam will now escape the knife
edge. This gives a varying intensity of the illumination on the screen.

9. Laser techniques
Application of lasers has provided the most powerful and reliable optical method of measuring velocity, direction and turbulence in liquids and gases over a wide range. In this method a laser beam is focused in the flow field (test section) where measurement of velocity, turbulence etc. is required. The scattered light from the minute solid particles in the flow is utilized as a signal for velocity measurement by employing a number of optical and electronic equipment such as special lenses, beam splitters, photo detectors, signal processors, timing devices, data acquisition system and a computer.

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation; this is a strong source of monochromatic and coherent light. In this light emitted from one atom of the gas is employed lo amplify the original light. Helium-Neon lasers are commonly used in the range 0.5-100 milli watts they have comparatively lower cost and higher degree of reliability. Argon-ion lasers are used in higher power ranges i.e. 5 m watts-15 watts. CO2 lasers have a range of power between 1 and 100 watts. Higher power lasers produce greater noise level in the system which interferes with the signal.

The laser beam has a very high intensity of light, which can be damaging to the eyes and skin. It can also start spontaneous combustion of inflammable material. Therefore proper precautions must be taken while using a laser system. Solid particles in the flow act as scattering points at the measuring stations. If they are too small having density close to that of the flow their velocity can be taken as equal to the flow velocity; this condition is satisfied to a great extent, in liquid flows. In air flows the small naturally occurring solid particles should act as scattering point Very small particles may not produce a signal of sufficient strength and would be lost in the "system noise"; very large size particles
will give erroneous results.
Artificial seeding plant can also be employed to supply solid particles of
the desired size (about one micron).

Advantages of laser techniques

Lasers have wide applications in measurements in turbo machinery, wind tunnels, water tunnels, combustion studies, heat exchangers and many areas in aerospace and nuclear engineering. Their main advantages are:

• They employ a non-intrusive method which does not disturb the flow.
• They can measure velocities in regions which are inaccessible by other
devices. They offer a valuable device for boundary layer measurements
• No calibration is required; their working is independent of pressure
temperature and the density of the fluid.
• They can be used in a wide range of velocity (0.1-300 m/s); their
frequency response is very high.
• Velocity varies linearly with the signal over wide range.
• They can be easily interfaced with a computer.

Some of the disadvantages include their high cost, complex optical and electronic equipment, and requirement of well trained and skilled operators Installation of a laser system requires considerable preparation. In some cases a seeding plant is also needed which further adds to the already prohibitively high cost.

10. Particle Image Velocimetry (PIV)

Introduction
Particle image Velocimetry is usually a planar laser light sheet technique in which the light sheet is pulsed twice, and images of fine particles lying in the light sheet are recorded on a video camera or a photograph. The displacement of the particle images is measured in the plane of the image and used to determine the displacement of the particles in the flow. The most common way of measuring displacement is to divide the image plane into small interrogation spots and cross correlate the images from the two time exposures. The spatial displacement that produces the maximum cross-correlation statistically approximates the average displacement of the particles in the interrogation cell. Velocity associated with each interrogation spot is just the displacement divided by the time between the laser pulses.

If the velocity component perpendicular to the plane is needed, a stereographic system using two lenses can be used. Typically, the PIV measures on a 100 x 100 grid with accuracy between 0.2% and 5% of full scale and spatial resolution ~1mm. But, special design allow for larger and smaller values. Framing rates of most PIV cameras are of order 10Hz, compatible with pulse rates of Nd: Yag lasers, which is too slow for most cinematic recording. Special systems using rapidly pulsed metal vapor lasers and fast cinematic cameras or special high speed video cameras are able to measure up to ~10,000 frames per second. Micro PIV systems have been constructed to measure velocities in cells as small as a few microns.

Particle Image Velocimetry (PIV) is a whole-flow-field technique providing instantaneous velocity vector measurements in a cross-section of a flow. Two velocity components are measured, but use of a stereoscopic approach permits all three velocity components to be recorded, resulting in instantaneous 3D velocity vectors for the whole area. The use of modern CCD cameras and dedicated computing hardware, results in real-time velocity maps.

Features
• the technique is non-intrusive and measures the velocities of micron-sized particles following the flow.
• Velocity range from zero to supersonic.
• Instantaneous velocity vector maps in a cross-section of the flow.
• All three components may be obtained with the use of a stereoscopic arrangement
• With sequences of velocity vector maps, statistics, spatial correlations and other relevant data are available.
Results are similar to computational fluid dynamics, i.e. large eddy simulations, and real-time velocity maps are an invaluable tool for fluid dynamics researchers.

Principle
In PIV, the velocity vectors are derived from sub-sections of the target area of the particle-seeded flow by measuring the movement of particles between two light pulses:

The flow is illuminated in the target area with a light sheet. The camera lens images the target area onto the CCD array of a digital camera. The CCD is able to capture each light pulse in separate image frames.

Once a sequence of two light pulses is recorded, the images are divided into small subsections called inter-rogation areas (IA). The interrogation areas from each image frame, I1 and I2, are cross-correlated with each other, pixel by pixel.

The correlation produces a signal peak, identifying the common particle displacement, ΔX. An accurate measure of the displacement - and thus also the velocity is achieved with sub- pixel interpolation
A velocity vector map over the whole target area is obtained by repeating the cross-correlation for each interrogation area over the two image frames captured by the CCD camera.

The correlation of the two interrogation areas, I1 and I2, results in the particle displacement X, represented by a signal peak in the correlation C (X).
PIV images are visual, just follow the seeding
Recording both light pulses in the same image frame to track the movements of the particles gives a clear visual sense of the flow structure. In air flows, the seeding particles are typically oil drops in the range 1 µm to 5 µm.
For water applications, the seeding is typically polystyrene; polyamide or hollow glass spheres in the range 5 µm to 100 µm. Any particle that follows the flow satisfactorily and scatters enough light to be captured by the CCD camera can be used.
The number of particles in the flow is of some importance in obtaining a good signal peak in the cross-correlation. As a rule of thumb, 10 to 25 particle images should be seen in each interrogation area.

Double-pulsed particle images.
When the size of the interrogation area, the magnifications of the imaging and the light-sheet thickness are known, the measurement volume can be defined.

Spatial resolution and dynamic range
Setting up a PIV measurement, the side length of the interrogation area, dIA, and the image magnification, s’/s are balanced against the size of the flow structures to be resolved. One way of expressing this is to require the velocity gradient to be small within the interrogation area:

The highest measurable velocity is constrained by particles traveling further than the size of the inter-rogation area within the time, Δt. The result is lost correlation between the two image frames and thus loss of velocity information. As a rule of thumb:

When the size of the interrogation area, the magnification of the imaging and the light-sheet thickness are known, the measurement volume can be defined.

The third velocity component
In normal PIV systems, the third velocity component is ’’invisible’’ due to the geometry of the imaging. This third velocity component can be derived by using two cameras in a stereoscopic arrangement.

Experimental set-up for stereoscopic PIV measurements of the flow behind a car model.

11. Computer Graphics Flow Visualization
Experimental flow visualization is a starting point for flow visualization using computer graphics. The process of computer visualization is described in general, and applied to CFD. The heart of the process is the translation of physical to visual variables. Fluid mechanics theory and practice help to identify a set of ‘standard’ forms of visualization To prepare the flow data to be cast in visual form, several types of operations may have to be performed on the data

The Flow Visualization Process

Scientific visualization with computer-generated images can be generally conceived as a three-stage pipeline process We will use an extended version of this process model here.

• Data generation:
Production of numerical data by measurement or numerical simulations. Flow data can be based on flow measurements, or can be derived from analysis of images obtained with experimental visualization techniques as described earlier, using image processing. Numerical flow simulations often produce velocity fields, sometimes combined with scalar data such as pressure, temperature, or density.

• Data enrichment and enhancement:
Modification or selection of the data, to reduce the amount or improve the information content of the data. Examples are domain transformations, sectioning, thinning, interpolation, sampling, and noise filtering.

Visualization mapping:
translation of the physical data to suitable visual primitives and attributes. This is the central part of the process; the conceptual mapping involves the ‘design’ of a visualization: to determine what we want to see, and how to visualize it. Abstract physical quantities are cast into a visual domain of shapes, light, colour, and other optical properties. The actual mapping is carried out by computing derived quantities from the data suitable for direct visualization. For flow visualization, an example of this is the computation of particle paths from a velocity field.

• Rendering: transformation of the mapped data into displayable images. Typical operations here are viewing transformations, lighting calculations, hidden surface removal, scan conversion, and filtering (anti-aliasing and motion blur).

• Display: showing the rendered images on a screen. A display can be direct output from the rendering process, or be simply achieved by loading a pixel file into a frame buffer; it may also involve other operations such as image file format translation, data (de)compression, and colour map manipulations. For animation, a series of precomputed rendered images may be loaded into main memory of a workstation, and displayed using a simple playback program.

The style of visualization using numerically generated data is suggested by the formalism
underlying the numerical simulations. The two different analytical formulations of flow: Eulerian and Lagrangian, can be used to distinguish two classes of visualization styles:

• Eulerian: physical quantities are specified in fixed locations in a 3D field. Visualization
tends to produce static images of a whole study area. A typical Eulerian visualization is an arrow plot, showing flow direction arrows at all grid points.

• Lagrangian: physical quantities are linked to small particles moving with the flow through an area, and are given as a function of starting position and time. Visualization often leads to dynamic images (animations) of moving particles, showing only local information in the areas where particles move.

FIGURES:

Wake behind an automobile (tuft grid method)

)

Visualization with dye to study water flow in a river model
(Courtesy Delft Hydraulics)

Conclusions

In the preceding sections, we have reviewed different aspects of flow visualization mainly that of experimental visualization methods and an introduction have been made into the computer graphics flow visualization techniques. The connection between experimental and computer-aided flow visualization is now beginning to develop. The current strong demand for new flow visualization techniques, especially for large scale 3D numerical flow simulations, can only be satisfied by combining the efforts of fluid dynamics specialists, numerical analysts, and computer graphics experts. Additional knowledge will be required from perceptual and cognitive psychology, and artists and designers can also contribute to this effort.

Flow visualization will not be restricted to techniques for giving an intuitively appealing,
general impression of flow patterns, but will increasingly focus on more specific physical flow phenomena, such as turbulence, separations and reattachments, shock waves, or free liquid surfaces. Also, purely visual analysis of flow patterns will be increasingly complemented by algorithmic techniques to extract meaningful patterns and structures, that can be visualized separately.

Before they can be used as reliable research tools, the visualization techniques themselves
must also be carefully tested and validated. As we have seen in the previous sections, visualization involves a sequence of many processing steps, where approximations are frequently used and numerical errors can easily occur.

An important issue following development of visualization techniques, is the design and
implementation of flow visualization systems. Research in computer graphics flow visualization is still in its early stages, and especially 3D flow field visualization is still very much an open problem. At present, this is one of the great challenges of scientific visualization. This calls for a cooperative effort in the development of new
techniques at all stages of the flow visualization process.

References

JOURNAL PAPERS

1- Fluid Flow Visualization
Frits H. Post, Theo van Walsum
Delft University of Technology, The Netherlands*
Published in: Focus on Scientific Visualization, H. Hagen, H. Müller, G.M. Nielson (eds.), Springer Verlag, Berlin, 1993, pp. 1-40 (ISBN 3-540-54940-4)

2- Accuracy Of Pressure Sensitive Paint AIAA Journal, Vol. 39, No.1, January 2001

3- 9th International Symposium On Flow Visualisation, 2000
Flow around a three-dimensional bluff Body
S. Krajnovi´c 1and L. Davidson2

BOOKS
Compressible fluid flow YAHYA

Batchelor, G.K. (1967) An Introduction to Fluid Dynamics, Cambridge University Press

E-BOOK
Elsevier publication Fluid Flow Visualization

ERGONOMIC SEAT DESIGN

2010-08-07T05:15:00.000-07:00

CONTENTS

Topic Page Number

1. Abstract…………………………………………………………………1

2. Ergonomics………………………………………………………………

3. Ergonomic Products……………………………………………………..

4. Uses of Ergonomics……………………………………………………..

5. Seat Design………………………………………………………………

6. Anthropometric aspects…………………………………………………

7. Seat Foam………………………………………………………………..

8. Conclusion………………………………………………………………

9. Bibliography…………………………………………………………….

ABSTRACT

The advancements made in the field of technology have helped the automotive sector in last decade, which has been its key customer. Safety and comfort of the passengers has emerged as one of the prime concerns for the vehicle manufacturers due to the stringent government regulations, which are updated with time.

The paper provides a brief overview of the conditions under which the body is completely comfortable. Hence they have been taken into account while designing the seats. The proper design of seats increases the aesthetics and ergonomics of the vehicle and also add to its ability as a safety feature. The feasibility of implementation of such sophisticated seats in Indian conditions has also been gauged.

ERGONOMICS .. ??

The term ergonomics comes from the Greek syllables “ERGON” which means “WORK”, AND “NOMOS” which means “LAWS”, first appeared in a Polish article published in 1857. The study of human factors did not gain much attention until World War 11. Accidents with military equipments were often blamed on human errors, but the investigations revealed that some were caused by poorly designed controls. The modern discipline ergonomics was born in United Kingdom on July 12, 1949, at a meeting of those interested in human work problems in the British navy. At another meeting held on February, 16, 1950, the term ergonomics was formally adopted for this growing discipline.

Today in the United States, ergonomics professionals belong to Human Factors and Ergonomics Society (HFES), an organization with over 5000 members interested in topics ranging from aging to aerospace to computers. Ergonomic design make consumer products safer, easier to use, and more reliable.

“Ergonomics or human factors are the scientific discipline concerned with the understanding of interactions among humans and other elements of a system.” i.e. it deals with the scientific study of the relationship between the humans and its environment. It is “fitting a job to a worker.”

ERGONOMICALLY DESIGNED PRODUCTS

An ergonomically designed toothbrush has a broad handle for easy grip, a bent neck for easier access to back teeth, and a bristle head shaped for better tooth surface contact. Ergonomic design has dramatically changed the interior appearance of automobiles. The steering wheel once a solid awkward disc – is now larger and padded for an easier, more comfortable grip. Its center is removed to improve the driver’s view of the instruments on the dashboard. Larger, contoured seats, adjustable to suit a variety of body sizes and posture preferences, have replaced the small, upright seats of the early automobiles. Equipped with seatbelts and airbags that prevent the face and neck from snapping backwards in the event of a collision, modern automobiles are not only comfortable but they are also safer. Virtually, all automotive and component manufacturers already recognize ergonomics as an important part of the vehicle design process.

An ergonomically designed chair

APPLICATIONS OF ERGONOMICS
Size and shape
Some years ago, researchers compared the relative positions of the controls on a lathe with the size of an average male worker. It was found that the lathe operator would have to stoop and move from side to side to operate the lathe controls. An ‘ideal’ sized person to fit the lathe would be just 4.5 feet tall, 2 feet across the shoulders and have an arm span of eight feet
This example epitomizes the shortcoming in design when no account has been taken of the user. People come in all shapes and sizes, and the ergonomist takes this variability into account when influencing the design process.
The branch of ergonomics that deals with human variability in size, shape and strength is called anthropometry.
Vision
Vision is usually the primary channel for information, yet systems are often so poorly designed that the user is unable to see the work area clearly. Many workers using computers cannot see their screens because of glare or reflections. Others, doing precise assembly tasks, have insufficient lighting and suffer eyestrain and reduced output as a result.

Sound
Sound can be a useful way to provide information, especially for warning signals. However, care must be taken not to overload this sensory channel. A recent airliner had 16 different audio warnings, far too many for a pilot to deal with in an emergency situation. A more sensible approach was to have just a few audio signals to alert the pilot to get information guidance from a visual display.

Job design
One goal of ergonomics is to design jobs to fit people. This means taking account of differences such as size, strength and ability to handle information for a wide range of users. Then the tasks, the workplace and tools are designed around these differences. The benefits are improved efficiency, quality and job satisfaction. The costs of failure include increased error rates and physical fatigue - or worse.
Human error
In some industries the impact of human errors can be catastrophic. These include the nuclear and chemical industries, rail and sea transport and aviation, including air traffic control.
When disasters occur, the blame is often laid with the operators, pilots or drivers concerned - and labeled 'human error'. Often though, the errors are caused by poor equipment and system design.
Ergonomists working in these areas pay particular attention to the mental demands on the operators, designing tasks and equipment to minimize the chances of misreading information or operating the wrong controls, for example.

SEAT DESIGN.

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INTRODUCTION

Drivers spend a great deal of time behind the wheel and encounter a wide range of road conditions. Consequently, they are frequently exposed to shocks when their vehicles encounter irregularities. Shocks are transmitted to the driver when the seat suspension runs out of a travel, a phenomenon called as “bottoming” and “topping”. Heavy drivers who adjust the seat height away from the centre of seat travel are at increased risk of bottoming and topping. Researchers generally agree that exposure to shock increases the risk of spinal injury and lower back pain for drivers. Extremely high shock levels, such as those encountered in an accident, can cause compressive fracture of the spine, while chronic exposure to lower levels can lead to disc degeneration and lower back pain. In addition to increased health risks, drivers who experience frequent bottoming and topping report increased levels of fatigue. Topping and bottoming also presents a safety risk, as these events can cause the driver to temporarily lose control of the vehicle as his feet and hands are thrown off the pedals and steering wheel.

PASSIVE SEAT DESIGN

Today, most driver seats have an air – ride suspension and a passive damper to isolate the driver from vibration. The seats are typically designed to isolate the driver from moderate levels of vibration between 4 and 8 Hz, because the human body is most sensitive to seat vibrations in this range. However, seat suspensions designed to effectively isolate moderate vibration at 4 – 8 Hz are too soft to prevent the suspension from bottoming and topping when the vehicle encounters severe road conditions. Although some seat designs employ elastomer snubbers to absorb some of the impact energy of bottoming and topping, snubbers generally do not provide adequate protection for the driver. In addition, when a seat bottoms out, energy is stored in the snubbers and air spring and then released, propelling the seat and driver upward and often causing the suspension to top out. Stiffening the spring and / or damper provides additional protection from bottoming and topping, but at the expense of overall vibration isolation. Thus, passive seat design always sacrifice some degree of either vibration or shock isolation.
ANTHRAPOMETRY
In order to design a seat it is necessary to consider the structure of the human body. Various aspects such as seat height, width, depth, backrest and armrest depend on the dimensions of the body. The further discussion aims at understanding the anthropometrics of seat design.
The branch of ergonomics that deals with human variability in size, shape and strength is called anthropometry. Tables of anthropometric data are used by ergonomists to ensure that places and items that they are designing fit the users.
ANTHRAPOMETRIC ASPECTS OF SEAT DESIGN

SEAT HEIGHT ( H )

As the size of the seat height increases, beyond the popliteal height of the user, pressure is felt on the underside of the thighs. The resulting reduction of circulation to lower extremities may lead to ‘pins and needles’, swollen feet and considerable discomfort. As the height decreases the user will (a) tend to flex the spine more (due to the need to achieve an acute angle between thigh and trunk); (b) experience greater problems in standing up and sitting down, due to the distance through which his centre of gravity must move; and (c) require greater leg room. In general, therefore the optimal seat height for many purposes is close to the popliteal height and where this cannot be achieved a seat that is too slow is preferable to one that is high. If it is necessary to make a seat higher than this, shortening the seat and rounding off its front edge in order to minimize the under – thigh pressure may mitigate the ill effects. It is of overriding importance that the height of a seat should be enough for comfortable driving.

SEAT DEPTH (D)

If the depth is increased beyond the buttock – popliteal length, the user will – not be able to engage the backrest effectively without unacceptable pressure on the backs of the knees. Furthermore, the deeper the seat, the greater are the problems of standing up and sitting down. The lower limit of seat depth is less easy to define. As little as 300 mm will still support the ischial tuberosities and may well be satisfactory in some circumstances. Tall people some – times complain that the seats of easy chairs are too short – an inadequate backrest may well be to blame.
SEAT WIDTH

For purposes of support a width that is some 25 mm less on either side than the maximum breadth of the hips is all that is required – hence 350 mm will be adequate. However, clearance between armrests must be adequate for the largest user. In practice, allowing for clothing and leeway, a minimum of 500 mm is required .

BACKREST DIMENSIONS (C)

The higher the backrest, the more effective it will be in supporting the weight of the trunk. This is always desirable but in some circumstances other requirements such as the mobility of the shoulders may be more important. We may distinguish three varieties of backrest, each of which may be appropriate under certain circumstances : the low – level backrest; the medium – level backrest and the high – level backrest.

The low – level backrest provides support for the lumbar and lower thoracic region only and finishes below the level of the shoulder blades, thus allowing freedom of movement for shoulder and arms. e.g. Old – fashioned typists chairs generally had low – level backrests. To support the lower back and leave the shoulder regions free, an overall backrest height (C) of about 400 mm is required.

The medium – level backrest also supports the upper back and shoulder regions. Most modern seats fall into this category. For support to mid – thoracic level an overall backrest height of about 500 mm is required and for full shoulder support about 650 mm. A figure of 500 mm is often quoted for office chairs.

The high – level backrest gives full head and neck support – for the 95th percentile man an overall backrest height of 900 mm is required. Whatever its height, it will generally be preferable and sometimes essential for the backrest to be contoured to the shape of the spine, and in particular to give ‘positive support’ to the lumbar region in the form of a convexity or pad. To achieve this end, the backrest should support you in the same place as you would support yourself with your hands to ease an aching back.

A medium – or high – level backrest should be flat or slightly concave but the contouring of the backrest should in no cases be excessive in fact a curve that is too pronounced is probably worse than no curve at all. It was found that a lumbar pad that protrudes 40 mm from the main plane of the backrest at its maximum point would support the back in a position that approximates to that of normal standing.

BACKREST ANGLE OR RAKE (A)

As the backrest angle increases, a greater proportion of the weight of the trunk is supported – hence the compressive force between the trunk and pelvis is diminished. Furthermore, increasing the angle between trunk and thighs improves lordosis. However, the horizontal component of the compressive force increases. This will tend to drive the buttocks forward out of the seat counteracted by (a) an adequate seat tilt; (b) high – friction upholstery; (c) muscular effort from the subject. Increased rake also leads to increased difficulty in the stand – up sit – down action. Interaction of these factors, together with a consideration of task demands, will determine the optimal rake, which will commonly be between 100° and 110°. A pronounced rake is not compatible with a low – or medium – backrest since the upper parts of the body becomes highly unstable.

SEAT ANGLE OR TILT (B)

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A positive seat angle helps the user to maintain good contact with the backrest and helps to counteract any tendency to slide out of the seat. Excessive tilt reduces hip/ trunk angle and ease of standing up and sitting down. For most purposes 5 - 10 is a suitable compromise.

ARMRESTS

Armrests may give additional postural support and be an aid to standing up and sitting down. Armrests should support the fleshy part of the forearm, but unless very well padded they should not engage the bony parts of the elbow where the highly sensitive unlar nerve is near the surface; a gap of perhaps 100 mm between the armrest and the seatback may, therefore, be desirable. If the chair is to be used with a table the armrest should not limit access, since the armrest should not, in these circumstances, extend more than 350 mm in front of the seat back. An elbow rest hat is somewhat lower than sitting elbow height is probably preferable to one that is higher, if a relaxed posture is to be achieved. An elbow rest 200 – 250 mm above the seat surface is generally considered suitable.

LEGROOM

In a variety of sitting workstations the provision of adequate lateral, vertical, and forward legroom are essential if the user is to adopt a satisfactory posture.

Lateral legroom

Lateral legroom (e.g. the ‘knee hole’ of a desk) must give clearance for the thighs and knees.

Vertical legroom

Requirements will, in some circumstances, be determined by the knee weight of a tall user. Alternatively, thigh clearance above the highest seat position may be more relevant – adding the 95th percentile male popliteal height and thigh thickness gives a figure of 700 mm. Standards quote a minimum of 650mm for a normal seat.

Forward legroom

This is most difficult thing to calculate. At knee level clearance is determined by buttock – knee length from the back of a fixed seat. In this case clearance is determined by buttock – knee length minus abdominal depth, which will be around 425 mm for a male who is a 95th percentile in the former and a 5th percentile in the latter. At floor level an additional 150 mm clearance for the feet gives a figure of 795 mm from the seat back or 575 mm from the dashboard. All of these figures are based on the assumption of a 95th percentile male sitting on a seat that is adjusted to approximately his own popliteal height, with his lower legs vertical. If the seat height is in fact lower than this he will certainly wish to stretch his legs forward. A rigorous calculation of the 95th percentile clearance requirements in these circumstances would be complex but an approximate value may be derived as follows.
Consider a person of buttock – popliteal length B, popliteal height P, and foot length F sitting on a seat height H. He stretches out his legs so that his popliteal region is level with the seat surface. The total horizontal distance between buttocks and toes (D) is approximated by
D = B+ (P2 - H2)1/2 + F
(Ignoring the effects of ankle flexion.) Hence, in the extreme case, of a male who is a 95th percentile in the above dimensions, sitting on a seat that is 400mm in height requires a total floor level clearance of around 1190mm from the seat back or 970 mm from the table edge. (if he is also a 5th percentile in abdominal depth). Such a figure is needlessly generous for most purposes; most ergonomic sources quote a minimum clearance value of between 600 and 700 mm from the table edge. (Standards quote minima of 450 mm at the underside of the desktop and 600 mm at floor level and for 150 mm above).

SEAT FOAM

The photograph shows the seat foam sectioned down the centerline. The angle of the seat surface is about 17 from the horizontal with an extra slightly softer area to resist softer slipping of the seat bones. The area behind the seat bones has been carefully designed to provide an upward force on the buttock behind the seat bones to provide extra pelvic support, i.e. to resist backward rolling of the pelvis. To make this part of the foam feel soft, although the foam is hard, there is a gap between the foam and the steel of the seat pan.
If the various synthetic materials available they prefer FLEXIBLE POLYURETHANE FOAM (FPF). The reasons for this selection and the properties of this material have been discussed below.

FLEXIBLE POLYURETHANE FOAM:

Comfort, durability, safety and economy of operation are requirements of every modern mode of transportation. Manufacturers of private and commercial vehicles meet these prerequisites by using flexible polyurethane foam (FPM) in seating systems. It is one of the most versatile manufacturing materials today with proven reliability and flexibility. Polyurethane foam can be formulated to dampen the vibration that causes discomfort for the operator of a vehicle effectively.

Improvements and refinements to the “miracle material” introduced in the early 1950’s continue to expand FPF use and add valuable benefits within the transportation industry. Protecting the environment by recycling vehicle seats to keep them out of landfills is of paramount importance. Elimination of springs in vehicular seating has helped cut the cost of recovery for recycling by about two – thirds. However, the move to deep, all – foam seating brings challenges as well as progress. New research focuses on FPF varieties that dampen the vibration created by the dynamics of the vehicle and irregularities of the roadbed. Some designers specify that a seat should be highly resilient. Others are much more concerned about vibration – dampening qualities of the seat. The two specifications appear to be in opposition, but methods have been developed control vibration and provide resiliency.

H – POINT AND TRANSMISSIVITY

Transmissivity is the transportation industry’s term for the amount of vibration transmitted through the seating platform to the driver by the motion of the vehicles.

H – Point is the term used by the industry to identify the height at which the driver has adequate visibility for safety. The H – point is influenced by several situations that may develop in the foam with extended use. The primary influence is creep (settling or compression); which, in turn, is influenced by the amount of “work” put into the foam as measured by dynamic modulus (a measuring of the dynamic firmness), and dynamic hysteresis (a measuring of the change in dynamic firmness, providing information about the foam’s ability to maintain original dampening properties).

MECHANICAL EQUIVALENT OF A SEAT

Spring and dashpot models are used to predict foam-cushioning behavior.

ACTIVE SEAT DESIGN:

The active Management System of seat design overcomes the limitations of passive suspensions by sensing changing vibration characteristics and instantly adjusting damping force, providing effective vibration damping and shock protection across a much wider range of road conditions and driver weight than passive systems. This system consists of a controllable damper filled with magnetorheological fluid (“MR fluid”), a sensor arm that measures the position of the seat suspension, a controller with a programmed algorithm that adjusts the damping force in response to changes in seat position. The Motion system senses suspension position and adjusts damping force 500 times per second.
The system includes a ride mode switch with three settings (firm, medium, and soft) to allow the driver to easily adjust the feel of the ride. Testing performed by vibration experts on a popular on – highway seat model showed that replacing the standard passive shock absorber with Motion Master reduced the Vibration Dose Value and maximum acceleration (or “shock”) transmitted to a 200 – pound driver by up to 40% and 49%, respectively.

CONCLUSION

Though the condition of Indian roads is improving, the uncomfortability and danger caused to the passengers is not a hidden fact. In such a scenario the advancements made in the field of automobile design should be included in all the cars introduced on the Indian roads. Though this may increase the cost of production marginally, the aesthetics and ergonomics of the vehicle improve. This also increases the comfort level of the vehicle and provides a sense of satisfaction to the customers. Market research has showed that the purchasing power of an Indian has increased over the past few years. Hence he certainly wouldn’t mind spending the extra bit on his comfort. Eventually it is the customer who is the king in this liberalized economy and any loss to the customer is loss to the company. Driver comfort and accessibility of the vehicle’s controls during the car’s operation maximizes the performance capabilities of the car.

“Customers value Ergonomics and they are ready to pay for it”

BIBLIOGRAPHY

• www. motion – master. com
• www. pfa. org
• “THE MECHANICAL DESIGN PROCESS” a book by DAVID G. ULLMAN

Electronic Stability Program

2010-08-07T05:13:00.002-07:00

CONTENTS

 INTRODUCTION
 WHAT IS ESC
 IMPORTANCE
 COMPONENTS
 WORKING
 ADVANTAGES
 APPLICATION
 SUMMARY

Electronic Stability Program (ESP)

Electronic Stability Program (ESP) is an interactive high-tech safety system that significantly improves the stability of a vehicle in all driving situations .When starting off, When driving it self and when braking and so increases the driver’s chances of avoiding a potential accident. ESP helps keep the driver in control of the vehicle even in critical situations.
ESP is based on already familiar components; the anti-lock brake system (ABS) and traction control (TCS) and also include electronic brake power distribution (EBD) and engine drag torque control (EDC).
ESP is an active safety system which improves vehicle stability in all driving conditions. It operates by actuating the brakes individually on one or more wheels on the front or rear axle. ESP stabilizes the vehicle when cornering, braking ,or during non-driven coasting to keep it on the road and in the desired line.
ESP is a registered trademark of the Robert Bosch GmbH and used originally for Mercedes-Benz.
ESP compares the driver's intended direction in steering and braking inputs, to the vehicle's response, via lateral acceleration, rotation (yaw) and individual wheel speeds. ESP then brakes individual front or rear wheels and/or reduces excess engine power as needed to help correct understeer (plowing) or overseer (fishtailing). ESP also integrates all-speed traction control, which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels, and/or reduces excess engine power, until control is regained. ESP cannot override a car's physical limits. If a driver pushes the possibilities of the car's chassis and ESP too far, ESP cannot prevent an accident.
Stability control equipment is now generally known as electronic stability control or ESC, a category recognized by the Society of Automotive Engineers. Electronic stability control combines anti-lock brakes, traction control and yaw control (yaw is spin around a vertical axis). To grasp how it works, think of steering a canoe. If you want the canoe to turn or rotate to the right, you plant the paddle in the water on the right to provide a braking moment on the right side. The canoe pivots or rotates to the right. ESC fundamentally does the same to assist the driver.
The electronic stability program (ESP) is a further enhancement to the anti-lock braking system (ABS) and traction control system (TCS). The ESP is designed to detect a difference between the driver's control inputs and the actual response of the vehicle. When differences are detected, the system intervenes by providing braking forces to the appropriate wheels to correct the path of the vehicle. This automatic reaction is engineered for improved vehicle stability, particularly during severe cornering and on low-friction road surfaces, by helping to reduce over-steering and under-steering.

To implement ESP functionality, additional sensors must be added to the ABS system. A steering wheel angle sensor is used to detect driver input with a yaw rate sensor and a low-G sensor that measure the vehicle response. Some ESP systems include a connection to the powertrain controller of the vehicle to enable reductions in engine torque when required.

As soon as skidding becomes imminent, the ESP Electronic Stability Program prevents it immediately. ESP continually monitors where the driver is steering and where the vehicle is actually going. When instability threatens, ESP selectively can brake each wheel individually, and intervene in the engine-management system. ESP stabilizes the vehicle and makes it more controllable in critical situations.
Rapid intervention: briefly applied braking pressure keeps the car on track
One of the strengths of the Electronic Stability Program is the speed with which it works: the sensing of oversteer and understeer, and the automatic braking intervention, are all completed within fractions of a second. For example if the rear of the car starts to swing out when taking a corner too fast, the ESP microcomputer first of all reduces engine power, thus increasing the lateral forces at the rear wheels. If this is not enough to eliminate the skidding tendency, the system also applies the brakes to the outer front wheel. The braking counteracts the critical rotational movement and restores stability. The simultaneous reduction in speed has further benefits for safety

Fig 1. Under steering drive
When ESP corrects the vehicle , it is not a one-off event which is completed after a brief application of the brakes. The stabilization is an ongoing process which is continuously adapted to take account of situational changes in the dynamics of the vehicle, until the risk of skidding is eliminated. This adaptive control requires the sensors and actuators in the Electronic Stability Program to react and adapt with extreme speed. The system has to cope not only with fast lane changes or patches of black ice, it must also function whatever the carload or tyre tread depth.
ESP was developed and tested with the aid of the most advanced techniques available, which systematically evaluated all potential malfunctions. Using these techniques, every conceivable system error was analyzed and methods were developed to eliminate the risk of malfunction. Amongst other things, the individual ESP components carry out self-checking routines at regular intervals. For example the vitally important yaw sensor is checked each time it supplies information, at intervals of just 20 milliseconds. The switch disables ESP's capability to reduce the engine torque. It also reduces the ESP intervention threshold to about 20%

How do I know ESP is working?
ESP monitors the vehicle's response to the driver's steering and braking inputs to detect oversteer or understeer. If sensors detect that a skidding condition is developing, ESP brakes individual front or rear wheels and/or reduces excess power as needed to help keep the vehicle going in the direction the driver is steering.
ESP could be realized especially through the remarkable progress in modern microelectronics. Sensors constantly record the driver and vehicle behavior and send their data to an electronic control unit. It compares the current driving condition with an appropriate nominal condition for the respective situation, and thus detects impending swerving within fractions of a second. If the car deviates from the calculated “ideal line”, ESP intervenes according to a special logic, and helps to keep the vehicle on track through accurately proportioned brake impulses at the front and rear axle as well as a reduction in engine torque. Thus, the system helps to correct driving errors and swerving movements, that are caused by slipperiness, wetness, gravel or other adverse road conditions. The stabilization takes place permanently – within the physical limits – and adjusts to the vehicle movements caused by the respective situation.
The triangle in the center of the speedometer flashes when ESP intervenes; either with ESP switched on or off. It's a reminder to adjust your speed to the prevailing road conditions, usually by reducing it. If instead one "steps on it", with ESP ON, the engine power may be reduced to prevent a potentially critical situation.
Electronic stability program
The standard-fitted ESP system selectively applies braking forces to the front and rear wheels in such a way as to reduce the risk of skids and slides and help the driver maintain control in critical situations. The system extends the technology of the anti-lock braking and acceleration skid control systems with a range of additional sensors which are used principally to detect yaw motion.
The ESP computer continuously compares the actual behaviour of the vehicle with the computed ideal values. The moment the car deviates from the direction intended by the driver, specially developed control logic causes the system to intervene with split-second speed to bring the car back on track. It does this in two ways:
1)Precisely controlled braking at one or more wheels 2)Reducing engine power.
ESP in this way helps to stabilize the vehicle in critical situations.

Active safety systems help prevent accidents]

1) Antilock braking system ABS
2) Traction control system TCS

Antilock Braking System (ABS)

Laying the groundwork for stability control, in the mid-80s Bosch brought the antilock braking system (ABS) to market through Mercedes and BMW. As most consumers probably know by now, ABS has become a standard feature on many new cars. It works by sensing and preventing wheel lock-up, thereby improving the vehicle's traction and enhancing steerability during hard braking.
1) Prevents the wheels from locking and thus allows avoiding obstacles.
2) The vehicle remains under control even while braking on one-sided slippery road.
3) The stopping distance is usually shortened compared to locked wheels

Traction Control System (TCS)
1) Fast interventions in engine management and brakes prevent the driven wheels from spinning
2) Safe drive off is possible even on one-sided slippery road
3) TCS prevents the vehicle from skidding when accelerating too much in a turn.

What does ESP do?
ESP actively enhances vehicle stability (staying in lane and in direction)

1) Through interventions in the braking system or the engine management.
2) To prevent critical situations (i.e. skidding), that might lead
to an accident
3) To minimize the risk of side crashes.

What is so special about ESP?
ESP watches out:-
1) Surveys the vehicle’s behavior (longitudinal and lateral dynamics)
2) Watches the driver’s commands (Steering angle, brake pressure, engine torque)
3) Is continuously active in the background.

ESP knows:

Recognizes critical situations –in many cases before the driver does
Considers the possible ways of intervening:
Wheel-individual brake pressure application Intervention in the
engine management.
Frequent cause for accidents:
The driver loses control of his vehicle. I.e. through
1) Speeding
2) Misinterpretation of the course or the road condition
3) Sudden swerving.
25% of all accidents involving severe personal injury are caused by skidding.
(Source: GDV – General Association of German Insurance Companies)

60% of all accidents with fatal injuries are caused by side crashs. These side crashs are mainly caused by skidding because of excessive speed, driving errors or excessive steering movements Source: GDV – General Association of German Insurance Companies)

What are the components of ESP?
The Bosch ESP components:

1) Hydraulic modulator with attached ECU
2) Wheel-speed sensors
3) Steering-angle sensor
4) Yaw-rate and lateral acceleration sensor
5) Communication with engine management.
First generation: complex hydraulic system develops braking pressure
The central control unit of the first-generation ESP system comprised two microprocessors, each with 48 kilobytes of memory, and the hydraulic system consisted of a pressurising pump, a charge piston and a central hydraulic unit. The pressurising pump was required for fast and reliable development of braking pressure under all temperature conditions. The hydraulic unit distributed the pressure individually to the wheels

WORKING

The heart of ESP is a yaw velocity sensor which resembles the ones used in aircraft and space vehicles. Like a compass, it constantly monitors the exact altitude of the car and registers every incipient spin. Other sensors report how high the current brake pressure is, what the position of the steering wheel is, how great the lateral acceleration is, what the speed is and how big the difference in wheel speed is. Whenever handling becomes instable, the necessary commands are executed and the vehicle is brought under control in a fraction of a second.
The ESP continuously compares the actual driving condition conveyed by the sensor with the driver’s intention. The software recognizes where the driver wants to steer via the anti-lock brake system sensors from the speeds of the four wheels and by the steering movement. This is recorded by another sensor mounted on the steering column. If there is now a difference between the driver’s intent determined in a vehicle model inside the computer and the current driving condition, which cannot be compensated without increased effort by the driver, ESP becomes active—upto 150 times per second. If there is a tendency to understeer, ESP brakes the wheel on the inside of curve as a priority and brings the car back on to the desired course. If the vehicle is oversteering toward the edge of the road, ESP brakes the outside of the car generating a moment opposed to the yawing moment that results in a driving condition that is easy to correct.

ESP works according the principle of an “observer”: Sensors acquire driver and vehicle behavior, send their data to a powerful microcomputer, that is loaded with a mathematical model. Thus, the actual state of the vehicle is compared with a nominal state appropriate for the respective situation, and impending swerving is detected.

From a physical standpoint, that swerving is nothing else than the turning of the vehicle about its own vertical axis. The faster that turning takes place, the greater the swerving movement and accident risk. Only: For the reliable measurement of the rotational speed, a complicated system was required, which then only existed in aerospace technology: a so-called turning or yaw rate sensor, which was too susceptible to breakdown and too expensive for automotive applications
however. Therefore, the experts developed a comparable measuring element for the stability program, which consists of a small hollow cylinder made of steel. Quartzes excite it to defined vibrations,that shift through the rotational movement of the vehicle. To compensate for that shift, an electrical potential was needed, whose value is the measuring signal for the rotational speed of the car.
In addition to the rotational speed, the ESP computer processes additional sensor information through the respective desire of the driver and the actual behavior of the vehicle:

The steering angle sensor measures the turn-in of the steering wheel and thus acquires where the driver wants to go.

The wheel speed sensors register the speed of the vehicle and the tendency of the wheels to loose adhesion with the road surface.

The lateral acceleration sensor detects when the vehicle is drifting off laterally.

The rotational speed sensor is the heart of the electronic stability program. It measures the rotational movement of the vehicle. If it deviates from the calculated “ideal line”, impending swerving is detected.

The admission pressure sensor detects the brake pressure input by the driver. In addition, the ESP ECU is connected with the engine and automatic transmission per CAN data bus (Controller Area Network), so that it also receives the current data about engine torque, gas pedal position and gear ratio at any time.

Constant Control: ESP Is Ready in Any Driving Situation

While driving, the ESP computer constantly compares the actual vehicle behavior with the programmed nominal values. If the vehicle deviates from the safe “ideal line”, the system intervenes with lightning speed according to a specially developed logic, and can bring the vehicle back onto the right course in two ways: Through exactly measured out brake impulses at the front or rear axle, and through reduction of the engine torque. Here, within the limits of physics, ESP corrects driving errors as well as swerving movements caused by ice, wetness, gravel or other adverse road surface conditions, where the driver

Normally hardly has a chance anymore to keep his vehicle on track through steering or braking maneuvers. Therefore, the system – compared with traction control – is always ready: While braking, during acceleration or when coasting.

As soon as skidding becomes imminent, the ESP Electronic Stability Program prevents it immediately. ESP continually monitors where the driver is steering and where the vehicle is actually going. When instability threatens, ESP selectively can brake each wheel individually, and intervene in the engine-management system. ESP stabilizes the vehicle and makes it more controllable in critical situations.
Advantages of ESP
1) Improves moving-off and acceleration capabilities by increasing traction; especially useful on road surfaces with different levels of grip and when cornering.
2) Improves active dynamic safety, since only a wheel which is not spinning can provide optimum traction with no loss of lateral stability.
3) Automatically adapts the engine torque to suit the ability of the wheels to transmit this to the road when the driver applies too much throttle.
4) Reduces the danger of traction loss under all road conditions by automatically stabilizing the vehicle during braking, acceleration and in spins.
5) Significantly improves the directional stability of the vehicle when cornering-up to the limit range.

.

CONCLUSION
. Numerous international studies have confirmed the effectiveness of ESC in helping the driver maintain control of the car, help save lives and reduce the severity of crashes. In the fall of 2004 in the U.S., the National Highway and Traffic Safety Administration confirmed the international studies, releasing results of a field study in the U.S. of ESC effectiveness. NHTSA concluded that ESC reduces crashes by 35%. The prestigious Insurance Institute for Highway Safety later issued their own study that concluded the widespread application of ESC could save 7,000 lives a year. That makes ESC the greatest safety equipment development since seat belts, according to some experts. Other manufacturers use electronic stability control systems under different marketing names:
ESP reduces the danger of spinning in curves, in avoidance maneuvers or during braking, and supports the driver in better controlling critical situations. “The current analysis of the accident statistics shows, that ESP makes an important contribution to accident prevention, and is therefore as significant for traffic safety as ABS, seat belt and airbag,”
Practice shows that vehicle dynamic control systems like ESP are capable of making skidding avoidable or at least increase control. With their widespread introduction a substantial decrease in the number of serious accidents could be expected.
RESIKO-Survey of GDV – General Association of German Insurance Companies)

REFERENCES

• ‘Robert Bosch GmbH-systems and products for Automobile Manufacturer.
• Vehicle stability enhancement systems-TRAXXAR
• ESP-Electronic stability program by Bosch.
• www.autoweb.com.au
• www.answers.com

ELECTRON FREEDOM FABRICATION PROCESS

2010-08-07T05:13:00.001-07:00

INTRODUCTION

Solid freeform fabrication (SFF) encompasses a class of processes that can be used to design and construct parts using a layer-additive approach. SFF processes are an outgrowth of rapid prototyping processes such as stereolithography for plastics and welding repair techniques employing laser, electron beam, or arc welding for repairing metal seal knife edges, turbine blade tips, or tooling dies. Current development efforts are expanding these repair techniques and applying principles from computer-aided design (CAD) and manufacturing as well as from rapid prototyping for wider applications. These development efforts are resulting in the production of a new class of SFF layer-additive processes to build structural metallic parts directly from CAD data rather than the traditional material removal approach.

ADVANTAGES

SFF offers numerous advantages. At the core of these are reduced production and material costs, reduced development and lead times, and improved performance. However, not all of the current SFF processes are equally suited to provide all of these advantages. Factors such as efficiency, deposition rates, material compatibility, and process quality must be considered to assess the feasibility of inserting such processes successfully into a production environment.

Direct cost savings can be realized through repair and salvage of parts, reduced machining time, and reduced waste. SFF can be used to repair broken or out-of-tolerance parts at a fraction of the cost of remanufacturing. This can be particularly significant when there is a large investment, either in capital expenditures, high value materials, or large amounts of time already invested in a part. SFF processes can be used to build an entire structure, or to add detailed features to a simplified casting or forging. However, the replacement technology must be cost-competitive. Thus, issues such as high deposition rates, process efficiencies, process quality, and material compatibility are paramount to insertion of a new technology into a competitive metals forming market. Implementing these processes can thereby reduce the material wasted during machining operations, reduce lead time and raw material costs by reducing billet sizes, and enable production of a generic, simplified part by conventional methods with addition of specific details at a laser time. Besides the raw material cost savings, there is an ease in handling smaller billets of raw feedstock and the by-products or scrap produced from a less-extensively machined part.

In addition to lead time reduction, SFF can also enable reduction in design cycle time. SFF permits direct production of prototype parts from a CAD file. Production of prototypes enables rapid product development, testing and insertion of improved designs into the existing production environment. This also allows flexibility in design for either unique part production or simplified part design in which detailed locations for items such as flanges, bosses, nozzles, or other features can be changed and modified late in the design cycle. Thus, SFF can provide better opportunity for optimization of designs by allowing more time for determining details.

SFF also offers the potential for improved performance through control of microstructures and compositions at a much finer scale than parts machined from thick products. Typical thick sections have high degrees of microstructural inhomogeneity, leading to anisotropic mechanical properties. This is a direct result of differences in cooling rates and an inability to impart work evenly through a thick section. Working with smaller billets in conjunction with layer-additive processes can result in more optimal microstructural features. Potentially improving the mechanical properties of the resultant part as compared to a similar part machined from a thick section billet. Finally, compositional gradients offer improved performance and reduced cost by allowing grading from an inexpensive material at the surface for enhanced wear resistance, corrosion resistance, etc.
SOLID FREEFORM FABRICATION PROCESSES

Rapid prototyping is an emerging field which encompasses numerous different techniques and resulting product forms. Of specific interest are processes that are capable of producing fully dense metallic and hybrid parts in which the resulting parts may be used for loaded structure. Binderless processes are attractive because they eliminate contaminants and minimize secondary processing. Layer additive techniques offer the potential for graded microstructures and compositions, and production of near net shapes with minimal secondary processing required.

Over the past several years, a number of SFF processes have been developed to directly produce structural metallic parts. Several processes such as Selective Laser Sintering (SLS) and Electron Beam Melting (EBM) operate in a powder bed, tracing the part in a layer of powder with a high energy beam and repeating for subsequent layers. These processes may require secondary processing to produce fully-dense components. Other emerging SFF processes that focus on low heat inputs include Precision Metal Deposition (PMD), laser deposition with flat wire and ultrasonic consolidation (UC) of layered metal foils to form 3-D parts using ultrasonic welding, a solid state process. Direct laser deposition processes, including Direct Metal Deposition (DMD), Laser Additive Manufacturing (LAM) and Laser Engineered Net Shaping (LENS), feed powder directly into a molten pool created by a laser. Electron beam freeform fabrication is another recently developed process, similar to direct laser deposition but employing a focused electron beam and wire feedstock. Many of these processes are complementary and selection of the appropriate process is dependent upon the desired applications.

Direct laser deposition, one of the most mature of the SFF processes, was introduced around 1991 and has been the focus of extensive research activity at many institutions. A laser beam, typically either CO2 or Nd:YAG, is used to create a small molten pool on a metallic substrate in an inert atmosphere. Metallic powder is fed into the molten pool to build up a part, resulting in fully dense, structural parts directly produced from CAD models without molds, tooling, or machining (except for some finish machining to get final tolerance and surface finishes). Feedstock material is usually pre-alloyed powder, although elemental powder blends are also used. This process results in near net shaped parts with fine grained microstructures due to rapid solidification kinetics and a small melt pool.

Most commercial laser based systems have limited size build envelopes and operate at low deposition rates, limiting application on large parts. Typically these processes use a tightly (approximately 0.05cm (0.02 inch) diameter) focused beam which enables fine details to be fabricated. However, there is a tradeoff between feature size and deposition rate, with fine feature size resulting in low deposition rates (8 to 33 cm3/hr (0.5 to 2 in3/hr) and low powder capture efficiencies, typically less than 50%. Energy efficiency of laser processes tends to be low; less than 10% of the input energy is converted to beam energy, and much of the beam energy may be reflected from the part (up to 98% in the case of highly reflective materials such as aluminium and copper). Diode laser based systems have improved energy efficiencies approaching 40% but still exhibit the same reflectance losses as other lasers.

ELECTRON BEAM DEPOSITION

Electron beam freeform fabrication (EBF) is an emerging cross-cutting technology for producing structural metal parts. The process can be used to build a complex, unitized part in a layer-additive fashion, although the more immediate payoff is for use as a manufacturing process for adding details to components fabricated from simplified castings and forgings or plate products. Figure 1 shows a schematic of the primary elements of an EBF system. EBF employs a high power electron beam in a vacuum environment (1  10-4 torr or lower).

Wire feedstock is used due to difficulties feeding powder in a vacuum since the carrier gas used to assist powder delivery will be ionized in the electron beam. Operation in a vacuum ensures a clean process environment and eliminates the need for a consumable shield gas as is typically used in laser deposition systems. The EBF process is nearly 100% efficient in feedstock consumption and approaches 95% efficiency in power usage. The electron beam couples well with any electrically conductive material, including highly reflective alloys, such as aluminium and copper. A variety of weldable alloys can be processed using EBF; further development is required to determine if non-weldable alloys cam also be deposited. Demonstrated deposition rates for EBF are 330 to 2500 cm/hr (20 to 150 in3/hr), with lower resolution in the ability to build fine details. Experiments are planned with the fine diameter wires to attempt to construct fine details and large diameter wires to increase deposition rate, process efficiency, and material compatibility for insertion into the production environment.

Recent work with the EBF system at NASA Langley Research Center has focused on understanding the process and characterizing the resulting microstructures and mechanical properties to optimize the process for 2219 Al and Ti-6-4. Aluminium alloy 2219, which has a nominal composition of A1-6 wt % Cu, is a common aerospace alloy with excellent weldability and good strength and toughness. Ti-6A1-4V is also commonly used in aerospace structures for high temperature applications and where its excellent strength and corrosion resistance are required. Extensive work has been done with Ti-6-4 in the laser deposition arena, providing a baseline for comparison with the EBF process.

A fundamental examination of the effect of processing parameters (translation speed and wire feed rate) for 2219 Al was conducted to establish some basic processing microstructure-mechanical property relationships. In this work, one of these two variables was continuously changed, while the beam power and the other variable were held constant. The resulting deposit dimensions, microstructures, and tensile properties were documented. Over the range of parameters tested, microstructures varied from a fine-grain equiaxed grain structure to a solidification microstructure with larger grain sizes and dendritic grown, as shown in Fig. 2. This shows the range of microstructures obtained over a wide processing envelope. The light bands are dendrites formed in the interpass region where portions of a previously deposited layer remelted during deposition of the following layer.

Increasing translation speed resulted in a decrease in both width and height of the deposited layer. Higher translation speed produced more rapid cooling and resulting in a homogeneous microstructure with smaller equiaxed grains (see fig. 2). Increasing the wire feed rate resulted in a narrowing of the deposit width and an increase in the deposit height. At higher wire feed rates, the cooling rate increased providing a smaller equiaxed grain structure with good homogeneity and no evidence of dendrite growth in the interpass region as compared to the microstructure developed at the lower wire feed rate.

Fig. 3 shows the ultimate tensile strength 0.2% offset yield strength, and total elongation to failure for EBF 2219 Al deposits as compared to typical handbook data for sheet and plat products. The data for the as-deposited 2219 Al were averaged over duplicate tests for seven combinations of beam power, translation speed, and wire feed rate. Deposit the wide range of processing conditions, the majority of the as-deposited 2219 Al data fell in a tight band, as shown by the range bars in fig. 3. The properties of as-deposited 2219 Al were immediate to those for annealed (O temper) and solutionized and naturally aged (T4 temper) 2219 Al sheet and plate. The 2219 Al deposits that were heat treated to the T62 temper also had a very tight data range and were equivalent to typical handbook properties for 2219-T62 sheet and plate product.

Similar work is now underway with Ti-6-4. The Ti-6-4 microstructrue comprises extremely large columnar grains growing epitaxially from the substrate, as shown in Figure 4a. at higher magnification, as shown in Figure 4b, alpha-beta laths typical of the microstructures of alpha + beta titanium alloys can be seen. Brice and coworkers have also researched Ti-6-4 EBF3 deposition with similar results; the room temperature tensile properties of Ti-6-4 deposits were comparable to or better than properties for wrought products. They also reported that a Ti-6-4 F-22 AMAD bracket produced by EBF3 successfully completed a two lifetime broad spectrum fatigue test with adequate residual tensile strength.

In addition to processing-microstructure-property correlation, process programmability and control are currently being explored. Several 2219 Al parts demonstrating different deposition schemes are shown in Figure 5. Low and high deposition rates have been achieved, ranging from rates of 160 cm3/hr to 1300cm3/hr (10 in3/hr to 80in3/hr), with a change in deposits width from 0.25 cm to 1.25 cm (0.1 to 0.5 inches) for the low and high deposition rated, respectively. The cylinder in Figure 5a shows an EBF3 part built using a high deposition rate. The square box in Figure 5b demonstrates the ability to change the motion vector of the part without a corresponding change to the wire feed orientation so that the entry point of the wire varies from the leading edge to the side or trailing edge of the molten pool. This had very little impact on the deposit except for a slight pushing of the puddle by the entering wire. This flexibility is significant because it enables simplified programming and construction of detailed parts. The airfoil-shaped pylon in Figure 5c demonstrates an ability to program and build a part with more complex curvature than the other round square shapes built. The vase shaped part shown in Figure 5d demonstrates the ability to build an unsupported overhang (50 degrees on the part shown) in either an expanding or contracting wall. Finally, a mixer in Figure 5e has been built to show transition from a circular part to a fluid edge.

All part built to date have been near-net shape, requiring a final finishing step to obtain final surface finish and contour. Four identical pylons were finished using a variety of techniques and compared to an as-built pylon to demonstrate the ability to perform finishing operations. The 2219 Al EBF3 part were successfully finished using conventional milling, were electric discharge machining (EDM), glass bead blasting, and electron beam glazing. The as-built EBF3 part had good localized surface irregularity (waviness) and mild tensile residual stresses. Machinability of the EBF3 parts was comparable to standard wrought product for both the milling and wire EDM processes. Milling resulted in the best surface finish over long and short ranges and induced compressive residual stresses. Wire EDM induced high compressive residual stresses in the EBF32219 Al, but the surface finish required additional work to achieve adequate smoothness. Bead blasting was not aggressive enough to eliminate EBF3 surface features, but succeeded in inducing compressive residual stresses. Electron beam glazing (using a defocused electron beam with the same EBF3 equipment) produced a flat surface with fine grained equiaxed microstructure at the surface, but did not significantly change the residual stress state of the as-built part. These experiments demonstrated that EBF3 parts can be finished using conventional machining operations. In addition, electron beam glazing is promising for production of net shaped parts using EBF3 and secondary processing in the same equipment.

FUTURE PLAN

Researchers are developing the EBF3 process for manufacture and repair of aerospace structures. Materials of interest include aluminum alloys for subsonic aircraft and spacecraft, and titanium alloys, nickel-based alloys, titanium aluminides, and metal matrix composites (including titanium matrix composites) for hot structures and launch vehicles. In addition, we have interest in high strength steels such as Vascomax and 15-5 PH for production of wind tunnel models.

Future efforts will concentrate on understanding and improving various aspects of the EBF3 process. Closed loop control and modeling of the process are important to ensure high quality and repeatability for certification of the process for applications on primary or secondary aerospace structures. A deeper understanding of the processing-microstructure-property relationships is necessary to support this development for continued process refinement. Process technique will be developed to enable building parts with complex geometry, improved surface quality and minimized residual stresses. Expanding the range of deposition rates and levels of detail achievable in a single system are also of interest to enhance the process flexibility. Finally, exploitation of the layer-additive nature of the process to develop functionally graded parts will broaden the utility of the EBF3 process. Ultimately, our goal is to develop the EBF3 process into a robust industrial process for application in a variety of industries.
SUMMARY

EBF3 is a new layer additive process with high potential for use in numerous structural metallic applications. EBF3 offers cost and lead time reductions in production of parts and performance improvements through optimized alloy chemistries and microstructures. Microstructures and mechanical properties obtained in aluminum and titanium alloys have demonstrated the potential for achieving a wide microstructural range with properties comparable to those of wrought product forms. EBF3 offers viable solutions to issues of deposition rate, process efficiency, and material compatibility for insertion into the production environment. Although further process development and understanding is required, no barriers are evident to prevent the maturation of EBF3 into a competitive commercial process.

REFERENCES

1. Seras, J.E., direct Laser Powder Deposition – KAPL Report No. KAPL – P – 00311, (1999).
2. “Electron Beams: Useful for More than Just Microscopes,” European tool and Mouldmaking, March/April 2002, http://www.toolmodekaling.com/magazine/magdetail.php?company.
3. Rabinovich, J., “Net Shape Manufacturing with Metal Alloys,”advanced materials & processes, 161:1, 47 & 86, (2003).
4. White, D.R., “Ultrasonic Consolidation of Aluminum Tooling,” Advanced Materials & Processes, 161:1, 64-65, (2003).
5. Sandia National Lab Laser Engineered Net Shaping CRADA No. SC96/01462, (1999).
6. Dave, V.R., Matz. J.E., and Eagar, T.W., Electron Beam Solid Freedom Fabrication of Metal Parts,” Proceedings of 6th SFF Symposium, 64-71, (1995).
7. Taminger, K.M.B. and Hafley, R.A., “characterization of 2219 Aluminum Produced by Electron Beam Freeform Fabrication,” Proceedings of 13th SFF Symposium, 482-489, (2002).
8. Brice, C.A., et al., “Rapid Prototyping and Freeform Fabrication via Electron Beam Welding Deposition,” Proceeding of Welding conference, (2002).
9. Mayer, L.W., Alcoa Green Letter: Alcoa Aluminum Alloy 2219, (1967).

Electrical Discharge Machining

2010-08-07T05:11:00.002-07:00

INTRODUCTION

Electrical Discharge Machining (EDM) is a controlled metal removal process that is used to remove metal by means of electric spark erosion. The English scientist Priestley first reported the erosive effect of electrical discharges in 1770.In this process, an electric spark is used as the cutting tool to cut the work piece to produce finished part. The metal removal process is performed by applying an electrical discharge of pulsed, high frequency alternating current or direct current through the electrode to the workpiece.The electrode location is controlled by the machine and is positioned so as not to contact the workpiece.A precise controlled space is maintained, allowing the spark to discharge its current from the electrode to the work piece through an insulated dielectric fluid of oil or water. This removes tiny particles of metal from the work piece.

EDM PROCESS

With the EDM process, both the work piece material and the electrode material must be conductors of electricity. The EDM process can be used in two different ways:

Figure.1

1. CONVENTIONAL EDM
In the EDM process, an electric spark is used to cut the workpiece, which takes the shape opposite to that of the cutting tool or electrode. The electrode and work piece are submerged in dielectric fluid, which is generally light lubricating oil. This dielectric fluid should be a non conductor (or poor conductor) of electricity. A servo mechanism maintains a gap of about 0.01 to 0.02 mm between the electrode and workpiece, preventing them from contacting each other.

Figure.2

2. WIRE-CUT EDM
The wire-cut EDM is discharge machine that uses CNC movement to produce the desired contour or shape. It does not require a special shaped electrode; instead it uses continuous traveling vertical wire under tension as the electrode. The electrode or cutting wire can be made of brass, copper or any other electrically conductive materials ranging in diameter from0.04 to 0.41 mm.The paths the wire follows is computer controlled along two axes (XY) contour, cutting a narrow slot through the work piece. This controlled movement is continuous and simultaneous in increments of 0.001 mm.Any contour may be cut to high degree of accuracy and is repeatable for any number of successive parts.The dielectric fluid maintains the proper conductivity between the wire and the work piece, and assists in reducing the heat caused by the spark.

Figure.3

Figure.4
DIELECTRIC FLUIDS
During the EDM process the work piece and electrode are submerged in the dielectric oil, which is an electrical insulator that helps to control the arc discharge. The dielectric oil that provides a means of flushing is pumped through the arc gap. This removes suspended particles of work piece material and electrode from the work cavity, insulates against premature discharging and helps to cool the electrode and work piece.

FLUSHING
One of the most important factors in a successful EDM operation is removal of the particles (chips) from the working gap. Flushing these particles out of the gap between the work piece and the electrode are very important to prevent them from forming bridges that cause short circuits. These arcs can burn holes in the work piece and in the electrode.EDMs have a built-in power adaptive control system that increases the pulse spacing as soon as this happens and reduces or shuts off the power supply.

IMPROVEMENT OF EDM PERFORMANCE

Rough machining gives poor surface finish due to micro cracks and pores, also finish machining gives better finish but in that case material removal rate(MRR) or machining speed is very less. Hence various monitoring and control systems were suggested such as continuous gap monitoring system, servo and pulse adaptive control system, knowledge based control system etc.It is very difficult to achieve higher cutting speed and better surface finish simultaneously. Hence it is considered as multi criteria optimization problem. Classical approach suggested by Fisher and Yates is inefficient because it considers one factor only at a time.Taguchi method also can optimize one factor either MRR or surface finish (SF) at a time. Hence it is supplemented with various supportive techniques such as fuzzy logic, grey relational analysis, two-phase parameter design, artificial neural network (ANN) and various combination methods.
Wire Electric Discharge Machining (WEDM) process is one of the important non traditional machining processes. It is used to machine hard materials, complex shapes and contours which are difficult by conventional methods. Particle swarm optimization (PSO) and Memetic algorithm (MA) based optimization procedures have been developed to optimize machining parameters viz.machining speed, pulse on time, pulse off time and peak current by using two response equations for material removal rate and surface roughness. The objective function considered for optimization is maximization of material removal rate and minimization of surface roughness. The objective function is solved by taking combined objective function (weight age given 50% to MRR and 50% to SR) i.e. minimization of MRR and SR.The output results of these two algorithms are compared.

Gap monitoring system identifies major gap states and thus differentiates between normal spark and harmful spark. The gap voltage and current signal have been modelled and analyzed mathematically by DDS (data dependent system).Radio and high frequency monitoring detects high frequency signal on the gap voltage. It can also provide pulse control to machine power generator.
Adaptive control for EDM adjusts the machine parameters such as servo settings, pulse off time, flushing rate etc as per the requirements so as to achieve optimal process performance i.e. maximum MRR and minimum tool wear ratio and desired integrity.
EDM fuzzy logic servo control system is capable of monitoring the gap states. Conventional EDM servo control systems, due to the lack of precise information of gap states (such as gap open, normal and harmful discharges etc) are unable to provide any action for avoiding the harmful acing. Servo feed and fuzzy logic strategy together encounters all measured gap parameters and thus makes the system capable to respond to all monitored gap signals in order to avoid arc damage and improve machining rate and work piece quality.
These monitoring and control system were not only complicated bit also costly and hence many times not economically feasible. Hence an experimental approach for parameter design was suggested.
Evaluation of machining performance in EDM is based on performance characteristics such as MRR, SR, electrode wear rate (EWR) and spark gap (SP) often called as uncontrollable factors. Various machining parameters such as peak voltage, pulse on time, pulse off time, peak current spark gap set voltage, wire feed rate, and wire tension over which an operator has sufficient control are referred as controllable parameters.

1. FUZZY LOGIC

Fuzzy model was developed with input parameters like tool-work piece combinations, tool area, tool wear, peak current and output parameters such as off time(microseconds),spark gap(mm) and servo sensitivity(milli volt/sec).Information obtained from the experimental model was,MRR is inversely proportional to quality. Increasing current (Ip) increases MRR but increases depth of heat affected zones. For finishing operation, productivity is determined by required surface finish, also for finish machining pulse recurrence frequency can be increased but it increases total and unit energy consumption. Setting off tool wear is sufficient as it determines accuracy and economy of operation and tool consumption. Higher off time decreases machining efficiency while too short off time prevents complete de-ionization of previously formed discharge channel causing abnormal discharges, which adversely affect tool wear, accuracy and surface finish. Hence optimum off time should be maintained. For optimum efficiency spark gap should be constant.
A fuzzy logic unit comprises of a fuzzifier, membership functions, a fizzy rule base, an inference engine and defuzzifier.First the fuzzyfier uses membership functions to fuzzyfy the signal to noise ratios. Next the inference engine performs fuzzy reasoning on fuzzy rules to generate a fuzzy value. Finally the defuzzifier converts the fuzzy value into a multi-response performance index. In the experiment two inputs X1(EWR) and X2(MRR) are given and one output (MRPI) i.e.Y is worked out.

Figure.5

Fig. Structure of the two input one output fuzzy logic unit.
X1=S/N ratio of first quality characteristic.
X2=S/N ratio of second quality characteristic.
Y=multi response performance index (MRPI)
Then MRPI for different levels of parameter is calculated. Larger the MRPI smaller is the variance. Based on ANOVA results it has been found out that work piece polarity; discharge current and open discharge voltage are significant parameters affecting multiple performance characteristics. The levels of these parameters are optimized. Experimental result shows and confirms that EWR is decreased from 29.9% to 20.7% and MRR is increased from 0.00159 to 0.00383 gm/min.

2. GREY RELATIONAL ANALYSIS

It can also be considered as one of approaches for solving the problem of multiple responses in EDM.A higher value of grey relational grade means that the corresponding process parameter is closer to the optimal value. Thus optimization of the complicated multiple process responses can be converted into optimization of a single grey relational grade.C.L.Lin, J.L.Lin and T.C.Ko carried out experimentation on SKD 11 alloy steel (12 mm diameter) using L-9 orthogonal array to optimize MRR, EWR and SR.The mathematical treatment is given out to calculate grey relational value Xi (k) for EWR, SR and MRR.Grey relational coefficient is then worked out. Averaging all grey relational coefficients, grey relational grade (yi) is obtained.
A higher value of grey relational grade represents a stronger relational degree between the reference sequence and the given sequence. Also the higher value of the grey relational grade indicates the closeness of process parameters closer to the optimum level. Calculations using grey relational analysis are simpler, straight forward than fuzzy based Taguchi method for optimizing the EDM process with multiple process responses.

3. TWO PHASE PARAMETER DESIGN

Two phase parameters designed strategy using Taguchi technique develops a robust high speed and high quality EDM process. A system with dynamic characteristics is no longer suitably designed using the conventional Taguchi approach, which is based on static characteristic. In actual practice the energy transmission of any system does not happen as designed or intended as there may be noise factors disturbing the system. The reality of the system therefore consists of non linear effects between input and output. Hence two phase parameter strategy with double signals for process optimization was proposed.

Figure.6

The result of the two phase dynamic experiment shows that the factor pulse on time, low voltage electric current high voltage sparking current have maximum influence on EDM process robustness. The factor pulse on time and low voltage electric current are controlling factors for EDM machining speed. The final product dimension can be further adjusted to the desired dimension using the second ideal function model. This method is simple, effective and efficient in developing a robust, high speed and high quality machining process.

4. ARTIFICIAL NEURAL NETWORK (ANN)

ANN can also model the multi objective optimization problem. ANN is a logical structure in which multiple processing elements communicate with each other through the interconnections between the processors. A feed forward back propagation learning algorithm that uses a gradient search technique to minimize the mean square deviation between the actual output and the desired output patterns is used to solve multi criteria problem.Dr.Bhattacharya carried out an experimental investigation of two response parameter i.e. cutting speed, surface roughness on Electra supercut-734 with titanium aluminide alloy as a work piece material.
The experimental results are first used to train the neural network. For training the network in cumulative learning; the delta weights are accumulated and the weights are adjusted until a complete set of input and output pairs are presented to the network. ANN model is then tested and varied for its performance by using training data. Initially three levels of six different input parameters (Ton, Toff, SP, Wt, SV, flow rate of dielectric fluid) which are then increased up to five for generating more number of optimum points, so as to give 15625 different combinations and hence the use of ANN model is highly justified as it is not feasible to carry out 15625 experiments. ANN gives important combinations to be worked out and further optimizes the system.

5. COMBINATION METHODS

Combination of EDM and ball burnishing machining (BBM) for surface improvement by modifying the micro structure of the machined surface (i.e.minimise surface roughness) eliminates micro cracks and pores. In this arrangement two ZnCr2 balls of 5 mm diameters attached with tool applies force to form a deformation layer and ultimately produces reinforced surfaces. Improved surface roughness ratio (ISRR) is then calculated as

(SRedm—SRedm+bbm)*100
ISRR= _____________________ %
SRedm
Where SRedm+bbm=Surface roughness obtained by combining EDM&BBM
SRedm=Surface roughness obtained by conventional EDM (micrometer Ra)
Thus combination of EDM&BBM is a feasible process for obtaining fine finishing and surface modifications. This method is found to be effective for eliminating the micro cracks and pores caused during machining.

MATHEMATICAL MODEL OF WEDM

(A). RESPONSE EQUATION FOR MRR

MRR=1.6184-0.0404{[(A-1.375)2 /0.01]-(8/12)}-0.0138(B-20)-0.0465{[(D-3.5)2/0.25]-(8/12)} ---- (1)
It is evident from the above response equation for MRR that out of four input operating parameters considered only three parameters namely machining speed, pulse on time and peak current are significant in MRR.

(B). RESPONSE EQUATION FOR SURFACE ROUGHNESS

Ra= 1.6592+0.687[A-1.375][1-4.07(D-3.5)-0.0061[C-20]+0.0374[((D-3.5)2-(8/12--------- (2)
It is evident that from the above equation out of four operating parameters considered only three parameters viz. machining speed, pulse off time and peak current are significant in surface roughness.

(C). COMBINED OBJECTIVE FUNCTION (COF)

COF= [WF1*Ra/Ra*]-[WF2*MRR/MRR*] -------- (3)
Where WF1=weight age factor 1=0.5
WF2=weight age factor 2=0.5
Ra*=2, surface roughness limitation in micro meter.
Ra*=2, MRR limitation in mm3/min.
The COF considered for optimization are maximization of MRR and minimization of surface roughness.

6. PARTICLE SWARM OPTIMIZATION (PSO)
PSO was developed by Dr.Eberhart and Dr.Kennedy in 1995.PSO is initialized with a group of random particles and then searches for optima by updating generations. In every iteration each particle is updated by following two “best” values. The first one is the best solution (fitness) it has achieved so far. This value is called pbest.Another best value that is tracked by the particle swarm optimizer is the best value, obtained so far by any particle in the population. This best value is a global best called gbest.When a particle takes a part of the populations its topological neighbours,the best value is a local best and is called lbest.After finding the two best values, the particle updates its velocity and position with following equation (a)&(b).
V[ ]=C1*rand( )*(pbest[ ]-present[ ])+C2*rand( )*(gbest[ ]*(gbest[ ]-present[ ]) ------ (a)
Present [ ] =persent [ ] +V [ ] ------ (b)
V [ ] is the particle velocity.
Persent [ ] is the current particle (solution).
Rand ( ) is a random number between 0&1.
C1, C2 are velocity factors.
Velocity values for C1=2.25, C2=3.25

Figure.7

6.1. IMPLEMENTATION OF PARTICLE SWARM ALGORITHM

The four WEDM parameters such as machining speed, pulse on time, pulse off time and peak current are considered as particle. The four particles are initialized using the following formulae.
Machining speed (A) =A min-{(A max-A min)*ran (0-1)}
Pulse on time (B) =B min + {(B max –B min)*ran (0-1)}
Pulse off time(C) =C min+ {(C max-C min)*ran (0-1)}
Peak current (D) =D min+ {(D max-D min)*ran (0-1)}
After initializing each particle in the first iteration, MRR, SR is calculated. Then pbest &gbest are chosen in the first iteration. In the second iteration each particle of the first iteration are updated using velocity formula (a) & (b).Then pbest & gbest are chosen in the second iteration. This process is continued in all iteration.

7. MEMETIC ALGORITHM (MA)

The combination of local search operators with a global search technique has provided very good results in certain optimization problems. The resulting algorithm from such an approach is termed as memetic algorithm. Particle swarm optimizer (global search) &simulated annealing (local search) are combined. The memetic approach takes the concept of evolution. It combined with an element of local search. PSO employs the basic operational steps of population initialization, updating the particles position by acceleration. An additional component of the algorithm is the notion that each individual can be readily improved upon.

Figure.8

7.1. SIMULATED ANNEALING

It is a point by point method. The algorithm begins with an initial point and a high temperature T.A second point is created at random in the vicinity of the initial point and the difference in the function values (E) at these two points is calculated. If the second point has small function value, otherwise point is accepted with the probability exp {-∆E/T}.This completes one iteration of the simulated annealing procedure. In the next generation another point is created at random in the neighborhood of the current point & the metropolis algorithm is used to accept or reject the point. The algorithm is terminated when a sufficiently small temperature is obtained or a small enough change in function values is found.

7.2. IMPLEMENTATION OF MEMETIC ALGORITHM

The four WEDM parameters are initiated the initial population as explained in PSO.MRR, Ra&COF are calculated using the formulae (1), (2) & (3) respectively and algorithm explained in simulated annealing. Then pbest&gbest values were chosen using PSO algorithm. In the second iteration each particle of first iteration is updated using velocity formulae (a) & (b).Then MRR, Ra, COF are calculated using SA.Then pbest, gbest values are chosen. Thus the entire iteration is continued with the same procedure.

RESULT AND DISCUSSION

PSO technique produces maximum combined objective function value at initial iteration and minimum COF value in the subsequent iterations. MA produces varying COF value in the initial stages &middle stages. At the end of the iterations MA produces better results i.e. minimum COF values.

Figure.9

Figure.10

CONCLUSION
Taguchi method which is supplemented with various supportive techniques minimizes the complexities involved in setting the process parameters so as to satisfy multi objective optimization for maximum MRR&minimum SR and power consumption simultaneously. PSO and MA based procedures used to optimize WEDM parameters viz. machining speed, pulse on time, pulse off time and peak current by taking COF.From the test analysis, it is evident that PSO technique yields better results than MA.This optimization process is easy to use and very simple to implement and efficient in handling COF.

REFERENCES

Journal: MANUFACTURING TECHNOLOGY TODAY (MTT)
CMTI, A NICMAP Publication, Volume 3, July 2004. (pp 11-21).
Books: 1. R.K.Jain, “Production Technology”, Khanna Publishers.
2. HMT Production Technology, Tata McGraw-Hill.
3. Steve Krar& Arthur Gill, “Exploring Advanced Manufacturing
Technology”, Industrial Press Inc.
Websites: www.charmillesus.com
www.makino.com

ELECTRIC DRIVES

2010-08-07T05:11:00.001-07:00

INTRODUCTION

Machining time per work piece represents one of the most important parameters in the area of manufacturing technology with respect to attainable productivity and is the sum of cutting and non-cutting time for a specific work piece. One way to improve productivity is to reduce both these time parameters. The non-cutting times mainly comprises the time required for positioning and tool changes. Clearly increasing the positioning speed and acceleration of the machining tool by properly designing the drive, decrease non-cutting time and increase in productivity can be achieved. In a general machine tool the feed rate during machining is appropriate. During other movements the feed rate is high. In the Electro Mechanical drive system discussed here the feed unit is equipped with 2 motors one (brake motor) for rapid advance &other (standard motor) for slow feed as shown in fig .1b.It is designed in such a way that movement at feed rate is restricted to cutting length while all idle distance are traveled at rapid traverse rate.

The fine boring machine consist of bed, table, lead, screw, brake motor, slow feed motor & two spindle one at each side of the fine boring machine as shown in fig 1b.

FIGURE. (1b)

The main functions of table drive are the following (fig 1a):

1. Job that is fixed on table is moved from left to right fast called as rapid advance (RA).
2. Boring using right spindle take place slowly (SF).
3. Table is moved from right to left fast (Rapid Return-RR).
4. Boring take place left spindle slowly (SF).
5. Ttable brought to home position fast (RR).

FIGURE (1a)

CONCEPT OF ELECTRIC DRIVE

In many of the industrial applications an electric motor is the most important component. A complete production unit consists of primarily of three basic components; an electric motor, an energy transmitting drive and the working (or driven) machine.

An electric motor is source of motive power. An energy-transmitting device delivers power from electric motor to the driven machine (or the load) it usually consists of shaft, belt, chain, rope, etc. A working machine is the driven machine that performs the required production process. Examples of working machines are lathes, centrifugal pumps, drilling machines, boring machines, etc. An electric motor together with its control equipment and energy-transmitting device forms an electric drive. An electric drive together with its working machine constitutes an electric drive system. A ceiling fan motor with its speed regulator but without blades is an example of electric drive. Other examples of electric drives are: - a food mixer without food to be processed, a motor and Conveyer belt without any material on its belt. Some examples of electric drive systems are: a ceiling fan motor with regulator and also with blades, a food mixer with food to be processed, a motor and conveyer belt with material on its belt and so on.

Figure shows an electric drive system. The electric drive, consisting of electric motor, its power controller and energy-transmitting shaft

BORING

Boring is a machining process in which internal surfaces of revolution are generalized with a single point cutting tool. The term `boring` is applicable to enlarging an existing drilled or cored hole and it also includes machining of blind holes, holes with contoured bores and bores with steps, under cuts, etc.

FINE BORING MACHINE

Fine boring machines are precision boring machines built to machine components requiring high degree of accuracy and surface finish. The boring spindle, which is the heart of these machines, can be of a ball, roller bearing, hydrostatic, or air bearing type. On these machines, diamond tools can be use to achieve high degree of accuracy and surface finish.

ELECTRO MECHANICAL DRIVE SYSTEM FOR FINE BORING MACHINE

OPERATION OF DRIVE SYSTEM

The total drive system consists of a brake motor, slow feed motor, lead screw, guide ways and table. Brake motor is meant for rapid feed rate when table travels the idle distance. When the table has moved the idle distance, the brake motor will be switched off. Slow feed motor will be switched on. The table moves slowly. The sequence of operations is controlled by limit switches. The operations controlled by limit switches are explained below (refer fig.1c).

1, 2, 3, 4-LIMIT SWITCHES
FIGURE (1c)
First brake motor is switched on and Rapid table movement follows. Spindle motor is also on. Limit switch 1 is on. When the table moves left to right and meets limit switch by trip dog brake motor stops. Slow feed motor is on. Table is under slow feed job facing right side spindle. Limit switch 2 is on. When the t able moves and meets limit switch 2 slow feed motors is off. Spindle also off.

Next brake motor is switched on in the reverse direction. Table under rapid rate. Limit switch 3 is on. When table moving towards left touches limit switches 3 and brake motor stops. Slow feed motor is on. Table is under slow feed and job facing the left spindle. When table meets limit switch 4, slow feed is off. Brake motor is on. Table comes to home position. This is the cycle of events that tables placed in a fine boring machine drive system under operation.

GEAR ARRANGEMENT

The gear box is designed for transmitting power from brake motor to lead screw via sun and planet gear during rapid advance and transmitting power from slow feed motor to lead screw via change gear, bevel gears and sun & planet gear during slow feed. By varying the change gears during slow feed as many as 45 feeds can be obtained.

FIGURE (2a)
First when the brake motor rotates it transmits power to gear A. From gear A it is transmitted to B (spur gear) .The speed reduces. From B it is transmitted to gear C (sun gear) &C to D (planet gear) D to 9, 9 to 10 and 10 to 8. From 8 power is transmitted to lead screw 12 via 10A and 11 as shown in figure.

FIGURE (2b)

FIGURE (2c)
Now the lead screw rotates at rapid feed rate. When the lead screw rotates table gets linear motion and moves towards the spindle. When it reaches near the spindle, the brake motor is switched off and slow feed motor is switched on. The power is transmitted from standard motor (slow feed motor) to change gear 1. From spur gear 1 power is transmitted to spur gear 2 and speed is reduced considerably. Again the speed is reduced by transmitting via gears 3,4,5 and 6.Bevel gears 7 is fixed at the other side of spur gear. From bevel gear 7 power is transmitted to bevel gear 8 in perpendicular direction. From, bevel gear 8 power is transmitted through sun and planet gears C, D, 9, 10 and 10A, level to lead screw 12 and table gets slow feed.

CALCULATION OF RAPID FEED

The rapid rate is got from Brake Motor rotating at 1500 rpm. The power is transmitted from brake Motor to lead screw 12 via C, D, 9, 10A, 11 as shown in fig. 2.

From fig. 2 the gear ratio for rapid rate
= (ZA / ZB) * (ZC / ZD) * (Z9 / Z10) * (Z10A / Z11)

This is calculated as follows:

The gear ratio = (26/51)*(20/13)*(13/22)*(22/53)
= 0.192378

Pitch of screw = 8
No. of start = 2

Multiply the gear ratio by 1500, rpm of brake motor and pitch of lead screw thread and no. of start, we get rapid rate
= 0.192378*1500*8*2 mm/min
= 4617 mm/min
= 4.6 m/min
So the rapid rate at which the table will be moving is 4.6 m/min. During rapid rate only the brake motor will be switched on. The slow feed motor will be switched off. So there will be no power transmission to the gears meant for slow feed.

CALCULATION OF SLOW FEED

Slow feeds obtained from slow feed motor. Power is first transmitted from slow feed motor to gear 8 via, gears 1,2,3,4,5,6,7(ref fig 2). From gear 8 power is transmitted through sun and planet gears CD, 9, 10 then from 10 to 10A and 11 &12 leads screw.
The speed ratio after passing through sun and planet gear is got from table1. The type of planetary gearing as shown in fig3 is compound planetary drive with two sun wheels. From the table1, for the present application, drive no.2 is selected.

Among the fixed ratio drive possibilities,

The transmission ratio I = (rpm of driver /rpm of driven). Is got as
= Z10ZD/ (Z10ZD-ZCZ9)
(Refer drive no.2 in table 1& fig 2&3)

ZC = 20, Z10 = 22, ZD =13, Z9 =13

The speed ratio after passing through planet gear is
=22*13/ (22*13-20*13)
= 286/26 =1:11

Table 1 Fixed ratio drive possibilities (Compound planetary drive with two sun gears-fig 3)

Drive No. 1 2 3 4 5 6
Fixed Member 1 1 2 2 4 4
Driver 2 4 1 4 1 2
Driven 4 2 4 1 2 1
Transmission ratio I
=(Rpm of driver/rpm of driven) 1=(ZCZD/
Z10ZD) Z10ZD/(Z10ZD-ZCZ9) 1-(Z10ZD)/ZCZ9) (ZCZ9)/
(ZCZ9-Z10ZD) (Z10ZD)/
(ZCZD) (ZCZ9)/
(Z10ZD)

The speed is reduces 11 times after passing through sun and planet gear CD 9 &10.we can get as many as 45 feed rate using change gears and with and without reductor.

The gear ratio for slow feed can be obtained from fig.2 as
(Z1/Z2)*(Z3/Z4)*(Z5/Z6)*(Z7/Z8)*(1/11)
(The speed ratio after passing through sun and planet gear) *(Z10A/Z11)

In this (Z7/Z8)*(1/11)*(Z10A/Z11) is common for all 45 feeds.

They are (30/47)*(1/11)*(22/53)*(Z5/Z6)

Are change gears, which will be changed each time, when different feeds required. The different change gears starting from
(15/67) 0 (54/29) are shown in table 2.

As per table 2, first 15 feeds are obtained with gear pair.

Z1/Z2 = 41/41, Z3/Z4 = 41/41
Z5/Z6 change gears

By varying change gear we can get first 15 speeds.
For example the feed rate 129 mm/min is obtained from
(41/41)*(41/41)*(15/67)*(30/47)*(1/11)*(22/53)*1500

(Rpm of slow feed motor)*8 (pitch of the lead screw)*2(no of start -double start)
= 129 mm/min

Next 15 feed rates are obtained by putting
Z1/Z2 = 18/64, Z3/Z4 = 15/67

Z5/Z6 change gears

By varying change gears we can get next 15 feeds. For example the feed rate 8 mm/min.is obtained from
(18/64)*(15/67)*(15/67)*(30/47)*(1/11)*(22/53)

For example the feed rate 36mm/min is obtained from
=8 mm/min
Table 2 Different Slow Feeds

Change Gear 5 Change Gear 6 Slow Feed MM/Min
Number of Teeth Z5 Number of Teeth Z6 Z5 / Z6 Range without Reductor and with 41/41*41/41 Range with Reductor 18/64 with gear pair
15*67 41*41
15 67 15/67 129 8 36
18 64 18/64 162 10 45
22 60 22/60 212 13 59
26 57 26/57 263 16 74
29 54 29/54 310 19 87
32 51 32/51 363 23 102
35 48 35/48 421 26 118
37 45 37/45 475 29 133
41 41 41/41 578 36 162
43 39 43/39 637 40 180
45 37 45/37 703 44 200
48 35 48/35 792 49 222
51 32 51/32 921 57 259
54 29 54/29 1076 67 302

Next 15 feed rates are obtained by keeping
Z1/Z2 = 18/64, Z3/Z4=41/41

Z5/Z6 change gears

By varying change gears we can get next 15 feed rates.

For example the feed rate 36 mm/min is obtained from
(18/64)*(41/41)*(15/67)*(30/47)*(1/11)*(22/53)*1500*8*2
=36 mm/min
CYCLE TIME OF FEED

The cycle times of doing the five operations are calculated as follows. The job selected is shown in fig 4. The component taken for the boring is the cylinder of one type of I.C. engine. The bore 500.05 is made on fine boring machine. The cylinder is having a length of 70 mm.

Cutting speed = 90 m/min for material cast iron and cutter carbide tip

Figure 4

Details of the component bored in fine boring machine

Material: cast iron
Component name: cylinder for I.C Engine
All dimensions are in mm

Cutting speed = (DN/1000)
= 90 m/min

Dia of bore D = 50 mm

N = (90*1000)/ (*50)
= 600 rpm.

Feed rate for fine boring 0.05 mm/rev. (normal feed for fine boring operation)

Feed /min = 600*0.05
= 30 mm/min

Bore length = 70 mm

Machining time = (70/30)*60
= 140 secs.

Rapid rate = 4600 mm/min
Rapid travel = 300 mm

Time for rapid travel = (300/4600)*60
= 4 sec.

Time for feed

Table from home position to right = 4secs
Right side boring = 140 secs
Right to left = 8 secs
Left side boring = 140 secs
Left to home position = 4 secs
Total = 296 secs
Cycle time for fine boring using Electro Mechanical Drive System = 296 secs

COST OF DRIVE SYSTEM

1. Raw material cost Rs. 47530
2. Bought out Rs. 28150
3. Imported Rs. 3295
4. Sub contract Rs. 1960

Labour cost

5. Manufacturing Rs. 1, 02160
6. Assembly cost Rs. 25520
7. Pattern cost Rs. 25000

Production cost =1+5+6+7 = 200210

Factory cost Rs. 200210

Cost price 10% added Rs. 220231 (200210+20021)

Bought out + imported + sub contract = 33405

Total cost Rs. 253636

Cost of Electro Mechanical Drive System = Rs. 2, 53,636

CONCLUSION

The electro mechanical drive system is designed to operate at rapid feed rate of 4.6 m/min and 45 m/min slow feeds. Since the non-cutting time is reduced considerably the over all cycle time is reduced. So the productivity is increased. The cost of drive system is justifiable. For stepped drive this is the best drive. The only the advantage is that the gear changing is little tiresome when change in feed rate is required unlike step less drive where speed changing is very easy. This same design can be tried in other special purpose and other machine tools also.

REFERENCE

1. Dr.P.S.Bimbhra, Power Electronics text book, Khanna Publishers
(2003), Pg-460
2. R.Henry Xavier and Dr K.V.Thyagarajan, Manufacturing Technology Today, volume-3, August 2004, Page No-13 to 17.
3. T.P.S.Iyer, Production Technology,HMT Publication Ltd,New Delhi

Effect of elevated piston temperature on combustion chamber deposit growth

2010-08-07T05:09:00.000-07:00

ABSTRACT
Combustion chamber deposits are found in all internal combustion engines. When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. The factors influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. One way to discourage deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced.
In these attempts is made to investigate the effects of wall temperature on deposit growth, without the use of ceramic coatings on the combustion chamber surfaces. Also methods for monitoring combustion chamber deposit growth as a function of metal wall temperature are described. In this, a composite piston design was developed to control and monitor surface temperature. The design incorporated ceramic wafers of varying thickness encapsulated between a metal cap and piston top. The cap was fitted with surface-mounted thermocouples to measure wall temperatures. An accelerated test cycle was used to accumulate deposits. There is a description of methodology employed in raising the wall temperature and monitoring deposit growth. After stabilization of deposit growth a physical and chemical analysis of deposits from different locations were also conducted.

INTRODUCTION
Combustion chamber deposits are recognized as a major contributor to the deterioration of SI engine performance . Their build-up leads to reduced air mass flow rates, increased charge emissions, and increased tendency for knock. The primary mechanism of formation of fuel deposits is condensation of the high boiling point components, such as aromatics, and their carbonization while in the liquid phase. The amount of air mixed with the fuel has been found to be critical to the deposit growth in engines. Therefore, oxidative fuel pyrolysis better describes the mechanism of deposit formation. With increased wall temperature, hydrocarbon condensation tendencies decrease, and therefore deposit formation is reduced. Deposits on hot surfaces, such as the exhaust valve of the spark plug, are primarily composed of oil-based inorganic compounds. Deposit growth in the end gas region, the region with the coolest surfaces, is typically higher than in any other portion of the combustion chamber, end chamber deposits also have lower oxygen and higher carbon content than elsewhere in the combustion chamber.
The purpose of this experiment is to investigate the effects of wall temperature on deposit growth, without the use of ceramic coatings on the combustion chamber surfaces. This study monitors in -situ combustion chamber deposit growth, as a function of metal wall temperature, and attempts to determine the critical wall temperature for no growth a composite piston design was developed to control and monitor surface temperature. The design incorporated ceramic wafers of varying thickness encapsulated between a metal cap and piston top. The cap was fitted with surface-mounted thermocouples to measure wall temperatures. An accelerated test cycle was used to accumulate deposits. This also contains the methodology employed in raising the wall temperature and monitoring deposit growth.

COMBUSTION CHAMBER DEPOSITS
Combustion chamber deposits are found in essentially all internal combustion engines. Their influence can be seen in many aspects of engine performance. Deposits form on all engine surfaces that are in contact with fuel or fuel air mixture at any point in the cycle. The mechanism by which these deposits form from fuel are not well understood .the effect of deposit include increased engine NO emissions, octane requirement increase and changes in flame speed and thermal efficiency.
The factors influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. These factors affect the rate of deposit formation and removal and the structure of deposits. To create a deposit control strategy needed is the magnitude and direction of these various effects over a wide range of fuel types and engine conditions.

The chemical and thermo physical properties deposits depend on fuel and oil composition, wall temperature, engine operating conditions, and engine design. The carbon to hydrogen (C/H) ration of the deposits indicates the relative proportion of fuel and oil contribution to the deposits. A low carbon to hydrogen ratio indicates deposit constituents are mostly oil based, and originate from oil cracking on the wall. A high carbon to hydrogen ratio indicates the deposits are primarily fuel derived. In general, deposits collected from engines that operate under normal conditions are primarily fuel derived.
OCTANE REQUIREMENT INCREASE
The actual octane requirement of a vehicle is called octane number requirement. A new engine require a fuel of octane number 6-9 lower than the same engine running for a long time. This octane requirement increase is due to the formation of a mixture of organic and inorganic deposits resulting from fuel and the lubricant. When using unleaded fuel two-thirds of the octane requirement is caused by deposit accumulation in the end gas region.
EFFECT OF COMBUSTION CHAMBER DEPOSITS
The effect of combustion chamber deposits include octane requirement increases, decreased volumetric efficiency, increased thermal efficiency due to insulation of the cylinder, combustion chamber deposit interference(CCDI) and combustion chamber flaking.

As deposits build up on the combustion chamber surfaces, the minimum fuel octane number needed to avoid engine knock increases. In modern engines this increase is approximately 4 to 5 octane numbers on average as the deposits build up to their equilibrium thickness. Combustion chamber deposit interference is the result of physical contact between deposits on the piston top and cylinder head. Combustion chamber deposit flaking causes low compression pressures due to improper sealing of the valves.
EXPERIMENTAL SETUP AND PROCEDURE
THE ENGINE CONFIGURATION
The investigation was performed using a Waukesha, single cylinder, split head, variable compression ratio, Cooperative Fuel Research (CFR) engine. Engine motoring and loading was handled by a General Electric DC dynamometer with 20 hp motoring and 35 hp absorbing capacity. The CFR’s intake manifold was modified to incorporate a throttle body in order to regulate engine load. An active magnetic pickup, mounted in close proximity to the dynamometer shaft, was used to measure engine speed. The dynamometer was controlled with a Dyne Systems DYN-LOC IV controller

The fuel delivery system was converted from the standard CFR system to a modern electronic fuel injection setup which was comprised of an automotive fuel fitter and pump, along with a Bosch fuel injector and pressure regulator. The fuel injector was installed in the in take manifold where the CFR injector was normally fitted. The ignition system consisted of a single pole, ignition coil and a TFI module that was used to trigger coil discharge. A fuel/spark controller was developed to control timing of the fuel injector and initiate coil discharge so as to achieve desired fuel flow rate and spark timing.

Engine oil and water jacket cooling was provided by tube type heat exchangers. The jacket water consisted of a mixture of approximately 80 percent water and 20 percent ethylene glycol. Engine oil temperature and jacket water temperatures were measured with K-type thermocouples. During testing, oil temperature in the crankcase sump was maintained at 90± 20 ºC. The jacket water temperature stabilized to 100 ºC in 15 minutes after starting the engine.

Air flow was measured with an ASME 5/8 inch metering orifice with flange mounted pressure taps. Fuel flow rate was measured with a calibrated burette Cylinder pressure was measured with a water cooled piezoelectric transducer mounted in the knock sensor hole of he head. The transducer was cleaned and covered with high temperature silicone RTV.
CONTROL AND MEASUREMENT OF PISTON SURFACE TEMPERATURES
Deposit growth was investigated on the top surface of the piston, which typically accounts for two-thirds of the deposit growth in the combustion chamber.A composite piston design was developed to control and monitor surface temperature. The design incorporated a ceramic wafer between an added iron cap and the standard iron piston top. The ceramic wafer was fabricated from a glass/ceramic material with low conductivity of 1.38 W/m. ºC, and high compression strength of 344 Mpa, and excellent machinability. The wafer measured 76.2mm in diameter, and 1.0, 2.0, or 3.0 mm in thickness. By varying the thickness of the ceramic wafer, the surface temperature of the cap could be increased from its baseline value. Predictions ware generated through a one-dimensional heat transfer analysis of the composite piston design, based on an assumed transient heat flux on its combustion surface.

A series of caps was machined from ferromagnetic iron, with each cap having a matching pocket to a seat a given ceramic wafer. For all caps, the distance between the top surface and its pocket was maintained at 4 mm for structural support. The cap was secured to the standard piston by countersunk fasteners. The CFR cast iron piston was used because its material closely matched the piston cap material. Since the iron piston has four compression rings and only one oil ring, the connecting rod oil jet, which is normally used for cooling the piston’s underside, was sealed off to avoid excess oil consumption in the combustion chamber.

Surface-mounted thermocouples were mounted flush with the cap surface to allow monitoring of its temperature during engine operation. Four constantan wires were affixed to the cap at 36.5 mm radially from the iron wire. The J-type thermocouple wire used was 24 gauge and has a peak temperature range of 700 ºC. The wires were fitted in the cap through counter-bored and counter sunk holes. The wires were bonded to the cap by welding the wire end into the countersunk holes.
TRANSMISSION OF ELECTRICAL SIGNALS-
Due to the harsh environment of high accelerations and temperatures, the piston assembly was meticulously wired to insure electrical continuity between the cap’s thermocouples and the connecting road. Augat electrical connectors which forming good electrical contact with 24-gage copper wire, were placed in the piston top to serve as an electrical socket for the thermocouple wires. Standard 26-gauge copper wire, which was secured to the connector with silver solder, was used to continue transmission of the electric signals. An RTD was placed next to a protruding Augat connector on the piston’s underside to establish the reference junction temperature. The RTD and all wires were bonded to the piston with epoxy.

A stainless steel band was used to provide a path between the piston and the connecting rod. The band was mechanically secured to the piston’s skirt and the connecting rod. Finely stranded copper wires were guided along the band’s outside surface and held with high-strength RTV and segmented high-strength heat shrink tubing. After passing under two aluminum plates which were fastened to the connecting rod’s shank, the wires were eventually routed to the end cap of the connecting rod. In order to establish electrical continuity of the thermocouple signals from the end cap of the connecting rod to an external data acquisition system, a mechanical telemetry linkage system was designed. The system works on the concept of classical four bar linkage. The longest possible wire life was achieved by minimizing angular deflection and by maximizing the transmission angle between adjoining linkage members. This reduced bending of wires at linkage joints, thus promoting longer wire life.
TEST PROCEDURE
A transient test cycle, appropriate for a single-cylinder engine, was designed for the test The test schedule was broken down into four and one half hour test cycles, followed by engine cool down to ambient temperature. Within each test cycle, a repeated fifteen minute test segment was conducted. One and one half minutes were spent at idle, thirteen minutes at low load, and one half minute at a high load. At the beginning of each test, the engine was warmed up at 800 rpm for twenty minutes.

The four and one half hour test cycle was repeated as many times as needed for establishing well defined growth patterns. For each four and one half hour test cycle, fast response, pressure and temperature data were recorded every half hour during the 1800 rpm segment. Additional measurements included airflow, oil and cooling water temperatures, exhaust temperature, and intake pressure. Fuel consumption measurements were documented periodically during testing.

At the end of testing with a given cap, the cylinder head was removed, and the deposit thickness on the head, valves, bore, ports and piston were recorded. Deposits were removed from the cylinder head, valves and ports. Then the valves were lapped and the engine was reassembled for further testing. All piston configurations were tested with a base premium unleaded fuel without reformer bottoms. The 3 mm cap test was repeated with the unleaded fuel doped with reformer bottoms.
IN-SITU MONITORING OF DEPOSIT GROWTH
A technique for in-situ monitoring of deposit growth is through measurement of local surface temperature using thermocouples affixed to the combustion surface. As deposits build up on the surface and form an insulation barrier, heat flow is reduced from the combustion gases to the wall. The restriction in heat flow reduces the wall’s surface temperature which is measured by the surface-mounted thermocouple. The rate of change of wall surface temperature is thus indicative of the rate of deposit growth. The surface temperature has been found to decrease almost linearly until deposit growth has stabilized, from then on, the surface temperature remains relatively constant.

Temperature gradients and stabilized growth periods have been found to be greatly influenced by the fuel’s hydrocarbon structure. Fuels with aromatic hydrocarbons, toluene and xylene, measured higher surface temperature gradients, during the first three hours of testing, than fuels containing paraffins, like iso-octane. The higher the boiling point of aromatic components, the faster the deposit growth, and the lower the measured wall temperature

Initially the baseline cap was run for a 42 hour deposit growth test. Recorded temperature histories exhibited two distinct temperature discontinuities at the 10th and 22nd hour. The first temperature discontinuity was due to the thermocouple wires and connectors being coated with a carbonaceous film, as a result of combustion gases penetrating into crevices of the contact surface between piston and cap. The gap was seated with a thin layer of high temperature RTV applied on the lower surface of the cap. The second temperature discontinuity was associated with vibration in the flat head fasteners. This was corrected by the use of flat head lock washers with the fasteners. After this, the first 12hours of the baseline test were repeated.

Regional differences in the measured rate of temperature decay are attributed to differences in deposit composition and thermal properties at the different locations. There is an accelerated deposit build-up in the regions surrounding thermocouples 3 and 4 (under the intake valve). The differences are driven by regional variations in wall surface temperature and changes in the C/H composition of deposits. The surface-averaged wall temperature of the baseline cap decreased linearly over time, at a rate of 0.38oC/hr.

EFFECT OF ELEVATED PISTON TEMPERATURE ON DEPOSIT GROWTH
TEST USING UNLEADED FUEL
Caps insulated with a1, 2 and 3 mm ceramic wafer were tested with the base unleaded fuel without reformer bottoms. An overall test period of 18hours was used to define deposit growth patterns. Local and averaged surface temperature histories of the insulated caps are compared with those of the baseline cap. Insulating the piston cap raised the initial temperature of the surface from an average of 215 ºC to 317 ºC for 3 mm cap .Elevating the initial temperature of the cap reduced the rate of decay with time, from –0.38 ºC/hr (baseline) to 0.02 ºC/hr for the last 11hours of the test with the 3mm insulated cap. This shows an overall decrease in deposit growth with elevated piston temperature

The discontinuity in the surface temperature gradients of the 3mm cap is that light engine knock was experienced after 6hour of testing with the unleaded fuel without additives. Spark timing was then retarded by three crank angle degrees to eliminate knock, and the test was continued. A thermocouple histories in the 3mm insulated cap shows surface temperatures to decrease at a rapid rate, particularly in the end gas region of thermocouples 2 & 3, between the second and sixth hour. This decrease indicates accelerated early deposit growth, with the largest concentration in the end gas region. Deposit growth causes an increase in gas temperature, which leads to knock. The high thermal stresses crated by the knocking condition cause deposit flaking, or random removal of deposits. Once flaking occurred, deposit accumulation on the exposed surfaces was retarded. A deposit film remained on the cap’s surface leads to periodic reoccurrence of knock and flaking, this shows the observed fluctuations in surface temperature after the sixth hour of testing.

There is a slightly positive slopes for the recorded temperature change at locations 2 and 3. This is attributed to , an inability to take data during the first one hour of testing, when a relatively large deposit accumulation occur at those locations, and difficulties during the first four-and-a- half hour test cycle. Data with the second test cycle establish negative (or close to zero) slopes. A little deposit growth is experienced with the 2 mm insulated cap, by an average rate of temperature decay of 0.06 ºC/hr. With further increase in cap insulation, the mean temperature gradient during the last seven hours of testing was –0.02 ºC/hr, indicating negligible deposit growth with the 3mm insulated cap. An average wall temperature of 320 ºC identifies a critical point above which the base unleaded fuel does not form deposits.

Results through in-situ monitoring of deposits using unleaded fuel yielded a critical surface temperature of 3200C.
TESTS USING FUELS WITH REFORMER BOTTOMS
Reformer bottoms are large hydrocarbon molecules which have poor oxidation characteristics, and thus enhance deposit growth rate. This is also affected by potential changes in the thermal properties of fuel deposits.

Testing with the reformer bottoms fuel was conducted for only eleven hours. The average wall temperatures for the reformer bottoms test were compiled from thermocouples 1 and 3.No knock occurred during testing of the 3 mm insulated cap with the reformer bottoms fuel. The linear decay in the average temperature of the piston surface (at a rate of 0.350 C/hr) shows a steady deposit growth. Reformer bottoms can promote deposit growth under operating conditions at which no deposits are formed with the base fuel.

The wall surface temperature for the reformer bottoms test was approximately 8 ºC lower than that for the base fuel test, after one hour of testing. This difference can be accounted for by a 4 o C lower inducted air temperature for the reformer bottoms test. The other differences are a result of differences in thermal properties of deposits from the two fuels. The deposit layer from the reformer bottoms fuel experiences a lower temperature swing during the cycle, and a lower peak surface temperature, this also leads to a lower mean wall temperature and thus increased deposit growth. The deposit growth is effectively controlled by the temperature at the deposit surface. The temperature difference (5 0C) between the peak temperatures at the gas-exposed surface of deposits from unleaded fuels with and without reformer patterns, shows differences in deposit growth patterns.
TEST ANALYSIS OF DEPOSITS
PHYSICAL ANALYSIS
A physical analysis of deposits is important in fully characterizing deposit growth patterns. At the end of each test schedule, overall observations were made concerning the color and texture of deposits in each of the four cap quadrants. In addition deposit thickness measurements were made with a Titan ZDM-1 microscope. This information was useful in correlating deposit growth and change in wall restricted within a square region defined by the thermocouple locations. The exact locations on the cap surface where deposit thickness measurements were taken.

Deposit thickness measurements are taken for various caps. At the baseline 12 hour test deposits in cap regions 1, 2, and 4 appeared as dark down in color with a sooty texture, while region 3 deposits had a lighter shade of brown and a crusty texture. After 18 hours of testing, the 1 mm insulated cap was covered with a deposit coating of a lighter shade of brown. In regions 1 & 4, deposits were observed to be denser and more sooty than those in regions 2 & 3, the regions 2 & 3 had a gritty texture. Compared to the 1 mm insulated cap which collected an average deposit thickness of 6.28 m, the 2mm cap had a reduced deposit growth (1.83 µm on average), particularly in region 2 where no deposits had accumulated . The deposits on the remaining three quadrants of the cap had a light- brown metallic color with a gritty texture. The 3mm cap exhibited almost negligible deposit accumulation after 18 hours of testing. In regions 3 & 4, the cap surface seen under a rough and gritty texture whereas regions 1 & 2 were covered by a thin, smooth, brownish white deposit film.

The exhaust valve maintained a white color in all cases, at the end of each test with the unleaded fuel (without reformer bottoms).The intake valve color changed from a dark brown to a light gray as the piston surface temperature increased. At the end of the 3 mm insulated cap test, the exhaust valve had a clear evidence of deposit flaking. This is due to high surface temperature as well as engine knock.

The average deposit thickness was found to decrease at 3.38 µm per millimeter of ceramic insulation. Low temperature regions, such as under the intake valve, were not always found to be covered under the thickest deposit coating. Thicker deposits accumulated on the cap for the longer test period. After 42 hours more deposits were found under the intake valve (region 3). Deposit flaking under the intake valve, where there is a tendency for large accumulation of deposits, resulted in removal of excessive deposit build-up with a long test period.

After 11 hours of testing with the reformer bottoms fuel, the 3mm cap accumulated a deposit layer with an average thickness of 0.47 µm, 55% more than the layer accumulated after testing the unleaded fuel without additives for 18 hours. Aside from the poor oxidation properties of the reformer bottoms, the differences in these growth patterns are attributed to differences in thermal properties of the two types of deposits. Deposits from the reformer bottoms fuel were primarily centered in regions 3 & 4, as well as the edges of regions 1 & 2. They were identified with a dark brown color, and a rough, sooty texture. The intake valve from the reformer bottoms test accumulated a dark brown deposit layer. The exhaust valve appeared to maintain a light brown appearance. Deposit flaking was not found on this component.

Insulating the piston cap had a noticeable impact on deposit characteristics. The deposits were found to progress from a dark brown color with a sooty texture ( baseline cap ) to light-brown pigment with a gritty texture (3 mm cap ) Deposit growth on the cylinder head, showed similar trends. Deposits on the 3 mm insulated cap from the reformer bottoms fuel test exhibited comparable characteristics to those formed on the baseline cap using unleaded fuel without reformer bottoms.
CHEMICAL ANALYSIS
A carbon to hydrogen (C/H) ratio analysis indicate the relative proportion of fuel and oil in the deposits, as well as the mechanism of deposit formation. The analysis reveals that deposits in the end gas region have the highest fuel content, as a result of deposition of unburned hydrocarbon products on the end gas region surfaces. The region between the spark plug and the intake valve has lower fuel content than the end gas region, and higher oil content. Since the former region runs approximately 16 ºC hotter than the latter region, this behavior can be attributed to fuel vaporization on the higher temperature surfaces. The deposits collected near the cap’s edge in the end gas region present the highest oil content. Excess oil on the cylinder liner accumulates on the latter region of cap during the piston’s travel.

Mole fraction of carbon and hydrogen in the deposits collected under the exhaust valve portion of the end gas region (region 2) for each cap configuration tested with unleaded fuel without additives, shows an increase in the concentration of carbon within the deposits. The C/H ratio decreases with increased surface temperature. As wall surface temperature elevate, more oil contributes to deposits. A decreasing C/H ratio with increasing wall temperature indicates that deposit growth primarily originates from oil cracking on the wall. Deposits collected on high temperature, combustion chamber walls were composed mostly of inorganic compounds, such as those preset in engine lubrication. Deposits collected on cooler surfaces have been composed primarily of carbon.
CORRELATION OF TEMPERATURE DECAY AND DEPOSIT GROWTH
An analysis was performed that, measured changes in temperature over a given test period were normalized with respect to the measured deposit thickness at the corresponding location. The all four thermocouple locations were considered for the base unleaded fuel tests with the baseline metal cap (for 12 hours) and the 1mm insulated cap (for 18 hours). For all except one case, there appears to be a strong correlation between measured temperature decay and associated deposit thickness.
The effective conductivity of the deposits collected at a given location is nearly constant during the accumulation period. This holds true as long as there is no drastic change in local composition of deposits while increasing piston operating temperature. For the case of the 1mm cap, the region between the spark plug and the intake valve (region 4) progressively accumulated deposits of lower fuel content and higher oil content, with increasing piston temperatures.

DEPOSIT CONTROL
When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. Deposits form on all engine surfaces that are in contact with fuel or fuel-air mixture at any point in the cycle. These deposits have significant effects. The deposit layer on the cylinder wall prevents the coolant that runs through the engine from bringing down the temperature inside the cylinder. Due to the increased temperatures, parts of the fuel-air mixture may ignite before the flame front reaches them, causing the engine to knock. Another effect of the raised temperatures is increased production of pollutants such as nitrogen oxides inside the engine cylinder. One way to discourage deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced. Deposits on hot surfaces such as exhaust valves or ceramic of the spark plug are composed of oil based inorganic compounds. Deposit growth in the end gas region (region with coolest surfaces) is typically higher than in any other portion of combustion chamber.
Disadvantage of increasing wall temperature is that, if defects the overall goal of keeping cylinder temperatures down.

CONCLUSION
Combustion chamber deposits are found in essentially all internal combustion engines. When fuel and air burn inside an internal combustion engine, deposits form on the walls inside the cylinder. Factors that influencing deposit formation are changes in fuel composition, coolant temperatures, engine speed and load, and spark timing. These affect the rate of deposit formation and removal and the structure of the deposits. Deposits form on all engine surfaces that are in contact with fuel or fuel-air mixture at any point in the cycle. These deposits have significant effects. The deposit layer on the cylinder wall prevents the coolant that runs through the engine from bringing down the temperature inside the cylinder. Due to the increased temperatures, parts of the fuel-air mixture may ignite before the flame front reaches them, causing the engine to knock. Another effect of the raised temperatures is increased production of pollutants such as nitrogen oxides inside the engine cylinder.
One way to avoid deposit formation is to prevent condensation. Raising the wall temperature prevent condensation. With increased wall temperature, hydrocarbon condensation tendencies decreases and thus deposit formation is reduced. The unleaded fuel would not condense into a carbonaceous film once a critical wall temperature is reached. Reformer bottoms yielded a 55 percentage increase in deposit thickness compared to base unleaded fuel. This difference was due to poor oxidation properties of reformer bottoms. Elevating wall temperature increases the carbon to hydrogen ratio in the composition of deposits. Deposits in the end gas region are mostly fuel derived.
Disadvantage of increasing wall temperature is that, if defects the overall goal of keeping cylinder temperatures down.

REFERENCES
 Christopher Forssen o’Brien , “ Combustion chamber deposit research.”
 Energy laboratory research And related activities at the MIT , “ Inside engine cylinders; cleaner walls for lower emissions, higher efficiency”
 Chevron U S A , “Gasoline vehicles deposit control.”
 The engineering society for advancing mobility land sea air and space, “Effect of elevated piston temperature on combustion chamber deposit growth ” SAE Technical paper series ,940948,1994

CAMLESS ENGINE

2010-08-07T05:07:00.000-07:00

INTRODUCTION

The cam has been an integral part of the IC engine from its invention. The cam controls the “breathing channels” of the IC engines, that is, the valves through which the fuel air mixture (in SI engines) or air (in CI engines) is supplied and exhaust driven out. Besieged by demands for better fuel economy, more power, and less pollution, motor engineers around the world are pursuing a radical “camless” design that promises to deliver the internal – combustion engine’s biggest efficiency improvement in years. The aim of all this effort is liberation from a constraint that has handcuffed performance since the birth of the internal-combustion engine more than a century ago. Camless engine technology is soon to be a reality for commercial vehicles. In the camless valve train, the valve motion is controlled directly by a valve actuator – there’s no camshaft or connecting mechanisms .Precise electrohydraulic camless valve train controls the valve operations, opening, closing etc. The seminar looks at the working of the electrohydraulic camless engine, its general features and benefits over conventional engines. The engines powering today’s vehicles, whether they burn gasoline or diesel fuel, rely on a system of valves to admit fuel and air to the cylinders and let exhaust gases escape after combustion. Rotating steel camshafts with precision-machined egg-shaped lobes, or cams, are the hard-tooled “brains” of the system. They push open the valves at the proper time and guide their closure, typically through an arrangement of pushrods, rocker arms, and other hardware. Stiff springs return the valves to their closed position. In an overhead-camshaft engine, a chain or belt driven by the crankshaft turns one or two camshafts located atop the cylinder head.
A single overhead camshaft (SOHC) design uses one camshaft to move rockers that open both inlet and exhaust valves. The double overhead camshaft (DOHC), or twin-cam, setup does away with the rockers and devotes one camshaft to the inlet valves and the other to the exhaust valves.

Such valve trains, as they are known, are complicated but reliable. Yet they have the major disadvantage of inflexibility. Valve timing, valve lift, and event duration are all fixed values specific to the camshaft design. Like a very simple software program that contains only one set of instruction, the cams always open and close the valves at the same precise moment in each cylinder’s constantly repeated cycle of fuel-air intake, compression, combustion, and exhaust. They do so regardless of whether the engine id idling or spinning at maximum rpm. As a result, engine designers can achieve optimum performance at only one speed. An engine designed for impressive high-rpm power may be a wimp at low rpm, and vice versa.
Some automakers have tried to get around that limitation with mechanisms that “phase”, or shift, the rotational position of the camshafts as rpm varies, Honda uses a system called VTEC. At faster engine speeds, it hydraulically brings extra sets of cam lobes and rockers into play to help the motor breathe more deeply and make more power. Clever as they are, these schemes are limited by their reliance on hard-metal parts of fixed geometry, and thus can only approximate the benefits of a dream long held by mechanical engineers: infinite variation of the timing, lift, and duration of valve openings to get the best performance across the whole rpm range.
The camless engine would be the latest in a series of changes that have made internal –combustion engines increasingly clean, efficient, and responsive to the driver’s right foot. The camless valve train, which eliminates the mechanical linkage by using a separate controller/actuator to move the valves, allows the optimization of the exhaust and intake valve timing, motion, and activation for individual valve. Various studies have shown that a camless valve train can alleviate many of engine design tradeoffs by supplying extra degrees of freedom to the overall power train system.

WORKING OF PUSH ROD ENGINE

Pushrod engines have been installed in cars since the dawn of the horseless carriage. A pushrod is exactly what its name implies. It is a rod that goes from the camshaft to the top of the cylinder head which push open the valves for the passage of fuel air mixture and exhaust gases. Each cylinder of a pushrod engine has one arm (rocker arm) that operates the valves to bring the fuel air mixture and another arm to control the valve that lets exhaust gas escape after the engine fires. There are several valve train arrangements for a pushrod.

Crankshaft
Crankshaft is the engine component from which the power is taken. It receives the power from the connecting rods in the designated sequence for onward transmission to the clutch and subsequently to the wheels. The crankshaft assembly includes the crankshaft and bearings, the flywheel, vibration damper, sprocket or gear to drive camshaft and oil seals at the front and rear.

Camshaft
The camshaft provides a means of actuating the opening and controlling the period before closing, both for the inlet as well as the exhaust valves, it also provides a drive for the ignition distributor and the mechanical fuel pump.

The camshaft consists of a number of cams at suitable angular positions for operating the valves at approximate timings relative to the piston movement and in the sequence according to the selected firing order. There are two lobes on the camshaft for each cylinder of the engine; one to operate the intake valve and the other to operate the exhaust valve.
Working

When the crank shat turn the cam shaft the cam lobs come up under the valve lifter and cause the lifter to move upwards. The upward push is carried by the pushrods through the rocker arm. The rocker arm is pushed by the pushrod, the other end moves down. This pushes down on the valve stem and cause it to move down thus opening the port. When the cam lobe moves out from under the valve lifter, the valve spring pulls the valve back upon its seat. At the same time stem pushes up on the rocker arm, forcing it to rock back. This pushes the push rods and the valve lifter down, thus closing the valve. The figure-1,2 shows cam-valve arrangement in conventional engines

Figure-1 Figure-2
Single cam and valve conventional valve train mechanism

Since the timing of the engine is dependent on the shape of the cam lobes and the rotational velocity of the camshaft, engineers must make decisions early in the automobile development process that affect the engine’s performance. The resulting design represents a compromise between fuel efficiency and engine power. Since maximum efficiency and maximum power require unique timing characteristics, the cam design must compromise between the two extremes.
This compromise is a prime consideration when consumers purchase automobiles. Some individuals value power and lean toward the purchase of a high performance sports car or towing capable trucks, while others value fuel economy and vehicles that will provide more miles per gallon.
Recognizing this compromise, automobile manufacturers have been attempting to provide vehicles capable of cylinder deactivation, variable valve timing (VVT), or variable camshaft timing (VCT). These new designs are mostly mechanical in nature. Although they do provide an increased level of sophistication, most are still limited to discrete valve timing changes over a limited range.

AN OVERVIEW OF CAMLESS ENGINE

To eliminate the cam, camshaft and other connected mechanisms, the
Camless engine makes use of three vital components – the sensors, the electronic control unit and the actuator

Mainly five sensors are used in connection with the valve operation. One for sensing the speed of the engine, one for sensing the load on the engine, exhaust gas sensor, valve position sensor and current sensor. The sensors will send signals to the electronic control unit.

The electronic control unit consists of a microprocessor, which is provided with a software algorithm. The microprocessor issues signals to the solid-state circuitry based on this algorithm, which in turn controls the actuator, to function according to the requirements.
Camless valve train

In the past, electro hydraulic camless systems were created primarily as research tools permitting quick simulation of a wide variety of cam profiles. For example, systems with precise modulation of a hydraulic actuator position in order to obtain a desired engine valve lift versus time characteristic, thus simulating the output of different camshafts. In such systems the issue of energy consumption is often unimportant. The system described here has been conceived for use in production engines. It was, therefore, very important to minimize the hydraulic energy consumption.

Hydraulic pendulum

The Electro hydraulic Camless Valve train, (ECV) provides continuously variable control of engine valve timing, lift, and velocity. It uses neither cams nor springs. It exploits the elastic properties of a compressed hydraulic fluid, which, acting as a liquid spring, accelerates and decelerates each engine valve during its opening and closing motions. This is the principle of the hydraulic pendulum. Like a mechanical pendulum," the hydraulic pendulum involves conversion of potential energy into kinetic energy and, then, back into potential energy with minimal energy loss". During acceleration, potential energy of the fluid is converted into kinetic energy of the valve. During deceleration, the energy of the valve motion is returned to the fluid. This takes place both during valve opening and closing. Recuperation of kinetic energy is the key to the low energy consumption of this system.. Figure 7 illustrates the hydraulic pendulum concept. The system incorporates high and low-pressure reservoirs. A small double-acting piston is fixed to the top of the engine valve that rides in a sleeve. The volume above the piston can be connected either to a high- or a low-pressure source. The volume below the piston is constantly connected to the high-pressure source. The pressure area above the piston is significantly larger than the pressure area below the piston. The engine valve opening is controlled by a high-pressure solenoid valve that is open during the engine valve acceleration and closed during deceleration. Opening and closing of a low-pressure solenoid valve controls the valve closing. The system also includes high and low-pressure check valves.

Figure 7. Hydraulic Pendulum.

During the valve opening, the high-pressure solenoid valve is open, and the net pressure force pushing on the double-acting piston accelerates the engine valve downward. When the solenoid valve closes, pressure above the piston drops, and the piston decelerates pushing the fluid from the lower volume back into the high-pressure reservoir. Low-pressure fluid flowing through the low-pressure check valve fills the volume above the piston during deceleration. When the downward motion of the valve stops, the check valve closes, and the engine valve remains locked in open position. The process of the valve closing is similar, in principle, to that of the valve opening. The low-pressure solenoid valve opens, the pressure above the piston drops to the level in the low pressure reservoir, and the net pressure force acting on the piston accelerates the engine valve upward. Then the solenoid valve closes, pressure above the piston rises, and the piston decelerates pushing the fluid from the volume above it through the high-pressure check valve back into the high-pressure reservoir. The hydraulic pendulum is a spring less system. Figure 8 shows idealized graphs of acceleration, velocity and valve lift versus time for the hydraulic pendulum system. Thanks to the absence of springs, the valve moves with constant acceleration and deceleration. This permits to perform the required valve motion with much smaller net driving force, than in systems which use springs. The advantage is further amplified by the fact that in the spring less system the engine valve is the only moving mechanical mass. To minimize the constant driving force in the hydraulic pendulum the opening and closing accelerations and decelerations must be equal (symmetric pendulum).

Figure 8. Dynamic characteristics of hydraulic pendulum.

Valve opening and closing

A more detailed step-by-step illustration of the valve opening and closing process is given in Figure 9. It is a six-step diagram, and in each step an analogy to a mechanical pendulum is shown. In Step 1 the opening (high-pressure) solenoid valve is opened, and the high-pressure fluid enters the volume above the valve piston. The pressure above and below the piston become equal, but, because of the difference in the pressure areas, the constant net hydraulic force is directed downward. It opens the valve and accelerates it in the direction of opening. The other solenoid valve and the two check valves remain closed. In Step 2 the opening solenoid valve closes and the pressure above the piston drops, but the engine valve continues its downward movement due to its momentum. The low-pressure check valve opens and the volume above the piston is filled with the low-pressure fluid. The downward motion of the piston pumps the high-pressure fluid from the volume below the piston back into the high-pressure rail. This recovers some of the energy that was previously spent to accelerate the valve. The ratio of the high and low-pressures is selected so, that the net pressure force is directed upward and the valve decelerates until it exhausts its kinetic energy and its motion stops. At this point, the opening check valve closes, and the fluid above the piston is trapped. This prevents the return motion of the piston, and the engine valve remains fixed in its open position trapped by hydraulic pressures on both sides of the piston. This situation is illustrated in Step 3, which is the open dwell position. The engine valve remains in the open dwell position as long as necessary. Step 4 illustrates the beginning of the valve closing. The closing (low-pressure) solenoid valve opens and connects the volume above the piston with the low-pressure rail. The net pressure force is directed upward and the engine valve accelerates in the direction of closing, pumping the fluid from the upper volume back into the low-pressure reservoir. The other solenoid valve and both check valves remain closed during acceleration. In Step 5 the closing solenoid valve closes and the upper volume is disconnected from the low-pressure rail, but the engine valve continues its upward motion due to its momentum. Rising pressure in the upper volume opens the high-pressure check valve that connects this volume with the high-pressure reservoir. The upward motion of the valve piston pumps the fluid from the volume above the piston into the high-pressure reservoir, while the increasing volume below the piston is filled with fluid from the same reservoir. Since the change of volume below the piston is only a fraction of that above the piston, the net flow of the fluid is into the high-pressure reservoir. Again, as it was the case during the valve opening, energy recovery takes place. Thus, in this system the energy recovery takes place twice each valve event. When the valve exhausts its kinetic energy, its motion stops, and the check valve closes. Ideally, this should always coincide with the valve seating on its seat. This, however, is difficult to accomplish. A more practical solution is to bring the valve to a complete stop a fraction of a millimeter before it reaches the valve seat and then, briefly open the closing solenoid valve again. This again connects the upper volume with the however, is difficult to accomplish. A more practical solution is to bring the valve to a complete stop a fraction of a millimeter before it reaches the valve seat and then, briefly open the closing solenoid valve again. This again connects the upper volume with the low-pressure reservoir, and the high pressure in the lower volume brings the valve to its fully closed position. Step 6 illustrates the valve seating. After that, the closing solenoid valve is deactivated again. For the rest of the cycle both solenoid valves and both check valves are closed, the pressure above the valve piston is equal to the pressure in the low-pressure reservoir, and the high pressure below the piston keeps the engine valve firmly closed.

Valve motion control

Varying the activation timing of both solenoids varies the timing of the engine valve opening and closing. This, of course, also vanes the valve event duration. Valve lift can be controlled by varying the duration of the solenoid voltage pulse. Changing the high pressure permits control of the valve acceleration, velocity, and travel time. The valve can be deactivated during engine operation by simply deactivating the pair of solenoids which control it. Deactivation can last any number of cycles and be as short, as one cycle.
Increasing the number of valves in each cylinder does not require a corresponding increase in the number of solenoid valves. The same pair of solenoid valves, which controls a single valve, can also control several valves running in-parallel. Thus, in a four-valve engine a pair of solenoid valves operates two synchronously running intake valves, and another pair runs the two exhaust valves.

UNEQUAL LIFT MODIFIER - In a four-valve engine an actuator set consisting of two solenoid valves and two check valves controls the operation of a pair of intake or a pair of exhaust valves. Solenoids and check valves are connected to a common control chamber serving both valves (Figure 10). In a four-cylinder engine there is a total of eight control chambers connected to eight pairs of valves. For each pair, the volumes below the hydraulic pistons are connected to the high pressure reservoir via a device called the lift modifier. In a neutral position the modifier does not affect the motion of the valves, and activation of the solenoid valves moves both engine valves in unison
.
Figure 10. Paired valves with unequal lift control.

To enhance the ability to vary the intake air motion in the engine cylinder, it is often desirable to have unequal lift of the two intake valves, or even to keep one of the two valves closed while the other opens. In some cases it may also be used for paired exhaust valves. The lift modifier is then used to restrict the opening of one the paired valves. The modifier is shown schematically in Figure 11 as a Rotating rod with its axis of rotation perpendicular to the plane of the drawing. The rod is installed in the cylinder head between the two intake valves. A cutout in the rod forms a communication chamber connected to the volumes below the hydraulic pistons of both intake valves. The communication chamber is always connected to the high pressure reservoir. In the case A the modifier is in the neutral position, and both valves operate in unison. In the case B the modifier rod is shown turned 90 degrees clockwise. The exit of oil from the volume below the hydraulic piston in the valve No. 1 is blocked and the valve cannot move in the direction of opening. However, the entry of oil into the volume below the hydraulic piston is permitted by a one-way valve installed in the modifier rod. This guarantees that, whenever deactivation takes place, the valve No. 1 will close and remain closed, while the valve No.2 continues its normal operation. If the modifier rod is turned 90 degrees counter-clockwise (from the position shown in the case A), the valve No.2 is deactivated, while the valve No. 1 would continue normal operation. In the case C the lift of one of the valves is reduced relative to the second one. The rod is turned a smaller angle so that the exit of oil from the valve No. 1 into the communication chamber is not completely blocked, but the flow is significantly throttled. As a result, the motion of the valve No. 1 is slowed down and its lift is less than that of the valve No.2. Varying the angular position of the modifier rod 26 varies the degree of oil throttling, thus varying the lift of the valve No. 1.

Figure 11. Unequal lift control.

DESIGN APPROACH FOR CAMLESS ENGINE

The camless engine was created on the basis of an existing four-cylinder, four-valve engine. The original cylinder head with all the valves, springs, camshafts, etc. was replaced by a new cylinder head assembly fully integrated with the camless valvetrain. The camshaft drive was eliminated, and a belt-driven hydraulic pump was added. There was no need for lubrication, and the access for engine oil from the engine block to the cylinder head was closed off. No other changes to the engine have been made.

Cylinder head

Two cross sections of the cylinder head are shown in Figure 12. The aluminum casting is within the original confines and contains all hydraulic passages connecting the system components. The high- and low-pressure hydraulic reservoirs are integrated into the casting. The reservoirs and the passages occupy the upper levels of the cylinder head and are part of the hydraulic system. The hydraulic fluid is completely separated from the engine oil system. A finite element analysis was used to assure the cylinder head integrity for fluid pressures of up to 9 MPa. The lower level of the head contains the engine coolant.

Figure 12. Cross sections of cylinder head.

Figure 13. Cylinder head with cover removed.

The engine valves, the check valves and the modifiers are completely buried in the body of the head. The solenoid valves are installed on the top of the cylinder head and are kept in their proper locations by a cylinder head cover. Hydraulic and electric connections leading to the hydraulic pump and the electronic controller, respectively, are at the back end of the cylinder head. The height of the head assembly is approximately 50 mm lower than the height of the base engine head. Figure 13 is a photograph of the head on the engine with the head cover removed. 27

COMPONENTS OF CAMLESS ENGINE

Main components of a camless engine are-Engine valve, solenoid valve, high pressure pump, low pressure pump, cool down accumulator, etc.

Engine valve – A cross section of the engine valve assembly is shown in Figure 14. The valve piston is attached to the top of the valve, and both the valve and the piston can slide inside a sleeve. The sleeve openings above and below the valve piston allow the hydraulic fluid to enter and exit. A seal in the lower part of the sleeve prevents leakage of fluid into the intake or exhaust port. A leak-off (not shown) unloads the seal from excessive pressure, which otherwise increases friction. There is a tight hydraulic clearance between the valve and the sleeve. However, the clearance between the sleeve and the cylinder head is relatively large, which improves the centering of the valve in its seat Circulation of hydraulic fluid through the chambers above and below the valve piston cools and lubricates the valve. All the forces acting on the valve are directed along its axis. Absence of side forces reduces stresses, friction and wear.

Figure 14. Engine valve
Solenoid valve – Figure 15 shows a cross section of the solenoid valve. The solenoid has conically shaped magnetic poles. This reduces the air gap at a given stroke. The normally-closed valve is hydraulically balanced during its movement. Only a slight unbalance exists in the fully-open and the fully-closed positions. A strong spring is needed to obtain quick closing time and low leakage between activations. The hydraulic energy loss is the greatest during the closing of either the high- or the low-pressure solenoid, because it occurs during the highest piston velocity. Thus, the faster the solenoid closure, the better the energy recovery. The valve lift and the seat diameter are selected to minimize the hydraulic loss with a large volume of fluid delivered during each opening. Both high-pressure and low-pressure solenoid valves are of the same design.

Figure 15. Solenoid valve.

Lift modifier - The design of the lift modifier permits a simultaneous hydraulic control of a group of modifiers with a single pulse-width modulated solenoid-valve that adjusts the pressure in a control gallery.

Hydraulic system

A diagram of the hydraulic system is shown in Figure 16. An engine-driven variable-displacement pump automatically adjusts its output to maintain the required pressure. The high-pressure and the low-pressure reservoirs are connected to all corresponding locations serving the high- and the low-pressure solenoids and the check valves.

Figure 16. Hydraulic System.

High pressure pump: the quantity of fluid delivered by the high pressure pump with the actual needs of the system at various engine speeds and loads is critical to assuring low energy consumption. To conserve the mechanical power needed to drive the pump, its hydraulic output should closely match the needs. A variable displacement, high efficiency, axial plunger-type pump was initially selected for that reason. Taking into account the prohibitively high cost of such pump for automotive applications, a low-cost variable capacity pump was conceived. A cross section of the pump is shown in Figure 17. The pump has a single eccentric-driven plunger and a single normally-open solenoid valve. During each down stroke of the plunger the solenoid valve is open, and the plunger barrel is filled with hydraulic fluid from the low pressure branch of the system. During the upstroke of the plunger, the fluid is pushed back into the low pressure branch, as long as the solenoid valve remains open. Closing the solenoid valve causes the plunger to pump the fluid through a check valve into the high pressure branch of the system. Varying the duration of the solenoid voltage pulse varies the quantity of the high-pressure fluid delivered by the pump during each revolution.

Figure 17. High pressure pump.

Low pressure pump - A small electrically driven pump picks up oil from the sump and delivers it to the inlet of the main pump. Only a small quantity of oil is required to compensate for the leakage through the leak-off passage, and to assure an adequate inlet pressure for the main pump. Any excess oil pumped by the small pump returns to the sump through a low-pressure regulator. A check valve 1 assures that the inlet to the main pump is not subjected to pressure fluctuations that occur in the low-pressure reservoir.

Cool down accumulator - The system also includes a cool-down accumulator that, during normal operation, is fully charged with oil under the same pressure as in the inlet to the main pump. When the engine stops running, the oil in both the high- and the low-pressure branches cools off and shrinks. As the system pressure drops, the accumulator discharges oil into the system, thus compensating for the shrinkage and preventing formation of pockets of oil vapor. The high-pressure branch is fed from the accumulator through a check valve 2 that is installed in-parallel to the main pump. The low-pressure branch is fed through an orifice that is installed in-parallel to the check valve 1. The orifice is small enough to prevent pressure wave propagation through it during each engine cycle, but sufficient to permit slow flow of oil from the accumulator to the reservoir. In some applications, the orifice can be incorporated directly in the check valve. After the oil in the system has cooled off, the accumulator maintains the system at above atmospheric pressure by continuously replenishing the oil that slowly leaks out through the leak-off passage. When the engine is restarted, the accumulator is recharged again. If the engine is not restarted for a very long time, as it is the case when a vehicle is left in a long-term parking, the accumulator will eventually become fully discharged. In that case, the pressure in the accumulator drops to an unacceptable level, and a pressure sensor, that monitors the accumulator pressure, sends a signal to the engine control system which reactivates the electric pump for a short period of time to recharge the accumulator. This process can be repeated many times, thus maintaining the system under a low level of pressure until the engine is restarted. After the engine restarts it takes less than one revolution of the main pump to restore the high pressure. Operating the hydraulic system in a closed loop contributes to low energy consumption. The amount of hydraulic power consumed by the system is determined by the flow of fluid from the high- to the low-pressure reservoir times the pressure differential between the outlet from and the inlet to the high pressure pump. A small loss is also associated with leakage. There are good reasons to use high hydraulic pressure in the system, one of them being the need to maintain a high value of the bulk modulus of the oil. In a closed-loop system the pressure in the low-pressure reservoir can also be quite high, although lower than in the high-pressure reservoir (thus the pressure in the low-pressure rail is low only in relative terms). Hence, the system can operate with very high hydraulic pressure, and yet the energy consumption remains modest due to a relatively low pressure differential. The ratio of high pressure to low pressure must be sufficiently higher than the ratios of the pressure areas above and below the valve piston to assure reliable engine valve closure.

TESTING AND DEVELOPMENT

The development of the camless valve train is a gradual process, involving design, testing, evaluation, and redesign of various components and subsystems. The initial laboratory testing was conducted with a single-valve test installation and was intended to verify the ability of the system to operate reliably and repeatable at wide range of speeds and valve lifts and event durations. Figure 18 illustrates a 9 mm valve lift obtained in a test fixture at a given crank angle duration and 1500, 4000 and 8000 engine rpm. The high pressure was selected to assure a sufficiently fast motion of the valves at the maximum engine speed. As the speed is reduced the lift profile becomes trapezoidal with progressively steeper slopes. Testing and development of a system with two intake or two exhaust valves running in parallel was dedicated primarily to developing independent lift control for each individual valve. Since the two valves are controlled by the same pair of solenoids, the nominal lift of both valves is determined by the solenoid voltage-pulse duration. The action of the lift modifier is superimposed over the solenoid action and permits an independent and continuously variable reduction of lift for either of the paired valves, while the other valve remains at the computer controlled lift. Figure 19 shows the traces of two hydraulically-paired valves with maximum lift set to 4 mm. The valves are operated in the near synchronous mode (bottom), or with a small reduction of one of the lifts (middle), or with a nearly deactivated lift (top).

Figure 18. Lift traces of engine valve.

Figure 19. Traces of unequally set lifts.
A substantial amount of work was devoted to obtaining a quiet seating of engine valves. The previously described hydraulic pendulum was capable of producing the quiet seating only with a high precious of lift control and low cycle-to-cycle lift variability. However, a small deviation from a finely-tuned low-noise operation resulted in a noisy operation. As a practical solution, a hydraulic snubbing action was introduced. The snubbing takes place in the last 0.2 - 0.4 mm of closing and reduces the sensitivity to seating control parameters with minimum interference with hydraulic energy recovery (Figure 20). This keeps the valve seating velocity at 0.1 m/s or less.

Figure 20. Quiet seating control.

At the time of preparation of this paper only a limited amount of engine dynamometer testing has been conducted on a firing engine. Figure 21 shows part-load pressure-volume diagrams obtained with conventional and late intake valve closing. At 1500 rpm and 4 bar IMEP the engine ran essentially unthrottled. A number of system improvements are planned for the near future. The cylinder head structure will be reinforced to handle higher hydraulic pressures. This will allow to minimize the effect of air content in the fluid on the bulk modulus. The pressures in both the high- and the low-pressure reservoirs will be increased by equal amounts in order not to increase the hydraulic energy consumption. The control chamber volume will be minimized, and the performance of the hydraulic pendulum optimized to increase the hydraulic energy efficiency. Solenoid and driver circuit optimization is also planned.

Figure 21. Pressure-Volume Diagram.

ADVANTAGES OF CAMLESS ENGINE

` Electro hydraulic camless valve train offers a continuously variable and independent control of all aspects of valve motion. This is a significant advancement over the conventional mechanical valve train. It brings about a system that allows independent scheduling of valve lift, valve open duration, and placement of the event in the engine cycle, thus creating an engine with a totally uncompromised operation. Additionally, the ECV system is capable of controlling the valve velocity, perform selective valve deactivation, and vary the activation frequency. It also offers advantages in packaging. Freedom to optimize all parameters of valve motion for each engine operating condition without compromise is expected to result in better fuel economy, higher torque and power, improved idle stability, lower exhaust emissions and a number of other benefits and possibilities. Camless engines have a number of advantages over conventional engines.
In a conventional engine, the camshaft controls intake and exhaust valves. Valve timing, valve lift, and event duration are all fixed values specific to the camshaft design. The cams always open and close the valves at the same precise moment in each cylinder’s constantly repeated cycle of fuel-air intake, compression, combustion, and exhaust. They do so regardless of whether the engine is idling or spinning at maximum rpm. As a result, engine designers can achieve optimum performance at only one speed. Thus, the camshaft limits engine performance in that timing, lift, and duration cannot be varied.
But in a cam less engine, any engine valve can be opened at any time to any lift position and held for any duration, optimizing engine performance. The valve timing and lift is controlled 100 percent by a microprocessor, which means lift and duration can be changed almost infinitely to suit changing loads and driving 0conditions. The promise is less pollution, better fuel economy and performance.
Another potential benefit is the cam less engine’s fuel savings. Compared to conventional ones, the cam less design can provide a fuel economy of almost 7- 10% by proper and efficient controlling of the valve lifting and valve timing. The implementation of camless design will result in considerable reduction in the engine size and weight. This is achieved by the elimination of conventional camshafts, cams and other mechanical linkages. The elimination of the conventional camshafts, cams and other mechanical linkages in the camless design will result in increased power output.
The better breathing that a camless valve train promotes at low engine speeds can yield 10% to 15% more torque. Camless engines can slash nitrogen oxide, or NOx, pollution by about 30% by trapping some of the exhaust gases in the cylinders before they can escape. Substantially reduced exhaust gas HC emissions during cold start and warm-up operation.
The combustion process can be optimized by changing the composition of the cylinder charge by varying the intake valve opening and exhaust valve-closing timing as a function of load and speed. Under full load conditions the maximum volumetric efficiency is increased by optimized timing for intake valve. Another potential benefit is the elimination of external EGR. The EGR system is used to reduce or NOx emissions. This is achieved by diluting the intake charge with exhaust gas. Due to the absence of oxygen exhaust gas itself will not burn; it lowers the combustion temperature thereby reducing the information of NOx. In the camless design there is no need of external EGR. The intake charge can be diluted by trapping some exhaust gas inside the engine cylinder by the earlier closing of the exhaust valve. For this purpose extra sensors are to be placed in the exhaust manifold to detect the presence of NOx in the exhaust gas.
The most intriguing prospect is momentarily shutting off individual engine cylinders by stopping their fuel supply and cracking open their valves to spoil the compression. It’s a way to save fuel when an engine is running under a light load. The electronics are so fast that it should be able to selectively shut off cylinders in a way that will be imperceptible to the driver.

CONCLUSIONS

1. An electro hydraulic camless valve train was developed for a camless engine. Initial development confirmed its functional ability to control the valve timing, lift, velocity, and event duration, as well as to perform selectively variable deactivation in a four-valve multicylinder engine.
2. The system employs the hydraulic pendulum principle, which contributes to low hydraulic energy consumption.
3. The electro hydraulic valve train is integral with the cylinder head, which lowers the head height and improves the engine packaging.
4. Review of the benefits expected from a camless engine points to substantial improvements in performance, fuel economy, and emissions over and above what is achievable in engines with camshaft-based valve trains.
5. The development of a camless engine with an electro hydraulic valve train described in this report is only a first step towards a complete engine optimization. Further research and development are needed to take full advantage of this system exceptional flexibility.

BIBLIOGRAPHY
• Michael M.Schechter and Michael B.Levin “Camless Engine”
SAE paper 960581
• P. Kreuter, P. Heuser, and M. Schebitz, "Strategies to Impove SI-Engine Performance by Means of Variable Intake Lift, Timing and Duration", SAE paper 920449.
• K. Hatano, k. Lida, H. Higashi, and S. Murata, “Development of a New Multi-Mode Variable Valve Timing Engine”,SAE paper930878
• J-C. Lee, C-W. Lee, and J. Nitkiewitz, “The Application of a Lost Motion VVT System to a DOHC SI Engine”,SAE paper 950816
• John B. Heywood, “Internal combustion engine fundamentals”
• William H. crouse. “Automotive mechanics.”
• John Steven Brader ,A Thesis on Development of a Piezoelectric Controlled Hydraulic Actuator for a Camless Engine
• mwww.machinedesign.com
• www.halfbakery.com
• www.deiselnet.com
• www.greendieseltechnology.co
• www.me.sc.edu

ABSTRACT

An engine with an electro hydraulic camless valve train, capable of total valve motion control, has many advantages other than the conventional engine. The system uses neither cam nor springs, which reduces the engine height and weight Hydraulic forces both open and closes the valves. During valve acceleration, potential energy of compressed fluid is converted into kinetic energy of the valve. During deceleration, the energy of valve motion is returned to the fluid. The System offers a continuously variable and independent control of virtually all parameters of valve motion .This permits optimization of valve events for each operating condition without any compromise.

AUTOMATIC HEAD LIGHT DIPPER UNIT

2010-08-07T05:05:00.002-07:00

INTRODUCTION

The number of vehicles on our roads is burgeoning day by day. This is turn forced almost all this vehicle manufactures to think about the extra safety instruments and electronic controls to attach with these products for giving the users a safety derived in all road conditions through a mass flow traffic. If asked, one should always mention that the right driving is very cumbersome due to the dazzling light problems and the frequent dipping of headlights by manual means that often causes fatigue to the driver particularly at the time of peak traffic. So naturally to get rid of this perennial problem, an automatic mechanism has to come up to dip the headlamp automatically whenever required.
For keeping a motor vehicle under perfect control and reins of the driver, different types of controls and accessories are provided in an automobile around the driver’s seat, on the dashboard and at the footboard. There are controls like clutch, brake pedal, accelerator pedal, and sharing the same importance, the dimmer switch is changed with time, and its pace in the filed of automobile safety is one of the uppermost.
Simply, an automatic dipper is a unit, which can automatically judge when the headlight beam needs to be lowered, and which dip the headlamp from which beam to a dipped beam. As the dipper unit is well connected to the lighting system of the vehicle, we have to look short into the type and construction of a head light before discussing the wiring diagram or the construction of Automatic dippers.

HEADLAMPS

The modern lighting system consists of switches, lamps, wiring harness, and fuses or circuit breakers. It may be mentioned that the primary purpose of the headlight design is to produce illumination over considerable distance ahead of the vehicle and enable the driver to drive at reasonable speeds at night with safety. But the provision should also be made that the drivers of other vehicles coming from the opposite direction to not experience a glare. For this purpose a dipped or meeting beam is also provided for maintaining the reasonable speed with safety without dazzling the coming driver. To prevent dazzle to the on coming driver during particularly misty or hazy conditions the light about the horizontal should be cut off. This is called dipping of the head light beam.
In an average car, the lighting system consumes about 70 – 75% of electrical energy when driven at night. In terms of amperage the consumption may be from 24 – 40 A at night for al purposes including the radio, heater, and transmission controls.
Light Source
There are two kinds of light sources, namely, the one that emits light and the other that reflects light. In the case of headlamp used in automobiles, both the things are combines in A. The filament of the electric lamp is the primary source, while the reflector is referred to as the secondary source. The intensity, colour and distribution are the important characteristics of any light source.
The headlight is composed of three elements:
1. The light filament that gives off light when a current flows through it.
2. The parabolic reflector that reflect the light in front: and
3. The lens that refracts of distorts the light beam into an illuminating pattern.
Construction
The present day headlights are the outcome of a lot of research and development. Earlier a single electric bulb of the carbon filament type was employed. The bulb was placed at the focus of a parabolic silvered reflector in order to give a parallel beam of light. The following figure shows a parabolic reflector with bulb, the lines showing light rays emitted from the filament of the bulb in all directions. This type of headlight given a parallel light beam, that saves greater illumination nearer the axis. It may be mentioned that the bulb itself and the intensity of light fall off towards the outer portion of the beam block a small amount of light.
From figure it may be seen that if the bulb filament is moved from position ‘d’, the focus of reflector, to a position ‘a’, the light beam ‘abc’ will no longer be a parallel one but will become divergent. On the contrary, if the filament is moved to position ‘f’ the beam will take the course a shown by ‘fbg’ and will meet at a point on the axis of the bulb. It may be mentioned that by a single adjustment of the bulb, the beam cane be concentrated at a ore-determined distance ahead of the vehicle in order to give a spot light effect.
Formerly the headlight was provided with certain means of adjusting the bulb holder with respect to the reflector along with the bulb axis in order to focus it. It had to be done up every time the bulb was changed. This was essential, otherwise it would cause increased dazzle to other motorists. The filament is encased in an airtight bulb in order to prevent burning up of the white-hot filament because of oxygen in the air. The reflector is generally of polished metal and it throws all the light rays into a cylindrical beam.
The lens is made up of a number of glass prisms molded together and they bend the beam of light into an oval pattern which is aimed ahead of the vehicle and somewhat in the downward direction. A part of the light is spread out in front of the vehicle for providing local illumination, whereas the rest of it is focused into a hot spot that provides distant illumination.
The first major advancement in headlight design took place with the introduction of pre-focused bulbs. It has two filaments, one for normal driving and the other for city driving or for overtaking. These days even two sets of headlights are used for the above said purposes. Generally a foot selector switch is provided, which enables the driver to select either the normal driving or the passing beam.

The parabolic reflector showing light
rays emitted from the filament of the bulb

The effect of changing the position of
filament on the nature of the light beam

Sealed-Beam Headlights
In a sealed beam headlight, the filament and the reflector along with the lens are sealed in an airtight unit. The front face of the sealed beam unit is a lens, which is fused to the reflector after the two filament units, has been inserted through the center of the reflector and sealed in position. The complete unit is then evaluated and filled with inert gas. With these units the only service required is to aim them. This type of headlight introduced in 1940 in the U.S.A.
Sealed beam headlights have the following advantages:
1. The glass unit is self-contained with accurately focused filaments.
2. Dust, moisture, etc. are prevented from entering from the back of the lens and the reflector.
3. A greater amount of light is provided in the beam because, of the absence of a filament bulb and
4. The beam of light obtained is greatly improved due to the pre-focused filament and permanently bright reflector.
It is essential to have a provision for horizontal and vertical adjustment of the beam by titling the sealed beam unit in its body housing. Two adjusting screws, as shown in the following figure, generally do it. Fig. shows an improved version of a selected beam unit with the provision of a metal mask or shield in front of the upper filament to prevent stray light rays from escaping upwards and reflecting back to the eyes of the driver. This type of headlights gives a brighter beam pattern and further reduces the repair and maintenance time. Such type of units are, however, more expensive or replace than plain or pre-focused type of units. Recently headlights of 50-60 W for the lower filament and 40-45 for the upper filament have been used, thus increasing their light output.

Control of Headlight Beam
The circular beam can be spread horizontally to any desired extent with the help of prisms, molded in the inside of the headlight cover glass, as shown in the figure. The horizontal light intensity can be controlled in any desired way by a suitable design of the headlight. The circular beam can also be controlled in the vertical direction with the help of prisms molded in front of the glass, thus redirecting the light rays in the downward direction. This way the downward reflected beam does not obstruct the vision of the other road users coming from the opposite side. With these two combinations, any required main beam illumination, combined with side illumination nearer to the vehicle can be produced.

RECENT DEVELOPMENTS

Technology improves day and day in the field of automobile headlamp construction and it left out the earlier single electric bulb of the carbon filament type and in place modern sealed beam headlights are using nowadays. The light circuits of today’s vehicles can consist of more that 50 light bulbs and hundreds of feet of wiring. Incorporated within these circuits are circuits’ protector, relays, switches lamps, and connectors. In addition more sophisticated lighting systems use computers and sensors. The lighting circuit consists of an array of interior and exterior lights, courtesy lights and so on. Federal laws largely regulate the lighting circuits, so the systems are similar between the various manufactures.

Halogen lamps

The halogen lamps are mostly introduced and consist of tungsten filaments in the atmosphere of some halogen element such as chlorine, bromine, or iodine. The tungsten evaporated from the filaments reacts with halogen gas to form tungsten halide, which is decomposed back into halogen and tungsten due to high temperature at the filaments, thus causing the tungsten to get redeposit on the filaments. In this way the life of the bulb is increased.

Besides, the filament can operate at still higher temperature, which increases its light intensity. However, the halogen attacks metals at cold temperatures. Thus other metals within the enclosure, viz. the metal shield and the second filament, which is not being used, are attacked by the halogen. To avoid this happening, pure halogen is replaced by dibromomethane gas, which does not cause deterioration of the cold metals. With these headlamps quartz glass is used since ordinary glass tends to crack due to higher operating temperature.

Composite headlights

Many of today’s vehicles have a halogen head light system using a replaceable bulb. This system is called composite headlights. By using the composite headlight system, vehicle manufacturers are able to produce any style of headlight lens by desire. This improves the aerodynamics, duel economy, and styling of the vehicle. Many manufacturers vent the composite headlight housing because of the increased amount of the heat developed by these bulbs. Because the housing is vented, condensation is not harmful to the bulb and does not affect the headlight operation. When the headlights are turned on, the heat generated from the halogen bulbs will dissipate the condensation quickly. On systems using non-vented composite headlights, condensation is not considered normal. The assembly should be replaced.

HID Headlamps

High Intensity Discharge (HID) headlamps are the latest headlight development. These headlamps put out three times more light and twice spread on the road then conventional halogen headlamps. They also use about two-thirds less power to operate will last two to three times larger. HID lamps produce light in tooth ultraviolet and visible wavelengths. This advantage allows highway signs and other reflective materials to glow. This type lamp first appeared on select models from BMW in 1993, Ford in 1995, and Porche in 1996.

These lamps do not relay on growing filament for light. Rather light is provided as a high voltage bridges an air gap between two electrodes. The presence of inert gas amplifies the light given off by the arching. More than 15,000 volts are used to jump the gap between the electrodes. To provide this voltage, only about 80 volts is required to keep current flow across the gap. The great light output of these lamps allows the headlamp assembly to be smaller and lighter. These advantages allow designers more flexibility in body designs as they attempt to make their vehicles more aerodynamic and efficient.

HEADLIGHT DAZZLE

The dazzle effect is one of the major problems faced by a driver in night driving. So one has to stop the high intensity light from the eyes of the incoming driver or road users to prevent the dazzle effect. Automatic Dipper is one such mechanism, which is employed for safety night driving without the intense dazzling effects. Without much efforts from the driver which otherwise has to dim the lights every seconds by manual means may lead to fatigue to the driver especially during peak traffics. So it will be better to know ‘what is meant by dazzle?’ and ‘what all devices are often used in preventing dazzle effect?’ before mentioning the advantages and uses of an auto dipper.

The problem of headlight dazzle is linked with many factors of which, the human eyes is the most important. In fact, it is the final judge in respect of dazzle and illumination. It may be mentioned that for driving, bright illumination is essential. In short, condition of illumination, should be such that there is clear vision for all motorists. Dazzle is nothing but brightness, which causes interference with vision. The various factors, which govern it, are: brightness, contrast, and the angle subtended by the bright area on the eye. It is the contrast between the bright and dark areas, which is one of the main causes of dazzle. However, it is difficult to lay down in terms of quantity the fixed ratio of the brightness of the two areas which is likely to produce or eliminate the effect of dazzle since it is controlled by the brightness of the lighter of the two areas. The ratio between the absolute black area and a dimly lit area may be quite great but there will be no dazzle effect. Further, an intensity bright area with very dark surroundings, does not give a dazzling effect.
The dazzling effect can be prevented by,
• Reducing the brightness of the headlights of the vehicles.
• Stopping high intensity light from entering the yes of on-coming drivers or road users.
• Reducing the contrast between the surrounding area and the headlight of the vehicle.

DIPPING OF HEADLIGHTS

When the vehicle is driven on the highways, it is required that light beam should be of high density and should illuminate the road at a distance sufficiently ahead. However when a vehicle coming in the opposite direction approaches a vehicle fitted with such headlights, driver of that vehicle will experience a glare, which will blind him. To avoid this, a separate filament is fitted at such a position that that light beam from this filament is deflected both down and sideways so that the driver of the oncoming car is not blinded. Some of the ways in which this can be achieved are shown in the following figure.

The main filament may be placed at the focus with the dipper filament slightly above it or the main filament and the dipper filament may be placed slightly below and above the focus respectively, with the reflector tilted. Another popular method is to place the main filament at the focus and the dipper filament slightly in front of the same with a mental shield placed below the dipper filament. In this only this upper half of converging beam comes out of the reflector. Thus it prevents the other rays from setting reflected from the lower half of the reflector and emerging in the upward direction to cause glare. The beam (main or dipper) are selected by the driver y means of a foot operated or steering column mounted stick type dimmer switch but in case of automatic dippers the light from the oncoming vehicle will trigger the dipper unit. The illumination of road by main bam and the dipper beam is shown in the above figure.

Bifocal Bulb

In the earlier days, a dipping reflector was used as one of the popular anti-dazzle devices. In this case, the movement of the reflector within the headlight casing dipped the headlight beam. The solenoid, mounted at the back of the reflector, controlled the movement of the reflector.

The bifocal both is an extensively used anti-dazzle device in the U.S.A and the U.K this type of both has two filaments, one being either in front of or above the other filament. The following figure shows this type of a bulb.

It will be seen that a metal shield is provided below the forward filament. Its main purpose is to prevent the light rays from the filament striking the lower half of the reflector. Switching over from one filament to the other may provide the normal and dipped beams. The figure & shows the manner in which the headlight beam is dipped while changing over the normal to the dipped beam. The bifocal bulb is simple in installation and is also an effective method of dipping the beam of the headlight.

Two Filament Bulbs

In two filaments modern headlights there uses a two-filament bulb with a fixed reflector. In this case, one filament is meant for the dipping beam and the other main beam filament is beneath it and it is located at the focus of the reflector. The nature of the dipped beam can be controlled by the help of prisons and lenses provided at the front cover of the headlight.

Anti-dazzle Devices
Most of the modern anti dazzle devices depend upon the redirection of the light rays. This can be achieved by various ways as by lenses, by specially designed reflectors, by bulbs of special design or by dipping reflector mechanisms. Now it is common practice to control the beam from the driver’s seat, as and when required. If the initial focusing of the lamp is correct, the dazzle effect is considerably reduced and at the same time it provides sufficient illumination for the driver.

In the case, the upper and the lower levels of the reflector are displaced by an amount equal to the filament length. It results in projection of light rays parallel and downwards and not upwards. It may be noted the correct focusing of the filament with respect to the two halves of the reflector will greatly help in the elimination of these upward rays.

Methods of getting dipped beams Bifocal bulb and the manner in which the headlight beam is dipped

A double – filament lamp

AUTOMATIC DIPPER (AUTRONIC DYE)

Autronic dipper

An autronic dipper is a unit which can automatically judge when the head light beam needs to be lowered. The auto dippers are basically switches, which dip the headlamp from high beam to a dipped beam if a certain amount of light falls on its photo sensor. This is a system, which electronically selects the proper headlamp beam for country driving. It holds the lights on upper, or high, beam until a car trigger the system so that it shifts the headlamps to the lower beam. When the other car had passed, the system electronically shifts the headlamps back to the upper beam.

Location

As the operation of the auto dipper trigger out only when the light from the on-coming vehicles falls directly on the photo sensor unit, it has to be ideally located in a place where the light beams can freely entered without any obstruction. Commonly auto dipper meters from the ground. The suggested position for passenger cars is in the place between windshield and rear position f cabin rear view mirror.

Applications

Some American manufactures have first used photoelectric cells for automatic dipping of headlights. In the ‘Autronic Eye’, the photoelectric cell senses the intensity of light from the oncoming vehicles and dips the heedful accordingly; the driver does not have to control the headlights. This type of system is very successful on American roads. But on Indian roads with frequent curves etc., especially in case of rural areas and with non-uniform light intensities automatic dipper has got not much use. But in high way driving through level straight roads having a large number of vehicles and without having sharp turns etc., the automatic dipper helps the drivers in eliminating the fatigue of operating the dipper switch intensity level will always be there for satisfying he minimum intensity needed for the system to function even on small breathing turns which is often seen in high ways.

Possibility of Manual Override

As the automatic dipper is particularly designed and good for the high way driving, but the vehicle is meant for all type of roads, and for facing some particular situation where the driver needs more light to see by etc., manual override is also fitted with the automatic dipper unit by which the driver can operate the heedful becomes manually leaving out the auto system inoperative. The driver has a sensitivity control, which allows adjustment of the system to the surrounding light.

The override system can be used when the oncoming driver does not dim, the driver needs more light to see by and also on rural road where not much vehicles are there at night and also sharp turns are there.

WORKING OF AUTO DIPPER

Automatic headlight dipping automatically switches the headlight from high beam to beams when light from oncoming vehicle strikes the photocell or phototube (Photo amplifier) of the vehicle. Thus we can select the proper headlight during country driving and it saves the driver from the trouble of depressing the foot switch for lowering this headlight beam. It holds the lights on the upper beam until the vehicle approaches from the other direction. And also the moment the other car passes by, it shifts automatically the headlights back to upper beam. The auto dipper is a device, which is highly immune to lights from street lamps, roadside light sources and other manual sources of light.

Modern automatic dipping systems use solid-state circuiting and electromagnet relays to control the beam switching. Most systems consist of the following major components.
1. Light sensitive photocell
2. High-low beam relay
3. Sensitivity control
4. Amplifier
5. Dimmer and auxiliary foot switch
6. Wiring harness.

We can analyze the working of the system by considering the following schematic circuit diagram of the auto-dipper.

The phototube is a variable resistor that used light to change the existence. The phototube amplifier is usually mounted behind the front grill or on the one side of the dashboard or in the rear view mirror support where it will be in limn with the light from the vehicle approaching from the opposite direction. The sensitivity control sets the intensity level at which the photocell amplifier will energize. This control of set by the driver and is located next to, or is a part of, the headlight switch assembly. The sensitivity control is a potentiometer that allows the driver to adjust the sensitivity of the automatic dipper (dimmer) system to surrounding ambient light conditions. The driver is able to adjust the sensitivity level of the system by rotating the control knob. An increase in the sensitivity level will make the headlights switch to the low beams sooner (approaching vehicle is further away). A decrease in the sensitivity level will switch the headlight to low beams when the approaching vehicle is closer. If the knob is located at full counter clockwise position, the system enters manual override. The high-low rely is a single pole, double throw unit that provides the switching of the headlight beams.

When the light from the oncoming strikes the light sensitive plate provided in it, an electric current is released. When the oncoming vehicle is nearing, its strong light sets the amplifier unit into operation. A special electronic tube is contained in the amplifier unit know as thyraton, which amplifies the current entering its grid. The thyraton greatly amplifies the current provided by the phototube. It becomes strong enough to put the power relay unit into operation.

Schematic Circuit Diagram of an Autronic Eye

The windings of the power relay are connected to the thyraton. There are two sets of points provided when the upper contacts are closed, the high filament of the headlight is connected to the battery. When the lower contacts are closed, the low filaments are connected to the battery. Depending upon the strength f the current from the thyraton, the points open and close lighting the upper or lower beam.

An auxiliary foot switches also provided in addition to this arrangement which this the driver can hold the upper beam on, even though the auto-dipper has operated, this shifting the headlights to the lower beam. This switch is used when signaling to the other motorists.

The above figure shows the simplified schematic diagram of the auto-dipper (autronic eye). The switches, resistance units, and other components are not shown. The curve in the phototube indicates the light sensitive plate. The dotted line in the thyraton unit indicates the grid.

CONCLUSION

Newer and better technologies always come with time and it will help in reducing the manual labor and difficulties in the sectors where it is made use. And in our case, the auto dipper can perform a great deal in reducing the manual efforts and fatigue of drivers in dipping the headlamp frequently while driving through highways full of moving vehicles. However, vehicles employed with automatic dippers are not very often seen in our cities, and it may be due to lack of information about the system and also because of giving attention to the people saying that it is not at all practicable in our highways. Yes, of course it has got some drawbacks like that one which is most common, when we drive the vehicle fitted with automatic dippers on a road in which different types of vehicles and hence varying light intensities cause frequent flickering of the headlight. And also the operation of the system eliminated or reduced by devising newer methods and technologies. The one nowadays available is only useful in highways and straight width roads.

Truly speaking, auto dippers are devices, which will attain more and more importance in the forthcoming years. In short, it is a device with a very bright future. The number of vehicles and the condition of the roads are improving very fast and the day is near, when the driving regulation, nature of traffic etc., are growing up to the levels which is already their in countries like America who successfully using auto dippers in their highways.

REFERENCES

1 AUTOMOTIVE ELECTRICITY, ELECTRONICS AND COMPUTER CONTROLS
- Barry Hollem Beak
2 AUTOMOTIVE ELECTRICAL EQUIPMENT – P.L. Kohli
3 AUTOMOBILE ENGINEERING – Kirpal Singh
4 AUTOMOBILE ENGINEERING – R.B. Gupta

ABSTRACT

The number of vehicles on our roads is burgeoning day by day. This is turn forced almost all this vehicle manufactures to think about the extra safety instruments and electronic controls to attach with these products for giving the users a safety derived in all road conditions through a mass flow traffic. If asked, one should always mention that the right driving is very cumbersome due to the dazzling light problems and the frequent dipping of headlights by manual means that often causes fatigue to the driver particularly at the time of peak traffic. So naturally to get rid of this perennial problem, an automatic mechanism has to come up to dip the headlamp automatically whenever required. For keeping a motor vehicle under perfect control and reins of the driver, different types of controls and accessories are provided in an automobile around the driver’s seat, on the dashboard and at the footboard. Simply, an automatic dipper is a unit, which can automatically judge when the headlight beam needs to be lowered, and which dip the headlamp from which beam to a dipped beam. As the dipper unit is well connected to the lighting system of the vehicle, we have to look short into the type and construction of a head light before discussing the wiring diagram or the construction of Automatic dippers.

JAGADEESH CHANDRA BABU K.P
02107022

CONTENTS

1) INTRODUCTION 1
2) HEADLAMPS 2
3) RECENT DEVELOPMENTS 7
4) HEADLIGHT DAZZLE 9
5) DIPPING OF HEADLIGHTS 10
6) AUTOMATIC DIPPER 13
7) WORKING OF AUTOM DIPPER 15
8) CONCLUSION 19
9) REFERENCES 20

MPFI

2010-08-07T05:05:00.001-07:00

1. INTRODUCTION

Petrol vehicles uses device called carburetor for supplying the air fuel mixture in correct ratio to cylinders in all rpm ranges. due to construction of the carburetor is relatively simple, it has been used almost exclusively on gasoline engines in the past. However in response to recent demands for cleaner exhaust emission, more economical fuel consumption, improved drivability, etc., the carburetor now must be equipped with various compensating devices, making it more complex system.
So In place of the carburetor, therefore, the MPFI (multi point fuel injection) system is used, assuring proper air fuel ratio to the engine by electrically injecting fuel in accordance with various driving conditions.
MPFI system injects fuel into individual cylinders, based on commands from the ‘on board engine management system computer’ – popularly known as the Engine Control Unit/ECU. These techniques result not only in better ‘power balance’ amongst the cylinders but also in higher output from each one of them, along with faster throttle response. The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions.

2. MAIN COMPONENTS OF MPFI SYSTEM
This system has four major components they are:
a) Air intake system
b) Fuel delivery system
c) Electronic control system
2.1. Air intake system
. The air (corresponding to the throttle valve opening) is filtered by the air cleaner, passes through the throttle body, and is distributed by the intake manifold and finally drawn into each combustion chamber. When the lAC valve is opened according to the signal from ECM, the air bypasses the1hrottle valve through bypass passage and is finally drawn into the intake manifold
a. Throttle body
. The throttle body consists of the main bore, air bypass passage and the following parts. Throttle valve, which is interlocked with the accelerator pedal and controls the amount of the intake air. TP sensor which detects the throttle valve opening and sends a signal to ECM. lAC valve, which supplies the bypass, air depending on Engine condition.

b. Idle air control valve
The lAC valve controls opening of the bypass air passage. The air bypasses the throttle valve through bypass passage and is finally drawn into the intake manifold. Opening and closing of the valve itself is determined by

operation of the magnet, which is connected to it. The magnet operates according to electric current from ECM.
2.2. Fuel delivery system
The fuel in the fuel tank is pumped up by the fuel pump, filtered by fuel filter and fed under pressure to each injector through the delivery 'pipe. As the fuel pressure applied to the injector is always kept a certain amount higher than the pressure in the intake manifold by the fuel pressure regulator, the fuel is injected into the intake port of the cylinder head when the injector opens according to the injection signal form ECM. The fuel relieved by the fuel pressure regulator return through the fuel return to the fuel tank.
a. Fuel pump
The electrical fuel pump located on the fuel tank consists of armature, magnet, impeller, brush, check valve etc.The ECM controls its operation. When the power is supplied to the fuel pump, the motor in the pump runs and so does the impeller. This causes a pressure difference to occur between both sides of the impeller, as there are many grooves around it. Then the fuel is drawn through the inlet port, and with its pressure increases,
It is discharged through the outlet port, The fuel pump also has a check valve to keep some pressure in the fuel feed line even when the fuel pump is stopped.

b. Pressure regulator system

The fuel pressure regulator is diaphragm operated relief valve consisting of diaphragm, spring and valve. It keeps the fuel pressure applied to the injector 2.9Kglcm^2 higher than intake manifold at all times, The pressure applied to the upper chamber of the fuel pressure regulator intake manifold pressure and that to the lower chamber is fuel pressure. When the fuel pressure rises more than 2,9Kg/cm2 higher than the intake manifold pressure, the fuel pushes the valve in the regulator open and excess fuel return to the fuel tank through return line.
c. Injector
Each cylinder has one injector. Which is installed between the intake manifold delivery pipe. It is an electromagnetic type injection nozzle, which injects fuel into the intake port of the cylinder head according to the signal from ECM. When the solenoid coil of the injector is energised by ECM, it becomes an Electro magnet and attracts the plunger. At the same time, the ball valve which is incorporated with the plunger opens and the injector which is under the fuel pressure injects fuel. As the lift stroke of the ball valve of the injector is set constant, the amount of fuel injected at one time is determined by the length of the time during which the solenoid is energized

2.3. Electronic control system

The electronic control system consist of various sensors which detect the state of engine and driving conditions, ECM which controls various devices according to the signals from the sensors and Various controlled devices. The systems are
 Fuel injection control system
 Idle speed control system
 Fuel pump control system,
 Ignition control system,
 Radiator fan control system,

Fuel injection control system

The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions. It uses the sequential multi-port fuel injection system, which injects fuel into each intake port of the cylinder head. In this system ECM controls the time and timing of the fuel injection from the fuel injector into the cylinder head intake port according to the signals from the various sensors so that suitable air/fuel mixture is supplied to the engine in each driving condition. The factors to determine the injection time are the basic injection time which is calculated on the basis of the engine speed and the intake manifold pressure and various compensation which are determined according to the signals from various sensors that detect the state of the engine and driving conditions.

Idle speed control system

This system controls the bypass airflow by means of ECM & lAC valve for the following purposes. To keep the engine idle speed as specified at all times. The engine idle speed can vary due to load applied to engine, to improve starting performance of the engine to compensate air fuel mixture ratio when -decelerating, to improve drivability while engine is warmed up. lAC valve operates according to duty signal sent from ECM. ECM detects the engine condition by using the signals from various signals and switches and controls the bypass airflow by changing lAC valve opening. When the vehicle is at a stop, the throttle valve is at the idle position and the engine is running, the engine speed is kept at a specified idle speed.

Fuel pump control system

ECM controls ON/OFF operation of the fuel pump by turning it ON, the fuel pump relay under any of the conditions. For two seconds after ignition switch ON. While cranking engine (while engine start signal is inputted to ECM). While crankshaft position sensor or camshaft - position sensor signal is inputted to ECM.

Ignition control system

This system controls electronically the time of electric current flow to ignition primary coil as well as ignition timing. ECM judges the engine and vehicle conditions by using signals from various sensors, selects the

most suitable electric current flow time and ignition timing for that engine and vehicle conditions from among those Prestored in its memory and sends an ignition signal to the igniter in ignition coil assembly. Controls of this system include three different types as follows. Ignition timing control at engine start, ignition timing control after engine start, electric current flow time control.

Radiator fan control system

This system controls operation (ON/OFF) of the radiator fan motor. Radiator fan motor is turned ON and OFF by its relay when ECM controls. Radiator fan motor turned ON at below 98°C and OFF at below 93°C
a. Engine Control Module (ECM)

ECM is installed to the underside of the instrument panel at the passenger's seat side. ECM is a precision unit consisting of microcomputer, analogue/digital converter input/output unit etc. It is an essential part of the electronic control system for its functions include not only such a major function as to control fuel injector, lAC valve, fuel pump relay, etc. But, also on-board diagnostic system (self-diagnosis function) and fail-safe function.

WORKING OF MPFI.

b. On-Board diagnostic system

ECM diagnosis troubles which may occur in the area including the following parts when the ignition switch is ON and the engine is running, and indicates the result by turning on or flashing malfunction indicator lamp (CHECK ENGINE LIGHT)
1. Oxygen sensor 2. Engine coolant temp sensor.3.TP sensor 4. IATsensor.5.MAP sensor
6.CMP sensor. 7. VS sensor. 8. CKP sensor. (MY 416).9 CPU of ECM. ECM and malfunction indicator lamp (MIL) operate as follows Malfunction indicator lamp lights when the ignition switch is turned ON but engine at stop with the diagnosis switch terminal ungrounded regardless of the condition of electronic fuel injection system. This is only to check the malfunction indicator lamp bulb and its circuit.If the above

areas of electronic fuel injection system; is free from any trouble after the engine start while engine is running. Malfunction indicator lamp turns OFF. When ECM detects a trouble which has occurred in the above areas, it makes malfunction indicator lamp turn ON while the engine is running to warn the driver of such occurrence of trouble and at the same time is stores the trouble area in ECM back-up memory. The memory is kept as it is even if the trouble was only temporary and disappeared immediately. And it is not erased unless the power to ECM is shut off for specified time 60 sec. or longer. ECM also indicates trouble area in memory by means of flashing of malfunction indicator lamp at the time of inspection.
. Fail- safe function
Even when a trouble has occurred in such area of electronic fuel injection system that includes the following parts and a failure signal is sent to ECM. control over the injector, idle air control valve and others is maintained on the basis of the standard signals and/or CPU. This function is called failsafe function. Thus with this function a certain level of engine performance is available even when some failure occurs in such area and disability in running is avoided.

3. EMISSION CONTROL SYSTEM

The need to control the emissions from automobiles gave rise to the computerization of the automobile. Hydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vaporization of gasoline and from the crankcase of

the automobile. Manufacturers’ are adding of pollution control devices and the creation of a self adjusting engine. 1981 saw the first of these self adjusting engines. They were called feedback fuel control systems.
Emission control in Petrol engine passenger cars
A petrol engine without emission control produces large emissions of nitrogen oxides and unburnt hydrocarbons. The technology that manufacturers have used to meet stiffer emission requirements is the three-
way catalytic converter and new technology such as MPFI, it maintain proper air fuel mixture at stoichiometric ratio by the use of sensors in the engine, there by ensuring proper combustion of the air fuel mixture due to this it reduces the emissions from the vehicles.

3.1 Catalytic converter
Automotive emissions are controlled in three ways, one is to promote more complete combustion so that there are less by products. The second is to reintroduce excessive hydrocarbons back into the engine for combustion and the third is to provide an additional area for oxidation or combustion to occur. This additional area is called a catalytic converter. The catalytic converter looks like a muffler. It is located in the exhaust system ahead of the muffler. Inside the converter are pellets or a honeycomb made of platinum or palladium. The platinum or palladium are used as a catalyst ( a catalyst is a substance used to speed up a chemical process). As hydrocarbons or carbon monoxide in the exhaust are passed over the catalyst, it is chemically oxidized or converted to carbon dioxide and water. As the converter works to clean the exhaust, it develops heat. The dirtier the exhaust, the harder the converter works and the more heat that is developed. In some cases the converter can be seen to glow from excessive heat. If the converter works this hard to clean a dirty exhaust it will destroy itself. Also leaded fuel will put a coating on the platinum or palladium and render the converter ineffective.
Catalytic oxidizers are used in most cars around the world. Because catalytic oxidizers cannot operate in the presence of lead, their introduction caused leaded gasoline to be phased out. Ideally the byproducts of an automobile engine are only carbon dioxide, water, and some nitrogen. This is similar to the chemical output of animals. But in practice, the combustion process in an engine is never 100% efficient, leaving behind hot, yet unburned hydrocarbons. Oxidizer fitted to a car’s tailpipe rapidly oxidizes a large percentage of the remaining unburnt hydrocarbons, resulting in cleaner emissions. However, the speed at which catalytic oxidizers must operate to catch unburnt hydrocarbons before they fly out the tailpipe puts limits on how efficient the oxidation process can be.

3.2 EU emission standards for petrol vehicles.

standards NOx (g/kWh) HC (g/kWh) PM (mg/kWh)
Euro I (1992-93) 9.0 1.23 400
Euro II 1995-96) 7.0 1.1 150
Euro III (2000) 5.01 0.662 100/1603
Euro IV (2005) 3.51 0.462 20/303
Euro V (2008) 2.01 0.462 20/303

3.3 Evaporative emission control system

The evaporative emission control system is used to prevent emission of fuel vapour.the vapour generated in the fuel tank while driving or the
Engine at a stop passes through a tank pressure control valve and enters the EVAP canister were the charcoal absorbs the stores the fuel vapour. The EVAP canister purge valve is controlled by ECM according to signals from various sensors.

4. SENSORS USED IN MPFI.
1 Manifold absolute pressure (MAP) sensor
This sensor senses pressure change in the intake manifold and converts it into voltage Change. It consists of a semi-conductor type pressure converting element, which converts a pressure change into an electrical change and, an electronic circuit which amplifies and corrects the electric change. The ECM sends a 5-volt reference voltage to the pressure sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes By monitoring the sensor output voltage ,ECM knows the manifold pressure, ECM uses the voltage signal from the pressure sensor as one of the signals to control fuel injector.

2. Throttle position sensor

The throttle position sensor is connected to the throttle valve shaft on the throttle body, and detects throttle valve opening, the throttle opening is detected by the potentiometer. A 5-volt reference Voltage is applied to the sensor from ECM and as Brush moves over the print resistance according
to the throttle valve opening, the output voltage varies accordingly. By monitoring sensor output voltage, ECM detects the throttle valve opening. ECM uses the signal from TP sensor as one of the signals to control various devices.

3 Intake air temperature sensor

Located on the air cleaner outlet hose, this sensor constantly measures the
Temperature of the air entering there and converts a change in the air temperature
Into that in resistance through its thermistor. That is, as is temperature lowers, resistance increases and as it rises, resistance decreases. As air density of the intake air varies with Variation in temperature, ECM, by monitoring the resistance, adjusts the amount of fuel injection according to the air temperature

4 Engine coolant temperature sensor

Incorporated with coolant temperature. Gauge and installed to thermostat case, this sensor measures the temperature of the engine coolant and converts its change into that in resistance through the thermistor like the air temperature sensor, by monitoring the resistance of the coolant temperature sensor, ECM detects the engine coolant temperature and that affects most systems under the control of ECM.

5 Oxygen sensor

The oxygen sensor is installed on the exhaust manifold to detect the concentration of oxygen in the exhaust gases. in order of engines equipped with the three- way catalytic converter to achieve their best exhaust emission purification performance, it is necessary for the air-fuel ratio to be kept within a narrow range near the theoretical air-fuel ratio The oxygen sensor senses whether the air-fuel ratio is richer on leaner than the theoretical air-fuel ratio, The oxygen sensor is located in the exhaust manifold and consists of an element made of zirconium dioxide (zrO2, a kind of ceramic material) This element is coated on both inside and outside with a thin layer of platinum. Atmospheric air is introduced into the inside of the sensor, and outside of the sensor is exposed to the exhaust gases. If the Oxygen concentration on the inside surface of the zirconium element differs greatly from that on the outside surface at high temperatures, the zirconium element generate a voltage when the air-fuel mixture is lean there is lot of oxygen in the exhaust gas, so there is a little difference between oxygen concentration inside and outside the sensor element. Thus the voltage generated by the zirconium element is low if the air-fuel mixture is rich; the oxygen in the exhaust has almost disappears. This creates a large difference in the oxygen concentrations inside and outside the sensor and voltage generated by the zirconium element is large. The ECM uses this signal to increase or reduce the injection volume to keep the air-fuel ratio at an even value near the stoichiometric air-fuel ratio.

6 Vehicle speed sensor

The vehicle speed sensor, located on the transmission gearbox or speedometer, Generates a signal in proportion to the vehicle speed. Receiving this signal, the speedometer uses it for operation of its indicator and also converts it into to the ON/OFF signal by doubling the cycle. This signal is sent to ECM where it is used as one of the signals to control various devices.

7. Camshaft position sensor

The sensor is mounted on the sensor case (distributor less ignition case) on tile camshaft let side for distributor less ignition vehicle and other vehicles on the distributor. The signal rotor is press-fitted onto the camshaft (distributor less ignition vehicle) and other vehicles on the distributor shaft. As the sensor has a built-in hall element and a waveform forming circuit, it converts changes in the magnetic flux caused by rotation of the signal rotor into electric pulse signals, Using this signal and the signal from the CKP sensor (if equipped), ECM identifies the cylinder whose piston is in the compression stroke.

8. Crank shaft position sensor

The sensor consists of magnet and coil. It is mounted on oil pan with specified air gap between the sensor core end and crankshaft timing belt pulley tooth. As the crankshaft turns, AC voltage is generated in the sensor. ECM uses this signal as: Engine speed, Cylinder identification.

5. ADVANTAGES OF MPFI
1) More uniform A/F mixture will be supplied to each cylinder; hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this the life of engine components is improved.

(2) No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system.

(3) Immediate response, in case of sudden acceleration / deceleration.

(4) Since the engine is controlled by ECM* (Engine Control Module), more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level.

(5) The mileage of the vehicle will be improved.

6. CONCLUSION

Almost all vehicles in India are changing to the mpfi because of law emissions, improved mileage and drivability since the engine is controlled by micro computer more accurate amount of a/f mixture will be supplied and as a result complete combustion will take place. this leads to effective utilization of fuel supplied and hence low emission level. it reduces wastage of fuel by the use of sensors and other control systems

7. BIBLIOGRAPHY

 Automotive technology –Jack erjavec
 Automobile engineering – Anil chhakra
 Automobile engineering-V.Ganesh
 www.howstuffworks .com
 www.indiacar.com

anti-lock braking system

2010-08-07T05:03:00.002-07:00

1. INTRODUCTION

Car manufacturers world wide are vying with each other to invent more reliable gadgets there by coming closer to the dream of the ‘Advanced safety vehicle’ or ‘Ultimate safety vehicle’, on which research and development has been going on for the past several year. Most of the newer vehicle models offer ABS as either standard or optional equipment .Wheel lockup during braking causes skidding which in turn cause a loss of traction and vehicle control. This reduces the steering ability to change direction. So the car slides out of control. But the road wheel that is still rotating can be steered. That is what ABS is all about. With such a system, the driver can brake hard, take the evasive action and still be in control of the vehicle in any road condition at any speed and under any load. ABS does not reduce stopping distance, but compensates the changing traction or tyre loading by preventing wheel lockup.
During panic braking when the wheels are about to lockup, sensors sense that the wheel has just begun turning slower than others on the vehicle. So they momentarily reduce braking force on the affected wheel. This prevents sliding of the wheels on the pavement. When the wheel resumes rolling, full braking force is again applied. ABS repeats the process until there is no longer any need for modulated braking. ABS acts faster than any driver could, pumping the brakes several times per second. Depending on the type of system, ABS adjusts the braking force at each wheel or set of wheels, whereas a driver’s foot on the brake pedal operates all the brakes at once in normal braking.

2. CONCEPT OF ABS

The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If the vehicle have been stuck on ice and if the wheels are spinning then the vehicle have no traction. This is because the contact patch is sliding relative to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop. Good drivers have always pumped the brake pedal during panic stops to avoid wheel lock up and the loss of steering control. ABS simply gets the pumping job done much faster and in much precise manner than the fastest human foot.

3. PRINCIPLES OF OPERATION OF SIMPLE HYDRAULIC BRAKING SYSTEM.

A simple braking system consists of a master cylinder, and four wheel cylinders. Every wheel cylinder contains two pistons which move out words when the hydraulic fluid flows from the master cylinder to the wheel cylinders through the suitable pipes or lines.

Springs are used to hold the brake shoes on all four wheels. When the brake pedal is pressed the piston in the master cylinder forces the liquid out of the cylinder. This liquid presses the two pistons in the wheel cylinders outwards. These two pistons push the brake shoes out words. The brake shoes in turn press against the brake drums; this stops the brake drum which will be rotating.
When the brake pedal is released the master cylinder is pushed backwords.This is done by a spring fitted in the master cylinder. The springs of the brake shoe brings the shoes closer. The liquid in the wheel cylinder is pushed outwards through the pipes. It returns through the pipes to the master cylinder. This is how the hydraulic system of the four wheels operates

3.1 Master cylinder

It consists of a reservoir feedhole, bypass port, primarypiston, secondary piston .The liquid in the reservoir flows through bypass port to the master cylinder. When the pedal is pressed the primary piston moves to the left .when it crosses the bypass port the liquid is forced along the pipe lines to the wheel cylinders. When the pedal is released the primary piston is moved back wards .it is the spring, which pushes the piston back wards. At the same time a partial vacuum is developed in the space previously occupied by the spring.

4. PRINCIPLES OF ABS

The brakes of vehicle not equipped with ABS will almost immediately lock the wheels, when the driver suddenly applies the brake. In this case the vehicle slides rather than rolls to a stop. The skidding and lack of control was caused by the locking of wheels. The release and reapply of the brake pedal will avoid the locking of the wheels which in turn avoid the skidding. This is exactly what an antilock braking system does.

4.1 Pressure modulation
When the brake pedal is pumped or pulsed the pressure is quickly applied and released at the wheels. This is called pressure modulation. Pressure modulation works to prevent the wheel locking. ABS can modulate the pressure to the brake as often as 15 times per seconds. By modulating the pressure to the brakes the friction between the tires and the road is maintained and the vehicle is able to come to the controllable stop.

Steering is another important consideration. As long as a tire doesn’t slip it goes only in the direction in which it is turned. But once it is skid it has little or no directional stability.
The Maneuverability of the vehicle is reduced if the front wheels are locked and the stability of the vehicle is reduced if the rear wheels are locked.
ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tyre and it there by ensures maneuverability and stability of the vehicle. ABS control module calculates the slip rate of the wheels based on the vehicle speed and speed of the wheels, and then it controls the brake fluid pressure to attain the target slip rate.

During ABS operation, the target slip rate can be from 10 to 30%. 0% slip means the wheel is rolling freely, while 100 % means the wheel is fully locked. A slip rate of 25 % means the velocity of a wheel is 25 % less than that of a freely rolling wheel at the same vehicle speed.

5. ABS COMPONENTS

Many different ABS are found on today’s vehicles. These designs are varied by their basic layout, operation and components. The ABS components can be divided into two categories.
1. Hydraulic components
2. Electrical/electronic components
Besides these normal and conventional brake parts are part of the overall brake system.
5.1 Hydraulic components
• Accumulator
An accumulator is used to store hydraulic fluid to maintain high pressure in the brake system and provide the residual pressure for power assisted braking. Normally the accumulator is charged with nitrogen gas and is an integral part of the modulator unit.

• Antilock hydraulic control valve assembly

This assembly controls the release and application of the brake system pressure to the wheel brake assemblies. It may be of integral type and non integral type. In integral type the unit is combined with the power boost and master cylinder unit into one assembly. The non integral type is mounted externally from the master cylinder /power booster unit and is located between the master cylinder and wheel brake assembly. Both types generally contain solenoid valve that control the releasing, holding and applying of brake system pressure.

• Booster pump
The booster pump is an assembly of an electric motor and pump. The booster pump is used to provide pressurized hydraulic fluid ABS. The pumps motor is controlled by systems control unit.
• Booster/Master cylinder assembly
It is referred as the hydraulic unit, contains the valves and pistons needed to modulate hydraulic pressure in the wheel circuit during the ABS operations.
• Fluid accumulator
Different than a pressure accumulator, fluid accumulator temporarily store brake fluid, that is removed from the wheel brake unit during ABS cycle. This fluid is then used by pump to build pressure for the brake hydraulic system.
• Hydraulic control unit
This assembly contains solenoid valve, fluid accumulator, pump and electric motor. The unit may have one pump and one motor or it have one motor and two pumps.
• Main Valve
This is a two position valve and is also controlled by ABS control module and is open only in the ABS mode. When open pressurized brake fluid from the booster circuit is directed into the master circuit to prevent excessive pedal travel.
• Modulator unit
The modulator unit controls the flow of pressurized brake fluid to the individual wheel circuits. Normally the modulator is made up of solenoid that open and close valves, several valves that control flow of fluid to wheel brake units and electrical relays that activate or deactivate the solenoids through the commands of the control module. This unit may also be called the hydraulic actuator, hydraulic power unit or the electro hydraulic control valve.

• Solenoid valves
The solenoid valves are located in the modulator unit and are electrically operated by signals from the control module. The control module switches the solenoids on or off to increase, decrease, or maintain the hydraulic pressure to the individual wheel units.
• Wheel circuit valves
Two solenoid valves are used to control each circuit or channel. One controls the inlet valve of the circuit, the controls the outlet valve .the position is determined by the control module. Outlet valves are normally closed and inlet valves are normally open. Valves are activated when abs control module switches 12 volts to the circuit solenoids. During normal driving the circuits are not activated.
5.2 Electrical\ electronic components

• ABS control module
This small computer is normally mounted inside the trunk on the wheel housing, mounted to the master cylinder or is part of the hydraulic control unit. It monitors system operation and controls antilock function when needed. The module relies on input from the wheel speed sensors and feedback from the hydraulic unit to determine if the abs is operating correctly and to determine when the anti lock mode is required.
• Brake pedal sensor
The antilock brake pedal sensor switch is normally closed. When the brake pedal exceeds the antilock brake pedal sensor switch setting during an antilock stop, the antilock brake control module senses that the antilock brake pedal sensor switch is open and grounds the pump motor relay coil. This energizes the relay and turns the pump motor on. When the pump motor is running, the hydraulic reservoir is filled with high pressure brake fluid and the brake pedal will be pushed up until antilock brake pedal sensor switch closes. when the antilock brake pedal sensor switch closes , the pump motor is turned off and the brake pedal will drop some with each abs control cycle until the antilock brake pedal sensor switch opens and the pump motor is turned on again .this minimizes pedal feedback during abs cycling .
• Pressure differential switch
It is located in the modulator unit. This switch sends a signal to the control module whenever there is an undesirable difference in the hydraulic pressures with in the brake system.
• Relays
Relays are electromagnetic devices used to control a high current circuit with a low current switching circuit. In abs relays are used to switch motors and solenoids. A low current signal from the control module energizes the relays that complete the electrical circuit for the motor or solenoid.
• Toothed ring
It can be located on an axle shaft, differential gear or a wheels hub. This ring is used with conjunction with the wheel speed sensor. The ring has a number of teeth around its circumference. As the ring rotates and each tooth passes by the wheel speed sensor, an ac voltage signal is generated between the sensor and tooth.
• Wheel speed sensor
It is mounted near the different toothed ring. As the rings teeth rotate past the sensor an ac voltage is generated. as the teeth move away from the sensor, the signal is broken until the next tooth comes close to the sensor .the end result is a pulsing signal that is sent to the control module. The control module translates the signal in to wheel speed. The sensor is normally a small coil of wire with a permanent magnet in its center.

6. TYPES OF ANTILOCK BRAKE SYSTEMS
One of the classifications of abs is integral and non integral type.
Integral type they combine the master cylinder, hydraulic booster and abs hydraulic circuit in to single hydraulic assembly.
In non integral type they use a conventional vacuum-assist booster and master cylinder. In addition they can be classified according to the control they provide.

6.1. Four channel, four sensors ABS

This is the best scheme. There is speed sensor on all four wheels and a separate valve for all the four wheels. With this set up the controller monitors each wheel individually to make sure it is achieving maximum braking force.

6.2. Three channel, three sensor ABS

This scheme is commonly found on pick up trucks with four wheels ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheel is located in the rear axle.
This system provides individual control of the wheels, so they can both achieve maximum braking force. The rear wheels however are monitored together, they both have to start to lock up before the abs will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.

6.3. One channel, one sensor abs

This scheme is commonly found on pick up trucks with rear wheel abs .it has one valve ,which controls both rear wheels , and one speed sensor, located in the rear axle . This system operates the same as the rear end of the rear channel system. The rear wheels are monitored together and both have to start to lock up before the abs kicks in. in this system is also possible that one of the rear wheels will lock reducing brake effectiveness.

7. FOUR WHEEL SYSTEM
The hydraulic circuit for this type of system is an independent four channel type. One for each wheel. The hydraulic control unit is a separate unit. Normal braking is accompanied by conventional vacuum power assist brake system.
The system prevents wheel lock up during an emergency stop by modulating brake pressure. It allows the driver to maintain steering control and stop the vehicle in the shortest possible distance under most conditions. During ABS operation the driver will sense a pulsation in the brake pedal and clicking sound.

7.1 Operation
The ABS control module calculates the slip rate of the wheels and control the brake fluid pressure to attain the target slip rate if the control module senses that the wheel is about to lock based on input sensor data, it pulses the normally open inlet solenoid valve closed for that circuit. This prevents any more fluid from entering that circuit. ABS control module then looks at the sensor signal from the effected wheel again. If that wheel is still decelerating faster than other three wheels it opens the normally closed out let solenoid valve for that circuit. This dumps any pressure that is trapped between the closed inlet valve and the brake back to the master cylinder reservoir. Once the effected wheel returns to the same speed as the other wheel, the control module returns the valve to the normal condition allowing fluid flow to the effected brake.
Based on the input from vehicle speed and the wheel speed sensor, the control module calculates the slip rate of each wheel, and transmits a control signal to the modulator unit solenoid valve when the slip rate is high.
Wheel speed at each wheel is measured by variable reluctance sensors and sensor indicators. The sensors operate on magnetic induction principles.

As the teeth on brake sensor indicators rotate past the sensors, ac current is generated. The ac frequency changes in accordance with the wheel speed. The ABS control unit detects the wheel sensor signal frequency and there by detects wheel speed.

7.2 FUNCTIONAL DIAGRAM OF FOUR CHANNEL ABS

8. ADVANCEMENTS IN ABS
Some systems, which work with the ABS, are Automatic traction control and Automatic stability control, which are discussed below.

8.1 AUTOMATIC TRACTION CONTROL (ATC)

Automatic traction control systems apply the brakes when a drive wheel attempts to spin and lose traction. The system works best when one drive wheel is working on a good traction surface and the other is not. The system also works well when the vehicle is accelerating on slippery road surfaces, especially when climbing hills. ATC is most helpful on four wheel or all wheel drive vehicles in which loss of traction at one wheel could hamper driver control.
During road operation the ATC system uses an electronic control module to monitor the wheel speed sensors. If a wheel enters a loss of traction situation, the module applies braking force to the wheel in trouble. Loss of traction is identified by comparing the vehicle speed to the speed of the wheel. If there is a loss of traction the speed of the wheel will be greater than expected for the particular vehicle speed. ABS and ATC systems can be integral and uses the common valves.
These systems are designed to reduce wheel slip and maintain traction at the drive wheels when the road is wet or snow covered. The control module monitors wheel speed. If during acceleration the module detects drive wheel slip and if brakes are not applied, the control module enters into the traction control mode. The inlet and outlet solenoid valves are pulsed and allow the brake to be quickly applied and released.

In some systems when a loss of traction is sensed, it not only cycles the brakes but signals the engine control module to retard ignition timing and partially close the throttle as well, which in turn reduces engine output.
Many systems are equipped with a dash mounted warning light to alert the driver that the system is operating. There will also be a manual cut off switch so that the driver can turn off ATC operation.

8.2 AUTOMATIC STABILITY CONTROL

Like ATC, the stability control systems are linked with the ABS. it can also be called Electronic Stability Programme (ESP). Stability control systems momentarily apply the brakes at any one wheel to correct over steer or under steer. The control unit receives signals from the typical sensors plus a yaw, lateral acceleration (G-force) and a steering angle sensor.
The system uses the angle of the steering wheel and the speed of the four wheels to calculate the path chosen by the driver. It then looks at lateral G-forces and vehicle yaw to measure where the vehicle is going. (Yaw is defined as the natural tendency for a vehicle to rotate on its vertical center axis). So it is also called Yaw control.

Under steer is the condition in which the vehicle is slow to respond to steering changes. Over steer occurs when the rear wheels try to swing around causing the car to spin. When the system senses under steer in a turn the brake at the inside rear wheel is applied. During over steer the outside front brake is applied. Relaying on the input from the sensors and computer programming the system calculates if the vehicle is going exactly in the same direction in which it is being steered. In case of any difference between what the driver is asking and what the vehicle is doing, the system corrects the situation by applying one of the right or left brakes.

9. ADVANTAGES OF ABS
 It allows the driver to maintain directional stability and control over steering during braking
 Safe and effective
 Automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance.
 ABS absorbs the unwanted turbulence shock waves and modulates the pulses thus permitting the wheel to continue turning under maximum braking pressure.

Disadvantages
 It is very costly
 Maintenance cost of a car equipped with ABS is more.

10. CONCLUSION

ABS has been so far developed to a system, which provides rapid, automatic braking in response to signs of incipient wheel locking by alternatively increasing and decreasing hydraulic pressure in the brake line
Statistics show that approximately 40 % of automobile accidents are due to skidding. These problems commonly occur on vehicle with conventional brake system which can be avoided by adding devices called ABS
If there is an ABS failure, the system will revert to normal brake operation. Normally the ABS warning light will turn on and let the driver know there is a fault

Bibliography

 Automotive technology –Jack erjavec
 Automobile engineering – kirpal Singh
 www.howstuffworks .com

ABSTRACT

Anti-Lock Braking Systems (ABS) are designed to maintain driver control and stability of the car during emergency braking. Locked wheels will slow a car down but will not provide steering ability. ABS allows maximum braking to be applied while retaining the ability to 'steer out of trouble'
The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop.
An ABS system monitors four wheel speed sensors to evaluate wheel slippage. Slip can be determined by calculating the ratio of wheel speed to vehicle speed, which is continuously calculated from the four individual wheel speeds. During a braking event, the function of the control system is to maintain maximum possible wheel grip on the road - without the wheel locking - by adjusting the hydraulic fluid pressure to each brake by way of electronically controlled solenoid valves.

CONTENTS

1. INTRODUCTION 1
2. CONCEPT OF ABS 2
3. HYDRAULIC BRAKING SYSTEM 3
4. PRINCIPLES OF ABS 5
4.1 Pressure modulation
5. ABS COMPONENTS 7
5.1 Hydraulic components
5.2 Electrical\ electronic components
6. TYPES OF ANTILOCK BRAKE SYSTEMS 11
6.1. Four channel, four sensors ABS
6.2. Three channel, three sensor ABS
6.3. One channel, one sensor abs
7. FOUR WHEEL SYSTEM 12
8. ADVANCEMENTS IN ABS 15
8.1 automatic traction control
8.2 automatic stability control
9. ADVANTAGES OF ABS 19
10. CONCLUSION 20
11. BIBLIOGRAPHY 21

EXHAUST GAS RECIRCULATION

2010-08-07T05:03:00.001-07:00

1. INTRODUCTION
All internal combustion engines generate power by creating explosions using fuel and air. These explosions occur inside the engine's cylinders and push the pistons down, which turns the crankshaft. Some of the power thus produced is used to prepare the cylinders for the next explosion by forcing the exhaust gases out of the cylinder, drawing in air (or fuel-air mixture in non-diesel engines), and compressing the air or fuel-air mixture before the fuel is ignited.

Fig 1. Working of four stroke engine.

There are several differences between diesel engines and non-diesel engines. Non-diesel engines combine a fuel mist with air before the mixture is taken into the cylinder, while diesel engines inject fuel into the cylinder after the air is taken in and compressed. Non-diesel engines use a spark plug to ignite the fuel-air mixture, while diesel engines use the heat created by compressing the air in the cylinder to ignite the fuel, which is injected into the hot air after compression. In order to create the high temperatures needed to ignite diesel fuel, diesel engines have much higher compression ratios than
gasoline engines. Because diesel fuel is made of larger molecules than gasoline, burning diesel fuel produces more energy than burning the same volume of gasoline. The higher compression ratio in a diesel engine and the higher energy content of diesel fuel allow diesel engines to be more efficient than gasoline engines.
1.1. Formation of Nitrogen Oxides (NOx)
The same factors that cause diesel engines to run more efficiently than gasoline engines also cause them to run at a higher temperature. This leads to a pollution problem, the creation of nitrogen oxides (NOx). You see, fuel in any engine is burned with extra air, which helps eliminate unburned fuel from the exhaust. This air is approximately 79% nitrogen and 21% oxygen.
When air is compressed inside the cylinder of the diesel engine, the temperature of the air is increased enough to ignite diesel fuel after it is ignited in the cylinder. When the diesel fuel ignites, the temperature of the air increases to more than 1500F and the air expands pushing the piston down and rotating the crankshaft.

Fig 2. NOx formation zone.

Generally the higher the temperature, the more efficient is the engine
1. Good Performance
2. Good Economy
Some of the oxygen is used to burn the fuel, but the extra is supposed to just pass through the engine unreacted. The nitrogen, since it does not participate in the

combustion reaction, also passes unchanged through the engine. When the peak temperatures are high enough for long periods of time, the nitrogen and oxygen in the air combines to form new compounds, primarily NO and NO2. These are normally collectively referred to as “NOx”.

1.2. Problems of NOx
Nitrogen oxides are one of the main pollutants emitted by vehicle engines. Once they enter into the atmosphere, they are spread over a large area by the wind. When it rains, water then combines with the nitrogen oxides to form acid rain. This has been known to damage buildings and have an adverse effect on ecological systems.
Too much NOx in the atmosphere also contributes to the production of SMOG. When the sunrays hit these pollutants SMOG is formed. NOx also causes breathing illness to the human lungs.

1.3. EPA Emission Standards
Since 1977, NOx emissions from diesel engines have been regulated by the EPA
(Environmental Protection Agency). In October 2002, new NOx standards required the
diesel engine industry to introduce additional technology to meet the new standards

The EPA has regulated heavy duty diesel engines since the 1970s. The following chart shows the trend to ever-lower emissions. Understanding the details of the chart is not of interest to most truckers. Even though the emissions standards become increasingly more difficult to meet, the diesel engine industry has always been able to continue to improve engine durability, reliability, performance, and fuel economy. A quick look at the bottom right hand side of the chart also shows that emissions from diesel engines built in 2007 and beyond will approach zero.

Fig 3. EPA Heavy Duty Engine Emission Standards

1.4. How can NOx be reduced?
Since higher cylinder temperatures cause NOx, NOx can be reduced by lowering cylinder temperatures. Charge air coolers are already commonly used for this reason.
Reduced cylinder temperatures can be achieved in three ways.
• Enriching the air fuel (A/F) mixture.
• Lowering the compression ratio and retarding ignition timing.
• Reducing the amount of Oxygen in the cylinder

Enriching the air fuel (A/F) mixture to reduce combustion temperatures. However, this increases HC and carbon monoxide (CO) emissions. Also Lowering the compression ratio and Retarded Ignition Timing make the combustion process start at a less than the optimum point and reduces the efficiency of combustion.

Fig 4. NOx reduction by lowering the temperature

These techniques lowers the cylinder temperature, reducing NOx, but it also reduces fuel economy and performance, and creates excess soot, which results in more frequent oil changes. So, the best way is to limit the amount of Oxygen in the cylinder. Reduced oxygen results in lower cylinder temperatures. This is done by circulating some exhaust gas and mixing it into the engine inlet air. This process is known as Exhaust Gas Recirculation.

2. EXHAUST GAS RECIRCULATION
Exhaust Gas Recirculation is an efficient method to reduce NOx emissions from the engine. It works by recirculating a quantity of exhaust gas back to the engine cylinders. Intermixing the recirculated gas with incoming air reduces the amount of available O2 to the combustion and lowers the peak temperature of combustion. Recirculation is usually achieved by piping a route from the exhaust manifold to the intake manifold. A control valve within the circuit regulates and times the gas flow.

2.1. Uses of Exhaust Gas Recirculation
First, exhaust gas recirculation reduces the concentration of oxygen in the fuel-air mixture. By replacing some of the oxygen-rich inlet air with relatively oxygen-poor exhaust gas, there is less oxygen available for the combustion reaction to proceed. Since the rate of a reaction is always dependent to some degree on the concentration of its reactants in the pre- reaction mix, the NOx-producing reactions proceed more slowly, which means that less NOx is formed.
In addition, since there is less oxygen available, the engine must be adjusted to inject less fuel before each power stroke. Since we are now burning less fuel, there is less heat available to heat the fluids taking place in the reaction. The combustion reaction therefore occurs at lower temperature. Since the temperature is lower, and since the rate of the NOx-forming reaction is lower at lower temperatures, less NOx is formed.

2.2. Basic Parts Of EGR
There are 3 basic parts of EGR
• EGR Valve
• EGR Cooler
• EGR Transfer Pipe
Typical Four Stroke Diesel Engine with Basic Parts of EGR
Figure 5

When EGR is required engine electronic controls open the EGR valve. The exhaust gas then flows through the pipe to the cooler. The exhaust gases are cooled by water from the truck cooling system. The cooled exhaust gas then flow through the EGR transfer pipe to the intake manifold.

Figure 6

2.3. EGR Operating Conditions
There are three operating conditions. The EGR flow should match the conditions
1. High EGR flow is necessary during cruising and midrange acceleration
2. Low EGR flow is needed during low speed and light load.
3. No EGR flow should occur during conditions when EGR flow could adversely affect the engine operating efficiency or vehicle drivability. ie, during engine warm up, idle, wide open throttle, etc.

2.4. EGR Impact on ECS
The ECM (Electronic Control Machine) considers the EGR system as an integral part of the entire ECS. Therefore the ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods of high EGR flow. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can actually be enhanced when the EGR system is functioning as designed.

2.5. EGR Theory of Operation
The purpose of the EGR system is to precisely regulate the flow under different operating conditions. The precise amount of exhaust gas must be metered into the intake manifold and it varies significantly as the engine load changes. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can be enhanced. For this an ECM (Electronic Control Machine) is used to regulate the EGR flow. When EGR is required ECM opens the EGR valve.The ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods EGR flowThe exhaust gas then flows through the pipe to the cooler. The exhaust gases are cooled by water from the vehicle’s cooling system. The cooled exhaust gas then flow through the EGR transfer pipe to the intake manifold.

Fig 7. Relationship between EGR Ratio and Load

4. EGR LIMITS
This is based on an experiment conducted. The research objective is to develop fundamental information about the relationship between EGR parameters and diesel combustion instability and particulate formulation so that options can be explored for maximizing the practical EGR limit, thereby further reducing nitrogen oxide emissions while minimizing particulate formation. A wide range of instrumentation was used to
acquire time-averaged emissions and particulate data as well as time-resolved combustion, emissions, and particulate data. The results of this investigation give insight into the effect of EGR level on the development of gaseous emissions as well as mechanisms responsible for increased particle density and size in the exhaust. A sharp increase in hydrocarbon emissions and particle size and density was observed at higher EGR conditions while only slight changes were observed in conventional combustion parameters such as heat release and work. Analysis of the time-resolved data is ongoing.

The objective of this work is to characterize the effect of EGR on the development of combustion instability and particulate formation so that options can be explored for maximizing the practical EGR limit. We are specifically interested in the dynamic details of the combustion transition with EGR and how the transition might be altered by appropriate high-speed adjustments to the engine. In the long run, we conjecture that it may be possible to alter the effective EGR limit (and thus NOx performance) by using advanced engine control strategies.

Experiments were performed on a 1.9 liter, four-cylinder Volkswagen turbo-charged direct injection engine under steady state, low load conditions. Engine speed was maintained constant at 1200 rpm using an absorbing dynamometer and fuel flow was set to obtain 30% full load at the 0% EGR condition. A system was devised to vary EGR by
manually deflecting the EGR diverter valve. The precise EGR level was monitored by comparing NOx concentrations in the exhaust and intake. NOx concentrations were used because of the high accuracy of the analyzers at low concentrations found in the intake over a wide range of EGR levels.

4.1. Combustion Characterization with HC and NOx Emissions
Steady state measurements were made of CO, CO2, HC, NOx, and O2 concentrations in the raw engine-out exhaust using Rosemount and California Analytical analyzers. Crank angle resolved measurements were also made of HC concentration in the exhaust using a Fast Flame Ionization Detector. The HC sampling probe was located in the exhaust manifold and the data were recorded.

Fig 8. Trade-off between HC and NOx concentration as a function of EGR Level

Time-averaged HC and NOx concentrations in the raw engine-out exhaust are shown in the Figure versus EGR level. This figure shows NOx concentration decreasing and HC increasing with increasing EGR as would be expected. Note the sudden increase in HC and leveling-off in NOx at approximately 45% EGR, where there appears to be a significant shift in combustion chemistry. This major transition is in sharp contrast to the slight changes observed in the integrated pressure parameters, HR and IMEP. Because of the suddenness of the emissions change at 45% EGR, it is clear that dynamic engine behavior at or above this operating point will be highly nonlinear. Thus it is imperative that any control strategies being considered should be able accommodate such behavior.

4.2. Combustion Characterization with PM
Our measurements have identified significant changes in PM emissions with EGR level as was expected. Similar to the gaseous emissions (e.g., HC and NOx), there was a sharp increase in PM at a critical EGR level. This critical level corresponding to a sharp increase in PM was observed in mass concentration, particle size, and particle density.
a) Mass Concentration
A Tapered Element Oscillating Microbalance (TEOM) was used to measure particulate mass concentration and total mass accumulation as a function of time. A sample of diluted exhaust is pulled through a 12 mm filter to the end of a tapered quartz element. The frequency of the element changes with mass accumulation. The instrument has approximately 3 sec resolution on mass concentration.

Particle mass concentration and total mass accumulation were measured on dilute exhaust using the TEOM. Mass accumulation rates were calculated based on over 100 mass data points and are shown in the figure as a function of EGR level. Mass accumulation rates begin to increase significantly at 30% EGR and continue to increase rapidly until the maximum EGR level. The intersection of the particulate mass and NOx curves represents a region where the engine out particulate mass and NOx concentration are minimized for this engine condition.

Fig 9. Relation of PM Accumulation Rate and NOx emission with EGR.

b) Particle Size
A Scanning Mobility Particle Sizer (SMPS) was used to measure the steady state size distribution of the particulates in the exhaust stream. The particles are neutralized and then sorted based on their electrical mobility diameter. The range of the SMPS was set at 11 nm – 505 nm.

Particle sizing was performed on dilute exhaust using the SMPS. Number concentration vs. particle diameter is shown in the figure for several EGR levels. Two aspects of the data stand out. The first is the increasing number concentration with level of EGR. The second is the increasing particle size. Note that the particle size at the peak concentration increases by a factor of approximately two between 30% and 53% EGR.

Fig 10. Time-averaged size distributions as measured by the SMPS.

The likely mechanism for particle growth is the reintroduction of particle nuclei into the cylinder during EGR. The recirculating exhaust particles serve as sites for further condensation and accumulation leading to larger particles. A significant fraction of the measured size distribution appears larger than the 500 nm upper bound of the SMPS for the highest EGR rates. This is significant because these particles contain much of the exhaust particulate mass.

The frequency plot in the figure illustrates the disappearance of small particles and the growth of much larger particles. The divergence between the curves for particles > 100 nm and particles 60-100 nm increases significantly at 30% EGR and continues to increase. The figure does appear to show that the smallest particles are contributing to the growth of the largest ones. The increase in larger particles is less steep than the increase in particle mass in the figure.

Fig 11. Frequency of occurrence of particle size classes as a function of EGR.

4.3. NOx reduction effect of EGR
Fig. 12 shows the typical NOx reduction effect of EGR at the mid-speed range of the test engine.Under all load conditions, the amount of NOx decreases as the EGR rate increases. The graph also shows that the NOx reduction curves with the 0 % EGR point as the origin slope downward at different angles according to the load; the higher the load, the steeper the angle. In other words, the NOx reduction effect at the same EGR rate
increases as the engine load becomes higher.

Fig.12. Relationship between EGR rate and NOx

It is generally known that there are two reasons to reduce NOx by EGR. The first of them is the reduction of combustion temperature. The addition of exhaust gases to the intake air increases the amount of combustion- accompanying gases (mainly CO2), which in turn increases the heat capacity and lowers the combustion temperature. The second effect is the reduction of oxygen concentration in the intake air, which restrains the generation of NOx. Fig. 13 shows the NOx emission test results as a function of the concentration of oxygen in the intake air/EGR gas mixture. This graph shows that the NOx reduction rate depends mostly on oxygen concentration, and not on the engine load or EGR rate.

Fig 2 Relationship between oxygen concentration and NOx reduction

Fig.13 shows the results of NOx emission tests conducted while varying both the engine operating conditions and EGR rate, in which the test results shown in Fig. 13 are merged. As in Fig.13, almost all the data are on or in a single curve, indicating that there is a strong correlation between the oxygen concentration and NOx reduction rate. The reason for this is thought to be as follows: In Fig.12, the NOx reduction rate under a certainload is different from that under another load even when the EGR rate remains the same because the difference in load causes a difference in the amount of combustion-accompanying gases and oxygen concentration in EGR gas, which in turn changes the oxygen concentration in the intake gas (mixture of intake air and EGR gas).
5. INTERNAL EGR
When a fraction of the combustion products is still present in the cylinder at the moment that the exhaust valves close, the mixture at the beginning of the next engine cycle will consist of air and fuel, as well as combustion products. These products are called internal EGR (in contrast to external EGR, which means that exhaust gases are recycled to the intake system, after which they mix with the air and fuel.) The fraction of internal EGR that is present in the cylinder at the beginning of the compression stroke is mainly dependent on the timing of the intake and exhaust valves.

The valve timing of traditional engines, such as the Diesel and Otto engines, is such that the fraction of exhaust gases (or residuals) at the start of the cycle is as small as possible. Traditional engines have Residual Gas Fractions (RGF) in the range 5-15 mass%.

6. TECHNICAL ISSUES

6.1. Combustion Contamination
Exhaust gas from any combustion process may have certain contaminants, including acid forming compounds, unburned and partially burned hydrocarbons, air pollutants, and liquid water. These contaminants can be successfully reintroduced into the combustion chamber but may lead, over time, to serious combustion degradation and instability, and shorter component life. Such effects need to be fully understood and documented, and appropriate improvements made to the combustion process to protect the customer’s investment and maintain true long-term emissions compliance. This activity would be a key element of any major engine manufacturer’s development process.

6.2. Control System Stability
Control systems for modern engines have been developed over two decades and involve integrated strategies to adjust air/fuel ratio, ignition timing, and air flow rates to maintain emissions control at varying loads, speeds, and fuel conditions. These systems are at the heart of successful engine operation today and are vital to satisfactory long term operation. Adding EGR into the combustion process introduces further complexity that must be carefully integrated into the entire engine control system approach for successful operation over a wide range of conditions. For instance, if fuel quality changes over time, the air/fuel ratio, ignition timing, air system rates, and the EGR rate must be adjusted accordingly to keep the combustion system stable and emissions in compliance. On the other hand, if the engine’s load changes rapidly from part load to full load and back to part load, the EGR system dynamics must be included in the overall control strategy response to make sure the engine operates smoothly during this transition.

6.3. Materials and Durability
EGR systems may decrease long-term life of the components affected, including the EGR coolers and control valves, the pistons and cylinder heads, exhaust manifolds and sensors, as well as the post engine catalyst. Operating a few hundred hours per year may not lead to any significant materials degradation in the overall lifespan of an engine. However, continuous duty applications at 8500 hours per year may cause near term emissions noncompliance and longer term materials breakdown, shorter component life, and even unexpected, catastrophic engine failures. To minimize or eliminate the potentially negative impacts of EGR on engine components, compatible components and designs must be used that often require thousands of hours of lab and field test operation for validation. Although both expensive and time consuming, such efforts are a necessary part of proving any new combustion design including EGR systems. Therefore, major engine manufacturers worldwide need to plan for and execute these tests in order to develop the materials needed for successful EGR applications.

6.4. Liquid Dropout
During exhaust gas recirculation, the gasses must be cooled with an external cooler before being reintroduced into the cool inlet manifold of an engine. The cooling process for the EGR may result in liquids being formed in the return lines, depending on temperatures and local humidity, much as liquids are formed in the tailpipe of an automobile at certain conditions. This liquid dropout could be a continuous stream that needs to be carefully understood and managed with the needs of the local environment in mind. While there may be ways to reintroduce this liquid into the combustion process, doing so may create further problems with combustion and lead to other emissions complications and instability. As such, managing liquid dropout needs careful study and development in an integrated development program.

7. CONCLUSION
Thus, as seen that using Exhaust Gas Recirculation Technique in engines, the emissions are vary much controlled due to lesser amounts of NOx entering the atmosphere. Thus the emission levels to be maintained are attained by the engines. As seen, Exhaust Gas Recirculation is a very simple method. It has proven to be very useful and it is being modified further to attain better standards. This method is very reliable in terms of fuel consumption and highly reliable. Thus EGR is the most effective method for reducing the nitrous oxide emissions from the engine exhaust. Many of the four wheeler manufacturers used this technique like Ford Company, Benz Motors etc to improve the engine performance and reduce the amount of pollutants in the exhaust of the engine.

Ejection seat

2010-08-07T05:01:00.000-07:00

1. INTRODUCTION
Almost since the first days of flight man has been concerned with the safe escape from an aircraft which was no longer flyable. Early escape equipment consisted of a recovery parachute only. As aircraft performance rapidly increased during World War II, it became necessary to assist the crewmen in gaining clear safe separation from the aircraft. This was accomplished with an ejector seat which was powered by a propellant driven catapult - the first use of a propulsive element in aircrew escape. . Since then, this collection of componentry has evolved through several generations into today's relatively complex systems which are highly dependent upon propulsive elements. Ejection seats are one of the most complex pieces of equipment on any aircraft, and some consist of thousands of parts. The purpose of the ejection seat is simple: To lift the pilot straight out of the aircraft to a safe distance, then deploy a parachute to allow the pilot to land safely on the ground.

2. A LITTLE HISTORY OF AIRCRAFT ESCAPE SYSTEM
The first operational use of a propulsive element to assist an aircrew to escape from an aircraft apparently occurred during World War II. It appears that the country to receive credit for the first operational system was Germany, as it is known that approximately 60 successful ejections were made from German aircraft during World War II. It is interesting to note, however, that the first aircraft ejection seat was designed and tested (successfully) with a dummy in 1910 by J. S. Zerbe in Los Angeles, California. This was one year before the first parachutist successfully, jumped from an aircraft. Another country involved in early ejection seat work was Sweden. Initial experiments were made by SAAB in 1942 using propellant powered seats. The first successful dummy in-flight ejection was on 8 January 1942. A successful live ejection was made on 29 July 1946.At the end of World War II both the British and Americans acquired German and Swedish ejection seats and data. This information and equipment added impetus to their efforts. The first live flight test in England occurred on 24 July 1946 when Mr. Bernard Lynch ejected from a Meteor III aircraft at 320 mph IAS at 8,000 feet, using a prototype propellant powered seat. On 17 August 1946 First Sergeant Larry Lambert ejected from a P61B at 300 mph IAS at 7,800 feet to become the first live in-flight US ejection test.

3. BASIC COMPONENTS
To understand how an ejection seat works, you must first be familiar with the basic components in any ejection system. Everything has to perform properly in a split second and in a specific sequence to save a pilot's life. If just one piece of critical equipment malfunctions, it could be fatal. Like any seat, the ejection seat's basic anatomy consists of the bucket, back and headrest. Everything else is built around these main components.
Here are key devices of an ejection seat:
• Catapult
• Rocket
• Restraints
• Parachute
This early propulsive element has been called a gun or catapult and, is in essence, a closed telescoping tube arrangement containing a propellant charge to forcibly extend the tubes, thereby imparting the necessary separation velocity to the "ejector seat" and its contents .The rocket is a propulsive device in the seat. The catapult remained as the initial booster to get the seat/man mass clear of the cockpit, while the rocket motor came on line, once clear of the cockpit, to act in a sustainer mode. The restraint system for the crue member is the protective devices to avoid injury while ejecting the seat. Harness straps can be tightened and body position can be adjusted to reduce injury from the forces encountered during ejection. Leg lifting devices and arm and leg restraints are provided to prevent limb flail injuries due to windblast forces. The limb restraints

do not require the crew to hook up as they enter the aircraft and do not restrict limb movement during normal flight operations. Parachute helped the pilot to land safely on ground.
4. EJECTION-SEAT TERMS
Bucket - This is the lower part of the ejection seat that contains the survival equipment.
Canopy - This is the clear cover that encapsulates the cockpit of some planes; it is often seen on military fighter jets.
Catapult - Most ejections are initiated with this ballistic cartridge.
Drogue parachute - This small parachute is deployed prior to the main parachute; it designed to slow the ejection seat after exiting the aircraft.
Egress system - This refers to the entire ejection system, including seat ejection, canopy jettisoning and emergency life-support equipment.
Environmental sensor - This is an electronic device that tracks the airspeed and altitude of the seat.
Face curtain - Attached to the top of some seats, pilots pull this curtain down to cover his or her face from debris. This curtain also holds the pilot's head still during ejection.
Recovery sequencer - This is the electronic device that controls the sequence of events during ejection.

Rocket catapult - This is a combination of a ballistic catapult and an under seat rocket unit.
Underseat rocket - Some seats have a rocket attached underneath to provide additional lift after the catapult lifts the crewmember out of the cockpit.
Vernier rocket - Attached to a gyroscope, this rocket is mounted to the bottom of the seat and controls the seat's pitch.
Zero-zero ejection - This is an ejection on the ground when the aircraft is at zero altitude and zero airspeed.

5. PHYSICS OF EJECTING
Ejecting from an airplane is a violent sequence of events that places the human body under an extreme amount of force. The primary factors involved in an aircraft ejection are the force and acceleration of the crewmember. To understand the forces in the ejection we want to know the following.
Frames of Reference - refers to the orientation of the object in relation to some reference. This way up/down, left/right, and front/back can be defined so others understand the position. In ejections, the following convention is used:
The primary vector acceleration axes are defined relative to the crewman's spinal axis (+Gz, positive spinal, eyeballs down; -Gz, negative spinal, eyeballs up; +Gx, positive fore-and-aft, eyeballs in; -Gx, negative fore-and-aft, eyeballs out; +Gy, positive lateral, eyeballs left; -Gy, negative lateral, eyeballs right).
Forces and G's - Newton's second law states that the force on a body is a function of the mass it contains and the acceleration it undergoes. It is represented in an equation as
Force = Mass * Acceleration [F=MA].
The acceleration is usually measured in terms of the G, or gravity, force equivalent. For each 32 feet/second^2 or 9.8 meter/second^2, one experiences 1 G of acceleration. A rocket assisted seat has a G rating of 5-10, while a pure catapult seat would be in the 10-20 G range.

G's and speed - To determine the speed of the seat at any point in time, one solves the Newton equation knowing the force applied and the mass of the seat/occupant system. The only other factors that are needed are the time for the force to be applied and the initial velocity present (if any). This all works together in the following equation:
Speed (final) = Acceleration * Time + Speed (initial)
[V(f) = AT + V(i)]
Initial velocity may involve the climb or sink rate of the aircraft, but most likely involves velocity resulting from a previous ejection force. For example, in most current seats, the ejection in a two step process where an explosive catapult removes the seat from the aircraft then a rocket sustainer gives final separation. So to solve this seat system, the Newton equation would be solved twice. Once with a V(i) of zero for the catapult and a second time where the initial velocity would be the speed at which the seat left the catapult.
Seat speed, aircraft speed, & aircraft size - All the above parameters, force, mass, time, and seat sequencing, need to be considered when the system is applied to an operating aircraft. A seat speed needs to be high enough to give a reasonable separation distance between the occupant and the aircraft. At the same time, the operating time needs to be short enough to move the person out of danger and allow all actions to take place. But as speed goes up and time goes down, the G force may become excessive. Therefore distance and time have to be balanced to provide a system that will operate swiftly, provide adequate separation,

and not impose an undue G load on the seat occupant. This relationship is given in the following equation:
Distance = 1/2 * Acceleration * Time^2 + Speed (initial) * Time
[D = 1/2AT^2 + V(i)T]
Pilot size and weight - No discussion has been made about the occupant of the seat. This is important since the mass of the pilot will ultimately have an effect on the acceleration. There are three things determining the mass to be ejected and two of them are essentially constant. These are seat mass, equipment mass, and pilot/occupant mass. The seat mass is composed of the seat itself, any pyrotechnics that eject with it, the survival kit, and the parachute.
These weights can vary greatly. For the Martin Baker H-7 seat as installed in the F-4 phantom they were as follows, seat = 193 pounds (88 kg), survival kit = 40 pounds (18 kg), and parachute = 20 pounds (9 kg). Looking at the McDonnell Douglas ACES II seat, the seat weight drops to about 150 pounds (68 kg) with the other factors remaining essentially constant. For seats used in some aircraft, weight is even less as the survival kit may be deleted since the aircraft is only used for flight test or over land where rescue is immediately available.
Equipment mass is what the pilot brings on board. The clothing worn by the occupant does not count, however the G suit, torso harness, life preserver, and helmet would. Depending on the aircraft and the occupant that may be 30-50 more pounds (14-22 kg) of weight.

The pilot mass is the largest variable since the seat mass will be determined by the aircraft and the equipment mass determined by the mission. When preparing for the addition of women pilots, the United States Air Force revised its pilot weight data and found a 5th percentile pilot to be a weight of 103 pounds (47 kg) and a 95th percentile pilot to be 205 pounds (93 kg). This difference in mass will produce a significant difference in the forces involved
Pilot position and seat actuation - As noted above, wind blast is a factor during an ejection. From the beginning, efforts were made to keep limbs and the head in place during the ejection event. The first step was using the inertia reel straps and having the pilot lock the harness prior to activation of the seat. As seats became more automatic, gas pressure from seat activation was used to retract and lock the reel. This helped to insure the hips and torso were tight against the seat.
The head and arms received attention next. Seats designed on both sides of the Atlantic settled on the face curtain as a means of seat activation and protection for the occupant. Hands grasped a set of handles mounted at the top and pulled down. The extended curtain helped hold thehead back and gave some wind blast protection. The arms were also tight against the body and, with muscles under tension, less likely to be out of position. A similar idea was the use of the center pull handle. By grasping in a two hand grip, the hands and arms are again inside the body and protected from wind blast. The final option is the side firing levers. Some designers feel that moving the hands up to a face curtain or into the center for the handle wastes valuable time. Therefore side firing handles

put the hands and arms in an anatomically stable position and also reduce reaction time when the need to eject arises.
The final appendages to consider are the legs and feet. Some seats, such as the Escapac and ACES II, attempt to passively control them through the use of high sides that keep the knees together and prevent the legs from abducting. Martin - Baker and Stencel have favored the use of a strap and garter assembly that attaches to the aircraft, passes through pulleys attached to the seat, and connects to the ankle of the occupant. As the seat moved up the rails, the cords tighten and pull the feet and legs into the bottom of the seat.

6. THE WORKING OR EJECTION SEQUENCES
A typical ejection sequence includes the following functions which occur generally in the order listed below:
6. 1. Seat activation: Seats are activated through different methods. Some have pull handles on the sides or in the middle of the seat. Others are activated when a crew member pulls a face curtain down to cover and protect his or her face.
6.2. Canopy or hatch jettison: Prior to the ejection system launching, the canopy has to be jettisoned to allow the crewmember to escape the cockpit. There are at least three ways that the canopy or ceiling of the airplane can be blown to allow the crewmember to escape:
• Lifting the canopy - Bolts that are filled with an explosive charge are detonated, detaching the canopy from the aircraft. Small rocket thrusters attached on the forward lip of the canopy push the transparency out of the way of the ejection path.
• Shattering the canopy - To avoid the possibility of a crewmember colliding with a canopy during ejection, some egress systems are designed to shatter the canopy with an explosive. This is done by installing a detonating cord or an explosive charge around or across the canopy. When it explodes, the fragments of the canopy are moved out of the crewmember's path by the slipstream.

• Explosive hatches - Planes without canopies will have an explosive hatch. Explosive bolts are used to blow the hatch during an ejection.
6.3. Seat ejection/crewmember extraction: In modern ejection seat there is a two stage propulsion system for Seat ejection/ crewmember extraction. The catapult remained as the initial booster to get the seat/man mass clear of the cockpit, while the rocket motor came on line, once clear of the cockpit, to act in a sustainer mode. When combined into a single unit, this propulsive element was termed the rocket catapult.
6.4. Drogue parachute deployment: This small parachute is deployed prior to the main parachute; it designed to slow the ejection seat after exiting the aircraft. Once out of the plane, a drogue gun in the seat fires a metal slug that pulls the drogue parachute, out of the top of the chair. This slows the person's rate of descent and stabilizes the seat's altitude and trajectory. After a specified amount of time, an altitude sensor causes the drogue parachute to pull the main parachute from the pilot's chute pack. At this point, a seat-man-separator motor fires and the seat falls away from the crewmember. The person then falls back to Earth as with any parachute landing.
6.5. Seat man separation: Test flights and operational experience showed that some aspects could be safely automated. One of the main ones was the removal of the occupant from the seat. Multiple methods have been used ranging from simple to complex. The simplest is gravity. The lap belt and shoulder restraints are released and the seat will drop away of its own accord. In some cases this is assisted. The original Escapac seat used a rubber bladder system and a bottle of nitrogen. When

the time delay expired, a bell crank rotated pulling retaining pins from the straps and puncturing the bottle. High pressure gas inflated bladders in the bottom and back of the seat, pushing the occupant away.
There was a small probability of collision following the split. Therefore, in later versions of the seat, the gas assembly was replaced by a downward firing rocket at the top of the seat to insure a positive separation distance.
6.6. Recovery parachute deployment and inflation: The altitude of parachute deployment is an important issue. Above 10 000 feet there is insufficient oxygen in the air (reduced altitude thins the air) to maintain consciousness. If the parachute opens too high, the occupant may become hypoxic and pass out. To alleviate this problem, many seats added a barostatic sensor to the parachute assembly. If below the preferred height, chute deployment would occur without delay. If above the appropriate height, a delay was initiated until the altitude conditions were met. One would think that the delay would not be needed since supplemental oxygen could be included as a part of the seat. However, masks can be ripped off by wind blast. Therefore altitude restrictions and opening the chute at the correct height is still important.
6.7. Parachute Descent and Landing: This phase of the ejection sequence is critical to the outcome of the entire process of escape and yet 90 per cent of all non-fatal injuries associated with escape occur during landing. Although the techniques of landing by parachute are easily taught and simulated by jumps from training towers, the incidence of sprained or fractured ankles is estimated to be 50 per thousand descents . The correct

procedures for parachute landing are taught aircrew during several phases of their training.

7. THE ACES II EJECTION SEAT

The Advanced Concept Ejection Seat (ACES) was designed to be rugged and lightweight compared to earlier systems. It also was designed to be easy to maintain and updatable.
It includes the following features:
• Electronic Sequencing and timing
• Auto sensing of egress conditions
• Parachute reefing to control opening at all speed ranges
• Multi-Mode operation for optimum recovery of the crewman

The ACES II is a third-generation seat, capable of ejecting a pilot from zero-zero conditions up to maximum altitude and airspeeds in the 250 knots (288 mph / 463 kph) range. The peak catapult acceleration is about 12gz. The ACES II has three main operating modes, one each for the low speed/low altitude, medium speed, and high speed/high altitude.
• Mode 1: low altitude, low speed - Mode 1 is for ejections at speeds of less than 250 knots (288 mph / 463 kph) and altitudes of less than 15,000 feet (4,572 meters). The drogue parachute doesn't deploy in mode 1.
• Mode 2: low altitude, high speed - Mode 2 is for ejections at speeds of more than 250 knots and altitudes of less than 15,000 feet.
• Mode 3: high altitude, any speed - Mode 3 is selected for any ejection at an altitude greater than 15,000 feet.
Deployment is delayed by the sequencer until the seat-man package reaches either Mode 2, or Mode 1 conditions, whichever comes first.
Seat modes are selected by the sequencer based on atmospheric conditions, and the modes vary depending on differences in the conditions such as apparent airspeed and apparent altitude.
7.1 Recovery Sequencing Subsystem
Seat functions are normally activated by the Recovery Sequencing Subsystem which consists of the environmental sensing unit , and the recovery sequencing unit, an electronic box located inside the seat rear on the right hand side. The environmental sensing unit consists of two altitude compensated dynamic pressure transducers, and two static pressure

transducers. The dynamic pressure sensor (pitot tubes) are located on or near the headrest and read the air pressure as the seat exits the aircraft. The pressure differential between them and the ambient (static) sensors behind the seat is compared by the recovery sequencing unit to determine what operating mode the sequencer should select.
7.2 Ejection control handles
Firing of the seat is normally by pulling one of the ejection control handles mounted on the seat bucket sides. (On ACES seats fitted to F-16s and F-22s the ejection control handle is located in the center of the front of the seat bucket) The side pull handles are mechanically linked so that raising one will lift the other as well. Raising the handles actuates a pair of initiators via mechanical linkages.
7.3 Stapac Package
One particularly unique feature to the ACES II is the STAPAC package. STAPAC is a vernier rocket motor mounted under the seat near the rear. It is mounted on a tilt system controlled by a basic pitch-rate gyro system. This system is designed to help solve one of the great problems inherent to ejection seat systems. Center of mass/Center of gravity is extremely important in terms of keeping the thrust of the booster rocket from inducing a tumble. Rocket nozzles for the main boost of a seat are aligned to provide thrust through the nominal center of gravity of the seat-man package. The STAPAC provides a counter force to prevent extreme pitching in cases where the CG is off by up to +2 inches. The yellow flag is a safety pin preventing accidental firing of the STAPAC.

7.4 Survival kit
Another unusual feature is related to the survival kit. In most ejection seats the survival kit is a rigid fiberglass box that makes up the seat inside the seat bucket. The ACES II survival kit is a soft pack that is stored under a fiberglass seat lid that is hinged at the front. When the pilot separates from the seat, the straps that connect him to the survival kit lift the seat lid up and forward. The seat kit then slips free from the rear end.
7.5 Inertia Reel Harness Assembly
The Inertia Reel Harness Assembly is located in the center of the seat back just below the headrest. The inertia reel fulfills two functions: (1) it acts like the shoulder belt in a car, restraining the pilot against a 2gx forward (-x) motion. (2) upon ejection, it retracts the pilot to an upright posture to minimize the possibility of spinal damage due to spinal misalignment upon catapult ignition. On the left side of the seat bucket there is a handle which allows the crew member to manually lock the reel prior to intense maneuvers or landing to prevent possible injuries.
7.6 Drogue System
The Drogue System consists of a hemisflo chute, a small extraction chute, and the Drogue Mortar. The drogue mortar is fired in Mode 2 and Mode 3 to slow and stabilize the seat-man package. This is intended to prevent or limit the injuries to the crewmember as he/she is exposed to the windblast after exiting the aircraft. The mortar fires a 1.2 Lb slug of metal that draws the extraction chute out which by means of a lanyard deploys the drogue chute. The extraction chute is packed in a small wedge-shaped

container on the upper left rear of the seat covered with metalized fabric. The lanyard is also covered in the metalized fabric. The drogue mortar is below this, and the drogue is packed in the metal covered box below this. The lid to the drogue is retained by a small plunger unit that is held in place by machining on the slug and released when the mortar fires.
7.7 Safety Lever
The seat is made safe by means of a Safety Lever on the left side of the seat bucket which prevents the seat from being fired when the lever is in the up/forward position. When it is down/back flat against the side of the bucket, it allows the seat to be fired.
7.8 Emergency Manual Chute Handle
The Emergency Manual Chute Handle is located on the right hand side of the seat bucket, and functions to fire the main chute mortar and initiate seat separation in case of failure of the electronic sequencer. Unlike other seats, the manual chute handle is inhibited in the aircraft and prevents the systems from functioning while the seat is still in the rails. In the event of ground egress, the crewman would have to unstrap the two shoulder harness connections, the two seat kit connections and the lap belt prior to egressing the aircraft. Given the 0-0 capability of the seat, in any case requiring extremely rapid egress, ejection would be a viable alternative.

7.9 Emergency oxygen system
The emergency oxygen system consists of an oxygen bottle attached to the seat back, an automatic activation lanyard, and a manual pull ring. As the seat rises up the rails, the lanyard activates the oxygen bottle and allows the crewman access to oxygen as long as he is still connected to the seat. During an in-flight emergency that does not require ejection, the oxygen bottle provides breathable air for enough time to return the aircraft to 10000 feet or below where the atmosphere is thick enough for the pilot to breath.

CONCLUSION
The ejection seat has evolved into a complicated system with subsystems. Seat improvement has improved the odds of survival, and expanded boundary limits for successful ejection. The ability of the seat to monitor environmental factors has allowed better control inputs, improving seat stability. The incidence of ejection injuries is reduced by employing a complex acceleration profile. The profile is impulsive and of high amplitude at the beginning and end of the acceleration period, while relatively smooth and of low amplitude during the interposed major time segment.
The next generation of escape systems will use controllable propulsion systems to provide safe ejection over the expanded aircraft flight performance envelopes of advanced aircraft. Continued research will only enhance the capability of future ejection systems. Current research efforts are being directed toward solving the problems associated with high speed and high altitude ejections. So we can expect that in the future more advanced ejection seats will evolve which will be more safer and will save many valuable lives.

REFERENCE
1. www.howstuffworks.com
2. www.ejectionsite.com
3. www.showcase.netin.net/web/herker/ejection
4. www.fas.org

ABSTRACT

Almost since the first days of flight man has been concerned with the safe escape from an aircraft which was no longer flyable. Early escape equipment consisted of a recovery parachute only. As aircraft performance rapidly increased during World War II, it became necessary to assist the crewmen in gaining clear safe separation from the aircraft. This was accomplished with an ejector seat which was powered by a propellant driven catapult - the first use of a propulsive element in aircrew escape. . Ejection seats are one of the most complex pieces of equipment on any aircraft, and some consist of thousands of parts. The purpose of the ejection seat is simple: To lift the pilot straight out of the aircraft to a safe distance, then deploy a parachute to allow the pilot to land safely on the ground.
Like any seat, the ejection seat's basic anatomy consists of the bucket, back and headrest. Everything else is built around these main components. There are many models of ejection seats manufactured by different companies and ACES II is one such important model.

EXPRESSOR

2010-08-07T05:00:00.001-07:00

INTRODUCTION

In earlier locomotives we used only air brakes. For that a compressor is needed to produce compressed air. But after 1980, almost all of the locomotives have dual brake systems, i.e. air brake is used for application of brakes in the locomotive (engine) and vacuum brakes are used for the application of brakes in the wagons or compartments. For that we need compressed air for air brake and high vacuum for vacuum brake.
A simple compressor cannot provide high compressed air and high vacuum. For obtaining these two, we need a compressor and an exhauster together. For that we use a single unit system known as EXPRESSOR, in the dual brake locomotives.
Therefore expressor is simply expressed as

EXhauster + comPRESSOR = EXPRESSOR

COMMON FEATURES OE EXPRESSOR

Expressor is a reciprocating type system. It has six cylinders, which are arranged in a ‘W’ type manner i.e., two cylinders are in a vertical position and four in a V shape. It is an air-cooled system with forced feed lubrication. For cooling purpose a fan is used which is of a forced draught type, mounted on the crankshaft. The oil fill capacity is 30 litres; the oil grade being Servo press 150-IOC.

TYPES OF EXPRESSOR

Expressors are generally classified on the basis of the number of cylinders they have and out of which how many are used as compressors. The three main classifications are:

1) 6CD 4UC: - Here, the expressor totally consists of six cylinders of which two cylinders are compressors. These two provide compressed air for the actuation of air brakes and other four are the exhausters.

6CD 4UC

2) 6CD 3UC: - Here the expressor totally consists of six cylinders in which three cylinders provide compressed air for air brakes and other three help in the creation of vacuum for the actuation of vacuum brakes.

3) 3CD B: - This type of expressor consists of three cylinders, which bare used only as compressors. This type of expressor is not capable of producing exhaust though it is termed as an expressor. This system is presently not used in dual brake system and is limited only in locomotives having air brakes only

The different types of expressor are shown in the following page. As the construction and working of the two expressors are in the similar fashion, the construction and working of only 6CD 4UC is explained in this seminar.

6CD 4UC EXPRESSOR

MAIN PARTS: -

1. CRANK CASE
2. CYLINDER AND CYLINDER HEAD
3. INLET AND DISCHARGE VALVE
4. AIR INTAKE AND STRAINER ASSEMBLY
5. PISTON AND CONNECTING ROD
6. CRANK SHAFT
7. INTERCOOLER
8. UNLOADER VALVE
9. SAFETY VALVE
10. CRANK CASE VACUUM MAINTAINING VALVE

The description of the parts is as follows.

CRANK CASE

The crankcase is the main body of the expressor to which all the cylinders are connected. The crankshaft is mounted centrally in the crankcase. One side of the crankcase is fully closed and the other side fully open, through which the crankshaft extends out words, on which the drive for the expressor is given. On the closed side the fan is fitted for cooling purpose. Inside the crankcase, the lube oil is filled. The oil fill capacity is 30 liters. On the inner side of the crankcase oil pump is fitted, which helps to circulate the lube oil under pressure.

CYLINDER AND CYLINDER HEAD

The 6CD 4UC expressor consists of six cylinders in which four are uncompressors. They are used to create vacuum for the actuation of vacuum brake. They are arranged in ‘V’ type manner with a pair of cylinders on the two sides of the crankcase. The other two cylinders are the compressor used for providing the compressed air. They are mounted vertically on the top of the crankcase so that the six cylinders together form a ‘W’ pattern. Of the two compressors one is a low-pressure cylinder and the other is a high-pressure cylinder.
The low-pressure cylinder head has two inlet and two delivery valves whereas the high-pressure cylinder has an inlet valve and a delivery only. Each exhauster cylinder head consists of two inlet and two delivery valves.

INLET AND DISCHARGE VALVES

The inlet and discharge valves used in expressor are of concentric disc valve type. The assembly is shown in the figure. Care should be taken when cleaning and assembling the different parts of the inlet and discharge valves so that a mix up does not occur, as these parts are not interchangeable.
The inlet valves of the L.P. cylinder and H.P. cylinder are fitted with suction unloader valves as a measure. This control enables the compressor to be operated continuously with out stopping.

AIR INTAKE STRAINER ASSEMBLY

An air intake strainer is mounted on the inlet of the L.P. cylinder head means of stud and nut. A minimum space of 160 mm is required to remove the element from the air intake strainer.
The strainer element is made up of spirally wound steel wire mesh. The layers of dust can be cleaned by dislodging the element from the air intake strainer and by using compressed air. Thus we can prevent the impurities from entering into the compressor

PISTON AND CONNECTING ROD

The low pressure and exhauster pistons are made of aluminium alloy and the high-pressure piston is made of high quality cast iron. High quality cast iron is used so as to withstand very high pressure produced in the high-pressure cylinder. For every piston there are four rings; two compression rings and two oil control rings. The compression rings used in the piston are of two types. The first compression ring provided on the top of the piston does a stepped compression ring follow a plain compression ring. Together with theses two compression rings, a plain oil control ring is provided at the top, where as the second slotted oil ting is provided at the bottom of the piston to ensure added safety.

The connecting rods are made of forged steel, which are identical. Three of them are mounted on each crank pin of the crankshaft. The small end of the connecting rod is provided with bush bearings. Inner bearing of the big end of the connecting rod can be easily replaced in case of necessity during repair.

CRANK SHAFT

The crankshaft of the expressor is directly coupled to the diesel engine. The crankshaft is supported on two main double row ball bearings for frictionless operation. On the other end of the crankshaft is mounted a fan which is provided for cooling purposes. The crank consists of two bearing seats, which support the main double row ball bearings. The crankshaft consists of crank pins on which the connecting rods are mounted. Oil seats fixed at the outer position of the two bearings prevent the atmospheric air from entering into the crankcase and also prevent the oil from leaking out. The drive to the gear type oil pump, fixed to the inner side of the crankcase is provided from the crankshaft via the gear train

drive. For the proper working of the expressor, the crankshaft should be balanced in both static and dynamic conditions so that proper pressure can be maintained. Counter weights are provided to the crankshaft at proper positions to enable it’s balancing.

INTER COOLER

The inter cooler I provided for the cooling of compressed air. It is provided in between the low pressure and high-pressure cylinders. It consists of 24 tubes on one side and 21 on the other. The air coming from the low-pressure cylinder first enters the inter cooler through the side having 24 tubes, reaches the side having 21 tubes and then enters the high-pressure cylinder. Thus, the air which enters the inter cooler (radiator type) gets cooled before going into the high-pressure cylinder. The cooling improves the volumetric efficiency of the compressor. The fan and the finned tubes of the inter cooler increases the cooling efficiency.

UNLOADER VALVE

The unloader is used to unload the excess air sucked by the compressor after the preset pressure in the main air tank is reached. The inlet valves of the low and high-pressure cylinders are fitted with unloaders controlled by the governor. The inlet valve gets opened when the designed pressure in the tank is reached and air gets unloaded through the air filters of the compressor.

SAFETY VALVE

The safety valve which is fitted in the inter cooler manifold is used to blow out the excess air if the pressure exceeds 3.2 bars in the inter cooler. If there is symptom of choking, found in the inter cooler or the suction valves of the high-pressure cylinder, care should be taken to ensure the tightness of the cap nut of the safety valves.

CRANK CASE VACUUM MAINTAINING VALVE

It is also known as breather valve. Partial vacuum is developed in the crank -case by connecting the crankcase to the inlet manifold of the exhauster by means of a pipe through the vacuum-maintaining valve.

The piston in the vacuum maintaining valve moves up when the pressure is built up in the crank case assisted by spring force which opens the port connecting the rank case to inlet manifold of the exhauster, there by evacuating the crank case. When the vacuum in the crankcase reaches a predetermined level as set, it is maintained at that level by the piston moving down and cutting off the connection to the vacuum manifold.

WORKING OF AN EXPRESSOR (6CD 4UC)

PROCESS OF AIR COMPRESSION

When drive is given to the expressor through the crankshaft, the piston of the low-pressure cylinder moves towards the bottom dead center (B D C). The combined action of the delivery valve return spring and the pressure differential developed between discharge manifold and the low-pressure cylinder closes the delivery valve. At the same time, inlet valves open due to the pressure differential developed between the inside and outside of the low-pressure cylinder.
The atmospheric air is sucked into the low-pressure cylinder through air filter, which is fitted to the suction side of the low-pressure cylinder head. During the upward motion of the piston, the combined action of the inlet valve spring and the pressure difference developed between the inside and outside of the low-pressure cylinder closes the inlet valves. The air, which is trapped in the cylinder, gets compressed. The compressed air forcibly opens the delivery valves due to the formation of pressure differential, which has been developed between the discharge manifold and the cylinder. The compressed air is delivered into the discharge manifold through the delivery valves. It then reaches the inter-cooler through the discharge manifold.
The air coming from the low-pressure cylinder first enters the inter-cooler through the side having 24 tubes, then passes through the side having 21 tubes and reaches the high-pressure cylinder. During compression in the low-pressure cylinder, the temperature of the compressed air is increased. Further compression of this air in the high-pressure cylinder is effective only if the temperature of this air is lowered, or else more work will have to be done on this air, which will lead to reduction in efficiency. To prevent this, we use an inter-cooler, which reduces the temperature of the compressed air coming from the low-pressure cylinder and thus increases the volumetric efficiency of the compressor. The fan and the finned tubes of the inter-cooler increase the efficiency of cooling. The cooled compressed air gets compressed to a higher pressure in the high- pressure cylinder and is delivered to the air receiver. This compressed air developed by the compressor is used for the application of brakes for the locomotive, horns and wind- screen vipers.

WORKING OF AN EXHAUSTER

When vacuum brake is applied, air is entered into the vacuum lines. For further application of this vacuum brake, the air present in the vacuum lines should be removed so that the vacuum tank is connected to the exhauster. The air present in the vacuum brake pipe is sucked into the inlet of the exhauster head, which is connected by the inlet manifold. The cylinder heads of all the exhauster cylinders
are provided with two inlet and two delivery valves. During the downward motion of the piston, i.e. moving to B D C, air is sucked through the inlet valves of the exhauster cylinder. The pressure differential developed between the exhauster cylinder and vacuum brake pipe makes the inlet valve open, during which the double action of delivery valve spring and pressure differential developed between the inside and outside of the exhauster cylinders keep the delivery valves closed. When the piston moves to T D C, the air is compressed to a pressure, which is comparatively higher than the atmospheric pressure. The delivery valves open and the air escapes through the manifold to the atmosphere. The process is continued, until the vacuum is attained to 585mm or 23” of mercury.

LUBRICATION IN EXPRESSOR

For efficient working of the expressor, the lubrication should be very good. The expressor lubrication system is piloted by gear train driven type oil pump. From the crank- case, the lubricating oil is fed to the pump through the oil strainer assembly. The oil pump, which is fixed to the inner side of the crankcase, circulates the oil under pressure. The gear train drive from the crankshaft of the expressor enables the driven gear mounted o one of the two gears of the oil pump, to pump the oil through the system. An oil strainer is provided, which is fitted with two wire meshes and which face the inner side of the crank case bottom. It filters the oil to prevent the ingress of external agents like dust and other solid particles from entering the pump and the lubricating system. The pump due to the meshing of gears takes up the filtered oil, and the delivery port takes the oil up, through the groove in the distributing ring.
Through the distributing ring, the lubrication oil flows to each crank pin in the crankshaft through the oil holes drilled in it. Axially drilled holes through each crank pin are connected to the distributing holes. The oil lubricates the inner bearings of their respective six connecting rods through the grooves provided on its top half in all the connecting rods. The hole drilled through the connecting rod carries the oil to the small end to lubricate the gudgeon pin. A relief valve fitted on the body of the oil pump, maintains the oil pressure between 4 and 6 bars. In case, the oil pressure exceeds, the oil relief valve opens and allows the oil to pass out of the pump, thus maintaining the set pressure. An oil pressure indicator valve, which is mounted on the side cover of the crankcase, helps to ensure the line pressure of the oil system. A tube is connected from the crankcase body to the oil gauge through which the gauge senses the pressure recommended oil pressure is a minimum of 4 bars at idle and 6 bars at full load. Oil seats fixed at the outer position of the two bearings prevent the atmospheric air entering inside the crankcase. Oil level can be checked visibly, and by the dipstick through the transparent oil level indicator, fitted on the side cover of the crankcase. Oil will overflow while filling, when the maximum level is reached.

TECHNICAL DATA (6CD 4UC)

01 MODEL TRC 155*615
02 TYPE RECIPROCATING,’W’TYPE,.AIR COOLED,FORCED FEED LUBRICATION
03 NORMAL WORKING PRESSURE Psi 140
04 FREE AIR DELIVERY 2.833 m3/min
05 RATED SPEED Rpm 1000
06 SPEED RANGE Rpm 400-1100
07 DISPLACEMENT Rpm AIR VACUUM
CFM LPM CFM LPM
400 61.35 1740 245.8 6959
500 76.69 2180 307.0 8693
750 115.03 3270 460.5 13039
1000 153.5 4349 614.0 17398
1025 157.4 4457 629.8 17833
08 TYPE OF CONFIGURATION VERTICAL LP & HP CYLINDERS, ‘V’ VACUUM CYLINDERS
09 COMPRESSION STAGE Nos 2
10 CYLINDERS Nos LP-1, HP-1, VACUUM-4
11 CYLINDER SIZE & STROKE mm 196.85 * 107.95 * 142.87
12 TYPE OF PISTON RING Dia (197) 5 Nos Dia (108) 1 No
a. PLAIN COMPRESSION 1 1
b. STEPPED COMPRESSION 1 1
c. SLOTTED OIL CONTROL 2 2
13 TYPE OF VALVES CONCENTRIC TYPE, DISC VALVE
14 DIRECTION OF ROTATION ANTI-CLOCKWISE FROM DRIVE END
15 TYPE IF LUBRICATION FORCED FEED
16 SHAFT HORSE POWER @ 1000 RPM
a. 140 Psi Air, 0” Vacuum BHP 115
b. 23” Vacuum BHP 60
17 TYPE OF COOLING FAN
18 TYPE OF FAN FORCED DRAUGHT, MOUNTED ON CRANKSHAFT
19 OIL FILL CAPACITY Lts 30
20 GRADE OF OIL Servo Press 150-IOC
21 LUBE OIL PRESSURE 4 to 5 min, 6 to 7 max Kgf/cm2
22 LUBE OIL PUMP DRIVE GEAR, MOUNTED ON CRANKSHAFT
23 SAFETY VALVE SET PRESSURE, HP-Inlet Psi 50
24 OVERALL DIMENSION mm 1207 * 1410 * 1000
25 NET WEIGHT Kg 865 approx

CONCLUSION

Thus, in locomotives, where high efficiency braking and dual system are required for both air and vacuum braking, the use of expressor is seen to produce the best results. Further, Its use can be extended in future, to heavy- duty automobiles, which may require the use of dual braking.

BIBILIOGRAPHY

ELGI- EXPRESSOR MANUAL
THOMAS BELL - LOCOMOTIVE BRAKES & ALLIED SYSTEMS
KASI VISWANATHAN -ALL ABOUT LOCOMOTIVES
TRIVEDI -BRAKING SYSTEMS IN INDIAN RAILWAYS

WEB BASED
www.dias.net/compressor/exhauster
www.howstuffworks.com
www.irfca.org

Ceramic Disc Brakes

2010-08-07T04:59:00.001-07:00

INTRODUCTION

One of the most important control system of an automobile is BRAKE SYSTEM .They are required to stop the vehicle within the smallest possible distance and is done by converting kinetic energy of the vehicle into heat energy which is dissipated into atmosphere.
The main requirements of brakes are given below:-
1. The brakes must be strong enough to stop the vehicle within the minimum possible distance in an emergency. But this should also be consistent with safety. The driver must have a proper control over the vehicle during emergency braking and the vehicle must not skid.
2. The brakes must have good antifade characteristics and their effectiveness should not decrease with constant prolonged application.

The actual stopping distance of vehicle while braking depends on the following factors:-
1. Vehicle speed
2. Condition of the road surface
3. Condition of tyre tread
4. Coefficient of friction between the tyre tread and the road surface
5. Coefficient of friction between the brake drum/disc and brake lining/friction pad
6. Braking force applied by the driver

TYPES OF BRAKES
The brakes for automotive use may be classified according to the following consideration

1. Purpose
a). Service or primary brakes
b). Parking or secondary brakes

2. Construction
a). Drum brakes
b). Disc brakes

3. Method of Actuation
a). Mechanical Brakes
b). Hydraulic Brakes
c). Electric Brakes
d). Vacuum Brakes
e). Air Brakes
4. Extra Braking Effort
a). Servo Brakes or Power assisted brakes
b). Power Operated Brake
DISC BRAKES
As shown in fig a disc brake consists of a cast iron disc bolted to the wheel hub and a stationary housing called caliper. The caliper is connected to some stationary part of the vehicle, like the axle casing or the stub axle and is cast in two parts, each part containing a piston. In between each piston and disc there is a friction pad held in position by retaining pins, spring plates etc., passages are drilled in the caliper for the fluid to enter or leave each housing. These passages are also connected to another one for bleeding.
When the brakes are applied hydraulically actuated pistons move the friction pads into contact with the disc, applying equal and opposite forces the later. On releasing the brakes the rubber sealing rings act as return springs and retract the pistons and the friction pads away from the disc.
CONSTRUCTIONAL FEATURES
Two types brake discs are generally used the solid type and the ventilated type. The ventilated type more efficient since it provides better cooling. But they are thicker and heavier than solid type, they are liable to wrap at severe braking conditions, the dirt accumulates in the vents which affects cooling and apart produces wheel imbalance.
The discs of the brakes are made of pearlite gray cast iron. The material is cheap and has good antiwear properties. Cast steel discs have also been employed in certain cases, which wear still less and provide higher coefficient of friction. Their main drawback is the non uniform frictional behavior.
The other materials used for the manufacture of disc are
1. Aluminium
2. Ceramic

Obviously, cast-iron disc is the heaviest part of a brake - about 8 kg each, or 32 kg per car. Aluminium alloy discs are used in the Lotus Elise. Though light, they were less resistant to heat and fade, thus more powerful Elises still employ conventional cast-iron disc.
In contrast, carbon-fiber disc is most heat-resisting yet is by far the lightest, however, it requires very high working temperature, and otherwise braking power and response will be unacceptable.
Ceramics are inorganic, non-metallic materials that are processed and used at high temperatures. They are generally hard brittle materials that withstand compression very well but do not hold up well under tension compared to the metals. They are abrasive-resistant, heat resistant (refractory) and can sustain large compressive loads even at high temperatures. The nature of the chemical bond in the ceramics is generally ionic in character, and the anions play an important role in determination of the properties of the material. Typical anions present are carbides, borides, nitrides and oxides. The different types of ceramics are clays, refractories, glasses etc.
Cast iron has been the material of choice for brakes rotors since the introduction of disc brakes during the 50’s.Elise made a new era, being the first road production road car to use aluminium metal matrix composite discs inserted on four wheels. Aluminium is better rotor material than cast iron due to two main reasons: its density is as one third as cast iron but its thermal conductivity is three times greater. These factors made it possible to construct a much lighter brake disc.

COMMPARISON OF CERAMIC BRAKES
AND CONVENTIONAL BRAKE DISC
Until now brake discs have been made up of grey cast iron, but these are heavy which reduces acceleration, uses more fuel and has a high gyroscopic effect.
Ceramic disc brake weigh less than carbon/carbon discs but have the same frictional values with more initial bite and cost a fraction of price. Carbon /carbon discs are used only in Formula 1 racing cars etc, because it is so expensive. More over ceramic brake discs are good even in wet conditions which carbon / carbon disc notoriously fails to do.
But comparing their weight, you will see right away that we are looking at two different worlds, with ceramic brake discs more than 61 per cent lighter than conventional cast iron discs. In practice

this reduces the weight of the car, depending on the size of the brake discs, by up to 20 kg. And apart from saving fuel, resulting in better and lower emission for the same mileage, this also means a reduction in unsprung masses with a further improvement of shock absorber response and behavior. Another is the manufacturer can add more safety features without adding to current weight.

MANUFACTURING OF CERAMIC BRAKE DISCS
In the earlier days, the brake discs were made from the conventional brittle ceramic materials would have disintegrated into a thousand pieces under slightest pressure.
The research division of Daimler Chrysler has developed techniques to make carbon fiber reinforced brake discs which avoid the brittleness problem. In the earlier days, long carbon fibers were used. Later the use of short carbon fibers increased the efficiency.
The composites for producing fiber reinforced ceramic brake discs are short carbon fibers, carbon powder, and resin mix. The process involves first compressing the carbon fibers, carbon powder and the resin mix together and then sintering at1000 degree Celsius. In the furnace a stable carbon frame work created. This consists of carbon fibers in a carbon matrix. Once cooled this material can be ground like wood and the break disk obtains its final shape.
Together with silicon the ground break disk blank is then inserted into the furnace a second time. The pores in the carbon framework absorb the silicon melt like a sponge; the fibers themselves remain unaffected by this process.

The ceramic material is created when the matrix carbon combines with liquid silicon. This fiber reinforced ceramic material cools over night and the gleaming dark grey break disk is ready.
Resin is a binder, which holds the different constituents together. Resins are of two types : 1.Thermosetting resins
2. Thermoplastic resins.
Thermoplastic resins are those, which can be softened on heating harden on cooling. Repeated heating and cooling does not affect their chemical nature of materials. These are formed by addition polymerization and have long chain molecular structure.

Thermosetting resins are those resins which, during molding process (by heating) get hardened and once they have solidified, they cannot be softened i.e. they are permanent setting resins. Such resins during moldings, acquire three dimensional cross linked structure with predominantly strong covalent bonds. They are formed by condensation polymerization and are stronger and harder than thermoplastic resins. They are hard, rigid, water resistant and scratch resistant.
COATING OF CERAMICS ON CONVENTIONAL BRAKE DISC
Earlier brake disc have been made of grey cast iron, but these are heavy which reduces acceleration, uses more fuel, etc. The new technology developed by Freno Ltd uses metal matrix composite for the disk, basically an alloy of aluminum for lightness and silicon carbide for strength. However it was found that, the ceramic additive made the disk highly abrasive and gave a low and unstable coefficient of friction. So it was realized that the surface had to be engineered in some way to overcome this problem. After experiments, Sulzer Metco Ltd found an answer in the form of a special ceramic coating. They developed thermal spray technology as well as manufacturing plasma surface engineering machinery used for the task and coating materials.
In use, the ceramic face requires a special carbon metallic friction pad, which deposits a layer of material on the brake disc. This coupling provides the required conditions of exceptional wear resistance, high and stable coefficient of friction.
The coated matrix composite discs were first used on high performance motor cycles, where the reduced gyroscopic effect had the additional advantage of making the cycles easier to turn.

Another company named Lanxide used aluminium as the disc material. To provide necessary abrasion resistance, aluminium discs have to be reinforced with a ceramic material, hence metal composite. They used silicon carbide also to increase the strength.

PORSCHE CERAMIC DISC BRAKES (P C C B)
After a long period of research and tests Porsche has developed new high performance disc brakes, P C C B (Porsche Ceramic Composite Brakes). Porsche has succeeded as the first car manufacturer in the world to develop ceramic brake discs with involute cooling ducts for an efficient cooling. The new brake system offers a substantial improvement in the car braking technology and sets entirely new standards in terms of decisive criteria such as braking response, fading stability, and weight and service life.

PORSCHE CERAMIC COMPOSITE BRAKE

Porsche's new brake system also offers obvious advantages in emergencies at low speeds: In such a case emergency application of the brakes with PCCB technology does not require substantial pedal forces or any technical assistance serving to build up maximum brake forces within fractions of a second. Instead, the Porsche Ceramic Composite Brake ensures maximum deceleration from the start without requiring any particular pressure on the brake pedal. And the new brake system is just as superior in its response under wet conditions, since the new brake linings cannot absorb water in the same way as conventional linings. The final point, of course, is that the cross-drilled brake discs help to optimize the response of the brakes also in wet weather.
The process involves heating carbon powder, resin and carbon fibers in a furnace to about 1700 degree Celsius and is a high vaccum process.

P C C B FITTED IN PORSCHE 911 TURBO

ADVANTAGES OF CERAMIC BRAKE DISCS

1. Ceramic brake discs are 50% lighter than metal brake discs. As a result, they can reduce the weight of car by up to 20kg. In case of a high speed ICE like train with 36 brake discs, these savings amount to 6 tons. And apart from saving fuel, this also means a reduction in unsprung masses with a further improvement of shock absorber response and behavior.
2. The ceramic brake disc ensures very high and, in particular, consistent frictional values

throughout the entire deceleration process. With Porsche ceramic brake discs, a car was able to decelerate from 100Km to 0Km in less than 3 seconds. In the case of Daewoo’s Nexia, it takes about 4 seconds to stop the vehicle.
3. Brake temperature - a factor crucial to stopping distances with metal brake discs - is now only a minor factor, both the brake lining and ceramic brake disc retaining their high level of friction regardless of whether they are hot or cold. This not only shortens stopping distances by a couple of - often decisive - meters, but also spares the driver unpleasant surprises whenever having to apply the brakes, say, from a high speed.
4. Ceramics retain their resistance up to 2000 degree celcius.Only if the temperature is excess of this, they loose their dimensional stability.
5. Initial field studies have shown that ceramic brake discs can still reliably bring an automobile to standstill even after 300,000 kilometers. Brake disc changes will in future be unnecessary.
6. They are not subject to wear, are maintenance free and are heat and rust resistant.
7. Heavily commercial vehicles can be braked safely over long distances without having to undergo brake maintenance. This dispenses with the need for expensive maintenance.
8. Ceramic brake discs do not rust under high oxygen concentration.
9. Ceramic brake discs do not warp or wear under constant use.
10. Dry and wet performances are excellent. Ceramics are water proof materials and the brake pads always remain dry.

APPLICATION
It was first introduced in Formula One, but applying to road cars seems impractical (F1 cars have warm up lap to bring the discs into appropriate working temperature), although the short-lived French sports car specialists Venturi made history by applying it to its road cars in the mid-90s

Porsche's fastest production model, the 911 Turbo, with a top speed of 305 km/h (189 mph) and acceleration from rest to 100 km/h (62 mph) in 4.2 s. Its engine is a 3.6-L producing 309 kW (420 hp), with maximum torque of 560 N•m (413 lb•ft) available from 2700 rpm is available with new Porsche Ceramic Composite Brake System.

PORSCHE 911 TURBO

PORSCHE 911 GT2
The new 911 GT2 comes with the most effective braking system ever featured on a production Porsche: the Porsche Ceramic Composite Brake (PCCB) - a powerful new technology designed to cope with even the most extreme conditions on racetrack and road?
Mercedes-Benz’s the futuristic Vision GST concept car features 22 inch wheels, 'butterfly' doors, three-dimensional instruments, a 360 horsepower 5.5 litre V8 engine, and carbon-fiber reinforced ceramic disc brakes.Mercedes Benz SLR IS ALSO available with ceramic disc brakes.

DISADVANTAGES
The main disadvantage of ceramic brake discs is their high initial cost. Initially the ceramic matrix composite brake discs will be more expensive than the current technology metal ones due to the low manufacturing volumes and high cost of production. But , because of the advantages listed above , the ceramic brakes will workout to be cheaper in the long run.

CONCLUSION
Ceramic brake discs due to its advantages over the conventional brake discs are going to be the brake discs for cars in future. The special combination in the ceramic brake discs had turned the conventional brake disc into a material most suited for making brake discs. With the success of this in Porsche turbo car , many other racing cars and commercial vehicles are going to implement the ceramic disc in their cars.

REFERENCES
1. AUTOMOTIVE MECHANICS – CROUSE / ANGLIN
2. http://www.hinduonnet.com/thehindu/2000/05/25/ceramic brake disc
3. Automotive Engineering International Online Global Viewpoints, Nov_ 1999
4. http://www.porsche.com
5. http://www.daimlerchrysler.com
6. http://www.mercedesbenz.com
7. http://www.howstuffworks.com

SOLAR CARS

2010-08-07T04:57:00.001-07:00

1. AN OVERVIEW
A solar car is a vehicle, which is powered by sun’s energy. A solar car is a light weight, low power vehicle designed and built with a single purpose in mind – racing. They have limited seating (usually one, sometimes two people), they have very little cargo capacity, and they can only be driven during the day. It does, however, offer an excellent opportunity to develop future technologies that can be applied to practical applications.

Figure 1: Energy Flow Diagram of a Solar Car
The main component of a solar car is its solar array, consisting of photovoltaic cells, which collect the energy from the sun and converts it into

usable electrical energy. The energy is passed either to the battery for storage, or to the motor to run the car, though a device called power tracker, which convert it into the required voltage. The decision on whether to transfer the power to the motor or battery is made by a small onboard computer called the motor controller. It is responsible for sending the electricity smoothly to the motor when the accelerator is depressed, controlling the torque that goes to the motor such that the car maintains the desired speed. Some cars also use a process called regenerative braking, which allows some of the kinetic energy stored in the vehicle’s translating mass to be stored in the battery when the car is slowing down.
A solar car is made up of many components that have been integrated together so that they work as a single system. For the ease of explanation it has been broken down into five primary systems:
• Driver Controls & Mechanical Systems
• Electrical System
• Drive Train
• Solar Array
• Body and Chassis

2. DRIVER CONTROLS & MECHANICAL SYSTEMS
Solar cars do have some of the standard features found in conventional cars, such as turn signals (front & rear), brake lights, accelerator, rear view mirrors, fresh air ventilation, and usually cruise control. The drivers and passengers are protected safety harnesses and helmets. Drivers and passengers can look forward to uncomfortable seats, cramped positioning, and high cockpit temperatures as these cars have very few amenities for the driver.
2.1 REAR VISION:
Mirrors mounted to a car's exterior greatly increase aerodynamic drag; therefore, an out-of-the–box thinking is required to find a solution. SUNRUNNER, a solar car developed by the University of Michigan in 1995, utilized a fibre optic cable connecting an eyepiece in the driver's area to a lens located in an aerodynamic fin mounted on top of the canopy. MAIZE & BLUE, a later model developed by the University, on the other hand, chose an electronic system consisting of a miniature camera installed in the car's trailing edge and a pocket television in the driver's area. Some cars also have externally mounted mirrors of mirrors within a bubble canopy.
2.2 VENTILATION:
High temperatures are obviously bad for the driver (and passenger), but they are also bad for electrical and electronic components as high temperatures will generally reduce the efficiency and shorten the life of solar cells, batteries, motors, motor controllers and other electronic equipment.

Figure 2: The comfortable interior temperature and air flow rate as a function of outside temperature

Something like 10 kilograms of air would typically have to be provided every minute to approach passenger car comfort levels. Obviously, that's seldom feasible in a solar car due to the drag that it might impose on the vehicle, if such cooling flows are not also required by electrical, electronic and mechanical components of the vehicle.
Vehicle designers usually use the same airflow several times over as it passes through the vehicle; for example cooling driver, electronics, electrics and motor sequentially. Placing a sizeable air inlet at the forward stagnation point of the vehicle minimises drag due to the opening. 'NACA ducts’ are an alternative for getting air into the car if there's a reasonably-flat, external surface nearby that doesn't have significant divergent (or convergent) flow.
The mechanical systems of a solar car are designed to minimize friction and weight while maintaining the strength needed to handle the various road conditions. Lightweight metals like titanium and composites are commonly used to maximize the strength-to-weight ratio. It includes:

2.3 STEERING:
The major design factors for steering are reliability and efficient performance. The steering system is designed with precise steering alignment because even small misalignments can cause significant losses and increase tire wear. Different cars use different steering mechanisms depending on their budget and other considerations. The SUNRUNNER utilized a rack and pinion system that was attached to the steering arms by means of tie rods. TESSERACT, a single-seat high performance solar racecar, uses a centre mounted handlebars, much like that on bicycles that connect to a rack-and-pinion steering system.
2.4 BRAKES:
To maximize efficiency, the brakes are designed to move freely, eliminating brake drag, which is caused by brake pads rubbing against the brake surface. Hydraulic disc brakes are commonplace in solar cars because of their adjustability and good braking power. As a supplemental system, some teams have regenerative braking which allows some of the kinetic energy stored in the vehicle’s translating mass to be stored in the battery when the car is slowing down. Here the car's motor becomes a generator as regenerative braking is applied and adds energy to the batteries during deceleration. Both MAIZE& BLUE and SUNRUNNER had hydraulic disc brakes while only SUNRUNNER used regenerative braking.
2.5 SUSPENSION:
Of the available front suspension variants, MacPhearson struts or double A arms are most common in solar cars. A MacPhearson strut requires a large vertical clearance since it is positioned perpendicular to the ground. Double A arms require less vertical clearance, but consist of more components. Depending

upon the design a suitable one is chosen. The most common rear suspension is a trailing arm, similar to that found in motorcycles. Due to a single degree of motion, the trailing arm suspension allows for convenient packaging of dampers and the drivetrain.
2.6 WHEELS:
Wheels, however, are the least efficient part of a solar car due to rolling resistance. About one third of the energy used by a solar car is lost due to this factor. Due to this limitation, contact with the ground should be minimized.
Solar cars typically have three or four wheels. The common three-wheel configuration is two front wheels and one rear wheel (usually the driven wheel). Four-wheel vehicles are sometimes configured like a conventional vehicle (with one of the rear wheels being driven). Other four-wheel vehicles have the two rear wheels close together near the centre (similar to the common three wheel configuration).
Solar car wheel designs are similar to those of bicycle tires. Generally, the wheel's rims and hubs are aluminium while the spokes are made of steel. A Mylar film is placed over the spokes to increase aerodynamic efficiency. Pneumatic tires are preferred over solid rubber tires because they weigh less and provide a smoother ride. The best tires currently available are the Bridgestone Ecopia tires made for solar cars. They are very thin and operate at over one hundred pounds/inch pressure.

3. ELECTRICAL SYSTEM
The heart of a solar car is the electrical system, which is made up of batteries and power electronics. Power electronics include the peak power trackers, the motor controller, and the data acquisition system. The primary function of the power electronics is to monitor and control the electricity within the system.
3.1 BATTERIES:
A solar car uses the battery pack to store energy, which will be at a later time. The battery pack is made up of several individual modules wired together to generate the required system voltage. The types of batteries used include:
• Lead-Acid
• Nickel-Metal Hydride (NiMH)
• Nickel-Cadmium (NiCad)
• Lithium Ion
The NiCad, NiMH, and Lithium batteries offer improved power to weight ratio over the more common Lead-Acid batteries, but are more costly to maintain.
The battery pack is made up of several individual modules wired together to generate the required system voltage. Typically, teams use system voltages between 84 and 108 volts, depending on their electrical system. For example, Tesseract uses 512 li-ion batteries, broken down into twelve modules, which are each equivalent to a car battery, but only weigh 5 lbs each. Through an innovative pack design, the batteries are ventilated with even airflow to minimize temperature differences between the modules.

3.2 PEAK POWER TRACKERS:
The peak power trackers condition the electricity coming from the solar array to maximize the power and deliver it either to the batteries for storage or to the motor controller for propulsion. When the solar array is charging the batteries, the peak power trackers help to protect the batteries from being damaged by overcharging. Peak power trackers can be very lightweight and commonly reach efficiencies above 95%.
A maximum power point tracker (MPPT) is a DC-DC converter that matches the output of a PV string to the battery voltage in a way that maximises the power generated by the PV string.
The power generated by a PV string depends on the operating voltage. PV power increases steadily with operating voltage to a maximum, and then drops off rapidly as the voltage is increased further to the open-circuit voltage. A tracker allows the PV string to always operate at the most efficient point, independently of the battery voltage. For example, if your battery voltage is 100V and the ideal operating point for an array string is 2A x 120V = 240W, the tracker output will be 2.4A x 100V = 240W. In practice, there is always a small loss of 1-2% due to inefficiencies in the tracker electronics.
MPPTs are of three types:
• down (buck) converters, which convert the PV voltage to a lower battery voltage;
• up (boost) converters, which convert the PV voltage to a higher battery voltage; and
• dual (buck-boost) converters, which will convert either way, though usually with a penalty in efficiency.

3.2.1 FINDING THE MAXIMUM POWER POINT: There are two methods to find the maximum power point.
1. Open-circuit voltage tracking: The tracker periodically measures the open circuit voltage, VOC, of the PV string, then sets the operating voltage to Vmp = k VOC, where k is a constant. The method is simple, and reasonably effective. This method is used by AERL trackers.
2. Power tracking: The tracker measures changes in output power as it makes small changes to the operating point, and adjusts the operating point to maximise output power.
3.3 MOTOR CONTROLLERS:
This component performs the complex task of deciding how much current actually reaches the motor at a given time. This determination of current by the motor controller allows the car to accelerate, decelerate, or stay at a constant speed. The better motor controllers are up to 90% efficient.
3.4 TELEMETRY:
A team's telemetry system is used for data acquisition. A commercial or custom system monitors conditions such as speed, battery voltage, power collection and consumption, and motor temperature. The system then relays that information to the driver and team strategists. Most telemetry systems allow for two-way data transmissions and are based on microcontrollers and radio modems.

4. DRIVE TRAIN
The drive train will consist of the electric motor and the means by which the motor's power is transmitted to the wheel causing the vehicle to move. Due to the low amount of power generated (less than 5 hp) usually only one wheel in the rear of the car is driven by the electric motor. The motor types that have been used in solar cars include
• brushed DC motors
• DC brushless motors
• induction motors
DC brushless motors are commonplace in solar car racing. Rare-earth, permanent magnets mounted on the rotor, reacts to magnetic fields produced by the motor's windings. Three-phase windings allow the rotor remain at constant torque. A motor controller sends signals to the windings, regulating the magnetic field around the rotor. The most common type of motor used in solar cars is the dual-winding DC brushless. It is fairly lightweight and can reach efficiencies of 98% at their rated rpm.
The dual-winding motor is sometimes used as an electronic transmission. Switching between the dual windings changes the speed rating of the motor. The low speed windings provide high torque for starting and passing, while the high speed windings have higher efficiencies and are best for cruising.
There are several variations of two basic types of transmissions used in solar cars.
1. single reduction direct drive
2. variable ratio belt drive
3. hub motor

In the past, the most common type was the direct drive transmission where the motor is connected to the wheel through a chain or belt with a single gear reduction. This is a reliable and easily maintained transmission if special care is taken when aligning the components. Efficiencies above 75% can be achieved when designed properly.
For a variable ratio belt drive, gear ratio changes as the speed of the motor increases. This gives the motor more starting torque at lower speeds, but still allows the car to run efficiently at higher speeds. Variable belt drives require precise alignment and careful setup to work efficiently.
A hub motor eliminates the need for any external transmission because the motor shaft is connected directly to the wheel hub. This greatly increases the efficiency of the drive train and reduces the number of moving parts necessary to drive the wheel. A hub motor uses low rpm to account for the lack of gear reduction, which tends to drop their efficiency slightly, but they still can achieve efficiencies in excess of 95%.

5. SOLAR INSOLATION
The energy from the sun strikes the earth throughout the entire day. However, the amount of energy changes due to the time of day, weather conditions and geographic location. The amount of available solar energy is known as the solar insolation or irradiance and is most commonly measured in watts per meter squared or W / m 2.

Figure 3: Typical solar insolation for a sunny day.
Solar irradiance is generally modelled as having three components:
• direct beam irradiance,
• diffuse irradiance, from the sky, and
• reflected irradiance, from the ground.

The sum of these components is called global irradiance. The irradiance that will fall on a surface depends on the many factors, including:
• the day of the year
• the position of the sun in the sky
• the inclination of the surface
• cloud cover.
These factors should be taken into account while designing the solar array.

6. SOLAR ARRAY
Solar cells or photovoltaics collect the energy from the sun and converts it into usable electrical energy. They are made from silicon by joining an n-type and a p-type silicon semiconductor, creating an electron rich and an electron poor layer. When sunlight strikes the cell, photons cause atoms of the semiconductor to free electrons, leaving behind positive charges. The flow of electrons thus created constitutes an electromotive force that drives the current to charge a battery or power a motor.
The cell's positive contact is on the bottom while the negative contact, or bus bar, is located on the top of the cell. Each cell produces approximately .5 volts and 3 amps of current. Connecting the cells in series, i.e., positive to negative, increases voltage. Parallel connections, i.e., negative to negative and positive to positive, increase current. Therefore, connecting the cells in various series and parallel configurations produces modules of different voltages and currents.

Figure 4: Schematic Diagram of a Solar

Figure 5: Solar Cell Diagram
Cells can be grouped into space grade and terrestrial grade categories:
• Space grade cells are up to 29% efficient, and are used mainly in satellite production due to their high cost. These high efficiency cells cost in excess of $500 per square inch.
• Terrestrial grade cells having a efficiency of 14%, are much cheaper causing them to be the cells of choice for solar cars. Each cell measures 10cm x 10cm, costs approximately $6.00, and produces 1.5 watts of power.
A large number of solar cells are wired together to form a solar array. The entire solar cells together form the solar array. Solar cells should also be divided into several zones. For example, if you have 750 solar cells, you might want to wire 3 sets of 250 cells, each zone producing about 125 volts. If one zone fails, two other zones are still producing power. SUNRUNNER'S array consisted of 14,057 razor blade sized, 16% efficient space grade cells.
The cells are extremely fragile. So many engineers put them through a process called encapsulation. Doing so strengthens solar cell durability, but decreases the efficiency. Encapsulation is the process of coating the cells with a tougher material like resins or sandwiching it between two sheets of fibre glass,

which prevents the cells from being damaged. For cells 14% efficient, encapsulation would reduce the overall efficiency to12.5%.
6.1 PRACTICALPROBLEMS WITH USING SOLAR CELLS
6.1. 1 I-V CURVES AND SERIES MISMATCH:
All silicon solar cells put out a voltage of about 0.5V. This is because they're a kind of diode, and this is analogous to the forward break over voltage of the diode. Now, if you have several cells in series and they're all the same they'll all give the same current, and the voltage from all the cells will add up neatly. But they're not all the same. The silicon is doped very subtly differently from cell to cell, or the purity of the silicon varies, or different cells are at different temperatures. Ss some cells will give more current than others. In a series string, they can't because all the cells are constrained to give exactly the same current. This will cause many of our cells to run sub-optimally. So after the cells are tabbed, they are measured, and grouped like with like.
6.1. 2 CURVED ARRAYS:
The next hazard is curves on the array. Many arrays are not perfectly flat, which means that not all cells are receiving the same amount of sunlight. They have to be arranged in such a way that all the cells in the strings receive approximately the same illumination. A common way to achieve this would be to run each string parallel to the long axis of the car, so that all the cells in a string are pointing in approximately the same direction. Several strings are often wired together to form a section or panel that has a voltage close to the nominal battery voltage.

6.1. 3 SHADOWS AND BROKEN CELLS:
Sometimes there will be shadows on the array. This could be caused by the driver bubble, or by trees or other obstructions near the road, or by passing traffic. When a cell in a string is shaded, its output goes down. Since the other cells continue to force current through it, this cell actually dissipates power instead of generating, and it gets dissipated as heat. Now that this cell is warmer, it's less efficient than the others, and so even when the light comes back, it'll want to generate less current, which means it'll wind up dissipating some power as heat. This is called Thermal runaway. This is prevented in the following way:
Every cell (or, more often, every small group of cells) has a diode across it. When a cell in that group is shaded, current flows through the diode. If you have 60 cells in your string, and they're in groups of 6, then when a single cell is shaded, your output voltage will drop by 10%, as the bypass diode for that group comes into play, and your current output will drop not at all. This is better than having your voltage drop 0.6V for the dark cell, and having your current output drop by some large amount, as current is forced through the dark cell.
The other time that the bypass diodes come in handy is when a cell gets damaged. This may be due to a stone being flicked up from the road, a camera falling out of someone's pocket or a small child running up the array. The damaged cell may go open-circuit, meaning that without the bypass diode, output from the string would drop to zero. With the bypass, output drops only proportionately to the percentage of cells bypassed.

6.2 LIMITATIONS:
To put the limitations of a solar car in perspective, a simple calculation will suffice. Only 1000 W/m2 of energy reaches the earth’s surface in an hour of “peak sun”. This term can be thought of as the amount of sunlight that reaches a sunny area on cloudless, summer day around noon. An average solar array configuration span 8m, meaning the total amount of energy hitting the solar car during peak sun is 8KWh/m2. Of this energy, average solar cells are only able to convert 12.5% to electricity. As a result, the total amount of converted energy available to a car consists of 1 KW/h, approximately the same amount of energy used to run a hairdryer.
With cars running on 700-1500 Watts, efficiency is hypercritical. Therefore, advances in all aspects of engineering, from mechanical to electrical to materials and computer science are the key. The three primary areas of energy loss consist of aerodynamic drag, braking, and rolling resistance. To minimize aerodynamic drag, engineers make solar cells as sleek as possible. Rolling resistance is proportional to weight. Hence solar cars should be engineered to be very light.

7. BODY & CHASSIS
The most distinctive part of solar cars is their bodies. The sleek and exotic shapes are eye catching. The main goals when designing the body are to minimize the aerodynamic drag, maximize the exposure to solar insolation, minimize weight, and maximize safety.

Figure 6: Body and Chassis of a Solar Car

7.1 BODY SHAPES
Although cars differ in design, their shapes can be grouped into four categories. A unified aero body and panel allows for a small frontal area, low weight, and a wide range of visibility around the canopy. Fixed or tilting, flat panels with a separate driver cab are simple, lightweight, and inexpensive to construct; however, aerodynamic efficiency is compromised due to exposed suspension components and vulnerability to cross winds. Catamaran shapes offer reduced frontal area and low aerodynamic drag. For north/south race routes, the curved array becomes very powerful in the early morning and late afternoon as the sun travels across the horizon. Finally, are uniquely designed vehicles whose aerodynamic efficiency and power collection capabilities differ from design to design. MAIZE & BLUE and SUNRUNNER were catamaran shaped.

Figure 8: Body shapes of common solar cars

7.2 CHASSIS
Generally, there are three types of chassis used in solar cars:
1. space frame
2. semi-monocoque or carbon beam
3. monocoque
A space frame uses a welded tube structure to support the loads and the body. The body is a lightweight, non-load bearing, composite shell that is attached to the chassis separately. The semi-monocoque or carbon beam chassis uses composite beams and bulkheads to support the loads and is integrated into a non-load bearing composite belly pan. The top sections of the car are often separate body pieces that are attached to the belly pan. A monocoque chassis uses the body structure to support the loads. Many solar cars use a combination of the chassis categories mentioned above. The image above is an example of a semi-monocoque chassis with an integrated space frame used to protect the driver.

8. MATERIALS USED
A composite material is the combination of a filler material sandwiched between layers of a structural material. Carbon fibre, Kevlar and fibreglass are common composite structural materials. Honeycomb and foam are common composite filler materials. These materials are bonded together using epoxy resins and in the cases of Kevlar and carbon fibre, can obtain impressive strengths (equal to steel) but remain very lightweight. SUNRUNNER used Kevlar as the fabric with a Nomex honeycomb spacer while MAIZE& BLUE used carbon fibre fabric.
9. FALLING SHORT
There are several characteristics that a commercially viable car must have. Commercial cars typical can hold at least 4 passengers. It must be extremely reliable, comfortable, and be able to function on its own. It must also be able to maintain the required speed. In addition, commercial cars typically have amenities such as air conditioning, radio, and power locks and windows. Solar vehicles when driven on highways, experienced many flat tires and often were incapable of maintaining highway speeds of fifty-five miles per hour. With the energy available to solar cars, the type of amenities described above is impossible. The car is also a very cramped one. Hence it failed to break into the commercial car market as of now

10. THE FUTURE
10.1 IN THE SHORT TERM
One plausible market for solar vehicles is a terrestrial application of the rovers that NASA uses in space for data collection in a hot, sun rich area where manual labor is difficult. The vehicles would recharge autonomously, and the driver’s discomfort would not be an issue because there would not be a driver. In addition, these vehicles could be kept lightweight and simple without a need for too many amenities.
10.1.1 CARRY-OVER OF EXPERTISE:
The solar car rush brought substantial advances to the design of electric vehicles, starting with the use of solar power. It led to better motors, better use of batteries, and better motor controller design which have been adopted by some electrical vehicle manufacturers.
10.1.2 COMPOSITE HULL CAR:
Another key area that has been charging ahead is the composite hull car. Composites were not only lighter, but they also made cars safer than their steel counterparts.
10.1.3 HARNESSING SOLAR POWER
Solar cars also helped spread the word about the use of harnessing solar power. By spreading the word about solar energy in this exciting way, the cars contributed to the rise in the use of solar cells for other, more practical uses. Lastly, it created a sport that has an educational as well as a social benefit.

10.2 IN THE LONG RUN
Whatever be its limitations, the future is definitely full of promise for the solar cars. It took us about a hundred years after electricity was invented, to develop a commercially viable electric vehicle. Similarly solar cars too need a suitable incubation period, to successfully foray into the commercial vehicle segment.
With the crude prices hitting upwards of $50 a barrel and still looking bullish, it is certain that the current preference for petroleum based automobiles will change in the not too distant future. The solar car with no fuel expenses will certainly be preferred for short distance commutation in the future. Though it may offer only a significantly reduced performance compared to the conventional vehicle it will then be looked upon as a cost effective option.
Also, there are many areas of the solar car, which can be improved upon, starting with the solar array. At present the solar array is only 12.5% efficient. What would be the case if it were made atleast 50% efficient? I’m sure that much of the current problems in solar cars can be overcome.

CONCLUSION
The solar cars are used exclusively for racing in tournaments, at present. Though they have been around for about twenty five years now, the technology is still in the developmental stages. Hence they can not be used as a practical means of transport. The challenge lies in making it a viable means of transport. Further research is needed in this regard to improve solar panels, reduce weight, to improve reliability and to reduce the cost. Research is being carried out on many semi-conductors and their alloys to develop more efficient solar cells. It can be safely assumed that with the advent of mass production there would be greatly reduced. Thus this technology will definitely live up to its potential some time in the future.

CONTENTS
1. AN OVERVIEW
2. DRIVER CONTROL AND MECHANICAL SYSTEMS
3. ELECTRICAL SYSTEMS
4. DRIVE TRAIN
5. SOLAR ARRAY
6. BODY AND CHASIS
7. CONCLUSION

ABSTRACT
A solar car is a vehicle, which is powered by sun’s energy. A solar car is a light weight, low power vehicle designed and built with a single purpose in mind – racing. Solar cells or photovoltaics collect the energy from the sun and converts it into usable electrical energy When sunlight strikes the cell, photons cause atoms of the semiconductor to free electrons, leaving behind positive charges. The flow of electrons thus created constitutes an electromotive force that drives the current to charge a battery or power a motor.This technology will definitely live up to its potential some time in the future.

REFERANCE

1. www.wikipedia.org
2. www.solarcars.com
3. Britannica encyclopedia

HYWI CAR

2010-08-07T04:54:00.000-07:00

1. INTRODUCTION

Automobiles as we know today are very complicated machines even though their basic purpose is transportation. The fundamental processes that a car performs are acceleration of wheel speed, their control through braking, the turning of the wheels with the help of the steering mechanism & so on. Given that the overall function of a car is so basic it seems a little strange that almost all cars have the same collection of complex devices crammed under the hood and the same general mass of mechanical and hydraulic linkages running throughout. So considering these facts, automotive engineers for many years, pondered over the question as to why do cars need all these complicated machinery at all. And funnily they found that cars actually don’t need all these gizmos and in the future they won’t need these.
This seminar deals with such a futuristic vision which the automotive engineers at GM (General Motors) have realized. The HY WIRE concept car the name symbolizes the combination of hydrogen as fuel for the fuel cell propulsion system, and the replacement of conventional mechanical and hydraulic control linkages for steering, braking and other control systems by a drive-by-wire system. "By combining fuel cell and by-wire technology, we've packaged this vehicle in a new way, opening up a new world of chassis architectures and customized bodies for individualized expressions and . It is a significant step towards a new kind of automobile that is substantially more friendly to the environment and provides consumers positive benefits in driving dynamics, safety and freedom of individual expression”.
The car is derived from GM’s previous concept of a drive-able fuel cell vehicle called the Autonomy which was debuted at the 2002 North American Motor Show in Detroit. GM does not hope to be selling these cars immediately, due to certain unavoidable hindrances but they are optimistic of seeing these vehicles on the road in the next decade or two.

2. CONCEPT OF HY-WIRE CAR

Conventional cars possess other complex machinery in addition to the ‘heart’ of the car i.e. the IC engine such as carburetor, gearbox, ignition systems, radiator etc. If you've ever looked under the hood of a car, you know an internal combustion engine requires a lot of additional equipment to function correctly. No matter what else they do with a car, designers always have to make room for this equipment. The same goes for mechanical and hydraulic linkages. The basic idea of this system is that the driver maneuvers the various actuators in the car (the wheels, brakes, etc.) more or less directly, by manipulating driving controls connected to those actuators by shafts, gears and hydraulics. In a rack-and-pinion steering system, for example, turning the steering wheel rotates a shaft connected to a pinion gear, which moves a rack gear connected to the car's front wheels. In addition to restricting how the car is built, the linkage concept also dictates how we drive: The steering wheel, pedal and gear-shift system were all designed around the linkage idea.
The defining characteristic of the Hy-wire (and its conceptual predecessor, the AUTOnomy) is that it doesn't have either of these two things. Instead of an engine, it has a fuel cell stack, which powers an electric motor connected to the wheels. Instead of mechanical and hydraulic linkages, it has a drive by wire system -- a computer actually operates the components that move the wheels, activate the brakes and so on, and based on input from an electronic controller. This is the same control system employed in modern fighter jets as well as many commercial planes. The result of these two substitutions is a very different type of car -- and a very different driving experience. There is no steering wheel, there are no pedals and there is no engine compartment. In fact, every piece of equipment that actually moves the car along the road is housed in an 11-inch-thick (28 cm) aluminum chassis -- also known as the skateboard -- at the base of the car. Everything above the chassis is dedicated solely to driver control and passenger comfort.

Skate board chassis

This means the driver and passengers don't have to sit behind a mass of machinery. Instead, the Hy-wire has a huge front windshield, which gives everybody a clear view of the road. The floor of the fiberglass-and-steel passenger compartment can be totally flat, and it's easy to give every seat lots of leg room. Concentrating the bulk of the vehicle in the bottom section of the car also improves safety because it makes the car much less likely to tip over.
But the coolest thing about this design is that it lets you remove the entire passenger compartment and replace it with a different one. If you want to switch from a van to a sports car, you don't need an entirely new car; you just need a new body (which is a lot cheaper).
Before we get to the further features of the car, we will discuss about the 2 most defining technologies that make up the HY WIRE car i.e. the drive by wire system & Hydrogen fuel cell technology.

3. GM HY-WIRE CONCEPT CAR

• HISTORY

General Motors, the American automobile behemoth, is essentially the company bringing out the HY WIRE car. But this was not the first alternate fuel powered vehicle that they were bringing out. GM’s overarching advanced technology strategy for propulsion systems was designed to build capability for increased power and energy efficiency and reduced emissions with the long-term vision of making the transition to hydrogen-fueled fuel cell powered vehicles that emit only clean water and offer twice the energy efficiency of traditional engines. This technology development focuses on fuel cell power systems, hydrogen production (electrolysis and fuel processing), electric drive control and system integration, hydrogen storage, and affordability.
At the 2002 North American International Motor Show at Detroit, GM unveiled the AUTOnomy car which was the first purpose-designed vehicle combining the benefits of fuel cells and drive by wire technology. Discarding the restrictions of conventional vehicle design based around the internal combustion engine, the vehicle consists of an innovative, skateboard-like chassis, incorporating all the running gear, such as fuel cell powered electric drive, steering and braking systems, onto which a variety of different body styles, from a two-seater sports car to a people carrier, can be placed as required.
The GM Hy-wire incorporates the features first envisioned in the AUTOnomy concept vehicle. All of the touring sedan's propulsion and control systems are contained within an 11-inch-thick skateboard-like chassis, maximizing the interior space for five occupants and their cargo. GM designers and engineers in the United States developed the vehicle chassis and body design, as well as the engineering and electrical system integration. Engineers at GM's research facility in Mainz-Kastel, Germany, integrated the fuel-cell propulsion system, which is the same system used in the HydroGen3 concept, based on an Opel Zafira and shown at the 2001 Frankfurt Motor Show. American designers also worked closely with Italian design house Stile Bertone in Turin, where the body was built. The SKF Group, headquartered in Sweden, developed the by-wire technology in the Netherlands and in Italy.

• What led to this name?

GM originally dubbed its working concept for a drive-by-wire fuel-cell car the AUTOnomy, to highlight the flexibility of the computer control and switch able car bodies. When it came time to name the actual drivable version, the design team recruited a group of kids, ranging from six to 15 years old, to come up with interesting possibilities. Hy-wire, because it nicely summarized the hydrogen-fuel-cell and drive-by-wire concepts at the vehicle's core.

4. DRIVE BY WIRE

Drive-By-Wire technology is the incorporation of electrical devices to supplant the use of mechanical linkages within a vehicle. This implementation can use electro hydrostatic. Electro pneumatic or electromechanical means. Drive-by-wire systems are forecast to replace many of the traditional hydraulic and mechanical systems in vehicles. Originally known as ‘fly-by-wire’ because it was used in fighter jets & for other aviation purposes. The past few years has seen its introduction into military vehicles (such as tanks etc.) and heavy vehicles (like Caterpillars). The drive-by-wire system follows closely the fly-by-wire concepts used successfully by the aerospace industry for many years. In conventional control, the movements the driver makes with the steering wheel are transmitted mechanically via the steering column to the steering rack and then to the front wheels. In a by-wire system, the driver’s physical movement on the steering wheel is sensed and converted into a digital electronic signal that is transmitted to a smart electro-mechanical actuation unit (SEMAU) that controls the wheels. The same principle can be applied to the braking and gearbox systems.
Like so many of today's technologies, drive-by-wire is primarily a response to tightening emission standards. As with fuel injection and integrated engine controllers, drive-by-wire systems improve engine efficiency while cutting vehicle emissions. They do this by replacing clunky and inaccurate mechanical systems with highly advanced and precise electronic sensors. Currently, drive-by-wire applications are being used to replace the throttle-cable system on newly developed cars like the models already mentioned.
These systems work by replacing conventional throttle-control systems. Instead of relying on a mechanical cable that wind from the back of the accelerator pedal, through the vehicle firewall, and onto the throttle body, drive-by-wire consists of a sophisticated pedal-position

Sensor that closely tracks the position of the accelerator and sends this information to the Engine Control Module (ECM). This is superior to a cable-operated throttle system for the following reasons:

1. By eliminating the mechanical elements and transmitting a vehicle's throttle position electronically.Thedrive-by-wire greatly reduces the number of moving parts in the throttle system. This means greater accuracy, reduced weight, and, theoretically, no service requirements (like oiling and adjusting the throttle cable).
2. The greater accuracy not only improves the driving experience (increased responsiveness and consistent pedal feel regardless of outside temperature or pedal position), but it allows the throttle position to be tied closely into ECM information like fuel pressure, engine temperature and exhaust gas re-circulation. This means improved fuel economy and power delivery as well as lower exhaust emissions.
3. With the pedal inputs reduced to a series of electronic signals, it becomes a simple matter to integrate a vehicle's throttle with non-engine specific items like ABS, gear selection and traction control. This increases the effectiveness of these systems while further reducing the amount of moving parts, service requirements and vehicle weight.
For the driver, the most striking aspects of the interior design of the vehicle are the absence of pedals and steering column. This creates considerably more space inside the car. Drive-by-wire technology eliminates heavy, space-consuming hydraulic and mechanical components, and it has positive environmental implications through the elimination of brake fluids, as well as significant safety benefits.
Electro-mechanical control could allow the steering column and pedals to be removed, a significant potential for improving passive safety for the driver in case of a crash.
In this concept vehicle, the driver’s control system combines all the controls that the driver needs in a single unit. Throttle, braking and steering are presented as hand controls. Gear selection is made by a button system that is familiar from the world of motor racing. Lights, windscreen wipers, audio, heating and air conditioning are all located within the driver’s immediate reach. The right and left steering control yokes, which are linked, have a travel of +/- 20 degrees. The amount of “feel” experienced by the driver is fully programmable, as is the relationship between the movement of the yokes and the movement of the front wheels. For the Filo, the steering actuator fits into the original platform’s sub-frame assembly.

• What does it do to the car?
• Increases responsiveness of the system, leading to better steering & braking.
• Negates the usage of a steering column & reduces the number of moving parts.
• It has positive environmental implications through the elimination of brake fluids, as well as significant safety benefits.
•Increased capability due to fault monitoring and diagnostics

• What does it mean for driver?
• Enhanced driving experience
• Less tiring
• Provides more space for passengers upfront due to absence of steering column & associated linkages.
• Less or nil maintenance due to near absence of any moving parts

5. FUEL CELL POWER
A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into water, producing electricity and heat in the process. It is very much like a battery that can be recharged while you are drawing power from it. Instead of recharging using electricity, however, a fuel cell uses hydrogen and oxygen. A fuel cell provides a DC (direct current) voltage that can be used to power motors, lights or any number of electrical appliances. There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by the type of electrolyte they use. Some types of fuel cells show promise for use in power generation plants. Others may be useful for small portable applications or for powering cars. The proton exchange membrane fuel cell (PEMFC) is one of the most promising technologies. This is the type of fuel cell that will end up powering cars, buses and maybe even your house. The proton exchange membrane fuel cell (PEMFC) uses one of the simplest reactions of any fuel cell. It is the type of fuel cell used in the Hy-Wire car.

First, let's take a look at what's in a PEM fuel cell. We can see there are four basic elements of a PEMFC:
The anode, the negative post of the fuel cell, has several jobs. It conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit. It has channels etched into it that disperse the hydrogen gas equally over the surface of the catalyst. The cathode, the positive post of the fuel cell, has channels etched into it that distribute the oxygen to the surface of the catalyst. It also conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water. The electrolyte is the proton exchange membrane. This specially treated material, which looks something like ordinary kitchen plastic wrap, only conducts positively charged ions. The membrane blocks electrons. The catalyst is a special material that facilitates the reaction of oxygen and hydrogen. It is usually made of platinum powder very thinly coated onto carbon paper or cloth. The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the PEM.

• Working:

The pressurized hydrogen gas (H2) enters the fuel cell on the anode side. This gas is forced through the catalyst by the pressure. When an H2 molecule comes in contact with the platinum on the catalyst, it splits into two H+ ions and two electrons (e-). The electrons are conducted through the anode, where they make their way through the external circuit (doing useful work such as turning a motor) and return to the cathode side of the fuel cell.
Meanwhile, on the cathode side of the fuel cell, oxygen gas (O2) is being forced through the catalyst, where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts the two H+ ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H2O).
This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack.
PEMFCs operate at a fairly low temperature (about 176 degrees Fahrenheit, 80 degrees Celsius), which means they warm up quickly and don't require expensive containment structures. Constant improvements in the engineering and materials used in these cells have increased the power density to a level where a device about the size of a small piece of luggage can power a car.
Chemistry of a Fuel Cell
Anode side:
2H2 => 4H+ + 4e-
Cathode side:
O2 + 4H+ + 4e- => 2H2O
Net reaction:
2H2 + O2 => 2H2O

We learned in the last section that a fuel cell uses oxygen and hydrogen to produce electricity. The oxygen required for a fuel cell comes from the air. In fact, in the PEM fuel cell, ordinary air is pumped into the cathode. The hydrogen is not so readily available, however. Hydrogen has some limitations that make it impractical for use in most applications. For instance, you don't have a hydrogen pipeline coming to your house, and you can't pull up to a hydrogen pump at your local gas station.
Hydrogen is difficult to store and distribute, so it would be much more convenient if fuel cells could use fuels that are more readily available. This problem is addressed by a device called a reformer. A reformer turns hydrocarbon or alcohol fuels into hydrogen, which is then fed to the fuel cell. Unfortunately, reformers are not perfect. They generate heat and produce other gases besides hydrogen. They use various devices to try to clean up the hydrogen, but even so, the hydrogen that comes out of them is not pure, and this lowers the efficiency of the fuel cell.
Some of the more promising fuels are natural gas, propane and methanol. Many people have natural-gas lines or propane tanks at their house already, so these fuels are the most likely to be used for home fuel cells. Methanol is a liquid fuel that has similar properties to gasoline. It is just as easy to transport and distribute, so methanol may be a likely candidate to power fuel-cell cars.

• Application Of Fuel Cells :

As we've discussed, fuel cells could be used in a number of applications. Each proposed use raises its own issues and challenges.
Automobiles:
Fuel-cell-powered cars will start to replace gas- and diesel-engine cars in about 2005. A fuel-cell car will be very similar to an electric car but with a fuel cell and reformer instead of batteries. Most likely, you will fill your fuel-cell car up with methanol, but some companies are working on gasoline reformers. Other companies hope to do away with the reformer completely by designing advanced storage devices for hydrogen.
Portable Power:
Fuel cells also make sense for portable electronics like laptop computers, cellular phones or even hearing aids. In these applications, the fuel cell will provide much longer life than a battery would, and you should be able to” recharge" it quickly with a liquid or gaseous fuel.
Buses:
Fuel-cell-powered buses are already running in several cities. The bus was one of the first applications of the fuel cell because initially, fuel cells needed to be quite large to produce enough power to drive a vehicle. In the first fuel-cell bus, about one-third of the vehicle was filled with fuel cells and fuel-cell equipment. Now the power density has increased to the point that a bus can run on a much smaller fuel cell.
Home Power Generation:
This is a promising application that you may be able to order as soon as 2002. General Electric is going to offer a fuel-cell generator system made by Plug Power. This system will use a natural gas or propane reformer and produce up to seven kilowatts of power (which is enough for most houses). A system like this produces electricity and significant amounts of heat, so it is possible that the system could heat your water and help to heat your house without using any additional energy.

6. FEATURES OF THE HY-WIRE CAR

• POWER TRANSMISSION:

The components which comprise the power transmission mechanism are the Hydrogen fuel cell stack & the 3-phase ac motor. We have discussed the working of the fuel cell just before. Now the reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack. The fuel-cell stack in the Hy-wire is made up of 200 individual cells connected in series, which collectively provide 94 kW (125 bhp) of continuous power and 129 kW (173 bhp) at peak power. This system delivers DC voltage ranging from 125 to 200 volts, depending on the load in the circuit. Three cylindrical storage tanks made by Quantum Fuel Systems Technologies Worldwide, Irvine, CA, rated at 5,000 psi (350 bar) so far provide a range of about 100 km (60 miles), with refueling in five minutes. But judging from earlier comments by GM's vice president of research and development, Larry Burns, higher-pressure tanks of 10,000 psi are
Under consideration. The motor controller boosts this up to 250 to 380 volts and converts it to AC current to drive the three-phase electric motor that rotates the wheels (this is similar to the system used in conventional electric cars).
The electric motor's job is to apply torque to the front wheel axle to spin the two front wheels. The control unit varies the speed of the car by increasing or decreasing the power applied to the motor. When the controller applies maximum power from the fuel-cell stack, the motor's rotor spins at 12,000 revolutions per minute, delivering a torque of 159 pound-feet. A single-stage planetary gear, with a ratio of 8.67:1, steps up the torque to apply a maximum of 1,375 pound-feet to each wheel. That's enough torque to move the 4,200-pound (1,905-kg) car 100 miles per hour (161 kph) on a level road. Smaller electric motors maneuver the wheels to steer the car, and electrically controlled brake calipers bring the car to a stop.

• CONTROL:

The Hy-wire's "brain" is a central computer housed in the middle of the chassis. It sends electronic signals to the motor control unit to vary the speed, the steering mechanism to maneuver the car, and the braking system to slow the car down.
At the chassis level, the computer controls all aspects of driving and power use. But it takes its orders from a higher power -- namely, the driver in the car body. The computer connects to the body's electronics through a single universal docking port. This central port works the same basic way as a USB port on a personal computer: It transmits a constant stream of electronic command signals from the car controller to the central computer, as well as feedback signals from the computer to the controller. Additionally, it provides the electric power needed to operate all of the body's onboard electronics. Ten physical linkages lock the body to the chassis structure. The driver's control unit, dubbed the X-drive, is a lot closer to a video game controller than a conventional steering wheel and pedal arrangement. The controller has two ergonomic grips, positioned to the left and right of a small LCD monitor. To steer the car, you glide the grips up and down lightly -- you don't have to keep rotating a wheel to turn, you just have to hold the grip in the turning position. To accelerate, you turn either grip, in the same way you would turn the throttle on a motorcycle; and to brake, you squeeze either grip.
Electronic motion sensors, similar to the ones in high-end computer joysticks, translate this motion into a digital signal the central computer can recognize. Buttons on the controller let you switch easily from neutral to drive to reverse, and a starter button turns the car on. Since absolutely everything is hand-controlled, you can do whatever you want with your feet. The 5.8-inch (14.7-cm) color monitor in the center of the controller displays all the stuff you'd normally find on the dashboard (speed, mileage, fuel level). It also gives you rear-view images from video cameras on the sides and back of the car, in place of conventional mirrors. A second monitor, on a console beside the driver, shows you stereo, climate control and navigation information.
Since it doesn't directly drive any part of the car, the X-drive could really go anywhere in the passenger compartment. In the current Hy-wire sedan model, the X-drive swings around to either of the front two seats, so you can switch drivers without even getting up. It's also easy to adjust the X-drive up or down to improve driver comfort, or to move it out of the way completely when you're not driving.
One of the coolest things about the drive-by-wire system is that you can fine-tune vehicle handling without changing anything in the car's mechanical components -- all it takes to adjust the steering, accelerator or brake sensitivity is some new computer software. In future drive-by-wire vehicles, you will most likely be able to configure the controls exactly to your liking by pressing a few buttons, just like you might adjust the seat position in a car today. It would also be possible in this sort of system to store distinct control preferences for each driver in the family.

Block figure of the Hy Wire Skateboard Chassis

7. TECHNICAL SPECIFICATIONS

• Top speed: 100 miles per hour (161 kph)

• Weight: 4,185 pounds (1,898 kg)

• Chassis length: 14 feet, 3 inches (4.3 meters)

• Chassis width: 5 feet, 5.7 inches (1.67 meters)

• Chassis thickness: 11 inches (28 cm)

• Wheels: eight-spoke, light alloy wheels.

• Tires: 20-inch (51-cm) in front and 22-inch (56-cm) in back

• Fuel-cell power: 94 kilowatts continuous, 129 kilowatts peak

• Fuel-cell-stack voltage: 125 to 200 volts

• Motor: 250- to 380-volt three-phase asynchronous electric motor

• Crash protection: front and rear "crush zones" (or "crash boxes") to absorb impact energy

• Related GM patents in progress: 30

• GM team members involved in design: 500+

8. A FEW CONCERNS

The big concern with drive-by-wire vehicles is safety. Since there is no physical connection between the driver and the car's mechanical elements, an electrical failure would mean total loss of control. In order to make this sort of system viable in the real world, drive-by-wire cars will need back-up power supplies and redundant electronic linkages. With adequate safety measures like this, there's no reason why drive-by-wire cars would be any more dangerous than conventional cars. In fact, a lot of

Designers think they'll be much safer, because the central computer will be able to monitor driver input. Another problem is adding adequate crash protection to the car. The other major hurdle for this type of car is figuring out energy-efficient methods for producing, transporting and storing hydrogen for the onboard fuel-cell stacks. With the current state of technology, actually producing the hydrogen fuel can generate about as much pollution as using gasoline engines, and storage and distribution systems still have a long way to go. For that and other reasons, GM is still exploring other storage techniques such as metal hydrides. To make fuel cell cars attractive, they must match current life time expectations of 150,000 miles or more and GM is pretty optimistic about that aspect. Says Larry Burns “….other than the flow of electrons and protons, the only moving parts will be the wheels, the suspension and the compressor, so it should have a pretty good life." In terms of production volumes, Burns said some 55 million cars are added each year to the global car park, minus "the old ones that are being retired. By 2010 we estimate the industry will be producing about 70 million a year." And how many of these might be fuel cell vehicles? "We see affordable and compelling vehicles as possible by 2010," said Burns. A decade after that he expects "we will move to high penetration, "probably hundreds of thousands of units in the 2020 time frame." Not all stacks will go to transportation because there may be other, stationary applications, but that order of magnitude, says Burns, "makes a lot of sense." Hy-wire is likely to spawn changes in other vehicles, and the first commercial one may not necessarily look like Hy-wire, according to Burns: "we might find fuel cells in conventional vehicles," for example, as well as by-wire technology. Big economies of scales are likely to be derived from the skateboard chassis concept: Today, says Burns, GM has to design and build 12-14 different "platforms" to cover the entire market. But with the skateboard, "there will be fewer platforms" - maybe only two or three. And fuel cell stacks can be "snapped together" - from 10 kW for a house to 1,000 kW for a locomotive.
So will we ever get the chance to buy a Hy-wire? General Motors says it fully intends to release a production version of the car in 2010, assuming it can resolve the major fuel and safety issues. But even if the Hy-wire team doesn't meet this goal, GM and other automakers are definitely planning to move beyond the conventional car sometime soon, toward a computerized, environmentally friendly alternative. In all likelihood, life on the highway will see some major changes within the next few decades.
Hy-wire on the road

Hy-Wire’s X-Drive

The Interiors of the Hy-wire

9. CONCLUSION

The technology is extremely interesting to people in all walks of life because it offers a means of making power more efficiently and with less pollution. But the coolest thing about this design is that it lets you remove the entire passenger compartment and replace it with a different one. If you want to switch from a van to a sports car, you don't need an entirely new car; you just need a new body (which is a lot cheaper).
The GM concept provides much more value than just zero emissions and twice the fuel economy .It would provide very affordable all-wheel drive, unprecedented safety and comfort, and no oil changes, maintenance worries or trips to the gas station.

10. Bibliography

• www.HowStuffWorks.com

• www.Edmunds.com

• www.Sciam.com

• www.PopSci.com

• www.gm.com

• www.CarDesignNews.com

• www.AutoIntell.com

• www.AutocarIndia.com

• www.BSMotoring.com

• www.TheCarConnection.com

• http://evolution.skf.com/gb/

CONTENTS

1. Introduction 1
2. Concept of Hy-wire car 2
3. GM Hy -wire concept car 4
• History
4. Drive by wire 5
• Working
• Applications
5. Fuel cell power 8
6. Features of hy-wire car 13

• power transmission
• control
7. Technical specifications 16
8. Few concerns 17
9. Conclusion 20
10. Bibliography 21

ABSTRACT

Automobiles as we know today are very complicated machines even though their basic purpose is transportation. The fundamental processes that a car performs are acceleration of wheel speed, their control through braking, the turning of the wheels with the help of the steering mechanism & so on.
The name symbolizes the combination of hydrogen as fuel for the fuel cell propulsion system. The replacement of conventional mechanical and hydraulic control linkages for steering, braking and other control systems by a drive-by-wire system. By combining fuel cell and by-wire technology, this vehicle packaged in a new way, opening up a new world of chassis architectures and customized bodies for individualized expressions.
The car is derived from GM’s previous concept of a drive-able fuel cell vehicle called the Autonomy which was debuted at the 2002 North American Motor Show in Detroit. GM does not hope to be selling these cars immediately, due to certain unavoidable hindrances but they are optimistic of seeing these vehicles on the road in the next decade or two.

Saab Combustion Control system

2010-08-07T04:51:00.000-07:00

INTRODUCTION
The Saab Combustion Control (SCC) system is a new engine control system developed to lower fuel consumption while radically reducing the exhaust emissions, but without impairing engine performance. By mixing a large proportion of exhaust gases into the combustion process, the fuel consumption can be reduced by up to 10 percent, at the same time lowering the exhaust emissions to a value below the American Ultra Low Emission Vehicle 2 (ULEV2) requirements that will come into force in the year 2005. Compared to today's Saab engines with equivalent performance, this will almost halve the carbon monoxide and hydrocarbon emissions, and will cut the nitrogen oxide emissions by 75 percent.

THREE MAIN COMPONENTS OF THE SCC CONCEPT

The SCC system is based on a combination of direct injection of petrol (gasoline), variable valve timing and variable spark gap. Unlike the direct injection systems available on the market today, the SCC system puts to use the benefits of direct injection, but without disturbing the ideal air-to-fuel ratio (14.6:1 = lambda 1) necessary for a conventional three-way catalytic converter to perform satisfactorily.

THE MOST IMPORTANT COMPONENTS OF THE SCC SYSTEM ARE:

Air-assisted fuel injection with turbulence generator The injector unit and spark plug are integrated into one unit known as the spark plug injector (SPI). The fuel is injected directly into the cylinder by means of compressed air. Immediately before the fuel is ignited, a brief blast of air creates turbulence in the cylinder, which assists combustion and shortens the combustion time.

1. Air-Assisted Fuel Injection with Turbulence Generator

The injector unit and spark plug are integrated into one unit known as the spark plug injector (SPI). The fuel is injected directly into the cylinder by means of compressed air. Immediately before the fuel is ignited, a brief blast of air creates turbulence in the cylinder, which assists combustion and shortens the combustion time.

2. Variable Valve Timing

The SCC system uses camshafts with variable cams to enable the opening and closing of the inlet and exhaust valves to be steplessly varied. This allows exhaust gases to be mixed into the combustion air in the cylinder, which puts to use the benefits of direct injection while maintaining the stoichiometric value under
almost all operating conditions. Up to 70 percent of the cylinder contents during combustion consist of exhaust gases - the exact proportion depending on the prevailing operating conditions.

3. Variable spark plug gap with high spark energy

The spark plug gap is variable between 1 and 3.5 mm. The spark is struck from a central electrode in the spark plug injector either to a fixed earth electrode at a distance of 3.5 mm or to an earth electrode on the piston. The variable spark gap together with a high spark firing energy (80 mJ) is essential for igniting an air/fuel mixture that is so highly diluted with exhaust gases.

CATALYTIC CONVERTOR

IMPORTANCE OF CATALYTIC CONVERTOR

The three-way catalytic converter is still the most important single exhaust emission control component. During normal operation, it will catalyze up to 99 percent of the harmful chemical compounds in the exhaust gases. The inside of the catalytic converter consists of a perforated core, the walls of which are coated with a precious metal catalyst (platinum and rhodium). The total area of the catalyst is equivalent to the area of three football pitches. The precious metal coating traps carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) in the exhaust gases and enables these substances to react with one another so that the end product will be carbon dioxide (CO2), water (H2O) and nitrogen (N2).

WEAKNESS OF CATALYTIC CONVERTOR

Although it is highly effective in neutralizing the harmful substances in the exhaust gases, the catalytic converter suffers certain limitations. For the three-way catalyst to be fully effective, its temperature must be around 400 degrees C. So the catalyst has no emission control effect immediately after the engine has been started from cold (the concept of 'starting from cold' is not related to the weather conditions or the ambient temperature, but in this context denotes all starting circumstances in which the engine coolant temperature is below 85 degrees C).
Moreover, the proportion of free oxygen in the exhaust gases must be kept constant. The amount of oxygen, in turn, is decided by the air/fuel ratio in the cylinder during combustion. The ideal ratio is 1 part of fuel to 14.6 parts of air (stoichiometric). If the mixture is richer, i.e. if the proportion of fuel is higher, the emissions of carbon monoxide (CO) and hydrocarbons (HC) will increase. If the mixture is leaner, i.e. if the amount of fuel is lower, the nitrogen oxide (NOx) emissions will increase. The catalytic converter has no influence on the carbon dioxide (CO2) emissions, which are directly proportional to the fuel consumption. The greater the amount of fuel used, the higher the carbon dioxide emissions.
Much of the work of designing less polluting petrol engines therefore has two objectives - to achieve the lowest possible fuel consumption, and to ensure that the catalyst is at optimum working conditions during most of the operating time. These are the guidelines that have been followed in the development of the SCC system.

DIRECT INJECTION

In an engine with a conventional injection system, the petrol is injected into the intake manifold, where it is mixed with the combustion air and is drawn into the cylinder. But part of the petrol is deposited on the sides of the intake manifold, and extra fuel must then be injected, particularly when the engine is started from cold, to ensure that the necessary amount of fuel will reach the cylinder.
Direct injection of petrol was launched a few years ago by some car makers as a way of lowering the fuel consumption. Since petrol is injected directly into the cylinder, the fuel consumption can be controlled more accurately, and the amount of fuel injected is only that necessary for each individual combustion process. In such cases, the entire cylinder is not filled with an ignitable mixture of fuel and air, and it is sufficient for the fuel/air mixture nearest to the spark plug to be ignitable. The remainder of the cylinder is filled with air.

HIGHER NOX

This leaner fuel/air mixture results in lower fuel consumption under certain operating conditions, but makes it impossible to use a conventional three-way catalytic converter to neutralize the nitrogen oxide emissions. A special catalytic converter with a 'nitrogen oxide trap' must be used instead.

Compared to conventional three-way catalytic converters, these special converters suffer a number of major disadvantages. In the first place, they are more expensive to produce, since they have higher contents of precious metals. Moreover, they are more temperature-sensitive and need cooling when under heavy load, which is usually done by injecting extra fuel into the engine. The nitrogen oxide trap must also be regenerated when full, i.e. the nitrogen oxide stored must be removed, which is done by the engine being run briefly on a richer fuel/air mixture. Both cooling and regeneration have a significant effect on the fuel consumption.
In addition, special catalytic converters of this type are sensitive to sulphur, and the engine must therefore be run on fuel with extremely low sulphur content. The petrol desulphurizing process causes higher carbon dioxide emissions from the refinery.

DIRECT INJECTION AND STOICHIOMETRIC

In evolving the SCC system, Saab engineers have developed a way of putting to use the benefits of direct injection, while still maintaining stoichiometric mixtures. Compressed air is used to inject the fuel directly into the cylinder through the spark plug injector. However, unlike other direct injection systems, the cylinder is still supplied with only a sufficient amount of air to achieve a stoichiometric air/fuel ratio. The remainder of the cylinder is filled with exhaust gases from the previous combustion process. The benefit of using exhaust gases instead of air for making up the cylinder fill is that the exhaust gases are inert. They add no oxygen to the combustion process, and they therefore do not affect the stoichiometric ratio. So the SCC system does not need a special catalytic converter and performs well with a conventional three-way catalyst. Moreover, the exhaust gases are very hot, and they therefore occupy a large volume, while also providing a beneficial supply of heat to the combustion process.

REDUCED PUMPING LOSSES

At the same time, the SCC system contributes towards minimizing the pumping losses. These normally occur when the engine is running at low load and the throttle is not fully open. The piston in the cylinder then operates under a partial vacuum during the suction stroke in order to draw in the air. The principle is roughly the same as when you pull out a cycle pump plunger while shutting off the air opening with your thumb. The extra energy needed for pulling down the piston causes increased fuel consumption.

In an SCC engine, the cylinder is supplied with only the amount of fuel and air needed for the operating conditions at any particular time. The remainder of the cylinder is filled with inert exhaust gases. The pumping losses are reduced since the engine need not draw in more air than that necessary for achieving stoichiometric mixtures.

DIFFERENT SPARKS

The fuel/air mixture in the cylinders of a car with an SCC system consists mainly of exhaust gases and air. The exhaust gases account for 60 - 70 percent of the combustion chamber volume, while 29 - 39 percent is air, and less than 1 percent is occupied by the petrol. The exact relationships depend on the prevailing operating conditions. As a general rule, a higher proportion of exhaust gases is used when the engine is running at low load, and a lower proportion when it is running at high load.

An ignition system that provides good spark firing quality is needed to ignite a gas mixture consisting of such a high proportion of exhaust gases and to ensure that the mixture will burn sufficiently quickly. A large amount of energy must be applied locally in the combustion chamber. In the SCC system, this is achieved by employing a variable spark gap and a high spark firing energy (80 mJ).
The spark gap is variable between 1 and 3.5 mm. At low load, the spark is fired from the central electrode in the spark plug injector to a fixed earth electrode at a distance of 3.5 mm. At high load, the spark is fired somewhat later, and the gas density in the combustion chamber is then too high for the spark to bridge a gap of 3.5 mm. A pin on the piston is then used instead as the earth electrode. Following the laws of physics, the spark will be struck to the electrode on the piston as soon as the gap is less than 3.5 mm.

WORKING OF THE SCC ENGINE
• Expansion Stroke

1. The air/fuel mixture burns. The combustion heat causes the pressure of the gas mixture to rise, which presses the piston downwards.

• Exhaust stroke

2. The exhaust valves open when the piston has reached the bottom of its stroke. Most of the exhaust gases are discharged through the exhaust ports due to the pressure difference between the interior of the cylinder and the outside of the gas ports. This takes place during a short period when the piston is at the Bottom Dead Centre.

The remainder of the exhaust gases is discharged through the exhaust ports as the piston moves up.

3. Just before the piston reaches Top Dead Centre, petrol is injected into the cylinder through the spark plug injector. The inlet valves open at the same time. Exhaust gases mixed with petrol are discharged through both the exhaust and the inlet ports. The prevailing operating conditions determine the exact length of time during which the opening of the exhaust and inlet valves overlaps (and thus the proportion of exhaust gases that will remain in the combustion chamber during combustion).

• Intake stroke

4. The piston moves downwards. The exhaust and inlet valves are open. The mixture of exhaust gases and petrol is drawn back from the exhaust ports into the cylinder. A large proportion of the exhaust gas/petrol mixture flows up into the inlet ports.

5. The piston continues on its downward travel. The exhaust valves close but the inlet valves remain open, and part of the exhaust gas/petrol mixture that flowed up into the inlet manifold is drawn back into the cylinder.

6. The piston approaches Bottom Dead Centre. All of the exhaust gas/petrol mixture has now been drawn back into the cylinder, and during the final phase of the inlet stroke, the air needed for combustion is drawn in (14.6 parts of air for every part of fuel).

• Compression stroke
7. The inlet valves close. The piston moves upward, and the mixture of exhaust gases, air and petrol is compressed. About half-way up the compression stroke (about 45 degrees of crankshaft rotation), and before the spark has ignited the air/petrol mixture, the spark plug injector delivers a blast of air into the cylinder. The air blast creates the turbulence needed to facilitate combustion and shorten the combustion time.

8. Just before the piston has reached Top Dead Centre, a spark from the electrode of the spark plug injector ignites the air/petrol mixture, and the next expansion stroke begins. The exact instant of ignition is determined by the prevailing operating conditions.

Depending on when the ignition instant occurs, the spark is fired either to the fixed electrode across a gap of 3.5mm or to the electrode in the piston. The spark follows the laws of physics and is fired to the piston as soon as the piston electrode is closer than 3.5mm to the centre electrode. As a general rule, the spark is fired to the fixed electrode at low load and to the piston electrode at high load.

CONCLUSION
The Saab Combustion Control system has been developed at the Saab Engine Development Department, which is also the Centre of Expertise for the development of turbocharged petrol engines in the GM Group. The variable spark gap in the SCC system is a further development of the spark-to-piston concept that Saab unveiled at the Frankfurt Motor Show in 1995. In the air-assisted direct injection system, Saab engineers are cooperating with the Australian company Orbital.
The SCC system is a 'global' engine system, since it meets the demands in the USA, where greatest emphasis is placed on limiting the nitrogen oxide and hydrocarbon emissions, and also those in Europe, where greater emphasis is placed on the carbon dioxide emissions. The SCC system will be launched in the next generation of Saab cars.

BIBLIOGRAPHY

1. www.autospeed.com
2. Advanced Engine Technology – Heinz Heisler

ABSTRACT

The Saab Combustion Control (SCC) System is a new engine control system developed to lower fuel consumption while radically reducing the exhaust emissions but without impairing engine performance. By mixing a large proportion of exhaust gases into the combustion process, the fuel consumption can be reduced by up to 10 percent, at the same time and also lowers the exhaust emissions. Compared to today’s engines, this will almost halve the carbon monoxide and hydrocarbon emissions, and will cut the nitrogen oxide emissions by 75 percent.

The SCC system is based on a combination of direct injection of petrol (gasoline), variable valve timing and variable spark gap. Unlike the direct injection systems available on the market today, the SCC system puts to use the benefits of direct injection, but without disturbing the ideal air to fuel ratio necessary for a three way catalytic convertor to perform satisfactorily.

CONTENTS

1. Introduction 1
2. Components of SCC System 2
3. Catalytic Converter 4
• Importance
• Weakness
4. Direct Injection 6
5. Higher NOx 6
6. Direct Injection and Stoichiometric 8
7. Reduced Pumping Losses 9
8. Different Sparks 10
9. Working of the SCC Engine 11
10. Conclusion 17
11. Bibliography 18

electronic cooling system

2010-08-07T04:37:00.000-07:00

1. INTRODUCTION
Electronic equipment has made its way in to practically every aspect of modern life, from toys to high power computer. Electronic components depend on the passage of electric current and they become potential sites for excessive heating since the current flow through a resistance is accompanied by heat generation. Continued miniaturization of electronic system has resulted in a dramatic increase in the heat generated per unit volume. Unless properly designed and controlled; high rates heat generation result in high operating temperatures for electronic equipment, which jeopardizes its safety and reliability. Thermal management is a challenging field that the developments and improvements in thermal management hardware have assisted the electronics packaging community by enabling higher heat fluxes in ever-smaller packaging volumes The growth of commercial electronics coupled with the need for better cooling, has enabled some thermal management technologies to move from expensive aerospace technologies to costs that are viable for commercial packaging.

HISTORY
The story of packaging in the past decade is tightly coupled to the continuous and rapid development of integrated circuit technology as exemplified by Moore's Law (i.e., the number of transistors in an IC doubles every 18 months).
Once the integrated circuit was invented, it was an inevitable trend that more and more of the functionality of a given electronic system would be integrated into fewer and fewer chips. The increased functionality led to requirements for greater I/O (input-output) connections and greater power. Packaging, as always, had to satisfy the role of an enabling technology to allow the full performance potential of a semiconductor to be realized in a given application. Package technology experienced dramatic changes to keep pace with these rapid changes in IC functionality.

Packaging technology trends

2. THERMAL INTERFACE MATERIAL
Thermal interface material (TIM) is essential when two or more solid surfaces are in the heat path. Standard machined surfaces are rough and wavy, leading to relatively few actual contact points between surfaces. The insulating air gaps created by multiple voids of "contacting" hard surfaces are simply too large a thermal barrier for even modest power applications. The first tactic in overcoming this barrier is to fill the voids and eliminate air by introducing a third material to the heat path that is fluidic and wets the surfaces. As shown in Figure 1, a thermal interface material essentially changes the thermal path between rough-surfaced solids from conduction through point contacts and air to conduction entirely through solids

fig.1 fig.2

An important property of any TIM is its thermal conductivity. In addition to thermal performance, TIM’S are selected on several other critical criteria as well. Ease of use in assembly and rework are important in high-end applications, as is long-term stability (reliability). Elastomeric pads were developed as an alternative to early grease solutions, largely for the manufacturing advantages they offered. Phase change materials emerged as a technology that captured the thermal performance advantage of grease and combined it with the assembly ease of a solid pad
3. HEAT SINKS
Heat sinks are needed when the heat transfer to the ambient air directly from the top of the package or via the system board is not sufficient to keep the semiconductor device within the allowable temperature range.

Heat sink with folded fins

The increase in power across all applications involving ICs led to the more frequent need for heat sinks It gave more flexibility in managing heat loads far beyond the original design intent of a system.

Pin fin heat sink
An example is on a graphics processor in an expansion card in a PC. The mainstay in the heat sink industry: the extruded aluminum heat sink was supplanted in higher power applications. For a given heat sink form factor, its thermal performance can be enhanced, in general, by the following two approaches:
1. Increasing the thermal conductance of components comprising the heat sink.
2. Increasing the fin area exposed to the airflow.

4. FANS

Developments in fan technology closely paralleled developments in heat sinks. Fans have been subject to the same cost sensitivity and form factor demands as heat sinks. For example, miniature fans are now being used in laptop computers. Since fans are active devices, noise and long-term reliability are further considerations.

The heat removal capability of a heat sink is directly proportional to the mass flow of air through its fin structure. A simple way of getting higher thermal performance from a heat sink is by pushing more air through it. However, in life, nothing is free, so using a fan at a higher pressure drop leads to greater power consumption in moving the air and greater noise. This is the inevitable struggle in fan usage.

5. HEAT PIPES
To cool electronic components, one can use air and liquid coolers as well as coolers constructed on the principle of the phase change heat transfer in closed space; i.e., immersion, thermosyphon, and heat pipe coolers. Each of these methods has its merits and draw-backs because, in the choice of appropriate cooling, one must take into consideration not only the thermal parameters of the cooler but also design and stability of the system, durability, technology, price, application, etc. they are most effective and have great potential as power levels and volume requirements increase. For these reasons heat pipes have been applied up to now mainly in applications with special working conditions and requirements, such as in space thermal control, in aircraft devices, in traction drives in audio amplifiers, in cooling of closed cabinets in harsh environmental conditions, etc. Heat pipes, because of their high thermal conductivity, provide an essential isothermal environment with very small temperature gradients between the individual components. The high heat transfer characteristics, the ability to maintain constant evaporator temperatures under different heat flux levels, and the diversity and variability of evaporator and condenser sizes make the heat pipe an effective device for the thermal control of electronic components

Heat Pipe Operation
Heat pipes are sealed vacuum vessels that are partially filled with a working fluid, typically water in electronic cooling, which serves as the heat transfer medium. The heat pipe envelope is made of copper in a myriad of shapes including cylindrical, rectangular, or any other enclosed geometry. The wall of the envelope is lined with a wick structure, which provides surface area for the evaporation/condensation cycle and capillary capability. Since the heat pipe is evacuated and then charged with the working fluid prior to being sealed, the internal pressure is set by the vapor pressure of the working fluid.
As heat is applied to the surface of the heat pipe, the working fluid is vaporized (Figure 1). The vapor at the evaporator section is at a slightly higher temperature and pressure than other areas. This creates a pressure gradient that forces the vapor to flow to the cooler regions of the heat pipe. As the vapor condenses on the heat pipe walls, the latent heat of vaporization is transferred to the condenser. The capillary wick then transports the condensate back to the evaporator section. This closed loop process continues as long as heat is applied.

Figure 1. As heat is applied to the surface of the heat pipe, the working fluid is vaporized.
For a heat pipe to function properly, the net capillary pressure difference between evaporator (heat source) and condenser (heat sink) must be greater than the sum of all pressures losses occurring throughout the liquid and vapor flow paths. This relationship, referred to as the capillary limitation, can be expressed mathematically as follows.

Pcmax is the maximum capillary pressure difference generated within the capillary wicking structure between the evaporator and condenser, Pl and Pv are the viscous pressure drops occurring in the liquid and vapor phases, respectively, and Pg represents the hydrostatic pressure drop.
When the maximum capillary pressure is equal to or greater than the sum of these pressure drops, the capillary structure can return an adequate amount of working fluid (priming or repriming of the heat pipe) to prevent the evaporator wicking structure from drying out. When the sum of all pressure drops exceeds the maximum capillary pumping pressure, the working fluid is not supplied rapidly enough to the evaporator to compensate for the liquid loss through vaporization, and the wicking structure becomes starved of liquid and dries out (depriming of the heat pipe). This condition, referred to as capillary limitation, varies according to the wicking structure, working fluid, evaporator heat flux, operating temperature, and body forces .

6. PULSATING HEAT PIPE.
Although a plethora of designs of classical heat pipes are available, recent industry trends have frequently shown the limitations of these conventional designs. This has led to the evolution of novel concepts fitting the needs of present industry demands. A relatively new and emerging technology, Pulsating or Loop-type Heat Pipes (PHP), as proposed by Akachi represent one such field of investigation. This range of devices is projected to meet all present and possibly future specific requirements of the electronics cooling industry, owing to favorable operational characteristics coupled with relatively cheaper costs.
Although grouped as a subclass of the overall family of heat pipes, the subtle complexity of internal thermo-fluidic transport phenomena is quite unique, justifying the need for a completely different research outlook. A comprehensive theory of operation and a reliable database or tools for the design of PHPs according to a given microelectronics-cooling requirement still remain Unrealized

7. HIGH POWERED CHIP COOLING
There was a demand for increased packaging density and performance reasserted itself and heat flux is again increasing dramatically. This has prompted many to ask what the practical limits of air-cooling are and when is it necessary resort to some form of liquid cooling?

8. AIR COOLING
With standard fans a maximum heat transfer coefficient of maybe 150 W/m2K can be reached with acceptable noise levels, which is about 1 W/cm2 for a 60°C temperature difference

MCM air cooled heat sink configuration.

9. INDIRECT LIQUID COOLING
Indirect liquid cooling schemes are denoted by the presence of distinct physical barriers between the chip and the liquid. Several possible implementations are illustrated in Figure 4. The most conservative implementation is to attach a separable cold plate to a lidded module (Figure 4a). When greater thermal performance is desired, the interface between the cold plate and the module can be eliminated by integrating the cold plate with the module (Figure 4b). Taking the concept to the limit, chip-scale high performance cold plates of the type discussed in Reference [4] can be attached directly to the chips (Figure 4c).

Figure 4. Indirect liquid cooling schemes: (a) separable module cold plate, (b) integral module cold plate, and (c) individual chip-scale cold plates.

10. DIRECT LIQUID COOLING
Direct liquid (immersion) cooling brings the coolant in direct contact with the back of the chip. Historically, the coolant considered was a dielectric (e.g., fluorocarbon coolants or FCs) primarily because it would also be in direct contact with the chip interconnects and substrate top surface metallurgy (TSM). For this exercise, it is assumed that water can be brought in direct contact with the back of the chip. Obviously a seal or barrier preventing water from contacting the interconnects or TSM is needed. For now, it is assumed that such a seal/barrier is technically feasible.

Figure 5. Direct liquid spray cooling of chips on an MCM.
For the dielectric cooling cases, a few different options may be considered. For example, droplets of a dielectric coolant may be

sprayed on the chip surface as shown in Figure 5. Based upon values reported in the literature spray cooling with a fluorocarbon liquid (i.e., FC-72) is capable of supporting heat fluxes up to 50 to 60 W/cm2 while limiting chip junction temperatures to 85°C. Jet impingement of a dielectric liquid on the chip surface may also be considered (Figure 6). Researchers have reported chip heat fluxes approaching 120 W/cm2 and a chip to liquid temperature difference of 60°C while cooling a 6 x 6 mm silicon chip with a single jet of FC-72 liquid at a flow rate of 2.2 x 10-4 m3/s [8]. It is expected that for the chip size under consideration here, the same heat flux and temperature difference could be achieved with four jets and a liquid flow rate per chip of 8.8 x 10-4 m3/s. Alternatively, the dielectric coolant flow could be directed through a micro channel heat sink attached directly to the chip as shown in Figure 7. As with indirect liquid cooling, single phase convection heat transfer is assumed. It is also assumed that a metal chip-to-heat sink interface of 2.5°C-mm2/W is the best achievable for the heat sink attach.

Figure 6. Direct liquid jet impingement.

Figure 7. Direct liquid cooling with a dielectric coolant and a micro channel heat sink attached directly to the chip.
Ultimately, given that an adequate chip to liquid seal can be provided, direct jet impingement of water on the back of the chip may be considered. For this case a recently published correlation for multiple jets is used to predict water jet impingement cooling performance.
For these various options, the chip heat removal capability for a 60°C chip to liquid inlet temperature difference is estimated to be 60, 120, 300, and 460 W/cm2 for spray cooling, dielectric jet impingement cooling, forced convection dielectric cooling with a heat sink attached to the chip, and water jet impingement, respectively.

11. PIEZO FANS
Piezoelectric fans are low power, small, relatively low noise, solid-state devices that recently emerged as viable thermal management solutions for a variety of portable electronics applications including laptop computers and cellular phones. Piezoelectric fans utilize piezoceramic patches bonded onto thin, low frequency flexible blades to drive the fan at its resonance frequency. The resonating low frequency blade creates a streaming airflow directed at electronics components.
12. MICROCHANNELS AND MINICHANNELS
The term 'micro' is applied to devices having hydraulic diameters of ten to several hundred micrometers, while 'mini' refers to diameters on the order of one to a few millimeters. In many practical cases, the small flow rate within micro-channels produces laminar flow resulting in a heat transfer coefficient inversely proportional to the hydraulic diameter. In other words, the smaller the channel, the higher the heat transfer coefficient. Unfortunately, the pressure drop increases with the inverse of the second power of the channel width, keeping the mass flow constant, and limiting ongoing miniaturization in practice.

13. NANOLIGHTNING
It is based on 'micro-scale ion-driven airflow' using very high electric fields created by nanotubes. As shown in Figure 5, the ionized air molecules are moved by another electric field, thereby inducing secondary airflow. Cooling a heat flux level of 40 W/cm2 has been reported.

Figure 5. 'Nanolightning' sketch

14. CONCLUSION
A comparison of the heat removal capability in terms of chip heat flux for the module cooling concepts discussed is shown in Figure 8

Figure 8. Comparison of heat removal capability.
A number of approaches show interesting industrial potential for the cooling of high-power electronics. For heat flux densities up to and maybe even beyond 50 W/cm2 air-cooling may remain the cooling option of choice. For heat fluxes over 100 W/cm2, some form of liquid-cooling appears to be the most viable option. Several papers have demonstrated solutions that may be industrially feasible for application in the range between 500 and 1000 W/cm2. Considering the range of efforts underway to extend conventional cooling technologies, as well as develop new ones, the future seems bright for accommodating high-heat flux applications.

15. REFERENCES
 CENGEL Y A - Fundamentals of heat and mass transfer

 ALLEN.D.KRAUS AND D.Q.KERN- Extended surface heat transfer

 ASME Journal of heat transfer , January-2005