AutoKriti 7.0

OUR VISIONThe prime objective of SAEINDIA NIT Kurukshetra Collegiate club is to provide a platform to the budding engineers and help them to practically apply the theoretical knowledge; to bring dynamism in their vision and thinking; to find solutions to the existing problems by encouraging collaboration between the minds of future engineers and with pioneers of the industry. The idea, vision and objectivity of the club and its working can be uniformly summarized under the club motto – Ignite to Achieve. autokriti 7.0 Index 1. Introduction to Automotive………………………………………………………………………………………….4 1.1 Automotive………………………………………………………………………………. 4 1.2 Automobile………………………………………………………………………………. 4 1.3 Components of an automobile………………………………………………….. .............4 2. Basic terminology……………………………………………………………………..……………5 2.1 Vehicle axis system…………………………………………………………...…………5 2.2 Some common terms used in automobiles………………………………........................5 3. Chassis………………………………………………………………………………………….….6 3.1 Types of chassis………………………………………………………………………...6 4. Aerodynamic fundamentals………………………………………………………………………………...…….8 4.1 Introduction……………………………………………………………………..………8 4.2 Aerodynamic forces……………………………………………………………....…….8 5. Engine……………………………………………………………………………………………..9 5.1 Introduction…………………………………………………………………..………...9 5.2 External and internal combustion engines...............…………………………......……..9 5.3 Classification of engines…………………………………………………………..........9 5.4(a) Petrol engine…………………………………………………………………...……11 5.4(b)Diesel engine...............................................................................................................11 5.5 Fuel injection……………………………………………………………………..……18 5.6 Turbochargers and superchargers……………………………………………...............20 5.7 Petrol engine v/s Diesel engine………………………………………………...............23 6. Transmission……………………………………………………………………………….……..24 6.1 Clutch……………………………………………………………………….………….24 6.2 Types of clutches…………………………………………………………….…………24 6.3 Gear Ratio………………………………………………………………………………25 6.4 Types of transmission………………………………………………………....………..25 6.5 Differential………………………………………………………………….…………..31 6.6 Types of driveline…………………………………………………………….…...… .. 33 7.Electronics in cars............................................................................................................................. 35 7.1 Engine........................................................................................................................... 35 7.2 Transmission............................................................................................................ ...... 36 7.3 Chassis electronics....................................................................................................... . 36 7.4 Active Safety............................................................................................................... ... 37 7.5 Driver Assistance............................................................................................................37 7.6 Passenger comfort........................................................................................................... 37 8. Suspension system…………………………………………………………………………........ 38 8.1 Objectives of suspension system…………………………………………………....... 38 8.2 Fundamental concepts……………………………………………………………....….38 8.3 Type of suspension......................................................................................................... 40 8.4 Magnetic suspension........................................................................................................43 2 autokriti 7.0 9 8.5 Hydro-pneumatic suspension..........................................................................................43 8.6 Motion ratio.....................................................................................................................43 8.7 Modern suspension trends...............................................................................................44 Steering system……………………………………………………………..........…….............…45 9.1 Fundamental……………………………………………………........................………45 9.2 Steering behaviour…………………………………………………………....….……..46 9.3 Type of steering system…………………………………………………....…….……..47 9.4 Steering geometry............................................................................................................47 9.5 Steering ratio..................................................................................................................48 9.6 Power steering.................................................................................................................48 10 Wheel…………………………………………………………………………………………......50 10.1 Tyre type………………………………………………………….........……………..50 10.2 Tyre properties……………………………………………………………………..…50 10.3 Tyre size notation……………………………………………………………………..51 10.4 The wheel assembly…………………………………………………………..………52 11 Brakes………………………………………………………………………………..……………53 11.1 Introduction……………………………………………………………………………53 11.2 Brake fade…………………………………………………………………………..…53 11.3 Types of brakes…………………………………………………………………..……53 11.4 Methods to reduce brake fade…………………………………………………............54 11.5 Types of calipers…………………………………………………………………........55 11.6 Hydraulic brakes……………………………………………………………………....56 11.7 Inboard brakes...............................................................................................................56 11.8 Brake biasing.................................................................................................................56 11.9 Proportioning valve…………………….......................................................................56 11.10 Anti-lock braking system……………………………………………........................57 11.11 Types of brake fluid…………………………………………………………………57 # Common abbreviations……………………………………………………………………………..58 # Appendix……………………………………………………………………………………………60 # Test Yourself……………………………………………………………………………………….60 3 Engine design 4. INTRODUCTION TO AUTOMOTIVE 1. A passengers and goods.”self”) and the Latin mobilis (“movable”). After that the automobile became a primary mode of transportation for all countries. Automotive engineering includes: 1. via the French automobile.autokriti 7. Drive train Engineering 1. Further developments led to the introduction of modern gasoline or petrol fuelled internal combustion engine in 1885.2 Automobile:The word automobile comes. Mechanical Engineering 2. from the Ancient Greek word αύτός (autόs.0 1. natural or LPG gas etc. meaning a vehicle that moves itself. Vehicle Dynamics 3. The first practical automobile with a petrol engine was built by Karl Benz in1885 in Mannheim. Each of these vehicles is operated by engine which consumes gasoline (petrol). Germany.1 Automotive: It is a branch of engineering dealing with automobiles or anything automatically in motion. In 1806. diesel. Benz was granted a patent for his automobile. Francois Issac de Rivaz of Switzerland invented an internal combustion engine that used a mixture of hydrogen and oxygen for fuel. 1.3 COMPONENTS OF AN AUTOMOBILE The main units of an automobile are:         The super structure or chassis The power plant or engine Transmission system or power train Steering system Suspension system Brakes Wheels Electrical system Figure 1 -Various components of an automobile 4 . 2.1 Longitudinal axis:The line passing between the contact patches of left and right wheel is track width of vehicle. Figure 2 –Axes of motion of a vehicle 5 .1Vehicle axes system 2. experiences yaw movement. 2.1. 2.1 Wheel base:Wheel base is the longitudinal distance measured between contact patches of front to rear wheel.2.2. represented by Y axis.2.3 Turning radius:It is actually a misnomer as it is the diameter of the circle of the outside wheels that a car turns through while turning at full lock.4 Indicated Power:Indicated power is the 2. through the front and rear roll centre of the vehicle (vehicle rolls about this line) represented as Xaxis.0 2. 2.2 Some common terms used in automobiles: 2.1. 2.3 Vehicle axis:Axis about which vehicle power actually developed by the engine cylinder.2 Track width:The lateral distance 2.2 Lateral axis:Axis about which vehicle pitches.4 Brake horse power (bhp): BHP is the power available at the crankshaft. BASIC TERMINOLOGY 2.2.autokriti 7.1. 2. tubular space frame and backbone chassis provides only the stress members and need to build the body around them.1. Figure 5 –Monocoque chassis of Lamborghini Aventedor 6 .3 Ladder chassis load and also the longitudinal forces caused by acceleration and braking. though circular section provides the maximum strength. motor racing engineers developed a 3 dimensional design . monocoque chassis is already incorporated with the body in a single piece. The lateral and cross members provide resistance to lateral forces produced during cornering and further increase torsional rigidity. and other pieces are pressed by big stamping machines.autokriti 7. CHASSIS 3.1 Type of chassis 3. It is actually made by welding several pieces together. which is the largest piece. Tubular space frame chassis employs dozens of circular-section tubes. They deal with the Figure 4 –Tubular frame chassis of a formula SAE car These tubes are welded together and form a very complex structure.1.0 3. The floor-pan. Fig. The longitude members are the main stress bearing members. For higher strength required by high performance sports cars. a square section can also be used for easier connection to the body panels.1 Ladder Chassis Indicated by its name. 3. looks like a ladder .Tubular space frame. 3.3 Monocoque frame chassis Monocoque is a one-piece structure which defines the overall shape of the car.two longitudinal rails interconnected by several lateral and cross braces.2 Tubular Space Frame As ladder chassis is not strong enough. They are spot welded together by robot arms.1. While ladder. tubular space frame chassis usually incorporate a strong structure under both doors hence result in difficult access to the cabin. 5 Backbone frame chassis A strong tubular backbone (usually in rectangular section) connects the front and rear axle and provides nearly all the mechanical strength. rear-wheel drive layout. extruded sections are connected by complex aluminium die casting. It is very complex and production cost is far higher than steel monocoque.1. then cooked in a big oven for 3 hours at 120°C and 90 psi pressure. The whole drive-train. The steel tubes are placed in a die which defines the desired shape. which defines the shape of the panel. Carbon-fiber panels are made by growing carbonfiber sheets on either side of an aluminium foil. 3.1. engine and suspensions are connected to both ends of the backbone. is stacked with several layers of carbon fiber sheets impregnated with resin. Inside which there is space for the drive shaft in case of front-engine. the carbon fiber layers will be melted and form a uniform. They all are made of high-strength aluminium alloy. After that. which expands the latter to the inner surface of die. although most of them simultaneously use other kinds of carbonfiber in even larger amount. usually made of glass-fibre. At the highly 7 . then fluid at very high pressure will be pumped into the tubes.1. vacuum die cast components and aluminium sheets of different thicknesses. By the Hydro form technique thin steel tubes are used.4 ULSAB Monocoque chassis (Ultra-Light Steel Auto Body) Pressing sheet metal to make chassis creates inhomogeneous thickness at the edges hence to maintain minimum thickness designers have to choose a thicker sheet metal. It is strong enough for smaller sports cars but not up to the job for high-end ones. 3. The body is built on the backbone. The thickness of steel tube remains uniform which results in lighter design. rigid body panel. the foil.6 Aluminium space frame chassis It consists of extruded aluminium sections.autokriti 7. 3. Figure 7–Carbon fiber chassis of a super sports car Figure 6 –Backbone chassis 3.1.7 Carbon fiber monocoque The carbon fiber called Kevlar offers highest rigidity-to-weight ratio.0 stressed corners and joints. Kevlar can be found in the body panels of many exotic cars. 28% at a speed of 60 km/h with the drag coefficient reduced to 0.2.Drag forces with (upper) and without (lower) spoiler 4. Slope angle of 15degree consistently reduces drag. The lift at the rear of the vehicle which reduces traction and stability is variable with vehicle design.336 from 0. which means.3 Lift The fluid flow follows Bernoulli’s equation for automotive aerodynamics.2. P (static) +P (dynamic) =P (total) 4. After body is the measure contributor of drag as it contains a separation zone.14L of petrol for every full tank refill. The pressure difference between the top and the bottom of the vehicle causes a lift force.1 INTRODUCTION Following section covers different types of aerodynamic forces deployed in a vehicle. such that the angle of overall wind force is much greater than the relative wind angle. after-body. yaw and noise hence decreases fuel economy.28%. Figure 8 .2. In case of a strong cross wind the side force is greater than the drag force.1 Side force: The lateral wind component will impose a side force on the vehicle. 4.2 DRAG: It is the largest and most important aerodynamic force encountered by a passenger car at normal highway speed. The force due to friction of air interacts with the moving vehicles and causes drag. there is a saving of 2. under body and skin friction. Figure 9 –Uplift produced due to airflow 2 DA=½ (ρV )CDA CD=Aerodynamic drag co-efficient A=Front area of vehicle ρ=Air density Modifications in TATA NANO have shown a drag reduction of 14. ½(ρv2) is the dynamic pressure of the air.0 4. pitch. thereby reducing the fuel consumption allotted to external body by an amount of approximately 14. The drag properties of a car are characterised by the value of product of co-efficient of drag and front area of the vehicle.392. lift (or downward). AERODYNAMIC FUNDAMENTALS 4. Front lift that reduces steering controllability is reduced by deploying a front bumper spoiler and by rear ward inclination of front surface.2 AERODYNAMIC FORCES It plays a major role in high performance cars through its contribution to Road load. 8 . 4. handling etc. This lift can be reduced by spoilers etc. These forces are significant as they influences driving stability and handling through reduced control forces available at tires. attempting to change the direction of travel. More than 65% of drag arises from the body (fore-body.autokriti 7. momentum role. 5. W. The water turns to steam in a boiler and expands greatly in volume. Reciprocating engines have different layouts or cylinder configurations such as straight. X etc. an engine with rotary pistons was invented which is called Wankel engine.1b Reciprocating Engine A Steam engine is an external combustion engine in which heat is supplied to the working fluid from fuel burned outside the engine. usually via pistons or turbines. 5. H.autokriti 7. ENGINE 5.1 INTRODUCTION  Engine is a machine designed to convert chemical energy of the fuel into useful mechanical motion.3.2a EXTERNAL COMBUSTION ENGINES: Figure 10 –A 4-stroke wankel engine 5.2b INTERNALCOMBUSTION ENGINES: An internal combustion engine is also a heat engine that burns fuel containing chemical energy to get heat energy and then converts this heat energy into mechanical energy.0 5.2 EXTERNAL & INTERNAL COMBUSTION ENGINES: 5. V configuration is mostly used. 5. U.3 CLASSIFICATION OF ENGINES: 5. But now it is not used because of its sealing and leakage problem. and can be used to generate mechanical power. V.1a Rotary Engines Reciprocating Engine In order to reduce engine components and produce more compact engine and to reduce losses caused by alternating movements in traditional engine. A Reciprocating engine also known as a piston engine is a heat engine that uses one or more reciprocating pistons to convert pressure on piston into a rotating motion.3. 5.1 ON THE BASIS OF BASIC Figure11 –Various configurations of an engine ENGINE DESIGN:  Rotary Engine 9 .3. 5. The temperature and pressure 10 .autokriti 7.3.3.3 ON THE BASIS OF IGNITION: 5. As the piston reaches near top position spark plug produces an electric spark. The piston is forced to move upwards because of the momentum gained.2b Four stroke engine In four stroke engines the piston reciprocates four times in the cylinder. Since the 4-stroke engine produces two rotations of the crankshaft while 2stroke engine produces single rotation each time the fuel is burnt. b) Compression stroke: After this the inlet valve gets closed. c)Power stroke: During this stroke the inlet and exhaust valve remains closed. W16 configuration is used in BUGATTI VEYRON.3. Carburetor now decides in what ratio gasoline/petrol and air should be mixed. Now the exhaust valve closes and the intake valve opens. The four strokes are as follows: a) Suction or intake stroke: Figure 12 –Working cycle of a 4-stroke engine Initially when engine is started piston moves downwards towards bottom of the cylinder which creates low pressure at top. As their name implies. 5. the efficiency of 4-stroke engines is greater than 2-stroke engines. These are called petrol or gasoline engines because petrol is used in these engines. After this the four strokes of the engine are repeated again and again. d)Exhaust stroke: In this stroke the exhaust valve remains open at the start.2a Two stroke engine In 2-stroke engines intake and exhaust valves are replaced by openings in the lower portion of the cylinder wall. During the latter part of the power stroke. The hot gases expand and force the piston to move downwards.3. and then the intake port allowing the fresh air-fuel mixture to rush in and drive most of the remaining exhaust gases out of the cylinder.3a SPARK IGNITION In SI engines.2 On the basis of working cycle 5.0 inside the cylinder increases due to compression caused. the burning of the fuel occurs by a spark generated by a spark plug located in the cylinder head of engine. The piston now moves towards the top of cylinder and compresses the fuel mixture to one tenth of its initial volume.3. the piston uncovers first the exhaust port. Combustion is started by an ignition system that fires a high voltage spark. Due to this intake valve opens and the fuel mixture containing petrol vapours and air are sucked in by the cylinder. The piston is linked to the piston rod and the piston rod to the crank shaft. This forces gases to move through the exhaust valve into the atmosphere. 5. Due to this fact they are called SI engines. The spark produced causes explosion of fuel. allowing the exhaust gases to be partially expelled. operation of 4-stroke engine have four basic steps. The mixture is then compressed as the piston moves upwards during the compression stroke and is subsequently ignited by a spark plug. 3. So petrol engines are called internal-combustion engines. 5. Within the engine burning of fuel mixed with air causes hot gases to expand against parts of the engine and force them to move. the cooling system of the CI engine can be of smaller dimensions. the SI engine cannot operate. It uses petrol called as gasoline in USA as a fuel.autokriti 7.0 6. • The third. its maintenance cost is less than that of the SI engine. whereas the CI engine.3b COMPRESSION IGNITION In CI engines. therefore. 5. Thus the temperature of the fuel increases and it starts burning. hence these engines are called CI engines. 11 . The fuel (diesel) for the CI engine is cheaper than the fuel (petrol) for SI engine. Many car manufacturers follow that way.3 7. ignition or carburetor system. Petrol Engine was introduced by the German engineers Gottlieb Daimler and Karl Benz in 1885. has less risk of failure. Why are Diesel engines still popular? Compression ratio of TATA INDICA is 22:1 • The first. the turbo-supercharging diesel engine can surely play the role of “fire-starter”. Compression ratio of TATA NANO is 10. Reliability of the CI engine is much higher than that of the SI engine. The torque characteristics of the CI engine are more uniform which results in better top gear performance. the burning of the fuel occurs because of the high pressure exerted on the fuel. on condition of quality oil fueling and maintenance on the regular base diesel engine can operate up to half-million kilometers without capital repair. COMPARISON OF CI AND SI ENGINES • Secondly. the ecological regulations are kept in foreign countries and the owners of ecology-friendly autos have discounts on assurance and other taxes.Consequently. the heat loss to the cylinder walls is less in the CI engine than that of the SI engine. the specific fuel consumption of the CI engine is low. 9. On part load. And that is the sure gain. 3. The fuel is compressed to high pressures. 1. owing to the design of the single carburetor and the intake manifold. The distribution of fuel to each cylinder is uniform as each of them has a separate injector. The fire risk in the CI engine is minimised due to the absence of the ignition system. 5. The CI engine has the following advantages over the SI engine. whereas the SI engine requires warming up. The CI engine can be switched over from part load to full load soon after starting from cold. 8. 4. It is considered as one of biggest achievement in the automotive field. The expansion ratio of the CI engine is higher than that of the SI engine.4(a) PETROL ENGINE 2. whereas in the SI engine the distribution of fuel mixture is not uniform.4(b)Diesel engine The diesel engine (also known as a compressionignition or 'CI' engine) is an internal combustion engine in which ignition of the fuel that has been injected into the combustion chamber is initiated by 5. with a separate fuel injector for each cylinder. Petrol engines are compact and light in weight for the power they produce. Since the servicing period of the fuel injection system of CI engine is longer. This is because in case of the failure of the battery. form the Figure 14 –Cylinder block of a 4 cylinder engine Within the cylinder. 5. injector location holes. The diesel engine has the highest thermal efficiency (engine efficiency) of any practical internal or external combustion engine due to its very high compression ratio and inherent lean burn which enables heat dissipation by the excess air.1 Cylinder head The cylinder head is a casting bolted to the top of the cylinder block. combustion chamber and valve ports. Both spark-ignition and compression-ignition cylinder blocks are similar but later blocks are relatively heavier and stronger to withstand high compression ratios and internal pressure. toughness.4. TATA NANO has 624cc. combustion process produces rapid and periodic rises in temperature and pressure. All the engine parts are mounted on it or in it and this holds the parts in alignment.2 Cylinder block The cylinder block is the portion of the engine between the cylinder head and sump.3 Crank case and Crank shaft upper face of combustion chamber. The cylinder head is detachable for easy access to the valves and piston tops and to facilitate machining of the cylinder bore.0 the high temperature which a gas achieves when greatly compressed (adiabatic compression). the spark plug are also located within the head casting. hardness.4. 2cylinder engine which gives 32. Large diameters holes in the block castings from the cylinder bores required to guide the pistons.5bhp power @5500 rpm and 45Nm torque@3500rpm TATA INDICA has 1405cc. These induce circumferential and mechanical properties such as strength.autokriti 7. and The crankcase supports the individual main journals and bearings of the crankshaft and also 12 . The coolant passages.4. and corrosion and wear resistance. cavities. intake and exhaust ports.4 cylinder engine which gives 84bhp power @6000 rpm. 120Nm Torque @3500 rpm Basic Engine Parts 5. Figure 13 –Cylinder head of a 4 cylinder engine 5. The front end of the crankshaft. on which the lobes are ground. FUNCTION When the fuel is ignited in the combustion chamber in presence of highly compressed air. These shafts are machined from hollow steel tubing. Each camshaft operates two of the valves.4. This is accomplished by having the connecting rods (which are attachéd to the pistons) connect to the crankshaft in an offset manner. fan. one camshaft handles the intake valves. to drive the camshaft. turns the sprocket.rocker shaft and springs. or timing gear. the resulting explosions forces the pistons downward with tremendous force. which is one of a series of links between pistons and the drive wheels. 5. plus a lobe for fuel pump actuation and a drive gear for the distributor. is a one piece art located in the bottom end of the engine that harnesses the huge forces produced by the explosions in the combustion chamber. The camshaft operates cam followers that in turn operate the rest of the valve train. known as the snout.autokriti 7. Camshafts do their work through Rocker shaft provides a rigid pivot support for the rocker arms. which is toothed. For lubrication purpose radial 13 .4 Cam shaft Rocker shaft Its job is to open and close the valves at just the right time during engine rotation. It is now used in high performance cars. Single Overhead Camshaft is used in both TATA Nano and TATA Indica 5. allowing the starter motor to rotate the crankshaft.4. Dual overhead camshaft(DOHC):The main benefit of dual overhead cams is that they allow an engine to have four valves per cylinder. On single camshaft engines there are twice as many lobes as there are cylinders. The other end of the crankshaft is connected to the flywheel.5 Rocker shafts and rocker arm assembly Rocker arm assembly consists of rocker arm. The camshaft itself is forged from one piece of steel. The camshaft drives the distributor to electrically synchronize spark ignition. water pump and power steering. The function of the crankshaft is to change the up-down motion of the pistons to a rotating motion.0 eccentric maintains the alignment of the journal axes of rotation as they are subjected to rotary and “lobes” that Figure 16 –Camshaft of a 4 cylinder engine Figure 15 –Crank shaft of a 4 cylinder engine actuate the components of the valve train. pulley that runs a belt connected to the alternator. and one handles the exhaust valves. reciprocating inertia forces and the periodic torque impulses. These are mounted and clamped on cast-iron or aluminium alloy pedestals. Rocker arm comes in contact with the valves as directed by the rotation of the camshaft. The crankshaft. which are generally fitted between each pair of rocker-arms. so that as they go up and down their angle changes. so that maximum power and efficient cleanout of exhaust can be obtained. these twoholes must align. Figure 20 –Piston & its Gudgeon pin The gudgeon-pin(piston pin) connects the piston and connecting rod. It is supported in holes bored in the piston at right angles to the piston axis atabout mid height position. The piston starts. and both end of the shaft are plungged to prevent the oil leakage. weight and thermal expansion control. and the centre portion 14 . the shaft is case-hardened to withstand the rubbing action. accelerates and stops twice in each crankshaft revolution. Figure 17 –A rocker shaft After machining. When reassembling the rockers and shaft. Rocker-arm A rocker-arm rockes or oscillates about its pivot and relays the push rod up-and-down movement to the stem of the poppet valve. It generally acts as a bearing for the gudgeon pin. a temperature gradient of about 150 k from the head of the piston to its bottom is experienced.6 Piston The automotive engine piston converts the combustion pressure to a force on the crankshaft. Therefore this arm acts as a rocking beam. The inertial force depends on the piston and less inertia permits higher engine operating speeds. This reciprocating action of the piston produces large inertial forces. design of a piston is based on a compromise between strength.4. Figure 19–Piston & its parts Figure 18 –A rocker arm assembly 5. During operation of the piston. It must transmit thegas load to the small end of the connecting rod. Functions of a piston in brief are:   It must form a sliding gas and oil tight seal within the cylinder. This hole matches with a corresponding radial hole in the shaft. to restore oil supply to the shaft.0 holes are drilled through rocker-shaft to align with each rocker arm.autokriti 7. Also it has to support piston sealing rings. One of the support pedestals normally incorporates a vertical drilled hole to supply the oil from the camshft to the hollow rocker shaft. Therefore. These layouts are differentiated by the location of the camshaft within the engine: A push rod is a straight stem with a roller ball at each end. the push rod drops back to its original starting point. 15 . while others are fabricated in three pieces that include the stem with welded roller balls at each end. and the camshafts. Technologies such as Solenoids are used to individually actuate the valves. As the cam turns farther. Cam less:this layout uses no camshafts at all. lifters. DID YOU KNOW? Only about 15% of chemical energy gets converted to useful kinetic energy of the vehicle. This action opens an intake or exhaust valve in the cylinder head of the engine.8 Valve train and Valve timings The valve train consists of valves. For this movement. The small end of the connecting rod reciprocates and the large end follows the crank pin rotational pattern. controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close duration is controlled by the camshaft that is syncronized to the crankshaft by a chain or belt. This relaxes pressure Cam-in-block:the camshaft is located within the engine block. Each connecting rod is fastened to the piston pins and to the crank pin(journal) of the crank shaft by a plain split bearing. This hinged joint transfers directly the gas thrust from the pistons to the connecting rod and allows the rod to pivot relative to the cylinder axis with an oscillating motion. or indirectly via pushrods and rocker arms. Connecting rod The connecting rod joins the piston to the crankshaft and transfers piston reciprocating force to crankshaft rotation. on the rocker arm and the valve closes. Some push rods are fabricated in one piece.autokriti 7.4. each of which vary slightly in layout but still perform the task of opening and closing the valves at the time necessary for proper operation of the engine. Figure 21 –Valve train with pushrods 5.7 Push Rod Valve trains are built in several configurations. as well as the geometry of the valve train.0 of the gudgeon pin passes through the connecting rod small-end eye.4. the connecting rod should be as light as possible. 5. depending on the design) is located above the valves within the cylinder head. As the offset lobe of the cam contacts the lower ball. Because they often require pushrods they are often called pushrod engines. and operates directly on the valves. the push rod is forced up and lifts the rocker arm. Valve train opening/closing and duration. rockerarms. and operates either indirectly or directly on the valves. The engine will not start or run without push rods. pushrods. Function The roller ball at the lower end of the push rod rides on the lobes of the camshaft. Overhead Camshaft:The camshaft (or camshafts. The upper ball seats into a recessed cup on the underside of a rocker arm. 9 Sump or oil pan The sump is attached to the bottom of the cylinder block underneath the crankcase. let’s show piston motion as a circle. This is called valve overlap. the intake valve usually opens earlier than top dead centre. the intake and exhaust valve are open at the same time for few degrees around TDC. fuel economy or emissions.The system has a verified fuel consumption reduction of 12-17 percent. It is increasingly being used in combination with variable valve lift systems. combustion pressures have dropped considerably and little power is lost by letting the exhaust gases have more time to exit.  This make valve opens 16° before the piston reaches top dead centre and it closes 55° after bottom dead centre.    By the time the piston is at 55° before BDC on the power stroke. Theoretically speaking the intake valve opens at top dead centre. The stem of the valve usually rides up and down a provision incorporated into the head itself that is machined called a valve guide. each stroke is shown as a semi-circle. and closes at bottom dead centre and the exhaust valve opens at bottom dead centre. Two-stroke engines use a power valve system to get similar results to VVT. In the simple cycle. however. When an intake valve closes after BDC and the exhaust valve closes after TDC. Figure 22 –Intake and exhaust valve The poppet valve also has great flow characteristics and provides a good means to direct fluid flow into the combustion chamber. the poppet vave is most common because this offers readonable weight. ranging from mechanical devices to electro-hydraulic and cam less systems. To see how valve timing works in a 4-stroke engine cycle.autokriti 7. On the exhaust stroke. There are many ways in which this can be achieved. This gives exhaust gases more time to leave. VVT (Variable Valve Timing) In internal combustion engines. and stays open a little past bottom dead centre. and is often used to improve performance.  The exhaust valve opens 55° before bottom dead centre and stays open until 16° past top dead centre. this is located in the cylinder head on all the engines. and closes at top dead centre before the new air fuel mixture enters the cylinder. The functions of the sump are:  To store the engine’s lubrication oil for circulation within the lubrication system. rotary and poppet type valves. DID YOU KNOW? The Free Valve concept by Koenigsegg offers the unique ability to have independent control of the intake and exhaust valve can be independently programmed. When an intake valve opens before TDC and the exhaust valve opens before BDC.0  Intake and Exhaust Valves Now-a-days. 16 . variable valve timing (VVT) is the process of altering the timing of a valve lift event. The exhaust valve opens a little before bottom dead centre and stays open a little past top dead centre. In practice. it is called lead. Among the commonly used sleeve. good strength and good heattransfer characteristics. 5. it is called lag.4. autokriti 7.0   rotating at a fairly uniform speed under a substantially constant load, it is necessary to provide it with a flywheel. A flywheel is an inertial energy-storage device. It absorbs mechanical energy and serves as a reservoir, storing energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than the supply. To collect the oil draining from the sides of the crankcase walls and if ejected directly from the journal bearings. To provide a centralized storage area for any contaminants like liquid fuel, water, combustion products blown past the piston ring, and worn metal particles.  To provide a short recovery period for the hot churned up and possibly aerated oil before it is re-circulated in the lubrication system. Functions and Operation The main function of a fly wheel is to smoothen out variations in the speed of a shaft caused by torque fluctuations. If the source of the driving torque or load torque is fluctuating in nature, then a flywheel is usually called for. Many machines have load patterns that cause the torque time function to vary over the cycle. Internal combustion engines with one or two cylinders are a typical example. Piston compressors, punch presses, rock crushers etc. are the other systems that have fly wheel. Flywheel absorbs mechanical energy by increasing its angular velocity and delivers the stored energy by decreasing its velocity. Figure 23 –Oil sump of an engine The sump generally has a shallow downward slope at one end, which changes into a relatively deep but narrow-walled reservoir at the other end. The incoming oil flows towards the deep end, where it submerges the pick-up pipe and strainer of the lubricating system. A drain plug is located at the lowest level in the sump for easy drainage of used oil. 5.4.11 Spark Plugs All spark plugs share the same basic design and construction. The high voltage from your vehicle's high-tension electrical system is fed into the terminal at the top of the spark plug. It travels down through the core of the plug and arrives at 5.4.10 Flywheel In a combustion engine, & especially in one with one or two cylinders, energy is imparted to the crankshaft intermittently, & in order to keep it Figure 25 –Spark plug of a petrol engine the centre electrode at the bottom where it jumps to the ground electrode creating a spark. The crush Figure 24 –Flywheel of an engine 17 autokriti 7.0 washer is designed to be crushed by tightening the spark plug down when it's screwed into the cylinder head, and as such, it helps keep the screw threads under tension to stop the spark plug from shaking loose or backing out. The insulator basically keeps the high-tension charge away from the cylinder head so that the spark plug doesn't ground before it gets a chance to generate the spark. This type of plug is known as a projected nose type plug, because the tip extends below the bottom of the spark plug itself. The other main type of spark plug has the centre electrode recessed into the plug itself and merely grounds to the collar at the bottom. The advantage of the projected nose type is that the spark is better exposed to the fuel-air mixture. just enough fuel to get into the cylinders to keep the engine ticking over. Figure 26 –Cut through diagram of a Carburetor 5.5 FUEL INJECTION INTRODUCTION 5.4.12 Carburetor Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive engines, having replaced carburetors during the 1980s and 1990s.Edward Butler, from Erith, Kent, and Henri Tenting, from Paris, were the first two men to develop a fuel injection system for the internal combustion engine in 1883 and 1891, respectively. A carburetor is basically a shaped tube. The shape of the tube is designed to swirl the incoming air and generate a vacuum in a section called the venturi pipe (or just the venturi). In the side of the venturi is a fuel jet which is basically a tiny hole connected to the float chamber via a pipe. It has a miniscule hole in the end of it which determines the flow of fuel through it. The fuel is pulled through the jet by the vacuum created in the venturi. At the bottom of the tube is a throttle plate or throttle butterfly which is basically a flat circular plate that pivots along its centre line. It is connected mechanically to the accelerator pedal or twist-grip throttle via the throttle cable. The more you push on the accelerator or twist open the throttle, the more the throttle butterfly opens. This allows more air in which creates more vacuum, which draws more fuel through the fuel jet and gives a larger fuel-air charge to the cylinder, resulting in acceleration.When the throttle is closed, the throttle butterfly in the carburetor is also closed. This means the engine is trying to suck fuel-air mix and generating a vacuum behind the butterfly valve so the regular fuel jet won't work. To allow the engine to idle without shutting off completely, a second fuel jet known as the idle valve is screwed into the venturi downwind of the throttle butterfly. This allows The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream. Figure 27 - cut through diagram of a typical fuel injector 18 autokriti 7.0 WORKING: MPFI is used in TATA NANO & Indirect Injection in used in TATA INDICA The Fuel Injection System as the name suggests is mainly consists of an Injector, a valve with a small nozzle at the extreme end which is responsible to supply the fuel to the combustion chamber with force resulting the atomization of the fuel, this force is generated from the fuel pump which is generally placed inside the fuel tank, the atomized fuel is easier to burn when combined with the radical oxygen molecules of the air intake creating an optimum fuel and air ratio hence resulting into increased fuel efficiency with remarkably cleaner emission. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressured fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel as fine a mist as possible so that it can burn easily. 3. Direct Injection In Direct injection fuel is directly injected into the combustion chamber. It suffers from an extraordinarily high back-pressure due to its placement, as well as other severe disadvantages. Because of the exposure of the injector tips to the combustion process, carbon build-ups easily clog the injector tips. TYPES OF FUEL INJECTION 1.Single-Point, Central Fuel Injection or Throttle Body Injection (TBI) Figure 28 – a) Single point fuel injection b) Multi point fuel injection c) Direct injection Single-point simply replaces the carburetor with one or two fuel-injector nozzles in the throttle body, which is the throat of the engine’s air intake manifold. The system injects fuel into the throttle body (a wet system), so fuel can condense and cling to the walls of the intake system. 4. Programmed Fuel Injection (Pgm-FI) The PGM-FI system precisely controls fuel injection to match engine requirements, reducing emissions and increasing driveability. The electric fuel pump supplies fuel to the pressure regulator. The fuel injectors are electric solenoid valves which open and close according to signals received from the Electronic Control Unit (ECU). The ECU has sensors which measure the temperatures of the engine, coolant, oil, and outside air as well as pressure sensors to monitor oil and barometric pressure. Based on these readings and the location of the throttle, the ECU calculates how much oxygen and fuel should be mixed for optimal and efficient performance. The ECU receives input from various sensors to determine engine operating conditions. This allows the ECU to determine the correct amount of fuel to be injected by its pre-set program. 2. Multi-Point Fuel Injection (MPFI) Multi-point fuel injection devotes a separate injector nozzle to each cylinder, right outside its intake port, which is why the system is sometimes called Port injection. The injector sprays gasoline into the air inside the intake manifold. The gasoline mixes with the air in a reasonably uniform manner. This mixture of gasoline and air then passes through the intake valve and enters into the cylinder. The main advantage is that MPFI meters fuel more precisely than do TBI designs, better achieving the desired air/fuel ratio and improving all related aspects. Also, it virtually eliminates the possibility that fuel will condense or collect in the intake manifold. 19 Turbochargers are a type of forced induction system. This can significantly improve the power-to-weight ratio for the engine. this engine gives a better power output. In homogeneous operation. GDI engine operate with lean mixture and unthrottled at part loads. They compress the air flowing into the engine. Indirect injection diesels can still be found in the many ATV diesel applications. In all cylinder A/F ratio is lean and A/F ratio can access until 40/1.0 5. Air/Fuel (A/F) ratio in cylinder vary. 20 . Gasoline direct injection system assisted by turbulence. 5.1 TURBOCHARGER A turbo can significantly boost an engine's horsepower without significantly increasing its weight. in other places is lean. which in turn spins an air pump. quieter running engine. The evaporation of the fuel cools the intake charge. which reduces the efficiency by 5–10%. In road-going vehicles most prefer the greater efficiency and better controlled emission levels of direct injection. A turbocharged engine produces more power overall than the same engine without the In order to achieve this boost. called a pre combustion chamber or ante-chamber. using a single orifice tapered jet injector. fuel starts injecting into cylinder at intake stroke at full loads. and restricting the combustion burn. mixture in front of spark plug is rich. In GDI engine.29 Indirect Injection System 5.Indirect Injection System An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber. Therefore. The fuel. At this condition. which is injected in the intake stoke. evaporates in the cylinder. the temperatures in the turbine are also very high. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder. assisted by turbulence created in the chamber.000 rpm .500 psi).000 rpm).6. which is the huge benefit that makes turbos so popular. And since it is hooked up to the exhaust. where combustion begins and then spreads into the main combustion chamber. This system allows for a smoother. and more air means that more fuel can be added. Mechanical injection systems allowed high-speed running suitable for road vehicles (typically up to speeds of around 4. that is. quietrunning vehicles with a simple mechanical system.that's about 30 times faster than most car engines can go. The turbine in the turbocharger spins at speeds of up to 150.6 TURBOCHARGER & SUPERCHARGER charging. The pre-chamber had the disadvantage of increasing heat loss to the engine's cooling system. and because combustion is Fig. as the GDI engine operates with homogeneous charge and stoichiometric or slightly rich mixture. fuel is injected into cylinder before spark plug ignites at low and medium loads.autokriti 7. 6. 1. injector pressures can be lower. this operation provide significant improvements in fuel economy. the turbocharger uses the exhaust flow from the engine to spin a turbine. you get more power from each explosion in each cylinder. At full load. The cooling effect permits higher compression ratios and increasing of the volumetric efficiency and thus higher torque is obtained. about 100 bar (10 MPa.[51] Indirect injection engines are cheaper to build and it is easier to produce smooth. low-velocity air stream through a process called diffusion. It is the job of the turbine housing to guide the exhaust gas into the turbine wheel. The compressor also consists of two parts: the compressor wheel and the compressor housing. mainly by reducing their weight. low-pressure air stream into a highpressure. Ceramic turbine blades are lighter than the steel blades used in most turbochargers. the highvelocity spinning draws in air and compresses it.7 psi at sea level. you would expect to get 50 percent more power.autokriti 7. The typical boost provided by a turbocharger is 6 to 8 pounds per square inch (psi). They also allow a slightly smaller. One sure way to reduce the inertia of the turbine and compressor is to make the turbocharger smaller. A small turbocharger will provide boost more quickly and at lower engine speeds. Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. further reducing turbo lag. One way to decrease turbo lag is to reduce the inertia of the rotating parts. so you might get a 30 to 40percent improvement instead. The energy from the exhaust gas turns the turbine wheel. and as the turbine turns the compressor wheel. Since normal atmospheric pressure is 14. Figure 30 –Turbocharger plumbing in a car Turbochargers allow an engine to burn more fuel and air by packing more into the existing cylinders. you can see that you are getting about 50 percent more air into the engine. and start providing boost earlier. Therefore.0 pushed into the engine. This allows the turbine and compressor to accelerate quickly. allowing the engine to burn more fuel to produce more power. The turbine consists of the turbine wheel and the turbine housing. The compressor wheel is attached to the turbine by a forged steel shaft. lighter shaft to be used. Working A turbocharger is made up of two main sections: the turbine and the compressor. They are super-precise bearings made of advanced materials to handle the speeds and temperatures of the turbocharger. This helps the turbocharger accelerate more quickly. and the gas then exits the turbine housing through an exhaust outlet area. The compressor housing then converts the highvelocity. Figure 31 –Inside a turbocharger One of the main problems with turbochargers is that they do not provide an immediate power boost when you step on the gas. They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. This allows the turbine to spin up to speed faster. It's not perfectly efficient. which reduces turbo lag. but may not be able to provide much boost at higher engine speeds. The compressed air is 21 . The compressor’s mode of action is opposite that of the turbine. This chemically correct mixture -14 parts air to one part fuel -. which wraps around a pulley that is connected to a drive gear. So some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine. The drive gear. Making the drive gear larger than the compressor gear causes the compressor to spin faster. In high-altitude situations. Turbochargers are powered by the mass-flow of exhaust gases driving a turbine. which means that it loses its density and cannot expand as much during the explosion. which use the exhaust gases to power the compressor. providing a boost.2 Supercharger A supercharger is a great way to achieve forced air induction.is essential for an engine to operate efficiently. Both superchargers and turbochargers do this. a supercharger delivers higher-pressure air to the engine so it can operate optimally. But you can't simply pump more fuel into the engine because an exact amount of oxygen is required to burn a given amount of fuel. Figure 32 –Cut through diagram of a supercharger Working As the air is compressed. 22 . it gets hotter. For a supercharger to work at peak efficiency. where engine performance deteriorates because the air has low density and pressure. Most are driven by a belt. In fact. The bottom line: To put in more fuel. except air passes through the inside as well as the outside of the intercooler. and when air heats up.0 5. it expands." its official name. Fig. This forces more air into the engine. Superchargers are powered mechanically by beltor chain-drive from the engine's crankshaft. in turn. Unlike turbochargers. This means that it can't create as much power when it's ignited by the spark plug. 5. superchargers draw their power directly from the crankshaft. you have to put in more air. The difference between the two devices is their source of energy.33 Intercooler An intercooler or charge air cooler is an additional component that looks something like radiator. rotates the compressor gear. and the power of the engine is increased. more fuel can be added to the charge. With the additional air in the boost. it heats up.6.autokriti 7. The intake air passes through sealed passageways inside the cooler. To pressurize the air.6. A supercharger is any device that pressurizes the air intake to above atmospheric pressure. the term "turbocharger" is a shortened version of "turbo-supercharger. Getting more fuel into the charge would make for a more powerful explosion. not necessarily more air pressure.3 Intercooler When air is compressed.more rapidly than the engine itself. the compressed air exiting the discharge unit must be cooled before it enters the intake manifold. That's the job of the supercharger. a supercharger must spin rapidly -. the goal is to get more air molecules into the cylinder. without creating a vacuum. Superchargers increase intake by compressing air above atmospheric pressure. 7. The diesel engine would be steady and carry heavier loads to longer distances. 5.7 PETROL ENGINE DIESEL ENGINE Diesel engine would pull heavy loads easily than a petrol engine. instead it has got carburetor and ignition coil.Which is more than Engine’s RPM 5. which is denser and contains more air molecules than warmer air. No spark is required. Diesel engine petrol engine 1 It has got carburetor. Sr. the air and fuel mixture is ignited using a spark plug and burns expanding and forcing the piston down. 7 8 9 10 Its compression ratio varies from 5:1 to 8:1. ignition coil and spark plug. Engine weight per horse-power is high. Operating cost is high.no. 5. Engine weight per horsepower is comparatively low.000 RPM. causing it to burn and force the piston down. Thermal efficiency varies from 25 to 32%. Torque produced is less even. In diesel engine. Though the pick-up of a petrol engine would be much more than of a diesel engine. DID YOU KNOW? 5. the intercooled system will put in 7 psi of cooler air.7. It has got no fuel injection pump and injector.7. v/s 5. Air fuel mixture is compressed in the combustion chamber when it is ignited by an electric spark. 6 Fuel is injected in combustion chamber where burning of fuel takes places due to heat of compression. 5 It has got ‘fuel injection pump’ and injector.0 2. 2 3 4 It has got no carburetor.autokriti 7.4 LOAD CARRYING CAPACITY Superchargers can spin at speeds as high as 50. fuel is injected at a high pressure into the hot. 5. Torque produced is even. The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it goes into the engine.1 EXPANSION STROKE 1. Operating cost is low. Only air is sucked in cylinder in suction stroke. so a diesel engine would last longer than a petrol engine. No intercooler is used in tata indica while cooler air from outside is blown across fins by engine cooling fan. 23 .3 WEIGHT Petrol engines are lighter than diesel engines. Thermal efficiency varies from 32 to 38%. In petrol engine.000 to 65. ignition coil & spark plug. Its compression ratio varies from 14:1 to 22:1 It uses diesel oil as fuel. It uses petrol (gasoline) or power kerosine as fuel. compressed air in the cylinder. Mixture of fuel and air is sucked in the cylinder in suction stroke. This means that if the turbocharger is operating at a boost of 7 psi.5 FUEL EFFICIENCY Diesel engines have better fuel efficiency as compared to petrol due to the fact that they have higher compression ratio.7.7.2 LIFE Petrol destroys lubrication and burns the engine whereas diesel doesn’t. When you press on the clutch. Springs inside the clutch plate absorb the initial shock of the clutch touching the flywheel and as you take your foot off the clutch pedal completely. 6. The flywheel is attached to the end of the main crank and the clutch plates are attached to the gearbox lay shaft using a spline.TRANSMISSION spinning on the end of the engine crank but it no longer drives the gearbox because the clutch plates aren't pressed up against it.1 Multi-plate clutches Adding plates to a clutch unit to form a multi-plate clutch will increase its torque capacity.2. the flywheel. So as the engine turns. An internally-splined hub on each disc mates with the splines on the transmission input shaft. The diaphragm springs are connected to the inside of the clutch cover with a bolt/pivot arrangement that allows them to pivot about the attachment bolt.2 Types of Clutches 6.1 CLUTCH A clutch is a mechanical device that engages and disengages the power transmission. without increasing spring strength or clutch diameter. clutch cover.As you start to release the clutch pedal. This clutch assembly has more than two friction discs. diaphragm springs and pressure plate are all spinning together. The friction material on the clutch plate is what grips the back of the flywheel and causes the input shaft of the gearbox to spin at the same speed. The separator plate locates on driving pins on the flywheel. with friction material riveted to both sides of each. especially from driving shaft to driven shaft. A cast-iron separator plate fits between each disc. This release of pressure allows the clutch plates to disengage from the flywheel. These in turn pivot on their pivot points against the inside of the clutch cover. The pressure plate spring 24 . the clutch cover is bolted to the flywheel so it turns with the flywheel.autokriti 7.0 6. The clutch pedal is connected either mechanically or hydraulically to a fork mechanism which loops around the throw-out bearing. the pressure plate and the clutch plate(s). Figure 34 –Components of a diaphragm spring clutch In the diagram here. 6. pulling the pressure plate away from the back of the clutch plates. the flywheel. and sit at traffic lights without stopping the engine. in turn pushing them against the flywheel again. The clutch is what enables you to change gears. the clutch is firmly pressed against it. pressure is released on the throwout bearing and the diaphragm springs begin to push the pressure plate back against the back of the clutch plates. The clutch is composed of three basic elements. The ends of the diaphragm springs are hooked under the lip of the pressure plate. The flywheel keeps Figure 35 –Components of a Multi-plate clutch This friction unit is between the flywheel and the pressure plate when the pressure plate assembly is bolted to the flywheel. the fork pushes on the throw-out bearing and it slides along the lay shaft putting pressure on the innermost edges of the diaphragm springs. A dry clutch. From the input gear to the secondary gear.3 Centrifugal Clutch A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts. the ratio is 20/10 = 2:1. When the central shaft spins fast enough.4. Figure 37 –Figure depicting gear ratios 6.1a Constant Mesh type Gearbox You can see the helical gears meshing with each other. a secondary gear with 20 teeth and a final gear with 30 teeth. 6. In this example. The output shaft is the upper shaft in this image. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil). From the second gear to the final gear.2. 6.5:1.it's the one connected to the clutch .autokriti 7. which connect to a clutch shoe. 25 .0 then provides a frictional clamping force on each mating surface.1 Manual Transmission 6. imagine an input gear with 10 teeth. You can see 5 helical gears and 3 sets of selector forks. i.4 Types of Transmission 6. as the name implies.4.2 Wet & Dry Clutches A wet clutch is immersed in a cooling lubricating fluid that also keeps surfaces clean and provides smoother performance and longer life. the input gear has to turn three times. with the driving shaft nested inside the driven shaft. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of housing. stacking multiple clutch discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged. weighted arms in the clutch swing outward and force the clutch to engage. however. or 3:1. The input of the clutch is connected to the engine crankshaft while the output may drive a shaft.ultimately you need the ratio of input to output. literally.5):1. Wet clutches. the springs extend causing the clutch shoes to engage the friction face. 6. tend to lose some energy to the liquid. For example. The total gear ratio for this system is (2*1. This also neatly shows how you can do the calculation and misses the middle gear ratios .2.3 Gear ratio Gear ratio is defined as the ratio of the speed of the input shaft to that of the output shaft. the ratio is 30/20 = 1.the one driven directly by the engine. As engine rpm increase. Well look at the output shaft. the final output is 30 and the original input is 10.e. dry. 30/10 = 3/1 = 3:1. is not bathed in liquid and should be. The lower shaft in this image is called the layshaft . to turn the output gear once. It is calculated as the ratio of the number of teeth on the output gear to the number on the input gear. At the most basic level that tells you this is a 5-speed box (note that my example has Figure 36 –Parts of a Centrifugal clutch On the centre shaft there are an assorted number of extension springs. The image here shows the same gearbox as above modified to have a reverse gear.1c Synchromesh gearbox Fig.4. Typically. when the gearstick is moved to select fourth gear. 39 –Gear selection in a constant mesh gearbox A synchro is a device that allows the dog gear to come to a speed matching the helical gear before the dog teeth attempt to engage. there will be three gears that mesh together at one point in the gearbox instead of the customary two. the selector fork slides backwards. sliding the dog gears back and forth. Because the reverse gear is spinning in the opposite direction. When you move the gear stick. In this way.Therefore they actually spin around the output shaft without turning it. The dog gears are mounted to the output shaft on a splined section which allows them to slide back and forth. when you let the clutch out. With the clutch engaged. All the This locks it to the dog gear which itself is locked to the output shaft with the splines. Figure 40 –Idler gear being used to reverse direction of motion causes the last helical gear on the output shaft to spin in the opposite direction to all the others.a dog gear is slid into place with a selector fork. but there will be a small gear in between them called the idler gear. 6. When the clutch is let out and the engine drives the layshaft. a series of mechanical pushrod connections move the various selector forks. Look closely at the selector forks. There will be a gear each on the layshaft and output shaft.Observing the close-up of the area between third and fourth gear.autokriti 7.0 no reverse gear). you'll see they are slipped around a series of collars with teeth on the inside. the layshaft is always turning. all the gears turn as before but now the second helical gear is locked to the output shaft and it is fourth gear. This slides the dog gear backwards on the splined shaft and the dog teeth engage with the teeth on the front of the helical fourth gear. you 26 . The inclusion of this extra mini gear Figure 38 –A constant mesh gearbox helical gears on the layshaft are permanently attached to it so they all turn at the same rate. Those are the dog gears and the teeth are the dog teeth.1b Reverse Gear Reverse gear is normally an extension of everything you've learned above but with one extra gear involved. The principle of engaging reverse is the same as for any other gear .4. They mesh with a series of gears on the output shaft that are mounted on sliprings. 6. the gearbox output shaft spins the other way in reverse. the more the speed of the output shaft and free-spinning helical gear are equalised before the teeth engage. To the left is a colour-coded cutaway part of my example gearbox. continuously variable transmissions don't have a gearbox with a set number of gears. One of the pulleys. As the two pulleys change their radii relative to one another. the synchro brings the layshaft to the right speed for the dog gear to mesh. centrifugal force or spring tension to create the force necessary to adjust the pulley halves. The green cone-shaped area is the syncho collar. is connected to the crankshaft of the engine. The more contact it makes. but it is freespinning once the clutch has been operated. the other decreases its radius to keep the belt tight. The driving pulley is also called the input pulley or variator because it's where the energy from the engine enters the transmission.4. most common type of CVT operates on an ingenious pulley system that allows an infinite variability between highest and lowest gears with no discrete steps or shifts. which means they don't have interlocking toothed wheels. When the two cones of the pulley are far apart (when the diameter increases). they create an infinite 6. Because the gears are meshed all the time. known as the drive pulley (or driving pulley). and the radius of the belt loop going around the pulley gets larger. This means that the layshaft is now spinning at a different speed to the engine. It's attached to the red dog gear and slides with it. When the cones are close together (when the diameter decreases).0 don't need to 'blip' the throttle and double-clutch to change gears because the synchro does the job of matching the speeds of the various gearbox components for you. either bringing the engine to the same speed as the layshaft or vice versa depending on engine torque and vehicle speed. A variable-input "driving" pulley. the belt rides lower in the groove. The second pulley is called the driven pulley because the first pulley is turning it. Each pulley is made of two 20-degree cones facing each other. the driven pulley transfers energy to the driveshaft. The variable-diameter pulleys are the heart of a CVT. As an output pulley. it makes friction contact with the conical hole. The layshaft is usually connected to the engine. the belt rides higher in the groove.2 Continuously Variable Transmission Unlike traditional automatic transmissions. but that's OK because the clutch gently equalises the speed of the engine and the layshaft. the output shaft is always turning (because ultimately it is connected to the wheels). and the radius of the belt loop going around the pulley gets smaller. The 27 . Most CVTs only have three basic components: A high-power metal or rubber belt. Figure 42 –CVT at low and high speeds CVTs may use hydraulic pressure. If the car is moving. but the three components described above are the key elements that enable the technology to work. A belt rides in the groove between the two cones. An output "driven" pulley CVTs also have various microprocessors and sensors. When one pulley increases its radius.autokriti 7. Figure 41 –Cone shaped synchro collars As it approaches the helical gear. at any engine or vehicle speed. Input Output Stationary Calculation Sun (S) Planet Ring (R) Carrier (C) 1 + R/S Planet Ring (R) Carrier (C) Sun (S) Sun (S) Planet -R/S Carrier (C) Ring (R) Gear Ratio 3. Choosing which piece plays which role determines the gear 28 .4:1 Figure 43 –Sun and Planet gears arrangement in an automatic transmission TATA NANO has Synchromesh on all forward gears. While in an automatic transmission. Automatic Transmission uses a torque converter instead of a clutch. which in turn allows the rear pulley to close up and lower the gearing. then the rotational speed of the driven pulley decreases.0 number of gear ratios -. In the arrangement shown we have two sets of planet gears that are arranged as inner and outer planets and the inner one are shorter and only engage the smaller sun gear and the outer planet gears. resulting in a higher gear. When you roll off the throttle. the ring gear. There are several other ratios that can be gotten out of this planetary gear set. the output or can be held stationary.autokriti 7. Once you put the transmission into drive. when the pitch radius is small on the driving pulley and large on the driven pulley. Any planetary gearset has three main components: The sun gear. but the output direction is reversed. the same set of gears produces all of the different gear ratios. And then the outer planet gear in turn rotates the larger sun gear at the bottom and the outermost ring gear. 6. sliding halves of the pulley.4:1 1 / (1 + S/R) 0.the output speed is slower than the input speed.3 Automatic Transmission Automatic transmission is totally different from manual transmission. Each of these three components can be the input. everything else is automatic.4. but these are the ones that are relevant to automatic transmission. the centrifugal force is reduced and the spring loaded rollers drop back. It has one ring gear that is always the output of the transmission. resulting in a lower gear. allowing the front pulley to open slightly. For example. 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. ratio for the gearset. then the rotational speed of the driven pulley increases. There is no clutch pedal and no gear shifter in an automatic transmission car. It has 4speed manual transmission Also. Notice that the first gear ratio listed above is a reduction -. the planet gears and the planet gears' carrier. CVT has an infinite number of gears that it can run through at any time. It looks like a single planetary gearset but actually behaves like two planetary gearsets combined. Sliding mesh on reverse gear with overdrive on 4th gear. The last is a reduction again. We can get lots of different gear ratios out of this gearset.from low to high and everything in between. The planetary gearset is the device that makes this possible in an automatic transmission. The second is an overdrive -the output speed is faster than the input speed. When the pitch radius is large on the driving pulley and small on the driven pulley.71:1 -2. locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. But in the Compound Planetary Gearset there are two sun gears and two sets of intermeshing planet gears. In this system we can now have four forward gear ratios and one reverse gear. which allows the belt to ride lower within the springloaded. the fluid around the impellar rotates in the same direction.Fluid strikes the curved vane of the stator causing the one way clutch to lick the stator and redirect the fluid at the impellar vanes in the direction of the engine rotation. See Figure 1-13. When the vehicle is stopped. A hydraulic pump in the transmission forces fluid into the converter.the turbines curved inner surface directs the fluid at the vanes of the stator.autokriti 7. These clutches are actuated by the valve body (see below). and the blade set connected to the input shaft is called the turbine. One set of blades is driven by the engine. As the impellar and turbine approach the same speed. See Figure 114. Planetary gear train It Consists of planetary gear sets as well as clutches and bands. while allowing another member to rotate. Inside the converter. The blade set connected to the engine is called the impeller. Power is transmitted from the impeller to the turbine through the fluid. and a set of planetary gearsets to provide a range of gear ratios. The blade set connected to the engine is called the impeller.releasing the one way clutch and allows the stator to freewheel. it strikes the turbine blades. As the fluid is thrown from the impeller blades.44 Torque converter 2. the fluid from the impeller continues to strike the turbine. When it reaches the interior of the turbine. When the impellar is driven by the engine crankshaft.Torque Converter Fluid couplings and torque converters are fluidfilled units installed between the engine’s crankshaft and the transmission. thereby transmitting torque and producing gear reductions or overdrive ratios.it flows inward along the vanes of the turbine. altering the speed of rotation of the output shaft depending on which planetary gears are locked. and the other set of blades is connected to the transmission’s input shaft. These are the mechanical systems that provide the various gear ratios. but the fluid allows enough slippage between the impeller and the turbine to prevent engine stalling. fluid strikes the back of the stator vanes. A hydraulic pump in the transmission forces fluid into the converter. One set of blades is driven by the engine. using a fluid coupling or torque converter. the fluid is spun by the impeller blades. one of two types of clutches or bands are used to hold a particular member of the planetary gearset motionless. the fluid is spun by the impeller blades.Fluid couplings and torque converters are fluid-filled units installed between the engine’s crankshaft and the transmission.fluid is forced out away from the impellar towards the turbine.0 .as impellar speed increases 29 . To effect gear changes. Hydraulic automatic transmissions consist of three major components: 1.The fluid strikes the vanes of turbine causing it to rotate in the same direction as the impellar. Fig. After the fluid dissipates its energy against the vanes of the turbine. As the fluid is thrown from the impeller blades.as speed increases further. They consist of two sets of blades. Hydraulic automatic transmissions The predominant form of automatic transmission is hydraulically operated. it strikes the turbine blades.centrifugal force causes the fluid to flow outward from the center of the impellar. They consist of two sets of blades. increasing engine torque. and the other set of blades is connected to the transmission’s input shaft.being mounted to the transmission body. Inside the converter.fluid will strike the vanes of the stator and limit engine rpm and upper engine performance.Unless the stator freewheels. and the blade set connected to the input shaft is called the turbine. however. The outer shaft is hollowed out. The clutch itself is actuated by electronic equipment that can synchronize the timing and the torque required to make gear shifts quick and smooth. gears can be changed without interrupting the power flow from the engine to the transmission. the DCT splits up odd and even gears on two input shafts. making room for an inner shaft. The system is designed to provide a better driving experience.0 their sequence controlled by the transmission's internal programming. a gearbox. Principally. Unlike a conventional manual gearbox. which is nested inside. Using this arrangement. a type of device known as a sprag or roller clutch is used for routine upshifts/downshifts. This removes the need for a clutch pedal while the driver is still able to decide when to change the gear. third and fifth gears.autokriti 7. Notice that one clutch controls second. A dual-clutch gearbox uses two clutches. A standard manual transmission can't do this because it must use one clutch for all odd and even gears. processors.especially in cities where congestion frequently causes stop-and-go traffic patterns. AMTs have been used in racing cars for many years. Hydraulic controls uses special transmission fluid sent under pressure by an oil pump to control various clutches and bands modifying the speed of the output depending on the cars running condition. Dual Clutch Transmission An AMT is composed of a dry clutch. and ease of use. Fig. AUTOMATED MANUAL TRANSMISSION 3. Sophisticated electronics and hydraulics control the clutches. but has no clutch pedal. In a DCT. the clutches operate independently.46 Shift buttons on the steering wheel of a FIAT Bravo Benefits of AMT Changing gears without using a foot to • operate the clutch Figure45 – Basic arrangement of a 6-speed dual clutch transmission • No engine or gear modifications The diagram shows this arrangement for a typical 6-speed DCT. third and fifth. A two-part transmission shaft is at the heart of a DCT. while the inner shaft feeds first. The outer hollow shaft feeds second. while the other controls the even gears. That's the trick that allows lightning-fast • Less physical or psychological stress • More comfortable than manual transmissions 30 .cost. gear changes and keeps power delivery constant. One clutch controls the odd gears. (DCT) A dual-clutch transmission offers the function of two manual gearboxes in one. just as they do in a standard automatic transmission. while another independent clutch controls first. but only recently have they become feasible for use in everyday vehicles with their more stringent requirements for reliability. fourth and sixth gears. and an embedded dedicated control system that uses electronic sensors. fourth and sixth gears. which houses all of its gears on a single input shaft. and actuators to actuate gear shifts on the driver’s command. is what gives that final gear reduction. neither drive pinion is trying to spin any differently from the other. one connected to each axle. Commercial DCT systems include the Direct-Shift Gearbox by Volkswagen Group and the Dual Dry Clutch Transmission by FIAT Group travel at a lower speed. As the input pinion spins. The input pinion gear is the gear that is driven from the drive-train typically the output shaft from the transmission. If your car did not have a differential. Open differentials have e a few essential components. It drives the ring gear which. differential is used.5. Fig. forced to spin at the same speed. The wheels that travel a shorter distance 6. so the 31 . containing two captive pinion gears that are intermeshed with the two output pinion gears. SensoDrive by Citroen. 2Tronic by Peugeot. Attached to the ring gear is the cage. Sequential Manual Gearbox by BMW. AMT systems are currently installed by several automakers under different commercial names. and EasyTronic by Opel. the wheels would have to be locked together.5 DIFFERENTIALS Car wheels spin at different speeds. 47 Differential The captive pinions are free to rotate how they wish. being larger. especially when turning.0 • More “fun” factor compared to fully automatic transmissions. The ring gear spins.autokriti 7. When the vehicle is travelling in a straight line. such as SeleSpeed by FIAT. illustrated below. This would make turning difficult and hard on your car.1 Open differential Open differentials are most commonly used and they supply the same amount of torque to each output. and that the inside wheels travel a shorter distance than the outside wheels. it meshes with the ring gear. Driven wheels are linked together so that a single engine and transmission can turn both wheels. Each wheel travels a different distance through the turn. For the car to be able to turn. spinning the cage and the two captive pinions. 6. one of the wheels spins more quickly than the other. However. the wheel on the ice spins and the wheel on the road doesn't. then all the input gets redirected to the drive Pinion that has the least resistance. allowing the two drive pinions to spin at slightly different speeds while still transmitting torque to them.autokriti 7. it’s a good idea to try to pull away in second gear – that gives the limited-slip differential a chance to do its job. only the wheel on the ice will spin. it holds the ring gear solid.2 Limited slip Differentials The simplest form of limited-slip differential is designed to combat the scenario outlined above.These push the drive pinions outwards where the second extra clement comes into play . The vehicle doesn't go anywhere because all the engine power is directed to the wheel with least resistance . This is where the limited slip differentials are of great help.0 captive pinions don't spin and the turning of the ring gear is translated directly to both drive pinions.the one on the ice. 6. This means that the clutch is always going to try to behave as if the car was moving in a straight line by attempting to make both output pinions spin at the same speed as the ring gear and cage. This also explains why a two-wheel-drive vehicle can get into trouble when one wheel has less friction with the ground than the other. the captive pinions spin in opposite directions. and the other wheel on the axle spins the other way around. To get around this. The stiffness of the spring pack coupled with the friction of the clutch pack together determines the amount of torque required to overcome the clutch. These are connected to the drive-shafts to the wheels so effectively that the ring gear spins the wheels at the same speed that it is turning. This is why when you gun a two-wheel-drive car with one wheel on ice and the other on the road. when a car with a LSD goes into a corner. Imagine the same scenario on a four-wheel-drive vehicle that has open differentials on the front and rear. With low engine revs and steady throttle control. If you're off-roading in such a vehicle and get it into a situation where one front wheel and one rear wheel 32 . With a limited slip differential.clutch packs. At this point. the captive pinions come into play. The render here shows the generic open differential Figure 48 –An open differential The open differential cannot compensate for this. It still has all the components of an open differential but there are two crucial extra elements. thus allowing them to turn at different speeds again. If the engine is revved hard though it can still generate sufficient torque to overcome the clutch pack and once again. One can check whether a vehicle's differential is working properly by jacking the driven axle up off the ground and spinning one wheel. Physically there's not a lot of difference in the design of a limited-slip differential and an open differential.5. because of the packs even though one wheel differential is going to attempt to spin both drive pinions at the same speed. there are enough forces at play that the drive Pinions begin to slip against the clutch material. are off the ground. Now gearbox is stationary. If one drive pinion is held solid compared to the other. The first are spring pressure plates which are a pair of springs and pressure plates nestled in the cage between the two drive pinions. When the vehicle starts to turn a corner. The backside of the drive pinions have friction material on them which presses against clutch plates built into the cage. the wheel on the road will get enough spin to move the vehicle forwards. you're stuck. This forces both wheels to turn in unison.6. they apply the same rotational force. even if one is entirely stationary.It turns 10 percent faster than the drive shaft.2 Four wheel Drive A vehicle with a four wheel drive (4WD) has a drive train that can send power to all the four wheels.0 from above modified to be a LSD. it allows each wheel to rotate at different speeds (such as when negotiating a turn). An open (or unlocked) differential always provides the same torque (rotational force) to each of the two wheels. This provides maximum traction for offroading. So although the wheels can rotate at different speeds. Other vehicles have a selective arrangement that permits the diver to shift from 4WD to 2WD and back according to driving conditions. thus avoiding tire scuffing. 6. (Refer appendix-3 DID YOU KNOW? In AUDI’s sport differential a superposition gear comprising two sun gears and an internal gear was mounted on the left and the right of a conventional rear differential.2). on that axle. It also provides maximum traction when the road surface is slippery or covered with ice or snow.autokriti 7. A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft.(Refer appendix 1. A locking differential is a variation on the standard automotive differential. If one of the driven wheels comes off the ground.1 Two-Wheel drive Figure 49 –Exploded view of a limited slip differential This is by far the most common type of drive-train in any car today. which in turn drives those wheels. 6. and the other spinning. A locking differential may provide increased traction compared to a standard or open differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel. regardless of the traction available to either wheel individually. The engine drives the gearbox which sends its output to an open differential either on the front or rear axle. Some vehicles have a four wheel drive system that engages automatically or remains engaged all the time.6. Figure 50 – Cut section view of a locking differential 33 . or gets on a slippery surface like ice. the car gets stuck because all the torque is being sent to that wheel while the other three sit there helpless.6 TYPES OF DRIVELINE 6.When the differential is open. in this case called a transaxle – is attached directly to the engine. The system then seamlessly determines the optimal amount of front and rear torque to apply for the given conditions to reduce wheel-slip and even to prevent slip from occurring in the first place. the computerized AWD system electronically activates an electromagnet in the clutch pack to push the clutch plates together and drive the rear wheels. The system reacts within milliseconds to distribute up to 100 percent of the available torque to the rear wheels. there is an electromagnetically activated clutch pack called a power transfer unit that is attached between the transmission and the rear drive axle. as said earlier. steering angle and wheel speed to determine the vehicle conditions and the driver’s intent. All Wheel Drive The transmission . However. The drive axles to the front wheels are attached directly to the transaxle. It does so when sensors detect wheel slip in the front wheels. AWD operates a lot like a frontwheel. Then. or.drive vehicle with much of the power sent to the front wheels.0 3.aUtOKRITI 7. Under normal driving conditions. In order to activate the rear wheels. will act preemptively to prevent slip from happening in the first place. 34 . the AWD system continuously monitors throttle position.  Regeneration of oxidation catalytic converter: The electronic controller. typically a 32-bit processor. fuel atomization. based on a feedback system from the oxygen sensor.  Lambda control: It controls the ratio of air and fuel going into the cylinders after checking the amount of oxygen coming out through exhaust.  Cooling system control: It monitors the temperature of various parts of the engine and maintains the safety level of the temperature.  Throttle control: After stepping on accelerator pedal.aUtOKRITI 7. as the engine itself is a very fast and complex part of the automobile. air-fuel ratio etc. 5. maintains the A/F ratio within a narrow range around the stoichiometric point.  OBD (On-Board Diagnostics): It is basically DAQ (Data acquisition) system which collects data (temperature. instead of opening the throttle a signal is sent to electronic control unit.Automotive electronics or automotive embedded systems are distributed systems. Engine electronics 2. which takes inputs into account as well as outside variables to open the throttle for optimum efficiency and performance. Of all the electronics in any car the computing power of the engine control unit is the highest. and according to different domains in the automotive field. In a diesel engine:  Fuel injection rate: The purpose of the fuel injection system is to deliver fuel into the engine cylinders. NOx control: Analysis of exhaust gas to determine combustion efficiency and pollutants. Engine controls demand one of the highest real time deadlines. while precisely controlling the injection timing.  Emission control. and other parameters. 6. 7.0 6. A modern car may have up to 100 ECU's and a commercial vehicle up to 40. Transmission electronics 3. One of the major things that has helped automobiles to provide more safety and convenience is electronics. the auto industry has revolutionized the way people travel from place to place. Chassis electronics Active safety Driver assistance Passenger comfort Entertainment systems 7. From the creation of the Electronic Fuel Injection to the popular Global Positioning System found in many cars today.1 Engine One of the most demanding electronic parts of an automobile is the engine control unit.) from various sensors and informs the user about the running status of the car and any abnormality. car manufacturers have been able to offer a wide variety of services that many new automobile owners appreciate. It controls such things as: 35 . With the advances in technology and electronics. to assure maximum catalyst efficiency. 4. they can be classified into: In a petrol engine: 1. Electronics in cars Automobiles have come a long way since their beginning in the late 19th century. for example. understeer or oversteer during poorly judged turns on slippery roads. and also many semi-automatic transmissions having a fully automatic clutch or a semi-auto clutch (declutching only). Automatic transmissions use controls for their operation. because steering input may not always be directly indicative of the intended direction of travel (i. ESP – Electronic Stability Program: ESC intervenes only when it detects a probable loss of steering control. The sensors are so sensitive. The engine control unit and the transmission control exchange messages. Conversely. sensor signals and control signals for their operation.e. if the ECU detects a wheel turning significantly faster than the others. and at least two hydraulic valves within the brake hydraulics. All-wheel 36 drive (AWD) vehicles often have an electronically controlled coupling system in the transfer case or transaxle engaged (active part-time AWD). four wheel speed sensors.aUtOKRITI 7. the car is understeering or oversteering and ESC activates one of the front or rear brakes to rotate the car back onto its intended course.3 Chassis Electronics   ABS . or hydroplaning. if a car is making a left turn and begins to understeer (the car plows forward to the outside of the turn) ESC activates the left rear brake. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. which will help turn the car left. if it detects a wheel rotating significantly slower than the others.  TCS – Traction Control System: When the traction control computer (often incorporated into another control unit. the wheel then turns faster. EBD – Electronic Brake Distribution: EBD may work in conjunction with ABS and Electronic Stability Control ("iESC") to minimize yaw accelerations during turns.e. and the actuation is so quick that the system may correct direction before the driver reacts.0 7. Some anti-lock systems can apply or release braking pressure 15 times per second. For example. controlled drifting).Anti-lock Braking System: Typically ABS includes a central electronic control unit (ECU). ESC compares the steering wheel angle to vehicle turning rate using a yaw rate sensor. such as the ABS module) detects one or more driven wheels spinning significantly faster than another. when the vehicle is not going where the driver is steering. opposing the skid and bringing the vehicle back in line with the driver's commanded direction. when skidding during emergency evasive swerves. thus reducing the braking force on that wheel. mainly the shifting of the gears for better shift comfort and to lower torque interrupt while shifting. or locked-up tighter (in a true full-time set up driving all wheels with some power all the time) to supply nonslipping wheels with torque. The ECU constantly monitors the rotational speed of each wheel. This may happen.  7. . and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis. brake hydraulic pressure to the wheel is increased so the braking force is reapplied. a condition indicative of impending wheel lock. ESC may also intervene in an unwanted way during highperformance driving. If the yaw sensor detects more/less yaw than the steering wheel angle should create. it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel. it invokes the ABS electronic control unit to apply brake friction to wheels spinning with lessened traction. slowing down the wheel. ESC estimates the direction of the skid. i.2 Transmission These control the transmission system. Braking action on slipping wheel(s) will cause power transfer to wheel axle(s) with traction due to the mechanical action within the differential. adjusts beam automatically Automatic cooling .temperature adjustment 37 .aUtOKRITI 7.6 Passenger comfort      Automatic climate control Electronic seat adjustment with memory Automatic wipers Automatic headlamps .5 Driver assistance  Lane assist system  Speed assist system Blind spot detection Park assist system Adaptive cruise control system    7.0 7.4 Active safety : These systems are always ready to act when there is a collision in progress or to prevent it when it senses a dangerous situation:    Air bags Hill descent control Emergency brake assist system 7. 2. Wheel 9.2.2. Rack and pinion 8. Where this line meets the centreline of the vehicle is the roll centre. 8. it is clear that the centre of gravity of the car will be located at where mass is most highly concentrated. hubs. Toe link 6. Essentially. In other words the suspension links the wheels of car to the chassis and aims to give the car the best possible handling qualities.4 Roll centre: When a car experiences centrifugal cornering forces the sprung mass between both the front and rear axles will tend to rotate around a centre which is also located in a transverse plane to the axles. Upright 5. which for a race car is typically around the engine and associated drive components.52 Roll centre 38 . These points are called the roll centres. Suspension arm 4. This weight is much larger than the unsprung weight as it consists of weight from the majority of car components which would include the chassis. fuel.51 Suspension components Fig. These tendencies give rise to an uncomfortable ride and also cause additional stress in the automobile frame and body.2 Sprung weight: Sprung weight is the portion of total car weight which is supported by the suspension springs. springs and shocks as well as the suspension links. It is also expected that all accelerative forces experienced by a vehicle will act through its centre of gravity. Rocker 2. it would be able to balance with no rotational movement.1 Unsprung weight : The unsprung weight of a vehicle is the fraction of the total weight that is not supported by the suspension springs and will usually consist of the wheels. All the parts which perform the function of isolating the vehicle body from the road shocks collectively called a suspension system. Tyre 8.SUSPENSION SYSTEM: INTRODUCTION:- 8.3 Centre of gravity (CG): The definition of centre of gravity for a car is no different than that of a simple object such as a cube.2. Fig. driver. pitch. 8. engine. gearbox and other components housed in the chassis. 1. it is a 3 dimensional balance point where if the car was suspended by. 8. The key components of these systems are numbered and listed below. roughly 50% of the weight due to drive shafts. Coil over shock absorber 7. lines corresponding with the angle of the upper and lower linkages are extended until they meet at a point which is called the instantaneous centre. Tie rod 11.2 FUNDAMENTAL CONCEPTS: The automobile chassis is mounted on the axles. Push rod 3.First. not direct but through some form of springs.aUtOKRITI 7. This is done to isolate the vehicles body from the road shocks which may be in the form of bounce.1 OBJECTIVE OF SUSPENSION SYSTEM:The function of a suspension system for a road vehicle is quite simple. Recognising this concept.0 8. brakes and lastly. 8. hub carriers. That is to reduce the shock and vibration experienced by occupants due to irregularities on the driving surface and to ensure all wheels maintain contact with the driving surface to promote stability and control of the vehicle. and roll. Steering arm 10. From this instantaneous centre a straight line is then drawn back to a point defined by the middle of the tyre’s contact patch. tires. 8.2. Fig. a left hand corner and from the left to the right in a right hand corner. The bar is also constrained by mounts featured on the chassis which allow rotation of the bar as the car wheels oscillate up and down. Where dampers come in is then to stop this post bump extension of the springs such that the car’s body stays at a roughly constant height. Bump occurs when the wheels hit a bump on the track surface whereas droop occurs when the wheels drop into a depression in the track surface.12 Springs and dampers Dampers and springs go hand in hand. Bump and droop movements also associate with the suspension travel terms.7 Dynamic load transfer Dynamic load transfer “is the load transferred from one wheel to another due to the moments about the vehicle’s centre of gravity or its roll centres as the vehicle is accelerated in one sense or another.5 Roll axis: The roll axis is the line that would connect the roll centre at the front axle to roll centre at the rear axle.11 Bump and droop Bump and droop are positions of independent suspension under certain scenarios.2. As a vehicle navigates a corner the car will tilt toward the outside of the turn as the suspension on that side of the car experiences the largest forces.8 Longitudinal load transfer Longitudinal load transfer is the result of the cars mass accelerating from the front of the vehicle to the back or the back to the front under accelerating or braking respectively. This force is sometimes strong enough to put the vehicle’s wheels in full droop.2.10 Dive and squat Dive and squat are fundamentally the same concept except reversed. load is merely transferred from the wheels at one end of the car to the wheels at the other end” 8. It is important to mention that “The total weight of the vehicle does not change. rebound and jounce where jounce describes the upwards movement of the wheel or movement in bump while rebound describes the downwards travel of the wheel or droop movement.2.2.0 8.” Fig. 8. 8. It can only be applied to independent suspension systems and mounts to both ends of the lower suspension arms.aUtOKRITI 7. These principles are best seen on the figure below with the bump condition on the left and the droop on the right.54 Bump and Droop 8. Dive is where the front end of the dips down under braking due to the longitudinal weight transfer from the back of the car to the front acting on the front springs. Without dampers the vehicle body would continue to oscillate up and down at its natural frequency after travelling over a disturbance in the road.2.6 Anti-roll bar :The anti-roll bar or anti-sway bar is a type of spring which is often incorporated into a suspension design where higher roll stiffness is required than is able to be supplied by the existing springs that act on each individual wheel. The damper 8. Squat is where the back springs are compressed due to longitudinal weight transfer from the front of the car to the back which in effect causes the end of the vehicle to depress towards the ground plane.53 Anti-Roll bar 8. as when compressed the springs store large amounts of kinetic energy which when released. forces the springs to extend back to their full length. the springs absorb shocks whereas the dampers dampen the energy stored in the springs as they absorb these shocks.2.2.9 Lateral load transfer In essence the lateral load transfer experienced by a vehicle is the same principle as the longitudinal transfer only just rotated 90 degrees such that load is either transferred from the right to the left under 39 . 2. Easy control over the roll centre height by changing the geometry of control arms. The amount of scrub radius depends upon the steering axis inclination. If the scrub radius is positive the wheel tends to toe-out. 8.55 Spring and Dampers 8. still used in light and heavy tricks. 8. It is measured in mm. larger deflection and Fig. It is commonly used in rear suspension of cars and trucks.1 Dependent suspension system: Wheels are mounted on a rigid beam. where both would theoretically touch the road. The track width will change as the suspension travel and this change is known as tire scrub. which are compliant vertically and stiff horizontally.  The springs are pin connected to the chassis at one end and to a pivoted link at the other. 2. Independent suspension system: In this type of suspension system motion of wheel pair is independent. 3. applying any movement of one wheel to be transmitted to the other and producing roll or bump steer and camber change.2.0 achieves its function through the use of oil or gas which is forced (as the spring compresses or extends) through a small valve which is often adjustable to alter how stiff the suspension performs.14 Scrub Radius The scrub radius is the distance in front view between the king pin axis and the centre of the contact patch of the wheel. If the scrub radius is zero the wheel keeps its straight position.3.57 Hotchkiss drive 8.56 Scrub Radius 1. Hotchkiss Drive  Axle is mounted on longitudinal leaf springs.2.3. Scrub radius is positive when the tyre centre line inside the steering axis. The kingpin axis is the line between the upper and lower ball joints of hub.13 Track width & tire scrub The track width is a measure of the distance between the centre of the tire contact patches at the front and rear of the vehicle. Fig. the wheel offset and suspension height. it provides better ride and handling. without any tendency to toe-in or toe-out. Fig. 40 . A.  Used widely in rear axles of passenger cars. so that a disturbance at one wheel is not directly transmitted to the other wheel.3 TYPES OF SUSPENSION:8.aUtOKRITI 7.If the scrub radius is negative the wheel tends to toe-in. 59 Macpherson strut c. It consists of upper and lower wishbone arms pivoted to the frame member. The upper link is typically the shorter one in order to induce a negative camber angle when the car hits a bump and either a negative or positive camber when the linkages go into droop. In this wheels are mounted Equal length and parallel arms: This geometry is created when the upper and lower 41 .0 greater roll stiffness for given suspension vertical rate. the shock absorber is compressed thus reducing the effect of forces induced by the ground surface that are felt by the chassis. when the vehicle’s sprung mass rolls a certain amount. this design is where the arms are of unequal length but still remain parallel. Fig . This system is simple than wishbone type arrangement also camber does not change when the wheels moves up and down. the wheels are forced into camber angles defined by the roll direction of the car however this time the positive camber of the outside wheel is reduced and the negative camber of the inside wheel increased. b. As the wheels move up and down there is no wheel camber change but there is notable track width change. This design has a number of benefits including the fact that it provides a large amount of room for adjustment. wishbone linkages are made the same length and thus form a parallelogram. Here it is seen that as the wheel moves up. The amount of camber change will be governed by the relative lengths of the upper and lower linkages. Further still. Swinging half axle suspension: A swing axle is a simple type of independent suspension designed. The ends of the two wishbone arms and top end of the shock absorber will mount to the chassis. This condition is not to be desired as the contact patch of the tire becomes reduced. Wishbone type suspension: This wishbone type is the most popular independent suspension system. Only lower wishbone are used. the camber will change by the exact same amount with the outside wheel cambering in the positive direction. These variations include: Fig. but these also resist acceleration. To allow the wheels to be steered. Unequal length and Parallel arms: As the name denotes. A strut containing shock absorber and the spring carries also the stub axles on which the wheel is mounted. On the other hand. Macpherson Strut: It is most widely used layout.58 Double wishbone Under the double wishbone configuration there are also a number of geometry variations that can be used to alter the vehicles handling properties.aUtOKRITI 7. These arms resemble letter ‘A’ of the Roman alphabet due to which these are also referred to as ‘A-arms’. large lateral space requirements and the fact that they can sometimes be quite heavy which adds to the sprung weight of the car. has high strength and rigidity. allows decent tyre camber control resulting in enhanced handling characteristics. the wishbone arms feature ball joints on the top and bottom so that the upright can pivot and rotate as needed. Like before. These arms transmit the vehicle load to springs. braking and cornering forces. the double wishbone also holds a number of disadvantages which comprise of relatively higher build and installation costs. diminishing the amount of grip available to the vehicle. a. aUtOKRITI 7. one method may integrate better much better than the other. It is therefore not uncommon to see a vehicle utilising a push system at one end of the car and a pull at the other. Multi-link suspension: Multi-link suspension configurations are in no way as developed as the double wishbone or trailing/semi trailing arm configurations that are used today however their implementation in modern vehicles has seen some very good performance. These may be viewed on the following figure and as seen. Semi trailing arm: The semi trailing arm suspension mechanism pictured in the following figure is a transformation of the trailing arm design. The main disadvantage of this system is up and down movement of the wheel. Fig. This results in sudden loss in traction. besides cornering the car is lifted due to a so called jacking effect which produces positive camber on the outer wheel. because the camber change to vary. it is important to realise that from a side view it is apparent that the wheelbase will alter as the suspension moves up and down. These systems take the basic double e. which are pivoted on their ends to the chassis member at the middle of the car. when in use on the rear of a car is the fact that it does not affect the path of the tyre in the lateral direction as the suspension linkages are parallel to the length of the vehicle and thus the front or rear of the car.0 rigidly on the half axles. This change from the normal trailing arm has been to improve the adjustability of the kinematic characteristics particularly in rear wheel applications. What type of mechanism is used will depend on the layout of the vehicle and the desired loading paths for the suspension design. Trailing Link suspension: The trailing arm suspension design uses the same fundamental concepts as the double wishbone setup although rotated 90 degrees so that the axle position is behind the holding points for the suspension linkages.60 Swinging half-axle suspension d. Fig. the rear wheels will only appear to move up and down and have no apparent rotation. 61 Fig. However.63 Semi-Trailing Arm PULL g. One benefit the system has 42 .62 Trailing arm f. PUSH Fig. Push and Pull Rod suspension: Currently there are two main approaches to designing the inboard suspension system which are the push and pull variations. will operate using the same fundamental principles whereby up and down wheel movement is transmitted to the shock absorber by means of a rocker arm. 0 wishbone set up and add arms.67 Motion Ratio During suspension travel the motion of the geometry causes these motion ratios to change. In the displacer unit. in an off road suspension. Fig.aUtOKRITI 7. this motion ratio will be progressive allowing the springs and dampers increasing leverage on the wheel during compression. add extra pivot points in the linkage system itself.66 Hydro-pneumatic suspension It is a method by which an object is suspended with no support other than magnetic field. modify mounting locations and in some cases.64 Multi-Link Suspension 8. 8.65 Magnetic Suspension 43 . Magnetic force is used to counteract the effects of the gravitational and any other accelerations. Fig. This lever arm through which both spring and damping forces act on the wheel.6 Motion ratio: Since the coil over is never directly connected to the wheel itself. The two primary issues involved in magnetic suspension are lifting forces: providing an upward force sufficient to counteract gravity. the spring acts on the wheel through the lever arm. Ideally. As there is no set standard for these multi-link mechanisms it is quite hard to explain how they function. rubber is used as a spring whereas fluid under pressure acts as damping medium. Typically packaging issues can limit the progressiveness of motion ratio dynamics. The displacer units are all interconnected by means of fluid. 8. and stability: ensuring that the system does not spontaneously slide or flip into a configuration where the lift is neutralized.5 Hydro pneumatic suspension: In this system a displacer unit is fitted at each of the four wheels. and Fig. can be described as the motion ratio. dynamic and highcapacity suspension that offers superior ride quality on a variety of surfaces. The purpose of this system is to provide a sensitive. Magnetic suspension systems generally consist of four dampers with magnetorheological (MR) fluid.4 Magnetic suspension: Fig. It was also used on Berlient trucks and has more recently been used on Mercedes Benz cars. One of these systems which is produced by Mercedes Benz on the SL500 model is shown over the page on figure. 37 to 0. Such systems are usually introduced in premium cars from where they come to the mainstream models.aUtOKRITI 7. Some of such technologies are: 1.e. Do you know. Wishbone Type with Macpherson Strut. 4. Lower Wishbone.? TATA INDICA has Front Independent.35. Using air springs to vary ride height according to requirements. 8. Jeep Gran Cherokee's Quadra-Life air suspension can vary the vehicle's height by 104 mm from an off-road' mode which lifts it 66 run higher than the normal. Antiroll bar. Adjustable shock absorber damping on Grand Cherokee. Semi Trailing arm with coil spring & gas filled shock absorbers type. on Land Rover Range Rover & LR4.8 Modern Suspension Trends: Active suspension systems. Q7 is lowered automatically from it static height by 34. to a park mode which lets it down by 38 mm fit in garages. increasing damper heat and decreasing performance..0 motion ratios that are very high (shock has very little leverage on wheel) will increase the needed spring rates.8 mm. Mercedes-Benz ML550 and Jeep Grand Cherokee. which lowers its drag coefficient from 0.g. i. It even lowers 15 mm automatically at highway speeds to reduce drag coefficient. This high motion ratio will also require more force to be absorbed by the fluid damper. McPherson Strut with gas filled dampers and anti-roll bar type. Active antiroll bars on Mercedes and Jeep. LAMBORGHINI-pushrod-suspension 44 . Besides. And rear suspension consists of Independent.. And rear Semi Trailing Arm with Coil Spring. Audi Q7.. overall shock output force and also increase the bending stress in the link carrying the shock absorber load. Audi s air suspension varies its height by 95 mm between the lifted and the lowered modes. a driver-selectable dynamic driving mode drops the ride height by 15 mm lowering the centre of gravity an improving handling. 3. Rear air springs to compensate for loads as on Lexus LX 570. 2. e. TATA NANO has front suspension consists of Independent. the ones in which desired suspension characteristics as per requirements are achieved during running by means of computer controlled actuators. For high speed driving on expressways. with the ground plane.1. In this system the rotary motion of steering wheel is converted into angular motion of road wheels. A positive camber is the opposite of this.1 FUNDAMENTAL CONCEPTS Fig. connected to tie rods 9.” Positive kingpin is when the kingpin axis angles in towards the centre of the vehicle whereas negative inclination is the opposite. It is the lateral measurement between the meeting point of the centre of the tyre’s contact patch and the kingpin axis. Increasing positive camber will enlarge the slip angle for a specific cornering force. by increasing negative camber the opposite will occur with a higher cornering force and less time for the car to break away.70 Scrub radius 45 . STEERING SYSTEM Caster angle also relates to the kingpin or steering axis although describes the angle of it when The primary function of steering system is to achieve angular motion of the wheels to negotiate a turn.aUtOKRITI 7. On the other hand.1 Camber angle: 9. Convention is that positive offset will be when the kingpin offset is outboard of the kingpin axis. ahead viewing the vehicle from side on. Secondary functions of steering system are:  To provide directional stability while going straight. Another term that is often associated with the caster angle is the caster offset or mechanical trail. It is stated that the “kingpin inclination is the angle.In a vehicle with negative caster angle.69 Caster angle 9. Fig. decrease the largest possible cornering force possible by the vehicle but will also slow down the onset of ‘breakaway’ which is assumed to mean the car starting to slide. connected to track rod  Steering arm. the camber angle is the angle that the inclination of the vehicle’s tyres makes with the vertical axis. between the vertical and the steering (kingpin) axis. viewed in end elevation. It is positive when the kingpin axis meets the ground ahead of the vertical axis drawn through the wheel centre . Another key parameter that is linked to kingpin inclination is kingpin offset or scrub radius.3 Kingpin inclination: As shown on the following figure. it is the angle that the kingpin axis makes with the vertical.68 Camber angle Fig. As seen in figure.  To minimize tire wear. In this case the camber is negative as the top of the tyre leans in towards the centre of the car. recovery after Steering system consists of following components  Steering wheel  Steering column connect the steering wheel to track rod  Tie rods.0 9.1.2 Caster angle: 9. the steering wheels will tend to self-align as the vehicle moves forward.  To facilitate straight completing a turn.1. 2. This concept is seen below. At this point the mechanical grip of the front tyres can simply be overpowered and they start to lose grip (for example on a wet or greasy road surface).71Toe in and Toe out 9. toe change and the inertias of the sprung mass. When the slip angle of the front wheels are less than those of the rear. Toe out on the other hand will produce some very unstable behaviour under these conditions when the slip angle of the more heavily laden wheel increases. It means your car turn more sharply than it should for a given rotation of steering wheel.2.2.73 Understeer 9. radius of turn is increased . Overseer is brought on by the car losing grip on the rear wheels as the weight 9.1. Understeer can be brought on by all manner of chassis. toe in will provide greater straight line stability whereas a controlled amount of toe out can improve the car’s turn in ability to a corner. In normal you-and-me driving. it means crashing at the outside of the corner. When the front wheels point away from each other.Understeer is so called because the car steers less than you want it to.1 Bump Steer Bump steer is the phenomenon that occurs when the front wheels of a vehicle vary their toe angle’s as the suspension moves up and down. 9. eliminating deflection in the suspension and associated chassis mounting components. the car goes where it's pointed far too efficiently and you end up diving into the corner much more quickly than you had expected.4 Toe angle: Toe angle is the angle that a wheel makes with a line drawn parallel to the length of the car. Generally designers will opt for toe in for the reason being that when the vehicle experiences an upsetting force such as a bump or a wind gust. centre of gravity height. In general. Bump steer can be used to the designers benefit by altering the response of the vehicle while cornering. Fig.aUtOKRITI 7. 46 .2. Fig. suspension and speed issues but essentially it means that the car is losing grip on the front wheels.2 Roll Steer Roll steer is “The self-steering action of any automobile in response to lateral acceleration and consists of slip angle changes due to camber change.” This effect will be present in all double wishbone set ups although can be limited by reducing the gross weight of the car. The end result is that the car will start to take the corner very wide. Over steer is the opposite of understeer.72 Slip angle This principle is best demonstrated by observing figure below which also highlights the lateral forces imposed on the wheel as it corners.4 Over steer & Understeer When the slip angle of front wheels are greater than those of the rear wheels . With over steer. Fig. radius of turn is decreased. the vehicle is said to have toe in.0 8. the toe in will promote stability as the front wheels naturally want to steer into a location central to the car’s body. and lastly.3 Slip Angle Slip angle is the angle made by the direction of the tyre contact patch with the direction of overall velocity of vehicle. the condition is called toe out whereas when the front wheels point inwards. by adjusting bump steer. when viewed from above. potentially causing the car to dart around even under no steering input resulting in highly unwanted driver uncertainty and poor handling feel.2 STEERING BEHAVIOURS 9. 76 Rack and Pinion 9. this geometry is simply called Ackermann geometry. It prevents slipping of tyres because in this geometry all the tyres turn about a common point. The pinion gear is attached to the steering shaft.  It provides a gear reduction. A simple approximation to perfect Ackermann geometry be generated by moving the steering pivot points inward so as to lie on alien drawn between the steering arm and the centre of the rear axle.74 Oversteer 9. Without countersteering the end result in racing is that the car will spin and end up going off the inside of the corner backwards. buses.1 Pitman arm steering system: A pitman arm consists of steering system involves the use of a steering gear box that is connected to the steering wheel by the steering column at its one end and at its other end it is connected to the tie rods. connects to each end of the rack.3.4. The rack-and-pinion gear set does two things:  It converts the rotational motion of the steering wheel into the linear motion needed to turn the wheels.75 Pitman Arm 9. It is a trapezoidal geometry. with each end of the rack protruding from the tube.3 TYPES OF STEERING SYSTEM 9. resulting in the rear kicking out in the corner.1 Ackermann geometry: When we turn the steering of a car then as expected by a layman both the tyre turn by same angle but in reality there is difference in the angle turn by both of the tyres. difference between the angle is depends on the percentage of Ackermann. A rod. For example if we turn the steering wheel of the car to a left turn then the inner tyre turn by a larger angle than the outer tyre.3.this type of steering system is generally used in heavy duty trucks. Fig. Fig. steering wheel. The tie rod at each end of the rack connects to the steering arm on the spindle. A rack-and-pinion gear set is enclosed in a metal tube.0 is transferred off them under braking. When you turn the 47 . the gear spins. Perfect Ackermann geometry can only be achieved at static condition and at full lock Fig.4 STEERING GEOMETRY There are three type of steering geometry  Ackermann geometry  Anti-Ackermann geometry  Parallel geometry 9. making it easier to turn the wheels.aUtOKRITI 7. The track rod is supported in its place but idler arms . moving the rack.2 Rack and pinion type steering system: Rack-and-pinion steering is quickly becoming the most common type of steering on cars. Rack and pinion systems give a much better feel for the driver. It is actually a pretty simple mechanism. called a tie rod. small trucks and SUVs. There are two types of power steering system.3 Parallel geometry: Basically the angle turn by the both tyres during turning is same. In steering system. to set a perfect negative percentage of antickermann is mainly depend on the tyre data. at high speed turn main load carry by the outer tyres. it means that if you turn the steering wheel by 20 degrees then therein wheels only turn 1 degree. The basic principle of a hydraulic power steering system is an ordinary hydro mechanical servo parallel to a pure mechanical connection. first you have to analyse the tyre data curves and then according to your requirement a percentage of antiackermann can be set. The lock to lock angle of steering wheel is the twice of the product of the steering ratio and lock angle of front wheels. This geometry is generally used in formula one racing cars to take sharp turns at High speed. power steering system has developed. means angle difference between wheels is vary it is not a constant quantity. the reduction of steering effort is accomplished by using a hydraulic system.6. The steering wheel operates valve to control flow to the Cylinder. the more fluid valves allow 9. 48 .6 Power steering: Negative Ackermann is simply called antiackermann. normally with the possibility to cope with higher forces or torque. In this geometry both the tyres turn at same angle on steering. To alleviate this. A hydro mechanical servo is a system that copies an operator applied movement. Decrement in turning radius is caused by slip angle effect. Fig.4.77 Ackermann Geometry 9. reducing turning effort is also a main motive.0 condition if Ackermann set is 100%. The hydraulic pressure typically comes from a gyrator vane pump driven by the vehicles’ engine. if the steering arm angle is 90 degrees. by enhancing the turning of outer wheel turning radius can be improved but as we are talking about slip angle. For example : if the steering ratio of any car is 20:1 .2 Anti-Ackermann geometry: 9. larger tire cross-sections and front wheel drive. A double acting hydraulic cylinder applies a force to the steering gear. While turning Ackermann percentage varies. the effort tom turn the steering wheel manually increased.5 Steering ratio: It is defined as the angle turned by the steering wheels on the to the angle turn by the wheels on the ground.aUtOKRITI 7. It uses hydraulic pressure supplied by an engine driven pump to assist the motion of turning the steering wheel.as the vehicle become heavier and switched to front wheel drive. 9. Fig. The more torque the driver applies to the steering wheel and column.1 Hydraulic power steering (HPS): Power steering has become a necessary component in modern cars of all sizes due to high axel weight. the wheels being used for steering will always be parallel to each other.78 Parallel Geometry 9. In this geometry turning radius is small as compared to Ackermann geometry because in this geometry outer wheel turn more than the inner one. This is the simplest mechanism of steering but turning radius is quite large in this type according to the wheelbase of the car. In most medium and larger cars.4. which in turn steer the road wheels. Disadvantage of this geometry is that after a limit outer wheel start slipping during turning. Fig. since the electric power steering motor only needs to provide assistance when the steering wheel is turned. 9.6.6. Pressure relief valve prevents a dangerous build-up of pressure when the hydraulic cylinders piston reaches the end of its stroke. the flow rate they deliver is directly proportional to the speed of the engine.aUtOKRITI 7.3 Steering Column: The steering column is a part of steering system that connect steering wheel to the steering mechanism or transferring the driver's input torque from the steering wheel.79 Electronic Power Steering 49 . 9.80 Steering Column TATA NANO uses a mechanical rack and pinion gear with steering column. In EPS the assist level is easily turn able to the vehicle type. Since the hydraulic pumps are positively displacement type. whereas the hydraulic pump must run constantly. Generally in commercial cars universal joint is used to connect steering wheel and steering mechanism. road speed.0 through the cylinder. Fig.2 Electronic power steering (EPS): It is more efficient than the hydraulic power steering. and even driver preference. It’s steering ratio is 16:1 & TATA INDICA uses Power Assisted Rack and Pinion Hydraulic/Mechanical and 4-spoke collapsible steering wheel. Because this would be undesirable. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid. and so the more force is applied to steer the wheels. a restricting orifice and flow control valve direct some of the pump’s engine speeds. This means that at high engine speeds the steering would naturally operate faster than at low speed. 1.1 Radial tyres: radial tyres construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approx. 10.0 10. Load carrying: The tyre is subjected to alternating stresses during each revolution of the wheel. Uniform wear: To maintain the non-skidding property. Fig. disadvantage of radial tyre includes a harder ride at low speed on rough roads. it is desirable that the desirable should be minimum. so that the final tyre design must incorporate an optimum combination of all these. Tyre noise: The tyre noise may be in the form of definite pattern sing. The wheel is one of the main component of the wheel and axle which is one of the six simple machines. The ribbed tread patterns help to achieve this. the advantage of construction include longer tread life. It is seen that the synthetic tyres consume more power while rolling than the ones made out of natural rubber. 3. 10. it is very essential that the wear on the tyre tread must be uniform. usually at angles in range of 30 to 40 degrees. allow heavy objects to be moved easily facilitating movement or transportation while supporting a load. fabric. the design allows the entire body to flex easily. 1. 2. wire and other chemical compounds. 10.2 Tyre properties: The tyres for automotive use have many tough functions to perform. 4. The tyre material and design must be able to ensure that the tyre is able to sustain these stresses. This power comes from the engine fuel and should be the least possible. In all these cases. Disadvantage of bias tyre: increased rolling resistance and less control and traction at high speed.1. 5.1 Tyre type The material of modern pneumatic tyre are synthetic rubber. decreased self-cleaning ability and lower grip ability at low speed. WHEEL some desirable properties. right angles to the centreline of the tread. better steering control and lower rolling resistance. Power consumption: The automotive tyre does absorb some power which is due to friction between the tread rubber and road surface and also due to hysteresis loss on account of the tyre being continuously fixed and released. a sequel or a loud road. Non skidding: This is one of the most important tyre properties. in conjunction with axles. natural rubber.81 Radial tyres 10.2 Bias tyres: Bias tyre construction utilizes body ply cords that extend diagonally from bead to bead. wheels. for which they must possess 50 . It is seen that some of these properties are conflicting with others. with successive plies laid at opposing angles forming a crisscross pattern to which tread is applied .aUtOKRITI 7. The tread provide traction while the body provide containment for a quantity of compressed air. A wheel is a circular component that is intended to rotate on an axial bearing. The tread pattern on the tyre must be suitably designed to permit least amount of skidding even on wet road. 0 10.25mm . to know what that means. It is speed Check out tire looking at it head on (or known as the aspect ratio. unstressed and you're percentage of the width.aUtOKRITI 7. 120. This is known this case. . and he will. (section This is This tells you that the tire sidewall when it's height). expressed as a the is a radial construction. as the section width.3 Tyre size notations: When you look at your car and discover that it is shod with a nice. but worn set of 185-65HR13’s (from the tire marking). You’ll cough up and drive away safe in the knowledge that he’s just put some more rubber on each corner of the car that has the same shamanic symbols on it as those he took off. 65% of 185mm is tire. Any tire mechanic will tell you that he can replace them. So what does it all means? This is the width in mm of This is the ratio of the height of the tire from sidewall to the tire sidewall. 51 This is the diameter in inches of the rim of the wheel that the tire has been designed to fit on. In of the construction if you want top-down).the section height. when the brakes are applied it clamps onto the rotor/disk(2) and thus slows down the wheel. ROTOR(2) The rotor or disk is attached into the hub of the wheel and the first impact of the brake comes oto it and further stop the wheel.82 Wheel Assembly 52 . 4.aUtOKRITI 7. 2. CALIPER(3) The brake caliper is mounted onto the knickle (6) and thus remain stationary . Fig. KNUCKLE(4) Knuckle is the stationary part and support the suspension and steering system . the knuckle is attached to one of the edges of a bearing using a sleeve or directly. HUB(1) The hub serves as housing for the wheels’s bearing (5) and spacers and is the central support around which the entire wheel revolves on the axle.0 WHEEL ASSEMBLY 1. 3. creating friction. hence the pad loose contact with the rotor thus reducing the amount of friction. The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge. When you apply the brakes. When the brake is applied against the component are already so hot that they cannot absorb more heat. When you are travelling at speeds your vehicle has kinetic energy. When the brake is applied the shoes are expand outward to press against the inside of the drum. The leading edge is the term given to the part of the brake pad which does contact the drum.3.2 BRAKE FADE With continuous use the brake shoes in the drum brake or brake pads in adisc brake will get heated and get no time to cool.   They should stop the vehicle within minimum possible distance To increase the maneuverability by locking all the 4 wheels together in the least time possible. This gas forms a thin layer between the two while trying to escape. The result is very similar to hydroplaning.0 released.autokriti 7.3. which create heats. This transfers kinetic energy that slows you down. it's the part of the pad closest to the actuator. Once this lot starts to get too hot the resin holding the pad material starts vaporising forming a gas. simple geometry means that the entire brake pad cannot contact the brake drum. 11. Figure 83 –Cut section view of drum brakes 11. 11. BRAKES 11. the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction. In every brake pad there is a friction which is held together with resin.1a Drum brakes – single leading edge The "single leading edge" refers to the number of parts of the brake shoe which actually contact the spinning drum. When the actuator is twisted it is forced against a brake shoes and in turn forces them to expand outwards.3 TYPES OF BRAKES 11. Because the brake shoe pivots at one end. and in the case of a single leading edge system.1 Drum Brakes Two semi-circular brake shoes sit inside a spring drum which is attached to the wheel. 11. The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are Fig.84 Drum Brakes 53 .1 INTRODUCTION Brakes are essentially a mechanism to change energy types. which means more heat. and instead of the brake shoes. Hence the name is double leading edge. three. The drilled holes give more bite. you now have brake calliper assemblies. The hydraulic pressure create by moving a piston toward the slave cylinder compresses the fluid evenly. and they also allow the gas to vent from between the pads. Where more force is required.3b Drum brakes.autokriti 7. to result in a movement of the slave cylinder. So each brake pad has now one leading and one trailing edge. Instead of the drum.0 11.also known as one or two-pot callipers. but by varying the comparative surface area of the master cylinder or each slave cylinder. Figure 85 –Disc brake assembly Disc brakes are again a two-part system. grooved-drilled rotors which give more bite hence more friction as they pass between the brake pads. the more friction is generated. which mean there are two leading edges. The movement of piston inside master cylinder is transferred through the hydraulic fluid. you have a disc or rotor. There are some other types of rotors such as grooved. which is why you'll find disc brakes on the front of almost every car and motorbike built today.2 MASTER CYLINDER The master cylinder is a control device that converts force provided by the driver at the brake pedal into hydraulic pressure.4. Now when the brakes are applied.2 DISC BRAKE Disc brakes are an order of magnitude better at stopping vehicles than drum brakes.3. Because there are two brake shoes. Figure 86 –Drilled rotor 11. such as one or more slave cylinder.4. 54 .1 Drilled Rotors Drilled rotors are typically used in race cars. there are two brake pads. 11. Sportier vehicles with higher speeds need better brakes to slow them down. Standard disc brakes have one or two cylinders in them . in order to move other devices which are located at the other end of the hydraulic system. one will vary the amount of force and displacement applied to each slave cylinder.double leading edge 11. the shoes are pressed outwards at two points. 11. but also allow air currents (eddies) to blow through the brake disc to assist cooling and ventilating gas. which slows you down. clamping them together around the spinning rotor.1.4 METHODS TO REDUCE BRAKE FADE The drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator. which means more kinetic energy transfer. or more cylinders can be used. The harder they clamp together. The calliper assemblies contain one or more hydraulic pistons which push against the back of the brake pads. most high performance cars use fixed calipers with multi positions on either side of calipers to generate higher application forces that the performance of vehicle requires.3 TANDEM MASTER CYLINDER Tandem master cylinder is characterized by two pistons operating in series within a common bore. 11. Force from the brake pedal will be transmitted mechanically through piston 1 to piston 2. weight transfer forward and rear wheels lose some of their much needed traction. Although overall braking performance will be severely compromise.2 FLOATING CALIPER Floating calipers can slide side to side on its mounting surface. fluid displaced and pressurized by first piston also causes movement of a second piston. each piston drives its brake pad into contact with the rotor. 11. the rear brakes will still be functional provided sufficient pedal travel 55 . When the brakes are applied. The pedal will need to travel further than normal to fully engage the rear brakes. It requires minimum of two piston one on each side. Second piston applies the vehicle’s rear brakes. Thus the piston is required only on one side.1 FIXED CALIPER Fixed calipers are rigidly fixed to its mounting surface.autokriti 7. each person drives its corresponding brake pad into contact with the rotor. piston one 11. will move forward until it contacts piston 2. As the car is slowing. In normal operation.87 Master cylinder is available.If a leak is develop in the front brakes system. Also. Most passenger cars use floating because fewer components are involved than fixed calipers. When the brakes are applied.5.5 TYPES OF CALIPERS The following two illustration show how a tandem isolates leaks in the front and rear brakes plumbing respectively . This results in the reaction force that causes with the rotor. 11.in rear wheel drive applications the piston that’s located closer to the pedal applies the vehicle’s front brakes.4.5. it should be appreciated that trying to stop quickly with just the rear brakes is very tricky because the rear tires will easily reach the point of lock up. and the brakes are fully applied.0 Fig. This sliding motion brings the opposite pad in contact with the rotor. On the other hand. Because of the arrangement of the slave cylinder. E. Regardless of what type of brakes a car has. If the brakes are still applied as the car turns into the corner.8 BRAKE BIASING This is an adjustment of the relative amount of hydraulic pressure applied to the front versus the rear brake calipers and pads. They are joined together with hydraulic hose and filled with non-compressible hydraulic fluid. or squeeze the brake lever. Because the brake fluid does not compress.10 ANTI LOCK BRAKING SYSTEM (ABS) ABS is a form of electronic braking which was invented to help driver to steer the vehicle under heavy braking and preventing the wheels from locking. That slave assembly is either connected to a lever to activate the brakes. Inboard brakes are fitted to a driven axle of the car. as a car decelerates. Single circuit hydraulic systems have three basic components.autokriti 7. In practice. the brake-bias setting will also have an effect on the car’s turn-in balance.9 PROPORTIONING VALVE 11. that pressure is instantaneously transferred through the hydraulic brake line to the slave cylinder where it acts on another piston assembly. This is 56 . is the brake caliper itself. the rear brakes require less force than the front brakes. while decreasing their grip at the rear of the car. as this no longer includes the brake discs and calipers. the slave cylinder and the reservoir.g. 11. it is normal for inboard brakes to be mounted rigidly with respect to the body of the vehicle. The goal is to adjust the proportion of the braking forces between front and rear (brake bias) in order to maximize overall braking efficiency. heat from the brakes can be transferred back in to the brake fluid. pads and piston area is often different requiring different amounts of pressure for the same braking power. pushing it out. 11.7 INBOARD BRAKES Proportioning valve reduces the pressure in the rear brakes lines. It is an automobile technology wherein the brake disc(s) is mounted on the chassis of the vehicle. or more commonly. Most have thus been used for rear-wheel drive cars. More weight means more brake force can be applied. load transfers to the front tires. The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. rather than directly on the wheel hubs. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. with the slave cylinder being the piston that acts directly on the brake pads. The wheels don’t enclose the brake mechanism allowing greater flexibility in wheel offset and placement of suspension members. For equal braking force applied at all four wheels during a stop. As during heavy braking there is a chance that wheel stop rotating before the car comes to rest this happens because the braking force on the wheel is not 11. the size of the front and rear brake rotors. The advantage is a reduction in the unsprung weight of the wheel hubs. The brake bias is indicated as a percentage which represents the relative amount of brake pressure applied from the master cylinder(s) to the front brakes. In addition. which generally improves their grip. often to the differential casing. the rear wheels would lock up before the front wheels.6 HYDRAULIC BRAKES This type of brakes system is used on most cars and motorbikes today. 52% would indicate that the front brakes are receiving 52% of the brake pressure and the rear brakes would be receiving 48%. When you press your foot on the brake. 11.0 needed to optimize the braking power. as they require a drive shaft to link the wheels to the brakes. you compress a small piston assembly in the master cylinder.the master cylinder. it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel. which leads to greater stopping distance and loss in control over vehicle. A kinetic energy recovery system is an automotive system for recovering a moving vehicle kinetic energy under braking. brakes hydraulic pressure to the wheel is increased so the braking force is reapplied. If the ECU detects any wheel rotating faster than the other. The recovered energy is stored in a battery or a reservoir (for example a flywheel or high voltages batteries) for later use under acceleration. This system is also known as KERS (kinetic energy recovery system). Counter torque provide by this system charges the batteries during braking and provide acceleration of up to 120KW and 2MJ of energy per lap.autokriti 7. 11.0 transferred efficiently to stop the vehicle due to fact that tire is sliding On the road. or the power units. The main characteristics of this type brake fluid are as follows: The electronic control unit constantly monitors the rotational speed of each wheel. if any wheel rotating slower than the other. 57 . This process is repeated continuously at the rate of 16 times per second. slowing down the wheel. One of the most innovative aspects has actually been the integration of braking system with the power unit.11 TYPES OF BRAKE FLUIDS       Poly-glycol based Most commonly used Compatible with one another Inexpensive Destroy paints Ruined by moisture  DOT 5     The main characteristics of DOT 5 type of brake fluids are: Silicon based Used only for heavy duty applications Not compatible with 4 and 5 Very expensive Does not damage paint Where DOT – department of transportation  DOT 3 AND 4 DO YOU KNOW? The revolution in formula 1 in 2014 is not just about the engines. the then turn faster. autokriti 7.0 COMMON ABBREVIATION 4WD FOUR WHEEL DRIVE I-VTEC DOHC INTELLIGENT VARIABLE(VALVE) TIMING (AND LIFT) ELECTRONIC CONTROL DOUBLE OVERHEAD CAMSHAFT DCT DUAL CLUTCH TRANSMISSION AMT AUTOMATIC MANUAL TRANSMISSION MPFI MULTI POINT FUEL INJECTION DTS-I DIGITAL TWIN SPARK IGNITION ACC AUTOMATIC CRUISE CONTROL CVT CONTINUOUSLY VARIABLE TRANSMISSION EBC ELECTRONIC BRAKE CONTROL ECU ELECTRONIC CONTROL UNIT A/T AUTOMATIC TRANSMISSION ICE INTERNAL COMBUSTION ENGINE LSD LIMITED SLIP DIFFERENTIAL LSUV LUXURY SPORT UTILITY VEHICLE CC CENTIMETER CUBIC TDC TOP DEAD CENTRE BDC BOTTOM DEAD CENTRE ABS ANTILOCK BRAKE SYSTEM RWD REAR WHEL DRIVE IRS INDEPENDENT REAR SUSPENSION EPS ELECTRIC POWER STEERING 58 . autokriti 7.0 4WD FOUR WHEEL DRIVE AWD ALL WHEEL DRIVE SUV SPORT UTILITY VEHICLE I-VTEC INTELLIGENT VARIABLE(VALVE) TIMING (AND LIFT) ELECTRONIC CONTROL OHV OVERHEAD VALVES SOHC SINGLE OVERHEAD CAMSHAFT DOHC DOUBLE OVERHEAD CAMSHAFT DCT DUAL CLUTCH TRANSMISSION AMT AUTOMATIC MANUAL TRANSMISSION MPFI MULTI POINT FUEL INJECTION DTS-I DIGITAL TWIN SPARK IGNITION ACC AUTOMATIC CRUISE CONTROL CVT CONTINUOUSLY VARIABLE TRANSMISSION EBC ELECTRONIC BRAKE CONTROL ECU ELECTRONIC CONTROL UNIT ICE INTERNAL COMBUSTION ENGINE LSD LIMITED SLIP DIFFERENTIAL LSUV LUXURY SPORT UTILITY VEHICLE CC CUBIC CENTIMETER TDC TOP DEAD CENTRE BDC BOTTOM DEAD CENTRE ABS ANTILOCK BRAKE SYSTEM RWD REAR WHEL DRIVE IRS INDEPENDENT REAR SUSPENSION EPS ELECTRIC POWER STEERING KERS KINETIC ENERGY RECOVERY SYSTEM CRDI COMMON RAIL DIRECT INJECTION 59 . Difference between trailing arm and semi trailing arm? 13. What is the function of anti-roll bar ? 5. What is overdrive? 4. Why synchromesh device usually not used for reverse gear? 6. What is the function of a stator in torque converter? 7. Why is the unsprung weight kept as low as possible? 3. What is the function of a stator in torque converter? 23. What is the firing order of a V-8 engine? 18. What is a limited slip differential? 26. Difference between trailing arm and semi trailing arm? 29. What are the effects of scrub radius? 11. Is six stroke engines possible? If yes then how? 9. What is octane number and factors for its determination? 17. What is the function of a differential in cars? 10. The purpose of wings in formula one cars? 14.autokriti 7. What are the effects of scrub radius? 27. What cause YAW moment in the vehicle? 28. Why mobile oil is added in a two stroke engine but not in four stroke? 60 . Why two compression rings in piston are placed in the opposite direction? 19. Why is the unsprung weight kept as low as possible? 20. What is the advantage of using pull rod suspension over push rod? 24. Why synchromesh device usually not used for reverse gear? 22. Which causes YAW moment in the vehicle? 12. The purpose of wings in formula one cars? 30. Is six stroke engine possible? If yes then how? 25. Difference between turbocharger and supercharger? 15. What is the advantage of using pull rod suspension over push rod? 8. What is the function of anti-roll bar? 21. How trains turn on the rail tracks without differential? 16. What are the advantages of helical gears over spur gears? 2.0 APPENDIX TEST YOURSELF 1.