Two-stroke petrol engine.

Piston rising, compressing mixture above, decreasing pressure below. All ports closed.

Piston passing TDC, mixture above piston ignited, fresh mixture entering crankcase.

Piston moving downward. The fresh mixture in the crankcase has been compressed. The piston has just uncovered the exhaust port, and is about to uncover the transfer port.

Piston passing BDC exhaust and transfer port open. Fresh mixture entering cylinder via transfer port, directed to top of cylinder by deflection on piston, driving out burnt gas through exhaust port.

Four-stroke cycle petrol spark-ingniton engine.

Induction stroke : inlet valve opens and exhaust valve closed mixture of air and fuel entering cylinder. Piston moving downward.

The compression stroke :both valves closed. Mixture compressed into top of cylinder. Piston moving upward.

Power stroke :both valves closed, mixture burnt. Piston forced down cylinder.

Exhaust stroke :exhaust valve opens, burnt gases forced out of cylinder. Piston moving upward.

Cold start devices.

The first diesel engines had simple cold start devices which fell into two categories :

  1. Cold start via glow plugs.
  2. Manifold heater via flame injector.

Cold start device: a component that’s used to preheat the air entering the combustion chamber of a diesel compression-ignition engine. This is required to ensure that the air reaches the self-ignition temperature of the diesel fuel when it is injected into the chamber; the cold start devices also help to reduce smoke emissions from the cold engine.

Superchargers :

Turbines driven by a belt from the engine, forcing air into the combustion chamber and allowing more fuel to be injected and burnt, which in turn generate more power.

Turbocharger :

Turbines driven by the exhaust gases, forcing air into the combustion chamber and allowing more fuel to be injected and burnt, which in turn generate more power.

Testing electrial/electronic system.

As in the case of many other electronic components, ECUs can easily be damaged by workshop test equipment, so care must be exercised when testing any part connected to an ECU.

An ECU can be damaged by :

  1. Boost starting – using a high -speed battery charger for starting an engine.
  2. Electric welding -induced voltage from an electric welding plant will damage a semiconductor, so disconnect the battery earth so isolate the ECU before any welding.
  3. Steam cleaning -heat and steam will damage an ECU.

How to depressurise a fuel system.

Working on a pressurised fuel system can be dangerous, so the system should be depressurised for components to be removed safely. This can be done easily by removing the fuel pump fuse and starting the engine; this will run until the fuel in the system is used up. As the pump is not running, no fresh fuel is pumped from the tank. The filter, fuel lines, pressure rail and injectors are then purged, depressurising the system.

EVAP system fault.

Commonly, the purge valve might become faulty, causing the engine vacuum to draw the fuel directly into the engine, enriching the mixture. When inspecting the carbon carnister, if it is full of fuel and extremely heavy, this could indicate a possible fault with the purge valve.

Air/fuel mixture .

The air/fuel mix supplied to the engine must :

  1. Be of a proportion of 14.7 parts air to 1 part petrol.
  2. Produce low levels of CO, NOx and HC.
  3. Be calibrated for economy, performance and meet legislative requirements.

Control of Cam phasing.

The electronic control of cam phasing varies according to the manufacturer, but the system operates in one of the following ways :

  1. Electromagnetic solenoids are switched on and off to allow oil flow in different directions to rotate a vane.
  2. Electronic control of oil pressure.

In both of these the PCM receives inputs from the following sensors to determine whether it should operate or not :

  1. Camshaft position sensor.
  2. Crankshaft position sensor.
  3. Engine RPM sensor.
  4. MAP(maniford absolute pressure).

Phase angle :

The time period from when the camshaft starts to open the valve to the time when the valve is closed. The time period is measured in degrees of rotation.

Cam phasing :

The moving of the camshaft from its original opening/closing point to an earlier or later point. The actual time the valve is opened by the cam remains the same.

Valve overlap :

The period of time when both the inlet valves and the exhaust valve are open. This extends from just before TDC to just after TDC.

Combustion phrases.

A spark-ingniton engine combustion process can be split into three phrases :

  • Ignition delay .
  • Rapid pressure rise or uncontrolled combustion .
  • After burning or late burning.

Ignition delay is the period between the spark occurring and the start of the pressure rise above compression pressure (about 20bar or 294psi).

Rapid pressure rise is the period when the pressure in the combustion chamber starts to rise above compression pressure to the peak combustion pressure (about 60bar or 882psi).

After burning or late burning is the period between the peak combustion pressure, to the point where the exhaust valve opens.

Combustion process .

During normal operating conditions the compressed air/fuel ,at the stoichiometric ratio (14.7:1),is ignited by a high -voltage spark jumping the gap at the electrodes of the spark plug. This produces a flame, which travels across the combustion chamber at a regular and smooth rate. The full combustion process take place within 3-4ms (milliseconds). The rapid expansion of gas and the increase in the pressure and heat within the chamber gives a smooth and steady downward push to the piston. This pressure will be dependent on a number of factors, but can reach 70bars (1029psi).

Stoichiometric ratio :the ideal air/fuel ratio for the most efficient combustion (14.7:1)

Construction and working of manual window regulating mechanism.

In cars and in some luxury vehicles, the window glasses can be operated for opening and closing to some extent as per the necessity. This can be done of manually or by using a single button of at each window or by using a panel of button at the control of the driver. In the older days only manually operated window regulating mechanism were being used. There will be handle inside the door to regulate it. This can be operated manually by rotating the handle to the extent required. There will be a wheel inside of door panel which is connected to this handle.


The exhaust from the cylinder passes through the turbine blades, causing the turbine to spin.

There are two main types ;axial and radial flow used. Material :k18(special types of stainless steel). Number of blades :12numbers. Wheel diameter :40 mm.

Turbocharging principles.

The air is pressurized by the compressor. The air cooler brings the air to a high density to the engine by decreasing the temperature. A part of the exhaust gas energy is treated by the turbine. The turbine power is transmitted to the compressor through the rotating shaft. The engine can work at a high power density without increase of the thermal load.

Flexible coupling.

A flexible coupling permits with in certain limits relative rotation and variations in the alignment of shafts. Pin (bolts) covered by rubber washer /bush is used connect flanges with nuts. The rubber washers /bushes act as a shock absorber and insulator.

Rigid coupling.

Rigid coupling are used when precise shaft alignment is required. Simple in design and are more rugged. Generally able to transmit more power than flexible coupling. Shaft misalignment cannot be compensated.

Uses of coupling.

  • To provide connection for shafts of units that are made separately.
  • To allow misalignment of the shaft or to introduce mechanical flexibility.
  • To reduce the transmission of shock loads.
  • To introduce protection against overload.
  • To alter the vibrations characteristics.

Method of door locking mechanism.

Almost in all kinds of automobiles, the door locking mechanism is just closing the door and the lock will be automatically operated for unlocking any of the following method may be applied.

  • With a key.
  • By pressing unlock button inside the vehicle.
  • By using a combination lock outside the door.
  • By pulling up the knob inside the door panel.
  • With keyless entry remote control.
  • By a signal from control center.

Some of the vehicle, are having different methods of self check for door locking. It will warn you if is not properly locked by lightning the body light or beeping a horn etc. In power lock mechanism, body controller monitors are the possible sources of locking and unlocking signals. There will be actuator in the door and a latch will be connected to the locking handle. When the actuator moves, it connects the handle to lock the door. To unlock it the body controller supplies power to the door lock actuated for timed interval. A key less remote entry device consist of a fob in the key ring and a radio receiver controller inside the car, which opens and closes the car door on the receipt of a signal from the fob.

Seat, door and window mechanism.

Construction and working of door lock mechanism : In automobiles the doors play an important role of closing of the vehicle for protecting passengers and cargo as the case may be. In cargo transport vehicles ,the doors are closed as plain doors by using simple plain tower locking mechanism. In cars and luxury vehicles, the door locking provision is almost vehicles separately. In some door locking mechanism locks are provided outward and in some other vehicles inward direction. In some recent model they are operated with remote control.

Air brakes.

The manufacturer of braking system offers a variety of air brakes equipment. However, the simplest system consist of an air compressor, a brake valve, series of brake chambers, unloader valve, a pressure gauge and a safety valve. These are all connected by lines of tubing. The other braking system may have additional components such as stop light switch, low pressure indicator, an air supply valve to supply air for tyre inflation, a quick release valve to release air quickly from the front brakes chambers when pedal is released, a limiting valve for limiting the maximum pressure in the front brake chambers and a relay valve to help in quick admission and release of air from rear brake chambers. The compressor sends compressed air to the reservoirs which are connected to the brake valve. The lines of tubing from the brake valve extend to the front and rear brake chambers. When the drive depresses the pedal, it operates the brake valve thus admitting compressed air to all the brake chambers. The compressed air operates the diaphragm of the brakes chambers thereby applying the brakes.

Bleeding of brakes in hydraulic brakes.

In hydraulic brakes, the removal of air from the entire hydraulic system starting from master cylinder to different wheel cylinder is known as brake bleeding. It includes the following process:

  1. At first check all the pipe lines and junction boxes from master cylinder to wheel cylinder. Whether there is any leak among them.
  2. Ask one person to pump the brake pedal and keep it in pressing position.
  3. The second person should loosen the bleeding nipple at the back plate of the wheel cylinder position.
  4. Keep the bleeding nipple in open until the air bubbles disappear and the brake fluid comes out with a force. Collect the brake fluid in a glass tumbler.
  5. Then tighten the bleeding nipple.
  6. Repeat this process in all the wheel cylinder starting from the farthest wheel to the master cylinder and ending with the nearest wheel.
  7. Make sure that the level of brake fluid in master cylinder is 1/4 less than the top covers while filling it.

Wheel cylinder.

Wheel cylinder or slave cylinder assist the main cylinder in covering the pressure of the piston inside it and push the brake shoes attached to it. Some of the wheel cylinder having one piston and some having two pistons. The wheel cylinder having one piston will operate only one brake shoes and the two wheel cylinder are require to operate two brake shoes. In some wheel cylinder, both brake shoes are operated as they are having two piston in them. When brakes are applied the brake fluid enter into the cylinder through a brake pipe lines. It causes to force out the piston. This motion is transmitted to brake shoes causing them to expand against the running wheel drum to hold it tightly and stop it.

Master cylinder.

It is the most important part of the hydraulic braking system. It contains two main chambers.

  1. Fluid reservoir -which stores the brake fluid in it.
  2. Barrel -which is compressor and develops pressure in brake fluid.
  1. Reservoir : The reservoir also contains two parts. The larger part is called filter or intake port and the smaller portions is called bypass port through which the returned fluid from the system will enter into reservoir from barrel.
  2. Barrel :in the barrel of master cylinder the parts are :
  1. Primary cup.
  2. Secondary cup.
  3. Return springs.
  4. Retaining spring.
  5. Check valve.

When the brake pedal is applied the push rod will push the piston of master cylinder and the there by the pressure is applied on the hydraulic brakes fluid. The pressurized brake fluid will enter into system through check valves which does not allow the fluid to return back. This causes the pressure on the system and applying brakes at the wheel cylinder.

Construction and working of hydraulic brakes.

The hydraulic brakes are being operated in the Pascal’s law which states that “The pressure on any liquid is equally transmitted to all the direction at the same time “. In the same manner the pressure of brake pedal which is applied on the brake fluid in the master cylinder is transmitted to all the four wheels cylinder with equal pressure and at the same time. In this way the brake shoes which are attached to the wheels cylinder are expanded and thus the brakes are applied. The parts of hydraulic braking system one :

  1. Brake pedal .
  2. Pull and push rod.
  3. Master cylinder.
  4. Brake pipe lines.
  5. Wheel cylinder.
  6. Brake shoes.

When the brake pedal is applied the piston inside the master cylinder in pushed forward and it caused the pressurized brake fluid moves forward to all the four wheels cylinder at the same time with the same pressure. There at the wheel cylinder the brake shoes will be expanded with the developed pressure in the wheel cylinder. All the wheel cylinder will be operated at the same time according to pascal’s law. This is how the brakes are applied while releasing the brakes with contracting of the brake shoes with spring force the brake fluid in the wheel cylinder will try to go back to the master cylinder. As there is no pressure on the position of the master cylinder, the brake fluid push the check valve of master cylinder and the enter into the reservoir through the barrel and by pass valve of master cylinder.

Construction and working of mechanical, hydraulic and air brakes.

Construction and working of mechanical brakes : these brakes are operated completely through mechanical links and lever. These are applied in two wheelers and these wheeler. These are also applied in four wheeler as parking or emergency brakes. In the wheels drum there are two brake shoes which are linked closely by a retracting spring. There will be a can between the two shoes. When brake pedal is applied, the can will rotate causing the brake shoes expand against the force of the returning spring. This causes the shoe to rub against rotating wheels drum and thereby stopping it. When brake pedal is released, the can inside wheel drum will come back to its position causing the brake shoes to come back with the presence of returning position and thus releasing brakes.

Drum brakes.

In this type of brakes, a brake drum is attached concentric to the axle hub whereas on the axle casing is mounted a back plate. In case of front axle, the brake plate are bolted to the steering knuckle. The back plate is made of pressed steel and is ribbed to increase rigidity and to provide support for the expanding brake shoes. These brakes are also known as internal expanding brakes.

Disc brakes.

The disc brake consist a cast iron disc bolted to the wheel hub and a stationary housing called calliper. The calliper is connected to some stationary part of vehicle, like axle casing or the stab axle and is cast in two parts, each part containing a piston. In between each piston and the disc, there is a friction pad held in position by retaining pins, spring plates etc. When the brakes are applied, hydraulically actuated piston move the friction pad into contact with the disc, applying equal and opposite forces on the later. On releasing brakes, the rubber sealing rings act as return springs and retract the pistons and the friction pads away from the disc.

Stopping time and stopping distance.

The stopping time and stopping distance shows the efficiency of brakes. The maximum retarding force applied by the brake at the wheels, F, depends upon the coefficient of friction between the road and tyre surface u and the component of the weight of the vehicle on the wheel, w.


In actual practice 100% of the brakes efficiency is not used. The stopping time and distance depends upon :

  1. Vehicle speed.
  2. Condition of road surface.
  3. Condition of tyres tread.
  4. Coefficient of friction between the tyre tread and road surface.
  5. Coefficient of friction between the brakes drum and brake lining (in case of drum brakes).
  6. Coefficient of friction between the disc and the friction pad (in case of disc brakes).
  7. Brake force applied by the driver.

However ,during emergency braking, the reaction of the driver and response time of the brakes also play an important role. The total stopping distance in case of emergency braking may be divided into three parts :

  1. Distance traveled during the reaction time of the driver.
  2. Distance traveled between the time elapsed between driver pressing the brake pedal and actual application of brakes at wheels.
  3. Net stopping distance, depending upon the deceleration.

Keeping all the factors in view, the assumed brake efficiencies for some of the vehicle may be like the valves given in the table approximately. These values depends upon the distance traveled during the reaction time of the driver and distance traveled between applying pedal and actual application of brakes at wheels.

Functions of brakes.

  1. To slow down or to stop the vehicle as and when required.
  2. To control the vehicle when the vehicle is rolling down on a slope road downward.
  3. To travel smoothly and safely even in heavy flow of traffic by controlling the movement of the vehicle.

Braking system.

In automobiles brakes play important role in slowing down and stopping of the vehicles as and when required by the driver. Fundamentally the brakes are of two types :internal expanding and external contracting type. Different types of brakes are used in different vehicles as per the requirements. According to application, the brakes are of different types -mechanical, hydraulic air, vacuum, air assisted hydraulic.

Steering defects – wheel wobble and shimmy.

Wheel wobble and shimmy : when the vehicle go through an uneven or rough road, the front wheel will get shaken for a while. This problem can also be seen when the vehicle is slowing down. This problem may caused by the following reasons.

  1. Unbalanced wheels – the wheels should be balanced at wheel balance.
  2. Unevenly worn out tyres – rotate the tyres or replace with the new ones if necessary.
  3. Inoperative shock absorber -replace them.
  4. Incorrect toe in -adjust the toe in.
  5. Loose spring u bolt -tighten.
  6. Loose steering linkages -tighten.
  7. Worn out kingpin steering linkages -tighten or replace as per the necessity wheel bearings, steering gear.
  8. Inoperative stabilizer -replace.

Toe out.

Toe out is the difference in angles between the two front wheels and the car frame during turns. The steering system is designed to the turn the inside wheel through a larger angle than the outside wheel when making a turn. The toe out is secured by providing the proper relationship between steering knuckle arms, tie rods and pitman arm (drop arm).

Toe -in.

It is the inward tilting of front wheels at the front so that the distance between the front wheels at the front is less than the distance between at the front wheels at the rear when viewed from the top. The amount of the toe -in is usually 3 to 5 mm. The toe in is provided to ensure parallel rolling of the front wheels to stabilize steering and prevent side slipping of the front wheels and thereby prevent excessive tyre wear.

Kingpin inclination or steering axis inclination.

It is the angle between the vertical line and the center of the kingpin the steering axis when viewed from the front. The kingpin inclination, in the combination with caster angle, is used to provide directional stability. It also reduces steering effort particularly when the vehicle is stationary. It reduces tyre wear also. The kingpin inclination in modern vehicle ranges from 4 degrees to 8 degrees. It is also known as steering axis inclination.

Camber angle.

It is the angle between the centre line of the tyre and the vertical. When viewed from the front of the vehicle when the angle is outward, so that the wheels are farther apart at the top the camber is positive, when the angle is inward, so that the wheels are closer at the top, the camber is negative. The usual value of camber angle should not exceed 2 degrees. When the camber angle is positive, it causes slip out prevention lightens perpendicular load and lessen the required steering effort. If it is a zero camber, it prevents uneven wear of tyres. When the camber angle is negative, the camber thrust increases with increase in tyre inclination relative to the road surface.

Caster angle.

It is the angel of tilting the king pin axis either forward or backwards from the vertical line. This tilting is known as caster. The angle between the vertical line and the king pin centre line in the plane of the wheel (when viewed from the side) is called the Caster angle. When the top of the kingpin is backward, the caster angle is positive, and when it is forward, the caster angle is negative. Usually the caster angle in modern vehicle ranges from 2 to 8 degrees. The main purpose of caster angle is to create self centering effect in the steering. It provides the directional stability. It positive caster increases the efforts required to steer and tries to keep the wheels straight ahead. In heavy duty trucks negative caster is preferred. This makes the steering easier.

Steering geometry -caster, camber, kingpin inclination, toe -in and toe -out.

Steering geometry :it refers to the positioning of the front wheels and steering mechanism that gives the vehicle directional stability, promotes ease of steering and reduces tyre wear to a minimum. It also refers to angular relationship between the front wheels and parts attached to the front wheels, frame of the vehicle. It depends upon the following terms. Caster angle, camber angle, kingpin inclination, toe -in and toe -out on turn.

Under steering, over steering and turning radius.

While taking a turn, the wheels are not always pointing in direction in which the vehicle is moving, due to distortion of tyretread. The angle between the wheel inclination and the path taken by the wheel is known as slip angle. When the slip angle is greater at the rear than that of the front, the vehicle tends to over steer the vehicle is to turn into the curve more than the driver intended. When the slip angle is smaller at the rear than at the front, the vehicle tends to under steer. The under steer is most commonly preferred because correction by the driver involves rotating the steering wheel a little more in the direction of the turn. It can be noted that the slip angle is affected by the road camber side winds, tyre inflation and the vibrations in the load on either the front or rear axle.

Turning radius : turning radius is the radius of the circle on which the outside front wheels moves when the front wheels are turned to their extreme outer position. This radius is 5 to 7m for buses and trucks. The turning radius is usually proportioned to the wheels base of the vehicle, because the maximum rotation of the steering knuckle is seldom more than 35 degrees.

Conventional steering linkages.

When the steering wheel is turned to the left or right, the pitman arm swing from one side to the other. This movement of the pitman arm gives angular movement to the front wheels through the steering linkages. The most commonly used steering linkages is the conventional steering linkages. The pitman arm (drop arm) is connected directly by a connecting link namely drag link to a steering knuckle arm attached to the left hand steering knuckle. The motions is carried across from this arm to a steering arm on the right side steering knuckle by means of the rod. The drag link and drop arm (pitman arm) are mounted on the left side of the frame. In some designs the drag link is connected between the drop arm and right steering knuckle arm by locating drop arm beneath the steering gear. In direct cross type steering linkages, the pitman arm is connected directly to one and of the rod which its turn is connected to another. The other ends of the rod are connected to the steering arms.

Steering linkages.

The steering linkage is a connection of various links between the steering gear box and the front wheels. The motions of pitman arm of the gear box is transferred to the steering knuckle of the front wheels through the steering linkages. When the steering wheel is turned to the left or right, the pitman arm swing from one side to the other. This movement of the pitman arm gives angular movement to the front wheels through the steering linkages.

Power steering.

The power steering system provides additional assistance to the turning effort applied to the manual steering system. The power steering is of two types – hydraulic and electric /electronic. A hydraulic -electric hybrid system is also possible. A hydraulic power steering (HPS) used hydraulic pressure applied by on engine driven pump to assist the motion of turning the steering wheel. Electric power steering (EPS) is more effective than the hydraulic power steering since the electric power steering motor only needs to provide assistance when the steering wheel turned where as the hydraulic pump must run constantly. The main components of an integral power steering system consist of a hydraulic pump assembly connected with hoses. A rotary valve power steering gear for the integral system using recirculating ball type worm and wheel steering gear is most commonly used one.

Types of steering system.

The steering system is said to be of different types according to its position along with the vibrations of the front wheels. When deflection of the steered wheels due to road surface is transmitted through the steering linkages and steering gear box to the steering wheel, the system is said to be reversible steering. If every small imperfections of the road surface cause the steering to rotate it is known as reversible steering. But it is not advisable. Some degree of reversibility is needed so that the wheels will find to strength up after negotiating a bending. This effect is called a semi reversible. When steered wheels do not cause any deflects due to road irregularities it is known as irreversible steering. The semi reversible steering is always desired.

Rack and pinion steering gear.

In this steering gear, a pinion is mounted at the end of the steering inner column. It engages the rack which has ball joints at each end to allow the raise and fall of the wheel, the rods are connected with ball joint to the sub axles. The rotary movement of steering wheel turn the pinion which moves the rack sideways parallel to tie rod.

Recirculating ball steering gear.

In this steering gear there will be some steel balls in the grooves of steering inner column which move along with the steering worm. This enables to control the friction among them and there by reducing noise. It increases the mechanical advantage of the operator for easy and smooth operation of steering.

Cam and lever steering gear.

In this type of steering gear, a special worm called Cam is located at the end of inner column which it attached to column in the steering gear. When the worm is rotated, the lever is also moved in the groove provided in the worm. This causes the lever to swing through an arc.

Worm and sector steering gear.

In this type of steering gear, there will be worm at the bottom end of the steering inner column and a part of sector shape is there in the steering gear housing. The worm meshes with sector and it moves by the rotation of worm and thereby moving drop arm which is attached to it

Worm and roller steering gear.

In this steering gear, there will be a worm at the bottom end of inner column and a roller is there in the steering gear box. When the worm rotates, the roller which is attached to it also rotates causing the roller to rotate and thereby moving drop arm

Worm and wheel steering gear.

In this type of steering gear box there will be worm at the bottom end of steering inner column. This worm meshes with a wheel in steering gear box housing. When steering wheel turned, the steering column revolves and the wheel is rotated along with it. This causes the drop arm to move and thereby drag link and other steering linkages like tie rods king pin etc.

Steering system : requirements of vehicle steering system.

The steering system of a vehicle is having the following requirement.

  1. It should be able to turn the vehicle with more mechanical advantage and less efforts.
  2. It should turn the wheel within shortest time possible.
  3. There should be self centering action in the steering geometry.
  4. It should be certain degree irreversible so that the shock of the road surface are not transmitted to the hands of the driver.

Different bodies used in automobiles.

The automobile bodies are designed according to the requirements of the vehicle. According to design and requirements of the vehicle, there are different types of automobiles bodies.

  1. Car.
  2. Straight truck or Punjab truck body.
  3. Truck with half body.
  4. Platform type truck.
  5. Tractor.
  6. Tractor with articulated trailer.
  7. Tanker.
  8. Bus.
  9. Dumper truck.
  10. Delivery van.
  11. Station wagon.
  12. Pick up van.
  13. Jeep.
  14. Long wheel base truck etc.

Various loads acting on the chassis frame.

  1. Stationary loads namely the loads of permanent attachment like all the parts of the chassis, body etc.
  2. Short duration loads while turning, braking etc.
  3. Momentary loads while quick acceleration, sudden braking etc.
  4. Loads applied while crossing roads of irregularities and uneven surfaces.
  5. Loads caused by sudden accidents, head on collisions.
  6. Loads caused by irregular and overloading of vehicle.

Types of chassis frame.

There are different types of chassis frame sections. Channel section, box section, tubular section. The conventional frame is also known as non -load carrying frame. In this type of frame, the load on the vehicle are transferred to the suspension by the frame which is the main skeleton of the vehicle. The channel section is used in long members and box section in short members. Tubular section is used now a days is three wheeler, scooter, matadors and pick up vans. The frame should be strong enough to bear load while sudden brakes and accidents.

The functions of the Chassis frame.

  1. To carry all the stationary loads attached to it and loads of passengers and cargo carried in it.
  2. To withstand torsional vibrations caused by the movement of the vehicle.
  3. To withstand the centrifugal force caused by cornering of the vehicle.
  4. To control the vibrations caused by the running of the vehicle.
  5. To withstand bending stresses due to rise and fall of the front and rear axles.

Layout of chassis and its main components.

“Chassis “a French term which means the complete automobile without body and it includes all the systems like power plant, transmission, steering, suspension, wheels tyres, auto electric system etc. If body is also attached to it then it is known as the particular vehicle as per the shape and design of the body.

Introduction of chassis frame.

Chassis frame is the basics frame work of the automobile. It supports all the parts of the automobile attached to it. It is made of drop forged steel. All the parts related to automobile are attached to it only. All the system related to automobile like power plant, transmission, steering, suspension, braking system etc are attached to and supported by it only.

Torsion bar.

In independent suspension system, the torsion bar is attached to the axle with the king pin of the front axle. The torsion bar axles the shock by moving in certain angle with the axle. It is almost being used along with any kind of independent suspension system. It is used along with rubber torsion units.

Stabilizer bar.

A stabilizer or a sway bar, is necessarily used in all independent front suspension units. It reduces the tending the vehicle to roll or tip and either side when taking a turn. This tendency has been increased due to the use of softer springs and independent front end suspension. A stabilizer is simply a bar of long steel with arms at each and connected to the lower wishbone arm of independent suspension or to the axle. It is supported by bush bearings fixed to the frame and is parallel to the cross member. When both the wheels deflect up or down by the same amount the stabilizer bar simply turns in the bearings. When only one wheel deflects then only one end of stabilizers moves, thus twisting the stabilizer which acts as a springs between two sides of independent suspension system. In this way, the stabilizer reduces rolling or tipping of the vehicle on curves.

Hydraulic shock absorber.

The shock absorber develop resistance to the springs by forcing a fluid through check valves and small holes. ‘Double “acting shock absorber offer resistance both during compression and rebound of the spring. The ‘double ‘acting hydraulic telescopic shock absorber are commonly used. Its upper eye is connected to the axle and the lower eye to the chassis frame.

Need of shock absorber.

Shock absorber compresses with the road shocks and rebalances while traveling on uneven roads due to usage of this, the effect of road shocks is required by the shock absorber suddenly and releases slowly whole traveling on uneven roads.

Helical springs.

The helical springs are preferably used in combination with independent suspension system. The length and diameter of the spring wire greatly affects the stiffness of the spring. But the length is controlled by the diameter of the coil and the number of active coils.

Coil springs.

Coil spring is made of a length of special spring steel, usually round in section which is wound in the shape of coil. The ends of coil springs are kept flat so that could seat properly. They can store twice energy per unit volume in comparison to leaf spring. To seat the coil spring pan shaped brackets or spring seats are attached to the axles. This suspension is also used in combination with torque tube or torque rod.

Leaf springs.

The leaf springs are of different types namely -full elliptic, three quarter elliptic, semi elliptic, quarter elliptic transverse. In almost all automobiles which are having conventional suspension system the semi elliptic leaf springs are most commonly used. The leaf springs are made of long flat strip steel. Several strips are placed one on the other and held together by means of centre bolt and champs. Each strip is called leaf. There is one main leaf which is extended to full length. Each succeeding leaf is shorter than the proceeding one. The main leaf contains eyes are both ends for making connections with the frame. The entire set is fitted from the chassis frame by hanging with a shackle at one side and the other side is fixed to frame. During jerks, the leaf spring bounces and each strip flexes and rebounces again and again.

Types of springs -laminated spring, coil spring, helical spring.

The springs support the chassis frame. The entire weight of the vehicle live engine, power train, body, passengers, cargo etc, falls on the chassis frame. The spring damp the road shocks transmitted to the wheels as they travel over the road thereby protecting the units supported directly by the frame. The springs are placed between the chassis frame and the axle.

Requirements of automobiles suspension system.

The automobile suspension system is having the following requirement .

  1. To have minimum deflection to the vehicles with required stability.
  2. To have minimum wheel hop.
  3. To safeguard the occupants and cargo against road shocks.
  4. To minimize the effects of stresses due to road shocks on the mechanism of the vehicle.
  5. To keep the body perfect in level while traveling over rough and uneven roads.
  6. To keep the body of the vehicle safe from road shocks.

Sliding pillar system.

In this system the pillar or elongated king pin is attached to the wheels and slides up and down in the axle type beam a fixed rigidly to the vehicle frame.

Trailing link system.

The trailing link independent suspension use parallelogram linkages lying beside the frame side members usually a horizontal coil springs is used in this type of suspension system. During compression and rebound, the spring winds and unwinds. In some vehicles the torsion bar may also be fitted instead of horizontal coil spring.

Wishbone arm system.

Wishbone arm system type independent suspension system is most popular type of all independent suspension system. In this system transverse springs along with coil springs are mostly used. In European cars, torsion bars instead of coil springs are used. In this system there are two suspension or control arms are used in each side of the vehicle. There arms are are like two legs of chicken wishbone or better ‘V’. These wishbone arms are connected with chassis frame on the open end. The closed end spread out of the chassis frame. One arm is below whereas the other is above the frame. The closed ends of both upper and lower suspension arms are connected with steering knuckle support to which the steering knuckle is attached by means of kingpin. A coil spring is placed between the frame and the lower wishbone arm. Mostly the open end of upper control arm is connected with the shock absorber shaft which is fitted at the frame when there is a bump, the wheels tends to go up, the control since the shock absorber is fitted with the upper control arm, it damps the vibrations set up in the coil spring due to road irregularities.

Conventional suspension system.

In this suspension system. The wheels are fitted on the beam type which are attached to the chassis frame through road springs. In this type of suspension, the effect on one wheel is directly transmitted to the other side of the wheel through the axle.