Functions of the automobile components

FUNCTIONS OF THE AUTOMOBILE COMPONENTS

1. Engine

The engine consists of a cylinder, piston, valves, valve operating mechanism, fuel injector, radiator fan, fuel feed pump, oil pump, etc. The engine components are explained in Chapter 17.

The explosive power of the air-fuel mixture drives the piston. The piston turns a crankshaft to which it is connected. Thus, the linear motion of the piston is converted into rotary motion of the crankshaft, resulting in the rotary motion of the wheels of an automobile.

A number of systems are necessary to make an engine work. A lubrication system is needed to reduce friction and prevent engine wear. A cooling system is required to keep the engine's temperature within safe limits. The engine must be provided with a proper amount of air and fuel by a fuel system.

The air-fuel mixture must be ignited inside the cylinder at just the right time by an ignition system. An electrical system is required to operate the cranking motor that starts the engine and also provide electrical energy to operate engine accessories.

2. Lubrication System

An engine has many moving metallic parts. The relative motion between the moving parts leads to friction, heat generation, wear and loss of power in engine. Oil is circulated between the moving parts to prevent metal-to-metal contact which leads to wear.

. The primary function of a lubricant is to reduce friction and power loss. The secondary function of a lubricant is to act as a coolant and also as a sealing medium to prevent leakages. The commonly used lubricating systems are splash system and forced feed system. The major parts which require lubrication are cylinder walls, piston, cooling fan, ignition mechanism and bearings of crankshaft and connecting rod.

3. Cooling system

The fuel is burnt inside the cylinder of an internal combustion engine to produce power. The temperature attained can be as high as 1600° C and this is greater than the melting point of engine parts. This increase of temperature directly affects the engine performance and the life of the engine parts.

The cooling system keeps the engine operating at an optimum temperature for efficient operation under all conditions. Whatever the driving conditions may be, the system is designed to prevent both overheating and overcooling.

The cooling system helps to dissipate surplus heat for protection of engine components like cylinder, cylinder head, piston, piston rings, and valves and also aids in maintaining the lubricating property of oil inside the engine. The systems adopted for cooling are (i) Air cooled system and (ii) Water cooled system.

Air cooled system: The system in which heat is directly dissipated into the air around the cylinder wall is called air cooled system. In order to increase the heat transfer rate, metallic fins are provided on the outer surface of the cylinder as shown in Fig. 2. This type of cooling is used for smaller capacity engines used in scooters and motor cycles.

Water cooled system: Water is used as a cooling medium. It is circulated through special cooling passages present in the engine. It is used for medium and large capacity engines, viz., cars, buses, trucks, etc.

4. Fuel system

The main function of a fuel supply system is to provide fuel to the injection system. The rate and pressure with which the fuel is supplied should be sufficient to meet engine demands under all conditions of load, speed and gradients encountered by the vehicle. The fuel system must also have enough reserve fuel for several miles of vehicle operation.

5. Ignition system

The fuel supplied to the combustion chamber must be ignited to deliver power. The purpose of the ignition system is to provide assistance for the combustion of fuel. The assistance is provided either by a high voltage spark or self-ignition in each of the engine's cylinders at the right time so that the airfuel mixture can burn completely.

In a spark-ignition engine, an electric spark is used for ignition purpose. The compressionignition engine does not require a separate ignition system because the ignition takes place by compression of the air-fuel mixture to a higher pressure.

6. Electrical system

The engine's electrical system provides energy to operate a starter motor and power all the accessories. Its main components are battery, alternator, starter motor, ignition coil and heater.

7. Chassis

A chassis is a skeletal frame on which various mechanical parts like engine, tires, axle assemblies, brakes, steering etc. are bolted. The frame provides a foundation for the engine and body of the vehicle. It is constructed from square or hollow cylindrical steel members strong enough to support the weight of the body and other components. They are welded or bolted together to give the final shape.

The engine is mounted on the frame with rubber pads to absorb and dampen vibrations. The frame is supported on wheel axles by means of springs. The frame shown in Fig. 1 consists of two long members and four cross members.

8. Suspension system

The function of the suspension system is to absorb vibrations due to the up and down motion of wheels caused by the irregularities in the road surface. The springs, connecting linkages, and shock absorber comprise the suspension system of a vehicle.

The suspension system is broadly classified into two types:

Rigid system: The springs are attached to a rigid beam axle. It is mostly used in the front axle of commercial vehicles and in the rear axle of all types of vehicles.

Independent system: It does not have a rigid axle. Each wheel is free to move vertically without any reaction on its mating wheel. It is mostly used in small cars to provide more comfort.

9. Power train

The power train consists of components that generate power and deliver it to the wheels of an automobile. This includes the engine, transmission, drive shafts, differential and the final drive to drive wheels.

10. Clutch

The purpose of clutch is to temporarily disconnect the engine from wheels. When clutch is in the engaged position, the engine power flows to the transmission through it. When gears are to be changed while the vehicle is running, the clutch permits temporary decoupling of engine and wheels so that gears can be shifted. Such disengagement of the power train from the engine is essential while changing the gear or stopping the vehicle.

11. Drive shaft

The drive shaft or propeller shaft connects the gearbox and the differential unit. The drive shaft has universal joints at its ends.

12. Differential

A differential is a mechanical element made up of several gears. It transmits power from the driveshaft to the drive wheels. The main function of differential is to allow the drive wheels to turn at different speeds allowing the wheels to go around corners.

13. Axle

The axle is a shaft on which a pair of wheels is mounted. The wheels are provided with the required drive through these axles.

A portion of the weight of vehicle is transmitted to the wheels through an axle. The front axle performs several functions. It carries the weight of the front of the vehicle and also takes horizontal and vertical loads when vehicle moves on bumpy roads. When brakes are applied on front wheels, it endures bending and torsional stresses. It is generally made by drop forging of steel to achieve higher strength. It is robust in construction.

14. Wheels

The wheels of an automobile take the load of the vehicle and also produce tractive force to move the vehicle. The wheels are also used for retardation and stopping the vehicle.

15. Steering system

The steering system is used for changing angular motion of the front wheel so that the vehicle can negotiate a turn. It also provides directional stability to the vehicle when the vehicle moves ahead in straight line. The major requirement of any steering mechanism is that it should be precise and easy to handle. Moreover, the front wheels should have a tendency to return to the straight-ahead position after a turn.

The most conventional steering arrangement is to turn the front wheels using a hand-operated steering wheel which is positioned in front of the driver, via the steering column. The schematic diagram of the steering system is shown in Fig. 3. The track rod and link rod connect the steering arms to the steering wheels through a steering box.

A gear mechanism in the steering gear box is used to increase the steering effort provided by the driver. Vehicle steering is not only required on a curved road but also while maneuvering on busy traffic roads.

16. Braking system

The brakes are required for slowing down or stopping a moving vehicle by reducing its kinetic energy. The braking system is essential for the safety of passengers, and passers-by on roads. It may be operated mechanically or hydraulically. Most of the braking systems in use today are of the hydraulic type.

All brakes consist of two members, one rotating and the other stationary. There are various means by which the two members can be brought in contact, thus reducing the speed of the vehicle.

The major components of the braking system are: brake pedal, master cylinder, wheel cylinders, brake drum, brake pipe, brake shoes and linkages. The components present in a hydraulic braking system are illustrated in Fig. 4.

As the vehicle loads and speeds have increased over years, there is a necessity for improving the braking performance. In order to meet such requirement, power brakes are now being preferred. Power brakes are a system of hydraulics which utilize vacuum and air pressure to provide most of the braking effort.

Hand brake or parking brake is mechanically operated. The mechanism consists of a handoperated lever and a locking mechanism that will keep it engaged until manually released. It is used for parking the vehicles on sloppy surfaces and also in case of emergency.