Layout of an Automobile

The layout of different types of vehicles is different. A private car which is to carry upto eight persons is generally four seater.

Fig. 1 Layout of a car

1-Frame; 2-Wheels; 3-Radiator; 4-Engine; 5-Clutch and gearbox; 6-Propellershaft; 7-Universal joint; 8-Differential, Rear Axle; 9-Fuel tank; 10-Front axle; 11-Steering; 12-Road springs; 13-Exhaust/silencer

                The layout of a car is shown in Fig. 1. It shows the position of the main parts of an automobile. It consists of engine located at the front of the vehicle, followed by a clutch, gear box, propeller shaft, universal joint, differential, back axle etc. The radiator is located in front of the engine. Various other parts of the vehicle shown in the layout are dynamo, horn, steering box, fan, timing gear, carburetor, air filter, gear control, steering wheel, cylinder, petrol tank, rear axle, back axle. The drive from universal joint of the propeller shaft. From the propeller shaft it is conveyed to the rear universal joint through a sliding splined type of joint. The bevel gear of the short shaft is driven by the rear universal joint. This bevel gear meshes with a larger bevel gear which drives the two rear axle shafts through a differential gear.

                The layout also consists of independent front-wheel springing with quarter-elliptic leaf springs, steer, steering column bevel-gear control and hydraulic braking system.

                The wheels which are four in number are fitted below the car chassis to support the load of the vehicle and passengers as well as to run the car. They ate fitted with hollow rubber tyres filled with air in rubber tubes under sufficient pressure necessary for carrying the load. The shocks caused by road irregularities are absorbed by them. By fitting springs between the wheels and the vehicle allowing the vertical movement of wheels in relation to vehicle, greater part of unevenness of road surfaces is taken care of.

                Front axle is used for steering front wheels carried on stub axles swiveling upon king pins at the axle extremities.

              Steering arms and a track rod link the two stub axles together for swiveling them by a steering wheel about the king pins. The steering wheel linked to one of the stub axles by a shaft, a gear box and a suitable linkage is operated by the driver’s hand wheel. Previously the axle-a one piece beam was used to support the vehicle through springs. An arrangement known as independent front suspension has replaced the axle and spring arrangement. Under the control of springs, the wheels are free to rise and fall vertically independently of each other.

                For fixing rear wheels, a tube like shaft enclosing driving shafts with suitable bearings for rotating the wheels is used. It is enlarged at the center for enclosing the final-drive gears used for providing main speed reduction between the engine and the driving wheels. The change of direction of the drive from the fore and aft line of the propeller shaft to the transverse line of the axle shafts is also provided by this tube known as rear axle.

                When going round a curve, the inner wheel has to travel a smaller distance in comparison to the outer wheel. But both the rear wheels would rotate at the same speed if they are connected by a shaft. This rotation of both the wheels would result in slip-ping of one or both of them on the road surface causing excessive tryre wear as well as severe twisting loads on the shaft. More-over, the two wheels of the exactly similar diameter (which is not usually so) can only turn at the same speed without slip on the straight road. Tyres fitted on the opposite sides may be of different states of wear and even tyre of same nominal diameter made by different or same manufacturer may differ in actual dimensions or may not be exactly similar. Due to change of rolling radius (the distance from the wheel center to the ground the effective size of the tyre may be altered by different inflation pressure also.

                Each wheel is provided with its own separate half shaft connected by a differential gear and meeting at about the center of the axle. The wheels are free to rotate at different speeds although they are provided with equal drive by the differential gear.

                For preventing the transmission of shock from uneven road surfaces to the vehicle, springs are used to support the vehicle on the axle. In order to allow for the vertical movements of the wheels relative to the frame as well as to allow the parts of the shaft to operate at different angle, another increasingly used arrangement is used. It consists of mounting the final-drive gears and the differential gear in a casing attached to the frame with independently sprung wheels attached to them by means of shafts through devices called universal joints.

                Power unit consists of an internal combustion engine. It is usually mounted at the point end of the car. The clutch and the gear box are placed immediately behind it. The three components, engine, clutch and gear box are assemble into a single unit.

                For connecting the output shaft of the gear box to the rear axle, a long shaft known as propeller shaft is used. This shaft is either enclosed in a tubular casing or kept exposed or opened with a universal joint fitted at each end for allowing the changes in the shaft alignment with the rise and fall of the rear axle due to road surface variations. Universal joints cannot be eliminated even if the final drive gears are fixed to the frame with the wheel springing independently. Neither the misalignment resulting from the flexing of the vehicle structure over bumpy road surfaces can be avoided nor the precise alignment if can be ensured without them.

                For controlling the movement of the vehicles or to stop them, efficient braking system is a necessity for a vehicle. Brakes attached to each of the four wheels are of two types. In the initial type, a pair of shoes carried on a stationary plate is expanded in contact with a rotating drum mounted on the wheels to arrest the motion of the drum. In the modern type of brakes, one or more pairs of pads are carried in a caliper attached to the axle or wheel supporting linkage. The sides of the dis mounted on the wheel are griped by these pads. By applying pressure on a pedal, the brakes are applied. A hand lever acting through a separate linkage and locked in the on position is used.

                For operating the brake, either mechanical or hydraulic system is used. Mechanical system requiring gearing system for mechanical and hydraulic fluid for the hydraulic brakes are used.