Usually the cabin is attached to the powered unit through hinges. Double duckers, earth moving equipment, dumpers, etc. are the examples of this category. 3. Heavy tractor vehicles: These are used for moving heavy loads at low speeds. Agricultural tractors and earth moving equipment are the examples of this category. CLASSIFICATION i) Based on use: a) Scooter, motor cycle, moped; b) Auto; c) Cars, mini bus; d) Bus, lorry, truck e) Tractor, earth-moving equipment like scrapper, dumper, etc. ii) Based on capacity: a) Light transport vehicle car, jeep; b) Medium transport vehicle Tempo, minibus.
c) Heavy transport vehicle Bus, lorry, truck iii) Based on fuel: a) Steam; b) Petrol; c) Diesel; d) Gas gas turbine driven truck iv) Based on drive mechanism: a) Left hand drive mechanism American b) Right hand driven mechanism Indian c) Front wheel drive mechanism Volks Wagon d) Rear wheel drive mechanism All Indian vehicles e) All four wheel drive mechanism Jeep. v) Based on number of wheels: a) Two wheelers: Scooters, motor cycle, moped b) Three wheelers: Auto, Tempo c) Four wheelers: Car, jeep, minibus d) Six wheelers: Bus, lorry, truck vi) Based on transmission system:
a) Conventional; b) Semi-automatic; c) Automatic vii) Based on suspension system: a) Conventional: uses leaf springs b) Independent: uses coil springs & torsion springs. LAYOUT OF AN AUTOMOBILE: Fig. Layout of an automobile Layout of an automobile consists of a frame on which the engine and the bodywork are fitted. The engine with its cooling, lubrication, ignition or fuel injection and fuel supply system is fitted at the front end of the frame. A radiator is provided in front of the engine to cool the circulating water.
A clutch to engage and disengage the drive when changing gears or stopping the vehicle, a gear box to change the torque on the road wheels depending on load requirements through different gear ratios, a propeller shaft to transmit the power from the gear box to the final drive along with an universal joint at either end to take care of the difference in elevation of the gear box and differential and as well as to take care changes in shaft alignment due to road surface condition, a differential to turn the rear wheels at different speeds when the automobile is taking turns, two half shafts to rotate the wheels, are provided with the engine to constitute a power transmission or train.
An electrical system (1) to develop electrical energy through the engine operated dynamo (generator), (2) to start the engine through an electrical motor and battery, (3) to provide the power for horn, wind screen wiper, head lights, trafficators (indicator lights) etc. is provided on the layout. Both the front and rear axles are fixed to frame through spring suspension system to provide cushioning from road shocks. Wheels support the load of the vehicle and passengers and run the vehicle. Hollow rubber tyre along with rubber tubes filled with air under pressure support the load.
To control the movement of vehicle, a breaking system is provided. A brake drum with friction material lined brake shoes in each wheel provides the necessary braking action whenever the shoes are squeezed on the drum. The front axle is so designed to provide steering through various linkages. A steering mechanism is used to steer the vehicle on level road and to negotiate bends and curves in the road. Frame is used to support the power train and other components. The final bodywork is built on the frame. The assembled vehicle without body is called the chassis. Clutch
Clutch is a mechanism, which enables the rotary motion of one shaft to be transmitted, when desired, to a second shaft the axis of which is coincident with that of the first. Torque transmission, gradual engagement, heat dissipation, dynamic balancing, vibration damping size, clutch free pedal play, ease of operation are some of the requirements of a clutch. Clutch is a mechanism, which connects or disconnects the transmission of power from crankshaft to the gearbox. It is fitted between the rear end of the crankshaft (where a flywheel is connected) and the gearbox. The following are the main types of clutches: a) Friction clutches.
b) Fluid flywheel The friction clutches work on the fact that friction is caused when two rotating discs come into contact with each other. On the other hand, the fluid flywheel works on the transfer of energy from one rotor to the other by means of some fluid. Friction clutches may be dry or the wet type. In an overwhelming majority of vehicles, the dry type of clutch is sued because of mainly the lower coefficient of friction in the wet type. Principle of friction clutches: The principle of a friction clutch may be explained by means of figure shown below. Let shaft A and disc C be revolving at some speed, say N r.
p. m. Shaft B and the disc D keyed to it are stationary; initially when the clutch is not engaged (Fig. a). Now apply some axial force W to the disc D so that it comes in contact with disc C. As soon as the contact is made the force of friction between C and D will come into play and consequently the disc D will also start revolving. The speed of d depends upon the friction force present, which in turn, is proportional to the force W applied. If W is increased gradually, the speed of D will be increased correspondingly till the stage comes when the speed of D becomes equal to the speed of C.
Then the clutch is said to be fully engaged (Fig. b). Let W = axial load applied µ = coefficient of friction T = torque transmitted R = effective mean radius of friction surface. Then T = µ W R Thus we see that the torque transmitted by a friction clutch depends upon 3 factors i. e. , µ , W and R. This means that increasing any or all of the above factors would increase the amount of torque, which a clutch can transmit. (W a driver can exert without undue strain; R space availability). Gearbox The object of the gearbox is to enable the driver to adjust the traffic effort to meet the total (air +gradient + rolling) resistance of the vehicle at any moment and accelerate or decelerate the vehicle as desired.
The driver does the change from one gear ratio to the other, through a gear-shifting lever. One reverse gear is also provided with medium and large transport vehicles to drive the vehicle in opposite direction. Propeller shaft It is a universally joined shaft. Its function is to transmit the power from the gearbox to the final drive. Universal joint The rear axle moves up and down due to the unevenness in the road. Because of this, the propeller shaft fitted to the rear axle must be free to move up & down.
To permit the turning of the propeller shaft under these conditions and to take care the difference in elevation between the gear box and the differential, universal joints are fitted at each end of the propeller shaft. Differential gear The differential gear carries the power from the propeller shaft to the rear wheel axle. It helps the two rear wheels to turn at different speeds when rounding a curve. The outer wheel must over-run the inner wheel when taking the turn. The differential gear also ensures that the final output torque is equally distributed between the two wheels. Hydraulic brake system
In hydraulic brakes, the pedal force is transmitted to the brake shoe by means of a confined liquid called brake fluid. The force applied to the pedal is multiplied and transmitted to all the brake shoes by a system of force transmission based on Pascals principle (confined liquids transmit pressure without loss equally in all direction). The hydraulic braking system consists a master cylinder and piston, which are connected by tubing to hydraulic wheel cylinders at each of the four wheels as shown in figure. The pistons of these cylinders move out to apply the pressure to the wheel brakes.
The system is filled with liquid under light pressure of about 0. 5 kg/cm2 when the brakes are not in operation. This is to ensure that the cups of the wheel cylinder are kept expanded in order to prevent the air from entering the cylinders when the brakes are released. The liquid is usually a mixture of glycerin and alcohol or castor oil and some additives. Each wheel brake comprises a cylindrical brake drum, which is mounted on the inner side of the wheel and revolves with it, and two brake shoes which are mounted inside the brake drums and do not rotate. The shoes are fitted with a heat and wear resisting brake lining on their outer surfaces.
These non-rotating shoes are forced out against the inner surface of the revolving brake drum to slow down or stop its motion by the action of the hydraulic wheel cylinders when the brakes are applied. Differential When the car is taking a turn, the outer wheels have to travel greater distance as compared to the inner wheels in the same time. If, therefore, the car has a solid rear axle only and no other device, there will be a tendency for the wheels to skid. Hence if the wheel skidding is to be avoided, some mechanism must be incorporated in the rear axle, which should reduce the speed of the inner wheels when taking turns; it should be at the same time keep the speeds of both the wheels on the rear axle same when going straight ahead.
Such a device, which serves both of the above functions, is called a differential. It should be noted that though the differential serves to change the speeds, the torques supplied to either wheel remain essentially equal. To understand the principle on which differential works, consider the figure shown. To the crown wheel is attached a cage contains the gear mechanism as shown. The crown wheel is further free to rotate on the rear axle shafts. Sun gears are mounted on the end of each half shaft.
When the vehicle is going straight, the cage and the inner gears rotate as a single unit and the two half shafts revolve at the same speed. In this situation, there is no relative movement among the various differential gears. To understand what happens when the vehicle is taking a turn, assume that the cage is stationary. Then turning one Sun gear will cause the other to rotate in the opposite direction. That means that if left Sun gear rotates n times in a particular time, the right Sun gear will also rotate n times in the same period but, of course, in the opposite direction.
This rotation is superimposed on the normal wheel speed when the vehicle is taking a turn. Thus, for example, consider a vehicle with wheel speed N rpm going straight. When it takes a turn towards right, there will be a resistance to the motion of the right wheel and as a result of differential action, if the right wheel rotates back at n rpm, then the left wheel will rotate forward at n rpm. This will give the resultant speed of the left wheel as (N+n) and that of the right wheel as (N-n) rpm. Half shaft B Cage Half shaft Crown wheel Bevel pinion Planet pinion C A P Sun gear.