THE TRANSMISSION OF A SYSTEM

The transmission of a system is used to carry power from the engine to the drive wheels.
The major transmissions are       (i) Gear box (also called the transmission)
                     (ii) Propeller shaft or drive shaft.
                     (iii) Clutch
The main function of a transmission system
*To safe guide the engine from over load when starting.
*To connect the engine to the drive wheel without shock.
*To turn the drive wheel through the right angle.
*To disconnect engine from the road wheel when desired.
*To reduce the engine speed in fixed ratio.
*To vary the leverage between the engine and the drive wheels.
*To provide provision for the flexing of the road spring which cause relative movement between the engine and the drive wheel
*To provide provision for the drive wheels so that that they may rotate at various speeds while taking turns.
                CLUTCH
Vehicle with a manual transmission have a clutch. Its function is to transporarily disconnected the engine from the wheel such as disengagement of the power train from the engine is essential while changing the gear or while stopping the vehicle.
               
GEAR BOX (TRANSMISSION)
The main function of the gear box or transmission is to provide the necessary variation to the torque applied by the engine to the wheels this is achieved by changing the gearing ratio between the engine output shaft and the drive shaft.

                BEVEL PINION AND CROW WHEEL if
These are used turn the drive round through 900 and also provide a permanent reduction in speed. The permanent reduction is necessary because of the fact the speed of the engine has to be maintained at optimum level at all times, yet a minimum value of torque has to be made available at the wheels.

                UNIVERSAL JOINTS
These provide for the relative movement between the engine and drive wheel due to flexing of the spring

                PROPELLER SHAFT (DRIVE SHAFT)
It connects the gear box and the differential unit.

                DEFFERENTIAL
The function of the differential is to split the power received from the propeller shaft to the rear axles shaft. It allows the rear wheels to be driven at different speeds when the vehicle takes a turn or falls into a ditch.
There are three types of drive trains: rear wheel drive, front wheel drive and four wheel drive.



REAR WHEEL DRIVE VEHICLE
In a car has the engine mounts either long way or sideways. The engine mount is usually tall which wheel are the drive wheels. These are the wheel that moves the car. If the engine is mounted in a long ways, it has longitudinal mounting and the car usually has rear drive wheels. The power flower through the transmission propeller shaft to the rear drive wheels.
ADVANTAGE OF REAR DRIVE WHEEL (RDW)
The layout of a rear wheel drive car is much closer to an even fore and aft weight distribution as more of the engine can lie between the front and rear wheels drive and the transmission is moved much farther back.
No torque steer.
During heavy acceleration, weight is placed on the rear or driving wheels which improve traction.
Better braking.
Better handing in dry conditions.

DISADVANTAGE OF REAR DRIVE WHEEL (RDW)

In creased weight.
Improper weight distributed when loaded.
Under heavy acceleration over steer and fishtailing may occur.
Higher initial purchase price.
The long propeller shaft (on front engine cars) adds to drive train elasticity.
On snow, ice and sand, rear-wheel drive loses its traction advantage to front or all-wheel drive vehicles which have weight in the driven wheels.

        (2) FRONT WHEEL DRIVE VEHICLE
An engine that mounts sideways at the front vehicle has transverse mounting with front wheel drive (FWD). Engine power flower through the trans axle to the front wheels.
ADVANTAGE FRONT WHEEL DRIVE (FWD)
(1) No need to devote inferior space for the propeller shaft tunnel or rear differential there by increasing the volume available for passenger and cargo.
(2) Improved fuel efficiency due to  less weight .
(3) Fewer components usually mean lower weight .
(4) It’s easier to correct trailing throttle or trailing brake over steer.
(5)The wheelbase can be extended without building a longer propeller shaft.

                 DISAVANTAGE OF FRONT WHEEL DRIVE (FWD)
Torque steer is the tendency for some front – wheel drive car to pull to the left or right under heard acceleration
Lack of weight shifting will limit the acceleration of a front – wheel drive vehicle. In vehicle weight shifting’s back during acceleration giving more traction the rear wheels. This is one of the reason why nearly all racing cars are rear – wheel drive
In some towing situations, front wheel drive cars can be at a traction disadvantage
Due to geometry and packaging constraints, the constant – velocity joints attached to the wheel hub have a tendency to wear out much earlier than the universal joints typically used I n their rear wheel drive counterparts
The transverse engine layout restricts the size of the engine that can be placed in modern engine compartments, so it is rarely adopted by powerful luxury and sport car
Its layout always use a transverse engine (“east – west”) installation, which limits the amount by which front wheels can turn, thus increasing the  turning circle of a front wheel drive one with the same wheelbase.

FOUR WHEEL DRIVE VEHICLE: military vehicles or jeeps have all the four wheels as drive wheels. In this there is a transfer case box in addition which divides the torque equally between the front and the rear axles. In terms of handling traction and performance, four wheel drive system generally have most of the advantage of both front wheel drive and rear wheel drive.
ADVANTAGE OF FOUR WHEEL DRIVE
Traction is nearly doubled compared to a two wheel drive layout. Given sufficient power, this result in unparalleled acceleration and drive anility on surface with less than ideal grip, and superior engine braking on loose surfaces.
Handling characteristic in normal conditions can be configured to emulate FWD or RWD or some mixture even to switch between these behaviors according to circumstance. Hence a 4WD car can be driven more safely at higher speeds by inexpert motorists than 2WD designs.
DISADVANTAGE OF FOUR WHEEL DRIVE
The handbrake cannot be used to induce over-steer for manicuring purposes as the drive train couples the fronts and rear axles together.
   THE AUXILIARIES
Auxiliaries refer to the electrical equipment which is common to all types of vehicle. The engine provides the power to move the can However’ electricity powers most devices on the car. These are classified as:
 Supply system: the car has two sources of electric. One is battery and the other is alternator in the charging system the battery supplies electricity while the engine is off and for cranking the engine. After the engine start, the alternator recharges the battery and supplied power for the electricity to crank the alternator recharges the battery and supplied power for the electricity to load
Starting motor: it requires electricity to crank the engine
Ignition system: it requires electricity to deliver sparks to the cylinders
Ancillary derives: such as light, horns, radio and air – conditioner all require electricity to operate
THE CONTROLS
Steer system: the steering system enable the driver to turn the front wheel to the left or right. This change the direction of a vehicle travel steering system. Stand at steering wheel in the front of the driver. Steering can be either manual or power assisted in manual steering, as the steering wheel is moved one way or the other a shaft is rotated in the steering gearbox. A gear converts the steering wheel action to the front wheels. In power assisted steering wheel turn, a power steering pump supplied hydraulic pressure, which more the connecting rods. In the way driver want to go not use muscle power. The hydraulic pressure provides the force.
Barks: barks stop forward motion of a car or it Bering it rest. Through the friction the can be drum brakes disc brakes or a combination of the two they can be manually applied or power assisted. Drum brakes operates by actuating metal shoes to which asbestos composition liming are attached. The friction between lining and drum stops the rotation of the drum. The disc brake work in similar way two linings, one on each side of the disc, squeeze the rotation disc (or rotor) to step the rotation of the wheel to move the brake shoes, hydraulic pressure from the master cylinder passes through steed lines to wheel cylinders. the wheel cylinders piston push the shoes into drum or disc in most cars today, this force is increased by a power booster,

THE SUPERSTRUCTURE
The main purpose of superstructure or car body is to provide accommodation for the driver and passengers, with suitable protection against wind and weather. The degrees of comfort provided depend upon the type of car and it cost. The modern automobile body is constructed of sheet formed to the required shape in giant punch presses. Most of the body components are welded together to from a light rattle free unit.