Transverse Engine Front Wheel Drive

transmits the drive from the gearbox mainshaft (output shaft) A universal joint fitted to both ends of the propshaft allows the engines turning motion to be sent through varying angles The Propeller Shaft transmits the drive from the gearbox mainshaft (output shaft) to the final drive pinion,it is made of tubular section to reduce weight and is balanced to reduce vibration The distance between gearbox and rear axle changes due to suspension movement

Universal Joints A universal joint is a device that can transmit (send) the engines turning effort/motion (torque) through varying angles. A shaft which receives its drive from a Hooke type universal joint, varies its speed when rotating, fitting a second universal joint restores a constant rotational speed. The vehicles propshaft is fitted with two Hooke type universal joints Front wheel drive arrangements use a constant – velocity type universal joint, as this joint does not cause a change in the speed of rotation (velocity) of the driveshaft not matter what the angle

The Final Drive Rear Axle, Rear Wheel Drive Front Wheel Drive Transaxle Before reaching the the road wheels, the engines drive has to pass through the final drive which is located in the rear axle on RWD vehicles and in the transaxle in FWD vehicles. Its main purpose is to turn the drive through 90 degrees in RWD layouts and reduce to the speed of the propshaft or driveshafts (FWD) to a speed suitable for the road wheels e.g. if the engine flywheel is rotating at 6000 rev/min, this has to reduced before being passed to the road wheels, which even at 70mph may only be rotating at 1000 rev/min. The gear ratio provided by the final drive reduces the speed and increases the engine torque, however unlike the gearbox this ratio is fixed.

Transmission/Final Drive/Rear Wheel Drive (Crown Wheel and Pinion) Bevel gears mesh (contact) at a 90 degree angle The teeth on the gears may be straight or curved. Crown Wheel Pinion Straight tooth bevel – the pinion is fitted on the centre line of crown wheel, cheap to produce, high efficiency but noisy. Spiral bevel – quiet in operation but has high tooth pressures

Transmission/Final Drive/Rear Wheel Drive (Crown Wheel and Pinion) Hypoid – the pinion is fitted below the centre line of the crown wheel, the propshaft can be set lower.The pinion is very strong and quiet in operation. Special high pressure oil is required as well as strong bearings. Hypoid has a low mechanical efficiency. Transmission/Final Drive/Rear Wheel Drive (Crown Wheel and Pinion)

The Differential When the car goes round a bend, the inner wheel has to travel a shorter distance than the outer. If both driven wheels were rotated by one solid shaft, they would have to rotate at the same speed, causing the inner wheel to skid, resulting in excessive tyre wear and poor handling. To prevent this, the drive from the engine is divided by the differential between two halfshafts or driveshafts. Each shaft is driven independently by the differential,so as the inner wheel slows, the outer speeds up, one disadvantage of the this arrangement is that if one wheel looses grip and just spins, the other will not be driven,possilby leaving the vehicle unable to move The Outer Wheel Travels A Greater Distance

Operation Of The Differential When travelling in a straight line, equal force is applied to both sun gears(which drive the half shaft/drive shafts) by the planet gears, which rotate with the crown wheel, but do not turn on their own pivots. When cornering equal force is still applied to both sun gears, but to allow for the change in speed and distance the inner wheel has to travel, the planet gears start to turn on their own pivots and rotate around the sun gears. Operation Of The Differential