Differential and Axle shaft

1   Differential

When a vehicle is cornered the inner wheel moves through a shorter  distance than the outer  wheel. This means that the inner wheel must slow  down and the outer wheel must speed up. From  this it follows that if the  drive wheels were coupled directly to the crown wheel or, less commonly   the  worm wheel of the final drive, enforced scrubbing of the tyres would  occur during cornering as  the wheels sought to rotate at different speeds. This would result in not only rapid wearing of the  tyres, but also a virtually unmanageable vehicle.

In practice, the drive wheels are coupled to the final drive through  separate driving shafts and  a differential gear, a device which not only  accommodates the differing speeds of the drive wheels  but also  equalizes  all times the axle torque distributed between them.

The principle of the bevel type differential can be seen if the unit is considered as two discs and  a lever. When the vehicle is travelling straight, the lever will divide the driving force  equally and both dises will move the same amount. When the vehicle corners, the driving force will  still be divided equally but the inner disc will now move through a smaller distance; this will cause  the lever to pivot about its center which will prize forward the outer disc to give it a greater move- ment. This action shows that the torque applied to each driving wheel is always equal, hence the  differential is sometimes called a torque equalizer.

2 Axle Shaft and Rear Hub Arrangement

The axle shaft (half shaft) connects the differential sun wheel to the road wheel. Most  vehicle use " banjo" type of rear axle casing, so the axle shaft is  splined to the differential to  shaft to be withdrawn