Working Of DIFFERENTIAL Gear box For Automobile Vehicles

When a four wheeler (car) takes a turn, the outer wheel turns faster than inner wheel. Thus, there is relative movement between inner and outer wheel. The function of the differential is to permit the relative movement between inner and outer wheels when vehicle negotiates (takes) a turn. The torque transmitted to each rear wheel is equal in this case, although their speed is different.

The differential is made up of a system of gears which connect the propeller shaft and rear axles. It is a part of inner axle housing assembly. The assembly consists of differential, rear axles, wheels and bearings.

Construction and Working

Differential Gear Box
Differential Gear Box 
The construction of a simple differential is shown in Figure . It consists of sun gears, planet pinion, a cage, a crown wheel and a bevel pinion. A sun gear is attached to inner end of each rear axle (half shaft). A cage is attached on left axle. A crown gear is attached to the cage and the cage rotates with the crown gear. The crown gear is rotated by the bevel pinion. Crown gear and cage remain free on the left rear axle. Two planet pinions are on a shaft which is supported by the cage. The planet pinions mesh with the sun gears. The rear wheels are attached to outer ends of two rear axles. When the cage rotates, sun gears rotate. Thus, the wheels also rotate. In case one inner wheel runs slower than other when the vehicle takes a turn, the planet gears spin on their shaft, transmit more rotary motion to outer wheel. When vehicle runs in straight line, the crown gear, cage, planet pinions and sun gears turn together as a unit. Thus there is no relative motion.


There are three types of differential :
(a) Conventional type,
(b) Non-slip or self locking type, and
(c) Double reduction type.

1) Conventional Type
Conventional type differential described in Section 5.6 delivers same torque to each rear wheel. If any of the wheels slips due to any reason the wheel does not rotate and vehicle does not move.
2) Non-slip or Self Locking Type
Non-slip or self locking type differential overcomes this drawback. It construction is similar to that of conventional type differential. But, two sets of clutch plates are provided additionally. Also, the ends of planet shafts are left loose in notches provided on the differential cage.
3) Double Reduction Type
Double reduction type differential provides further speed reduction by additional gear. This type of differential is used in heavy duty automobiles which require larger gear reduction between engine and wheels.
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