# Differential Gear of an Automobile

The differential gear used in the rear drive of an automobile is shown in fig:

## Function of Differential Gear:

1. To transmit motion from the engine shaft to the rear driving wheels and

2. To rotate the rear wheels at different speeds while the automobile is taking a turn.

## Explain the Differential Gear of an Automobile:

As long as the automobile is running on a straight path, the rear wheel are driven directly by the engine and speed of both the wheels is same. But when the automobile is taking a turn, the outer wheel will run faster than the inner wheel because at that time the outer rear wheel has to cover more distance than the inner rear wheel. This is achieved by epicyclic gear train with bevel gears as shown in fig:

The bevel gear A known as pinion. It is keyed to the propeller shaft driven from the engine shaft through universal coupling. This gear A drives the gear B known as crown gear which rotates freely on the axle P. Two equal gears C and D are mounted on two separate parts P and Q of the rear axles respectively. These gears, in turn, mesh with equal pinions E and F which can rotate freely on the spindle provided on the arm attached to gear B.

When the automobile runs on a straight path, the gears C and D must rotate together. These gears are rotated through the spindle on the gear B. The gears E and F don’t rotate on the spindle. But when the automobile is taking a turn, the inner wheel should have lesser speed than the outer rear wheel and due to relative speed of the inner and outer gear D and C. The gears E and F start rotating about the spindles axis and at the same time revolve about the axle axis.