Mar
21
2015

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What’s a Differential and Why Does It Matter?

A differential is a type of simple planetary gear that consists of a drive shaft as the input and two drive wheels as the outputs. The differential has the property that angular velocity of the carrier is the mean average of the angular velocities of the annular and sun gears.

**There are two basic types of differentials**
Epicyclic/planetary differential: This differential uses an epicyclic gearing to split and asymmetrically apportion torque between the rear and the front axles. In some vehicles, an epicyclic differential interconnects the engine, motor generators and the drive wheels. The advantage of an epicyclic differential is that it is relatively compact along the axis length (the sun gear shaft).
Spur gear differential. This differential is composed of spur gears only. It is made of two equally sized spur gears, one for each half shaft, with a gap between them. There is a rotating carrier on the same axis as the two shafts. Torque from a transmitter rotates this carrier.

**Differentials are very important especially in the automobile industry**
They allow the outer drive wheel to rotate faster that the inner drive wheel when a vehicle is turning, making the wheel traveling around the outer turning curve roll further and faster than the other. The input rotational speed of the drive shaft is equivalent to the average of the rotational speed of the two driving wheels. Therefore, an increase in velocity of one wheel is balanced by a reduction in velocity of the other.
A differential connects the input shaft to the pinion. The differential may connect to half shafts inside a drive shafts connecting to the rear wheel drive vehicles.
For front wheel drive vehicles, the pinion is found on the end of the prime shaft of the gear box. The differential is usually enclosed in the same casing as the gearbox. Front wheel drive vehicles have individual drive shafts to each wheel.
Differentials also have non-automotive uses. They can be used in performing analog arithmetic. Two of the three differential drive shafts are rotated through angles representing two numbers. The angle of the third shaft’s rotation represents the sum of the difference of the two input numbers.
Anti-kythera mechanism uses a differential gear to control a sphere representing the moon from the difference between the moon and the sun position pointers. This Mechanism graphically shows the phase of the moon at that particular point. Differentials can also be used to calculate the direction in which a gun should be aimed.

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Last Updated on 03 May 2015