A differential is a device, usually but not necessarily employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways. In one way, it receives one input and provides two outputs; this is found in most vehicles. In the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.
In an car and other wheeled vehicles, the differential allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them.
Types of Differential
Epicyclic gearing is used here to split torque asymmetrically.The input shaft is the green hollow one, the yellow is the low torque output and the pink is the high torque output. The force applied in the yellow and the pink gears is the same, but since the arm of the pink one is 2x-3x bigger the torque will be 2x-3x higher.
An epicyclic differential uses epicyclic gears to split torque asymmetrically between the front and rear axles. An epicyclic differential is at the heart of the Toyota Prius automotive drive train, where it interconnects the engine, motor-generators, and the drive wheels (which have a second differential for splitting torque as usual). It has the advantage of being relatively compact along the length of its axis (that is, the sun gear shaft).
Epicyclic gears are also called planetary gears because the axes of the planet gears revolve around the common axis of the sun and ring gears that they mesh with and roll between. In the image, the yellow shaft carries the sun gear which is almost hidden. The blue gears are called planet gears and the pink gear is the ring gear or annulus.
This is another type of differential that was used in some early automobiles, more recently the Oldsmobile Toronado, as well as other non-automotive devices. It consists of spur gears only.
A spur-gear differential has two equal-sized spur gears, one for each half-shaft, with a space between them. Instead of the miter gear assembly (the "spider") at the center of the differential, there is a rotating carrier on the same axis as the two shafts. Power from a prime mover or transmission, such as the drive shaft of a car, rotates this carrier.
Mounted in this carrier are one or more pairs of identical pinions, generally longer than their diameters, and typically smaller than the spur gears on the individual half-shafts. Each pinion pair rotates freely on pins supported by the carrier. Furthermore, the pinions pairs are displaced axially, such that they mesh only for the part of their length between the two spur gears. The remaining length of a given pinion meshes with the nearer spur gear on its axle. Therefore, each pinion couples that spur gear to the other pinion, and in turn, the other spur gear.
When the drive shaft rotates the carrier, its relationship to the gears for the individual wheel axles is the same as that in a miter-gear differential. differentialis an unit which supply the equa speed in runing condition but in case of veichile take a turan that time it not divided equal speed itprovide one is slower & oter is faster as compare to other wheel
Steam engine differential
Details required to explain this photo opposite
Part extract of wikipedia article (to define a commonly used term) See http://en.wikipedia.org/wiki/Differential_(mechanical_device) For full article.