How does a differential work?

Answer 1

From Wikipedia: The following description of a differential applies to a "traditional" rear- or front-wheel-drive car or truck: Power is supplied from the engine, via the transmission or gearbox, to a drive shaft (British term: propeller shaft, more commonly abbreviated to "prop-shaft"), which runs to the differential. A spiral bevel pinion gear at the end of the propeller shaft is encased within the differential itself, and it meshes with the large spiral bevel ring gear (British term: crown wheel). (The ring and pinion may mesh in hypoid orientation, not shown.) The ring gear is attached to a carrier, which holds what is sometimes called a spider, a cluster of four bevel gears in a rectangle, so each bevel gear meshes with two neighbors and rotates counter to the the third, that it faces and does not mesh with. Two of these spider gears are aligned on the same axis as the ring gear and drive the half shafts connected to the vehicle's driven wheels. These are called the side gears. The other two spider gears are aligned on a perpendicular axis which changes orientation with the ring gear's rotation. These two gears are just called pinion gears, not to be confused with the main pinion gear. (Other spider designs employ different numbers of pinion gears depending on durability requirements.) As the carrier rotates, the changing axis orientation of the pinion gears imparts the motion of the ring gear to the motion of the side gears by pushing on them rather than turning against them (that is, the same teeth stay in contact), but because the spider gears are not restricted from turning against each other, within that motion the side gears can counter-rotate relative to the ring gear and to each other under the same force. Thus, for example, if the car is making a turn to the right, the main ring gear may make 10 full rotations. During that time, the left wheel will make more rotations because it has further to travel, and the right wheel will make fewer rotations as it has less distance to travel. The side gears will rotate in opposite directions relative to the ring gear by, say, 2 full turns each (4 full turns relative to each other), resulting in the left wheel making 12 rotations, and the right wheel making 8 rotations. The rotation of the ring gear is always the average of the rotations of the side gears. This is why if the wheels are lifted off the ground with the engine off, and the drive shaft is held (preventing the ring gear from turning inside the differential), manually rotating one wheel causes the other to rotate in the opposite direction by the same amount. When the vehicle is traveling in a straight line, there will be no differential movement of the planetary system of gears other than the minute movements necessary to compensate for slight differences in wheel diameter, undulations in the road (which make for a longer or shorter wheel path), etc.

Answer 2

The differential gears, commonly referred to as the "rear end," in a vehicle serves to convert the rotating motion of the driveshaft from the engine and converts it to motion that can be used to power the vehicle forward or backward. The differential gear is position under the vehicle at the rear, dead center between the rear wheels. The differential gear is a large cog or wheel that has grooves carved around the edge. These grooves line up with the grooves on the rear axle on which the rear wheels are mounted. The engine runs, turns the crankshaft, which spins the driveshaft, which is connected to the differential gear or rear end. The rear end then transfers the motion to the rear axle, which makes the rear wheels turn.