The differential transmission shall distribute the torque when multi-track vehicles with two drive wheels or four-wheel drive and at the same time rotational speed differences compensate, e.g. when cornering. It thus reduces the wear of possibly scraping tyres.
It is also called 'differential'. The spur-wheel differential uses planet gears to compensate, however, this mostly occurs through four bevel wheels (picture above) which are all meshed with each other.
The drive takes place via the casing (picture 2) on two opposing to each other compensating bevel wheels. When driving straight ahead they do not rotate. The whole bevel wheel gear-set revolves as a block and transmits the torque to both axle shaft wheels evenly.
Only when there are rotational speed differences (e.g., when cornering) between the two axle shaft wheels, both differential bevel pinions rotate in opposite direction on their shafts in the casing. The torque is always evenly distributed to both driven wheels. The wheel with the greatest slip determines the transferable torque. It is the highest when the slip of both wheels is about 0% - precisely 0% is impossible when driving. To prevent wheel-spinning of a driven wheel, and to achieve the transferable torque, a differential lock is necessary.
With rotational speed differences between the side gears, the one wheel rotates accordingly slower as the other wheel rotates faster. In extreme cases, one wheel stands still, while the other turns twice as fast. Differential gears also exists between the axles of a permanent all-wheel drive. The picture above shows that also the middle rotational speeds of the front and rear axles differ when cornering. 05/15