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Differential unit for a rear-wheel drive car, built by ZF c. 2004 Differential gears (in yellow) in a punched tape reader, built by Tally c. 1962 A differential is a gear train with three drive shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others.
The predecessor of modern electronic traction control systems can be found in high-torque, high-power rear-wheel-drive cars as a limited slip differential.A limited-slip differential is a purely mechanical system that transfers a relatively small amount of power to the non-slipping wheel, while still allowing some wheel spin to occur.
A locking differential is a mechanical component, commonly used in vehicles, designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel ...
Viscous couplings are used as the center differential in cars such as the Toyota Celica GT-Four, and also as a limited slip differential (LSD) in rear axles. They offer a cheaper way to implement four-wheel-drive than technologies like the mechanical-transfer Torsen differentials.
When cornering, the inner and outer wheels rotate at different speeds, because the inner wheels describe a smaller turning radius. The electronic differential uses the steering wheel command signal and the motor speed signals to control the power to each wheel so that all wheels are supplied with the torque they need.
If the traction difference exceeds the TBR, the outer tire gets the tractive torque of the inner wheel multiplied by the TBR, and the remaining applied torque to the differential contributes to wheel spin up. When a Torsen differential is employed, the slower-moving wheel always receives more torque than the faster-moving wheel.
A torque vectoring differential requires an electronic monitoring system in addition to standard mechanical components. This electronic system tells the differential when and how to vary the torque. Due to the number of wheels that receive power, a front or rear wheel drive differential is less complex than an all-wheel drive differential.
In 1932, Ferdinand Porsche designed a Grand Prix racing car for the Auto Union company. The high power of the design caused one of the rear wheels to experience excessive wheel spin at any speed up to 160 km/h (100 mph). In 1935, Porsche commissioned the engineering firm ZF to design a limited-slip differential to improve performance.