torsen automatically locking differential
The Torsen differential is a mechanical self-locking centre differential which regulates the power between the front and rear axles according to demand. The word "Torsen" is made up of the words "torque" and "sensing", indicating that the differential operates on the basis of torque sensing. It responds to varying rotational forces between the input and output shafts (front and rear axle). This enables variable distribution of the driving torque between the axles. On a Torsen differential the two output gears are interconnected by worm gears. They limit high differential rotation speeds, but still balance the speeds when cornering.
The main disadvantage of the Torsen differential is when no torque is sensed on one of the axles, the differential does not lock. Torsen differential is not capable of transferring 100% of torque to one of the axles. In real life this means that when a single axle loses grip completely (very low traction on ice, or if wheels raised in the air) the car is not able to move.
See Audi Q5 quattro vs. BMW X3 xDrive rollers test
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The original Torsen T-1 (Type A) uses crossed axis helical gears to increase internal friction. The Type I can be designed for higher torque bias ratios than the Type II, but typically has higher backlash and the potential for Noise, Vibration, and Harshness (NVH) issues, and requires a precise setup/installation.
Figure: T-1 (Type A) (47KB)
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