How does a Torsen differential limit slip between the wheels?

A Torsen differential limits slip between the wheels through a torque-sensing mechanism that relies on worm gears and spur gears. Unlike an open differential, which transmits equal torque to both wheels regardless of traction, a Torsen differential biases torque towards the wheel with more traction. A Torsen differential uses sets of worm gears and spur gears to connect the two axles. The worm gears can only transmit torque from the carrier to the side gears (axles), not from the side gears back to the carrier. This creates a "torque bias ratio." When one wheel starts to slip, the Torsen differential senses the reduced torque on that wheel. Due to the worm gear design, it resists the difference in torque between the two wheels. This resistance causes more torque to be transferred to the wheel with better traction. The amount of torque bias is determined by the torque bias ratio, which is a design parameter of the differential. For example, a Torsen differential with a 3:1 torque bias ratio can transmit up to three times more torque to the wheel with traction than to the wheel that is slipping. This significantly improves traction and acceleration, especially in slippery conditions. Unlike locking differentials, a Torsen differential operates smoothly and automatically without any driver intervention. It also allows for some differential action during cornering, unlike a fully locked differential. However, a Torsen differential requires some torque on both wheels to function. If one wheel is completely off the ground and has zero traction, it will not be able to transfer any torque to the other wheel. For example, if a tractor with a Torsen differential has one wheel lifted completely off the ground, it will behave like an open differential, and the tractor will not be able to move forward.