Torsen differentials are a derivative of open differentials. They derive their name from their function - Torque-Sensing. When the torque going to both outputs is the same, a Torsen differential essentially works just like an open differential. The change comes when the torque going to each output begins to change, for example as a result of a slippery road surface under one wheel. When this happens, what's known as an Invex gear train (inside the differential) begins to bind together.