US Patent 7481307 Torque transmission apparatus

The torque transmission apparatus is simple, small and light and has a clutch unit to receive thrust and transmit torque between rotary members, a differential screw mechanism to convert rotational force into the thrust applied to the clutch unit, and an electric motor to produce the rotational force. The differential screw mechanism has a driving screw and driven screws. The driving screw is rotatably and axially movably supported on a rotary drive shaft of the electric motor. The driven screws mesh with the driving screw and are rotatably and axially immovably supported. The meshing driving screw and driven screws are rotated to axially move the driving screw and apply engaging force to the clutch unit.