Patent ID: 8721481

Claim:
A motor unit comprising: a motor shaft for receiving a motor provided driving force; an auxiliary shaft for receiving an externally provided driving force: a first torque transmission path for transferring the externally provided driving force to a drive mechanism; a second torque transmission path for transferring the motor provided driving force to said drive mechanism, the second torque transmission path comprising the motor shaft and a gear mechanism mechanically coupling the motor shaft to the drive mechanism; wherein a first one way drive means is provided in the first torque transmission path between the auxiliary shaft and the drive mechanism such that when the drive mechanism is being driven by the motor provided driving force through the second torque transmission path, the auxiliary shaft is able to freewheel, wherein the gear mechanism has a reduction gear ratio and operates to transfer the motor provided driving force from the motor shaft to the drive mechanism at said reduction gear ratio, the gear mechanism comprising a planetary gear mechanism having a planet gear whose axis of rotation is offset by a predetermined amount with respect to the axis of rotation of the motor shaft; the planet gear being rotatably supported on an eccentric wheel whereby the planet gear is made to rotate as the eccentric wheel rotates and whereby the position of the axis of rotation of the planet gear changes relative to the axis of rotation of the motor shaft as the planet gear rotates such that the varying position of the axis of rotation of the planet gear defines a circle centered on the axis of rotation of the motor shaft, said circle having a radius equal to the predetermined amount.