A power transfer device for the mobility of a wheelchair for the physically challenged on inclined planes comprises a winch (58) driven by a motor (60). The winch (58) comprises a belt reel (62) rotationally connected to the motor (60), a drive belt (64) wound round the reel (62) and equipped with at least one hook (66) for fastening to the wheelchair (2), and a control unit (68) for driving the motor (60). The power transfer device also comprises a command device (70) which can be connected to the control unit (68) and which can be operated manually by a user in order to allow the user to adjust the advancing speed of the wheelchair (2) in real time.
