Hilfsantrieb für Fahrrad

摘要

A power assist apparatus of a power assisted bicycle comprises a crank shaft (33) extending in the transverse direction of the body of the bicycle and rotatably driven by a footpedal- propelling, an electric motor for generating an assist power, a power composition shaft (84) rotatably supported and extending in parallel with the crank shaft, a footpedal- propelling power transmission mechanism (102) for transmitting the footpedal-propelling power to the power composition shaft at a right angle to the axis of the power composition shaft, an assist power transmission mechanism (101) for transmitting the assist power to the power composition shaft at a right angle to the axis of the power composition shaft in the direction opposite to the direction in which the footpedal-propelling power is transmitted, a power composition output mechanism (103) for outputting the rotating power of the power composition shaft to a driven wheel, a moment sensor for sensing a moment difference between two moments acting on the power composition shaft from two opposite directions when the footpedal-propelling power and the assist power are transmitted, and a control unit (41) for calculating the assist ratio of the assist power to the footpedal-propelling power based on the magnitude and direction of the moment difference coming in from the moment sensor (106) and controlling the output of the electric motor so that the assist ratio is kept constant.