Power unit for motor-assisted bicycle

摘要

To minimize the generation of a gear noise from a reduction gear train in a power unit for a motor-assisted bicycle, the reduction gear train being provided between a power transmitting member and an electric assisting motor, the power transmitting member being rotatably supported to a casing and operatively connected to a rear wheel, for transmitting torque from a crankshaft, the electric assisting motor being mounted to the casing and having a motor shaft whose axis is parallel to the axis of the crankshaft, the axial length of the motor along the axis of the motor shaft being smaller than the axial length of the crankshaft. At least an outer circumferential portion of at least one specific gear 76 of plural gears 74, 76, 77, 78, 81, and 82 constituting a reduction gear train 57 is formed of a synthetic resin.