DRIVING FORCE ASSISTING DEVICE FOR MOTOR ASSISTED BICYCLE

PROBLEM TO BE SOLVED: To provide a driving force assisting device suitable for a motor assisted bicycle and miniaturized by centralizing the mass of the driving force assisting device. SOLUTION: In a motor assisted bicycle assisting manual force to travel by transmitting driving force of a pedal manual driving means to a driving wheel through a driving transmission means and transmitting the driving force of a motor to the driving transmission means, the driving transmission means integrally has a pedal shaft 15 journalling a large diameter gear 31 through a one-way clutch 30, and a small diameter gear 32 provided with a torque detecting means 36 on a shaft to detect the deformation quantity deformed by manual force applied to the pedal shaft 15, as manual torque, and meshed with the large diameter gear 31 on the upper reaches of the torque detecting means 36. The driving transmission means is provided with power transmission shafts 33, 34 supporting a gear 55a for inputting the driving force of the motor 22 to the shaft through a one-way clutch 56, on the lower reaches of the torque detecting means 36. Unit cases 14, 18 rotatably supporting the pedal shaft 15 support the power transmission shafts 33, 34, and the motor 22 is integrally held behind the pedal shaft 15 and in front of a rear wheel 10.