Patent ID: 6851497

Claim:
A power-assisted bicycle operable to provide an assisting power in accordance with a pedaling power acting on a drive shaft, comprising: a ratchet gear for transmitting a one-way rotation of said drive shaft to a sprocket, said ratchet gear including: a tooth part having a plurality of ratchet teeth; and a piece part having a plurality of ratchet pieces arranged such that said ratchet pieces engage said ratchet teeth during the one-way rotation and disengage said ratchet teeth during rotation in a direction opposite the one-way rotation, one of said tooth part and said piece part being mounted on said drive shaft via a rotation-prevention system operable to prevent rotation of said one of said tooth part and said piece part relative to said drive shaft and operable to allow sliding axial movement of said one of said tooth part and said piece part relative to said drive shaft, the other of said tooth part and said piece part being connected to said sprocket, said tooth part and said piece part being arranged such that a position of said piece part changes relative to a position of said tooth part according to a pedaling force in a direction of the one-way rotation; a detection system for detecting a physical parameter that varies due to the change of the position of said piece part relative to the position of said tooth part; and a control system for controlling the assisting power based at least in part on the physical parameter detected by said detection system.