A ratchet clutch is an overrunning clutch, divided into two types of external and internal ratchet clutch. Common internal ratchet ratchet clutch clutch ratchet, clutch, clutch bearing PIN pin, clutch spring and pawl and the round form. In the presence of springs, and pawls on the front-end is always, Embedded in the teeth of the ratchet slot. When the engine starts, the ratchet clockwise rotation under connecting shaft, and rotate pawl. In clutch device PIN of role Xia, pawl led dial round rotating, at ratchet clutch device in closing state; Dang launched started Hou, dial round and pawl reached must of speed, in centrifugal force of role Xia, pawl end dumped out, to clutch device PIN for Center rotating, pawl front-end overcome clutch device spring of stretch Hou and ratchet tooth slot slot end of separation, pawl in off open State, Ratchet and dial round to their of speed rotating, non interference. Ratchet clutch is widely used on the bike to achieve one-way transmission for bicycle wheel.