US Patent 7721621 Bicycle shift control mechanism

A bicycle shift control mechanism that has an operating member, a wire take up member, a positioning ratchet and a position maintaining pawl. The operating member is movable between a rest position, a shift wind position and a shift releasing position. The positioning ratchet includes a plurality of winding teeth, a plurality of positioning teeth and a plurality of movement restricting teeth. The positioning teeth and the movement restricting teeth are non-concentrically arranged to form stair shaped arrangements. The position maintaining pawl selectively holds and releases the positioning ratchet upon movement of the operating member from the rest position.