Patent ID: 8616649

Claim:
A pivotal device of a vehicle seat having a lock mechanism, comprising: a disc-shaped ratchet and a guide that are axially fitted on and mounted to each other, such that the ratchet and the guide radially support each other while being rotatable relative to each other; a plurality of pawls supported by the guide and positioned around a circumferential surface of the guide, each of the pawls having external teeth adapted to mesh with internal teeth formed in a radially outer portion of the ratchet as each of the pawls move outward in radial directions of the guide, so as to inhibit the ratchet and the guide from rotating relative to each other; and an operating cam operable to push the plurality of pawls radially outward, relative to the guide, wherein at least one of the plurality of pawls is divided obliquely into a first part and a second part in a circumferential direction of the guide, the first and second parts being adapted to move in opposite circumferential directions when the operating cam pushes the at least one pawl radially outward, so that the at least one pawl increases a width thereof and is brought into meshing engagement with the internal teeth of the ratchet while eliminating clearances in the circumferential direction between the at least one pawl and the guide, and a protrusion is provided on the guide, and the operating cam is arranged to ride on the protrusion during movement thereof to push the plurality of pawls radially outward, so that reaction force is applied from the protrusion to the at least one pawl so as to push the at least one pawl to an overshoot position located radially outwardly of a position at which the at least one pawl meshes with the internal teeth, and the ratchet is pressed radially against the guide.