Patent ID: 7144082

Claim:
A seat reclining apparatus for a vehicle, comprising: a base member connected to one of a seat cushion and a seat back rotatably fixed to the seat cushion; a rotational member having an internal gear formed at an inner peripheral surface of the rotational member, the rotational member being connected to other of the seat cushion and the seat back and rotatable relative to the base member in a peripheral direction of the rotational member; a lock tooth having an external gear which is engageable with the internal gear, the lock tooth being swingable in directions in which the external gear is engaged with and disengaged from the internal gear; a shaft section having an inner peripheral side guide surface for swinging the lock tooth along an arcuate orbit, the shaft section being formed integral with the base member; a pair of guide sections each of which has an outer peripheral side guide surface for swinging the lock tooth along the arcuate orbit and is formed integral with the base member and located in vicinity of opposite ends of the arcuate orbit; and a cam for biasing the lock tooth to engage the external gear with the internal gear, wherein the lock tooth has an outer peripheral side slide surface formed facing one of the guide sections on a side of the shaft section with respect to the external gear and slidably contacted with the outer peripheral side guide surface of the one of the guide sections; the one of the guide sections has a backup surface for receiving a load from the lock tooth when the load is high; the lock tooth has a contact face facing the backup surface through a clearance, so that a rotational load for rotating the rotational member relative to the base member is received by the shaft section and the one of the guide sections when the rotational load acts, wherein the one of the guide sections has a step portion formed between the outer peripheral side guide surface and the backup surface; the lock tooth includes a protruding section which faces the step portion and is located between the outer peripheral side slide surface and the contact face, so that a reactive force which the protruding section receives from the step portion when the protruding section is brought into contact with the step portion is directed a onto side of the cam with respect to a tangential plane to a bearing surface of the lock tooth, the tangential plane passing the step portion, the bearing surface being slidably contacted with the inner peripheral side guide surface of the shaft section.