Vehicle seat reclining device

1. A seat reclining device for swingably connecting a seat back to a seat cushion, the seat reclining device comprising:

a base member connected to one of the seat back and the seat cushion;

a rotating member connected to the other of the seat back and the seat cushion, the rotating member being rotatable relative to the base member, an internal gear being formed on an inner peripheral surface of the rotating member;

a lock tooth having an external gear, which is engageable with the internal gear of the rotating member, the lock tooth being swingable in directions of engaging and disengaging the external gear with and from the internal gear, the lock tooth having a bearing portion which has an arc shaped bearing surface;

a shaft portion integrally formed with the base member, the shaft portion having an inner-periphery guiding surface, wherein the bearing surface of the lock tooth slides in contact with the inner-periphery guiding surface of the shaft portion, the shaft portion being aligned with the external gear along a circumferential direction about a rotational center of the rotating member;

a pair of guide portions integrally formed with the base member;

a cam pushing the lock tooth to engage the external gear with the internal gear; and

a weak portion which is formed at an end portion of the lock tooth opposite to the external gear across the shaft portion, and induces a breakage or deformation of the end portion.

2. The seat reclining device as claimed in claim 1 , wherein the lock tooth has a slide outer-peripheral surface which slides in contact with an outer-periphery guiding surface of one of the guide portions, at a diametrically inner position of the lock tooth about the rotational center of the rotating member, and the weak portion is disposed at a diametrically outer position of the lock tooth about the rotational center of the rotating member.

3. The seat reclining device as claimed in claim 1 , wherein the weak portion is formed by decreasing a width of the end portion of the lock tooth as compared with other portions of the lock tooth.

4. The seat reclining device as claimed in claim 1 , wherein the weak portion is made soft in strength as compared with other portions of the lock tooth.

5. The seat reclining device as claimed in claim 1 , wherein the lock tooth is supported by the shaft portion and one of the guide portions when a load of that relatively rotates the rotating member with respect to the base member occurs.

6. The seat reclining device as claimed in claim 5 , wherein both end portions of the inner-periphery guiding surface of the shaft portion act as a pair of guide contact surfaces in contact with the lock tooth.

7. The seat reclining device as claimed in claim 6 , wherein a projection for absorbing stress is integrally formed with the shaft portion at one of the guide contact surfaces opposite to the external gear.

8. The seat reclining device as claimed in claim 7 , wherein an inner-periphery side clearance is formed between the inner-periphery guiding surface and the bearing surface of the lock tooth opposite to the inner-periphery guiding surface, and between the pair of the guide contact surfaces.

9. The seat reclining device as claimed in claim 8 , wherein an outer-periphery guiding surface for sliding in contact with the lock tooth is formed on a surface of one of the guide portions facing with the lock tooth, and an outer-periphery side clearance is formed at an inner gear side of the outer-periphery side guide surface and between the one of the guide portions and the lock tooth.

10. A vehicle seat reclining device comprising:

a seat cushion;

a seat back swingably connected to the seat cushion;

a base member connected to one of the seat back and the seat cushion;

a rotating member connected to the other of the seat back and the seat cushion, the rotating member being rotatable relative to the base member, an internal gear being formed on an inner peripheral surface of the rotating member;

a lock tooth having an external gear, which is engageable with the internal gear of the rotating member, the lock tooth being swingable in directions of engaging and disengaging the external gear with and from the internal gear, the lock tooth having a bearing portion which has an arc shaped bearing surface;

a shaft portion integrally formed with the base member, the shaft portion having an inner-periphery guiding surface, wherein the bearing surface of the lock tooth slides in contact with the inner-periphery guiding surface of the shaft portion; and

a cam pushing the lock tooth to engage the external gear with the internal gear;

wherein the lock tooth has a weak portion which is formed at an end portion of the lock tooth opposite to the external gear across the shaft portion, and which induces a breakage of deformation of the end portion.