Automotive seat reclining device

1. An automotive seat reclining device for holding a seat back at a desired angle with respect to a seat cushion, comprising:

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

a pivot member coupled to the other of the seat cushion and the seat back, being pivotable relative to the base member and having gear teeth;

a shaft member integrally formed with the base member;

a lock member being swingable around the shaft member and having a shaft bearing surface and lock teeth engageable with the gear teeth;

a cam member for causing the lock member to swing along an arc path around the shaft member in a direction that brings the lock teeth into engagement with the gear teeth to prevent a pivotal movement of the pivot member relative to the base member and in a direction that disengages the lock teeth from the gear teeth to allow a pivotal movement of the pivot member relative to the base member; and

first and second guide members formed integrally with the base member at locations adjacent to respective ends of the swing path of the lock member so as to guide the lock member along the swing path and, under the application of a load that forces the pivot member to pivot relative to the base member, support the lock member by the shaft member and the second guide member,

wherein the shaft member has a shaft surface facing the shaft bearing surface of the lock member and including a pair of shaft surface sections to guide the lock member along the swing path and a stress absorbing protrusion formed integrally with one of the shaft surface sections located on an opposite side of the shaft member from the lock teeth.

2. The automotive seat reclining device according to claim 1 , wherein there is a gap left between the shaft bearing surface of the lock member and the shaft surface of the shaft member at a location between the stress absorbing protrusion and the other of the shaft surface sections.

3. The automotive seat reclining device according to claim 2 , wherein the gap becomes wider as the distance from the stress absorbing protrusion decreases.

4. The automotive seat reclining device according to claim 1 , wherein there is a gap left between portions of the lock member and the second guide member facing each other at a location adjacent to the gear teeth.

5. An automotive seat reclining device for holding a seat back at a desired angle with respect to a seat cushion, comprising:

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

a pivot member coupled to the other of seat cushion and the seat back, being pivotable relative to the base member and having gear teeth;

a shaft member formed integrally with the base member and having a cylindrical shaft surface;

a lock member being swingable along a path around the shaft member and having a shaft bearing surface facing the shaft surface, a pair of first and second opposite end surfaces positioned on the swing path of the lock member and lock teeth formed in the second end surface to be engageable with the gear teeth;

a cam member for causing the lock member to swing along the path around the shaft member in a direction that brings the lock teeth into engagement with the gear teeth to prevent a pivotal movement of the pivot member relative to the base member and in a direction that disengages the lock teeth from the gear teeth to allow a pivotal movement of the pivot member relative to the base member;

first and second guide members formed integrally with the base member at locations adjacent to the first and second end surfaces of the lock member, respectively, so as to guide the lock member along the path around the shaft member; and

a stress absorbing protrusion formed integrally with the shaft surface on an opposite side of the shaft member from the lock teeth.

6. The automotive seat reclining device according to claim 5 , wherein the shaft surface includes a shaft surface section positioned adjacent to the second end surface of the lock member to make sliding contact with the shaft bearing surface of the lock member and the stress absorbing protrusion has an end to make sliding contact with the shaft bearing surface of the lock member.

7. The automotive seat reclining device according to claim 6 , wherein there is a gap left between the shaft bearing surface of the lock member and the shaft surface of the shaft member at a location between the protrusion and the shaft surface section.

8. The automotive seat reclining device according to claim 7 , wherein the gap becomes wider as the distance from the protrusion decreases.

9. The automotive seat reclining device according to claim 5 , wherein there is a gap left between portions the lock member and the second guide member facing each other at a location adjacent to the gear teeth.