1. Field of the Invention Deferent
The present invention relates to seat reclining mechanisms for adjusting a tilt angle of a seat back of a seat (e.g., a vehicle seat). More particularly, the present invention relates to seat reclining mechanisms that have a high load resistance when the seat back is tilted.
2. Description of the Related Art
Typically, a vehicle seat comprises a seat back and a seat cushion. The seat back and the seat cushion are rotatably interconnected via a seat reclining mechanism for adjusting a tilt angle of the seat back. Such a seat reclining mechanism is taught, for example, by Japanese Laid-Open Patent Publication Number 2002-119349.
The known seat reclining mechanism includes a pair of opposing disk-shaped housings, i.e., a first or stationary housing and a second or rotational housing. The first housing is affixed to the vehicle seat cushion. The second housing is affixed to the vehicle seat back. The first and second housings are circumferentially connected by an annular fastener or clip ring along peripheral edges thereof, so that the second housing can move or rotate around a rotational shaft relative to the first housing.
The seat reclining mechanism further includes a locking means that can prevent the second housing from rotating relative to the first housing, so as to lock the seat reclining mechanism. The locking means essentially consists of a cam member and two pairs of slide pawls that are received within the housings. The cam member is secured to or integrally formed with the rotational shaft, so as to rotate with the rotational shaft. The slide pawls are slidably received between guide members that are formed within the first housing, so as to radially move on the first housing. As will be recognized, the slide pawls are appropriately shaped such that “desired clearances” are produced between the slide pawls and the guide members. In addition, each of the slide pawls is provided with a convex toothed portion.
When the rotational shaft is rotated to a locking position, the pawls are radially moved outward by the cam member, so that the respective convex toothed portions of the pawls engage a concave toothed portion that is circumferentially formed over an inner circular surface of the second housing peripheral edge. In this state, the second housing (i.e., ratchet) is prevented from rotating relative to the first housing, so that the seat reclining mechanism is locked. As a result, the seat back is locked in position relative to the seat cushion.
Often times, when the seat back is locked, a substantial force can be unexpectedly applied to the seat reclining mechanism in a direction to forwardly tilt the seat back relative to the seat cushion. The force may act as a rotational moment or torque that may force the second housing to rotate relative to the first housing. As a result, the slide pawls may be forced against the corresponding guide members. That is, such a force may be exerted on and received by the four slide pawls. However, if the clearances formed between the slide pawls and the guide members are not equal to each other (i.e., if the clearances have manufacturing variations), such a force is concentrated on only a specific slide pawl that corresponds to the smallest clearance. That is, the force is not evenly received by the four slide pawls. Consequently, the seat reclining mechanism may not achieve the best performance. Many approaches have been made in order to reduce the variations among the clearances. However, all of the approaches have resulted in an increased manufacturing cost.