1. Field of the Invention
The present invention relates to a seat back of vehicle seat with a movable headrest. In particular, the invention is directed to a structure of seat back of seat for vehicle which permits a headrest mounted in the seat back to be displaceable in forward and upward directions in response to a rear-end collision occurred to the vehicle.
2. Description of Prior Art
Among vehicle seats with headrest, there has been known a vehicle seat of such type that, responsive to a rear-end collision, a headrest mounted thereon is subjected to forward movement under a backward force of inertia applied from a lumbar part of the occupant and moved toward a head portion of occupant on the seat. For example, the Japanese Laid-Open Patent Publication No. 2001-26232 discloses the vehicle seat of this kind. According thereto, the seat back thereof includes a seat back frame and an auxiliary frame, such that a lower portion of the auxiliary frame is rotatably connected via a lower link with the seat back frame. A headrest is fixed on the top of the auxiliary frame to support a head of seat occupant, while a pressure receiving portion is provided in the lower region of the auxiliary frame at a point where a lumbar part of the seat occupant is positioned. Normally, the auxiliary frame is set at a given lower home position and the headrest is thus set at a lower home position. When a rear-end collision occurs, a backward load is applied to that pressure receiving portion from the seat occupant's lumbar part which is moved backwardly under a backward inertia of the seat occupant. Then, due to such backward load, the auxiliary frame is rotated in forward and upward direction relative to the lower link, which causes simultaneous forward and upward displacement of both headrest from the lower home position, thereby providing a quick support to the occupant's head and upper body portion.
In the foregoing conventional seat back structure, the auxiliary frame is movably supported by an upper guide pin and a lower link with respect to the seat back frame, such the upper guide pin is slidably engaged in a guide hole formed in the seat back frame, whereas the lower link is movably connected with the seat back frame. Due to such arrangement, the auxiliary frame and headrest are merely free to move either in a forward and upward direction or a backward and downward direction, along a given path, without any means for restricting the movement of the auxiliary frame itself. Thus, when a rear-end collision occurs, a head of seat occupant is certainly given a quick support by the forward and upward movement of the headrest, but, shortly after that emergency headrest support, the auxiliary frame is abruptly moved back, or moved in the backward and downward direction, under a backward inertia of the seat occupant's upper body portion, as a result of which, the headrest is also abruptly returned to the lower home position. Consequently, it is highly possible that the seat occupant's head will be abruptly inclined backwards to receive a great impact, and therefore, the seat occupant's head and neck portion will be seriously damaged. This requires an improvement of seat back structure to prevent such abrupt return of the auxiliary frame or headrest in order to protect the seat occupant's head and neck portion.
In view of the afore-stated drawbacks, it is a purpose of the present invention to provide an improved seat back structure in a vehicle seat, which effectively prevent the above-discussed abrupt return of the auxiliary frame or headrest in the case of rear-end collision.
In order to achieve such purpose, a seat back structure in vehicle seat in accordance with the present invention is basically comprised of:
Other various features and advantages will become apparent from reading of the description hereinafter, with reference to the annexed drawings.
Referring to
Designation (12) denotes a headrest provided on the auxiliary frame (16). Namely, the headrest (12) has a pair of headrest stays (22) (22), each being securely inserted in the respective pair of known cylindrical holders (20) (20) fixed to the horizontal top portion (16b-1) of the upper frame member (16b) of the auxiliary frame (16). As understandable from
The foregoing two-frame construction of seat back (SB), i.e. the combination of seat back frame (14) and auxiliary frame (16), is however known from the previously noted Japanese Laid-Open Patent Publication No. 2001-26232. Likewise as in such prior art, the auxiliary frame (16) is displaceable responsive to a rear-end collision so as to cause forward displacement of the headrest (12) toward a head of seat occupant. In brief, subject to a rear-end collision occurring, a backward inertia is generated at a seat occupant's lumbar part (designated by (PL) in
In accordance with the present invention, as generically indicated in
As far as the
It should be noted that the term, “forward” or “forwardly”, refers to a side (FW) forwardly of the backrest framework (BF) or seat back (SB), whereas the term, “backward”, “backwards”, or “backwardly”, refers to a side (BW) backwardly of the backrest framework (BF).
Now, a specific description will be made of the seat back structure in the present invention.
For simplicity, a description will be made only of left-side half of the backrest framework (BF); namely, a left-side upper guide element (24), a left-side lower link element (26), and a left-side biasing element (36).
As seen in
As shown in
As best seen in
More specifically, the guide bracket (40) has an upper end portion (40a) and a lower end portion (40b), and the guide hole (40h) is formed in a main body area of the guide bracket (40) between those upper and lower end portions (40a) (40b) so as to extend substantially along the longitudinal direction of the guide bracket (40). The lower end portion (40b) of guide bracket (40) is rotatably connected with the inward surface of upper region (14a-1) of seat-back-frame lateral frame member (14a) by means of pivot pin (42), as shown in
The guide pin (42) is fixed in the upper region of the lateral frame member (16a) of auxiliary frame (16) so as to project outwardly therefrom. Such outwardly projected guide pin (42) is in a sliding engagement in the guide hole (40h) of guide bracket (40).
In this respect, as illustrated, both guide bracket (40) and guide hole (40h) extend vertically alongside of the auxiliary frame lateral frame member (16a) within the seat back (SB), so that the auxiliary frame (16) is displaceable along a predetermined path through sliding movement of the guide pin (42) along such vertical guide hole (40h) in conjunction with concurrent rotation of the lower link member (26) relative to the second bolt (30). This action in turn causes displacement of the headrest (12) between the home position (NP) and upwardly displaced point (UP), as will be described later.
The buffer member (48) has a forward end (48a) and a backward end (48b), and is formed with a hole (48h) in the forward end (48a) thereof. As illustrated, the forward end (48a) of buffer member (48) is securely connected, at the hole (48h) thereof, with the upper end portion (40a) of guide bracket (40) by means of a pin (46). It is observed that the backward end (48b) of buffer member (48) projects backwardly from that guide bracket upper end portion (40a), thus facing toward the backwardly facing flange portion (14aF) of lateral frame member (14a) of seat back frame (14). The buffer member (48) per se is in a slidable contact with the inward surface of upper region (14a-1) of seat-back-frame lateral frame member (14a).
Hence, both guide pin (42) and lower link member (26) are arranged in the above-described manner between the two lateral frame members (14a) and (16a) respectively of the seat back frame (14) and auxiliary frame (16).
In this respect, it is to be seen that the first bolt (28) is a pivotal support point of the lower link member (26) with respect to the seat back frame (14), while the second bolt (30) is a pivotal support point of that lower link member (26) with respect to the auxiliary frame (16).
At the lower home position (NP) of the headrest (12) as in
It is noted here that the biasing force or contractive force of the extension coil spring (36) is set to such a degree at which the spring (36) will not be stretched by a load which is normally applied from a seat occupant's dorsal part (PD) to the backrest frame (BF) as well as a load normally applied from a seat occupant's lumbar part (PL) to the pressure receiving member (18).
With the above-described arrangement, as indicated in
Thus, the auxiliary frame (16) is immediately displaced in forward and upward directions, along a predetermined path, due to the accelerated anticlockwise rotation of the lower link member (26) under the anticlockwise biasing force of extension coil spring (36) as well as to the rectilinear upward movement of the guide pin (42) along the guide hole (40h). With such controlled displacement of auxiliary frame (16), the headrest (12) is immediately displaced from the lower home position (NP) toward the upwardly displaced point (UP) for providing quick and stable support to the seat occupant' head (PH).
But, although the seat occupant's head (PH) is received and supported by the headrest (12) as such, an excessive backward inertia of the seat occupant (P), which is inevitably caused by the rear-end collision, creates and applies a great backward load to both of the headrest (12) and auxiliary frame (16), with the result that the headrest (12) is about to be abruptly inclined backwards from the emergency head support position (at UP), as indicated by the arrow (Y) in
At this moment, however, in accordance with the present invention, the auxiliary frame (16) is displaced backwardly relative to the pivotal support point (at 30) at the backward end portion (26b) of lower link member (26), while being prevented against downward displacement under the anticlockwise biasing force of extension coil spring (36) whose line of force (36a) is disposed backwardly of the pivotal support point (at 28). With such backward displacement of auxiliary frame (16), a corresponding backward load is applied to the guide pin (42) in the guide hole (40h) of guide bracket (40) (the guide pin (42) is contacted with the guide hole upper edge (40h-2)), and therefore, the upper end portion (40a) of the guide bracket (40) is simultaneously rotated clockwise or backwardly relative to the lower pivot point (at the bolt 44), which in turn causes simultaneous backward movement of the damper member (48), so that the backward end (48b) of that particular buffer member (48) is immediately brought to contact with the flange portion (14aF) of the seat-back-frame lateral frame member (14a), as can be seen from
Accordingly, the abrupt backward displacement of the auxiliary frame (16) is decelerated and slowly stopped due to a buffering effect of the foregoing buffer member (48), which means that the headrest (12) is slowly inclined in the backward direction, thereby insuring to protect the seat occupant's head (PH) as well as his or her neck portion against damage and injury. Further, at that time, the auxiliary frame (16) is also abruptly displaced downwardly due to the backward inertia and downward load or weight of seat occupant (P), but, such abrupt downward displacement of the auxiliary frame (16) is decelerated and slowly done under the anticlockwise biasing force of the extension coil spring (36) which attempts to give a counterforce against the downward displacement of auxiliary frame (16).
It is to be also appreciated that the above-described mechanism for changing the direction of biasing force of the biasing element (at 36) by displacing the line of force (36a) relative to the pivotal support point (at 28) is of a quite simplified structure and effective for rapid displacement of the headrest (12) to the emergency head support point (at UP).
While having described the present invention thus far, it should be understood that the invention is no limited to the illustrated embodiment, but, any modification, replacement and addition may be applied thereto without departing from the scopes of the appended claims.