Vehicle seat

A seat back has a seat back frame, a plane spring structure, and a headrest provided at the upper end of a seat back frame. The plane spring structure has left and right side wires, and horizontal wires extending in the horizontal direction. Connection wires are provided between the seat back frame and plane spring structure. First end portions and second end portions of the connection wires function as detachable portions. At least one of these detachable portions is detached from the seat back frame or plane spring structure by the load applied to the seat back, when a vehicle is bumped from behind.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-284262, filed Oct. 31, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle seat having a headrest.

2. Description of the Related Art

There has been proposed a headrest drive capable of moving a headrest forward to hold an occupant's head when a vehicle is bumped from behind. For example, Jpn. Pat. Appln. KOKAI Publication No. 11-268566 (patent document 1) discloses a conventional headrest drive, in which a connection member is arranged in the lower part of a bracket to support a stay of a headrest. The connection member is provided with a pressure-receiving member. In this conventional example, when an occupant is pressed to a seat back upon a collision, the pressure-receiving member is pressed rearward, the connection member is driven, and the headrest is moved forward.

Jpn. Pat. Appln. KOKAI Publication No. 2001-58533 (patent document 2) discloses another conventional headrest drive, in which a pressure-receiving member is arranged above an S-shaped spring of a seat back. In this conventional example, the pressure-receiving member is fixed to the lower part of a headrest holder bracket. When a vehicle is bumped from behind, the pressure-receiving member is pushed rearward by the load applied to a seat back from an occupant, and a headrest is moved forward.

It is known that when a vehicle is bumped from behind, a vehicle seat having a headrest drive behaves as shown inFIG. 7. InFIG. 7, the characteristic curve A drawn by a solid line indicates rearward movement (X-amount) of an occupant's head with time. The characteristic curve B drawn by a broken line indicates rearward movement (X-amount) of a headrest with time. At a point of intersection C of the characteristic curves A and B, the occupant's head contacts the headrest.

In a vehicle seat having a headrest drive, a characteristic curve includes a flat part F (shown inFIG. 7) showing a relatively small increase in the X-amount of a headrest. The time taken by the occupant's head to contact the headrest (the time from a collision to the point C) can be shortened by the flat part F.

Jpn. Pat. Appln. KOKAI Publication No. 2007-106378 (patent document 3) discloses another vehicle seat, which has a connection member to connect the upper part of a seat back frame to the upper part of a plane spring structure, and a shock-absorbing part provided in the connection member. According to the patent document 3, a vehicle seat facilitates rearward movement of an occupant upon a collision from behind.

In the vehicle seat with a headrest drive incorporated in a seat back as described in the patent documents 1 and 2, the weight of a seat is increased by the weight of a headrest drive. The structure of a headrest drive is complicated, and the seat cost is increased.

In the vehicle seat described in the patent document 3, a shock-absorbing part is provided in a connection member provided in the upper part of a seat back. In this structure, the shock-absorbing part cannot function effectively, when a relatively large load is applied to the lower half part of a seat back from the part around an occupant's waist upon a collision from behind. Namely, when a seat back is moved rearward by the load applied to a seat back, a headrest is also moved rearward, and a head support function equivalent to the movable headrest drive is not obtained.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a vehicle seat having a headrest, which has a simple structure compared with a headrest drive, and supports quickly the head of an occupant when a vehicle is bumped from behind.

According to an aspect of the invention, there is provided a vehicle seat comprising a seat cushion on which an occupant sits; a seat back which is provided at the rear of the seat cushion, and is provided with a seat back frame having left and right side frame units; a headrest which is provided at the upper end of the seat back frame; left and right side wires which are provided inside the seat back frame, and extended in the vertical direction; a plane spring structure having horizontal wires provided between the side wires at some intervals in the vertical direction; connection wires provided between the seat back frame and plane spring structure; and a pad member provided on the front side of the plane spring structure, wherein the connection wires have detachable portions. The detachable portions are detached from the plane spring structure or seat back frame by the load applied to the seat back from an occupant sitting on the seat cushion, when a vehicle is bumped from behind. The detachable portions are formed at the end portions of the connection wires for example.

According to the invention, when a vehicle is bumped from behind, the detachable portions are detached from a plane spring structure or a seat back frame by the load applied from an occupant to the seat back. Therefore, the rearward movement of the seat back is restricted, and an occupant's head can contact the headrest within a short time. The rearward movement of the occupant's head is quickly stopped by the headrest. The vehicle seat of the invention is simple in the structure compared with a headrest drive, and quickly holds an occupant's head.

The detachable portions of the connection wires are configured to disengage from the plane spring structure or seat back frame, when the load applied to the seat back is over 150 kgf and below 800 kgf, for example. The detachable portions of the connection wires are U-shaped hooks, for example. In a preferable embodiment of the invention, the upper end portion of the plane spring structure is secured to the upper part of the seat back frame, and the connection wires are arranged in the lower half part of the plane spring structure. A preferable embodiment may have the upper side connection wires arranged in the upper half part of the plane spring structure, and the lower side connection wires arranged in the lower half part of the plane spring structure, wherein when the load is applied to the seat back, at least the lower side connection wires are detached.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will be explained hereinafter with reference toFIG. 1toFIG. 6.

FIG. 1shows a vehicle seat10. The vehicle seat10comprises a seat cushion11, and a seat back12provided at the rear of the seat cushion11. A slide mechanism13is provided on the lower side of the seat cushion11. The slide mechanism13has a fixed rail14, a movable rail15, and a lock mechanism (not shown). The fixed rail14is fixed to the floor of a vehicle (not shown). The movable rail15is movable in the longitudinal direction of a vehicle with respect to the fixed rail14. The lock mechanism has a function to fix the movable rail15to the fixed rail14. InFIG. 1, the longitudinal direction of a vehicle is indicated by the arrow X.

The seat cushion11comprises a seat cushion frame20, a spring unit21, a pad member22, and a cover member23. The spring unit21includes S-springs secured to the seat cushion frame20. The pad member22is provided on the spring unit21. The cover member23covers the outer surface of the pad member22. The movable rail15of the slide mechanism13is fixed to the seat cushion frame20.

The seat back12comprises a seat back frame30, a plane spring structure31, a pad member32, and a cover member33. The pad member32is provided on the front side of the plane spring structure31. The cover member33covers the pad member32. The seat back12is fixed to the rear of the seat cushion frame20. The seat back12is changeable in the longitudinal inclination angle by a hinge unit35having a reclining mechanism.

FIG. 2shows a seat back frame30, and a plane spring structure31. The seat back frame30comprises left and right side frame units40and41, an upper frame unit42, and a lower frame unit43. The side frame units40and41formed by pressing a steel sheet metal, for example. The upper frame unit42connects the upper parts of the side frame units40and41. The lower frame unit43connects the lower parts of the side frame units40and41. A headrest bracket45is fixed to the upper frame unit42. The seat back frame is substantially a rigid structure.

As shown inFIG. 1, a headrest50is provided at the upper end of the seat back12. The headrest50comprises a headrest main body51, and left and right stays52. The headrest main body51is provided at the upper end portion of the seat back12. The stay52extends downward from the headrest main body51. The headrest bracket45is provided in the seat back frame30. The stay52is inserted into the headrest bracket45, and can be fixed at a desired height by a not-shown stopper mechanism.

As shown inFIG. 2, the plane spring structure31comprises left and right side wires60and61provided on both sides, a center cord62provided at the center, and horizontal wires63. The horizontal wires63are provided between the side wires60and61. The side wires60,61and center cord62extend in the vertical direction. The horizontal wires63extend in the horizontal direction. The plane spring structure31is arranged inside the seat back frame30. The plane spring structure31supports a rearward load applied from the waist and back of an occupant sitting on the seat cushion11.

The horizontal wires63are arranged at some intervals in the vertical direction of the plane spring structure31. The horizontal wires63are made of spring steel wire with a diameter smaller than that of the side wires60and61. Both ends of each horizontal wire63are fixed to the side wires60and61. Each horizontal wire63has a projected portion64which is projected upward. The projected portion64is formed horizontally symmetrical on both sides of the center cord62. The projected portion64is formed on the same plane. Therefore, the plane spring structure31is shaped like a mat having a substantially plane surface. The projected portion64may be S-shaped or Z-shaped. The horizontal wires63may be shaped straight.

The upper end portions60aand61aof the side wires60and61are secured to the upper part of the seat back frame30through a support wire65. The support wire65is arranged in the upper part of the seat back frame30. The lower ends of the side wires60and61are set free without being secured to the seat back frame30. Therefore, when a rearward load is applied from the seat back12to the plane spring structure31, the whole plane spring structure31can be moved a little in the longitudinal direction around the upper end portions60aand61aof the side wires60and61acting as fulcrums. Besides, a lower half part31bof the plane spring structure31can be moved a little farther than an upper half part31a.

FIG. 3shows a part of the seat back frame30and plane spring structure31.FIG. 4is a transverse sectional view of the seat back frame30.

Side wires60and61are arranged on both sides of the plane spring structure31. These side wires60and61are secured to the seat back frame30through connection wires71,72,73and74. More specifically, the upper half part31aof the plane spring structure31is supported by the side frame units40and41through the upper side left and right connection wires71and72. The lower half part31bof the plane spring structure31are supported by the side frame units40and41through the lower side left and right connection wires73and74.

The connection wires71,72,73and74are formed by bending a metal wire such as a steel wire with a diameter smaller than that of the side wires60and61in the following manner. Namely, the connection wires71,72,73and74have U-shaped hook-like first end portions71a,72a,73aand74a, U-shaped hook-like second end portions71b,72b,73band74b, and straight linear portions71c,72c,73cand74c. The straight linear portions71c,72c,73cand74care formed between the first end portions71a,72a,73aand74aand second end portions71b,72b,73band74b. The first end portions71a,72a,73aand74aand second end portions71b,72b,73band74bfunction as detachable portions.

The first end portions71a,72a,73aand74aare wound and secured to the side wires60and61of the plane spring structure31, as partially shown inFIG. 3. The side frame units40and41of the seat back frame30have holes81,82,83and84. The second end portions71b,72b,73band74bare inserted into these holes81,82,83and84, thereby they are secured to the side frame units40and41.

The first end portions71a,72a,73aand74afunction as detachable portions. When a tensile load larger than a predetermined value is applied to the connection wires71,72,73and74, the curved ends of these first end portions are deformed and extended, and the first end portions are detached from the side wires60and61of the plane spring structure31.

The second end portions71b,72b,73band74bfunction also as detachable portions. When a tensile load larger than a predetermined value is applied to the connection wires71,72,73and74, the curved ends of these second end portions are deformed and extended, and the second end portions are detached from the holes81,82,83and84of the seat back frame30.

As indicated by the curves No.1to No.11inFIG. 5, the connection wires71,72,73and74have characteristics so as to be detached from the plane spring structure31or seat back frame30, when a load over 150 kgf (1470N) and below 900 kgf (8820N) is applied to the seat back12and the seat back12is bent to 65 to 85 mm.

For example, in the example indicated by the curve No.1inFIG. 5, when a load of 400 kgf (3920N) is applied to the seat back12and the seat back12is deformed to 65 mm, one of first and portions73aand74aof the lower side connection wires73and74was detached from the plane spring structure31. Therefore, the load is temporarily decreased when the seat back is deformed to about 65 mm. But, the plane spring structure31is maintained to be supported by the other not-detached end portion, pad member32, and cover member33, so that the load is increased again. The curves No.1to No.11indicate such characteristics.

In this embodiment, the lower side connection wires73and74supporting the lower half part31bof the plane spring structure31were detached from the plane spring structure31. The reason is that the load applied from the waist of an occupant to the lower half part of the seat back12was larger than the load applied to the upper half part of the seat back12, the upper end portions60aand61aof the side wires60and61of the plane spring structure31are secured to the upper part of the seat back frame30, and the lower half part31bof the plane spring structure31is movable more easily than the upper half part31a.

By extending both ends of the horizontal wire63, the horizontal wire63may be formed in one body with the connection wires connected to both ends of the horizontal wire. At the end of the connection wire, a hook-like detachable portion detachable from the seat back frame upon a collision from behind is formed. In this case, the diameters of the horizontal wire63and connection wire become the same.

Next, an explanation will be given on the function of the vehicle seat10configured as described hereinbefore.

When a vehicle provided with the seat10is bumped from behind, a rearward load is transmitted to the seat back12from an occupant sitting on the seat cushion11. The load is applied to the plane spring structure31, and the plane spring structure31is bent. When the load exceeds a predetermined value, at least one of the first end portions71a,72a,73aand74aof the connection wires71,72,73and74are detached from the plane spring structure31, or one of the second end portions71b,72b,73band74bis detached from the seat back frame30. In this embodiment, at least one of the first end portions73aand74aof the lower side connection wires73and74which support the lower half part of the plane spring structure31was detached from the plane spring structure31.

InFIG. 6, the characteristic curve A drawn by a solid line indicates movement (X-amount) with time of an occupant's head in the longitudinal direction upon a collision from behind. The characteristic curve L1drawn by a broken line indicates movement (X-amount) with time of the headrest50having the connection wires71,72,73and74of this embodiment in the longitudinal direction.

According to this embodiment, when a vehicle is bumped from behind, at least one of the connection wires73and74is detached from the plane spring structure31. Therefore, the relative movement of the side wires60and61, center cord62and horizontal wire63, which are moved back by the load from an occupant, with respect to the seat back frame30is increased. Therefore, the X-amount of the headrest50connected to the seat back frame30through the headrest bracket45is restricted, and the characteristic curve L1includes a flat portion F in which the X-amount of the headrest is relatively small.

Therefore, according to this embodiment, the time taken by the occupant's head to be held by the headrest (the time from a collision to the point C) can be reduced. This is effective to decrease a whiplash injury.

The characteristic curve L2drawn by a chain double-dashed line inFIG. 6indicates the measurement result of the seat back in a comparative example using a connection wire having no detachable portions. In this comparative example, a connection wire is arranged connected not to detach from a seat back frame and plane spring structure. The characteristic curve L2in the comparative example indicates that the X-amount of the headrest is increased at a substantially constant ratio, as the load is increased. Therefore, the characteristic curve L2in the comparative example indicates that the time taken by the occupant's head to be held (the time from a collision to the point C′) is longer than in the characteristic curve L1.

InFIG. 5, the examples indicated by the curves No.1to No.11indicate seat backs configured so that a detachable portion of a connection wire is detached by a load of 150 to 900 kgf. According to the experiment done by the inventor, these seat backs could generate a flat portion F in the characteristic curve L1(shown inFIG. 6) indicating the X-amount of a headrest, as in the seat back having a headrest drive. A head holding effect equivalent to a headrest drive could not be obtained in a seat back, in which a connection wire is not detached by the above range of load.

As explained herein, the seat back12of this embodiment is configured so that when a vehicle is bumped from behind, at least one of the detachable portions of the connection wires71,72,73and74is detached from the plane spring structure31or seat back frame30by the load applied to the seat back12upon a collision. Therefore, comparing with a conventional seat back using a headrest drive, the structure and operation principle are simple, and an occupant's head is held when a vehicle is bumped from behind. Further, the weight and number of parts are not increased from those of a conventional seat back.

The invention may be embodied by appropriately changing the constituent elements such as a seat back frame, plane spring structure, pad member and detachable portion of a connection wire. For example, it is possible to provide a portion corresponding to a connection wire in a part of a horizontal wire by extending both ends of a horizontal wire, and to provide a detachable portion that can be detached from a seat back frame, at the end of the connection wire frame.