Abstract:
A detector for detecting the load applied to a passenger seat of an automobile equipped with an air bag. The load detector includes a sensor bracket having a deformation portion that deforms in accordance with the amount of the load. A strain sensor is arranged on the deformation portion to detect the degree of deformation of the deformation portion. A force limiter bracket is located adjacent to the sensor bracket to limit deformation of the deformation portion within a predetermined range. An anchor bracket is formed integrally with the force limiter bracket and is connected to a seat belt.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a vehicle seat, and more particularly, to a vehicle seat having a passenger detector. 
     A vehicle equipped with an air bag is typically provided with a passenger detector, or a load detector. The passenger detector detects whether a passenger is sitting on a seat or the passenger&#39;s weight. The amount of gas generated to inflate the air bag is adjusted in accordance with the detection. 
     Japanese Unexamined Patent Publication No. 11-1153 describes a detector employing a load cell to detect the weight applied by a vehicle seat. The load cell is located between a rail, which supports the seat, and a mount bracket, which secures the rail to the passenger compartment floor. 
     Japanese Unexamined Patent Publication No. 11-1154 describes a detector employing a link unit to detect the load applied to a seat cushion. The link unit is located between the seat cushion and a frame, which supports the seat cushion. The link unit is pivoted in accordance with the load of the seat cushion. The load detector detects the seat load based on the position of the link unit. 
     Japanese Unexamined Patent Publication NO. 11-94637 also describes a detector employing a link unit to detect the load applied to a seat cushion. The link unit is located between a slide rail and the seat cushion. The load detector detects the seat load based on the position of the link unit. 
     However, the conventional load detectors are complicated and large. Further, the accuracy of the conventional load detectors is relatively low. 
     Generally, the retaining force produced by a seat belt acts on the seat. This may result in the load detector inaccurately detecting the passenger&#39;s weight. Further, when a child safety seat is mounted on the vehicle seat, a large load is applied to the vehicle seat. Thus, a load detector that is not affected by the restraining force of a seat belt has been sought after. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a vehicle seat having a simple and highly accurate passenger detector. 
     To achieve the above object, the present invention provides a vehicle seat including a seat cushion and a load detector for detecting the load applied to the seat cushion. The load detector includes a sensor bracket having a deformation portion, which is deformed in accordance with the degree of the load. A strain sensor is arranged on the deformation portion to detect the degree of deformation of the deformation portion. A force limiter bracket is adjacent to the sensor bracket to limit deformation of the deformation portion within a predetermined range. An anchor bracket is formed integrally with the force limiter bracket. The anchor bracket is attached to a seat belt. 
     A further aspect of the present invention provides a vehicle seat arranged on an upper support that moves along a lower support, which is fixed to the floor of a passenger compartment. The seat includes a seat cushion, a seat frame for supporting the seat cushion, and a load detector arranged between the upper support and the seat frame to detect the load applied to the seat cushion. The load detector includes a sensor bracket having a deformation portion, which is deformed in accordance with the degree of the load, and first and second connecting holes. A strain sensor is arranged on the deformation portion to detect deformation of the deformation portion. A force limiter bracket is located adjacent to the sensor bracket. The force limiter bracket has a fastening hole and a restricting hole. The force limiter bracket limits deformation of the deformation portion within a predetermined range. A first bolt is fitted in the first connecting hole and the restricting hole to fix the sensor bracket to the seat frame. A second bolt is fitted in the second connecting hole and the fastening hole to fix the second bracket to the upper support. An anchor bracket is formed integrally with the force limiter bracket and attached to a seat belt. 
     Another aspect of the present invention provides a load detector arranged between a vehicle seat and the floor of a passenger compartment to detect the load applied to the seat. The load detector includes a sensor bracket having a deformation portion, which is deformed in accordance with the degree of the load, and first and second connecting holes. A strain sensor is arranged on the deformation portion to detect deformation of the deformation portion. A force limiter bracket is located adjacent to the sensor bracket. The force limiter bracket has a fastening hole aligned with the force connecting hole and a restricting hole aligned with the second connecting hole. The force limiter bracket limits deformation of the deformation portion within a predetermined range. An anchor bracket is formed integrally with the force limiter bracket and attached to a seat belt. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a perspective view showing a vehicle seat according to a first embodiment of the present invention; 
     FIG. 2 is a schematic side view showing the frame of the seat of FIG. 1; 
     FIG. 3 is a front view showing a rear load detector; 
     FIG. 4 is a side view showing the rear load detector; 
     FIG. 5 is a cross-sectional view of the rear load detector taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is a cross-sectional view showing the rear load detector and taken along line  6 — 6  of FIG. 3; 
     FIG.  7 ( a ) is a front view showing a front load detector; 
     FIG.  7 ( b ) is a side view showing the front load detector; 
     FIG.  8 ( a ) is a front view showing a rear sensor bracket; 
     FIG.  8 ( b ) is a side view showing the rear sensor bracket; 
     FIG.  9 ( a ) is a front view showing a force limiter bracket; 
     FIG.  9 ( b ) is a cross-sectional view showing the force limiter bracket and taken along line  9   b — 9   b  of FIG.  9 ( a ); 
     FIG. 10 is a front view showing a rear load detector according to a second embodiment of the present invention; 
     FIG. 11 is a side view showing the rear load detector of FIG. 10; 
     FIG. 12 is a cross-sectional view showing the rear load detector and taken along line  12 — 12  of FIG. 10; 
     FIG. 13 is a cross-sectional view showing the rear load detector and taken along line  13 — 13  of FIG. 10; 
     FIG.  14 ( a ) is a front view showing a force limiter bracket of the second embodiment; and 
     FIG.  14 ( b ) is a cross-sectional view showing the force limiter bracket and taken along line  14   b — 14   b  of FIG.  14 ( a ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An automobile seat  1  according to a first embodiment of the present invention will now be described with reference to the drawings. 
     As shown in FIG. 1, the seat  1  is supported on two base frames  2  and includes a seat cushion  7  and a seatback  8 . The two base frames  2  are parallel and are secured to the floor of a passenger compartment. Two base brackets  3  are fixed to each base frame  2 . Each pair of the base brackets  3  supports a lower support  4 , which is lower rail in this embodiment. The lower support  4  has a U-shaped slide groove  5 . A pair of upper supports  6 , which are upper rails in this embodiment, are attached to the seat  1 . Each of the upper supports  6  is received in and can slide along the slide groove  5  of an associated one of the lower supports  4 . 
     FIG. 2 shows the frame of the seat  1 . A seat frame  9  supports the seat cushion  7  and the seatback  8 . A front load detector  10  and a read load detector  11  are arranged between each of the upper supports  6  and the seat frame  9 . The structure of the left front load detector  10  is a mirror-image of the structure of the right front load detector  10 . The structure of the left rear load detector  11  is a mirror-image of the structure of the right rear load detector  11 . Thus, only the right front and rear load detectors  10 ,  11  will be discussed below. 
     With reference to FIGS.  7 ( a ) and  7 ( b ), the front load detector  10  includes a front sensor bracket  12  and a front strain sensor (strain detecting element)  13 . The front sensor bracket  12  has an upper portion  14 , a lower portion  15  and a bent deformation portion  16 . The deformation portion  16  extends continuously between the upper and lower portions  14 ,  15 . The strain sensor  13  is affixed to the deformation portion  16 . An upper bolt hole  17  extends through the upper portion  14 , and a lower bolt hole  18  extends through the lower portion  15 . The upper and lower portions  14 ,  15  are respectively fastened to the seat frame  9  and the upper support  6  by bolts  19  that are inserted through the upper and lower bolt holes  17 ,  18 . The front load detector  10  connects and determines the distance between the seat frame  9  and the upper support  6 . 
     The deformation portion  16  is deformed in accordance with the load applied to the seat cushion  7 . The front strain sensor  13  electrically detects the degree of deformation of the deformation portion  16  and provides a detection signal to a controller (not shown). 
     As shown in FIG. 4, the rear load detector  11  includes a rear sensor bracket  21 , a force limiter bracket (deformation restriction plate)  22 , and a rear strain sensor (strain detecting element)  23 . 
     With reference to FIGS.  8 ( a ) and  8 ( b ), the rear sensor bracket  21  has a bent deformation portion  24 , a lower portion  25  extending downward from the deformation portion  24 , and an upper portion  28  extending upward from the deformation portion  24 . The rear strain sensor  23  is affixed to the deformation portion  24 . A pair of lower bolt holes  26  and a nut hole  27  extend through the lower portion  25 . The diameter of the nut hole  27  is greater than that of the lower bolt holes  26 . A pair of upper bolt holes  29  extend through the upper portion  28 . The upper end of the upper portion  28  is bent so that it extends substantially parallel to the deformation portion  24 . 
     The deformation portion  24  is deformed in accordance with the degree of the load acting on the seat cushion  7 . The rear strain sensor  23  electrically detects the degree of deformation of the deformation portion  24  and provides a detection signal to the controller. 
     When an excessive load acts on the seat cushion  7 , the force limiter bracket  22  limits the deformation of the rear sensor bracket  21  so that the deformation is within a predetermined range. As shown in FIGS.  5  and  9 ( a ), a pair of fastening holes  31  extend through the lower portion of the force limiter bracket  22 . The diameter of the fastening hole  31  is substantially the same as the diameters of the lower bracket bolt holes  26  and support holes  32 , which are formed at the rear portion of the upper support  6 . The rear sensor bracket  21  and the force limiter bracket  22  are fastened to the upper support  6  by fasteners, which are bolts  33  and nuts  34  is this embodiment. The heads of the bolts  33  are located on one side of the force limiter bracket  22 , and the deformation portion  24  is located on the other side of the force limiter bracket  22 . The diameter of the bolts  33  is substantially the same as the diameters of the bolt holes  26 ,  31 ,  32 . Accordingly, there is no space between the bolts  33  and the corresponding walls of the bolt holes  26 ,  31 ,  32 . 
     Referring to FIG.  9 ( a ), two elongated holes (movement restriction holes)  35  extend through the force limiter bracket  22  in correspondence with the upper bracket bolt holes  29  and frame bolt holes  36 . The width and length of the elongated holes  35  is greater than the diameters of the upper bracket bolt holes  29  and the frame bolt holes  36 . As shown in FIG. 5, a cylindrical spacer  37  is extended through each elongated hole  35 . The spacer  37  is fitted on a connecting bolt  38  and forms a gap between the seat frame  9  and the rear sensor bracket  21 . The outer diameter of the spacer  37  is smaller than the width and length of the elongated holes  35 . Accordingly, the movement of the spacer  37  is tolerated in the elongated hole  35 . In other words, the movement of the spacer  37  is restricted within a predetermined area by contact between the outer surface of the spacer  37  and the wall of the elongated hole  35 . Thus, the walls of the elongated holes  35  are referred to as movement restriction surfaces. 
     Nuts  39  are fastened to the connecting bolts  38  to secure the rear sensor bracket  21  to the seat frame  9 . More specifically, the connecting bolts  38  are inserted through the corresponding upper bracket bolt holes  29 , the elongated holes  35 , and the frame bolt holes  36  and fastened by the nuts  39 . The rear load detector  11  connects and determines the distance between the seat frame  9  and the upper support  6 . 
     An anchor projection  40  projects away from the rear sensor bracket  21  at the middle portion of the force limiter bracket  22 . The anchor projection  40  has an anchor bolt hole  41 . An anchor nut  42  is welded to the inner surface of the anchor projection  40 . The outer diameter of the anchor nut  42  is smaller than the diameter of the nut hole  27 . This enables the anchor nut  42  to move within the nut hole  27 . 
     When in use, a seat belt  43  is fastened to a belt anchor  44  (FIG.  1 ). Referring to FIG. 6, the belt anchor  44  is connected to the anchor projection  40  by an anchor bracket  45 . A bolt hole  46  extends through the anchor bracket  45 . The diameter of the bolt hole  46  is substantially the same as the anchor bolt hole  41 . An anchor bolt  47  is inserted through the bolt holes  46 ,  41  and fastened to the anchor nut  42 . This secures the belt anchor  44  to the force limiter bracket  22 . 
     In the first embodiment, as viewed in FIG. 1, the anchor bracket  45  is connected to the force limiter bracket  22  of the right rear load detector  11 . The anchor bracket  45  is not connected to the left rear load detector  11 . 
     The seat  1  of the first embodiment has the advantages described below. 
     (1) The load applied to the upper surface of the seat cushion  7  is transferred to the seat frame  9  thereby deforming the front and rear deformation portions  16 ,  24 . The degree of deformation of each deformation portion  16 ,  24  is detected by the associated strain sensors  13 ,  23 . Thus, the front and rear load detectors  10 ,  11  detect whether a passenger is sitting on the seat  1 . 
     (2) The force limiter bracket  22  prevents excessive deformation of the sensor bracket  21  and thus maintains the desired detection characteristics of the rear strain sensor  23 . When a relatively large load is applied to the seat cushion  7 , the spacers  37  contact the bottom wall of the associated elongated holes  35 . This restricts further deformation of the rear deformation portion  24 . As a result, the detection characteristics of the rear strain sensor  23  remain unaffected. 
     (3) The anchor bracket  45  of the seat belt  43  is easily connected to the force limiter bracket  22 . For example, by fixing the anchor bracket  45  to the force limiter bracket  22  beforehand, the anchor bracket  45  may be connected to the seat  1  by merely connecting the force limiter bracket  22  to the seat  1 . This decreases the time for installing the seat  1 . 
     (4) The rear sensor bracket  21  and the force limiter bracket  22  are fixed to the upper support  6  by a single connection bolt  33 . Further, the procedure for connecting the rear sensor bracket  21  to the seat frame  9  is performed with the connecting bolts  38  inserted in the elongated holes  35 . Accordingly, the attachment of the rear sensor bracket  21  and the attachment of the force limiter bracket  22  are performed simultaneously. This decreases the assembly time of the seat  1 . 
     (5) The anchor bracket  45  is connected to the force limiter bracket  22  only by the anchor bolt  47 . Thus, the anchor bracket  45  may be connected to either one of the force limiter brackets  22  located on the left side and the right side of the seat  1 . 
     An automobile seat  1  according to a second embodiment of the present invention will now be described with reference to FIGS. 10 to  14 . The seat  1  of the second embodiment is substantially the same as that of the first embodiment except for a force limiter bracket  52  of a rear load detector  51 . 
     As shown in FIGS. 10 and 11, the rear load detector  51  includes the force limiter bracket  52 . Referring to FIGS.  14 ( a ) and  14 ( b ), two elongated holes (movement restriction holes)  53  extend through the lower portion of the force limiter bracket  52 . The width and length of each elongated hole  53  is greater than the diameter of the lower bracket bolt holes  26 . 
     With reference to FIG. 12, the connecting bolts  33  are inserted through the corresponding holes  26 ,  32 ,  53  and fastened by the nuts  34 . This connects the rear sensor bracket  21  to the upper support  6 . A cylindrical spacer  54  is arranged in each elongated hole  53  between the head of the corresponding bolt  33  and the rear sensor bracket  21 . 
     The diameter of the bolts  33  is substantially the same as the diameters of the bolt holes  26 ,  32 . Accordingly, there is no space between the bolts  33  and the walls of the bolt holes  26 ,  32 . The outer diameter of each spacer  54  is smaller than the width and length of the associated elongated hole  53 . This forms a space between the spacer  54  and the wall of the elongated hole  53 . Thus, the movement of the spacer  54  is tolerated in the elongated hole  53 . In other words, the movement of the spacer  54  is restricted within a predetermined area by contact between the outer surface of the spacer  54  and the wall of the elongated hole  53 . 
     Two fastening holes  55  are formed at the upper portion of the force limiter bracket  52  in correspondence with the upper bracket bolt holes  29  and the frame bolt holes  36 . The diameter of the fastening holes  55  is substantially the same as the diameter of the upper bracket bolt holes  29 . 
     The connecting bolts  38  are inserted through the corresponding upper bolt holes  29 , the fastening holes  55 , and the frame bolt holes  36  and fastened by the nuts  39 . This connects the rear sensor bracket  21  and the force limiter bracket  52  to the seat frame  9 . The diameter of the connecting bolts  38  is substantially the same as the diameters of the bolt holes  29 ,  36 ,  55 . Thus, there is no space between the connecting bolts  38  and the walls of the bolt holes  26 ,  31 ,  32 . The rear load detector  51  connects and determines the distance between the seat frame  9  and the upper support  6 . 
     With reference to FIGS.  13  and  14 ( a ), an anchor projection  56  projects away from the rear sensor bracket  21  at the middle portion of the force limiter bracket  52 . The anchor projection  56  has an anchor bolt  57  located at a position corresponding to the nut hole  27 . The anchor bracket  45  of the belt anchor  44  is connected to the anchor projection  56 . The anchor nut  42 , which is aligned with the anchor bolt hole  57 , is fixed to the inner surface of the anchor projection  56 . The outer diameter of the anchor nut  42  is smaller than the diameter of the nut hole  27 . This enables the anchor nut  42  to move within the nut hole  27 . In other words, the nut hole  27  restricts the movement of the anchor nut  42  within a predetermined area. 
     In addition to the five advantages of the first embodiment, the seat of the second embodiment has the following advantage. 
     (6) The force limiter bracket  52  is directly connected to the seat frame  9  but not to the upper support  6 . Further, the belt anchor  44  is directly connected to the seat frame  9 , which supports the seat cushion  7 . Since the restraining force of the seat belt  43  is directly applied to the seat frame  9 , the restraining force does not deform the rear sensor bracket  21 . This enables accurate detection of only the load applied by a passenger sitting on the seat  1 . For example, if the seat belt  43  is used to fasten a child safety seat to the seat  1 , the restraining force of the seat belt  43  does not affect the rear load detector  51 . Thus, the load of only the passenger sitting on the child safety seat is accurately detected. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     Instead of using the fastening bolt  47 , the anchor belt  45  may be welded to the force limiter brackets  22 ,  52 . 
     The elongated holes  35 ,  53  may have a slot-like shape. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.