Abstract:
A frame-based occupant weight estimation apparatus for a vehicle seat includes a compliant linkage assembly that translates vertically applied seat loads to a horizontal plane, where the horizontal forces are measured by a set of force sensors. A compliant member, which may be a spring or a linkage arm, preloads the force sensors to enable off-loading detection, and an overload device securely anchors the seat to the vehicle floor without interfering with normal load measurement.

Description:
TECHNICAL FIELD 
     This invention is directed to apparatus for detecting the weight of an occupant of a motor vehicle seat for purposes of determining whether and how forcefully to deploy supplemental restraints, and more particularly to apparatus for measuring forces applied to a frame of the vehicle seat. 
     BACKGROUND OF THE INVENTION 
     Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criterion to distinguish between an adult and an infant or small child. 
     Most prior weight estimation techniques involve installing a pressure sensitive element such as a variable resistance pad or a fluid filled bladder in or under a vehicle seat cushion, and utilizing the pressure measurement as an indication of occupant weight. See, for example, the U.S. Pat. Nos. 5,474,327, 5,987,370, 6,246,936, 6,101,436 and 6,490,936, assigned to the assignee of the present invention and incorporated by reference herein. 
     Alternatively, the occupant weight may be measured with one or more load cells that sense the forces (strain or pressure) that the seat applies to a bracket that supports the seat on the vehicle floor. See, for example, the Publication Nos. 41520, 41542, 41549 and 41559 from the November, 1998 issue of Research Disclosure. Since the “frame-based” load cell configurations become part of the supporting structure of the seat, they tend to be relatively bulky and/or expensive to produce. Accordingly, what is needed is a frame-based occupant weight estimation apparatus that is simple and inexpensive to produce, and that does not compromise the structural integrity of the seat. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved frame-based occupant weight estimation apparatus for a vehicle seat, including compliant linkage assemblies interposed between the seat frame and floor brackets bolted to the vehicle floor. The compliant linkage assemblies translate vertically applied seat loads to a horizontal plane (that is, parallel to the vehicle floor), where the horizontal forces are measured by a set of force sensors. In each assembly, a compliant member, which may a spring or a linkage arm, preloads the force sensor to enable off-loading detection, and an overload device securely anchors the seat to the floor bracket without interfering with normal load measurement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a side-view diagram of a vehicle seat incorporating the frame-based occupant weight estimation apparatus of the present invention. 
         FIG. 2  is a diagram of the electrical components of the apparatus of  FIG. 1 . 
         FIG. 3  depicts a first alternate linkage assembly for the apparatus of  FIG. 1 . 
         FIG. 4  depicts a second alternate linkage assembly for the apparatus of  FIG. 1 . 
         FIG. 5  depicts a third alternate linkage assembly for the apparatus of  FIG. 1 . 
         FIG. 6  depicts a fourth alternate linkage assembly for the apparatus of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly to  FIGS. 1 and 2 , the reference numeral  10  generally designates a vehicle seat, including seat and backrest cushions  10   a ,  10   b  supported on a frame including a set of mounting brackets  12 . The seat  10  is secured to the vehicle floor  14  by a pair of laterally spaced floor brackets  16 ,  18  that are bolted to floor  14 , and a set of linkage assemblies  20  are interposed between the seat frame mounting brackets  12  and the floor brackets  16 ,  18  for supporting the seat  10  and estimating the weight of a seat occupant. In the illustrated embodiment, there are four seat mounting brackets (left front, right front, left rear and right rear) and four associated linkage assemblies, but only the left-front and left-rear seat mounting brackets  12 ,  12 ′ and the left-front and left-rear linkage mechanisms  20 ,  20 ′ are visible in the drawings. As indicated in  FIG. 1 , the front and rear linkage assemblies  20 ,  20 ′ are mirror image but otherwise identical. Accordingly, the following description of the linkage assembly  20  applies equally to linkage assembly  20 ′ as well as the right-front and right-rear linkage assemblies. 
     The linkage assembly  20  includes first and second linkage arms  22  and  24  rotatably coupled at one end to a pin  26  secured to the seat frame mounting bracket  12 . The other end of arm  22  is rotatably coupled to a pin  28  secured in a mounting bracket  30  of floor bracket  16 , and the other end of arm  24  is rotatably coupled to a pin  32  secured to a slider block  34  that is supported on the base of floor bracket  16  for linear movement substantially parallel to the vehicle floor. The weight of the seat  10  and a spring  36  bias the slider block  34  into engagement with a force sensor  38  which is disposed between slider block  34  and a central post  40  of floor bracket  16 . The force sensor  38  may be a strain gauge device or load cell such as those produced and sold by Panasonic Corporation or Texas Instruments Corporation, and produces an electrical output signal functionally related to the force applied to it by slider block  34 . 
     The bias or preload force applied to force sensor  38  is particularly important in frame-based occupant weight estimation because it enables off-loading detection. This can occur, for example, when the occupant leans back in the seat  10 , reducing the force measured by the linkage assemblies coupled to mounting brackets on the front of the seat  10 . Due to the preload force, such off-loading can be measured and taken into consideration in the weight estimation calculations. 
       FIG. 2  depicts the force sensor layout for the embodiment of  FIG. 1 , with the force sensors  38   a  and  38   b  being disposed in the floor bracket  16 , and the force sensors  38   c  and  38   d  being disposed in the floor bracket  18 . The co-located sensors  38   a ,  38   b  are electrically coupled to a first connector  42 , while the co-located sensors  38   c ,  38   d  are electrically coupled to a second connector  44 . The connectors  42  and  44 , in turn are electrically coupled to a microcontroller (uC)  46 , which may be located beneath the seat  10  as shown or at a remote location. The microcontroller  46  processes the output signals produced by the sensors  38   a ,  38   b ,  38   c ,  38   d  to determine corresponding weights attributable to a seat occupant, and sums the weights to determine the occupant weight or weight classification for purposes of deciding whether and how forcefully to deploy supplemental restraints designed to protect the occupant from serious injury in a crash event. 
       FIG. 3  depicts an alternate embodiment in which a spiral torsion spring  48  is used in place of the linear coil spring  36  of  FIG. 1 . In this case, the spring  48  imparts a moment to the arm  22  which tends to make the arms  22  and  24  co-linear. Additionally,  FIG. 3  depicts an overload plate  50  for limiting upward movement of the seat  10   a  with respect to the floor brackets  16 ,  18  in the event of a crash. Of course, overload plates  50  are preferably installed at each of the four seat frame mounting brackets  12 ,  12 ′. The plate  50  is anchored on a post  52  formed on floor bracket  16 , and has an elongated aperture  54  through which the pin  26  extends. The pin  26  does not contact the plate  50  in normal operation, but contacts the plate  50  when a strong upward force is applied to seat  10 . The plate  50  is applicable to each of the various embodiments depicted herein, but has been omitted from the other embodiments so as not to obscure the linkage mechanism elements. 
       FIG. 4  depicts an alternate embodiment in which the arm  24 ′ of linkage assembly  20  is compliant instead of rigid. In this case, the arm  24 ′ biases the slider block  34  against the sensor  38 , and no external spring is required. Also, the arm  22  could be compliant instead of, or in addition to, the arm  24 ′, if desired. 
       FIG. 5  depicts an alternate embodiment in which the linkage assembly  20  includes two additional arms  60  and  62 . The arms  60  and  62  are rotatably co-joined at pin  64 , the arm  60  also being rotatably coupled to the pin  28  of floor bracket  16 , and the arm  62  also being rotatably coupled to the pin  32  of slider block  34 . This arrangement requires additional space under the seat  10 , but reduces frictional losses. As with the other embodiments, one or more of the bars/arms  22 ,  24 ,  60 ,  62  can be compliant to provide the desired bias or preload on sensor  38 , or the bias can be provided by an external spring as shown in  FIGS. 1 and 3 . 
     Finally,  FIG. 6  depicts an alternate embodiment in which the linkage assembly  20  is a compliant one-piece device that applies a compressive force to the sensor  38  in relation to occupant weight. The device  20  includes first and second lever arms  70  and  72  rotatably coupled to the pins  26  and  28  of seat frame mounting bracket  12  and floor bracket  16 . The lever arms  70  and  72  are joined at a fulcrum which defines the slider block  74 , and a circumferential arm  76  joined to the lever arms  70  and  72  provides a reaction surface  78  for the force sensor  38 . 
     In summary, the present invention provides a seat frame-based occupant weight estimation apparatus including a compliant linkage assembly that translates vertical force associated with occupant weight to a horizontal force that is sensed by a pre-loaded force sensor. The several different embodiments each include a linkage mechanism coupling the seat mounting bracket to a floor bracket, and an overload mechanism for limiting upward movement of the seat with respect to the floor bracket. Each linkage assembly includes a slider block that exerts a compressive force on the respective force sensor, and the sum of the measured forces is indicative of occupant weight. 
     Advantageously, the linkage assemblies depicted in  FIGS. 1 ,  3 ,  4  and  5  can be configured in accordance with the teachings of U.S. Pat. No. 5,649,454, co-assigned to Purdue Research Foundation and the assignee of the present invention and incorporated by reference herein, so that the preload force applied to sensor  38  is substantially constant. This can be particularly significant in an automotive environment, as the preload bias force would otherwise vary as the linkage arms expand and contract with changes in the passenger compartment temperature. Essentially, the bias force exerted by the spring  36  or  48 , or by the compliant linkage arm  24 ′ should be designed to have a null (i.e., zero bias force) condition when the linkage arms  22 ,  24  are collinear with the path of movement of slider block  34 , and the length of the linkage arms should be designed so that the bias force is substantially constant for any position of the arms  22 ,  24 . A detailed description of the linkage arm dimensional considerations is set forth in the aforementioned U.S. Pat. No. 5,649,454, which is incorporated by reference herein. 
     While illustrated in respect to the illustrated embodiments, it will be recognized that various modifications in addition to those mentioned above may occur to those skilled in the art. For example, the seat  10  may be supported by a greater or lesser number of linkage assemblies, the linkage assemblies may be oriented laterally with respect to the seat  10 , and so on. Accordingly, it will be understood that devices incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.