Abstract:
An over-travel protection device is provided for placing in a load path between a load cell and an object being weighed. The device has a first member positioned to be in the load path and a second member also positioned to be in the load path. The second member is arranged to cooperate with the first member to transfer load force from the object to the load cell. The first and second members define a space between one another and a compressible member is disposed in the space between the first member and the second member. A retaining member is adapted to limit separation displacement between the first and second members.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to methods of attaching an occupant classification sensor to a vehicle, and more particularly to methods of preventing over-extension or over-compression of the sensor. 
     BACKGROUND 
     A common type of occupant classification sensor uses a load cell to determine the weight of a vehicle occupant. The sensor is located in a load path between an occupant&#39;s seat and the vehicle floor. While the occupant is seated his weight causes a load beam within the cell to deflect. A sense element is mounted to the load beam and is deflected therewith. The sense element converts this deflection into an electrical property indicative of the occupant&#39;s weight. If the load beam is subjected to a large enough force, however, it may be deflected beyond its range of elasticity and assume a permanent deflection or “offset”. This offset is undesirable and, depending on the magnitude of offset and the ability of other electronics in the occupant classification system to compensate for it, may result in a need to replace the sensor. 
     It is therefore desirable to provide a method for mounting an occupant classification sensor which prevents over-deflection of the sensor&#39;s load beam or similar deflecting member. 
     SUMMARY OF THE INVENTION 
     Accordingly, an aspect of the present invention is to provide a method for mounting an occupant classification sensor which limits movement of the sensor&#39;s load beam or other deflecting member. 
     In accordance with these aspects, an over-travel protection device for placing in a load path between a load cell and an object being weighed is presented. The device has a first member adapted for placing in the load path and a second member also adapted for placing in the load path. An elastic member is disposed between the first member and the second member, and a retaining member is adapted to limit separation displacement between the first and second members. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of an over-travel protection device connected to an occupant classification sensor, and 
         FIG. 2  shows a partial cross-section view of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning to  FIG. 1 , an over-travel protection device (OTP)  1  is shown attached to an occupant classification sensor  3 . A pair of bolts  6  secure OTP  1  to a load beam  8  of sensor  3  and a seat base  10 . Seat base  10  and a seat rail  18  are omitted from  FIG. 1  to provide an unobstructed view of OTP  1 . A bushing  12  and washer  14  are provided at each bolt  6  location to evenly distribute the bolt&#39;s clamping load through beam  8 . A bolt  16  is provided for attaching OTP  1  to a seat rail  18 . The OTP  1  has a shunt body  20  with a pair of threaded openings  22  for receiving bolts  6  and a third opening  24  for receiving top member  25 . A lateral clearance  28  is defined by top member  25  and the perimeter of third opening  24 . 
     Turning to  FIG. 2 , a cross section diagram of an OTP  1  is shown arranged in a load path between a seat rail  18  and a seat base  10 . Occupant classification sensor  3  is also arranged in the load path between the OTP  1  and the seat base  10 . 
     In pertinent part, load beam  8  of the occupant classification sensor (OCS)  3  is secured to the seat base  10  at each end by bolts  6 . Each bolt  6  is coaxially aligned with a washer  14  and a bushing  12 , and is threadably secured to shunt body  20 . Seat base  10  is clamped between the shunt body  20  and the bushings  12 , thereby securing the OTP  1  and OCS  3  to seat base  10 . The bushings  12  and washers  14  further operate to minimize residual forces in beam  8  due to torque forces applied by bolts  6 . An orifice is provided at the center of beam  8  for receiving bushing  12 , which is coaxially aligned with a washer  14 . 
     OTP  1  has a stud  30  with an integral bolt  32 , which provides an attachment point for the load beam  8 . Integral bolt  32  protrudes through a bushing  12  and a washer  14 . Nut  34  is threaded to the integral bolt  32  and compresses the assembly of beam  8 , bushing  12  and washer  14 , against a shoulder  36  of stud  30 . A retaining lip  38  extends radially to the outer periphery of stud  30 . 
     The OTP  1  also has a top member  25  with a threaded opening  23  disposed therein, which provides an attachment point for the seat rail  18 . Bolt  16  secures seat rail  18  to the top member  25 . Bolt  16  may also secure a seat motion component  42 , such as a movement member for power seats. In one aspect of the invention the threaded opening  23  is coaxial with integral bolt  32  of the stud  30 . 
     Looking briefly to within dashed oval A, a portion of the top member  25  is shown prior to a crimping operation. A crimp flange  44  is provided at the outer periphery of top member  25 . A compressible element  46 , such as made from a rubber material, is disposed within a cavity defined by the adjacent portions of top member  25 , stud  30 , and retaining lip  38 . During manufacture of the OTP  1 , crimp flange  44  is crimped radially inward to become retaining ledge  44 ′ as shown in dashed circle B. The retaining ledge  44 ′ is dimensioned to capture retaining lip  38  within the radially outer portion of top member  25 , thereby limiting separation displacement between top member  25  and stud  30 . 
     An shunt body  20  has a cavity for receiving top member  25 , which protrudes from opening  24 . A shunt ledge  54  extends over a shoulder formed in top member  25 . An upper vertical clearance  50  is provided between the shunt ledge  54  and seat rail  18 , and a lower vertical clearance  52  is provided between the shunt ledge  54  and the shoulder of top member  25 . 
     In operation, an OTP  1  is placed at a mounting point for a vehicle seat. At the mounting point, the vehicle seat (not shown) is engaged with seat rail  18 , and seat base  10  is made fast to the vehicle floor. The OTP  1  and OCS  3  are secured between the seat rail  18  and seat base  10 . When an occupant is seated, the occupant&#39;s weight is distributed among several, usually four, vehicle seat mounting points. A portion of the occupant&#39;s weight is shown as force F, which is approximately equally distributed through the load path to seat base  10  via bolts  6 . 
     For levels of force F which are within the predetermined operating range of OCS  3 , the force is applied to the load beam  8  via a path through the top member  25 , compressible element  46 , and stud  30 . As force F is applied, the seat rail  18  deflects vertically by an amount Δx together with the columnar assembly of the top member  25 , compressible element  46 , and stud  30 . As the columnar assembly deflects vertically, one of the upper or lower vertical clearances  50 ,  52  gradually closes depending on whether F is positive (downward) or negative (upward) respectively. The load beam  8 , which is connected to stud  30 , also deflects vertically by Δx. 
     In accordance with the present invention, the unloaded height of upper and lower vertical clearances  50 ,  52  is determined by the maximum allowable positive and negative deflections of load beam  8 , respectively. When a force F is applied that would otherwise deflect the load beam  8  beyond its maximum allowable deflection, one of the clearances  50 ,  52  closes against shunt ledge  54  and prevents over-deflection of the load beam. For example, when an excessive positive, or downward, force F is applied to the seat rail  18 , the seat rail deflects downward and lands against shunt ledge  54 , thereby closing upper vertical clearance  50  and limiting deflection of the load beam  8 . The portion of force F which would otherwise over-deflect load beam  8  is thereby shunted through shunt body  20  to the seat base  10 , protecting the load beam  8  from over-deflection in the positive direction. Similarly, when an excessive negative, or upward, force F is applied to the seat rail  18 , the seat rail deflects upward and lands the shoulder of top member  25  against shunt ledge  54 , thereby closing lower vertical clearance  52  and limiting deflection of the load beam  8 . The portion of force F which would otherwise over-deflect load beam  8  is shunted through shunt body  20  to the seat base  10 , protecting the load beam  8  from over-deflection in a negative direction. 
     If an offset load component, such as a force perpendicular to force F, is applied to the seat rail, load beam  8  experiences a bending moment as indicated by moment arrows M. In this situation, deflection of load beam  8  is also limited. As the offset force increases, top member  25  moves laterally until lateral clearance  28  closes when top member  25  comes to rest against shunt body  20 . A small portion of the lateral force acts upon load beam  8  through top member  25 , compressible member  46 , and stud  30 . The more significant remainder of the lateral force is shunted to seat base  10  via shunt body  20 , thereby protecting load beam  8  from an excessive bending moment. Compressible element  46  may also be used to absorb all or some of lateral displacement of top member  25 , thereby limiting lateral displacement of stud  30 . Compressible element  46  also effectively prevents load beam  8  from being influenced by forces other than F. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.