Abstract:
A seat suspension arrangement intended to provide greater protection for occupants of a vehicle seat in the event of a rearward collision in a motor vehicle, comprises a platform element intended to be supported in the frame of the back rest of a vehicle seat in order to provide support for the seat upholstery, the platform element comprising side rails ( 1 ) between which are coupled sinuous wire springs ( 3 ) and a plurality of link means ( 6, 300, 301, 302 ) by means of which the platform element may be suspended in the frame of a vehicle seat. At least some of the link means ( 300, 301, 302 ) are designed to collapse under abnormal load such as would occur in a vehicle collision from the rear, to allow the platform element to move relatively to the seat frame and thus to provide protection for the seat occupant against rearward impact.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to PCT/EP02/13452 filed on Nov. 28, 2002; which claims priority to Great Britain Patent 0227534.5 filed Nov. 26, 2002; which claims priority to Great Britain Patent 0128417 filed Nov. 28, 2001. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an improved seat suspension arrangement, more especially of the kind intended for use in the backrest of a vehicle seat. 
   2. Related Art 
   In the vehicle seat, it is well known to provide support for the upholstery of the seat by means of a platform element that is suspended between two opposite side elements of a seat frame in such a manner as to provide resilient support for the upholstery. Arrangements are known in which the platform element is flexible but substantially inextensible, and wherein tension springs are provided to support the platform element between the side elements of the seat frame. Other arrangements are known wherein the platform element itself is resiliently extensible in a transverse direction, and in that case the platform element can be attached to side elements of the seat frame by link means that are substantially inextensible. Platform elements of the latter kind are known, for example, from EP-A-0128407 (see  FIG. 2 ) and GB-A-2316604 (see  FIG. 1 ). 
   Safety requirements in relation to vehicle seats become increasingly more rigorous, and thus, in the design of vehicle seats, those skilled in the art are constantly seeking measures that may be adopted in order to reduce personal injury that may occur to occupants of the seats in the event of a motor vehicle accident. 
   It has, for example, been proposed that the frames of vehicle seats should be adapted to allow a limited collapse in the event of the application of sudden loads exceeding those occurring in normal use, in order, for example, to reduce injury to an occupant due to sudden forward acceleration of the seat. This may occur, for example, if a motor vehicle is subjected to a sudden impact from the rear when a following vehicle collides therewith. 
   Arrangements for providing for the collapse of vehicle seat frames, are, however, of complicated construction and are thus relatively expensive. 
   Other arrangements for collapse of seat suspension assemblies have also been proposed but are also relatively complicated, see for example WO 99/29536 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a simplified means that will enable the occupant of a vehicle seat to be cushioned from a sudden forward acceleration applied to the vehicle seat frame, for example as a result of a collision. 
   The invention provides a seat suspension arrangement comprising: a seat back platform element having a side margin; and a collapsible extensible link means connected to the side margin, the link means substantially restraining the side margin from displacement during normal loading conditions and yielding under abnormal loading conditions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further preferred features and attendant advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which, 
       FIG. 1  is a front elevation of a seat back rest incorporating an arrangement of known type referred to above, 
       FIG. 2  is a diagrammatic view illustrating an occupant of a vehicle seat shown in the normal seated position, 
       FIG. 3  is a view similar to  FIG. 2  but showing the occupant of a conventional vehicle seat in a position that would normally occur after the vehicle has been involved in a collision from the rear, 
       FIG. 4  is a diagrammatic view similar to  FIG. 2  but showing the position of the occupant of a vehicle seat after a vehicle has been involved in a rearward collision when occupying a vehicle seat in accordance with the present invention, 
       FIG. 5  is a perspective view showing one example of a link means for securing a platform element to a seat frame in accordance with the present invention, 
       FIGS. 6–10  are similar views of alternative forms of link means, 
       FIG. 11  is a perspective view of the links means shown in  FIG. 10  taken from the opposite side, 
       FIG. 12  is a side elevation of a link means as shown in  FIG. 9  or  FIGS. 10 and 11 , but in a deformed state such as would occur after a vehicle has been involved in a collision from the rear, 
       FIG. 13  is a perspective view of a link means for incorporation in a cable adjustment mechanism of a seat arrangement as shown in  FIG. 1 , 
       FIG. 14  is a front view of one embodiment of platform element of a seat arrangement according to the invention shown equipped with link means of kinds shown in  FIGS. 9–11 , 
       FIG. 15  is a graph showing force deflection characteristics of seat suspension arrangements under conditions of abnormal load that would occur during a vehicle collision, 
       FIG. 16  is a similar view showing force deflection characteristics in the upper region of a seat suspension arrangement in accordance with the invention, 
       FIG. 17  is a similar view showing force deflection characteristics in the middle part of a seat suspension arrangement in accordance with the invention, 
       FIG. 18  is a further similar view showing force deflection characteristics in the lower part of a seat suspension arrangement in accordance with the invention, and 
       FIG. 19  is a view similar to  FIG. 18  but showing force deflection characteristics in the lower part of a suspension arrangement in accordance with the invention, when equipped with link means of the kind shown in  FIGS. 10 and 11  of the drawings. 
   

   Referring to  FIG. 1 , which illustrates an arrangement as shown in GB-A-2316604, it will be seen that a platform element comprises a pair of side rails  1  interconnected by a plurality of transverse supporting wires  3  that are angled at  3 A so that they form sinuous wire springs allowing for limited transverse stretching of the platform element. The arrangement of the sinuous wire springs may, for example, be such that they can be extended to a point at which the wires adopt almost a straight line under the maximum load normally expected upon the seat. At this point the platform element will be resistant to further resilient extension, and forces placed on the platform element will be transmitted directly to wire links  6  coupling the platform element to a seat frame  5 . In a known vehicle seat, the system presented by the platform element and the wire links securing it to the seat frame will present a substantially rigid and inextensible system and will thus transfer to the occupant of the seat any abnormal force of acceleration such as may occur as a result of an impact upon the motor vehicle from the rear. 
   The effect of an impact from the rear on the occupant of a vehicle seat of conventional construction is illustrated diagrammatically in  FIGS. 2 and 3 .  FIG. 2  shows the posture of an occupant of a vehicle seat when seated in a normal travelling position. For simplicity, there is shown in the drawing only a back rest  200  of the vehicle seat, that, in known manner, will incorporate the seat frame and platform element of an arrangement as shown in  FIG. 1 , the platform element itself being illustrated diagrammatically at  201 . As illustrated in  FIG. 2 , an angle u 1  is defined between the axis  202  of the upper legs of the occupant and the spine  203 . 
   As illustrated in  FIG. 3 , in the event of a vehicle collision involving an impact from the rear, the seat back will collapse into the position shown in  FIG. 3 , the seat back  200  and the platform element  201  being forced backwardly and effectively pivoting rearwardly about the base of the seat. This has the result that there is a sudden increase in the angle between the legs and the spine of the seat occupant that will cause potential injury. An object of the arrangement according to a preferred embodiment of the invention is to allow a controlled collapse of the platform element relatively to the seat frame in such a manner as to avoid such a sudden change in the posture of the occupant of a seat. As shown in  FIG. 4 , it would be desirable that, in the event of a vehicle collision, the back rest  200  of the vehicle seat on the one hand, and the platform element  201  on the other be allowed to collapse in different directions, in order to enable the torso of the occupant of the seat to be cushioned in rearward movement, without substantially changing the relative positions of the legs and spine of the occupant of the seat. Thus, as shown in  FIG. 4 , although the back rest  200  has been forced rearwardly into a reclining position, the platform element  201  has moved rearwardly relatively to the seat back  200  in such a manner that whereas the upper portion of the platform element has moved rearwardly through a distance shown as d 1 , the lower part of the platform element has moved through a greater distance d 2  so that the attitude of the platform element relatively to the legs of the occupant of the seat remains substantially unchanged. 
   As will be described below, this object can be achieved by replacing the known wire links  6  of the conventional construction shown in  FIG. 1  by means of modified link means that are capable of extension under abnormal load. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the arrangement according to the invention, an extensible link means may take various forms and may be designed to collapse under load in such a manner that the increase in length of the link means in proportion to the applied load is either linear, or non-linear. The manner in which the platform element of the seat arrangement yields under abnormal load may thus be tailored to an optimum condition that may be determined by trial and experiment. 
   In  FIG. 5  for example, there is a shown a wire link  10 , one end of which is anchored around a side rail  20  of a platform element of the kind shown in GB-A-2316604, and the other end  10 A of which is hooked for insertion in an appropriate anchorage point provided on a side member of the seat frame. Between the two ends of the wire link an intermediate portion  10 B is angled to form a loop that can extend under a load determined by the material and dimensions of the wire link  10 . 
     FIG. 6  shows another arrangement wherein the side rail  20  of the platform element is engaged by hooked ends  30  of a U-shaped wire yoke  31 . A wire link  11  of which a free end is linked to seat frame in a manner not illustrated is wound around an intermediate portion of the yoke  31 , as illustrated at  40 , and is extended to provide a hooked end  12  that terminates in spaced relation to the side rail  20 . Thus, when the platform element is placed under abnormal load, the side rail  20  is allowed to yield relatively to the seat frame until the hooked portion  12  of the wire link  11  engages the side rail  20  in order to provide additional restraint. Such yielding of the side rail  20  is allowed owing to the fact that the portion  40  of the wire  11  will unroll around the yoke  31  under tension and/or the yoke  31  itself will bend. The precise action will be dependent upon the relative diameters of the wires  11  and  31  which can be selected to give the desired result. 
   In the arrangement of  FIG. 7 , the side rail  20  is engaged by a metal strap  50  of which a free end is anchored to the seat frame in a manner not shown. The metal strap is looped around the side rail  20  and a T-shaped tongue  51  thereof is arranged to engage through a correspondingly shaped slot  52 . Under abnormal load, the portion of the strap  50  that is looped around the side rail  20  can extend by unrolling of the loop in the strap  50  until the T-shaped head of the tongue  51  is trapped at the end of the slot  52 . 
   In  FIG. 8 , a metal strap  60  has looped ends  61  and  62  for respective engagement with the side rail of a platform element and with the frame of a seat, and incorporates an S-shaped centre portion  63  that can extend under load. 
   In  FIG. 9 , the side rail  20  is engaged by a wire link  70  that is similar to the link  10  of  FIG. 5 , with the exception that a looped portion  70 A is of S-shaped rather than U-shaped configuration. 
     FIGS. 10 and 11  show another arrangement wherein a wire link  80  has a looped end  81  for engagement around the side rail of a platform element, and a hooked end  82  for engagement within a seat frame. An intermediate looped portion  80 A is formed in an S-shaped similar to the link of  FIG. 9 , but the respective ends of the S-shaped link are interconnected by a further wire link  90  that is looped around the first link  80  in the manner illustrated. This has the effect that extension of the wire link  80  is prevented until the load transmitted between the respective ends thereof is sufficient to unroll a hooked end of the interconnecting link  90  and allow the S-shaped loop to expand. This arrangement is such as to modify the relationship between the linear extension of the link  80  and the applied load, in such a manner that the load reaches a peak value at which the link  90  fails, before the link  80  is allowed to expand. Continued expansion of the link  80  then occurs. This particular characteristic is such as to allow a controlled collapse of the platform element that is believed to be particularly effective in preventing the transfer of shocks to the occupant of a seat in the event of an accidental collision. 
   It will be appreciated that although the deformable links referred to above may be formed of spring steel as in the case of existing links conventionally used, the deformation that is required to achieve the desired extension of the links, under abnormal load, is not resilient extension in the manner of a normal spring but is effected by plastic deformation of the material of the link beyond its yield point.  FIG. 12  shows for example the permanently deformed condition of a link of the kind shown in  FIGS. 9–11  after it has been subjected to an abnormal load. 
   Referring to  FIG. 13  there is shown a further embodiment of the invention that comprises a modified clip for use in the known arrangement of adjustable back rest as shown in  FIG. 1 . It will be seen from  FIG. 1  that side rails  1  of the platform element, in addition to being linked to the seat frame  5  by means of the inextensible links  6 , are further linked to the frame by means of Bowden cables, the inner cores of which are anchored to the seat frame  5  and then passed via outer sheaths  8  to an adjustment mechanism  10 . The outer sheaths  10  of the Bowden cables are anchored at their free ends in clips  7  that extend around the side rails  1 . This arrangement has the effect that when the inner cores  9  of the Bowden cables are subjected to tension by the adjustment mechanism  10 , the free ends of the sheaths  8  are drawn towards the seat frame  5  and carry with them the clips  7  that are anchored around the side rails  1  of the platform element. Thus the transverse wires  3  of the platform element are subjected to additional tension in the lumbar region of the backrest for the purpose of providing lumbar adjustment. 
   In the known arrangement it would clearly be desirable to provide for controlled collapse of the means linking the side rails  1  to the seat frame  5  also in the lumbar region of the platform element, in addition to the regions supported by the links  6 . 
   Referring to  FIG. 13  it can be seen that a clip element  107  has a configuration generally similar to that of the clips  7  of  FIG. 1 , comprising a pair of spaced hook portions  108  for snap engagement over the side rails  1  of the platform element shown in  FIG. 1 , and a further hook portion  109  extending from the opposite margin of the clip and incorporating an anchorage  110  in the form of an aperture designed for engagement with an appropriately shaped mounting at the end of a sheath  8  of the Bowden cable mechanism shown in  FIG. 1 . 
   The clip  107  is thus of generally U-shaped configuration, and, in the base of the U there is provided a longitudinally extending slit  111  that forms a point of weakness. Therefore when the Bowden cable mechanism shown in  FIG. 1  is placed under tension, this tension is transmitted from the seat frame  5  to the hooked portion  109  and thence to the side rail  1  of the platform element via the transversely extending base of the U and the hooked portions  108 . Since the longitudinal slit  111  forms a point of weakness in the base of the U, the clip element becomes deformed under excessive load, by spreading apart of the opposite longitudinal boundaries of the slit  111 , thus allowing the hooked portion  109  to yield relatively to the hooked portions  108 , upon the corresponding deformation of the base of the U. Thus, a controlled yielding of the platform element can be achieved in the region in which lumbar adjustment is provided by the Bowden cables  8 , 9 , in addition to the regions at which yielding may be allowed for by link elements as described with reference to  FIGS. 5 to 11 . 
   As already mentioned, the use of extensible links in accordance with the invention enables a suspension assembly including a platform element to be tailored to provide for a progressive deflection of the platform element under abnormal load, and by selection of appropriate forms of link means energy absorbent elements can be created that will absorb energy by extending under certain levels of force. As will be understood by one skilled in the art, tuning of the deflection characteristics of the suspension arrangement can be achieved by varying the shape of the extensible links, by varying the diameter of the wire from which such links are formed, by varying the number of links coupling the platform element to the seat frame, by varying the number of cross wires in the platform element itself and-the distance between cross wires, by providing additional link means as indicated in  FIGS. 10 and 11  and by varying the diameter of the extra link means provided. 
   Referring to  FIG. 15  there is shown for comparison, force deflection curves illustrating the deflection of the platform element of a seat suspension arrangement under conditions of normal and abnormal load, wherein the applied force in kilonewtons is represented on the abscissa and the corresponding deflection of the platform element in millimeters is represented on the ordinate. 
   The curve A represents an ideal force deflection characteristic of a vehicle seat suspension arrangement designed to collapse in the manner illustrated in  FIG. 4 . Thus, in a first section of the curve A extending from its origin to point  2  and indicated as zone  1 , the seat assembly should have a normal resilient deflection characteristic representing the comfort zone in which forces occurring on the seat assembly in normal use are absorbed resiliently. However, in the event of a rearward collision, the force exerted upon the seat will increase rapidly in the section of the curve between point  2  and point  3 . In this region, the deflection of the seat assembly should remain almost the same as force thereon increases. When the force upon the seat assembly reaches a given threshold, the seat assembly should then allow increasing deflection of the platform element whilst the force upon the seat assembly remains substantially the same, as indicated by the section of the curve A extending between points  3  and  4 . In practice, it is difficult to achieve this ideal deflection characteristic. However, characteristics approximating to the ideal curve can be achieved by selection of appropriate link means positioned at relevant points on the platform element of the seat. Thus, curve B illustrates a force deflection characteristic that may be achieved when conventional link means are used in any given part of the seat, whereas curve C illustrates a curve that may be achieved when, in the same part of the seat, a platform element is linked to the seat frame by extensible links in accordance with the invention. 
   A seat assembly that is tailored to give such differing force deflection characteristics between upper, middle and lower portions of the platform element is illustrated diagrammatically in  FIG. 14 , wherein a platform element of the general construction shown in  FIG. 1  and comprising side rails  1  interconnected by transverse supporting wires  3  is provided with link means that differ to provide different extension characteristics as desired for the respective portions of the seat assembly. Thus, for example, at the upper region of the platform element the side rails  1  are provided with the conventional linking hooks  6  of the kind that are not intended to extend significantly under abnormal loads. At middle and lower regions of the seat assembly the platform element is provided with link means  300 ,  301  that have the general form shown in  FIG. 9  of the drawings but are tailored to provide correspondingly desired extension characteristics. At the base of the platform element, the side rails  1  are provided with link means  302  having the form shown in  FIGS. 10 and 11  of the drawings. 
   Corresponding deflection characteristics of such a seat suspension arrangement are shown in the graphs of  FIGS. 16–19 , wherein  FIG. 16  illustrates the deflection characteristic in the upper region of the platform element connected to the seat frame by links  6 ,  FIG. 17  represents the extension characteristic in the middle portion of the platform element connected to the seat frame by means of the links  300 ,  FIG. 18  represents the extension characteristic of the platform element in the lower region coupled to the seat frame by links  301 , and  FIG. 19  represents the force deflection characteristic in the region of the platform element linked to the seat i frame by links  302 . It will be seen that in  FIG. 19  the deflection curve includes discontinuities indicated at the points x, these points representing positions in the curve at which the additional wire links that are shown as  90  in  FIGS. 10 and 11  are caused to fail.