Abstract:
An adjustable lumbar support, for use in the back rest of a seat, includes a flexible band which in use extends longitudinally across the back rest so that opposite ends of the band are adjacent respective opposite sides of the back rest and further includes adjusting means operable to vary the extent to which the flexible band is able to curve rearwardly relative to the seat back rest. The flexible band includes a plurality of elongate members which are spaced along, and extend transversely with respect to, the longitudinal extent of the band, and a respective resiliently compressible bridging element joining together successive elongate members. Each elongate member is sufficiently flexible whereby at least some of the elongate members are adapted to bend resiliently at opposite end portions thereof, and thereby to bend rearwardly to conform substantially to the shape of and provide resilient support for the lumbar region of an occupant of the seat, as the adjusting means is operated to reduce the extent to which the flexible band curves rearwardly.

Description:
FIELD OF THE INVENTION 
   This invention relates to an improved lumbar support for use in the back rest of a seat, chair and the like. The invention is particularly suited for use with seats for vehicles of all kinds, including land vehicles, water borne vehicles and aircraft. For ease of description, the invention will be hereinafter described with particular reference to vehicle seats. 
   BACKGROUND TO THE INVENTION 
   It is well known to provide adjustable lumbar supports in vehicle seats, especially in the seat to be occupied by the vehicle driver. Usually lumbar supports are adjustable to assist in combating driver fatigue by the driver being able to adjust the support to suit his or her individual comfort requirements. Most supports conform to one of two principal types, namely vertically adjustable and horizontally adjustable supports. 
   The vertically adjustable type of lumbar support has a thin, usually rectangular form provided by a sheet of resilient material or a mesh or grid of resilient elongate members of metal or plastics material. With this type, an actuator is operable to vary the spacing between upper and lower edges of the support to adjust the extent to which the support bows or flexes forwardly about a laterally extending line. 
   The horizontally adjustable type of lumbar support has the form of a flexible band which extends longitudinally between opposite sides of a vehicle seat frame. An actuator is operable to adjust the depth of rearward curvature of the band, about a vertical line, against pressure applied by an occupant of the seat, such as by adjusting the effective longitudinal length of the band. 
   With the vertically adjustable type, the forward bowing or flexing causes lower portion of the padding and covering at the front of the seat back to be correspondingly pushed forward, as the support adopts a shape which is complementary to the lumbar region of an occupant of the seat. The arrangement is such that the seat back can have a thickness or depth which is substantially independent of the presence of the lumbar support. Thus, in line with the trend to reduce weight and maximise available space, such as in a land vehicle cabin, a designer&#39;s freedom in creating a seat back is not compromised by the need to allow for the thickness of a lumbar support of this type. 
   In the case of the horizontally adjustable type of lumbar support, a substantially greater thickness needs to be accommodated by the seat back rest. This is because the band has a significant effective depth due to it having a front face which has a convex form conforming somewhat to the lumbar region of standardized occupant. The lumbar support of this type therefore necessitates a thicker seat back rest and therefore limits the extent to which the seat back thickness can be reduced. Thus, it is not possible to reduce the thickness of the seat back rest to much less than the front-to-back thickness of the seat frame and, as will be appreciated, it is the seat back thickness within the frame of a front seat which determines the maximum available space for the knees of a rear seat passenger. 
   The greater thickness required for horizontally adjustable lumbar supports results from them conforming to the curvature of an occupant&#39;s back as a consequence of the designed shape of the flexible band. That is, the flexible band as produced has a front face which is shaped to complement that curvature. Specifically the front face is curved with respect to a horizontal centre line so as to be arcuate in end elevation, whereby as mounted on a seat frame, upper and lower edges of the flexible band are located rearwardly with respect to the centre line. This form of front face is necessary since operation of an actuator to vary the length flexible band acts to vary the curvature of the band somewhat circumferentially with respect to the waist of an occupant, rather than to conform the band to the curvature of the lumbar region. 
   In essence, the vertically adjustable type of lumbar support is conformable to the curvature of an occupant&#39;s lumbar region during adjustment, whereas the horizontally adjustable type has a flexible band which is pre-shaped to conform to that region. 
   It is an object of the present invention to provide a lumbar support of the horizontally adjustable type which is conformable during adjustment to the curvature of the lumbar region of the occupant of a seat. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention provides an adjustable lumbar support for use in the back rest of a seat, wherein the lumbar support includes a flexible band which in use extends longitudinally across the back rest so that opposite ends of the band are adjacent respective opposite sides of the back rest and further includes adjusting means operable to vary the extent to which the flexible band is able to curve rearwardly relative to the seat back rest; wherein the flexible band includes a plurality of elongate members which are spaced along, and extend transversely with respect to, the longitudinal extent of the band, and a respective resiliently compressible bridging element joining together successive elongate members; and wherein each elongate member is sufficiently flexible whereby at least some of the elongate members are adapted to bend resiliently at opposite end portions thereof, and thereby to bend rearwardly to conform substantially to the shape of and provide resilient support for the lumbar region of an occupant of the seat, as the adjusting means is operated to reduce the extent to which the flexible band curves rearwardly. 
   The flexible band is longitudinally resiliently compressible, due to the bridging elements being resiliently compressible. Most preferably each bridging element comprises a resilient spring element. Each spring element, when compressed longitudinally of the band, resiliently biases apart the successive elongate members it bridges whereby the elements act to maintain or restore the length, and hence act to maintain or restore the extent of rearward curvature, of the flexible band. The adjusting means acts against the bias of the spring elements in operating to decrease the extent of rearward curvature of the band by causing the spring elements to compress and thereby decrease the effective length of the band. 
   Each spring element most preferably has the form of a pair of oppositely acting leaf springs and hereinafter is described as such. With that form, the leaf springs of each pair most preferably are joined together at respective ends while each spring is joined intermediate its ends to a respective one of the successive elongate members bridged by the spring element. However the converse is possible in that the leaf springs of each pair may be joined together intermediate their ends in a back to back arrangement, with each spring of the pair having both of its ends joined to a respective elongate member. In each case, the spring element preferably is integrally formed and may be assembled with elongate members to form the flexible band. However, the entire flexible band most preferably is integrally formed. 
   The flexible band most conveniently is made of a suitable polymeric material such as polypropylene. Preferably the band is formed by injection moulding, whether of separate components to be assembled together or as an integrally formed band. 
   As indicated, the flexible band of the lumbar support of the present invention is able to conform substantially to the shape of the lumbar region of an occupant of a seat in which the support is provided as the adjusting means is operated to reduce the extent to which the flexible band curves rearwardly. The flexible band conforms by the elongate elements bending resiliently at opposite end portions. The bending is in response to pressure applied to the band by the body of the occupant as the band is drawn against the occupant&#39;s lumbar region. However, the arrangement is such that in the absence of applied pressure, such as due to there not being a seat occupant, the end portions of the elongate members do not bend as the adjusting means acts to reduce the extent to which the band curves rearwardly. The band then is able to be drawn to a condition in which it has negligible rearward curvature, preferably such that the band is able exhibit a substantially planar front face, Particularly where this is the case, the flexible band is able to have an effective depth between front and rear faces which is small compared to the above-mentioned known horizontally adjustable lumbar supports. Thus, the flexible band may have a thickness of from about 3 to 6 mm. However, even with such thickness, the band can be of relatively light weight and provide efficient material usage, in being of thin wall construction. Thus, in one form, each elongate member may comprise a thin elongate plate provided with strengthening ribs, such as on a rear face of the plate. Alternatively, each elongate member may be of a skeletal, open-mesh or grid-like structure. 
   Where each elongate member comprises a thin plate provided with strengthening ribs, the resistance they exhibit to resilient bending at opposite end portions is, in large part, determined by the depth of the strengthening ribs. The depth of the ribs therefore is chosen such that the resistance to bending is sufficient to ensure that, in conforming to the lumbar region of an occupant of the seat, the end portions of the elongate members contribute to the occupant&#39;s awareness of support. Achieving a sufficient level of resistance to bending necessitates a suitable balance being achieved between the thickness of the plate, the number, form and disposition of the ribs and relevant characteristics of the material of which the elongate member is made. Similar considerations apply to the elongate members of a skeletal, open-mesh or grid-like structure. 
   Particularly where the flexible band is to have a relatively small effective depth, it is preferred that the bridging elements do not exceed the longate members in depth. Where each bridging element has the form of a pair of opposed leaf springs, each half may have a depth which is greater than its thickness in a direction longitudinally of the band. For a given material of which the bridging elements are made, the depth and thickness of each half of the bridging elements are determined by the resilient biasing force the bridging element is to be able to exert. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate a preferred embodiment of the lumbar support of the present invention. The detailed description of the drawings is to assist with an appreciation of the construction and function of the lumbar support. In the drawings: 
       FIG. 1  is a perspective view from the front of a lumbar support according to an embodiment of the invention, shown in a first condition; 
       FIG. 2  corresponds to  FIG. 1  but shows the lumbar support in a second condition; 
       FIG. 3  is a rear elevational view of the lumbar support of the embodiment of  FIG. 1  shown in an extended, unmounted condition; 
       FIGS. 4  to  7  each shows a respective termination for a lumbar support according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1  to  3 , there is shown a part of a seat back frame F for a vehicle. The frame F has laterally spaced, upwardly extending side sections S jointed together at the top of frame F by a cross-bar (not shown). Mounted between sections S of frame F, there is a lumbar support  12  according to an embodiment of the present invention. The lumbar support  12  includes an elongate flexible band  16  having a respective connecting tongue or section  18  at each end by which it is coupled to a respective side section S of frame F. The support  12  further includes an actuator system  20  shown in FIG.  3 . 
   The flexible band  16  is integrally formed by injection moulding from a suitable polymeric material such as polypropylene. Band  16  comprises a plurality of elongate members  24  and bridging elements  26 . The members  24  extend laterally with respect to the longitudinal extent of, and an uniform intervals along, band  16 . A respective element  26  interconnects successive members  24 , while a respective connector portion  28  interconnects the member  24  nearest each end of band  16  to the adjacent end tongue  18 . 
   Band  16 , as produced, is such that the front face of each member  24  and each element  26  is able to be substantially in a common plane as depicted in FIG.  3 . Each member  24  has a front face defined by a thin plate  30  such as of 0.7 to 1.2 mm thick. However, as seen in  FIG. 3 , each member  24  is stiffened at the rear of plate  30  by a plurality of ribs or fins  32  which extend along a major part of the length of its plate  30 . The ribs  32  have a width dimension perpendicularly of the plate  30  which is greater than the plate thickness, such that the members  24  may have a thickness of about 3 to 6 mm. Also, each connector portion  28  has a front face defined by a similarly thin plate  34  which is braced by short transverse ribs  36 , while end tongues  18  have the form of a strap of similar thickness to the plate  34 . 
   Each bridging element  26  is compressible longitudinally of band  16  as a result of element  26  comprising a spring element having a pair of spring members  38 . As a consequence of elements  26  being compressible, the length of flexible band  16  is able to be varied between the length shown in  FIGS. 1 and 3  and the reduced length shown in FIG.  2 . The length of band  16  is able to be varied in response to variation in the extent to which band  16  curves rearwardly of frame F, between sections S, from a maximum condition of rearward curvature such as shown in  FIG. 1  to a condition of zero or negligible curvature such as shown in FIG.  2 . 
   In the arrangement of  FIGS. 1  to  3 , the spring members  38  of each pair have the form of opposed leaf springs. At their upper and lower ends, the members  38  are joined together at  40  and  41 , respectively. Intermediate their ends, each member  38  of a pair thereof is joined at  42  to a respective one of the successive elongate members  24  between which the respective bridging element  26  is provided. 
   In the arrangement shown, each spring member  38  has a width in the front to rear direction of band  26  which corresponds substantially to the thickness of elongate members  24 , such as from 3 to 6 mm. Each member  38  has a thickness in the longitudinal direction of band  16  which is less than its depth, such as of about 0.7 to 1.2 mm. However, other relative depth and thickness dimensions are possible, with these being chosen for a given material of which band  16  is made to achieve a required level of resilient compressibility for elements  26 . 
   Alternative arrangements are possible for elements  26 . Thus, for example, rather than springs  38  being opposed and joined together at their ends, they may be in back to back relationship relative to that shown. That is, each spring  38  of a pair may be in the position located by the other, with each of its ends joined to a respective member  24  and the members  38  of the pair joined to each other in a back to back relationship, at a location intermediate the ends of each of them. 
   Still further alternatives are detailed later herein. 
   The actuator system  20  of lumbar support  12  has an actuator device  44  and a Bowden cable system  46 . The actuator device  44  is operable to adjust the flexible band  16  between the respective conditions shown in  FIGS. 1 and 2 . For this, device  44  is mounted in a fixed location by lugs  48  and, by rotating a handle  50  relative to housing  52 , device  44  moves a cable  54  of system  46  longitudinally within a sleeve  56  of system  46 . The direction of movement of cable  54  in sleeve  56  is determined by the direction of rotation of handle  50 . 
   The device  44  can take a variety of forms. A preferred example is disclosed in our co-pending U.S. patent application Ser. No. 10/618,821 by Macaulay and Harris, entitled “Cable Actuator for Lumbar Support”, filed Jul. 15, 2003, the disclosure of which is incorporated herein. Further examples are disclosed in U.S. Pat. No. 5,638,722 to Klingler; U.S. Pat. No. 6,053,064 to Gowing et al; and U.S. Pat. No. 6,520,580 to Hong, the disclosure of each of which also is incorporated herein by reference. 
   As shown in  FIG. 3 , the cable  54  of Bowden system  46  extends beyond the end of sleeve  56  remote from actuator device  44 . The cable  54  and sleeve  56  extend through a slot  58  in a first end section  18  of band  16 . The sleeve ends at a cylindrical termination  60  which is secured by a snap fit between fingers  62  defined at the back of the connector portion  28  adjacent to the first end section  18 . The cable  54  extends through the termination  60  and along a longitudinal centre region of band  16 . A termination  64  secured on the free end of cable  54  is secured by a snap fit between fingers  63  defined at the back of the connector portion  28  which is remote from the portion  28  at which termination  60  is held. 
   Considering the lumbar support as seen in  FIG. 3 , the arrangement is such that, by rotating handle  50  in a direction causing cable  54  to be retracted into sleeve  56 , the effective length of flexible band  16  is reduced. This reduction results from tension in cable  54  compressing the bridging elements  26 , to cause resilient flexing of spring members  38  and a reduction in the spacing between successive elongate members  24 . If handle  50  then is rotated in the reverse direction, to cause cable  54  to extend further from sleeve  56 , band  16  is able to recover to the condition shown in  FIG. 3  by members  38  recovering substantially to their unstressed condition. 
   The length of band  16  is such that, when mounted on frame F with members  38  substantially unstressed, band  16  is able to curve rearwardly of frame F as shown in FIG.  1 . That is, the length of the section of band  16  between side sections S of frame F is greater than the spacing between section S. The arrangement is such that, as handle  50  of actuator device  44  is rotated to retract cable  54  into sleeve  56 , to thereby compress elements  26 , the extent of rearward curvature of band  16  is able to be progressively reduced until it is is negligible or substantially zero, as shown in FIG.  2 . In this regard, it is to be appreciated that the reference to rearward curvature is in relation to the longitudinal extent of band  16 , as distinct from curvature of elongate members  24  as described in the following. 
   As shown in  FIG. 1 , each elongate member  24  is in a condition in which the front face of its plate  30  is substantially planar. However, due to the rearward curvature of band  16  as shown in  FIG. 1 , the front face of each plate  30  is in a respective plane, rather than in a common plane as in the condition shown in FIG.  3 . Whether the front face of each plate  30  remains planar as the rearward curvature of band  16  is reduced to zero depends on whether or not there is an occupant in the seat in which support  12  is provided. Where there is no seat occupant, each plate is able to be brought into a position similar to that shown in  FIG. 2 , but with the front face of each plate  30  substantially co-planar. Where there is an occupant in the seat, reduction in the rearward curvature becomes progressively more strongly resisted by the occupant&#39;s body. As a consequence, the upper and lower end portions of at least some members  24  are resiliently bent rearwardly, as depicted in  FIG. 2 , by reaction forces generated by the occupant&#39;s body acting to cause the end portions to bend to conform to the shape of the lumbar region of the occupant. Thus, the front face of at least some members  24  cease to be planar and adopt convex forms as shown in FIG.  2 . 
   The bending of the end portions of members  24 , of course, necessitates band  16  being at an appropriate height on sections S of the seat back frame F, at which the mid-region of the members  24  is aligned with the hollow of the occupant&#39;s back at the lumbar region. Also, bending of the end portions of members  24  is assisted by cable  54  extending across a mid-region of each member  24  such that both opposite end portions of each member  24  are free to resiliently bend rearwardly. Also, as the end portions bend resiliently, they are able to recover so that members  24  resume the shape shown in  FIG. 1 , as actuator device  44  is operated to increase the extent of rearward curvature of band  16 . This recovery results from the band  16  moving away from the occupant&#39;s lumbar region and ceasing to be forced to conform to the shape of that region. 
   As best seen in  FIGS. 1 and 2 , the ribs  32  of elongate members  24  and the members  38  of elements  26  are notched to accommodate and centrally locate is cable  54 . The cable  54  is thereby effectively able to be retained in position by the combined action of tension in cable  54  and the resilience of bridging elements  26 . 
   The form of connection to each side section S is shown in  FIG. 4  for the end of band  16  remote from actuator device  34 . As indicated by this, the end tongue  18  extends around to the outer side face of the respective side section S of frame F. The tongue  18  is secured by a screw, rivet or other suitable fastener (not shown) applied through hole  65  of tongue  18  into frame section S. An alternative is shown in  FIG. 5 , in which the tongue  18  of band  16  extends around a major part of the circumference of frame section S. As shown in  FIG. 5 , the tongue  18  is secured by a screw  66 , rivet or other suitable fastener, extending through tongue  18  into the inner side face of section S. As shown in  FIG. 4 , the respective tongues  18  may be strengthened around the holes  18   a  by bead or rib formations  68 . 
   A further variant is shown in FIG.  6 . This differs principally in that tongue  18   a  increases in width to its free end and accommodates a laterally spaced pair of attachment holes  65   a . The tongue  18   a  may wrap around a frame section S to the outer side face, as in  FIG. 4 , or the tongue  18   a  of  FIG. 6  may be secured by screws or other fasteners to the front or rear face of a section S (not shown). 
   An alternative approach is shown in FIG.  7 . In this, tongue  18   b  has a number of raised tabs  69  spaced across the lateral extent of its free end. The tabs define holes which are aligned with each other and through which a stiff wire connector  70  extends. The connector  70  has a part rectangular form to define two opposed legs  72  which are able to hook into tabs or holes found in a frame section S (not shown). 
   In  FIGS. 5 and 7 , the respective elongate member  24 ,  24   b  nearest to the end of flexible band  16 ,  16   b  shown is in the condition illustrated in FIG.  2 . That is, the opposite end portions of the respective member  24 ,  24   b  are shown bent rearwardly, as in conforming to a seat occupant&#39;s lumbar region.  FIG. 5  is from the rear and hence shows the concave rear face rather than the convex front face evident in FIG.  7 . 
   In addition to the form of elements  26  as described with reference to  FIGS. 1  to  3 , and the alternative detailed above of an arrangement having members  38  in a back to back relationship, still further alternatives are possible. Thus, in relation to elements  26  as shown in  FIGS. 1  to  3 , one further alternative would be similar, but comprising a pair of spring elements of a V-shape which point away from each other. In this case, each spring element would have a respective end connected to each elongate member, with a short spacing between the ends of each of the elements such that they are connected only through the elongate members. This readily can be appreciated from  FIGS. 1  to  3  by considering the notches in which cable  54  is accommodated as extending across the side of each member  24  to the front face. A still further alternative can be appreciated from the back to back arrangement for members  38 , the still further alternative comprising a pair of spring elements of a V-shape which point towards each other, with their apices close to each other but not connected together. Again, the elements would be connected only through the elongate members. 
   Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.