SEAT WITH DYNAMIC BACKREST PORTION

Abstract: A seat comprises a frame (10), a sitting portion (12) yieldably carried on the frame so as to be displaceable downwardly under the weight of a sitter when seated thereon, a backrest (14) which includes at least a lower, lumbar region supporting part (16), and an L-shaped force transference lever (24) which is pivotally supported on a convex cam (22) secured on the frame, and which is pivotally secured at its lower free end to the rearward part of the sitting portion (12), and at its upper free end to the lower part (16) of the backrest. An intermediate part (18) of the backrest is also pivotally secured to the upper end of the lever (24) so as to be displaceable with the part (16), that intermediate part (18) being hinged to the lower margin of an upper part (20) of the backrest, which part is itself slidably mounted in slots (30) at the top of the seat frame. A sitter thus provides a supporting force for the lumbar region of his back, which force is always related to the sitter's weight and his movements in the seat.

Description: SEAT WITH DYNAMIC BACKREST PORTION TECHNICAL FIELD This invention relates to a seat or seating system for use in static locations, as in the home or office, or in vehicles such as cars, boats and aeroplanes, which seat or seating system has a backrest portion arranged to support the lumbar region of a sitter's back. BACKGROUND ART Seats are structures commonly used by people in a wide variety of situations and circumstances to sit upon. These structures consist of at least a sitting surface or portion, which is essentially horizontal and provides support for the thighs and buttocks of a seated person (the sitter), and a backrest portion which is essentially at an angle of 90 degrees or more to the seating portion and which supports parts of the back of the sitter. A variety of methods have been employed to enhance the degree of support that a particular seat or chair can give to sitters of different shapes and sizes. Such methods typically include the use of (a) upholstery incorporating flexible materials such as foam rubber, (b) springs and other flexible devices and materials for mounting various components to the frame or to each other, and (c) means for adjusting the positional relationship of the various components relative to one another. However, all such methods have only limited value, in that they provide good and positive support to the spine of a seated person for as long as the person remains in the optimum position for which the seat in question was designed. If the sitter changes his or her position - an absolute necessity if the sitter is to remain comfortable and relaxed for any length of time - the supportive function of the seat is lost. DISCLOSURE OF THE INVENTION According to the present invention, there is provided a seat which comprises a seat frame; a substantially horizontal sitting portion on which a sitter may sit, said portion being yieldably carried on said seat frame so as to assume, under the weight of a sitter seated thereon, a displaced position relative to said frame, which position is dependent on the weight of the sitter; an upright backrest portion against which a sitter seated on said sitting portion may recline to support the sitter's back, which backrest portion is adjustably carried on said seat frame; a backrest adjusting means carried on said seat frame and coupled to said backrest portion, for effecting adjustment of the position of said backrest portion relative to said frame, which backrest adjusting means is responsive to displacement of said sitting portion under the weight of a sitter seated thereon, and is arranged to adjust, in response thereto, said position of said backrest portion in dependence upon said weight of a said sitter and in a manner such as to urge said backrest portion against, and so provide support for, a predetermined region (preferably the lumbar region) of the sitter's back, which support is related to, and increases with increase in, the sitter's weight. Preferably, said sitting portion is pivotally secured at a forward part thereof to said frame at a position thereon remote from said backrest portion, and is yieldably carried at a rearward part thereof on said frame at a position thereon near said backrest portion; and said backrest adjusting means is coupled to said sitting portion at said rearward part thereof. In one preferred embodiment of the present invention, said sitting portion is yieldably carried at said rearward part thereof by at least one lever, preferably two similar levers, each of which interconnects said sitting and backrest portions and each of which is pivotally supported on said seat frame at a position intermediate the points of connection of said lever with said portions. Preferably, said point of connection of each said lever with said sitting portion is fixed in position relative to said sitting portion, and each said lever is pivotally supported on said seat frame at a position thereon which moves forwardly relative to said sitting portion as said sitting portion is displaced downwardly under the weight of a sitter seated thereon. Preferably, each said lever is pivotally supported on said seat frame by means of two cooperating cam surfaces provided respectively on said lever and said seat frame, one said cam surface being planar, and the other cam surface being convex towards the planar cam surface; said planar cam surface is provided on said lever and faces downwardly; and said convex cam surface is provided on said seat frame and is convex upwardl . Preferably, each said lever is generally L-shaped and comprises conjoined short and long arms, the short arm having its free end connected to said sitting portion and being pivotally carried on said seat frame, and the long arm having its free end connected to said backrest portion. In an alternative arrangement, said point of connection of each said lever with said sitting portion is fixed in position relative to said sitting portion, and said lever is pivotally supported on said seat frame at a position thereon which moves rearwardly relative to said sitting portion as said sitting portion is displaced downwardly under the weight of a sitter seated thereon. In that alternative arrangement, each said lever is preferably pivotally supported on said seat frame by means of a cam surface and a cooperating cam follower; and said cam surface is provided on said seat frame, is planar and faces upwardly, and said cam follower is provided on said lever and rests on said cam surface. Preferably, each such lever is generally T-shaped and comprises a short cross bar from which a long staff projects; the free end of each said long staff is pivotally coupled with said backrest portion; and one free end of each said cross bar pivotally engages with said sitting portion, whilst the other free end of each said cross bar carries said cam follower. In another preferred arrangement according to the present invention, said backrest adjusting means includes a position sensing means carried on said seat frame and coupled with said sitting portion so as to be responsive to displacement of said sitting portion relative to said seat frame, which sensing means is arranged to produce an output signal dependent upon said displaced position of said sitting portion; an actuating means carried on said seat frame and coupled with said backrest portion so as to position said backrest portion relative to said frame in accordance with an input signal supplied thereto; and a signal transmitting means for transmitting said output signal or a signal dependent thereon to said actuating means so as to serve therein as said input signal. Preferably, said actuating means comprises an electrically energisable actuating motor, preferably one controlled by a closed loop control means. In one preferred arrangement said actuating motor comprises a stepper motor, and said signal transmitting means is arranged to supply a series of electric pulses to said stepper motor, in which series the number of pulses is dependent upon the displacement of said sitting portion as sensed by said sensing means. Alternatively, said actuating means may comprises a fluid pressure operated actuating motor operating under the control of electric and/or fluid pressure control signals. According to another preferred feature of the present invention, there is provided an acceleration limiting means pivotally carried on said seat frame and coupled with said backrest portion or with the or each said lever so as to be responsive to accelerations of said backrest portion relative to said frame, said acceleration limiting means being adapted to control or limit the rate at which the backrest portion may accelerate relative to said seat frame when said sitting portion or said seat frame is subjected to undesirably high accelerating forces. Preferably, said acceleration limiting means is adapted to lock said backrest portion against further movement relative to said seat frame whenever the acceleration of said backrest relative to said seat frame tends to exceed a predetermined high value. Preferably, said backrest portion is pivotally connected to said backrest adjusting means. Said backrest portion may also be pivotally carried on said seat frame, so that said adjusting means is effective to adjust the angular disposition of said backrest portion relative to said seat frame. An additional backrest portion may also be provided, and be carried on said seat frame or on an upright extension of said sitting portion; in which case said backrest portion may be pivotally connected to said additional backrest portion. Said additional backrest portion may also be hingedly or slidably carried on said seat frame; and when hingedly carried thereon, it may also be pivotally coupled with said backrest adjusting means so as to be displaced thereby. Said additonal backrest portion may also comprise two component parts which are hinged one on the other. Other preferred features of the present invention will be perceived from a reading of the description that follows hereafter, and from the claims appended at the end of that description. Various preferred embodiments of the present invention will now be described by way of example and with reference to the accompanying diagrammatic drawings in which: - BRIEF DESCRIPTION OF DRAWINGS Figure 1 shows schematically and in side elevation one embodiment of the present invention; Figure 2 shows in like manner a second embodiment of the present invention; Figures 3 to 8 show in like manner various modified forms of that second embodiment; Figure 9 shows in like manner a third embodiment which comprises a modified form of the first embodiment. BEST MODES FOR CARRYING OUT THE INVENTION From what has been said above, it will be appreciated that in a practical form of seat embodying the present invention, the seat comprises a sitting surface or portion, a backrest portion and a seat frame structure; the sitting portion and the backrest portion are mounted to the frame structure in such manner as to allow relative movement between the sitting and backrest portions within predetermined limits; and the sitting portion and the backrest portion are coupled together by means of a force transferring device (Involving for example levers, cables, pulleys, and electric, hydraulic and/or pneumatic actuating means) which will effect a transference of part of the sitter's weight (ie a transfer of a predetermined proportion of the force acting on the sitting portion when a sitter sits thereon) into the backrest portion, so that the backrest or a part thereof exerts a supporting force against the lumbar region of the sitter, in a predetermined magnitude, over the entire path along which the backrest portion can move. The path of movement of the sitting portion is essentially vertical (ie parallel to the gravitational force 'G' ); and the path of movement of the backrest is essentially perpendicular to the plane of the sitter's back, and may vary with seats designed for different purposes. The backrest may consist of a lower part situated only at approximately the height of the lumbar region of the sitter, or it may consist of such a lower part and an upper part which itself may comprise a single component or a number of inter¬ connected components. The force transference is intended to occur primarily and mainly via that lower part of the backrest, the said upper part of the backrest being mounted to the frame in such a manner that it does not move at all in relationship to the sitting portion, or that it moves significan ly less in relationship to the sitting portion when compared with the movement of the lower, lumbar-supporting part of the backrest. As an optional provision for specific uses, the lumbar supporting section of the backrest may be connected to the seat frame structure by a shock absorbing device or/and by a device which can arrest the backrest in any position and render it immobile or reduce its freedom of mobility. Such a device may be activated, optionally, manually by the sitter , or automatically by a ' mechanism (such as an inertia-type acceleration sensor) which will cause the device to lock whenever acceleration or deceleration rates and forces exceed predetermined safe values, as may be experienced in cars and other vehicles, boats and aeroplanes. Referring now to Figure 1, the seat there shown comprises a frame 10, a sitting surface or portion- 12, a backrest 14 made up of lower, middle and upper parts 16, 18, 20, a cam 22, a force transference device 24 in the form of an L-shaped lever, and an optional inertia- type locking device 26. The parts of the backrest are interconnected by means of hinges (or equivalent hinging means) 28, and the upper part 20 slidably connects with vertical slots 30 formed in the upper part of the frame 10 by means of gliders or rollers 32. The force transference lever 24 is seated on the cam 22, which is itself carried on a horizontal member of the frame 10; is connected by hinges 34 at the end of its short arm to the sitting portion 12 and by other hinges 36 at the end of its long arm to the lower backrest part 16; and is pivotally connected at the end of its long arm to the frame 10 via the inertia- locking device 26 by other hinges 38 . The force Fw, indicated at 40 and produced by the weight of a person 42 (the sitter) occupying the seat, acts vertically on the sitting portion 12, which being hinged along its front edge at 44, for movement in the direction of arrow 46 about the transverse axis 48, effects movement of the force transference lever 24 in the direction indicated by the arrow 50 around a transverse axis 52. That movement in turn causes the lower backrest part 16 to move towards the lumbar region of the sitter 42 and there exert a force Fb, as indicated at 54. That force Fb is determined by the magnitude of the force Fw and the relative sizes of the dimensions 'L' (indicated at 56), *dl* (indicated at 58), and 'd2' (indicated at 60). The force Fb will be a small proportion of the force Fw produced by the sitter, so that the lumbar support exerted on the sitter by the lower part 16 of the backrest will be small for a sitter of light weight, and correspondingly larger for a sitter of greater weight . The cam 22 can be shaped if desired in such a way that the distance 'dl' (indicated at 58) decreases when the sitting portion 12 moves in the direction of the arrow 46 about the hinge axis 48, and vice versa, so that the lumbar support force Fb increases progressively when the lower backrest part 16 is pushed backwards by the sitter when he reclines thereon and rests his back on the backrest 14. Furthermore, the position of the cam 22 on the seat frame relative to the hinging axis 52 of the L-shaped lever 24 on the sitting portion 12 can be made adjustable, so as to vary the dimension 'dl' and thereby alter the proportionality between the gravitational and lumbar support forces 'Fw' and ' Fb' . Whilst the lower part 16 of the backrest 14 is directly and wholly displacable by the L-shaped lever 24, the middle part 18 of the backrest is moved against the back of the sitter to a much lesser extent by movement of that lever 24, whereas the upper part 20 of the backrest is moved only in a vertical direction, as indicated by the arrow 61, by movement of the lever 24. Hence, it will be appreciated that the support for the sitter's back is applied where it is most needed, namely in the lumbar region. The inertia type locking device 26 is effective to inhibit and/or restrict movement of the force transference lever 24 and the associated parts of the backrest 14 whenever the acceleration of that lever (whether caused by a sudden change in the position of the sitter on the seat or in the position of the seat frame 10 itself) exceeds a predetermined high value. The cam 22 may be secured Instead, if desired, to the underside of the force transference lever 24, and caused to rock on the adjacent planar surface of the seat frame 10. Referring now to the second embodiment of Figure 2, and the various modified forms thereof shown in the Figures 3 to 8, (and using the references of Figure 1 for the same or analogous features) the seats there shown likewise each comprise a seat frame 10, a sitting portion 12, a backrest 14 comprising at least a lower backrest portion 16 (or a portion analogous thereto), and a force transference lever 24; and in some of the modified forms of seat the backrest includes an upper backrest portion as will be referred to later. These seats are generally the same as that shown in the Figure 1, but differ principally in that the L-shaped lever 24 of Figure 1 has been replaced by an inverted T-shaped lever 24 having a short cross bar 24A and a long staff 24B projecting therefrom. The free end of the long staff is pivotally connected to the lower backrest portion 16, whilst one free end of the cross bar is pivotally connected to the rearward part of the sitting portion 12 at hinge 34, whilst the other free end of the cross bar carries a small roller 62 which constitutes a cam follower resting on a planar cam surface 64 formed on a horizontal part of the seat frame . It will be appreciated that when the sitting portion 12 is displaced by the weight of a sitter 42, the position on the seat frame at which the T-shaped force transference lever 24 is carried moves progressively rearwardly, which is unlike the corresponding movement in the embodiment of Figure 1 of the position at which the L-shaped lever 24 is supported on its seat frame. Whereas the seat of Figure 2 has only the lower, lumbar-supporting backrest portion 16, the seats of the Figures 3 to 8 have the additional backrest portions as set out below: - In Figure 3, an upper, fixed backrest portion 66 is secured on the upper rearward part of the seat frame 10 for supporting the upper part of the back of the sitter. In Figure 4, an upper, fixed backrest portion 68, similar to that of the Figure 3, has been secured instead to a rear, upright extension of the sitting portion 12. In Figure 5, the force transference lever 24 carries a roller 70 which engages the rear face of an elongated backrest portion 72 which is pivotally suspended at its upper end from the top of the rearward part of the seat frame. In Figure 6, the backrest comprises upper and lower portions 74, 76 which are hinged one on the other, and which are suspended from a hinge 78 carried on the upper part of the seat frame. The upper end of the force transference lever 24 carries a roller 80 which engages the rear surface of the lower backrest portion 76. In Figure 7, an elongate backrest portion 82 is pivotally and slidably engaged at its upper end in slots 84 formed in the upper part of the seat frame, and is pivotally connected near its lower end to the upper end of the force transference lever 24. In Figure 8, an upper backrest portion 86 is pivotally and slidably engaged in slots 88 formed in the upper part of the seat frame, and has its lower part pivotally secured to the upper end of a double-ended lever 90. The lower end of that lever 90 is pivotally connected to a lumbar-supporting backrest portion 92, whilst a central part of that lever is pivotally connected to the upper end of the force transference lever 24. It will be appreciated that in some practical forms of the various seats embodying the systems described above, the seat frame may comprise an assembly of two similar frame sides spaced apart by various transverse members; and the force transference system may likewise comprise an assembly of two similar levers spaced apart by various transverse members, each such lever interconnecting the sitting and backrest portions and being carried on a cam (or an analogous part) which is itself carried on the associated frame side. Figure 9 shows an alternative form of the seat shown in the Figure 1. In that alternative seat, the sitting portion 12 is yieldably supported at its rearward part on a resilient support means (not shown) carried by the seat frame. The sitting portion also rests on a load sensing device 94 which is carried on a horizontal part of the seat frame 10, and is arranged to produce an electrical output signal whose magnitude is dependent upon the force applied to the load sensing device by the sitting portion when a person is seated thereon. That output signal is transmitted via a signal transducing and transmitting means 96, which is arranged to supply in response to such signal a train of electrical output pulses to an electrical actuating motor 98 of the stepper kind. The number of pulses in that train is dependent on the size of the output signal supplied by the load sensing device. That motor is pivotally interconnected between the seat frame 10 and the lumbar-supporting backrest portion 16, and is arranged so as to adjust when energised the position of that backrest portion in accordance with the number of input pulse signals received from the transmission means 96. Hence, the position to which the lumbar-supporting backrest portion 16 is driven in response to a displacement of the sitting portion 12 by a sitter is dependent on the weight of the sitter, and any other forces applied to the sitting portion by the sitter. This alternative form of force transference system has operating characteristics which are similar to those of the seat of Figure 1 employing a mechanical force transference system. The operating characteristic (relating the lumbar support to the sitter's weight) of the seat of Figure 9 may be adjusted by adjusting the input-output transfer characteristic of the transducer- transmission means 96. Furthermore, that means 96 may be arranged to incorporate feedback or other means for inhibiting, or limiting the rate of, further movement of the lumbar-supporting backrest portion 16 whenever the rate of relative movement of the sitting portion and the seat frame exceeds an unsafe high value. Equivalent force transference systems may involve instead the use of fluid pressure operated and/or controlled actuating devices for moving the lumbar- supporting backrest portion 16 in response to the force exerted on the sitting portion 12 by a sitter when sitting thereon.

Claims: CLAIMS 1. A seat comprising a seat frame; a substantially horizontal sitting portion on which a sitter may sit, said portion being yieldably carried on said seat frame so as to assume, under the weight of a sitter seated thereon, a displaced position relative to said frame, which position is dependent on the weight of the sitter; an upright backrest portion against which a sitter seated on said sitting portion may recline to support the sitter's back, which backrest portion is adjustably carried on said seat frame; a backrest adjusting means carried on said seat frame and coupled to said backrest portion, for effecting adjustment of the position of said backrest portion relative to said frame, which backrest adjusting means is responsive to displacement of said sitting portion under the weight of a sitter seated thereon, and is arranged to adjust, in response thereto, said position of said backrest portion in dependence upon said weight of a said sitter and in a manner such as to urge said backrest portion against, and so provide support for, a predetermined region of the sitter's back, which support is related to, and increases with increase in, the sitter's weight . 2. A seat according to claim 1, wherein said backrest portion is positioned relative to said sitting portion so as to provide support for the lumbar region of said sitter's back. 3. A seat according to claim 1 or 2, wherein said sitting portion is pivotally secured at a forward part thereof to said frame at a position thereon remote from said backrest portion, and is yieldably carried at a rearward part thereof on said frame at a position thereon near said backrest portion; and said backrest adjusting means Is coupled to said sitting portion at said rearward part thereof. 4. A seat according to claim 3, wherein said sitting portion is yieldably carried at said rearward part thereof by at least one lever which interconnects said sitting and backrest portions and which is pivotally supported on said seat frame at a position intermediate the points of connection of said lever with said portions . 5. A seat according to claim 4, wherein said point of connection of said lever with said sitting portion is fixed in position relative to said sitting portion, and said lever is pivotally supported on said seat frame at a position thereon which moves forwardly relative to said sitting portion as said sitting portion is displaced downwardly under the weight of a sitter seated thereon. 6. A seat according to claim 5, wherein said lever is pivotally supported on said seat frame by means of two cooperating cam surfaces provided respectively on said lever and said seat frame. 7. A seat according to claim 6, wherein one said cam surface is planar, and the other cam surface is convex towards the planar cam surface. 8. A seat according to claim 7, wherein said planar cam surface is provided on said lever and faces downwardly, and said convex cam surface is provided on said seat frame and is convex upwardly. 9. A seat according to claim 8, wherein said lever is generally L-shaped and comprises conjoined short and long arms, the short arm having its free end connected to said sitting portion and being pivotally carried on said seat frame, and the long arm having its free end connected to said backrest portion. 10. A seat according to claim 4, wherein said point of connection of said lever with said sitting portion is fixed in position relative to said sitting portion, and said lever is pivotally supported on said seat frame at a position thereon which moves rearwardly relative to said sitting portion as said sitting portion is displaced downwardly under the weight of a sitter seated thereon. 11. A seat according to claim 10, wherein said lever is pivotally supported on said seat frame by means of a cam surface and a cooperating cam follower. 12. A seat according to claim 11, wherein said cam surface is provided on said seat frame and faces upwardly, and said cam follower is provided on said lever and rests on said cam surface. 13. A seat according to claim 12, wherein said cam surface is planar. 14. A seat according to claim 11, wherein said lever is generally T-shaped and comprises a short cross bar from which a long staff projects, and wherein the free end of said long staff is pivotally coupled with said backrest portion, and one free end of said cross bar pivotally engages with said sitting portion and the other free end of said cross bar carries one of said cam surface and cooperating cam follower. 15. A seat according to claim 1, wherein said backrest adjusting means includes a position sensing means carried on said seat frame and coupled with said sitting portion so as to be responsive to displacement of said sitting portion relative to said seat frame, which sensing means is arranged to produce an output signal dependent upon said displaced position of said sitting portion; an actuating means carried on said seat frame and coupled with said backrest portion so as to position said backrest portion relative to said frame in accordance with an input signal supplied thereto; and a signal transmitting means for transmitting said output signal or a signal dependent thereon to said actuating means so as to serve therein as said input signal. 16. A seat according to claim 15, wherein said actuating means comprises an electrically energisable actuating motor. 17. A seat according to claim 16, wherein said actuating motor comprises a stepper motor, and said signal transmitting means is arranged to supply a series of electric pulses to said stepper motor, in which series the number of pulses is dependent upon the displacement of said sitting portion as sensed by said sensing means. 18. A seat according to claim 15, wherein said actuating means comprises a fluid pressure operated actuating motor. 19. A seat according to any preceding claim, including an acceleration limiting means pivotally carried on said seat frame and coupled with said backrest portion or with said lever so as to be responsive to accelerations of said backrest portion relative to said frame, said acceleration limiting means being adapted to control or limit the rate at which the backrest portion may accelerate relative to said seat frame when said sitting portion or said seat frame is subjected to undesirably high accelerating forces. 20. A seat according to claim 19, wherein said acceleration limiting means is adapted to lock said backrest portion against further movement relative to said seat frame whenever the acceleration of said backrest relative to said seat frame tends to exceed a predetermined high value. 21. A seat according to any preceding claim, wherein said backrest portion is pivotally connected to said backrest adjusting means. 22. A seat according to claim 21, wherein said backrest portion is also pivotally carried on said seat frame, so that said adjusting means is effective to adjust the angular disposition of said backrest portion relative to said seat frame. 23. A seat according to claim 21, wherein there is provided an additional backrest portion which is carried on said seat frame or on an upright extension of said sitting portion. 24. A seat according to claim 23, wherein said backrest portion is pivotally connected to said additional backrest portion. 25. A seat according to claim 24, wherein said * additional backrest portion is hingedly or slidably carrled on said seat frame. 26. A seat according to claim 23, wherein said additional backrest portion is hingedly carried on said seat frame, and is pivotally coupled with said backrest adjusting means so as to be angularly displaced thereby. 27. A seat substantially as hereinbefore described with reference to and as illustrated by any single figure or group of associated figures of the accompanying diagrammatic drawings. 28. Any and every aspect and/or combination of features not otherwise specifically claimed of the seats hereinbefore described with reference to and as illustrated by the accompanying diagrammatic drawings.

Inventors: ANDERLE EKKEHARD, ANDERLE, EKKEHARD
Applicants: ANDERLE EKKEHARD, ANDERLE, EKKEHARD
Application year: 1985
Main classification: A47C1
IPC codes: A47C1, A47C7