Patent Publication Number: US-7896376-B2

Title: Wheelchair

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of European Patent Application Number 06405395.2, filed Sep. 18, 2006, the contents of which are fully incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a wheelchair and to a support device for supporting a seat on an axle of a wheelchair. 
     BACKGROUND 
     U.S. Pat. No. 6,168,178 describes a wheelchair in which the chassis of the wheelchair can be converted from a rigid chassis to a suspension chassis and vice versa. However, the conversion is quite labour-intensive and complex as it implies the removal or addition of several components. Furthermore, the device disclosed in this reference does not allow to adjust further parameters of the wheelchair, such as seat height. Furthermore, mechanical forces are disadvantageously distributed in this device. 
     SUMMARY 
     The present invention seeks to improve comfort for wheelchair users and in particular to solve the problem of shock loads transmission into the spinal and skeleton parts of the human body. Furthermore, the present invention seeks to provide devices and components for wheelchairs that take individual preferences of a wheelchair user into account. An objective is thus to provide a wheelchair or wheelchair components that permit easy adaptations to the surface on which said wheelchair is intended to roll or to other varying circumstances. In particular, it is an objective of providing components for a wheelchair, which can easily be replaced according to the wheelchair user&#39;s needs, preferably by the wheelchair user alone. 
     Accordingly, it is an objective of the present invention to provide means for adjusting the height of the seat surface of a wheelchair. It is also an objective to provide for the possibility of adjusting the shock absorbing and springing characteristics of a wheelchair. The latter may be important to adapt the wheelchair according to the weight of the user, according to the surface on which the wheelchair is rolling and also to individual preferences of the user. 
     In general, the present invention relates to non-motorized wheelchairs. Such wheelchairs are generally hand driven and are advantageously light in weight. It is thus a further objective to provide a wheelchair that is optimised in terms of material utilisation and provides for high stability at relatively low weight. 
     The present invention relates to a wheelchair comprising a seat with a rear part and a front part, two left and right main wheels, connected by a transversal axle, and left and right lateral frame elements, wherein said seat is supported at its rear part on said transversal axle and at its front part on said lateral frame elements, respectively, at a left side and a right side of the front part of the seat, and wherein said lateral frame elements converge towards the rear part of the seat. 
     In another aspect, the present invention relates to a support device for supporting a seat on an axle of a wheelchair, comprising an exchangeable intermediate element detachably fixed at one of its ends to a chassis of the seat and at its other end to the axle and wherein the intermediate element can be selected according to preferences of a user of the wheelchair. 
     In a further aspect, the present invention provides a wheelchair comprising a seat and two main wheels connected by an axle and further comprising a support device according to the invention, wherein said support device is detachably fixed at one of its end to a chassis of the seat and at its other end to the axle through a center part attached to the middle part of said axle, said center part being arranged to receive the rear ends of two left and right main frame elements of the wheelchair. 
     In yet another aspect, the present invention provides a support structure for connecting an axle of a wheelchair to a chassis of a seat of the wheelchair, said support structure comprising a support device according to the invention and a center part attached to the middle of the axle, said center part being arranged to receive the rear ends of two left and right main frame elements of the wheelchair. 
     The term “frame element”, in the context of the present invention, refers to oblong, longish structures capable of assuming a support function, such as, for example, tubes, struts, bars, rods, and the like. In other words, the cross-section and the material constitution of the frame element is not relevant, as long as the support function can be accomplished. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the accompanying drawings, following description, and appended claims. 
         FIG. 1  shows a three quarter bottom front view of the wheelchair of the present invention comprising a first embodiment of the support device of the invention. 
         FIG. 2  is a close front view of a first embodiment of a support device according to the present invention. 
         FIG. 3  is a longitudinal vertical section of the embodiment of  FIG. 2 . 
         FIG. 4A  is a perspective view of a central part for pivotally lodging the support device of the present invention. 
         FIG. 4B  is a horizontal section of the central part of  FIG. 4A . 
         FIG. 4C  is a vertical, lateral section of the central part at line B-B shown in  FIG. 4B . 
         FIG. 5A  is a perspective view of the pivot part of the support device of the present invention. 
         FIG. 5B  is a longitudinal vertical section of the pivot part of  FIG. 5A . 
         FIG. 6A  is a perspective view of the lower part of the fixing element of the support device of the present invention. 
         FIG. 6B  is a vertical transverse section of the lower part of  FIG. 6A . 
         FIG. 7A  is a perspective view of the upper part of the fixing element of the support device of the present invention. 
         FIG. 7B  is a vertical transverse section of the upper part of  FIG. 7A . 
         FIG. 8  is a close front view of a second embodiment of a support device according to the present invention. 
         FIG. 9  is a close front view of a third embodiment of a support device according to the present invention. 
         FIG. 10  is a longitudinal vertical section of the embodiment of  FIG. 9 . 
         FIG. 11  is a close front view of a fourth embodiment of a support device according to the present invention. 
         FIG. 12  is a longitudinal vertical section of the embodiment of  FIG. 11 . 
         FIG. 13  is a close front view of a fifth embodiment of a support device according to the present invention. 
         FIG. 14  shows a three quarter bottom front view of a second embodiment of the wheelchair of the present invention, in which the rear part of the seat is supported by a pair of articulated supports. 
         FIG. 15  is a close partial rear view of the wheelchair according to the embodiment of  FIG. 14 . 
         FIG. 16  is a close partial rear view of a third embodiment of the wheelchair of the present invention, in which the rear part of the seat is supported by a pair of spring and shock absorber devices. 
         FIG. 17  is a close partial rear view of a fourth embodiment of the wheelchair of the present invention, in which the rear part of the seat is supported by a pair of vertically arranged struts. 
         FIG. 18  is a close partial rear view of a fifth embodiment of the wheelchair of the present invention, in which the rear part of the seat is supported by a v-shaped device. 
     
    
    
     DESCRIPTION 
     Various embodiments according to the present invention will be now described by way of example with reference to the appended drawing figures. 
       FIG. 1  shows a wheelchair  1  according to the present invention. The wheelchair is hand-driven. As usual in wheelchairs, there is a seat  2  for accommodating a wheelchair user, said seat comprising a seat surface  13  and a backrest  12 . The perspective of a user seated in the wheelchair defines the left, right, front and rear sides of the wheelchair. Given that  FIG. 1  represents a front view, the right side of  FIG. 1  corresponds to the left side of the wheelchair and vice versa. Left and right main wheels  3 ,  4 , are connected at their central points by a transversal axle  5 . The wheels are equipped with parallel-grip-rings for manual propulsion. Left and right frame tubes  6 ,  7 , emerge from below the seat towards left and right front sides of the wheelchair. 
     The frame tubes  6 ,  7  are bent, with a rear section  106 ,  107  of each frame tube  6 ,  7 , respectively, being defined as the section extending from the bend to the rear ends of the frame tubes  6 ,  7 , and with a front section  106 ′,  107 ′ of each frame tube  6 ,  7 , being defined as the section extending from the bend to the front ends of the frame tube,  6 ,  7 , respectively. The front ends of the frame tubes  6 ,  7  extend downwardly in the front part of the wheelchair. 
     While each left and right frame tubes  6 ,  7 , is preferably provided as a single-pieced, bent tube, with the bend defining rear and front sections  106 ,  106 ′, and  107 ,  107 ′, respectively, of each frame tube, it is of course possible to provide rear and front sections of each frame tube as two or even more part pieces, which are attached to each other, be it rigidly, by welding, for example, or adjustably. For example, according to a variant, the front section  106 ′,  107 ′ of each left and right frame tube could be pivotally connected to the respective rear section  106 ,  107 , the latter thus being a separate piece. This may provide further possibilities of adjustment. 
     Laterally at said front sections  106 ′,  107 ′, towards their bottom ends, support structures for lodging left and right castor wheels  8 ,  9 , respectively, are attached, for example, by welding, to each left and right frame tube  6 ,  7 . A U-shaped foot-rest  11  connects the left and right frame tubes  6 ,  7  at their bottom ends. The outer tube circumference of the foot-rest  11  is equal or slightly smaller than the inner circumference of the front sections  106 ′,  107 ′ of the left and right main frame tubes at their bottom ends. In this way, the left and right lateral parts of the foot-rest  11  telescopically slide within the front sections  106 ′,  107 ′ of the left and right frame tubes  6 ,  7 , the latter being arranged in parallel at their bottom ends. A number of holes present in the left and right tubes of the U-shaped foot-rest allows for adjustment of foot-rest height, by tightening a screw extending from borings in the front sections  106 ′,  107 ′ of left and right frame tubes,  6 ,  7 , respectively, through said holes in the left and right lateral tubes of the foot rest. 
     As is also visible in  FIG. 1 , the rear sections  106  and  107  of the left and right frame tubes,  6 ,  7 , converge towards their rear ends, where they are fixed to axle  5  of the wheelchair  1 . In a position which lies in between the rear ends of the rear sections  106 ,  107 , in the mid-point of axle  5 , a support device  10  comprising a spring can be seen. At its upper end, said spring is linked to a tube  15 , which is part of the seat chassis  14 , namely of the rear part of said chassis. 
     From  FIG. 1 , the important role of the two frame tubes  6 ,  7  can be recognized, as these tubes provide, along with the horizontal, transversal axle  5 , the overall framework of the wheelchair. As indicated, both left and right frame tubes are attached with their rear sections  106 ,  107  to the left and the right side of the middle point of the axle  5 , leaving the middle zone of the axle  5  for bearing the support device. From their rear ends, the frame tubes extend forwardly and slightly upwardly, diverging towards the lateral left and right front ends of the seat, where they bend downwardly. Shortly before bending downwards, towards the front end of the rear sections  106 ,  107  of the frame tubes each left and right frame tube,  6 ,  7 , is attached to the chassis of the seat of the wheelchair, namely to left and right seat tubes, respectively. As can be discerned in  FIG. 1 , the front sections  106 ′,  107 ′ of the lateral frame tubes also converge towards their respective bottom ends, albeit to a less extent than their rear counterparts  106 ,  107 . This converging, non-parallel disposition of the front sections  106 ′,  107 ′ has the advantage that lateral space for the castor wheels  8 ,  9  is provided, so that the lateral dimension of the wheelchair  1  does not substantially vary from rear to front. 
     Accordingly, the seat  2 , in  FIG. 1 , is supported at three positions, namely at a central position, substantially vertically above the axle  5 , by the support device  10 , and at two lateral positions, near the front of the upper parts of the frames tubes  6 ,  7 , respectively, corresponding to the left and right sides towards the front of the seat. The unusual arrangement of the left and right frame tubes, being attached with their rear ends close to the middle point of the axle  5 , reminds of legs of a spider. 
     As illustrated on  FIGS. 2 and 3  the first embodiment of the support device  10  of the present invention comprises an intermediate element, located between a pivot part  23 , pivoting into a seat provided in a central part  20  fixed to the axle  5 , and a fixing element  24  attached to the seat tube  15 . The intermediate element comprises a spring  28  and a shock absorber element  29 , the shock absorber element (e.g., an elastomer element) being located in the lacuna provided by the spiral turns of the spring  28 . At their bottom ends, the spring  28  and the shock absorber element  29  are seated on pivot part  23 , which is pivotally attached to the axle  5  by means of a center part  20  mounted around the axle  5  and which will be described in detail later. The pivoting axis of pivot part  23  is parallel to axle  5 . The center part  20  also harbors, on left and right sides of the pivot part  23 , the rear ends of the rear left and right sections  106 ,  107 , respectively, of the frame tubes. A longitudinal slot  17  in the center part  20  is visible extending from left to right along the axle  5 . This slot is necessary for tightening the center part  20  around axle  5 , while permitting some adjustment of the center part to the diameter of the axle  5 . 
     At their top ends, the spring  28  and shock absorber element  29  abut to the lower part  26  of fixing element  24 , which will also be described in more detail later. 
     As can be seen in  FIG. 3 , a fixing screw  30  extends along the central axis of the support device, through a central hole provided in the pivot part  23  and a central boring  95  provided in the shock absorber element  29 . The screw  30  is anchored in the boring  95  of lower part  26  of fixing element  24 , the head  31  of the screw  30  abutting upon an inner sleeve  35  of pivot part  23 . In this way, the screw  30 , when tightened by a thread or nut present in fixing element  24 , attaches the support device of the invention  23 ,  10 ,  24  to the seat tube  15 , the pivot part being itself pivotally attached to the center part  20  attached on the middle of axle  5 . A ring  32  is preferably located between the head  31  of screw  30  and sleeve  35 . 
     With respect to the pivotal attachment of the pivot part  23 , left and right pins  36 ,  37 , are seated in left and right borings,  38 ,  39 , respectively, provided in the center part  20  and oriented in parallel to axle  5 . As is better visible in  FIG. 4A to 4C , these left and right borings,  38 ,  39 , are located at the bottom of left and right supports  66 ,  77 , intended to receive the left and right frame tubes, respectively. 
     The pins  36 ,  37  extend from their respective borings  38 ,  39  in the center part  20  towards each other, into corresponding borings provided in the centrally located pivot part  23 , thus providing a pivoting articulation for the pivot part  23 . 
     While pins  36 ,  37  penetrate into a substantial part of pivot part  23 , to provide sufficient footing for the pivoting articulation, they do not extend through it entirely, but leave a free space  33  in the center, to permit access to the head  31  of screw  30 . As will be discussed further below, the free space  33  is helpful when exchanging the intermediate element  10 . Furthermore, the free space  33  may be temporarily occupied by the head  31  of screw  30 , when the latter is descending upon compression of spring  28  and shock absorber element  29 , upon absorption of shocks experienced by the wheelchair. 
     The left and right pins  36 ,  37 , each comprise a head,  42 ,  43 , each of which is threaded in the lateral boring  45 ,  46 , the central borings  38 ,  39 , housing the axel-forming part of the pins  36 ,  37 . 
       FIG. 3  also shows that pivot part  23  comprises, on its top vertical end, even and substantially horizontal surfaces  47  and  48 , on which the shock absorber element  29  and spring  28  bear. Both surfaces  47 ,  48 , if viewed from top, have the form of a ring, with surface  47 , on which the shock absorber element  29  bears, having a central opening for the passage of the screw  30 . Surface  48  is situated laterally and lower than surface  47  with a radial dimension substantially corresponding to the thickness of the spring  30 . 
     The bottom end of lower part  26  of fixing element  24  substantially mirrors the dimensions of the top vertical end of pivot part  23 , thus providing ring-shaped surfaces  49  and  53 . With screw  30  anchored in fixing element  24 , spring  28  is stably clamped between surfaces  48  and  53  of the pivot part and the fixing element, respectively. Lateral displacement of the spring being prevented by the vertical offset of surfaces  47  and  49 , respectively. The shock absorber element  29 , on the other hand, is clamped between inner, ring-shaped surfaces  47  and  49 , and further stabilised by annular protrusions  54  and  55  of the pivot part  23  at the shock absorber element&#39;s bottom end and on the fixing element  24  at the shock absorber element&#39;s upper end, respectively, said protrusions preventing lateral displacement of the shock absorber element  29 . 
     The central part  20  is better represented on  FIGS. 4A ,  4 B and  4 C. It can be seen that the central part  20  is provided in a single piece. It comprises a free space  16  intended to receive the pivot part  23  and which is sufficiently deep to allow for pivoting of the latter. This free space  16  is actually created by the gap between the left and right cylindrical structures  66 ,  77 , intended to receive the rear left and right sections  106 ,  107 , respectively, of the frame tubes  6  and  7 . Openings of the left and right borings  38 ,  39  are also visible. The distal ends of the cylindrical structures  66 ,  77 , have diameters slightly smaller or equal to the internal diameter of the left and right rear sections  106 ,  107 , respectively, permitting telescopically setting said sections  106 ,  107 , and thereby, the frame tubes  6 ,  7 , onto said cylindrical support structures. Left and right holes  61 ,  62 , in each support structure  66 ,  77  allow for detachably attaching said sections  106 ,  107  to said support structures  66 ,  77 , for example, by means of a screw or a pushable pin. The cylindrical hollow  63 , designed to harbor axle  5  is also visible. Also, slot  17  and opening  70  are visible. 
     Left and right borings  65 ,  67  are intended to house screws to permit tightening of the central part  20  around axle  5  (see  FIG. 3 ), while diminishing the breadth of slot  17  ( FIG. 4A ). 
       FIG. 4C  shows the vertical orientation of boring  67  and the position of slot  17 , thus illustrating that central part  20  will be tightened around axle  5  when a screw is tightened in boring  67 , compressing slot  17  and thus diminishing the dimension of cylindrical hollow  63 , intended to harbor axle  5 . A thread for said screw (both not shown in  FIG. 4C ) may be present in the upper end of boring  67 . 
       FIGS. 5A and 5B  show further details of pivot part  23 . An annular protrusion  54  surrounding boring  75 , in which the screw  30  (not visible) is to be held, is provided on top of pivot part. Ridge  76  illustrates the vertical offset between ring-shaped surfaces  47  and  48 , which is relevant for preventing lateral movements of intermediate part  10 , when placed between pivot part  23  and the lower part  26  of fixing element  24  (not shown). Borings  72  and  73  are intended to harbor the central ends of pins  36 ,  37 . 
     Details of the lower part  26  and upper part  25  composing the fixing element  24  forming a clamp around seat tube  15  are shown in  FIGS. 6A and 6B  and in  FIGS. 7A and 7B , respectively. 
     In  FIG. 6A , the concave surface  80 , having a circular form in cross-section, is visible. This concave surface  80  is designed to fit with the diameter of the seat tube  15  (not shown) and, when harboring said tube, covers about half of its circumference. In the center of said concave surface  80 , the extension of boring  95  is visible, in which screw  30  is to be harbored and tightened by means of a thread. The fixing element  24  has a hinge-joint configuration, with a hinge being formed between lower part  26  and upper part  25 , by means of hinge-joint elements  81 ,  82 , with a common central axis, but leaving a gap between them for inserting a corresponding hinge-joint provided in the upper part  25  ( FIG. 7 ). Borings  83  are provided in the other (front) side of concave surface  80 , which comprise threads so as to fix said upper part  25  by means of screws to said lower part  26  at the front side of the fixing element  24  (not shown). 
     In  FIG. 6B , the situation of the even ring-shaped surfaces  53 ,  49  is indicated. Also, the protrusion  55  is visible, in which a boring  95  for harboring the screw  30  extends (not shown). The section provided in  FIG. 6B  is slightly lateral and extends vertically along one of the borings  83 , thus showing the orientation of the latter in the lower part  26 . 
     As illustrated by  FIGS. 7A and 7B , the upper part  25  mainly forms a concave surface  90 , which is intended to harbor about half of the circumference of the seat tube  15  (not shown), the other half being covered by concave surface  80  of lower part  26  (see  FIGS. 6A and 6B ). The hinge-joint element  84 , visible in a central position at the rear part of the upper part  25  is adjusted to fit between hinge-joint elements  81 ,  82 , of lower part  26  and to thus form the hinge joint with the latter, a pin or axle being placed so as to extend through holes  85  and  86  of the hinge-joint elements of the upper and lower parts  25  and  26 , respectively. In both,  FIGS. 7A and 7B , the openings  27  for a screw to be placed are shown, with the head of said screw abutting against surface  87 . Said screw will extend through borings  83  ( FIGS. 6A  and B) and thus permit tightening fixing element  24  around seat tube  15 . 
       FIG. 8  show a second embodiment of the support device of the present invention. In this embodiment, a washer  40  is placed between the intermediate element comprising the spring  28  and the shock absorber element  29 , and the lower part  26  of the fixing element  24 . With the washer  40  at this position, the distance between axle  5  and seat tube  15  is increased by the thickness of the washer  40 , thus increasing the rear seat height of the wheelchair. 
     It is clear that washers of various thickness can be used for increasing rear seat height. However, the washer could also be used to keep rear seat height constant when a spring and/or shock absorber element smaller than that shown in  FIG. 2  is used. Springs of different strengths can thus be employed without affecting rear seat height. Accordingly, the combination of intermediate element  10  and washer  40  allows various adjustments according to the wheelchair user&#39;s preferences. 
       FIGS. 9 and 10  show a third embodiment of the support device of the present invention. Instead of a spring/shock absorber element, the intermediate element consists in a rigid element  50 . The rigid element  50  is put in place when the spring and shock absorbing function is not desired. 
     As is better shown in  FIG. 10 , the rigid element  50  resembles a hollow column, with the screw  30  extending along the central, vertical axe of said column. In this embodiment, rear seat height is adjusted to a relatively low level, rigid element  50  being shorter than the spring  28  in  FIG. 3 . For this reason, small washers  51  are situated between the head  31  of screw  30  and sleeve  35 , to account for the length of screw  30 . Instead of small washers  51 , a shorter screw  30  could, of course, be used with the same result. However, as the situation is in  FIG. 10 , the head  31 , abutting against a ring  52 , for example, a washer, situated below small washers  51 , is now situated lower in pivot part  23  and occupies nearly all space ( 33  in  FIG. 3 ) provided between the central ends of pins  36  and  37 . 
     Similar to the situation in  FIG. 3 , the vertically offset, ring-shaped surfaces  47 ,  48  on the pivot part  23  and  49 ,  53  on the lower part  26  of fixing element  24  provide for the lateral stabilisation of the intermediate element  10 , here rigid element  50 . 
     The rear seat height may be adjusted by using rigid elements of different lengths and/or by using washers as discussed hereunder. 
       FIGS. 11 and 12  show a fourth embodiment similar to that of  FIGS. 9 and 10 , but with increased rear seat height, due to the presence of washer  60  placed above rigid element  50 , and below fixing element  24 . As in the embodiments with the spring and/or the shock absorber element, the washer is clamped, together with the rigid element  50 , by screw  30  (not visible), between pivot part  23  and fixing element  24 , thus heightening the overall position of seat tube  15  with respect to axle  5 , and, in consequence with respect to the ground on which the wheelchair is placed. 
     The purpose of washer  60  is to increase the distance provided by intermediate element, here rigid element  50 . In this embodiment, contrary to the one of  FIG. 10 , only one, instead of two small washers  51 , is placed between head  31  of screw  30  and the inner sleeve  35  of pivot part  23 , because of the increased distance, resulting in increased rear seat height, provided by the combination of rigid element  50  and washer  60 . The washer  60  has an upper profile that fits the profile of the lower end of lower part  26  of fixing element  24 , and a lower profile that fits the profile of the upper end of intermediate element, here rigid element  50 . 
       FIG. 13  shows a fifth embodiment of the support device of the present invention, comprising two washers  60 ,  100  positioned directly above and below, respectively, of rigid element  50 , thus further increasing rear seat height. The lower washer  100  is, in this case, placed between pivot part  23  and rigid element  50 . 
     The advantages of the support device of the present invention in terms of adjusting parameters of the wheelchair will now be described. 
     The support device of the present invention allows adjustment of rear seat height and of absorption characteristics. 
     Accordingly, the intermediate element ( 28 ,  29 ,  50 ) can be easily removed, replaced and or supplemented with washers  40  to increase rear seat height. To this end, the head  31  of screw  30 , situated in pivot part  23 , is accessible and can be loosened with a suitable tool, by the wheelchair user or technical staff of a wheelchair vendor. Screw  30  being loosened, fixing element  24  can be manually separated from said screw and pivot part  23 . The latter can be pivoted towards the front of the wheelchair and the intermediate element, for example, a spring  28  and a shock absorber  29  may be further supplemented with a washer  40 , or may be replaced by a rigid element  50 , with or without washer  60 ,  100 . Once all desired replacements or supplements being put on pivot part  23 , the latter is pivoted back to its substantially vertical position and the lower part  26  of fixing element  24  is fitted unto exchanged and/or supplemented intermediate element. Then, screw  30  is again tightened to clamp the intermediate element, with or without washers, between pivot part  23  and fixing element  24 , thus connecting the seat tube  15  to axle  5 . 
     Absorption parameters of the wheelchair may be adjusted by selecting suitable intermediate elements. A spring  28  can be used alone, but preferably in combination with a shock absorber element  29 , the latter having the purpose of absorbing shocks. Of course, springs of different strengths and elastomers of different materials, such as rubbers, or gas filled shock absorbers exhibiting different absorbing characteristics may be selected according to the wheelchair users preferences or physical properties, for example, according to the weight of the wheelchair user. Also, rigid elements  50  may be used to provide intermediate element, thus minimizing shock absorption and cushioning properties of the support device and providing an overall wheelchair nearly devoid of these properties. The later may be desired if the wheelchair is to be used on even, flat surfaces and/or if loss of kinetic energy by absorption is to be prevented, for example, in wheelchair races. It should further be noted that the above described arrangement combining the intermediate element (spring  28  and shock absorber  29 ) with the related design of the left and right frame tubes  6 ,  7  is unique in the wheelchair industry. This for reasons that, for the first time, special attention is given to solve the problem of shock loads transmission into the spinal and skeleton parts of the human body. By means of an oriented non-swinging spring/damper concept, the vibrations induced during wheelchair movements are absorbed and, accordingly, not transmitted into the spinal and skeleton parts of the human body. 
     The embodiment of the wheelchair of  FIG. 14  differs from the wheelchair shown in previous figures in that the central support device  10  is absent, and the function of supporting the seat  2  of the wheelchair at its rear part is accomplished by a pair of left and right articulated supports  110 ,  120 , respectively. As can be seen in  FIG. 14 , the articulated supports are disposed laterally on the transversal axle  5 , vertically below tubes of the chassis  14  of the seat, said tubes of the chassis extending on the lateral left and right side on the bottom of the seat  2  in the driving direction (rear-to-front). The rear part of the chassis  14  of the seat  2  is supported at two lateral positions, instead of a single central position as was the case with the embodiment of  FIGS. 1-13 . As a consequence, the stability of the seat is increased. In particular, lateral oscillations are avoided. 
     The support elements  110 ,  120  of the embodiment of  FIG. 14  are shown in greater detail in  FIG. 15 , where the different components making up the articulation in these supports are well visible. Each left and right articulated support  110 ,  120 , respectively, comprises an attachment  111 ,  121 , which at least partly clamped to transversal axle  5 , at left and right lateral positions of the axle, close to the left and right rear wheels (not represented in  FIG. 15 ). The attachments  111 ,  121 , in  FIG. 15  have the configuration of clamps provided with an oblong, fortified section, extending in an upward direction. At its top end, each attachment  111 ,  121 , is pivotally attached to a link element  112 ,  122 , respectively, which in turn is pivotally attached to the chassis  14  of the seat, at lateral left and right positions of the chassis  14 /seat  2 . In the embodiment shown in  FIG. 15 , a second transversal axle  130  is provided. The left and right link elements  112 ,  122  are perpendicular to this second transversal axle  130  and are rigidly fixed to it at its distal left and right ends, forming altogether a Π-shaped element. This element is attached to the chassis  14  of the seat, at suitable left and right fixing plates  112 ,  124 , so that the second transversal axle  130  is oriented horizontally, in parallel to the transversal axle  5 . In this way, stable pivotal hinges  116 ,  126  are formed at the left and the right side of the chassis  14  with the second transversal axle  130  coordinating the pivoting movements of the left and right link elements  112 ,  122 , preventing independent pivoting movement of the latter around pivoting hinges  116 ,  126 , or  115 ,  125 , respectively. 
     As the skilled person will appreciate, the lateral articulated supports  110  and  120 , enable the adjustment of a number of parameters of the wheelchair according to the embodiment of  FIGS. 14 and 15 . Firstly, if the different elements  111 ,  112  and  114  on the left, and  121 , 122  and  124  on the right side of the wheelchair are rigidly attached to each other, by tightening screws at the pivoting hinges  115 ,  116 ,  125 ,  126 , respectively, the height of the rear part of the seat  2  can be adjusted, namely by adjusting the angle between attachments  115 ,  125  and link elements  112 ,  122 , before tightening said screws. Furthermore, it is possible to adjust the rear-to-front position of the seat  2  on the overall wheelchair, namely by moving the fixing points  117 ,  127 , at which the front part of the seat  2  is attached to the lateral frame tubes  6 ,  7 , at lateral left and right front sides of the seat  2 . Since the pivoting hinges  115 ,  125  and  116 ,  126  of the articulated supports  110 ,  120  are also adjustable, the overall rear-to-front position of the seat  2  supported on the left and right frame tubes  6 ,  7  and on the transversal axle  5  can be adjusted according to a user&#39;s preferences. 
     The third embodiment of a wheelchair according to the invention shown in  FIG. 16  differs from the embodiment of  FIGS. 14 and 15  in that a pair of left and right substantially vertically arranged spring and shock absorber devices  140 ,  150  replace the articulated supports of  FIG. 15 . 
     A second transversal axle  160  (corresponding to the axis  130  of  FIG. 15 ) is attached to the chassis  14  of the seat  2  through attachment surfaces provided by small left and right plates  114 ,  124 . Ring-shaped clamps are disposed on the distal ends of the left  145 ,  114  and of the right  155 ,  156  spring/shock absorber devices  140 ,  150 , respectively, and are designed to connect each device  140 ,  150  with a lower end to the transversal axle  5 , and with the upper end to said second transversal axle  160 , thus providing a support for the seat  2  on the transversal axle  5 . 
     Advantageously, the embodiment shown in  FIG. 16  has increased shock absorbing properties and may be preferred if a wheelchair is intended or prepared for uneven surfaces, for example, for an off-road excursion. The shock absorbing and spring properties are generally preferred for reasons of increased comfort. 
     As a variation of the embodiment shown in  FIG. 16 , it is, of course at the option of the skilled person to employ only a spring or a shock absorber alone on each left and right support position, to use other kinds of elastomers or to attach springs and shock absorbers at different positions, preferably along the transversal axle  5 . 
       FIG. 17  shows a further embodiment, in which the rear end of the seat  2  is supported on the transversal axle  5  by rigid vertical left and right struts (tubes)  170 ,  180 , attached laterally on the transversal axle  5  by left and right clamps  171 ,  181 , respectively, and directly attached to lateral tubes of the chassis  14  of the seat  2  by suitable attachments. In this embodiment, the height of the seat  2  can be adjusted by exchanging vertical tubes  170 ,  180  by corresponding shorter or larger tubes. 
     A still further embodiment of the wheelchair of the invention is shown in  FIG. 18 , where an inversed, V-shaped device  190  connects the transversal axle  5  to a cross-tube  195  of the chassis  14  of the seat  2 . The v-shaped device comprises two legs,  196 ,  197 , which at the point of their attachment to each other, are attached to the cross-tube  195  of the chassis  14 . The distal ends of the legs  196 ,  197  are each attached to the transversal axle  5  by a suitable left and right clamps  191 ,  192  forming part of the v-device. In the device shown in  FIG. 18 , the distal ends of the legs are oriented downwards, so that they are connected with the transversal axle  5  at lateral left and right positions of the transversal axle  15 . 
     As a variant of the embodiment of  FIG. 18 , the skilled person could also envisage a non-inversed v-shaped device, with the meeting point of the two lateral legs  196 ,  197  being connected to the center part  20 ′, in a way similar to the support device  10  shown in  FIGS. 1-13 . The separate, distal ends of the legs of the v-shaped device could then be attached to lateral tubes of the chassis  14  of the seat. 
     In the embodiments of the wheelchair shown in  FIGS. 14 to 18 , a center part  20 ′ is still present, for attaching the rear sections  106  and  107  of the left and right frame tubes  6 ,  7  to the transversal axle  5 . It differs from the center part  20  of the embodiment of  FIGS. 1 to 13  in that a central support device  10  is not present, as the support of the rear part of the seat  2  is accomplished by other structural elements described above with reference to  FIGS. 14 to 18 . 
     While the invention is described herein in conjunction with one or more exemplary embodiments, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, exemplary embodiments in the preceding description are intended to be illustrative, rather than limiting, of the spirit and scope of the invention. More specifically, it is intended that the invention embrace all alternatives, modifications, and variations of the exemplary embodiments described herein that fall within the spirit and scope of the appended claims or the equivalents thereof. Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. §112, ¶6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. §112, ¶6.