Abstract:
A wheelchair suspension system includes a suspension member which clamps to longitudinal bars of the wheelchair frame located below the seat of the wheelchair. The suspension member is elongate with upper and lower parallel leaf springs extending between the opposing ends of the suspension member. An axle support member is hinged to each end of the suspension member, by pivotal connection to each of the leaf springs. Each axle support member receives the axle of one of the opposing large rear wheels of the wheelchair. As the large wheels encounter uneven areas on the ground surface on which the wheelchair moves, the leaf springs flex reducing vibrations and shock to the wheelchair occupant. The axle support members maintain their generally upright orientation as the leaf springs flex so that camber angle of the rear wheels does not change.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from copending provisional patent application entitled WHEELCHAIR SUSPENSION SYSTEM, Ser. No. 61/115,364 filed Nov. 17, 2008. The disclosure of provisional patent application Ser. No. 61/115,364 is hereby incorporated in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention pertains to wheelchairs and particularly to suspension of the large rear wheels of wheelchairs which are manually operable. 
         [0003]    In the typical manual wheelchair each rear wheel is a large wheel mounted to the frame of the wheelchair without any provision for absorption of shocks or damping of vibration of the wheelchair. In such a wheelchair, shocks and vibrations arising from irregularities and defects in the traveled surface are transmitted through the rear wheels to the wheelchair occupant. These shocks and vibrations contribute to spasms and back pain in wheelchair users. Studies have shown that low back pain is a common problem among people with disabilities who use wheelchairs. 
         [0004]    One attempt to reduce shocks and vibrations to wheelchair users is shown in U.S. Pat. No. 4,455,031 wherein a shock absorber interconnects the seat of the wheelchair with a frame on which the large rear wheels are mounted. My U.S. Pat. No. 7,032,917 issued Apr. 25, 2006 discloses a solution to shock absorption in which separate suspension devices interconnect the rear wheel hubs to side frame members of the wheelchair frame. Additional solutions reducing vibration and shock to the body of wheelchair users are desirable. 
       SUMMARY 
       [0005]    The present invention provides a rear suspension for a wheelchair which can be retrofitted to a wheelchair or installed at initial manufacture. The invention is directed toward a manually operated wheelchair, especially a sport wheelchair, which is driven by the rider pushing the large rear wheels by hand. The present invention provides a shock absorbing apparatus which isolates the large rear wheels from the wheelchair frame to reduce the shock and vibration felt by the user of a wheelchair traversing a surface. 
         [0006]    The instant invention includes a suspension member which clamps to central longitudinal bars of the wheelchair frame, the longitudinal bars being located below the seat of the wheelchair. The suspension member is elongate, with mounting elements for the opposing large rear wheels of a manual wheelchair at opposing ends of the suspension member. Axle support plates are hinged to the opposing ends of the suspension member such that these axle support plates receive the axles of the hubs of the large rear wheels. The suspension includes upper and lower mounting blocks which receive the horizontal tubular frame members of the wheelchair frame and clamp the horizontal tubular frame members to the suspension member. 
         [0007]    The rear suspension may flex vertically while the axle support plates remain in a substantially vertical orientation throughout such flexure. As a result, camber angle of the rear wheels retained to the suspension member does not change because of vertical flexure of the suspension. 
         [0008]    The suspension system includes an upper leaf spring and a lower leaf spring separated by an upper mounting element and a lower mounting element which are identical except one is an inversion of the other. The upper and lower mounting elements are formed with semi-cylindrical openings in them such that the upper and lower mounting elements can capture and retain the longitudinal frame bars between them. The upper leaf spring and lower leaf spring are slightly curved at rest and both leaf springs remain substantially parallel to one another. 
         [0009]    An upper plate is centered atop the upper leaf spring and a lower plate is centered below and touching the lower leaf spring. The upper plate and lower plate are best composed of aluminum so that the weight of the suspension remains minimal. Voids in the upper plate and lower plate serve to lessen the weight of the plates. The upper and lower plates retain the upper and lower leaf springs to the mounting elements by plural bolts passing from upper plate through to the lower plate. 
         [0010]    It is an object of the invention to provide a shock absorbing apparatus to reduce the transmission of bumps and shocks from the large rear wheels of a wheelchair to the rider in the wheelchair. 
         [0011]    It is a further object of the invention to provide an improved manual wheelchair which is less uncomfortable for the user to ride over irregular surfaces. 
         [0012]    It is also an object of the invention to provide a shock absorbing rear suspension which can be easily added to an existing wheelchair. 
         [0013]    These and other objects will become apparent from examination of the description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0014]      FIG. 1  is a side elevation of a wheelchair with wheel spoke and seat elements omitted, the wheelchair being equipped with the invention which is mounted to the axles of the large rear wheels. 
           [0015]      FIG. 2  is a front perspective of a wheelchair with parts thereof omitted, the wheelchair equipped with a first embodiment suspension system attached to the rear wheels. 
           [0016]      FIG. 3  is a rear elevation of a wheelchair equipped with the suspension system of  FIG. 2 , with parts of the wheelchair omitted for clarity. 
           [0017]      FIG. 4  is a front left perspective view of the first embodiment of the suspension member. 
           [0018]      FIG. 5  is a front elevation of the suspension member of  FIG. 4 . 
           [0019]      FIG. 6  is an enlarged perspective of a lower mounting element of the invention. 
           [0020]      FIG. 7  is a front elevation of a second width-adjustable embodiment of a suspension system for a wheelchair. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  discloses a wheelchair  3  which comprises large rear wheels of which left side rear wheel  16  is seen in this figure. The wheelchair frame  7  is supported on the rear wheels and by front casters, of which caster  9  on left side of wheelchair  3  can be observed in  FIG. 1 . Caster  9  is connected to lower end  11  of front frame element  15  which is oriented generally vertically. Front frame element  15  is joined to wheelchair frame  7  at front end  25  thereof. All parts of wheelchair frame  7  are preferably tubular and of light weight metals. Wheelchair frame  7  includes rear frame assembly  26  which comprises lower longitudinal elongate tubular member  24  as well as intermediate side bar  17  and upper side bar  19 , all of which extend longitudinally forward of upright rear frame element  21 . Mirror images of lower tubular member  24 , intermediate side bar  17  and upper side bar  19  are provided on the opposing side of wheelchair frame  7  as will be seen in  FIGS. 2 ,  3 . A seat cushion and seat cushion support structure have been omitted but would be supported by intermediate side bars  17 ,  37  (See  FIG. 2 ). 
         [0022]    As seen in  FIG. 1 , rear wheel  16  supports wheelchair frame  7  at axle  12  thereof. Suspension invention  2  interconnects axle  12  to wheelchair frame  7  by attachment to lower tubular frame member  24  and its parallel twin member  22  (See  FIG. 2 ). 
         [0023]      FIGS. 2 and 3  illustrate the new rear suspension  2  shown mounted to the lower frame  5  of a wheelchair  3 . The wheelchair  3  is provided with opposing wheels  14 ,  16  which serve as the rear wheels of the wheelchair  3 . Rear wheels  14 ,  16  may be manually driven by the user and will be manually driven when operated by a wheelchair athlete. Wheelchair  3  also comprises rear frame assembly  26  which includes elongate tubular frame members  22 ,  24  which are substantially laterally parallel and horizontally disposed when wheelchair  3  rests on a horizontal surface. Each of horizontal tubular frame members  22 ,  24  is disposed slightly above the axles  10 ,  12  of rear wheels  14 ,  16  of wheelchair  3  due to the interconnection of the tubular frame members  22 ,  24  to wheel axles  10 ,  12  by suspension  2 . Tubular frame members  22 ,  24  extend horizontally forward of lower cross bar  23  of seat support frame member  26 . Tubular frame members  22 ,  24  include angled segments  83 ,  85  respectively which effect lateral divergence of tubular frame members  22 ,  24  at forward segments  82 ,  84  thereof such that forward segments  82 ,  84  are laterally parallel to one another. Upper cross bar  27  interconnects upright bar members  29 ,  31  of rear frame assembly  26 . 
         [0024]    The rear suspension  2  includes opposing axle support plates  6 ,  8  which receive the axles  10 ,  12  of the rear wheels  14 ,  16  of the wheelchair  3 . Wheel hubs  33 ,  35  are freely rotatable about axles  10 ,  12 . The rear suspension  2  includes upper and lower mounting elements  18 ,  20  which receive horizontal tubular frame members  22 ,  24  which extend forward from rear frame assembly  26  of wheelchair  3 . 
         [0025]    The rear suspension  2  may flex vertically while axle support plates  6 ,  8  remain in a substantially vertical orientation throughout such flexure. As a result, camber angle of the rear wheels  14 , 16  does not change because of vertical flexure of the suspension  2 . 
         [0026]    In  FIGS. 4 and 5 , the first embodiment of the rear wheel suspension system  2  for a wheelchair is shown isolated from the wheelchair itself. The suspension system  2  comprises an upper leaf spring  30  and a lower leaf spring  32  separated by an upper mounting element  18  and a lower mounting element  20 . The upper leaf spring  30  and lower leaf spring  32  are slightly curved at rest and both leaf springs  30 ,  32  remain substantially in parallel with one another whether at rest or when flexed. Each leaf spring  30 ,  32  is substantially elongate and of thickness which is substantially less than the traverse dimension thereof. Each leaf spring  30 ,  32  is made of spring steel or other material which will flex but return to its original longitudinal curvature at rest. 
         [0027]    The upper leaf spring  30  and lower leaf spring  32  further comprise first ends  34 ,  44  and second ends  36 ,  46 . Each first end  34 ,  44  and second end  36 ,  46  comprises a pivot axle bearing housing  38 . Referring specifically to  FIG. 5 , each pivot axle bearing housing  38  receives a pivot pin  40  within bushing  48 . Pivot pin  40  is retained at its opposing ends to the axle support plates  6 ,  8 . Therefore, each pivot axle bearing housing  38  may rotate about the pivot pin  40  received within it as the upper leaf spring  30  and lower leaf spring  32  flex, allowing the axle support plates  6 ,  8  to which the pivot pins  40  are retained to remain in a selected substantially vertical orientation regardless of the flexure of the leaf springs  30 ,  32 . Each of leaf springs  30 ,  32  extend from first axle support plate  6  to opposing axle support plate  8 . 
         [0028]    Again referring to  FIGS. 4 and 5 , an upper plate  50  is preferably centered atop the upper leaf spring  30  and a lower plate  52  is preferably centered underneath and touching the lower leaf spring  32 . The upper plate  50  and lower plate  52  are preferably rigid and may be made of a metal and in the preferred embodiment the upper plate  50  and lower plate  52  are composed of aluminum. The voids  54  in the upper plate  50  and lower plate  52  serve to lessen the weight of the plates  50 ,  52 . Ribs  58  extending along each plate  50 ,  52  are integral therewith to provide additional rigidity to plates  50 ,  52 . 
         [0029]    Upper plate  50 , upper leaf spring  30 , upper and lower mounting elements  18 ,  20 , lower leaf spring  32 , and lower plate  52  are held together by plural bolts  56  passing from upper plate  50 , through upper leaf spring  30 , upper mounting element  18 , lower mounting element  20 , lower leaf spring  32  and joined to lower plate  52 . Referring again to  FIGS. 2 and 3 , upper and lower mounting elements  18 ,  20  clamp about the horizontal tubular frame members  22 ,  24  of frame  7  of wheelchair  3 . Plural bolts  56  may be adjusted to properly secure the horizontal tubular frame members  22 ,  24  to suspension system  2 . Passageways  64 ,  66  are provided to receive the parallel longitudinal tubular frame members  22 ,  24 . Gaps  68 ,  70  remain at sides of passageways  64 ,  66  to allow tolerance to clamp tubular frame members  22 ,  24  securely. Gaps  68 ,  70  are provided by forming upper mounting element  18  and lower mounting element  20  such that when brought together, gaps  68 ,  70  remain. 
         [0030]    Weight saving voids  72  are formed through mounting blocks  18 ,  20  to reduce weight. 
         [0031]    A threaded opening  60  in each of axle support plates  6 ,  8  is configured to receive the axles  10 ,  12  of wheelchair  3 . Axle support plates  6 ,  8  each contain transverse passageways  84  and end voids  86  to reduce weight further. 
         [0032]    Upper and lower mounting elements  18 ,  20  are each preferably formed as a shell with end voids  74  between first vertical wall  76 ,  77  and opposing second vertical wall  78  (opposing wall of upper mounting element  18  hidden) of each mounting elements  18 ,  20 . Large void openings are provided laterally through the assembled upper and lower mounting elements  18 ,  20 . 
         [0033]    Each of mounting elements  18 ,  20  is further machined or otherwise formed with tapered ends  80  to allow leeway for flexure of leaf springs  30 ,  32 . Similarly each plate  50 ,  52  is tapered at opposing ends such that a gap  82  remains between leaf springs  30 ,  32  and the opposing ends  80  of blocks  50 ,  52 , again to allow space for leaf springs  30 ,  32  to more easily flex. 
         [0034]      FIG. 6  is an enlarged perspective of the lower mounting element  20  of the suspension  2 . It should be understood that upper mounting element  18  is an inverted duplicate of lower mounting element  20 . Lower mounting element  20  comprises an elongate base  90  with voids  74 ,  91  therethrough to reduce the weight of lower mounting element  20 . Preferably mounting element  20  is formed of a lightweight metal such as aluminum. Mounting element  20  is preferably symmetrical about its center segment  92 . Side walls  93 ,  94  upstand from the base  90  at opposing edges thereof. Voids  72 ,  74  are formed in each side wall  93 ,  94 , again to reduce weight without sacrificing rigidity. Each sidewall  93 ,  94  is provided with a semi-cylindrical recess  95  which in cooperation with the identical recess of the upper mounting element  18  creates tubular member receiving passageways  60 . (See  FIGS. 4 and 5 ). 
         [0035]    Each opposing end  80  of base  90  is tapered such that ends  80  are not coplanar with the remainder of underside of base  90 , the tapered ends  80  allowing movement of a leaf spring  30 ,  32  when such leaf spring  30 ,  32  flexes. Each end  80  of base  90  juts a short distance via protruding edge  98  beyond the adjacent sidewall  93 ,  94 . 
         [0036]    Bolt passageways  96  pass vertically through sidewalls  93 ,  94  to accommodate bolts  56  which are used to secure the plates  50 ,  52 , leaf springs  30 ,  32  and mounting elements  18 ,  20  together. Adjacent bolt passageways  96  are abutment surfaces  97  which come into abutment with identical surfaces on the upper mounting element  18  when the mounting elements  18 ,  20  are assembled. Abutment surfaces  97  cause gaps  68 ,  70  to exist when upper and lower mounting elements  18 ,  20  are brought into abutment. (See  FIG. 5 ). 
         [0037]      FIG. 7  diagrammatically illustrates an alternative embodiment wheelchair suspension system  102  in which an upper pair of leaf spring members  130  and  131  are retained to frame mounting elements  118 ,  120 , preferably by mounting bolts (hidden from view). Similarly and symmetrically, paired leaf spring members  132 ,  133  are retained to lower frame mounting element  120  by mounting bolts. Additionally, an upper retaining member  150  and a lower retaining member  152  assist in retaining leaf spring members  130 ,  131  and  132 ,  133  to frame mounting elements  118 ,  120 . Each frame mounting element  118 ,  120  is equivalent to the mounting element  18  shown in  FIG. 6 . Bolts passing from upper retaining member  150  to lower retaining member  152  serve to retain leaf spring members  130 ,  131  and  132 ,  133  to frame mounting elements  118 ,  120 , and to secure wheelchair frame members within openings  126 ,  128  formed by recesses in mounting elements  118 ,  120 . Central void  127  created when mounting elements  118 ,  120  are assembled reduces the weight of material, preferably aluminum, of upper and lower frame mounting blocks  118 ,  120 . 
         [0038]    The alternative embodiment wheelchair suspension system  102  permits separation adjustment of leaf spring members  130 ,  131  and  132 ,  133  to allow selective widening of wheelchair suspension system  102  for wider frame wheelchairs by allowing leaf spring members  130 ,  131  and  132 ,  133  to be adjusted inwardly or outwardly and still to be retained to frame mounting elements  118  and  120 . In particular, each leaf spring member  130 ,  131 ,  132 ,  133  includes a proximal end  230 ,  231 ,  232 ,  233  respectively, with the proximal ends  230 ,  231  of leaf spring members  130 ,  131  selectively continuously adjustable between a spaced apart positioning as seen in  FIG. 7  to the proximal ends  230 ,  231  being in abutment. Likewise, each of leaf spring members  132 ,  133  includes a proximal end  232 ,  233  which opposes the proximal end of the other leaf spring member  132 ,  133 . Leaf spring members  132 ,  133  likewise may be adjusted to any spacing between proximal ends  232 ,  233  thereof being in abutment to a spaced apart opposition as illustrated in  FIG. 7 . After desired adjustment of spacing between proximal ends  230 ,  231 , and spacing between proximal ends  232 ,  233 , bolts (not seen) may be tightened to apply clamping force of upper plate  150  and lower plate  152  to secure leaf spring members  130 ,  131 ,  132 ,  133  to upper frame mounting elements  118 ,  120 . 
         [0039]    Axle support plate  106  is hingedly retained to each of distal ends  134 ,  136  of upper leaf spring member  130  and lower leaf spring member  132  by use of cylindrical bearings  140 ,  142  which may be formed by roll turning distal ends  134 ,  135  of the leaf members  130 ,  131  and likewise the distal ends  136 ,  137  of leaf spring members  132 ,  133 . Similarly, opposing axle support plate  108  is hingedly fixed to each of distal ends  135 ,  137  of upper leaf spring member  131  and lower leaf spring member  133  by use of hinge pins  144  through cylindrical bearings  141 ,  143 . Wheelchair axles  110 ,  112  are screw threaded into axle support plates  106 ,  108 , respectively with threaded openings  160  therein disposed such that the wheels mounted on axles  110 ,  112  are supported at a desired camber angle. The camber angle of support plates  106 ,  108  may be adjusted by sliding leaf springs  130 ,  131  inward or outward. Flexure of leaf spring members  130 ,  131  and  132 ,  133  of suspension system  102  does not cause variation in the camber angle of the wheels mounted on axles  110 ,  112 , due to the parallelism of leaf spring members  130   132 , and  131 ,  133 , and due to their hinged connection to axle supports plates  106 ,  108 . 
         [0040]    Tapers  180  at corners of upper and lower mounting block members  118 ,  120  and reduced thickness at upper and lower plates  150 ,  152 , at each end thereof, allow room for flexing movement of leaf springs  130 ,  131 ,  132  and  133 . 
         [0041]    In operation, as large rear wheels  14 ,  16  encounter uneven support surfaces, any upward thrust is attenuated by flexure of leaf springs  30 ,  32  as axle support plate  6  or axle support plate  8  is forced upward. Because leaf springs  30 ,  32  of suspension  2  or leaf spring members  130 ,  131 ,  132 ,  133  of alternate embodiment suspension  102  are formed of spring steel or other material which will flex but return to its original shape, the upward thrust of either rear wheel  14 ,  16  will be diminished when it reaches rear frame assembly  26  on which the wheelchair user is seated. 
         [0042]    The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations of the embodiments are possible in light of the above disclosure or such may be acquired through practice of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and by their equivalents.