Abstract:
A wheelchair suspension system includes suspension members that interact to cause a positive movement of the suspension members to urge the drive wheels into contact with the ground. The resilient suspension system comprises a drive wheel suspension member for supporting a drive wheel and a front wheel suspension member for supporting a front wheel. The drive wheel suspension member and the front wheel suspension member are each adapted to be movably attached to the wheelchair frame. Each suspension member cooperates with a resilient element to resist movement of the suspension members relative to the frame. The suspension members are adapted to cooperate with each other in response to movement of the suspension members relative to the frame to urge the drive wheel into contact with the ground.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application is a continuation copending U.S. patent application Ser. No. 09/134,286, filed on Aug. 14, 1998 now U.S. Pat. No. 6,070,898. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to wheelchair suspension systems and more particularly, to resilient independent suspension members that have the ability to interact with one another to improve drive wheel traction. 
     Conventional wheelchairs include side frames and a seat assembly supported by the side frames. Drive wheels and front casters are attached to the side frame. The drive wheels may be driven by the wheelchair occupant or by an electrical motor. Anti-tip wheels are often provided rearward of the drive wheels. The anti-tip wheels are adapted to engage the ground to prevent the wheelchair from tipping over. 
     The drive wheels, casters, and anti-tip wheels of traditional wheelchairs are rigidly attached to the side frames. Rigidly attached wheels and casters typically fail to maintain contact with the ground as the wheelchair negotiates obstacles or irregular ground surfaces. Moreover, such wheels and casters provide an abrupt jolt to the wheelchair occupant as the wheels and casters engage the ground. 
     To overcome this problem, pivotal suspension members have been provided for supporting the wheels and casters. Such suspension members are adapted to pivot about a common transverse axis to permit the wheels to maintain contact with the ground. The suspension members may be spring-biased to absorb shock and provide greater comfort for the wheelchair occupant. In addition to absorbing shock, the spring-biased suspension members further insure that substantially all the wheels and casters maintain contact with the ground. Some suspension members provide variable rate resistance to movement. The resistance progressively increases as the suspension members move. The rate of resistance may increase non-linearly. It is well known to use elastomeric elements to bias suspension members. The elastomeric elements cooperate with the frame and suspension members to resist rotational movement of the suspension members. 
     While the advancements in suspension members have progressed towards maintaining ground contact, such advancements have limited application. Maintaining ground contact is still a problem when negotiating obstacles or irregular ground surfaces because of the passive movement of the suspension members. The passive movement has a limited effect on improving the traction of the drive wheels. 
     What is needed is a wheelchair suspension system that has suspension members interacting to positively urge the drive wheel suspension members into contact with the ground and thus improve the traction of the drive wheels. 
     SUMMARY OF THE INVENTION 
     This invention is directed towards a wheelchair suspension system that includes suspension members that interact to cause a positive movement of the suspension members to urge the drive wheels into contact with the ground. The resilient suspension system comprises a drive wheel suspension member for supporting a drive wheel and a front wheel suspension member for supporting a front wheel. The drive wheel suspension member and the front wheel suspension member are each adapted to be movably attached to the wheelchair frame. Each said suspension member cooperates with a resilient element to resist movement of the suspension members relative to the frame. The suspension members are adapted to cooperate with each other in response to movement of said suspension members relative to the frame to urge the drive wheel into contact with the ground. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear perspective view of a base frame assembly for use with a wheelchair suspension system according to the invention. 
     FIG. 2 is a rear perspective view of the base frame assembly shown in FIG. 1, further showing resilient suspension members attached to the base frame assembly for supporting drive wheels and drive motors, front casters, and anti-tip wheels. 
     FIG. 3 is an exploded perspective view of a resilient rear suspension member of the invention. 
     FIG. 4 is an enlarged sectional view of a portion of the resilient rear suspension member shown in FIG.  3 . 
     FIG. 5 is an enlarged sectional view of a portion of a resilient drive wheel suspension member of the invention. 
     FIG. 6 is an enlarged side elevational view of the resilient drive wheel suspension member shown in FIG. 2 attached to a portion of the side of the base frame assembly. 
     FIG. 7 is an elevational view of the base frame assembly showing relative locations of the resilient drive wheel suspension member, the resilient front suspension member, and the resilient rear suspension member. 
     FIG. 8 is an exploded perspective view of the resilient drive wheel suspension member shown in FIGS. 2,  6 , and  7 . 
     FIG. 9 is an elevational view of another alternative resilient element. 
     FIG. 10 is an elevational view of yet another alternative resilient element. 
     FIG. 11 is an elevational view of still another alternative resilient element. 
     FIG. 12 is a perspective view of an alternative resilient drive wheel suspension member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in FIG. 1 a power wheelchair base frame assembly  10  for supporting a wheelchair seat assembly (not shown). It should be understood that the base frame assembly  10  could be adapted to support any number of suitable wheelchair seat assemblies. It should also be understood that a wheelchair seat assembly could be attached to the base frame assembly  10  in any suitable manner. 
     The base frame assembly  10  has opposite sides  12 ,  14 , a front end  16 , and a rear end  18 . A footrest  26  (shown in FIG. 2) extends from the front end  16  of the base frame assembly  10 . The base frame assembly  10  further includes an upper frame structure  20  and a lower frame structure  22 . The upper frame structure  20  includes opposite sides  24 ,  28  and a front end  30 . The lower frame structure  22  includes opposite sides  32 ,  34 , a front end  36 , and a rear end  38 . The upper frame structure  20  is spaced apart from the lower frame structure  22  and fixed relative to the lower frame structure  22  by vertically extending structural elements  40 ,  42 . The vertically extending structural elements  40 ,  42  have lower ends  46 ,  48  connected to corners of the lower frame structure  22  and upper ends  50 ,  52  connected to corners of the upper frame structure  20 . This configuration forms a base frame assembly  10  having a substantially rectangular construction. A substantially planar panel  54  is rigidly connected to the opposite sides  32 ,  34 , the front end  36 , and the rear end  38  of the lower frame structure  22  so as to be rigidly supported by the lower frame structure  22 . The planar panel  54  is provided to support a battery (not shown). It should be understood that this base frame assembly  10  described is for merely illustrative purposes and that the invention may be adapted for use with other wheelchair frame assemblies. 
     As shown in FIG. 2, the base frame assembly  10  supports independent resilient suspension members, generally indicated at  56 ,  58  and  60  (shown more clearly in FIG.  7 ). The independent resilient suspension members include resilient front suspension members  56 , resilient rear suspension members  58 , and resilient drive wheel suspension members  60 . The resilient drive wheel suspension members  60  are attached to opposite sides  12 ,  14  of the base frame assembly  10 . The resilient front suspension members  56  are attached to the base frame assembly  10  in front of the drive wheel suspension members  60 . The resilient rear suspension members  58  are attached to the base frame assembly  10  reward of the resilient drive wheel suspension members  60 . 
     Each of the resilient suspension members  56 ,  58 ,  60  supports a wheel. For example, each of the resilient front suspension members  56  supports a front wheel  62 . The front wheels  62  are preferably casters. Each of the resilient rear suspension members  58  supports a rear wheel  64 . The rear wheels  64  may also be casters. Lastly, each of the resilient drive wheel suspension members  60  supports a drive wheel  66 . The drive wheels  66  are preferably driven by a prime mover, such as the electric motor assembly  68  shown. The electric motor assembly  68  may be controlled by an electrical controller  44  responsive to the occupant&#39;s voice or to signals produced by a control wand supported on the armrest (not shown) of the wheelchair. The armrest could be an integral part of the wheelchair seat assembly. 
     An example of a resilient suspension member is shown in FIG.  3 . Although the resilient suspension member shown is a resilient rear suspension member  58 , the resilient front suspension member  56  is configured in a similar manner. The resilient rear suspension member  58  includes an outer structural member  70  and an inner structural member  72  disposed within the outer structural member  70 . It is preferable that the outer structural member  70  and the inner structural member  72  be metal. However, it is conceivable that other materials may be suitable for carrying out the invention. Although the outer structural member  70  and the inner structural member  72  are substantially square, other geometric shapes may be employed. As shown in FIG. 4, the outer structural member  70  is positioned out of phase relative to the inner structural member  72  so as to form a plurality of pockets  74  between the outer structural member  70  and the inner structural member  72 . Although the outer structural member  70  is positioned forty-five degrees out of phase relative to the inner structural member  72 , other phase angles may be suitable for carrying out the invention. The relative positions of the outer structural member  70  and the inner structural member  72  may largely depend on the geometric shapes of the structural members  70 ,  72 . A resilient element  76  is disposed within each of the pockets  74 . The resilient element  76  is preferably an elastomeric material. Rubber or vulcanized rubber may be a suitable material. It should be understood that the resilient element  76  may be a natural or synthetic material. Urethanes or other polymers may be suitable for carrying out the invention. The inner structural member  72  is rotatable relative to the outer structural member  70  along an axis of rotation, indicated at A in FIG.  7 . The resistance of the resilient element  76  to compression limits the rotation or torsional movement of the inner structural member  72 . 
     As shown in FIG. 3, a set of spaced apart tabs, generally indicated at  78 , extends from an outer surface of the outer structural member  70 . The tabs  78  are provided to engage the rear end  38  of the lower frame structure  22 , as is clearly shown in FIG.  2 . The tabs  78  have holes  98  which co-align with corresponding holes (not shown) in the rear end  38  of the lower frame structure  22  to receive a fastener (not shown) for affixing the outer structural member  70  to the base frame assembly  10 . The resilient front suspension member  56  may be attached to the front end  16  of the base frame assembly  10 , as shown in FIG. 7, in a similar manner as well. 
     Continuing with reference to FIG. 3, a lever  80  is shown attached to the inner structural member  72 . The lever  80  is provided for supporting the rear wheel  64  (shown in FIG.  2 ). The rear wheel  64  is supported at an end  82  of the lever  80  remote from the inner structural member  72 . The lever  80  may support the rear wheel  64  in any conventional manner. For example, a caster housing  84  may be provided at the end  82  of the lever  80  for rotatably receiving a caster stem (not shown). An annular space (not shown) may be defined between an inner surface of the housing  84  and the caster stem to receive bearings (also not shown). 
     An end  83  of the inner structural member  72  remote from the lever  80  has a threaded bore  86  for receiving a threaded stud  88 . The threaded stud  88  extends through a cap  90  for the outer structural member  70 , and further through a series of washers  92 . A lock nut  96  is engageable with the threaded stud  88  so as to confine the outer structural member  70  between the lever  80  and the cap  90 . Linear bearings  91 ,  93  may be employed between the lever  80  and the structural members  70 ,  72 , and further between the inner structural member  72  and the cap  90  to eliminate or reduce axial frictional forces. It should be understood that other friction reduction elements, such as nylon washers (not shown), may be employed as well. 
     It should be noted with reference to FIG. 7, that the resilient front suspension members  56  and the resilient rear suspension members  58  are attached to the base frame assembly  10  at different relative elevations. It should also be noted that the lengths of the levers  80 ,  81  and the angular displacement of the levers  80 ,  81  vary between the resilient front suspension members  56  and the resilient rear suspension members  58 . It should further be noted that the front wheels  62  and the rear wheels  64  may be of different dimensions. These characteristics are dependent on one another and may be largely dependent on other physical characteristics of the wheelchair as well. 
     Unlike the resilient rear suspension members  58 , the resilient front suspension members  56  each supports a traction ramp  100 . The traction ramps  100  are preferably welded to the resilient front suspension members  56 . However, it should be understood that the traction ramps  100  may be attached in any suitable manner. 
     The resilient drive wheel suspension members  60  are configured in a manner similar to that of the resilient rear suspension members  58  and the resilient front suspension members  56 . As shown in FIG. 8, the resilient drive wheel suspension members  60  each includes an outer structural member  102  and an inner structural member  104  disposed within the outer structural member  102 . A plurality of pockets  106  (more clearly shown in FIG. 5) are defined between the outer structural member  102  and the inner structural member  104 . A resilient element  108  is disposed within each of the pockets  106  (also shown more clearly in FIG.  5 ). The resilient element  108  is preferably an elastomeric material. As set forth above, the resilient element  108  may be rubber or vulcanized rubber. The resilient element  108  may be a natural or synthetic material. Urethane or other polymers may be suitable for carrying out the invention. The inner structural member  104  is rotatable relative to the outer structural member  102  along an axis of rotation, indicated at B in FIG. 7, and the resistance of the resilient element  108  to compression limits such rotation. 
     A set of spaced apart tabs, generally indicated at  110 , extends from the outer structural member  102 . The tabs  110  are provided to support the electric motor assembly  68 . Hence, the tabs  110  define a motor mount. The tabs  110  have holes  115  that co-align with corresponding holes (not shown) in the electric motor assembly  68  (shown in FIG. 2) and are adapted to receive fasteners (not shown) for affixing the electric motor assembly  68  to the tabs  110 . 
     The outer structural member  102  is disposed between two spaced apart brackets  112 . Spacers may be provided between the inner structural member  104  and the brackets  112  so as to center the outer structural member  102  between the brackets  112 . The brackets  112  shown are triangular shaped and have an offset upper end  111 . The offset upper end  111  is provided to compensate for the difference in the axial width of the outer structural member  102  and the sides  24 ,  28  of the upper frame structure  20  of the base frame assembly  10  to which the brackets  112  attach. The offset upper end  111  of each of the brackets  112  have holes  117  that co-align with holes (not shown) in the opposite sides  24 ,  28  of the upper frame structure  20 . Threaded fasteners  116  pass through the holes  117  in the brackets  112  and further through the holes in the sides  24 ,  28  of the upper frame structure  20 . The threaded fasteners  116  are engageable with lock nuts  118  to attach the brackets  112  to the upper frame structure  20  (as shown in FIG.  6 ). 
     An axial bore  120  passes through the inner structural member  104 . A threaded fastener  122  passes through the brackets  112 , the inner structural member  104 , and a series of washers  121 ,  123  and spacers  125 . A lock nut  113  engages the threaded fastener  122  to retain the outer structural member  102  within the inner structural member  104  and between the brackets  112 . 
     The resilient elements  76 ,  108  set forth above each preferably have a cross-section larger than the cross-section of the pockets  74 ,  106  so as to be compressed when in the pockets  74 ,  106 . The resilient elements  76 ,  108  may be formed integrally with one another, as shown in the drawings, or may be separate cylindrically shaped resilient members (not shown) independent of one another. Resilient elements  76 ,  108  formed integrally with one another may be more effective in restricting the rotational displacement of the inner structural members  72 ,  104  relative to the outer structural members  70 ,  102 . 
     It should be understood that the invention is not limited to resilient elements that are an extruded elastomer. An elastomer may be injected into the pockets  74 ,  106 . An injected elastomer would bond to the outer structural members  70 ,  102  as well as the inner structural members  72 ,  104 . 
     It should also be understood that the resilient suspension members in the foregoing description are merely illustrative and that other resilient suspension configurations may be suitable for carrying out the invention. For example, an annular resilient element may be provided in an annular pocket defined between cylindrical inner and outer structural members. The annular resilient element may be in the form of a Torsilastic spring manufactured by B F Goodrich in Akron, Ohio. A resilient element in the form of a spring  124  is shown in FIG. 9. A resilient member in the form of a hydraulic actuator  126  is shown in FIG.  10 . FIG. 11 shows a resilient material  128  intermediate a displaceable structural member, such as the resilient drive wheel suspension member  60 , and a fixed structural member, such as one of the sides  24  of the upper frame structure  20  of the base frame assembly  10 . Each of these configurations may be suitable for carrying out the invention. 
     As shown in FIG. 12, the resilient drive wheel suspension members  60  may be provided with a traction link arm  130  for supporting a traction link roller  132 . The traction link roller  132  is rotatable about an axis of rotation C that is spaced apart and substantially parallel to the axis of rotation B of the resilient drive wheel suspension member  60 . The traction link roller  132  is adapted to cooperate with or engage the traction ramp  100 . The traction link arm  130 , the traction link roller  132 , and the traction ramp  100  cooperatively form a traction linkage assembly, generally indicated at  134  (shown in FIG.  7 ). The traction linkage assembly  134  insures that a continuous contact is maintained between the drive wheels  66  and the ground. 
     The operation of the suspension system will be best understood with reference to FIG.  7 . As the wheels  62 ,  64 ,  66  rotate in the direction of the arrows D, the wheelchair progresses forward in the direction of the arrow E. The resilient suspension members  56 ,  58 ,  60  absorb shock sustained by the wheelchair when traversing an irregular ground surface to provide comfortable transportation. This is accomplished because of the compressive and decompressive nature of the resilient elements  76 ,  108 . The front wheels  62  are spaced apart from the drive wheels  66  sufficiently to reduce the risk of the wheelchair tipping forward. Likewise, the rear wheels  64  are spaced apart from the drive wheels  66  sufficiently to reduce the risk of the wheelchair tipping rearward. Note that clearance is provided between the traction link roller  132  and the traction ramp  100 . As the wheelchair encounters an obstacle, the resilient front suspension members  56  pivot about an axis of rotation in the direction of the arrow F. As this occurs, the resilient front suspension members  56  approach the traction link rollers  132 . Upon contacting the traction ramps  100 , the traction link rollers  132  progress up the traction ramps  100  and the resilient drive wheel suspension members  60  pivot about the axis of rotation B in the direction of the arrow G. As this occurs, the drive wheels  66  are forced downward so as to remain in contact with the ground. As the wheelchair tips rearward, the rear wheels  64  maintain contact with the ground. The resilient rear suspension members  58  may pivot about the axis of rotation A in the direction of the arrow H so as to absorb shock encountered by rearward tipping. Upon overcoming the obstacle, the resilient suspension members  56 ,  58 ,  60  return to a normal position. It should be understood that, as the wheelchair tips rearward, the resilient elements  76 ,  108  are compressed. As the wheelchair overcomes the obstacle, the resilient elements  76 ,  108  are decompressed. The resistance to compression increases as the compression increases so as to smoothly absorb shock or abrupt jolts. Likewise, the resistance to compression decreases as the resilient elements  76 ,  108  decompress to smoothly urge the resilient suspension members  56 ,  58 ,  60  back to a normal position. 
     It should be clear that the front wheels  62  reduce the risk of the wheelchair tilting forward. The resilient rear suspension members  58  function to support anti-tip wheels to limit the amount of rearward tipping of the wheelchair. 
     A separate and independent resilient suspension member for each wheel permits each of the six wheels to react to irregular ground surfaces independent of all the other wheels. However, it is to be understood that an independent resilient suspension member need not be provided for all of the wheels. For example, independent resilient suspension members may be provided for the front wheels  62  only. However, such a configuration would not permit the drive wheels  66  to pivot. It should also be understood that a resilient suspension member may be provided to support a single wheel, like a single front wheel  62  or a single rear wheel  64 . One advantage to having six wheels is that the drive wheels  66  may be centrally located along the opposite sides  12 ,  14  of the base frame assembly  10  between the front and rear wheels  62 ,  64 . 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.