Abstract:
A wheelchair suspension system comprises a suspension assembly disposed adjacent to each wheel of the wheelchair, and attached to an interconnecting the axle of the wheels to the wheelchair frame. Each of the suspension assemblies includes a front bracket and a rear bracket, wherein the front bracket is attached to the wheelchair frame and the rear bracket is attached to the axle. Top and bottom generally L-shaped arms each are pivotally attached to each of the brackets in a diametrically opposed fashion, and an elastomeric spring is disposed between and interconnects the arms. When one or more of the wheels encounters a bump in a travel surface of the wheelchair, the arms pivot about the brackets, remain parallel to each other, and move closer together to compress the spring which absorbs a significant amount of shock caused by the bump. Further, the wheelchair has a frame with a pair of frame extensions that are supported by a transversely extending camber bar that journals the axles of thee wheelchair drive wheels. The drive wheels can be variably positioned with respect to the front casters by means of the frame extensions.

Description:
CROSS-REFERENCE 
     This is a divisional of application Ser. No. 09/191,332, filed on Nov. 13, 1998 now U.S. Pat. No. 6,161,856, of Christopher J. Peterson for WHEELCHAIR SUSPENSION SYSTEM. 
     1. Field of the Invention 
     The invention relates to lightweight wheelchairs used for sports. More particularly, the present invention is directed to a wheelchair frame, which includes a pair of frame extension members that permit adjustment of the center of gravity by changing the length of the distance between the drive wheels and the front wheels. 
    
    
     BACKGROUND OF THE INVENTION 
     2. Background Art 
     Since the inception of the wheelchair, manufacturers and users of this device have continually attempted to improve its comfort, operation, portability, and appearance. One area of ongoing concern is the capability of the wheelchair to exhibit excellent shock absorption characteristics while at the same time being cost-effective and light-weight. A suspension system, of the type similar to those that can be found on other types of wheeled vehicles such as cars and trucks, is incorporated in a vehicle for several reasons. One reason is to absorb shocks and thereby insulate from shocks the people and/or cargo being carried by the vehicle. For example, during use of a wheelchair, small bumps, depressions or other irregularities on the surface on which the wheelchair is traveling can cause such shocks. Another common objective of a vehicle suspension that also applies to wheelchairs is to maintain all of the wheels of the vehicle on the ground when such relatively small bumps or depressions are encountered, in order to maintain steering control and stability of the vehicle. However, unfortunately, many known suspension systems are too expensive and/or too heavy for incorporation into many of today&#39;s lightweight and relatively inexpensive wheelchairs. 
     The present invention solves the above-described problems by incorporating a relatively simple, inexpensive, lightweight, yet effective suspension assembly adjacent to each wheel of the wheelchair, which in turn provides a relatively large amount of substantially vertical wheel displacement for absorbing shocks and for maintaining the steering control and stability of the wheelchair. 
     SUMMARY OF INVENTION 
     Objectives of the present invention include providing a wheelchair suspension system which absorbs and insulates the occupant of the wheelchair from shocks when relatively small bumps, depressions or other irregularities in a travel surface are encountered by the wheelchair. 
     Another objective of the present invention is to provide such a wheelchair suspension system in which all wheels of the wheelchair are maintained in constant contact with the travel surface when such bumps, depressions or other irregularities in the travel surface are encountered by the wheelchair, thereby maintaining occupant steering control and stability of the wheelchair. 
     A further objective of the present invention is to provide such a wheelchair suspension system which is economical to manufacture and install on a wheelchair, lightweight and reliable in use. 
     These objectives and advantages are obtained by the wheelchair suspension system of the present invention, the general nature of which may be stated as including at least one suspension system for a wheelchair, the suspension system including at least one suspension assembly interconnecting a frame of the wheelchair to an axle of at least one wheel of the wheelchair, the suspension assembly including top and bottom arms, each of the arms being pivotally and operatively attached at each of its ends to the frame and the axle; and a spring disposed between and attached to each of the arms, so that when the wheel encounters a bump in a travel surface, the arms pivot, the spring compresses and the axle moves in a substantially vertical upward direction, and when the wheel encounters a depression in a travel surface, the arms pivot, the spring is placed in tension and the axle moves in a substantially vertical downward direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the invention, illustrative of the best mode in which applicants has contemplated applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a rear perspective view showing one type of wheelchair on which the suspension system of the present invention is incorporated; 
     FIG. 2 is an enlarged view similar to FIG. 1, but with one of the wheels of the wheelchair removed to reveal the suspension assembly disposed adjacent to the removed wheel; 
     FIG. 3 is a left-hand side view of the wheelchair shown in FIG. 2; 
     FIG. 4 is an enlarged front perspective view of the suspension system of the present invention, shown mounted on the axle of the wheelchair and with other parts of the wheelchair removed; 
     FIG. 5A is an enlarged fragmentary side view of one of the suspension assemblies of the suspension system, shown mounted on the axle and the frame of the wheelchair, and with other parts of the wheelchair removed; 
     FIG. 5B is a rear perspective view of the parts shown in FIG. 5A; 
     FIG. 6A is an enlarged view similar to FIG. 5A, but without showing any portion of the wheelchair frame, and showing the substantially vertical upward displacement of the axle when a bump is encountered in the travel surface of the wheelchair; and 
     FIG. 6B is a view similar to FIG. 6A, and showing the substantially vertical downward displacement of the axle when a depression is encountered in the travel surface of the wheelchair. 
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The suspension system of the present invention is indicated generally at  10 , and is shown in FIG. 1 incorporated into a wheelchair  11  having a frame  12  and an axle  13 . As best shown in FIGS. 2 and 4, suspension system  10  includes a pair of suspension assemblies  15  which are identical in structure and operation, so that only one suspension assembly will be described hereinbelow. Suspension assembly  15  includes a front bracket  16  and a frame extension  14  for attaching the suspension assembly to wheelchair frame  12 , a rear bracket  17  for attaching the suspension assembly to one end of wheelchair axle  13 , top and bottom arms  18   a  and  18   b , respectively, each of which is pivotally attached to the front and rear brackets, and a spring  19  disposed between and interconnecting the top and bottom arms. Suspension assembly  15  is a trailing arm type suspension assembly, but it is understood that the concepts of the present invention also are applicable to leading arm or transverse arm suspension assemblies. 
     Suspension system  10  of the present invention is shown in FIGS. 1 through 3 incorporated into wheelchair  11  of the type which generally is considered to be a lightweight sport wheelchair useful in outdoor and indoor sporting activities. However, it is understood that the present invention can be utilized on other types of wheelchairs, including non-rigid or folding wheelchairs which are free of an axle which extends between and interconnects the two main wheels of the wheechair, thereby making the wheelchair collapsible. However, so that one environment in which suspension system  10  can be used will be better understood, wheelchair  11  will be described in greater detail. As set forth hereinabove, wheelchair  11  includes frame  12  and axle  13 . Wheelchair  11  further includes a seat  25  mounted on frame  12 , wherein the seat includes a horizontal bottom portion.  26  and a vertical back support  27 . A manually operable drive wheel  28 , of a type which is well known in the wheelchair art, is mounted on each end of axle  13  in a usual manner. A pair of swivel casters  29  is mounted in spaced-apart relationship on the front of frame  12  forwardly from wheels  28 . A footrest  30  also is mounted on the front of frame  12  between casters  29 . It should be noted that wheelchair  11  of the type shown in FIGS. 1 to  3  typically is utilized in sporting activities such as basketball and the like, due to its light weight and stability as well as its ability to withstand side loads because of the interconnection of wheels  28  by axle  13 . Moreover, it is understood that in this type of sport wheelchair  11 , wheels  28  each are conventionally mounted on frame  12  with a camber (not shown), that is, the bottom portions of the wheels are set apart a greater transverse distance than are the top portions of the wheels. 
     Suspension assembly  15  and its incorporation into wheelchair  11  now will be described in detail. The components of suspension assembly  15  are formed of any suitable sturdy material such as metal, except where noted. Top and bottom suspension assembly arms  18   a, b  each is a generally L-shaped member (FIG.  5 A). Each L-shaped arm  18   a, b  includes an elongated section  35  and a short section  36 . Each short arm section  36  is formed with a cutout  37  (FIG. 5B) and a pair of spaced-apart transversely aligned openings (not shown). Similarly, each elongated arm section  35  is formed with a cutout  38  (FIG. 4) and a pair of spaced-apart transversely aligned openings (not shown). 
     Front bracket  16  is formed with a first pair of spaced-apart upwardly extending ears  40  and a second pair of spaced-apart downwardly extending ears  41  (FIG.  4 ). Each ear  40 ,  41  is formed with an opening (not shown), and each pair of ears is spaced apart a distance wherein the outermost surface of each ear abuts an innermost surface of its respective arm cutout  37 ,  38 . The openings of first pair of ears  40  are aligned with top arm elongated section  35  openings and the openings of second pair of ears  41  are aligned with bottom arm short section  36  openings. A suitable fastener  42  is passed through the aligned openings of top arm elongated section  35  and first pair ears  40  to pivotally secure top arm  18   a  to bracket  16 . Similarly, another fastener  42  is passed through the aligned openings of bottom arm short section  36  and second pair ears  41  to pivotally secure bottom arm  18   b  to bracket  16 . Bracket  16  also is formed with a central opening  43  (FIG. 5B) for insertion of the rear end of frame extension  14 , and the front end of the frame extension is inserted into frame  12 . More specifically, wheelchair frame  12  and frame extension  14  each is formed of a tube-shaped metal, and-the outside diameter of extension  14  is nominally smaller than the inside diameter of a rearwardly extending frame tube  44  and central bracket opening  43 . The rear end of extension  14  is immovably secured in bracket opening  43  by any suitable means such as welding, and the front end of the extension is adjustably secured in the frame tube by a cam clamp mechanism  45  of a type that is well known to the art and to the literature (FIGS. 2,  3 ,  5 A and  5 B) However, although clamp  45  is preferred, it is understood that any type of clamp mechanism, set screw or the like could be used to adjustably secure extension tube  14  within frame tube  44 . It should further be appreciated that the depth of insertion of each extension tube  14  within its respective frame tube  44  determines the front-rear position of wheels  28  relative to frame  12  and seat  25 , thereby determining the center of gravity of wheelchair  11 . 
     Rear bracket  17  similarly is formed with a first pair of spaced-apart upwardly extending ears  50  and a second pair of spaced-apart downwardly extending ears  51  (FIGS.  4  and  5 B). Each ear  50 ,  51  is formed with an opening (not shown), and each pair of ears is spaced apart a distance wherein the outermost surface of each ear abuts an innermost surface of its respective arm cutout  37 ,  38 . The openings of first pair of ears  50  are aligned with top arm short section  36  openings and the openings of second pair of ears  51  are aligned with bottom arm elongated section  35  openings. A fastener  42  is passed through the aligned openings of top arm short section  36  and first pair ears  50  to pivotally secure top arm  18   a  to bracket  17 . Similarly, another fastener  42  is passed through the aligned openings of bottom arm elongated section  35  and second pair ears  51  to pivotally secure bottom arm  18   b  to bracket  17 . The rear surface of bracket  17  is attached to a saddle  52  such as by welds (not shown), and the saddle in turn is similarly attached to a cam clamp mechanism  53  which in turn is slidably mounted on the end of axle  13 . 
     Spring  19  includes top and bottom cylindrical-shaped solid members  61 ,  62 , respectively, with each member being formed of an elastomer having a type A durometer of from about 50 to about 100, preferably from about 60 to about 90, and most preferably from about 70 to about 80. An isolation plate  60  is disposed between and interconnects top and bottom members  61 ,  62  to provide additional stability to spring  19 . As best shown in FIGS. 4 and 6A, spring  19  is mounted on and extends between elongated section  35  of top and bottom arms  18   a, b  by a pair of fasteners  65  of a type which are well known to one skilled in the spring art. 
     The operation of suspension system  10  of the present invention, and in particular each suspension assembly  15  thereof, can now be described. In its resting position, as best shown in FIG. 5A, a horizontal distance between the rear surface of bracket  16  and a central axis of axle  13  is represented by D. Moreover, a vertical distance between the central axis of axle  13  and a central axis of frame extension  14  is represented by H. In addition, a distance between the lowermost and uppermost surfaces of elongated sections  35  of top and bottom arms  18   a, b , respectively, is represented by A. It can be seen in FIG. 6A that when a bump is encountered by one or both wheels  28  of wheelchair  11 , arms  18  pivot about brackets  16  and  17  at fasteners  42  as axle  13  moves upward in response to the bump. This pivoting action causes arms  18   a, b  to visibly move close together from distance A (FIG. 5A) to distance A−z, where z is variable, and spring  19  correspondingly is compressed to absorb the shock of wheel  28  moving over the bump. However, elongated section  35  of each arm  18  remains parallel to the elongated section of the other arm, thereby enabling a relatively large amount of vertical travel H+y, where y is variable, of axle  13  and only a nominal amount of horizontal travel D−x, where x is variable, of the axle, thereby providing efficient absorption of up to about 50% of the shock by suspension assembly  15 . 
     Turning now to FIG. 6B, it can be seen that when one or both wheels  28  of wheelchair  11  encounters a depression in the travel surface of the wheelchair, arms  18  again pivot about brackets  16 ,  17  at fasteners  42  as axle  13  moves downward in response to the depression. This pivoting action causes arms  18   a, b  to visibly move farther apart from distance A to distance A+z, and spring  19  correspondingly is placed under tension to absorb the shock of wheel  28  dropping into the depression. Elongated section  35  of each arm  18  again remains parallel to the elongated section of the other arm, thereby enabling a relatively large amount of vertical travel H−y of axle  13  and only a nominal amount of horizontal travel D+x of the axle, again resulting in efficient absorption of up to about 50% of the shock by suspension assembly  15 . 
     In accordance with one of the main features of the present invention, it should be understood that the displacement of axis  13  in a substantially vertical direction when a bump or depression is encountered in the travel surface of wheelchair  11 , is an important factor in maintaining the center of gravity of the occupied wheelchair. This substantially vertical axle displacement also aids in keeping all of the wheels of the wheelchair in contact with the travel surface, to maintain the stability and steering control of the wheelchair. Moreover, suspension assembly  15  prevents axle  13  from traveling substantially in an arc, which in turn prevents toe-in of the already cambered wheels, which in turn also aids in maintaining all of the wheels in contact with the travel surface when irregularities in that surface are encountered. 
     Thus, it can be seen that the suspension system  10  of the present invention is useful on wheelchairs of any type to provide shock absorption and stability to the wheelchair when bumps, depressions or other irregularities in the travel surface of the wheelchair are encountered. Moreover, it can be seen that suspension system  10  is economical to make and install, reliable in use, and lightweight and easy to maintain. 
     Accordingly, the wheelchair suspension system of the present invention is simplified, provides an effective, safe, inexpensive and efficient suspension system which achieves all of the enumerated objectives, provides for eliminating difficulties encountered with prior wheelchair suspension systems, and solves problems and obtains new results in the art. 
     In the foregoing description, certain terms have been used for brevity, clarity, and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries and principle pies of the invention, the manner in which the wheelchair suspension system is constructed, arranged, and used, the characteristics of the construction and arrangement, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts, and combinations are set forth in the appended