WHEELCHAIR SUSPENSION SYSTEM

Abstract: A wheelchair suspension system comprises a suspension assembly disposed adjacent to each wheel of the wheelchair, and attached to and interconnecting the axle (13) of the wheels to the wheelchair frame. Each of the suspension assemblies includes a front bracket (16) and a rear bracket (17), wherein the front bracket (16) is attached to the wheelchair frame and the rear bracket (17) is attached to the axle (13). Top and bottom generally L-shaped arms (35) each are privotally attached to each of the brackets in a diametrically opposed fashion, and an elastomeric spring (19) 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 move closer together to compress the spring. Conversely, when one or more of the wheels encounters a depression, the arms move farther apart to place tension on the spring. The pivoting parallel arrangement of arms and brackets enables displacement of the axle in a substantially vertical, relatively large distance when one or more of the wheels encounter an irregularity in the wheelchair travel surface, which in turn maintains stability and steering control of the wheelchair by keeping the wheels in contact with the travel surface.

Description: WHEELCHAIR SUSPENSION SYSTEM BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to suspension systems and in particular to a suspension system for a wheelchair. More particularly, the present invention is directed to a suspension system for a wheelchair, which provides for a relatively large amount of substantially vertical travel of the wheels of the wheelchair when bumps, depressions or other irregularities in the wheelchair travel surface are encountered by the wheels. 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'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 wheel- chair 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 draw- ings 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 draw- ings. 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 1 1 having a frame 1 2 and an axle 1 3. As best shown in FIGS. 2 and 4, suspension system 1 0 includes a pair of suspension assemblies 1 5 which are identical in structure and operation, so that only one suspension assembly will be described hereinbelow. Suspension assembly 1 5 includes a front bracket 1 6 and a frame extension 14 for attaching the suspension assembly to wheelchair frame 1 2, a rear bracket 17 for attaching the suspension assembly to one end of wheelchair axle 1 3, top and bottom arms 1 8a and 1 8b, respectively, each of which is pivotally attached to the front and rear brackets, and a spring 1 9 disposed between and interconnecting the top and bottom arms. Suspension as- sembly 1 5 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 1 1 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 wheel- chair, thereby making the wheelchair collapsible. However, so that one environment in which suspension system 10 can be used will be better understood, wheelchair 1 1 will be described in greater detail. As set forth hereinabove, wheelchair 1 1 includes frame 1 2 and axle 1 3. Wheelchair 1 1 further includes a seat 25 mounted on frame 1 2, 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 1 3 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 1 2 between casters 29. It should be noted that wheelchair 1 1 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 1 3. Moreover, it is understood that in this type of sport wheelchair 1 1 , wheels 28 each are conventionally mounted on frame 1 2 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 1 5 and its incorporation into wheelchair 1 1 now will be described in detail. The components of suspension assembly 1 5 are formed of any suitable sturdy material such as metal, except where noted. Top and bottom suspension assembly arms 1 8a, b each is a generally L-shaped member (FIG. 5A). Each L-shaped arm 18a, 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 1 6 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 1 8a to bracket 1 6. 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 1 8b to bracket 1 6. Bracket 1 6 also is formed with a central opening 43 (FIG. 5B) for insertion of the rear end of frame extension 1 4, and the front end of the frame extension is inserted into frame 1 2. More specifically, wheelchair frame 1 2 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, 5A and 5B) 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 1 2 and seat 25, thereby determining the center of gravity of wheelchair 1 1 . Rear bracket 1 7 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 5B). 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 1 8a to bracket 1 7. 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 18b to bracket 1 7. The rear surface of bracket 1 7 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 1 3. Spring 1 9 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 1 9. As best shown in FIGS. 4 and 6A, spring 1 9 is mounted on and extends between elongated section 35 of top and bottom arms 1 8a, 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 1 5 thereof, can now be described. In its resting position, as best shown in FIG. 5A, a horizontal distance between the rear surface of bracket 1 6 and a central axis of axle 1 3 is represented by D. Moreover, a vertical distance between the central axis of axle 1 3 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 1 8a, 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 1 1 , arms 18 pivot about brackets 1 6 and 1 7 at fasteners 42 as axle 1 3 moves upward in response to the bump. This pivoting ac- tion causes arms 1 8a, b to visibly move close together from distance A (FIG. 5A) to distance A-z, where z is variable, and spring 1 9 correspondingly is compressed to absorb the shock of wheel 28 moving over the bump. However, elongated section 35 of each arm 1 8 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 1 3 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 1 5. Turning now to FIG. 6B, it can be seen that when one or both wheels 28 of wheelchair 1 1 encounters a depression in the travel surface of the wheelchair, arms 18 again pivot about brackets 1 6, 17 at fasteners 42 as axle 1 3 moves downward in response to the depression. This pivoting action causes arms 1 8a, b to visibly move farther apart from distance A to distance A + z, and spring 1 9 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 1 3 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 1 3 in a substantially vertical direction when a bump or depression is encountered in the travel surface of wheelchair 1 1 , 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 1 5 prevents axle 1 3 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 in- tended 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 princi- 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 claims.

Claims: WHAT IS CLAIMED IS: 1 . A suspension system for a wheelchair, said suspension system including: a) at least one suspension assembly interconnecting a frame of said wheelchair to an axle of at least one wheel of the wheelchair, said suspension assembly including, i) top and bottom arms, each of said arms being pivotally and operatively attached at each of its ends to said frame and said axle; and ii) a spring disposed between and attached to each of said arms, so that when said wheel encounters a bump in a travel surface, the arms pivot, said spring compresses and the axle moves in a substantially vertical upward direc- tion, and when said wheel encounters a depression in a travel surface, said arms pivot, the spring is placed in tension and said axle moves in a substantially vertical downward direction. 2. The suspension system for a wheelchair of Claim 1 , in which each of said arms generally is L-shaped; and in which said L- shaped arms generally are diametrically opposed. 3. The suspension system for a wheelchair of Claim 2, in which said wheelchair includes a front end and a rear end; in which each of said L-shaped arms includes an elongated section and a short section; and in which said top arm short section extends in a rearward direction and said bottom arm short section extends in a frontward direction. 4. The suspension system for a wheelchair of Claim 3, in which each of said L-shaped arms is pivotally attached to spaced apart front and rear brackets; in which said elongated section of each of said L-shaped arms remains parallel to the elongated section of the other arm during pivoting of said arms; in which said rear bracket is immovably attached to said axle; and in which said front bracket is immovably attached to said wheelchair frame. 5. The suspension system for a wheelchair of Claim 4, in which said front bracket is immovably attached to an extension member of said wheelchair frame; in which said wheelchair frame exten- sion member is telescopically adjustably engaged with said wheelchair frame, for selectively adjusting the location of said axle relative to a seat back support mounted on said wheelchair frame. 6. The suspension system for a wheelchair of Claim 1 , in which said spring is formed of an elastomer having a type A durome- ter of from about 50 to about 100; and in which said spring absorbs up to about fifty percent of a force of a shock caused by a bump or a depression in said wheelchair travel surface. 7. The suspension system for a wheelchair of Claim 6, in which said spring durometer is from about 60 to about 90. 8. The suspension system for a wheelchair of Claim 7, in which said spring durometer is from about 70 to about 80. 9. The suspension system for a wheelchair of Claim 1 , in which said suspension system includes a pair of suspension assemblies; in which each of said suspension assemblies is attached to said axle of a pair of spaced-apart wheels; and in which each of the sus- pension assemblies is disposed adjacent to a respective one of said pair of wheels. 1 0. A main frame for a wheelchair having a front end and a rear end, said wheelchair main frame including: a) at least one rearwardly extending frame extension member having a front end and a rear end, said extension member front end being adjustably attached to said main frame and said extension member rear end being attached to a transversely extending axle of at least one wheel of the wheelchair, so that said axle can be selectively positioned relative to the main frame front and rear ends for adjusting the center of gravity of the wheelchair. 1 1 . The wheelchair main frame of Claim 1 0, which includes a pair of spaced-apart frame extension members; in which said wheelchair includes a pair of spaced-apart wheels; and in which each of said frame extension members is located adjacent to a respective one of said wheels. 1 2. The wheelchair main frame of Claim 1 0, in which said main frame and said frame extension member each is formed of tubular metal; in which the outside diameter of the frame extension mem- ber is nominally smaller than the inside diameter of the main frame; and in which said frame extension member is telescopically engaged with the main frame. 1 3. The wheelchair main frame of Claim 1 2, in which a cam clamp device is slidably disposed about said main frame and said telescopically engaged extension member, for clamping the main frame against the extension member to secure the extension member in a selected position, and for unclamping said main frame from said extension member to enable selective positioning of the extension mem- ber within the main frame.

Inventors: PETERSON CHRISTOPHER J, PETERSON, CHRISTOPHER, J.
Applicants: INVACARE CORP, INVACARE CORPORATION
Application year: 1999
Main classification: A61G5
IPC codes: A61G5, B60G9, B60G11