Abstract:
An all terrain adapter for a wheelchair that removably clamps onto the foot support of the wheelchair and supports a relatively large diameter, slightly inclined swivelling nose gear wheel at an extended distance from the foot support to stabilize the wheelchair when it is being pushed over soft or uneven surfaces and which swivels around when the wheelchair is moved forward to lift the front wheels of the wheelchair clear of the ground.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part application of application Ser. No. 11/820,632, filed Jun. 19, 2007 now U.S. Pat. No. 7,735,847, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to wheelchairs and more particularly to a terrain adapter for wheelchairs. 
     BACKGROUND OF THE INVENTION 
     Conventional, user propelled wheelchairs have a seat frame, relatively large diameter rear wheels, typically from 22 inches to 26 inches, which often have a rim that the user can push to rotate the wheels and thus propel the wheelchair, and a pair of front or caster wheels that are considerably smaller in diameter than the rear or driving wheels, typically between 2 to 10 inches and more commonly 2 to 6 inches. These wheelchairs can also be pushed from behind. However, when an attempt is made to propel or manipulate such wheelchairs on rough terrain or soft terrain, where the vehicle&#39;s front wheels either encounter obstructions or sink into the terrain then movement and control of the wheelchair becomes extremely difficult and hazardous. The front wheels can unintentionally be directed in other than the desired direction of movement. Pushing a wheelchair on any surface that is not smooth is both tiring and can be enough to upset the balance of the user or pusher and result in stopping or worse, the user falls out of the wheelchair. This is particularly true for terrain such as sand, snow, ice, and mud, which require extreme strength and physical dexterity to safely propel and guide the wheelchair. Such rough terrain is often unavoidable in daily life situations for a disabled person in a wheelchair. While many of these problems can be overcome simply by increasing the diameter of the front wheels, there are substantial disadvantages to doing so. Compared to small diameter front wheels, the large diameter front wheels are more difficult to propel over normal surfaces which are essentially smooth and hard, are difficult to turn, and allow less clearance for feet positioned on foot plates. 
     There are known, specialized wheelchairs such as three wheeled sport wheelchairs, some of which are discussed further herein, that can help eliminate some of the above described problems in travelling over rough surfaces, however, typically these wheelchairs are expensive, bulky, and not conveniently suited for travel over smooth, everyday terrain, such as in buildings, homes or the like. 
     There is a need for a simple, easy to use, easy to install and remove, portable, light weight, low cost, safe, attractive, and durable attachment for wheelchairs to safely and easily negotiate difficult terrain. Such a device should improve handling and personal safety for an individual propelling such wheelchairs, occupants of such wheelchairs, and individuals in the vicinity of such wheelchairs. The device should be capable of use on snow, sand, ice, mud and other terrain, and the like, where wheels ordinarily sink into the terrain, and/or otherwise become directed in a direction other than the desired direction of travel of such wheelchairs, and make wheeled transportation otherwise difficult or impossible, and hazardous, and be easy to use. The device should be of simple construction, easy to manufacture, and easily installable as a retrofit on existing wheelchairs or in new installations during construction and fabrication of such wheelchairs, adjustable and installable for different wheel sizes and on different types of wheelchairs. 
     Different wheels, skids, skis and other adaptations for wheelchairs have heretofore been known, however, none of these adequately satisfies these aforementioned needs: 
     U.S. Pat. No. 5,116,067 (Johnson) discloses a wheelchair having a support structure that attaches to standard wheelchair wheels for providing mobility and allowing interchangeability of accessories to change the support structure for sporting events, such as water and snow skiing. The wheelchair has a frame and sockets to replace attachable wheels with water and snow skis. 
     U.S. Pat. No. 4,141,566 (Banes et al) discloses a sled frame for releasable attachment of a wheelchair. The sled frame has a body portion supporting a pair of laterally spaced, horizontally disposed support members which, in turn, are sized to be disposed between the wheels of a wheelchair to support the frame of the wheelchair on the sled. The support members are each provided with a plurality of locking devices which releasably engage the frame of the wheelchair to securely lock the wheelchair to the sled. 
     U.S. Pat. No. 5,076,390 (Haskins) discloses a wheelchair having a foldable frame with an interlinked system of parallelogram linkages which can be readily collapsed for travel and to provide access to otherwise restricted areas. 
     U.S. Pat. No. 5,983,452 (McGovern) discloses wheel and skid for replacement of each front wheel of a wheelchair. Each skid has a saucer-shaped base that expands the contact area of each front wheel to prevent it from sinking into the terrain, and/or otherwise become directed in a direction other than the desired direction of travel. The base has a slot, a wheel assembly having a wheel, the slot having the wheel of the wheel assembly protruding therethrough, and a fastener for fastening the wheel assembly to the wheel skid. This device is not intended to be easily installable and removable when rough terrain is encountered. Instead, it is generally permanently kept on the wheelchair which complicates folding the wheelchair and providing foot spacing on the foot support. 
     U.S. Pat. No. 5,427,398 (Weybrecht) discloses set of wide auxiliary wheels or wheel extensions so that the wheelchair can be much more easily used off road. An anti-tip over wheel can also be attached to the back of the wheelchair. In general, although these modifications can be added or removed to the wheelchair to adapt it to rough terrain, they generally require the assistance of an abled person, or at least they can not be conveniently added or removed by the user of the wheelchair while he or she is seated in it. 
     U.S. Pat. No. 4,132,423 (Chant) discloses pivoting rocker shaped struts that attach to the front of a wheelchair to enable the small front wheels of the wheelchair to negotiate side-walk curbs or the like. The struts can be either permanently attached or removably attached. However useful these devices may be for negotiating curbs or similar obstructions, they are of no great help in soft terrain or over surfaces having holes. 
     U.S. Pat. No. 6,869,084 (Volk) discloses a wheelchair wherein the front wheels have been replaced by skids. This adaptation is not designed to be easily installable and removable. 
     A recent innovation is a wheelchair adapter denoted model “Magelan MTC” (ModuleToutChemin) by the French company Magelan and marketed in the USA under the trademark “Freedom Wheel” by a Spokes-&#39;n-Motion of Denver, Colo. This adapter comprises a Y-shaped frame that must first be attached to the front bars of a wheelchair using two grips. A nose gear wheel attached to the front of the frame is thereafter extended downward by the occupant of the wheelchair by turning a hand crank. The diameter of the nose gear wheel is large compared to the diameters of the conventional wheelchair front wheels. As the nose gear wheel is cranked downward, it tilts the wheelchair back and lifts the much smaller front wheels clear of the ground. The relatively large diameter nose gear wheel is able to roll over soft surfaces or uneven surfaces. The device can be quickly attached and detached by the wheelchair occupant, however, it is relatively large and cumbersome and requires horizontally actuated, leftside and rightside clamping devices, thus generally requiring that the wheelchair occupant have the full use of both arms to push the clamping devices closed. Further, the process of lifting the wheelchair front wheels clear of the ground is cumbersome and time consuming. 
     For the foregoing reasons, there is a need for a simple, easy to use, easy to install and remove, portable, light weight, low cost, safe, attractive, and durable device to facilitate maneuvering of manually propelled wheelchairs on difficult terrain. Such a device should improve handling and personal safety for an individual propelling such wheelchairs, occupants of such wheelchairs, and individuals in the vicinity of such wheelchairs. 
     The device should be capable of use on snow, sand, ice, mud and other uneven terrain, and the like, where wheels ordinarily sink into the terrain, and/or otherwise become directed in a direction other than the desired direction of travel of such wheelchairs, and make wheeled transportation otherwise difficult or impossible, and hazardous. The device should be of light weight, simple construction, easy and economical to manufacture, easily installable as a retrofit on existing wheelchairs of all sizes and types, and easy and safe to use. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     In view of the above-described disadvantages with present systems, it is an object of the embodiments of the present invention to provide an all terrain adapter for a wheelchair. 
     It is another object of the present invention to provide an adapter for a wheelchair that increases the stability of the wheelchair when traveling over uneven surfaces or soft surfaces. 
     It is yet another object of the present invention to provide a light weight all terrain adapter for a wheelchair. 
     It is still another object of the invention to provide an all terrain adapter for a wheelchair that can be easily and safely installed and removed by the occupant of the wheelchair while he or she is seated in the wheelchair and using only one arm. 
     The above and other objects are achieved by the present invention of an all-terrain adapter for a wheelchair of the type having a seat frame, including a foot support, and large rear wheels and smaller front wheels mounted to the seat frame for allowing the wheelchair to be rolled over a surface. The adapter includes a strut for removable attachment at one end to the foot support, a single nose gear wheel having a diameter that is at least ten inches, a swivel mount for attaching the nose gear wheel to another end of the strut so that the nose gear wheel swivels about an axis that is slightly inclined from the vertical, attachment means for attaching and detaching the one end of the strut to the foot support, and wherein the front wheels of the wheelchair are lifted from the surface and remain suspended above the surface by the action of propelling the wheelchair in the forward direction to cause the nose gear wheel to swivel in a direction that shortens the wheelbase of the wheelchair between the nose gear wheel and the rear wheels. 
     In the preferred embodiments the mechanism for attaching the one end of the strut to the foot support includes a hand operated clamp. 
     In one preferred embodiment, the strut follows a first hypothetical, curved line that is offset from the nose gear wheel and the swivel mount is below a second, hypothetical horizontal line that intersects the top of the nose gear wheel when it the adapter is attached to the wheelchair. 
     Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which: 
         FIG. 1  is a vertical side view of an all terrain adapter for a wheelchair according to a first embodiment of the present invention; 
         FIGS. 2 and 3  are vertical side views that illustrate the method of attaching the first embodiment of the present invention to a wheelchair; 
         FIG. 4  is vertical side view that illustrate an all terrain wheelchair adapter of a second embodiment of the present invention; and 
         FIGS. 5A and 5B  are vertical side views illustrating the all terrain wheelchair adapter of the second embodiment of the present invention before and after being mounted on a wheelchair. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The adapter of the present invention includes a frame that easily attaches to the foot support of the wheelchair and raises the front wheels off the ground as the wheelchair is rolled forward. A slightly canted nose gear wheel attached to the frame extends the wheelbase making the chair more stable pushing over rough surfaces and provides a larger wheel in front to roll over surfaces that would normally upset the wheelchair. 
     Referring now to  FIGS. 1 and 2 , there is shown a first preferred embodiment of the invention comprised of a one piece adapter  100 . The adapter  100  attaches to a conventional wheelchair  110  having relatively small front wheels  112 , much larger rear wheels  114 , and a foot support  116  having a forward bar  116   a  and a rear bar  116   b . The bars  116   a  and  116   b  are parallel to each other and extend horizontally across the front of the wheelchair frame. The adapter  100  comprises a fixture  120  that has a rectangular cross-section and is provided with a fork opening  122  at one end that engages with the rear bar  116   b  of the wheelchair foot support  116 . The fixture  120  also has a downwardly extending notch  124  spaced forward of the fork  122  for engaging with the forward bar  116   a  of the wheelchair foot support  116 . 
     Mounted on the fixture  120  is a hand operated clamp  130  that has a handle  132  and hook  134  and a four bar linkage  136  between the handle  132  and the hook  134 . The hook  134  is positioned just beneath the notch  124  and has an adjustable clamping plate  135  that, when the clamp  130  is closed, presses tightly against foot support forward bar  116   a  in the notch  124 , locking the fixture  120  onto the wheelchair foot support  116 . The clamp  130  can operate other than as shown in the figure, provided that the same clamping action results. In the preferred embodiment the clamp  130  is a pull action, vertical latch clamp manufactured by De-Sta-Co company of Auburn Hills, Mich. By acting in a vertical plane, the wheelchair occupant is better able to use his or her weight in actuating the clamping mechanism, as compared to a horizontal action clamp. Also, the clamp can be actuated with only one arm. 
     The adapter  100  further comprises an S shaped support or strut  150  that is rigidly attached at one end to the fixture  120  and extends upwardly from it. At the other end of the strut  150  is a swivel mount  152 . A nose gear wheel  160  is mounted in a fork  162  for rotation in the swivel mount  152 . The swivel mount  152 , either due to the angle of attachment of the fixture  120  to the wheelchair  110 , the shape of the strut  150 , the mounting angle of the swivel mount  152  on the strut  150 , or a combination of all of these factors, preferably provides a steering axis  104  that is canted slightly rearwardly from the vertical  102 . The angle of this cant defines the caster angle α and is preferably between 5° to 10° from the vertical. A caster angle is defined as the angle that the steering axis makes with the horizontal or vertical, depending on convention. The steering axis  104  is the axis about which the fork  162  pivots. This caster angle could be made to be adjustable by making adjustable the angle of attachment of the fixture  120  to the wheelchair  110 , the shape of the strut  150 , the mounting angle of the swivel mount  152  on the strut  150 , or a combination of all of these. 
     The nose gear wheel assembly  160  includes the fork  162 , that has one end mounted for rotation in the swivel mount  152 , and a pair of parallel legs  164  that extend downwardly and slightly rearwardly from the swivel mount  152  (as viewed in  FIG. 1 ) and straddle a wheel  166  that has a relatively large diameter compared to the front wheels  112 . In the preferred embodiment, the diameter of the nose gear wheel is between 10″ and 16″ and is preferably 12″. The angle of inclination of the legs  164  is about 27° from the vertical that helps determine a positive trail, which is defined as the horizontal distance from where the steering axis intersects the ground to where the wheel  166  touches the ground. The horizontal trail in the disclosed embodiments is approximately 3″. The wheel  166  can include a pneumatic tire and is rotatably mounted about an axle  168  extending between the forks  164 . 
     When the nose gear wheel  160  is traveling in the forward, i.e., the leading direction, the trail of the legs  164  will cause a rotational torque to be exerted on the fork  162  so that it rotates to position itself as shown in  FIG. 1  with the wheel axle  168  at its closest point to the wheelchair  110 . Taking the distance between the axle of the rear wheels and the axle  168  as the wheelbase of the terrain adapted wheelchair  110 , the effect is to minimize this wheelbase. (This is not to be confused with the fact that the terrain adapted wheelchair has a longer wheelbase than the non-adapted conventional wheelchair). When the nose gear wheel  160  is travelling in the opposite direction, i.e., the rearward direction, the position of the fork  162  is rotated 180° from that shown in  FIG. 1  so that the axle  168  is moved farther away from the axle of the rear wheels, thereby lengthing the wheelbase of the terrain adapted wheelchair  110 . However, because of the caster angle, lengthening the wheelbase has the effect of lowering the foot support  116 . 
     Referring now more particularly to  FIGS. 2 and 3 , to install the adapter  100 , the user slides it in-between his or her feet and engages the parallel bars  116   b  and  116   a  of the wheelchair foot support  116  with the fork  122  and notch  124 , respectively, on the fixture  120 . The adapter  100  is then lowered to the ground with the nose gear wheel  160  swiveled ahead of the support  150 , as shown in  FIG. 2 . The lever  132  is then pulled to cause the hook  134  and clamping plate  135  to clamp against the front bar  116   a  and both secure the adapter  100  to the wheelchair foot support  116  and to slightly lift some of the weight of the wheelchair  110  from the front wheels  112 . The lever  132  is an over-center design and locks into the ready position. When the wheelchair  110  is pushed forward, the nose gear wheel  160  swivels 180° so that it trails behind the front end of the support  150 , as shown in  FIG. 3 . As explained above, this shortens the wheelbase of the terrain adapted wheelchair  110  and thereby lifts the front wheels  112  clear of the ground, placing all of the front weight of the wheelchair  110  on the nose gear wheel  160 . To remove the adapter  100 , the user simply moves wheelchair  110  in the rearward direction to return the nose gear wheel to the rotational position shown in  FIG. 2 , thereby dropping the front wheels  112  to the ground, moves the lever  132  back to unclamp the adapter  100  from the front bar  116   a , thereby returning the front weight of the wheelchair  110  to the front wheels  112 , and disconnects the adapter  100  from the wheelchair  110 . It is the combination of engaging the lever  132  and then moving the wheelchair  110  in the forward direction to swivel the nose gear wheel  160  that makes lifting the front wheels  112  clear of the ground so relatively effortless for the wheelchair user. Alternatively, as illustrated in  FIG. 10 , the adapter  100  can be left mounted in an up position stowed and locked between the user&#39;s legs by means of a latch or other type of fastening (not shown). 
     It will be noted that when the wheelchair  110  travels in the rearward direction, the nose gear wheel  160  swivels in such a manner to lower the front wheels  112  to the ground or nearly to the ground, however, this is of no concern because the weight of the wheelchair  110  is still primarily apportioned between the rear wheels  114  and the nose gear wheel  160 . The rear wheels  114 , because of their relatively large diameters, are easily able to roll over obstacles or soft terrain without upsetting the balance of the wheelchair. That is, during rearward travel there is no tendency for the front wheels  112  to dig in or be stopped by irregularities in the surface. 
     Referring now to  FIGS. 4 ,  5 A and  5 B, there is shown an adapter  200  according to a second embodiment of the invention. This embodiment is similar in all respects to the first embodiment and attaches and operates in the same manner to lift the front wheels of the wheelchair from the ground surface when the wheel chair is propelled forward after the adapter is attached to the wheelchair. The adapter  200  attaches to the conventional wheelchair  110  having relatively small front wheels  112 , much larger rear wheels  114 , and a foot support  116  having a forward bar  116   a  and a rear bar  116   b . The adapter  200  comprises a fixture  220  that engages with the rear bar  116   b  and the forward bar  116   a  of the wheelchair foot support  116  in a manner similar to the adapter  100  of the first embodiment, as shown in  FIG. 5A . 
     Mounted on the fixture  220  is a hand operated clamp  230  that locks the fixture  220  to the wheelchair bars  116   a  and  116   b  in an manner similar to the claim  130  of the first embodiment. 
     The adapter  200  further comprises a curved support or strut  250  that is rigidly attached at one end to the fixture  220  and extends upwardly from it. At the other end of the strut  250  is a swivel mount  252 . A nose gear wheel  260  is mounted on an axle in a fork  262  for rotation about the swivel mount  252 . The nose gear wheel  260  can include a pneumatic tire. The swivel mount  252 , either due to the angle of attachment of the fixture  220  to the wheelchair  110 , the shape of the strut  250 , the mounting angle of the swivel mount  252  on the strut  250 , or a combination of all of these factors, preferably provides a steering axis that is canted slightly rearwardly from the vertical (with respect to the ground). The angle of this cant defines the caster angle α (as shown in  FIG. 1 ) and is preferably between 5° to 10° from the vertical. A caster angle is defined as the angle that the steering axis makes with the horizontal or vertical, depending on convention. As in the embodiment shown in  FIG. 1 , the steering axis is the axis about which the fork  262  pivots. This caster angle could be made to be adjustable by making adjustable the angle of attachment of the fixture  220  to the wheelchair  110 , the shape of the strut  250 , the mounting angle of the swivel mount  252  on the strut  250 , or a combination of all of these. After the adapter  200  is attached to the wheelchair  110 , it operates functionally in the same manner as the adapter  100  to lift the front wheels  112  of the wheelchair  110  clear of the ground when the wheelchair  110  is moved forward, as shown in  FIG. 5B . 
     The primary differences between the adapters  100  and  200  are in the ergonomic design of the adapter  200 . The strut  250  is curved to closely follow the contour of the nose gear wheel  260  so that it takes less space than the strut  150 . The location of the swivel mount  252  is lower than the top of the nose gear wheel  260  when the adapter is attached to the wheelchair  110 . This and the fact that the strut  250  has a rounded, i.e., round or oval cross-section, makes it less likely that the user will have his or her fingers pinched between the nose gear wheel, the swivel mount, and/or the strut when the adapter  200  is attached and detached from the wheelchair  110 . Also, there are no sharp edges to injure the user if the user were to fall on the adapter  200 . The legs of the fork  262  are flat and arc-shaped, giving them greater torsional rigidity but with less mass, thus less weight and lower manufacturing costs, than the legs  164  of the fork  162 . Lastly, the adapter  200  is more visually appealing than the adapter  100 . 
     Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.