Abstract:
A level on a wheelchair allows the cambered rear wheels to be easily adjusted to eliminate toe-in/toe-out. The level comprises a ball encased in a curved track. The curve track is formed in a clear housing that mounts to the underside of a wheelchair camber tube or wheel axle. The camber tube or wheel axle is rotated until the ball aligns with an indicator mark indicating that toe-in/out has been eliminated from the cambered wheels.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/608,311, filed on Sep. 9, 2004. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     This invention relates in general to land vehicles and more particularly, to personal mobility vehicles. Most particularly, the invention relates to wheelchairs having camber tubes for supporting manually driven wheels.  
         [0003]     Manual, or non-powered, wheelchairs typically comprise a seating surface, a backrest, and a wheelchair frame that is supported by rear wheels, and front casters. Wheelchairs often incorporate a number of adjustments that allow the wheelchair to be customized to fit a particular user size. Typically, manual wheelchairs provide a height adjustment in the rear wheels and/or the front casters. The rear wheels of the wheelchair may be cambered, or angled, with respect to a vertical plane. A wheelchair with a large camber angle has more responsive turning, which is beneficial in sports applications. A wheelchair with little to no camber angle has a smaller overall width and thus greater maneuverability in tight confines.  
         [0004]     When an adjustment is made to the rear wheel height or front caster height on a wheelchair with cambered wheels, the rear wheels will toe-in or toe-out. That is to say, the rear wheels become misaligned with respect to horizontal. This misalignment is undesirable because it increases rolling friction. If the rear wheels are raised or the front casters are lowered, the rear wheels will toe-in. Conversely, if the rear wheels are lowered or the front casters are raised, the rear wheels will toe-out. This occurs because the axis of the camber is no longer aligned horizontally. To correct this misalignment the camber tube must be rotated about its axis in order to re-align the camber angle with respect to horizontal. Typically, a horizontal or vertical reference plane is provided on the camber tube to indicate when the camber angle is aligned horizontally. When a horizontal reference plane is provided, a user would hold a bubble level on this surface and rotate the camber tube until the plane is level. When a vertical reference plane is provided, a user would hold a 90-degree angle between the reference plane and the ground and rotate the camber tube until the plane is vertical. Such an adjustment is difficult because it requires additional tools and several hands to perform the operation. U.S. Pat. No. 4,852,899 discloses the use of a spirit or bubble level that is permanently mounted to the top of a camber tube. This invention facilitates toe-in and toe-out adjustment, wherein the user rotates the camber tube until the bubble level is centered. However, because the bubble level is on top of the camber tube, the seating surface blocks the user&#39;s view of the bubble level. This makes the invention awkward to use, particularly when the camber tube is situated very close to the seating surface.  
         [0005]     What is needed is a camber tube level indicator that can be viewed easily from the side of the wheelchair or from below.  
       SUMMARY OF INVENTION  
       [0006]     The present invention is directed towards a level that meets the foregoing needs. The level on a wheelchair comprises a ball encased in a curved track. The curve track is formed in a clear housing that mounts to the underside of a wheelchair camber tube or wheel axle. The camber tube or wheel axle is rotated until the ball aligns with an indicator mark indicating that toe-in/out has been eliminated from the cambered wheels.  
         [0007]     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 DRAWINGS  
       [0008]      FIG. 1  is a front perspective view of a portion of a wheelchair having a camber tube, and a camber tube level according to the invention.  
         [0009]      FIG. 2A  is a side elevational view of the camber tube and the camber tube level shown in  FIG. 1 .  
         [0010]      FIG. 2B  is a front elevational view of the camber tube and the camber tube level shown in  FIG. 2A .  
         [0011]      FIG. 3A  is a side elevational view of a camber tube and a camber tube level according to another embodiment of the invention.  
         [0012]      FIG. 3B  is a front elevational view of the camber tube and the camber tube level shown in  FIG. 3A .  
         [0013]      FIG. 4A  is a side elevational view of a camber tube and a camber tube level according to still another embodiment of the invention.  
         [0014]      FIG. 4B  is a front elevational view of the camber tube and the camber tube level shown in  FIG. 4A .  
         [0015]      FIG. 5A  is a side elevational view of a camber tube and a camber tube level according to yet another embodiment of the invention.  
         [0016]      FIG. 5B  is a front elevational view of the camber tube and the camber tube level shown in  FIG. 5A . 
     
    
     DETAILED DESCRIPTION  
       [0017]     Referring now to the drawings, there is illustrated in  FIGS. 1, 2A  and  2 B there is illustrated a camber tube level indicator or level  10  comprising a housing  12  that is adapted to be mounted to a rear wheel axle or camber tube  14  of a wheelchair. The housing  12  is preferably a clear plastic housing, which is adapted to be mounted to an underside  14   a  of the camber tube  14 . The camber tube  14  can be mounted to the wheelchair in any suitable manner; such as by using one or more clamps, such as the clamps  16  shown. The clamps  16  shown, when loosened, permit the camber tube  14  to be rotated about the axis A 1  of the camber tube  14 . The housing  12  of the illustrated embodiment has an internal curved or curved shaped track  12   a , as shown in  FIG. 2A . A material or object, such as cylindrical or spherical ball  18  or other rolling device, is adapted to rest upon the track  12   a , and may freely roll or travel to the lowest position on the track  12   a  due to gravity. The track  12   a  is of preferably a substantially constant radius R, with the axis A 2  of the radius R being parallel with the axis A 1  of the camber tube  14 . The housing  12  preferably has a center mark  12   b  that is adapted to align with the location of the ball  18  along the track  12   a  when the camber tube  14  is oriented horizontally. To make toe-in and toe-out adjustments, a user could rotate the camber tube  14  within the clamps  16  until the ball  18  rolls or travels and settles in a position coincident with the center mark  12   b . The curved track  12   a  preferably has a radius R that is sufficiently large to provide the level  10  with accuracy when making this adjustment.  
         [0018]     The housing  12  is preferably designed so that the housing  12  can be easily installed on a camber tube  14 . The track  12   a  is preferably opened at a top of the track  12   a  so that the ball  18  may be captured between the housing  12  and the camber tube  14  when installed. The track  12   a  and the camber tube  14  preferably cooperate to form a closed cavity  12   d , where the ball  18  may reside inside the track  12   a  and not be easily contaminated by dust, fluids, or other contaminants. The housing  12  may be mounted to the camber tube  14  using screws, bolts, pop rivets, adhesives, or other suitable fasteners or means.  
         [0019]     The camber tube level  10  facilitates toe-in and toe-out adjustment by providing an easily viewable reference to indicate when the camber tube  14  has been rotated to a level position. No additional tools are required, and the level  10  may be easily viewed from the side or from below the wheelchair. This is particularly advantageous, considering that a wheelchair is most frequently set on a level workbench or table when adjustments are made. The camber tube level  10  can be provided with the wheelchair, pre-installed on the camber tube  14 , or it can be sold as an after market add-on feature that can be sized for standard camber tube diameters.  
         [0020]     Another embodiment of the invention is shown in  FIGS. 3A and 3B , wherein a housing  20  is provided with a slot  20   a . The housing  20  may be made from an opaque plastic. The slot  20   a  may serve as a window through which to view the ball  18 .  
         [0021]     Still another embodiment of the invention is shown in  FIGS. 4A and 4B , wherein a curved glass vial  22  may be installed into a housing  24 . The housing  24  is preferably a plastic housing having a viewing window  24   a . The vial  22  may have a material, such as a ball  18  and/or a liquid  26  therein. The liquid  26  may serve to dampen the motion of the ball  18  and allow the ball  18  to settle more quickly to the lowest position within the vial  22 . An indicator mark  24   b  may be provided on the housing  24  to show when the camber tube  14  is oriented horizontally or substantially horizontally.  
         [0022]     Yet another embodiment of the invention is shown in  FIGS. 5A and 5B , wherein a vial  28 , which is preferably a curved glass vial, is installed into a housing  30 , which is preferably a plastic housing with a viewing window  30   a . The vial  28  preferably contains a material, such as two liquids  32 ,  34  that have different densities and thus do not intermix. The less dense liquid  32  is preferably clear. The more dense liquid  34  is preferably opaque. The more dense liquid  34  is adapted to settle to a lowest point along the curved glass vial  28 . An indicator mark  28   a  is preferably on the vial  28  to show when the camber tube  14  is oriented horizontally or substantially horizontally.  
         [0023]     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.