Abstract:
A seat is pivotally connected to a frame of a wheelchair and is connected by one or more resilient supports. Each support includes a housing attached to either the seat or the frame and a bracket arrangement attached to the other of those wheelchair components. A spring biases the bracket arrangement with respect to the housing and an adjuster enables the force of the spring to be varied to alter resiliency of the support.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to wheelchairs, and more particularly to the seat and seat supports of the wheelchair. 
   2. Description of the Related Art 
   Wheelchairs are commonly used by people who are unable to walk. The typical wheelchair has tubular metal frame with large rear wheels at each side and smaller front wheels which typically swivel. In its simplest form, the seat of the wheelchair comprises a sheet of material hung between two horizontal arms of the frame and a similar vertical sheet of material strung between two vertical posts at the rear of the wheelchair. Such sheets of material are flexible thereby conforming to the contour of the user&#39;s body. 
   This simple seat arrangement can aggravate certain medical conditions of some wheelchair users, especially those with spinal abnormalities or injuries. In any case, this basic seat is not very comfortable for users who sit in the wheelchair for prolonged periods of time. As a consequence, padded seats with foam cushions for the seat bottom and back have been developed. The bottom and back cushions are contoured to the general shape of the human anatomy for improved comfort. The elements of this seat are rigidly secured to the frame of the wheelchair. 
   Although the more elaborate seats offer increased comfort because of the foam cushions, their secure attachment to the wheelchair frame provides relatively rigid support for the user. Therefore, there still exists a need for a more comfortable wheelchair seating system, especially one that can be adjusted to the preferences of each user. 
   SUMMARY OF THE INVENTION 
   A seat assembly for a wheelchair comprises a seat that preferably is pivotally connected to a frame of the wheelchair. One or more resilient supports are disposed between the frame and the seat so as to allow relative motion there between. 
   Each support includes a housing attached to either the seat or the frame and a bracket arrangement that is attached to the other of the seat and the frame. A spring biases the bracket arrangement with respect to the housing. An adjuster is provided to vary the force that the spring exerts between the first bracket arrangement and the first housing to thereby adjust resiliency of the support. 
   In a preferred embodiment of the seat assembly the spring is within the housing which has a pair of longitudinal apertures on opposite sides. The bracket arrangement extends through both of the longitudinal apertures and engages an end of the spring. The adjuster has a threaded shaft that extends into a threaded aperture in either the housing or the bracket arrangement, wherein screwing the threaded shaft into and out of the threaded aperture varies the force exerted by the spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric frontal view of a wheelchair with a seat support system according to the present invention; 
       FIG. 2  is a side view showing an adjustable support that connects the rear of the seat to the wheelchair frame; 
       FIG. 3  isometric view of the adjustable support; and 
       FIG. 4  is a cross section view through a portion of the adjustable support. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With initial reference to  FIG. 1 , a wheelchair  10  has a tubular metal frame  12  that includes two horizontal members  14  and  15  and a pair of vertical posts  16  and  17  which bend into handles  18  and  19 . A seat  20  of the wheelchair comprises a seat bottom  22  and a seat back  24  in a substantially orthogonal orientation to each other. Both the seat bottom and back  22  and  24  comprise cushions that are contoured to conform to the curvature of a wheelchair user&#39;s buttocks and back, respectively. These cushions are supported on a curved. plastic shell  26 , however other seat constructions may be used. For example, the seat bottom  22  and back  24  may be mounted independently to the wheelchair frame  12 , in which case different supports described herein can be employed to separately attach the seat bottom and back. Therefore, as used herein the term “seat structure” refers to seat bottom or the seat back individually, as well as a combination of the seat bottom and back. 
   The seat  20  is attached to the frame  12  by a resilient support system that provides a degree of shock absorption as the wheelchair rolls along. The front section of the seat  20  is pivotally connected to each of the horizontal members  14  and  15  of the frame  12  by pins  28  with only one pin being visible in  FIG. 1 . The coupling by the pins  28  allows the seat  20  to pivot about a transverse horizontal axis  29  with respect to the frame  12 . 
   With reference to  FIGS. 2 and 3 , the rear of the seat  20  is coupled to the horizontal frame members  14  and  15  by separate supports  30 . Each support  30  includes an L-shaped first bracket  32  having one leg attached to the bottom section of the seat shell  26  by two machine screws  33  that extend through slots  35  in the leg. With additional reference to  FIG. 4 , a spring cartridge  34  has an L-shaped second bracket  36  from which a bolt  38  projects through one of a plurality of open slots  39  in the other leg of the first bracket  32 . A knob  40  is threaded onto the bolt  38  to secure the first and second brackets  32  and  32  together in an adjustable manner. A third bracket  42  is attached to one end of the spring cartridge  34  and clamps around a horizontal transverse member  44  of the wheelchair frame  12 . 
   The details of the spring cartridge  34  are shown in the cross-sectional diagram in  FIG. 4 . The spring cartridge  34  has a tubular housing  46  with a closed end  48  that has a centrally located aperture  50 . A coil spring  52  is located within the bore  54  of the housing  46 , abutting the closed end  48 . A pair of slots  56  extend longitudinally through the wall on opposite sides of the housing with the slots opening through the open end  58 , (see also  FIGS. 2 and 3 ). 
   The second bracket  36  has an aperture  60  in one leg, allowing the end  62  of that leg to be slidably received within the longitudinal slots  56 . That end  62  of the second bracket  36  has a threaded aperture within which an adjusting screw  64  is received. The head of the adjusting screw  64  is larger than the inner diameter of the coil spring  52  so that the screw head engages the exposed end of that spring. 
   The open end  58  of the housing  46  is closed by a cap  66  that is held in place by a pair of machine screws  59  that extend through apertures in the wall of the housing. The cap  66  has an internal recess  68  for receiving the threaded end of the adjusting screw  64 . The flat external surface of the cap  66  has a threaded aperture that receives a machine screw  70  which holds the third bracket  42  on the end of the spring cartridge  34 . 
   When the seat  20  of the wheelchair  10  is empty, the spring  52  extends fully which pushes the adjusting screw  64  and the second bracket  36  upward within the cartridge housing  46 , until the internal end  62  of that bracket abuts the inner surface of the cap  66 . When a person sits in the seat  20  of the wheelchair  10 , the added weight on the seat is transferred through the first and second L-shaped brackets  32  and  36  to the coil spring  52  within the housing  46 . This weight exerts a downward force which compresses the spring  52 , causing the seat to lower slightly with respect to the frame  12  of the wheelchair. This downward motion continues until the spring force equals the downward force from the seat. 
   By inserting an allen wrench through the aperture  50  in the closed end  48  of the housing  46 , the adjusting screw  64  can be moved into and out of the aperture in the internal end  62  of the second bracket  36 . This adjustment varies the preload force of the coil spring  52  and thus the amount of travel which occurs when a person sits on the wheelchair seat  20 . By adjusting the spring force in this manner, the amount of bounce, or resiliency, of the wheelchair seat  20  with respect to the frame  12  can be varied as desired to accommodate the preference of the user. 
   The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.