Abstract:
A simple, durable, lightweight, economical wheelchair is disclosed that offers full convertibility from rigid frame to folding and vice versa, without sacrificing advantages of either design. In addition, it allows conversion to sports, companion, pediatric, front wheel drive, etc. as well as customizing to suit the end user&#39;s needs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to wheelchairs and, more specifically, to convertible wheelchairs. All frame components are designed to accept parts for both the folding and rigid frame wheelchairs. Tubular components are designed to be easily attached to other members with the special connector fittings allowing for further conversion to other desirable designs. 
     2. Description of the Prior Art 
     Two different methods have been used in the design and production of manual wheelchairs. The most common is the folding cross brace wheelchair. This design utilizes a welded cross brace mechanism, allowing the wheelchair to fold similar to a director&#39;s chair (from side to side). The main advantage of this method is that the wheelchair can be easily folded by most users. The disadvantage of this design is low energy efficiency due to its loose construction since a part of the energy used to propel the wheelchair is transferred to the frame rather than the wheels. 
     A second popular design is the rigid frame wheelchair. In this design the cross brace mechanism is replaced with tubular crossbars welded to the side frames of the wheelchair. The advantage of this design is its energy efficiency. However, this wheelchair does not fold as compactly as the cross brace chair for easy travel, storage or transportation. 
     The above-described designs have a problem in common—welded construction. The welded construction makes it extremely difficult, if not impossible, to adapt the wheelchair to the end user&#39;s changing needs and environment. Conversion from rigid frame to folding wheelchair is virtually impossible. In addition, welding creates a heat-affected zone weakening the frame tube around the welded joint, which is a main cause for structural failure in wheelchairs. 
     For the majority of wheelchair users it is necessary to have both wheelchairs—the rigid frame and the folding one. The folding wheelchair is more convenient for travel and indoor use, whereas the chair must be folded and stored. The rigid wheelchair is better suited for outdoors and a more active lifestyle. Unfortunately, it is not economically feasible for most users to own both wheelchairs. 
     Some wheelchair manufacturers build both folding and rigid frame chairs. There is a number of folding wheelchairs that use the conventional crossbrace design. Rigid chairs exist that are of a modular design and can change the width of the wheelchair with little difficulty. There is a design that converts from a user propelled to an assistant propelled wheelchair (U.S. Pat. No. 5,294,141). There is also a wheelchair that converts the riding position from the standard seating position to a recumbent position (U.S. Pat. No. 5,011,175). There is a weld-free folding wheelchair which folds in a non-conventional manner but is not convertible (U.S. Pat. No. 4,682,783). Another wheelchair design appears to be of a weld-free design that allows the wheelchair to adjust to different needs by use of special shaped bars and plates but is not a convertible wheelchair (U.S. Pat. No. 5,743,545). There are several U.S. patents that claim the chair to be modular, allowing for different components to be used to build the chair to the user&#39;s needs. Among these is a rigid frame wheelchair (U.S. Pat. No. 5,421,598), but again this wheelchair does not convert to folding. There are no wheelchairs known to exist at this time that can fully convert from a rigid frame to folding frame. 
     In U.S. Pat. No. 5,253,888, issued to the assignee of the subject invention, a rigid frame weld-free wheelchair is disclosed that utilizes a series of special clamping members for clamping tubes to each other. However, such weld-free construction had some disadvantages. A series of specially designed clamps had to be utilized which were not universal to all designs, making further conversion and design changes virtually impossible. Also, by virtue of the clamp designs, numerous bolts were required that were clearly visible and detracted from the appearance of the wheelchair. 
     It is possible for one wheelchair to have all of the advantages of both the folding and the rigid chairs while eliminating the disadvantages of each. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a convertible wheelchair that does not have the disadvantages inherent in prior art wheelchairs. 
     It is an object to provide a convertible wheelchair utilizing standard [???] components which can be used for both folding and rigid frame wheelchair design. 
     It is another object of this invention to provide a durable, lightweight and economical wheelchair that can be quickly and easily converted by a layman from a folding frame to a rigid frame and vice versa. 
     It is still another object of the invention to provide a wheelchair that can be easily converted to a sport type wheelchair. 
     It is yet another object of the invention to provide a wheelchair that can be easily converted to a companion chair. 
     It is a further object of the invention to provide a wheelchair that can be easily converted to a front wheel drive wheelchair. 
     It is still a further object of the invention to provide a wheelchair that can be easily converted to a pediatric wheelchair. 
     It is yet a further object of the invention to provide a wheelchair that can be easily converted to a hand cycle with optional attachment. 
     It is an additional object of the invention to provide a wheelchair that can be easily converted to a lever driven wheelchair with optional attachment. 
     It is still an additional object to provide convertible wheelchairs that can be converted with the use of simple tools. 
     In order to achieve the above objects of this invention, as well as others that will become apparent hereinafter, the convertible wheelchair of the present invention has a pair of like side frame assemblies spaced from each other and each including a generally horizontal seat tube and a generally horizontal bottom tube below said seat tube. Each of these seat and bottom tubes has front and rear ends. A generally vertical backrest tube has a lower end proximate to said rear ends of said seat and bottom tubes and an upper end extending upwardly of said set tube and forming handgrips. 
     A caster assembly for each side frame assembly carries a caster wheel and has a generally upwardly extending shaft portion. Connecting means is provided for rigidly clamping respective rear ends of the seat and bottom tubes and the lower ends of the backrest tubes, for rigidly clamping the respective front ends of the seat and bottom tubes and caster assembly shaft portion, and for rigidly connecting said conversion means to frame assemblies. A footrest means is secured to the seat tube, and a conversion means selectively converts the connection between the side frame assemblies to convert the wheelchair from a folding wheelchair to a rigid wheelchair and vice versa. 
     Conversion means may include pivotally connected elongate means having ends pivotably connectable to the side frame assemblies for selectively replacing the transverse tube means and for permitting the side frame assemblies to move from the width position of the wheelchair to proximate positions in the collapse condition of the wheelchair, or a kit consisting of at least two transverse members including at least two elongate rigid tubes having a length substantially corresponding to the normal operative width of the wheelchair and at least one set of pivotably connected members that can pivot relative to each other. 
     The convertible wheelchair frame is made up of left and right side frame assemblies, two push handle assemblies, upholstery and removable folding or rigid crossbars (all assemblies are weld-free). Specially designed fittings are used to provide for a secure fastening internally between mating tubes. These fittings are used throughout all assemblies where two or more tubes mate up. These fittings shall be referred to as connector fittings throughout this text. Each side frame assembly is provided with mounting holes to assemble the wheelchair as either folding or rigid. The folding crossbar assemblies have T-fittings at the lower end which are a sliding fit to the lower side frame assembly tubes. At the top of the crossbars are seat tubes held in place perpendicular to the crossbar by the connector fittings. Each seat tube is assembled with a multi position insert that is used to attach the seat tube to the crossbar and to assemble the seat upholstery. There are holes in the crossbars near the center. These holes are the location where a pair of crossbars are bolted together and act as the pivot point when folding. These crossbars are slid onto the lower frame tube and held in place with retaining rings fastened through holes in the tube. This maintains proper horizontal position. There are also holes near the top of the crossbars, these holes are fastened to links which pivot on the side frame assemblies. The links hold the wheelchair frame assemblies parallel when the chair is in both the open (riding) and folding (storage) positions. When the wheelchair is in the open (riding) position, the seat tubes nest into saddles fastened to each side frame assembly. This nesting along with the tension of the upholstery creates a solid box frame giving the chair the feel and performance associated with rigid frame wheelchairs. 
     Conversion to a rigid frame type wheelchair is accomplished by removing the folding crossbars, links, retaining rings and seat upholstery, and installing rigid crossbars. There are two types of rigid crossbars. The lower crossbars are straight tubes. The upper crossbars have a bend at both ends to give clearance at the seat and back upholstery. Each of the rigid crossbars is assembled with the connector fittings. The seat inserts are removed from the seat tubes and inserted into the upper frame tubes of the side frame assemblies. The top rigid cross tubes are attached to each side frame at the appropriate holes with the connector fittings. Inserts are inserted into the lower side frame tubes and the lower crossbars are fastened in place. 
     Conversion from rigid to folding is done in the reverse order. 
     The backrest of the wheelchair may be adjusted to varying heights as may be required by the user or to a folding back for the rigid frame version for ease of transportation and storage. Each side frame has an insert in the back at the seat level that is used to fasten the backrest tubes to the frame. Changing heights can be done by removing two fasteners on either side and the back upholstery and replacing with the new backrest tubes and upholstery. To replace the fixed back with a folding back, the back insert is replaced in the frame with the proper insert for folding. The backrest tube is assembled to the folding hinge plates and all to the frame assemblies are assembled. All components are modular, allowing for simple alteration of the seat width and depth and back height. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The benefits of the construction herein disclosed will become apparent to those skilled in the art from the following detailed description of a presently preferred embodiment, having reference to accompanying drawings wherein: 
     FIG. 1 is a rear elevation view if a wheelchair assembled with folding crossbars in accordance with the invention: 
     FIG. 2 is a side elevation view of the wheelchair shown in FIG. 1 with folding crossbars, shown with rear wheels removed: 
     FIG. 3 is a top plan view of the wheelchair shown in FIGS. 1 and 2, with folding crossbars (upholstery removed for clarity); 
     FIG. 4 is a rear elevation view of the wheelchair assembled with rigid cross tubes: 
     FIG. 5 is a side elevation view of the wheelchair shown in FIG. 4 assembled with rigid cross tubes (upholstery removed for clarity); 
     FIG. 6 is a top plan view of the wheelchair shown in FIGS. 4 and 5 assembled with rigid cross tubes (upholstery removed for clarity): 
     FIG. 7 is a fragmentary, exploded perspective view of the connector fitting used in the wheelchair shown in FIGS.  1 - 6 : 
     FIGS. 8 a  and  8   b  are side and top elevation views of optional flip up footplate assemblies, 
     FIG. 9 is an exploded partial side view of a rigid frame wheelchair with optional wheel camber plate; 
     FIG. 10 is a fragmentary exploded perspective view of the caster bearing housing assembly; 
     FIG. 11 is a side elevation view of a wheelchair assembled with a lever drive kit; and 
     FIG. 12 is a side elevation view of a wheelchair assembled with a hand cycle attachment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the figures, in which identical or similar parts are designated by the same reference numerals throughout, and first referring to FIGS. 1,  2  and  3 , a folding wheelchair in accordance with the present invention is generally designated by the reference numeral  10 . 
     The chair  10  has a pair of like side frame assemblies  12  spaced from each other and including a generally horizontal top tube  14  and a generally horizontal bottom tube  16  below the top tube. The top and bottom tubes have front or distal ends  14   a ,  16   a  and rear or proximal ends  14   b ,  16   b . Top and bottom tubes are joined at front ends  14   a ,  16   a  using connector fittings  20 . The top tube  14  and the bottom tube  16  are secured to each other at front  14   a ,  16   a  and at the rear  14   b ,  16   b  using connector fittings  20 . The top tube  14  has a row of holes  14   c  for seat attachment when converted to a rigid frame wheelchair. 
     The chair also has like crossbar assemblies  22  including an angular crossbar tube  24  and a generally horizontal seat tube  26 . There is an insert tube  28  located inside of the seat tube which has threaded holes for multiple connections coinciding with holes in the upper frame  14  and seat tubes  26  which include seat to crossbar and seat upholstery on both the folding and the rigid wheelchair. The seat tube  26  and cross tubes  24  are joined at the upper ends  24   a  of the cross tubes offset from the center of the seat tube  26 . The tubes are attached using connector fittings  20 . The lower ends  24   b  of the crossbar tubes are inserted into T-fittings  30  with the through hole parallel to the seat tube  26 . Each T-fitting has a sliding fit relative to the lower side frame tube  16 . The crossbar assemblies  22  are installed over the lower side frame tube  16  in opposing directions (left side with longer portion of seat tube to rear, right side longer portion to front) with seat upholstery holes  26   a  pointing upward. Each crossbar assembly  22  is held in position by retaining rings  32 . Crossbar links  34  are installed over the top frame tube  14  and held in place with retaining rings  32 . The hole at the small end of the crossbar links  34  are fastened to the opposing crossbar tube  24  at the upper ends  24   a . The crossbar links  34  maintain a parallel relationship between side frame assemblies when the wheelchair is in either the open or folded position. Seat tube saddles  36  are also assembled to the top frame tube  14 . The seat saddles are a snap fit with the seat tubes  26 , when the wheelchair is in the open position the seat tubes rest in the saddles and lock the frame rigidly. The seat upholstery  76  is secured to the seat tube with screws at upholstery holes  26   a.    
     Each side frame assembly  12  has a back tube stiffening insert  40  secured near the top of the vertical component of the bottom frame tube end  16   b  and protruding upward. Back upholstery  78  is assembled over a pair of push handle tubes  38  and secured with screws near the top of each push handle tube end  38   a . Push handles are assembled over the top of the back tube stiffener insert  40  abutting the top of the vertical component of the bottom frame tube  16   b . The assembly is secured with fastener through holes in each tubular member. Hand grips  80  are installed over the top ends of each push handle tube  38 . 
     A caster assembly is generally designated by the reference numeral  42  and includes a downwardly extending open fork member  44  that receives and supports a caster wheel  46  by means of a transverse axle  48 . Extending upwardly from the fork member  44  is a solid shaft portion  50  rotatably supported about its axis in bearings  84 , as will be described below. 
     A caster bearing housing  74  (See FIG. 10) is mounted on the bottom frame tube  16  near the front of the tube  14   a . The caster bearing housing has a threaded hole  74   a  on one end and a slot  74   b  on the opposite side with perpendicular serrations  74   c  crossing the slot. The caster bearing housing is secured to the bottom frame tube through the hole end. The caster bearing housing  74  is free to rotate vertically about the hole. A mating serrated cam  82  is secured over the slot in the caster bearing housing  74  and when properly placed maintains a vertical posture for the caster fork stem  50 . 
     The caster bearing housing  74  has both an upper and lower bearing pocket  74   d ,  74   e  into which radial bearings  84  are pressed. 
     The vertical solid shaft  50  of the caster assembly  42  is inserted through the bearings  84  pressed into the caster bearing housing  74 . The top of the caster stem is threaded to enable securing to the caster bearing housing with a locking nut. The caster assembly  42  is horizontally rotatable about the bearings and stem. 
     Footrest assembly  52  includes extension tubes  54 , which are telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A transverse tube  56  is secured to one extension tube  54  at its lower end and nests into a fitting  58  on the opposite extension tube. A footrest  60  is secured to the transverse tube  56  (FIGS. 2 and 3) by means of footrest clamps  62 . A belt or strap  64  extends between opposing extension tubes  54  and is positioned above the footrest  60  to serve as a foot support and to prevent the legs from slipping rearwardly off of the footrest. 
     An alternate footrest assembly  66  is shown in FIG.  8 . This assembly includes extension tubes  68 , which are telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A flip up footplate  70  is secured to the lower end of the extension tube  68 . It is free to rotate upward toward the extension tube. The footplate  70  is limited in rotation downward to a position perpendicular to the extension tube  68 . A belt or strap  72  is attached to the inner and outer rear corners of the foot plate  70   a  with a studs  74 ′ (see FIG. 2) and loops around the footrest extension tube  68  positioned above the footplate. 
     The vertical component of the bottom frame tube  16   c  has a series of holes to which are mounted a pair of rear wheel mounting plates  84 ′ and a wheel plate bushing  86  which is captured between the pair of plates. The position of the axle mounting plates on the bottom frame tube determines the wheelchair rear seat height and seat angle. An axle bushing  88  is installed through the wheel mount plates  84 ′ and wheel plate bushings  86  secured on the back side with a nut. Axles  90  (not shown) support the rear wheels  92  and insert into axle bushing  86 . Rear wheels are rotatable vertically about the axles. 
     FIG. 9 shows an optional wheel attachment which consists of an axle plate tube  94  mounted between the top frame tube  14  and the bottom frame tube  16  at  14   b ,  16   c . The axle plate tube is secured to the frame tubes with connecting fittings  20  at both ends. Spanning between the axle plate tube  94  and the vertical component of the bottom tube  16  is a generally horizontal axle camber plate  86 ′. The axle camber plate has a series of holes through which the wheel axle bushing  88  is secured. Positioning of the wheel bushing in the holes in the axle camber plate  86 ′ determine the center of gravity of the wheelchair. Angling the lower edge of the axle camber plate  86 ′ outward creates camber to the rear wheels which aids in stability and performance. 
     Now referring to FIGS. 4,  5  and  6 , a rigid wheelchair in accordance with the present invention is generally designated by the reference numeral  110 . 
     The wheelchair  110  has a pair of like side frame assemblies  120  spaced from each other and including the same components as the previous folding wheelchair side frame assemblies, upper tube  14 , lower tube  16  and connector fittings  20 . To convert the folding wheelchair  10  to a rigid wheelchair  110 , the following components are removed from the folding wheelchair: seat upholstery  76 , crossbar assemblies  22  (including crossbar tubes  24 , seat tube  26  and tee fitting  30 , see FIG.  1 , 2  and  3 ), crossbar links  34 , seat tube saddles  36  and retaining rings  32 . The insert tubes  28  in the seat tubes are removed and reinstalled in the top tube  14  of the rigid side frame assemblies  120 . The upper frame tubes  14  and lower frame tubes  16  mount to one another with connector fittings  20  at the front at  14   a  and  16   a  and at the rear at  14   b  and  16   c . This allows the top frame  14  to at the same seat height from the floor as the seat tube  26  on the folding frame wheelchair  10 . Threaded inserts  122  are installed into the lower frame tubes  16  at holes  16   d  aligning holes. Straight crossbar tubes  124  are installed at the holes  16   d  and  16   e  with the special connector fittings and screws. Formed cross tubes  126  are installed on the upper frame tubes  14  at  14   d  and  14   e  using special connector fittings and screws. The insert  28  has corresponding threaded holes to  14   d  and  14   e  to which the formed cross tubes  126  are attached. An additional formed cross tube  126  is attached to the push handle tubes  38  at  38   b  using special fittings  20  and screws. 
     An optional folding back assembly  130  may be attached to the rigid frame wheelchair  110 . The push handle tubes  38   a  are removed from the side frame assembly  120  by removing the screws at  38   a . The back insert  40  is removed and replaced with a new insert  128 . Insert  134  is added to the bottom of each push handle  38  at holes  38   a . Screws are used to attach back hinge plates  132  to the push handles at  38   a  and to the top frame tube  14  at  14   f . A removable pin through the hinge plates  132  and the top of the lower frame tube  16   b  at hole  16   f.    
     The footrest assembly  52  or  66  are the same as those used on the folding frame wheelchair  10  or an optional rigid footrest assembly  134 ′ may be used on the rigid frame wheelchair  110 . This assembly consists of a generally u-shaped tubular footrest tube  136 . Each parallel leg  136   a  and  136   b  of the footrest tube has a series of holes through both walls of the tube. Each of the parallel legs are telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A footrest  60  is secured to the horizontal potion of the u-shaped footrest tube  136  by means of footrest clamps  62 . A belt or strap  64  extends between opposing parallel legs of the footrest tube  136  and is positioned above the footrest  60  to serve as a foot support and to prevent the legs from slipping rearwardly off of the footrest. 
     The above mentioned procedure is to convert a folding wheelchair  10  into a rigid frame wheelchair  110 . The reverse procedure would be used to convert rigid to folding. 
     All frame components are designed to accept parts for both the folding  10  and rigid frame  110  wheelchairs. Tubular components are designed to be easily attached to other members with the special connector fittings  20 . 
     This design offers a simple, durable, lightweight, affordable wheelchair. It can be quickly and easily converted from a folding to a rigid frame wheelchair and vice versa. The design has the following features: 
     1. A simple and unique method of conversion; 
     2. Modular construction; 
     3. No welded or brazed joints; 
     4. Lightweight construction; and 
     5. Ability to adapt to any end user&#39;s needs. 
     While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications will be effected within the spirit and scope of the invention as described herein and as defined in the appended claims.