Interlocking Foldable Wheelchair Construction

The present invention relates to a foldable wheelchair having an improved, lightweight construction employing an interlocking technique. More particularly, it relates to a wheelchair construction comprising substantially rigid panels connected by an interlocking button and rod means to produce a folding wheelchair without a separate framework.

Standard wheelchair construction comprises a welded tubular metal frame having seat and back elements of flexible material or fabric spanning the space between either side of the frame. Although foldable and of relatively light weight, such construction is inherently unstable and subject to weakening and breakage, predominantly at the weld locations and through the fabric elements. Furthermore, the initial construction and subsequent repair of such wheelchairs is expensive and requires technical expertise associated with bending and welding of tubular steel.

The present invention provides a simple and inexpensive construction for a wheelchair which may be assembled by relatively unskilled persons and which permits easy repair of broken parts. These parts include left and right side panels and at least two seat panels which together form the primary structure of the chair. These panels are made of a substantially rigid material, preferably injection molded polymer resin, and are held together in a chair configuration by means of interlocking fasteners. Additional frame stability is achieved by an interlocking pivotable lower support member, and a foldable stay member between the side panels. Wheels are attached in a conventional manner which permits vertical adjustment of the chair.

Foldable wheelchairs made from modular panels have been proposed before; however, they suffer from various drawbacks or design deficiencies. For example, U.S. Pat. No. 4,625,984 to Kitrell, discloses a folding wheelchair having two side frames connected by hinged foot and back panels. This design, however, includes a tubular metal framework in the side frames and requires that the seat be totally removed in order to fold. Furthermore, a wheel and belt motive system adds to the complexity of the construction.

U.S. Pat. No. 4,770,432 to Wagner, discloses a foldable wheelchair constructed of panels of skinned polymeric foam which are secured together by piano type hinges. These hinges require continued maintenance and add to the skill and cost required in assembly and maintenance.

U.S. Pat. No. 4,917,395 to Gabriele, discloses a wheelchair having a hinge construction between the side panels and seat and back panels which is an integrally molded part of the respective panels providing both bearing and support surfaces. Although providing relative ease of assembly, such an integral hinge means requires complete replacement of a panel should one portion of a hinge surface fail thus increasing the cost of repair. Additionally, individual parts of this construction are not interchangeable from left to right.

Thus, there is a need for a foldable wheelchair construction which is simple, rugged and inexpensive and requires little skill to construct or maintain. The wheelchair of the present invention provides such a construction with the added convenience of being adaptable to almost any material from wood to metal to plastic and which provides for relative ease of assembly and maintenance.

As described, the wheelchair of this invention is particularly adapted for ease of construction and maintenance by relatively unskilled persons and comprises side and seat panels, preferably of molded material, connected together in interlocking fashion by means of easily installed and replaced buttons and rods. The combination of these interlocking buttons and rods provides an improved structural stability whereby a stable vertical alignment is maintained at all times to reduce rolling resistance and tire drag. This, in turn, virtually eliminates the primary causes of wheelchair failure or repair which are wheel bearing failure, seat fabric replacement and frame cracks or broken welds brought about by excessive horizontal forces in the frame.

The primary pieces in the wheelchair construction of this invention are the two side panels and at least two seat panels which are hinged together. Each of the seat panels is hinged to one of the side panels by the interlocking buttons and rods and, when the chair is open, are at right angles to the side pieces. The interlock between the seat panels and the buttons and rods forms a tension/compression balance between the side pieces and the interlocking buttons and rods which prevents the seat from collapsing and reinforces the structural stability of the chair.

It is therefore an object of this invention to provide a foldable wheelchair construction which is easily assembled and repaired.

It is a further object to provide such a construction which results in a foldable wheelchair having improved structural stability.

It is a still further object to provide a foldable wheelchair construction which is fabricated from molded parts without welding or screws to maintain its structural integrity.

And it is an even further object to provide a foldable wheelchair construction which is lightweight and employs an interlocking button and rod technique for its assembly, whereby such assembly and subsequent maintenance and repair are easily accomplished by persons without specialized skills.

Further objects and advantages will become evident from the following drawings and description.

FIG. 1 is an oblique view of a wheelchair constructed according to the present invention with arm rest assemblies removed for clarity.

FIG. 2 is a front view of the wheelchair of FIG. 1 with foot rest assemblies removed for clarity.

FIG. 3 is a top view of a wheelchair of the present invention illustrating an alternative seat construction.

FIG. 4 is a cross section of a seat panel/side panel interlocking construction taken along line 4--4 of FIG. 2.

FIG. 5 is a cross section through the interlocking construction of two seat panels taken along line 5--5 of FIG. 3.

FIG. 6 is a cross section through the interlocking construction of two seat panels taken along line 6--6 of FIG. 3.

FIG. 7 is a planar view of a side panel of the wheelchair construction of the present invention.

FIG. 8 is a planar top view of a seat panel of the wheelchair construction of FIG. 3.

FIG. 9 is a planar side view of the seat panel of FIG. 8.

FIG. 10 is a planar end view of the seat panel of FIG. 8.

FIG. 11 is a planar side view of a lower support element employed in the wheelchair construction of this invention.

FIG. 12 is a planar top view of the lower support element of FIG. 11.

FIG. 13 is a cross section of the seat panel/side panel/button interlock construction of the present invention taken along line 13--13 of FIG. 4.

FIG. 14 is a cross section of the seat panel/side panel interlock construction of the present invention taken along line 14--14 of FIG. 4.

FIG. 15 is a side view of a rectangular seat panel/side panel interlock button employed in the construction of this invention.

FIG. 16 is a top view of the button of FIG. 15.

FIG. 17 is a side view of a cylindrical support member interlock button employed in the construction of this invention.

FIG. 18 is a top view of the button of FIG. 17.

FIG. 19 is an end view of the button of FIG. 17.

FIG. 20 is a planar view of a front caster plate of the wheelchair of this invention.

FIG. 21 is a longitudinal cross-section of the caster plate taken through line 21--21 of FIG. 20.

FIG. 22 is a top view of a foot rest assembly of the wheelchair of this invention.

FIG. 23 is an oblique view of the upstanding portion of a side panel illustrating the arm rest assembly of the wheelchair.

FIG. 24 is an exploded oblique view of the armrest assembly of FIG. 23.

FIG. 25 is a detail view of the attachment of armrest assembly to the wheelchair.

The wheelchair construction of the present invention eliminates the need for a welded frame and, instead, comprises left and right side panels 1, 2 and at least one each of left and right seat panels 3, 4. Each side panel 1, 2 has attached to it a large diameter rear wheel assembly 5, and a small diameter, vertically pivotable, front caster wheel assembly 6. As shown in FIGS. 1 and 2, the overall construction also includes a back support 7 connected to each side panel 1, 2 and spanning the space between upwardly extending portions of those panels when the chair is erected. Back support 7 is preferably a flexible material, such as a textile fabric, as normally used in tubular frame wheelchairs. A further foldable stay member 8 is positioned between the upwardly extending portions of each side panel 1, 2 and folds downward about the center pivot 31a when the chair is folded. A simple spring latch 32 or detent locks the stay member 8 in place when the chair is erected for use. A pivotable lower support assembly 9 is positioned between side panels 1, 2 beneath seat panels 3, 4. This assembly 9 provides additional vertical stability to the side panels 1, 2 and prevents the weight of the user from spreading the lower half of the chair out of vertical alignment.

FIG. 7 illustrates the basic configuration of side panels 1, 2, arbitrarily left side panel 1 of FIG. 1; right side panel 2 is identical, side panels 1, 2 being formed so as to be interchangeable. Side panel 1 is substantially L-shaped comprising a lower portion 1a having attachment areas for seat panels 3, 4, lower support 9, front caster and rear wheel assemblies 5, 6 and footrest assemblies 38, and an upstanding portion 1b providing handles 14 and attachment locations for backrest 7, folding stay 8 and arm rest assemblies 56.

As noted previously, the construction method employs buttons and rods which interlock with and secure seat panels 3, 4, lower support assembly 9, foldable stay 8, front caster assemblies 38, foot rest assemblies 39 and arm rest assemblies 56 to side panels 1, 2. Accordingly, side panels 1, 2 are provided with apertures therethrough in the attachment areas for the respective buttons. Apertures 10 are for seat panel attachment buttons 17, apertures 11 for lower support 9 attachment, apertures 12 for front caster and footrest assemblies 38, 39 attachment, apertures 13 are for rear wheel assembly 5 attachment and aperture 16 is for foldable stay member 8 attachment. Area 15 along the forward edge of upper portion 1b is where backrest 7 is attached. The interlocking construction of this invention may be used for attaching backrest 7. Alternatively, backrest 7 may be attached by other means such as standard screws, a sliding bar and channel, heavy duty snaps, etc. Slot 53 is for attachment of the upper portion of an arm rest and is elongated to allow adjustment of the arm rest height. Aperture 54 adjacent the lower end of slot 53 provides an attachment point for a lower portion of the arm rest which serves to stabilize the upper portion.

FIGS. 15 through 19 illustrate the two types of buttons employed in the wheelchair construction of this invention; rectangular seat panel attachment buttons 17 in FIGS. 15 and 16, and cylindrical support member buttons 18 in FIGS. 17 through 19. Both types of buttons comprise an enlarged head 17a, 18a and an elongated shaft 17b, 18b extending therefrom. The heads 17a, 18a are enlarged to extend laterally beyond the shafts 17b, 18b and thereby form a perimeter flange 17c, 18c which butts against the surface of side panel 1, 2 when the buttons are inserted through the respective apertures of panels 1, 2. Shafts 17b, 18b are preferably about two inches long and the perimeter flanges 17c, 18c of heads 17a, 18a preferably extend at least one quarter inch beyond the shaft surfaces. Rectangular buttons 17 are also used in the foot rest assemblies as shown in FIG. 22.

As shown by FIGS. 17 and 18, cylindrical buttons 18 have a substantially uniform size, the shaft 18b being a right cylinder preferably one inch in diameter. A flat surface 18e about one-eighth inch deep is cut into the end of the cylinder opposite head 18a. This flat surface 18e runs parallel to the central axis of shaft 18b and is about one half the length thereof. In contrast, rectangular buttons 17 have a shaft 17b which has a greater width than thickness, preferably in a ratio of 2:1 with a width of two inches and a thickness of one inch. The upper edge of the end of shaft 17b opposite the head 17a has a radius 17e while the lower end edge is square. Each type of button is also provided with a through channel 17d, 18d through its width at the end thereof opposite the head 17a, 18a. The end of shaft 18b of cylindrical support button 18 is preferably left square and channel 18d is perpendicular to flat surface 18e which provides an orientation and smooth surface for pieces that rotate about a rod inserted in channel 18d. These channels in the buttons accept attachment rods whereby the various panels or support members are secured to their respective side panels 1, 2. Attachment rods preferably have a knurled surface for a tight press-fit within channels 17d, 18d, of the buttons. Alternatively, other means of maintaining the rods in place, such as cotter pins or c-clips may be used.

FIGS. 8 through 10 illustrate a preferred form of seat panels 3, 4 as used in the embodiment of FIG. 3 and the following description, though given in terms of side panel 1 and seat panel 3, is applicable to either left 3 or right 4 seat panels and their attachment to left 1 or right 2 side panels, inasmuch as seat panels 3, 4, like side panels 1, 2, are identical. The seat portion of the chair may be constructed from just two panels, left 3 and right 4 as shown in FIG. 1, or from a plurality of narrower panels of the style shown in FIGS. 8 through 10, as shown in the construction of FIG. 3. Whichever style is used, the overall relationship between the left and right seat panels 3, 4 and these panels with their respective side panels 1, 2 is the same. Referring to FIGS. 8-10, each seat panel 3 comprises a molded panel having a planar upper surface 19 and a relieved lower surface 20. The relieved areas 20a of lower surface 20, shown by dotted lines in FIGS. 8 and 9, reduce the overall mass of the seat panels 3, 4 without sacrificing strength. A first end 21 of seat panel 3 is fashioned for attachment to side panel 1 by means of rectangular attachment buttons 17 and is provided with a notch 22 corresponding in width and depth to the shaft 17b of rectangular attachment button 17 extending through aperture 10 of seat panel 1. On either side of notch 22 are ears 23 which will flank shaft 17b of rectangular attachment button 17 when the seat panel 3 and side panel 1 are assembled. Such assembly is shown in cross section in FIGS. 4, 13 and 14. Ears 23 are provided with a horizontal through channel 24 corresponding in size and relative location to channel 17d of rectangular button 17 through which an attachment rod 25 is inserted to secure rectangular button 17 to seat panel 3 in a hinging manner. The upper edge 23a of ears 23 is given a radius so that seat panel 3 may pivot relative to side panel 1 about the rod 25 which is inserted through channel 24. The radius 17e of rectangular button 17 further facilitates this pivoting motion. The end face 23b of ears 23 is substantially perpendicular to upper surface 19 to butt against the inner surface of side panel 1 when seat panel 3 is lowered into a position for use. In constructions using only two seat panels, one left 3 and one right 4, the first end 21 of the seat panel will have a plurality of spaced notches 22 corresponding to the number and placement of attachment apertures 10 in side panels 1, 2. This construction is illustrated in FIG. 1. The alternative construction of FIG. 3 employs four narrower panels of the type depicted in FIG. 8 for each side of the seat wherein each seat panel 3, 4 has only one notch 22, the panel dimensions being such that the grouping of panels provides a uniform surface for an occupant to sit on.

FIGS. 13 and 14 are particularly illustrative of the relationship between seat panel 3, side panel 1 and rectangular button 17. Referring to these figures, as well as FIG. 4, it is seen that rectangular attachment buttons 17 are inserted into apertures 10 of side panel 1 from the outer side. Apertures 10 are preferably formed with a recess 30 about their perimeter corresponding to the dimensions of the head 17a of rectangular button 17 so that the head 17a will be slightly recessed into side panel 1. Because it is preferred that one molded panel can serve as either a left 1 or right 2 side panel, the recess 30 is provided on both sides of the panel 1 as most clearly shown in FIG. 13. The shaft 17b of each rectangular button 17 extends through aperture 10 and fits into notch 22 of seat panel 3. When channels 17d of rectangular buttons 17 and channel 24 of seat panel 3 are lined up, rod 25 is inserted to secure the assembly and serve as a hinge pin for pivoting of seat panel 3 relative to side panel 1. The radius edges 17e and 23a of rectangular buttons 17 and seat panel 3 respectively are uppermost so that seat panel 3 will pivot upward relative to side panel 1 when the wheelchair is folded. When the wheelchair is in the open position, the seat panel 3 and side panel 1 will have the relationship shown in FIGS. 13 and 14 with the end surfaces 23b of seat panel 3 butting against the inner surface of side panel 1. Furthermore, the inner face 22a of notch 22 will butt against the end of shaft 17b of rectangular button 17. In this manner a positive stop is provided for seat panel 3 against side panel 1 providing increased support for the user and increased stability to the chair since the force exerted by a person sitting in the chair will be transmitted by seat panel 3 as an outward or pushing lateral force to side panel 1 through ears 23 and as an inward or pulling lateral force through rectangular buttons 17. This combination of outwardly and inwardly directed lateral forces works to provide a tension/compression balance between the side pieces 1, 2 and the seat panels 3, 4 thereby improving structural stability and rigidity by reduction of the horizontal wobble which often occurs in standard tubular frame chairs.

The second end 26 of seat panel 3 is provided with a plurality of alternating ears 27 and notches 28 which will mate with corresponding ears and notches on a right side seat panel 4 in an interdigitating manner as shown in FIGS. 1 and 3. The arrangement of ears 27 and notches 28 is such that the same panel may serve as a left 3 or right 4 panel thereby reducing the numbers and varieties of parts required for the chair. Such interdigitation of left and right seat panels 3, 4 provides a hinge structure along the center line of the seat to permit folding when the wheelchair is collapsed. As with ears 23 on the first, side panel attachment, end 21 of seat panel 3, ears 27 have a horizontal through channel 29 which accepts an attachment rod 31 to secure left and right seat panels together and serve as a hinge pin. This relationship is best shown in FIGS. 3, 5 and 6. Since seat panels 3, 4 pivot upwards with respect to side panels 1, 2 when the chair is folded, the respective pivoting of the seat panels to each other about rod 31 is downward. For this reason, the lower edge of interdigitating ears 27 is given a radius 27a. To provide a positive stop along the centerline hinge formed by the attachment of seat panels 3, 4 to each other, the end surfaces 27b of ears 27 and the inner surfaces 28a of notches 28 are each perpendicular to the upper surface 19 of seat panels 3, 4 and butt against each other when the chair is open as shown in FIGS. 5 and 6. FIG. 5 is a cross section through seat panels 3, 4 and shows an ear 27 of seat panel 3 in a notch 28 of seat panel 4, while FIG. 6 is a similar cross section showing an ear 27 of seat panel 4 in a notch 28 of seat panel 3.

As with the securement of attachment rods in buttons 17, 18, rods 25 and 31 are also preferably knurled, at least at the ends, for a tight press-fit within the channels 24 and 29 of the seat panels 3,4.

The button and pin method of interlocking attachment is also used to secure the foldable stay member 8, the lower support assembly 9 and the front caster and foot rest assemblies 38 and 39 to the side panels 1, 2. In each of these instances the cylindrical support buttons 18 depicted in FIGS. 17 through 19 are used.

As shown in FIGS. 2 and 3, foldable stay member 8 comprises two relatively pivoting bars 8a, 8b, one end of each bar being attached to a respective side panel 1, 2 the opposite ends being joined in pivotal relationship by a common pivot pin 31a inserted into lined up apertures, this pin preferably being a rigid plastic and having its ends flared to hold it in place. Pin 31a provides a pivot means for foldable stay member 8 in the same manner that rod 31 provides a pivot for seat panels 3, 4. Stay member 8 folds downward when the chair is closed and is provided with a latch means comprising a spring loaded clip 32 or other detent means to secure the bars 8a, 8b of stay member 8 in a horizontal position when the chair is open. Bars 8a and 8b are identical, the end opposite the central pivot pin 31a aperture being provided with an attachment pivot pin 33 extending perpendicularly therefrom. Pin 33 is sized to fit in the channel 18d in shaft 18b of cylindrical support buttons 18 which are inserted through aperture 16 in upstanding portion 1b of side panel 1. Since side panel 2 is identical to side panel 1 it will have a corresponding aperture 16. Stay 8 is preferably attached relative to panels 1, 2 so that one attachment pivot pin 33 points rearward and the other points forward as is more clearly shown in FIG. 3. Pin 33 may be made so that it is longer than the width of button shafts 18b and may be provided with means to prevent it from pulling out of the channels 18d. Such means may be in the form of cotter pins inserted through the ends of the pin 33 or C-clips which fit into a circumferential groove in the end of the pin 33. Alternatively, cooperating detents may be provided on the pin 33 and in channels 18d to prevent pulling out of pin 33. Or pin 33 may be formed to have a snug, press-fit relationship within channels 18d of cylindrical buttons 18 while still permitting rotation therein. Preferably, the outer end of each bar 8a, 8b is given a radius 8c at the lower corner to facilitate the pivoting of these bars relative to the side panels 1, 2 the upper corner being straight to provide a contact surface against panels 1, 2 so bars 8a and 8b can pivot in only one direction, preferably downward.

Lower support assembly 9 is provided for additional support to maintain the vertical alignment of side panels 1, 2 and comprises identical pivot arms 9a, 9b, support pivot rod 9c and attachment pins 9d. The arrangement of these parts relative to themselves and the rest of the wheelchair is shown most clearly in FIG. 2 and the detail of the pivot arms themselves is shown in FIGS. 11 and 12. As is readily seen, pivot arms 9a, 9b are elongated members, the ends of which are laterally displaced relative to each other about the mid-point of the arm thus giving each arm a modified "S" shape. Each end of arm 9a, 9b has a body 35, 36 each of which is provided with a through channel 37 perpendicular to the longitudinal axis of the arm 9a, 9b and in the plane of the lateral displacement. In this manner when the support 9 is assembled as shown in FIG. 2, each arm will have a low end and a high end with channels 37 in each knob being vertically oriented. Body 35 of each arm 9a, 9b, which will be the outer end, is provided with a flat stay surface 35a to butt against the surface of side panels 1, 2 when the chair is open thereby assisting in maintaining proper spacing of side panels 1, 2 and providing added stability. Inasmuch as arms 9a, 9b are identical, only one part type need actually be fabricated, the two arms 9a, 9b comprising lower support assembly 9 merely being inverted relative to each other. Furthermore, channels 37 preferably have a diameter identical to that of channel 18d in shaft 18b of cylindrical button 18 which button type is used to attach support assembly 9 to side panels 1, 2.

The central pivot element of lower support assembly 9 is support pivot rod 9c which comprises a rod sized to fit within through channels 37 of bodies 36 of arms 9a, 9b. Pivot rod 9c fits into aligned channels 37 of bodies 36 of arms 9a and 9b respectively as shown in FIG. 2, the arms being free to pivot thereabout. As with the attachment of stay 8 and pin 31a described above, the ends of pivot rod 9c may be enlarged to hold rod 9c in place. Alternatively, pivot rod 9c and bodies 36 may have cooperating detents or other locking means or may rely on a snug fit to maintain relative positions and prevent arms 9a, 9b and support pivot rod 9c from separating. The outer ends of arms 9a, 9b attach to side panels 1, 2 by means of attachment pins 9d inserted into the channels 37 in the respective bodies 35, the ends of pins 9d being confined in channels 18d of upper and lower cylindrical buttons 18 inserted through apertures 11 in side panels 1, 2. Arms 9a, 9b are free to pivot about pins 9d while pins 9d are preferably secured into channels 18d by means of cooperating detents or locking pins, clips or a press-fit as in the manner of pins 33 of stay 8 or seat attachment rods 25 and 31. As with the other buttons 17 and 18 used to fasten seat panels 3, 4 and stay 8 to side panels 1, 2, cylindrical buttons 18 used to hold pins 9d and, thereby, secure support assembly 9 to side panels 1, 2 are inserted through their respective apertures 11 in side panels 1, 2 from the outer side of each panel.

The caster wheel assemblies 38 for each side panel 1, 2 comprise a caster plate 40 and caster wheel 6 attached to the inner face of each side panel as shown in FIG. 1. The assembly is held in place against the inner surface of the side panel by a cylindrical button 18 passing through the lower of apertures 12 in the side panel and aperture 41 in the caster plate 40. An interconnect rod 42 is inserted into channel 43 in caster plate 40 and through channel 18d of cylindrical button 18. Aperture 41 in caster plate 40 is provided with a flat 41a corresponding to surface 18e on cylindrical button 18 so that channel 18d is properly oriented with channel 43 to accept interconnect rod 42. The other end of interconnect rod 42 mates with channel 18d of a cylindrical button 18 inserted in the upper one of apertures 12 in the side panel. Upper and lower apertures 12 are oriented so as to be in line at an angle of 13.degree. rearward of vertical. As with the other attachment rods, interconnect rod 42 is provided with means to ensure its retention by cylindrical buttons 18 and caster plate 40. These means are preferably such as to provide a tight press-fit in the channels 18d and channel 43 and may comprise knurling of the rod or other means of expanding the end portions of the rod for a tight fit or cooperating detents. As shown in FIGS. 20 and 21, the caster plates 40 themselves comprise a substantially trapezoidal plate body 40a, the wider edge of which is curved to correspond to the curvature of the lower forward corner of side panels 1, 2. Extending laterally from plate body 40a along this edge is flange 40b which will butt against the lower front edge of side panels 1, 2. Flange 40b is provided with two locating pins 44 which extend upward therefrom and engage corresponding holes 45 in the lower front edge of side panels 1, 2 to accurately position caster plates 40 relative to side panels 1, 2. Unlike the other elements of this wheelchair, caster plates 40 are formed as individual right and left units, although the fabrication procedure is identical for each.

The caster assemblies 38 together with the interconnect rods 42 and cylindrical buttons 18 used to attach them to side panels 1, 2 reinforce the lower front corner of the side panels by effectively doubling the thickness of the panels at that point. Such reinforcement is necessary in view of the severe stress and vibration to which the forward corners are subjected. The caster wheels 6 like the rear wheels 5 are attached to metal plates which can be adjusted for the proper height with the rear wheels. Preferably, three height adjustments are provided to correspond with those of the rear wheels, such attachment and height adjustment preferably comprising bolts penetrating the side panels 1, 2 and caster plates 40.

Associated with the caster assemblies 38 are foot rest assemblies 39 comprising a foot rest attachment arm 46 and foot rest plate 47. As with side panels 1, 2 and seat panels 3, 4, foot rest attachment arm 46 and plate 47 are identical pieces for both left and right sides. Foot rest attachment arm 46 comprises a substantially inverted "L" shaped piece wherein the horizontal arm 46a has a cylindrical end 48, the longitudinal axis of which is substantially parallel to the axis of the vertical arm 46b. The cylindrical end 48 has a longitudinal through channel 49 with a diameter corresponding to that of the interconnect rods 42 of the caster assemblies 38. The opposite end of the foot rest attachment arm 46 is provided with an aperture 50 sized to accept the shaft 17b of a rectangular button 17 for attachment of foot rest plate 47.

Foot rest plate 47 is similar to seat panels 3, 4 and is pivotally mounted to the lower end of foot rest attachment arm 46 by button 17 and attachment rod 51 in the same manner that seat panels 3, 4 are attached to side panels 1, 2. The primary difference is that left and right foot rest plates 47 are not connected to each other at their adjacent edges as seat panels 3, 4 are. Each foot rest plate 47 comprises a substantially rectangular panel, one short edge of which is provided with a pair of ears 52 which are spaced apart a distance corresponding to the width of button shaft 17b. Horizontal through channels 52a in ears 52 correspond to channel 17d of rectangular button 17 to accept an attachment rod 51. As with other such rods in this construction, rod 51 is provided with means to cause its retention within the through channels 52a and channel 17d while permitting foot rest plate 47 to pivot relative to attachment arm 46. Preferably, such means comprises knurled portions at the ends of rod 51 within through channels 52 a. Other means may include cotter pins, c-clips, detents and the like. Ears 52 have a radius on their upper edges permitting plate 47 to pivot relative to arm 46 and a perpendicular end face to butt against the surface of arm 46 when plate 47 is lowered to its use position in the same manner as ends 21 of seat panels 3, 4.

Foot rest assemblies 39 are attached to the wheel chair at the time caster wheel assemblies 38 are mounted, the interconnect rods 42 passing through longitudinal through channels 49 of foot rest attachment arms 46. In this manner, foot rest assemblies 39 are maintained at the same angle of 13.degree. relative to the vertical as caster assembly interconnect rods 42, this angle provides the most comfortable position for the feet in relation to the seat of the wheelchair. Foot rest assemblies 39 are also capable of pivoting about interconnect rods 42 into a storage position underneath the wheelchair seat with foot rest plates 47 pivoted upward against their respective attachment arms 46. The height of foot rest assemblies 39 is adjustable by sliding the attachment arms 46 up or down the interconnect rods 42, any height above the caster plate 40 being maintained by means of "C" shaped collars snapped over the rod between caster plate 40 and cylindrical end 48 of foot rest attachment arm 46. The "C" shaped collars may be provided in various lengths; however 1/2" segments should normally be sufficient to provide variable heights with multiple segments being stacked for greater heights.

Slot 53 and aperture 54 in upstanding portion 1b of side panel 1 provide an attachment location for armrest assembly 56 as shown in FIG. 23. The height of arm rest assembly 56 is adjustable within the length of slot 53 by means of plug 55 insertable in slot 53 as shown in FIGS. 23 and 25. As with the collars used to adjust the height of the foot rest assemblies, plug 55 is preferably provided in 1/2" segments which can be snapped together as needed.

Referring to FIG. 24, it is seen that arm rest assembly 56 comprises two portions; arm rest 57 and support rod 58. Arm rest 57 preferably comprises an elongated rod 59 one end of which is padded 60 preferably with a foam material. At the opposite end of rod 59 from padding 60 is fitting 61 which comprises pin 62 extending perpendicularly to the axis of armrest 57. Support rod 58 likewise comprises an elongated rod 63 having a fitting 64 at one end. In this instance fitting 64 comprises a 90.degree. member with rod 63 inserted into one end while the opposite end comprises a socket 65 sized to accept pin 62. Preferably, pin 62 and socket end 65 of fitting 64 include cooperating means whereby pin 62 and socket 65 interconnect in a locking manner to permit arm rest 57 and support rod 58 to be assembled for use on the right or left side of the wheelchair. This cooperating means may take the form of a twist-lock or bayonet mechanism employing lugs on pin 62 which mate in slots in the interior of socket 65. Other interconnect means may be employed as long as they permit assembly of armrest 57 and support rod 58 in one of two orientations for right or left side usage and allow relative rotation of arm rest 57 and support rod 58 from vertical to horizontal but limit such rotation so that, when in the down position, arm rest 57 is parallel to seat panels 3, 4 when the chair is open. Preferably, the vertical position is such that arm rest 57 will be parallel to upper portion 1b of side panel 1. also, arm rest 57 is preferably of sufficient length to extend forward to a point substantially even with the front edge of the wheelchair.

Arm rest assembly 56 attaches to the wheelchair by means of a cylindrical support button 18 inserted through aperture 54 in upstanding portion 1b. Armrest assembly 56 is inserted through slot 53 from the outer surface of side panel 1 so that support rod 58 extends downward adjacent the inner surface of side panel 1. Cylindrical support button 18 is inserted through aperture 54 with through channel 18d oriented to accept rod 63 as shown in FIG. 25. Rod 63 is of sufficient length to engage button 18 even when armrest 56 is adjusted to the maximum height allowable by the length of slot 53, such adjustment being effected by means of plug 55 against which fitting 64 rests. An alternative procedure for assembly of armrest assembly 56 to the wheelchair comprises inserting button 18 through aperture 54 followed by insertion of rod 63 into through channel 18d so that socket end 65 of fitting 64 extends through slot 53. In this instance, fitting 64 may be provided with flattened areas 66 on opposite sides to key fitting 64 into slot 53. Armrest 57 is then connected to support rod 58 by means of pin 62 and its related interconnect means.

Backrest 7 comprises a flexible fabric panel sized to span the space between the upstanding portions 1b, 2b of side panels 1, 2 forward of slot 53 and armrest support rod 58 to provide support for the occupant's back. This panel may be provided with mounting strips on each end whereby the panel is attached to side panels 1, 2. The simplest method of attaching backrest 7 to side panels 1, 2 is to make these mounting strips out of a material which will accept and hold screws and to attach the backrest 7 by means of such screws driven through side panels 1, 2 at the backrest mounting location 15 and into the mounting strips. Alternatively, snaps or other fastening means as currently employed in wheel chair construction may be used to attach backrest 7.

Rear wheels 5 are attached to side panels 1, 2 at location 13 thereof which is preferably internally reinforced. Attachment is by means of a standard anodized aluminum plate which fits into the recess at location 13 and is held in place by bolts passing through the plate and the panel. Multiple holes are provided in the side panel to allow adjustment of wheel height.

Alternatively, front casters 6 may be attached to panels 1, 2 in the same manner as rear wheels 5 by means of metal plates bolted directly to panels 1, 2 without the benefit of intervening caster plates 40. In this instance interconnect rods 42 and the associated cylindrical support buttons 18 inserted in apertures 12 will serve only to provide pivoting attachment of foot rest assemblies 39 to side panels 1, 2. This method of attachment of casters 6 should be used only when the construction and material of side panels 1, 2 is of sufficient strength to take the stress and vibration to which the forward corners of the panels are subjected.

The above described construction provides a wheelchair which is both sturdy and inexpensive to maintain and repair. In addition, the chair is foldable to permit storage or transportation in a flat folded condition. When the chair is to be folded, the latch 32 on support stay 8 is released and the two side panels 1, 2 brought together. Backrest 7, being of a flexible material, will fold easily as stay 8 folds downward about pins 33, the individual bars 8a, 8b of stay 8 folding downward relative to each other about pivot pin 31. At the same time, seat panels 3, 4 pivot upward relative to panels 1, 2 about rods 25 and fold downward relative to each other about rod 31. Meanwhile, support assembly 9 will fold forwardly or rearwardly, the arms 9a, 9b pivoting relative to each other about pivot support 9c and relative to side panels 1, 2 about pins 9d. Unfolding the chair reverses the action of the parts with the stay 8 and seat panels 3, 4 opening out to their extended positions and the support assembly 9 pivoting out to its central position under the seat panels, the stay surfaces 35a of each arm butting against their respective side panels 1, 2 thus restricting further spreading of the lower portions of side panels 1, 2 and maintaining vertical stability of the chair. At full extension latch 32 on stay 8 will lock the stay and the chair in the open position. Furthermore, the weight of the occupant applied to the seat panels 3, 4 will set up the tension/compression force balance between the seat panels 3, 4 and side panels 1, 2 through the abutting end faces 23b of ears 23 and the inner surfaces of side panels 1, 2 and between the heads 17a of buttons 17 and the outer surfaces of panels 1, 2.

In the event a part needs replacing it is a simple matter to disassemble the chair, replace the part and reassemble the chair. In fact, in most instances complete disassembly would not be necessary. For example, if a seat panel required replacement it would only be necessary to remove rod 31 and one of rods 25, depending on whether it was a left or right seat panel, remove the defective panel and replace it with a new one, followed by reinsertion of the rods.

The side panels, seat panels, foot rest elements, caster plates, support members, connector buttons and attachment and interconnect rods may be fabricated from a variety of rigid materials such as wood, plastic, metal, reinforced plastics, composites and the like. Preferably, the panels, plates, supports, and buttons are molded from reinforced polymers with the side panels preferably shaped by compression molding over a reinforcing core. The attachment and interconnect rods are preferably steel but may be reinforced polymer or the like so long as they possess sufficient rigidity.

The foregoing is a description of the preferred embodiment of the wheelchair construction of the present invention. Other embodiments and modifications will be apparent to those of ordinary skill in the art in light of the foregoing description and are deemed to be included within the scope of the following claims.