Abstract:
A tilt-in-place wheelchair having adjustable wheelbase includes front and rear side frames, hinged cross members supported on the frames, an adjustment rail supported on the frames for rotation relative to the frames, a block slideably supported on the rail and hinged to one pair of cross members, a latch supported on the rail and adapted for releasable engagement with the rail so that the block is alternately fixed to the rail to maintain the width of the wheelbase or released from the rail to allow adjustment of the wheelbase.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of wheelchairs and other wheeled apparatus for transporting people. 
     2. Description of the Prior Art 
     Wheelchairs having a fixed wheelbase width require large main wheels to provide needed stability against overturning. However, the width of such chairs and their wheel size present difficulties in maneuvering the chair in confined spaces such as in washrooms, aircraft, and offices, through doorways, and along narrow aisles. 
     U.S. Pat. No. 6,164,674 describes a wheelbase adjustable wheelchair. A linkage between two side frames includes two cross members. One end of each being pivotally supported to a side frame on each side of the chair. The cross members are attached mutually at a point of intersection, the other end of each cross member sliding on the opposite side frame. 
     PCT International Patent Application WO 99/37265 describes a wheelchair having lower and upper side frames, the upper frame being tiltable with respect to the lower frame, ground wheels mounted on the lower frames, and seating and backrest support carried on the upper frames. The upper frame, and the seating and backrest supports are foldable laterally inward regardless of the tilted position of the upper frame. 
     U.S. Pat. No. 4,603,890 discloses a wheelchair having forward and rearward side frames that are telescopically interconnected so that the length of the frame can be adjusted. A cross brace connecting the side frames permits folding the chair laterally A cross brace mechanism adjusts the width of the chair without adjusting its height. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a wheelchair, the width of whose wheelbase is adjustable. This feature permits the user to readily narrow the chair&#39;s width when narrow doorways and passageways are confronted. 
     It is another object of the invention to provide a wheelchair having a set of anti-tilting wheels that apply a stabilizing, restoring force to the chair when it is tilted backward. This feature permits safe, reliable backward tilting of the chair by the occupant to avoid or pass-over obstructions at the front caster wheels. 
     A tilt-in-place wheelchair having adjustable wheelbase includes front and rear side frames, hinged cross members supported on the frames, an adjustment rail supported on the frames for rotation relative to the frames, a block slideably supported on the rail and hinged to one pair of cross members, a latch supported on the rail and adapted for releasable engagement with the rail so that the block is alternately fixed to the rail to maintain the width of the wheelbase or released from the rail to allow adjustment of the wheelbase. 
     In realizing these objects and advantages a tilt-in-place wheelchair according to the present invention includes a first side frame; a first side frame; a second side frame substantially parallel to the first side frame and spaced laterally therefrom; a first pair of cross members, mutually pivotally interconnected at an inner end thereof and foldable about the pivotal interconnection, a first member of the first pair coupled to and pivotably supported on the first side frame for variable angular positions, a second member of the first pair being coupled to and pivotably supported on the second side frame for variable angular position; a second pair of cross members spaced longitudinally from said first pair of cross members, mutually pivotally interconnected at an inner end thereof and foldable about the pivotal interconnection, a first member of the second pair coupled to and pivotally supported on the first side frame for variable angular position, a second member of the second pair pivotally being coupled to the second side frame for variable angular position; means for adjusting and releasably holding the first pair of cross members and second pair of cross members at predetermined angular positions relative to the first and second side frames; a first tilt wheel extending outward from, and pivotably supported on the first side frame, continually biased resiliently downward toward ground contact and opposing displacement upward away from ground contact; and a second tilt wheel extending outward from, and pivotably supported on the second side frame, continually biased resiliently downward toward ground contact and opposing displacement upward away from ground contact. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an isometric side view of a wheelchair according to this invention tilted backward and positioned to mount an obstruction. 
     FIG. 2 is a top view showing the side rails, cross members and width-adjustment mechanism of the wheelchair of FIG.  1 . 
     FIG. 3 is an isometric side view showing the cross members and width-adjustment mechanism. 
     FIG. 4 is an isometric view showing the wheelchair width at an intermediate position. 
     FIG. 5 is an isometric view similar to that of FIG. 4 showing the wheelchair expanded to its maximum width. 
     FIG. 6 is an isometric view showing an adjustment block surrounding an adjustment rail and carrying a latch for engaging the rail. 
     FIG. 7 is an isometric side view showing an alternate form of an adjustment block and latch. 
     FIG. 8 is an isometric side view showing the collar and latch of FIG.  7 . 
     FIG. 9 is a side isometric view showing the latch of FIG.  6 . 
     FIG. 10 is an isometric side view showing the adjustment rail of FIG.  6 . 
     FIG. 11 is a front view of an adjustment block showing a spring-loaded pin for engaging the adjustment rail. 
     FIG. 12 is a side view of a retractable spring-loaded pin of FIG.  11 . 
     FIG. 13 is an isometric view of the adjustment block, latch and adjustment rail of FIG.  6 . 
     FIG. 14 is an isometric view of the adjustment block, latch and adjustment rail of FIG.  7 . 
     FIG. 15 is an isometric side view showing a tilt wheel pivotally supported on a frame. 
     FIG. 16 is an isometric view of the wheelchair showing the tilt wheel retracted and the wheelchair folded to its minimum width. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, first and second parallel side frames  20 ,  22  are shown substantially mutually aligned axially and extending axially forward from mounting plates  24 ,  26  located at the rear of the side frames. Each side frame  20 ,  22  rotatably supports a front caster wheel  28 ,  30 . Mounting plate  26  rotatably supports primary wheel  34  and pivotally supports a tilt wheel  36 . Similarly, plate  24  rotatably supports a first primary wheel  32  and pivotally supports a first tilt wheel  38 . 
     Vertically directed struts  40 ,  42 , adapted to support the back of the chair, extend vertically upward from the upper rails of the first and second side rails  20 ,  22 . 
     FIG. 1 shows the wheelchair tipped rearward so that the front caster wheels are located above a curb or similar obstruction, and the tilt wheels are contacting, or nearly contacting, the ground to prevent the wheelchair from tipping rearward. In this position, the wheelchair disposed so that the first and second primary wheels can roll over the obstruction. 
     Referring now to FIGS. 2 and 3, a first pair  44  of a cross members or frames  46 ,  48 , pivotably supported at the forward end of the side frames, are mutually connected end-to-end near the center of the space between the side rails for pivoting movement. Cross member  46  is pivotally connected at  52  and  54  to the upper and lower longitudinal rails of side frame  20 . Similarly, cross member  48  is pivotally connected at  56 ,  58  to the upper and lower longitudinal rails of side frame  22 . 
     A second pair  60  of cross members  62 ,  64  located toward the rear of side rails  20 ,  22 . and spaced longitudinally from the first pair of cross members  44 , are mutually pivotally connected end-to-end at  65 . Cross member  62  is pivotally connected at  64 ,  66  to the upper and lower longitudinal rails of side frame  20 ; cross member  64  is pivotally connected at  68 ,  70  to the upper and lower rails of side frame  22 . In this way, the cross members of the first pair  44  and second pair  60  can pivot for a variable angular position with respect to the side frames. The lateral space between the side frame, or width of the chair, is determined by the angular position of the cross members and the extent to which they are folded. For example, FIG. 5 shows the front of pair  44  of cross members and the rear pair  60  extending substantially mutually parallel and perpendicular to the side frames so that the wheelchair attains its maximum width. But in FIG. 4, the front pair of cross members  44  and rear pair  60  are partially folded, and the angular position of the cross members is other than substantially perpendicular to the plane of the side rails  20 ,  22 . In the position of FIG. 4, the wheelchair has a reduced width compared to the maximum width of FIG.  5 . 
     The front pair  44  of cross members is pivotally connected to the forward end  72  of an adjustment rail  74 , and the rear pair  60  of cross members  62 ,  64  is pivotally connected to the rearward end  76  of adjustment rail  74 . The inner ends of the forward frames  46 ,  48  that comprise the forward cross member pair  44  are formed with upper and lower devices  76 ,  78 , and the forward end of rail  74  is formed with two devices  80 , each of devices being formed with an open-ended through hole that receives a pin to permits hinged rotation of the frames  46 ,  48  relative to rail  74 . Similarly, each of the rear frames  62 ,  64 , which comprise the rear cross member pair  60 , is formed with an upper device  82  and a lower device  84 . The rearward end of rail  74  is also formed with a device  86  located between the upper and lower devices  82 ,  84 , each of these mutually aligned devices being formed with an open-ended through hole that receives a pin to permit hinged rotation of the frames. 
     Frame  64  is also formed with an upper device  88 , a lower device  90 , each formed with a through hole having an open end. An adjustment strut  92  pivotally connected on adjustment block  94  includes a device  96  located between devices  88 ,  90  and aligned so that a pin can be inserted through the devices  88 ,  96 ,  90  to permit strut  92  to rotate relative to frame  64 . Similarly, adjustment strut  98  is formed with a device  100  located between an upper clevice  102  and a lower clevice  104 , formed on frame  62 . A pin is inserted between clevices  102 ,  100  and  104  to permit strut  98  to rotate relative to frame  62 . 
     Preferably the lengths of cross members  46  and  62  are mutually substantially equal, the lengths of cross members  48  and  64  are mutually substantially equal, and the lengths of struts  92  and  98  are mutually substantially equal. The length of the first side frame  20  between the points where cross members  46  and  62  are coupled to frame  20  is substantially equal to the length of the second side frame  22  between the points where cross members  48  and  64  are coupled to frame  22 . 
     Adjustment block  94  is supported on rail  74  for sliding movement along the axis of the rail. This movement of block  94  changes the angular position of frames  62  and  64  about the side rails  20  and  22 , thereby forcing adjustment rail  74  longitudinally relative to block  94  so that the angular position of frames  46  and  48  changes with the change of angular position of frames  62 ,  64  and the longitudinal position of block  94 . In this way, cross member pairs  44 ,  60  are folded and extended according to the position of block  94  on rail  74  in order to change the width of the wheelchair. 
     Referring next to FIG. 7, adjustment block  94  is formed with two upper devices  110  and two lower devices  112 , a device of each lateral pair, located on opposite lateral sides of the center line of rail  74 . A pin, passing through those clevices, hinges each attachment strut  92 ,  98  on block  94 . Rail  74  supports block  94  so that the block can slide longitudinally to a position limited by the located of a collar  114 , whose position on rail  74  is fixed by a set screw, bolt or similar attachment  116 , which engages rail  74  and fixes the position of collar  114 . The upper surface of block  94  pivotally supports a latch  118  having a blocking surface  120 . When the latch is in position shown in FIG. 7, surface  120  engages the end face of collar  114 , thereby releaseably fastening block  94  to rail  74 , but not locking the block to the rail. In order to change the width of the wheelchair, latch  118  can be pivoted at its pinned connection on block  94  out of engagement with collar  114 . When this occurs, the latch  118  and block  94  can be moved as a unit away from the position of the collar. The longitudinal position of the collar on rail  74  can be changed by loosening attachment  116 , sliding the collar along rail  74 , and reattaching the collar to the rail by tightening attachment  116 . 
     Referring now to FIGS. 6,  9  and  10 , an alternate adjustment rail  124  is formed with a series of radially directed holes  126 , spaced longitudinally along the rail and angularly about the axis of the rail. Alternatively, the holes  126  can form a spiral pattern on the outer surface of rail  124 , the spiral extending around the rail and along its length. Collar  128 , located at an axial end of rail  124 , supports the rail for rotation about its axis and is formed with a series of radially directed hole  130  spaced angularly about the axis. The opposite end of the rail  124  is supported on the front pair  44  of cross members for rotation about its axis. Holes on collar  128  are sized and located to receive a radial pin  131  that passes through holes  130  and through a similar series of holes formed on the end of rail  124 . Pin  131  fixes the angular position of rail  124  with respect to the wheelchair and collar  128 . Preferably the angular position of the holes  126  is aligned with the angular position of holes  130  so that the latch pin  136  will readily engage holes  126 . 
     A latch  132  is pivotally mounted on block  94  by a pin that passes through a hole  134  on the latch. As the latch is rotated about the axis of hole  134 , pin  136 , located on the end of latch  132 , is brought into engagement with any of holes  126  located on rail  124 . When this engagement occurs, block  94  is releasably fastened to rail  124  at a fixed longitudinal position, whereby the width of the wheelchair is held in position. In order to change the width of the wheelchair, latch  132  is rotated to bring pin  136  out of engagement with a hole  126 , and block  94  is displaced along rail  124 , rail  124  is rotated to bring a different hole into alignment with pin  136 , and the latch is pivoted to engage pin  136  and a new hole of rail  124 . 
     FIG. 14 shows adjustment rail  74  journalled in a collar  76  formed integrally with a plate  140  that includes right-hand and left-hand devices  8 , located between the upper clevices  82  and lower devices  84  on frames  62  and  64 . The pin that engages the devices  82 ,  84 ,  86  permits the frames  62 ,  64  to rotate relative to plate  140  and rail  74 , as FIG. 3 shows. 
     FIG. 11 shows an alternative adjustment block  142  surrounding rail  124 . A retractable bolt  146  is urged radially toward rail  124  and into engagement with a hole  126  on the rail by a helical coil spring  148 . A cable  150 , attached to a handle or grip  152 , can be pulled upward against the force of spring  148  to disengage bolt  146  from the hole of rail  124 , thereby permitting the load block  142  to be moved longitudinally. 
     FIG. 12 shows a side view of block  142 , spring  148 , cable  150 , bolt  146 , and handle  152 , which can be gripped manually and pulled against the force of spring  148  to disengage bolt  146  from hole  126  on rail  124 . 
     Preferably each adjustment rail is marked on its outer surface at points spaced along its length with a scale comprising a scribed line and a number or legend that indicates the actual width or relative width of the wheelbase that corresponds to placing the adjustment block at the position of the line, number or legend. 
     FIG. 15 shows frame  62  pivotally supported for rotation about a pin  65 , which passes through the upper longitudinal rail  160  and lower rail  162  of the side frame  20 . Mounting plate  24  supports the left-hand side main wheel  32  and carries a stopper surface  164 , engaged by the end of an anti-tipping bar  166 , which is pivotally supported on mounting plate  24  by a laterally directed pin  168  that passes through bar  166  and plate  24 . A spring  170  urges the anti-tipping bar  166  to rotate about pin  168  toward contact with the ground. As the chair rotates, e.g. when the occupant attempts to clear an obstruction, such as that shown in FIG. 1, the load applied by spring  170  to bar  166  operates to stabilize the chair and to prevent its overturning. The arrangement of FIG. 15 is typical of both sides of the chair; therefore, two spring loaded anti-tipping bars bias two tilt wheels toward ground contact to apply a restoring force to the chair tending to prevent tip-over. 
     When the wheelchair assumes the position of FIG. 1, tilt wheel  38  is maintained in contact with the ground due to the force of spring  170 , but the chair rotates counterclockwise when viewed from the right-hand side, against the resilient force of spring  170  until the end  172  of bar  166  contacts stopper  164 . Contact between bar  166  and the stopper surface limits the extent to which the chair can rotate. Thereafter, further backward tilting of the chair is prevented due to contact of the tilt wheels with ground, and contact of bar  166  with stopper  164 . 
     Anti-tipping bars  166 ,  167  can be biased toward ground contact by coupling a pneumatic or hydraulic cylinder and a piston moving within the cylinder between bars  166 ,  167  and side frames  20 ,  22 . The piston will be biased in response to movement of the rails relative to the frames by compressed fluid in the cylinder toward ground contact. EPO Patent 0 45 171 B1 describes a piston and cylinder applied to a wheelchair assembly for a different purpose than this. 
     FIG. 16 shows the wheelchair folded to its minimum width, rails  40 ,  42  folded forward, and tilt wheels  36 ,  38  and bars  166  folded forward due to the force of spring  170 . 
     Although the form of the invention shown and described here constitutes the preferred embodiment of the invention, it is not intended to illustrate all possible forms of the invention. Words used here are words of description rather than of limitation. Various changes in the form of the invention may be made without departing from the spirit and scope of the invention as disclosed.