Abstract:
A manual propulsion mechanism for wheelchairs utilizes a lever pivotally mounted to the hub of each rear wheel such that the wheelchair user can propel the chair with push/pull movements of the levers. Forward and reverse propulsion directions are accomplished by a system of one-way reversible clutches contained in the propulsion wheel hubs which also allow the levers to be operationally disconnected such that the chair can freewheel. Operator control of direction shifting is through pivoting motions imparted to the grip handles of the propulsion levers. In a preferred embodiment, improved ergonomics for propulsion direction changes are made possible by coordinating the direction of the shift pivot motion with the push/pull movement of the levers. This allows the operator to retain a comfortable, stable grip on the grip handle while simultaneously propelling and controlling direction of movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED R&amp;D 
       [0002]    Not Applicable 
       REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM 
       [0003]    Not Applicable 
         [0004]    This invention relates to manual wheelchair drive mechanisms. 
       BACKGROUND OF THE INVENTION 
       [0005]    Wheelchairs are typically intended to provide independent mobility for persons without the use of their legs, and provide means of utilizing arm movement to cause rotation of one or more wheels of the wheelchair. In the commonest and simplest form, round pushrims of slightly smaller diameter than the propelling wheels are fixed to the said propelling wheels, such that the user may conveniently grasp the pushrims to exert a rotational torque to the driving wheels through the pushrims. Although such means of propelling is simple, light in weight, and inexpensive, problems with pushrims include placing the users hand near the tires of the driving wheels which may be dirty, requiring considerable grip strength to grasp the pushrim, and repetitive motion injuries from the non-optimal bio-mechanics of grasping and pushing the pushrims. Efforts to provide solutions to these problems have often included lever drive mechanisms that allow the user to propel with reciprocating rowing type of motion. The levers can be located such that the pushing and pulling on the grip portion of the input lever provides improved biomechanics and keeps the users hand away from the driving wheels. Torque transmission from the input lever to the driving wheels typically involves some type of clutch action such that the wheelchair can be propelled in both forward and reverse directions. In this type of drive mechanism a means must be provided to allow the user to select either forward or reverse, and also to disengage the drive mechanism so that the wheelchair can be pushed by a caregiver. 
       PRIOR ART 
       [0006]    To this point in the state of the art, lever drive mechanisms have all had deficiencies that limit general acceptance by potential users. These deficiencies include being too heavy, too bulky, having non-ergonomic forward/reverse shifting control inputs, and being obtrusive in appearance. Many levers drive inventions depend on a lever that is pivotally mounted forward of the rear drive wheels and that transmits torque to the drive wheels by way of chains, belts, or gear racks. Representative of this type of lever drive arrangement are U.S. Pat. Nos. 6,234,504, 5,007,655, and 4,652,026. This style of lever drive is exceptionally obtrusive in appearance, needlessly heavy, and has not been accepted by the user community. 
         [0007]    Another style of lever drive incorporates the drive lever pivot spindle into the rear drive wheel hub. Although potentially less obtrusive than the forward mount lever arrangement discussed above, the bulky physical size of current hub mount lever drive mechanisms causes them to be placed on the outside of the driving wheel, and thus are still objectionably obtusive. Additionally, this placement causes the width of the wheelchair to increase, which is problematic for passing through typical doorways. U.S. Pat. No. 7,261,309 shows a wheelchair lever drive that is placed on the outside of each rear drive wheel. It uses roller clutches to effect forward/reverse directional control that are shifted in rotational sense by a handgrip  47  actuated pinion  17  that runs against a mating gear portion  2 A on shift cage  2  of the clutch in the transmission. The relative pitch diameters necessary to the use of this pinion/gear arrangement result in less angular movement of shift cage  2  than is input by handgrip  47 . Further, the connection between handgrip  47  and pinion  17  is cable  49 . This arrangement causes the torsional compliance of cable  49  to add angular lost motion to the shift angle input the user must apply to the handgrip. This results in an awkwardly large angle through which the user must rotate the handgrip in order to affect change of direction, forward/reverse or reverse/forward shifts. In wheelchair operation change of direction shifts are very frequent, and this large angle of rotation forces the user to continually adjust their hand position on the grip of the propulsion lever. This condition significantly impairs the user experience, and predisposes users to forego using a lever drive wheelchair, other benefits notwithstanding. Additionally this invention uses multiple springs  5  of unusual and complex shape to cause rollers  3  to contact cam points  52  of cam disc  50  portion of the mechanism. Cam points  52  are of complex geometry and require high precision machining and grinding processes to fabricate. This results in an expensive clutch and control arrangement, not well suited to low production uses such as wheelchairs. 
         [0008]    Various roller clutch mechanisms are known to the art, but fail to adequately address wheelchair lever drive needs. U.S. Pat. No. 6,210,300 presents a roller clutch invention that uses formed cam surfaces on the inside diameter portion of the outer member of the clutch, with the rollers biased by individual springs. This type of clutch is complex and problematically expensive to manufacture in small quantities for wheelchair applications. 
         [0009]    U.S. Pat. No. 6,953,412 discloses a reversible one-way clutch which incorporates cammed surfaces on either the outer periphery of an inner race, or the inner periphery of an outer race, in combination with cylindrical rollers, a cage portion containing said rollers and biasing springs for each roller, and a biasing plate  96  which functions to move the bias springs such that the clutch functions in either forward or reverse. It also, like other similar one-way reversible clutches, depends on a plurality of individual springs,  114 , generally either one or two per roller, to achieve torque transmission in a selectable direction of rotation. Due to the dependence on individual springs for roller biasing, the arrangement thus taught is limited to a bi-state operation, as the springs will push the rollers either one direction on the other, and are not intended or able to achieve an intermediate position. Therefore, either CW torque transmission with freewheeling CCW is achieved, or CCW torque transmission with freewheeling CW, thus lacking a neutral position allowing freewheeling both CW and CCW. Unique to this arrangement is the further incorporation of a biasing plate  96  to effect movement of the plurality of springs from one torque transmission state to the reverse. This arrangement as presented is of greater complexity and cost than is needed for wheelchair transmissions. 
         [0010]    U.S. Pat. No. 5,765,669 teaches a reversible clutch type mechanism with features similar to U.S. Pat. No. 6,953,412 and U.S. Pat. No. 6,210,300 in that it incorporates rollers that can be positioned such that torque transmission in selected direction can be achieved. It also use a complex formed spring cage to position the rollers with respect to the cammed surfaces. 
         [0011]    State of the art lever drives, such as taught by U.S. Pat. No. 7,261,309, typically use a lever grip arrangement in which the grip interfaces for the user&#39;s hands are placed coaxially with the long axis of the lever. This arrangement is inherently biomechanically sub-optimal, in that it requires an unnecessarily large flexure of the wrist during the push/pull propulsion motion. Additionally, by using a rotation of the grip interface to effect forward/reverse shifting, it further causes the user wrists to be placed at non-optimal angles relative to the stress of pushing and pulling for propulsion. 
         [0012]    Consequently it may be seen that many inventions relating to lever drive wheelchair propulsion, and reversible clutching mechanisms utilizing rollers, springs, cages, and cammed surfaces are known. However, the specific biomechanical challenges of manual wheelchair propulsion by lever drive have not adequately addressed by the state of the art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present invention furthers the state of the art by providing a lever propulsion direction selection means for manual wheelchairs that allows improved biomechanics of directional control shifting, forward/reverse and reverse/forward. Operator directional control input through the pivoting of the propulsion lever handgrip uses intuitive pivoting motions which result in a reduced user training period and more confident control of the wheelchair. Precise control of wheelchair positioning is further improved by incorporation of simple brake operation means into the handgrip interface as a rotation of the handgrip. 
         [0014]    This pivoting handgrip directional shifting combined with brake operation by handgrip rotation allows the operator to maintain a non-changing- hand grip position such that propulsion movement of the levers may be comfortably simultaneous with direction shifting and braking. 
       OBJECTS OF THE INVENTION 
       [0015]    It is therefore an object of this invention to provide a wheelchair lever drive propulsion mechanism that addresses the shortcomings in the state of the art mentioned above. 
         [0016]    A further object of this invention is to provide a method to propel a wheelchair by means of a lever which can selectively rotate the wheelchair drive wheels either forward or reverse by the respective push or pull stroke of the lever, as well as a means to decouple the lever such that the wheelchair can freewheel, be propelled by conventional pushrims, or be moved by a caregiver. 
         [0017]    A further object of this invention is to provide a lever drive propulsion mechanism that does not increase the width of the wheelchair. 
         [0018]    A further object of this invention is to provide a lever drive propulsion mechanism that is positioned to the inside of the rear wheels of the wheelchair. 
         [0019]    A further object of this invention is to provide an ergonomically and biomechanically improved method of selecting the direction of lever drive wheelchair propulsion. 
         [0020]    A further object of the invention is to provide a reversible one-way roller clutch system that can be shifted from one direction of rotation to the reverse of that by a pivoting control movement of the lever handgrip. 
         [0021]    A further object of the invention is to provide a reversible one-way roller clutch system that provides a neutral position in which the clutch input and output elements can freewheel with respect to each other in either direction of rotation. 
         [0022]    Another object of the invention is to provide a spring urged shifting mechanism that will maintain the reversible clutch in constant engagement in either forward or reverse position. 
         [0023]    Another object of the invention is to provide a shifter over-travel compensation means that will protect the reversible clutch shifting mechanism from damage by shift input motions of excessive excursion and force. 
         [0024]    Another object of the invention is provide a handgrip by which by which a user of the invention can change the relative sense of the propulsion rotation, select a transmission neutral which decouples the levers from the propelling wheels, and can effect braking of the wheelchair. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE INVENTION 
         [0025]      FIG. 1  is a perspective view from the right side of a typical manual wheelchair frame with the lever drive system of this invention installed. 
           [0026]      FIG. 2  is a front view of a typical manual wheelchair frame with the lever drive system of this invention installed. 
           [0027]      FIG. 3A  shows the lever drive shifted from reverse propulsion. 
           [0028]      FIG. 3B  shows the lever drive system shifted for neutral. 
           [0029]      FIG. 3C  shows the lever drive system shifted for forward propulsion. 
           [0030]      FIG. 4  contains two perspective views of a left side lever drive system with some components removed for clarity in illustrating the shifting system. 
           [0031]      FIG. 5  is perspective view of the lever drive system with some components removed to illustrate the brake design. 
           [0032]      FIG. 6A  shows the reversible clutch detail with the clutch shifted to transmit CW torque while overrunning in the CCW direction. 
           [0033]      FIG. 6B  shows the reversible clutch detail with the clutch shifted to neutral position in which it will overrun in both CW and CCW directions. 
           [0034]      FIG. 6C  shows the reversible clutch detail with the clutch shifted to transmit CCW torque while overrunning in the CW direction. 
           [0035]      FIG. 7  is side view with a partial cutaway to illustrate adjustment of the brake cable. 
           [0036]      FIG. 8  shows two views illustrating the design of the shift overtravel compensation system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    With reference to  FIGS. 1 through 3 , a typical wheelchair  1  is shown with a preferred embodiment of the wheelchair lever drive system installed on a typical wheelchair frame. It can be seen that propulsion lever assemblies  32  are placed to the inside of rear drive wheels  2 . This position is preferable to outside placement as it allows handgrip assemblies  46  to be closer together side-to-side in an ergonomically advantageous position and does not increase the overall width of the wheelchair. It also makes the overall lever drive mechanism aesthetically less obtrusive, a feature shown by independent survey to be important to users. Lever propulsion motion arrows  13  indicate the approximate arc of reciprocating motion that the user would impart to lever assemblies  32  when propelling wheelchair  1 . 
         [0038]    With reference to  FIGS. 3A ,  3 B, and  3 C, a wheelchair user would grasp grip  4  and push or pull, thus imparting a propelling motion shown by arrow  13 , and could, as desired, impart a directional shift motion shown by circular arrow  8 . As shown by arrow  8 , the shift motion can be relatively either a CW pivot of grip  4  and grip mount  6  about the long axis of lever  7 , or CCW. A CW rotation  9  selects forward propulsion, and a CCW rotation  10  selects reverse propulsion. It may also be understood from this figure that for the user to comfortably shift directions, shift pivot motion  8  must be of small angular excursion so as to not overstress the user&#39;s wrist. Inherent to the transmission described in this invention, the handgrip central axis is fixed at an angle to the long axis of lever  7 , and offset laterally from the long axis such that pushing force applied to handgrip  4  causes a biasing resultant that tends to maintain the shifting mechanism in forward propulsion position. Conversely, pulling motions tend to maintain reverse propulsion position. 
         [0039]    In  FIG. 2  and  FIG. 5 , the braking movement of handgrip  4  and grip mount  6  are shown by curved arrow  5 . In a preferred embodiment, braking motion  5  is an inward rotation of handgrip  4  and grip mount  6  about a pivot axis in trunnion  11  placed at the top of lever  7 . This placement of grip mount  6  pivot axis causes the weight of the users forearm to impart a pivot motion in the opposite sense of brake motion  5  such that when not actively braking grip  4  and grip mount  6  are returned to a non-braking ready position. 
         [0040]      FIG. 4  shows a close-up view of left side lever assembly  32  with some components removed to better illustrate the shifting system. Curved arrow  13  indicates propulsion motion while curved arrow  8  illustrates the pivoting shift motion. Trunnion  11  and shift shaft  27  with associated grip mount  6  and hand grip  4  are rotatably fixed at the top end of lever  7 , itself fixed to the top end of lever mount  19  which is removably fixed to clutch cam  23  which is rotatably mounted by rotating bearings in wheel hub  14 , not shown. The shifting operations which will be described now can take place simultaneously with propulsion of the wheelchair as depicted by arrow  13 . Again with reference to  FIG. 4 , when forward propulsion is desired, a CW twisting pivot motion applied to handgrip  4  would cause grip mount  6 , trunnion  11 , and shift shaft  27  to rotate along with pawl  26  which is fixed to the lower end of shift shaft  27 . This CW pivot rotation of pawl  26  causes a rotation of clutch cage  24  and associated clutch rollers  25  about the periphery of clutch cam  23  such that propulsion torque resulting in forward motion is transmitted from lever assembly  32  to wheel hub  14 , not shown. While shifted as described above, motion of the lever assembly in the opposite direction would result in an overrunning of the clutch described, and allows a return motion of lever assembly  32  to ready it for the next forward propulsion motion. 
         [0041]    It may be understood that imparting a CCW twisting pivot shift input motion in place of the CW shift input motion just described will cause torque transmission to be of opposite sense to that described above and result in reverse propulsion. The arrangement is such that the sequence as described above is appropriate for use on both left and right sides of a wheelchair frame. 
         [0042]    With reference to  FIG. 5  a preferred embodiment of the braking motion of grip  4  and grip mount  6  is illustrated by curved arrow  5 . The braking operation which will be described now can take place simultaneously with wheelchair propulsion as depicted by arrow  13 . At any time during propulsion or at rest, handgrip  4  and grip mount  6  can be rotated inwardly as shown by arrow  5  such that cable  17  is pulled upwardly through cable sheath  16 . Cable sheath  16  is terminated at the upper end by a typical cable sheath socket  36 incorporated into the upper end of lever  7  and at the lower end by a typical cable sheath socket fixed to one of a pair of crossed brake band levers  20 . Brake cable  17  is adjustably fixed at the upper end to grip mount  6 . See  FIG. 7 . At the lower end cable  17  is fixed to one of a pair of crossed brake band levers  20 . It may be seen, then, that as braking input motion  5  pulls cable  17  upwardly through cable sheath  16 , crossed brake band levers  20  are drawn closer together causing brake band  15  to be constricted about the projecting braking portion  33  of wheel hub  14 , thus restraining rotation of wheel hub  14  relative to lever assembly  32 . 
         [0043]      FIGS. 6A ,  6 B, and  6 C illustrate the operation of the bidirectional clutch assembly of the invention. Note that  FIG. 4  illustrates the connection of grip  4  and grip mount  6  to clutch cam  23 . In  FIG. 6A  moveable clutch cage  24  is rotated slightly CCW from neutral such that rollers  25  are placed to transmit CW torque from clutch cam  23 , indicated by dotted lines as a  12  sided polygon, to wheel hub  14 . In  FIG. 6B  clutch cage  24  is shown in a neutral position such that torque is not transmitted in either direction, and wheel hub  14  can turn independently of lever assembly  32 . In  FIG. 6C  clutch cage  24  is shown shifted slightly CW from neutral such that rollers  25  are placed to transmit CCW torque from clutch cam  23  to wheel hub  14 . 
         [0044]      FIG. 7  shows the upper end of flexible brake cable  17  with cable end button  35  terminated in cable adjuster  12  axially adjustable within grip mount  6 . In a preferred embodiment, cable adjuster  12  comprises a socket with an outside threaded portion and an inside hole with a slot by which cable  17  and cable end button  35  can be installed. Cable sheath  16  is shown terminated in upper cable socket mount  36 . Rotation of threaded cable adjuster  12  in grip mount  6  results in axial movement of cable  17  such that brake band  15  can be adjusted for proper operation. 
         [0045]    With reference to  FIG. 8A , a centerline cutaway about the long axis of lever assembly  32  shows the trunnion rotation limiter arrangement. Also in  FIG. 8A  are shown view A-A crosswise cutaway sections illustrating the shifting components first in a neutral position and then with trunnion  11  rotated through the full trunnion excursion “a”. A shift detent mechanism is provided that will bias the shifting mechanism to maintain either forward or reverse propulsion positions. The twisting pivot motion describes allows the detent to be overcome such that a shift to different propulsion mode can be effected. Shift detent balls  38  urged by associated shift detent springs  39  engage a plurality of shift detents  40 . Detents  40  are provided corresponding to reverse, neutral, and forward shift positions. In view A-A detent ball  38  can be seen engaged in center position detent  40  by spring  39 , thus holding trunnion  11  in a center position corresponding to neutral. In upper view A-A trunnion  11  is shown rotated through angle “a” about cylindrical trunnion arbor portion  37  and is held in that position by the engagement of ball  38  in the associated corner detent  40 . Trunnion arbor portion  37  also incorporates angled flank portions  45  act to limit the rotational excursion of trunnion  11  to angle “a”. In  FIG. 8B  shift shaft  27  with flatted tang portion  41  is shown with associated shift overtravel compensator springs  42  placed to either side. Springs  42  are retained and adjustably compressed by adjusting screws  44 . Spring buttons  43  may optionally be employed to ameliorate the contact between the face of springs  42  and shift shaft tang  41 . In view B-B of  FIG. 8B , are shown crosswise section views depicting the shifting components first in a neutral position and then with trunnion  11  rotated through the full trunnion excursion “a”. In this view the angle necessary to accomplish shifting of reversible clutch cage  24  from neutral to either forward or reverse is indicated at “b”. Angles “a” and “b” are chosen such that “b” is less than “a” so that rotation of trunnion  11  through angle “a” will first rotate shift shaft  27  through angle “b” and then further rotation of trunnion  11  will cause shift overtravel compensator springs  43  to be compressed. This compression of springs  43  has the effect of making the interaction of the shifting components less critical, and to protect the shifting components from the high forces applied to the hand grip and lever assembly during propulsion. It also has the effect of causing trunnion  11 , when detented at angle “a”, to maintain a spring generated torque reaction on tang portion of  41  of shift shaft  27 . This torque applied to shift shaft  27  has the effect of maintaining a controlled torque which acts to urge clutch cage  34  such that it is firmly but compliantly maintained in either reverse or forward position.