Patent Publication Number: US-7717447-B2

Title: Propulsion aid

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority filing benefit of International PCT Application PCT/GB2004/003848 filed Sep. 9, 2004, and published under PCT 21(2) in the English language; Great Britain Patent Application Serial No. 0321474.9 filed Sep. 12, 2003; and Great Britain Patent Application Serial No. 0406148.7 filed Mar. 18, 2004. 
   The present invention relates to an apparatus and method for propelling a vehicle. More specifically, but not exclusively, the apparatus and method relate to a propulsion aid for use with a wheelchair. 
     FIGS. 1   a  and  1   b  show a known method for propelling a wheelchair. The wheelchair  4  is provided with a seat for use by a wheelchair user  2 , a pair of front wheels  6  and a pair of rear wheels  8  notably mounted to the wheelchair about an axle  12 . An annular ring  10 , known as a hand rim  10 , is fixedly attached to each of the rear wheels  8 , in such a way that the hand rim  10  is concentric with the wheel. 
   To facilitate movement of the wheelchair the wheelchair user  2  grips the hand rim  10  at a point substantially vertically above the axle  12  of the rear wheels  8 , as shown in  FIG. 1   a . The user  2  then rotates the hand rims  10  in a forward direction. Since the hand rims  10  are fixedly attached to the rear wheels  8 , rotation of the hand rims  10  causes rotation of the rear wheels of the wheelchair  4  in a forward direction. When the rear wheels  8  have moved through an angle of anything up to approximately 120°, the wheelchair user  2  releases his grip on the hand rims  10 . The precise angle will vary depending on a number of factors, including; the range of movement of the wheelchair user, the desired speed of movement and any incline being ascended or descended.  FIG. 1   b  illustrates the end point of the motion. When the user  2  releases his grip, the wheelchair  4  may continue to freewheel. To achieve continuous propulsion, the wheelchair user  2  returns to the beginning of the cycle and again grips the hand rims  10  above the axle  12  as shown in  FIG. 1   a , and repeats the motion described above. 
   To provide backwards motion, the wheelchair user  2  performs the reverse of the above motion, gripping the hand rims  10  at the point illustrated in  FIG. 1   b  and rotating them towards the position shown in  FIG. 1   a.    
   If the wheelchair user  2  wants to turn the wheelchair  4 , he grips one hand rim  10  at the end of the motion and the opposing hand rim  10  at the start of the motion. The hand rims  10  are then rotated in opposite directions and the wheelchair  4  turns accordingly. 
   To reduce the velocity of the wheelchair  4 , or to stop the motion of the wheelchair, the user  2  grips the hand rims  10  as they rotate. This process introduces friction to the hand rims  10  and slows the wheelchair  4 . If the grip is not released this action will eventually result in the wheelchair coming to a halt. 
   As will be appreciated, a great deal of upper body strength is required for a wheelchair user  2  to manoueuvre the wheelchair  4 . Consequently, a wheelchair user  2  suffering from certain conditions, such as cerebral palsy, may be unable to propel a wheelchair  4  of this type. Furthermore, because a large amount of force may be required to propel the wheelchair  4 , in particular when ascending inclines, the wheelchair user  2  may quickly become exhausted. Another problem is that since the wheelchair user  2  needs to adjust their grip on the hand rim  10  between the start and end of the motion they may get their fingers caught in the rear wheel  8 , resulting in injury. In addition, the hands may suffer abrasion, or become dirty, from gripping the hand rims  10 . An additional problem is that wheelchair users lacking grip strength, for example arthritis sufferers, may not be able to grip the hand rim sufficiently to transmit sufficient torque to the wheels 
   In an attempt to overcome these problems a number of designs have been suggested which provide an alternative propulsion mechanism. 
   One such design is shown in U.S. Pat. No. 5,988,661, in which there is described a device for manually propelling a wheelchair. The device comprises a drive arm which is mounted to the wheel of the wheelchair so as to be manually pivotable by the wheelchair user about a pivot axis coincident with the axis of rotation of the wheel. The drive arm is mounted to the rear axle using an extended axle bolt, which replaces the originally provided axle bolt. However, one disadvantage of having to remove the original axle bolt is that axle dimensions differ between different designs of wheelchair the receiving aperture in the drive arm cannot be universally applicable. A second disadvantage is that it is not possible for the wheelchair user to be seated in the wheelchair while the drive arm is being fixed in place. A yet further disadvantage is that when the rear axle is removed, the wheels will require realigning and this may take some time. It is even possible that, since wheelchairs are subject to stringent regulatory controls, the replacement of an axle bolt will not be permitted if the wheelchair is to comply with the necessary regulatory controls. It would therefore be desirable to provide a mechanism which overcomes these disadvantages whilst still providing an improved propulsion device. 
   In GB-A-2278582 an alternative design is described in which a drive disc is fastened to the rear wheel of a wheelchair by a circular plate and a cylindrical casing. The cylindrical casing is attached to the spokes of the rear wheel by means of a plurality of chucks. These chucks project from an inner facing wall of the cylindrical casing and each receives a spoke of the rear wheel. After the chucks have been mounted to the spokes they are fastened using screws thereby firmly retaining the cylindrical casing to the wheel. As the drive disc is rotated, either by hand or by an insertable lever, torque is transferred to the spokes of the wheel causing the wheel to rotate. Although this design avoids the problem of the device being attached to the rear axle, it nevertheless produces forces on the spokes which they were not designed to withstand. In particular, the application of excessive torque may lead to buckling of the spokes. As will be appreciated, an alternative method of attaching an enhanced propulsion mechanism is required. 
   Broadly speaking, existing designs for providing enhanced propulsion to wheelchairs use one of two mechanisms for transmitting torque from a drive arm to the rear drive wheel. In the first group, a driving block transmits torque to the tyre of the rear wheel. For example, in GB-A-2213438 a device is described in which a driving block is pivotally mounted on a drive arm so that it is selectively engageable with the tyre of the rear wheel. Thus, pivoting the drive arm, with the driving block engaged on the tyre, rotates the wheel and propels the wheelchair. Similarly, U.S. Pat. No. 5,232,236 provides a leveraged hand propeller comprising a tyre engaging gripper (driving block) which, when engaged with the tyre, transmits sufficient torque to rotate the rear wheel. 
   An alternative means of transmitting torque is by providing a mechanism which engages with the hand rim of the rear wheel rather than with the tyre. In U.S. Pat. No. 5,988,661 there is described a mechanism comprising friction pads which, when hand pressure is applied to the drive arm, engage with the hand rim. Thus, when the drive arm is pivoted in a forward direction, torque is transmitted to the hand rim and the wheel rotates. In an alternative design described in WO 98/03142 there is provided a propulsion assembly which includes a lever arm and a crank handle at the end of the lever arm. The crank handle further comprises friction pads for engaging the hand rims of the wheelchair. When the occupant of the wheelchair applies a force in a forward direction relative to the wheelchair frame the friction pads come into contact with the hand rims. Continued forward motion causes the hand rims to move in a forward direction and the wheelchair will advance. 
   There are a number of problems associated with both of the above methods. Firstly, neither the tyres nor the hand rims were designed to be subjected to the frictional forces required to transmit sufficient torque to cause rotation of the rear wheels. There is therefore a risk that the force applied through the driving blocks/frictional pads will damage these components. In particular, the hand rims are not usually fixed to the wheel in such a way as to withstand the rotational and frictional forces required to produce rotation of the rear wheels in this manner. In addition, the hand rims and tyres may suffer severe wear from the frictional pads which may in turn compromise the functionality of the wheelchair. Excess wear will also result in the components requiring more frequent replacement than would otherwise be necessary. It would therefore be desirable to provide an enhanced propulsion mechanism which overcomes the problems associated with the prior art methods of torque transmission. 
   A number of designs have been previously disclosed which are able to provide propulsion in both the forward and reverse directions. WO 98/03142 describes a manual propulsion assembly in which the top of the lever arm provides a hand grip which can be rotated between a first position to provide forward motion and a second position to provide rearward motion. However, constant pressure is required to maintain the frictional pad in contact with the tyre during either forward or rearward motion while, in order to return the lever arm to the starting position, it is necessary to release this pressure. This means that frequent movement of the wrist is required to engage and disengage the frictional pads. In addition, wrist strength is required to maintain the frictional pad in contact with the tyre to enable torque transmission. Similarly, U.S. Pat. No. 5,988,661 describes an assembly where a wheelchair user is required to apply hand pressure to the drive arm to force the frictional pads into contact with the hand rim of the wheelchair. In order to allow the drive arm to return to the start of its travel the hand pressure is released from the lever. Therefore, once again a repeated gripping motion is required to actuate the device. One problem in using such devices is that the repeated gripping motion may cause repetitive strain injury in users. It is also possible that wheelchair users may not have sufficient hand or wrist strength to enable them to provide the necessary pressure for engagement of the frictional pads with either the tyres or the hand rims. It would therefore be desirable to provide an improved mechanism which does not require so much strength in the hands or wrist of the wheelchair user and which reduces the risk of repetitive strain injury. 
   In addition, it would also be desirable to provide a handle which provides enhanced hand/arm ergonomics during use of the propulsion apparatus. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention there is provided a propulsion apparatus mountable to a vehicle, the vehicle comprising at least one ground engaging wheel having an axis of rotation and the propulsion apparatus comprising; a first portion adapted to be statically attached at a location remote from said axis to either a rim of said wheel or to a structural member projecting from a plane defined by said wheel, the structural member being rigidly attached to the wheel; a second portion pivotal about an axis coincident with said rotational axis of said wheel; and coupling means interposed between said first and second portion such that pivotal movement of said second portion about said axis causes said first portion to rotate thereby propelling the vehicle. 
   Preferably the first portion carries means for location of said second portion such that the axis of rotation of the second portion is coincident with the axis of the wheel. 
   According to a second aspect of the present invention there is provided a propulsion apparatus for a vehicle, the vehicle comprising at least one ground engaging wheel and the propulsion apparatus comprising: a first portion adapted to be mounted to or formed integrally with the wheel; a second portion drivingly connected to said first portion and pivotable about an axis coincident with a rotational axis of said wheel; one of said first and second portions comprising a continuous contact surface; and coupling means carried by either the first or the second portion and selectively engageable with said continuous contact surface such that, when engaged, pivotal movement of the second portion about said axis causes said first portion to rotate thereby propelling the vehicle. 
   In one embodiment the first portion comprises the continuous contact surface and the coupling means is carried by the second portion. 
   In an alternative embodiment the second portion comprises the continuous contact surface and the coupling means is carried by the second portion; and said apparatus further comprises means to key the contact surface with respect to the first portion. 
   According to a third aspect of the present invention there is provided a wheel of a vehicle comprising: a first portion statically mounted to or formed integrally with said wheel, the first portion comprising a lever arm receiving portion and a continuous contact surface, the lever arm receiving portion being adaptable to receive a lever arm such that the lever arm is pivotable about an axis coincident with an axis of rotation of said wheel; the continuous contact surface being adapted to be selectively engageable with coupling means carried by said lever arm such that, when engaged, pivotal movement of the lever arm about said axis causes the wheel to rotate thereby propelling the vehicle. 
   According to a fourth aspect of the present invention there is provided a propulsion apparatus mountable to a vehicle, the vehicle comprising at least one ground engaging wheel and the propulsion apparatus comprising a first portion adapted to be mounted to the wheel or formed integrally therewith; a second portion comprising a lever arm pivotable about a first axis coincident with a rotational axis of the wheel; and coupling means interposed between said first and second portions such that pivotal movement of said lever arm about said first axis causes said first portion to rotate thereby propelling the vehicle; the lever arm having a handle pivotable about a second axis transverse to a longitudinal axis of the lever arm so as to provide an ergonomic hand movement for a user. 
   Advantageously the first portion or the second portion has a continuous contact surface and the coupling means is carried by either the first portion or the second portion, the coupling means being selectively engageable with the continuous contact surface such that, when engaged, pivotal movement of the second portion about said axis causes said first portion to rotate thereby propelling the vehicle. 
   Advantageously the first portion is adapted to be statically attached at a location remote from said axis to either a rim of said wheel or to a structural member projecting from a plane defined by said wheel, the structural member being rigidly attached to the wheel. 
   Preferably the second portion comprises a lever arm. 
   More preferably the lever arm comprises a handle, the handle being pivotable about an axis transverse to a longitudinal axis of the lever arm, so as to provide an ergonomic hand movement for a user. 
   Preferably the first portion is statically attached to the wheel at discrete locations. 
   Preferably the first portion is statically attached to said wheel by a plurality of attachment spokes, said attachment spokes being radially extendable from a central hub. 
   More preferably, said attachment spokes are provided at an end remote from said hub with a respective channel shaped member adapted to at least partially receive said rim or structural member. 
   In one configuration the channel shaped members preferably include a deformable insert adapted to conform under compression to the shape of said rim or structural member. 
   Preferably the deformable insert is formed of a high friction material. 
   Advantageously the attachment spokes are pivotally connected at a radially inner end to a respective intermediate member and said intermediate members are pivotally connected to a hub mounted actuating member at circumferentially spaced locations, the attachment spokes being constrained for radial motion such that rotation of the actuating member causes the attachment spokes to extend or retract depending on the sense of the rotation and the extent of rotation of the actuating member may be limited by the engagement of a projection within a slot. 
   In a preferred embodiment in moving the attachment spokes from a retracted position to a fully extended position, the location at which each intermediate member is pivotally connected to the actuating member moves circumferentially past the location at which the same intermediate member is pivotally connected to the associated attachment spoke such that the attachment spokes are retained in the fully extended position by means of an over-centering arrangement. 
   Advantageously, the second portion is releasably connectable to said first portion. 
   Preferably the coupling means comprises rolling support means adapted to frictionally engage the continuous contact surface. 
   In a preferred embodiment when the second portion is pivoted about said axis in a first direction, the rolling support means is selectable to frictionally engage the continuous contact surface to cause the rotation of the first portion in one sense and, when the second portion is pivoted about said axis in a second direction, opposite to said first direction, the rolling support means is selectable frictionally engage the continuous contact surface and cause the rotation of the first portion in an opposite sense. 
   Advantageously, the coupling means comprises a pair of drive surfaces disposed on opposite sides of a pivot such that only one of said drive surfaces may be brought into frictional engagement with the continuous contact surface at a time. 
   Preferably as the second portion is pivoted about said axis, the engagement of one of said pair of drive surfaces with the continuous contact surface causes the rotation of the first portion in a first sense while the engagement of the other of said pair of drive surfaces with the continuous contact surface causes the rotation of the first portion in the opposite sense. 
   More preferably one of said pair of drive surfaces is biased towards the continuous contact surface in preference to the other, the biased drive surface engaging the continuous contact surface to propel the vehicle in a forward direction upon pivotal movement of the second portion about said axis. The biasing of said one of said drive surfaces may be overcome by selective manipulation of a handle and the handle may be adapted so that said manipulation is by the rotation of said handle about a longitudinal axis of said lever arm. 
   Advantageously each drive surface is associated with a respective rolling support means, the rolling support means contacting the continuous contact surface when said associated drive surface is in the proximity of the continuous contact surface, the rolling support means and associated drive surface being coupled such that the drive surface frictionally engages with the continuous contact surface when the associated rolling support means is rotated in a first direction and disengages the continuous contact surface when the associated rolling support means is rotated in an opposite direction. 
   Preferably a second pair of drive surfaces disposed on opposite sides of a second pivot, the two pairs of drive surfaces being pivotally interconnected so as to form a parallelogram-type mechanism in which diagonally opposite drive surfaces move together into and out of frictional engagement with the continuous contact surface. 
   In a preferred embodiment, the second portion comprises two or more parts, at least one of the parts being releasably connectable to said other parts. 
   Advantageously the invention also provides a variable drive ratio of propulsion speed of the vehicle to power input by a user of said vehicle. In a preferred embodiment the lever arm is adapted to have a working length that is selectively adjustable such that as the working length of the lever arm is adjusted a drive ratio of propulsion speed of the vehicle to power input by a user of said vehicle is varied. 
   Advantageously, the lever arm is collapsible from an in use configuration to a stored configuration such that when collapsed said lever arm has a radial extent less than the radius of said wheel. 
   Preferably at least a part of said lever arm is adapted to collapse telescopically. 
   Alternatively or additionally the lever arm may further comprise a hinge at a location spaced radially inwardly of the rim of the wheel. 
   In a preferred embodiment the handle of the lever arm comprises an arcuate housing fixedly attached to one end of the lever arm and a D-shaped grip comprising an arcuate portion slidably received within the arcuate housing and a grip portion external of the arcuate housing and interconnecting opposite ends of the arcuate portion. 
   Preferably the handle rotates inwardly to provide a means of selectively engaging and disengaging said coupling means. 
   Advantageously the second portion further comprises a brake, said brake comprising at least one braking surface moveable between an operable position, in which the braking surface engages the continuous contact surface to slow rotation, and an inoperable position, in which the braking surface is not so engaged; and means for selectively moving said braking surface between said operable and inoperable positions. Preferably the means for activating said brake are provided on said handle. 
   In a preferred embodiment the handle is movable about the axis transverse to the longitudinal axis of the lever arm such that movement of the handle to an activating position provides the means for activating said brake. Alternatively, the braking means are provided on said lever arm, said lever arm being inwardly pivotable such that said braking means is brought into contact with said wheel or said structural member. 
   According to a fifth aspect of the present invention there is provided a vehicle having at least one ground engaging wheel and a propulsion apparatus as previously discussed. 
   Preferably a separate propulsion apparatus is provided on opposite sides of said vehicle. More preferably the vehicle is a wheelchair. 
   According to a sixth aspect of the present invention there is provided a lever arm for use with a vehicle, the vehicle comprising at least one ground engaging wheel and a lever arm receiving portion statically mounted to or formed integrally with said wheel, one of said lever arm and said lever arm receiving portion comprising a continuous contact surface, said lever arm being detachably mountable to said lever arm receiving portion, so as to be pivotable about an axis coincident with an axis of rotation of said wheel and carrying coupling means selectively engageable with said continuous contact surface such that, when engaged, pivotal movement of the lever arm about said axis causes the wheel to rotate thereby propelling the vehicle. 
   Advantageously the lever arm comprises a handle pivotal about a second axis transverse to a longitudinal axis of said lever arm so as to provide an ergonomic hand movement for a user. 
   Advantageously the lever arm is releasably connectable to said lever arm receiving portion. 
   The lever arm may carry coupling means in any form previously described. 
   Preferably the lever arm comprises two or more parts, one of said parts being releasably connectable to said other parts. 
   Advantageously the lever arm is adapted to have a working length that is selectively adjustable such that as the working length of the lever arm is adjusted a drive ratio of propulsion speed of the vehicle to power output by said user of said vehicle is varied. 
   Advantageously the lever arm as claimed in any of claims  45  to  49 , wherein said lever arm is collapsible from an in use configuration to a stored configuration such that when collapsed said lever arm has a radial extent less than the radius of said wheel. 
   In a preferred embodiment at least a part of said lever arm adapted to collapse telescopically. Alternatively or additionally the lever arm further comprises a hinge at a location spaced radially inwardly of the rim of the wheel. 
   Preferably the handle comprises an arcuate housing fixedly attached to one end of the lever arm and a D-shaped grip comprising an arcuate portion slidably received within the arcuate housing and a grip portion external of the arcuate housing and interconnecting opposite ends of the arcuate portion. 
   Preferably the handle rotates inwardly to provide a means of engaging and disengaging said coupling means. 
   Advantageously the lever arm further comprises a brake, said brake comprising at least one braking surface moveable between an operable position, in which the braking surface engages the continuous contact surface to slow rotation, and an inoperable position, in which the braking surface is not so engaged; and means for selectively moving said braking surface between said operable and inoperable positions. Preferably the means for activating said brake are provided on the handle. More preferably the handle is moveable about the axis transverse to the longitudinal axis of the lever arm such that movement of the handle to an activating position provides the means for activating said brake. 
   Alternatively braking means are provided on said lever arm, said lever arm being inwardly rotatable such that said braking means is brought into contact with said wheel or a structural member positioned from the plane of said wheel. 
   According to a seventh aspect of the present invention there is provided a method of propelling a vehicle, the method comprising the steps of: 
   a) providing a propulsion apparatus as claimed in any of claims  1 ,  3 ,  6  or  7 ; 
   b) connecting said propulsion apparatus to said wheel; 
   c) pivoting said second portion of the propulsion apparatus such that said first portion of the propulsion apparatus is rotated, thereby rotating the wheel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIGS. 1   a  and  1   b  show a wheelchair user propelling a wheelchair according to a known method; 
       FIG. 2  shows a perspective view of a rear wheel of a wheelchair in combination with a propulsion apparatus, the propulsion apparatus being in accordance with a preferred embodiment of the present invention; 
       FIG. 3  shows a perspective view of a first embodiment of a hub portion of a propulsion apparatus according to the present invention; 
       FIG. 4   a  shows a rear view of the hub portion of  FIG. 3 , with a back plate of the hub portion removed and an actuating disc shown in ghost; 
       FIG. 4   b  shows an exploded view of the hub portion of  FIG. 3 ; 
       FIG. 5  shows a perspective view of a tool for use with the actuating disc of  FIG. 4   a;    
       FIG. 6   a  shows a sectional view through a trough shaped moulding in contact with a rim of the rear wheel; 
       FIG. 6   b  shows a sectional view of the trough shaped moulding of  FIG. 6   a  not in contact with the rear wheel; 
       FIG. 7  shows a perspective view of a further embodiment of a hub portion, formed integrally with a wheel, of a propulsion apparatus according to the present invention; 
       FIG. 8  shows a perspective view of second component of the propulsion apparatus according to the present invention; 
       FIG. 9   a  shows a front view of a propulsion apparatus according to the present invention and having a partially removable lever arm part; 
       FIG. 9   b  shows a front view of the removable lever arm part of  FIGS. 9   a  and  9   c;    
       FIG. 9   c  shows a front view of a wheel according to the present invention having an integral lever arm receiving portion and a lever arm portion which has a part of the lever arm being removable; 
       FIG. 10   a  shows a further embodiment of a propulsion apparatus having a partially removable lever arm part; 
       FIG. 10   b  shows a front view of the removable lever arm part of  FIGS. 10   a  and  10   c;    
       FIG. 10   c  shows a front view of a wheel according to a further embodiment having an integral lever arm receiving portion and a lever arm portion which has a part of the lever arm being removable; 
       FIG. 11   a  shows a side view of a propulsion apparatus having collapsible lever arm in an operable position; 
       FIG. 11   b  shows a side view of the propulsion apparatus of  FIG. 11   a  with the lever arm in a stored position; 
       FIG. 12  shows a catch for securing the lever arm of  FIGS. 11   a  and  11   b  in the stored position; 
       FIG. 13  shows a perspective view of a drive mechanism according to the present invention; 
       FIG. 14  shows a plan view of the drive mechanism of  FIG. 13  with a front plate of the drive mechanism removed for clarity; 
       FIG. 15  shows a pin block assembly contained within a lever arm according to the present invention, with the outer casing of the arm removed for clarity; 
       FIG. 16  shows a detailed view of a pin arrangement contained within the drive mechanism of  FIG. 13 ; 
       FIG. 17  shows a perspective view of the drive mechanism of  FIG. 3  when inserted in the second component of the propulsion apparatus shown in  FIG. 7 ; 
       FIG. 18  shows an exploded view of a jammer assembly of the drive mechanism shown in  FIG. 13 ; 
       FIG. 19   a  shows a plan view of an upper surface of the jammer shown in  FIG. 18 ; 
       FIG. 19   b  shows a plan view of the underside of the jammer shown in  FIG. 18 ; 
       FIG. 19   c  shows a section A-A through the jammer of  FIG. 19   b;    
       FIG. 20  shows a perspective view of the jammer assembly of  FIG. 18  when assembled; 
       FIGS. 21   a  and  21   b  show, in more detail, the drive mechanism of  FIG. 13  when attached to the hub portion of  FIG. 3 ; 
       FIGS. 22   a - d  show the approximate orientation of the propulsion apparatus of  FIG. 2  throughout a cycle,  FIG. 22   a  depicting approximately the start of a cycle and  FIG. 22   d  depicting approximately the end of a cycle; 
       FIG. 23  shows an exploded side view of a propulsion apparatus according to the present invention; 
       FIG. 24  shows an exploded side view of a propulsion apparatus according to an alternative embodiment of the present invention; 
       FIG. 25   a  shows a front view of a lever arm portion according to the present invention having an alterable length; 
       FIG. 25   b  shows the lever arm portion of  FIG. 25   a  with an altered length; 
       FIG. 26  shows a detailed view of the lever arm portion of  FIGS. 25   a  and  25   b;    
       FIG. 27   a  shows a detailed view of the internal working of the lever arm portion of  FIGS. 25   a  and  25   b  in a clamped position; 
       FIG. 27   b  shows a detailed view of the internal working of the lever arm portion of  FIGS. 25   a  and  25   b  in an operable position; 
       FIG. 28   a  shows a detailed side view of a handle of the propulsion apparatus of  FIG. 2  at approximately the start of a cycle; 
       FIG. 28   b  shows a detailed side view of the handle of the propulsion apparatus of  FIG. 2  at approximately the end of a cycle; 
       FIG. 29  shows a section C-C through a Cantilever Roller as shown in  FIG. 28   a;    
       FIG. 30  shows a section through the handle of  FIGS. 28   a  and  28   b , with the handle in a fully extended position; 
       FIG. 31  shows a perspective rear view of the drive mechanism of  FIG. 9 ; and 
       FIGS. 32   a  and  32   b  show a braking mechanism according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION 
   As previously discussed,  FIGS. 1   a  and  1   b  show a wheelchair  4 , which is provided with a seat for use by a wheelchair user  2 , a pair of front wheels  6  and a pair of rear wheels  8  rotatably mounted to the wheelchair about an axle  12 . The wheelchair  4  shown in  FIGS. 1   a  and  1   b  is also provided with a pair of hand rims  10 . 
     FIG. 2  shows a rear wheel  8  of a wheelchair  4  in combination with a propulsion apparatus  20  in accordance with the present invention. 
   The propulsion apparatus  20  comprises a hub portion  22  and a second portion  23 . The second portion  23  comprises a drive mechanism containment portion  70 , a lever arm  140  and a handle  160  at an end of the lever arm remote from the drive mechanism containment portion. 
   Although the propulsion apparatus  20  may be formed separately from the wheel, thereby enabling the propulsion apparatus to be retrofitted to existing wheelchairs, it will be understood that in other embodiments the propulsion apparatus may be formed as part of the wheel assembly so as not to be separable therefrom. 
     FIG. 3  shows the hub portion  22  without the second portion  23  attached. As can be seen, the hub portion  22  comprises a circular aperture  24 , bounded by an outwardly extending cylindrical wall  26 . The hub portion  22  is positioned such that the centre of the aperture  24  lies on an axis defined by the axle  12  of the rear wheel  8 . An annular flange  28  extends radially outwardly from the cylindrical wall  26  and merges with an outwardly extending annular hub rim  30 , defined by a radially inner surface  32  and a radially outer surface  34 . The radially inner surface  32  is connected to the radially outer surface  34  by a rim surface  36 . While the hub rim  30  is concentric with the cylindrical wall  26 . 
   The hub portion  22  further comprises a plurality of hub attachment spokes  38 . Each hub attachment spoke  38  comprises a base portion  40  and an attachment arm  42 , the base portion being formed integrally with and merging with the outer surface  34  of the hub portion  22 . The attachment arm  42  is carried by the base portion  40  and extends radially outwardly therefrom to terminate in a trough shaped moulding  44  remote from the hub portion  22 . 
   An example of a suitable mechanism for attaching the hub part  22  to the rear wheel  18  is shown in  FIGS. 4   a  and  4   b . In this example an actuating disc  48  is provided in the hub portion  22  and is located on an outwardly facing surface  29  of the flange  28 . As shown in  FIG. 4   b , the actuating disc  48  has projections  49  which extend inwardly from a rear surface  51  of the actuating disc towards the hub portion  22 . Although three projections  49  are shown, it will be understood that the number of projections may vary depending on the number of attachment arms  42 . Turning to  FIG. 4 , the flange  28  is provided with a number of cutout sections  53  arranged circumferentially about the central axis. Although the cutout sections  53  are shown to have an arcuate form it will be understood that they may take other forms and may, for example be rectangular cutouts and arranged tangentially at spaced locations about a circumference. Although there are six cutout sections  53  shown in  FIG. 4   a , it will be understood that the number of cutout sections may vary. For example, there may be three cutout sections  53  corresponding to the three attachment arms  42 . The projections  49  extend through a respective one of the cutout sections  53  where upon they are pivotally connected to one end of a respective projecting plate  50 . Each projecting plate  50  acts as a first toggle plate and the number of projecting plates  50  correspond to the number of hub attachment spokes  38 . Each projecting plate  50  is pivotally connected at an end remote from the projection  49  to a respective one of the attachment arms  42  using a toggle joint  54 . The attachment arms  42  are constrained to reciprocate in a radial direction by a restraining guide  56  provided within the base portion  40 . The actuating disc  48  further comprises circumferentially spaced tool location apertures  52  which are adapted to receive a corresponding number of tool projections  66  of a tool  60  shown in  FIG. 5 . Although three tool location apertures  52  are shown, it will be understood that the number and spacing of these tool location apertures may vary. 
   The tool shown in  FIG. 5  is made of a one piece construction and is sized to fit within the hub rim  30 . The tool  60  comprises a handle  62  and a body  64  having a central aperture  65 . The aperture  65  is sized to allow the cylindrical wall  26  of the hub portion  22  to protrude therethrough when the tool  60  is being used to attach the hub portion  22  to the rear wheel  8 . A plurality of tool projections  66  are provided to correspond with the tool location apertures  52  provided in the actuating disc  48 . 
   A trough shaped moulding  44  provided at one end of an attachment arm  42  is shown in more detail in  FIGS. 6   a  and  6   b .  FIG. 6   a  shows a section through the trough shaped moulding  44  prior to the moulding being brought into contact with an inner rim  14  of the rear wheel  8 . The trough shaped moulding  44  may be designed to correspond to the shape of a specific inner rim  14 . However, to provide enhanced attachment characteristics and to negate the requirement for a specifically shaped moulding, the trough shaped moulding  44  is preferably provided with a moulding insert  46  which is made of a material capable of conforming to the shape of the inner rim  14 . Preferably the moulding insert  46  is formed of a high-friction material such as polyurethane to provide enhanced attachment properties. The moulding insert  46  may be retained within the trough shaped moulding  44  by any known means such as, for example, by means of an adhesive. Alternatively or in addition the moulding insert  46  may be keyed into the trough shaped moulding  44 . In another arrangement, the moulding insert  46  may simply be placed in position prior to use thereby relying on the high friction characteristic of the material for the retention of the insert within the moulding. 
     FIG. 6   b  shows the trough shaped moulding  44  in contact with the inner rim  14  of the rear wheel  8  and under compression. It will be noted that the moulding insert  46  has taken up a shape which conforms to the inner rim  14 . 
   The method of attaching the hub portion  22  to the rear wheel  8  will now be described with reference to  FIGS. 4 to 6 . 
   In order to attach the hub portion  22  to the rear wheel  8  the tool  60  is orientated such that the projections  66  are received within the tool location apertures  52  and the cylindrical wall  26  is received within the aperture  65 . The hub portion  22  and tool  60  are then offered up to the rear wheel of a wheelchair so that the axle  12  passes through or else is aligned with circular aperture  24 . The tool  60  is then rotated in the direction shown by arrow A in  FIG. 4   a . As the actuating disc  48  rotates it actuates the toggle joints  54  causing the constrained attachment arms  42  to slide in a radially outwardly direction with respect to the base portions  40 . As the attachment arms  42  extend radially outwardly the trough shaped mouldings  44 , and the moulding inserts  46  contained therein, are brought into contact with the inner rim  14  of the rear wheel  8 . The contact force between the attachment arm  42  and the wheel  8  causes the moulding insert  46  to conform to the shape of the inner rim  14 . The tool  60  is then removed and the over-centering effect of the toggle joints  54  retains the attachment arms  42  in the extended position, thereby selectively retaining the hub portion  22  with respect to the rear wheel  8  and maintaining the moulding inserts  46  in static contact with the inner rim  14 . 
   The hub portion  22  may be removed from the wheel  8  by inserting the tool  60  and rotating the actuating disc  48  in the opposite direction to return the attachment arms  42  to their retracted positions. 
   Although the hub portion  22  is shown as having three hub attachment spokes  38 , regularly spaced at 120° intervals, it will be apparent that the number and spacing of the hub attachment spokes can be varied and still provide a suitable fixation to the inner rim  14  of the rear wheel  8 . Likewise, it will be apparent that the hub portion  22  may alternatively be attached to the hand rim  10  using the same method as described above. In this alternative, the trough shaped moulding  44  will be sized to fit around an inner rim  11  of the hand rim  10 . 
   As stated previously, in another embodiment the propulsion apparatus  20  may be permanently attached to the rear wheel  8  of the wheelchair  4 . Under such circumstances the hub attachment spokes  38  may be formed integrally with the wheel rim  14  or permanently attached using a method such as welding. It will also be apparent that other methods of releasably attaching the hub portion  22  to the inner rims  14  or  11  are envisaged, for example by the use of screws. In any event, the hub portion  22  may be incorporated in the wheel design and permanently attached to the wheel. 
     FIG. 7  shows an embodiment of the present invention where a propulsion apparatus  120  is formed as part of the wheel assembly. Since many features of the propulsion apparatus  120  are comparable to those of propulsion apparatus  20 , the same reference numerals will be used with the stem numeral ‘1’ being used to indicate this embodiment. 
   This embodiment differs from the previously discussed embodiments in that there are no hub attachment spokes for securing the hub portion  122  to the wheel. Instead, the hub portion  122  forms an integral part of the wheel hub, with wheel spokes  127  radiating from the outer surface  134  of an annular hub rim  130 . 
   At the centre of the hub portion  122  an aperture  129  allows the wheel to be fixed to the axle using any acceptable method, for example by utilization of a nut or screw. 
   The hub portion  122  may further comprise an inner cylinder  126 , this inner cylinder is configured to allow access to the axle for the purpose of attaching the wheel to wheelchair, but is otherwise configured in a similar fashion to that discussed in relation to the previous embodiment. 
     FIG. 7  shows the hub portion  122  without the second portion  23  attached for clarity. However, the second portion  23 , may be releasably connectable to or integral with the hub portion  122 . It will be understood that all the variations discussed subsequently in relation to the second portion  23 , drive mechanism  70  and the relationship of the second portion  23  to the hub portion  22  are envisaged as being suitable for use with any of the previously discussed embodiments of the hub portion  22  or  122 . 
     FIG. 8  shows the second portion  23  of the propulsion apparatus  20 . As previously mentioned, although this second portion  23  is shown as being separable from the hub portion  22 , it is to be understood that the propulsion apparatus  20  may be so adapted that the second component  23  is not removable from the hub portion  22 . 
   However, one advantage of providing a two piece propulsion apparatus  20  is that the second portion  23  may be removed and the wheelchair  4  will then revert to the functionality of the traditional wheelchair design depicted in  FIGS. 1   a  and  1   b . Alternatively, the second portion  23  may be made up of two or more parts and these parts can be releasably connectable. For example a part or whole of the lever arm  140  may be removable, when removed the drive mechanism containment portion  70  will remain attached to the hub portion  22 . Examples of configurations in which either the whole or a part of the lever arm  140  is removed are shown in  FIGS. 9A ,  9 B, and  9 C and  10 A,  10 B and  10 C. It will be understood that there are other configurations which can be used in addition to those shown in the aforementioned Figures. An alternative method of achieving this is to provide a lever arm  140  which is provided with a hinge at a point radially inward of the hand rim  10 . This would enable the lever arm  140  to be folded into a compact configuration allowing access to the hand rim  10 , while negating the requirement to physically remove the second portion  23  from the wheelchair. A further alternative would be to form the handle of an outer member and an inner member telescopically received within the outer member (not shown). When the handle is in use, the inner member may be extended and secured in a usable length using any suitable method. For example, ball bearings locatable in apertures on the outer member. When the lever is not in use and it is desired to revert the wheelchair to the functionality of the traditional wheelchair design the inner member may be telescopically received within the outer member, and preferably secured, to reduce the length of the lever to less than the radius of the hand rim  10  or wheel  8  as desired. 
   In a further alternative a combination of a telescopically receivable inner member and a pivotable outer member of the lever arm is envisaged.  FIG. 11A  shows a configuration when arranged for use with an inner member  140   a  extending radially outwardly from the axis defined by the wheel axle and  FIG. 11B  shows the configuration when the inner member  140   a  is stored. In the configuration shown in  FIG. 11   a  the inner member  140   a  is slidably received within an outer member  140   b . The outer member  140   b  comprises an upper portion  140   c  and a lower portion  140   d . The lower portion  140   b  is pivotally attached at one end to the second portion  23 . Preferably the pivot biases the lower portion  140   d  to extend outwardly from the plane of the wheel at an angle α to the axis defined by the wheel axle when in use. An example of a suitable pivot is a torsion spring. At the opposite end of the lower portion  140   d  to the pivot the lower portion  140   d  merges with the upper portion  140   c  which turns through an angle to extend substantially parallel to the plane of the wheel in a direction radially outwardly from the axis defined by the wheel axle when in use. As shown in  FIG. 11   a , in use, the inner member  140   a  extends from the upper portion  140   c  so that the user can hold the handle  160  and operate the propulsion apparatus  20 . 
   When it is desired to propel the wheelchair in the traditional manner, i.e. using the hand rim  10 , it is apparent that it is necessary to store the lever arm  140  so that the hand rim  10  can be easily accessed. 
     FIG. 11   b  shows a configuration where the lever arm  140  is stored so that the hand rim  10  can be accessed. The inner portion  140   a  is slid into the upper portion  140   c , and the outer member is pivoted inwardly towards the rear wheel  8 , thereby increasing the angle between axis defined by the wheel axle and the lower portion  140   d  to β (β&gt;α). The relative lengths of the inner member  140   a , upper portion  140   c  and lower portion  140   d  are chosen so that when the inner member  140   a  is received within the upper portion  140   c , and the lower member  140   b  is pivoted inwardly, the length of the lever arm  140  is less than the radius of the hand rim  10 . Once the lever arm  140  has been collapsed and pivoted inwardly it is secured in the “stored” position, for example using a catch hook,  141  as shown in  FIG. 12 , which is preferably sprung, or other suitable attachment mechanism. 
   When the propulsion apparatus  20  is provided as a two part construction, the second component  23  is attached to the hub component  22  using a quick release pin  67 , which is shown in  FIG. 16 . It will be understood however, that other attachment mechanisms may be used, such as for example a locking nut and bolt. The quick release pin  67  comprises two ball bearings  68  mounted in the quick release pin. The ball bearings  68  are connected to a central release button  69 , which is shown in  FIG. 8 . 
   In use, actuation of the central release button  69  causes the two ball bearings  68  to retract inwardly into the pin  67 , whilst remaining captive. The quick release pin  67  is then inserted into the cylindrical wall  26  of the hub portion  22 . When the central release button  69  is released the ball bearings  68  move radially outwardly into the configuration shown in  FIG. 16  and are received in corresponding apertures or recesses (not shown) provided in the cylindrical wall  26  of the hub portion  22  thereby securing the second portion  23  to the hub portion  22 . 
   The second component  23  comprises a drive mechanism containment portion  70 , a lever arm  140  which is attached to the drive mechanism containment portion  70  and a handle  160  which is attached to the lever arm  140  at a location remote from the drive mechanism containment portion  70 . 
   Each of the above components will now be described in further detail with reference to  FIGS. 13-22 . 
     FIG. 13  shows a drive mechanism  72  prior to assembly into the drive mechanism containment portion  70 . The drive mechanism  72  comprises four jammer assemblies  74   a - d . The jammer assemblies  74   a - d  are configured in two pairs,  74   a  and  74   b  constitute a first pair and  74   c  and  74   d  constitute a second pair. The individual jammer assemblies in each of the pairs are connected by jammer attachment plates  76   a  and  76   b . The drive mechanism  72  further comprises a back plate  78  which is in the form of a disc. The back plate  78  comprises locator holes  80  and screw holes  82 . When assembled, the locator holes  80  and screw holes  82  are aligned with locator dowels  98  and threaded holes respectively both of which are provided in the drive mechanism containment portion  70  as shown in  FIG. 16 . A front plate  84  is provided and the jammer attachment plates  76   a  and  76   b  are pivotally attached to the front and back plates  78  and  84  by means of respective pivot pins  86   a  and  86   b . The front and back plates  84  and  78  further comprise respective, mutually aligned central apertures,  88  and  90 , which correspond with the central axis of the drive mechanism containment portion  70 . 
   A pin  92  and spring  94  are located in a pin housing  96 , positioned between the back plate  78  and front plate  84 . Also shown in  FIG. 8  are brake mechanisms  180   a  and  180   b . However, all these features will be described in more detail below. 
     FIG. 14  shows the drive mechanism with the front plate  84  removed for the sake of clarity. As can be seen, the jammer attachment plates  76   a  and  76   b  are interconnected by two linkage plates  77  to form a parallelogram shift mechanism  79 . One of the linkage plates  77  incorporates the pin housing  96 , which will be described in more detail below. The linkage plates  77  are pivotally connected at opposite ends to the jammer attachment plates  76   a  and  76   b  and are designed so as not to obstruct the central apertures  88  and  90  provided in the front and back plates  84  and  78 . 
     FIG. 15  shows a mechanism for lateral movement of the pin  92 . The pin  92  is connected to a pin block  146 . In  FIG. 15  the longitudinal axis of the pin  92  is in a direction that extends out of the page. The pin block  146  is constrained to move in a rectilinear motion substantially perpendicular to the longitudinal axis of the lever arm  140  by block guide rails  148  which are attached to the lever arm  140 . The pin block  146  is attached at one end to a direction selecting cable  142 . The direction selecting cable  142  extends away from the pin block  146 , around a pulley  144  and then extends substantially parallel to the longitudinal axis of the lever arm  140  before being connected to the handle  160  in such a way that inward rotation of the handle will exert a pull on the cable. 
     FIG. 16  shows the pin housing  96  in more detail. The pin housing  96  forms part of one of the linkage plates  77  and thereby forms a part of the parallelogram shift mechanism  79 . An aperture  97  is provided within the pin housing  96  and serves to locate spring  94 . The spring  94  is connected at one end to a spring block  95 , which in turn is attached to the lever arm  140 . The aperture  97  also comprises a second portion  93  through which the pin  92  extends. Thus the action of the spring  94  is to urge an opposite end of the aperture  97  away from the spring block  95  and so bias the parallelogram shift mechanism  79  (including the jammer attachment plates  76   a  and  76   b ) in a particular direction. However, upon inward rotation of the handle  160 , the cable  142  pulls pin  92  against the action of the spring  94  thereby biasing the parallelogram shift mechanism  79  in the opposite direction. 
     FIG. 17  shows the drive mechanism  72  positioned within the drive mechanism containment portion  70 . The locator dowels  98  project inwardly from an inner surface of the drive mechanism containment portion  70  and are received within the locator holes  80  in the back plate  78 . At the same time the threaded screw holes provided in the drive mechanism containment portion  70  are aligned with the screw holes  82  in the back plate  78  to receive threaded screws  100 . 
     FIGS. 18 ,  19   a ,  19   b ,  19   c  and  20  show one jammer assembly  74  in more detail. The jammer assembly  74  comprises a jammer  99 , having in side view an essentially teardrop shape. The jammer  99  comprises a substantially planar first surface  102  from which projects a curved side wall  104  which gives the jammer its distinctive teardrop shape. At one end the current side wall  104  is intersected by a substantially planar end face  100 . A second jammer surface  106  opposite the first is divided into two different surface portions  106   a  and  106   b  which lie in two different planes and are interconnected by a step  108 . As shown in  FIGS. 18 and 19   b , the step  108  takes an arcuate form corresponding to the outer circumference of a wheel  110 . At the same time the height of the step  108 , that is the distance between the first surface portion  106   a  and the second surface portion  106   b , corresponds to the axial dimension H of the wheel  110 . The jammer assembly  74  further comprises a shaft  113 , a shaft sleeve  114  and a “one way” roller clutch  116 . The second surface portion  106   b  comprises a through bore  118  which has two keys  120  which correspond with key slots  122  in the shaft sleeve  114 . An annular part of the second surface portion  106   b  provides a location of the roller clutch and a step  126  connects the roller clutch surface  124  with a platform  128  for the wheel  110 .  FIG. 20  shows the jammer assembly  74  following assembly and as it is configured in the drive mechanism  72 . 
     FIGS. 21   a  and  21   b  show the interaction of the drive mechanism  72  and the inner surface  32  of the hub rim  30 . 
   The operation of the drive mechanism  72  will now be described with reference to  FIGS. 21   a  and  21   b  and  FIG. 22 . One cycle for forward motion will be described in detail. If continuous propulsion of the wheelchair is desired in the forward direction the cycle is simply repeated. 
   The parallelogram shift mechanism  79  is biased for forward motion as a default as a result of the action of spring  94 . As such the jammer assemblies  74   a  and  74   c  are in contact with the hub rim  30 . The driving motion will be described with reference to a single jammer assembly,  74   a , although it will be apparent that the description will apply in a similar fashion to the other contacting jammer assembly,  74   c . The remaining two jammer assemblies  74   b  and  74   d  are not in contact with the hub rim  30  when the drive mechanism  72  is configured for forward motion. 
     FIGS. 22   a - d  show the position of the lever arm  140  throughout one complete cycle. The start of the cycle is shown in  FIG. 22   a , where it can be seen that the lever arm  140  is positioned at an angle of approximately 330°, clockwise from the vertical. As the lever arm  140  is pivoted in a forward direction, as shown in  FIGS. 22   b - d , the contact between the wheel  110  and the inner surface  32  of the hub rim  30  causes the wheel  110  to rotate in the same direction as the lever arm. The rotation of the wheel  110  causes the one way roller clutch  116  to rotate in its operational direction and the clutch therefore transmits the motion to the shaft sleeve  114 , which rotates in the same direction. Since the shaft sleeve  114  is keyed into the jammer  99  by the interengagement of the keys  120  and the key slots  122 , the rotation of the shaft sleeve causes the jammer  99  to rotate in the same rotational direction as the wheel  110 . This rotation will drive the jammer  99  into the hub rim  30  to provide a locking relationship between the jammer  99  and the hub rim  30 . Further rotation of the lever arm  140  in the forward direction will result in a transfer of torque to the hub rib  30  via the jammer assembly  74 . This will force the hub rim  30 , and therefore the hub portion  22 , to rotate in a forward direction. Since the hub portion  22  is fixed statically to an inner rim  14  of the rear wheel  8  via the trough shaped moulding  44 , this rotation will in turn be transmitted to the rear wheel  8 . The result is a forward rotation of the rear wheel  8  which propels the wheelchair in a forward direction. 
   Once the end of a cycle is reached, for example at an approximate angle of 60° clockwise from the vertical as shown in  FIG. 22   d , the lever arm  140  is returned to the beginning of the cycle and the cycle repeated for continuous propulsion. 
   Between cycles the lever arm  140  is rotating in the opposite direction to the direction of motion. During this time the wheel  110  will also rotate in the opposite direction to the direction of motion. However, since the roller clutch  116  is only operational in one direction, in this example in the forward direction, no torque is transmitted to the jammer  99 . This means that the jammer  99  will rotate away from and out of engagement with the inner surface  32  of the hub rim  30 . As a result the jammer  99  provides no torque to the hub rim  30  neither does it provide any frictional resistance inhibiting further rotation. The rear wheel  8  is therefore able to continue to rotate in a forward direction, in a so-called “freewheel” motion. 
   Should it be desired to rotate the rear wheel  8  in a reverse direction the direction selecting cable  142  is activated by rotating the handle  160  inwardly. The cable  142  pulls the pin block  146  causing it to move. The pin block  146  will slide, since it is constrained by the block guide rails  148 , in a direction as depicted by the arrow B in  FIG. 15 , Referring now to  FIG. 16  it will be apparent that the movement of the pin  92  in the direction shown by the arrow B causes the spring  94  to compress against the spring block  95 . This in turn causes the parallelogram shift mechanism  79  to move in the direction of the arrow C. This releases the jammer assemblies  74   a  and  74   c  from their contact with the inner surface  32  of the hub rim  30  and instead brings the jammer assemblies  74   b  and  74   d  into engagement with the inner surface  32 . Rotational movement of the lever arm  140  in a rearward direction will then force the jammers  99  of these assemblies into contact with the inner rim  32 , resulting in a rearward rotation of the wheel  8  by the same mechanism as previously described. 
   In an alternative embodiment of the present invention, a contact wheel may replace the jammer assembly  74 . Preferably, the contact wheel may be made of a high friction material to provide enhanced frictional contact with the hub rim  30 . Advantageously, the contact wheel may also be made of a material capable of deformation to provide an increased contact surface with the hub rim  30 . In this embodiment only one contact wheel will be required for both forward and rearward rotation of the rear wheel  8 , although it will be understood that more than one contact wheel may be provided if desired. In order to provide forward rotation the contact wheel contacts the hub rim  30  and the lever arm  140  is pivoted in a forward direction. The contact wheel will therefore rotate in a forward direction, thereby transmitting torque to the hub rim  30  and the rear wheel  8 . The handle  160  is then be rotated inwardly to disengage the contact wheel from the hub rim  30  allowing the rear wheel  8  to freewheel whilst the lever arm  140  is returned to the start of the motion. The handle  160  is then rotated outwardly again and the contact wheel reengages the hub rim  30 . For continuous forward motion this cycle is repeated. For rearward motion, the handle is rotated inwardly and the lever arm  140  moved to the end of the motion while the contact wheel is disengaged from the hub rim  30 . The handle  160  is then rotated outwardly again and the contact wheel is brought into engagement with the hub rim  130 . The lever arm  140  is then pivoted in a rearward direction and, as with the description of forward motion, torque is transmitted to provide rearward rotation of the rear wheel  8 . 
   It will be understood that the described drive mechanisms, i.e. the jammers and contact wheels, are examples only and that other mechanisms for transferring torque in a forward or rearward direction whilst being capable of allowing freewheeling, such as the use of clutches, is also envisaged. 
   In a further alternative embodiment of the present invention, a two stage inward rotation of the handle  160  provides first a neutral stage, in which the none of the jammer assemblies  74   a - d  are in engagement with the hub rim  30 , and a second reverse stage, in which jammer assemblies  74   b  and  74   d  engage the hub rim  30 . In such an embodiment the jammer assemblies  74  may once again take the form a contact wheel. As before, the contact wheel may preferably be made of a high friction material to provide enhanced frictional contact with the hub rim  30 . Advantageously, the contact wheel may also be made of a material capable of deformation to provide an increased contact surface with the hub rim  30 . Advantageously, more than one contact wheel may be arranged in a parallelogram shift mechanism  79  as previously described, providing at least one contact wheel for forward motion and at least one contact wheel for rearward motion. Although the torque transmission will be similar to that described in previous embodiments, the freewheeling motion will be provided by inwardly rotating the handle  160  to put the drive mechanism  72  into the first neutral stage, in which none of the contact wheels are in contact with the hub rim  30 . 
   Although the drive mechanism containment portion  70  is described as being a part of the second portion  23 , it will also be understood that the drive mechanism  72  may be contained within the hub portion  22  and activated when the second portion  23  is attached. 
   In summary,  FIG. 23  shows a hub portion  22  and a second portion  23  which comprises a lever arm  140 . The second portion  23  further comprises a drive mechanism  72  and the hub portion  22  has a hub rim  30  with an inner surface  32 . The interaction between the drive mechanism  72  and the inner surface  32  provides the driving connection by which the torque is transmitted from the second portion  23  to the rear wheel  8 . 
     FIG. 24  shows an alternative embodiment in which the second portion  23  comprises both the drive mechanism  72  and an annular surface  32 ′. The drive mechanism  72  interacts with the annular surface  32 ′ to transmit torque. In this alternative embodiment the second portion  23  is statically attached to the hub portion  22 , for example by the use of splines  71  being provided on an exterior surface  73  of the annular surface  32 ′ which are inserted into corresponding grooves  75  in the hub portion  22 . It will also be understood that other methods of keying the second portion  23  to the hub portion  22  are also acceptable. 
   An advantage of housing the drive mechanism  72  within a drive mechanism containment portion  70  of the second portion  23  is that, when the second portion  23  is removed from the hub portion  22  the drive mechanism  72  is also removed. This means that the weight of both the second portion  23  and the drive mechanism  72  are removed. Therefore, if the wheelchair user wishes to propel the wheelchair in the traditional manner, having removed the second portion  23 , they will not have to contend with the extra weight of the drive mechanism  72 . Furthermore, if the second portion  23  also comprises the annular rim  32 ′, when the second portion  23  is removed, for example for propulsion of the wheelchair in the traditional manner, the weight of the propulsion apparatus  20  retained in/on the rear wheel  8  will be further reduced. 
   A further advantage of housing both the drive mechanism  72  and annular rim  32 ′ in the second portion  23  is that when the second portion  23  is removed neither of the drive surfaces are exposed, meaning that the possibility of dirt ingress, which could effect their performance, is minimized. 
   A yet further advantage of having a detachable second portion  23  is that when the second portion  23  is removed the width of the wheelchair will be reduced. This will be useful when negotiating narrow gaps, such as doorways. 
   In a yet further embodiment both the annular surface  32  and a drive mechanism  72 ′ may be contained within the hub portion  22 . In this embodiment the second portion  23  is statically attached to the drive mechanism  72 ′, to activate the interaction of the drive mechanism  72 ′ and annular surface  32  to transmit torque. 
   An advantage of retaining the drive mechanism  72 ′ within the hub portion  22  is that when the second portion  23  is removed, for example to reduce the width of the wheelchair for negotiating narrow gaps, it will not include the weight of the drive mechanism  72 ′. This means that the second portion  23  can be more easily manoeuvred by the wheelchair user. 
   One method for varying the drive ratio of propulsion speed of the vehicle to power input by the user is to use gearing systems. An alternative method is to use a variable length lever arm, and this alternative will now be described in more detail. 
   As has been previously discussed, the lever arm  140  may be collapsible by telescopically receiving an inner member inside an outer member to reduce the length of the lever arm  140 . This system can also be adapted so that the lever arm  140  can have a variable radial length, the working length, (rather than just “in use” and “stored” lengths), for example by the provision of a plurality of apertures at varying distances along the outer member for engagement with ball bearings on the inner member. The working length being the distance between the point at which the user applies an input force and the axle of the wheel. 
     FIGS. 25   a  and  b  show a further example of how the lever arm  140  may be varied in length. In this example the lever arm  140  is comprised of first and second tubular members  140   e  and  140   f  which are preferably joined at an end remote from the handle  160 . The first and second tubular member  140   e  and  140   f  are slidably received in corresponding cylindrical bores (not shown) which pass through a housing portion  143  on the second portion  23 . 
   In one embodiment, as shown in  FIG. 26 , the configuration further includes springs  145   a  and  145   b  to aid in the control of the sliding of the first and second tubular members  140   e  and  140   f  within the cylindrical bores. 
   The first and second tubular members  140   e  and  140   f  may be held in a desired position within the cylindrical bores by means of clamps  147   a  and  147   b  as shown in  FIG. 27A . When it is desired to alter the length of the lever arm  140  the clamps  147   a  and  147   b  are released, as shown in  FIG. 27B , so that the first and second tubular members  140   a  and  140   f  are free to slide. Once the desired length is achieved then the clamps  147   a  and  147   b  are activated to clamp the tubular members  140   e  and  140   f  so that the lever arm  140  is prevented from sliding. 
   One method of activating and releasing the clamps  147   a  and  147   b  is to attach them to a cable (not shown) which is activated by movement of the handle  160 , or a lever attached thereto. However, it will be appreciated that other mechanisms for holding the lever arm  140  at a desired length and of releasing it for sliding movement may also be used. 
   The use of a lever arm with a variable working length enables the user to vary the drive speed and load effort without the use of a gearing mechanism. If the user shortens the length of the lever arm  140  and maintains a constant speed of reciprocation of the lever arm, then the speed of rotation of the rear wheel  8  will increase. However, the input force required by the user will increase. Conversely, if the user increases the length of the lever arm  140  and maintains a constant speed of reciprocation, then the speed of rotation of the rear wheel  8  will decrease, as will the required input force exerted by the user. It is therefore apparent that the use of a variable length lever arm enables the drive ratio of propulsion speed/input force to be altered without the use of complex gearing systems. The handle  160  will now be described with reference to  FIGS. 19   a ,  19   b ,  20  and  21 . 
     FIG. 28   a  shows the handle  160  at the start of a cycle, i.e. in the position shown in  FIG. 27   a , while  FIG. 28   b  shows the handle  160  at the end of a cycle, i.e. in the position shown in  FIG. 27   d . The handle  160  is attached to the lever arm  140  and comprises a handle housing  162  which is shown as being formed integrally with the lever arm. However, it will be appreciated that the handle housing  162  may be formed separately and only later attached to the lever arm  140  if desired. The handle  160  further comprises a semi-circular annular ring  164 . A slot  166  extends through a minor arc of the semi-annular ring  164  and serves to locate a number of cantilever rollers  168 . A section through one of the rollers  168  is shown in  FIG. 28  to illustrate how the roller is located within the semi-annular ring  164 . The handle  160  further comprises a hand piece  170  which is connected to opposite ends of the semi-annular ring  164  and is shown to have an ergonomically designed taper from the ends of the hand piece towards the centre. However, it will be appreciated that the hand piece may take other forms, and may for example in some embodiments comprise a straight cylindrical bar. 
     FIG. 30  shows a section through the handle  160  and handle housing  162 . As can be seen the semi-annular ring  164  is supported by two rollers  172 , which are secured to the handle housing  162 . The rollers  172  are positioned so as to maintain contact with an outer surface  174  of the semi-annular ring  164  throughout the travel of the handle  160 . 
   During one cycle the handle  160  will rotate through the handle housing  162  as shown in  FIGS. 21   a - d . The motion of the handle  160  provides an ergonomic hand movement which will be described further with reference to  FIGS. 28   a ,  28   b  and  30 . 
   As the lever arm  140  is pivoted in a forward direction the user maintains a grip on the hand piece  170  and the semi-annular ring  164  moves through the handle housing  162  supported by the rollers  172  until it reaches the configuration shown in  FIG. 28   b . The range of motion is limited by a stop, not shown, which is provided within the handle housing  162  to limit the travel of the semi-annular ring  164 . At the end of one cycle the user returns the lever arm  140  to the start of the cycle and the handle will smoothly return to the position shown in  FIG. 28   a.    
   The handle  160  further comprises a mechanism for applying a braking force against the motion of the wheelchair.  FIG. 30  shows a brake actuation mechanism  182  provided in the handle  160 . The semi-annular ring  164  is provided with a profile  174  at an end which comes into contact with the lever arm  140 . The lever arm  140  comprises a brake roller  184  mounted to a pivot lever  186 . The pivot lever  186  pivots about a pivot pin  188 . The pivot lever  186  is shown as being substantially “L” shaped. However, it will be apparent that other shapes may be used. At an end of the pivot lever  186  remote from the brake roller  184  and on the opposite side of the pivot pin  188  an attachment point  190  is provided for securely attaching a brake cable  192  which runs through the lever arm  140  and is connected to a brake control mechanism  194  housed in the drive mechanism containment portion  70 . 
     FIG. 31  shows the rear side of the back plate  78  of the drive mechanism  72  and illustrates the brake control mechanism  194  in more detail. The brake control mechanism  194  is attached to the rear side of the back plate  78  and comprises a horizontal plate  196  connected to the brake cable  192  and the back plate  78 . The horizontal plate  196  merges at opposite ends with downwardly and outwardly depending plates  198   a  and  198   b  which in turn merge with substantially vertically downwardly depending plates  200   a  and  200   b . The downwardly and outwardly depending plates  198   a  and  198   b  each comprise a respective vertical slot  202   a  and  202   b  in which is received a respective pin  203  which extend rearwardly from the back plate  78 . The vertical plates  200   a  and  200   b  are attached to respective brake arms  204   a  and  204   b . Brake shoe attachments  206   a  and  206   b  are provided at an end of the brake arms  204   a  and  204   b  remote from the vertical plates  200   a  and  200   b.    
   Looking now at  FIG. 13 , it can be seen that a brake slot  208  is provided in the back plate  78  of the drive mechanism  72 . The brake shoe attachments  206   a  and  206   b  extend through the brake slot  208  to attach the brake arms  204   a  and  204   b  to brake shoes  210   a  and  210   b.    
   Although in what follows only one of the brake mechanisms  180  will be described, nevertheless it will be apparent that the description will equally apply to the other, opposing brake mechanism. 
   The brake shoe  210  comprises an inner shoe plate  212 , which is disposed substantially perpendicularly to the back plate  78  of the drive mechanism  72 . The inner shoe plate merges at either end with opposite ends of a curved plate section  214 . A brake pad  216  is fixed to the curved plate section  214  by means of interlocking keys  218  and key slots  220 . 
   The braking process will now be described with reference to  FIGS. 30 ,  32   a  and  32   b . The handle  160  is rotated such that the cam profile  174  provided in the handle  160  contacts the brake roller  184  thereby causing the pivot lever  186  to pivot about the pivot pin  188 . As the pivot lever  186  pivots the attachment point  190  moves in a direction away from the drive mechanism  72 . Since the brake cable  192  is attached to the attachment point  190 , the brake cable is also moved in a direction away from the drive mechanism  72 . The arrows D in  FIG. 31  show how, as the brake cable  192  moves, the horizontal plate  196  and the attached plates  198  and  200  move. This movement is constrained to be in a direction parallel to that of the brake cable  192  by virtue of the receipt of the pins  203  in the slots  202   a  and  202   b . The movement of the vertical plate  200  is transmitted to the brake arms  204   a  and  204   b . However, since the brake shoe attachment  206   a  and  206   b  are restrained within the brake slot  208  the motion is converted to one urging the brake shoes  210   a  and  210   b  in a radially outward direction as shown by arrows E in  FIG. 30 . The result of this movement is that the brake pads  216  are forced into contact with the inner surface  32  of the hub rim  30 . The friction provided between the brake pads  216  and hub rim  30  acts to slow the motion of the hub rim and therefore the rear wheel  8 . If the contact between the brake pads  216  and hub rim  30  is maintained the frictional contact will slow the movement of the wheelchair, eventually bringing it to a stop. 
   Once the handle  160  is released, thereby releasing the contact between the cam profile  174  and the brake roller  184 , the brake cable  192  will also be released. The mechanism will then be reversed such that the brake pad  216  is released from contact with the hub rim  30  and motion of the rear wheel  8  may be resumed. 
   Although a manual wheelchair has been described, it will be understood that this invention is equally applicable to a hybrid wheelchair, i.e. a wheelchair that also has the capability of motorised propulsion. 
   Alternative ways of transmitting torque to the hub portion  22  may also be used. Thus the frictional system described above could be replaced by one based on positive engagement. For example, the hub rim  30  could take a toothed form and the driving mechanism could be provided by intermeshing teeth. Thus the hub rim  30  could comprise an annular rack and the driving mechanism one or more interengaging gear wheels. 
   Additionally, other methods of braking may be used. For example, in an alternative embodiment a brake lever may be provided whereby a friction pad is provided on an inner side of the lever arm. The lever arm  140  may be hinged at the end where it is attached to the drive mechanism containment portion enabling the arm to be inclined towards the wheel. In this embodiment the lever arm may be pulled inward to bring the friction pad into contact with either the hand rim or the wheel to slow down rotation of the wheel. Alternatively, the inward motion of the lever arm  140  may engage a pair of drum style rotary brakes. 
   Although the present invention is described as being for use with a wheelchair, it will be understood that it is equally applicable to other manually propelled vehicles, for example trolleys, which would benefit from an enhanced propulsion mechanism.