WO2003065963A1

WO2003065963A1 - Propulsion device

Info

Publication number: WO2003065963A1
Application number: PCT/GB2003/000631
Authority: WO
Inventors: David Stanley Davies; Gavin Mckinnell; Peter William Gillett; Angus Paul Steele
Original assignee: Sunrise Medical Limited
Priority date: 2002-02-09
Filing date: 2003-02-07
Publication date: 2003-08-14
Also published as: GB0203109D0; AU2003208409A1

Abstract

A propulsion device comprising: a stationary part adapted to be fitted to a vehicle and including a hub portion (11-13, 20) and support portions (30, 31) spaced from the hub portion and disposed circumferentially therearound; a ground-engaging wheel rim (16, 17) portion; bearing means (55-57) carried by said support portions and supporting the wheel rim portion for rotation about said hub portion; motor means (73) carried by said stationary part and drivingly engaged with said wheel rim portion; and energy storage means carried by said stationary part for energising said motor means.

Description

Title: Propulsion Device

Description of Invention

This invention relates to a propulsion device which has been designed with the object of being able to be fitted to a user-propelled wheelchair in place of each of the conventional propulsion wheels thereof, thereby converting the wheelchair to a powered chair.

User-propelled wheelchairs conventionally have a pair of relatively large diameter propulsion wheels as well as a pair of small diameter castor wheels. The propulsion wheels, which may be at the rear of the wheelchair in the vicinity of the seat thereof, have hand rims which can be grasped by the user, and by which the user of the wheelchair can propel and manoeuvre the wheelchair using the strength of his or her arms to rotate the wheels.

Power driven wheelchairs of various configurations are well known, for use by persons who are not able to propel a wheelchair themselves in the above way or even for persons who are able to propel themselves but for use over long distances or challenging terrain. Such purpose designed power wheelchairs are however usually of much heavier construction and of course have to have an electric motor or motors, electrical power storage batteries, controllers and the like. Thus they are not in general able to be readily folded and/or dismantled for storage or transportation for example in the luggage compartment of an automobile.

There have been proposed propulsion assistance devices for user- propelled wheelchairs, but in general all such known devices have required structural alterations of the manual wheelchair to enable fitment of the propulsion device. Usually they have required the provision of means for accommodating electrical power storage batteries in the frame structure of a wheelchair, e.g. under the seat thereof, It has been proposed (in US 6 155 367) that electrical power storage batteries can be accommodated in a hub portion of a powered wheel device to be fitted in place of a wheel of a user-propelled wheelchair, but the problem with this is that the space available in the hub of the wheel is severely limited. Hence the device described in US 6 155 367 is intended primarily for assisting manual propulsion of a wheelchair, rather than being able in itself to be the main means of propulsion of a wheelchair.

It is broadly the objective of the present invention to provide a propulsion device suitable for use in a user-propelled wheelchair in place of the conventional hand operated wheels thereof, which is self contained (with the possible exception of a control means as referred to hereafter) and does not require any or any substantial modification of the wheelchair. In being suitable for this purpose, it is to be appreciated that a device in accordance with the invention may be suitable for the propulsion of things other than wheelchairs, e.g. goods or luggage carts and trolleys, baby carriages, or possibly even bicycles or tricycles.

According to one aspect of the invention, we provide a propulsion device comprising: a stationary part adapted to be fitted to a vehicle and including a hub portion and support portions spaced from the hub portion and disposed circumferentially therearound; a ground-engaging wheel rim portion; bearing means carried by said support portions and supporting the wheel rim portion for rotation about said hub portion; motor means carried by said stationary part and drivingly engaged with said wheel rim portion; and energy storage means carried by said stationary part for energising said motor means.

The bearing means may comprise a number of bearing elements respectively carried by said support portions; each bearing element may comprise a roller element which is rotatably carried by the support portion. Each such roller element may have a peripheral groove, wherein a formation extending radially inwardly of the ground-engaging wheel rim portion engages. Such radially inwardly extending formations may comprise a rib, which may have an inner periphery of an increased cross section, foπning a track which engages in said grooves in the roller elements.

In another of the embodiments of the invention described hereafter, there is a stationary rim portion carried by said support portions and provided with said bearing means. In this embodiment, each bearing element comprises a roller element which is rotatably carried by the stationary rim portion, and each such roller element may then comprise proposed support surfaces engaging complementary bearing surface portions provided on the ground engaging wheel rim portion. Each roller element may be generally diabolo shaped.

At least one of the bearing elements may be biased, e.g. by spring means, radially outwardly into engagement with the ground engaging wheel rim portion. This enables the taking up of production tolerances which may arise in directions radially of the wheel rim portion, so that the latter is always effectively constrained to rotate accurately about the hub portion.

At least one of said support portions may carry two of the bearing elements, engaging the wheel rim portion at positions spaced circumferentially thereof. In this case, preferably the two bearing elements are carried with their rotational axis at fixed positions relative to one another, by a support element which is moveable, e.g. pivotable about an axis substantially parallel to the rotational axis of the roller elements, relative to the support portion. This enables the bearing elements to self-align with the wheel rim portion, so that both engage it correctly.

It may be the bearing elements carried by such support element which are biased radially outwardly into engagement with the wheel rim portion, e.g. by having the support element biased radially outwardly relative to the hub portion. The ground engaging wheel rim portion preferably is provided with a tyre (solid or possibly pneumatic): preferably it also carries a hand grip rim enabling manual propulsion of a wheelchair to which the device is fitted, if required.

Preferably the motor means is an electric motor, and the energy storage means comprises one or more rechargeable electrical storage batteries. However in its broadest aspect the invention may utilise some other power source.

Preferably the motor means is drivingly engageable with the ground engaging wheel rim portion by way of clutch means enabling such engagement to be established or discontinued as required. Such clutch means may be manually operable, so that if required a wheelchair fitted with the device according to the invention can be propelled and manoeuvred manually without the "drag" or braking effect of an electric motor remaining in driving connection with the ground engaging wheel part of the device.

The driving connection established between the motor means and the ground engaging wheel rim portion may also include a torque-limiting means for protecting against overload under certain conditions. Such torque-limiting means may be combined with the clutch means: in the embodiment described hereafter torque is transmitted between two axially-adjacent elements disposed on a shaft and having their adjacent faces provided with formations which transmit torque between the members when they are spring urged into engagement with one another but which, under excess torque, are able to move axially apart until the formations disengage. For manual disengagement when required, a manually-operable member such as a lever may be provided to move the members away from one another against their engaging spring.

The driving engagement with the ground engaging wheel rim portion may be established by way of gear teeth provided on the latter, and may in one embodiment be provided on an internal surface of the wheel rim portion between the bearing surfaces thereof. However it would be within the broadest scope of the invention for a frictional driving connection to be established with the ground engaging part.

The stationary part of the device is preferably adapted to be fitted to a frame part of a vehicle such as a wheelchair by virtue of the provision at its hub portion at an axle member engageable with a wheelchair in the same manner as an axle member of a conventional user-rotatable wheel. Such an axle member may be adapted to fit in an aperture or socket in the vehicle frame part, and may have quick-release fastening means associated therewith to facilitate removal and fitting of the device, as when the wheels might be removed from a wheelchair for storage or transportation.

Preferably a torque reaction stop member is provided, engageable with a frame part of a vehicle such as a wheelchair to prevent the stationary part of the device from rotating when in use. Preferably the stop member is adjustably positioned in relation to the stationary part of the device.

A rechargeable electrical battery pack constituting the energy storage means may be quickly detachable from and replaceable to the device, e.g. to lessen its weight for easy handling, or to be removed for charging away from the device or from a wheelchair to which the device is fitted. Preferably such a battery pack has engagement with the device by way of a plug and socket means incorporating electrical contacts.

The configuration of the stationary part may comprise the hub portion in its centre and a number of spoke elements extending generally radially outwards therefrom to said stationary rim portion. This should provide sufficient space for accommodation of a battery pack of reasonable electrical capacity in the sector between two adjacent such spoke elements.

It will be appreciated that certain details of the invention set forth above may themselves constitute independent inventions, not in combination with any or all of the other features set forth. For example, the arrangement of the hub portion, support portions spaced therefrom, ground-engaging wheel rim portion and bearing means carried by the support portions and supporting the wheel rim portion for rotation about the hub portion, may be useable in a supporting assembly for, e.g. a wheelchair, which may be used in place of a conventional wheel thereof.

In this case, the arrangement of roller elements engaging the wheel rim portion may be in any of the configurations above described.

The invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 is a perspective view, from one side, of a first embodiment of propulsion device in accordance with the invention;

Figure 2 is a perspective view from the other side of the device;

Figure 3 is an exploded perspective view showing principal elements of the device;

Figure 4 is a section through a drive-transmitting part of the device;

Figure 5 is a perspective view of part of a further embodiment of propulsion device in accordance with the invention;

Figure 6 is a broken-away perspective view of a roller element of the embodiment of Figure 5; and

Figure 7 is a perspective view illustrating the cross-sectional shape of the wheel rim portion of the embodiment of Figure 5.

Referring to the drawings, a propulsion device comprises a stationary part including a hub portion 10 from which spoke elements 11, 12, 13 extend generally radially outwardly to a stationary rim portion indicated generally at 14. Rotatable about the stationary part is a ground engaging part indicated generally at 15, which comprises a tyre 16 (solid or pneumatic) on a rotatable rim portion 17.

The hub portion 10 comprises a central region 20 of a member indicated generally at 21 in Figure 3, the spoke elements 11, 12, 13 extending radially outwardly from the portion 20. The component may be a casting of metal e.g. an aluminium alloy, or possibly a moulding of a suitable plastics material. The central part 20 is in the form of a web and is held between two support members 22, 23 secured together by bolts as 22a passing through apertures in the web portion 20. An axle member 25 passes through a bush 24a in aligned apertures in the members 22, 23 and the web portion 20, and is engageable in a socket aperture in the frame of a wheelchair, in the same manner as the axle of a conventional manually rotatable wheel is fitted thereto. The axle member 25 preferably has quickly-detachable fastening means associated therewith to enable it to be rapidly fitted to and removed from the wheelchair when required. Member 23 has an outwardly extending arm portion 26 which supports, adjustably by way of a slot 27 in the arm portion 26, a torque reaction peg 28 engageable with a suitable part of a wheelchair frame at a distance from the axle member 24, to prevent the stationary parts of the device from rotating under torque reaction when the device is being used to propel the wheelchair.

The stationary rim portion 14 comprises two circular components indicated generally at 30, 31 disposed in back to back relationship and secured to one another. The general form of the member 30 is that it comprises a generally cylindrical wall portion 32 with, at one end, a radially inwardly extending flange portion 33 and, at the opposite end a radially outwardly extending flange portion 34. Similarly the member 31 comprises a wall portion 35 and flange portions, 36 and 37. The members 30, 31 are secured together with the flange portions 33, 36 in face-to-face engagement with one another, held thus by a number of bolts as 38 passing through apertures in the flange portions 33, 36. The member 30 has three substantially equally circumferentially spaced inwardly extending lug formations 39, 40, 41 and the member 31 is similarly provided with lug formation 42, 43, 44. Lug formations 39, 42 abut to provide a recess or socket for receiving a formation 45 at the end of spoke portion 11; similarly the lug formations 40, 43 receive a formation 46 on spoke portion 12 and the lug formations 41, 44 receive a formation 47 on the end of spoke portion 13. Further fasteners as indicated at 49 in relation to lug formation 39 pass through aligned apertures in the lug formations and in the formations at the ends of the spoke portions: thus the stationary rim portion is securely fixed to the hub and spoke component 21.

Radially outwardly of the lug formations 39 to 41 and 42 to 44 the members 30, 31 are provided with aligned somewhat U-shaped recesses as indicated at 50, 51, 52 for the component 31. In each of the three such aligned recesses there is provided a respective bearing element as indicated at 55, 56, 57 in Figure 3. The bearing elements 55 to 57 are rotatably supported about respective shafts or pins as 55 a, b, c carried between the members 30, 31 and extending axially across the recesses therein. Each of the bearing members 55 to 57, as seen most clearly in relation to the member 55, is somewhat diablo- shaped in cross section with two opposed tapering faces 58, 59 with a cylindrical face 60 there between.

The rotatable rim portion 17 has, in its interior, gear teeth 65 and on opposite sides thereof inclined annular end faces one of which is indicated at 66. These end faces as 66 are engaged by the facing tapering surfaces 58, 59 of the bearing elements 55 to 57 so that the rim portion 17 is rotatable about the stationary rim portion 30, 31 being supported at three points spaced circumferentially thereabout. The face as 60 of each of the bearing members 55 to 57 provides a clearance from the gear teeth 65. The flanges 34, 37 of the members 30, 31 respectively extend radially outwardly beyond the faces as 66 of the rim 17 and lie axially closely adjacent the rim so that the faces 66 and teeth 65 are concealed.

Adjacent the lug formations 40, 43 the members 30, 31 respectively have aligned cut-out portions 70, 71 which afford access to the gear teeth 65 for driving engagement therewith by a drive gear 72. The gear 72 forms the output from an assembly of an electric drive motor 73 and reduction gear box 74, which is secured to the member 31, and drives the gear 72 by way of a clutch arrangement to be described hereafter. The members 30, 31 are further provided with similar recesses adjacent the lug formations 41, 44: these further recesses are provided to enable the drive motor to be assembled to the device in a different position depending on whether the device is intended to be used on the left hand side or right hand side of a wheelchair.

Referring now to Figure 4 of the drawings, this shows in diagrammatic cross section one possible arrangement by which drive gear 72 may be drivingly connected to the motor and gear box 73, 74. In this drawing, an output shaft 80 extends from the gear box 74 into a housing indicated generally at 81 which is positioned in relation to the recesses 70, 71 so as to present the drive gear 72 to the internal gear teeth 65 of the rotatable rim portion 17 through an opening in the side of the housing 81. The shaft extends across the housing 81 and is supported in a bearing 82 at the opposite end of the housing to that at which the gear box 74 is attached. Gear 72, which is formed on a somewhat cup-shaped member is supported relative to the shaft 80 by a radial and thrust bearing assembly 83 and is fast with a clutch member 84 having clutch formations 85 in the form of radially extending V-section teeth or serrations on its annular axially presented face surrounding the shaft 80.

Axially adjacent the clutch member 84, and rotationally fast with but axially slideable on the shaft 80 by virtue of engaging the latter through splines 86 is a further clutch member 87. The clutch member 87 has formations 88 complementary to the formations 85 and facing the latter. Clutch member 87 is urged axially into engagement with clutch member 84 by a compression spring 89 abutting a thrust bearing 90 within the clutch member 87.

Torque can thus be transmitted between the clutch members 84, 87 by virtue of their engaging formations 85, 88 under the axial force exerted by spring 89. The configuration of the formations 85, 88 however is such that if too great a torque is attempted to be transmitted the clutch member 87 can move axially away from the member 84 against the spring 89, to discontinue the driving connection between them. To disconnect the driving connection when required, if for example the wheelchair is to be propelled or manoeuvred manually without operation of the propulsion device, the clutch member 87 can be axially disengaged from the member 84 by operation of a yoke 91 which engages a collar 92 on the clutch member 87 and is operable by a suitable hand control knob or lever not shown.

Electrical power for the motor 73 is taken from a battery pack indicated generally at 100, accommodated in the sector between spoke elements 11, 13. The battery pack 100, comprising a number of rechargeable electrical storage batteries of any suitable type, comprises a casing containing the batteries which fits in a correspondingly-shaped recess provided in a member 101 which fits closely within the sector-like space bounded by the spoke elements 11, 13 and the part of the stationary rim portion 14 extending therebetween, and the casing has a nose portion 102 which fits in a corresponding recess in the member 101. Electrical contacts are provided on the nose portion 102 which when the battery is fitted make electrical engagement with complementary contacts in the member 101: a lever 103 operates an over-centre catch mechanism indicated generally at 104 to retain the battery pack to the member 101 and ensure effective electrical contact at the nose portion 102 of the battery pack.

Appropriate wiring (not shown) will of course be provided for conveying electrical power from the battery pack to the motor of the device. A battery pack may be charged in situ in which case a suitable charging plug/socket connector may be provided or a battery pack may be removed from the device for charging and replace when charged or substituted by another pack which has been charged.

It is of course also necessary that control means be provided to enable the user of a wheelchair or other vehicle provided with a device to control the operation of the motors of the two devices at opposite sides of the chair so as to command propulsion and steering as required. Such a controller may be of the "joystick" type well known for control of power wheelchairs: such a controller may be removably mounted on a wheelchair when it is to be fitted with propulsion devices in accordance with the invention, and preferably has detachable e.g. plug and socket connections with both the propulsion devices of the chair so that it may remain in position even when the devices are removed for storage or transportation of the wheelchair or if the user-operated wheels of the wheelchair are fitted for any reason.

An alternative arrangement for a controller is that it may be mounted on a member extending from the stationary part of the device to a position in which it is accessible to and operable by the user of a wheelchair or other vehicle to which the propulsion device is fitted.

Referring now to Figures 5 to 7 of the drawings, a further embodiment of propulsion device in accordance with the invention comprises a stationary part which has a hub portion 110 from which spoke elements 111, 112, 113 extend radially outwardly to respective support portions indicated generally at 114, 115, 116. Rotatable about the stationary part is a ground-engaging wheel rim portion 117 which carries a tyre (solid or pneumatic) (not shown).

The hub portion 110 where the spoke elements 111, 112, 113 converge, is constituted by a generally central part of a component which may be a casting of metal, e.g. an aluminium alloy or possibly a moulding of a suitable plastics material. Where the spoke elements converge there is a supporting plate 122 bolted through to a similar such plate at the opposite side of the hub portion, the two plates being bolted together through the innermost parts of the spoke elements in similar manner to the support members 22, 23 in the embodiment of Figures 1 to 4. A bush 124 for an axle member is provided, the axle member providing for connection to a wheelchair frame in the same manner as above described, preferably with the provision of quickly-detachable fastening means. An extension 126 of the plate 122 carries a torque reaction peg 128. The spoke elements 112, 113 end in respective forks as indicated at 130 for the spoke element 112. Between the limbs of the fork 130 there is rotatably mounted a support roller element 131, the roller element having a central bearing carried on a pin or bolt 130a extending between the limbs of the fork. A roller element 132 is carried in like manner by the spoke element 113.

The spoke element 111 is provided at its outermost end, instead of a fork as 130, with a support element 135 which itself is provided with two roller elements 136, 137 which are of smaller diameter than the roller elements 131, 132. The support element 135 is carried by an elongate shaft 138 of square or other non-circular cross-sectional shape, which extends into a correspondingly- sectioned socket in the spoke element 111. The shaft 138 is able to move lengthwise of the spoke element 111 and is spring biased radially outwardly of the propulsion device, i.e. lengthwise of the spoke element 111. The support element 135 is pivotably carried by the shaft 138 about an axis provided by a connecting bolt or pin 139, this axis being parallel to the rotational axes of the roller element 137, 136 and indeed to those of the other roller element 131, 132.

One of the roller element 131, 132 or 136, 137 is shown in a partly broken-away view in Figure 6. This shows that it has a peripheral groove 140, of a cross-section which is generally V-shaped with a rounded base.

Figure 7 shows, in a broken-away perspective view, part of the wheel rim 117, illustrating its cross-sectional shape. Its outermost periphery comprises two spaced walls 141, 142 with a well 143 therebetween, these features providing for fitment of a solid or pneumatic tyre. Radially inwardly of the walls 141, 142, there are respectively oppositely axially facing grooves 144, 145, and radially inwardly of these grooves there are respective gear teeth parts 146, 147. The two gear teeth parts 146, 147 are separated by a central radially inwardly extending rib 148 whose internal periphery has a support track 149 of bulbous part-circular cross sectional shape. This track 149 engages with the peripheral groove as 140 of the respective roller elements 131, 132, 136, 137.

The wheel rim portion 117 is thus supported by the roller elements for rotation about the hub portion 110. The radially outwards spring biasing of the support element 135 for the roller elements 136, 137, and the ability of the support element 135 to pivot at 139 relative to the shaft 138, means that the rotatable wheel rim portion is contacted by all the roller elements, and any radial production tolerances are accommodated. The inability of the non- circular shaft 138 to rotate relative to the spoke element 111 about its own longitudinal axis means that the rim portion is effectively held in alignment to rotate about the axis of the device, and resists becoming misaligned when for example a wheelchair to which the device is fitted is being steered or is travelling on a non-even surface.

For driving the wheel rim portion 117, an electric drive motor would be provided which may be like that described above at 73, 74 and may include a drive arrangement somewhat as that shown in Figure 4. In this case, however, a drive gear would be provided which preferably is wide enough to have respective parts to engage the gear teeth 146, 147, with a space therebetween to accommodate the rib 148 and track 149. The motor and reduction gearbox assembly would be carried by a supporting structure indicated generally at 150, secured to the fork which carries the roller element 132.

Although not illustrated in the drawings, the support portions which carry the rollers by which the wheel rim portion 117 is rotatably supported may also carry a stationary rim portion which acts as a cover substantially to exclude dust and dirt from the gear teeth 146, 147 and the track 149 on the interior of the rim portion. Such a cover, which may be of annular form or comprise part annular regions extending between the support portions, may have respective lip portions which extend into the recesses 144, 145 to provide an adequately effective barrier against the access of dirt to the gear teeth and track. For providing an electrical power supply for the drive motor, a battery pack would be accommodated between spoke elements 111 - 113, possibly in a similar arrangement to that in the embodiment of Figures 1 - 4. A control means would also be provided.

Although not shown in the drawings, the rotatable wheel rim portion 17 or 117 desirably is provided with a manually-graspable rim by which the user of a wheelchair can propel and manoeuvre it if the need arises without use of the electrically powered propulsion devices.

In the present specification "comprises" means "includes or consists of and "comprising" means "including or consisting of.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A propulsion device comprising: a stationary part adapted to be fitted to a vehicle and including a hub portion and support portions spaced from the hub portion and disposed circumferentially therearound; a ground-engaging wheel rim portion; bearing means carried by said support portions and supporting the wheel rim portion for rotation about said hub portion; motor means carried by said stationary part and drivingly engaged with said wheel rim portion; and energy storage means carried by said stationary part for energising said motor means.

2. A propulsion device according to Claim 1 wherein said bearing means comprises a number of bearing elements respectively carried by said support portions.

3. A device according to Claim 2 wherein each bearing element comprises a roller element rotatably carried by the support portion.

4. A device according to Claim 3 wherein each roller element has a peripheral groove, wherein a formation extending radially inwardly of said wheel rim portion engages.

5. A device according to Claim 4 wherein said formation comprises a rib.

6. A device according to Claim 5 wherein said rib has an inner periphery of an increased cross-section forming a track, engaging in said grooves in the roller elements.

7. A device according to Claim 1 wherein there is a stationary rim portion carried by said support portions and provided with said bearing means.

8. A device according to Claim 7 wherein the bearing means comprises a number of bearing elements circumferentially spaced about the stationary rim portion and engaging a bearing surface on the ground engaging wheel rim portion to support the latter.

9. A device according to Claim 8 wherein each bearing element comprises a roller element rotatably carried by the stationary rim portion.

10. A device according to Claim 9 wherein each roller element comprises opposed support surfaces engaging complementary bearing surface portions on the ground engaging wheel rim portion.

11. A device according to Claim 10 wherein each roller element is generally diabolo-shaped.

12. A device according to any one of Claims 2 to 6 wherein at least one of said bearing elements is biased radially outwardly into engagement with said wheel rim portion.

13. A device according to any one of Claims 2 to 6, or Claim 12 wherein one of said support portions carries two of said bearing elements, engaging the wheel rim portion at positions spaced circumferentially thereof.

14. A device according to Claim 13 wherein said two bearing elements are carried with their rotational axes at fixed positions relative to one another, by a support element movably supported by said support portion.

15. A device according to Claim 14 wherein said support element is pivotable about an axis substantially parallel to the rotational axes of the roller elements.

16. A device according to Claim 15 wherein said support element is biased radially outwardly relative to the hub portion.

17. A device according to any one of the preceding claims wherein said ground engaging wheel rim portion is provided with a tyre.

18. A device according to any one of the preceding claims wherein the ground-engaging wheel rim portion carries a hand grip rim.

19. A device according to any one of the preceding claims wherein the motor means is an electric motor, and the energy storage means comprises one or more rechargeable electrical storage batteries.

20. A device according to any one of the preceding claims wherein the motor means is drivingly engageable with the ground-engaging wheel rim portion by way of clutch means.

21. A device according to Claim 20 wherein said clutch means is manually operable.

22. A device according to any one of the preceding claims wherein said motor means is drivingly engageable with the ground-engaging wheel rim portion by way of torque-limiting means.

23. A device according to Claim 22 as appendant to Claim 20 or Claim 21 wherein said clutch means is also said torque-limiting means.

24. A device according to Claim 23 wherein said clutch means comprises two axially-adjacent elements having adjacent faces provided with formations for transmitting torque there between said members being spring urged into engagement with one another but able to move axially apart under excess torque.

25. A device according to any one of the preceding claims wherein said driving engagement with the ground engaging wheel rim portion is established by way of gear teeth on the latter.

26. A device according to any of the preceding claims wherein said stationary part comprises an axle member engageable with a wheelchair or the like in the same manner as an axle member of a user-rotatable wheel.

27. A device according to Claim 26 wherein said axle member is adapted to fit in an aperture in the wheelchair frame.

28. A device according to Claim 26 or Claim 27 comprising quick release fastening means associated with said axle member.

29. A device according to any one of the preceding claims wherein a torque reaction stop member is provided, engageable with a frame part of a wheelchair or the like to prevent the stationary part of the device from rotating when in use.

30. A device according to Claim 29 wherein said stop member is adjustably positioned in relation to the stationary part of the device.

31. A device according to any one of the preceding claims wherein said stationary part comprises the hub portion in its centre and a number of spoke elements extending generally radially outwardly therefrom to said support portions.

32. A device according to Claim 31 as appendant directly or indirectly to Claim 19 wherein said electrical storage batteries are accommodated in the sector between two adjacent said spoke elements.

33. A device according to Claim 32 wherein said electrical storage batteries are quickly detachable from and replaceable to the device.

34. A device according to Claim 33 wherein said batteries engage the device by way of plug and socket means incorporating electrical contacts.

35. A device according to any one of the preceding claims further comprising control means for controlling operation of said motor means.

36. A device according to Claim 35 wherein said control means is detachably connected to said motor means.

37. A device according to Claim 35 where said control means is carried by the stationary part of the device.

38. A wheelchair provided with two propulsion devices according to any one of the preceding claims.

39. A support device for a vehicle, comprising: a stationary part adapted to be fitted to the vehicle, and including a hub portion and support portions spaced from the hub portion and disposed circumferentially therearound; a ground-engaging wheel rim portion; and bearing elements carried by the support portions and supporting the wheel rim portion for rotation thereabout; wherein at least one of said bearing elements is biased radially outwardly into engagement with the wheel rim portion.

40. A support device for a vehicle, comprising: a stationary part adapted to be fitted to the vehicle, and including a hub portion and support portions spaced from the hub portion and disposed circumferentially therearound; a ground-engaging wheel rim portion; and bearing elements carried by the support portions and supporting the wheel rim portion for rotation thereabout; wherein at least one of the support portions carries two bearing elements spaced circumferentially of the wheel rim portion.

41. A support device according to Claim 40 wherein said bearing elements are biased radially outwardly into engagement with the wheel rim portion.

42. A support device according to Claim 41 wherein said two bearing elements are carried in a fixed position relative to one another, and are movable together to align with the wheel rim portion.

43. A support device for a vehicle, comprising: a ground-engaging wheel rim portion; a stationary part fitted or adapted to be fitted to the vehicle, and including support portions spaced circumferentially around the interior of the wheel rim portion; and bearing elements carried by the support portions and supporting the wheel rim portion for rotation thereabout; wherein at least one of said bearing elements is biased radially of the wheel rim portion into engagement therewith.

44. A support device for a vehicle, comprising: a ground-engaging wheel rim portion; a stationary part fitted or adapted to be fitted to the vehicle, and including support portions spaced circumferentially around the interior of the wheel rim portion; and bearing elements carried by the support portions and supporting the wheel rim portion for rotation thereabout; wherein the bearing elements comprise roller elements each having a peripheral groove, wherein a track formation in the interior of the wheel rim portion engages.

45. A support device according to claim 44 wherein the track formation is afforded by a rib extending radially inwardly of the wheel rim portion.

46. A propulsion or support device substantially as herein described with reference to and/or as shown in the accompanying drawings.

47. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.