Field

The present disclosure relates to a wheel and to an expandable member. The wheel and expandable member have been developed primarily for use on wheelchairs, and will be described hereinafter with reference to this application. However, it will be appreciated that the wheel and/or expandable member may also be used in other applications, such as on tracked motor vehicles, including military vehicles, robotic vehicles, exploratory vehicles, and agricultural vehicles, toys, robots, children's prams and strollers, supermarket trolleys, wheeled baggage, or in machinery where the wheel or track system may be used as a drive mechanism.

Background

Known wheelchair wheels include a frame comprising a circular rim, a hub located centrally within the rim and spokes extending radially between the hub and the rim. A pneumatic tyre is engaged on the rim. A disadvantage of known wheelchair wheels is that they have a small surface contact area (footprint) with the ground, which results in low traction and makes climbing stairs extremely difficult, if not impossible.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Summary In a first aspect, the present disclosure provides a wheel comprising: a wheel assembly adapted for rotational connection relative to a vehicle body; a hub located centrally in the wheel assembly for connection to an axle; a wheel rim extending around the wheel assembly; and a mechanism associated with the wheel assembly and operable to reconfigure a traction member associated with the wheel assembly between a retracted configuration and a deployed configuration, wherein a length of the traction member adapted to contact the ground in the retracted configuration is less than a length of the traction member adapted to contact the ground in the deployed configuration.

A floor may extend around a periphery of the wheel rim, generally transverse to a plane defined by the wheel rim, and a wheel well may be defined between the rim and the floor, the wheel well being adapted to receive the traction member.

The deployed configuration of the traction member may comprise a substantially linear ground engaging portion.

The mechanism may comprise an arm hingedly connected at one end relative to the vehicle body, and a roller may be rotatably connected to an opposite end of the arm for engaging the traction member.

A said traction member may be received in the wheel well, the traction member comprising: a plurality of interconnected engagement elements movable relative to each other in a direction between a retracted configuration and an expanded configuration to facilitate reconfiguration of the traction member between the retracted and deployed states; at least one resilient member interconnecting the engagement elements, the resilient member biasing the engagement elements toward the retracted configuration; at least one limiting member interconnecting the engagement elements for defining the maximum extent of the expanded configuration.

A hand rim may be connected to the wheel assembly and a gear train may interconnect the hand rim and. the traction member. In a first gear setting associated with the retracted configuration of the traction member, the gear train may provide a gear ratio of approximately 1 :1 between the hand rim and the traction member, and, in a second gear setting associated with the deployed configuration of the traction member, the gear train may provide a gear ratio of between 5: 1 and 15:1 between the hand rim and the traction member to reduce the amount of manual effort required on the hand rim to rotate the wheel rim. In other embodiments, moving the traction member into the retracted configuration automatically disengages the gear train from the hand rim and moving the traction member into the deployed configuration automatically engages the gear train with the hand rim.

A frame may support the wheel assembly, the frame being adapted for fixed connection to the vehicle body, and a self-levelling mechanism may extend between the frame and a bracket for connecting the frame to the vehicle, for adjusting an angle between the frame and the bracket to retain a user seat in the vehicle within a predetermined angle range relative to horizontal.

In the retracted configuration, the traction member may be level with or elevated relative to a ground engaging portion of the wheel assembly, and in the deployed configuration, a ground engaging portion of the traction member may extend from the wheel assembly, such that the wheel assembly is raised relative to a ground engaging portion of the traction member.

In another aspect, there is provided a wheelchair including a wheel as defined in the first aspect above. The wheelchair may comprise a frame supporting the wheel assembly, the frame being adapted for fixed connection to the vehicle body, and a self-levelling mechanism comprising an actuator extending between the frame and a bracket for connecting the frame to a body of the wheelchair, for adjusting an angle between the frame and the bracket to retain a scat of the wheelchair within a predetermined angle range relative to horizontal.

A tilt sensor may be provided for sensing a value indicative of an inclination angle of ground being traversed by the wheelchair,

A controller may be responsive to the tiJt sensor for controlling actuation of the actuator for adjusting the angle between the frame and the bracket to maintain the angle within the predetermined range.

The predetermined angle range relative to horizontal may be adjusted based on the value sensed by the tilt sensor.

In a yet further aspect, there is provided an expandable member comprising: a plurality of interconnected engagement elements movable relative to each other in a direction between a retracted configuration and an expanded configuration; at least one resilient member interconnecting the engagement elements, the resilient member biasing the engagement elements toward the retracted configuration; at least one limiting member interconnecting the engagement elements for defining the maximum extent of the expanded configuration. The engagement elements may include gripping portions extending substantially normal to said direction.

The resilient member may be formed from a material selected from the group consisting of: silicone and elasticised fabric.

The limiting member may be formed from a material selected from the group consisting of: medium density polyethylene (MDPE) and webbing. The limiting member may be pleated when the engagement elements are in their retracted configuration to allow the engagement elements to move into their expanded configuration.

The engagement elements may be interconnected so as to form a continuous loop.

Another aspect of the present disclosure provides a wheel comprising: a frame adapted for fixed connection to a vehicle body; a wheel assembly rotatably connected to the frame; a hub located centrally in the wheel assembly for connection to an axle; a wheel rim extending around the wheel assembly and adapted to receive an expandable member; at least one expanding mechanism extendable between the frame and the expandable member, the expanding mechanism being movable relative to the frame, between a disengaged configuration and an engaged configuration, to expand the expandable member into an expanded shape.

The wheel rim preferably defines a plane. A floor preferably extends generally transverse to, and around a periphery of, the wheel rim. A wheel well is preferably defined between the rim and the floor, the wheel well being adapted to receive the expandable member. The expanded shape of the expandable member is preferably non-circular. More preferably, the expanded shape includes a substantially linear portion. The linear portion is preferably a ground engaging portion of the wheel. The expanded shape is preferably of substantially triangular configuration. In the expanded shape, at least part of the expandable member preferably extends from the wheel rim. A self-levelling mechanism preferably extends between the frame and a bracket for connecting the frame to the vehicle, for adjusting an angle between the frame and the bracket to retain a user seat in the vehicle within a predetermined angle range relative to horizontal. The predetermined angle range is preferably between approximately -5 degrees and +5 degrees when the wheel is traversing substantially horizontal ground. The predetermined angle range is preferably between 0 degrees and +/-20 degrees, and more preferably approximately 12 degrees, when the wheel is traversing an incline. The self-levelling mechanism preferably includes a tilt sensor for sensing a value indicative of the inclination angle of the ground being traversed. A controller is preferably responsive to the tilt sensor for controlling actuation of. an actuator for adjusting the angle between the frame and the bracket. The expanding mechanism preferably comprises an arm hingedly connected at one end to the frame. The arm is preferably hingedly moveable in a plane parallel to the plane defined by the wheel rim. A roller is preferably rotatably connected to an opposite end of the arm for engaging the expandable member. The roller is preferably rotatable in a plane parallel to the plane defined by the wheel rim. The roller preferably includes a roller rim and a roller floor extending generally normal to the roller rim. The roller floor preferably includes openings engageable by the expandable member. The roller floor is preferably defined by a plurality of pins, preferably in the form of rivets, extending from the roller rim. The pins preferably have heads on their free ends for guiding the expandable member. The expandable member is preferably engaged by the roller and guided between the roller rim and the heads of the pins when the expanding mechanism moves the expandable member into the expanded shape. An actuating mechanism is preferably provided between the frame and the arm to rotate the arm. The actuating mechanism may, for example, comprise a worm drive, an electro-hydraulic actuator or one or more gear wheels engaged with a gear wheel on the arm. In other embodiments, the expanding mechanism comprises a linear actuator connected at one end to the frame and at the other end to a roller for engaging the expandable member. The expanding mechanism preferably includes two of the arms, each arm preferably having an associated actuating mechanism. An electronic controller is preferably provided for controlling the expanding mechanism. A control panel is preferably connected to the controller for receiving commands from a user.

In the disengaged configuration, the expanding mechanism is preferably located within a periphery of the wheel rim. The wheel floor preferably includes openings meshingly engageable by the expandable member. The wheel floor is preferably defined by a plurality of pins, preferably in the form of rivets, extending from the wheel rim. The expandable member preferably engages the pins, so as to be driven by the pins upon rotation of the wheel rim. An expandable member is preferably received in the wheel well. The expandable member preferably comprises: a plurality of interconnected engagement elements movable relative to each other in a direction between a retracted configuration and an expanded configuration; at least one resilient member interconnecting the engagement elements, the resilient member biasing the engagement elements toward the retracted configuration; at least one limiting member interconnecting the engagement elements for defining the maximum extent of the expanded configuration.

The engagement elements preferably include gripping portions extending substantially normal to said direction. The engagement elements preferably have a substantially trapezoidal cross-section, with the gripping portions defining opposite sides of the engagement elements. The engagement elements are preferably formed from a resilient material. In a preferred form, the engagement elements are formed from a rubber material, In some embodiments, the engagement elements are formed from composite materials. For example, the engagement elements may include a rigid plate embedded in a resilient material. The rigid plate may be formed from steel, aluminium, carbon fibre, or another suitable structural material. The engagement elements preferably include a hollow core. The engagement elements preferably include an arcuate outer surface extending between the gripping portions. The radius of the arcuate surface is preferably greater than 200mm and preferably less than 400mm. In a preferred form, the radius of the arcuate surface is between 290mm and 320mm.

The resilient member is preferably formed from a material selected from the group consisting of: silicone and elasticised fabric.

The limiting member is preferably formed from a material of relatively low elasticity. The limiting member may be formed from medium density polyethylene (MDPE) or from webbing; for example Dyneema, Nylon, Polyester, or Kevlar webbing. The limiting member is preferably pleated when the engagement elements are in their retracted configuration to allow the engagement elements to move into their expanded configuration.

Mechanical fasteners preferably extend between the resilient member, the limiting member and the engagement elements to connect these components together.

The mechanical fasteners may be tri-fold rivets. However, nuts and bolts can be used to connect the components together in other embodiments. In further embodiments, bolts may engage a thread in the engagement elements to connect the components together.

A plurality of lugs may extend from a side of the expandable member opposite the engagement elements. Bach of the lugs may be connected to a respective one of the engagement elements. The lugs may be connected to the engagement elements by mechanical fasteners extending between the lugs, the resilient member, the limiting member and the engagement elements. The lugs may be adapted to transmit a driving force from a driving element to the expandable member, The engagement elements are preferably interconnected so as to form a continuous loop. A hand rim is preferably connected to the wheel rim. A gear train is preferably provided between the hand rim and the wheel rim. In a first gear setting, the gear train provides a gear ratio of approximately 1 : 1 between the hand rim and the wheel rim. In a second gear setting the gear train is preferably adapted to provide a gear ratio of between 5: 1 and 15: 1 between the hand rim and the wheel rim to reduce the amount of manual effort required on the hand rim to rotate the wheel rim. The gear train preferably includes a series of planetary gears. The planetary gears preferably include a sun gear connected to the hand rim and a ring gear connected to the wheel rim. At least one intermediate gear preferably meshingly engages the sun gear and the ring gear. In the first gear setting, the planetary gears are preferably locked to provide the approximately 1 :1 gear ratio between the hand rim and the wheel rim. A geared reduction handle is preferably provided to facilitate manual selection of the first gear setting and the second gear setting. The geared reduction handle preferably requires application of a predetermined force for movement between the first gear setting and the second gear setting. The predetermined force is preferably between 2 and 6 N.m, and more preferably approximately 3.5 N.m. In other embodiments, a worm drive may be used instead of the planetary gears.

A ratchet mechanism is preferably provided to rotationally lock the wheel rim to the frame to prevent the wheel rim rotating due to gravity. The ratchet mechanism is preferably actuated when the expanding mechanism is actuated. The ratchet mechanism preferably includes a ratchet pin fixedly connected to the frame and engageable with spaced apertures in the wheel rim. The pin is preferably biased toward engagement with the apertures by a solenoid. In a first direction of wheel rotation, the bias applied by the solenoid can be overcome by user rotation of the wheel rim. In a second direction of wheel rotation, the bias applied by the solenoid cannot be overcome by user rotation of the wheel rim and the pin is preferably disengageable from the wheel rim by a user operating a control panel to actuate the solenoid and retract the pin. A second pin and an associated second solenoid are preferably fixedly connected to the frame. The second pin is preferably also engageable with the spaced apertures in the wheel rim. When the wheel is rotating in the second direction of wheel rotation with the expanding mechanism actuated, the ratchet pin and second pin preferably alternately engage the apertures in the wheel rim to control the speed of rotation of the wheel rim. The ratchet pin and second pin are preferably controlled by a controller to engage the apertures in the wheel rim once in approximately every 1 to 5 degrees, and more preferably approximately once in every 1.5 degrees, of rotation of the wheel rim. The ratchet pin and/or second pin are also preferably adapted for use as brakes for the wheel rim.

An opening is preferably provided in the frame to allow the expanding mechanism to move between the disengaged configuration and the engaged configuration.

A further aspect of the present disclosure provides an expandable member comprising: a plurality of interconnected engagement elements movable relative to each other in a direction between a retracted configuration and an expanded configuration; at least one resilient member interconnecting the engagement elements, the resilient member biasing the engagement elements toward the retracted configuration; at least one limiting member interconnecting the engagement elements for defining the maximum extent of the expanded configuration.

The engagement elements preferably include gripping portions extending generally transverse to said direction. The engagement elements preferably have a substantially trapezoidal cross-section, with the gripping portions defining opposite sides of the engagement elements. The engagement elements are preferably formed from a resilient material. The engagement elements may be formed from a rubber material. In some embodiments, the engagement elements are formed from composite materials. For example, the engagement elements may include a rigid plate embedded in a resilient material. The rigid plate may be formed from steel, aluminium, carbon fibre or another suitable structural material. The engagement elements may include a hollow core. The engagement elements may include an arcuate outer surface extending between the gripping portions. The radius of the arcuate surface may be greater than 200mm and preferably less than 400mm. In an embodiment, the radius of the arcuate surface is between 290mm and 320mm.

The resilient member may be formed from a silicone material. However, in other embodiments, the resilient member is formed from an elasticised fabric material.

The limiting member is preferably formed from a material of relatively low elasticity. The limiting member may be formed from medium density polyethylene

(MDPE). In other embodiments, however, the limiting member is formed from webbing; for example Dyneema, Nylon, Polyester, or Kevlar webbing. The limiting member is preferably pleated when the engagement elements are in their retracted configuration to allow the engagement elements to move into their expanded configuration. Mechanical fasteners may extend between the resilient member, the limiting member and the engagement elements to connect these components together. The mechanical fasteners may be tri-fold rivets. However, nuts and bolts can be used to connect the components together in other embodiments. In further embodiments, bolts may engage a thread in the engagement elements to connect the components together.

A plurality of lugs may extend from a side of the expandable member opposite the engagement elements. Each of the lugs may be connected to a respective one of the engagement elements. The lugs may be connected to the engagement elements by mechanical fasteners extending between the lugs, the resilient member, the limiting member and the engagement elements. The lugs may be adapted to transmit a driving force from a driving element to the expandable member.

The engagement elements are preferably interconnected so as to form a continuous loop.

A still further aspect of the present disclosure provides a wheel comprising: a frame adapted for fixed connection to a vehicle body; a wheel assembly rotatably connected to the frame; a hub located centrally in the wheel assembly for connection to an axle; at least one locking member connected to one of the frame and the wheel assembly and selectively engageable with the other of the frame and the wheel assembly to lock the frame and the wheel assembly against relative rotation,

An actuator may be associated with the locking member for selectively engaging the locking member with the other of the frame and the wheel assembly.

Two of the locking members may be provided. Each of the locking members may have an associated actuator. The locking members may be alternately selectively engageable with the other of the frame and the wheel assembly.

Another aspect of the present disclosure provides a wheel comprising: a wheel assembly; a hub located centrally in the wheel assembly for connection to an axle; a planetary gear train mounted on the wheel assembly, gears of the gear train being selectively lockable to provide a first gear setting and selectively releasable to provide a second gear setting.

A gear reduction handle may be mounted to the planetary gear train for facilitating manual transition between the first gear setting and the second gear setting.

Yet another aspect of the present disclosure provides a wheelchair comprising a wheel as defined in any one of the first, third or fourth aspects above. Brief Description of the Drawings

Preferred embodiments of a wheel and expandable member therefor will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is an exploded perspective view of the wheel; Fig. 2 is an outer side assembled perspective view of the wheel of Fig. 1 with its expandable member in an unexpanded state;

Fig. 3 is an inner side assembled perspective view of the wheel of Fig. 1 with its expandable member in an unexpanded state;

Fig. 4 is an outer side assembled perspective view of the wheel of Fig. 1 with its expandable member in an expanded state;

Fig. 5 is an inner side assembled perspective view of the wheel of Fig. 1 with its expandable member in an expanded state;

Fig. 6 is an enlarged exploded perspective view of the expandable member of the wheel of Fig. 1 ; Figs. 7A to 7F are schematic views of the wheel of Fig. 1 climbing a set of stairs;

Figs. 8Λ to 8G are schematic views of the wheel of Fig. 1 descending a set of stairs; and

Figs. 9 and 10 are schematic views of an alternative wheelchair embodiment, shown, respectively, in a retracted configuration and a deployed configuration.

Detailed Description of Preferred Embodiments

Referring to the drawings, and initially to Figs. 1 to 5, there is shown a wheel 10 comprising a frame 12 adapted for fixed connection to the body of a wheelchair. A wheel assembly 14 is rotatably connected to the frame 12. A hub 16 is located centrally in the wheel assembly 14 for connection, to an axle assembly. The axle assembly comprises a bracket 20 for fixed connection to the wheelchair body and an axle pin 22, which extends through the hub 16 and engages the bracket 20 for rotationally connecting the wheel assembly 14 to the bracket 20.

A wheel rim 28 extends around the wheel assembly 14 and defines a plane. A floor 30 extends generally transverse to, and around a periphery of, the wheel rim 28. The wheel floor defined by a plurality of pins 30, in the form of rivets, extending from the wheel rim 28. Openings 31 are defined between the pins 30. A wheel well 32 is defined between the rim 28 and the floor 30. An expandable member, in the form of a traction member 34, is received in the wheel well 32. The traction member 34 engages the pins 30 and the openings 31 , so as to be driven thereby upon rotation of the wheel rim 28.

Referring to Fig. 6, the traction member 34 ^° comprises a loop formed from a plurality of interconnected engagement elements 34a movable relative to each other in a direction between a retracted configuration and an expanded configuration. A resilient member, in the form of a loop of silicone material 34b, interconnects the engagement elements 34a. The resilient member 34b biases the engagement elements 34a toward the retracted configuration. A limiting member, in the form of a loop of medium density polyethylene (MDPE) 34c, interconnects the engagement elements 34a for defining the maximum extent of the expanded configuration. The limiting member 34c is pleated when the engagement elements 34a are in their retracted configuration to allow the engagement elements 34a to move into their expanded configuration.

The engagement elements 34a include gripping portions 34d extending substantially transverse to the direction of extension of the traction member 34 (i.e. generally outwardly). The engagement elements 34a have a substantially trapezoidal cross-section, with the gripping portions 34d defining opposite sides of the engagement elements 34a. The engagement elements 34a are formed from a resilient rubber material and include a hollow core. The engagement elements 34a include an arcuate outer surface 34e, having a radius of approximately 305mm, extending between the gripping portions 34d.

A plurality of lugs 34f extend from a side of the expandable member 34 opposite the engagement elements 34a. Each of the lugs 34f is connected to a respective one of the engagement elements 34a by a mechanical fastener, in the form of a tri-fold rivet (not shown), which extends between the lug 34f, the resilient member 34b, the limiting member 34c and into the engagement element 34a. The lugs 34f are adapted to transmit a driving force from a driving element, in the form of pins 31, to the traction member 34 to rotate the traction member 34.

Referring again to Figs. 1 to 5, an expanding mechanism is extendable between the frame 12 and the traction member 34, The expanding mechanism is movable relative to the frame, between a disengaged configuration, as shown in Figs. 2 and 3, and an engaged configuration, as shown in Figs. 4 and 5, to expand the traction member 34 into a deployed configuration in ^' which the traction member 34 has an expanded shape. The expanding mechanism comprises arms 36, each hingedly connected at one end to the frame 12. The arms 36 are hingedly movable in a plane parallel to the plane defined by the wheel rim 28. A roller 38 is rotatably connected to an opposite end of the arms 36 for engaging the _, traction member 34. The roller 38 is also rotatable in a plane parallel to the plane defined by the wheel rim 28. The roller 38 includes a roller rim 40 and a roller floor, defined by a plurality of pins 42 (in the form of rivets), extending generally normal from the roller rim 40. The roller floor includes openings 44, defined between the pins 42, engageable by the traction member 34. The pins 42 have heads on their free ends for guiding the traction member 34. The traction member 34 is engaged by the roller 38 and guided between the roller rim 40 and the heads of the pins 42 when the expanding mechanism moves the traction member 34 into the expanded shape shown in Figs. 4 and 5. Openings 45 are provided in the frame 12 to allow the rollers 38 to pass therethrough during movement of the arms 36 between the disengaged configuration and the engaged configuration of the expanding mechanism.

An actuating mechanism 46 is provided between the frame 12 and each of the arms 36 to rotate the arm 36. The actuating mechanism 46 comprises an electro- hydraulic actuator having a motor and worm drive gearbox. An electronic controller 48 is provided for controlling deployment and retraction of the arms 36 of the expanding mechanism via the actuating mechanism 46. As best seen in Figs. 3 and 5, a control panel 50 (see Figs. 3 and 5) is connected to the controller 48 for receiving commands from a user. The expanded shape of the traction member 34, with the arms 36 in the deployed configuration as shown in Figs. 4 and 5, is generally triangular and includes a substantially linear ground engaging portion 51 , which facilitates stabilising the wheel 10 when traversing uneven terrain. In the expanded shape, parts of the traction member 34 extend from the wheel rim 28. The limiting member 34c defines the maximum length of the expandable member 34 to ensure that the expandable member 34 does not over-extend and disengage from the pins 30.

As shown in Figs. 2 and 3, in the disengaged configuration of the expanding- mechanism, with the arms 36 retracted, the expanding mechanism is located within a periphery of the wheel rim 28. A hand rim 52 is connected to the wheel rim 28. A gear train is provided between the hand rim 52 and the wheel rim 28. In a first gear setting, the gear train provides a gear ratio of approximately 1 :1 between the hand rim 52 and the wheel rim 28. In a second gear setting the gear train is adapted to provide a gear ratio of between 5: 1 and 15:1 between the hand rim 52 and the wheel rim 28 to reduce the amount of manual effort required on the hand rim 52 to rotate the wheel rim 28. The gear train includes a series of planetary gears including a sun gear (not shown) connected to an inner side of the hand rim 52 and a ring gear 56 connected to the wheel rim 28. Intermediate gears 58 meshingly engage the sun gear 54 and the ring gear 56. In the first gear setting, the planetary gears are locked to provide the approximately 1 :1 gear ratio between the hand rim 52 and the wheel rim 28. A geared reduction handle 60 is provided to facilitate manual selection of the first gear setting and the second gear setting. The geared reduction handle 60 requires application of a predetermined force of approximately 3.5 N.m for movement between the first gear setting and the second gear setting. This predetermined force reduces the likelihood of accidental movement between the first and second gear settings and also provides a user with positive feedback that the change from one gear setting to the other has been effected.

A self- levelling mechanism is provided between the frame 12 and the bracket 20 for adjusting an angle between the frame 12 and the bracket 20. This adjustment facilitates retaining the wheel chair seat within a predetermined angle range relative to horizontal when traversing uneven ground or when climbing or descending stairs or other inclines. The predetermined angle range is between approximately -5 degrees and +5 degrees when the linear ground engaging portion 51 is substantially horizontal. The predetermined angle range is a recline of approximately 12 degrees when the wheel chair is traversing an incline and the linear ground engaging portion 51 is inclined. The self-levelling mechanism includes an actuator comprising a ring gear 62 on the bracket 20, which is meshingly engaged by a drive gear 64. The drive gear 64 is fixedly connected to the frame 12 and is drivable by a worm gear (not shown) to rotate the frame 12 relative to the bracket 20. The self-levelling mechanism also includes a tilt sensor (not shown) for sensing an inclination angle of the linear ground engaging portion 51. The controller 48 is responsive to the tilt sensor (not shown) for controlling actuation of the worm gear (not shown).

As shown in Fig. 1, a ratchet mechanism is provided to rotationally lock the wheel πm 28 to the frame 12 to prevent the wheel rim 28 rotating due to gravity. The ratchet mechanism is actuated when the expanding mechanism is actuated to deploy the arms 36. The ratchet mechanism includes a locking member, in the form of a ratchet pin 66, fixedly connected to the frame 12 and engageable with spaced apertures 68 in the wheel rim 28 . The pin 66 is biased toward engagement with the apertures 68 (see Fig. 5) by a solenoid 70. In a first direction of wheel rotation, when the wheel chair is being wheeled uphill, the bias applied by the solenoid 70 can be overcome by user rotation of the wheel rim 28. This allows the wheel 10 to be rotated relative to the wheelchair body whilst the user is applying effort to the wheel rim 28, but engages the pin 66 with the apertures 68 when the user ceases applying effort to prevent the wheelchair from rolling back down the hill. In a second direction of wheel rotation, when the wheelchair is being wheeled downhill, the bias applied by the solenoid 70 cannot be overcome by user rotation of the wheel rim 28 and the pin 66 is disengageable from the wheel rim 28 by the user operating the control panel 50 to signal the controller 48 to actuate the solenoid 70 and retract the pin 66. A second pin 72 and an associated second solenoid 74 are fixedly connected to the frame 12. The second pin 72 is also engageable with the spaced apertures 68 in the wheel rim 28.

When the wheel 10 is rotating downhill in the second direction of wheel rotation with the expanding mechanism actuated to deploy the arms 36, the ratchet pin 66 and pin 72 are controlled by the controller 48 to alternately engage the apertures 66 in the wheel rim 28 to control the speed of rotation of the wheel rim 28. The ratchet pin 66 and second pin 72 engage the apertures 68 in the wheel rim 28 once in approximately every 1.5 degrees of rotation of the wheel rim 28. The ratchet pin 66 and second pin 72 are also adapted for use as brakes for the wheel rim 28. To actuate the pins for use as brakes, the user presses a brake button on the control panel 50, which disengages the solenoids 70 and 74 and biases the pins 66, 72 into engagement with the wheel rim 28 to engage one of the pins with the apertures 68. The body of a wheelchair typically includes an upright tubular member to which an axle pin of the wheelchair wheel is connected. To connect the wheel 10 to the wheelchair body, a. semicircular groove 76 on the bracket 20 is engaged with the upright tubular member of the wheelchair body. The axle pin 22 is then installed through the hand rim 52, the wheel rim 28, the frame 12 and ^' the bracket 20, and is engaged with the upright tubular member of the wheelchair.

When a wheelchair with wheels 10 attached is traversing substantially level ground, the expanding member would typically be in its disengaged configuration, as shown in Figs. 2 and 3, with the arms 36 retracted.

When the wheelchair 100 is traversing an incline, such as a set of stairs 78 as shown in Fig. 7A to 7F, the expanding mechanism is engaged, with the arms 36 deployed to expand the traction member 34 to increase the size of the footprint of the ground engaging portion 51. The wheelchair 100 approaches the incline in a reverse direction as shown in Fig. 7A. At the base of the incline, the user presses a button on the control panel 50, which signals the controller 48 to actuate actuating mechanisms 46 to deploy the arms 36 and expand the traction member 34 into the expanded configuration shown in Figs. 7B to 7E. With the arms 36 deployed, the traction member 34 adopts its triangular configuration, in which the engagement elements 34a are spaced apart to increase the surface area of the traction member 34 to assist in gripping the stairs 78, The large footprint of the ground engaging portion 51 also facilitates stabilising the wheelchair 100 when traversing the stairs 78. The user engages the second gear setting by turning the geared reduction handle 60. The user then reverses the wheelchair until the wheels 10 engage the base of the stairs 78. As the wheelchair starts to tip forward as it climbs the stairs 78, the self-levelling mechanism is automatically engaged to recline the wheelchair by approximately 12 degrees and to maintain this angle of recline during ascent up the stairs 78. During the ascent, the gripping portions 34d of the engagement elements 34a engage the stairs 78. Between each of the user's driving strokes on hand rim, the ratchet pin 66 of each wheel 10 engages an aperture 68 in the wheel rim 28 to lock the wheel 10 against rotation to prevent the wheelchair from rolling back down the stairs 78. At the top of the stairs 78, as shown in Figs. 7E and 7F, the user presses a button on the control panel 50 to signal the controller 48 to actuate actuating mechanisms 46 to retract the arms 36 and retract the traction member 34 into the unexpanded configuration. With the arms 36 retracted, the self-levelling mechanism is deactivated, such that the wheelchair is no longer reclined. When the arms 36 are retracted, solenoids 70 and 74 are deactivated to retract the pins 66 and 72 out of engagement with the apertures 68 in the wheel rim 28. Operation of the wheelchair with wheels 10 on a decline is shown in Figs 8A to

8G. Downhill operation is similar to uphill operation as described above. However, in downhill operation, the wheelchair is initially reclined by an angle of approximately 35 degrees. As shown in the transition between Figs. 8C and 8D, once a sensor in the wheels 10 senses that more than approximately half of the user's weight is over the edge of the top stair 78, the controller 48 controls the self-levelling mechanism to adopt a recline angle of approximately 12 degrees and to retain this recline angle for the remainder of the descent. Also, in downhill operation, when the arms 36 are deployed, the controller 48 controls alternate engagement and retraction of pins 66 and 72 through solenoids 70 and 74 to control the speed of descent of the wheelchair. In downhill operation, either the first or second gear setting can be used, since gravity drives the wheelchair down the decline and the pins 66 and 72 control the descent rate.

It will be appreciated that the illustrated wheel 10 provides numerous advantages over conventional wheelchair wheels. In particular, the wheel 10 facilitates traversing of inclines and descents, including stairs, in non-powered wheelchairs. The increased footprint provided by expanded configuration of the traction member 34 is also advantageous where the user wishes to traverse uneven, soft or slippery terrain. The wheel 10 also has advantages of improved control and safety. The gearing arrangement disclosed also facilitates a reduction in the effort required by a user when traversing inclines, declines and difficult terrain. The unexpanded circular configuration of the wheel 10 facilitates speed and comfort on level ground, with relatively quick and easy conversion to the expanded triangular tracked configuration when difficult terrain is encountered. The design of the wheel 10 is also such that its dimensions are substantially the same as those of a conventional wheelchair wheel (i.e. width of approx 1 13mm from point of engagement with the wheelchair body and diameter, with arms 36 retracted, of approximately 610mm). An alternative embodiment of a wheelchair according to the present disclosure is shown schematically in Figs. 9 and 10. The alternative embodiment shares many features in common with the earlier described embodiment, where corresponding reference numerals indicate corresponding features with corresponding functions. In the alternative embodiment of Figs. 9 and 10, however, the expandable member 34 is replaced with a non-elasticised traction member 134. The traction member 134 extends around a plurality of rollers 180 mounted on arms 36. In the retracted configuration of Fig. 9, the arms 36 and traction member 134 are located within the perimeter of the wheel assembly and a ground engaging portion 382 of the traction member is elevated relative to a ground engaging portion 184 of the wheel assembly. Accordingly, no length of the traction member 134 is available for contact with the ground. However, when the arms 34 and reconfigured into the deployed configuration of Fig. 10, the ground engaging portion 182 of the traction member is lower than the ground engaging portion 184 of the wheel assembly. Accordingly, in the deployed configuration, a substantial ground engaging length of the traction member 134 is available for ground contact, Also, as shown in Fig. 10, a gear train, comprising sprockets 186 and chain 188, is provided between the hub 16 and the traction member 134. As will be appreciated, rotation of the hub 16 is driven by manual effort on the hand rim (not shown). Moving the traction member 134 into the retracted configuration of Fig. 9 automatically disengages the gear train from the hand rim and moving the traction member 134 into the deployed configuration of Fig. 10 automatically engages, via the hub 16, the gear train with the hand rim.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the specific embodiments without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Examples of modifications included in other embodiments (not shown) include, but are not limited to:

• the expanding mechanism comprising a linear actuator connected at one end to the frame ] 2 and at the other end to a roller for engaging the traction member 34;

• the engagement elements 34a being formed from composite materials (for example, a rigid plate of steel, aluminium, carbon fibre or other suitable structural material embedded in a resilient material);

• the resilient member 34b being formed from an elasticised fabric material; • the limiting member 34c being formed from webbing; for example Dyneema, Nylon, Polyester, or Kevlar webbing;

• the resilient member 34b and/or limiting member 34c being discrete lengths of material extending between adjacent engagement elements 34a, instead of being a continuous loop; « the engagement elements 34a, resilient member 34b, limiting member 34c and lugs 34f being interconnected by nuts and bolts, or by bolts engaging a thread in the engagement elements 34a;

• a worm drive being used between the hand rim 52 and wheel rim 28 instead of the planetary gears; • scaling up of the wheel, for example for use in larger vehicles or machinery;

• scaling down of the wheel, for example for use in toys or trolleys;

• providing tracks of different widths to facilitate traversal of the wheelchair over different terrain (eg. narrow tracks for roads and footpaths and wider tracks for sandy, snowy or uneven terrain); and/or • modification of the engagement elements 34a to provide increased traction and/or load bearing capacity.