WO2008065407A1

WO2008065407A1 - Vehicle wheel

Info

Publication number: WO2008065407A1
Application number: PCT/GB2007/004581
Authority: WO
Inventors: Vincente Osmar Rodrigues
Original assignee: Royal College Of Art; Vincente Osmar Rodrigues
Priority date: 2006-11-29
Filing date: 2007-11-29
Publication date: 2008-06-05

Abstract

A variable diameter/width wheel for a vehicle is provided that has an axis of rotation and comprising: a rim, a hub configured for attachment to an axle or shaft, the hub comprising a first part (20) and a second part (22) that are both arranged on the said rotational axis, and arching members (7) having first and second ends and being connected at the first end to the first hub part and at the second end to the second hub part, so that the arching members extend outwardly in an arc between the first and second hub members and form or support the wheel rim, The first and second hub parts (20, 22) can be moved towards or away from each other to change the shape of the arc of the arching members (7) and the two hub parts are lockable in a fixed position relative to each other to maintain a given arc shape. Moving the hub parts (20, 22) towards each other makes the arc shape of the arching members taller and thinner, thereby increasing the diameter of the wheel and decreasing its width while moving the hub parts (20, 22) away from each other makes the arc shape shorter and wider, thereby decreasing the diameter of the wheel and increasing its width.

Description

VEHICLE WHEEL

Technical Background

The present invention relates to a vehicle wheel having a variable diameter and width.

Background Art

The provision of a wheel for a vehicle having a variable diameter is known. For example, US-A-3802743 describes a variable diameter wheel having a rim made up of individual segments. Each segment is supported by a piston that can be moved from a retracted position, where the wheel diameter is small, to an extended position, where the wheel diameter is large. This arrangement is used to allow vehicles to traverse the contours of a steep hill without tilting or tipping by making the wheel higher up the hill small and the wheel further down the hill large.

EP-A-0665128 describes a vehicle wheel having a number of sliders that can be extended by means of hydraulic pressure to increase the outer diameter of the wheel.

US-2004036347 describes a vehicle having a number of tyres, each having different road gripping characteristics. A desired tyre is selected by inflating it so that it has a larger diameter than the other tyres and therefore engages the road in preference to the other tyres.

US-1980314 and GB-251256 disclose a vehicle wheel with a rim whose diameter can be reduced to simplify the changing of a tyre. Once the tyre has been fitted, the rim is expanded to its original diameter. Neither contemplates operating the wheel with the reduced diameter.

US-756290 discloses a wheel whose diameter can be adjusted by altering the length of adjustable wheel spokes. GB-1078817 discloses a wheel having a segmented rim in which the segments of the rim are support on a two-part wheel hub by spokes that are not in alignment with the wheel radius. The overall diameter of the wheel can be adjusted by means of the two-part hub; the parts of the hub can be pivoted about the wheel axis relative to each other and thereby bring the spokes into closer alignment with the wheel radius (thereby increasing the wheel diameter) or out of alignment with the wheel radius (thereby decreasing the wheel diameter).

US-2916331 discloses an elliptical wheel having a segmented rim whose segments are moved in an elliptical path to mimic a tracked vehicle.

Disclosure of Invention

The present invention provides a wheel of variable diameter which, in addition to changing its diameter, can also change its width, thereby increasing the area of the wheel that engages the ground. Thus, the wheel of the present invention can be adjusted to increase a vehicle's performance according to the terrain over which it is travelling. For example, on a hard surface, a large diameter wheel with a low footprint area (i.e. area where the wheel and ground are in contact) can be used whereas on soft, yielding ground, a smaller diameter wheel with a larger width can be provided that has a larger footprint area and will prevent the wheel from sinking into the ground.

In accordance with the present invention there is provided a variable diameter and width wheel for a vehicle, the wheel having an axis of rotation and comprising: a rim, a hub configured for attachment to an axle or shaft, the hub comprising a first part and a second part that are both arranged on the said rotational axis, and at least one arching member having first and second ends and being connected at the first end to the first hub part and at the second end to the second hub part, wherein the arching member extends outwardly in an arc between the first and second hub members and forms or supports the wheel rim, wherein the first and second hub parts can be moved relative to each other to change the shape of the arc of the at least one arching member, and wherein the two hub parts are lockable in a fixed position relative to each other.

The term "arc" is not used in its strict mathematical sense (i.e. part of the circumference of a circle) but in its wider sense to mean an arch or curve. The at least one arching members may be made up of a plurality of flexible hoops spaced radially around the hub and extending radially outward from the hub. Alternatively the at least one arching member may be a hollow annular flexible tyre having a central opening defined by two internal rims. These rims form the said two ends of the arching member that are connected to the first and second hub parts so that, as the two hub parts are moved relative to each other, the width and diameter of the tyre will change.

If the arched member(s) do not prevent material, e.g. soil, mud, water etc, penetrating into the interior of the wheel, as is the case when the arched members are hoops, an outer covering may be provided that at least partly overlies the arched member(s) and that is deformable to adopt the shape outlined by the arched member(s). The outer covering may be sealed to form a pneumatic cushion for the vehicle but generally the pressure inside the cover will be low enough so that contact is maintained between the arched members and the covering.

Likewise, when the arched member is in the form of a tyre, the tyre can be pneumatically inflated, e.g. by including an inner tube within the tyre or by sealing a cavity within the tyre, e.g. the tyre may have a toroidal shape, enclosing a pressurisable annular cavity within the tyre, which would eliminate the necessity of a inner tube.

As mentioned, the first and second hub parts are movable with respect to each other and the direction of relative movement is, in one embodiment, along the said axis of rotation of the wheel. To this end, at least one of the hub parts may be movable along a rod that lies on the rotational axis. This movement can be achieved in a number of ways, e.g. by means of a pneumatic or hydraulic ram or by providing the rod with a screw thread that is engaged by the movable hub part so that the movable hub part may be driven along the rod by turning the rod, e.g. with the aid of a motor.

In one embodiment, only one of the hub parts is movable while the other is not, e.g. it is in a fixed location with respect to a vehicle.

The present invention also provides a vehicle provided with one or more wheels as described above. The primary use of the wheel of the present invention is for off road vehicles, for example agricultural vehicles, where varying under-wheel conditions may be encountered and where it is important that the wheels should not sink into the ground or compact the soil more than necessary and where the wheels can often slip in muddy conditions. The wheel may be used both on vehicles that are self-propelled or those that are not. However, the wheel can also be used for on-road vehicles as well.

Detailed Description of Drawings There will now be described, by way of example only, various embodiments of wheels in accordance with the present invention, by reference to the accompanying drawings in which:

Figure 1 is an exploded view of a wheel in accordance with the present invention; Figure 2 is a side elevation of the wheel of Figure 1 ;

Figure 3 is an end view of the wheel of Figures 1 and 2;

Figure 4 is a perspective view of the wheel of Figures 1 to 3;

Figures 5 to 7 are perspective views of various parts of the wheel shown in Figure 4; Figure 8 is a perspective view of part of a wheel in accordance with the present invention suitable for use on water to provide buoyancy to a vehicle and also to provide additional support and extra load-carrying capacity;

Figure 9 is a side elevation of the wheel in accordance with the present invention and is similar to that of Figure 4 but incorporates a floatation bladder as shown in Figure 8;

Figure 10a is a side elevation and Figure 10b is a perspective view of the wheel of Figure 4 but including a cover for use on water or land, especially on moisturized mud ;

Figure 11 (a) to (c) are photographs showing the wheel of Figures 1 to 10 in a large diameter/narrow configuration (Figure 11 (a)), in a small diameter/wide configuration (Figure 11(c)) and in an intermediate configuration (Figure 11 (b));

Figure 12 is a sectional view through a rim of a wheel in accordance with the present invention;

Figure 13 is a view of a hub part of the wheel. Figure 14 is an exploded perspective view of a second embodiment of the mechanism of the present invention for changing the diameter and width of a wheel;

Figure 15 is a detailed part of the mechanism shown in Figure 14;

Figure 16 shows the mechanism of Figure 14 fully assembled, but component 103 is shown partly broken away;

Figure 17 shows a wheel of the present invention, which incorporates the mechanism of Figures 14 to 16;

Figure 18 is a vertical sectional view of the wheel of Figure 17 but without the mechanism of Figures 14 to 17 and Figures 19 and 20 are exploded perspective view of many of the components of the wheel of Figures 14 to 18 showing two methods of attachment to a vehicle.

Detail description of the best mode of putting the invention into operation Referring initially to Figure 2, there is shown a wheel in accordance with the present invention that has a cage 24 composed of thirty six equi-spaced, radially extending hoops 7 that arch between a first hub part 20 and a second hub part 22. A rod 1 extends through the first hub part 20 into the second hub part 22. The hoops are made of helical steel springs steel filled by wire rope obtained by cutting the spring to the desired length and threading a section of wire rope with the same length and internal diameter as the spring through the centre of the spring. However, the hoops may be made of any material that is strong, stiff and resilient enough to support the loads imposed on the wheels, while also being flexible to allow the diameter of the wheel to be changed as discussed below.

The component parts of the wheel will be described in further details initially with reference to Figures 1 to 11 and 13. From these drawings, it can be seen that the rod 1 extends along the rotary axis of the cage 24 of hoops.

The rod 1 includes a section 26 at one end of the rod that incorporates a helical groove 27; the rod also includes a stop section 28 at the opposite end of the rod to the helical groove 27.

The wheel is constructed on the rod 1 and, starting from the left hand side of the rod as seen in Figures 1 and 2, there is a spacer cylinder 2, which is made of metal, e.g. steel, or of a strong plastic material, for example PPS (poly(p-phenylene sulfide), POM (polyoxymethylene) or a metallic polymer alloy, e.g. a pure iron powder uniformly dispersed in a insulating plastic binder. The spacer cylinder 2 abuts the stop section 28 of the rod and limits the longitudinal movement of a cylinder 3, which has a central bore 30 that fits on the helical section 26 of the rod 1. Within the bore 30, there are provided a number of ball bearings that stand proud of the bore 30 and that are configured to run in the helical groove 27 of rod section 26. Accordingly, when the rod 1 is twisted about its central axis, the cylinder 3 moves axially along the rod 1 either towards the stop 28 or away from the stop, depending on the direction in which the rod is turned. The cylinder 3 may conveniently be composed of plastic, e.g. PPS, POM or metallic polymer alloy although it can also be made of metal, for example steel.

The cylinder 3 has a flange 32 at one end that is secured to a circular connector 4 of hub part 20 by means of screws (see Figure 5) that pass through the flange 32 and engage in screw holes (not visible in Figure 1 and 6) in the hub connector 4. The hub connector 4 includes thirty six equally spaced socket holes 34 around a cylindrical outer face. The socket holes 34 together accommodate one end of each of the hoops 7 that together form the cage 24. The ends of the hoops are secured in the holes by bolts (not visible) that are present in an array of holes 35 (see Figure 13) positioned on the external side of the hub connector 4, the bolts engaging the hoops perpendicularly. Alternatively, as described below, the ends of the hoops may be secured by profiling their terminal ends and holding the profiled ends captive in correspondingly shaped sockets in the wheel hub connector 4. The hub connector 4 may be made of a tough plastic material such as POM or metal, for example steel.

The internal side of the hub connector 4, i.e. the side facing the cage 24, is provided with arms 36 (see Figures 1 , 5 and 6) that define between them a recess that holds a bearing 6. On the opposite side of the cage 24, there is a second connector 5 of the second hub part 22 having an identical construction to the hub connector 4. In other words, hub connector 5 has thirty six socket holes 34 provided around a cylindrical outer surface, into which the other ends of the hoops 7 are secured in the same manner as described above. In the same way, the hub connector 5 has arms 36 that provide a recess for holding a further bearing 6'. The rod, which is rotatable on the bearings, passes through bearing 6 and the helically grooved end of the rod 1 is retained in the bearing 6'. The end of the rod 1 is fixed to the inner part of the bearing 6' by means of a simple locker steel ring (not shown). The bearings 6 and 6'are held captive within the hub connectors 4,5 by means of three bolts equally positioned around the outer part of the bearings 6,6' in arms 36 of the hub connectors.

Rings 9 and 10, which may be made of metal, e.g. steel, are secured to the respective external faces of the hub connectors 4,5 via bolts passing though holes in the external rings 9, 10 and secured in corresponding blind threaded holes in the hub connectors 4, 5. Internal rings 11, 12 are likewise secured via bolts to the inside faces of the hub connector 4, 5. When the wheel is in use supporting the weight of a vehicle, and especially when the vehicle is moving, the hoops exert a large lateral load on the side walls of the thirty six equally spaced socket holes 34. The rings 9, 10, 11 and 12 provide reinforcement to the hub connectors 4, 5 and assist in avoiding breakage of the holes 34 by these large lateral forces. In addition, they provide a clamping arrangement for securing an internal inflatable bag 13; the bag fits within the cage 24 and the ends of the bag are clamped between the ring 11 and the hub connector 4, at one end of the bag, and between the ring 12 and the hub connector 5, at the other end. To assist in the clamping, the two ends of the inflatable bag 13 may be secured to bag rings 14, 15 and it is the bag rings 14, 15 that are clamped between the internal rings 11 , 12 and their respective hub connectors 4, 5, thereby providing a gas-tight seal around the two ends of the inflatable bag 13.

The inner inflatable bag 13 is provided to protect the rod 1 from dirt or other debris and also to improve the wheel's performance when under an extra heavy load, once inflated; this improvement in performance under a heavy load is brought about because the inflated bag can support the hoops 7 and so reduce the motion resistance of the wheel. Also the bag supports the hoops if subject to a high pressure that, without the bag 13, would lead to excessive deformation of the hoops. The bag 13 can be inflated by air introduced via a valve (not shown). The bag 13 can also provide buoyancy for amphibious vehicles. Instead of the inflatable bag 13, a hollow cylindrical casing can be used to enclose the rod 1 (see below).

An external stretchable covering 16 can be placed outside the cage 24 and the two mouths of the covering may be clamped between the rings 9, 10 and their respective hub connectors 4, 5. Awheel including such a stretchable covering is shown in Figures 10a and 10b. The external stretchable cover 16 is used to provide buoyancy to the wheel when used in connection with an amphibious vehicle. It will adapt to the shape of the cage 24 when the shape of the wheel is altered, as described below, without the necessity of being inflated. Both the internal bag 13 and the external cover 16 may be used.

A series of spacer elements 8 are provided on alternate hoops 7 to keep the hoops separate and prevent them from becoming entangled with each other.

Figure 4 shows the completed wheel in perspective, while Figure 5 shows the wheel without the cage 24. Further details of the two hub connectors 4,5 are shown in

Figure 6 while the cage itself is shown in Figure 7. Figure 8 shows the wheel without the cage but including the internal bag 13, which is shown partially inflated. Figure 9 shows the wheel of Figure 8 but with the cage 24 and Figure 10 shows the wheel covered by the covering 16.

In use, the diameter and width of the wheel can be changed, as shown in Figures 11 , a, b and c. Figure 11a shows the wheel with the largest diameter but narrowest width and Figure 11c shows the wheel with the smallest diameter and the largest width. Figure 11 b shows the wheel in an intermediary position. The change of diameter can be brought about by turning the rod 1 within the bearings 6,6' relative to the rest of the wheel. If one starts with the arrangement shown in Figure 11 c, turning the rod causes the cylinder 3 provided with ball bearings in its internal bore 30 to move axially along the rod 1 towards the cage 24 as a result of the engagement of the internal ball bearings within the helical groove 27 in section 26 of the rod 1. The cylinder does not twist as it does so because of its connection to the cage 24 via the hub connector 4. As the cylinder 3 moves axially along the rod 1 , it pushes the hub connector 4 in the same direction. Because the hub connector 5 does not move along the rod, the action of turning the rod within the bearings 6 causes the separation between the hub connectors 4 and 5 to be reduced, which causes the hoops 7 to flex and adopt a more arched profile, thereby increasing the diameter of the wheel and reducing its width. Turning the rod in the opposite direction increases the separation between the hub connectors 4, 5 and increases the width of the wheel. The rod 1 can be remotely rotated by means of an assembly that includes an electric motor and a gear box; the assembly may be attached to the rod 1 at its stop end 28. A clutch arrangement (or other manner of breaking and forming the drive between the rod 1 and the gearbox) can be interposed between the rod 1 and the motor/gearbox so that the rod can be decoupled from the motor/gearbox while the vehicle is in motion and coupled to the motor/gearbox while the diameter/width of the wheel is being changed. It will be appreciated that the rod 1 rotates with the rest of the wheel when the vehicle is in motion. Therefore, it is possible to change the diameter/width of the wheel in accordance with the present invention while the wheel is still fitted to a vehicle. If the hub part 20 is moved along the rod 1 by another mechanism, e.g. a pneumatic or hydraulic ram, then it would be possible to change the diameter/width of the wheel while it is still moving. As an alternative to having to use a gearbox, the motor can remain coupled to the gears at all times using an arrangement having the threaded rod 101 rotating around the solid rod 160, as discussed in further detail below.

The wheel may be attached to the end of an axle of a vehicle in a large number of alternative ways, for example through an adapter (not shown) that is attached to, or integral with, one of the discs 9 or 10. This adapter would be attached both to the vehicle axle, for example by bolts such as those customarily used to attach car tyres to car axles. The adaptor may be of a hollow rounded shape to accommodate the end 28 of the rod 1 , the spacer cylinder 2 and the bored cylinder 3 and optionally a mechanism for turning the rod, e.g. a flat upright gear.

The hoops can be replaced by a single hollow tyre of annular shape. In this case, as shown in Figure 12, the inner rim 52 can be clamped to the hubs 20, 22. Such a tyre can be formed, for example, by embedding the hoops 7 in a flexible material, for example, hardened (e.g. vulcanised) rubber. The tyre may be inflatable internally, in which case the internal cavity may be sealed or an inflatable inner may be provided, if necessary. Thus the cross section of the tyre may be closed, e.g. by a flexible wall shown schematically by broken line 53 in Figure 12, forming an annular cavity 55 within the torus-shaped tyre. The flexible wall may be a concertina or bellows wall, such as a wall 200 described in connection with Figure 18. Alternatively, the tyre may be sufficiently resilient to support the weight of the vehicle without internal pneumatic pressure as a result of the strength of the sidewalls of the tyre. A further embodiment is shown in connection with Figure 14. In Figure 14, parts having the same function as the parts in Figure 1 embodiment are indicated by the Figure 1 reference number plus 100 so that, for example, the hub part 20 of the Figure 1 embodiment becomes the hub part 120 of the Figure 14 embodiment.

In the embodiment shown in Figure 14, there are two hub parts 120, 122 that are connected together by hoops 107 in the same manner as shown in Figure 1 , although the hoops are omitted from Figure 14 for the sake of clarity.

The threaded rod 101 is, in Figure 14, hollow and contains a solid rod 160; the solid rod 160 is held by the two hub parts and the threaded rod 101 is rotatable about the fixed rod 160. The left hand hub part 120 shown in Figures 14 and 15 includes a hub connector 104, which consists of an outer ring 104a and an inner nine-segment ring 104b. In this embodiment, the hoops 107 have shaped terminal ends that fit within correspondingly shaped recesses 162 in the rings 104a and 104b. The rings are bolted together by passing bolts through the though-holes 164b in the ring 104b to engage in threaded blind holes 164a in ring 104a. In this way, the ends of the hoops (not shown) are held captive within the hub connector 104. As indicated above, ring 104b is, in fact, made up of nine segments each of which is individually bolted to the ring 104a; the advantage of this arrangement is that, if one of the hoops is damaged, it can be replaced merely by unbolting the segment of the ring 104b that holds it in place, which avoids unbolting all of the bolts holding ring 104b and ring 104a together. Naturally, the number of segments used in ring 104b can be different from nine and will generally depend on the number of hoops provided in the wheel.

As shown in Figures 14 and 15, a flanged bearing 106 is provided to allow the threaded rod 101 to rotate relative to the hub part 120. Also threaded on the rod 101 is a cylinder or sleeve 103 which contains ball bearings 163; these ball bearings are located in the threads of rod 101 and are retained in place by the sleeve 103, which is closed by a plate 166. The sleeve 103, the plate 166 and the bearing 106 are secured to the outer ring 104a using bolts passed through holes 165 in the bearing 106, holes 167 in the plate 166 and holes (not visible) in a flange 170 of the sleeve 103. Therefore, the ball bearings 168 are held captive within the sleeve 103 so that, as the rod 101 is rotated, the hub part 104 together with the bearing 106, the plate 166 and the sleeve 103 are moved axially along the rod in a direction that depends on the direction of rotation of the rod 101. Using this mechanism, the separation between the hub parts 120 and the hub part 122 can be varied to alter the diameter and width of the wheel in the manner described in connection with Figures 1 to 13.

Turning to consider the second hub part 122, which is shown in Figure 14, the hub connectors 105a and 105b are identical to hub connectors 104a and 104b and so will not be described in further detail except to say that they hold the other end of the arched hoops 107.

A tube 171 is provided that has the same external and internal diameters as the threaded rod 101 and is designed to support the inner rod 160 at its right hand end as shown in Figure 14. The tube passes through the ring 105b and is fixed to the ring 105a of the hub connector 105; thus the tube 171 is fixed with respect to the hub part 105. The rod 160 is also secured to the hub part 105, e.g. using bolts. The tube 171 passes through a bearing 106', through a plate 172, which is identical to plate 166, and through a flanged sleeve 174, which has an opening 175 through which the tube 171 passes. The end of the tube fits snugly in the flanged sleeve 174, which is thereby supported and positioned by the tube 171. Although a bearing 106' is used, it can be replaced by a flanged collar since the rod 160 does not rotate within the bearing 106' and the bearing is used to match bearing 106 and avoid the stocking of an additional part for the wheel.

Holes are provided in the flange 173 of the sleeve 174 and corresponding holes are provided in the plate 172 and a flange on the bearing 106; these components are secured to the outer ring 105a by means of bolts passing through the holes.

The sleeve 174 has a platform 177 on which is secured an electric motor 176, which drives a bevelled wheel 178 in either a clockwise or an anti-clockwise direction. The bevelled wheel 178 in turn drives a second bevelled gear wheel 180, which is fixed onto the end of the rod 101 (see Figure 16). Therefore, by driving the gear wheel 180 using the electric motor, it is possible to rotate the rod 101 and thereby advance the left-hand hub part 120 along the rod 101, the direction of advance being dependent on the direction of rotation of the gear wheel 180. Power to the motor 176 can be provided via a bushing (not shown) incorporated in hub part 120 or 122. In the same manner as described above in connection with the embodiments of Figures 1 to 13, the width of a wheel having a mechanism as shown in Figures 14 to 16 can be increased or decreased by increasing or decreasing the separation between the hub parts 120, 122 by means of the electric motor 176 and the rod 101. A reduction of the distance between the hub parts 120, 122 decreases the width of the wheel and increases its height, while an increase in the distance between the hub parts 120, 122 increases the width of the wheel and reduces its height.

The inner rod 160 is secured to the hub part 105a. In use, the rod 160 is held at one end by a bearing 250, which allows all the components of the wheel, including the rod 160, to rotate when the wheel turns. In an alternative embodiment the rod 160 may be stationary with respect to the vehicle and the rest of the wheel rotates about the rod 160. The bearing 250 is connected to a fixed axle 255 (Figure 19) or a suspension 260 (Figure 20).

When adjusting the diameter of the wheel, the motor 176 rotates the gears 178, 180, which in turn rotate the grooved rod 101. These are the only components to rotate during the adjustment of the wheel width and diameter. The rotation of the rod 101 causes the hub part 104 to move towards or away from the hub part 105 as has already been described, thereby causing the height of the hoops 107 to increase or decrease, depending on whether the hub part 104 is brought closer to, or pushed away from hub part 105 (respectively). During diameter/width adjustment, the rod 180 turns with the helically grooved rod 101.

As an alternative to the cover arrangement 16 shown in Figure 10, a covering 116, e.g. made of vulcanised rubber, provided with a tread may be used as shown in Figure 17. In Figure 17, parts of hoops 107 are shown, which pass through slots or openings in raised elements 190 of the covering. Such an arrangement provides not only for the separation of the hoops in place as separators 8 as shown in Figure 2 but also provides a tread to the tyre. This can be achieved by threading the hoops through the slots or openings in the raised elements 190 before being secured in one or other or both of the hub connectors 104, 105. Alternatively, the hoops 107 can be incorporated as part of the covering 116 during its manufacture; for example the cover 16 may be moulded in situ around the hoop and then subject to an after- treatment, e.g. vulcanisation. The internal rim 152 of the covering 116 (see Figure 19) rests in a groove 195 to hold the covering 116 in place on the rim. In such an arrangement, which is similar to that depicted in Figure 12, it is not necessary for the ends of the hoops 107 to be secured in the connectors 104,105.

Turning now to Figure 18, there is shown a cross-section through a wheel of the present invention, although the internal mechanism shown in Figure 14 has been omitted for the sake of clarity. As can be seen, the wheel includes a telescopic tube 192 made of metal, steel or strong plastic. The telescopic tube 192 protects the internal mechanism from dirt and prevents contact between it and the tyre 116 or hoops 107, to prevent the mechanism being damaged in use. The tube is provided with end plates 194 that are bolted to the outside of the hub parts 120, 122 using bolt holes visible in Figure 19 in the hub connector part 105a and corresponding bolt holes in the end plates 192. The telescopic tube can expand and contract in length as the wheel changes its configuration between large diameter/narrow and small diameter/wide.

The tyre of Figure 18 may also include a bellows or concertina arrangement 200 formed by five small diameter steel rings 202 and three large diameter rings 204, which are linked together by flexible segments 206, which may be made of rubber, thereby forming the bellows 200. The outer rings 202 of the bellows may be secured to a flange 203 (see also Figure 19) to seal the bellows with respect to the tyre 116 to provide an annular airtight compartment 208 between the bellows 200 and the tyre 116. Here, it should be emphasised that the hoops 107 do not extend through the airtight compartment 208 but rather extends outside the covering 116 and the compartment through the raised elements 190 (see Figure 17). The compartment 208 can be inflated though a valve of conventional design (not shown) to support the wheel. The bellows can extend and contract as the wheel is moved between its small diameter and large diameter configurations.

The wheel of Figures 14 to 18 is secured to a vehicle in the same manner as described above with respect to the wheel of Figures 1 to 13 or as illustrated in Figures 19 and 20. When the wheel has a relatively small diameter and a relatively great width, the area of the wheel that is in contact with the ground (which will be referred to as the "footprint" of the wheel) is greater than is the case when the diameter of the wheel is relatively large and the width is relatively small. The greater the area of the footprint, the smaller is the pressure exerted by the wheel on the ground. Accordingly, in ground that tends to yield, e.g. waterlogged ground, sand or broken-up soil, it is advantageous to use the wider/smaller diameter configuration, which prevents the wheel sinking into the ground and/or minimises the compaction caused by the wheel. However, on hard ground, where the wheel will not readily sink in, either the large diameter/small width configuration or the small diameter/large width configuration could be used (or any intermediate diameter/width). When moving over different terrains, it is possible to change the diameter of the wheel without stopping to fit new wheels.

The change of diameter of the wheel will also affect the ability of the wheel to grip the ground and therefore affects the drive that is able to be transmitted through the wheel. Thus on steep hills or muddy/slippery surfaces, a large footprint is desirable to increase the drive of the wheel and decrease slippage, which can be achieved by increasing the width of the wheel and reducing the diameter.

The change of the diameter of a driven wheel will obviously affect the speed of the vehicle, for a given engine speed and gear box setting. Thus, the smallest diameter wheel will tend to drive the vehicle at a slower speed than the largest diameter wheel. In addition, the larger diameter wheel is likely to provide lower fuel usage.

As a result of its larger footprint, the smaller diameter/wider wheel will tend to dig into broken ground less than the larger diameter wheel and this will reduce its tendency to "plough" into the ground and therefore reduce its resistance in rolling over the ground.

The wheel of the present invention finds particular application for agricultural transportation or in other applications in which a vehicle moves over open ground and off road driving. It can be attached either to a driven axle or shaft of a vehicle or to a non-driven axle or shaft, i.e. it is an idling wheel. The idling wheel can either be part of a self- propelled vehicle or a non-self propelled vehicle e.g. a trailer.

The wheels of the present invention can form all or only some of the wheels of the vehicle.

Two or more wheels in accordance with the present invention could be attached side by side along the same axle or shaft, thereby increasing the thrust achievable by the wheel and halving the pressure exerted by the wheel on the ground. The wheels can be operated independently and adopt different configuration. For example, one could be of a relatively large width/small diameter while the other could be of a relatively small width and large diameter. Such an arrangement will improve the thrust and decrease the slippage provided by the wheel having the relatively large diameter while, at the same time, improving the weight distribution through the smaller diameter/larger width wheel.

The present invention can also be applied to track vehicles such that the track passes around one or more of the wheels of the present invention. In this case, the speed of the vehicle can be altered by changing the diameter of a wheel of the present invention when acting as a track drive wheel.

In the embodiment shown in Figure 11 , the width of the wheel at its maximum can be approximately three times the width at its minimum.

Claims

1. A wheel of variable diameter and width for a vehicle, the wheel having an axis of rotation and comprising: a rim, a hub configured for attachment to an axle or shaft, the hub comprising a first part and a second part that are both arranged on the said rotational axis, and at least one arching member having first and second ends and being connected at the first end to the first hub part and at the second end to the second hub part, wherein the arching member extends outwardly in an arc between the first and second hub members and forms or supports the wheel rim, wherein the first and second hub parts can be moved relative to each other to change the shape of the arc of the at least one arching member, and wherein the two hub parts are lockable in a fixed position relative to each other.

2. A vehicle wheel as claimed in claim 1 , wherein the at least one arching members comprises a plurality of flexible hoops spaced around the hub and extending radially outward from the hub.

3. A vehicle wheel as claimed in claim 2, which includes an outer covering that at least partly overlies the said hoops and that is deformable to adopt the shape outlined by the hoops.

4. A vehicle wheel as claimed in claim 3, wherein the hoops pass through part of the outer covering.

5. A vehicle wheel as claimed in claim 4, which includes raised sections through which the hoops pass.

6. A vehicle wheel as claimed in claim 4 or claim 5, wherein the hoops are integral with the outer covering.

7. A vehicle wheel as claimed in any of claims 2 to 6, wherein each hoop has profiled ends that are anchored in correspondingly profiled sockets within the hub.

8. A vehicle wheel as claimed in any preceding claim, which includes an inflated or inflatable container or compartment located within the confines of the at least one arching member, wherein the container or compartment is sealed and can be pneumatically inflated.

9. A vehicle wheel as claimed in claim 8 which includes a wall extending between the first and second hub parts, e.g. in the form of a bellows, and wherein the said compartment is formed between the wall and the covering.

10. A vehicle wheel as claimed in claim 1 , wherein the at least one arching member comprises a hollow annular flexible tyre having a central opening defined by two internal rims forming the said two ends of the arching member, and wherein the first and second hub parts are each connected to one of the internal rims.

11. A vehicle wheel as claimed in claim 9, wherein the tyre is sealed and can be pneumatically inflated.

12. A vehicle wheel as claimed in any preceding claim, wherein the first and second hub parts are movable with respect to each other in a direction along the said axis of rotation of the wheel.

13 A vehicle wheel as claimed in any preceding claim, which includes a rod and wherein at least one of the hub parts is movable along the rod.

14. A vehicle wheel as claimed in claim 13, wherein the rod has a screw thread and wherein the said at least one movable hub part is engaged on the screw thread so that, as the rod is turned, the said at least one movable hub part is driven along the rod.

15. A vehicle wheel as claimed in claim 14, wherein the screw threaded rod is at least partly hollow and contains a member about which the threaded rod can rotate.

16. A vehicle wheel as claimed in any of claims 13 to 15, wherein the rod is rotatable by motor to move the at least movable hub part along the rod.

17. A vehicle wheel as claimed in preceding claim, wherein one of the first and second hub parts is in a fixed location and the other is movable to change the diameter and width of the wheel.

18. A vehicle wheel as claimed in any of claims 12 to 17 which includes means for moving the first and second hub parts with respect to each other.

19. A vehicle wheel as claimed in claim 18 wherein the means for moving the first and second hub parts with respect to each other extends between the first and second hub parts and wherein the wheel further includes a telescopic tube surrounding said moving means.

20. A vehicle including one or more wheel as claimed in any preceding claim.