Abstract:
The present invention discloses a tyre whose stiffness in its radial direction varies around its circumference. Preferably, the tyre is adapted to fit one or more wheels of a stair-climbing vehicle and its radial stiffness varies so as to allow the tyre to grip one or more stairs in use.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a tyre and related apparatus for a remotely operated vehicle. In particular, the present invention relates predominantly, but not exclusively, to a tyre that is adapted to cope with undulating terrain such as stairs, kerbs, and rough ground; to wheels fitted with the tyre; and to remotely operated vehicles fitted with such wheels.  
       BACKGROUND ART  
       [0002]     Before the present invention, it was possible for remotely-operated vehicles to cope with undulating terrain, but in order to obtain the traction required it was necessary to ensure that their tyres were only partially pneumatically filled. The consequence of this is that the tyres then only had a short life span in use.  
         [0003]     There remains a need to provide a resilient tyre that can cope with undulating terrain. Stairs and kerbs present difficulties, as does some terrain such as sand, shingle, mud, rough ground and rubble.  
       SUMMARY OF THE INVENTION  
       [0004]     It is thus an aim of the present invention to provide an improved tyre without the disadvantages of the prior art. Typically, such an improved tyre should allow remotely-operated vehicles to cope with difficult terrain more efficiently.  
         [0005]     In a first aspect, the present invention therefore provides a tyre adapted to fit one or more wheels of a remotely operated vehicle whose stiffness in its radial direction varies around its circumference.  
         [0006]     Preferably, the tyre is non-pneumatic. That is, it may comprise parts that are not inflated, but are solid although resiliently deformable.  
         [0007]     Preferably, the tyre&#39;s radial stiffness varies so as to allow the tyre to grip one or more stairs in use. This enables efficient leverage for climbing sets of stairs to be provided.  
         [0008]     In one embodiment, the variable stiffness is effected by a localised reduction in stiffness in one or more discrete zones around the circumference of the tyre. Usually, the discrete zones are regularly spaced around the circumference of the tyre. Preferably, each discrete zone is formed of a collapsible area of resilient means.  
         [0009]     Typically, the number of discrete zones is: 
        (a) one or more;     (b) five or more; or     (c) no greater than 100.        
 
         [0013]     In another embodiment, the tyre comprises an inner ring of one or more sprockets encased in an outer ring of a resilient material. The outer ring of resilient material allows the tyre to grip one or more stairs in use, whilst the sprockets encourage the wheel to move so that an adjacent thicker portion of resilient material is engaged with each stair.  
         [0014]     In another variation, the one or more inner sprockets may be sandwiched between two or more outer layers of resilient material. Alternatively, the one or more inner sprockets may be arranged beside a single layer of resilient material.  
         [0015]     Preferably, the sprockets are composed of polymer and/or the resilient material is rubber.  
         [0016]     In another embodiment, a discrete, sprung tooth may pass from each sprocket in a radial direction towards the circumferential edge of the overlying outer ring of resilient material. Here, the sprung tooth is able to move radially to allow the outer surface above the tooth to engage a stair in use.  
         [0017]     In yet another embodiment, the one or more collapsible areas include at least one internal compartment within the resilient material. As an internal compartment engages a stair (or other point load) it collapses so as to grip the stair and provide stair climbing leverage.  
         [0018]     The at least one compartments may be filled with a material of lower stiffness, or may alternatively be empty.  
         [0019]     Preferably, each compartment is adapted to collapse in use as the area around it encounters a point load.  
         [0020]     In a second aspect, the present invention provides a wheel comprising a tyre as described above.  
         [0021]     In a third aspect, the present invention provides a vehicle comprising a wheel as described above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;  
         [0023]      FIG. 1  shows a side view of a first embodiment of the present invention in which an internal sprocket is encased in an outer layer of resilient material;  
         [0024]      FIG. 2A  illustrates a plan view of a second embodiment in which an inner sprocket is sandwiched between two layers of resilient material;  
         [0025]      FIG. 2B  illustrates a plan view of a related, third embodiment in which an inner sprocket is bounded by a single outer layer of resilient material;  
         [0026]      FIG. 3  depicts a version of the embodiment shown in  FIG. 1 ;  
         [0027]      FIG. 4  shows a sprung-tooth sprocket arrangement of yet another embodiment;  
         [0028]      FIG. 5  illustrates an arrangement in which the resilient material comprises inner compartments according to yet another embodiment;  
         [0029]      FIG. 6  shows a view from the side of a further embodiment of tyre;  
         [0030]      FIG. 7  shows a view from the side of a related embodiment;  
         [0031]      FIG. 8  shows a view from the circumference f the embodiment of  FIG. 6  or  7 ;  
         [0032]      FIGS. 9 and 10  show views of the reaction of the tyres of  FIGS. 6 and 7  to flat and point loads respectively; and  
         [0033]      FIG. 11  shows yet a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0034]     In the following description, the embodiments will be described in the context of climbing stairs, a significant problem in the known art. However, it will be appreciated that similar technical difficulties apply to the other contexts discussed above, and it should therefore be understood that the described embodiments are equally applicable to and advantageous in other forms of undulating terrain.  
         [0035]     In  FIG. 1 , a wheel  10  is shown having a tyre  12 , comprising an inner aluminium sprocket  14  covered in an outer encasement of resilient material  16 . In use, when the wheel  10  encounters a stair, the resilient material  16  will deform radially inwards towards the centre of the wheel  10 . The tyre  12  will grip the stair if sufficient deformation occurs. This happens when the teeth of the sprocket  14  are aligned such that deformation can continue in between the teeth. If alignment is not so, the wheel  10  will slip around, driven until alignment is correct, and the tyre  12  can grip accordingly.  
         [0036]     Thus, when presented with a series of steps, the wheel essentially presents the toothed arrangement of the stiffer aluminium sprockets  14 . When running on a flat surface, on the other hand, the wheel can present the softer smooth surface of the resilient material  16 . Thus, the wheel has stair-climbing ability but can also provide a smooth ride.  
         [0037]     The tyre  12  has a continuous rim formed by a band  18  of resilient material. This provides some circumferential rigidity to the tyre, to offer a smoother ride over flat surfaces.  
         [0038]     In another example, shown in  FIGS. 2A  and B, the inner sprocket  20  may be either sandwiched between two outer layers of resilient material  22  (see  FIG. 2A ) or bounded by just one such layer (see  FIG. 2B ). Operation of the tyre is the same as described above.  
         [0039]      FIG. 3  shows a further embodiment in which the sprocket  32  extends right out to the surface of the tyre such that less resilient material  34  is present. This likewise operates in the same manner.  
         [0040]     In  FIG. 4 , another arrangement is shown. Here a tooth  36  is attached to a hollow section of the sprocket  38  by a spring means  40  within a channel  42 . This tooth  36  will offer some additional resilience when rolling on flat ground but will be circumferentially rigid when engaging the edge of a step by virtue of its location in the channel  42 .  
         [0041]     The further example illustrated in  FIG. 5  shows a tyre  50  having a plurality of inner compartments  52 . At least an outer section  54  of the tyre is composed of resilient material, in which the compartments  52  are formed. Thus, when the tyre  50  encounters a stair  56 , the relevant compartment  58  collapses, thus allowing for deformation of the rim  54  so that the stair  56  may be gripped. Should no compartment be aligned with the stair  56 , the tyre  50  will slip until such correct alignment is in fact present.  
         [0042]     As shown in  FIG. 5 , slits  60  extend from the compartments  52  towards the rim of the tyre. In this case, the slits extend through the outer section  54  but stop short of a circumferential cover  62 . These slits may assist in encouraging the described deformation of the tyre. However, in many instances they may be superfluous.  
         [0043]      FIGS. 6 and 7  show a still further embodiment. This resembles the embodiment of  FIG. 5  in that the tyre  62  has compartments within the resilient material, but is distinguished by the compartments being arranged as a number of spaced open ‘cells’  64  arranged on a pitch circle close to its outer circumference. A second group of cells  66  are arranged on a smaller pitch circle, positioned ½ of one pitch out from the outer group  64 . This allows the web of material left present between the outer cells  64  to collapse into the cavity of the inner cell  66 , equalising the compliance of the tyre when rotating and thus transitioning from cell to web. This keeps the vibration induced by the rolling tyre to a minimum.  
         [0044]     The number, shape of cells and material hardness may be varied to provide tyres with specific characteristics. In this example, 10 equally spaced cells  64 ,  66  are provided in each group. However, this could be adjusted as required.  
         [0045]     The tyre is moulded around a rigid interface ring or hub  68  that maintains it roundness in operation. Various alternative forms of hub  70  are possible, as shown in  FIG. 7 .  
         [0046]     The exterior circumference of the tyre  62  can be provided with a thread pattern  72 , as shown in  FIG. 9 .  
         [0047]     In use, as shown in  FIGS. 9 and 10 , the tyre can display smoother rolling characteristics due to the double layer of cells  64 ,  66 .  FIG. 9  shows the tyre  62  on a flat surface  74 , with various cells  76   a ,  76   b ,  76   c  being deformed under the load although the aggregate radial stiffness throughout the tyre  62  is generally the same at all circumferential points. As a result, the tyre  62  rolls smoothly.  
         [0048]     As shown in  FIG. 10 , however, the varying radial stiffness in the outer section of the tyre  62  means that the outer cells  64  thus deform in on themselves when point loads  78  are applied against them, such as stair treads and kerbs. This allows the tyre  62  to grip in a positive manner and gain traction enabling a vehicle to climb the obstacle  78 .  
         [0049]     In  FIG. 11 , a further embodiment is shown in which the wheel  80  comprises discrete outer  82  and inner  84  bands of aluminium bent so as to provide some resiliency in their arrangement around a central hub  86 . The outermost surfaces of both the outer  82  and inner  84  bands are covered in a layer of more resilient material  88  such as rubber. In use, the inner bands  84  prove to be more deformable than their outer band  82  counterpart by virtue of the different profiles. Thus, when they engage a stair the edge thereof can be gripped between bands.  
         [0050]     Thus, the present invention provides a tyre which is simple to construct at minimal cost, yet effectively and efficiently allows vehicles to climb stairs (etc) without the tyre perishing quickly. Preferred embodiments of the tyre are able to; 
        Maintain radial compliance (deformation) when climbing kerbs, stairs, and obstacles.     Increase transverse stiffness, thus reducing tyre roll with respect to the rim when cornering.     Be impervious to puncture damage.     Maintain or exceed the vibration-damping characteristics of known tyres.     Reduce friction when cornering (again attributable to the high transverse stiffness) as compared to low-inflation pneumatic tyres     Remain unaffected by external pressure changes. (e.g. during or after transportation by air)     Require little or no maintenance (such as re-inflation).        
 
         [0058]     It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.