A Wheel Attachment

Field of the Invention

The present invention relates to a wheel attachment. More specifically the present invention relates to a wheel attachment for retrofitting to the wheel of a vehicle so as to provide additional traction or to distribute the weight of the vehicle over a larger surface area.

Background of the Invention

Wheeled vehicles often experience difficulties when crossing soft surfaces such as mud or sand or when crossing slippery surfaces such as snow, ice or mud. For example, wheels may sink into soft ground, impeding the progress of the vehicle and potentially resulting in the vehicle becoming stuck or bogged down.

In order to prevent wheels sinking into soft surfaces, vehicle users have had to replace their wheels, or the tyres thereof with specialised wheels with increased surface areas so as to distribute the weight of the vehicle over a larger surface area.

This is time consuming and may be expensive and/or may require specialised tools in addition to the specialised wheels.

The present invention provides a wheel attachment which may be retrofitted to a wheel quickly and easily so as to improve its performance on soft and/or slippery ground.

Another aim of the invention is to provide a wheel attachment which may be retrofitted to a wheel without complicated tools or specialist wheel changing equipment so that the wheel attachment can be fitted in situ.

Prior Art

German Utility Model DE2031 8409 U1 (RUEMMELEIN ANDREAS) discloses an inflatable auxiliary wheel for securing to small wheels using a tensioning cable.

German Patent Application DE2940604 A1 (SNELL THOMAS BARTLETT) discloses a front wheel attachment for a tractor comprising a frusto-conical body mounted on a wheel using a bracket bolted to the hub of the wheel.

Japanese Patent Application JP20051 19626 A (SHIMIZU TAKAO) discloses an attachment for attaching to the outside of a wheel by nuts and bolts.

European Patent Application EP1 943107 A2 (BIESSE PHILIPPE) discloses an anti- sink rim for attaching to the outward facing rim of a wheel using specially adapted bolts.

Summary of the Invention

According to a first aspect of the invention there is provided a wheel attachment comprising: an attachment means for attaching to a wheel, and a plurality of spars connected to the attachment means, the spars at least partially enclosing a volume of space dimensioned to receive a bladder. In use, wheel attachments may be attached to one or more wheels of a vehicle by their attachment means and one or more bladders may be arranged and/or inflated within the volumes of space at least partially enclosed by their spar lengths. The bladders may each act to increase the effective surface area of the wheels and/or may brace against the spars such that they engage or lock the attachment means onto the wheel.

In some embodiments, the wheel attachment may be a wheel extension for spreading the load of a vehicle. For example, the wheel attachment may be a wheel extension for retrofitting to the wheel of a vehicle so as to distribute the weight of the vehicle over a larger surface area.

Alternatively, or additionally, the wheel attachment may be a wheel attachment for providing additional traction to a wheel on slippery surfaces such as ice, snow or mud. Such a wheel attachment may provide ridges on or may otherwise modify the surface of, a wheel to which it is attached. For example, the wheel attachment may comprise one or more elements, such as spar portions which may in use extend over the rim or tyre of the wheel to which the wheel attachment is attached. In such embodiments a bladder received by the volume of space, at least partially defined by the spars, preferably braces against the spars so as to maintain the wheel attachment in its deployed configuration and/or attached to the wheel.

The spars may be elongate members, such as bars, arms or strips of material, which may be bent, curved or otherwise shaped such that they may be arranged to define and/or at least partially enclose a volume of space in use. Ideally the spars are arcuate and/or shaped to engage with, and/or attach to the wheel; and/or to retain and/or at least partially surround the bladder. The spars may be formed from, or may comprise a composite material, such as a carbon fibre laminate material; metal, such as steel or aluminium; a synthetic plastics material; a carbon fibre reinforced polymer; or any combination of these materials.

The spars may be directly connected to the attachment means or may be connected to some other component of the wheel attachment, such as an adaptor, which is itself connected to the attachment means.

In other embodiments, individual spars may be connected to individual elements of the attachment means, and the combined spars and the elements of the attachment means to which they are connected may be separated one from another by other components of the wheel attachment. The connections may be rigid, such that the location and orientation of the spars with respect to the attachment means are fixed; alternatively, the connections may allow one, some, or all of the spars to be displaceable with respect to the attachment means. For example, the connections may comprise hinges or other mechanical bearings which allow the orientation and/or the location of the spars with respect to the attachment means, or components thereof to be adjusted. Such an adjustable arrangement may allow the at least partial enclosure of the volume of space to be opened and closed, for example, so as to facilitate the installation of a bladder therein.

In preferred embodiments, the spars and the attachment means may be formed integrally with each other, and/or individual spars may be formed integrally with individual components of the attachment means. In some such embodiments, one, some, or all of the spars may define all or part of the attachment means.

The volume of space at least partially enclosed by the spars may be enclosed to the extent that when a bladder located within the volume of space is inflated to substantially fill the volume of space, the spars retain the bladder within the volume of space. The volume of space may be enclosed to the extent that a bladder substantially fills the volume of space, and/or such that in order to remove a bladder it has to be at least partially deflated. In some embodiments, the spars may entirely enclose the volume of space and may be connected one to another at their distal ends.

In some embodiments, the spars when deployed may at least partially enclose a volume of space which may expand or contract as the spars or portions thereof are displaced, In such embodiments the volume of space may be expandable by inflating a bladder within the volume of space such that it displaces the spars or portions thereof outwards. In some embodiments, displacing the spars so to expand the volume of space may cause the attachment means to which the spars are connected to engage with or lock onto a wheel in use. For example, the wheel attachment may comprise spars with first portions for enclosing the volume of space and second portions on opposite sides of pivot points for attaching to the wheel. In use the volume of space may be expanded by displacing the first portions outwards thereby causing the second portions (which may be, may be defined by, or may be comprised by the attachment means) to be displaced inwards such that they grip the wheel or a tyre thereof.

Other components of the wheel attachment may also form part of the at least partial enclosure of the volume of space. For example, the wheel attachment may comprise a plate from which the spars extend. The plate may define an end boundary of the volume of space with the spars defining boundaries for the volume extending from the plate.

The spars preferably define a cage for retaining the bladder within the volume so that the boundaries of the cage ideally at least partially enclose the volume. For example, in some embodiments the wheel attachment may comprise a plurality of spars which in use extend away from the wheel and which curve or bend such that their ends meet at a point away from the wheel, thereby defining a cage. The distal spar ends may be adjacent one another; may contact one another; may be fixed to, or may be releasably attached one to another. In some embodiments, the cage may entirely enclose the volume of space.

In use, the volume of space at least partially enclosed by the spars may be substantially circularly symmetric about an axis of rotation of the wheel. This allows a substantially circularly symmetric bladder to be installed in the volume of space, and the overall wheel attachment to be substantially circularly symmetric. This may also allow the wheel attachment to increase the rolling surface area of a wheel without undue negative impacts on the performance of the wheel.

The volume of space may be located adjacent to, may extend from, and may be at least partially enclosed by the outer face of the wheel. In some embodiments, one, some, or all of the spars comprise a first portion for at least partially enclosing the volume of space and a second portion for engaging with the wheel, The second portions of the spars may be for attaching the wheel attachment to a wheel, They may surround, partially enclose and/or interlock with all of, portions of, or individual components of the wheel.

In some embodiments, the second portions may be comprised by, may define or may constitute the attachment means, Alternatively, or additionally, the attachment means may comprise clamps, ties, screws, grips, bolts, washers, hooks, straps, and/or magnetic or interference fit attachment means, which may attach the wheel attachment to the wheel.

The first and second portions may be distinct, may be separated by some other portion of the spar, or may overlap, such that a portion of the spar engages with the wheel and forms a part of the at least partially enclosed volume of space. The spar portions are preferably lengths of the spars.

In some embodiments, the first portions may be at, and/or may extend from first ends of the spar, and the second portions may be at, and/or may extend from second ends of the spar.

The first portions may be for enclosing, or partially enclosing the volume of space, for retaining or locating the bladder, may extend from the outer face of the wheel and may define a cage which may enclose the volume of space and may retain the bladder. In embodiments where the wheel attachment is for a wheel extension for spreading the load of a vehicle, the first portions of the spars may be arranged to define a portion of a rolling surface of an extension, other portions of which may be defined by the exterior surface of the bladder.

The second portions of the spars may locate the wheel attachment with respect to the wheel, may engage with the wheel such that the wheel attachment rotates with the wheel, and/or may attach the wheel attachment to the wheel. In some embodiments, the second portions may cover or extend over a portion of the rim or tyre of the wheel, and/or may engage directly with the tyre of the wheel and may thereby attach the wheel attachment to the wheel.

In some embodiments the second portions of the spars may cover or extend over a portion of the rim or tyre of wheel such that they provide additional traction to the wheel. For example, the second portions may form protrusions or bumps on the rolling surface of the wheel, this may improve the performance of the wheel on slippery surfaces in a similar manner to snow chains,

The wheel attachment may comprise a spar retainer which may engage with the spars intermediate their first and second portions. In alternative embodiments the spar retainer may engage with the first portions of the spars, with the second portions of the spars, or in an overlapping region comprised by both the first and second spar portions.

The spar retainer may engage with the spars when the wheel attachment is assembled, when the wheel assembly is attached to the wheel, and/or when a bladder is received or inflated within the volume of space defined by the spars. In some embodiments, the spar retainer may be disengage-able from the spars. The spar retainer may be disengaged from the spars in order to attach the wheel attachment to a wheel, for example to allow second portions of the spars to displaced such that they can fitted around the wheel or such that a bladder may be inserted into the volume of space at least partially enclosed by the spars.

The spar retainer may retain the spars in an arrangement where first portions of the spars at least partially enclose the volume of space, and the second portions of the spars engage the wheel. For example, the spar retainer may press the second portions of the spars against portions of the wheel, such that the spars are braced in a position where the first portions of the spars at least partially enclose the volume of space.

In some embodiments, the spars may be fixed to, be releasably connected to, interlock with, be connected by flexible ligatures to, and/or fit through apertures in the spar retainer. The spars may be rigidly arranged with respect to the spar retainer, or may be displaceable with respect to the spar retainer, the spars may be linearly displaceable between a plurality of locations in contact with or engaging with the spar retainer, may be displaceable into and out of contact or engagement with the spar retainer, and/or the spars may pivot about the spar retainer.

In some embodiments, the spar retainer may be actuated so as to disengage with and/or release the spars. When the spars are released by the spar retainer, the wheel attachment may be released from the wheel, and/or a bladder contained within the volume of space may be released from the spars. The spar retainer may be actuated so as to disengage with and/or release the spars, by opening one or releasable connectors, thereby either disassembling the spar retainer or releasing connections between the spar retainer and the spars, alternatively the release/disengagement may be actuated by a controlled detonation.

In some embodiments, the wheel attachment comprises a spar retainer releasing means. The spar retainer releasing means may be a means of breaking the spar retainer, for example the spar retainer may comprise explosive which may be detonated automatically or remotely in order to sever a spar retainer ring. Such an arrangement enables rapid release of the attachment means, ideally whilst the vehicle to which they are connected is still moving.

The spars may comprise bends intermediate their first and second portions which engage with the spar retainer.

The insides of the bends may define indentations in the outer surface of the spars inside which elements of the spar retainer may be arranged thereby interlocking the spars with the spar retainer. An element of the spar retainer may contact the insides of the bend and press the spars against some other objects, such as the wheel, the bladder, or another element of the spar retainer. The presence of an element of the spar retainer within the inside of the bend may prevent the spars from being displaced out of an arrangement where they are attached to the wheel and/or where they are retaining a bladder within the volume of space defined by the first portions of the spars. The spar retainer may comprise, protrusions, hooks, bars or other elements which in use are inserted into or are located within the inside of the bend so as to retain the spars. In some embodiments, the portions of the spars which engage with the spar retainer may be defined by, or may be located at the ends of, branches extending from the spars.

The spars may be pivot-able about the elements of the spar retainer located inside the bends. The wheel attachment may be thereby arranged such that when the second portion of a spar is displaced outwards (away from the axis of rotation of the wheel) the first portion is displaced inwards (towards the axis of rotation of the wheel). Therefore, the presence of the wheel within the second portions may prevent the first portions being displaced outwards, and/or the presence of an inflated bladder within the first portions may prevent the second portions from being displaced outwards.

The spar retainer may act as a fulcrum about which the spars are able to pivot.

For example, the wheel attachment may be attached to a wheel with the bladder either uninflated or absent from the volume of space. This may allow the first portions to be displaced inwards, thereby displacing the second portions outwards such that they can fit around the wheel. The bladder may then be inserted into, or inflated within the insides of the first portions, thereby pressing them outwards, pressing the second portions inwards against the exterior of the wheel and attaching the wheel attachment to the wheel, The wheel attachment may then be removed by either deflating the bladder or by releasing the spar retainer.

In some embodiments, the spars and/or the bladder may be shaped and/or arranged such that the bladder (or a portion thereof) contacts the outer face of the wheel when located and/or inflated within the spars or first portions thereof. When the bladder is inflated within the spars and/or first portions thereof the bladder may exert a force or pressure upon the outer face of the wheel. This may displace the wheel attachment outwards along the axis of rotation of the wheel, and/or may press elements of the wheel attachment which engage with the inner surface of the wheel (such as elements of second portions of the spars) against the inner surface of the wheel (or a tyre comprised thereby).

In alternative embodiments, the spars may comprise other elements specifically shaped to engage with the spar retainer, such as hooks, apertures, loops or other engagement means. In some embodiments the spars may be connected to the spar retainer by flexible linkages such as clips, quick release clips, cables, chains or loops of flexible material, this may allow the spars to be displaced and to rotate with respect to the spar retainer.

In some embodiments, the spar retainer may be a shaped band of material and may be a ring or other closed loop. The closed loop or ring may be circular, or may comprise a plurality of corners or vertices. The number of corners or vertices may be equal to the number of spars, for example the spar retainer comprised by a wheel attachment with four spars may be square, diamond, super-ellipse, or squircle shaped. The closed loop or ring may surround the spars in use, may engage with indents or attachment means comprised by the spars, or may pass through apertures through the spars.

In some embodiments, the spar retainer may be tubular and may engage with a portion of the length of the spars. In some embodiments, the spars may comprise an elongate portion between the first and second spar portion which may be surrounded by a tubular spar retainer. The tubular spar retainer may be cylindrical, or may comprise a cross section with a plurality of straight edges which may extend along the length of the spar retainer. The spar retainer may comprise a number of edges equal to the number of spars, for example a tubular spar retainer comprised by a wheel attachment with four spars may be cuboid, and/or may have a square, diamond, super-ellipse, or squircle shaped cross section.

In some embodiments, the spar retainer may be a plate or panel which engages with the spars directly or indirectly. The plate or panel shaped spar retainer may comprise one or more apertures formed therethrough and/or one or more other aperture defining elements such as eyelets, clips or D-rings attached to the plate or panel.

The apertures formed through the plate or panel and/or defined by the aperture defining elements may be for receiving the spars themselves or may be for receiving and connecting to flexible linkages which are connected to the spars. In some embodiments, the spars are adapted to be inserted through the apertures in use and ideally to interlock with the apertures. For example, the spars may comprise hooks or clips for connecting to the apertures. In other embodiments, the spars are connected to the apertures by elongate flexible linkages such as chains, cables, cords, loops or other flexible linkages which may be received by apertures or notches in the spars. The spar retainer may separate the volume of space enclosing first spar portions and/or the bladder from the wheel. In some embodiments, the spar retainer may space the first spar portions apart from the wheel along the axis of rotation of the wheel, for example so as to prevent the bladder or the spars from contacting the wheel arch of a vehicle when turning.

Wheel attachments may be provided with different sized or shaped spars and/or spar retainers; and/or which space apart the first portions of the spars and/or the bladder out different distances along the axis of rotation of the wheel. For example, wheel attachments for attachment to the front wheels of vehicles may space the first spar portions and/or bladder out further such that it does not contact the wheel arch when the front wheels are turned during steering.

In some embodiments, the portions of the spars with which the spar retainer engages may have a lower radius (as measured from the axis of rotation of the wheel) than the first and or second portions of the spars. This may prevent this portion of the wheel attachment which may be located adjacent to the outer face of the wheel, from contacting the wheel arch of a vehicle in use.

Ideally the spar retainer may comprise or may be formed from a flexible or deformable material, such as a composite, wire or fibre, and is resiliently deformable. This may accommodate stretching of the spar retainer and may enable impact and/or shock absorption.

The size of the spar retainer may be adjustable, for example to allow the same set of spars to be attached to differently sized wheels. The length, radius, and/or circumference of a ring, closed loop, or tubular shaped spar retainer may be adjustable. Alternatively, the spar retainer may be replaceable with one or more differently sized and/or dimensioned spar retainers.

The spar retainer may have an adjustable diameter by way of a circumferential adjuster. Alternatively, or additionally, the spar retainer may be supplied in different lengths or may be adjustable lengthwise in order to accommodate various sized wheels. In some embodiments, the fulcrum about which the spars pivot may be provided by a ring, or a spacer bracket or another type of anchor point which may engage with the spars and/or the wheel.

The spar retainer may be, or may comprise, a spacer bracket which may lengthen the spar retainer and so hold the first spar portions and/or the bladder at a distance away from the wheel thereby ensuring that the arcuate portions of the spars and the bladder do not contact or impinge upon the wheel arches of the vehicle, which might otherwise impede steering.

In some embodiments, the spar retainer may be attachable to the wheel, for example the spar retainer may comprise ties, brackets, clips, clamps, bolts, or washers which engage with wheel nuts.

In some embodiments, the spar retainer may be a ring which may surround the spars, may contact the outer surfaces of the spars and may be located within the inside of bends comprised by the spars, thereby engaging with the spars. The ring may thereby maintain the spars against the wheel and/or a bladder located within the volume of space at least partially enclosed by the first portions of the spars.

The ring may be located against, near to, adjacent to, and/or in a parallel plane to the outer face of the wheel.

In alternative embodiments, the spar retainer may be, or may comprise a chain, a tie, a plurality of rings or closed loops, or a body with a plurality of spar retaining means such as clips or apertures.

In some embodiments, the spar retainer is circularly symmetric about an axis of rotation of the wheel. The spar retainer may thereby retain the spars in a circularly symmetric arrangement and the entire wheel arrangement may thereby be circularly symmetric so as to improve the efficiency of the wheel.

In use the spars may be distributed around the circumference of the spar retainer, the circumference of the wheel, and/or the circumference of a cross section through the bladder orthogonal to the axis of rotation of the wheel.

In some embodiments, the profile of the spars may comprise an arcuate or substantially semi-circular length, connected to a first substantially straight length by a substantially full angled bend, the first substantially straight length being connected to a second substantially straight length by a substantially right angled bend, and the second substantially straight length being connected to a third substantially straight length by a substantially right angled bend.

The arcuate or substantially semi-circular length may be comprised by the first portion for at least partially enclosing the volume of space, the substantially full angled bend may be comprised by the spar locator engaging element, and the first, second and third substantially straight lengths may be comprised by the second portion for engaging with the wheel.

In some embodiments, the attachment means may comprise a plurality of spar portions for engaging with the wheel.

The spar portions comprised by the attachment means may attach the wheel attachment to a wheel. They may surround, partially enclose and/or interlock with all of, portions of. or individual components of the wheel. Alternatively, or additionally, the attachment means may comprise clamps, ties, screws, grips, bolts, washers, hooks, straps, and/or magnetic or interference fit attachment means.

In some embodiments, one, some, or all of the spar portions comprised by the attachment means may be portions of the spars for at least partially enclosing the volume of space comprised by the wheel attachment. The spars comprised by the wheel attachment may comprise portions which engage with the wheel and portions which at least partially enclose the volume of space, these portions may be distinct, or may overlap.

Alternatively, the spar portions comprised by the wheel attachment may be comprised by different spars to those which at least partially enclose the volume of space. One, some or all of the spars which comprise the spar portions comprised by the wheel attachment means may be attached to one, some or all of the spars for at least partially enclosing the volume of space. Alternatively, both sets of spars may be connected to one or more other elements of the wheel attachment, such as a plate or ring which separates the volume of space from the attachment means.

One, some, or all of spar portions comprised by the attachment means may comprise substantially U-shaped portions. In some embodiments, the spar portions comprised by the attachment means may be substantially U-shaped spar portions. In some embodiments, the U-shaped portions may be the second portions of the spars.

The U-shaped portions may be U-shaped brackets. The U-shaped portions may be for engaging with a wheel or portions thereof, for example the U-shaped portions may be for, or may be dimensioned to receive or fit over the rim or tyre of a wheel.

The attachment means may comprise a plurality of U-shaped spar portions which fit over the rim or tyre of a wheel at a plurality of points around its circumference so as to secure the wheel attachment to the wheel.

In use, substantially U-shaped portions of the spar portions comprised by the attachment means may contact the inner face, rim and outer face of the exterior of a wheel. The U-shaped portions of the spar portions may be adjustable in size, for example the width of the U-shape may be adjustable so as to allow the U-shaped portions to fit securely around the rims of a variety of differently sized wheels.

The base of the U-shape of the U-shaped portion may define a ground contacting portion, which may in use be arranged over the ground contacting portion of the wheel (such as the rim or a portion of a tyre). The ground contacting portion may be substantially flat, may have treads or grips formed on its outer surface and may be adjustable in width so as to fit onto wheels of different sizes. The ground contacting portion may protrude or extend radially outwards from the wheels such that it may provide additional traction to the wheel in the same manner as a snow chain.

The spar portions comprised by the attachment means may be shaped such that in use they contact the inner face of the wheel, the rim of the wheel and the outer face of the wheel.

In some embodiments, the spars, or first portions thereof may be arcuate. The arcuate spars or spar portions may be semi-circular. The arcuate spars or spar portions may be dimensioned to at least partially enclose a volume of space to enclose a substantially rounded bladder, and/or may be dimensioned to retain a substantially rounded bladder.

The volume of space enclosed by the spars, or first portions thereof may be substantially spherical, cylindrical, conical, frusto-conical, capsule-shaped, ellipsoid- shaped or superegg-shaped.

The boundaries of the volume of space may be defined and/or at least partially enclosed by the spars or first portions thereof, by the spar retainer and/or by the outer face of the wheel. For example, in an embodiment where the volume of space is substantially cylindrical, one flat end wall of the cylindrical volume may be defined by the outer face of the wheel, by a ring or disc-shaped spar retainer held against the outer face of the wheel by the attachment means, and by a plurality of spar lengths which extend substantially radially from the spar retainer. The radially extending spar lengths may be bent by approximately 90 degrees before extending outwards from the wheel parallel to the axis of rotation of the wheel, so as to define the curved wall of the cylindrical volume. The ends of the spars may be bent by approximately 90 degrees to extend radially inwards towards the axis of rotation of the wheel so as to define the distal flat end of the cylindrical volume.

The bladder received by the volume of space may be substantially spherical, cylindrical, conical, frusto-conical, capsule-shaped, ellipsoid-shaped, superegg- shaped, and/or of substantially the same shape as the volume of space when inflated.

The volume of space may be adjacent to, may be coaxial to, may extend from, and/or may be at least partially defined and/or enclosed by the outer face of the wheel.

The spars may be substantially flat and may be arranged such that a normal to the flat surface of the spar lies within the plane which contains both the axis of rotation of the wheel and a central lengthwise axis of the spar. The spars may be substantially flat or planar. Therefore, the spars may comprise flat surfaces for contacting the ground, for contacting the outer surfaces of the wheel, and/or for contacting the outer surfaces of the bladder. In use the spars or first portions thereof may conform to and/or be coplanar with the outer surface of the bladder, and spar portions comprised by the attachment means may conform to and/or be coplanar with the outer surfaces of the wheel.

Portions of the outer surfaces of the spars (those facing away from the axis of rotation of the wheel) which in use contact the ground may have treads and/or studs formed thereon. These may include portions of the spars which contact the furthermost radially extending (from the axis of rotation of the wheel) portions of the bladder, and portions which contact, extend over, or cover portions of the rim or tyre of the wheel.

In some embodiments, more of, a majority of, or all of the outer surface of the spars may have treads and/or studs formed thereon. In some embodiments, all of the outer surface of the first portion of the spars may have treads and/or studs formed thereon and/or all of the outer surface of the spar portion comprised by the attachment means may have treads and/or studs formed thereon.

Alternatively, or additionally, the outer surfaces of the spars or first portions thereof may have fins and/or paddles formed thereon.

The spars or first portions thereof may comprise flexible portions which may extend from their first ends, or the ends distal from the wheel and the attachment means. Flexible spars may allow the wheel attachments to more effectively absorb shocks or to absorb the unevenness of off-road terrain.

In some embodiments, the attachment means may attach to the rim of the wheel, to the spokes of the wheel, to the hub of the wheel, or to any combination thereof. The attachment means may comprise spar portions which interlock with the wheel or components thereof, may comprise clamps, grips, or ties which may be secured to components of the wheel. Alternatively, or additionally the wheel connector may comprise washers and/or bolts which may allow the wheel attachment to be screwed onto a wheel, for example the wheel attachment means may comprise washer portions through which the bolts which secure a wheel to a vehicle may be inserted such that these bolts also secure the wheel attachment to the wheel.

The wheel attachment may comprise three or more spars. In preferred embodiments, the wheel attachment comprises at least four spars.

The spars may be substantially flat. In some embodiments, the spars may be formed from flat strips of material which may be bent about axis perpendicular to the length, width and/or the axis of rotation of the wheel, so as to adopt a shaped profile which may at least partially enclose a volume of space, may retain a bladder, may interlock with the spar retainer, may engage with the wheel, and/or may attach the wheel attachment to the wheel.

The spars may comprise, and/or may be formed from a composite material. Such a composite material may be a carbon fibre laminate material. The use of composite materials may allow all or a portion of the spars to flex. In some embodiments, the spars may be adjustable, for example different length first spar portions may be used in combination with differently sized second portions for engaging with the wheels.

Differently sized spars may allow differently sized bladders to be used and/or may allow the wheel attachment to be attached to differently sized wheels.

In some embodiments, inserts may be provided, and/or comprised by the wheel attachment which may be inserted into the attachment means, or spar portions thereof, so as to allow them to be used with differently sized and/or dimensioned wheels.

In some embodiments, in use the spars, first portions thereof, and/or the bladder may have a radius from the axis of rotation of the wheel substantially equal to that of the wheel, such that the wheel attachment provides an extension for the wheel along the wheel's axis of rotation. In alternative embodiments, the radius of the spars or first portions thereof, and of the bladder, from the axis of rotation of the wheel may be greater than that of the wheel . This may provide additional elevation with respect to uneven terrain or soft ground over which a vehicle is travelling.

In other embodiments, the bladder, the volume of space defined by the spars, and the spars or portions thereof which define the volume of space may extend radially from the axis of rotation of the wheel to which the wheel attachment is attached substantially less than the rim or tyre of the wheel. This may be so that they do not contact the ground themselves, for example in embodiments wherein the wheel attachment is a snow chain alternative comprising spar portions which extend over and provide additional grip to the rim or tyre of the wheel, rather than being an extension for the wheel.

The wheel attachment may comprise a bladder which may in use be located inside the volume of space defined by the spars or first portions thereof. In use the wheel attachment may retain the bladder within the spars or first portions thereof, the bladder may be retained adjacent the wheel so as to define an increased rotating surface area.

In some embodiments a bladder comprised by the wheel extension may be constructed from a tyre, which may be a tyre of substantially the same dimensions as a tyre comprised by a wheel which the attachment means attaches the attachment to.

Such a bladder may be formed by enclosing the two circular apertures on either side of the tyre which are bounded by the annular beads of the tyre, which may define a bladder with a single generally cylindrical cavity. The bladder may comprise two rings which may each be arranged such that they contact the inside of the bead of one of the sides of the tyre and may extend into the circular aperture bounded by said bead. The bladder may further comprise two plates which may be arranged such that they each covers one of the two apertures bounded by one of the two beads of the tyre and may contact the outside of the bead and/or a ring extending into the aperture as described above. The plates may be domed and may be concave or convex when viewed from outside the bladder. The plates may each be connected to a ring, for example by a plurality of bolts. The bladder may be inflatable. In some embodiments, the bladder may be self- inflating and/or may comprise a plurality of isolated separately inflatable or self- inflating chambers, so as to minimise the risk of a puncture deflating the bladder. The bladder may be inflated by air, or some other compressed gas. In alternative embodiments, the bladder may be water inflatable, may contain compressible foam or may comprise a deformable or compressible foam and/or plastic structure

The outer surface of the bladder may have treads formed thereon.

In some embodiments, the outer surface of the bladder and/or the outer surface of the spars may have fins formed thereon. The inflatable bladder retaining wheel attachment may allow a vehicle to which they are attached to float and to act as a waterborne or amphibious vehicle. The fins may provide traction and/or propulsion for the vehicle.

In some embodiments, the wheel attachment may comprise one or more paddles, and/or one or more paddle wheels, which may be located at distal ends of spars from wheel, and/or intermediate the first and second portions of the spars, The paddles/ and or paddle wheels may provide propulsion to a waterborne vehicle when the wheels to which the wheel attachments are affixed are rotated.

In some embodiments, the spars, first portions thereof, and/or second portions thereof may comprise a rim, lip or ridge which may extend from the outer surface of the spars. The rim lip or ridge may extend along the length of the spar or first or second portions thereof, may extend radially outwards (with respect to the axis of rotation of the wheel in use), and/or may be substantially at right angles to the outer surface of the spars. These rims, lips or ridges may provide additional traction on soft surfaces, for example on soft snow or powder.

In some embodiments, the bladder may comprise, or may be contained within a reinforced jacket. For example, the reinforced jacket may be reinforced with carbon fibres; graphene; and/or Kevlar (RTM). Alternatively, or additionally the bladder, or an outer surface thereof may be formed from a reinforced material; Kevlar (RTM); graphene; a carbon fibre fabric; or any combination thereof. In other embodiments, the bladder may be contained within a flexible and/or collapsible case or other protective enclosure.

The outer surface of the reinforced jacket or case may have treads, studs, grips, fins, rims, lips, paddles and/or ridges formed thereon.

In some embodiments the bladder, the outer surface of the bladder or the reinforced jacket or case may comprise connection means for engaging with or connecting to the spars, first portions thereof, the spar retainer, and/or the wheel, Alternatively, or additionally the spars, first portions thereof, spar retainer or wheel attachment means may comprise means for connection with the bladder, outer surface thereof, and/or the reinforced jacket. The connection means may be grips, clips, ties, magnets, hook and loop connectors, interlocking means, members and matching recesses, or any combination thereof. In some embodiments, the spars, first or second portions thereof, the outer surface of the bladder, and/or of the reinforced jacket or case may comprise means to connect to their outer surface, such as attachment points for snow chains.

In some embodiments, the volume of space may be dimensioned to receive a plurality of bladders, the spars or first portion thereof may locate and/or retain a plurality of bladders. In some embodiments, the wheel attachment may comprise a plurality of bladders which may have any of the optional features described above. The wheel attachment may comprise bladder locating means which may be located within the volume of space and may be supported by the spars, by the attachment means, and/or by the spar retainer. One, some or all of the bladders may be modified, adapted, or comprise any of the features, as described above.

Preferred embodiments of the invention will now be described, by way of example, with reference to the Figures, in which:

Brief Description of the Figures

Figure 1 A is an overall view of a variant of a first wheel attachment comprising alternative extended spars attached to a wheel with the bladder absent;

Figure 1 B is an overall view of a first wheel attachment attached to a wheel with the bladder absent;

Figure 1 C is an overall plan view of vehicle with two first wheel attachments and two variant first wheel attachments attached, illustrating how the variant wheel attachments retain the bladders at a distance from the vehicle to facilitate turning;

Figure 2 is a second overall view of the first wheel attachment attached to the wheel with the bladder absent;

Figure 3 is an overall view of the first wheel attachment attached to the wheel with the bladder present;

Figure 4 is a first end view of the first wheel attachment attached to the wheel with the bladder present;

Figure 5 is a second end view of the first wheel attachment attached to the wheel with the bladder present;

Figure 6A is an overall view of a first wheel attachment removed from the wheel and partially disassembled with two of its spars removed;

Figures 6B and 6C are overall views of the spars removed from the partially disassembled first wheel attachment shown in Figure 6A;

Figure 6D is an overall view of an alternative extended spar comprising an extended recess portion for retaining the bladder at a distance from the vehicle;

Figure 7 is an overall view of a vehicle being driven across soft terrain without the use of wheel attachments; Figure 8 is an overall view of a vehicle being driven across soft terrain with a first wheel attachment fitted to each wheel;

Figure 9 is an overall view of a second wheel attachment attached to a wheel;

Figure 1 0A is a cross-sectional view of the second wheel attachment attached to a wheel;

Figure 10B is a partial cross-sectional view of the second wheel attachment being attached to a wheel;

Figure 1 1 is an exploded view of the second wheel attachment;

Figure 12 is an overall view of a third wheel attachment attached to a wheel;

Figure 1 3A is a cross-sectional view of the third wheel attachment being attached to a wheel;

Figure 1 3B is a cross-sectional view of the third wheel attachment attached to a wheel;

Figure 14 is an exploded view of the third wheel attachment;

Figure 15A is a detailed overall view of a spar of the third wheel attachment;

Figure 1 5B is a detailed view of a portion of a spar of the third wheel attachment; and

Figure 15C shows two detailed view of the end of a spar of the third wheel attachment being received by a track of the third wheel attachment.

Detailed Description of the Figures

Referring to the figures generally there are shown a plurality of wheel attachments 1 00, 600, 1 100 according to the present invention, each of the wheel attachments comprising four spars 200, 700, 1200, a spar retainer 300, 800, 1800, and optionally an inflatable bladder 400, 900, 1400. In use the wheel attachments 100, 600, 1 100 are attached to wheels 500, 1000, 1500.

Referring to Figures 1 to 8 there are shown variants of a first wheel extension attachment 1 00 according to the present invention comprising four spars 200, 200A, a ring-shaped spar retainer 300, and optionally an inflatable bladder 400. In use the wheel extension 1 00 may be attached to a wheel 500 so as to increase the effective surface are of the wheel 500, and thereby spread the weight of a vehicle to which the wheel is attached.

A first variant of the first wheel extension 1 00 with shorter spars 200 is shown assembled in Figures 1 B, 2, 3, 4, 5 and 8 and is shown disassembled in Figures 6A, 6B and 6C. A second variant of the first wheel extension 1 00 wherein the spars have been replaced with alternative extended spars 200A is shown in Figure 1 A; the alternative extended spars 200A are shown in Figure 6D. Figure 1 C shows a vehicle with first and second variants of the first wheel extension 1 00 attached thereto, and Figure 8 shows a vehicle with a first variant of the wheel attachment attached thereto.

The spars 200 each comprise a first portion 220 for defining and partially enclosing a volume of space within which the bladder 400 is retained, a second portion 240 for engaging and connecting to the wheel 500, and a bend 260 which connects the first and second portions 220, 240 and which engages with the ring-shaped retainer 300.

The alternative extended spars 200A comprise similarly dimensioned first portions 220A for defining and partially enclosing the volume of space within which the bladder 400 is retained, and similarly dimensioned second portions 240A for engaging with and connecting the wheel 500. The alternative spars 200A further comprise elongate intermediate portions 260A which connect the first portions 220A and the second portions 240A, and which in use engage with the ring-shaped retainer 300 (or alternatively, multiple ring-shaped retainers 300, or a differently shaped retainer). The spars 200, 200A are formed from flat elongate strips of material which are bent so as to have a shaped profile comprising the first portion 220, 220A, the second portion 240, 240A and the bend 260, or intermediate portion 260A. The material may be a composite laminate material.

The first portions 220, 220A of the spars 200, 200A are arcuate and extend between first ends 222, 222A of the spars and the bends 260, or intermediate portions 260A. In the illustrated embodiment, the first portions 220, 220A are substantially semicircular.

In use, the first portions 220, 220A of the spars 200, 200A surround a volume of space within which the bladder 400 may be retained. The spars 200, 200A may be distributed around the circumference of the ring-shaped retainer 300 and the circumference of the wheel such that the four first portions 220, 220A define a cage within which the bladder may be retained. The first ends 222, 222A of the spars 200, 200A meet at a point on the axis of rotation of the wheel 500 a distance away from the outer surface of the wheel 500.

When the bladder 400 is inflated within the first portions 220, 220A of the spars 200, 200A such that it fills the volume defined and partially enclosed by the first portions 220, 220A, the first portions 220, 220A are substantially coplanar with the outer surface of the bladder 400.

The second portions 240, 240A of the spars are U-shaped and extend between second ends 242, 242A of the spars and the bends 260, or the intermediate portions 260A. The U-shaped second portions 240, 240A comprise three substantially straight lengths connected by two substantially right angled bends.

In use the second portions 240, 240A engage with the rim of the wheel 500. The U- shaped portions 240, 240A fit over the rim or tyre of the wheel 500, such that they contact the inner face, the rim, and the outer face of the wheel 500. In use the second portions 240, 240A may be distributed about the rim of the wheel 500 so as to secure the wheel extension 1 00 to the wheel 500. When the wheel extension 100 is attached to the wheel 500, the second portions 240, 240A may conform to and may be substantially coplanar with the outer surface of the wheel.

The end length of the first portion 220, 220A distal from the first end 222, 222A of the spar 200, 200A, runs substantially parallel to the end length of the second portion 240, 240A distal from the second end 242, 242A of the spar 200, 200A.

In the shorter spars 200, these two parallel end lengths are connected to each other by the bend 260 such that they define the sides of a notch formed in the outer surface of the spars 200 with which the ring-shaped spar retainer 300 may engage in use. In the alternative extended spars 200A, these two parallel end lengths are connected to each other by the intermediate portion 260A of the spar. The intermediate portion 260A is substantially parallel to the middle length of the second portion 240A and the axis of rotation of the wheel 500 and is substantially at right angles to the two parallel end lengths which it interconnects.

The intermediate portion 260A separates the first portions 220A and the bladder 400 from the wheel 500 and the second portions 240A, locating the bladder 400 further away from the wheel 500. The alternative elongated spars 200A may distribute the weight of a vehicle over a larger area , and may prevent the wheel attachment 100 from contacting the wheel arch of vehicles during steering. In some circumstances, alternate extended wheel attachments 200A may be attached to the front wheels of a vehicle (such that they do not contact a wheel arch when the front wheels are turned during steering), and regular shorter wheel attachments 200 may be attached to the rear wheels. Figure 1 C shows a vehicle with wheel attachments 100 comprising the alternative extended spars 200A attached to each of the front wheels 500, and wheel attachments 1 00 comprising the shorter spars 200 attached to each of the rear wheels 500.

The ring-shaped retainer 300 is a ring torus with a major radius approximately half that of the wheel 500 and slightly less than that of the inside of the bend 260, or intermediate portion 260A, and slightly less than half the width of the notch defined between the first portions 220 and the second portions 240 in the shorter spars 200.

In use, the four shorter spars 220 are inserted partially through the ring-shaped spar retainer 300 and are then engaged with the spar retainer 300, such that the spar retainer 300 is in contact with the insides of the bends 260 comprised by the spars 200. In this configuration, the spars 200 are able to pivot about the ring-shaped spar retainer 300, and are also able to be displaced around the circumference of the ring of the spar retainer 300.

When the alternative extended spars 200A are used, they are inserted partially through the ring-shaped spar retainer 300 (or in further alternative embodiments a tubular spar retainer) and are then engaged with the spar retainer 300, such that the spar retainer 300 is in contact with the outer surface of the intermediate portion 260A, between the first and second portions 220A, 240A of the spar 200A. The intermediate portion 260A defines an indent in the profile of the alternative extended spar 200A with reduced radius (from the axis of rotation of the wheel 500) within which the spar retainer 300 is retained.

In such an arrangement, the first ends 222, 222A of the spars 200, 200A are located near, adjacent and/or in contact with each other and a point on the axis of rotation of the wheel.

The wheel extension attachment 1 00 may then be attached to a wheel 500, for example, by rotating the spars 200, 200A around the ring shaped spar retainer 300, until they are all on one side of the ring of the spar retainer 300, fitting the U-shaped second portions 240, 240A of the spars 200, 200A over the rim of the wheel, then rotating the spars 200, 200A back around the wheel 500 and the ring of the spar retainer 300, such that they are equally distributed around the circumference of the wheel 500 and the spar retainer 300 (such an assembled embodiment may be seen in Figures 1 A, 1 B, and 2). In this arrangement, the spars 200 hold the spar retainer 300 against the outer face of the wheel 500.

Alternatively, if the second portions 240, 240A are sufficiently large with respect to the wheel 500, the spars may be distributed around the circumference of the spar retainer 300 and then pivoted with respect to the spar retainer 300, such that the second portions 240, 240A are spread outwards, and the first portions 220, 220A are pushed inwards. The second portions 240, 240A may then be fit over the rim of the wheel 500 before being pressed against the wheel 500, thereby pivoting the first portions 220, 220A back outwards.

The bladder 400 may either be inserted before the spars 200, 200A are rotated back around to be equally distributed about the circumferences (in which case it may be inserted substantially inflated), or may be inserted between the spars 200, 200A after they have been distributed about the circumferences (in which case it must be inserted while substantially deflated). The bladder may then be inflated such that it expands and presses against the insides the of the first portions 220, 220A of the spars and against the outer face of the wheel 500.

The pressure exerted by the inflated bladder 400 on the outer face of the wheel pushes wheel extension attachment 1 00 outwards along the axis of rotation of the wheel 500 and ensures that the parts of the second spar potions 240, 240A adjacent the second spar ends 242, 242A are pressed against the inner face of the wheel 500.

The pressure exerted by the inflated bladder 400 on the inner surfaces of the first portions 220, 220A of the spars 200, 200A press the first portions 200, 220A radially outwards away from the axis of rotation of the wheel 500. This causes the second portions 240, 240A of the spar 200, 200A to be pressed radially inwards against the rim of the wheel 500.

The pressure of the inflated bladder 400 thereby secures the wheel extension attachment 1 00 to the wheel 500.

A wheel extension attachment 1 00 comprising the additional elongated spars 200A may comprise a specially shaped bladder 400 which in use fills the space between and first portions of the spars 220, 220A, the intermediate portions 260A and the outer face of the wheel 500. This may allow or ensure that the bladder 400 presses against the outer face of the wheel 500 when it is inflated. Alternatively multiple bladders 400 may be used, for example a first approximately spherical bladder 400 located between the first portions 220A of the spars 200A, and a second approximately cylindrical bladder 400 located between the intermediate portions 260A.

Figure 7 shows a vehicle weighing approximately 1600kg with four tyres whose area of contact with the ground is approximately 25cm wide and 25 cm long. The pressure exerted on the ground by the vehicle is therefore approximately 16000/0.25 = 64000 Pa.

Figure 8 shows the same vehicle with a wheel extension attachment 100 attached to each tyre, thereby increasing the effective surface area in contact with the ground. The bladders 400 held by the wheel attachments are approximately spherical with a circular footprint with a diameter of approximately 0.75m. Each of the wheel extensions weighs approximately 25kg. The pressure exerted on the ground by the vehicle with the extensions attached is therefore approximately 17000/(0.25+1 .767... ) = 8427.749... Pa.

Therefore, the vehicle fitted with the wheel attachments exerts only approximately 1 3.168... % of the pressure exerted by the vehicle without the attachments, thereby enabling it to be driven across much softer terrain with the attachments fitted than without.

Referring to Figures 9 to 1 1 , there is shown a second wheel extension attachment 600 according to the present invention comprising four spars 700, a spar retainer disc 800, and an inflatable bladder 900. In use the wheel extension 600 may be attached to a wheel 1 000 so as to increase the effective surface are of the wheel 1 000, and thereby spread the weight of a vehicle to which the wheel is attached.

The spars 700 each comprise a central straight length 740 which in use contacts the rolling surfaces of the wheel 1000 and the bladder 900, a central branch 762 at right angles the central straight length, a bladder face plate contacting length 720 extending at right angles to the central straight length from a first end thereof and, a tab for contacting an inner face of the wheel 742 extending at right angles to the central straight length from a second end thereof. The first and second ends of the central straight lengths being opposite ends thereof, and the central branch 762, the bladder face plate contacting length 720 and an imaginary line along the centre of the tab being substantially parallel to each other. Consequently, the spars 700 have generally W- shaped profiles.

The spars each define two generally U-shaped indents. The first such indent is bounded by the bladder contacting length 720, the central branch 762 and a first portion of the central straight length 740 extending therebetween. This generally U- shaped indent contacts and fits over the rim of the bladder 900 in use, as shown in Figure 1 0A.

The second generally U-shaped indent is defined between the tab for contacting an inner face of the wheel 742, the central branch 762 and a second portion of the central straight length extending therebetween. This generally U-shaped indent contacts and fits over the rim of the wheel 1 000 in use, as shown in Figures 10A.

The spar retaining disc 800 is a substantially circular flexible disc which in use is arranged between the wheel 1000 and the bladder 900. The spar retaining disc 800 comprises four apertures 820 adjacent and spaced around its circumference. A looped flexible ligature 760 passes through each aperture 820 in the disc 800 and through an aperture formed through the central branch 762 of one of the spars 700. As such each spar 700 is flexible attached to the spar retaining plate 800 such that it can be displaced and pivoted with respect to the disc 800.

The bladder 900 is constructed by enclosing a tyre 920 of substantially the same size and shape of that of the wheel 1000. The bladder 900 comprises the tyre 920, two rings 940, and two domed plates 960, 961 .

The exploded view of Figure 1 1 only shows one of the four spars 700 and shows a duplicate of one of the looped flexible ligatures 760. Figure 1 1 does not show the flexible connections 980 between the two domed plates 960, 961 .

The bladder 900 is formed by enclosing the two circular apertures on either side of the tyre 920 which are bounded by the annular beads of the tyre 920, so as to define a bladder with a single generally cylindrical cavity. The two rings 940 are each arranged such that they contact the inside of the bead of one of the sides of the tyre 920 and extend into the circular aperture bounded by said bead. Each of the two domed plates 960, 961 is arranged such it covers one of the two apertures bounded by one of the two beads of the tyre and contacts the outside of the bead as well as the ring 940 extending into the aperture.

A plurality of bolts 966 extend through apertures in the domed plates 960, 961 into apertures in the rings 940 so as to connect the domed plates 960, 961 to the rings 940 and to grip the beads of the tyre 920 between them and to define an air-tight seal across the aperture bounded by the bead and covered by the domed plates 960, 961 . In some variants of the wheel extension the apertures through the domed plates 960, 961 and the rings 940 may be threaded, in other variants the bolts may be held in position by nuts arranged on the inner surfaces of the rings 940. Figure 1 1 shows the inner domed plate 961 connected to the inner ring 940.

Figure 10A shows a variant of the wheel extension where the two domed plates 960 and 961 are arranged facing the same direction, such that when viewed from outside the bladder 900 the domed plate 960 distal from the wheel 1 000 is convex and the domed plate 961 located closer to the wheel 1 000 and adjacent the spar retaining plate 800 is concave. In other embodiments both of the domed plates 960, 961 may be arranged such that they are convex when viewed from outside the bladder 900.

The domed plate 960 distal from the wheel 1 000 comprises an air valve 964 at its centre for inflating or deflating the bladder. This plate 960 further comprises four radial tracks 962 with C-shaped cross sections spaced apart such that each track is at 90 degrees to two other tracks and opposite a third track. The end 722 of each bladder face contacting length 720 which is distal from the remainder of the spar 700 comprises a pair of protrusions 723 which are received by the tracks 962 such that the end of the spar is slideable lengthwise into, out of and along the tracks but is not displaceable out the tracks in any other direction. The bladder further comprises flexible connections 980 which may be fibrous ligatures, cables, straps or chains between the two plates 960, 961 which are extended when the bladder is inflated and restrain the plates to prevent overloading the spars 700 when the bladder 900 is inflated to normal tyre pressures as shown in Figure 10A.

Figure 10B shows the wheel extension 600 with a partially evacuated bladder 900 in the process of being fitted onto a wheel 1000. The partially evacuated bladder 900 allows the spars 700 to be pivoted such that their first generally U-shaped indents between their central branches 762 and their bladder face plate contacting lengths 720 are closer together and their second generally U-shaped indents between their central branches 762 and tabs 742 are further apart, with their track engaging ends722 being located close to the centre of the outer domed plate 960. This allows the spars 700 to fit their second ends and second generally U-shaped portions over the wheel 1 000. Partially evacuating the air from the bladder 900 may advantageously provide the force required to deform the tyre 920 of the bladder thereby allowing the tab comprising ends 742 of the spars 700 to be placed over the wheel 1 000 as seen in Figure 1 0B.

The bladder 900 may then be inflated, displacing the domed plates 960, 961 apart and inflating the bladder 900. This displaces the first generally U-shaped portions of the spars 700 apart, consequently pivoting the spars at their flexible loops 760 such that their second generally U-shaped portions are displaced together onto the rim of the wheel 1 000, thereby gripping and attaching the wheel extension attachment 600 onto the wheel 1000 such that it generally doubles the surface area in contact with the ground in use. The fully inflated and attached arrangement of the wheel extension 600 and the wheel 1 000 is shown in Figure 9 and 10A.

Referring to Figures 1 2 to 1 5C, there is shown a third wheel attachment 1 100 according to the present invention. The third wheel attachment 1 1 00 is not a wheel extension and is intended to provide additional traction to a wheel 1 500 on slippery surfaces such as snow, ice, or mud. This allows the wheel attachment 1 100 to provide additional traction in a similar manner to a snow chain.

The wheel attachment 1 1 00 comprises four spars 1 200, a bladder 1400, a rigid external bladder cover 1960 and a flexible internal disc 1 800 which acts as a spar retainer and as an internal protective cover for the bladder 1400. In use the wheel attachment 1 100 is attachable to a wheel 1500.

The spars 1 200 each comprise a first length 1 220 for contacting the outer face of the tyre 1 500 and the external bladder cover 1960, and a central length 1 240 at right angles to the first length 1220 for contacting the rim or rolling surface of the tyre of the wheel 1500. The spars 1200 further comprise a tab at an end 1242 The spars 1 200 each comprise a central length 1 240 for contacting the rim or rolling surface of the tyre of the wheel 1 500; first length 1 220 for contacting the outer face for the tyre of the wheel 1 500 and the external bladder cover 1960; and a tab 1242 for contacting the inner face of the tyre of the wheel 1 500. The first length 1 220 and the tab 1 242 extend at right angles from first and second ends of the central length of the spar 1 200 respectively, such that the first length 1220 is parallel to an imaginary length along the centre of the tab 1 242. Consequently, the spars define generally U-shaped profiles which in use fit over the rim of the wheel 1 500.

The exploded view of Figure 14 only shows one of the four spars 1 200, and duplicates one of the looped flexible ligatures 1260

The external bladder cover 1960 and the flexible disc 1 800, fit together and are connectable to each other over the bladder 1 400 such that they define a bladder case. The flexible disc 1800 is arranged adjacent the wheel 1500 in use and comprises either four D-rings 1 820 attached to and spaced around its circumference (as shown in Figure 14) or four apertures 1820 adjacent to and spaced around its circumference (as shown in Figures 1 3A, 1 3B and 15B).

A looped flexible ligature 1 260 passes through each aperture 1 820 or D-ring 1 820 and in use fits into a notch 1262 formed in the outer edge the spar 1200 adjacent the corner of the central and first lengths of the spar 1 200. The arrangement of a flexible ligature 1 260 is shown in detail in Figure 1 5B.

The dome shaped rigid external bladder cover 1 960 is arranged distal from the wheel 1 500 and comprises an aperture 1342 at its centre for an air valve 1 964 to extend through. The external bladder cover 1 960 further comprises four radial tracks 1 962 with C-shaped cross sections spaced apart such that each track is at 90 degrees to two other tracks and opposite a third track. The distal end 1222 of each first length 1 220 of the spars 1200 comprises a pair of protrusions 1223 which are received by the tracks 1 962 such that the end 1222 of the spar 1 200 is slideable lengthwise into, out of and along the tracks but is not displaceable out the tracks in any other direction. Figure 1 5C shows protrusions 1223 and the end 1 222 of a spar 1 200 being received within a track 1962.

The flexible inner disc 1800 may be formed of rubber and may comprise a reinforcing ring attached to or embedded within its circumference.

The bladder 1400 is generally disc shaped and comprises a central air valve 1964 which extends through the central aperture 1342 in the outer bladder cover 1 960. Figure 13A shows the wheel attachment 1 1 00 being fitted onto a wheel 1500 with the bladder 1 400 partially deflated. In such an arrangement the flexible disc 1800 is relatively flat such that the spars 1200 are able to move freely on the flexible ligatures 1 260, allowing their tabbed ends 1242 to be displaced apart such that the wheel attachment fits over the rim of the wheel 1 500.

In use, the bladder is inflated such that inner disc 1 800 becomes distended, decreasing the radial distance between the axis of rotation of the wheel and the D- rings 1 820 or apertures 1 820. The external bladder cover 1960 is simultaneously displaced outward from the wheel 1 500 by the outward expansion of the bladder 1 400, thereby displacing the protrusion 1 223 comprising spar ends 1 222 radially outward from the central valve 1964 along the spar tracks 1 962. The tabbed spar ends 1242 are consequently drawn together on the far side of the wheel 1 500. This causes the spars 1 200 to grip the wheel 1 500 locking the wheel attachment 1 1 00 onto the wheel 1 500. This arrangement is shown in Figure 1 3B.

In this arrangement the spars 1200 provide ridges on the rolling surface of the tyre of the wheel 1500, thereby providing grip on slippery surfaces such as snow, ice, or mud. This allows the wheel attachment 1 100 to act in a similar manner to snow chains.

It is understood that the invention is not intended to be limited to the illustrated embodiments described above, and any suitable modifications may be made to the described embodiment which fall within the scope of the invention as defined by the claims. For example, the illustrated embodiments may be modified to include optional features described in the summary of the invention or features of one of the other embodiments. For example, the invention may be deployed with amphibious vehicles or used to provide amphibious capability to non-amphibious vehicles.