FIELD OF THE INVENTION This invention relates to a traction affording device for fitment to a motor vehicle driven wheel, and generally (in the absence of a lockable or limited slip differential) to each of a pair of driven wheels, in order to provide traction in slippery or unstable ground such as mud, sand and the like.

BACKGROUND TO THE INVENTION In the event that the driven wheels of a vehicle enter a region of slippery or unstable ground such as mud, sand or the like, it is a regular occurrence that the continued application of driving force to the wheels simply causes them to dig themselves deeper into the mud or sand thereby creating a situation in which the vehicle is thoroughly stuck. Recovery from such a position generally requires outside assistance, in particular, a suitable vehicle to tow the one that is stuck out of the mud or sand unless the stuck vehicle itself, is fitted with some sort of winch device which would be, to say the least, unusual.

One solution that has, in times gone by, proved to be reasonably popular, if not entirely effective, is for the driven wheels of the vehicle to be fitted with chains. This is extremely difficult and messy to implement, in situ ; the chains must be appropriately dimensioned for the particular size and configuration of wheel ; and the solution is not entirely effective, as indicated above. In any event, tensioning of such chains is generally troublesome to achieve

OBJECT OF THE INVENTION It is accordingly an object of this invention to provide a traction affording device for a motor vehicle driven wheel that will be effective in use and that will be relatively easy to fit to such wheel.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a traction affording device of the type operatively comprising a plurality of angularly spaced tread engaging members extending transverse to the circumference of a tire tread, the device being characterised in that it comprises an attachment assembly including at least three generally equally angularly spaced radially extending arms having inner and outer ends, the radially inner ends being interconnected optionally by way of a base, and the radially outer ends each being operatively associated with a transverse tread engaging member, and wherein the effective length of at least one of said arms is adjustable relative to the others and has associated therewith means for urging the outer end of such arm radially inwards towards the other tread engaging members to operatively cause frictional engagement between all of the tread engaging members and the tread of an associated tire.

Further features of the invention provide for each of the radially extending arms to be radially adjustable in length, preferably telescopically adjustable; for the means for urging the outer ends of the arms inwards to cause the tread engaging members to operatively frictionally engage the tire tread to be a flexible tension element, typically a stranded steel cable, attached to a central tensioning hub at one end and at the other end to a remote part of the associated arm or tread engaging member ; for each tread engaging member to have at its free end, a generally radially inwardly directed stop; for the length of each of the tread engaging members to be adjustable, preferably telescopically, to accommodate different widths of tires between the stop and

the associated arm; for the hub to be rotatable by means of a suitable wheel spanner and to have a pawl and ratchet assembly associated therewith for maintaining tension in the tension members; and for each of the arms to be resiliently biased to an extended condition in which case the means for urging the outer ends inwardly operates against such biasing.

In one embodiment of the invention a tension element such as a steel cable is attached to the stop in each case so that tension on the associated tension element will cause both the length of the tread engaging member and the length of the associated radially extending arm to be urged to a contracted position in which the stop engages the side of a tire opposite the arm and the arm causes the tread engaging member to engage the tread of an associated tire, in use.

In an alternative embodiment of the invention a tension element such as a steel cable is attached to an outer part of each telescopically retractable arm to enable contraction of the arms to be effected and a screw threaded fastener is arranged to enable clamping of the stop against the side wall of a tire, in use.

It is a further feature of the invention that the base be provided with an axially aligned, outwardly extending reel that can be used as the reel of a winch arrangement for pulling on an associated wheel by way of a cable fixed to a stationary anchor point some distance away from the vehicle, in use.

The invention also provides an attachment assembly suitable for use in a device as defined above, the attachment assembly being characterised in that it includes at least three generally equally angularly spaced radially extending arms having inner and outer ends, the radially inner ends being interconnected optionally by way of a base, and the radially outer ends being adapted for attachment to a transverse tread engaging member, and wherein the effective length of at least one of said arms is adjustable relative to the

others and has associated therewith means for urging the outer end of such arm radially inwards to operatively cause contraction of a circle joining the outer ends of the three arms.

Further features of this aspect of the invention provide for the outer end of each arm to have associated therewith a hook for cooperation with a transverse tire engaging member in the form of a chain or other articulated member. Other features of the attachment assembty wi) t be quite apparent from the foregoing features of the device itself.

In order that the above and other features of the invention may be more fully understood a number of different embodiments thereof ill now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE POINGS Figure 1 is a schematic elevation of one embodiment of the invention illustrating its position relative to a wheel, in use; Figure 2 is a schematic sectional view taken along line II-II in Figure 1 and showing only the. one radially extending arm and associated parts ; Figure 3 is a schematic elevation showing the interrelationship of the three tensioning cables and their associated hub; Figure 4 is a schematic detailed elevation showing the pawl, ratchet and nut assembly for rotating the hub illustrated in Figures 1 and 3; Figure 5 is a schematic elevation illustrating an auxiliary reel coaxial with the base and adapted for use as a winch arrangement

Figure 6 is a cross-section through a second embodiment of the invention; Figure 7 is an elevation of the embodiment illustrated in Figure 6; Figure 8 is a schematic three-dimensional view of an attachment assembly for use in combination with a chain or like articulated assembly that defines the tread engaging members; Figure 9 is a schematic three-dimensional view of the attachment assembly illustrated in Figure 8 in combination with a dedicated chain assembly; Figure 10 is an elevation of an enhanced fin or paddle assembly in association with a tread engaging member in a condition ready for installation ; and, Figure 11 is a view similar to Figure 10 but showing the associated stop in its operative position.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the embodiment of the invention illustrated in Figures 1 to 4 of the drawings, a friction affording device according to the invention, generally indicated by numeral (1) in Figure 1, comprises an attachment assembly that includes a central base (2) with three equally angularly spaced radially extending composite arms (3). Each of the composite arms (3) is radially telescopically extensible by virtue of each arm having a tubular base part (4) into which is received a telescopically movable outer arm part (5).

Each outer arm part has, at its outer extremity, a transverse tread engaging member (6) that is also tubular so as to receive, telescopically, a stem (7) carrying at its opposite end an inwardly directed stop (8) that is generally parallel to the radially extending arm (3) and axially spaced therefrom.

The inner end of the stem (7) has anchored to it, one end (9) of a flexible stranded steel cable (10) that extends around the corner (11) joining the tread engaging member with the outer arm part (5). The other end (12) of each cable is anchored to a rotatable hub (13) located at the centre of the base.

The hub is rotatable by means of a nut formation (14) extending axially outwards at one end thereof, the nut formation being configured to be rotatable by means of a conventional motor vehicle wheel spanner. The hub also has fixed thereto a ratchet wheel (15) that cooperates with a pawl (16) to hold the hub in a position in which the cables are under tension applied utilizing the wheel spanner.

The above arrangement is such that pulling radially inwards on each of the cables tends to simultaneously pull the stop member towards the arm so that it engages the inner side wall (17) of a tire (18) and simultaneously withdraws the outer arm part radially inwards to cause the associated tread engaging member to firmly engage the tread (19) of the tire.

In order to install the device on a tire, with the cables in a loosened condition, the device is positioned on the tire with the three tread engaging members extending over the tire tread and the stop members located on the inside of the tire. The hub is then rotated by means of the wheel spanner in order to draw the three stops against the inner sidewall of the tire and simultaneously draw the tread engaging members onto the tire tread so that the device is firmly attached to the tire and is rotatable in unison therewith. Clearly the

pawl is spring biased towards engagement with the ratchet wheel to prevent tension being released.

It will be understood that the tread engaging members will provide substantial traction that can be enhanced to any extent necessary by providing radially outwardly directed fins or paddles (20) on the radially outer edge of the tread engaging member.

In order to remove the device from a wheel the spanner is employed to urge the hub and ratchet wheel sufficiently against the tension in the cables to enable the pawl to be disengaged from the ratchet wheel whereupon the arms can be extended and the stops disengaged from the sidewall to remove the device from the wheel.

Figure 5 illustrates an auxiliary feature of the invention in which a reel (21) is provided to extend outwards from the base (22), and the reel can be used to wind cable (23) onto itself with the cable being attached to a fixed object (24) such as a tree or the like. This has the effect of pulling on the wheel when it is rotated and, accordingly pulling the vehicle generally horizontally towards the tree.

Turning now to the embodiment of the invention illustrated in Figures 6 and 7, the stem is replaced by a telescopically movable tube (25) that carries a transverse tubular stop (26) at its free end. In this case the steel cable (27) pulls exclusively on the outer part (28) of the arm (29), in each case, in order to contract for the arms to draw the tread engaging members into contact with the tire. The distance between the outer part of the arm and the stop is, in this case, adjustable by means of a screw threaded bolt (30) extending centrally down the composite tread engaging member (31) of which the telescopically movable tube (25) is a part. Accordingly, in this case, the device is clamped onto the sidewalls by rotating the bolt (30) as may be required.

Another feature of this embodiment of the invention is that the telescopically extensible arms are resiliently biased to the extended condition by means of springs (32) so that the steel cable operatively retracts the arms against the action of the resilient bias.

Clearly, in order to install the device of the second embodiment of the invention on a tire (33) the device is firstly positioned relative to the tire with the three composite tread engaging members located opposite the tire tread. In order assist in doing this, the tubular stops could be rotatable to a position in which they extend in a generally circumferential direction and they may subsequently be rotated to the generally radially extending condition once the tread engaging members are located opposite the tire trade. This initial location of the device is greatly facilitated by the fact that the arms are biased to the extended condition thereby ensuring that the tread engaging members do not foul against the tire.

The arms are then retracted by rotating the nut on the drum so that the composite tread engaging members (31) frictionally engage the tire tread.

The tubular stops (26) are then clamped against the sidewalls of the tire by tightening the bolts (30).

Turning now to Figure 8 of the accompanying drawings, there is illustrated an attachment assembly, generally indicated by numeral (33), that has a central hub assembly (34) as described above, and three telescopically retractable radially extending arms (35).

In this instance, the outer part (36) of each arm has an inwardly directed hook (37) associated therewith. The hook is configured so that it can cooperate with a conventional tire chain assembly (not shown) to draw it tightly into engagement with the tread of a tire.

Alternatively, and as illustrated in Figure 9, a dedicated chain assembly (39) may be provided for use with the attachment assembly illustrated in Figure 8, the chain assembly comprising three chain limbs (40) adapted to operatively extend across the tire tread and whereof the operatively inner ends are interconnected by a triangular tension ring arrangement (41) adapted to encircle the vehicle axle, in use. The tension ring arrangement has an opening link (42) to enable it to be installed around the vehicle axis, for use.

It will be understood that numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof. In particular, the device could be made to be collapsible for transport and storage purposes in which case the outer arm parts could be removable from the base part and could, indeed, the made so as to be nested with each other, or with the base part which could also be collapsible.

Still further, the fin or paddle arrangement could be enhanced relative to that described with reference to, and as illustrated in, Figure 2, and could assume the form illustrated in Figures 10 and 11. In this instance, the fin (43) is slidable axially on the tread engaging member (44) so as to be removable from its and as and when necessary, and the fin has its own inwardly inclined locator stop (45) for cooperation with the inner edge of the tread, as shown in Figure 11. The fin is, however, non-rotatable relative to the tread engaging member (44).

The stop (46) for engaging the inner sidewall of a tire, in use, is, however, rotatable between a position in which it extends approximately circumferentially for purposes of fitting onto a tire, as illustrated in Figure 10, and one in which it extends operatively radially inwards as illustrated in Figure 11 as described previously. The clamping of the stop (46) is achieved using a bolt (47) that operates in a manner that will be quite apparent from the aforegoing.

The particular advantage of this fin arrangement is that the fin itself can be easily included, or removed, as and when required, depending on the terrain to be negotiated simply by removing the bolt completely and allowing the stop and fin to be installed or removed from the tread engaging member.

Numerous other variations may be made without departing from the scope of the invention.

The invention therefore provides an extremely simple and effective traction affording device that can be easily and swiftly fitted in an appropriate format to a vehicle tire and that accommodates a wide range of different sizes and widths of tires.