The present invention relates to a device for use with inflatable tyres mounted on vehicle wheels, fitted within a tyre that enables the wheel to run with a deflated tyre. Such devices are known as Vun-flat' devices.

Run flat devices are designed to resist the effects of sudden deflation when a tyre is punctured, such that the tyre does not become shredded or thrown off a, say, metal wheel.

It is known to provide run-flat devices for wheels in which the run flat device is fitted within a tyre to a metal rim of a wheel . The run flat device is in the form of an annular body adapted to slip circumferentially on the metal rim when the tyre deflates and the tyre is brought into contact with an outer face of the annular body of the run flat device. This slippage allows the tyre to slip on the wheel rim whilst ensuring little or no slippage of the tyre relative to the outer circumference of the annular body of the run-flat device.

According to a first aspect the present invention a run flat device for fitting to the outer circumference of a wheel inside an inflatable tyre, comprises a resilient substantially annular body having a central axis, the body having, in radial section, an upper portion from which depend first and second side legs, one or both sides of the body being provided with a foot or feet extending from a free end of each of the side legs, wherein the upper portion and the side legs of the body define a recess shaped to direct a component of force applied radially inward with respect to the central axis and outward axially through the one or more feet.

Preferably one or both of the side legs extend uninterrupted along a substantial part of a circumferential length of the annular body. More preferably, one or both of the side legs extend along the circumferential length of the body.

Preferably, one or both of the feet extends uninterrupted along at least part of a circumferential length of the side legs. More preferably still, one or both of the feet extend along the circumferential length of the side legs.

Preferably the side legs are of corresponding section.

Preferably an inner surface of each of said side legs terminates at a crack inhibitor formation. More preferably the crack inhibitor formation is of circular section joining the legs to one another.

Preferably the legs are of constant section between the crack inhibitor formation and the feet. Alternatively, the legs are of varying section between the crack inhibitor formation and the feet. Preferably the inner surface of one or more legs tapers reducing the section of the leg or legs toward the respective flange. Preferably, the annular body comprises a split ring. Alternatively, the annular body comprises a plurality of arcuate segments. Preferably the annular body comprises three arcuate segments.

Preferably each of the plurality of segments are identical in shape.

Preferably a clamping means located between adjacent segments imparts to each segment a circumferential clamping force and an axial clamping force to urge the segments circumferentially and axially towards each other.

Preferably a lubricant is located on an outer surface of the run flat device.

According to a second aspect of the invention a wheel assembly comprises a wheel rim and an inflatable tyre, a run-flat device according to the first aspect of the invention fitted to the wheel rim and a lubricant provided between the run flat device and an inner surface of the tyre.

Preferably, the lubricant between the run flat device and an inner surface of the tyre is a high temperature grease.

Preferably, the lubricant between the run flat device and an inner surface of the tyre is provided on the inner surface of the tyre. Preferably, the run flat device acts on deflation of the tyre to prevent relative movement of a periphery of the tyre with respect to the wheel rim.

According to a third aspect of the invention, a method of forming a wheel assembly comprises the steps of

providing a wheel having a rim and a rear rim portion, a front rim portion releasably securable to the rim, a run flat device in accordance with a first aspect of the invention, and a tyre having front and rear side walls;

locating the run flat device within the tyre;

urging the tyre and associated run flat device axially over the wheel rim; and

securing the front rim portion to the wheel rim.

This has as an advantage that the resilient nature of the run flat device means that force applied as the front wall of the tyre is urged axially is exerted on the adjacent leg and transferred to the other leg which in turn urges the rear side wall towards and subsequently into contact with the rear rim portion.

Preferably a lubricant is provided on an inner rim of the tyre prior to location of the run flat device within the tyre.

The invention will now be described, by way of example only, in relation to the attached Figures, in which Figure 1 shows a sectional view through a wheel fitted with a tyre and a run flat device in accordance with the present invention; and

Figure 2 shows a perspective view of a run flat device in accordance with the present invention;

Figure 3 shows a perspective view of a segment of a run-flat device in accordance with the present invention; and

Figure 4 shows a view corresponding to that of Figure 1.

Referring first to Figure 1, there is shown schematically a sectional view through a wheel assembly 2. The wheel assembly 2 comprises a demountable metal wheel 4 of three piece construction, a tyre 6 and a run-flat device 8. The wheel 4 comprises a central wheel portion 10, a rim 12 including a rear rim portion 14 and a front rim portion 16. The central wheel portion 10 incorporates a circumferentially extending foot 18 to which the rim 12 is permanently secured in any suitable manner. In use, the central wheel portion 10 is secured by way of an inner surface to a wheel hub of a vehicle (not shown) in any suitable manner, for example by way of studs and nuts, or by way of threaded studs (not shown). The front rim portion 16 is releasably secured in relation to the wheel rim 12 in any suitable manner, for example by way of locking pins or bolts 20.

The run flat device 8 comprises a resilient substantially annular body 50 of generally top hat section. The body 50 is formed of an upper portion 56 from which depend first and second side legs 58,60, with feet 52,54 extending to each side from a free end of each of the side legs 58,60. As may be seen from the Figures the feet 52,54 extend and are directed axially outward . The upper portion 56 and first and second side legs 58,60 define a cut-away central portion or recess 70 within the body 50 of each segment 28. As may be seen from Figures 2 and 3, the cut-away central portion or recess 70 extends along the length of the body 50 of each segment.

In Figure 1, it can be seen that the recess comprises an upper generally circular portion 72 bounded to each side by the side legs 58,60. It will be understood that the circular portion 72 acts as a crack inhibitor and that other shapes will be suitable for the upper portion of the recess 70. In the illustrated embodiment, beneath the crack inhibitor portion, the side legs 58,60 are of uniform thickness and the body 50 is provided with an internal radius 74 on an inner surface and an external radius 76 on the outer surface where the side legs 56,60 transition into the respective feet 52,54.

In the illustrated embodiment both side legs correspond . In an alternative embodiment, this is not the case.

Where the wheel 4 is fitted with a conventional inflation valve (not shown) aligned generally with the centre of the wheel rim 12, the inflation valve will be located within the cut-away portion 70 of the segments 28 of the run flat device 8. Such an embodiment has as an advantage that any circumferential alignment of the run flat device 8 will allow the tyre readily to be inflated. The tyre 6 and the run flat device 8 are located over the metal wheel 4 prior to placing in position of the front rim portion 16. This may conveniently be achieved by locating the run flat device 8 within the tyre 6 and then urging the tyre 6 and associated run flat device 8 axially onto the wheel rim 12 (as indicated by arrow A in Figure 1).

The resilient nature of the body 50 of the run flat device means that as an axial force is applied to the outer tyre wall 22 and into the first leg 58 of the run flat device 8, as the first leg 58 moves into the part of the recess 70 between the first leg 58 and the second leg 60 the run flat device 8 transfers the axial force from the first leg 58 to the second leg 60, causing the second leg 60 to urge the adjacent tyre wall 24 axially along the rim such that as the run flat device 8 is urged axially onto and along the wheel rim 12 the rear wall 24 of the tyre 6 is urged towards and against the rear rim portion 14 of the wheel. It will be understood that as the force is applied the resilient nature of the run flat device 8 will cause the run flat device 8 to shuffle into position (as indicated by the arrows B).

When the front rim portion 16 is then secured in place against the wheel rim 12 the resilient nature of the body 50 of the run flat device 8 causes the run flat device 8 to act as a bead retainer holding a periphery 66 of the front and rear side walls 22,24 of the tyre 6 against the corresponding front and rear portions 14,16 of the wheel 4. The tyre 6 can then be inflated. In a preferred embodiment an inner portion of the tyre 6 is provided with a lubricant, such as a high temperature grease, prior to location of the tyre 6 on the wheel 4. In use the forces acting on the grease will tend to spread the grease over an inner surface 62 of a rim of the tyre 6.

Turning to Figure 2 a perspective view of a preferred embodiment of the run flat device 8 is shown. The run flat device 8 comprises an annular body 26 having a number of segments 28, three in the illustrated embodiment. For ease of manufacture, the segments 28 are identical in form, one of which is shown in Figure 3 (hidden surfaces are shown by dashed lines). The segments 28 may be used for a left-hand or right- hand wheel without adaptation.

The segments 28 are formed of any suitable material having resilient properties. The segment material conveniently also possesses enhanced ballistic and shock absorption properties. In the illustrated embodiment, each segment 28 is generally arcuate having a first stepped end 30 and a second stepped end 32. As may be seen from Figure 2 the first end 30 of each segment 28 fits to the second end 32 of an adjacent segment 28. Each stepped end 30,32 comprises a forwardly extending convex portion 34 and recessed concave portion 36, the concave portion 36 fitting the adjacent convex portion 34, leaving a circumferential gap between the convex portion 34 and the concave portion 36.

It can be seen that the feet 52,54 extend uninterrupted around the circumferential length of each segment. In an alternative embodiment (not shown) one or both of the feet of one or more of the segments may take a different form. By way of example, a foot may be formed with interruptions along its length. One or more of the interruptions may extend into an adjacent leg to lighten the segment to produce a succession of depending circumferential legs depending circumferentially from the body 50. The section of dependent legs on a side of the body 50 need not be of identical section. Where each side of the run flat device is provided with a succession of circumferential legs, the legs to each side of the body may be aligned circumferentially with one another or offset in whole or in part. The succession of circumferential legs may be of equal circumferential dimension and/or circumferential spacing or differing circumferential dimension and/or circumferential spacing.

In an alternative embodiment, a lubricant in the form of a low friction material is provided on an upper surface of one or more of the segments. In a further embodiment the lubricant is provided on an upper surface of each segment. In a still further embodiment the lubricant is provided as a split band fitted to the segments when they have been fitted in place about the wheel rim.

Returning to the illustrated embodiment, each forwardly extending convex portion 34 is provided with two parallel through bores 38,40 (Figure 3) recessed on an outer face for receiving in use clamping means in the form of parallel bolts 42,44 and anti-vibration washers 46. The use of two parallel bolts 42,44 prevents, or at least severely restricts, relative pivoting of the segments 28. The bolts 42,44 also provide clamping both in a circumferential direction and in an axial direction (in a direction along the axis of rotation of the wheel assembly 2). In use the clamping arrangement prevents the segments 28 twisting out of alignment with the wheel 4 when the deflated tyre 6 contacts an outer surface 82 of the run flat device 8.

In use, the wheel assembly 2 is normally as in Figure 1 with the tyre 6 inflated. When the tyre 6 deflates, as for example in the event of a puncture, an inner surface 62 of the tyre rim 64 is forced towards the outer surface 82 of the upper portion 56 of the run-flat device 8 in the region where the tyre 6 contacts the road to exert an inward force thereon (as indicated by arrow C in Figures 1 and 4). The lubricant, such as grease, between the inner surface 62 of the tyre rim 64 and the outer surface 82 of the run flat device 8 will cause the tyre rim 64 repeatedly to skid circumferentially in relation to the outer surface 82 of the run flat device 8 as the wheel 4 rotates.

The side feet 52,54 function first as tyre bead retainers that stop the sidewalls of the tyre collapsing inward away from the side rim portions 14,16 of the wheel 4 when the tyre 6 is deflated. However, in addition, due to the cross sectional shape of the body 50 of the run flat device 8, when the tyre 6 is urged radially inwards towards and exerts a force radially inwards upon the resilient run flat device 8, due to the resilient nature of the segments, a component of the force will also be directed through the side feet 52,54 outward toward the front and rear wheel rim portions 14,16 (arrows D in Figure 4) producing a clamping action to prevent relative movement of the periphery 66 of the tyre walls 22,24 with respect to the run-flat device 8 and the wheel rim portions 14,16. By preventing movement of the periphery 66 of the tyre walls 22,24 with respect to the wheel rim portions 12,14, the tyre 6 does not rotate in relation to the rotating wheel 4. Relative movement between the tyre 6 and the wheel 4 occurs only in the region where the tyre 6 contacts the road or ground beneath the vehicle to which the wheel is fitted, due to the skidding action between the inner surface 62 of the tyre 6 and the outer surface 82 of the run-flat device 8, the skidding action being enabled by the presence of the lubricant between the tyre 6 and the run-flat device 8.

While described in relation to three piece demountable wheels, the present invention also has application for two piece bolt together wheels.