BACKGROUND TO THE INVENTION The desirability of fitting vehicles with tyres that can be driven on even after they have lost their air pressure is well known. Many forms of"run-flat"tyres have been proposed.

For example it has been proposed to fill tyre casings with foamed plastic material so that, in the event of a puncture, the foamed plastic prevents collapse of the tyre. Thus the casing can be driven on without damage until a repair facility can be reached.

The desirability of fitting certain vehicles with puncture proof tyres is also well known. Such tyres are desirable on vehicles which are used to carry VIP's where kidnapping is a risk, and on security vehicles which carry valuables where robbery is a threat. In both cases the vehicle can be disabled by puncturing its tyres. Security vehicles are often of the type which carry cash between banks and their customers, and are a prime target for robbers.

BRIEF DESCRIPTION OF THE INVENTION According to one aspect of the present invention there is provided a tyre comprising a shell of resiliently flexible sheet material which has first and second portions constituting the side walls of the tyre and a third portion which joins radially outer ends of said first and second portions and which has, on the radially outer face thereof, a bonded-on sleeve of tyre compound with a tread pattern in its radially outer face.

The tyre can include a flange along the circumferentially extending radially inner edge of each of said first and second portions which flanges permit the shell to be secured to a wheel rim. Preferably said flanges extend axially of the tyre from the inner peripheries of said first and second portions and have apertures in them through which fastening elements can be passed.

To assist in keying the sleeve to the shell the shell can have holes in it through which the tyre compound of said sleeve has passed to form protrusions.

Said first and second portions can each have a groove in their axially outer faces, each groove being circular and extending around the respective first and second portion radially outwardly of said inner edge of that portion.

A casing of tyre compound can be bonded to said shell, the casing comprising said sleeve and side walls which are bonded to said first and second

portions.

In this form there can be beads along the radially inner edges of said side walls of the casing, there being reinforcing cords in said beads.

The material of said shell is preferably spring steel or polycarbonate.

In a specific form said third portion is constituted by a circular spine and said first and second portions by ribs protruding from each side of the spine.

According to a further aspect of the present invention there is provided a tyre and a rim construction, the tyre comprising a shell of resiliently flexible sheet material which has first and second portions constituting the side walls of the tyre and a third portion which joins radially outer ends of said first and second portions and which has, on the radially outer face thereof, a bonded-on sleeve of tyre compound with a tread pattern in its radially outer face and the rim construction including a rim and means for securing said shell to said rim.

Said shell can have a flange along the circumferentially extending radially inner edge of each of said first and second portions, said means being constituted by fastening elements each of which passes through said rim and through one of said flanges.

In the preferred form said first and second portions each have a groove in and a rib on their axially outer faces, each groove and rib being circular and extending around the respective first and second portion radially outwardly of said inner edge of that portion, and wherein said rim has circumferentially extending recesses in which said ribs of the first and second portions are seated and circumferentially extending protrusions which seat in the grooves of said first and second portions.

To improve keying of the shell to the sleeve, said shell can have holes in it through which the tyre compound of said sleeve has passed to form protrusions which key said sleeve to said shell.

In another form said combination includes a casing of tyre compound, the casing comprising said sleeve and side walls which are bonded to said first and second portions, there being beads along the radially inner edges of said side walls of the casing and there being reinforcing cords in said beads, said beads being in circumferentially extending recesses in said rim and said means being constituted by fastening elements which pass through said shell and said rim and fasten said shell to said rim.

To secure the tyre to the rim a plurality of circumferentially spaced brackets can be fastened to said rim, said flanges being between the brackets and the rim and being held in place by the brackets. In this construction each bracket

can be channel shaped and include an axially extending web which is fastened to the rim and two radially outwardly directed end walls, said flanges being between the rim and said end walls.

To inhibit rotation of the tyre on the rim a plurality of locking elements can be provided which protrude radially outwardly from the radially outer face of said rim, said casing and said shell, or said shell, having notches in the radially inner periphery thereof for receiving said locking elements.

In another form there is provided a plurality of brackets which are fastened to said rim and span between said casing side walls, said brackets pressing said beads into said recesses.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:- Figure 1 is a radial section through a tyre in accordance with the present invention, Figure 1 also showing the rim to which the tyre is fitted; Figure 2 is a radial section and showing another form of tyre and rim; Figures 3 and 4 are radial sections illustrating further forms of tyre and rim; Figure 5 illustrates a double tyre and double rim for a truck;

Figures. 6 and 7 are radial sections illustrating two further forms of tyre and rim ; Figure 8 is a detail of part of a further rim and tyre; Figure 9 is an elevation of the tyre of Figure 8; Figure 10 is a detail of part of another rim and tyre; Figure 11 is a pictorial view of the rim of Figure 10; Figure 12 is a detail of another rim and tyre; Figure 13 is a pictorial view showing a tyre with part of its casing removed to show its shell ; and Figure 14 is a diagram showing another form of tyre shell.

DETAILED DESCRIPTION OF THE DRAWINGS Referring firstly to Figure 1 the tyre illustrated is generally designated 10 and the rim on which it is mounted is generally designated 12. The tyre and rim constitute a vehicle wheel construction.

The tyre 10 comprises a spring steel or polycarbonate inner shell 14 having the general profile of a conventional tyre. Along its radially inner edges there are flanges 16 and 18 which are configured to match the co-operating parts of the rim 12. More specifically, the flanges 16 and 18 include cylindrical portions 16.1 and 18.1 and flanges 16.2 and 18.2 which are of radially inwardly curving configuration when viewed in radial section. Two series of nuts 20 and bolts 22 secure the shell 14 to the rim 12. The nuts 20 are tack welded or otherwise secured to the cylindrical

portions 16.1 and 18.1 to facilitate assembly.

The shell 14 can, if of spring steel, be manufactured in one piece or in two identical halves which are then welded together. The weld line is at W. If the shell is of polycarbonate it is made in one piece.

A sleeve 24 of tyre compound is vulcanized (or otherwise bonded) to the shell 14, the sleeve 24 having a tread pattern at 26. A steel belt and/or a Nylon belt is incorporated into the tyre at 28 between the shell 14 and the sleeve 24.

Holes 30 are formed in the shell 14 so that, as the sleeve 24 is vulcanised onto the shell, the tyre compound enters the holes and forms protrusions with oversized heads 32 on the inside of the shell. This assists in keying the shell and sleeve together.

The shell has first and second portions 15.1,15.2 constituting the side walls of the tyre and a third portion 15.3 which joins the radially outer ends of the portions 15.1,15.2. The sleeve 24 is bonded onto the radially outer face of the portion 15.3 and has the tread patten 26 in its radially outer face.

The rim 12 comprises two components 34 and 36. The component 34 is of generally drum-like form having at one end a portion which provides a recess 38 and a short cylindrical section 40 to which the shell 14 is bolted. At the other end

the component includes a radially inwardly directed flange 42.

The component 36 comprises a disc-like flange 44 which is secured by bolts 46 to the flange 42. Axial projections 48 on the radial inner edge of the flange 44 enter notches in the edge of the flange 42. The component 36 further includes a short cylindrical section 50 to which the shell 14 is bolted and an axial end section 52 which bounds another recess 38.

The shell is configured so that it has two circumferentially extending ribs 54 which enter the recesses 38. Adjacent the ribs in the axially outer faces of the portions 15.1,15.2 there are circular grooves 55 which receive the edge portions of the components 34 and 36. The grooves are radially outwardly of the inner edges of the portions 15.1,15.2.

The tyre does not require inflation as the shell 14 supports the sleeve 24 and permits the tyre to flex when the tyre runs over rough roads. However, if desired the tyre can also be inflated and a valve for this purpose is shown at 56.

In Figure 2 parts which correspond to those of Figure 1 have been designated with like reference numerals. In this form the portions 16.2 and 18.2 are omitted.

The sleeve 24 is formed with beads 58 along the edges thereof. The

beads 58 are in circumferentially extending recesses 60 formed in the shell 14.

Steel cords 62 reinforce the beads 58. The holes 30 are in this form provided not only under the tread pattern 26 but also through the parts of the shell 14 which bound the recesses 60.

In Figure 3 the recesses 60 and beads 58 are omitted and the holes 30 are made somewhat bigger so that more tyre compound passes through to form oversized heads 32. The shell has portions 16.1,18.1 and flanges 16.2,18.2.

The tyre of Figure 4 includes a shell 64 which is within a tyre casing comprising a sleeve 66 in which the tread pattern is formed and side walls 68.

Those parts in Figure 4 which have counterparts in Figures 1 to 3 have been designated by the same reference numerals to which the suffix. 4 has been added.

The side walls are bonded to the first and second portions 15.1,15.2.

In Figure 4 the side walls 68 have beads 70 along the radially inner edges thereof in which beads there are reinforcing cords 72. The beads 70 are in the recesses 38.4 of the rim 12.4. The shell 64, which is secured to the rim 12.4 by the nuts and bolts 20.4 and 22.4, holds the beads 70 in the recesses 38.

Figure 5 shows a double rim construction for a truck. The tyres on the rims are of the same construction as those shown in Figure 4. Like parts have been designated with the same reference numerals plus the suffix. 5.

Figure 6 shows a construction similar to that of Figure 3. In this form a series of circumferentially spaced brackets 74 are provided around the rim 12.5.

The brackets 74 have radially outwardly directed end walls at each end thereof and the brackets 74 trap the shell's flange portions 16.6 and 18.6 between themselves and the rim 12.6. The brackets 74 are secured to the rim by two self tapping studs 78.

In Figure 7 the brackets 74 are held in place by a single stud 78 and the tyre is constructed as shown in Figure 4.

In Figures 1 to 3 and 6 the shell is exposed in the area of its side walls.

To conceal the stainless steel or polycarbonate shell's side walls it can have a decorative and protective rubber coating sprayed on or otherwise secured thereto.

In Figure 8 a rim is designated 300 and a tyre 302. The tyre 302 is constructed as shown in Figure 4 and its shell is designated 304. Circumferentially spaced around the rim 300 are a plurality of locking elements 306 (see also Figure 11). The elements 306 are fixed to and protrude from the radially outer face of the rim 300.

The shell 304 has, on each of its inner peripheries, notches 308 which receive the elements 306. The notches are best seen in Figure 9. Inter- engagement between the locking elements and the notches prevents the tyre

dragging on the rim and thus rotating with respect to it. In Figure 9 the inner edge of the tyre bead 310 is shown as a dotted circle.

In Figure 10 the configuration differs from that. in Figure 9 in that the bead 310 and the radially inner edge of the shell 304 are both notched to receive the locking elements 306. The notches of the shell are again shown at 308 and the notches of the bead 310 are shown at 312. Tapering studs 314 screwed into the rim 300 force the inner periphery of the shell 304 against the bead 310.

Figure 12 shows a bracket 316 which extends across the wheel in the axial direction to press the shell 304 against the beads 310 and thus the beads 310 into the recesses 318 provided therefor in the rim 300. A number of brackets 316 are spaced apart circumferentially around the wheel. Each bracket includes a bar 320 and two plates 322 which are configured to fit against the shell 304 and rim 300.

Self tapping studs 324 screwed through the rim 300 and into the plates 322 secure the brackets 316 to the rim. The plates 322 are notched at 326 to receive the elements 306.

In Figure 13 the polycarbonate or steel shell 328 is shown as having a spine 330 with ribs 332 protruding from each edge thereof. In another form, which has not been illustrated, the gaps designated 334 between adjacent ribs are replaced by slits in the material of the shell. Thus each rib 332 abuts the adjacent rib 332.

In Figure 14 the slits between ribs are designated 336 and are of a sinusoidal configuration.