NZ200323A - Pneumatic tyre sidewall tensioned by inflatable pocket below tread - Google Patents

Description

200323 Divided out of Patent Appl. No. 188202 PriorMy Datsfs): . ;7.7 Complete Specification Filed: Glass: ikQ^/A',- ■ ■ h J pj^rj, v 'E8 15 fi jJ t,1 S Cf £ J i«3 L' 9 iL* Cb i w * /£$V P.O. , ivo: .-s -i.il. 84 Under the provisions of Regulation 23 (I) the Specification has been ante-dated to jbSU 19S8L.

N.Z. NO.

NEW ZEALAND Patents Act 19 5 3 ■> COMPLETE SPECIFICATION 4T J F ^ 1 . - ▼ -Initials **t V\ 1 APR i<2$2 "IMPROVEMENTS TO TYRE AND WHEEL ASSEMBLIES." We, DUNLOP LIMITED, a British Company of Dunlop House, Ryder Street, St. James's, London S.W.1.ENGLAND do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- ~ 1 ~ (Followed by 1A.) 200323 ,iA IMPROVEMENTS TO TYRE AND WHEEL ASSEMBLIES This invention relates to type and wheel assemblies and to tyres for vehicles.

In conventional pneumatic tyre and wheel assemblies air pressure is utilised to tension the carcass and when load is applied to the assembly the carcass tension near that part of the tyre contacting the ground is progressively reduced so that effective load bearing support is obtained by the carcass tension in other parts of the tyre. Conventional pneumatic tyres are subject to complete loss of effective load support in the event of loss of air -■? pressure. Conventional solid tyres support load by subjecting the tyre to compressive loads in the ground contacting portion of the tyre. Such solid tyres are, however, prone to heat build-up and are therefore subject to limitations of speed and load.

It is known that if the sidewalls of a pneumatic tyre are provided with an inherent degree of pretension, effective load support is not completely lost if the tyre is deflated. However previous tyres or tyre and rim assemblies including pretensioned sidewalls have suffered from various disadvantages.

For example it is known from U K Patent No 6961 of 1896 to insert in the cavity between tyre and wheel rim a steel strip of rectangular cross-section, of width slightly less than the tyre tread width, and length equal to several times the tyre tread circumference. Such a strip has an inherent tendency to unwind (acting as a large spring) and thus applied a radially outwards force beneath the tyre tread causing the tyre sidewalls to be placed in tension. It is also known to replace the tread reinforcing belt (the "breaker") of a radial ply tyre by a metal hoop, of width substantially equal to that of the belt but of greater diameter, again to place the sidewalls in tension. In both instances the use of a solid metal strip which prevents local deflection of the tyre tread in a radial'direction substantially reduces the ride comfort of the tyre. 2.

Alternatively it is known from U.K. Patent No. 28233 of 1903 to tension the sidewalls by causing radially inward displacement of the tyre beads. However, this is difficult to achieve in practice since the bead wire has to be made discontinuous in order to allow its diameter to be reduced on radially-inward displacement.

It is an object of the present invention to provide a tyre or a tyre and wheel rim assembly which does not suffer from these disadvantages.

In accordance with the invention a tyre and wheel assembly comprises a wheel rim including two circumferentially-extending bead seats and a tyre comprising two circumferentially-extending bead regions each retained upon a respective bead seat by a continuous bead ring which is substantially inextensible and incompressible circumferentially of the tyre, a circumferentially-extending tread-capable of- local radial deflection, and two load-carrying sidewalls each of which is straight or includes a substantial portion of its length which is straight, when an axial cross-section of the tyre is considered, each having a radially-innermost edge and a radially-outermost edge, the radially-outermost edge being attached to a respective edge of the tread and the radially-innermost edge being attached to a respective edge of the bead region, each sidewall comprising reinforcement which extends between said edges and which is pretensioned in the unladen state of the assembly by introduction of a fluid under pressure into a cavity beneath the tread in only the radially outer part of the chamber formed between the tyre and the rim, and having a height less than the tyre sectional height.

If the tyre is pneumatic, the reinforcement may be pretensioned before the chamber is inflated.

The tread is preferably reinforced by a breaker extending like a belt around the tyre.

High tensile strength, low elongation reinforcement materials are preferred to reinforce the sidewalls so that N.z. PA 22, 200323 M °nv7.?- 3. when the assembly is subjected to load in use the tension forces in the reinforcement in the deflected ground contacting sector of the assembly are immediately reduced near to zero.

The reinfrocement may be cords or wires extending radially or at an angle to the radial direction. The cords or wires may be part of a ply or plies of woven or non-woven material but preferably comprise a substantially radially extending ply of conventional substantially 10 weftless tyre cord fabric.

According to a further aspect of the invention a tyre comprises two circumferentially-extending bead regions each reinforced by a continuous bead ring which is substantially inextensivle and incompressible circumfer-15 entially of the tyre, a circumferentially-extending tread capable of local radial deflection, two load-carrying sidewalls each having a radially-innermost edge and a radially-outermost edge, the radially-outermost edge being attached to a respective edge of the tread and the 20 radially-innermost edge being attached to a respective bead region, each sidewall comprising reinforcement which extends between said edges and which is pretensioned when the tyre is mounted on a rim and in the unladen state by introduction of a fluid under pressure into a cavity 25 beneath the tread in only the radially outer part of the chamber formed by the tyre, and having a height less than :the tyre sectional height.

The tyre tread may be reinforced by a breaker which is capable of circumferential expansion. Preferably the 30 sidewalls are reinforced by cords or wires which are continuous from one bead region to the other, said cords radially overlying the breaker in the tread region of the tyre carcass.

The cavity may be air or liquid filled and it is 35 preferred to pressurise only the cavity and not the main chamber formed between tyre and rim which should be close am^en"k pressure.

The cavity may be supported by a hoop which may be 200323 - 4. substantially rigid. For example, the hoop may be a simple steel hoop or may be formed by a thicker hoop of softer material which may be reinforced by more conventional means similar to conventional tyre breakers. A suitable choice of material and design may allow the natural frequency of the hoop to be varied to provide harmonic damping so that the tyre .can be tuned for various vehicle application. The cavity is effectively a generally flat tube between the breaker and the hoop and the overall effect is to provide at each edge of the tread region a stiffened ring one for each sidewall.

The edges of the cavity may be formed with a reversed curvature such that the fluid pressure in the cavity tends to straighten the edges. This effect increases still further the stiffening forces applied to the edges of the tread.

An alternative support for the tread edges comprises a circular cross-section tube provided radially beneath a substantially transversely rigid breaker which tube is helically wound with a reinforcement laid at a high angle such that inflation of the tube causes its main radius to enlarge without any substantial change in cross-sectional area to that radially outward stabilising forces are applied by the reinforced tube to the centre of the breaker and the transverse stiffness of the breaker thus provides the required tread edge region support.

In this arrangement again only the tube need be pressurised and the main tyre cavity is not so pressurised. Pressurised gas or liquids may be used to radially expand the tube.

The tube length may be several times that of the tread and is. helically coiled to extend both underneath and across the width of the tread.

Some embodiments of the present invention will now be described, by way of example only, in conjunction with the attached diagrammatic drawings in which Figure 1 shows a cross-section of a tyre of an assembly according to a first embodiment 200323 of the present invention to show details of the tread region and carcass radially outwards force being applied to the tyre breaker; Figure 2 shows a modified form of the assembly shown in Figure 1; Figure 3 shows a cross-section of a tyre of an assembly according to a second embodiment of the invention.

Figure 1 shows a tyre having a hoop 60 which is relatively rigid and may, for example, comprise a flat steel strip shaped into a hoop which is moulded into an inner wall 61 of tubular cavity 62. The cavity 62 is of a similar width to the tread region 63 of the tyre and a 15 breaker 64 is provided in the radially outermost wall of the cavity 62. The breaker 64 is basically a conventional tyre breaker but is capable of sufficient circumferential expansion to allow the reinforcement tension to be created and in addition is made substantially rigid in the 20 transverse direction by, for example, an additional reinforcement ply laid at 90° to the circumferential direction. The remainder of the tyre comprises straight sidewalls 65, bead regions 66 and a radial ply reinforced carcass P which has the ply cords extending from bead to 25 bead and passing through the tread region of the tyre over the breaker 64 as shown.

It is a feature of this arrangement that the relatively small cross-section radius of the edges of the cavity do not bulge sideways and that they therefore 30 prevent any lateral pressure being applied to the sidewalls. These are therefore able to remain straight under the ^ influence of the radial tension only.

In use of the assembly shown in Figure 1 the main annular chamber 67 of the tyre is not inflated, but only 35 the thin, flat annular cavity 62.

If a radial sidewall tension Fq is created in the reinforcement without pressurising the cavity 62, the tyre ^is then similar to a conventional tyre and a compressive 200323 ■ 6. circumferential stress T is created in the breaker where: T ow T = Breaker Stress R = ~~<-E _ R Breaker Radius F = Sidewall Tension per Unit o * Length of Breaker circumference.

If the breaker is sufficiently resistant to compression this balance of forces is stable and the tyre functions in this state.

However, when the cavity 62 is pressurised then the above equation becomes: T ^ = FW ~2Fq where P = excess pressure m the cavity and W = width of cavity and the compressive stress (T negative) in the breaker is reduced or even converted to a tensile stress (T positive).

Thus support for the breaker is provided by the pressure of the cavity 62 and the edges are supported to ,. cf - provide the support for the sidewalls.

This example is very efficient in that the pneumatic stiffness at a given pressure may be more than twice that ■ of a more conventional tyre, allowing very much larger loads to be carried.

Figure 1 shows the tubular cavity and hoop as integral with the tyre tread region. This is not essential although it minimises relative movement and friction. It is an advantage in some cases to reinforce at least the edges of the tube with,.for example, cords wound at nearly 90° to the circumferential direction. The radial thickness of the tube cavity should be at least equal to the normal working deflection so that the inner, rigid hoop is not normally deflected. The hoop itself is required to be relatively rigid to support the compressive stress created by air pressure (and which must not be supported by the sides of the tube). A steel hoop is adequate but it is an advantage to use a thicker hoop of softer material which will survive the occasional large deflection. The mass of the hoop can be varied over a wide range. It is possible therefore to 200323 • 7. adjust the frequency of its modes of vibration independently of those of the tyre leading to the possibility of creating a harmonic damper for some of the tyre vibration frequencies. It will therefore be possible to 'tune' the tyre for better comfort.

Figure 2 shoes a similar tyre in which the edges E?" of the flat tube 62 are not reinforced but thickened and . of reversed curvature.

These edges constitute "arches" and can retain the'' air pressure. The thrust of the arches provides additional support at the edges of the breaker 64 where the casing tension tends to pull inward. It helps therefore to give a "flat" breaker and make the contact pressure distribution more even.

Figure 3 shows a tyre of a second embodiment in which the breaker 64 is capable of sufficient circumferential expansion to allow the reinforcement tension to be created and, on inflation, pressed outwardly by a tube T which is helically wound with reinforcement cords disposed at a high angle such that inflation causes the main radius to increase without any substantial change in cross-sectional area.

For a 90° reinforcement the equilibrium shape is close to a circle while for lower angles a flattened elliptical shape may be obtained which presses against a greater proportion of the width of the breaker inner surface.

Alternatively a number of smaller coils of tube may be used to obtain a more even coverage of the breaker inner surface or a longer length arranged in a plurality of coils extending across the width of the tread.

For all of the tyres described a large sidewall pretension tends to pull the breaker inwards at one or two points across the width while the pressurised cavity applies a force outwards over the whole width. These forces tend to bend the breaker cross-section.

Since the breaker is a hoop this bending implies extensions and compressions in the circumferential direction 200323 8. additional to the strains caused by bending into and out of the contact patch.

It is an advantage to minimise transverse bending by designing for increased transverse rigidity.

For example a solid hoop of nylon moulded to a wavy shape would have a very high transverse rigidity. So too would crimped sheet steel or a hoop assemblied from alternate sectors of rigid and soft material. /■ c. 'ty loo 313 9.

Claims (30)

WHAT WE CLAIM IS:

1. A tyre and wheel assembly comprising a wheel rim including two circumferentially-extending bead seats and a tyre comprising two circumferentially-extending bead regions each retained upon a respective bead seat by a continuous bead ring which is substantially inextensible and incompressible circumferentially of the tyre, a circumferentially-extending tread capable of local radial deflection, and two load-carrying sidewalls each of which is straight or includes a substantial portion of its length which is straight, when an axial cross-section of the tyre is considered, each sidewall having a radially-innermost edge and a radially-outermost edge, the radially-outermost edge being attached to a respective edge of the tread and the radially-innermost edge being attached to a respective edge of the bead region, each sidewall comprising reinforcement which extends between said edges and which is pretensioned in the unladen state of the assembly by introduction of a fluid under pressure into a cavity beneath the tread in only the radially outer part of the chamber formed between the tyre and the rim, and having a height less than the tyre sectional height.

2. A tyre and wheel assembly according to Claim 1 in which the tyre is pneumatic and the reinforcement is pretensioned before the chamber is inflated.

3. A tyre and wheel assembly according to Claim 1 or Claim 2 wherein the reinforcement comprises cords or wire extending radially of the assembly.

4. A tyre and wheel assembly according to any one of Claims 1-3 wherein the reinforcement comprises cords or wire extending at an angle to the radial direction.

5. A tyre and wheel assembly according to any one of the preceding claims wherein the tread is reinforced by a breaker which is capable of circumferential expansion.

6. A tyre and wheel assembly according to Claim 5 wherein the sidewalls are reinforced by cords or wires which are continuous 2 2 JUL 1983 c. 0 'J j 2 3 10. from one bead region to the other, said cords or wires radially overlying the breaker in the tread region of the tyre.

7. A tyre and wheel assembly according to any one of the preceding claims wherein only the cavity is pressurised.

8. A tyre and wheel assembly according to any one of the preceding claims wherein the sidewalls of the cavity are formed with a reverse curvature which tend to straighten when the cavity is pressurised.

9. A tyre and wheel assembly according to any one of the preceding claims wherein the cavity is supported by a hoop.

10. A tyre and wheel assembly according to Claim 9 wherein the hoop is substantially rigid.

11. A tyre and wheel assembly according to either one of. Claims 9 or 10 wherein the tubular cavity extends circumferent-ially around the tyre and has a width substantially equal to the width of the tread, and a radial height substantially less than the tyre sectional height, the hoop being located in the radially inner surface wall of the tubular cavity and having an axial dimension similar to the axial width of said cavity.

12. A tyre and wheel assembly according to any one of Claims 1-7 wherein the cavity is defined by a circular cross-section tube helically wound with reinforcement.

13. A tyre and wheel assembly according to any one of Claims 1-7 wherein the cavity is defined by a tube of length greater than the tread circumference, the tube being helically coiled beneath and across the width of the tread.

14. A tyre comprising two circumferentially-extending bead regions each reinforced by a continuous bead ring which is substantially inextensible and incompressible circumferentially of the tyre, a circumferentially-extending tread capable of local radial deflection, two load-carrying sidewalls each of which is straight or includes a substantial portion of its length which is straight or includes a substantial portion of a length which is straight, when an axial cross-section of the tyre is considered, each sidewall having a radially-innermost edge and a radially-outermost edge, the radially-outermost edge being attached to a respective edge of the tread and the 12 OCT 1983 200323 radially-innermost edge being attached to a respective bead region, each sidewall comprising reinforcement which extends between said edges and which is pretensioned when the tyre is mounted on a rim and in the unladen state by introduction of a fluid under pressure into a cavity beneath the tread in only the radially outer part of the chamber formed by the tyre and having a height less than the tyre sectional height.

15. A tyre according to Claim 14 wherein the reinforcement comprises cords or wires extending radially.

16. A tyre according to Claim 14 wherein the reinforcement comprises cords or wires extending at an angle to the radial direction.

17. A tyre according to any one of Claims 14-16 wherein the tread is reinforced by a breaker which is capable of circumferential expansion.

18. A tyre according to Claim 17 wherein the sidewalls are reinforced by cords or wires which are continuous from one bead region to the other, said cords or wires radially overlying the breaker in the tread region of the tyre.

19. A tyre according to any one of Claims 14-18 wherein the sidewalls of the cavity are formed with a reverse curvature which tend to straighten when the cavity is pressurised.

20. A tyre according to any one of Claims 14-19 wherein the cavity is supported by a hoop.

21. A tyre according to Claim 20 wherein the hoop is substantially rigid.

22. A tyre according to either one of Claims 20 or 21 wherein the tubular cavity extends circumferentially around the tyre and has a width substantially equal to the width of the tread, and a radial height substantially less than the tyre sectional height, the hoop being located in the radially inner surface wall of the tubular cavity and having an axial dimension similar to the axial width of said cavity.

23. A tyre according to any one of Claims 14-19 wherein the cavity is defined by a circular cross-section tube helically wound with reinforcement.

24. A tyre according to any one of Claims 14-19 wherein the 12. 2005 cavity is defined by a tube of length greater than the tread circumference, the tube being coiled helically beneath and across the width of the tread.

25. A tyre siobstantially as described herein with reference to and as shown in Figure 1.

26. A tyre siobstantially as described herein with reference to and as shown in Figure 2.

27. A tyre substantially as described herein with reference to and as shown in Figure 3.

28. A tyre and wheel rim assembly including a tyre substantially as described herein with reference to Figure 1.

29. A tyre and wheel rim assembly including a tyre substantially as described herein with reference to Figure 2.

30. A tyre and wheel rim assembly including a tyre substantially as described herein with reference to Figure 3. DUNLOP LIMITED By Their Attorneys HENRY HUGHES LIMITED