IE41532B1 - Tyres - Google Patents

Abstract

Tyres incorporating an additional hoop of rubber on the underside of the tread zone and in a state of compression which establishes and sustains a state of tension in an inextensible reinforcing structure contained in the carcass between the compressed rubber and the outer tread. The hoop can be incorporated in both pneumatic and solid tyred wheels. The performance limit of a tyre is approximately determined by the value of TL2HS/MA, where T = radial thickness of the tyre, L = vertical loading on the tyre, H is a hysteresis loss factor, S is a function of rolling speed (viz rate of flex per unit time), M = modulus of the rubber, A = effective area of rolling contact. Unlike higher levels of cross-linking, precompression increases M without a corresponding increase in H, hence raising the performance limit for a tyre of given dimensions.

Description

This invention relates to tyres.

According to the invention there is provided a tyre including as integral parts of its structure the following: a) a tread portion of elastomeric material b) bracing the tread portion and radially inwardly of it an annular reinforcing structure which is substantially inextensible in both its circumferential and its transverse directions^and, c) radially inwardly of the annular reinforcing structure a hoop of rubber which in the unloaded and, if appropriate, uninflated state of the tyre, is maintained in a compressed condition by the annular reinforcing structure.

There can be ambiguity in describing the state of stress or strain of a sample of rubber. It is to be noted, therefore, that in this specification the term compressed as applied to rubber refers to any state of strain in which the largest boundary stress components acting on the sample of rubber are directed so as to tend to produce a compressive strain.

The tyre may be a solid or cushion tyre, in which substantially the whole of a vertical load is borne by the rubber7 or may be a pneumatic tyre in which air pressure within the tyre assists in supporting the load. In either case the incorporation of the hoop of pre-compressed rubber into the tyre results in an increase in the load carrying capacity of the tyre whilst minimising the attendant difficulties of heat generation normally resulting from 2. additions! rubber being incorporated into the tyres.

At the same time the comfort of the tyre, i.e, the ability to absorb road obstacles without transmitting unpleasant vibrations to the a:;le, and thence to vehicle and occupants, can be maintained and in some cases) improved, The invention will now be described in more detail with reference to the accompanying drawings of which:Figure 1 shows the stages in the manufacture of a solid tyre according to this invention; Figure 2 illustrates another method of making a solid tyre including pre-compressed rubber? Figure 3 illustrates a possible cross-sectional configuration for the hoop; Figure ' illustrates a further method of making a non-pneumatic tyre containing hoops of compressed rubber; Figure 5 illustrates the application of the hoop in a pneumatic tyre and Figure 6 is a graph showing the effect of the precompressed rubber on the response to vertical and horizontal vibration of a pneumatic tyre.

The performance of solid elastomeric tyres is limited in speed and lead-carrying capacity by the hysteresis of the materia 1-3 rued in their construction. The limitations are approximately according to the equation: vs.

LIMIT 3, 42.532 Τ = Radial thickness of the tyre L - Vertical load on the tyre II - Hysteresis loss factor of the tyre rubber S - Speed (deflection cycles/unit time) M = Modulus of elasticity of the rubber A = Effective area of contact patch The limit referred to above depends on the effective rate of cooling of the particular tyre involved.

This invention is concerned with improving the load carrying capacity of the tyres by pre-stressing a hoop of rubber in the tyre in compression.

The value of pre-compression can be understood in general terms by reference to the above equation since the effect of the pre-compression in the rubber is to increase the modulus of elasticity (M) without increasing the Hysteresis loss factor H. Thus pre-compressing reduces the value of T L HS and therefore allows a greater load L to be MA carried by the tyre without exceeding the limit.

It will be appreciated that this equation represents a simplified approximation of the situation in a tyre. Depending upon the manner of manufacture of the tyre the degree of pre-compression may not be uniform throughout the compressed rubber. In general, however, it is preferred that no part of the hoop of pre-compressed rubber is pre-compressed by more than 30%. The average pre-compression over the whole of the hoop of pre-compressed rubber is preferably in the range 10% to 20% although lower pre-compressions than this may also have value, especially in pneumatic tyres as is 4. described later in this specification.

It is also to be noted chat the higiier tiie modules of elacticity the rubber the lower the degree of pre-compression required for a given effect on load capability.

Figure 1 shows how a solid tyre containing a hoop of pre-compressed rubber can be made. Part (a) shows a precurod belt 1 consisting of, for example, cross-biased plies of textile or steal cords embedded in rubber compound as used in the breakers of conventional radial tyres. This belt will form a suitable annular reinforcing structure in the tyre·.

Figure 1 (b) shows the main body 2 or cushion of the tyre which is cured to ε larger external diameter than the internal diameter of the reinforcing structure .

Figure 1 (a shows the cushion 2 after it has been compressed and fitted inside the belt 1. It is necessary to make soma provision for fixing this in place. However, conventional bonding techniques or even mating ridges and grooves are adequate because the pre-compression of fas rubber in the cushion urges it outwardly into the reinforcing structure and thus urges the two surfaces together.

Figure I (d) shows a cross-section through the finished tyre. The dotted line outlines a tread layer 3 which has not been shown in the previous sketches.

There is no pre-compression in the tread layer 3 illustrated in part (d) and this region is still subject to the original limits before pre-compression. This is not a critical problem because for the tread layer 3 the thickness 1 can be very small and the Modulus M can be very large . without impairing the ability of the tyre to cushion obstacles. This function is now performed separately by the material comprising the hoop.

In practice therefore, the use of the pre-compressed 5 rubber increases the load-carrying/speed capability for a given size of solid tyre.

So far only the simplest design and the simplest method of manufacture have been described.

It is however possible to make the tyre in one 10 operation by building and curing it inside out as in Figure 2(a) where the tread 4 is inwardly of a belt 5 and the cushion 6 is the outermost portion. After this it is turned inside out as in Figure 2(b)Since as shown in Figure 2(a) and 2(b) the method 15 gives an undesirable pre-stretch in the tread as well as pre-compressing the cushion it is preferred to apply the tread after turning inside out an assembly of the annular reinforcing structure and the cushion.

If desired it would be possible to make the tyre 20 turning only the cushion inside out before fitting the hoop and tread.

By many of these routes the pre-compression in the cushion would be found to increase towards the centre and it is possible to exploit this by using a cross-section with sloping sides, triangular or trapezoidal.

Figure 3(a) shows a hoop of rubber having in section a triangular outline before turning inside out. The sloping faces are concave. 6. out.

J Ά S 3 S Figure 3(b) shows tho same section after turning inside The sloping surfaces havo now bulged outwards and are less concave. This concavity helps to avoid tensile stresses and fatigue cracking.

A preferred method for the manufacture of a solid tyre in accordance with the invention which does not involve inversion of any of the components is illustrated in Figures 4a and 4bo The tyre is manufactured in the cross-sectional shape shown in Figure 4a and consists of a tread portion lo, an inextensible annular reinforcement 11 and a pair of solid rubber tyre components 12 and 13 which are moulded to the interior of the reinforcement but splay outwards radially inwardly. As shown in Figure 4b the tyre is used on a divided rim 14 which has the same, diameter as the internal diameter of the two rubber components 12 and 13 as moulded. In mounting the tyre on the rim the components 12 and 13 are drawn together to form a substantially solid tyre. In this step these components are forced to reduce their raaial length in crosssection and thus become pre-compressed.

Figure 5a shows a cross-section of a radial ply pneumatic tyre on a rim.

Figure 5b shows a cross·-section of a hoop of elastomer of larger diameter than the inside surface of the breaker region tiie hoop saving a cross-sectional shape wnirii tapers towards the rotational axis of tne tyre.

Figure 5c shows the hoop bonded in place on the inside surface -.4 tne breaker.

To the scale shown this modification is capable of increasing the load capability of the tyre by about 20% 44532 without the major increase in hysteretic energy loss usually associated with thick inner linings.

The effect of the hoop of compressed rubber on the ride comfort of a pneumatic tyre is illustrated by the following example.

Two 155-12 Dunlop SP Sport textile radial tyres were fitted with hoops of rubber positioned beneath the crown region on the interior of the tyre. In one case the hoop was not pre-stressed and in the other it was. The amount of pre-stress in the latter case was of the order of 4%. The rubber used in the hoops was a natural rubber compound of the formulation given below in the Table.

TABLE Parts bv Weight SMR 20 100 Flectol flakes 2.5 Nonox ZA 1.0 Mineral oil 5.0 ZnO 4.0 Stearic acid 1.0 GPF Black 65.0 Sulphur 3.0 Santocure 1.0 PVI 50 0.8 /sMR 20 is a standard Malaysian Natural Rubber.

Flectol flakes are a proprietory product consisting of (2,2,4 trimethyldihydroquinoline).

Nonox ZA is Phenyl Isopropyl p-phenylene diamine (IPPD). 8.

Santocure is H.cyclohexyl benzthiazolo sulphenamide (CBS) PVJ 50 is 50% eye Johexyl thiophthaI imide 4 50% inert inorganic filler).

The hardness of the compound was 64° BS and its modulus 5 of elasticity was 7.00 MN/met.re measured dynamically at 15 Hz and 10% amplitude i.e. oscillating between 0 and 10% elongation. The load deflection curves were plotted for each tyre and it was found that at a scheduled pressure of 20 p.s.i. the tyre with the pre-stressed hoop exhibited a load deflection IO curve about 7% steeper than the control without precompression i.e. the tyre with tho pre-stroesed hoop of rubber was deflected less by a given load than the control..

The vibration transmission of the tyres was measured by mounting the tyres inflated to 20 p.s.i on a laboratory Maclipherson strut type suspension, rotating the tyres under a load of 550 lbs. on a slatted drum to vibrate the tyres and measuring the induced acceleration of the axle of the wheel on which the tyre was mounted over a wide range of frequencies of excitation. For both radial (or vertical) acceleration V A and longitudinal acceleration L A the results for the prestressed hoop are plotted in Figure 6 as a ratio of the accelerations transmitted by the tyre containing the precompressed rubber and the tyre containing unpre-compressed rubber respectively against the frequency of vibration to which the tyre was submitted i.e. the excitation frequency.

The shaded areas represent the parts of the frequency range over which the tyre containing pre-stressed rubber gave a better performance.

. Longitudinal acceleration is particularly important because vehicle designers are subject to greater restriction in the design of suspension stiffness in this direction than in the vertical direction.

The pre-stressed hoop shows a clear advantage in reduced vibration transmission over most of the frequency range for the longitudinal effect.

Claims (14)

1. WHAT we claim is:1. A tyre including as integral parts of its structure the following: a) a tread portion of elastomeric material b) bracing the tread portion and radially inwardly of it an annular reinforcing structure which is substantially inextensible in both its circumferential and its transverse directions,and, c) radially inwardly of the annular reinforcing structure a hoop of rubber which in the unloaded and, if appropriate, uninflated state of the tyre, is maintained in a compressed condition by the annular reinforcing structure..

2. A tyre according to claim 1 which comprises a substantially solid, non-pneumatic, tyre,

3. A tyre according to claim 2 in which the tread portion has a radial thickness less than that of the hoop of compressed rubber.

4.. A tyre according Lo claims 1, 2 or i in which the tyre, as moulded, comprises a pair of solid annular rubber tyre components which splay axially outwardly and radially inwardly from the annular reinforcing structure to permit their being compressed by being forced together between the annular reinforcing structure and a wheel rim.

5. A tyre according to claim 1, which comprises a pneumatic tyre, the hoop of rubber being situated at the crown of the tyre.

6. A tyre according to claim 5 which comprises a pair of 11. reinforced beads and a carcass construction made up of cords extending in substantially radial planes from bead to bead.

7. A tyre according to claim 6 in which the hoop of rubber has a cross-sectional shape which tapers towards the 5 rotational axis of the tyre.

8. A tyre according to any one of claims 1 to 4 in which the average compression in the hoop of rubber is in the range 10% to 20%.

9. A tyre according to any one of the preceding claims 10. In which no part of the hoop of rubber is compressed to a degree which is greater than 30%.

10. A tyre substantially as described herein with reference to Figures 1, 2 or 3 of the accompanying drawings.

11. A tyre substantially as described herein with 15 reference to Figure 4 of the accompanying drawings.

12. A tyre substantially as illustrated herein in Figure 5 of the accompanying drawings.

13. A method for the manufacture of a tyre substantially as described herein with reference to Figure 4 of the 20 accompanying drawings.

14. A pneumatic tyre substantially as described in the foregoing example.