GB2064445A

GB2064445A - Pneumatic Tyre Breakers

Info

Publication number: GB2064445A
Application number: GB8038530A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1979-12-06
Filing date: 1980-12-01
Publication date: 1981-06-17
Also published as: FR2473426A1; FI64768C; IT8026439A0; FI803730L; GB2064445B; SE8008568L; FR2473426B1; JPS5695704A; DE3046005A1; MY8500370A; ZA807483B; AU539314B2; JPH0319083B2; DE3046005C2; IT1134590B; FI64768B; AU6512180A

Abstract

A tyre has a tread reinforcing breaker formed by at least two cross- laid plies 1, 2 of metal reinforcement cables and at least one edge ply, e.g. 3, formed by circumferentially extending reinforcement members. The or each edge ply may have a modulus greater than 5,000 daN/cm and may comprise reinforcement members of aromatic polyamide, or of a material with a large initial elongation under stress. The or each edge ply may be located radially outwardly of the cross-laid plies as shown or between these plies. The tyre may have a radial carcass and an aspect ratio less than 100%. <IMAGE>

Description

SPECIFICATION Pneumatic Tyre The present invention relates to a pneumatic tyre with a reinforcing breaker play, intended in particular, but not exclusively, for heavy commercial vehicles, and comprising a radial carcass with a low aspect ratio, i.e. less than 100%, possibly falling to 30%.

Tyres of this type may be used in particular for semi-trailers. In the case of multi-axle semitrailers, the tyres, owing to their location, can undergo very high transverse loading which frequently may cause scrubbing, resulting in premature failure due to ply separation at the edges of the breaker.

On the other hand, and especially when a low aspect ratio tyre is to be made, it has been noticed that after vulcanization and inflation of the cover, undesirable deformation of the tyre cross-section has occurred.

According to the present invention, a tyre having a tread reinforcing breaker wherein the breaker comprises at least two plies of metal reinforcement cables each ply being laid so that its cables cross the cables of the next adjacent ply and at least one edge ply comprising longitudinally extending reinforcement members made up of high modulus reinforcement elements.

Preferably, the longitudinally extending reinforcement members are embedded in a rubber compound and the elements may also have the characteristic of a large initial elongation such that the elements extend when a small tensile load is applied but resist further extension.

The reinforcement members of the edge ply or plies may comprise a winding of a band formed by at least two parallel reinforcing elements or may comprise a single reinforcing element helically wound.

The edge ply or plies may be radially above, the crossed plies or between the crossed plies.

The modulus M of a ply of wires can be characterised by the ratio dL F/- L in which F is the force necessary to extend the corresponding cables, with a width of 1 cm and a length L, by a length dL, and for an elongation dL L equal to 90% of the elongation at rupture. In the case of a tyre intended for commercial vehicles, the modulus M is considered to be high if it is greater than 5000 daN/cm.

The result of the invention is an improvement in the performance of the reinforcing belt particularly with respect to non-separation of the edges of the breaker ply, and a tyre casing having an inflated transverse section of satisfactory shape, free from the undesirable deformation of the section existing in the earlier technology.

Other characteristics and advantages of the invention will appear in the following description of particular embodiments, given by way of non-limiting example, in conjunction with the attached diagrammatic drawings, in which: Figure 1 is a developed view of a reinforcing belt subjected to a transverse force; Figure 2 shows a section of a tyre with a reinforcing belt in accordance with the invention; Figure 3 is a graph showing measurements of the strength of wires used for the manufacture of tyres; Figure 4 shows a second embodiment of a tyre crown in section; Figure 5 shows a third embodiment of a tyre crown in section; Figure 6 shows a fourth embodiment of a tyre crown in section; and Figure 7 shows a fifth embodiment of a tyre crown in section.

A reinforcing belt subjected to a lateral force when the tyre is skidding or scrubbing can be compared with a beam loaded at the centre. The reinforcement of the edges of the breaker ply in accordance with the invention confers on this ply a high resistance to bending under such loading conditions.

A developed portion of the reinforcing belt according to the invention is shown in Figure 1. This reinforcement consists of two crossed plies of metal wires 1 and 2, known from earlier technology, and two longitudinally extending border plies 3 and 4 constituted, for example, by high modulus reinforcing elements such as metal wires or cables, preferably with "high initial elongation." Of course these plies can be constituted by aromatic polyamide cabling, or any equivalent high modulus material.

In the case of a tyre subjected to scrubbing, the arrows A symbolize the forces originating from the structure of the casing which surrounds and supports the breaker ply and arrow B symbolises the resuitant of the friction forces of the tyre on the ground due to its transverse displacement during scrubbing.

Figure 2 represents in section a tyre according to the invention having an aspect ratio of 40%.

The tyre shown includes a radial carcass 5, the plies of which at their ends embrace two bead wires 6.

The tread 7 includes grooves which are not shown in the drawing.

The breaker ply comprising the two crossed plies 1 and 2 is reinforced near its edges by two longitudinal plies 3 and 4 of wires, the object of which is to reinforce the resistance of the belt to mechanical loads resulting from scrubbing. The wires used to form the two longitudinal plies 3 and 4 have a high modulus M, which, in the case of commercial vehicle tyres, means that the modulus is greater than 5000 daN/cm.

Figure 3 shows graphically measurement of strength made on different types of wires used in the manufacture of tyres. To make these measurements, tension is applied with increasing force, by means of a dynamometer, up to the breaking point of the wire. During each measurement, a record is made of the values of the force applied, expressed in daN, and the corresponding elongations in percentages.

Curve A in Figure 3 relates to a normal metal cable in the form 7x3x0.20 mm. Its elongation at rupture is 2.2%, and the force corresponding to 90% of this value (1.98%) is 164 daN.

Curve B shows the development of the elongation as a function of the force applied to a 3x7x0.22 mm cable "of high initial elongation." As appears in the diagram, curve B shows a development which is different from curve A although the structures of the two cables are relatively close. At the commencement of traction, cable B has an elongation very much greater than that of cable A, then, when the elongation reaches 5 or 6%, it behaves identically. The elongation at rupture is 9.1%, and the force corresponding to 90% of this value (8.6%) is 1 65 daN.

Curve C relates to a 3 xl 650 dtex aromatic polyamide cable. Cables of this type are marketed for example by the Du Pont Nemours Company under the name "Kevlar". This cable is made adhesive with a view to ensure the adhesion of the rubbery mixes. In the case of this cable, the elongation at rupture is 4%, the force corresponding to 90% of this value being 42 daN.

In Figure 3, curve D relates to a 2x 1400 dtex cable in nylon fibres. Its elongation at rupture being 19.6%, and the force corresponding to 90% of this value (17.6%) being 20 daN. Cables of types A, B, C and D are currently used in the tyre industry. Preferably, a ply is formed by laying mutually parallel cables in a rubbery mix. The modulus of the ply thus defined, given by the formula dL Fl- L for dL =90% L of the elongation at rupture is then calculated directly from the mechanical characteristics of the wires and their density in the ply.

The table below summarises the calculations given for each of the types of cable measured previously: Density Elongation % at Force for elongation Cable per cm 90% rupture at 90% rupture Ply modulus A 4.5 1.98 164 daN/cm 37272 daN/cm B 4.5 8.6 165 8634 C 9 3.6 42 10500 D 9 17.6 20 1023 As stated above, one of the requirements of the invention is that the modulus M of the ply of cables must be high, for example higher than 5000 daN/cm. Under these conditions, it can be seen that only cables A, B and C, with an appropriate density in the ply allow a sufficiently high modulus to be obtained.

Preferably, a chosen cable will have identical characteristics to those represented by curve B, having a phase of rapid elongation from 2 to 10% followed by a phase of reduced elongation, cables of this type being called "Cables with large initial elongation." In the following Figures, special embodiments of the invention have been represented concerning the arrangements of the reinforcing plies relative to the crossed plies constituting the breaker ply itself.

Figure 4 represents a second embodiment in which the longitudinal edge plies 3 and 4 are arranged between the crossed plies 1 and 2 constituting the breaker ply.

In Figure 5, the plies 3 and 4 are arranged above the crossed plies 8, 9 and 10. In this Figure, the two-ply band shown previously has been replaced by three triangulated plies 8,9 and 10, the innermost ply 8, for example, having metal wires orientated at 680 relative to the equatorial plane of the tyre, the second ply 9 having metal cables arranged at 220 and crossing those of the first, the outermost ply 10 also having cables at 220 but crossing those of ply 9.

Figure 6 represents another variant in which the longitudinal reinforcing plies 3 and 4 are arranged laterally on the upper crossed ply 10, this ply of course crossing one of plies 9 and 8 as before, the whole constituting the reinforcing band.

In Figure 7, the longitudinal plies 3 and 4 are included within the rubber of the tyre, as in Figure 6, but they are enveloped by a ply 11 of the breaker ply reinforced by metal cables parallel to those of one of the crossed plies 8, 9 or 10. Ply 11 covers all the others, with overlapping as shown in Figure 7, although a similar construction without overlapping is also possible. Such an additional ply 11 can be used with any of the variants already described.

The longitudinal reinforcing plies can be obtained by calendering with an appropriate mixture of rubber compound mutually parallel wires or cables. The band thus obtained is then rolled at least one on the edges of the breaker ply, its ends overlapping or not. They can also be obtained by winding in a helix one or more wires or cables which are coated with rubber compound prior to winding.

The longitudinal reinforcing plies 3 and 4 are generally off-set inwards relative to the second ply of the band, but they can also overlap it on both sides.

The longitudinal reinforcing plies may be laid flat on the band during its make-up. They can also be laid on the previously curved or shaped band. They can be assymetrical in width, in their nature or the density of their cables, or in position.

31 5/70 R 22.5 tyre casings have been made in conformity with the teaching of the present invention. The radial casing included a single ply reinforced by metal cables in accordance with a known process. The band included: for the main part, two plies reinforced by 7x4x0.22 mm wrapped metal cables orientated at 22C relative to the equatorial plane of the tyre, mutually crossed and 200 mm wide for the inner ply and 225 mm wide for the outer ply, an extra ply, centrally positioned above the outer crossed ply. Its metal reinforcing cables had a wrapped 7x3x0.20 mm structure; they were inclined at 22C to the equatorial plane, in the same direction as the outer crossed ply, in the subject of the invention, the lateral reinforcement, a 3x7x0.22 mm metal cable "with large initial elongation" wound from the edge of the extra ply up to a distance of 55 mm inwards from the edge of the outer crossed ply i.e. over a width of 52.5 mm. The pitch of winding was 4.5 cm.

Tested on a rolling road at a speed of 50 kph and with overloads in excess of 60% relative to the loads published by ETRTO, they gave results very superior to those obtained with casings of normal design. During very severe tests on vehicles, such tyres, subjected to considerable scrubbing, have been used up to full wear without exhibiting separation of the edges of the breaker ply.

Claims

1. A tyre having a tread reinforcing breaker wherein the breaker comprises at least two plies of metal reinforcement cables each ply being laid so that its cables cross the cables of the next adjacent ply and at least one edge ply comprising longitudinally extending reinforcement members made up of high modulus reinforcement elements.

2. A tyre according to claim 1 wherein the edge ply is formed by longitudinally extending reinforcement members embedded in a rubber compound.

3. A tyre according to claims 1 or 2, characterised in that the metal elements forming the abovementioned longitudinal ply have a large initial elongation.

4. A tyre according to claim 1, characterised in that the above-mentioned longitudinal ply is constituted by parallel elements of aromatic polyamide.

5. A tyre according to any one of claims 1 to 4, characterised in that the above-mentioned reinforcing elements are wires, cables or strands.

6. A tyre according to any one of the preceding claims, characterised in that each longitudinal ply is obtained by winding at least one band formed by an assembly of two or more parallel reinforcing elements.

7. A tyre according to any one of the preceding claims, characterised in that the longitudinal ply is obtained by helically winding a reinforcing element.

8. A tyre according to any one of the preceding claims, characterised in that the bands constituting the said longitudinal plies exhibit an overlap of the ends on themselves.

9. A tyre according to any one of the preceding claims, characterised in that the lateral reinforcing plies are placed radially above the said crossed plies.

10. A tyre according to any one of claims 1 to 7, characterised in that the lateral reinforcing plies are placed between two crossed plies forming the reinforcing band.

11. A tyre according to any one of claims 1 to 9, characterised in that the axially inner edge of the said longitudinal plies is situated between the axially outer edge and the equatorial line of the said band.

12. A tyre according to any one of the preceding claims, characterised in that the axially outer edge of the said longitudinal plies coincides with the axially outer edge of one of the plies of the said band.

13. A tyre according to any one of the preceding claims, characterised in that a ply of strands or cables wholly overlaps the assembly formed by the said band and the said longitudinal ply.

14. A tyre constructed and arranged substantially as described herein and illustrated in Figures 2 or 4 or 5 or 6 or 7 of the accompanying drawings.