Lighter hybrid bead wire for tyre

Abstract

A bead wire for a tire includes a core, an outer layer, and at least one intermediate layer. The core includes at least one yarn of a multifilament textile fiber embedded in an organic matrix. The outer layer includes an outer-layer metal wire wound around the core. Each intermediate layer includes an intermediate-layer metal wire wound around the core. Each intermediate layer is disposed between the core and the outer layer.

Claims

1. A bead wire for a tyre, the bead wire comprising: a core that includes a single yarn of a multifilament textile fibre embedded in an organic matrix, the multifilament textile fibre including a plurality of elementary filaments; an outer layer including an outer-layer metal wire wound around the core; and at least one intermediate layer, each intermediate layer including an intermediate-layer metal wire wound around the core, wherein the core forms a monolithic torus having no macroscopic joint corresponding to a joining of ends to form the torus, wherein the multifilament textile fibre is embedded in the organic matrix such that the elementary filaments are positioned side by side, and wherein each intermediate layer is disposed between the core and the outer layer.

2. The bead wire according to claim 1, wherein a ratio of a contribution of the core to a mass of the bead wire to a contribution of the core to a force at break of the bead wire is less than 1.

3. The bead wire according to claim 2, wherein the ratio of the contribution of the core to the mass of the bead wire to the contribution of the core to the force at break of the bead wire is greater than or equal to 0.25.

4. The bead wire according to claim 1, wherein a material of which the yarn is made has a yield strength greater than or equal to 800 MPa, measured in accordance with a standard ISO 14125 at 23 C.

5. The bead wire according to claim 1, wherein a material of which the yarn is made has a Young's modulus less than or equal to 100 GPa, measured in accordance with the standard ISO 14125 at 23 C.

6. The bead wire according to claim 1, wherein a contribution of the core to a force at break of the bead wire is greater than or equal to 5%.

7. The bead wire according to claim 6, wherein the contribution of the core to the force at break of the bead wire is less than or equal to 75%.

8. The bead wire according to claim 1, wherein a contribution of the core to a mass of the bead wire is greater than or equal to 7%.

9. The bead wire according to claim 8, wherein the contribution of the core to the mass of the bead wire is less than or equal to 75%.

10. The bead wire according to claim 1, wherein a ratio of a diameter of a torus defined by the core to a diameter of a torus defined by the bead wire is greater than or equal to 0.25.

11. The bead wire according to claim 1, wherein a force at break of the bead wire is greater than or equal to 200 kN.

12. The bead wire according to claim 1, wherein a diameter of the yarn is between 6 and 20 mm.

13. The bead wire according to claim 1, wherein a diameter of each elementary filament is between 2 and 30 m.

14. The bead wire according to claim 1, wherein the multifilament textile fibre includes more than 10 elementary filaments.

15. The bead wire according to claim 1, wherein the multifilament textile fibre is chosen from a group of fibres consisting of: glass fibres, carbon fibres, silica fibres, ceramic fibres, and mixtures thereof.

16. The bead wire according to claim 1, wherein the organic matrix is a thermoset type of matrix.

17. A tyre comprising at least one bead wire, each bead wire including: a core that includes a single yarn of a multifilament textile fibre embedded in an organic matrix, the multifilament textile fibre including a plurality of elementary filaments; an outer layer including an outer-layer metal wire wound around the core; and at least one intermediate layer, each intermediate layer including an intermediate-layer metal wire wound around the core, wherein the core forms a monolithic torus having no macroscopic joint corresponding to a joining of ends to form the torus, wherein the multifilament textile fibre is embedded in the organic matrix such that the elementary filaments are positioned side by side, and wherein each intermediate layer is disposed between the core and the outer layer.

18. The tyre according to the claim 17, wherein the tyre is an aircraft tyre.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood on reading the following description, which is given solely by way of nonlimiting example, with reference to the drawings in which:

(2) FIG. 1 is a perspective view of a tyre according to the invention;

(3) FIGS. 2 and 3 are views in section perpendicular to the axis of the bead wire (which is assumed to be straight and at rest) of bead wires according to the first and second embodiments, respectively, of the invention;

(4) FIG. 4 is a view in section perpendicular to the axis of the bead wire (which is assumed to be straight and at rest) of a prior art bead wire.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(5) FIG. 1 shows a tyre according to the invention, denoted by the general reference 10. In this case, the tyre 10 is intended to be fitted on an aircraft and has dimensions of 4617 R20. As a variant, the tyre 10 is intended to be fitted on a terrestrial vehicle, for example a vehicle of the heavy goods vehicle type.

(6) The tyre 10 has a crown 12 reinforced by a crown reinforcement 14, two sidewalls 16 and two beads 18, each of these beads 18 being reinforced with an annular bead wire 20. The crown 14 is surmounted by a tread, not shown in this schematic figure. A carcass reinforcement 22 is wound around the two bead wires 20 in each bead 18 and comprises a turn-up 24 disposed towards the outside of the tyre 20, which is shown fitted onto a wheel rim 26 here. The carcass reinforcement 22 is made up of at least one ply reinforced with cords. The reinforcement 22 is of the radial type. As a variant, the reinforcement 22 is made up of at least two plies reinforced with cords and is of the bias belted type.

(7) Each bead wire 20 has a toroidal overall shape and has an approximately circular cross section. As a variant, the bead wire 20 has a polygonal, for example square, rectangular or hexagonal cross section or even an elliptical or oblong cross section.

(8) FIG. 2 shows a bead wire 20 according to a first embodiment of the invention.

(9) The bead wire 20 comprises a core 30 and four layers C1, C2, C3, C4. The diameter Dt of the torus defined by the bead wire 20 is equal to 21.3 mm. The bead wire 20 is of the multilayer type.

(10) The core 30 comprises a single yarn and in this case consists of a single yarn B. The diameter of the yarn B is between 6 and 20 mm, preferably between 6 and 10 mm.

(11) The yarn B forms a monolithic torus. The core 30 has an approximately circular cross section and the diameter Da of the torus defined by the core 30 is equal to 8.90 mm. The core 30 is made of a core material Ma and comprises a multifilament textile fibre embedded in an organic matrix. The multifilament textile fibre is a glass fibre and the organic core matrix is a thermoset resin. The multifilament textile fibre is continuous. As a variant, the textile fibre is discontinuous.

(12) The glass fibre comprises more than 10 elementary glass filaments, preferably more than 100 and more preferably more than 1000 elementary filaments arranged side by side and thus more or less parallel to one another, apart from the occasional overlap. The diameter of each elementary filament of the textile fibre is between 2 and 30 m. The glass fibre used may be of the E or R type.

(13) The thermoset resin is of the vinyl ester type. Without this definition being limiting, the vinyl ester resin is preferably of the epoxy vinyl ester type. Use is more preferably made of a vinyl ester resin, in particular of the epoxy type, which, at least in part, is based on novolac (also known as phenoplast) and/or bisphenol (that is to say is grafted onto a structure of this type), or preferably a vinyl ester resin based on novolac, bisphenol, or novolac and bisphenol, as described for example in applications EP 1 074 369 and EP 1 174 250. An epoxy vinyl ester resin of the novolac and bisphenol type has shown excellent results; by way of examples, the vinyl ester resins ATLAC 590 or ATLAC E-Nova FW 2045 from the company DSM (both diluted with styrene) may be mentioned in particular. Such epoxy vinyl ester resins are available from other manufactures, such as Reichhold, Cray Valley, UCB.

(14) The core 30 is manufactured for example by impregnation of the fibre as described in document U.S. Pat. No. 3,730,678, or by injection of the organic matrix into a mould in which the fibre has previously been placed, or as described in document EP1167080.

(15) Each layer C1 to C4 comprises a metal wire wound in a helix around the core 30. The wire of the intermediate layer C1 is wound in contact with the core 30. Each wire of each intermediate layer C2, C3 is wound in contact with the layer C1, C2, respectively. The wire of the outer layer C4 is wound in contact with the layer C3. The two ends of each wire of each layer C1 to C4 are connected by means of sleeves.

(16) All of the wires have a more or less identical diameter Df equal to 1.55 mm. Each wire is made of a steel of which the carbon content is greater than or equal to 0.7% by weight of the steel, preferably greater than or equal to 0.8% and more preferably greater than or equal to 0.9%, in this case equal to 0.9%. Each wire of each layer C1 to C4 is wound over a number of turns, for example over 19, 25, 31 and 37 turns, respectively, such that each layer is saturated, that is to say there is not enough room between adjacent windings to be able to insert an additional winding.

(17) FIG. 3 shows a bead wire 20 according to a second embodiment of the invention. Elements similar to those shown with reference to the previous embodiment are denoted by identical references.

(18) In contrast to the bead wire according to the first embodiment, the bead wire 20 according to the second embodiment comprises an intermediate layer C1 and an outer layer C2. The wire of each layer C1, C2 is wound over a number of turns, over 38 and 44 turns, respectively. Thus, the diameter Dt of the torus defined by the bead wire 20 is equal to 21.3 mm. The diameter Da of the torus defined by the core 30 is equal to 16 mm. Each wire has a diameter Df equal to 1.3 mm.

(19) In a third embodiment (not illustrated), the core 30 forms a winding having a number of coils. In this case, the core 30 comprises a number of coils of a single yarn B. These coils have an axis in common with that of the bead wire 20. Thus, each coil has a circular overall shape in projection in a plane perpendicular to the axis of the bead wire.

(20) Traverse winding of the yarn B over a number of turns is carried out such that the core 30 has a substantially polygonal, in this case triangular, cross section. The yarn B is made of the core material Ma described in the previous embodiments. The diameter of each coil B is between 2.5 and 10 mm, preferably between 2.5 and 4 mm.

(21) In a fourth embodiment (not illustrated), the core 30 comprises a plurality of separate yarns B1, B2, B3. Each yarn B1, B2, B3 forms a monolithic torus of which the axis is in common with that of the bead wire 20. The core 30 thus comprises a plurality of monolithic toruses that are juxtaposed parallel to one another. The toruses are side by side such that the core 30 has a substantially polygonal, in this case triangular, cross section.

(22) All of the yarns B1, B2, B3 are made of the same core material. For example, the yarns B1, B2, B3 are made of the material Ma of the yarn B. As a variant, the yarns B1, B2, B3 are made of at least two different core materials, each of the materials comprising at least one multifilament textile fibre embedded in an organic matrix. The diameter of each yarn B1, B2, B3 is between 2.5 and 10 mm, preferably between 2.5 and 4 mm.

(23) The tyre 10 illustrated in FIG. 1 comprises two bead wires 20 according to the first embodiment. A similar tyre 10 according to a second embodiment (not shown) comprises two bead wires 20 according to the second embodiment.

(24) FIG. 4 shows a prior art bead wire denoted by the general reference 100.

(25) In contrast to the bead wire according to the invention, the bead wire 100 comprises a metal core 102 made of a steel having a carbon content equal to 0.1%. The diameter Da of the torus defined by the core 102 is equal to 5 mm.

(26) The bead wire 100 comprises six layers C1 to C6, namely five intermediate layers C1 to C5 and an outer layer C6. The wire of the intermediate layer C1 has a diameter equal to 1.55 mm and each wire of each intermediate layer C2 to C5 and outer layer C6 has a diameter equal to 1.3 mm. Each wire of each layer C1 to C6 is made of steel having a carbon content equal to 0.7%. The diameter of the torus Dt defined by the bead wire 100 is equal to 21.3 mm.

(27) Comparative Measurements

(28) The bead wires 20, 20 according to the first and second embodiments and the prior art bead wire 100 were compared. The tyres 10, 10 according to the first and second embodiments and a prior art tyre comprising two prior art bead wires 100 were also compared.

(29) Residual force at break measurements were carried out following low-speed running. The tyre comprising the bead wire is mounted on landing gear of a predetermined aeroplane and the latter taxis, simulating the phases prior to takeoff and following landing of the aeroplane. The taxiing is carried out under predetermined high loads and for a predetermined time. Next, the bead wire is removed from the tyre and the force at break under tension is measured according to the bead wire tensile test described above. The force at break thus measured is the residual force at break, denoted Fmr. When the relative unit is greater than 1, the bead wire tested has lost, proportionately to its initial force at break, less force at break than the bead wire 100. Conversely, when the relative unit is less than 1, the bead wire tested has lost, proportionately to its initial force at break, more force at break than the bead wire 100.

(30) The characteristics resulting from the measurements carried out are summarized in Table 1 below.

(31) TABLE-US-00001 TABLE 1 Bead wire tested Bead wire 100 Bead wire 20 Bead wire 20 Mass 3.6 kg 3 kg 2.2 kg Force at break (Fm) 320 kN >320 kN 300 kN Burst pressure >61 bar >61 bar >61 bar Residual force at break 1 1 1 (Fmr) as relative unit Yield strength of the 700 MPa >1000 MPa >1000 MPa core material (Re) Young's modulus (E) 205 GPa 40 GPa 40 GPa Diameter of the bead 21.3 mm 21.3 mm 21.3 mm wire (Dt) Diameter of the core 5 mm 8.9 mm 16 mm (Da) Rd = Da/Dt 0.23 0.42 0.75 Contribution of the 2% 13% 45% core to the force at break of the bead wire (Rf) Contribution of the 7% 7% 28% core to the mass of the bead wire (Rm) R = Rm/Rf 3.5 0.54 0.62

(32) The bead wires 20, 20 make it possible, at constant diameter, to maintain excellent mechanical characteristics, in particular force at break, while reducing the mass of the prior art bead wire by 17% (first embodiment) and 39% (second embodiment).

(33) Furthermore, each tyre 10, 10 has a burst strength identical to the prior art tyre. The residual force at break Fmr of each bead wire 20, 20 is identical to that of the bead wire 100, that is to say that the bead wire tested has lost, proportionately to its initial force at break, as much force at break as the bead wire 100.

(34) The force at break Fm of each bead wire 20, 20 is greater than or equal to 200 kN, preferably greater than or equal to 260 kN for the second embodiment and more preferably greater than or equal to 320 kN for the first embodiment. Thus, with a mass much less than that of the bead wire 100, each bead wire 20, 20 has a force at break that is more or less equivalent (second embodiment) or even greater (first embodiment).

(35) The core material of each bead wire 20, 20 has a yield strength Re measured in accordance with the standard ISO 14125 at 23 C. greater than or equal to 800 MPa, preferably greater than or equal to 1000 MPa and more preferably greater than or equal to 1200 MPa.

(36) The core material Ma of each bead wire 20, 20 has a Young's modulus E measured in accordance with the standard ISO 14125 at 23 C. less than or equal to 100 GPa, preferably less than or equal to 75 GPa and more preferably less than or equal to 50 GPa.

(37) The ratio Rd of the diameter Da of the torus defined by the core 30 to the diameter Dt of the torus defined by each bead wire 20, 20 is greater than or equal to 0.25, preferably greater than or equal to 0.4 for the first embodiment and more preferably greater than or equal to 0.6 for the second embodiment.

(38) The contribution Rf of the core 30 to the force at break Fm of the bead wire 20 is greater than or equal to 5% for the first embodiment, preferably greater than or equal to 15% and more preferably greater than or equal to 40% for the second embodiment. This contribution Rf is less than or equal to 75% for each bead wire 20, 20.

(39) At an equal contribution of the core to the mass of the bead wire, the core of each bead wire 20, 20 has a much greater contribution to the force at break of the bead wire, i.e. around 7 times greater than that of the bead wire 100.

(40) The contribution of the core to the force at break is multiplied by 22 when going from the bead wire 100 to the bead wire 20 according to the second embodiment, while the contribution of the core to the mass of the bead wire is only multiplied by 4.

(41) The contribution Rm of the core 30 to the mass of the bead wire 20 is greater than or equal to 7% for the first embodiment, preferably greater than or equal to 15% and more preferably greater than or equal to 25% for the second embodiment. This contribution Rm is less than or equal to 75% for the bead wires 20, 20.

(42) The ratio R of the contribution Rm to the contribution Rf is strictly less than 1, preferably less than or equal to 0.8 and more preferably less than or equal to 0.7 for the bead wires 20, 20. This ratio R is greater than or equal to 0.25, preferably greater than or equal to 0.4 and more preferably greater than or equal to 0.5. Thus, R lies in the range [0.5; 0.7] for the bead wires 20, 20.

(43) The invention is not limited to the embodiments described above.

(44) Specifically, the bead wire according to the invention can be fitted on a tyre other than a tyre for an aircraft. For example, the bead wire may be intended for a tyre for industrial vehicles chosen from vans, heavy vehiclesi.e. metro vehicles, buses, road transport vehicles (lorries, tractors, trailers), off-road vehicles, agricultural or construction plant machinery, and other transport or handling vehicles.

(45) In one embodiment, the core comprises a plurality of separate yarns that are assembled by cabling or twisting.

(46) Moreover, the characteristics of the different embodiments can be combined with one another in any way, as long as they are compatible with one another.

(47) It will be noted that it is possible to use a bead wire for a tyre, comprising: a core, at least one outer layer comprising an outer-layer wire wound around the core, at least one intermediate layer comprising an intermediate-layer wire wound around the core, said intermediate layer being disposed between the core and the outer layer,
wherein the ratio of the contribution of the core to the mass of the bead wire to the contribution of the core to the force at break of the bead wire is strictly less than 1, preferably less than or equal to 0.8 and more preferably less than or equal to 0.7, independently of the fact that the bead wire comprises: a core comprising at least one yarn of a multifilament textile fibre embedded in an organic matrix, at least one outer layer comprising an outer-layer metal wire wound around the core, at least one intermediate layer comprising an intermediate-layer metal wire wound around the core, said intermediate layer being disposed between the core and the outer layer.