Tire Comprising Working Layers Formed by Individual Wires

Abstract

Tire comprising a crown reinforcement formed of three working layers having between ends thereof two layers of rubber compound Ci. Thickness of the three working layers is <5 mm with individual metal wires as reinforcing elements of diameter <0.50 mm and a distance therebetween being strictly <1 mm. The axial width of each working layer is >60% that of the tread. Distance d.sub.i between two working layers separated by a layer of rubber compound Ci and measured at the end of the axially narrowest working layer in contact therewith is such that 0.5<d.sub.i<2.5 mm, and, in a meridian plane, the thickness of at least one layer of rubber compound Ci is substantially constant over the axial width between the axially inner end of a layer of rubber compound Ci and the end of the axially narrowest working layer in contact therewith.

Claims

1. A tire with a radial carcass reinforcement for a vehicle of the heavy duty type comprising a crown reinforcement comprising at least three working crown layers of reinforcing elements, crossed from one layer to the other, making with the circumferential direction angles of between 10 and 45, which is itself capped radially by a tread, said tread being connected to two beads by two sidewalls, at least two layers of rubber compound being arranged between the ends of said at least three working crown layers, wherein, in a meridian plane, the thickness of said at least three working crown layers, measured in the equatorial plane, is less than 5 mm, wherein the reinforcing elements of said at least three working crown layers are individual metal wires of diameter less than 0.50 mm, wherein the distance between the reinforcing elements, measured along the normal to the direction of the mean line of the wire, is strictly less than 1 mm, wherein the axial width of each of said at least three working crown layers is greater than 60% of the axial width of the tread, wherein at least a distance d.sub.i between two working layers separated by a layer of rubber compound and measured at the end of the axially narrowest working layer in contact with it is such that 0.5<d.sub.i<2.5 mm, and wherein, in a meridian plane, the thickness of at least one layer of rubber compound is substantially constant over the axial width comprised between the axially inner end of one layer of rubber compound and the end of the axially narrowest working layer in contact therewith.

2. The tire according to claim 1, wherein the diameter of the individual metal wires of said at least three working crown layers is greater than or equal to 0.25 mm.

3. The tire according to claim 1, a working crown layer of reinforcing elements comprising two skim layers between which the reinforcing elements are positioned, wherein the skim thickness measured in a radial direction on each side of a reinforcing element is less than 0.30 mm.

4. The tire according to claim 1, wherein the stiffness per unit width of each of the working crown layers is comprised between 35 and 70 daN/mm.

5. The tire according to claim 1, wherein the crown reinforcement comprises four working crown layers of reinforcing elements and wherein three layers of rubber compound are respectively arranged between the ends of said four working crown layers.

6. The tire according to claim 5, wherein the distance d.sub.i between two working layers separated by one of the three layers of rubber compound and measured at the end of the axially narrowest working layer in contact therewith is such that 0.5<d.sub.i<2 mm and wherein, in a meridian plane, the thickness of each of the three layers of rubber compound is substantially constant over the axial width comprised between its axially inner end and the end of the axially narrowest working layer in contact therewith.

7. The tire according to claim 1, wherein the tensile modulus of elasticity at 10% elongation of at least one layer is less than 8 MPa and wherein the maximum value of tan(), denoted tan().sub.max, of the at least one layer is less than 0.100.

8. The tire according to claim 7, wherein said at least one layer of rubber compound is an elastomeric compound based on natural rubber or on synthetic polyisoprene with a majority of cis-1,4 chains, and possibly on at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of a blend being present in a majority proportion relative to the proportion of the other diene elastomer or elastomers used, and on a reinforcing filler composed: a) either of carbon black with a BET specific surface of greater than 60 m.sup.2/g, i. used at a content of between 20 and 40 phr when the oil absorption number (COAN) of the carbon black is greater than 85, ii. used at a content of between 20 and 60 phr when the oil absorption number (COAN) of the carbon black is less than 85, b) or of carbon black with a BET specific surface of less than 60 m.sup.2/g, whatever its oil absorption number, employed at a content of between 20 and 80 phr and preferably between 30 and 50 phr, c) or of a white filler of silica and/or alumina type comprising SiOH and/or AlOH surface functional groups, selected from the group consisting of precipitated or fumed silicas, aluminas and aluminosilicates, or alternatively carbon blacks modified during or after the synthesis having a BET specific surface of between 30 and 260 m.sup.2/g, employed at a content of between 20 and 80 phr and preferably between 30 and 50 phr, d) or of a blend of carbon black described in (a) and/or of carbon black described in (b) and/or a white filler described in (c), in which the overall content of filler is between 20 and 80 phr and preferably between 40 and 60 phr.

9. The tire according to claim 1, said at least three working crown layers each being formed of reinforcing elements inserted between two skim layers of rubber compound, wherein the tensile modulus of elasticity at 10% elongation of at least one skim layer of at least one working crown layer is less than 8.5 MPa and wherein the maximum value of tan(), denoted tan().sub.max, of said at least one skim layer of at least one working crown layer is less than 0.100.

10. The tire according to claim 9, wherein said at least one skim layer of at least one working crown layer is an elastomeric compound based on natural rubber or on synthetic polyisoprene with a majority of cis-1,4 chains, and possibly on at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of a blend being present in a majority proportion relative to the proportion of the other diene elastomer or elastomers used, and on a reinforcing filler composed: a) either of carbon black with a BET specific surface of greater than 60 m.sup.2/g, i. used at a content of between 20 and 40 phr when the oil absorption number (COAN) of the carbon black is greater than 85, ii. used at a content of between 20 and 60 phr when the oil absorption number (COAN) of the carbon black is less than 85, b) or of carbon black with a BET specific surface of less than 60 m.sup.2/g, whatever its oil absorption number, employed at a content of between 20 and 80 phr and preferably between 30 and 50 phr, c) or of a white filler of silica and/or alumina type comprising SiOH and/or AlOH surface functional groups, selected from the group consisting of precipitated or fumed silicas, aluminas and aluminosilicates, or alternatively carbon blacks modified during or after the synthesis having a BET specific surface of between 30 and 260 m.sup.2/g, employed at a content of between 20 and 80 phr and preferably between 30 and 50 phr, d) or of a blend of carbon black described in (a) and/or of carbon black described in (b) and/or a white filler described in (c), in which the overall content of filler is between 20 and 80 phr and preferably between 40 and 60 phr.

11. The tire according to claim 1, wherein the crown reinforcement is supplemented by a layer of circumferential reinforcing elements.

12. The tire according to claim 11, wherein the layer of circumferential reinforcing elements is radially positioned between two working crown layers.

13. The tire according to claim 11, wherein the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation in the range from 10 to 120 GPa and a maximum tangent modulus of less than 150 GPa.

14. The tire according to claim 1, wherein the crown reinforcement is supplemented radially on the outside by at least one additional ply, referred to as a protective ply, of reinforcing elements which are oriented with respect to the circumferential direction at an angle of between 10 and 45 and in the same direction as the angle formed by the reinforcing elements of the working crown layer radially adjacent to it.

Description

[0126] Other advantageous details and features of the invention will become evident hereinbelow from the description of the exemplary embodiments of the invention, with reference to FIGS. 1 and 2, which represent:

[0127] FIG. 1: a schematic meridian view of a tire according to a first embodiment of the invention,

[0128] FIG. 2: a schematic meridian view of a tire according to a second embodiment of the invention,

[0129] FIG. 3: a schematic meridian view of a tire according to a third embodiment of the invention,

[0130] FIG. 4: a schematic meridian view of a tire according to the prior art.

[0131] In order to make them easier to understand, the figures have not been drawn to scale. The figures depict only a half-view of a tire, which extends symmetrically with respect to the axis XX, which represents the circumferential median plane, or equatorial plane, of a tire.

[0132] In the figures, the tires 1-41, of size 385/55 R 22.5, have an aspect ratio H/S equal to 0.55, H being the height of the tire 1-41 on its mounting rim and S its maximum axial width. The said tires 1-41 comprise a radial carcass reinforcement 2-42 anchored in two beads, not depicted in the figures. The carcass reinforcement 2-42 is formed of a single layer of metal cords. They further comprise a tread 5-45.

[0133] In FIG. 1, the carcass reinforcement 2 is hooped according to the invention by a crown reinforcement 4 formed radially, from the inside to the outside: [0134] of a first working layer 41 formed of metal wires oriented at an angle equal to 18, [0135] of a second working layer 42 formed of metal wires oriented at an angle equal to 18, [0136] of a third working layer 43 formed of metal wires oriented at an angle equal to 18, [0137] of a protective layer 45 formed of 6.35 elastic metal cords parallel to the metal wires of the working layer 43.

[0138] The metal wires that make up the reinforcing elements of the three working layers are wires of the UHT type having a diameter of 0.35 mm. Wires of SHT type or of higher grades may also be used. They are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the wire, equal to 0.35 mm.

[0139] The axial width L.sub.41 of the first working layer 41 is equal to 300 mm.

[0140] The axial width L.sub.42 of the second working layer 42 is equal to 320 mm.

[0141] The axial width L.sub.43 of the third working layer 43 is equal to 300 mm.

[0142] The axial width L.sub.45 of the protective layer 45 is equal to 220 mm.

[0143] The axial width of the tread L.sub.5 is equal to 312 mm.

[0144] The thickness of the three working crown layers, measured in the equatorial plane, is equal to 2.5 mm and therefore less than 5 mm.

[0145] According to the invention, two layers of rubber compound C1, C2 respectively provide decoupling of the ends of the working crown layers 41, 42 and 43.

[0146] The zone of engagement of the layer C1 between the two working crown layers 41 and 42 is defined by its thickness and more specifically by the radial distance d.sub.1 between the end of the layer 42 and the layer 41. The radial distance d1 is equal to 2 mm, which corresponds to a thickness of the layer C1 equal to 1.5 mm. In accordance with the invention, the thickness of the layer C1 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C1 and the end of the axially narrowest working layer 42.

[0147] Regarding the layer C2 between the two working crown layers 42 and 43, this is defined on the one hand by its thickness and more specifically the radial distance d.sub.2 between the end of the layer 42 and the layer 43 and on the other hand by its shape which is irregular in a meridian view, this shape being thickest at the end of the layer 42, its thickness decreasing down to values of the order of 0.5 mm at its ends. The radial distance d.sub.2 is equal to 3.5 mm, which corresponds to a thickness of the layer C2 equal to 2.7 mm.

[0148] In FIG. 2, the carcass reinforcement 22 is hooped according to the invention by a crown reinforcement 24 formed radially, from the inside to the outside: [0149] of a first working layer 241 formed of metal wires oriented at an angle equal to 18, [0150] of a second working layer 242 formed of metal wires oriented at an angle equal to 18, [0151] of a third working layer 243 formed of metal wires oriented at an angle equal to 18, [0152] of a fourth working layer 244 formed of metal wires oriented at an angle equal to 18, [0153] of a protective layer 245 formed of 6.35 elastic metal cords parallel to the metal wires of the working layer 244.

[0154] The metal wires that make up the reinforcing elements of the four working layers are wires of the UHT type having a diameter of 0.35 mm. Wires of SHT type or of higher grades may also be used. They are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the wire, equal to 0.35 mm.

[0155] The axial width L.sub.241 of the first working layer 241 is equal to 300 mm.

[0156] The axial width L.sub.242 of the second working layer 242 is equal to 320 mm.

[0157] The axial width L.sub.243 of the third working layer 243 is equal to 300 mm.

[0158] The axial width L.sub.244 of the fourth working layer 244 is equal to 280 mm.

[0159] The axial width L.sub.245 of the protective layer 245 is equal to 220 mm.

[0160] The axial width of the tread L.sub.25 is equal to 312 mm.

[0161] The thickness of the four working crown layers, measured in the equatorial plane, is equal to 3.3 mm and therefore less than 5 mm.

[0162] According to the invention, three layers of rubber compound C1, C2, C3 respectively provide decoupling of the ends of the working crown layers 241, 242, 243 and 244.

[0163] The zone of engagement of the layers C1 and C3 respectively between the two working crown layers 241, 242 and 243, 244 is defined by their thicknesses and more specifically the respective radial distances d.sub.1 and d.sub.3 between the end of the layer 242 and the layer 241, and between the end of the layer 243 and the layer 244. The radial distances d1 and d.sub.3 are equal to 2 mm, which corresponds to a thickness of the layers C1 and C3 equal to 1.5 mm. In accordance with the invention, the thickness of the layer C1 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C1 and the end of the axially narrowest working layer 42 in contact therewith. Likewise, the thickness of the layer C3 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C3 and the end of the axially narrowest working layer 43 in contact therewith.

[0164] Regarding the layer C2 between the two working crown layers 242 and 243, this is defined on the one hand by its thickness and more specifically the radial distance d.sub.2 between the end of the layer 242 and the layer 243 and on the other hand by its shape which is irregular in a meridian view, this shape being thickest at the end of the layer 42, its thickness decreasing down to values of the order of 0.5 mm at its ends. The radial distance d.sub.2 is equal to 3.5 mm, which corresponds to a thickness of the layer C2 equal to 2.7 mm.

[0165] In FIG. 3, the carcass reinforcement 32 is hooped according to the invention by a crown reinforcement 34 formed radially, from the inside to the outside: [0166] of a first working layer 341 formed of metal wires oriented at an angle equal to 18, [0167] of a second working layer 342 formed of metal wires oriented at an angle equal to 18, [0168] of a third working layer 343 formed of metal wires oriented at an angle equal to 18, [0169] of a fourth working layer 344 formed of metal wires oriented at an angle equal to 18, [0170] of a protective layer 345 formed of 6.35 elastic metal cords parallel to the metal wires of the working layer 344.

[0171] The metal wires that make up the reinforcing elements of the four working layers are wires of the UHT type having a diameter of 0.35 mm. Wires of SHT type or of higher grades may also be used. They are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the wire, equal to 0.35 mm.

[0172] The axial width L.sub.341 of the first working layer 341 is equal to 300 mm.

[0173] The axial width L.sub.342 of the second working layer 342 is equal to 320 mm.

[0174] The axial width L.sub.343 of the third working layer 343 is equal to 300 mm.

[0175] The axial width L.sub.344 of the fourth working layer 344 is equal to 280 mm.

[0176] The axial width L.sub.245 of the protective layer 245 is equal to 220 mm.

[0177] The axial width of the tread L.sub.25 is equal to 312 mm.

[0178] The thickness of the four working crown layers, measured in the equatorial plane, is equal to 3.3 mm and therefore less than 5 mm.

[0179] According to the invention, and as in the case with FIG. 2, three layers of rubber compound C1, C2, C3 respectively provide decoupling of the ends of the working crown layers 341, 342, 343 and 344.

[0180] In the case of FIG. 3, the three layers C1, C2, C3 are substantially identical.

[0181] The zone of engagement of the layers C1, C2 and C3 respectively between the two working crown layers 341 and 342, 342 and 343, 343 and 344 is defined by their thicknesses and more specifically the respective radial distances d.sub.1, d.sub.2 and d.sub.3 between the end of the layer 342 and the layer 341, between the end of the layer 342 and the layer 343, and between the end of the layer 343 and the layer 344. The radial distances d.sub.1, d.sub.2 and d.sub.3 are equal to 2 mm, which corresponds to a thickness of the layers C1, C2 and C3 equal to 1.5 mm. In accordance with the invention, the thickness of the layer C1 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C1 and the end of the axially narrowest working layer 342 in contact therewith. Likewise, the thickness of the layer C2 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C3 and the end of the axially narrowest working layer 342 in contact therewith. Likewise again, the thickness of the layer C3 is substantially identical in a meridian view over the axial width between the axially inner end of the layer C3 and the end of the axially narrowest working layer 343 in contact therewith.

[0182] In FIG. 4, the carcass reinforcement 42 is hooped by a crown reinforcement 44 formed radially, from the inside to the outside: [0183] of a first triangulation layer 440 formed of non-wrapped 9.35 metal cords oriented at an angle equal to 50, [0184] of a first working layer 441 formed of non-wrapped 9.35 metal cords, which are continuous across the entire width of the ply, and oriented at an angle equal to 18, [0185] of a second working layer 442 formed of non-wrapped 9.35 metal cords which are continuous over the entire width of the ply, which are oriented at an angle equal to 18 and which are crossed with the metal cords of the layer 441, [0186] of a protective layer 443 formed of elastic 6.35 metal cords.

[0187] The inextensible 9.35 metal cords of the working layers 441 and 442 are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the wire, equal to 1 mm.

[0188] The axial width L.sub.440 of the triangulation layer 440 is equal to 302 mm.

[0189] The axial width L.sub.441 of the first working layer 441 is equal to 318 mm.

[0190] The axial width L.sub.442 of the second working layer 442 is equal to 296 mm.

[0191] The axial width L.sub.443 of the protective layer 443 is equal to 220 mm.

[0192] The axial width of the tread L.sub.45 is equal to 312 mm.

[0193] The thickness of the three crown layers 440, 441, 442, measured in the equatorial plane, is equal to 6.5 mm.

[0194] Over the remaining width that the two working layers have in common, the two working layers 441, 442 are separated by the layer of rubber compound C. The layer C is defined on the one hand by its thickness and more specifically the radial distance d between the end of the layer 442 and the layer 441 and on the other hand by its shape which is irregular in a meridian view, this shape being thickest at the end of the layer 442, its thickness decreasing down to values of the order of 0.5 mm at its ends. The radial distance d is equal to 3.5 mm, which corresponds to a thickness of the layer C equal to 2.7 mm.

[0195] The preparation of tires according to the invention has demonstrated a simplifying of the manufacture, conditioning and storage of the layers Ci of rubber compound as semi-finished product before preparing a tire. The preparation itself of the tire is also simplified, the positioning and the accuracy of positioning of the said layers Ci being simpler as a result of their homogeneous form concerning their cross section.

[0196] The combined mass of the four working layers 341, 342, 343 and 344 of the tire according to the invention, produced as depicted in FIG. 3, including the mass of the metal wires and of the skim compounds, thus amounts to 6.3 kg. The mass of the tire according to the invention, produced as depicted in FIG. 2, is equal to 61 kg.

[0197] The combined mass of the crown layers 440, 441, 442 of the tire, produced as depicted in FIG. 3, including the mass of the metal cords and of the skim compounds, amounts to 12.6 kg. The mass of the tire, produced as depicted in FIG. 3, is equal to 67 kg.

[0198] Tests were conducted on tires produced in accordance with FIG. 3, the tire produced in accordance with FIG. 4 being the reference tire.

[0199] First endurance tests were conducted on a test machine, each tire being made to roll in a straight line at a speed equal to the maximum speed rating (or speed index) specified for the said tire under an initial load of 4000 kg which was progressively increased to reduce the duration of the test.

[0200] Other endurance tests were conducted on a test machine, a transverse force and a dynamic overload being applied to the tires in a cyclic manner. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

[0201] The tests thus carried out showed that the distances covered during each of these tests are substantially identical for the tires according to the invention and the reference tires. It is thus apparent that the tires according to the invention exhibit performance in terms of endurance which is substantially the equivalent of that of the reference tires.

[0202] Other tests were carried out to evaluate the wear performance of the tires under actual conditions on vehicles. The running conditions, in particular the circuit followed, are determined so as to be representative of a particular type of use, in this instance use of the motorway type that is more disadvantageous as regards uneven wear. At the end of the running, the wear on the tires according to the invention was found to be more even, indicating potential for increased life.

[0203] Measurements of rolling resistance were also made.

[0204] These tests are carried out with tires according to the invention while varying the characteristics of the compounds of the layers C1, C2, C3, in particular their tensile moduli of elasticity at 10% elongation and the tan().sub.max values, in accordance with the invention.

[0205] Other tests are also carried out with tires according to the invention while also varying the characteristics of the skim layer compounds of the working layers, in particular their tensile moduli of elasticity at 10% elongation and the tan().sub.max values, in accordance with the invention.

[0206] The various compounds used are listed below, the tensile modulus of elasticity at 10% elongation and the tan().sub.max and P60 values being expressed for each.

TABLE-US-00001 Compound Compound R1 R2 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 NR 100 100 100 100 100 100 100 Black N347 52 50 33 Black N683 44 30 Black N326 47 Silica 165G 46 Antioxidant (6PPD) 1 1.8 1.5 1 2 1 1 Stearic acid 0.65 0.6 0.9 0.65 1 0.65 0.65 Zinc oxide 9.3 9.3 7.5 9.3 8 9.3 9.3 Cobalt salt (CoAcac) 1.12 1.12 1.12 1.1 1.12 1.12 Cobalt salt 4.5 (CoAbietate) Silane-on-black 8.3 Sulfur 6.1 5.6 4.5 6.1 4.8 6.1 6.1 Accelerator DCBS 0.93 0.8 0.8 0.93 0.93 0.93 Accelerator TBBS 1.01 Coaccelerator DPG 1.1 Retarder CTP PVI 0.25 0.15 0.25 0.2 0.25 0.25 MA.sub.10 (MPa) 10.4 8.5 5.99 5.56 7.25 6.16 4.4 tan ().sub.max 0.130 0.141 0.099 0.074 0.063 0.056 0.030 P60 (%) 22.9 24.5 18.7 14.9 13.3 12.2 8.5

[0207] The values of the constituents are expressed in phr (parts by weight per hundred parts of elastomers).

[0208] As regards the reference tire, denoted T1, the layer C is made of the compound R2 and the skim layers of the working layers 441, 443 are made of the compound R1.

[0209] Different tires according to the invention were tested.

[0210] A first series of tires S1 in accordance with the invention (FIG. 3) was prepared with layers C1, C2, C3 made of the compound R2, the skim layers of the working layers being made of the compound R1.

[0211] A second series of tires S2 in accordance with the invention (FIG. 3) was prepared with layers C1, C2, C3 made of the compounds 1 to 5, the skim layers of the working layers being made of the compound R1.

[0212] A third series of tires S3 in accordance with the invention (FIG. 3) was prepared with layers C1, C2, C3 made of the compound R2, the skim layers of the working layers being made of the compounds 1 to 5.

[0213] A fourth series of tires S4 in accordance with the invention (FIG. 3) was prepared with layers C1, C2, C3 made of the compounds 1 to 5, the skim layers of the working layers also being made of the compounds 1 to 5. Some tires of this series S2 were prepared with identical compounds for the layers C1, C2, C3 and the skim layers of the working layers and others with different compounds.

[0214] The results of the measurements are shown in the following table; they are expressed in kg/t, a value of 100 being assigned to the tire T1.

TABLE-US-00002 Tire T1 Tire S1 Tire S2 Tire S3 Tire S4 100 100 99 97 96