Tire comprising a layer of circumferential reinforcing elements

Abstract

A tire having a crown reinforcement formed of at least two working crown layers having unequal axial widths, a layer C of rubber mixture being positioned between at least the ends of the said at least two working crown layers, and the crown reinforcement having at least one layer of circumferential reinforcing elements positioned radially between two working crown layers. The distance d between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the layer C of rubber mixture is such that 1.1<d<2.2, being the diameter of the reinforcing elements of the said at least one layer of circumferential reinforcing elements, and, in a meridian plane, the thickness of the layer C of rubber mixture is substantially uniform.

Claims

1. A tire comprising: a radial carcass reinforcement comprising a crown reinforcement comprising; at least two working crown layers of reinforcing elements crossed from one layer to the other while forming, with a circumferential direction, angles of between 10 and 45 , wherein the at least two working crown layers have unequal axial widths, a layer C of rubber mixture being positioned between at least the ends of the at least two working crown layers, at least one layer of circumferential reinforcing elements positioned radially between two working crown layers, wherein the distance d between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the layer C of rubber mixture is such that 1.1<d<2.2, being the diameter of the reinforcing elements of the at least one layer of circumferential reinforcing elements, and wherein, in a meridian plane, the thickness of the layer C of rubber mixture does not vary by more than 0.3 mm over the axial width between the axially interior end of the layer C and the end of the axially narrowest working layer, wherein the axial widths of the working crown layers radially adjacent to the layer of circumferential reinforcing elements are greater than the axial width of the layer of circumferential reinforcing elements, and wherein the working crown layers adjacent to the layer of circumferential reinforcing elements on either side of an equatorial plane and, in an immediate axial extension of the layer of circumferential reinforcing elements, coupled over an axial width, in order to be subsequently decoupled by said layer C of rubber mixture of at least over the remainder of the width common to the two working layers, a tread, the tread being joined to two beads via two sidewalls, and wherein the tread radially tops the crown reinforcement.

2. The tire according to claim 1, wherein the tensile modulus of elasticity at 10% elongation of the layer C of rubber mixture is less than 8 MPa and in that the maximum tan(d) value, denoted tan(d).sub.max, of the layer C of rubber mixture is less than 0.100.

3. The tire according to claim 2, wherein the layer C of rubber mixture is an elastomeric mixture based on natural rubber or on synthetic polyisoprene comprising predominantly cis-1,4 enchainments and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene, in the case of a blend, being present at a predominant content with respect to the content of other diene elastomer(s) used, and on a reinforcing filler consisting: a) either of carbon black with a BET specific surface of greater than 60 m.sup.2/g, i. employed at a content of between 20 and 40 phr when the structural index of the carbon black using Compressed Oil Absorption Number (COAN) is greater than 85, ii. employed at a content of between 20 and 60 phr when the structural index of the carbon black (COAN) is less than 85, b) or of carbon black with a BET specific surface of less than 60 m.sup.2/g, whatever its structural index, employed at a content of between 20 and 80 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, 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.

4. The tire according to claim 2, further comprising at least one layer of rubber mixture B bordering the end of a working crown layer, wherein the tensile modulus of elasticity at 10% elongation of the at least one layer of rubber mixture B is less than 8 MPa and wherein the maximum tan(d) value, denoted tan(d).sub.max, for the layer of rubber mixture B is less than 0.100.

5. The tire according to claim 2, wherein the at least two working crown layers are each formed of reinforcing elements inserted between two calendering layers of rubber mixture, wherein the tensile modulus of elasticity at 10% elongation of at least one calendering layer of at least one working crown layer is less than 8.5 MPa and wherein the maximum tan(d) value, denoted tan(d).sub.max, of the at least one calendering layer of at least one working crown layer is less than 0.100.

6. The tire according to claim 5, wherein the at least one calendering layer of at least one working crown layer is an elastomeric mixture based on natural rubber or on synthetic polyisoprene predominantly comprising cis-1,4 enchainments and optionally at least one other diene elastomer, wherein the natural rubber or the synthetic polyisoprene, in the case of a blend, is present at a predominant content with respect to the content of other diene elastomer(s) used, and on a reinforcing filler consisting: a) either of carbon black with a BET specific surface of greater than 60 m.sup.2/g, i. employed at a content of between 20 and 40 phr when the structural index of the carbon black using Compressed Oil Absorption Number (COAN) is greater than 85, ii. employed at a content of between 20 and 60 phr when the structural index of the carbon black (COAN) is less than 85, b) or of carbon black with a BET specific surface of less than 60 m.sup.2/g, whatever its structural index, employed at a content of between 20 and 80 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, 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.

7. The tire according to claim 5, wherein the difference between the tensile modulus of elasticity at 10% elongation of the layer C of rubber mixture and the tensile modulus of elasticity at 10% elongation of the at least one calendering layer of at least one working crown layer is less than 2 MPa.

8. The tire according to claim 1, wherein the said reinforcing elements of at least one working crown layer are saturated layered cords, at least one inner liner being sheathed with a layer consisting of a polymeric composition, such as a non-crosslinkable, crosslinkable or crosslinked rubber composition.

9. The tire according to claim 1, wherein the difference between the axial width of the axially widest working crown layer and the axial width of the axially narrowest working crown layer is between 10 and 30 mm.

10. The tire according to claim 1, wherein the axially widest working crown layer is radially interior to the other working crown layers.

11. The tire according to claim 1, wherein the reinforcing elements of the at least one layer of circumferential reinforcing elements are metal reinforcing elements exhibiting a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

12. The tire according to claim 1, wherein the reinforcing elements of the working crown layers are inextensible.

13. The tire according to claim 1, wherein the angle formed by the reinforcing elements of the working crown layers with the circumferential direction is less than 30.

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

15. A tire comprising: a radial carcass reinforcement comprising a crown reinforcement comprising; at least two working crown lavers of reinforcing elements crossed from one layer to the other while forming, with a circumferential direction, angles of between 10 and 45 , wherein the at least two working crown layers have unequal axial widths, a layer C of rubber mixture being positioned between at least the ends of the at least two working crown lavers, at least one layer of circumferential reinforcing elements positioned radially between two working crown layers, wherein the distance d between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the layer C of rubber mixture is such that 1.1 <d<2.2 , being the diameter of the reinforcing elements of the at least one layer of circumferential reinforcing elements, and wherein, in a meridian plane, the thickness of the layer C of rubber mixture does not vary by more than 0.3 mm over the axial width between the axially interior end of the layer C and the end of the axially narrowest working layer, and a triangulation layer formed of metal reinforcing elements forming, with the circumferential direction, angles greater than 60, a tread, the tread being joined to two beads via two sidewalls, and wherein the tread radially tops the crown reinforcement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantageous details and characteristics of embodiments of the invention will emerge below from the description of the implementational examples of the invention, with reference to FIGS. 1 and 2, which represent:

(2) FIG. 1, a meridional view of a diagram of a tire according to an embodiment of the invention,

(3) FIG. 2, a meridional view of a diagram of a tire according to a second embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(4) The figures are not represented to scale in order to make them easier to understand. The figures represent 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.

(5) In FIG. 1, the tire 1, of dimension 315/70 R 22.5, has an aspect ratio H/S equal to 0.70, H being the height of the tire 1 on its mounting rim and S being its maximum axial width. The said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not represented in the figure. The carcass reinforcement is formed of a single layer of metal cords. This carcass reinforcement 2 is hooped by a crown reinforcement 4 formed radially, from the inside to the outside: of a first working layer 41 formed of non-hooped inextensible metal cords 9.28 which are continuous over the entire width of the ply and which are oriented with an angle equal to 24, of a layer of circumferential reinforcing elements 42 which is formed of metal cords made of steel 2123, of bimodulus type, of a second working layer 43 formed of non-hooped inextensible metal cords 9.28 which are continuous over the entire width of the ply, which are oriented with an angle equal to 24 and which are crossed with the metal cords of the layer 41, of a protective layer 44 formed of elastic metal cords 6.35.

(6) The crown reinforcement is itself topped by a tread 5.

(7) The maximum axial width S of the tire is equal to 317 mm.

(8) The axial width L.sub.41 of the first working layer 41 is equal to 252 mm.

(9) The axial width L.sub.43 of the second working layer 43 is equal to 232 mm. The difference between the widths L.sub.41 and L.sub.43 is equal to 15 mm.

(10) With regard to the axial width L.sub.42 of the layer of circumferential reinforcing elements 42, it is equal to 194 mm.

(11) The final crown ply 44, referred to as protective ply, has a width L.sub.44 equal to 124 mm.

(12) In accordance with the embodiments of the invention, a layer of rubber mixture C will decouple the ends of the working crown layers 41 and 43.

(13) The region of engagement of the layer C between the two working crown layers 41 and 43 is defined by its thickness and more specifically the radial distance d between the end of the layer 43 and the layer 41 and by the axial width D of the layer C between the axially inner end of the said layer C and the radially outer end of the working crown layer 43. The radial distance d is equal to 2 mm, which corresponds to a thickness of the layer C equal to 1.2 mm. In accordance with the invention, the thickness of the layer C is substantially identical in a meridional view over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer.

(14) The diameter of the circumferential reinforcing elements of the layer 42 is equal to 1.35 mm. The distance d is thus equal to 1.48 times the diameter 0 of these elements.

(15) The axial distance D is equal to 20 mm, i.e. approximately 19 times the diameter .sub.2 of the reinforcing elements of the working ply 42, the diameter .sub.2 being equal to 1.07 mm.

(16) In FIG. 2, the tire 1 differs from that represented in FIG. 1 in that the two working layers 41 and 43 are, on each side of the equatorial plane and axially in the extension of the layer of circumferential reinforcing elements 42, coupled over an axial width 1: the cords of the first working layer 41 and the cords of the second working layer 43, over the axial coupling width 1 of the two layers, are separated radially from one another by a rubber layer, the thickness of which is minimal and corresponds to twice the thickness of the rubber calendering layer of the non-hooped metal cords 9.28 of which each working layer 41, 43, is formed, i.e. 0.8 mm. Over the remaining width common to the two working layers, the two working layers 41, 43 are separated by the layer of rubber mixture C, the thickness of the said layer C increasing on proceeding from the axial end of the coupling region to the end of the narrowest working layer 43. The layer C advantageously has a sufficient width to radially overlap the end of the widest working layer 41, which is, in this case, the working layer radially closest to the carcass reinforcement.

(17) The preparation of tires according to the invention has demonstrated a simplifying of the manufacture, conditioning and storage of the layer C of rubber mixture as semi-finished product before preparing the tire. The preparation itself of the tire is also simplified, the positioning and the accuracy of positioning of the said layer C being simpler as a result of its homogeneous form concerning its cross section.

(18) Despite the presence of an additional layer of circumferential reinforcing elements in the architecture of the tire, it appears that, for some dimensions of tires, the manufacturing costs may be reduced by virtue of these simplifications to manufacturing, management and processing of the layer C of rubber mixture.

(19) Furthermore, tests have been carried out with different tires prepared according to the invention in accordance with the representation of FIG. 1 and compared with a first reference tire not comprising layers of circumferential reinforcing elements and comprising a layer C of rubber mixture not in accordance with that of the invention and exhibiting a distance d equal to 3.5 mm and a rounded profile of its cross section.

(20) In addition, tests are carried out with tires according to the invention while varying the characteristics of the mixtures of the layer C, in particular their tensile moduli of elasticity at 10% elongation and the tan().sub.max values, in accordance with the invention.

(21) Other tests are also carried out with tires according to the invention while also varying the characteristics of the calendering layers mixtures of the working layers 41 and 43, in particular their tensile moduli of elasticity at 10% elongation and the tan().sub.max values, in accordance with the invention.

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

(23) TABLE-US-00001 Mixture R1 Mixture R2 Mixture 1 Mixture 2 Mixture 3 Mixture 4 Mixture 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 (6 PPD) 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 Sulphur 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 M.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 L60 (%) 22.9 24.5 18.7 14.9 13.3 12.2 8.5

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

(25) As regards the reference tire, the layer C is composed of the mixture R2 and the calenderings of the working layers are composed of the mixture R1.

(26) Different tires according to embodiments of the invention were tested.

(27) A first series of tires S1 in accordance with embodiments of the invention was prepared with a first layer C composed of the mixture R2, the calenderings of the working layers being composed of the mixture R1.

(28) A second series of tires S2 in accordance with embodiments of the invention was prepared with a first layer C composed of the mixtures 1 to 5, the calenderings of the working layers being composed of the mixture R1.

(29) A third series of tires S3 in accordance with embodiments of the invention was prepared with a first layer C composed of the mixture R2, the calenderings of the working layers being composed of the mixtures 1 to 5.

(30) A fourth series of tires S4 in accordance with embodiments of the invention was prepared with a first layer C composed of the mixtures 1 to 5, the calenderings of the working layers also being composed of the mixtures 1 to 5. Some tires of this series S2 were prepared with identical mixtures for the layer C and the calenderings of the working layers and others with different mixtures.

(31) First endurance tests were carried out on a test machine which made each of the tires run in a straight line at a speed equal to the maximum speed index prescribed for the said tire under an initial load of 4000 kg which was gradually increased in order to reduce the duration of the test.

(32) Other endurance tests were carried out on a test machine which cyclically applies a transverse load and a dynamic overload to the tires. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

(33) The tests thus carried out showed that the distances travelled during each of these tests are at least as great for the tires according to the invention as the reference tires. It is thus apparent that the tires according to the invention exhibit a performance in terms of endurance which is at least as good as that of the reference tires. The series of tires S2 and S4 prepared in accordance with the invention exhibited in particular superior results.

(34) Other running tests were carried out on non-bituminous surfaces consisting of stones particularly aggressive towards the treads of the tires.

(35) The latter tests showed that, after identical distances travelled, the tires according to embodiments of the invention and more particularly those of the S3 and S4 series exhibit fewer and less significant detrimental changes than those of the reference tires.

(36) These tests show in particular that, in addition to the design of the tires according to embodiments of the invention, which allows the form of the layer C of rubber mixture in accordance with the invention to be simplified, the combination of this form of the layer C with a decrease in the modulus of elasticity of the layer of rubber mixture C and of those of the calenderings of the working crown layers results in a satisfactory endurance performance when a layer of circumferential reinforcing elements is present.

(37) Furthermore, rolling resistance measurements were carried out. These measurements related to a first reference tire T1 as described above, to a second reference tire T2 identical to the above and additionally comprising a layer of circumferential reinforcing elements identical to that of the tires according to the invention, to a tire of the S1 series, to a tire of the S2 series, the layer C of which is composed of the mixture 1, to a tire of the S3 series, the calendering layers of which are composed of the mixture 1, and to a tire of the S4 series, the layer C of which and the calendering layers of which are composed of the mixture 1.

(38) The results of the measurements are presented in the following table; they are expressed in kg/t, a value of 100 being assigned to the tire T1.

(39) TABLE-US-00002 Tire T1 Tire T2 Tire S1 Tire S2 Tire S3 Tire S4 100 101 100 98 97 95