Tire comprising a layer of circumferential reinforcement elements

Abstract

The invention relates to a tire comprising a crown reinforcement formed of at least two working crown layers each formed of reinforcing elements inserted between skim layers of rubber compound, a first layer S of polymer compound being in contact with at least one working crown layer and in contact with the carcass reinforcement and the crown reinforcement comprising at least one layer of circumferential reinforcing elements. In accordance with the invention, the elastic modulus under tension at 10% elongation of at least one skim layer of at least one working crown layer is less than 8.5 MPa, the maximum value of tan(), denoted tan()max of the said at least one skim layer of at least one working crown layer is less than 0.100, and the complex dynamic shear modulus G*, measured at 10% and 60 C. on the return cycle, of the said first layer S of polymer compound is greater than 1.35 MPa.

Claims

1. Tire with a radial carcass reinforcement comprising a crown reinforcement formed of at least two working crown layers each formed of reinforcing elements inserted between two skim layers of rubber compound, crossed from one layer to the other making with the circumferential direction angles comprised between 10 and 45, a first layer of polymer compound being in contact with at least one working crown layer and in contact with the carcass reinforcement, said first layer of polymer compound extending axially as far as at least the axial end of the tread, said tread radially capping the crown reinforcement and being connected to two beads by two sidewalls, the crown reinforcement comprising at least one layer of circumferential reinforcing elements, wherein the elastic modulus under tension at 10% elongation of at least one skim layer at least one working crown layer is less than 8.5 MPa, 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, and wherein the complex dynamic shear modulus, measured at 10% and 60 C. on the return cycle, of said first layer of polymer compound is greater than 1.35 MPa, wherein the tire further comprises a second layer of polymer compound axially in contact with the first layer of polymer compound radially between the carcass reinforcement and the radially innermost layer of reinforcing elements of the crown reinforcement, and wherein the complex dynamic shear modulus, measured at 10% and 60 C. on the return cycle, of said second layer of polymer compound is greater than 1.35 MPa.

2. The tire according to claim 1, wherein the complex shear modulus G*, measured at 10% and 60 C. on the return cycle, of the first layer of polymer compound is less than 2 MPa.

3. The tire according to claim 1, wherein the maximum value of tan(), denoted tan().sub.max of the first layer of polymer compound is less than 0.100.

4. The tire according to claim 1, wherein said first layer of polymer compound comprises a reinforcing filler made up of: a) either carbon black with a BET specific surface area of between 30 and 160 m.sup.2/g, used in a content equal to or greater than 15 phr and less than or equal to 28 phr, b) or a white filler of the silica and/or alumina type comprising SiOH and/or AlOH surface functional groups selected from the group formed of precipitated or pyrogenated silicas, aluminas or aluminosilicates or alternatively carbon blacks modified during or after synthesis with a specific surface area of between 30 and 260 m.sup.2/g used at a content greater than or equal to 15 phr and less than or equal to 55 phr, c) or a blend of carbon black described at (a) and a white filler described at (b), in which the overall filler content is greater than or equal to 15 phr and less than equal to 50 phr and the white filler phr content is greater than or equal to the phr content of carbon black minus 5.

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

6. The tire according to claim 1, wherein the complex shear modulus, measured at 10% and 60 C. on the return cycle, of the second layer of polymer compound is less than 2 MPa.

7. The tire according to claim 1, wherein the maximum value of tan(), denoted tan()max, of the second layer of polymer compound is less than 0.100.

8. The tire according to claim 1, wherein said second layer of polymer compound comprises a reinforcing filler made up of: a) either carbon black with a BET specific surface area of between 30 and 160 m.sup.2/g, used in a content equal to or greater than 15 phr and less than or equal to 28 phr, b) or a white filler of the silica and/or alumina type comprising SiOH and/or AlOH surface functional groups selected from the group formed of precipitated or pyrogenated silicas, aluminas or aluminosilicates or alternatively carbon blacks modified during or after synthesis with a specific surface area of between 30 and 260 m.sup.2/g used at a content greater than or equal to 15 phr and less than or equal to 55 phr, c) or a blend of carbon black described at (a) and a white filler described at (b), in which the overall filler content is greater than or equal to 15 phr and less than equal to 50 phr and the white filler phr content is greater than or equal to the phr content of carbon black minus 5.

9. The tire according to claim 1, wherein the said reinforcing elements of at least one working crown layer are cords with saturated layers, at least one internal layer being sheathed by a layer made of a polymer composition such as a non-crosslinkable, crosslinkable or crosslinked rubber composition.

10. The tire according to claim 1, wherein the layer of circumferential reinforcing elements is placed radially between two working crown layers.

11. The tire according to claim 1, 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 comprised between 10 and 120 GPa and a maximum tangent modulus 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 crown reinforcement is supplemented radially on the outside by at least one additional ply, referred to as a protective ply, of reinforcing elements referred to as elastic elements, which are oriented with respect to the circumferential direction at an angle of between 10 and 45 in the same direction as the angle formed by the inextensible elements of the working ply radially adjacent to it.

14. The tire according to claim 1, wherein the crown reinforcement further comprises a triangulation layer formed of metallic reinforcing elements making angles greater than 60 with the circumferential direction.

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

16. The tire according to claim 1, wherein the said reinforcing elements of at least one working crown layer are cords with saturated layers, at least one internal layer being sheathed by a layer made of a polymer composition such as a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantageous features of the invention will become apparent hereinafter from the description of exemplary embodiments of the invention, with reference to FIGS. 1 and 2 which depict:

(2) FIG. 1: a schematic meridian view of a tire according to one embodiment of the invention,

(3) FIG. 2: a schematic meridian view of a tire according to a second embodiment of the invention.

(4) In order to make them easier to understand, the figures are not shown to scale. The figures depict only half a view of a tire which extends symmetrically with respect to the axis XX that represents the circumferential meridian plane, or equatorial plane, of a tire.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) In FIG. 1, the tire 1, of size 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 fixed in two beads, not shown 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-wrapped inextensible 9.28 metal cords, which are continuous across the entire width of the ply, and oriented at an angle equal to 24, of a layer of circumferential reinforcing elements 42, formed of 2123 steel metal cords, of the bimodulus type, of a second working layer 43 formed of non-wrapped inextensible 9.28 metal cords, which are continuous across the entire width of the ply, oriented at an angle equal to 24, and crossed with the metal cords of the layer 41, of a protective layer 44 formed of elastic 6.35 metal cords.

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

(7) The maximum axial width 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) As for the axial width L.sub.42 of the layer of circumferential reinforcing elements 42, this is equal to 194 mm.

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

(12) According to the invention, the elastic modulus under tension at 10% elongation of the skim layers of each of the working layers 41 and 43 is equal to 6 MPa.

(13) According to the invention, a first layer S of rubber compound is placed between the carcass reinforcement 2 and the first working layer 41.

(14) In FIG. 2, the tire 1 differs from the one depicted in FIG. 1 in that a second layer G axially extends the first layer S, radially between the carcass reinforcement 2 and the first working layer 41.

(15) Tests have been conducted with various tires produced according to the invention as depicted in FIG. 1, and compared against reference tires also as depicted in FIG. 1.

(16) Tests have in particular been performed varying the characteristics of the skim compounds of the working layers 41 and 43, notably their elastic modulus values under tension at 10% elongation and the value of tan().sub.max and the characteristics of the compounds of the layer S, notably the complex dynamic shear modulus G*, measured at 10% and 60 C. on the return cycle.

(17) The various compounds used are listed below.

(18) TABLE-US-00001 Compound Compound R1 R2 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 NR 100 100 100 100 100 100 100 100 Black N347 52 33 Black N683 44 30 Black N326 47 5 Black N330 35 Silica 165G 46 40 Antioxidant 1 0.7 1.5 1 2 1 1 1.5 (6PPD) Stearic acid 0.65 1.4 0.9 0.65 1 0.65 0.65 1 Zinc oxide 9.3 2.1 7.5 9.3 8 9.3 9.3 5 Cobalt salt 1.12 1.12 1.12 1.1 1.12 1.12 (CoAcac) Cobalt salt (CoAbietate) Silane-on-black 8.3 5 Sulphur 6.1 2.15 4.5 6.1 4.8 6.1 6.1 1.75 PEG 2.5 Accelerator DCBS 0.93 0.8 0.93 0.93 0.93 Accelerator TBBS 1.01 Accelerator CBS 1 0.9 Coaccelerator 1.1 0.34 DPG Retarder CTP 0.25 0.08 0.15 0.25 0.2 0.25 0.25 PVI) MA.sub.10 (MPa) 10.4 3.4 5.99 5.56 7.25 6.16 4.4 4.3 tan().sub.max 0.130 0.074 0.099 0.074 0.063 0.056 0.030 0.087 P60 (%) 22.9 11.3 18.7 14.9 13.3 12.2 8.5 16.5 G* 10% at 60 C. 1.25 1.55 (return cycle)

(19) The values for the constituent ingredients are expressed in phr (parts by weight per hundred parts of elastomer).

(20) Various reference tires were tested.

(21) First reference tires T1 have working layers, the skims of which are made of the compound R1 and the first layer S of the compound R2.

(22) Second reference tires T2 have working layers, the skims of which are made of the compounds 1 to 5 and the first layer S of the compound R2.

(23) Various tires according to the invention were tested.

(24) Tires S1 according to the invention were produced with working layers, the skims of which are made of the compounds 1 to 5 and a first layer S of the compound 6.

(25) The first endurance tests were run on a test machine that forced each of the tires to run in a straight line at a speed equal to the maximum speed rating prescribed for the said tire (the speed index) under an initial load of 4000 kg progressively increased in order to reduce the duration of the test.

(26) It was found that all the tires tested exhibited substantially comparable results.

(27) Other endurance tests were conducted on a test machine that cyclically imposed a transverse loading and a dynamic overload on the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires.

(28) The distances covered varied from one type of tire to another, failures occurring as a result of degradation of the rubber compounds at the ends of the working layers. The results are set out in the table which follows with reference to a base 100 fixed for the reference tire T1.

(29) TABLE-US-00002 Tire T1 Tire T2 Tire S1 100 85 105

(30) Other running tests were performed on unsurfaced roads made up of stones particularly aggressive towards tire treads.

(31) These last tests demonstrated that after covering identical distances, the tires according to the invention exhibit instances of damage that are fewer in number and less substantial than those of the reference tires.

(32) These tests notably show that the design of the tires according to the invention makes it possible to reduce the elastic modulus of the skims of the working crown layers without adversely affecting endurance performance when a layer of circumferential reinforcing elements is present.

(33) Moreover, rolling resistance measurements were taken. These measurements applied to all of the tires described hereinabove.

(34) The results of the measurements are given in the table below: they are expressed in kg/t, a value of 100 being assigned to the tire T1.

(35) TABLE-US-00003 Tire T1 Tire T2 Tire S1 100 98 98

(36) The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this feature or combination of features is not explicitly stated in the examples.