Tire comprising a layer of circumferential reinforcing elements

Abstract

Tire comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements. First layer C of rubber compound is placed between ends of the two working crown layers. Second layer S of polymer compound is in contact with at least one working crown layer and with the carcass reinforcement. The crown reinforcement includes at least one layer of circumferential reinforcing elements. The elastic modulus under tension at 10% elongation of first layer C is less than 8 MPa, the maximum value of tan() of first layer C is less than 0.100. The second layer S is made up of a filled elastomer blend having a macro dispersion coefficient Z greater than or equal to 65 and a maximum tan() value less than 0.100, and its complex dynamic shear modulus G*, measured at 10% and 60 C. on the return cycle, is greater than 1.35 MPa.

Claims

1. A tire with a radial carcass reinforcement comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements, crossed from one layer to the other making with the circumferential direction angles comprised between 10 and 45, a first layer of rubber compound being placed between at least the ends of said at least two working crown layers, a second layer of polymer compound being in contact with at least one working crown layer and in contact with the carcass reinforcement, said second 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 metallic circumferential reinforcing elements, wherein the elastic modulus under tension at 10% elongation of the first layer of rubber compound is less than 8 MPa, wherein the maximum value of tan (), denoted tan().sub.max, of the first layer of rubber compound is less than 0.100, wherein said second layer of polymer compound is made up of a filled elastomeric compound having a macro dispersion coefficient greater than or equal to 65 and a maximum tan () value, denoted tan()max, less than 0.100 and wherein the complex dynamic shear modulus G*, measured at 10% and 60 C. on the return cycle, of said second layer of polymer compound is greater than 1.35 MPa and less than 2 MPa.

2. The tire according to claim 1, wherein the elastomer compound of the second layer of polymer compound comprises, by way of reinforcing filler, at least carbon black used at a content comprised between 10 and 50 phr, and wherein the carbon black has a BET specific surface area greater than 90 m.sup.2/g.

3. The tire according to claim 1, wherein the elastomer compound of the second layer of polymer compound comprises a blend of carbon black, of BET specific surface area greater than 90 m.sup.2/g, and of a white filler, wherein the reinforcing filler is used at a content comprised between 10 and 60 phr, and wherein the ratio of carbon black to white filler is greater than 2.7.

4. Tire according to claim 1, wherein the layer of rubber compound 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.

5. The tire according to claim 1, said at least two working crown having unequal axial widths, wherein a third layer of rubber compound separates the axially widest working crown layer from the end of the second working crown layer, wherein the axially outer end of said third layer of rubber compound is situated at a distance away from the equatorial plane of the tire that is less than the distance separating the end of the axially widest reinforcing elements ply from said plane, wherein said third layer of rubber compound is radially separated, at least in part, from the skim L of said second working crown layer by the first layer of rubber compounds, and wherein said first and third layers of rubber compound and said skim respectively having elastic modulus values under tension at 10% elongation denoted MP, MC and ML, such that MLMC>MP.

6. The tire according to claim 1, the tire comprising a fourth layer of polymer compound axially in contact with the second layer of polymer compound radially between the carcass reinforcement and the radially innermost layer of reinforcing elements of the crown reinforcement, wherein said fourth layer of polymer compound is made up of a filled elastomer compound having a macro dispersion coefficient greater than or equal to 65 and a maximum tan () value, denoted tan()max, less than 0.100 and wherein the complex dynamic shear modulus measured at 10% and 60 C. on the return cycle, of said fourth layer of polymer compound is greater than 1.35 MPa.

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

8. The tire according to claim 6, wherein the elastomer compound of the fourth layer of polymer compound comprises, by way of reinforcing filler, at least carbon black used at a content comprised between 10 and 50 phr, and wherein the carbon black has a BET specific surface area greater than 90 m.sup.2/g.

9. The tire according to claim 6, wherein the elastomer compound of the fourth layer of polymer compound comprises by way of a blend of carbon black, of BET specific surface area greater than 90 m.sup.2/g, and of a white filler, wherein the reinforcing filler is used at a content comprised between 10 and 60 phr, and wherein the ratio of carbon black to white filler is greater than 2.7.

10. The tire according to claim 6, wherein the elastomer compound of the fourth layer of polymer compound comprises, by way of reinforcing filler, at least carbon black used at a content comprised between 10 and 50 phr, and wherein the carbon black has a BET specific surface area greater than or equal to 120 m.sup.2/g.

11. The tire according to claim 6, wherein the elastomer compound of the fourth layer of polymer compound comprises by way of a blend of carbon black, of BET specific surface area greater than or equal to 120 m.sup.2/g, and of a white filler, wherein the reinforcing filler is used at a content comprised between 10 and 60 phr, and wherein the ratio of carbon black to white filler is greater than 2.7.

12. The tire according to claim 1, said at least two working crown layers each being formed of reinforcing elements inserted between two skim layers of rubber compound, wherein 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 and wherein the maximum value of tan(), denoted tan()max, of said at least one skim layer of at least one working crown layer is less than 0.100.

13. The tire according to claim 12, wherein the said at least one skim layer of at least one working crown layer is an elastomer compound based on natural rubber or based on synthetic polyisoprene with a predominance of cis-1,4 chains and possibly at least one other diene elastomer, natural rubber or synthetic polyisoprene in the case of a blend being present at a content that predominates over the content of the other diene elastomer or elastomers used and of a reinforcing filler made up of: a) either carbon black of BET specific surface area 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 carbon black with 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 functional groups at the surface, selected from the group formed of precipitated or pyrogenated silicas, aluminas or aluminosilicates or alternatively still carbon blacks modified during or after the 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 blend the overall filler content is between 20 and 80 phr.

14. The tire according to claim 12, wherein said at least one skim layer of at least one working crown layer is an elastomer compound based on natural rubber or based on synthetic polyisoprene with a predominance of cis-1,4 chains and possibly at least one other diene elastomer, natural rubber or synthetic polyisoprene in the case of a blend being present at a content that predominates over the content of the other diene elastomer or elastomers used and of a reinforcing filler made up of: e) either carbon black of BET specific surface area 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, f) or carbon black with 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, g) or a white filler of the silica and/or alumina type comprising SiOH and/or AlOH functional groups at the surface, selected from the group formed of precipitated or pyrogenated silicas, aluminas or aluminosilicates or alternatively still carbon blacks modified during or after the 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, h) 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 blend the overall filler content is between 40 and 60 phr.

15. 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.

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

17. 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.

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

19. Tire according to claim 1, wherein the layer of rubber compound 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: e) 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, f) 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, g) 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, h) 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.

20. 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 to 3 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) FIG. 3: a schematic meridian view of a tire according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) 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.

(6) 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.

(7) The crown reinforcement is itself capped by a tread 5.

(8) The maximum axial width of the tire is equal to 317 mm

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

(10) 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

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

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

(13) According to the invention, a first layer of rubber compound C decouples the ends of the working crown layers 41 and 43.

(14) The zone of engagement of the layer C between the two working crown layers 41 and 43 is defined by its thickness or, more precisely, 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 comprised between the axially inner end of the said layer C and the end of the radially outer working crown layer 43. The radial distance d is equal to 3.5 mm, namely approximately 2.1 times the diameter .sub.2 of the reinforcing elements of the working crown layer 43, the diameter .sub.2 being equal to 1.65 mm. The axial distance D is equal to 20 mm, namely approximately 12 times the diameter .sub.2 of the reinforcing elements of the working crown layer 43.

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

(16) In FIG. 2, the tire 1 differs from the one depicted in FIG. 1 in that the ends of the working crown layers 41 and 43 are decoupled by a stack of two radially superposed layers. A third layer of rubber compound P in contact with the working crown ply 41 is positioned radially between the said working crown layer 41 and the first layer of rubber compounds C such that the said third layer P caps the end of the axially narrowest working crown layer 43.

(17) In FIG. 3, the tire 1 differs from the one depicted in FIG. 1 in that a fourth layer G axially extends the second layer S, radially between the carcass reinforcement 2 and the first working layer 41.

(18) 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.

(19) Tests have notably been performed varying the characteristics of the compounds of the layer C, 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.

(20) Further tests have also been performed with tires by also 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 tan().sub.max value, according to the invention.

(21) The various compounds used are listed below, expressing, for each case the elastic modulus under tension at 10% elongation and the values tan().sub.max and P60.

(22) TABLE-US-00001 Compound Compound Compound R1 R2 R3 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 NR 100 100 100 100 100 100 100 100 100 Black N347 52 50 33 Black N683 44 30 Black N326 47 Black N330 35 Black N234 35 Silica 165G 46 5 Antioxidant 1 1.8 0.7 1.5 1 2 1 1 1.7 (6PPD) Stearic acid 0.65 0.6 1.4 0.9 0.65 1 0.65 0.65 0.5 Zinc oxide 9.3 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 4.5 (CoAbietate) Silane-on-black 8.3 Sulphur 6.1 5.6 2.15 4.5 6.1 4.8 6.1 6.1 3.13 Accelerator DCBS 0.93 0.8 0.8 0.93 0.93 0.93 Accelerator TBBS 1.01 Accelerator CBS 1 1.10 Coaccelerator 1.1 DPG Retarder CTP 0.25 0.08 0.15 0.25 0.2 0.25 0.25 PVI) MA.sub.10 (MPa) 10.4 8.5 3.4 5.99 5.56 7.25 6.16 4.4 3.5 tan().sub.max 0.130 0.141 0.074 0.099 0.074 0.063 0.056 0.030 0.080 P60 (%) 22.9 24.5 11.3 18.7 14.9 13.3 12.2 8.5 12 G* 10% at 60 C. 1.25 1.43 (return cycle) Z coefficient 60 65 Bound rubber 27.5 48.1

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

(24) Various reference tires were tested.

(25) First reference tires T1 have a first layer C made of the compound R2, the skims of the working layers being made of the compound R1 and the second layer S of the compound R3.

(26) Second reference tires T2 have a first layer C made of the compounds 1 to 5, the skims of the working layers being made of the compound R1 and the second layer S of the compound R3.

(27) Third reference tires T3 have a first layer C made of the compounds 1 to 5, the skims of the working layers being made of the compounds 1 to 5 and the second layer S of the compound R3.

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

(29) A first series of tires S1 according to the invention was produced with a first layer C made of the compounds 1 to 5, the skims of the working layers being made of the compound R1 and a second layer S of the compound 6.

(30) A second series of tires S2 according to the invention was produced with a first layer C made of the compounds 1 to 5, the skims of the working layers also being made of the compounds 1 to 5 and the second layer S being made of the compound 6. Certain tires of this series S2 were produced with the same compounds for the first layer C and the skims of the working layers, and others with different compounds.

(31) 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.

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

(33) 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.

(34) The distances covered varied from one type of tire to another, failures occurring from 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.

(35) TABLE-US-00002 Tire T1 Tire T2 Tire T3 Tire S1 Tire S2 100 90 80 110 100

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

(37) These last tests demonstrated that after covering identical distances, the tires according to the invention, and more particularly those of series S2, exhibit instances of damage that are fewer in number and less substantial than those of the reference tires.

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

(39) 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.

(40) TABLE-US-00003 Tire T1 Tire T2 Tire T2 Tire S1 Tire S2 100 99 96 99 96

(41) 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.