Tire comprising a layer of circumferential reinforcing elements

Abstract

A tire comprising a crown reinforcement formed from at least two working crown layers of reinforcing elements and at least one layer of circumferential reinforcing elements, wherein, the tensile modulus of elasticity at 10% elongation of at least one skim coat of at least one working crown layer is greater than 9 MPa and the maximum value of tan(), denoted tan()max, of said skim coat is less than 0.100.

Claims

1. A tire with a radial carcass reinforcement, comprising: a crown reinforcement formed from at least two working crown layers of reinforcing elements, with one layer crossing the next at angles in the range from 10 to 45 with the circumferential direction, said at least two working crown layers each being formed of reinforcing elements inserted between two skim coats of rubber mixture, and including a layer of circumferential reinforcing elements, wherein the tensile modulus of elasticity at 10% elongation of at least one skim coat of at least one working crown layer is greater than 9 MPa, wherein the maximum value of tan denoted tan max, of said at least one skim coat of at least one working crown layer is less than 0.100, wherein said at least one skim coat of at least one working crown layer is an elastomeric mixture based on: natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains, and optionally 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 carbon black with a BET specific surface of less than or equal to 44 m.sup.2/g, regardless of its structural index, used in a proportion of 40 to 100 phr, and a tread radially capping the crown reinforcement and joined to two beads via two sidewalls.

2. The tire according to claim 1, further comprising a layer C of rubber mixture placed between at least ends of said at least two working crown layers, and wherein said at least two working crown layers having unequal axial widths, wherein a distance d between an end of an axially narrowest working layer and a working layer separated from the axially narrowest working layer by the layer C of rubber mixture is such that 1.1<d<2.2, where is the diameter of the reinforcing elements of said at least one layer of circumferential reinforcing elements and wherein, in a meridian plane, a thickness of the layer C of rubber mixture is substantially constant over an axial width between an axially inner end of the layer C and the end of the axially narrowest working layer.

3. The tire according to claim 1, wherein said reinforcing elements of at least one working crown layer are saturated layered cords, wherein at least one inner layer is sheathed in a layer formed by a polymeric composition that is a non-cross-linkable, cross-linkable or cross-linked rubber composition.

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

5. The tire according to claim 1, wherein said at least two working crown layers have different axial widths, wherein the difference between an axial width of an axially widest working crown layer and an axial width of an axially least wide working crown layer is in the range of 10 to 30 mm.

6. The tire according to claim 5, wherein the axially widest working crown layer lies radially inside the other working crown layers.

7. The tire according to claim 1, wherein axial widths of the working crown layers radially adjacent to the layer of circumferential reinforcing elements are greater than an axial width of said layer of circumferential reinforcing elements.

8. The tire according to claim 7, wherein the working crown layers adjacent to the layer of circumferential reinforcing elements are coupled over an axial width, on either side of the equatorial plane and in the immediate axial extension of the layer of circumferential reinforcing elements, and are subsequently decoupled by profiled elements of rubber mixture at least over the remainder of the width common to said two working layers.

9. The tire according to claim 1, wherein the reinforcing elements of said 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.

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

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

12. The tire according to claim 1, wherein the crown reinforcement is supplemented on its radially outer side by at least one additional layer, called the protective layer, of elastic reinforcing elements, oriented with respect to the circumferential direction at an angle in the range from 10 to 45 and in the same direction as the angle formed by inextensible elements of the working layer which is radially adjacent to the protective layer.

13. The tire according to claim 1, wherein the crown reinforcement further includes a triangulation layer formed from metallic reinforcing elements forming angles of more than 60 with the circumferential direction.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other characteristics and advantages of the invention will be made clearer by the following description of exemplary embodiments of the invention, with reference to FIGS. 1 to 3, which show:

(2) in FIG. 1, a meridian view of a tire layout according to an embodiment of the invention,

(3) in FIG. 2, a meridian view of a tire layout according to a second embodiment of the invention, and

(4) in FIG. 3, a meridian view of a tire layout according to a third embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(5) In order to simplify the understanding of the figures, they are not shown to scale. The figures shown only a half-view of a tire which extends symmetrically about the axis XX which represents the circumferential mid-plane, or equatorial plane, of a tire.

(6) In FIG. 1, the tire 1, with a size of 315/70 R 22.5, has a shape ratio H/S equal to 0.70, where H is the height of the tire 1 on its mounting rim and S is its maximum axial width. Said tire 1 comprises a radial carcass reinforcement 2 fixed in two beads, not shown in the figure. The carcass reinforcement is formed by a single layer of metal cords. This carcass reinforcement 2 is wrapped with a crown reinforcement 4, formed radially, from the inside to the outside, from: a first working layer 41 formed from inextensible metal cords 9.28 which are not wrapped, these cords being continuous over the whole width of the layer and orientated at an angle of 24, a layer of circumferential reinforcing elements 42 formed from metal cords made of 2123 steel, of the bi-modulus type, a second working layer 43 formed from inextensible metal cords 9.28 which are not wrapped, these cords being continuous over the whole width of the layer, being orientated at an angle of 24, and crossing over the metal cords of the layer 41, and a protective layer 44 formed from elastic 6.35 metal cords.

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

(8) The maximum axial width S 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.

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

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

(13) A layer of rubber mixture C is also present for decoupling of the ends of the working crown layers 41 and 43.

(14) The area of engagement of the layer C between the two working crown layers 41 and 43 is defined by its thickness, or more precisely by 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 said layer C and the end of the radially outer working crown layer 43. The radial distance d is equal to 3.5 mm. The axial distance D is equal to 20 mm.

(15) In FIG. 2, the tire 1 differs from that of FIG. 1 in the shape of the layer C which is substantially flat. The radial distance d is equal to 2 mm, corresponding to a thickness of the layer C equal to 1.2 mm. According to the variant of the invention shown in FIG. 2, the thickness of the layer C is substantially identical in a meridian view over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer.

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

(17) In FIG. 3, the tire 1 differs from that shown in FIG. 1 in that the two working layers 41 and 43 are coupled over an axial width 1, on either side of the equatorial plane and axially in the extension of the layer of circumferential reinforcing elements 42: 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 layer of rubber whose thickness is minimal and is equal to twice the thickness of the rubber skim coat of the non-wrapped 9.28 metal cords from which each working layer 41, 43 is formed, that is to say 0.8 mm. Over the remainder of the 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 said layer C increasing from the axial end of the coupling area to the end of the least wide working layer 43. The length of the layer C is advantageously sufficient to radially cover the end of the widest working layer 41, which in this case is the working layer radially nearest to the carcass reinforcement.

(18) Tests have been conducted with different tires made according to the invention as shown in FIGS. 1 and 2, and with control tires.

(19) The different mixtures used in these tires to form the skim coat mixtures of the working layers are listed below, the tensile modulus of elasticity for each mixture at 10%elongation being stated, together with the values of tan().sub.max and P60.

(20) TABLE-US-00001 Mixture R1 Mixture 1 NR 100 100 Black N347 52 Black N683 63 Antioxidant (6PPD) 1 1 Stearic acid 0.65 0.65 Zinc oxide 9.3 9.3 Cobalt salt (AcacCo) 1.12 1.12 sulphur 6.1 6.1 Accelerator DCBS 0.93 0.93 Retarder CTP (PVI) 0.25 0.25 MA.sub.10 (MPa) 10.4 10.03 tan().sub.max 0.130 0.092 P60 (%) 22.9 17.4

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

(22) Regarding the control tire T1, this has no circumferential reinforcing elements and the skim coats of the working layers are formed from the mixture R1.

(23) A first tire P1 according to the invention as shown in FIG. 1 was made with skim coats of the working layers made of the mixture R1.

(24) A second tire P2 according to the invention was made with skim coats of the working layers made of the mixture R1 and with a layer C of rubber mixture having a distance d equal to 3.5 mm and having a flat cross-sectional profile as shown in FIG. 2.

(25) 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 said tire under an initial load of 4000 kg which was progressively increased to reduce the duration of the test.

(26) 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 conducted on the tires according to the invention in conditions identical to those used for the control tires.

(27) The tests conducted in this way demonstrated that the distances traveled by the tires according to the invention in each of these tests were at least as great as, or even greater than, the distances traveled by the control tire T1. It appears, therefore, that the performance of the tires according to the invention is at least as good as that of the control tires.

(28) These tests demonstrate, notably, that the design of the tires according to the invention makes it possible to use skim coats of the working crown layers combining a tensile modulus of elasticity at 10% elongation of more than 9 MPa and a value of tan().sub.max of less than 0.100, and possibly associated with a layer C having a flat profile, without detracting from performance in terms of endurance when a layer of circumferential reinforcing elements is present.

(29) Measurements of rolling resistance were also made. These measurements were made on a first control tire T1 as described above, on a second control tire T2 identical to the former but further including a layer of circumferential reinforcing elements identical to those of the tires according to the invention, and also on the tires P1 and P2 according to the invention.

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

(31) TABLE-US-00002 Tire T1 Tire T2 Tire P1 Tire P2 100 101 99 98