PNEUMATIC TIRE COMPRISING LOW-CARBON CARCASS REINFORCING CORDS AND HAVING REDUCED THICKNESSES OF RUBBER MIXTURES

Abstract

The tire has a radial carcass reinforcement which includes at least one layer of metal reinforcing elements. The tire also has a crown reinforcement, itself capped radially with a tread. The tread is joined to two beads via two sidewalls. The metal reinforcing elements of at least one layer of the carcass reinforcement are cords include several steel threads having a weight content of carbon C such that 0.01%C<0.4%. The cords exhibit, in the permeability test, a flow rate which is strictly greater than 20 cm.sup.3/min, and the thickness of the rubber compound between the inner surface of the tire cavity and the point of a metal reinforcing element of the carcass reinforcement that is closest to the inner surface of the cavity is less than 3.2 mm.

Claims

1- A tire having a radial carcass reinforcement which includes at least one layer of metal reinforcing elements, said tire comprising a crown reinforcement, itself capped radially with a tread, said tread being joined to two beads via two sidewalls, wherein the metal reinforcing elements of at least one layer of the carcass reinforcement are cords consisting of several steel threads having a weight content of carbon C such that 0.01%C<0.4%, wherein said cords of at least one layer of the carcass reinforcement exhibit, in the permeability test, a flow rate strictly greater than 20 cm.sup.3/min and wherein the thickness of the rubber compound between the inner surface of the tire cavity and the point of a metal reinforcing element of the carcass reinforcement that is closest to said inner surface of the cavity is less than or equal to 3.2 mm.

2- The tire according to claim 1, the rubber compound between the tire cavity and the reinforcing elements of the radially innermost carcass reinforcement layer consisting of at least two layers of rubber compound, wherein the radially innermost layer of rubber compound has a thickness less than or equal to 1.5 mm.

3- The tire according to claim 1, the rubber compound between the tire cavity and the reinforcing elements of the radially innermost carcass reinforcement layer consisting of at least two layers of rubber compound, wherein the layer of rubber compound radially adjacent to the radially innermost layer of rubber compound has a thickness less than or equal to 1.7 mm.

4- The tire according to claim 1, wherein said steel threads have a maximum tensile strength R, expressed in MPa, such that R175+930.0600.Math.ln(d) and R1500 MPa, d being the diameter of said steel threads.

5- The tire according to claim 1, wherein said steel threads have a weight content of chromium Cr such that Cr<12%.

6- The tire according to claim 1, wherein the metal reinforcing elements of at least one layer of the carcass reinforcement are layered metal cords of [L+M] or [L+M+N] construction of use as reinforcing element in a tire carcass reinforcement, comprising a first layer C1 of L threads of diameter d.sub.1, with L ranging from 1 to 4, surrounded by at least one intermediate layer C2 of M threads of diameter d.sub.2 wound together in a helix at a pitch p.sub.2, with M ranging from 3 to 12, said layer C2 possibly being surrounded by an outer layer C3 of N threads of diameter d.sub.3 wound together in a helix at a pitch p.sub.3, with N ranging from 8 to 20.

7- The tire according to claim 6, wherein the diameter of the threads of the first layer (C1) is between 0.10 and 0.4 mm, and wherein the diameter of the threads of the layers (C2, C3) is between 0.10 and 0.4 mm.

8- The tire according to claim 1, wherein the crown reinforcement is formed of at least two working crown layers of reinforcing elements that are crossed from one layer to the other and form, with the circumferential direction, angles of between 10 and 45.

9- The tire according to claim 1, wherein the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

10- 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 reinforcing elements, that 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 inextensible elements of the working ply which is radially adjacent thereto.

11. The tire according to claim 1, wherein the crown reinforcement also comprises a triangulation layer formed of metal reinforcing elements that form angles of more than 60 with the circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Further details and advantageous features of the disclosure will become apparent from the following description of exemplary embodiments of the disclosure, with reference to FIGS. 1 to 2, which depict:

[0081] FIG. 1: a meridian view of a diagram of a tire according to an embodiment of the disclosure,

[0082] FIG. 2: an enlarged partial view of a part of the diagram of FIG. 1.

[0083] In order to make them easier to understand, the figures have not been drawn to scale.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

[0084] In FIG. 1, the tire 1, of size 295/80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3 around bead wires 4. The carcass reinforcement 2 is formed of a single layer of metal cords 11 and of two calendering layers 13. The carcass reinforcement 2 is wrapped by a crown reinforcement 5, itself capped by a tread 6. The crown reinforcement 5 is formed radially, from the inside towards the outside: [0085] of a triangulation layer formed of non-wrapped 9.28 inextensible metal cords, oriented at an angle equal to 65, [0086] of a first working layer formed of non-wrapped inextensible 11.35 metal cords which are continuous across the entire width of the ply, oriented at an angle equal to 26, [0087] of a second working layer formed of non-wrapped 11.35 inextensible metal cords, which are continuous over the entire width of the ply, oriented at an angle equal to 18, and crossed with the metal cords of the first working layer, [0088] of a protective layer formed of non-wrapped elastic 6.35 metal cords which are continuous across the entire width of the ply, oriented at an angle equal to 18 in the same direction as the metal cords of the second working layer.

[0089] The combination of these layers, constituting the crown reinforcement 5, is not depicted in detail in the figures.

[0090] FIG. 2 illustrates an enlargement of region 7 in FIG. 1 and in particular indicates the thickness E of rubber compound between the inner surface 10 of the tire cavity 8 and the point 12 of a reinforcing element 11 that is closest to the surface 10. This thickness E is equal to the length of the orthogonal projection of the point 12 of a reinforcing element 11 that is closest to the surface 10 onto the surface 10. This thickness E is the sum of the thicknesses of the various rubber compounds placed between the reinforcing element 11 of the carcass reinforcement 2; it corresponds, on the one hand, to the thickness of the calendering layer 13 radially on the inside of the carcass reinforcement and, on the other hand, to the thicknesses e.sub.1, e.sub.2 of the various layers 14, 15 of rubber compound that form the internal wall of the tire 1. These thicknesses e.sub.1, e.sub.2 are moreover equal to the length of the orthogonal projection of a point on one surface onto the other surface of the respective layer 14 or 15 concerned.

[0091] These thickness measurements are carried out on a cross section of the tire, the latter consequently not being fitted or inflated.

[0092] The value of E measured is equal to 2.4 mm.

[0093] The values of e.sub.1 and e.sub.2 are respectively equal to 1.4 mm and 1 mm.

[0094] The cords of the carcass reinforcement of the tire 1 are non-wrapped layered cords of 1+6+12 structure, consisting of a central nucleus formed of a thread, of an intermediate layer formed of six threads and of an outer layer formed of twelve threads.

[0095] It exhibits the following characteristics (d and p in mm): [0096] 1+6+12 structure; [0097] d.sub.1=0.20 (mm); [0098] d.sub.2=0.18 (mm); [0099] p.sub.2=10 (Mm); [0100] d.sub.3=0.18 (mm); [0101] p.sub.2=10 (mm); [0102] (d.sub.2/d.sub.3)=1;
with d.sub.2 and p.sub.2 respectively the diameter and the helical pitch of the intermediate layer and d.sub.3 and p.sub.3 respectively the diameter and the helical pitch of the threads of the outer layer.

[0103] The steel threads constituting the cords of the carcass reinforcement have a weight content of carbon C equal to 0.21%.

[0104] The maximum tensile strength of the steel threads constituting the cords of the carcass reinforcement is equal to 2750 MPa.

[0105] In the permeability test, the cords extracted from the tire exhibit a flow rate equal to 22 cm.sup.3/min and hence greater than 20 cm.sup.3/min.

[0106] Tests have been carried out on tires P produced according to the disclosure in accordance with the depiction in FIGS. 1 and 2, and other tests have been carried out with what are referred to as reference tires R.

[0107] These reference tires R differ from the tires P according to the disclosure by cords of the carcass reinforcement comprising a sheathing layer around the inner layers and steel threads constituting the cords of the carcass reinforcement having a weight content of carbon C equal to 0.58% and a maximum tensile strength equal to 2830 MPa.

[0108] The core of the reference tire cord composed of the central nucleus formed of a thread and of the intermediate layer formed of the six threads is sheathed with a rubber composition based on unvulcanized diene elastomer (in the raw state). The sheathing is obtained via a head for extrusion of the core composed of the thread surrounded by the six threads, followed by a final operation in which the 12 threads are twisted or cabled around the core thus sheathed.

[0109] Endurance testing with running on an external roller with a circumference equal to 8.5 meters was carried out, with the tires being subjected to a load of 4176 daN and a speed of 40 km/h, with oxygen-doped inflation of the tires to 10.2 bar. These tests were carried out in a temperature-controlled chamber at 15 C. The tests were carried out for the tires according to the disclosure under conditions identical to those applied to the reference tires. The running operations are halted as soon as the tires exhibit carcass reinforcement degradation.

[0110] The distance traveled is measured until the tire exhibits a degradation. The measurements illustrated below are referenced to a base 100 for the reference tire.

TABLE-US-00001 R P km 100 125

[0111] These results show that, under particularly severe running conditions, the tires according to the disclosure have better performance in terms of endurance than the reference tires. The faults in the latter are due to localized oxidation of elastomeric mixtures in the carcass reinforcement. Such faults only appear in the tires according to the disclosure at higher distances. Moreover, it appears that the use of cords, the steel threads of which have a low carbon content, makes it possible to push the risks associated with fatigue-corrosion or fatigue-fretting-corrosion phenomena back to a level that is at least as good as heavily penetrated cords or cords comprising an elastomeric mixture deposited during the manufacture of the cords at the inner layers.