TIRE COMPRISING CARCASS REINFORCEMENT CABLES HAVING A LOW CARBON CONTENT

Abstract

The tire has a radial carcass reinforcement, the seat diameter of which is less than or equal to 19.5 inches, the carcass reinforcement has metal reinforcing elements which are layered cords that include several steel threads. The steel threads have a weight content of carbon C such that 0.01%C<0.4%. The at least one carcass reinforcement layer has a breaking force per unit width of between 20 daN/mm and 50 daN/mm, and the diameter of the cords is less than 0.7 mm.

Claims

1. A tire having a radial carcass reinforcement which includes at least one layer of metal reinforcing elements, the seat diameter of which is less than or equal to 19.5 inches, 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 said at least one layer of the carcass reinforcement are layered cords consisting of several steel threads having a weight content of carbon C such that 0.01%C<0.4%, wherein said at least one carcass reinforcement layer having a breaking force per unit width of between 20 daN/mm and 50 daN/mm and wherein the diameter of said cords is less than 0.7 mm.

2. The tire according to claim 1, wherein said steel threads have a maximum tensile strength R, expressed in MPa, such that R175+930.C-600.ln(d) and R1500 MPa.

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

4. 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.

5. The tire according to claim 4, 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.

6. The tire according to claim 1, wherein the metal reinforcing elements of said at least one layer of the carcass reinforcement are non-wrapped cords exhibiting, in the permeability test, a flow rate of less than 20 cm.sup.3/min.

7. The tire according to claim 6, wherein the metal reinforcing elements of said at least one layer of the carcass reinforcement are cords having at least two layers and wherein at least one inner layer is sheathed with a layer consisting of a rubber composition which is crosslinkable or crosslinked, preferably based on at least one diene elastomer.

8. The tire according to claim 6, wherein the cords exhibit, in the permeability test, a flow rate of less than 10 cm.sup.3/min and preferably of less than 2 cm.sup.3/min.

9. The tire according to claim 1, wherein the thickness of 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 3.2 mm.

10. 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 of less than 1.5 mm.

11. 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 of less than 1.7 mm.

12. 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.

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

14. 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.

15. 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 DRAWING

[0109] Further details and advantageous features of the disclosure will become apparent from the following description of exemplary embodiments of the disclosure, with reference to the FIGURE which depicts a meridian view of a diagram of a tire according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

[0110] In order to make it easier to understand, the FIGURE has not been drawn to scale.

[0111] In the FIGURE, the tire 1, of size 215/75 R17.5, 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: [0112] of a triangulation layer formed of non-wrapped 9.28 inextensible metal cords, oriented at an angle equal to 65, [0113] of a first working layer 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 26, [0114] of a second working layer formed of non-wrapped 9.28 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, [0115] 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.

[0116] The combination of these layers, constituting the crown reinforcement 5, is not depicted in detail in the figures.

[0117] The cords of the carcass reinforcement of the tire 1 are non-wrapped layered cords of 3+9 structure, consisting of a central nucleus formed of three threads, of an outer layer formed of nine threads.

[0118] It exhibits the following characteristics (d and p in mm):

[0119] 3+9 structure;

[0120] d.sub.1=0.18 (mm);

[0121] p.sub.1=6.5 (mm);

[0122] d.sub.2=0.18 (mm);

[0123] p.sub.2=12.5 (mm);

[0124] (d.sub.1/d.sub.2)=1;

with d.sub.1 and p.sub.1 respectively the diameter and the helical pitch of the inner layer and d.sub.2 and p.sub.2 respectively the diameter and the helical pitch of the threads of the outer layer.

[0125] The diameter of the carcass reinforcement cords is equal to 0.66 mm.

[0126] The steel threads constituting the cords of the carcass reinforcement have a weight content of carbon C equal to 0.21%.

[0127] The maximum tensile strength of the steel threads constituting the cords of the carcass reinforcement is equal to 2750 MPa.

[0128] In the permeability test, the cords extracted from the tire have a flow rate of greater than 20 cm.sup.3/mn.

[0129] The breaking force of the carcass reinforcement cords is equal to 74.5 daN.

[0130] The carcass reinforcement layer 2 is formed of the cords described above distributed with a pitch equal to 1.6 mm.

[0131] The breaking force per unit width of the carcass reinforcement layer is equal to 46.6 daN/mm.

[0132] Tests have been carried out on tires P produced according to the disclosure in accordance with the depiction in the figure, and other tests have been carried out with what are referred to as reference tires R.

[0133] These reference tires R differ from the tires P according to the disclosure by carcass reinforcement cords distributed with a pitch equal to 1.25 mm and the steel threads constituting the carcass reinforcement cords having a weight content of carbon C equal to 0.58% and a maximum tensile strength equal to 2830 MPa.

[0134] The breaking force per unit width of the carcass reinforcement layer of the reference tires R is equal to 59.6 daN/mm.

[0135] The variation in the weight thus obtained according to the disclosure compared to the tires R is equal to 0.3 kg. This corresponds to a weight gain of 1.2% relative to the overall weight of the tire. The cost of the tire is thus reduced by 1.5%.

[0136] 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 1999 daN and a speed of 40 km/h, with oxygen-doped inflation of the tires to 7.8 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.

[0137] The distance travelled 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 100 150

[0138] 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 the cords of the carcass reinforcement. Such faults only appear in the tires according to the disclosure at higher distances.