Tire Comprising Reduced Rubber Mixture Thicknesses and Sheathed Casing Framework Reinforcement Elements

Abstract

A tire having a radial carcass reinforcement having at least one layer of metal reinforcing elements. The tire includes a crown reinforcement, itself radially capped by a tread. The tread is connected to two beads by two sidewalls. The reinforcing elements of at least one layer of the carcass reinforcement have at least one filamentary element and at least one sheath covering the at least one filamentary element. The at least one sheath includes at least one layer of a thermoplastic polymer composition. The thickness of rubber compound between the internal surface of the tire cavity and the point of a metal reinforcing element of the carcass reinforcement that is closest to the internal surface of the cavity is less than or equal to 3.8 mm.

Claims

1. A tire having a radial carcass reinforcement comprised of at least one layer of metal reinforcing elements, said tire comprising a crown reinforcement, itself radially capped by a tread, said tread being connected to two beads by two sidewalls, wherein the reinforcing elements of at least one layer of the carcass reinforcement are comprised of at least one filamentary element and at least one sheath covering said at least one filamentary element, said at least one sheath comprising at least one layer of a thermoplastic polymer composition, and wherein the thickness of rubber compound between the internal surface of the tire cavity and the point of a metal reinforcing element of the carcass reinforcement that is closest to said internal surface of the cavity is less than or equal to 3.8 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 being comprised of at least two layers of rubber compound, wherein the radially innermost layer of rubber compound has a thickness less than 1.7 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 being comprised 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 1.7 mm.

4. The tire according to claim 1, wherein the mean thickness of the sheath at the back of each filamentary element is between 1 m and 2 mm.

5. The tire according to claim 1, wherein the thermoplastic polymer composition comprises a thermoplastic polymer, a functionalized diene elastomer, a poly(p-phenylene ether) or a mixture of these materials.

6. The tire according to claim 1, wherein each filamentary element comprises an assembly of individual metal threads.

7. 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 that are usable as reinforcing elements in a tire carcass reinforcement, having 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 being surrounded by an external 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.

8. The tire according to claim 7, wherein the diameter of the threads of the first layer (C1) is between 0.10 and 0.5 mm, and wherein the diameter of the threads of the layers (C2, C3) is between 0.10 and 0.5 mm.

9. The tire according to claim 7, wherein the helical pitch at which said threads of the external layer (C3) are wound is between 8 and 25 mm.

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

11. The tire according to claim 1, wherein the crown reinforcement furthermore has at least one layer of circumferential reinforcing elements.

12. 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 10and 45 and in the same direction as the angle formed by the inextensible elements of the working ply radially adjacent to it.

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

Description

[0078] In order to make them easier to understand, the figures are not shown to scale.

[0079] In FIGS. 1a and 1b, the tire 1, of size 315/70 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 hooped by a crown reinforcement 5, itself capped by a tread 6. The crown reinforcement 5 is formed radially, from the inside towards the outside: [0080] 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 of 18, [0081] of a second 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 of 18 and crossed with the metal cords of the first working layer, [0082] of a protective layer formed of elastic 635 metal cords.

[0083] This combination of layers constituting the crown reinforcement 5 is not shown in detail in the figures.

[0084] FIG. 1b illustrates an enlargement of region 7b in FIG. 1a and notably indicates the thickness E of rubber compound between the internal surface 10 of the tire cavity 8 and the point 12 of a reinforcing element 11 that is closest to said 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 said surface 10 onto the surface 10. This thickness E is the sum of the thicknesses of the various rubber compounds placed between said 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 inner 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 in question.

[0085] The thickness measurements are taken on a cross section of the tire, the latter consequently not being fitted or inflated.

[0086] The value E measured is equal to 3.8 mm.

[0087] The values of e.sub.1 and e.sub.2 are respectively equal to 1.7 mm and 1.7 mm.

[0088] FIG. 2 illustrates a schematic depiction of a reinforcing element 21 of the carcass reinforcement. It comprises at least one filamentary element 211 and at least one sheath 212 covering the filamentary element 211. The sheath 212 comprises at least one layer 25 of a thermoplastic polymer composition.

[0089] The filamentary element 211 is made up of an assembly of individual metal threads.

[0090] The filamentary element 211 is a non-wrapped layered cord of 1+6+12 structure, made up of a central nucleus formed of a thread 22, an intermediate layer formed of six threads 23 and an external layer formed of twelve threads 24.

[0091] It has the following features (d and p in mm): [0092] 1+6+12 structure; [0093] d.sub.1=0.20 (mm); [0094] d.sub.2=0.18 (mm); [0095] p.sub.1=10 (mm); [0096] d.sub.3=0.18 (mm); [0097] p.sub.2=10 (mm); [0098] (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 external layer.

[0099] The sheath 212 has a mean thickness G at the back of each filamentary element 211 equal to 150 m.

[0100] The layer 25 of the thermoplastic polymer composition comprises a thermoplastic polymer, a functionalized diene elastomer, a poly(p-phenylene ether) or a mixture of these materials. In this case, the thermoplastic polymer composition comprises a thermoplastic polymer, for example polyamide 66. Optionally, the thermoplastic polymer composition may comprise a functionalized diene elastomer, for example a stirene thermoplastic comprising an epoxide, carbonyl, anhydride or ester function and/or a poly(p-phenylene ether).

[0101] The layer 25 of the thermoplastic polymer composition can also advantageously be covered with a layer of adhesive (not shown in FIG. 2) providing adhesion.

[0102] Tests have been carried out on tires produced according to the invention 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.

[0103] These reference tires differ from the tires according to the invention by way of carcass reinforcement cords that do not have the sheath 212 and by the fact that the thickness E of rubber compound between the internal surface of the tire cavity and the point of a reinforcing element that is closest to said surface is equal to 5.5 mm, each of the thicknesses e.sub.1 and e.sub.2 being equal to 2.5 mm.

[0104] Rolling road endurance tests were carried out on a test machine which applies a load of 4415 daN and a speed of 40 km/h on the tires, with oxygen-doped inflation of the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires. The running operations were halted as soon as the tires exhibit carcass reinforcement degradation or after a given distance covered.

[0105] The tests thus carried out showed that the distances covered during each of these tests are favorable for the tires according to the invention; specifically, some of the tires exhibited degradation of the reinforcing elements of the carcass reinforcement while, for others, the tests had to be halted on account of excessive degradation. As far as the tires according to the invention are concerned, for the same distances covered, the reinforcing elements of the carcass reinforcement did not exhibit any damage.

[0106] Other endurance tests with running on a drive axle of a vehicle were carried out, with the tires being subjected to a load of 3680 daN and a speed of 40 km/h, with the tires inflated to 0.2 bar. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires. The running operations are carried out over a distance of 12 000 km or are halted as soon as the tires exhibit carcass reinforcement degradation.

[0107] The tests thus carried out showed that the distances covered during each of these tests are substantially equivalent for the tires according to the invention and the reference tires.

[0108] Moreover, the manufacturing costs of the tires according to the invention are not as high, the cost of materials being 6% lower in the case of the tires according to the invention.

[0109] Moreover, the tires according to the invention have the advantage of being less heavy, with a 5% lightening of weight compared with the reference tires.