Three-layered metal cable for tire carcass reinforcement

1. A multi-strand steel cable comprising, as an elementary strand, a three-layered cable, wherein the three-layered cable includes:

an inner layer C 1 , which includes from 1 to 4 wires L having a diameter d 1 ;

an intermediate layer C 2 , which surrounds the inner layer C 1 , wherein the intermediate layer C 2 includes from 3 to 12 wires M having a diameter d 2 , and wherein the wires M are wound together in a helix at a pitch p 2 ;

an outer layer C 3 , which surrounds the intermediate layer C 2 , wherein the outer layer C 3 includes from 8 to 20 wires N having a diameter d 3 , wherein the wires N are wound together in a helix at a pitch p 3 , and wherein the wires M of the intermediate layer C 2 and the wires N of the outer layer C 3 are wound in a same direction of twist; and

at least one of: a first rubber sheath, which is positioned between the inner layer C 1 and the intermediate layer C 2 , and a second rubber sheath, which is positioned between the intermediate layer C 2 and the outer layer C 3 , wherein the first and second rubber sheaths are formed of a cross-linkable or cross-linked rubber composition that includes at least one diene elastomer.

2. A multi-strand steel cable according to claim 1 , wherein the at least one diene elastomer of the rubber sheath is selected from a group of elastomers that includes polybutadienes, natural rubbers, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures thereof.

3. A multi-strand steel cable according to claim 2 , wherein the at least one diene elastomer is selected from a group of elastomers that includes natural rubbers, synthetic polyisoprenes, and mixtures thereof.

4. A multi-strand steel cable according to claim 3 , wherein the at least one diene elastomer is a natural rubber.

5. A multi-strand steel cable according to claim 1 , wherein the rubber composition includes carbon black as a reinforcing filler.

6. A multi-strand steel cable according to claim 1 , wherein the rubber composition has, in a cross-linked state, a secant tensile modulus that is less than 20 MPa.

7. A multi-strand steel cable according to claim 6 , wherein the secant tensile modulus is less than 12 MPa.

8. A multi-strand steel cable according to claim 1 ,

wherein the steel cable is incorporated into a carcass reinforcement ply of a tire that includes a rubber matrix, and

wherein the rubber matrix of the carcass reinforcement ply includes substantially a same rubber composition as the rubber composition of each of the first and second rubber sheaths of the three-layered cable.

9. A multi-strand steel cable according to claim 1 , wherein the outer layer C 3 is a saturated layer.

10. A multi-strand steel cable according to claim 1 , wherein the first rubber sheath covers the inner layer C 1 .

11. A multi-strand steel cable according to claim 1 , wherein the first rubber sheath is structured to separate adjacent wires of the wires M in the intermediate layer C 2 .

12. A multi-strand steel cable according to claim 1 , wherein the second rubber sheath separates adjacent wires of the wires N of the outer layer C 3 and covers a radial inner half-circumference of each wire N of the outer layer C 3 .

13. A multi-strand steel cable according to claim 1 , wherein the intermediate layer C 2 includes 6 or 7 of the wires M.

14. A multi-strand steel cable according to claim 1 , wherein:

0.10 mm<d 1 <0.28 mm;

0.10 mm<d 2 <0.25 mm;

0.10 mm<d 3 <0.25 mm;

M=6 or M=7; and

5π(d 1 +d 2 )<p 2 ≦p 3 <5π(d 1 +2d 2 +d 3 ).

15. A multi-strand steel cable according to claim 14 , wherein:

if M is 6, then a ratio (d 1 /d 2 ) is from 1.10 to 1.40; and

if M is 7, then the ratio (d 1 /d 2 ) is from 1.40 to 1.70.

16. A multi-strand steel cable according to claim 15 , wherein p 2 =p 3 .

17. A multi-strand steel cable according to claim 16 , wherein the outer layer C 3 has a substantially circular cross-section.

18. A multi-strand steel cable according to claim 1 , wherein the inner layer C 1 includes 1 wire L.

19. A multi-strand steel cable according to claim 18 , wherein a wire composition of the three-layered cable includes one of:

6 wires for the wires M in the intermediate layer C 2 , and 10 wires for the wires N in the outer layer C 3 ;

6 wires for the wires M in the intermediate layer C 2 , and 11 wires for the wires N in the outer layer C 3 ;

6 wires for the wires M in the intermediate layer C 2 , and 12 wires for the wires N in the outer layer C 3 ;

7 wires for the wires M in the intermediate layer C 2 , and 11 wires for the wires N in the outer layer C 3 ;

7 wires for the wires M in the intermediate layer C 2 , and 12 wires for the wires N in the outer layer C 3 ; and

7 wires for the wires M in the intermediate layer C 2 , and 13 wires for the wires N in the outer layer C 3 .

20. A multi-strand steel cable according to claim 19 , wherein the intermediate layer C2 includes 6 wires for the wires M, and the outer layer C 3 includes 12 wires for the wires N.

21. A multi-strand steel cable according to claim 14 , wherein:

0.18 mm<d 1 <0.24 mm;

0.16 mm<d 2 ≦d 3 <0.19 mm; and

5 mm<p 2 ≦p 3 <12 mm.

22. A multi-strand steel cable according to claim 14 , wherein:

0.18 mm<d 1 <0.24 mm;

0.16 mm<d 2 ≦d 3 <0.19 mm; and

20 mm<p 2 ≦p 3 <30 mm.

23. A multi-strand steel cable according to claim 1 , wherein each of the first and second rubber sheaths has an average thickness of from 0.010 mm to 0.040 mm.

24. A multi-strand steel cable according to claim 1 , wherein the wire or wires L, the wires M, and the wires N include carbon steel.

25. A multi-strand steel cable according to claim 24 , wherein a carbon content of the carbon steel is from 0.4% to 1.0%.