MULTI-STRAND CABLE OF 1XN STRUCTURE FOR PROTECTIVE REINFORCEMENT OF A TIRE

Abstract

A method is provided for manufacturing a multistrand cable having a 1×N structure and including a single layer of N strands wound in a helix. Each strand includes an internal layer of M internal threads and an external layer of P external threads. The method includes a step of individually assembling each of the N strands, during which, in chronological order, the M internal threads are wound, the P external threads are wound, and the M internal threads and the P external threads are elongated such that a structural elongation associated with the P external threads of each strand is greater than or equal to 0.05%. The method further includes a step of collectively assembling the N strands, during which the N strands are wound to form the cable.

Claims

1-21. (canceled)

22. A method for manufacturing a multistrand cable having a 1×N structure and including a single layer of N strands wound in a helix, in which each strand includes an internal layer of M internal threads wound in a helix and an external layer of P external threads wound in a helix around the internal layer, the method comprising steps of: individually assembling each of the N strands by twisting, during which, in chronological order: the M internal threads are wound in a helix to form the internal layer, the P external threads are wound in a helix around the internal layer, and the M internal threads and the P external threads are elongated such that a structural elongation (Asp) associated with the P external threads of each strand is greater than or equal to 0.05%; and collectively assembling the N strands by twisting, during which the N strands are wound in a helix to form the cable.

23. The method according to claim 22, wherein the structural elongation (Asp) of each strand associated with the P external threads is greater than or equal to 0.07%.

24. The method according to claim 22, wherein the structural elongation (Asp) of each strand associated with the P external threads is greater than or equal to 0.09%.

25. The method according to claim 22, wherein a structural elongation (As) of each strand is greater than or equal to 0.10%.

26. The method according to claim 22, wherein a structural elongation (As) of each strand is greater than or equal to 0.20%.

27. The method according to claim 22, wherein, during the step of individually assembling each of the N strands, the M internal threads and the P external threads are elongated such that each thread of the P external threads has an elongation length greater than an elongation length of each thread of the M internal threads.

28. The method according to claim 22, wherein the M internal threads and the P external threads are elongated by applying an additional twist to each strand after the P external threads have been wound in a helix around the internal layer.

29. The method according to claim 28, wherein the additional twist is applied to each strand using a member that is mounted to rotate about an axis of rotation (X) substantially parallel to a direction (D) in which each strand passes through the member.

30. The method according to claim 29, wherein the member includes at least one pulley around at least a part of which each strand is made to pass.

31. The method according to claim 30, wherein the member includes at least two pulleys arranged such that each strand follows a path that defines at least one loop around at least one of the pulleys.

32. The method according to claim 22, wherein, during the step of individually assembling each of the N strands, a tensile force is applied to the internal layer and a tensile force is applied to the external layer, with the tensile force applied to the internal layer being greater than the tensile force applied to the external layer.

33. The method according to claim 22, wherein, during the step of collectively assembling the N strands: the N strands are wound in a helix at a pitch p3, the N strands are overtwisted so as to obtain a temporary pitch p3′<p3, and the N strands are untwisted to the pitch p3 so as to obtain a residual torque of substantially zero.

34. The method according to claim 22, wherein: during the step of individually assembling each of the N strands, the M internal threads and the P external threads are wound at intermediate pitches p1′ and p2′, respectively, and during the step of collectively assembling the N strands, the N strands are wound at a pitch p3 such that the M internal threads and the P external threads have final pitches p1 and p2, respectively, satisfying a relationship of p2/p2′<p1/p1′.

35. The method according to claim 22, wherein: during the step of individually assembling each of the N strands, the M internal threads and the P external threads are wound at intermediate pitches p1′ and p2′, respectively, and during the step of collectively assembling the N strands, the N strands are wound at a pitch p3 such that the M internal threads and the P external threads have final pitches p1 and p2, respectively, satisfying a relationship of 1.3×p2/p2′<p1/p1.

36. A strand comprising: an internal layer of M internal threads wound in a helix; and an external layer of P external threads wound in a helix around the internal layer, wherein a structural elongation (Asp) associated with the P external threads is greater than or equal to 0.05%.

37. A multistrand cable having a 1×N structure, the cable comprising a single layer of N strands wound in a helix, wherein: each strand includes an internal layer of M internal threads wound in a helix and an external layer of P external threads wound in a helix around the internal layer, and the cable is produced by a method that includes steps of: individually assembling each of the N strands by twisting, during which, in chronological order: the M internal threads are wound in a helix to form the internal layer, the P external threads are wound in a helix around the internal layer, and the M internal threads and the P external threads are elongated such that a structural elongation (Asp) associated with the P external threads of each strand is greater than or equal to 0.05%, and collectively assembling the N strands by twisting, during which the N strands are wound in a helix to form the cable.

38. The multistrand cable according to claim 37, wherein N=3.

39. The multistrand cable according to claim 37, wherein N=4.

40. The multistrand cable according to claim 37, wherein M=3, 4, or 5.

41. The multistrand cable according to claim 37, wherein M=3.

42. The multistrand cable according to claim 37, wherein P=7, 8, 9, 10, or 11.

43. The multistrand cable according to claim 37, wherein P=8.

44. The multistrand cable according to claim 37, wherein the external layer of each strand is not compact.

45. The multistrand cable according to claim 37, wherein the M internal threads are wound in a helix at a pitch p1, with p1 being in a range of 3 mm to 11 mm.

46. The multistrand cable according to claim 37, wherein the M internal threads are wound in a helix at a pitch p1, with p1 being in a range of 5 mm to 9 mm.

47. The multistrand cable according to claim 37, wherein the P external threads are wound in a helix at a pitch p2, with p2 being in a range of 6 mm to 14 mm.

48. The multistrand cable according to claim 37, wherein the P external threads are wound in a helix at a pitch p2, with p2 being in a range of 8 mm to 12 mm.

49. The multistrand cable according to claim 37, wherein the N strands are wound in a helix at a pitch p3, with p3 being in a range of 10 mm to 30 mm.

50. The multistrand cable according to claim 37, wherein the N strands are wound in a helix at a pitch p3, with p3 being in a range of 15 mm to 25 mm.

51. A tire for a civil engineering vehicle, the tire comprising a multistrand cable having a 1×N structure, the cable including a single layer of N strands wound in a helix, wherein: each strand includes an internal layer of M internal threads wound in a helix and an external layer of P external threads wound in a helix around the internal layer, and the cable is produced by a method that includes steps of: individually assembling each of the N strands by twisting, during which, in chronological order: the M internal threads are wound in a helix to form the internal layer, the P external threads are wound in a helix around the internal layer, and the M internal threads and the P external threads are elongated such that a structural elongation (Asp) associated with the P external threads of each strand is greater than or equal to 0.05%, and collectively assembling the N strands by twisting, during which the N strands are wound in a helix to form the cable.

Description

[0074] The invention will be better understood from reading the following description, which is given solely by way of non-limiting example and with reference to the drawings in which:

[0075] FIG. 1 is a simplified view in section of a tire according to the invention;

[0076] FIG. 2 is a detail view of the part I of the tire in FIG. 1;

[0077] FIG. 3 is a schematic view in section perpendicular to the axis of the cable (which is assumed to be straight and at rest) of a cable according to a first embodiment of the invention;

[0078] FIG. 4 is a schematic view in section perpendicular to the axis of the cable (which is assumed to be straight and at rest) of a cable according to a second embodiment of the invention;

[0079] FIGS. 5 and 6 are schematic views of an installation for implementing the method according to the invention;

[0080] FIG. 7 is a schematic view of an element of the installation in FIG. 5; and

[0081] FIG. 8 is a graph illustrating force-elongation curves for a strand of one of the cables according to the invention in FIGS. 3 and 4 and of a prior art strand.

EXAMPLE OF TIRES AND CABLES ACCORDING TO THE INVENTION

[0082] A frame of reference X, Y, Z corresponding to the usual axial, radial and circumferential orientations, respectively, of a tire has been depicted in the figures.

[0083] FIGS. 1 and 2 show a tire for a civil engineering-type vehicle, for example of the “dumper” type, denoted by the overall reference 10. Thus, the tire 10 has a size of the W R U type, for example 40.00 R 57 or 59/80 R 63.

[0084] In a manner known to a person skilled in the art, W:

[0085] when it is in the form H/B, denotes the nominal aspect ratio H/B as defined by the ETRTO (H being the height of the section of the tire and B being the width of the section of the tire) and,

[0086] when it is in the form H.00 or B.00, in which H=B, H and B being as defined above. U represents the diameter, in inches, of the rim seat on which the tire is intended to be mounted, and R denotes the type of carcass reinforcement of the tire, in this case radial. U≧35, preferably U≧49 and more preferably U≧57.

[0087] The tire 10 has a crown 12 reinforced by a crown reinforcement 14, two sidewalls 16 and two beads 18, each of these beads 18 being reinforced with a bead wire 20. The crown 12 is surmounted by a tread 22. The crown reinforcement 14 is arranged radially on the inside of the tread 22. A carcass reinforcement 24, arranged radially on the inside of the crown reinforcement 14, is anchored in each bead 18, in this case wrapped around each bead wire 20 and comprises a turn-up 26 disposed towards the outside of the tire 10, which is shown mounted on a rim 28 here.

[0088] The carcass reinforcement 24 comprises at least one carcass ply 30 comprising reinforcing elements known as carcass reinforcing elements (not shown). The carcass reinforcing elements make an angle greater than or equal to 65°, preferably greater than or equal to 80°, with respect to the circumferential direction Z of the tire 10. Examples of such carcass reinforcing elements are described in the documents EP0602733 and also EP0383716.

[0089] The tire 10 also comprises a sealing ply 32 made up of an elastomer, for example of butyl, (commonly known as “inner liner”) which defines the radially internal face 34 of the tire 10 and which is intended to protect the carcass ply 30 from the diffusion of air coming from the space inside the tire 10.

[0090] The crown reinforcement 14 comprises, radially from the outside to the inside of the tire 10, a protective reinforcement 36 arranged radially on the inside of the tread 22, a working reinforcement 38 arranged radially on the inside of the protective reinforcement 36 and a hoop reinforcement 39 arranged radially on the inside of the working reinforcement 38. Thus, the protective reinforcement 36 is interposed radially between the tread 22 and the working reinforcement 38.

[0091] The protective reinforcement 36 comprises first and second protective plies 42, 44, the first protective ply 42 being arranged radially on the inside of the second protective ply 44. The first and second protective plies 42, 44 comprise reinforcing elements known as protective reinforcing elements (not shown).

[0092] The protective reinforcing elements are arranged side by side parallel to one another in a main direction substantially perpendicular to the overall direction in which these reinforcing elements extend. The protective reinforcing elements are crossed from one protective ply 42, 44 to the other. Each protective reinforcing element, in this case the overall direction in which these reinforcing elements extend, makes an angle at least equal to 10°, preferably in the range from 10° to 35° and more preferably from 15° to 30°, with the circumferential direction Z of the tire 10. In this case, the angle is equal to 24°.

[0093] With reference to FIG. 3, each protective reinforcing element comprises a multistrand cable 46 of 1×N structure. The cable 46 comprises a single layer 48 of N strands 50 wound in a helix at a pitch p3. The N strands 50 are wound in a Z or S direction.

[0094] Each strand 50 comprises an internal layer 52 of M internal threads 54 wound in a helix at a pitch p1 and an external layer 56 of P external threads 58 wound in a helix around the internal layer 52 at a pitch p2. In this case, each strand 50 is made up of the internal layer 52 and of the external layer 56. Each strand 50 therefore has no wrapping wire.

[0095] Each internal thread 54 and external thread 58 has a diameter ranging from 0.12 mm to 0.50 mm, preferably from 0.25 mm to 0.45 mm, and more preferably from 0.30 to 0.40 mm and in this case equal to 0.35 mm. Each internal thread 54 and external thread 58 is metallic, in this case made of HT (“High Tensile”) grade steel having a breaking strength equal to 2765 MPa. Other grades of steel can of course be used. In further embodiments, the diameter of the internal threads 54 can be different from the diameter of the external threads 58.

[0096] The external layer 56 of each strand 50 is not compact and unsaturated.

[0097] The winding pitch p1 of the M internal threads 54 ranges from 3 to 11 mm, preferably from 5 to 9 mm and in this case is equal to 6.7 mm. The winding pitch p2 of the P external threads 58 ranges from 6 to 14 mm, preferably from 8 to 12 mm and in this case is equal to 10 mm. Finally, the winding pitch p3 of the N strands 50 ranges from 10 to 30 mm, preferably from 15 to 25 mm and in this case is equal to 20 mm.

[0098] The internal threads 54, the external threads 58 and the N strands are wound in the same direction, Z or S.

[0099] In the first embodiment illustrated in FIG. 3, N=3 or N=4, and in this case N=4. Also, M=3, 4 or 5 and in this case M=3. Finally, P=7, 8, 9, 10 or 11 and in this case P=8.

[0100] In the second embodiment of the cable 46 illustrated in FIGS. 4, N=3, M=3 and P=8.

[0101] Returning to FIG. 2, the working reinforcement 38 comprises first and second working plies 60, 62, the first working ply 60 being arranged radially on the inside of the second working ply 62. The first and second working plies 60, 62 comprise reinforcing elements known as working reinforcing elements (not shown).

[0102] The working reinforcing elements are arranged side by side parallel to one another in a main direction substantially perpendicular to the overall direction in which these reinforcing elements extend. The working reinforcing elements are crossed from one working ply 60, 62 to the other. Each working reinforcing element, in this case the overall direction in which these reinforcing elements extend, makes an angle at most equal to 60°, preferably in the range from 15° to 40°, with the circumferential direction Z of the tire 10. In this case, the angle of the reinforcing elements of the first working ply is equal to 19° and the angle of the reinforcing elements of the second working ply is equal to 33°.

[0103] Examples of such working reinforcing elements are described in the documents EP0602733 and also EP0383716.

[0104] The hoop reinforcement 39, also known as limiting block, the function of which is to partially absorb the mechanical stresses due to inflation, comprises first and second hooping plies 64, 66, the first hooping ply 64 being arranged radially on the inside of the second hooping ply 66.

[0105] Each hooping ply 64, 66 comprises metal hoop reinforcing elements (not shown), for example metal cables, as described in FR 2 419 181 or FR 2 419 182, that make an angle at most equal to 10°, preferably in the range from 5° to 10°, with the circumferential direction Z of the tire 10. In this case, the angle is equal to 8°. The hoop reinforcing elements are crossed from one hooping ply 64, 66 to the other.

Example of a Method for Manufacturing a Multistrand Cable According to the Invention

[0106] FIGS. 5, 6 and 7 illustrate an installation 68 for manufacturing the cable 46 as described above.

[0107] The installation 68 comprises an installation 70 for manufacturing each strand 50, shown in FIG. 5, and an installation 72 for assembling the strands 50, shown in FIG. 6.

[0108] It will be recalled that there are two possible techniques for assembling metal threads: [0109] Either by cabling: in which case the threads undergo no twisting about their own axis, on account of a synchronous rotation before and after the assembling point; [0110] Or by twisting: in which case the threads undergo both a collective twist and an individual twist about their own axis, thereby generating an untwisting torque on each of the threads and on the strand or the cable itself.

[0111] In accordance with the invention, the method according to the invention uses twisting and not cabling.

[0112] The installation 70 for manufacturing each strand 50 comprises, from upstream to downstream in the direction in which the strand 50 passes, means 74 for feeding the M internal threads 54, means 76 for assembling the M internal threads 54 by twisting, means 77 for setting the assembled M internal threads in rotation, means 78 for feeding the P external threads 58, means 80 for assembling the P external threads 58 around the internal layer 52 by twisting, means 81 for setting each strand 50 in rotation, means 82 for elongating the M internal threads and the P external threads, means 83 for tensioning the strand 50 and means 84 for storing the strand 50.

[0113] The assembly 72 for assembling the strands 50 comprises, from upstream to downstream in the direction in which the cable 46 passes, means 86 for feeding the N strands 50, means 88 for assembling the N strands 50 together by twisting, means 89 for setting the cable 46 in rotation, means 93 for aerating and balancing the cable, means 90 for tensioning the cable 46 and means 91 for storing the cable 46.

[0114] With reference to FIG. 5, the means 74 for feeding the M internal threads 54 comprise reels 92 for unwinding each internal thread 54. The means 76 for assembling the M internal threads comprise a distributor 94 and an assembly guide 96 defining an assembly point P1. The means for setting in rotation 77 comprise two flywheels 97 arranged downstream of the assembly point P1. A rotary feed is thus spoken of.

[0115] The means 78 for feeding the P external threads 58 comprise reels 98 for unwinding each external thread 58. The means 80 for assembling the P external threads comprise a distributor 100 and an assembly guide 102 defining an assembly point P2. The means for setting in rotation 81 comprise two flywheels 103 arranged downstream of the assembly point P2. Rotary reception is thus spoken of.

[0116] With reference to FIG. 7, the means 82 for elongating the M internal threads and the P external threads comprise a member 104 that is mounted so as to rotate about an axis of rotation X substantially parallel to the direction D in which each strand 50 passes through the member 104. The member 104 that is mounted so as to rotate comprises at least one pulley 106, around at least a part of which each strand 50 is made to pass. In the present case, the member 104 that is mounted so as to rotate comprises several pulleys, in this case two pulleys 106. In the member 104, each strand 50 follows a path defining at least one loop around at least one of the pulleys 106. In this case, each strand follows a path defining an “8” on its side and is wrapped around each pulley 106. In this case, the member 104 is a two-pulley twister.

[0117] The means 83 for tensioning each strand 50 comprise one or more winches 108 and the means 84 for storing each strand 50 comprise a reel 110 for winding each strand 50.

[0118] Each strand 50 is in this case assembled by twisting.

[0119] With reference to FIG. 6, the means 86 for feeding the N strands 50 comprise reels 112 for unwinding each strand 50. The means 88 for assembling the N strands 50 together comprise a distributor 114 and an assembly guide 116 defining an assembly point P3. The means 89 for setting the cable 46 in rotation comprise two flywheels 118 arranged downstream of the assembly point P3. The aerating and balancing means 93 comprise an upstream twister 124 and a downstream twister 126. The means 90 for tensioning the cable 46 comprise one or more winches 120 and the means 91 for storing the cable 46 comprise a reel 122 for winding the cable 46.

[0120] A method for manufacturing the cable 46 that is implemented by means of the installation 68 described above will now be described.

[0121] The method comprises two steps of assembling by twisting. The first step is a step of individually assembling each of the N strands 50 by twisting that is implemented by the installation means 70. The second step is a step of collectively assembling the N strands 50 by twisting that is implemented by the installation means 72.

[0122] During the first step of individually assembling by twisting, the M internal threads 54 are wound in a helix, at an intermediate pitch p1′, in order to form the internal layer 52. In this case, p1′=10 mm.

[0123] Then, still in this first step of individually assembling by twisting, the P external threads 58 are wound in a helix, at an intermediate pitch p2′, around the internal layer 52. In this case, p2′=20 mm.

[0124] Next, still in this first step of individually assembling, the M internal threads 54 and the P external threads 58 are elongated such that each P external thread 58 has an elongation length greater than an elongation length of each M internal thread 54. The M internal threads 54 and the P external threads 58 are elongated by plastic deformation by means of the means 82. In the present case, the M internal threads 54 and the P external threads 58 are elongated by plastic deformation by applying an additional twist to each strand 50 after the P external threads 58 have been wound in a helix around the internal layer 52. Then, each strand 50 that is thus obtained is stored on the storage means 84. The additional twist is applied by regulating the value of the speed of rotation of the rotating member 104 about the axis X. A person skilled in the art will know how to find the value of this speed of rotation depending on the desired lengths of elongation.

[0125] During the step of individually assembling each of the N strands 50, a tensile force T1 is applied to the internal layer 52. During this step of individually assembling each of the N strands 50, a tensile force T2 is also applied to the external layer 56. The tensile force T1 applied to the internal layer 52 is greater than the tensile force T2 applied to the external layer 56.

[0126] During the second step of collectively assembling the N strands 50, N strands 50 are wound in a helix, at the pitch p3, to form the cable at the pitch p3, as illustrated in FIG. 6. To this end, during the step of collectively assembling the N strands 50, the N strands 50 are first of all wound in a helix at the pitch p3. Then, by means of the upstream twister 124, the N strands 50 are overtwisted so as to obtain a temporary pitch p3′<p3. Next, the N strands 50 are untwisted to the pitch p3 so as to obtain a residual torque of substantially zero by means of the downstream twister 126.

[0127] During this second step of collectively assembling the N strands 50, the N strands are wound at the pitch p3 such that the M internal threads 54 and the P external threads 58 have final pitches p1 and p2, respectively, satisfying p2/p2′<p1/p1′, preferably 1.3.Math.p2/p2′<p1/p1′. In this case, p1=6.7 mm and p2=10 mm

Comparative Tests

[0128] A prior art cable C0 and three cables 46, 47 and 49 according to the invention were compared in the following text. The characteristics of these cables C0, 46 and 47 are compiled in Table 1 below.

[0129] The cable C0 was manufactured using a method in accordance with the prior art, that is to say without a step of elongating the M internal threads and the P external threads. The prior art method is associated with the reference “1”.

[0130] The cables 46, 47 and 49 according to the invention were manufactured by implementing a method according to the invention. Each cord 46 and 49 is obtained by implementing the above-described method according to the invention, which is associated with the reference “2”, wherein, during the step of individually assembling each of the N strands, a tensile force is applied to the internal layer that is greater than the tensile force applied to the external layer. The cord 47 is obtained by implementing a method according to the invention, which is associated with the reference “3”, wherein, during the step of individually assembling each of the N strands, the same tensile force is applied to the internal layer and to the external layer.

[0131] Each cord tested has the following final pitches p1, p2 and p3: p1=6.7 mm, p2=10 mm and p3=20 mm.

[0132] Force at break, denoted Fm (maximum load in N), is measured under tension in accordance with standard ISO 6892-1, October 2009, on cables directly produced by the manufacturing method.

[0133] The number of instances of emergence of internal threads per metre of strand

[0134] Ns is measured by disassembling the cable tested and counting, for each strand, the number of instances of emergence of internal threads. Thus, for N strands, a total number of instances of emergence of internal threads per metre of cable is obtained. By dividing this total number by N, the number Ns of instances of emergence of internal threads per metre of strand is obtained.

[0135] The number of instances of bowing of internal threads that is observed per meter of strand Nf is also measured in a similar manner. Bowing corresponds to an abnormally large curvature of a thread without this otherwise constituting a radial emergence.

[0136] Since they do not have or virtually do not have instances of emergence of internal threads, the cables 46, 47 and 49 do not have a variable diameter. Thus, all the problems linked to this variation in the diameter of the cable are avoided, thereby making it less tedious to manufacture and reducing its cost.

[0137] On comparing the cables 46 (method 2) and 47 (method 3), it will be noted that applying, during the step of individually assembling each of the N strands (cable 46, method 2), a tensile force to the internal layer that is greater than the tensile force applied to the external layer makes it possible to reduce even further the number of instances of bowing Nf of internal threads compared with a method comprising an assembly step during which the tensile force applied to the internal layer is equal to the tensile force applied to the external layer (cable 47, method 3). The fact that the cable 49 (method 2) has a number of instances of bowing Nf equal to that of the cable 47 (method 3) is linked to the fact that the associated structural elongation Asp associated with the P external threads of the cable 49 is less than that of the cable 47, this favouring the occurrence of instances of bowing compared with the cable 47.

[0138] FIG. 8 shows the force-elongation curve I of a strand (3+8)×0.35 of the cable C0 and the force-elongation curve II of a strand of the cable 46. Each of these curves represents the variation in the elongation A (in %, on the abscissa) depending on the force F (in newtons, on the ordinate) applied thereto. This force-elongation curve is obtained under experimental conditions in accordance with the standard ISO 6892-1, October 2009.

[0139] It will be noted that each curve comprises three parts. The first part corresponds to the moving of the M internal threads towards one another. The second part corresponds to the moving of the P external threads towards one another. The third part corresponds to the elastic elongation of the M internal threads and P external threads. For each of the parts, the tangent to this part has been drawn. Thus, the tangent to the first part intersects the abscissa axis at a point Asi corresponding to the structural elongation associated with the spacing apart of the M internal threads. The tangent to the second part intersects the abscissa axis at a point Ase, the difference Ase-Asi corresponding to the structural elongation Asm associated with the spacing apart of the M internal threads. The tangent to the third part intersects the abscissa axis at a point As, the difference As-Ase corresponding to the structural elongation Asp associated with the spacing apart of the P external threads.

[0140] It will be noted that the spacing apart of the P external threads of the strand of curve II makes it possible to obtain a strand having much greater structural elongation associated with the P external threads than the strand of curve I. Specifically, the structural elongation Asp associated with the P external threads of the strand of curve II is greater than or equal to 0.05%, or even greater than or equal to 0.07%, preferably greater than or equal to 0.09%. In the present case, the structural elongation Asp associated with the P external threads of the strand of curve II is greater than or equal to 0.15%, or even greater than or equal to 0.20%, preferably greater than or equal to 0.25%. In this case, Asp=0.31%.

[0141] It will also be noted that the structural elongation As of the strand of curve II is much greater than the structural elongation of the strand of curve I. Specifically, the elongation As of the strand of curve II is greater than or equal to 0.10%, preferably greater than or equal to 0.15% and more preferably greater than or equal to 0.20%. In the present case, the elongation As of the strand of curve II is greater than or equal to 0.25%, preferably greater than or equal to 0.30% and more preferably greater than or equal to 0.35%. In this case, As=0.43%.

[0142] Moreover, it is noted that, with an identical structure, the cables 46, 47 and 49 allow a minimum increase of 5% in force at break compared with the cable C0. A posteriori, the inventors originating the invention have discovered that, on the one hand, in the cable C0, the internal threads emerging between the external threads rubbed between the latter, resulting in a drop in the force at break of the cable. On the other hand, the inventors hypothesize, a posteriori, that since the M internal threads do not have any excess length in the cable according to the invention, said M internal threads contribute, when the cable is tensioned, to the mechanical strength of the cable at the same time as the P external threads. By contrast, in the prior art cable, the M internal threads have an excess length, these M internal threads not being involved, when the cable is tensioned, in the mechanical strength of the cable at the same time as the P external threads, this reducing the force at break of the prior art cable compared with the cable of the invention.

TABLE-US-00001 TABLE 1 Steel Fm Ase As Asp Ns Nf Cable Structure Method grade N % % % m.sup.−1 m.sup.−1 C0 4 × (3 + 8) × 0.35 1 HT 9173 0.05 0.09 0.04 20 >20 46 4 × (3 + 8) × 0.35 2 HT 9612 0.12 0.43 0.31 0 2 47 4 × (3 + 8) × 0.35 3 HT 9495 0.24 0.35 0.11 0 4 49 4 × (3 + 8) × 0.35 2 HT 9450 0.11 0.20 0.09 0 4

[0143] The invention is not limited to the embodiments described above.

[0144] Specifically, each strand could also comprise an intermediate layer, interposed between the internal layer and the external layer, the threads of the intermediate layer being wound in a helix around the internal layer and the threads of the external layer being wound in a helix around the intermediate layer. In this embodiment, the cable is made up of the internal layer, of the intermediate layer and of the external layer.