HIGHLY COMPRESSIBLE OPEN REINFORCING CORD

Abstract

A cord (50) comprises a single layer (52) made up of N helically wound metal filamentary elements (54) having an outer diameter D, the metal filamentary elements (54) defining an internal enclosure (58) of the cord of diameter Dv. Each metal filamentary element (54) has a diameter Df and a helix radius of curvature Rf. With this cord (50), D, Dv, Df and Rf being expressed in millimeters: 0.10≤Jr≤0.25, 9≤Rf/Df≤30, and 1.60≤Dv/Df≤3.20, where Jr=N/(π*(D−Df))×(Dh×Sin(π/N)−(Df/Cos(αx π/180))) and α is the helix angle, expressed in degrees, of each metal filamentary element (54).

Claims

1.-15. (canceled)

16. A cord comprising a single layer made up of N helically wound metal filamentary elements having an outer diameter D, each metal filamentary element describing, when the cord extends in a substantially rectilinear direction, a helical path about a main axis substantially parallel to the substantially rectilinear direction, such that, in a section plane substantially perpendicular to the main axis, a distance between a center of each metal filamentary element and the main axis is equal to half a helix diameter Dh and is substantially constant and identical for all the metal filamentary elements, the metal filamentary elements defining an internal enclosure of a cord of diameter Dv, each metal filamentary element having a diameter Df and a helix radius of curvature Rf defined by Rf=P/(π×Sin(2α)), where P is a pitch of each metal filamentary element expressed in millimeters and a is a helix angle of each metal filamentary element, wherein, with Dh, D, Dv, Df and Rf being expressed in millimeters:
0.10≤Jr≤0.25
9≤Rf/Df≤30, and
1.60≤Dv/Df≤3.20, where Jr=N/(π*(D−Df))×(Dh×Sin(π/N)−(Df/Cos(α×π/180))), a is the helix angle, expressed in degrees, of each metal filamentary element and Dv=Dh−Df.

17. The cord according to claim 16, wherein 0.14≤Jr≤0.25.

18. The cord according to claim 16, wherein 9≤Rf/Df≤25.

19. The cord according to claim 16, wherein 1.70≤Dv/Df≤3.20.

20. The cord according to claim 16, wherein the helix radius of curvature Rf is such that 4.10 mm≤Rf≤5.30 mm.

21. The cord according to claim 16, wherein the helix diameter Dh of each metal filamentary element is such that 0.70 mm≤Dh≤1.60 mm.

22. The cord according to claim 16, wherein Df is such that 0.10 mm≤Df≤0.50 mm.

23. The cord according to claim 16, wherein Dv is such that Dv≥0.50 mm.

24. The cord according to claim 16, wherein each metal filamentary element is wound at a pitch P such that 3 mm≤P≤15 mm.

25. The cord according to claim 16, wherein D≤2.10 mm.

26. The cord according to claim 16, wherein a ratio K of the pitch P to the diameter Df of each metal filamentary element, P and Df being expressed in millimeters, is such that 19≤K≤44.

27. The cord according to claim 16, wherein the helix angle α is such that 13°≤α≤30°.

28. The cord according to claim 16, wherein the cord has a structural elongation As such that As≥1.5%, the structural elongation As being determined by applying the standard ASTM D2969-04 of 2014 to the cord so as to obtain a force-elongation curve, the structural elongation As being equal to elongation, in %, corresponding to a projection onto an elongation axis of intersection between a tangent to a structural portion of the force-elongation curve and a tangent to an elastic portion of the force-elongation curve.

29. The cord according to claim 16, wherein the cord has, once embedded in a crosslinked standard elastomeric matrix having a modulus in extension at 10% elongation ranging from 5 MPa to 10 MPa, a modulus of elasticity in extension greater than or equal to 100 GPa, the modulus of elasticity in extension at 10% elongation being determined according to the standard ASTM D2969-04 of 2014.

30. A tire comprising the cord according to claim 16, the cord embedded in an elastomeric matrix.

Description

[0615] The invention will be understood better on reading the following description, which is given purely by way of non-limiting example and with reference to the drawings, in which:

[0616] FIG. 1 is a view in radial section of a tyre according to a first embodiment of the invention;

[0617] FIG. 2 is a cutaway view of the tyre in FIG. 1 illustrating the projection onto the equatorial circumferential plane E of the hooping filamentary reinforcing elements, of the working filamentary reinforcing elements and of the carcass filamentary reinforcing elements;

[0618] FIG. 3 is a view of the carcass filamentary reinforcing elements arranged in the sidewall of the tyre in FIG. 1 in projection onto the median plane M of the tyre;

[0619] FIG. 4 is a view in cross section perpendicular to its axis of a cord according to a first embodiment of the invention (assumed to be rectilinear and at rest);

[0620] FIG. 5 shows a stress-elongation curve of the cord in FIG. 4;

[0621] FIG. 6 shows a stress-elongation curve of the cord in FIG. 4, embedded in a crosslinked standard elastomeric matrix;

[0622] FIGS. 7 to 14 show an installation and a method for manufacturing the cord in FIG. 4;

[0623] FIG. 15 is figure similar to FIG. 4 of a cord according to a second embodiment;

[0624] FIGS. 16 and 17 are curves similar to those in FIGS. 5 and 6 of the cord according to the second embodiment;

[0625] FIG. 18 is a view similar to the one in FIG. 1 of a tyre according to a second embodiment of the invention;

[0626] FIGS. 19 and 20 are views similar to those in FIGS. 2 and 3 of the tyre in FIG. 18 according to the second embodiment of the invention.

TYRE ACCORDING TO A FIRST EMBODIMENT OF THE INVENTION

[0627] FIGS. 1 and 2 show a reference frame X, Y, Z corresponding to the usual axial (X), radial (Y) and circumferential (Z) directions, respectively, of a tyre.

[0628] FIG. 1 schematically shows a view in radial section of a tyre according to the invention denoted by the general reference 10. The tyre 10 substantially exhibits revolution about an axis substantially parallel to the axial direction X. The tyre 10 is in this case intended for a passenger vehicle.

[0629] With reference to FIGS. 1 and 2, the tyre 10 has a crown 12 comprising a crown reinforcement 14 comprising a working reinforcement 15 comprising two working plies 16, 18 comprising working filamentary reinforcing elements 46, 47, respectively, and a hoop reinforcement 17 comprising a single hooping ply 19 comprising at least one hooping filamentary reinforcing element 48. The crown reinforcement 14 is in this case made up of the working reinforcement 15 and the hoop reinforcement 17. The crown reinforcement 14 extends in the crown 12 in the circumferential direction Z of the tyre 10. The crown 12 comprises a tread 20 arranged radially on the outside of the crown reinforcement 14. In this case, the crown 12 is made up of the tread 20 and the crown reinforcement 14. In this case, the hoop reinforcement 17, in this case the hooping ply 19, is radially interposed between the working reinforcement 15 and the tread 20. In this case, the working reinforcement 15 comprises only two working plies 16, 18 and the hoop reinforcement 17 comprising a single hooping ply 19. In this case, the working reinforcement 15 is made up of the two working plies 16, 18 and the hoop reinforcement 17 is made up of the hooping ply 19. The crown reinforcement 14 is made up of the working reinforcement 15 and the hoop reinforcement 17. The crown 12 is in this case made up of the tread 20 and the crown reinforcement 14.

[0630] The tyre 10 also comprises two sidewalls 22 extending the crown 12 radially towards the inside. The tyre 10 also has two beads 24 radially on the inside of the sidewalls 22, each having an annular reinforcing structure 26, in this case a bead wire 28, surmounted by a mass of filling rubber 30 on the bead wire, and also a radial carcass reinforcement 32. Each sidewall 22 connects each bead 24 to the crown 12.

[0631] The carcass reinforcement 32 has a carcass ply 34 comprising a plurality of carcass filamentary reinforcing elements 44, the carcass ply 34 being anchored to each of the beads 24 by a turnup around the bead wire 28 so as to form, in each bead 24, a main strand 38 extending from the beads through the sidewalls towards the crown 12, and a turnup strand 40, the radially outer end 42 of the turnup strand 40 being radially on the outside of the annular reinforcing structure 26. The carcass reinforcement 32 thus extends from the beads 24 in and through the sidewalls 22, and into the crown 12. The carcass reinforcement 32 is arranged radially on the inside of the crown reinforcement 14 and the hoop reinforcement 17. The crown reinforcement 14 is therefore radially interposed between the carcass reinforcement 32 and the tread 20. The carcass reinforcement 32 comprises a single carcass ply 34. In this case, the carcass reinforcement 32 is formed by the carcass ply 34. The carcass reinforcement 32 is arranged so as to be directly radially in contact with the crown reinforcement 14 and the crown reinforcement 14 is arranged so as to be directly radially in contact with the tread 20.

[0632] The tyre 10 also comprises an airtight internal layer, preferably made of butyl, that is situated axially on the inside of the sidewalls 22 and radially on the inside of the crown reinforcement 14 and extends between the two beads 24.

[0633] Each working ply 16, 18, hooping ply 19 and carcass ply 34 comprises an elastomeric matrix in which reinforcing elements of the corresponding ply are embedded. Each elastomeric matrix of the working plies 16, 18, hooping ply 19 and carcass ply 34 is based on a conventional elastomeric composition for the skim coating of reinforcing elements conventionally comprising a diene elastomer, for example natural rubber, a reinforcing filler, for example carbon black and/or silica, a crosslinking system, for example a vulcanizing system, preferably comprising sulphur, stearic acid and zinc oxide, and possibly a vulcanization accelerant and/or retarder and/or various additives.

[0634] With reference to FIGS. 2 and 3, each carcass filamentary reinforcing element 44 extends axially from one bead 24 of the tyre 10 to the other bead 24 of the tyre 10. Each carcass filamentary reinforcing element 44 makes an angle A.sub.C greater than or equal to 80°, preferably ranging from 80° to 90°, with the circumferential direction Z of the tyre 10 in the median plane M and equatorial circumferential plane E of the tyre 10, in other words in the crown 12 and in each sidewall 22.

[0635] With reference to FIG. 2, the working filamentary reinforcing elements 46, 47 of each working ply 16, 18 are arranged side by side in a manner substantially parallel to one another. Each working filamentary reinforcing element 46, 47 extends axially from one axial end of the working reinforcement 15 of the tyre 10 to the other axial end of the working reinforcement 15 of the tyre 10. Each working filamentary reinforcing element 46, 48 makes an angle ranging from 10° to 40°, preferably ranging from 20° to 30° and in this case equal to 26° with the circumferential direction Z of the tyre 10 in the median plane M. The orientation of the angle S made by the working filamentary reinforcing elements 46 with the circumferential direction Z of the tyre 10 in the working ply 16 is opposite to the orientation of the angle Q made by the working filamentary reinforcing elements 47 with the circumferential direction Z of the tyre 10 in the other working ply 18. In other words, the working filamentary reinforcing elements 46 in one working ply 16 are crossed with the working filamentary reinforcing elements 47 in the other working ply 18.

[0636] With reference to FIG. 2, the single hooping ply 19 comprises at least the hooping filamentary reinforcing element 48 obtained by embedding the cord 50 in an elastomeric matrix based on the elastomeric composition of the hooping ply 19 and as illustrated in FIG. 4 and described in more detail below. Being embedded in the matrix of the hooping ply 19, the cord 50 within the tyre 10 comprises a filling material for the internal enclosure 58 based on the elastomeric composition of the hooping ply 19, this filling material 53 being situated in the internal enclosure 58 of the cord 50. In this instance, the hooping ply 19 comprises a single hooping filamentary reinforcing element 48 wound continuously over an axial width L.sub.F of the crown 12 of the tyre 10. Advantageously, the axial width L.sub.F is less than the width L.sub.T of the working ply 18. The hooping filamentary reinforcing element 48 makes an angle A.sub.F strictly less than 10° with the circumferential direction Z of the tyre 10, preferably less than or equal to 7°, and more preferably less than or equal to 5°. In this instance, the angle is in this case equal to 5°.

[0637] The carcass filamentary reinforcing elements 44 and working filamentary reinforcing elements 46, 47 are arranged, in the crown 12, so as to define a triangle mesh in projection onto the equatorial circumferential plane E in the radial direction of the tyre.

[0638] Each carcass filamentary reinforcing element 44 is a textile filamentary element and conventionally comprises two multifilament strands, each multifilament strand being made up of a spun yarn of polyester, in this case PET, monofilaments, these two multifilament strands being individually overtwisted at 240 turns.Math.m.sup.−1 in one direction and then twisted together at 240 turns.Math.m.sup.−1 in the opposite direction. These two multifilament strands are wound in a helix around one another. Each of these multifilament strands has a count equal to 220 tex.

[0639] Each working filamentary reinforcing element 46, 47 is a metal filamentary element and in this case is an assembly of two steel monofilaments that each have a diameter equal to 0.30 mm, the two steel monofilaments being wound together at a pitch of 14 mm.

CORD ACCORDING TO A FIRST EMBODIMENT OF THE INVENTION

[0640] With reference to FIG. 4, the cord 50 according to the invention comprises a single layer 52 of helically wound metal filamentary elements 54. In this instance, the cord 50 is made up of the single layer 52, in other words the cord 50 does not comprise any other metal filamentary element than those of the layer 52. The layer 52 is made up of N helically wound metal filamentary elements, N ranging from 3 to 18, preferably from 5 to 12, more preferably from 6 to 9 and in this case N=9. The cord 50 has a main axis A extending substantially parallel to the direction in which the cord extends along its greatest length. Each metal filamentary element 54 of the layer 52 describes, when the cord 50 extends in a substantially rectilinear direction, a helical path about the main axis A substantially parallel to the substantially rectilinear direction, such that, in a section plane substantially perpendicular to the main axis A, the distance between the centre of each metal filamentary element 54 of the layer 52 and the main axis A is substantially constant and identical for all the metal filamentary elements 54 of the layer 52. This constant distance between the centre of each metal filamentary element 54 of the layer 52 and the main axis A is equal to half the helix diameter Dh.

[0641] In the embodiment illustrated, each metal filamentary element 54 comprises a single metal monofilament 56. Each metal filamentary element 54 also comprises a layer (not shown) of a metal coating comprising copper, zinc, tin, cobalt or an alloy of these metals, in this case brass. Each metal monofilament 56 is made of carbon steel and has a tensile strength in this case equal to 3200 MPa.

[0642] The diameter Df of each metal filamentary element 54 is such that 0.10 Df 0.50 mm, preferably 0.15 mm≤Df≤0.50 mm and more preferably 0.15 mm≤Df≤0.45 mm, and, in this first embodiment such that 0.15 mm≤Df≤0.35 mm. In this instance, Df=0.20 mm for all the metal filamentary elements 54. Each metal filamentary element 54 is without preforming marks.

[0643] The cord 50 has a diameter D such that D 2.10 mm, preferably 0.90 mm≤D≤2.10 mm and more preferably 0.95 mm≤D≤2.05 mm, and, in this first embodiment such that 0.95 mm≤D≤1.20 mm. In this instance, D=1.04 mm.

[0644] Advantageously, each metal filamentary element 54 is wound at a pitch P such that 3 mm≤P≤15 mm, preferably 5 mm≤P≤13 mm, more preferably 7 mm≤P≤11 mm, and, in this first embodiment 7 mm≤P≤8.5 mm. In this instance, P=7.8 mm.

[0645] The ratio K of the pitch P to the diameter Df of each metal filamentary element, P and Df being expressed in millimetres, is such that 19≤K≤44, preferably 20≤K≤40, more preferably 23≤K≤39, and, in this first embodiment such that 23≤K≤40 and preferably 25≤K≤39. In this instance, K=39.

[0646] The cord 50 according to the first embodiment has a structural elongation As such that As≥1.5%, preferably 1.5%≤As≤5.0%, more preferably 1.9%≤As≤4.5% and in this case equal to 2.2%. As described above, the value As is determined by plotting a force-elongation curve of the cord 50, applying the standard ASTM D2969-04 of 2014. The curve obtained is shown in FIG. 5. The structural elongation As is determined by determining the projection onto the elongation axis of the intersection between the tangent to the structural portion of the force-elongation curve and the tangent to the elastic portion of the force-elongation curve.

[0647] The helix angle α of each metal filamentary element is such that 13°≤α≤30°, preferably 17°≤α≤26° and in this first embodiment such that 13°≤α≤19.5° and preferably 17°≤α≤19.5°. In this instance, as described above, with the characteristics of the cord 50, α(1)=17.76°, α(2)=18.23° and α(3)=α=18.26°.

[0648] Each metal filamentary element 54 has a helix radius of curvature Rf such that 4.10 mm≤Rf≤5.30 mm and in this first embodiment 4.10 mm≤Rf≤4.25 mm. The radius of curvature Rf is calculated using the relationship Rf=P/(π×Sin(2α)). Since in this case P=7.8 mm and α=18.26°, Rf=4.18 mm.

[0649] The helix diameter Dh of each metal filamentary element is such that 0.70 mm≤Dh≤1.60 mm, preferably 0.75 mm≤Dh≤1.60 mm, more preferably 0.80 mm≤Dh≤1.60 mm and in the first embodiment such that 0.70 mm≤Dh≤0.90 mm, preferably 0.75 mm≤Dh≤0.90 mm, more preferably 0.80 mm≤Dh≤0.90 mm. The helix diameter Dh is calculated using the relationship Dh=P×Tan(α)/π. Since in this case P=7.8 mm and α=18.26°, Dh=0.82 mm.

[0650] The metal filamentary elements 54 define an internal enclosure 58 of the cord 50 of diameter Dv. The enclosure diameter Dv is calculated using the relationship Dv=Dh−Df, in which Df is the diameter of each metal filamentary element and Dh is the helix diameter. Advantageously, Dv is such that Dv≥0.50 mm and preferably 0.50 mm≤Dv≤1.20 mm and in the first embodiment 0.50 mm≤Dv≤0.70 mm, preferably 0.50 mm≤Dv≤0.65 mm. In this case, since Dh=0.82 mm and Df=0.20 mm, Dv=0.62 mm.

[0651] According to the invention, 9≤Rf/Df≤30, preferably 9≤Rf/Df≤25, more preferably 9≤Rf/Df≤22 and in the first embodiment 12≤Rf/Df≤30, preferably 12≤Rf/Df≤25, more preferably 12≤Rf/Df≤22. In this case, Rf/Df=20.7. According to the invention, 1.60≤Dv/Df≤3.20, preferably 1.70≤Dv/Df≤3.20, and in this case Dv/Df=3.10.

[0652] Also, 0.10≤Jr≤0.25 where Jr=N/(π*(D−Df))×(Dh×Sin(π/N)−(Df/Cos(α×π/180))), preferably 0.14≤Jr≤0.25 and in this case Jr=0.24.

[0653] The cord 50 has a modulus of elasticity in extension of the structural portion of less than or equal to 15 GPa, preferably ranging from 2 GPa to 15 GPa, and in this case equal to 5 GPa. Furthermore, the cord 50 has a modulus of elasticity in extension of the elastic portion of greater than or equal to 50 GPa, preferably ranging from 50 GPa to 180 GPa. In the first embodiment, the modulus of elasticity in extension of the elastic portion ranges from 130 to 180 GPa, and is in this case equal to 160 GPa.

[0654] With reference to FIG. 6, the modulus of the cord 50, embedded in a crosslinked standard elastomeric matrix as described above and having a modulus in extension at 10% elongation ranging from 5 MPa to 10 MPa, has a modulus of elasticity in extension greater than or equal to 100 GPa, preferably ranging from 100 GPa to 180 GPa, more preferably from 110 GPa to 180 GPa, and in this case equal to 145 GPa.

METHOD FOR MANUFACTURING THE TYRE ACCORDING TO THE FIRST EMBODIMENT

[0655] The tyre 10 is manufactured using the method described below.

[0656] First of all, the working ply 18 and the carcass ply 34 are manufactured by arranging the filamentary reinforcing elements of each ply parallel to one another and embedding them, for example by skim coating, in an uncrosslinked composition comprising at least an elastomer, the composition being intended to form an elastomeric matrix once crosslinked. A ply known as a straight ply, in which the filamentary reinforcing elements of the ply are parallel to one another and are parallel to the main direction of the ply, is obtained. Then, if necessary, portions of each straight ply are cut at a cutting angle and these portions are butted against one another so as to obtain a ply known as an angled ply, in which the filamentary reinforcing elements of the ply are parallel to one another and form an angle with the main direction of the ply equal to the cutting angle.

[0657] Then, an assembly method is implemented, during which the hoop reinforcement 17, in this case the hooping ply 19, is arranged radially on the outside of the working reinforcement 15. In this instance, in a first variant, a strip with a width B significantly less than L.sub.F is manufactured, in which the hooping filamentary reinforcing element 48 formed by a cord 50 is embedded in the elastomeric matrix based on the uncrosslinked elastomeric composition of the strip, and the strip is wound helically through several turns so to obtain the axial width L.sub.F. In a second variant, the hooping ply 19 having a width L.sub.F is manufactured in a similar manner to the carcass and working plies and the hooping ply 19 is wound through one turn over the working reinforcement 15. In a third variant, the hooping filamentary reinforcing element 48 formed by the cord 50 is wound radially on the outside of the working ply 18, and then a layer based on the uncrosslinked elastomeric composition of the hooping ply 19, in which the hooping filamentary reinforcing element 48 formed by the cord 50 will be embedded during the curing of the tyre, is deposited on top. In the three variants, the bonded filamentary reinforcing element 48 formed by the cord 50 is embedded in a composition in order to form, at the end of the method for manufacturing the tyre, the hooping ply 19 comprising the hooping filamentary reinforcing element 48 formed by the cord 50.

[0658] Then, the carcass reinforcement, the working reinforcement, the hoop reinforcement and the tread are arranged so as to form a green form of tyre in which the compositions of the elastomeric matrices have not yet been crosslinked and are in an uncured state.

[0659] Next, the green form of tyre is shaped so as to at least radially enlarge the green form of tyre. Finally, the compositions of the shaped green form of tyre are crosslinked, for example by curing or vulcanization, so as to obtain the tyre in which each composition exhibits a crosslinked state and forms an elastomeric matrix based on the composition.

INSTALLATION AND METHOD FOR MANUFACTURING THE CORD ACCORDING TO THE FIRST EMBODIMENT

[0660] FIG. 7 shows an installation for manufacturing the cord 50. The installation is denoted by the overall reference 100.

[0661] The installation 100 comprises first of all means for 110 supplying a transitory assembly 220 comprising at least one, and in this case consisting of a layer 130 made up of M′>1 metal filamentary elements 54 helically wound around a transitory core 160. The transitory assembly 220 shown in FIG. 9 comprises the layer 130 made up of the M′ metal filamentary elements 54 and the transitory core 160, the M′ metal filamentary elements 54 being helically wound around the transitory core 160. In this case, the transitory assembly 220 consists of the layer 130 made up of the M′=7 metal filamentary elements 54 and of the transitory core 160, the M′ metal filamentary elements 54 being helically wound around the transitory core 160. The transitory core is in this case a textile filamentary element, more particularly in this case a polyester textile multifilament strand having a count of 334 tex and a diameter of approximately equal to 0.60 mm.

[0662] The supply means 110 comprise means 120 for feeding in the M′ metal filamentary elements 54 and the transitory core 160. The supply means 110 also comprise means 180 for assembling, by twisting, the M′ metal filamentary elements 54 together in the layer 130 of M′ metal filamentary elements 54 around the transitory core 160 so as to form the transitory assembly 220. Furthermore, the supply means 110 comprise means 200 for twist-balancing the transitory assembly 220. On exiting the means 200, each metal filamentary element 54 of the transitory assembly 220 is, in this case, assembled at a transitory pitch of 5 mm. The transitory helix diameter of each metal filamentary element 54 of the transitory assembly 220 is, in this case, substantially equal to 0.80 mm.

[0663] Downstream of the supply means 110, considering the direction of travel of the metal filamentary elements, the installation 100 comprises means 240 for separating the transitory assembly 220 into a first split assembly 250, a second split assembly 270 and the transitory core 160 or one or more ensembles comprising the transitory core 160, in this case the transitory core 160.

[0664] The first split assembly 250, shown in FIG. 10, consists of a layer 260 made up of M1′≥1 helically wound metal filamentary element(s) 54. In this case, M1′=4. The M1′ metal filamentary elements originate from the layer 130 of the transitory assembly 220.

[0665] The second split assembly 270, shown in FIG. 12, consists of a layer 330′ made up of M2′>1 helically wound metal filamentary elements 54. In this case, M2′=5. The M2′ metal filamentary elements originate from the layer 130 of the transitory assembly 220.

[0666] Downstream of the supply means 110, the means 240 for separating the transitory assembly 220 into the first split assembly 250, the second split assembly 270 and the transitory core 160 comprise means 720 for separating the transitory assembly 220 into the first split assembly 250 and a split ensemble 330 comprising at least one layer 330′ made up of M4′=3 metal filamentary elements 54 helically wound around the transitory core 160, the M4′ metal filamentary elements 54 originating from the layer 52 made up of the M′>1 metal filamentary elements 54 of the transitory assembly 220. The split ensemble 330 thus comprises the layer 330′ and the transitory core 160, the M4′ metal filamentary elements 540 being helically wound around the transitory core 160. In this case, the split ensemble 330 is made up of the layer 330′ and of the transitory core 160, the M′4 metal filamentary elements 54 being helically wound around the transitory core 160. In this case, the separation means 720 comprise means 720′ for splitting the transitory assembly 220 into the first split assembly 250 and the split ensemble 330.

[0667] The means 240 for separating the transitory assembly 220 into the first split assembly 250, the second split assembly 270 and the transitory core 160 comprise means 740 for separating the split ensemble 330 into the second split assembly 270 and the transitory core 160. In this case, the separation means 740 comprise means 740′ for splitting the split ensemble 330 into the second split assembly 270 and the transitory core 160.

[0668] In this embodiment, the separation means 720 are arranged upstream of the separation means 740.

[0669] Downstream of the separation means 240, the installation 100 comprises means 370 for reassembling the first split assembly 250 with the second split assembly 270 to form the layer 52 made up of N helically wound metal filamentary elements 54. The separation means 240 and the reassembly means 370 are arranged such that M1′+M2′=M′. In this particular instance, on account of the elastic springback of each metal filamentary element 54 in response to the twisting step, the pitch of each metal filamentary element 54 of the transitory assembly 220 passes from the transitory pitch equal to 5 mm to the pitch P in this case equal to 7.8 mm. A person skilled in the art knows how to determine what transitory pitch to apply in order to obtain the desired pitch P.

[0670] The helix diameter Dh of each metal filamentary element 54 in the cord 50 is in this case substantially greater than the transitory helix diameter of each filamentary element 54 in the transitory assembly 220, on account of the elastic springback. The greater the degree of twist, the greater the extent to which the helix diameter Dh of each metal filamentary element 54 in the cord 50 exceeds the transitory helix diameter of each filamentary element 54 in the transitory assembly 220. A person skilled in the art knows how to determine the transitory helix diameter to be applied in order to obtain the desired helix diameter Dh, depending on the degree of twist and on the nature of the transitory core. The same goes for the enclosure diameter.

[0671] The supply means 110, the separation means 240 and the reassembly means 370 are arranged such that all the N metal filamentary elements 54 have the same diameter Df=0.20 mm, are helically wound at the same pitch P=7.8 mm and have the same helix diameter Dh=0.82 mm.

[0672] Downstream of the reassembly means 370, when considering the direction of travel of the metal filamentary elements 54, the installation 100 comprises means 380 for maintaining the rotation of the cord 50 about their direction of travel.

[0673] Downstream of the rotation-maintaining means 380, when considering the direction of travel of the metal filamentary elements 54, the installation 100 comprises means 390 for twist-balancing the cord 50.

[0674] Downstream of the twist-balancing means 390, when considering the direction of travel of the metal filamentary elements 54, the installation 100 comprises means 400 for storing the cord 50.

[0675] The installation 100 also comprises means G for guiding, D for paying out, and T for applying tension to the filamentary elements and assemblies, as are conventionally used by those skilled in the art, for example pulleys and capstans.

[0676] The feed means 120 in this case comprise nine spools 410 for storing each filamentary element 54 and one spool 410 for storing the transitory core 160. In FIG. 7, for the sake of clarity, only two of the nine spools 410 have been depicted.

[0677] The assembly means 180 comprise a distributor 420 and an assembly guide 440. The assembly means 180 comprise means 460 for twisting the M′ metal filamentary elements 54 and the transitory core 160. The twisting means 460 comprise a twisting device 480, also more commonly known to those skilled in the art as a “twister”, for example a four-pulley twister. Downstream of these twisting means 460, the twist-balancing means 200 comprise a twister 500, for example a four-pulley twister. Finally, downstream of the twister 480, the assembly means 180 comprise a bow 520 and a pod 530 bearing the final twist-balancing means 390 and the storage means 400. The bow 520 and the pod 530 are mounted with the ability to rotate so as to retain the pitch of assembly of the cord 50.

[0678] FIG. 13 depicts the splitting means 720. The transitory assembly 220 progresses in an upstream direction of travel X. After passing through the splitting means 720, the split ensemble 330 progresses in a downstream direction of travel X2 and the first split assembly 250 progresses in a downstream direction X1. The splitting means 720 comprise guide means 570 allowing, on the one hand, translational movement of the split ensemble 330 and of the first split assembly 250 in the downstream directions X2, X1, respectively, and, on the other hand, rotation of the split ensemble 330 and of the first split assembly 250 about the downstream directions X2, X1, respectively. In this particular instance, the means 570 comprise an inclined rotary roller 600. The splitting means 740 are analogous to the splitting means 720 described hereinabove. During the method, the first split assembly 250 comes into contact with the roller 600 downstream of the point of splitting into the split ensemble 330 and the first split assembly 250.

[0679] FIG. 14 depicts the reassembly means 370. The first split assembly 250 progresses in an upstream direction of travel Y1. The second split assembly 270 progresses in an upstream direction of travel Y2. The cord 50 progresses in a downstream direction of travel Y. The reassembly means 370 comprise guide means 590 allowing, on the one hand, translational movement of the first and second split assemblies 250, 270 in the downstream directions Y1, Y2, respectively, and, on the other hand, rotation of the first and second split assemblies 250, 270 about the downstream directions Y1, Y2, respectively. In this particular instance, the means 590 comprise an inclined rotary roller 610. During the method, the first split assembly 250 comes into contact with the roller 610 upstream of the point of reassembly of the first and second split assemblies 250, 270.

[0680] The rotation-maintaining means 380 comprise a twister 620, for example a four-pulley twister, for maintaining the rotation of the cord 50 about the downstream direction Y respectively. The final twist-balancing means 390 also comprise a twister 630, for example a four-pulley twister. The storage means 400 in this case comprise a spool 640 for storing the cord 50.

[0681] In order to recycle the transitory core 160, the installation 100 comprises guide means G for guiding the transitory core 160 between, on the one hand, an exit 680 from the separation means 240, in this instance downstream of the splitting means 740 and, on the other hand, an entry 700 into the assembly means 180.

[0682] It will be noted that the installation 100 has no preforming means, particularly means for individually preforming the filamentary elements 54, arranged upstream of the assembly means 180.

[0683] The various means 240, 720, 740, 370 and the various assemblies and ensembles 220, 250, 270, 330 are depicted schematically in FIG. 8 in which the arrows indicate the direction of travel of these assemblies and ensembles from downstream towards upstream.

[0684] The method for implementation of the installation 100 described hereinabove will now be described. The method allows the manufacture of the cord 50 described hereinabove.

[0685] First of all, the filamentary elements 54 and the transitory core 160 are paid out from the feed means 120, in this instance the spools 410.

[0686] Next, the method comprises a step 1000 of supplying the transitory assembly 220 comprising, on the one hand, a step of assembly by twisting the M′ metal filamentary elements 54 in a single layer of M′ metal filamentary elements 54 around the transitory core 160 and, on the other hand, a step of twist-balancing the transitory assembly 220 carried to out by means of the twister 500.

[0687] The method comprises a step 1100 of separating the transitory assembly 220 into the first split assembly 250, the second split assembly 270 and the transitory core 160 or one or more ensembles comprising the transitory core 160, in this case the transitory core 160.

[0688] Downstream of the supply step 1000, the step 1100 of separating the transitory assembly 220 into the first split assembly 250, the second split assembly 270 and the transitory core 160 comprises a step 1210 of separating the transitory assembly 220 into the first split assembly 250 and the split ensemble 330. In this case, the separation step 1210 comprises a step 1210′ of splitting the transitory assembly 220 into the first split assembly 250 and the split ensemble 330.

[0689] The step 1100 of separating the transitory assembly 220 into the first split assembly 250, the second split assembly 270 and the transitory core 160 comprises a step 1230 of separating the split ensemble 330 into the second split assembly 250 and the transitory core 160. In this case, the separation step 1230 comprises a step 1230′ of splitting the split ensemble 330 into the second split assembly 270 and the transitory core 160.

[0690] The separation step 1210 takes place upstream of the separation step 1230.

[0691] Downstream of the separation step 1100 and the splitting steps 1210 and 1230, the method comprises a step 1400 of reassembling the first split assembly 250 with the second split assembly 270 to form the layer 52. The separation step 1100 and the reassembly step 1400 are carried out such that M1′+M2′=M′.

[0692] Note also that M′=6, M′=M4′+M1′, M4′=M2′, N=6, M1′=3, M2′=3.

[0693] The method also comprises steps of maintaining the rotation of the cord 50 about its direction of travel. These rotation-maintaining steps are carried out downstream of the step of separating the transitory assembly 220 by the means 380. A final twist-balancing step is performed, using the means 390. Finally, the cord 50 is stored on the storage spools 640.

[0694] As regards the transitory core 160, the method comprises a step of recycling the transitory core 160. During this recycling step, the transitory core 160 is recovered downstream of the separation step 1100, in this case downstream of the splitting step 1230, and the transitory core 160 previously recovered is reintroduced upstream of the assembly step 180. This recycling step is continuous.

[0695] It will be noted that the method thus described does not have steps of individually preforming each of the metal filamentary elements 54.

CORD ACCORDING TO A SECOND EMBODIMENT OF THE INVENTION

[0696] A second embodiment of a cord of the tyre according to the invention will now be described. This cord, denoted by the reference 50′, is shown in FIG. 15. Elements similar to those of the first embodiment that are shown in the previous figures are denoted by identical references.

[0697] The cord 50′ comprises a single layer 52 of helically wound metal filamentary elements 54. The layer 52 is made up of N=8 helically wound metal filamentary elements. The cord 50′ is intended to reinforce a tyre for industrial vehicles chosen from vans, heavy-duty vehicles, for example light rail vehicles, buses, heavy road transport vehicles (lorries, tractors, trailers).

[0698] In the embodiment illustrated, each metal filamentary element 54 comprises a single metal monofilament 56. Each metal filamentary element 54 also comprises a layer (not shown) of a metal coating comprising copper, zinc, tin, cobalt or an alloy of these metals, in this case brass.

[0699] The diameter Df of each metal filamentary element 54 is such that 0.10 mm≤Df≤0.50 mm, preferably 0.15 mm≤Df≤0.50 mm and more preferably 0.15 mm≤Df≤0.45 mm, and, in this second embodiment such that 0.22 mm≤Df≤0.50 mm, preferably 0.22 mm≤Df≤0.45 mm, more preferably 0.30 mm≤Df≤0.45 mm. In this instance, Df=0.35 mm for all the metal filamentary elements 54. Each metal filamentary element 54 is without preforming marks.

[0700] The cord 50′ has a diameter D such that D 2.10 mm, preferably 0.90 mm≤D≤2.10 mm and more preferably 0.95 mm≤D≤2.05 mm, and, in this second embodiment such that 1.15 mm≤D≤2.10 mm and preferably 1.15 mm≤D≤2.05 mm. In this instance, D=1.55 mm.

[0701] Advantageously, each metal filamentary element 54 is wound at a pitch P such that 3 mm≤P≤15 mm, preferably 5 mm≤P≤13 mm, more preferably 7 mm≤P≤11 mm, and, in this second embodiment, 7.5 mm≤P≤11 mm. In this instance, P=10.5 mm.

[0702] The ratio K of the pitch P to the diameter Df is such that 19≤K≤44, preferably 20≤K≤40, more preferably 23≤K≤39, and, in this second embodiment such that 19≤K≤35 and preferably 23≤K≤30. In this instance, K=30.

[0703] The cord 50′ according to the second embodiment has a structural elongation As such that As≤1.5%, preferably 1.5%≤As≤5.0%, more preferably 1.9%≤As≤4.5% and in this case equal to 2.0%. As described above, the value As is determined by plotting a force-elongation curve of the cord 50′, applying the standard ASTM D2969-04 of 2014. The curve obtained is shown in FIG. 16.

[0704] The helix angle α of each metal filamentary element is such that 13°≤α≤30°, preferably 17°≤α≤26° and, in this second embodiment such that 18.5°≤α≤30° and preferably 18.5°≤α≤26°. In this instance, as described above, with the characteristics of the cord 50′, α(1)=18.99°, α(2)=19.66° and α(3)=α=19.71°.

[0705] Each metal filamentary element 54 has a helix radius of curvature Rf such that 4.10 mm≤Rf≤5.30 mm. Since in this case P=10.5 mm and α=19.71°, Rf=5.27 mm.

[0706] The helix diameter Dh of each metal filamentary element is such that 0.70 mm≤Dh≤1.60 mm, preferably 0.75 mm≤Dh≤1.60 mm, more preferably 0.80 mm≤Dh≤1.60 mm and in the second embodiment such that 0.85 mm≤Dh≤1.60 mm, preferably 1.15 mm≤Dh≤1.60 mm, more preferably 1.20 mm≤Dh≤1.60 mm. Since in this case P=10.5 mm and α=19.71°, Dh=1.20 mm.

[0707] Advantageously, Dv is such that Dv≥0.50 mm and preferably 0.50 mm≤Dv≤1.20 mm and in the second embodiment 0.50 mm≤Dv≤1.20 mm, preferably 0.65 mm≤Dv≤1.20 mm. In this case, since Dh=1.20 mm and Df=0.35 mm, Dv=0.85 mm.

[0708] According to the invention, 9≤Rf/Df≤30, preferably 9≤Rf/Df≤25, more preferably 9≤Rf/Df≤22 and in the second embodiment 9≤Rf/Df≤15. In this case, Rf/Df=15. Likewise, according to the invention, 1.60≤Dv/Df≤3.20, preferably 1.70≤Dv/Df≤3.20 and more preferably 1.70≤Dv/Df≤3.05, and in this case Dv/Df=2.42.

[0709] Likewise, 0.10≤Jr≤0.25, preferably 0.14≤Jr≤0.25 and in this case, Jr=0.18.

[0710] The cord 50′ has a modulus of elasticity in extension of the structural portion of less than or equal to 15 GPa, preferably ranging from 2 GPa to 15 GPa, and in this case equal to 7 GPa. Furthermore, the cord 50′ has a modulus of elasticity in extension of the elastic portion of greater than or equal to 50 GPa, preferably ranging from 50 GPa to 180 GPa. In the second embodiment, the modulus of elasticity in extension of the elastic portion ranges from 80 to 130 GPa, and is in this case equal to 109 GPa.

[0711] With reference to FIG. 17, the the cord 50′, embedded in a crosslinked standard elastomeric matrix as described above and having a modulus in extension at 10% elongation ranging from 5 MPa to 10 MPa, has a modulus of elasticity in extension greater than or equal to 100 GPa, preferably ranging from 100 GPa to 180 GPa, more preferably 110 GPa GPa to 180 GPa, and even more preferably 120 GPa to 180 GPa. In this embodiment, the cord 50′ has a modulus of elasticity in extension equal to 140 GPa.

[0712] The cord 50′ is manufactured using, mutatis mutandis, an installation and a method similar to those used for the manufacture of the cord 50.

TYRE ACCORDING TO A SECOND EMBODIMENT OF THE INVENTION

[0713] FIGS. 18 to 20 show a tyre 10′ according to a second embodiment of the invention. In these figures, elements similar to those of the tyre 10 according to the first embodiment are denoted by identical references.

[0714] The tyre 10′ substantially exhibits revolution about an axis substantially parallel to the axial direction X. The tyre 10′ is in this case intended for a passenger vehicle.

[0715] The tyre 10′ has a crown 12 comprising a tread 20 and a crown reinforcement 14 extending in the crown 12 in the circumferential direction Z.

[0716] The crown reinforcement 14 comprises a working reinforcement 15 comprising a single working ply 18 and a hoop reinforcement 17 comprising a single hooping ply 19. In this case, the working reinforcement 15 is made up of the working ply 18 and the hoop reinforcement 17 is made up of the hooping ply 19. The crown reinforcement 14 is made up of the working reinforcement 15 and the hoop reinforcement 17.

[0717] The crown reinforcement 14 is surmounted by the tread 20. In this case, the hoop reinforcement 17, in this case the hooping ply 19, is radially interposed between the working reinforcement 15 and the tread 20. The crown 12 is in this case made up of the tread 20 and the crown reinforcement 14.

[0718] The tyre 10′ comprises two sidewalls 22 extending the crown 12 radially towards the inside. The tyre 10′ also has two beads 24 that are radially on the inside of the sidewalls 22 and each have an annular reinforcing structure 26, in this instance a bead wire 28, surmounted by a mass of filling rubber 30, and also a radial carcass reinforcement 32. The crown reinforcement 14 is situated radially between the carcass reinforcement 32 and the tread 20. Each sidewall 22 connects each bead 24 to the crown 12.

[0719] The carcass reinforcement 32 has a single carcass ply 34. In this case, the carcass reinforcement 32 is formed by the carcass ply 34. The carcass reinforcement 32 is anchored in each of the beads 24 by being turned up around the bead wire 28 so as to form, within each bead 24, a main strand 38 extending from the beads 24 through the sidewalls 22 and into the crown 12, and a turnup strand 40, the radially outer end 42 of the turnup strand 40 being radially on the outside of the annular reinforcing structure 26. The carcass reinforcement 32 thus extends from the beads 24 through the sidewalls 22 and into the crown 12. In this embodiment, the carcass reinforcement 32 also extends axially through the crown 12. The crown reinforcement 14 is radially interposed between the carcass reinforcement 32 and the tread 20. The carcass reinforcement 32 is arranged so as to be directly radially in contact with the crown reinforcement 14 and the crown reinforcement 14 is arranged so as to be directly radially in contact with the tread 20. More particularly, the single hooping ply 19 and the single working ply 18 are advantageously arranged so as to be directly radially in contact with one another.

[0720] Each working ply 18, hooping ply 19 and carcass ply 34 comprises an elastomeric matrix in which one or more reinforcing elements of the corresponding ply are embedded.

[0721] With reference to FIG. 19, the single carcass ply 34 comprises carcass filamentary reinforcing elements 44. Each carcass filamentary reinforcing element 44 extends axially from one bead 24 of the tyre 10 to the other bead 24 of the tyre 10. Each carcass filamentary reinforcing element 44 makes an angle A.sub.C1 greater than or equal to 55°, preferably ranging from 55° to 80° and more preferably from 60° to 70°, with the circumferential direction Z of the tyre 10 in the median plane M of the tyre 10′, in other words in the crown 12. With reference to FIG. 20, which is a simplified view in which, given the scale, all the carcass filamentary reinforcing elements 44 are shown parallel to one another, each carcass filamentary reinforcing element 44 makes an angle A.sub.C2 greater than or equal to 85° with the circumferential direction Z of the tyre 10′ in the equatorial circumferential plane E of the tyre 10′, in other words in each sidewall 22.

[0722] In this example, it is adopted by convention that an angle oriented in the anticlockwise direction from the reference straight line, in this case the circumferential direction Z, has a positive sign and that an angle oriented in the clockwise direction from the reference straight line, in this case the circumferential direction Z, has a negative sign. In this instance, A.sub.C1=+67° and A.sub.C2=+90°.

[0723] With reference to FIG. 19, the single working ply 18 comprises a plurality of working filamentary reinforcing elements 46. The working filamentary reinforcing elements 46 are arranged side by side in a manner substantially parallel to one another. Each working filamentary reinforcing element 46 extends axially from one axial end of the working reinforcement 15 of the tyre 10 to the other axial end of the working reinforcement 15 of the tyre 10. Each working filamentary reinforcing element 46 makes an angle A.sub.T greater than or equal to 10°, preferably ranging from 30° to 50° and more preferably from 35° to 45°, with the circumferential direction Z of the tyre 10′ in the median plane M. Given the orientation defined above, A.sub.T=−40°.

[0724] The single hooping ply 19 comprises at least one hooping filamentary reinforcing element 48. In this instance, the hooping ply 19 comprises a single hooping filamentary reinforcing element 48 wound continuously over an axial width L.sub.F of the crown 12 of the tyre 10′ such that the axial distance between two adjacent windings is equal to 1.3 mm. Advantageously, the axial width L.sub.F is less than the width L.sub.T of the working ply 18. The hooping filamentary reinforcing element 48 makes an angle A.sub.F strictly less than 10° with the circumferential direction Z of the tyre 10′, preferably less than or equal to 7°, and more preferably less than or equal to 5°. In this instance, A.sub.F=+5°.

[0725] It will be noted that the carcass filamentary reinforcing elements 44, working filamentary reinforcing elements 46 and hooping filamentary reinforcing elements 48 are arranged, in the crown 12, so as to define a triangle mesh in projection onto the equatorial circumferential plane E in the radial direction of the tyre. In this case, the angle A.sub.F and the fact that the orientation of the angle A.sub.T and the orientation of the angle A.sub.C1 are opposite with respect to the circumferential direction Z of the tyre 10′ make it possible to obtain this triangle mesh.

[0726] Each carcass filamentary reinforcing element 44 is a textile filamentary element and conventionally comprises two multifilament strands, each multifilament strand being made up of a spun yarn of polyester, in this case PET, monofilaments, these two multifilament strands being individually overtwisted at 240 turns.Math.m.sup.−1 in one direction and then twisted together at 240 turns.Math.m.sup.−1 in the opposite direction. These two multifilament strands are wound in a helix around one another. Each of these multifilament strands has a count equal to 220 tex.

[0727] Each working filamentary reinforcing element 46 is a metal filamentary element and in this case is an assembly of two steel monofilaments that each have a diameter equal to 0.30 mm, the two steel monofilaments being wound together at a pitch of 14 mm.

[0728] The hooping filamentary reinforcing element 48 is obtained by embedding the cord 50 in an elastomeric matrix based on the elastomeric composition of the hooping ply 19.

[0729] The tyre 10′ is manufactured by implementing a method similar to the method for manufacturing the tyre 10. In order to form the triangle mesh of the tyre 10′, a specific assembly method is implemented, as described in EP1623819 or in FR1413102.

[0730] Comparative Tests

[0731] We tested various cords A to W intended to reinforce a tyre for passenger vehicles, cords A to L preferably being intended to reinforce tyres for passenger vehicles, but also for two-wheel vehicles, and cords K to W preferably being intended to reinforce a tyre for industrial vehicles.

[0732] Among cords A to W, the following are distinguished: [0733] cords A, which are not in accordance with the invention and were obtained by implementing a conventional cabling assembly method of the prior art, [0734] cords D to I and M, which are not in accordance with the invention and were obtained by implementing the prior art method described in WO2016083265 and WO2016083267, [0735] cords J, K, N, T, U and V, which are not in accordance with the invention and were obtained by implementing the method comprising a reassembly step described hereinabove, [0736] cords B, C, L, O, P, Q, R, S and W, which are in accordance with the invention and were obtained by implementing the method comprising a reassembly step described hereinabove, Each cord C and W forms the cord 50, 50′ described above, respectively.

[0737] For each metal cord, the following were measured: the diameter Df of each metal filamentary element, expressed in millimetres, the number N of metal filamentary elements, the pitch factor K equal to the ratio of the pitch P to Df, the helix angle α expressed in degrees, the pitch P of each metal filamentary element, expressed in millimetres, the helix diameter Dh, expressed in millimetres, the enclosure diameter Dv, expressed in millimetres, the helix radius of curvature Rf, expressed in millimetres, the ratio Rf/Df, the ratio Dv/Df, the structural elongation As, expressed in %, the diameter D of the cord, expressed in millimetres, the linear density expressed in grammes per metre, the relative radial clearance Jr and a compressibility indicator ε.sub.c determined as follows.

[0738] The compressibility indicator ε.sub.c is measured on a test specimen with a rectangular section with an area of 12 mm×8 mm and with a height equal to 20 mm. The test specimen comprises an elastomeric matrix which has, in the cured state, a modulus equal to 10 MPa (in this case a modulus representative of the modulus of the compositions used in tyres—in other fields, other moduli could be envisaged) and in which the metal cord to be tested is embedded such that the axis of the cord is coincident with the axis of symmetry of the test specimen. Two support plates with an area of 20 mm×20 mm are adhesively bonded to each face of the rectangular section of the test specimen, each face having been carefully ground beforehand. Each support plate is then connected to a test machine having a movable crosshead usable in tension or in compression (machine from Zwick or Instron for example). The test specimen (resting on one of the 20 mm×20 mm plates) is placed on a support with a diameter of 30 mm having a horizontal support face, the support itself being fastened to a lower crosshead of the test machine. Positioned under the movable crosshead of the machine is a load sensor carrying a second support with a diameter equal to 30 mm, the support face of which, which is also horizontal, is positioned facing the first support face. The distance that separates the two horizontal supports is therefore variable as per the movement of the movable crosshead. This distance takes, as first value, a value such that the test specimen can fit without load between the two supports with a diameter of 30 mm, then takes a second value for exerting a preload of 0.1 N, and will then decrease to a speed of 3 mm/mn until the end of the test, which is stopped after the test specimen has been squashed by 10% of its initial height. The force-compression curve is obtained at 20° C. The contribution of the load of the matrix to the corresponding deformations is subtracted from the value of the load of the test specimen (starting from a force-compression curve of a single block made only of matrix). The value of maximum deformation at which buckling takes place, this being a critical deformation beyond which the load decreases when the test specimen bends, corresponds to the value of the maximum load, of this new curve. The compressibility indicator ε.sub.c is equal to the value of this recorded critical deformation.

[0739] The results of all these measurements are collated in Table 1 below. As regards the compressibility indicator ε.sub.c, it is estimated that satisfactory longitudinal compressibility is obtained for values of ε.sub.c≥3.5. The longitudinal compressibility is favoured all the more, the higher the value of ε.sub.c. The indication NT indicates that the cord was not tested.

[0740] On comparing cords A, B and C, is noted that cord A has a relative radial clearance that is too large on account of a linear density that is too low relative to its diameter. The relative radial clearance of cord C is greater than that of cord B, which results in a diameter greater than that of cord B for identical linear densities. Cords B and C have excellent longitudinal compressibility.

[0741] On comparing cords D to L, it is noted that cord L has the best compromise between linear density, outer diameter and longitudinal compressibility. To be specific, even though cords D, E and F have a longitudinal compressibility greater than that of cord L, cords D, E and F have much lower linear densities for outer diameters of the same order of magnitude as cord L. Cords G, H, J and K have a longitudinal compressibility lower than that of cord L on account of an enclosure diameter which is much too small, causing the filamentary elements to move closer to the axis of the cord and thus making them more sensitive to buckling. Although cords G and H have satisfactory longitudinal compressibility and a diameter smaller than that of cord L, their linear density is largely insufficient to provide sufficient reinforcement. Cords J and K have diameters of the same order of magnitude as cord L but linear densities significantly lower than cord L and therefore offer insufficient reinforcement. As for cord I, this has a linear density less than that of cord L and a significantly greater diameter.

[0742] On comparing cords M to W, it is noted that cords O to S and W have the best compromise between linear density, outer diameter and longitudinal compressibility. Cords M, N, T and U have a linear density that is too low for their diameter compared to cords O to S and W. As for cord V, this has insufficient longitudinal compressibility on account of a helix radius of curvature and a relative radial clearance that are too small, making cord V too sensitive to buckling.

[0743] It will be noted that, on comparing cords P and Q and S, cords P and S have a longitudinal compressibility greater than that of cord Q on account of a greater enclosure diameter and therefore a relative radial clearance that is also greater.

[0744] It will be noted that, on comparing cords R and S, cord R has a linear density significantly greater than that of cord S, an identical diameter and a barely lower longitudinal compressibility.

TABLE-US-00001 TABLE 1 Df N K α P Dh Dv Rf Rf/Df Dv/Df As D Ml Jr ε.sub.c A 0.2 5 25 20.1 5 0.58 0.38 2.47 12.4 1.91 3.8 0.78 1.3 0.35 <5 B 0.2 9 39 17.9 7.8 0.80 0.60 4.25 21.2 3.01 2 1 2.3 0.23 4.5 C 0.2 9 39 18.3 7.8 0.82 0.62 4.18 20.9 3.10 2.2 1.04 2.3 0.24 5 D 0.3 3 27 18.5 8.1 0.86 0.56 4.29 14.3 1.88 4.4 1.15 1.74 0.48 >10 E 0.32 3 25 17.9 8 0.82 0.50 4.35 13.6 1.58 3.9 1.15 2 0.43 9 F 0.32 4 25 19.3 8 0.89 0.57 4.09 12.8 1.78 4.1 1.15 2.66 0.45 7 G 0.32 4 25 16.4 8 0.75 0.43 4.70 14.7 1.34 2.5 1.07 2.61 0.33 5.5 H 0.32 4 25 15.2 8 0.69 0.37 5.04 15.8 1.16 1.9 1.01 2.6 0.29 3.5 I 0.32 4 25 21.0 8 0.98 0.66 3.81 11.9 2.05 5.2 1.29 2.69 0.46 NT J 0.32 5 25 18.0 8 0.83 0.51 4.33 13.5 1.59 2.6 1.15 3.34 0.29 6 K 0.32 6 25 17.9 8 0.82 0.50 4.36 13.6 1.57 1.6 1.15 4.01 0.17 5.2 L 0.32 6 25 19.0 8 0.88 0.56 4.14 12.9 1.74 2.2 1.2 4.04 0.22 7 M 0.38 5 25 19.9 9.5 1.09 0.71 4.73 12.4 1.88 3.7 1.47 4.71 0.35 NT N 0.45 5 25 20.1 11.25 1.31 0.86 5.56 12.4 1.91 3.8 1.78 6.75 0.35 5 O 0.45 6 23 21.3 10.35 1.29 0.84 4.87 10.8 1.86 3 1.75 8.17 0.23 4.5 P 0.45 7 23 23.3 10.35 1.42 0.97 4.54 10.1 2.15 3 1.88 9.67 0.20 4.2 Q 0.45 7 23 21.7 10.35 1.31 0.86 4.81 10.7 1.91 1.9 1.77 9.55 0.14 3.5 R 0.45 8 23 25.5 10.35 1.57 1.12 4.25 9.4 2.49 3 2.03 11.23 0.16 4.7 S 0.45 7 23 25.4 10.35 1.56 1.11 4.26 9.5 2.47 4.5 2.03 9.83 0.25 5 T 0.45 6 23 25.5 10.35 1.57 1.12 4.25 9.4 2.49 6 2.03 8.42 0.35 5.3 U 0.45 5 23 25.8 10.35 1.59 1.14 4.21 9.4 2.53 7.5 2.03 7.02 0.44 5.7 V 0.45 8 18 29.7 8.1 1.47 1.02 3.00 6.7 2.26 1.9 1.88 11.7 0.08 3 W 0.35 8 30 19.7 10.5 1.20 0.85 5.27 15.0 2.42 2 1.55 6.37 0.18 >4