IMPROVED ARAMID TEXTILE CORD WITH AN AT LEAST TRIPLE TWIST

Abstract

A cord (30) has a triple twist (T1, T2, T3) and comprises an assembly (25) consisting of N=3 strands (20a, 20b, 20c) twisted together with a twist T3 in a direction D2, each strand consisting of M=2 pre-strands, which are themselves twisted together with a twist T2 (T2a, T2b, T2c) in a direction D1 opposite to D2, each pre-strand itself consisting in a yarn that has been previously twisted about itself with a twist T1 in the direction D1, wherein each yarn consists of elementary monofilaments of aromatic polyamide or aromatic copolyamide. Each yarn has a count varying from 90 to 130 tex.

Claims

1.-15. (canceled)

16. A cord with a triple twist comprising an assembly consisting of N=3 strands twisted together with a twist T3 in a direction D2, each strand consisting of M=2 pre-strands, which are themselves twisted together with a twist T2 in a direction D1 opposite to D2, each pre-strand itself consisting in a yarn that is twisted about itself with a twist T1 in the direction D1, wherein each yarn consists of elementary monofilaments of aromatic polyamide or aromatic copolyimide, each yarn having a count ranging from 90 to 130 tex.

17. The cord according to claim 16, wherein each yarn has a count ranging from 100 to 120 tex.

18. The cord according to claim 16, wherein each pre-strand has a twist factor K1 ranging from 2 to 80.

19. The cord according to claim 16, wherein each strand has a twist factor K2 ranging from 10 to 150.

20. The cord according to claim 16, wherein the cord has a twist factor K3 ranging from 50 to 500.

21. The cord according to claim 16, wherein T2 is greater than T1.

22. The cord according to claim 16, wherein T3 is greater than T2.

23. The cord according to claim 16, wherein a sum T1+T2 ranges from 0.8 times T3 to 1.2 times T3.

24. The cord according to claim 16, wherein the cord has an apparent toughness greater than or equal to 115 daN.Math.mm.sup.2.

25. The cord according to claim 16, wherein the cord has a diameter less than or equal to 1.03 mm.

26. A semi-finished article or product comprising a polymer matrix in which at least one cord according to claim 16 is embedded.

27. A tire comprising the cord according to claim 16.

28. A tire comprising a crown reinforcement comprising a hoop reinforcement comprising a hooping ply comprising at least one hoop reinforcement textile filamentary element forming an angle that is strictly less than 10 with a circumferential direction of the tire, the or each hoop reinforcement textile filamentary element being formed by the cord according to claim 16.

29. The tire according to claim 28 further comprising a crown comprising a tread, two sidewalls, and two beads, each sidewall connecting each bead to the crown, the crown reinforcement extending in the crown in the circumferential direction of the tire.

30. The tire according to claim 29 further comprising a carcass reinforcement anchored in each of the beads and extending in the sidewalls and in the crown, the crown reinforcement being radially interposed between the carcass reinforcement and the tread.

Description

[0087] The invention and its advantages will be readily understood in the light of the detailed description and the non-limiting examples of embodiment that follow, and of FIGS. 1 to 6, relating to these examples, which show schematically (without being to any specific scale unless indicated otherwise): [0088] in cross section, a conventional multifilament textile fibre (or yarn), firstly in the initial state (5), that is to say with no twist, and then after a first operation of twisting T1 in the direction D1 to form a yarn twisted about itself, or a pre-strand (10) (FIG. 1); [0089] in cross section, the assembly of 2 yarns (10a, 10b) as above, acting as pre-strands (previously twisted according to T1a, T1b in the same direction D1), which are assembled by a second operation of twisting T2, still in the same direction D1, to form a strand (20) intended for the cord according to the invention (FIG. 2); [0090] in cross section, the assembly (25) of 3 strands (20a, 20b, 20c) as above (previously twisted according to T2a, T2b, T2c in the same direction D1), which are assembled by a third operation of twisting T3, this time in the direction D2 opposite to the direction D1, to form a triple-twist (T1, T2, T3) cord (30) according to the invention (FIG. 3); [0091] a view in a section perpendicular to the circumferential direction of a tyre according to the invention (FIG. 4); [0092] a cut-away view of the tyre of FIG. 4, showing the projection on to the circumferential equatorial plane E of the hooping reinforcing filamentary elements, the working reinforcing filamentary elements and the carcass reinforcing filamentary elements (FIG. 5); [0093] a view of the carcass reinforcing filamentary elements arranged in the sidewall of the tyre of FIG. 4 in projection on the median plane M of the tyre (FIG. 6).

[0094] Firstly, FIG. 1 shows schematically, in cross section, a conventional multifilament textile fibre 5, also called a yarn (yarn in English), in the initial state, that is to say without any twist; in a well-known way, such a yarn is formed by a plurality of elementary monofilaments 50, typically ranging from several tens to several hundreds, having a very fine diameter which is usually less than 25 m. Here, each yarn 5 is formed by elementary monofilaments of aromatic polyamide or aromatic copolyamide, and has a count varying from 90 to 130 tex, preferably from 100 to 120 tex, and more preferably equal to 110 tex.

[0095] During a first twist operation T1 (first twist), expressed in turns per metre, ranging from 10 to 350 turns.Math.m.sup.1, preferably from 20 to 200 turns.Math.m and more preferably from 105 to 135 turns.Math.m.sup.1, and here equal to 120 turns.Math.m.sup.1, in direction D1 (here Z), the initial fibre 5 is converted into a fibre twisted about itself, called a pre-strand 10. In this pre-strand 10, the elementary monofilaments 50 are thus subjected to a spiral deformation about the fibre axis (or pre-strand axis).

[0096] As shown in FIG. 2, each of the M=2 pre-strands 10a, 10b is characterized by a specific first twist T1 (here, for example, T1a, T1b) which may be equal (in the general case, that is to say that here, for example, T1a=T1b) or different from one strand to another. Here, each of the M=2 pre-strands 10a, 10b has a twist factor K1 ranging from 2 to 80, preferably from 6 to 70, and more preferably from 30 to 40, and here equal to 33.

[0097] Then, again with reference to FIG. 2, the M=2 pre-strands 10a, 10b are themselves twisted together in the same direction D1 (here, Z) as before, with an intermediate twist T2 (second twist) ranging from 25 to 470 turns.Math.m.sup.1, preferably from 35 to 400 turns.Math.m.sup.1 and more preferably from 170 to 190 turns.Math.m.sup.1, and here equal to 180 turns.Math.m.sup.1, to form a strand 20.

[0098] As shown in FIG. 3, each of the N=3 strands 20a, 20b, 20c is characterized by a specific second twist T2 (here, for example, T2a, T2b, T2c) which may be equal (in the general case, that is to say that here, for example, T2a=T2b=T2c) or different from one strand to another. Here, each of the N=3 strands 20a, 20b, 20c has a twist factor K2 ranging from 10 to 150, preferably from 20 to 130, and more preferably from 69 to 86, and here equal to 70. It should be noted that T2=180 turns.Math.m.sup.1 is greater than T1=120 turns.Math.m.sup.1.

[0099] Then, again with reference to FIG. 3, the N=3 pre-strands 20a, 20b, 20c are themselves twisted together in the direction D2, opposite to D1 (here, S), with a final twist T3 (third twist) ranging from 30 to 600 turns.Math.m.sup.1, preferably from 80 to 500 turns.Math.m.sup.1 and more preferably from 310 to 370 turns.Math.m.sup.1, and here equal to 300 turns.Math.m.sup.1, to form the assembly 25 of the cord 30 according to the invention. The cord 30 then has a twist factor K3 ranging from 50 to 500, preferably from 80 to 230, and here equal to 203.

[0100] It should be noted that T3=300 turns.Math.m.sup.1 is greater than T2=180 turns.Math.m.sup.1. Additionally, T2 ranges from 0.2 times T3 to 0.95 times T3, preferably from 0.4 times T3 to 0.8 times T3. Here, T2=0.60 times T3.

Additionally, the sum T1+T2 ranges from 0.8 times T3 to 1.2 times T3, preferably from 0.9 times T3 to 1.1 times T3, and here T1+T2=T3.

[0101] In a first embodiment, the cord 30 is formed by the raw assembly 25. This is known as a raw cord. A raw cord is such that the constituent elementary monofilaments of the cord result from the method of manufacturing the cord without the elementary monofilaments being covered by any coating having an adhesive function. Thus a raw cord may be bare, that is to say the constituent material or materials of the cord are not coated with any coating, or may be sized, that is to say coated with a sizing compound having the function, notably, of facilitating the sliding of the constituent material or materials of the cord during the process of its manufacture and preventing the accumulation of electrostatic charges.

[0102] In a second embodiment, the cord 30 comprises the assembly 25 and an outer layer of an adhesive compound. This is known as an adherized cord. Thus, after the manufacture of the raw assembly 25, the raw assembly 25 is coated with an outer layer of a thermo-crosslinked compound and the raw assembly 25 coated with the outer layer is heat-treated so as to crosslink the adhesive compound to produce the adherized assembly 25, which then forms the cord 30.

[0103] In a third embodiment, the cord 30 comprises the assembly 25 and two layers of adhesive compounds. Thus, after the manufacture of the raw assembly 25, the raw assembly 25 is coated with an intermediate layer of a first thermo-crosslinked adhesive compound, and the raw assembly 25 coated with the intermediate layer is heat-treated so as to crosslink the first adhesive compound to produce a pre-adherized assembly 25. The pre-adherized assembly 25 is then coated with an outer layer of a second thermo-crosslinked adhesive compound and the pre-adherized assembly 25 coated with the outer layer is heat-treated so as to crosslink the second adhesive compound to produce the adherized assembly 25, which then forms the cord 30.

[0104] The cord 30 has an apparent toughness which is greater than or equal to 115 daN.Math.mm.sup.2, or preferably greater than or equal to 130 daN.Math.mm.sup.2, and here equal to 135 daN.Math.mm.sup.2. The cord 30 has a diameter which is less than or equal to 1.03 mm, or preferably less than or equal to 1.00 mm and more preferably less than or equal to 0.98 mm, and here equal to 0.97 mm.

[0105] FIGS. 4 to 6 show a reference frame X, Y, Z corresponding to the usual axial (X), radial (Y) and circumferential (Z) directions, respectively, of a tyre.

[0106] FIG. 4 shows a tyre according to the invention and denoted by the general reference 100. The tyre 100 substantially exhibits revolution about an axis substantially parallel to the axial direction X. The tyre 100 is in this case intended for a passenger vehicle.

[0107] The tyre 100 has a crown 120 comprising a tread 200 and a crown reinforcement 140 extending in the crown 120 in the circumferential direction Z.

[0108] The crown reinforcement 140 comprises a working reinforcement 160 comprising a single working ply 180 and a hoop reinforcement 170 comprising a single hooping ply 190. Here, the working reinforcement 160 consists of the working ply 180 and the hoop reinforcement 170 consists of the hooping ply 190.

[0109] The crown reinforcement 140 is surmounted by the tread 200. Here, the hoop reinforcement 170, in this case the hooping ply 190, is radially interposed between the working reinforcement 160 and the tread 200.

[0110] The tyre 100 comprises two sidewalls 220 extending the crown 120 radially inwards. The tyre 100 also comprises two beads 240 that are radially on the inside of the sidewalls 220 and each comprise an annular reinforcing structure 260, in this instance a bead wire 280, surmounted by a mass of filling rubber 300, and also a radial carcass reinforcement 320. The crown reinforcement 140 is situated radially between the carcass reinforcement 320 and the tread 200. Each sidewall 220 connects each bead 240 to the crown 120.

[0111] The carcass reinforcement 320 has a single carcass ply 340. The carcass reinforcement 320 is anchored in each of the beads 240 by being turned up around the bead wire 280 so as to form, within each bead 240, a main strand 380 extending from the beads 240 through the sidewalls 220 and into the crown 120, and a turnup strand 400, the radially outer end 420 of the turnup strand 400 being radially on the outside of the annular reinforcing structure 260. The carcass reinforcement 320 thus extends from the beads 240 through the sidewalls 220 as far as into the crown 120. In this embodiment, the carcass reinforcement 320 also extends axially through the crown 120. The crown reinforcement 140 is radially interposed between the carcass reinforcement 320 and the tread 200.

[0112] Each working ply 180, hooping ply 190 and carcass ply 340 comprises an elastomeric matrix in which one or more reinforcing elements of the corresponding ply are embedded.

[0113] With reference to FIG. 5, the single carcass ply 340 comprises carcass reinforcing filamentary elements 440 anchored in each bead 240 and extending from one to the other bead of the tyre 100, passing through each sidewall 220 and the crown 120. Each carcass reinforcing filamentary element 440 forms 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 100 in the median plane M of the tyre 100, in other words in the crown 120.

[0114] With reference to FIG. 6, which is a simplified view in which, given the scale, all the carcass reinforcing filamentary elements 440 are shown parallel to one another, each carcass reinforcing filamentary element 440 makes an angle Ace greater than or equal to 85 with the circumferential direction Z of the tyre 100 in the equatorial circumferential plane E of the tyre 100, in other words in each sidewall 220.

[0115] 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.

[0116] With reference to FIG. 5, the single working ply 180 comprises working reinforcing filamentary elements 460. The single working ply being axially delimited by two axial edges B, axially defining the width L.sub.T of the working ply 180, each axial edge B is arranged radially outside each sidewall 220. The working reinforcing filamentary elements 460 extend from one axial edge B to the other axial edge B of the single working ply 180.

[0117] Each carcass reinforcing filamentary element 460 forms an angle AT 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 100 in the median plane M. Given the orientation defined above, A.sub.T=40.

[0118] The single hooping ply 190 comprises at least one hooping reinforcing textile filamentary element 480. In this instance, the hooping ply 190 comprises a single hooping reinforcing textile filamentary element 480 wound continuously over an axial width L.sub.F of the crown 120 of the tyre 100. Advantageously, the axial width L.sub.F is less than the width L.sub.T of the working ply 180. The hooping reinforcing textile filamentary element 480 forms an angle A.sub.F strictly smaller than 10 with the circumferential direction Z of the tyre 100, preferably smaller than or equal to 7, and more preferably smaller than or equal to 5. In this instance, A.sub.F=+5.

[0119] Note that the carcass reinforcing filamentary elements 440, working reinforcing filamentary elements 460 and hooping reinforcing filamentary elements 480 are arranged, in the crown 120, so as to define, in projection onto the equatorial circumferential plane E, a triangle mesh. Here, 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 to the circumferential direction Z of the tyre 100, enable this triangular mesh to be obtained.

[0120] Each carcass reinforcing filamentary element 440 conventionally comprises two multifilament strands, each multifilament strand consisting of a yarn of polyester monofilaments, here PET, these two multifilament strands being overtwisted individually to 240 turns.Math.m1 in one direction and then twisted together to 240 turns.Math.m1 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.

[0121] Each working reinforcing filamentary element 460 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.

[0122] The hooping reinforcing textile filamentary element 480 is formed by the cord 30 according to the invention described previously.

[0123] The tyre 100 is manufactured using the below-described method.

[0124] Firstly, the working ply 180 and the carcass ply 340 are manufactured by arranging the reinforcing filamentary elements of each ply parallel to one another and embedding them, by calendering for example, in an uncrosslinked compound comprising at least an elastomer, the compound being intended to form an elastomeric matrix when crosslinked. A ply called a straight ply is obtained, in which the reinforcing filamentary elements of the ply are parallel to one another and are parallel to the main direction of the ply. Then, if necessary, portions of each straight ply are cut off at a cutting angle and these portions are abutted against one another so as to obtain what is called an angle ply, in which the reinforcing filamentary elements of the ply are parallel to one another and form an angle with the main direction of the ply equal to the cut-off angle.

[0125] Then, an assembly method as described in EP1623819 or in FR1413102 is implemented.

[0126] During this assembly method, the hoop reinforcement 170, in this case the hooping ply 190, is arranged radially on the outside of the working reinforcement 160. In this case, in a first variant, a bead of width B significantly less than L.sub.F is manufactured, in which the hooping reinforcing textile filamentary element 480 formed by the cord 30 according to the invention is embedded in an uncrosslinked compound, and the bead is rolled up helically for several turns to obtain the axial width L.sub.F. In a second variant, the hooping ply 190 having a width L.sub.F is manufactured in a similar manner to the carcass and working plies and the hooping ply 190 is wound through one turn over the working reinforcement 160. In a third variant, the hooping reinforcing textile filamentary element 480 formed by the cord 30 according to the invention is rolled up radially outside the working ply 180, and then a layer of a compound, in which the hooping reinforcing textile filamentary element 480 formed by the cord 30 according to the invention during the curing of the tyre will be embedded, is deposited thereon. In all three variants, the adherized reinforcing textile filamentary element 480 formed by the cord 30 is embedded in a compound to form, on completion of the tyre manufacturing method, the hooping ply 190, comprising the hooping reinforcing textile filamentary element 480 formed by the cord 30 according to the invention.

[0127] After a step of laying the tread 200, the tyre is then obtained, in which the compositions of the elastomeric matrices are not yet crosslinked and are in an uncured state. This is what is known as a green form of the tyre.

[0128] Finally, the compositions are crosslinked, for example by curing or vulcanization, in order to obtain the tyre in which the compositions are in a crosslinked state. During this curing step, the tyre of which the elastomeric matrices are in the uncured state is expanded radially, circumferentially and axially, for example by pressurizing an inflating membrane, so as to press the tyre against the surfaces of a curing mould.

[0129] Comparative Tests

[0130] Because of its special construction, the cord of the invention has notably improved tensile properties, as demonstrated by the following examples of embodiment.

[0131] A comparison was made between five triple-twist cords having different constructions, not conforming to the invention (cords E1, E2, E3 and E4) and conforming to the invention (cord 30).

[0132] The construction of each cord and its final properties are summarized in Table 1 below.

[0133] The initial yarns are, as is known, available commercially, in this case being sold by DuPont under the trade name Kevlar or by Teijin under the trade name Twaron.

[0134] For each cord, the breaking strength (Fr) and the apparent diameter () were measured. The apparent toughness () was deduced from these. The values of breaking strength and apparent toughness are also shown in base 100 relative to cord E1.

[0135] Also shown are the cord density and the lay-up pitch required to produce a ply whose calenderability factor varies from 4.8 to 4.9, these two values not differing significantly and corresponding to a ply that can be manufactured in existing industrial conditions and has correctly formed links of polymeric material between the adjacent cords. The calenderability factor is defined as the ratio between the diameter of the cord and the difference between the lay-up pitch in the ply and the diameter of the cord. For the proposed plies, the breaking strength of the ply (Rn), expressed in daN per mm of ply, was also calculated.

[0136] The endurance in flexion and compression was also evaluated. In fact, for cords intended, notably, for reinforcing tyre structures, the endurance or fatigue resistance may be analysed by subjecting these cords to various known laboratory tests, notably the fatigue test known by the name of the belt test, sometimes called the Shoe Shine test (see for example EP 848 767, U.S. Pat. Nos. 2,595,069, 4,902,774, and the ASTM D885-591 standard, revised 67T), in which test the cords, previously coated, are incorporated into a rubber article that is cured. The principle of the belt test, firstly, is as follows: the belt comprises two layers of textile filamentary elements, the first layer comprising the cords whose performance is to be evaluated, embedded at a pitch of 1.25 mm in two skims of compound, each measuring 0.4 mm, and a second stiffening layer for preventing the elongation of the first layer, this second layer comprising relatively rigid textile filamentary elements and comprising two aramid strands of 167 tex each, twisted together with a twist of 315 turns per metre and embedded at a pitch of 0.9 mm in two skims of compound, each measuring 0.3 mm. The axis of each cord is orientated in the longitudinal direction of the belt. This belt is then subjected to the following stresses: the belt is drawn cyclically around a roller of given diameter, using a crank and crankshaft system, in such a way that each elementary portion of the belt is subjected to a tension of 15 daN and undergoes cycles of variation of curvature causing it to pass from an infinite radius of curvature to a given radius of curvature, in this case 20 mm, in the course of 190,000 cycles, at a frequency of 7 Hz. This variation of curvature of the belt causes the cord on the inner layer, which is closer to the roller, to undergo a given rate of geometric compression depending on the diameter of the chosen roller. At the end of this stressing, the cords are extracted by stripping from the inner layer, and the residual breaking strength of the fatigued cords is measured. From this is deduced the residual apparent toughness () and the loss, expressed in %, of apparent toughness during the test. The greater the loss, the less satisfactory is the endurance of the cord.

[0137] The construction denoted A55/1/3/4-Z120/Z180/S300 of the cord E1 signifies that this cord is a triple-twist (T1, T2, T3) cord produced by an operation of final twisting (T3=300 turns.Math.m.sup.1, direction S) of 4 different strands, each of which has been prepared in advance by an operation of intermediate twisting (T2=180 turns.Math.m.sup.1) in the reverse direction (direction Z) of 3 pre-strands, each of these 3 pre-strands consisting of a 1 single yarn consisting of elementary monofilaments of aromatic polyamide, in this case the aramid (A) with a count of 55 tex that has previously been twisted about itself in a first twisting operation T1=120 turns.Math.m.sup.1 in the same direction (direction Z) as for the pre-strands. The other notations of the cords E2 to E4 and 30 enable the constructions corresponding to these cords to be identified mutatis mutandis.

[0138] It is important to note that all the cords E1 to E4 and 30 are characterized by final twist factors K3 that are very similar and provide assurance that the superior properties of the cords according to the invention are due to the specific combination of the count of its yarns and the values of N and M, and not to other characteristics such as the twists T1, T2 and T3.

[0139] With the exception of cord 30, none of the tested cords is based on yarns consisting of elementary monofilaments of aromatic polyamide or aromatic copolyamide, having a count varying from 90 to 130 tex, in this case from 100 to 120 tex and equal to 110 tex. Cords E1 to E4 all have yarns either with lower counts (E1, E3 and E4) or with a higher count (E2). Only the cord 30 according to the invention has a construction in which M=2 and N=3 and in which each yarn has a count ranging from 90 to 130 tex.

[0140] In fact, cord E1 has a construction in which M=3 and N=4, resulting in the best breaking strength Fr and the best apparent toughness a obtained among the tested cords. However, another effect of the M=3 and N=4 constructions is that, on the one hand, this cord becomes more costly to manufacture because it requires numerous modifications to the existing twisting machinery, and, on the other hand, it is necessary to use a relatively lengthy manufacturing process and numerous twisting machines simultaneously, since this cord is based on 12 yarns. Above all, the loss in cord E1 is greatest out of all the tested cords.

[0141] Cord E2 has a construction in which N=M=2. In an attempt to compensate for a relatively small number of yarns, cord E2 comprises yarns having a count of 167 tex. The N=M=2 construction of cord E2 enables it to be manufactured on the existing twisting machinery without modifying the machinery, while allowing the use of a method which is relatively fast and also requires a very low number of machines because of the low number of yarns used for the cord (4 for cord E2, as against 12 for cord E1 and 9 for cord E4). However, the use of a relatively high count results, on the one hand, in the lowest apparent toughness a among the tested cords, and, on the other hand, in a relatively large diameter and therefore a relatively low ply breaking strength Rn. Furthermore, the loss in cord E2 is relatively high.

[0142] Cord E3 has a construction in which M=2 and N=3, enabling the count of each yarn to be reduced by comparison with cord E2. The M=2 and N=3 construction of cord E3 enables it to be manufactured on the existing twisting machinery without modifying the machinery, while allowing the use of a method which is relatively fast and also requires a low number of machines because of the low number of yarns used for the cord (6 for cord E3, as against 12 for cord E1 and 9 for cord E4). Thus cord E3 has a relatively small diameter, but at the cost of a lower apparent toughness a than cord E1 and a ply strength Rn comparable to that of cord E2, that is to say relatively low. Furthermore, the loss in cord E3 is relatively high.

[0143] By contrast with the cord E1, the construction of the core E4 is such that M=N=3, enabling it to be manufactured on the existing twisting machinery without modifying the machinery. By contrast with the cord E2, the diameter of the cord E4 is smaller than that of the cord E1. As a consequence of the reduced diameter, by contrast with the cords E2 and E3, the cord E4 has an apparent toughness equivalent to that of the cord E1. Additionally, by contrast with the cords E2 and E3, the ply breaking strength Rn is kept at a satisfactory level with respect to the cord E1. Finally, and especially, the cord E3 has a much better endurance than that of the cords E1, E2 and E3. However, the construction M=N=3 also has the effect of it being necessary either to use a relatively long manufacturing process or to use numerous twisting machines simultaneously since the cord is based on 9 yarns.

[0144] Finally, the cord 30 according to the invention has the best compromise between controlled diameter, improved endurance and very easy manufacture. This is because, by contrast with cords E1 and E4, the construction of the cord 30 according to the invention is such that M=2 and N=3 and enables it to be manufactured on the existing twisting machinery without modifying the machinery, while allowing the use of a method which is relatively fast and also requires a very low number of machines because of the low number of yarns used for the cord (6 for cord 30 according to the invention, as against 12 for cord E1 and 9 for cord E4). By contrast with cord E2, the diameter of the cord 30 according to the invention is equivalent to that of cord E1. Such a diameter makes it possible to avoid increasing the ply thickness, the weight of the latter, and the hysteresis of the tyre, and therefore the rolling resistance of the tyre. Furthermore, by contrast with cords E2 and E3, the ply breaking strength Rn is kept at a satisfactory level relative to cord E1. Above all, the cord 30 shows a much better endurance than that of cords E1, E2 and E3.

[0145] In conclusion, by virtue of the invention, it is now possible, for the same given final twist, to retain the properties of compactness and to improve the endurance in flexion and compression of the textile cords, and to improve further the architecture of the tyres to be reinforced with these cords, without the need to make numerous modifications to the existing manufacturing machinery, while also using a method which is fast and requires a very small number of machines, owing to the low number of yarns on which the cord is based.

[0146] The invention is not limited to the embodiments described above. In fact, an embodiment in which the working reinforcement comprises two working plies may be conceivable. In this embodiment, each carcass reinforcement filamentary element forms an angle greater than or equal to 80, preferably ranging from 80 to 90, with the circumferential direction of the tyre in the median plane of the tyre and in the equatorial circumferential plane of the tyre. In this way, a tyre having a radial carcass reinforcement both in the sidewalls and in the crown is obtained. In this embodiment, each working ply comprises several, preferably metal, working reinforcement filamentary elements arranged side by side substantially parallel to one another. Such working reinforcement filamentary elements form an angle ranging from 10 to 40, preferably ranging from 20 to 30 with the circumferential direction of the tyre.

[0147] Advantageously, the angles formed by the working reinforcement elements of the two plies are oriented in opposite directions. In other words, the working reinforcement elements of the two plies are crossed from one working ply to the other. In this embodiment, as in the embodiment described in more detail above, the hoop reinforcement filamentary element(s), the working reinforcement filamentary elements and the carcass reinforcement filamentary elements are advantageously arranged so as to define, in projection onto the equatorial circumferential plane, a triangle mesh.

TABLE-US-00001 TABLE 1 E1 E2 E3 E4 30 A55/1/3/4 A167/1/2/2 A84/1/2/3 A55/1/3/3 A110/1/2/3 Name Z120/Z180/S300 Z120/Z180/S300 Z120/Z180/S300 Z140/Z200/S340 Z120/Z180/S300 Count of each yarn 55 167 84 55 110 M 3 2 2 3 2 N 4 2 3 3 3 T1 (turns.m.sup.1) 120 120 120 140 120 T2 (turns; m.sup.1) 180 180 180 200 180 T3 (turns; m.sup.1) 300 300 340 340 300 K1 23 41 29 27 33 K2 61 87 61 68 70 K3 203 204 201 199 203 Fr (daN) 116.5 88.1 73.7 87.0 99.7 Fr (base 100) 100 76 63 75 86 Diameter (mm) 0.96 1.01 0.84 0.84 0.97 (daN/mm2) 161 110 133 157 135 (base 100) 100 68 83 98 84 Density (cords/dm) 86 81 99 98 86 Laying pitch (mm) 1.16 1.22 1.01 1.01 1.17 Calenderability factor 4.8 4.8 4.9 4.9 4.9 Rn (daN/mm) 100.4 72.2 72.9 86.1 85.2 (daN/mm2) 90 65 82 109 90 Drop-off (%) 44 41 38 31 33