REINFORCING ELEMENT, ELASTOMER COMPOSITE AND TIRE COMPRISING SAID REINFORCING ELEMENT

Abstract

The reinforcing element (45) comprises an assembly (49) made up: of a multifilament strand made of aromatic polyamide or aromatic copolyamide (46) and of a multifilament strand made of polyester (48). The two strands (46, 48) are wound in a helix around one another, and the reinforcing element (45) is twist-balanced. The twist factor K of the reinforcing element (45) ranges from 5.5 to 6.5 where K is defined by the formula: K=(RTi.sup.1/2)/957 in which R is the twist of the reinforcing element (45) expressed in twists per metre and Ti is the sum of the counts of the multifilament strands of the reinforcing element (45) in tex.

Claims

1.-22. (canceled)

23. A reinforcing element comprising an assembly made up of: a multifilament strand made of aromatic polyamide or aromatic copolyamide; and a multifilament strand made of polyester, wherein the two multifilament strands are wound in a helix around one another and the reinforcing element is twist-balanced, the twist factor K of the reinforcing element ranging from 5.5 to 6.5 with K being defined by the formula:
K=(RTi.sup.1/2)/957 in which R is the twist of the reinforcing element expressed in twists per meter and Ti is the sum of the counts of the multifilament strands of the reinforcing element in tex.

24. The reinforcing element according to claim 23, wherein the twist factor K of the reinforcing element ranges from 5.5 to 6.5, the value 5.5 being excluded.

25. The reinforcing element according claim 23, wherein the twist of the reinforcing element ranges from 275 to 365 twists per meter.

26. The reinforcing element according to claim 23, wherein a count of the multifilament strand made of aromatic polyamide or aromatic copolyamide ranges from 140 to 210 tex.

27. The reinforcing element according to claim 23, wherein a count of the multifilament strand made of polyester ranges from 100 to 210 tex.

28. The reinforcing element according to claim 23, wherein an initial tensile modulus of the reinforcing element ranges from 5.0 to 10.5 cN/tex.

29. The reinforcing element according to claim 23, wherein a final tensile modulus of the reinforcing element ranges from 14.0 to 21.5 cN/tex.

30. The reinforcing element according to claim 23, wherein a ratio of a final tensile modulus to an initial tensile modulus ranges from 2.10 to 2.75.

31. An elastomer composite comprising at least one reinforcing element according to claim 23 embedded in an elastomer composition.

32. The elastomer composite according to claim 31, wherein a density of reinforcing elements in the composite ranges from 80 to 145 reinforcing elements per decimeter of composite.

33. The elastomer composite according to claim 31, wherein a ratio of the diameter of the reinforcing element to the thickness of the composite is less than 0.65.

34. The elastomer composite according to claim 31, wherein a diameter of the reinforcing element is less than or equal to 0.95 mm.

35. The elastomer composite according to claim 31, wherein the thickness of the composite is less than or equal to 1.45 mm.

36. A tire comprising a carcass reinforcement comprising at least one carcass ply, wherein the at least one carcass ply is obtained from an elastomer composite according to claim 31.

37. The tire according to claim 36, wherein the carcass reinforcement comprises a single carcass ply.

38. The tire according to claim 36, wherein the carcass ply is obtained from the elastomer composite by shaping a green tire.

39. The tire according to claim 36 further comprising two sidewalls, each sidewall having a mean thickness F, measured in a median tangential plane T of the tire of less than 10 mm.

40. The tire according to claim 36, wherein the tire is designed to run flat.

41. The tire according to claim 40 further comprising a sidewall insert positioned axially on the inside of the carcass reinforcement.

42. The tire according to claim 40 further comprising two sidewalls, each sidewall having a mean thickness F, measured in a median tangential plane T of the tire of greater than or equal to 10 mm.

Description

[0075] The invention will be better understood in the light of the following description, which is given solely by way of non-limiting example and with reference to the drawings in which:

[0076] FIG. 1 is a view in radial section of a tyre according to a first embodiment of the invention;

[0077] FIG. 2 illustrates a composite that can be used to obtain a carcass ply of the tyre of FIG. 1;

[0078] FIG. 3a illustrates a view, in cross section on III-III, of the composite of FIG. 2;

[0079] FIG. 3b is a view, similar to that of FIG. 3a, of a composite of the prior art;

[0080] FIG. 4 illustrates a detail view of a reinforcing element of the tyre of FIG. 1, and of the composite of FIG. 2;

[0081] FIG. 5 is an enlargement of a view in cross section of a reinforcing element according to the invention; and

[0082] FIGS. 6 and 7 are views similar to that of FIG. 1 of tyres respectively according to second and third embodiments of the invention.

[0083] When using the term radial, a distinction should be made between several different uses of the word by the person skilled in the art. Firstly, the expression refers to a radius of the tyre. It is in that sense that a point A is said to be radially inside a point B (or radially on the inside of the point B) if it is closer to the axis of rotation of the tyre than is the point B. Conversely, a point C is said to be radially outside a point D (or radially on the outside of the point D) if it is further from the axis of rotation of the tyre than is the point D. Progress radially inwards (or outwards) will mean progress towards smaller (or larger) radii. It is this sense of the word that applies also when radial distances are being discussed.

[0084] A radial cross section or radial section here means a cross section or a section in a plane which contains the axis of rotation of the tyre.

[0085] The median circumferential plane M of the tyre is the plane which is normal to the axis of rotation of the tyre and which is situated equidistantly from the annular reinforcing structures of each bead.

[0086] As already described hereinabove, the median tangential plane T of the tyre is the plane perpendicular to the median circumferential plane M and radially equidistant from a first tangential plane T1 passing through the external surface of the tread and from a second tangential plane T2 passing through the radially internal end of the tyre.

[0087] An axial direction is a direction parallel to the axis of rotation of the tyre.

[0088] A circumferential direction is a direction which is perpendicular both to a radius of the tyre and to the axial direction.

[0089] As already described hereinabove, F is the mean thickness of the sidewall of the tyre measured in the median tangential plane, namely the distance measured between the external wall and the internal wall of the tyre in the median tangential plane. This thickness is a mean thickness because it is calculated over 5 values measured on 5 sections uniformly circumferentially distributed over the tyre.

[0090] In the present application, unless specified otherwise, any range of values denoted by the expression from a to b means the range of values ranging from the end point a to the end point b, i.e. including the strict end points a and b.

[0091] Tyre According to a First Embodiment of the Invention

[0092] A frame of reference X, Y, Z corresponding to the usual respectively axial (X), radial (Y) and circumferential (Z) directions of a tyre has been depicted in the figures.

[0093] FIG. 1 schematically depicts a view in radial section of a tyre according to a first embodiment of the invention and 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 here is intended for a passenger vehicle. The tyre 10 has an aspect ratio ranging from 30 to 55, and preferably from 30 to 50. In this particular instance, the tyre is of the size 245/40 R18 and therefore has an aspect ratio equal to 40. The tyre 10 according to the first embodiment is not designed to run flat.

[0094] The tyre 10 comprises a crown 12 comprising a crown reinforcement 14 comprising a working reinforcement 15 comprising two working plies 16, 18 of working reinforcing elements and a hoop reinforcement 17 comprising a hooping ply 19 of hoop reinforcing elements. The crown reinforcement 14 is surmounted by a tread 20 arranged radially on the outside of 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.

[0095] The tyre also comprises two sidewalls 22 extending the crown 12 radially inwards. The tyre 10 further comprises two beads 24 radially on the inside of the sidewalls 22 and each comprising an annular reinforcing structure 26, in this instance a bead wire 28, surmounted by a mass of bead apex filling rubber 30, and also a radial carcass reinforcement 32.

[0096] The carcass reinforcement 32 comprises at least one carcass ply comprising several reinforcing elements, the ply being anchored to each of the beads 24 by a turn-up around the bead wire 28, so as to form, within each bead 24, a main strand 38 extending from the beads through the sidewalls towards the crown 12, and a turn-up strand 40, the radially outer end 42 of the turn-up 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 as far as into the crown 12. The carcass reinforcement 32 is arranged radially on the inside of the crown reinforcement 14 and of the hoop reinforcement 17. The carcass reinforcement 32 comprises a single carcass ply 34.

[0097] The tyre 10 also comprises an airtight inner liner 43, preferably made of butyl, located axially on the inside of the sidewalls 22 and radially on the inside of the crown reinforcement 14 and extending between the two beads 24.

[0098] The mean thickness F of each sidewall 22 of the tyre 10, measured in the median tangential plane T, is less than 10 mm. In this particular instance, the mean thickness F is equal here to 5 mm.

[0099] Each working ply 16, 18, hooping ply 19 and carcass ply 34 comprises a polymer composition in which reinforcing elements of the corresponding ply are embedded. Each polymer composition, here an elastomer composition, of the working plies 16, 18, hooping ply 19 and carcass ply 34 is made from a conventional composition for the skimming 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 vulcanization system, preferably comprising sulfur, stearic acid and zinc oxide, and possibly a vulcanization accelerator and/or retarder and/or various additives.

[0100] Composite According to the Invention

[0101] A composite from which the carcass ply 34 is obtained will now be described with reference to FIGS. 2, 3a and 4.

[0102] The composite comprises several reinforcing elements. The reinforcing elements are arranged side-by-side and parallel to one another in a main direction D substantially perpendicular to the overall direction G in which the reinforcing elements of the carcass ply extend, the overall direction G making an angle ranging from 80 to 90 with the circumferential direction Z of the tyre 10 once the composite that forms the carcass ply 34 is in the tyre 10. In this particular instance, the overall direction G makes an angle substantially equal to 90 with the circumferential direction Z of the tyre 10 once the composite that forms the carcass ply 34 is in the tyre 10.

[0103] A reinforcing element 45 and the corresponding assembly 49 will be described hereinbelow. A composite 36 corresponding to the reinforcing element 45 will also be described.

[0104] Nature of the Strands of the Reinforcing Element

[0105] As depicted schematically in FIG. 4, the reinforcing element 45 comprises an assembly 49 made up of a multifilament strand made of aromatic polyamide or of aromatic copolyamide 46 and a multifilament strand made of polyester 48, the two strands 46, 48 being wound in a helix one around the other. The reinforcing element 45 is twist-balanced. For the sake of the accuracy of the description, FIG. 5 is a view in cross section of the reinforcing element 45 according to the invention, in which the monofilaments of each of the strands can be discerned.

[0106] The aromatic polyamide selected is, in this instance, preferably a para-aramid known by the Teijin company trade name of Twaron 1000. The polyester is polyethylene terephthalate (PET) known by the Hyosung or Hailide company trade name of PET HMLS (High Module Low Shrinkage).

[0107] In certain embodiments which have not been depicted, the reinforcing element 45 comprises, in addition to the assembly 49, a layer of an adhesive composition coating the assembly 49.

[0108] Count of the Reinforcing Element

[0109] The count of the multifilament strand 46 made of aromatic polyamide or aromatic copolyamide ranges from 140 to 210 tex, preferably from 150 to 190 tex, and more preferably from 160 to 180 tex.

[0110] In the reinforcing element 45, the count of the strand 46 is equal to 167 tex.

[0111] The count of the multifilament strand 48 made of polyester ranges from 100 to 210 tex, preferably from 120 to 190 tex, more preferably from 130 to 180 tex, more preferably still from 160 to 180 tex.

[0112] In the reinforcing element 45, the count of the strand 48 is equal to 167 tex.

[0113] Twist of the Reinforcing Element

[0114] In the reinforcing element 45, the twist of the reinforcing element ranges from 275 to 365 twists per metre, preferably from 275 to 350 twists per metre, and more preferably from 300 to 330 twists per metre. In this particular instance, the twist of the reinforcing element 45 is equal to 315 twists per metre.

[0115] Initial and Final Modulus of the Reinforcing Element

[0116] The initial tensile modulus of each reinforcing element 45 ranges from 5.0 to 10.5 cN/tex.

[0117] In the reinforcing element 45, the initial tensile modulus of the reinforcing element advantageously ranges from 5.7 to 8.5 cN/tex, preferably from 6.2 to 7.8 cN/tex, and more preferably from 6.8 to 7.5 cN/tex. In this particular instance, the initial modulus of the reinforcing element 45 is equal to 7.2 cN/tex.

[0118] The final tensile modulus of the reinforcing element 45 ranges from 14.0 to 21.5 cN/tex.

[0119] In the reinforcing element 45, the final tensile modulus of the reinforcing element advantageously ranges from 15.0 to 19.0 cN/tex, preferably from 15.8 to 18.5 cN/tex, and more preferably from 16.6 to 17.9 cN/tex. In this particular instance, the final modulus of the reinforcing element 45 is equal to 16.9 cN/tex.

[0120] The ratio of the final modulus to the initial modulus ranges from 2.10 to 2.75.

[0121] In the reinforcing element 45, the ratio of the final modulus to the initial modulus advantageously ranges from 2.15 to 2.45, preferably from 2.20 to 2.40 and more preferably from 2.25 to 2.40. In this particular instance, the ratio of the final modulus to the initial modulus of the reinforcing element 45 is equal to 2.34.

[0122] Twist Factor of the Reinforcing Element

[0123] The twist factor K of the reinforcing element 45 ranges from 5.5 to 6.5.

[0124] Preferably, in the reinforcing element 45, the twist factor K belongs to the interval ]5.5; 6.5] (which means to say excluding the value 5.5), preferably from 5.6 to 6.1, and more preferably still from 5.9 to 6.1. In this particular instance, the twist factor K of the reinforcing element 45 is equal to 6.0.

[0125] Geometric Characteristics of the Composite

[0126] Returning to FIG. 3a, the composite 36 has a thickness E and the reinforcing element 45 has a diameter d. The diameter d corresponds to the diameter of the theoretical circle inside which the reinforcing element can be inscribed. In this FIG. 3a, each strand has deliberately been depicted schematically for the sake of simplifying the description. FIG. 5 illustrates the reinforcing element 45 as it actually would appear.

[0127] The diameter of the reinforcing element 45 is less than or equal to 0.95 mm, preferably less than or equal to 0.80 mm, more preferably less than or equal to 0.70 mm. The reinforcing element 45 has a diameter d=0.67 mm.

[0128] The thickness E of the composite 36 is less than or equal to 1.45 mm, preferably less than or equal to 1.30 mm, more preferably less than or equal to 1.20 mm. The reinforcing element 45 has a thickness E=1.10 mm.

[0129] Thus, the ratio d/E is strictly less than 0.65, preferably less than or equal to 0.62. The reinforcing element 45 has a ratio d/E=0.61.

[0130] The density of the reinforcing element 45 in the composite 36 ranges from 90 to 130 reinforcing elements per decimetre of each composite 36, preferably from 100 to 125 reinforcing elements per decimetre of the composite 36, and more preferably from 105 to 120 reinforcing elements per decimetre of the composite 36. For the composite 36, the density of reinforcing elements 45 is equal to 110 reinforcing elements per decimetre of composite 36.

[0131] FIG. 3a depicts the pitch P which is the distance separating two analogous points of two adjacent reinforcing elements 45. The pitch P is generally referred to as the laying pitch at which the reinforcing elements are laid in the composite. The pitch P and the density of reinforcing elements per decimetre of composite are such that the density of reinforcing elements per decimetre of composite is equal to 100/P.

[0132] The density of reinforcing elements and the thickness which are described hereinabove are, as explained previously, the density of reinforcing elements 45 and the thickness E of the composite 36. In the tyre 10, as the carcass ply 34 is obtained from the composite 36 by shaping a green tyre, the density of reinforcing elements and the thickness of the carcass ply 34 differ from those of the composite and vary according to their distance away from the axis of revolution of the tyre. These variations are notably dependent on the shape factor of the green form of the tyre and also on the geometry thereof. A person skilled in the art will be able, notably on the basis of the shape factor of the green form of the tyre and of the geometry thereof, to determine the characteristics of the corresponding composite.

[0133] Method for Manufacturing the Reinforcing Element

[0134] As described hereinabove, the reinforcing element 45 is twist-balanced, which means to say that the two multifilament strands are wound with substantially the same twist and that the twist of the monofilaments in each multifilament strand is substantially zero. In a first step, each spun yarn of monofilaments (more properly referred to as a yarn) is first of all twisted individually on itself with an initial twist equal to 315 twists per metre in a given direction, in this instance the Z direction, to form a strand or overtwist (more properly referred to as a strand). Then, during a second step, the two strands are then twisted together with a final twist equal to 315 twists per metre in the S direction to obtain the assembly of the reinforcing element (more properly referred to as a cord).

[0135] In later steps, each assembly is coated with an adhesive composition, for example an adhesive composition of the RFL (Resorcinol-Formaldehyde-Latex) type, and undergoes heat treatment steps in order to at least partially crosslink the adhesive composition.

[0136] Method for Manufacturing the Composite According to the Invention

[0137] The composite 36 is manufactured by embedding several reinforcing elements 45 in the elastomer composition, for example by skimming. During such a skimming step, which is well known to those skilled in the art, reinforcing elements are moved along, and two strips made of an elastomer composition, and referred to as skims, are brought in, one on each side of the reinforcing elements, so that the reinforcing elements are sandwiched between the two skims. The reinforcing elements are thus embedded in the elastomer composition.

[0138] Method for Manufacturing the Tyre According to the Invention

[0139] The method for manufacturing the tyre is the one conventionally used by those skilled in the art. During the course of this method and as already described hereinabove, various plies and composite, including the composites according to the invention which is intended to form the carcass ply 34 of the tyre 10, are successively laid, during a first series of tyre building steps. The green form thus obtained is then shaped. Next, other plies and composites intended to form the crown 12 of the tyre 10 are laid. Finally, the green form thus obtained is vulcanized in order to obtain the tyre 10.

[0140] Tyre According to a Second Embodiment of the Invention

[0141] FIG. 6 depicts a tyre according to a second embodiment of the invention. Elements similar to those of the first embodiment are denoted by identical references.

[0142] Unlike the tyre 10 according to the first embodiment, the tyre 10 according to the second embodiment has an aspect ratio higher than or equal to 55, preferably ranging from 55 to 75. In this particular instance, the tyre is of the size 205/55 R16 and therefore has an aspect ratio equal to 55.

[0143] Tyre According to a Third Embodiment of the Invention

[0144] FIG. 7 depicts a tyre according to a third embodiment of the invention. Elements similar to those of the first embodiment are denoted by identical references.

[0145] Unlike the tyre 10 according to the first embodiment, the tyre 10 according to the third embodiment is a tyre designed to run flat. Thus, the tyre is configured in such a way as to withstand a load corresponding to a portion of the weight of the vehicle during a run-flat situation, namely with a pressure substantially equal to atmospheric pressure.

[0146] The tyre 10 according to the third embodiment comprises two self-supporting sidewalls 22 extending the crown 12 radially inwards. For this purpose, the tyre 10 comprises two sidewall inserts 50, axially on the inside of the carcass reinforcement 32 and axially on the outside of the airtight inner liner 43. Thus, the sidewall inserts 50 are positioned axially between the carcass reinforcement 32 and the airtight inner liner 43.

[0147] These inserts 50 with their characteristic crescent-shaped radial cross section are intended to reinforce the sidewalls 22. Each insert 50 is made from a specific elastomer composition. Document WO 02/096677 gives several examples of specific elastomer compositions that can be used to form such an insert. Each sidewall insert 50 is capable of contributing towards withstanding a load corresponding to a portion of the weight of the vehicle during a run-flat situation.

[0148] Unlike in the first embodiment of the tyre, each sidewall 22 has a mean thickness F, measured in the median tangential plane T, that is greater than or equal to 10 mm. In this particular instance, the mean thickness F is equal here to 17 mm.

[0149] Comparative Tests and Measurements

[0150] By way of a comparative example, FIG. 3b depicts a composite of the prior art denoted by the general reference NT of a tyre of the prior art. The composite NT comprises reinforcing elements ET each comprising an assembly made up of two multifilament strands made of polyester which are assembled with one another and wound in a helix around one another at a twist of 270 twists per metre. Each reinforcing element ET is twist-balanced. Each multifilament strand of the reinforcing element ET has a count equal to 334 tex.

[0151] Use was also made of a control composite NT comprising control reinforcing elements ET each comprising an assembly made up of a multifilament strand made of aromatic polyamide or aromatic copolyamide, and a multifilament strand made of polyester which are assembled with one another and wound in a helix around one another at a twist of 290 twists per metre. Each reinforcing element ET is twist-balanced. The multifilament strand of aromatic polyamide or aromatic copolyamide, in this case para-amide identical to that of the reinforcing element 45, has a count equal to 167 tex. The multifilament strand of polyester, in this case of PET identical to that of the reinforcing element 45, has a count equal to 144 tex.

[0152] Comparison Between Reinforcing Elements

[0153] Table 1 summarizes the characteristics of the reinforcing element 45 of the tyre 10 according to the invention, of the control reinforcing element ET and of the reinforcing element ET of the prior art. The force at break measurements are taken under tensile testing according to standard ISO 6892, 1984.

TABLE-US-00001 TABLE 1 ET ET 45 Nature of the strands PET/PET p-Aramid/ p-Aramid/ PET PET Initial modulus at 20 C. (cN/tex) 5.0 8.2 7.2 Final modulus at 20 C. (cN/tex) 3.6 18.9 16.9 Ratio of final modulus to initial 0.72 2.29 2.34 modulus at 20 C. Twist (t/m) 270 290 315 Count of the strands (tex) 334/334 167/144 167/167 Twist factor K 7.3 5.3 6.0 Force at break (daN) 40 36.8 39.6

[0154] Note that the reinforcing element 45 has initial and final modulus values that are significantly higher than those of the reinforcing element of the prior art ET.

[0155] The force at break value of the reinforcing element 45 is high enough to effectively combat road hazards. It will be noted that the force at break of the reinforcing element 45 is greater than that of the control reinforcing element ET and is almost dentical to that of the reinforcing element ET.

[0156] Comparison of the Composites

[0157] The composite 36 according to the invention comprising reinforcing elements 45 was compared with the control composite NT comprising the control reinforcing elements ET and a composite NT of the prior art comprising reinforcing elements ET. The geometric characteristics of these composites are collated in Table 2 below.

TABLE-US-00002 TABLE 2 Composite NT NT 36 Reinforcing element ET 44 45 Density (reinforcing 80 116 110 elements/dm) Diameter d of the 0.96 0.65 0.67 reinforcing element (mm) Thickness E of the 1.47 1.16 1.10 composite (mm) Ratio d/E 0.65 0.56 0.61 Force at break of the 320 427 436 composite (daN/cm)

[0158] Note that the reinforcing element ET of the prior art has a diameter d very much greater than that of the reinforcing elements 45 of the composite according to the invention. The composite 36 according to the invention is far thinner than the composite NT and than the composite NT. The ratio d/E of the composite 36 is smaller than the ratio d/E of the composite of the prior art which means that the composite 36 is lighter in weight.

[0159] It will be noted that, in addition to being more lightweight, the composite 36 has a significantly higher force at break than the composite NT and than the composite NT.

[0160] Force at Break of the Reinforcing Elements

[0161] Table 3 gives the force at break of reinforcing elements comprising a multifilament strand made of aramid (Twaron 1000 by the company Teijin) having a count equal to 167 tex and a multifilament strand made of PET (PET HMLS by the company Hyosung) having a count equal to 144 tex, the two strands being wound in a helix one around the other and each reinforcing element being twist-balanced. The twist was varied in such a way as to vary the twist factor K from 3.7 to 7.0. The force at break measurements are taken under tensile testing according to standard ISO 6892, 1984.

TABLE-US-00003 TABLE 3 Twist factor K 3.7 4.0 4.2 4.6 5.0 5.3 5.5 5.6 5.9 6.3 6.6 7.0 Force at 38.1 39.3 38.5 38.2 37.0 36.8 37.0 36.6 37.0 36.8 34.2 34.9 break (daN)

[0162] Table 4 then gives the force at break of reinforcing elements comprising a multifilament strand made of aramid (Twaron 1000 by the company Teijin) having a count equal to 167 tex and a multifilament strand made of PET (PET HMLS by the company Hailide) having a count equal to 167 tex, the two strands being wound in a helix one around the other and each reinforcing element being twist-balanced. The twist was varied in such a way as to vary the twist factor K from 4.6 to 7.0. The force at break measurements are taken under tensile testing according to standard ISO 6892, 1984.

TABLE-US-00004 TABLE 4 Twist factor K 4.6 4.8 5.2 5.3 5.5 5.7 6.0 6.5 7.0 Force at 42.0 41.1 40.1 40.7 40.0 39.8 39.6 39.7 37.1 break (daN)

[0163] Tables 3 and 4 show that, for a given count, in the interval of twist factors K ranging from 5.5 to 6.5, the force at break of each reinforcing element is substantially constant. Thus, as described hereinabove, in the selected twist-factor interval, the tyre designer can adapt other characteristics of the reinforcing element, notably the twist, to suit the use or uses for which the tyre is intended, notably in order to vary the durability as explained hereinbelow.

[0164] Durability of the Reinforcing Elements

[0165] The durability of the reinforcing element 45 was compared against that of other aramid/PET reinforcing elements I, II, III and ET. The reinforcing elements II and 45 are in accordance with the invention. The reinforcing elements I, III and ET are not in accordance with the invention. In order to evaluate durability, reinforcing elements were embedded in an elastomer composition in order to form a test specimen in the form of a strip with a thickness equal to 30 mm which was cycled around a cylindrical bar. After 190,000 cycles, the final force at break of each reinforcing element was measured. The drop-off, corresponding to the loss, as a %, in the force at break after the 190,000 cycles, was then calculated. The higher the drop-off, the lower the durability. The results of the tests and the characteristics of the reinforcing elements tested are collated in Table 5 below.

TABLE-US-00005 TABLE 5 Reinforcing element I II III ET 45 Count of aramid/ 167/167 167/167 167/144 167/144 167/167 PET strands (tex) Twist factor K 5.3 5.7 7.0 5.3 6.0 Initial force at break 40.7 39.8 34.9 36.8 39.6 (daN) Final force at break 18.2 23.2 27.5 18.7 28.0 (daN) Drop-off (%) 55.3 41.7 21.2 49.2 29.3

[0166] The results for the reinforcing elements II and 45 show that, for given strand counts, within the twist-factor K interval ranging from 5.5 to 6.5, the durability can be varied according to the desired use of the tyre, for example by varying the twist. Thus, the tyre designer can vary the durability according to the specific use for which the tyre is intended, for example a sporting use by increasing the twist, or alternatively may select a durability compatible with most present-day tyre uses, by selecting a lower twist.

[0167] These results show that the reinforcing element 45 has both a relatively high initial force at break and a durability close to that of the reinforcing element III having a much higher twist factor. Moreover, in the twist-factor K interval ranging from 5.5 to 6.5, the initial force at break is far higher than that of the reinforcing element III that has a twist factor above the interval.

[0168] Comparison of the Tyres

[0169] The tyre 10 according to the invention was compared against a tyre PT of the prior art comprising a carcass ply obtained from the composite NT.

[0170] The masses of the tyres 10 and PT were compared by weighing the tyres tested. The results of this test are collated in Table 6 below.

TABLE-US-00006 TABLE 6 Tyre PT 10 Mass 10.27 kg 10.06 kg

[0171] Thus it is noted that the tyre 10 exhibits a lower mass in comparison with the tyre of the prior art PT.

[0172] The invention is not limited to the embodiments described above.

[0173] In embodiments not described hereinabove, the tyre may have an aspect ratio ranging from 60 to 70.

[0174] It will also be possible to combine the characteristics of the various embodiments and alternative forms described or envisaged hereinabove, provided that these characteristics are compatible with one another.