TYRE FOR VEHICLE WHEELS

Abstract

A tyre for vehicle wheels comprises a support structure and a tread band arranged in a radially outer position with respect to the support structure. The support structure comprises a plurality of hybrid reinforcing cords (10). Each of the hybrid reinforcing cords (10) has at least two strands (20) twisted together with a predetermined twisting pitch. Each of said at least two strands (20) comprises at least one monofilament textile wire (21) and at least one multifilament textile yarn (22) comprising a plurality of textile filaments (22a). In any cross section of the hybrid reinforcing cord (10), said at least one monofilament textile wire (21) is at least partially embedded in the filaments (22a) of said at least one multifilament textile yarn (22).

Claims

1-16. (canceled)

17. The tyre for vehicle wheels, comprising a support structure and a tread band arranged in a radially outer position with respect to the support structure, wherein the support structure comprises a plurality of hybrid reinforcing cords, each of the hybrid reinforcing cords having at least two strands twisted together with a predetermined twisting pitch (P), wherein each of the at least two strands comprises: at least one monofilament textile wire; and at least one multifilament textile yarn comprising a plurality of textile filaments; wherein, in any cross section of the hybrid reinforcing cord, the at least one monofilament textile wire is at least partially embedded in the filaments of the at least one multifilament textile yarn.

18. The tyre according to claim 17, wherein, in any cross section of the hybrid reinforcing cord, at least 50% of an outer surface of the monofilament textile wire is embedded in the filaments of the at least one multifilament textile yarn.

19. The tyre according to claim 17, wherein the at least one monofilament textile wire is twisted on itself with a predetermined first torsion pitch (T).

20. The tyre according to claim 19, wherein the first torsion pitch (T) is equal to the predetermined twisting pitch (P).

21. The tyre according to claim 17, wherein the at least one multifilament textile yarn is substantially parallel to the at least one monofilament textile wire.

22. The tyre according to claim 17, wherein the filaments of the at least one multifilament textile yarn are helically wound on the at least one monofilament textile wire with a predetermined winding pitch (W).

23. The tyre according to claim 22, wherein the winding pitch (W) is equal to the twisting pitch (P).

24. The tyre according to claim 17, wherein the at least one monofilament textile wire is made of one or more of aliphatic polyamide fibers, polyester fibers, polyaryletherketone fibers, and mixtures thereof.

25. The tyre according to claim 17, wherein the filaments of the at least one multifilament textile yarn are made of one or more of aromatic polyamide fibers, aliphatic polyamide fibers, polyester fibers, polyketone fibers, polyvinylalcohol fibers, cellulose fibers, glass fibers, carbon fibers, and mixtures thereof.

26. The tyre according to claim 17, wherein each of the at least two strands comprises a single monofilament textile wire and a single multifilament textile yarn.

27. The tyre according to claim 17, wherein the at least one monofilament textile wire has a diameter ranging from about 0.10 mm to about 0.70 mm.

28. The tyre according to claim 17, wherein the at least one multifilament textile yarn has a linear density ranging from about 400 dTex to about 4000 dTex.

29. The tyre according to claim 17, wherein the support structure comprises: a carcass structure comprising at least one carcass layer having opposite end edges turned around respective annular anchoring structures to define, on opposite sides with respect to an equatorial plane (X) of the tyre, respective bead structures; and a crossed belt structure arranged in a radially outer position with respect to the carcass structure and in a radially inner position with respect to the tread band; wherein the plurality of hybrid reinforcing cords are arranged in at least one of: the carcass structure; the belt structure; and at least one stiffening layer associated with the at least one carcass layer at or close to a respective turned end edge.

30. The tyre according to claim 17, wherein two or more of the hybrid reinforcing cords comprise at least one metallic wire helically wound around the at least two strands twisted together.

31. The tyre according to claim 30, wherein the at least two strands are twisted together according to a predetermined twisting direction, and wherein the at least one metallic wire is wound on the at least two strands twisted together with a winding direction opposite to the predetermined twisting direction.

32. A hybrid reinforcing cord comprising: at least two strands twisted together with a predetermined twisting pitch (P), wherein each of the at least two strands comprises: at least one monofilament textile wire; at least one multifilament textile yarn comprising a plurality of textile filaments; wherein, in any cross section of the hybrid reinforcing cord, the at least one monofilament textile wire is at least partially embedded in the filaments of the at least one multifilament textile yarn.

Description

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0122] Further features and advantages of the tyre of the present invention will become clearer from the following detailed description of preferred embodiments thereof, made with reference to the attached drawings. In such drawings:

[0123] FIG. 1 is a schematic partial half cross-section view of a portion of a tyre according to an embodiment of the present invention;

[0124] FIG. 2 is a schematic side view of a segment of a first embodiment of a hybrid reinforcing cord used in the tyre of FIG. 1;

[0125] FIG. 3 is an enlarged schematic view of a cross section of the hybrid reinforcing cord of FIG. 2 incorporated in a portion of the tyre of FIG. 1, such a cross section being taken on the section plane S-S drawn in FIG. 2;

[0126] FIG. 4 is a schematic perspective view of the hybrid reinforcing cord of FIG. 2 in which part of its components have been removed to show other components which otherwise would be hidden;

[0127] FIG. 5 is a schematic perspective view of a second embodiment of the hybrid reinforcing cord of FIG. 2 in which part of its components have been removed to show other components which otherwise would be hidden;

[0128] FIG. 6 is a schematic side view of a segment of a second embodiment of a hybrid reinforcing cord used in the tyre of FIG. 1.

[0129] For the sake of simplicity, FIG. 1 shows only a part of an embodiment of a tyre 100 in accordance with the present invention, the remaining part, which is not shown, being substantially identical and being arranged symmetrically with respect to the equatorial plane M-M of the tyre.

[0130] The tyre 100 shown in FIG. 1 is, in particular, an embodiment of a tyre for four-wheeled vehicles.

[0131] Preferably, the tyre 100 is a HP or UHP tyre for sports and/or high or ultra-high performance automobiles.

[0132] In FIG. 1 “a” indicates an axial direction, “c” indicates a radial direction, “M-M” indicates the equatorial plane of the tyre 100 and “R-R” indicates the rotation axis of the tyre 100.

[0133] The tyre 100 comprises at least one support structure 100a and, in a radially outer position with respect to the support structure 100a, a tread band 109 made of elastomeric material.

[0134] The support structure 100a comprises a carcass structure 101, in turn comprising at least one carcass layer 111.

[0135] Hereinafter, for the sake of simplicity of presentation, reference will be made to an embodiment of the tyre 100 comprising a single carcass layer 111. However, it is understood that what is described has analogous application in tyres comprising more than one carcass layer.

[0136] The carcass layer 111 has axially opposite end edges engaged with respective annular anchoring structures 102, called bead cores, possibly associated with an elastomeric filler 104. The area of the tyre 100 comprising the bead core 102 and the possible elastomeric filler 104 forms an annular reinforcing structure 103 called “bead structure” and intended to allow the tyre 100 to be anchored on a corresponding mounting rim, not shown.

[0137] The carcass layer 111 comprises a plurality of reinforcing cords 10′ coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material.

[0138] The carcass structure 101 is of the radial type, i.e. the reinforcing cords 10′ are arranged on planes comprising the rotation axis R-R of the tyre 100 and substantially perpendicular to the equatorial plane M-M of the tyre 100.

[0139] Each annular reinforcing structure 103 is associated with the carcass structure 101 through folding back (or turning) of the opposite end edges of the at least one carcass layer 111 around the bead core 102 and the possible elastomeric filler 104, so as to form the so-called turnings 101a of the carcass structure 101.

[0140] In an embodiment, the coupling between carcass structure 101 and annular reinforcing structure 103 can be carried out through a second carcass layer (not shown in FIG. 1) applied in a radially outer position with respect to the carcass layer 111.

[0141] An anti-abrasion strip 105 is arranged at each annular reinforcing structure 103 so as to surround the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103, thus being located between the latter and the rim of the wheel when the tyre 100 is mounted on the rim. Such an anti-abrasion strip 105 can however not be provided.

[0142] The support structure 100a comprises, in a radially outer position with respect to the carcass structure 101, a crossed belt structure 106 comprising at least two belt layers 106a, 106b arranged in a radial juxtaposition over one another.

[0143] The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10a, 10b. Such reinforcing cords 10a, 10b have an orientation inclined with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle comprised between about 15° and about 45°, preferably between about 20° and about 40°. For example, such an angle is equal to about 30°.

[0144] The support structure 100a can also comprise a further belt layer (not shown) arranged between the carcass structure 101 and the radially innermost belt layer of the aforementioned belt layers 106a, 106b and comprising a plurality of reinforcing cords having an orientation inclined with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle equal to about 90°.

[0145] The support structure 100a can also comprise a further belt layer (not shown) arranged in a radially outer position with respect to the radially outermost belt layer of the aforementioned belt layers 106a, 106b and comprising a plurality of reinforcing cords having an orientation inclined with respect to the circumferential direction of the tyre 100, or to the equatorial plane M-M of the tyre 100, by an angle comprised between about 20° and about 70°.

[0146] The reinforcing cords 10a, 10b of a belt layer 106a, 106b are parallel to one another and have a crossed orientation with respect to the reinforcing cords of the other belt layer 106b, 106a.

[0147] In ultra-high performance tyres, the belt structure 106 can be a turned crossed belt structure. Such a belt structure is made by arranging at least one belt layer on a support element and turning the opposite lateral end edges of said at least one belt layer. Preferably, at first a first belt layer is applied on the support element, then the support element is radially expanded, then a second belt layer is applied on the first belt layer and finally the opposite axial end edges of the first belt layer are turned over the second belt layer to at least partially cover the second belt layer, which is the radially outermost layer. In some cases, a third belt layer can be arranged on the second belt layer. Advantageously, the turning of the axially opposite end edges of a belt layer over another belt layer arranged in a radially outer position thereof imparts greater reactivity and responsiveness of the tyre when cornering.

[0148] The support structure 100a comprises, in a radially outer position with respect to the crossed belt structure 106, at least one zero degrees reinforcing layer 106c, commonly known as “zero degrees belt”. It comprises reinforcing cords 10c oriented in a substantially circumferential direction. Such reinforcing cords 10c thus form an angle of a few degrees (typically lower than about 10°, for example comprised between about 0° and 6°) with respect to the equatorial plane M-M of the tyre 100.

[0149] The reinforcing cords 10a, 10b, 10c are coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material.

[0150] The tread band 109 made of elastomeric material is applied in a radially outer position with respect to the zero degrees reinforcing layer 106c, as well as other constituent semi-finished products of the tyre 100.

[0151] Respective sidewalls 108 made of elastomeric material are also applied on the side surfaces of the carcass structure 101, in an axially outer position with respect to the carcass structure 101 itself. Each sidewall 108 extends from one of the lateral edges of the tread band 109 up to the respective annular reinforcing structure 103.

[0152] The anti-abrasion strip 105, if provided, extends at least up to the respective sidewall 108.

[0153] In some specific embodiments, like the one shown and described here, the rigidity of the sidewall 108 can be improved by providing a stiffening layer 120, generally known as “flipper” or additional strip-like insert, and which has the function of increasing the rigidity and integrity of the annular reinforcing structure 103 and of the sidewall 108.

[0154] The flipper 120 is wound around a respective bead core 102 and the elastomeric filler 104 so as to at least partially surround the annular reinforcing structure 103. In particular, the flipper 120 surrounds the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103.

[0155] The flipper 120 is arranged between the turned end edge of the carcass layer 111 and the respective annular reinforcing structure 103. Usually, the flipper 120 is in contact with the carcass layer 111 and the annular reinforcing structure 103.

[0156] In some specific embodiments, like the one shown and described here, the bead structure 103 can also comprise a further stiffening layer 121 that is generally known by the term “chafer”, or protective strip, and which has the function of increasing the rigidity and integrity of the annular reinforcing structure 103.

[0157] The chafer 121 is associated with a respective turned end edge of the carcass layer 111 in an axially outer position with respect to the respective annular reinforcing structure 103 and extends radially towards the sidewall 108 and the tread band 109.

[0158] The flipper 120 and the chafer 121 comprise reinforcing cords 10d (in the attached figure those of the flipper 120 are not visible) coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material.

[0159] The tread band 109 has, in a radially outer position thereof, a rolling surface 109a intended to contact the ground. The rolling surface 109a has circumferential grooves (not shown in FIG. 1) formed thereon, which are connected by transversal notches (not shown in FIG. 1) so as to define on the rolling surface 109a a plurality of blocks of various shapes and sizes (not shown in FIG. 1).

[0160] A sub-layer 107 is arranged between the crossed belt structure 106 and the tread band 109.

[0161] In some specific embodiments, like the one shown and described here, a strip 110 consisting of elastomeric material, commonly known as “mini-sidewall”, can possibly be provided in the connection area between the sidewalls 108 and the tread band 109. The mini-sidewall 110 is generally obtained through co-extrusion with the tread band 109 and allows an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108.

[0162] Preferably, an end portion of the sidewall 108 directly covers the lateral edge of the tread band 109.

[0163] In the case of tubeless tyres, a layer of rubber 112, generally known as “liner”, can also be provided in a radially inner position with respect to the carcass layer 111 to provide the necessary impermeability to the inflation air of the tyre 100.

[0164] At least some of the reinforcing cords 10′ (preferably all of the reinforcing cords 10′ provided in the carcass layer 111) and/or the reinforcing cords 10a, 10b (preferably all of the reinforcing cords 10a provided in the belt layer 106a and all of the reinforcing cords 10b provided in the belt layer 106b, even in the case in which the belt structure 106 is a turned crossed belt structure) and/or the reinforcing cords 10c of the flipper 120 and/or of the chafer 121 are hybrid reinforcing cords 10 of the type shown in FIGS. 2-6 and described below.

[0165] The reinforcing cords 10c, on the other hand, are preferably non-hybrid reinforcing cords, i.e. they are made of a single textile material, preferably aramid or nylon.

[0166] With reference to FIGS. 2-4, the hybrid reinforcing cord 10 comprises two strands 20 twisted together with a predetermined twisting pitch P.

[0167] Preferably, the two strands 20 are identical to each other. Therefore, only one of them will be described hereinafter.

[0168] As shown in FIGS. 3 and 4, the strand 20 comprises a single monofilament textile wire 21 and a single multifilament textile yarn 22 defined by a plurality of filaments 22a. Each strand 21 can however comprise more than one monofilament textile wire 21 and more than one multifilament textile yarn 22.

[0169] In any cross section of the reinforcing cord 10, the monofilament textile wire 21 is embedded in the filaments 22a of the multifilament textile yarn 22.

[0170] In the embodiment shown in FIGS. 3 and 4, the monofilament textile wire 21 is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 22a of the multifilament textile yarn 22 and, therefore, the aforementioned filaments 22 are arranged around the monofilament textile wire 21 so as to completely surround the monofilament textile wire 21.

[0171] Therefore, in FIG. 2, the monofilament textile wire 21 is not visible since it is entirely covered by the filaments of the multifilament textile yarn 22.

[0172] Although the embodiment of FIGS. 2-4 (and as will be seen hereinafter also the embodiment of FIG. 5 and FIG. 6) in which the monofilament textile wire 21 is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 22a of the multifilament textile yarn 22 is particularly preferred, embodiments are equally preferred in which, in any cross section of the reinforcing cord 10, the monofilament textile wire 21 is only partially embedded in the filaments 22a of the multifilament textile yarn 22, and in particular those in which at least 50% of the outer surface of the monofilament textile wire 21 is embedded in the filaments 22a of the multifilament textile yarn 22.

[0173] The monofilament textile wire 21 extends along a longitudinal direction A, shown in FIG. 2.

[0174] The mutual arrangement of the monofilament textile wire 21 and of the filaments 22a of the multifilament textile yarn 22 along the longitudinal direction A can be such that the monofilament textile wire 21 extends substantially parallel to the filaments 22a of the multifilament textile yarn 22, as shown in FIG. 4, or such that the filaments 22a of the multifilament textile yarn 22 are helically wound on the monofilament textile wire 21 with a predetermined winding pitch W that, preferably, is equal to the twisting pitch P.

[0175] In this last case, the direction of twisting of the two strands 20 is preferably the same as that of winding of the filaments 22a of the multifilament textile yarn 22 on the monofilament textile wire 21, but it is possible to foreseen opposite directions.

[0176] The twisting pitch P is preferably comprised between about 1 mm and about 20 mm, more preferably between about 2 mm and about 15 mm, for example equal to about 12.5 mm.

[0177] FIG. 5 shows an embodiment of the hybrid reinforcing cord 10 that differs from the one shown in FIGS. 2 and 3 only in that the monofilament textile wire 21 is twisted on itself with a predetermined torsion pitch T.

[0178] Preferably, the torsion pitch T is equal to the twisting pitch P.

[0179] The direction of torsion of the monofilament textile wire 21 can be equal or opposite to that of the twisting of the two strands 20.

[0180] The monofilament textile wire 21 is made of aliphatic polyamide fibers, for example Nylon 6, Nylon 6.6, Nylon 4.6, Nylon 4.10, Nylon 10.10, Nylon 11, Nylon 12, Nylon 6.10, Nylon 6.12, or polyester fibers, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or polyaryletherketone fibers, for example polyetheretherketone (PEEK), or mixtures thereof.

[0181] The filaments 22a of the multifilament textile yarn 22 are made of aromatic polyamide fibers, or aliphatic polyamide fibers, for example Nylon 6, Nylon 6.6, Nylon 4.6, Nylon 4.10, Nylon 10.10, Nylon 11, Nylon 12, Nylon 6.10, Nylon 6.12, or polyester fibers, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or polyketone fibers, or polyvinylalcohol fibers, or cellulose fibers, for example rayon or lyocell), or glass or carbon fibers, or any mixture of the aforementioned fibers, or assemblies of mixed fibers comprising two or more of the materials listed previously. Such assemblies of mixed fibers are indicated hereinafter with the term “commingled fibers”.

[0182] In the case of “commingled fibers”, the fibers of the filaments 22a can for example comprise: [0183] 50% of Aramid with linear density equal to about 1100 dTex and 50% of PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 2200 dTex”); [0184] 43% of Aramid with linear density equal to about 840 dTex and 57% of PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 1940 dTex”); [0185] 33% of Aramid with linear density equal to about 550 dTex and 67% of PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 1650 dTex”).

[0186] Irrespective of the specific type of textile material used for the filaments 22a of the multifilament textile yarn 22, such a material is suitably subjected to adhesivization to be made adhesive on the surface so as to offer adequate adhesivity to the surrounding elastomeric material. Typically, the adhesivization can be carried out through coating with an adhesive substance or through a chemical or physical treatment.

[0187] For example, the adhesivization is carried out through immersion of the hybrid reinforcing cord 10, after having twisted together the two strands 20, in a solution comprising the adhesive substance.

[0188] The monofilament textile wire 21 preferably has a diameter comprised between about 0.10 mm and about 0.70 mm, more preferably between about 0.15 mm and about 0.50 mm, also depending on the material from which it is made and the area of the tyre 100 in which the hybrid reinforcing cord 10 are arranged.

[0189] The multifilament textile yarn 22 preferably has a linear density comprised between about 400 dTex and about 4000 dTex, preferably between about 800 dTex and about 2500 dTex, also depending on the material from which it is made and the area of the tyre 100 in which the hybrid reinforcing cord 10 are arranged.

[0190] In specific embodiments, only the reinforcing cords 10′, and not also the reinforcing cords 10a, 10b and 10d, or vice-versa, are hybrid reinforcing cords 10 of the type described above.

[0191] In other specific embodiments, only the reinforcing cords 10a, and not also the reinforcing cords 10′, 10b, 10d or vice-versa, are hybrid reinforcing cords 10 of the type described above.

[0192] In some embodiments, only the reinforcing cords 10a and/or 10b, and not also the reinforcing cords 10′ and 10d, are hybrid reinforcing cords 10 of the type described above.

[0193] In further other embodiments, only the reinforcing cords 10d, and not also the reinforcing cords 10′, 10a and/or 10b, are hybrid reinforcing cords 10 of the type described above.

[0194] When the reinforcing cords 10d are hybrid reinforcing cords 10 of the type described above, such hybrid reinforcing cords 10 can be used only in the flipper 120 (if provided and when the chafer is not provided or is provided and comprises non-hybrid reinforcing cords), only in the chafer 121 (if provided and when the chafer is not provided or is provided and comprises non-hybrid reinforcing cords), or both in the flipper 120 and in the chafer 121 (if both are provided).

[0195] FIG. 6 shows an embodiment of the hybrid reinforcing cord 10 that differs from that of the previous figures only in that the hybrid reinforcing cord 20 also comprises a metallic wire 30 helically wound around the two strands 20 twisted together.

[0196] In the embodiment shown, the winding direction of the metallic wire 30 is opposite to the twisting direction of the two strands 20.

[0197] The winding of the metallic wire 30 has a winding pitch preferably comprised between about 2 mm and about 10 mm, more preferably between about 3.5 mm and about 5 mm, for example equal to about 4 mm.

[0198] The Applicant has made some samples of hybrid reinforcing cords 10 for the carcass structure 101, for the crossed belt structure 106 and for the stiffening layers 120, 121 of the tyre 100 of the present invention.

[0199] For being used in the carcass structure 101 of a tyre 100 of the type shown in FIG. 1, and thus intended to be used in high and ultra-high performance automobiles as defined above, a hybrid reinforcing cord 10 has been made comprising two strands 20 twisted together, each of the strands comprising a monofilament textile wire 21 made of nylon and having a diameter equal to about 0.23 mm and a multifilament textile yarn 22 made of nylon and having a linear density equal to about 940 dTex. Hereinafter, such a cord is indicated with 2×(Ny 0.23 mm+Ny 940 dTex).

[0200] For being used in the carcass structure of a tyre intended to be used in high performance sports motorcycles, a hybrid reinforcing cord 10 has been made comprising two strands 20 twisted together, each of the strands comprising a monofilament textile wire 21 made of nylon and having a diameter equal to about 0.23 mm and a multifilament textile yarn 22 made of aramid and having a linear density equal to about 1100 dTex. Hereinafter, such a hybrid reinforcing cord 10 is indicated with 2×(Ny 0.23 mm+Ar 1100 dTex).

[0201] Another example of hybrid reinforcing cord 10 made by the Applicant, preferably for an application in the carcass structure of high and ultra-high performance automobiles and/or high performance sports motorcycles, is the 2×(Ny 0.21 mm+Ny 1400 dTex), i.e. it comprises two strands 20 twisted together, each of the strands comprising a monofilament textile wire 21 made of nylon and having a diameter equal to about 0.21 mm and a multifilament textile yarn 22 made of nylon and having a linear density equal to about 1400 dTex.

[0202] For being used in the crossed belt structure 106 of a tyre 100 of the type shown in FIG. 1, and thus intended to be used in high and ultra-high performance automobiles as defined above, a hybrid reinforcing cord 10 has been made comprising two strands 20, each of the strands comprising a monofilament textile wire 21 made of PET and having a diameter equal to about 0.30 mm and a multifilament textile yarn 22 made of aramid and having a linear density equal to about 1680 dTex. Hereinafter, such a hybrid reinforcing cord 10 is indicated with 2×(PET 0.30 mm+Ar 1680 dTex).

[0203] Again for being used in the crossed belt structure 106 of a tyre 100 of the type shown in FIG. 1, a hybrid reinforcing cord has been made comprising three strands 20 twisted together, each of the strands comprising a monofilament textile wire 21 made of PET and having a diameter equal to about 0.40 mm and a multifilament textile yarn 22 made of aramid and having a linear density equal to about 1100 dTex. Hereinafter, such a hybrid reinforcing cord 10 is indicated with 3×(PET 0.40 mm+Ar 1100 dTex).

[0204] The Applicant has also made reinforcing cords 10 for the stiffening layer 121 of the tyre 100. Such reinforcing cords 10 have the same structure and are made with the same materials described above with reference to the crossed belt structure 106.

Comparative Tests

[0205] On some of the reinforcing cords 10 described above the Applicant has carried out comparative tests with respect to conventional reinforcing cords. Some of such tests are discussed below.

[0206] A test was carried out for measuring the hysteresis (energy dissipated as a result of the friction between the wires/filaments) of a piece of 200 mm of a hybrid reinforcing cord of type 2×(Ny 0.23 mm+Ny 940 dTex) with respect to the hysteresis of a piece of 200 mm of a conventional reinforcing cord made by twisting together two strands of nylon 1400 dTex.

[0207] Both of the pieces described above were subjected to 100 cycles of traction and compression through a Zwick dynamometer, subjecting the aforementioned pieces to a load increasing up to 12 N between a maximum elongation of 1.5% (equal to 3 mm) and a minimum elongation of 0.5% (equal to 1 mm), with an application speed of the traction/compression equal to 50 mm/min. The average of the measurements carried out gave as an indicative value of the energy dissipated a value equal to 2.45 for the conventional reinforcing cord and equal to 2.24 for the hybrid reinforcing cord of type 2×(Ny 0.23 mm+Ny 940 dTex), confirming the better behaviour of the hybrid reinforcing cord of the invention in terms of hysteresis with respect to a conventional reinforcing cord comprising only a multifilament textile yarn. Hence the advisability of using the hybrid reinforcing cord of type 2×(Ny 0.23 mm+Ny 940 dTex) in the carcass structure of the tyre.

[0208] The hybrid reinforcing cord of type 2×(Ny 0.23 mm+Ny 940 dTex) was also subjected to a comparative test for measuring the flexional rigidity thereof (i.e. the capability of withstanding flexing stresses). For this purpose a specimen of vulcanized elastomeric material comprising a plurality of hybrid reinforcing cords of type 2×(Ny 0.23 mm+Ny 940 dTex), with thread count equal to 108 cords/dm, and a specimen of vulcanized elastomeric material comprising a plurality of conventional reinforcing cords, each of the cords comprising two strands of nylon 1400 dTex, with thread count equal to 112 cords/dm were made.

[0209] Both of the specimens described above were subjected to a ring crush test as follows: the specimens were folded and welded to create respective rings having a diameter of 80 mm. Such specimens were subjected to an initial pretensioning of 0.5 N and to a squashing of 25 mm, with a compression speed of 100 mm/min.

[0210] The specimen comprising the hybrid reinforcing cords of type 2×(Ny 0.23 mm+Ny 940 dTex) withstood a maximum force of 0.282 N, whereas the specimen comprising the conventional reinforcing cords withstood a maximum force of 0.243 N, confirming the better behaviour of the hybrid reinforcing cord of the invention in terms of flexional rigidity with respect to a conventional reinforcing cord comprising only a multifilament textile yarn. Hence the advisability of using the hybrid reinforcing cord of type 2×(Ny 0.23 mm+Ny 940 dTex) in the carcass structure of the tyre.

[0211] The Applicant also carried out comparative tests to measure the flexional rigidity of a hybrid reinforcing cord of type 2×(PET 0.30 mm+Ar 1680 dTex) with respect to that of a conventional reinforcing cord. For this purpose, a specimen of vulcanized elastomeric material comprising a plurality of hybrid reinforcing cords of type 2×(PET 0.30 mm+Ar 1680 dTex), with thread count equal to 70 cords/dm (7 cords in 1 cm), and a specimen of vulcanized elastomeric material comprising a plurality of conventional metallic reinforcing cords, each of the cords comprising 3 steel wires of 0.22 mm twisted together were made, the latter specimen comprising 11 cords in 1 cm.

[0212] Both of the specimens described above were subjected to a ring crush test as described above.

[0213] The specimen comprising the hybrid reinforcing cords of type 2×(PET 0.30 mm+Ar 1680 dTex) withstood a maximum force of about 3.2 N, whereas the specimen comprising the conventional metallic reinforcing cords withstood a maximum force of about 2.3 N, confirming the better behaviour of the hybrid reinforcing cord of the invention in terms of flexional rigidity with respect to a conventional metallic reinforcing cord. Hence the advisability of using the hybrid reinforcing cord of type 2×(PET 0.30 mm+Ar 1680 dTex) in the belt structure of the tyre, as well as also in the chafer and/or flipper.

[0214] The present invention has been described with reference to some preferred embodiments. Different changes can be made to the embodiments described above, while still remaining within the scope of protection of the invention, defined by the following claims.