HYBRID CORD AND TYRE WITH SUCH CORD

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 having a plurality of monofilament textile wires (20) twisted to at least one multifilament textile yarn (30). In any cross section of the hybrid reinforcing cord (10), at least one portion of at least one monofilament textile wire (20) of said plurality of monofilament textile wires (20) defines a first radially outer surface portion of the hybrid reinforcing cord (10) and at least one portion of said at least one multifilament textile yarn (30) defines a second radially outer surface portion of the hybrid reinforcing cord (10).

Claims

1-16. (canceled)

17. A 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 having a plurality of monofilament textile wires twisted to at least one multifilament textile yarn, wherein, in any cross section of the hybrid reinforcing cord, at least one portion of at least one monofilament textile wire of the plurality of monofilament textile wires defines a first radially outer surface portion of the hybrid reinforcing cord and at least one portion of the at least one multifilament textile yarn defines a second radially outer surface portion of the hybrid reinforcing cord.

18. The tyre according to claim 17, wherein the first radially outer surface portion is defined by at least one portion of at least two of the monofilament textile wires.

19. The tyre according to claim 17, wherein the plurality of monofilament textile wires are twisted together with a predetermined first twisting pitch (P1) to form a strand of monofilament textile wires, and the at least one multifilament textile yarn is twisted together with the strand of monofilament textile wires with a predetermined second twisting pitch (P2).

20. The tyre according to claim 17, wherein at least one first monofilament textile wire of the plurality of monofilament textile wires is twisted together with the at least one multifilament textile yarn with a predetermined first twisting pitch (P1) to form a strand of mono-multifilament textile wires and at least one second monofilament textile wire of the plurality of monofilament textile wires is twisted together with the strand of mono-multifilament textile wires with a predetermined second twisting pitch (P2).

21. The tyre according to claim 17, wherein each monofilament textile wire of the plurality of monofilament textile wires is twisted together with at least another monofilament textile wire of the plurality of monofilament textile wires and to the at least one multifilament textile yarn with a predetermined twisting pitch (P1) to form a strand of mono-multifilament textile wires.

22. The tyre according to claim 17, wherein each monofilament textile wire of the plurality of monofilament textile wires is made of one or more of aliphatic polyamide fibres, polyester fibres, polyaryletherketone fibres, and mixtures thereof.

23. The tyre according to claim 17, wherein the at least one multifilament textile yarn comprises textile filaments made of one or more of aromatic polyamide fibres, aliphatic polyamide fibres, polyester fibres, polyketone fibres, polyvinyl alcohol fibres, cellulose fibres, glass fibres, carbon fibres, and mixtures thereof.

24. The tyre according to claim 17, wherein each monofilament textile wire of the plurality of monofilament textile wires has a diameter ranging from about 0.1 mm to 1 mm.

25. The tyre according to claim 17, wherein the hybrid reinforcing cord comprises a number of monofilament textile wires ranging from 2 to 10.

26. 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 4500 dTex.

27. The tyre according to claim 17, wherein the hybrid reinforcing cord comprises a number of multifilament textile yarns ranging from 1 to 4.

28. The tyre according to claim 17, wherein at least some of the hybrid reinforcing cords comprise at least one metallic wire helically wound around the plurality of monofilament textile wires and the at least one multifilament textile yarn.

29. The tyre according to claim 17, wherein the at least one multifilament textile yarn comprises at least one textile monofilament and a plurality of textile filaments, wherein in any cross section of the hybrid reinforcing cord, the at least one textile monofilament is at least partially incorporated among the textile filaments.

30. The tyre according to claim 17, wherein the support structure comprises: a carcass structure comprising at least one carcass layer having opposite end edges associated with respective annular anchoring structures to define, on opposite sides with respect to an equatorial plane (M-M) of the tyre, respective bead structures; and a 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 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 end edge of the at least one carcass layer.

31. The tyre according to claim 30, wherein the belt structure comprises a zero-degree reinforcing layer arranged in a radially inner position with respect to the tread band, and wherein the zero-degree reinforcing layer comprises a plurality of the hybrid reinforcing cords.

32. A hybrid reinforcing cord comprising: a plurality of monofilament textile wires and at least one multifilament textile yarn twisted to the plurality of monofilament textile wires, wherein, in any cross section of the hybrid reinforcing cord, at least one portion of at least one monofilament textile wire of the plurality of monofilament textile wires defines a first radially outer surface portion of the hybrid reinforcing cord and at least one portion of the at least one multifilament textile yarn defines a second radially outer surface portion of the hybrid reinforcing cord.

Description

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0124] Further characteristics 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:

[0125] FIG. 1 is a schematic partial half cross-section view of a portion of a tyre according to an embodiment of the present invention;

[0126] FIG. 2 is a schematic side view of a piece of a first embodiment of a hybrid reinforcing cord used in the tyre of FIG. 1;

[0127] FIG. 3 is a schematic enlarged view of a cross section of the hybrid reinforcing cord of FIG. 2, such a cross section being taken on the section plane S-S drawn in FIG. 2;

[0128] FIG. 4 is a schematic side view of a piece of a second embodiment of a hybrid reinforcing cord used in the tyre of FIG. 1;

[0129] FIG. 5 is a schematic enlarged view of a cross section of the hybrid reinforcing cord of FIG. 4, such a cross section being taken on the section plane S-S drawn in FIG. 4;

[0130] FIG. 6 is a schematic side view of a piece of a second embodiment of a hybrid reinforcing cord used in the tyre of FIG. 1.

[0131] 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.

[0132] The tyre 100 shown in FIG. 1 is, in particular, an embodiment of a tyre for four-wheeled vehicles.

[0133] Preferably, the tyre 100 is a HP or UHP tyre for sports and/or high or ultra-high performance automobiles.

[0134] 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.

[0135] 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 in elastomeric material.

[0136] The support structure 100a comprises a carcass structure 101, in turn comprising at least one carcass layer 111.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In an embodiment, the coupling between the carcass structure 101 and the annular reinforcing structure 103 can be made through a second carcass layer (not shown in FIG. 1) applied in a radially outer position with respect to the carcass layer 111.

[0143] 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 arranged between the latter and the rim of the wheel when the tyre 100 is mounted on the rim. Such an anti-abrasion strip 105 may, however, not be provided.

[0144] 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 radially superimposed over one another.

[0145] The belt layers 106a, 106b comprise a plurality of reinforcing cords 10a, 10b, respectively. 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°.

[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 may 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 arranged on the support element, then the support element is radially expanded, then a second belt layer is arranged on the first belt layer and finally the opposite axial end edges of the first belt layer are turned on the second belt layer to at least partially cover the second belt layer, which is the radially outermost one. 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 on another belt layer arranged in a radially outer position imparts greater reactivity and responsiveness of the tyre when entering a bend.

[0148] The support structure 100a comprises, in a radially outer position with respect to the crossed belt structure 106, at least one zero-degree 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 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 is made of elastomeric material, like other semi-finished products constituting the tyre 100, and is applied in a radially outer position with respect to the zero-degree reinforcing layer 106c.

[0151] Respective sidewalls 108 made of elastomeric material are also applied onto 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 may also comprise a further stiffening layer 121 that is generally known with 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 figures 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, said grooves being 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] An underlayer 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 optionally 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 of 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 of the reinforcing cords 10c of the zero-degree reinforcing layer 106c, and/or of the reinforcing cords 10d 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] With reference to FIGS. 2 and 3, the hybrid reinforcing cord 10 comprises three monofilament textile wires 20 twisted to one another and a multifilament textile yarn 30 twisted to the three monofilament textile wires 20 with a predetermined twisting pitch and defined by a plurality of filaments 32.

[0166] Preferably, the three monofilament textile wires 20 are identical. Therefore, only one of them will be described hereinafter.

[0167] The aforementioned reinforcing cord 10 can be made in various ways.

[0168] A first way provides for an initial twisting of the three monofilament textile wires 20 with a twisting pitch P1 to form a strand of monofilament textile wires 20. Thereafter, such a strand is twisted with the multifilament textile yarn 30 with a twisting pitch P2 that can be equal to or different from the twisting pitch P1.

[0169] A second way provides for an initial twisting of one or more of the monofilament textile wires 20 with the multifilament textile yarn 30 with a twisting pitch P1 to form a strand of mono-multifilament textile wires. Thereafter, such a strand is twisted with another monofilament textile wire 20 with a twisting pitch P2 that can be equal to or different from the twisting pitch P1.

[0170] A third way provides for a single twisting operation in which each of the monofilament textile wires 20 is twisted together with the other monofilament textile wires 20 and with the multifilament textile yarn 30 with a predetermined twisting pitch P1 to form a strand of mono-multifilament textile wires.

[0171] In the embodiment shown in FIGS. 2 and 3, each monofilament textile wire 20 is, in any cross-section of the reinforcing cord 10 (like for example that of FIG. 3), and preferably in all of the cross-sections of the reinforcing cord 10, arranged externally with respect to the filaments 32 of the multifilament textile yarn 30.

[0172] The mutual arrangement of the monofilament textile wires 20 and of the multifilament textile yarn 30 is such that a first radially outer surface portion of the hybrid reinforcing cord 10 is defined by a portion of each of the three monofilament textile wires 20 and a second radially outer surface portion of the hybrid reinforcing cord 10 is defined by a portion of the multifilament textile yarn 30.

[0173] For example, about 50% of the outer surface of the hybrid reinforcing cord 10 is defined by the multifilament textile yarn 30 and the remaining about 50% is defined by the monofilament textile wires 20.

[0174] In the example shown in FIGS. 2 and 3, each of the three monofilament textile wires 20 is in mutual contact with the other two monofilament textile wires and only two of the three monofilament textile wires 20 are in contact with the multifilament textile yarn 30.

[0175] The monofilament textile wires 20 and the multifilament textile yarn 30 extend along a longitudinal direction A, shown in FIG. 2.

[0176] The twisting pitch P1 is preferably comprised between about 2 mm and about 20 mm, more preferably between about 3 mm and about 10 mm, for example equal to about 3.5 mm.

[0177] Each monofilament textile wire 20 is made of fibres made of aliphatic polyamide, 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 of polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or of polyaryletherketone fibres, for example polyether ether ketone (PEEK), or mixtures thereof.

[0178] The filaments 32 of the multifilament textile yarn 30 are made of aromatic polyamide fibres, or of aliphatic polyamide fibres, 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 of polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or of polyketone fibres, or of polyvinyl alcohol fibres, or of cellulose fibres, for example rayon or lyocell), or of glass or carbon fibres, or any other mixture of the aforementioned fibres, or assemblies of mixed fibres comprising two or more of the materials listed above. Such assemblies of mixed fibres are indicated hereinafter with the term “commingled fibres”.

[0179] In the case of “commingled fibres”, the fibres of the filaments 32 can for example comprise: [0180] 50% Aramid with linear density equal to about 1100 dTex and 50% PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 2200 dTex”); [0181] 43% Aramid with linear density equal to about 840 dTex and 57% PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 1940 dTex”); [0182] 33% Aramid with linear density equal to about 550 dTex and 67% PET with linear density equal to about 1100 dTex (such an assembly is indicated hereinafter as “Commingled 1650 dTex”).

[0183] Irrespective of the specific type of textile material used for the filaments 32 of the multifilament textile yarn 30, such a material is suitably superficially adhesivised 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.

[0184] For example, the adhesivization is carried out through immersion of the hybrid reinforcing cord 10, after having twisted together the monofilament textile wires 20 with the multifilament textile yarn 30, in a solution comprising the adhesive substance.

[0185] Each monofilament textile wire 20 preferably has a diameter comprised between about 0.1 mm and about 1 mm, more preferably between about 0.2 mm and about 0.5 mm, also depending on the material from which it is made and the area of the tyre 100 in which the hybrid reinforcing cords 10 are arranged.

[0186] The multifilament textile yarn 30 preferably has a linear density comprised between about 400 dTex and about 4500 dTex, preferably between about 800 dTex and about 4000 dTex, also depending on the material from which it is made and the area of the tyre 100 in which the hybrid reinforcing cords 10 are arranged.

[0187] In specific embodiments, only the reinforcing cords 10′, and not also the reinforcing cords 10a, 10b, 10c and 10d, or vice-versa, are hybrid reinforcing cords 10 of the type described above.

[0188] In other specific embodiments, only the reinforcing cords 10a, and not also the reinforcing cords 10′, 10b, 10c, 10d or vice-versa, are hybrid reinforcing cords 10 of the type described above.

[0189] In some embodiments, only the reinforcing cords 10a and/or 10b, and not also the reinforcing cords 10′, 10c and 10d, are hybrid reinforcing cords 10 of the type described above.

[0190] In yet other embodiments, only the reinforcing cords 10d, and not also the reinforcing cords 10′, 10a, 10b and/or 10c, are hybrid reinforcing cords 10 of the type described above.

[0191] 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 flipper 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).

[0192] FIGS. 4 and 5 show an embodiment of the hybrid reinforcing cord 10 that differs from that of the previous figures only in that the multifilament textile yarn 30 comprises a monofilament textile wire 31 incorporated among the filaments 32.

[0193] 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 10 also comprises a metallic wire 50 helically wound around the monofilament textile wires 20 twisted together with the multifilament textile yarn 30.

[0194] In the illustrated embodiment, the winding direction of the metallic wire 50 is opposite to the twisting direction of the monofilament textile wires 20 which are twisted together with the multifilament textile yarn 30.

[0195] The winding of the metallic wire 50 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.

[0196] The Applicant has made some samples of hybrid reinforcing cords 10 for the carcass structure 101, for the crossed belt structure 106, for the zero-degree reinforcing layer 106c and for the stiffening layers 120, 121 of the tyre 100 of the present invention.

[0197] For the use 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 three monofilament textile wires 20 made of nylon and each having a diameter equal to about 0.21 mm twisted with a multifilament textile yarn 30 made of nylon and having a linear density equal to about 1400 dTex. Such a reinforcing cord is briefly identified as: Ny 3×0.21 mm+Ny 1400 dTex.

[0198] For the use 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 three monofilament textile wires 20 made of PET and each having a diameter equal to about 0.40 mm twisted with a multifilament textile yarn 30 made of aramid and having a linear density equal to about 1100 dTex. Such a reinforcing cord is briefly identified as: PET 3×0.40 mm+Ar 1100 dTex.

[0199] For the use in the zero degrees belt layer 106c 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 each of which comprising two monofilament textile wires 20 made of PET and each having a diameter equal to about 0.20 mm, the two strands being twisted to a multifilament textile yarn 30 made of aramid. The multifilament textile yarn 30 has a linear density equal to about 1100 dTex. Such a reinforcing cord is briefly identified as: PET 2×(2×0.20 mm)+Ar 1100 dTex.

[0200] The Applicant has also made reinforcing cords 10 for the stiffening layer 120 or 121 of the tyre 100. Such reinforcing cords 10 have the same structure and are made of the same materials described above with reference to the crossed belt structure 106.

Comparative Tests

[0201] On some of the reinforcing cords 10 described above the Applicant has carried out comparative tests with respect to conventional reinforcing cords currently used by the Applicant and currently deemed suitable for ensuring the desired driving performance and the desired behaviour of the tyre. Some of such tests are discussed hereinafter.

[0202] A test has been carried out in order to measure the hysteresis (energy dissipated after friction between the wires/filaments) of a piece of 200 mm of a hybrid reinforcing cord of the type Ny 3×0.21 mm+Ny 1400 dTex with respect to the hysteresis of a piece of 200 mm of a conventional reinforcing cord made by twisting together two yarns of nylon 1400 dTex (identified here as: 2×Ny 1400 dTex).

[0203] The reinforcing cords of both the pieces described above had substantially the same weight and the same volume and both of the pieces had substantially the same amount of elastomeric material. Therefore, both of the pieces described above had substantially the same weight.

[0204] Such pieces were subjected to 100 traction and compression cycles through a Zwick dynamometer, stressing the aforementioned pieces with 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) and 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 2.05 for the conventional reinforcing cord and equal to 2.24 for the hybrid reinforcing cord of the type Ny 3×0.21 mm+Ny 1400 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 multifilament textile yarns. This confirmed that it is advisable using the hybrid reinforcing cord of type Ny 3×0.21 mm+Ny 1400 dTex in the carcass structure of the tyre.

[0205] The Applicant has also carried out comparative tests to measure the bending stiffness of a hybrid reinforcing cord of the type PET 3×0.40 mm+Ar 1100 dTex with respect to that of a conventional reinforcing cord made of steel of the type 3×0.175 mm. For this purpose a test piece made of vulcanized elastomeric material comprising a plurality of hybrid reinforcing cords of the type PET 3×0.40 mm+Ar 1100 dTex, with thread count equal to 80 cords/dm (8 cords in 1 cm), and a test piece made of vulcanized elastomeric material comprising a plurality of conventional reinforcing cords made of steel of the type 3×0.175 mm, with thread count equal to 130 cords/dm (13 cords in 1 cm) were made.

[0206] The test piece comprising the hybrid reinforcing cords of the type PET 3×0.40 mm+Ar 1100 dTex had a thickness of elastomeric material equal to about 1.30 mm and a weight equal to about 1480 g/m.sup.2, whereas the test piece comprising the conventional metallic reinforcing cords had a thickness of elastomeric material equal to about 0.80 mm and a weight equal to about 1470 g/m.sup.2.

[0207] Both of the test pieces described above were subjected to a ring compression test as follows: the test pieces were folded and welded to create respective rings having a diameter of 80 mm. Such test pieces were subjected to an initial pretensioning of 0.5 N and to a crushing of 25 mm, with a compression speed of 100 mm/min.

[0208] The test piece comprising the hybrid reinforcing cords of the type PET 3×0.40 mm+Ar 1100 dTex withstood a maximum force of about 0.95 N, whereas the test piece comprising the conventional metallic reinforcing cords withstood a maximum force of about 0.86 N, confirming the better behaviour of the hybrid reinforcing cord of the invention in terms of bending stiffness with respect to a conventional metallic reinforcing cord. This confirmed that it is advisable using the hybrid reinforcing cord of the type PET 3×0.40 mm+Ar 1100 dTex in the belt structure of the tyre, as well as in the chafer and/or flipper.

[0209] The Applicant has also carried out comparative tests to measure the resistance to compression stresses of a hybrid reinforcing cord of the type PET 3×0.40 mm+Ar 1100 dTex with respect to that of conventional reinforcing cords made of steel of the type 3×0.175 mm.

[0210] The Applicant has indeed observed that, particularly with reference to the belt structure and to the chafer and/or flipper, among the stresses that can shorten the lifetime of the reinforcing cords dynamic compression stresses are of particular relevance. In particular, when subjected to repeated compression stresses, the reinforcing cords used in the aforementioned structural components of the tyre deform forming waves that lead to “unravelling”, i.e. to the separation of the single wires/yarns, with consequent damaging of the tyre.

[0211] In order to evaluate the behaviour of the reinforcing cords with respect to the aforementioned compression stresses two test pieces were made each comprising two strips of vulcanized elastomeric material, each strip comprising a plurality of parallel reinforcing cords and the two strips being arranged inclined with respect to one another by an angle equal to about 30°.

[0212] One of the two test pieces (hereinafter indicated as “test piece A”) comprised hybrid reinforcing cords of the type PET 3×0.40 mm+Ar 1100 dTex, with thread count equal to 80 cords/dm (8 cords in 1 cm), whereas the other test piece (hereinafter indicated as “test piece B”) comprised conventional reinforcing cords made of steel of the type 3×0.175 mm, with thread count equal to 130 cords/dm (13 cords in 1 cm).

[0213] The test piece A had a thickness of elastomeric material equal to about 1.30 mm and a weight equal to about 1480 g/m.sup.2, whereas the test piece B had a thickness of elastomeric material equal to about 0.80 mm and a weight equal to about 1470 g/m.sup.2.

[0214] The two test pieces were vulcanized at 170° C. for 10 minutes and conditioned at room temperature for 16 hours.

[0215] Each of the two test pieces was subjected to bending/compression cycles in a testing machine of the De Mattia type until breaking occurred.

[0216] The test piece A resisted for a time period greater than about 40% with respect to that of the test piece B. This confirmed that it is advisable using the hybrid reinforcing cord of type PET 3×0.40 mm+Ar 1100 dTex in the belt structure of the tyre, as well as in the chafer and/or flipper.

[0217] In general, the comparative tests discussed above highlighted how, being substantially equal the weight of the semi-finished product that contains the reinforcing cords: [0218] the hybrid reinforcing cords of the type Ny 3×0.21 mm+Ny 1400 have a better behaviour in terms of hysteresis with respect to that of the conventional reinforcing cords of the type 2×Ny 1400 dTex, therefore being suitable for being used in the carcass structure of tyres; [0219] the hybrid reinforcing cords of the type PET 3×0.40 mm+Ar 1100 dTex have a better behaviour in terms of bending stiffness and resistance to compression stresses with respect to that of the conventional reinforcing cords made of steel of the type 3×0.175 mm currently used in the belt structure, as well as in the chafer and/or flipper, therefore being suitable for being used in the belt structure, as well as in the chafer and/or flipper, of tyres.

[0220] 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.