TYRE FOR VEHICLE WHEELS

Abstract

A tyre for vehicle wheels comprises a carcass structure including at least one carcass ply having a plurality of hybrid reinforcing cords (10). Each hybrid reinforcing cord (10) comprises at least two strands (20a, 20b) twisted together with a predetermined twisting pitch (P). Each of said at least two strands (20a, 20b) comprises at least one monofilament textile wire made of polyester fibres and at least one multifilament textile yarn (22a, 22b) comprising a plurality of textile filaments (23a, 23b) made of aramid and/or polyester and/or rayon fibres. In any cross section of the hybrid reinforcing cord (10), said at least one monofilament textile wire is at least partially embedded in the filaments (23a, 23b) of said at least one multifilament textile yarn (22a, 22b).

Claims

1.-15. (canceled)

16. A tyre for vehicle wheels, comprising: a carcass structure comprising at least one carcass ply having a plurality of hybrid reinforcing cords, wherein each hybrid reinforcing cord comprises 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 made of polyester fibers; at least one multifilament textile yarn comprising a plurality of textile filaments made of aramid fibers, polyester fibers, rayon fibers, or combinations thereof; 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.

17. The tyre according to claim 16, wherein in any cross section of at least one segment of the hybrid reinforcing cord, the at least one monofilament textile wire is completely embedded in the filaments of the at least one multifilament textile yarn.

18. The tyre according to claim 16, wherein the at least one monofilament textile wire has a diameter ranging from 0.15 mm to 0.50 mm.

19. The tyre according to claim 16, wherein the at least one multifilament textile yarn has a linear density ranging from 840 dtex to 2100 dtex.

20. The tyre according to claim 16, wherein the at least one carcass ply has a thread count greater than 70 cords/dm and lower than, or equal to, 95 cords/dm.

21. The tyre according to claim 16, wherein the at least one carcass ply has a thickness ranging from 0.7 mm to 1.5 mm.

22. The tyre according to claim 16, wherein the carcass structure comprises a single carcass ply.

23. The tyre according to claim 16, wherein each hybrid reinforcing cord comprises only two strands.

24. The tyre according to claim 23, wherein each of the two strands comprises a single monofilament textile wire and a single multifilament textile yarn.

25. The tyre according to claim 16, wherein each of the two strands comprises at least two ends twisted together, wherein each of the at least two ends comprises, in any cross section of the hybrid reinforcing cord, at least one monofilament textile wire at least partially embedded in the filaments of at least one multifilament textile yarn

26. The tyre according to claim 25, wherein each of the at least two ends comprises a single monofilament textile wire and a single multifilament textile yarn.

27. The tyre according to claim 25, wherein each of the two strands comprises only two ends.

28. The tyre according to claim 16, wherein the tyre has one of the following speed codes: “T”, “U”, “H”, “V”, “Z”, “W”, “Y”, according to the E.T.R.T.O. standard.

29. The tyre according to claim 16, wherein the tyre is a self-supporting tyre.

30. 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 made of polyester fibers; at least one multifilament textile yarn comprising a plurality of textile filaments made of aramid fibers, polyester fibers, rayon fibers, or combinations thereof; 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

[0141] 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:

[0142] FIG. 1 is a schematic partial half-cross section view of a portion of a tyre according to an embodiment of the present invention;

[0143] FIG. 2 is a schematic side view of a segment of a first embodiment of a hybrid reinforcing cord used in the carcass structure of the tyre of FIG. 1;

[0144] 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 carcass structure of the tyre of FIG. 1, such a cross section being taken on the section plane S-S drawn in FIG. 2;

[0145] 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 components that otherwise would be hidden;

[0146] 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 components that otherwise would be hidden;

[0147] FIG. 6 is an enlarged schematic view of a cross section of a further embodiment of a hybrid reinforcing cord which can used in the carcass structure of the tyre of FIG. 1.

[0148] For the sake of simplicity, FIG. 1 shows only a part of an exemplary 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.

[0149] The tyre 100 shown in FIG. 1 is, in particular, an exemplary embodiment of a tyre for four-wheeled vehicles.

[0150] Preferably, the tyre 100 is a HP or UHP tyre for high or ultra-high-performance sports automobiles, both electric and non-electric.

[0151] In particular, the tyre 100 carries one of the following speed codes: “T”, “U”, “H”, “V”, “Z”, “W”, “Y”, according to the E.T.R.T.O. standard.

[0152] 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.

[0153] The tyre 100 comprises a carcass structure 101 of the radial type, which in turn comprises at least one carcass ply 111.

[0154] Hereinafter, for the sake of simplicity of presentation, reference will be made to an embodiment of the tyre 100 comprising a single carcass ply 111 (mono-ply tyre). However, it is understood that what is described with respect to the carcass ply 111 also applies to each carcass ply of tyres comprising more than one carcass ply, except when indicated otherwise. Indeed, there are embodiments of the tyre 100 of the invention in which the carcass structure 101 comprises for example two carcass plies 111 (two-ply tyre).

[0155] The carcass ply 111 comprises a plurality of reinforcing cords 10′ coated with, or embedded in, a layer of cross-linked elastomeric material. In the case in which the tyre 100 is of the two-ply type, the reinforcing cords of a first carcass ply can be substantially parallel to those of the other carcass ply or inclined with respect to those of the other carcass ply by an angle lower than 40°.

[0156] The carcass ply 111 preferably has a thread count greater than 70 cords/dm and lower than, or equal to, 95 cords/dm, more preferably comprised between 75 cords/dm and 90 cords/dm. For example, in a preferred embodiment of the tyre 100 of the invention, the aforementioned thread count is equal to 85 cords/dm.

[0157] The carcass ply 111 preferably has a thickness comprised between 0.7 mm and 1.5 mm, more preferably between 0.9 mm and 1.3 mm. For example, in the aforementioned preferred embodiment of the tyre 100 of the invention, the aforementioned thickness is equal to 1.1 mm.

[0158] The carcass ply 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 which is called “bead structure” and which is intended to allow the tyre 100 to be anchored on a corresponding mounting rim, not shown.

[0159] Each annular reinforcing structure 103 is associated with the carcass structure 101 by folding back (or turning) the opposite end edges of the at least one carcass ply 111 around the bead core 102 and the possible elastomeric filler 104, so as to form the so-called turns 101a of the carcass structure 101.

[0160] In an embodiment, the coupling between carcass structure 101 and annular reinforcing structure 103 can be made through a layer (not shown in FIG. 1) applied in a radially outer position with respect to the carcass ply 111.

[0161] An anti-abrasion strip 105 is arranged at each annular reinforcing structure 103 so as to wrap around the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103, thus being placed 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.

[0162] The tyre 100 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 radial juxtaposed with respect to one another.

[0163] The belt layers 106a, 106b respectively comprise a plurality of reinforcing cords 10a, 10b. Such reinforcing cords 10a, 10b have an orientation which is 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 15° and 45°, preferably between 20° and 40°. For example, such an angle is equal to 30°.

[0164] The tyre 100 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 which is 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 90°.

[0165] The tyre 100 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 20° and 70°.

[0166] 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.

[0167] 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 deposited on the support element, then the support element is radially expanded, then a second belt layer is deposited on the first belt layer and finally the opposite axial end edges of the first belt layer are turned onto the second belt layer to at least partially cover the second belt layer, which is the radially outermost one. In some cases, it is possible to arrange a third belt layer 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 with respect to the first one provides the tyre with a greater reactivity and responsiveness when tackling a bend.

[0168] The tyre 100 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 10°, for example comprised between 0° and 6°) with respect to the equatorial plane M-M of the tyre 100.

[0169] The reinforcing cords 10a, 10b, 10c are coated with an elastomeric material or embedded in a matrix of cross-linked elastomeric material.

[0170] A tread band 109 made of elastomeric material is applied in a radially outer position with respect to the zero degrees reinforcing layer 106c.

[0171] Respective sidewalls 108 made of elastomeric material are also applied on the lateral 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.

[0172] The anti-abrasion strip 105, if provided, extends at least up to the respective sidewall 108.

[0173] In some specific embodiments, like the one herein shown and described, the rigidity and integrity of the annular reinforcing structure 103 and of the sidewall 108 can be improved by providing a stiffening layer 120, generally known as “flipper” or additional strip-like insert.

[0174] 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 wraps around the annular reinforcing structure 103 along the axially inner, axially outer and radially inner areas of the annular reinforcing structure 103.

[0175] The flipper 120 is arranged between the turned end edge of the carcass ply 111 and the respective annular reinforcing structure 103. Usually, the flipper 120 is in contact with the carcass ply 111 and the annular reinforcing structure 103.

[0176] In some specific embodiments, like the one shown and described here, the annular reinforcing structure 103 can also comprise a further stiffening layer 121 that is generally known by the name “chafer”, or protective strip, and which has the function of increasing the rigidity and integrity of the annular reinforcing structure 103.

[0177] The chafer 121 is associated with a respective turned end edge of the carcass ply 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.

[0178] 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.

[0179] The tread band 109 has, in a radially outer position thereof, a rolling surface 109a intended to come into contact with the ground. Circumferential grooves (not shown in FIG. 1) are formed on the rolling surface 109a,such 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).

[0180] A sub-layer 107 is arranged between the crossed belt structure 106 and the tread band 109.

[0181] In some specific embodiments, like the one shown and described herein, a strip 110 consisting of elastomeric material, commonly known as “mini-sidewall”, can possibly be provided in the connection area between the sidewall 108 and the tread band 109. The mini-sidewall 110 is generally obtained through co-extrusion with the tread band 109 and it allows an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108.

[0182] Preferably, an end portion of the sidewall 108 directly covers the lateral edge of the tread band 109.

[0183] In the case of tubeless tyres, like the one herein shown and described, a layer of rubber 112, generally known as “liner”, can also be provided in a radially inner position with respect to the carcass ply 111 to supply the necessary air tightness to the inflation air of the tyre 100.

[0184] In the case of self-supporting tyres, a reinforcing insert made of elastomeric material (not shown) is arranged in an axially outer position with respect to the liner 112 and in an axially inner position with respect to the sidewall 108, the reinforcing insert being configured to prevent the yielding or the swelling of the sidewall 108 when the tyre is deflated.

[0185] At least some of the reinforcing cords 10′ of the carcass structure 101 (preferably all of the reinforcing cords 10′) are hybrid reinforcing cords 10 of the type shown in FIGS. 2-6 and described below.

[0186] The reinforcing cords 10a, 10b, 10c and 10d can also be hybrid reinforcing cords 10 of the type shown in FIGS. 2-6 or reinforcing cords of a different type.

[0187] With reference to FIGS. 2-4, the hybrid reinforcing cord 10 comprises two strands 20a, 20b twisted together with a predetermined twisting pitch P.

[0188] Preferably, the two strands 20a, 20b are identical.

[0189] As shown in FIGS. 3 and 4, each strand 20a, 20b comprises a single monofilament textile wire 21a, 21b and a single multifilament textile yarn 22a, 22b defined by a plurality of filaments 23a, 23b. Each strand 20a, 20b could however comprise more than one monofilament textile wire and more than one multifilament textile yarn.

[0190] In any cross section of the reinforcing cord 10, the monofilament textile wire 21a, 21b is embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0191] In the embodiment shown in FIGS. 3 and 4, the monofilament textile wire 21a, 21b is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b and, therefore, the aforementioned filaments 23a, 23b are arranged around the respective monofilament textile wire 21a, 21b so as to completely surround the monofilament textile wire 21a, 21b.

[0192] Therefore, in FIG. 2, the monofilament textile wires 21a, 21b are not visible since they are entirely covered by the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0193] Although the embodiment of FIGS. 2-4 (and also that of FIG. 5, as discussed below) wherein the monofilament textile wire 21a, 21b is, in any cross section of the reinforcing cord 10, completely embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b is particularly preferred, other embodiments are deemed equally preferred wherein, in any cross section of the reinforcing cord 10, the monofilament textile wire 21a, 21b is only partially embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b, and in particular wherein at least 50% of the outer surface of the monofilament textile wire 21a, 21b is embedded in the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b.

[0194] The monofilament textile wires 21a, 21b extend along a longitudinal direction A, shown in FIG. 2.

[0195] The mutual arrangement of the monofilament textile wires 21a, 21b and of the filaments 23a, 23b of the multifilament textile yarn 22a, 22b along the longitudinal direction A can be such that the monofilament textile wires 21a, 21b extend substantially parallel to the filaments 23a, 23b of the multifilament textile yarn 22a, 22b of the respective strand 20a, 20b, as shown in FIG. 4, or such that the filaments 23a, 23b of the multifilament textile yarn 22a, 22b are wound in a helix on the respective monofilament textile wire 21a, 21b with a predetermined winding pitch W which, preferably, is equal to the twisting pitch P.

[0196] In this last case, the twisting direction of the two strands 20a, 20b is preferably the same as the winding direction of the filaments 23a, 23b of the multifilament textile yarn 22a, 22b on the monofilament textile wire 21a, 21b, but it is possible to have opposite directions.

[0197] The twisting pitch P is preferably comprised between 1 mm and 20 mm, more preferably between 2 mm and 15 mm, for example equal to 12.5 mm.

[0198] FIG. 5 shows an embodiment of a hybrid reinforcing cord 10 that differs from the one shown in FIGS. 2-4 only in that the monofilament textile wires 21a, 21b are twisted on themselves with a predetermined twisting pitch T.

[0199] Preferably, the twisting pitch T is equal to the twisting pitch P.

[0200] The twisting direction of the monofilament textile wires 21a, 21b can be the same as or opposite to the twisting direction of the two strands 20a, 20b.

[0201] The monofilament textile wires 21a, 21b are made of polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or mixtures thereof.

[0202] The filaments 23a, 23b of each multifilament textile yarn 22a, 22b are made of aramid fibres or polyester fibres, for example polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), or rayon fibres, or any mixture of the aforementioned fibres.

[0203] Irrespective of the specific type of textile material used for the filaments 23a, 23b of the multifilament textile yarns 22a, 22b, such a material is suitably made adhesive on the surface so as to offer an adequate adhesivity to the surrounding elastomeric material. Typically, the adhesive treatment can be carried out through coating with an adhesive substance or through a chemical or physical treatment.

[0204] For example, the adhesive treatment is carried out through immersion of the hybrid reinforcing cord 10 in a solution comprising the adhesive substance after having twisted together the two strands 20a, 20b.

[0205] The monofilament textile wires 21a, 21b preferably have a diameter comprised between 0.15 mm and 0.50 mm, more preferably between 0.20 mm and 0.40 mm. For example, in a preferred embodiment of the carcass structure 101 of the tyre 100 the aforementioned diameter is equal to 0.30 mm.

[0206] The multifilament textile yarns 22a, 22b preferably have a linear density comprised between 840 dtex and 2100 dtex, preferably between 940 dtex and 1840 dtex. For example, in a preferred embodiment of the carcass structure 101 of the tyre 100 the aforementioned linear density is equal to 1100 dtex.

[0207] In a preferred embodiment of the hybrid reinforcing cord 10 shown in FIGS. 2-5 and used in the aforementioned preferred embodiment of the carcass structure 101 of the tyre 100, the hybrid reinforcing cord 10 has two strands 20a, 20b twisted together. In each strand 20a, 20b, the monofilament textile wires 21a, 21b are made of PET fibres and have a diameter equal to 0.30 mm, whereas the multifilament textile yarns 22a, 22b are made of aramid and have a linear density equal to 1110 dtex. In such a hybrid reinforcing cord 10, for example, 310 twists have been imparted in the right-handed direction (Z) to the multifilament textile yarn 22a, 22b and to the monofilament textile wire 21a, 21b of each of the two strands 20a, 20b, whereas 180 twists have been imparted in the left-handed direction (S) to each of the two strands 20a, 20b. Such a reinforcing cord can therefore be indicated with (PET0.30+AR1100)×2 310Z/180S.

[0208] Another preferred embodiment of the hybrid reinforcing cord 10 shown in FIGS. 2-5 differs from the one described above only in that the multifilament textile yarns 22a, 22b are made of rayon and have a linear density equal to 1840 dtex. In such a hybrid reinforcing cord 10, for example, 300 or 310 twists have been imparted in the right-handed direction (Z) to the multifilament textile yarn 22a, 22b and to the monofilament textile wire 21a, 21b of each of the two strands 20a, 20b, whereas 180 twists have been imparted in the left-handed direction (S) to each of the two strands 20a, 20b. Such reinforcing cords can therefore be indicated with (PET0.30+RY1840)×2 300Z/180S and (PET0.30+RY1840)×2 310Z/180S, respectively.

[0209] Another preferred embodiment of the hybrid reinforcing cord 10 shown in FIGS. 2-5 differs from the one described above only in that the multifilament textile yarns 22a, 22b made of rayon have a linear density equal to 1220 dtex. In such a hybrid reinforcing cord 10, for example, 300 twists have been imparted in the right-handed direction (Z) to the multifilament textile yarn 22a, 22b and to the monofilament textile wire 21a, 21b of each of the two strands 20, 20b, whereas 150 twists have been imparted in the left-handed direction (S) to each of the two strands 20a, 20b. Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)×2 300Z/150S.

[0210] In another preferred embodiment of the hybrid reinforcing cord 10 shown in FIGS. 2-5, the two strands 20a, 20b are not identical. For example, while in both the strands 20a, 20b the monofilament textile wires 21a, 21b are made of PET fibres and have a diameter equal to 0.30 mm, the multifilament textile yarn 22a of a strand 20a is made of rayon and has a linear density equal to 1220 dtex and the multifilament textile yarn 22b of the other strand 20b is made of rayon and has a linear density equal to 1840 dtex. In such a hybrid reinforcing cord 10, for example, 300 twists have been imparted in the right-handed direction (Z) to the multifilament textile yarn 22a, 22b and to the monofilament textile wire 21a, 21b of each of the two strands 20a and 20b, whereas 150 twists have been imparted in the left-handed direction (S) to each of the two strands 20a, 20b. Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)+(PET0.30+RY1840) 300Z/150S.

[0211] The Applicant has also made hybrid reinforcing cords in accordance with the present invention by twisting together three strands. For example, in an embodiment of such a type of hybrid reinforcing cord each strand comprises a monofilament textile wire made of PET fibres and having a diameter equal to 0.30 mm and a multifilament textile yarn made of rayon and having a linear density equal, for example, to 1220 dtex. In such hybrid reinforcing cords, for example, 300 twists have been imparted in the right-handed direction (Z) to the multifilament textile yarn and to the monofilament textile wire of each of the three strands, whereas 150 twists have been imparted in the left-handed direction (S) to each of the three strands. Such a reinforcing cord can therefore be indicated with (PET0.30+RY1220)×3 300Z/150S.

[0212] FIG. 6 shows another preferred embodiment of a hybrid reinforcing cord 10 which can used in the carcass structure 101 of tyres 100 in accordance with the present invention, preferably of the self-supporting type.

[0213] The hybrid reinforcing cord 10 of FIG. 6 differs from the one shown in FIGS. 2-4 only in that the strand 20a comprises two monofilament textile wires 21a of the type described above and two multifilament textile yarns 22a of the type described. Similarly, the strand 20b comprises two monofilament textile wires 21b of the type described above and two multifilament textile yarns 22b of the type described above. The empty space at the centre of the hybrid reinforcing cord 10 shown in FIG. 6 in reality will be occupied by the filaments 23a and 23b of the multifilament textile yarns 22a, 22b.

[0214] The strand 20a comprises two ends 20a′ twisted together with a twisting pitch that can be the same as, or different from, the twisting pitch of the two strands 20a, 20b. Similarly, the strand 20b comprises two ends 20b′ twisted together with a twisting pitch that can be the same as, or different from, the twisting pitch of the two ends 20a′.

[0215] Each of the two ends 20a′ of the strand 20a comprises a monofilament textile wire 21a at least partially embedded in the filaments 23a of a multifilament textile yarn 22a. Similarly, each of the two ends 20b′ of the strand 20b comprises a monofilament textile wire 21b at least partially embedded in the filaments 23b of a multifilament textile yarn 22b.

[0216] In a preferred embodiment of the hybrid reinforcing cord 10 shown in FIG. 6, the monofilament textile wires 21a, 21b are made of PET fibres and have a diameter equal to 0.30 mm, whereas the multifilament textile yarns 22a, 22b are made of aramid and have a linear density equal to 1110 dtex. In such a hybrid reinforcing cord 10, for example, 310 twists have been imparted in the right-handed direction (Z) to the ends 20a′, 20b′ of each strand 20a and 20b, whereas 280 twists have been imparted in the left-handed direction (S) to each of the two strands 20a, 20b. The reinforcing cord can therefore be indicated with 2×2(PET0.30+AR1100) 310Z/280S.

COMPARATIVE TESTS

[0217] The Applicant has carried out various comparative tests adapted to compare the behaviour of tyres made in accordance with the present invention with that of reference tyres successfully produced and commercialized by the Applicant.

[0218] Self-Supporting Tyres

[0219] In a first series of tests aimed to evaluate the suitability of the tyre of the present invention for being used as self-supporting tyre and to satisfy the continuous need of reducing emissions of CO.sub.2 into the atmosphere (hereinafter indicated as “environmental need”), the Applicant compared a reference self-supporting tyre of the type 245/45R18 100Y XL, commercialized with the trademark Cinturato P7™ RUNFLAT and having a carcass structure including reinforcing cords made of rayon and, in the sidewalls, reinforcing inserts made of elastomeric material with a high modulus having a thickness equal to 7 mm (hereinafter such a tyre is indicated with P1), with the following two tyres: [0220] a tyre that differs from the tyre P1 solely in that it has, in the sidewalls, reinforcing inserts made of elastomeric material having a lower thickness, equal to 6 mm (hereinafter such a tyre is indicated with P2); [0221] a tyre made in accordance with the present invention and that differs from the tyre P1 solely in that it has, in its carcass structure, hybrid reinforcing cords as defined above and, in the sidewalls, reinforcing inserts made of elastomeric material having a low modulus, and thus with a low hysteresis, and a thickness equal to 8 mm (hereinafter such a tyre is indicated with INV).

[0222] The reinforcing cords of the carcass structure of the tyres P1 and P2 were of the type RY1840×2 (48Z×48S), i.e. each of them comprising two multifilament textile yarns made of rayon twisted together, in which 48 twists have been imparted in the right-handed direction (Z) to each multifilament textile yarn and 48 twists have been imparted in the left-handed direction (S) to the reinforcing cord. Such reinforcing cords were arranged in the carcass structure with a thread count equal to 120 cords/dm.

[0223] The hybrid reinforcing cords of the carcass structure of the tyre INV were of the following type: (PET0.30+AR1680)×2 310Z/180S, i.e. each of them comprising two strands, each strand comprising two monofilament textile wires made of PET having a diameter equal to 0.30 mm and a multifilament textile yarn made of aramid having a linear density equal to 1680 dtex. The two strands were twisted together by imparting 310 twists in the right-handed direction (Z), whereas each multifilament textile yarn was twisted to the respective monofilament textile wire by imparting 180 twists in the left-handed direction (S). Such hybrid reinforcing cords were arranged in the carcass structure with a thread count equal to 85 cords/dm.

[0224] The Applicant measured the rolling resistance of the tyres P1, P2 and INV in accordance with EU Regulation no. 1235/2011 and obtained the values given in Table 1 below.

TABLE-US-00001 TABLE 1 P1 P2 INV 6.3 6.1 6.1

[0225] The Applicant has therefore verified that the tyres P2 and INV satisfy the aforementioned environmental need. The good behaviour of the tyre P2 was expected by virtue of the reduction of thickness of the reinforcing insert made of elastomeric material, whereas the good behaviour of the tyre INV confirms the intuition of the Applicant that it is possible to reduce the rolling resistance of a tyre by increasing the rigidity of its carcass structure and reducing the hysteresis.

[0226] With the aim to evaluate the suitability of the tyres P2 and INV for being used as self-supporting tyres, the Applicant carried out an outdoor test on a circuit by mounting the tyres P1, P2 and INV on the left rear wheel of a BMW series 5 and applying a vertical load of 570 Kg on the aforementioned wheel.

[0227] The Applicant verified that, while the tyre P2 allowed to travel for a few km with the tyre deflated, much less than with the tyre P1 and such as not to allow use of the tyre P2 as self-supporting tyre, the tyre INV allowed to travel with the tyre deflated a distance that is absolutely comparable with that of the tyre P1.

[0228] Such tests therefore confirmed the suitability of the tyre of the present invention both for being used as self-supporting tyre and for satisfying the need of reducing emissions of CO.sub.2 into the atmosphere.

[0229] Standard Tyres

[0230] In a second series of tests, carried out on standard tyres, i.e. not self-supporting, and aimed to evaluate the performance of the tyre of the present invention, the Applicant compared a reference tyre of the type 215/45 R17 91Y XL, commercialized with the trademark Cinturato P7™ and having a carcass structure including reinforcing cords made of rayon and a rigid tread band (hereinafter such a tyre is indicated with P1*), with a tyre made in accordance with the present invention (hereinafter such a tyre is indicated with INV*). The latter differs from the tyre P1* only in that it has, in its carcass structure, hybrid reinforcing cords as defined above and a tread band less rigid than that of the tyre P1*.

[0231] The reinforcing cords of the carcass structure of the tyre P1* were identical to those described above with reference to the tyres P1 and P2. Such reinforcing cords were arranged in the carcass structure with a thread count equal to 120 cords/dm

[0232] The hybrid reinforcing cords of the carcass structure of the tyre INV* were identical to those described above with reference to the tyre INV. Such hybrid reinforcing cords were arranged in the carcass structure with a thread count equal to 85 cords/dm.

[0233] The reference tyre is a tyre appreciated by customers for its excellent behaviour on dry and wet road surfaces in terms of drivability and braking.

[0234] The choice of providing in the tyre of the invention a tread band less rigid than that of the reference tyre was made to compensate for the greater rigidity of the carcass structure of the tyre of the invention with respect to that of the carcass structure of the reference tyre. The Applicant indeed wanted to carry out comparative tests based on the same vertical rigidity.

[0235] The tyres P1* and INV* were mounted on a Mini Cooper S, the front tyres being inflated to 2.6 bar and the rear tyres being inflated to 2.2 bar, and subjected to the judgement of a test driver who carried out a series of laps of a circuit.

[0236] The judgement provided by the test driver is given in Table 2 below, where the symbol “=” indicates an excellent judgement and the symbol “+” indicates an improvement with respect to the reference tyres.

TABLE-US-00002 TABLE 2 P1* INV* Straight-line travel on uneven surface = + Straight-line travel on regular surface = + Response to steering = + Steering torque = + Required steering angle = + Change of direction = + Comfort = = Rolling noise = = Insertion (Turn-in) = + Understeering = + Oversteering = + Throttle Release = + Progressivity in the loss of grip = + (Breakaway) Recovery = + Controllability = + Lateral Grip = +

[0237] Table 2 shows how the tyre of the invention offered improved results with respect to the already excellent results of the reference tyre in all performance categories, without having any worsening in the other categories.

[0238] Some data detected during circuit laps carried out with tyres P1* and INV* and with reference tyres are given in Table 3 below, wherein also in this case the symbol “=” indicates a value, considered excellent, obtained with the reference tyres and the symbol “+” indicates an improvement with respect to the reference tyres.

TABLE-US-00003 TABLE 3 P1* INV* Braking in the dry = + at 100 kph [m] Braking in the wet = + at 80 kph [m] Lap time in the wet = + [min/s]

[0239] The data of table 3 show an excellent behaviour of the tyre of the invention in terms of braking on a dry road surface, braking on a wet road surface and time taken to complete a lap of the circuit on a wet road surface. The excellent behaviour during braking is a consequence of the possibility of using in the tyres of the invention tread bands that are less rigid than those of the reference tyres. This is thanks to the greater rigidity of the carcass structure of the tyres of the invention with respect to that of the carcass structure of the reference tyres.

[0240] The present invention has been described with reference to some preferred embodiments. Different modifications can be brought to the embodiments described above, still remaining within the scope of protection of the invention which is defined by the following claims.