TYRE FOR VEHICLE WHEELS

Abstract

A tyre (1) for motorcycles comprises a carcass structure (2), a belt structure (10) applied in radially outer position with respect to the carcass structure (2), a tread band (11) applied in radially outer position with respect to the belt structure (10), wherein the carcass structure (2) comprises at least one carcass ply (3). The carcass ply (3) comprises a plurality of reinforcing cords (20) comprising a first end (21) and a second end (22) twisted together, wherein the first end (21) is a hybrid yarn (23) comprising a plurality of first filaments (24) mixed with a plurality of second filaments (25), wherein the filaments of the plurality of first filaments (24) are made from a single material having a first modulus and wherein the filaments of the plurality of second filaments (25) are made from a single material having a second modulus different from the first modulus. The second end (22) is a textile yarn (28) comprising a plurality of third filaments (29) made from at least one material having a third modulus.

Claims

1. Tyre (1) for vehicle wheels, comprising: a carcass structure (2); a belt structure (10) applied in radially outer position with respect to the carcass structure (2); a tread band (11) applied in radially outer position with respect to the belt structure (10); wherein the carcass structure (2) comprises at least one carcass ply (3); wherein the carcass ply (3) comprises a plurality of reinforcing cords (20) comprising a first end (21) and a second end (22) twisted together; wherein the first end (21) is a hybrid yarn (23) comprising a plurality of first filaments (24) mixed with a plurality of second filaments (25), wherein the filaments of the plurality of first filaments (24) are made from a single material having a first modulus and wherein the filaments of the plurality of second filaments (25) are made from a single material having a second modulus different from the first modulus, wherein the second end (22) is a multi-filament textile yarn (28) comprising a plurality of third filaments (29) made from at least one material having a third modulus.

2. Tyre (1) for vehicle wheels according to claim 1, wherein said third modulus is greater than or equal to said first modulus.

3. Tyre (1) for vehicle wheels according to claim 1 or 2, wherein said second modulus is less than said first modulus.

4. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of first filaments (24) are made from a single material having a high modulus.

5. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of second filaments (25) are made from a single material having a low modulus.

6. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of first filaments (24) are made from a single material having a high modulus, the filaments of the plurality of second filaments (25) are made from a single material having a low modulus and the filaments of the plurality of third filaments (29) are made from at least one material having a high modulus.

7. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of first filaments (24) are made from aramidic material.

8. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of second filaments (25) are made from a material selected from the group comprising: polyethylene terephthalate (PET), polyethylene napthalate (PEN), Nylon, Rayon.

9. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of third filaments (29) are made from aramidic material.

10. Tyre (1) for vehicle wheels according to claim 8, wherein the filaments of the plurality of second filaments (25) are made from polyethylene terephthalate (PET).

11. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the filaments of the plurality of first filaments (24) are mixed with the filaments of the plurality of second filaments (25) in a proportion of 50% by weight.

12. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the hybrid yarn (23) is obtained from a first yarn (26) comprising said plurality of first filaments (24) and from a second yarn (27) comprising said plurality of second filaments (25); the multi-filament textile yarn (28) of the second end (22) having a count equal to or greater than that of the first yarn (26).

13. Tyre (1) for vehicle wheels according to claim 12, wherein the count of the first yarn (26) is comprised between about 840 dtex and about 2200 dtex.

14. Tyre (1) for vehicle wheels according to claim 12 or 13, wherein the count of the second yarn (27) is comprised between about 840 dtex and about 2200 dtex.

15. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the number of reinforcing cords (20) of the carcass ply (3) per decimeter is comprised between about 80 and about 120.

16. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the first end (21) and the second end (22) are twisted on themselves with a predetermined number of twists per meter.

17. Tyre (1) for vehicle wheels according to any one of the previous claims, wherein the first end (21) and the second end (22) are twisted on themselves with an equal number of twists per meter.

18. Reinforcing cord (20) for a tyre (1) for vehicle wheels comprising a first end (21) and a second end (22) twisted together, wherein the first end (21) is a hybrid yarn (23) comprising a plurality of first filaments (24) mixed with a plurality of second filaments (25), wherein the filaments of the plurality of first filaments (24) are made from a single material having a first modulus and wherein the filaments of the plurality of second filaments (25) are made from a single material having a second modulus different from the first modulus, wherein the second end (22) is a multi-filament textile yarn (28) comprising a plurality of third filaments (29) made from at least one material having a third modulus.

19. Reinforcing cord (20) according to claim 18, wherein said first modulus and said third modulus are greater than said second modulus.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0123] Further features and advantages of the tyre of the present invention will become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the attached drawings only as an example and not for limiting purposes. In such drawings:

[0124] FIG. 1 is a schematic partial half cross section view of a portion of a tyre according to an embodiment of the present invention;

[0125] FIG. 2 is a schematic side view of a segment of a first embodiment of a reinforcing cord used in the tyre of FIG. 1;

[0126] FIG. 3 is an enlarged schematic view of a cross section of an end of the reinforcing cord of FIG. 2;

[0127] FIG. 4 is an enlarged schematic view of two yarns able to be used to make the end of the reinforcing cord of FIG. 3; and

[0128] FIG. 5 is an enlarged schematic view of a cross section of the reinforcing cord of FIG. 2.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0129] In FIG. 1, reference numeral 1 wholly indicates a tyre for vehicle wheels according to the present invention. In the specific example of FIG. 1, the tyre 1 is a tyre specifically intended to be used on the wheel of a high-performance motorcycle. However, the following can be applied, except when explicitly indicated otherwise, to a tyre for wheels of other types of vehicles.

[0130] An equatorial plane X and a rotation axis Z perpendicular to the equatorial plane X are defined in the tyre 1. An axial (or transversal, or lateral) direction, substantially parallel to the rotation axis Z and a circumferential (or longitudinal) direction, substantially parallel to the equatorial plane X and corresponding to the rolling direction of the tyre 1 are also defined.

[0131] The tyre 1 comprises a carcass structure 2 in turn comprising at least one carcass ply 3 comprising a plurality of reinforcing cords according to the invention arranged parallel to one another.

[0132] Preferably, the carcass structure 2 comprises two carcass plies 3 juxtaposed over one another.

[0133] The carcass structure 2 has, in an axial section thereof, a substantially toroidal configuration.

[0134] The carcass structure 2 comprises a crown portion 4 symmetrically arranged with respect to the equatorial plane X, and opposite lateral portions 5 arranged on axially opposite sides to the crown portion 4.

[0135] The illustrated carcass structure 2 comprises a carcass ply 3 extending axially from a lateral portion 5 of the carcass structure 2 to the opposite lateral portion 5.

[0136] The carcass ply 3 is preferably coated, on the radially inner wall, by a sealing layer 6, so-called “liner”, essentially consisting of a layer of airtight elastomeric material, adapted for ensuring the hermetic seal of the tyre 1 itself once inflated.

[0137] The carcass ply 3 is engaged, at the respective axially opposite lateral edges 3a, with respective annular reinforcing structures 7, typically called “bead cores”.

[0138] Each lateral edge 3a of the carcass ply 3 is turned around a respective bead core 7.

[0139] A tapered elastomeric filler 8 that occupies the space defined between the carcass ply 3 and the respective turned lateral edge 3a is applied on the outer perimeter edge of the bead cores 7.

[0140] In an alternative embodiment that is not illustrated, the carcass ply 3 has its opposite lateral edges 3a associated without turning with particular annular reinforcing structures provided with two metallic annular inserts. In this case, a filler made from elastomeric material can be arranged in axially outer position with respect to the first annular insert. The second annular insert, on the other hand, is arranged in axially outer position with respect to the end of the carcass ply 3. Finally, in axially outer position with respect to said second annular insert, and not necessarily in contact with it, there can be a further filler that finishes off the annular reinforcing structure.

[0141] The area of the tyre comprising the bead core 7 and the elastomeric filler 8 forms the so-called “bead”, globally indicated in FIG. 1 with 9, intended for anchoring through elastically forced fitting of the tyre on a corresponding mounting rim, not illustrated.

[0142] In radially outer position with respect to the aforementioned carcass structure 2, there is a belt structure 10. The belt structure 10 is arranged at at least one portion of the crown portion 4.

[0143] The belt structure 10 of the tyre 1 is of the zero degrees type. It is formed by winding onto the crown portion 4 of the carcass structure 2 one or more layers comprising a single reinforcing cord 10a, or a band-like element reinforced with rubber fabric comprising a plurality of reinforcing cords 10a arranged adjacent in the axial direction, to form a plurality of turns substantially oriented according to the circumferential direction of the tyre 1 (preferably with an angle comprised between 0° and 5° with respect to the equatorial plane X). In the case in which a reinforced band-like element is used, it can comprise up to seven reinforcing cords 10a, more preferably two or three or four reinforcing cords 10a.

[0144] Preferably, the winding defined by the turns extends axially over the entire crown portion 4, with a winding pitch that can be constant or variable in the axial direction.

[0145] Preferably, the reinforcing cords 10a of the belt structure 10 are made from metallic material. Even more preferably, the reinforcing cord 10a is made through wires of steel having high carbon content, in other words wires of steel with a carbon content over 0.60%-0.90%.

[0146] The belt structure 10 can also comprise one or more support layers made from elastomeric material (not illustrated) arranged between the layer of reinforcing cords 10a and the carcass ply 3 and on which the turns are wound. Such a layer/layers can extend over a surface having an axial extension substantially corresponding to the surface on which the turns extend.

[0147] In radially outer position with respect to the belt structure 10 there is a tread band 11, by means of which the contact of the tyre 1 with the road surface takes place.

[0148] The tread band 11 can have a tread pattern defined by a plurality of grooves 12 variously spread over the different areas of the tyre.

[0149] The tyre 1 can also comprise, at each of the opposite lateral portions 5 of the carcass structure 2, a respective sidewall 13 that extends from the tread band 11 to the bead 9 of the tyre 1.

[0150] The tyre 1 represented in FIG. 1 is, as stated, for wheels of high-performance motorcycles and is distinguished by a high transversal curvature (and therefore by a high curvature ratio) and, preferably, recessed sidewalls.

[0151] Preferably, the curvature ratio is greater than 0.200, more preferably greater than 0.250. Such a curvature ratio is typically less than 0.800. Preferably, the curvature ratio is comprised respectively between about 0.200 and about 0.500 for a rear tyre and between about 0.350 and about 0.600 for a front tyre.

[0152] With reference to FIG. 1, the term tyre with low or recessed sidewalls is meant to indicate a tyre in which the ratio between the distance H-H1 and the height H, measured on the equatorial plane X between the radially highest point of the tread band 11 and the fitting diameter, substantially defined by the reference line L passing through the beads 9 of the tyre, is preferably less than 0.65, more preferably less than 0.6, for example equal to 0.55.

[0153] The carcass ply 3 of the carcass structure 2 is preferably made from elastomeric material and comprises a plurality of reinforcing cords 20 that are preferably arranged substantially parallel to one another and oriented along a substantially axial direction. More preferably, each reinforcing cord 20 belongs to a respective radial plane of the tyre 1.

[0154] The carcass structure 2 is therefore a radial carcass structure.

[0155] In the embodiment illustrated in FIG. 1 all of the reinforcing cords 20 belong to a single carcass ply 3.

[0156] In an alternative embodiment that is not illustrated, the carcass structure 2 comprises at least two carcass plies 3 radially juxtaposed over one another and the reinforcing cords 20 are always arranged substantially parallel to one another and oriented along a substantially axial direction.

[0157] In another embodiment that is not illustrated the carcass structure 2 comprises at least two carcass plies 3 radially juxtaposed over one another, each comprising a plurality of reinforcing cords 20 arranged substantially parallel to one another. Said at least two carcass plies 3 are crossed over one another so that the reinforcing cords 20 of a first ply are inclined with respect to the reinforcing cords 20 of the second carcass ply and to the equatorial plane X.

[0158] In the first carcass ply the reinforcing cords 20 are arranged so as to form an angle with the equatorial plane X comprised in the range between about 10° and about 70°, preferably between about 15° and about 45°.

[0159] In the second carcass ply the reinforcing cords 20 are arranged so as to form an angle with the equatorial plane X comprised in the range between about 10° and about 70°, preferably between about 15° and about 45°.

[0160] The reinforcing cords 20 of the second carcass ply are arranged in an opposite manner with respect to the reinforcing cords 20 of the first carcass ply. In other words, the aforementioned reinforcing cords 20 have the same amount of inclination with respect to the equatorial plane X, but have opposite orientation.

[0161] Each reinforcing cord 20 comprises a first end 21 and a second end 22 twisted together, as schematically indicated in FIG. 2.

[0162] The twists (TPM) per meter of the first end 21 on the second end 22, or of the second end 22 on the first end 21, are comprised between about 100 and about 500, more preferably between about 280 and about 380.

[0163] The first end 21 is a hybrid yarn 23 consisting of a plurality of first filaments 24 and of a plurality of second filaments 25 mixed together, as illustrated in FIG. 3.

[0164] The hybrid yarn 23 that makes the first end 21 is obtained from a first yarn 26 and from a second yarn 27, each made up of a plurality of filaments 24, 25 of a respective single material (as schematized in FIG. 4). The filaments 24, 25 of the first and second yarn 26, 27 are mixed through an operation known as “commingling” and described in document WO 2009/052844 to the same Applicant.

[0165] As an example, a process for making the hybrid yarn 23 provides that the first yarn 26 and the second yarn 27 are conveyed and brought towards one another inside a duct of an airjet device inside which pressurized air is introduced through one or more nozzles. The air separates the single filaments 24, 25 of each of the first 26 and second yarn 27 and mixes them forming the single hybrid yarn 23.

[0166] In the embodiment according to the present description, which as already stated is relative to a tyre for wheels of high-performance motorcycles, the first filaments 24 are made from material with high modulus, preferably aramidic material, for example aromatic polyamide (Aramid), and the second filaments 25 are made from polyethylene terephthalate (PET).

[0167] In other embodiments not described in detail, the first filaments 24 can be made from material with low modulus, and the second filaments 25 can be made from material with high modulus.

[0168] It is also possible to provide that the first filaments 24 are made from material with high modulus and that the second filaments 25 are also made from material with high modulus, provided that the material that makes the first filaments 24 has a different modulus from the material that makes the second filaments 25.

[0169] Furthermore, it is possible to provide that the first filaments 24 are made from material with low modulus and that the second filaments 25 are also made from material with low modulus, provided that the material that makes the first filaments 24 has a different modulus from the material that makes the second filaments 25.

[0170] In the embodiment described in detail, the first filaments 24 of the first yarn 26 are mixed with the second filaments 25 of the second yarn 27 in proportions of 50% by weight.

[0171] The count of the first yarn 26 is comprised between about 840 dtex and about 2200 dtex.

[0172] The count of the second yarn 27 is comprised between about 840 dtex and about 2200 dtex.

[0173] The count of the first 26 and second yarn 27, in the preferred embodiment of the invention, is the same and is equal to about 1100 dtex.

[0174] The hybrid yarn 23 is twisted on itself with a number of twists per meter comprised between about 310 and about 410.

[0175] Preferably, the number of twists per meter of the hybrid yarn 23 is comprised between 320 and 360.

[0176] Even more preferably, the number of twists per meter of the hybrid yarn 23 is equal to 330 or 340.

[0177] With reference to FIG. 5, the second end 22 of the reinforcing cord 21 comprises a textile yarn 28 comprising third single filaments 29.

[0178] The third filaments 29 are, in the embodiment described here in detail, made from aramidic material, for example aromatic polyamide (Aramid).

[0179] In other embodiments, the third filaments 29 can be made from any other material with high modulus or from material with low modulus.

[0180] In the embodiment described in detail, the count of the textile yarn 28 of the second end 22 is comprised between about 1100 dtex and about 2200 dtex and preferably it is about 1670 dtex.

[0181] The textile yarn 28 is twisted on itself with a number of twists per meter comprised between about 310 and about 410.

[0182] Preferably, the number of twists per meter of the textile yarn 28 is comprised between 320 and 360.

[0183] Even more preferably, the number of twists per meter of the textile yarn 28 is equal to about 330 or 340.

[0184] Preferably, the number of twists per meter of the hybrid yarn 23 and of the textile yarn 28 is the same.

[0185] Preferably, the hybrid yarn 23 is twisted on itself with a different number of twists per meter from the number of twists per meter with which the first end 21 is twisted together with the second end 22.

[0186] Preferably, the textile yarn 28 is twisted on itself with a different number of twists per meter from the number of twists per meter with which the first end 21 is twisted with the second end 22.

[0187] The number of reinforcing cords 20 of the carcass ply 3 arranged per decimeter (also called thread count), measured along a circumferential direction, is comprised between about 80 and about 120, preferably between about 97 and about 110.

[0188] The reinforcing cord 20 preferably has the following mechanical characteristics.

[0189] Elongation less than or equal to 1% when subjected to a load less than or equal to 20 N.

[0190] Elongation less than or equal to 3% when subjected to a load of about 100 N.

[0191] Tensile strength greater than about 300 N.

[0192] The Applicant has carried out some comparative tests to evaluate the performance of tyres comprising, in the respective carcass structures, reinforcing cords in accordance with the present invention in comparison with a reference tyre comprising, in its carcass structure, reinforcing cords made from only Aramid.

[0193] In particular, the test tyre described below and the reference tyre are distinguished from one another substantially only for the different reinforcing cords used in the carcass structure. All of the tyres comprise a zero degrees belt structure with identical metallic reinforcing cords. The reference tyre, in the carcass structure, comprises used reinforcing cords of type AR 1100×2(45×45) F80, in other words reinforcing cords made up of two yarns made from Aramid with count 1100 dtex each twisted on itself with 450 twists per meter, twisted together and in which the thread count of the reinforcing cords is equal to 80.

[0194] The test tyre comprises reinforcing cords 20 in the carcass structure of type:

(AR+PET)/AR 2200/1670(33/33×33) F110.

[0195] They are reinforcing cords 20 in accordance with the present invention in which the hybrid yarn 23 is obtained from a first yarn 26 comprising first filaments 24 made from Aramid and from a second yarn 27 comprising second filaments 25 in PET in which the first filaments 24 are mixed with the second filaments 25 in a proportion of 50% by weight.

[0196] The second end 22 is made from a textile yarn 28 comprising only filaments 29 made from Aramid.

[0197] The count of the first 26 and of the second yarn 27 is the same and is equal to 1100 dtex.

[0198] The count of the textile yarn 28 is equal to 1670 dtex.

[0199] The number of twists on itself of the hybrid yarn 23 is equal to 330 per meter. The number of twists on itself of the textile yarn 28 is equal to 330 per meter.

[0200] The thread count of the reinforcing cord 20 is equal to 110.

[0201] TEST 1

[0202] A track test carried out by a driver showed, with respect to the reference tyre, better grip on the asphalt of the test tyre, a better lap time around the track, better driving precision, better thrust provided by the rear wheel and better stability of alignment of the motorcycle.

[0203] TEST 2

[0204] The reinforcing cords of the carcass structure of the reference tyre and those of the test tyre were subjected to a same stress test. At the end of the stress test the tensile strength of the reinforcing cord was evaluated, so as to evaluate the mechanical fatigue behavior thereof. The stress test was carried out as described hereinafter.

[0205] The tyre (both the test one and the reference one) has dimensions 200/65R17 and was mounted on a hub with camber 45 degrees, inflated to a pressure of 1.6 bar and made to rotate on a road wheel of 1.8 meters in diameter at a speed of 120 km/h with a load of 250 kg, at controlled room temperature (25+/−2° C.) for one hour.

[0206] The test concluded positively since from a visual inspection the tyre (both the test one and the reference one) did not show clear failures at the end of the test.

[0207] After the stress test, the tyre (both the test one and the reference one) was sent to the laboratory to analyze the mechanical characteristics of the reinforcing cords. In particular, reinforcing cords of the carcass were manually extracted. The extracted reinforcing cords were subjected to traction testing with a dynamometer (Instron) to measure the rupture load thereof in the section corresponding to the engaged side of the cover during testing.

[0208] From 10 tyres identical to the one used in the stress test but not subjected to stress test reinforcing cords were extracted, which were also subjected to traction testing. From the comparison between the measured rupture loads, the degradation of the tensile strength of the reinforcing cords in percentage terms was obtained.

[0209] After having subjected the test tyre and the reference tyre to stress testing, the tensile strength of the reinforcing cords of the test tyre was between about 150 N and about 190 N, whereas the tensile strength of the reinforcing cords of the reference tyre was between about 70 N and about 130 N. The tensile strength of the reinforcing cords was again about 300 N for the reinforcing cords of the reference tyre and about 345 N for the reinforcing cords of the test tyre.

[0210] In percentage degradation terms of the tensile strength, the reinforcing cord of the test tyre has a degradation comprised between about 45% and about 57%, whereas the reinforcing cord of the reference tyre has a degradation comprised between about 57% and about 77%.

[0211] It was thus found that the reinforcing cords of the test tyre, made in accordance with the present invention, are capable of withstanding a greater number of stress cycles with respect to the reinforcing cords of the reference tyre.

[0212] Of course, those skilled in the art can bring further modifications and variants to the tyre 1 described above in order to satisfy specific and contingent application requirements, said variants and modifications in any case being encompassed by the scope of protection as defined by the following claims.