Tyre for motor vehicles and process for building a tyre for motor vehicles

Abstract

A tyre for motor vehicles comprises a carcass structure (2) comprising a first carcass ply (3) and a second carcass ply (4), a reinforcing layer (8) comprising at least one reinforcing cord (9) wound in a plurality of circumferential coils and arranged in a radially outer position to the carcass structure (2) and in contact with the carcass structure (2), a tread band (10) applied in a radially outer position to the reinforcing layer (8) and in contact with the reinforcing layer (8). The first carcass ply (3) has a first end flap (3A) engaged with a first annular anchoring structure (5A) and a second end flap (3B) spaced from a second annular anchoring structure (5B). The second carcass ply (4) has a first end flap (4A) engaged with the second annular anchoring structure (5B) and a second end flap (4B) spaced from the first annular anchoring structure (5A). The first carcass ply (3) and the second carcass ply (4) are superimposed on each other in an overlapping area located below the tread band (10).

Description

[0001] “Tyre for motor vehicles and process for building a tyre for motor vehicles”

[0002] DESCRIPTION

[0003] Technical field of the invention

[0004] The present invention relates to a tyre for motor vehicles and to a process for building a tyre for motor vehicles. In particular, the present invention relates to a beltless tyre comprising two carcass plies, each of which extends partially between an annular structure and the opposite one.

[0005] Definitions

[0006] A “beltless” tyre means a tyre having a carcass structure, a tread band and a reinforcing structure between the carcass structure and the tread band comprising at least one reinforcing cord, the reinforcing structure being formed by at least one reinforcing layer, wherein in said at least one reinforcing layer said at least one reinforcing cord present is oriented at 0° + / - 10° with respect to the circumferential direction of the tyre; i.e. a tyre without a belt structure arranged between the carcass structure and the tread band comprising distinct belt strips provided with reinforcing cords parallel in each strip and crossed with those of the adjacent strip. By “curvature ratio” in relation to a tyre it is meant the ratio between the distance of the radially outermost point of the tread band from the line passing through the laterally opposite ends of the tread band itself, measured on a radial plane of the tyre, and the distance measured along the tyre cord between said ends.

[0007] By “motor vehicle tyre” it is meant a tyre whose curvature ratio is indicatively less than 0.15, preferably between 0.03 and 0.1 , more preferably close to 0.05.

[0008] The terms “radial”, “axial” and “circumferential” refer to an axis of rotation of a tyre or an axis of rotation of a building drum.

[0009] By “radial plane” it is meant a plane in which the axis of rotation of the tyre or building drum lies.

[0010] “Tyre middle plane” means a plane equidistant from the tyre beads and orthogonal to the axis of rotation of the tyre. “Axial distance”, “axial extension” and “axial width” are measured along respective directions parallel to the axis of rotation of the tyre or building drum.

[0011] The “axial width of the tread band” of a tyre means the width of the semi-finished product constituting the tread band present in the finished tyre.

[0012] The term “end flap” of the carcass ply means a portion of the carcass ply that includes one of the axial ends.

[0013] By end flap “spaced” from the annular anchoring structure, it is meant that such end flap is not engaged with the respective annular anchoring structure.

[0014] The “tensile load - elongation" curve of a reinforcing cord means the curve drawn on a graph which has the elongation (for example the percentage elongation) of the reinforcing cord on the abscissa axis and the tensile force exerted on the reinforcing cord on the ordinate (for example expressed in N).

[0015] The “tensile load - elongation” curve for metallic cords is obtained according to the BISFA standard - Internationally agreed methods for testing steel tyre cords 1995, chapter E6.

[0016] The “tensile load - elongation” curve for textile cords is obtained according to the BISFA standard - Testing method for polyamide filament yarns 2004, chapter 7.

[0017] By “density” it is meant the number of cords present per unit of width, for example 1 dm.

[0018] By “textile cord” it is meant a cord made of a thread or several threads of textile material.

[0019] By “hybrid cord” it is meant a cord made of threads of at least two different textile materials.

[0020] By “metallic cord” it is meant a cord made of one or more metallic threads.

[0021] Prior art

[0022] A tyre for motor vehicles generally comprises a carcass structure associated with a belt structure.

[0023] The carcass structure comprises one or more carcass plies having respectively opposite terminal flaps engaged with respective annular anchoring structures, called bead cores, associated with a filling insert. The tyre area comprising the bead core and the filling insert forms a bead structure intended for anchoring tyre onto a corresponding mounting rim. The belt structure comprises several belt layers placed layers placed in radial overlap with respect to each other and with respect to the carcass structure, having metallic or textile or hybrid reinforcing cords with a crossed orientation with respect to a circumferential development direction of the tyre. A tread band is arranged in a radially outer position with respect to the belt structure.

[0024] Tyres are also known whose carcass plies have end flaps engaged with only one of the annular anchoring structures.

[0025] Document WO2014 / 130215A1 illustrates a tyre having a first carcass ply, a second carcass ply and a belt. The first carcass ply extends from a first bead, along a first sidewall, and ends at a point inside the tread band of the tyre. The second carcass ply extends from a second bead, along a second sidewall, and ends at a point inside the tread band of the tyre. The belt has a first edge and a second edge. The first carcass ply has an end point offset with respect to the second edge by a distance of 0 to 5 inches. The second carcass ply has an end point offset with respect to the first edge by a distance of 0 to 5 inches.

[0026] Document EP1985468A1 illustrates a tyre having a belt and a carcass structure comprising a first ply and a second ply. The first and second plies are arranged one above the other but offset with respect to a central radial axis of the tyre. Each of the first and second plies mentioned above is wound around a single bead core placed on one side of the tyre. The ends of the first ply and of the second ply are arranged under the belt. The first ply and the second ply may differ in that the reinforcements are arranged at different angles with respect to each other. Reinforcements may be oriented radially in the first ply and diagonally in the second ply.

[0027] Document US6267166B1 illustrates a tyre having a belt assembly with steel cords arranged at 23° with respect to a circumferential direction of the tyre and crossed with each other. The tyre further comprises a single-ply carcass reinforcement which extends from a respective outer bead core (with respect to a vehicle on which the tyre is mounted) to an inner shoulder area and comprises reinforcing cords deposited at an angle of 85° - 90° with respect to the circumferential direction of the tyre. An inner reinforcement comprises a carcass ply wound around the inner bead core to form an inner ply and an outer ply on the sidewall which end at an edge of the tread. Document US3363660A illustrates a tyre comprising a belt and a carcass. The carcass is made up of plies comprising a rubberised fabric with cords which extend at an angle of 80° - 90° with respect to the equatorial median plane of the tyre. The belt is made of a weftless fabric with cords oriented circumferentially or forming a small angle with respect to the equatorial median plane. In one example, the carcass comprises an inner ply and two outer plies. The two outer plies are joined to each other below the belt and at the median equatorial plane.

[0028] Summary

[0029] The adoption of the strip (layered) belt structure provided with reinforcing cords crossed with respect to each other in the tyres was necessary to satisfy the request to adapt the tyres to the ever-increasing performance of motor vehicles and to improve the driving features in terms, for example, of stiffness, driving stability and driving readiness.

[0030] Tyres with a belt structure having belt layers having cross-oriented cords are in fact normally capable of providing a greater drift force, for the same drift angle, compared to beltless tyres. Tyres with such a belt structure are also normally capable of providing a greater self-aligning moment at low drift angles than beltless tyres.

[0031] For several years the Applicant has paid attention to the environmental impact exerted directly and indirectly by tyres during their use. In particular, in order to contain the consumption of motor vehicles which have an impact on energy consumption and also on the emission of carbon dioxide into the atmosphere, the Applicant produces tyres with low rolling resistance, i.e. tyres with a fuel efficiency class equal to “A” (according to the European Regulation EU 2020 / 740).

[0032] In this context, the Applicant has set itself the objective of further reducing the rolling resistance of tyres, for example but not exclusively intended to equip new hybrid and fully electric motor vehicles, particularly for autonomous driving, in order to reduce the environmental impact.

[0033] In particular, the Applicant has set itself the goal to achieve the above objective without compromising the performance and driving features of modern tyres, in particular tyres provided with a crossed belt structure.

[0034] The Applicant has unexpectedly found that the above objectives may be solved by adopting a particular beltless structure. More precisely, the Applicant has found that the above-mentioned objectives may be achieved by means of a beltless tyre which combines two carcass plies arranged asymmetrically with a reinforcing layer provided with a reinforcing cord wound in a plurality of circumferential coils.

[0035] According to a first aspect thereof, the present invention relates to a tyre for motor vehicles.

[0036] Preferably, the tyre for motor vehicles has a curvature ratio of less than 0.15.

[0037] Preferably, the tyre comprises a carcass structure, a tread band and a reinforcing structure between the carcass structure and the tread band comprising at least one reinforcing cord, the reinforcing structure being formed by at least one reinforcing layer, wherein in said at least one reinforcing layer said at least one reinforcing cord present is wound in a plurality of circumferential coils and is oriented at 0° + / - 10° with respect to the circumferential direction of the tyre.

[0038] Preferably, said carcass structure comprises a first carcass ply and a second carcass ply.

[0039] Preferably, said carcass structure comprises a first annular anchoring structure and a second annular anchoring structure.

[0040] Preferably, the first carcass ply has a first end flap engaged with the first annular anchoring structure and a second end flap, opposite the first end flap, spaced from the second annular anchoring structure.

[0041] Preferably, the second carcass ply has a first end flap engaged with the second annular anchoring structure and a second end flap, opposite the first end flap, spaced from the first annular anchoring structure.

[0042] Preferably, the first carcass ply and the second carcass ply are superimposed on each other in an overlapping area located below the tread band.

[0043] Preferably, said reinforcing layer has an axial width.

[0044] Preferably, an edge of the second end flap of the first carcass ply and a respective second lateral edge of said reinforcing layer are separated by a first axial distance. Preferably, an edge of the second end flap of the second carcass ply and a respective first lateral edge of said reinforcing layer are separated by a second axial distance.

[0045] Preferably, a ratio between the first axial distance and the axial width of the reinforcing layer is between 0.0 and 0.22. Preferably, a ratio between the second axial distance and the axial width of the reinforcing layer is between 0.0 and 0.22.

[0046] According to a second aspect thereof, the present invention relates to a process for building a beltless tyre for vehicle wheels.

[0047] Preferably, the tyre for motor vehicles has a curvature ratio of less than 0.15.

[0048] Preferably, the process comprises: placing in a radially outer position to a building drum a first carcass ply having a first end flap and a second end flap axially opposite the first end flap.

[0049] Preferably, the process comprises: placing in a radially outer position to the building drum and the first carcass ply a second carcass ply having a first end flap and a second end flap axially opposite to the first end flap.

[0050] Preferably, the first carcass ply and the second carcass ply are partly superimposed on each other in an overlapping area.

[0051] Preferably, the first end flap of the first carcass ply is axially spaced from the second end flap of the second carcass ply.

[0052] Preferably, the first end flap of the second carcass ply is axially spaced from the second end flap of the first carcass ply.

[0053] Preferably, the process comprises: associating a first annular anchoring structure to the first end flap of the first carcass ply and associating a second annular anchoring structure to the first end flap of the second carcass ply.

[0054] Preferably, the process comprises: shaping the carcass structure.

[0055] Preferably, the process comprises: applying a reinforcing layer in a position radially outer to the carcass structure.

[0056] Preferably, the reinforcing layer comprises at least one reinforcing cord.

[0057] Preferably, applying the reinforcing layer comprises: winding said at least one reinforcing cord into a plurality of circumferential coils.

[0058] Preferably, the process comprises: applying a tread band in a position radially outer to the reinforcing layer.

[0059] Preferably, at the end of the building process and after a moulding and vulcanisation step, the reinforcing layer has an axial width.

[0060] Preferably, an edge of the second end flap of the first carcass ply and a respective second lateral edge of said reinforcing layer are separated by a first axial distance. Preferably, an edge of the second end flap of the second carcass ply and a respective first lateral edge of said reinforcing layer are separated by a second axial distance.

[0061] Preferably, a ratio between the first axial distance and the axial width of the reinforcing layer is between 0.0 and 0.22.

[0062] Preferably, a ratio between the second axial distance and the axial width of the reinforcing layer is between 0.0 and 0.22.

[0063] The Applicant believes that the present invention allows for a drastic reduction in the rolling resistance of tyres.

[0064] The Applicant has also verified that the present invention allows performance and driving features suitable for the equipment of modem motor vehicles.

[0065] In particular, the Applicant has verified that the tyres made in accordance with the present invention are capable of providing a drift force suitable for daily road use.

[0066] The present invention, in at least one of the above aspects thereof, may exhibit one or more of the following preferred features.

[0067] Preferably, the reinforcing layer is arranged in contact with said carcass structure.

[0068] Preferably, the tread band is applied in contact with said reinforcing layer.

[0069] Preferably, the carcass plies present in the carcass structure are two in number: the first carcass ply and the second carcass ply.

[0070] Preferably, the first axial distance and the second axial distance are equal to each other or different.

[0071] Preferably, a ratio between the first axial distance and the axial width of the reinforcing layer is between 0.02 and 0.12.

[0072] Preferably, a ratio between the second axial distance and the axial width of the reinforcing layer is between 0.02 and 0.12.

[0073] Preferably, a ratio between the first axial distance and the tyre width is between 0.0 and 0.18.

[0074] Preferably, a ratio between the second axial distance and the tyre width is between 0.0 and 0.18.

[0075] Preferably, said edge of the second end flap of the first carcass ply lies axially further from a middle plane of the tyre than the respective second lateral edge.

[0076] Preferably, a ratio of the first axial distance to the axial width of the reinforcing layer is equal to or less than 0.03. Preferably, said edge of the second end flap of the second carcass ply lies axially further from a middle plane of the tyre than the respective first lateral edge.

[0077] Preferably, a ratio of the second axial distance to the axial width of the reinforcing layer is equal to or less than 0.03.

[0078] Preferably, said edge of the second end flap of the first carcass ply lies axially closer to a middle plane of the tyre than the respective second lateral edge.

[0079] Preferably, a ratio of the first axial distance to the axial width of the reinforcing layer is equal to or less than 0.22, more preferably equal to or less than 0.12.

[0080] Preferably, said edge of the second end flap of the second carcass ply lies axially closer to a middle plane of the tyre than the respective first lateral edge.

[0081] Preferably, a ratio of the second axial distance to the axial width of the reinforcing layer is equal to or less than 0.22, more preferably equal to or less than 0.12.

[0082] Preferably, each of said first carcass ply and second carcass ply comprising a plurality of cords.

[0083] Preferably, the cords of the first carcass ply and the second carcass ply are crossed over each other in the overlapping area.

[0084] Preferably, in said overlapping area, the cords of each of the first carcass ply and second carcass ply delimit with a circumferential direction of the tyre a respective angle between 25° and 80°.

[0085] Preferably, such angle is between 45° and 75°.

[0086] Preferably, such angle is between 60° and 65°.

[0087] Preferably, the angle delimited by the cords of the first carcass ply with the circumferential direction of the tyre is equal to or different from the angle delimited by the cords of the second carcass ply with said circumferential direction of the tyre.

[0088] Preferably, in the overlapping area, the cords of the first carcass ply and the second carcass ply form a crossing angle with each other between 50° and 160°. Preferably, the crossing angle is between 90° and 150°.

[0089] Preferably, the crossing angle is between 120° and 130°.

[0090] Preferably, at a first sidewall of the tyre, each of the cords of the first carcass ply lies in a radial plane or in a plane delimiting an angle of less than 5° with a radial plane intersecting said cord. Preferably, at a second sidewall of the tyre, each of the cords of the second carcass ply lies in a radial plane or in a plane delimiting an angle of less than 5° with a radial plane intersecting said cord.

[0091] Preferably, the second end flap of the first carcass ply and the second end flap of the second carcass ply both lie below the tread band.

[0092] Preferably, the overlapping area has an axial extension and a ratio of an axial width of the reinforcing layer to the axial extension is between 0.9 and 1 .8.

[0093] Preferably, the tread band has an axial width and a ratio of the axial width of the tread band to the axial extension is between 1 .0 and 1 .9.

[0094] Preferably, a ratio of a width of the tyre to the axial extension is between 1 .2 and 2.3.

[0095] Preferably, the second end flap of the first carcass ply and the second end flap of the second carcass ply both lie below the reinforcing layer.

[0096] Preferably, the tyre comprises a first sidewall and a second sidewall.

[0097] Preferably, only the first carcass ply is associated with the first sidewall and only the second carcass ply is associated with the second sidewall.

[0098] Preferably, said at least one reinforcing cord has a predefined percentage elongation.

[0099] Preferably, said at least one reinforcing cord has a “tensile load - elongation” curve comprising a first section, placed upstream of the predefined percentage elongation, a second section, placed downstream of the predefined percentage elongation and a third connecting section placed between the first section and the second section.

[0100] Preferably, a second slope of the second section is greater than a first slope of the first section.

[0101] Preferably, a ratio of the second slope of the second section to the first slope of the first section is greater than 5.

[0102] Preferably, a ratio of the second slope of the second section to the first slope of the first section is less than 50.

[0103] Preferably, said at least one reinforcing cord is metallic or hybrid.

[0104] Preferably, the reinforcing layer comprises said at least one reinforcing cord immersed in a layer of elastomeric material.

[0105] Preferably, the circumferential coils of said at least one reinforcing cord delimit, with the circumferential direction, an angle comprised between 0° and 5°. Preferably, a density of the circumferential coils of said at least one reinforcing cord in the reinforcing layer is between 40 coils / dm and 130 coils / dm, more preferably it is between 75 coils / dm and 115 coils / dm.

[0106] Preferably, it is provided to apply the reinforcing layer in a radially outer position to the carcass structure in contact with said carcass structure.

[0107] Preferably, it is provided to apply the tread band in a radially outer position to the reinforcing layer in contact with said reinforcing layer.

[0108] Preferably, said edge of the second end flap of the first carcass ply lies axially further from a middle plane of the tyre than the respective second lateral edge and a ratio of the first axial distance to the axial width of the reinforcing layer is equal to or less than 0.03.

[0109] Preferably, said edge of the second end flap of the second carcass ply lies axially further from a middle plane of the tyre than the respective first lateral edge and a ratio of the second axial distance to the axial width of the reinforcing layer is equal to or less than 0.03.

[0110] Preferably, said edge of the second end flap of the first carcass ply lies axially closer to a middle plane of the tyre than the respective second lateral edge and a ratio of the first axial distance to the axial width of the reinforcing layer is equal to or less than 0.22, more preferably equal to or less than 0.12.

[0111] Preferably, said edge of the second end flap of the second carcass ply lies axially closer to a middle plane of the tyre than the respective first lateral edge and a ratio of the second axial distance to the axial width of the reinforcing layer is equal to or less than 0.22, more preferably equal to or less than 0.12.

[0112] Preferably, each of said first carcass ply and second carcass ply comprises a plurality of cords.

[0113] Preferably, the cords of the first carcass ply and the second carcass ply are crossed over each other in the overlapping area.

[0114] Preferably, in said overlapping area and before shaping, the cords of each of the first carcass ply and second carcass ply delimit with a circumferential direction of the building drum a respective angle between 50° and 82°.

[0115] Preferably, said angle with respect to the circumferential direction of the building drum is between 59° and 79°.

[0116] Preferably, said angle with respect to the circumferential direction of the building drum is between 69° and 72°. Preferably, in the overlapping area and before shaping, the cords of the first carcass ply and the second carcass ply form a crossing angle with each other between 100° and 164°.

[0117] Preferably, the crossing angle before shaping is between 118° and 158°.

[0118] Preferably, the crossing angle before shaping is between 138° and 144°.

[0119] Preferably, the first carcass ply has a first area comprising the first end flap and a second area comprising the second end flap.

[0120] Preferably, the cords in the first area have a different orientation than the cords in the second area.

[0121] Preferably, before shaping, the cords in the first area delimit an angle between 90° and 95° with the circumferential direction of the building drum.

[0122] Preferably, before shaping, the cords in the second area delimit said respective angle with the circumferential direction of the building drum.

[0123] Preferably, the second carcass ply has a first area comprising the first end flap and a second area comprising the second end flap.

[0124] Preferably, the cords in the first area have a different orientation than the cords in the second area.

[0125] Preferably, before shaping, the cords in the first area delimit an angle (ε’) between 90° and 95° with the circumferential direction of the building drum.

[0126] Preferably, the cords in the second area delimit said respective angle with the circumferential direction of the building drum.

[0127] Preferably, once the tread band has been applied, the second end flap of the first carcass ply and the second end flap of the second carcass ply both lie below said tread band.

[0128] Preferably, applying the reinforcing layer comprises: placing said reinforcing layer against the second end flap of the first carcass ply or against the second end flap of the second carcass ply.

[0129] Preferably, applying the reinforcing layer comprises: winding, in coils placed in side by side relationship, an elongated continuous element comprising said at least one reinforcing cord around the shaped carcass structure.

[0130] Preferably, a density of the reinforcing cords in the continuous elongated element is between 40 coils / dm and 130 coils / dm, more preferably between 75 coils / dm and 115 coils / dm. Further features and advantages will become more apparent from the detailed description of preferred but non-exclusive embodiments of a tyre for motor vehicles and of a process for building a tyre for motor vehicles according to the present invention.

[0131] Description of the figures

[0132] Such description is given hereinafter with reference to the accompanying drawings, provided only for illustrative and, therefore, non-limiting purposes, in which:

[0133] - Figure 1 illustrates a half-section along a radial plane of a tyre for motor vehicles according to the present invention;

[0134] - Figure 2 is an enlarged portion of Figure 1 ;

[0135] - Figures 3 and 4 are enlarged portions of respective variants of the tyre in Figure 1 ;

[0136] - Figures 5 and 6 are schematic top views of the tyre shown in the preceding figures according to two respective embodiments and with some parts removed to better highlight others;

[0137] - Figure 7 is an enlarged portion of the half-section of Figure 1 ;

[0138] - Figures 8 - 11 illustrate the respective steps of a building process of the tyre of the preceding figures;

[0139] - Figure 12 illustrates a building drum in one of the building steps;

[0140] - Figures 13 and 14 are two schematic top views of the building drum of Figure 12 used for building the embodiments of Figures 5 and 6;

[0141] - Figure 15 illustrates a continuous elongated element used to make the tyre referred to in the preceding figures;

[0142] - Figure 16A illustrates a “tensile load - elongation” curve of a possible reinforcing cord of a tyre referred to in the preceding figures;

[0143] - Figure 16b illustrates a “tensile load - elongation” curve of a different reinforcing cord of a tyre referred to in the preceding figures;

[0144] - Figure 17 is a graph showing rolling resistance coefficients of tyres according to the present invention;

[0145] - Figure 18 illustrates drift forces of the tyres in Figure 17 and a reference tyre; - Figure 19 illustrates the drift stiffnesses of the tyres in Figure 17 and the reference tyre as a function of the vertical load;

[0146] - Figure 20 is a graph showing rolling resistance coefficients of further tyres according to the present invention;

[0147] - Figure 21 illustrates drift forces of the tyres in Figure 20 and a reference tyre;

[0148] - Figure 22 illustrates the drift stiffnesses of the tyres in Figure 20 and the reference tyre as a function of the vertical load;

[0149] - Figure 23 is a graph showing rolling resistance coefficients of other tyres according to the present invention;

[0150] - Figure 24 illustrates drift forces of the tyres in Figure 23 and a reference tyre;

[0151] - Figure 25 illustrates the drift stiffnesses of the tyres in Figure 23 and the reference tyre as a function of the vertical load.

[0152] Detailed description

[0153] Figure 1 illustrates a half-section along a radial plane of a tyre 1 for motor vehicles according to the present invention. The tyre 1 for motor vehicles shown in Figure 1 has a curvature ratio of approximately 0.05.

[0154] The tyre 1 comprises a carcass structure 2, comprising a first carcass ply 3 and a second carcass ply 4.

[0155] The first carcass ply 3 has its own first end flap 3A engaged with a first annular anchoring structure 5A, called bead core, associated with a first filling insert 6A. The second carcass ply 4 has its own first end flap 4A engaged with a second annular anchoring structure 5B associated with a second filling insert 6B.

[0156] The two areas of the tyre 1 each comprising the annular anchoring structure 5A, 5B and the filling insert 6A, 6B form a first and a second bead structure 7A, 7B intended for anchoring the tyre 1 on a corresponding mounting rim, not illustrated.

[0157] A second end flap 3B of the first carcass ply 3, axially opposite to the first end flap 3A, is not engaged with the second annular anchoring structure 5B but is instead spaced from the latter. A second end flap 4B of the second carcass ply 4, axially opposite to the first end flap 4A, is not engaged with the first annular anchoring structure 5A but is instead spaced from the latter. The carcass structure 2 is associated with a reinforcing layer 8 (zero degree layer) comprising at least one reinforcing cord 9 wound in a plurality of circumferential coils arranged in a radially outer position with respect to the carcass structure 2 (better shown in Figure 7). The reinforcing layer 8 preferably lies in contact with the carcass structure 2. The circumferential coils are arranged so as to form an angle preferably of between 0° and 5° with a circumferential direction “C” of the tyre 1. The density of the circumferential coils of the reinforcing cord 9 in the reinforcing layer 8 is between 40 coils / dm and 130 coils / dm, more preferably between 75 coils / dm and 115 coils / dm.

[0158] A tread band 10 is applied in a position radially outer to the reinforcing layer 8, made of an elastomeric compound like other semi-finished products making up tyre 1 . The tread band 10 is preferably positioned against the reinforcing layer 8.

[0159] The tyre 1 according to the invention is not provided with a belt structure comprising strips or layers provided with parallel reinforcing cords in each strip / layer and crossed with those of the adjacent strip / layer, i.e. it is of the beltless type.

[0160] On the lateral surfaces of the carcass structure 2, each extending from one of the lateral edges of the tread band 10 up to the respective bead structure 7A, 7B, a first sidewall 11A and a second sidewall 11 B of elastomeric compound are also applied in an axially outer position.

[0161] A layer of waterproof elastomeric material 12, generally known as a “liner”, which provides the necessary impermeability to the inflation air of the tyre 1 , is arranged in a radially inner position with respect to the first carcass ply 3. The waterproof elastomeric material layer 12 is preferably applied against the carcass structure 2. The first end flap 3A of the first carcass ply 3 is wound around the respective first annular anchoring structure 5A. Starting from said first annular anchoring structure 5A, the first carcass ply 3 extends along the first sidewall 11A up to under the tread band 10 and, in all the non-limiting embodiments illustrated, the second end flap 3B of the first carcass ply 3 is placed in a position radially inside the tread band 10, i.e. under the tread band 10. Therefore, the first sidewall 11A is associated with only the first carcass ply 3.

[0162] The first end flap 4A of the second carcass ply 4 is wound around the respective second annular anchoring structure 5B. Starting from said second annular anchoring structure 5B, the second carcass ply 4 extends along the second sidewall 11 B up to under the tread band 10 and, in all the non-limiting embodiments illustrated, the second end flap 4B of the second carcass ply 4 is placed in a position radially inside the tread band 10, i.e. under the tread band 10. Therefore, the second sidewall 11 B is associated with only the second carcass ply 4.

[0163] Therefore, the first carcass ply 3 and the second carcass ply 4 are superimposed on each other in an overlapping area located below the tread band 10. In such overlapping area, the first carcass ply 3 is radially inside and the second carcass ply 4 is radially outside. In such overlapping area, the first carcass ply 3 preferably lies in contact with the layer of waterproof elastomeric material 12 placed radially inside and the second carcass ply 4 preferably lies in contact with the reinforcing layer 8 placed radially outside.

[0164] As illustrated in Figures 1 , 5 and 6, the overlapping area has an axial extension “L1”, the reinforcing layer 8 has an axial width “L2”, the tread band 10 has an axial width “L3” and the tyre 1 has a width “L4”.

[0165] A ratio of the axial width “L2” of the reinforcing layer 8 to the axial extension “L1” is between 0.9 and 1 .8; a ratio of the axial width “L3” of the tread band 10 to the axial extension “L1” is between 1 .0 and 1 .9; a ratio of the width “L4” of the tyre 1 to the axial extension “L1” is between 1.2 and 2.3.

[0166] The reinforcing layer 8 has a first lateral edge 8A and a second lateral edge 8B axially opposite the first lateral edge 8A. The first lateral edge 8A is coupled to the first sidewall 11A. The second lateral edge 8B is coupled to the second sidewall 11 B.

[0167] One edge of the second end flap 3B of the first carcass ply 3 and the second lateral edge 8B of the reinforcing layer 8 are separated by a first axial distance “D1” (Figures 1 - 4). One edge of the second end flap 4B of the second carcass ply 4 and the first lateral edge 8A of the reinforcing layer 8 are separated by a second axial distance “D2” (Figures 1 - 4). A ratio (in absolute value) of the first axial distance “D1” to the axial width “L2” of the reinforcing layer 8 is between 0.0 and 0.22. A ratio (in absolute value) of the second axial distance “D2” to the axial width “L2” of the reinforcing layer 8 is between 0.0 and 0.22.

[0168] A ratio of the first axial distance “D1” to the width “L4” of tyre 1 is between 0.0 and 0.18. A ratio of the second axial distance “D2” to the width “L4” of tyre 1 is between 0.0 and 0.18. In the embodiments of Figures 1 , 2 and 3, the second end flap 3B of the first carcass ply 3 is placed in a radially inner position with respect to the reinforcing layer 8, i.e. it does not protrude axially beyond the reinforcing layer 8, and the second end flap 4B of the second carcass ply 4 is also placed in a radially inner position with respect to the reinforcing layer 8. Said edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 therefore lie axially closer to a middle plane “M” of the tyre 1 than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8. Preferably, in such embodiments, a ratio of the first axial distance “D1” to the axial width “L2” of the reinforcing layer 8 is equal to or less than 0.22 and / or a ratio of the second axial distance “D2” to the axial width “L2” of the reinforcing layer 8 is equal to or less than 0.22.

[0169] In the variant of Figure 4, the second end flap 3B of the first carcass ply 3 protrudes axially beyond the reinforcing layer 8 and so does (although not illustrated in Figure 4) the second end flap 4B of the second carcass ply 4. Therefore, said edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 lie axially further from the middle plane “M” than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8. Preferably, in such embodiments, the ratio of the first axial distance “D1” to the axial width “L2” of the reinforcing layer 8 is equal to or less than 0.03 and / or the ratio of the second axial distance “D2” to the axial width “L2” of the reinforcing layer 8 is equal to or less than 0.03.

[0170] The following Table 1 reports, as a non-limiting example, the sizes of the tyres 1 illustrated in Figures 1 , 2, 3 and 4. The positive sign of D1 and D2 means that said edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 are farther from the middle plane “M” of the tyre 1 than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8 (as in Figure 4). The negative sign of D1 and D2 means that said edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 are closer to the middle plane “M” of the tyre 1 than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8 (as in Figures 1 , 2 and 3).

[0171] Table 1

[0172] Although in the accompanying figures, the first axial distance “D1” and the second axial distance “D2” are illustrated as identical, it is possible that in the same tyre 1 they are different from each other.

[0173] The first carcass ply 3 and the second carcass ply 4 each comprise a plurality of cords 13, 14 parallel to each other and covered by or immersed in elastomeric material. Such parallel cords 13, 14 of the first carcass ply 3 and of the second carcass ply 4 may be textile and / or hybrid.

[0174] As visible in Figure 5, which schematically illustrates the first carcass ply 3 and the second carcass ply 4 together with the reinforcing layer 8, the cords 13 of the first carcass ply 3 are inclined, with respect to the circumferential direction “C” of the tyre 1 , by a respective angle a measured in an anti-clockwise direction and the cords 14 of the second carcass ply 4 are inclined, with respect to the aforementioned circumferential direction “C”, by a respective angle β measured in a clockwise direction. Therefore, in the overlapping area, the cords 13 of the first carcass ply 3 are crossed with respect to the cords 14 of the second carcass ply 4. The cords 13 of the first carcass ply 3 delimit a crossing angle with the cords 14 of the second carcass ply 4: Δ = α + β. The angles α and β are between 25° and 80°, preferably between 45° and 75°, more preferably between 60° and 65°. The crossing angle Δ is between 60° and 160°, preferably between 90° and 150°, more preferably between 120° and 130°. In the accompanying figures, the angles α and β are equal to each other but in other embodiments they may also be different from each other.

[0175] The above illustrated values of the angles α , β and Δ are those formed by the cords in the finished tyre 1 , i.e. shaped and vulcanised, and may differ from the angles of the cords of the first carcass ply 3 and of the second carcass ply 4 when said plies 3, 4 are deposited on a building drum 15, i.e. before the carcass structure 2 is shaped.

[0176] In this regard, a process for building a tyre 1 for vehicle wheels according to the invention is illustrated in Figures 8 to 11 .

[0177] Such process comprises: depositing on a radially outer surface of the building drum 15 a layer of waterproof elastomeric material 12 optionally provided, at opposite axial ends, with elastomeric material intended to form portions of the first sidewall 11 A and of the second sidewall 11 B and / or of the first bead structure 7A and of the second bead structure 7B.

[0178] Such process further comprises: depositing the first carcass ply 3 in a radially outer position to the building drum 15, depositing the second carcass ply 4 in a radially outer position to the building drum 15 and to the first carcass ply 3, so that the first end flap 3A of the first carcass ply 3 is axially spaced from the second end flap 4B of the second carcass ply 4, the first end flap 4A of the second carcass ply 4 is axially spaced from the second end flap 3B of the first carcass ply 3 and the first carcass ply 3 and the second carcass ply 4 are partially overlapped in the overlapping area (Figures 12, 13 and 14). The first carcass ply 3 and the second carcass ply 4 are preferably applied in contact with the waterproof elastomeric material layer 12.

[0179] The first annular anchoring structure 5A is then associated with the first end flap 3A of the first carcass ply 3 with the respective first filling insert 6A and the second annular anchoring structure 5B is associated with the first end flap 4A of the second carcass ply 4 with the respective second filling insert 6B. The first annular anchoring structure 5A and the second annular anchoring structure 5B are arranged in a radially outer position with respect to the opposite axial ends of the waterproof elastomeric material layer 12.

[0180] A half-section of the resulting carcass structure 2 is shown in Figure 8. In this step, the carcass structure 2 is substantially cylindrical in shape. In such cylindrical shape, that is, immediately after the deposition on the building drum 15 and before a shaping step, in the overlapping area, the cords 13, 14 of the first carcass ply 3 and of the second carcass ply 4 delimit with a circumferential direction “X” of the building drum 15 the respective angles α' and β' and form the crossing angle Δ' between them (Figures 13 and 14). The values of such angles differ slightly from the values of such angles α and β and Δ in the finished tyre 1 . The respective angles α' and β' of the cylindrical carcass structure 2 are between 50° and 82°, preferably between 59° and 79°, more preferably between 69° and 72°, and the crossing angle Δ' is between 100° and 164°, preferably between 118° and 158°, more preferably between 138° and 144°.

[0181] Figure 14 illustrates a variant in which the first carcass ply 3 has a first area comprising the first end flap 3A and a second area comprising the second end flap 3B. In the first area, the cords 13 have a different orientation compared to the cords 13 placed in the second area (multi-angular ply). Similarly, the second carcass ply 4 has a first area comprising the first end flap 4A and a second area comprising the second end flap 4B and the respective cords 14 have a different orientation in the first area compared to the cords placed in the second area (multi- angular ply).

[0182] For example, the cords 13, 14 of the first carcass ply 3 and of the second carcass ply 4 placed in the respective first areas delimit with the circumferential direction “X” of the building drum 15 an angle Ω between 90° and 95° while in the respective second areas the cords 13, 14 of the first carcass ply 3 and of the second carcass ply 4 have the angles α’ and β’, Δ’ illustrated above.

[0183] According to the process, the carcass structure 2 is then shaped by bringing the first annular anchoring structure 5A and the second annular anchoring structure 5B axially closer to each other and by radially expanding, for example by means of pressurised gas, a portion of the carcass structure 2 located at the overlapping area of the first carcass ply 3 and the second carcass ply 4 (Figure 9).

[0184] Figure 6 illustrates the shaped tyre 1 corresponding to the variant of Figure 14 wherein, at the first sidewall 11A of the tyre 1 , each of the cords 13 of the first carcass ply 3 lies in a radial plane or in a plane delimiting with a radial plane intersecting said cord an angle of less than 5° and at the second sidewall 11 B of the tyre 1 , each of the cords 14 of the second carcass ply 4 lies in a radial plane or in a plane delimiting with a radial plane intersecting said cord 14 an angle of less than 5°.

[0185] A continuous elongated element 16 (partially illustrated in Figure 15) which comprises one or more of the aforementioned reinforcing cords 9 embedded in or covered by elastomeric material 17 is then wound around the carcass structure 2 and preferably in contact with the carcass structure 2, in coils placed close to each other or partially overlapping. The deposition of the continuous elongated element 16 forms the reinforcing layer 8 (Figure 10).

[0186] Before shaping, the overlapping area of the first and second carcass plies 3, 4 has an axial extension “L'1”, which may be slightly different from the axial extension “L1” in the finished tyre 1.

[0187] The continuous elongated element 16 preferably comprises a number of reinforcing cords 9 between 1 and 500. In the exemplary embodiment of Figure 15, the continuous elongated element 16 has a flattened section and comprises reinforcing cords 9 arranged side by side. A density of the reinforcing cords 9 in the continuous elongated element 16 is preferably between 40 cords / dm and 130 cords / dm, for example equal to 75 cords / dm. The winding of the continuous elongated element 16 also arranges the reinforcing cords 9 according to the aforementioned plurality of circumferential coils.

[0188] In the illustrated exemplary embodiments, the continuous elongated element 16, and hence the reinforcing layer 8, is placed against the second carcass ply 4 and the second end flap 4B of the second carcass ply 4. In the embodiment of Figure 1 , the reinforcing layer 8 is also applied against a portion of the first carcass ply 3 close to the second end flap 4B of the second carcass ply 4.

[0189] During deposition, the continuous elongated element 16 is placed under tension so as to give said continuous elongated element 16 and the respective reinforcing cords 9 a percentage elongation, which is substantially maintained once the continuous elongated element 16 is wound and applied around the carcass structure 2.

[0190] Each reinforcing cord 9 has a predefined percentage elongation Sp between 1 % and 5%, preferably between 1.5% and 4.5%. Such reinforcing cord 9 also has a “tensile load - elongation” curve comprising a first section “T1”, located upstream of the predefined percentage elongation “Sp” and provided with a first slope measured in a first point “P1”, and a second section “T2”, placed downstream of the predefined percentage elongation “Sp” and provided with a second slope measured at a second point “P2”, where the second slope is greater than the first slope. In other words, the reinforcing cord 9 increases its stiffness when it is stretched beyond the predefined percentage elongation “Sp”. Given that in the finished tyre 1 the reinforcing cord 9 has such predefined percentage elongation “Sp”, then this means that when, during the rolling of the tyre 1 on the road, said tyre 1 deforms so as to put the reinforcing cord 9 under traction or portions thereof, then the reinforcing cord 9 behaves as if it had a high stiffness corresponding to the slopes of the second section “T2”.

[0191] An example of such a “tensile load - elongation” curve is illustrated in the graph in Figure 16a which reports on the abscissa the percentage elongation (%) of a possible reinforcing cord 9 usable according to the invention and on the ordinate the tensile force (expressed in Newton).

[0192] The first section “T1” is delimited between the zero elongation and the first point “P1” of the “tensile load - elongation” curve, the second section “T2” develops downstream of the second point “P2” of the “tensile load - elongation” curve, a third connecting section “K” is delimited between the first point “P1” and the second point “P2”. The first section “T1” and the second section “T2” of the “tensile load - elongation” curve are connected by the third connecting section “K” with an increasing slope. The third connecting section “K” forms a sort of elbow or knee with a concavity facing upwards. The “tensile load - elongation” curve in Figure 16a refers to a 3x4x0.20 HEHT steel metal cord.

[0193] The “tensile load - elongation” curve in Figure 16a has the first section “T1” with the concavity facing downwards, followed by the third connecting section “K” with the concavity facing upwards and then by the second section “T2” with the concavity facing first upwards and then downwards. The curve in Figure 16a therefore has an inflection point between the first section “T1” and the third connecting section “K” and an inflection point at the beginning of the second section “T2”. The first point “P1” corresponds to the first point of the “tensile load - elongation” curve encountered, starting from zero elongation, in which the concavity of the “tensile load - elongation” curve is facing upwards. In the graph of Figure 16a, the first point “P1” is placed just after the inflection point of the first section “T1”. The second point “P2” is the inflection point at the beginning of the second section “T2”.

[0194] In Figure 16a, the predefined percentage elongation Sp corresponds to the elongation placed at the intersection between a first tangent to the “tensile load - elongation” curve in the first point “P1” and a second tangent to the “tensile load - elongation” curve in the second point “P2”. In the graph of Figure 16a, the predefined percentage elongation “Sp” is equal to approximately 1.7% and a force F corresponding to such predefined percentage elongation “Sp” is equal to approximately 60 N.

[0195] A further example of such a “tensile load - elongation” curve is illustrated in the graph in Figure 16b which shows on the abscissa the percentage elongation (%) of a different possible reinforcing cord 9 usable according to the invention and on the ordinate the tensile force.

[0196] The “tensile load - elongation” curve in Figure 16b refers to a hybrid cord of the AR / NY 1100 / 1400 type.

[0197] Also in this case, the first section “T1” is delimited between the zero elongation and the first point “P1” of the “tensile load - elongation” curve, the second section “T2” develops downstream of the second point “P2” of the “tensile load - elongation” curve, a third connecting section “K” is delimited between the first point “P1” and the second point “P2”. The first section “T1” and the second section “T2” of the “tensile load - elongation” curve are connected by the third connecting section “K” with an increasing slope. The third connecting section “K” forms a sort of elbow or knee with a concavity facing upwards.

[0198] The “tensile load - elongation” curve in Figure 16b has the first section “T1” with the concavity facing downwards, followed by the third connecting section “K” with the concavity facing upwards and then by the second section “T2”, which unlike the curve in Figure 16a, has a concavity always facing upwards (up to the breaking load). As for Figure 16a, the first point “P1” corresponds to the first point of the “tensile load - elongation” curve encountered, starting from zero elongation, in which the concavity of the “tensile load - elongation” curve is facing upwards. Unlike Figure 16a, the second point “P2” of the “tensile load - elongation” curve in Figure 16b is the point with maximum concavity.

[0199] In the graph of Figure 16b, the predefined percentage elongation “Sp” is equal to approximately 4.27 % and a force F corresponding to such predefined percentage elongation “Sp” is equal to approximately 33 N.

[0200] A ratio between the second slope and the first slope of the “tensile load - elongation” curve of the reinforcing cord 9 usable according to the invention is preferably greater than 5, more preferably between 5 and 50, even more preferably it is between 5 and 35. For example, the first slope of the first section “T1” is preferably comprised between 1 and 25 N / elongation % and the second slope of the second section “T2” is preferably comprised between 35 and 500 N / elongation %. In the example of the graph of Figure 16aA, the first slope of the first section “T1” is approximately 20 N / % elongation and the second slope of the second section “T2” is approximately 470 N / % elongation, so the aforementioned ratio is approximately 24. In the example of the graph of Figure 16bA, the first slope of the first section “T1” is approximately 7 N / % elongation and the second slope of the second section “T2” is approximately 38 N / % elongation, so the aforementioned ratio is approximately 5.4.

[0201] Finally, the tread band 10 is placed around the reinforcing layer 8. The tread band 10 is applied against the reinforcing layer 8 (Figure 11 ). Once the tread band 10 has been applied, the second end flap 3B of the first carcass ply 3 and the second end flap 4B of the second carcass ply 4 both lie below said tread band 10.

[0202] Finally, the first sidewall 11A is applied against the first carcass ply 3, between the tread band 10 and the first bead structure 7A and the second sidewall 11 B is applied against the second carcass ply 4, between the tread band 10 and the second bead structure 7B.

[0203] Test 1

[0204] Five tyres B, C, D, E, F according to the invention were compared by means of a finite element simulation (FEA) with a reference tyre A having a low rolling resistance value of approximately 6 N / kN.

[0205] All the tyres A, B, C, D, E, F represent a beltless model in size 215 / 60 R17, i.e. without a belt structure comprising layers with reinforcing cords crossed with each other and arranged between the carcass structure and the tread band. All tyres A, B, C, D, E, F include a zero-degree reinforcing layer between the carcass structure and the tread band comprising AR / NY 1100 / 1400 type reinforcing cords whose “tensile load - elongation” curve is illustrated in Figure 16b.

[0206] The reference tyre A is a simulated tyre with only two carcass plies, in which the two carcass plies have crossed cords forming, with a circumferential direction “C” of the tyre and in a crown area located at the tread band, an angle of 62°. Both carcass plies are engaged with the two annular anchoring structures.

[0207] The five tyres B, C, D, E, F comprise only two carcass plies and each carcass ply is engaged with only one annular anchoring structure. The two carcass plies have crossed cords that form a circumferential direction “C” of the tyre and an angle of 62° in the overlapping area.

[0208] The five tyres B, C, D, E, F differ from each other in the position of the edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 with respect to the reinforcing layer 8, i.e. in the first axial distance “D1” and in the second axial distance “D2”, where D1 is equal to D2, as illustrated in the following Table 2. The positive sign of D1 and D2 means that the edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 are farther from the middle plane “M” of the tyre 1 than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8 (as in Figure 4). The negative sign of D1 and D2 means that the edges of the second end flap 3B of the first carcass ply 3 and of the second end flap 4B of the second carcass ply 4 are closer to the middle plane “M” of the tyre 1 than the respective first lateral edge 8A and second lateral edge 8B of the reinforcing layer 8 (as in Figures 1 , 2 and 3).

[0209] Table 2

[0210] Figure 17 shows the rolling resistance coefficient RR of tyres B, C, D, E, F. The rolling resistance coefficient has been normalised by assigning the value 100 to reference tyre A. As may be seen, all tyres B, C, D, E, F have a RR (RRB= 75.4, RRC= 70.8, RRD= 68.8, RRE= 68.8, RRF= 71.2) lower than the rolling resistance coefficient RR of reference tyre A (RRA = 100). The lowest coefficients are those of tyres D and E with D1 and D2 equal to -10 mm and -5 mm respectively. As may be observed, for all the cases analysed the rolling resistance values are exceptionally low considering that they are compared with those of the aforementioned reference tyre A.

[0211] Figure 18 illustrates the drift forces Fs (in Newton) as a function of the drift angle SA of the tyres A, B, C, D, E, F at a vertical load of 600 kg corresponding to the working conditions of a wheel on the external side of the curve. Figure 19 illustrates the drift stiffness as a function of the vertical load of tyres A, B, C, D, E, F.

[0212] All tyres B, C, D, E, F have a lower drift stiffness than the reference tyre A, i.e. a lower reactivity when cornering. The drift force deficit Fs for tyres B, C, D, E, F is however such that it does not give rise to a significant penalty in non-sporty driving on the road.

[0213] Test 2

[0214] Four tyres G, H, I (same as E), J according to the invention were compared via a finite element simulation (FEA) with the reference tyre A of Test 1 .

[0215] The four tyres G, H, I, J comprise only two carcass plies and each carcass ply is engaged with only one annular anchoring structure. They include a zero-degree reinforcing layer between the carcass structure and the tread band comprising AR / NY 1100 / 1400 type reinforcing cords whose “tensile load - elongation” curve is illustrated in Figure 16b. The two carcass plies have crossed cords in the overlapping area. The two carcass plies have the first axial distance “D1” equal to the second axial distance “D2” and equal to - 5 mm.

[0216] The four tyres G, H, I, J differ from each other in the angles α and β formed, in the overlapping area, by the reinforcing cords 13, 14 with the circumferential direction “C” of tyre 1 .

[0217] Table 3

[0218] Figure 20 illustrates the rolling resistance coefficient RR of tyres G, H, I, J. The rolling resistance coefficient has been normalised by assigning the value 100 to the reference A. As may be seen, all tyres G, H, I, J have a RR (RRG= 82.8, RRH= 72.3, RRI= 68.8, RRJ= 72.3) lower than the rolling resistance coefficient RR of the reference tyre A (RRA= 100). The minimum value of the rolling resistance coefficient RR is obtained with the angles α and β equal to 62° (tyre I equal to tyre E).

[0219] Even in these cases, the rolling resistance values are all exceptionally low, considering the reference tyre.

[0220] Figure 21 illustrates the drift forces Fs (in Newton) as a function of the drift angle SA of the tyres A, G, H, I, J at a vertical load of 600 kg corresponding to the working conditions of a wheel on the external side of the curve. The figure illustrates the drift stiffness as a function of the vertical load of the tyres A, G, H, I, J.

[0221] All tyres G, H, I, J have a lower drift stiffness than the reference tyre A, i.e. a lower reactivity when cornering. The drift force deficit Fs for tyres G, H, I, J is however such that it does not give rise to a significant penalty in non-sporty driving on the road.

[0222] Test 3

[0223] Three tyres K, L, M according to the invention were compared via a finite element simulation (FEA) with the reference tyre A from Tests 1 and 2.

[0224] The three tyres K, L, M comprise only two carcass plies and each carcass ply is engaged with only one annular anchoring structure. They include a zero-degree reinforcing layer between the carcass structure and the tread band comprising AR / NY 1100 / 1400 type reinforcing cords whose “tensile load - elongation” curve is illustrated in Figure 16b. The two carcass plies have crossed cords in the overlapping area. Each of the two carcass plies is of the multi-angular type, as illustrated in Figures 6 and 14. In particular, each of the two carcass plies at the first sidewall 11A and the second sidewall 11 B, the cords 13, 14 of the first carcass ply 3 and of the second carcass ply 4 lie in respective radial planes. Furthermore, the two carcass plies of the three tyres K, L, M have the first axial distance “D1” equal to the second axial distance “D2” and equal to - 5 mm.

[0225] The three tyres K, L, M differ from each other in the angles α and β formed, in the overlapping area, by the reinforcing cords 13, 14 with the circumferential direction “C” of tyre 1 .

[0226] Table 4

[0227] Figure 23 shows the rolling resistance coefficient RR of the K, L, M tyres. The rolling resistance coefficient has been normalised by assigning the value 100 to the reference A. As may be seen, all the K, L, M tyres have a RR (RRK= 92.3, RRL= 75.3, RRM= 74.0) lower than the rolling resistance coefficient RR of the reference tyre A (RRA= 100). The minimum value of the rolling resistance coefficient RR is obtained with the angles α and β equal to 62° (tyre M). Also in this test, in the various cases analysed, the rolling resistance values are always lower and in some cases exceptionally low compared to the reference tyre.

[0228] Figure 24 illustrates the drift forces Fs (in Newton) as a function of the drift angle SA of the tyres A, K, L, M at a vertical load of 600 kg corresponding to the working conditions of a wheel on the external side of the curve. Figure 25 illustrates the drift stiffness as a function of the vertical load of tyres A, K, L, M.

[0229] All tyres K, L, M have a lower drift stiffness than the reference tyre A, i.e. a lower reactivity when cornering. The drift force deficit Fs for tyres K, L, M is however such that it does not give rise to a significant penalty in non-sporty driving on the road.

Claims

CLAIMS1 . Tyre for motor vehicles, having a curvature ratio of less than 0.15, said tyre comprising a carcass structure (2), a tread band (10) and a reinforcing structure between carcass structure (2) and tread band (10) comprising at least one reinforcing cord (9), the reinforcing structure being formed by at least one reinforcing layer (8), wherein in said at least one reinforcing layer (8) said at least one reinforcing cord (9) present is wound in a plurality of circumferential coils and is oriented at 0° + / - 10° with respect to the circumferential direction of the tyre, wherein: said carcass structure (2) comprises a first carcass ply (3), a second carcass ply (4), a first annular anchoring structure (5A) and a second annular anchoring structure (5B); wherein the first carcass ply (3) has a first end flap (3A) engaged with the first annular anchoring structure (5A) and a second end flap (3B), opposite the first end flap (3A), spaced from the second annular anchoring structure (5B); wherein the second carcass ply (4) has a first end flap (4A) engaged with the second annular anchoring structure (5B) and a second end flap (4B), opposite the first end flap (4A), spaced from the first annular anchoring structure (5A); wherein the first carcass ply (3) and the second carcass ply (4) are superimposed on each other in an overlapping area located below the tread band (10); wherein said reinforcing layer (8) has an axial width (L2); wherein an edge of the second end flap (3B) of the first carcass ply (3) and a respective second lateral edge (8B) of said reinforcing layer (8) are separated by a first axial distance (D1 ); wherein an edge of the second end flap (4B) of the second carcass ply (4) and a respective first lateral edge (8A) of said reinforcing layer (8) are separated by a second axial distance (D2); wherein a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is between 0.0 and 0.22 and a ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is between 0.0 and 0.22.

2. Tyre according to claim 1 , wherein said edge of the second end flap (3B) of the first carcass ply (3) lies axially further from a middle plane (M) of the tyre (1)than the respective second lateral edge (8B ) and a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.03; wherein said edge of the second end flap (4B) of the second carcass ply (4) lies axially further from a middle plane (M) of the tyre (1 ) than the respective first lateral edge (8A) and a ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.03.

3. Tyre according to claim 1 or 2, wherein said edge of the second end flap (3B) of the first carcass ply (3) lies axially closer to a middle plane (M) of the tyre (1 ) than the respective second lateral edge (8B) and a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.22; wherein said edge of the second end flap (4B) of the second carcass ply (4) lies axially closer to a middle plane (M) of the tyre (1 ) than the respective first lateral edge (8A) and a ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.22.

4. Tyre according to claim 3, wherein the ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.12 and the ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.12.

5. Tyre according to one of claims 1 to 4, wherein each of said first carcass ply (3) and second carcass ply (4) comprises a plurality of cords (13, 14), the cords (13, 14) of the first carcass ply (3) and the second carcass ply (4) being crossed with each other in the overlapping area.

6. Tyre according to claim 5, wherein, in the overlapping area, the cords (13, 14) of each of the first carcass ply (3) and second carcass ply (4) delimit with a circumferential direction (C) of the tyre (1) a respective angle (a, β) between 25° and 80°.

7. Tyre according to one of claims 1 to 6, wherein the second end flap (3B) of the first carcass ply (3) and the second end flap (4B) of the second carcass ply (4) both lie below the tread band (10).

8. Tyre according to one of claims 1 to 7, wherein the overlapping area has an axial extension (L1 ) and a ratio of an axial width (L2) of the reinforcing layer (8) to the axial extension (L1 ) is between 0.9 and 1.8; wherein the tread band (10) has an axial width (L3) and a ratio of the axial width (L3) of the tread band (10) to the axial extension (L1 ) is between 1.0 and 1.9; wherein a ratio of a width (L4) of the tyre (1 ) to the axial extension (L1 ) is between 1 .2 and 2.3.

9. Tyre according to one of claims 1 to 8, wherein said at least one reinforcing cord (9) has a predefined percentage elongation (Sp); said at least one reinforcing cord (9) having a “tensile load - elongation” curve comprising a first section (T1), placed upstream of the predefined percentage elongation (Sp), a second section (T2), placed downstream of the predefined percentage elongation (Sp), and a third connecting section (K) placed between the first section (T1 ) and the second section (T2); wherein a second slope of the second section (T2) is greater than a first slope of the first section (T 1 ).

10. Process for building a beltless tyre for motor vehicles having a curvature ratio of less than 0.15, wherein the process comprises:- placing in a radially outer position to a building drum (15) a first carcass ply (3) having a first end flap (3A) and a second end flap (3B) axially opposite the first end flap (3A);- placing in a radially outer position to the building drum (15) and to the first carcass ply (3) a second carcass ply (4) having a first end flap (4A) and a second end flap (4B) axially opposite the first end flap (4A); wherein the first carcass ply (3) and the second carcass ply (4) partially overlap each other in an overlapping area; wherein the first end flap (3A) of the first carcass ply (3) is axially spaced from the second end flap (4B) of the second carcass ply (4) and wherein the first end flap (4A) of the second carcass ply (4) is axially spaced from the second end flap (3B) of the first carcass ply (3);- associating a first annular anchoring structure (5A) to the first end flap (3A) of the first carcass ply (3) and associating a second annular anchoring structure (5B) to the first end flap (4A) of the second carcass ply (4);- shaping the carcass structure (2);- applying a reinforcing layer (8) radially outer to the carcass structure (2), wherein the reinforcing layer (8) comprises at least one reinforcing cord (9) and wherein applying the reinforcing layer (8) comprises: winding said at least one reinforcing cord (9) in a plurality of circumferential coils;- applying a tread band (10) in a radially outer position to the reinforcing layer (8); wherein, at the end of the building process and after a moulding and vulcanisation step, the reinforcing layer (8) has an axial width (L2), wherein an edge of the second end flap (3B) of the first carcass ply ( 3) and a respective second lateral edge (8B) of said reinforcing layer (8) are separated by a first axial distance (D1 ); wherein an edge of the second end flap (4B) of the second carcass ply (4) and a respective first lateral edge (8A) of said reinforcing layer (8) are separated by a second axial distance (D2), wherein a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is between 0.0 and 0.22 and a ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is between 0.0 and 0.22.

11. Process according to claim 10, wherein said edge of the second end flap (3B) of the first carcass ply (3) lies axially further from a middle plane (M) of the tyre (1 ) than the respective second lateral edge (8B ) and a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.03; wherein said edge of the second end flap (4B) of the second carcass ply (4) lies axially further from a middle plane (M) of the tyre (1 ) than the respective first lateral edge (8A) and a ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.03.

12. Process according to claim 10 or 11 , wherein said edge of the second end flap (3B) of the first carcass ply (3) lies axially closer to a middle plane (M) of the tyre (1 ) than the respective second lateral edge (8B) and a ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.22; wherein said edge of the second end flap (4B) of the second carcass ply (4) lies axially closer to a middle plane (M) of the tyre (1 ) than the respective first lateral edge (8A) and a ratio of the second axial distance (D2) and the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.22.

13. Process according to claim 12, wherein the ratio of the first axial distance (D1 ) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.12; wherein the ratio of the second axial distance (D2) to the axial width (L2) of the reinforcing layer (8) is equal to or less than 0.12.

14. Process according to one of claims 10 to 13, wherein each of said first carcass ply (3) and second carcass ply (4) comprises a plurality of cords (13, 14), the cords (13, 14) of the first carcass ply (3) and the second carcass ply (4) being crossed with each other in the overlapping area.

15. Process according to claim 14, wherein, in the overlapping area and before shaping, the cords (13, 14) of each of the first carcass ply (3) and second carcass ply (4) delimit with a circumferential direction (X) of the building drum (15) a respective angle (α’, β’) between 50° and 82°.

16. Process according to one of claims 14 or 15, wherein the first carcass ply (3) has a first area comprising the first end flap (3A) and a second area comprising the second end flap (3B); wherein the cords (13) in the first area have a different orientation than the cords (13) in the second area; wherein, before shaping, the cords (13) in the first area delimit an angle (Ω) between 90° and 95° with the circumferential direction (X) of the building drum (15) and the cords (13) in the second area delimit said respective angle (α’, β’) with the circumferential direction (X) of the building drum (15); wherein the second carcass ply (4) has a first area comprising the first end flap (4A) and a second area comprising the second end flap (4B); wherein the cords (14) in the first area have a different orientation than the cords (14) in the second area; wherein, before shaping, the cords (14) in the first area delimit an angle (Ω) between 90° and 95° with the circumferential direction (X) of the building drum (15) and the cords (14) in the second area delimit said respective angle (α’, β’) with the circumferential direction (X) of the building drum (15).

17. Process according to one of claims 10 to 16, wherein, once the tread band (10) has been applied, the second end flap (3B) of the first carcass ply (3) and thesecond end flap (4B) of the second carcass ply (4) both lie below said tread band (10).

18. Process according to one of claims 10 to 17, wherein applying the reinforcing layer (8) comprises: winding an elongated continuous element (16) comprising said at least one reinforcing cord (9) around the shaped carcass structure (2).

19. Process according to one of claims 10 to 18, wherein said at least one reinforcing cord (9) is metallic or hybrid.

Images