WO2023242787A1 - Tyre for vehicle wheels - Google Patents

Abstract

A tyre for vehicle wheels comprises, in a central annular portion (A) of its tread band (110), a central circumferential groove (115) extending on axially opposite parts with respect to the equatorial plane (E) of the tyre, a circumferential row of first blocks (125) having a respective axially inner side (126) delimited by the central circumferential groove (115) and a respective axially outer side (127) delimited by a respective first circumferential groove (120) and a circumferential row of second blocks (155) having a respective axially inner side (156) delimited by the central circumferential groove (115) and a respective axially outer side (157) delimited by a respective second circumferential groove (160) arranged on the axially opposite part to the respective first circumferential groove (120) with respect to the central circumferential groove (115). The axially inner side (126; 156) of each of the first blocks (125) and second blocks (155) comprises, in the circumferential direction, respective opposite free ends (126a, 126b; 156a, 156b) and a respective central portion (126c; 156c). The first blocks (125) are circumferentially offset with respect to the second blocks (155) so that the opposite free ends (126a, 126b) of each of the first blocks (125) are arranged at the central portions (156c) of two circumferentially consecutive second blocks (155) and the opposite free ends (156a, 156b) of each of the second blocks (155) are arranged at the central portions (126c) of two circumferentially consecutive first blocks (125).

Description

Tyre for vehicle wheels

DESCRIPTION

The present invention relates to a tyre for vehicle wheels.

The tyre of the invention is preferably a tyre intended to be used on low-grip road surfaces, in particular on icy and possibly snow-covered road surfaces, for example as an alternative to studded tyres when and where their use is not permitted.

Preferably, the tyre of the invention is intended to be used in high and ultra-high performance vehicles, commonly defined as "HP" or "UHP" tyres. Such tyres are in particular those that allow speeds greater than 190 km/h, up to more than 300 km/h to be reached.

Examples of "HP" or "UHP" tyres are those having speed codes "T", "U", "H", "V", "Z","W", "Y", according to the E.T.R.T.O. standard (European Tyre and Rim Technical Organisation). Typically, such tyres have a width of radial section equal to or greater than 185 mm, preferably comprised between 195 mm and 385 mm, more preferably comprised between 195 mm and 355 mm, and are mounted on rims having fitting diameters equal to or greater than 13 inches, preferably not greater than 24 inches, more preferably comprised between 16 inches and 23 inches.

Throughout the present description and in the following claims, when reference is made to certain values of certain angles, these values are deemed to be absolute values, i.e. both positive values and negative values with respect to a reference plane or direction, unless specified otherwise.

Moreover, when reference is made to any range of values comprised between a minimum value and a maximum value, the aforementioned minimum and maximum values are deemed to be included in the aforementioned range, unless expressly stated to the contrary. Moreover, all of the ranges include any combination of the described minimum and maximum values and include any intermediate range, even if not specifically expressly described.

Even if not expressly indicated, any numerical value is deemed to be preceded by the term "about" to also indicate any numerical value that differs slightly from that described, for example to take into account the dimensional tolerances typical of the field of reference.

Hereinafter, the following definitions apply.

The term "equatorial plane" of the tyre is used to indicate a center plane perpendicular to the rotation axis of the tyre.

The terms "radial" and "axial" and the expressions "radially inner/outer" and "axially inner/outer" are used with reference to a direction substantially parallel to the equatorial plane of the tyre and to a direction substantially perpendicular to the equatorial plane of the tyre, respectively, i.e. to a direction substantially perpendicular to the rotation axis of the tyre and to a direction substantially parallel to the rotation axis of the tyre, respectively.

The expressions "axially outer" and "axially inner" indicate a position farther from, and closer to, the equatorial plane, respectively. Correspondingly, the expressions "axially outermost" and "axially innermost" indicate a position farthest from, and closest to, the equatorial plane with respect to a reference element, respectively. Thus, for example, a first portion of tread band is axially outermost with respect to a second portion of tread band if the axial distance of the first portion of tread band from the equatorial plane is greater than that of the second portion of tread band. Similarly, a first portion of tread band is axially innermost with respect to a second portion of tread band if the axial distance of the first portion of tread band from the equatorial plane is less than that of the second portion of tread band.

The term "parallel" is used to indicate not only a condition of perfect parallelism, but also a condition slightly diverging from that of perfect parallelism, for example by an angle not greater than 5°.

The term "perpendicular" is used to indicate not only a condition of perfect perpendicularity or orthogonality, but also a condition slightly diverging from that of perfectly perpendicularity or orthogonality, for example by an angle not greater than 5°.

The term "circumferential extension" of the tyre, or of the tread band or of portions thereof, is used to indicate the extension in plan of the radially outermost surface of the tyre, or of the tread band or of portions thereof, on a plane tangent to the tyre.

The term "radial section" of the tyre is used to indicate a section taken on a plane orthogonal to the equatorial plane and containing the rotation axis of the tyre.

The term "circumferential dimension" is used to indicate a dimension measured along a direction lying on, or parallel to, the equatorial plane.

The term "groove" is used to indicate a recess formed on the tread band and having a width greater than or equal to 2 mm. More preferably, the groove has a depth greater than, or equal to, 3 mm.

The term "circumferential groove" is used to indicate a groove that extends along one or more directions oriented, with respect to the equatorial plane, according to an angle not greater than 45°. In the case in which the circumferential groove is formed of various differently- oriented lengths, the term "circumferential length" is used to indicate a length of groove that extends along a direction oriented, with respect to the equatorial plane, according to an angle not greater than 45°.

The term "transversal groove", or "transversal length" of a groove, is used to indicate a groove, or a length of groove, which extends along a direction oriented, with respect to a plane orthogonal to the equatorial plane, according to an angle not greater than 45°.

The term "sipe" is used to indicate a hollow formed on the tread band and having a width less than 2 mm.

The term "width" of a groove or of a sipe is used to indicate a dimension measured at a point of the groove or of the sipe along a direction orthogonal to the direction along which the groove or the sipe extends at that point. For example, the width of a circumferential groove parallel to the equatorial plane is measured along a direction orthogonal to the circumferential direction, whereas the width of a transversal groove parallel to the rotation axis of the tyre is measured along a direction orthogonal to the axial direction.

The term "block" is used to indicate a portion of tread band delimited by grooves and not by sipes. In the case in which the block is positioned on the axially outermost portion of the tread band, it is delimited in the axial direction on one part by the axially outermost side of the tread band and, on the other part, by a groove.

The term "free end" of a block or of a side of the block along a predetermined direction is used to indicate a point of the block or of the side of the block taken along that direction and arranged at an area of the tread band in which two grooves delimiting the block intersect.

The term "substantially concave profile" of a side of a block with respect to the equatorial plane is used to indicate the profile of a side that, along a circumferential direction, has opposite free ends and a central portion, wherein at least one of the opposite free ends is proximal to the equatorial plane and the central portion is distal from the equatorial plane.

The equatorial plane is deemed "entirely contained" in a central circumferential groove (or the central circumferential groove is deemed to "entirely contain" the equatorial plane) when the equatorial plane is arranged with respect to the blocks proximal to it so that none of such blocks has block portions that extend both from one side of the equatorial plane and from the other side of the equatorial plane or, in other words, when none of the aforementioned blocks crosses the equatorial plane from one side to the other side.

The "depth" of the tread band, or of the grooves, or of the sipes, is measured at a groove or sipe along a direction substantially perpendicular to the bottom of the groove or of the sipe.

The term "tread pattern" is used to indicate the whole of blocks and grooves provided on the tread band.

The term "void to solid ratio" is used to indicate the ratio between the overall surface of the grooves, excluding the sipes, of a certain annular portion of the tread band of the tyre (possibly of the entire tread band) and the surface of said certain portion of tread band (possibly of the entire tread band).

The term "footprint" of the tyre is used to indicate the portion of tyre that is in contact with the ground or road surface when the tyre is mounted on a rim of a wheel and a predetermined vertical load is exerted on the tyre. In the case in which grooves are provided on the tread band of the tyre, the footprint also includes such grooves.

The term "pitch" referred to the tread band is used to indicate a portion of tread band that is repeated substantially equal to itself many times along the entire circumferential extension of the tyre. Pitches having different circumferential dimensions can be provided in a tyre.

The term "axial extension" of a zig-zag trajectory is used to indicate the width in the axial direction of the portion of tread band including such a trajectory.

The expression "mirroring shape" referred to two blocks is used to indicate that the two blocks have substantially identical shape but mutual arrangement such that a first block of said two blocks can be substantially overlapped to the other block only after a rotation of 180° of the first block with respect to its barycentric axis. If the two blocks are circumferentially offset with respect to each other, the two blocks can substantially be overlapped to each other after a relative displacement in the circumferential direction by an amount such as to eliminate such offsetting.

Tyres for icy and/or snow-covered road surfaces are described for example in JP 2019137090A, JP 2020100191A, US 20200298627A1, WO 201901789A1, WO 201901790A1, JP 2020199841A, US 5591280A, JP 2017088021A, EP 3421264B1. Such tyres have a tread band comprising a plurality of circumferential and transversal grooves that define in the tread band a plurality of blocks provided with sipes.

The Applicant has focused its attention on tyres intended to equip high and ultra-high performance vehicles and to be used on road surfaces that are in low-grip conditions due to the presence of ice and possibly snow.

Such a type of tyre requires a high ability to adhere to the icy and possibly snow-covered road surface, so as to be able to effectively discharge to the ground the high drive torque to which they are subjected and, therefore, to achieve an effective traction and braking.

The Applicant has observed that in order to allow the aforementioned tyres to offer the desired grip to the icy/snow-covered road surface it is advisable both to provide a footprint in which the mutual contact surface between tread band and road surface is sufficiently large, so as to increase the surface at which an effective transfer of the drive torque to the ground occurs during travel, and to distribute the contact pressures as evenly as possible inside the footprint, so as to tend towards the optimal travel condition, in which the same contact pressure acts in all of the areas in which the tread band is in contact with the road surface. For this reason, the tread band of the aforementioned tyres typically has a plurality of blocks delimited by circumferential and transversal grooves.

The Applicant has thought how to enlarge the mutual contact surface between road surface and tread band at the central annular portion of the latter and thus tend towards the desired even distribution of contact pressures in the footprint of the tyre.

The Applicant has thought that in order to achieve this objective it is necessary to reduce the void to solid ratio at least at the central annular portion of the tread band.

With particular reference to tyres provided with a central circumferential groove arranged at the equatorial plane and with rows of blocks arranged on opposite parts with respect to the equatorial plane, the Applicant has thought that such a reduction of the void to solid ratio can be achieved by reducing the size of the voids inevitably provided between one row of first blocks arranged on one part of the equatorial plane and a row of second blocks arranged on the opposite part of the equatorial plane.

The Applicant has realised that it is possible to reduce the size of the aforementioned voids by providing the axially inner sides of the aforementioned first and second blocks with a substantially concave profile with respect to the equatorial plane along the circumferential direction and by circumferentially offsetting the aforementioned first blocks with respect to the aforementioned second blocks so that the opposite free ends of the axially inner sides of each of said first blocks are arranged at the central portions of the axially inner sides of two circumferentially consecutive second blocks and the opposite free ends of the axially inner sides of each of said second blocks are arranged at the central portions of the axially inner sides of two circumferentially consecutive first blocks.

The Applicant has thus found that the provision in the central annular portion of the tread band of at least two circumferential rows of blocks arranged on axially opposite parts with respect to the equatorial plane and each having :

- an axially inner side having a central portion distal from the equatorial plane and opposite free ends, at least one of which is proximal to the equatorial plane, such an axially inner side being delimited by a central circumferential groove that extends on axially opposite parts with respect to the equatorial plane,

- an axially outer side delimited by a respective circumferential groove, and

- opposite sides in the circumferential direction delimited by respective transversal grooves that extend from a portion of said tread band arranged at the central circumferential groove up to close to the sidewalls, and the offset arrangement of such two rows of blocks in the circumferential direction so that the opposite free ends of the blocks of one row are arranged at the central portions of two circumferentially consecutive blocks of the other row and vice-versa, makes it possible to reduce the size of the aforementioned voids which are close to the equatorial plane and, consequently, to increase the surface with blocks at the central annular portion of the tread band. This provides such a central annular portion with the ability to deform sufficiently, during travel, both in the axial direction and in the circumferential direction at the footprint of the tyre, maintaining a large mutual contact area between road surface and tread band in the central area, to the benefit of the grip on icy and possibly snow-covered road surfaces.

The present invention relates to a tyre for vehicle wheels comprising a tread band extending between opposite sidewalls.

Preferably, the tread band comprises a central annular portion and opposite shoulder annular portions.

Preferably, each shoulder annular portion is adjacent to a respective sidewall of said opposite sidewalls.

Preferably, said central annular portion comprises a central circumferential groove.

Preferably, said central circumferential groove extends on axially opposite parts with respect to an equatorial plane.

Preferably, said central annular portion comprises a circumferential row of first blocks.

Preferably, said first blocks have a respective axially inner side delimited by said central circumferential groove.

Preferably, said first blocks have a respective axially outer side delimited by a respective first circumferential groove.

Preferably, each of said first blocks is delimited in a circumferential direction by respective lengths of opposite first transversal grooves.

Preferably, said first transversal grooves extend from a portion of said tread band arranged at said central circumferential groove up to a first shoulder annular portion.

Preferably, said first transversal grooves extend up to an axially outer end of said first shoulder annular portion.

Preferably, said central annular portion comprises a circumferential row of second blocks.

Preferably, said second blocks have a respective axially inner side delimited by said central circumferential groove.

Preferably, said second blocks have a respective axially outer side delimited by a respective second circumferential groove arranged on an axially opposite part to said first circumferential groove with respect to the central circumferential groove.

Preferably, each of said second blocks is delimited in a circumferential direction by respective lengths of opposite second transversal grooves.

Preferably, said second transversal grooves extend from a portion of said tread band arranged at said central circumferential groove up to a second shoulder annular portion arranged on the axially opposite side to said first shoulder annular portion with respect to the central circumferential groove.

Preferably, said first transversal grooves extend up to an axially outer end of said second shoulder annular portion.

Preferably, the axially inner side of each of said first blocks comprises, in the circumferential direction, respective opposite free ends, at least one of which being proximal to the equatorial plane.

Preferably, the axially inner side of each of said second blocks comprises, in the circumferential direction, respective opposite free ends, at least one of which being proximal to the equatorial plane.

Preferably, the axially inner side of each of said first blocks comprises, in the circumferential direction, a respective central portion distal from the equatorial plane.

Preferably, the axially inner side of each of said second blocks comprises, in the circumferential direction, a respective central portion distal from the equatorial plane.

Preferably, said first blocks are circumferentially offset with respect to said second blocks.

Preferably, said offsetting is such that the opposite free ends of each of said first blocks are arranged at the central portions of two second circumferentially consecutive blocks.

Preferably, said offsetting is such that the opposite free ends of each of said second blocks are arranged at the central portions of two first circumferentially consecutive blocks.

The Applicant believes that a tread band made in accordance with what has been described above has a central annular portion capable of deforming sufficiently both in the axial direction and in the circumferential direction at the footprint during travel of the tyre. This makes it possible to achieve the desired increase of the contact surface with the road surface at the footprint and the desired even distribution of contact pressures inside the footprint, providing the tyre with a high ability to adhere on low-grip road surfaces.

The present invention can have at least one of the preferred characteristics described hereinafter.

Preferably, the other of the opposite free ends of the axially inner side of each of said first blocks is distal from the equatorial plane.

Preferably, the other of the opposite free ends of the axially inner side of each of said second blocks is distal from the equatorial plane.

In this way, the width of the central circumferential groove varies progressively in the circumferential direction going from a free end of the axially inner side of a first block towards the central portion of the aforementioned side of the first block (and thus progressively going from the central portion of the axially inner side of a second block towards a free end of the aforementioned side of the second block) and from the central portion of the axially inner side of the first block towards the other free end of the aforementioned side of the first block (and thus from a free end of the axially inner side of a further block which is circumferentially consecutive to the previous second block towards the central portion of the axially inner side of such a further second block). Such a change in width actually causes a reduction of the void to solid ratio at the equatorial plane of the tyre and, consequently, an increase in the mutual contact surface between road surface and tread band at the central annular portion of the latter, to the benefit of the behavior of the tyre on low-grip road surfaces.

In different embodiments, the other of the opposite free ends of the axially inner side of each of said first blocks is proximal to the equatorial plane.

In different embodiments, the other of the opposite free ends of the axially inner side of each of said second blocks is proximal to the equatorial plane. Preferably, said first blocks have a substantially quadrangular shape.

Preferably, said second blocks have a substantially quadrangular shape.

Preferably, said first blocks have a shape mirroring that of said second blocks.

Thanks to the aforementioned provisions the first and second blocks provide the tread band with the ability to deform substantially uniformly along two orthogonal directions, to the benefit of the grip on icy and possibly snow-covered road surfaces. An advantageous distribution of the blocks in the circumferential and transversal direction is also obtained, with consequent benefits also with respect to the noise caused by the rolling of the tyre.

Preferably, each transversal groove extends from the equatorial plane up to a respective sidewall of the tyre. In this way, the evacuation of water from the footprint is facilitated when the tyre travels on wet road surfaces.

More preferably, each transversal groove has, at said central annular portion, a first inclination with respect to a direction orthogonal to the equatorial plane and, at the opposite shoulder annular portions, an inclination that is lesser than said first inclination and that progressively decreases getting closer to the respective sidewall.

Preferably, close to the equatorial plane each transversal groove is inclined with respect to a direction orthogonal to the equatorial plane by an angle greater than 20°.

Preferably, such an angle is less than 45°.

In preferred embodiments, the aforementioned angle is comprised between 20° and 45°, for example equal to 37°.

Preferably, close to the respective sidewall each transversal groove is substantially perpendicular to the equatorial plane.

Preferably, said central circumferential groove extends along a first zig-zag trajectory.

Preferably, said first zig-zag trajectory is defined by a plurality of first circumferential lengths inclined on one part with respect to the equatorial plane and by a plurality of second circumferential lengths inclined with respect to said first circumferential lengths, more preferably substantially parallel to the equatorial plane.

Preferably, each of said second circumferential lengths connects two consecutive first circumferential lengths.

The zig-zag shape of the central circumferential groove increases the ability of the tread band to deform along different directions.

Preferably, said central circumferential groove has, along said first circumferential lengths, a non-constant width.

Preferably, said central circumferential groove has, along said second circumferential lengths, a non-constant width.

Such a change in width is obtained by providing end portions of the aforementioned first and second blocks proximal to the equatorial plane and central portions of the aforementioned first and second blocks distal from the equatorial plane, as described above.

Preferably, said first circumferential lengths have a circumferential dimension substantially equal to that of said second circumferential lengths.

Preferably, said first circumferential lengths are substantially parallel to each other.

Preferably, said second circumferential lengths are substantially parallel to each other.

Preferably, said first circumferential lengths delimit both a first portion of the axially inner side of respective first blocks and a first portion of the axially inner side of respective second blocks.

Preferably, said second circumferential lengths delimit both the remaining portion of the axially inner side of said first blocks and the remaining portion of the axially inner side of said second blocks.

Preferably, said first portion of the axially inner side of said first blocks extends from one of the opposite free ends of the respective first block up to the central portion of the respective first block.

Preferably, said remaining portion of the axially inner side of said first blocks extends from the other of the opposite free ends of the respective first block up to the central portion of the respective first block.

Preferably, said first portion of the axially inner side of said second blocks extends from one of the opposite free ends of the respective second block up to the central portion of the respective second block.

Preferably, said remaining portion of the axially inner side of said second blocks extends from the other of the opposite free ends of the respective second block up to the central portion of the respective second block.

Preferably, said first portion of the axially inner side of said first block is substantially parallel to the equatorial plane.

Preferably, said remaining portion of the axially inner side of said first block is inclined with respect to the equatorial plane by a first angle greater than 5°.

Preferably, said remaining portion of the axially inner side of said first block is inclined with respect to the equatorial plane by a first angle less than 15°.

In preferred embodiments, said first angle is comprised between 5° and 15°.

Preferably, said remaining portion of the axially inner side of said second block is substantially parallel to the equatorial plane.

Preferably, said first portion of the axially inner side of said second block is inclined with respect to the equatorial plane by a second angle greater than 5°.

Preferably, said first portion of the axially inner side of said second block is inclined with respect to the equatorial plane by a second angle less than 15°.

In preferred embodiments, said second angle is comprised between 5° and 15°.

In particularly preferred embodiments, said second angle is substantially equal to said first angle.

Preferably, each of said first transversal grooves comprises a respective first transversal length arranged between two respective first circumferential grooves.

Preferably, the first circumferential grooves and the first transversal lengths follow each other in an alternating manner along a second zigzag trajectory.

Preferably, said second zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

Preferably, said first circumferential grooves are substantially parallel to each other.

Preferably, said first transversal lengths are substantially parallel to each other.

Preferably, said first circumferential grooves are inclined with respect to the equatorial plane on the same part as the first circumferential grooves.

Preferably, each first block of said circumferential row of first blocks comprises a respective axially outer side delimited only by a respective first circumferential groove.

Preferably, said axially outer side is inclined with respect to the equatorial plane by a third angle greater than 5°.

Preferably, said axially outer side is inclined with respect to the equatorial plane by a third angle less than 25°.

In preferred embodiments, said third angle is comprised between 5° and 25°. Preferably, said first transversal lengths are inclined with respect to the equatorial plane by a fourth angle greater than 20°.

Preferably, said first transversal lengths are inclined with respect to the equatorial plane by a fourth angle less than 45°.

In preferred embodiments, said fourth angle is comprised between 20° and 45°.

Preferably, each of said second transversal grooves comprises a respective second transversal length arranged between two respective second circumferential grooves.

Preferably, the second circumferential grooves and the second transversal lengths follow each other in an alternating manner along a third zig-zag trajectory.

Preferably, said third zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

Preferably, said third zig-zag trajectory has an axial extension substantially equal to that of said second zig-zag trajectory.

Preferably, said second circumferential grooves are substantially parallel to each other.

Preferably, said second transversal lengths are substantially parallel to each other.

Preferably, said second circumferential grooves are inclined with respect to the equatorial plane on the opposite part with respect to said first circumferential grooves.

Preferably, said second transversal lengths are inclined with respect to the equatorial plane on the opposite part with respect to said first transversal lengths.

Preferably, each second block of said circumferential row of second blocks comprises a respective axially outer side delimited only by a respective second circumferential groove.

Preferably, said axially outer side is inclined with respect to the equatorial plane by a fifth angle greater than 5°.

Preferably, said axially outer side is inclined with respect to the equatorial plane by a fifth angle less than 15°.

In preferred embodiments, said fifth angle is comprised between 5° and 15°.

In particularly preferred embodiments, said fifth angle is substantially equal to said third angle.

Preferably, said second transversal lengths are inclined with respect to the equatorial plane by a sixth angle greater than 20°.

Preferably, said second transversal lengths are inclined with respect to the equatorial plane by a sixth angle less than 45°.

In preferred embodiments, said sixth angle is comprised between 20° and 45°.

In particularly preferred embodiments, said sixth angle is substantially equal to said fourth angle.

Preferably, the axially outer side of each of said second blocks is inclined with respect to the equatorial plane on the opposite part with respect to the axially outer side of each of said first blocks.

Preferably, said central annular portion comprises a circumferential row of third blocks arranged between said first circumferential grooves and third circumferential grooves arranged in an axially outer position with respect to said first circumferential grooves.

Preferably, said central annular portion comprises a circumferential row of fourth blocks arranged between said second circumferential grooves and fourth circumferential grooves arranged in an axially outer position with respect to said second circumferential grooves.

The provision of blocks also at the axially outermost annular portions of the central annular portion of the tread band provides said central annular portion with a distribution of blocks in the circumferential and transversal direction, with consequent benefits not only in terms of uniformity and constancy of performance during travel on icy and possibly snow-covered surfaces, but also with respect to the noise caused by the rolling of the tyre.

Preferably, said third blocks are circumferentially offset with respect to said first blocks.

Preferably, said third blocks are substantially axially aligned with said second blocks.

Preferably, said fourth blocks are circumferentially offset with respect to said second blocks.

Preferably, said fourth blocks are substantially axially aligned with said first blocks.

Preferably, said third blocks have a substantially quadrangular shape.

Preferably, said fourth blocks have a substantially quadrangular shape.

Preferably, said third blocks have a shape mirroring that of said fourth blocks.

Preferably, each of said first transversal grooves comprises a respective third transversal length arranged between two respective third circumferential grooves.

Preferably, the third circumferential grooves and the third transversal lengths follow each other in an alternating manner along a fourth zig-zag trajectory.

Preferably, said fourth zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

Preferably, said fourth zig-zag trajectory has an axial extension substantially equal to that of said second zig-zag trajectory.

Preferably, each third block of said circumferential row of third blocks comprises a respective axially inner side delimited only by a respective first circumferential groove. Preferably, said third circumferential grooves are substantially parallel to each other.

Preferably, said third circumferential grooves are substantially parallel to said first circumferential grooves.

Preferably, said third transversal lengths are substantially parallel to each other.

Preferably, said third transversal lengths are inclined with respect to the equatorial plane by said fourth angle.

Preferably, each third block of said circumferential row of third blocks comprises a respective axially outer side delimited only by a respective third circumferential groove.

Preferably, the axially outer side of each of said third blocks is substantially parallel to the axially outer side of each of said first blocks.

Preferably, each of said second transversal grooves comprises a respective fourth transversal length arranged between two respective fourth circumferential grooves.

Preferably, the fourth circumferential grooves and the fourth transversal lengths follow each other in an alternating manner along a fifth zig-zag trajectory.

Preferably, said fifth zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

Preferably, said fifth zig-zag trajectory has an axial extension substantially equal to that of said third zig-zag trajectory.

Preferably, each fourth block of said circumferential row of fourth blocks comprises a respective axially inner side delimited only by a respective second circumferential groove.

Preferably, said fourth circumferential grooves are substantially parallel to each other.

Preferably, said fourth circumferential grooves are substantially parallel to said second circumferential grooves. Preferably, said fourth transversal lengths are substantially parallel to each other.

Preferably, said fourth transversal lengths are inclined with respect to the equatorial plane by said sixth angle.

Preferably, each fourth block of said circumferential row of fourth blocks comprises a respective axially outer side delimited only by a respective fourth circumferential groove.

Preferably, the axially outer side of each of said fourth blocks is substantially parallel to the axially outer side of each of said second blocks.

Preferably, each of said shoulder annular portions comprises a plurality of respective blocks.

Preferably, the equatorial plane of the tyre is entirely contained in the central circumferential groove.

According to the Applicant, such a provision increases the deformability of the first and second blocks in the circumferential direction. Indeed, in this way possible interference between the first blocks and the second blocks at the respective axially inner sides is avoided when such blocks deform in the circumferential direction. Such interference would obstruct the free deformation of the blocks in the circumferential direction.

Preferably, the tread band has a void to solid ratio less than, or equal to, 0.30. The Applicant has found that such a provision makes it possible to maximize the contact area between tread band and road surface at the footprint, to the benefit of the grip on icy road surfaces.

Preferably, said void to solid ratio is greater than, or equal to, 0.24.

Preferably, said void to solid ratio is comprised between 0.24 and 0.30.

Preferably, the tread band has a tread pattern comprising a number of pitches greater than, or equal to, 54, more preferably greater than, or equal to, 56. The Applicant has found that such a provision makes it possible to improve traction and braking on snow-covered road surfaces.

Preferably, the tread band has a tread pattern comprising a plurality of first pitches having a first circumferential dimension.

Preferably, the tread pattern comprises a plurality of second pitches having a second circumferential dimension different from the first circumferential dimension.

Preferably, the tread pattern comprises a plurality of third pitches having a third circumferential dimension different from said first circumferential dimension.

Preferably, said third circumferential dimension is different from said second circumferential dimension.

According to the Applicant, the provision of at least two types of pitches of different dimensions produces beneficial effects with respect to noise from rolling. By providing three types of pitches of different dimensions such beneficial effects are even greater. Indeed, in this way it is possible to properly alternate the various pitches along the circumferential extension of the tyre (for example through suitable frequency optimization software) and increase the difference in dimension between a shorter pitch and a longer pitch, in order to avoid generating undesirable frequency repetitions that would result in an increase in noise from rolling.

Preferably, at least some of said first blocks, more preferably all of said first blocks, comprise a plurality of respective sipes.

This is in order to also achieve an excellent behavior on snow, particularly with reference to traction and braking.

Moreover, the provision of sipes in the blocks in combination with the provision of a tread pattern having at least two pitches of different dimension allows a better distribution of the sipes on the tread band in the circumferential direction, further improving the behavior on snow. Preferably, at least some of said second blocks, more preferably all of said second blocks, comprise a plurality of respective sipes.

Preferably, the sipes of the first blocks are identical to the sipes of the second blocks.

Preferably, said sipes extend along non-rectilinear trajectories on a radially outer surface of the respective first blocks.

Preferably, said sipes extend along non-rectilinear trajectories on a radially outer surface of the respective second blocks.

Preferably, said sipes extend along a non-planar surface in the radial direction.

Therefore, the sipes have a substantially three-dimensional shape. Such a shape ensures that an interlocking is created between the two portions of block separated by a first sipe, avoiding an excessive deformation of the block.

Preferably, at least some of said third blocks and/or fourth blocks, more preferably all of said third blocks and/or fourth blocks, comprise a plurality of sipes.

Preferably, at least some of said first blocks, more preferably all of said first blocks, comprise a first tapered portion at said central circumferential groove.

Preferably, at least some of said first blocks, more preferably all of said first blocks, comprise a second tapered portion at an adjacent transversal groove.

The Applicant has verified that the provision of the aforementioned tapered portions in a first block allows gripping on the snow-covered road surface of the edges of the circumferentially adjacent block and of the axially adjacent block that would otherwise be "hidden" by the aforementioned first block, thus increasing the gripping effect on the snow both in the circumferential direction and in the transversal direction without, at the same time, weakening the first block. Preferably, at least some of said second blocks, more preferably all of said second blocks, comprise a first tapered portion at said central circumferential groove.

Preferably, at least some of said second blocks, more preferably all of said second blocks, comprise a second tapered portion at an adjacent transversal groove.

Preferably, said first tapered portions are in a block portion having a dimension greater than that where said second tapered portions are.

Preferably, at least some of said third blocks, more preferably all of said third blocks, comprise at least one first tapered portion at said first circumferential groove.

Preferably, at least some of said fourth blocks, more preferably all of said fourth blocks, comprise at least one first tapered portion at said second circumferential groove.

Preferably, at least some of said third blocks, more preferably all of said third blocks, comprise at least one second tapered portion at an adjacent transversal groove.

Preferably, at least some of said fourth blocks, more preferably all of said fourth blocks, comprise at least one second tapered portion at an adjacent transversal groove.

Preferably, the tread band has, close to said opposite shoulder annular portions, a depth that is less than that at said central annular portion. Such a provision contributes to keep the noise from rolling down.

Further characteristics and advantages of the present invention will be more evident from the following description of preferred embodiments thereof made with reference to the appended drawings. In such drawings:

- figure 1 is a schematic perspective view of a tyre in accordance with the present invention;

- figure 2 is a view of an enlarged portion of the tyre of figure 1; - figures 3a and 3b are enlarged views of a portion of the central part of a central annular portion of the tread band of the tyre of figure 1;

- figures 4a and 4b are enlarged view of portions of the opposite lateral parts of the central annular portion of the tread band of the tyre of figure 1;

- figure 5 is a further view of an enlarged portion of the tread band of the tyre of figure 1;

- figure 6 schematically shows the footprint of the tyre of figure 1.

In figure 1, a tyre in accordance with the present invention is indicated with 100. The tyre 100 is, in particular, an HP or UHP tyre for sports and/or high or ultra-high performance vehicles and is intended to be used on low-grip road surfaces, in particular on icy and possibly snow- covered road surfaces.

The tyre 1 comprises a carcass structure 103, a belt structure (not visible) arranged in a radially outer position with respect to the carcass structure 103 and a tread band 110 made of elastomeric material and arranged in a radially outer position with respect to the belt structure.

The tread band 110 extends between opposite sidewalls 105 (only one of which is visible in figure 1) also made of elastomeric material.

Each sidewall 105 is applied on a respective lateral surface of the carcass structure 103, in an axially outer position with respect to the carcass structure 103 itself, and extends from such a lateral surface up to the tread band 110.

As shown in figure 2, the tread band 110 comprises a central annular portion A that extends from axially opposite parts with respect to an equatorial plane E of the tyre 100 and two shoulder annular portions SI, S2 arranged on axially opposite parts with respect to the axially central annular portion A.

Each shoulder annular portion SI, S2 is adjacent to a respective sidewall 105. The depth of the tread band 110 at the central annular portion A is greater than that at the shoulder annular portions SI, S2. Such a depth preferably progressively decreases going from the central annular portion A towards the opposite shoulder annular portions SI, S2.

In a preferred embodiment, the depth of the tread band 110 is equal to 8.5 mm at the central annular portion A and equal to 7.5 mm at the shoulder annular portions SI, S2.

With reference to figure 2, the central annular portion A comprises a central circumferential groove 115 that extends on axially opposite parts with respect to the equatorial plane E, a plurality of first circumferential grooves 120 arranged on one part with respect to the central circumferential groove 115 and a plurality of second circumferential grooves 160 arranged on an axially opposite part to the plurality of first circumferential grooves 120 with respect to the central circumferential groove 115.

The central annular portion A further comprises a plurality of third circumferential grooves 140 arranged in an axially outer position with respect to the plurality of first circumferential grooves 120 and a plurality of fourth circumferential grooves 180 arranged in an axially outer position with respect to the plurality of second circumferential grooves 160.

The first circumferential grooves 120 are substantially parallel to each other.

The second circumferential grooves 160 are substantially parallel to each other and inclined on the opposite part to the first circumferential grooves 120 with respect to the equatorial plane E.

The third circumferential grooves 140 are substantially parallel to each other and inclined with respect to the equatorial plane E on the same part as the first circumferential grooves 120. Preferably, the third circumferential grooves 140 are substantially parallel to the first circumferential grooves 120. The fourth circumferential grooves 180 are substantially parallel to each other and inclined on the opposite part to the first circumferential grooves 120 with respect to the equatorial plane E. Preferably, the fourth circumferential grooves 180 are substantially parallel to the second circumferential grooves 160.

The angle of inclination of the first circumferential grooves 120 with respect to the equatorial plane E is preferably comprised between 5° and 25°, for example equal to 15°.

In an embodiment, the equatorial plane E is entirely contained in the central circumferential groove 115.

The tread band 110 comprises a plurality of first transversal grooves 210 that extend on one side with respect to the equatorial plane E (to the left of the equatorial plane E in figure 2) from an axially central portion of the tread band 110 which is close to the central circumferential groove 115 up to an axially outer end of the shoulder annular portion SI.

The first transversal grooves 210 are substantially parallel to each other.

The tread band 110 further comprises a plurality of second transversal grooves 220 that extend on the other side with respect to the equatorial plane E (to the right of the equatorial plane E in figure 2) from an axially central portion of the tread band 110 which is close to the central circumferential groove 115 up to an axially outer end of the shoulder annular portion S2.

The second transversal grooves 220 are substantially parallel to each other.

In the embodiment shown in the attached figures, each first transversal groove 210 extends, on one side of the equatorial plane E, from the central circumferential groove 115 up to the respective sidewall 105 and each second transversal groove 220 extends, on the other side of the equatorial plane E, from the central circumferential groove 115 up to the opposite sidewall 105.

The transversal grooves 210 are circumferentially offset with respect to the transversal grooves 220.

The first transversal grooves 210 are connected to the first circumferential grooves 120 and to the third circumferential grooves 140.

The second transversal grooves 220 are connected to the second circumferential grooves 160 and to the fourth circumferential grooves 180.

At the central annular portion A each transversal groove 210, 220 is inclined with respect to a direction orthogonal to the equatorial plane E by an angle comprised between 20° and 45°, for example equal to 37°.

Such an angle of inclination decreases at the respective shoulder annular portions SI, S2 to then become substantially equal to zero progressively going towards the respective sidewall 105, so that, close to the respective sidewall 105, each transversal groove 210, 220 is substantially perpendicular to the equatorial plane E.

The aforementioned grooves 115, 120, 140, 160, 180, 210, 220 delimit a plurality of blocks, as described hereinafter.

The central circumferential groove 115 and the first circumferential grooves 120 delimit on axially opposite parts a circumferential row of first blocks 125 having a substantially quadrangular shape. Such first blocks 125 are delimited on circumferentially opposite parts by respective lengths of two circumferentially consecutive transversal grooves 210.

The central circumferential groove 115 and the second circumferential grooves 160 delimit on axially opposite parts a circumferential row of second blocks 155 having a substantially quadrangular shape and mirroring the shape of the first blocks 125. The second blocks 155 are delimited on circumferentially opposite parts by respective lengths of two circumferentially consecutive transversal grooves 220. The second blocks 155 are circumferentially offset with respect to the first blocks 125.

The first circumferential grooves 120 and the third circumferential grooves 140 delimit on axially opposite parts a circumferential row of third blocks 135 having a substantially quadrangular shape. Such third blocks 135 are delimited on circumferentially opposite parts by respective lengths of the two aforementioned circumferentially consecutive transversal grooves 210.

In the embodiment shown in the attached drawings, the third blocks 135 are offset in the circumferential direction with respect to the first blocks 125 and substantially aligned in the axial direction with the second blocks 155.

The second circumferential grooves 160 and the fourth circumferential grooves 180 delimit on axially opposite parts a circumferential row of fourth blocks 175 having a substantially quadrangular shape and substantially mirroring the shape of the third blocks 135. The fourth blocks 175 are delimited on circumferentially opposite parts by respective lengths of the aforementioned two circumferentially consecutive transversal grooves 220.

The fourth blocks 175 are circumferentially offset with respect to the third blocks 135.

In the embodiment shown in the attached drawings, the fourth blocks 175 are offset in the circumferential direction with respect to the second blocks 155 and substantially aligned in the axial direction with the first blocks 125.

Further blocks 190, 195 are provided at the shoulder annular portions SI, S2, as described hereinafter.

A row of further blocks 190 is delimited on axially opposite parts by the third circumferential grooves 140 and by one of the two sidewalls 105. Such further blocks 190 are delimited on circumferentially opposite parts by respective lengths of two circumferentially consecutive transversal grooves 210.

A row of further blocks 195 is delimited on axially opposite parts by the fourth circumferential grooves 180 and by the other of the two sidewalls 105. Such further blocks 195 have a shape substantially mirroring that of the blocks 190 and are delimited on circumferentially opposite parts by respective lengths of two circumferentially consecutive transversal grooves 220.

The blocks 195 are circumferentially offset with respect to the blocks 190.

With reference to figures 3a and 3b, each of the first blocks 125 comprises a respective axially inner side 126 delimited by the central circumferential groove 115 and a respective axially outer side 127 delimited by a first circumferential groove 120.

Similarly, each of the second blocks 155 comprises a respective axially inner side 156 delimited by the central circumferential groove 115 and a respective axially outer side 157 delimited by a second circumferential groove 160.

The axially inner side 126 of the blocks 125 comprises, in the circumferential direction, a free end 126a proximal to the equatorial plane E, an opposite free end 126b distal from the equatorial plane E and a central portion 126c distal from the equatorial plane E.

Similarly, the axially inner side 156 of the blocks 155 comprises, in the circumferential direction, a free end 156a proximal to the equatorial plane E, an opposite free end 156b distal from the equatorial plane E and a central portion 156c distal from the equatorial plane E.

The circumferential offsetting of the first blocks 125 with respect to the second blocks 155 is such that the opposite free ends 126a, 126b of each of the first blocks 125 are arranged at the central portions 156c of two circumferentially consecutive second blocks 155 and the opposite free ends 156a, 156b of each of the second blocks 155 are arranged at the central portions 126c of two circumferentially consecutive first blocks 125.

With reference to figure 4a, each of the third blocks 135 comprises a respective axially inner side 136 delimited by a first circumferential groove 120 and a respective axially outer side 137 delimited by a third circumferential groove 140. The latter also delimits the axially inner side 191 of the further blocks 190.

Similarly, with reference to figure 4b, each of the fourth blocks 175 comprises a respective axially inner side 176 delimited by a second circumferential groove 160 and a respective axially outer side 177 delimited by a fourth circumferential groove 180. The latter also delimits the axially inner side 196 of the further blocks 195.

In the embodiment shown in the drawings, the axially outer sides 127 of the first blocks 125 and the axially inner sides 136 of the third blocks are substantially parallel and inclined with respect to the equatorial plane E by an angle of inclination equal to that of the first circumferential grooves 120 (figure 3b). Preferably, each circumferential groove 120 delimits the entire axially outer side 127 of a respective first block 125 and the entire axially inner side 136 of a respective third block 135.

In the embodiment shown in the drawings, the axially outer sides 157 of the second blocks 155 and the axially inner sides 176 of the fourth blocks 175 are substantially parallel and inclined with respect to the equatorial plane E by an angle of inclination equal to that of the second circumferential grooves 160 (figure 3b). Preferably, each circumferential groove 160 delimits the entire axially outer side 157 of a respective second block 155 and the entire axially inner side 176 of a respective fourth block 175.

In the embodiment shown in the drawings, the axially outer sides 137 of the third blocks 135 and the axially inner sides 191 of the blocks 190 are substantially parallel and inclined with respect to the equatorial plane E by an angle of inclination equal to that of the third circumferential grooves 140 (figure 4a). Preferably, each circumferential groove 140 delimits the entire axially outer side 137 of a respective third block 135 and the entire axially inner side 191 of a respective block 190.

In the embodiment shown in the drawings, the axially outer sides 177 of the fourth blocks 175 and the axially inner sides 196 of the blocks 195 are substantially parallel and inclined with respect to the equatorial plane E by an angle of inclination equal to that of the fourth circumferential grooves 180 (figure 4b). Preferably, each circumferential groove 180 delimits the entire axially outer side 177 of a respective fourth block 175 and the entire axially inner side 196 of a respective block 195.

The axially outer side of the blocks 190 and 195 is, on the other hand, delimited by the respective sidewalls 105.

With reference to figures 3a and 3b, the central circumferential groove 115 extends along a first zig-zag trajectory defined by a plurality of first circumferential lengths 115a substantially parallel to each other and inclined on one part with respect to the equatorial plane E and by a plurality of second circumferential lengths 115b substantially parallel to each other and inclined with respect to the first circumferential lengths 115a, in particular substantially parallel to the equatorial plane E. Each of the second circumferential lengths 115b connects two consecutive first circumferential lengths 115a and vice-versa.

The first circumferential lengths 115a are inclined with respect to the equatorial plane E on the same part as the first circumferential grooves 120.

The second circumferential lengths 115b are inclined with respect to the equatorial plane E on the same part as the second circumferential grooves 160.

The angle of inclination of the first circumferential lengths 115a with respect to the equatorial plane E is preferably less than that of the first circumferential grooves 120, more preferably comprised between 5° and 15°, for example equal to 9°.

The angle of inclination of the second circumferential lengths 115b with respect to the equatorial plane E is preferably less than that of the second circumferential grooves 160, more preferably comprised between 5° and 15°, for example equal to 9°.

The first circumferential lengths 115a delimit both the portions of the axially inner sides 126 of the first blocks 125 that extend from the respective free ends 126a up to the respective central portions 126c of the first blocks 125, and the portions of the axially inner sides 156 of the second blocks 155 that extend from the respective free ends 156b up to the respective central portions 156c of the second blocks 155.

The second circumferential lengths 115b delimit both the portions of the axially inner sides 126 of the first blocks 125 that extend from the respective free ends 126b up to the respective central portion 126c of the first blocks 125, and the portions of the axially inner sides 156 of the second blocks 155 that extend from the respective free ends 156b up to the respective central portions 156c of the second blocks 155.

The portion of the axially inner side 126 of each of the first blocks 125 that extends from the free end 126a up to the central portion 126c is inclined with respect to the equatorial plane E by an angle equal to the angle of inclination of the first circumferential lengths 115a of the central circumferential groove 115 with respect to the equatorial plane E.

The portion of the axially inner side 156 of each of the second blocks 155 that extends from the free end 156a up to the central portion 156c is inclined with respect to the equatorial plane E by an angle equal and opposite to the angle of inclination of the first circumferential lengths 115a. The second circumferential lengths 115b of the central circumferential groove 115 are substantially parallel with respect to the equatorial plane E.

The portion of the axially inner side 126 of each of the first blocks 125 that extends from the free end 126b up to the central portion 126c and the portion of the axially inner side 156 of each of the second blocks 155 that extends from the free end 156b up to the central portion 156c are substantially parallel to the equatorial plane E.

As a result of the geometry of the axially inner sides 126 of the first blocks 125 and of the axially inner sides 156 of the second blocks 155 described above, the central circumferential groove 115 has a nonconstant width in the circumferential direction both along the first circumferential lengths 115a and along the second circumferential lengths 115b.

With reference to figure 4a, each first transversal groove 210 comprises first transversal lengths 210a arranged between two respective first circumferential grooves 120.

The first transversal lengths 210a and the first circumferential grooves 120 follow each other in an alternating manner along a second zig-zag trajectory having an axial extension greater than that of the first zig-zag trajectory.

With reference to figure 4b, each second transversal groove 220 comprises second transversal lengths 220a arranged between two respective second circumferential grooves 160 and inclined with respect to the equatorial plane E on the opposite part to the first transversal lengths 210a.

The second transversal lengths 220a and the second circumferential grooves 160 follow each other in an alternating manner along a third zigzag trajectory having an axial extension greater than that of the first zigzag trajectory, preferably equal to that of the second zig-zag trajectory.

The angle of inclination of the circumferential grooves 160 is preferably equal to that of the circumferential grooves 120. With reference to figure 4a, each first transversal groove 210 further comprises third transversal lengths 210b arranged between two respective third circumferential grooves 140 and inclined with respect to the equatorial plane E on the same part as the first transversal lengths 210a.

The third transversal lengths 210b and the third circumferential grooves 140 follow each other in an alternating manner along a fourth zig-zag trajectory having an axial extension greater than that of said first zig-zag trajectory, preferably equal to that of the second zig-zag trajectory.

With reference to figure 4b, each second transversal groove 220 further comprises fourth transversal lengths 220b arranged between two respective fourth circumferential grooves 180 and inclined with respect to the equatorial plane E on the opposite part to the first transversal lengths 210a.

The fourth transversal lengths 220b and the fourth circumferential grooves 180 follow each other in an alternating manner along a fifth zigzag trajectory having an axial extension greater than that of the first zigzag trajectory, preferably equal to that of the third zig-zag trajectory.

As shown in figure 2, in an embodiment thereof, the tyre 100 has, in each of the blocks 125, 135, 155, 175, 190, 195 described above, a plurality of respective sipes LI.

Preferably, the sipes LI have a three-dimensional shape, i.e. they extend along a non-rectilinear trajectory on the radially outer surface of the blocks 125, 135, 155, 175, 190, 195 and along a non-planar surface in the radial direction.

The sipes LI of the blocks 125 are preferably identical to the sipes LI of the blocks 155 but oriented on opposite parts to the latter with respect to the equatorial plane E.

The sipes LI of the blocks 125 are preferably identical to the sipes LI of the blocks 175 but oriented on opposite parts to the latter with respect to the equatorial plane E.

The sipes LI of the blocks 190 are preferably identical to the sipes LI of the blocks 195 but oriented on opposite parts to the latter with respect to the equatorial plane E.

The sipes LI of the blocks 125 extend along an at least partially zigzag path along a trajectory substantially parallel to those of the respective lengths 210a of the transversal grooves 210.

Similarly, the sipes LI of the blocks 155 extend along an at least partially zig-zag path along a trajectory substantially parallel to those of the respective lengths 220a of the transversal grooves 220.

The sipes LI of the blocks 190 extend along an at least partially zigzag path along a trajectory substantially parallel to those of the respective end lengths of the transversal grooves 210.

Similarly, the sipes LI of the blocks 195 extend along an at least partially zig-zag path along a trajectory substantially parallel to those of the respective end lengths of the transversal grooves 220.

The sipes LI of the blocks 135 extend along an at least partially zigzag path along a trajectory inclined with respect to a plane orthogonal to the equatorial plane E on the opposite part with respect to the respective lengths 210b of the transversal grooves 210.

The sipes LI of the blocks 175 extend along an at least partially zigzag path along a trajectory inclined with respect to a plane orthogonal to the equatorial plane E on the opposite part with respect to the respective lengths 220b of the transversal grooves 220.

With reference to figure 5, each of the blocks 125, 135, 155, 175,

190, 195 comprises a respective first tapered portion 126', 136', 156', 176', 191', 196' on the respective axially inner side 126, 136, 156, 176,

191, 196 and a respective second tapered portion 125', 135', 155', 175', 190', 195' at the side of the block adjacent to a respective transversal groove 210, 220 (the lower one with reference to the orientation of the tyre 100 shown in the attached figures).

The first tapered portions 126', 136', 156', 176', 191', 196' are arranged in a portion of the respective block 125, 135, 155, 190, 195 having a dimension greater than that of the block portion where the second tapered portions 125', 135', 155', 175', 190', 195' are arranged. In particular, the first tapered portions 126', 136', 156', 176', 191', 196' have a dimension greater than that of the second tapered portions 125', 135', 155', 175', 190', 195'. More in particular, the dimension of the first tapered portions 126', 136', 156', 176', 191', 196' is greater than half the dimension of the respective blocks 125, 135, 155, 190, 195, whereas the dimension of the second tapered portions 125', 135', 155', 175', 190', 195' is less than half the dimension of the respective blocks 125, 135, 155, 190, 195.

Each of the aforementioned first tapered portions 126', 136', 156', 176', 191', 196' and second tapered portions 125', 135', 155', 175', 190', 195' has a substantially triangular shape, with a vertex, corresponding to the highest point of the ramp, on the radially outer surface of the respective blocks 125, 135, 155, 190, 195 and progressively widen going away from the vertex moving parallel to the adjacent groove. The angle of inclination of the aforementioned first tapered portions 126', 136', 156', 176', 191', 196' and second tapered portions 125', 135', 155', 175', 190', 195 with respect to the radially outer surface of the respective blocks 125, 135, 155, 190, 195 is preferably comprised between 20° and 50°, for example equal to 30°.

As a result of the provision of all of the blocks described above the tread band 110 has a void to solid ratio less than, or equal to, 0.30, preferably comprised between 0.24 and 0.30.

The arrangement of the aforementioned blocks and of the aforementioned grooves is such that the tread pattern comprises a number of pitches greater than, or equal to 54, for example equal to 68.

In particular, as schematically shown in figure 2, three different types of pitches Pl, P2, P3 are provided that differ from each other in that they have different circumferential dimensions.

The pitches Pl, P2 and P3 are properly alternated in the tread pattern according to a predetermined sequence, for example obtained through a suitable software. Figure 2 indicates, purely as an example, a part of a possible sequence.

COMPARATIVE TESTS

The Applicant made some tyres in accordance with the present invention having a size 205/55 R16. Such tyres are indicated hereinafter with INV.

Such tyres had identical structure and dimensions to those of a tyre of the Applicant valued by customers for its excellent behavior on low- grip road surfaces, in particular on icy and possibly snow-covered road surfaces. Such a tyre hereinafter is indicated with Ref.

The tyres INV thus differed from the tyres Ref. only for the different tread pattern.

Outdoor comparative tests were carried out between the tyres INV and the tyres Ref.

The tests were carried out by mounting the aforementioned tyres, inflated with the same inflation pressure on identical wheel, on the wheels of a same vehicle in substantially identical weather conditions.

The behavior of the tyres INV and Ref. was evaluated, asking the driver for an opinion. In particular, the items listed in table 1 below were evaluated, where the qualitative opinion given by the driver is also provided.

In table 1, "=" indicates the positive opinion obtained by the tyres Ref. and "+" indicates an improvement with respect to the tyres Ref.

Table 1

Table 1 shows how the tyres INV offered improved performance with respect to that of the tyres Ref., in particular with reference to traction and braking on icy road surfaces and to traction on snow-covered road surfaces, having a substantially identical behavior to that of the tyres Ref. as far as braking on snow-covered road surfaces is concerned. The Applicant has thus had confirmation of the fact that the particular tread pattern adopted in the tyres of the invention effectively makes it possible to obtain the desired improvement of performance on low-grip road surfaces.

The excellent behavior of the tyre of the invention on low-grip road surfaces is also confirmed by the shape of its footprint, shown in Figure 6. Such a footprint is obtained in particular by subjecting the tyres INV to a vertical load of 450 Kg.

It can be seen that the footprint has a substantially elliptical shape with a very regular perimeter edge. This confirms the fact that the contact surface with the road surface is maximized, as desired for tyres intended to be used on low-grip road surfaces. The substantial uniformity of the grey color on the entire footprint also demonstrates a regular and uniform distribution of the contact pressures inside the footprint, this feature being equally desired in tyres intended for use on low-grip road surfaces.

Of course, those skilled in the art can bring further modifications and variants to the tyre of the present invention described above in order to satisfy specific and contingent application requirements, these variants and modifications in any case being within the scope of protection as defined by the following claims.

Claims

1. Tyre (100) for vehicle wheels, comprising a tread band (110) extending between opposite sidewalls (105), wherein the tread band (110) comprises a central annular portion (A) and opposite shoulder annular portions (SI, S2), each shoulder annular portion (SI, S2) being adjacent to a respective sidewall (105), wherein said central annular portion (A) comprises:

- a central circumferential groove (115) extending on axially opposite parts with respect to an equatorial plane (E);

- a circumferential row of first blocks (125) having a respective axially inner side (126) delimited by said central circumferential groove (115) and a respective axially outer side (127) delimited by a respective first circumferential groove (120), wherein each of said first blocks (125) is delimited in a circumferential direction by respective lengths of opposite first transversal grooves (210) extending from a portion of said tread band (110) arranged at said central circumferential groove (115) up to an axially outer end of a first shoulder annular portion (SI);

- a circumferential row of second blocks (155) having a respective axially inner side (156) delimited by said central circumferential groove (115) and a respective axially outer side (157) delimited by a respective second circumferential groove (160) arranged on an axially opposite part to said first circumferential groove (120) with respect to the central circumferential groove (115), wherein each of said second blocks (155) is delimited in the circumferential direction by respective lengths of opposite second transversal grooves (220) extending from a portion of said tread band (110) arranged at said central circumferential groove (115) up to an axially outer end of a second shoulder annular portion (S2) arranged on the axially opposite part to said first shoulder annular portion (SI) with respect to the central circumferential groove (115); wherein the axially inner side (126) of each of said first blocks (125) comprises, in the circumferential direction, respective opposite free ends (126a, 126b), at least one of which being proximal to the equatorial plane (E), and a respective central portion (126c) distal from the equatorial plane (E); wherein the axially inner side (156) of each of said second blocks (155) comprises, in the circumferential direction, respective opposite free ends (156a, 156b), at least one of which being proximal to the equatorial plane (E), and a respective central portion (156c) distal from the equatorial plane (E); wherein said first blocks (125) are circumferentially offset with respect to said second blocks (155) so that the opposite free ends (126a, 126b) of each of said first blocks (125) are arranged at the central portions (156c) of two circumferentially consecutive second blocks (155) and the opposite free ends (156a, 156b) of each of said second blocks (155) are arranged at the central portions (126c) of two circumferentially consecutive first blocks (125).

2. Tyre (100) according to claim 1, wherein said central circumferential groove (115) extends along a first zig-zag trajectory defined by a plurality of first circumferential lengths (115a) inclined on one part with respect to the equatorial plane (E) and a plurality of second circumferential lengths (115b) inclined with respect to said first circumferential lengths (115a), wherein each of said second circumferential lengths (115b) connects two consecutive first circumferential lengths (115a).

3. Tyre (100) according to claim 1 or 2, wherein each of said first transversal grooves (210) comprises a respective first transversal length (210a) arranged between two respective first circumferential grooves (120) and wherein the first circumferential grooves (120) and the first transversal lengths (210a) follow each other in an alternating manner along a second zig-zag trajectory.

4. Tyre (100) according to claim 3 when depending on claim 2, wherein said second zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

5. Tyre (100) according to any one of the previous claims, wherein each of said second transversal grooves (220) comprises a respective second transversal length (220a) arranged between two respective second circumferential grooves (160) and wherein the second circumferential grooves (160) and the second transversal lengths (220a) follow each other in an alternating manner along a third zigzag trajectory.

6. Tyre (100) according to claim 5 when depending on claim 2, wherein said third zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

7. Tyre (100) according to any one of the previous claims, wherein said central annular portion (A) comprises:

- a circumferential row of third blocks (135) arranged between said first circumferential grooves (120) and third circumferential grooves (140) arranged in an axially outer position with respect to said first circumferential grooves (120);

- a circumferential row of fourth blocks (175) arranged between said second circumferential grooves (160) and fourth circumferential grooves (180) arranged in an axially outer position with respect to said second circumferential grooves (160).

8. Tyre (100) according to claim 7, wherein each of said first transversal grooves (210) comprises a respective third transversal length (210b) arranged between two respective third circumferential grooves (140) and wherein the third circumferential grooves (140) and the third transversal lengths (210b) follow each other in an alternating manner along a fourth zig-zag trajectory.

9. Tyre (100) according to claim 8 when depending on claim 2, wherein said fourth zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

10. Tyre (100) according to any one of claims 7 to 9, wherein each of said second transversal grooves (220) comprises a respective fourth transversal length (220b) arranged between two respective fourth circumferential grooves (180) and wherein the fourth circumferential grooves (180) and the fourth transversal lengths (220b) follow each other in an alternating manner along a fifth zig-zag trajectory.

11. Tyre (100) according to claim 10 when depending on claim 2, wherein said fifth zig-zag trajectory has an axial extension greater than that of said first zig-zag trajectory.

12. Tyre (100) according to any one of the previous claims, wherein said equatorial plane (E) is entirely contained in said central circumferential groove (115).

13. Tyre (100) according to any one of the previous claims, wherein the tread band (110) has a void to solid ratio less than, or equal to, 0.30.

14. Tyre (100) according to any one of the previous claims, wherein the tread band (110) has a tread pattern comprising a number of pitches (Pl, P2, P3) greater than, or equal to, 54.

15. Tyre (100) according to claim 13, wherein the tread band (110) has a tread pattern comprising a plurality of first pitches (Pl) having a first circumferential dimension, a plurality of second pitches (P2) having a second circumferential dimension different from the first circumferential dimension, and a plurality of third pitches (P3) having a third circumferential dimension different from said first circumferential dimension and second circumferential dimension.

16. Tyre (100) according to any one of the previous claims, wherein each of said first blocks (125) and second blocks (155) comprises a plurality of sipes (LI).

17. Tyre (100) according to claim 16, wherein said sipes (LI) extend along non-rectilinear trajectories on a radially outer surface of the respective first blocks (125) and second blocks (155) and along a non- planar surface in a radial direction.

18. Tyre (100) according to any one of the previous claims, wherein each of said first blocks (125) and second blocks (155) comprises a first tapered portion (126'; 156') at said central circumferential groove (115).

19. Tyre (100) according to any one of the previous claims, wherein each of said first blocks (125) and second blocks (155) comprises a second tapered portion (125'; 155') at an adjacent transversal groove (210; 220).

20. Tyre (100) according to any one of the previous claims, wherein the tread band (110) has, close to said opposite shoulder annular portions (SI, S2), a depth that is less than that at said central annular portion (A).