Tire for vehicle wheels

Abstract

A tyre for vehicle wheels, comprising a tread band (2) on which a plurality of first pairs of main grooves are defined, formed by a first main groove (10) and a second main groove (20) extending from a first shoulder region (4) and a second shoulder region (5) towards a central region (6); a plurality of second pairs of main grooves (30, 40) arranged alternately with respect to the first pairs of main grooves, formed by a third main groove (30) and a fourth main groove (40) extending from the first shoulder region (4) and the second shoulder region (5) towards the central region (6); a plurality of third pairs of main grooves (50, 60) formed by a fifth main groove (50) and a sixth main groove (60) extending between two consecutive first main grooves (10) and between two consecutive second main grooves (20), respectively, and having a slope smaller than the first and second main grooves (10, 20), respectively, but coinciding with the first and second main grooves (10, 20). Each pair of consecutive first main grooves (10) delimit, in the circumferential direction: a first group of shoulder blocks (110) and a second group of shoulder blocks (120) separated from each other by the third main groove (30); and a first group of central blocks (100) separated from the first group of shoulder blocks (110) and the second group of shoulder blocks (120) by the fifth main groove (50).

Description

TECHNICAL FIELD

[0001] The present invention relates to a tyre for vehicle wheels, in particular to a winter tyre. BACKGROUND

[0002] The tyre generally comprises a carcass structure annularly shaped about an axis of rotation and comprising at least one carcass ply having end flaps joined in respective annular anchoring structures, known as bead cores.

[0003] In a radially external position with respect to the carcass structure, a belt structure is provided, which, in the case of a tyre for motor vehicles, comprises at least two radially superimposed strips of rubberized fabric provided with reinforcing cords, generally made of metal and arranged parallel to each other in each strip, but crossed with respect to the cords of the adjacent strip, preferably symmetrically with respect to the equatorial plane of the tyre.

[0004] Preferably, the belt structure also comprises, in the radially external position, at least under the ends of the belt strips, a third layer of fabric or metal cords arranged in the circumferential direction (0°). In the case of tyres of the tubeless type, there is also a radially inner layer, known as "liner", which has impermeable characteristics, in order to obtain the air tightness of the tyre itself.

[0005] In a radially external position with respect to the belt structure, a tread band is applied, made of elastomeric material and on which a tread surface is defined, intended for contact with the road surface.

[0006] In order to obtain sufficient grip even on wet road surfaces, the tyre has a tread band provided with grooves having various shapes and geometries, which delimit portions of the tread band intended for contact with the ground, known as blocks.

[0007] The main function of the grooves is to allow the water present between the tyre surface and the road surface to be expelled during their mutual contact, thus preventing the hydrostatic pressure due to the impact of the water on the tyre in progress from causing the tyre to even partially lift from the road surface with the consequent loss of control of the vehicle.

[0008] In the case of winter tyres, small notches, known as "sipes", are generally formed on the blocks of the tread band, which extend from the tread surface of the tyre towards the inside of the block. The function of the sipes is to provide additional gripping elements in the case of travel on snow-covered road surfaces and to retain a certain amount of snow, thus improving the grip on the road surface.

[0009] In addition, the blocks of the tread band can also be provided with studs, which, since a part of them protrude from the tread band, improve the grip characteristics on icy road surfaces.

[0010] The overall configuration of the tread band defined by the assembly of grooves and blocks forms the tread pattern.

[0011] WO 2020012277 in the name of the same Applicant describes a winter tire whose tread pattern is formed by a respective plurality of shoulder blocks and central blocks arranged in succession along the circumferential development of the tread band.

[0012] The term "circumferential" direction means a direction substantially parallel to the direction of rotation of the tire, or at most slightly inclined (at most about 5°) with respect to the direction of rotation of the tire.

[0013] The term "axial" direction means a direction substantially parallel to the axis of rotation of the tire, or at most slightly inclined (at most about 5°) with respect to the axis of rotation of the tire. The axial direction is substantially perpendicular to the circumferential direction.

[0014] The term "equatorial plane" of the tire means the central plane perpendicular to the axis of rotation of the tire.

[0015] The term "central region" of the tread band means the portion of the tread band which extends circumferentially around the equatorial plane of the tire over a width of at least 30% of the width of the tread band, preferably over a width comprised between 40% and 60% of the width of the tread band.

[0016] The central region can extend symmetrically with respect to the equatorial plane or can not extend symmetrically with respect to the equatorial plane.

[0017] The term "shoulder region" of the tread band means the portion of the tread band which extends circumferentially in axially outer positions of the tread band at opposite sides of the central region up to the axial end of the tread band.

[0018] Preferably, each shoulder region extends over a width equal to at least 10% of the width of the tread band.

[0019] The term "groove" means a recess formed in the portion of the tread band and having a width greater than or equal to 1.5 mm.

[0020] A groove is said to be "circumferential" when it extends along a direction which is parallel or at most slightly inclined (at most by an angle of less than 5°) with respect to the circumferential direction.

[0021] A groove is said to be "transversal" when it extends along a direction which is inclined by an acute angle with respect to the circumferential direction of at least greater than 10°.

[0022] The term "sipe" means a recess formed in the portion of the tread band and having a width less than 1.5 mm, preferably less than or equal to 1 mm.

[0023] The width of the sipes and grooves should be measured at a depth greater than or equal to 1 mm, preferably greater than or equal to 1.5 mm.

[0024] If the width of a groove or sipe varies along its longitudinal development, the average width is considered and its value is obtained as the average of the different width values, appropriately weighted according to the relative longitudinal range. For example, if a groove has a width of 5 mm over 80% of its longitudinal range and a width of 3 mm over the remaining 20%, the average width to be considered is 5 x 0.8 + 3 x 0.2 = 4.6 mm.

[0025] Similarly, if the width of a groove, in particular of a transverse groove, varies along the length of the tread band according to the pitch to which it belongs, the average value is considered.

[0026] When the groove depth is at least 5 mm, the groove is defined as a "primary" groove. Preferably, the width of the primary groove is at least 3 mm.

[0027] When the groove depth is less than 5 mm, the groove is defined as a "secondary" groove.

[0028] Preferably, the width of the secondary groove is less than 4 mm.

[0029] The inclination of a groove with respect to the circumferential direction identified on the tread band is defined by the acute angle formed by the groove and the circumferential direction. As a particular case, the inclination of a groove extending parallel to the axis of the tyre with respect to the circumferential direction is 90°.

[0030] When considered in a Cartesian plane positioned on the tread band (with the longitudinal axis parallel to the circumferential direction and the transverse axis parallel to the axis of the tyre), two (or more) transverse grooves are "inclined in a consistent manner" if the trend of both (or all) grooves is increasing or decreasing.

[0031] Thus, two transverse grooves are "inclined in an inconsistent manner" when, when considered in this Cartesian plane, the trend of the two grooves is increasing for one groove and decreasing for the other groove.

[0032] Two grooves are "substantially aligned" when the value of the longitudinal axis offset of the two grooves is less than the width of the largest groove, at least in the region of their respective ends facing each other.

[0033] Two grooves are "successive" when, considering the rotation of the tyre along either of its two directions of rotation, the two grooves are arranged one after the other on the tread surface. In particular, two grooves having the same configuration are successive when no other groove having the same configuration is arranged between them.

[0034] In particular, when the grooves are arranged in succession according to a predetermined circumferential distance pattern, a plurality of grooves can develop along the circumference of the tread band to be arranged in "regular succession" on the tread surface.

[0035] The term "block" is intended to mean a portion of the tread band delimited by at least one groove, preferably by at least two distinct grooves, and defining on its radially outer surface a portion of the tread band intended for contact with the road surface.

[0036] The block is therefore considered both as a portion of the tread band with closed profile delimited by three or more grooves and as a circumferential rib delimited by a pair of grooves developing around the circumference of the tread band.

[0037] The blocks formed in the central region of the tread band are defined as "central blocks", while the blocks formed in the shoulder region of the tread band are defined as "shoulder blocks".

[0038] When calculating the area of the radially outer surface of a group of blocks, the potential internal grooves are not considered with respect to the surface involved by the group of blocks.

[0039] The term "tread pattern" is intended to mean the overall configuration of the tread band, defined by the grooves and by the assembly of the blocks delimited by said grooves.

[0040] The tread pattern is of the "oriented" type when it is configured to be mounted on a vehicle so as to rotate along a preferred direction of travel.

[0041] A "module" of the tread pattern is defined by the minimum portion of the tread band extending between the axial ends of the tread band, the configuration of which is repeated in succession along the development of the circumference of the tread band so as to form said tread band.

[0042] Furthermore, while maintaining the same basic configuration, the modules can have slightly different circumferential dimensions (called "pitch") from one another, for example modules with two, three or four different pitches can be used on the tread band, said pitches being combined with one another in various ways.

[0043] The module can be formed by two or more basic portions (or sub-modules) extending between the two axial ends of the tread band and arranged within each module in the same successive arrangement.

[0044] In this case, it is provided that each basic portion can have the same basic configuration in different modules, but with slightly different circumferential dimensions (i.e. "pitch") from one another, so that each module can be formed by basic portions with different pitches.

[0045] Two or more directions or two or more elements extending in respective directions, such as, for example, two or more grooves, are "substantially parallel" when they are inclined with respect to each other by an angle of less than 10°, preferably less than 5°.

[0046] The lengths of two or more elements are "substantially equal" when their respective lengths differ by at most a range of 10% of the maximum length.

[0047] Two or more elements or groups of elements are considered "substantially symmetrical" with respect to a symmetry plane even if they are slightly misaligned with respect to each other in a direction parallel to the symmetry plane. For example, two grooves or two blocks or two groups of blocks are symmetrical with respect to the equatorial plane even if they are spaced apart in the circumferential direction by a range of less than the range of the tread pattern pitch, which may, for example, correspond to the circumferential distance between two consecutive main grooves. In absolute terms, the circumferential distance of two substantially symmetrical elements is less than 50 mm, preferably less than 40 mm.

[0048] Two elements, such as, for example, two blocks or two grooves, are "axially misaligned" or "misaligned with respect to the axial direction" when they are spaced apart from each other in the circumferential direction of the tread band. SUMMARY

[0049] Applicant has initially observed that the level of performance of a tyre on a snowy surface depends to some extent on the number and range of sipes formed in the blocks. In particular, Applicant has noted that, for the same tread pattern, blocks in which more sipes are formed are able to provide a better behaviour on snow.

[0050] However, Applicant has also observed that the presence of sipes weakens the structure of the blocks, making them less rigid and thus reducing the ability of the blocks to withstand external stresses, in particular tangential stresses.

[0051] As a result of this weakening, during braking, acceleration or cornering, the blocks can undergo a corresponding deformation, thus causing the blocks to be partially lifted from the road surface, with the result that the contact area between the blocks and the road surface is reduced and thus the total frictional force exerted by the tyre on the road surface is reduced.

[0052] Applicant has also observed that the lower rigidity of the blocks can also have a negative impact on the level of performance of a studded tyre.

[0053] In fact, Applicant has verified that studs fixed on easily deformable blocks not only have a poorer grip on icy surfaces, but can also be more easily pulled out of their seats, thus causing the studs to be detached from the tread band and thus causing an irreversible loss of efficiency when driving on icy surfaces.

[0054] In fact, the Applicant has verified that the ability of the tyre to keep the studs inside the seats suitably provided in the tread band is a key parameter for a studded tyre to obtain a sufficient performance level during its service life.

[0055] The Applicant has also observed that how to respond to this requirement is usually achieved by shaping and dimensioning the seats for receiving the studs and the portions of the studs intended to be received in the seats so as to highly interfere with the movements that can occur when the studs exit the seats.

[0056] However, the Applicant has verified that these arrangements have limitations and can not be sufficient due to the need to insert the studs into the respective seats during the tyre production steps.

[0057] Therefore, the Applicant has thought that, in order to improve the grip behaviour of the studs and their ability to be kept inside the seats, the tread pattern can be advantageously configured so as to limit as much as possible the excessive local deformations of the tread band, in particular of the individual blocks.

[0058] To achieve this goal, the Applicant has thought that the configuration of the tread pattern must not only have as high as possible stiffness characteristics, but also must make the stiffness of the different areas of the tread band as uniform as possible, so that the possible tangential stresses are distributed in the most uniform way possible.

[0059] To meet both requirements, without compromising the ability to expel water from the tread band, the Applicant has thought that it can be possible to use grooves with greater depth in order to define on the tread band relatively large areas, and grooves with smaller depth within said large areas in order to define two or more blocks.

[0060] From this, the Applicant has obtained greater freedom in designing the tread pattern, being able to configure the large areas formed by a plurality of blocks with homogenous characteristics with respect to each other (for example, similar surface extent), even in the presence of a plurality of blocks that, taken individually, can be very different from each other.

[0061] Finally, the Applicant has found that, by defining on the tread band in a suitable way a respective plurality of main grooves that extend from the shoulder areas towards the equatorial plane and that are connected to each other so as to define a first group of shoulder blocks and a second group of shoulder blocks that are circumferentially alternated with respect to each other and a first group of central blocks axially internal and adjacent to the two groups of shoulder blocks, a tread pattern is obtained that is suitable to withstand the tangential stresses in a uniform way, thus preventing excessive local deformations of the blocks and therefore increasing the ability to keep the studs inside the respective receiving seats.

[0062] In particular, in its first aspect, the present application relates to a tyre for vehicle wheels, comprising a tread band.

[0063] Preferably, a first shoulder region and a second shoulder region axially opposite each other and a central region interposed between said first shoulder region and said second shoulder region are defined on the tread band.

[0064] Preferably, a plurality of first pairs of main grooves is defined on the tread band, arranged in a regular succession along the circumferential development of said tread band.

[0065] Preferably, each first pair of main grooves is formed by a first main groove extending from said first shoulder region towards said central region and by a second main groove extending from said second shoulder region towards said central region.

[0066] Preferably, the inclination of said first main groove with respect to said circumferential direction decreases from said first shoulder region towards said central region.

[0067] Preferably, the inclination of said second main groove with respect to said circumferential direction decreases from said second shoulder region towards said central region.

[0068] Preferably, said first main groove comprises an axially inner end connected to said second main groove.

[0069] Preferably, said second main groove comprises an end portion located axially internally and extending between said first main groove and a further first main groove belonging to a subsequent first pair of main grooves.

[0070] Preferably, a plurality of second pairs of main grooves is defined on the tread band, arranged in a regular succession along the circumferential development of said tread band.

[0071] Preferably, said second pairs of main grooves are arranged on the tread band in alternating positions with respect to said first pairs of main grooves.

[0072] Preferably, each second pair of main grooves is formed by a third main groove extending from said first shoulder region towards said central region and by a fourth main groove extending from said second shoulder region towards said central region.

[0073] Preferably, the inclination of said third main groove with respect to said circumferential direction decreases from said first shoulder region towards said central region.

[0074] Preferably, the inclination of said fourth main groove with respect to said circumferential direction decreases from said second shoulder region towards said central region.

[0075] Preferably, a plurality of third pairs of main grooves is defined on the tread band, said plurality of third pairs of main grooves being arranged in a regular succession along the circumferential development of said tread band.

[0076] Preferably, each third pair of main grooves is formed by a fifth main groove and a sixth main groove.

[0077] Preferably, said fifth main groove extends between two first main grooves of said first pairs of main grooves which are mutually consecutive.

[0078] Preferably, said fifth main groove is connected to an axially inner end of said third main groove.

[0079] Preferably, said fifth main groove has a slope with respect to said circumferential direction which is less than that of said first main grooves.

[0080] Preferably, said fifth main groove has a slope which is coincident with that of said first main grooves.

[0081] Preferably, said sixth main groove extends between two second main grooves of said first pairs of main grooves which are mutually consecutive.

[0082] Preferably, said sixth main groove is connected to an axially inner end of said fourth main groove.

[0083] Preferably, said sixth main groove has a slope with respect to said circumferential direction which is less than that of said second main grooves.

[0084] Preferably, said sixth main groove has a slope which is coincident with that of said second main grooves.

[0085] Preferably, each pair of consecutive first main grooves delimits, circumferentially, a first group of shoulder blocks and a second group of shoulder blocks.

[0086] Preferably, said first group of shoulder blocks and said second group of shoulder blocks extend from said first shoulder region towards said central region.

[0087] Preferably, said first group of shoulder blocks and said second group of shoulder blocks are mutually separated by said third main groove.

[0088] Preferably, each pair of consecutive first main grooves delimits, circumferentially, a first group of central blocks separated from said fifth main groove by said first and second groups of shoulder blocks.

[0089] Applicant believes that a tyre configured according to the above aspects of the present application advantageously allows to provide a substantially uniform behaviour in the various regions of the tread band when subjected to axial and circumferential tangential stresses.

[0090] Thus, when the tread band is provided with sipes and studs, the tyre has an optimal behaviour on mutually different road surfaces (dry road surface and wet road surface and snow-covered road surface or icy road surface).

[0091] More in detail, the Applicant believes that the provision of the main grooves allows to quickly discharge water from the central region towards the opposite shoulder regions. In particular, this behaviour is induced by the first pair of main grooves, which are mutually connected and connected to the first pair of consecutive transversal grooves in the region of their axially inner end. In this way, a network of channels is formed in which water can be collected and quickly conveyed towards the shoulder regions.

[0092] Furthermore, the first pair of main grooves is separated by a second pair of main grooves, which are also intended to discharge water towards the shoulder regions, but are not mutually connected, thus preventing the central region from being weakened.

[0093] Finally, the substantial uniformity of the behaviour of the tread band with respect to the tangential stresses allows to advantageously use the tread pattern of the tyre of the present application as a basis for studded tyres.

[0094] In the above aspects, the present application can have at least one of the additional preferred features indicated below.

[0095] In some embodiments, each pair of consecutive second main grooves delimit, in the circumferential direction, a third group of shoulder blocks and a fourth group of shoulder blocks.

[0096] Preferably, said third group of shoulder blocks and said fourth group of shoulder blocks extend from said second shoulder region towards said central region.

[0097] Preferably, said third group of shoulder blocks and said fourth group of shoulder blocks are mutually separated by said fourth main groove.

[0098] Preferably, each pair of consecutive second main grooves delimits, in the circumferential direction, a second group of central blocks.

[0099] Preferably, said second group of central blocks is separated from said third group of shoulder blocks and said fourth group of shoulder blocks by said sixth main groove.

[0100] Thereby, the above technical advantages can be obtained over the entire tread surface.

[0101] Preferably, when considered as a whole, the first group of shoulder blocks, the second group of shoulder blocks and the first group of central blocks extend from the axial end of the tread band up to the equatorial plane or in its immediate vicinity.

[0102] In some embodiments, said first group of shoulder blocks is substantially symmetrical with respect to said third group of shoulder blocks about said equatorial plane.

[0103] In some embodiments, said second group of shoulder blocks is substantially symmetrical with respect to said equatorial plane with respect to said fourth group of shoulder blocks.

[0104] In some embodiments, said first group of center blocks is substantially symmetrical with respect to said equatorial plane with respect to said second group of center blocks.

[0105] In this way, the configuration of the first group of shoulder blocks, of the second group of shoulder blocks and of the first group of center blocks is provided in a substantially symmetrical manner on the two halves of the tread band, so as to make the tread band obtain particularly balanced performances.

[0106] In some embodiments, said first group of shoulder blocks is formed by a first pair of shoulder blocks.

[0107] Preferably, the blocks of said first group of shoulder blocks are separated by a first secondary groove, which extends between said first main groove and said third main groove.

[0108] In this way, the blocks forming the first group of shoulder blocks are separated from each other by a groove of small depth (less than 5 mm), so as to be connected with respect to each other and therefore not to be easily deformed as a whole.

[0109] In some embodiments, said first secondary groove is parallel to said fifth main groove.

[0110] In some embodiments, said second group of shoulder blocks is formed by a second pair of shoulder blocks.

[0111] Preferably, the blocks of said second group of shoulder blocks are separated by a second secondary groove, which extends between said third main groove and said further first main groove subsequent to said first main groove.

[0112] In this way, the blocks forming the second group of shoulder blocks are separated from each other by a groove of small depth (less than 5 mm), so as to be connected with respect to each other and therefore not to be easily deformed as a whole.

[0113] In some embodiments, said second secondary groove is parallel to said fifth main groove.

[0114] In some embodiments, said second secondary groove is aligned with said first secondary groove.

[0115] In this way, a single direction of outflow of water from the first and second group of shoulder blocks towards the first and third main grooves is defined, so as to facilitate the rapid expulsion of water therefrom when driving on wet road surfaces.

[0116] In some embodiments, said first group of center blocks is formed by a first pair of center blocks.

[0117] Preferably, the blocks of said first group of center blocks are separated by a third secondary groove.

[0118] In this way, the blocks forming the first group of central blocks are separated from each other by grooves of small depth (less than 5 mm) so as to be connected to each other in opposition and therefore not to be easily deformed as a whole.

[0119] Preferably, said third grooves extend between said first main groove and said fifth main groove.

[0120] Preferably, said third grooves are inclined in a non-uniform manner with respect to said fifth main groove.

[0121] Preferably, said third grooves are aligned with end portions of a further second main groove.

[0122] In some embodiments, said first pair of central blocks is formed by a first central block located axially internally and a second central block located axially externally with respect to the first central block.

[0123] Preferably, said first central block has a V shape and comprises: an apex, said apex being directed towards said first shoulder region; and a pair of branches, said pair of branches extending in respective directions towards said second shoulder region and having opposite inclinations with respect to said circumferential direction.

[0124] Preferably, said second central block has a substantially triangular shape.

[0125] In some embodiments, each third main groove is substantially parallel to said first main groove.

[0126] In some embodiments, each fourth main groove is substantially parallel to said second main groove.

[0127] In some embodiments, said third group of shoulder blocks is formed by a third pair of shoulder blocks.

[0128] Preferably, the blocks of said third group of shoulder blocks are separated by fourth grooves, said fourth grooves extending between said second main groove and said fourth main groove.

[0129] In this way, the blocks forming the third group of shoulder blocks are separated from each other by grooves of small depth (less than 5 mm) so as to be connected to each other in opposition and therefore not to be easily deformed as a whole.

[0130] In some embodiments, said fourth grooves are parallel to said sixth main groove.

[0131] In some embodiments, said fourth group of shoulder blocks is formed by a fourth pair of shoulder blocks.

[0132] Preferably, the blocks of the fourth group of shoulder blocks are separated by a fifth groove extending between the fourth primary groove and the further second primary groove subsequent to the second primary groove.

[0133] In this way, the blocks forming the fourth group of shoulder blocks are mutually separated by grooves of smaller depth (less than 5 mm) so as to be connected to each other and therefore not easily deformable as a whole.

[0134] In some embodiments, the fifth groove is parallel to the sixth primary groove.

[0135] In some embodiments, the fifth groove is aligned with the fourth groove.

[0136] In this way, a single outflow direction of water from the third group of shoulder blocks and the fourth group of shoulder blocks towards the second primary groove and the fourth primary groove is defined, thus facilitating the rapid drainage thereof from the wet road surface when travelling thereon.

[0137] In some embodiments, the second group of central blocks is formed by a second pair of central blocks.

[0138] Preferably, the blocks of the second group of central blocks are separated by a sixth groove.

[0139] In this way, the blocks forming the second group of central blocks are mutually separated by grooves of smaller depth (less than 5 mm) so as to be connected to each other and therefore not easily deformable as a whole.

[0140] Preferably, the sixth groove extends between the second primary groove and the sixth primary groove.

[0141] Preferably, the sixth groove is inclined in a non-uniform manner with respect to the sixth primary groove.

[0142] In some embodiments, the second pair of central blocks is formed by a third central block located axially internally and a fourth central block located axially externally with respect to the third central block.

[0143] Preferably, the third central block has a V shape and comprises a vertex directed towards the second shoulder region and a pair of branches extending in respective directions towards the first shoulder region and having opposite inclinations with respect to the circumferential direction.

[0144] In this way, the third central block is substantially mirrored with respect to the first central block, despite being staggered with respect to the axial direction.

[0145] Preferably, one branch of each first central block is partially received in the concavity of the third central block.

[0146] Preferably, one branch of each third central block is partially received in the concavity of the first central block.

[0147] In this way, the first and third central blocks partially embed one another, mutually assisting in withstanding the tangential stresses.

[0148] Preferably, the apices of said first central block are aligned in a circumferential direction.

[0149] Preferably, the apices of said third central block are substantially aligned in a circumferential direction.

[0150] Preferably, said fourth central block has a substantially triangular shape.

[0151] Preferably, each of said first main grooves comprises a first portion having a curvilinear development extending from said first shoulder region towards the equatorial plane of the tread band, and an inclination with respect to said circumferential direction which substantially decreases from said first shoulder region towards said central region.

[0152] Preferably, each of said second main grooves comprises a first portion having a curvilinear development extending from said second shoulder region towards the equatorial plane of the tread band, and an inclination with respect to said circumferential direction which substantially decreases from said second shoulder region towards said central region.

[0153] Preferably, said first portion of said first main grooves and said first portion of said second main grooves are inclined with respect to said circumferential direction in a non-uniform manner.

[0154] In this way, the discharge of water from the central region towards the respective shoulder regions is particularly facilitated when the tyre is rotated in a predetermined direction corresponding to the preferred direction of progression.

[0155] Preferably, said first portion of each of said first and second main grooves has a curvilinear development without any inflection points.

[0156] Preferably, the inclination with respect to said circumferential direction of said first portion of each of said first main grooves in the region of said first shoulder region and / or of said first portion of each of said second main grooves in the region of said second shoulder region is defined by an angle comprised between 70° and 90°.

[0157] Preferably, the inclination with respect to said circumferential direction of said first portion of each of said first and / or second main grooves in the region of said central region is defined by an angle comprised between 20° and 40°.

[0158] In this way, the rapid discharge of water from the central region towards the shoulder regions is thus promoted, while maintaining a high level of resistance of the shoulder regions to the tangential transverse stress.

[0159] Preferably, each of the first main grooves has a width that decreases from the first shoulder region towards the equatorial plane.

[0160] Preferably, each of the second main grooves has a width that decreases from the second shoulder region towards the equatorial plane.

[0161] In this way, on the one hand, the outflow of water from the central region towards the respective shoulder region is promoted, and on the other hand, the stiffness of the first and second groups of central blocks, respectively, is increased.

[0162] Preferably, each of the first main grooves and / or second main grooves and / or third main grooves and / or fourth main grooves and / or fifth main grooves and / or sixth main grooves has a variable width comprised between 3 mm and 10 mm.

[0163] Preferably, each of the first main grooves and / or second main grooves and / or third main grooves and / or fourth main grooves and / or fifth main grooves and / or sixth main grooves has a depth comprised between 6 mm and 12 mm, more preferably between 7 mm and 10 mm.

[0164] Preferably, each of the first secondary grooves and / or second secondary grooves and / or third secondary grooves and / or fourth secondary grooves and / or fifth secondary grooves and / or sixth secondary grooves has a variable width comprised between 2 mm and 5 mm.

[0165] Preferably, each of the first secondary grooves and / or second secondary grooves and / or third secondary grooves and / or fourth secondary grooves and / or fifth secondary grooves and / or sixth secondary grooves has a depth comprised between 2.5 mm and 4.5 mm.

[0166] Preferably, in each first pair of main grooves, the first main groove and the second main groove are axially staggered.

[0167] Preferably, in each second pair of main grooves, the third main groove and the fourth main groove are axially staggered.

[0168] Thereby, since the impacts of the edges of the respective grooves with the ground are staggered with respect to each other, the noise generated by the tyre when rolling on the ground is advantageously reduced, thus reducing the intensity of the overall noise generated.

[0169] Preferably, the third main groove and the fourth main groove have a substantially symmetrical course with respect to the circumferential direction.

[0170] In some embodiments, the end portion of the second main groove extends to cross the equatorial plane of the tread band, preferably in a zigzag manner.

[0171] Preferably, the end portion of the second main groove comprises a first segment extending from the first main groove towards the first shoulder region.

[0172] Preferably, the end portion of the second main groove comprises a second segment, which continues the first segment to extend, more preferably towards the second shoulder region.

[0173] Preferably, the end portion of the second main groove comprises a third segment, which continues the second segment to extend, more preferably towards the first shoulder region up to the other first main groove.

[0174] Preferably, the first and third segments of the end portion are substantially parallel.

[0175] In some embodiments, the depth of the secondary grooves is less than 50% of the depth of the main grooves.

[0176] In some embodiments, the fifth main groove is inclined with respect to the circumferential direction by an angle comprised between 5° and 25°, preferably of about 15°.

[0177] In some embodiments, the first secondary groove and / or the second secondary groove and / or the fourth secondary groove and / or the fifth secondary groove are inclined with respect to the circumferential direction by an angle comprised between 5° and 25°, preferably of about 15°.

[0178] In some embodiments, the third secondary groove and / or the sixth secondary groove are inclined with respect to the circumferential direction by an angle comprised between 25° and 45°, preferably of about 35°.

[0179] In some embodiments, the first set of shoulder blocks, the second set of shoulder blocks and the first set of center blocks define respective radially outer surfaces thereon, and each of the radially outer surfaces has a respective area which differs from an average value of the areas of the radially outer surfaces by a value less than 30% of the average value, preferably by a value less than 25% of the average value.

[0180] In some embodiments, each of the first set of shoulder blocks, the second set of shoulder blocks and the first set of center blocks defines a respective radially outer surface thereon, and each of the radially outer surfaces of the blocks has a respective area which differs from an average value of the areas of the radially outer surfaces of the blocks by a value less than 30% of the average value, preferably by a value less than 25% of the average value.

[0181] In some embodiments, said tread band is defined with a tread pattern formed by the whole of the grooves and the whole of the blocks; and with modules defined by the minimum portion of the tread band extending between the axial ends of the tread band, the configuration of said modules being successively repeated along the circumferential development of the tread band so as to form said tread pattern.

[0182] Preferably, said modules are formed by the portion of the tread band located between two pairs of said first pairs of main grooves, one after the other.

[0183] Preferably, said modules are formed by a first elementary portion extending from said first pair of main grooves up to said second pair of main grooves and a second elementary portion extending from said second pair of main grooves up to said first pair of main grooves, one after the other.

[0184] In some embodiments, on at least some of the blocks defined on said tread band, more preferably on all of the blocks defined on said tread band, a respective plurality of sipes is formed.

[0185] In some embodiments, on at least some of the blocks defined on said tread band, a block is provided. BRIEF DESCRIPTION OF DRAWINGS

[0186] The features and advantages of the application will be better understood from the detailed description of several preferred embodiments thereof, illustrated by way of non-limiting example in the accompanying drawings in which:

[0187] - Figure 1 is a front view of a tyre for vehicle wheels constructed in accordance with the present application;

[0188] - Figure 2 is Figure 1 a partial front view of a first construction variant of the tyre of

[0189] - Figure 3 is Figure 1 a schematic view, drawn to an enlarged scale and planarly developed, of a main portion of the tread band of the tyre of

[0190] - Figure 4 is a schematic view, drawn to an enlarged scale, of a portion of the tread band representing a module of the tread band of the tyre of Figure 1 DETAILED DESCRIPTION

[0191] With reference to the drawings, the tyre for vehicle wheels constructed in accordance with the present application is indicated as a whole with the reference number 1.

[0192] ​The tyre 1 comprises a tyre structure as such (not shown in the figures) and a tread band 2 on which a tread surface 3 is defined, arranged in a radially external position with respect to the tread band 2 and intended for contact with the road surface.

[0193] The tyre 1 has a substantially annular shape as such, developing around an axis of rotation, defining on the tread surface 3 an axial direction Y parallel to the axis of rotation, and an equatorial plane X passing through said axial direction, perpendicular to the axis of rotation and defining on the tread surface 3 a circumferential direction parallel to the equatorial plane.

[0194] The tread band 2 has a width L determined as the maximum width of the tread band intended for contact with the ground in standard conditions of use.

[0195] The tyre 1 is a directional tyre, in which a preferred rolling direction of the tyre is defined, indicated in the figures with the arrow F.

[0196] On the tread band 2 there are also defined: a first shoulder region 4 delimited on the axially external side by a first lateral edge 4a of the tread band 2; a second shoulder region 5 axially opposite the first shoulder region 4 and delimited on the axially external side by a second lateral edge 5a of the tread band 2; and a central region 6 interposed between the first shoulder region 4 and the second shoulder region 5 and extending so as to span the equatorial plane X.

[0197] On the tread band 2 there are defined a plurality of first pairs of main grooves, arranged successively and regularly along the circumferential development of the tread band 2 and extending transversely from the opposite shoulder regions 4 and 5 towards the equatorial plane X.

[0198] In particular, each first pair of main grooves is formed by a first main groove 10 extending transversely from the first shoulder region 4 towards the central region 6 and by a second main groove 20 extending transversely from the second shoulder region 5 towards the central region 6.

[0199] Each first main groove 10 comprises a first portion 11 extending from an axially external end 10a open at the first lateral edge 4a of the first shoulder region 4 up to an axially internal end 10b open at the second main groove 20.

[0200] In particular, the first main groove 10 joins the second main groove 20 shortly after crossing the equatorial plane X. The first portion 11 has a curvilinear course without any inflection points and has a general inclination with respect to the circumferential direction which decreases from the first shoulder region 4 towards the central region 6, starting from an inclination of about 80° in the region of the axially internal end 10a up to an inclination of about 30° in the region of the axially internal end 10b.

[0201] Each second main groove 20 comprises a first portion 21 extending from an axially outer end 20a, which is open at the second lateral edge 5a of the second shoulder region 5, up to a junction with respect to the axially inner end 10b of the first main groove 10.

[0202] Similarly to the first portion 11 of the first main groove 10, the first portion 21 of the second main groove 20 also has a curvilinear development without any inflection points and with a general decrease in the inclination with respect to the circumferential direction from the second shoulder region 5 towards the central region 6, starting from an inclination of about 80° in the region of the axially inner end 20a up to an inclination of about 30° in the region of the abutment position with the axially inner end 10b of the first main groove 10.

[0203] Each second main groove 20 also comprises an end portion 22, which is axially internal and continues the extension of the first portion 21 up to its axially inner end 20b, which is open in an additional first main groove 10, which is subsequent to the first main groove 10, which forms a first pair of main grooves together with the second main groove 20.

[0204] The end portion 22 of each second main groove 20 has a zigzag configuration and comprises a first segment 23, which continues the first portion 21 towards the first shoulder region 4, a second segment 24, which continues the first segment 23 towards the second shoulder region 5, and a third segment 26, which continues the second segment 24 towards the first shoulder region 4 up to the axially inner end 20b. In particular, the third segment 26 is joined with the additional first main groove 10 shortly after crossing the equatorial plane X.

[0205] Thereby, on the first portion 11 of the additional first main groove 10, and therefore on the first portion 11 of each first main groove 10, there is still defined an inner end region 15, which is delimited by the end 20a of the second main groove 20 and the axially inner end 10b of the first main groove 10.

[0206] The first segment 23, the second segment 24 and the third segment 26 are substantially rectilinear, more particularly they are curved with a radius of curvature comprised between 120 mm and 150 mm and extend so as to cross the equatorial plane X of the tread band 2 and are inclined in an alternating manner with respect to the circumferential direction. In particular, the first segment 23 and the third segment 26 are substantially parallel to each other and the second segment 24 and the inner end region 15 of the first main groove 10 are also substantially parallel.

[0207] Therefore, in this way, a zigzag is formed and is defined by the inner end region 15 of the first main groove 10, the first segment 23 of the end portion 22, the second segment 24 of the end portion 22 and the third segment 26 of the end portion 22.

[0208] This fold line develops continuously along the entire circumferential extent of the equatorial plane X and passes through said equatorial plane in each of its successive portions.

[0209] Thus, the first 10 and second 20 main grooves of each first pair have a substantially similar profile, in which the relevant portions of the respective first 11 and second 21 portions are substantially symmetrical with respect to the equatorial plane X and have a concavity directed towards the same side of the tread band 2.

[0210] However, the second main grooves 20 are axially staggered with respect to the first transverse grooves 10. In fact, the respective axially outer ends 10a and 20a are staggered by a value comprised between 5 mm and 20 mm, preferably between 10 mm and 20 mm, measured in the circumferential direction.

[0211] A plurality of second pairs of main grooves is also defined on the tread band 2, which are arranged successively and regularly along the circumferential development of the tread band 2, their position being alternated with respect to the first pairs of main grooves 10 and 20.

[0212] Each second pair of main grooves is formed by a third main groove 30 extending from the first shoulder region 4 towards the central region 6 and a fourth main groove 40 extending from the second shoulder region 5 towards the central region 6.

[0213] In particular, each third main groove 30 extends between an axially outer end 30a, which opens in the first shoulder region 4, and an axially inner end 30b.

[0214] Similarly, each fourth main groove 40 extends between an axially outer end 40a, which opens in the second shoulder region 5, and an axially inner end 40a.

[0215] The third 30 and fourth 40 main grooves have a similar curvilinear profile, which is substantially parallel to the first 10 and second 20 main grooves, respectively.

[0216] Furthermore, the third 30 and fourth 40 main grooves, although axially staggered with respect to each other, are substantially symmetrical with respect to the equatorial plane X. In particular, the respective ends 30a and 40a are staggered by a value comprised between 5 mm and 20 mm, preferably between 10 mm and 20 mm, measured in the circumferential direction.

[0217] Advantageously, the second segment 24 of the end portion 22 is located on the theoretical extension of the third main groove 30, even in the absence of a contact point between these grooves.

[0218] Similarly, the third segment 26 of the end portion 22 is also located on the theoretical extension of the fourth main groove 40.

[0219] A plurality of third pairs of main grooves is also defined on the tread band 2, which are arranged successively and regularly along the circumferential development of the tread band 2.

[0220] Each third pair of main grooves is formed by a fifth main groove 50 and a sixth main groove 60, which are substantially mutually symmetrical with respect to the equatorial plane X, although they are axially staggered.

[0221] In particular, each fifth main groove 50 extends between two mutually successive first main grooves 10 and, in a central region thereof, said fifth main groove is connected to the axially inner end 30b of a third main groove 30.

[0222] Each fifth main groove 50 is inclined with respect to the circumferential direction X in a manner coinciding with the first main grooves 10, but with an angle smaller than these first main grooves 10, for example of the order of 15°.

[0223] Similarly, each sixth main groove 60 extends between two mutually successive second main grooves 20 and, in a central region thereof, said sixth main groove is connected to the axially inner end 40b of a fourth main groove 40.

[0224] Each sixth main groove 60 is inclined with respect to the circumferential direction X in a manner coinciding with the second main grooves 20, but with an angle smaller than these second main grooves 20, for example of the order of 15°.

[0225] All the first main grooves 10, second main grooves 20, third main grooves 30, fourth main grooves 40, fifth main grooves 50 and sixth main grooves 60 have a depth of about 8.5 mm. Furthermore, the first main grooves 10, second main grooves 20, third main grooves 30 and fourth main grooves 40 have a variable width which decreases from the respective axially outer end towards the axially inner end. In particular, the width of these main grooves varies from about 7 mm to 10 mm in the region of the respective shoulder region up to values of about 3.5 mm to 5 mm in the central region 6.

[0226] The fifth main grooves 50 and the sixth main grooves 60 have a variable width comprised between 2.5 mm and 4 mm.

[0227] The configuration of the main grooves listed above defines on the tread band 2 a number of block groups, which will be described in greater detail below.

[0228] Each pair of successive first main grooves 10 delimits, circumferentially, a first group of shoulder blocks 110, a second group of shoulder blocks 120 separated from the first group of shoulder blocks 110 by the third main grooves 30, and a first group of central blocks 100 separated from the first group of shoulder blocks 110 and from the second group of shoulder blocks 120 by the fifth main grooves 50.

[0229] Similarly, each pair of consecutive second primary grooves 20 delimit a third group of shoulder blocks 130, a fourth group of shoulder blocks 140 separated from the third group of shoulder blocks 130 by a fourth primary groove 40, and a second group of center blocks 150 separated from the third and fourth groups of shoulder blocks 130, 140 by a sixth primary groove 60.

[0230] Since the primary grooves delimiting the block groups are substantially symmetrical with respect to the equatorial plane, the third group of shoulder blocks 130, the fourth group of shoulder blocks 140 and the second group of center blocks 150 are substantially symmetrical with respect to the first group of shoulder blocks 110, the second group of shoulder blocks 120 and the first group of center blocks 100, respectively.

[0231] The first group of center blocks 100 is separated from the second group of center blocks 150 by the end portion 22 of the second primary groove 20.

[0232] It can be noted that all the block groups are delimited by primary grooves and separated from each other by primary grooves, thus having a relatively large depth.

[0233] The first group of shoulder blocks 110 is formed by a first pair of shoulder blocks 111, 112 separated from each other by a first secondary groove 16 extending between the first primary groove 10 and the third primary groove 30.

[0234] Similarly, the second group of shoulder blocks 120 is formed by a second pair of shoulder blocks 121, 122 separated from each other by a second secondary groove 25 extending between the third primary groove 30 and an additional first primary groove 10 subsequent to the first primary groove 10.

[0235] The first secondary groove 16 and the second secondary groove 25 are substantially aligned with each other and substantially parallel to the fifth primary groove 50.

[0236] The third group of shoulder blocks 130 is formed by a third pair of shoulder blocks 131, 132 separated from each other by a fourth secondary groove 45 extending between the second primary groove 20 and the fourth primary groove 40.

[0237] Similarly, the fourth group of shoulder blocks 140 is formed by a fourth pair of shoulder blocks 141, 142 separated from each other by a fifth secondary groove 55 extending between the fourth primary groove 40 and an additional second primary groove 20 subsequent to the second primary groove 20.

[0238] The fourth secondary groove 45 and the fifth secondary groove 55 are substantially aligned with each other and substantially parallel to the sixth primary groove 60.

[0239] The first set of central blocks 100 is also formed by a pair of blocks, in particular, it is formed by a first axial inner central block 101 and a second central block 102, which is axially external with respect to the first central block 101 and is separated from the first central block 101 by a third secondary groove 35.

[0240] The third secondary groove 35 extends between the first primary groove 10 and the fifth primary groove 50, it being inclined in a non-conformal manner with respect to the fifth primary groove 50, the angle of inclination being approximately 35°.

[0241] The first central block 101 has a V-shaped shape and comprises a vertex, which is directed towards the first shoulder region 4, and a pair of branches, which extend towards the second shoulder region 5 along respective directions having opposite inclinations with respect to the circumferential direction.

[0242] The second central block 102 has a substantially triangular shape, the largest side of which faces the axially inner blocks 112 and 122 of the first and second set of shoulder blocks 110 and 120, respectively.

[0243] Similarly, the second set of central blocks 150 is formed by a third central block 151, which is axially internal, and a fourth central block 152, which is axially external with respect to the third central block 151, and the fourth central block is separated from the third central block 151 by a sixth secondary groove 65.

[0244] The sixth secondary groove 65 extends between the second primary groove 20 and the sixth primary groove 60, it being inclined in a non-conformal manner with respect to the sixth primary groove 60, the angle of inclination being approximately 35°.

[0245] The third central block 151 has a V-shaped shape and comprises a vertex, which is directed towards the second shoulder region 5, and a pair of branches, which extend towards the first shoulder region 4 along respective directions having opposite inclinations with respect to the circumferential direction.

[0246] The fourth central block 152 has a substantially triangular shape, the largest side of which faces the axially inner blocks 132 and 142 of the third and fourth set of shoulder blocks 130 and 140, respectively.

[0247] The fourth, fifth and sixth secondary grooves 45, 55 and 65 are substantially symmetrical with respect to the equatorial plane X to the first, second and third secondary grooves 16, 25 and 35, respectively, although they are axially staggered with respect to each other.

[0248] In this way, each block is substantially symmetrical with respect to the equatorial plane to another block of the tread band 2.

[0249] In particular, each third central block 151 is substantially a mirror image of the first central block 101, although staggered with respect to the axial direction.

[0250] Each third central block 151 and each first central block 101 has a respective concavity directed towards the other and is partially aligned not only in the axial direction Y but also in the circumferential direction X. In other words, the respective projections of the first central blocks 101 and of the third central blocks 151 in the circumferential direction partially overlap. In particular, the branch of each first central block 101 is partially received in the concavity of the third central block 151 and vice versa, the branch of each third central block 151 is partially received in the concavity of the first central block 101.

[0251] All first secondary grooves 16, second secondary grooves 25, third secondary grooves 35, fourth secondary grooves 45, fifth secondary grooves 55 and sixth secondary grooves 65 have a depth of about 4 mm and a variable width comprised between about 2.5 mm and 4 mm.

[0252] The blocks and grooves identified above define, as a whole, the tread pattern of the tyre 1.

[0253] The tread pattern is formed by repeating, in a successive and continuous manner, a single module M formed by the portion of the tread band located between two successive first pairs of main grooves 10 and 20.

[0254] Each module M is in turn formed by a first elementary portion extending from the first pair of main grooves 10 and 20 up to the second pair of main grooves 30 and 40 and by a second elementary portion extending from the second pair of main grooves 30 and 40 up to the successive first pair of main grooves 10 and 20.

[0255] Each first elementary portion and each second elementary portion can have a circumferential dimension corresponding to a long pitch or a value corresponding to a short pitch smaller than the long pitch.

[0256] In particular, the long pitch is about 30% greater than the short pitch.

[0257] Each module M can be formed by a first elementary portion and by a second elementary portion having a short pitch or a long pitch combined with each other in various ways, so that on the tread pattern there are modules having a first elementary portion and a second elementary portion both having a long pitch, or modules having a first elementary portion and a second elementary portion both having a short pitch, or modules having a first elementary portion having a short pitch and a second elementary portion having a long pitch, or finally modules having a first elementary portion having a long pitch and a second elementary portion having a short pitch.

[0258] On all the blocks there are formed the above-mentioned sipes which improve the performance level of the tyre on snowy road conditions.

[0259] In particular, on the blocks of the first group 100 and of the second group 150, sipes are formed which extend substantially in the axial direction Y, while on the axially internal blocks of the groups of shoulder blocks 110, 120, 130 and 140, sipes are formed which develop in a transverse direction with respect to the main development direction of the block (defined by the development direction of the first or second main groove), and on the axially external blocks of the groups of shoulder blocks 110, 120, 130 and 140, sipes are formed which extend in a direction substantially parallel to the main development direction of the block (also defined by the direction of the first or second main groove).

[0260] A plurality of studs 200 can also be provided in suitable positions on the different blocks of the tread band 2 of the tyre 1, as shown in Figure 2 A construction variant of the tyre 1 is visible in the figures, in order to make it particularly suitable for travel on icy surfaces.

[0261] Each group of shoulder blocks and each group of central blocks defines a respective radially external surface which in fact constitutes a portion of the tread surface 3.

[0262] Thanks to the above-described configuration of the grooves and of the blocks, each of the radially external surfaces of the first group of shoulder blocks 110, of the second group of shoulder blocks 120 and of the first group of central blocks 100 differs from the average value of the radially external surfaces by a value less than 25%.

[0263] Not only this, but also the blocks forming the different shoulder groups have respective radially external surfaces which differ from the average value of the radially external surfaces of the blocks by a value less than 25%.

[0264] Obviously, thanks to the above-described symmetry relationships, the same relationships between the radially external surfaces also apply to the third group of shoulder blocks 130 and to the fourth group of shoulder blocks 140 and to the second group of central blocks 150.

[0265] In this way, the tread band 2 is subdivided into areas (groups of blocks) in contact with the road surface, which have substantially uniform areas.

[0266] This makes the tread band react to the tangential stresses in a substantially uniform manner, preventing excessive local deformations which could compromise the road grip of the tyre 1, and in the case of studded tyres, allows to reduce the possibility of extraction of the studs from the respective seats.

[0267] Example

[0268] A tyre having dimensions 205 / 55 R16 was constructed according to the above-described embodiment of the present application.

[0269] Table 1 below lists the respective ranges of the radially outer surfaces of the first set of shoulder blocks 110, the second set of shoulder blocks 120 and the first set of central blocks 100, as well as the percentage difference of the surface range of each set of blocks with respect to the average of these surface ranges.

[0270] In the specific example of a tire used here, this average is approximately 1185 mm 2 .

[0271]

[0272] Table 1

[0273] It will be noted that the percentage difference of the radially outer surfaces of the blocks of each set with respect to the average of the surfaces is less than 25% of the average, so that the surface range of each set of blocks in contact with the road is substantially the same, thereby providing a substantially uniform resistance to the tangential stresses.

[0274] Table 2 below lists the respective ranges of the radially outer surfaces of the blocks forming the first set of shoulder blocks 110, the second set of shoulder blocks 120 and the first set of central blocks 100, as well as the percentage difference of the range of each block with respect to the average of the ranges of the blocks.

[0275] In this particular case, this average is approximately 593 mm 2 .

[0276]

[0277] Table 2

[0278] It will also be noted in this case that the percentage difference of the radially outer surfaces of the blocks of each set with respect to the average of the surfaces is less than 25% of the average, so that the surface of each block in contact with the road is substantially the same as the other blocks, thereby providing a substantially uniform resistance to the tangential stresses.

[0279] Table 3 below lists the stiffness values calculated by finite element simulation for the first set of shoulder blocks 110, the second set of shoulder blocks 120 and the first set of central blocks 100, respectively, as well as the percentage difference of the stiffness values of each set of blocks with respect to the average of these stiffness values. The stiffness value is defined as the ratio of the reaction force exerted by the block on the road to the movement imposed on the block itself.

[0280]

[0281] Table 3

[0282] It can thus be observed that the stiffness values of the sets of blocks are globally similar when the tangential stresses to which the sets of blocks are subjected have an axial direction and when these tangential stresses have a circumferential direction.

[0283] The uniformity of the stiffness values between the different block groups is reflected in the uniformity of the behavior of the tread band, thus conferring to the tire a number of important advantages, including better road grip (whatever the road surface), better results in terms of tire wear, greater stud support (in the case of tires with studs), which becomes evident as greater stud retention capacity and higher grip efficiency on icy roads.

Claims

1. Tyre for vehicle wheels, comprising a tread band (2) on which there are defined: - a first shoulder region (4) and a second shoulder region (5) axially opposite each other; - a central region (6) interposed between the first shoulder region (4) and the second shoulder region (5); - a plurality of first pairs of main grooves arranged in regular succession along a circumferential direction of the tread band, each first pair of main grooves being formed by: i. a first main groove (10) extending from the first shoulder region (4) toward the central region (6) and decreasing in inclination with respect to the circumferential direction from the first shoulder region (4) toward the central region (6); and ii. a second main groove (20) extending from the second shoulder region (5) towards the central region (6) and having a decreasing inclination with respect to the circumferential direction from the second shoulder region (5) towards the central region (6); wherein, the first main groove (10) comprises an axially inner end (10b) connected to the second main groove (20), and wherein the second main groove (20) comprises an end portion (22) located axially inside and extending between the first main groove (10) and a further first main groove belonging to a subsequent first pair of main grooves, - a plurality of second pairs of main grooves arranged in regular succession along the circumferential direction of the tread band in alternating positions with respect to the first pairs of main grooves (10, 20), each second pair of main grooves being formed by: i. a third main groove (30) extending from the first shoulder region (4) towards the central region (6) and having a decreasing inclination with respect to the circumferential direction from the first shoulder region (4) towards the central region (6); and ii. a fourth main groove (40) extending from the second shoulder region (5) towards the central region (6) and having a decreasing inclination with respect to the circumferential direction from the second shoulder region (5) towards the central region (6), - a plurality of third pairs of main grooves arranged in regular succession along the circumferential direction of the tread band, each third pair of main grooves being formed by: i. a fifth main groove (50) extending between two first main grooves (10) of the first pairs of main grooves in succession with each other and connected to an axially inner end (30b) of the third main groove (30), and having an inclination with respect to the circumferential direction smaller than and coinciding with that of the first main groove (10), and ii. a sixth main groove (60) extending between two second main grooves (20) of the first pairs of main grooves in succession with each other and connected to an axially inner end (40b) of the fourth main groove (40), and having an inclination with respect to the circumferential direction smaller than and coinciding with that of the second main groove (20), wherein each pair of consecutive first main grooves (10) delimit, in circumferential direction: a first group of shoulder blocks (110) and a second group of shoulder blocks (120) extending from the first shoulder region (4) towards the central region (6) and separated from each other by the third main groove (30); and a first group of central blocks (100) separated from the first and second groups of shoulder blocks (110, 120) by the fifth main groove (50).

2. Tire according to claim 1, wherein, each pair of consecutive second main grooves (20) delimit, in circumferential direction: a third group of shoulder blocks (130) and a fourth group of shoulder blocks (140) extending from the second shoulder region (5) towards the central region (6) and separated from each other by the fourth main groove (40); and a second group of central blocks (150) separated from the third and fourth groups of shoulder blocks (130, 140) by the sixth main groove (60).

3. The tire of claim 2, wherein, The first, second and first groups of shoulder blocks (110, 120, 100) are substantially symmetrical with respect to the equatorial plane of the tyre with respect to the third, fourth and second groups of shoulder blocks (130, 140, 150), respectively.

4. Tyre according to any one of claims 1 to 3, wherein, The first group of shoulder blocks (110) is formed by a first pair of shoulder blocks (111, 112) separated by a first secondary groove (16) extending between the first main groove (10) and the third main groove (30).

5. The tire of claim 4, wherein, The first secondary groove (16) is parallel to the fifth main groove (50).

6. The tire of any one of claims 1 to 3, wherein, The second group of shoulder blocks (120) is formed by a second pair of shoulder blocks (121, 122) separated by a second secondary groove (25) extending between the third main groove (30) and the other first main groove subsequent to the first main groove (10).

7. The tire of claim 6, wherein, The second secondary groove (25) is parallel to the fifth main groove (50).

8. The tire of claim 6, wherein, The first group of shoulder blocks (110) is formed by a first pair of shoulder blocks (111, 112) separated by a first secondary groove (16) extending between the first main groove (10) and the third main groove (30); and wherein the second secondary groove (25) is aligned with the first secondary groove (16).

9. The tire of any one of claims 1 to 3, wherein, The first group of central blocks (100) is formed by a first pair of central blocks (101, 102) separated by a third secondary groove (35).

10. Tire according to claim 9, wherein, The third secondary groove (35) extends between the first main groove (10) and the fifth main groove (50).

11. The tire of claim 9, wherein, The third secondary groove (35) is inclined in a non-uniform manner with respect to the fifth main groove (50).

12. The tire of claim 9, wherein, The third secondary grooves (35) are aligned with the end portions of the other second primary grooves.

13. Tire according to any one of claims 1 to 3, wherein, Each third primary groove (30) is substantially parallel to the first primary groove (10).

14. Tire according to any one of claims 1 to 3, wherein, Each fourth primary groove (40) is substantially parallel to the second primary groove (20).

15. Tire according to any one of claims 1 to 3, wherein, The end portion (22) of the second primary groove (20) extends in a zigzag manner so as to cross the equatorial plane of the tyre.

16. A tire according to any one of claims 1 to 3, wherein, The end portion (22) of the second primary groove (20) comprises a first segment (23) extending from the first primary groove (10) towards the first shoulder region (4), a second segment (24) extending from the first segment (23) towards the second shoulder region (5) and a third segment (26) extending from the second segment (24) towards the first shoulder region (4) up to the other first primary groove.

17. The tire of claim 16, wherein, The first segment (23) and the third segment (26) of the end portion (22) are substantially parallel.

18. The tire of claim 4, wherein, The depth of the first secondary grooves is less than 50% of the depth of each of the primary grooves.

19. A tire according to any one of claims 1 to 3, wherein, The fifth primary groove (50) is inclined with respect to the circumferential direction by an angle comprised between 5° and 25°.

20. The tire of claim 9, wherein, The third secondary grooves (35) are inclined with respect to the circumferential direction by an angle comprised between 25° and 45°.

21. The tire of any one of claims 1 to 3, wherein, A respective radially outer surface is defined on the first group of shoulder blocks (110), on the second group of shoulder blocks (120) and on the first group of central blocks (100), and each of the radially outer surfaces has a respective area, the difference between the area of each of the radially outer surfaces and the average of the areas of the radially outer surfaces being less than 30% of the average.

22. A tyre according to any one of claims 1 to 3, wherein, A respective radially outer surface is defined on each of the blocks of the first group of shoulder blocks (110), on each of the blocks of the second group of shoulder blocks (120) and on each of the blocks of the first group of central blocks (100), and each of the radially outer surfaces of the blocks has a respective area, the difference between the area of each of the radially outer surfaces of the blocks and the average of the areas of the radially outer surfaces of the blocks being less than 30% of the average.

23. The tire of any one of claims 1 to 3, wherein, The depth of each primary groove is comprised between 6 mm and 12 mm.

24. The tire of claim 4, wherein, The depth of the first secondary grooves is comprised between 2.5 mm and 4.5 mm.

25. The tire of claim 6, wherein, The depth of the second secondary grooves is less than 50% of the depth of each of the primary grooves.

26. The tire of claim 9, wherein, The depth of the third secondary grooves is less than 50% of the depth of each of the primary grooves.

27. The tire of claim 6, wherein, The depth of the second secondary grooves is comprised between 2.5 mm and 4.5 mm.

28. The tire of claim 9, wherein, The depth of the third secondary grooves is comprised between 2.5 mm and 4.5 mm.

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