Tyre for vehicle wheels

Abstract

Tyre for vehicle wheels, the tyre comprising a tread band (2) on which are defined: a plurality of first pairs of main grooves 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 pair of main grooves, the second pairs of main grooves being formed by third and fourth main grooves (30, 40) extending from the first and second shoulder regions (4, 5) toward 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 successive first main grooves (10) and two successive second main grooves (20), respectively, and having a smaller inclination than the first and second main grooves (10, 20), respectively, but coincide with the first and second main trenches (10, 20). Each pair of consecutive first main grooves (10) circumferentially delimits: a first set of shoulder blocks (110) and a second set of shoulder blocks (120) separated from each other by a third main groove (30); and a first set of central blocks (100) separated from the first set of shoulder blocks (110) and the second set of shoulder blocks (120) by fifth main grooves (50).

Description

Technical Field

[0001] The present invention relates to a tire for a vehicle wheel, and more particularly to a winter tire. Background Art

[0002] A tire generally includes a carcass structure that is formed annularly about a rotational axis and includes at least one carcass ply having end flaps joined in respective annular anchoring structures (called bead cores).

[0003] A belt structure is provided at a radially outer position relative to the carcass structure. In the case of a motor vehicle tire, the belt structure includes at least two radially superposed rubberized fabric strips provided with reinforcing cords, which are generally made of metal and are arranged parallel to each other in each strip but cross the cords of adjacent strips, preferably symmetrically with respect to the equatorial plane of the tire.

[0004] Preferably, the belt structure also includes a third ply of fabric or metal cords arranged circumferentially (0 degrees) at least below the ends of the belt strips in a radially outer position. In a tubeless-type tire, there is also a radially inner layer called a "liner" that has an impermeable property in order to obtain the airtightness of the tire itself.

[0005] A tread band is applied at a radially outer position relative to the belt structure. The tread band is made of an elastomeric material and defines a tread surface intended for contact with the road surface on the tread band.

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

[0007] The main function of the grooves is to allow the drainage of the water present between the tire surface and the road surface during their mutual contact, thereby preventing the hydrostatic pressure caused by the impact of the water on the advancing tire from causing the tire to even partially lift off the road surface and as a result causing the vehicle to lose control.

[0008] In the case of a winter tire, small notches, called "sipes", are generally formed on the blocks of the tread band and extend from the tread surface of the tire towards the interior of the blocks. The function of the sipes is to provide additional gripping elements in the case of traveling on a snow-covered road surface and to retain a certain amount of snow, thereby improving the grip on the road surface.

[0009] In addition, studs can be provided on the blocks of the tread band, which improve the gripping characteristics on an icy road surface since a part of them projects from the tread band.

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

[0011] WO 2020012277 under the same applicant describes a winter tire, the tread pattern of which is formed by a plurality of corresponding shoulder blocks and central blocks arranged successively along the circumferential development of the tread band.

[0012] The term "circumferential" direction refers to a direction that is substantially parallel to the rotation direction of the tire, or a direction that is inclined at most slightly (up to about 5°) relative to the rotation direction of the tire.

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

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

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

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

[0017] The term "shoulder region" of the tread band refers to such a portion of the tread band that extends circumferentially at the axially outer positions of the tread band on the opposite sides of the central region up to the axially ends of the tread band.

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

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

[0020] When the groove extends in the circumferential direction or is inclined at most less than 5° relative to the circumferential direction, the groove is called a "circumferential" groove.

[0021] When the groove extends along a direction inclined at an acute angle of at least greater than 10° relative to the circumferential direction, the groove is called a "lateral" groove.

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

[0023] The width of the knife groove and the groove shall 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 the groove or the knife groove varies along its longitudinal development, the average width is considered and its value is obtained as the average of different width values, which are appropriately weighted according to the relevant longitudinal range. For example, if the width of the groove is 5 mm over 80% of its longitudinal range and 3 mm over the remaining 20%, the average width to be considered is 5×0.8 + 3×0.2 = 4.6 mm.

[0025] Similarly, if the width of the groove (especially the width of the transverse groove) varies along the tread band according to the length of 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 "main" groove. Preferably, the width of the main 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 the 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 special case, the inclination of a groove extending parallel to the tire axis with respect to the circumferential direction is 90°.

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

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

[0032] When the offset value of the longitudinal axes of two grooves is less than the width of the largest groove at least in the region of their corresponding facing ends, the two grooves are "substantially aligned".

[0033] Considering the rotation of the tire in either of its two rotational directions, when two grooves are arranged one after another on the tread surface, the two grooves are "successive". In particular, when no other grooves with the same configuration are provided between two grooves with the same configuration, the two grooves with the same configuration are successive.

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

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

[0036] Thus, a block is considered both a portion of the tread band with a closed contour delimited by three or more grooves and a circumferential rib delimited by a pair of grooves developing circumferentially around the tread band.

[0037] A block formed in the central region of the tread band is defined as a "central block", while a block formed in the shoulder region of the tread band is defined as a "shoulder block".

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

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

[0040] When the tread pattern is configured to be mounted on a vehicle so as to rotate along a preferred direction of travel, the tread pattern belongs to the "directional" type of tread pattern.

[0041] A "module" of the tread pattern is defined by the smallest portion of the tread band extending between the axial ends of the tread band, the configuration of which module develops successively and repeats circumferentially along the tread band so as to form said tread band.

[0042] Furthermore, while maintaining the same basic configuration, the modules can have circumferential dimensions (referred to as "pitches") that are slightly different from each other. For example, on the tread band, modules with two, three or four different pitches can be used, and the pitches are combined with each other in various ways.

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

[0044] In this case, it is stipulated that each basic part can have the same basic configuration in different modules, but the circumferential dimensions (i.e., "pitches") are slightly different from each other, such that each module can be formed by basic parts with different pitches.

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

[0046] When the corresponding lengths of two or more elements differ by at most a range equal to 10% of the maximum length, the lengths of these two or more elements are "substantially equal".

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

[0048] When two elements (such as, for example, two blocks or two grooves) are spaced apart from each other in the circumferential direction of the tread band, they are "axially offset" or "offset with respect to the axial direction". Summary of the Invention

[0049] The applicant has preliminarily observed that the performance level of a tire on a snow-covered surface depends to a certain extent on the number and extent of the sipes formed in the blocks. In particular, the applicant has noted that, for the same tread pattern, blocks in which more sipes are formed provide better behavior on snow.

[0050] However, the 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, especially tangential stresses.

[0051] Due to this weakening, during braking, acceleration or cornering, the blocks may undergo corresponding deformations, thus causing the blocks to lift off the road surface portion, resulting in a reduction in the contact area between the blocks and the road surface and thus a reduction in the total frictional force exerted by the tire on the road surface.

[0052] The applicant has also observed that the lower stiffness of the blocks can also have a negative impact on the performance level of studded tires.

[0053] In fact, the applicant has confirmed that studs fixed to deformable blocks not only have poor grip on an icy surface, but may also be more easily pulled out of their seats, resulting in the studs detaching from the tread band and thus causing an irreversible loss of efficiency when driving on an icy surface.

[0054] In fact, the Applicant has demonstrated that the ability of the tyre to keep the studs in seats properly arranged in the tread band is a key parameter for the studded tyre to obtain an adequate level of performance during its useful life.

[0055] The Applicant has also observed that responding to this requirement is usually achieved by shaping and dimensioning the seat for receiving the cleat and the portion of the cleat intended to be received in the seat so as to create a high degree of interference with the movements that may occur when the cleat leaves the seat.

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

[0057] The Applicant has therefore considered that, in order to improve the gripping behaviour of the stud and its ability to remain in the seat, it may be advantageous to configure the tread pattern so as to limit as much as possible excessive local deformations of the tread band, and in particular of the individual blocks.

[0058] To achieve this aim, the Applicant has considered that the tread pattern should be configured not only to have the highest possible stiffness characteristics, but also to make the stiffness as uniform as possible in the different areas of the tread band, so as to distribute possible tangential stresses in the most uniform way possible.

[0059] In order to meet these two requirements, without compromising the ability to drain water from the tread band, the Applicant has considered that it would be possible to use grooves of greater depth in order to define a relatively large area on the tread band, while grooves of smaller depth could be used within said large area in order to define two or more blocks.

[0060] The Applicant has thus gained greater freedom in designing the tread pattern, being able to configure large areas formed by a plurality of blocks to have mutually homogeneous properties (e.g. similar surface extent) even though, in the presence of a plurality of blocks, said blocks individually may differ greatly from one another.

[0061] Finally, the Applicant has discovered that by defining in a suitable manner on the tread band a corresponding plurality of main grooves which extend from the shoulder region towards the equatorial plane and which are connected to one another so as to define a first group of shoulder blocks and a second group of shoulder blocks which alternate circumferentially with respect to one another and a first group of central blocks which are axially inside and adjacent to the two groups of shoulder blocks, a tread pattern is obtained which is suitable for withstanding tangential stresses in a uniform manner, thereby preventing excessive local deformation of the blocks and thereby increasing the ability to retain the studs in the corresponding receiving seats.

[0062] In particular, in its first aspect, the present invention relates to a tire for a vehicle wheel, said tire comprising a tread band.

[0063] Preferably, a first shoulder region and a second shoulder region that are axially opposite to each other and a central region 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 are defined on the tread band, and the plurality of first pairs of main grooves develop circumferentially along the tread band and are arranged in a regular successive manner.

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

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

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

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

[0069] Preferably, the second main groove includes an end portion that is axially internal and extends between the first main groove and another first main groove belonging to a subsequent first pair of main grooves.

[0070] Preferably, a plurality of second pairs of main grooves are defined on the tread band, and the plurality of second pairs of main grooves develop circumferentially along the tread band and are arranged in a regular successive manner.

[0071] Preferably, the second pairs of main grooves are arranged on the tread band at alternating positions with respect to the 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 the central region and a fourth main groove extending from said second shoulder region towards the central region.

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

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

[0075] Preferably, a plurality of third pairs of main grooves are defined in the tread band, and the plurality of third pairs of main grooves extend circumferentially along the tread band and are arranged in a regular successive manner.

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

[0077] Preferably, the fifth main groove extends between two first main grooves in the mutually successive first pair of main grooves.

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

[0079] Preferably, the fifth main groove has an inclination smaller than that of the first main groove with respect to the circumferential direction.

[0080] Preferably, the fifth main groove has an inclination consistent with that of the first main groove.

[0081] Preferably, the sixth main groove extends between two second main grooves in the mutually successive first pair of main grooves.

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

[0083] Preferably, the sixth main groove has an inclination smaller than that of the second main groove with respect to the circumferential direction.

[0084] Preferably, the sixth main groove has an inclination consistent with that of the second main groove.

[0085] Preferably, each pair of successive first main grooves circumferentially defines a first set of shoulder blocks and a second set of shoulder blocks.

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

[0087] Preferably, the first set of shoulder blocks and the second set of shoulder blocks are separated from each other by the third main groove.

[0088] Preferably, each pair of successive first main grooves circumferentially defines a first set of central blocks, and the first set of central blocks is separated from the fifth main groove by the first set of shoulder blocks and the second set of shoulder blocks.

[0089] The applicant believes that a tire constructed according to the above aspects of the present invention advantageously allows for providing a substantially uniform behavior when subjected to axial tangential stress and circumferential tangential stress in various regions of the tread band.

[0090] Therefore, when the tread band is provided with grooves and studs, the tire has an optimal behavior on mutually different road surfaces (dry road surfaces, wet road surfaces, and snow-covered or icy road surfaces).

[0091] More specifically, the applicant believes that the provision of the main grooves allows water to be rapidly discharged from the central region towards the opposite shoulder regions. In particular, this behavior is caused by the first pair of main grooves, which are interconnected in the region of their axial inner ends and connected to the first pair of successive transverse grooves. In this way, a network of channels is formed in which water can be collected and rapidly conveyed towards the shoulder regions.

[0092] In addition, 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 interconnected, thus preventing the central region from being weakened.

[0093] Finally, the substantially uniform behavior of the tread band with respect to the tangential stress allows the tread pattern of the tire according to the invention to be advantageously used as a basis for a studded tire.

[0094] In the above aspects, the invention can have at least one of the following additional preferred features.

[0095] In some embodiments, each pair of successive second main grooves circumferentially delimits a third set of shoulder blocks and a fourth set of shoulder blocks.

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

[0097] Preferably, the third set of shoulder blocks and the fourth set of shoulder blocks are separated from each other by the fourth main groove.

[0098] Preferably, each pair of successive second main grooves circumferentially delimits a second set of central blocks.

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

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

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

[0102] In some embodiments, the first set of shoulder blocks is substantially symmetric with respect to the third set of shoulder blocks about the equatorial plane.

[0103] In some embodiments, the second set of shoulder blocks is substantially symmetric about the equatorial plane with respect to the fourth set of shoulder blocks.

[0104] In some embodiments, the first set of central blocks is substantially symmetric about the equatorial plane with respect to the second set of central blocks.

[0105] In this way, the configurations of the first set of shoulder blocks, the second set of shoulder blocks, and the first set of central blocks are arranged in a substantially symmetric manner on the two halves of the tread band, so that the tread band obtains particularly balanced performance.

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

[0107] Preferably, the blocks in the first set of shoulder blocks are separated by a first groove that extends between the first main groove and the third main groove.

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

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

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

[0111] Preferably, the blocks in the second set of shoulder blocks are separated by a second groove that extends between the third main groove and the other first main groove subsequent to the first main groove.

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

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

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

[0115] Thereby, a single outflow direction of water from the first and second sets of shoulder blocks towards the first and third main grooves is defined, thus facilitating the rapid drainage of water from them when driving on a wet road surface.

[0116] In some embodiments, the first set of central blocks is formed by a first pair of central blocks.

[0117] Preferably, the blocks in the first set of central blocks are separated by a third groove.

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

[0119] Preferably, the third groove extends between the first main groove and the fifth main groove.

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

[0121] Preferably, the third groove is aligned with an end portion of another second main groove.

[0122] In some embodiments, the 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, the first central block has a V shape and includes: a vertex pointing to the first shoulder region; and a pair of branches extending in respective directions towards the second shoulder region and having opposite inclinations with respect to the circumferential direction.

[0124] Preferably, the second central block has a generally triangular shape.

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

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

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

[0128] Preferably, the blocks in the third set of shoulder blocks are separated by a fourth groove that extends between the second main groove and the fourth main groove.

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

[0130] In some embodiments, the fourth groove is parallel to the sixth main groove.

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

[0132] Preferably, the blocks in the fourth set of shoulder blocks are separated by a fifth groove that extends between the fourth main groove and the other second main groove subsequent to the second main groove.

[0133] In this way, the blocks forming the fourth set of shoulder blocks are separated from each other by grooves having a relatively small depth (less than 5 mm) so as to be connected to each other relatively and thus the whole is not easily deformed.

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

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

[0136] Thereby, a single outflow direction of water from the third set of shoulder blocks and the fourth set of shoulder blocks towards the second main groove and the fourth main groove is defined, thereby facilitating the rapid discharge of water from it when driving on a wet road surface.

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

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

[0139] In this way, the blocks forming the second set of central blocks are separated from each other by grooves having a relatively small depth (less than 5 mm) so as to be connected to each other relatively and thus the whole is not easily deformed.

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

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

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

[0143] Preferably, the third central block has a V shape and includes: a vertex pointing 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, although being in a staggered state with respect to the axial direction, the third central block is substantially mirror-image with respect to the first central block.

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

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

[0147] In this way, the first central block and the third central block are partially embedded in each other and assist each other to withstand tangential stress.

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

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

[0150] Preferably, the fourth central block has a generally triangular shape.

[0151] Preferably, each of the first main grooves includes a first portion having a curved path that extends from the first shoulder region toward the equatorial plane of the tread band and whose inclination with respect to the circumferential direction generally decreases from the first shoulder region toward the central region.

[0152] Preferably, each of the second main grooves includes a first portion having a curved path that extends from the second shoulder region toward the equatorial plane of the tread band and whose inclination with respect to the circumferential direction generally decreases from the second shoulder region toward the central region.

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

[0154] In this way, when the tire rotates in a predetermined direction corresponding to the preferred forward direction, the discharge of water from the central region toward the corresponding shoulder regions is particularly promoted.

[0155] Preferably, the first portions of each of the first main grooves and the second main grooves have a curved path without any inflection points.

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

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

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

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

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

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

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

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

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

[0165] Preferably, each of the first and / or second and / or third and / or fourth and / or fifth and / or sixth grooves has a depth 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] Thus, since the impacts of the edges of the corresponding grooves with the ground are staggered with each other, the noise generated when the tire rolls on the road surface is advantageously reduced, thereby reducing the intensity of the overall noise generated.

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

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

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

[0172] Preferably, the end portion of the second main groove includes a second segment that continues the extension of the first segment, more preferably extending towards the second shoulder region.

[0173] Preferably, the end portion of the second main groove includes a third segment that continues the extension of the second segment, more preferably extending towards the first shoulder region until the other first main groove.

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

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

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

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

[0179] In some embodiments, corresponding radially outer surfaces are defined on the first set of shoulder blocks, the second set of shoulder blocks, and the first set of central blocks, and each of the radially outer surfaces has a corresponding area that differs from the average value of the areas of the radially outer surfaces by a value less than 30% of the average value, preferably less than 25% of the average value.

[0180] In some embodiments, corresponding radially outer surfaces are defined on each block of the first set of shoulder blocks, the second set of shoulder blocks, and the first set of central blocks, and each of the radially outer surfaces of the blocks has a corresponding area that differs from the average value of the areas of the radially outer surfaces of the blocks by a value less than 30% of the average value, preferably less than 25% of the average value.

[0181] In some embodiments, a tread pattern is defined on the tread band, the tread pattern being formed by the overall of all the grooves and all the blocks; and a module is defined, the module being formed by a smallest part of the tread band extending between the axial ends of the tread band, the configuration of the module repeating successively along the circumferential development of the tread band so as to form the tread pattern.

[0182] Preferably, the module is formed by a part of the tread band located between two pairs of said first main grooves that are successive to each other.

[0183] Preferably, the module is formed by a first basic part extending from the first pair of main grooves to the second pair of main grooves and a second basic part extending from the second pair of main grooves to the successive first pair of main grooves.

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

[0185] In some embodiments, blocks are provided on at least some of the blocks defined on the tread band. Description of the Drawings

[0186] With reference to the attached drawings, the features and advantages of the present invention will be better understood from the detailed description of several preferred embodiments of the present invention shown by way of non-limiting examples, in which:

[0187] - Figure 1 is a front view of a tire for a vehicle wheel constructed according to the present invention;

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

[0189] - Figure 3 is Figure 1 a schematic view of a main part of the tread band of the tire of

[0190] - Figure 4 is a schematic view of a part of the tread band drawn to an enlarged scale, which part of the tread band represents Figure 1 the module of the tread band of the tire of Detailed Description

[0191] With reference to the attached drawings, a tire for a vehicle wheel constructed according to the present invention is generally designated by the reference numeral 1 as a whole.

[0192] The tire 1 includes a tire structure (not shown in the drawings) that is conventional per se and a tread band 2, on which a tread surface 3 is defined, the tread surface being arranged at a radially outer position relative to the tread band 2 and intended for contact with the road surface.

[0193] The tire 1 has a conventional generally annular shape that develops around a rotation axis, an axial direction Y parallel to the rotation axis is defined on the tread surface 3, and an equatorial plane X passes through the axial direction, the equatorial plane being perpendicular to the rotation axis and defining a circumferential direction parallel to the equatorial plane on the tread surface 3.

[0194] The tread band 2 has a width L that is determined as the maximum width by which the tread band is intended to come into contact with the ground under standard use conditions.

[0195] The tire 1 is an oriented tire, in which a preferred rolling direction of the tire is defined, the rolling direction being indicated by an arrow F in the figure.

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

[0197] On the tread band 2, a plurality of first pairs of main grooves are defined, the plurality of first pairs of main grooves developing circumferentially along the tread band 2 and being arranged successively and regularly, 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 that extends transversely from the first shoulder region 4 towards the central region 6 and a second main groove 20 that extends transversely from the second shoulder region 5 towards the central region 6.

[0199] Each first main groove 10 includes a first portion 11 that extends from an axially outer end 10a that is open at the first lateral edge 4a of the first shoulder region 4 until an axially inner end 10b that is open at the second main groove 20.

[0200] In particular, the first main groove 10 joins the second main groove 20 shortly after passing through the equatorial plane X. The first portion 11 has a curved course without any inflection points and the inclination with respect to the circumferential direction generally decreases from the first shoulder region 4 towards the central region 6, starting from an inclination of approximately 80° in the region of the axially inner end 10a until an inclination of approximately 30° in the region of the axially inner end 10b.

[0201] Each second main groove 20 includes a first portion 21 that extends from an axial outer end 20a that opens at a second lateral edge 5a of the second shoulder region 5 until a connection portion relative to the axial inner end 10b of the first main groove 10.

[0202] Similar to the first portion 11 of the first main groove 10, the first portion 21 of the second main groove 20 also has a curved path without any inflection points and the inclination with respect to the circumferential direction generally decreases from the second shoulder region 5 towards the central region 6, starting from an inclination of approximately 80° in the region of the axial inner end 20a until an inclination of approximately 30° in the region of the contiguous position with the axial inner end 10b of the first main groove 10.

[0203] Each second main groove 20 further includes an end portion 22 that is located axially inward and continues the extension of the first portion 21 until its axial inner end 20b opens into an additional first main groove 10 that follows the first main groove 10, and the first main groove 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 broken-line configuration and includes: a first segment 23 that continues the first portion 21 towards the first shoulder region 4; a second segment 24 that continues the first segment 23 towards the second shoulder region 5; and a third segment 26 that continues the second segment 24 towards the first shoulder region 4 until the axial inner end 20b. In particular, the third segment 26 is connected to the additional first main groove 10 shortly after passing through the equatorial plane X.

[0205] Thus, an inner end region 15 is still defined on the first portion 11 of the additional first main groove 10 and thus on the first portion 11 of each first main groove 10, and the inner end region is bounded by the end 20a of the second main groove 20 and the axial 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 straight-line shaped. More specifically, they are bent with a radius of curvature between 120 mm and 150 mm, and extend so as to straddle the equatorial plane X of the tread band 2, and are alternately inclined in a non-uniform 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 broken line is formed in a zigzag manner and the broken line 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] The broken line develops continuously along the entire circumferential range of the equatorial plane X and crosses the equatorial plane in each of its successive parts.

[0209] Therefore, the first main groove 10 and the second main groove 20 in each first pair have substantially similar orientations, where the relevant parts of the corresponding first parts 11 and 21 are substantially symmetric with respect to the equatorial plane X and have a concave shape pointing to the same side of the tread band 2.

[0210] However, the second main groove 20 is axially offset with respect to the first transverse groove 10. In fact, the offset value between the corresponding axial outer ends 10a and 20a is between 5 mm and 20 mm, preferably between 10 mm and 20 mm, and this value is measured in the circumferential direction.

[0211] A plurality of second pairs of main grooves are also defined on the tread band 2, and the plurality of second pairs of main grooves are arranged successively and regularly along the circumferential direction of the tread band 2, and their positions are alternating with respect to the first pair 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 open 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 open in the second shoulder region 5 and an axially inner end 40a.

[0215] The third main groove 30 and the fourth main groove 40 have similar curved orientations, and the third main groove and the fourth main groove are substantially parallel to the first main groove 10 and the second main groove 20 respectively.

[0216] In addition, although the third main groove 30 and the fourth main groove 40 are axially offset from each other, they are substantially symmetric with respect to the equatorial plane X. In particular, the offset value between the corresponding ends 30a and 40a is between 5 mm and 20 mm, preferably between 10 mm and 20 mm, and this value is measured in the circumferential direction.

[0217] Advantageously, even though there is no contact point between these grooves, the second segment 24 of the end portion 22 is located on the theoretical extension of the third main groove 30.

[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] On the tread band 2, a plurality of third pairs of main grooves are further defined, and the plurality of third pairs of main grooves are arranged successively and regularly along the circumferential direction 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. Although they are axially offset, they are substantially symmetric with respect to each other about the equatorial plane X.

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

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

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

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

[0225] The depths of 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 are about 8.5 mm. In addition, the first main grooves 10, second main grooves 20, third main grooves 30 and fourth main grooves 40 have variable widths, and the widths decrease from the corresponding axial outer ends towards the axial inner ends. In particular, the widths of these main grooves vary from about 7 mm to 10 mm in the regions corresponding to the shoulder regions to a value 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 variable widths between 2.5 mm and 4 mm.

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

[0228] Each pair of successive first main grooves 10 circumferentially defines 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 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.

[0229] Similarly, each pair of successive second main grooves 20 circumferentially defines 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 main groove 40, and a second group of central blocks 150 separated from the third group of shoulder blocks 130 and the fourth group of shoulder blocks 140 by a sixth main groove 60.

[0230] Since the main grooves defining the block groups are substantially symmetric 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 central blocks 150 are substantially symmetric with respect to the first group of shoulder blocks 110, the second group of shoulder blocks 120, and the first group of central blocks 100, respectively.

[0231] The first group of central blocks 100 and the second group of central blocks 150 are separated by an end portion 22 of the second main groove 20.

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

[0233] The first group of shoulder blocks 110 is formed by a first pair of shoulder blocks 111, 112 which are separated from each other by a first groove 16 that extends between the first main groove 10 and the third main groove 30.

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

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

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

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

[0238] The fourth groove 45 and the fifth groove 55 are substantially aligned with each other and are substantially parallel to the sixth main 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 axially internal central block 101 and a second central block 102. The second central block is axially external to the first central block 101 and is separated from the first central block 101 by a third groove 35.

[0240] The third groove 35 extends between the first main groove 10 and the fifth main groove 50. The third groove is inclined in a non-uniform manner with respect to the fifth main groove 50, and the inclination angle is approximately 35°.

[0241] The first central block 101 has a V-shaped configuration and includes: a vertex that points towards the first shoulder region 4; and a pair of branches that extend in respective directions having opposite inclinations with respect to the circumferential direction towards the second shoulder region 5.

[0242] The second central block 102 has a generally triangular shape, and its longest side faces the axially internal blocks 112 and 122 of the first set of shoulder blocks 110 and the second set of shoulder blocks 120, respectively.

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

[0244] The sixth groove 65 extends between the second main groove 20 and the sixth main groove 60. The sixth groove is inclined in a non-uniform manner with respect to the sixth main groove 60, and the inclination angle is approximately 35°.

[0245] The third central block 151 has a V-shaped configuration and includes: a vertex that points towards the second shoulder region 5; and a pair of branches that extend in respective directions having opposite inclinations with respect to the circumferential direction towards the first shoulder region 4.

[0246] The fourth central block 152 has a generally triangular shape, and its longest side faces the axially internal blocks 132 and 142 of the third set of shoulder blocks 130 and the fourth set of shoulder blocks 140, respectively.

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

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

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

[0250] Each third central block 151 and each first central block 101 have corresponding concave shapes that point towards each other and are at least partially aligned not only in the axial direction Y but also in the circumferential direction X. In other words, the corresponding projections of the first central block 101 and the third central block 151 in the circumferential direction partially overlap. In particular, the branches of each first central block 101 are at least partially received in the concave shape of the third central block 151, and vice versa, the branches of each third central block 151 are at least partially received in the concave shape of the first central block 101.

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

[0252] The blocks and grooves identified above generally define the tread pattern of the tire 1.

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

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

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

[0256] In particular, the long pitch is approximately 30% more than the short pitch.

[0257] Each module M can be formed by a first basic portion and a second basic portion that have short pitches or long pitches combined with each other in various ways such that modules having first basic portions and second basic portions that all have long pitches, or modules having first basic portions and second basic portions that all have short pitches, or modules having a first basic portion with a short pitch and a second basic portion with a long pitch, or finally modules having a first basic portion with a long pitch and a second basic portion with a short pitch are provided on the tread pattern.

[0258] The above-mentioned sipes are formed on all of the blocks, and the sipes improve the performance level of the tire in snowy road conditions.

[0259] In particular, on the blocks of the first set of blocks 100 and the second set of blocks 150, there are formed knife grooves extending substantially along the axial direction Y, while on the axial inner blocks of the set of shoulder blocks 110, 120, 130 and 140, there are formed knife grooves developing along the transverse direction with respect to the main development direction of the blocks (defined by the development direction of the first or second main groove), and on the axial outer blocks of the set of shoulder blocks 110, 120, 130 and 140, there are formed knife grooves extending in a direction substantially parallel to the main development direction of the blocks (also defined by the direction of the first or second main groove).

[0260] A plurality of studs 200 can also be provided at appropriate positions on different blocks of the tread band 2 of the tire 1, as Figure 2 can be seen in the construction variant of the tire 1 shown, so as to make it particularly suitable for traveling on icy surfaces.

[0261] On each set of shoulder blocks and each set of central blocks, there is defined a corresponding radially outer surface, which in fact constitutes a part of the tread surface 3.

[0262] Due to the configuration of the above-mentioned grooves and blocks, each of these 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 differs from the average value of these radially outer surfaces by a value less than 25%.

[0263] Moreover, each of the blocks forming different shoulder groups also has a corresponding radially outer surface, which differs from the average value of the radially outer surfaces of these blocks by a value less than 25%.

[0264] Obviously, due to the above-mentioned symmetry relationship, the same relationship between the radially outer surfaces also applies to the third set of shoulder blocks 130 and the fourth set of shoulder blocks 140 and the second set of central blocks 150.

[0265] In this way, the tread band 2 is subdivided by the main grooves into areas (block groups) in contact with the road surface, which have a substantially uniform area.

[0266] This enables the tread band to respond to the tangential stress in a substantially uniform manner, thereby preventing excessive local deformation that may damage the road grip of the tire 1, and in the case of a studded tire, allowing a reduction in the possibility of the studs being pulled out from the corresponding seats.

[0267] Example

[0268] A tire of size 205 / 55R16 is constructed according to the above-described embodiment of the present invention.

[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, and the percentage differences of the surface ranges of each block set relative to the average of these surface ranges.

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

[0271] Block group <![CDATA[Surface (mm 2 )]]> Percentage difference relative to the average value First set of shoulder blocks 1104 -6.8％ Second set of shoulder blocks 1313 +21.6％ First set of central blocks 1138 -7.9％

[0272] Table 1

[0273] It will be noted that the percentage values by which the radially outer surfaces of the blocks in each group differ from the surface average are less than 25% of the average, such that the surface ranges of each group of blocks in contact with the road surface are substantially the same, thereby providing a substantially uniform resistance to tangential stress.

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

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

[0276] Block <![CDATA[Surface (mm 2 )]]> Percentage difference relative to the average value Axial outer blocks of the first set of shoulder blocks 543 -8.3％ Axial inner blocks of the first set of shoulder blocks 561 -5.4％ Axial outer blocks of the second set of shoulder blocks 733 +23.7％ Axial inner blocks of the second set of shoulder blocks 580 -2.1％ Axial outer blocks of the first set of central blocks 504 -15％ Axial inner blocks of the first set of central blocks 635 +7.1％

[0277] Table 2

[0278] In this case, it can also be noted that the percentage values by which the radially outer surfaces of the individual blocks in each group of blocks differ from the surface average are less than 25% of the average, such that the surfaces of each block in contact with the road surface are substantially the same as those of the other blocks, thereby providing a substantially uniform resistance to tangential stress.

[0279] Table 3 below lists respectively the stiffness values of the first set of shoulder blocks 110, the second set of shoulder blocks 120, and the first set of central blocks 100 obtained by finite element simulation calculations, and the percentage differences of the stiffness values of each group of blocks relative 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 motion applied to the block itself.

[0280] Block group <![CDATA[Stiffness (N / mm 3* 100)]]> Percentage difference relative to the average value First set of shoulder blocks 14.6 +0.01％ Second set of shoulder blocks 14.5 -0.79％ First set of central blocks 14.7 +0.85％

[0281] Table 3

[0282] Thus, it can be observed that the stiffness values of the block groups are generally similar when the tangential stresses applied to the block groups have an axial direction and when these tangential stresses have a circumferential direction.

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

Claims

1. A tire for a vehicle wheel, the tire comprising a tread band (2), on which are defined: - a first shoulder region (4) and a second shoulder region (5) axially opposite each other; - a central region (6) between the first shoulder region (4) and the second shoulder region (5); - a plurality of first pairs of main grooves, the plurality of first pairs of main grooves extending circumferentially along the tread band in a regular successive manner, each first pair of main grooves being formed by the following grooves: i. The first main groove (10) extends from the first shoulder region (4) towards the central region (6) and the inclination with respect to the circumferential direction decreases from the first shoulder region (4) towards the central region (6); and ii. a second main groove (20), the second main groove extending from the second shoulder region (5) towards the central region (6) and having an inclination with respect to the circumferential direction that decreases from the second shoulder region (5) towards the central region (6); wherein the first main groove (10) includes an axially inner end (10b) connected to the second main groove (20), and wherein the second main groove (20) includes an end portion (22) that is axially internal and extends between the first main groove (10) and another first main groove belonging to a subsequent first pair of main grooves, - a plurality of second pairs of main grooves, the plurality of second pairs of main grooves extending circumferentially along the tread band in a regular successive manner in alternating positions with respect to the first pair of main grooves (10, 20), each second pair of main grooves being formed by the following grooves: i. a third main groove (30), the third main groove extending from the first shoulder region (4) towards the central region (6) and having an inclination with respect to the circumferential direction that decreases from the first shoulder region (4) towards the central region (6); and ii. a fourth main groove (40), the fourth main groove extending from the second shoulder region (5) towards the central region (6) and having an inclination with respect to the circumferential direction that decreases from the second shoulder region (5) towards the central region (6), - a plurality of third pairs of main grooves, the plurality of third pairs of main grooves extending circumferentially along the tread band in a regular successive manner, each third pair of main grooves being formed by the following grooves: i. a fifth main groove (50), the fifth main groove extending between two first main grooves (10) of successive first pairs of main grooves and connected to the axially inner end (30b) of the third main groove (30), and having an inclination with respect to the circumferential direction that is less than that of the first main groove (10) and is consistent with that of the first main groove (10), and ii. a sixth main groove (60), the sixth main groove extending between two second main grooves (20) of successive first pairs of main grooves and connected to the axially inner end (40b) of the fourth main groove (40), and having an inclination with respect to the circumferential direction that is less than that of the second main groove (20) and is consistent with that of the second main groove (20), Among them, each pair of successive first main grooves (10) circumferentially defines: a first group of shoulder blocks (110) and a second group of shoulder blocks (120), the first group of shoulder blocks and the second group of shoulder blocks extending from the first shoulder region (4) towards the central region (6) and being separated from each other by the third main groove (30); a first group of central blocks (100), the first group of central blocks being separated from the first group of shoulder blocks (110) and the second group of shoulder blocks (120) by the fifth main groove (50).

2. The tire according to claim 1, wherein, Each pair of successive second main grooves (20) circumferentially defines: a third group of shoulder blocks (130) and a fourth group of shoulder blocks (140), the third group of shoulder blocks and the fourth group of shoulder blocks extending from the second shoulder region (5) towards the central region (6) and being separated from each other by the fourth main groove (40); a second group of central blocks (150), the second group of central blocks being separated from the third group of shoulder blocks (130) and the fourth group of shoulder blocks (140) by the sixth main groove (60).

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

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

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

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

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

8. The tire according to claim 6 or 7, wherein, The second groove (25) is aligned with the first groove (16).

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

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

11. The tire according to claim 9 or 10, wherein, The third groove (35) is inclined with respect to the fifth main groove (50) in a non-uniform manner.

12. The tire according to claim 9 or 10 or 11, wherein, The third groove (35) is aligned with the end portion of another second main groove.

13. The tire according to any one of the preceding claims, wherein, Each third main groove (30) is substantially parallel to the first main groove (10).

14. The tire according to any one of the preceding claims, wherein, Each fourth main groove (40) is substantially parallel to the second main groove (20).

15. The tire according to any one of the preceding claims, wherein, The end portion (22) of the second main groove (20) extends in a zigzag manner so as to straddle the equatorial plane (X) of the tread band (2).

16. The tire according to any one of the preceding claims, wherein, The end portion (22) of the second main groove (20) includes a first segment (23) extending from the first main groove (10) towards the first shoulder region (4), a second segment (24) continuing the first segment (23) and extending towards the second shoulder region (5), and a third segment (26) continuing the second segment (24) and extending towards the first shoulder region (4) until the other first main groove.

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

18. The tire according to any one of claims 4 to 17, wherein, The depth of each of the secondary grooves is less than 50% of the depth of each of the main grooves.

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

20. The tire according to any one of the preceding claims, wherein, The third secondary groove (35) is inclined at an angle between 25° and 45° with respect to the circumferential direction.

21. The tire according to any one of the preceding claims, wherein, Corresponding radially outer surfaces are defined on the first set of shoulder blocks (110), the second set of shoulder blocks (120) and the first set of central blocks (100), and each of the radially outer surfaces has a corresponding area that differs from the average value of the areas of the radially outer surfaces by a value less than 30% of the average value.

22. The tire according to any one of the preceding claims, wherein, Corresponding radially outer surfaces are defined on each of the blocks in the first set of shoulder blocks (110), the second set of shoulder blocks (120) and the first set of central blocks (100), and each of the radially outer surfaces of the blocks has a corresponding area that differs from the average value of the areas of the radially outer surfaces of the blocks by a value less than 30% of the average value.

23. The tire according to any one of the preceding claims, wherein, The depth of each main groove is between 6 mm and 12 mm.

24. The tire according to any one of claims 4 to 23, wherein, The depth of each secondary groove is between 2.5 mm and 4.5 mm.

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