WO2024127200A1

WO2024127200A1 - Tyre for vehicles wheels

Info

Publication number: WO2024127200A1
Application number: PCT/IB2023/062452
Authority: WO
Inventors: Giovanni Casarotto; Riccardo Guerra; Diego Ettore Speziari
Original assignee: Pirelli Tyre S.P.A.
Priority date: 2022-12-13
Filing date: 2023-12-11
Publication date: 2024-06-20

Abstract

A tyre for vehicle wheels, comprising a tread band (2), on which there are defined a plurality of first groups of shoulder blocks (110) which extend from a first shoulder region (4) towards a central region (6) of the tread band (2), a plurality of second groups of shoulder blocks (120) which extend from the first shoulder region (4) towards the central region (6) and which alternate with the first groups of shoulder blocks (110), and a plurality of first groups of central blocks (100) which are adjacent and axially internal with respect to a respective first group of shoulder blocks (110) and a respective second group of shoulder blocks (120). The groups of blocks (110, 120, 100) are separated from each other by at least one main groove (10, 30, 50) while the blocks (111, 112; 121, 122; 101, 102) inside each group of blocks are separated from each other by at least one secondary groove (16, 25, 35). The areas of the respective radially external surfaces of the groups of blocks differ from a mean value of the areas of these radially external surfaces by a value less than 30% of said mean value.

Description

Tyre for vehicle wheels

The present invention relates to a tyre for vehicle wheels, in particular a winter tyre. A tyre generally comprises a carcass structure which is toroidally shaped about a rotation axis and which comprises at least one carcass ply which has end flaps which are engaged in respective annular anchoring structures, called bead cores.

In a radially external position with respect to the carcass structure, there is provided a belt structure comprising, in the case of tyres for cars, at least two radially superimposed strips of rubber-coated fabric which is provided with reinforcement cords, usually made of metal, which are arranged in each strip parallel with each other but in a crosswise manner relative to the cords of the adjacent strip, preferably symmetrically with respect to the equatorial plane of the tyre.

In a radially external position, the belt structure preferably further also comprises, at least at the ends of the belt strips underneath, a third layer of textile or metal cords, which are arranged circumferentially (at 0 degrees). In tyres of the tubeless type, there is further present a radially internal layer, called a liner, which has characteristics of impermeability in order to ensure the air-tightness for the tyre itself. In a radially external position with respect to the belt structure, there is applied a tread band which is made from an elastomer material and on which a tread surface which is intended for contact with the road surface is defined.

The tyres, in order to ensure adequate road grip even on a wet road surface, have a tread band which is provided with grooves of various shapes and geometries, which delimit tread band portions which are intended for contact with the ground, called blocks.

The main function of the grooves is to allow the discharge of the water present between the surface of the tyre and the road surface during mutual contact, preventing the hydrostatic pressure resulting from the impact of the water against the advancing tyre from being able to cause even partial lifting of the tyre off the road surface and the consequent loss of control of the vehicle.

In the case of winter tyres, there are generally formed on the blocks of the tread band small notches, called "sipes", which extend from the tread surface of the tyre towards the interior of the block. The objective of the sipes is to provide additional gripping elements in the event of travel on snow-bound surfaces and to retain a specific quantity of snow, thereby improving the grip with respect to the road surface. Furthermore, there may be provided on the blocks of the tread band studs which, thanks to a portion thereof projecting from the tread surface, improve the grip characteristics on ice-bound road surfaces.

The overall configuration of the tread band defined by the whole of the grooves and blocks constitutes the tread pattern.

WO 2020012277, in the name of the same Applicant, describes a winter tyre, the tread pattern of which is formed by respective pluralities of shoulder blocks and central blocks which are successively arranged along the circumferential development of the tread band.

The term "circumferential" direction is intended to be a direction which is generally parallel with the rotation direction of the tyre or, at most, slightly inclined (at most by approximately 5°) with respect to the rotation direction of the tyre.

The term "axial" direction is intended to be a direction which is substantially parallel with the rotation axis of the tyre or, at most, slightly inclined (at most by approximately 5°) with respect to the rotation axis of the tyre. The axial direction is generally perpendicular to the circumferential direction.

The term "equatorial plane" of the tyre is intended to be a centre plane which is perpendicular to the rotation axis of the tyre.

The term "central region" of the tread band is intended to be a tread band portion which extends circumferentially about an equatorial plane of the tyre over a width of at least 30% of the width of the tread band, preferably over a width between 40% and 60% of such a width.

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

The term "shoulder regions" of the tread band is intended to be the tread band portions which extend circumferentially at the opposite sides of the central region in an axially external position of the tread band as far as the axial ends of the tread band.

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

The term "groove" is intended to be a recess which is formed in a tread band portion and which has a width greater than or equal to 1.5 mm.

A groove is referred to as being "circumferential" when it extends in a circumferential direction or at most is inclined at an angle less than 5° with respect to the circumferential direction.

A groove is referred to as being "transverse" when it extends in a direction which is inclined with respect to the circumferential direction by an acute angle greater than at least 10°.

The term "sipe" is intended to be a recess which is formed in a tread band portion and which has a width less than 1.5 mm, preferably less than or equal to 1 mm.

The width of sipes and grooves is intended to be measured at a depth greater than or equal to 1 mm, preferably greater than or equal to 1.5 mm.

If the width of the groove or the sipe varies along the longitudinal development thereof, the mean width, the value of which is obtained as a mean of the various width values which are suitably weighted in accordance with the relative longitudinal extents, is considered. For example, if a groove has a width of 5 mm over 80% of the longitudinal extent thereof and a width of 3 mm for the remaining 20%, the mean value of the width to be considered will be equal to 5 x 0.8 + 3 x 0.2 = 4.6 mm.

Similarly, if the width of a grove, particularly a transverse groove, varies along the tread band in accordance with the length of the pitch to which it belongs, the mean value is considered.

A groove is defined as being a "main" groove when it has a depth of at least 5 mm. Preferably, a main groove has a width of at least 3 mm.

A groove is defined as being a "secondary" groove when it has a depth less than 5 mm. Preferably, a secondary groove has a width less than 4 mm.

The inclination of a groove with respect to a circumferential direction defined on the tread band is defined by the acute angle formed by the groove with the circumferential direction. As a particular case, a groove which extends parallel with the axis of the tyre will have an inclination of 90° with respect to the circumferential direction.

Two (or more) transverse grooves are inclined "in a concordant manner" when the progression thereof is, for both, increasing or decreasing when considered in a Cartesian plane which is positioned on the tread band (tangentially thereto) with the axis of the ordinate parallel with the circumferential direction and the axis of the abscissa parallel with the axis of the tyre.

Consequently, two transverse grooves are inclined "in a discordant manner" when the progression thereof is, when considered in this Cartesian plane, increasing for one groove and decreasing for the other groove.

Two grooves are "substantially aligned" when, at least in the region of the respective ends thereof facing each other, the longitudinal axes thereof are staggered by a value less than the width of the largest groove. Two grooves are "successive" when they are arranged on the tread surface one after the other, considering the rotation of the tyre in any one of the two rotation directions. In particular, two grooves of the same configuration are successive when other grooves of the same configuration are not provided between them.

In particular, a plurality of grooves may be arranged on the tread band in "regular succession" along the circumferential development of the tread band when the grooves are arranged in succession in accordance with a predefined pattern of circumferential distances.

The term "block" is intended to be understood to be a tread band portion which is delimited by at least one groove, preferably by at least two different grooves, in which there is defined, on the radially external surface, a tread band portion intended for contact with the road surface.

Therefore, there are considered to be blocks both a tread band portion with a closed contour which is delimited by three or more grooves and a circumferential rib which is delimited by a pair of grooves which develop circumferentially about the tread band. A block which is formed in the central region of the tread band is defined as a "central block" while a block which is formed in a shoulder region of the tread band is defined as a "shoulder block".

The area of the radially external surface of a group of blocks is calculated without considering the surface affected by the possible internal grooves with respect to the group of blocks.

The term "tread pattern" is intended to be the overall configuration of the tread band as defined by the assembly of the grooves and blocks which are delimited thereby. A tread pattern is of the "directional" type when it is configured to be mounted on the vehicle so as to rotate in a preferential travel direction.

A "module" of the tread pattern is defined by the minimum tread band portion which extends between the axial ends of the tread band, the configuration of which is successively repeated along the circumferential development of the tread band so as to form said tread pattern.

Furthermore, while maintaining an identical basic configuration, the modules can have a circumferential dimension (called the "pitch") which is slightly different with respect to each other, for example, on a tread band there can be used modules having two, three or four different pitches which are combined with each other in various manners.

A module may be formed by two or more elementary portions (or sub-modules) which extend between the two axial ends of the tread band and which are arranged in the same succession inside each module.

In this case, there is provision for each elementary portion to be able to have in different modules the same basic configuration but circumferential dimensions (that is to say, "pitches") which are slightly different from each other so that each module may be formed by elementary portions with different pitches.

Two or more directions, or two or more elements which extend in respective directions, such as, for example, two or more grooves, are "substantially parallel" when they are inclined relative to each other by an angle less than 10°, preferably less than 5°.

Two or more elements have a "substantially equal" length when the respective lengths differ from each other at most by an extent equal to 10% of the greatest length.

Two or more elements or groups of elements are considered to be "substantially symmetrical" with respect to a plane of symmetry even when they are slightly staggered relative to each other in a direction parallel with the plane of symmetry. For example, two grooves or two blocks or two groups of blocks are symmetrical with respect to the equatorial plane even when they are spaced apart in the circumferential direction by a value less than the value of a pitch of the tread pattern, wherein a pitch may, for example, correspond to the circumferential distance between two successive main grooves. In absolute terms, the circumferential distance of two substantially symmetrical elements is less than 50 mm, preferably less than 40 mm.

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

The Applicant has initially observed that the performance levels of a tyre on snowbound roads depend in a relevant manner on the quantity and the extent of the sipes which are formed on the blocks. In particular, the Applicant has noted that, for the same tread pattern, a block on which more sipes are formed is able to provide better behaviour on snow.

However, the Applicant has further observed that the presence of the sipes weakens the structure of the block, making it less rigid and therefore reducing the capacity of the block to withstand the external stresses, in particular the tangential stresses.

As a result of this weakening, in the event of braking, acceleration or travel round bends, the block may become deformed to a relevant extent, bringing about a partial lifting of the block from the road surface with a resultant reduction of the contact area between the block and road surface and, consequently, also of the total friction force applied by the tyre to the road surface.

Furthermore, the Applicant has observed that the lesser rigidity of the blocks can also negatively influence the performance levels of studded tyres.

In fact, the Applicant has verified that a stud which is fixed to a block which is very deformable not only is less effective in gripping ice-bound surfaces but can also be more readily extracted from its seat, bringing about the detachment of the stud from the tread band and consequently an irreversible loss of efficiency during travel on an ice-bound road surface.

In fact, the Applicant has verified that the capacity of the tyre to retain the studs inside the seats which are suitably provided in the tread band is a critical parameter for obtaining adequate performance levels of the studded tyres during the servicelife thereof.

The Applicant has further observed that the response to this requirement is generally achieved by forming and sizing the receiving seat of the stud and the stud portion which is intended to be received in the seat so as to bring about a high level of interference during the possible movement when the stud leaves the seat.

However, the Applicant has verified that these arrangements have limitations as a result of the need to have to insert the studs in the respective seats during the production step of the tyre and that they may be insufficient.

Therefore, the Applicant has perceived that, in order to increase the efficiency of the action of gripping of the studs and the capacity for retaining them inside the seats, it may be advantageous to configure the tread pattern in such a manner as to limit the excessive local deformations of the tread band to the greatest possible extent, in particular in terms of the individual blocks.

In order to achieve this objective, the Applicant has perceived that the tread pattern must be configured so as to have characteristics of rigidity which are not only as high as possible but also homogeneous as far as possible in the different regions of the tread band so that the possible tangential stresses are distributed in the most uniform manner possible.

In order to comply with both requirements, without thereby impairing the capacity for discharging the water from the tread band, the Applicant has thought that it may be possible to use grooves with a greater depth in order to define on the tread band macro-regions which are relatively extensive and inside which there may be used grooves with a lesser depth in order to define two or more blocks.

The Applicant has thereby obtained a greater freedom in designing the tread pattern, being able to configure macro-regions which are formed by a plurality of blocks having homogeneous characteristics with respect to each other, for example, a similar surface extent, even in the presence of blocks which, when taken individually, may be substantially different from each other.

Finally, the Applicant has found that, by defining on the tread band a first group of shoulder blocks and a second group of shoulder blocks which alternate in circumferential succession with respect to each other, and a first group of central blocks which are axially inside and adjacent to the two groups of shoulder blocks, all separated from each other by one or more main grooves, that is to say, with a great depth, and inside which the individual blocks are separated from each other by one or more secondary grooves, that is to say, with a reduced depth, there is obtained a tread pattern which is suitable for complying in a homogeneous manner with the tangential stresses, preventing excessive local deformations of the blocks and thus increasing the capacity for retaining the studs inside the respective receiving seats. In particular, in one aspect thereof, the invention relates to a tyre for vehicle wheels comprising a tread band.

Preferably, there are defined on the tread band a first shoulder region and a second shoulder region which are axially opposite each other and a central region which is interposed between said first shoulder region and said second shoulder region. Preferably, a plurality of first groups of shoulder blocks are defined on the tread band. Preferably, each first group of shoulder blocks extends from said first shoulder region towards said central region of said tread band.

Preferably, a plurality of second groups of shoulder blocks are defined on the tread band.

Preferably, each second group of shoulder blocks extends from said first shoulder region towards said central region of said tread band.

Preferably, each first group of shoulder blocks and each second group of shoulder blocks are successively arranged in alternation along the circumferential development of said tread band.

Preferably, a plurality of first groups of central blocks which are successively arranged along the circumferential development of said tread band are defined on the tread band. Preferably, each first group of central blocks is adjacent and in an axially internal position with respect to a respective first group of shoulder blocks and a respective second group of shoulder blocks.

Preferably, the blocks of each first group of shoulder blocks are separated from each other by at least one secondary groove.

Preferably, the blocks of each second group of shoulder blocks are separated from each other by at least one secondary groove.

Preferably, the blocks of each first group of central blocks are separated from each other by at least one secondary groove.

Preferably, each second group of shoulder blocks is separated from two first groups of shoulder blocks adjacent thereto by at least one main groove.

Preferably, each first group of central blocks is separated from a first group of shoulder blocks and from a second group of shoulder blocks adjacent thereto by at least one main groove.

Preferably, there are defined on said first group of shoulder blocks, said second group of shoulder blocks and said first group of central blocks respective radially external surfaces, each of said radially external surfaces having a respective area which differs from a mean value of the areas of said radially external surfaces by a value less than 30% of said mean value.

The Applicant considers that the tyre which is constructed according to the above- mentioned aspect of the invention advantageously allows the acquisition, in the different regions of the tread band, of a substantial homogeneity of behaviour when it is subjected to tangential stresses, whether they are axial stresses or circumferential stresses.

The tyre thereby has optimum behaviour on mutually different road surfaces, on wet surfaces and on dry ones, and on snow-bound or icy road surfaces, wherein the tread band is provided with sipes and studs.

Furthermore, the substantial homogeneity of behaviour of the tread band with respect to the tangential stresses allows advantageous use of the tread pattern of the tyre of the invention as a valid basis for a studded tyre. In fact, the uniform rigidity of the groups of blocks, by avoiding localized zones with great deformability, increases the capacity for retention of the studs in the respective seats by preventing the loss thereof.

The present invention, in the above-mentioned aspect, may have at least one of the additional preferred features indicated below.

In some embodiments, each of said areas of the radially external surfaces differs from said mean value by a value less than 25% of said mean value.

In some embodiments, there are further defined on said tread band a plurality of third groups of shoulder blocks which are successively arranged along the circumferential development of said tread band.

Preferably, each third group of shoulder blocks extends from said second shoulder region towards said central region.

In some embodiments, there are further defined on said tread band a plurality of fourth groups of shoulder blocks which are successively arranged along the circumferential development of said tread band.

Preferably, each fourth group of shoulder blocks extends from said second shoulder region towards said central region.

Preferably, each fourth group of shoulder blocks is arranged along the circumferential development of said tread band in a position alternating with one of said third groups of shoulder blocks.

In some embodiments, there are further defined on said tread band a plurality of second groups of central blocks which are successively arranged along the circumferential development of said tread band.

Preferably, each second group of central blocks is adjacent and in an axially internal position with respect to a respective third group of shoulder blocks and a respective fourth group of shoulder blocks.

Preferably, the blocks of each third group of shoulder blocks are separated from each other by at least one secondary groove.

Preferably, the blocks of each fourth group of shoulder blocks are separated from each other by at least one secondary groove.

Preferably, the blocks of each second group of central blocks are separated from each other by at least one secondary groove.

Preferably, each fourth group of shoulder blocks is separated from two third groups of shoulder blocks adjacent thereto by at least one main groove.

Preferably, each second group of central blocks is separated from a third group of shoulder blocks and a fourth group of shoulder blocks adjacent thereto by at least one main groove.

Preferably, there are defined on said third group of shoulder blocks, said fourth group of shoulder blocks and said second group of central blocks respective radially external surfaces.

Preferably, each of said radially external surfaces has a respective area which differs from a mean value of the areas of said radially external surfaces by a value less than 30% of said mean value.

In some embodiments, each third group of shoulder blocks is substantially symmetrical, except for an axial offset, with respect to a first group of shoulder blocks. In some embodiments, each fourth group of shoulder blocks is substantially symmetrical, except for an axial offset, with respect to a second group of shoulder blocks.

In some embodiments, each second group of central blocks is substantially symmetrical, except for an axial offset, with respect to a first group of central blocks. In this manner, the configuration of the first group of shoulder blocks, the second group of shoulder blocks and the first group of central blocks is set out in a substantially symmetrical manner on both halves of the tread band, thereby obtaining a behaviour of the tread band which is particularly balanced.

In some embodiments, there is defined on said tread band a plurality of first pairs of main grooves which extend from said first shoulder region and from said second shoulder region towards said central region and which are arranged in regular succession along the circumferential development of said tread band.

Preferably, there is defined on said tread band a plurality of second pairs of main grooves which extend from said first shoulder region and from said second shoulder region towards said central region and which are arranged in regular succession along the circumferential development of said tread band.

Preferably, said second pairs of main grooves are arranged in an alternating position with respect to said first pairs of main grooves.

In some embodiments, said plurality of first pairs of main grooves and said plurality of second pairs of main grooves separate said plurality of first groups of shoulder blocks from said plurality of said second shoulder blocks.

In some embodiments, said plurality of first pairs of main grooves and said plurality of second pairs of main grooves separate said plurality of third groups of shoulder blocks from said plurality of fourth groups of shoulder blocks.

Preferably, each first pair of main grooves is formed by a first main groove which extends from said first shoulder region towards said central region and by a second main groove which extends from said second shoulder region towards said central region. More preferably, said first main groove comprises an axially internal end which is connected to said second main groove.

In some embodiments, said second main groove comprises an end part, which is axially internal and which extends between said first main groove and a further first main groove which belongs to a subsequent first pair of main grooves.

Preferably, said end part separates said first group of central blocks from said second group of central blocks.

In some embodiments, each second pair of main grooves is formed by a third main groove which extends from said first shoulder region towards said central region and by a fourth main groove which extends from said second shoulder region towards said central region.

In some embodiments, each third main groove is substantially parallel with said first main groove.

In some embodiments, each fourth main groove is substantially parallel with said second main groove.

In some embodiments, there are defined on said tread band a plurality of third pairs of main grooves which are arranged in regular succession along the circumferential development of said tread band.

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

Preferably, said fifth main groove separates said first group of central blocks from said first group of shoulder blocks and from said second group of shoulder blocks.

Preferably, said sixth main groove separates said second group of central blocks from said third group of shoulder blocks and from said fourth group of shoulder blocks.

Preferably, said fifth main groove extends between two first main grooves of said mutually successive first pairs of main grooves.

Preferably, said fifth main groove is connected to an axially internal end of said third main groove.

Preferably, said fifth main groove has an inclination, with respect to said circumferential direction, which is less than said first main grooves. Preferably, said fifth main groove has an inclination which is concordant with said first main grooves. Preferably, said sixth main groove extends between two second main grooves of said mutually successive first pairs of main grooves.

Preferably, said sixth main groove is connected to an axially internal end of said fourth main groove. Preferably, said sixth main groove has an inclination, with respect to said circumferential direction, which is less than said second main grooves.

Preferably, said sixth main groove has an inclination which is concordant with said second main grooves.

Preferably, said first main groove and said third main groove extend from said first shoulder region towards said central region with an inclination, with respect to said circumferential direction, which decreases from said first shoulder region towards said central region.

Preferably, said second main groove and said fourth main groove extend from said second shoulder region towards said central region, with an inclination, with respect to said circumferential direction, which decreases from said second shoulder region towards said central region.

In some embodiments, each first group of shoulder blocks is formed by a first pair of shoulder blocks which are separated by a first secondary groove.

In this manner, the blocks which form the first group of shoulder blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

Preferably, said first secondary groove extends between said first main groove and said third main groove.

Preferably, said first secondary groove is parallel with said fifth main groove.

In some embodiments, each second group of shoulder blocks is formed by a second pair of shoulder blocks which are separated by a second secondary groove.

In this manner, the blocks which form the second group of shoulder blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

Preferably, said second secondary groove extends between said third main groove and said further first main groove subsequent to said first main groove.

Preferably, said second secondary groove is parallel with said fifth main groove.

Preferably, said second secondary groove is aligned with said first secondary groove. In this manner, there is defined a single direction for the outflow of the water from the first group of shoulder blocks and the second group of shoulder blocks towards the first main groove and the third main groove, promoting the rapid discharge thereof in the event of travel on a wet surface.

In some embodiments, said first group of central blocks is formed by a first pair of central blocks which are separated by a third secondary groove. In this manner, the blocks which form the first group of central blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

Preferably, said third secondary groove extends between said first main groove and said fifth main groove.

Preferably, said third secondary groove is inclined in a discordant manner with respect to said fifth main groove.

In some embodiments, said first pair of central blocks is formed by a first, axially internal central block and by a second, axially external central block with respect to the first central block.

Preferably, said first central block has a V-shaped configuration and comprises a vertex which is directed towards said first shoulder region and a pair of branches which extend towards said second shoulder region in respective directions with an opposite inclination with respect to said circumferential direction.

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

In some embodiments, there are defined on each block of said first group of shoulder blocks, said second group of shoulder blocks and said first group of central blocks respective radially external surfaces and each of said radially external surfaces of said blocks has a respective area which differs from a mean value of the areas of said radially external surfaces of said blocks by a value less than 30% of said mean value, preferably less than 25%.

Preferably, the first group of shoulder blocks, the second group of shoulder blocks and the first group of central blocks extend, when considered as a whole, from one axial end of the tread band as far as the equatorial plane or the immediate vicinity thereof.

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

Preferably, the blocks of said third group of shoulder blocks are separated from a fourth secondary groove which extends between said second main groove and said fourth main groove.

In this manner, the blocks which form the third group of shoulder blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

In some embodiments, said fourth secondary groove is parallel with said sixth main groove. In some embodiments, said fourth group of shoulder blocks is formed by a fourth pair of shoulder blocks.

Preferably, the blocks of said fourth group of shoulder blocks are separated by a fifth secondary groove which extends between said fourth main groove and said additional second main groove subsequent to said second main groove.

In this manner, the blocks which form the fourth group of shoulder blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

In some embodiments, said fifth secondary groove is parallel with said sixth main groove.

In some embodiments, said fifth secondary groove is aligned with said fourth secondary groove.

In this manner, there is defined a single direction for the outflow of the water from the third group of shoulder blocks and the fourth group of shoulder blocks towards the second main groove and the fourth main groove, promoting the rapid discharge thereof in the event of travel on a wet surface.

In some embodiments, said second group of central blocks is formed by a second pair of central blocks.

Preferably, the blocks of said second group of central blocks are separated by a sixth secondary groove.

In this manner, the blocks which form the second group of central blocks are separated from each other by a groove with a small depth, less than 5 mm, so as to be relatively connected to each other and therefore generally less deformable.

Preferably, said sixth secondary groove extends between said second main groove and said sixth main groove.

Preferably, said sixth secondary groove is inclined in a discordant manner with respect to said sixth main groove.

In some embodiments, said second pair of central blocks is formed by a third, axially internal central block and by a fourth, axially external central block with respect to the third central block.

Preferably, said third central block has a V-shaped configuration and comprises a vertex which is directed towards said second shoulder region and a pair of branches which extend towards said first shoulder region in respective directions with an opposite inclination with respect to said circumferential direction.

In this manner, the third central blocks are substantially specular with respect to the first central blocks, though staggered with respect to the axial direction.

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

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

In this manner, the first central blocks and the third central blocks are partially embedded one in the other, mutually assisting in withstanding tangential stresses. Preferably, the vertices of said first central blocks are aligned in a circumferential direction.

Preferably, the vertices of said third central blocks are substantially aligned in a circumferential direction.

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

Preferably, each of said first main grooves comprises a first part with a curvilinear progression which extends from said first shoulder region towards an equatorial plane of said tread band and which has an inclination with respect to said circumferential direction which generally decreases from said first shoulder region towards said central region.

Preferably, each of said second main grooves comprises a first part with a curvilinear progression which extends from said second shoulder region towards an equatorial plane of said tread band and which has an inclination with respect to said circumferential direction which generally decreases from said second shoulder region towards said central region.

Preferably, said first part of said first main groove and said first part of said second main groove are inclined in a discordant manner with respect to said circumferential direction.

In this manner, the discharge of the water from the central region towards the respective shoulder regions is particularly promoted when the tyre is rotated in a predefined direction corresponding to the preferred advance direction.

Preferably, said first parts of each of said first and second main grooves have a curvilinear progression without any inflection points.

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

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

In this manner, the rapid discharge of the water is promoted from the central region towards the shoulder regions while maintaining, at the same time, a high level of resistance of the shoulder regions to transverse tangential stresses.

Preferably, each of said first main grooves has a width which decreases from said first shoulder region towards said equatorial plane.

Preferably, each of said second main grooves has a width which decreases from said second shoulder region towards said equatorial plane.

In this manner, on the one hand, there is promoted the outflow of the water from the central region towards the respective shoulder regions and, on the other hand, there is increased the rigidity of the first group of central blocks and the second group of central blocks, respectively.

Preferably, each of said 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 between 3 mm and 10 mm.

Preferably, each of said 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 between 6 mm and 12 mm, more preferably between 7 mm and 10 mm.

Preferably, each of said 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 between 2 mm and 5 mm.

Preferably, each of said 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 between 2.5 mm and 4.5 mm.

Preferably, in each first pair of main grooves said first main groove and said second main groove are axially staggered.

Preferably, in each second pair of main grooves said third main groove and said fourth main groove are axially staggered.

In this manner, the noise produced by the rolling of the tyre on the road surface is advantageously reduced because the impacts of the edges of the respective grooves with the ground are staggered relative to each other, decreasing the intensity of the noise which is generally generated.

Preferably, said third main grooves and said fourth main grooves have a substantially symmetrical progression with respect to said circumferential direction.

In some embodiments, said end part of said second main groove extends so as to straddle an equatorial plane of said tread band, preferably in a zigzag manner.

Preferably, said end part of said second main groove comprises a first portion which extends from said first main groove towards said first shoulder region.

Preferably, said end part of said second main groove comprises a second portion which extends in continuation of said first portion, more preferably it extends towards said second shoulder region.

Preferably, said end part of said second main groove comprises a third portion which extends in continuation of said second portion, more preferably it extends towards said first shoulder region as far as said additional first main groove.

Preferably, said first portion and said third portion of said end part are substantially parallel.

In some embodiments, said secondary grooves have a depth less than 50% of the depth of said main grooves.

In some embodiments, said fifth main groove is inclined with respect to said circumferential direction by an angle between 5° and 25°, preferably approximately 15°.

In some embodiments, said first secondary groove and/or said second secondary groove and/or said fourth secondary groove and/or said fifth secondary groove are inclined with respect to said circumferential direction by an angle between 5° and 25°, preferably approximately 15°.

In some embodiments, said third secondary groove and/or said sixth secondary groove are inclined with respect to said circumferential direction by an angle between 25° and 45°, preferably approximately 35°.

In some embodiments, there is defined on said tread band a tread pattern which is formed by the whole of all the grooves and all the blocks and a module which is formed by the minimum tread band portion which extends between the axial ends of the tread band, the configuration of which is repeated successively along the circumferential development of the tread band so as to form said tread pattern.

Preferably, said module is formed by the tread band portion between two of said first pairs of main grooves which are mutually successive.

Preferably, said module is formed by a first elementary portion which extends from said first pair of main grooves as far as said second pair of main grooves and by a second elementary portion which extends from said second pair of main grooves as far as said successive first pair of main grooves.

In some embodiments, respective pluralities of sipes are formed on at least some blocks which are defined on said tread band and more preferably on all the blocks which are defined on said tread band.

In some embodiments, studs are provided on at least some blocks which are defined on said tread band.

The features and advantages of the invention will be better appreciated from the detailed description of a number of preferred embodiments thereof which are illustrated by way of non-limiting example with reference to the appended drawings, in which:

- Figure 1 is a front view of a tyre for vehicle wheels constructed according to the present invention;

- Figure 2 is a partial front view of a first construction variant of the tyre of Figure 1;

- Figure 3 is a schematic view, drawn to an enlarged scale and developed in a plane, of a significant portion of the tread band of the tyre of Figure 1;

- Figure 4 is a schematic view, drawn to an enlarged scale, of a tread band portion illustrating a module of the tread band of the tyre of Figure 1.

With reference to the appended Figures, there is generally designated 1 a tyre for vehicle wheels constructed according to the present invention.

The tyre 1 comprises a tyre structure which is conventional per se and which is not illustrated in the appended Figures and a tread band 2, on which there is defined a tread surface 3 which is arranged in a radially external position with respect to the tread band 2 and which is intended for contact with a road surface.

The tyre 1 has a conventional shape which is generically toroidal and which develops about a rotation axis, defining on the tread surface 3 an axial direction Y which is parallel therewith and which is passed through by an equatorial plane X which is perpendicular to the rotation axis and which defines on the tread surface 3 a circumferential direction which is parallel therewith.

The tread band 2 has a width L which is defined as the maximum width of the tread band which is intended for contact with the ground in conditions of standard use.

The tyre 1 is a tyre of the directional type, wherein there is defined a preferential rolling direction of the tyre which is indicated in the Figures with the arrow F.

There is further defined on the tread band 2 a first shoulder region 4 which is delimited at the axially external side by a first lateral edge 4a of the tread band 2, a second shoulder region 5 which is axially opposite the first shoulder region 4 and which is delimited at the axially external side by a second lateral edge 5a of the tread band 2, and a central region 6 which is interposed between the first and second shoulder regions 4 and 5 and which extends so as to straddle the equatorial plane X. There are defined on the tread band 2 a plurality of first pairs of main grooves which are successively and regularly arranged along the circumferential development of the tread band 2 and which extend transversely from the opposite shoulder regions 4 and 5 towards the equatorial plane X.

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

Each first main groove 10 comprises a first part 11 which extends from an axially external end 10a which opens at the first lateral edge 4a of the first shoulder region 4 as far as an axially internal end 10b which opens at the second main groove 20.

In particular, the first main groove 10 joins the second main groove 20 shortly after crossing the equatorial plane X. The first part 11 has a curvilinear progression without any inflection points with an inclination with respect to the circumferential direction which 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 internal end 10a up to an inclination of approximately 30° in the region of the axially internal end 10b.

Each second main groove 20 comprises a first part 21 which extends from an axially external end 20a which opens at the second lateral edge 5a of the second shoulder region 5 as far as the junction with respect to the axially internal end 10b of the first main groove 10.

Similarly to the first part 11 of the first main groove 10, the first part 21 of the second main groove 20 also has a curvilinear progression without any inflection points with an inclination with respect to the circumferential direction which 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 axially internal end 20a up to an inclination of approximately 30° in the region of the abutment location with the axially internal end 10b of the first main groove 10.

Each second main groove 20 further comprises an end part 22 which is axially internal and which extends in continuation from the first part 21 until opening with an axially internal end 20b thereof in an additional first main groove 10, subsequent to the first main groove 10 which forms the pair of first main grooves together with the second main groove 20.

The end part 22 of each second main groove 20 has a configuration with a broken line and comprises a first portion 23 which extends in continuation of the first part 21 towards the first shoulder region 4, a second portion 24 which extends in continuation of the first portion 23 towards the second shoulder region 5 and a third portion 26 which extends in continuation of the second portion 24 towards the first shoulder region 4 as far as the axially internal end 20b. In particular, the third portion 26 joins the additional first main groove 10 shortly after crossing the equatorial plane X.

There thereby remains defined on the first part 11 of the additional first main groove 10 and, consequently, on the first part 11 of each first main groove 10 an internal end region 15 which is delimited by the end 20a of the second main groove 20 and the axially internal end 10b of the first main groove 10.

The first portion 23, the second portion 24 and the third portion 26 are substantially rectilinear, more specifically they are curved 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 inclined alternately in a discordant manner with respect to the circumferential direction. In particular, the first portion 23 and the third portion 26 are substantially parallel with each other and the second portion 24 and the internal end region 15 of the first main groove 10 are also substantially parallel.

In this manner, therefore, a broken line is formed in a zigzag manner and is defined by the internal end region 15 of the first main groove 10, the first portion 23 of the end part 22, the second portion 24 of the end part 22 and the third portion 26 of the end part 22.

This broken line develops continuously along the entire circumferential extent of the equatorial plane X, crossing it in each successive part thereof.

The first and second main grooves 10 and 20 of each first pair therefore have generally similar progressions with a relevant portion of the respective first parts 11 and 21 which are substantially symmetrical with respect to the equatorial plane X and with concavities which are directed at the same side of the tread band 2. However, the second main groove 20 is axially staggered with respect to the first transverse groove 10. In fact, the respective axially external ends 10a and 20a are staggered by a value between 5 and 20 mm, preferably between 10 mm and 20 mm, which is measured in the circumferential direction.

There are further defined on the tread band 2 a plurality of second pairs of main grooves which are arranged successively and regularly along the circumferential development of the tread band 2, in a position alternating with respect to the first pairs of main grooves 10 and 20.

Each second pair is formed by a third main groove 30 which extends from the first shoulder region 4 towards the central region 6 and by a fourth main groove 40 which extends from the second shoulder region 5 towards the central region 6.

In particular, each third main groove 30 extends between an axially external end 30a which opens in the first shoulder region 4 and an axially internal end 30b.

Similarly, each fourth main groove 40 extends between an axially external end 40a which opens in the second shoulder region 5 and an axially internal end 40a.

The third and fourth main grooves 30 and 40 have a similar curvilinear progression which is substantially parallel with the first and second main grooves 10 and 20, respectively.

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

Advantageously, the second portion 24 of the end part 22 is located on the theoretical extension of the third main groove 30 even if there are no contact points between these grooves.

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

There are further defined on the tread band 2 a plurality of third pairs of main grooves which are arranged successively and regularly along the circumferential development of the tread band 2.

Each third pair 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.

In particular, each fifth main groove 50 extends between two first mutually successive main grooves 10 and in a central region it is connected to the axially internal end 30b of the third main groove 30. Each fifth main groove 50 is inclined with respect to the circumferential direction X in a manner concordant with the first main grooves 10 but at an angle less than these first main grooves 10, for example, approximately 15°.

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

Each sixth main groove 60 is inclined with respect to the circumferential direction X in a manner concordant with the second main grooves 20 but at an angle less than these second main grooves 20, for example, approximately 15°.

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 approximately 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 external ends towards the axially internal ends. In particular, the width of these main grooves varies from approximately 7 mm to 10 mm in the region of the respective shoulder region up to a value of from 3.5 mm to 5 mm in the central region 6.

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

The configuration of main grooves set out above defines on the tread band 2 several pluralities of groups of blocks which are described in greater detail below.

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

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

As a result of the substantial symmetry with respect to the equatorial plane of the main grooves which delimit them, the third group of shoulder blocks 130, the fourth group of shoulder blocks 140 and the second group of central blocks 150 are substantially symmetrical with respect to the first group of shoulder blocks 110 with respect to the second group of shoulder blocks 120 and the first group of central blocks 100, respectively.

The first group of central blocks 100 and the second group of central blocks 150 are separated from each other by the end part 22 of the second main groove 20.

It may be noted that all the groups of blocks are delimited and separated from each other by main grooves, therefore at a relatively great depth.

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 secondary groove 16 which extends between the first main groove 10 and the third main groove 30.

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 secondary groove 25 which extends between the third main groove 30 and the additional first main groove 10, subsequent to the first main groove 10.

The first secondary groove 16 and the second secondary groove 25 are substantially aligned with each other and substantially parallel with the fifth main groove 50.

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 secondary groove 45 which extends between the second main groove 20 and the fourth main groove 40.

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 secondary groove 55 which extends between the fourth main groove 40 and the additional second main groove 20, subsequent to the second main groove 20.

The fourth secondary groove 45 and the fifth secondary groove 55 are substantially aligned with each other and substantially parallel with the sixth main groove 60.

The first group 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 by a second central block 102 which is axially external with respect to the first central block 101 and which is separated from the first central block 101 by a third secondary groove 35.

The third secondary groove 35 extends between the first main groove 10 and the fifth main groove 50 which is inclined in a discordant manner with respect to the fifth main groove 50, at an angle of approximately 35°.

The first central block 101 has a V-shaped configuration 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 in respective directions with opposite inclinations with respect to the circumferential direction. The second central block 102 has a substantially triangular shape with the largest side facing the axially internal blocks 112 and 122 of the first and second groups of shoulder blocks 110, 120, respectively.

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

The sixth secondary groove 65 extends between the second main groove 20 and the sixth main groove 60 which is inclined in a discordant manner with respect to the sixth main groove 60, at an angle of approximately 35°.

The third central block 151 has a V-shaped configuration 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 in respective directions with opposite inclinations with respect to the circumferential direction.

The fourth central block 152 has a substantially triangular shape with the largest side facing the axially internal blocks 132 and 142 of the third and fourth groups of shoulder blocks 130, 140, respectively.

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

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

In particular, each third central block 151 is substantially specular to a first central block 101 although staggered with respect to the axial direction.

Each third central block 151 and each first central block 101 have the respective concavities directed towards each other and are further partially aligned not only in the axial direction Y but also in the circumferential direction X. In other words, the respective projections in the circumferential direction of the first central block 101 and the third central block 151 are partially superimposed. In particular, a branch of each first central block 101 is partially received in the concavity of a third central block 151 and, vice versa, a branch of each third central block 151 is partially received in the concavity of a first central block 101.

All the 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 approximately 4 mm and a variable width between approximately 2.5 mm and 4 mm.

The blocks and the grooves identified above generally define the tread pattern of the tyre 1.

The tread pattern is formed by the repetition in a successive and continuous manner of a single module M which is formed by the tread band portion between two first successive pairs of main grooves 10 and 20.

Each module M is in turn formed by a first elementary portion which extends from a first pair of main grooves 10 and 20 as far as the second pair of main grooves 30 and 40 and by a second elementary portion which extends from the second pair of main grooves 30 and 40 as far as the first successive pair of main grooves 10 and 20.

Each first elementary portion and each second elementary portion may have a circumferential dimension which corresponds to a long pitch or a value corresponding to a short pitch, which is less than the long pitch.

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

Each module M may be formed by a first elementary portion and a second elementary portion having a short pitch or a long pitch which are combined with each other in various manners so that there are provided on the tread pattern modules having both the first and second elementary portions with a long pitch, or modules having both the first and second elementary portions with a short pitch, or modules having the first elementary portion with a short pitch and the second elementary portion with a long pitch or, finally, modules having the first elementary portion with a long pitch and the second elementary portion with a short pitch.

There are formed on all the blocks indicated above sipes which promote the performance levels of the tyre in snow-bound road conditions.

In particular, there are formed on the blocks of the first and second groups of blocks 100 and 150 sipes which develop substantially in the axial direction Y while there are formed on the axially internal blocks of the groups of shoulder blocks 110, 120, 130 and 140 sipes which develop in a transverse direction with respect to the main development direction of the blocks (defined by the development direction of the first or second main grooves) and on the axially external blocks of the groups of shoulder blocks 110, 120, 130 and 140 there are formed sipes which develop in a direction substantially parallel with the main development direction of the blocks (also defined by the direction of the first or second main grooves). Ther may further be provided on the tread band 2 of the tyre 1, in a suitable position on the different blocks, a plurality of studs 200, as can be seen in the construction variant of the tyre 1 illustrated in Figure 2, so as to make it particularly suitable for travel even on icy surfaces.

There remains defined on each group of shoulder blocks and on each group of central blocks a respective radially external surface which in fact constitutes a portion of the tread surface 3.

As a result of the configuration of grooves and blocks described above, each of these radially external surfaces of the first group of shoulder blocks 110, second group of shoulder blocks 120 and first group of central blocks 100 differs from the mean value of these radially external surfaces by a value less than 25%.

Not only this, the individual blocks which form the different shoulder groups also have a respective radially external surface which differs from the mean value of the radially external surfaces of these blocks by a value less than 25%.

Evidently, as a result of the relationships of symmetry described above, the same relationships between radially external surfaces also apply to the third and fourth groups of shoulder blocks 130, 140 and to the second group of central blocks 150.

In this manner, the tread band 2 is subdivided by the main grooves into contact regions with the road surface (the groups of blocks) with a substantially homogeneous area.

This allows the tread band to react to the tangential stresses in a substantially homogeneous manner, preventing the occurrence of excessive local deformations which can impair the road-holding of the tyre 1 and, in the case of a studded tyre, allows a reduction in the possibility of the studs being extracted from the respective seat.

EXAMPLE

A tyre with a measurement of 205/55 R.16 has been constructed according to the embodiment of the invention described above.

In Table 1 below, there are set out the respective extents of the radially external surfaces of the first group of shoulder blocks 110, second group of shoulder blocks 120 and the first group of central blocks 100 and the percentage difference of the surface extent of each group of blocks with respect to the mean value of these surface extents.

In the specific example of a tyre used here, this mean value is approximately 1185 mm².

Table 1

It will be noted that the radially external surfaces of the individual groups of blocks differ from the mean value of the surfaces by a percentage value less than 25% of the mean value so that each group of blocks moves into contact with the road surface with a surface having substantially the same extent, thereby providing a substantially homogeneous resistance to the tangential stresses.

In Table 2 below, there are set out the respective extents of the radially external surfaces of the individual blocks which form the first group of shoulder blocks 110, second group of shoulder blocks 120 and the first group of central blocks 100, respectively, and the percentage difference of the extent of each block with respect to the mean value of the extents of the blocks.

In the specific case, this mean value is approximately 593 mm².

Table 2

In this case, it may also be noted that the radially external surfaces of the individual blocks of each group of blocks differ from the mean value of the surfaces by a percentage value less than 25% of the mean value so that each block comes into contact with the road surface with a surface which is substantially equal to the other blocks, thereby providing a substantially homogeneous resistance to the tangential stresses.

In Table 3 below, there are set out values of rigidity which are calculated by means of simulation with finite elements of the first group of shoulder blocks 110, second group of shoulder blocks 120 and first group of central blocks 100, respectively, and the percentage difference of the rigidity values of each group of blocks with respect to the mean value of these rigidity values. The rigidity values are defined as the ratio between the reaction force which a block applies to the road and the movement which is imposed on the block itself.

Table 3

Therefore, it may be observed that the groups of blocks have rigidity values which are generally similar, both when the tangential stresses to which they are subjected have an axial direction and when these tangential stresses have a circumferential direction.

This homogeneity of the rigidity values between the different groups of blocks is reflected in a uniformity of behaviour of the tread band, conferring on the tyre a number of important advantages including better road-holding, irrespective of the road surface, better results in terms of wear of the tyre, greater support of the studs (in the case of studded tyres), which becomes evident as a greater capacity for retention of the studs and a greater gripping efficiency on icy roads.

Claims

CLAIMS re for vehicle wheels, comprising a tread band (2), on which there are defined:

- a first shoulder region (4) and a second shoulder region (5) which are axially opposite each other;

- a central region (6) which is interposed between said first shoulder region (4) and said second shoulder region (5);

- a plurality of first groups of shoulder blocks (110) which are successively arranged along the circumferential development of said tread band (2), each first group of shoulder blocks (110) extending from said first shoulder region (4) towards said central region (6),

- a plurality of second groups of shoulder blocks (120) which are successively arranged along the circumferential development of said tread band (2), each second group of shoulder blocks (120) extending from said first shoulder region (4) towards said central region (6) and being arranged along the circumferential development of said tread band in an alternating position with one of said first groups of shoulder blocks (110),

- a plurality of first groups of central blocks (100) which are successively arranged along the circumferential development of said tread band (2), each first group of central blocks (100) being adjacent and in an axially internal position with respect to a respective first group of shoulder blocks (110) and a respective second group of shoulder blocks (120), wherein:

- the blocks (111, 112) of each first group of shoulder blocks (110) are separated from each other by at least one secondary groove (16),

- the blocks (121, 122) of each second group of shoulder blocks (120) are separated from each other by at least one secondary groove (25),

- the blocks (101, 102) of each first group of central blocks (100) are separated from each other by at least one secondary groove (35),

- each second group of shoulder blocks (120) is separated from two first groups of shoulder blocks (110) adjacent thereto by at least one main groove (10, 30),

- each first group of central blocks (100) is separated from a first group of shoulder blocks (110) and from a second group of shoulder blocks (120) adjacent thereto by at least one main groove (50) and - there are defined on said first group of shoulder blocks (110), said second group of shoulder blocks (120) and said first group of central blocks (100) respective radially external surfaces, each of said radially external surfaces having a respective area which differs from a mean value of the areas of said radially external surfaces by a value less than 30% of said mean value.

2. A tyre according to claim 1, wherein each of said areas of the radially external surfaces differs from said mean value by a value less than 25% of said mean value.

3. A tyre according to claim 1 or claim 2, wherein there are further defined on said tread band (2):

- a plurality of third groups of shoulder blocks (130) which are successively arranged along the circumferential development of said tread band (2), each third group of shoulder blocks (130) extending from said second shoulder region (5) towards said central region (6),

- a plurality of fourth groups of shoulder blocks (140) which are successively arranged along the circumferential development of said tread band (2), each fourth group of shoulder blocks (140) extending from said second shoulder region (5) towards said central region (6) and being arranged along the circumferential development of said tread band (2) in a position alternating with one of said third groups of shoulder blocks (130),

- a plurality of second groups of central blocks (150) which are successively arranged along the circumferential development of said tread band (2), each second group of central blocks (150) being adjacent and in an axially internal position with respect to a respective third group of shoulder blocks (130) and a respective fourth group of shoulder blocks (140), wherein:

- the blocks (131, 132) of each third group of shoulder blocks (130) are separated from each other by at least one secondary groove (45),

- the blocks (141, 142) of said fourth group of shoulder blocks (140) are separated from each other by at least one secondary groove (55),

- the blocks (151, 152) of said second group of central blocks (150) are separated from each other by at least one secondary groove (65),

- each fourth group of shoulder blocks (140) is separated from two third groups of shoulder blocks (130) adjacent thereto by at least one main groove (20, 40),

- each second group of central blocks (150) is separated from a third group of shoulder blocks (130) and by a fourth group of shoulder blocks (140) adjacent thereto by at least one main groove (60), and

- there are defined on said third group of shoulder blocks (130), said fourth group of shoulder blocks (140) and said second group of central blocks (150) respective radially external surfaces, each of said radially external surfaces having a respective area which differs from a mean value of the areas of said radially external surfaces by a value less than 30% of said mean value.

4. A tyre according to claim 3, wherein each third group of shoulder blocks (130) is substantially symmetrical, except for an axial offset, with respect to a first group of shoulder blocks (110).

5. A tyre according to claim 3 or 4, wherein each fourth group of shoulder blocks (140) is substantially symmetrical, except for an axial offset, with respect to a second group of shoulder blocks (120).

6. A tyre according to any one of claims 3 to 5, wherein each second group of central blocks (150) is substantially symmetrical, except for an axial offset, with respect to a first group of central blocks (100).

7. A tyre according to any one of claims 3 to 6, wherein there is defined on said tread band (2):

- a plurality of first pairs of main grooves (10, 20) which extend from said first shoulder region (4) and from said second shoulder region (5) towards said central region (6) and which are arranged in regular succession along the circumferential development of said tread band (2), and

- a plurality of second pairs of main grooves (30, 40) which extend from said first shoulder region (4) and from said second shoulder region (5) towards said central region (6) and which are arranged in regular succession along the circumferential development of said tread band (2) in an alternating position with respect to said first pairs of main grooves (10, 20), wherein said plurality of first pairs of main grooves (10, 20) and said plurality of second pairs of main grooves (30, 40) separate said plurality of first groups of shoulder blocks (110) from said plurality of said second shoulder blocks (120), and said plurality of third groups of shoulder blocks (130) from said plurality of fourth groups of shoulder blocks (140).

8. A tyre according to claim 7, wherein each first pair of main grooves is formed by:

- a first main groove (10) which extends from said first shoulder region (4) towards said central region (6) and by

- a second main groove (20) which extends from said second shoulder region (5) towards said central region (6); said first main groove (10) comprising an axially internal end (10b) which is connected to said second main groove (20).

9. A tyre according to claim 7 or 8, wherein said second main groove (20) comprises an end part (22), which is axially internal and which extends between said first main groove (10) and a further first main groove which belongs to a subsequent first pair of main grooves, said end part (22) separating said first group of central blocks (100) from said second group of central blocks (150).

10. A tyre according to any one of claims 7 to 9, wherein each second pair of main grooves is formed by a third main groove (30) which extends from said first shoulder region (4) towards said central region (6) and by a fourth main groove (40) which extends from said second shoulder region (5) towards said central region (6).

11. A tyre according to any one of claims 3 to 10, wherein there are defined on said tread band (2) a plurality of third pairs of main grooves (50, 60) which are arranged in regular succession along the circumferential development of said tread band, each third pair of main grooves being formed by:

- a fifth main groove (50) which separates said first group of central blocks (100) from said first group of shoulder blocks (110) and from said second group of shoulder blocks (120) and by

- a sixth main groove (60) which separates said second group of central blocks (150) from said third group of shoulder blocks (130) and from said fourth group of shoulder blocks (140).

12. A tyre according to claim 11, wherein said fifth main groove (50) extends between two first main grooves (10) of said mutually successive first pairs of main grooves and is connected to an axially internal end (30b) of said third main groove (30).

13. A tyre according to claim 11 or 12, wherein said fifth main groove (50) has an inclination, with respect to said circumferential direction, which is less than said first main grooves (10) and which is concordant with said first main grooves (10).

14. A tyre according to any one of claims 11 to 13, wherein said sixth main groove (60) extends between two second main grooves (20) of said mutually successive first pairs of main grooves and is connected to an axially internal end of said fourth main groove (40).

15. A tyre according to any one of claims 11 to 14, wherein said sixth main groove (60) has an inclination, with respect to said circumferential direction, which is less than said second main grooves (20) and which is concordant with said second main grooves (20).

16. A tyre according to any one of claims 10 to 15, wherein said first main groove (10) and said third main groove (30) extend from said first shoulder region (4) towards said central region (6) with an inclination, with respect to said circumferential direction, which decreases from said first shoulder region (4) towards said central region (6).

17. A tyre according to any one of claims 10 to 16, wherein said second main groove (20) and said fourth main groove (40) extend from said second shoulder region (5) towards said central region (6), with an inclination, with respect to said circumferential direction, which decreases from said second shoulder region (5) towards said central region (6).

18. A tyre according to any one of the preceding claims, wherein each first group of shoulder blocks (110) is formed by a first pair of shoulder blocks (111, 112) which are separated by a first secondary groove (16).

19. A tyre according to claim 18, wherein said first secondary groove (16) extends between said first main groove (10) and said third main groove (30).

20. A tyre according to claim 18 or 19, wherein said first secondary groove (16) is parallel with said fifth main groove (50).

21. A tyre according to any one of the preceding claims, wherein each second group of shoulder blocks (120) is formed by a second pair of shoulder blocks (121, 122) which are separated by a second secondary groove (25).

22. A tyre according to claim 21, wherein said second secondary groove (25) extends between said third main groove (30) and said further first main groove subsequent to said first main groove (10).

23. A tyre according to claim 21 or 22, wherein said second secondary groove (25) is parallel with said fifth main groove (50).

24. A tyre according to claim 21 or 22 or 23, wherein said second secondary groove (25) is aligned with said first secondary groove (16).

25. A tyre according to any one of the preceding claims, wherein said first group of central blocks (100) is formed by a first pair of central blocks (101, 102) which are separated by a third secondary groove (35).

26. A tyre according to claim 25, wherein said third secondary groove (35) extends between said first main groove (10) and said fifth main groove (50).

27. A tyre according to claim 25 or 26, wherein said third secondary groove (35) is inclined in a discordant manner with respect to said fifth main groove (50).

28. A tyre according to any one of the preceding claims, wherein there are defined on each block of said first group of shoulder blocks (110), said second group of shoulder blocks (120) and said first group of central blocks (100) respective radially external surfaces, each of said radially external surfaces of said blocks having an area which differs from a mean value of the areas of said radially external surfaces of said blocks by a value less than 30% of said mean value.

29. A tyre according to any one of the preceding claims, wherein each main groove has a depth between 6 mm and 12 mm.

30. A tyre according to any one of the preceding claims, wherein each secondary groove has a depth between 2.5 mm and 4.5 mm.