Vehicle wheel tyre

Abstract

A tire (1) comprises a plurality of blocks (5) defined on a tread band (2) and at least one first sipe (10) and one second sipe (10a) formed on each block (5). The first sipe (10) extends along a first longitudinal direction (A) and comprises: a first linear portion (11) extending substantially along the first longitudinal direction (A) towards a first edge (8) of the block (5); only one single-wave portion (12) extending as a continuation of the first linear portion (11) and having a distance from the first edge (8) of 5% to 40% of the distance between the first edge (8) and the opposite second edge (9); and a second linear portion (13) extending towards the second edge (9) as a continuation of the single-wave portion (12). Similarly, the second sipe (10a) extends along a second longitudinal direction (B) and comprises: a first linear portion (11) extending substantially along the second longitudinal direction (B) towards a second edge (9) of the block (5); only one single-wave portion (12) extending as a continuation of the first linear portion (11) and having a distance from the second edge (9) of 5% to 40% of the distance between the first edge (8) and the second edge (9); and a second linear portion (13) extending towards the first edge (8) as a continuation of the single-wave portion (12).

Description

Technical Field

[0001] The present invention relates to tyres for vehicle wheels, in particular the present invention relates to winter tyres. Background Art

[0002] The tyre generally comprises a carcass structure in the shape of a torus about an axis of rotation and comprising at least one carcass ply having end edges engaged in respective annular anchoring structures, called bead cores.

[0003] In a radially external position relative to the carcass structure a belt structure is arranged, which in the case of a car tyre comprises at least two radially superposed rubberised fabric strips provided with reinforcing cords, which are generally made of metal and which are arranged parallel to one another in each strip but crossed with respect to the cords of adjacent strips, preferably symmetrically with respect to the equatorial plane of the tyre.

[0004] Preferably, the belt structure also comprises, in a radially external position, at least on the end of the lower belt strip, a third layer of textile or metal cords arranged circumferentially (at 0 degrees). In tubeless type tires, there is also a radially internal layer called "liner", which has an impermeability in order to ensure the airtightness of the tire itself.

[0005] In a radially outer position with respect to the belt structure there is applied a tread band made of elastomeric material and defining thereon a tread surface intended for contact with the road surface.

[0006] In order to obtain sufficient road grip also on wet roads, the tyres have a tread band provided with grooves of various shapes and geometries, the main purpose of which is to allow the drainage of water present between the tyre surface and the road surface during mutual contact.

[0007] The grooves generally define a plurality of blocks on the tread band, each of which comprises a radially outer surface intended to come into contact with the road surface and thus forming part of the tread surface of the tyre. Each block is also at least partially delimited by one or more walls defined by the grooves surrounding the walls.

[0008] In some cases, the wall of the block or a portion thereof is connected to the tread surface of the block by means of a chamfer, which is generally formed by a plane appropriately inclined relative to the wall and the tread surface and defines the edge of the block.

[0009] In the case of winter tyres, small recesses are usually formed on the blocks of the tread band, which are called "sipes", extending from the tread surface of the tyre towards the inside of the blocks. The function of the sipes is to provide additional gripping elements in the case of driving on snowy roads and to retain a certain amount of snow, thereby improving the grip relative to the road surface. The sipes may have a variety of different configurations, for example, they may have a straight or curved or wavy progression.

[0010] The term "circumferential" direction means a direction pointing substantially in the direction of rotation of the tyre or in any case a direction slightly inclined (at most about 5°) relative to the direction of rotation of the tyre.

[0011] The term "axial" direction means a direction substantially parallel to the axis of rotation of the tyre or at most slightly inclined (up to about 5°) relative to this axis of rotation of the tyre. The axial direction is generally perpendicular to the circumferential direction.

[0012] The term "radial" direction refers to a direction intersecting the axis of rotation of the tire perpendicularly, or a direction at most slightly inclined (for example at most about 5°) relative to a direction perpendicular to the axis of rotation of the tire.

[0013] The term "equatorial plane" of the tire means the axial centerline plane perpendicular to the tire's axis of rotation.

[0014] The term "groove" refers to a recess formed in the tread band portion and extending along a main longitudinal direction and having a width greater than or equal to 1.5 mm. Preferably, the depth of the groove is at least 3 mm.

[0015] The term "sipe" means a recess formed in the tread band portion and extending along a main longitudinal direction and having a width less than 1.5 mm.

[0016] The “longitudinal development direction” of the sipe is defined by the linear progression of the sipe in the radially external surface region of the block.

[0017] The term "block" means the portion of the tread band intended for contact with the road surface, which is delimited over the entire circumference by one or more grooves and, where applicable, by the axial ends of the tread band.

[0018] Thus, a block may be considered both as a portion of the tread band having a closed outline delimited by three or more grooves and as a circumferential rib delimited by a pair of grooves developing circumferentially around the tread band.

[0019] A "central block" is defined as a block not bounded by the axial ends of the tread band, whereas a block partially bounded by one of the axial ends of the tread band is defined as a "shoulder block".

[0020] The term "wall" of a block refers to a surface that extends generally from the bottom of a groove delimiting the block toward the tread surface portion of the block.

[0021] The term "edge" of a block refers to the area of ​​the block joining the wall of the block to the tread surface portion of the block.

[0022] The edge may be formed by a corner if the wall intersects the tread surface portion directly, or it may be formed by a connecting surface connecting the wall to the tread surface portion, which connecting surface is defined as a "chamfer".

[0023] Two or more linear distances, such as, for example, two or more distances between sipes or between sipe elements, have "substantially equal" lengths when the respective lengths differ from each other by no more than 10% of a maximum length.

[0024] Two or more directions or two or more elements extending in respective directions, such as, for example, two or more sipes or parts thereof, are "substantially parallel" when they are inclined relative to each other at an angle of less than 10°, preferably less than 5°.

[0025] The inclination of the first direction relative to the second direction, for example, the inclination of the direction of the sipe portion relative to the longitudinal development direction of the sipe, is defined by the acute angle formed by the first direction and the second direction. As a special example, when the first direction is perpendicular to the second direction, the inclination is 90°.

[0026] Two or more directions or two or more elements extending along respective directions (such as, for example, two or more sipes or portions thereof) are inclined in a "consistent manner" relative to the other direction, in the case where the trends of the two or more directions are both increasing or both decreasing when considered on a Cartesian plane containing the two or more directions and whose abscissa axis is parallel to the other direction. For example, two different portions of the sipe extending along the longitudinal development direction of the sipe are inclined in a consistent manner relative to the longitudinal development direction of the sipe, in the case where the trends of the two or more directions are both increasing or both decreasing when considered on a Cartesian plane containing the two or more directions and whose abscissa axis is parallel to the longitudinal development direction of the sipe.

[0027] Thus, two or more directions or two or more elements extending along respective directions (such as, for example, two or more sipes or portions thereof) are inclined in an "inconsistent manner" with a tendency, when considered on this Cartesian plane, to increase for one or more of said directions and to decrease for one or more other directions of said directions.

[0028] The term "peak" defined on a sipe or a portion thereof means the maximum area or the minimum area defined on a linear segment of the sipe or said portion thereof when considering said linear segment on a Cartesian plane, the abscissa axis of said Cartesian plane being positioned in the longitudinal development direction of the sipe.

[0029] Two sipe portions spaced apart from each other are "substantially aligned" when, at least in the region of their respective two ends facing each other, their longitudinal directions are as follows:

[0030] - Alignment; or,

[0031] - if the respective longitudinal directions are incident on each other, the longitudinal directions are inclined by an angle of less than 10°, preferably less than 5°, or

[0032] If the respective longitudinal directions are parallel to one another, said longitudinal directions are offset by a value less than 1.5 mm.

[0033] Two sipes are “consecutive” when they are arranged one after the other on the tread surface of a block, taking into account a direction perpendicular to the longitudinal development direction of at least one of the two sipes.

[0034] The term "single wave portion" of the sipe means the section of the linear trend of the sipe at the radially external surface of the block having a first wave crest and a second wave crest which are consecutive and in opposite directions with respect to the longitudinal development of the sipe itself.

[0035] The sipe formed on the block divides the block into two block parts having respective mutually facing surfaces.

[0036] A sipe is defined as "complex type" when at least one of the mutually facing surfaces of the block has at least one projection and another of these surfaces has a corresponding recess capable of at least partially receiving this projection. In other words, the corresponding projections in a plane perpendicular to the radial direction of the two blocks separated by the sipe at least partially overlap in the region of the projection and the corresponding recess.

[0037] In this way, a relative movement of the two block parts in the radial direction is hindered by the interference between the two block parts in the region of the projections and recesses.

[0038] Complex type sipes are also known in the art as "three-dimensional" sipes.

[0039] A sipe is defined as being of “simple type” when, on the mutually facing surfaces of the block portions, there are no projections and / or recesses which interfere with each other during the relative movement of the two block portions in the radial direction.

[0040] Examples of sipes configured in various ways are described in, for example, EP 3375639, US 5198047, US 2021 / 0107319, EP 3867081A1, JP 6946658, JP 2018020689, US 3799231, US 20030029537, US 2005 / 0150581, EP 0598300, US 5327953 and US 5591280. Summary of the invention

[0041] The Applicant has observed that the performance level of a tyre on snowy roads depends largely on the number and extent of the sipes formed on the blocks, so that for the same tread pattern, blocks formed with a plurality of sipes can provide better snow performance.

[0042] However, the Applicant has also observed that the presence of the sipes weakens the structure of the block, making it less rigid and thus reducing its ability to withstand external stresses, especially tangential stresses.

[0043] Due to this weakening, during braking, acceleration or cornering, the block may deform in a relevant way, causing it to be partially lifted from the road surface, resulting in a reduction in the contact area between the block and the road surface, and thus also in a reduction in the total friction force exerted by the tire on the road surface.

[0044] The Applicant has demonstrated that the cause of this weakening of the block is related to the fact that the sipe subdivides the block into two parts which can slide relative to one another in the region of the sipe.

[0045] In particular, the Applicant has observed that this sliding occurs in a direction parallel to the separation surface of the two portions and that said sliding can therefore always be considered as the synthesis of movements in two main directions defined on the separation surface: a first direction extending perpendicular to the tread surface from the bottom of the sipe (generally coinciding with the radial direction of the tread band) and a second direction parallel to the longitudinal development direction of the sipe.

[0046] The Applicant has demonstrated that it is possible to improve the resistance of the blocks in the area of ​​the sipe by preventing or limiting to the greatest extent possible the possibility of mutual sliding along these two main directions.

[0047] The Applicant has observed that complex type sipes, having a profile provided with protuberances and corresponding recesses, are able to resist mutual sliding of block portions, in particular movements along the first direction identified above. However, providing a profile of this type is not always sufficient to effectively resist sliding behaviour along the second direction identified above (parallel to the longitudinal development direction of the sipe), in particular in the area of ​​the tread surface.

[0048] The Applicant has therefore observed that, in order to counteract this type of slip, it is generally known to configure the sipes to have an undulating linear progression, for example in a zigzag manner.

[0049] The Applicant has also observed that, in order to obtain a sufficiently effective resistance action, this wavy linear progression must extend over a large part of the longitudinal development of the sipe, providing a plurality of undulations having a substantially symmetrical form.

[0050] However, the Applicant has demonstrated that the resistance to tangential sliding of the block parts provided by this configuration is not always effective.

[0051] Furthermore, the Applicant has also observed that, in the possible case where the sipe opens at the edge of a block, the stiffness of the block itself will further decrease in a consistent manner in the region of this edge.

[0052] The Applicant has therefore identified the need to provide a block in which a sipe is formed with a reduced number of waves and which is also provided with good stiffness properties.

[0053] In order to meet this requirement, the Applicant has realised that, due to the presence of the sipes, the most critical areas on the block structure are the edge areas (where, in particular, some of the sipes may be open), and that sliding of the block portion in the longitudinal development direction of the sipes can therefore also be effectively resisted by a single sipe portion configured in a wavy manner, provided that the single sipe portion is positioned near the edge.

[0054] Finally, the Applicant has found that the above-mentioned problem of being subjected to tangential stresses is solved by a block provided with a pair of sipes, wherein each sipe of the pair has only one single wave portion interposed between linear portions, and wherein the first sipe has a separate single wave portion near a first edge of the block, and the second sipe has a separate single wave portion near a second edge of the block.

[0055] In particular, in a first aspect thereof, the present invention relates to a tyre for vehicle wheels, said tyre comprising a tread band and a tread surface, said tread surface being radially external with respect to said tread band.

[0056] Preferably, the tread band has a plurality of blocks defined thereon.

[0057] Preferably, at least one first sipe and at least one second sipe are formed on each of the plurality of blocks.

[0058] Preferably, said at least one first sipe is consecutive with respect to said at least one second sipe.

[0059] Preferably, said first sipe opens at said tread surface so as to define a first longitudinal development direction of said first sipe.

[0060] Preferably, the first longitudinal direction intersects a first edge and a second edge of the block.

[0061] Preferably, said second sipe opens at said tread surface so as to define a second longitudinal development direction of said second sipe.

[0062] Preferably, the second longitudinal direction intersects the first edge and the second edge of the block.

[0063] Preferably, said first sipe comprises a first linear portion extending substantially along said first longitudinal direction towards said first edge of said block.

[0064] Preferably, the first linear portion of the first sipe is a straight line or a curve, and its minimum curvature radius is not less than 20 mm.

[0065] Preferably, said first sipe comprises a single wave portion extending as a continuation of said first linear portion of said first sipe.

[0066] Preferably, said first sipe comprises only one single wave portion.

[0067] Preferably, the distance between the single wave portion of the first sipe and the first edge measured along the first longitudinal direction is between 5% and 40% of the distance between the first edge and the second edge measured along the first longitudinal direction.

[0068] Preferably, said first sipe comprises a second linear portion extending towards said second edge as a continuation of said single wave portion.

[0069] Preferably, the second linear portion of the first sipe is a straight line or a curve, and its minimum curvature radius is not less than 20 mm.

[0070] Preferably, said second sipe comprises a first linear portion extending substantially along said second longitudinal direction towards said second edge of said block.

[0071] Preferably, the first linear portion of the second sipe is a straight line or a curve, and its minimum curvature radius is not less than 20 mm.

[0072] Preferably, said second sipe comprises a single wave portion extending as a continuation of said first linear portion of said second sipe.

[0073] Preferably, said second sipe comprises only one single wave portion.

[0074] Preferably, the distance between said single wave portion of said second sipe and said second edge measured along said second longitudinal direction is between 5% and 40% of the distance between said first edge and said second edge measured along said second longitudinal direction.

[0075] Preferably, said second sipe comprises a second linear portion extending towards said first edge as a continuation of said single wave portion.

[0076] Preferably, the second linear portion of the second sipe is a straight line or a curve, and its minimum curvature radius is not less than 20 mm.

[0077] The Applicant believes that, thanks to these characteristics, it is possible to effectively resist the sliding behaviour of the block portions separated by the sipe, even with only one single wave portion, thus allowing, under the same other conditions, to obtain a more rigid block and one that can offer better behaviour on dry and icy roads.

[0078] It may be noted that the distance of the single wave portion from the first edge is measured from the center point of the single wave portion at the first edge or the distance of the single wave portion from the second edge is measured from the center point of the single wave portion at the second edge.

[0079] The present invention in the above aspects may have at least one of the following additional preferred features.

[0080] In some embodiments, said first linear portion of said first sipe opens at said first edge of said block.

[0081] In some embodiments, said first linear portion of said second sipe opens at said second edge of said block.

[0082] In some embodiments, the distance between the single wave portion of the first sipe and the first edge measured along the first longitudinal direction is 25% to 35% of the distance between the first edge and the second edge measured along the first longitudinal direction.

[0083] In some embodiments, the distance between the single wave portion of the second sipe and the second edge measured along the second longitudinal direction is 25% to 35% of the distance between the first edge and the second edge measured along the second longitudinal direction.

[0084] In some embodiments, the single wave portion of the first sipe comprises a first segment inclined relative to the first longitudinal direction.

[0085] Preferably, said first segment extends from said first linear portion of said first sipe up to a first wave crest of said single wave portion.

[0086] Preferably, said single wave portion of said first sipe comprises a second segment inclined with respect to said first longitudinal direction.

[0087] Preferably, the second segment extends from the first wave peak to a second wave peak of the single wave portion.

[0088] Preferably, the second wave peak is defined on an opposite side of the first wave peak with respect to the first longitudinal direction.

[0089] Preferably, said single wave portion of said first sipe comprises a third segment inclined with respect to said first longitudinal direction.

[0090] Preferably, the third segment extends from the second wave peak to the second linear portion of the first sipe.

[0091] Preferably, the second segment of the single wave portion is inclined at an angle relative to the first longitudinal direction that is greater than the angles at which the first segment and the third segment of the single wave portion are inclined relative to the first longitudinal direction.

[0092] Thanks to this particular configuration, the Applicant believes that the single wave portion of the first sipe confers sufficient rigidity to the block, in particular in the region of its first edge, to withstand in a particularly effective way the tangential stresses relative to the tread surface.

[0093] In some embodiments, said single wave portion of said second sipe comprises a first segment inclined relative to said second longitudinal direction.

[0094] Preferably, said first segment extends from said first linear portion of said second sipe up to a first wave crest of said single wave portion.

[0095] Preferably, said single wave portion of said second sipe comprises a second segment inclined with respect to said second longitudinal direction.

[0096] Preferably, the second segment extends from the first wave peak to a second wave peak of the single wave portion.

[0097] Preferably, the second wave peak is defined on an opposite side of the first wave peak with respect to the second longitudinal direction.

[0098] Preferably, said single wave portion of said second sipe comprises a third segment inclined with respect to said second longitudinal direction.

[0099] Preferably, the third segment extends from the second wave peak to the second linear portion of the second sipe.

[0100] Preferably, the second segment of the single wave portion is inclined at an angle relative to the second longitudinal direction that is greater than the angles at which the first segment and the third segment of the single wave portion are inclined relative to the second longitudinal direction.

[0101] Thanks to this particular configuration, the Applicant believes that the single wave portion of the second sipe confers sufficient rigidity to the block, in particular in the region of its second edge, to withstand in a particularly effective way the tangential stresses relative to the tread surface.

[0102] Therefore, the first sipe and the second sipe preferably have a similar configuration, which is formed by a single wave portion between the first linear portion and the second linear portion.

[0103] In some embodiments, in said first sipe, said first segment of said single wave portion is inclined with respect to said first longitudinal direction at an angle comprised between 20° and 45°, more preferably at about 24°.

[0104] In some embodiments, in said first sipe, said third segment of said single wave portion is inclined with respect to said first longitudinal direction at an angle comprised between 20° and 45°, more preferably at about 24°.

[0105] In some embodiments, in said first sipe, said second segment of said single wave portion is inclined with respect to said first longitudinal direction at an angle comprised between 60° and 90°, preferably at about 80°.

[0106] In some embodiments, in the first sipe, the distance between the first wave peak and the first longitudinal direction is substantially equal to the distance between the second wave peak and the first longitudinal direction. Preferably, the distance is between 0.5 mm and 1.5 mm, more preferably about 1 mm.

[0107] In some embodiments, in said second sipe, said first segment of said single wave portion is inclined with respect to said second longitudinal direction at an angle comprised between 20° and 45°, more preferably at about 24°.

[0108] In some embodiments, in said second sipe, said third segment of said single wave portion is inclined with respect to said second longitudinal direction at an angle comprised between 20° and 45°, more preferably at about 24°.

[0109] In some embodiments, in said second sipe, said second segment of said single wave portion is inclined with respect to said second longitudinal direction at an angle comprised between 60° and 90°, preferably at about 80°.

[0110] In some embodiments, in the second sipe, the distance between the first wave peak and the second longitudinal direction is substantially equal to the distance between the second wave peak and the second longitudinal direction. Preferably, the distance is between 0.5 mm and 1.5 mm, more preferably about 1 mm.

[0111] Preferably, in the first sipe or the second sipe, the first segment and the third segment of the single wave portion are inclined in a consistent manner relative to each other.

[0112] Preferably, in the first sipe or the second sipe, the second segment of the single wave portion is inclined in a non-uniform manner with respect to the first segment and the third segment of the single wave portion.

[0113] In some embodiments, in the first sipe or the second sipe, the first segment and the third segment of the single wave portion are substantially parallel to each other.

[0114] In some embodiments, in the first sipe or the second sipe, a length of the first segment of the single wave portion is substantially the same as a length of the third segment of the single wave portion.

[0115] Preferably, in the first sipe or the second sipe, the length of the first segment and the third segment of the single wave portion is between 1.5 and 3 mm, more preferably the distance is about 2 mm.

[0116] In some embodiments, in the first sipe or the second sipe, the length of the second linear portion is at least 50% greater, preferably at least 100% greater, more preferably at least 200% greater relative to the first linear portion.

[0117] In this way, the single wave portion of the first sipe is greatly offset from the centre relative to the first and second portions, allowing it to be positioned at the edge of the block where it can perform the function of reinforcing the block in an even more effective manner.

[0118] In some embodiments, the first longitudinal direction is substantially parallel to the second longitudinal direction.

[0119] Preferably, in the first sipe or the second sipe, the length of the first linear portion is between 2 mm and 5 mm.

[0120] Preferably, in the first sipe or the second sipe, the depth in the region of the first linear portion is smaller than the depth in the region of the single wave portion.

[0121] In this way, the reinforcing effect of the block in the region of the first linear portion is advantageously increased.

[0122] In some embodiments, said second linear portion of said first sipe opens at said second edge of said block.

[0123] In some embodiments, said second linear portion of said second sipe opens at said first edge of said block.

[0124] Preferably, in the first sipe or the second sipe, the length of the second linear portion is between 4 mm and 25 mm.

[0125] In some embodiments, in the first sipe, the second linear portion is substantially aligned with the first linear portion along the first longitudinal direction.

[0126] In some embodiments, in the second sipe, the second linear portion is substantially aligned with the first linear portion along the second longitudinal direction.

[0127] In some embodiments, the first peak portion of the first sipe and the first peak portion of the second sipe are laterally offset on the same side relative to the first longitudinal direction of the first sipe and the second longitudinal direction of the second sipe, respectively.

[0128] In other words, the first, second and third segments of the first sipe are inclined in a non-uniform manner with respect to the first or second longitudinal direction with respect to the first, second and third segments of the second sipe, respectively.

[0129] In this way, the respective second segments of the first and second sipes, intended to provide maximum resistance to longitudinal sliding of the block parts, are inclined in a non-uniform manner relative to each other so as to render the stiffness of the block substantially uniform when it is subjected to tangential stresses parallel to and oriented in opposite directions to the first or second longitudinal directions.

[0130] In some embodiments, at least three sipes are formed in succession to each other on the block, and the at least three sipes are formed alternately and successively by one of the first sipes and one of the second sipes.

[0131] In some embodiments, a central block is formed on said tread band which is delimited only by one or more grooves.

[0132] In some embodiments, each central block of said tread band comprises at least one of said first sipes and at least one of said second sipes.

[0133] In some embodiments at least 80% of the sipes formed in the central block of said tread band having a length greater than a minimum predetermined value, more preferably all of the sipes are either one of said first sipes or one of said second sipes.

[0134] Preferably, the minimum predetermined value is between 5 mm and 15 mm, for example approximately 10 mm.

[0135] In this way, the sipe extends far enough to be able to have a configuration in which a single wave portion is interposed between two linear portions of suitable dimensions.

[0136] In some embodiments, said at least one first sipe and said at least one second sipe are of complex type. BRIEF DESCRIPTION OF THE DRAWINGS

[0137] The characteristics and advantages of the present invention will be better understood by referring to the detailed description of several preferred embodiments of the invention shown by way of non-limiting examples with reference to the accompanying drawings, in which:

[0138] - Figure 1 is a schematic elevational view of a tread band portion of a tire for a vehicle wheel manufactured in accordance with the present invention;

[0139] - Figure 2 is Figure 1 A schematic front view, drawn on an enlarged scale, of first and second sipes formed on a block of a tire. DETAILED DESCRIPTION

[0140] With reference to the accompanying drawings, generally designated 1 therein is a tire (not shown in its entirety) for vehicle wheels manufactured in accordance with the present invention.

[0141] The tyre 1 has a conventional substantially toroidal shape, developed around an axis of rotation and defining an axial direction Y of the tyre, through which passes an equatorial plane X perpendicular to the axis of rotation.

[0142] The tyre 1 comprises a tread band 2 on which is defined a tread surface 3 arranged in a radially outer position with respect to the tread band 2 and intended for contact with a road surface.

[0143] For example, the nominal section width of tire 1 is about 205 mm and the rim diameter is 16 inches.

[0144] The tread band 2 still defines a central region extending circumferentially symmetrically near the equatorial plane X and a pair of shoulder regions, which extend at axially opposite sides of the central region to corresponding axial ends 2a of the tread band 2.

[0145] A plurality of grooves are formed on the tread band 2, each of which is marked 4 and which define a corresponding plurality of central blocks 5 formed in a central region of the tread band 2 and a plurality of shoulder blocks 6 formed in a shoulder region of the tread band 2, and the shoulder blocks are defined in their axially outer regions by the axial ends 2a of the tread band 2.

[0146] In the embodiment described here, the grooves 4 have a depth between 3 mm and 9 mm and a width between 2.5 mm and 9.5 mm.

[0147] For example, Figure 1 The central blocks 5 and the shoulder blocks 6 are schematically shown, it being understood that the same considerations apply analogously to all other central blocks and other shoulder blocks 6 formed in the tread band 2 .

[0148] The central block 5 is defined with: a tread surface portion 3, which is defined on the radially outer surface of the central block and is intended for contact with the road surface; a first edge 8 and a second edge 9 opposite to the first edge 8, the first edge and the second edge connecting the tread surface portion 3 of the central block 5 with the wall of the corresponding groove 4.

[0149] The first edge 8 and the second edge 9 together delimit the tread surface portion 3 of the central block 5 and may be fully or partially chamfered.

[0150] A plurality of first sipes 10 and a plurality of second sipes 10 a are formed on each central block 5 in an alternating manner.

[0151] The first sipes 10 extend along respective first longitudinal directions A, whereas the second sipes 10a extend along respective second longitudinal directions B. All first longitudinal directions A and second longitudinal directions B are substantially parallel to each other.

[0152] In the illustrated embodiment of the central block 5 , the first longitudinal direction A and the second longitudinal direction B are inclined by about 60° relative to the equatorial plane X, but these directions can have different inclinations and can be parallel to the axial direction Y.

[0153] The first sipes 10 and the second sipes 10a are formed on the central block 5 in an alternating manner and are preferably equidistant, for example, at a spacing between about 5 mm and about 6 mm.

[0154] The first sipe 10 and the second sipe 10a follow one after another and have a similar structure, as will be explained in more detail below.

[0155] from Figure 2 As can be better seen in FIG. 5 , each first sipe 10 extends in the first longitudinal direction A beyond the central block 5 so as to open at the first edge 8 and at the second edge 9 .

[0156] Each first sipe 10 includes a first linear portion 11 opening at the first edge 8 , a single wave portion 12 extending as a continuation of the first linear portion 11 , and a second linear portion 13 extending as a continuation of the single wave portion 12 and opening at the second edge 9 .

[0157] Both the first linear portion 11 and the second linear portion 13 are substantially straight and aligned along the first longitudinal direction A.

[0158] The length of the second linear portion 13 may be greater than that of the first linear portion 11 , preferably, it is at least 50% greater than the first linear portion 11 , more preferably at least 100% greater, even more preferably at least 200% greater.

[0159] The length of the first linear portion 11 is between 2 mm and 5 mm, while the length of the second linear portion 13 is between 4 mm and 25 mm.

[0160] The single wave portion 12 includes:

[0161] a first substantially rectilinear segment 14 extending from the first linear portion 11 up to the first wave crest 15 and inclined relative to the first longitudinal direction A;

[0162] a second substantially rectilinear segment 16 extending from the first wave peak 15 as far as a second wave peak 17 defined on the opposite side of the first wave peak 15 with respect to the first longitudinal direction A; and

[0163] a third substantially rectilinear segment 18 which extends from the second wave crest 17 as far as the second linear portion 13 and which is inclined relative to the first longitudinal direction A.

[0164] The first segment 14 and the third segment 18 are substantially parallel to each other and are inclined by about 24° with respect to the first longitudinal direction A. Furthermore, the first segment 14 and the third segment 18 have substantially equal lengths, which are about 2 mm.

[0165] The second section 16 is inclined by approximately 80° with respect to the first longitudinal direction A in a manner that is not consistent with the first section 14 and the third section 18 with respect to the first longitudinal direction A.

[0166] The distances of the first wave crest 15 and the second wave crest 17 from the first longitudinal direction A are substantially the same and are respectively equal to about 1 mm.

[0167] Thus, the single wave portion 12 is substantially symmetrical with respect to the point where the second segment 16 intersects the first longitudinal direction A defined by the first linear portion 11 and the second linear portion 13 .

[0168] Each first sipe 10 has a width of about 0.5 mm and a variable depth between 2 mm (at the end areas of the first sipe, in particular at the first linear portion 11) and 7 mm (at the single wave portion 12 and the central area of ​​the first sipe 10).

[0169] Each first sipe 10 is also preferably of complex type, having along its radial profile one or more protuberances and corresponding recesses which hinder the free sliding in radial direction of the portions of the central block 5 separated by the same first sipe 10 .

[0170] As mentioned above, the second sipes 10a are similar to the first sipes 10. In fact, in each second sipe 10a, a first linear portion 11 can be identified, followed by a single wave portion 12 and thus by a second linear portion 13, which is longer than the first linear portion 11.

[0171] Each second sipe 10a differs from any first sipe 10 in that, in the second sipe 10a, the first linear portion 11 opens at the second edge 9 (as well as at the first edge 8), and the second linear portion 13 opens at the first edge 8 (as well as at the second edge 9).

[0172] Due to the fact that the first sipes 10 and the second sipes 10a are arranged in an alternating manner, the single wave portions 12 of the first sipes 10 and the second sipes 10a are positioned in an alternating manner near the first edge 8 and near the second edge 9 so as to reinforce the two edges of the central block 5 in a substantially homogeneous manner.

[0173] Furthermore, the first wave peak 15 of each first sipe 10 and the first wave peak 15 of each second sipe 10a are laterally offset relative to the respective longitudinal directions A and B on the same side.

[0174] This configuration is obtained by configuring the sipes 10 and 10a in such a way that the first, second, and third segments 14, 16, 18 of the first sipe 10 are inclined in a non-uniform manner relative to the first longitudinal direction A relative to the first, second, and third segments 14, 16, 18 of the second sipe 10a.

[0175] Preferably, at least 80% of the sipes formed on the central block 5 are first sipes 10 or second sipes 10a, provided that their total length is greater than a minimum value of about 10 mm.

[0176] In the case where a smaller sipe is provided on the central block 5, as Figure 1 The case of a corner region is shown, in which the sipe is referenced 19 , which sipe may have a different configuration, for example straight or wavy with a single crest.

[0177] A plurality of third sipes 20 are formed on the shoulder blocks 6 , and extend parallel to each other along corresponding third longitudinal development directions A′, which are usually different from the first longitudinal direction A and the second longitudinal direction B.

[0178] The third sipe 20 is similar to the first and second sipes 10 and 10a formed on the central block 5, but unlike the first and second sipes 10 and 10a having only one single wave portion 12, the third sipe 20 has two single wave portions.

[0179] Therefore, each third tread groove 20 includes: a first linear portion 21, which opens at the first edge 7 of the shoulder block 6; a first single wave portion 22, which extends as a continuation of the first linear portion 21; a second linear portion 23, which extends as a continuation of the first single wave portion 22; a second single wave portion 24, which extends as a continuation of the second linear portion 23; and a third linear portion 25, which extends as a continuation of the second single wave portion 24 to the axial end 2a of the tread band 2.

[0180] It may be noted that the third linear portion 25 may be considered as a first linear portion of the second single-wave portion 24 , and the second linear portion 23 is common to the single-wave portions 22 and 24 .

[0181] The single wave portions 22 and 24 of the third sipe 20 are completely similar to the single wave portion 12 described in detail above with reference to the first and second sipes 10, 10a.

[0182] The Applicant has verified that the central block 5 provided with a plurality of first and second sipes as described above has the best resistance to tangential stresses directed along the longitudinal development direction, thus improving the performance level on icy and dry roads.

[0183] In particular, the central block 5 has optimal stiffness and behaviour uniformity characteristics in the region of the edges 8 and 9 .

[0184] Of course, in order to meet specific and accidental application requirements, those skilled in the art may make additional modifications and variations to the above invention, which are still included in the protection scope defined by the appended claims.

[0185] For example, the number of first sipes and / or second sipes present on the central block may be different from the number described above.

Claims

1. A tire (1), comprising a tread band (2), a tread surface (3) located radially outward relative to the tread band, a plurality of blocks (5) defined on the tread band (2), and at least one first sipe (10) and one second sipe (10a), the first sipe and the second sipe being successive to each other and formed on each of the plurality of blocks (5), the first sipe (10) and the second sipe (10a) opening at the tread surface (3) so as to define a first longitudinal direction (A) of development of the first sipe (10) and a second longitudinal direction (B) of development of the second sipe (10a), respectively, the first longitudinal direction (A) and the second longitudinal direction (B) intersecting a first edge (8) and a second edge (9) of the block (5), wherein: The first tread groove (10) comprises: - a first linear portion (11) extending substantially along the first longitudinal direction (A) towards the first edge (8) of the block (5), - only one single wave portion (12) extending as a continuation of the first linear portion (11) and being at a distance from the first edge (8) measured along the first longitudinal direction (A) of 5% to 40% of the distance between the first edge (8) and the second edge (9) measured along the first longitudinal direction (A), and - a second linear portion (13) extending towards the second edge (9) as a continuation of the single-wave portion (12), Wherein, the second tread groove (10a) comprises: - a first linear portion (11) extending substantially along the second longitudinal direction (B) towards the second edge (9) of the block (5), - only one single wave portion (12) extending as a continuation of the first linear portion (11) and being at a distance from the second edge (9) measured along the second longitudinal direction (B) of 5% to 40% of the distance between the first edge (8) and the second edge (9) measured along the second longitudinal direction (B), and - a second linear portion (13), which extends towards the first edge (8) as a continuation of the single-wave portion (12), and wherein the first linear portion (11) and the second linear portion (13) of the first sipe (10) and the second sipe (10a) are straight lines or curves, whose minimum curvature radius is not less than 20 mm.

2. The tire (1) according to claim 1, wherein: The distance between the single wave portion (12) of the first sipe (10) and the first edge (8) measured along the first longitudinal direction (A) is 25% to 35% of the distance between the first edge (8) and the second edge (9) measured along the first longitudinal direction (A).

3. The tire (1) according to claim 1 or 2, wherein: The distance between the single wave portion (12) of the second sipe (10a) and the second edge (9) measured along the second longitudinal direction (B) is 25% to 35% of the distance between the second edge (9) and the first edge (8) measured along the second longitudinal direction (B).

4. Tyre (1) according to any one of the preceding claims, wherein: The single wave portion (12) of the first sipe (10) comprises: a first section (14) which is inclined relative to the first longitudinal direction (A) and which extends from the first linear portion (11) to a first wave crest (15), a second section (16) which is inclined relative to the first longitudinal direction (A) and extends from the first wave crest (15) to a second wave crest (17) which is defined on the opposite side of the first wave crest (15) relative to the first longitudinal direction (A), and - a third section (18) which is inclined relative to the first longitudinal direction (A) and extends from the second wave crest (17) to the second linear portion (13).

5. Tyre (1) according to any one of the preceding claims, wherein: The single wave portion (12) of the second sipe (10a) comprises: a first section (14) which is inclined relative to the second longitudinal direction (B) and which extends from the first linear portion (11) to a first wave crest (15), a second segment (16) which is inclined relative to the second longitudinal direction (B) and extends from the first wave crest (15) to a second wave crest (17) which is defined on the opposite side of the first wave crest (15) relative to the second longitudinal direction (B), and - a third section (18) which is inclined relative to the second longitudinal direction (B) and extends from the second wave crest (17) to the second linear portion (13).

6. The tire according to claim 4 or 5, wherein: The second segment (16) of the single-wave portion (12) is inclined at an angle relative to the first longitudinal direction (A) or the second longitudinal direction (B), respectively, which is greater than the angle at which the first segment (14) and the third segment (18) are inclined relative to the first longitudinal direction or the second longitudinal direction.

7. The tire (1) according to claim 4 or 5, wherein: The first segment (14) and the third segment (18) of the single wave portion (12) are inclined at an angle between 20° and 45° relative to the first longitudinal direction (A) or the second longitudinal direction (B), respectively.

8. The tire (1) according to claim 4 or 5, wherein: The second segment (16) of the single wave portion (12) is inclined at an angle between 60° and 90° relative to the first longitudinal direction (A) or the second longitudinal direction (B), respectively.

9. Tyre (1) according to any one of claims 4 to 8, wherein: In the first sipe (10) or the second sipe (10a), the first segment (14) and the third segment (18) of the single wave portion (12) are substantially parallel.

10. Tyre (1) according to any one of claims 4 to 9, wherein: In the first sipe (10) or the second sipe (10a), the length of the first segment (14) of the single wave portion (12) is substantially the same as the length of the third segment (18) of the single wave portion (12).

11. Tyre (1) according to any one of claims 4 to 10, wherein: In the first sipe (10) or the second sipe (10a), the distance between the first wave peak (15) and the first longitudinal direction (A) or the second longitudinal direction (B) and the distance between the second wave peak (17) and the first longitudinal direction (A) or the second longitudinal direction (B) are substantially the same.

12. Tyre (1) according to any one of the preceding claims, wherein: In the first sipe (10) or the second sipe (10a), the length of the second linear portion (13) is at least 50% greater than that of the first linear portion (11).

13. Tyre (1) according to the preceding claim, wherein: In the first sipe (10) or the second sipe (10a), the length of the second linear portion (13) is at least 100% greater than that of the first linear portion (11).

14. Tyre (1) according to the preceding claim, wherein: In the first sipe (10) or the second sipe (10a), the length of the second linear portion (13) is at least 200% greater than that of the first linear portion (11).

15. Tyre (1) according to any one of the preceding claims, wherein: The first longitudinal direction (A) is substantially parallel to the second longitudinal direction (B).

16. Tyre (1) according to any one of the preceding claims, wherein: In the first sipe (10) or the second sipe (10a), the length of the first linear portion (11) is between 2 mm and 5 mm.

17. Tyre (1) according to any one of the preceding claims, wherein: In the first sipe (10) or the second sipe (10a), the depth in the region of the first linear portion (11) is smaller than the depth in the region of the single wave portion (12).

18. Tyre (1) according to any one of the preceding claims, wherein: The first linear portion (11) of the first sipe (10) opens at the first edge (8) of the block (5).

19. Tyre (1) according to any one of the preceding claims, wherein: The first linear portion (11) of the second sipe (10a) opens at the second edge (9) of the block (5).

20. Tyre (1) according to any one of the preceding claims, wherein: The second linear portion (13) of the first sipe (10) opens at the second edge (9) of the block (5).

21. Tyre (1) according to any one of the preceding claims, wherein: The second linear portion (13) of the second sipe (10a) opens at the first edge (8) of the block (5).

22. Tyre (1) according to any one of the preceding claims, wherein: In the first sipe (10) or the second sipe (10a), the length of the second linear portion (13) is between 4 mm and 25 mm.

23. Tyre (1) according to any one of the preceding claims, wherein: In said first sipe (10), said second linear portion (13) is substantially aligned with said first linear portion (11) along said first longitudinal direction (A).

24. Tyre (1) according to any one of the preceding claims, wherein: In the second sipe (10a), the second linear portion (13) is substantially aligned with the first linear portion (11) along the second longitudinal direction (B).

25. Tyre (1) according to any one of claims 4 to 24, wherein: The first wave peak (15) of the first sipe (10) and the first wave peak (15) of the second sipe (10a) are respectively laterally offset on the same side relative to the first longitudinal direction (A) of the first sipe (10) and the second longitudinal direction (B) of the second sipe (10a).

26. Tyre (1) according to any one of the preceding claims, wherein: At least three sipes are formed in succession on the block (5), and the at least three sipes are formed alternately and successively by one of the first sipes (10) and one of the second sipes (10a).

27. The tire according to any one of the preceding claims, wherein: Central blocks (5) are formed on said tread band (2) and are delimited only by one or more grooves (4), each central block (5) comprising at least one of said first sipes (10) and at least one of said second sipes (10a).

28. Tyre (1) according to claim 27, wherein: At least 80% of the sipes formed on said central block (5) of said tread band (2) and having a length greater than a minimum predetermined value are one of said first sipes (10) or one of said second sipes (10a).

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