Tyre for vehicle wheels

Abstract

A tyre (1) for vehicles wheels comprises a tread band (2), on which there are defined main pair of grooves (10, 20) between which a first secondary main groove (30), and a first and second block (60, 70) delimited by the pair of main grooves and separated from each other by the first secondary groove (30). Both the edge (61) of the first block (60) and the edge (71) of the second block (70) facing the first secondary groove (30) comprise at least three edge portions, adjacent to each other and comprising at least a first edge portion (61a; 71a) defined by a chamfer and at least a second edge portion (61b; 71b) defined by an angular edge, alternating with each other. Each first edge portion (61a) of the first block (60) is aligned with a second edge portion (71b) of the second block (70), and each second edge portion (61b) of the first block (60) is aligned with a first edge portion (71a) of the second block (70).

Description

[0001] TYRE FOR VEHICLE WHEELS

[0002] DESCRIPTION

[0003] The present invention concerns a tyre for vehicle wheels, in particular a winter tyre. A tyre generally comprises a carcass structure shaped toroidally around a rotation axis and including at least one carcass ply having end flaps which are engaged in respective annular anchoring structures, called bead cores.

[0004] In a position radially external to the carcass structure, a belt structure is provided comprising, in the case of car tyres, at least two radially superimposed strips of rubberised fabric provided with reinforcing cords, usually metallic, arranged in each strip parallel to each other but crossed with respect to the cords of the adjacent strip, preferably symmetrically with respect to the equatorial plane of the tyre.

[0005] Preferably, the belt structure further comprises in a radially external position, at least on the ends of the underlying belt strips, also a third layer of textile or metallic cords, arranged circumferentially (at 0 degrees). In tubeless type tyres, there is also a radially internal layer, called the "liner", which has waterproofing characteristics to obtain the air sealing of the tyre itself.

[0006] In a position radially external to the belt structure, a tread band, made of elastomeric material, is applied on which a tread surface intended for contact with the road surface is defined.

[0007] The tyres, in order to obtain adequate grip even on a wet road surface, have a tread band provided with grooves of various shapes and geometry whose main function is to allow the evacuation of the water present between the surface of the tyre and the road surface at the time of mutual contact, preventing the hydrostatic pressure deriving from the impact of the water against the forward travelling tyre from causing the tyre to lift even partially from the road surface and the consequent loss of control of the vehicle (a phenomenon known as "aquaplaning'").

[0008] The grooves formed in the circumferential direction also affect the directionality and travel stability characteristics of the tyre in relation to the ability of the tyre to bear the tangential stresses parallel to the rotation axis of the tyre.

[0009] The grooves formed in the transverse direction, in turn, affect the traction characteristics of the tyre, i.e. the ability to transmit the tangential stresses parallel to the travel direction to the road surface, in particular during the acceleration and braking of the vehicle.

[0010] The grooves, overall, define on the tread band a plurality of blocks, each of which comprises a radially external surface intended for contact with the road surface, and which, therefore, forms a portion of the tread surface of the tyre. Each block is furthermore delimited, at least partially, by one or more walls of the grooves that surround it.

[0011] In some cases, a wall of a groove, or a portion thereof, is connected to the tread surface of the block by a chamfer, typically formed by a plane, suitably inclined with respect to the wall and the tread surface, defining an edge of the block.

[0012] In the case of winter tyres, small notches, known as "sipes", are generally cut into the tread blocks of the tread band, extending from the tread surface of the tyre towards the inside of the block, the function of the sipes is to provide additional grip when driving on snow-covered surfaces and to retain a certain amount of snow, thereby improving grip with the road surface.

[0013] With "circumferential" direction is intended to mean a direction generally oriented according to the rotation direction of the tyre, or, in any case, slightly inclined (at most at about 10°) with respect to the rotation direction of the tyre.

[0014] The term "axial" and the expressions "axially internal / external" are used with reference to the axial direction of the tyre, i.e. to a direction parallel to the rotation axis of the same or at most inclined at 5° with respect to it. The axial direction is generally perpendicular to the circumferential direction.

[0015] With the term "equatorial plane" of the tyre is intended to mean an axial centre line plane perpendicular to the rotation axis of the tyre.

[0016] With "shoulder regions" of the tread band, is intended to mean the portions of tread band that extend circumferentially in a position axially external to the tread band itself.

[0017] Preferably, each shoulder region extends over a width equal to at least 10% of the width of the tread band, more preferably equal to at least 20% of the width of the tread band.

[0018] Preferably, each shoulder region extends over a width less than 30% of the width of the tread band, more preferably less than 25% of the width of the tread band.

[0019] With "equatorial region" of the tread band is intended to mean the portion of tread band extending circumferentially in a symmetrical manner around the equatorial plane and delimited on its axially opposed sides by said shoulder regions.

[0020] The term "groove" is intended to mean a cavity formed in a portion of tread band, having a width greater than or equal to 1.5 mm, and preferably a depth greater than 3 mm.

[0021] The terms "transverse" and "transversely" indicate a direction inclined with respect to the circumferential direction by an acute angle greater than at least 10°.

[0022] The term "sipe" is intended to mean a cavity formed in a portion of tread band, having a width less than 1.5 mm, preferably less than or equal to 1 mm.

[0023] With "block" is intended to mean a portion of tread surface that is delimited by at least one groove, preferably by at least two distinct grooves, on which there is defined, on the radially external surface thereof, a portion of tread surface intended for contact with the road surface.

[0024] The "wall" of a groove refers to the area generally extending towards the tread surface from a groove bottom.

[0025] The "edge" of a block is defined as the region of the block that joins a wall of a groove delimiting the block with the portion of the block's tread surface. The edge as defined above is to be understood as separate from the wall, i.e. the edge is not part of the wall.

[0026] When the block is completely delimited by grooves, the edge then defines the perimeter contour of the portion of tread surface of the block.

[0027] The edge, or a part of it, may be formed by an angular edge, where the wall directly intersects the portion of tread surface, or it may be formed by a connecting surface that connects the wall with the portion of tread surface.

[0028] The "chamfer" of a block is understood to be this connecting surface.

[0029] Preferably the chamfer is formed by a flat surface, but it can also take on a rounded shape.

[0030] If the chamfer is formed by a flat surface, the chamfer is inclined with respect to both the tread surface and the groove wall.

[0031] The width of a chamfer is defined as the measurement of the width of the orthogonal projection of the chamfer on the tread surface calculated in a direction perpendicular to the longitudinal direction of the edge on which the chamfer is formed.

[0032] It should be noted that the "length" of an element, e.g. an edge or a portion thereof, is the measurement of the prevailing dimension of that element.

[0033] The expression length "substantially equal / equal to", relating to two or more elements, is used when their respective lengths differ from each other by, at most, 10% of the greater length.

[0034] Two or more directions, or two or more elements extending along respective directions, such as two or more sipes, are "substantially parallel" when they are inclined to each other by an angle of less than 10°, preferably less than 5°.

[0035] A groove is said to be a "main groove" when it extends transversely from a shoulder region to an equatorial region of the tread band. Preferably, a main groove extends on the tread band so as to cover at least 30% of the width of the tread band, more preferably at least 40% of the width of the tread band.

[0036] Preferably, a main groove is open at an axial end of the tread band.

[0037] Preferably said main grooves have a decreasing inclination with respect to an equatorial plane of the tread band from the shoulder region towards the equatorial region.

[0038] Preferably, a main groove has a depth of at least 5 mm.

[0039] Preferably, a main groove has a width of at least 3 mm, more preferably of at least 5 mm.

[0040] A groove is said to be a "secondary groove" when it extends between a pair of main grooves.

[0041] Two or more elements of the tread band, e.g. two edge portions of respective blocks, are "aligned" according to an "alignment direction" when the orthogonal projections of those elements in a plane perpendicular to the alignment direction overlap by at least 80%, and more preferably by at least 90%, of the smaller projection.

[0042] With "tread pattern" is intended to mean the overall configuration of the tread band as defined by the set of grooves and blocks delimited by them.

[0043] WO 2016\189418, in the name of the same Applicant, describes a winter tyre comprising a plurality of transverse grooves, arranged in succession along the circumferential extension of the tyre, joined together by secondary grooves defining a plurality of blocks aligned along the direction of the transverse grooves and separated from each other by the secondary grooves.

[0044] WO 2023 / 238027, on behalf of the same Applicant, describes a winter tyre in which, in some blocks, the edges comprise alternating portions of chamfers and angular edges.

[0045] The Applicant has noted that the performance of a tyre on a snow-covered surface depends heavily on the ability of the tread band to retain snow on its outer surface, so as to take advantage of the greater coefficient of friction present between snow and snow than between rubber and snow.

[0046] The Applicant has verified that the function of retaining snow on the tread surface is generally delegated to the provision of sipes on the blocks, so that, with the same tread pattern, a block on which more sipes are provided is able to offer better behaviour on snow.

[0047] However, the Applicant has also noted that the presence of the sipes weakens the structure of the block, making it less rigid and thus decreasing the block's ability to withstand external stresses, in particular tangential stresses.

[0048] Due to this weakening, during braking, acceleration or on bends, the block can be deformed, causing partial lifting of the block from the road surface with a consequent reduction in the contacting area between block and road surface and in the overall frictional force exerted by the tyre on the road surface.

[0049] In other words, the Applicant has verified that the provision of a high number of sipes on a block, while on the one hand improving the behaviour of the block on snowy surfaces, can penalise the performance of the block in terms of grip on both dry and wet road surfaces.

[0050] The Applicant las also noted that the amount of snow retained on the tread surface depends not only on the quantity and extension of the sipes on the blocks, but also on the quantity and configuration of the grooves delimiting the blocks.

[0051] The Applicant therefore has preliminarily realised that in order to improve the performance of the tyre on snowy surfaces without increasing the number and extension of the sipes, it might be useful to modify the conformation of the edges of the blocks so as to increase the number of gripping edges of the tread band on the snow.

[0052] In particular, the Applicant has observed that a chamfer formed on a portion of the edge of a block and adjacent to a "sharp-angular edge" edge portion, i.e. defined by the intersection of the wall of the groove delimiting the block with the tread surface of the block, defines additional gripping angular edges precisely at the end of the sharp-angular edged portion facing the chamfered edge portion.

[0053] The Applicant has then verified that by configuring the edge of a block with an alternation of chamfered and sharp-angular edged portions, new gripping angular edges were obtained without excessively diminishing the tread surface of the block. The Applicant also perceived that the conformation of the edges of the blocks could also be advantageously used to improve the snow-holding capacity within the groove which these blocks face.

[0054] Finally, the Applicant has found that in a tread pattern comprising a pair of blocks separated from each other by a groove in which both edges of the blocks facing the groove are configured with an alternation of chamfered portions and angular edge portions such that each chamfered portion of one edge corresponds to an angular edge portion of the other edge and vice versa, the snow-holding capacity within the groove itself is significantly increased and, consequently, the performance of the tyre on snowy surfaces is improved.

[0055] In particular, in a first aspect thereof, the invention concerns a tyre for vehicle wheels comprising a tread band on which a first main groove and a second main groove are defined.

[0056] Preferably, a first secondary groove is defined on said tread band.

[0057] Preferably, said first secondary groove extends between said first main groove and said second main groove.

[0058] Preferably, a first block and a second block aligned along an alignment direction are defined on said tread band.

[0059] Preferably, said alignment direction is defined by said first main groove and second main groove.

[0060] Preferably, said first block and second block are delimited at a pair of opposing sides by said first main groove and by said second main groove, respectively.

[0061] Preferably, said first block and second block are separated from each other by said first secondary groove.

[0062] Preferably, a first edge of said first block facing said first secondary groove is defined on said tread band.

[0063] Preferably, said first edge of said first block comprises at least three edge portions, adjacent to each other.

[0064] Preferably said at least three edge portions of said first block comprise at least a first edge portion, defined by a chamfer, and at least a second edge portion, defined by an angular edge.

[0065] Preferably, said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0066] Preferably, a first edge of said second block facing said first secondary groove is defined on said tread band.

[0067] Preferably, said first edge of said second block comprises at least three edge portions, adjacent to each other.

[0068] Preferably said at least three edge portions of said second block comprise at least a first edge portion, defined by a chamfer, and at least a second edge portion, defined by an angular edge.

[0069] Preferably, said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0070] Preferably, each first edge portion of said first block is aligned according to said alignment direction with a second edge portion of said second block. Preferably, each second edge portion of said first block is aligned according to said alignment direction with a first edge portion of said second block.

[0071] Thanks to these characteristics, snow is retained more effectively on the tyre's tread surface.

[0072] In fact, the Applicant considers that snow present in a section of the secondary groove delimited laterally by a chamfered portion of one edge and the angular edge portion of the other edge is pushed by the wall of the groove with the angular edge portion against the chamfered edge portion, getting stuck between the angular edges adjacent to the chamfered edge portion.

[0073] Furthermore, the Applicant noted that this alternating configuration of chamfered portions angular edge portions, defines a slightly curved, S-shaped profile of the groove itself and considers that this configuration further improves the retention of snow within the groove.

[0074] The present invention, in the aforesaid aspect, may have at least one of the further preferred features set out below.

[0075] In some embodiments, said first secondary groove and said second main groove are substantially parallel.

[0076] Preferably, said first main groove is extended to an equatorial plane of the tread band.

[0077] In some embodiments, said first main groove and said second main groove have a width between 3 mm and 11 mm.

[0078] Preferably, said first main groove and said second main groove have a width which decreases from a first end thereof which is defined in said shoulder region to a second end thereof which is defined in said equatorial region.

[0079] In some embodiments, said first main groove and said second main groove are formed in alternating succession along the entire circumferential development of said tread band.

[0080] In some embodiments, said first main groove and said second main groove have a depth greater than 5 mm, preferably greater than 7 mm, more preferably of about 9 mm.

[0081] In some embodiments, said first main groove and said second main groove have a greater depth than said first secondary groove.

[0082] In some embodiments, said first secondary groove has a depth comprised between 3 mm and 5 mm, preferably around 4 mm.

[0083] In some embodiments, said first secondary groove has a width between 2 mm and 3 mm.

[0084] In some embodiments, each first edge portion of said first defined block has a length substantially equal to said second edge portion of said second block aligned with it.

[0085] In some embodiments, each second edge portion of said first block has a length substantially equal to said first edge portion of said second block aligned with it.

[0086] In other words, the first edge portions and the second edge portions facing the first secondary groove and aligned according to the alignment direction of the two blocks have essentially the same length.

[0087] In this way, the action exerted on the snow in the secondary groove by the respective edge portions is homogeneous, increasing the snow-holding capacity within the groove.

[0088] In some embodiments, said at least a first edge portion of said first block and said at least a second edge portion of said first block have the same length. Preferably, all the first edge portions and second edge portions of said first edge have a length comprised between 4 and 6 mm, e.g. approximately 5 mm.

[0089] In some embodiments, said at least a first edge portion of said second block and said at least a second edge portion of said second block have the same length. Preferably, all the first edge portions and second edge portions of said second edge have a length comprised between 4 and 6 mm, e.g. approximately 5 mm.

[0090] In other words, the first edge of the first block and / or the first edge of the second block are equally divided into one or more first edge portions and one or more alternating second edge portions.

[0091] In some embodiments, said first edge or said second edge, in other words the chamfered portion of the respective edge, comprises a surface inclined with respect to the tread surface by an angle comprised between 30° and 60°, preferably about 45°.

[0092] In some embodiments, said first portion of said first edge or said second edge, in other words the chamfered portion of the respective edge, has a width comprised between 0.5 mm and 3 mm.

[0093] In some embodiments, there is formed a plurality of sipes open on said first edge of said first block.

[0094] Preferably, said plurality of sipes separates, on the first edge of said first block, said at least one first edge portion from said at least one second edge portion.

[0095] In this way, the "natural" subdivision of the edge of the block into adjacent portions defined by the provision of the sipes on the block is exploited. In some embodiments, said plurality of sipes of said first block extends parallel to said alignment direction.

[0096] In other embodiments, said plurality of sipes of said first block extends transversely to said alignment direction, except for an end region, open on said first edge, substantially parallel to said alignment direction.

[0097] In some embodiments, a second secondary groove separating said second block from a third block extends between said first main groove and said second main groove. Preferably, said third block is aligned with said second block according to said alignment direction.

[0098] In some embodiments, said second block comprises a second edge facing said secondary groove.

[0099] Preferably, said second edge of the second block comprises at least three edge portions, adjacent to each other and comprising at least a first edge portion defined by a chamfer and at least a second edge portion defined by an angular edge, wherein said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0100] In some embodiments, in said second block, each first edge portion defined on said second edge is aligned, according to said alignment direction, with a second edge portion defined on said second edge.

[0101] In some embodiments, in said second block, each second edge portion defined on said second edge is aligned, according to said alignment direction, with a first edge portion defined on said second edge.

[0102] In this way, each first portion defined on the first edge corresponds to a second portion defined on the second edge aligned according to the alignment direction and vice versa.

[0103] In some embodiments, said third block comprises a first edge facing said second secondary groove and comprising at least three edge portions, adjacent to each other and comprising at least a first edge portion defined by a chamfer and at least a second edge portion defined by an angular edge, wherein said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0104] Preferably, each first edge portion of said third block is aligned according to said alignment direction with a second edge portion defined on said second edge of said second block.

[0105] Preferably, each second edge portion of said third block is aligned according to said alignment direction with a first edge portion defined on said second edge of said second block.

[0106] In this way, by reproducing on the second secondary groove the configuration provided in the first secondary groove, the snow-holding capacity of the second secondary groove is also improved.

[0107] In some embodiments, on said second block, a plurality of sipes is formed open on said first edge of said second block.

[0108] Preferably, said plurality of sipes separates, on the first edge of said second block, said at least one first edge portion from said at least one second edge portion.

[0109] Preferably, said plurality of sipes on said second block is open on said second edge of said second block.

[0110] Preferably, said plurality of sipes separates, on the second edge of the second block, said at least one first edge portion from said at least one second edge portion.

[0111] In some embodiments, said plurality of sipes of said second block extends parallel to said alignment direction.

[0112] In other embodiments, said plurality of sipes of said second block extends transversely to said alignment direction, except for an end region, open on said first edge of said second block, substantially parallel to said alignment direction.

[0113] In some embodiments, a third secondary groove separating said third block from a fourth block extends between said first main groove and said second main groove. Preferably, said fourth block is aligned with said third block according to said alignment direction.

[0114] In some embodiments, said third block comprises a second edge facing said third secondary groove.

[0115] Preferably, said second edge of the third block comprises at least three edge portions, adjacent to each other and comprising at least a first edge portion defined by a chamfer and at least a second edge portion defined by an angular edge, wherein said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0116] In some embodiments, in said third block, each first edge portion defined on said first edge is aligned, according to said alignment direction, with a second edge portion defined on said second edge.

[0117] In some embodiments, in said third block, each second edge portion defined on said first edge is aligned, according to said alignment direction, with a first edge portion defined on said second edge.

[0118] In some embodiments, said fourth block comprises a first edge facing said third secondary groove and comprising at least three edge portions, adjacent to each other and comprising at least a first edge portion defined by a chamfer and at least a second edge portion defined by an angular edge, wherein said at least a first edge portion and said at least a second edge portion are alternating with each other.

[0119] Preferably, each first edge portion of said fourth block is aligned according to said alignment direction with a second edge portion defined on said second edge of said third block.

[0120] Preferably, each second edge portion of said fourth block is aligned according to said alignment direction with a first edge portion defined on said second edge of said third block.

[0121] In this way, by also reproducing on the third secondary groove the configuration provided in the first and / or second secondary groove, the snow-holding capacity of the third secondary groove is also improved.

[0122] In some embodiments, on said third block, a plurality of sipes is formed open on said first edge of said third block.

[0123] Preferably, said plurality of sipes separates, on the first edge of the third block, said at least one first edge portion from said at least one second edge portion.

[0124] Preferably, said plurality of sipes on said third block is open on said second edge of said third block.

[0125] Preferably, said plurality of sipes separates, on the second edge of the third block, said at least one first edge portion from said at least one second edge portion.

[0126] In some embodiments, said plurality of sipes of said third block extends parallel to said alignment direction.

[0127] In other embodiments, said plurality of sipes of said third block extends transversely to said alignment direction, except for an end region, open on said first edge of said third block, substantially parallel to said alignment direction.

[0128] In some embodiments, on said fourth block, a plurality of sipes is formed open on said first edge of said fourth block.

[0129] Preferably, said plurality of sipes separates, on the first edge of the fourth block, said at least one first edge portion from said at least one second edge portion.

[0130] Preferably, said plurality of sipes on said fourth block is open on a second edge of said fourth block.

[0131] Preferably, in said fourth block, said second edge is opposed to said first edge along said alignment direction.

[0132] Preferably, said plurality of sipes separates, on the second edge of the fourth block, at least one first edge portion from said at least one second edge portion.

[0133] In some embodiments, said plurality of sipes of said fourth block extends parallel to said alignment direction.

[0134] In other embodiments, said plurality of sipes of said fourth block extends transversely to said alignment direction, except for an end region, open on said first edge of said fourth block, substantially parallel to said alignment direction.

[0135] In some embodiments, said first block is axially external with respect to said second block.

[0136] In some embodiments, said second block is axially external with respect to said third block.

[0137] In some embodiments, said third block is axially external with respect to said fourth block.

[0138] In some embodiments, said fourth block is crossed by an equatorial plane of the tread band.

[0139] In some embodiments, said first block is delimited by an axial end of said tread band. In some embodiments, all the edges of the blocks facing said first secondary groove, said second secondary groove and said third secondary groove have the same total number of first and second edge portions, preferably three or four, more preferably three.

[0140] In some embodiments, the edges of the blocks facing said first secondary groove have a total number of first and second edge portions greater than the total number of first and second edge portions of the edges of the blocks facing said third secondary groove.

[0141] The characteristics and advantages of the invention will become clearer from the detailed description of an embodiment shown, by way of non-limiting example, with reference to the appended drawings wherein:

[0142] - Figure 1 is a schematic front view of a significant portion of tread band, extended on a plane, of a tyre for vehicle wheels made in accordance with the present invention,

[0143] - Figure 2 is a schematic view on an enlarged scale of a portion of the tread band of the tyre in Figure 1,

[0144] - Figure 3 is a perspective view of part of the portion of tread band in Figure 2, and

[0145] - Figure 4 is a sectional view along line IV-IV in Figure 2.

[0146] With reference to the accompanying figures, 1 globally denotes a tyre for vehicle wheels made in accordance with the present invention. The tyre 1 has a conventional generally toroidal shape extended around a rotation axis, defining an axial direction Y of the tyre, and crossed by an equatorial plane X, perpendicular to the rotation axis.

[0147] The tyre 1 comprises a tread band 2 on which a tread surface 3 is defined which is arranged in a position that is radially external to the tread band 2 and intended for contact with a road surface.

[0148] The tread band 2 has a width L and extends axially between a first axial end 2a and an opposite second axial end 2b.

[0149] The tyre 1 has, for example, a nominal section width of about 225 mm with a shoulder diameter of 17 inches.

[0150] An equatorial region 4, which extends circumferentially and symmetrically around the equatorial plane X, as well as a first shoulder region 5 and a second shoulder region 6, which extend respectively at the axially opposite sides of the equatorial region 4, in a position axially external to the same tread band 2 up to the respective axial ends 2a, 2b of the tread band 2, remain defined on the tread band 2.

[0151] The equatorial region 4 extends indicatively over a width equal to about 60% of the width of the tread band 2.

[0152] On the tread band 2, a plurality of grooves of various dimensions and configurations are formed which delimit a plurality of blocks, so as to define, overall, the tread pattern of the tyre 1.

[0153] In particular, the tread pattern has a modular configuration in which some pitches M are defined, repeated in succession along the circumferential extension of the tread band 2 according to an appropriate sequence.

[0154] The different pitches M all have the same general configuration of grooves and blocks but differ slightly in terms of circumferential dimensions.

[0155] An example of a pitch M, represented in enlarged scale in Figure 2, comprises a first main groove 10 and a second main groove 20, which both extend from the first axial end 2a of the tread band 2 up to the equatorial region 4, crossing the first shoulder region 5.

[0156] In particular, the first main groove 10 extends between a first, axially external end 11, which open at the first axial end 2a of the tread band 2, and a second, axially internal end 12, which closes an end section 13 of the first main groove 10 that extends in a zig-zag manner along the equatorial plane X.

[0157] The second main groove 20 extends between a first, axially external end 21, which opens at the first axial end 2a of the tread band 2, and a second, axially internal end 22, which converges into the end section 13 of the first main groove 10.

[0158] Corresponding main grooves 10a and 20a extend from the second axial end 2b of the tread band 2 up to the equatorial region 4, crossing the second shoulder region 6.

[0159] The course of the main grooves 10a, 20a is substantially similar to that of the first and second main groove 10, 20, so the following detailed description of the main grooves 10 and 20 may also refer, mutatis mutandis, to the main grooves 10a, 20a. The two pairs of main grooves 10, 20 and 10a, 20a, are in fact substantially symmetrical with respect to the equatorial plane X, apart from a slight circumferential offset and apart from the end section 13 of the first main groove 10, on which the main grooves 10a and 20a also converge.

[0160] The first main groove 10 and the second main groove 20 have a slightly curvilinear course, with an inclination with respect to the equatorial plane X that decreases from the shoulder region 5 up to the equatorial region 4.

[0161] The first main groove 10 and the second main groove 20 have a substantially constant depth of, for example, approximately 8.8 mm, while they have a decreasing width from their first end 11, 21, where it is between 7 mm and 11 mm, to the end section 13 and the second end 22, respectively, where it is between 3.5 mm and 5.5 mm.

[0162] A first secondary groove 30, a second secondary groove 40 and a third secondary groove 50 further extend between the first main groove 10 and the second main groove 20, as well as between the second main groove 20 and the first main groove 10 of the next pitch M.

[0163] In particular, the first secondary groove 30 is defined in an axially external position, for delimiting the first shoulder region 5 from the equatorial region 4, the third secondary groove 50 is defined in an axially internal position and the second secondary groove 40 is defined in an intermediate position between the other two secondary grooves 30 and 50.

[0164] The first secondary groove 30 extends along a curvilinear direction between a first and second end open on the first main groove 10 and the second main groove 20, respectively.

[0165] The first secondary groove 30 has a substantially constant depth and width, for example equal to about 4 mm and about 3.5 mm, respectively.

[0166] The first secondary groove 30 comprises a bottom 31 from which a pair of walls 32 rises towards the tread surface 3, with a substantially constant inclination, slightly divergent with respect to the radial direction of the tyre, with which it forms an angle comprised between about 2° and about 10°.

[0167] The first secondary groove 30, moreover, is crossed by a sipe 33, blind, which is formed longitudinally on its bottom.

[0168] The second secondary groove 40 extends in a substantially rectilinear manner between a first and a second end, which are open on the first main groove 10 and the second main groove 20, respectively.

[0169] The second secondary groove 40 has a substantially constant width, e.g. approximately 2.5 mm, like the first secondary groove 30, and a substantially constant depth of approximately 4 mm at one of its central regions, while its opposing end regions are chamfered towards the respective main grooves 10 and 20.

[0170] The second secondary groove 40 comprises a bottom 41 from which a pair of walls 42 rises towards the tread surface 3, with a substantially constant inclination, slightly divergent with respect to the radial direction of the tyre, with which it forms an angle comprised between about 2° and about 10°.

[0171] The third secondary groove 50 extends in a substantially rectilinear manner, substantially parallel to the second secondary groove 40, between a first and a second end, which are open on the first main groove 10 and the second main groove 20, respectively.

[0172] The third secondary groove 50 has a width and depth greater than the width and depth of the first secondary groove 30 and the second secondary groove 40.

[0173] In particular, the third secondary groove 50 has a substantially constant width, e.g. about 3.5 mm, and a substantially constant depth, e.g. about 7 mm at one of its central regions, while its opposing end regions are chamfered towards the bottom of the respective main grooves 10 and 20.

[0174] The third secondary groove 50 comprises a bottom 51 from which a pair of walls 52 rises towards the tread surface 3, with a substantially constant inclination, slightly divergent with respect to the radial direction of the tyre, with which it forms an angle comprised between about 2° and about 10°.

[0175] Between each main groove 10a and the main groove 20a, as well as between the main groove 20a and the main groove 10a of the next pitch M, there are formed corresponding secondary grooves 30a, 40a and 50a which are entirely similar to the first secondary groove 30, to the second secondary groove 40 and to the third secondary groove 50, respectively.

[0176] The first and second main grooves 10 and 20 delimit laterally, from the axial end 2a to the equatorial plane X, a first block 60, a second block 70, a third block 80 and a fourth block 90, aligned along an alignment direction A, defined by the longitudinal extension of the main grooves 10, 20, and separated from each other by the secondary grooves 30, 40 and 50.

[0177] Naturally, the main grooves 10a and 20a and the secondary grooves 30a, 40a and 50a delimit the corresponding blocks 60a, 70a, 80a and 90a, which are entirely analogous to the blocks 60, 70, 80 and 90 described in detail below.

[0178] The first block 60, axially external to the other blocks delimited by the first and second main grooves 10 and 20 and crossed by the axial end 2a of the tread band 2, comprises a first edge 61, facing the first secondary groove 30.

[0179] The first edge 61 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. approximately 5 mm, formed by two first edge portions 61a, both defined by a chamfer, interspersed with a second edge portion 61b in turn defined by an angular edge.

[0180] The two first edge portions 61a are substantially identical to each other, with the chamfer formed by a substantially flat surface, about 1 mm wide, and inclined at about 45°, extending between the portion of tread surface 3 of the first block 60 and the wall 32 of the first groove 30. The second edge portion 61b, on the other hand, is formed by the intersection of the wall 32 of the first groove 30 with the tread surface portion 3 of the first block 60.

[0181] On the first block 60 there is a pair of sipes 62 extending parallel to the alignment direction A and open on the first edge 61 to separate the first edge portion 61a from the second edge portion 61b.

[0182] The second block 70, axially internal to the first block 60, comprises a first edge 71, facing the first secondary groove 30 on the opposite side of the first edge 61 of the first block 60.

[0183] The first edge 71 of the second block 70 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. equal to about 5 mm, formed by two second edge portions 71b, both defined by an angular edge deriving from the intersection of the wall 32 with the tread surface portion 3, interspersed with a first edge portion 71a, in turn defined by a chamfer extending to connect the wall 32 with the tread surface portion 3.

[0184] The first edge portions 61a and 71a of the first block 60 and the second block 70 respectively are substantially identical to each other, as are the second edge portions 61b and 71b of the first block 60 and the second block 70. The two second edge portions 71b of the second block 70 are aligned according to the alignment direction A with a respective first edge portion 61a of the first block 60, while the first edge portion 71a of the second block 70 is aligned according to the alignment direction A with the second edge portion 61b of the first block 60.

[0185] The second block 70 also comprises a second edge 73, opposing the first edge 61 with respect to the alignment direction A, and facing the second secondary groove 40.

[0186] The second edge 73 of the second block 70 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. about 5 mm, formed by two first edge portions 73a interspersed with a second edge portion 73b. The first two edge portions 73a are defined by a chamfer extending at a junction between the wall 42 of the second secondary groove 40 and the tread surface portion 3 of the second block 70, while the second edge portion 73b, in turn, is defined by an angular edge resulting from the intersection of the wall 42 with the tread surface portion 3 of the second block 70.

[0187] The arrangement of the first and second edge portions 73a, 73b of the second edge 73 of the second block 70, thus follows that of the first edge 61 of the first block 60. A pair of sipes 72 extending parallel to the alignment direction A and open on both the first edge 71 and the second edge 73, so as to separate the first edge portions 71a, 73a from the second edge portions 71b, 73b, is formed on the second block 70. Thus, in the second block 70, each first edge portion 71a defined on the first edge 71 is aligned, according to the alignment direction A, with a second edge portion 73b defined on the second edge 73, just as each second edge portion 71b defined on the first edge 71 is aligned, according to the alignment direction A, with a first edge portion 73a defined on the second edge 73.

[0188] The third block 80, axially inner from the second block 70, comprises a first edge 81, facing the second secondary groove 30 opposite the second edge 73 of the second block 70.

[0189] The first edge 81 of the third block 80 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. equal to about 5 mm, formed by two second edge portions 81b, both defined by an angular edge deriving from the intersection of the wall 42 with the tread surface portion 3, interspersed with a first edge portion 81a, in turn defined by a chamfer extending to connect the wall 42 with the tread surface portion 3.

[0190] The first edge portions 73a and 81a of the second block 70 and the third block 80 respectively are substantially identical to each other, as are the second edge portions 73b and 81b of the second block 70 and the third block 80.

[0191] The two second edge portions 81b of the third block 80 are aligned according to the alignment direction A with a respective first edge portion 73a of the second edge 73 of the second block 70, while the first edge portion 81a of the third block 80 is aligned according to the alignment direction A with the second edge portion 73b of the second edge 73 of the second block 70.

[0192] The third block 80 also comprises a second edge 83, opposing the first edge 81 with respect to the alignment direction A, and facing the third secondary groove 50.

[0193] The third edge 83 of the second block 80 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. about 5 mm, formed by two first edge portions 83a interspersed with a second edge portion 83b. The first two edge portions 83a are defined by a chamfer extending at a junction between the wall 52 of the third secondary groove 50 and the tread surface portion 3 of the third block 80, while the second edge portion 83b, in turn, is defined by an angular edge resulting from the intersection of the wall 52 with the tread surface portion 3 of the third block 80.

[0194] The arrangement of the first edge portions 83a and the second edge portions 83b of the second edge 83 of the third block 80 thus follows that of the first edge 61 of the first block 60 and the second edge 73 of the second block 70.

[0195] A pair of sipes 82 extending parallel to the alignment direction A and open on both the first edge 81 and the second edge 83, so as to separate the first edge portions 81a, 83a from the second edge portions 81b, 83b, is formed on the third block 80. Thus, it will be noted that, in the third block 80, each first edge portion 81a defined on the first edge 81 is aligned, according to the alignment direction A, with a second edge portion 83b defined on the second edge 83, just as each second edge portion 81b defined on the first edge 81 is aligned, according to the alignment direction A, with a first edge portion 83a defined on the second edge 83.

[0196] The fourth block 90, axially inner from the third block 80, comprises a first edge 91, facing the third secondary groove 50 opposite the second edge 83 of the third block 80.

[0197] The first edge 91 of the fourth block 90 is subdivided into three edge portions, adjacent to each other and having substantially the same length, e.g. equal to about 5 mm, formed by two second edge portions 91b, both defined by an angular edge deriving from the intersection of the wall 52 with the tread surface portion 3, interspersed with a first edge portion 91a, in turn defined by a chamfer extending to connect the wall 52 with the tread surface portion 3.

[0198] The first edge portions 83a and 91a of the third block 80 and the fourth block 90 respectively are substantially identical to each other, as are the second edge portions 83b and 91b of the third block 80 and the fourth block 90.

[0199] The two second edge portions 91b of the fourth block 90 are aligned according to the alignment direction A with a respective first edge portion 83a of the second edge 83 of the third block 80, while the first edge portion 91a of the fourth block 90 is aligned according to the alignment direction A with the second edge portion 83b of the second edge 83 of the third block 80.

[0200] The fourth block 90 also comprises a second edge 93, opposing the first edge 91 with respect to the alignment direction A, and facing the end section 13 of the first main groove 10.

[0201] The second edge 93 of the fourth block 90 is subdivided into three edge portions, adjacent to each other and of substantially the same length, e.g. approximately 5 mm, formed by two first edge portions 93a, both defined by a chamfer, interspersed with a second edge portion 93b, in turn defined by an angular edge.

[0202] A pair of sipes 92 extending parallel to the alignment direction A and open on both the first edge 91 and the second edge 93, so as to separate the first edge portions 91a, 93a from the second edge portions 91b, 93b, is formed on the fourth block 90. Thus, it will be noted that, in the fourth block 90, each first edge portion 91a defined on the first edge 91 is aligned, according to the alignment direction A, with a second edge portion 93b defined on the second edge 93, just as each second edge portion 91b defined on the first edge 91 is aligned, according to the alignment direction A, with a first edge portion 93a defined on the second edge 93.

[0203] As can also be seen in the portion of tread band shown in Figure 1, the different circumferential dimension between the pitches M can lead to variations in the number of edge portions into which each edge of the blocks facing a secondary groove is divided, so that this number can be different from three, for example four.

[0204] In particular, it is possible that in some pitches M, the edges 61 and 71 of the blocks 60 and 70 facing the first secondary groove 30 are subdivided into four first and second edge portions and the edges 83 and 91 of the blocks 80 and 90 facing the third secondary groove 50 are divided into three first and second edge portions.

[0205] The tests carried out by the Applicant on a tyre made according to the preferred example described above have shown excellent behaviour both on snowy road surfaces and on dry road surfaces and, again, on wet road surfaces.

[0206] Naturally, those skilled in the art may make further modifications and variants to the above-described invention with the purpose of meeting specific and contingent application needs, variants and modifications in any case falling within the scope of protection as defined by the successive claims.

Claims

CLAIMS1. Tyre (1) for vehicles wheels comprising a tread band (2), on which there are defined:- - a first main groove (10) and a second main groove (20),- - a first secondary groove (30) which extends between said first main groove (10) and said second main groove (20),- - a first block (60) and a second block (70) which are aligned in an alignment direction (A) which is defined by said first main groove and second main groove, said first block and second block being delimited at a pair of opposite sides by said first main groove (10) and by said second main groove (20), respectively, and being separated from each other by said first secondary groove (30),- - a first edge (61) of said first block (60) facing said first secondary groove (30) and comprising at least three edge portions, which are adjacent to each other and which comprise at least one first edge portion (61a) which is defined by a chamfer and at least one second edge portion (61b) which is defined by an angular edge, alternating with each other,- - a first edge (71) of said second block (70) facing said first secondary groove (30) and comprising at least three edge portions, which are adjacent to each other and which comprise at least one first edge portion (71a) which is defined by a chamfer and at least one second edge portion (71b) which is defined by an angular edge, alternating with each other, wherein each first edge portion (61a) of said first block (60) is aligned in said alignment direction (A) with a second edge portion (71b) of said second block (70), and each second edge portion (61b) of said first block (60) is aligned in said alignment direction (A) with a first edge portion (71a) of said second block (70).

2. Tyre according to claim 1, wherein each first edge portion (61a) of said first block (60) has a length which is substantially identical to said second edge portion (71b) of said second block (70) aligned thereto.

3. Tyre according to claim 1 or 2, wherein each second edge portion (61b) of said first block (60) has a length which is substantially identical to said first edge portion (71a) of said second block (70) aligned thereto.

4. Tyre according to any one of the preceding claims, wherein said at least one first edge portion (61a) of said first block (60) and said at least one second edge portion (61b) of said first block (60) have the same length.

5. Tyre according to any one of the preceding claims, wherein said at least one first edge portion (71a) of said second block (70) and said at least one second edge portion (71b) of said second block (70) have the same length.

6. Tyre according to any one of the preceding claims, wherein there is formed on said first block (60) a plurality of sipes (62) which open at said first edge (61) of said first block (60) so as to separate said at least one first edge portion (61a) from said at least one second edge portion (61b).

7. Tyre according to any one of the preceding claims, wherein there is formed on said second block (70) a plurality of sipes (72) which open at said first edge (71) of said second block (70) so as to separate said at least one first edge portion (71a) from said at least one second edge portion (71b).

8. Tyre according to any one of the preceding claims, wherein a second secondary groove (40) which separates said second block (70) from a third block (80) extends between said first main groove (10) and said second main groove (20).

9. Tyre according to claim 8, wherein said third block (80) is aligned with said second block (70) in said alignment direction (A).

10. Tyre according to claim 8 or 9, wherein said second block (70) comprises a second edge (73) which faces said second secondary groove (40) and which comprises at least three edge portions, which are adjacent to each other, and which comprises at least one first edge portion (73a) which is defined by a chamfer and at least one second edge portion (73b) which is defined by an angular edge, alternating with each other.

11. Tyre according to claim 10, wherein, in said second block (70), each first edge portion (71a) which is defined on said first edge (71) is aligned, in said alignment direction (A), with a second edge portion (73b) which is defined on said second edge (73) and each second edge portion (71b) which is defined on said first edge (71) is aligned, in said alignment direction (A), with a first edge portion (73a) which is defined on said second edge (73).

12. Tyre according to claim 10 or 11, wherein said third block (80) comprises a first edge (81) which faces said second secondary groove (40) and which comprises at least three edge portions, which are adjacent to each other and which comprise at least one first edge portion (81a) which is defined by a chamfer and at least one second edge portion (81b) which is defined by an angular edge, alternating with each other, and wherein each first edge portion (81a) of said third block (80) is aligned in said alignment direction (A) with a second edge portion (73b) whichis defined on said second edge (73) of said second block (70), and each second edge portion (81b) of said third block (80) is aligned in said alignment direction (A) with a first edge portion (73a) which is defined on said second edge (73) of said second block (70).

13. Tyre according to any one of claims 10 to 12, wherein said plurality of sipes (72) which is formed on said second block (70) open at said second edge (73) of said second block (70) so as to separate said at least one first edge portion (73a) from said at least one second edge portion (73b) which are defined on said second edge (73).

14. Tyre according to any one of claims 8 to 13, wherein a third secondary groove (50) which separates said third block (80) from a fourth block (90) extends between said first main groove (10) and said second main groove (20).

15. Tyre according to claim 14, wherein said fourth block (90) is aligned with said third block (80) in said alignment direction (A).

16. Tyre according to claim 14 or 15, wherein said third block (80) comprises a second edge (83) which faces said third secondary groove (50) and which comprises at least three edge portions, which are adjacent to each other and which comprise at least one first edge portion (83a) which is defined by a chamfer and at least one second edge portion (83b) which is defined by an angular edge, alternating with each other.

17. Tyre according to claim 16, wherein, in said third block (80), each first edge portion (81a) which is defined on said first edge (81) is aligned, in said alignment direction (A), with a second edge portion (83b) which is defined on said second edge (83) and each second edge portion (81b) which is defined on said first edge (81) is aligned, in said alignment direction (A), with a first edge portion (83a) which is defined on said second edge (83).

18. Tyre according to any one of claims 14 to 17, wherein said fourth block (90) comprises a first edge (91) which faces said third secondary groove (50) and which comprises at least three edge portions which are adjacent to each other and which comprise at least one first edge portion (91a) which is defined by a chamfer and at least one second edge portion (91b) which is defined by an angular edge, alternating with each other, and wherein each first edge portion (91b) of said fourth block (90) is aligned, in said alignment direction (A), with a second edge portion (83b) which is defined on said second edge (83) of said third block (80), and each second edge portion (91b) of said fourth block (90) is aligned, insaid alignment direction (A), with a first edge portion (83a) which is defined on said second edge (83) of said third block (80).

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