Tyre

Abstract

A tyre (1) comprising a tread band (2) comprising: - a plurality of grooves (4A), - a plurality of blocks (5A, 5B, 5C) delimited at least by a first pair of said plurality of grooves (4A), and - a plurality of sipes (10) extending, on said plurality of blocks (5A, 5B, 5C), from a radially outer surface of said tread band (2) to a radially inner surface of the tread band (2). Each sipe (10) extends along a predetermined trajectory and comprises: - an upper portion (101) located at said radially outer surface of said tread band (2) and having, along said predetermined trajectory, a substantially sinusoidal wave pattern having a first amplitude (A') and a first period (P'); and - a lower portion (102) located at said radially inner surface of said tread band (2) and having, along said predetermined trajectory, a respective substantially sinusoidal wave pattern having a second amplitude (A") and a second period (P").

Description

[0001] Tyre

[0002] Description

[0003] Field of the Invention

[0004] The present invention relates to a tyre, in particular a winter tyre.

[0005] More specifically, the invention concerns a winter tyre with improved performance, especially on snow-covered and / or icy road surfaces.

[0006] Prior Art

[0007] In a typical configuration, a tyre generally comprises a carcass structure, toroidally shaped around a rotation axis, on which a belt structure is applied in a radially outer position, and, further superposed, a tread band made of elastomeric material, on which a tread surface is defined for contact with the road surface.

[0008] On the tread band, a plurality of grooves with a circumferential and / or transverse pattern is typically defined, delimiting a corresponding plurality of blocks which, together, define the tread pattern of the tyre.

[0009] The characteristics of the tread pattern, and in particular the quantity and configuration of the grooves and blocks provided on the tread surface, primarily determine the performance of the tyre in terms of road behavior, especially with respect to the possible different conditions of the road surface itself.

[0010] To improve the performance of a tyre on snow-covered surfaces, small cuts called "sipes" can also be formed on the blocks of the tread band, extending from the tread surface of the tyre towards the interior of the block. The function of the sipes is generally to provide additional gripping elements on the snow-covered surface and to retain a certain amount of snow, thereby improving grip, traction, and / or braking on snow- covered road surfaces. It is known, in fact, that snow-to-snow friction (i.e., between the snow retained inside the sipes and the snow-covered road surface) is greater than rubber-to-snow friction (i.e., between the tread band and the snow-covered road surface).

[0011] Nowadays, various types of winter tyres are known, having blocks comprising sipes.

[0012] An example is disclosed in International Publication W02023119019A1, in the name of the same Applicant, which describes a winter tyre whose blocks are provided with sipes.

[0013] Other examples of winter tyres whose blocks are provided with three-dimensional sipes are disclosed in International Patent Applications WO 2012 / 164449 and WO 2012 / 164450, respectively, also in the name of the same Applicant, in which sipes with a variable longitudinal pattern are described, for example straight or wavy, depending on the depth of the sipes.

[0014] Summary of the Invention

[0015] In this description and in the following claims, the following definitions will be applied.

[0016] The term "radial" and the expressions "radially inner / outer" are used with reference to the axis of rotation of the tyre, while the terms "circumferential" and "circumferentially" are used with reference to the direction of the annular development of the tyre, that is, the rolling direction of the tyre, which corresponds to a direction lying on a plane coincident with or parallel to the equatorial plane of the tyre.

[0017] In particular: the term "radial direction" is used to indicate a direction substantially perpendicular to the axis of rotation of the tyre, or in any case lying on a plane containing the axis of rotation of the tyre and moving away from it;

[0018] The term "circumferential direction" is used to indicate a direction substantially parallel to the rolling direction of the tyre, or inclined with respect to the rolling direction by an angle less than 45°.

[0019] The term "groove" means a recess formed on the tread surface, having at least one portion with a width of at least 1.5 mm. Preferably, said groove has a minimum depth of about 3 mm. The term "sipe" means a recess formed in a portion of the tread band having a maximum width between about 0.1 mm and 1.5 mm.

[0020] Such sipe, depending on the performance required of the tyre, extends along a trajectory defined by a straight line, a curved line, or a broken line, where the term "broken line" is used to indicate a line composed of two or more consecutive straight and / or curved lines that are inclined with respect to each other (e.g., zig-zag).

[0021] The term "chamfer" means that the transition portion created between a radially extended surface of the block formed by the sipe and the portion of tread surface at the block forms a surface rather than an edge.

[0022] For example, the transition portion may be an inclined surface.

[0023] In other words, the edge that would structurally be created due to the presence of the sipe, as a transition portion between the radially extended surface of the block and the surface of the block arranged on the tread, is eliminated / chamfered and replaced by a surface. In this way, the radially extended surface of the block moves away from its reference plane up to the portion of tread surface at the block, forming the chamfer.

[0024] The term "sipe trajectory" is used to indicate the path or direction along which the sipe extends between its two opposite ends.

[0025] The term "sipe cross-section" is used to indicate a section of the sipe formed on a plane perpendicular to the trajectory of the sipe.

[0026] The term "sipe transverse dimension" is used to indicate the width of the sipe measured in a cross-section of the sipe taken at a given point along the trajectory.

[0027] Each sipe divides the block in which it is formed into two block portions having respective mutually facing surfaces.

[0028] These surfaces extend along a respective "reference plane" incident to the tread surface and coincident with the surface net of any protrusions and recesses.

[0029] A sipe is "three-dimensional" when at least one of the mutually facing surfaces of the block portions has at least one protrusion, while the other of said surfaces has a corresponding recess, adapted to at least partially accommodate said protrusion. In other words, the respective projections of the two block portions separated by the sipe, along any direction lying on each reference plane at the protrusion and the corresponding recess, are at least partially overlapped.

[0030] In this way, as will be better explained below, a relative movement of the two block portions along a direction lying on the reference plane is hindered by the interference between the two block portions at the protrusion and the recess.

[0031] The Applicant has first verified that providing the blocks with three-dimensional sipes increases their stiffness when subjected to shear stresses, thereby improving the performance of the tyre on dry or wet road surfaces, both in braking and in traction and cornering.

[0032] At the same time, however, the Applicant has verified that this increase in block stiffness, due to the presence of three-dimensional sipes, corresponds to a reduced mobility of the adjacent block portions, thus reducing the efficiency in retaining snow and therefore the performance of the tyre on snow-covered surfaces.

[0033] Furthermore, the Applicant has also verified that the geometry of the three- dimensional sipes currently used, in particular due to the presence of sharp edges at the protrusions / recesses, mechanically generates pressure peaks in these areas, as well as at the tread surface, due to resulting phenomena of catching / lifting in the sipe, respectively between one surface of the block and the adjacent one, which locally increase the stress and create areas of discontinuity with increased contact pressure of the tyre with the ground, with a consequent decrease in friction and grip of the tyre, for example, on icy ground.

[0034] The Applicant has felt the need to provide a design in which the geometry of such three-dimensional sipes is, in general, less impactful on the contact pressure of the tyre with the ground, improving the performance of the tyre on snow-covered and / or icy ground, not only when the tyre is new but also throughout its life.

[0035] The Applicant has found that a three-dimensional sipe having, along its trajectory, a substantially sinusoidal wave pattern, with an oscillation amplitude that differs between a radially outer surface of the tread band and a radially inner surface, gives rise to a "variable wave" structure along the radial direction that allows the characteristics of the sipe in this direction to be maintained homogeneously throughout the life of the tyre, and to reduce discontinuities and localized increases in stress and pressure, while maintaining the functionality of the sipe as the depth of the tread band decreases, i.e., as the tyre wears.

[0036] In a first aspect, the invention relates to a tyre comprising a tread band.

[0037] Preferably, the aforementioned tread band comprises a plurality of grooves and a plurality of blocks delimited by at least one pair of said plurality of grooves.

[0038] Furthermore, preferably, said tread band comprises a plurality of sipes extending on the plurality of blocks respectively along a predetermined trajectory, from a radially outer surface of the tread band to a radially inner surface of the tread band.

[0039] Each sipe advantageously comprises opposite side walls extending parallel to each other, in which, in each section perpendicular to said predetermined trajectory, each of said opposite side walls comprises at least one male-female coupling comprising:

[0040] - at least one protrusion formed on a first wall of said opposite side walls towards a second wall of said opposite side walls and, in correspondence with said at least one protrusion, at least one recess formed on said second wall of said opposite side walls away from said first block wall of said opposite side walls.

[0041] Each sipe further comprises an upper portion located at the radially outer surface of the tread band.

[0042] Furthermore, each sipe comprises a lower portion located at the radially inner surface of the tread band.

[0043] Advantageously, the aforementioned upper portion of the sipe has, along the aforementioned predetermined extension trajectory, a substantially sinusoidal wave pattern with a first amplitude and a first period. Also advantageously, the lower portion of the sipe has, along the predetermined extension trajectory, a respective substantially sinusoidal wave pattern with a second amplitude and a second period.

[0044] Preferably, the first amplitude is different from the second amplitude; preferably, the first period is equal to the second period.

[0045] Advantageously, the different oscillation of the sinusoid between the upper and lower portions, combined with at least one male-female coupling in the radial direction of the sipe, structurally creates interlocks that are maintained over time as the tread depth decreases with tyre wear.

[0046] Advantageously, the residual oscillation of the sipe trajectory in its lower portion allows, despite tyre wear, snow to continue to become trapped along a sinusoidal trajectory that has a greater extension than would be the case with the same trajectory along a straight line. This advantageously results in an increase in the efficiency of the sipes on snow towards the end of the tire's service life.

[0047] In a first preferred variant, the first amplitude is greater than the second amplitude.

[0048] Advantageously, the first amplitude of the sinusoid, being greater than the second amplitude of the sinusoid, combined with at least one male-female coupling in the radial direction of the sipe, creates interlocks that are structurally deeper at the radially outer surface of the tread band and less deep at the radially inner surface of the tread band.

[0049] These interlocks, due to tyre wear, become progressively less deep.

[0050] The wear of the tread, in turn, results in a progressive decrease in its thickness and a progressive increase in its stiffness.

[0051] Thanks to this, the block at the radially inner surface of the tread does not require stiffening of the same intensity as that provided by the deep interlocks at the radially outer surface of the tread; on the contrary, the decrease in the depth of the interlocks in the lower portion of the sipe allows adequate mutual mobility of the opposite side walls of the sipe even when the tyre is worn, which is advantageous for snow retention during driving on snow-covered surfaces.

[0052] Advantageously, each sipe comprises a plurality of male-female couplings.

[0053] Preferably, this plurality of male-female couplings preferably comprises an even number of male-female couplings.

[0054] Advantageously, an even number of male-female couplings ensures that the sipe behaves in the same way regardless of the rolling or mounting direction of the tyre.

[0055] Preferably, in each section perpendicular to said predetermined trajectory, the sipe has, from said radially outer surface of said tread band to said radially inner surface of the tread band, a substantially sinusoidal pattern.

[0056] Preferably, said upper portion has a respective first radial dimension in which each sipe has, along said predetermined trajectory, said substantially sinusoidal wave pattern having said first amplitude and said first period.

[0057] Preferably, said lower portion has a respective second radial dimension in which said sipe has, along said predetermined trajectory, said sinusoidal wave pattern having said second amplitude and said second period.

[0058] Preferably, the second radial dimension is greater than the first radial dimension.

[0059] Preferably, each sipe comprises, between the upper portion and the lower portion, an intermediate portion.

[0060] Preferably, the intermediate portion has a respective third radial dimension in which said sipe comprises at least one male-female coupling.

[0061] Preferably, the third radial dimension is greater than the first radial dimension and the second radial dimension.

[0062] Preferably, in each section perpendicular to said predetermined trajectory, at said intermediate portion, the sipe has a respective first transverse dimension that is substantially constant along said third radial dimension.

[0063] In further preferred, but not limiting, embodiments, in each section perpendicular to the predetermined trajectory, the lower portion of the sipe is bounded inferiorly by a curved lower surface.

[0064] Advantageously, the curved lower surface has a second transverse dimension greater than or equal to the respective first transverse dimension.

[0065] Preferably, the lower portion is substantially defined by an arc of a circle having a determined radius.

[0066] Advantageously, in each section perpendicular to said trajectory, the curved lower surface is connected to said intermediate portion by a fillet radius.

[0067] Advantageously, the fillet radius is greater than said determined radius.

[0068] Preferably, the ratio between said fillet radius and said determined radius is greater than or equal to 2.

[0069] Still more preferably, the ratio between said fillet radius and said determined radius is less than or equal to 6.

[0070] For example, the ratio between said fillet radius and said determined radius may be equal to 4.

[0071] In this way, in the lower portion of the sipe, a substantially "drop-shaped" structure is created which, due to its geometry, improves the durability of the lower portion itself, reducing the risk of tears and / or cracks in this delicate region, which is more subject to such phenomena due to the stresses encountered during the life of the tyre.

[0072] Brief Description of the Figures

[0073] The features and advantages of the invention will become more apparent from the detailed description of a preferred embodiment, provided by way of example and not limitation, with reference to the accompanying drawings, in which:

[0074] - Figure 1 schematically shows a view of a block comprising a plurality of sipes according to the present invention;

[0075] - Figure 2 shows a perspective view of a sipe according to the present invention;

[0076] - Figure 3 is a side view of the sipe of Figure 2;

[0077] - Figure 4A is a schematic top view of the sipe of Figure 2, in which the trajectory of the sipe at the tread surface is visible; - Figure 4B is a schematic top view of the sipe of Figure 2 but in a radially inner position, in which the trajectory of the sipe in the radially inner position relative to the tread surface is visible;

[0078] - Figure 5A is a view of a cross-section of the sipe taken along line B in Figures 4A and 4B;

[0079] - Figure 5B is a view of a cross-section of the sipe taken along line C in Figures 4A and 4B;

[0080] - Figure 5C is a view of a cross-section of the sipe taken along line D in Figures 4A and 4B;

[0081] - Figure 5D is a view showing a superposition of the sections in Figures 5A-5C;

[0082] - Figure 6A is a view of a cross-section of a second embodiment of a sipe according to the present invention, taken along line B in Figures 4A and 4B;

[0083] - Figure 6B is a view of a cross-section of the sipe according to the second embodiment, taken along line C in Figures 4A and 4B;

[0084] - Figure 6C is a view of a cross-section of the sipe according to the second embodiment, taken along line D in Figures 4A and 4B;

[0085] - Figure 6D is a view showing a superposition of the sections in Figures 6A-6C;

[0086] - Figures 7A and 7B are schematic radial sectional views of the block of Figure 1 comprising, respectively, known three-dimensional sipes and the sipes according to the present invention;

[0087] - Figure 7C shows a graph illustrating the comparison between the deformation resistance of the block according to Figure 7A and the block according to Figure 7B.

[0088] Detailed description

[0089] With reference to the accompanying figures, the numeral 1 generally indicates a tyre made in accordance with the present invention.

[0090] The tyre 1 comprises a tyre structure, itself conventional and not shown in the attached figures, as well as a tread band 2, arranged in a radially outer position on the tyre 1 and on which a tread surface is defined.

[0091] On the tread band 2, a plurality of grooves is formed, indicated in Figure 1 by the reference numeral 4.

[0092] In preferred embodiments, said plurality of grooves comprises at least one pair of grooves 4.

[0093] More specifically, in a first embodiment of the tyre 1 according to the present invention, said at least one pair of grooves 4 delimits a plurality of blocks 5.

[0094] As shown in Figure 1, a plurality of sipes 10 is formed on the plurality of blocks 5, which extend on said plurality of blocks 5 respectively along a predetermined trajectory Y, visible by way of example in Figures 1 and 2.

[0095] Advantageously, the sipes of said plurality of sipes 10 extend on said plurality of blocks from a radially outer surface of said tread band 2 to a radially inner surface of said tread band 2.

[0096] Generally, as shown in the figures, the sipe 10 is of the three-dimensional type. Thus, the sipe 10 comprises opposite side walls 11, 12 that extend substantially parallel to each other, in which, in each section perpendicular to said predetermined trajectory, each of said opposite side walls 11, 12 comprises at least one male-female coupling.

[0097] Advantageously, such a male-female coupling comprises:

[0098] - at least one protrusion 15 formed on a first wall 11 of said opposite side walls towards a second wall 12 of said opposite side walls and, in correspondence with said at least one protrusion 15,

[0099] - at least one recess 16 formed on said second wall 12 of said opposite side walls away from said first block wall 11 of said opposite side walls.

[0100] As shown in Figures 2, 3, 5, and 6, each sipe comprises an upper portion 101 located at the radially outer surface of the tread band 2.

[0101] Advantageously, as shown in Figure 4A, such sipe, along its extension direction Y, at the upper portion 101, has a substantially sinusoidal wave pattern having a first amplitude A'. Preferably, said first amplitude A' is greater than or equal to 0.8 mm.

[0102] Preferably, said first amplitude A' is less than or equal to 2 mm.

[0103] More preferably, said first amplitude A' is between 1 mm and 1.5 mm, inclusive.

[0104] Advantageously, in the embodiment described above along said predetermined trajectory, at the upper portion 101, said sipe with a substantially sinusoidal wave pattern has a first period P'.

[0105] Preferably, said first period P' is greater than or equal to 2.5 mm.

[0106] Preferably, said first period P' is less than or equal to 4 mm.

[0107] More preferably, said first period P' is between 2.5 mm and 3.5 mm, inclusive.

[0108] As shown in Figures 2, 3, 5, and 6, each sipe 10 further comprises a lower portion 102 located at the radially inner surface of the tread band 2.

[0109] Advantageously, as shown in Figure 4B, such sipe, along said predetermined trajectory, at the lower portion 101, has a substantially sinusoidal wave pattern having a second amplitude A".

[0110] Preferably, said second amplitude A" is greater than or equal to 0.3 mm.

[0111] Preferably, said second amplitude A" is less than or equal to 1 mm.

[0112] More preferably, said second amplitude A" is between 0.3 mm and 0.8 mm, inclusive.

[0113] As shown in Figures 4A and 4B, said first amplitude A' is different from the second amplitude A".

[0114] Advantageously, the different oscillation of the sinusoid between the upper and lower portion, combined with at least one male-female coupling in the radial direction of the sipe, structurally creates interlocks that are maintained over time, as the tread depth decreases with tire wear.

[0115] Advantageously, the residual oscillation of the sipe trajectory in the respective lower portion still allows, despite tire wear, snow to continue to become trapped along a sinusoidal trajectory, increasing the efficiency of the sipe on snow towards the end of the tire's life. Preferably, the first amplitude A' is greater than the second amplitude A" of the wave.

[0116] In this way, advantageously, at the tread surface, deeper interlocks are created, which become progressively less deep as the sipe wears, but the reduced thickness of the residual tread ensures that it maintains adequate stiffness thanks to its reduced thickness, without the need to further stiffen it with deep interlocks.

[0117] Advantageously, in the embodiment described above along said predetermined trajectory, at the lower portion 102, said sipe with a substantially sinusoidal wave pattern has a second period P".

[0118] Preferably, said second period P" is greater than or equal to 2.5 mm.

[0119] Preferably, said second period P" is less than or equal to 4 mm.

[0120] More preferably, said second period P" is between 2.5 mm and 3.5 mm, inclusive. Preferably, said first period P' is equal to said second period P".

[0121] Preferably, as shown in the figures, said sipe 10 comprises a plurality of malefemale couplings.

[0122] With reference to Figure 3 and Figures 5A-5D and 6A-6D, said plurality of malefemale couplings comprises an even number of couplings, so that said sipe 10 operates in the same way regardless of the direction of rotation or mounting of the tyre.

[0123] Preferably, said plurality of male-female couplings has, in the radial direction, a substantially sinusoidal pattern.

[0124] Advantageously, the difference in amplitude between the sinusoid of the upper portion A' and the sinusoid of the lower portion A" combined with the male-female couplings in the radial direction of the sipe 10, gives rise to a three-dimensional "variable wave" structure in the radial direction, which allows the functionality of the sipe to be maintained during the life of the tyre, while at the same time reducing localized increases in stress and pressure, thus improving its functionality and performance on ice.

[0125] As shown by way of example in Figures 2 and 3, preferably the upper portion 101 of the sipe 10 has a first radial dimension H'.

[0126] By way of example only, said first radial dimension H' is greater than or equal to

[0127] 1 mm.

[0128] Advantageously, said first radial dimension H' is less than or equal to 3.5 mm.

[0129] Advantageously, said first radial dimension H' is between 1 mm and 3.5 mm.

[0130] Preferably, said first radial dimension H' is equal to 1 mm.

[0131] Preferably, in said first radial dimension H', each sipe 10 has, along the predetermined trajectory, the sinusoidal pattern having the first amplitude A' and the first period P', as described above.

[0132] With reference to the same figures, the lower portion 102 has a respective second radial dimension H".

[0133] By way of example only, said second radial dimension H" is greater than or equal to

[0134] 2 mm.

[0135] Advantageously, said second radial dimension H" is less than or equal to 4.5 mm.

[0136] Advantageously, said second radial dimension H" is between 2 mm and 4.5 mm.

[0137] Preferably, said second radial dimension H" is equal to 2 mm.

[0138] Preferably, in said second radial dimension H", each sipe 10 has, along the predetermined trajectory, the sinusoidal pattern having the second amplitude A" and the second period P", as described above.

[0139] In preferred embodiments, the second radial dimension H" is greater than said first radial dimension H'.

[0140] In the embodiment shown in the figures, the sipe 10 comprises, between the upper portion 101 and said lower portion 102, an intermediate portion 103.

[0141] Advantageously, and preferably, the intermediate portion 103 has a respective third radial dimension H'" in which said sipe 10 comprises the plurality of male-female couplings.

[0142] By way of example only, said third radial dimension H'" is greater than or equal to 1.1 mm. Advantageously, said third radial dimension H'" is less than or equal to 5.1 mm.

[0143] Advantageously, said third radial dimension H'" is between 1.1 mm and 5.1 mm.

[0144] Advantageously, said third radial dimension H'" is equal to 4.1 mm.

[0145] In the embodiment under consideration, said third radial dimension H'" is greater than said first radial dimension H' and said second radial dimension H".

[0146] As shown in Figures 2, 5B, and 6B, in each section perpendicular to the predetermined trajectory, the sipe has a respective first transverse dimension T'.

[0147] In a first embodiment, as shown in Figure 5B, said transverse dimension T' is substantially constant in said third radial dimension H'" of the sipe 10.

[0148] In further embodiments, said first transverse dimension T' is also substantially constant in said first radial dimension H' of said upper portion 101 of the sipe 10.

[0149] In a second embodiment, as shown in Figure 6B, said first transverse dimension T' is substantially constant up to a depth between 60% and 80% of the depth of the sipe 10 in the radial direction.

[0150] Preferably, said first transverse dimension T' is greater than or equal to 0.2 mm.

[0151] Preferably, said first transverse dimension T' is less than or equal to 1 mm.

[0152] More preferably, said first transverse dimension T' is between 0.2 mm and 0.6 mm, inclusive.

[0153] In a further embodiment, not shown in the figures, said first transverse dimension T' at said first radial dimension H' is different from the first transverse dimension T' at said third radial dimension H'".

[0154] According to a first example, not shown in the figures, said first transverse dimension T' at said first radial dimension H' is greater than the first transverse dimension T' at said third radial dimension H'", for example due to the presence of a chamfer or taper of the upper portion 101 of the sipe 10 at the tread surface 2.

[0155] According to a further example, not shown in the figures, said first transverse dimension T' at said first radial dimension H' may be less than the first transverse dimension T' at said third radial dimension H'", for example due to the presence of a narrowing of the upper portion 101 of the sipe 10 at the tread surface 2.

[0156] As shown in Figures 2, 5B, and 6B, in each section perpendicular to said predetermined trajectory, at the second radial dimension H" the sipe has a respective second transverse dimension T".

[0157] Preferably, said second transverse dimension T" is greater than or equal to 0.2 mm.

[0158] Preferably, said second transverse dimension T" is less than or equal to 2.0 mm.

[0159] More preferably, said second transverse dimension T" is between 0.8 mm and 1.2 mm, inclusive.

[0160] Advantageously, as shown by way of example in Figures 5B and 6B, the lower portion 102 of said sipe 10, in each section perpendicular to said predetermined trajectory, comprises a curved lower surface 102A.

[0161] In the embodiment shown in Figures 5A-5D, the curved lower surface 102A has said second transverse dimension T" which is substantially equal to the respective first transverse dimension T'.

[0162] In the further embodiment shown in Figures 6A-6D, the curved lower surface 102A has said second transverse dimension T" which is greater than the respective first transverse dimension T'.

[0163] With reference to Figure 6B, advantageously the curved lower surface 102A is defined by a portion of a circumference arc having a determined radius R.

[0164] In preferred embodiments, said radius R corresponds to about half of said second transverse dimension T".

[0165] Also as shown in Figure 6B, in each section perpendicular to said trajectory, the curved lower surface 102A is connected to said intermediate portion 103 via a fillet radius R*.

[0166] Preferably, said fillet radius R* is greater than or equal to 0.4 mm.

[0167] Preferably, said fillet radius R* is less than or equal to 4 mm.

[0168] More preferably, said fillet radius R* is between 0.4 mm and 4 mm, inclusive.

[0169] Preferably, said fillet radius R* is greater than said determined radius R. Still more preferably, the ratio between said fillet radius R* and said determined radius R is greater than or equal to 2.

[0170] Preferably, the ratio between said fillet radius R* and said determined radius R is less than or equal to 6.

[0171] For example, the ratio between said fillet radius R* and said determined radius R may be equal to 4.

[0172] In this embodiment, advantageously, in the lower portion 102 of the sipe 10, a substantially "drop-shaped" structure is created which, during deformation of the block 5 and, consequently, of the sipe 10, improves the durability of said lower portion 102 of the sipe 10, reducing the risk of the formation of tears and / or cracks that could weaken this area.

[0173] Finally, with reference to Figures 7A-7B, there are shown, purely for illustrative purposes of the properties of the sipe 10 according to the present invention, radial sectional views of blocks comprising, respectively, three-dimensional sipes 10' as, for example, those described in the prior art document W02023119019A1 cited above, compared with the sipes 10 as previously described according to the present invention, both in a rest condition (i.e., the block is not subject to deformations D representative of an acceleration or braking condition).

[0174] In Figure 7C, a graph is shown illustrating the comparison of the behavior of block 5' according to Figure 7A, thus comprising sipes 10' of known type, and block 5 according to Figure 7B, thus comprising sipes 10 according to the present invention, when subjected to deformations D representative of an acceleration or braking condition.

[0175] In more detail, the data relating to the deformation of block 5' of Figure 7A are represented in the graph of Figure 7C by a dashed line, while the data relating to block 5 of Figure 7B are represented in the graph of Figure 7C by a solid line.

[0176] As can be seen, for increasing deformations D (abscissa axis, increasing values in the direction of the arrow in the figure) of the blocks, the values of reaction force F of the block (ordinate axis, increasing values in the direction of the arrow in the figure) are higher; therefore, the resistance to deformation opposed by block 5 of Figure 7B is greater than the resistance opposed by block 5' of Figure 7A.

[0177] This leads to a high rigidity of the block obtained with a much lower degree of deformation of the block.

[0178] In fact, as can be seen for example from the line indicated with Z in the graph of Figure 7C, at the same value of deformation D, the values of reaction force F of the block and, therefore, of resistance to deformation of the block itself, are higher in the case of block 5 of Figure 7B compared to the case of block 5' of Figure 7A. Moreover, as can be seen from the graph, the blocks 5' of Figure 7A will always have a resistance to deformation that is lower than that of the blocks 5 of Figure 7B, even for higher deformation values.

[0179] This property makes it possible to achieve good performance on dry or wet road surfaces, while at the same time maintaining good performance on snowy road surfaces. This advantageous property also allows block 5 of Figure 7B to achieve better grip, particularly on icy ground, since the higher stiffness of block 5 in question means that it deforms less, creating fewer discontinuities and less increase in localized stress and pressure that would otherwise impair the grip of the block on this type of surface.

Claims

CLAIMS1. Tyre (1) comprising a tread band (2) comprising:- a plurality of grooves (4A),- a plurality of blocks (5A, 5B, 5C) delimited at least by a first pair of said plurality of grooves (4A), and- a plurality of sipes (10) extending on said plurality of blocks (5A, 5B, 5C) respectively along a predetermined trajectory, from a radially outer surface of said tread band (2) to a radially inner surface of the tread band (2), each sipe (10) comprises opposite side walls (11, 12) parallel to each other in which, in each section perpendicular to said predetermined trajectory, each of said opposite side walls (11, 12) comprises at least one male-female coupling comprising:- at least one protrusion (15) formed on a first wall (11) of said opposite side walls towards a second wall (12) of said opposite side walls and, in correspondence with said at least one protrusion (15),- at least one recess (16) formed on said second wall (12) of said opposite side walls away from said first block wall (11) of said opposite side walls each sipe (10) further comprises,- an upper portion (101) located at said radially outer surface of said tread band (2) and having, along said predetermined trajectory, a substantially sinusoidal wave pattern having a first amplitude (A') and a first period (P'); and- a lower portion (102) located at said radially inner surface of said tread band (2) and having, along said predetermined trajectory, a respective substantially sinusoidal wave pattern having a second amplitude (A") and a second period (P"), wherein said first amplitude (A') is different from said second amplitude (A") and said first period (P') is equal to said second period (P").

2. Tyre (1) according to the preceding claim, characterized in that said first amplitude(A') is greater than said second amplitude (A ) of the wave.

3. Tyre (1) according to at least one of the preceding claims, characterized in that each sipe (10) comprises a plurality of male-female couplings.

4. Tyre (1) according to the preceding claim, characterized in that said plurality of malefemale couplings comprises an even number of male-female couplings.

5. Tyre (1) according to claim 3 or 4, characterized in that in each section perpendicular to said predetermined trajectory, the sipe (10) has, from said radially outer surface of said tread band (2) to said radially inner surface of the tread band (2), a substantially sinusoidal pattern.

6. Tyre (1) according to at least one of the preceding claims, characterized in that:- said upper portion (101) has a relative first radial dimension (H') in which each sipe (10) has, along said predetermined trajectory, said substantially sinusoidal wave pattern having said first amplitude (A') and said first period (P');- said lower portion (102) has a relative second radial dimension (H"), in which each sipe (10) has, along said predetermined trajectory, said sinusoidal wave pattern having said second amplitude (A") and said second period (P").

7. Tyre (1) according to at least one of the preceding claims, characterized in that said sipe (10) comprises an intermediate portion (103) between said upper portion (101) and said lower portion (102).

8. Tyre (1) according to the preceding claim, characterized in that said intermediate portion (103) has a relative third radial dimension (H'") in which said sipe (10) comprises said at least one male-female coupling.

9. Tyre (1) according to the preceding claim, characterized in that, in each section perpendicular to said predetermined trajectory, at said intermediate portion (103), said sipe (10) has a relative first transverse dimension (T') that is substantially constant along said third radial dimension (H'").

10. Tyre (1) according to at least one of the preceding claims, characterized in that, in each section perpendicular to said predetermined trajectory, said lower portion (102)of said sipe (10) comprises a curved lower surface (102A).

11. Tyre (1) according to the preceding claim, characterized in that said curved lower surface (102A) has a second transverse dimension (T") greater than or equal to said relative first transverse dimension (T').

12. Tyre (1) according to the preceding claim, characterized in that said second transverse dimension (T") is defined by a first circumferential portion having a determined radius (R).

13. Tyre (1) according to at least one of the preceding claims, characterized in that, in each section perpendicular to said trajectory, said curved lower surface (102A) is connected to said intermediate portion (103) via a fillet radius (R*).

14. Tyre (1) according to claims 12 and 13, characterized in that the ratio between said fillet radius (R*) and said determined radius (R) is between 2 and 6, endpoints included.

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