Tyre with soft tread and stiff tread pattern

Abstract

The tyre (10) comprises a tread (14) comprising an axially central portion (P0) comprising incisions referred to as deep incisions, each deep incision of the axially central portion (P0) having a depth Hi such that Hi / Hs ≥ 50%, where Hs is the tread pattern height. The axially central portion (P0) of the tread layer (141) comprises an elastomeric material (M1) having a complex dynamic shear modulus G*_1 such that G*_1 ≤ 1.50 MPa, a glass transition temperature Tg_1 such that Tg_1 ≤ -23°C. Each deep incision has a variable depth such that the deep incisions (40) of the axially central portion (P0) collectively have a mean volume bridging rate greater than or equal to 25%.

Description

Pneumatic tire with soft tread and rigid tread pattern

[0001] The present invention relates to a tire. By tire is meant a bandage intended to form a cavity by cooperating with a support element, for example a rim, this cavity being capable of being pressurized to a pressure higher than atmospheric pressure. A tire according to the invention has a structure of substantially toroidal shape of revolution around a main axis of the tire.

[0002] The state of the art is known of 4-season, all-season or winter tires for passenger vehicles comprising a crown comprising a tread and a crown reinforcement. Winter tires are identified in particular by an M+S marking (M+S being the acronym for "Mud + Snow") and / or 3PMSF (3PMSF being the acronym for "3 Peak Mountain Snow Flake"). 4-season or all-season tires, due to their performance on snow, also have the M+S and / or 3PMSF markings. On the contrary, a summer tire does not have an M+S marking or a 3PMSF marking. Such tires are described in particular in W02021 / 005295 respectively.

[0003] These tires offer excellent grip performance on snowy surfaces. However, it is desirable to further improve these performances. However, it has been observed that the improvement in these performances on snowy surfaces comes at the expense of the tire's behavior, particularly due to a reduction in the tire's drift stiffness as well as wear resistance.

[0004] The aim of the invention is to provide a tire with improved performance on snowy ground without degrading its behavior or its resistance to wear.

[0005] For this purpose, the subject of the invention is a tire comprising a tread carrying a tread surface, the tread comprising a tread layer carrying at least part of the tread surface, the tread comprising an axially central portion extending over an axial width equal to 80% of the axial width of the tread surface and axially centered on the median plane of the tire, the axially central portion of the tread comprising at least one deepest cut of the axially central portion having a depth Hs, the axially central portion of the tread comprising so-called deep incisions, each deep incision of the axially central portion having a depth Hi such that Hi / Hs > 50%, the axially central portion of the tread layer comprising an elastomeric material,the elastomeric material having a complex dynamic shear modulus G*_1 measured according to ASTM D-5992-96, at a temperature of 60°C and at a frequency, of 10Hz under a stress equal to 0.7 MPa such that G*_1 < 1.50 MPa, the elastomeric material having a glass transition temperature Tg_1 such that Tg_1 < - 23°C, and each deep incision of the axially central portion extending in a general direction on the rolling surface, each deep incision having a variable depth along the general direction of said incision so that all of the deep incisions of the axially central portion have an average bridging volume ratio greater than or equal to 25%.

[0006] The tire according to the invention has improved performance on snowy ground and undegraded behavior and wear.

[0007] Indeed, the inventors behind the invention found that certain properties of the elastomeric material necessary for achieving grip performance on snowy ground, here the complex dynamic shear modulus G*_1 and the glass transition temperature Tg_1, led to a reduction in the rigidity of the elastomeric material. This reduction in rigidity leads to increased deformation of the elastomeric material, in particular under high stress as is the case when cornering, which deteriorates the behavior of the tire as well as the wear resistance. In order to compensate for the deterioration in the behavior of the tire and the wear resistance, the inventors, independently of the properties of the elastomeric material, found that a tread having a particularly rigid tread pattern made it possible to limit the deformation of the tread as a whole and thus to compensate for the low intrinsic rigidity of the elastomeric material.

[0008] The inventors have further identified that the average bridging volume ratio of the deep incisions of the axially central portion was, apart from the elastomeric material, the parameter having the most influence on increasing the rigidity of the tread. Thus, the invention proposes a relatively high average bridging volume ratio of the deep incisions of the axially central portion.

[0009] The bridging volume ratio represents the volume proportion of material connecting the two main lateral faces of a deep incision. To determine the average bridging volume ratio, the individual bridging volume ratio of each of the deep incisions of the axially central portion is determined and the arithmetic mean is taken. The individual bridging volume ratio of a deep incision is equal to 1-ViA / t with: - See the empty volume of the deep incision, - Vt the theoretical volume of a theoretical deep incision whose depth is constant and equal to the maximum depth of the deep incision.

[0010] The complex shear modulus G* and the glass transition temperature are properties well known to those skilled in the art and are measured on a Metravib VA4000 type viscoanalyzer using specimens extracted from the tire. The response of the specimens subjected to sinusoidal stress in alternating simple shear is recorded at a frequency of 10 Hz under a stress equal to 0.7 MPa. A temperature scan is carried out between -60°C and 100°C at a speed of 1.5°C / min. The specimen is of cylindrical section as described in ASTM D 5992 - 96 (version published in September 2006, initially approved in 1996) in Figure X2.1 (circular embodiment) and has a diameter of 10 mm [0 to + 0.04 mm] and a thickness of 2 mm [1.85-2.20]. The dynamic shear complex modulus G* at 60°C is the value of G* measured when the temperature is equal to 60°C. The glass transition temperature Tg is equal to the temperature for which the value of tanD is maximum.The tangent of the phase angle D between the force exerted on the sample and its displacement reflects a dynamic loss and is equal to the ratio G” / G'.

[0011] Conventionally, the rolling surface on a tire mounted on a measuring rim and inflated to the nominal pressure (250 kPa or 290 kPa depending on whether it is a standard or reinforced tire) can be determined within the meaning of the ETRTO standard manual ("European Tire and Rim Technical Organization"), 2021 as being the surface in contact with the ground when the tire is loaded to 80% of its load capacity within the meaning of the ETRTO standard manual, 2021, a load then representing conditions of use normally encountered.

[0012] A cut-out has, on the rolling surface, two main characteristic dimensions: a width and a curvilinear length such that the curvilinear length is at least twice the width. A cut-out is therefore delimited by at least two main lateral faces determining its curvilinear length and connected by a base, the two main lateral faces being distant from each other by a non-zero distance, called the width of the cut-out.

[0013] A cutout is either a groove or an incision and forms a space opening onto the rolling surface.

[0014] An incision is such that the distance between the main lateral faces is suitable to allow at least partial contact of the main lateral faces delimiting said incision when passing through the contact area, in particular when the tire is in new condition and under normal driving conditions, including in particular the fact that the tire is at nominal load and nominal pressure.

[0015] A groove is such that the distance between the main side faces is such that these main lateral faces cannot come into contact with each other under normal driving conditions, including in particular the fact that the tire is at nominal load and nominal pressure.

[0016] The width of a cutout is, on a new tire, the maximum distance between the two main lateral faces measured, by default and in the case where the cutout does not include a chamfer, at a radial dimension coincident with the rolling surface, and by default and in the case where the cutout includes a chamfer, at the radial dimension most radially outer of the cutout and radially inner of the chamfer. The width is measured substantially perpendicular to the main lateral faces. If a width other than the default width is specified, for example a width at a particular dimension, the width is equal to the smallest distance between the two main lateral faces at the particular dimension of the cutout.

[0017] The depth of a cut is, on a new tire, the maximum radial distance between the bottom of the cut and its projection onto the ground when the tire is rolling. The maximum value of the depths of the cuts is called the tread height.

[0018] The general direction of a cutout is, on the rolling surface, the direction defined by the line equidistant from the main side walls of the cutout.

[0019] The mean direction of a cut is, on the rolling surface, the straight line joining the two ends of the cut.

[0020] In embodiments for optionally improving braking on dry ground, the or each cutout is provided with chamfers. A chamfer may be a straight chamfer or a rounded chamfer. A straight chamfer is formed by a flat face inclined relative to the leading or trailing face which it extends to the leading or trailing edge circumferentially delimiting the cutout. A rounded chamfer is formed by a curved face connecting tangentially to the leading or trailing face which it extends. A chamfer is characterized by a height and a width equal respectively to the radial distance and to the distance in a direction perpendicular to the leading or trailing faces between the common point between the leading or trailing face extended by the chamfer and the leading or trailing edge circumferentially delimiting the cutout.

[0021] The tire according to the invention has a substantially toric shape around an axis of revolution substantially coincident with the axis of rotation of the tire. This axis of revolution defines three directions conventionally used by those skilled in the art: an axial direction, a circumferential direction and a radial direction.

[0022] By axial direction is meant the direction substantially parallel to the axis of revolution of the tire or mounted assembly, i.e. the axis of rotation of the tire or mounted assembly. The mounted assembly includes the tire mounted on a mounting support, for example a rim.

[0023] Circumferential direction means the direction which is substantially perpendicular to both the axial direction and a radius of the tire or mounted assembly (in other words, tangent to a circle whose center is on the axis of rotation of the tire or mounted assembly).

[0024] Radial direction means the direction along a radius of the tire or mounted assembly, i.e. any direction intersecting the axis of rotation of the tire or mounted assembly and substantially perpendicular to this axis.

[0025] By median plane of the tire (noted M), we mean the plane perpendicular to the axis of rotation of the tire which is located at the axial midpoint of the two beads and passes through the axial center of the crown.

[0026] By equatorial circumferential plane of the tire, we mean, in a meridian section plane, the plane passing through the equator of the tire, perpendicular to the median plane and to the radial direction. The equator of the tire is, in a meridian section plane (plane perpendicular to the circumferential direction and parallel to the radial and axial directions) the axis parallel to the axis of rotation of the tire and located equidistant between the radially outermost point of the tread intended to be in contact with the ground and the radially innermost point of the tire intended to be in contact with a support, for example a rim.

[0027] Meridian plane means a plane parallel to and containing the axis of rotation of the tire or mounted assembly and perpendicular to the circumferential direction.

[0028] By radially inner, respectively radially outer, is meant closer to the tire's axis of rotation, respectively further from the tire's axis of rotation. By axially inner, respectively axially outer, is meant closer to the tire's median plane, respectively further from the tire's median plane.

[0029] By bead is meant the portion of the tire intended to allow the tire to be attached to a mounting support, for example a wheel comprising a rim. Thus, each bead is in particular intended to be in contact with a hook on the rim allowing it to be attached.

[0030] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from more than a to less than b (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict limits a and b).

[0031] In optional embodiments in which the deep incisions are relatively deep and result in a reduction in tread stiffness making the invention even more advantageous, Hi / Hs > 60%, preferably Hi / Hs > 70%.

[0032] Preferably and optionally, each deep incision of the axially central portion has a depth ranging from 5.0 mm to the sculpture height Hs, preferably ranging from 6.0 mm to the sculpture height Hs and more preferably ranging from 6.5 mm to the sculpture height Hs.

[0033] Preferably and optionally, each deep incision of the axially central portion has a width ranging from 0.2 mm to 2.0 mm, preferably from 0.2 mm to 1.5 mm and more preferably from 0.2 mm to 1.0 mm.

[0034] Advantageously but optionally, the tread height ranges from 5.5 mm to 9.0 mm and preferably from 8.0 mm to 9.0 mm.

[0035] In certain optional embodiments, the tread comprising regulatory wear indicators defining a theoretical regulatory wear surface parallel to the tread surface of the tire in new condition and passing through the most radially external point of each regulatory wear indicator of the axially central portion, each deep incision of the axially central portion has a bottom of which at least one portion is arranged radially inside the theoretical regulatory wear surface.

[0036] Such deep incisions ensure that, as long as the tire wear is below a regulatory wear threshold, the incisions will be present on the tread surface. This guarantees long-lasting performance on snowy ground regardless of tire wear.

[0037] Such wear indicators are required, for example, by United Nations regulations R30 and R54, the United States of America FMVSS139 or China GB97743 and are intended to indicate to the tire user a regulatory wear threshold of the tire beyond which it is risky to drive. Thus, these wear indicators are referred to as regulatory wear indicators. Each regulatory wear indicator is formed by a protuberance extending radially over a radial height substantially equal to 1.6 mm.

[0038] In advantageous and optional embodiments, G*_1 < 1.30 MPa, preferably G*_1 < 1.00 MPa and more preferably G*_1 < 0.94 MPa.

[0039] The lower the complex dynamic shear modulus G*_1, the better the snow grip performance. In addition, the inventors also found that the lower the complex dynamic shear modulus G*, the better are the wet grip performance. Thus, reducing the value of the complex dynamic shear modulus G*_1 can simultaneously improve the snow and wet grip performance.

[0040] In these embodiments, advantageously, G*_1 > 0.50 MPa, preferably G*_1 > 0.70 MPa. It will be preferable to have a G*_1 which is not too small so as to maintain an intrinsic rigidity of the elastomeric material making it possible to obtain behavior as good as possible and wear as reduced as possible.

[0041] In advantageous and optional embodiments, the elastomeric material has a glass transition temperature Tg_1 such that -35°C < Tg_1 < -25°C, preferably -30°C < Tg_1 < -25°C.

[0042] Snow grip performance increases with decreasing glass transition temperature. Wet grip performance increases with increasing glass transition temperature. Thus, it is preferable to choose the glass transition temperature in a temperature range where both wet and snow grip performance are best in view of the performance compromise desired by the tire designer. In all cases, such ranges lead to a decrease in the rigidity of the elastomeric material, which the invention makes it possible to compensate for.

[0043] In preferred and optional embodiments, the average bridging volume ratio is greater than or equal to 30%, preferably 35%.

[0044] The higher the average bridging rate, the more the tread becomes stiffer, which further compensates for the low stiffness of the elastomeric material.

[0045] In advantageous and optional embodiments, the average bridging volume ratio is less than or equal to 50%, preferably 45%.

[0046] If the average bridging rate becomes too high, there is a risk of reducing the tire's performance on snowy ground due to the reduced mobility of the edges of the deep incision. This reduction in performance on snowy ground is especially noticeable when the tire is worn.

[0047] In advantageous and optional embodiments, each deep incision of the axially central portion has a bottom having a radial profile arranged so that at least first and second points of the bottom are arranged on either side of a third point of the bottom in the mean direction in which said deep incision extends, each first and second point being arranged, relative to the rolling surface, at a depth strictly less than the depth at which the third point is arranged.

[0048] In preferred variants of these embodiments, the depth of at least one, preferably each, of the first and second points coincides with a minimum depth of said deep incision. Still in preferred variants, the depth of the third point coincides with a maximum depth of said deep incision. Finally, still in preferred variants, each first and second point coincides with each end of the bottom of said deep incision in the mean direction.

[0049] In advantageous and optional embodiments, the radial bridging distance between the maximum depth and the minimum depth of each deep incision of the axially central portion is equal to, on average, at least 50%, preferably at least 55%, more preferably at least 60% of the maximum depth of said incision.

[0050] The radial distance represents the bridging height and, together with the values ​​described above, ensures significant stiffening of the tread.

[0051] To determine the average of the ratio between the radial distance and the minimum depth, the radial distance and the minimum depth of each of the deep incisions of the axially central portion of the tread are determined and the arithmetic mean is taken.

[0052] In advantageous and optional embodiments, each deep incision of the axially central portion extends in a mean direction on the rolling surface forming, with the axial direction, an angle ranging from 25° to 40°, preferably from 27° to 37°.

[0053] The smaller the angle formed by the mean direction with the axial direction, the more the tread is stiffened in the axial direction and therefore the more the tire behavior is improved, especially under strong drift. Conversely, the larger the angle formed by the general direction with the axial direction, the more the tread is stiffened in the circumferential direction and therefore the more the performance on snowy ground, especially braking, is improved. The angles of the embodiments described make it possible to obtain an excellent compromise between behavior and these other performances.

[0054] Obviously for those skilled in the art, the angle considered is the angle, in absolute value, the smallest of the two angles defined between the reference line, here the axial direction of the tire, and the average direction in which the deep incision extends on the rolling surface.

[0055] In advantageous and optional embodiments, the axially central portion comprises at least one bread, the or each bread comprising several incisions deep incisions made in said bread and extending substantially parallel to each other in a mean direction on the rolling surface, the mean distance, in a direction perpendicular to the mean direction, between two adjacent deep incisions made in said bread ranges from 2.0 mm to 5.0 mm, preferably from 2.0 mm to 4.0 mm and more preferably from 2.0 mm to 3.0 mm.

[0056] Thus, the tire includes a relatively high density of deep incisions which further improves performance on snowy ground.

[0057] By substantially parallel to each other, we mean that the average directions of each of the deep incisions are parallel to within plus or minus 15°. The average distance is an arithmetic mean of the distances separating two successive incisions in the direction perpendicular to the average direction.

[0058] In preferred and optional embodiments, the elastomeric material has a dynamic loss tanDMAX23 measured according to ASTM D-5992-96, at a temperature of 23°C and at a frequency of 10Hz, less than or equal to 0.40.

[0059] A relatively low dynamic loss tanDMAX23 helps reduce the tire's rolling resistance.

[0060] The dynamic loss tanDMAX23 is yet another dynamic property well known to those skilled in the art and is measured on the same viscoanalyzer of the Metravib VA4000 type using specimens extracted from the tire. The specimen has a cylindrical section as described in the ASTM D 5992 - 96 standard (version published in September 2006, initially approved in 1996) in figure X2.1 (circular embodiment) and has a diameter of 10 mm [0 to + 0.04 mm] and a thickness of 2 mm [1.85-2.20]. The response of the specimen subjected to a sinusoidal stress in alternating simple shear, at the frequency of 10 Hz under determined temperature conditions (here 23 ° C) according to the ASTM D1349-99 standard, is recorded. A strain amplitude sweep is carried out from 0.1% to 100% (forward cycle), then from 100% to 0.1% (return cycle).The tangent of the phase angle D between the force exerted on the sample and its displacement reflects a dynamic loss and is equal to the ratio G” / G'. The maximum value tanDMAX of the tangent of the phase angle D observed on the deformation return cycle is recorded.

[0061] In advantageous variants, the tread comprises: - a radially outer rolling layer carrying at least part of the rolling surface and comprising the elastomeric material, and - a radially inner wearing course arranged at least partly radially inside the radially outer wearing course.

[0062] The radially inner tread layer is intended to, before reaching a regulatory wear threshold, carry at least part of the rolling surface. In other words, the radially inner tread layer is intended, after a predetermined wear of the tire, to carry at least part of the rolling surface and therefore to be in contact with the ground on which the tire is rolling.

[0063] In these advantageous variants, the radially internal rolling layer optionally comprises an internal elastomeric material having a complex dynamic shear modulus G*_2 such that G*_2 > G*1, G*_2 being measured according to the ASTM D-5992-96 standard, at a temperature of 60°C and at a frequency of 10Hz under a stress equal to 0.7 MPa.

[0064] A value of G*_2 greater than that of G*_1 makes it possible to obtain a tread layer, thanks to the radially internal layer, improving the behavior of the tire when new, and in any case as long as the radially external layer is not completely worn. The complex dynamic shear modulus G*_2 is determined as described previously.

[0065] In these advantageous variants, we optionally have G*_2 > 1.10, preferably G*_2 > 1.15. Thus, the higher the value of G*_2, the more rigid the radially internal layer is and makes it possible to improve the behavior of the tire, in particular when new and in any case as long as the radially external layer is not completely worn.

[0066] In these advantageous variants, the internal elastomeric material optionally has a glass transition temperature Tg_2 such that -45°C < Tg_2 < - 25°C, preferably -40°C < Tg_2 < -30°C. Thus, the grip performance on snowy ground is maximized even once the tire has advanced wear. The glass transition temperature Tg_2 is determined as described above.

[0067] In other variations, the tread comprises: - a radially outer rolling layer carrying at least part of the rolling surface and comprising the elastomeric material, and - a radially inner support layer arranged at least partly radially inside the radially outer wearing course.

[0068] In these other variants, the support layer is not intended to carry at least part of the rolling surface until the regulatory wear threshold is reached. Thus, the support layer, unless it exceeds the regulatory wear threshold, will never be in contact with the ground on which the tire is rolling.

[0069] In optional embodiments, the volumetric notch rate of the tread is greater than or equal to 28%, preferably 35%.

[0070] The tread of a tire is all the more rigid as its volumetric notch ratio is low. Indeed, the less the tread is notched, the less it is likely to deform under the effect of forces, in particular at the level of its cuts which form zones very favorable to deformation. Thus, the invention, by stiffening the crown thanks to the relatively high average bridging ratio, is particularly advantageous in the case of a relatively notched tread.

[0071] The volumetric notch rate of the tread is the ratio of the total volume of the tread cutouts in the new condition to the total volume of the tread in the new condition but not including any cutouts. The tread is axially delimited by two planes perpendicular to the axis of rotation of the tire and passing through the axial edges of the tread surface. In order to measure such a volumetric notch rate, one of the methods described in WO2021 / 089958 may in particular be used.

[0072] Optionally and preferably, the tire is for a vehicle selected from passenger vehicles, light commercial vehicles and camper vans and even more preferably the tire according to the invention is for a passenger vehicle.

[0073] A passenger vehicle tire is a passenger car or passenger car tire as defined in the ETRTO standard manual, 2021. Such a tire has a section in a meridian cutting plane characterized by a section height H and a nominal section width SW within the meaning of the ETRTO standard manual, 2021. More preferably and optionally, the passenger vehicle tires to which the invention will advantageously be applied are such that the H / SW ratio, expressed as a percentage, is at most equal to 90, preferably at most equal to 80 and more preferably at most equal to 70 and is at least equal to 20, preferably at least equal to 30, and the nominal section width SW is at least equal to 115 mm, preferably at least equal to 155 mm and more preferably at least equal to 175 mm and at most equal to 385 mm, preferably at most equal to 315 mm, more preferably at most equal to 285 mm.In addition, the hook diameter D, defining the diameter of the rim on which the tire is mounted, is at least 12 inches, preferably at least 16 inches and at most 24 inches, preferably at most 21 inches. The nominal section width SW, the nominal aspect ratio H / SW and the hook diameter D are those of the dimension marking on the sidewall of the tire and comply with the ETRTO 2021 standard manual.

[0074] A light commercial vehicle or motorhome tyre is as defined in the ETRTO standard manual in sections 10 to 12 of the commercial vehicle tyre part.

[0075] Preferably and advantageously, the tire bears an M+S and / or 3PMSF marking. Such a marking is generally affixed to at least one of the sidewalls of the tire. So-called "winter" tires are notably identified by an M+S marking (M+S being the acronym for "Mud + Snow") and / or 3PMSF (3PMSF being the acronym for "3 Peak Mountain Snow Flake"). So-called "4-season" or "all-season" tires, due to their performance on snow, also have the M+S and / or 3PMSF markings. On the contrary, a so-called "summer" tire does not have an M+S marking or a 3PMSF marking.

[0076] In advantageous and optional embodiments, the tread comprises first and second axially lateral portions arranged axially outside the axially central portion and on either side of the axially central portion relative to the median plane, each first and second axially lateral portion comprising incisions extending in a mean direction on the tread surface forming, with the axial direction, an angle less than or equal to 45°, preferably less than or equal to 30° and more preferably less than or equal to 15°.

[0077] Each first and second axially lateral portion has a lesser thickness of material than the axially central portion, in particular due to the meridian curvature of the tread surface. Thus, the impact of the elastomeric material of each first and second axially lateral portion on the behavior of the tire is less than that of the axially central portion. It is thus possible to use incisions whose orientation has no influence on the behavior or performance on snowy ground. Here, such angles will be preferred, which make it possible to reduce the noise generated by the tread.

[0078] In preferred embodiments, the tread comprises first and second lateral main cutouts, each first and second lateral main cutout extending: - axially from an axially outer end of each first and second main lateral cutout to an axially inner end of each first and second main lateral cutout, the axially outer end of each first main lateral cutout being arranged on one side of the median plane of the tire, the axially outer end of each second main lateral cutout being arranged on the other side of the median plane of the tire, - circumferentially from a circumferentially first azimuth of the axially inner end to a circumferentially second azimuth of the axially outer end, the circumferentially first azimuth entering the contact area with the rolling ground of the tire before the circumferentially second azimuth when the tire is mounted on a vehicle moving forward, each first and second main lateral cutout extends axially from each axially outer end to each axially inner end over at least 30% of the axial width of the tread surface, the tread comprising first and second sets of at least one loaf, each first and second set of loaves being delimited circumferentially at least in part by a pair of respectively first and second circumferentially successive main lateral cutouts,the deep incisions being made in the part of each first and second set extending in the axially central portion.,

[0079] In preferred variants, each first and second main lateral cutout extends axially from the axially outer end to the axially inner end in a mean direction forming, with the circumferential direction, a mean angle ranging from 40° to 70°.

[0080] Preferably and optionally, each first and second lateral main cutout has a width ranging from 2.0 to 15.0 mm, preferably from 5.0 to 12.0 mm.

[0081] Preferably and optionally: - each first and second main lateral cutout has a depth greater than or equal to 75% and more preferably 90% of the sculpture height Hs, and / or - each first and second main lateral cutout has a depth ranging from 5.0 mm to the tread height Hs, preferably ranging from 6.0 mm to the tread height Hs and more preferably ranging from 6.5 mm to the tread height Hs.

[0082] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which: Figure 1 is a view, in a meridian section plane, of a tire according to the invention, Figure 2 is a top view of the tread of the tire of Figure 1, Figure 3 is a detail view of a set of tread blocks of the tire of Figure 1, Figures 4 and 5 are perspective views of a deep incision of the tread of Figure 1, and Figure 6 is a perspective view of a theoretical volume of a theoretical deep incision corresponding to the deep incision of Figures 4 and 5 and whose depth is constant and equal to the maximum depth of the deep incision of Figures 4 and 5.

[0083] The figures show a reference X, Y, Z corresponding to the usual axial (Y), radial (Z) and circumferential (X) directions of a tire.

[0084] With reference to Figures 1 and 2, the tire according to the invention is designated by the general reference 10. The tire 10 has a substantially toric shape around an axis of revolution substantially parallel to the axial direction Y. The tire 10 is intended for a passenger vehicle and has dimensions 205 / 55R16. The tire 10 is a winter tire bearing an M+S and 3PMSF marking. The tire 10 is shown in new condition, that is to say not yet having been driven. The tire 10 has a direction of rotation R indicating the direction in which, once mounted on the vehicle, the tire 10 must rotate when the vehicle is moving forward.

[0085] The tire 10 comprises a tread 14 intended to come into contact with a ground when rolling. The tire 10 further comprises a conventional structure, such as for example described in applications WO2021250331, WO2022074341 or WO2022069819.

[0086] The tread 14 comprises a rolling surface 16 via which the tread 14 is intended to come into contact with the ground when the tire 10 rolls on the ground. The rolling surface 16 is delimited axially by first and second axial edges 18, 20.

[0087] The tread 14 comprises an axially central portion PO and first and second axially lateral portions P1, P2 arranged axially outside the axially central portion PO on either side axially of the axially central portion PO relative to the median plane M of the tire 10. The axially central portion PO has an axial width L0 equal to 80% of the axial width L of the tread surface 16 and is centered on the median plane M of the tire 10. Each first and second axially lateral portions P1, P2 respectively have an axial width L1, L2 equal to 10% of the axial width L of the rolling surface 16.

[0088] Referring to Figure 1, the tread 14 comprises a radially outer tread layer 141 carrying the tread surface 16 of the tire in the new condition and a radially inner tread layer 142 arranged at least partly radially inside the radially outer tread layer 141. The radially outer tread layer 141 comprises an elastomeric material M1. The radially inner tread layer 142 comprises an inner elastomeric material M2. The radially outer layer 141 and the radially inner tread layer 142 are separated by an interface 143 represented by a dashed line in Figure 1. Each axially central portion PO and each first and second axially lateral portions P1, P2 comprises the radially outer tread layer 141 and therefore the elastomeric material M1.Each axially central portion PO and each first and second axially lateral portions P1, P2 also comprises the radially internal rolling layer 142 and therefore the elastomeric material M2.

[0089] The tread 14 comprises regulatory wear indicators 12 defining a theoretical regulatory wear surface 121 parallel to the tread surface 16 of the tire 10 in the new condition and passing through the most radially external point of each regulatory wear indicator of the tread 14. The theoretical regulatory wear surface 121 is shown in dotted lines in Figure 1.

[0090] The elastomeric material M1 has a complex dynamic shear modulus G*_1 measured according to ASTM D-5992-96, at a temperature of 60°C and at a frequency of 10Hz under a stress equal to 0.7 MPa such that G*_1 < 1.50 MPa, preferably G*_1 < 1.30 MPa, more preferably G*_1 < 1.00 MPa and even more preferably G*_1 < 0.94 MPa. Here, G*_1=0.90 MPa. The elastomeric material M1 has a glass transition temperature Tg_1 such that Tg_1 < -23°C, preferably -35°C < Tg_1 < -25°C and more preferably -30°C < Tg_1 < -25°C and here Tg_1= -27°C. The elastomeric material M1 has a dynamic loss tanDMAX23 measured according to the ASTM D-5992-96 standard, at a temperature of 23°C and at a frequency of 10Hz less than or equal to 0.40 and here equal to 0.38. The elastomeric material M1 may be designed from the elastomeric materials described in particular in WO 2021 / 005295.

[0091] The internal elastomeric material M2 has a complex dynamic shear modulus G*_2 measured according to ASTM D-5992-96, at a temperature of 60°C and at a frequency of 10Hz under a stress equal to 0.7 MPa such that G*_2 > G*_1 and such that G*_2 > 1.10, preferably G*_2 > 1.15. Here, G*_2=1.15 MPa. The internal elastomeric material M2 has a glass transition temperature Tg_2 such that -45°C < Tg_2 < -25°C, preferably -40°C < Tg_2 < -30°C and here Tg_2= - 35°C. The elastomeric material M2 may be designed from the elastomeric materials described in particular in W02020 / 099789.

[0092] With reference to figures 1, 2 and 3, the tread 14 comprises first and second main lateral cutouts 22, 24. The tread 14 also comprises first and second sets 32, 34 of several loaves 36, 38. The axially central portion PO comprises incisions 40 made in the axially central portion and here in loaves 36, 38 of the part of each first and second set 32, 34 extending into the axially central portion PO. The axially central portion PO also comprises incisions 42 separating each bread 36, 38 from the adjacent bread or breads of the same set 32, 34. The tread 14, here each first and second axially lateral portions P1, P2 and more precisely the part of each first and second set 32, 34 extending in each first and second axially lateral portions P1, P2 also comprises incisions 44.

[0093] Each first main lateral cutout 22 extends axially from an axially outer end 22A to an axially inner end 22B. The axially outer end 22A is arranged on a first side of the median plane M. Similarly, each second main lateral cutout 24 extends axially from an axially outer end 24A to an axially inner end 24B. The axially outer end 24A is arranged on the second side of the median plane M, i.e. on the other side than the side where the axially outer end 22A is arranged.

[0094] Each first and second main lateral cutout 22, 24 extends axially from the axially outer end 22A, 24A to the axially inner end 22B, 24B in a mean direction forming, with the circumferential direction X, an average angle ranging from 40° to 70° and here equal on average to 45°.

[0095] Each first set 32 ​​is circumferentially delimited at least in part by a pair of first circumferentially successive main lateral cutouts 22. Each second set 34 is circumferentially delimited at least in part by a pair of second circumferentially successive main lateral cutouts 24.

[0096] Each first lateral main cutout 22 extends circumferentially from a circumferentially first azimuth AZ1 of the axially inner end 22B to a circumferentially second azimuth AZ2 of the axially outer end 22A. The circumferentially first azimuth AZ1 enters the contact area with the rolling ground of the tire 10 before the circumferentially second azimuth AZ2 when the tire 10 is mounted on a vehicle moving forward and respecting its direction of rotation R. Similarly, each second main lateral cutout 24 extends circumferentially from a circumferentially first azimuth AZ1' of the axially inner end 24B to a circumferentially second azimuth AZ2' of the axially outer end 24A. The circumferentially first azimuth AZ1' enters the contact area with the rolling ground of the tire 10 before the circumferentially second azimuth AZ2' when the tire 10 is mounted on a vehicle moving forward and respecting its direction of rotation R.

[0097] Each first and second main lateral cutout 22, 24 extends axially in a main direction forming, with the circumferential direction X, a decreasing angle when moving from each axially outer end 22A, 24A towards each axially inner end 22B, 24B over at least 75%, here over 100%, of the curvilinear length of each first and second main lateral cutout 22, 24.

[0098] Each first and second lateral main cutout 22, 24 has a width ranging from 2.0 to 15.0 mm, preferably from 5.0 to 12.0 mm. Each first and second lateral main cutout 22, 24 has a depth greater than or equal to 75% and more preferably 90% of the tread height Hs and ranging from 5.0 mm to the tread height Hs, preferably ranging from 6.0 mm to the tread height Hs and more preferably ranging from 6.5 mm to the tread height Hs. The tread height Hs ranges from 5.5 mm to 9.0 mm and preferably from 8.0 mm to 9.0 mm. Here, the tread height Hs and the depth of each first and second lateral main cutout 22, 24 is substantially equal to 8.8 mm. Thus each first and second main lateral cutout 22, 24 constitutes the deepest cutout of the axially central portion PO.

[0099] Each incision 40 has a depth Hi such that Hi / Hs > 50%, preferably Hi / Hs > 60% and more preferably Hi / Hs > 70%. For this reason, each incision 40 is referred to as a deep incision. Each deep incision 40 of the axially central portion PO has a depth ranging from 5.0 mm to the tread height Hs, preferably ranging from 6.0 mm to the tread height Hs and more preferably ranging from 6.5 mm to the tread height Hs. Here, each deep incision 40 has a depth varying from 6.5 mm to 7.5 mm depending on whether it is arranged close to or far from the median plane M. Each deep incision 40 of the portion axially central portion PO has a width ranging from 0.2 mm to 2.0 mm, preferably from 0.2 mm to 1.5 mm and more preferably from 0.2 mm to 1.0 mm and here equal to 0.4 mm. Each deep incision 40 of the axially central portion PO extends in a mean direction Di on the rolling surface 16 forming, with the axial direction Y, an angle ranging from 25° to 40°, preferably from 27° to 37° and here equal to 35°.

[0100] Each incision 42 is substantially parallel to each incision 40 adjacent to it and therefore extends in a mean direction on the rolling surface 16 forming, with the axial direction Y, an angle ranging from 25° to 40°, preferably from 27° to 37° and here equal to 35°. Each incision 42 has a width strictly greater than the width of each incision 40, ranging from 1.0 mm to 3.0 mm and here equal to 1.7 mm. Each incision 42 has a depth strictly less than the depth of each incision 40. The depth of each incision 42 is strictly less than 50% of the tread height Hs and here ranges from 1.0 mm to 4.0 mm and here equal to 3.0 mm.

[0101] Each incision 44 extends in a mean direction on the rolling surface 16 forming, with the axial direction Y, an angle less than or equal to 45°, preferably less than or equal to 30° and more preferably less than or equal to 15°. Each incision 44 has a width ranging from 0.2 mm to 2.0 mm, preferably from 0.2 mm to 1.5 mm and more preferably from 0.2 mm to 1.0 mm.

[0102] With reference to Figure 3, the deep incisions 40 made in each bread 36, 38 extend substantially parallel to each other in the mean direction Di on the rolling surface 16. The mean distance Dm, in a direction Dp perpendicular to the mean direction Di, between two adjacent deep incisions 40 made in said bread 36, 38 ranges from 2.0 mm to 5.0 mm, preferably from 2.0 mm to 4.0 mm and more preferably from 2.0 mm to 3.0 mm. In Figure 3, several distances D1, D2, D3, D4 have been measured between the deep incisions 40 of a second element 34 and the mean Dm of which is equal to 2.7 mm.

[0103] Due to the large number of cutouts described above, the volumetric notch rate of the tread 14 is greater than or equal to 28%, preferably 35%.

[0104] Each deep incision 40 will now be described in more detail with reference to FIGS. 4, 5 and 6. Each deep incision 40 of the axially central portion PO extends in a general direction Dg on the rolling surface 16. Each deep incision 40 has a variable depth along the general direction Dg of said deep incision 40. Each deep incision 40 of the axially central portion PO has a bottom 400 having a radial profile arranged so that at least first and second points 401, 402 of the bottom 400 are arranged on either side of a third point 403 of the bottom 400 along the average direction Di along which said deep incision 40 extends. Each first and second point 401, 402 is arranged, relative to the rolling surface 16, at a depth Psup strictly less than the depth Hi at which the third point 403 is arranged. Here, the depth of each of the first and second points 401, 402 coincides with a minimum depth Psup of said deep incision 40. The depth of the third point 403 coincides with a maximum depth Hi of said deep incision 40. Each first and second point 401, 402 coincides with each end E1, E2 of the bottom 400 of said deep incision along the average direction Di.

[0105] As can be seen in Figure 1, each bottom 400 has at least one portion arranged radially inside the theoretical regulatory wear curve 121.

[0106] The radial bridging distance Dr between the maximum depth Hi and the minimum depth Psup of each deep incision 40 of the axially central portion PO is equal to, on average, at least 50%, preferably at least 55% and more preferably at least 60% of the maximum depth Hi of said incision 40. For the deep incision 40 shown in Figures 4 to 6 (and in which the proportions are not respected), Hi = 7.5 mm, Psup = 2.5 mm so that Dr = 5.0 mm and Dr / Hi = 67%. On average, Dr / Hi is here equal to 64%

[0107] The deep incision 40 creates an empty volume Vi in the axially central part PO. This empty volume Vi is delimited radially by the rolling surface 16 and by the bottom 400. This empty volume Vi is delimited radially by the main faces of the axially central part in which the deep incision 40 is made. This empty volume Vi is shown in Figure 5, here equal to 19.7 mm3.

[0108] In Figure 6, a volume Vt is represented which is the theoretical volume of the theoretical deep incision whose depth is constant and equal to the maximum depth of the deep incision 40, i.e. Hi. Here, Vt=33.9 mm3.

[0109] The value of 1-Vi / Vt is equal to an individual bridging volume ratio of the deep incision 40. For the deep incision previously described, 1-Vi / Vt=42%. By averaging the individual bridging volume ratios of all the deep incisions 40 of the axially central portion PO, an average bridging volume ratio is obtained. All the deep incisions 40 of the axially central portion PO have an average bridging ratio greater than or equal to 25%, preferably greater than or equal to 30% and more preferably 35%. The average bridging volume ratio is less than or equal to 50%, preferably 45%. Here, the average bridging volume ratio is equal to 42%.

[0110] COMPARATIVE TESTS

[0111] Control tires T0, T1, T2, T3, T4 and tire 10 were compared according to the first embodiment.

[0112] The T0 tire is a tire marketed under the MICHELIN ™ brand in the ALPIN 6 ™ range. The T0 tire comprises a radially outer tread layer comprising an elastomeric material having a complex dynamic shear modulus G* measured according to ASTM D-5992-96, at a temperature of 60°C and a frequency of 10Hz under a stress equal to 0.7 MPa equal to 0.95 MPa and a glass transition temperature Tg= -22°C. The T0 tire comprises a radially inner tread layer comprising an elastomeric material having a complex dynamic shear modulus G* measured according to ASTM D-5992-96, at a temperature of 60°C and a frequency of 10Hz under a stress equal to 0.7 MPa equal to 1.10 MPa and a glass transition temperature Tg=-30°C.

[0113] The tire T1 is identical to the tire T0 except for the elastomeric material of the radially inner tread layer 142 which is the elastomeric material M2 of the tire 10.

[0114] The T2 tire is identical to the T0 tire except for the elastomeric material of the radially outer tread layer 141 which is the elastomeric material M1 of the tire 10.

[0115] The T3 tire is identical to the T0 tire except for the tread pattern which is that described previously, notably with deep incisions in the axially central portion presenting an average bridging volume rate greater than or equal to 25%.

[0116] The T4 tire is identical to the 10 tire except for the tread pattern which is that of the T0 tire, notably with deep incisions in the axially central portion and has an average bridging volume rate of less than 15%.

[0117] Various tests were carried out, the results of which are shown in Table 1 below, in which, unless otherwise stated, a value above 100 indicates an improvement in performance and a value below 100 indicates a deterioration in performance.

[0118] Several tests were carried out on snowy ground: a braking test during which a vehicle traveling at 50 km / h braked in a straight line and the distance required to reach the speed of 5 km / h with an ABS system was measured, a traction test during which the acceleration of a vehicle was measured between 10% and 60% slippage without driving assistance devices, in particular without anti-skid devices, a subjective transverse grip test taking into account the average time taken to complete three laps of a snowy circuit and the vehicle's behavior.

[0119] The average of these different tests on snowy ground was calculated under the name TEST1 in Table 1.

[0120] There is also a machine behavior test to measure the drift stiffness. In Table 1, this test is called TEST 2. The tire is rolled at a constant speed, here 80 km / h, on a suitable automatic machine (a "ground-plane" type machine marketed by the company MTS), varying the load noted "Z", under a drift angle of 1 degree, and the drift thrust was continuously measured and the drift stiffness noted "D" (corrected for the zero drift thrust) was identified, by recording the transverse force on the wheel as a function of this load Z using sensors. We then obtain, for a chosen load, in particular as a function of the tire's load index, a drift stiffness value.

[0121] A road wear test was carried out in which the distance travelled by a tyre to reach a wear level corresponding to the regulatory wear indicator is measured. In Table 1, this test is referred to as TEST 3. Table 1

[0122] Table 1 shows that the use of a radially external wearing course having a lower dynamic shear complex modulus G* than that of the T0 tire makes it possible to significantly improve the performance on snowy ground in TEST 1. However, this improvement visible on the T2, T4 and 10 tires is to the detriment of the behavior performance of the tire in TEST 2, the decrease of which is compensated by the use of a more rigid sculpture whose deep incisions of the axially central portion have a relatively high average bridging volume ratio as shown by the comparison between, on the one hand, the T2, T3, T4 tires and, on the other hand, the 10 tire according to the invention.

[0123] It should also be noted that the use of a radially internal tread layer with a relatively low glass transition temperature improves the performance on snowy ground of T1, T4 and 10 tires in TEST 4.

[0124] The invention is not limited to the embodiments previously described.

Claims

CLAIMS 1. A tire (10) comprising a tread (14) carrying a tread surface (16), the tread (14) comprising a tread layer (141) carrying at least a portion of the tread surface (16), the tread (14) comprising an axially central portion (PO) extending over an axial width (LO) equal to 80% of the axial width (L) of the tread surface (16) and axially centered on the median plane (M) of the tire, the axially central portion (PO) of the tread (14) comprising at least one deepest cutout (22, 24) of the axially central portion (PO) having a depth Hs, the axially central portion (PO) of the tread (14) comprising so-called deep incisions (40), each deep incision (40) of the axially central portion (PO) having a depth Hi such that Hi / Hs > 50%,the axially central portion (PO) of the rolling layer (141) comprising an elastomeric material (M1), characterized in that: the elastomeric material (M1) has a complex dynamic shear modulus G*_1 measured according to the ASTM D-5992-96 standard, at a temperature of 60°C and at a frequency of 10Hz under a stress equal to 0.7 MPa such that G*_1 < 1.50 MPa, the elastomeric material (M1) has a glass transition temperature Tg_1 such that Tg_1 < -23°C, and each deep incision (40) of the axially central portion (PO) extending in a general direction (Dg) on ​​the rolling surface (16), each deep incision (40) has a variable depth along the general direction (Dg) of said incision (40) so that all of the deep incisions (40) of the axially central portion (PO) has an average volumetric bridging rate greater than or equal to 25%., 2. Tire (10) according to the preceding claim, wherein the tread (14) comprising regulatory wear indicators (12) defining a theoretical regulatory wear surface (121) parallel to the tread surface (16) of the tire (10) in the new condition and passing through the most radially external point of each regulatory wear indicator (12) of the axially central portion (PO), each deep incision (40) of the axially central portion (PO) has a bottom (400) of which at least one portion is arranged radially inside the theoretical regulatory wear surface (121).

3. Tire (10) according to any one of the preceding claims, in which G*_1 < 1.30 MPa, preferably G*_1 < 1.00 MPa and more preferably G*_1 < 0.94 MPa.

4. Tire (10) according to any one of the preceding claims, in which the elastomeric material (M1) has a glass transition temperature Tg_1 such that -35°C < Tg_1 < -25°C, preferably -30°C < Tg_1 < -25°C.

5. Tire (10) according to any one of the preceding claims, in which the average bridging volume ratio is greater than or equal to 30%, preferably 35%.

6. Tire (10) according to any one of the preceding claims, in which the average bridging volume ratio is less than or equal to 50%, preferably 45%.

7. A tire (10) according to any one of the preceding claims, wherein each deep incision (40) of the axially central portion (PO) has a bottom (400) having a radial profile arranged so that at least first and second points (401, 402) of the bottom are arranged on either side of a third point (403) of the bottom in the mean direction (Di) in which said deep incision (40) extends, each first and second point (401, 402) being arranged, relative to the rolling surface (16), at a depth strictly less (Psup) than the depth (Hi) at which the third point (403) is arranged.

8. Tire (10) according to any one of the preceding claims, in which the radial bridging distance (Dr) between the maximum depth (Hi) and the minimum depth (Psup) of each deep incision (40) of the axially central portion (PO) is equal to, on average, at least 50%, preferably at least 55%, more preferably at least 60% of the maximum depth (Hi) of said incision (40).

9. Tire (10) according to any one of the preceding claims, in which each deep incision (40) of the axially central portion (PO) extends in a mean direction (Di) on the rolling surface forming, with the axial direction (Y), an angle ranging from 25° to 40°, preferably from 27° to 37°.

10. A tire (10) according to any one of the preceding claims, wherein the axially central portion (PO) comprises at least one loaf (36, 38), the or each loaf (36, 38) comprising several deep incisions (40) made in said loaf (36, 38) and extending substantially parallel to each other in a mean direction (Di) on the rolling surface (16), the mean distance, in a direction perpendicular (Dp) to the mean direction (Di), between two deep incisions (40) adjacent spaces formed in said bread (36, 38) ranges from 2.0 mm to 5.0 mm, preferably from 2.0 mm to 4.0 mm and more preferably from 2.0 mm to 3.0 mm.

11. Tire (10) according to any one of the preceding claims, in which the elastomeric material (M1) has a dynamic loss tanDMAX23 measured according to standard ASTM D-5992-96, at a temperature of 23°C and at a frequency of 10Hz, less than or equal to 0.

40.

12. Tire (10) according to any one of the preceding claims, in which the axially central portion (PO) comprises: - a radially outer rolling layer (141) carrying at least part of the rolling surface (16) and comprising the elastomeric material (M1), and - a radially inner wearing course (142) arranged at least partly radially inside the radially outer wearing course (141).

13. Tire (10) according to the preceding claim, in which the radially inner tread layer (142) comprises an inner elastomeric material (M2) having a complex dynamic shear modulus G*_2 such that G*_2 > G*1, G*_2 being measured according to standard ASTM D-5992-96, at a temperature of 60°C and at a frequency of 10Hz under a stress equal to 0.7 MPa.

14. A tire (10) according to any one of the preceding claims, wherein the tread (14) comprises first and second axially lateral portions (P1, P2) arranged axially outside the axially central portion (PO) and on either side of the axially central portion (PO) relative to the median plane (M), each first and second axially lateral portion (P1, P2) comprising incisions (44) extending in a mean direction on the tread surface (16) forming, with the axial direction (Y), an angle less than or equal to 45°, preferably less than or equal to 30° and more preferably less than or equal to 15°.

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