TIRE WITH A TREAD THAT OFFERS IMPROVED ENDURANCE PROPERTIES

Abstract

The invention relates to a tire whose tread has at least one groove on the bottom of which at least one protrusion of material is present. According to the invention, the tread is made of a first elastomeric compound, and at least a portion of the bottom of said at least one groove, surrounding the junction areas between said at least one protrusion and the bottom of said at least one groove, is made of a second elastomeric compound with a thickness of at least 1 mm, the second elastomeric compound having a tear coefficient at least 20% higher than the tear coefficient of the first elastomeric compound. Figure for the abstract: Fig 2

Description

Title of the invention: TYRE WHOSE TREAD HAS ENDURANCE PROPERTIES IMPROVED

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly a tire intended to equip vehicles carrying heavy loads and traveling at high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally speaking, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles of between 10° and 45° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcement elements, called elastic.It may also comprise a layer of low-extensibility metal wires or cables forming an angle of between 45° and 90° with the circumferential direction, this ply, called the triangulation ply, being radially located between the carcass reinforcement and the first crown ply called the working ply, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which, under the various stresses to which it is subjected, exhibits little deformation, the triangulation ply having the essential role of absorbing the transverse compression forces to which all the reinforcing elements in the area of ​​the crown of the tire are subjected.

[0003] Cables are said to be inextensible when said cables exhibit, under a tensile force equal to 10% of the breaking force, a relative elongation at most equal to 0.2%.

[0004] Cables are said to be elastic when said cables exhibit, under a tensile force equal to the breaking load, a relative elongation at least equal to 3% with a maximum tangent modulus less than 150 GPa.

[0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the range +2.5°, -2.5° around 0°.

[0006] The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the direction of tire rolling.

[0007] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

[0008] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it.

[0009] The axis of rotation of the tire is the axis around which it rotates in normal use.

[0010] A radial or meridian plane is a plane that contains the axis of rotation of the tire.

[0011] The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of tire rotation and which divides the tire into two halves.

[0012] Some current tires, called "road tires", are intended to travel at high speed and over increasingly long distances, due to the improvement of the road network and the growth of the motorway network throughout the world. All of the conditions under which such a tire is called upon to travel undoubtedly allow an increase in the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter and in particular of the crown reinforcement is penalized.

[0013] There are indeed constraints at the level of the crown reinforcement and more particularly shear constraints between the crown layers, combined with a non-negligible rise in the operating temperature at the level of the ends of the axially shortest crown layer, which result in the appearance and propagation of cracks in the rubber at the level of said ends.

[0014] In order to improve the endurance of the crown reinforcement of the type of tire studied, solutions relating to the structure and quality of the layers and / or profiles of rubber mixtures which are arranged between and / or around the ends of the plies and more particularly the ends of the axially shortest ply have already been provided.

[0015] It is known in particular to introduce a layer of rubber mixture between the ends of the working layers to create decoupling between said ends to limit shear stresses. Such decoupling layers must however have very good cohesion. Such layers of rubber mixtures are for example described in patent application WO 2004 / 076204.

[0016] The tires thus produced effectively make it possible to improve performance, particularly in terms of endurance.

[0017] Furthermore, it is known to produce tires with a very wide tread or to give tires of a given size greater load capacities to introduce a layer of circumferential reinforcing elements. Patent application WO 99 / 24269 describes, for example, the presence of such a layer of circumferential reinforcing elements.

[0018] The layer of circumferential reinforcing elements is usually constituted by at least one metal cable wound to form a turn whose laying angle relative to the circumferential direction is less than 2.5°.

[0019] In combination with this internal tire structure, it is known to provide the tread, that is to say the part of the tire intended to come into contact with the ground during rolling and to wear during rolling, with a sculpture formed of relief elements delimited by cutouts whether they are circumferential, transverse or oblique in orientation. The objective of such a sculpture is to give the tread good performance when rolling on dry roads and on water-covered roads, particularly in wet weather.

[0020] For the purposes of the invention, a cutout generically designates either a groove or an incision and corresponds to the space delimited by walls of material facing each other and spaced apart from each other by a non-zero distance (called "width of the cutout"). What differentiates an incision from a groove is precisely this distance; in the case of an incision, this distance is appropriate to allow at least partial contact of the opposite walls delimiting said incision at least when passing into contact with the roadway. In the case of a groove, the walls of this groove cannot come into contact with each other under normal driving conditions.

[0021] For the purposes of the invention, a cutout of circumferential or longitudinal orientation is a cutout whose mean plane of at least a portion of the walls of said cutout forms an angle with a longitudinal plane of less than 10°. This angle formed with a longitudinal plane may be oriented in one direction or the other relative to said longitudinal plane. A cutout of longitudinal orientation may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0022] For the purposes of the invention, a transversely oriented cutout is a cutout whose mean plane of at least a portion of the walls of said cutout forms an angle with a radial plane of less than 35°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. A transversely oriented cutout may also be a cutout which runs continuously on either side of a mean plane as just described; it may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0023] For the purposes of the invention, an obliquely oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a radial plane of between 35° and 80°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. A cutout of oblique orientation can also be a cutout which runs continuously on either side of a mean plane as just described; it can also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0024] In the case of grooves, it is usual to provide for the presence of indentations at the bottom of these grooves. Indentations are protrusions made of material whose height is less than the depth of the groove. They can have different functions. They can be provided to provide rigidity by providing support to the walls of the grooves when they undergo deformations during rolling. They can also be provided to allow the ejection of stones which obstruct the grooves during rolling.

[0025] When rolling tires thus produced subjected to constraints that are particularly stressful for the tread, in particular in terms of violent impacts for example on sidewalks, damage to the tread has appeared, resulting in particular in the tearing of blocks of rubber.

[0026] An aim of the invention is to provide tires whose tread endurance properties are improved regardless of the use, the properties in particular of wear and overall endurance of the tire being preserved for usual uses.

[0027] This object is achieved according to the invention by a tire with a radial carcass reinforcement comprising a crown reinforcement, itself radially capped with a tread, said tread being joined to two beads by means of two sidewalls, said tread comprising a tread surface intended to come into contact with a roadway and form a contact surface, said tread having a plurality of cutouts consisting of at least one groove consisting of two walls opening onto the tread surface and a surface connecting the two walls forming the bottom of said at least one groove, at least one protuberance made of material being present on the bottom of said at least one groove, the height of said protuberance being greater than 10% of the depth of said at least one groove and less than the height of said at least one groove, the width of said protuberance,measured in a direction normal to the walls of said at least one groove, being greater than or equal to 40% of the width of said at least one groove, measured in a direction normal to the walls of said at least one groove, and less than said width of said at least one groove, and said protuberance being connected to the bottom of said at least one groove by junction zones, the tread being made up of at least a first elastomeric mixture forming at least part of the rolling surface when the tire is, new, at least a portion of the bottom of said at least one groove surrounding the junction zones between said at least one protuberance and the bottom of said at least one groove being made of a second elastomeric mixture over a thickness of at least 1 mm and the second elastomeric mixture having a tear coefficient (expressed in N / m) at least 25% greater than the tear coefficient of the first elastomeric mixture, the tear coefficient being the product of the breaking force per unit of thickness (expressed in N / mm of thickness) by the elongation at break (expressed in %), measured at 100°C.

[0028] For the purposes of the invention, the depth of a groove is the radial distance measured on a new tire between the surface of the tread and the radially innermost point of said groove.

[0029] For the purposes of the invention, the height of a protuberance present on the bottom of a groove is the radial distance measured on a new tire between the radially outermost point of said protuberance and the radially innermost point of said groove.

[0030] For the purposes of the invention, the widths of the protrusions and of the grooves are measured in a direction normal to the walls of the grooves on a new tire.

[0031] The thickness of the second elastomeric mixture is measured locally in a direction normal to the surface of the wall of said at least one circumferential groove.

[0032] The breaking force per unit thickness and the elongation at break, in tearability, are measured on a specimen stretched at 500 mm / min to cause the specimen to break on a dynamometric machine for tensile tests, equipped with a system for measuring and acquiring the force and the displacement of the moving crosshead. The tensile specimen consists of a parallelepipedal rubber plate, with a thickness equal to 2.5 mm, a length equal to 145 mm and a width equal to 10 mm. Before starting the test, three very fine notches perpendicular to the length of the specimen are made using a razor blade to a depth of 3 mm, on one edge of the specimen, one in the middle and the other two on either side of the first and 6 mm apart from it. The force (expressed in N per mm of thickness of the specimen) to be exerted to obtain rupture is determined and the elongation at rupture is measured (expressed in %).The test was conducted in air at a temperature of 100°C. High values ​​indicate good cohesion of the rubber composition although there are signs of cracking.

[0033] According to a first embodiment of the invention, said at least one groove is a longitudinally oriented groove.

[0034] According to a second embodiment of the invention, said at least one groove is a transversely oriented groove.

[0035] According to a third embodiment of the invention, said at least one groove is a groove of oblique orientation.

[0036] The tires thus produced according to the invention effectively allow driving in particularly demanding conditions without seeing any tearing on the tread appearing in comparison with tires of more usual design.

[0037] The inventors believe they have demonstrated that when driving in conditions that are particularly stressful for the tread with tires of conventional design, the tears that occur on the tread seem to begin at the junction zones between a protuberance and the bottom of a groove. The inventors believe they interpret this phenomenon because of these junction zones which are conducive to the appearance of longitudinal breaks during violent impacts. During driving, the tire having suffered attacks on the tread such as impacts, these breaks lead to the tearing of a part of the tread.

[0038] The presence of a mixture in accordance with the invention at least locally in the zone sensitive to the appearance of breaks makes it possible to limit or at least delay the appearance of breaks and therefore reduces the risks of tearing off part of the tread whatever the driving conditions.

[0039] According to a preferred embodiment of the invention, the entire bottom and walls of said at least one groove are made of the second elastomeric mixture over a thickness of at least 1 mm so that the second mixture forms the complete surface of said at least one groove.

[0040] This preferred embodiment of the invention simplifies the production of the tire according to the invention, the second mixture being positioned before molding according to the knowledge of a person skilled in the art to obtain the tire according to the invention after curing and molding of the tread forming the sculpture.

[0041] According to a preferred embodiment of the invention, the thickness of the second elastomeric mixture is less than 5 mm, without taking into account the volume of the protuberance which may be made up of this second mixture. The volume of the second mixture thus remains limited in comparison with the volume of the first mixture which thus contributes mainly to the desired properties of the tread such as grip and wear.

[0042] According to an alternative embodiment of the invention, said at least one protuberance present in said at least one groove is continuous over the length of said groove. In the case of a circumferential groove, said protuberance is continuous over the circumference of the tire.

[0043] According to another variant embodiment of the tire, said at least one pro tuber present in said at least one groove is discontinuous along the length of said groove. According to this embodiment variant, the protrusion advantageously creates a pattern which is repeated along the length of the groove to ensure its function along the length of the groove.

[0044] According to a preferred embodiment of the invention, the second elastomeric mixture has a tear coefficient at least 50% higher and preferably still at least 100% higher than the tear coefficient of the first elastomeric mixture.

[0045] According to an advantageous variant of the invention, the first elastomeric mixture has a maximum value of tan(ô), noted tan(ô)max, less than 0.25.

[0046] The loss factor tan(ô) is a dynamic property of the rubber compound layer. It is measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 2 mm thick and 78 mm2 in cross-section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 60°C. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 1% (return cycle). For the return cycle, the maximum value of tan(ô) observed, noted tan(ô)max, is indicated.

[0047] In the case where the thickness of the material is between 1 and 2 mm, the loss factor tan(ô) is measured according to the same method and under the same conditions, as described previously, on a sample of vulcanized composition which is in the form of a cylindrical test piece 1 mm thick and 78 mm2 in cross-section. Rolling resistance is the resistance that appears when the tire rolls. It is represented by the hysteretic losses linked to the deformation of the tire during a revolution. The frequency values ​​linked to the revolution of the tire correspond to values ​​of tan(ô) measured between 30 and 100°C. The value of tan(ô) at 60°C thus corresponds to an indicator of the rolling resistance of the tire while rolling.

[0049] Furthermore, the tests carried out have shown that the rolling resistance properties are preserved or even improved by the choice of the second elastomeric mixture, the latter being able to have better rolling resistance performances than the first elastomeric mixture.

[0050] Advantageously according to the invention, the first elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising a copolymer based on styrene and butadiene and at least one reinforcing filler.

[0051] By “elastomer matrix” or “elastomeric matrix” is meant all of the elastomer(s) present in the rubber composition.

[0052] By “diene” elastomer (or indistinctly rubber), whether natural or synthetic, must be understood an elastomer consisting at least in part (i.e. a homopolymer or a copolymer) of diene monomer(s) (i.e., bearing(s) two carbon-carbon double bonds, conjugated or not).

[0053] By copolymer based on styrene and butadiene is meant here a copolymer of at least one styrene monomer and at least one butadiene monomer (and of course also any mixture of such copolymers); in other words, said copolymer based on styrene and butadiene comprises by definition at least styrene units (derived from the styrene monomer) and butadiene units (derived from the butadiene monomer).

[0054] Advantageously according to the invention, the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising, predominantly, natural rubber for at least 80% and at least one reinforcing filler.

[0055] According to a preferred embodiment of the invention, the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising 100% natural rubber.

[0056] The rubber compositions according to the invention of the first mixture or of the second mixture may comprise one or more reinforcing fillers.

[0057] Any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition which can be used in particular for the manufacture of tires, can be used, for example an organic filler such as carbon black, an inorganic filler such as silica or even a mixture of these two types of fillers.

[0058] Suitable carbon blacks are all carbon blacks, in particular the blacks conventionally used in tires or their treads. Among the latter, mention will be made more particularly of the reinforcing carbon blacks of the 100, 200, 300 series, or the blacks of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as for example blacks NI 15, N134, N234, N326, N330, N339, N347, N375, N550, N683, N772).

[0059] By "reinforcing inorganic filler" is meant here any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called "white" filler, "light" filler or even filler "non-black" ("non-black filler") as opposed to carbon black; this inorganic filler being capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcing function, a conventional pneumatic grade carbon black. Such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (OH) on its surface, requiring to be used as a reinforcing filler the use of a coupling agent or system intended to ensure a stable chemical bond between the filler and the elastomeric matrix.

[0060] Suitable inorganic reinforcing fillers include siliceous mineral fillers, preferably silica (SiO2). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both less than 450 m2 / g, preferably from 30 to 400 m2 / g, in particular between 60 and 300 m2 / g.

[0061] Of course, the term inorganic reinforcing filler also means mixtures of different reinforcing inorganic fillers, in particular highly dispersible silicas as described above or a mixture of inorganic fillers of the siliceous type and non-siliceous inorganic fillers. As non-siliceous inorganic fillers, mention may be made of mineral fillers of the aluminous type, in particular alumina (A12O3) or aluminum (oxide)hydroxides, or even reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087. The non-siliceous inorganic fillers, when present, are in the minority in the reinforcing filler.

[0062] The physical state in which the inorganic reinforcing filler is present is indifferent, whether in the form of powder, microbeads, granules, or even beads.

[0063] Those skilled in the art will understand that, as a filler equivalent to the reinforcing inorganic filler described in this paragraph, a reinforcing filler of another nature, in particular organic such as carbon black, could be used, provided that this reinforcing filler is covered with an inorganic layer such as silica, or else comprises functional sites on its surface, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. By way of example, mention may be made, for example, of carbon blacks for tires as described, for example, in patent documents WO 96 / 37547, WO 99 / 28380.

[0064] According to a variant of the invention, the reinforcing filler of the first mixture and / or of the second mixture is predominantly carbon black, that is to say that it comprises more than 50% (>50%) by weight of carbon black relative to the total weight of reinforcing filler. Optionally according to this variant, the reinforcing filler may also comprise silica or another reinforcing inorganic filler.

[0065] According to another variant of the invention, the reinforcing filler of the first mixture and / or of the second mixture consists of carbon black.

[0066] According to another variant of the invention, the reinforcing filler of the first mixture and / or the second mixture is predominantly an inorganic reinforcing filler (preferably silica), i.e. it comprises more than 50% (>50%) by weight of an inorganic reinforcing filler such as silica relative to the total weight of the reinforcing filler. Optionally, according to this variant, the reinforcing filler also comprises carbon black. According to this option, the carbon black is used at a rate less than or equal to 20 phr, more preferably less than or equal to 10 phr (for example, the carbon black rate may be in a range from 0.5 to 20 phr, in particular from 1 to 10 phr). In the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon blacks are benefited from, without otherwise penalizing the typical performances provided by the reinforcing inorganic filler.

[0067] The elastomeric compositions of the tread of the tire according to the invention may optionally also comprise all or part of the usual additives, known to those skilled in the art and usually used in treads, such as for example processing aids, fillers (reinforcing or non-reinforcing, other than those mentioned above), pigments, protective agents such as antiozone waxes, chemical antiozonants (6PPD, TMQ), antioxidants, anti-fatigue agents and reinforcing resins (such as those described for example in application WO 02 / 10269).

[0068] According to an alternative embodiment of the invention, the crown reinforcement of the tire is formed from at least two working crown layers of reinforcing elements.

[0069] According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

[0070] The metallic elements are preferably steel cables.

[0071] Advantageously according to the invention, the reinforcing elements of the working crown layers of the crown reinforcement are crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction.

[0072] Advantageously still according to the invention, the working crown reinforcement comprises a layer of circumferential reinforcing elements, preferably arranged radially between two working crown layers.

[0073] According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

[0074] A preferred embodiment of the invention further provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0075] According to any one of the embodiments of the invention mentioned above, the crown reinforcement can also be completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic reinforcing elements made of steel making, with the circumferential direction, an angle greater than 45° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0076] Other advantageous details and characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to Figures 1 and 2 which represent: - [Fig.l], a meridian view of a diagram of a tire according to the invention, - [Fig.2], a radial sectional view of a groove of a tire according to the invention.

[0077] The figures are not shown to scale to simplify understanding.

[0078] In [Fig.l], the tire 1, of dimension 315 / 70 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3 by turning around rods 4. The carcass reinforcement is formed of a single layer of metal cables. This carcass reinforcement 2 is hooped by a crown reinforcement 5, formed radially from the inside to the outside: - a first working layer formed of non-fretted 9.35 inextensible metal cables, continuous over the entire width of the sheet, oriented at an angle equal to 22°, - a layer of circumferential reinforcing elements formed of 21x23 steel metal cables, - a second working layer formed of non-fretted 9.35 inextensible metal cables, continuous over the entire width of the sheet, oriented at an angle equal to 18° and crossed with the metal cables of the first working layer, - a protective layer formed from elastic metal cables 6.35.

[0079] All of these layers forming the crown reinforcement 5 are not shown in the figures.

[0080] The crown reinforcement is itself capped with a tread having a surface 6 intended to come into contact with the ground. The surface 6 of the tread is formed of four circumferential grooves 7 forming circumferential ribs or ribs 8 constituting the tread. At the bottom of the circumferential grooves 7 are shown indentations 9. These indentations 9 are continuous around the wheel. They could also according to other embodiments be discontinuous; they could also not be present in all the grooves.

[0081] In [Fig.2], a circumferential groove 7 is schematically represented in cut along a radial plane, this showing a step 9 made of material on the bottom of said groove 7.

[0082] The circumferential groove 7 has a depth d7 equal to 14.5 mm. The indent 9 has a height d9 equal to 11.5 mm. The indent 9 thus has a height d9 equal to 79% of the depth d7 of the circumferential groove 7 and therefore greater than 10%. The circumferential groove 7 has a width d7 equal to 15.2 mm. The indent 9 has a width d9 equal to 8.7 mm. The indent 9 thus has a width d9 equal to 57% of the width d7 of the circumferential groove 7 and therefore greater than 40%.

[0083] The tread is mainly made up of a first mixture. In [Fig.2], a thickness E of a second mixture forming the wall 10 of the circumferential groove 7 is also shown.

[0084] The average thickness E of the second mixture is equal to 2 mm. This thickness E is measured in the direction normal to the inner surface of the circumferential groove 7.

[0085] Tests are carried out with tires according to the invention.

[0086] The same tests are carried out with reference tires. The reference tires differ from the tires according to the invention by the absence of the second mixture, that is to say that the tread is entirely made up of the first mixture.

[0087] The different mixtures used for the treads are listed below: Piesuser Mixture Second- Mixture NR (0 8$ W BR Q) 20 SB£(3) 2G (4) Nos Ni 15 (5) 4? Faraæsîsi® * 1 Anfeesydast (6P?Es) (7) ■s L5 Acæ&steœ' CSS (S) 1.1 0.7 CT?® Stearic acid (10) U ? 5 Oxysfe cæ zIkc (î 4 S oufte sïhîùl e 11 £ (1) Natural rubber (2) 98% neodymium polybutadiene of 1,4-cis unit; Tg=-108°C (3) Anionic styrene-butadiene copolymer containing 15% by weight of styrene unit and 24% vinyl of the butadiene part (Tg -65°C) (4) Carbon black grade N 134 according to ASTM D-1765 -2017 (5) Carbon black grade NI 15 according to ASTM D-1765 -2017 (6) SER 6266 from SER (7) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine “Santoflex 6PPD” from Flexys (8) N-cyclohexyl-2-benzothiazol-sulfenamide “Santocure CBS” from Flexsys (9) N-cyclohexylthio-phthalimide (CTP / PV1) marketed by Shandong Derek New Materials Co. (10) Stearic acid “Pristerene 4931” from Uniqema (11) Industrial grade Zinc Oxide from Umicore

[0088] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0089] The measured properties are expressed in the following table for each of the mixtures: First Mixture Second Mixture berce to rapterè cl 388 w AUcagesnaÈ to rupture f •:18ÿ Coefficient of 822 aïs

[0090] Initial endurance tests were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 4000 kg, gradually increased to reduce the duration of the test.

[0091] Other endurance tests were carried out on a test machine cyclically imposing a transverse force and a dynamic overload on the tires. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

[0092] The tests thus carried out have shown that the distances covered during each of these tests are at least as great or even greater for the tires according to the invention than the reference tires.

[0093] A final test aimed at reproducing sidewalk impacts that could be suffered by the tires was carried out.

[0094] This test consists of a preliminary step of driving for an hour and a half at 120 km / h, the tires being subjected to a load of 4000 kg.

[0095] The vehicle then follows a trajectory causing the tires to pass over a sidewalk with a height of between 15 cm and 20 cm.

[0096] The tires are made to follow three different trajectories in succession in order to have more or less pronounced overlaps of a few centimeters of the tire tread on the pavement at a speed of 10 km / h. These three successive trajectories are reproduced four times in order to thus make twelve passes on the pavement.

[0097] The entire test is repeated so that each tire undergoes it twice.

[0098] At the end of these tests, the tires are checked by shearography and corticated to analyze possible damage. This is a visual analysis to compare possible cracks and their propagation. The tires are rated and compared with each other. A score above 100 corresponds to a less damaged tire. A value of 100 is assigned to the reference tire that is the most damaged. Reference tire Invention tire Note WG Greater than 13Û

[0099] At the end of the rolling, the tires according to the invention show less extensive damage than the reference tires.

[0100] Furthermore, rolling resistance measurements were carried out.

[0101] The test results are presented in the following table. Rolling resistance measurements are expressed in kg / t, with a value of 100 being assigned to the reference tire. Values ​​above 100 show better rolling resistance performance. Tire reference Tire Invention Rolling resistance 100 101

[0102] It emerges from these tests that the tires according to the invention make it possible to maintain, or even slightly improve, the performance in terms of rolling resistance compared to the reference tire.

Claims

1.

2.

3. Claims A pneumatic tire with a radial carcass reinforcement comprising a crown reinforcement, itself radially capped with a tread, said tread being joined to two beads by means of two sidewalls, said tread comprising a tread surface intended to come into contact with a roadway and form a contact surface, said tread having a plurality of cutouts consisting of at least one groove consisting of two walls opening onto the tread surface and a surface connecting the two walls forming the bottom of said at least one groove, at least one protuberance made of material being present on the bottom of said at least one groove, the height of said protuberance being greater than 10% of the depth of said at least one groove and less than the height of said at least one groove, the width of said protuberance,measured in a direction normal to the walls of said at least one groove, being greater than or equal to 40% of the width of said at least one groove, measured in a direction normal to the walls of said at least one groove, and less than said width of said at least one groove, and said protuberance being connected to the bottom of said at least one groove by junction zones, characterized in that the tread is made up of at least a first elastomeric mixture forming at least part of the rolling surface when the tire is new,in that at least a portion of the bottom of said at least one groove surrounding the junction zones between said at least one protuberance and the bottom of said at least one groove is made of a second elastomeric mixture over a thickness of at least 1 mm and in that the second elastomeric mixture has a tear coefficient (expressed in N / m) at least 25% greater than the tear coefficient of the first elastomeric mixture, the tear coefficient being the product of the breaking force per unit of thickness (expressed in N / mm of thickness) by the elongation at break (expressed in %), measured at 100°C., Tire according to claim 1, characterized in that said at least one groove is a longitudinally oriented groove. Tire according to claim 1, characterized in that said at least one groove is a transversely oriented groove.

4. A tire according to claim 1, characterized in that said at least one groove is an obliquely oriented groove.

5. Tire according to one of claims 1 to 4, characterized in that the entire bottom and walls of said at least one groove are made of the second elastomeric mixture over a thickness of at least 1 mm.

6. Tire according to one of claims 1 to 5, characterized in that the thickness of the second elastomeric mixture is less than 5 mm.

7. A tire according to one of the preceding claims, characterized in that said at least one protuberance present in said at least one groove is continuous along the length of said groove.

8. Tire according to one of claims 1 to 6, characterized in that said at least one protuberance present in said at least one groove is discontinuous along the length of said groove.

9. Tire according to one of the preceding claims, characterized in that the second elastomeric mixture has a tear coefficient at least 50% higher than the tear coefficient of the first elastomeric mixture.

10. Tire according to one of the preceding claims, characterized in that the first elastomeric mixture has a maximum value of tan(ô), noted tan(ô)max, less than 0.

25.

11. Tire according to one of the preceding claims, characterized in that the first elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising a copolymer based on styrene and butadiene and at least one reinforcing filler.

12. Tire according to one of the preceding claims, characterized in that the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising, as a majority, natural rubber for at least 80% and at least one reinforcing filler.

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