Tire with improved endurance performance

Abstract

The invention relates to a tire (1) with a radial carcass reinforcement, two working crown layers (41, 42). According to the invention, the rubber mixture constituting said layer C comprises a composition comprising 50 to 70 pce of reinforcing fillers, including at least 20 pce of pyrolysis carbon black. Figure for the abstract: Fig 1

Description

Title of the invention: Tire with improved endurance performance

[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 tangent to the periphery of the tire and defined by the rolling direction of the tire.

[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 tire's axis of rotation.

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

[0012] The term “modulus of elasticity” of a rubber mixture means a secant modulus of extension at 10% elongation and at room temperature.

[0013] With regard to rubber compositions, the secant modulus of elasticity at 10% elongation is the elastic modulus of the mixture measured during a uniaxial tensile experiment, at an elongation value of 0.1 (i.e. 10% elongation, expressed as a percentage). A constant uniaxial tensile speed is imposed on the test piece, and its elongation and stress are measured. The measurement is carried out using an INSTRON type tensile machine, at a temperature of 23°C, and a relative humidity of 50% (ISO 23529 standard). The conditions for measuring and using the results to determine the elongation and stress are as described in standard NF ISO 37: 2012-03. The stress is determined for an elongation of 0.1 and the secant modulus of elasticity is calculated at 10% elongation by dividing this stress value by the elongation value.The person skilled in the art will know how to choose and adapt the dimensions of the test piece according to the quantity of mixture accessible and available, particularly in the case of taking samples from a finished product such as a tire.

[0014] 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 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] Patent FR 1 389 428, to improve the resistance to degradation of rubber compounds located in the vicinity of the crown reinforcement edges, recommends the use, in combination with a low hysteresis tread, of a rubber profile covering at least the sides and marginal edges of the crown reinforcement and consisting of a low hysteresis rubber compound.

[0019] Patent FR 2 222 232, to avoid separations between crown reinforcement plies, teaches coating the ends of the reinforcement in a rubber mattress, the Shore A hardness of which is different from that of the tread surmounting said reinforcement, and greater than the Shore A hardness of the rubber mixture profile arranged between the edges of the crown reinforcement plies and the carcass reinforcement.

[0020] The tires thus produced effectively make it possible to improve performance, particularly in terms of endurance.

[0021] Furthermore, the use of tires on heavy goods vehicles of the "site approach" type leads to the tires being subjected to shocks when driving on stony ground. These shocks are of course detrimental to performance in terms of endurance.

[0022] It is also known to those skilled in the art to increase the number of plies constituting the crown reinforcement to improve the endurance of the tire with regard to such impacts.

[0023] The presence of one or more layers of additional reinforcing elements leads to a greater mass of the tire and to higher tire manufacturing costs.

[0024] The inventors have in particular demonstrated that when driving on surfaces that are extremely demanding for tires, the endurance performance of such tires could be degraded, for example in driving conditions combining the speed of the vehicle, the load carried by the tire and the nature of the ground, which is particularly aggressive, in particular at the shoulders of the tire. It is indeed possible to observe a degradation of performance in terms of endurance, for example when driving at relatively high speed on construction site approach type surfaces which are very aggressive for the tire.

[0025] The inventors have thus set themselves the mission of providing tires for "Heavy Goods" vehicles, for example of the "construction site approach" type, whose endurance performance with regard to impacts suffered on the tread is improved whatever the nature of the ground and the driving conditions.

[0026] This object is achieved according to the invention by a tire comprising a radial carcass reinforcement, said tire comprising a crown reinforcement comprising two working crown layers, each formed of reinforcing elements inserted between two calendering layers of rubber mixture crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction, said angles being oriented on either side of the circumferential direction, a layer C of rubber mixture being arranged between at least the ends of said at least two working crown layers, the crown reinforcement being capped radially with a tread, said tread being joined to two beads by means of two sidewalls, the rubber mixture constituting said layer C comprising a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0027] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant the part, by mass per hundred parts by mass of elastomer or rubber, the two terms being synonymous.

[0028] In certain embodiments, the composition comprises from 50 to 70 phr of reinforcing fillers, the reinforcing fillers being pyrolysis carbon black. It must then be understood that the composition comprises pyrolysis carbon black as the only reinforcing fillers (the composition therefore does not comprise inorganic reinforcing fillers and other organic reinforcing fillers).

[0029] The reinforcing fillers may be as described below.

[0030] For the purposes of the present invention, the term "pyrolysis carbon black" means a carbon black resulting from a process for pyrolyzing a material comprising at least one carbon polymer and a carbon black, hereinafter the material to be pyrolyzed, for example in the context of recycling such a material. The physical state in which the material to be pyrolyzed is present is indifferent, whether in the form of powder, granules, strips, or any other form, in the crosslinked or non-crosslinked state.

[0031] Preferably, the material to be pyrolyzed can be recovered from manufactured articles or products generated during their manufacture / production (such as by-products or offcuts); these manufactured articles can be chosen from the group consisting of tires, solid tires, industrial conveyor belts, transmission belts, rubber seals, carbon pipes outcushion, shoe soles and windshield wipers. More preferably still, the pyrolysis carbon black usable in the context of the present invention is a carbon black obtained from a pyrolysis process in which the material to be pyrolyzed comes from manufactured articles chosen from the group consisting of tires and solid tires.

[0032] Pyrolysis in the context of the present invention means any type of thermal decomposition in the absence of oxygen and the raw material of which is the material to be pyrolyzed as defined above. Pyrolysis carbon blacks are therefore distinguished from so-called industrial and / or ASTM grade carbon blacks in that the carbon raw material used for pyrolysis is a material comprising at least one carbon polymer and a carbon black and not materials derived from petroleum fractions or from coal or from oils of natural origin.

[0033] The pyrolysis carbon blacks which can be used in the context of the present invention are distinguished from known carbon blacks such as industrial carbon blacks, in particular so-called “fumac” carbon blacks, in particular by a higher ash content.

[0034] Preferably, the pyrolysis carbon black usable in the context of the present invention has an ash content ranging from 5 to 30% by weight, more preferably less than 25% by weight, more preferably less than 22% by weight, relative to the total weight of the pyrolysis carbon black.

[0035] Preferably, the pyrolysis carbon black usable in the context of the present invention has a sulfur content greater than 2% by weight, preferably ranging from 2.5 to 5% by weight, relative to the total weight of the pyrolysis carbon black.

[0036] Preferably, the pyrolysis carbon black usable in the context of the present invention has a zinc content greater than or equal to 2% by weight, preferably ranging from 2.5 to 8% by weight, relative to the total weight of the pyrolysis carbon black.

[0037] Preferably, the pyrolysis carbon black usable in the context of the present invention has a specific surface area STSA measured according to the ASTM D 6556-2021 standard within a range from 20 to 200 m2 / g, more preferably from 30 to 90 m2 / g.

[0038] Preferably, the pyrolysis carbon black usable in the context of the present invention has a void volume measured according to standard ASTM D7854 (2018) and at a pressure of 50 MPa within a range from 30 to 60 ml / 100g, more preferably from 35 to 55 ml / 100g.

[0039] The ash content is determined by calcination in platinum capsules in a muffle furnace at 825°C according to the following protocol. A capsule is previously identified before each series of measurements and is tared to the nearest 0.1 mg and the mass is noted PO. 5 g of pyrolysis carbon black sample are placed in the capsule and weighed precisely to within 0.1 mg; this mass is noted PI. The capsule and its contents are pre-calcined using a Bunsen burner until fumes appear and the product ignites. Once the product has completely burned, the capsule and its contents are placed in a muffle furnace heated to 825 °C for 1 h. After 1 h, the capsule is removed from the furnace and immediately placed in a desiccator at room temperature. When the capsule and the ash have returned to room temperature, the capsule is weighed again to obtain the mass P2. Finally, it is possible to obtain the ash content (% ash) using the formula below: P2 - PO % ash ~------x 100 PI -Pü

[0040] The zinc content in the pyrolysis carbon black is determined after calcination of the sample, then recovery of the ash in an acid medium and determination by ICP-AES (inductively coupled plasma atomic emission spectroscopy). The ash is obtained by carrying out the above protocol. Approximately 100 mg of ash (test sample) is taken and placed in a PFA (perfluoroalkoxy) tube for a HotBlock hot plate. 8 mL of 37% concentrated hydrochloric acid, 3 mL of 65% concentrated nitric acid and 0.5 mL of 40% hydrofluoric acid are then added. The tube is closed with its cap and heated at 130°C for 2 hours. After cooling, the contents are then transferred using ultrapure water into a 100 mL PTFE (polytetrafluoroethylene) volumetric flask already containing 2 g of boric acid (to neutralize the hydrofluoric acid). The volume is topped up with ultrapure water to the mark.The solution obtained is diluted by 100, by taking 1 mL in a 100 mL PFTE flask, previously containing 8 mL of 37% concentrated hydrochloric acid, 3 mL of 65% concentrated nitric acid, 0.5 mL of 40% hydrofluoric acid and 2 g of boric acid. This diluted solution is then filtered through a 0.45 pm GHP syringe filter before being analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Before analyzing the diluted solution, at least 5 standards are analyzed by ICP-AES at zinc concentrations of 0, 0.5, 1, 2 and 5 mg / L. These standards were prepared in 100 mL volumetric flasks, by diluting a certified commercial solution to a zinc concentration of 1 g / L.

[0041] These volumetric flasks contain in advance 8 mL of 37% concentrated hydrochloric acid, 3 mL of 65% concentrated nitric acid, 0.5 mL of 40% hydrofluoric acid and 2 g of boric acid. The standard solutions are analyzed by ICP-AES at a wavelength of XZn = 202.613 nm. For each standard concentration (c), the intensity of the zinc signal IZn is plotted on a graph IZn = f(c), which corresponds to the calibration line (of type y = ax + b). The sample solution (diluted solution) of The unknown concentration is then measured under the same conditions as the standards. The measured intensity is related to the concentration using the calibration line obtained previously. The concentration [c]ash in % by mass is thus obtained directly from the software, since the test sample and volume have been previously recorded. The zinc concentration in the pyrolysis black [c]black in % by mass is obtained using the following equation: [Close-up ~ Hosncires * 100 *% ash

[0042] The determination of the sulfur content in pyrolysis carbon blacks is carried out by LECO furnace. LECO sulfur analyzers are designed to measure, in particular, the sulfur content in organic and / or inorganic materials by combustion and non-dispersive infrared detection. Before carrying out the measurement of the sulfur content on the sample, cleaning of the nacelles and calibration of the furnace are carried out. The nacelles for LECO furnace are previously cleaned: this involves analyzing the empty nacelle, under the same conditions as the samples. The preparation of the calibration curve is done from a commercial standard called "BBOT" whose purity is greater than 99.99% and whose carbon (C), hydrogen (H), nitrogen (N), oxygen (O) and sulfur (S) content is guaranteed. This content is as follows: C%: 72.52; H% 6.09; N% 6.51; 0% 7.43 and S% 7.44. Approximately 10 ± 3, 20 ± 3 and 40 ± 3 mg of BBOT are weighed in a basket.The standard / boat assembly is introduced into the combustion furnace, regulated at 1350 C under pure oxygen. The combination of the furnace temperature and the analysis flow rate causes the combustion of the sample and the release of sulfur and / or carbon in the form of SO2(g). After a time of 20 s, oxygen begins to flow through the "lance" to accelerate the combustion of difficult-to-burn materials. The sulfur and / or carbon, in the form of SO2(g), are carried by an oxygen flow through the infrared detection cells. The instrument software plots a straight line connecting the mass of standard introduced and the observed response (area) on the detector. This gives a calibration straight line. After carefully cleaning the sampling equipment, approximately 80 + 5 mg of pyrolysis carbon black are weighed exactly and introduced into a LECO furnace boat.

[0043] The area of ​​the observed SO2 peak is related to the concentration using the calibration line. The instrument software then calculates the mass % of sulfur in the sample using the mass of the sample introduced into the basket.

[0044] Pyrolysis carbon blacks are marketed, for example, by the company BlackBear under the reference “BBCT30” or by the company Scandinavian Enviro Systems under the reference “P550”.

[0045] The angles of the working crown layers, expressed in degrees, are measured on a section of the tire. According to the invention, the angle measurements are taken at the circumferential median plane. These measurements can also be taken by radiography.

[0046] The layer C of rubber mixture makes it possible to obtain a decoupling of said working crown layers in order to distribute the shear stresses over a greater thickness.

[0047] For the purposes of the invention, working crown layers are said to be coupled if the respective reinforcing elements of each of the layers are separated radially by a distance less than the average diameter of the circle circumscribed by the reinforcing elements, said rubber thickness being measured radially between the respectively radially upper and lower generatrices of said reinforcing elements.

[0048] The average diameter of the circle circumscribed by the reinforcing elements is defined as being the average diameter of the circles circumscribed by the reinforcing elements of each of the working crown layers.

[0049] According to a preferred embodiment of the invention, the layer C of rubber mixture is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used.

[0050] Among the diene elastomers that can be used in blending with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, mention may be made of a polybutadiene (BR) preferably with a majority of cis-1,4 chains, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers may be elastomers modified during polymerization or after polymerization by means of branching agents such as divinylbenzene or star-forming agents such as carbonates, halotins, halosilicones or even by means of functionalization agents leading to grafting onto the chain or at the end of the chain of oxygenated carbonyl, carboxyl functions or even an amine function such as for example by the action of dimethyl or diethylamino benzophenone.In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains with one or more of the diene elastomers mentioned above, the natural rubber or synthetic polyisoprene is preferably used at a majority rate and more preferably at a rate greater than 70 pce.

[0051] Also preferably, the layer C of rubber mixture, in addition to the black of pyrolysis carbon, comprises a reinforcing filler consisting of: a - either carbon black used at a rate of between 20 and 50 phr, and preferably between 30 and 40 phr, b - or a white filler of silica and / or alumina type comprising SiOH and / or A10H surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m2 / g used at a rate of between 20 and 50 phr, and preferably between 30 and 40 phr, c - or a blend of carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 20 and 50 phr, and preferably between 30 and 40 phr.

[0052] The BET specific surface measurement is carried out according to the method of BRUNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938, corresponding to the NFT 45007 standard of November 1987.

[0053] In the case of using a clear filler or white filler, it is necessary to use a coupling and / or covering agent chosen from agents known to those skilled in the art. Examples of preferred coupling agents that may be mentioned are sulfurized alkoxysilanes of the bis-(3-trialkoxysilylpropyl) polysulfide type, and among these, in particular bis-(3-triethoxysilylpropyl) tetrasulfide marketed by the company DEGUSSA under the names Si69 for the pure liquid product and X50S for the solid product (50 / 50 blend by weight with black N330). Examples of covering agents include a fatty alcohol, an alkylalkoxysilane such as a hexadecyltrimethoxy or triethoxysilane respectively marketed by the DEGUSSA Company under the names Sill6 and Si216, diphenylguanidine, a polyethylene glycol, a silicone oil possibly modified by means of OH or alkoxy functions.The covering and / or coupling agent is used in a weight ratio relative to the filler of > 1 / 100 and < 20 / 100, and preferably between 2 / 100 and 15 / 100 when the light filler represents the entire reinforcing filler and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and light filler.

[0054] As other examples of reinforcing fillers having the morphology and the SiOH and / or A1OH surface functions of the silica and / or alumina type materials previously described and which can be used according to the invention as a partial or total replacement for these, mention may be made of carbon blacks modified either during the synthesis by addition to the furnace feed oil of a silicon and / or aluminum compound or after the synthesis by adding, to an aqueous suspension of carbon black carbon in a solution of sodium silicate and / or aluminate, an acid so as to at least partially cover the surface of the carbon black with SiOH and / or A1OH functions. As non-limiting examples of this type of carbon fillers with SiOH and / or A1OH functions on the surface, mention may be made of the CSDP type fillers described in Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, California, May 6-9, 1997 as well as those of patent application EP-A-0 799 854.

[0055] When a clear filler is used as the sole reinforcing filler, the hysteresis and cohesion properties are obtained by using a precipitated or pyrogenic silica, or a precipitated alumina or an aluminosilicate with a BET specific surface area of ​​between 30 and 260 m2 / g. As non-limiting examples of this type of filler, mention may be made of silicas KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HLSIL 2000 from PPG, etc.

[0056] The results obtained with tires in accordance with the invention have effectively demonstrated that the performance in terms of endurance can be improved, whatever the nature of the ground and the driving conditions. The endurance properties of the crown of the tire, in particular with regard to impacts appearing on the edge of the tread, in particular at the shoulders of the tire, are improved whatever the nature of the ground and the driving conditions.

[0057] The inventors believe that these results can be interpreted by the presence of pyrolysis black used as a filler within layer C. The inventors have been able to demonstrate that the presence of pyrolysis black in the rubber mixture constituting layer C gives it higher elongation at break values ​​than with more usual mixtures. Usually, during impacts comparable to those observed when driving on stony ground, more specifically impacting the shoulders of the tire, the rupture of reinforcing elements, if it occurs, is observed on the radially innermost layer and more specifically at its ends. These findings seem to indicate that in the face of this type of attack, the presence of pyrolysis black in the rubber mixture constituting layer C makes it possible to improve the endurance performance of the tire.

[0058] Preferably, the thickness of the layer C of rubber mixture, measured at the end of the narrowest working crown layer of the two working crown layers considered, will preferably be between 30% and 80% of the overall thickness of rubber mixture between cable generatrices respectively of the two working crown layers: a thickness of less than 30% not allowing conclusive results to be obtained, and a thickness of more than 80% being useless with regard to the improvement in the resistance to separation between layers and de- advantageous from a cost point of view.

[0059] More preferably, the axial width D of the layer of rubber mixture C between the axially innermost end of said layer of rubber mixture C and the axially narrowest end of the working crown layer is such that: 3.02 < D < 25.02 with 02, diameter of the reinforcing elements of the axially narrowest working crown layer. Such a relationship defines an engagement zone between the rubber compound layer C and the axially narrowest working crown layer. Such an engagement below a value equal to three times the diameter of the reinforcing elements of the axially narrowest working layer may not be sufficient to obtain decoupling of the working crown layers, in particular to obtain attenuation of the stresses at the end of the axially narrowest working crown layer. A value of this engagement greater than twenty times the diameter of the reinforcing elements of the axially narrowest working layer may lead to too great a reduction in the drift stiffness of the tire crown reinforcement.

[0060] Preferably, the axial width D of the rubber mixture layer C between the axially innermost end of said rubber mixture layer C and the axially narrowest end of the working crown layer is greater than 5 mm.

[0061] The invention also preferably provides that the thickness of the layer of rubber mixture C, at the axially outer end of the axially narrower working crown layer, has a thickness such that the radial distance d between the two working crown layers, separated by the layer of rubber mixture C, satisfies the relationship: 3 / 5.02 < d < 5.02 with 02, diameter of the axially narrowest working crown ply reinforcement elements.

[0062] The distance d is measured from cable to cable, that is to say between the cable of a first working layer and the cable of a second working layer. In other words, this distance d encompasses the thickness of the rubber mixture layer C and the respective thicknesses of the calendering rubber mixtures, radially outside the cables of the radially inner working layer and radially inside the cables of the radially outer working layer.

[0063] The various thickness measurements are carried out on a meridian section of a tire, the tire therefore being in an uninflated state.

[0064] According to an advantageous embodiment of the invention, the top layer of axially widest work is radially inside the other working crown layers.

[0065] According to an alternative embodiment of the invention, at least one calendering layer of at least one working crown layer is made up of a rubber mixture comprising a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0066] According to a preferred embodiment of this variant of the invention, the rubber mixture of the calendering layers of said two working crown layers comprises a composition comprising 50 to 70 phr of reinforcing fillers, including at least 20 phr of pyrolysis carbon black.

[0067] The inventors thus note that the rubber mixtures based on pyrolysis black from the calenderings of the working crown layers associated with the mixtures of layer C, in accordance with the invention according to this variant embodiment of the invention, lead to a conservation, or even an improvement, of the endurance performance of the tire in an even more marked manner.

[0068] According to a preferred embodiment of this variant of the invention, said at least one calendering layer of at least one working crown layer is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used.

[0069] Also preferably, said at least one calendering layer of at least one working crown layer, in addition to the pyrolysis carbon black, comprises a reinforcing filler consisting of: a - either by carbon black used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, b - either by a white filler of silica and / or alumina type comprising SiOH and / or A1OH surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m2 / g used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, c - either by a blend of carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 20 and 50 pce, and preferably between 30 and 40 pce.

[0070] According to one embodiment of the invention, the elastomeric mixture constituting said at least one calendering layer of at least one working crown layer is identical to the elastomeric mixture of layer C, arranged between at least the ends of said two working crown layers.

[0071] The metallic elements are preferably steel cables.

[0072] According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

[0073] A preferred embodiment of the invention also 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 of 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.

[0074] 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 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0075] Other advantageous details and characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to [Fig. 1] which represents a meridian view of a diagram of a tire according to an embodiment of the invention.

[0076] [Fig.l] is not shown to scale to simplify understanding. [Fig.l] only represents a half-view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of a tire.

[0077] In [Fig.l], the tire 1 is of dimension 295 / 80 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not shown in [Fig.l]. The carcass reinforcement is formed of a single layer of metal cables. This carcass reinforcement 2 is hooped by a crown reinforcement 4, formed radially from the inside to the outside: - a triangulation layer 45 formed of inextensible metal cables 9.28 not hooped, oriented at an angle equal to 65°, - a first working layer 41 formed of inextensible metal cables 11.35 not hooped, continuous over the entire width of the sheet, oriented at an angle equal to 26°, - a second working layer 42 formed of inextensible metal cables 11.35 not hooped, 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 44 formed of elastic metal cables 6.35 not hooped, continuous over the entire width of the sheet, oriented at an angle equal to 18° in the same direction as the metal cables of the second working layer.

[0078] The crown reinforcement is itself topped with a tread 5.

[0079] The tire is inflated to a pressure of 8.5 bars.

[0080] The axial width L4i of the first working layer 41 is equal to 221 mm.

[0081] The axial width L42 of the second working layer 42 is equal to 202 mm.

[0082] The axial width of the tread L5 is equal to 242 mm.

[0083] The maximum axial width L is equal to 300 mm.

[0084] According to the invention, a first layer of rubber mixture C decouples the ends of the working crown layers 41 and 42.

[0085] The engagement zone of the layer C between the two working crown layers 41 and 42 is defined by its thickness or more precisely the radial distance d between the end of the layer 42 and the layer 41 and by the axial width D of the layer C between the axially inner end of said layer C and the end of the radially outer working crown layer 42. The radial distance d is equal to 2.8 mm, i.e. approximately 2.1 times the diameter 02 of the reinforcing elements of the working crown layer 42, the diameter 02 being equal to 1.35 mm. The axial distance D is equal to 19 mm, i.e. approximately 14 times the diameter 02 of the reinforcing elements of the working crown layer 42.

[0086] According to the invention, layer C consists of an elastomeric mixture comprising a pyrolysis black.

[0087] Different tires according to the invention are compared to reference tires of the same size.

[0088] First tires II according to the invention comprise a layer C made up of mixtures 1, 2, or 3 and calendering layers made up of mixture RL

[0089] Second tires 12 according to the invention comprise a layer C and calendering layers made up of mixtures 1, 2, or 3.

[0090] The reference tires T1 differ from the tires II according to the invention by the nature of the mixtures of layer C, these being made up of the mixture R2.

[0091] The different mixtures used are listed below, expressing for each the secant modulus of elasticity at 10% elongation, the elongation at break. M&aage RI Méîssige. R2 MèWge 1 KR IDG 100:.W Black N34”' 52. 53 NckRCB 60 (SPfD) 15. 15 1.5 Stearic acid 3.35 0.5 Ziîic oxide 93 RS '7.5 • SeWCçWtÇ^^ 1.12 1.12 1.12 scivdce 61 5.6 4.5: Access 0.93 OS OS Delay ateia CTP PVT) 0.25 0.25 6.15 10.4 S.5 6.Ï at Break (W 2S0 323 444:

[0092] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0093] Initial endurance tests, particularly thermally demanding, 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.

[0094] Other endurance tests, particularly requiring mechanical stress, 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.

[0095] The tests thus carried out showed that the distances covered during each of these tests are substantially identical for the tires according to the invention and the reference tires.

[0096] Tests aimed at characterizing the breaking strength of a tire crown reinforcement subjected to impacts were also carried out. These tests consist of: rolling a tire, inflated to a recommended pressure and subjected to a recommended load, over a cylindrical obstacle or indenter with a diameter equal to 1.5 inches, or 38.1 mm, with a hemispherical head, and of a determined height. The trajectory of the tire is adjusted so that the axis of the obstacle corresponds to the position of one of the axially outermost ribs on the tread. The breaking strength is characterized by the critical height of the indenter, i.e. the maximum height of the indenter resulting in a total rupture of the crown reinforcement, i.e. the rupture of all the crown layers. The values ​​express the energy required to obtain rupture of the crown block. The values ​​are expressed from a base 100 corresponding to the value measured for the reference tire TL II 125 12 130 Reference Tl 100

[0097] These results show that the breaking energy during an impact on the surface of the tread of the tires II and 12 according to the invention is greater than that of the tire TL

[0098] Final endurance tests aimed at reproducing driving conditions combining the vehicle speed and the particularly aggressive nature of the ground have been carried out. These tests thus reproduce extreme conditions, particularly for "Heavy Goods" vehicles of the "site approach" type.

[0099] These last tests consist of reproducing twenty-five times a rolling phase of 2 hours at 100 km / h on a circuit under the load and pressure conditions indicated on the tire followed by a rolling phase of 12 minutes at 35 km / h on a stony track.

[0100] The low speed rolling phase on a stony track is intended to penalize endurance following repeated impacts on the tread.

[0101] The purpose of the high-speed running phase on a circuit is to increase the temperature of the tire. This makes the tire more sensitive to the effects of repeated impacts on the tread and this promotes the propagation of cracks initiated in the running phase on a stony track.

[0102] At the end of the rolling, the tires are checked by shearography and dissected to analyze any possible damage. This is a visual analysis allowing comparison of 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 given to the most damaged tire. Note Il 110 12 130 Reference Tl 100

[0103] At the end of the rolling, the tires according to the invention II and 12 present less extensive damage than the reference tires T1.

[0104] During these last endurance tests, the temperature of the tires at the ends of the crown block was measured following the first rolling phase of 2 hours at 100 km / h on the circuit. Temperature II 93 °C 12 9(TC Reference Tl 97^0

[0105] These results show that the tires according to the invention actually have lower temperatures than the reference tires.

[0106] It emerges from these tests that the tires according to the invention make it possible to improve the performance in terms of impact resistance in a satisfactory manner while presenting satisfactory endurance performance.

Claims

Claims

1. A tire (1), comprising a radial carcass reinforcement (2), said tire comprising a crown reinforcement (4), comprising two working crown layers of reinforcing elements (41, 42) inserted between two calendering layers of rubber compound, crossed from one layer to the other making angles of between 10 and 45° with the circumferential direction, said angles being oriented on either side of the circumferential direction, a layer C of rubber compound being arranged between at least the ends of said two working crown layers, the crown reinforcement (4) being radially capped with a tread (5), said tread being joined to two beads (3) by means of two sidewalls, characterized in that the rubber compound constituting said layer C comprises a composition comprising 50 to 70 phr of reinforcing fillers, of which at least 20 pce of pyrolysis carbon black.

2. Tire according to claim 1, characterized in that the pyrolysis carbon black has an ash content ranging from 5 to 30% by weight, preferably less than 25% by weight, more preferably less than 22% by weight, relative to the total weight of the pyrolysis carbon black, the ash content being determined by calcination in platinum capsules in a muffle furnace at 825°C according to the protocol presented in the description.

3. Tire according to claim 1 or 2, characterized in that the pyrolysis carbon black has a sulfur content greater than 2% by weight, preferably ranging from 2.5 to 5% by weight, relative to the total weight of the pyrolysis carbon black, the determination of the sulfur content in the pyrolysis carbon blacks being carried out by LECO oven according to the method presented in the description.

4. Tire (1) according to one of claims 1 to 3, characterized in that the pyrolysis carbon black has a zinc content greater than or equal to 2% by weight, preferably ranging from 2.5 to 8% by weight, relative to the total weight of the pyrolysis carbon black, the determination of the zinc content being carried out after calcination of the sample, then recovery of the ashes in an acid medium and dosage by ICP-AES (inductively coupled plasma atomic emission spectroscopy) according to the method presented in the description.

5. Tire according to one of the preceding claims, characterized in that said layer C is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of a blend being present at a majority rate compared to the rate of the other diene elastomer(s) used.

6. Tire (1) according to one of the preceding claims, characterized in that the layer C of rubber mixture, in addition to the pyrolysis carbon black, comprises a reinforcing filler consisting of: a - either carbon black used at a rate of between 20 and 50 phr, and preferably between 30 and 40 phr, b - or a white filler of silica and / or alumina type comprising SiOH and / or A1OH surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m2 / g used at a rate of between 20 and 50 phr, and preferably between 30 and 40 phr, c - either a blend of carbon black described in (a) and a white filler described in (b), in in which the overall charge rate is between 20 and 50 pce, and preferably between 30 and 40 pce.

7. Tire (1) according to one of the preceding claims, characterized in that at least one calendering layer of at least one working crown layer is made up of a rubber mixture comprising a composition comprising 50 to 70 pce of reinforcing fillers, including at least 20 pce of pyrolysis carbon black.

8. Tire (1) according to claim 7, characterized in that said at least one calendering layer of at least one working crown layer (41, 42) is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used.

9. Tire (1) according to one of claims 7 or 8, characterized in that said at least one calendering layer of at least one working crown layer, in addition to the pyrolysis carbon black, comprises a reinforcing charge consisting of: a - either by carbon black used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, b - either by a white filler of silica and / or alumina type comprising SiOH and / or A10H surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino-silicates or even carbon blacks modified during or after synthesis with a BET specific surface area of ​​between 30 and 260 m2 / g used at a rate of between 20 and 50 pce, and preferably between 30 and 40 pce, c - either by a blend of carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 20 and 50 pce, and preferably between 30 and 40 pce.

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