Tyre comprising layer of circumferential reinforcing elements

Abstract

The invention relates to a tyre (1) with a radial carcass reinforcement, said tyre (1) comprising two working crown plies (41, 42) and a layer (43) of circumferential reinforcing elements. According to the invention, the rubber mixture constituting the layer C comprises a composition comprising from 40 phr to 70 phr of a reinforcing filler, said reinforcing filler comprising at least 20 phr of pyrolytic carbon black.

Description

TECHNICAL FIELD

[0001] The present invention relates to a tire having a radial carcass reinforcement, and more particularly to a tire intended to be mounted on a vehicle (such as, for example, a truck, a tractor, a trailer or a bus) carrying heavy loads and traveling at a constant speed. BACKGROUND ART

[0002] Generally, in tires for heavy-duty vehicles, the carcass reinforcement is anchored in the two bead areas on both sides and is covered radially by a crown reinforcement composed of at least two superimposed layers formed by filaments or cords, the filaments or cords being parallel within each layer and crossing from one layer to another, forming an angle between 10° and 45° with the circumferential direction. The working layer forming the working reinforcement may also be covered by at least one layer called a protection layer, the protection layer being formed by preferably metallic and extensible reinforcing elements (called elastic reinforcing elements). It may also include a layer of metallic filaments or cords having low extensibility, the metallic filaments or cords forming an angle between 45° and 90° with the circumferential direction, and this ply is called a chafer ply and is located radially between the carcass reinforcement and the first crown ply (called the working ply), the carcass reinforcement and the first crown ply being formed by parallel filaments or cords with an absolute value of the angle of at most 45°. The chafer ply and at least the working ply together form a chafer reinforcement, the chafer reinforcement having almost no deformation under the various stresses it undergoes, and the chafer ply being basically used to absorb the lateral compressive forces applied to all the reinforcing elements in the crown area of the tire.

[0003] When a cord shows a relative elongation of at most 0.2% under a tensile force equal to 10% of the breaking force, the cord is called inextensible.

[0004] When a cord shows a relative elongation of at least 3% and a maximum tangent modulus of less than 150 GPa under a tensile force equal to the breaking load, the cord is called elastic.

[0005] A circumferential reinforcing element is a reinforcing element forming an angle within the range of +2.5° to -2.5° (relative to 0°) with the circumferential direction.

[0006] The circumferential direction or longitudinal direction of the tire is the direction tangent to the outer circumference of the tire and defined by the traveling direction of the tire.

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

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

[0009] The axis of rotation of a tire is the axis about which the tire rotates during normal use.

[0010] A radial plane or a meridional plane is a plane containing the axis of rotation of the tire.

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

[0012] The "modulus of elasticity" of a rubber compound shall be understood as the secant modulus of elongation at 10% elongation and ambient temperature.

[0013] For a rubber composition, the secant modulus of elasticity at 10% elongation is the modulus of elasticity measured for the compound at an elongation value of 0.1 (i.e., 10% elongation, expressed as a percentage) during a uniaxial tensile test. A uniaxial tension is applied to the specimen at a constant rate, and the elongation and the force are measured. The measurement is carried out using a tensile testing machine of the INSTRON type 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 the stress are as described in NF ISO 37 standard: 2012 - 03. The stress at 0.1 elongation is determined, and the secant modulus of elasticity at 10% elongation is calculated by determining the ratio of this stress value to the elongation value. A person skilled in the art will know how to select and adjust the dimensions of the specimen according to the available and usable amount of the compound, especially in the case where the specimen is taken from a finished product such as a tire.

[0014] Due to the improvement of the road network and the expansion of the global highway network, some tires currently called "road tires" are designed to travel longer distances at higher speeds. Since the wear on the tires is reduced, the combined conditions of travel of such tires can undoubtedly increase the number of kilometers traveled; on the other hand, the durability of such tires, especially the durability of the crown reinforcement, is adversely affected.

[0015] This is because there are stresses in the crown reinforcement, more specifically shear stresses between the crown layers, and these stresses, combined with a non - negligible increase in the operating temperature at the ends of the axially shortest crown layers, result in the appearance of cracks in the rubber and their propagation at said ends.

[0016] In order to improve the durability of the crown reinforcement of the type of tire under study, solutions have been proposed related to the structure and quality of rubber compound layers and / or shaping elements arranged between and / or around the ends of the ply (more specifically the ends of the axially shortest ply).

[0017] It is a well-known practice to introduce a layer of rubber compound between the ends of the working layer in order to create a decoupling between said ends and thus limit the shear stress. However, this decoupling layer needs to have very good cohesion. For example, such a layer of rubber compound is described in patent application WO 2004 / 076204.

[0018] In order to improve the resistance to degradation of the rubber compound located near the edge of the crown reinforcement, patent FR 1 389 428 proposes using a rubber forming element in combination with a low hysteresis tread, said rubber forming element covering at least the sides and the edge of the crown reinforcement and being made of a rubber compound with low hysteresis.

[0019] In order to avoid separation between the plies of the crown reinforcement, patent FR 2 222 232 teaches covering the ends of the reinforcement with a rubber pad, the Shore A hardness of said rubber pad being different from the Shore A hardness of the tread covering said reinforcement and being greater than the Shore A hardness of the forming element of the rubber compound arranged between the edge of the carcass reinforcement and the plies of the crown reinforcement.

[0020] The tires thus produced can effectively improve the performance, especially in terms of durability.

[0021] Moreover, in order to produce tires with a very wide tread or to give greater load-bearing capacity to tires of a certain size, it is a known practice to introduce a layer of circumferential reinforcement elements. For example, patent application WO 99 / 24269 describes the presence of such a layer of circumferential reinforcement elements.

[0022] The layer of circumferential reinforcement elements generally consists of at least one metal cord, said metal cord being wound to form a coil with a laying angle with respect to the circumferential direction of less than 2.5°.

[0023] The use of tires on heavy-duty vehicles of the "job-site supply" type means that the tires are subjected to impact loads when driving over stony ground. These impact loads will of course have an adverse effect on the performance in terms of durability.

[0024] The inventors have particularly found that when driving on a ground that exerts great stress on the tires, the durability performance of such tires may decrease (especially at the shoulders of the tires), for example, it may decrease under particularly severe driving conditions that combine vehicle speed, the load borne by the tires, and the nature of the ground. In fact, for example, when driving at a relatively high speed on a ground of the job-site supply type that is very demanding on the tires, a decrease in durability performance can be observed. Summary of the Invention

[0025] Thus, the inventors set themselves the task of providing tyres for "heavy-duty" vehicles (such as vehicles of the "site supply" type) which, regardless of the nature of the ground and the driving conditions, have improved durability with respect to the impact loads to which the tread is subjected and exhibit improved performance in terms of rolling resistance.

[0026] According to the invention, this object is achieved by a tyre comprising a radial carcass reinforcement, said tyre comprising a crown reinforcement which comprises two working crown layers and at least one circumferential reinforcement element layer, each working crown layer being formed by reinforcement elements which are interposed between two surface layers of rubber compound, cross from one layer to the other and form an angle between 10° and 45° with the circumferential direction, the angles α1 and α2 being respectively oriented on either side of the circumferential direction, a rubber compound layer C being arranged between at least the ends of the at least two working crown layers, the crown reinforcement being radially covered by a tread which is connected to two beads via two sidewalls, the rubber compound forming the layer C comprising a composition comprising from 40 phr to 70 phr of reinforcing filler, the reinforcing filler comprising at least 20 phr of pyrolytic carbon black.

[0027] The expression "parts by weight per hundred parts by weight of elastomer" (or phr) is to be understood as meaning parts by mass per hundred parts by mass of elastomer or rubber (the two terms being synonymous).

[0028] In certain embodiments, the composition comprises from 40 phr to 70 phr of reinforcing filler, the reinforcing filler being pyrolytic carbon black. Thus, it should be understood that the composition comprises pyrolytic carbon black as the sole reinforcing filler (thus, the composition does not contain any inorganic reinforcing fillers and other organic reinforcing fillers).

[0029] The reinforcing filler can be as described below.

[0030] Within the meaning of the present invention, the term "pyrolytic carbon black" is understood to mean carbon black produced by the pyrolysis process (for example in the case of the recycling of such materials) of a material comprising at least one carbon-based polymer and carbon black (hereinafter referred to as the material to be pyrolysed). The physical state of the material to be pyrolysed provided, whether in the form of powder, granules, strips or any other form, and whether in a crosslinked state or not, is not important.

[0031] Preferably, the material to be pyrolysed can be recovered from manufactured articles or products (such as by-products or waste) produced during their manufacture / production; these manufactured articles can be selected from pneumatic tyres, non-pneumatic tyres, industrial conveyor belts, conveyor belts, rubber gaskets, rubber hoses, shoe soles and windscreen wipers. Even more preferably, the pyrolytic carbon black which can be used within the scope of the present invention is carbon black obtained by the pyrolysis process of a material to be pyrolysed derived from manufactured articles selected from pneumatic tyres and non-pneumatic tyres.

[0032] Within the scope of the present invention, pyrolysis means any type of thermal decomposition carried out under anaerobic conditions, and its raw material is the material to be pyrolyzed as defined above. Therefore, pyrolytic carbon black is different from so-called industrial carbon black and / or ASTM grade carbon black in that the carbon-based raw material used for pyrolysis is a material containing at least carbon-based polymers and carbon black, rather than a material derived from petroleum fractions or oils from coal or natural sources.

[0033] The pyrolytic carbon black that can be used within the scope of the present invention is particularly different from known carbon blacks (such as industrial carbon black, especially "furnace black") in that its ash content is higher than that of the said "furnace black". Relative to the total weight of the "furnace black", the ash content of the "furnace black" is less than 1% by weight.

[0034] Preferably, relative to the total weight of the pyrolytic carbon black, the ash content of the pyrolytic carbon black that can be used within the scope of the present invention ranges from 5% by weight to 30% by weight, more preferably less than 25% by weight, and still more preferably less than 22% by weight.

[0035] Preferably, relative to the total weight of the pyrolytic carbon black, the sulfur content of the pyrolytic carbon black that can be used within the scope of the present invention is greater than 1.5% by weight, preferably greater than 2% by weight, and more preferably ranges from 2.5% by weight to 5% by weight.

[0036] Relative to the total weight of the "furnace black", the sulfur content of the "furnace black" is less than 1.2% by weight.

[0037] Preferably, relative to the total weight of the pyrolytic carbon black, the zinc content of the pyrolytic carbon black that can be used within the scope of the present invention is greater than or equal to 2% by weight, preferably ranges from 2.5% by weight to 8% by weight.

[0038] Relative to the total weight of the "furnace black", the zinc content of the "furnace black" is substantially zero and particularly less than 0.5% by weight.

[0039] Preferably, the STSA specific surface area of the pyrolytic carbon black that can be used within the scope of the present invention measured according to standard ASTM D6556-2021 is between 20 m 2 / g and 200 m 2 / g, more preferably between 30 m 2 / g and 90 m 2 / g.

[0040] Preferably, the void volume of the pyrolytic carbon black that can be used within the scope of the present invention measured according to standard ASTM D7854 (2018) at a pressure of 50 MPa is in the range of 30 ml / 100 g to 60 ml / 100 g, more preferably in the range of 35 ml / 100 g to 55 ml / 100 g.

[0041] The ash content was determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the following protocol. Before each series of measurements, the platinum dish was pre-determined and the tare weight of the platinum dish was weighed to an accuracy of within 0.1 mg, and the mass was designated as P0. A 5 g sample of pyrolytic carbon black, accurately weighed to within 0.1 mg, was placed into the platinum dish; this mass was designated as P1. The platinum dish and its contents were pre-calcined using a Bunsen burner until smoke appeared and the product ignited. After the combustion of the product was complete, the platinum dish and its contents were placed into a muffle furnace heated to 825 °C for 1 h. After 1 h, the platinum dish was removed from the furnace and immediately placed into a desiccator at ambient temperature. When the platinum dish and the ash had returned to ambient temperature, the platinum dish was weighed again to obtain the mass P2. Finally, the ash content (ash %) could be obtained using the following formula:

[0042]

[0043] After the sample was calcined, the ash was taken up in an acidic medium and the zinc content in the pyrolytic carbon black was determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) analysis. The ash was obtained by carrying out the above protocol. Approximately 100 mg of the ash (test sample) was taken and placed into a PFA (Perfluoroalkoxy) tube for a HotBlock hotplate. Then 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid and 0.5 ml of 40% hydrofluoric acid were added. The tube was closed using a tube stopper and heated at 130 °C for 2 h. After cooling, the contents were then transferred to a 100 ml PTFE (Polytetrafluoroethylene) volumetric flask that already contained 2 g of boric acid (for neutralizing the hydrofluoric acid) using ultrapure water. Ultrapure water was added up to the calibration mark. The solution obtained was diluted 100-fold by taking 1 ml of the solution and placing it into a 100 ml PFTE volumetric flask that already contained 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. Then, before analysis by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), the diluted solution was filtered through a 0.45 μm GHP syringe filter. Before analyzing the diluted solution, at least 5 calibration standards with zinc concentrations of 0 mg / l, 0.5 mg / l, 1 mg / l, 2 mg / l and 5 mg / l were analyzed by ICP-AES. These calibration standards were prepared by diluting a commercial solution with a certified zinc concentration of 1 g / l in a 100 ml volumetric flask.

[0044] These volumetric flasks already contain 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 solution was analyzed by ICP-AES at a wavelength of λZn = 202.613 nm. For each standard concentration (c), the intensity of the zinc signal IZn was plotted on the IZn = f(c) curve, which corresponds to a calibration line (type y = ax + b). Then, the sample solution of unknown concentration (diluted solution) was measured under the same conditions as the standard sample. The measured intensity was related to the concentration using the previously obtained calibration line. Since the sample and volume were pre-recorded, the concentration [c] was directly obtained by software. 灰分 (in mass %). The zinc concentration [c] in the pyrolytic carbon black was obtained by the following equation: 炭黑 (in mass %):

[0045] [c] 炭黑 = [c] 灰分 * 100 * ash content %

[0046] The sulfur content in the pyrolytic carbon black was determined by a LECO furnace. The LECO sulfur analyzer is designed to measure the sulfur content in organic materials and / or inorganic materials, especially by combustion and non-dispersive infrared detection. Before measuring the sulfur content in the sample, the boat was cleaned and the furnace was calibrated. The boat used for the LECO furnace was pre-cleaned: this involved analyzing an empty boat under the same conditions as the sample. A calibration curve was prepared based on a commercial standard sample called "BBOT" (its purity is greater than 99.99%, and the contents of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S) are ensured). These contents are as follows: C% 72.52; H% 6.09; N% 6.51; O% 7.43, and S% 7.44. Weigh approximately 10 ± 3 mg, 20 ± 3 mg, and 40 ± 3 mg of BBOT on the boat. The standard sample / boat assembly was placed into the combustion furnace and adjusted to 1350 °C under pure oxygen. The combination of the furnace temperature and the analysis flow rate caused the combustion of the sample, and sulfur and / or carbon were released in the form of SO2(g). After 20 s, oxygen began to flow through the lance, thus accelerating the combustion of materials that are difficult to burn. Sulfur and / or carbon in the form of SO2(g) were entrained by the oxygen flow through the infrared detection unit. The software of the instrument plotted a straight line that related the mass of the introduced standard sample to the response (area) observed on the detector. Thus, the calibration line was obtained. After thoroughly cleaning the sampling equipment, approximately 80 ± 5 mg of pyrolytic carbon black was weighed and placed into the boat used for the LECO furnace.

[0047] The area of the SO2 peak observed was related to the concentration through the calibration line. The software of the instrument then calculated the weight % of sulfur in the sample based on the weight of the sample placed into the boat.

[0048] Pyrolytic carbon black is sold, for example, by BlackBear under the reference number "BBCT30", or by Scandinavian EnviroSystems under the reference number "P550".

[0049] The angle of the working crown ply (expressed in degrees) is measured on the cross-section of the tire. According to the invention, the angle is measured at the circumferential mid-plane. These measurements can also be carried out by radiography.

[0050] Advantageously, according to the invention, the maximum value of tan(δ) of said ply C (denoted as tan(δ) max ) is less than 0.130, preferably less than 0.100.

[0051] The loss factor tan(δ) is a dynamic property of the rubber compound ply. It is measured on a viscometer (Metravib VA4000) according to the ASTM D5992-96 standard. Recording the response of a sample of the vulcanized composition (with a thickness of 2 mm and a cross-section of 78 mm 2 in the form of a cylindrical specimen) subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz at a temperature of 100 °C. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 1% (return cycle). For the return cycle, the maximum observed tan(δ) value is shown, denoted as tan(δ) max .

[0052] In the case where the thickness of the material is between 1 mm and 2 mm, the loss factor tan(δ) is measured on a sample of the vulcanized composition in the form of a cylindrical specimen (with a thickness of 1 mm and a cross-section of 78 mm 2 ) according to the same method as described above and under the same conditions.

[0053] Rolling resistance is the resistance that occurs when the tire rolls. Rolling resistance is represented by the hysteresis losses associated with the deformation of the tire during rotation. The frequency value associated with the rotation of the tire corresponds to the tan(δ) value measured between 30 °C and 100 °C. Thus, the tan(δ) value at 100 °C corresponds to the rolling resistance index when the tire rolls.

[0054] The rubber compound ply C can decouple the working crown ply, so that the shear stress is distributed over a greater thickness.

[0055] In the meaning of the present invention, the working crown ply is said to be coupled if the distance by which the corresponding reinforcing elements of each ply are radially separated is less than the average diameter of the circle circumscribing the reinforcing elements, the rubber thickness being measured radially between the upper and lower generatrices of the corresponding reinforcing elements.

[0056] The average diameter of the circle circumscribing the reinforcing elements is defined as the average diameter of the circle circumscribing the reinforcing elements of each working crown ply.

[0057] According to a preferred embodiment of the invention, the rubber blend layer C is an elastomeric blend based on natural rubber or on synthetic polyisoprene having mainly cis-1,4 bonds, and optionally on at least one other diene elastomer, in the case of a blend, the natural rubber or synthetic polyisoprene being present in a major amount relative to the amount of one or more other diene elastomers used.

[0058] Among the diene elastomers which can be used in blend with natural rubber or synthetic polyisoprene having mainly cis-1,4 bonds, mention may be made preferably of polybutadiene (BR) having mainly cis-1,4 bonds, styrene-butadiene copolymers (SBR) in solution or emulsion, butadiene-isoprene copolymers (BIR) and styrene-butadiene-isoprene terpolymers (SBIR). These elastomers may be elastomers modified during or after polymerization by a branching agent (such as divinylbenzene) or a star-branching agent (such as a carbonate, a tin halide or a silicon halide), or elastomers modified by a functionalizing agent so as to graft an oxycarbonyl or carboxyl functional group or an amine functional group to the chain or the chain ends, for example by the action of dimethylaminobenzophenone or diethylaminobenzophenone. In the case of a blend of natural rubber or synthetic polyisoprene having mainly cis-1,4 bonds with one or more of the abovementioned diene elastomers, the natural rubber or synthetic polyisoprene is preferably used in a major amount, more preferably in an amount greater than 70 phr.

[0059] Also preferably, in addition to the pyrolytic carbon black, the rubber blend layer C further comprises a reinforcing filler consisting of:

[0060] a) carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0061] b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, the white filler being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0062] c) or a blend of the carbon black described in (a) and the white filler described in (b), wherein the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

[0063] The BET specific surface area is measured by the Brunauer, Emmet and Teller method described in "The Journal of the American Chemical Society" (Volume 60, page 309, February 1938), which corresponds to the NFT 45007 standard of November 1987.

[0064] If a transparent filler or a white filler is used, a coupling agent and / or a covering agent selected from reagents known to those skilled in the art must be used. As examples of preferred coupling agents, mention may be made of alkoxysilane sulfides of the bis(3-trialkoxysilylpropyl) polysulfide type, in particular bis(3-triethoxysilylpropyl) tetrasulfide sold by Degussa under the names Si69 (pure liquid product) and X50S (solid product (blended 50 / 50 by weight with N330 carbon black)). As examples of covering agents, mention may be made of fatty alcohols, alkylalkoxysilanes (such as hexadecyltrimethoxysilane or hexadecyltriethoxysilane sold by Degussa under the names Si116 and Si216 respectively), diphenylguanidine, polyethylene glycol or silicone oils optionally modified by OH or alkoxy functional groups. The covering agent and / or the coupling agent are used in a weight ratio of ≥1 / 100 and ≤20 / 100 relative to the filler, preferably between 2 / 100 and 15 / 100 when the transparent filler constitutes all of the reinforcing filler, and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and a transparent filler.

[0065] As other examples of reinforcing fillers having the above morphology and SiOH and / or AlOH surface functional groups of materials of the silica and / or alumina type and which can be used as partial or total substitutes for these materials according to the invention, mention may be made of carbon blacks which are modified during the synthesis by adding a compound of silicon and / or aluminum to the feedstock oil of the furnace or after synthesis by adding an acid to an aqueous suspension of carbon black in a sodium silicate and / or sodium aluminate solution, so as to at least partially cover the surface of the carbon black with SiOH and / or AlOH functional groups. As non-limiting examples of carbon-based fillers of this type having SiOH and / or AlOH functional groups on the surface, mention may be made of the fillers of the CSDP type described in Document No. 24 of the ACS Rubber Division Meeting (Anaheim, California, May 6 - 9, 1997), and those fillers in patent application EP-A-0799 854.

[0066] When using a transparent filler as the sole reinforcing filler, by using a BET specific surface area of 30 m 2 / g to 260 m 2 / g to obtain hysteresis properties and cohesive properties. As non-limiting examples of fillers of this type, mention may be made of silica KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HI-SIL 2000 from PPG, etc.

[0067] The results obtained with the tire according to the invention have effectively demonstrated that the performance in terms of durability can be improved, regardless of the nature of the ground and the running conditions, and the performance in terms of rolling resistance is improved. In particular, the endurance performance of the crown of the tire is improved with respect to the impact loads at the tread edges, especially at the shoulders of the tire, regardless of the nature of the ground and the running conditions.

[0068] The inventors believe that these results can be explained by the presence of pyrolytic carbon black used as filler in layer C. The inventors have been able to demonstrate that the presence of pyrolytic carbon black in the rubber compound constituting layer C gives said layer C elongation at break values higher than those of more conventional compounds. Typically, if an impact load similar to that observed when driving over stony ground is applied, more specifically to the shoulders of a tire, the rupture of the reinforcing elements, if such rupture occurs, is found in the radially innermost layer, more specifically at its ends. These observations seem to indicate that the presence of pyrolytic carbon black in the rubber compound constituting layer C makes it possible to improve the endurance performance of the tire in the face of this type of attack.

[0069] The use of pyrolytic carbon black in layer C also results in a reduced stiffness of the rubber compound layer C. This lower stiffness compared to more common compounds is a factor that is detrimental to the durability of the tire when subjected to high stresses, such as when running at sustained speeds.

[0070] A more conventional tire design effectively provides a layer of rubber compound arranged between the ends of the working crown layers, whose secant modulus of elasticity at 10% elongation is greater than 8.5 MPa, in particular in order to be able to limit the shear stresses between the ends of the working crown layers, said working crown layers having a very low circumferential stiffness at their ends. Such a modulus, which is generally even greater than 9 MPa, makes it possible to prevent cracks from starting and propagating in the rubber compound at the ends of said working crown layers, more particularly at the ends of the narrowest working layers.

[0071] The inventors have demonstrated that the layer of circumferential reinforcing elements enables the selection of a rubber compound having a lower modulus of elasticity for layer C without compromising the durability of the tire.

[0072] The inventors have also demonstrated that the cohesion of layer C according to the invention remains satisfactory.

[0073] Within the meaning of the present invention, a cohesive rubber compound is a rubber compound that is particularly resistant to cracking. Thus, the cohesion of the compound is evaluated by means of fatigue cracking tests carried out on "PS" (pure shear) specimens. The test consists in determining the variation of the crack propagation rate "Vp" (nm / cycle) as a function of the energy release rate "E" (J / m 2 ) after notching the specimen. The experimental range covered by the measurements is the temperature in the range from -20 °C to +150 °C, using an atmosphere of air or nitrogen. The stress on the specimen is a dynamic displacement with an amplitude between 0.1 mm and 10 mm applied in the form of a pulsed stress load ("half-sine" tangent signal), where the pause time is equal to the pulse duration; the frequency of the signal is on average about 10 Hz.

[0074] The measurements include three parts:

[0075] · Adaptation of the "PS" specimen to 1000 cycles at 27% deformation.

[0076] · Energy characterization to determine the "E" = f(deformation) law. The energy release rate "E" is equal to W0*h0, where W0 = energy supplied to the material per cycle and per unit volume, h0 = initial height of the specimen. Thus, the acquisition of "force / displacement" data gives the relationship between "E" and the amplitude of the stress load.

[0077] · Measuring the crack after notching the "PS" specimen. The data collected are used to determine the variation of the crack propagation rate "Vp" as a function of the applied stress load level "E".

[0078] The inventors have particularly demonstrated that the presence of at least one circumferential reinforcing element layer contributes to reducing the variation of the cohesion of layer C. This is because a more conventional tire design particularly includes a rubber compound layer arranged between the ends of the working crown layer having a secant modulus of elasticity at 10% elongation greater than 8.5 MPa, which causes a variation in the cohesion of the rubber compound layer arranged between the ends of the working crown layer, and the cohesion tends to become weaker. The inventors have found that the presence of at least one circumferential reinforcing element layer (which limits the shear stress between the ends of the working crown layer and limits the temperature rise) results in a slight variation in the cohesion of layer C. Thus, the inventors believe that the cohesion of layer C (which is less than that present in more conventional tire designs) is satisfactory in the tire design according to the invention.

[0079] In addition, the combination of the lower stiffness compound of layer C based on pyrolytic carbon black with the circumferential reinforcing element layer helps to limit the temperature rise generated when subjected to shear stress.

[0080] The blend with lower stiffness based on pyrolytic carbon black in layer C (a blend based on pyrolytic carbon black may seemingly impair the durability of the tire under extreme usage conditions) actually enables the durability performance of the tire to be maintained or even improved. The inventors believe that this result can be explained by the fact that, in the presence of the circumferential reinforcing element layer, the blend with lower stiffness based on pyrolytic carbon black in layer C affects the crown temperature of the tire, and the combination of these factors seemingly reverses the expected impact on durability.

[0081] Compared with tires having a more conventional design, the performance in terms of rolling resistance is also improved with respect to these not-too-high operating temperatures.

[0082] Preferably, the thickness of the rubber blend layer C measured at the end of the narrowest operating crown layer among the two operating crown layers considered is preferably between 30% and 80% of the total thickness of the rubber blend between the cord generatrices of each of the two operating crown layers: a thickness less than 30% does not yield conclusive results, and a thickness greater than 80% is useless for improving the resistance to separation between the layers and is also disadvantageous in terms of cost.

[0083] Also preferably, the axial width D of the rubber blend layer C between the axially innermost end of the rubber blend layer C and the end of the axially narrowest operating crown layer satisfies:

[0084] 3·φ2 ≤ D ≤ 25·φ2

[0085] where φ2 is the diameter of the reinforcing element of the axially narrowest operating crown layer. This relationship defines the joint area between the rubber blend layer C and the axially narrowest operating crown layer. Such a joint less than three times the diameter of the reinforcing element of the axially narrowest working layer may not be sufficient to obtain the decoupling of the operating crown layer, especially to obtain a reduction in stress at the end of the axially narrowest operating crown layer. A value of such a joint greater than twenty times the diameter of the reinforcing element of the axially narrowest working layer may lead to an excessive reduction in the camber stiffness of the tire crown reinforcement.

[0086] Preferably, the axial width D of the rubber blend layer C between the axially innermost end of the rubber blend layer C and the end of the axially narrowest operating crown layer is greater than 5 mm.

[0087] The present invention also preferably provides, at the axially outer end of the axially narrowest operating crown layer, a rubber blend layer C, and the thickness of the rubber blend layer C satisfies that the radial distance d between the two operating crown layers separated by the rubber blend layer C satisfies the following relationship:

[0088] 3 / 5·φ2 < d < 5·φ2

[0089] where φ2 is the diameter of the reinforcing element of the axially narrowest operating crown ply.

[0090] The distance d is measured from cord to cord (i.e., between the cords of the first working ply and the cords of the second working ply). In other words, this distance d includes the thickness of the rubber compound layer C and the respective thicknesses of the rubber surface compound located radially outside the cords of the radially inner working ply and radially inside the cords of the radially outer working ply.

[0091] The various thickness measurements are made on a meridian cross-section of the tire, so the tire is in an uninflated state.

[0092] According to an advantageous embodiment of the invention, the axially widest working crown ply is located radially inside another working crown ply.

[0093] According to a variant of an embodiment of the invention, at least one surface layer of at least one working crown ply is made of a rubber compound having a composition comprising 40 phr to 70 phr of reinforcing filler, the reinforcing filler including at least 20 phr of pyrolytic carbon black.

[0094] According to a preferred embodiment of this variant of the invention, the rubber compounds of the surface layers of the two working crown plies have a composition comprising 40 phr to 70 phr of reinforcing filler, the reinforcing filler including at least 20 phr of pyrolytic carbon black.

[0095] Generally, the elastic secant modulus of the surface layer of the working crown ply at 10% elongation is greater than 10 MPa. Such an elastic modulus is required in order to be able to limit the compression of the reinforcing elements of the working crown ply, particularly when the vehicle is moving along a winding route, in a parking lot or when passing through a circuitous route. This is because the shear action in the axial direction acting on the tread in the area of contact with the ground causes compression of the reinforcing elements of the working crown ply.

[0096] The inventors have also demonstrated that the circumferential reinforcing element layer can use a rubber compound based on pyrolytic carbon black, which has a lower elastic modulus, without compromising the durability of the tire due to the compression of the reinforcing elements of the working crown ply as described above.

[0097] Furthermore, the combination of the pyrolytic carbon black-based rubber compound of the calendered surface layer of the working crown ply and the circumferential reinforcing element layer, like layer C, helps to limit the temperature rise generated when subjected to shear stress.

[0098] Furthermore, the inventors have observed that, in the presence of the circumferential reinforcing element layer, the combination of the pyrolytic carbon black-based rubber compound of the calendered surface layer of the working crown ply in this variant of the embodiment of the invention and the compound of layer C according to the invention enables the durability performance of the tire to be maintained, or even improved, and even more significantly improved. This unexpected result is due in particular to the combined effect on the tire crown temperature.

[0099] According to a preferred embodiment of this variant of the invention, at least one surface layer of the at least one working tread layer is an elastomeric compound, the elastomeric compound being based on natural rubber or on synthetic polyisoprene having predominantly cis-1,4 bonds and optionally on at least one other diene elastomer, and in the case of a blend, the natural rubber or synthetic polyisoprene being present in a major content relative to the content of one or more other diene elastomers used.

[0100] Also preferably, in addition to pyrolytic carbon black, the at least one surface layer of the at least one working tread layer further comprises a reinforcing filler consisting of:

[0101] a) carbon black used in a content between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0102] b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, the white filler being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in a content between 20 phr and 50 phr, preferably between 30 phr and 40 phr,

[0103] c) or a blend of the carbon black described in (a) and the white filler described in (b), wherein the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

[0104] According to one embodiment of the invention, the elastomeric compound constituting at least one surface layer of the at least one working tread layer is the same as the elastomeric compound of layer C arranged between at least the ends of the two working tread layers.

[0105] According to an advantageous embodiment variant of the invention, the axial width of the circumferential reinforcing element layer is greater than 0.5×S.

[0106] S is the maximum axial width of the tire when the tire is mounted on its service rim and inflated to its recommended pressure.

[0107] The axial width of the reinforcing element layer is measured in the cross-section of the tire, so the tire is in an uninflated state.

[0108] According to a preferred embodiment of the invention, the circumferential reinforcing element layer is arranged radially between two working tread layers.

[0109] According to this embodiment of the invention, the circumferential reinforcing element layer can limit the compressive action on the reinforcing elements of the carcass reinforcement to a greater extent than a similar layer located radially outside the working layer. It is preferably separated from the carcass reinforcement in the radial direction by at least one working layer, thereby limiting the stress on the reinforcing elements and avoiding excessive fatigue of the reinforcing elements.

[0110] Advantageously according to the invention, the axial width of the working crown layer adjacent to the at least one circumferential reinforcing element layer in the radial direction is greater than the axial width of the at least one circumferential reinforcing element layer, and preferably, on each side of the equatorial plane and in the immediate axial extension of the at least one circumferential reinforcing element layer, the working crown layer adjacent to the at least one circumferential reinforcing element layer is joined in terms of axial width and then separated by the rubber compound layer C at least over the remaining width common to the two working layers.

[0111] According to an advantageous embodiment of the invention, the reinforcing elements of the at least one circumferential reinforcing element layer are metal reinforcing elements, and the metal reinforcing elements have a secant modulus at 0.7% elongation between 10 GPa and 120 GPa and a maximum tangent modulus less than 150 GPa.

[0112] According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 100 GPa and greater than 20 GPa, preferably between 30 GPa and 90 GPa, and even more preferably less than 80 GPa.

[0113] Also preferably, the maximum tangent modulus of the reinforcing elements is less than 130 GPa, and more preferably less than 120 GPa.

[0114] The above moduli are measured on a curve of tensile stress versus elongation (the curve is determined using a preload of 20 MPa), and the tensile stress corresponds to the measured tension corrected for the metal cross-section of the reinforcing element. The measurement is made on the cords taken from a part of the circumferential reinforcing element layer that extends axially towards the inside of the layer with an axial width of 50 mm from the axial end of the layer.

[0115] The moduli of the same reinforcing elements can be measured on a curve of tensile stress versus elongation (the curve is determined using a preload of 10 MPa), and the tensile stress corresponds to the measured tension corrected for the entire cross-section of the reinforcing element. The entire cross-section of the reinforcing element is the cross-section of a composite element composed of metal and rubber, and the rubber has penetrated into the reinforcing element especially during the curing of the tire.

[0116] According to this constitution related to the entire cross-section of the reinforcing element, the reinforcing elements in the axially outer part and the middle part of at least one circumferential reinforcing element layer are metal reinforcing elements, and the metal reinforcing elements have a secant modulus at 0.7% elongation between 5 GPa and 60 GPa and a maximum tangent modulus less than 75 GPa.

[0117] According to a preferred embodiment, the secant modulus of the reinforcing element at 0.7% elongation is less than 50 GPa and greater than 10 GPa, preferably between 15 GPa and 45 GPa, and even more preferably less than 40 GPa.

[0118] Also preferably, the maximum tangent modulus of the reinforcing element is less than 65 GPa, and more preferably less than 60 GPa.

[0119] According to a preferred embodiment, the reinforcing elements of at least one circumferential reinforcing element layer are such metal reinforcing elements that the curve of the tensile stress varying with the relative elongation shows a gentle gradient for smaller elongations and a steeper gradient that is substantially constant for larger elongations.

[0120] The above respective characteristics of the reinforcing element are measured on the reinforcing element taken from the tire.

[0121] According to the present invention, the reinforcing element that is more particularly suitable for preparing at least one circumferential reinforcing element layer is, for example, the assembly of formula 21.23, and the structure of formula 21.23 is 3×(0.26 + 6×0.23)4.8 / 7.5SS; this ply cord is composed of 21 basic filaments of formula 3×(1 + 6), where three strands are twisted together, each strand is composed of 7 filaments, the diameter of one filament forming the middle core is equal to 26 / 100 mm, and the diameter of the six winding filaments is equal to 23 / 100 mm. This cord has a secant modulus at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, and these moduli are measured on the curve of the tensile stress varying with the elongation determined using a 20 MPa preload, and the tensile stress corresponds to the measured tension corrected for the metal cross-section of the reinforcing element. On the curve of the tensile stress varying with the elongation determined using a 10 MPa preload (the tensile stress corresponds to the measured tension corrected for the entire cross-section of the reinforcing element), this cord of formula 21.23 has a secant modulus at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

[0122] Similarly, another example of a reinforcing element is a component of formula 21.28, the structure of formula 21.28 being 3×(0.32 + 6×0.28)5.6 / 9.3SS. This cord has a secant modulus at 0.7% equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, these moduli being measured on a curve of tensile stress versus elongation determined using a 20 MPa preload, the tensile stress corresponding to the measured tension corrected for the metal cross-section of the reinforcing element. On a curve of tensile stress versus elongation determined using a 10 MPa preload (the tensile stress corresponding to the measured tension corrected for the overall cross-section of the reinforcing element), this cord of formula 21×28 has a secant modulus at 0.7% equal to 27 GPa and a maximum tangent modulus equal to 49 GPa.

[0123] Using such a reinforcing element in at least one circumferential reinforcing element layer makes it possible in particular to maintain a satisfactory stiffness of the layer (even after the shaping and curing steps of a conventional production method).

[0124] According to a second embodiment of the invention, the circumferential reinforcing element can be formed from non-extendable metal elements which are cut so as to form portions whose length is much less than the shortest layer perimeter but preferably greater than 0.1 times said perimeter, the cuts between said portions being axially offset relative to one another. Also preferably, the tensile elastic modulus per unit width of the additional layer is less than the tensile elastic modulus measured under the same conditions for the most extensible working crown layer. Such an embodiment makes it possible to impart in a simple manner a certain modulus to the circumferential reinforcing element layer, said modulus being easily adjustable (by choosing the spacing between the portions of the same row), but always less than the modulus of a layer composed of the same but continuous metal elements, the modulus of the additional layer being measured on a vulcanized layer of cut elements taken from the tire.

[0125] According to a third embodiment of the invention, the circumferential reinforcing element is a corrugated metal element, the ratio a / λ of the amplitude to the wavelength being at most equal to 0.09. Preferably, the tensile elastic modulus per unit width of the additional layer is less than the tensile elastic modulus measured under the same conditions for the most extensible working crown layer.

[0126] The metal element is preferably a steel cord.

[0127] According to a preferred embodiment of the invention, the reinforcing element of the working crown layer is a non-extendable metal cord.

[0128] Preferred embodiments of the present invention also supplement the radially outer side of the crown reinforcement by means of at least one additional layer (referred to as a protective layer) having so-called elastic reinforcement elements, the elastic reinforcement elements being oriented at an angle between 10° and 45° with respect to the circumferential direction and the direction of the angle being the same as the angle formed by the inextensible elements of the working layer radially adjacent thereto.

[0129] According to any of the above embodiments of the present invention, the crown reinforcement can also be supplemented on the radially inner side between the carcass reinforcement and the radially inner working layer closest to the carcass reinforcement by means of a triangular layer having inextensible metal reinforcement elements, the inextensible metal reinforcement elements being made of steel, forming an angle greater than 60° with the circumferential direction and the direction of the angle being the same as the angle formed by the reinforcement elements of the layer radially closest to the carcass reinforcement layer. Description of the Drawings

[0130] Other details and advantageous features of the present invention will become apparent hereinafter from the description of the exemplary embodiments of the present invention given with reference to the accompanying drawings, which show a meridian view of a tire design according to an embodiment of the present invention.

[0131] For easier understanding, the drawings are not drawn to scale. The drawings show only a half view of the tire, which extends symmetrically about an axis XX', which represents the circumferential median plane or equatorial plane of the tire. Detailed Description

[0132] In the drawings, the tire 1 has a size of 315 / 70R 22.5. The tire 1 includes a radial carcass reinforcement 2 anchored in two beads (not shown in the figures). The carcass reinforcement is formed of a single layer of metal cord. This carcass reinforcement 2 is hoop-shaped by a crown reinforcement 4, which is formed radially from the inside out by:

[0133] - A first working layer 41, the first working layer 41 being formed of metal cords oriented at an angle equal to 22°,

[0134] - A circumferential reinforcement element layer 43, the circumferential reinforcement element layer 43 being formed of steel metal cords of type 21.23,

[0135] - A second working layer 42 formed of metal cords, the metal cords being oriented at an angle equal to 18° and crossing the metal cords of layer 41, and the cords of each of the working layers 41, 42 being oriented on both sides of the circumferential direction,

[0136] - A protective layer 44 formed of elastic 6.35 metal cords, wherein the distance between the reinforcing elements measured along a direction perpendicular to the bisector of the cords is equal to 2.5 mm, and the elastic 6.35 metal cords are oriented at an angle equal to 18° on the same side as the cords of the second working layer.

[0137] The metal cords of the reinforcing elements constituting the two working layers are cords of formula 9.35. They are distributed in each working layer at a distance equal to 2.2 mm between the reinforcing elements, said distance being measured along a direction perpendicular to the bisector of the cords.

[0138] The crown reinforcement itself is covered by a tread 5.

[0139] The tire is inflated to a pressure of 9 bar.

[0140] The axial width L of the first working layer 41 41 is equal to 252 mm.

[0141] The axial width L of the second working layer 42 42 is equal to 232 mm.

[0142] The axial width L of the circumferential reinforcing element layer 43 43 is equal to 194 mm.

[0143] The axial width L5 of the tread is equal to 266 mm.

[0144] The maximum axial width L is equal to 315.9 mm.

[0145] According to the invention, the first rubber compound layer C provides decoupling at the ends of the working crown layers 41 and 42.

[0146] The layer C is defined in the joining region between the two working crown layers 41 and 42 by its thickness, or more precisely by the radial distance d between the ends of layer 42 and layer 41 and the axial width D of layer C between the axial 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 φ2 of the reinforcing elements of the working crown layer 42, and the diameter φ2 is equal to 1.35 mm. The radial distance D is equal to 19 mm, i.e., approximately 14 times the diameter φ2 of the reinforcing elements of the working crown layer 42.

[0147] According to the invention, the layer C is made of an elastomeric compound containing pyrolytic carbon black.

[0148] Various tires according to the invention were compared with various reference tires of the same dimensions.

[0149] The first tire I1 according to the invention has a layer C made of compound 1 and a surface layer made of compound R1.

[0150] The second tire I2 according to the invention has a layer C and a surface layer made of the compound 1.

[0151] The first reference tire T1 differs from the tire I1 according to the invention in the properties of the compound for the layer C, and these layers C are made of the compound R1.

[0152] The various compounds used are listed below, and each compound shows the secant modulus of elasticity, elongation at break, and tan(δ) at 10% elongation max values.

[0153] Compound R1 Compound 1 NR 100 100 Carbon black N347 52 Carbon black RCB 60 Antioxidant (6PPD) 1.5 1.5 Stearic acid 0.65 0.9 Zinc oxide 9.3 7.5 Cobalt salt (AcacCo) 1.12 1.12 Sulfur 6.1 4.5 Accelerator DCBS 0.93 0.8 CTP blocker (PVI) 0.25 0.15 <![CDATA[MA 10 (MPa)]]> 10.4 6.1 Elongation at break (%) 280 444 <![CDATA[tan(δ) max > 0.13 0.08

[0154] The values of the components are expressed in phr (parts by weight per hundred parts of elastomer).

[0155] The pyrolytic carbon black (carbon black RCB) contains 20% ash, 1.8% sulfur, and 4.5% zinc.

[0156] The carbon black N347 contains 0.5% ash, 1% sulfur, and 0% zinc.

[0157] The content of the various components other than carbon black in the compound I1 is adjusted according to the knowledge of those skilled in the art, so as to obtain similar temperature and curing time conditions for various tires, and the properties of the tires can be compared.

[0158] The first (especially heat - required) durability test is carried out on a testing machine. Each tire rolls in a straight line at a speed equal to the maximum speed rating (or speed index) specified for the tire under an initial load of 4000 kg. In order to shorten the duration of the test, the initial load is gradually increased.

[0159] Other (especially mechanically - required) durability tests are carried out on a testing machine, and a lateral force and a dynamic over - load are applied to the tire in a cyclic manner. The tires according to the invention are tested under the same conditions as those applied to the reference tire.

[0160] The tests thus carried out show that the distances covered by the tires according to the invention and the reference tires are substantially the same in each of these tests.

[0161] Tests were also carried out to characterize the breaking strength of the tire crown reinforcement subjected to impact loads. These tests consisted of running a tire inflated to the recommended pressure and subjected to the recommended load on a cylindrical obstacle or indentor tool, the obstacle or indentor tool having a diameter equal to 1.5 inches (i.e., 38.1 mm), a hemispherical head and a given height. The trajectory of the tire was adjusted so that the axis of the obstacle corresponded to the position of one of the axially outermost ribs of the tread. The breaking strength was characterized by the critical height of the indentor tool, i.e., the maximum height at which the indentor tool caused complete breakage of the crown reinforcement (i.e., breakage of all crown plies). These values represent the energy required to break the crown blocks. These values are expressed relative to a base number 100 (which corresponds to the value measured for the reference tire T1).

[0162] I1 125 I2 130 Reference T1 100

[0163] These results show that the breaking energy of tires I1 and I2 according to the invention is higher than that of tire T1 in the case of impact loads on the tread surface.

[0164] Final durability tests were carried out to reproduce the driving conditions combining vehicle speed and particularly adverse ground. Thus, these tests reproduce the extreme conditions especially for "heavy-duty load" vehicles of the "site supply" type.

[0165] This final test includes: a stage of driving on a test track at 100 km / h for 2 hours under the load and pressure conditions marked on the tire, and then a stage of driving on a stony road at 35 km / h for 12 minutes, repeated 25 times.

[0166] The purpose of the stage of driving at low speed on the stony road is to have an adverse effect on durability due to repeated impact loads on the tread.

[0167] The purpose of the stage of driving at high speed on the test track is to raise the temperature of the tire. This makes the tire more sensitive to the effects of repeated impact loads on the tread and promotes the propagation of cracks initiated during the stage of driving on the stony road.

[0168] At the end of the run, the tires were inspected using shearography and peeled so that any damage could be analyzed. This is a visual analysis, allowing comparison between any cracks and crack propagation. The tires were scored and compared with each other. A score greater than 100 corresponds to a tire with less damage. The most severely damaged tire received a score of 100.

[0169] Fraction: I1 110 I2 130 Reference T1 100

[0170] At the end of the run, tires I1 and I2 according to the invention showed a lower degree of damage than the reference tire T1.

[0171] During these final durability tests, after driving for 2 hours on a circuit at 100 km / h in the first stage, the temperature of the tire at the end of the tread block portion is measured.

[0172] Temperature I1 90℃ I2 87℃ Reference T1 94℃

[0173] These results show that the temperature exhibited by the tire according to the present invention is not actually as high as that of the reference tire.

[0174] In addition, the rolling resistance is measured.

[0175] The rolling resistance of each tire is measured under the same driving conditions in accordance with Regulation No. 117 of the United Nations Economic Commission for Europe (UNECE). The measurement results are expressed in kg / t, and a value of 100 is assigned to tire T1. A value greater than 100 indicates better performance in terms of rolling resistance.

[0176] T1 I1 I2 Rolling resistance 100 102 105

[0177] It is clearly seen from these tests that the tire according to the present invention can improve the performance in terms of rolling resistance and impact load resistance in a satisfactory manner, while exhibiting satisfactory durability performance.

Claims

1. A tire (1) comprising a radial carcass reinforcement (2), said tire comprising a crown reinforcement (4), said crown reinforcement (4) comprising two working crown layers (41, 42) having reinforcing elements and at least one circumferential reinforcing element layer (43), said reinforcing elements being inserted between two surface layers of rubber compound, crossing from one layer to the other and forming an angle between 10° and 45° with the circumferential direction, said angle being oriented on both sides of the circumferential direction, a rubber compound layer C being arranged between at least the ends of said two working crown layers, said crown reinforcement (4) being radially covered by a tread (5), said tread being connected to two beads (3) via two sidewalls, characterized in that, The rubber compound constituting the layer C contains a composition comprising 40 phr to 70 phr of reinforcing filler, and the reinforcing filler includes at least 20 phr of pyrolytic carbon black.

2. The tire according to claim 1, wherein, Relative to the total weight of the pyrolytic carbon black, the ash content of the pyrolytic carbon black ranges from 5 wt% to 30 wt%, preferably less than 25 wt%, more preferably less than 22 wt%. The ash content is determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the method described in the specification.

3. The tire according to claim 1 or 2, characterized in that, Relative to the total weight of the pyrolytic carbon black, the sulfur content of the pyrolytic carbon black is greater than 1.5 wt%, preferably greater than 2 wt%, and preferably ranges from 2.5 wt% to 5 wt%. The sulfur content in the pyrolytic carbon black is determined by a LECO furnace according to the method described in the specification.

4. The tire (1) according to any one of claims 1 to 3, characterized in that, Relative to the total weight of the pyrolytic carbon black, the zinc content of the pyrolytic carbon black is greater than or equal to 2 wt%, preferably ranges from 2.5 wt% to 8 wt%. The zinc content is determined by analyzing the ash absorbed in an acidic medium after calcining the sample and by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) according to the method described in the specification.

5. The tire according to any one of the preceding claims, characterized in that, The layer C is an elastomeric compound, and the elastomeric compound is based on natural rubber or on synthetic polyisoprene mainly having cis-1,4 bonds, and optionally based on at least one other diene elastomer. In the case of a blend, the content of natural rubber or synthetic polyisoprene is present in a major amount relative to the content of one or more other diene elastomers used.

6. The tire (1) according to any one of the preceding claims, characterized in that, In addition to the pyrolytic carbon black, the rubber compound layer C further contains a reinforcing filler composed of: a) Carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, c) Or a blend of the carbon black described in (a) and the white filler described in (b), where the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

7. The tire (1) according to any one of the preceding claims, characterized in that, At least one surface layer of at least one working tread layer is made of a rubber compound having a composition comprising 40 phr to 70 phr of reinforcing filler, and the reinforcing filler includes at least 20 phr of pyrolytic carbon black.

8. The tire (1) according to claim 7, characterized in that, The at least one surface layer of at least one working tread layer (41, 42) is an elastomeric compound, and the elastomeric compound is based on natural rubber or on synthetic polyisoprene mainly having cis-1,4 bonds, and optionally based on at least one other diene elastomer. In the case of a blend, the content of natural rubber or synthetic polyisoprene is present in a major amount relative to the content of one or more other diene elastomers used.

9. The tire (1) according to any one of claims 7 and 8, characterized in that, In addition to the pyrolytic carbon black, the at least one surface layer of at least one working tread layer further contains a reinforcing filler composed of: a) Carbon black used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, b) or a white filler of the silica and / or alumina type having SiOH and / or AlOH surface functional groups with a BET specific surface area between 30 m 2 / g and 260 m 2 / g, selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and used in an amount between 20 phr and 50 phr, preferably between 30 phr and 40 phr, c) Or a blend of the carbon black described in (a) and the white filler described in (b), where the total filler content is between 20 phr and 50 phr, preferably between 30 phr and 40 phr.

10. The tire (1) according to any one of the preceding claims, characterized in that, The axial width of the two working tread layers (41, 42) is greater than the axial width of the at least one circumferential reinforcing element layer (43).

11. The tyre (1) according to any one of the preceding claims, characterised in that, The at least one circumferential reinforcing element layer (43) is located radially between the two working tread layers (41, 42).

12. The tire (1) according to any one of the preceding claims, characterized in that, The reinforcing elements of the at least one circumferential reinforcing element layer (43) are metal reinforcing elements, and the metal reinforcing elements have a secant modulus at 0.7% elongation between 10 GPa and 120 GPa and a maximum tangent modulus less than 150 GPa.

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