Lightweight pneumatic tire comprising layer of circumferential reinforcing elements

Abstract

The invention relates to a pneumatic tire (1) having a radial carcass reinforcement, two working crown plies (41, 42) and a circumferential reinforcing element ply (43), the two working crown plies (41, 42) and the circumferential reinforcing element ply (43) being the only layers for forming the crown reinforcement (4) over at least 75% of a width L5 of the tread (5), the absolute value of the difference between the angle alpha 2 and the absolute value of the angle alpha 1 is larger than 7 degrees, the absolute value of the angle alpha 2 is larger than the absolute value of the angle alpha 1, and the average angle alpha meets the relational expression 13 + 131 * exp (-L / 100) lt; [alpha] [lt]; and 28 + 110 * exp (-L / 100). According to the invention, the rubber mixture constituting said ply C comprises a composition comprising from 40 phr to 70 phr of a reinforcing filler, said reinforcing filler comprising at least 10 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, which is formed by preferably metallic and extensible reinforcing elements (called elastic reinforcing elements). It may also include a layer of metallic filaments or cords with low extensibility, which form an angle between 45° and 90° with the circumferential direction. 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 form a triangular reinforcement, which has very little deformation under the various stresses it undergoes, and the chafer ply is basically used to absorb the lateral compressive forces applied to all the reinforcing elements in the tire crown area.

[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] Circumferential reinforcing elements are reinforcing elements that form 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 a tire is the direction tangent to the outer circumference of the tire and defined by the direction of travel of the tire.

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

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

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

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

[0011] The circumferential median plane or the equatorial plane is a plane that is perpendicular to the axis of rotation of the tire and divides 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 measurements are carried out at a temperature of 23 °C and a relative humidity of 50% (standard ISO 23529) using a tensile testing machine of the INSTRON type. The conditions for measuring and using the results to determine the elongation and the stress are as described in the 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 amount of compound available and usable, particularly 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 referred to as "road tires" are designed to travel longer distances at higher speeds. Since the wear on the tires is reduced, this combination of driving conditions for such tires undoubtedly enables an increase in the number of kilometers traveled; on the other hand, the durability of such tires, particularly 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 following: cracks appear in the rubber and propagate at these ends.

[0016] In order to improve the durability of the crown reinforcement of the type of tire under study, solutions have been proposed that relate to the structure and quality of the rubber compound layer and / or the forming element 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 ply 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 carcass 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 carcass 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 in order 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 so as to form a coil with a laying angle relative to the circumferential direction of less than 2.5°.

[0023] In addition, 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] For those skilled in the art, it is also a known practice to increase the number of plies constituting the crown reinforcement in order to improve the durability of the tires with respect to these impact loads.

[0025] The presence of one or more additional reinforcement element layers results in a greater tire mass and a higher tire manufacturing cost.

[0026] A tire is also known from document WO 2017 / 149223, in which the crown reinforcement of the tire is lightened while also improving the durability properties of the tire with respect to such impact loads. However, the inventors have found that when traveling on a ground that exerts a great stress on the tire, the durability performance of such a tire may be reduced (especially at the shoulders of the tire), for example, under particularly severe driving conditions combining vehicle speed, the load borne by the tire, and the nature of the ground. In fact, for example, when traveling at a relatively high speed on a ground of the type supplied to construction sites, which is very demanding on the tire, a reduction in durability performance can be observed. Summary of the Invention

[0027] Therefore, the inventors set themselves the task of providing a tire for "heavy-duty" vehicles (such as vehicles of the "construction site supply" type), which has a limited total mass and whose durability performance with respect to the impact loads experienced by the tread is improved regardless of the nature of the ground and the driving conditions, and which exhibits improved performance in terms of rolling resistance.

[0028] According to the present invention, this object has been achieved by a tire comprising a radial carcass reinforcement intended to be mounted on a deep groove rim of the 15° deep groove type, the tire comprising a crown reinforcement, the crown reinforcement comprising two working crown layers and at least one circumferential reinforcement element layer, each working crown layer being formed by reinforcement elements which are inserted between two surface layers of rubber compound, cross from one layer to the other, and form an angle (α1, α2) greater than 8° with the circumferential direction, the angles α1 and α2 being oriented on either side of the circumferential direction respectively, 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, the tread being connected to two beads via two sidewalls, the two working crown layers and the at least one circumferential reinforcement element layer being the only layers used to form the crown reinforcement over at least 75% of the axial width of the crown reinforcement, the absolute value of the angle α2 formed by the reinforcement elements of the radially outermost working crown layer with the circumferential direction being greater than the angle α1 formed by the reinforcement elements of the radially innermost working crown layer with the circumferential direction, the absolute value of the difference between the absolute values of the angles α2 and α1 being greater than 7°, and the average angle α satisfying the following relationship:

[0029] 13 + 131*exp(-L / 100) < α < 28 + 110*exp(-L / 100),

[0030] α is defined by the relation α = Arctan((tan(|α1|)*tan(|α2|))1 / 2), L is the maximum width of the tire measured in the axial direction and expressed in mm, and the composition comprised in the rubber compound forming said layer C comprises from 40 phr to 70 phr of reinforcing filler, said reinforcing filler comprising at least 10 phr of pyrolytic carbon black.

[0031] Within the meaning of the present invention, a deep groove rim or a safety bulge deep groove rim of the 15° deep groove type is a one-piece rim as defined in the ETRTO, in which the seat intended to receive the tire bead has a truncated conical shape, the angle formed with the axial direction being substantially equal to 15°. These seats are also extended by a rim flange with a reduced height compared to the flange of a flat rim (the rim seat of which has a substantially cylindrical shape).

[0032] 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).

[0033] In certain embodiments, the composition comprises from 40 phr to 70 phr of reinforcing filler, said 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 comprise any inorganic reinforcing filler and other organic reinforcing fillers).

[0034] The reinforcing filler may be as described below.

[0035] 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 a material) of a material comprising at least one carbon-based polymer and carbon black (hereinafter called the material to be pyrolyzed). Whatever its form, whether powder, granule, strip or any other form, and whether in a crosslinked state or not, the physical state of the material to be pyrolyzed provided is not important.

[0036] Preferably, the material to be pyrolyzed may 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 tires, non-pneumatic tires, industrial conveyor belts, conveyor belts, rubber gaskets, rubber hoses, shoe soles and windshield wipers. Even more preferably, the pyrolytic carbon black usable within the scope of the present invention is carbon black obtained by the pyrolysis process of a material to be pyrolyzed originating from manufactured articles selected from pneumatic tires and non-pneumatic tires.

[0037] Within the scope of the present invention, pyrolysis means any type of thermal decomposition carried out under anaerobic conditions, the raw material of which is the material to be pyrolyzed as defined above. Thus, pyrolytic carbon black differs 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 derived from coal or natural sources.

[0038] The pyrolytic carbon black that can be used within the scope of the present invention differs particularly 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". With respect to the total weight of the "furnace black", the ash content of the "furnace black" is less than 1% by weight.

[0039] Preferably, with respect 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, still more preferably less than 22% by weight.

[0040] Preferably, with respect 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.

[0041] With respect to the total weight of the "furnace black", the sulfur content of the "furnace black" is less than 1.2% by weight.

[0042] Preferably, with respect 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.

[0043] With respect 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.

[0044] Preferably, the ST SA 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 in the range of 20 m 2 / g to 200 m 2 / g, more preferably in the range of 30 m 2 / g to 90 m 2 / g.

[0045] 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.

[0046] The ash content was determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the following protocol. Prior to each series of measurements, the platinum dish was pre-determined and the tare weight of the platinum dish was weighed to within 0.1 mg, and the mass was designated as P0. A 5 g sample of pyrolytic carbon black weighed to within 0.1 mg was placed into the platinum dish; this weight 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:

[0047]

[0048] 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 performing the above protocol. Approximately 100 mg of ash (test sample) was taken and placed into a PFA (Perfluoroalkoxy) tube for a HotBlock hot plate. 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 hydrofluoric acid) using ultrapure water. The solution was diluted to the mark using ultrapure water. 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, prior to analysis by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), the diluted solution was filtered through a 0.45 μm GHP syringe filter. Prior to analysis of 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 commercially available solution with a certified zinc concentration of 1 g / l in a 100 ml volumetric flask.

[0049] 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 is analyzed by ICP - AES at a wavelength of λZn = 202.613 nm. For each standard concentration (c), the intensity IZn of the zinc signal is plotted on a curve of IZn = f(c), which corresponds to a calibration line (of the y = ax + b type). Then, the sample solution of unknown concentration (diluted solution) is measured under the same conditions as the standard samples. The measured intensity is related to the concentration using the previously obtained calibration line. Since the sample and volume are pre - recorded, the concentration [c] is directly obtained by software. 灰分 (in mass %). The zinc concentration [c] in the pyrolytic carbon black is obtained by the following equation 炭黑 (in mass %):

[0050] [c] 炭黑 = [c] 灰分 * 100 * ash content %

[0051] The sulfur content in the pyrolytic carbon black is 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 boats are cleaned and the furnace is calibrated. The boats used for the LECO furnace are pre - cleaned: this involves analyzing an empty boat under the same conditions as the sample. A calibration curve is prepared based on a commercial standard sample called "BBOT" (whose purity is greater than 99.99% and ensures the contents of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S)). 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 boats. The standard sample / boat assembly is placed into the combustion furnace and adjusted to 1350 °C under pure oxygen. The combination of the furnace temperature and the analysis flow rate causes the combustion of the sample and releases sulfur and / or carbon in the form of SO2(g). After 20 s, oxygen starts to flow through the lance, thus accelerating the combustion of difficult - to - burn materials. The sulfur and / or carbon in the form of SO2(g) is entrained by the oxygen flow through the infrared detection unit. The software of the instrument plots a straight line that relates the mass of the introduced standard sample to the response (area) observed on the detector. Thus, the calibration line is obtained. After thoroughly cleaning the sampling equipment, weigh approximately 80 ± 5 mg of the pyrolytic carbon black and place it into the boat used for the LECO furnace.

[0052] The area of the SO2 peak observed is related to the concentration through the calibration line. Using the mass of the sample placed in the boat, the instrument software then calculates the mass % of sulfur in the sample.

[0053] Pyrolytic carbon black is sold, for example, by BlackBear under the reference number "BBCT30" or by Scandinavian EnviroSystems under the reference number "P550".

[0054] According to ETRTO, the maximum width L of the tyre is measured on a tyre mounted on its nominal rim and inflated to its nominal pressure and is expressed in millimetres.

[0055] The angles α1 and α2 (expressed in degrees) are measured in the cross-section of the tyre. According to the invention, the angles are measured in the circumferential median plane.

[0056] Advantageously, according to the invention, the maximum value of tan(δ) of the layer C (designated as tan(δ) max ) is less than 0.130, preferably less than 0.100.

[0057] The loss factor tan(δ) is a dynamic property of the rubber compound layer. It is measured on a viscometer (Metravib VA4000) according to the standard ASTM D 5992-96. The response of a sample of the vulcanised composition (cylindrical specimen with a thickness of 2 mm and a cross-section of 78 mm 2 ) subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz at a temperature of 100 °C is recorded. 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 value of tan(δ) is shown, designated as tan(δ) max .

[0058] 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 vulcanised 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.

[0059] The rolling resistance is the resistance that occurs when the tyre rolls. The rolling resistance is represented by the hysteresis losses associated with the deformation of the tyre during rotation. The frequency value associated with the rotation of the tyre corresponds to the value of tan(δ) measured between 30 °C and 100 °C. Thus, the value of tan(δ) at 100 °C corresponds to the rolling resistance index when the tyre rolls.

[0060] The rubber compound layer C can decouple the working crown layer, so that the shear stress is distributed over a greater thickness.

[0061] Within the meaning of the present invention, a working crown ply is said to be joined 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 corresponding upper and lower generatrices of the reinforcing elements.

[0062] 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.

[0063] According to a preferred embodiment of the invention, the rubber compound layer C is an elastomeric compound based on natural rubber or on synthetic polyisoprene having predominantly cis-1,4 bonds and optionally on at least one other diene elastomer, natural rubber or synthetic polyisoprene being present in a major amount relative to the content of one or more other diene elastomers used in the blend.

[0064] Among the diene elastomers which can be used in blend with natural rubber or synthetic polyisoprene having predominantly cis-1,4 bonds, mention may be made preferably of polybutadiene (BR) having predominantly 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 such that an oxycarbonyl or carboxyl functional group or an amine functional group is grafted onto the chain or the chain ends by the action of, for example, dimethylaminobenzophenone or diethylaminobenzophenone. In the case of a blend of natural rubber or synthetic polyisoprene having predominantly cis-1,4 bonds with one or more of the abovementioned diene elastomers, natural rubber or synthetic polyisoprene is preferably used in a major amount, more preferably in an amount greater than 70 phr.

[0065] Also preferably, in addition to the pyrolytic carbon black, the rubber compound layer C further comprises a reinforcing filler consisting of:

[0066] a) carbon black used in an amount between 30 phr and 60 phr, preferably between 30 phr and 50 phr,

[0067] b) or a BET specific surface area between 30 m 2 / g and 260 m 2a white filler of the silica and / or alumina type with SiOH and / or AlOH surface functional groups between / g, said white filler being selected from precipitated silica or pyrogenic silica, alumina or aluminosilicate, or carbon black modified during or after synthesis, and being used in a content between 30 phr and 60 phr, preferably between 30 phr and 50 phr,

[0068] 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 30 phr and 60 phr, preferably between 30 phr and 50 phr.

[0069] 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 standard NFT 45007 of November 1987.

[0070] 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 an example of a preferred coupling agent, alkoxysilane sulfides of the bis(3-trialkoxysilylpropyl) polysulfide type can be mentioned, in particular bis(3-triethoxysilylpropyl) tetrasulfide sold by Degussa under the names Si69 (pure liquid product) and X50S (solid product (blended with N330 carbon black at 50 / 50 by weight)). As an example of a covering agent, fatty alcohols, alkylalkoxysilanes (such as hexadecyltrimethoxysilane or hexadecyltriethoxysilane sold by Degussa under the names Si116 and Si216 respectively), diphenylguanidine, polyethylene glycol or silicone oil optionally modified by OH or alkoxy functional groups can be mentioned. 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 accounts for all of the reinforcing filler, and between 1 / 100 and 20 / 100 when the reinforcing filler consists of a blend of carbon black and transparent filler.

[0071] As other examples of reinforcing fillers having the above morphology and SiOH and / or AlOH surface functional groups of silica and / or alumina type materials 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 aluminium to the feedstock oil of the furnace or after synthesis by adding an acid to an aqueous suspension of the carbon black in a solution of sodium silicate and / or sodium aluminate, 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, 6 - 9 May 1997), and those in patent application EP-A-0799 854.

[0072] When using a transparent filler as the sole reinforcing filler, hysteresis properties and cohesion properties are obtained by using precipitated silica or pyrogenic silica or precipitated alumina or aluminosilicate having a BET specific surface area between 30 m 2 / g and 260 m 2 / g. 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.

[0073] The results obtained with the tyres according to the invention have effectively demonstrated that, regardless of the nature of the ground and the driving conditions, in the case of weight reduction of the tyre crown reinforcement, the performance in terms of durability can be improved and the performance in terms of rolling resistance can be improved. Moreover, the weight reduction of the tyre crown reinforcement is accompanied by a simplification of the manufacturing process and a reduction in the manufacturing cost.

[0074] Unexpectedly, the results effectively show that the weight of the tyre according to the invention can be reduced by reducing the number of layers constituting the tyre crown reinforcement, while improving in particular the durability of the tyre crown with respect to the impact loads to which the tread edges (especially at the shoulders of the tyre) are subjected, regardless of the nature of the ground and the driving conditions.

[0075] In particular, those skilled in the art know that, in order to improve the durability performance of the tyre crown reinforcement with respect to this type of impact load, the usual practice is to increase the number of layers of reinforcing elements and to increase the stiffness of the compound used to decouple the ends of the reinforcing element layers.

[0076] The inventors believe that these results can be explained by the fact that the angle formed by the reinforcing elements of the radially innermost working crown layer with the circumferential direction is an angle whose absolute value is smaller than the angle formed by the reinforcing elements of the radially outermost working crown layer, and there is pyrolytic carbon black used as a filler within layer C. They found that the smaller angle of the reinforcing elements of the radially innermost working crown layer seems to cause a delay in the absorption of tension by the reinforcing elements when such impact loads occur. Also, the inventors have demonstrated that the presence of pyrolytic carbon black in the rubber compound constituting layer C results in a higher elongation at break value for said rubber compound than for more common compounds. Generally, if the impact load is the impact load observed when driving over a stony ground, more specifically impacting the shoulder of the tire, the breakage of the reinforcing elements (if such breakage occurs) is found in the radially innermost layer, more specifically at its ends. These observations seem to indicate that in the face of this type of attack, the difference in the angles of the reinforcing elements between the two working crown layers and the presence of pyrolytic carbon black in the rubber compound constituting layer C enable the improvement of the durability performance of the tire and, at the same time, reduce the number of layers in the crown reinforcement.

[0077] The value by which the average angle α increases compared to the more commonly known values of conventional tires for this type of application further improves certain properties of the tire. The presence of said at least one circumferential reinforcing element layer allows the average angle α of the reinforcing elements of the two working crown layers to be greater than the average angle defined by the reinforcing elements of the two working crown layers in more conventional tires. This is because the circumferential stiffness provided by the presence of said at least one circumferential reinforcing element layer enables an increase in the average angle formed by the reinforcing elements of each working crown layer with the circumferential direction. Thus, when driving under heavy loads or when the angle formed with the forward direction of travel is very large, said average angle seems to be beneficial for the operation of the tire, especially its maneuverability. Therefore, the inventors have demonstrated that the dynamic performance of the tire (especially the cornering stiffness) is maintained or even improved regardless of the use.

[0078] The inventors also believe that they have revealed the following fact: the absolute value of the angle formed by the reinforcing elements of the radially innermost working crown layer with the circumferential direction is smaller than the angle formed by the reinforcing elements of the radially outermost working crown layer, resulting in the reinforcing elements of the radially innermost working layer being subjected to high stress loads under extreme stress loads (especially when driving at a constant speed), which may have an adverse impact on the performance in terms of durability.

[0079] The use of pyrolytic carbon black in layer C also results in a reduction in the stiffness of the rubber compound layer C. This lower stiffness is another factor that is adverse to the durability of this radially innermost working crown layer when subjected to high stress (such as when driving at a constant speed) compared to more common compounds.

[0080] More conventional tire designs effectively provide a layer of rubber compound disposed between the ends of the working crown ply, having a secant modulus of elasticity at 10% elongation greater than 8.5 MPa, particularly in order to be able to limit the shear stress between the ends of the working crown ply, which has a very low circumferential stiffness at its ends. This modulus (which is typically even greater than 9 MPa) prevents cracking from starting and spreading in the rubber compound at the ends of the working crown ply (more particularly at the ends of the narrowest working ply).

[0081] The inventors have demonstrated that the circumferential reinforcement element ply can select a rubber compound for layer C with a lower modulus of elasticity without compromising the durability of the tire.

[0082] The inventors have also demonstrated that the cohesion of layer C according to the invention remains satisfactory.

[0083] 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 ) over a temperature 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 dwell time is equal to the pulse duration; the frequency of the signal is on average approximately 10 Hz.

[0084] The measurement comprises three parts:

[0085] · Adaptation of the "PS" specimen to 1000 cycles at 27% deformation.

[0086] · 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, and 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.

[0087] · Measurement of 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".

[0088] The inventors have specifically demonstrated that the presence of at least one circumferential reinforcing element layer helps to reduce the variation in the cohesion of layer C. This is because, in more conventional tire designs, a layer of rubber compound disposed between the ends of the working crown layer typically has a secant modulus of elasticity at 10% elongation greater than 8.5 MPa, which causes a change in the cohesion of the rubber compound layer disposed 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 change in the cohesion of layer C. Therefore, the inventors believe that the cohesion of layer C (which is less than that in more conventional tire designs) is satisfactory in the tire design according to the present invention.

[0089] In addition, the combination of the lower stiffness compound of layer C based on pyrolytic carbon black and the circumferential reinforcing element layer helps to limit the temperature rise generated when subjected to shear stress.

[0090] Moreover, the weight reduction of the crown reinforcement results in a decrease in the total thickness of the tire crown. The inventors have also demonstrated that when driving at a constant speed, the temperature of the tire crown is lower compared to tires with more conventional designs.

[0091] The combination of the weight-reduced crown reinforcement according to the present invention and the lower stiffness compound of layer C based on pyrolytic carbon black (a compound based on pyrolytic carbon black may seemingly impair the durability of the tire under extreme use conditions) actually enables the durability performance of the tire to be maintained or even improved. The inventors believe that this result can be explained as on the one hand, the weight-reduced design of the crown reinforcement has a cumulative effect on the tire crown temperature, and on the other hand, in the presence of a circumferential reinforcing element layer, the presence of a lower stiffness compound based on pyrolytic carbon black in layer C, and the combination of these factors seems to reverse the expected effect on durability.

[0092] Compared to tires with more conventional designs, the performance in terms of rolling resistance is also improved relative to these not-too-high operating temperatures.

[0093] Preferably, the thickness of the rubber compound layer C measured at the ends of the narrowest working crown layer among the two working crown layers considered is preferably between 30% and 80% of the total thickness of the rubber compound between the cord generatrices of each of the two working 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 layers and is also disadvantageous in terms of cost.

[0094] Also preferably, the axial width D of the rubber compound layer C between the axially innermost end of the rubber compound layer C and the end of the axially narrowest working crown layer satisfies:

[0095] 3.φ2 ≤ D ≤ 25.φ2

[0096] Where φ2 is the diameter of the reinforcing element of the axially narrowest working tread crown layer. This relationship defines the joint area between the rubber compound layer C and the axially narrowest working tread crown layer. Such a joint that is less than three times the diameter of the reinforcing element of the axially narrowest working layer may not be sufficient to obtain the detachment of the working tread crown layer, especially in order to obtain a reduction in stress at the ends of the axially narrowest working tread crown layer. Such a joint value that is greater than twenty times the diameter of the reinforcing element of the axially narrowest working layer may result in an excessive reduction in the camber stiffness of the tire crown reinforcement.

[0097] Preferably, the axial width D between the axially innermost end of the rubber compound layer C and the end of the axially narrowest working tread crown layer is greater than 5 mm.

[0098] The present invention also preferably provides a rubber compound layer C at the axially outer end of the axially narrowest working tread crown layer, and the thickness of the rubber compound layer C satisfies the following relationship for the radial distance d between the two working tread crown layers separated by the rubber compound layer C:

[0099] 3 / 5.φ2 < d < 5.φ2

[0100] Where φ2 is the diameter of the reinforcing element of the axially narrowest working tread ply.

[0101] The distance d is measured from cord to cord (i.e., between the cords of the first working layer and the cords of the second working layer). In other words, the distance d includes the thickness of the rubber compound layer C and the corresponding thicknesses of the rubber surface compound along the radial direction outside the cords of the radially inner working layer and inside the cords of the radially outer working layer.

[0102] Various thickness measurements are made on the meridian cross-section of the tire, so the tire is in an uninflated state.

[0103] Advantageously according to the present invention, the fracture potential index F2 / FR2 of the radially outermost working layer is less than 1 / 6, where:

[0104] FR2 is the breaking force of each cord of the radially outermost working layer under uniaxial extension,

[0105] F2 = p2*Tc*[(tan(|α1|) / (tan(|α1|)+tan(|α2|))) / cos 2 (|α2|)+C F , where

[0106] Tc = 0.078*P*Rs*(1-(Rs 2 -R L 2) / (2*Rt*Rs)),

[0107] P is the nominal inflation pressure of the tire according to ETRTO,

[0108] C F = 0.00035 * (min((L - 80) / sin(|α1|), (L - 80) / sin(|α2|), 480) - 480),

[0109] p2 is the pitch of the laying of the reinforcing elements of the radially outermost working tread ply, the pitch being measured perpendicular to the reinforcing elements at the circumferential mid-plane,

[0110] Rs = Re - Es,

[0111] Re is the outer radius of the tire, measured at the radially outermost point on the tread surface of the tire, the surface being extrapolated to fill any voids that may be present,

[0112] Es is the radial distance between the radially outermost point of the tire and its orthogonal projection on the radially outer surface of the reinforcing elements of the radially innermost working tread ply,

[0113] R L is the average value of the radii of the axially outermost points of the main part of the carcass reinforcement ply on each side of the tire,

[0114] Rt is the radius of the circle passing through the following three points, the three points being located on the outer tread surface outside the void and defined by axial distances from the shoulder end equal to 1 / 4, 1 / 2, and 3 / 4 of the axial width of the tread, respectively.

[0115] The thickness Es and the pitch p2 are measured in the cross-section of the tire and are expressed in millimeters.

[0116] According to the present invention, the meridian cross-section of the tire is defined such that the centroids of the bead wires form an axially oriented straight line, the distance between the centroids being equal to the width of the nominal rim J increased by 20 mm and minus twice the distance measured axially between the centroid of the bead wire and the point on the outer surface of the tire.

[0117] The inventors have also found that by choosing the absolute value of the difference between the absolute values of the above-mentioned angles α1 and α2 and combining it with the average angle α and the fracture potential index F2 / FR2 (as defined in this advantageous embodiment of the present invention), it is possible to dispense with the protective layer that is usually radially mounted on the outside of other layers of the crown reinforcement. Such a layer is usually present so that it can be sacrificed in the case where the tire is subjected to an attack of the cutting type, which can damage the integrity of the metal reinforcement elements through a corrosion phenomenon related to the fatigue of the reinforcement elements. The inventors have actually found that when the tire is inflated or when it is used in normal driving, the reinforcement elements of the radially outermost working crown layer of the tire according to the present invention are subjected to less stress than the reinforcement elements of the radially outermost working crown layer of a more conventional tire; the more conventional tire shows a smaller angular difference in absolute value between the reinforcement elements of the different working layers, the absolute value of the angle formed by the reinforcement elements of the radially innermost working layer being greater than or equal to the angle formed by the reinforcement elements of the radially outermost working layer, and the fracture potential index F2 / FR2 being higher. Therefore, the reinforcement elements of the radially outermost working crown layer of the tire according to the present invention have significantly better durability than those of a more conventional tire; thus, the inventors have found that the protective layer can be omitted, which helps to reduce the weight of the tire and limit the temperature rise in the crown area of the tire.

[0118] According to a preferred embodiment of the present invention, the absolute value of the difference between the absolute values of the angles α2 and α1 is greater than or equal to 10°, preferably greater than 14°. According to this embodiment and based on the explanations provided above, the durability performance of the reinforcement elements of the radially outermost working layer can be further improved and / or the performance of the tire with respect to impact loads (such as the impact loads experienced when driving over a stony ground) can be further improved.

[0119] Preferably, the absolute value of the difference between the absolute values of the angles α2 and α1 is less than 25°, more preferably less than 20°. Above these values, the tire is prone to uneven wear under certain use conditions.

[0120] Also advantageously according to the present invention, the fracture potential index F2 / FR2 of the radially outermost working layer is less than 1 / 8. Such a fracture potential index F2 / FR2 further helps to improve the durability performance of the reinforcement elements of the radially outermost working layer during tire use.

[0121] Preferably according to the present invention, the fracture potential index F1 / FR1 of the radially innermost working layer is less than 1 / 3, where:

[0122] FR1 is the breaking force of each cord of the radially innermost working layer under uniaxial extension,

[0123] F1 = p1 * Tc * [(tan(|α2|) / (tan(|α1|) + tan(|α2|))) / cos 2 (|α1|) + C F , where

[0124] p1 is the pitch of the laying of the reinforcing elements of the radially innermost working tread layer, the pitch being measured perpendicular to the reinforcing elements at the circumferential mid-plane.

[0125] Also preferably, the fracture potential index F1 / FR1 of the radially innermost working layer is at least 30% higher than the fracture potential index F2 / FR2 of the radially outermost working layer.

[0126] According to an advantageous embodiment of the invention, the axially widest working tread layer is located radially inside another working tread layer.

[0127] According to a preferred embodiment for optimizing the reduction of the tire crown thickness according to the invention, the two working tread layers and the at least one circumferential reinforcing element layer are the only layers used to form the crown reinforcement over the entire axial width of the crown reinforcement.

[0128] According to a variant of the embodiment of the invention, at least one surface layer of at least one working tread layer is made of a rubber compound, the composition of which comprises 40 phr to 70 phr of reinforcing filler, the reinforcing filler comprising at least 10 phr of pyrolytic carbon black.

[0129] According to a preferred embodiment of this variant of the invention, the rubber compounds of the surface layers of the two working tread layers have a composition comprising 40 phr to 70 phr of reinforcing filler, the reinforcing filler comprising at least 10 phr of pyrolytic carbon black.

[0130] Generally, the elastic secant modulus of the surface layer of the working tread layer at 10% elongation is greater than 10 MPa. Such an elastic modulus is required to be able to limit the compression of the reinforcing elements of the working tread layer, especially 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 the compression of the reinforcing elements of the working tread layer.

[0131] 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 tread layer as described above.

[0132] In addition, the combination of the pyrolytic carbon black-based rubber compound of the calendered surface layer of the working tread layer and the circumferential reinforcing element layer helps to limit the temperature rise generated when subjected to shear stress, like layer C.

[0133] Accordingly, the inventors have also found that in the presence of the circumferential reinforcement element layer, the combination of the pyrolytic carbon black-based rubber compound of the calendered surface layer of the working crown layer, layer C according to the invention, and the weight reduction design of the crown reinforcement in the variant of this embodiment of the invention enables the durability performance of the tyre to be maintained, or even improved, and even more significantly improved. This unexpected result is due in particular to the combined effect on the tyre crown temperature.

[0134] According to a preferred embodiment of this variant of the invention, the at least one surface layer of the at least one working crown layer is an elastomeric compound based on natural rubber or on synthetic polyisoprene having mainly cis-1,4 bonds and optionally based on at least one other diene elastomer, and in the case of a blend, the natural rubber or synthetic polyisoprene is present in a major amount relative to the content of the one or more other diene elastomers used.

[0135] Also preferably, in addition to the pyrolytic carbon black, the at least one surface layer of the at least one working crown layer further comprises a reinforcing filler consisting of:

[0136] a) carbon black used in an amount between 30 phr and 60 phr, preferably between 30 phr and 50 phr,

[0137] 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 aluminium silicate, or carbon black modified during or after synthesis, and used in an amount between 30 phr and 60 phr, preferably between 30 phr and 50 phr,

[0138] 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 30 phr and 60 phr, preferably between 30 phr and 50 phr.

[0139] According to one embodiment of the invention, the elastomeric compound constituting the at least one surface layer of the at least one working crown layer is the same as the elastomeric compound of layer C arranged between at least the ends of the two working crown layers.

[0140] According to an advantageous embodiment variant of the invention, the axial width of the circumferential reinforcement element layer is greater than 0.5×S.

[0141] S is the maximum axial width of the tyre when the tyre is mounted on its service rim and inflated to its recommended pressure.

[0142] The axial width of the layer of reinforcing elements is measured in the cross-section of the tyre, the tyre being in the deflated state.

[0143] According to a preferred embodiment of the invention, the circumferential layer of reinforcing elements is arranged radially between two working crown layers.

[0144] According to this embodiment of the invention, the circumferential layer of reinforcing elements can limit to a greater extent the compressive action on the reinforcing elements of the carcass reinforcement than a similar layer located radially outside the working layer. It is preferably separated radially from the carcass reinforcement by at least one working layer, thereby limiting the stress on the said reinforcing elements and avoiding excessive fatigue of the reinforcing elements.

[0145] Also advantageously according to the invention, the axial width of the working crown layer adjacent in the radial direction to the said at least one circumferential layer of reinforcing elements is greater than the axial width of the said at least one circumferential layer of reinforcing elements, and preferably, on each side of the equatorial plane and in the immediate axial extension of the said at least one circumferential layer of reinforcing elements, the working crown layer adjacent to the said at least one circumferential layer of reinforcing elements 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.

[0146] According to an advantageous embodiment of the invention, the reinforcing elements of the at least one circumferential layer of reinforcing elements are metal reinforcing elements having a secant modulus at 0.7% elongation between 10 GPa and 120 GPa and a maximum tangent modulus of less than 150 GPa.

[0147] 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, even more preferably less than 80 GPa.

[0148] Also preferably, the maximum tangent modulus of the reinforcing elements is less than 130 GPa, more preferably less than 120 GPa.

[0149] The above moduli are measured on a curve of tensile stress as a function of elongation (the curve being determined using a preload of 20 MPa), the tensile stress corresponding to the measured tension corrected for the metal cross-section of the reinforcing elements. The measurement is made on cords taken from the tyre on a portion of the circumferential layer of reinforcing elements extending axially towards the inside of the layer with an axial width of 50 mm from the axial end of the layer.

[0150] The modulus of the same reinforcing element can be measured on a curve of tensile stress versus elongation (the curve being determined using a preload of 10 MPa), the tensile stress corresponding 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 consisting of metal and rubber, the rubber having penetrated the reinforcing element in particular during the curing of the tyre phase.

[0151] According to this constitution related to the entire cross-section of the reinforcing element, the reinforcing elements in the axially outer part and the intermediate part of at least one circumferential reinforcing element layer are metal reinforcing elements, the metal reinforcing elements having a secant modulus at 0.7% elongation between 5 GPa and 60 GPa and a maximum tangent modulus of less than 75 GPa.

[0152] 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, even more preferably less than 40 GPa.

[0153] Also preferably, the maximum tangent modulus of the reinforcing element is less than 65 GPa, more preferably less than 60 GPa.

[0154] 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 tensile stress versus relative elongation thereof shows a gentle gradient for smaller elongations and a steeper, substantially constant gradient for larger elongations.

[0155] The above respective characteristics of the reinforcing element are measured on a reinforcing element taken from a tyre.

[0156] 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 stranded cord is composed of 21 basic filaments of formula 3×(1 + 6), in which three strands are twisted together, each strand is composed of 7 filaments, the diameter of a single filament forming the middle core is equal to 26 / 100 mm, and the diameters of the six winding filaments are 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 tensile stress varying with 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 tensile stress varying with elongation determined using a 10 MPa preload (the tensile stress corresponds to the measured tension corrected for the overall 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.

[0157] Similarly, another example of a reinforcing element is the assembly of formula 21.28, and the structure of formula 21.28 is 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, and these moduli are measured on the curve of tensile stress varying with 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 tensile stress varying with elongation determined using a 10 MPa preload (the tensile stress corresponds 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.

[0158] Using such a reinforcing element in at least one circumferential reinforcing element layer is particularly capable of maintaining a satisfactory stiffness of the layer (even after the forming and curing steps of the conventional production method).

[0159] According to a second embodiment of the present invention, the circumferential reinforcing element may be formed by non-extendable metal elements which are cut so as to form portions having a length much smaller 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 for the most extensible working crown ply under the same conditions. Such an embodiment makes it possible to impart to the circumferential reinforcing element layer a certain modulus in a simple manner, which modulus can be easily adjusted (by choosing the spacing between the portions of the same row), but which is always less than the modulus of a layer consisting of the same but continuous metal elements, the modulus of the additional layer being measured on a vulcanized layer of cut-out elements taken from the tyre.

[0160] According to a third embodiment of the present 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 for the most extensible working crown ply under the same conditions.

[0161] The metal element is preferably a steel cord.

[0162] According to a preferred embodiment of the present invention, the reinforcing element of the working crown ply is a non-extendable metal cord. Description of the drawings

[0163] By reference Figure 1 to the description of the exemplary embodiments of the present invention given below, other details and advantageous features of the present invention will become apparent, the Figure 1 showing a meridional view of a tyre design according to an embodiment of the present invention.

[0164] For easier understanding, Figure 1 the drawing is not to scale. The drawing shows only half of the tyre, which extends symmetrically about an axis XX' which represents the circumferential median plane or equatorial plane of the tyre. Detailed description

[0165] In Figure 1 it, the dimensions of the tyre 1 are 315 / 70R 22.5. The tyre 1 comprises a radial carcass reinforcement 2 anchored in two beads (not shown in the figure). The carcass reinforcement is formed by a single layer of metal cords. This carcass reinforcement 2 is hoop-reinforced by a crown reinforcement 4 which, radially from the inside outwards, is formed by:

[0166] - a first working layer 41 formed by metal cords oriented at an angle of 18°,

[0167] - The circumferential reinforcement element layer 43, which is formed of steel metal cord of type 21.23,

[0168] - The second working layer 42 formed of metal cord, the metal cord being oriented at an angle equal to 30° and crossing the metal cord of layer 41, and the cords of each of the working layers 41, 42 being oriented on both sides in the circumferential direction.

[0169] The metal cords of the reinforcement elements constituting the two working layers are cords of formula 9.35. They are distributed within each working layer at a distance equal to 2.2 mm between the reinforcement elements, said distance being measured along a direction perpendicular to the bisector of the cord.

[0170] The crown reinforcement itself is covered by the tread 5.

[0171] The tire is inflated to a pressure of 9 bar.

[0172] The axial width L of the first working layer 41 41 is equal to 252 mm.

[0173] The axial width L of the second working layer 42 42 is equal to 232 mm.

[0174] The axial width L of the circumferential reinforcement element layer 43 43 is equal to 194 mm.

[0175] The axial width L5 of the tread is equal to 266 mm.

[0176] The maximum axial width L is equal to 315.9 mm.

[0177] According to the invention, the first rubber compound layer C provides a decoupling of the ends of the working crown layers 41 and 42.

[0178] 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 by the axial width D of the layer C between the axial inner end of the 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 reinforcement element of the working crown layer 42, the diameter φ2 being equal to 1.35 mm. The radial distance D is equal to 19 mm, i.e. approximately 14 times the diameter φ2 of the reinforcement element of the working crown layer 42.

[0179] The combined mass of the two working layers 41, 42 and the circumferential reinforcement element layer 43 (including the mass of the metal cord and the surface compound) thus totals 10.1 kg.

[0180] According to the invention, the layer C is made of an elastomeric compound containing pyrolytic carbon black.

[0181] The difference between the angle formed by the cords of the first working crown ply and the circumferential direction and the angle formed by the cords of the second working crown ply and the circumferential direction is equal to 12°.

[0182] The average angle is equal to 23.4°, and is significantly between 18.6° and 32.7°.

[0183] The measured value of Re is equal to 508.5 mm.

[0184] The measured value of Es is equal to 22.5 mm.

[0185] The average value R of the measured radius L is equal to 401.3 mm.

[0186] The value Rt determined on the tire is equal to 792 mm.

[0187] The calculated value of Tc is equal to 308 N / mm.

[0188] C F The calculated value of is equal to -0.0029.

[0189] The value of F1 is equal to 477.2 N.

[0190] The value of F2 is equal to 323.3 N.

[0191] The breaking forces FR1 and FR2 of the reinforcing elements of the working crown ply are equal to 2950 N.

[0192] The fracture potential index F2 / FR2 is equal to 11%.

[0193] The fracture potential index F1 / FR1 is equal to 16.2%.

[0194] The fracture potential index F1 / FR1 is 48% higher than the fracture potential index F2 / FR2.

[0195] Various tires according to the invention have been compared with various reference tires of the same size.

[0196] The first tire I1 according to the invention has a layer C made of compound 1 and a surface layer made of compound R1.

[0197] The second tire I2 according to the invention has a layer C made of compound 1 and a surface layer.

[0198] The first reference tire T1 differs from the tire I1 according to the invention in the properties of the compound for the layer C, which layers C are made of compound R1.

[0199] 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.

[0200] 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

[0201] The values of the components are expressed in phr (parts by weight per hundred parts of elastomer).

[0202] The pyrolytic carbon black (carbon black RCB) contains 20% ash, 1.8% sulfur, and 4.5% zinc.

[0203] The carbon black N347 contains 0.5% ash, 1% sulfur, and 0% zinc.

[0204] The contents of the various components in Compound I1 other than carbon black are 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.

[0205] The second reference tire T2 differs from the reference tire T1 in that the crown reinforcement they have is formed radially from the inside to the outside by:

[0206] - A first working layer formed of metal cords, the metal cords being oriented at an angle equal to 22° on the same side as the cords of the triangular layer with respect to the circumferential direction,

[0207] - A circumferential reinforcement element layer formed of steel metal cords of type 21.23,

[0208] - A second working layer formed of metal cords, the metal cords being oriented at an angle equal to 18° and crossing the metal cords of the first working layer, and the cords of each layer in the working layer are oriented on both sides of the circumferential direction respectively,

[0209] - A protective layer formed of elastic 6.35 metal cords, wherein the distance between the reinforcement elements measured along the 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.

[0210] The metal cords of the two working layers are cords of type 9.35. They are distributed in each working layer at a distance equal to 2.5 mm between the reinforcement elements, and the distance is measured along the direction perpendicular to the cord bisector.

[0211] The reference tire T2 is inflated to a pressure of 9 bar.

[0212] The axial width of the first working layer is equal to 252 mm.

[0213] The axial width of the second working layer is equal to 232 mm.

[0214] The axial width of the circumferential reinforcing element layer 53 is equal to 194 mm.

[0215] The axial width of the protective layer is equal to 188 mm.

[0216] The combined mass of the working layer, the protective layer and the circumferential reinforcing element layer of the reference tire T2 (including the mass of the metal cord and the surface compound) totals 12.2 kg.

[0217] The absolute value of the difference between the absolute value of the angle formed by the cords of the first working crown layer and the circumferential direction and the absolute value of the angle formed by the cords of the second working crown layer and the circumferential direction is equal to 4°.

[0218] The average angle is equal to 19.9°.

[0219] The value of F1 is equal to 410 N.

[0220] The value of F2 is equal to 424 N.

[0221] The values of F1 and F2 are obtained by finite element simulation. The large number of reinforcing ply layers in the crown makes it impossible to use a simple analytical model.

[0222] The breaking forces FR1 and FR2 of the reinforcing elements of the working crown layer are equal to 2600 N.

[0223] The breaking potential index F2 / FR2 is equal to 16.3%.

[0224] The breaking potential index F1 / FR1 is equal to 15.8%.

[0225] The breaking potential index F1 / FR1 is 3% higher than the breaking potential index F2 / FR2.

[0226] 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.

[0227] Other (especially mechanically - required) durability tests are carried out on a testing machine. A lateral force and a dynamic over - load are applied to the tire in a cyclic manner. The tire according to the invention is tested under the same conditions as those applied to the reference tire.

[0228] The tests thus carried out show that the distances covered by the tire according to the invention and the reference tire in each of these tests are substantially the same.

[0229] 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 over a cylindrical obstacle or indentor tool having a diameter equal to 1.5 inches (i.e., 38.1 mm), with 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, which is the maximum height at which the indentor tool causes 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 T2.

[0230] I1 125 I2 130 Reference T1 120 Reference T2 100

[0231] These results show that, despite the reduction in the weight of the tire (in particular by reducing the mass of its crown reinforcement), the breaking energy of the tread surface of tires I1 and I2 according to the invention under impact loads is higher than that of the tread surface of the reference tire T2 under impact loads and higher than that of the tread surface of tire T1 under impact loads.

[0232] Final durability tests were carried out to reproduce driving conditions combining vehicle speed and particularly adverse ground. Thus, these tests reproduce the extreme conditions specifically for "heavy-duty load" vehicles of the "site supply" type.

[0233] 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 indicated on the tire, followed by a stage of driving on a stony road at 35 km / h for 12 minutes, repeated 25 times.

[0234] The purpose of the stage of driving at low speed on the stony road is to have an adverse effect on durability due to the repeated impact loads on the tread.

[0235] 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.

[0236] At the end of the run, the tire was inspected using speckle shearing interferometry and peeled so that any damage could be analyzed. This is a visual analysis, allowing a 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.

[0237] Fraction I1 115 I2 135 Reference T1 100 Reference T2 100

[0238] At the end of the run, tyres I1 and I2 according to the invention show a lower degree of damage than reference tyres T1 and T2.

[0239] During these final endurance tests, after driving for 2 hours on a circular track at 100 km / h in the first stage, the temperature of the tyre at the end of the tread blocks is measured.

[0240] Temperature I1 90℃ I2 87℃ Reference T1 94℃ Reference T2 99℃

[0241] These results show that the temperature exhibited by the tyres according to the invention is not actually as high as that of the reference tyres.

[0242] In addition, the rolling resistance is measured.

[0243] The rolling resistance of each tyre is measured under the same driving conditions in accordance with United Nations Economic Commission for Europe (UNECE) Regulation No. 117. The measurement results are expressed in kg / t, and a value of 100 is assigned to tyre T1. A value greater than 100 indicates better performance in terms of rolling resistance.

[0244] T1 T2 I1 I2 Rolling resistance 100 98 102 104

[0245] It is clear from these tests that the tyres according to the invention are able to improve the performance in terms of rolling resistance and shock load resistance in a satisfactory manner while exhibiting satisfactory durability performance.

Claims

1. A tire (1) including a radial carcass reinforcement (2) intended to be mounted on a deep groove rim of the 15° deep groove type, said tire including a crown reinforcement (4), said crown reinforcement (4) including 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 (α1, α2) greater than 8° with the circumferential direction, said angles α1 and α2 being oriented on either side of the circumferential direction respectively, 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, wherein: - said two working crown layers (41, 42) and said at least one circumferential reinforcing element layer (43) are the only layers used to form the crown reinforcement (4) over at least 75% of the axial width of the crown reinforcement (5), - the absolute value of the angle (α2) formed by the reinforcing elements of the radially outermost working crown layer (42) with the circumferential direction is greater than the angle (α1) formed by the reinforcing elements of the radially innermost working crown layer (41) with the circumferential direction, - the absolute value of the difference in absolute values between the angle (α2) and the angle (α1) is greater than 7°, - the average angle α satisfies the following relationship: 13 + 131*exp(-L / 100) < α < 28 + 110*exp(-L / 100), α is defined by the relation α = Arctan((tan(|α1|)*tan(|α2|)) 1 / 2 ), where L is the maximum width of the tyre measured in the axial direction and expressed in mm characterized in that the composition of the rubber compound forming said layer C contains 40 phr to 70 phr of reinforcing filler, said reinforcing filler including at least 10 phr of pyrolytic carbon black.

2. The tire according to claim 1, characterized in that, The ash content of said pyrolytic carbon black ranges from 5 wt% to 30 wt%, preferably less than 25 wt%, more preferably less than 22 wt%, relative to the total weight of the pyrolytic carbon black, and 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, The sulfur content of said pyrolytic carbon black is greater than 1.5 wt%, preferably greater than 2 wt%, preferably in the range of 2.5 wt% to 5 wt%, relative to the total weight of the pyrolytic carbon black, and the sulfur content in said 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, The zinc content of said pyrolytic carbon black is greater than or equal to 2 wt%, preferably in the range of 2.5 wt% to 8 wt%, relative to the total weight of the pyrolytic carbon black, and the zinc content is determined by analyzing the ash absorbed in an acidic medium after calcination of 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 claims 1 to 4, characterized in that, Said layer C is an elastomeric compound, said elastomeric compound being based on natural rubber, or on synthetic polyisoprene mainly having cis - 1,4 bonds, and optionally based on at least one other diene elastomer, and in the case of a blend, 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 claims 1 to 5, characterized in that, In addition to the pyrolytic carbon black, the rubber compound layer C further comprises a reinforcing filler consisting of: a) carbon black used in an amount between 30 phr and 60 phr, preferably between 30 phr and 50 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 a content between 30 phr and 60 phr, preferably between 30 phr and 50 phr, 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 30 phr and 60 phr, preferably between 30 phr and 50 phr.

7. The tire (1) according to any one of claims 1 to 6, characterized in that, The fracture potential index F2 / FR2 of the radially outermost working tread layer (42) is less than 1 / 6, where: FR2 is the breaking force of each cord of the radially outermost working tread layer under uniaxial extension, F2 = p2 * Tc * [(tan(|α1|) / ((tan(|α1|) + tan(|α2|))) / cos 2 (|α2|) + C F , where Tc = 0.078 * P * Rs * (1 - (Rs 2 - R L 2 ) / (2 * Rt * Rs)), P is the tire nominal inflation pressure according to ETRTO, C F = 0.00035 * (min((L - 80) / sin(|α1|), (L - 80) / sin(|α2|), 480) - 480), p2 is the spacing of the reinforcing elements laid in the radially outermost working tread layer, measured perpendicular to the reinforcing elements at the circumferential midplane, Rs = Re - Es, Re is the outer radius of the tire, measured at the radially outermost point on the tread surface of the tire, and the surface is extrapolated to fill any voids that may exist, Es is the radial distance between the radially outermost point of the tire and its orthogonal projection on the radially outer surface of the reinforcing elements of the radially innermost working tread layer, R L is the average value of the radii of the axially outermost points on each side of the tire, Rt is the radius of the circle passing through three points located on the outer tread surface outside the void, defined by axial distances from the shoulder end equal to 1 / 4, 1 / 2, and 3 / 4 of the axial width of the tread, respectively.

8. The tire (1) according to claim 7, characterized in that, The fracture potential index F2 / FR2 of the radially outermost working tread layer (42) is less than 1 / 8.

9. The tire (1) according to any one of claims 7 and 8, characterized in that The fracture potential index F1 / FR1 of the radially innermost working tread layer (41) is less than 1 / 3, where: FR1 is the breaking force of each cord of the radially innermost working layer under uniaxial extension, F1 = p1 * Tc * [(tan(|α2|) / ((tan(|α1|) + tan(|α2|))) / cos 2 (|α1|) + C F , where p1 is the spacing of the reinforcing elements laid in the radially innermost working tread layer, measured perpendicular to the reinforcing elements at the circumferential midplane.

10. The tire (1) according to claim 9, characterized in that, The fracture potential index F1 / FR1 of the radially innermost working layer (41) is at least 30% higher than the fracture potential index F2 / FR2 of the radially outermost working layer (42).

11. The tire (1) according to any one of the preceding claims, characterized in that, The two working tread layers (41, 42) and the at least one circumferential reinforcing element layer (43) are the only layers used to form the tread reinforcement over the entire axial width of the tread reinforcement (4).

12. 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 a reinforcing filler, the reinforcing filler including at least 10 phr of pyrolytic carbon black.

13. The tire (1) according to claim 12, characterized in that, The at least one surface layer of at least one working tread layer (41, 42) is an elastomeric compound based on natural rubber or on synthetic polyisoprene having predominantly cis-1,4 bonds and optionally based on at least one other diene elastomer, and in the case of a blend, the natural rubber or synthetic polyisoprene is present in a major amount relative to the content of the one or more other diene elastomers used.

14. The tire (1) according to any one of claims 12 and 13, characterized in that, In addition to the pyrolytic carbon black, the at least one surface layer of at least one working tread layer further comprises a reinforcing filler consisting of: a) Carbon black used in a content between 30 phr and 60 phr, preferably between 30 phr and 50 phr, b) or a white filler of 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 aluminum silicate, or carbon black modified during or after synthesis, and used in a content between 30 phr and 60 phr, preferably between 30 phr and 50 phr, 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 30 phr and 60 phr, preferably between 30 phr and 50 phr.

15. 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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