TIRE WITH IMPROVED ENDURANCE PERFORMANCE IN THE TOP AREA

Abstract

The invention relates to a tire (1) comprising a crown reinforcement (4) formed of at least two working crown layers (41, 43). According to the invention, the calendering layers of the working crown layers (41, 43) are made of an elastomeric compound comprising a silica-type filler with a specific surface area BET of between 50 and 150 m² / g and the FWHM / Dmode ratio obtained from the mass distribution curve as a function of the diameter of the silica-type filler particles is greater than or equal to 0.77. Figure for the abstract: Fig 2

Description

Title of the invention: TIRE WITH IMPROVED ENDURANCE PERFORMANCE IN THE TOP AREA

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

[0002] Generally, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These layers, called working layers, forming the working reinforcement, may be further covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, called elastic elements.It may also include a layer of wires or metal cables forming an angle of between 45° and 90° with the circumferential direction. This layer, called the triangulation layer, is radially located between the carcass reinforcement and the first crown layer, called the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement, which exhibits little deformation under the various stresses it is subjected to. The essential role of the triangulation layer is to resist the transverse compression forces to which all the reinforcing elements are subjected in the crown area of ​​the tire.

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

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

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

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

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

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

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

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

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

[0012] Some current tires, known as "road" tires, are designed to travel at high average speeds and over increasingly long distances, due to improvements in the road network and the growth of the motorway network worldwide. The overall conditions under which such a tire is expected to operate undoubtedly allow for an increase in the number of kilometers traveled, as tire wear is reduced. This increase in lifespan in terms of kilometers, combined with the fact that such operating conditions are likely to result in relatively high crown temperatures under heavy loads, necessitates at least a proportional increase in the endurance potential of the tire's crown reinforcement.

[0013] Indeed, there are stresses at the level of the top reinforcement, and more specifically shear stresses between the top layers, which, in the case of an excessive rise in operating temperature at the ends of the axially shorter top layer, result in the appearance and propagation of cracks in the rubber at said ends. The same problem exists in the case of the edges of two layers of reinforcing elements, the other layer not necessarily being radially adjacent to the first.

[0014] In order to improve the endurance of the crown reinforcement of the tires, French application FR 2 728 510 proposes to have, on the one hand between the carcass reinforcement and the working layer of crown reinforcement, radially closest to the axis of rotation, an axially continuous layer, formed of inextensible metal cables making an angle of at least 60° with the circumferential direction, and whose axial width is at least equal to the axial width of the shortest working crown layer, and on the other hand between the two working crown layers an additional layer formed of metal elements, oriented substantially parallel to the circumferential direction.

[0015] In addition, patent application WO 99 / 24269 proposes, in particular, on either side of the equatorial plane and in the immediate axial extension of the water table additional reinforcement elements substantially parallel to the circumferential direction, to couple, over a certain axial distance, the two top working layers formed of reinforcement elements crossed from one layer to the next and then to decouple them by rubber compound profiles at least over the remainder of the common width of said two working layers.

[0016] Furthermore, the use of tires on heavy-duty vehicles of the "construction site approach" type leads to the tires being subjected to stress when driving on stony ground. This stress is obviously detrimental to performance in terms of endurance.

[0017] Indeed, these aggressions crack the tire tread, and the cracks propagate to the crown reinforcement during rolling. These cracks then allow oxidizing agents such as air and water to penetrate, which can then cause corrosion of the metallic reinforcement elements of the crown reinforcement.

[0018] If, in conjunction with these tread aggressions, the tire is subjected to violent shocks during such driving on stony ground, the risk of breakage of reinforcement elements of the crown reinforcement is increased.

[0019] One object of the invention is thus to provide tires for "Heavy Goods Vehicles", whose performance in terms of endurance of the crown reinforcement is improved and whose resistance properties to aggressions in particular when driving on stony ground are satisfactory.

[0020] This objective is achieved according to the invention by a tire for heavy-duty vehicles, with a radial carcass reinforcement comprising a crown reinforcement formed of at least two working crown layers, each comprising metallic reinforcing elements inserted between two calendered layers of elastomeric compound, the crown reinforcement being radially capped by a tread, said tread being joined to two beads by means of two sidewalls, at least the outermost radially calendered layer of at least the outermost radially working crown layer being an elastomeric compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of cutting being present at a major rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous-type filler, with a specific surface area BET between 50 and 150 m2 / g, used at a rate between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of the siliceous-type filler particles obtained according to ISO 20927 of 2019 on the , diameter Dmode, expressed in nm, of siliceous-type charge particles at maximum distribution being greater than or equal to 0.77.

[0021] The specific surface area measurement BET of siliceous type filler is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, more specifically according to the French standard NF ISO 9277 of December 1996.

[0022] The mass distribution curve as a function of the diameter of siliceous filler particles is obtained in accordance with ISO 20927:2019 using a method for determining the dimensional distribution by centrifugal disk, known as the CPS (Centrifuge Particle Size) method. The FWHM width, expressed in nm, is determined by measuring the width of the curve at 50% of the maximum distribution value. The diameter Dmode, expressed in nm, of the siliceous filler particles at the maximum distribution corresponds to the abscissa of the maximum distribution on the curve.

[0023] Advantageously according to the invention, the FWHM / Dmode ratio of the distribution width FWHM measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of siliceous-type filler particles, reinforcing at least said outermost radially calendered layer of at least the outermost radially working top layer, obtained according to ISO 20927 of 2019 on the diameter Dmode of siliceous-type filler particles, reinforcing at least said outermost radially calendered layer of at least the outermost radially working top layer, at the maximum distribution is greater than or equal to 0.80.

[0024] Advantageously still according to the invention, the siliceous type filler of the elastomeric mixture constituting at least said radially outermost calendering layer of at least the radially outermost working top layer has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

[0025] Preferably according to the invention, the silica-type filler of the elastomeric mixture constituting at least said radially outermost calendering layer of at least the radially outermost working top layer is a cut of two silicas.

[0026] When using siliceous fillers, it is necessary to use a coupling and / or coating agent chosen from those known to those skilled in the art. Examples of preferred coupling agents include sulfide alkoxysilanes of the bis-(3-trialcoxysilylpropyl) polysulfide type, and among others These include bis-(3-triethoxysilylpropyl) tetrasulfide, marketed by DEGUSSA under the brand name Si69. Examples of covering agents include fatty alcohols, alkylalkoxysilanes such as hexadecyltrimethoxy or triethoxysilane (marketed by DEGUSSA under the brand names Sillô and Si216, respectively), diphenylguanidine, polyethylene glycol, and silicone oil, possibly modified with OH or alkoxy groups. The covering and / or coupling agent is used in a mass ratio to the filler of between 0.2% and 0.15%.

[0027] Among the diene elastomers that can be used in cutting with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, we can mention a polybutadiene (BR) preferably with a majority of cis-1,4 chains, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers can be modified elastomers during polymerization or after polymerization by means of branching agents such as divinylbenzene or star-forming agents such as carbonates, halotins, halosilicons or by means of functionalizing agents leading to grafting onto the chain or at the end of the chain of oxygenated carbonyl, carboxyl functions or of an amine function such as for example by the action of dimethyl or diethylaminobenzophenone.In the case of natural rubber or synthetic polyisoprene blends with a majority of cis-1,4 chains and one or more of the diene elastomers mentioned above, natural rubber or synthetic polyisoprene is preferably used in a majority proportion and more preferably in a proportion greater than 70%.

[0028] The results obtained with tires conforming to the invention have indeed shown that the performance in terms of endurance of the crown reinforcement is improved and exhibits a satisfactory resistance to aggressions or shocks suffered for example when driving on stony ground.

[0029] The tests carried out showed that the use of the elastomeric mixtures according to the invention comprising a silica or a cutting of silicas to produce at least the outermost radially calendered layer of at least the outermost radially working top layer makes it possible to improve the properties of the tire in terms of the endurance of the top reinforcement.

[0030] The inventors believe they have demonstrated, in particular, that the choice of mixtures according to the invention for producing at least the outermost radially said calendered layer of at least the outermost radially working top layer and, in particular, having the properties of the reinforcing charge according to The invention makes it possible to limit the propagation speeds of cracks appearing during rolling at the ends of the layers of reinforcing elements.

[0031] Furthermore, the inventors believe that the hydrophilic nature of the reinforcing fillers defined according to the invention makes it possible to limit the risk of corrosion of the working reinforcement elements when cracks originate on the surface of the tread, allowing the passage of oxidizing agents such as water and air. Thus, under high stress, the reinforcing elements appear to exhibit better resistance to failure. The failure phenomena of the reinforcing elements of the top working layers during particularly stressful rolling are therefore postponed to cases of even higher stress.

[0032] Advantageously according to the invention, the entire calendering layer of the working top layers consists of an elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of cutting being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a silica-type filler, with a specific surface area BET of between 50 and 150 m2 / g, used at a rate of between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and the FWHM / Dmode ratio of the distribution width measured at 50% of the maximum distribution, expressed in nm,(FWHM) on the mass distribution curve as a function of the diameter of siliceous-type filler particles obtained according to ISO 20927 of 2019 on the diameter of siliceous-type filler particles at maximum distribution, expressed in nm, (Dmode) is greater than or equal to 0.77. ,

[0033] According to a preferred embodiment of the invention, the maximum value of tan(ô), denoted tan(ô)max, of at least the outermost radially calendered layer of at least the outermost radially working top layer, is less than or equal to 0.11.

[0034] Preferably, the set of calendering layers of the working vertex layers has a maximum value of tan(ô), denoted tan(ô)max, less than or equal to 0.11.

[0035] The loss factor tan(φ) is a dynamic property of the rubber compound layer. It is measured on a viscoelastic analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a vulcanized composition sample (cylindrical specimen 2 mm thick and 78 mm² in cross-section) subjected to sinusoidal loading in alternating simple shear at a frequency of 10 Hz and a temperature of 100°C is recorded. A strain amplitude sweep is performed from 0.1 to 50% (forward cycle), then from 50% to 1% (reverse cycle). The results The variables used are the complex dynamic shear modulus (G*) and the loss factor tan(θ) measured over the return cycle. For the return cycle, the maximum observed value of tan(θ) is indicated, denoted tan(θ)max.

[0036] In the case where the thickness of the material is between 1 and 2 mm, the loss factor tan(ô) is measured according to the same method and under the same conditions, as described above, on a sample of vulcanized composition which is in the form of a cylindrical specimen 1 mm thick and 78 mm2 in cross-section.

[0037] Rolling resistance is the resistance that appears when the tire is rolling. It is represented by the hysteretic losses related to the deformation of the tire during one revolution. The frequency values ​​related to the tire's revolution correspond to tan(φ) values ​​measured between 30 and 100°C. The tan(φ) value at 100°C thus corresponds to an indicator of the tire's rolling resistance.

[0038] The inventors have further demonstrated that the choice of mixtures according to this preferred embodiment of the invention to produce at least the outermost radially calendered layer of at least the outermost radially working top layer makes it possible to improve the tire's rolling resistance properties, due to the relatively low value of the maximum value of tan(ô), denoted tan(ô)max.

[0039] According to certain embodiments of tires, layers of elastomeric materials may be provided to cover the ends of the working top layers of the crown reinforcement. These layers are usually called rim layers.

[0040] Advantageously according to the invention, when these edge layers are present, they are made of the same mixture as the calendering layers of the top working layers.They are therefore made up of an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and possibly at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of cutting being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous type filler, with a specific surface area BET between 50 and 150 m2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the FWHM / Dmode ratio of the distribution width measured at 50% of the maximum distribution, expressed in nm, (FWHM) on the mass distribution curve as a function of the diameter of the siliceous type filler particles obtained according to the ISO 20927 of 2019 standard on particle diameter. of siliceous type charge at maximum distribution, expressed in nm, (Dmode) is greater than or equal to 0.77.

[0041] According to a first embodiment of the invention, a layer C of elastomeric blend being disposed between at least the ends of said at least two top working layers, said layer C is a layer of elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of cutting being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous-type filler, with a specific surface area BET of between 50 and 150 m2 / g, used at a rate of between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and the FWHM / Dmode ratio of the distribution width FWHM, expressed in nm,measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of siliceous-type filler particles obtained according to ISO 20927 of 2019 on the diameter Dmode, expressed in nm, of siliceous-type filler particles at the maximum distribution is greater than or equal to 0.77.

[0042] Advantageously according to the invention, the FWHM / Dmode ratio of the distribution width measured at 50% of the maximum distribution (FWHM) on the mass distribution curve as a function of the diameter of the siliceous-type filler particles reinforcing said elastomeric mixture layer C obtained according to ISO 20927 of 2019 on the diameter of the siliceous-type filler particles, reinforcing said elastomeric mixture layer C, at the maximum distribution (Dmode) is greater than or equal to 0.80.

[0043] Advantageously, according to the invention, the siliceous-type filler of the elastomeric mixture constituting said layer C has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

[0044] Preferably according to the invention, the siliceous type filler of the elastomeric mixture constituting said layer C is a cutting of two silicas.

[0045] According to a preferred embodiment of the invention, the maximum value of tan(ô), denoted tan(ô)max, of said layer C is less than or equal to 0.11.

[0046] As in the case of at least one calendering layer of at least one top working layer, the use of an elastomeric compound layer C according to the invention will make it possible to improve the tire's endurance properties.

[0047] Preferably, the thickness of layer C of the rubbery mixture, measured at the end of the narrower of the two working top layers of The working top thickness considered will preferably be between 30% and 80% of the overall thickness of the rubber compound between the cable generators of the two working top layers respectively: a thickness less than 30% does not allow for conclusive results, and a thickness greater than 80% is useless with regard to improving resistance to separation between layers and disadvantageous from a cost point of view.

[0048] Preferably, the axial width D of the rubbery mixture layer C, between the innermost axial end of said rubbery mixture layer C and the narrowest axial end of the top working layer, is such that: 3*02 < D < 25*02 with 02 being the diameter of the reinforcement elements of the axially narrowest working crown layer. This relationship defines an engagement zone between the rubber compound layer C and the axially narrowest working crown layer. Such an engagement below a value equal to three times the diameter of the reinforcement elements of the axially narrowest working layer may not be sufficient to achieve decoupling of the working crown layers, particularly to mitigate stresses at the end of the axially narrowest working crown layer. An engagement value exceeding twenty times the diameter of the reinforcement elements of the axially narrowest working layer can lead to an excessive reduction in the drift stiffness of the tire crown reinforcement.

[0049] Preferably, the axial width D of the rubbery mixture layer C between the innermost axial end of said rubbery mixture layer C and the narrowest axial end of the top working layer is greater than 5 mm.

[0050] The invention further preferably provides that the thickness of the rubbery mixture layer C, at the axially outer end of the axially narrowest working top layer, has a thickness such that the radial distance d between the two working top layers, separated by the rubbery mixture layer C, satisfies the relation: 3 / 5*02 <d< 5*02 with 02, diameter of the reinforcement elements of the axially least wide working top sheet.

[0051] The distance d is measured from cable to cable, that is, between the cable of a first working layer and the cable of a second working layer. In other words, this distance d encompasses the thickness of the rubber compound layer C and the respective thicknesses of the calendered rubber compounds, radially external to the cables of the radially inner working layer and radially inner to the cables of the radially outer working layer.

[0052] The various thickness measurements are taken on a cross-section of a tire, the tire therefore being in a deflated state. The cut is advantageously made by water jet without brushing to avoid any risk of cord bulging.

[0053] According to a second embodiment of the invention, the top reinforcement comprising a layer of circumferential reinforcing elements associated with an elastomeric blend, said elastomeric blend associated with the circumferential reinforcing elements is an elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of cutting being present at a majority rate relative to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous-type filler, with a specific surface area BET of between 50 and 150 m2 / g, used at a rate of between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and the FWHM / Dmode ratio of the distribution width FWHM, expressed in nm,measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of siliceous-type filler particles obtained according to ISO 20927 of 2019 on the diameter Dmode, expressed in nm, of siliceous-type filler particles at the maximum distribution is greater than or equal to 0.77.

[0054] Advantageously according to the invention, the FWHM / Dmode ratio of the FWHM distribution width measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of the siliceous-type filler particles reinforcing said elastomeric mixture associated with the circumferential reinforcing elements obtained according to ISO 20927 of 2019 on the diameter Dmode of the siliceous-type filler particles reinforcing said elastomeric mixture associated with the circumferential reinforcing elements at the maximum distribution is greater than or equal to 0.80.

[0055] Advantageously still according to the invention, the siliceous type filler of the elastomeric mixture associated with the circumferential reinforcing elements has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

[0056] Preferably according to the invention, the siliceous type filler of the elastomeric mixture associated with the circumferential reinforcing elements is a cutting of two silicas.

[0057] According to a preferred embodiment of the invention, the maximum value of tan(ô), denoted tan(ô)max, of said elastomeric mixture associated with the circumferential reinforcing elements is less than or equal to 0.11.

[0058] According to a first embodiment of this second variant of the invention, the elastomeric mixture associated with the circumferential reinforcing elements is a gumming mixture associated with the circumferential reinforcing elements by extrusion when, for example, these circumferential reinforcing elements are put in place by winding unit wires.

[0059] According to a second embodiment of this second variant of the invention, the elastomeric mixture associated with the circumferential reinforcing elements is in the form of calenders to be associated with the circumferential reinforcing elements to form strips of several circumferential reinforcing elements when, for example, these strips of circumferential reinforcing elements are put in place by winding.

[0060] According to a third embodiment of this second variant of the invention, the elastomeric mixture associated with the circumferential reinforcing elements is in the form of calenders to be associated with the circumferential reinforcing elements to form a layer of circumferential reinforcing elements when, for example, such a layer of circumferential reinforcing elements is put in place by winding on a single turn of tire.

[0061] According to a preferred embodiment of the invention, a layer of circumferential reinforcing elements is radially arranged between two working top layers.

[0062] According to this embodiment of the invention, the layer of circumferential reinforcing elements makes it possible to limit the compressive stresses on the carcass reinforcement elements to a greater extent than a similar layer placed radially outside the working layers. It is preferably radially separated from the carcass reinforcement by at least one working layer so as to limit the stresses on said reinforcing elements and prevent excessive fatigue.

[0063] Advantageously still according to the invention, the axial widths of the radially adjacent working top layers to the layer of circumferential reinforcing elements are greater than the axial width of said layer of circumferential reinforcing elements.

[0064] According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa.

[0065] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 100 GPa and greater than 20 GPa, preferably between 30 and 90 GPa and preferably still less than 80 GPa.

[0066] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and preferably even less than 120 GPa.

[0067] The moduli expressed above are measured on a tensile stress-elongation curve determined with a preload of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. The measurements are carried out on cables extracted from the tire on a portion of the layer of circumferential reinforcing elements extending from an axial end of said layer over an axial width of 50 mm towards the interior of said layer.

[0068] The moduli of the same reinforcing elements can be measured on a tensile stress-elongation curve determined with a preload of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall cross-section of the reinforcing element. The overall cross-section of the reinforcing element is the cross-section of a composite element made of metal and rubber, the latter having notably penetrated the reinforcing element during the curing phase of the tire.

[0069] According to this formulation relating to the overall section of the reinforcing element, the reinforcing elements of the axially external parts and of the central part of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation between 5 and 60 GPa and a maximum tangent modulus less than 75 GPa.

[0070] According to a preferred embodiment, the secant modulus of the 0.7% elongation reinforcement elements is less than 50 GPa and greater than 10 GPa, preferably between 15 and 45 GPa and even more preferably less than 40 GPa.

[0071] Preferably also, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and preferably even less than 60 GPa.

[0072] According to a preferred embodiment, the reinforcement elements of at least one layer of circumferential reinforcement elements are metallic reinforcement elements having a tensile stress curve as a function of relative elongation having small slopes for small elongations and a substantially constant and large slope for larger elongations.

[0073] The different characteristics of the reinforcement elements stated above are measured on reinforcement elements taken from tires.

[0074] Reinforcing elements more particularly adapted to the production of at least one layer of circumferential reinforcing elements according to the invention Examples include assemblies of formula 21.23, whose construction is 3x(0.26+6x0.23) 4.8 / 7.5 SS; this stranded cable consists of 21 elementary wires of formula 3 x (1+6), with 3 twisted strands each made up of 7 wires, one wire forming a central core with a diameter of 26 / 100 mm, and 6 wound wires with a diameter of 23 / 100 mm. Such a cable exhibits a secant modulus at 0.7% of 45 GPa and a maximum tangent modulus of 98 GPa, measured on a tensile stress-elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. On a tensile stress-as-elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall section of the reinforcement element, this cable of formula 21.23 has a secant modulus at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

[0075] Similarly, another example of a reinforcing element is an assembly of formula 21.28, whose construction is 3x(0.32+6x0.28) 5.6 / 9.3 SS. This cable has a secant modulus at 0.7% of 56 GPa and a maximum tangent modulus of 102 GPa, measured on a tensile stress-strain curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension referred to the metal cross-section of the reinforcing element. On a tensile stress-strain curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension referred to the overall cross-section of the reinforcing element, this cable of formula 21.28 has a secant modulus at 0.7% of 27 GPa and a maximum tangent modulus of 49 GPa.

[0076] The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain satisfactory layer stiffnesses even after the shaping and baking steps in conventional manufacturing processes.

[0077] According to a second embodiment of the invention, the circumferential reinforcing elements can be formed from inextensible metallic elements and cut to form sections of length much shorter than the circumference of the shortest layer, but preferably longer than 0.1 times said circumference, the cuts between sections being axially offset from one another. Even more preferably, the tensile modulus of elasticity per unit width of the additional layer is lower than the tensile modulus of elasticity, measured under the same conditions, of the most extensible top working layer. Such an embodiment makes it possible to easily impart to the layer of circumferential reinforcing elements a modulus that can readily be adjusted (by choosing the intervals between sections of the same row), but in all cases lower than the modulus of the layer made up of the same metallic elements but continuous, the modulus of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

[0078] According to a third embodiment of the invention, the circumferential reinforcing elements are corrugated metallic elements, the ratio a / / of the wave amplitude to the wavelength being at most equal to 0.09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working top layer.

[0079] As in the case of at least one calendering layer of at least one top working layer, the use of an elastomeric compound, associated with circumferential reinforcing elements, according to the invention will improve the tire's endurance properties and provide satisfactory resistance to aggressions or shocks suffered, for example, when driving on stony ground.

[0080] According to a third embodiment of the invention, it is planned to combine the first and second embodiments of the invention relating respectively to the use of an elastomeric mixture layer C and the use of an elastomeric mixture associated with circumferential reinforcing elements in combination with at least one calendered layer of at least one working top layer according to the invention.

[0081] According to other embodiments of the invention, particularly to reduce the number of elastomeric compounds used in the tire, at least one calendered layer of the carcass reinforcement, and advantageously all calendered layers of the carcass reinforcement, are made of an elastomeric compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene, in the case of a blend, being present at a higher proportion than the proportion of the other diene elastomer(s) used, and a reinforcing filler consisting of a silica-type filler with a specific surface area BET of between 50 and 150 m² / g, used at a proportion of between 20 and 80 parts per liter, and preferably between 30 and 50 parts per liter, and the FWHM / Dmode ratio of the width FWHM distribution, expressed in nmmeasured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of siliceous-type filler particles obtained according to ISO 20927 of 2019 on the diameter Dmode, expressed in nm, of siliceous-type filler particles at maximum distribution being greater than or equal to 0.77.

[0082] Advantageously according to the invention, the FWHM / Dmode ratio of the distribution width measured at 50% of the maximum distribution (FWHM) on the mass distribution curve as a function of the diameter of the siliceous-type filler particles, reinforcing the elastomeric mixture of the calendering layers of the carcass reinforcement, obtained according to ISO 20927 of 2019 on the diameter of the siliceous-type filler particles, reinforcing the elastomeric mixture of the calendering layers of the carcass reinforcement, at the maximum distribution (Dmode) is greater than or equal to 0.80.

[0083] Advantageously still according to the invention, the siliceous type filler of the elastomeric mixture constituting the calendering layers of the carcass reinforcement has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

[0084] Preferably according to the invention, the siliceous type filler of the elastomeric mixture constituting the calendering layers of the carcass reinforcement is a cut of two silicas.

[0085] According to a preferred embodiment of the invention, the maximum value of tan(ô), denoted tan(ô)max, of the calendering layers of the carcass reinforcement is less than or equal to 0.11.

[0086] According to yet other embodiments of the invention, in particular to further reduce the number of elastomeric compounds used in the tire, an elastomeric compound layer being in contact with at least one working apex layer and in contact with the carcass reinforcement, said elastomeric compound layer extending axially to at least the axial end of the tread, said elastomeric compound layer in contact with at least one working apex layer and in contact with the carcass reinforcement is made up of an elastomeric compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally of at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of cutting being present at a major rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a silica-type filler, with a specific surface area BET between 50 and 150 m2 / g, used at a rate between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and the FWHM / Dmode ratio of the distribution width FWHM, expressed in nm, measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of the silica-type filler particles obtained according to ISO 20927:2019 on the diameter Dmode, expressed in nm, of the silica-type filler particles at the maximum distribution being greater than or equal to 0.77.

[0087] Advantageously according to the invention, the FWHM / Dmode ratio of the distribution width measured at 50% of the maximum distribution (FWHM) on the mass distribution curve as a function of the diameter of the siliceous-type filler particles, reinforcing the elastomeric mixture of said elastomeric mixture layer in contact with at least one working top layer and in contact with the carcass reinforcement, obtained according to ISO 20927 of 2019 on the diameter of the siliceous-type filler particles, reinforcing the elastomeric mixture of the calendering layers of the carcass reinforcement, at the maximum distribution (Dmode) is greater than or equal to 0.80.

[0088] Advantageously, according to the invention, the siliceous type filler of the elastomeric mixture constituting said elastomeric mixture layer in contact with at least one working top layer and in contact with the carcass reinforcement has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

[0089] Preferably according to the invention, the siliceous type filler of the elastomeric mixture constituting said elastomeric mixture layer in contact with at least one working top layer and in contact with the carcass reinforcement is a cut of two silicas.

[0090] According to a preferred embodiment of the invention, the maximum value of tan(ô), denoted tan(ô)max, of said elastomeric mixture layer in contact with at least one working top layer and in contact with the carcass reinforcement is less than or equal to 0.11.

[0091] According to one embodiment of the invention, the reinforcing elements of said at least two top working layers are crossed from one layer to the other by making angles with the circumferential direction between 10° and 45°.

[0092] Preferably, the reinforcing elements of said at least two top working layers are inextensible.

[0093] A preferred embodiment of the invention further provides that the top reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of reinforcement elements oriented with respect to the circumferential direction with an angle between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0094] Advantageously according to the invention, the reinforcing elements of said at least one protective layer are elastic.

[0095] The protective layer may have an axial width less than the axial width of the narrowest working layer. Said protective layer may also have a axial width greater than the axial width of the narrowest working layer, such that it covers the edges of the narrowest working layer.

[0096] Other variants may further provide that the top reinforcement can be supplemented between the core reinforcement and the innermost radially internal working layer of said core reinforcement by a triangulation layer of inextensible steel reinforcing elements forming an angle greater than 45° with the circumferential direction and in the same direction as the angle formed by the reinforcing elements of the layer radially closest to the core reinforcement. Advantageously, said triangulation layer consists of two half-layers positioned axially on either side of the circumferential median plane.

[0097] Other advantageous details and features of the invention will become apparent from the description of exemplary embodiments of the invention with reference to Figures 1 and 2, which represent: [Fig. 1], a meridian view of a diagram of a tire according to an embodiment of the invention, [Fig.2], a mass distribution curve as a function of the diameter of the reinforcing loads.

[0098] Fig. 1 is not shown to scale for ease of understanding. The figure represents only a half-view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of a tire.

[0099] In [Fig. 1], the tire 1 is size 315 / 70 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two flanges, not shown in the figure. The carcass reinforcement is formed of a single layer of metal cords. This carcass reinforcement 2 is bound by a vertex reinforcement 4, formed radially from the inside out: - a first working layer 41 formed of metal cables oriented at an angle of 18°, - a layer of circumferential reinforcing elements 43 formed of 21x23 steel wire cables, - of a second working layer 42 formed of metal cables oriented at an angle equal to 30° and crossed with the metal cables of layer 41, the cables of each of the working layers 41, 42 being oriented on either side of the circumferential direction.

[0100] The metal cables constituting the reinforcement elements of the two working layers are cables of formula 9.35. They are distributed in each of the layers of work with a distance between the reinforcement elements, measured along the normal to the direction of the mean line of the cable equal to 2.2 mm.

[0101] The top reinforcement is itself capped with a tread 5.

[0102] The tire is inflated to a pressure of 9 bars.

[0103] The axial width L4i of the first working layer 41 is equal to 252 mm.

[0104] The axial width L42 of the second working layer 42 is equal to 232 mm.

[0105] The axial width L43 of the layer of circumferential reinforcing elements 43 is equal to 194 mm.

[0106] According to the invention, a layer of rubbery mixture C decouples the ends of the top working layers 41 and 42.

[0107] The engagement zone of layer C between the two working top layers 41 and 42 is defined by its thickness, or more precisely, the radial distance d between the end of layer 42 and layer 41, and by the axial width D of layer C between the inner axial end of said layer C and the radially outer end of the working top layer 42. The radial distance d is equal to 2.8 mm, or approximately 2.1 times the diameter 02 of the reinforcing elements of the working top layer 42, the diameter 02 being equal to 1.35 mm. The axial distance D is equal to 19 mm, or approximately 14 times the diameter 02 of the reinforcing elements of the working top layer 42.

[0108] Fig. 2 illustrates a mass distribution curve 6 (expressed as relative mass) as a function of the diameter of siliceous-type filler particles (expressed in nm), obtained in accordance with ISO 20927 of 2019 according to a method for determining the dimensional distribution by centrifugal disk, known as the CPS method (“Centrifuge Particle Size”).

[0109] The FWHM width, expressed in nm, is determined by measuring the width of the curve at 50% of the maximum value of distribution 7.

[0110] The diameter Dmode, expressed in nm, of the siliceous type charge particles at the maximum distribution corresponds to the abscissa of the maximum distribution 7 on the curve 6.

[0111] Different tires according to the invention are compared to different reference tires of the same size. All of these tires conform to the representation in [Fig. 1].

[0112] The different mixtures used are listed below, expressing for each of the mixtures comprising a siliceous type filler the specific surface area BET, the width FWHM, the diameter Dmode, as well as the ratio FWHM / Dmode. SSxSïïSc s w. : w ■ O SS ■S? ! SSW 4S Sï sakw î SS SK s ;VS ï. dî x: Sx - * ss SS U LS $S<,ïxL:s <S: Sx*:-: ; ?:. ? s S S. S SS SK SS. 4. S CS S.<x<:v4:SSSÂr $ SSS JS !S.:$ X: x HET (sE / gl •SS SS"' xS S'Ls -SS P î SS’? * N <s.~r : sss

[0113] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers.

[0114] The first tires II according to the invention comprise calendering layers of the two working layers made up of the compound I, the layer C and the elastomeric compound associated with the circumferential reinforcing elements being made up of the compound RI.

[0115] Second tires 12 according to the invention comprise calendered layers of the two working layers and layer C made up of mixture I, the elastomeric mixture associated with circumferential reinforcing elements being made up of the RI mixture.

[0116] Third tires 13 according to the invention comprise calendered layers of the two working layers and the elastomeric mixture associated with the circumferential reinforcing elements made up of mixture I, layer C being made up of mixture RI.

[0117] Fourth tires 14 according to the invention comprise calendered layers of the two working layers, layer C and the elastomeric mixture associated with the circumferential reinforcing elements made up of mixture I.

[0118] The first reference tires Tl differ from the tires II according to the invention by the nature of the mixtures of the calendering layers of the two working layers, these being made up of the RI mixture; the calendering layers of the two working layers, the C layer and the elastomeric mixture associated with the circumferential reinforcing elements are thus made up of the RI mixture.

[0119] Second reference tires T2 include calendered layers of the two working layers, layer C and the elastomeric mixture associated with the circumferential reinforcing elements made up of the R2 mixture.

[0120] Third reference tires T3 comprise calendered layers of the two working layers, layer C and the elastomeric mixture associated with the circumferential reinforcing elements made of the R3 mixture.

[0121] Tests were carried out with the tires made according to the invention II, 12, 13 and 14 and with the reference tires T1, T2 and T3.

[0122] Initial endurance tests were carried out on a test machine subjecting each tire to a straight-line roll on an inner flywheel with a 40m circumference, at a speed equal to the maximum speed index prescribed for said tire, under an initial load of 4230 kg, progressively increased to reduce the test duration. The tests were performed on the tires according to the invention under conditions identical to those applied to the reference tires.

[0123] The results are presented in the following table. The relative mileage of the tires before a crack appeared at the end of the crown reinforcement is denoted by , with a value of 100 being assigned to the reference tire TL TI 12 T3 II 12 13 14 100 90 80 100 110 100 110

[0124] Further endurance tests were carried out on a test machine that cyclically applied a transverse force and a dynamic overload to the tires. The tests were performed on the tires according to the invention under conditions identical to those applied to the reference tires.

[0125] The results are presented in the following table. The relative mileage of the tires before a crack appeared at the end of the crown reinforcement is denoted by , with a value of 100 being assigned to the reference tire TL Tl T3 II 12 13 14 100 105 106 105 130 110 130

[0126] Tests to characterize the rupture resistance of a tire crown reinforcement subjected to stress were carried out by driving vehicles over 20,000 km, performing driving cycles including a 10 km section at 80 km / h on a road, a 3 km section at 30 km / h on a gravel bed, and a 50 m section at idle in salt-saturated water. The tires were then stripped of their treads to expose the outermost radially exposed working layer in order to measure the lengths of corroded cords.

[0127] The results are presented in the following table. The performance index is the ratio between the total corroded length of the tested tire and that of the control tire TL Tl T2 T3 II 12 13 Ï4 100 110 110 110 110 110 115

[0128] In addition, rolling resistance measurements were carried out.

[0129] The measurement results are presented in the following table; they are expressed in kg / t, with a value of 100 assigned to the reference tire TL Tl T2 T3 II 12 13 14 100 100 103 100 105 100 105

Claims

Demands

1. Heavy-duty vehicle tire (1), with a radial carcass reinforcement (2) comprising a crown reinforcement (4) formed of at least two working crown layers (41, 43), each having metallic reinforcing elements inserted between two calendered layers of elastomeric compound, the crown reinforcement (4) being radially capped by a tread (5), said tread (5) being joined to two beads by means of two sidewalls, characterized in that at least the outermost radially calendered layer of at least the outermost radially working crown layer (43) is an elastomeric compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of cutting being present at a major rate compared to the rate of the other or other diene elastomers used and of a reinforcing filler consisting of a siliceous type filler, of specific surface area BET between 50 and 150 m2 / g, used at a rate between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and in that the FWHM / Dmode ratio of the FWHM width, expressed in nm, of distribution measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of the siliceous type filler particles obtained according to ISO20927 of 2019, to the Dmode diameter, expressed in nm, of the siliceous type filler particles at the maximum distribution, is greater than or equal to 0.

77.

2. Pneumatic (1) according to claim 1, characterized in that the FWHM / Dmode ratio is greater than or equal to 0.

80.

3. Pneumatic (1) according to claim 2, characterized in that the siliceous type filler of the elastomeric mixture constituting at least said radially outermost calendered layer of at least the radially outermost working top layer (43) has a specific surface area BET greater than 130 m2 / g, and preferably greater than 140 m2 / g.

4. Pneumatic (1) according to any one of claims 1 to 3, characterized in that the maximum value of tan(θ), denoted tan(θ)max, is at least the radially outermost calendered layer of at least the radially outermost working top layer (43), is less than or equal to 0.

11.

5. Pneumatic (1) according to any one of claims 1 to 4, characterized in that the silica-type filler of the elastomeric mixture constituting at least said radially outermost calendered layer of at least the radially outermost working top layer (43) is a cut of two silicas.

6. Pneumatic (1) according to any one of the preceding claims, a layer C of elastomeric blend being disposed between at least the ends of said at least two working top layers (41, 43), characterized in that said layer C is a layer of elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of cutting being present at a majority rate relative to the rate of the other diene elastomer(s) used, and a reinforcing filler consisting of a silica-type filler, with a specific surface area BET of between 50 and 150 m² / g, used at a rate of between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and in that the FWHM / Dmode ratio of the distribution width FWHM, expressed in nm,measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of siliceous-type filler particles obtained according to ISO 20927 of 2019, on the diameter Dmode, expressed in nm, of the siliceous-type filler particles at the maximum distribution, is greater than or equal to 0.

77.

7. Pneumatic (1) according to claim 6, characterized in that the maximum value of tan(ô), denoted tan(ô)max, of said layer C is less than or equal to 0.

11.

8. Pneumatic (1) according to any one of claims 6 or 7, characterized in that the silica-type filler of the elastomeric mixture constituting said layer C is a cutting of two silicas.

9. Pneumatic (1) according to any one of the preceding claims, the apex reinforcement (4) comprising a layer of circumferential reinforcing elements (42) associated with an elastomeric mixture, characterized in that said elastomeric mixture associated with the circumferential reinforcing elements is an elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene, in the case of a blend, being present at a higher proportion than the other diene elastomer(s) used, and a reinforcing filler consisting of a siliceous filler with a specific surface area BET between 50 and 150 m² / g, used at a proportion between 20 and 80 parts per cent, and preferably between 30 and 50 parts per cent, and in that the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the maximum distribution on the mass distribution curve as a function of the diameter of the siliceous filler particles obtained according to ISO 20927:2019, over the diameter Dmode, expressed in nmof siliceous-type charge particles at maximum distribution, is greater than or equal to 0.

77.

10. Pneumatic (1) according to claim 9, characterized in that the maximum value of tan(θ), denoted tan(θ)max, of the elastomeric mixture associated with the circumferential reinforcing elements is less than or equal to 0.11

11. Pneumatic (1) according to any one of claims 9 or 10, characterized in that the silica-type filler of the elastomeric mixture associated with the circumferential reinforcing elements is a cutting of two silicas.

12. Pneumatic (1) according to any one of the preceding claims, the top reinforcement (4) comprising at least one layer of circumferential reinforcing elements (42), characterized in that the layer of circumferential reinforcing elements (42) is radially arranged between two working top layers (41, 43).

13. Pneumatic (1) according to any one of the preceding claims, the top reinforcement (4) comprising at least one layer of circumferential reinforcing elements (42), characterized in that the reinforcing elements of at least one layer of circumferential reinforcing elements (42) are metallic reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

14. Pneumatic (1) according to any one of the preceding claims, characterized in that the reinforcing elements of said at least two top working layers (41, 43) are crossed from one layer to the other by making with the circumferential direction angles between 10° and 45°.

15. Pneumatic (1) according to any one of the preceding claims, characterized in that the reinforcing elements of said at least two working top layers (41, 43) are inextensible metal cables.

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