Tyre in which the crown area has improved endurance performance

Abstract

The invention relates to a tyre comprising a crown reinforcement (4) formed by at least two working crown plies (41, 42). According to the invention, the skim coats of the working crown plies consist of an elastomer blend comprising a siliceous filler with a BET specific surface area of between 50 and 150 m2 / g, and the FWHM / Dmode ratio obtained from the curve expressing mass distribution as a function of the diameter of the siliceous filler particles is greater than or equal to 0.77.

Description

TYRE WHOSE TOP AREA PRESENTS IMPROVED ENDURANCE PERFORMANCE

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

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

[0004] Cables are said to be elastic when, under a tensile force equal to the breaking load, the said cables exhibit 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 in the range + 2.5°, - 2.5° around 0°.

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

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

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

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

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

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

[0012] Some current tires, called "road tires", are designed to run at high average speeds and over increasingly long distances, due to the improvement of the road network and the growth of the motorway network throughout the world. All the conditions under which such a tire is called upon to run undoubtedly allow an increase in the number of kilometers traveled, since tire wear is less. This increase in service life in terms of kilometers, combined with the fact that such conditions of use are likely to result, under heavy load, in relatively high crown temperatures, requires an at least proportional increase in the endurance potential of the tire crown reinforcement.

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

[0014] In order to improve the endurance of the crown reinforcement of tires, French application FR 2 728 510 proposes to have, on the one hand between the carcass reinforcement and the working crown reinforcement ply, radially closest to the axis of rotation, an axially continuous ply, formed of inextensible metal cables making with the circumferential direction an angle at least equal to 60°, and whose axial width is at least equal to the axial width of the shortest working crown ply, and on the other hand between the two working crown plies an additional ply 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 additional ply of reinforcing elements substantially parallel to the circumferential direction, to couple, over a certain axial distance, the two working crown plies formed of reinforcing elements crossed from one ply to the next and then to decouple them by rubber compound profiles at least over the remainder of the width common to said two working plies.

[0016] Furthermore, the use of tires on heavy-duty vehicles of the "site approach" type leads to the tires being subjected to damage when driving on stony ground. These damages are of course detrimental to performance in terms of endurance.

[0017] In fact, these attacks crack the tire tread and the cracks propagate to the crown reinforcement during rolling. These cracks then open the way to oxidizing agents such as air and water which can then cause corrosion of the metal reinforcing elements of the crown reinforcement.

[0018] If, combined with these tread attacks, the tire is subjected to violent impacts during such rolling on stony ground, the risk of rupture of the crown reinforcement elements is increased.

[0019] One aim 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 attacks, particularly when driving on stony ground, are satisfactory.

[0020] This object is achieved according to the invention by a tire for a heavy goods vehicle, with a radial carcass reinforcement comprising a crown reinforcement formed from at least two working crown layers, each comprising metal reinforcing elements inserted between two calendering layers of elastomeric mixture, the crown reinforcement being radially capped with a tread, said tread being joined to two beads by means of two sidewalls, at least the radially outermost calendering layer of at least the radially outermost working crown layer being an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 10 m, 2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the ratio FWHM / D mo of the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of siliceous filler particles obtained according to ISO 20927 standard of 2019 on the diameter D mo of, expressed in nm, siliceous type filler particles at the maximum distribution being greater than or equal to 0.77.

[0021] The BET specific surface area measurement 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 precisely 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 of 2019 using a method for determining the size distribution by centrifugal disk, known as the CPS method ("Centrifuge Particle Size"). 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 distribution maximum corresponds to the abscissa of the distribution maximum on the curve.

[0023] Advantageously according to the invention, the FWHM / D ratio mo of the FWHM distribution width measured at 50% of the distribution maximum on the distribution curve mass as a function of the diameter of the siliceous type filler particles, reinforcing at least said radially outermost calendering layer of at least the radially outermost working crown layer, obtained according to ISO 20927 of 2019 on the diameter D mo of siliceous type filler particles, reinforcing at least said radially outermost calendering layer of at least the radially outermost working crown 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 crown layer has a BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m 2 / g.

[0025] Preferably 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 crown layer is a blend of two silicas.

[0026] In the case of using siliceous type fillers, it is necessary to use a coupling and / or covering agent chosen from agents known to those skilled in the art. Examples of preferred coupling agents that may be mentioned are sulfurized alkoxysilanes of the bis-(3-trialkoxysilylpropyl) polysulfide type, and among these in particular bis-(3-triethoxysilylpropyl) tetrasulfide marketed by the company DEGUSSA under the names Si 69. Examples of covering agents that may be mentioned are a fatty alcohol, an alkylalkoxysilane such as a hexadecyltrimethoxy or triethoxysilane respectively marketed by the company DEGUSSA under the names Si10 and Si216, diphenylguanidine, a polyethylene glycol, a silicone oil optionally modified by means of OH or alkoxy functions. The covering and / or coupling agent is used in a mass ratio to the filler of between 2 / 100 and 15 / 100.

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

[0028] The results obtained with tires conforming to the invention have effectively demonstrated that the performance in terms of endurance of the crown reinforcement is improved and presents satisfactory resistance to attacks or impacts suffered, for example, when driving on stony ground.

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

[0030] The inventors believe that they have in particular demonstrated that the choice of mixtures according to the invention to produce at least said radially outermost calendering layer of at least the radially outermost working crown layer and in particular having the properties of the reinforcing filler 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 risks of corrosion of the reinforcing elements of the working reinforcement during cracks initiated on the surface of the tread opening the passage to oxidizing agents such as water and air. Thus, during high stresses, the reinforcing elements seem to have better resistance to rupture. The phenomena of rupture of the reinforcing elements of the working top layers during particularly demanding rolling are thus pushed back to cases of even greater stress.

[0032] Advantageously according to the invention, all of the calendering layers of the working crown layers are 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 the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m 2 / 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 distribution maximum, 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 standard of 2019 on the diameter of the siliceous type filler particles at the distribution maximum, 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 radially outermost calendering layer of at least the radially outermost working crown layer, is less than or equal to 0.11.

[0034] Preferably, all of the calendering layers of the working crown layers have a maximum value of tan(ô), noted tan(ô)max, less than or equal to 0.11.

[0035] The loss factor tan(ô) is a dynamic property of the rubber compound layer. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized compound (cylindrical specimen 2 mm thick and 78 mm 2 of section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10Hz, at a temperature of 100°C. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 1% (return cycle). The results used are the complex dynamic shear modulus (G*) and the loss factor tan(ô) measured on the return cycle. For the return cycle, the maximum value of tan(§) observed, noted tan(ô) is indicated max .

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

[0037] Rolling resistance is the resistance that appears when the tire rolls. It is represented by the hysteretic losses linked to the deformation of the tire during a revolution. The frequency values ​​linked to the revolution of the tire correspond to values ​​of tan(ô) measured between 30 and 100°C. The value of tan(3) at 100°C thus corresponds to an indicator of the rolling resistance of the tire while rolling.

[0038] The inventors have also been able to demonstrate that the choice of mixtures according to this preferred embodiment of the invention to produce at least the radially outermost calendering layer of at least the radially outermost working crown layer makes it possible to improve the properties of the tire in terms of rolling resistance, due to the relatively low value of the maximum value of tan(§), noted tan(ô)max.

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

[0040] Advantageously according to the invention, when these edging layers are present, they are made of the same mixture as the calendering layers of the working crown layers. They are therefore made 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 the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m 2 / 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 distribution maximum, 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 standard of 2019 on the diameter of siliceous type filler particles at the maximum distribution, expressed in nm, (D mo of) is greater than or equal to 0.77.

[0041] According to a first variant embodiment of the invention, a layer C of elastomeric mixture being arranged between at least the ends of said at least two working crown layers, said layer C is a layer of elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m 2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the ratio FWHM / D moof the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of siliceous filler particles obtained according to ISO 20927 standard of 2019 on the diameter D mo of, expressed in nm, siliceous type filler particles at the maximum distribution is greater than or equal to 0.77.

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

[0043] Advantageously still according to the invention, the siliceous type filler of the elastomeric mixture constituting said layer C has a BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m 2 / g.

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

[0045] According to a preferred embodiment of the invention, the maximum value of tan(ô), noted 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 working crown layer, the use of a layer of elastomeric mixture C in accordance with the invention will make it possible to improve the properties of the tire in terms of endurance.

[0047] Preferably, the thickness of the layer C of rubber mixture, measured at the end of the narrowest working crown layer of the two working crown layers considered, will preferably be between 30% and 80% of the overall thickness of the rubber mixture between the cable generators of the two working crown layers respectively: a thickness of less than 30% not allowing conclusive results to be obtained, and a thickness of more than 80% being useless with regard to improving the resistance to separation between layers and disadvantageous from a cost point of view.

[0048] More preferably, the axial width D of the rubber mixture layer C between the axially innermost end of said rubber mixture layer C and the axially narrowest end of the working crown layer is such that: 3* < D < 25*(])2 with <|)2, diameter of the reinforcing elements of the axially narrowest working crown layer. Such a relationship defines an engagement zone between the rubber compound layer C and the axially narrowest working crown layer. Such an engagement below a value equal to three times the diameter of the reinforcing elements of the axially narrowest working layer may not be sufficient to obtain decoupling of the working crown layers, in particular to obtain attenuation of the stresses at the end of the axially narrowest working crown layer. A value of this engagement greater than twenty times the diameter of the reinforcing elements of the axially narrowest working layer may lead to too great a reduction in the drift stiffness of the tire crown reinforcement.

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

[0050] The invention also preferably provides that the thickness of the layer of rubber mixture C, at the axially outer end of the axially narrower working crown layer, has a thickness such that the radial distance d between the two working crown layers, separated by the layer of rubber mixture C, satisfies the relationship: 3 / 5*(|)2 < d < 5*<|)2 with <|)2, diameter of the reinforcing elements of the axially narrowest working crown layer.

[0051] The distance d is measured from cable to cable, i.e. 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 calendering rubber compounds, radially outside the cables of the radially inner working layer and radially inside the cables of the radially outer working layer.

[0052] The various thickness measurements are taken on a cross-section of a tire, the tire being in an uninflated state. The cut is advantageously carried out by water jet without brushing to avoid any risk of the cables bulging.

[0053] According to a second embodiment of the invention, the crown reinforcement comprising a layer of circumferential reinforcing elements associated with an elastomeric mixture, said elastomeric mixture associated with the circumferential reinforcing elements is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m 2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the ratio FWHM / D moof the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of siliceous filler particles obtained according to ISO 20927 standard of 2019 on the diameter D mo of, expressed in nm, siliceous type filler particles at the maximum distribution is greater than or equal to 0.77.

[0054] Advantageously according to the invention, the FWHM / D ratio moof the FWHM distribution width measured at 50% of the distribution maximum 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 the ISO 20927 standard of 2019 on the diameter Dmode of the siliceous type filler particles reinforcing said elastomeric mixture associated with the circumferential reinforcing elements at the distribution maximum 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 BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m 2 / g.

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

[0057] According to a preferred embodiment of the invention, the maximum value of tan(ô), noted tan(5)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 embodiment of the invention, the elastomeric mixture associated with the circumferential reinforcing elements is a rubber mixture associated with the circumferential reinforcing elements by extrusion when, for example, these circumferential reinforcing elements are put in place by winding unitary threads.

[0059] According to a second embodiment of this second variant embodiment 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 embodiment 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 the tire.

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

[0062] According to this embodiment of the invention, the layer of circumferential reinforcing elements makes it possible to limit the compression of the reinforcing elements of the carcass reinforcement 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 not to fatigue them excessively.

[0063] Advantageously still according to the invention, the axial widths of the working crown layers radially adjacent 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 of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

[0065] 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 and 90 GPa and more preferably less than 80 GPa.

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

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

[0068] The moduli of the same reinforcing elements can be measured on a tensile stress versus elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element. The overall section of the reinforcing element is the 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 outer 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 of between 5 and 60 GPa and a maximum tangent modulus of less than 75 GPa.

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

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

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

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

[0074] Reinforcing elements more particularly suitable for producing at least one layer of circumferential reinforcing elements according to the invention are, for example, assemblies of formula 21.23, the construction of which is 3x(0.26+6x0.23) 4.877.5 SS; this stranded cable is made up 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 equal to 26 / 100 mm and 6 wound wires with a diameter equal to 23 / 100 mm. Such a cable has a secant modulus at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, measured on a tensile stress versus elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension related to the metal section of the reinforcing element.On a tensile stress versus elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing 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 reinforcing elements is an assembly of formula 21.28, whose construction is 3x(0.32+6x0.28) 5.6 / 9.3 SS. This cable has a 0.7% secant modulus equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, measured on a tensile stress versus elongation curve determined with a prestress of 20 MPa, the tensile stress corresponding to a measured tension reduced to the metal section of the reinforcing element. On a tensile stress versus elongation curve determined with a prestress of 10 MPa, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element, this cable of formula 21.28 has a 0.7% secant modulus equal to 27 GPa and a maximum tangent modulus equal to 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 rigidities even after the shaping and curing steps in standard manufacturing processes.

[0077] According to a second embodiment of the invention, the circumferential reinforcing elements may be formed from inextensible metal elements and cut so as to form sections of length much less than the circumference of the shortest layer, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset from each other. More 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 crown layer.Such an embodiment makes it possible to confer, in a simple manner, on the layer of circumferential reinforcing elements a modulus which can easily be adjusted (by the choice of 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 but continuous elements, 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 metal elements, the ratio a / X of the corrugation amplitude over the wavelength being at most equal to 0.09. 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 working crown layer.

[0079] As in the case of at least one calendering layer of at least one working crown layer, the use of an elastomeric mixture, associated with the circumferential reinforcing elements, in accordance with the invention will make it possible to improve the properties of the tire in terms of endurance and makes it possible to provide satisfactory resistance to attacks or impacts suffered, for example, when driving on stony ground.

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

[0081] According to other embodiments of the invention, in particular to reduce the number of elastomeric mixtures used within the tire, at least one calendering layer of the carcass reinforcement and advantageously all the calendering layers of the carcass reinforcement are made up of an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m 2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of the siliceous type filler particles obtained according to the ISO 20927 standard of 2019 on the diameter Dmode, expressed in nm, of the siliceous type filler particles at the distribution maximum being greater than or equal to 0.77.

[0082] Advantageously according to the invention, the FWHM / D ratio moof the distribution width measured at 50% of the distribution maximum (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 the ISO 20927 standard 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 distribution maximum (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 BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m 2 / 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 blend of two silicas.

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

[0086] According to still other embodiments of the invention, in particular to reduce the number of elastomeric mixtures used within the tire, a layer of elastomeric mixture being in contact with at least one working crown layer and in contact with the carcass reinforcement, said layer of elastomeric mixture extending axially to at least the axial end of the tread, said layer of elastomeric mixture in contact with at least one working crown layer and in contact with the carcass reinforcement is made up of an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m, 2 / g, used at a rate between 20 and 80 pce, and preferably between 30 and 50 pce, and the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of the siliceous filler particles obtained according to the ISO 20927 standard of 2019 on the diameter D mo of, expressed in nm, siliceous type filler particles at the maximum distribution being greater than or equal to 0.77.

[0087] Advantageously according to the invention, the FWHM / D ratio moof the distribution width measured at 50% of the distribution maximum (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 crown layer and in contact with the carcass reinforcement, obtained according to the ISO 20927 standard 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 distribution maximum (Dmode) is greater than or equal to 0.80.

[0088] Advantageously still according to the invention, the siliceous type filler of the elastomeric mixture constituting said layer of elastomeric mixture in contact with at least at least one working crown layer and in contact with the carcass reinforcement has a BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m2 / g.

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

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

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

[0092] More preferably, the reinforcing elements of said at least two working crown layers are inextensible.

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

[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 an 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 still provide that the crown reinforcement can be completed between the carcass reinforcement and the innermost radially working layer. close to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 45° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement. Advantageously, said triangulation layer consists of two half-layers positioned axially on either side of the circumferential median plane.

[0097] Other advantageous details and characteristics of the invention will emerge below from the description of exemplary embodiments according to the invention with reference to figures 1 and 2 which represent: figure 1, a meridian view of a diagram of a tire according to an embodiment of the invention, figure 2, a mass distribution curve as a function of the diameter of the reinforcing fillers.

[0098] Figure 1 is not drawn to scale to simplify understanding. The figure represents only a half-view of a tire that extends symmetrically about the XX' axis, which represents the circumferential median plane, or equatorial plane, of a tire.

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

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

[0101] The crown frame itself is topped with a tread 5.

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

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

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

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

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

[0107] The engagement zone of the layer C between the two working crown layers 41 and 42 is defined by its thickness or more precisely the radial distance d between the end of the layer 42 and the layer 41 and by the axial width D of the layer C between the axially inner end of said layer C and the end of the radially outer working crown layer 42. The radial distance d is equal to 2.8 mm, i.e. approximately 2.1 times the diameter (|>2 of the reinforcing elements of the working crown layer 42, the diameter <|)2 being equal to 1.35 mm. The axial distance D is equal to 19 mm, i.e. approximately 14 times the diameter <|)2 of the reinforcing elements of the working crown layer 42.

[0108] Figure 2 illustrates a curve 6 of mass distribution (expressed in relative mass) as a function of the diameter of siliceous filler particles (expressed in nm), obtained in accordance with ISO 20927 of 2019 using a method for determining the dimensional distribution by centrifugal disc, 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 distribution value 7.

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

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

[0112] The different mixtures used are listed below, expressing for each of the mixtures containing a siliceous type filler the BET specific surface area, the FWHM width, the diameter D mo of, as well as the FWHM / D ratio mo of.

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

[0114] First tires II according to the invention comprise calendering layers of the two working layers consisting of mixture I, layer C and the elastomeric mixture associated with the circumferential reinforcement elements being consisting of mixture RI.

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

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

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

[0118] First reference tires T1 differ from 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 mixture RI; the calendering layers of the two working layers, the layer C and the elastomeric mixture associated with the circumferential reinforcement elements are thus made up of the mixture RI.

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

[0120] Third reference tires T3 comprise calendering layers of the two working layers, layer C and the elastomeric mixture associated with the circumferential reinforcement 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 requiring each of the tires to roll in a straight line, on an internal steering wheel with a development of 40m, at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 4230 kg, progressively increased to reduce the duration of the test. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

[0123] The results are presented in the following table. The mileage traveled by the tires before a crack appears at the end of the crown reinforcement is noted in relative terms, with a value of 100 being assigned to the reference tire TL

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

[0125] The results are presented in the following table. The mileage traveled by the tires before a crack appears at the end of the crown reinforcement is noted in relative terms, with a value of 100 being assigned to the reference tire TL

[0126] Tests to characterize the breaking strength of a tire crown reinforcement subjected to aggression were carried out by rolling with vehicles traveling for 20,000 km by performing rolling cycles including a section at 80 km / h on the road for 10 km, a section at 30 km / h on a bed of stones for 3 km and a section over 50 m at idle in salt-saturated water. The tires are then detreaded to reveal the radially outermost working layer to measure the lengths of corroded cables.

[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

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

[0129] The results of the measurements are presented in the following table; they are expressed in Kg / t, a value of 100 being attributed to the reference tire TL

Claims

CLAIMS 1 - Tire (1) for a heavy goods vehicle, with a radial carcass reinforcement (2) comprising a crown reinforcement (4) formed of at least two working crown layers (41, 43) each comprising metal reinforcing elements inserted between two calendering layers of elastomeric mixture, the crown reinforcement (4) being radially capped with a tread (5), said tread (5) being joined to two beads by means of two sidewalls, characterized in that at least the radially outermost calendering layer of at least the radially outermost working crown layer (43) is an elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer,natural rubber or synthetic polyisoprene in the case of blending being present at a majority rate compared to the rate of the other diene elastomer(s) used and a reinforcing filler consisting of a siliceous type filler, with a BET specific surface area of ​​between 50 and 150 m, 2 / g, used at a rate of between 20 and 80 pce, and preferably between 30 and 50 pce and in that the FWHM / D ratio mo of the FWHM width, expressed in nm, of distribution measured at 50% of the distribution maximum on the mass distribution curve as a function of the diameter of the siliceous type filler particles obtained according to the ISO20927 standard of 2019, on the diameter Dmode, expressed in nm, of the siliceous type filler particles at the distribution maximum, is greater than or equal to 0.

77. 2 - Tire (1) according to claim 1, characterized in that the FWHM / Dmode ratio is greater than or equal to 0.

80. 3 - Tire (1) according to claim 2, characterized in that the siliceous type filler of the elastomeric mixture constituting at least said radially outermost calendering layer of at least the radially outermost working crown layer (43) has a BET specific surface area greater than 130 m 2 / g, and preferably greater than 140 m 2 / g. 4 - Tire (1) according to one of claims 1 to 3, characterized in that the maximum value of tan(ô), noted tan(5)max, of at least the radially outermost calendering layer of at least the radially outermost working crown layer (43), is less than or equal to 0.

11. 5 - Tire (1) according to one of claims 1 to 4, characterized in that the siliceous type filler of the elastomeric mixture constituting at least said radially outermost calendering layer of at least the radially outermost working crown layer (43) is a blend of two silicas. 6 - Tire (1) according to one of the preceding claims, a layer C of elastomeric mixture being arranged between at least the ends of said at least two working crown layers (41, 43), characterized in that said layer C is a layer of elastomeric mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of 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 BET specific surface area of ​​between 50 and 150 m 2 / g, used at a rate of between 20 and 80 pce, and preferably between 30 and 50 pce and in that the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum 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 the siliceous-type filler particles at the distribution maximum, is greater than or equal to 0.

77. 7 - Tire (1) according to claim 6, characterized in that the maximum value of tan(ô), noted tan(5)max, of said layer C is less than or equal to 0.

11. 8 - Tire (1) according to one of claims 6 or 7, characterized in that the siliceous type filler of the elastomeric mixture constituting said layer C is a blend of two silicas. 9 - Tire (1) according to one of the preceding claims, the crown 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 mixture based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in the case of a blend being present at a majority rate compared to the rate of the other or other diene elastomers used and a reinforcing filler consisting of a filler of the type siliceous, with a BET specific surface area of ​​between 50 and 150 m 2 / g, used at a rate of between 20 and 80 pce, and preferably between 30 and 50 pce and in that the FWHM / Dmode ratio of the FWHM distribution width, expressed in nm, measured at 50% of the distribution maximum 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 the siliceous-type filler particles at the distribution maximum, is greater than or equal to 0.

77. 10 - Tire (1) according to claim 9, characterized in that the maximum value of tan(ô), noted tan(5)max, of the elastomeric mixture associated with the circumferential reinforcing elements is less than or equal to 0.11 11 - Tire (1) according to one of claims 9 or 10, characterized in that the siliceous type filler of the elastomeric mixture associated with the circumferential reinforcing elements is a blend of two silicas. 12 - Tire (1) according to one of the preceding claims, the crown 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 crown layers (41, 43). 13 - Tire (1) according to one of the preceding claims, the crown 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 - Tire (1) according to one of the preceding claims, characterized in that the reinforcing elements of said at least two working crown layers (41, 43) are crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction. 15 - Tire (1) according to one of the preceding claims, characterized in that the reinforcing elements of said at least two working crown layers (41, 43) are inextensible metal cables.

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