Optimized structure of a tire for civil engineering

Abstract

The present invention relates to a tyre (1) for civil engineering vehicles, said tyre (1) comprising a tread (2) intended to come into contact with the ground via a tread surface (21), said tread surface (21) having an axial end E1, the distance (11) in the meridian plane between the axial end E1 of the tread surface and the inner cavity (5) being at least equal to 120 mm. The tread (2) comprises two rubber compounds (23, 24): a first material intended to come into contact with the ground and a second so-called diffuser material (24) located radially inside the contact material (23). The thermal conductivity of the second rubber compound (24) is at least equal to 0.35 W / mK.

Description

Technical Field

[0001] The subject of this invention is radial tires intended for mounting on heavy-duty vehicles of the construction site type, and more specifically, the invention relates to the tread of such tires. Background Technology

[0002] Radial tires designed for use on heavy-duty vehicles intended for use on construction sites are designated as radial tires within the meaning of the standards of the European Tire and Rim Technology Organization (or ETRO).

[0003] For example, within the meaning of the ETRTO 2020 standard, radial tires for heavy-duty vehicles of the construction site type are intended to be mounted on rims with a diameter of at least 25 inches. More specifically, the present invention is intended for tires of large dump trucks of the construction site type, and therefore for tires with a rim diameter of at least 57 inches.

[0004] Because tires have a geometry that exhibits rotational symmetry about their axis of rotation, their geometry is typically described in the meridional plane, which contains the tire's axis of rotation. For a given meridional plane, the radial, axial, and circumferential directions represent the directions perpendicular to the tire's axis of rotation, parallel to the axis of rotation, and perpendicular to the meridional plane, respectively. The circumferential direction is tangent to the circumference of a circle.

[0005] In the following text, "radially inside" and "radially outside" mean "closer" to the tire's axis of rotation and "farther" from the tire's axis of rotation, respectively. "Axially inside" and "axially outside" mean "closer" to the tire's equatorial plane and "farther" from the tire's equatorial plane, respectively, where the tire's equatorial plane is a plane passing through the middle of the tread surface and perpendicular to the axis of rotation.

[0006] Typically, a tire includes a tread designed to contact the ground via a tread surface, with two axial ends of the tread connected to two beads via two sidewalls, the two beads providing a mechanical connection between the tire and a rim designed to mount the tire.

[0007] Radial tires also include a reinforcement consisting of a crown reinforcement located radially inside the tread and a carcass reinforcement located radially inside the crown reinforcement.

[0008] Radial tires for heavy-duty vehicles used in construction sites typically comprise at least one carcass layer. This carcass layer usually includes a metal reinforcement coated with an elastomeric or elastic polymer material (also known as a rubber compound), obtained through blending and referred to as a surface compound or surface rubber. The carcass layer includes a main section that connects two bead sections and typically forms a bead by wrapping around a generally metallic circumferential reinforcing element (called a bead cord) from the inside to the outside of each bead. The metal reinforcements of the carcass layer are substantially parallel to each other and form an angle between 80° and 90° with respect to the circumferential direction.

[0009] The crown reinforcement of radial tires for construction site vehicles comprises a stack of circumferentially extending crown layers located radially outside the carcass reinforcement. Each crown layer consists of a reinforcement of typically metal, which are parallel to each other and encapsulated in a polymer material of the type of elastomer or coated compound (or rubber).

[0010] In the tire crown layer, a protective layer and a working layer are usually distinguished. The protective layer constitutes a protective reinforcement and is located radially on the outermost side, while the working layer constitutes a working reinforcement and is located radially between the protective reinforcement and the carcass reinforcement.

[0011] The protective reinforcement, including at least one protective layer, primarily protects the working layer from mechanical or physical-chemical attacks that may propagate radially toward the interior of the tire through the tread.

[0012] The protective reinforcement typically comprises two radially stacked protective layers formed of elastic metal reinforcements that are parallel to each other in each layer and intersect from one layer to the other, forming an angle of at least 10° with respect to the circumferential direction.

[0013] The working reinforcement, typically comprising at least two working layers, serves to belt the tire and impart stiffness and road retention. The working reinforcement absorbs mechanical inflation stresses and driving-induced mechanical stresses, which are generated by tire inflation pressure and transmitted through the carcass reinforcement, and driving-induced mechanical stresses generated when the tire is on the ground and transmitted through the tread. A recurring problem with tire treads is rolling resistance and thermal effects, attributed to the thickness of these tires due to their very large tread thickness relative to tire size and the durability requirements of users.

[0014] The working reinforcement typically comprises two radially stacked working layers formed of inextensible metal reinforcements that are parallel to each other in each layer and intersect from one layer to the other, forming an angle of at most 50°, preferably at least 15° and at most 45°, with respect to the circumferential direction. This double-layer structure generally ensures sufficient edge bending stiffness for acceptable vehicle handling.

[0015] To reduce shear stress and heat generated by mechanical inflation stress transmitted to the working reinforcement, a known practice is to place a ring reinforcement radially on the outer side of the carcass reinforcement. The ring reinforcement (which at least partially absorbs mechanical inflation stress) improves the durability of the crown reinforcement by strengthening it. The ring reinforcement can be located radially inside the working reinforcement, between two working layers of the working reinforcement, or radially outside the working reinforcement.

[0016] In construction site applications, hoop reinforcements may comprise two radially stacked hoop layers formed of metal reinforcements, which are parallel to each other in each layer and intersect from one layer to the other, forming an angle of up to 10° with respect to the circumferential direction. Another embodiment of the hoop reinforcement comprises circumferentially wound hoop wires or continuous hoop strips, which form an angle of up to 5° with respect to the circumferential direction.

[0017] Regarding metal reinforcements, the mechanical characteristics of a metal reinforcement are represented by a curve (called a force-elongation curve) showing the change of tensile force (in N) applied to the metal reinforcement as a function of its relative elongation (in %). From this force-elongation curve, the mechanical tensile characteristics of the metal reinforcement are derived, such as structural elongation As (in %), total elongation at break At (in %), breaking force Fm (maximum load in N), and breaking strength Rm (in MPa). These characteristics are measured according to the 2014 standard ASTM D2969-04.

[0018] By definition, the total elongation At of a metal reinforcement is the sum of its structural elongation, elastic elongation, and plastic elongation (At = As + Ae + Ap) (especially at fracture), where each elongation is non-zero. The structural elongation As arises from the relative positioning of the metal wires constituting the metal reinforcement under low tensile force. The elastic elongation Ae arises from the actual elasticity of the metal of the metal wires constituting the metal reinforcement, which, when considered independently, exhibits metallic behavior following Hooke's law. The plastic elongation Ap arises from the plasticity of the metal of these wires when considered independently (i.e., irreversible deformation exceeding the yield point). These various elongations and their respective meanings are well known to those skilled in the art and are described, for example, in documents US5843583, WO2005 / 014925, and WO2007 / 090603.

[0019] A tensile modulus (in GPa) is also defined at each point on the force-elongation curve of the metal reinforcement, which represents the slope of the straight line tangent to the force-elongation curve at that point. In particular, the tensile modulus of the elastic linear portion of the force-elongation curve is called the tensile modulus of elasticity or Young's modulus.

[0020] In metal reinforcements, a distinction is usually made between elastic metal reinforcements (such as those used in protective layers) and non-stretchable or non-stretchable metal reinforcements (such as those used in working layers).

[0021] The elastic metal reinforcement in its non-rubberized state is characterized by a structural elongation As of at least 0.5% and a total elongation at break At of at least 3%. In addition, the tensile modulus of elasticity of the elastic metal reinforcement is at most 180 GPa, and is typically between 40 GPa and 150 GPa.

[0022] The inextensible metal reinforcement is characterized by a total elongation At of at most 0.2% under a tensile force equal to 10% of the breaking force Fm. Furthermore, the tensile modulus of the inextensible metal reinforcement is typically between 150 GPa and 200 GPa.

[0023] Another well-known method for improving rolling resistance and crown thermal effects is to reduce the hysteresis of materials in the crown, filler rubber, edge rubber at the ends of the crown layer, tread, and surface compound, but this list is not exhaustive. However, using materials with higher hysteresis at the crown to improve rolling resistance is completely counterintuitive. Summary of the Invention

[0024] The inventors’ goal is to improve the rolling resistance performance of construction site tires by using an elastomer material with better thermal conductivity in the tread (even if its hysteresis is worse).

[0025] According to the present invention, this objective has been achieved by a tire for a construction site type vehicle, wherein when the tire is mounted on a rim, the tire defines an inner cavity designed to receive inflation gas, the tire comprising: - Tread, the tread being designed to contact the ground via a tread surface having an axial end E1. - The tread has a wear limit for removal and comprises at least two rubber compounds: a first rubber compound (referred to as the contact material) and at least one second rubber compound (referred to as the diffusion material), the contact material being designed to contact the ground, and the diffusion material being located radially inside the recommended wear limit and the contact material. - A crown reinforcement, which is located radially inside the tread and radially outside the carcass reinforcement. - In the meridional plane, the distance between the axial end E1 of the tread surface and the inner cavity is at least 120 mm. - The thermal conductivity of the diffusion material is at least 0.35 W / mK. - The maximum radial thickness of the diffused material measured in the meridional plane (OYZ) is at least 10 mm.

[0026] This invention involves using a portion of the tread to better dissipate heat through a particularly high thermal conductivity (at least equal to 0.35 W / mK). This tends to improve tire curing and the overall performance of the tire's rubber compound. Specifically, the resulting improvement in rolling resistance is counterintuitive, and the inventors envision a significant reduction in the gradient phenomenon in the curing state of the rubber compound within the tire. Typically, in the case of construction tires, considering the varying crown thicknesses at the shoulder (the area near the axial end of the tread) and the center, for the rubber compound at the tire core to cure (fully cross-link), it is inevitable that the rubber compound in contact with the heating element of the mold will be in a higher curing state than the rubber compound in the center, which is therefore not optimal unless curing at low temperatures is possible, but the duration makes this approach impractical for industrial application. By placing a highly thermally conductive rubber compound near the heating element (particularly the portion of the mold that forms the grooves), the curing gradient must be sufficiently reduced to allow for measurement of the effect on the tire.

[0027] On the other hand, these highly thermally conductive materials do not possess sufficient properties to constitute the tread portion intended for contact with the ground, whether in terms of wear, rolling resistance, or impact resistance. They also lack the crack-resistant properties of compounds used near the ends of the crown ply. Therefore, it makes no sense to use them as crown filler rubber or crown release rubber. However, they can be used between tread contact materials and crown reinforcements.

[0028] This is effective as long as the tire is intended for use on construction sites and the distance between the axial end E1 of the tread surface and the inner cavity in the radial plane (OYZ) is at least 130 mm. For smaller tires (e.g., heavy-duty tires, whose curing time is sometimes 10 times shorter), the effect is almost imperceptible. On the other hand, in construction site type tires, the inventors were surprised to observe that rolling resistance was improved despite increased hysteresis in the rubber compound used. Construction site type tires can also be described as having a radial tread height of at least 65 mm, measured from the tread surface to the bottom of the groove. The recommended limits for removal are understood to mean, for example, the limits given by wear indicators present in the tread pattern, or the tire manufacturer's data (specific recommendations for tire removal based on expert opinion, which are not necessarily marked on the tire).

[0029] An advantageous solution is that the axial distance from the outermost axial end of the diffuser material to the central circumferential plane (OXZ) passing through the middle of the tread is at least 90% equal to the axial distance from the axial end E1 of the contact surface to the central circumferential plane (OXZ). Specifically, considering two characteristics (i.e., the maximum local thickness of the tire and the presence of elastomeric materials that sometimes contain silica (as described in document WO2023 / 110499 A1)), it is appropriate to place an elastomeric diffuser material that allows for better diffusion of curing heat at the ends of the crown layer, the size of which is proportional to the axial width of the tread. This diffusion can maintain or even shorten the curing time, thereby allowing the elastomeric material to achieve optimal curing (despite the local thickness of the tire). The invention remains effective even if the diffuser material does not form a continuous layer from one shoulder to the other on both sides of the meridional plane, because optimal curing of the tire depends on the curing of its thickest region, and therefore, for the crown, on the shoulders.

[0030] Advantageously, the diffuser material is continuous between the axial ends located on both sides of the equatorial plane (the central circumferential plane (OXZ) passing through the center of the tread), and the radial thickness of the diffuser material measured on the meridional plane (OXY) at the center of the tread is at least equal to 10 mm, preferably at least equal to 15 mm. Advantageously, the radial thickness of the diffuser material measured on the meridional plane (OXY) at the center of the tread is the minimum thickness of the diffuser material in its axial width, especially due to the crown thickness (which is the smallest at the center of the tread). This configuration of the diffuser material appears to allow for better relative curing in the center and shoulder. For a material that is a good conductor as an elastomer, the heat reaching the shoulder comes from the heat elements of the mold, but even more so from the central portion of the crown (where the temperature rises more rapidly due to its approximately 30% reduction in thickness). The minimum thickness makes the minimum heat flow have a visible effect.

[0031] Advantageously, the maximum radial thickness of the diffuser material measured in the meridional plane (OYZ) is at least 15 mm, preferably at least 40 mm. Starting from a maximum thickness of 10 mm of diffuser material at the tire shoulder, the curing time can be reduced by about 10 minutes, and a stable phase is reached up to a maximum thickness of about 40 mm of diffuser material. Beyond this thickness, the improvement in curing time and rolling resistance becomes more significant (curing time reduction exceeding 20 minutes), even though the hysteresis properties of the diffuser material are higher than those of the reference tire material. For diffuser material thicknesses less than 10 mm at the tire shoulder, the inventors have not observed any measurable significant effects.

[0032] Advantageously, when the tread includes grooves (which include walls and bottoms), the diffused material is located radially inside the bottom of all the grooves in the tread to avoid contact with the ground (which would lead to rapid wear).

[0033] Advantageously, the contact material contains at least 30 phr of silica. Given its insulating properties, contact materials containing at least 30 phr of silica are complex for use in construction sites. This is made possible if their hysteresis performance is lower than that of carbon black-based contact materials, and this is generally the case if they are configured for this purpose. Therefore, they can reduce rolling resistance, but their insulating properties prevent the dissipation of heat generated at the shoulder block. Tests have shown that the reduction in rolling resistance produced by these contact materials is accompanied by a 10°C increase in shoulder temperature, thus reducing tire durability to below reasonable levels. Furthermore, for a constant curing temperature, silica-based contact materials require a longer curing time of nearly 30 minutes. The use of graphite-based diffusion materials as defined in this invention avoids the adverse effects on curing time and shoulder temperature, and thus can benefit from the advantages of silica-based materials in terms of rolling resistance as contact materials.

[0034] The thermal conductivity level of the diffusion material has been obtained using an elastomer material based on at least one elastomer matrix, filler, and vulcanization system. The filler includes graphite and reinforcing filler. The elastomer matrix contains at least 50 phr (per hundred parts elastomer) of a diene elastomer selected from isoprene elastomers, butadiene elastomers, and mixtures of these diene elastomers. The reinforcing filler mainly comprises carbon black. The grain size Lc of the graphite ranges from 80 nm to 500 nm, more preferably from 90 nm to 400 nm, and even more preferably from 100 nm to 300 nm. The total content of the filler is less than or equal to 60 phr.

[0035] "Diene" elastomers (or indiscriminately, rubbers) (whether natural or synthetic) should be understood in a known manner to mean elastomers that are at least partially (i.e., homopolymers or copolymers) composed of diene monomer units (monomers with two conjugated or non-conjugated carbon-carbon double bonds). In this patent application, diene elastomers are defined as non-thermoplastic. Preferably, when diene elastomers are copolymers, they are random polymers. Diene elastomers can be classified into two categories: "substantially unsaturated" or "substantially saturated." "Substantially unsaturated" generally means diene elastomers that are at least partially derived from conjugated diene monomers and have a diene source (conjugated diene) unit content greater than 15% (mol%); therefore, diene elastomers such as butyl rubber or EPDM-type copolymers of diene and α-olefins do not fall into the foregoing definition but can be specifically referred to as "substantially saturated" diene elastomers (low or very low diene source unit content, always less than 15 mol%). The diene elastomers that can be used in the context of the diffusion material according to the invention are substantially unsaturated diene elastomers. Therefore, butyl elastomers cannot be used in this context because they are substantially saturated diene elastomers.

[0036] The elastomeric matrix of the diffusion material composition comprises at least 50 phr of a diene elastomer selected from isoprene elastomers, butadiene elastomers, and mixtures thereof. For example, the elastomeric matrix may comprise isoprene elastomers or mixtures thereof, butadiene elastomers or mixtures thereof, or even mixtures of isoprene and butadiene elastomers. These diene elastomers have a diene source (conjugated diene) unit content greater than 15 mol%. Therefore, the elastomeric matrix of the diffusion material composition comprises at least 50 phr of a diene elastomer with a diene source (conjugated diene) unit content greater than 15 mol%; this elastomer is selected from isoprene elastomers, butadiene elastomers, and mixtures thereof. In addition to the aforementioned diene elastomers, the elastomeric matrix may also comprise thermoplastic elastomers.

[0037] The elastomeric composition of the diffusion material comprises fillers, including reinforcing fillers and graphite. The term "filler" herein refers to any type of filler, whether reinforcing, unreinforcing, or inert. As reinforcing fillers, those skilled in the art know of carbon black, or inorganic reinforcing fillers of the silica or alumina type. As unreinforcing or inert fillers, those skilled in the art know of graphite, clay, talc, mica, etc. In this context, zinc oxide is not considered an unreinforcing filler. Zinc oxide is an activator of the vulcanization system. The total filler content in the elastomeric composition of the diffusion material (i.e., the sum of the reinforcing and unreinforcing filler contents) is less than or equal to 60 phr, preferably less than or equal to 55 phr, more preferably less than or equal to 50 phr, preferably in the range of 20 phr to 55 phr, and more preferably in the range of 25 phr to 50 phr. At this total filler content, a good trade-off is achieved between impact resistance, stiffness, fracture strain, and thermal conductivity, making it suitable for use in tire treads.

[0038] The elastomeric composition of the diffusion material includes a reinforcing filler, which primarily comprises carbon black. In addition to carbon black (which is the primary reinforcing filler), the elastomeric composition of the diffusion material may optionally include a second reinforcing filler, such as silica. The total content of the reinforcing filler (i.e., the sum of the carbon black content and the silica content (if present)) is less than or equal to 55 phr, more preferably less than or equal to 50 phr, more preferably less than or equal to 45 phr, and even more preferably less than or equal to 44 phr. This content of the reinforcing filler is advantageously greater than or equal to 20 phr, more preferably greater than or equal to 25 phr, and even more preferably greater than or equal to 30 phr. Preferably, the content of the reinforcing filler in the elastomeric composition is in the range of 20 phr to 55 phr, more preferably 25 phr to 50 phr, and even more preferably 30 phr to 45 phr.

[0039] Preferably, for the diffusion material, carbon black accounts for more than 55% by weight of the total weight of the reinforcing filler, even more preferably more than 60% by weight, even more preferably more than 80% by weight, and even more preferably 100% by weight of the total weight of the reinforcing filler.

[0040] Therefore, preferably, for the diffusion material, the content of reinforcing filler is less than or equal to 55 phr, more preferably less than or equal to 50 phr, more preferably less than or equal to 45 phr, and carbon black accounts for more than 55% by weight of the total weight of the reinforcing filler, even more preferably more than 60% by weight, even more preferably more than 80% by weight, even more preferably 100% by weight of the total weight of the reinforcing filler.

[0041] Even more preferably, the content of reinforcing filler in the elastomer composition of the diffusion material is in the range of 20 phr to 55 phr, more preferably 25 phr to 50 phr, more preferably 30 phr to 45 phr, and carbon black accounts for more than 55% by weight of the total weight of the reinforcing filler, even more preferably more than 60% by weight, even more preferably more than 80% by weight, even more preferably 100% by weight of the total weight of the reinforcing filler.

[0042] The diffusion material composition comprises at least one type of graphite. The elastomeric composition of the diffusion material may comprise a single type of graphite as described below or a mixture of multiple types of graphite as described below.

[0043] Graphite generally refers to a stack of graphene planes, a sheet of material about one atom thick in which carbon atoms are arranged in a substantially hexagonal lattice. Unlike carbon black, graphite has a crystalline structure. Graphite can be natural or synthetic. When graphite is synthetic, it can be obtained, in particular, through a complex process of baking petroleum coke at very high temperatures. Graphite is not considered a reinforcing filler and is therefore not taken into account when calculating reinforcing fillers. However, graphite is a filler and is therefore considered when calculating the total filler content.

[0044] The grain size (labeled Lc) of graphite that can be used in diffusion materials is in the range of 80 nm to 500 nm, more preferably 90 nm to 400 nm, and even more preferably 100 nm to 300 nm.

[0045] The BET specific surface area of ​​graphite that can be used in diffusion materials can reach 10 m². 2 / g to 50 m 2 / g, preferably 15 m 2 / g to 40 m 2 / g, or even more preferably 20 m 2 / g to 30 m 2 Within the range of / g.

[0046] The graphite particle size distribution D that can be used in this context 90 It can be in the range of 40 nm to 110 nm, more preferably 50 nm to 100 nm, and even more preferably 60 nm to 90 nm. 90 The 90th percentile of the mass distribution corresponding to particle size, i.e., 90% by mass of the particles have a particle size smaller than D. 90 The size, and 10% by mass of the particles have a size greater than D. 90 The size. D 90 It is expressed in nm.

[0047] The apparent density (Scott density) of graphite that can be used in diffusion materials can be greater than or equal to 0.10 g / cm³. 3 Preferably greater than 0.12 g / cm³ 3 .

[0048] Preferably, the graphite that can be used in the context of this invention is expanded graphite.

[0049] Preferably, the graphite content in the elastomer composition of the diffusion material is in the range of 1 phr to 12 phr, more preferably 1 phr to 11 phr.

[0050] Preferably, the mass ratio of graphite to carbon black in the elastomer composition is in the range of 0.05 phr to 0.5 phr, more preferably 0.06 phr to 0.4 phr.

[0051] Surprisingly, the inventors have confirmed that using elastomeric materials (which have a trade-off between stiffness, fracture strain and thermal conductivity) as diffusion materials within the scope mentioned produces the expected performance trade-off.

[0052] The method used to measure the BET specific surface area of ​​graphite is based on the adsorption isotherm of liquid nitrogen recorded at 77 K in the range of p / p0 = 0.04–0.26. The monolayer capacity can be determined following the procedure proposed by Brunauer, Emmett, and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309–319). The specific surface area can be calculated based on the cross-sectional area of ​​nitrogen molecules, the monolayer capacity, and the sample weight.

[0053] Apparent density (or Scott density) is determined according to standard ASTM B329-98 (2003) by passing dry graphite powder through a Scott volumetric meter.

[0054] The size of the crystals was determined by X-ray diffraction according to the ASTM D5187-10 method adapted by those skilled in the art for samples derived from tires.

[0055] Thermal conductivity is a physical quantity that characterizes a material's ability to transfer heat via conduction. It represents the amount of heat transferred per unit surface area per unit time under a temperature gradient of 1 Kelvin / m. It is expressed in W·m³. -1 ·K -1 Therefore, 1 W·m -1 ·K -1 Thermal conductivity is expressed in 1 m 2Heat is diffused through the material over a distance of 1 m over its surface area via thermal conduction. Thermal conductivity was measured at room temperature (23°C) using a Hotdisk TPS 2500 thermal analyzer equipped with a Type 5501 probe, according to standard ISO 22007-2:2015. The dimensions of the test specimens were adjusted by a person skilled in the art based on the amount of rubber removed from the cured tire.

[0056] To protect all tread layers (working layer, ring layer, and triangular layer) from impacts caused by driving on rocky surfaces, it is advantageous for the protective layer to have the maximum axial width of all tread layers. Advantageously, for construction site type tires optimized for this application of tread impact resistance, at least one reinforcing element of the protective layer has a diameter of at least 2.5 mm, a tensile modulus of at most 100 GPa, and the surface compound of the tread layer comprises natural rubber.

[0057] If the tread reinforcement includes at least one ring layer comprising a metal reinforcement forming an angle ATE of at most 10° with respect to a circumferential direction tangent to the tire's circumference, and the axial width of the ring layer is at most 0.7 times the axial width of the narrowest working layer, then the tread durability can be improved. The presence of such a ring layer limits the rise of the tire tread during inflation and enhances the effectiveness of other features of the invention.

[0058] The dynamic mechanical properties of the rubber composition (rubber type, compound) were measured on an adhesive specimen taken from a tire. The specimen was described, for example, in Figure X2.1 (circular version) of standard ASTM D 5992-96 (first adopted in 1996 and published in September 2006). If possible, the specimen diameter “d” was 10 mm [0 to +0.04 mm], and the thickness “L” of each portion of the rubber composition was 2 mm [1.85–2.20]. Those skilled in the art will recognize how to select and adjust the specimen size based on the amount of available and usable compound, particularly when the specimen is taken from a finished product such as a tire. These properties were measured on a Metravib VA4000 viscosity analyzer. The terms complex modulus, elastic modulus, and viscous modulus refer to dynamic properties known to those skilled in the art. The “complex modulus” G* is defined by the following relationship: G* Where G' represents the elastic modulus and G'' represents the viscous modulus. The phase angle δ between force and displacement (expressed as dynamic loss tanδ) is equal to the ratio G'' / G'. The response of a vulcanized rubber composition specimen subjected to simple alternating sinusoidal shear stress at a frequency of 10 Hz under stress applied symmetrically around its equilibrium position is recorded. The specimen is conditioned prior to temperature scanning measurements. For this purpose, the specimen is subjected to sinusoidal shear stress load at 10 Hz, 100% full-size deformation, and 100°C. Attached Figure Description

[0059] Referring to a tire with a size of 40.00R57, in Figure 1 Features of the invention are shown in (which are schematic and not drawn to scale).

[0060] Figure 1 The diagram shows a meridional cross-section of the tread of a tire (1) for heavy-duty vehicles used in construction sites, the tread containing a diffusion material (24) between a contact material (23) and a tread reinforcement (3). Of course, the invention is not limited to the single geometry shown; for example, and in an inexhaustible manner, various contact materials, diffusion materials with radially variable thickness along the axial direction, and various diffusion materials can be imagined. Detailed Implementation

[0061] therefore, Figure 1 The tire crown is shown, comprising a crown reinforcement (3) located radially inside the tread (2) and radially outside the carcass reinforcement (4). The crown reinforcement (3) radially comprises a protective reinforcement (31), a working reinforcement (32), and a ring reinforcement (33) from the outside to the inside. The protective reinforcement has two protective layers comprising mutually parallel elastic metal reinforcements coated with an elastomeric material or a coating compound. The working reinforcement (32) comprises two working layers, each with a non-stretchable metal reinforcement coated with an elastomeric material, parallel to each other, forming the same angle between 15° and 50° with the circumferential direction XX', and intersecting from one working layer to the other. The protective layer protrudes axially beyond the widest working layer (in this case, the innermost working layer radially). The hoop reinforcement (33) includes two hoop layers, each of which has a metal reinforcement coated with an elastomeric material, is parallel to each other, forms an angle between 5° and 10° with the circumferential direction XX', and intersects from one hoop layer to the other.

[0062] The tread includes a contact material (23) designed to contact the ground via a tread surface (21) having an axial end E1 and a tread height H. The contact material is located radially outside a diffusion material (24) located radially inside a wear limit (221) recommended for removal, which is indicated herein by a wear indicator at the bottom (222) of a groove or recess (22).

[0063] The tire defines an inner cavity (5) which is designed to receive inflation gas when the tire is mounted on the rim.

[0064] Figure 1 It shows: - The distance (11) between the axial end E1 of the tread surface (21) and the inner cavity (5); - The axial distance (112) from the axial end (241) of the diffusion material (24) to the central circumferential plane (OXZ) passing through the middle of the tread (2). - The axial distance (113) from the axial end E1 of the contact surface (21) to the central circumferential plane (OXZ).

[0065] The present invention is also applicable to tires with only 5 crown layers and 1 protective layer (which is not the widest crown layer among other possible structural variants included in the present invention).

[0066] Figure 1 Only one example of a possible structure for a construction site type tire is shown. The invention was tested or evaluated on a commercial “Michelin XDR3” tire with a size of 40.00R57. The distance (11) between the axial end E1 of the tread surface (21) and the inner cavity (7) in the radial plane (OYZ) is equal to 217 mm, and the tread height (H) is equal to 97 mm. The radial thickness of the diffuser material near the axial end E1 of the tread surface is equal to 48 mm, and the radial thickness at the center plane is equal to 23 mm.

[0067] For each test, the tire according to the invention was compared with a reference tire of the same size. Except for the diffusion material, the tread pattern, metal reinforcement elements, and elastomer materials were identical.

[0068] Reference tire R1 contains a standard graphite-free blend as the diffusion material, with a thermal conductivity of 0.28 W / mK and a maximum dynamic loss tanδ of 0.052 at 10 Hz and a temperature of 100°C (a commonly used measure of its hysteresis performance). Tire R1 has a contact material for hard surfaces and high-temperature mining environments, i.e., the contact material has a maximum dynamic loss tanδ of 0.063 measured at 10 Hz and a temperature of 100°C according to the same standard ASTM D 5992-96, and an elastic modulus G' of 1.141 MPa measured at 10 Hz and 10°C with 35% deformation according to standard ASTM D 5992-96.

[0069] The tire according to the invention is the same as tire R1, except that the diffusion material is a graphite material containing 7 phr, the anisotropic thermal conductivity of which is at least equal to 0.38 W / mK, average equal to 0.46 W / mK, and the maximum dynamic loss tanδ at 10 Hz and 100°C is equal to 0.055. The curing time is adjusted according to the thermal conductivity characteristics of the diffusion material and shortened by about 40 minutes.

[0070] Surprisingly, rolling resistance measurements showed that the tire according to the invention exhibited a 10% improvement in performance compared to tire R1, and an improvement of at least 10° in tread thermal effect, despite a significant 6% increase in the hysteresis of the diffusion material in the tire according to the invention compared to the diffusion material in tire R1. This demonstrates the advantages of the invention.

Claims

1. A tire (1) for a vehicle of the construction site type, said tire (1) defining an inner cavity (5) which, when the tire is mounted on a rim, is intended to receive inflation gas, said tire (1) comprising: - Tread (2), the tread (2) being designed to contact the ground via a tread surface (21) having an axial end E1, - The tread (2) has a wear limit (221) for removal and comprises at least two rubber blends (23, 24), namely a first rubber blend (23) referred to as a contact material and at least one second rubber blend (24) referred to as a diffusion material, the contact material being intended to contact the ground, and the diffusion material being located radially inside the recommended wear limit (221) and the contact material (23). - A crown reinforcement (3), which is located radially inside the tread (2) and radially outside the carcass reinforcement (4). - In the meridional plane, the distance (11) between the axial end E1 of the tread surface (21) and the inner cavity (5) is at least 120 mm. - Characterized by the fact that the thermal conductivity of the diffusion material (24) is at least equal to 0.35 W / mK, and the maximum radial thickness of the diffusion material (24) measured in the meridional plane (OYZ) is at least equal to 10 mm.

2. The tire according to claim 1, wherein, The radial tread height (H) of the tread is at least 65 mm.

3. The tire according to claim 1 or 2, wherein the tread includes a groove (22), the groove (22) including a wall and a bottom (222), wherein, The diffusion material (24) is located radially inside the bottom (222) of all grooves (22) of the tread (2).

4. The tire (1) according to any one of the preceding claims, wherein, The radial thickness (e) of the diffusion material (24) measured at the center of the tread in the meridional plane (OYZ) is at least 10 mm, preferably at least 15 mm.

5. The tire (1) according to any one of the preceding claims, wherein, The maximum radial thickness of the diffusion material (24) measured in the meridional plane (OYZ) is at least 15 mm, preferably at least 40 mm.

6. The tire (1) according to any one of the preceding claims, wherein, The axial distance (112) from the outermost axial end of the diffusion material (24) to the central circumferential plane (OXZ) passing through the middle of the tread (2) is at least 90% equal to the axial distance (113) from the axial end E1 of the contact surface (21) to the central circumferential plane (OXZ).

7. The tire (1) according to any one of the preceding claims, wherein, The contact material contains at least 30 phr of silicon dioxide.

8. The tire (1) according to any one of the preceding claims, wherein, The diffusion material (24) is based on at least one elastomer matrix, filler and vulcanization system, the filler comprising graphite and reinforcing filler, the elastomer matrix comprising at least 50 phr of diene elastomer selected from isoprene elastomer, butadiene elastomer and mixtures thereof, the reinforcing filler comprising primarily carbon black, the graphite having a grain size Lc in the range of 80 nm to 500 nm, more preferably 90 nm to 400 nm, more preferably 100 nm to 300 nm, and the total content of the filler being less than or equal to 60 phr.

9. The tire (1) according to claim 8, wherein, The total filler content of the diffusion material (24) is less than or equal to 55 phr, preferably less than or equal to 50 phr, preferably in the range of 20 phr to 55 phr, and more preferably in the range of 25 phr to 50 phr.

10. The tire (1) according to claim 8 or 9, wherein, The graphite contained in the diffusion material (24) has a BET specific surface area of ​​10 m². 2 / g to 50 m 2 / g, preferably 15 m 2 / g to 40 m 2 / g, or even more preferably 20 m 2 / g to 30 m 2 Within the range of / g.

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