Optimized architecture of civil engineering pneumatics

Abstract

Tire (1) for construction vehicle comprising two working layers (321, 322), comprising metallic reinforcements and at least two shrink-fit layers (331, 332), of axial widths less than those of the working layers (321, 322), and comprising metallic reinforcements, the innermost radial shrink-fit layer (332) being the shrink-fit layer of greatest axial width. At each axial end of the innermost radially enclosing layer (332), two contiguous rubber mixtures (51, 52, 61, 62), or decoupling mixtures, are arranged, one being radially inside the other, the decoupling mixture (51, 61) furthest radially from the end of the enclosing layer (332) has a dynamic modulus of elasticity measured at 23°C and 10% strain and at 10 Hz, at most equal to 0.7 times the dynamic modulus of elasticity of the decoupling mixture (52, 62) closest radially to the end of the innermost radially oriented shrinkage layer (332). Abstract figure: Figure 1.

Description

Title of the invention: Optimized architecture of civil engineering tires

[0001] The present invention relates to a radial tire, intended to equip a heavy vehicle of the civil engineering type, and more particularly concerns the top of such a tire.

[0002] Radial tires intended to equip a heavy vehicle of the civil engineering type are designated as such in the sense of the standard of the European Tyre and Rim Technical Organisation (European Tyre and Rim Technical Organisation) or ETRTO.

[0003] For example, a radial tire for heavy-duty construction equipment, as defined in ETRTO 2020, is intended to be mounted on a rim with a diameter primarily at least 24 inches. The invention is more particularly intended for tires for mining vehicles and therefore for tires with a diameter of at least 39 inches.

[0004] Since a tire has a geometry of revolution about an axis of rotation, the geometry of the tire is generally described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial, and circumferential directions respectively denote the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire, and perpendicular to the meridian plane. The circumferential direction is tangent to the circumference.

[0005] In what follows, the expressions "radially inside" and "radially outside" respectively mean "closer" and "further" from the axis of rotation of the tire. By "axially inside" and "axially outside," respectively, we mean "closer" and "further" from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tread surface and perpendicular to the axis of rotation.

[0006] Generally, a tire includes a tread, intended to come into contact with a ground via a tread surface, the two axial ends of which are connected via two sidewalls to two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] A radial tire further comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement.

[0008] The carcass reinforcement of a radial tire for heavy-duty construction vehicles typically comprises at least one carcass layer including reinforcements, generally metallic, coated with a polymeric material of the elastomeric or elastomeric type, obtained by mixing and called the coating compound or coating rubber. A carcass layer includes a main part, connecting the two beads and generally wrapping, within each bead, from the inside to the outside of the tire around a circumferential reinforcement element, most often metallic, called a bead, to form a inversion. The metallic reinforcements of a carcass layer are substantially parallel to each other and form an angle of between 80° and 90° with the circumferential direction.

[0009] The crown reinforcement of a radial tire for construction vehicles comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer consists of reinforcements, generally metallic, parallel to each other and coated with a polymeric material of the elastomer type or a coating compound (or rubber).

[0010] Among the top layers, we usually distinguish the working layers, which constitute the working reinforcement, and the shrink-fit layers, which constitute the shrink-fit reinforcement.

[0011] The working structure, often comprising at least two working layers, serves to encircle the tire and provide it with rigidity and road holding. It withstands both mechanical inflation stresses, generated by the tire's inflation pressure and transmitted by the carcass structure, and mechanical rolling stresses, generated by the tire rolling on a surface and transmitted by the tread. A recurring problem in tire crowns is shearing, due to rolling, of the rubber compounds, crown coating compounds, or other compounds at the crown edges.

[0012] The working reinforcement usually comprises two radially superimposed working layers, formed of non-extensible metallic reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles of at least 15°. The two-layer, constituted by these two working layers, generally ensures a level of edge bending sufficient for acceptable vehicle behavior.

[0013] To reduce the mechanical inflation stresses transmitted to the working reinforcement, a shrink-fit reinforcement is placed radially outside the carcass reinforcement. The shrink-fit reinforcement, whose function is to absorb at least part of the mechanical inflation stresses, improves the durability of the reinforcement. apex reinforcement by stiffening the apex reinforcement. The shrinkage reinforcement can be positioned radially inside the working reinforcement, between the two working layers of the working reinforcement, or radially outside the working reinforcement.

[0014] In civil engineering applications, the confinement reinforcement may comprise two radially superimposed confinement layers formed of metallic reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming angles of no more than 10° with the circumferential direction. Another embodiment of the confinement reinforcement consists of a circumferential winding of a confinement wire or a continuous confinement strip forming angles of no more than 5° with the circumferential direction.

[0015] To prevent damage to the working and reinforcement layers by stones and other indenters often found in mines, the top reinforcement also often includes protective layers, forming part of the protective reinforcement and radially external to the working reinforcement. The protective reinforcement often comprises two radially superimposed protective layers, formed of elastic metal reinforcements, parallel to each other in each layer and intersecting from one layer to the next, forming angles of at least 10° with the circumferential direction.

[0016] The failure modes of mining tire crowns are numerous, ranging from cracking of the compounds at the ends of the working layers, leading either to a crack on the shoulder or a separation between the working layers, causing the tire to split into two parts: the carcass on one side and the complementary crown portion on the other. Other failures include rupture of the protective layers followed by the working layers, resulting in leaks. Much more rarely, the tire is removed during maintenance inspection due to the presence of radially circumferential pockets outside the carcass layer, visible from inside the tire upon careful examination. This defect does not cause a loss of pressure or damage the carcass layer, but is sufficiently visible to necessitate tire removal.A careful examination of the tires shows that these pockets appear at the end of the innermost radially oriented liner layer, which is also the one with the greatest axial width.

[0017] The inventors have set themselves the objective, for a radial tire for a civil engineering type vehicle for mining vehicle, of reducing the probability of occurrence of circumferential pockets radially external to the carcass layer under the axial end of the innermost radially enclosing layer.

[0018] This objective has been achieved, according to the invention, by a tire for construction vehicles intended to be mounted on a rim of at least 39 inches, comprising: - a crown reinforcement, radially internal to a tread and radially external to a carcass reinforcement and comprising crown layers including metallic reinforcements surrounded by a rubber compound or coating compound, - the top reinforcement comprising at least two working layers, including metallic reinforcements, parallel to each other and forming, with the circumferential direction (XX') tangent to the circumference of the tire, an angle whose absolute value is at least equal to 15°, - the crown reinforcement comprising at least two shrink-fit layers, each shrink-fit layer having an axial width less than those of the working layers, and comprising metallic reinforcements, parallel to each other and forming, with the circumferential direction (XX') tangent to the circumference of the tire, an angle whose absolute value is at most equal to 10°, the innermost radially oriented shrink-fit layer being the shrink-fit layer with the greatest axial width, the innermost radially oriented shrink-fit layer being radially inner to the innermost radially oriented working layer, - the carcass reinforcement comprising at least one carcass layer including metallic reinforcements surrounded by a rubber compound or coating compound, - at each axial end of the innermost radially oriented reinforcement layer, between the coating compound of the innermost radially oriented reinforcement layer and the coating compound of the innermost radially oriented working layer and / or the outermost radially oriented carcass layer, two contiguous rubber compounds, or decoupling compounds, being arranged, one being radially internal to the other, - the decoupling compound furthest radially from the end of the innermost radially oriented compression layer, called the outer decoupling compound, having a dynamic modulus of elasticity measured at 23°C, 10% strain, and 10 Hz, not exceeding 0.7 times the dynamic modulus of elasticity measured at 23°C, 10% strain, and 10 Hz of the decoupling compound closest to the end of the innermost radially oriented compression layer, called the inner decoupling compound.

[0019] The inventors were surprised to find, particularly during customer visits, that tires were being removed from vehicles upon the appearance of secondary damage. They sought solutions to this new problem, including changing the types of cables and the lengths of the various crown layers, but each of these common solutions for this type of civil engineering crown introduced other sizing problems for the dimension in question.The inventors then had the idea of ​​decoupling the innermost radially enclosed shrink-fit layer from either the innermost radially enclosed working layer, or the carcass layer, or the . Two, the "or / and" meaning an inclusive "or," using two radially stacked rubber compounds, with the compound with the higher dynamic modulus of elasticity positioned in contact with the innermost radial end of the shrink-fit layer, and with a difference in dynamic modulus of elasticity of at least 30% between the two materials. According to calculations, this solution reduces the maximum stress levels on the rubber in this region by approximately 40%, despite the decrease in stiffness of one of the compounds, and thus further reduces the risk of pocketing.

[0020] The dynamic elastic moduli G' at 10% strain, at 23°C and at 10 Hz, are measured according to ASTM D 5992 - 96.

[0021] By contiguous rubber compounds, it is understood that on a meridian section, the most radially inner points of the most radially outer material are in contact with the most radially outer points of the most radially inner material and this at the level of the line perpendicular to the axis of rotation of the tire passing through the axial end of the most radially inner shrink-fit layer.

[0022] The reduction in stresses is even greater if this decoupling occurs on both sides of the innermost radially oriented end of the shrinkage layer. Thus, a preferred solution is that at each axial end of the innermost radially oriented shrinkage layer, between the coating mixture of the innermost radially oriented shrinkage layer and the coating mixture of the innermost radially oriented working layer, two contiguous rubber mixtures, or decoupling mixtures, are placed, one being radially oriented inside the other, and between the coating mixture of the innermost radially oriented shrinkage layer and the coating mixture of the outermost radially oriented carcass layer, two contiguous rubber mixtures, or decoupling mixtures, are placed, one being radially oriented inside the other, and each outer decoupling mixture,between the innermost radially enclosed shrink-fit layer and the outermost radially enclosed carcass layer, and between the innermost radially enclosed shrink-fit layer and the innermost radially enclosed working layer, has a dynamic modulus of elasticity measured at 23°C and 10% strain and 10Hz, not exceeding 0.7 times the dynamic modulus of elasticity measured at 23°C and 10% strain and 10Hz, of the inner decoupling mixture contiguous to the outer decoupling mixture considered.

[0023] Advantageously, on either side of a median plane perpendicular to the axis of rotation of the tire passing through the center of the tread, the axial distance between the axial end of the innermost radially enclosed layer and each axial end of each other enclosed layer is at least 20 mm. A smaller difference in the axial width of the enclosed layers implies either that the innermost radially enclosed layer has a lower axial width significantly increases the risk of pocket formation at this location in the tire, but in return, the shear increases at the level of the working layers, meaning that the outermost radially enclosing layers have a width such that the main risk in this area becomes the rupture of the metal reinforcements of said enclosing layers.

[0024] Preferably, the radial thickness of each outer decoupling mixture is between 40% and 150% of the radial thickness of the inner decoupling mixture contiguous to the outer decoupling mixture under consideration. For optimal operation of the invention, the rubbery mixtures should have a certain balance with respect to their respective thicknesses.

[0025] Advantageously, the radial distance between the axial end of the innermost radially oriented shrink-fit layer and the outermost radially oriented carcass layer, measured on the back of the metal reinforcements, is at least 7 mm. For the invention to be optimized, the thickness of the rubber compounds between the axial end of the innermost radially oriented shrink-fit layer and the carcass layer should be at least 7 mm.

[0026] Advantageously, each decoupling compound of the innermost radially enclosing layer has an axial width of at least 40 mm, preferably at least 70 mm. Indeed, the decoupling has significant effects if it is carried out over an axial width conforming to the dimensions of earthmoving tires.

[0027] It is also preferred that the axial distance between each axial end of the innermost radially enclosing layer and each axial end of each decoupling mixture of said enclosing layer be at least 10 mm. This condition allows for correct centering of the decoupling mixtures with respect to the axial end of the innermost radially enclosing layer.

[0028] Advantageously, each decoupling mixture in contact with the coating mixture of the innermost radially oriented shrinkage layer has at most the same dynamic modulus of elasticity measured at 23°C and 10% strain and 10 Hz as the coating mixture of the innermost radially oriented shrinkage layer. This also means that the coating mixture of the shrinkage layer has the same composition as the decoupling mixtures adjacent to it, for the sake of ease of industrialization.

[0029] This invention is particularly interesting for tires in which the metallic reinforcements of the tread layers form an angle of at least 40° with the circumferential direction (XX') tangent to the tire's circumference. The inventors have also noted that this condition exacerbates the stresses on the compound between the innermost radial reinforcement layer and the innermost radial tread layer, stresses which The invention helps to reduce this. This type of construction is particularly suited to vehicles with highly cambered tires. To avoid excessive shear, the working layers have very open angles of application to reduce shear at their ends. The circumferential forces are absorbed by the shrink-fit layers, resulting in increased shear at their ends, which must be reduced as the invention does.

[0030] Similarly, the invention is all the more interesting when the innermost radially working layer has a significant axial width. Thus, it is preferred that the half-difference between the axial width of the innermost radially working layer and the axial width of the innermost radially shrink-fit layer be at least 190 mm.

[0031] The features of the invention are illustrated by the schematic [Fig.1] not shown to scale, with reference to a tire of size 70 / 70R57.

[0032] Figure 1 shows a meridian section of the crown of a heavy-duty vehicle tire 1 for civil engineering purposes comprising a crown reinforcement 3, radially internal to a tread 2 and radially external to a carcass reinforcement 4. The crown reinforcement 3 comprises, radially from the outside in, a protective reinforcement 31, a working reinforcement 32 and a reinforcing reinforcement 33. The protective reinforcement has two protective layers 311 and 312 comprising elastic metal reinforcements embedded in an elastomeric material or coating mixture, parallel to each other. The working reinforcement 32 comprises two working layers 321, 322 whose metal reinforcements, embedded in an elastomeric material or rubbery mixture, are parallel to each other and form, with the circumferential direction XX', angles of at least 15°, and are crossed from one working layer to the next.The shrink-fit reinforcement 33 comprises two shrink-fit layers 331 and 332, whose respective metallic reinforcements, embedded in an elastomeric material, are parallel to each other and form an angle of no more than 10° with the circumferential direction XX'. These reinforcements are crossed from one shrink-fit layer to the next. The innermost radially positioned shrink-fit layer 332 has the greater axial width. Between the innermost radially positioned shrink-fit layer 332 and the frame layer 41 are two decoupling compounds 61 and 62, with compound 62 being radially external to compound 61, which has a dynamic modulus of elasticity at least 30% lower than the dynamic modulus of elasticity of the decoupling compound 62.Similarly, between the innermost radially enclosed layer 332 and the innermost radially enclosed working layer 322, there are two decoupling mixtures 51 and 52, 52 being radially enclosed within 51, which has a dynamic modulus of elasticity at least 30% lower than the dynamic modulus of elasticity of the decoupling mixture 52.

[0033] The invention also works with only 5 top layers and a protective layer that would not be overhanging as in [Fig.1].

[0034] Fig. 1 represents only one example among others of the possible architectures of the civil engineering tire. The invention has been tested or evaluated on tires of size 70.70R57. The tires according to the invention are compared to reference tires of the same size for each of the tests and analyses. The tread patterns of the different tires are the same. The reference tires and the tires according to the invention comprise 6 crown layers: • 2 innermost radial reinforcement layers, including the reinforcements metallic are made up of 189 wires of 0.23 mm arranged in a pitch of 5.1 mm and making an angle of +8° / -8° with the circumferential direction at the level of the equatorial plane, the layers being crossed with respect to each other, the innermost radially having an axial width of 800 mm and the outermost radially having an axial width of 712 mm. • 2 working layers, with metallic reinforcements made of 189 threads of 0.23 mm arranged at a 5.1 mm pitch and at an angle of +60° / -60° with the circumferential direction at the equatorial plane, the innermost radial working layer having an axial width of 1214 mm • 2 outermost protective layers, with reinforcements elastic metallic, made up of 24 wires of 0.26 mm, arranged at a pitch of 2.5 mm and making an angle of +16° / -16° with the circumferential direction at the level of the equatorial plane.

[0035] The tires of the invention are identical to the reference tires except that the tires according to the invention have decoupling rubbers with two materials between the innermost radially enclosing layer and the carcass layer, and the enclosing layer and the innermost radially enclosing working layer.

[0036] The radially decoupling materials closest to the shrink-wrap layer are identical to the rubber compound used to coat the shrink-wrap layer. The innermost radial compound has a maximum radial thickness of 2.5 mm for an axial width of 130 mm. The outermost radial compound has a maximum radial thickness of 8.5 mm for an axial width of 180 mm. The axial end of the innermost radially shrink-wrap layer and each axial end of each radially decoupling compound closest to said shrink-wrap layer are at least 50 mm apart axially.

[0037] The radially decoupling materials furthest from the shrink-fit layer have a dynamic modulus of elasticity 31% lower than the dynamic modulus of elasticity of the shrink-fit layer coating mixture. The mixture The innermost radially oriented layer has a maximum radial thickness of 2.5 mm for an axial width of 160 mm. The outermost radially oriented layer has a maximum radial thickness of 5.2 mm for an axial width of 160 mm. The axial end of the innermost radially oriented shrinkage layer and each axial end of each radially oriented decoupling layer closest to said shrinkage layer are at least 80 mm apart axially.

[0038] The invention makes it possible to reduce, based on calculations of rolling resistance at the tire's operating load and pressure when hot (8.95 bar and 136 tonnes), the stresses in the coating mixtures by 40%. This should significantly reduce the occurrence of damage, thus demonstrating the value of the invention.

Claims

1. Demands Tyre (1) for construction vehicle intended to be mounted on a rim of at least 39 inches, comprising: - a crown reinforcement (3), radially internal to a tread (2) and radially external to a carcass reinforcement (4) and comprising crown layers (311, 312, 321, 322, 331, 332) comprising metallic reinforcements surrounded by a rubber compound or coating compound, - the top reinforcement (3) comprising at least two working layers (321, 322), comprising metallic reinforcements, parallel to each other and forming, with the circumferential direction (XX') tangent to the circumference of the tire, an angle whose absolute value is at least equal to 15°, - the top reinforcement comprising at least two shrink-fit layers (331, 332), each shrink-fit layer (331, 332) having an axial width less than those of the working layers (321, 322), and comprising metallic reinforcements, parallel to each other and forming, with the circumferential direction (XX') tangent to the circumference of the tire, an angle whose absolute value is at most equal to 10°, the innermost radially oriented shrink-fit layer (332) being the shrink-fit layer with the greatest axial width, the innermost radially oriented shrink-fit layer being radially inner to the innermost radially oriented working layer, - the carcass reinforcement (4) comprising at least one carcass layer (41) comprising metallic reinforcements surrounded by a rubbery mixture or coating mixture, - characterized in that at each axial end of the innermost radially oriented shrink-fit layer (332), between the coating mixture of the innermost radially oriented shrink-fit layer (332) and the coating mixture of the innermost radially oriented working layer (322) and / or the outermost radially oriented carcass layer (41), are arranged two contiguous rubber mixtures (51, 52, 61, 62), or decoupling mixtures, one being radially oriented towards the other, - and in that the decoupling mixture (51, 61) furthest radially from the end of the innermost radially shrink-fit layer (332), called the outer decoupling mixture, has a dynamic modulus of elasticity measured at 23°C and 10% strain, at most equal to 0.7 times the dynamic modulus of elasticity measured at 23°C and 10% strain of the decoupling mixture (52, 62) most radially close to the end of the innermost radially enclosing layer (332), called the internal decoupling mixture.

2. A tire according to claim 1 wherein at each axial end of the innermost radially oriented shrink-fit layer (332), between the coating mixture of the innermost radially oriented shrink-fit layer (332) and the coating mixture of the innermost radially oriented working layer (322) are arranged two contiguous rubber compounds (51, 52), or decoupling compounds, one (51) being radially internal to the other (52), and between the coating mixture of the innermost radially oriented shrink-fit layer (332) and the coating mixture of the outermost radially oriented carcass layer (41), are arranged two contiguous rubber compounds (61, 62), or decoupling compounds, one (61) being radially internal to the other (62) and each decoupling compound (61.51) exterior,between the innermost radially enclosed shrink-fit layer (332) and the outermost radially enclosed frame layer (41), and between the innermost radially enclosed shrink-fit layer (332) and the innermost radially enclosed working layer (322), has a dynamic modulus of elasticity measured at 23°C and 10% strain, at most equal to 0.7 times the dynamic modulus of elasticity measured at 23°C and 10% strain of the inner decoupling mixture (52, 62) contiguous to the outer decoupling mixture considered.

3. Tire according to any one of claims 1 or 2, wherein on either side of a median plane perpendicular to the axis of rotation of the tire passing through the center of the tread, the axial distance between the innermost radially axial end of the innermost shrink-fit layer (332) and each axial end of each other shrink-fit layer (332) is at least 20 mm.

4. Pneumatic according to any one of the preceding claims wherein the maximum radial thickness of each outer decoupling mixture (51, 61) is between 40% and 150% of the maximum radial thickness of the inner and contiguous inner decoupling mixture (52, 62) to the outer decoupling mixture considered.

5. Pneumatic according to any one of the preceding claims, wherein the radial distance between the axial end of the innermost radially enclosed shrink-fit layer (312) and the outermost radially enclosed carcass layer (41), measured at the back of the metal reinforcements, is at least 7 mm.

6. Pneumatic according to any one of the preceding claims wherein each decoupling mixture (51,61, 52, 62) of the innermost radially enclosing layer has an axial width of at least 40 mm, preferably at least 70 mm.

7. Pneumatic according to any one of the preceding claims wherein the axial distance between each axial end of the innermost radially enclosing layer (312) and each axial end of each decoupling mixture (51, 52, 61, 62) of said enclosing layer, is at least equal to 10 mm.

8. Pneumatic according to any one of the preceding claims wherein each decoupling mixture (52, 62) in contact with the innermost radially enclosing layer coating mixture (312) has at most the same dynamic modulus of elasticity measured at 23°C and 10% strain as the innermost radially enclosing layer coating mixture (312).

9. A tire according to any one of the preceding claims, wherein the metallic reinforcements of the working layers form an angle with the circumferential direction (XX') tangent to the circumference of the tire, the absolute value of which is at least 40°

10. Pneumatic according to any one of the preceding claims wherein the half-difference between the axial width of the innermost radially working layer and the axial width of the innermost radially shrink-fit layer is at least equal to 190 mm.

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