Optimised architecture for a civil engineering tyre

Abstract

The invention relates to a tyre (1) for a civil engineering vehicle, wherein the tyre comprises two working layers (321, 322), comprising metal reinforcements, and at least two hooping layers (331, 332) with axial widths smaller than those of the working layers (321, 322) and comprising metal reinforcements, wherein the radially innermost hooping layer (332) is the hooping layer having the greatest axial width, and at each axial end of the radially innermost hooping layer (332), two contiguous rubber compounds (51, 52, 61, 62), or separating compounds, are arranged, one being radially inside the other. The separating compound (51, 61) radially farthest from the end of the hooping layer (332) has a dynamic modulus of elasticity, measured at 23°C, at 10% deformation, and at 10 Hz, at most equal to 0.7 times the dynamic modulus of elasticity of the separating compound (52, 62) radially closest to the end of the radially innermost hooping layer (332).

Description

[0001] Optimized architecture of civil engineering pneumatics

[0002] 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.

[0003] 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.

[0004] For example, a radial tire for heavy-duty construction equipment, as defined in the ETRTO 2020 standard, is intended to be mounted on a rim with a diameter primarily at least 24 inches. The invention is more specifically intended for tires for mining vehicles and therefore for tires with a diameter of at least 39 inches.

[0005] Since a tire has a geometry of revolution around an axis of rotation, its geometry is generally described in a meridian plane containing the tire's axis of rotation. For a given meridian plane, the radial, axial, and circumferential directions respectively denote the directions perpendicular to the tire's axis of rotation, parallel to the tire's axis of rotation, and perpendicular to the meridian plane. The circumferential direction is tangent to the circumference.

[0006] In what follows, the expressions "radially inside" and "radially outside" respectively mean "closer" and "further" from the tire's axis of rotation, respectively. "Axially inside" and "axially outside" mean "closer" and "further" from the tire's equatorial plane, respectively, the tire's equatorial plane being the plane passing through the middle of the tread and perpendicular to the axis of rotation.

[0007] Generally speaking, 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.

[0008] A radial tire also includes a reinforcing structure, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement.

[0009] The carcass reinforcement of a radial tire for heavy-duty vehicles, such as construction equipment, typically comprises at least one layer of casing consisting of reinforcements, generally metallic, coated with a polymeric material, such as an elastomer or elastomeric compound, obtained by mixing and called the casing compound or rubber compound. A casing layer includes a main section connecting the two bead sections and generally wrapping, within each bead section, 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 casing layer are essentially parallel to each other and form an angle of between 80° and 90° with the circumferential direction.

[0010] The crown reinforcement of a radial tire for construction vehicles comprises a series of crown layers extending circumferentially and radially outside the carcass reinforcement. Each crown layer consists of reinforcements, generally metallic, parallel to each other and coated with a polymeric material such as an elastomer or a compound (or rubber) coating.

[0011] Among the top layers, we usually distinguish between working layers, which constitute the working reinforcement, and shrink-fit layers, which constitute the shrink-fit reinforcement.

[0012] The tread, often comprising at least two layers, serves to encircle the tire and provide rigidity and road holding. It withstands both the mechanical stresses of inflation, generated by the tire's inflation pressure and transmitted by the carcass reinforcement, and the mechanical stresses of rolling, generated by the tire rolling over the road surface and transmitted by the tread. A recurring problem in tire crowns is shearing, caused by rolling, of the rubber compounds, whether they are the crown coating compounds or other compounds, at the crown edges.

[0013] The working reinforcement usually comprises two radially superimposed working layers, formed of non-extensible metal 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 structure, formed by these two working layers, generally ensures a sufficient level of edge bending for acceptable vehicle behavior.

[0014] To reduce the mechanical stresses of inflation 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 some of the mechanical stresses of inflation, improves the durability of the top reinforcement by stiffening it. The shrink-fit reinforcement can be positioned radially inside the working reinforcement, between the two working layers of the working reinforcement, or radially outside the working reinforcement.

[0015] In civil engineering applications, the confinement reinforcement may comprise two radially superimposed layers of confinement reinforcement, formed of parallel metallic reinforcements within 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.

[0016] To prevent damage to the working and reinforcement layers from stones and other indenters often found in mines, the top reinforcement frequently includes protective layers. These protective layers form part of the protective reinforcement and are radially external to the working reinforcement. The protective reinforcement often comprises two radially superimposed protective layers made of elastic metal reinforcements, parallel to each other within each layer and intersecting from one layer to the next, forming angles of at least 10° with the circumferential direction.

[0017] 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 section 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 circumferential pockets radially outside the carcass layer, visible from inside the tire upon careful examination. This defect does not cause pressure loss or damage to the carcass layer, but is sufficiently visible to warrant tire removal.A careful examination of the tires shows that these pockets appear at the end of the innermost radially enclosing layer, which is also the one with the greatest axial width.

[0018] The inventors 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 outside the carcass layer under the axial end of the innermost radially enclosing layer.

[0019] 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 tire carcass reinforcement, and comprising crown layers including metallic reinforcements surrounded by a rubber compound or coating compound. The crown layers comprise at least two working layers, including metallic reinforcements, parallel to each other and forming, with the circumferential direction tangent to the circumference of the tire, an angle whose absolute value is at least equal to 15°.The top layers further comprise at least two reinforcement layers, each reinforcement layer having an axial width less than that of the working layers, and comprising metallic reinforcements parallel to each other and forming, with the circumferential direction tangent to the circumference of the tire, an angle whose absolute value is at most 10°, the innermost radially reinforced layer being the reinforcement layer with the greatest axial width, the innermost radially reinforced layer being radially inner to the innermost radially reinforced working layer. The carcass reinforcement comprises at least one carcass layer comprising metallic reinforcements surrounded by a rubber compound or coating mixture.At each axial end of the innermost radially oriented shrinkage layer, between the coating compound of the innermost radially oriented shrinkage layer and the coating compound of the innermost radially oriented working layer and / or the outermost radially oriented carcass layer, are placed two contiguous rubber compounds, or decoupling compounds, one being radially internal to the other. Furthermore, the decoupling compound furthest radially from the end of the innermost radially oriented shrinkage layer, called the outer decoupling compound, has 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 shrinkage layer, called the inner decoupling compound.The dynamic elastic moduli G' at 10% strain, at 23°C and 10 Hz, are measured according to ASTM D 5992 - 96.

[0020] The inventors were surprised to find, particularly during customer visits, that tires were being removed from vehicles as soon as secondary damage appeared. They sought solutions to this new problem, including changing the types of cables and the lengths of the various top layers, but each of these common solutions for this type of civil engineering top layer introduced other sizing problems related to the dimension in question.The inventors then conceived the idea of ​​decoupling the innermost radially oriented rubber layer from either the innermost radially oriented working layer, the carcass layer, or both (the "or" signifying an inclusive "or"), by using two radially stacked rubber compounds. The compound with the higher dynamic modulus of elasticity was positioned in contact with the end of the innermost radially oriented rubber layer, 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.

[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 stress is even greater if this decoupling occurs on both sides of the innermost radial end of the shrinkage layer. Thus, a preferred solution is that at each axial end of the innermost radial end of the shrinkage layer, between the shrinkage layer coating and the innermost radial work layer coating, two contiguous rubber compounds, or decoupling compounds, are placed, one being radially inside the other; and between the shrinkage layer coating and the outermost radial carcass layer coating, two contiguous rubber compounds, or decoupling compounds, are placed, one being radially inside the other, and each outer decoupling compound,between the innermost radially enclosed shrinkage layer and the outermost radially enclosed carcass layer, and between the innermost radially enclosed shrinkage layer and the innermost radially enclosed working layer, has 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 inner decoupling mixture contiguous to the outer decoupling mixture considered. The dynamic elastic moduli G' at 10% strain, 23°C, and 10 Hz are measured according to ASTM D 5992-96.

[0023] Advantageously, on either side of a median plane perpendicular to the tire's axis of rotation and passing through the center of the tread, the axial distance between the axial end of the innermost radially oriented liner layer and each axial end of every other liner layer is at least 20 mm. A smaller difference in the axial width of the liner layers implies either that the innermost radially oriented liner layer has an axial width that significantly reduces the risk of pocket formation at that point in the tire, but in return increases shear stress at the working layers, or that the outermost radially oriented liner layers have a width such that the main risk in this area becomes the failure of the metal reinforcements of said liner layers.

[0024] Preferably, the radial thickness of each outer decoupling compound is between 40% and 150% of the radial thickness of the inner decoupling compound contiguous to the outer decoupling compound under consideration. For optimal operation of the invention, the rubber compounds should have a certain balance with respect to their respective thicknesses. Advantageously, the radial distance between the axial end of the innermost radially oriented reinforcement 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 reinforcement layer and the carcass layer should be at least 7 mm.

[0025] Advantageously, each decoupling compound of the innermost radially enclosing layer has an axial width of at least 40 mm, preferably at least 70 mm. This is because decoupling has significant effects when performed over an axial width that conforms to the dimensions of earthmoving tires.

[0026] 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.

[0027] 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, 10% strain, and 10 Hz as the coating mixture of the innermost radially oriented shrinkage layer. This also means that the shrinkage layer coating mixture has the same composition as the decoupling mixtures adjacent to it, for the sake of ease of industrialization.

[0028] This invention is particularly advantageous 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 radially reinforced layer and the innermost radially reinforced tread layer, stresses that the invention helps to reduce. This type of construction is particularly well-suited to vehicles with highly cambered tires. To avoid excessive shear, the tread layers have very open angles to reduce shear at their ends. The circumferential forces are absorbed by the reinforced layers, resulting in increased shear at their ends, which must be mitigated as the invention does.

[0029] 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 enclosing layer be at least 190 mm. The features of the invention are illustrated in the schematic Figure 1, which is not drawn to scale and refers to a 70 / 70R57 tire.

[0030] Figure 1 shows a meridional section of the crown of a heavy-duty construction vehicle tire 1 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 332 layer and the innermost radially enclosed working layer 322, two decoupling mixtures 51 and 52, the 52 being radially enclosed within the 51 which has a dynamic modulus of elasticity lower than at least 30% than the dynamic modulus of elasticity of the decoupling mixture 52.

[0031] The invention also works with only 5 crown layers and a protective layer that is not overhanging, as shown in Figure 1. Figure 1 represents only one example among others of the possible architectures of the earthmover 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 identical. The reference tires and the tires according to the invention comprise 6 crown layers, namely:

[0032] - 2 innermost radially enclosed layers of swaging, the metal reinforcements of which consist of 189 wires of 0.23 mm arranged at a pitch of 5.1 mm and making an angle of +87-8° with the circumferential direction at the level of the equator 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;

[0033] - 2 working layers, having metallic reinforcements consisting of 189 0.23 mm wires arranged at a 5.1 mm pitch and forming an angle of +607-60° with the circumferential direction at the equatorial plane, the innermost radially oriented working layer having an axial width of 1214 mm; and

[0034] - 2 outermost radially protective layers, having elastic metal reinforcements, made up of 24 wires of 0.26 mm, arranged at a pitch of 2.5 mm and making an angle of +167-16° 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 shrinkage layer are identical to the rubber compound used to coat the shrinkage layer. The innermost radial compound has a maximum radial thickness of 2.5 mm and an axial width of 130 mm. The outermost radial compound has a maximum radial thickness of 8.5 mm and an axial width of 180 mm. The axial end of the innermost radially shrinkage layer and each axial end of each radially decoupling compound closest to said shrinkage layer are at least 50 mm apart axially.

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

[0038] The invention allows for a 40% reduction in stresses within the tire coating mixture, based on calculations of rolling resistance at the tire's operating load and pressure (8.95 bar and 136 tonnes respectively). This should significantly reduce the occurrence of damage, thus demonstrating the invention's value.

Claims

Demands 1. Tire (1) for construction vehicles 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) of the tire and comprising crown layers (311, 312, 321, 322, 331, 332) comprising metallic reinforcements surrounded by a rubber compound or coating compound, in which the crown layers include: - 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°, and - at least two reinforcement layers (331, 332), each reinforcement 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 reinforcement layer (332) being the reinforcement layer with the greatest axial width, the innermost radially oriented reinforcement layer being radially inner to the innermost radially oriented working layer, wherein the carcass reinforcement (4) comprises at least one carcass layer (41) comprising metallic reinforcements surrounded by a rubber compound or coating compound, characterized in that, at each axial end of the innermost radially oriented reinforcement layer (332),between the coating mixture of the innermost radially enclosed reinforcement layer (332) and the coating mixture of the innermost radially enclosed working layer (322) and / or the outermost radially enclosed carcass layer (41), are arranged two contiguous rubber mixtures (51, 52, 61, 62), or decoupling mixtures, one being radially internal to the other, and in that the decoupling mixture (51, 61) furthest radially from the end of the innermost radially enclosed reinforcement layer (332), called the outer decoupling mixture, has a dynamic modulus of elasticity, measured according to ASTM D 5992-96 at 23°C and 10% strain, which is at most equal to 0.7 times a dynamic modulus of elasticity, measured according to ASTM D 5992-96 at 23°C and 10% strain, of the decoupling mixture (52, 62) closest radially to the end of the innermost radially oriented shrink-fit layer (332), called the internal decoupling mixture.

2. Pneumatic according to claim 1, wherein at each axial end of the innermost radially oriented shrink-fit layer (332), between the coating mixture of Between the innermost radially oriented shrinkage layer (332) and the innermost radially oriented working layer coating mix (322), two contiguous rubber mixtures (51, 52), or decoupling mixtures, are arranged, one (51) being radially oriented inside the other (52). Between the innermost radially oriented shrinkage layer coating mix (332) and the outermost radially oriented carcass layer coating mix (41), two contiguous rubber mixtures (61, 62), or decoupling mixtures, are arranged, one (61) being radially oriented inside the other (62). Each outermost decoupling mixture (61, 51) is placed between the innermost radially oriented shrinkage layer (332) and the outermost radially oriented carcass layer (41). of the innermost radially shrink-fit layer (332) and the innermost radially working layer (322), has a dynamic modulus of elasticity,measured according to ASTM D 5992-96 at 23°C and 10% strain, which is at most equal to 0.7 times a dynamic modulus of elasticity, measured according to ASTM D 5992-96 at 23°C and 10% strain, of the internal (52, 62) decoupling mixture contiguous with the external 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 coating mixture of the innermost radially oriented shrink-fit layer (312) has at most the same dynamic modulus of elasticity measured at 23°C and 10% strain than the coating mixture of the innermost radially enclosed shrink-fit layer (312).

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