Optimized architecture of civil engineering pneumatics

Abstract

A tire (1) for a mining construction vehicle comprising two protective layers (31) including elastic metallic reinforcements having an extension modulus of at least 40 GPa and at most 140 GPa, and two working layers. The diameter of the reinforcement elements of the outermost radially protective layer is at least 2.5 mm, and the reinforcement elements of the outermost radially protective layer form, with a circumferential direction (XX') tangent to the circumference of the tire, an angle APN whose absolute value is at least 35°. Abbreviated 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 relates more particularly to the crown reinforcement of a tire for a mining vehicle whether the mine is underground or open pit.

[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 vehicles of the civil engineering type, as defined by the ETRTO standard, is intended to be mounted on a rim whose diameter is at least 25 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. A carcass layer includes a main portion, 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 coating mixture.

[0010] Among the top layers, we usually distinguish the protective layers, which are part of the protective reinforcement and radially the outermost, and the working layers, which are part of the working reinforcement and radially located between the protective reinforcement and the carcass reinforcement.

[0011] The protective reinforcement, comprising at least one protective layer for certain applications, but comprising two protective layers for mining vehicles that travel on tracks or in tunnels very often obstructed by stones, sometimes large compared to the size of the tire. These protective layers essentially protect the working layers from mechanical or physico-chemical damage that could propagate radially through the tread towards the inside of the tire.

[0012] The protective reinforcement therefore comprises for mining tires two radially superimposed protective layers, formed of elastic 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 10°.

[0013] The working reinforcement, 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 reinforcement, and mechanical rolling stresses, generated by the tire rolling on a surface and transmitted by the tread. The crown reinforcement must also resist impacts and punctures, thanks to its intrinsic design, particularly its flexibility and, in particular, that of the protective structure. Furthermore, the tire must have sidewall flex, or lateral stiffness, to ensure proper vehicle handling on winding roads.

[0014] The working reinforcement typically comprises two radially superimposed working layers formed of non-extensible metallic reinforcements, parallel to each other within each layer and crossed from one layer to the next, forming, with the circumferential direction, angles preferably of at least 15° and at most 35° so as to resist the transverse forces and a portion of the circumferential forces. The two-layer structure, formed by these two working layers, generally ensures a sufficient level of edge bending for acceptable vehicle behavior.

[0015] To reduce the mechanical inflation stresses transmitted to the working reinforcement, it is known to place a shrink-fit reinforcement radially outside the carcass reinforcement. The shrink-fit reinforcement, whose function is to absorb at least some of the mechanical inflation stresses, 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.

[0016] 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.

[0017] With regard to metal reinforcements, a metal reinforcement is mechanically characterized by a curve representing the tensile force (in N) applied to the metal reinforcement as a function of its relative elongation (in %), known as the force-elongation curve. From this force-elongation curve, tensile mechanical characteristics of the metal reinforcement are deduced, such as the structural elongation As (in %), the total elongation at break At (in %), the breaking force Fm (maximum load in N), and the tensile strength Rm (in MPa), these characteristics being measured according to ASTM D 2969-04:2014.

[0018] The total elongation At of the metallic reinforcement is, by definition, the sum of its structural, elastic, and plastic elongations (At = As + Ae + Ap), and particularly at break where each of the elongations is non-zero. The structural elongation The elastic elongation (Ae) results from the relative positioning of the metal wires constituting the metal reinforcement under a slight tensile force. The elastic elongation (Ae) results from the elasticity of the metal wires themselves, considered individually, the metal's behavior following Hooke's law. The plastic elongation (Ap) results from the plasticity, that is, the irreversible deformation, beyond the elastic limit, of the metal wires considered individually. These different elongations, as well as their respective meanings, well known to those skilled in the art, are described, for example, in documents US5843583, WO2005 / 014925, and WO2007 / 090603.

[0019] A tensile modulus, expressed in GPa, is also defined at every point on the force-stretch curve of a metallic reinforcement. This modulus represents the slope of the line tangent to the force-stretch curve at that point. In particular, the tensile modulus of the linear elastic portion of the force-stretch curve is called the elastic tensile modulus or Young's modulus.

[0020] Among metallic reinforcements, a distinction is usually made between elastic metallic reinforcements, such as those used in protective layers to prevent the protective layers from absorbing tensile stresses, and non-stretchable or inextensible metallic reinforcements, such as those used primarily in working layers. The important point is that the protective layers be significantly more elastic than the working layers.

[0021] An elastic metal reinforcement, in its unglued state, is characterized by a structural elongation As of at least 0.5% and a total elongation at break At of at least 3%. Furthermore, an elastic metal reinforcement has a tensile elastic modulus of at most 180 GPa, and is usually between 40 GPa and 150 GPa.

[0022] A non-stretchable metal reinforcement is characterized by a total elongation At, under a tensile force equal to 10% of the breaking force Fm, at most equal to 0.2%. Furthermore, a non-stretchable metal reinforcement has an elastic modulus in tension usually between 150 GPa and 200 GPa.

[0023] The efforts of mining tire manufacturers in the continuous improvement of the reinforcing elements, metallic reinforcements, or cables in the protective layers have significantly improved the puncture resistance of tires from stones present on the ground over which they travel. These failures have clearly decreased, leading to an increase in the frequency of other unexpected failures, which are becoming problematic. This is the case with the formation of a crack that develops at the interface between the outermost radial protective layer and the tread, and which then propagates circumferentially until a portion of the tread detaches, resulting in the tire being removed.

[0024] The inventors have set themselves the objective, for a radial tire for a vehicle of the mining civil engineering type, of reducing the shear forces at the interface between the outermost radially protective layer without deteriorating the performance of resistance to aggressions.

[0025] This objective has been achieved, according to the invention, by a tire for mining construction vehicles intended to be mounted on a rim having a diameter at site of at least 25 inches, comprising: - a crown reinforcement, radially internal to a tread, having a tread height of at least 30 mm, and radially external to a carcass reinforcement and comprising crown layers including metallic reinforcements, - the crown reinforcement comprising two protective layers, the outermost radial layers of the crown layers, said protective layers comprising elastic metallic reinforcements having a modulus of extension of at least 40 GPa and at most 140 GPa, embedded in a rubber compound, called calendering compound, parallel to each other, and having a breaking strength FR, - the crown reinforcement comprising at least two working layers,each working layer being radially internal to the protective 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 least equal to 17°, - the diameter of the metallic reinforcements of the most radially outer protective layer being at least equal to 2.5 mm and the metallic reinforcements of the most radially outer protective layer forming, with a circumferential direction (XX') tangent to the circumference of the tire, an angle APN whose absolute value is at least equal to 40°.

[0026] The idea is to amplify the characteristics that have enabled the metallic reinforcements of the protective layers to withstand impacts during rolling, such as the diameter of the metallic reinforcements. This is achieved by using metallic reinforcements with a larger diameter than those used in state-of-the-art solutions, while simultaneously increasing the angle of the outermost radial layer of the protective layer so that its circumferential rigidity approaches as closely as possible the rigidity of its calendering compound. Thus, since the protective layers have reinforcing elements on the order of 2 mm, the invention requires that the reinforcing elements of the protective layer have a diameter of at least 2.5 mm and that the metallic reinforcements of the outermost radial layer form, with a circumferential direction (XX') tangent to the circumference of the tire, an angle APN whose absolute value is at least 40°. preferably at least 45°, preferably at least 55°. At a 40° angle, the circumferential stiffness of a top layer is less than 2% of the stiffness of said top layer at 0° and less than 50% to 10% of the circumferential stiffness for angles used in the state of the art. By thus reducing the circumferential stiffness of the outermost radially protective layer, the stiffness differential between the tread and the outermost radially protective layer is reduced, and consequently, the stresses at this interface are reduced accordingly. This reduction should allow for a noticeable improvement in resistance to circumferential crack propagation along the outermost radially protective layer following impact with an aggressive soil element.

[0027] This decrease in rigidity is even more significant at an angle of 45°, dropping by more than 50% compared to the value at 35°, and even more so at 55° where the rigidity of the protective layer becomes negligible. From the perspective of other performance aspects, further widening the angles is irrelevant because the protective layers do not experience increased tension due to the difference in rigidity of their metallic reinforcements compared to those of the working and reinforcement layers.

[0028] This modification is acceptable for mining tires, according to the inventors' knowledge, due to the specific conditions of their operation. Indeed, in other applications, objects on the ground that could damage the tire are stones that might damage the tread or break working layers, but not puncture the tire itself. Therefore, the use of large-diameter cables that can withstand being cut when rolling over the object is possible. This is not the case for applications where the risk to the tire in an aggressive environment is running over an indenter that could puncture the crown reinforcement and lead to a tire puncture.

[0029] To protect all the top layers (working layers, bracing layer, triangulation layer) from the hammering phenomenon caused by rolling on stony soils, it is advantageous that the outermost radially outer protective layer of the top layers has an axial width LPN greater than all the axial widths of the other top layers.

[0030] It is advantageous for the metal reinforcements of the outermost radially exposed protective layer to have a diameter of at least 2.5 mm, preferably at least 3.0 mm, and preferably at least 3.5 mm. Increasing the diameters allows for an increase in the breaking strength of the metal reinforcement and therefore the distance between the metal reinforcements for the same strength of the protective layer. Increasing the distance between the metal reinforcements of the The outermost radially exposed protective layer allows for a reduction in circumferential stiffness by increasing the percentage of compound within the protective layer. Indeed, the breaking strength of the metal reinforcements increases with the square of the diameter, and while maintaining the same breaking strength of the protective layer, the distance between the reinforcements increases linearly with the diameter. Therefore, by doubling the diameter, the distance between the metal reinforcements can be increased by approximately 3.5 times, thus increasing the calendering compound ratio and contributing to a reduction in the tire's circumferential stiffness. This allows for a reduction, taking into account the angle of the metal reinforcements relative to the circumferential direction, of the circumferential stiffness that influences the failure mode we wish to target.

[0031] For the same advantage, preferably the breaking strength FR of the metallic reinforcements of the outermost radially protective layer, is greater than 4000 N.

[0032] Advantageously, the spacing of the metal reinforcements in the outermost radially protective layer is greater than 0.70*FR / 1000 and less than 11*FR / 1000. The spacing of the metal reinforcements is defined as the distance in mm between each metal reinforcement, either between the centers of two directly adjacent metal reinforcements measured perpendicular to the reinforcements, or between two right or left edges of the cables of two directly adjacent metal reinforcements. This measurement is well known to those skilled in the art and can be taken on a protective layer sampled from the tire, by X-ray, or by any other suitable method on the cured tire. This formula is derived from experience and tested protective layers considered conclusive regarding puncture problems.

[0033] Advantageously, the protective layers, namely the outermost radially protective layer and the innermost radially protective layer, are identical in terms of the nature of the metal reinforcements, i.e., same architecture (same number of wires, same assembly, same manufacturing process), same pitch, same calendering mixture, same absolute value of the angle of the metal reinforcements with the circumferential direction, the metal reinforcements being crossed from one protective layer to the other to facilitate manufacturing. In particular, the metal reinforcements of the innermost radially protective layer have the same diameter and the same breaking strength as the metal reinforcements of the outermost radially protective layer.Similarly, it is advantageous that the spacing of the metal reinforcements in the innermost radially protective layer be equal to the spacing of the metal reinforcements in the outermost radially protective layer. Therefore, it is preferable that the angle formed by the metal reinforcements in the innermost radially protective layer be at least 35°, preferably at least 45°, and preferably at least 55°.

[0034] To reduce stress at the interface between the outermost radially protective layer and the rubber compound of the tread directly adjacent to it, it is advantageous for the stiffness of said compound to be close to the stiffness of the calendering compound. Thus, it is preferable that, with the tread directly adjacent to the outermost radially protective layer, the elastic modulus Mal measured at 10% elongation at 23°C of the rubber compound of the tread directly adjacent to the outermost radially protective layer at the center of the tread, be at least equal to 0.65 times the elastic modulus Ma2 measured at 10% elongation at 23°C of the calendering compound of the outermost radially protective layer.

[0035] It is advantageous that, when the metallic reinforcements of the protective layers have a peripheral layer of strands, the peripheral layer of strands of the metallic reinforcements of the protective layers be desaturated. “Desaturated layer” means that the diameter of the strands with respect to the perimeter where said peripheral strands are arranged is such that there is sufficient space between each strand to allow the calendering compound to penetrate the metallic reinforcement in order to protect all of these metallic reinforcements from corrosion. Indeed, saturated cables are not penetrated by gum, and if a crack forms in the calendering compound down to the peripheral layer of the metallic reinforcement, then water can enter the reinforcement and move within it, causing corrosion along its entire length.With a penetrated cable whose outer strand layer is desaturated, the crack reaches the metal reinforcement but does not allow water to penetrate the metal reinforcement, let alone circulate within it, as the metal reinforcement is impregnated with the calendering mixture. It is interesting that the same applies to the metal reinforcements of the working layers; namely, since the metal reinforcements of the working layers have an outer strand layer, the outer strand layer of the metal reinforcements of the working layers is desaturated.

[0036] The features of the invention are illustrated by the schematic [Fig.1] not shown to scale, with reference to a tire of size 29.5R29.

[0037] Figure 1 shows a meridional cross-section 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 comprises two protective layers 311 and 312 comprising elastic metallic reinforcements embedded in an elastomeric material or coating or calendering compound, parallel to each other and forming angles A11 and A12 respectively, with a circumferential direction XX'. tangent to the circumference of the tire, the protective layers are intersected from one protective layer to the next. The working reinforcement 32 comprises two working layers 321, 322 whose respective metal reinforcements are embedded in an elastomeric material, parallel to each other and forming, with the circumferential direction XX', angles of 24°, and are intersected from one working layer to the next. The shrink-fit reinforcement 33 comprises two shrink-fit layers 331, 332 whose respective metal reinforcements, embedded in an elastomeric material, parallel to each other and forming, with the circumferential direction XX', an angle between 5° and 10°, are intersected from one shrink-fit layer to the next.

[0038] The invention has been tested or evaluated on tires of size 29.5R29, 24.00R35, 27.00R49 and 50 / 80R57. The reference tires are commercial tires, the reference cable for the civil engineering tires of the Michelin ® brand tires considered as reference is an E24.26 elastic cable made up of 24 steel wires of 26 hundredths of a millimeter, whose extension modulus is equal to 80GPa. Its diameter is 1.97 mm and its breaking strength is 2550 N. These reinforcing elements are desaturated and therefore the calendering mixture penetrates to the core of the reinforcing element. This cable is used at a pitch of 2.5 mm, i.e. an inter-cable of 0.53 mm for a ply resistance of 1020 N / mm in a protective layer using two crossed layers making a very fine mesh relevant for certain tires of machinery on construction sites where there are nails, screws and other thin and sharp objects likely to puncture a tire.This type of object is not particularly dangerous for mining tires, whose tread depth is usually greater than the length of such objects, which are also rarely found in underground or surface mines. For example, the tread depth of mining tires is greater than 30 mm and often greater than 90 mm. The protective layers of these tires have reinforcing elements that form an angle of 24° with the circumferential direction. These reinforcing elements are staggered from one protective layer to the next. For these tires, these protective layers have significantly improved their impact resistance, resulting in excellent impact resistance.However, while the improvement in this performance has significantly reduced tire shrinkage due to apex impact problems, it has revealed another failure mode that is becoming increasingly common: the formation of circumferential pockets between the protective layer and the tread.

[0039] The invention was implemented using a reinforcing element 52.26 composed of 52 wires of 0.26 mm diameter, with an extension modulus of 68 GPa. These reinforcing elements are elastic and desaturated so that the mixture The calendering process penetrates to the core of the reinforcement elements. These elements have a diameter of 3.1 mm and a breaking strength of 6050 N. They were installed at a 5.9 mm pitch to provide a protective layer strength equivalent to that of the test piece, but with a 2.8 mm inter-strand spacing. Furthermore, the angle of the reinforcement elements of the outermost radial layer of the tires according to the invention with the circumferential direction is 50°.

[0040] The invention was tested in three ways: straight-line driving, braking, and tire drifting. Since the tires were of different sizes, the same braking force (Fx) and drift thrust (Fy) ratios relative to the nominal load were applied. During straight-line driving, the forces Fx and Fy were negligible, and the load (Fz) was equal to the tire's nominal load. During drifting, a Fy / Fz ratio of approximately 20% was used, and for braking, a Fx / Fz ratio of approximately 15% was used.

[0041] The reduction in maximum shear stress in the rubber compound at the interface with the outermost radially protective layer is on average 25% for the various tires and can reach 70%. With a more flexible protective layer and an increased angle, while maintaining the same level of rupture strength, we should obtain a crown impact resistance equivalent to that of the control tires. With such a significant reduction in shear deformation at the interface between the outermost radially protective layer and the tread, the resistance to pocketing should be improved accordingly. Thus, the invention enables an improvement in the crown resistance of mining tires.

Claims

Demands

1. A tire (1) for a mining construction vehicle intended to be mounted on a rim having a diameter at site of at least 25 inches, comprising: - a crown reinforcement (3), radially inward to a tread (2), having a tread height of at least 30 mm, and radially outward to a carcass reinforcement (4), and comprising crown layers (311, 312, 321, 322, 331, 332) comprising metallic reinforcements, - the crown reinforcement (3) comprising two protective layers (311, 312), the outermost radial layers of the crown layers, said protective layers comprising elastic metallic reinforcements having an extensibility modulus of at least 40 GPa and at most 140 GPa, embedded in a rubber compound, referred to as the calendering compound, parallel to each other, and having a breaking strength FR, - the reinforcement of apex comprising at least two working layers (321, 322), each working layer (321,322) being radially internal to the protective layers (311, 312) 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 least equal to 17°, - characterized in that the diameter of the metallic reinforcements of the outermost radially external protective layer (311) is at least equal to 2.5 mm and in that the metallic reinforcements of the outermost radially external protective layer (311) form, with a circumferential direction (XX') tangent to the circumference of the tire, an angle APN whose absolute value is at least equal to 40°.

2. Tire (1) according to claim 1, wherein the metallic reinforcements of the outermost radially protective layer (311), form, with a circumferential direction (XX') tangent to the circumference of the tire, an angle APN whose absolute value is at least equal to 45°, preferably at least equal to 55°.

3. Pneumatic (1) according to claim 1, wherein the metallic reinforcements of the outermost radially outer protective layer (311), have a diameter of at least 3.0 mm, preferably at least 3.5 mm.

4. Pneumatic (1) according to claim 1 or 2, wherein the breaking strength FR of the metallic reinforcements of the outermost radially protective layer (311), is greater than 4000 N.

5. Pneumatic (1) according to any one of the preceding claims, wherein the pitch of the metallic reinforcements of the outermost radially protective layer (311) is greater than 0.70*FR / 1000.

6. Pneumatic (1) according to any one of the preceding claims, wherein the pitch of the metallic reinforcements of the outermost radially protective layer (311), is less than ll*FR / 1000.

7. Pneumatic (1) according to any one of the preceding claims, wherein the metallic reinforcements of the innermost radially protective layer (312) have the same diameter and breaking strength as the metallic reinforcements of the outermost radially protective layer (311).

8. Pneumatic (1) according to any one of the preceding claims, wherein the pitch of the metal reinforcements of the innermost radially protective layer (312) is equal to the pitch of the metal reinforcements of the outermost radially protective layer (311).

9. Pneumatic (1) according to any one of the preceding claims, wherein the angle formed by the metallic reinforcements of the innermost radially protective layer (311) is at least equal to 40°, preferably at least equal to 45°, preferably at least equal to 55°.

10. Tire (1) according to any one of the preceding claims, the tread (2) being directly adjacent to the outermost radially outermost protective layer (311), wherein the elastic modulus Mal measured at 10% elongation at 23°C of the rubber compound of the tread (2) directly adjacent to the outermost radially outermost protective layer at the center of the tread, is at least equal to the elastic modulus Ma2 measured at 10% elongation at 23°C of the calendering compound of the outermost radially outermost protective layer (311).

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