Optimised structure of a civil engineering tire

Abstract

A tire (1) for a mine engineering vehicle comprises two protective layers (31) having elastic metal reinforcements, the modulus of extension of which is at least 40 GPa and at most 140 GPa, and two working layers. The diameter of the reinforcing elements of the radially outermost protective layer is at least equal to 2.5 mm and the reinforcing elements of the radially outermost protective layer form an angle APN with a circumferential direction (XX ') tangential to the circumference of the tire, the absolute value of the angle APN being at least 45°.

Description

Optimized architecture of civil engineering pneumatics

[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 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 (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 with a diameter of at least 25 inches.

[0004] A tire has a geometry of revolution around an axis of rotation. The tire's 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.

[0005] In what follows, the expressions "radially inward", respectively "Radially outside" means "closer" and "further" respectively from the tire's rotation axis. "Axially inside" and "axially outside" mean "closer" and "further" respectively from the tire's equatorial plane, the tire's equatorial plane being the plane passing through the middle of the tread and perpendicular to the rotation axis.

[0006] Generally speaking, a tire comprises a tread, designed to come into contact with the ground via a tread surface, the two axial ends of which are connected by 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 also includes a reinforcing structure, 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 vehicles, such as construction equipment, typically comprises at least one casing layer consisting of reinforcements, generally metallic, coated with a polymeric material, such as an elastomer or elastomeric compound, obtained by blending and called the casing 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 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 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 coating compound.

[0010] Among the top layers, we usually distinguish between the protective layers, which make up the protective reinforcement and are radially furthest outwards, and the working layers, which make up the working reinforcement and are radially located between the protective reinforcement and the carcass reinforcement.

[0011] The protective reinforcement, comprising at least one protective layer for certain applications, includes two protective layers for mining vehicles that travel on tracks or in tunnels frequently obstructed by rocks, sometimes large compared to the tire size. These protective layers primarily shield the working layers from mechanical or physicochemical damage that could propagate radially through the tread towards the inside of the tire.

[0012] The protective reinforcement for mining tires therefore comprises 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 tread reinforcement, often comprising at least two layers, serves to encircle the tire and provide it with 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. The tread reinforcement must also resist impacts and punctures, thanks to its inherent design, particularly its flexibility, and especially that of the protective reinforcement. Furthermore, the tire must exhibit sidewall flex, or lateral stiffness, to ensure proper vehicle handling on winding roads.

[0014] The structural reinforcement typically comprises two radially superimposed layers of non-extensible metal reinforcement, parallel to each other within each layer and crossed from one layer to the next, forming angles with the circumferential direction that are preferably at least 15° and at most 35°, in order to resist transverse forces and a portion of the circumferential forces. The two layers of structural reinforcement generally provide sufficient edge deflection for acceptable vehicle behavior.

[0015] To reduce the mechanical stresses of inflation 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 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.

[0016] 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.

[0017] Regarding 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, the 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 strength 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 metal reinforcement is, by definition, the sum of its structural, elastic, and plastic elongations (At = As + Ae + Ap), particularly at break, where each elongation is non-zero. The structural elongation As results from the relative positioning of the metal wires constituting the reinforcement under a small tensile force. The elastic elongation Ae results from the elasticity of the metal wires constituting the reinforcement, 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, W02005 / 014925, and W02007 / 090603.

[0019] At each point on the force-stretch curve of a metallic reinforcement, a tensile modulus, expressed in GPa, is also defined, representing the slope of the line tangent to the force-stretch curve at that point. In particular, we call The elastic modulus in extension, or Young's modulus, is the modulus in extension of the linear elastic part of the force-stretch curve.

[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 work layers. The important point is that protective layers are significantly more elastic than work 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 modulus of elasticity 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, and at most equal to 0.2%. Furthermore, a non-stretchable metal reinforcement has a tensile elastic modulus usually between 150 GPa and 200 GPa.

[0023] The efforts of mining tire manufacturers in the continuous improvement of reinforcement elements, such as metal reinforcements or cables in the protective layers, have significantly improved the tires' resistance to punctures from stones on the ground. While these punctures have clearly decreased, other unexpected failures have increased in frequency and become problematic. One such failure is the development of a crack at the interface between the outermost radial layer and the tread, which then propagates circumferentially until a portion of the tread detaches, leading to tire removal.

[0024] The inventors set themselves the objective, for a radial tire for a mining civil engineering vehicle, of reducing shear stresses 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 tread (2) having a tread height of at least 30 mm and a crown reinforcement, which is radially internal to the tread and radially external to a carcass reinforcement, and which comprises crown layers including metallic reinforcements. The crown reinforcement includes two protective layers which are the outermost radial layers of the crown layers, said protective layers comprising elastic metallic reinforcements having an elongation modulus 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 comprises at least two working layers, each working layer being radially inner 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 17°. The diameter of the metallic reinforcements of the outermost radially protective layer is at least 2.5 mm. The metallic reinforcements of the outermost radially protective layer form, with a circumferential direction tangent to the circumference of the tire, an angle APN whose absolute value is at least 45°.

[0026] The idea is to enhance the characteristics that enabled the metallic reinforcements in the protective layers to withstand impacts during rolling, such as the diameter of the metallic reinforcements. This is achieved by using larger diameter metallic reinforcements 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 stiffness approaches as closely as possible the stiffness of its calendered compound. Thus, since the protective layers have reinforcing elements on the order of 2 mm, the reinforcement elements of the protective layer must have a diameter of at least 2 mm in the invention.5 mm and that the metallic reinforcements of the outermost radially protective layer form, with a circumferential direction tangent to the circumference of the tire, an angle APN whose absolute value is at least equal to 45°, preferably at least equal to 50°, of. A preference for an angle of at least 55° is preferred. At an angle of 45°, the circumferential stiffness of a top layer is more than 2% less than the stiffness of said top layer at 0° and less than 50% to 10% less than 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 stiffness is even more significant at a 50° angle, dropping by more than 50% compared to 35°, and even more so at 55° where the stiffness of the protective layer becomes negligible. From a performance standpoint, further widening the angles is irrelevant because the protective layers do not experience increased tension due to the difference in stiffness between their metallic reinforcements and 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 the working layers, but not puncture the tire itself. Therefore, the use of large-diameter cables that can withstand being cut when rolling over such objects is feasible. 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 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 metallic 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 increases the breaking strength of the metallic reinforcement and therefore the spacing between the reinforcements for the same protective layer strength. Increasing the spacing between the metallic reinforcements of the outermost radially exposed protective layer reduces its circumferential stiffness by increasing the percentage of metal blending within the protective layer. Indeed, the breaking strength of the metallic reinforcements increases with the square of the diameter, and while maintaining the same breaking strength of the protective layer, the spacing between the reinforcements increases linearly with the diameter.Therefore, by doubling the diameter, we can increase the distance between the metal reinforcements by approximately 3.5 times, thereby increasing the calendering mixture ratio and contributing to a decrease in the tire's circumferential stiffness. This allows us to reduce, given the angle of the metal reinforcements relative to the circumferential direction, the circumferential stiffness that influences the failure mode we wish to address.

[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, in mm, of the metal reinforcements in the outermost radially protective layer is greater than 0.70*FR / 1000 and less than 1.1*FR / 1000, where FR is in N (Newtons). The spacing of the metal reinforcements is defined as the distance in mm between each reinforcement, either between the centers of two directly adjacent reinforcements measured perpendicular to the reinforcements, or between two right or left edges of the cords of two directly adjacent 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 and innermost radially protective layers—are identical in terms of the nature of their metal reinforcements, namely the same architecture (same number of wires, same assembly, same manufacturing process), same pitch, same calendering mixture, and the same absolute value of the angle of the metal reinforcements with the circumferential direction. The metal reinforcements are 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 breaking strength as the metal reinforcements of the outermost radially protective layer.Similarly, it is advantageous for the spacing of the metal reinforcements in the innermost radially oriented protective layer to be equal to the spacing of the metal reinforcements in the outermost radially oriented protective layer. Therefore, it is preferable that the angle formed by the metal reinforcements in the innermost radially oriented protective layer be at least 35°, preferably at least 45°, preferably at least 50°, and preferably at least 55°.

[0034] To reduce stress at the interface between the outermost radially protective layer and the tread compound directly adjacent to it, it is advantageous for the stiffness of this compound to be close to the stiffness of the calendering compound. Therefore, 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 tread compound directly adjacent to the outermost radially protective layer at the center of the tread be at least 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 strand layer, the peripheral strand layer 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 The calendering compound penetrates the metal reinforcement to protect it from corrosion. Saturated cables are not penetrated by the compound, and if a crack develops in the calendering compound extending to the outer layer of the metal reinforcement, water can enter and move through the reinforcement, causing corrosion along its entire length. With a penetrated cable whose outer layer of strands is desaturated, the crack reaches the metal reinforcement but prevents water from penetrating it, let alone circulating within it, as the metal reinforcement is impregnated with the calendering compound.It is interesting that the same applies to the metallic reinforcements of the working layers, namely that the metallic reinforcements of the working layers having a peripheral layer of strands, the peripheral layer of strands of the metallic reinforcements of the working layers is desaturated.

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

[0037] Figure 1 shows a meridional section of a heavy-duty vehicle tire 1 for civil engineering type 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 coated in an elastomeric material or coating or calendering mixture, parallel to each other and forming angles respectively Al 11 and Al 12, with a circumferential direction XX' tangent to the circumference of the tire, the protective layers being crossed 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 equal to 24°, and are intersecting from one working layer to the next. The confinement reinforcement 33 comprises two confinement layers 331, 332 whose respective metal reinforcements, embedded in an elastomeric material, are parallel to each other and forming, with. the circumferential direction XX', an angle between 5° and 10°, are crossed from one layer of shrinkage to the next.

[0038] The invention was tested or evaluated on tires of size 29.5R29, 24.00R35, 27.00R49 and 50 / 80R57. The reference tires are commercially available tires, the reference cable for the civil engineering tires of the Michelin ® brand tires considered as reference is an E24.26 elastic cable made 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 peak impact performance, resulting in excellent impact resistance.However, while the improvement in this performance has significantly reduced tire shrinkage on apex impact problems, it has revealed another mode of failure which tends to become predominant: the formation of circumferential pockets between the protective layer and the tread.

[0039] The invention was implemented using a 52.26 reinforcing element 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 calendering mixture penetrates to the core of the reinforcing elements. They have a diameter of 3.1 mm and a breaking strength of 6050 N. They were placed at a pitch of 5.9 mm for a protective layer resistance equivalent to that of the control but with a cable spacing of 2.8 mm. Furthermore, the angle of the reinforcement elements of the outermost radially protective layer of the tires according to the invention with the circumferential direction is equal to 50°.

[0040] The invention was tested in three modes: 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, the Fy / Fz ratio was approximately 20%, and for braking, the Fx / Fz ratio was approximately 15%.

[0041] The reduction in maximum shear stress in the tread at the interface with the outermost radially protective layer averages around 25% for different 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. Tyre (1) for mining construction equipment intended to be mounted on a rim having a diameter at site of at least 25 inches, comprising: - a tread (2) with a tread height of at least 30 mm, and - a crown reinforcement (3), which is radially internal to the tread (2) and radially external to a carcass reinforcement (4) and which comprises crown layers (311, 312, 321, 322, 331, 332) comprising metallic reinforcements, wherein the crown reinforcement (3) comprises two protective layers (311, 312) which are 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, called calendering compound, parallel to each other, and having a breaking strength FR, wherein the crown reinforcement comprises at least two working layers (321, 322), each working layer (321, 322) being radially internal to the protective layers (311, 312) and including parallel metallic reinforcements forming,with the circumferential direction (XX') tangent to the circumference of the tire, an angle whose absolute value is at least equal to 17°, in which the diameter of the metallic reinforcements of the outermost radially protective layer (311) is at least equal to 2.5 mm, and in which 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°.

2. Pneumatic (1) according to claim 1, wherein the metallic reinforcements of the outermost radially protective layer (311) form, with the circumferential direction (XX'), an angle APN whose absolute value is at least equal to 50°.

3. Pneumatic (1) according to claim 1, wherein the metallic reinforcements of the outermost radially protective layer (311) form, with the circumferential direction (XX'), an angle APN whose absolute value is at least equal to 55°.

4. Pneumatic (1) according to any one of the preceding claims, wherein the metallic reinforcements of the outermost radially protective layer (311) have a diameter of at least 3.0 mm, preferably at least 3.5 mm.

5. Pneumatic (1) according to any one of the preceding claims, wherein the breaking strength FR of the metallic reinforcements of the outermost radially protective layer (311) is greater than 4000 N.

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

7. Pneumatic (1) according to any one of the preceding claims, wherein the pitch, in mm, of the metallic reinforcements of the outermost radially protective layer (311), is less than 1.1 *FR / 1000 where FR is in N.

8. 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).

9. 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).

10. 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 50°, preferably at least equal to 55°.

11. Tire (1) according to any one of the preceding claims, wherein the tread (2) is directly adjacent to the layer of - 15 - outermost radially protective layer (311), and in which 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 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 protective layer (311).

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