Optimized structure of a tire for civil engineering

Abstract

The invention relates to a radial tyre (1) for heavy vehicles comprising at least two working layers (321, 322, 323, 324) whose reinforcing elements form an angle with the circumferential direction of at least 10° and at most 45°. The metal reinforcing elements of the crown layers of all the crown reinforcing elements are extensible, thus having a structure elongation As in the rubberized state removed from the polymer matrix of at least 0.5%, a total breaking elongation At of at least 3% and a tensile Young's modulus E of at most 150 GPa. For the two working layers, the axial width of the narrower layer is at least 60% of the width of the tread and the axial width of the wider layer is at least 70% of the width of the tread.

Description

Technical Field

[0001] The present invention relates to a radial tire intended for mounting on heavy-duty civil engineering vehicles, more particularly to heavy-duty vehicles or loaders for underground mining, and even more particularly to a crown reinforcement for said tire. Background Technology

[0002] Radial tires designed for mounting heavy-duty civil engineering vehicles are specified within the meaning of the European Tire & Rim Technology Organization (ETRTO) standard.

[0003] For example, within the meaning of the European Tire & Rim Technology Organization (ETRTO) standard, radial tires for heavy-duty civil engineering vehicles are intended to be mounted on rims with a diameter of at least 25 inches. While not limited to this type of application, the present invention describes radial tires intended to be mounted on loaders (vehicles used to transport materials extracted from underground mines) via rims with a diameter of at least 35 inches.

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

[0005] In the following text, "radial inner" and "radial outer" refer to "closer to the tire's axis of rotation" and "farther from the tire's axis of rotation," respectively. "Axial inner" and "axial outer" refer to "closer to the tire's equatorial plane" and "farther from the tire's equatorial plane," respectively. The tire's equatorial plane is a plane that passes through the middle of the tread surface and is perpendicular to the axis of rotation.

[0006] Typically, a tire includes a tread that is designed to contact the ground through its surface, and two axial ends of the tread are connected to two beads via two sidewalls, which provide a mechanical connection between the tire and a rim designed to mount the tire.

[0007] The radial tire further includes a reinforcing member consisting of a crown reinforcement located radially inside the tread and a carcass reinforcement located radially inside the crown reinforcement.

[0008] The carcass reinforcement of radial tires used in heavy-duty civil engineering vehicles typically comprises at least one carcass layer, which usually includes a metal reinforcement (or reinforcing element) coated with an elastomeric or elastic polymer material obtained through blending and referred to as a coated compound. The carcass layer includes the main portion that connects two beads together and typically forms a beaded edge by wrapping a circumferential metal reinforcing element, commonly referred to as a bead line, from the inside to the outside of each bead. The metal reinforcements of the carcass layer are substantially parallel to each other and form an angle between 85° and 95° with respect to the circumferential direction.

[0009] The crown reinforcement of radial tires for civil engineering vehicles comprises stacked crown layers extending circumferentially outward along the radial direction outside the carcass reinforcement. Each crown layer is typically composed of metal reinforcements parallel to each other and coated with an elastomeric or compound-type polymer material.

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

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

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

[0013] The function of a working reinforcement, comprising at least two working layers, is to surround the tire and ensure its stiffness and road retention. The working reinforcement absorbs mechanical inflation stress and mechanical stress caused by driving. The mechanical inflation stress is generated by the tire inflation pressure and transmitted through the carcass reinforcement, while the mechanical stress caused by driving is generated by the tire's movement on the ground and transmitted through the tread. Due to the inherent design of the working reinforcement and the protective reinforcement responsible for protecting other tread layers from external impacts, tears, or other punctures, the working reinforcement must further withstand oxidation, shock, and punctures.

[0014] The working reinforcement typically comprises two radially stacked working layers formed of non-extensible metallic reinforcements that are parallel to each other in each layer, intersecting from one layer to the other, and forming an angle of at most 60°, preferably at least 10° and at most 45°, with respect to the circumferential direction. To satisfactorily absorb radial and lateral forces, designers seek to maximize the stiffness and fracture strength of the reinforcing elements in the working layers.

[0015] To reduce the mechanical inflation stress transmitted to the working reinforcement, a known practice is to place a hoop reinforcement on the radially outer side of the carcass reinforcement. The function of the hoop reinforcement is to at least partially absorb the mechanical inflation stress, thereby improving the durability of the crown reinforcement by strengthening it. The hoop reinforcement can be located 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, hoop reinforcements may comprise two radially stacked hoop layers formed of metal reinforcements. These metal reinforcements are parallel to each other in each layer and intersect from one layer to the other, forming an angle of at most 10° but at least 5° with respect to the circumferential direction. In this configuration, the reinforcing elements of the hoop layers are arranged in layers, extending from one axial edge of the hoop layer to the other within a circle less than one revolution of the tire around its axis of rotation.

[0017] The hoop reinforcement may typically include a hoop layer, which is produced by circumferentially winding hoop wires or continuous hoop strips, the hoop wires or continuous hoop strips forming an angle of up to 5° with the circumferential direction.

[0018] Regarding metal reinforcements, their mechanical characteristics are defined by a so-called force-elongation curve, which shows the change in tensile force (in N) applied to the metal reinforcement as a function of its relative elongation (in %). From this force-elongation curve, the mechanical tensile characteristics of the metal reinforcement are derived (e.g., structural elongation As (in %), total elongation at break At (in %), breaking force Fm (maximum load, in N), and breaking strength Rm (in MPa)). These characteristics are measured according to ASTM D 2969-04, 2014.

[0019] By definition, the total elongation at break of a metal reinforcement, At, is the sum of its structural elongation, elastic elongation, and plastic elongation (At = As + Ae + Ap), and specifically, each elongation is non-zero at fracture. The structural elongation As originates from the relative positioning of the metal wires constituting the metal reinforcement under low tensile force. The elastic elongation Ae originates from the actual elasticity of the metal of the metal wires constituting the metal reinforcement (considered separately), whose behavior follows Hooke's law. The plastic elongation Ap originates from the plasticity of the metal of these metal wires (i.e., irreversible deformation exceeding the elastic limit), considered separately. These different elongations and their respective meanings are well known to those skilled in the art, for example, as described in US5843583, WO2005 / 014925, and WO2007 / 090603.

[0020] At each point on the force-elongation curve of the metal reinforcement, a tensile modulus, expressed in GPa, is defined, which represents the slope of the straight line tangent to the force-elongation curve at that point. In particular, the tensile modulus of the elastic linear portion of the force-elongation curve is called the tensile modulus of elasticity or Young's modulus.

[0021] In metal reinforcements, a distinction is typically made between stretchable metal reinforcements (such as those used in protective layers) and non-stretchable or non-stretchable metal reinforcements (such as those used in working layers).

[0022] The stretchable metal reinforcement in its non-rubberized state is characterized by a structural elongation As of at least 1% and a total elongation at break At of at least 3%. In addition, the tensile modulus of elasticity of the stretchable metal reinforcement is at most 180 GPa, and is typically between 40 GPa and 150 GPa.

[0023] In the rubberized state extracted from the polymer matrix (i.e., the tire), the stretchable metal reinforcement is characterized by a structural elongation As of at least 0.5% and a total elongation at break At of at least 3%. Furthermore, the tensile modulus or Young's modulus of the stretchable metal reinforcement in the rubberized state extracted from the polymer matrix is ​​at most 150 GPa, typically between 40 GPa and 120 GPa. The term "overstretchable" refers to a metal reinforcement with a structural elongation between 1% and 3%.

[0024] Non-extensible metal reinforcements are characterized in that, under a tensile force equal to 10% of the breaking force Fm, the total elongation at break At is at most 0.2%. Furthermore, the tensile modulus or Young's modulus of non-extensible metal reinforcements is typically between 150 GPa and 200 GPa.

[0025] When a tire drives over rocks or other more or less sharp objects present in an underground mine, where a loader is operating, the tire's tread is typically cut. These cuts may penetrate radially through the tire to the interior and, depending on the size of the object, puncture the tread reinforcement and carcass reinforcement assembly, resulting in pressure loss and tire failure. It is known to improve tire puncture resistance by using stretchable metal reinforcements in the protective layer, allowing the layer to better adapt to the shape of the obstacle; given the cost of these large tires and the frequency of these incidents, improved performance is always beneficial.

[0026] However, while these tire crown structures are effective against relatively small or medium-sized obstacles, they are less effective against larger obstacles present in mines. Specifically, in these cases, the force applied to the cords is greater than the cords' breaking strength, so the obstacle "cuts" through the reinforcing elements of the working layer. The stiffer these cords are, the more resistant they are to deformation exerted by the obstacle, the easier they are to cut.

[0027] For radial tires used in civil engineering vehicles, the inventors set a goal for themselves to reduce the risk of the tire crown being punctured when it drives over sharp rocks, while maintaining the good crack resistance of the crown and reducing the mass of the crown reinforcement. Summary of the Invention

[0028] According to the present invention, this objective has been achieved by a radial tire for civil engineering vehicles, said tire comprising:

[0029] • A crown reinforcement, located radially inside the tread with an axial width of Lbdr and radially outside the carcass reinforcement, comprising a crown layer with metal reinforcing elements.

[0030] The tire crown reinforcement includes at least one working reinforcement, which comprises at least two working layers. One working layer has a larger axial width of Ltmax, and the other working layer has a smaller axial width of Ltmin.

[0031] Each working layer includes metal reinforcement elements that are parallel to each other and form an orientation angle of at least 10° and at most 45° with respect to the circumferential direction. At least two angles of the two working layers have opposite signs.

[0032] • Each reinforcing element of each tread ply is characterized by structural elongation As, breaking force Fm (maximum load, in N), breaking strength Rm (in MPa), total elongation at break At, and tensile Young's modulus E, which are measured according to ASTM D 2696-04, 2014.

[0033] Each metal reinforcement element in each crown layer is extensible and has a structural elongation As of at least 0.5% in the rubberized state removed from the polymer matrix, a total elongation at break At of at least 3%, and a tensile Young's modulus E of at most 150 GPa.

[0034] • The axial width Ltmin of the working layer with a smaller axial width is at least equal to 60% of the tread axial width Lbdr (Ltmin ≥ 0.6 * Lbdr).

[0035] • The axial width Ltmax of the working layer with a large axial width is at least equal to 70% of the axial width Lbdr of the tread (Ltmin≥0.7*Lbdr).

[0036] In the tire of this invention, all metal reinforcements of the crown reinforcement are extensible or overstretchable, unlike prior art tires where at least the working ply is non-extensible to allow for sufficient circumferential and lateral stiffness. Surprisingly, this feature is not considered necessary in existing civil engineering tires. More importantly, the use of extensible cords in the working ply significantly increases the crown's puncture and crack resistance and saves weight. Due to the extensibility of the reinforcements, satisfactory rubber shear levels and crown stiffness can be maintained at the ends of the working ply, provided that the working ply has a minimum width relative to the tread width. Working ply with a larger axial width is typically at least 70% of the tread width, and working ply with a smaller axial width is at least 60% of the tread width. When the axial width of the lateral reinforcement layer with a smaller width is below this minimum axial width, the absorption of lateral forces is poor and the mechanical behavior of the tire deteriorates, particularly its crack resistance at the axial ends of the lateral reinforcement layer.

[0037] The inventors have observed that the functionality of the present invention is satisfactory regardless of the presence or absence of a ring layer. However, ring layers with strictly circumferential reinforcements present manufacturing limitations due to their low deformability; therefore, it is advantageous not to use them. This does not apply if the extendable reinforcement of the ring layer (if used) forms an angle of at least 5° with the circumferential direction as measured at the circumferential midplane. A crown layer comprising extendable or overextended reinforcements forming an angle of at least 45° and at most 70° with the circumferential direction can also be associated with the working layers and referred to as a triangular layer. The benefit of such a reinforcement layer is resistance to shear between at least two working layers and absorption of compressive forces typically absorbed by the carcass reinforcement. Different extendable reinforcements can also be used between the triangular layer and the working layers, particularly to make the outermost radially extending working layer more extendable and to protect the other layers when the crown is impacted.

[0038] Therefore, the invention can be implemented in several embodiments having two, three, four, or more working layers, optionally associated with one or two hoop layers and optionally with triangular layers, wherein the angles of the working layers have opposite signs from one working layer to another, or have different signs in pairs from one layer to another within each pair of layers, wherein the reinforcements in the hoop layers form an angle of at least 5° and at most 10° with respect to the circumferential direction, and the reinforcements in the triangular layers form an angle of at least 45° and at most 70° with respect to the circumferential direction. The outermost radial working layer can have greater extensibility than the innermost radial working layer.

[0039] Of all possible solutions, the crown reinforcement advantageously includes two working layers, especially for saving raw material resources.

[0040] For the purpose of saving raw materials, the crown reinforcement also advantageously includes two working layers and a third crown layer, wherein the extendable metal reinforcement forms an angle between 5° and 70° with the circumferential direction. In this case, the crown includes two working layers, and (depending on the selected angle) a ring layer, a third working layer, or a triangular layer.

[0041] Similarly, in order to save raw materials, the crown reinforcement advantageously includes four working layers.

[0042] Similarly, to save on raw materials, the crown reinforcement advantageously includes three working layers and a lateral crown layer with an extendable reinforcement forming an angle between 5° and 70° with the circumferential direction, the angles of the reinforcement with the circumferential direction having opposite signs from one working layer to another. In this case, the crown includes three working layers, and (depending on the selected angle) a ring layer, a fourth working layer, or a triangular layer.

[0043] An advantageous solution is that the crown reinforcement comprises at least two working layers and two transverse reinforcement layers, wherein the extendable reinforcements form an angle between 5° and 10° with the circumferential direction, and the angles of these reinforcements with the circumferential direction have opposite signs from one layer to the other.

[0044] To more effectively protect the crown reinforcement from impacts, especially when driving over obstacles that frequently occur on the ground, if the crown reinforcement comprises at least three crown layers, the structural elongation Asp of the reinforcing element of the outermost radial crown layer is advantageously at least equal to one percent plus the structural elongation Ast of the reinforcing element of the innermost radial working layer (Asp ≥ 1% + Ast), with each reinforcement in a rubberized state extracted from the polymer matrix. An advantageous version of the invention comprises a crown reinforcement having two layers (i.e., the outermost radial layer), wherein the structural elongation Asp of the reinforcing element is at least equal to one percent plus the structural elongation Ast of the reinforcing element of the innermost radial working layer (Asp ≥ 1% + Ast), with each reinforcement in a rubberized state extracted from the polymer matrix.

[0045] Preferably, the structural elongation As of the reinforcing element in each reinforcing layer is at least 85% and at most 110% of the structural elongation Ast of the reinforcing element in the innermost radial working layer, and each reinforcement is in a rubberized state extracted from the polymer matrix. Unless the outermost radial reinforcing layer has better extensibility, the respective total elongation of the reinforcements in each reinforcing layer is advantageously similar, such that the reinforcing layers exhibit similar behavior upon impact and absorb deformation in a balanced manner, thereby preventing premature failure of one or more layers upon impact with an obstacle.

[0046] Similarly, the Young's modulus Ef of the reinforcing element in each reinforcing layer is preferably at least 85% and at most 110% of the Young's modulus Et of the reinforcing element in the innermost radial working layer, and each reinforcing element is in a rubberized state extracted from the polymer matrix. As with the previous conditions, this condition allows for the balancing effect of the different crown layers, but in this case, from the perspective of stress rather than deformation.

[0047] Each stretchable metal reinforcement element in each tread ply, in its rubberized state extracted from the polymer matrix, advantageously possesses a structural elongation of at least 1% and at most 3%. This is the optimal range of structural elongation for the reinforcement of the ply to achieve best protection against punctures and impacts to the tread. If the structural elongation of the ply is excessive, the tire will deform excessively, and the tire's rubber material will also deform significantly during inflation, particularly reducing some crack resistance. For rubberized stretchable reinforcements extracted from the polymer matrix, 0.5% structural elongation is merely the lower limit of structural elongation and not the optimal value for improving tire puncture resistance.

[0048] Similarly, each extendable metal reinforcement element in each crown layer has a Young's modulus (Ef, Et) of at most 85 GPa and at least 50 GPa in the rubberized state after being removed from the polymer matrix, in order to achieve optimal behavior in terms of crack and puncture resistance. Attached Figure Description

[0049] Figure 1 (Illustrative and not drawn to scale) A tire with a reference size of 24.00R35 illustrates the features of the invention, showing a radial cross-section of the tire crown comprising four crown layers according to the invention. Detailed Implementation

[0050] Figure 1 Not all possibilities offered by the invention have been shown. For example, for versions of the invention comprising two working layers and one ring layer, various possible variations in the positions of the different ring layers and triangular layers included in the invention have not been shown.

[0051] Figure 1 A radial cross-section of a tire 1 for heavy-duty civil engineering vehicles is shown. The tire 1 includes a crown reinforcement 3 located radially inside the tread 2 and radially outside the carcass reinforcement 4. The crown reinforcement 3 includes crown layers 321, 322, 323, and 324, at least two of which are working layers. All crown layers 321, 322, 323, and 324 include extensible metal reinforcements coated with an elastic material and parallel to each other. For the working layers, the reinforcements form an angle between 10° and 45° with the circumferential direction XX' (tangent to the tire's circumference) and intersect from one layer to another. The axial width Lbdr of the tread, and the minimum axial width Ltmin and maximum axial width Ltmax of the working layers are also shown.

[0052] The invention was tested on a tire with a size of 24.00R35 and a tread axial width of 590 mm. In each test, the tire according to the invention was compared with a reference tire of the same size.

[0053] Regarding the puncture resistance of the tire crown, a quasi-static test was conducted using a cylindrical indentation tool with a circular base of 76.6 mm in diameter and a length of 300 mm. The end of the tool designed to contact the tire has an inclined plane on a plane of symmetry relative to the axis of the cylinder, with an angle of 46° at the top of the inclined plane.

[0054] The quasi-static test involves pushing an indenter into the tire at a speed of 50 mm / min. The tire is then compressed onto a flat surface with a force equal to the recommended load, and the tire is inflated to the recommended pressure. The indenter is pushed into the center of the contact patch. The test result is the puncture distance required to break the crown reinforcement. Results are given in a baseline of 100, where 100 is the result for a reference tire. A result greater than 100 indicates better performance.

[0055] The crack resistance of the tire crown (also known as the tread's resistance to cracking) is measured on a machine by testing two identical tires traveling over each other at 28 km / h (a reference tire on a reference tire, and the tire according to the invention on the tire according to the invention), with the tires inflated to 7.25 bar, a pressure of 20 tons. The test is stopped when one of the tires loses pressure. The result is the number of kilometers traveled before tire failure.

[0056] Except for the crown reinforcement, the reference tire and the tire according to the invention are identical. They have the same tread pattern, the same carcass layers with the same reinforcements, and the same rubber compound in different parts of the tire.

[0057] Regarding the crown reinforcement, radially from the outside to the inside, the reference tire consists of the following: a protective reinforcement, a working reinforcement, and a ring reinforcement:

[0058] The reinforcing elements of the protective layer are E24.26 stretchable cords (24 strands with a diameter of 26 mm), laid at a spacing of 2.5 mm. In their rubberized state after extraction from the polymer matrix, they have a structural elongation As of 0.6%, a total elongation at break At of 3.9%, and a Young's modulus of 75 GPa. They form a 24° angle with the circumferential direction and intersect from one layer to another. The axial width of the outermost radial layer is 520 mm, and the axial width of the next layer is 400 mm.

[0059] The reinforcing element of the working layer is 26.30 non-stretchable cord (26 filaments with a diameter of 30% mm), laid at a spacing of 3.4 mm. In its rubberized state after extraction from the polymer matrix, its structural elongation As is 0%, its total elongation at break At is 2.4%, and its Young's modulus is 180 GPa. The innermost radial layer forms an angle of -33° with the circumferential direction, and the outermost radial layer forms an angle of 19° with the circumferential direction, intersecting from one layer to the other. The axial width of the outermost radial layer is 380 mm, and the axial width of the other layer is 450 mm.

[0060] The reinforcing elements of the hoop layer are the same as those of the working layer, with the same laying spacing. They form an 8° angle with the circumferential direction and intersect from one layer to another. They are laid in the form of plywood layers. The axial width of the outermost radial layer is 200 mm, and the axial width of the other layer is 240 mm.

[0061] Due to the stiffness of the working layer and the hoop layer, it is impossible to make the hoop layer wider. If only the hoop layer is stretchable, they will no longer be effective.

[0062] Two versions of the invention (a so-called stretchable version, referred to as E, and two so-called overstretchable versions, referred to as HE1 and HE2, with HE2 having a reinforcement that is more overstretchable than HE1) were tested. For the three versions of the invention, E, HE1, and HE2, the structure of the crown reinforcement is the same, but the reinforcing elements for different crown layers are different. Radially from the outside to the inside, the crown reinforcement consists of the following:

[0063] • A working layer with an axial width of 380mm (i.e., 64% of the tread width) forming a 33° angle with the circumferential direction.

[0064] • A working layer with an axial width of 450mm (i.e., 76% of the tread width) forming an angle of -33° with the circumferential direction.

[0065] • A working layer with an axial width of 380mm (i.e., 64% of the tread width) forming a 33° angle with the circumferential direction.

[0066] • Working layer with an axial width of 450mm (i.e., 76% of the tread width) forming an angle of -33° with the circumferential direction.

[0067] For version E of the present invention, all layers of the crown reinforcement are produced from a reinforcement comprising E21.28 cords (21 filaments with a diameter of 28% mm) with a spacing of 2.4 mm, a structural elongation As equal to 0.5% in the rubberized state removed from the polymer matrix, a total elongation at break At equal to 3.3%, and a Young's modulus equal to 95 GPa.

[0068] For version HE1 of the present invention, all layers of the crown reinforcement are produced from a reinforcement comprising E24.35_1 cords (24 filaments with a diameter of 35% mm) with a layup spacing of 3.9 mm, a structural elongation As equal to 1.1% in the rubberized state extracted from the polymer matrix, a total elongation at break At equal to 4.3%, and a Young's modulus equal to 70 GPa. The elasticity and hyperelasticity of the cords (in other words, extensibility and hyperstretchability) are achieved by adjusting the arrangement of the filaments in the cords and the compound disposed between the filaments.

[0069] For version HE2 of the present invention, all layers of the crown reinforcement are produced from a reinforcement comprising E24.35_2 cords (24 filaments with a diameter of 35% mm) with a layup spacing of 4.2 mm, a structural elongation As equal to 1.6% in the rubberized state extracted from the polymer matrix, a total elongation at break At equal to 5.5%, and a Young's modulus equal to 50 GPa. The elasticity and hyperelasticity of the cords are achieved by adjusting the arrangement of the filaments in the cords and the compounding material disposed between the filaments.

[0070] During the structural elongation phase of the assembly of the stretchable or overstretchable cords of the reference tire or the tire according to the invention, its elastic modulus in the non-rubberized state is between 10 GPa and 20 GPa, and its elastic modulus in the rubberized state removed from the polymer matrix is ​​between 10 GPa and 30 GPa.

[0071] Regarding puncture resistance, the results showed that although the tire weight was reduced by decreasing the metal mass of the crown reinforcement, the critical height of the indentation tool increased significantly upon impact with the tread surface. Version E exhibited the same performance as the control tire, version HE1 showed a 10% improvement, and version HE2 showed a 20% improvement.

[0072] In tests relating to crown cracking or splitting, the tire according to the invention traveled the same number of kilometers as the reference tire before failure and exhibited the same performance.

[0073] In terms of performance related to tire weight, versions E and HE1 showed a 20% reduction in metallic weight, while version HE2 showed a 22% reduction, resulting in a weight reduction of approximately 100 kg for the tires tested.

[0074] Therefore, the proposed invention can achieve the same or improved puncture resistance of the tread, the same crack resistance of the tread reinforcement, and reduce the mass of the tread reinforcement, thereby reducing the mass of the tire.

Claims

1. Radial tyre (1) for civil engineering vehicles, comprising: • a tread (2) having an axial width Lbdr, • a carcass reinforcement (4), and • a single crown reinforcement (3) located radially inside the tread (2) and radially outside the carcass reinforcement (4), and consisting of crown layers having metal reinforcing elements in a polymer matrix, wherein said crown layers comprise at least two working layers (321, 322, 323, 324) constituting a working reinforcement (32) belonging to the single crown reinforcement, one of said at least two working layers being a greater axial width working layer (321) having an axial width Ltmax, the other of said at least two working layers being a smaller axial width working layer (322) having an axial width Ltmin, the metal reinforcing elements of each of said at least two working layers being parallel to each other and forming an orientation angle with the circumferential direction of the tyre at least equal to 10° and at most equal to 45°, the orientation angle of one of said at least two working layers having an opposite sign with respect to the orientation angle of the other of said at least two working layers, each metal reinforcing element of each crown layer having, in the rubberized state removed from the polymer matrix, a structural elongation As, a breaking force Fm (maximum load in N), a breaking strength Rm (in MPa), a total breaking elongation At and a tensile Young's modulus E, all measured according to ASTM D 2696-04 of 2014, characterized in that each metal reinforcing element of each crown layer is extensible, each extensible metal reinforcing element of each crown layer having a structural elongation As at least equal to 0.5%, a total breaking elongation At at least equal to 3% and a tensile Young's modulus E at most equal to 150 GPa, and in that the axial width Ltmin of the smaller axial width working layer (322) is at least equal to 60% of the tread axial width Lbdr, and in that the axial width Ltmax of the greater axial width working layer (321) is at least equal to 70% of the tread axial width Lbdr.

2. Tyre (1) according to claim 1, wherein, the crown layers consist of: - two working layers, and - a transversal reinforcement crown layer, the extensible metal reinforcing elements of which form an angle with the circumferential direction comprised between 5° and 70°.

3. Tyre (1) according to claim 1, wherein, the crown layers consist of four working layers (321, 322, 323, 324).

4. Tyre (1) according to claim 1, wherein, the crown layers comprise: - three working layers, and - a transversal reinforcement crown layer, the extensible metal reinforcing elements of which form an angle with the circumferential direction comprised between 5° and 70°, the angle of the extensible metal reinforcing elements with the circumferential direction having an opposite sign from one crown layer to another.

5. Tyre (1) according to claim 1, wherein, The crown layers consist of two working layers.

6. Tyre (1) according to any one of claims 1 to 5, wherein, The structural elongation As of the reinforcing elements of each crown layer is at least equal to 85% and at most equal to 110% of the structural elongation of the reinforcing elements of the radially innermost working layer of said at least two working layers.

7. Tyre (1) according to any one of claims 1 to 5, wherein, The tensile Young's modulus Ef of the reinforcing elements of each crown layer is at least equal to 85% and at most equal to 110% of the tensile Young's modulus of the reinforcing elements of the radially innermost working layer of said at least two working layers.

8. Tyre (1) according to any one of claims 1 to 5, wherein, The structural elongation As of each extensible metallic reinforcing element of each crown layer is at least equal to 1% and at most equal to 3%.

9. Tyre (1) according to any one of claims 1 to 5, wherein, The tensile Young's modulus of each extensible metallic reinforcing element of each crown layer is at most equal to 85 GPa and at least equal to 50 GPa.

10. Tyre (1) according to any one of claims 1 to 4, wherein, The crown layers comprise at least three crown layers, the structural elongation of the reinforcing elements of the radially outermost crown layer being at least equal to one percent plus the structural elongation of the reinforcing elements of the radially innermost working layer of said at least two working layers.

Images