Optimized structure of a tire for civil engineering

Abstract

The present invention relates to a radial tyre (1) for heavy vehicles, wherein the reinforcing elements of each bead layer (331, 332, 333) form an angle with the circumferential direction at most equal to 5°, the reinforcing elements of the transverse reinforcement layers (321, 322, 323) form an angle with the circumferential direction comprised between 10° and 45°, are extensible, so that in the rubberized state removed from the polymer matrix their structural elongation As is at least equal to 0.5%, their total elongation at break At is at least equal to 3% and their Young's modulus in traction E is at least equal to 150 GPa.

Description

Technical Field

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

[0002] The European Tire & Rim Technology Organization (ETRTO) standards specify radial tires designed for mounting on heavy-duty civil engineering vehicles.

[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 dump trucks, particularly on vehicles used for transporting materials extracted from quarries or open-pit mines, using rims with a diameter of at least 35 inches (potentially up to 57 inches, or even 63 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 or Young's modulus of the stretchable metal reinforcement is at most 180 GPa, and is typically between 40 GPa and 150 GPa.

[0023] In the rubberized state after being removed 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%, with the polymer matrix restricting some of the movement of the filaments responsible for the structural elongation. Furthermore, the tensile modulus or Young's modulus of the stretchable metal reinforcement in the rubberized state after being removed from the polymer matrix is ​​at most 150 GPa, typically between 40 GPa and 120 GPa.

[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 is at most 0.2%. Furthermore, the tensile modulus of non-extensible metal reinforcements is typically between 150 GPa and 200 GPa.

[0025] When a tire drives over a rock or other more or less sharp object present on the track of a dump truck, 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 hardness of the steel, 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 being punctured by sharp rocks when driving over them, while maintaining the good crack resistance of the tread and reducing the mass of the tread reinforcement. Summary of the Invention

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

[0029] • A crown reinforcement, which is located radially inside the tread with an axial width of Lbdr and radially outside the carcass reinforcement;

[0030] The crown reinforcement comprises at least two lateral reinforcement layers, one lateral reinforcement layer having a larger axial width of Ltmax, and the other lateral reinforcement layer having a smaller axial width of Ltmin.

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

[0032] The tread reinforcement includes at least one ring layer with a maximum axial width of Lfmax, the ring layer including extendable metal reinforcement elements that are parallel to each other and form an angle of at most 5° with respect to the circumferential direction (XX') of the tire.

[0033] The characteristics of each reinforcing element in each layer of the crown reinforcement are: 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, which are measured according to ASTM D2969-04 2014.

[0034] • Each extensible metal reinforcing element of each ring layer has a structural elongation Asf of at least 0.5% in the rubberized state after being removed from the polymer matrix, a total elongation at break Atf of at least 3%, and a tensile Young's modulus Ef of at most 150 GPa.

[0035] • The reinforcing elements of the transverse reinforcing layers (321, 322, 323) are extensible and have a structural elongation Asf of at least 0.5%, a total elongation at break Atf of at least 3%, and a tensile Young's modulus Ef of up to 150 GPa in the rubberized state after being removed from the polymer matrix.

[0036] In the tires of this invention, all metal reinforcements of the crown reinforcement are stretchable or overstretchable, unlike prior art tires where the working layer is non-stretchable to allow for sufficient circumferential and lateral stiffness. Surprisingly, in civil engineering tires, a non-stretchable working layer or lateral reinforcement layer is not necessarily required if it is associated with one or more ring layers having stretchable reinforcement elements. More importantly, using stretchable cords in the working layer (or the lateral reinforcement layer here) can significantly increase the puncture and crack resistance of the crown and can save weight.

[0037] In the prior art, the working layer and the protective layer differ not only in their relative positions but also in the fact that the protective layer is located radially on the outermost side and exhibits a stretchable behavior compared to the non-stretchable behavior of the working layer. In the simplest and most economical version in terms of quality and raw materials, the tire of the present invention has one or two ring layers and two stretchable lateral reinforcement layers, at least one of which is located radially outside the ring layer. In this case, according to prior art tire terminology, the radially outermost lateral reinforcement layer is the protective layer and possesses all the characteristics of a protective layer, except that it does not absorb any lateral forces, as in prior art tires, lateral forces are absorbed by the non-stretchable working layer. In this structure, the radially outermost lateral reinforcement layer acts as a protective layer in terms of impact and as a working layer in terms of absorbing lateral forces. Surprisingly, although all lateral reinforcement layers are stretchable, limited to the presence of one or more stretchable ring layers, the absorption of lateral forces ensures that the vehicle's behavior remains acceptable in civil engineering applications, and the crack resistance at the ends of the lateral reinforcement layers is maintained or even improved.

[0038] For this invention to function correctly, the hoop layer must be designed to provide satisfactory absorption of longitudinal forces. Therefore, an extendable reinforcement must be selected such that it forms an angle of at most 5° with the circumferential direction as measured in the circumferential midplane. Preferably, this structure is achieved by wrapping one or more reinforcements (particularly strips comprising multiple reinforcements) around the tire. Even when a single reinforcement is laid, the hoop layer is considered to comprise parallel metal reinforcements because the hoop layer effectively comprises multiple reinforcement channels or channels of the same reinforcement in its axial width, making it impossible to determine whether it is a single reinforcement or two reinforcements joined at the ends of the first reinforcement; this has no effect on tire behavior. Conventionally, the hoop layer is therefore considered to comprise multiple metal reinforcements. However, for this metal reinforcement angle, layered laying on an industrial scale is also possible instead of laying strips of reinforcement elements or multiple reinforcement elements, but this type of laying requires significant overlap at the longitudinal ends of the layers.

[0039] Preferably, the axial width Ltmin of the lateral reinforcement layer with a smaller axial width is at least equal to 70% of the tread axial width Lbdr, and more preferably at least equal to 80% of the tread axial width Lbdr. Since the lateral reinforcement layers are extensible, these layers are preferably joined at a minimum width of 70% (preferably 80%) of the tire crown width (i.e., tread width). When the axial width of the lateral reinforcement layer with a smaller width is less than this axial width, the absorption of lateral forces is poorer and the tire behavior deteriorates, while its crack resistance at the axial ends of the lateral reinforcement layer also deteriorates.

[0040] Advantageously, the axial width of at least one ring layer is at least 60% of the axial width of the tread, Lbdr, preferably at least 70% of the axial width of the tread, Lbdr. When the axial width of the ring layer with a larger width is less than this axial width, the absorption effect of longitudinal force is poor, and the shear force at the axial ends of the transverse reinforcement layer increases, making the tire more prone to cracking.

[0041] Preferably, the total elongation at break of the reinforcing element Atf of each ring layer and the total elongation at break of the reinforcing element Att2 of the second radially innermost transverse reinforcing layer are at least 85% and at most 110% of the total elongation at break of the reinforcing element Att1 of the radially innermost transverse reinforcing layer, and each reinforcing element is in a rubberized state extracted from the polymer matrix. If designers wish to further protect the tire from punctures, they increase the number of crown layers and the structural and total elongation of the radially outermost reinforcing layer that absorbs the impact first. If there is a difference in total elongation between different crown layers, the total elongation of the two radially innermost transverse reinforcing layers will therefore be smaller than that of the radially outermost crown layer. Therefore, the total elongation of each ring layer and the total elongation of the two radially innermost transverse reinforcing layers are preferably similar so that they exhibit similar behavior upon impact and absorb deformation in a balanced manner, thereby preventing one or the other layer from failing prematurely upon impact with an obstacle.

[0042] Similarly, the structural elongation Asf of the reinforcing element in each ring layer and the structural elongation Ast2 of the second radially innermost lateral reinforcing layer are preferably at least 85% and at most 110% of the structural elongation Ast1 of the reinforcing element in the radially innermost lateral reinforcing layer, with each reinforcing element in a rubberized state extracted from the polymer matrix. This allows for a balance of inflation and driving stresses among the different crown layers.

[0043] Similarly, the Young's modulus Ef of the reinforcing element of each ring layer and the Young's modulus Et2 of the reinforcing element of the second radially innermost transverse reinforcing layer (322) are preferably at least 85% and at most 110% of the Young's modulus Et of the reinforcing element of the radially innermost transverse reinforcing 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 different crown layers, but in this case, from the perspective of stress rather than deformation.

[0044] Advantageously, the reinforcing elements of the two innermost radial transverse reinforcement layers and the reinforcing elements of the hoop layer, in their rubberized state after being removed from the polymer matrix, each exhibit a structural elongation of at least 1% and at most 3%. This is the optimal range of structural elongation for the reinforcements of these layers to improve the puncture and impact resistance of the tire crown. If the structural elongation of the layers is excessive, the tire will deform excessively, and the tire's rubber material will also deform significantly during inflation, particularly reducing some of its crack resistance. For the rubberized, elongated reinforcements removed from the polymer matrix, a structural elongation of 0.5% is the lower limit of structural elongation and not the optimal value for improving tire puncture resistance.

[0045] Similarly, the reinforcing elements of the two innermost transverse reinforcing layers and the reinforcing elements of the hoop layer preferably have a Young's modulus of at most 85 GPa and at least 50 GPa in their rubberized state after being removed from the polymer matrix, in order to achieve optimal behavior in terms of crack resistance and puncture resistance.

[0046] If the tire's intended use does not involve the most aggressive applications in terms of impact from obstacles on the tread, then all reinforcing elements in all transverse reinforcement layers advantageously possess similar mechanical elongation and fracture properties, thus eliminating weak points in terms of impact resistance. This ensures that the tire's behavior remains as consistent as possible with changes in the drift angle applied to the tire and optimizes its crack resistance. In this case, to improve impact resistance, the total elongation at break of the reinforcing elements in each transverse reinforcement layer is advantageously at least 85% and at most 110% of the total elongation at break (Att) of the reinforcing elements in the innermost radial transverse reinforcement layer, with each reinforcement in a rubberized state extracted from the polymer matrix. Similarly, for the same purpose and optimal behavior, the structural elongation of the reinforcing elements in each transverse reinforcement layer is preferably at least 85% and at most 110% of the structural elongation (Ast) of the reinforcing elements in the innermost radial transverse reinforcement layer, with each reinforcement in a rubberized state extracted from the polymer matrix. Similarly, for optimal crack resistance, the Young's modulus of the reinforcing element in each transverse reinforcement layer is preferably at least 85% and at most 110% of the Young's modulus Et1 of the reinforcing element in the innermost radial transverse reinforcement layer, with each reinforcement in a rubberized state extracted from the polymer matrix. For the same application, the structural elongation of the reinforcing element in each transverse reinforcement layer in its rubberized state extracted from the polymer matrix is ​​advantageously at least 1% and at most 3%, which is the optimal range of structural elongation for the reinforcement of the layers to optimize protection while possessing other properties related to puncture resistance and impact resistance of the tread.

[0047] If the tire includes at least two lateral reinforcement layers and at least one ring layer in addition to the outermost radial crown layer, then both the lateral carcass layers and the ring layer can further enhance the protective effect of the outermost radial crown layer on the tire crown by increasing their elasticity relative to the other lateral reinforcement layers. For this purpose, the structural elongation Asp of the reinforcing element of the outermost radial crown layer in its rubberized state after being removed from the polymer matrix is ​​advantageously at least one percent equal to the structural elongation Ast of the reinforcing element of the innermost radial lateral reinforcement layer (Asp ≥ Ast + 1%). In this structure, the outermost radial crown reinforcement layer is preferably also the layer with the largest axial width, so that this last layer provides effective puncture resistance relative to small obstacles and protects the ends of the other lateral reinforcement layers from impact stress when driving over large rocks.

[0048] In a tire comprising at least three lateral reinforcement layers, where the structural elongation Asp of the outermost radial lateral reinforcement layer in its rubberized state after being removed from the polymer matrix is ​​greater than 110% (more particularly greater than said elongation plus 1%) of the structural elongation Ast of the innermost radial lateral reinforcement layer, all lateral reinforcement layers radially inner to the outermost radial lateral reinforcement layer advantageously exhibit similar elastic and fracture behavior, thereby keeping the tire behavior as consistent as possible with changes in the drift angle applied to the tire and optimizing its crack resistance. In this case, to optimize the crown's resistance to mechanical attack, the total fracture elongation of the reinforcing elements of each radially inner lateral reinforcement layer is advantageously at least equal to 85% and at most equal to 110% of the total fracture elongation Att of the reinforcing elements of the innermost radial lateral reinforcement layer, each reinforcement being in a rubberized state after being removed from the polymer matrix. Similarly, to improve road retention, the structural elongation of the reinforcing element in each radially innermost transverse reinforcing layer of the outermost radial reinforcing layer is preferably at least 85% and at most 110% of the structural elongation Ast of the reinforcing element in the innermost radial reinforcing layer, with each reinforcing element in a rubberized state extracted from the polymer matrix. Likewise, to improve crack resistance, the Young's modulus Ef of the reinforcing element in each radially innermost radial reinforcing layer of the outermost radial reinforcing layer is preferably at least 85% and at most 110% of the Young's modulus Et1 of the reinforcing element in the innermost radial reinforcing layer, with each reinforcing element in a rubberized state extracted from the polymer matrix. Under the same conditions, the structural elongation of the reinforcing element in each radially innermost radial reinforcing layer of the outermost radial reinforcing layer in the rubberized state extracted from the polymer matrix is ​​advantageously at least 1% and at most 3%, which is the optimal range of structural elongation for the reinforcing elements of the layers, to achieve optimal resistance to tread punctures and impacts in this configuration. Attached Figure Description

[0049] Indication Figures 1 to 8 The features of the invention are illustrated using a tire with a reference size of 24.00R35. These figures are not drawn to scale.

[0050] - Figures 1 to 5 According to the radial cross-section of the tire crown of the present invention, the tire crown comprises three transverse reinforcement layers and two ring layers, the positions of which vary according to the figure.

[0051] - Figure 6 According to the radial cross-section of the tire crown of the present invention, the tire crown comprises three transverse reinforcement layers and one ring layer.

[0052] - Figure 7 According to the radial cross-section of the tire crown of the present invention, the tire crown comprises three transverse reinforcement layers and three ring layers.

[0053] - Figure 8 According to the radial cross-section of the tire crown of the present invention, the tire crown comprises two transverse reinforcement layers and two ring layers. Detailed Implementation

[0054] These figures do not show all the possibilities offered by the present invention. For example, regarding the present invention as follows: Figure 8 The version shown includes two transverse reinforcement layers and two hoop layers. Many possible variations exist regarding the placement of the different layers included in the invention, which are not shown. However, preferably, the outermost radial reinforcement layer is a transverse reinforcement layer rather than a hoop layer, particularly as a barrier against sharp obstacles, because the orientation of the reinforcing elements in the hoop layer in the direction of travel makes them less effective at preventing penetration by sharp objects.

[0055] The figures show a radial cross-section of a tire 1 for heavy-duty civil engineering vehicles, the tire 1 including a crown reinforcement 3 located radially inside the tread 2 and radially outside the carcass reinforcement 4. The crown reinforcement 3 includes lateral reinforcement layers 321, 322, and in some figures, 323, each comprising an extendable metal reinforcement coated with an elastic material, parallel to each other and forming an angle between 10° and 45° with respect to the circumferential direction XX' (which is tangent to the tire's circumference). The metal reinforcements of the two innermost radial lateral reinforcement layers intersect from one layer to the other. The crown reinforcement also includes one, two, or three ring layers 331, 332, 333, each of which has an extendable metal reinforcement coated with an elastic material and is parallel to each other, forming an angle of at most 5° with respect to the circumferential direction XX'. The axial width of the tread, Lbdr, the maximum axial width of the ring layer, Lfmax, and the minimum and maximum axial widths, Ltmin and Ltmax, of the lateral reinforcement layers are also shown. In a structure with three lateral reinforcement layers, the outermost radial lateral reinforcement layer will advantageously be more extensible than the other lateral reinforcement layers, thus providing the tire with improved tread impact resistance, especially when all ring layers are radially inward.

[0056] The invention was tested on tires with a size of 24.00R35 and a tread width of 600 mm. In each test, the tire according to the invention was compared with a reference tire of the same size.

[0057] 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.

[0058] The quasi-static test involves pushing the 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.

[0059] 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 a tire according to the invention), with the tires inflated to 7.25 bar, a pressure of 20 tons. The test continues until one of the tires loses pressure. The result is the number of kilometers traveled before tire failure.

[0060] 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.

[0061] Regarding the crown reinforcement, from the outermost radial element to the innermost radial element, the reference tire consists of the following: protective reinforcement, working reinforcement, and ring reinforcement:

[0062] 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 extracted 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.

[0063] The reinforcing element of the working layer is 26.30 non-extensible 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.

[0064] 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.

[0065] 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 would no longer be effective.

[0066] Two versions of the invention (the so-called extended version, referred to as E, and the so-called over-extended version, referred to as HE) were tested. For both versions E and HE, the crown reinforcement is identical except for the reinforcing elements of different crown layers. From the outermost radial element to the innermost radial element, the crown reinforcement consists of the following:

[0067] • A transverse reinforcement layer forming a 33° angle with the circumferential direction and having an axial width of 520 mm.

[0068] • A transverse reinforcement layer that forms a 33° angle with the circumferential direction, intersects the first transverse reinforcement layer, and has an axial width of 472 mm.

[0069] • Two ring layers that form a 0° angle with the circumferential direction and have an axial width of 400 mm.

[0070] For version E of the present invention, all layers of the crown reinforcement are produced from reinforcement elements 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.

[0071] For version HE of the present invention, all layers of the crown reinforcement are produced from reinforcing elements comprising E24.35 cords (24 filaments with a diameter of 35% mm) with a layup spacing of 4.2 mm, having a structural elongation As equal to 1.1% in the rubberized state removed 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, or extensibility and hyperstretchability of the cords, are obtained by adjusting the arrangement of the filaments in the cords and the compound filling between the filaments.

[0072] During the structural elongation stage of the component 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.

[0073] Regarding puncture resistance, the results showed that although reducing the metal mass of the crown reinforcement reduced the tire's weight, the critical height of the indentation tool increased significantly upon impact with the tread surface. Version E showed a 10% improvement in performance, and Version HE showed a 20% improvement.

[0074] In tests related to tread cracking or splitting, the tire according to the invention traveled 20% more kilometers than the reference tire before failure, i.e., a 20% performance improvement.

[0075] In terms of performance related to tire weight, version E showed a 20% reduction in metal weight, and version HE showed a 22% reduction, resulting in a weight reduction of approximately 100 kg for the tested tires.

[0076] Therefore, the proposed invention enables the improvement of the puncture resistance of the tread and the crack resistance of the tread reinforcement, while reducing the mass of the tread reinforcement, thereby reducing the mass of the tire.

Claims

1. Radial tire (1) for civil engineering vehicles, comprising: • a tread (2) having an axial width Lbdr, • a carcass reinforcement (4), and • a single crown reinforcement (3) arranged radially inside the tread (2) and radially outside the carcass reinforcement (4), and consisting of: o at least two layers of transverse reinforcement (321, 322, 323) comprising a greater axial width layer of transverse reinforcement having an axial width Ltmax and a smaller axial width layer of transverse reinforcement (322) having an axial width Ltmin, and each of the at least two layers of transverse reinforcement (321, 322, 323) comprising metal transverse reinforcing elements parallel to each other and forming an orientation angle with the circumferential direction of the tire at least equal to 10° and at most equal to 45°, the orientation angle of one of the at least two layers of transverse reinforcement being opposite in sign to the orientation angle of the other of the at least two layers of transverse reinforcement, and o at least one bead layer (331, 332, 333) having a maximum axial width Lfmax and comprising metal bead reinforcing elements parallel to each other and forming an angle with the circumferential direction at most equal to 5°, wherein each of the transverse reinforcing elements and the bead reinforcing elements, in the rubberized state taken from the polymer matrix of the tire, has a structural elongation, a breaking force (maximum load in N), a breaking strength (in MPa), a total breaking elongation and a tensile Young's modulus, all measured according to ASTM D 2969-04 of 2014, wherein each bead reinforcing element is extensible, the structural elongation (Asf) of each bead reinforcing element being at least equal to 0.5%, the total breaking elongation (Atf) of each bead reinforcing element being at least equal to 3% and the tensile Young's modulus (Ef) of each bead reinforcing element being at most equal to 150 GPa, characterized in that each transverse reinforcing element is extensible, the structural elongation (Ast) of each transverse reinforcing element being at least equal to 0.5%, the total breaking elongation (Att) of each transverse reinforcing element being at least equal to 3% and the tensile Young's modulus (Et) of each transverse reinforcing element being at most equal to 150 GPa.

2. Tyre (1) according to claim 1, wherein, the axial width Ltmin of the smaller axial width layer of transverse reinforcement (322) being at least equal to 70% of the tread axial width Lbdr.

3. Tyre (1) according to either of Claims 1 and 2, wherein, the maximum axial width Lfmax of the at least one bead layer (331, 332, 333) being at least equal to 60% of the tread axial width Lbdr.

4. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers (321, 322, 323) comprise a first radially innermost transverse reinforcement layer (321) and a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and The tensile Young's modulus of the hoop reinforcement elements (Ef) and the tensile Young's modulus of the transverse reinforcement elements of the second radially innermost transverse reinforcement layer (322) (Et2) are at least equal to 85% and at most equal to 110% of the tensile Young's modulus of the reinforcement elements of the first radially innermost transverse reinforcement layer (321) (Et1).

5. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers (321, 322, 323) comprise a first radially innermost transverse reinforcement layer (321) and a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and The respective tensile Young's modulus of the transverse reinforcement elements of the first and second radially innermost transverse reinforcement layers (321, 322) (Ef, Et) and the tensile Young's modulus of the hoop reinforcement elements are at most equal to 85 GPa and at least equal to 50 GPa.

6. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers (321, 322, 323) comprise a first radially innermost transverse reinforcement layer (321) and a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and The respective structural elongation of the transverse reinforcement elements of the first and second radially innermost transverse reinforcement layers (321, 322) (Asf, Ast) and the structural elongation of the hoop reinforcement elements are at least equal to 1%.

7. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers (321, 322, 323) comprise a first radially innermost transverse reinforcement layer (321) and a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and The respective structural elongation of the transverse reinforcement elements of the first and second radially innermost transverse reinforcement layers (321, 322) (Asf, Ast) and the structural elongation of the hoop reinforcement elements are at most equal to 3%.

8. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers (321, 322, 323) comprise a first radially innermost transverse reinforcement layer (321) and a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and The structural elongation of the hoop reinforcement elements (Asf) and the structural elongation of the transverse reinforcement elements of the second radially innermost transverse reinforcement layer (322) (Ast2) are at least equal to 85% and at most equal to 110% of the structural elongation of the transverse reinforcement elements of the first radially innermost transverse reinforcement layer (321) (Ast1).

9. Tyre (1) according to either of Claims 1 and 2, wherein, The at least two transverse reinforcement layers comprise: - a first radially innermost transverse reinforcement layer (321), - a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and - a second radially innermost transverse reinforcement layer (322) located radially outward of the first radially innermost transverse reinforcement layer (321), and - an outer transverse reinforcing layer (323) located radially outside the first and second radially innermost transverse reinforcing layers and the at least one bead filler layer (331, 332, 333) and forming the radially outermost reinforcing layer for the crown reinforcement (3), and the structure elongation (Asp) of the transverse reinforcing elements of the outer transverse reinforcing layer (323) is at least equal to one percent plus the structure elongation (Ast) of the transverse reinforcing elements of the first radially innermost transverse reinforcing layer (321).

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