WO2023247257A1

WO2023247257A1 - Optimized architecture of a tyre of the heavy duty or civil engineering type

Info

Publication number: WO2023247257A1
Application number: PCT/EP2023/065756
Authority: WO
Inventors: Vincent Estenne
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2022-06-20
Filing date: 2023-06-13
Publication date: 2023-12-28
Also published as: FR3136701B1; FR3136701A1

Abstract

The invention relates to a radial tyre for a heavy vehicle of the heavy duty or civil engineering type, comprising two working layers (51, 52) comprising metal reinforcing elements forming, with the circumferential direction (XX'), an angle at least equal to 15° and at most equal to 45°, and at least one bracing layer (41, 42). Each bracing layer comprises metal reinforcing elements (411) forming, with the circumferential direction (XX'), an angle A which is variable according to the axial position. The angles Ae1, Ae2 at the two axial ends (412, 413) of the bracing layer (41, 42) are of the same orientation and have absolute values at most equal to 10°. The angle A has a maximum absolute value Am at an axial distance from the median plane (M) at most equal to 15% of the axial width of the bracing layer, Am being at least equal to the average of the absolute values of the angles Ae1, Ae2 plus 10°.

Description

Title: optimized architecture of heavy-duty or civil engineering type tires

[001] The subject of the present invention is a radial tire, intended to equip a heavy vehicle of the heavy goods vehicle or civil engineering type, and relates more particularly to the crown reinforcement of such a tire.

[002] Radial tires intended to equip a heavy vehicle of the heavy goods vehicle or civil engineering type, are designated within the meaning of the standard of the European Tire and Rim Technical Organization (European Tire and Rim Technical Organization) or ETRTO.

[003] For example, a radial tire for a heavy vehicle of the civil engineering type, within the meaning of the standard of the European Tire and Rim Technical Organization (ETRTO), is intended to be mounted on a rim whose diameter is at least equal to 25 inches. Although not limited to this type of application, the invention is described for a large radial tire intended to be mounted on a dumper, in particular vehicles for transporting materials extracted from quarries or surface mines, by intermediate of a rim whose diameter is at least equal to 35 inches and can reach 57 inches, or even 63 inches. The heavy-duty tires considered are intended to be mounted on a rim whose diameter is at least equal to 19.5 inches

[004] A tire having a geometry of revolution relative to an axis of rotation, the geometry of the tire is generally described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane. The circumferential direction is tangent to the circumference of the tire.

[005] In what follows, the expressions “radially interior”, respectively “radially exterior” mean “closer”, respectively “further from the axis of rotation of the tire. By “axially interior”, respectively “axially exterior”, we mean “closer”, respectively “further from the equatorial plane of the tire”, the equatorial plane of the tire being the plane passing through the middle of the rolling surface and perpendicular to the axis of rotation. By “an element A axially interior to an element B by an axial distance D”, we mean that element A is closer to the equator plane than element B and that the axial distance between the two elements is equal to the distance D. This type of sentence can be generalized with the radial and circumferential direction and the exterior versus interior position of one or the other of the elements.

[006] Generally, a tire comprises a tread, intended to come into contact with a ground via a rolling surface, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[007] A radial tire further comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially internal to the tread, and a carcass reinforcement, radially internal to the crown reinforcement.

[008] The carcass reinforcement of a radial tire for a heavy vehicle of the civil engineering or heavy goods vehicle type usually comprises at least one carcass layer comprising metal reinforcements, coated with a polymeric material of the elastomer or elastomeric type, obtained by mixing and called coating mixture. A carcass layer comprises a main part, connecting the two beads together and generally winding, in each bead, from the inside to the outside of the tire around a circumferential reinforcing element, most often metallic, called a bead, to form a reversal. The metal reinforcements of a carcass layer are substantially parallel to each other and form, with the circumferential direction, an angle of between 85° and 95°.

[009] The crown reinforcement of a radial tire for a heavy goods vehicle or civil engineering type vehicle comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each top layer is made up of generally metallic reinforcements, parallel between them and coated with a polymeric material of the elastomer type or coating mixture.

[010] 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%), called the force-elongation curve. From this force-elongation curve, the mechanical characteristics in tension of the metal reinforcement are deduced, such as the structural elongation As (in %), the total elongation at break At (in %), the force at break Fm (load maximum in N) and the breaking strength Rm (in MPa), these characteristics being measured according to standard ASTM D 2969-04 of 2014.

[011] The total elongation At of the metal reinforcement is, by definition, the sum of its structural, elastic and plastic elongations (At = As + Ae + Ap) and particularly at rupture where each of the elongations is non-zero. The structural elongation As results from the relative positioning of the metal wires constituting the metal reinforcement under a low tensile force. The elastic elongation Ae results from the very elasticity of the metal of the metal wires, constituting the metal reinforcement, taken individually, the behavior of the metal following a Hooke's law. The plastic elongation Ap results from the plasticity, that is to say the irreversible deformation, beyond the elastic limit, of the metal of these metal wires taken individually. These different extensions 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.

[012] We also define, at any point of the force-elongation curve of a metal reinforcement, an extension modulus, expressed in GPa, which represents the slope of the line tangent to the force-elongation curve at this point. In particular, the elastic modulus in extension or Young's modulus is called the extension modulus of the linear elastic part of the force-elongation curve.

[013] Among the metal reinforcements, a distinction is usually made between elastic metal reinforcements, such as those used in protective layers, and non-extensible or inextensible metal reinforcements. [014] An elastic metal reinforcement, in its gummed state from the tire, is characterized by a structural elongation As at least equal to 0.3% and a total elongation at break At at least equal to 2.5%. In addition, an elastic metallic reinforcement has an elastic modulus in extension at most equal to 150 GPa, and usually between 40 GPa and 130 GPa.

[015] An inextensible metal reinforcement is characterized by a total elongation At, under a tensile force equal to 10% of the breaking force Fm, at most equal to 0.3%. Furthermore, a non-extensible metal reinforcement has an elastic modulus in extension usually between 150 GPa and 200 GPa.

[016] Among the top layers, we usually distinguish the protective layers, constituting the protective reinforcement and radially the outermost, comprising elastic reinforcing elements (or reinforcements) and the working layers comprising inextensible reinforcing elements, constituting the working reinforcement and radially included between the protective reinforcement and the carcass reinforcement.

[017] The protective reinforcement, comprising at least one protective layer, essentially protects the working layers from mechanical or physicochemical attacks, likely to propagate through the tread radially towards the inside of the tire.

[018] The protective reinforcement comprises, for a civil engineering type tire, often two protective layers, radially superimposed, formed of elastic metal reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential steering, angles at least equal to 15° and often only one for a heavy-duty type tire.

[019] The working reinforcement, comprising at least two working layers, has the function of surrounding the tire and giving it rigidity and road holding. It includes both mechanical inflation stresses, generated by the inflation pressure of the tire and transmitted by the carcass reinforcement, and mechanical rolling stresses, generated by rolling the tire on a ground and transmitted by the tread . It must also resist oxidation and to impacts and perforations, thanks to its intrinsic design and that of the protective frame.

[020] The working reinforcement usually comprises two working layers, radially superimposed, formed of non-extensible metal reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles at most equal to 60°, and, preferably, at least equal to 15° and at most equal to 45°. To reduce shearing of rubber compounds, or rubber mixtures; at the axial ends of the working layers, it is customary to axially offset the position of said ends relative to each other. The crown reinforcement therefore usually comprises a working layer of greater axial width and a working layer of smaller axial width. The shears of the rubber compounds are maximum at the end of the working layer with the smallest axial width. In fact, these maximum shears due to the displacements of the end of the working layer of the smallest axial width are distributed over the radial thickness of the rubber compounds between the working layer of the smallest axial width and the working layer of the largest. axial width. These shears are amplified by the deformations of the working layer of greater axial width. Indeed, given the angle of the metal reinforcements crossed with the metal reinforcements of the working layer of smaller width, the working layer of greater axial width deforms in another direction, which increases the deformations of the rubber compounds . These shear maxima are generally reduced by adding a decoupling rubber between the end of the working layer of the smallest axial width and the working layer of the largest axial width. The end of the working layer with the greatest axial width is also subjected to strong shearing but generally of lesser amplitude given that for this end, the thickness of the rubber compounds is greater and the deformations are no longer amplified by the presence of the other working layer.

[021] To reduce the mechanical inflation and rolling stresses transmitted to the working reinforcement and the shears of the rubber mixture which covers them, it is known to arrange, radially outside the carcass reinforcement, a hooping reinforcement. The hooping reinforcement, whose function is to at least partially absorb the mechanical inflation stresses, improves the endurance of the crown reinforcement by stiffening the crown reinforcement. The shrink reinforcement can be positioned radially inside the working reinforcement, between the two working layers of the working reinforcement, or radially outside the working reinforcement.

[022] In heavy-duty type applications, the hooping reinforcement often includes a hooping layer constituted by the winding of a reinforcing element.

[023] In civil engineering type applications, the hooping reinforcement may comprise two hooping layers, radially superimposed, formed of metal reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles at most equal to 10°. To produce the shrink layers, on large diameter civil engineering tires, winding a layer of discontinuous reinforcing elements whose ends go from one axial edge of the layer to the other forming with the direction circumferential, an angle of between 7 and 9° is often preferred to the winding of a narrow strip of a few continuous reinforcing elements forming with the circumferential direction an angle of between 0° and 5° for reasons of productivity. In both cases, the shrink layers are of smaller axial width than the working layer of smaller axial width. In fact, the stresses due to rolling at the ends of the working layers are very high in traction and compression and lead to the rupture of the inextensible metal reinforcements arranged around the ends whose angles formed with the circumferential direction are less than 15°. Document WO2019/202239 discloses a usual architecture of civil engineering tires comprising two hooping layers of rigid reinforcing elements, radially internal to two working layers of rigid reinforcing elements radially internal to elastic protective layers, the two shrink layers having an axial width substantially less than the axial width of the working layers. This document presents an optimization of the protective layers in order to improve the resistance to summit attacks suffered by the civil engineering tires. In fact, civil engineering tires, and particularly those used in surface mines, are subject to attacks generally in the vicinity of working faces where the ore is more protruding. As the tread wears, the impact of the crown block's sinking stiffness on the tread cuts is felt. If the optimization proposed in the state of the art has its interest, its significant circumferential rigidity brought mainly by the hooping layers and mainly at the center of the top favors cuts in the tread and its irregular wear at the center and sometimes the total perforation of the summit block. It is well known to those skilled in the art that increasing the average angle of the hooping layers beyond 15° makes it possible to reduce the rigidity of the top but this reduces the endurance by promoting cracking at the ends of the working layers, but also at the end of the shrink layers themselves.

[024] These problems of crown aggression are found but at lower levels for heavy-duty tires, crown aggression generating more tearing of the tread than wear.

[025] The inventors set themselves the objective, for a civil engineering or heavy goods vehicle tire, of maintaining good endurance, particularly at the ends of the crown layers, of improving resistance to punctures by reducing the circumferential rigidity in the center while maintaining an effective shrinking action and for civil engineering tires to improve wear due to aggression.

[026] This objective was achieved, according to the invention, by a radial tire for a heavy vehicle of the heavy goods vehicle or civil engineering type comprising

• a crown reinforcement, radially Radial pneumatic tire for heavy vehicle of heavy goods vehicle or civil engineering type comprising

• a crown reinforcement, radially internal to a tread and radially external to a carcass reinforcement,

• A median plane perpendicular to the axis of rotation of the tire and passing through the middle of the tread,

• the top frame comprising, a working frame, • the working reinforcement comprising at least two working layers each comprising metallic reinforcing elements coated in an elastomeric material, parallel to each other, forming, with the circumferential direction (XX'), an angle at least equal to 15° and at most equal to 45°, said metal reinforcing elements being crossed from one working layer to the next,

• the crown reinforcement comprising a hooping reinforcement comprising at least one hooping layer, each hooping layer comprising metallic reinforcing elements coated in an elastomeric material, parallel to each other, and comprising two axial ends on either side of the median plane,

• the reinforcing elements of each hooping layer forming with the circumferential direction, at its two axial ends, angles, of the same orientation, and of absolute values at most equal to 10°,

• the angle formed by the metal reinforcing elements of a hooping layer with the circumferential direction (XX'), being variable from one axial end of said hooping layer to the other axial end, and has an absolute value maximum at an axial distance from the median plane at most equal to 15% of the axial width of said hooping layer,

• the maximum absolute value of said angle being at least equal to the average of the absolute values of the angles formed by the metallic reinforcing elements of said hooping layer with the circumferential direction (XX') at the two axial ends of said hooping layer, more 10°.

[027] The solution implemented makes it possible to better balance the circumferential rigidities axially by maintaining the rigidity near the axial ends of the working layers and reducing it in the center. The inventors started from the observation that the circumferential rigidities are too high at the center due to the shrink layers. On certain tires, the shrink layers are responsible for 5 sevenths of the circumferential rigidity at the center. Counter-intuitively given the rigidity of the reinforcing elements of the hooping layers, the invention consists of modifying the rigidity of at least one hooping layer in the center and maintaining their identical operation on their axial ends , in modifying the central angle formed by the reinforcing elements with the circumferential direction of at least one hooping layer.

[028] The reference civil engineering tires considered usually have two hooping layers radially internal to two working layers, themselves radially internal to two protective layers. The hooping layers of the reference civil engineering tires considered are made up of metallic reinforcing elements parallel to each other, coated with a rubber composition, going continuously from one axial end of the hooping layer to the other , and making a substantially constant angle with the circumferential direction, at most equal to 10° to allow effective hooping. The invention consists of modifying the angle of the reinforcing elements of at least one hooping layer, around the center of the tire, such that:

• the metallic reinforcing elements of at least one hooping layer form, with the circumferential direction (XX'), an angle varying from one axial end of said hooping layer to the other axial end,

• the angle formed by the metallic reinforcing elements of said hooping layer with the circumferential direction (XX'), having a maximum absolute value (Am) at an axial distance from the median plane at most equal to 15% of the axial width of said shrink layer, the maximum coinciding approximately with the center of the shrink layer in order to reduce the rigidity precisely where desired,

• the maximum absolute value of said angle being at least equal to the average of the absolute values of the angles formed by the metallic reinforcing elements of said hooping layer with the circumferential direction (XX') at the two axial ends of said hooping layer plus 10 °.

These conditions allow, on a variable angle hooping layer, to reduce the circumferential rigidity of the crown reinforcement in the center to around 20%. The same modification on two shrink layers allows a reduction in rigidity of 40%.

[029] Thus a preferred solution, for a tire whose crown reinforcement comprises at least two hooping layers, is that the angles formed by the metal reinforcing elements of said at least two hooping layers with the circumferential direction (XX' ), are variable from one axial end to the other of each hooping layer, have a maximum absolute value at an axial distance from the median plane at most equal to 15% of the axial width of said hooping layer considered, and that the maximum absolute values of said angles are at least equal to the average of the absolute values of the angles formed by the metallic reinforcing elements of the hooping layer considered with the circumferential direction (XX') at the two axial ends of said hooping layer, plus 10°. For a tire having two hooping layers, the angles of which are variable, if each maximum absolute value of said angles is at least equal to the average of the absolute values of the angles formed by the metal reinforcing elements of the hooping layer considered with the direction circumferential (XX') at the two axial ends of the hooping layer considered plus 16°, the drop in the total rigidity of the crown reinforcement at the center is at least equal to 50%, and for plus 25° respectively the drop in the total rigidity of the crown reinforcement in the center is at least equal to 65%.

[030] It is advantageous for the crown reinforcement to comprise two hooping layers for reasons of manufacturing cycle times and balance of the crown architecture, the angles formed by the reinforcing elements of the two hooping layers being of opposite signs.

[031] A preferred solution is that the absolute values of the angles (Ael, Ae2) formed by the metallic reinforcing elements of each hooping layer with the circumferential direction (XX'), at the two axial ends, are at least equal to 5 °. Below the hooping layers consist of a winding of a reinforcing element or a strip of reinforcing elements for which it is complex to vary the angle of the reinforcing elements of an axial end of the hoop layer considered at its other axial end. In this case there is one end of the reinforcing element at each axial end of the hooping layer considered. For angles at least equal to 5°, the hooping layers constituted by very numerous reinforcing elements distant from the adjacent reinforcing elements by a substantially constant circumferential pitch within manufacturing tolerances, each reinforcing element having an axial end at each axial end of the hooping layer. In this case to vary the angle of the reinforcing elements from an axial end of the hooping layer to another, it is sufficient for example to prepare the hooping layers on a rigid ring and to perform rotations around the axis of rotation of the drum between the central zone of the hooping layer and the axial zones , while moving the axial zones away from each other.

[032] An advantageous solution for protecting the hooping layers from attacks is for each hooping layer to be radially interior to the working layers.

[033] Preferably the metal reinforcing elements of the working layers have an extension modulus at least equal to 150 GPa, which corresponds to reinforcing elements of the inextensible working layers which have excellent endurance performance.

[034] A preferred solution is that the crown reinforcement comprises two protective layers, radially external to the working layers, each comprising metallic reinforcing elements coated in an elastomeric material, parallel to each other, forming, with the circumferential direction ( XX'), an angle at least equal to 15° and at most equal to 45°, said metal reinforcing elements being crossed from one protective layer to the next, and having an extension modulus at most equal to 150 GPa. The presence of protective layers whose reinforcing elements are elastic, very significantly improves the performance of civil engineering or heavy goods vehicle tires against perforation by stones.

[035] Advantageously to protect the ends of the hammering working layers against the stones of the rolling tracks, the most radially interior protective layer is the layer of the top reinforcement of greatest axial width.

[036] The characteristics of the invention are illustrated by Figures 1 and 2 schematically and not shown to scale, with reference to a tire of size 59/80 R63: Figure 1 represents a meridian section of a vertex of civil engineering pneumatics and Figure 2 a portion of a variable angle hooping layer.

[037] The figure shows a cutaway perspective view of the top of a tire presenting:

-a tread 10,

-sides 20, -a carcass reinforcement 30, comprising a carcass layer whose reinforcements form an angle close to 90° with the circumferential direction XX', -a hooping reinforcement 40, comprising two hooping layers 41 and 42, -a working reinforcement 50, comprising two working layers 51 and 52, and radially external to the hooping reinforcement 40, -a protective reinforcement 60, comprising two protective layers 61 and 62.

[038] In the state of the art, the angles formed by the reinforcing elements of the different top layers with the circumferential direction are substantially constant except for manufacturing variations. Indeed, during molding of the tire, the reinforcing elements deform and their angles can vary slightly from one axial position to another. In the tire according to the invention, in at least one hooping layer, the angle formed by the reinforcing elements with the circumferential direction varies from one axial end of the hooping layer considered to the other by at least 10 °. For reasons of readability, this variation is not shown in Figure 1.

[039] Figure 2 represents a portion of the hooping layer 41 with variable angle flat, of an axial width Lcf comprising reinforcing elements 411 parallel to each other, namely equidistant by a circumferential distance constant to manufacturing variations close. The angles of the reinforcing elements 411 of the hooping layer 41 vary from a value Ael at one axial end 412 of the hooping layer 41 to a value Ae2 at the other axial end 413, substantially identical here, passing through a maximum value Am in a central zone of the hooping layer. This zone has an axial width at most equal to 30% of Lcf, the maximum being at the furthest from the median plane (M) by an axial distance at most equal to 15% of Lcf. The angles vary here from 8° at the axial end of the hooping layer to approximately 37° in the center. Such a variation can be obtained from a hooping layer at a constant angle of 8° to which one end has been subjected to a relative displacement in relation to the other, both circumferentially and axially.

[040] The angles Ael, Ae2, and the angles of different vertex layers are measured by methods well known to those skilled in the art either by non-destructive testing means or by cutting the tire and accessing the different vertex layers. The same applies to the measurement of the axial widths of the different vertex layers usually measured on a meridian section. Unless the axial position of the measurement is specified, as for variable angle hooping layers, angle measurements are preferably made at the center of the top layer considered - most often at the median plane - or at the center of the axial part considered to give a reference value, the measured angle may vary slightly with the axial position of the measurement.

[041] The invention is compared to a market control tire ("Michelin 59/80R63 protection. The reinforcing elements of the hooping layers form angles of 8 and -8°. They are inextensible in 77.35, or 77 steel wires of 35 hundredths of a millimeter in diameter, for an extension module, measured on a cable taken from the tire, equal to 178 GPa, arranged in a pitch of 6.4 mm. The reinforcing elements of the working layers form angles of -33 and 24°. They are inextensible. The reinforcement elements of the protective layers are extensible and form angles of -33 and 33°.

[042] The control tires and according to the invention are identical except for the shrink layers. They have the same tread pattern and the same reinforcements for the carcass layer, the protective layers and the working layers and the same rubber compounds for the different parts of the tires.

[043] The invention was simulated on calculation tools. The simulations make it possible to evaluate the mechanical and thermal stresses on tires using the finite element technique in large displacement and large deformation, taking into account the mechanical and hysteretic characteristics of the materials.

[044] The objective of the invention is to reduce the circumferential rigidity at the center in order to improve wear and resistance to attacks and perforations. The drop in rigidity is estimated from the deformation of the crown block under the effect of an increase in pressure. The two hooping layers have variable angles, the angles at the axial ends of the hooping layers having an absolute value equal to 8° like the reference tires. Rigidity at the center of vertex is divided by a factor of 3.3, when the absolute value of the maximum angle at the center of the hooping layers is equal to 33, divided by 2.3 when the absolute value of the maximum angle at the center of the hooping layers is equal to 24 and divided by 1.4 when the absolute value of the maximum angle at the center of the hooping layers is equal to 18. The stiffness at the ends of the crown layers is maintained at the same value as for the reference tires. The average rigidity of the crown reinforcement is sufficient for the recovery of rolling forces. This reduction in rigidity at the center should allow a gain in perforation of the invention of between 20% and 40% depending on the maximum angles at the center of the hooping layers and the reduction in the chosen rigidity and should help to resolve the problems of irregular wear due to excessive rigidity in the center of the civil engineering indicator tire.

[045] Concerning the endurance of the crown, the safety coefficients (strength to rupture of the cable under maximum stresses) of the reinforcing elements of all the crown layers are at least equal to the minimum safety coefficient of the control tire. Likewise, the stresses on the rubber compositions at the ends of the working layers are substantially identical thanks to the axial parts of the hooping layers. From this point of view, the inventors expect an endurance performance at least equal to that of the control. The mass of the control tires and according to the invention are equivalent.

[046] All of these performances demonstrate the interest of the invention.

Claims

Claims Radial tire for heavy vehicle of heavy goods vehicle or civil engineering type including

• a crown reinforcement, radially internal to a tread (10) and radially external to a carcass reinforcement (30),

• A median plane (M) perpendicular to the axis of rotation of the tire and passing through the middle of the tread (10),

• the top frame comprising a working frame (50),

• the working reinforcement (50) comprising at least two working layers (51, 52) each comprising metallic reinforcing elements coated in an elastomeric material, parallel to each other, forming, with the circumferential direction (XX'), a angle at least equal to 15° and at most equal to 45°, said metal reinforcing elements being crossed from one working layer to the next,

• the crown reinforcement comprising a hooping reinforcement (40) comprising at least one hooping layer (41, 42), each hooping layer (41,42) comprising metallic reinforcing elements (411) coated in an elastomeric material , parallel to each other, and comprising two axial ends (412, 413) on either side of the median plane (M),

• the reinforcing elements of each hooping layer forming with the circumferential direction, at its two axial ends (412, 413) angles (Ael, Ae2), of the same orientation, and of absolute values at most equal to 10°,

• characterized in that the angle formed by the metal reinforcing elements of a hooping layer (41, 42) with the circumferential direction (XX'), is variable from an axial end of said hooping layer to the other axial end, and has an absolute value maximum (Am) at an axial distance from the median plane (M) at most equal to 15% of the axial width of said hooping layer,

• and in that the maximum absolute value (Am) of said angle is at least equal to the average of the absolute values of the angles (Ael, Ae2) formed by the metal reinforcing elements (411) of said hooping layer (41, 42 ) with the circumferential direction (XX') at the two axial ends (412, 413) of said hooping layer (41, 42), plus 10°. Tire according to claim 1 in which the crown reinforcement comprises at least two hooping layers (41, 42), the angles formed by the metal reinforcing elements (411) of said at least two hooping layers (41, 42) with the circumferential direction (XX'), being variable from one axial end to the other of each hooping layer (41, 42), having a maximum absolute value (Am) at an axial distance from the median plane (M) at most equal to 15% of the axial width of said hooping layer considered, the maximum absolute values (Am) of said angles being at least equal to the average of the absolute values of the angles (Ael, Ae2) formed by the metallic reinforcing elements (411 ) of the considered hooping layer (41, 42) with the circumferential direction (XX') at the two axial ends (412, 413) of said hooping layer (41, 42), plus 10°. Tire according to any one of claims 1 or 2 in which the crown reinforcement comprises two hooping layers (41, 42). Tire according to any one of the preceding claims in which the absolute values of the angles (Ael, Ae2) formed by the metal reinforcing elements (411) of each hooping layer (41, 42) with the circumferential direction (XX'), at the two axial ends (412, 413), are at least equal to 5°. Tire according to any one of the preceding claims in which each hooping layer (41, 42) is radially interior to the working layers (51, 52). Tire according to any one of the preceding claims in which the metallic reinforcing elements of the working layers (51, 52) have an extension modulus at least equal to 150 GPa. Tire according to any one of the preceding claims in which the crown reinforcement comprises two protective layers (61, 62), radially external to the working layers, each comprising metallic reinforcing elements coated in an elastomeric material, parallel to each other , forming, with the circumferential direction (XX'), an angle at least equal to 15° and at most equal to 45°, said metal reinforcing elements being crossed from one protective layer to the next, and having a modulus in extension at most equal to 150 GPa. Tire according to claim 7 above in which the most radially inner protective layer (61) is the layer of the crown reinforcement of greatest axial width.