Optimized structure of tyres of heavy or civil engineering type

Abstract

The invention relates to a radial tyre for a heavy vehicle of the heavy or civil engineering type, comprising two working layers (51, 52) comprising metal reinforcing elements forming an angle with the circumferential direction (XX ') of at least 15 DEG and at most 45 DEG, and at least one hoop layer (41, 42). The angle A formed by the metal reinforcing elements (411) included in each hoop layer with the circumferential direction (XX ') varies depending on the axial position. The angles Ae1, Ae2 of the two axial ends (412, 413) of the hoop layer (41, 42) have the same direction and have absolute values at most equal to 10 degrees. The angle A has a maximum absolute value Am at a position at an axial distance from the median plane (M) at most equal to 15% of the axial width of the hoop layer, Am being at least equal to the average value of the absolute values of the angles Ae1, Ae2 plus 10 degrees.

Description

Technical Field

[0001] The present invention relates to a radial tyre intended to be fitted to a heavy vehicle or civil engineering vehicle and more particularly to a crown reinforcement of such a tyre. Background Art

[0002] Radial tyres intended to be fitted to heavy vehicles or civil engineering vehicles are specified within the meaning of the European Tyre and Rim Technical Organisation (or ERTRO) standards.

[0003] For example, within the meaning of the European Tire and Rim Technical Organization (or ETRTO) standards, radial tires for heavy civil engineering vehicles are intended to be mounted on rims with a diameter at least equal to 25 inches. Although not limited to this type of application, the present invention is described for radial tires of large dimensions, intended to be mounted on dump trucks, in particular on vehicles used to transport materials extracted from quarries or open-pit mines, with rims with a diameter at least equal to 35 inches, possibly equal to 57 inches, or even equal to 63 inches.

[0004] Since the tire has a geometry that exhibits rotational symmetry about an axis of rotation, the geometry of the tire is usually described in a meridian plane containing the axis of rotation of the tire. For a given meridian plane, the radial direction, the axial direction and the circumferential direction respectively denote the direction perpendicular to the axis of rotation of the tire, the direction parallel to the axis of rotation of the tire and the direction perpendicular to the meridian plane. The circumferential direction is tangential to the circumference of the tire.

[0005] In the following, the expressions "radially inside" and "radially outside" mean "closer to the axis of rotation of the tire" and "further away from the axis of rotation of the tire", respectively. "Axially inside" and "axially outside" mean "closer to the equatorial plane of the tire" and "further away from the equatorial plane of the tire", respectively, the equatorial plane of the tire being the plane passing through the middle of the tread surface and perpendicular to the axis of rotation. "Element A is axially located on the inside of element B at an axial distance D" means that element A is closer to the equatorial plane than element B and the axial distance between the two elements is equal to the distance D. This type of expression can be generalized to radial and circumferential directions as well as to outer and inner positions of one element or the other.

[0006] Typically, a tire comprises a tread intended to come into contact with the ground through the tread surface, the two axial ends of which are connected by two sidewalls to two beads providing a mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] The radial tire further comprises a reinforcing reinforcement constituted by a crown reinforcement radially on the inside of the tread and a carcass reinforcement radially on the inside of the crown reinforcement.

[0008] The carcass reinforcement of a radial tire for civil engineering vehicles or heavy vehicles generally comprises at least one carcass layer comprising a metal reinforcement coated with a polymer material of an elastomeric or elastomeric type obtained by blending and referred to as a coating compound. The carcass layer comprises a main portion that connects two beads together and is generally wound around a circumferential reinforcing element, generally metal, called a bead wire, from the inside to the outside of the tire in each bead, thereby forming a bead. The metal reinforcements of the carcass layer are substantially parallel to each other and form an angle between 85° and 95° with the circumferential direction.

[0009] The crown reinforcement of a radial tire for heavy vehicles or civil engineering vehicles comprises a superposition of circumferentially extending crown layers radially outside the carcass reinforcement. Each crown layer is generally composed of metal reinforcements parallel to each other and coated with a polymer material of the elastomeric type or of the coating compound type.

[0010] The mechanical characteristics of the metal reinforcement are represented by a curve representing the tensile force (in N) applied to the metal reinforcement as a function of its relative elongation (in %), which is called the force-elongation curve. The mechanical tensile characteristics of the metal reinforcement, such as the structural elongation As (in %), the total elongation at break At (in %), the breaking force Fm (maximum load in N) and the breaking strength Rm (in MPa) are obtained from this force-elongation curve, which are measured according to the 2014 standard ASTM D 2969-04.

[0011] By definition, the total elongation At of a metal reinforcement is the sum of its structural elongation, elastic elongation and plastic elongation (At=As+Ae+Ap), in particular at fracture, where each elongation is non-zero. The structural elongation As results from the relative positioning of the metal wires constituting the metal reinforcement under low tensile forces. The elastic elongation Ae results from the actual elasticity of the metal of the individually considered metal wires constituting the metal reinforcement, the behavior of which follows Hooke's law. The plastic elongation Ap results from the plasticity (i.e., irreversible deformation beyond the elastic limit) of the metal of these individually considered metal wires. These different elongations and their respective meanings are well known to those skilled in the art and are described, for example, in documents US5843583, WO2005 / 014925 and WO2007 / 090603.

[0012] At each point on the force-elongation curve of the metal reinforcement, a tensile modulus expressed in GPa is also 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 elastic modulus or Young's modulus.

[0013] Among 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.

[0014] The elastic metal reinforcement extracted from the tire in the rubberized state 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, the elastic metal reinforcement has a tensile elastic modulus of at most 150 GPa, typically between 40 GPa and 130 GPa.

[0015] The inextensible metal reinforcement is characterized in that, under a tensile force equal to 10% of the breaking force Fm, the total elongation At is at most equal to 0.3%. In addition, the tensile elastic modulus of the inextensible metal reinforcement is generally between 150 GPa and 200 GPa.

[0016] In the crown layers, a distinction is generally made between a protective layer comprising elastic reinforcing elements (or reinforcements), which constitutes the protection reinforcement and is radially outermost, and a working layer comprising inextensible reinforcing elements, which constitutes the working reinforcement and is radially interposed between the protection reinforcement and the carcass reinforcement.

[0017] The protection reinforcement, which comprises at least one protective layer, substantially protects the working layers from mechanical or physicochemical attacks that could propagate through the tread radially towards the interior of the tire.

[0018] For civil engineering tires, the protective reinforcement generally comprises two radially superimposed protective layers formed by elastic metal reinforcements parallel to each other in each layer and crossing from one layer to another, making an angle at least equal to 15° with the circumferential direction, and for heavy-duty tires, the protective reinforcement generally comprises a single protective layer.

[0019] The function of the working reinforcement, which comprises at least two working layers, is to surround the tire and ensure its rigidity and road holding. The working reinforcement absorbs the mechanical stresses of inflation, which are generated by the tire inflation pressure and transmitted through the carcass reinforcement, and the mechanical stresses caused by running, which are generated by the running of the tire on the ground and transmitted through the tread. The working reinforcement also needs to withstand oxidation, impacts and perforations by its inherent design and that of the protective reinforcement.

[0020] The working reinforcement usually comprises two radially superimposed working layers, the working layers being formed by inextensible metal reinforcements, the inextensible metal reinforcements being parallel to each other in each layer and crossing from one layer to another, forming an angle with the circumferential direction of at most 60°, preferably at least 15° and at most 45°. In order to reduce the shear of the rubber compound (or rubber mixture) at the axial ends of the working layers, the positions of the ends are usually offset axially relative to each other. Therefore, the crown reinforcement usually comprises a working layer with a larger axial width and a working layer with a smaller axial width. At the end of the working layer with a smaller axial width, the shear of the rubber compound is maximum. This maximum shear, caused by the displacement of the end of the working layer with a smaller axial width, is distributed over the radial thickness of the rubber compound between the working layer with a smaller axial width and the working layer with a larger axial width. This shear is amplified by the deformation of the working layer with a larger axial width. Taking into account the angle at which the metal reinforcement crosses the metal reinforcement of the working layer with a smaller width, the working layer with a larger axial width is deformed in another direction, which increases the deformation of the rubber compound. These maximum shears are usually reduced by inserting a decoupling rubber between the working layer with the smaller axial width and the end of the working layer with the larger axial width. The end of the working layer with the larger axial width is also subjected to a stronger shear, but usually with a smaller amplitude, considering that for this purpose the thickness of the rubber compound is greater and the deformation is no longer amplified by the presence of the other working layers.

[0021] In order to reduce the inflation mechanical stresses and running stresses transmitted to the working reinforcement and the shear of the rubber mixture covering the working reinforcement, it is known practice to arrange a hoop reinforcement radially outside the carcass reinforcement. The function of the hoop reinforcement is to absorb the inflation mechanical stresses at least partially, which improves the durability of the crown reinforcement by strengthening the crown reinforcement. The hoop reinforcement can be located radially inside the working reinforcement, between two working layers of the working reinforcement, or radially outside the working reinforcement.

[0022] In heavy-duty applications, hoop reinforcements generally comprise a hoop layer formed by windings of reinforcing elements.

[0023] In civil engineering applications, the hoop reinforcement may include two radially superimposed hoop layers formed by metal reinforcements that are parallel to each other in each layer and cross from one layer to another, forming an angle of at most 10° with the circumferential direction. In order to form the hoop layer on a large diameter civil engineering tire, for reasons of productivity, it is more preferred to wind a layer of discontinuous reinforcement elements, whose ends extend from one axial edge of the layer to another axial edge, forming an angle of between 7° and 9° with the circumferential direction, rather than winding a narrow strip with several continuous reinforcement elements and forming an angle between 0° and 5° with the circumferential direction. In both cases, the axial width of the hoop layer is less than the working layer with a smaller axial width. The stress generated at the end of the working layer due to driving is very high, whether tensile stress or compressive stress, and causes the inextensible metal reinforcement arranged around the end to form an angle less than 15° with the circumferential direction to break. WO2019 / 202239 discloses a common structure of a civil engineering tire, the civil engineering tire comprising two hoop layers with rigid reinforcement elements, the hoop layers are radially located on the inner side of two working layers with rigid reinforcement elements, the working layers are radially located on the inner side of the elastic protective layer, and the axial width of the two hoop layers is substantially smaller than the axial width of the working layer. The document discloses optimizing the protective layer to improve the resistance of the crown of the civil engineering tire to attack. Civil engineering tires, especially tires for open-pit mines, are usually attacked near the working surface where the ore protrudes more. As the tread wears, the effect of the indentation stiffness of the crown block on the cut in the tread will become apparent. Although the optimization proposed in the prior art has its advantages, its huge circumferential stiffness (mainly provided by the hoop layer and mostly in the center of the crown) accelerates the uneven wear of the cut in the tread and its center, and sometimes even causes the crown block to be completely punctured. It is known to those skilled in the art that increasing the average angle of the hoop layers above 15° reduces the rigidity of the crown, but this can thus reduce durability by accelerating the rupture of the ends of the working layers and of the hoop layers themselves.

[0024] With heavier tires, these crown attack issues also occur, but to a lesser degree, with crown attack causing more tread chipping than wear. Summary of the invention

[0025] The inventors aimed to maintain satisfactory durability, especially at the ends of the crown layer, and to improve puncture resistance by reducing the circumferential stiffness in the center, while maintaining an effective hoop action for civil engineering tires or heavy-duty tires, and to improve the wear resistance of civil engineering tires against attacks.

[0026] According to the invention, this object has been achieved by a radial tire for heavy vehicles or civil engineering vehicles, comprising:

[0027] A crown reinforcement for a radial tire for a heavy vehicle or civil engineering vehicle, the radial tire comprising

[0028] a crown reinforcement situated radially on the inside of the tread and radially on the outside of the carcass reinforcement,

[0029] a median plane, which is perpendicular to the axis of rotation of the tyre and passes through the middle of the tread,

[0030] The crown reinforcement comprises a working reinforcement,

[0031] the working reinforcement comprises at least two working layers, each of which comprises metal reinforcement elements coated with an elastomeric material, the metal reinforcement elements being parallel to one another and forming an angle with the circumferential direction (XX') at least equal to 15° and at most equal to 45°, the metal reinforcement elements crossing from one working layer to another,

[0032] the crown reinforcement comprises a hoop reinforcement comprising at least one hoop layer, each hoop layer comprising metal reinforcing elements coated with an elastomeric material, the metal reinforcing elements being parallel to each other and comprising two axial ends situated on either side of a median plane,

[0033] the reinforcing elements of each hoop layer form, at their two axial ends, angles with the circumferential direction in the same direction and with an absolute value of at most 10°,

[0034] the angle formed by the metal reinforcement elements of the hoop layer with the circumferential direction (XX') varies from one axial end to the other of said hoop layer and has a maximum absolute value at an axial distance from the mid-plane that is at most equal to 15% of the axial width of said hoop layer,

[0035] The maximum absolute value of the angle is at least equal to the average of the absolute values ​​of the angles that the metal reinforcing elements of the hoop layer make with the circumferential direction (XX′) at the two axial ends of the hoop layer plus 10°.

[0036] The solution implemented makes it possible to improve the axial balance of the circumferential stiffness values ​​by maintaining the stiffness near the axial ends of the working layers and reducing the stiffness in the center. The inventors first observed that the circumferential stiffness values ​​in the center were too high due to the hoop layers. On some tires, the hoop layers are the source of five sevenths of the circumferential stiffness in the center. Counterintuitively, considering the stiffness of the reinforcing elements of the hoop layers, the invention consists in varying the stiffness at the center of at least one hoop layer and keeping its function the same at the axial ends by varying the angle that the reinforcing elements at the center of at least one hoop layer make with the circumferential direction.

[0037] The reference civil engineering tire under consideration generally has two hoop layers radially inside two working layers which in turn are radially inside two protective layers. The hoop layers of the reference civil engineering tire under consideration consist of mutually parallel metallic reinforcing elements and coated with a rubber composition, extending continuously from one axial end of the hoop layer to the other axial end and forming with the circumferential direction a substantially constant angle of at most 10°, so as to enable effective hooping. The invention consists in varying the angle of the reinforcing elements of at least one hoop layer near the center of the tire, so that:

[0038] the angle formed by the metal reinforcing elements of at least one hoop layer with the circumferential direction (XX') varies from one axial end to the other axial end of said hoop layer,

[0039] the angle formed by the metal reinforcement elements of the hoop layer with the circumferential direction (XX') has a maximum absolute value (Am) at an axial distance from the midplane that is at most equal to 15% of the axial width of the hoop layer, the maximum value being approximately the same as the value at the center of the hoop layer, so as to reduce the stiffness precisely where it is needed,

[0040] The maximum absolute value of the angle is at least equal to the average of the absolute values ​​of the angles that the metal reinforcing elements of the hoop layer make with the circumferential direction (XX′) at the two axial ends of the hoop layer plus 10°.

[0041] On the variable angle hoop layer, these conditions can reduce the circumferential stiffness at the center of the crown reinforcement by about 20%. The same changes to the two hoop layers result in a 40% reduction in stiffness.

[0042] Therefore, for a tire whose crown reinforcement comprises at least two hoop layers, a preferred solution is that the angle formed by the metal reinforcing elements of said at least two hoop layers with the circumferential direction (XX') varies from one axial end to the other of each hoop layer, has a maximum absolute value at a position at an axial distance from the mid-plane that is at most equal to 15% of the axial width of the hoop layer in question, and the maximum absolute value of said angle is at least equal to the average value of the absolute values ​​of the angles formed by the metal reinforcing elements of the hoop layer in question with the circumferential direction (XX') at the two axial ends of said hoop layer plus 10°. For a tire with two variable angle hoop layers, the total stiffness of the center of the crown reinforcement is reduced by at least 50% if each of the maximum absolute values ​​of said angles is at least equal to the average value of the absolute values ​​of the angles formed by the metal reinforcing elements of the hoop layer in question with the circumferential direction (XX') at the two axial ends of said hoop layer plus 16°, and the total stiffness of the center of the crown reinforcement is reduced by at least 65% if 25° is added.

[0043] Advantageously, for reasons of manufacturing cycle time and crown structural balance, the crown reinforcement comprises two hoop layers, the angles formed by the reinforcing elements of the two hoop layers having opposite signs.

[0044] A preferred solution is that the absolute value of the angle (Ae1, Ae2) formed by the metal reinforcing element of each hoop layer at two axial ends with the circumferential direction (XX') is at least equal to 5 °. Below 5 °, the hoop layer is composed of a winding of reinforcing elements or a strip of reinforcing elements, making it complicated to change the angle of the reinforcing element from one axial end of the hoop layer in question to its other axial end. In this case, an end of the reinforcing element is present at each axial end of the hoop layer in question. For an angle at least equal to 5 °, the hoop layer is composed of a large number of reinforcing elements, which are spaced at a substantially constant circumferential spacing from adjacent reinforcing elements within the manufacturing tolerance range, and each reinforcing element has an axial end at each axial end of the hoop layer. In this case, in order to change the angle of the reinforcing element from one axial end of the hoop layer to another axial end, for example, the hoop layer must be simply formed on a rigid ring and must be rotated around the axis of rotation of the drum between the central area and the axial area of ​​the hoop layer, while the axial areas are separated from each other.

[0045] An advantageous solution for protecting the hoop layers from attack is that each hoop layer is located radially within the working layer.

[0046] Preferably, the metal reinforcement elements of the working layers have a tensile modulus at least equal to 150 GPa, which corresponds to an inextensible reinforcement element of the working layer having excellent endurance properties.

[0047] A preferred solution is that the crown reinforcement comprises two protective layers radially on the outside of the working layers, each protective layer comprising metal reinforcing elements coated with an elastomeric material, parallel to one another, forming an angle with the circumferential direction (XX') of at least 15° and at most 45°, crossing from one protective layer to the other and having a tensile modulus of at most 150 GPa. The presence of a protective layer with elastic reinforcing elements greatly improves the performance of civil engineering or heavy-duty tires with respect to stone punctures.

[0048] Advantageously, in order to protect the ends of the working layers from being crushed by stones on the track on which they run, the radially innermost protective layer is the layer of the crown reinforcement having the greatest axial width. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In a schematic not drawn to scale Figure 1 and Figure 2The features of the invention are illustrated with reference to a tire of size 59 / 80R63. Figure 1 shows the meridian section of the crown of a civil engineering tire, Figure 2 A portion of a variable angle hoop layer is shown.

[0050] Figure 1 A cutaway perspective view of the crown of a tire is shown, the tire having:

[0051] -Tread 10,

[0052] - Sidewall 20,

[0053] a carcass reinforcement 30 comprising a carcass layer, the reinforcements of which make an angle close to 90° with the circumferential direction XX′,

[0054] a hoop reinforcement 40 comprising two hoop layers 41 and 42,

[0055] a working reinforcement 50 comprising two working layers 51 and 52 and situated radially on the outside of the hoop reinforcement 40 ,

[0056] A protective reinforcement 60 comprising two protective layers 61 and 62 . DETAILED DESCRIPTION

[0057] In the prior art, the angles formed by the reinforcing elements of the different crown layers with the circumferential direction are substantially constant within manufacturing tolerances. During the shaping of the tire, the reinforcing elements deform and their angles may vary slightly from one axial position to another. In at least one hoop layer of the tire according to the invention, the angle formed by the reinforcing elements with the circumferential direction varies by at least 10° from one axial end to the other of the hoop layer in question. For the sake of clarity, Figure 1 This change is not shown in FIG.

[0058] Figure 2A portion of a flatly laid variable angle hoop layer 41 is shown, which has an axial width Lcf and includes reinforcing elements 411 parallel to each other, i.e., equally spaced at a constant circumferential distance within a manufacturing tolerance. The angle of the reinforcing elements 411 of the hoop layer 41 changes from a value Ae1 at one axial end 412 of the hoop layer 41 through a maximum value Am at the central region of the hoop layer to a value Ae2 at another axial end 413, where the two values ​​Ae1 and Ae2 are substantially the same. The axial width of the central region of the hoop layer is at most equal to 30% of Lcf, and the maximum axial distance from the midplane (M) at the maximum value is at most equal to 15% of Lcf. Here, the angle changes from 8° at the axial end of the hoop layer to about 37° at the center. This change can be obtained using a hoop layer with a constant angle of 8°, wherein one end is applied with respect to the other end. Relative displacement in the circumferential direction and the axial direction.

[0059] The angles Ae1, Ae2 and the angles of the different crown layers are measured using methods known to those skilled in the art, either using non-destructive testing means or by cutting the tire and obtaining the different crown layers. The same applies to the measurement of the axial widths of the different crown layers, usually measured in a meridian section. Unless the axial position of the measurement is specified, for variable angle hoop layers, in order to obtain a reference value, it is best to measure the angle at the center of the crown layer in question (usually in the mid-plane) or at the center of the axial section in question, because the measured angle will vary slightly depending on the axial position of the measurement.

[0060] The present invention is compared with a commercially available control tire (Michelin 59 / 80R63 XDR3 MB4) of the same size, and the crown of the tire of the present invention is composed of two hoop layers, which are radially located on the inner side of two working layers, and the working layers are radially located on the inner side of two protective layers. The reinforcing elements of the hoop layer form an angle of 8° and -8°. The reinforcing elements of the hoop layer are 77.35 inextensible elements, that is, composed of 77 steel wires with a diameter of 35 hundredths of a millimeter, and the tensile modulus measured on the cord extracted from the tire is equal to 178GPa, arranged at a spacing of 6.4 millimeters. The reinforcing elements of the working layer form an angle of -33° and 24°. The reinforcing elements of the working layer are inextensible. The reinforcing elements of the protective layer are extensible and form an angle of -33° and 33°.

[0061] The control tire and the tire according to the invention are identical except for the hooping layer.The control tire and the tire according to the invention have the same tread pattern and the same reinforcements for the carcass layer, the protective layer and the working layers, and the same rubber compound for the different parts of the tire.

[0062] The invention is simulated on a computational tool. This simulation enables the mechanical and thermal stresses of the tire to be evaluated using large displacement and large deformation finite element methods, taking into account the mechanical and hysteresis properties of the material.

[0063] The object of the invention is to reduce the circumferential stiffness in the center in order to improve the wear resistance, impact resistance and puncture resistance. The reduction in stiffness is evaluated based on the deformation of the crown block under the influence of increased pressure. The two hoop layers have variable angles, the angle at the axial ends of the hoop layers having an absolute value equal to 8°, as in the reference tire. The stiffness of the center of the crown is divided by a factor of 3.3 when the absolute value of the maximum angle at the center of the hoop layer is equal to 33, by a factor of 2.3 when the absolute value of the maximum angle at the center of the hoop layer is equal to 24 and by a factor of 1.4 when the absolute value of the maximum angle at the center of the hoop layer is equal to 18. The stiffness of the ends of the crown layer remains the same value as in the reference tire. The average stiffness of the crown reinforcement is sufficient to absorb the driving forces. Depending on the maximum angle at the center of the hoop layer and the selected stiffness reduction, the reduction in stiffness at the center should increase the puncture resistance of the present invention by between 20% and 40%, and should help overcome the uneven wear problem caused by the excessive stiffness at the center of the control civil engineering tire.

[0064] With regard to the durability of the crown, the safety factor of the reinforcing elements of all crown layers (cord breaking strength at maximum stress) is at least equal to the minimum safety factor of the control tire. Similarly, due to the axial portion of the hoop layer, the stress of the rubber composition at the end of the working layer is substantially the same. From this point of view, the inventors expect at least the same durability performance as the control tire. The quality of the control tire and the tire according to the invention is equal.

[0065] All these performance aspects demonstrate the advantages of the present invention.

Claims

1. A radial tire for a heavy vehicle or a civil engineering vehicle, the radial tire comprising: a crown reinforcement located radially on the inside of the tread (10) and radially on the outside of the carcass reinforcement (30), a median plane (M), perpendicular to the axis of rotation of the tyre and passing through the middle of the tread (10), The crown reinforcement comprises a working reinforcement (50), the working reinforcement (50) comprising at least two working layers (51, 52), each working layer (51, 52) comprising metal reinforcing elements coated with an elastomeric material, the metal reinforcing elements being mutually parallel and forming an angle with the circumferential direction (XX') of at least 15° and at most 45°, the metal reinforcing elements crossing from one working layer to the other, The crown reinforcement comprises a hoop reinforcement (40), the hoop reinforcement (40) comprising at least one hoop layer (41, 42), each hoop layer (41, 42) comprising a metal reinforcement element (411) coated with an elastomeric material, the metal reinforcement elements (411) being parallel to each other and comprising two axial ends (412, 413) situated on either side of a median plane (M), the reinforcing elements at the two axial ends (412, 413) of each hoop layer form angles (Ae1, Ae2) of the same direction with the circumferential direction, said angles (Ae1, Ae2) having an absolute value at most equal to 10°, characterised in that the angle formed by the metal reinforcement elements of the hoop layer (41, 42) with the circumferential direction (XX') varies from one axial end to the other axial end of the hoop layer and has a maximum absolute value (Am) at an axial distance from the midplane (M) that is at most equal to 15% of the axial width of the hoop layer, and the maximum absolute value (Am) of the angle is at least equal to the average of the absolute values ​​of the angles (Ae1, Ae2) formed by the metal reinforcing element (411) of the hoop layer (41, 42) at the two axial ends (412, 413) of the hoop layer (41, 42) with the circumferential direction (XX') plus 10°.

2. The tire according to claim 1, wherein: The crown reinforcement comprises at least two hoop layers (41, 42), the angle formed by the metal reinforcing elements (411) of the at least two hoop layers (41, 42) with the circumferential direction (XX') varying from one axial end to the other axial end of each hoop layer (41, 42), having a maximum absolute value (Am) at a position at an axial distance from the middle plane (M) at most equal to 15% of the axial width of the hoop layer in question, the maximum absolute value (Am) of the angle being at least equal to the average of the absolute values ​​of the angles (Ae1, Ae2) formed by the metal reinforcing elements (411) of the hoop layer (41, 42) with the circumferential direction (XX') at the two axial ends (412, 413) of the hoop layers (41, 42) plus 10°.

3. The tire according to any one of claims 1 or 2, wherein: The crown reinforcement comprises two hoop layers (41, 42).

4. A tyre according to any one of the preceding claims, wherein: The metal reinforcement elements (411) of each hoop layer (41, 42) form, at both axial ends (412, 413), an angle (Ae1, Ae2) with the circumferential direction (XX') of at least 5° in absolute value.

5. A tyre according to any one of the preceding claims, wherein: Each hoop layer (41, 42) is located radially inside the working layer (51, 52).

6. A tyre according to any one of the preceding claims, wherein: The metal reinforcement elements of the working layers (51, 52) have a tensile modulus at least equal to 150 GPa.

7. A tyre according to any one of the preceding claims, wherein: The crown reinforcement comprises two protective layers (61, 62) radially outside the working layers, each comprising metal reinforcing elements coated with an elastomeric material, the metal reinforcing elements being parallel to one another and forming an angle with the circumferential direction (XX') of at least 15° and at most 45°, the metal reinforcing elements crossing from one protective layer to the other and having a tensile modulus of at most 150 GPa.

8. The tire according to claim 7, wherein: The radially innermost protective layer ( 61 ) is the layer of the crown reinforcement having the greatest axial width.

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