Optimized architecture of a civil engineering type tire

Abstract

The invention is a radial tire (1) for heavy vehicles, in which the reinforcing elements of each shrink-fit layer (331, 332, 333) form an angle with the circumferential direction of no more than 5°, and the reinforcing elements of the transverse reinforcement layers (321, 322, 323) form an angle with the circumferential direction of between 10° and 45°, are extensible and thus such that, in their gummed state extracted from a polymer matrix, their structural elongations As are at least equal to 0.5%, their total elongation At at break are at least equal to 3%, and their tensile Young's moduli E are at most equal to 150 GPa. Abstract figure: Figure 1

Description

Title of the invention: Optimized architecture of a civil engineering type tire

[0001] The present invention relates to a radial tire, intended to equip a heavy vehicle of the civil engineering type and relates more particularly to the crown reinforcement of such a tire.

[0002] Radial tires intended to equip a heavy vehicle of the civil engineering type are designated in accordance with the standard of the European Tyre and Rim Technical Organisation or ETRTO - European Tyre and Rim Technical Organisation.

[0003] For example, a radial tire for heavy-duty construction equipment, as defined by the European Tyre and Rim Technical Organisation (ETRTO) standard, is intended to be mounted on a rim with a diameter of at least 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, particularly vehicles for transporting materials extracted from quarries or surface mines, by means of a rim with a diameter of at least 35 inches and up to 57 inches, or even 63 inches.

[0004] Since a tire has a geometry of revolution about an axis of rotation, the tire's geometry is generally described in a meridian plane containing the tire's axis of rotation. For a given meridian plane, the radial, axial, and circumferential directions respectively denote the directions perpendicular to the tire's axis of rotation, parallel to the tire's axis of rotation, and perpendicular to the meridian plane. The circumferential direction is tangent to the tire's circumference.

[0005] In what follows, the expressions "radially inside" and "radially outside" respectively mean "closer" and "further" from the axis of rotation of the tire. By "axially inside" and "axially outside," respectively, we mean "closer" and "further" from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tread surface and perpendicular to the axis of rotation.

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

[0007] A radial tire further comprises a reinforcing frame, consisting of of a crown reinforcement, radially inside the tread, and of a carcass reinforcement, radially inside the crown reinforcement.

[0008] The carcass reinforcement of a radial tire for heavy-duty construction vehicles typically comprises at least one carcass layer including reinforcements, or reinforcing elements, generally metallic, coated with a polymeric material of the elastomeric or elastomeric type, obtained by mixing and called the coating compound. A carcass layer includes a main portion, connecting the two beads to each other and generally wrapping, within 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 inversion. The metallic reinforcements of a carcass layer are substantially parallel to each other and form an angle of between 85° and 95° with the circumferential direction.

[0009] The crown reinforcement of a radial tire for construction vehicles comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer consists of reinforcements, generally metallic, parallel to each other and coated with a polymeric material of the elastomer type or coating mixture.

[0010] Among the top layers, we usually distinguish the protective layers, which are part of the protective reinforcement and radially the outermost, and the working layers, which are part of the working reinforcement and radially located between the protective reinforcement and the carcass reinforcement.

[0011] The protective reinforcement, comprising at least one protective layer, essentially protects the working layers from mechanical or physicochemical aggressions, which may propagate through the tread radially towards the inside of the tire.

[0012] The protective reinforcement often comprises two radially superimposed protective layers, formed of extensible metallic reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles of at least 10°.

[0013] The working reinforcement, comprising at least two working layers, serves to encircle the tire and provide it with rigidity and road holding. It withstands both mechanical inflation stresses, generated by the tire's inflation pressure and transmitted by the carcass reinforcement, and mechanical rolling stresses, generated by the tire rolling on a surface and transmitted by the tread. Furthermore, it must resist oxidation, impacts, and punctures, thanks to its intrinsic design and that of the protective reinforcement responsible for protecting the other top layers from external damage and tears. or other perforations.

[0014] The working reinforcement usually comprises two radially superimposed working layers formed of non-extensible metallic reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles of at most 60°, and preferably at least 10° and at most 45°. For good resistance to radial and transverse forces, designers seek to maximize the stiffness and breaking strength of the reinforcement elements of the working layers.

[0015] To reduce the mechanical inflation stresses transmitted to the working reinforcement, it is known to place a shrink-fit reinforcement radially outside the carcass reinforcement. The shrink-fit reinforcement, whose function is to absorb at least some of the mechanical inflation stresses, improves the durability of the top reinforcement by stiffening it. The shrink-fit reinforcement can be positioned radially inside the working reinforcement, between the two working layers of the working reinforcement, or radially outside the working reinforcement.

[0016] In civil engineering applications, the tire reinforcement may comprise two radially superimposed layers of reinforcement, formed of metallic reinforcements, parallel to each other in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles of at most 10° but at least 5°. In this case, the reinforcement elements of the tire layers are laid in layers and extend from one axial edge to the other of said tire layers in less than one revolution of the tire on its axis of rotation.

[0017] The shrink-fitting armature can usually include a shrink-fitting layer made by circumferentially winding a shrink-fitting wire or a continuous shrink-fitting strip, forming angles of no more than 5° with the circumferential direction.

[0018] With regard to metal reinforcements, a metal reinforcement is mechanically characterized by a curve representing the tensile force (in N) applied to the metal reinforcement as a function of its relative elongation (in %), known as the force-elongation curve. From this force-elongation curve, tensile mechanical characteristics of the metal reinforcement are deduced, such as the structural elongation As (in %), the total elongation at break At (in %), the breaking force Fm (maximum load in N), and the tensile strength Rm (in MPa), these characteristics being measured according to ASTM D 2969-04:2014.

[0019] The total elongation at break At of the metallic reinforcement is, by definition, the sum of its structural, elastic, and plastic elongations (At = As + Ae + Ap), and particularly at break where each of the elongations is non-zero. The structural elongation As results from the relative positioning of the metallic wires constituting the Metallic reinforcement under a low tensile force. The elastic elongation Ae results from the elasticity of the metal wires constituting the metallic reinforcement, taken individually, the behavior of the metal following Hooke's law. The plastic elongation Ap results from the plasticity, that is, the irreversible deformation, beyond the elastic limit, of the metal in these individual wires. These different elongations, as well as their respective meanings, well known to those skilled in the art, are described, for example, in documents US5843583, WO2005 / 014925 and WO2007 / 090603.

[0020] A tensile modulus, expressed in GPa, is also defined at every point on the force-stretch curve of a metallic reinforcement. This modulus represents the slope of the line tangent to the force-stretch curve at that point. In particular, the tensile modulus of the linear elastic portion of the force-stretch curve is called the elastic tensile modulus or Young's modulus.

[0021] Among metallic reinforcements, a distinction is usually made between extensible metallic reinforcements, such as those used in protective layers, and non-extensible or inextensible metallic reinforcements, such as those used in working layers.

[0022] A stretchable metal reinforcement, in its unglued 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, a stretchable metal reinforcement has an elastic modulus or Young's modulus in extension of at most 180 GPa, and usually between 40 GPa and 150 GPa.

[0023] In its gummed state extracted from a polymer matrix, namely a tire, an elastic 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%, the polymer matrix blocking part of the movement of the fibers responsible for the structural elongation. Furthermore, an elastic metal reinforcement has, in its gummed state extracted from a polymer matrix, an elastic modulus or Young's modulus in tension of at most 150 GPa, and usually between 40 GPa and 120 GPa.

[0024] A non-stretchable 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 0.2%. Furthermore, a non-stretchable metal reinforcement has an elastic modulus in tension usually between 150 GPa and 200 GPa.

[0025] When a tire is driven over stones or other sharp or less sharp objects on the tracks used by dump trucks, the top of the tire is frequently subjected to cuts that can penetrate it radially inwards and, depending on the size of the object, pierce the entire crown and carcass reinforcement, causing a loss of pressure and failure of the pneumatic. The use of expandable metallic reinforcement in the protective layers is known to improve the resistance of tires to punctures by allowing better adaptation of said protective layer to the shape of the obstacle, however given the cost of these large tires and the frequency of these incidents, it is always useful to improve performance.

[0026] However, while these top-mounted structures are effective against relatively small or medium-sized obstacles, they prove less effective against larger obstacles found in mines. Indeed, in these cases, the forces exerted on the cables exceed the hardness of the steel, and the obstacle then 'cuts' the reinforcing elements of the working layers, all the more easily because these cables are rigid and resist the deformation imposed by the obstacle.

[0027] The inventors have set themselves the objective, for a radial tire for civil engineering type vehicle, of reducing the risk of tire perforation following damage to the tread when driving over sharp stones while maintaining good performance in cracking of the crown by allowing a reduction in the mass of the crown reinforcement.

[0028] This objective has been achieved, according to the invention, by a radial tire for a construction vehicle comprising: • a crown reinforcement, radially internal to a tread of axial width Lbdr and radially external to a carcass reinforcement, • the apex reinforcement comprising at least two layers of transverse reinforcement, one with a greater axial width of Ltmax and one with a smaller axial width of Ltmin, • each layer of transverse reinforcement comprising parallel metallic reinforcement elements forming, with the circumferential direction, oriented angles of at least 10° and at most 45°, with at least two angles of two layers of transverse reinforcement being of opposite sign, • the top reinforcement comprising at least one reinforcement layer with a maximum axial width Lfmax comprising extensible metallic reinforcement elements, parallel to each other and forming, with a circumferential direction (XX') of the tire, an angle of at most equal to 5°, • Each reinforcement element in each layer of the top reinforcement is characterized by a structural elongation As, a breaking force Fm (maximum load in N), a breaking strength Rm (in MPa), a total elongation at break At, and a tensile Young's modulus; these ca- characteristics being measured according to ASTM D 2969-04 of 2014, • each extensible metallic reinforcement element of each reinforcement layer having, in its gummed state extracted from a polymer matrix, a structural elongation Asf of at least 0.5%, a total elongation Atf at break of at least 3% and a Young's modulus in tension Ef of at most 150 GPa, • the reinforcement elements of the transverse reinforcement layers (321, 322, 323) being extensible, having, in their gummed state extracted from a polymeric matrix, a structural elongation Ast of at least 0.5%, a total elongation Att at break of at least 3% and a Young's modulus Et in tension of at most 150 GPa.

[0029] The invention consists of a tire in which all the metallic reinforcements of the crown reinforcement are extensible or hyperextensible, unlike prior art tires whose working layers are inextensible in order to allow for adequate circumferential and transverse rigidity. Surprisingly, on civil engineering tires, having inextensible working layers or transverse reinforcements, if they are combined with one or more reinforcement layers whose reinforcing elements are extensible, is not essential. Moreover, using extensible cords for the working layers—or in this case, transverse reinforcement layers—allows for substantial gains in crown puncture resistance and crack resistance, with a possible reduction in weight.

[0030] In the prior art, what differentiates the working layers from the protective layers, besides their relative positions (the protective layers being the outermost radial layers), is the difference in the inextensible behavior of the working layers when the protective layers are extensible. In one of the simplest and most economical versions in terms of mass and therefore raw material, the invention consists of a tire having one or two compression layers and two layers of extensible transverse reinforcement, at least one of which is radially external to the compression layers.In this case, according to the terminology of state-of-the-art tire design, the outermost radially oriented transverse reinforcement layer is a protective layer; it possesses all the characteristics of one, except that a protective layer does not absorb any transverse forces, these being absorbed by the inextensible working layers in state-of-the-art tires. However, in this configuration, the outermost radially oriented transverse reinforcement layer acts as both a protective layer against impacts and a working layer with respect to absorbing transverse forces. Surprisingly, although all the transverse reinforcement layers are extensible, but only to the extent that there is one or more extensible reinforcement layers, the absorption of transverse forces is... such as in civil engineering applications, the vehicle behavior remains acceptable and the resistance to cracking at the end of the transverse reinforcement layers is maintained or even improved.

[0031] For the invention to function correctly, the shrink-wrapping layer(s) must ensure proper absorption of longitudinal forces. Therefore, expandable reinforcements must be used, the angles of which with the circumferential direction, measured at the level of the median circumferential plane, are no more than 5°. Preferably, this configuration is achieved by wrapping one or more reinforcements, particularly with a strip containing several reinforcements, around the tire. Even when a single reinforcement is used, the shrink-wrapping layer(s) are considered to comprise parallel metallic reinforcements. The shrink-wrapping layer effectively contains, within its axial width, a significant number of reinforcement passes or passes of the same reinforcement, without it being possible to determine whether it is a single reinforcement or two reinforcements joined at the end of the first, as this point has no influence on the tire's behavior.By convention, the reinforcement layer(s) are therefore considered to comprise several metal reinforcements. However, for such angles of metal reinforcement, layer-by-layer installation, rather than wrapping a single reinforcement element or a strip of several reinforcement elements, is also feasible on an industrial scale; however, this installation requires significant overlap of the layer at its longitudinal ends.

[0032] Preferably, the axial width Ltmin of the transverse reinforcement layer with the smallest axial width is at least equal to 70% of the axial width Lbdr of the tread, and preferably at least equal to 80% of the axial width Lbdr of the tread. Since the transverse reinforcement layers are extensible, it is preferable that the coupling of these layers occur over a minimum width of 70%, and preferably 80%, of the width of the tire's crown, i.e., the width of the tread. Below this axial width of the smallest transverse reinforcement layer, the transverse forces are less effectively resisted, the tire's behavior deteriorates, as does its performance in terms of cracking at the axial ends of the transverse reinforcement layers.

[0033] It is advantageous for the axial width of at least one reinforcement layer to be at least 60% of the axial width Lbdr of the tread, and preferably at least 70% of the axial width Lbdr of the tread. Below this axial width of the widest reinforcement layer, longitudinal stresses are less effectively resisted, and shear stresses at the axial ends of the transverse reinforcement layers increase, making the tire more susceptible to cracking.

[0034] Preferably, the total elongation Atf at the rupture of the reinforcing elements The total elongation (Att2) at break of the reinforcement elements in the second, innermost radially positioned transverse reinforcement layer, and the total elongation (Att2) at break of the reinforcement elements in the innermost radially positioned transverse reinforcement layer, are at least 85% and at most 110% of the total elongation (Attl) at break of the reinforcement elements in the innermost radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. If the designer wishes to provide greater protection against punctures, they will increase the number of top layers and the structural and total elongation of the outermost radially positioned reinforcement layer, the one that first absorbs impacts. Thus, if there is a difference in total elongation between the different top layers, the two innermost radially positioned transverse reinforcement layers will have a lower total elongation than the outermost radially positioned top layer.Therefore, it is preferable that the total elongation of each layer of shrinkage and of the two innermost transverse reinforcement layers be close so that in the event of an impact, they behave similarly and absorb deformations in a balanced way, thus avoiding premature failure of one or the other of said layers under impact with an obstacle.

[0035] Similarly, it is preferable that the structural elongation Asf of the reinforcing elements of each shrink-fit layer and the structural elongation Ast2 of the second, innermost, radially positioned transverse reinforcement layer be at least 85% and at most 110% of the structural elongation Asti of the reinforcing elements of the innermost, radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. This allows for balanced operation of the various top layers with respect to inflation and rolling stresses.

[0036] Similarly, it is preferable that the Young's modulus Ef of the reinforcing elements of each shrink-fit layer and the Young's modulus Et2 of the reinforcing elements of the second, innermost, radially positioned transverse reinforcement layer (322) be at least 85% and at most 110% of the Young's modulus Et of the reinforcing elements of the innermost, radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. This condition, like the previous one, allows for good functional balance of the different top layers, but in this case from the point of view of stresses rather than strains.

[0037] It is advantageous that the reinforcing elements of the two innermost radially transverse reinforcement layers and the reinforcement layers have, in their gummed state extracted from a polymer matrix, respective structural elongations of at least 1% and at most 3%, which is the optimal range for the Structural elongation of the reinforcement layers is necessary for improved resistance to punctures and impacts on the crown. If the structural elongation of these layers is too high, the tire will deform excessively, and the rubberized materials of the tire will also deform significantly upon inflation, reducing their resistance, particularly to cracking. A structural elongation of 0.5% for rubberized stretch reinforcements extracted from a polymer matrix, which is a lower limit for structural elongation, is not optimal for improved tire puncture resistance.

[0038] Similarly, it is preferable that the reinforcing elements of the two innermost radially transverse reinforcement layers and of the shrink-fit layers have, in their gummed state extracted from a polymeric matrix, respective Young's moduli of at most equal to 85 GPa and at least equal to 50 GPa, for optimal behavior with respect to the same performance.

[0039] In the case where the tire is dedicated to uses not including the most aggressive uses in terms of impacts of the top by obstacles, it is advantageous that all the reinforcing elements of all the transverse reinforcement layers have similar mechanical characteristics in elongation and rupture in order to have no weak link in the resistance to aggression, so that the behavior of the tire remains as constant as possible depending on the angle of drift applied to it and so that its resistance to cracking is optimized.In this case, for improved impact resistance, it is advantageous that the total elongation at break of the reinforcing elements in each transverse reinforcement layer be at least 85% and at most 110% of the total elongation at break (Att) of the reinforcing elements in the innermost radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. Similarly, for the same applications and optimal performance, it is preferable that the structural elongation of the reinforcing elements in each transverse reinforcement layer be at least 85% and at most 110% of the structural elongation (Ast) of the reinforcing elements in the innermost radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix.Similarly, for optimized crack resistance, it is preferable that the Young's modulus of the reinforcing elements in each transverse reinforcement layer be at least 85% and at most 110% of the Young's modulus Etl of the reinforcing elements in the innermost radially positioned transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. In the same application, it is advantageous for the reinforcing elements in each transverse reinforcement layer to have, in their gummed state extracted from a polymer matrix, elongations. respective structural elongations of at least 1% and at most 3%, which is the optimal range for the structural elongations of the reinforcements of said layers for optimized protection with other performance against perforations and impacts on the top.

[0040] It is possible to further specialize the role of the outermost radially outer crown reinforcement layer, whether it is a transverse reinforcement layer or a reinforcing layer, in crown protection by increasing its elasticity relative to the other transverse reinforcement layers, provided that the tire, in addition to this outermost radially outer crown layer, also comprises at least two transverse reinforcement layers and at least one reinforcing layer. To achieve this, it is advantageous for the reinforcing elements of the outermost radially outer crown layer, in their gummed state extracted from a polymer matrix, to have a structural elongation Asp at least equal to one percent plus the structural elongation Ast of the reinforcing elements of the innermost radially inner transverse reinforcement layer. (Asp > Ast + 1%).Preferably in this configuration, the outermost radially positioned apex reinforcement layer is also the one with the greatest axial width so that this last layer provides effective puncture resistance against small obstacles and to protect the ends of the other transverse reinforcement layers against hammering stresses when passing over large stones.

[0041] In the case of a tire comprising at least 3 layers of transverse reinforcements and whose reinforcements of the outermost radially external transverse reinforcement layer, in their gummed state extracted from a polymeric matrix, have a structural elongation Asp greater than 110% of the structural elongation Ast of the innermost radially internal transverse reinforcement layer and more particularly greater than said elongation plus 1%, it is advantageous that all the radially internal transverse reinforcement layers to the outermost radially external transverse reinforcement layer have similar elastic and rupture behaviors so that the behavior of the tire remains as constant as possible depending on the drift angle applied to it and so that its resistance to cracking is optimized.In this case, to optimize resistance to mechanical stress at the apex, it is advantageous that the total elongation at break of the reinforcing elements of each radially inner transverse reinforcement layer, relative to the outermost radially outermost transverse reinforcement layer, be at least 85% and at most 110% of the total elongation at break of the reinforcing elements of the innermost radially inner transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. Similarly, for improved road handling, it is preferable that the structural elongation of the reinforcing elements of each... The Young's modulus Ef of the reinforcement elements in each radially innermost transverse reinforcement layer, relative to the outermost radially outermost transverse reinforcement layer, should be at least 85% and at most 110% of the structural elongation Ast of the reinforcement elements in the innermost radially innermost transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix. Similarly, for improved crack resistance, it is preferable that the Young's modulus Ef of the reinforcement elements in each radially innermost transverse reinforcement layer, relative to the outermost radially outermost transverse reinforcement layer, should be at least 85% and at most 110% of the Young's modulus Etl of the reinforcement elements in the innermost radially innermost transverse reinforcement layer, each reinforcement being in its gummed state extracted from a polymer matrix.In the same case, it is advantageous that the reinforcing elements of each layer of radially inner transverse reinforcements to the outermost radially outer transverse reinforcement layer, in their gummed state extracted from a polymeric matrix, have structural elongations of at least 1% and at most 3%, which is the optimal range for the structural elongations of the reinforcements of said layers for optimized resistance in this configuration against perforations and impacts on the top.

[0042] The features of the invention are illustrated by the schematic figures 1 to 8, which are not shown to scale, with reference to a tire of size 24.00R35: • Figures 1 to 5: meridian section of a tire crown according to the invention comprising three layers of transverse reinforcements and two layers of shrinkage, the position of which varies according to the figures. • [Fig.6]: Meridian section of a tire apex according to the invention comprising three layers of transverse reinforcements and one layer of shrinkage. • [Fig. 7]: Meridian section of a tire apex according to the invention comprising three layers of transverse reinforcement and three layers of shrinkage. • [Fig. 8]: Meridional cross-section of a tire crown according to the invention comprising two transverse reinforcement layers and two shrink-fit layers.

[0043] The figures do not fully represent the possibilities offered by the invention. For example, for a version of the invention comprising two transverse reinforcement layers and two shrink-fit layers as shown in [Fig. 8], there are numerous possible variations in the positioning of the different layers included in the invention that are not shown. It is nevertheless preferable that the outermost radial reinforcement layer be a transverse reinforcement layer and not a shrink-fit layer, particularly to block sharp obstacles, as the orientation of the reinforcement elements of the shrink-fit layers in the direction of travel makes them less effective at stopping the penetration of a sharp obstacle.

[0044] In the various figures, a meridian section of a tire 1 for heavy vehicle of civil engineering type is shown, comprising a crown reinforcement 3, radially internal to a tread 2 and radially external to a carcass reinforcement 4. The crown reinforcement 3 comprises transverse reinforcement layers 321, 322 and, for some figures, 323, comprising extensible metal reinforcements embedded in an elastomeric material, parallel to each other and forming an angle between 10° and 45°, with a circumferential direction XX' tangent to the circumference of the tire, the metal reinforcements of the two most radially internal transverse reinforcement layers being crossed from one layer to the next.The crown reinforcement also includes one, two, or three reinforcement layers 331, 332, 333, whose respective extensible metallic reinforcements, embedded in an elastomeric material, are parallel to each other and form an angle of no more than 5° with the circumferential direction XX'. Also shown are the axial width of the tread Lbdr, the maximum axial width of the reinforcement layers Lfmax, and the minimum axial widths Ltmin and maximum axial widths Ltmax of the transverse reinforcement layers. In a configuration with three transverse reinforcement layers, the outermost radial reinforcement layer will advantageously be more extensible than the other transverse reinforcement layers in order to provide the tire with improved crown resistance, especially if all the reinforcement layers are radially internal to it.

[0045] The invention was tested on 24.00R35 tires with a tread width of 600 mm. The tires according to the invention are compared to reference tires of the same size for each of the tests.

[0046] Regarding the performance of the resistance of the top to perforation, quasi-static tests are carried out using a cylindrical indenter 300 mm long, with a circular base of diameter 76.6 mm, the end of which, intended to come into contact with the tire, is beveled by planes, symmetrical with respect to the axis of the cylinder, the tip of the bevel having an angle of 46°.

[0047] The quasi-static test involves driving the indenter in at a speed of 50 mm / min. The tire is crushed on a flat surface with a force equal to the recommended load, the tire being inflated to the recommended pressure. The indenter is driven into the center of the contact area. The test result is the penetration distance required to break the top reinforcement. The results are given on a scale of 100, where 100 is the result for the reference tire. A result greater than 100 indicates better performance.

[0048] Endurance performance against crown cracking, also known as crown cleavage, is measured in machine tests where two tires of the same type (reference on reference, invention on invention) roll one on top of the other at the At a speed of 28 km / h, with the tires inflated to 7.25 bar and a crushing force of 20 t, the test is conducted until one of the tires loses pressure. The result considered is the number of kilometers traveled before the tire failure.

[0049] The reference tires and the tires according to the invention are identical except for the crown reinforcement. They have the same tread pattern and the same reinforcements for the carcass layer and the same rubber compounds for the different parts of the tire.

[0050] Regarding the crown reinforcement, the reference tires consist, from the outermost radially outer element to the innermost radially inner element, of a protective reinforcement, a working reinforcement, and a reinforcing reinforcement: • The reinforcement elements of the protective layers are E24.26 expandable cables (24 strands of 0.26 mm diameter), with a laying pitch of 2.5 mm, their structural elongation As being equal, in their gummed state extracted from a polymer matrix, to 0.6%, their total elongation at break At being equal to 3.9%, and their Young's modulus being equal to 75 GPa. They form an angle of 24° with the circumferential direction and are crossed from one layer to the other. The outermost radially outer layer has an axial width of 520 mm, the other 400 mm. • The reinforcement elements of the working layers are inextensible 26.30 cables (26 strands, each 0.3 mm in diameter), with a laying pitch of 3.4 mm. Their structural elongation (As), in their gummed state extracted from a polymer matrix, is 0%, their total elongation at break (At) is 2.4%, and their Young's modulus is 180 GPa. They form an angle of -33° for the innermost radial layer and 19° for the outermost radial layer with the circumferential direction and are crossed from one layer to the next. The outermost radial layer has an axial width of 380 mm, and the outermost layer has an axial width of 450 mm. • The reinforcement elements of the shoring layers are identical to the reinforcement elements of the working layer, with the same spacing. They form an 8° angle with the circumferential direction and are intersected from one layer to the next. They are laid in a sheet pattern. The outermost radial layer has an axial width of 200 mm, the other 240 mm.

[0051] Given the rigidities of the working layers and the shrink-fit layers, it is not possible to widen the shrink-fit layers. If only the shrink-fit layers are extensible, they have no effect.

[0052] The invention has been tested in two versions, a so-called extensible version, referred to as E, and a so-called hyperextensible version, referred to as HE. For both versions E and HE of the invention, The top reinforcement is identical except for the reinforcing elements of the different top layers. The top reinforcement is composed from the outermost radially outer element to the innermost radially inner element: • A layer of transverse reinforcements forming an angle of 33° with the circumferential direction, with an axial width of 520 mm, • A layer of transverse reinforcements forming an angle of 33° with the circumferential direction, crossed with the first layer of transverse reinforcements, and 472 mm in axial width. • Two layers of shrink-fitting forming an angle of 0° with the circumferential direction, with an axial width of 400 mm,

[0053] For version E of the invention, all layers of the top reinforcement are made with reinforcement elements consisting of E21.28 cables (21 wires of 28 hundredths of a millimeter in diameter) laid at a pitch of 2.4 mm, and whose structural elongation As, in their gummed state extracted from a polymeric matrix, is equal to 0.5%, the total elongation at break At is equal to 3.3% and the Young's modulus is equal to 95 GPa.

[0054] For the HE version of the invention, all the layers of the top reinforcement are made with reinforcing elements consisting of E24.35 cables (24 wires of 0.35 mm diameter) laid at a 4.2 mm pitch, and whose structural elongation As, in their gummed state extracted from a polymer matrix, is equal to 1.1%, the total elongation at break At is equal to 4.3%, and the Young's modulus is equal to 70 GPa. The elasticity and hyperelasticity, or extensibility and hyperextensibility of the cables are obtained by working on the arrangement of the wires in the cable and also the mixture disposed of between the wires.

[0055] The modulus of elasticity during the structural elongation phase of the set of stretchable or hyperstretchable cables of the reference tires or according to the invention, is between 10 and 20 GPa in their ungummed state, and between 10 and 30 GPa in their gummed state extracted from a polymeric matrix.

[0056] Regarding penetration resistance performance, the results show that, despite a weight reduction in the tire through a decrease in the metallic mass of its crown reinforcement, the critical height of the indenter during an impact on the tread surface is significantly higher. The E version shows a 10% performance improvement and the HE version a 20% improvement.

[0057] Regarding the tests for cracking or splitting of the crown, the tires according to the invention perform 20% more kilometers than the reference tire before its failure, i.e. an increase in performance of 20%.

[0058] Regarding tire mass performance, the E version shows a 20% reduction in metal mass and the HE version a 22% reduction, i.e., for the The tested tire resulted in a weight reduction of approximately 100 kg.

[0059] The invention as proposed therefore makes it possible to improve the resistance to puncture at the apex, the resistance of the apex reinforcement to cracking while reducing the mass of the apex reinforcement and therefore the mass of the tire.

Claims

1. Demands Radial tire (1) for construction equipment type vehicle comprising: • a crown reinforcement (3), radially internal to a tread (2) of axial width Lbdr and radially external to a carcass reinforcement (4), • the apex reinforcement (3) comprising at least two layers of transverse reinforcement (321, 322, 323), one with a greater axial width of Ltmax and one with a smaller axial width (322) of Ltmin, • each layer of transverse reinforcements (321, 322, 323) comprising metallic reinforcement elements, parallel to each other, forming, with the circumferential direction, oriented angles of at least 10° and at most 45°, at least two angles of two layers of transverse reinforcements being of opposite sign, • the top reinforcement comprising at least one reinforcement layer (331, 332, 333) of a maximum axial width Lfmax comprising extensible metallic reinforcement elements, parallel to each other and forming, with a circumferential direction (XX') of the tire, an angle of at most equal to 5°, • each reinforcement element of each layer of the top reinforcement being characterized by a structural elongation As, a breaking strength Fm (maximum load in N), a breaking strength Rm (in MPa), a total elongation at break At and a tensile Young's modulus, these characteristics being measured according to ASTM D 2969-04 of 2014, • each extensible metallic reinforcement element of each reinforcement layer (331, 332, 333) having, in its gummed state extracted from a polymeric matrix, a structural elongation Asf of at least 0.5%, a total elongation Atf at break of at least 3% and a Young's modulus in tension Ef of at most 150 GPa, • Characterized in that the reinforcing elements of the transverse reinforcing layers (321, 322, 323) are extensible, having, in their gummed state extracted from a polymeric matrix, a structural elongation Ast at least equal to 0.5%, a total elongation Att at break of at least 3% and a Young's modulus Et in tension of at most 150 GPa, • Characterized in that all the metallic reinforcements of the top reinforcement are extensible.

2. Tire (1) according to claim 1, wherein the axial width Ltmin of the transverse reinforcement layer of smallest axial width (322) is at least equal to 70% of the axial width Lbdr of the tread (Ltmin >0.7*Lbdr), preferably at least equal to 80% of the axial width Lbdr of the tread (Ltmin >0.8*Lbdr).

3. Tire (1) according to any one of claims 1 or 2, wherein the axial width of at least one shrink-fit layer (331, 332, 333) is at least equal to 60% of the axial width Lbdr of the tread (Lfmax >0.6*Lbdr) and preferably at least equal to 70% of the axial width Lbdr of the tread (Lfmax >0.7*Lbdr).

4. Pneumatic (1) according to any one of the preceding claims, wherein the Young's modulus Ef of the reinforcing elements of each reinforcement layer (331, 332, 333) and the Young's modulus Et2 of the reinforcing elements of the second, innermost radially transverse reinforcement layer (322) are at least equal to 85% and at most equal to 110% of the Young's modulus Etl of the reinforcing elements of the innermost radially transverse reinforcement layer (321) (0.85*Etl <Ef <1.10*Etl etO.85*Etl <Et2 <1.10*Etl), chacun des renforts étant dans son état gommé extrait d’une matrice polymérique.

5. Pneumatic (1) according to any one of the preceding claims wherein the reinforcing elements of the two innermost radially transverse reinforcing layers (321, 322) and of the reinforcing layers (331, 332, 333) have, in their gummed state extracted from a polymeric matrix, respective Young's moduli (Ef, Et) of at most 85 GPa and at least 50 GPa.

6. Radial tire (1) according to any one of the preceding claims wherein the reinforcing elements of the two innermost radially transverse reinforcing layers (321, 322) and of the shrink-fit layers (331, 332, 333) have, in their gummed state extracted from a polymeric matrix, respective structural elongations (Asf, Ast) of at least 1%.

7. Pneumatic (1) according to any one of the preceding claims wherein the reinforcing elements of the two innermost radially transverse reinforcing layers (321, 322) and of the shrink-fit layers (331, 332, 333) have, in their gummed state extracted from a polymeric matrix, respective structural elongations (Asf, Ast) not more than 3%.

8. Pneumatic (1) according to any one of the preceding claims, wherein the structural elongation Asf of the reinforcing elements of each reinforcement layer (331, 332, 333) and the structural elongation Ast2 of the second, innermost, radially displaced transverse reinforcement layer (322) are at least equal to 85% and at most equal to 110% of the structural elongation Asti of the reinforcing elements of the innermost, radially displaced transverse reinforcement layer (321) (0.85*Ast <Asf <1.10* Ast), chacun des renforts étant dans son état gommé extrait d’une matrice polymérique.

9. Pneumatic (1) according to any one of claims 1 to 6, wherein the outermost radially external top reinforcement layer is radially external to at least two transverse reinforcement layers and at least one reinforcing layer, the reinforcement elements of the outermost radially external top layer (323), in their gummed state extracted from a polymer matrix, have a structural elongation Asp at least equal to one percent plus the structural elongation Ast of the reinforcement elements of the innermost radially internal transverse reinforcement layer (321). (Asp>Ast+1%).

Images