FR3089876A1 - Tire for civil engineering vehicle comprising a two-dimensional paving protection frame - Google Patents

Abstract

The present invention relates to a tire, intended to equip a civil engineering vehicle, and more particularly relates to its protective frame. To increase the resistance to attack by its protective frame, when rolling over sharp stones, the reinforcements of each protective layer (51) are two-dimensional elements (511) each having a unitary section Se and two to two separate , each two-dimensional element (511) is inscribed in a minimum disc having a center O and a diameter D both at least equal to 0.1 times L, expressed in mm, and 30 mm, and the centers O of the minimum discs circumscribed at two-dimensional elements (511) are positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling. Figure for the abstract: Fig 1

Description

Description

Title of the invention: Tire for civil engineering vehicle comprising a protective framework with two-dimensional paving

The present invention relates to a tire, intended to equip a civil engineering vehicle, and relates more particularly to its crown reinforcement, and even more particularly to its protective reinforcement.

Typically a tire for a civil engineering vehicle, within the meaning of the European Tire and Rim Technical Organization or ETRTO standard, is intended to be mounted on a rim whose diameter is at least 25 inches and can reach 63 inches. In addition, such a tire is intended to be subjected to heavy loads and to roll on aggressive soils.

In general, a tire having a geometry of revolution relative to an axis of rotation, its geometry is generally described in a meridian plane containing its axis of rotation. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation, parallel to the axis of rotation and perpendicular to the meridian plane. 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”, is meant “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.

A tire comprises a tread, intended to come into contact with a ground by means of a tread surface, the two axial ends of which are connected by means of two sidewalls with two beads ensuring the connection mechanical between the tire and the rim on which it is intended to be fitted.

[0005] A radial tire also comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially internal to the tread, and a carcass reinforcement, radially internal to the crown reinforcement.

The carcass reinforcement of a radial tire for a civil engineering vehicle usually comprises at least one carcass layer comprising generally metallic reinforcements, coated with a polymeric material of elastomer or elastomer type, obtained by mixing and usually called mixture coating. 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 reinforcement element, most often metallic, called bead wire, 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 close to 90 °, between 85 ° and 95 °.

The crown reinforcement of a radial tire for a civil engineering vehicle comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each top layer consists of generally metallic reinforcements, which are parallel to each other and coated with a polymeric material of the elastomer or coating mixture type.

Among the top layers, there are usually the protective layers, constituting the protective armature and radially outermost, and the working layers, constituting the working armature and radially between the protective reinforcement and the carcass reinforcement.

The protective reinforcement, comprising at least one protective layer, essentially protects the working layers from mechanical or physicochemical attack, liable to spread through the tread radially towards the inside of the tire. The protective reinforcement often comprises two protective layers, radially superimposed, formed of elastic metallic reinforcements, mutually parallel in each layer and crossed from one layer to the next, forming, with the circumferential direction, angles at least equal. at 10 °.

The working frame, comprising at least two working layers, has the function of encircling the tire and giving it rigidity and road holding. It takes up both mechanical inflation stresses generated by the inflation pressure of the tire and transmitted by the carcass reinforcement, and mechanical rolling stresses generated by the rolling of the tire on a ground and transmitted by the strip of rolling. It must also resist oxidation and impact and puncture, thanks to its intrinsic design and that of the protective frame. The working reinforcement usually comprises two working layers, radially superposed, usually formed of non-extensible metallic reinforcements, mutually parallel 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 °.

The metal reinforcements constituting the various carcass or crown layers are metallic cables made up of an assembly of metallic wires, most often made of steel.

When rolling the tire on more or less sharp stones, present on the tracks on which the civil engineering vehicles circulate, the tread of a tire is frequently subjected to cuts capable of passing through it radially towards the inside to the protective reinforcement, which prevents the propagation of cracks resulting from cuts to the working reinforcement: the protective reinforcement thus acts as a shield against mechanical attack of the working frame.

The inventors have set themselves the objective, for a radial tire for a civil engineering vehicle, of increasing the resistance to attack by its protective reinforcement, and consequently that of its crown reinforcement, during rolling on sharp stones.

This objective was achieved, according to the invention, by a tire for a civil engineering vehicle comprising a crown reinforcement, radially internal to a tread and radially external to a carcass reinforcement:

the crown reinforcement comprising, radially from the outside towards the inside, a protective reinforcement and a working reinforcement,

the protective reinforcement comprising at least one protective layer comprising reinforcements coated in an elastomeric material,

the protective layer having an axial width L and a circumferential surface S, the working reinforcement comprising at least two working layers each comprising reinforcements coated in an elastomeric material,

the reinforcements of each protective layer being two-dimensional elements each having a unitary surface Se and two by two separate,

- each two-dimensional element being inscribed in a minimal disk having a center O and a diameter D both at least equal to 0.1 times L, expressed in mm, and 30 mm

- And the centers O of the minimum disks circumscribed to the two-dimensional elements being positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling.

A protective layer according to the invention comprises two-dimensional reinforcements, most often but not necessarily metallic, distributed in regular paving, replacing the usual one-dimensional reinforcements, generally made up of cables, most often metallic, parallel to each other and forming , with the circumferential direction of the tire, a given angle. The advantage of a regular paving of two-dimensional elements is to present sufficient local surfaces opposing mechanical resistance to the penetration of the stones present on the ground and thus allowing the distribution of the resulting indentation forces.

By two-dimensional element means a three-dimensional element having a smaller dimension, called thickness E, much less than the other two dimensions, typically at most equal to 2% of each of the other two dimensions. The other two dimensions define the unit area Se of the two-dimensional element.

The two-dimensional elements are two by two separate, that is to say separated from each other by an elastomeric coating material, which avoids any overlapping between them and guarantees independent mechanical operation of each two-dimensional element and a local resumption of efforts.

Still according to the invention each two-dimensional element is inscribed in a minimum disc having a center O and a diameter D both at least equal to 0.1 times L, expressed in mm, and 30 mm, a minimum disc being the smallest disk containing the two-dimensional element. In other words, the inventors estimated that the surface of the smallest disc containing the two-dimensional element, which is an increase in the unit area Se of the two-dimensional element, was a technical characteristic relevant with respect to the geometry of the element. two-dimensional, allowing an excess estimate of the unit area Se. A minimum disc diameter at least equal to the greater of the following two values: 10% of the axial width L of the protective layer and 30 mm, representing the average dimension of the stones likely to attack the tread of the tire, was considered optimal by the inventors to provide sufficient local protection.

Still according to the invention, the centers O of the minimum disks circumscribed to the two-dimensional elements are positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling. This regular paving allows a homogeneous mechanical operation of the protective shield. Furthermore, the shape of the regular polygons is optimized so as to maximize the number of two-dimensional elements per unit area of the protective layer, or coverage rate.

Preferably the sum of the elementary surfaces Se of the two-dimensional elements is at least equal to 0.50 times the circumferential surface S of the protective layer. In other words, the recovery rate, defined as the ratio between the sum of the elementary surfaces Se of the two-dimensional elements, that is to say the total surface of the reinforcements, and the circumferential surface S of the protective layer , that is to say of the developed surface of the protective layer in the circumferential direction, must at least be equal to 50% to ensure the targeted shield effect.

Advantageously, each two-dimensional element is inscribed in a minimal disk having a center O and a diameter D at most equal to 0.2 times L, expressed in mm. Beyond this value, the protective layer becomes too rigid both with respect to the meridian bending of the top of the tire, around a circumferential direction of the tire, and with respect to the circumferential bending from the top of the tire, around an axial direction of the tire. In other words, the meridian and circumferential flattening of the top of the tire would be penalized.

Each two-dimensional element advantageously has a thickness E at least equal to 0.2 mm. Below this value, the two-dimensional element is insufficiently rigid to ensure its function as a physical barrier to the penetration of an indenter.

Each two-dimensional element still advantageously has a thickness E at most equal to 0.5 mm. Above this value, the two-dimensional element is too rigid, which penalizes the rigidities of meridian and circumferential bending of the crown reinforcement.

According to a preferred embodiment, each two-dimensional element is a disk of center O and of diameter D. In this case, the two-dimensional element is coincident with the minimum disk in which it is inscribed. The advantage of a circular contour makes it possible to avoid angular points capable of creating local stresses which can cause a rupture of the angular points or a decohesion between the two-dimensional element and the elastomeric coating material, at the angular points.

Preferably, the material constituting each two-dimensional element is a metal, preferably a stainless steel or a low carbon steel, that is to say with a carbon content at most equal to 0.2% carbon in mass. Metal, and in particular steel, is a material commonly used in the tire field, and compatible with an elastomeric coating material with suitable coatings well known in the state of the art. Stainless steel and low carbon steel were chosen preferentially because of their resilience, that is to say their ability to absorb shocks.

According to a particular embodiment, each two-dimensional element is pierced with holes. The presence of holes, allowing the elastomeric coating material to pass, allows better mechanical anchoring of the two-dimensional element to the elastomeric coating material.

According to a first embodiment of the tiling of two-dimensional elements, the centers O of the minimum disks circumscribed to the two-dimensional elements are positioned at the vertices of identical equilateral triangles. This pattern with equilateral triangles makes it possible to minimize the distance between two neighboring two-dimensional elements and to optimize the recovery rate of the protective layer.

According to a second embodiment of the tiling of two-dimensional elements, the centers O of the minimum disks circumscribed to the two-dimensional elements are positioned at the vertices of identical squares. This pattern with squares also makes it possible to have a small distance between two neighboring two-dimensional elements and to optimize the recovery rate of the protective layer.

For a tire according to the invention, comprising a first and a second radially superposed protective layers, the centers of the minimum discs circumscribed to the two-dimensional elements of the second protective layer are advantageously offset axially and circumferentially relative to those of the first layer of protection. A shift between the centers of these minimum disks, assumed to be of the same size between the first and second protective layers, makes it possible to have a partial superposition between the respective two-dimensional elements of each layer and therefore to constitute an almost continuous protective shield and d '' provide more mechanical resistance.

Most often the metal reinforcements of the working layers are cables parallel to each other.

The characteristics of the invention are illustrated by Figures 1 to 6 schematic and not shown to scale:

Figure 1: Meridian section of a tire for a civil engineering vehicle according to the invention.

Figure 2: Perspective view of a protective layer with two-dimensional elements.

Figure 3: Top view of a protective layer with two-dimensional elements. Figure 4: Two-dimensional disk-shaped element.

Figure 5: Two-dimensional disc-shaped element with holes.

Figure 6: Superimposition of two protective layers with offset of their respective two-dimensional elements.

Figure 1 is a meridian section of a tire 1 for a civil engineering vehicle according to the invention. The tire 1 comprises a crown reinforcement 3, radially internal to a tread 2 and radially external to a carcass reinforcement 4. The crown reinforcement 3 comprises radially from the outside inwards, a protective reinforcement 5 and a working armature 6. In the particular embodiment of the invention shown, the protective armature 5 comprises a protective layer 51 comprising reinforcements 511 coated in an elastomeric material, the protective layer 51 having an axial width L and a circumferential surface S (not shown). The working frame 6 comprises two working layers 61 each comprising reinforcements 611 of the metal cable type coated in an elastomeric material. According to the invention, the reinforcements of each protective layer 51 are two-dimensional elements 511 each having a unitary section Se and two by two separate, each two-dimensional element 511 is inscribed in a minimum disc having a center O and a diameter D at the times at least equal to 0.1 times L, expressed in mm, and 30 mm and the centers O of the minimum disks circumscribed to the two-dimensional elements 511 are positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling.

Figure 2 is a perspective view of a protective layer 51 with monthly bidi elements 511, having the shape of a disc having a center O and a diameter D. The centers O of two-dimensional elements 511 in the form of disk are positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling. In the embodiment shown in Figure 2, the regular paving consists of identical equilateral triangles.

Figure 3 is a top view of a protective layer 51 with two-dimensional elements 511, having the shape of a disc having a center O and a diameter D. The centers O of the two-dimensional elements 511 in the form of a disc are positioned at the vertices of identical regular polygons, so that the two-dimensional elements constitute a regular tiling. In the embodiment shown in Figure 3, the regular paving consists of identical equilateral triangles.

FIG. 4 represents a preferred embodiment of a two-dimensional disk-shaped element having a center O and a diameter D. The thickness E of the two-dimensional element is small compared to the diameter D, typically at most equal to 2% of D. Preferably, each two-dimensional element 511 has a thickness E at least equal to 0.2 mm and at most equal to 0.5 mm, to guarantee optimal rigidity of the two-dimensional element making it possible to ensure its function as a physical barrier to an indenter without penalizing the rigidities of meridian and circumferential bending of the crown reinforcement.

FIG. 5 represents a variant of the preferred embodiment of a two-dimensional disc-shaped element having a center O and a diameter D, presented in FIG. 4, with holes 512. The presence of holes 512, letting the elastomeric coating material, allows better mechanical anchoring of the two-dimensional element 511 with the elastomeric coating material.

Figure 6 is a top view of a protective frame 5 consisting of a first and a second protective layer 51 radially superimposed, in which the centers of the two-dimensional elements 511 in the form of a disc of the second layer of protection 51 (in solid lines) are offset axially and circumferentially with respect to those of the first protective layer 51 (in dotted lines. This offset between the centers of these discs of the same diameter D makes it possible to have a partial superposition between the respective two-dimensional elements of each layer and therefore to constitute an almost continuous protective shield and to provide more mechanical resistance.

The invention has been more particularly studied for a tire with a size of 24.00R35. The crown reinforcement of such a tire comprises, radially from the outside to the inside, a protective reinforcement and a working reinforcement. The work reinforcement comprises two working layers comprising reinforcements of the metallic wire structure type (3 + 9 + 14) * 0.30 ER, constituted by 26 steel wires having a diameter of 0.30 mm and hooped. These metallic cables, parallel to each other, form, with the circumferential direction, an angle equal to 19 ° for one working layer and equal to 34 ° for the other working layer, and are crossed from one working layer to the next. Two protective armor variants have been studied. A first variant of protective frame comprises three radially superposed protective layers. Each protective layer has an axial width L equal to 400 mm and comprises two-dimensional disc-shaped elements having a thickness E equal to 0.4 mm and a diameter D equal to 70 mm. The centers O of the two-dimensional disc-shaped elements being positioned at the vertices of equilateral triangles, having a side length equal to 76 mm, so as to constitute a regular paving. The recovery rate of a protective layer, equal to the ratio between the sum of the unit areas Se of the two-dimensional elements and the circumferential surface S of the protection layer, is equal to 60%. In addition, each two-dimensional disc-shaped element is pierced with seven holes. Two types of materials making up the two-dimensional elements were tested: stainless steel and low-carbon steel. The second variant of protective reinforcement is distinguished from the first variant by the radial superposition of four protective layers comprising two-dimensional disc-shaped elements having a thickness E equal to 0.3 mm and a diameter D equal to 70 mm.

The effectiveness of a protective reinforcement according to the invention, in terms of a mechanical shield against obstacles, was quantified by tests of perforation of the tire, by rolling over standardized obstacles. These standardized obstacles are hemispherical head thrusters, having a variable diameter and height. Typically, the diameter of a polar varies between 0.5 inches and 3 inches, for a height between 25 mm to 500 mm. The tire to be tested is mounted on the rim of a Dumper type vehicle and inflated to a recommended pressure. Several successive passages on a polar having a given diameter are carried out with a progressive increase in the height of the polar. The test ends when you end up rolling on a fleece high enough to perforate the top of the tire under test. During the test, a device makes it possible to measure the maximum forces generated at the center of the wheel. At the end of the test, the forces measured at the center of the wheel are represented as a function of the height of the polar. Indentation rigidity is the ratio between the variation in vertical force measured at the center of the wheel and the variation in height of the thrust, between the initial state and the perforation of the tire. This test was carried out for a tire according to the invention and a reference tire of the state of the art. For protective reinforcements having substantially equal masses of metal reinforcements, a gain of 30% in perforation, corresponding to a 30% increase in the polar height necessary for perforation, was measured for a tire according to the invention by compared to the reference tire.

Claims (1)

Claims [Claim 1] Tire (1) for a civil engineering vehicle comprising a crown reinforcement (3), radially internal to a tread (2) and radially external to a carcass reinforcement (4), the crown reinforcement (3) comprising , radially from the outside to the inside, a protective reinforcement (5) and a working reinforcement (6), the protective reinforcement (5) comprising at least one protective layer (51) comprising reinforcements ( 511) coated with an elastomeric material, the protective layer (51) having an axial width L and a circumferential surface S, -the working frame (6) comprising at least two working layers (61) each comprising reinforcements (611) coated in an elastomeric material, characterized in that the reinforcements of each protective layer (51) are two-dimensional elements (511) each having a unitary section Se and two by two separate, in that each two-dimensional element (511) is inscribed in a minimum disc having a center 0 and a diameter D both at least equal to 0.1 times L, expressed in mm, and 30 mm and in that the centers 0 of the minimum disks circumscribed to the two-dimensional elements (511) are positioned at the vertices of identical regular polygons , so that the two-dimensional elements constitute a regular tiling. [Claim 2] A tire (1) for a civil engineering vehicle according to claim 1, in which the sum of the elementary surfaces Se of the two-dimensional elements (511) is at least equal to 0.50 times the circumferential surface S of the protective layer (51). [Claim 3] Tire (1) for a civil engineering vehicle according to either of Claims 1 and 2, in which each two-dimensional element (511) is inscribed in a minimum disk having a center O and a diameter D at most equal to 0.2 times L, expressed in mm. [Claim 4] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 3, in which each two-dimensional element (511) has a thickness E at least equal to 0.2 mm. [Claim 5] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 4, in which each two-dimensional element (511) has a thickness E at most equal to 0.5 mm. [Claim 6] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 5, in which each two-dimensional element (511) is a disc of center 0 and of diameter D. [Claim 7] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 6, in which the material constituting each two-dimensional element (511) is a metal, preferably stainless steel or a low carbon steel. [Claim 8] Tire (1) for a civil engineering vehicle according to any one of Claims 1 to 7, in which each two-dimensional element (511) is pierced with holes (512). [Claim 9] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 8, in which the centers 0 of the minimum disks circumscribed by the two-dimensional elements (511) are positioned at the vertices of identical equilateral triangles. [Claim 10] A tire (1) for a civil engineering vehicle according to any one of claims 1 to 8, in which the centers 0 of the minimum disks circumscribed by the two-dimensional elements (511) are positioned at the vertices of identical squares. [Claim 11] Tire (1) for a civil engineering vehicle according to any one of Claims 1 to 10, comprising a first and a second protective layer (51) radially superimposed, in which the centers of the minimum discs circumscribed by the two-dimensional elements (511) of the second protective layer (51) are offset axially and circumferentially relative to those of the first protective layer (51). 1/4