FR3064212A1 - PNEUMATIC SUMMIT REINFORCEMENT COMPRISING A TOP WORK LAYER AND A LAYER OF CIRCUMFERENTIAL ELEMENTS - Google Patents

Abstract

A tire, wherein the carcass reinforcement reinforcing members are oriented in a radial direction in the sidewalls of the tire, comprises a crown reinforcement consisting of a working crown layers of reinforcing elements with the circumferential direction an angle (α2) between 25 ° and 55 ° and a layer of circumferential reinforcing elements. According to the invention, in the zone of the summit, the reinforcing elements of said layer of the carcass reinforcement make with the circumferential direction an angle (a1) such that the average angle α defined by the Arctan relation ((tan ( | α1 |) * tan (| α2 |)) 1/2) is between 30 and 67 ° and, radially inside the crown reinforcement, the tire comprises a layer of textile reinforcing elements whose Secant modulus at 1% extension is less than 75 GPa, the utilization ratio of the fracture potential F2 / FR2 of the working layer being less than 1/10.

Description

Holder (s): COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares.

Extension request (s)

Agent (s): MANUF FSE PNEUMATIQUES MICHELIN Limited partnership with shares.

SUMMIT FRAME OF TIRE CONSISTING OF A LAYER OF WORKING SUMMIT AND A LAYER OF CIRCUMFERENTIAL ELEMENTS.

FR 3 064 212 - A1

The invention relates to a tire, the reinforcing elements of the carcass reinforcement oriented in a radial direction in the sidewalls of the tire, comprising a crown reinforcement constituted by a working crown layers of reinforcing elements making with the circumferential direction an angle (cz2) between 25 ° and 55 ° and of a layer of circumferential reinforcing elements.

According to the invention, in the region of the apex, the reinforcing elements of said layer of the carcass reinforcement form with the circumferential direction an angle (al) such that the mean angle a defined by the relation Arctan ((tan ( | cz1 |) * tan (| cz2 |)) ^1/2 ) is between 30 and 67 ° and, radially inside the crown reinforcement, the tire comprises a layer of textile reinforcing elements, the secant module at 1% extension is less than 75 GPa, the utilization ratio of the F2 / FR2 breaking potential of the working layer being less than 1/10.

-1 TIRE SUMMIT FRAME CONSTITUTED

A LAYER OF WORK TOP AND A

LAYER OF CIRCUMFERENTIAL ELEMENTS The present invention relates to a tire, with a radial carcass reinforcement and more particularly a tire intended to equip vehicles carrying heavy loads, such as, for example trucks, tractors, trailers or road buses.

In general, in heavy goods vehicle tires, the carcass reinforcement is anchored on either side in the zone of the bead and is radially surmounted by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles between 10 ° and 45 ° with the circumferential direction. Said working layers, forming the working reinforcement, can also be covered with at least one so-called protective layer and formed of reinforcing elements advantageously metallic and extensible, called elastic. It can also include a layer of metal wires or cables making an angle of between 45 ° and 90 ° with the circumferential direction, this layer, called triangulation, being radially located between the carcass reinforcement and the first crown layer called work, formed of parallel wires or cables having angles at most equal to 45 ° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which has, under the various stresses which it undergoes, little deformation, the triangulation ply having the essential role of resuming the transverse compressive forces which is the 'object the set of reinforcing elements in the area of the top of the tire.

Cables are said to be inextensible when said cables have, under a tensile force equal to 10% of the breaking force, a relative elongation at most equal to 0.2%.

Cables are said to be elastic when said cables have, under a tensile force equal to the breaking load, a relative elongation at least equal to 3% with a maximum tangent modulus less than 150 GPa.

-2 [0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the interval + 2.5 °, - 2.5 ° around 0 °.

The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular thereto.

The axis of rotation of the tire is the axis around which it rotates in normal use.

[0010] A radial or meridian plane is a plane which contains the axis of rotation of the tire.

The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

With regard to metallic wires or cables, the measures of breaking strength (maximum load in N), of breaking strength (in MPa), of elongation at break (total elongation in%) and of module (in GPa) are carried out in traction according to ISO 6892 standard of 1984.

Certain current tires, known as road tires, are intended to travel at high average speeds and on increasingly long journeys, due to the improvement of the road network and the growth of the motorway network in the world. All of the conditions, under which such a tire is called to roll, undoubtedly allows an increase in the number of kilometers traveled, the wear of the tire being less. This increase in service life in terms of kilometers, combined with the fact that such conditions of use are likely to result, under heavy load, in

-3 relatively high crown temperatures, requires an at least proportional increase in the endurance potential of the crown reinforcement of the tires.

There are in fact constraints at the level of the crown reinforcement and more particularly shear stresses between the crown layers which, in the case of too high a rise in the operating temperature at the ends of the axially shortest crown layer results in the appearance and propagation of cracks in the rubber at the level of said ends. The same problem exists in the case of edges of two layers of reinforcing elements, said other layer not necessarily being radially adjacent to the first.

In order to improve the endurance of the crown reinforcement of tires, French application FR 2 728 510 proposes to have, on the one hand between the carcass reinforcement and the armature working ply of apex, radially closest to the axis of rotation, an axially continuous ply, formed of inextensible metallic cables making with the circumferential direction an angle at least equal to 60 °, and whose axial width is at least equal to the axial width of the shortest working crown ply, and on the other hand between the two working crown plies an additional ply formed of metallic elements, oriented substantially parallel to the circumferential direction.

In addition, French application WO 99/24269 proposes in particular, on either side of the equatorial plane and in the immediate axial extension of the additional ply of reinforcing elements substantially parallel to the circumferential direction, to couple, over a certain axial distance, the two working crown plies formed of reinforcing elements crossed from one ply to the next, then decoupling them by profiles of rubber mixture at least over the remainder of the width common to said two work tablecloths.

In addition, the use of tires on heavy goods vehicles of the "construction site approach" type leads to the tires being subjected to shocks when driving on stony ground. These shocks are of course harmful in terms of endurance performance.

It is also known to a person skilled in the art to increase the number of plies constituting the crown reinforcement in order to improve the endurance of the tire with regard to such shocks.

Whatever one of these solutions as presented above, the presence of one or more layers of additional reinforcing elements leads to a greater mass of the tire and to higher costs of manufacturing the tires.

An object of the invention is to provide tires for HGV vehicles, for example of the "construction site approach" type, the endurance performance of which is maintained or even improved, in particular with regard to the shocks sustained on the tread and of which the overall mass is reduced.

This object is achieved according to the invention by a tire for a heavy goods vehicle, with a carcass reinforcement consisting of a layer of metallic reinforcing elements oriented in a radial direction in the sidewalls of the tire, comprising a reinforcement crown comprising a working crown layer of metallic reinforcing elements forming with the circumferential direction an angle (a2) of between 25 ° and 55 °, said working crown layer being centered on the circumferential median plane, the reinforcement crown being capped radially by a tread, said tread being joined to two beads via the two sides, the crown reinforcement being completed by at least one layer of metallic circumferential reinforcing elements, and on a part centered on the circumferential median plane of axial width less than the width of said working crown layer, the reinforcing elements of lad ite layer of the carcass reinforcement making with the circumferential direction an angle (al) such that the mean angle (a) defined by the relation

Arctan ((tan (| ocl |) * tan (| oc2 |)) ^1/2 ) is between 30 and 67 °, said angles al and a2 being oriented on either side of the circumferential direction, radially to l inside the crown reinforcement, the tire comprising a layer of textile reinforcing elements whose secant modulus at 1% of extension is less than 75 GPa, the ratio of use of the rupture potential F2 / FR2 of the working layer being less than 1/10, in which:

-5FR2 is the breaking force in uniaxial extension of the reinforcing elements of the working layer, expressed in N,

F2 = 0.1 * P * Qs * p ₂ / [(sin (| oc2 |) + tan (| ocl |) * cos (| a2 |)) * sin (| oc2 |)], with

P: inflation pressure, expressed in bar,

Qs = (Rs ² -RL ² ) / (2 * Rs), p ₂ : the pitch of laying the reinforcing elements of the working crown layer, measured perpendicular to the reinforcing elements at the circumferential median plane,

Rs = Re - Es,

Re: outside radius of the tire measured at the radially outermost point on the surface of the tire tread, said surface being extrapolated to fill any gaps,

Es: radial distance between the radially outermost point of the tire and its orthogonal projection on the radially outer face of a reinforcement element of the working crown layer,

RL: mean of the radii of the axially outermost points on each side of the tire, the thickness Es and the pitch p ₂ are measured on a section of the tire and are expressed in millimeters.

The angles al and a2, expressed in degrees, are also measured on a section of the tire. The angle measurements are according to the invention carried out at the level of the circumferential median plane.

The measurements of the radii Re, RL and Rt are carried out on a tire mounted on its nominal rim and inflated to the nominal pressure.

With regard to textile threads or cables, the mechanical properties are measured on fibers which have been subjected to prior conditioning. By pre-conditioning, the fibers are stored for at least 48 hours, before measurement, in a standard atmosphere according to the European standard NF EN ISO 139 (temperature of 20 +/- 2 ° C; relative humidity of 65 +/- 4 % RH). Properties

-6 mechanicals in extension (breaking strength, elongations under load) are measured according to a specific measurement method using calibrated static traction machines of the INSTRON or ZWICK brand. The wires are pulled over an initial length between jaws of 400 mm at a nominal speed of 200 mm / min.

The expression of the test results depends on the wire tested: the test result can be either a single individual value or the average of 5 individual values.

The mechanical properties of the textile reinforcing elements are measured on a new tire.

According to a preferred embodiment of the invention, the module of the textile reinforcing elements is less than 30 Gpa.

More preferably, the elongation at break of the textile reinforcing elements is greater than 3.5% and more preferably still greater than 8%.

Advantageously according to the invention, the working crown layer is radially external to said at least one layer of circumferential reinforcing elements.

The results obtained with tires in accordance with the invention have effectively demonstrated that the performance in terms of endurance can be improved, in particular when driving on stony ground, the crown reinforcement of the tire being lightened. The lightening of the crown reinforcement of the tire is accompanied by a simplification of manufacturing and a reduction in manufacturing costs.

Against all expectations, the results have effectively demonstrated that the tires according to the invention can be lightened by reducing the number of layers making up the crown reinforcement while retaining or even improving the endurance properties of the crown of the tire especially with regard to shocks appearing on the tread, for example when driving on stony ground. It is in fact known to those skilled in the art that in order to improve the endurance performance of the crown reinforcement of a tire with regard to this type of impact, it is customary to increase the number of layers of reinforcing elements.

The inventors intend to interpret these results because of the angle formed with the circumferential direction by the reinforcing elements of the carcass reinforcement layer in the region of the crown of the tire, these functionally substituting for elements of a working top layer. It seems according to the inventors that it is thus possible that the carcass reinforcement layer plays the role of a working layer, the reinforcing elements of which would be crossed with the elements of the working crown layer in the crown area. the tire as provided by the tire according to the invention.

The inventors still note that it is possible to do without a protective layer. Such a layer is usually present in order to be sacrificed in the event of attacks by the tire of the cut type which may alter the integrity of metallic reinforcing elements by corrosion phenomena associated with the fatigue of said reinforcing elements. The inventors do make the observation that the reinforcing elements of the working crown layer, which is in a radially outermost position of a tire according to the invention, are less stressed when the tire is inflated or when it is use in normal driving as the reinforcing elements of a radially outermost working crown layer of a more usual tire on the one hand because of the presence of the layer of circumferential reinforcing elements and on the other hand due to the relatively low utilization ratio of the rupture potential F2 / FR2 compared to a conventional tire. The reinforcing elements of the working crown layer of a tire according to the invention thus have much higher endurance properties than those of a more common tire; the inventors thus make the observation that the removal of the protective layer is made possible and makes it possible to contribute to the lighter weight of the tire.

Regarding the layer of textile reinforcing elements, this gives an additional mass to the tire which is relatively negligible as regards the reinforcing elements. The inventors have been able to demonstrate that its presence within the tire has no functional effect during the use of the tire. The presence of this layer of textile reinforcing elements allows the reorientation of the reinforcing elements of the carcass reinforcement layer in the area of the top of the tire. During the manufacture of the tire, the reinforcing elements of the layer

-8 carcass reinforcement are initially oriented to form an angle between 80 ° and 90 ° with the circumferential direction. After the carcass reinforcement layer and the textile reinforcement elements have been laid and before the crown reinforcement has been placed, the tire blank thus formed is shaped to pass from a cylindrical structure to a toric structure. The inventors have shown that the presence of the textile reinforcing elements allows the local reorientation of the reinforcing elements of the carcass reinforcement layer during this shaping phase.

According to the invention, the layer of textile reinforcing elements can be radially external to the carcass reinforcement layer.

Advantageously according to the invention, the layer of textile reinforcing elements is radially internal to said layer of carcass reinforcement. According to such an advantageous embodiment of the invention and in particular to further limit the mass of the tire, the layer of textile reinforcing elements replaces one of the layers of elastomeric mixture which is usually located between the surface of the wall of the tire. tire cavity and carcass reinforcement. According to such an embodiment of the invention, the calendering layers of the layer of textile reinforcing elements advantageously consist of an elastomeric mixture which has the properties of the usual mixture layer for which it replaces. It may be an example of an elastomeric mixture which reacts with oxygen to limit the migration of the latter from the tire cavity to the metal reinforcing elements of the tire.

According to a preferred embodiment of the invention, the textile reinforcing elements of the layer of textile reinforcing elements are distributed with pitch between 1.4 and 3.0 mm. Such steps of distribution of the textile reinforcing elements make it possible to optimize the compromise between the action of the textile reinforcing elements to redirect the reinforcing elements of the carcass reinforcement layer in the region of the top of the tire during the phase of conformation during manufacture of the tire and the mass added to the tire.

Advantageously still according to the invention, the ratio of use of the F2 / FR2 breaking potential of the radially outermost working layer is less than 1/15.

Such a utilization ratio of the F2 / FR2 rupture potential further contributes to improving the

-9 endurance performance of the reinforcing elements of the radially outermost working layer when the tire is used.

According to a preferred embodiment of the invention, the average angle ocl formed by the reinforcing elements of the carcass reinforcement layer is greater than 75 ° on either side of the circumferential median plane in two parts axially inside the ends of the working layer and each of said two parts having an axial width of between 10 mm and 35 mm. More preferably, the mean angle al is greater than 82 ° on these two parts. The usual inflation pressures for HGV tires impose an orientation in the radial direction to the reinforcing elements of the carcass reinforcement layer at the shoulders of the tire and in particular when the working layer is no longer radially superimposed on the carcass reinforcement layer. It is therefore preferable to provide these two parts, which are similar to transition zones between the part of the carcass reinforcement layer centered on the equatorial plane and the parts of the carcass reinforcement layer present in the sidewalls. tire.

The axial width of the layer of textile reinforcing elements is thus advantageously narrower than the axial width of the working layer, with an axial width of between 14 and 80 mm. It is still advantageously narrower than the layer of circumferential reinforcing elements.

According to an advantageous alternative embodiment of the invention, said at least one layer of circumferential reinforcing elements has an axial width greater than 0.5xL.

L is the maximum axial width of the tire, when the latter is mounted on its service rim and inflated to its recommended pressure.

The axial widths of the layers of reinforcing elements are measured on a cross section of a tire, the tire therefore being in an uninflated state.

According to an advantageous embodiment of the invention, the reinforcing elements of said at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant module with 0.7% elongation between 10 and 120 GPa and a maximum tangent modulus less than 150

GPa.

According to a preferred embodiment, the module secing reinforcement elements at 0.7% elongation is less than 100 GPa and more than 20 GPa, preferably between 30 and 90 GPa and more preferably less than 80 GPa .

Also preferably, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and more preferably still less than 120 GPa.

The modules expressed above are measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa reduced to the metal section of the reinforcing element, the tensile stress corresponding to a measured tension reduced to the metal section of the reinforcing element.

The modules of the same reinforcement elements can be measured on a tensile stress curve as a function of the elongation determined with a preload of 10 MPa reduced to the overall section of the reinforcement element, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element. The overall section of the reinforcing element is the section of a composite element made of metal and rubber, the latter having notably penetrated the reinforcing element during the curing phase of the tire.

According to this formulation relating to the overall section of the reinforcing element, the reinforcing elements of the axially outer parts and of the central part of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant module with 0.7% elongation between 5 and 60 GPa and a maximum tangent module less than 75 GPa.

- n According to a preferred embodiment, the module secing reinforcement elements at 0.7% elongation is less than 50 Gpa and greater than 10 GPa, preferably between 15 and 45 GPa and more preferably less than 40 GPa.

Also preferably, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and more preferably still less than 60 GPa.

According to a preferred embodiment, the reinforcing elements of said at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a tensile stress curve as a function of the relative elongation having slight slopes for low elongations and a substantially constant and steep slope for higher elongations. Such reinforcing elements of the additional ply are usually called bimodule elements.

According to a preferred embodiment of the invention, the substantially constant and steep slope appears from a relative elongation of between 0.1% and 0.5%.

The different characteristics of the reinforcing elements set out above are measured on reinforcing elements taken from tires.

Reinforcement elements more particularly suitable for producing at least one layer of circumferential reinforcement elements according to the invention are, for example, assemblies of formula 21.23, the construction of which is 3x (0.26 + 6x0.23)

4.4 / 6.6 SS; this stranded cable consists of 21 elementary wires of formula 3 x (1 + 6), with 3 twisted strands together, each consisting of 7 wires, a wire forming a central core with a diameter equal to 26/100 mm and 6 wires wound from diameter equal to 23/100 mm. Such a cable has a 0.7% secant module equal to 45 GPa and a maximum tangent module equal to 98 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa reduced to the section of metal of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a pre-stress of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a

- 12 measured voltage reduced to the overall section of the reinforcing element, this cable of formula 21.23 has a secant module at 0.7% equal to 23 GPa and a maximum tangent module equal to 49 GPa.

In the same way, another example of reinforcing elements is an assembly of formula 21.28, the construction of which is 3x (0.32 + 6x0.28) 6.2 / 9.3 SS. This cable has a 0.7% secant module equal to 56 GPa and a maximum tangent module equal to 102 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa reduced to the section of metal of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a prestress of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element reinforcement, this cable of formula 21.28 has a 0.7% secant module equal to 27 GPa and a maximum tangent module equal to 49 GPa.

The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain stiffnesses of the satisfactory layer even after the shaping and baking steps in usual manufacturing processes.

According to a second embodiment of the invention, the circumferential reinforcing elements can be formed of inextensible metallic elements and cut so as to form sections of length much less than the circumference of the shortest layer, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset with respect to each other. More preferably still, the modulus of elasticity in traction per unit of width of the additional layer is less than the modulus of elasticity in traction, measured under the same conditions, of the layer of working crown most extensible. Such an embodiment makes it possible to confer, in a simple manner, on the layer of circumferential reinforcing elements a module which can easily be adjusted (by the choice of the intervals between sections of the same row), but in all cases lower that the layer module

- 13 made up of the same metallic but continuous elements, the modulus of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

According to a third embodiment of the invention, the circumferential reinforcement elements are corrugated metal elements, the ratio a / λ of the amplitude of ripple over the wavelength being at most equal to 0, 09. Preferably, the tensile elasticity modulus per unit of width of the additional layer is less than the tensile elasticity modulus, measured under the same conditions, of the most extensible working crown layer.

According to one embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metallic cables.

According to an advantageous embodiment of the invention, the working crown layer and said layer of circumferential reinforcing elements are the only layers present to constitute the crown reinforcement over at least 80% of the axial width of the top reinforcement. This advantageous embodiment of the invention goes in the direction of an even greater lightening of the tire.

According to other alternative embodiments of the invention shifting the compromise in performance of the tire in a less favorable manner as regards lightening, the crown reinforcement comprises an additional layer, called a protective layer, radially external to the working crown layers, preferably centered on the circumferential median plane. The reinforcing elements of such a protective layer are preferably so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle between 25 ° and 55 ° and in the same direction as the angle formed by the elements. reinforcement of the working layer. More preferably, the reinforcing elements of such a protective layer are parallel to the reinforcing elements of the working layer.

Other variants may also provide that the crown reinforcement can be completed between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of elements of

- 14 inextensible metallic steel reinforcement making, with the circumferential direction, an angle greater than 45 ° and in the same direction as that of the angle formed by the elements of the carcass reinforcement at the equatorial plane. According to a preferred embodiment according to these alternative embodiments, at the equatorial plane, the angle formed by the reinforcing elements of the triangulation layer with the circumferential direction the angle is greater than that formed by the reinforcing elements the carcass reinforcement layer with the circumferential direction. Advantageously, said triangulation layer consists of two half-layers positioned axially on either side of the circumferential median plane.

The tire according to the invention may also include one or more layers of additional circumferential reinforcing elements, advantageously consisting of two half-layers positioned axially on either side of the circumferential median plane.

Other advantageous details and characteristics of the invention will emerge below from the description of an exemplary embodiment of the invention with reference to the figure which represents a meridian view of a diagram of a tire according to a embodiment of the invention.

The figure is not shown to scale to simplify understanding. The figure represents only a half-view of a tire which extends symmetrically with respect to the axis XX ’which represents the circumferential median plane, or equatorial plane, of a tire.

In the figure, the tire 1, of dimension 12 R 22.5, has an aspect ratio H / L equal to 0.90, H being the height of the tire 1 on its mounting rim and L its maximum axial width. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not shown in the figure. The carcass reinforcement 2 is formed from a single layer of metal cables. They also have a tread 5.

In the figure, the carcass reinforcement 2 is hooped in accordance with the invention by a crown reinforcement 4, formed radially from the inside to the outside:

- 15 of a layer of circumferential reinforcing elements 41 formed of metal cables made of 21x28 steel, of the bi-module type, of a working layer 42 formed of metal cables oriented at an angle equal to 45 °.

The metal cables constituting the reinforcing elements of the layer of circumferential reinforcing elements are spaced from each other by 2 mm, according to the normal to the direction of the mean line of the cables.

The metal cables constituting the reinforcing elements of the working layer are cables of formula 9.35. They are distributed in the working layer with a distance between the reinforcing elements, measured according to the normal to the direction of the mean line of the cable equal to 2 mm and form an angle a2 with the circumferential direction equal to 45 °.

Radially under the carcass reinforcement 2, a layer of textile reinforcing elements 6 is arranged in accordance with the invention.

The textile reinforcing elements are PET cables (polyethylene terephthalate) of 144/2 title. They form an angle with the circumferential direction equal to 51 ° and are distributed with a distance between the reinforcing elements, measured according to the normal to the direction of the mean line of the cable equal to 2 mm.

Such cables have a module of 4.3 GPa and therefore less than 75 GPa.

Such cables have an elongation at break of 13% and therefore greater than

3.5%.

The tire is inflated to a pressure of 9 bars.

The axial width L of the layer of circumferential reinforcing elements is equal to 158 mm.

The axial width L ₄₂ of the working layer 42 is equal to 202 mm.

- 16 The axial width L _g of the layer of textile reinforcing elements 6 is equal to 146 mm.

The axial width of the tread L ₅ is equal to 215 mm.

The axial width L is equal to 302 mm.

The cumulative mass of the working layer 42 and the layer of circumferential reinforcing elements 41 and the layer of textile reinforcing elements 6, comprising the mass of cables and calendering mixtures, thus amounts to 6.9 Kg.

The angle al formed by the reinforcing elements of the carcass reinforcement layer 2 with the circumferential direction at the equatorial plane is equal to 70 °. The reinforcing elements of the carcass reinforcement layer 2 form this angle al over a width substantially equal to L ₆ .

The average angle a is equal to 58.9 ° and is well between 30 ° and 67 °.

Over a width 1, measured along the curvilinear abscissa of the carcass reinforcement layer, substantially equal to 29 mm, axially inside one end of the working layer 42, the mean angle ocl formed by the reinforcing elements of the carcass reinforcement layer 2 with the circumferential direction has a value equal to 83 °.

Beyond the end of the working layer 42, the mean angle al formed by the reinforcing elements of the carcass reinforcement layer 2 with the circumferential direction has a value greater than 88 °.

The measured value of Re is equal to 541.7 mm.

The measured value of Es is equal to 22.3 mm.

The average value RL of the radii measured is equal to 410 mm.

The calculated value of Qs is equal to 97.9 mm.

The value of F2 is equal to 94 N.

- 17 The breaking force of the reinforcing elements of the working crown layer FR2 is equal to 2600 N.

The utilization ratio of the F2 / FR2 rupture potential is equal to 3.6%.

The tire according to the invention is compared to a reference tire of the same dimension which differs from the tire according to the invention by the absence of the layer of textile reinforcing elements and its crown reinforcement formed radially from the inside to outside:

a triangulation layer, consisting of two half plies, formed of inextensible metallic cables 9.28 non-hooped, oriented at an angle equal to 65 °,

- a first working layer formed of metallic cables oriented at an angle equal to 26 °, a second working layer formed of metallic cables oriented at an angle equal to 18 ° and crossed with the metallic cables of the first working layer, the cables of each of the working layers being oriented on either side of the circumferential direction, with a protective layer formed of elastic metallic cables 6.35.

The metal cables of the two working layers are cables of formula 9.35. They are distributed in each of the working layers with a distance between the reinforcing elements, measured according to the normal to the direction of the mean line of the cable equal to 2.5 mm.

The reference tire is inflated to a pressure of 9 bars.

The overall axial width of the triangulation layer is equal to 180 mm, each of the half-plies having a width equal to 60 mm.

The axial width of the first working layer is equal to 220 mm.

The axial width of the second working layer is equal to 200 mm.

The axial width of the protective layer is equal to 136 mm.

- 18 The cumulative mass of the working layers of the reference tire, the protective layer and the triangulation layer, comprising the mass of the metallic cables and calendering mixtures, amounts to 10.0 Kg.

Tests were carried out with tires produced according to the invention in accordance with FIG. 1 and with the reference tire.

First endurance tests were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load of 3550 Kg gradually increased to reduce the duration of the test.

Other endurance tests were carried out on a test machine which cyclically imposed transverse force and dynamic overload on the tires. The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires.

The tests thus carried out have shown that the distances traveled during each of these tests are substantially identical for the tires according to the invention and the reference tires. It therefore appears that the tires according to the invention have performances substantially equivalent in terms of endurance to those of the reference tires when running on bituminous soils.

Tests aimed at characterizing the breaking strength of a tire crown reinforcement subjected to shocks were also carried out. These tests consist in rolling a tire, inflated to a recommended pressure and subjected to a recommended load, over a cylindrical obstacle or indentor with a diameter equal to 1.5 inches, or 38.1 mm, and of a determined height. The breaking strength is characterized by the critical height of the indentor, that is to say the maximum height of the indentor causing a total rupture of the crown reinforcement, that is to say of the rupture of all the top layers. The values express the energy necessary to obtain the rupture of the vertex block. The values are expressed from a base 100 corresponding to the value measured for the reference tire.

Reference 100 Invention 115

These results show that despite the tire being lightened by a reduction in the mass of its crown reinforcement, the energy at break during an impact on the surface of the tread is significantly higher.

Claims (8)

1 - Tire for heavy goods vehicle type, with carcass reinforcement consisting of a layer of metallic reinforcing elements oriented in a radial direction in the sidewalls of the tire, comprising a crown reinforcement comprising a working crown layer of metallic reinforcing elements forming with the circumferential direction an angle (a2) of between 25 ° and 55 °, said working crown layer being centered on the circumferential median plane, the crown reinforcement being radially capped with a tread , said tread being joined to two beads by means of two sides, characterized in that the crown reinforcement is completed by a layer of metallic circumferential reinforcing elements, in that, on a part centered on the circumferential median plane of axial width less than the width of said working crown layer, the reinforcing elements nt of said layer of the carcass reinforcement make with the circumferential direction an angle (al) such that the mean angle a defined by the relation Arctan ((tan (| ocl |) * tan (| oc2 |)) ^{1 / 2} ) is between 30 and 67 °, in that said angles a1 and a2 are oriented on either side of the circumferential direction, in that, radially inside the crown reinforcement, the tire comprises a layer of textile reinforcing elements whose secant modulus at 1% of extension is less than 75 GPa, in that the utilization ratio of the breaking potential F2 / FR2 of the working layer is less than 1/10 , in which : FR2 is the breaking force in uniaxial extension of the reinforcing elements of the working layer, expressed in N, F2 = 0.1 * P * Qs * p ₂ / [(sin (| oc2 |) + tan (| ocl |) * cos (| oc2)) * sin (| oc2 |)], with P: inflation pressure, expressed in a bar, Qs = (Rs ² -RF ² ) / (2 * Rs), p ₂ : the pitch of laying the reinforcing elements of the working crown layer, measured perpendicular to the reinforcing elements at the circumferential median plane, Rs = Re - Es, Re: outside radius of the tire measured at the radially outermost point on the surface of the tire tread, said surface being extrapolated to fill any gaps, -21 Es: radial distance between the radially outermost point of the tire and its orthogonal projection on the radially outer face of a reinforcement element of the working crown layer, RL: average of the radii of the axially outermost points on each side of the 5 pneumatic. 2 - A tire according to claim 1, characterized in that the working crown layer is radially external to the layer of circumferential reinforcing elements. 3 - A tire according to one of claims 1 or 2, characterized in that the layer of 10 working crown and said layer of circumferential reinforcing elements are the only layers present to constitute the crown reinforcement over at least 80% of the axial width of the crown reinforcement. 4 - A tire according to one of the preceding claims, characterized in that the layer of textile reinforcing elements is radially inside the carcass reinforcement. 15 5 - A tire according to one of the preceding claims, characterized in that the elongation at break of the textile reinforcing elements is greater than 3.5% and preferably greater than 8%. 6 - A tire according to one of the preceding claims, characterized in that the textile reinforcing elements of the layer of textile reinforcing elements are 20 distributed with pitch between 1.4 and 3.0 mm. 7 - A tire according to one of the preceding claims, characterized in that the utilization ratio of the F2 / FR2 breaking potential of the working layer is less than 1/15. 25 8 - A tire according to one of the preceding claims, characterized in that the ocl angle formed by the reinforcing elements of the carcass reinforcement layer is greater than 75 ° on either side of the circumferential median plane on two parts axially inside the ends of the working layer and in that each of said two parts has an axial width between 10 mm and 35 mm. -229 - A tire according to one of the preceding claims, characterized in that the reinforcing elements of the working crown layer are inextensible metallic cables. 10 - A tire according to one of the preceding claims, characterized in that the 5 reinforcing elements of said at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant module with 0.7% elongation between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa. 1/1