WO2019048762A1

WO2019048762A1 - Lightweight tyre

Info

Publication number: WO2019048762A1
Application number: PCT/FR2018/052144
Authority: WO
Inventors: William License; Patrick DAYET; Orel FOURNIER
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2017-09-06
Filing date: 2018-09-03
Publication date: 2019-03-14

Abstract

The invention relates to a tyre (1) for a heavy goods vehicle, which is designed to be mounted on a 15° drop centre-type hollow wheel rim (J). According to the invention, the two working crown layers (61, 62) and at least one layer (63) of circumferential reinforcing elements are all that are provided to form the crown reinforcement over at least 40% of the width of the tread (5), the absolute value of the difference between the absolute values of the angles α2 and α1 being greater than 7°, α2 being greater than α1 in terms of absolute value, the mean angle α satisfying the relationship 14+131*exp(-L/100) < α < 28+110*exp(-L/100) and, in a meridian section of the said tyre, the turn-up (7) of the carcass reinforcing layer and the main part (2) of the carcass reinforcing layer being the only layers of reinforcing elements with an elongation at break of less than 6% present in the sidewall.

Description

PNEUMATIC ALLEGE

The present invention relates to a tire, radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads and rolling at a high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] In general, in heavy-vehicle tires, the carcass reinforcement is anchored on both sides in the bead zone and is radially surmounted by a crown reinforcement consisting of at least two layers, superimposed and formed of son or parallel cables in each layer and crossed from one layer to the next in making with the circumferential direction angles between 10 ° and 45 °. Said working layers, forming the working armature, can still be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcing elements, called elastic elements. It may also comprise a layer of metal wires or cables forming with the circumferential direction an angle of between 45 ° and 90 °, this so-called triangulation ply being radially located between the carcass reinforcement and the first crown ply of 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 it undergoes, few deformations, the triangulation ply having the essential role of taking up the transverse compression forces of which the object all the reinforcing elements in the area of the crown 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 elastic when said cables have under tensile force equal to the breaking load a relative elongation of at least 3% with a maximum tangent modulus of less than 150 GPa. [0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the range + 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.

[0007] 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.

A radial or meridian plane is a plane which contains the axis of rotation of the tire. The circumferential mid-plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

As regards the metal wires or cables, the measurements of force at break (maximum load in N), tensile strength (in MPa), elongation at break (total elongation in%) and of module (in GPa) are made in traction according to the ISO 6892 standard of 1984.

As regards the rubber compositions, the modulus measurements are made in tension according to the AFNOR-NFT-46002 standard of September 1988: the secant modulus is measured in second elongation (ie, after an accommodation cycle). nominal (or apparent stress, in MPa) at 10% elongation (normal conditions of temperature and hygrometry according to AFNOR-NFT-40101 of December 1979).

During the manufacture of such tires, the last step is to bake the tire to allow the crosslinking and / or vulcanization of different constituent polymeric mixtures of the tire. This step of baking the tire is a a step that immobilizes the tire for several minutes and is considered as such a relevant step in relation to the productivity relating to the manufacture of a tire. In addition, this step which is done at a high temperature is energy consuming. These cooking times may also lead to having to increase the number of tools to avoid having to create temporary stocks of products waiting for their cooking, these stocks only increasing if the number of tools is not adapted. An increase in the number of cooking tools necessarily leads to additional costs due to machines, energy consumption and congestion. The duration of the cooking is in particular imposed by the time required to obtain constituent materials with the desired properties knowing that the crosslinking and / or vulcanization does not proceed in the same way for mixtures radially or axially apparent that for internal mixtures. In the same way, the crosslinking and / or vulcanization varies according to the nature and the thicknesses of the mixtures. The parts of the tire which have the largest thicknesses are on the one hand the top and more particularly the shoulders of the tire and on the other hand the areas of the beads of the tire.

The thickness of the crown of the tire is defined in particular by the number of layers of reinforcing elements which form the crown reinforcement of the tire, the thicknesses of the different layers of surrounding polymeric mixtures being adapted.

The thickness of the zones of the beads is defined by all the constituents of said zones which are layers of reinforcing elements and layers of polymeric mixtures, the increase in the number of layers of reinforcing elements leading to more often than not an increase in the number of layers of polymeric mixtures. The size of the bead wire, and more precisely its section, is more usually defined by the size and use of the tire and is not very variable for a given tire whatever the orientation chosen in terms of design of these bead areas.

It is known that those areas of the tire which are among the thickest consist of polymeric mixtures whose vulcanization times some are going to be among the longest because of their distance from heat sources. These areas of the tire which are among the thickest and require minimum vulcanization times for the overall baking of the tire.

On the other hand, some current tires, called "road", are intended to run at high average speeds and on longer and longer journeys, because of the improvement of the road network, the growth of motorway network in the world and the emergence of increasingly autonomous driving vehicles. The set of 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 the life expectancy in terms of kilometers, combined with the fact that such conditions of use are likely to result, under heavy load, in relatively high peak temperatures, require an at least proportional increase in the endurance potential of the crown of the tires.

There are indeed constraints at 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 crown. these crown layers result in the appearance and propagation of cracks in the rubber at said ends.

In order to improve the endurance of the tire crown reinforcement, the French application FR 2 728 510 proposes to have, on the one hand, between the carcass reinforcement and the reinforcing steel reinforcing ply. radially closest to the axis of rotation, an axially continuous sheet formed of non-extensible metal cables forming an angle of at least 60 ° with the circumferential direction, and whose axial width is at least equal to the axial width the shortest working crown ply, and secondly between the two working crown plies an additional ply formed of metal elements, oriented substantially parallel to the circumferential direction.

In addition, the 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, on a certain axial distance, the two working crown plies formed of reinforcing elements crossed from one ply to the next one and then decoupling them by rubber mixing profiles at least over the remainder of the width common to said two working plies.

In addition, certain uses of tires on vehicles for trucks such as "site approach" leads the tires to suffer shocks when driving on stony ground. These shocks are of course detrimental to performance in terms of endurance.

It is still known to those skilled in the art to increase the number of webs constituting the crown reinforcement to improve the endurance of the tire with respect to such shocks. Such tires usually still include at the beads one or more layers of reinforcing elements called stiffeners. These layers are usually made of reinforcing elements oriented relative to the circumferential direction of an angle less than 45 °, and usually less than 25 °. These reinforcing element layers have the particular function of limiting the longitudinal displacements of the constituent materials of the bead relative to the rim of the wheel to limit premature wear of said bead. They also make it possible to limit the permanent deformation of the bead on the rim hook, due to the dynamic creep phenomenon of the elastomeric materials. This deformation of the bead can prevent tire retreading when it is excessive. They further contribute to the protection of the beads of the tire against the aggressions suffered during the assembly and disassembly of the tires on the rims.

Furthermore, in the case of anchoring the carcass reinforcement made around a rod, which consists in winding at least part of the carcass reinforcement around a rod in each of the beads forming a reversal extending more or less in the sidewall, layers of reinforcing elements or stiffener further prevent or delay the unwinding of the carcass reinforcement during accidental and excessive heating of the rim.

These layers of reinforcing elements or stiffeners are most often arranged axially outside the overturning of the carcass reinforcement and extend. on a height in the upper flank to that of the upturn including to cover the free ends of the reinforcing elements of said reversal.

Such tire designs are for example described in FR 2779387 or US 2006/0000199.

The presence of these layers of reinforcing elements or stiffeners complicates the design of these areas of the beads of the tire. The presence of an additional layer on the one hand and its arrangement with respect to the overturning of the carcass reinforcement and the rod on the other hand lead to a design requiring additional rubber mixes to separate the ends of the layers and to ensure the desired positioning of the different ends.

Whatever one of these solutions as presented above, the presence of one or more layers of additional reinforcing elements leads to a larger mass of the tire and to higher tire manufacturing costs, on the one hand because of the additional layers and on the other hand because of longer cooking time.

It is also known to those skilled in the art that it may be desirable to modify the tire designs in particular for the purpose of improving performance in terms of rolling resistance leading to lightening of the tire.

Such lightening may concern the top but then care must be taken to maintain tire performance in terms of acceptable endurance.

The application WO2013053879 describes for example a tire whose crown reinforcement comprises a layer of circumferential reinforcing elements whose presence can reduce the number of layers of reinforcing elements and consequently the volume of polymeric mixtures or the size of the reinforcing elements of certain layers of reinforcing elements, in particular their diameter, and therefore the thicknesses of the polymer mixtures forming these layers. The lightening of the tire may still relate to the bead areas but again it must be ensured to maintain tire performance in terms of acceptable endurance.

It is for example known from the patent application WO 10/055118 to use carcass reinforcement cables strongly penetrated by polymeric mixtures, these being advantageously positioned within the cable during its manufacture, for to reduce the volumes of certain constituent polymeric mixtures of the tire or to remove layers of polymeric mixtures usually provided for protecting the reinforcing elements of the carcass reinforcement during the use of the tire. Such embodiments can help lighten the tires.

Such tire designs can lead to a reduction in the baking time of the tire to result in the good vulcanization of the polymeric mixtures ensuring the desired properties of the tire. This reduction in cooking time also leads to energy costs for the production of tires which can be reduced or even to an improved productivity due to the time of occupation of the reduced baking molds.

When the decreases in thickness concern both the crown area of the tire and the area of the beads of the tire, it must be ensured that the desired cooking times are well respected in each of the zones. It is for example known from US 4568259 structures of complex tire baking molds to allow different heat transfer depending on the areas of the tires. Such molds are complex to achieve and further lead to more expensive tire manufacturing processes.

It is also known to those skilled in the tire that it is possible to modify the time required for the polymerization of the mixtures by the addition of accelerator or vulcanization retarder. Such examples are for example described in the journals of the Techniques of the engineer "Rubber: methods of obtaining and properties" under reference AM7705 VI of January 10, 2015 from "Materials Plastics and Composites" by Yves Zélicourt and "Raw materials of rubber "under the reference AM8010 VI of December 10, 2016 from" Materials Plastics and Composites "by Claude Janin. It is thus possible to modify the polymer mixtures in the crown and the zones of the bead of the tire in order to adapt the times necessary for the polymerization, with the risk, however, of modifying the properties of the tires because of these constituents. In addition, the production costs may be increased, in particular because the mixtures will have to be adapted according to the size; this means that different polymeric mixtures must be manufactured and stored in order to achieve different tire sizes.

The inventors have thus given themselves the mission of designing lightened tires whose performance including endurance are preserved and whose manufacturing costs are reduced.

This object is achieved according to the invention by a tire for heavy vehicle type vehicle, intended to be mounted on a hollow rim type 15 ° drop center, radial carcass reinforcement, consisting of a single layer of carcass reinforcement formed of reinforcement elements inserted between two polymer blend calendering layers, said tire comprising a crown reinforcement comprising two working crown layers of reinforcement elements crossed from one web to another by making with the circumferential direction of the angles (a1, a2) greater than 8 °, said angles a1 and a2 being oriented on either side of the circumferential direction, and at least one layer of circumferential reinforcing elements, the crown reinforcement being capped radially with a tread, said tread being joined to two beads by means of two sidewalls, the layer of reinforcing elements of the armature re carcass being anchored in each of the beads by turning around a bead wire to form a reversal of the carcass reinforcement, said overturning of the carcass reinforcement being separated from the carcass reinforcement by a first layer of mixture ( s) polymer (s) extending radially from the bead wire to at least the end of the upturn and said overturning of the carcass reinforcement being axially outwardly in contact with a second layer of polymeric mixture, itself even at least in contact with a third layer of polymeric mixture forming the outer surface of the tire in the region of the bead, said third layer of polymeric mixture being intended in particular to come into contact with the rim, said third layer of polymeric mixture being radially outwardly in contact with a fourth layer of polymeric mixture forming the outer surface of a flank: the two working crown layers and said at least one layer of circumferential reinforcing elements being only present to constitute the crown reinforcement over at least 40% of the axial width of the crown reinforcement,

- The reinforcing elements of the radially outermost working layer forming an angle a2 with the circumferential direction higher in absolute value than the angle α1 formed by the reinforcing elements of the radially innermost working layer with the circumferential direction the absolute value of the difference between the absolute values of the angles a2 and al being greater than 7 °,

the average angle a satisfying the relation:

14 + 131 * exp (-L / 100) <a <28 + 110 * exp (-L / 100), a being defined by the relation Arctan ((tan (| al |) * tan (| a2 |)) ^{1 / 2} ), where L is the maximum width of the tire measured in the axial direction and expressed in mm,

in a meridian section of said tire, the radially outer end of the first layer of polymeric mixture (s) being radially external to the end of the upturn of the carcass reinforcement layer,

in a meridian section of said tire, the radially outer end of the second layer of polymeric mixture being radially external to the end of the upturn of the carcass reinforcement layer,

in a meridian section of said tire, the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the rod being between 25 and 40% of the distance between the point axially the outermost of the main portion of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the rod,

in a meridian section of said tire, said first layer of polymeric mixture (s) having a thickness, measured in the normal direction to the reinforcing elements of the main part of the carcass reinforcement layer and passing through the end of the upturn of the carcass reinforcement layer between 30 and 60% of the distance between the reinforcing elements of the main part of the carcass reinforcement layer and the external surface of the tire measured in the direction of measurement of the carcass reinforcement layer. the thickness of the first layer of polymer mixture (s) passing through the end of the upturn of the carcass reinforcement layer, in a meridian section of said tire, the ratio of the distance between the reinforcing elements of the main portion of the carcass reinforcement layer and the external surface of the tire measured along said measurement direction of the thickness of the first layer; polymeric mixture (s) passing through the end of the upturn of the carcass reinforcement layer over the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribed to the rod being less than 0.5,

the overturning of the carcass reinforcement layer and the main part of the carcass reinforcement layer being the only layers of reinforcing elements whose elongation at break is less than 6% present in a zone of the sidewall constituting at least 90% of the sidewall surface radially between the end of the upturn of the carcass reinforcement layer and the radially outermost point of the bead wire,

the tensile modulus of elasticity at 10% elongation of the first and second polymeric mixture layers being less than or equal to the modulus of elasticity under tension at 10% of elongation of the calendering of the reinforcing layer of carcass and greater than or equal to 30% of the modulus of elasticity under tension at 10% of elongation of the calender of the carcass reinforcement layer.

Within the meaning of the invention, a hollow rim type 15 ° drop center or wedged seat rim is a monobloc rim, as defined in the ETRTO, whose seats for receiving the beads of the tire have a shape frustoconical, the angle formed with the axial direction being substantially equivalent to 15 °. These seats are also extended by hooks de rim rim of reduced height compared to hooks flat base rims whose rim seats have substantially cylindrical shapes.

The width L and the different radii are measured on a tire mounted on its nominal rim and inflated to its nominal pressure, and are expressed in millimeters.

The angles a1 and a2, expressed in degrees, are also measured on a section of the tire. The angle measurements are according to the invention made at the circumferential mid-plane.

Advantageously, the angle α1 of the radially innermost working layer is less than 20 ° to ensure a better transition with the layer of circumferential reinforcing elements. The position of the axially outermost point of the main portion of the carcass reinforcement layer is determined on a tire mounted and inflated according to the nominal conditions. This measurement can for example be performed using a tomography technique. The positions of the radially innermost and radially outermost points of the circle circumscribing the rod are determined on a section of a tire, the spacing of the beads of which is the same as when the tire is mounted on the rim. recommended by ETRTO, as it is neither mounted nor inflated. The distance between the axially outermost point of the main portion of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the rod is measured on a tire mounted and inflated according to the nominal conditions. This measurement can be performed for example according to a tomography technique. The other distances, in particular measured from the radially innermost point of the circle circumscribing the rod, may also be measured according to a tomography technique or are measured on a section of a tire, the spacing of the beads of which is the same as when the tire is mounted on the mounting rim recommended by the ETRTO, which is neither mounted nor inflated. Within the meaning of the invention, the first layer of polymer (s) mixture (s) may consist of several polymeric mixtures whose stiffness properties and more specifically whose tensile modulus of elasticity at 10% of lengthening may vary. In the case of several polymeric mixtures constituting the first layer, they advantageously form a gradient of decreasing stiffness from the bead wire towards the radially outer end of said first layer.

Advantageously, the tire according to the invention is intended to be inflated to an inflation pressure P greater than or equal to 6.5 bar.

Preferably according to the invention, said at least one layer of circumferential reinforcing elements is continuous axially and preferably still centered on the circumferential median plane. Preferably according to the invention, the reinforcing elements of said two working crown layers are metallic.

The inventors have demonstrated that a tire thus produced according to the invention can be manufactured at a lower cost compared to usual practices. It is for example possible to reduce the cooking time of said tire for temperature and pressure conditions given in the baking mold.

The tire thus defined according to the invention actually has in comparison with more conventional tires both a top and lightened areas of beads whose cooking times necessary to obtain the desired properties are substantially equivalent for the top and the bead areas and less than the cooking times of the more usual tires. This reduction in cooking times is related to the better temperature rise of the polymer blends due to the lower thicknesses.

The tire thus defined according to the invention reduces the cooking time without the need for an adaptation of one or the other of the polymer mixtures to reduce or increase the time required for vulcanization which furthermore would be different depending dimensions of the tire. Nor is it necessary to design complex and expensive molds with different materials to obtain locally varying and once again specific thermal conductivities in terms of design as a function of tire size.

Moreover, the lightening of the crown reinforcement and the areas of the bead of the tire is accompanied by a simplification of manufacture and a reduction in manufacturing costs.

Against all expectations, the results have indeed shown that the tires according to the invention can be reduced by reducing the number of constituent layers of the crown reinforcement while maintaining or even improving the endurance properties of the tire crown. in particular against shocks occurring on the tread for example when driving on stony ground. It is indeed known to those skilled in the art that to improve the endurance performance of the crown reinforcement of a tire with respect to this type of shock, it is customary to increase the number of layers of reinforcing elements.

The inventors think to interpret these results because of the angle formed with the circumferential direction by the reinforcing elements of the radially innermost working crown layer which is smaller in absolute value than that formed by the elements of reinforcing the radially outermost working crown layer. They found that this smaller angle seems to cause a delay in the tensioning by the reinforcing elements during such an impact. Usually, during shocks comparable to those observed during a taxiing on stony ground the breaking of reinforcing elements if it occurs is observed on the radially innermost layer. These findings seem to indicate that in the face of this type of attack, the difference in angle of the reinforcing elements between the two working crown layers makes it possible to improve the endurance performance of the tire while reducing the number of layers of the tire. crown frame. Advantageously according to the invention, the utilization ratio of the fracture potential F 2 / FR 2 of the radially outermost working layer being less than 1/6, in which:

FR2 is the force in uniaxial extension of the cables of the radially outermost working layer, F2 = p ₂ * Te * [(tan (| al |) / (tan (| al |) + tan (| a2 |) )) / cos ² (| a2 |) + C _F ], with

Te = 0.078 * P * Rs * (l- (Rs ² -RL ² ) / (2 * Rt * Rs)),

P: the inflation pressure of the tire, expressed in bar,

C _F = 0.00035 * (min ((L-80) / sin (| al |), (L-80) / sin (| a2 |), 480) -480), p ₂ : the laying pitch of the elements of reinforcing the radially outermost working crown layer, measured perpendicularly to the reinforcing elements at the circumferential mid-plane,

Rs = Re - Es,

Re: outer radius of the tire measured at the radially outermost point on the surface of the tread of the tire, said surface being extrapolated to fill any cavities, Es: radial distance between the radially outermost point of the tire and its orthogonal projection on the radially outer face of a reinforcing element of the radially innermost working crown layer,

RL: average of the radii of the axially most outlying points of the main part of the carcass reinforcement layer on each side of the tire,

Rt: the radius of the circle passing through three points on the outer surface of the tread outside the troughs, defined from a shoulder end at respective axial distances equal to ¼, ½ and ¾ of the width axial of the tread.

The thickness Es and the pitch p ₂ are measured on a section of the tire and are expressed in millimeters.

The inventors further note that the choice of the absolute value of the difference between the absolute values of the above-mentioned angles α1 and α2 associated with the average angle α and the utilization ratio of the rupture potential F2 / FR2 such as that defined according to this advantageous embodiment of the invention may allow to eliminate the protective layer usually placed radially outside the other layers of the crown reinforcement. Such a layer is usually present to be sacrificed in the event of an attack of the tire-type cuts that can alter the integrity of metal reinforcing elements by corrosion phenomena associated with the fatigue of said reinforcing elements. The inventors actually observe that the reinforcement elements of the radially outermost working crown layer, of a tire according to the invention, are less stressed during inflation of the tire or during its use in normal running than the reinforcing elements of a radially outermost working crown layer of a more usual tire; such a more usual tire has an angle of the reinforcing elements of the radially innermost working layer greater than or equal in absolute value to that of the reinforcing elements of the radially outermost working layer, a utilization ratio of higher fracture potential F2 / FR2 and most often absolute differences in angles between the reinforcement elements of the different smaller working layers. The reinforcing elements of the radially outermost working crown layer of a tire according to the invention thus have endurance properties which are much greater than those of a more usual tire; the inventors thus make the observation that the removal of the protective layer is made possible and can contribute to the lightening of the tire. In addition, the presence of said at least one layer of circumferential reinforcing elements allows a mean angle to reinforcing elements of the two working crown layers greater than the average angle defined by the reinforcing elements of the two top layers. working in the more usual tires. Indeed, the circumferential stiffness provided by the presence of said at least one layer of circumferential reinforcing elements makes it possible to increase the angles formed by the reinforcing elements of each of the working crown layers with the circumferential direction, said angles seeming thus favoring the operation of the tire and particularly its maneuverability during driving under heavy loads or with an angle formed with the very important direction of advance. The inventors have thus been able to demonstrate that the dynamic properties of the tire, in particular the rigidity of drift, are preserved or even improved whatever the use. According to a preferred embodiment of the invention, the absolute value of the difference between the absolute values of the angles α 2 and α 1 is greater than or equal to 10 ° and preferably greater than 14 °. According to this embodiment, and in accordance with the interpretations given above, it will be possible to further improve the endurance performance of the reinforcing elements of the radially outermost working layer and / or to further improve the performance of the tire. with regard to shocks such as those suffered while taxiing on stony ground.

[0065] Preferably, the absolute value of the difference between the absolute values of the angles a2 and a1 is less than 25 ° and more preferably less than 20 °. Beyond these values, the tire could be subject to irregular wear under certain conditions of use.

[0066] More preferably according to the invention to further improve the performance of the tire with respect to shocks such as those experienced while driving on stony ground, the average angle has satisfied the relationship: a> 20 + 164 * exp (-L / 100).

Advantageously again according to the invention, the utilization ratio of the fracture potential F2 / FR2 of the radially outermost working layer is less than 1/8. Such a ratio of utilization of the rupture potential F2 / FR2 further contributes to improving the endurance performance of the reinforcing elements of the radially outermost working layer when using the tire.

Preferably, according to the invention, the utilization ratio of the fracture potential F1 / FR1 of the radially innermost working layer is less than 1/3, in which: FR1 is the breaking force in uniaxial extension of the cables from the radially innermost working layer,

Fl = pi * Te * [(tan (| a2 |) / (tan (| al |) + tan (| a2 |))) / cos ² (| al |) + C _F ], with pi: the step of placing reinforcing elements of the radially innermost working crown layer, measured perpendicularly to the reinforcing elements at the circumferential mid-plane.

More preferably, the utilization ratio of the fracture potential F1 / FR1 of the radially innermost working layer is at least 30% greater than the utilization ratio of the fracture potential F 2 / FR 2 of the radially the most external work. According to one embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

According to an advantageous embodiment of the invention, the two working crown layers and said at least one layer of circumferential reinforcing elements are only present to constitute the crown reinforcement on at least 60% of the axial width of the crown reinforcement and advantageously still at least 80% of the axial width of the crown reinforcement. These advantageous embodiments of the invention go in the direction of an even greater relief of the tire.

According to a preferred embodiment of the invention, optimizing the thinning of the crown of the tire, the two working crown layers and the said at least one layer of circumferential reinforcing elements are only present to constitute the reinforcement. vertex over the entire axial width of the crown reinforcement. According to an advantageous embodiment of the invention, said at least one layer of circumferential reinforcing elements has an axial width greater than 0.5xL.

The axial widths of the reinforcing element layers are measured on a cross section of a tire, the tire therefore being in a non-inflated state.

According to a preferred embodiment of the invention, the two working crown layers have different axial widths, the difference between the axial width of the axially widest working crown layer and the axial width of the working layer. axially the axially the least wide working vertex being between 10 and 30 mm.

According to a preferred embodiment of the invention, said at least one layer of circumferential reinforcing elements is radially disposed between two working crown layers.

According to this embodiment of the invention, said at least one layer of circumferential reinforcement elements makes it possible to limit more significantly the compression of the reinforcement elements of the carcass reinforcement than a similar layer. placed radially outside the working layers. It is preferably radially separated from the carcass reinforcement by at least one working layer so as to limit the stresses of said reinforcing elements and do not strain them too much.

Advantageously again according to the invention, the axial widths of the working crown layers radially adjacent to said at least one layer of circumferential reinforcing elements are greater than the axial width of said at least one layer of reinforcing elements. circumferentially and preferably, said working crown layers adjacent to said at least one layer of circumferential reinforcing elements are on either side of the equatorial plane and in the immediate axial extension of said at least one layer of circumferential reinforcement coupled over an axial width, to be subsequently decoupled by a layer of rubber mixture at least over the remainder of the width common to said two working layers. Within the meaning of the invention, working crown layers are said to be coupled if the respective reinforcing elements of each of the layers are separated radially by a distance less than the mean diameter of the circle circumscribed to the reinforcing elements, said thickness of rubber being measured radially between the respectively radially upper and lower generatrices of said reinforcing elements.

The average diameter of the circle circumscribing the reinforcing elements is defined as the average diameter of the circles circumscribed to the reinforcing elements of each of the working crown layers. The presence of such couplings between the working crown layers adjacent to said at least one layer of circumferential reinforcing elements makes it possible to reduce tension stresses acting on the axially outermost circumferential elements and located on the circumferential element. closer to the coupling.

The thickness of the decoupling profiles between the working crown layers, axially external to the coupling zone, measured at the ends of the least wide working ply, will be at least equal to two millimeters, and preferentially greater than 2.5 mm.

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

According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 100 GPa and greater 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 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. brought back to the metal section of the reinforcing member, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing member.

The modules of the same reinforcing elements can be measured 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 voltage brought back 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 in particular penetrated the reinforcing element during the baking phase of the tire.

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

According to a preferred embodiment, the secant modulus of the reinforcing 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 less than 60 GPa.

According to a preferred embodiment, the reinforcing elements of said at least one layer of circumferential reinforcing elements are metal reinforcing elements having a tensile stress curve as a function of the relative elongation having slight slopes to the low elongations and a substantially constant and strong slope for the higher elongations. Such reinforcing elements of the additional ply are usually referred to as "bi-module" elements.

According to a preferred embodiment of the invention, the substantially constant and strong slope appears from a relative elongation of between 0.1% and 0.5%. The various characteristics of the reinforcing elements mentioned above are measured on reinforcing elements taken from tires.

Reinforcement elements more particularly adapted to the production of at least one layer of circumferential reinforcing 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 strand cable consists of 21 elementary wires of formula 3 x (1 + 6), with 3 twisted strands each consisting of 7 wires, a wire forming a central core of diameter equal to 26/100 mm and 6 coiled wires of diameter equal to 23/100 mm. Such a cable has a secant module at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa brought back to the section. of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a preload of 10 MPa brought back to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the overall section of the element of reinforcement, this cable of formula 21.23 has a secant module at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

In the same way, another example of reinforcement 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 secant module at 0.7% equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, measured on a tensile stress curve as a function of the elongation determined with a preload of 20 MPa brought to the cross section. metal of the reinforcing element, the tensile stress corresponding to a measured voltage brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a preload of 10 MPa brought back to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the overall section of the element of reinforcement, this cable of formula 21.28 has a secant module at 0.7% equal to 27 GPa and a maximum tangent modulus 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 satisfactory layer stiffness even after the shaping and baking steps in conventional manufacturing processes. According to a second embodiment of the invention, the circumferential reinforcing elements may be formed of inextensible metal elements and cut so as to form sections of length much shorter than the circumference of the least long layer, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset with respect to each other. More preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working crown layer. Such an embodiment makes it possible to confer, in a simple manner, on the layer of circumferential reinforcement elements a module which can easily be adjusted (by the choice of intervals between sections of the same row), but in all cases weaker. the module of the layer consisting of the same metallic elements but continuous, the module 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 reinforcing elements are corrugated metal elements, the ratio a / λ of the waviness amplitude over the wavelength being at most equal to 0, 09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is smaller than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working crown layer. The tests carried out have furthermore shown that the zones of the beads of the tires thus produced according to the invention contribute to a decrease in the mass of the tires in comparison with tires of more conventional design, comprising, for example, layers of reinforcement type stiffeners, and have performance in terms of endurance of the bead zones, at least as good as those of said tires of more conventional design or higher. These results are all the more surprising that the tires according to the invention comprise a reversal of the carcass reinforcement layer whose end is in a relatively thin region of the bead in comparison with more design tires. usual. Indeed, it is customary to design tires with a relatively thick bead at the end of the upturn of the carcass reinforcement layer to increase the distance between the overturning of the carcass reinforcement layer and the main part. of the carcass reinforcement layer, and thus to best limit the shear stresses which are initiated between the main part of the carasse reinforcement layer and its reversal, in particular due to the de-axialization phenomena which appear during the rolling of the pneumatic.

The inventors have thus been able to demonstrate that the tires produced in accordance with the invention and which have in particular one end of the upturn of the carcass reinforcement layer in a relatively thin zone of the bead associated with the relative sizing and positioning of the various components of the bead area of the tire, allow to reduce the tire and against all odds to maintain properties in terms of endurance satisfactory, or even improve.

According to an advantageous embodiment of the invention, the first layer of polymer mixture (s) and / or the second layer of polymeric mixture comprise a reinforcing filler constituted by at least one white filler of silica type and and / or alumina comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or alternatively modified carbon blacks during or after synthesis. According to a preferred embodiment of the invention, said first layer of polymeric mixture (s) and / or second polymeric mixture layers are elastomeric mixtures based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages and possibly at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in case of cutting being present at a majority rate relative to the rate of the other diene elastomer or diene elastomers used and a reinforcing filler consisting of: a) either with a white filler of silica and / or alumina type comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or else modified carbon blacks during or after the synthesis, BET specific surface area between 30 and 260 m ² / g employed at a rate of between 20 and 80 phr, and preferably between 30 and 50 phr, b) by a cutting of a load blank described in (a) and carbon black, wherein the overall charge rate is between 20 and 80 phr, and preferably between 40 and 60 phr, the silica level on the overall charge rate being greater than 80 % and preferably greater than 90%.

BET specific surface measurement is performed according to the method of BRUNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938, corresponding to standard NFT 45007 of November 1987. [00105] In the case of using a clear charge or a white charge, it is necessary to use a coupling and / or recovery agent chosen among agents known to those skilled in the art. Examples of preferential coupling agents that may be mentioned are sulphurised alkoxysilanes of the bis (3-trialkoxysilylpropyl) polysulfide type, and of these, in particular, bis (3-triethoxysilylpropyl) tetrasulfide marketed by DEGUSSA under the Si69 denominations for pure liquid product and X50S for solid product (50/50 by weight blend with N330 black). Examples of coating agents that may be mentioned include a fatty alcohol, an alkylalkoxysilane such as hexadecyltrimethoxy or triethoxysilane respectively marketed by DEGUSSA under the names Sil16 and Si166, diphenylguanidine, a polyethylene glycol, a silicone oil which may be modified with OH or alkoxy functions. The covering agent and / or coupling agent is used in a weight ratio relative to the filler> at 1/100 and ≤ at 20/100, and preferably between 2/100 and 15/100 when the clear filler represents the all of the reinforcing filler and between 1/100 and 20/100 when the reinforcing filler is constituted by a carbon black and clear charge cutting. As other examples of reinforcing fillers having the morphology and the SiOH and / or AlOH surface functions of the silica and / or alumina materials previously described and that can be used according to the invention as partial or total replacement thereof , the modified carbon blacks may be mentioned either during the synthesis by addition to the furnace feed oil of a silicon and / or aluminum compound or after the synthesis by adding, to an aqueous suspension of carbon black in a solution of silicate and / or sodium aluminate, an acid so as to at least partially cover the surface of the carbon black of SiOH and / or AlOH functions. As non-limiting examples of this type of carbonaceous feedstock with SiOH and / or AlOH functions at the surface, mention may be made of the CSDP type feeds described in Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, California, May 6-9. 1997 as well as those of the patent application EP-A-0 799 854. As other non-limiting examples, mention may be made of the charges marketed by Cabot Corporation under the name EcoblackTM "CRX 2000" or "CRX4000", or else the fillers described in US2003040553, WO9813428; such a reinforcing filler preferentially contains a silica content of 10% by weight of the reinforcing filler.

When a clear filler is used as the sole reinforcing filler, the hysteresis and cohesion properties are obtained by using a precipitated or pyrogenic silica, or a precipitated alumina or even a BET specific surface alumino-silicate between 30 and 260 m ² / g. As non-limiting examples of this type of filler, mention may be made of the silicas KS404 from Akzo, Ultrasil VN2 or VN3 and BV3370GR from Degussa, Zeopol 8745 from Huber, Zeosil 175MP or Zeosil 1165MP from Rhodia, HI -SIL 2000 of the PPG Company etc.

Among the diene elastomers that can be used in a blend with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 linkages, mention may be made of a polybutadiene (BR), preferably with a majority of cis-1 linkages, 4, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers may be modified elastomers during polymerization or after polymerization by means of branching agents such as divinylbenzene or starch agents such as carbonates, halogenotins, halosilicons or else by means of functionalization leading to grafting on the chain or at the end oxygenated carbonyl, carboxyl or an amine functional chain such as for example by the action of dimethyl or diethylamino benzophenone. In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages with one or more of the diene elastomers mentioned above, the natural rubber or the synthetic polyisoprene is preferably used at a majority rate. and more preferably at a rate greater than 70 phr.

[00109] Said first and / or second layers of polymeric mixture thus formed impart greater rigidity to the more usual designs which make it possible to provide the tire bead regions with satisfactory bending stiffnesses in combination with the thicknesses of these areas which are reduced. compared to those of more usual tires.

[00110] Said first and / or second layers of polymeric mixture thus formed still have properties in terms of cohesion and thus improved resistance to cracking in comparison with more usual designs. The endurance properties of the areas of the beads of the tire are thus further strengthened.

For the purposes of the invention, a cohesive rubbery mixture is a rubbery mixture particularly resistant to cracking. The cohesion of a mixture is thus evaluated by a fatigue cracking test performed on a specimen "PS" (pure shear). It consists in determining, after notching the specimen, the crack propagation speed "Vp" (nm / cycle) as a function of the energy release rate "E" (J / m ² ). The experimental area covered by the measurement is in the range -20 ° C and + 150 ° C in temperature, with an air or nitrogen atmosphere. The biasing of the specimen is a dynamic displacement imposed amplitude ranging between 0.1mm and 10mm in the form of impulse-type stress (tangential "haversine" signal) with a rest time equal to the duration of the pulse; the frequency of the signal is of the order of 10 Hz on average.

[00112] The measurement comprises 3 parts:

• An accommodation of the "PS" test tube, from 1000 cycles to 27% deformation. • an energetic characterization to determine the law "E" = f (deformation). The energy release rate "E" is equal to W0 * h0, with WO = energy supplied to the material per cycle and per unit volume and hO = initial height of the test piece. The exploitation of acquisitions "force / displacement" thus gives the relation between "E" and the amplitude of the solicitation.

• The measurement of cracking, after notching of the "PS" test piece. The information collected leads to determining the propagation velocity of the crack "Vp" as a function of the imposed stress level "E".

According to a preferred embodiment of the invention, said first and second polymeric mixture layers are made with identical polymer mixtures, and preferably comprising a reinforcing filler consisting of at least one white filler of silica type and / or alumina comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or alternatively modified carbon blacks during or after synthesis.

According to a preferred embodiment of the invention, the modulus of elasticity under tension at 10% elongation of the calendering layers of the carcass reinforcement layer is between 4 and 16 MPa and preferably between 8 and 12 MPa. These values make it possible in particular to define the desired compromise between the endurance performance of the area of the beads of the tire and its performance in terms of rolling resistance. These values also allow, in the case of a crown reinforcement consisting solely of the two working layers, to ensure better cohesion between the crown reinforcement and the carcass reinforcement.

Advantageously according to the invention, the radially inner end of the second polymeric mixture layer is radially between the radially outermost point of the circle circumscribing the bead wire and the radially innermost point of the circle circumscribing the bead wire. . This positioning is determined on a section of a tire, the spacing of the beads is the same as when the tire is mounted on the mounting rim recommended by the ETRTO, it being neither mounted nor inflated. Advantageously again according to the invention, the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the bead wire is between 31 and 37% of the distance between the axially outermost point of the main part of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the bead wire.

According to an advantageous embodiment of the invention, in any meridian plane, in each bead, the tire comprises a compression frame surrounding the rod and a rubber mix volume directly in contact with the rod. Such a compression reinforcement allows during the use of the tire to limit the changes in shape of the rod and thus to maintain performance including satisfactory endurance. Indeed, the tire according to the invention whose structure leads to its lightening could, in some cases of use or types of rolling, lead to a geometric evolution in the bead area potentially harmful to the performance in terms of tire endurance . The presence of a restraining frame as proposed makes it possible to delay or even prevent such a geometrical evolution. Advantageously again according to the invention, the compression reinforcement consists of a layer of textile reinforcing elements of aliphatic polyamide type. Advantageously according to the invention, the rods are bundles bundles, that is to say, rods formed of an assembly of gummed son wrapped around a shape, preferably of hexagonal shape.

According to one embodiment of the invention, in particular to further improve the performance in terms of endurance of the tire, the carcass reinforcement is formed of cables whose structure is strongly penetrated by polymeric mixtures. They may for example be cables whose construction makes it possible to increase their penetrability by the polymeric mixtures. It can also be cables in which polymeric mixtures are inserted during the manufacture of the cables themselves. It is then for example cables with at least two layers, at least one inner layer being sheathed a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

According to other embodiments of the invention shifting the tire performance compromise less favorably as regards the lightening and the cooking / vulcanization time, the crown reinforcement comprises an additional layer, so-called protection, radially external to the working crown layers, preferably centered on the circumferential mid-plane. The reinforcing elements of such a protective layer are preferably so-called elastic reinforcing elements, oriented with respect to the circumferential direction with an angle of between 8 ° and 45 ° and in the same direction as the angle formed by the elements. reinforcing the working layer which is radially adjacent thereto. More preferably, the reinforcing elements of such a protective layer are parallel to the reinforcing elements of the working layer which is radially adjacent thereto.

Other variants may also provide that the crown reinforcement may be completed between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of elements of the carcass reinforcement. inextensible steel metal reinforcing making, with the circumferential direction, an angle greater than 45 ° and in the same direction as that of the angle formed by the reinforcing elements of the radially closest layer of the carcass reinforcement. Advantageously, said triangulation layer consists of two half-layers positioned axially on either side of the circumferential mid-plane.

Other details and advantageous features of the invention will emerge below from the description of the embodiments of the invention, in particular with reference to FIGS. 1 to 2 which represent: FIG. 1, a meridian view of a FIG. 2 shows an enlarged schematic representation of the zone of the bead of the tire of FIG. 1.

The figures are not shown in scale to simplify understanding. Figure 1 shows only a half-view of a tire which is extended symmetrically with respect to the axis XX 'which represents the circumferential mid-plane or equatorial plane of a tire.

[00126] Figure 1 illustrates a tire 1 of size 385/65 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads. The carcass reinforcement 2 formed of a single layer of metal cables, is wound in each of the beads 3 around a bead wire 4 and forms in each of the beads 3 a carcass reinforcement upturn 7 having an end 8. pneumatic tire still has a tread 5.

In Figure 1, the carcass reinforcement 2 is shrunk according to the invention by a crown reinforcement 6, formed radially from the inside to the outside: a first working layer 61 formed of cables 16 ° oriented metal, a layer of circumferential reinforcing elements 63 formed of 21x28 steel cables, of "bi-module" type, a second working layer 62 formed of metal cables oriented at an angle equal to 34 °, crossed with the metal cables of the first working layer 61, the cables of each of the working layers 61, 62 being oriented on either side of the circumferential direction.

The metal cables constituting the reinforcing elements 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 average line of the cable equal to 2.2 mm.

The metal cables constituting the reinforcing elements of the layer of circumferential reinforcing elements are spaced from each other by 2.4 mm, depending on the normal direction of the average line of the cables.

The tire is inflated to a pressure of 9 bar.

[00131] The axial width L of the first working layer 61 is equal to 295 mm. The axial width L _g2 of the second working layer 62 is equal to 276 mm.

The axial width L _g3 of the layer of circumferential reinforcing elements 63 is equal to 200 mm.

The axial width of the tread L ₅ is equal to 309 mm. [00135] The axial width L is equal to 384 mm.

The difference between the angles formed by the cables of the first working crown layer 61 with the circumferential direction and those of the cables of the second working crown layer 62 is equal to 18 °.

The average angle is equal to 23.7 ° and is well between 16.8 ° and 30.4 °.

[00138] The measured value of Re is equal to 533 mm.

The measured value of Es is equal to 20.3 mm.

The average value R _L of the measured rays is equal to 408 mm.

The value Rt determined on the tire is equal to 1145 mm.

The calculated value of Te is equal to 330.4 N / mm.

The calculated value of C _F is equal to 0.

The value of Fl is equal to 627.2 N.

The value of F2 is equal to 358.5 N.

The breaking forces of the reinforcing elements of the working crown layers FR1 and FR2 are equal to 2600 N.

The utilization ratio of the rupture potential F2 / FR2 is equal to 12.1%.

The utilization ratio of the rupture potential F1 / FR1 is equal to 21.2%.

The utilization ratio of the F1 / FR1 rupture potential is 75% greater than the utilization ratio of the F2 / FR2 rupture potential. [00150] The carcass reinforcement 2 consists of reinforcement elements between two calendering layers whose modulus of elasticity under tension at 10% elongation is equal to 9.8 MPa.

The reinforcement elements of the carcass reinforcement 2 are 19.18 cables whose elongation at rupture is equal to 2.5%.

[00152] The carcass reinforcement cables of the tire 1 are cables with a structure layer 1 + 6 + 12, not shrunk, consisting of a central core formed of a wire, an intermediate layer formed of six wires. and an outer layer of twelve wires.

[00153] Figure 1 illustrates the tire mounted on its nominal rim J; the axially outermost point E of the main part of the carcass reinforcement layer 2 is thus determined, the tire being inflated to its nominal pressure, for example by tomography.

[00154] FIG. 2 magnifies a schematic sectional representation of a bead 3 of the tire in which there is a portion of the carcass reinforcement layer 2 wound around a bead wire 4 to form an upturn 7 with one end 8.

In this FIG. 2, the circle T circumscribes the bead wire 4 and shows the radially innermost point A of said circle T. This point A is defined on a radial section of the tire, the spacing of the beads of which is the same as when the tire is mounted on the mounting rim recommended by the ETRTO, which is not mounted on a rim.

The outermost radially B point of the circle T is also determined. The distance dn between the point E and the point A is equal to 128 mm. The distance d _R between the point 8 and the point A is equal to 44 mm. The ratio of the distance d _R over the distance d _E is equal to 34% and therefore between 25 and 40%. The upturn 7 of the carcass reinforcement layer is separated from the main part of the carcass reinforcement layer 2 by a first layer of polymeric mixture 9, having a radially outer end 10 at a distance dio from the point A equal to 105 mm. The first polymeric compound layer 9 has an elastic modulus under tension at 10% elongation less than the modulus of elasticity under tension at 10% elongation of the calendering layers of the carcass reinforcement 2.

Axially on the outside of the upturn 7 of the carcass reinforcement layer is represented the second polymeric mixture layer 11, the radially outer end 12 of which is radially outwardly of the end 8 of the upturn 7. the carcass reinforcement layer at a distance of from point A equal to 112 mm. The radially inner end 13 of the second polymeric mixture layer 11 is radially between the points A and B, respectively radially the innermost and radially the outermost of the circle circumscribing the bead wire.

The second layer of polymeric mixture 11 has a modulus of elasticity under tension at 10% elongation lower than the elastic modulus under tension at 10% elongation of the calendering layers of the carcass reinforcement 2.

In contact with the second layer of polymeric mixture 11 and radially under the bead wire, there is the third layer of polymeric mixture 14, the axially outermost end 15 of which is radially inside the end 12 of the second layer of polymeric mixture 11.

The third layer of polymeric mixture 14 has a modulus of elasticity under tension at 10% elongation equal to 7.1 MPa.

[00165] Axially in contact with the second layer of polymeric mixture 11 and the third layer of polymeric mixture 14, is the fourth layer of polymeric mixture 16. The radially inner end 17 of the fourth layer of polymeric mixture 16 is radially at the end of the third layer of polymeric mixture 14.

The fourth layer of polymeric mixture 16 has a tensile modulus of elasticity at 10% elongation equal to 3.1 MPa. The first polymeric mixture layer 9 has a thickness Ei, measured in the normal direction to the reinforcing elements of the main part of the carcass reinforcement layer and passing through the end of the upturn of the reinforcing layer. carcass equal to 7.5 mm. The distance E ₂ between the reinforcing elements of the main part of the carcass reinforcement layer and the external surface of the tire measured along the measurement direction of the thickness Ei of the first polymeric mixture layer passing through the end of the upturn of the carcass reinforcement layer is equal to 20 mm. The ratio of the thickness Ei of the first layer 9 of polymer mixture over the distance E ₂ , measured between the reinforcing elements of the main part of the carcass reinforcement layer and the external surface of the tire, is equal to 38% and therefore between 30 and 60%.

The ratio of the distance E ₂ , measured between the reinforcing elements of the main part of the carcass reinforcement layer and the external surface of the tire, over the distance dR between the end of the reversal of the layer of carcass reinforcement and the radially innermost point of the circle circumscribing the rod is equal to 0.45 and therefore less than 0.5.

The cumulative mass of the two working layers 61, 62, and the layer of circumferential reinforcing elements 63 comprising the mass of the metal cables and calendering mixtures, amounts to 12.8 Kg.

The mass of the tire according to the invention is 67.2 Kg.

The various mixtures used to make the first and second layers 9 and 1 1 are listed below.

Mixture 1 Mixture 2

N 100 100

Black N330 40

Silica 165G 45 Antioxidant 1.30 1.7

Stearic acid 0.5 1

Zinc oxide 4 4.5

sulfur 3.12 1.9

CBS 0.60 1.9 Accelerator

Silane on black 9

PEG4000 1

MA ₁₀ (MPa) 3.7 5

P60 12.5 12.5

tan (6) "_" 80 ° C 0.080 0.080

The values of the constituents are expressed in phr (parts by weight per hundred parts of elastomers).

[00175] The loss factor tan (δ) is a dynamic property of the layer of rubber mix. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen with a thickness of 2 mm and a section thickness of 78 mm ² ) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 80. ° C. A strain amplitude sweep of 0.1 to 50% (forward cycle) and then 50% to 1% (return cycle) are performed. The results used are the complex dynamic shear modulus (G ^* ) and the loss factor tan (δ) measured on the return cycle. For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) _{max, is indicated} .

[00176] The rolling resistance is the resistance that appears when the tire is rolling. It is represented by the hysteretic losses related to the deformation of the tire during a revolution. The value of tan (δ) at 80 ° C corresponds to an indicator of the rolling resistance of the rolling tire.

[00177] It is still possible to estimate the rolling resistance by measuring energy losses by rebound energy samples imposed at temperatures of 60 ° C and expressed as a percentage. A first tire II, produced in accordance with the invention, comprises first and second layers made with the mixture 1 according to the invention.

A second tire 12, made in accordance with the invention, comprises first and second layers made with the mixture 2 according to the invention. The tires II and 12 according to the invention are compared with reference tires R, of the same size as the tires according to the invention. The reference tires R differ from the tire according to the invention on the one hand by its crown reinforcement formed radially from the inside to the outside: of a first working layer formed of metal cables oriented at an angle equal to 18 °, a layer of circumferential reinforcing elements formed of 21x23 steel cables, of the "bi-module" type, of a second working layer formed of metal cables oriented at an angle equal to 18 ° and crossed to the metal cables of the first working layer, the cables of each of the working layers being oriented on either side of the circumferential direction, a protective layer formed of elastic metal cables 6.35, whose distance between the reinforcing elements, measured according to the normal to the direction of the average line of the cable is equal to 2.5 mm, oriented an angle equal to 18 °, the same side as the cables of the second co workload.

The metal cables constituting the reinforcing elements 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 average line of the cable equal to 2.5 mm. The two working crown layers therefore differ from the working crown layers of the tire according to the invention only by the angles.

The metal cables constituting the reinforcing elements of the layer of circumferential reinforcing elements are spaced from each other by 2 mm, depending on the normal direction of the average line of the cables. [00183] The reference tire is inflated to a pressure of 9 bar.

The axial width of the first working layer is equal to 295 mm.

The axial width of the layer of circumferential reinforcing elements is equal to 194 mm.

The axial width of the second working layer is equal to 276 mm.

[00187] The axial width of the protective layer is equal to 188 mm.

The absolute value of the difference between the absolute values of the angles formed by the cables of the first working crown layer with the circumferential direction and those of the cables of the second working crown layer is equal to 0 °.

The average angle is equal to 18 °.

[00190] The value of Fl is equal to 401.8 N.

The value of F2 is equal to 401.8 N.

The utilization ratio of the rupture potential F2 / FR2 is equal to 15.4%.

The utilization ratio of the rupture potential F1 / FR1 is equal to 15.4%.

The utilization ratio of the rupture potential F1 / FR1 is identical to the utilization ratio of the rupture potential F2 / FR2.

The cumulative mass of the working layers of the reference tire R, the layer of circumferential reinforcing elements and the protective layer, comprising the mass of the metal cables and calendering mixtures, amounts to 16.7 Kg.

The reference tires R, on the other hand, differ from the tire according to the invention at the level of the bead zone. The reference tires R differ from the tires according to the invention by the presence of stiffeners in the area of the bead more usual with in particular a greater thickness of the bead at the end of the overturning of the reinforcing layer. carcass and first and second layers made with the mixture 1. Such a more usual bead zone further comprises a third layer, also consisting of the mixture 1, which is positioned between the radially outermost end of the stiffener and the end the overturning of the carcass reinforcement.

[00199] The mass of the reference tire R is 71.5 Kg.

The times required for the baking of the tires at a temperature of 145.5 ° C. on the mold side, 158 ° C. on the cavity side of the tire and at a pressure of 16 bar are given in the following table (they are expressed in minutes):

As explained above, the baking time of a tire is set by one and / or the other of the areas that are the area of the crown of the tire and the bead area of the same tire. By way of illustration, the table below gives the necessary cooking times for each of these two zones of the tire for the same three tires R, II and 12. As in the table above, the times are expressed in minutes for conditions identical to those described above.

Tests to test the endurance of the crown reinforcement were carried out with tires II and 12 made according to the invention and with the reference tires R. [00203] First endurance tests were carried out on a test machine requiring each tire to run a straight line at a speed equal to the maximum speed index prescribed for said tire (speed index), a regulated pressure of 9b, under an initial load of 3924 daN gradually increased to reduce the duration of the test.

[00204] Other endurance tests were performed on a test machine imposing cyclically a transverse force and a dynamic overload to 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 showed that the distances traveled during each of these tests are substantially identical for the tires II and 12 according to the invention and the tires of reference R. It therefore appears that the tires II and 12 according to the The invention has substantially equivalent performance in terms of endurance of the crown reinforcement to those of the reference tires R when running on bituminous soils.

[00206] Tests to characterize the breaking strength of a tire crown reinforcement subjected to shocks have also been carried out. These tests consist in rolling a tire, inflated to a recommended pressure and subjected to a recommended load, on an obstacle or cylindrical indenter of diameter equal to 1.5 inches, that is to say 38.1 mm, and of a determined height. The breaking strength is characterized by the critical height of the indenter, that is to say the maximum height of the indenter resulting in a total rupture of the crown reinforcement, that is to say of the breaking of all vertex layers. The values express the energy necessary to obtain the break of the vertex block. The values are expressed from a base 100 corresponding to the value measured for the reference tire R.

These results show that despite lightening of the tires II and 12 according to the invention, in particular by a reduction in the mass of the crown reinforcement, the energy at break during an impact on the surface of the tread is significantly higher.

[00208] Other endurance tests were carried out in order to test the endurance of the zones of the tire bead by rolling two planed tires on one another with a regulated pressure of 8.5 b, with an inflation of nitrogen and a load of 7455 daN at a speed of 30km / h. In addition, the tires were rolled for ten weeks at 60 ° C. with inflation with 50% oxygen at 8 ° C.

The tests were carried out for the tires II and 12 according to the invention with conditions identical to those applied to the tires of reference R.

The tests carried out for the reference tires R at performances establishing the base 100. The tests are stopped at the occurrence of a degradation of the low zone of the tire.

The results of the measurements are presented in the following table. They are expressed in relative distance, a value of 100 being attributed to the tire R.

Moreover, rolling resistance measurements have been carried out.

The results of the measurements are presented in the following table; they are measured in Kg / t, an index of 100 being assigned to the tire R.

Pneumatic R Pneumatic II Pneumatic 12

100 98 97

Claims

1 - Pneumatic tire for a truck-type vehicle, intended to be mounted on a 15 ° drop center hollow rim, with a radial carcass reinforcement, consisting of a single carcass reinforcement layer formed of reinforcement elements inserted between two polymeric blend (s) calendering layers, said tire comprising a crown reinforcement comprising two working crown layers of reinforcement elements crossed from one web to another by making angles with the circumferential direction (al, a2) greater than 8 °, said angles a1 and a2 being oriented on either side of the circumferential direction, and at least one layer of circumferential reinforcement elements, the crown reinforcement being capped radially with a tread, said tread being joined to two beads via two sidewalls, the layer of reinforcing elements of the carcass reinforcement being anchored in each of s rolls by turning around a bead wire to form a main portion of the carcass reinforcement layer extending from one rod to the other and a reversal of the carcass reinforcement layer in each of the beads, said reversal of the carcass reinforcement layer being separated from the main portion of the carcass reinforcement layer by a first layer of polymeric mixture extending radially from the bead wire to at least the end of the upturn of the bodyside layer; carcass reinforcement and said overturning of the carcass reinforcement layer being axially outwardly in contact with a second layer of polymeric mixture, itself at least in contact with a third layer of polymeric mixture forming the surface outside the tire in the region of the bead, said third layer of polymeric mixture being intended in particular to come into contact with the rim, said third layer of mixture in. lymérique being radially outwardly in contact with a fourth layer of polymeric mixture forming the outer surface of a flank, characterized in that:

said two working crown layers and said at least one layer of circumferential reinforcing elements are only present to constitute the crown reinforcement over at least 40% of the axial width of the crown reinforcement,

in that the reinforcing elements of the radially outermost working layer form an angle a2 with the circumferential direction greater than the angle α in absolute value formed by the reinforcement elements of the radially innermost working layer with the circumferential direction, in that the absolute value of the difference between the absolute values of the angles a2 and al is greater than 7 °,

in that the average angle has satisfied the relation:

in that in a meridian section of said tire: the radially outer end of the first layer of polymer mixture (s) is radially external to the end of the upturn of the carcass reinforcement layer,

the radially outer end of the second layer of polymeric mixture is radially external to the end of the upturn of the carcass reinforcement layer,

the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the bead wire is between 25 and 40% of the distance between the axially outermost point of the main part the carcass reinforcement layer and the radially innermost point of the circle circumscribing the bead wire,

said first polymeric mixture layer (s) has a thickness, measured in the direction normal to the reinforcing elements of the main portion of the carcass reinforcement layer and passing through the end of the uptake of the diaper layer; carcass reinforcement between 30 and 60% of the distance between the reinforcing elements of the main part of the carcass reinforcement layer and the outer surface of the tire measured in the direction of measurement of the thickness of the first layer of carcass reinforcement layer; polymeric mixture (s) passing through the end of the upturn of the carcass reinforcement layer,

the ratio of the distance between the reinforcing elements of the main part of the carcass reinforcement layer and the external surface of the tire measured in the said direction of measurement of the thickness of the first layer of polymer mixture (s) (s) ) passing through the end of the upturn of the carcass reinforcement layer over the distance between the end of the upturn of the reinforcing layer of carcass and the radially innermost point of the circle circumscribing the bead wire is less than 0.5,

the overturning of the carcass reinforcement layer and the main part of the carcass reinforcement layer are the only layers of reinforcement elements whose elongation at break is less than 6% present in an area of the constituent flank at less than 90% of the flank surface radially between the end of the upturn of the carcass reinforcement layer and the radially outermost point of the bead wire,

the tensile modulus of elasticity at 10% elongation of the first polymeric mixture layer (s) and the second polymeric mixture layer are less than or equal to the modulus of elasticity under tension at 10% of lengthening of the calender of the carcass reinforcement layer and greater than or equal to 30% of the modulus of elasticity under tension at 10% of elongation of the calandering of the carcass reinforcement layer. 2 - A tire according to claim 1, characterized in that the utilization ratio of the fracture potential F2 / FR2 of the radially outermost working layer is less than 1/6, in which:

FR2 is the breaking force in uniaxial extension of the cables of the radially outermost working layer, F2 = p ₂ * Te * [(tanfled |) / ((tan (| al |) + tan (| a2 |))) / cos ² (| a2 |) + C _F ], with

Te = 0.078 * P * Rs * (l- (Rs ² -RL ² ) / (2 * Rt * Rs)),

P: the inflation pressure of the tire expressed in bar,

C _F = 0.00035 * (min ((L-80) / sin (| al |), (L-80) / sin (| a2 |), 480) -480),

P2: the laying pitch of the reinforcing elements of the radially outermost working crown layer, measured perpendicularly to the reinforcing elements at the circumferential median,

Rs = Re - Es,

R _L : average of the radii of the axially outermost points on each side of the tire,

Rt: the radius of the circle passing through three points on the outer surface of the tread outside the troughs, defined from a shoulder end at respective axial distances equal to ¼, ½ and ¾ of the width of the tread.

3 - A tire according to one of claims 1 or 2, characterized in that said at least one layer of circumferential reinforcing elements is continuous axially and preferably centered on the circumferential mid-plane.

4 - A tire according to one of claims 1 to 3, characterized in that the reinforcing elements of said two working crown layers are metallic.

5 - tire according to one of claims 1 to 4, characterized in that the absolute value of the difference between the absolute values of the angles a2 and al is greater than or equal to 10 °, and preferably greater than 14 °.

6 - tire according to one of claims 1 to 5, characterized in that the average angle has satisfied the relationship: a> 20 + 164 * exp (-L / 100).

7 - tire according to one of claims 1 to 6, characterized in that the utilization ratio of the fracture potential F2 / FR2 of the radially outermost working layer is less than 1/8.

8 - A tire according to one of claims 1 to 7, characterized in that the utilization ratio of the fracture potential F1 / FR1 of the radially innermost working layer is less than 1/3, in which: FR1 is the breaking force in uniaxial extension of the cables of the radially innermost working layer,

Fl = pi * Te * [(tan (| a2 |) / ((tan (| al |) + tan (| a2 |))) / cos ² (| al |) + C _F ], with i: the laying pitch of the reinforcing elements of the radially innermost working crown layer, measured perpendicularly to the reinforcing elements at the circumferential mid-plane,

Te = 0.078 * P * Rs * (l- (Rs ² -RL ² ) / (2 * Rt * Rs)),

P: the inflation pressure of the tire expressed in bar,

Rs = Re - Es,

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

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

9 - A tire according to claim 8, characterized in that the utilization ratio of the rupture potential F1 / FR1 of the radially innermost working layer is at least

30% higher than the utilization ratio of the F2 / FR2 rupture potential of the radially outermost working layer.

10 - tire according to one of the preceding claims, characterized in that at most said two working crown layers and said at least one layer of circumferential reinforcing elements are only present to form the crown reinforcement on at least 60% of the axial width of the crown reinforcement, and preferably at least 80% of the axial width of the crown reinforcement.

11 - tire according to one of the preceding claims, characterized in that the two working crown layers and the said at least one layer of circumferential reinforcing elements are only present to form the crown reinforcement over the entire width axial of the crown reinforcement. 12 - A tire according to one of the preceding claims, characterized in that said at least one layer of circumferential reinforcing elements is radially disposed between the two working crown layers.

13 - tire according to one of the preceding claims, characterized in that the reinforcing elements of said at least one layer of circumferential reinforcing elements are metal reinforcing elements having a secant modulus at 0.7% elongation included between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa.

14 - A tire according to one of the preceding claims, characterized in that the first layer of polymer mixture (s) and / or the second layer of polymer mixture comprise a reinforcing filler consisting of at least one white filler of silica type and / or alumina comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or alternatively modified carbon blacks during or after synthesis.

15 - A tire according to claim 14, characterized in that said first layer of polymeric mixture (s) and / or second polymeric mixture layers are elastomeric mixtures based on natural rubber or synthetic polyisoprene with a majority of sequences cis-1,4 and optionally at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in case of cutting being present at a majority rate relative to the rate of the other diene elastomer or diene elastomers used; a reinforcing filler constituted: a) either by a white filler of silica and / or alumina type comprising SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or fumed silicas, aluminas or alumino silicates or else modified carbon blacks in process or after synthesis, having a BET specific surface area of between 30 and 260 m ² / g employed at a rate of is between 20 and 80 phr, and preferably between 30 and 50 phr, b) either by a cutting of a white filler described in (a) and of carbon black, in which the overall filler rate is between 20 and 80 phr, and preferably between 40 and 60 phr, the silica level on the overall charge rate being greater than 80% and preferably greater than 90%.