WO2019077273A1

WO2019077273A1 - Tyre having a reduced-weight bead region

Info

Publication number: WO2019077273A1
Application number: PCT/FR2018/052587
Authority: WO
Inventors: Luc Bestgen; William License; Jean-Luc Guerbert-Jubert
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2017-10-18
Filing date: 2018-10-17
Publication date: 2019-04-25

Abstract

The invention relates to a tyre with a radial carcass reinforcement (2), consisting of a single layer (2) of reinforcement elements, which is turned up around a bead wire (4) such as to be anchored in each of the beads (4a, 4b). According to the invention, the turn-up (7) of the carcass reinforcement layer and the main portion (2) of the carcass reinforcement layer are the only layers of reinforcement elements having elongation at break less than 6% present in the sidewall (3), and any point of the profile of the outer surface S of the tyre between points F and E is at a distance of less than 2.5 mm from the curve P defined by three arcs of circles (H1, H2, H3) connecting said first and second points F and E.

Description

PNEUMATIC WITH BOURRELET'S ZONE IS ALLEGEE

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 low extensibility wires or metal 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 ply of plywood. so-called working top, 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).

Such tires still usually comprise at the beads one or more layers of reinforcing elements called stiffeners. These layers are most often consist 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 low areas 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 disposed axially outside the overturning of the carcass reinforcement and extend over a height in the upper flank to that of the upturn, in particular to cover the ends. free reinforcement 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 to the bead wire on the other hand lead to a design requiring rubbery mixtures to separate the ends of layers and to ensure the desired positioning of the different ends. The inventors are thus given a mission to provide tires for vehicles "heavy-weight", whose endurance performance including endurance areas of the beads are preserved and whose design is simplified and advantageously whose mass overall tire is decreased.

This object has been achieved according to the invention by a tire, intended to be mounted on a hollow rim type 15 ° drop center, comprising a radial carcass reinforcement, consisting of a single carcass reinforcement layer formed reinforcement elements, said tire comprising a crown reinforcement, itself capped radially with a tread, said tread being joined to two beads by means of two sidewalls, the layer of reinforcement elements the carcass reinforcement being anchored in each of the beads 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 bead layer; carcass reinforcement 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 polymer mixture (s) radially extending from the bead wire to at least the end of the upturn of the carcass reinforcement layer and said upturn of the carcass reinforcement being axially outwardly in contact with a second layer polymeric mixture, itself 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 polymeric mixture layer being radially outwardly in contact with a fourth layer of polymeric mixture forming the outer surface of a sidewall, in a meridian section of said tire: the radially outer end of the first layer of mixture (s) polymer (s) being radially external to the end of the upturn of the carcass reinforcement layer,

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, 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 axially outermost point Z of the part main part of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the bead wire,

said first polymeric mixture layer (s) having 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 carcass reinforcement layer and the radially innermost point of the circle circumscribing the rod being less than 0.5 ,

the upturn of the carcass reinforcement layer and the main portion of the carcass reinforcement layer being the only layers of reinforcement elements whose elongation at break is less than 6% present in a zone 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 elastic modulus under tension at 10% elongation of the first layer of polymer mixture (s) and the second layer of polymer mixture being 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%> tensile modulus of elasticity at 10% elongation of the calender of the carcass reinforcement layer,

- any point of the profile of the outer surface S of the tire, between a first point F, itself defined by the intersection of an axially oriented straight line passing through the radially outermost point I of the rim hook J and the outer surface of the tire, and a second point E, which is the axially outermost point of the tire, being at a distance of less than 2.5 mm from a curve P defined by three arcs of circles connecting said first and second points F summer,

a first circle passing through the point F, its center being axially oriented towards the inside of the tire with respect to the point F,

a second circle passing through the point E, its center being axially oriented towards the inside of the tire with respect to the point E and on an axially oriented straight line passing through E,

a third circle being tangential to said first and second circles, its center being axially oriented towards the outside of the tire with respect to the two points of tangency with said first and second circles, said two points of tangency forming the two points of inflection of said curve P,

the four unknowns (the coordinates of the center of the first circle and the radii of the second and third circles) making it possible to define these circles being determined by 10 points of the surface S, intermediate between the points F and E, positioned at the relative curvilinear abscissa sin (i * 90deg / l 1), i being the point number, the abscissa 0 being that of the point E, the abscissa 1 being that of the point F, minimizing the sum of the distances between the ten intermediate points of the profile of the surface S and the curve P, the radial distance between the radially innermost inflection point of the curve P and the radially outermost point of the circle circumscribing the bead wire being less than the diameter of the circle circumscribing the bead wire,

the radial distance between the radially outermost point of inflection of the curve P and the point F is greater than 1.1 times the radial distance between the end of the upturn of the carcass reinforcement layer and the point F.

Within the meaning of the invention, a hollow rim typel5 ° 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 frustoconical shape , 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 meridian section of the tire is defined in accordance with the invention such that the barycentres of the rods form an axially oriented straight line, said centroids being distant from each other by a distance equal to the width of the nominal rim. J increased by 20 mm and decreased by twice the distance measured axially between a barycentre of a bead wire and a point of the outer surface of the tire.

The points E and F are determined on a tire mounted on its nominal rim and inflated to the nominal pressure.

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 bead wire may also be determined according to a tomography technique on a tire mounted and inflated according to the nominal conditions or are 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.

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, especially measured from the radially innermost point of the circle circumscribing the bead wire, can also be measured according to a tomography technique or are measured on a section of a tire, of which Bead spacing is the same as when the tire is mounted on the mounting rim recommended by ETRTO, which is therefore neither mounted nor inflated.

Regarding the determination of the four unknowns (the coordinates of the center of the first circle and the radii of the second and third circle) to define the circles that define the curve P, it is for example possible to use the software Catia Version 5 -6 Release 2016 Service Pack 4 from Dassault Systèmes, Generative Shape Design Workshop. We can build parametrically the three circles:

Circle Hl: creation of a point in the plane of the generator by these X and Y coordinates, and circle defined by its center (the point X, Y) and a point (the point F), Circle H2: creation of a point on curve (the axial line) at a distance D and from a circle defined by its center (the created point) and a point (the point E),

Circle H3: creation of the bitangent circle at H1 and H2 parameterized by its radius R.

A curve C consisting of the circle H1 of F at the point of tangency with H3, of H3 between these two points of tangency and of H2 is assembled between the point of tangency with H3 and the point E.

We create the 10 points on the generator and then an Objective parameter equal to the maximum distance of these points to the curve P.

The "Product Engineering Optimizer" workshop is then launched to minimize the Objective parameter by the simulated annealing (global optimization) method according to the four parameters (X, Y, D, R). To facilitate convergence, the parameters of the starting circles H1 and H2 are chosen to approach the target generator. For example, the X and Y coordinates correspond to the center of a circle passing through the point F and the two points among the ten closest to F.

It should be noted that in order to evaluate the maximum distance, the same method can be used with the objective of maximizing the distance of a point on the outer curve of the tire profile from the constructed curve, the point being constructed by its relative curvilinear abscissa (varies from 0 to 1).

Another example of a method for determining the four unknowns (the coordinates of the center of the first circle and the radii of the second and third circles) to define the circles that define the curve P is to use a discretization.

After having collected the coordinates of the ten points on the generator, it is written in an advanced programming language (C, Fortran, Java, Matlab, ...) a code discretizing the geometric curve P defined according to the parameters. For this construction, basic geometric constructions are used. This curve is discretized with a resolution around 10 points per mm. For each of the ten points on the generator, the distance to the geometric curve will be the smallest distance between this point and the set of discrete points. The objective is defined as being the maximum of the ten distances and a global optimization method is used to minimize the objective according to the parameters. As an overall optimization method, the simulated annealing method (S. Kirkpatrick, C. D. Gelatt and M. P. Vecchi, Optimization by Simulated Annealing, Science, Vol 220, pp. 671-680 (1983)) is particularly suitable.

To evaluate the maximum distance, it is necessary to discretize the outer curve of the tire in a thousand points and evaluate the distance between these points and the curve built.

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.

According to a preferred embodiment of the invention, in a meridian section, any point of the profile of the outer surface S of the tire between said first and second points F and E, is at a distance of less than 1.25 mm from the P curve connecting said first and second points F and E.

The tests have shown that the tires thus produced according to the invention and whose mass is less than that of tires of more conventional design, including in particular layers of reinforcing elements additional stiffeners type, show performance in terms endurance, especially in terms of endurance areas of the beads, at least as good as those of said tires of more conventional design or higher.

These results are all the more surprising that the more usual designs of this type of tires have a relatively thick bead area including to contain complementary elements such as stiffeners and allow to support the supports on the hooks at the lunches during rollings.

The inventors have thus been able to demonstrate that the tires made according to the invention and which have a relatively thin bead area associated in particular with the absence of layers of complementary reinforcing elements such as stiffeners, allow to lighten the tire and against all expectations to maintain properties in terms of satisfactory endurance, or even to improve.

The inventors believe to interpret this result because of the profile of the outer surface of the tire between the point F and the point E, defined above, which leads to a modification of the contact between the rim and the tire and more particularly to the contact zone between the rim hook and the part of the tire which bears against it during the crushing of the tire and rolling. The aforementioned contact area is indeed reduced compared to more usual designs, which limits the wear on the carriage and the wear due to the phenomena of de-axialization during rolling. This profile of the outer surface of the tire between the points E and F with a concave zone whose radially outer end which corresponds to the radially outer point of inflection of the curve P is radially distant from the end of the upturn of the tire. carcass reinforcement layer and leads to an optimization of the sharing between the meridian bending and the shearing of the first layer of polymer mixture (s) during the recovery of the tensions due to inflation by the reversal of the layer of carcass reinforcement; this particularly favors performance in terms of endurance. Furthermore, the position of the radially innermost inflection point of the curve P relatively close to the radially outermost point of the circle circumscribing the bead optimizes the bearing area of the tire on the rim. 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.

Moreover, this lightening of the bead area of the tire improves the hysteretic losses of the tire and therefore its performance in terms of rolling resistance. This effect is even more pronounced that the profile of the outer surface of the tire leads to a decrease in curvature variations in comparison with more usual designs as explained above.

According to a preferred embodiment of the invention, in a meridian plane, the portion of the outer surface S of the tire delimited between the intersection of the outer surface S of the tire with a first straight axially oriented and passing through the end of the overturning of the carcass reinforcement layer and the intersection of the outer surface S of the tire with a second straight axially oriented and passing through the radially outermost point of the circle circumscribing the bead wire fits by translation according to the axial direction in a surface defined between said first straight axially oriented and passing through the end of the overturning of the reinforcing layer of carcass, said second straight axially oriented and passing through the radially outermost point of the circle circumscribed to the bead wire and two curves parallel to the reinforcing elements of the overturning of the carcass reinforcement layer remote from the overturning of the reinforcing layer of carcass of twice the diameter of the reinforcing elements of the carcass reinforcement layer.

More preferably according to the invention, the two curves parallel to the reinforcing elements of the overturning of the carcass reinforcement layer are distant from the overturning of the carcass reinforcement layer by one and a half times (1, 5 times) the diameter of the reinforcing elements of the carcass reinforcement layer.

The distance between the upturn of the carcass reinforcement layer and one of the two curves parallel to the reinforcement elements of the carcass reinforcement layer is measured from the outer surface of the reinforcing element. closest to said curve parallel to the reinforcing elements of the upturn of the carcass reinforcement layer.

According to this preferred embodiment of the invention, the thickness of axially external elastomeric mixtures to the overturning of the carcass reinforcement layer is substantially constant and allows a homogeneous bending in this zone and is favorable to the performance in terms of endurance of said zone.

According to a preferred embodiment of the invention, the radial distance between the radially outermost point of inflection of the curve P and the point F is greater than 1.5 times the radial distance between the end of the reversal of the the carcass reinforcement layer and the point F. The radially outermost point of inflection of the curve P is all the more radially distant from the end of the upturn of the carcass reinforcement layer.

Also preferably according to the invention, the radial distance between the radially innermost inflection point of the curve P and the radially outermost point of the circle circumscribing the rod is less than 0.8 times the radial distance between the radially outermost point of the circle circumscribing the rod and the radially innermost point of the circle circumscribing the rod. This positioning of the point of inflection radially the innermost of the curve P closer to the bead further optimizes the bearing area of the tire on the rim.

Advantageously according to the invention, the radial distance between the radially outermost point of inflection of the curve P and the point F is greater than 50% of the radial distance between the point E and the point F.

Advantageously again according to the invention, the radius of the third circle is between 100% and 160% of the radius of the second circle.

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 consisting of 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 polymer mixture (s) and / or second layer of polymeric mixture 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 constituted: a) either by a white filler of silica and / or alumina type having SiOH and / or AlOH surface functional groups chosen from the group formed by precipitated or pyrogenic silicas, aluminas or alumino silicates or still well modified carbon blacks in course or after synthesis, BET specific surface area between 30 and 260 m ² / g used at a rate included in 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 charge rate is between 20 and 80 pce, and preferably between 40 and 60 phr, the silica level on the overall charge rate being greater than 80% and preferably greater than 90%.

The BET surface area measurement is carried out 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.

In the case of using clear charge or white charge, it is necessary to use a coupling agent and / or covering selected from 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 functions at the surface and / or AIOH, mention may be made of the CSDP type charges 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 nonlimiting examples, mention may be made of the charges marketed by Cabot Corporation under the name Ecoblack ™ "CRX 2000" or "CRX4000", or even the fillers described in publications 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 only reinforcing filler, the hysteresis and cohesion properties are obtained using a precipitated or fumed silica, or a precipitated alumina or even a BET surface area 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 a grafting on the chain or at the end of the chain of oxygen functions carbonyl, carboxyl or an amino function 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. Said first layer of polymeric mixture (s) and / or second layer of polymeric mixture thus formed imparts greater rigidity to the more usual designs which make it possible to provide the tire bead zones with satisfactory bending stiffnesses. combination with the thicknesses of these areas which are reduced compared to those of more usual tires.

[0058] Said first layer of polymeric mixture (s) and / or second layer 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.

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 W0 = 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 layer of polymer mixture (s) and second layer of polymeric mixture are made with identical polymer mixtures, and preferably comprising a reinforcing filler consisting of minus 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 progress or after the 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 bead wire and a rubber mix volume directly in contact with the bead wire. 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 especially in terms of endurance satisfactory. 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 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. This is for example of cables with at least two layers, at least one inner layer being sheathed with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one elastomer diene.

According to an alternative embodiment of the invention, the crown reinforcement of the tire is formed of at least two working crown layers of inextensible reinforcing elements, crossed from one layer to another by making with the circumferential direction angles between 10 ° and 45 °. According to other embodiments of the invention, the crown reinforcement further comprises at least one layer of circumferential reinforcing elements.

A preferred embodiment of the invention further provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called protective layer, of so-called elastic reinforcing elements, oriented with respect to the direction. circumferential with an angle between 10 ° and 45 ° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent thereto.

The protective layer may have an axial width smaller than the axial width of the least wide working layer. Said protective layer may also have an axial width greater than the axial width of the narrower working layer, such that it covers the edges of the narrower working layer and, in the case of the radially upper layer, being the smallest, as coupled, in the axial extension of the additional reinforcement, with the widest working crown layer over an axial width, to be subsequently, axially outside, decoupled from said widest working layer with profiles at least 2 mm thick. The protective layer formed of elastic reinforcing elements may, in the case mentioned above, be on the one hand possibly decoupled from the edges of said least wide working layer by profiles of thickness substantially less than the thickness. profiles separating the edges of the two working layers, and have on the other hand an axial width less than or greater than the axial width of the widest vertex layer.

According to any of the embodiments of the invention mentioned above, the crown reinforcement can be further completed, radially inwardly between the carcass reinforcement and the nearest radially inner working layer. of said carcass reinforcement, by a triangulation layer of steel non-extensible reinforcing elements making, with the circumferential direction, an angle greater than 60 ° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement. Other details and advantageous features of the invention will emerge below from the description of the exemplary embodiments of the invention, in particular with reference to FIGS. 1 to 5 which represent: FIG. 1, a meridian view of a diagram of a tire according to the invention, FIG. 2, an enlarged schematic representation of the external surface of the tire between the point F of the zone of the bead and the point E, FIG. 3, a schematic representation of the zone of the bead illustrating the zone. around the overturning of the carcass reinforcement layer, FIG. 4, a schematic representation of the zone of the bead illustrating other aspects of the invention, FIG. 5, a schematic representation of the zone of a bead of a tire. reference.

The figures are not shown in scale to simplify understanding.

In Figure 1, the tire 1 is of dimension 12 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads 3. The carcass reinforcement 2 is hooped at the top of the tire by a crown reinforcement 5, itself capped with a tread.

The carcass reinforcement 2, formed of a single layer of metal cables, is wound in each of the beads 3 around a rod 4a, 4b and forms in each of the beads 3 a reversal 7 of the layer of carcass reinforcement having one end 8.

The carcass reinforcement 2 consists of reinforcement elements between two calendering layers whose tensile modulus of elasticity 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%. The carcass reinforcement cables of the tire 1 are cables with 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.

[0081] Figure 1 illustrates the tire mounted on its nominal rim J; the axially outermost point Z of the main part of the carcass reinforcement layer 2 is determined, the tire being inflated to its nominal pressure, for example by tomography. The point E is the axially outermost point of the tire when it is mounted on its nominal rim J and inflated to its nominal pressure. The point F is defined by the intersection between the outer surface of the tire and the straight line, parallel to the axis of rotation, passing through the point I, radially outermost of the rim J.

FIG. 2 schematically illustrates the outer surface S of the tire between points E and F on a meridian section of the tire, defined so that the barycentres 6a, 6b of the rods 4a, 4b form an axially oriented straight line, said barycenters 6a. , 6b being spaced from each other by a distance equal to the width of the nominal rim J increased by 20 mm and reduced by twice the distance measured axially between a barycentre 6a, 6b of a bead wire 4a, 4b and a point on the outer surface of the tire.

On this meridian section, any point on the profile of the outer surface S of the tire between points F and E is at a distance less than 0.73 mm from a curve P defined by three arcs of circles connecting said first and second points. Party.

The first circle FL passes through the point F, its center being axially oriented towards the inside of the tire with respect to the point F. The radius Ri of the circle Hi is equal to 17 mm.

The second circle H ₂ passes through the point E, its center being axially oriented towards the inside of the tire with respect to the point E and on an axially oriented straight line passing through E. The radius R ₂ of the circle H ₂ is equal to 102 mm.

The third circle H ₃ is tangent to said first and second circles, its center being axially oriented towards the outside of the tire with respect to the two points of tangency M, N with said first and second circles, said two points of tangency. M, N forming the two points of inflection of said curve P. The radius R ₃ of the circle H ₃ is equal to 144 mm.

[0087] The radius R of the circle ₃ H ₃ is therefore between 100% and 160% of the radius R ₂ of the circle H _2.

The radial distance dEF between the point E and the point F is equal to 110.5 mm.

The radial distance dMF between the radially outermost point of inflection M of the curve P and the point F is equal to 79.5 mm.

The radial distance d F between the radially innermost point of inflection N of the curve P and the point F is equal to 3.2 mm.

The radial distance dgF between the end 8 of the upturn of the carcass reinforcement layer and the point F is equal to 29 mm.

FIG. 3 illustrates in enlarged manner a diagrammatic representation in section of a bead 3 of the tire 1, on which is represented the portion 30 of the outer surface S of the tire delimited between the intersection 31 of the outer surface S of the tire. pneumatic with a first straight line 32 oriented axially and passing through the end 8 of the upturn 7 of the carcass reinforcement layer and the intersection 33 of the outer surface S of the tire with a second straight line 34 oriented axially and passing through the point B radially outermost of the circle circumscribed to the rod.

In this Figure 3, is further shown the surface 35 defined between said first line 32, said second straight line 34 and the two curves 36, 37 parallel to the reinforcing elements of the upturn 7 of the carcass reinforcement layer.

Each of the curves 36, 37 is at a distance from the upturn of the carcass reinforcement layer equal to twice the diameter of the reinforcing elements of the carcass reinforcement layer, ie 1.8 mm.

In this figure, it is possible to note that a translation in the axial direction of the portion 30 is included in the surface 35 according to the invention. FIG. 4 illustrates in enlarged manner a diagrammatic sectional representation of a bead 3 of the tire 1, in which there is a portion of the carcass reinforcement layer 2 wound around a bead wire 4 to form a turnaround. 7 with one end 8.

In this figure 4, is shown the axially outermost point Z of the main portion of the carcass reinforcement layer 2; it is determined for example by tomography, the tire being inflated to its nominal pressure.

In this FIG. 4, 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.

We also determine the radially outermost point B of the circle T.

The distance dz between the point Z and the point A is equal to 128 mm.

The distance dR 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.

[00104] Axially outside the overturning 7 of the carcass reinforcement layer is represented the second layer of polymeric mixture 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 layer of polymeric mixture 11 is radially between the points A and B, respectively radially the innermost and radially the outermost of the circle circumscribing the rod.

The second layer of polymeric mixture 11 has an elastic modulus under tension at 10% elongation lower than the modulus of elasticity 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 polymer mixture 14 has a modulus of elasticity under tension at 10% elongation equal to 7.1 MPa.

[00108] 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 modulus of elasticity under tension 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 overturning 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 according to 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 upturn of the protective layer. 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 different mixtures used to make the first and second layers 9 and 1 1 are listed below.

The values of the constituents are expressed in phr (parts by weight per hundred parts of elastomers). The loss factor tan (δ) is a dynamic property of the layer of rubber mixture. 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} .

The rolling resistance is the resistance that appears when the tire rolls. 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.

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, made in accordance with the invention, comprises first and second layers made with the mixture 1 according to the invention.

A second tire 12, made according to 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 RI and R2.

The tires RI, an enlarged schematic representation of the region of the bead is shown in Figure 5, are tires of conventional design comprising stiffeners 18 and more usual bead areas with in particular a thicker bead thickness, with in particular a distance d _R between the end 8 of the upturn 7 of the carcass reinforcement layer 2 and the radially innermost point A of the circle T circumscribed at the bead wire 4 equal to 37% of the distance dz between the point axially the outermost Z of the main portion of the carcass reinforcement layer and the radially innermost point A of the circle T circumscribed to the bead wire and the first and second polymeric mixture layers 9 and 11 made with the mixture 1. Such a more usual bead region further comprises a third layer 50, also consisting of the mixture 1, which is positioned between the radially outermost end of the stiffener and the end of the upturn of the carcass reinforcement.

The tires R2 differ from the tires RI by the absence of stiffener 18 and the third layer 50.

Endurance tests were carried out by rolling two planed tires on one another with a regulated pressure of 5.5b, and a load of 4571 daN at a speed of 50km / h and at an ambient temperature. of 15 ° C for 20000 km.) The tires have previously been run for ten weeks at 60 ° C with inflation with 50% oxygen at 8b.

These tests are carried out by mounting the tires on rims of dimension 22.5x9.00, the surface roughness of the rim hook promotes abrasion of the tire.

The tests were carried out for the tires according to the invention with conditions identical to those applied to the reference tires RI and R2.

After a run of 20000 Km, the lost volume is measured in the tire area which comes into contact with the rim using a laser profilometer. And we check on meridian cuts if cracks appeared in the tire area radially inside the point E.

Regarding the lost volume measurement, the tests carried out for the reference tires R2 at performances establishing the base 100, the index of the other tires being the ratio between the lost volume of the tire R2 and the lost volume of the tire. concerned.

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 attributed to the tire Ri.

Pneumatic Ri Pneumatic R ₂ II 12

100 98 97 96

Claims

1 - Pneumatic tire (1) intended to be mounted on a 15 ° drop center hollow rim (J) comprising a radial carcass reinforcement (2) consisting of a single carcass reinforcement layer formed of elements reinforcement, said tire comprising a crown reinforcement (5), itself capped radially with a tread, said tread being joined to two beads by means of two sidewalls, the layer of reinforcing elements the carcass reinforcement being anchored in each of the beads by turning around a bead wire (4a, 4b) to form a main portion of the carcass reinforcement layer extending from one rod to the other and a reversal (7) of the carcass reinforcement layer in each of the beads, said reversal (7) of the carcass reinforcement layer being separated from the main portion of the carcass reinforcement layer by a first layer (9 ) of polymeric mixture (s) goes out ndant radially from the bead wire (4a, 4b) to at least the end (8) of the upturn (7) of the carcass reinforcement layer and said upturn (7) of the carcass reinforcement being axially towards the outside contact with a second layer (11) of polymeric mixture, itself at least in contact with a third layer (14) of polymeric mixture forming the outer surface of the tire in the region of the bead, said third layer (14) ) of polymeric mixture being intended in particular to come into contact with the rim (J), said third layer (14) of polymeric mixture being radially outwardly in contact with a fourth layer (16) of polymeric mixture forming the outer surface of a flank, in a meridian section of said tire, characterized in that in a meridian section of said tire: the radially outer end (10) of the first layer (9) of polymeric mixture (s) is radially ex at the end (8) of the upturn (7) of the carcass reinforcement layer,

the radially outer end (12) of the second polymeric compound layer (11) is radially external to the end (8) of the carcass reinforcement layer (7), the distance (d _R ) between the end (8) of the upturn (7) of the carcass reinforcement layer and the radially innermost point (A) of the circle (T) circumscribing the bead wire (4) is comprised between 25 and 40% of the distance (dz) between the axially outermost point (Z) of the main portion of the carcass reinforcement layer and the radially innermost point (A) of the circle (T) circumscribed in the rod (4), said first layer (9) of polymeric mixture (s) 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 (8) of the upturn (7) of the carcass reinforcement layer between 30 and 60% of the distance (E ₂ ) between the reinforcing elements of the main part of the reinforcement layer of carcass and the outer surface (S) of the tire measured in the direction of measurement of the thickness (Ei) of the first layer (9) of polymer mixture (s) passing through the end (8) of the upturn (7) of the carcass reinforcement layer,

the ratio of 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 in the said measurement direction of the thickness (Ei) of the first layer ( 9) of polymeric mixture (s) passing through the end (8) of the upturn (7) of the carcass reinforcement layer over the distance (d _R ) between the end (8) of the upturn (7). ) of the carcass reinforcement layer and the radially innermost point (A) of the circle (T) circumscribing the bead wire is less than 0.5,

the upturn (7) of the carcass reinforcement layer and the main portion of the carcass reinforcement layer are the only layers of reinforcing elements whose elongation at break is less than 6% present in an area of the carcass reinforcement layer; flank constituting at least 90% of the flank surface radially between the end (8) of the upturn (7) of the carcass reinforcement layer and the point (B) radially outermost of the bead wire ( 4),

the tensile modulus of elasticity at 10% elongation of the first layer (9) of the polymer mixture (s) and the second layer (11) of the polymer mixture are less than or equal to the modulus of elasticity under 10% elongation of the calender of the carcass reinforcement layer and greater than or equal to 30% of the modulus of elasticity under tension at 10% elongation of the calender of the carcass reinforcement layer.

any point on the profile of the outer surface S of the tire (1), between a first point F, itself defined by the intersection of an axially oriented line passing through the radially outermost point (I) of the rim hook (J) and the outer surface of the tire, and a second point (E), which is the axially outermost point of the tire, is at a distance of less than 2.5 mm from a curve (P) defined by three arcs of circles connecting said first and second points F and E, a first circle (Hi) passes through the point (F), its center being axially oriented towards the inside of the tire with respect to the point (F),

a second circle (H ₂ ) passes through the point (E), its center being axially oriented towards the inside of the tire with respect to the point (E) and on an axially oriented straight line passing through (E),

a third circle (H ₃ ) is tangent to said first and second circles (Hi, H ₂ ), its center being axially oriented towards the outside of the tire with respect to the two points of tangency (M, N) with said first and second circles (Hi, H ₂ ), said two points of tangency (M, N) forming the two points of inflection of said curve P,

the four unknowns (the coordinates of the center of the first circle (Hi) and the radii of the second and third circle (H ₂ , H ₃ )) making it possible to define these circles (Hi, H ₂ , H ₃ ) are determined by 10 points of the surface (S), intermediate between the points (F) and (E), positioned at the relative curvilinear abscissa sin (i * 90deg / l 1), i being the point number, the abscissa 0 being that of the point (E), the abscissa 1 being that of the point (F), minimizing the sum of the distances between the ten intermediate points of the profile of the surface (S) and the curve (P),

the radial distance between the radially innermost inflection point of the curve P and the radially outermost point of the circle circumscribing the bead wire is less than the diameter of the circle circumscribing the bead wire;

the radial distance between the radially outermost point of inflection of the curve P and the point F is greater than 1.1 times the radial distance between the end of the upturn of the carcass reinforcement layer and the point F. 2 - tire (1) according to claim 1, characterized in that in a meridian plane, the portion of the outer surface S of the tire delimited between the intersection of the outer surface S of the tire with a first straight axially oriented and passing through the end of the upturn of the carcass reinforcement layer and the intersection of the outer surface S of the tire with a second straight axially oriented and passing through the radially outermost point of the circle circumscribing the rod is registered by translation in the axial direction in a surface defined between said first straight axially oriented line and passing through the end of the upturn of the carcass reinforcement layer, said second straight axially oriented and passing through the radially outermost point of the circumcircle circle. rod and two curves parallel to the reinforcing elements of the reversal of the reinforcing layer of carcass remote from the overturning of the carcass reinforcement layer by twice the diameter of the reinforcing elements of the carcass reinforcement layer.

3 - tire (1) according to claim 1 or 2, characterized in that any point of the profile of the outer surface (S) of the tire between said first and second points (F) and (E), is at a distance less than 1.25 mm of the curve (P) connecting said first and second points (F) and (E).

4 - tire (1) according to one of the preceding claims, characterized in that the radial distance between the radially outermost point of inflection (M) of the curve P and the point F is greater than 1.5 times the radial distance between the end of the upturn of the carcass reinforcement layer and the point F.

5 - tire (1) according to one of the preceding claims, characterized in that the radial distance between the radially innermost inflection point (N) of the curve P and the point (B) radially outermost of the circle (T) circumscribed to the rod is less than 0.8 times the radial distance between the radially outermost point (B) of the circle circumscribing the bead wire and the radially innermost point (A) of the circle circumscribing the bead wire.

6 - tire (1) according to one of the preceding claims, characterized in that the radial distance between the radially outermost point of inflection (M) of the curve P and the point (F) is greater than 50% of the radial distance between point E and point F. 7 - tire (1) according to one of the preceding claims, characterized in that the radius (R ₃ ) of the third circle (H ₃ ) is between 100% and 160% of the radius (R ₂ ) of the second circle (H ₂ ).

8 - tire (1) according to one of the preceding claims, characterized in that the first layer of polymeric mixture (s) and / or the second layer of polymeric mixture comprise a reinforcing filler consisting of at least one 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 aluminosilicates or alternatively modified carbon blacks during or after synthesis. 9 - tire (1) according to claim 8, characterized in that said first layer of polymer mixture (s) and / or second layer of polymeric mixture are elastomeric mixtures based on natural rubber or synthetic polyisoprene 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 (s) used and 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 pyrogenic silicas, aluminas or aluminosilicates or else the modified carbon blacks in progress or after synthesis, with a BET specific surface area of between 30 and 260 m ² / g employed at a compound rate. 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 carbon black, in which the overall filler rate is between 20 and 50 phr, 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%.

10 - tire (1) according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the calender layers of the carcass reinforcement layer is between 4 and 16 MPa and preferably between 8 and 12 MPa. 11 - tire (1) according to one of the preceding claims, characterized in that the radially inner end of the second polymeric mixture layer is radially between the radially outermost point of the circle circumscribed to the rod and the point radially. the innermost of the circle circumscribed to the rod.

12 - tire (1) according to one of the preceding claims, characterized in that the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribing the rod is between 31 and 37% of 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 bead wire.

13 - tire (1) according to one of the preceding claims, characterized in that, 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 .

14 - tire (1) according to one of the preceding claims, characterized in that the rods are bundles packages, preferably hexagonal shape.