WO2019008247A1 - Tyre with a reduced-weight bead region - Google Patents

Abstract

The invention relates to a tire with a radial carcass reinforcement consisting of a single layer (2) of reinforcing elements anchored in each of the beads by turning around a bead wire. According to the invention, the upturn (8) of the carcass reinforcement layer and the main part (2) of the carcass reinforcement layer are the only layers of reinforcing elements whose elongation at break is less than at 6% present in the sidewall, said reversal and the main part are coupled then decoupled, and any point of the profile of the outer surface S of the tire between the points F and E, is at a distance of less than 2.5 mm from the curve P defined by three arcs of circles 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) Ie (s) extending radially from the bead wire to at least the end of the upturn of the carcass reinforcement layer, in a meridian section of said tire: 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 an area of the sidewall constituting at least 90% of the surface of the sidewall radially between the end the upturn of the carcass reinforcement layer and the radially outermost point of the bead wire,

 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 45 and 90% 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,

radially outwards, from a point C of the upturn of the carcass reinforcement layer situated at a distance from the radially innermost point of the circle circumscribing the rod between 30 and 55% of 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, the overturning of the reinforcing layer carcass layer and the main portion of the carcass reinforcement layer being coupled to form a coupling zone over a length of between 15 and 65% of the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribed to the bead wire, then to be decoupled by the first layer of polymer mixture (s),

any point on 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 and E,

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 orthogonal projection of the radially outermost point of inflection of the curve P on the main part of the carcass reinforcement layer being located in the coupling zone of the upturn of the carcass reinforcement layer and the main portion of the carcass reinforcement layer; 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 present 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, the spacing of the beads. is the same as when the tire is mounted on the mounting rim recommended by the ETRTO, which is 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 coordinates X and Y, and circle defined by its center (the point X, Y) and a point (the point F),

H2 circle: creation of a point on a curve (the axial line) at a distance D and a circle defined by its center (the point created) and a point (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 coordinates and Y 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) for defining 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 carcass reinforcement layer and the carcass reinforcement overturn are said to be coupled if the respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement overturn are separated by a substantially constant thickness of rubber mix and not more than 5 mm over more than 15% of the distance between the end of the carcass reinforcement overturn and the radially innermost point of the circumcircle the rod. The thickness of the rubber mixture separating the respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement overturn is measured in the normal direction to the reinforcing elements of the carcass reinforcement. Advantageously according to the invention, the respective reinforcement elements of the carcass reinforcement layer and the carcass reinforcement upturn are separated by a substantially constant thickness of rubber compound of at most 3.5 mm and preferably they are separated by a substantially constant rubber compound thickness of at least 0.8 mm and more preferably a substantially constant rubber compound thickness of at least 2.5 mm. Within the meaning of the invention, a substantially constant thickness of rubber compound separating the respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement upturn is a thickness that does not vary by more than 0.5. mm. The variations in thickness are then due to creep phenomena during the manufacture and baking of the tire. Within the meaning of the invention, the carcass reinforcement layer and the carcass reinforcement upturn are said to be decoupled if, radially outside the coupling zone, the thickness of the rubber mixture separating the elements respective reinforcement of the carcass reinforcement layer and the carcass reinforcement upturn is greater than that of the coupling zone. The respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement overturning are then advantageously separated by a rubber compound thickness of between 3 and 8 mm, said thickness of rubber compound being measured in the normal direction to reinforcement elements of the carcass reinforcement between the respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement overturning. Preferably according to the invention, in the decoupling zone, the respective reinforcement elements of the carcass reinforcement layer and the carcass reinforcement upturn are separated by at most 6 mm and preferably they are separated from each other. at least 4 mm.

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 on 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 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, and in particular in terms of endurance of the bead zones, at least as good as those of said tires of more conventional design, or even higher.

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

The inventors have thus been able to demonstrate that the tires made in accordance with 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 think 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 the outer surface of the tire between the points E and F with a concave zone whose radially outer end corresponds to the radially outermost point of inflection of the curve P on the main part of the carcass reinforcement layer and which is located in the coupling zone of the upturn of the carcass reinforcement layer and the main part of the carcass reinforcement layer also leads to an optimization of the division between the meridian flexion and the shear of the first layer of carcass reinforcement. polymeric mixture (s) during the recovery of the tensions due to inflation by the overturning of the carcass reinforcement layer; 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, moreover, all the more surprising that the more usual designs of the areas of the beads of this type of tire include a carcass reinforcement upturn such as the distance between the end of the turnaround of the carcass reinforcement and the radially innermost point of the circle circumscribing the rod is less than 45% of the distance between the axially outermost point of the main part of the carcass reinforcement layer and the radially innermost point the circle circumscribed to the bead wire to improve the performance of the tire in terms of endurance. Indeed, it is customary to design tires with a carcass reinforcement rollover of reduced length to increase the distance between the carcass reinforcement overturning and the carcass reinforcement, and thus to limit as much as possible the shear deformations which are initiated between the carasse reinforcement and its reversal in particular due to the de-radialization phenomena that appear during the rolling of the tire.

It is also common in the design of tires whose carcass reinforcement has a turnaround, intended in particular to be mounted on a hollow rim (15 ° drop center) or wedged seat rim and to equip vehicles carrying heavy loads, to avoid a connection and therefore even more a coupling of the overturning with the carcass reinforcement so as to prevent any risk of shear between the reinforcement carcass and its overturning which penalizes the first layer of polymeric mixture that separates them.

The inventors have thus been able to demonstrate that the tires made in accordance with the invention and which have in particular a reversal of the carcass reinforcement with a length greater than the most usual designs, a coupling of the reversal with the carcass reinforcement followed. a decoupling said reversal and the carcass reinforcement, associated with the outer profile of the low zone of the tire, allow to lighten the tire and against all odds to maintain properties in terms of endurance areas of satisfactory beads, to improve them. 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, the orthogonal projection of the radially outermost inflection point of the curve P on the overturning of the carcass reinforcement layer is located at a distance from the point radially on the more inside the circle circumscribed to the rod between 40 and 85% of the distance between the end of the upturn of the carcass reinforcement layer and the radially innermost point of the circle circumscribed to the bead wire. This embodiment further optimizes the recovery of tensions, during inflation, by the overturning 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 radially innermost inflection point of the curve P closer to the bead further optimizes the support zone of the tire on the rim. Advantageously according to the invention, the radius of the third circle is greater than twice the radius of the first circle.

Advantageously again according to the invention, the radius of the second circle is greater than twice the radius of the third circle.

According to a preferred embodiment of the invention, a fourth circle passing through the point Gi of the upturn of the carcass reinforcement layer located on the axial line passing through the radially outermost point of the circle circumscribing the rod, by the point G ₂ located on the overturning of the carcass reinforcement layer between the point Gi and the end of the upturn of the carcass reinforcement layer, at a distance from the point C equal to twice the decoupling thickness measured at point C, and by a point G ₃ of the upturn of the carcass reinforcement layer equidistant from the points Gi and G ₂ , the radius of the third circle being greater than the radius of the fourth circle and less than twice the radius of the fourth circle.

Advantageously according to this preferred embodiment of the invention, the radius of the third circle is less than 1.75 times the radius of the fourth circle and preferably less than 1.5 times the radius of the fourth circle.

According to this preferred embodiment of the invention, the radius of the third circle is greater but relatively close to that of the fourth circle to avoid the appearance of singular points that can lead to hinge phenomena unfavorable to the performance in terms of performance. endurance of the bead area of the tire. Indeed, this embodiment limits the thickness variations of the rubber compounds between the upturn of the carcass reinforcement layer and the outer surface of the tire in this region of the bead of the tire.

According to an advantageous embodiment of the invention, the decoupling zone may consist of a first portion, called transition, extending the coupling zone in which the thickness of the rubber mixture separating the respective reinforcing elements. of the carcass reinforcement layer and the carcass reinforcement upturn increases and of a second radially outermost part in which the thickness of the rubber mixture separates the respective reinforcement elements from the reinforcement layer. carcass reinforcement layer and carcass reinforcement overturning is substantially constant.

Decoupling between the upturn and the carcass reinforcement following the coupling zone is advantageously obtained by increasing the thickness of the first layer of polymer mixture (s). This decoupling makes it possible to compensate for the decrease in the tension in the reinforcement elements of the carcass reinforcement when approaching the end of its upturn to absorb the shear stresses between the carcass reinforcement and its reinforcement. turnaround.

Advantageously according to the invention, the decoupling length is between 5 and 40% of the distance between the end of the upturn of the carcass reinforcement and the radially innermost point of the circle circumscribing the rod and of preferably between 15 and 35% of the distance between the end of the upturn of the carcass reinforcement and the radially innermost point of the circle circumscribed to the bead wire.

Preferably according to the invention, the upturn of the carcass reinforcement and the carcass reinforcement are coupled over a length of between 25 and 40% of the distance between the end of the upturn of the carcass reinforcement. and the radially innermost point of the circle circumscribing the rod.

Advantageously according to the invention, 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.

According to an alternative embodiment of the invention in a meridian section of the tire beads, said reversal 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 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 sidewall, and according to the invention, in a meridian section of said tire, the end of the upturn of the carcass reinforcement is radially external to the radially outer end of the second layer of polymer mixture.

According to other embodiments of the invention, in a meridian section of the tire beads, the end of the upturn of the carcass reinforcement is radially internal to the radially outer end of the second layer. polymeric mixture.

Advantageously, according to other embodiments of the zones of the beads of the tire according to the invention, the radially outer end of the second polymeric mixture layer is radially external to the radially outer end of the third layer of mixture. polymer.

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.

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.

Preferably according to the invention, the modulus of elasticity under tension at 10% elongation of the first layer of polymer mixture (s) is less than or equal to the tensile modulus of elasticity at 10% of lengthening of the calendering of the carcass reinforcement layer. This choice makes it possible in particular to concentrate the shearing forces within the first layer of polymer mixture. More preferably according to the invention, the modulus of elasticity under tension at 10% elongation of the first layer of polymer mixture (s) is greater than 50% of the tensile modulus of elasticity at 10% of the calendering elongation of the carcass reinforcement layer and preferably is greater than 70% of the modulus of elasticity under tension at 10% elongation of the calendering of the carcass reinforcement layer. This choice makes it possible to maintain shear forces within the first layer of polymer mixture (s) while ensuring good endurance performance.

Advantageously according to the invention, the tensile modulus of elasticity at 10% elongation of the second polymeric mixture layer is less than 150% of the tensile modulus of elasticity at 10% elongation of the calender of the carcass reinforcement layer and preferably strictly less than 25 MPa; it is advantageously still superior to the modulus of elasticity under tension at 10% elongation of the first polymeric mixture layer. According to this advantageous embodiment of the invention, the second polymeric compound layer provides sufficient rigidity to ensure good endurance of the tire during the support on the rim hooks while ensuring satisfactory performance in terms of rolling resistance.

According to a preferred embodiment of the invention, to promote the compromise between endurance performance and rolling resistance, the modulus of elasticity under tension at 10% elongation of the first layer of mixture (s). ) the polymer (s) is greater than or equal to the modulus of elasticity under tension at 10% elongation of the third layer of polymeric mixture which itself is greater than or equal to the tensile modulus of elasticity at 10% elongation the fourth layer of polymeric mixture.

According to a preferred embodiment of the invention, in any meridian plane, a length of the carcass reinforcement overturned delimited radially between the end of said reversal and a point situated at a distance from the radially innermost point. of the circle circumscribing the bead wire equal to 65% of the distance between the end of the upturn of the carcass reinforcement and the radially innermost point of the circle circumscribing the bead wire, any point of the upturn of the carcass reinforcement is at a distance from the outer surface of the tire less than 10 mm. More preferably, any point of the upturn of the carcass reinforcement is at a distance from the surface external tire less than 10 mm over a length of carcass reinforcement overturned delimited radially between the end of said overturning and a point situated at a distance from the radially innermost point of the circle circumscribing the bead wire equal to 50% of the distance between the end of the upturn of the carcass reinforcement and the radially innermost point of the circle circumscribing the rod.

Advantageously again according to the invention, in any meridian plane, over a radial distance greater than 4 mm, and preferably greater than 10 mm, starting radially outside the end of the carcass reinforcement overturning and at a radial distance from the end of the carcass reinforcement upturn equal to 2.5 times the diameter of a reinforcing element of the carcass reinforcement and extending radially outwards, the thickness, measured according to the normal direction to the reinforcement elements of the carcass reinforcement upturn at the end of the carcass reinforcement upturn, the fourth layer of polymeric mixture forming the outer surface of a flank is substantially constant. Advantageously also according to the invention, in any meridian plane, over a radial distance greater than 4 mm, and preferably greater than 10 mm, starting radially inside the end of the carcass reinforcement overturning and at a radial distance from the end of the carcass reinforcement upturn equal to 2.5 times the diameter of a reinforcement element of the carcass reinforcement and extending radially inwards, the thickness, measured according to the normal direction to the reinforcement elements of the carcass reinforcement upturn at the end of the carcass reinforcement upturn, the fourth layer of polymeric mixture forming the outer surface of a flank is substantially constant.

For the purposes of the invention, the expression a substantially constant thickness means that it does not vary by more than 0.5 mm. These variations in thickness are due to creep phenomena during the manufacture and baking of the tire.

The fourth layer of polymeric mixture thus produced according to the invention seems to contribute to the better positioning of the first polymeric mixture layer and its implementation to ensure the coupling and decoupling of the carcass reinforcement layer. and the carcass reinforcement overturn. 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 changes in form 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 the other 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, so-called protective, of so-called elastic reinforcing elements, oriented relative 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 one of the embodiments of the invention mentioned above, the crown reinforcement may 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 embodiments of the invention, particularly with reference to FIGS. 1 to 4 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, an enlarged schematic representation of the zone of the bead, FIG. 4 is an enlarged schematic representation of the zone of a bead of a reference tire. 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 flipping 7 of the layer of carcass reinforcement having an end 8. [0085] 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 break 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. [0088] 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.

[0089] 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 of the profile of the outer surface S of the tire between the points F and E is at a distance of less than 0.95 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 16.5 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 134 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 39 mm. The radius R ₃ of the circle H ₃ is therefore much greater than 2 times the radius Ri of the circle

The radius R ₂ of the circle H ₂ is thus much greater than 2 times the radius R ₃ of the circle H ₃ . The circle H ₄ is defined as being the circle by the point Gi of the overturning of the carcass reinforcement layer situated on the axial line passing through the radially outermost point of the circle circumscribing the bead wire, by the point G ₂ located on the upturn of the carcass reinforcement layer between the point Gi and the end of the upturn of the carcass reinforcement layer, at a distance from the point C equal to twice the decoupling thickness measured at point C, and the point G ₃ of the upturn of the carcass reinforcement layer equidistant points Gi and G ₂ . The radius R ₄ of the circle H ₄ is equal to 25.3 mm.

The radius R ₃ of the circle H ₃ is greater than the radius R ₄ of a fourth circle H ₄ and less than 2 times the radius R ₄ of the circle H ₄ .

The radial distance between the radially innermost point of inflection N of the curve P and the radially outermost point B of the circle circumscribing the bead wire is equal to 2.8 mm and therefore less than the diameter of the circle circumscribed in FIG. rod which is equal to 16.5 mm.

The radial distance between the radially outermost point of inflection M of the curve P and the radially outermost point of the circle circumscribing the rod is equal to 29 mm.

The orthogonal projection M _P of the radially outermost point of inflection M of the curve P on the main part of the carcass reinforcement layer is according to the invention situated in the coupling zone of the reversal of the carcass reinforcement layer and the main part of the carcass reinforcement layer and more precisely at 63% of 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. [00101] FIG. 3 illustrates an enlarged schematic 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 3, 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 Figure 3, is further materialized the circle T circumscribing the rod 4 and appears 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. 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 radius of the circle T circumscribing the rod is equal to 8.25 mm.

[00104] The radially outermost point B of the circle T is also determined.

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

The distance d _R between the point 8 and the point A is equal to 90 mm.

The ratio of the distance d _R over the distance d _z is 70% and therefore between 45 and 90%.

The upturn 7 of the carcass reinforcement layer is coupled to the main part of the carcass reinforcement layer 2 from the point C, such that the distance between the point C and the point A is equal to 37 mm.

The ratio of the distance d _c over the distance d _R is equal to 41% and therefore between 30 and 55%.

The upturn 7 of the carcass reinforcement layer is then decoupled from the main part of the carcass reinforcement layer 2 from the point D, such that the distance d _D between the point D and the point A is equal to 66 mm and such that the coupling length between the point C and the point D is equal to 29 mm and therefore between 25 and 40% from the distance d _R. The coupling length is measured along the straight line through points C and D.

The coupling thickness between the main portion of the carcass reinforcement layer 2 and the upturn 7 of the carcass reinforcement layer, measured in the normal direction to the reinforcing elements of the main part of the layer of carcass reinforcement 2 between the respective reinforcement elements of the main part of the carcass reinforcement layer and the upturn of the carcass reinforcement layer, is substantially constant and equal to 2.9 mm.

The decoupling length between the point D and the point 8 is equal to 21 mm and therefore between 15 and 35% of the distance d _R. The decoupling length is measured along the line through points D and 8.

The upturn 7 of the carcass reinforcement layer is separated from the carcass reinforcement 2 by a first layer of polymeric mixture 9, having a radially outer end 10 at a dio distance from the point A equal to 117 mm. The first polymeric mixture layer 9 has a tensile modulus of elasticity at 10% elongation equal to 7.8 MPa and therefore less than the tensile modulus of elasticity at 10% elongation of the calendering layers of the reinforcement. carcass 2.

The first layer of polymeric mixture 9 is profiled to bear on the bead wire 4 and ensure the coupling and decoupling between the upturn of the carcass reinforcement layer 7 and the main part of the carcass reinforcement layer. 2.

Axially on the outside of the upturn 7 of the carcass reinforcement layer is represented the second layer of polymeric mixture 11, the radially outer end 12 of which is radially inside the end 8 of the upturn 7. the carcass reinforcement layer. 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 polymeric mixture layer 11 has an elastic modulus under tension at 10% elongation equal to 12.5 MPa and therefore greater than the modulus elasticity under tension at 10% elongation of the calender 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.

[00119] Axially in contact with the first polymeric mixture layer 9, the second polymeric mixture layer 11, and the third polymeric mixture layer 14, is the fourth polymeric mixture layer 16. The radially inner end 17 of the fourth layer of polymeric mixture 16 is radially inner to the end 15 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.

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. 15 ° C during 20000 km.

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

The tires 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 4, are tires of conventional design having stiffeners 18 and more usual bead areas including a greater thickness of the bead, with in particular a distance dR between the end 8 of the upturn 7 of the carcass reinforcement layer 2 and the point A radially the most inside the circle T circumscribed at the bead wire 4 equal to 37% of the distance dz between the axially outermost point Z of the main part of the carcass reinforcement layer and the radially innermost point A of the circle T circumscribed at the bead wire and first and second layers of polymeric mixture 9 and 11 whose modulus of elasticity under tension at 10% elongation is equal to 3.7 MPa.

The tires R2 differ from the tires RI by the absence of stiffener 18.

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 expressed in Kg / t, a value of 100 being attributed to the tire Ri.

Pneumatic Ri Pneumatic R ₂ Invention

100 98 96

Claims

1 - Pneumatic tire (1), intended to be mounted on a rim (J) hollow type 15 ° drop center), comprising a radial carcass reinforcement (2) consisting of a single carcass reinforcement layer formed of reinforcement elements, said tire comprising a crown reinforcement (5), itself capped radially with a tread, said tread being joined to two beads by means of two flanks, the layer of elements of reinforcing 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) 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, characterized in that in a meridian section of said tire: the upturn (7) of the carcass reinforcement layer and the main portion of the carcass reinforcement layer are the only layers of reinforcement elements whose elongation at break is less than 6% present in a zone of the sidewall constituting at least 90 % of the flank surface radially between the end (8) of the upturn (7) of the carcass reinforcement layer and the radially outermost point (B) of the bead wire, 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 circumscribed by the bead wire is between 45 and 90% 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) circumscribing the rod (4), radially outwardly from a point (C) of the upturn (7) of the carcass reinforcement layer located at a distance (d _c ) from the radially innermost point (A) of the circle (T) circumscribed to the rod (4) between 30 and 55% of 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 rod (4), the upturn (7) of the carcass reinforcement layer and the main portion of the carcass reinforcement layer are coupled to form a coupling zone over a length of between 15 and 65% of the distance (d _R ) between 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), then to be decoupled by the first layer (9). ) of polymeric mixture (s), any point of the profile of the outer surface S of the tire (1), between a first point F, itself defined by the intersection of a straight line of axial orientation, passing by the radially outermost point (I) of the rim hook (J) and the tire outer surface, and a second point (E), which is t the axially outermost point of the tire, is at a distance less than 2.5 mm from a curve (P) defined by three arcs of circles connecting said first and second points F and E, in that 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), in that 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), in that a third circle (H ₃ ) is tangent to said first and second circles (H ₁ , 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, in that the four unknowns (the coordinates of the center of the first circle (Hi) and the radii of the second and third circles (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 / ll), i being the point number, the abscissa 0 being the from point (E), the abscissa 1 being that of point (F), minimizing the sum of the distances between the ten intermediate points of the profile of the surface (S) and the curve (P), in that the radial distance between the radially innermost inflection point (N) of the curve P and the radially outermost point (B) of the circle (T) circumscribing the bead wire (4) is less than the diameter of the circle (T) circumscribed on the rod (4), in that the orthogonal projection (M _P ) of the radially outermost point of inflection (M) of the curve (P) on the main part of the carcass reinforcement layer is located in the coupling zone of the inversion ( 7) of the carcass reinforcement layer and the main part of the carcass reinforcement layer. 2 - tire (1) according to claim 1, 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 of less than 1.25 mm of the curve (P) connecting said first and second points (F) and (E). 3 - tire (1) according to claim 2, characterized in that the orthogonal projection (M _P ) of the radially outermost point of inflection (M) of the curve (P) on the upturn (7) of the carcass reinforcement is situated at a distance from the radially innermost point (A) of the circle circumscribed to the rod between 40 and 85% of 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 circumscribing the bead wire. 4 - tire (1) according to one of the preceding claims, characterized in that the radial distance between the radially innermost point of inflection (N) of the curve (P) and the point (B) radially the outermost the circle (T) circumscribed in the bead wire (4) is less than 0.8 times the radial distance between the radially outermost point (B) of the circle (T) circumscribing the bead wire (4) and the point (A) radially more inside the circle (T) circumscribed to the rod (4). 5 - tire (1) according to one of the preceding claims, characterized in that the radius (R ₃ ) of the third circle (H ₃ ) is greater than twice the radius (Ri) of the first circle (Hi). 6 - tire (1) according to one of the preceding claims, characterized in that the radius (R ₂ ) of the second circle (H ₂ ) is greater than twice the radius (R ₃ ) of the third circle (H ₃ ). 7 - tire according to one of the preceding claims, a fourth circle (H ₄ ) passing through the point (Gi) of the upturn (7) of the carcass reinforcement layer located on the axial line passing through the point (B). radially the outermost of the circle (T) circumscribing the rod (4), by the point (G ₂ ) located on the upturn (7) of the carcass reinforcement layer between the point (Gi) and the end ( 8) of the upturn (7) of the carcass reinforcement layer, at a distance from the point (C) equal to twice the decoupling thickness measured at the point (C), and by the point (G ₃ ) of the upturn (7) of the carcass reinforcement layer equidistant from the points (Gi) and (G ₂ ), characterized in that the radius (R ₃ ) of the third circle (H ₃ ) is greater than the radius (R ₄ ) of the fourth circle (H ₄ ) and less than twice the radius of the fourth circle. 8 - tire (1) according to claim 7, characterized in that the radius (R ₃ ) of the third circle (H ₃ ) is less than 1.75 times the radius of the fourth circle and preferably less than 1.5 times the radius of the fourth circle . 9 - tire (1) according to one of the preceding claims, characterized in that the decoupling length is between 5 and 40% of the distance (d _R ) between the end (8) of the upturn (7) of the carcass reinforcement and the radially innermost point (A) of the circle (T) circumscribing the rod (4), and preferably between 15 and 35% of the distance (d _R ) between the end (8) the upturn (7) of the carcass reinforcement and the radially innermost point (A) of the circle (T) circumscribing the rod (4). 10 - tire (1) according to one of the preceding claims, characterized in that the upturn (7) of the carcass reinforcement and the carcass reinforcement are coupled over a length of between 25 and 40% of the distance ( d _R ) between the end (8) of the upturn (7) of the carcass reinforcement and the point (A) radially innermost of the circle (T) circumscribed to the rod (4). 11 - tire (1) according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the calendering layers of the carcass reinforcement layer (2) is between 4 and 16 MPa and preferably between 8 and 12 MPa. 12 - tire (1) according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the first layer (9) of polymer (s) mixture (s) is lower or equal to the elastic modulus under tension at 10% elongation of the calendering of the carcass reinforcement layer (2). 13 - tire (1) according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the first layer (9) of polymer (s) mixture (s) is greater than 50% of the elastic modulus under tension at 10% elongation of the calender of the carcass reinforcement layer (2) and preferably is greater than 70% of the modulus of elasticity under tension at 10% elongation of the calendering of the carcass reinforcement layer (2). 14 - tire (1) according to one of the preceding claims, said reversal (7) of the carcass reinforcement layer being axially outwardly in contact with a second layer (11) of polymeric mixture, characterized in that that the modulus of elasticity under tension at 10% elongation of the second layer (11) of polymer mixture is less than 150%) of the modulus of elasticity under tension at 10% of elongation of the calendering of the layer of carcass reinforcement (2), preferably strictly less than 25 MPa and more preferably greater than the modulus of elasticity under tension at 10% elongation of the first (9) layer of polymeric mixture. 15 - tire (1) according to one of the preceding claims, characterized in that, in any meridian plane, over a length of the upturn (7) the carcass reinforcement layer defined radially between the end (8) of said reversal of the carcass reinforcement layer and a point located at a distance from the radially innermost point (B) of the circle (T) circumscribing the rod (4) equal to 65% of the distance (άκ) between the end (8) the upturn (7) of the carcass reinforcement layer and the radially innermost point (A) of the circle (T) circumscribing the bead wire (4), any point of the upturn (7) of the the carcass reinforcement is at a distance from the outer surface (S) of the tire less than 10 mm.