FR3050961A1 - PNEUMATIC WITH BOURRELET'S ZONE IS ALLEGEE - Google Patents

Abstract

The invention relates to a tire with radial carcass reinforcement, consisting of a single layer of reinforcing elements anchored in each of the beads by turning around a bead wire. According to the invention, the overturning of the carcass reinforcement and the carcass reinforcement are coupled then decoupled, the overturning of the carcass reinforcement and the carcass reinforcement are the only layers of reinforcing elements of which Breaking elongation is less than 6% present in the sidewall and the arrangement and the choice of polymeric mixtures of the tire bead area promote endurance performance.

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.

In general, in heavy-vehicle type tires, the carcass reinforcement is anchored on both sides in the region of the bead 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 presents, under the different 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.

[00051] 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.

[00071] The transverse or axial direction of the tire is parallel to the rotational axis of the tire.

[00081] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it.

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: measuring in second elongation (ie, after an accommodation cycle) the secant modulus nominal (or apparent stress, in MPa) at 10% elongation (normal conditions of temperature and hygrometry according to AFNOR-NFT-40101 of December 1979).

[0014] Such tires usually still comprise, at the level of the beads, a number of items of the type which are most frequently used, and which are most often constituted by reinforcing elements oriented with respect to the bead. 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.

[00151] 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, the 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 have thus given themselves the task of providing tires for "heavy-weight" vehicles, whose endurance performance, in particular the endurance of the zones of the beads, are preserved and whose design is simplified and advantageously whose overall mass of the tire is diminished.

This object has been achieved according to the invention by a tire intended to be mounted on a wedged seat rim, comprising a radial carcass reinforcement consisting of a single carcass reinforcement layer formed of inserted reinforcing elements. between two polymeric mixture calendering layers, 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 reinforcing elements of the carcass reinforcement being anchored in each of the beads by turning around a bead wire to form a reversal of the carcass reinforcement, said reversal of the carcass reinforcement being separated from the carcass reinforcement by a first polymeric compound layer extending radially from the bead wire to at least the end of the upturn and said directing the carcass reinforcement axially outwards 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 radially outer end of the first layer of polymer mixture is radially external to the end of the upturn of the carcass reinforcement, - the end of the upturn of the tire. carcass reinforcement is radially external to the radially outer end of the a second layer of polymeric mixture, the radially outer end of the second polymeric mixture layer is radially external to the radially outer end of the third polymeric mixture layer, the distance between the end of the upturn of the polymer reinforcement; carcass and the radially innermost point of the circle circumscribing the bead wire is between 50 and 90% of the distance between the axially outermost point of the tire and the radially innermost point of the circle circumscribing the bead wire, the reversal of the carcass reinforcement and the carcass reinforcement are the only layers of reinforcement elements whose elongation at break is less than 6% present in an area of the sidewall constituting at least 90% of the zone radially between end of the upturn and the radially outermost point of the circle circumscribed to the rod, and radially t to the outside, from a point C of the upturn located at a distance from the radially innermost point of the circle circumscribed to the rod between 30 and 55% of the distance between the end of the upturn of the reinforcement of carcass and the radially innermost point of the circle circumscribing the bead wire, the overturning of the carcass reinforcement and the carcass reinforcement are coupled over a length of between 15 and 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, then to be decoupled by the first layer of polymer mixture to the end of the upturn for a length of 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.

The position of the axially outermost point of the tire is determined on a tire mounted and inflated according to the nominal conditions.

The positions of the radially innermost and radially outermost points of the circle circumscribing the rod are determined on a section of a tire, the spacing of the beads of which is the same as when the tire is mounted on the rim. recommended by ETRTO, as it is neither mounted nor inflated.

In the same way, the different distances, in particular measured from the radially innermost point of the circle circumscribing the bead wire, are measured on a section of a tire, the spacing of which of the beads is the same as when the pneumatic is mounted on the mounting rim recommended by ETRTO, which is neither mounted nor inflated.

Within the meaning of the invention, the carcass reinforcement layer and the carcass reinforcement upturn are said to be coupled if the respective reinforcement elements of the carcass reinforcement layer and the carcass reinforcement upturn are 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 reinforcement elements of the carcass reinforcement layer and the carcass reinforcement upturn 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.

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

The tests have shown that the tires thus produced according to the invention and whose mass is lower than that of tires of more conventional design, for example comprising layers of additional reinforcing elements of the stiffener type, exhibit performance characteristics. terms of 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 carcass reinforcement overturn such that the distance between the end of the upturn of the carcass reinforcement and the point radially the more inside the circle circumscribed to the bead wire is less than 50% of the distance between the axially outermost point of the tire and the radially innermost point of the circle circumscribing the bead wire, in particular to improve the performance of the tire in terms of endurance . Indeed, it is customary to design tires with a carcass reinforcement turnaround of reduced length in order to increase the distance between the carcass reinforcement overturn and the carcass reinforcement, and thus to limit as much as possible the shear stresses 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.

[00301 H is also common in the design of tires whose carcass reinforcement has a turnaround, intended in particular to be mounted on a wedged seat rim and to equip vehicles carrying heavy loads, to avoid a rapprochement and therefore to so much more a coupling of the overturning with the carcass reinforcement so as to prevent any risk of shear between the carcass reinforcement and its overturning which penalizes the first layer of polymeric mixture which separates them.

The inventors have thus been able to demonstrate that the tires made according to 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 of said reversal and the carcass reinforcement, associated with the relative sizing and positioning of the various elements constituting the tire bead zone, make it possible to lighten the tire and against all odds to maintain properties in terms of endurance satisfying or even improving them.

Decoupling between the upturn and the carcass reinforcement following the coupling zone is obtained by increasing the thickness of the first layer of polymer mixture. 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 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, the radially inner end of the second polymeric mixture layer is radially between the radially outermost point of the circle circumscribing the rod and the radially innermost point of the circle circumscribing the rod. . 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 calender 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 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 is less than or equal to the modulus of elasticity under tension at 10% of elongation of the calender 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 polymeric mixture layer is greater than 50% of the modulus of elasticity under tension at 10% elongation of the calendering of the carcass reinforcement layer and preferably is greater than 70% of the modulus of elasticity under tension at 10% of elongation of the calender of the carcass reinforcement layer. This choice makes it possible to maintain the shear stresses within the first polymeric mixture layer while ensuring good endurance performance.

Advantageously according to the invention, the tensile modulus of elasticity at 10% elongation of the second layer of polymeric mixture is greater than the modulus of elasticity under tension at 10% elongation of the first layer of mixture polymeric and preferably strictly less than 25 MPa; it is advantageously still less than 150% of the elastic modulus under tension at 10% elongation of the calendering of the carcass reinforcement 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 tensile modulus of elasticity at 10% elongation of the first layer of polymer blend is greater or equal to the tensile modulus of elasticity at 10% elongation of the third layer of polymeric mixture which itself is greater than or equal to the modulus of elasticity under tension at 10% elongation of the fourth layer of polymer mixture .

According to a preferred embodiment of the invention, in any meridian plane, a length of carcass reinforcement overturn defined 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 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 outer surface of the tire less than 10 mm over a length of the carcass reinforcement upturn delimited radially between the end of said upturn and a point located 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 bead wire.

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 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 layer of polymeric mixture 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.

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 of the 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 protective layer of so-called elastic reinforcing elements oriented with respect to the circumferential direction. with an angle of 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 less 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 optionally decoupled from the edges of said least-extensive 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 inwards between the carcass reinforcement and the radially inner working layer closest to 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 in particular with reference to Figures 1 to 2 which represent: - Figurel, a meridian view of a diagram of a tire according to one embodiment of the invention, - Figure 2, an enlarged schematic representation of the bead area of the tire of Figure 1.

The figures are not shown in scale to simplify understanding.

Figure 1 shows only a half-view of a tire which extends symmetrically with respect to the circumferential mid-plane or equatorial plane of a tire.

In FIG. 1, the tire 1, of dimension 12 R 22.5, has a shape ratio H / L equal to 0.90, H being the maximum radial height of the tire 1 on its mounting rim and L its width. axial axis. 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 6.

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

The carcass reinforcement 2 consists of reinforcing elements between two calendering layers whose modulus of elasticity under tension at 10% elongation is equal to 9.8 MPa.

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

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

[0066] FIG. 1 illustrates the tire mounted on its nominal rim J; the axially outermost point E is thus determined, the tire being inflated to its nominal pressure.

FIG. 2 illustrates in enlarged manner a diagrammatic sectional representation of a bead 3 of the tire in which there is a portion of the carcass reinforcement layer 2 wound around a bead wire 4 to form an upturn 7 with one end 8.

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

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

The distance dE between point E and point A is equal to 120 mm.

The distance dR between the point 8 and the point A is equal to 87 mm.

The ratio of the distance dR over the distance dE is equal to 73% and therefore between 50 and 90%.

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

The ratio of the distance dc on the distance dR is equal to 43% and therefore between 30 and 55%.

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

The coupling thickness between the carcass reinforcement 2 and the upturn 7, measured in the normal direction to the reinforcement elements of the carcass reinforcement 2 between the respective reinforcing elements of the carcass reinforcement layer and the carcass reinforcement overturn, 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 dR. The decoupling length is measured along the line through points D and 8.

The carcass reinforcement upturn 7 is separated from the carcass reinforcement 2 by a first polymeric mixture layer 9, having a radially outer end 10 at a distance dio 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 provide the coupling and decoupling between the carcass reinforcement upturn 7 and the carcass reinforcement 2.

Axially outside the carcass reinforcement upturn 7 is represented the second polymeric mixture layer 11, the radially outer end 12 of which is radially inside the end 8 of the upturn 7. The end radially inner 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 a tensile modulus of elasticity at 10% elongation equal to 12.5 MPa and therefore greater than the modulus of elasticity under tension at 10% elongation of the first layer of polymer mixture. 9 which is equal to 7.8 MPa and less than 150% of the modulus of elasticity under tension at 10% elongation of the calendering layers of the carcass reinforcement 2 which is equal to 9.8 MPa.

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.

[0080] Axially in contact with the first polymeric mixture layer 9, the second polymeric mixture layer 11, the third polymeric mixture layer 14 and axially in contact with the carcass reinforcement upturn 7, is the fourth layer The radially inner end 17 of the fourth polymer blend layer 16 is radially inner at the end 15 of the third polymeric blend layer 14.

The fourth layer of polymeric mixture 16 has a modulus of elasticity under tension at 10% elongation equal to 3.1 MPa.

In areas located on either side of the end 8 of the carcass reinforcement upturn 7, the profile of the fourth polymeric mixture layer 16 is such that said fourth polymeric compound layer 16 has a thickness , measured in the normal direction to the reinforcing elements of the carcass reinforcement 2 at the end 8 of the upturn 7, substantially constant and equal to 3.3 mm, over two radial lengths of approximately 5 mm from each of the two points located on either side of the end 8 at distances of the said end 8 equal to 2.5 mm corresponding to more than 2.5 times the diameter of the carcass reinforcement cables, the latter being equal to 0.9 mm.

Tests have been carried out with tires Ii made according to the invention in accordance with the representation of Figures 1 and 2, tires h which differ from Ii and others with so-called reference tires R.

The tires I2 differ from the tires L by the use of a first layer of polymeric mixture whose modulus of elasticity under tension at 10% elongation is equal to 3.7 MPa and therefore less than 50% of that of the carcass reinforcement layer calendars which is equal to 9.8 MPa.

The reference tires R differ from the tires according to the invention by the presence of stiffeners and a more usual bead area with in particular a distance between the end of the upturn of the carcass reinforcement and the radially innermost point. of the circle circumscribing the bead equals 43% of the distance between the axially outermost point of the tire and the radially innermost point of the circle circumscribing the bead wire and a second layer of polymeric mixture whose modulus of elasticity under tension at 10% elongation is equal to 3.7 MPa and less than that of the carcass reinforcement layer calendars which is equal to 9.8 MPa.

Endurance tests were carried out by rolling two planed tires on one another with a regulated pressure of 8b, with a nitrogen inflation and a load of 6786 daN at a speed of 30km / h.

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

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

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

[00901] Furthermore, rolling resistance measurements have been carried out.

[00911 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 R.

Claims (11)

1 - Pneumatic tire, intended to be mounted on a wedged seat rim, comprising a radial carcass reinforcement, consisting of a single carcass reinforcement layer formed of reinforcement elements inserted between two polymeric mixture calendering layers, 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 reinforcing elements of the carcass reinforcement being anchored in each of the beads by turning around a bead wire to form a tilting of the carcass reinforcement, said tilting of the carcass reinforcement being separated from the carcass reinforcement by a first layer of radially extending polymeric mixture from the bead wire to at least the end of the upturn and said overturning of the carcass reinforcement being axial 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, characterized in that, in a meridian section of said tire, the radially outer end of the first layer of polymeric mixture is radially external to the end of the upturn of the carcass reinforcement, the end of the upturn of the carcass reinforcement is radially external to the radially outer end of the second layer of polymeric mixture, - the end radially outer surface of the second polymeric mixture layer is radially external to the radially outer end of the third polymeric mixture layer; - the distance between the end of the carcass reinforcement upturn and the radially innermost point of the circle; circumscribed between 50 and 90% of the distance between the axially outermost point of the tire and the radially innermost point of the circle circumscribing the bead wire, the overturning of the carcass reinforcement and the reinforcement of carcass are 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 zone between the end of the upturn and the radially most outside the rod, radially outwards, from a point C of the reversal located at a distance d radially the innermost point of the ring circumscribed circle between 30 and 55% of the distance between the end of the overturning of the carcass reinforcement and the radially innermost point of the circle circumscribed to the bead wire, the reversal of the carcass reinforcement and the carcass reinforcement are coupled over a length of between 15 and 65% of the distance between the end of the upturn of the carcass reinforcement and the radially innermost point of the circle circumscribed by the bead wire. , then to be decoupled by the first layer of polymer mixture to the end of the upturn for a length of between 5 and 40% of the distance between the end of the upturn of the carcass reinforcement and the radially most inside the circle circumscribed to the rod. 2 - tire according to claim 1, characterized in that the decoupling length is 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 circumscribing the rod. 3 - A tire according to one of claims 1 or 2, characterized in that the overturning 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 body. reversal of the carcass reinforcement and the radially innermost point of the circle circumscribing the rod. 4 - A tire 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 circumscribing the rod and the radially innermost point. from the circle circumscribed to the rod. 5 - tire 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 is between 4 and 16 MPa and preferably between 8 and 12 MPa. 6 - tire according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the first layer of polymer mixture is less than or equal to the modulus of elasticity under tension at 10% d elongation of the calendering of the carcass reinforcement layer 7 - tire according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the first polymeric mixture layer is greater than 50% of the modulus of elasticity under tension at 10% the calendering elongation of the carcass reinforcement layer is preferably greater than 70% of the tensile modulus of elasticity at 10% of the calendering elongation of the carcass reinforcement layer. 8 - A tire according to one of the preceding claims, characterized in that the modulus of elasticity under tension at 10% elongation of the second layer of polymer mixture is greater than the modulus of elasticity under tension at 10% elongation of the first layer of polymeric mixture and preferably strictly less than 25 MPa. 9 - A tire according to one of the preceding claims, characterized in that, in any meridian plane, a length of carcass reinforcement overturned delimited radially between the end of said reversal and a point located at a distance from the point radially more inside 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 overturning of the reinforcement of carcass is at a distance from the outer surface of the tire less than 10 mm. 10 - A tire 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 volume of rubber mix directly in contact with the rod. 11 - A tire according to one of the preceding claims, characterized in that the rods are bundles packages, preferably hexagonal shape.