TIRES WITH IMPROVED ROLLING RESISTANCE

Description

[0001] The present invention relates to a tire with a radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads and traveling at sustained speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] In general, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may be further covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of low-extensibility wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, known as the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement that exhibits minimal deformation under the various stresses it is subjected to. The triangulation layer's essential role is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area of ​​the tire.

[0003] Cables are said to be inextensible when, under a tensile force equal to 10% of the breaking force, said cables exhibit a relative elongation of no more than 0.2%.

[0004] Cables are said to be elastic when, under a tensile force equal to the breaking load, said cables exhibit a relative elongation of at least 3% with a maximum tangent modulus less than 150 GPa.

[0005] Circumferential reinforcement elements are reinforcement elements that make angles with the circumferential direction within the range of +2.5°, -2.5° around 0°.

[0006] The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the direction of rolling of the tire.

[0007] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

[0008] Radial direction is a direction that intersects the axis of rotation of the tire and is perpendicular to it.

[0009] The axis of rotation of the tire is the axis around which it rotates in normal use.

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

[0011] The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

[0012] Such tires typically still incorporate one or more layers of reinforcing elements, known as stiffeners, in the bead area. These layers are most often made up of reinforcing elements oriented at an angle of less than 45°, and more commonly less than 25°, relative to the circumferential direction. The function of these reinforcing layers is, in particular, to limit the longitudinal movement of the bead materials relative to the wheel rim, thereby preventing premature bead wear. They also help limit the permanent deformation of the bead on the rim hook, caused by the dynamic creep of the elastomeric materials. Excessive bead deformation can prevent tire retreading.They also contribute to protecting the tire bead areas from damage sustained during the mounting and dismounting of tires on rims.

[0013] Furthermore, in the case of carcass reinforcement anchoring made around a bead, which consists of wrapping at least part of the carcass reinforcement around a bead in each of the ridges by forming a turn extending more or less high in the sidewall, the layers of reinforcement or stiffening elements still make it possible to avoid or delay the unwinding of the carcass reinforcement during accidental and excessive heating of the rim.

[0014] These layers of reinforcement elements or stiffeners are most often arranged axially outside the reversal of the frame reinforcement and extend over a height in the side greater than that of the reversal in particular to cover the free ends of the reinforcement elements of said reversal.

[0015] Such tire designs are described for example in documents FR 2779387 or US 2006 / 0000199 or GB 2 065 573.

[0016] The presence of these layers of reinforcing elements or stiffeners contributes to thickening the bead area all the way down to the sidewall, towards the area of ​​the tire where it has its greatest axial width. This tire profile appears to be susceptible to brittleness in the tire under certain types of impacts during specific usage conditions.

[0017] In order to reduce the risk of damage to tires due to friction on curbs, it is known, in particular from documents WO 2020 / 012122 and WO 2020 / 012121, to propose tires having in the area of ​​the bead a recessed part which also leads to a reduction in the weight of the tire.

[0018] The inventors have nevertheless highlighted that under particularly severe driving conditions, especially in terms of load and / or inflation pressure, the performance in terms of rolling resistance was not at the expected level in view of this reduction in tire weight.

[0019] Document WO2021 / 126187 further describes a bead area of ​​a heavy-duty tire in which the filling compounds exhibit different stiffnesses.

[0020] The inventors have thus set themselves the mission of providing tires for "Heavy Goods Vehicles", whose endurance performance, in particular the endurance of the bead areas, is maintained, whose wear performance of the bead area is satisfactory and whose design allows for improved performance in terms of rolling resistance.

[0021] This objective has been achieved according to the invention by a tire comprising a radial carcass reinforcement, consisting of a carcass reinforcement layer formed of reinforcing elements, said tire comprising a crown reinforcement, itself radially capped by 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 folding around a bead to form a main part of the carcass reinforcement layer extending from one bead to the other and a folding of the carcass reinforcement layer in each of the beads, said folding of the carcass reinforcement being reinforced by at least one layer of reinforcing or stiffening elements,a first layer of polymeric mixture(s) being at least partly axially internal to the end of said fold of the carcass reinforcement layer, a second layer of polymeric mixture(s) being at least partly axially external to the radially external end of said stiffener, a third layer of polymeric mixture(s) forming the outer surface of the tire in the bead area, said third layer of polymeric mixture(s) being intended in particular to come into contact with the rim, said third layer of polymeric mixture(s) being radially outwards in contact with a fourth layer of polymeric mixture(s) forming the outer surface of a sidewall, the stiffener being axially separated from the fold of the carcass reinforcement layer by a fifth layer of polymeric mixture(s),the thickness of polymeric mixture(s) consisting of the third and / or fourth layer of polymeric mixture(s) forming the outer surface of the tire, measured radially outside the innermost radial point of the bead, being greater than or equal to 2 mm, and in a meridional section of said tire, , a sixth layer of polymer compound(s) occupying at least one radially bounded area between the outermost axial point F of the tire and a point H of the outer surface of the tire, said point H being radially outer to the end of the fold of the carcass reinforcement layer and radially outer to the radially outer end of the stiffener, said area being axially bounded between the polymer compound(s) consisting of the third and / or fourth layer of polymer compound(s), and the main part of the carcass reinforcement layer, the sixth layer of polymer compound(s) being at least 1.5 mm away from the radially outer end of the stiffener and at least 1.5 mm away from the end of the fold of the carcass reinforcement layer, the maximum value of tan(δ), denoted tan(δ)max, measured at 60°C, of ​​the sixth layer of polymer mixture(s) being less than 0.050 and the linearity ratio of the complex dynamic shear modulus G*, at a temperature of 23°C, of ​​the sixth layer of polymer mixture(s) being greater than 0.80, the linearity ratio being defined by the ratio of G* min on G* max , with G* min being the minimum value of the complex dynamic shear modulus G* for a strain of 1 to 100%, and G* max being the maximum value of the complex dynamic shear modulus G* for a strain of 1 to 100%.

[0022] The meridian section of the tire is defined according to the invention such that the barycenters of the beads form an axially oriented straight line, said barycenters being separated from each other by a distance equal to the nominal rim width J increased by 20 mm and decreased by twice the axially measured distance between a barycenter of a bead and a point on the outer surface of the tire.

[0023] The position of point F, axially the outermost of the tire, is determined on a tire mounted and inflated according to nominal conditions.

[0024] For the purposes of the invention, the thickness of polymeric mixture(s) consisting of the third and / or fourth layer of polymeric mixture(s) forming the outer surface of the tire is measured along the direction normal to the outer surface of the tire.

[0025] The loss factor tan(δ) is a dynamic property of the rubber compound layer. It is measured on a viscoelastic analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a vulcanized compound sample (a 2 mm thick cylindrical specimen with a cross-sectional area of ​​78 mm²) is recorded under sinusoidal alternating simple shear loading at a frequency of 10 Hz and a temperature of 60°C. A strain amplitude sweep is performed from 0.1% to 100% (forward cycle), then from 100% to 1% (reverse cycle). The results analyzed are the complex dynamic shear modulus (G*) and the loss factor tan(δ) measured during the reverse cycle. For the reverse cycle, the maximum observed value of tan(δ) is recorded, denoted tan(δ) max. For the measurement of the complex dynamic shear modulus (G*) according to the invention, the sinusoidal loading in simple alternating shear, at a frequency of 10Hz, is carried out at a temperature of 23°C.

[0026] According to the invention, said at least one layer of reinforcing or stiffening elements is made of metallic or textile reinforcing elements. In a first embodiment, the radially innermost end of said at least one layer of reinforcing or stiffening elements is radially external to the radially innermost point of the rod. In a second embodiment, the radially innermost end of said at least one layer of reinforcing or stiffening elements is radially internal to the radially innermost point of the rod. In a third embodiment, said at least one layer of reinforcing or stiffening elements is wrapped around the rod such that one of its ends is axially internal to the main part of the frame reinforcement layer.

[0027] For the purposes of this invention, the six polymer mixture layers correspond to volumes and should be understood as being able to be made from one or more polymer mixtures combined to constitute these volumes. These combinations can be made along axial and / or radial directions. Industrially, the six polymer layers correspond to semi-finished products previously prepared for tire manufacturing. When such a layer is made up of several polymer mixtures as described above, these polymer mixtures can each constitute a semi-finished product or be previously combined to form a single semi-finished product, advantageously produced by co-extrusion techniques that allow the different polymer mixtures to be combined.

[0028] Tests have shown that tires manufactured according to the invention exhibit significantly superior rolling resistance compared to more conventionally designed tires, as well as compared to tires with recessed and therefore lighter bead areas. Furthermore, the tires according to the invention exhibit satisfactory wear performance due to impacts and / or friction against curbs during normal driving conditions, and their durability, particularly in terms of bead area durability, is at least as good as that of more conventionally designed tires.

[0029] The inventors have demonstrated that tires made according to the invention and which have a bead area of ​​usual shape and a layer of polymer mixture(s) forming the outer surface of the tire of usual composition, although of reduced thickness compared to more usual designs, make it possible to obtain performance in terms of wear sufficient for usual uses.

[0030] Surprisingly, the inventors also highlighted that the tires according to the invention are more efficient in terms of rolling resistance than tires such as those described previously having a hollowed-out area in the bead area, despite the weight reduction of the latter.

[0031] The inventors believe they interpret this result concerning rolling resistance as the fact that the weight reduction linked to the hollowed-out part of the bead area of ​​the tires previously described allows a greater flexing of this part of the tire during its use, particularly in extreme conditions either in terms of load carried or in terms of inflation pressure, and therefore greater deformations of certain parts of the tire than in the case of tires of more usual design or than in the case of tires according to the invention.

[0032] Compared to a more conventional tire design, which lacks a hollow section in the bead area, the relatively high linearity of the complex dynamic shear modulus G* of the sixth layer, compared to that of the polymer compounds used in more conventional tires, leads to lower heat dissipation and therefore weaker hysteresis. The inventors believe this is due to the relatively large deformation of the tire at the level of the sixth layer, caused by the deformation of the tire as it presses against the rim edge during rolling contact.The Payne effect, being less pronounced for the compound constituting the sixth layer according to the invention than for the polymer compounds used in more conventional tires, appears to contribute to lower heat dissipation due to reduced hysteresis properties during a wheel rotation deformation cycle, with deformations being low opposite the contact patch and high within it. Furthermore, the Payne effect leads the inventors to believe that the lower low-strain stiffness of the compound constituting the sixth layer according to the invention, without altering the high-strain stiffness, linked to the relatively high linearity of the complex dynamic shear modulus G*, has no impact on the tire's durability properties, given the chosen location of the sixth layer.

[0033] According to a first embodiment of the invention, the sixth layer of polymer mixture(s) extends radially towards the radially inner end of the stiffener in an area axially outside the stiffener.

[0034] According to this first embodiment of the invention, the sixth layer of polymer mixture(s) extending axially outwards from the stiffener, it replaces at least in part the second layer of polymer mixture(s) and / or the third layer of polymer mixture(s) and / or the fourth layer of polymer mixture(s).

[0035] This first embodiment of the invention can increase the volume of the sixth layer of polymer mixture(s) and thus further improve the rolling resistance properties.

[0036] Advantageously according to this first embodiment of the invention, the radially innermost point of the sixth layer of polymeric mixture(s) is radially outside the radially innermost point of the rod.

[0037] The sixth layer of polymeric mixture(s) does not advantageously extend too far into the area of ​​the bead according to this first embodiment of the invention, due to the low rigidity of this sixth mixture with low deformation so as not to alter the holding of this area of ​​the tire, in particular during rim mounting.

[0038] According to a second embodiment of the invention, the sixth layer of polymer mixture(s) extends radially towards the rod in an axially internal zone at the reversal of the carcass reinforcement layer.

[0039] According to this second embodiment of the invention, the sixth layer of polymer mixture(s) extends axially between the reversal of the carcass reinforcement layer and the main part of the carcass reinforcement layer, replacing at least in part the first layer of polymer mixture(s).

[0040] As in the case of the first embodiment of the invention, this second embodiment of the invention can increase the volume of the sixth layer of polymer mixture(s) and thus further improve the rolling resistance properties.

[0041] According to other embodiments that further increase the volume of the sixth layer of polymer mixture(s) to improve rolling resistance properties, the invention provides a combination of the first and second embodiments of the invention described above. According to these other embodiments, the sixth layer of polymer mixture(s) extends both radially towards the radially inner end of the stiffener in an area axially outside the stiffener and radially towards the rod in an area axially inside the fold of the carcass reinforcement layer.

[0042] According to a preferred embodiment of the invention, the fifth layer of polymer mixture(s), located axially between the reversal of the carcass reinforcement layer and the stiffener, has a secant modulus of elasticity at 10% elongation greater than 6 MPa and preferably greater than 9 MPa.

[0043] For polymeric compounds, such as rubber compositions, the secant modulus of elasticity at 10% elongation is the elastic modulus of the compound measured during a uniaxial tensile test at an elongation value of 0.1 (i.e., 10% elongation, expressed as a percentage). A constant uniaxial tensile speed is applied to the specimen, and its elongation and the stress are measured. The measurement is performed using an INSTRON tensile testing machine at a temperature of 23°C and a relative humidity of 50% (ISO 23529). The measurement and data processing conditions for determining elongation and stress are as described in standard NF ISO 37:2012-03. The stress is determined for an elongation of 0.1 and the secant modulus of elasticity at 10% elongation is calculated by taking the ratio of this stress value to the elongation value.A person skilled in the art will know how to choose and adapt the dimensions of the test specimen according to the amount of mixture accessible and available, particularly in the case of taking samples from a finished product such as a tire.

[0044] The inventors advantageously chose a fifth layer with high rigidity to further improve the endurance performance of the tire in the bead area, this fifth layer compensating for the low rigidity of the sixth polymer compound, particularly during heavy braking.

[0045] According to another preferred embodiment of the invention, the polymer mixture present in a circle centered on the end of the stiffener and having a radius of at least 1.5 mm has a secant modulus of elasticity at 10% elongation greater than 6 MPa and preferably greater than 9 MPa.

[0046] According to yet another preferred embodiment of the invention, the polymer mixture present in a circle centered on the end of the reversal of the carcass reinforcement and having a radius of at least 1.5 mm has a secant modulus of elasticity at 10% elongation greater than 6 MPa and preferably greater than 9 MPa.

[0047] According to one or the other of these preferred embodiments of the invention, the choice of polymer blends, whose modulus of elasticity at 10% elongation is greater than 6 MPa and preferably greater than 9 MPa, contributes to an increase in stiffness in the areas defined by the circles centered on the ends of the stiffener or the reversible reinforcement of the frame. Indeed, in these areas, the inventors have notably demonstrated that the stiffness of the sixth layer was insufficient, particularly under significant braking stress.

[0048] These various preferred embodiments of the invention can advantageously be carried out simultaneously or in pairs. They are also advantageously carried out in conjunction with one or another of the variant embodiments of the invention presented previously.

[0049] According to an advantageous embodiment of the invention, the radially outer end of the stiffener is radially outer to the end of the fold in the carcass reinforcement layer. This embodiment prevents the respective ends of the stiffener and the fold in the carcass reinforcement layer from coinciding, as these ends are radially offset. Furthermore, the stiffener thus fully protects the fold in the carcass reinforcement layer, particularly with regard to contact with the rim hook and the pressure exerted on it when the tire is in motion.

[0050] According to other embodiments, the radially outer end of the stiffener is radially inner to the end of the reversal of the frame reinforcement layer.

[0051] According to an advantageous embodiment of the invention, in any meridian plane, in each bead, the tire comprises a restraint frame surrounding the rod and a volume of rubbery mixture directly in contact with the rod.

[0052] According to one embodiment of the invention, particularly to further improve the tire's durability, the carcass reinforcement is formed of cords whose structure is deeply penetrated by polymer blends. These cords may, for example, be constructed to increase their penetrability to polymer blends. Alternatively, they may be cords into which polymer blends are incorporated during the cord manufacturing process. In this case, they may be, for example, cords with at least two layers, at least one inner layer being sheathed with a layer made of a non-crosslinkable, crosslinkable, or crosslinked rubber composition, preferably based on at least one diene elastomer.

[0053] Such carcass reinforcement cables, exhibiting higher penetration rates than usual, can allow the tire to distribute deformation even better along its length, avoiding local concentrations that lead to small radii of curvature.

[0054] Indeed, the carcass reinforcement cables, as defined according to the invention, which are subjected to significant bending phenomena, particularly during impacts on sidewalks, can exhibit better resistance to these bending phenomena due to their penetration rate by the rubber compounds, which induces better homogeneity of deformation between the areas of the cable in extension and compression due to bending.

[0055] According to one embodiment of the invention, the crown reinforcement of the tire is formed of at least two working crown layers of advantageously inextensible reinforcing elements, crossed from one layer to the other making angles with the circumferential direction between 10° and 45°.

[0056] According to other embodiments of the invention, the top reinforcement also includes at least one layer of circumferential reinforcing elements.

[0057] A preferred embodiment of the invention further provides that the top reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented with respect to the circumferential direction 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 to it.

[0058] According to any one of the embodiments of the invention mentioned above, the top reinforcement can be further completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel 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.

[0059] Other advantageous details and features of the invention will become apparent from the description of examples of embodiments of the invention, particularly with reference to figures 1 to 5 which represent: figure 1 , a meridian view of a diagram of a pneumatic tire according to the invention, figure 2, a schematic representation of the area of ​​a ridge according to a first embodiment of the invention, figure 3 , a schematic representation of the area of ​​a ridge according to a second embodiment of the invention, figure 4 , a schematic representation of the area of ​​a ridge according to a third embodiment of the invention, figure 5 , a schematic representation of the area of ​​a ridge according to a fourth embodiment of the invention.

[0060] The figures are not shown to scale to simplify understanding.

[0061] There figure 1 represents only half a view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of the tire.

[0062] On the figure 1, the tire 1 is of size 315 / 70 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads 3. The carcass reinforcement 2 is clamped at the top of the tire by a crown reinforcement 5, itself capped with a tread 6.

[0063] The carcass reinforcement 2, formed of a single layer of metal cables, is wound in each of the ribs 3 around a rod 4 and forms in each of the ribs 3 a reversal 7 of the carcass reinforcement layer having an end 8.

[0064] Axially outside the inversion 7, there is a stiffener 9 whose radially outside end 10 is radially outside the end 8 of the inversion 7 of the reinforcement layer of the frame.

[0065] The meridian section is defined so that the barycentres of the strands 4 form an axially oriented straight line, said barycentres being separated from each other by a distance equal to the nominal rim width plus 20 mm and minus twice the axially measured distance between a barycentre of a strand 4 and a point on the outer surface of the tire.

[0066] Point F, axially the outermost point of the tire, is determined with the tire mounted / inflated under nominal conditions.

[0067] On the figure 2 , the reversal 7 of the carcass reinforcement layer is separated from the main part of the carcass reinforcement layer 2 by a first layer of polymeric mixture 11, having a radially external end 12 radially external to the ends of the stiffener 9 and the reversal 7 of the carcass reinforcement layer.

[0068] The first layer of polymer mixture 11 is profiled to bear against the rod 4, and to ensure decoupling between the inversion 7 of the carcass reinforcement layer and the main part of the carcass reinforcement layer 2.

[0069] Axially outside the stiffener 9 is represented the second layer of polymer mixture 13 whose radially outer end 14 is radially outer to the end 12 of the first layer of polymer mixture 11. The radially inner end 15 of the second layer of polymer mixture 13 is radially included between points A and B, respectively radially innermost and radially outermost of the rod 4.

[0070] In contact with the second layer of polymer mixture 13 and radially under the rod 4, we find the third layer of polymer mixture 16, whose outermost radial end 17 is radially internal to the end 14 of the second layer of polymer mixture 13 and radially external to the end 10 of the stiffener 9.

[0071] Axially in contact with the second polymer mixture layer 13, and the third polymer mixture layer 16, is the fourth polymer mixture layer 18. The radially inner end 19 of the fourth polymer mixture layer 18 is radially inner to the end 17 of the third polymer mixture layer 16 and radially inner to the ends 10 of the stiffener 9 and 8 of the turn 7 of the frame reinforcement layer.

[0072] The third polymer compound layer 16 and the fourth polymer compound layer 18 form the outer surface of the tire 1 in the area of ​​the tire bead 3. The thicknesses d1, d2, and d3 of the third polymer compound layer 16 and / or the fourth polymer compound layer 18, measured in the direction normal to the outer surface of the tire, are greater than 2 mm.

[0073] A fifth layer of polymer mixture 20 is partially present axially between the stiffener 9 and the turn 7 of the frame reinforcement layer.

[0074] According to the invention, a sixth polymer mixture layer 21 is axially positioned between the fourth polymer mixture layer 18 and the main part of the carcass reinforcement layer 2, said sixth polymer mixture layer 21 being radially between point F and a point H of the outer surface of the tire, said point H being radially outside the ends 10 and 8 of the stiffener 9 and the turn 7 of the carcass reinforcement layer and radially distant from these ends 10, 8 by at least 1.5 mm.

[0075] There figure 3 is a schematic representation of the area of ​​a bead according to a second embodiment of the invention and differs from the figure 1by a sixth layer of polymer mixture 321 which extends radially towards the radially inner end of the stiffener 39 in an area axially outside the stiffener 39. According to this embodiment, the sixth layer of polymer mixture 321 remains at least 1.5 mm away from the radially outer end 310 of the stiffener 39. For this purpose, the end 310 of the stiffener 39 is covered with a layer of polymer mixture 323, bordering the end 310 of the stiffener 39 and positioned axially outside the stiffener 39.

[0076] The presence of the polymer mixture layer 323 allows the tire to be designed with one or more polymer mixtures present in a circle Ca centered on the end 310 of the stiffener 39 and having a radius of at least 1.5 mm which have a secant modulus of elasticity at 10% elongation greater than 6 MPa, the sixth polymer mixture layer 321 being located outside this circle Ca.

[0077] Compared to the first embodiment, the sixth polymer mixture layer 321 replaces at least in part the second polymer mixture layer of the first embodiment of the invention, the polymer mixture layer 323 being similar to the second polymer mixture layer with a reduced volume.

[0078] Compared to the first embodiment, the sixth layer of polymer mixture 321 can still partially replace the third layer of polymer mixture 16 and / or the fourth layer of polymer mixture 18 depending on the desired volume of this sixth layer of polymer mixture 321.

[0079] There figure 4 is a schematic representation of the area of ​​a bead according to a third embodiment of the invention and differs from the figure 1by a sixth layer of polymeric mixture 421 extending radially towards the rod 44, in an area axially inside the fold 47 of the carcass reinforcement layer. According to this embodiment of the invention, the sixth layer of polymeric mixture 421 remains at least 1.5 mm from the end 48 of the fold 47 of the carcass reinforcement layer. To achieve this, the end 48 of the fold 47 of the carcass reinforcement layer is covered with a layer of polymeric mixture 424, bordering the end 48 of the fold 47 of the carcass reinforcement layer and axially inside the contact with the fold 47 of the carcass reinforcement layer.According to this embodiment of the invention, the sixth layer of polymer mixture 421 replaces at least in part the first layer of polymer mixture of the first embodiment of the invention, the layer of polymer mixture 424 being able to resemble the first layer of polymer mixture with a reduced volume.

[0080] The presence of the polymer blend layer 424 allows the tire to be designed with one or more polymer blends present in a circle Cb centered on the end 48 of the inversion 47 of the carcass reinforcement layer and having a radius of at least 1.5 mm which have a secant modulus of elasticity at 10% elongation greater than 6 MPa, the sixth polymer blend layer 421 being located outside this circle Cb.

[0081] In this embodiment example, to maintain endurance properties regardless of rolling conditions, the second polymer mixture layer 413, the fifth polymer mixture layer 420, axially between the stiffener 49 and the inversion 47 of the carcass reinforcement layer and the polymer mixture layer 424 are made with a polymer mixture having a secant modulus of elasticity at 10% elongation greater than 6 MPa.

[0082] There figure 5is a schematic representation of the area of ​​a bead according to a fourth embodiment of the invention combining the second and third embodiments presented above. According to this fifth embodiment, the sixth layer of polymer mixture 521 extends on the one hand, radially towards the radially inner end of the stiffener 59 in an area axially outside the stiffener 59 and on the other hand, radially towards the rod 54 in an area axially inside the turnover 57 of the carcass reinforcement layer.

[0083] According to this embodiment, the sixth layer of polymer mixture 521 remains at least 1.5 mm from the radially outer end 510 of the stiffener 59. To achieve this, the end 510 of the stiffener 59 is covered with a layer of polymer mixture 523, bordering the end 510 of the stiffener 59 and positioned axially outside the stiffener 59. The sixth layer of polymer mixture 521 also remains at least 1.5 mm from the end 58 of the fold 57 of the frame reinforcement layer. To achieve this, the end 58 of the fold 57 of the frame reinforcement layer is covered with a layer of polymer mixture 524, bordering the end 58 of the fold 57 of the frame reinforcement layer and positioned axially inside the fold 57 of the frame reinforcement layer.

[0084] The presence of the polymer mixture layers 523 and 524 allows the tire to be designed with one or more polymer mixtures present on the one hand in the circle Ca, centered on the end 510 of the stiffener 59 and having a radius of at least 1.5 mm, and on the other hand in the circle Cb, centered on the end 58 of the inversion 57 of the carcass reinforcement layer and having a radius of at least 1.5 mm, which have a secant modulus of elasticity at 10% elongation greater than 6 MPa, the sixth polymer mixture layer 521 being located outside these circles Ca and Cb.

[0085] In this embodiment example, to maintain endurance properties regardless of rolling conditions, the fifth polymer blend layer 520, axially between the stiffener 59 and the inversion 57 of the carcass reinforcement layer, the polymer blend layer 523 and the polymer blend layer 524 are made with a polymer blend having a secant modulus of elasticity at 10% elongation greater than 6 MPa.

[0086] The various polymer blends used to create the six polymer blend layers are listed below, with the secant modulus of elasticity under tension at 10% elongation, as well as the maximum tan(δ) values ​​and the linearity coefficient G*, expressed for each. The proportions of the different constituents in the compositions presented in the following table are expressed in parts per cubic meter (pce). First layer second layer third layer fourth layer fifth layer sixth layer NR 100 100 75 50 100 100 BR 25 50 Black N347 30 Black N330 40 Black N375 65 Black N234 35 Black N326 60 Black N550 175 Stearic acid 0.5 05 3 1 0.5 1 Zinc oxide 5 3.5 4 2.5 9 5 MES / HPD Oil 10 TAC OPF Resin 1 WAX 7132 1 1.5 Sulfur Soil 2H 1 1.5 Sulfur insol 20H 3 3 8 4 CBS Accelerator 1 0.5 1.5 1 1.5 DCBS Accelerator 1 Cobalt salt 2 tan(δ) max 60°C 0.06 0.08 0.24 0.12 0.13 0.02 G*min (MPa) 23°C 1.02 1.04 2.08 0.78 2.4 0.91 G*max (MPa) 23°C 1.76 2.05 18.41 1.82 10.6 1.03 Linearity Rate G* 23°C 0.58 0.51 0.11 0.43 0.23 0.88 MA 10 (MPa) 3.5 3.3 7 2.7 10 3.1

[0087] The polymer blends used for layers 323, 424, 523 and 524 are identical to the blend of the fifth layer.

[0088] Tests were carried out with tires according to the invention I1, I2, I3 and I4 designed respectively in accordance with figures 2 , 3 , 4 And 5 .

[0089] The tires according to the invention are compared, on the one hand, to reference R1 tires of a more conventional design. These tires are similar to the representation of the figure 1 the sixth layer of polymer mixture not existing.

[0090] On the other hand, they are compared to R2 reference tires, the sixth layer of polymeric mixture also being absent and the R2 reference tires having a hollowed-out bead area as described in patent application WO 2020 / 012122.

[0091] The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires R1 and R2.

[0092] Initial endurance tests were carried out by rolling two planed tires on top of each other with a regulated pressure of 8.5 bar, and a load of 7061 daN at a speed of 30 km / h and at an ambient temperature of 15°C for 20000 km.

[0093] The tires according to the invention exhibit results substantially identical to those of the reference tires R1 and R2.

[0094] Other tests were carried out to test the performance of resistance to impacts and / or friction on curb edges.

[0095] The R2 reference tires exhibit superior performance under extreme conditions. The tires according to the invention, on the other hand, demonstrate results substantially identical to those of the R1 reference tires.

[0096] In addition, rolling resistance measurements were carried out.

[0097] Rolling resistance measurements were performed on each tire under identical driving conditions, in accordance with United Nations Economic Commission for Europe (UNECE) Regulation No. 117. Measurement results are expressed in kg / t, with a value of 100 assigned to tire P1. Values ​​above 100 indicate better rolling resistance performance. R1 R2 I1 I2 I3 I4 Rolling resistance 100 100 102 103 105 106

[0098] These tests show that the tires according to the invention improve performance in terms of rolling resistance satisfactorily while also exhibiting satisfactory performance in endurance and shock resistance.

Claims

1. Tyre (1), comprising a radial carcass reinforcement (2) made up of a carcass reinforcement layer formed of reinforcing elements, said tyre comprising a crown reinforcement (5), itself capped radially by a tread (6), said tread (6) being connected to two beads (3) via two sidewalls, the layer of reinforcing elements of the carcass reinforcement being anchored in each of the beads by being turned up around a bead wire (4) to form a main part of the carcass reinforcement layer extending from one bead wire (4) to the other and a turn-up (7) of the carcass reinforcement layer (2) in each of the beads (3), said turn-up (7) of the carcass reinforcement being reinforced by at least one layer of reinforcing elements or stiffener (9), a first layer of polymer compound(s) (11) being at least partly axially on the inside of the end (8) of said turn-up (7) of the carcass reinforcement layer, a second layer of polymer compound(s) (13) being at least partly axially on the outside of the radially outer end (10) of said stiffener (9), a third layer of polymer compound(s) (16) forming the outer surface of the tyre in the region of the bead (3), said third layer of polymer compound(s) (16) being intended in particular to come into contact with the rim, said third layer of polymer compound(s) (16) being radially towards the outside in contact with a fourth layer of polymer compound(s) (18) forming the outer surface of a sidewall, the stiffener (9) being axially separated from the turn-up (7) of the carcass reinforcement layer by a fifth layer of polymer compound(s) (20), the thickness (d1, d2, d3) of polymer compound(s) consisting of the third layer of polymer compound(s) (16) and / or of the fourth layer of polymer compound(s) (18) forming the outer surface of the tyre, and measured radially on the outside of the radially innermost point (A) of the bead wire, being greater than or equal to 2 mm, in a meridian cross section of said tyre, - a sixth layer of polymer compound(s) (21) occupies at least one region radially between an axially outermost point F of the tyre and a point H on the outer surface of the tyre, said point H being radially on the outside of the end (8) of the turn-up (7) of the carcass reinforcement layer (2) and radially on the outside of the radially outer end (10) of the stiffener (9), said region being axially between the polymer compound(s) consisting of the third layer of polymer compound(s) (16) and / or of the fourth layer of polymer compound(s) (18) and the main part of the carcass reinforcement layer (2), - the sixth layer of polymer compound(s) (21) is spaced apart from the radially outer end (10) of the stiffener (9) by at least 1.5 mm and spaced apart from the end (8) of the turn-up (7) of the carcass reinforcement layer by at least 1.5 mm, said tyre being characterized in that the maximum value of tan(δ), denoted tan(δ)max, measured at 60°C in accordance with standard ASTM D 5992-96, of the sixth layer of polymer compound(s) (21) is less than 0.050 and in that the linearity of the complex dynamic shear modulus G*, at a temperature of 23°C, of the sixth layer of polymer compound(s) (21) is greater than 0.80, the linearity being defined by the ratio of G*min to G*max, with - G*min being the minimum value of the complex dynamic shear modulus G* for a strain of 1 to 100%, and - G*max being the maximum value of the complex dynamic shear modulus G* for a strain of 1 to 100%.

2. Tyre (1) according to Claim 1, characterized in that the sixth layer of polymer compound(s) (21) extends radially towards the radially inner end of the stiffener (9) in a region axially on the outside of the stiffener (9).

3. Tyre (1) according to Claim 2, characterized in that the radially innermost point of the sixth layer of polymer compound(s) (21) is radially on the outside of the radially innermost point (A) of the bead wire (4).

4. Tyre (1) according to one of Claims 1 to 3, characterized in that the sixth layer of polymer compound(s) (21) extends radially towards the bead wire (4) in a region axially on the inside of the turn-up (7) of the carcass reinforcement layer.

5. Tyre (1) according to one of the preceding claims, characterized in that the fifth layer of polymer compound(s) (20), situated axially between the turn-up (7) of the carcass reinforcement layer and the stiffener (9), has a secant elastic modulus at 10% elongation of greater than 6 MPa.

6. Tyre (1) according to one of the preceding claims, characterized in that the polymer compound present in a circle (Ca) centred on the radially outer end (10) of the stiffener (9) and having a radius of at least 1.5 mm has a secant elastic modulus at 10% elongation of greater than 6 MPa.

7. Tyre (1) according to one of the preceding claims, characterized in that the polymer compound present in a circle (Cb) centred on the end (8) of the turn-up (7) of the carcass reinforcement and having a radius of at least 1.5 mm has a secant elastic modulus at 10% elongation of greater than 6 MPa.

8. Tyre (1) according to one of the preceding claims, characterized in that the radially outer end (10) of the stiffener (9) is radially on the outside of the end (8) of the turn-up (7) of the carcass reinforcement layer.

9. Tyre (1) according to one of the preceding claims, characterized in that the reinforcing elements of the carcass reinforcement layer (2) are cords having at least two layers, at least one internal layer being sheathed with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

10. Tyre (1) according to one of the preceding claims, characterized in that, in any meridian plane, in each bead (3), the tyre (1) has a retention reinforcement surrounding the bead wire (4) and a volume of rubber compound in direct contact with the bead wire (4).