TIRES WITH OPTIMIZED ROLLING RESISTANCE PERFORMANCE WITHOUT IMPACTING INDUSTRIAL PRODUCTION

Description

Field of invention

[0001] The present invention relates to a tire for a motor vehicle whose rolling resistance performance is improved without degrading the industrial performance of its manufacture. The invention is more particularly suitable for a radial tire intended to equip a passenger vehicle or a van. Definitions

[0002] By convention, we consider a reference (O, OX, OY, OZ), whose center O coincides with the center of the tire, the circumferential directions OX, axial OY, and radial OZ respectively designate a direction tangent to the rolling surface of the tire according to the direction of rotation, a direction parallel to the axis of rotation of the tire, and a direction orthogonal to the axis of rotation of the tire.

[0003] By radially inner, respectively radially outer, we mean closer, respectively further from the axis of rotation of the tire.

[0004] Axially inner, respectively axially outer, means closer, respectively further from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tire tread and perpendicular to the axis of rotation of the tire.

[0005] The constitution of the tire is usually described by a representation of its constituents in a meridian plane, that is to say a plane containing the axis of rotation of the tire.

[0006] A tire comprises a crown, intended to come into contact with the ground via a tread, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] A radial tire further comprises a reinforcing reinforcement, consisting of a crown reinforcement, radially inside the tread, and a carcass reinforcement, radially inside the crown reinforcement.

[0008] The crown reinforcement of a radial tire comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer consists of reinforcements parallel to each other and coated with a polymeric material of the elastomer type or elastomeric mixture. The assembly consisting of the crown reinforcement and the tread is called the crown.

[0009] The carcass reinforcement of a radial tire usually comprises at least one carcass layer consisting of metallic or textile reinforcing elements coated in an elastomeric coating mixture. The reinforcing elements are substantially parallel to each other and form, with the circumferential direction, an angle of between 85° and 95°. The carcass layer comprises a main part, connecting the two beads together and wrapping, in each bead, around an annular reinforcing structure. The annular reinforcing structure may be a bead wire which comprises a circumferential reinforcing element, most often metallic, surrounded by at least one material, non-exhaustively elastomeric or textile. The wrapping of the carcass layer around the annular structure goes from the inside to the outside of the tire to form a turn-up, comprising an end.The turn-up, in each bead, allows the anchoring of the carcass reinforcement layer to the annular structure of the bead.

[0010] Each bead comprises a filler layer extending radially outwards the annular reinforcement structure. The filler layer consists of at least one elastomeric filler compound. The filler layer axially separates the main part and the turn-up of the carcass reinforcement.

[0011] Each bead also comprises a protective layer extending radially inwards from the sidewall and axially outwards from the turn-up. The protective layer is also at least partly in contact by its axially outward face with a hook of the rim. The protective layer is made of at least one protective elastomeric mixture.

[0012] Each bead may finally comprise a lateral reinforcement layer positioned between the sidewall and the turn-up of the carcass reinforcement. The external lateral reinforcement layer is made of at least one elastomeric mixture.

[0013] Each tire sidewall comprises at least one sidewall layer consisting of an elastomeric compound and extending axially towards the inside of the tire from an outer face of the tire, in contact with atmospheric air.

[0014] An elastomeric blend is an elastomeric material obtained by mixing its various constituents. An elastomeric blend typically comprises an elastomeric matrix with at least one diene elastomer of natural or synthetic rubber type, at least one reinforcing filler of carbon black type and / or silica type, a crosslinking system most often based on sulfur, and protective agents. For certain applications, the elastomers considered may also include thermoplastics (TPE).

[0015] The expression "based on" composition means a composition comprising the mixture and / or the reaction product of the different constituents used, some of these basic constituents being capable of, or intended to, react with each other, at least in part, during the different phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

[0016] By the expression "part by weight per hundred parts by weight of elastomer" (or pce), it is meant, within the meaning of the present invention, the part, by mass per hundred parts of elastomer present in the mixture composition considered.

[0017] An elastomeric mixture can be characterized mechanically, in particular after curing, by its dynamic properties, such as a dynamic shear modulus G*= (G'2+G''2)1 / 2, where G' is the elastic modulus of shear stiffness and G'' the viscous shear modulus, and a dynamic loss Tanδ=G'' / G'. The dynamic shear modulus G* and the dynamic loss Tanδ are measured on a Metravib VA4000 type viscoanalyzer, according to ASTM D 5992-96 standard. The response of a sample of vulcanized elastomeric mixture in the form of a cylindrical specimen 2 mm thick and 78 mm 2< in cross-section, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 100°C, is recorded. We perform a deformation amplitude sweep from 0.1% to 50% (forward cycle), then from 50% to 0.1% (return cycle). For the forward cycle, we indicate the maximum value of tan(δ) observed, noted Tan(δ) max.

[0018] "Handling" performance corresponds to the responses of a vehicle / tire assembly to multiple driver inputs (steering, acceleration, braking, etc.). Handling is essential both in terms of safety for the stability of the vehicle and for driving pleasure.

[0019] The tire plays a key role in road behavior because it ensures, at the end of the chain, the transmission of forces between the vehicle and the ground in order to maintain the trajectory defined by the driver.

[0020] When cornering, to keep the vehicle on a trajectory, it is necessary to generate a force equivalent to (but in the opposite direction) the centrifugal force that tends to eject the vehicle from the trajectory. This lateral force must be generated by the vehicle's 4 tires to overcome the centrifugal force.

[0021] The deformation of the rubber blocks in contact with the ground generates a lateral force. The mechanism that allows the tire to deform the rubber blocks when cornering is called drift. Drift is the angle between the direction of the wheel and the trajectory followed by the vehicle. When cornering, this angle is not zero in order to allow the tire to deform the rubber blocks of the tread and thus generate the necessary lateral forces.

[0022] Transverse drift stiffness is the variation of transverse forces generated in the contact patch of the moving tire crushed by the load carried, as a function of the drift angle applied to the tire. Transverse drift stiffness is expressed in Newtons per degree (N / °).

[0023] For small drift angles, i.e. angles less than 10°, the transverse force, in a direction parallel to the tire's axis of rotation, is proportional to the drift angle. The transverse drift stiffness is equal to this coefficient of proportionality.

[0024] Transverse drift stiffness is an essential physical quantity that connects the tire to the vehicle and determines the quality of the vehicle's behavior on the road.

[0025] Rolling resistance is another performance covered in the application. Rolling resistance is one of the forces that oppose the vehicle's movement. The rolling resistance coefficient of a tire (CR RR ) is the rolling resistance force related to the load carried by the tire. The coefficient is expressed in kg / t.

[0026] Rolling resistance is primarily related to tire deformation. For example, the beads associated with the sidewalls represent 20% to 30% of the tire's rolling resistance, while the tread contributes 60% to 80%.

[0027] Most often in this present patent application, the tire appears mounted on a rim. Said rim is chosen according to the specifications of the ETRTO (European Tire and Rim Technical Organization) standard which, for a given tire dimension, associates recommended rims. In general, several rim widths can be suitable for the same tire dimension. The part of the rim which interacts with the tire in the context of the invention is axisymmetric with respect to the axis of rotation of the tire. To describe the rim, it is sufficient to describe the generating profile in a meridian plane.

[0028] In a meridian plane, the rim comprises at least one hook located at an axial end, and connected to a seat which is intended to receive a face of the bead located most radially inward. Between the seat and the hook, there is a rectilinear portion which connects the rim hook to the seat by connecting fillets. The rim hook extended by the rectilinear portion axially limits the movement of the beads during inflation.

[0029] The fitability of the beads on a rim during inflation is also a performance that can be impacted by the invention. The fitability performance of the beads consists of evaluating the ability of the beads of a tire to be correctly installed on a rim during inflation. On the radially innermost face of the bead, the contact with the seat must be sufficient to prevent any leakage of the tire inflation air. In general, a contact pressure of at least 1.4 MPa is expected in this contact zone. The inflation pressure wedges the bead against the rim hook. Here again, the contact pressure on the hook must be sufficient to prevent the tire from coming off the rim, particularly during sharp turns at high speed. Observation methods, particularly radiographic methods, of the beads mounted on a rim make it possible to diagnose the quality of the fitment.

[0030] It is therefore possible to classify two tires according to their rim fitment performance. Prior art

[0031] Reducing greenhouse gas emissions from transportation is one of the major challenges facing vehicle manufacturers today. Tires represent a significant source of progress, through a reduction in rolling resistance, as this has a direct impact on the vehicle's fuel consumption. For example, a 20% reduction in a tire's rolling resistance saves approximately 3% of fuel per 100 km in a combined cycle.

[0032] There is still a need to reduce the rolling resistance of passenger car tires without degrading other performances, including industrial performances.

[0033] It has already been proposed to improve the rolling resistance of passenger vehicle tires by optimizing their beads. Document WO 2010 / 072736 teaches in particular the use of elastomeric compositions having low elastic shear stiffness moduli G' around 15 MPa and viscous moduli G" lower by more than 20% than the elastic shear stiffness moduli to obtain a significant reduction in rolling resistance.

[0034] This document also recommends further reducing rolling resistance by optimizing the geometry of the elastomeric compound layers whose elastic and viscous moduli satisfy the previous relationship. This optimization leads to shorter and wider elastomeric compound layer profiles than in traditional tires. In some cases, the difficulty of industrial implementation to manufacture these compound layer profiles is a major drawback of this approach.

[0035] Document FR2994127 describes an improvement to document WO 2010 / 072736, proposing to add a reinforcing reinforcement in the beads. The reinforcing reinforcement is formed from reinforcements coated in an elastomeric mixture.

[0036] The major drawback of this solution is a significant deterioration in industrial production costs with the introduction of new semi-finished products into the tire manufacturing process.

[0037] Other documents such as patent EP2657049B1 suggest reducing the hysteresis of the sidewall layer to gain rolling resistance by providing the sidewall layer with an appropriate chemical composition.

[0038] The sidewall layer performs several functions of the tire. The outer wall of the tire in contact with the ambient air, the sidewall layer must resist attacks from the ozone it contains. In urban driving, the sidewall layer must resist contact with pavements, which sometimes results in grating of the outer surface of the sidewall leading to premature wear.

[0039] Reducing rolling resistance by reducing the hysteresis of the elastomeric compound in the sidewall layer requires a chemical composition that is significantly different from the usual compositions for this item. Often, the search for a performance compromise between rolling resistance and other sidewall layer performances leads to elastomeric compounds whose use in industrial manufacturing degrades industrial performance.

[0040] Industrial performance refers to the ability of processes to produce a given volume of products while meeting quality, cost, and deadline requirements. Here, costs are related to material loss due to rejects and quality defects. Since the invention is an iso-process, only material costs are considered in industrial performance.

[0041] One of the stages in the manufacture of a tire consists of a molding phase in a curing mold. The tire blank after assembly of its components is placed in a closed hot mold, and a membrane positioned inside the mold and filled with a hot fluid deploys to press said tire against the interior walls of the mold so as to print the design of the sculpture on the tread and the markings on the sidewalls.

[0042] Markings include markings that provide technical information on product use, commercial information, and regulatory information. Regulatory information is mandatory and must meet specific requirements regarding font and character size.

[0043] Tires that have regulatory marking defects are rejected if they cannot be repaired, which increases material loss and degrades industrial performance.

[0044] The state-of-the-art tires are known from documents JP2006062379A, EP1640188A1 and DE112016000956T5.

[0045] The inventors set themselves the goal of creating a tire that improves the level of rolling resistance without degrading industrial performance. Statement of the invention

[0046] This goal was achieved by a passenger vehicle tire comprising in a meridian plane: two beads intended to be mounted on a rim, two layers of sidewalls connected to the beads, a crown comprising a tread, the crown having a first side connected to the radially outer end of one of the two layers of sidewalls and having a second side connected to the radially outer end of the other of the two layers of sidewalls; at least one carcass reinforcement extending from the two beads to the crown, the carcass reinforcement comprising a plurality of carcass reinforcement elements and being anchored in the two beads by an upturn around an annular reinforcement structure, so as to form in each bead a main part and an upturn;each sidewall layer consisting of two axially superimposed sub-layers, a first sidewall sub-layer FE1 delimited by a first axially outermost side constituting a sidewall of the tire in contact with the ambient air, and a second axially inner side defined so that said sidewall sub-layer FE1 has an average axial thickness E1, and occupying a volume V1; each sidewall layer also comprising a second sidewall sub-layer FE2, a first side of which coincides with the second side of the first sidewall sub-layer FE1, and a second axially inner side of which is at least partly in contact with the carcass reinforcement, said sidewall sub-layer FE2 having an average thickness E2, and occupying a volume V2; the thickness E1 of the first sidewall sub-layer FE1 is greater than or equal to 0.7 mm; the ratio V1 / (V1+V2) is less than or equal to 0.3;the elongation at break of the elastomeric mixture constituting the first sidewall sub-layer FE1 is greater than or equal to 200% measured at a temperature of 100°C; the dynamic loss of the second sidewall sub-layer FE2, Tan (δ) max is less than or equal to 0.10. ;

[0047] The principle of the invention is to reduce the hysteresis of the sidewall layer to reduce the rolling resistance of the tire without degrading other performances, in particular industrial performance. To achieve this, the functions of the sidewall are decoupled, considering the sidewall layer as a laminate with two sub-layers superimposed in the axial direction.

[0048] The average thickness E2 of the sub-layer FE2 is the average of the thicknesses measured along a straight line normal to the carcass reinforcement between a first and a second point at the intersections of said normal line and each of the first and second sides of said sub-layer FE2. The average thickness E1 of the sub-layer FE1 is defined equivalently.

[0049] The second sub-layer FE2 occupies the largest volume of elastomeric mixture among the two sub-layers. According to the invention, the volume V1 of the sub-layer FE1 is less than or equal to 30% of the total volume of the sidewall. As an illustration, on a passenger car tire size, 245 / 45 R18, at an ordinate corresponding to the middle of the sidewall layer in the meridian reference, E2 is 1.2 mm and E1 is 0.7 mm.

[0050] The dynamic loss of the sidewall sub-layer mixture FE2, Tan (δ) max is less than or equal to 0.10. This hysteresis condition, imposed on the second sub-layer, is motivated for a gain in rolling resistance.

[0051] The first sub-layer FE1 is intended to be in contact with the tire curing mold during the molding phase. The inventors have established a relationship between the ability of the first sub-layer FE1 to be demolded without molding defects, and the value of the hot elongation at break of said sub-layer. According to the invention, the elongation at break of the elastomeric mixture constituting the first sidewall sub-layer FE1 is greater than or equal to 200% measured at a temperature of 100°C.

[0052] A thickness E1 of the first sidewall sub-layer defined by a value in millimeters around 0.7 mm guarantees correct operation without premature wear of the tire sidewalls.

[0053] The combination of the choice of a sidewall layer in two sub-layers FE1, FE2, with a first sub-layer of significantly lower thickness with appropriate mechanical properties at break, and a second sidewall sub-layer of low hysteresis, leads to the tire of the invention which provides an improvement in rolling resistance without degrading industrial performance.

[0054] The invention provides other advantages: the first sub-layer FE1 which is in contact with the ambient environment is designed to also ensure the functions of mechanical and chemical protection against attacks from the ambient environment.

[0055] Chemical damage to sidewalls refers to the effects of prolonged exposure to sunlight, particularly the UV (ultraviolet) component of the light spectrum. UV light affects the splitting of the main polymer chain, leading to rapid degradation of the elastomer. This degradation manifests itself as surface cracks, often called crazing, and can allow water to penetrate, which leaches out soluble components and leads to the breakdown of product bonds.

[0056] To address this problem, the inventors incorporated chemical UV stabilizers into the FE1 sidewall undercoat formulation: carbon black is generally recognized as one of the most effective UV protection systems to use for elastomers. Similarly, ozone (a strong oxidant) can degrade elastomer components in the same way as UV. The inventors addressed this problem by using an antioxidant and by carefully choosing elastomers (saturated polymers).

[0057] Advantageously, from a process point of view, the two sidewall sub-layers (FE1, FE2) are obtained during manufacturing by a co-extrusion process. Co-extrusion techniques are now well mastered and make it possible to maintain identical manufacturing cycle times compared to a single-layer sidewall.

[0058] Different embodiments are proposed by the inventors in order in particular to guarantee the tire of the invention a level of transverse drift rigidity sufficient for good road behavior of the vehicle equipped with these tires.

[0059] Advantageously, the elastic modulus of shear stiffness of the second flank sub-layer FE2 is preferably within the range [1.5; 10] MPa and even more preferably is within the range [2.5; 10] MPa.

[0060] By assigning to the second sidewall sub-layer FE2 of a tire of the invention an elastomeric mixture having an elastic modulus of shear rigidity of up to 10 MPa, the transverse drift rigidity is improved compared to usual designs, useful for good road behavior of a vehicle equipped with these tires. Indeed, the usual design of the sidewalls aims for an elastic modulus of shear rigidity less than or equal to 1.5 MPa.

[0061] Furthermore, the beads of the tires of the invention are based in particular on a balance between the shear rigidities and the hysteresis of the elastomeric mixtures constituting them. The elastic modulus of shear rigidity G' of each sidewall sub-layer FE2 remains less than 10 MPa so that the hysteresis remains at a level measured by a value Tan(δ)max less than or equal to 0.10. The invention operates from an elastic modulus of shear rigidity of the sidewall layer greater than or equal to 1.5 MPa.

[0062] According to a preferred embodiment, each bead comprising a filling layer comprised at least in part between the main part of the carcass reinforcement, the turn-up of the carcass reinforcement and the radially outer portion of the annular reinforcement structure, the elastomeric mixture constituting the filling layer has a dynamic loss Tan(δ) max less than or equal to 0.1.

[0063] Increasing the shear stiffness elastic modulus of the elastomeric mixture of the FE2 sidewall sub-layer makes it possible to reduce the hysteresis of the filler layer. In the usual designs of beads, the skilled person chooses filler layers having a shear stiffness elastic modulus rather around 40 Mpa, and the dynamic loss is penalized.

[0064] The bead filler layer generally occupies a large volume and is subject to high shear deformations due to tension variations in the reinforcements of the main part of the carcass layer and its turning. The choice of a low hysteresis elastomeric compound helps to control the level of viscoelastic dissipation.

[0065] Advantageously, the bead comprises a lateral reinforcing layer consisting of an elastomeric mixture occupying a volume at least partly between the second sidewall layer and the turn-up of the carcass reinforcement.

[0066] According to the inventors, the lateral reinforcement layer of the bead complements the first filling layer to provide transverse rigidity. Depending on these material properties in terms of Tan(δ)max and dynamic shear stiffness, said reinforcement makes it possible to adjust the performance balance between rolling resistance and road behavior.

[0067] Advantageously, in a variant of this embodiment, said lateral reinforcement layer of at least one bead is made up of an elastomeric mixture whose dynamic loss Tan (δ) max is less than or equal to 0.10.

[0068] In this variant of the embodiment, the two layers of mixtures, namely the filler layer and the lateral reinforcement layer, verify the property of having a dynamic loss Tan (δ) max less than 0.10. The gain in rolling resistance is optimal, while having a road behavior of the tire mounted on the vehicle in accordance with expectations.

[0069] In another embodiment of the invention, in each bead a rim contact curve comprises the points of the tire in contact with the rim. Said rim contact curve connects a first point M1 of the tire axially positioned most externally, and in contact with the rim, and a second point M2 of the tire also in contact with the rim and located in the middle of the rectilinear portion connecting the hook to the seat of the rim. The length of said rim contact curve is the curvilinear distance from point M1 to point M2 along the contact curve.Said tire also comprising two sections in a vertical meridian section of the inflated tire, mounted on a rim, and crushed on a ground by a vertical load where the load, the inflation pressure, being determined in a specification standard such as ETRTO (European Tire and Rim Technical Organization); a first section being located in the contact patch, and a second section being located on the opposite side to the previous one with respect to the axis of rotation of the tire. In the first section located in the contact patch, in at least a first bead, the length of the rim contact curve, LADC, is measured.In the second section located opposite the contact patch relative to the axis of rotation of the tire, in at least one second bead, the length of the rim contact curve, LCJ, is measured, then the ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%.

[0070] In this embodiment, the rim contact variation rate of the tires of the invention is significantly higher than that observed on the tires of the state of the art.

[0071] When the inflated tire, mounted on a rim, is crushed by a load, the points of the tire in contact with the rim may vary from one meridian to another. It follows that the length of the rim contact curve as defined above also varies from one meridian to another.

[0072] The tire is designed so that the rim contact curve is as long as possible in the contact patch, compared to state-of-the-art tires, and more precisely in the meridian at the center of the contact patch. Under these conditions, the inventors estimate that the contribution of the rim contact to the drift rigidity is maximum.

[0073] In a meridian section of an inflated tire, mounted on a rim, and crushed by the load carried, we can see a first section of the tire which passes through the center of the contact patch. The contact patch is understood to mean all the points of the tire, at a given instant which are in contact with the crushing ground. The center of the contact patch is called the point of the contact air located on the vertical axis OZ. We can also see opposite the contact patch with respect to the axis of rotation OY of the tire another section of the tire which globally defines a deformed state similar to the state of axisymmetric inflation.

[0074] The rim contact variation rate corresponds to the maximum value of the change in rim contact lengths per wheel revolution.

[0075] According to the inventors, an essential step in the design of a tire of this embodiment consists in modifying its external profile in the area of ​​contact with the rim. Various solutions are possible, such as, for example, increasing the axial thickness of the sidewall layer at the junction with the protective layer. Other solutions consist in modifying the external profile so as to obtain a profile in the contact area with the same curvature as the rim hook. Yet another solution consists in inserting a compound cushion in the area at the junction of the sidewall and protective layers, at the rim hook. This compound cushion may preferably be made of the same compound as that of the sidewall layer so as to maintain the industrial cost price.The expectation with regard to this elastomeric mixture cushion is above all its elastic modulus of shear rigidity which advantageously could be for example equal to that of the sidewall layer.

[0076] Advantageously, the ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 40%, preferably greater than or equal to 50%, even more preferably greater than or equal to 60%.

[0077] The outer profile in the rim contact area can be modified to target a rim contact variation rate. It is therefore a lever for adjusting the transverse drift stiffness in the search for a performance compromise between rolling resistance and the tire's road behavior. The transverse drift stiffness is an increasing function of the rim contact variation rate. For rim contact variation rates greater than or equal to 60%, modifying the outer profile of the sidewall layer facilitates bead fitting, but rates that are too high, beyond 100%, could hinder fitment.

[0078] In addition to the main characteristics of the invention, the inventors have identified levers linked to the geometry of the bead compound layers to further optimize the tire's performance compromise with improved rolling resistance while having good road behavior.

[0079] Advantageously, the distance DRB being the radial distance from one end of the radially outer filling layer, said distance DRB is less than or equal to 50% of the radial height H of the tire.

[0080] The height H of the tire is the normal distance between a first straight line HH' parallel to the axis of rotation of the tire and tangent to the most radially inner point of the annular reinforcement structure, and a second straight line AA' also parallel to the axis of rotation of the tire and passing through the most radially outer point of the tread. The radial height H is measured on the tire mounted on a rim and inflated with a set pressure conforming to the ETRTO (European Rim and Tire Organization) specifications.

[0081] Advantageously, the distance DRI being the radial distance from a radially inner end of the lateral reinforcement layer to the line HH', said radial distance DRI is included in the interval [5%; 25%] of the radial height H of the tire.

[0082] Advantageously, the distance DRL being the radial distance from the radially outer end of the lateral reinforcement layer to the right (HH'), said radial distance DRL is greater than or equal to 25% of the radial height H of the tire.

[0083] The lateral reinforcing layer between the sidewall and the upturn of the carcass reinforcement contributes to the stiffness of the bead by reinforcing the first filling layer. According to the inventors, its positioning is adjusted by the DRI and DRL dimensions so as to resist the bending, extension-compression stresses of the bead when passing through the contact area.

[0084] In an advantageous embodiment of the invention, the upturn of the carcass reinforcement is pressed against the main part of the carcass reinforcement over its entire height radially outwards.

[0085] As mentioned above, the carcass reinforcement is made up of reinforcements coated between two layers of elastomeric compounds. The upturn of the carcass reinforcement is pressed against the main part of the carcass reinforcement, meaning that the upturn is in contact with the main part of the carcass reinforcement. The contact is made along a surface positioned between the two layers of coating of the carcass reinforcement.

[0086] In this configuration, the volume of the first layer of filler is limited to the strict minimum around the annular reinforcement structure. This configuration is very advantageous for reducing the rolling resistance of the bead.

[0087] In another embodiment, the tire comprises a bead reinforcement reinforcement axially external to the carcass reinforcement, and axially internal to the sidewall.

[0088] The bead reinforcement is made up of parallel reinforcements, coated between two layers of elastomeric compounds. The addition of this semi-finished product results in an additional manufacturing cost that must be compensated for. In order to limit the impact on the cost price of such a solution, this embodiment can be combined with the plating of the carcass reinforcement turn-over against the main part of the carcass reinforcement.

[0089] Advantageously, the elastomeric mixture constituting at least one layer among the filler layer, and / or the lateral reinforcement layer, and / or the second sidewall sub-layer FE2 has a composition based on a diene elastomer, a crosslinking system, a reinforcing filler, type Carbon Black 550, at an overall rate of between 50 and 75 pce.

[0090] Advantageously, the elastomeric mixture constituting the filler layer, the elastomeric mixture constituting the lateral reinforcement layer, and the elastomeric mixture constituting the sidewall sub-layer FE2 have the same composition.

[0091] By "diene" elastomer (or indistinctly rubber) is meant, in a known manner, an elastomer derived at least in part (i.e., a homopolymer or a copolymer) from diene monomers, i.e. monomers carrying two carbon-carbon double bonds, conjugated or not. The diene elastomer used is preferably chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), butadiene-styrene-isoprene copolymers (SBIR) and the compositions of these elastomers.

[0092] A preferred embodiment consists of using an “isoprenic” elastomer, that is to say a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the different copolymers of isoprene and the compositions of these elastomers.

[0093] The isoprene elastomer is preferably natural rubber or a synthetic polyisoprene of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. According to other preferred embodiments, the diene elastomer may consist, in whole or in part, of another diene elastomer such as, for example, an SBR elastomer (E-SBR or S-SBR) used in blend or not with another elastomer, for example of the BR type.

[0094] The rubber composition may also comprise all or part of the additives normally used in rubber matrices intended for the manufacture of tires, such as, for example, reinforcing fillers such as carbon black or inorganic fillers such as silica, coupling agents for inorganic filler, anti-aging agents, antioxidants, plasticizing agents or extender oils, whether the latter are aromatic or non-aromatic (in particular very weakly or non-aromatic oils, for example of the naphthenic or paraffinic type, with high or preferably low viscosity, MES or TDAE oils, plasticizing resins with a high Tg greater than 30°C), agents facilitating the implementation (processability) of the compositions in the raw state, tackifying resins, a crosslinking system based either on sulfur or on sulfur and / or peroxide donors, accelerators,vulcanization activators or retarders, antireversion agents, methylene acceptors and donors such as, for example, HMT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimide), known adhesion promoting systems of the metal salt type, for example, in particular cobalt or nickel salts., Brief description of the drawings

[0095] Other advantageous details and characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to the figures which represent meridian views of diagrams of a tire according to embodiments of the invention. The figures are not shown to scale to simplify understanding.

[0096] There Figure 1includes a view 1-A which shows a section of a tire of the invention in a meridian plane, and a view 1-B which represents an enlargement of a portion of the meridian view 1-A surrounded by a dashed circle showing the bead of a tire of the invention.

[0097] THE Figures 2-A, 2-B, 2-C, and 2-D show embodiments of the invention with modifications of the outer profile of the sidewall layers (FE1, FE2) to facilitate contact with the rim.

[0098] There Figure 3 represents a meridian section of the inflated tire, mounted on a rim and crushed by a load carried. We see a first section in the contact patch and a second section opposite the contact patch relative to the axis (OY). This figure illustrates the determination of the rate of variation of contact with the rim.

[0099] THE Figures 4-A and 4-B represent the visualization of the main dimensions of the tire bead. Detailed description of the invention

[0100] The invention was implemented on a passenger car tire of size 245 / 45R18, according to the ETRTO (European Rim and Tire Technical Organization) specification standard. Such a tire can carry a load of 800 kilos, inflated to a pressure of 250 kPa.

[0101] On the Figure 1-A , the general reference tire 1 comprises a carcass reinforcement 90 made up of reinforcements coated with rubber composition, and two beads 50 in contact with a rim 100. A zone 49 delimited by a dotted circle defines one of the two beads 50 of the tire, an enlargement of which is proposed on the Figure 1-B. The carcass reinforcement 90 is anchored in each of the beads 50. The tire further comprises a crown reinforcement 20 comprising two working layers 21, 22, and a hooping layer 23. Each of the working layers 21 and 22 is reinforced by wire reinforcement elements which are parallel in each layer and crossed from one layer to the other, making angles of between 10° and 70° with the circumferential direction. The hooping layer 23, arranged radially outside the crown reinforcement 20, this hooping layer 23 being formed of circumferentially oriented reinforcement elements wound in a spiral. A tread 10 is placed radially on the hooping layer 23; it is this tread 10 which ensures the contact of the tire 1 with a ground.The tire 1 shown is a “tubeless” tire: it includes an “inner rubber” 95 made of a rubber composition impermeable to the inflation gas, covering the inner surface of the tire.

[0102] The sidewall layer 30 comprises two sub-layers (FE1, FE2). The first sub-layer FE1 is positioned axially externally so as to constitute the sidewall of the tire in contact with the ambient environment. The second sub-layer FE2 32 is in contact at least in part with the carcass reinforcement 90. On the Figures 1-A and 1-B , the first sublayer FE1 has a dark background, while the second sublayer FE2 has a hatched background.

[0103] The portion of the rim 100 which interacts with the tire within the framework of the invention is axisymmetrical with respect to the axis of rotation of the tire.

[0104] In a meridian plane, the rim 100 comprises at least one hook 120 located at an axial end, and connected to a seat 110 which is intended to receive a face of the bead located most radially inward. Between the seat 110 and the hook 120, there is a rectilinear portion 130 which connects the rim hook 120 to the seat 110 by connecting fillets. The rim hook 120 extended by the rectilinear portion 130 axially limits the movement of the beads during inflation.

[0105] The bead 50 partly comprises a carcass reinforcement 90 which comprises a main part 52, then wraps around an annular reinforcement structure 51 to form a turn-up 53. A padding layer 70 is positioned between the main part 52 of the carcass reinforcement 90 and its turn-up 53. According to the embodiments, the bead 50 may comprise a lateral reinforcement layer 60, positioned axially outside the turn-up 53, and axially inside the sidewall layer 30. Axially the innermost of the bead 50, a sealing layer 95 constitutes the inner wall in contact with the internal inflation air.

[0106] Said bead 50 also comprises a protective layer 80 which is in axially external contact with a rectilinear portion 130 of the rim so as to limit the axial displacement of the bead. Said protective layer 80 also comprises a portion intended to be in contact with the rim at the rim seat 110. A sidewall layer 30 cooperates with the bead 50 and constitutes an external side wall.

[0107] On the Figure 2-A, the external profiles of a bead 50 of a tire according to a particular embodiment of the invention are shown in comparison with that of a tire of usual design. The bead 50 is shown in a section opposite the contact area. The two profiles differ in an area at the rim hook 120. Reference 30 indicates the profile of a tire of the state of the art, and reference 35 shows the modification of the profile made on the tire of the invention to facilitate contact with the rim 100.

[0108] On the Figure 2-B , we have the same representation as on the Figure 2-A , but the profiles are shown in the center of the contact patch with the ground. The tire is in contact with the entire rim hook 120 unlike the Figure 2-A The rim contact variation rate reflects this evolution of rim contact.

[0109] In another embodiment shown in the Figure 2-C , there is an elastomeric mixture cushion 40 (modification located at the radially inner end of the sidewall 30), intended to be in contact with the rim hook 120. The mixture cushion 40 is delimited radially internally by a curve which matches the profile of the rim hook 120. A first side of the elastomeric mixture cushion 40 has an appropriate geometric shape which anticipates contact with the curvature of the rim hook so as to match the shape of the rim hook 120 upon contact, a second side of the elastomeric mixture cushion extends an outer side of a sidewall in contact with the ambient air, a third side of the elastomeric mixture cushion 40 is in contact with the radially inner end of the sidewall and finally a fourth side of the elastomeric mixture cushion is in contact with the protective layer 80.

[0110] On the Figure 2-C, the rim contact curve extends from a first point M1 of the tire axially positioned most externally, and in contact with the rim, and a second point M2 of the tire also in contact with the rim and located in the middle of the rectilinear portion connecting the hook 120 to the seat 110 of the rim. The length of said rim contact curve is the curvilinear distance from point M1 to point M2 along the rim contact curve.

[0111] There Figure 2-D is a variant of the previous embodiment characterized by the presence of a lateral reinforcing layer 60 of the bead 50, positioned axially external to the turn-up 53 of the carcass reinforcement 90, and axially internal to the sidewall layer 30.

[0112] There Figure 3is a view in the vertical plane of a tire of the invention according to a previous embodiment. The tire is inflated, mounted on a rim 100 and crushed by the load carried 250 on a ground 200. A first meridian section can be seen in the contact area and a second meridian section opposite the contact area. In the first section located in the contact area, in at least one first bead, the length of the rim contact curve 100, LADC, is measured. In the second section in at least one second bead, the length of the rim contact curve, LCJ, is also measured. The ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%, and in the present case is equal to 62%.

[0113] On the Figure 4-A, the determination of the height H is illustrated. The height H of the tire is the normal distance between a first straight line HH' parallel to the axis of rotation of the tire and tangent to the radially innermost point of the annular reinforcement structure, and between a second straight line DD' also parallel to the axis of rotation of the tire and passing through the radially outermost point of the tread. The radial height H is measured on the tire mounted on a rim and inflated with a set pressure conforming to the ETRTO (European Rim and Tire Organization) specifications.

[0114] On the Figure 4-B the geometric parameters of the bead in connection with the invention have been represented. The heights are defined from the line HH', which is tangent to the rod 51 at its radially innermost point:

[0115] DRI is the radial distance from HH' of the radially inner end of the lateral reinforcement layer 60. The radial distance DRI is less than or equal to 20% of the radial height H of the tire, and is 5 mm in the example presented here;

[0116] DRL is the radial distance from the line HH' of the radially outer end of the lateral reinforcement layer 60. The radial distance DRL is greater than or equal to 25% of the radial height H of the tire and is 38 mm in the example presented here;

[0117] DRR is the radial distance from HH' of the end of the turn-up of the carcass reinforcement 90. The radial distance DRR being greater than or equal to 10% of the radial height H of the tire and is 20 mm in the example presented here;

[0118] DRB is the radial distance from HH' of the radially outer end of the packing layer 70, and is 28 mm in the example presented here.

[0119] Table No. 1 below gives the compositions of elastomeric mixtures of a tire of the invention. The main mixtures used are listed by expressing for each the main ingredients expressed in pce (part by weight per hundred parts by weight of elastomer): [Table 1] NR Elastomer (Natural Rubber) BR elastomer (Butadiene) Carbon black reinforcing filler Antioxidant agent Sulfur Accelerator Reinforcing resin e Hardener M1 100 0 75 (N326) 1.5 8.5 0.95 12 4.18 M2 100 0 75 (N326) 2 7.5 0.97 12 6.8 M3 35 65 30 (N550) 1.3 8.0 4.75 0 0 10 (Silica) M4 35 65 48 (N550) 5 1.4 1.4 18 0

[0120] The mixtures of the invention used in this example are based on natural rubber elastomer, or a blend of natural rubber and butadiene for mixtures M3 and M4, reinforced with carbon black. Plasticizers (reinforcing resin) are included in the composition to facilitate the processability of the mixtures. The mixtures also include vulcanizing agents, sulfur, accelerator, and protective agents.

[0121] The M4 mixture that constitutes the first layer of FE1 sidewall includes an antioxidant agent at 5 pce and carbon black at 48 pce, so as to guarantee protection against attacks due to exposure to light and ozone attack.

[0122] The associated mechanical and viscoelastic properties, measured at 23°C under a deformation amplitude of 10% are summarized in table no. 2: [Table 2] G' G" Tan (δ)max M1 46 7 0.2 M2 48 8 0.2 M3 2.47 0.06 0.03 M4 1.26 0.100 0.08

[0123] The M4 elastomeric compound has an elongation at break level of 300% measured at 100°C, while the elongation at break level of the M3 compound is 80% also measured at 100°C.

[0124] Tire configurations of the invention were tested to clearly highlight the performance provided by the invention. The results of these tests are compared with those obtained for control tires.

[0125] Witness T1 conforms to the Figures 1-A, and 1-B , corresponds to a tire of usual design which includes a filler layer made of the elastomeric compound M1, a lateral bead reinforcement layer made of the elastomeric compound M2, and the two sidewall sub-layers (FE1, FE2) made of the elastomeric compound M4. The profile of the sidewall layer is of usual design, that is to say it has not been modified to facilitate contact with the rim.

[0126] A second witness T2 takes up the specifications of T1, but the elastomeric mixtures of the two sidewall sub-layers are made up of the same M3 mixture.

[0127] The first tire P1 conforming to the invention uses the specifications of witness T1, but the first sidewall sub-layer FE1 is made of the M4 compound and the second sidewall sub-layer FE2 is made of the M3 compound.

[0128] Generally speaking, all tires conforming to the invention have the first sidewall layer FE1 consisting of the M4 mixture, and the second sidewall layer FE2 consisting of the M3 mixture.

[0129] The second tire P2 according to the invention contains a filler layer made of the mixture M3 and also contains a lateral reinforcement layer made of the mixture M2.

[0130] The third tire P3 according to the invention has the filler layer and the lateral reinforcement layer made of the same M3 mixture.

[0131] Finally, the fourth tire P4 of the invention differs from P3, by the modification of the profile of the sidewall layer for a rim contact variation rate greater than 30%.

[0132] The configurations of the tires P1, P2, and P3 of the invention are illustrated in Figure 1-B . As for the P4 configuration, illustrations can be seen on the Figures 2-A, 2-B, and 2-D .

[0133] The rim contact variation rate is 62% for P4, after a partial modification of the sidewall layer profile in the rim contact area, as shown in the Figures 2-A and 2-B .

[0134] Industrial performance is measured by the reject rate due to sidewall molding defects. None of the tires of the invention P1, P2, P3 and P4 have molding defects affecting the markings, and are satisfactory in industrial performance as T1. On the other hand, the control T2 with a single-layer sidewall made of the M3 compound leads to numerous rejects due to difficult demolding.

[0135] The rolling resistance test was carried out according to ISO 28580. For a tested tire, the result is the rolling resistance coefficient which represents the ratio of the force resisting the vehicle's forward movement by tire hysteresis divided by the load carried.

[0136] The transverse drift stiffness measurements were made on dedicated measuring machines such as those marketed by the company MTS.

[0137] A result above (respectively below) 100% means an improvement (respectively a deterioration) in the performance considered.

[0138] The results obtained are summarized in the following table no. 3: [Table 3] Rolling resistance Transverse drift stiffness T1 100 100 T2 102 101 P1 102 100 P2 104 100 P3 112 98 P4 111 101

[0139] All the tires of the invention achieve the desired compromise between rolling resistance and industrial performance. Rolling resistance is improved by 2% to 12% depending on the tested variants.

[0140] The transverse drift stiffness of the tires was measured. Tires P1 and P3 have a transverse drift stiffness of 100% and 98% respectively without perceptibly affecting the vehicle's behavior. Tires P2 and P4 have performances greater than or equal to the desired target.

[0141] All the tire variants in accordance with the invention presented are produced without any change in the processes and remain at a standard industrial cost price.

[0142] Furthermore, the invention can be generalized to other bead architectures than those described here, such as for example a bead having a first filling layer, and a second lateral reinforcement layer, even though the carcass reinforcement does not include a turn-up.

Claims

1. Tyre (1) for a passenger vehicle, comprising in a meridian plane: two beads (50) intended to be mounted on a rim, two sidewall layers (30) connected to the beads (50), a crown (20) comprising a tread (10), the crown (20) having a first side connected to the radially outer end of one of the two sidewall layers (30) and having a second side connected to the radially outer end of the other of the two sidewall layers (30); at least one carcass reinforcement (90) extending from the two beads (50) to the crown (20), the carcass reinforcement (90) comprising a plurality of carcass reinforcement elements and being anchored in the two beads (50) by a turn-up around an annular reinforcement structure (51), so as to form in each bead a main part (52) and a turn-up (53); each sidewall layer (30) consisting of two axially superposed sub-layers (FE1, FE2), a first sidewall sub-layer (FE1) delimited by a first axially outermost side constituting a lateral wall of the tyre in contact with the ambient air, and a second axially inner side defined such that said sidewall sub-layer (FE1) has an average axial thickness E1, and occupying a volume V1; each sidewall layer also comprising a second sidewall sub-layer (FE2), a first side of which coincides with the second side of the first sidewall sub-layer (FE1), and a second, axially inner side of which is at least partially in contact with the carcass reinforcement (50), said sidewall sub-layer (FE2) having an average axial thickness E2, and occupying a volume V2; the ratio V1 / (V1+V2) is less than or equal to 0.3 characterized in that the thickness E1 of the first sidewall sub-layer (FE1) is greater than or equal to 0.7 mm, , in that the elongation at break of the elastomer compound constituting the first sidewall sub-layer (FE1) is greater than or equal to 200% measured at a temperature of 100°C, and in that the dynamic loss of the second sidewall sub-layer (FE2), Tan(δ) max, is less than or equal to 0.10, the dynamic loss is measured on a Metravib VA4000 viscosity analyser in accordance with ASTM D 5992-96, the response of a sample of vulcanized elastomer compound in the form of a cylindrical test specimen 2 mm thick and 78 mm2 in cross section, subjected to sinusoidal loading in simple alternating shear stress at a frequency of 10 Hz, at a temperature of 100°C is recorded, a sweep is carried out in deformation amplitude from 0.1% to 50% outward cycle, then from 50% to 0.1% return cycle.

2. Tyre (1) according to Claim 1, wherein the elastic shear modulus of the second sidewall sub-layer FE2 is in the range [1.5; 10] MPa and preferably is in the range [2.5; 10] MPa.

3. Tyre (1) according to either of the preceding claims, each bead (50) comprising a filling layer (70) comprised at least in part between the main part of the carcass reinforcement (52), the turn-up (53) of the carcass reinforcement and the radially outer portion of the annular reinforcement structure, wherein the elastomer compound constituting the filling layer has a dynamic loss Tan(δ)max of less than or equal to 0.1, the dynamic loss is measured on a Metravib VA4000 viscosity analyser in accordance with ASTM D 5992-96, the response of a sample of vulcanized elastomer compound in the form of a cylindrical test specimen 2 mm thick and 78 mm2 in cross section, subjected to sinusoidal loading in simple alternating shear stress at a frequency of 10 Hz, at a temperature of 100°C is recorded, a sweep is carried out in deformation amplitude from 0.1% to 50% outward cycle, then from 50% to 0.1% return cycle.

4. Tyre (1) according to one of the preceding claims, wherein the bead comprises a lateral reinforcement layer (60) consisting of an elastomer compound occupying a volume comprised at least in part between the second sidewall layer (30) and the turn-up (53) of the carcass reinforcement.

5. Tyre (1) according to Claim 4, wherein the lateral reinforcement layer (60) of the bead consists of an elastomer compound whose dynamic loss Tan(δ)max is less than or equal to 0.10, the dynamic loss is measured on a Metravib VA4000 viscosity analyser in accordance with ASTM D 5992-96, the response of a sample of vulcanized elastomer compound in the form of a cylindrical test specimen 2 mm thick and 78 mm2 in cross section, subjected to sinusoidal loading in simple alternating shear stress at a frequency of 10 Hz, at a temperature of 100°C is recorded, a sweep is carried out in deformation amplitude from 0.1% to 50% outward cycle, then from 50% to 0.1% return cycle.

6. Tyre (1) according to one of the preceding claims, in each bead (50) a rim contact curve comprising the points of the tyre (1) in contact with the rim (100); said rim contact curve connecting a first point M1 of the tyre positioned outermost axially, and in contact with the rim, and a second point M2 of the tyre also in contact with the rim and situated in the middle of the rectilinear portion (130) connecting the flange (120) to the seat (110) of the rim; said tyre (1) also comprising two sections in a vertical meridian section of the inflated tyre, mounted on a rim, and compressed against the ground by a vertical load (250), where the load, the inflation pressure, are determined in a specification standard such as ETRTO (European Tyre and Rim Technical Organisation); a first section being located in the contact area, and a second section being located on the opposite side to the previous section in relation to the axis of rotation of the tyre; in the first section located in the contact area, in at least a first bead, the length of the rim contact curve, LADC, being measured; in the second section located opposite the contact area in relation to the axis of rotation of the tyre, in at least a second bead, the length of the rim contact curve, LCJ, being measured, wherein the ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%.

7. Tyre (1) according to the preceding claim, wherein the ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 40%, preferably greater than or equal to 50%, more preferably greater than or equal to 60%.

8. Tyre (1) according to one of the preceding claims, the distance DRB being the radial distance from a radially outer end of the filling layer (70), wherein said distance DRB is less than or equal to 50% of the radial height H of the tyre (1).

9. Tyre (1) according to one of Claims 4 to 8, the distance DRI being the radial distance from a radially inner end of the lateral reinforcement layer (60) to the straight line (HH'), wherein said radial distance DRI is in the range [5%; 20%] of the radial height H of the tyre (1).

10. Tyre (1) according to one of Claims 4 to 9, the distance DRL being the radial distance from the radially outer end of the lateral reinforcement layer (60) to the straight line (HH'), wherein said radial distance DRL is greater than or equal to 25% of the radial height H of the tyre (1).

11. Tyre (1) according to one of the preceding claims, wherein the turn-up (53) of the carcass reinforcement (90) is pressed against the main part (52) of the carcass reinforcement (90) over its entire height radially externally, the turn-up (53) of the carcass reinforcement (90) is pressed against the main part (52) of the carcass reinforcement (90).

12. Tyre (1) according to one of the preceding claims, wherein said tyre comprises a reinforcement of the bead (50) axially externally to the turn-up (53) of the carcass reinforcement (90), and axially internally to the sidewall (30).

13. Tyre (1) according to one of Claims 4 to 12, wherein the elastomer compound constituting at least one layer among the filling layer (70), and / or the lateral reinforcement layer (60) and / or the sidewall sub-layer (FE2) has a composition based on a diene elastomer, a crosslinking system, a reinforcing filler, carbon black type N550, at an overall rate of between 50 and 75 phr.

14. Tyre (1) according to Claim 13, wherein the elastomer compound constituting the filling layer (70), the elastomer compound constituting the lateral reinforcement layer (60), and the elastomer compound constituting the sidewall sub-layer (FE2) have the same composition.