Tire with optimized performance in rolling resistance and road handling

Abstract

The invention relates to a passenger car tire (1) whose rolling resistance performance has been improved without degrading its lateral stiffness. The bead (50) is made more flexible by the use of low-hysteresis materials. The lateral stiffness is compensated by the use of a rigid, low-hysteresis sidewall layer (30). The lower zone compound layers, having a viscoelastic loss Tan(δ)max less than or equal to 0.10, represent a volume between 30% and 90% of the total volume of the lower zone, and the elastic shear stiffness modulus G'(M3) of the sidewall layer is within the range [0.5; 10]. Abstract figure: Figure 1-A

Description

Title of the invention: Tire with optimized performance in rolling resistance and road handling. Field of the invention

[0001] The present invention relates to a tire for motor vehicles whose rolling resistance performance is improved without degrading lateral stiffness. The invention is particularly suited to a radial tire intended for use on a passenger car or van. Definitions

[0002] By convention, we consider a frame (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 in 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 inside, respectively radially outside, we mean closer, respectively further from the axis of rotation of the tire.

[0004] By axially inside, respectively axially outside, we mean 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 tread of the tire 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 includes a crown, intended to come into contact with a ground by means of a tread, the two axial ends of which are connected by means of two sidewalls to 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 and radially outside the carcass reinforcement. Each crown layer consists of parallel reinforcements coated with a polymeric material of the elastomeric type or an elastomeric blend. The assembly consisting of the crown reinforcement and the tread is called the crown.

[0009] The carcass reinforcement of a radial tire typically comprises at least one carcass layer made of metallic or textile reinforcing elements embedded in an elastomeric coating. The reinforcing elements are substantially parallel to each other and form an angle of between 85° and 95° with the circumferential direction. The carcass layer includes a main portion connecting the two beads and winding, within each bead, around an annular reinforcing structure. The annular reinforcing structure may be a bead comprising a circumferential reinforcing element, most often metallic, surrounded by at least one material, including but not limited to elastomeric or textile. The winding of the carcass layer around the annular structure proceeds from the inside to the outside of the tire to form a inversion, including one end.The reversal, in each bead, allows the carcass reinforcement layer to be anchored to the annular structure of the bead.

[0010] Each bead comprises a filling layer extending radially outwards from the annular reinforcing structure. The filling layer consists of at least one elastomeric filling compound. The filling layer axially separates the main part and the reversible part of the frame reinforcement.

[0011] Each rim also includes a protective layer extending radially inwards along the sidewall and axially outwards towards the rim. The protective layer is also at least partially in contact via its axially outwards face with a rim hook. The protective layer is made of at least one protective elastomeric compound.

[0012] Each bead may finally include a lateral reinforcing layer positioned between the side and the inversion of the frame reinforcement. The outer lateral reinforcing layer is made of at least one elastomeric compound.

[0013] Each tire sidewall comprises at least one sidewall layer made 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 defined as an elastomeric material obtained by mixing its various constituents. An elastomeric blend typically comprises an elastomeric matrix with at least one diene elastomer of the natural or synthetic rubber type, at least one reinforcing filler of the carbon black and / or silica type, a crosslinking system most often sulfur-based, and protective agents. For certain applications, the elastomers considered may also include thermoplastics (TPEs).

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

[0016] The expression "part by weight per hundred parts by weight of elastomer" (or pce) is to be understood in the context of the present invention as the part, by mass per hundred parts of elastomer present in the composition of the mixture considered.

[0017] An elastomeric compound can be mechanically characterized, particularly after curing, by its dynamic properties, such as a dynamic shear modulus G* = (G'² + G”²)l / ², where G' is the elastic shear stiffness modulus and G” is the viscous shear modulus, and a dynamic loss Tanô = G” / G'. The dynamic shear modulus G* and the dynamic loss Tanô are measured on a Metravib VA4000 viscoalyzer, according to ASTM D 5992-96. The response of a vulcanized elastomeric compound sample in the form of a cylindrical specimen 2 mm thick and with a cross-section of 78 mm², subjected to sinusoidal alternating simple shear loading at a frequency of 10 Hz and a temperature of 100°C, is recorded. An amplitude sweep is performed. deformation from 0.1% to 50% (outward cycle), then from 50% to 0.1% (return cycle). For the outward cycle, the maximum observed value of tan(θ) is indicated, denoted Tan(θ)max.

[0018] The "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 vehicle stability 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 its trajectory, a force equivalent to (but in the opposite direction to) the centrifugal force that tends to eject the vehicle from its trajectory must be generated. This lateral force must be generated by the vehicle's four tires to overcome the centrifugal force.

[0021] The deformation of the tread blocks in contact with the ground generates a lateral force. The mechanism that allows the tire to deform the tread 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 tread blocks and thus generate the necessary lateral forces.

[0022] Transverse drift stiffness is defined as the variation of the transverse forces generated in the contact area of ​​the moving tire compressed by the load, 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, parallel to the axis of rotation of the tire, is proportional to the drift angle. The transverse drift stiffness is equal to this proportionality coefficient.

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

[0025] Rolling resistance is another performance characteristic addressed in the application. Rolling resistance is one of the forces that oppose the forward motion of the vehicle. The rolling resistance coefficient of a tire (CRR) is the rolling resistance force expressed per unit load on the tire. The coefficient is expressed in kg / t.

[0026] Rolling resistance is essentially linked to tire deformation. For example, the sidewall beads account for 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 is shown mounted on a rim. This rim is chosen according to the specifications of the ETRTO (European Technical Organisation for Tyres and Rims) standard, which associates recommended rims with a given tire size. In general, several rim widths may be suitable for the same tire size. The part of the rim that interacts with the tire within the scope of the invention is axisymmetric with respect to the tire's axis of rotation. To describe the rim, it suffices 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, connected to a seat designed to receive a face of the rim bead located most radially inward. Between the seat and the hook, there is a straight portion that connects the rim hook to the seat by means of fillets. The rim hook, extended by the straight portion, axially limits the displacement of the rim beads during inflation.

[0029] The fitment of the tire beads on a rim during inflation is also a performance that can be impacted by the invention. The fitment performance of the tire beads consists of evaluating the ability of a tire's beads to seat correctly on a rim during inflation. On the innermost radial face of the bead, the contact with the seat must be sufficient to prevent any leakage of the tire's inflation air. Generally, a contact pressure of at least 1.4 MPa is expected in this contact area. The inflation pressure forces the bead against the rim hook. Here again, the contact pressure on the hook It must be sufficient to prevent the tire from coming off the rim, especially in sharp turns at high speed. Observation methods, particularly radiographic ones, of the beading mounted on a rim allow for the diagnosis of the mounting quality.

[0030] It is therefore possible to classify two tires according to their rim mounting performance. Previous technique

[0031] Reducing greenhouse gas emissions from transport 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 vehicle fuel consumption. For example, a 20% reduction in tire rolling resistance can save 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 their behavior on the vehicle.

[0033] It has already been proposed to improve the rolling resistance of passenger vehicle tires by optimizing their bead design. Document WO 2010 / 072736 specifically advises using elastomeric compositions with low elastic shear stiffness moduli G' around 15 MPa and viscous moduli G'' lower than 20% than the elastic shear stiffness moduli to achieve 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 preceding relationship. This optimization leads to shorter and wider elastomeric compound layer profiles than in traditional tires. In some cases, the difficulty of industrially implementing 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 reinforcing mesh to the ridges. The reinforcing mesh consists of reinforcements embedded in an elastomeric mixture.

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

[0037] The inventors have set themselves the objective of producing a tire that improves the level of rolling resistance without degrading vehicle behavior, and while controlling the associated manufacturing costs. Description of the invention

[0038] This goal has been 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 top comprising a tread, the top 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 frame reinforcement extending from the two ridges to the top, the frame reinforcement comprising a plurality of frame reinforcement elements and being anchored in the two ridges by a turning around an annular reinforcement structure, so as to form in each ridge a main part and a turning; two low zones as portions of the tire, positioned on either side of the radial axis OZ, a first low zone on one side of the radial axis OZ including the bead and at least part of the sidewall layer of this first side and a second low zone on the other side of the radial axis OZ including the bead and at least part of the sidewall layer of this second side; each lower zone having a meridian surface delimited by an axial line AA' passing at a radial distance equal to 70% of the distance H, where H is the radial distance between a first axial line HH' passing through the most radially internal point of the annular reinforcement structure, and between a second axial line DD' tangent to the tread at its most radially external point, and radially internally said meridian surface being delimited by the peripheral contour of the bead intended to be in contact with the rim; each lower zone occupying a volume obtained by rotating said meridian surface around the axis of rotation of the tire; the bead of each lower zone comprising at least one layer of padding included at least in part between the main part of the frame reinforcement, the reversal of the frame reinforcement and the radially outer portion of the annular reinforcing structure; elastomeric mixtures having an elastic modulus of shear stiffness and a viscoelastic loss measured according to ASTM D 5992-96, at 23°C, under a shear strain of 10%; said layers of mixtures in each lower zone having a viscoelastic loss Tan(ô)max less than or equal to 0.10, represent a volume between 30% and 90% of the total volume of said lower zone; the elastic shear stiffness modulus of each flank layer is within the range [0.5; 10] MPa.

[0039] The tires of the invention have two lower zones positioned on either side of the radial axis (OZ). The contour of each lower zone in a meridian plane comprises the axial line AA', the axially outer wall in contact with the ambient air of a portion of the sidewall layer, which extends radially inwardly through the outer periphery of the protective layer intended to be in contact with the rim. The contour of each lower zone continues as the axially inner wall of the bead in contact with the tire's inflation gas. In other words, the contour of the lower zone incorporates, at least in part, the outer contours of the sidewall layer and the outer contour of the bead, both of which are contained within the lower zone.

[0040] The volume of a low zone is the circumferential extension of its contour in a meridian plane defined above.

[0041] As defined, the lower zones represent 20% to 30% of the tire's rolling resistance. This contribution is mainly due to the viscoelastic dissipation of the larger volume elastomeric compounds with greater hysteresis.

[0042] During the rolling of an inflated tire mounted on a rim and compressed by the load it carries, the lower areas undergo cycles of intense flexural deformation resulting from the periodic passage through the contact patch. These deformations, combined with the hysteresis levels of the elastomeric compounds, are the cause of the viscoelastic dissipation of the lower areas.

[0043] The principle of the invention is to provide the elastomeric compound layers in the lower, larger volume zone with a hysteresis measured by a Tan(φ)max value less than or equal to 0.10, so as to reduce the viscoelastic dissipation of the bead and thus improve rolling resistance compared to conventional tire designs. Indeed, conventional bead designs use a shear stiffness modulus greater than 30 MPa for these elastomeric compound layers. However, such elastomeric compounds most often also have a hysteresis measured by a Tan(φ)max value significantly greater than 0.10.

[0044] In the case of the lower zones of the tires of the invention, between 30% and 90% of the volume of each lower zone is made up of low hysteresis elastomeric mixtures, i.e. mixtures with a hysteresis measured by a value of Tan(ô)max less than 0.10.

[0045] By applying an elastic mixture to the sidewall layer of a tire of the invention With a shear stiffness modulus of up to 10 MPa, lateral drift stiffness is maintained at a suitable level, essential for good vehicle handling. Indeed, conventional sidewall designs aim for a shear stiffness modulus of 1.5 MPa or less.

[0046] The combination of selecting elastomeric compounds with the largest volumes in the lower zone, exhibiting low hysteresis, and choosing a sidewall layer with a shear stiffness modulus of up to 10 MPa are the main characteristics that lead to the tire of the invention, which achieves a compromise between improving rolling resistance without compromising road handling. The sidewall layer of the tires of the invention, being stiffer than in conventional designs, compensates, for example, for the decrease in the shear stiffness modulus of the tread layer. Furthermore, the solutions implemented do not require major process changes, thus keeping the industrial production cost at a typical level.

[0047] Advantageously, the elastic shear stiffness modulus of the flank layer is preferably within the range [1.5; 10] MPa and even more preferably within the range [2.5; 10] MPa.

[0048] The sidewalls of the tires of the invention rely in particular on a balance between the shear stiffness and the hysteresis of the elastomeric compounds constituting them. The elastic shear stiffness modulus of each sidewall layer remains below 10 MPa so that the hysteresis remains at a level measured by a Tan(φ)max value less than or equal to 0.10. The invention operates from an elastic shear stiffness modulus of the sidewall layer greater than or equal to 0.5 MPa.

[0049] Preferably, said layers of mixtures of the lower zone having a viscoelastic loss Tan(ô)max less than or equal to 0.10, represent a volume between 40% and 90% of the total volume of the lower zone, and even more preferably a volume between 50% and 90% of the total volume of the lower zone.

[0050] The architecture of the lower zones varies depending on the presence of the elastomeric compound layers necessary for the proper functioning of the tire. In particular, the mounting rim diameter is a parameter that significantly impacts the bead architecture. For example, for rim diameters exceeding 16 inches, each bead often includes a lateral layer reinforcing the tread layer to efficiently transmit vehicle torque. This affects the volume of low-hysteresis compounds relative to the total volume of the lower zone. A 90% volume of low-hysteresis elastomeric compounds constitutes an upper limit, indicating that each lower zone also includes non-hysteresis materials. Conversely, for smaller rim diameters, the architecture of the lower zones can be simplified, and the proportion of compounds Low hysteresis relative to the total volume of each lower zone can reach a value of 40%.

[0051] Advantageously, the packing layer is made of an elastomeric mixture whose viscoelastic loss Tan(ô)max is less than or equal to 0.10.

[0052] The padding layer of the bead generally occupies a large volume and undergoes significant shear deformations due to variations in tension in the reinforcements of the main part of the carcass layer and its reversal. The choice of a low-hysteresis elastomeric compound helps to control the level of viscoelastic dissipation.

[0053] According to a particularly advantageous embodiment, the bead comprises a lateral reinforcement layer made of an elastomeric mixture occupying a volume at least partly between the side layer and the turning of the frame reinforcement.

[0054] According to the inventors, the lateral reinforcement layer of the bead, in addition to the first padding layer, provides transverse rigidity. Based on its material properties in terms of Tan(φ)max and dynamic shear stiffness, this reinforcement allows for adjusting the performance balance between rolling resistance and road handling.

[0055] Advantageously, in a variant of this embodiment, said lateral reinforcement layer of at least one bead is made of an elastomeric mixture whose viscoelastic loss Tan (ô) max is less than or equal to 0.10.

[0056] In this variant of the embodiment, the two layers of mixtures, namely the filling layer and the lateral reinforcement layer, verify the property of having a viscoelastic loss Tan (ô) max less than 0.10. The gain in rolling resistance is optimal, while having a road behavior of the tire mounted on the vehicle conforming to the expected.

[0057] 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 axially positioned, outermost point M1 of the tire, 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 straight portion connecting the hook to the rim seat. 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 meridional 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 Technical Organisation for Tyres and Rims); a first section being located in the contact area, and . A second section is located on the opposite side of the tire's rotation axis to the first. In the first section, located in the contact patch, the length of the rim contact curve, LADC, is measured in at least one bead. In the second section, located on the opposite side of the contact patch relative to the tire's rotation axis, the length of the rim contact curve, LCJ, is measured in at least one bead. The ratio of the difference in lengths of the rim contact curves of the two sections, i.e., 100*(LADC-LCJ) / LCJ, is greater than or equal to 30.

[0058] In this embodiment, the rate of variation of rim contact of the tires of the invention is significantly higher than that observed on the tires of the state of the art.

[0059] When an inflated tire mounted on a rim is compressed by a load, the points of the tire in contact with the rim can 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.

[0060] The tire is designed so that the rim contact curve is as long as possible in the contact area, compared to state-of-the-art tires, and more specifically in the meridian at the center of the contact patch. Under these conditions, the inventors believe that the contribution of the rim contact to the drift stiffness is maximized.

[0061] In a cross-section of an inflated tire mounted on a rim and compressed by the load it carries, a first section of the tire can be seen passing through the center of contact. The contact area is understood to be all the points of the tire, at a given instant, that are in contact with the ground. The center of contact is the point of the contact area located on the vertical axis OZ. Opposite the center of contact with respect to the axis of rotation OY of the tire, another section of the tire can also be seen, which overall defines a deformed state comparable to the axisymmetric inflation state.

[0062] The rate of change of rim contact corresponds to the maximum value of the evolution of rim contact lengths per wheel revolution.

[0063] According to the inventors, an essential step in the design of a tire of this embodiment consists of modifying its outer profile in the contact area with the rim. Various solutions are possible, such as increasing the axial thickness of the sidewall layer at the junction with the protective layer. Other solutions consist of modifying the outer profile so as to obtain a profile in the contact area with the same curvature as the rim hook. Yet another solution consists of inserting a compound cushion in the area at the junction of the sidewall and protective layers, at the rim hook. This cushion of The mixture can preferably be made from the same mixture as the flank layer in order to maintain industrial production costs. The key requirement for this elastomeric mixture cushion is its elastic shear stiffness modulus, which advantageously could be, for example, equal to that of the flank layer.

[0064] Advantageously, the ratio of the difference in 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, and even more preferably greater than or equal to 60.

[0065] The outer profile in the contact area with the rim can be modified to target a specific rim contact variation rate. This therefore provides a lever for adjusting the lateral drift stiffness in the search for a performance compromise between rolling resistance and tire handling. The lateral 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 mounting, but rates that are too high, exceeding 100%, could hinder mounting.

[0066] In addition to the main features of the invention, the inventors have identified levers related to the geometry of the bead's compound layers to further optimize the tire's performance compromise with improved rolling resistance while maintaining good road handling.

[0067] Advantageously, the DRB distance being the radial distance from one end of the radially outer packing layer, said DRB distance is less than or equal to 50% of the radial height H of the tire.

[0068] 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 innermost radial point of the annular reinforcement structure, and a second straight line DD' also parallel to the axis of rotation of the tire and passing through the outermost radial point of the tread. The radial height H is measured on the tire mounted on a rim and inflated to a target pressure conforming to ETRTO (European Tyre and Rim Organisation) specifications.

[0069] Advantageously, the DRI distance being the radial distance from a radially inner end of the lateral reinforcement layer to the line HH', said radial distance DRI is within the range [5%; 25%] of the radial height H of the tire.

[0070] Advantageously, since the DRL distance is 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 pneumatic.

[0071] The lateral reinforcement layer located between the side and the inversion of the carcass reinforcement contributes to the rigidity of the reinforcement bead to the first padding layer. According to the inventors, its positioning is adjusted by the dimensions DRI and DRL so as to resist the bending, extension-compression stresses of the bead when passing through the contact area.

[0072] In an advantageous embodiment of the invention, the reversal of the carcass reinforcement is pressed against the main part of the carcass reinforcement over its entire height radially outwards.

[0073] As mentioned above, the carcass reinforcement is formed of reinforcements embedded between two layers of elastomeric compounds. The reversible reinforcement is pressed against the main part of the carcass reinforcement, meaning that the reversible reinforcement is in contact with the main branch of the carcass reinforcement. This contact occurs along a surface positioned between the two coating layers of the carcass reinforcement.

[0074] In this configuration, the volume of the first layer of padding is limited to the bare minimum around the annular reinforcement structure. This configuration is very advantageous for reducing the rolling resistance of the bead.

[0075] In another embodiment, the tire includes a reinforcement of the bead axially external to the carcass reinforcement, and axially internally to the sidewall.

[0076] The reinforcement of the bead is formed of parallel reinforcements embedded between two layers of elastomeric compounds. The addition of this semi-finished product results in an increased manufacturing cost that must be offset. To limit the impact on the cost of such a solution, this embodiment can be combined with the reinforcement of the frame's reinforcement facing against the main part of the frame's reinforcement.

[0077] Advantageously, in each bead, the elastomeric mixture constituting at least one layer among the packing layer, and / or the lateral reinforcing layer, and / or the flank layer 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 parts per unit.

[0078] Even more advantageously, in each bead, the elastomeric mixture constituting the padding layer, the elastomeric mixture constituting the lateral reinforcement layer, and the elastomeric mixture constituting the flank layer have the same composition.

[0079] By "dienic" elastomer (or indistinctly rubber) is meant, in a known manner, an elastomer derived at least in part (i.e., a homopolymer or a co polymer) of diene monomers, that is to say, monomers bearing two carbon-carbon double bonds, conjugated or not. The diene elastomer used is preferentially 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 compositions of these elastomers.

[0080] A preferred embodiment consists of using an "isoprene" 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 various isoprene copolymers and the compositions of these elastomers.

[0081] The isoprene elastomer is preferably natural rubber or a synthetic polyisoprene of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes with a cis-1,4 linkage percentage (molar %) greater than 90% are preferably used, and more preferably greater than 98%. According to other preferred embodiments, the diene elastomer may be composed, in whole or in part, of another diene elastomer such as, for example, an SBR elastomer (E-SBR or S-SBR) used in blending or not with another elastomer, for example of the BR type.

[0082] The rubber composition may also include all or some of the additives commonly used in rubber matrices for the manufacture of tires, such as, for example, reinforcing fillers like carbon black or inorganic fillers like silica, coupling agents for inorganic fillers, anti-aging agents, antioxidants, plasticizing agents or extending 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 above 30°C), agents facilitating the processing of the compositions in the raw state, tackifying resins, a crosslinking system based on either sulfur or sulfur donors and / or peroxide, accelerators,Vulcanization activators or retarders, anti-reversion agents, methylene acceptors and donors such as HMT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimide), known adhesion-promoting systems such as metallic salts, particularly cobalt or nickel salts. Brief description of the drawings

[0083] Other details and advantageous features of the invention will become apparent from the description of exemplary embodiments of the invention with reference to the figures, which represent meridian views of diagrams of a tire according to one embodiment of the invention. The figures are not drawn to scale for the sake of simplicity.

[0084] Fig. 1 includes 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 a magnification of a portion of the meridian view 1-A surrounded by a circle of dashes showing a lower area of ​​a tire of the invention.

[0085] Figures 2-A, 2-B, 2-C, and 2-D show an embodiment of the invention with modifications to the external profile of the sidewall layer to facilitate contact with the rim.

[0086] Figure 3 shows a meridional cross-section of the inflated tire, mounted on a rim and compressed by a load. A first section is visible in the contact area, and a second section opposite the contact area with respect to the (OY) axis. This figure illustrates the determination of the rate of change of contact with the rim.

[0087] Figures 4-A and 4-B represent the visualization of the main ribs of the lower zone. Detailed description of the invention

[0088] The invention has been implemented on a passenger car tire of size 245 / 45R18, according to the ETRTO (European Technical Organisation for Wheels and Tyres) specification standard. Such a tyre can carry a load of 800 kg, inflated to a pressure of 250 kPa.

[0089] In [Fig. 1]-A, the general reference tire 1 comprises a carcass reinforcement 90 made of reinforcements coated with a rubber compound, and two beads 50 in contact with a rim 100. A zone 49 delimited by a dashed circle defines a lower zone of the tire, a magnified view of which is shown in [Fig. 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 reinforcement layer 23. Each of the working layers 21 and 22 is reinforced by wire reinforcement elements which are parallel within each layer and crossed from one layer to the next, making angles with the circumferential direction between 10° and 70°.The reinforcement layer 23, arranged radially outside the top reinforcement 20, is formed of circumferentially oriented, spirally wound reinforcing elements. A tread 10 is laid radially on the reinforcement layer 23; it is this tread 10 that provides contact between the tire 1 and the ground. The... The tire shown is a "tubeless" tire: it includes an "inner rubber" 95 in a rubbery composition impermeable to inflation gas, covering the inner surface of the tire.

[0090] The part of the rim 100 which interacts with the tire within the framework of the invention is axisymmetric with respect to the axis of rotation of the tire.

[0091] In a meridian plane, the rim 100 comprises at least one hook 120 located at an axial end and connected to a seat 110 intended to receive a face of the rim bead located most radially inwardly. Between the seat 110 and the hook 120, there is a straight portion 130 which connects the rim hook 120 to the seat 110 by means of fillets. The rim hook 120, extended by the straight portion 130, axially limits the displacement of the rim beads during inflation.

[0092] In [Fig. 1]-B, a general reference lower zone 55 is shown containing the flank layer 30 and the bead 50. The contour of the lower zone follows the external contours of the flank layer 30 at least in part and the external contour of the bead 50.

[0093] Said bead 50 includes in part a carcass reinforcement 90 which has a main part 52, then wraps around an annular reinforcing structure 51 to form a turret 53. A padding layer 70 is positioned between the main part 52 of the carcass reinforcement 90 and its turret 53. According to embodiments, the bead 50 may include a lateral reinforcing layer 60, positioned axially external to the turret 53, and axially internal to the side layer 30. Axially furthest inward to the bead 50, a sealing layer 95 constitutes the inner wall in contact with the internal inflation air.

[0094] Said bead 50 also includes a protective layer 80 which is in external axial contact with a straight portion 130 of the rim so as to limit the axial displacement of the bead. Said protective layer 80 also includes 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 lateral wall.

[0095] In [Fig.2]-A, the external profiles of a bead 50 of a A tire according to a particular embodiment of the invention compared to that of a conventionally designed tire. The bead 50 is shown in a section opposite the contact patch. The two profiles differ in an area at the rim hook 120. Reference numeral 30 indicates the profile of a prior art tire, and reference numeral 35 shows the modification of the profile made to the tire of the invention to facilitate contact with the rim 100.

[0096] In [Fig.2]-B, we have the same representation as in [Fig.2]-A, but the Profiles are shown at the center of the contact area with the ground. The tire is in contact with the entire rim hook 120, unlike in [Fig. 2]-A. The rate of change in rim contact reflects this evolution of the rim contact.

[0097] In another embodiment shown in [Fig.2]-C, there is an elastomeric blending cushion 40 (modification located at the radially inner end of the sidewall 30), intended to be in contact with the rim hook 120. The blending cushion 40 is radially delimited internally by a curve that follows the profile of the rim hook 120. A first side of the elastomeric blending cushion 40 has a suitable geometric shape that anticipates contact with the curvature of the rim hook so as to follow the shape of the rim hook 120 upon contact, a second side of the elastomeric blending cushion extends an outer side of a sidewall in contact with the ambient air, a third side of the elastomeric blending cushion 40 is in contact with the radially inner end of the sidewall and finally a fourth side of the elastomeric blending cushion is in contact with the protective layer 80.

[0098] In [Fig. 2]-C, the rim contact curve extends from a first point M1 of the tire, axially positioned furthest out and in contact with the rim, to a second point M2 of the tire, also in contact with the rim and located in the middle of the straight section connecting the hook 120 to the rim seat 110. The length of said rim contact curve is the curvilinear distance from point M1 to point M2 along the rim contact curve.

[0099] The [Fig.2]-D is a variant of the previous embodiment characterized by the presence of a lateral reinforcement layer 60 of the bead 50, positioned axially externally to the turn 53 of the frame reinforcement 90, and axially internally to the side layer 30.

[0100] Figure 3 is a vertical plane view of a tire of the invention according to a prior embodiment. The tire is inflated, mounted on a rim 100, and compressed by the load 250 on a surface 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 bead, the length of the rim contact curve 100, LADC, is measured. In the second section, in at least one bead, the length of the rim contact curve, LCJ, is also measured. The ratio of the difference in 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%.

[0101] Figure 4-A illustrates the determination of the height H. 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 innermost radial point of the The annular reinforcement structure is connected to a second straight line DD', also parallel to the tire's axis of rotation and passing through the outermost radial point of the tread. The radial height H is measured on the tire mounted on a rim and inflated to a target pressure conforming to ETRTO (European Tyre and Rim Organisation) specifications.

[0102] Figure 4-B shows the geometric parameters of the bead related to the invention. The heights are defined from the line HH', which is tangent to the rod 51 at its innermost radial point:

[0103] 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 5mm in the example shown here;

[0104] 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 shown here;

[0105] DRR is the radial distance from HH' of the end of the carcass reinforcement reversal 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;

[0106] DRB is the radial distance from HH' of the radially outer end of the packing layer 70, and is 28 mm in the example shown here.

[0107] Table 1 below gives the compositions of elastomeric mixtures of a lower zone of the invention. The principal mixtures used are listed, expressing for each the principal ingredients in wt. (parts by weight per hundred parts by weight of elastomer):

[0108] [Tables] NR elastomer (Natural UC rubber) BR elastomer (Butadien e) Reinforcing filler carbon black Anti-oxidant agent Sulfur Accelerator Reinforcing resin Hardener Ml 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) 10 (Silica) 1.3 8.0 4.75 0 0 M4 35 65 48 (N550) 5 1.4 1.4 18 0

[0109] The compounds of the invention used in this example are based on natural rubber elastomer, or on a blend of natural rubber and butadiene for compounds M3 and M4, reinforced with carbon black. Plasticizers (reinforcing resin) are included in the composition to facilitate the processability of the compounds. The compounds also include vulcanizing agents, sulfur, an accelerator, and protective agents. The associated mechanical and viscoelastic properties, measured at 23°C under a 10% strain amplitude, are summarized in Table 2:

[0110] [Table 2] G' G" Tan (ô)max Ml 46 7 0.2 M2 48 8 0.2 M3 2.47 0.06 0.03 M4 1.26 0.100 0.08

[0111] Tire configurations of the invention have been tested to clearly highlight the performance benefits of the invention. The results of these tests are compared to those obtained for control tires.

[0112] The witness Tl illustrated by figures 1-A and 1-B corresponds to a pneumatic which It comprises a padding layer made of the elastomeric compound M1, a lateral bead reinforcement layer made of the elastomeric compound M2, and a sidewall layer made of the elastomeric compound M4. The sidewall layer profile is of standard design, i.e., it has not been modified to facilitate contact with the rim.

[0113] A second witness T2 takes up the specifications of T1, but the elastomeric mixtures of packing and reinforcement are made up of the mixture M3.

[0114] The first PI tire conforming to the invention takes up the specifications of the T1 witness, but the sidewall layer and the lateral reinforcement layer are made of the M3 elastomeric mixture.

[0115] The second tire P2 according to the invention takes up the specifications of the witness T1, but the filling layer and the sidewall layer are made of the elastomeric mixture M3.

[0116] The third P3 tire according to the invention differs from the witness in that the elastomeric mixture layers of the padding, reinforcement and sidewall layers are made of the M3 elastomeric mixture.

[0117] Finally, the fourth tire P4 of the invention differs from P3, by the modification of the sidewall layer profile for a rim contact variation rate greater than 30%.

[0118] The tire configurations PI, P2, and P3 of the invention are illustrated in [Fig.1]-B. As for the P4 configuration, illustrations can be seen in Figures 2-A, 2-B, and 2-D.

[0119] The rate of variation of rim contact is 62% for P4, after a partial modification of the profile of the sidewall layer in the area of ​​contact with the rim, as shown in figures 2-A and 2-B.

[0120] For all tires of the invention, the proportion of elastomeric compounds with a hysteresis less than or equal to 0.10 is within the range [30%; 90%], as illustrated in the following table No. 3:

[0121] [Tables3] Tire configuration, low zone layers. With M3 compound. % Low zone volume. PI Sidewall layer + reinforcement layer 44 P2 Sidewall layer + filler layer 41 P3 Sidewall layer + filler layer + reinforcement layer 54 P4 Sidewall layer + filler layer + reinforcement layer + Modified rim contact zone profile 54

[0122] 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 of resistance to the forward movement of the vehicle by hysteresis of the tires divided by the load carried.

[0123] Transverse drift stiffness measurements were made on dedicated measuring machines such as those marketed by the company MTS.

[0124] A result greater than (respectively less than) 100% means an improvement (respectively a degradation) of the performance considered.

[0125] The results obtained are summarized in the following table no. 4:

[0126] [Tables4] Rolling resistance Transverse drift stiffness Tl 100 100 T2 110 96 PI 108 98 P2 104 100 P3 112 99 P4 111 102

[0127] All tires of the invention achieve the desired compromise between rolling resistance and controlled road handling, specifically lateral drift stiffness. Tires PI and P3 have a lateral drift stiffness of 98% and 99%, respectively, without noticeably affecting vehicle handling. Tires P2 and P4 have performance equal to or greater than the target sought.

[0128] All the tire variants according to the invention presented are produced without process changes and remain with a usual industrial cost price.

[0129] Furthermore, the invention can be generalized to other bead architectures than those described here, such as for example a bead having a first layer of padding, and a second lateral layer of reinforcement, even if the carcass reinforcement does not include a reversal.

Claims

Demands

1. Tire (1) for a passenger vehicle comprising in a meridian plane: two beads (50) intended to be mounted on a rim, two layers of sidewalls (30) connected to the beads (50), a top (20) comprising a tread (10), the top (20) having a first side connected to the radially outer end of one of the two layers of sidewalls (30) and having a second side connected to the radially outer end of the other of the two layers of sidewalls (30); at least one frame reinforcement (90) extending from the two ridges (50) to the top (20), the frame reinforcement (90) comprising a plurality of frame reinforcement elements and being anchored in the two ridges (50) by a turning around an annular reinforcement structure (51), so as to form in each ridge a main part (52) and a turning (53); two lower zones (55) as portions of the tire, positioned on either side of the radial axis (OZ) passing through the center O of the tire, a first lower zone on one side of the radial axis (OZ) including the bead (50) and at least part of the sidewall layer (30) of this first side and a second lower zone on the other side of the radial axis (OZ) including the bead and at least part of the sidewall layer of this second side; each lower zone (55) having a meridian surface delimited by an axial line (AA') passing at a radial distance equal to 70% of the distance H, where H is the radial distance between a first axial line (HH') passing through the most radially interior point of the annular reinforcement structure (51), and between a second axial line (DD') tangent to the tread at its most radially exterior point, and radially interior said meridian surface being delimited by the peripheral contour of the bead intended to be in contact with the rim; each lower zone occupying a volume obtained by rotating said meridian surface around the axis of rotation of the tire; the bead (50) of each lower zone (55) comprising at least one layer of padding (70) included at least in part between the main part of the frame reinforcement (52), the reversal of the frame reinforcement (53) and the radially outer portion of the structure annular reinforcement (51); each elastomeric compound of the tire having an elastic shear stiffness modulus and viscoelastic loss measured according to ASTM D 5992-96, at 23°C, under a shear strain of 10%, characterized in that each compound layer of each lower zone (55) having a viscoelastic loss Tan(ô)max less than or equal to 0.10, represents a volume between 30% and 90% of the total volume of said lower zone and in that the elastic shear stiffness modulus of each sidewall layer is within the range [0.5; 10] MPa.

2. Tire according to claim 1 wherein the elastic shear stiffness modulus of the sidewall layer is preferably within the range [1.5; 10] MPa and even more preferably within the range [2.5; 10] MPa.

3. Pneumatic according to any one of claims 1 or 2 wherein said layers of mixtures of the lower zone having a viscoelastic loss Tan(ô)max less than or equal to 0.10, represent a volume preferably between 40% and 90% of the total volume of the lower zone, and even more preferably a volume between 50% and 90% of the total volume of the lower zone.

4. Pneumatic (1) according to any one of the preceding claims wherein the packing layer is made of an elastomeric mixture whose viscoelastic loss Tan(ô)max is less than or equal to 0.

10.

5. Pneumatic (1) according to any one of the preceding claims, wherein the bead comprises a lateral reinforcement layer (60) made of an elastomeric mixture occupying a volume at least partly between the sidewall layer (30), and the reversal of the carcass reinforcement (53).

6. Pneumatic (1) according to claim 5, wherein the lateral reinforcement layer of the bead (60) is made of an elastomeric mixture whose viscoelastic loss Tan(ô)max is less than or equal to 0.

10.

7. A tire (1) according to any one of the preceding claims, in each bead (50) a rim contact curve comprising the points of the tire (1) in contact with the rim (100); said rim contact curve connecting a first axially positioned, outermost point M1 of the tire, 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 a straight portion (130) connecting the hook (120) to the seat (110) of the rim; said tire (1) also comprising two sections in a vertical meridian cut of the inflated tire, mounted on a rim, and crushed on a ground by a vertical load (250) where the load, the inflation pressure, being determined in a specification standard such as the ETRTO (European Technical Organisation for Tyres and Rims); a first section being located in the contact area, and a second section being located on the opposite side to the former with respect to the axis of rotation of the tire; 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 with respect to the axis of rotation of the tire, in at least a second bead, the length of the rim contact curve, LCJ, being measured, in which the ratio of the difference in lengths of the rim contact curves of the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 30.;

8. Pneumatic (1) according to the preceding claim, wherein the ratio of the difference 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, again preferably greater than or equal to 60.

9. Tire (1) according to any one of the preceding claims, the DRB distance being the radial distance from one end of the packing layer (70) radially outwards, in which said DRB distance is less than or equal to 50% of the radial height H of the tire (1).

10. Tire (1) according to any one of claims 5 to 9, the DRI distance being the radial distance from a radially inner end of the lateral layer (60) of reinforcement to the right (HH') in which said radial distance DRI is within the range [5%; 20%] of the radial height H of the tire (1).

11. Tire (1) according to any one of claims 5 to 10, the DRL distance being the radial distance from the radially outer end of the lateral reinforcement layer (60) to the right (HH'), wherein said radial distance DRL is greater than or equal to 25% of the radial height H of the tire (1).

12. Pneumatic (1) according to any one of the preceding claims, in which the reversal (53) of the frame reinforcement (90) is in contact with the main part (52) of the frame reinforcement (90) radially outwardly along said reversal (53).

13. Tire (1) according to any one of the preceding claims wherein said tire comprises a bead reinforcement (50) axially external to the reversal (53) of the carcass reinforcement (90), and axially internal to the sidewall (30).

14. Pneumatic (1) according to any one of claims 5 to 13, wherein in each bead, the elastomeric mixture constituting at least one layer among the packing layer (70), and / or the side reinforcement layer (60) and / or the sidewall layer (30) has a composition based on a diene elastomer, a crosslinking system, a reinforcing filler, type Carbon Black N550, at an overall rate of between 50 and 75 parts per annum.

15. Pneumatic according to claim 14, wherein, in each bead, the elastomeric mixture constituting the packing layer (70), the elastomeric mixture constituting the lateral reinforcement layer (60), and the elastomeric mixture constituting the sidewall layer (30) have the same composition.

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