Tire having optimized performance in terms of rolling resistance and grip

Abstract

The invention relates to a tire (1) for passenger vehicles, the performance of which has been improved in terms of rolling resistance without compromising the lateral drift stiffness. The bead (50) is softened by using a low hysteresis material. The lateral drift stiffness is compensated by using a rigid and low hysteresis sidewall layer (30). The volume of the layer of compound with a viscoelastic loss Tan(delta)max less than or equal to 0.10 in the lower region represents between 30% and 90% of the total volume of the lower region and the shear stiffness elastic modulus G'(M3) of the sidewall layer is in the range [0.5; 10].

Description

Technical Field

[0001] This invention relates to a tire for motor vehicles that improves rolling resistance without adversely affecting lateral slip stiffness. The invention is particularly applicable to radial tires intended for mounting in passenger vehicles or trucks.

[0002] definition

[0003] By convention, reference frames (O, OX, OY, OZ) are considered, where the center O coincides with the center of the tire. The circumferential direction OX, the axial direction OY, and the radial direction OZ refer to the directions tangent to the tire tread surface, parallel to the tire's axis of rotation, and perpendicular to the tire's axis of rotation, respectively, in the direction of rotation.

[0004] "Radially inside / inner side" and "radially outside / outer side" refer to being closer to and further away from the tire's axis of rotation, respectively.

[0005] "Inner / inner side" and "outer / outer side" in the axial direction refer to the plane closer to the tire's equatorial plane and the plane further away from the tire's equatorial plane, respectively. The tire's equatorial plane is a plane that passes through the middle of the tire tread and is perpendicular to the tire's axis of rotation.

[0006] The composition of a tire is usually described by the constituent components shown in the meridional plane (i.e., the plane containing the tire's axis of rotation).

[0007] The tire includes a tread designed to contact the ground via a tread, the two axial ends of which are connected to two beads via two sidewalls, the two beads providing a mechanical connection between the tire and a rim on which the tire is designed to be mounted.

[0008] Radial tires also include reinforcing members, which consist of a crown reinforcement located radially inside the tread and a carcass reinforcement located radially inside the crown reinforcement.

[0009] The crown reinforcement of a radial tire comprises overlapping crown layers extending circumferentially, which are located radially outside the carcass reinforcement. Each crown layer consists of mutually parallel reinforcements coated with an elastomeric or elastomeric compound type polymer material. The assembly consisting of the crown reinforcement and the tread is called the crown.

[0010] Radial tire carcass reinforcements typically include at least one carcass layer composed of metal or fabric reinforcing elements coated with an elastomeric compound. The reinforcing elements are substantially parallel to each other and form an angle between 85° and 95° with respect to the circumferential direction. Each carcass layer includes a main section that connects two beads to each other and is wound around an annular reinforcing structure within each bead. The annular reinforcing structure can be a bead line including circumferential reinforcing elements, typically made of metal and non-exhaustively surrounded by at least one elastomeric material or fabric. The carcass layer is wound around the annular structure from the inside to the outside of the tire, forming a crimp including the ends. The crimps in each bead allow the carcass reinforcement layer to be anchored to the annular structure of the bead.

[0011] Each bead includes a filler layer extending radially outward from the annular reinforcement structure. The filler layer consists of at least one elastomeric filler compound. The filler layer axially separates the main portion of the carcass reinforcement from the crimp.

[0012] Each tire bead also includes a protective layer that extends radially inward from the tire sidewall and is axially located outside the bead. The protective layer also contacts the rim flange at least partially via its axially outer surface. The protective layer consists of at least one protective elastomer compound.

[0013] Finally, each bead may include a lateral reinforcement layer located between the sidewall and the crimp of the carcass reinforcement. The outer lateral reinforcement layer consists of at least one elastomer compound.

[0014] Each tire sidewall includes at least one sidewall layer composed of an elastomer compound and extending axially from the outer surface of the tire (which is in contact with the atmosphere) toward the inner side of the tire.

[0015] Elastomer blends refer to elastomeric materials obtained by blending their various components. Elastomer blends typically comprise: an elastomeric matrix having at least one diene elastomer of the natural rubber or synthetic rubber type; at least one reinforcing filler of the carbon black type and / or silica type; a crosslinking system typically based on sulfur; and a protective agent. For some applications, the elastomers mentioned may also include thermoplastic materials (TPEs).

[0016] The statement “the composition is based on / based on a composition of…” should be understood to mean that the composition comprises a mixture of various components used and / or reaction products, some of which are capable of or intended to react with each other at least partially during various stages of the preparation of the composition, particularly during its crosslinking or vulcanization.

[0017] Within the meaning of this invention, the expression "parts by weight of 100 parts by weight of elastomer" (or phr) should be understood to mean the weight percentage of elastomer present in the considered compound composition per hundred parts.

[0018] The mechanical characteristics of elastomer blends, especially after curing, can be attributed to their kinetic properties, such as the kinetic shear modulus G* = (G'² + G”²)¹ / ² (where G' is the elastic shear modulus and G” is the viscous shear modulus) and the kinetic loss Tanδ = G” / G'. The kinetic shear modulus G* and kinetic loss Tanδ were measured according to ASTM D 5992-96 on a Metravib VA4000 viscometer. The response of vulcanized elastomer blend samples with a thickness of 2 mm and a diameter of 78 mm was recorded after being subjected to a simple alternating sinusoidal shear stress at 10 Hz and a temperature of 100 °C. 2 The test specimen is in the form of a cylindrical cross-section. Strain amplitude scans are performed from 0.1% to 50% (outward cycle) and then from 50% to 0.1% (backward cycle). For the outward cycle, the observed maximum value of tan(δ) is shown, which is denoted as Tan(δ)max.

[0019] "Handling performance" corresponds to the vehicle / tire assembly's response to various stresses induced by the driver (steering, acceleration, braking, etc.). Handling is crucial for safety, vehicle stability, and driving pleasure.

[0020] Tires play a crucial role in handling because they are at the end of the chain, ensuring the transmission of force between the vehicle and the ground to maintain the track defined by the driver.

[0021] During a turn, in order to keep the vehicle on the track, a force equal to (but in the opposite direction to) the centrifugal force is needed, which tends to move the vehicle away from the track. This lateral force must be generated by the vehicle's four tires to overcome the centrifugal force.

[0022] The deformation of the rubber tread in contact with the ground generates lateral force. The mechanism that allows the tire to deform the rubber tread during cornering is slip. Slip is the angle between the direction of the wheel and the track the vehicle is following. During cornering, this angle is not zero, allowing the tire to deform the rubber tread, thereby generating the required lateral force.

[0023] Lateral slip stiffness refers to the change in lateral force as the slip angle applied to the tire varies. This lateral force is generated in the contact patch of the moving tire under the load. Lateral slip stiffness is expressed in Newtons per degree (N / °).

[0024] For small slip angles, i.e., less than 10°, the lateral force in the direction parallel to the tire's axis of rotation is proportional to the slip angle. The lateral slip stiffness is equal to this proportionality factor.

[0025] Lateral slip stiffness is a very important physical variable that connects the tire to the vehicle and determines the vehicle's handling quality on the road.

[0026] Rolling resistance is another performance metric addressed in this application. Rolling resistance is one of the forces resisting the forward movement of a vehicle. The rolling resistance coefficient (C) of a tire... RR This is the rolling resistance relative to the load carried by the tire. This coefficient is expressed in kg / t.

[0027] Rolling resistance is essentially related to tire deformation. For example, the bead, which is associated with the sidewall, accounts for 20% to 30% of the tire's rolling resistance, while the tread accounts for 60% to 80%.

[0028] In this patent application, the tire is typically shown mounted on a rim. The rim is selected according to ETRTO (European Tyre and Rim Technology Organization) standards, which associate recommended rims with a given tire size. Generally, multiple rim widths can be used for the same tire size. Within the scope of this invention, the portion of the rim that interacts with the tire is axisymmetric with respect to the tire's axis of rotation. For the purpose of describing the rim, it is sufficient to depict the generatrix profile in the meridional plane.

[0029] In the meridional plane, the rim includes at least one flange located at one axial end and connected to a base designed to receive the radially innermost surface of the tire bead. A straight portion of the rim flange connecting to the base via a fillet is located between the base and the flange. The flange of the rim, extending from the straight portion, axially restricts the movement of the tire bead during inflation.

[0030] The adhesion of the tire bead to the rim during inflation is also a performance criterion that this invention can influence. Performance regarding bead adhesion includes assessing the tire's ability to be properly mounted on the rim during inflation. The innermost radial surface of the bead must be in full contact with the base to prevent any leakage of air used to inflate the tire. Typically, a contact pressure of at least 1.4 MPa is required in this contact area. The inflation pressure holds the bead against the rim flange. The contact pressure on the flange must also be sufficient to prevent the tire from detaching from the rim, especially during high-speed cornering. Devices for observing the bead mounted on the rim (particularly radiographic devices) allow for the diagnosis of installation quality.

[0031] Therefore, the two types of tires can be classified according to their mounting performance on the rim. Background Technology

[0032] Reducing greenhouse gas emissions from transportation is one of the major challenges facing vehicle manufacturers today. Significant progress has been made in tires by reducing rolling resistance, as rolling resistance has a direct impact on vehicle fuel consumption. For example, a 20% reduction in tire rolling resistance can result in approximately 3% fuel savings per 100 kilometers in a combined cycle.

[0033] It is still necessary to reduce the rolling resistance of passenger vehicle tires without adversely affecting their maneuverability on the vehicle.

[0034] It has been proposed to improve the rolling resistance of tires for passenger vehicles by optimizing the bead. WO2010 / 072736 specifically discloses the use of an elastomer composition to achieve a significant reduction in rolling resistance, the elastomer composition having a low elastic shear modulus G' of about 15 MPa and a viscous shear modulus G that is more than 20% lower than the elastic shear modulus.

[0035] It also recommends further reducing rolling resistance by optimizing the geometry of the elastomer compound layer with elastic and viscous moduli that satisfy the aforementioned relationship. This optimization results in a shorter and wider profile of the elastomer compound layer compared to conventional tires. In some cases, the difficulty of industrially manufacturing these compound layer profiles is a major drawback of this approach.

[0036] FR2994127 describes an improvement to WO 2010 / 072736 by proposing the addition of a reinforcing member to the tire bead. The reinforcing member is formed from a reinforcement coated with an elastomer compound.

[0037] The main drawback of this solution is that it significantly increases industrial manufacturing costs by introducing new semi-finished products into the tire manufacturing process.

[0038] The inventors set their own goal as producing a tire that improves rolling resistance without adversely affecting vehicle handling, while still controlling the associated manufacturing costs. Summary of the Invention

[0039] This objective is achieved by a tire for passenger vehicles, the tire comprising, in the meridional plane:

[0040] Two tire beads intended to be mounted on a rim, two sidewalls connected to the tire beads, and a tread including a tread crown having a first side connected to the radially outer end of one of the two sidewalls and a second side connected to the radially outer end of the other of the two sidewalls;

[0041] At least one carcass reinforcement extending from two beads to the crown, the carcass reinforcement comprising a plurality of carcass reinforcement elements and anchored in the two beads by wrapping around an annular reinforcement structure, thereby forming a main portion and a rolled edge in each bead;

[0042] The tire has two lower regions, which are portions of the tire located on both sides of the radial axis OZ. The first lower region located on the first side of the radial axis OZ includes the bead and at least a portion of the sidewall layer on the first side, and the second lower region located on the other side of the radial axis OZ includes the bead and at least a portion of the sidewall layer on the second side.

[0043] Each lower region has a meridional surface defined by an axial straight line AA' that passes through at a radial distance equal to 70% of a distance H, where H is the radial distance between a first axial straight line HH' and a second axial straight line DD' that passes through the innermost radial point of the annular reinforcement structure and the second axial straight line DD' that is tangent to the tread at the outermost radial point of the tread. The meridional surface is defined radially inward by the outer periphery of a bead intended to contact the rim.

[0044] Each lower region occupies the volume obtained by rotating the meridional surface around the axis of rotation of the tire;

[0045] Each lower region bead includes at least one filler layer, which is at least partially included between the main portion of the carcass reinforcement, the crimp of the carcass reinforcement, and the radially outer portion of the annular reinforcement structure;

[0046] The elastic shear modulus and viscoelastic loss of the elastomer compound were measured according to ASTM D5992-96 at 23°C and 10% shear strain.

[0047] The volume of the blend layer in each lower region where the viscoelastic loss Tan(δ)max is less than or equal to 0.10 accounts for between 30% and 90% of the total volume of the lower region;

[0048] The elastic shear modulus of each sidewall layer is in the range of [0.5; 10] MPa.

[0049] The tire of the present invention has two lower regions located on either side of a radial axis (OZ). The profile of each lower region in the meridional plane includes an axial straight line AA' and an axial outer wall of a portion of the sidewall ply in contact with ambient air, said axial outer wall extending radially inward from the outer periphery of a protective layer intended to contact the rim. The profile of each lower region is continued by an axial inner wall of the bead in contact with the tire's inflation gas. In other words, the profile of the lower region follows at least a portion of the outer profile of the sidewall ply and the outer profile of the bead, both of which are included in the lower region.

[0050] The volume of the lower region is the circumferential extension of its outline in the meridional plane as defined above.

[0051] Defined in this way, the lower region represents 20% to 30% of the tire's rolling resistance. This effect is primarily due to the viscoelastic dissipation of the elastomer blend, which has a larger volume and higher hysteresis.

[0052] When a pneumatic tire, mounted on a rim and compressed by a load, is in operation, the lower region undergoes cycles of high-amplitude bending strain due to periodic passage through the contact patch. These strains (related to the hysteresis level of the elastomer blend) result in viscoelastic dissipation in the lower region.

[0053] The principle of this invention is to enable the elastomeric compound layer in the lower region to have a hysteresis of less than or equal to 0.10, measured in Tan(δ)max, at maximum volume, thereby reducing viscoelastic dissipation of the bead and thus improving rolling resistance compared to conventionally designed tires. Conventional bead designs use elastomeric compound layers with an elastic shear modulus greater than 30 MPa. However, such elastomeric compounds typically also exhibit a hysteresis significantly greater than 0.10, measured in Tan(δ)max.

[0054] In the lower region of the tire of the present invention, 30% to 90% of the volume of each lower region is composed of a low-hysteresis elastomer compound, that is, a compound with a hysteresis of less than 0.10 as measured by the value of Tan(δ)max.

[0055] By configuring the sidewall layer of the tire of this invention with an elastomer compound having an elastic shear modulus of up to 10 MPa, lateral slip stiffness can be maintained at an appropriate level, thereby contributing to good vehicle handling. The conventional design target for the sidewall is an elastic shear modulus of less than or equal to 1.5 MPa.

[0056] The main feature of the tire of this invention is the combination of a low-hysteresis elastomer blend selected in the lower region at maximum volume with a sidewall layer having an elastic shear modulus of up to 10 MPa. This provides a trade-off between improved rolling resistance and adverse effects on handling. Compared to conventional designs, the stiffer sidewall layer of the tire of this invention, for example, compensates for the reduced elastic shear modulus of the filler layer. Furthermore, the implemented solution requires no significant changes to the process, thus keeping industrial manufacturing costs at a normal level.

[0057] Advantageously, the elastic shear modulus of the sidewall layer is preferably in the range of [1.5; 10] MPa, more preferably in the range of [2.5; 10] MPa.

[0058] The tire bead of this invention relies particularly on the balance between the shear stiffness and hysteresis of the elastomeric compound constituting the bead. The elastic shear modulus of each sidewall layer is maintained at less than 10 MPa so that the hysteresis is kept at a level less than or equal to 0.10 as measured by the value of Tan(δ)max. This invention works based on the sidewall layer's elastic shear modulus being greater than or equal to 0.5 MPa.

[0059] Preferably, the volume of the compound layer in the lower region with a viscoelastic loss Tan(δ)max less than or equal to 0.10 accounts for 40% to 90% of the total volume of the lower region, more preferably 50% to 90% of the total volume of the lower region.

[0060] The structure of the lower region can vary depending on the presence of the elastic compound layers required for proper tire operation. In particular, the diameter of the mounting rim is a parameter that significantly influences the bead structure. For example, for rims larger than 16 inches in diameter, each bead typically includes lateral layers to reinforce the filler layer and effectively transmit torque from the vehicle. The volume of the low-hysteresis compound relative to the total volume of the lower region is thus affected. A maximum of 90% volumetric content of the low-hysteresis elastomer compound is allowed, meaning that each lower region also includes non-hysteresis material. Conversely, for smaller rim diameters, the structure of the lower region can be simplified, with the low-hysteresis compound content reaching up to 40% relative to the total volume of each lower region.

[0061] Advantageously, the filler layer is composed of an elastomer compound whose viscoelastic loss Tan(δ)max is less than or equal to 0.10.

[0062] Due to the tension variations in the main body layers and the reinforcements of the bead, the filler layer typically occupies a large volume and bears significant shear strain. Selecting low-hysteresis elastomer blends helps control the level of viscoelastic dissipation.

[0063] According to a particularly advantageous embodiment, the bead includes a lateral reinforcement layer composed of an elastomeric compound that occupies at least a portion of the volume between the sidewall layer and the crimp of the carcass reinforcement.

[0064] According to the inventors, the lateral reinforcement layer of the bead provides additional lateral stiffness to the lateral stiffness provided by the first filler layer. Depending on the properties of these materials in terms of Tan(δ)max and dynamic shear stiffness, the reinforcement can adjust the performance balance between rolling resistance and handling.

[0065] Advantageously, in a variant of this embodiment, the lateral reinforcement layer of at least one bead is composed of an elastomer blend with a viscoelastic loss Tan(δ)max less than or equal to 0.10.

[0066] In this variant of the implementation, the two compound layers (i.e., the filler layer and the lateral reinforcement layer) satisfy the characteristic that the viscoelastic loss Tan(δ)max is less than 0.10. The improvement in rolling resistance is optimal, and the handling of the tire mounted on the vehicle is consistent with expectations.

[0067] In another embodiment of the invention, the rim contact curve in each bead includes the point where the tire contacts the rim. The rim contact curve connects a first point M1 and a second point M2 of the tire, the first point M1 being axially outermost and in contact with the rim, and the second point M2 also contacting the rim and located midway along the straight portion connecting the rim flange to the base. The length of the rim contact curve is the curved distance along the contact curve from point M1 to point M2. The tire also includes two sections in the vertical meridional plane of the pneumatic tire, which is mounted to the rim and compressed against the ground under a vertical load, wherein the load and inflation pressure are determined according to specifications such as ETRTO (European Tire and Rim Technology Organization) standards, the first section being located in the contact patch, and the second section being located on the opposite side of the former section relative to the tire's axis of rotation. In the first section located in the contact patch, the length LADC of the rim contact curve is measured in at least the first bead. In the second section, located relative to the axis of rotation of the tire and opposite to the contact surface, in at least the second tire bead, the length LCJ of the rim contact curve is measured, and the ratio of the difference in the lengths of the rim contact curves in the two sections, i.e., 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%.

[0068] In this embodiment, the rim contact variation rate of the tire of the present invention is much greater than the rim contact variation rate found in prior art tires.

[0069] When a pneumatic tire mounted on a rim is compressed under a load, the point of contact between the tire and the rim can vary depending on the meridian. Therefore, the length of the rim contact curve, as defined above, will also vary depending on the meridian.

[0070] The tire is designed such that the rim contact curve is as long as possible within the contact patch compared to prior art tires, and more specifically, as long as possible along the meridian at the center of the contact patch. Under these conditions, the inventors believe that the contribution of the rim contact to slip stiffness is at its highest.

[0071] In the meridional plane of a pneumatic tire mounted on a rim and compressed under a load, a first section of the tire passing through the center of the contact patch can be seen. The contact patch refers to all points on the tire that are in contact with the ground at a given moment, where the tire is compressed against the ground. The point of the contact patch located on the vertical axis OZ is called the center of the contact patch. Another section of the tire, opposite the contact patch with respect to the tire's axis of rotation OY, can also be seen, and the tire generally defines a deformation state similar to an axisymmetric inflation state.

[0072] The rate of change in rim contact corresponds to the maximum change in rim contact length per revolution of the wheel.

[0073] According to the inventors, the basic steps in designing a tire according to this embodiment include altering its external profile in the area contacting 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 involve altering the external profile to obtain a profile with the same curvature as the rim flange in the contact area. Another solution involves inserting a compound pad at the rim flange into the area at the junction between the sidewall layer and the protective layer. This compound pad can preferably be composed of the same compound as the sidewall layer to maintain industrial manufacturing costs. A key requirement for such an elastomeric compound pad is its elastic shear modulus, which advantageously can be, for example, the same as that of the sidewall layer.

[0074] Preferably, the ratio of the length difference of the rim contact curves in the two regions, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 40%, more preferably greater than or equal to 50%, and more preferably greater than or equal to 60%.

[0075] The outer profile of the area in contact with the rim can be altered to achieve a specific rim contact variation ratio. Therefore, it is a means of adjusting lateral slip stiffness when seeking a performance trade-off between rolling resistance and handling. Lateral slip stiffness is an increasing function of the rim contact variation ratio. For rim contact variation ratios greater than or equal to 60%, altering the outer profile of the sidewall layer makes bead installation easier, but excessively high ratios above 100% may reduce installability.

[0076] In addition to the main features of the invention, the inventors have also identified means associated with the geometry of the compound layer of the bead to further optimize the performance trade-offs of the rolling resistance-improved tire while maintaining good handling.

[0077] Advantageously, the distance DRB is the radial distance from the radial outer end of the filler layer, and the distance DRB is less than or equal to 50% of the radial height H of the tire.

[0078] The tire height H is the normal distance between a first straight line HH' and a second straight line DD'. The first straight line HH' is parallel to the tire's axis of rotation and tangent to the innermost radial point of the annular reinforcement structure. The second straight line DD' is also parallel to the tire's axis of rotation and passes through the outermost radial point of the tread. The radial height H is measured on the tire mounted on the rim and inflated to a reference pressure according to ETRTO (European Tyre and Rim Technology Organization) specifications.

[0079] Advantageously, the distance DRI is the radial distance from the radial inner end of the lateral reinforcement layer to the straight line HH', and the radial distance DRI is within the range of [5%; 25%] of the radial height H of the tire.

[0080] More advantageously, the distance DRL is the radial distance from the radial outer end of the lateral reinforcement layer to the straight line HH', and the distance DRL is greater than or equal to 25% of the radial height H of the tire.

[0081] In addition to the first filler layer, a lateral reinforcement layer, including the one between the sidewall and the crimp of the carcass reinforcement, also contributes to the stiffness of the bead. According to the inventors, its positioning is adjusted by dimensions DRI and DRL to withstand the bending and tensile-compressive stresses of the bead as it enters the contact patch.

[0082] In an advantageous embodiment of the invention, the rolled edge of the carcass reinforcement presses against the main portion of the carcass reinforcement over its entire radially outward height.

[0083] As described above, the carcass reinforcement is formed by a reinforcement layer sandwiched between two elastomeric compound layers. "The crimp of the carcass reinforcement presses against the main portion of the carcass reinforcement" means that the crimp contacts the main arm of the carcass reinforcement. This contact occurs on the surface located between the two coating layers of the carcass reinforcement.

[0084] In this configuration, the volume of the first filler layer is restricted to a strictly minimized size around the annular reinforcement structure. This configuration is highly advantageous for reducing the rolling resistance of the bead.

[0085] In another embodiment, the tire includes a reinforcement for reinforcing the bead, the reinforcement being located axially outside the carcass reinforcement and axially inside the sidewall.

[0086] The reinforcing members of the tire bead are formed by parallel reinforcing elements sandwiched between two layers of elastomeric compound. The addition of this semi-finished product incurs additional manufacturing costs that must be compensated for. To limit the impact of this solution on manufacturing costs, this implementation can be combined with pressing the crimp of the carcass reinforcement against the main portion of the carcass reinforcement.

[0087] Advantageously, in each bead, the elastomeric compound forming at least one of the filler layer and / or lateral reinforcement layer and / or sidewall layer has a composition based on: dioxane elastomer, crosslinking system, and reinforcing filler such as carbon black N550 in total content between 50 phr and 75 phr.

[0088] Even more advantageously, in each bead, the elastomeric compound forming the filler layer, the elastomeric compound forming the lateral reinforcement layer, and the elastomeric compound forming the sidewall layer have the same composition.

[0089] "Diene" elastomers (or equivalent rubbers) are understood, as is known, to mean elastomers in which at least a portion (i.e., homopolymers or copolymers) is derived from diene monomers (i.e., monomers with two conjugated or non-conjugated carbon-carbon double bonds). The diene elastomers used are preferably selected from polybutadiene (BR), natural rubber (NR), synthetic polyisoprene (IR), styrene-butadiene copolymer (SBR), butadiene-isoprene copolymer (BIR), styrene-isoprene copolymer (SIR), styrene-butadiene-isoprene copolymer (SBIR), and combinations thereof.

[0090] A preferred embodiment includes the use of "isoprene" elastomers, namely isoprene homopolymers or isoprene copolymers, in other words diene elastomers selected from natural rubber (NR), synthetic polyisoprene (IR), various isoprene copolymers, and combinations of these elastomers.

[0091] The isoprene elastomer is preferably natural rubber or cis-1,4-type synthetic polyisoprene. Among these synthetic polyisoprene, polyisoprene with a cis-1,4 bond content (mol%) of more than 90% is preferred, and more preferably more than 98%. According to other preferred embodiments, the diene elastomer may consist wholly or partially of another diene elastomer, such as an SBR (E-SBR or S-SBR) elastomer used with or without blending with another elastomer (e.g., BR type).

[0092] The rubber composition may also contain all or some of the additives commonly used in rubber matrices intended for the manufacture of tires, such as reinforcing fillers like carbon black or inorganic fillers like silica, coupling agents for inorganic fillers, anti-aging agents, antioxidants, plasticizers or thickening oils (whether the latter are aromatic or non-aromatic in nature (especially very weakly aromatic or non-aromatic oils, such as high-viscosity or preferably low-viscosity naphthenic or paraffinic types, MES or TDAE oils, plasticizing resins with a high Tg greater than 30°C)), agents that improve the processability (handleability) of the composition in the uncured state, tackifying resins, crosslinking systems based on sulfur or sulfur donors and / or peroxides, accelerators, vulcanization activators or retarders, anti-reversion agents, methylene acceptors and donors (e.g., HMT (hexamethylenetetramine) or HMMM (hexamethoxymethylmelamine)), reinforcing resins (e.g., resorcinol or bismaleimide), and tackifying systems of known metal salt types (e.g., especially cobalt or nickel salts). Attached Figure Description

[0093] Further details and advantageous features of the invention will become apparent below from the description of exemplary embodiments of the invention given with reference to the accompanying drawings, which depict meridional views of a tire schematic diagram according to one embodiment of the invention. For ease of understanding, the drawings are not shown to scale.

[0094] Figure 1-A The cross-section of the tire of the present invention in the meridional plane is shown. Figure 1-B It shows the meridian Figure 1-A An enlarged view of the portion surrounded by the dashed circle, showing the lower region of the tire of the present invention.

[0095] Figure 2-A , Figure 2-B , Figure 2-C and Figure 2-D An embodiment of the invention is shown, wherein the outer contour of the sidewall layer is varied to facilitate contact with the rim.

[0096] Figure 3The diagram shows a meridional cross-section of a pneumatic tire mounted on a rim and compressed by a load. A first section of the contact patch and a second section opposite the contact patch relative to the axis (OY) are visible. The figure illustrates the determination of the rate of change in contact with the rim.

[0097] Figure 4-A and Figure 4-B The main dimensions of the lower region are shown. Detailed Implementation

[0098] The invention has been implemented on a passenger vehicle tire with a size of 245 / 45R18, according to the specifications of ETRTO (European Tyre and Rim Technology Organization) standards. This tire can bear a load of 800 kg and is inflated to a pressure of 250 kPa.

[0099] exist Figure 1-A In the figure, the tire with overall reference numeral 1 includes a carcass reinforcement 90 and two bead 50s, the carcass reinforcement 90 being a reinforcement body coated with a rubber composition, and the bead 50 contacting the rim 100. The area 49 defined by the dashed circle defines the lower region of the tire. Figure 1-B An enlarged view is provided. The carcass reinforcement 90 is anchored in each bead 50. The tire further includes a crown reinforcement 20 comprising two working layers 21 and 22 and a hoop layer 23. Each of the working layers 21 and 22 is reinforced by filamentous reinforcing elements that are parallel within each layer and cross from one layer to the other, forming an angle between 10° and 70° with respect to the circumferential direction. A hoop layer 23 is arranged radially outward of the crown reinforcement 20, formed by reinforcing elements oriented circumferentially and spirally wound. A tread 10 is arranged radially on the hoop layer 23; the tread 10 provides contact between the tire 1 and the ground. The depicted tire 1 is a "tubeless" tire: it includes an "inner liner" 95 covering the inner surface of the tire, the inner liner 95 being made of a rubber composition impermeable to inflation gas.

[0100] Within the scope of this invention, the portion of the rim 100 that interacts with the tire is axisymmetric with respect to the tire's axis of rotation.

[0101] In the meridional plane, the rim 100 includes at least one flange 120 located at one axial end and connected to a base 110, the base 110 being designed to receive the radially innermost surface of the tire bead. A straight portion 130 connecting the rim flange 120 to the base 110 via a fillet is located between the base 110 and the flange 120. The flange 120 of the rim, extending from the straight portion 130, axially restricts the movement of the tire bead during inflation.

[0102] Figure 1-BThe lower region, indicated by overall reference numeral 55, includes the sidewall layer 30 and the bead 50. The outline of the lower region follows at least a portion of the outer outline of the sidewall layer 30 and the outer outline of the bead 50.

[0103] The bead 50 partially includes a carcass reinforcement 90, which comprises a main portion 52 and is then wound around an annular reinforcement structure 51 to form a rolled edge 53. A filler layer 70 is located between the main portion 52 of the carcass reinforcement 90 and its rolled edge 53. Depending on the embodiment, the bead 50 may also include a lateral reinforcement layer 60, which is axially located outside the rolled edge 53 and axially inside the sidewall layer 30. At the innermost axial direction from the bead 50, an airtight layer 95 forms an inner wall in contact with the internal inflation gas.

[0104] The bead 50 also includes a protective layer 80 that contacts the straight portion 130 of the rim on its axially outer side, thereby restricting axial movement of the bead. The protective layer 80 also includes a portion intended to contact the rim on the rim base 110. The sidewall layer 30 interacts with the bead 50 and forms an outer wall.

[0105] Figure 2-A The outer contour of a tire bead 50 according to a particular embodiment of the present invention is depicted compared to a conventionally designed tire bead. The bead 50 in the area opposite the contact patch is also depicted. The difference between the two contours lies in the area at the rim flange 120. Reference numeral 30 indicates the contour of a prior art tire, and reference numeral 35 shows the modification of the contour on the tire according to the present invention to facilitate contact with the rim 100.

[0106] Figure 2-B and Figure 2-A The same as shown, but it shows the outline in the center of the ground contact surface. Different from... Figure 2-A The tire contacts the entire rim flange 120. The rate of change in rim contact reflects this change in rim contact.

[0107] exist Figure 2-C In another depicted embodiment, an elastomeric compound pad 40 (a variant located at the radially inner end of the sidewall 30) is intended to contact the rim flange 120. The compound pad 40 is defined radially inner by a curve that closely follows the contour of the rim flange 120. A first side of the elastomeric compound pad 40 has a suitable geometry intended to contact the curved portion of the rim flange so as to closely follow the shape of the rim flange 120 upon contact; a second side of the elastomeric compound pad extends the outer side of the sidewall in contact with ambient air; a third side of the elastomeric compound pad 40 contacts the radially inner end of the sidewall; and a final fourth side of the elastomeric compound pad contacts the protective layer 80.

[0108] exist Figure 2-C In this design, the rim contact curve extends from a first point M1 on the tire to a second point M2 on the tire. The first point M1 is located on the outermost side of the axial direction and contacts the rim. The second point M2 also contacts the rim and is located in the middle of the straight section connecting the rim flange 120 to the base 110. The length of this rim contact curve is the curve distance from point M1 to point M2 along the rim contact curve.

[0109] Figure 2-D It is a variant of the previous embodiment, characterized by the presence of a lateral reinforcement layer 60 of the bead 50, which is located axially outside the rolled edge 53 of the carcass reinforcement 90 and axially inside the sidewall layer 30.

[0110] Figure 3 This is a vertical plan view of the tire of the present invention according to the foregoing embodiment. The tire is inflated, mounted on a rim 100, and compressed against the ground 200 by a load 250. A first meridian region and a second meridian region opposite the ground surface can be seen. In the first region located at the ground surface, the length LADC of the rim 100 contact curve is measured in at least the first bead. In the second region, the length LCJ of the rim contact curve is also measured in at least the second bead. The ratio of the difference in the lengths of the rim contact curves in the two regions, i.e., 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%, and in this case equals 62%.

[0111] Figure 4-A The determination of the height H is shown. The tire height H is the normal distance between a first straight line HH' and a second straight line DD', the first straight line HH' being parallel to the tire's axis of rotation and tangent to the innermost radial point of the annular reinforcement structure, and the second straight line DD' also being 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 the rim, the tire being inflated to a reference pressure according to ETRTO (European Tyre and Rim Technology Organization) specifications.

[0112] Figure 4-B The geometric parameters of the bead in relation to this invention are described. The height is defined from the straight line HH', which is tangent to the bead line 51 at its radially innermost point:

[0113] DRI is the radial distance from the inner radial end of the lateral reinforcement layer 60 to HH'. The radial distance DRI is less than or equal to 20% of the radial height H of the tire, which is 5 mm in the embodiment shown here;

[0114] DRL is the radial distance from the outermost radial end of the lateral reinforcement layer 60 to the straight line HH'. The radial distance DRL is greater than or equal to 25% of the radial height H of the tire, which is 38 mm in the embodiment shown here;

[0115] DRR is the radial distance from the end of the rolled edge of the carcass reinforcement 90 to HH'. The radial distance DRR is greater than or equal to 10% of the radial height H of the tire, which is 20 mm in the embodiment shown here;

[0116] DRB is the radial distance from the outer radial end of the filler layer 70 to HH', which is 28 mm in the embodiment shown here.

[0117] Table 1 below shows the composition of the elastomer compound for the lower region of the present invention. The main compounds used are listed, wherein the main component of each compound is expressed as phr (parts by weight / 100 parts by weight elastomer).

[0118] [Table 1]

[0119]

[0120] The formulations of the present invention used in this embodiment are based on natural rubber elastomers or blends of natural rubber and butadiene (for formulations M3 and M4), reinforced with carbon black. Plasticizers (reinforcing resins) are incorporated into the composition to improve the processability of the formulations. The formulations also contain vulcanizing agents (sulfur), accelerators, and protective agents. The relevant mechanical and viscoelastic properties, measured at 23°C and 10% strain amplitude, are summarized in Table 2.

[0121] [Table 2]

[0122] 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 construction of the tire of the present invention was tested, thereby clearly highlighting the performance provided by the present invention. These test results were compared with those obtained from a control tire.

[0124] Figure 1-A and Figure 1-B The comparison tire T1 shown corresponds to a tire comprising a filler layer composed of elastomer compound M1, a bead lateral reinforcement layer composed of elastomer compound M2, and a sidewall layer composed of elastomer compound M4. The profile of the sidewall layer is a conventional design, meaning it has not been altered to facilitate contact with the rim.

[0125] The second comparison tire T2 has the same specifications as T1, but the filler elastomer blend and the reinforcing elastomer blend are composed of blend M3.

[0126] The first tire P1 according to the present invention has the same specifications as the control tire T1, but the sidewall layer and the lateral reinforcement layer are composed of an elastomer compound M3.

[0127] The second tire P2 according to the present invention has the same specifications as the control tire T1, but the filler layer and sidewall layer are composed of an elastomer compound M3.

[0128] The third tire P3 according to the present invention differs from the control tire in that the elastomeric compound layer of the filler layer, the reinforcing layer and the sidewall layer is composed of elastomeric compound M3.

[0129] Finally, the fourth tire P4 of the present invention differs from P3 in that it alters the profile of the sidewall layer, resulting in a rim contact change ratio greater than 30%.

[0130] Figure 1-B The construction of tires P1, P2, and P3 of the present invention is shown. Figure 2-A , Figure 2-B and Figure 2-D The diagram showing the construction of P4 can be seen in the image.

[0131] like Figure 2-A and Figure 2-B The depicted rim contact change rate of P4 is 62% after the profile of the sidewall layer in the area in contact with the rim is partially modified.

[0132] As shown in Table 3 below, for all tires of the present invention, the content of elastomer blends with a hysteresis of less than or equal to 0.10 is in the range of [30%; 90%].

[0133] [Table 3]

[0134]

[0135] Rolling resistance testing is performed according to ISO 28580. For the tires tested, the result is a coefficient of rolling resistance, which represents the ratio of the resistance caused by tire hysteresis, which is opposite to the forward movement of the vehicle, to the load being carried.

[0136] Lateral slip stiffness is measured on a dedicated measuring machine (such as those sold by MTS).

[0137] A result greater than (or less than) 100% indicates an improvement (or deterioration) in the performance criterion under consideration.

[0138] The results are summarized in Table 4 below.

[0139] [Table 4]

[0140]

[0141]

[0142] All tires of this invention achieve the desired trade-off between rolling resistance and handling controlled by lateral slip stiffness. Tires P1 and P3 have lateral slip stiffness of 98% and 99%, respectively, without significantly affecting vehicle handling. Tires P2 and P4 offer performance superior to or equal to the desired outcome.

[0143] All variants of the tires disclosed in this invention are produced without altering the manufacturing process, thereby maintaining normal industrial manufacturing costs.

[0144] Furthermore, the present invention can be applied more broadly to other bead structures besides those described herein. For example, even if the carcass reinforcement does not include a rolled edge, the bead may have a first filler layer and a second lateral reinforcement layer.

Claims

1. A tire (1) for a passenger vehicle, comprising in the meridional plane: Two bead (50) intended to be mounted on a rim, two sidewalls (30) connected to the bead (50), and a crown (20) including a tread (10), the crown (20) having a first side connected to the radially outer end of one of the two sidewalls (30) and a second side connected to the radially outer end of the other of the two sidewalls (30); At least one carcass reinforcement (90) extends from two bead (50) to the crown (20), the carcass reinforcement (90) includes a plurality of carcass reinforcement elements and is anchored in the two bead (50) by wrapping around an annular reinforcement structure (51), thereby forming a main portion (52) and a serration (53) in each bead. Two lower regions (55) are portions of the tire located on either side of a radial axis (OZ) passing through the tire center O. The first lower region located on the first side of the radial axis (OZ) includes the bead (50) on the first side and at least a portion of the sidewall layer (30), and the second lower region located on the other side of the radial axis (OZ) includes the bead on the second side and at least a portion of the sidewall layer. Each lower region (55) has a meridional surface defined by an axial line (AA') that passes through at a radial distance equal to 70% of a distance H, where H is the radial distance between a first axial line (HH') and a second axial line (DD') that passes through the radial innermost point of the annular reinforcement structure (51) and the second axial line (DD') that is tangent to the tread at the radial outermost point of the tread, the meridional surface being defined radially inward by the outer periphery of a bead intended to contact the rim; Each lower region occupies the volume obtained by rotating the meridional surface around the axis of rotation of the tire; Each lower region (55) of the bead (50) includes at least one filler layer (70) which is at least partially included between the main portion (52) of the carcass reinforcement, the rolled edge (53) of the carcass reinforcement and the radially outer portion of the annular reinforcement structure (51); The elastic shear modulus and viscoelastic loss of each elastomer compound in the tire were measured at 23°C and 10% shear strain according to ASTM D 5992-96. The invention is characterized in that the volume of each compound layer in each lower region (55) with a viscoelastic loss Tan(δ)max less than or equal to 0.10 accounts for 30% to 90% of the total volume of the lower region, and the elastic shear modulus of each sidewall layer is in the range of [2.5; 10] MPa.

2. The tire according to claim 1, wherein, The volume of the blend layer in the lower region where the viscoelastic loss Tan(δ)max is less than or equal to 0.10 accounts for between 40% and 90% of the total volume of the lower region.

3. The tire (1) according to claim 1, wherein, The filler layer consists of an elastomer blend with a viscoelastic loss Tan(δ)max less than or equal to 0.

10.

4. The tire (1) according to claim 1, wherein, The bead includes a lateral reinforcement layer (60) composed of an elastomer compound and occupying at least part of the volume between the sidewall layer (30) and the rim (53) of the carcass reinforcement.

5. The tire (1) according to claim 4, wherein, The lateral reinforcement layer (60) of the bead is composed of an elastomer blend with a viscoelastic loss Tan(δ)max less than or equal to 0.

10.

6. The tire (1) according to claim 1, wherein, The rim contact curve in each bead (50) includes the point where the tire (1) contacts the rim (100), the rim contact curve connecting a first point M1 and a second point M2 of the tire, the first point M1 being located on the outermost side of the axial direction and in contact with the rim, the second point M2 also being in contact with the rim and located in the middle of the straight portion (130) connecting the flange (120) of the rim to the base (110); the tire (1) also includes two sections in the vertical meridional plane of the pneumatic tire being mounted on the rim and pressed against the ground by a vertical load (250), wherein the load and inflation pressure are determined according to specifications such as ETRTO (European Tire and Rim Technology Organization) standards, the first section being located in the ground contact area, and the second section being located on the opposite side of the former section relative to the axis of rotation of the tire; In the first section located at the contact surface, in at least the first tire bead, the length of the rim contact curve, LADC, is measured; In the second section, located relative to the axis of rotation of the tire and opposite to the contact surface, in at least the second tire bead, the length LCJ of the rim contact curve is measured, wherein the ratio of the difference in the lengths of the rim contact curves in the two sections, i.e., 100*(LADC-LCJ) / LCJ, is greater than or equal to 30%.

7. The tire (1) according to claim 6, wherein, The ratio of the length difference of the rim contact curves in the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 40%.

8. The tire (1) according to claim 1, wherein the distance DRB is the radial distance from the radial outer end of the filler layer (70), The distance DRB is less than or equal to 50% of the radial height H of the tire (1).

9. The tire (1) according to claim 4, wherein the distance DRI is the radial distance from the radially inner end of the lateral reinforcement layer (60) to the first axial straight line (HH'), wherein, The radial distance DRI is within the range of [5%; 20%] of the radial height H of the tire (1).

10. The tire (1) according to claim 4, wherein the distance DRL is the radial distance from the radially outer end of the lateral reinforcement layer (60) to the first axial straight line (HH'), wherein, The radial distance DRL is greater than or equal to 25% of the radial height H of the tire (1).

11. The tire (1) according to claim 1, wherein, The crease (53) of the carcass reinforcement (90) contacts the main part (52) of the carcass reinforcement (90) on the radially outer side along the crease (53).

12. The tire (1) according to claim 1, wherein, The tire includes a reinforcement for reinforcing the bead (50), the reinforcement being located axially outside the rim (53) of the carcass reinforcement (90) and axially inside the sidewall layer (30).

13. The tire (1) according to claim 4, wherein, In each bead, the elastomeric compound forming at least one of the filler layer (70) and / or lateral reinforcement layer (60) and / or sidewall layer (30) has a composition based on dioxane elastomer, crosslinking system, and reinforcing filler such as carbon black N550 in total content between 50 phr and 75 phr.

14. The tire (1) according to claim 13, wherein, In each bead, the elastomeric compound forming the filler layer (70), the elastomeric compound forming the lateral reinforcement layer (60), and the elastomeric compound forming the sidewall layer (30) have the same composition.

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