Tire having optimized rolling resistance performance without reducing industrial performance

Abstract

This invention relates to a tire whose rolling resistance is improved without reducing industrial performance. The sidewall (30) is made of two sub-layers. A first sub-layer (FE1) having a thickness E1 and a volume V1 provides the desired protective function of the sidewall as the outer wall of the tire, and a second sidewall sub-layer (FE2) having a thickness E2 and a volume V2 is optimized to have low hysteresis, thereby improving rolling resistance. The volume ratio of the two sub-layers (FE1, FE2) V1 / (V1+V2) is less than or equal to 0.3. The elongation at break of the FE1 blend measured at 100°C is greater than or equal to 200%, and the viscoelastic loss Tan(δ)max of the FE2 blend is less than or equal to 0.10.

Description

Technical Field

[0001] This invention relates to a tire for motor vehicles, which improves rolling resistance performance without compromising its manufacturing industrial performance. More specifically, this invention applies to radial tires intended for mounting in passenger vehicles or trucks.

[0002] definition

[0003] By convention, a reference frame (O, OX, OY, OZ) is considered, with the center O of the reference frame coinciding with the center of the tire. The circumferential direction OX, the axial direction OY, and the radial direction OZ represent the directions tangent to the tire's running surface according to the direction of rotation, the directions parallel to the tire's axis of rotation, and the directions perpendicular to the tire's axis of rotation, respectively.

[0004] Radial inner or radial outer refers to being closer to or further away from the tire's axis of rotation, respectively.

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

[0006] The structure of a tire is usually described by a schematic diagram of the tire's components 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 ensuring a mechanical connection between the tire and a rim designed to mount the tire.

[0008] The radial tire also includes a reinforcement, which consists 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 a stack of crown layers extending circumferentially, the crown layers being radially located outside the carcass reinforcement. Each crown layer consists of reinforcements parallel to each other and coated with a polymer material of the elastomer or elastomer blend type. The assembly consisting of the crown reinforcement and the tread is called the crown.

[0010] The carcass reinforcement of a radial tire typically comprises 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. The carcass layer includes a main section that connects two beads together and is wound around a ring-shaped reinforcement structure in each bead. The ring-shaped reinforcement structure can be a bead line comprising circumferential reinforcing elements, most typically metallic, and covered with at least one material, non-exhaustibly an elastomeric or fabric material. The carcass layer is wound around the ring-shaped structure from the inside to the outside of the tire to form a crimp including one end. The crimp in each bead allows the carcass reinforcement layer to be anchored within the ring-shaped structure of the bead.

[0011] Each bead includes a filler layer extending radially outward in an annular reinforcing structure. The filler layer consists of at least one elastomer filler compound. The filler layer axially separates the main portion of the carcass reinforcement from the rolled edge.

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

[0013] Each bead may ultimately include a lateral reinforcement layer located between the sidewall and the rolled edge of the carcass reinforcement. The outer lateral reinforcement layer consists of at least one elastomeric compound.

[0014] Each sidewall of the tire includes at least one sidewall layer made of an elastomer compound and extending axially toward the interior of the tire from the outer surface of the tire that is in contact with ambient air.

[0015] The term "elastomer compound" is understood to refer to an elastomeric material obtained by mixing its various components. Elastomer compounds typically comprise an elastomeric matrix, at least one carbon black-type and / or silica-type reinforcing filler, a crosslinking system, and a protective agent. The elastomeric matrix has at least one diene elastomer of the natural or synthetic rubber type, and the crosslinking system is typically a sulfur-based crosslinking system. For certain applications, the elastomer in question may also include a thermoplastic elastomer (TPE).

[0016] The term “based on” in a composition is understood to mean that the composition comprises a mixture and / or reaction products of various components used, some of which are capable (or intended) to react at least partially with each other during various stages of the composition’s manufacture, particularly during its crosslinking or vulcanization.

[0017] For the purposes of this invention, the expression “parts by weight / hundred parts by weight elastomer” (or phr) is understood to mean the weight percentage of each hundred parts of elastomer present in the compound composition under consideration.

[0018] Elastomer blends (especially after curing) can be mechanically characterized by their dynamic properties, such as dynamic shear modulus G* = (G'² + G”²)¹ / ² and dynamic loss Tanδ = G” / G', where G' is the elastic shear modulus and G” is the viscous shear modulus. The dynamic shear modulus G* and dynamic loss Tanδ were measured on a Metravib VA4000 viscometer according to ASTM D5992-96. Vulcanized elastomer blend samples (2 mm thick, 78 mm cross-section) were recorded in cylindrical specimen form subjected to a sinusoidal load of simple alternating shear stress at a frequency of 10 Hz at 100 °C. 2 The response was measured. The amplitude was scanned from 0.1% to 50% (outward loop) and then from 50% to 0.1% (backward loop). For the outward loop, the observed maximum value of tan(δ) was noted, denoted as Tan(δ). max .

[0019] "Handling" performance corresponds to the vehicle / tire components' response to multiple driver inputs (steering, acceleration, braking, etc.). Handling is crucial for vehicle stability, safety, and driving pleasure.

[0020] Tires play a crucial role in handling because they ensure the transmission of forces between the vehicle and the ground at the end of the chain, thus maintaining the trajectory defined by the driver.

[0021] When turning, in order for a vehicle to stay on track, a force equal to (but in the opposite direction to) the centrifugal force must be generated, which tends to cause the vehicle to deviate 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 portion in contact with the ground generates lateral force. The mechanism by which the rubber tread portion of the tire deforms during cornering is slip. Slip is the angle between the wheel direction and the vehicle's trajectory. During cornering, this angle is not zero, causing the rubber tread portion of the tire to deform and thus generating the necessary lateral force.

[0023] The lateral force generated in the contact patch of a moving tire, compressed by its load, varies with the slip angle applied to the tire and is called lateral slip stiffness. 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 an important physical parameter that connects the tire to the vehicle and determines the vehicle's handling quality on the road.

[0026] Rolling resistance is another performance aspect addressed in this application. Rolling resistance is a force that impedes the forward movement of a vehicle. The rolling resistance coefficient (C) of a tire... RR This represents the rolling resistance associated with the load carried by the tire. The coefficient is expressed in kg / t.

[0027] Rolling resistance is inherently related to tire deformation. As an example, the bead, which is associated with the tire 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 most common configuration is that the tire is mounted on a rim. The rim is selected according to the specifications of the ETRTO (European Tyre and Rim Technology Organization) standard, which recommends rims for specific tire sizes. Typically, multiple rim widths can be used for the same tire size. Within the scope of this invention, the rim portion that interacts with the tire is axisymmetric with respect to the tire's axis of rotation. To describe the rim, it is sufficient to describe the generatrix profile in the meridional plane.

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

[0030] The performance of the tire bead's fit on the rim during inflation is also a property that can be affected by this invention. Bead fit includes evaluating the tire's ability to properly mount the bead on the rim during inflation. Sufficient contact with the base is required on the innermost radial surface of the bead to prevent any leakage of tire inflation gas. Typically, a contact pressure of at least 1.4 MPa is desired in this contact area. Inflation pressure keeps the bead firmly against the rim flange. Furthermore, the contact pressure on the flange must be sufficient to prevent the tire from detaching from the rim, especially during sharp cornering at high speeds. Devices used to observe the bead mounted on the rim (especially radiographic devices) can determine the quality of the fit.

[0031] Therefore, tires can be classified into two types based on their rim mounting characteristics. Background Technology

[0032] Reducing greenhouse gas emissions during transportation is one of the major challenges facing vehicle manufacturers today. Tires are a significant source of progress (through reducing rolling resistance), as this has a direct impact on a vehicle's fuel consumption. For example, in a combined cycle, a 20% reduction in tire rolling resistance can save approximately 3% of fuel per 100km.

[0033] There is still a need to reduce the rolling resistance of passenger vehicle tires without compromising other performance levels (including industrial performance).

[0034] It has been proposed to improve the rolling resistance of tires used in passenger vehicles by optimizing the bead. Document WO 2010 / 072736 specifically teaches the use of an elastomer composition having a low shear stiffness modulus G' of about 15 MPa and a viscous modulus G' that is more than 20% smaller than the shear stiffness modulus, thereby achieving a significant reduction in rolling resistance.

[0035] The document also suggests further reducing rolling resistance by optimizing the geometry of the elastomer compound layer whose elastic modulus and viscous modulus 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, a major drawback of this approach is the difficulty in industrially manufacturing these compound layer profiles.

[0036] Document FR2994127 improves upon document WO 2010 / 072736 by proposing the addition of a reinforcement to the tire bead. The reinforcement is formed from a reinforcement coated with an elastomer compound.

[0037] The main drawback of this solution is the significant increase in industrial costs, as it introduces new semi-finished products into the tire manufacturing process.

[0038] Other literature (such as patent EP2657049B1) suggests reducing the hysteresis of the sidewall layer by setting a sidewall layer with an appropriate chemical composition, so as to increase rolling resistance.

[0039] The sidewalls perform multiple functions of a tire. Since the tire's outer wall is in contact with ambient air, the sidewalls must be able to withstand the effects of ozone contained within. In urban driving, the sidewalls must also withstand contact with paving surfaces, which can sometimes lead to friction on the outer surface of the sidewalls and cause premature wear.

[0040] Reducing rolling resistance by decreasing the hysteresis of the elastomer compound in the sidewall layer requires a chemical composition that is completely different from that commonly found in this field. Typically, seeking a trade-off between rolling resistance and other sidewall layer properties results in reduced industrial performance of the elastomer compound for use in industrial manufacturing.

[0041] Industrial performance refers to a process's ability to produce a given quantity of products while meeting quality, cost, and time requirements. Here, cost relates to material loss due to scrap caused by quality defects. Since this invention covers equivalent processes, only material costs are considered in industrial performance.

[0042] One of the steps in manufacturing a tire includes a molding stage in a curing mold. After assembling its components, the tire blank is placed in a closed, heated mold, and a film inside the mold, filled with hot fluid, unfolds to press the tire against the inner wall of the mold, imprinting tread patterns on the tire surface and markings on the tire sidewall.

[0043] The markings include those indicating technical information, commercial information, and regulatory information about the product. Regulatory information is mandatory and must meet specific requirements regarding font and character size.

[0044] Tires with defective regulatory markings are discarded if they cannot be repaired, which increases material loss and reduces industrial performance.

[0045] The inventors set a goal for themselves to produce tires that improve rolling resistance levels without compromising industrial performance. Summary of the Invention

[0046] This objective is achieved by passenger vehicle tires, which include, in the meridional plane:

[0047] Two bead layers, two sidewall layers, and a tread, wherein the two bead layers are intended to be mounted on a rim, the two sidewall layers are connected to the bead layers, and the tread includes a tread having a first side and a second side, the first side being connected to the radially outer end of one of the two sidewall layers and the second side being connected to the radially outer end of the other of the two sidewall layers.

[0048] 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 a crease around an annular reinforcement structure, thereby forming a main portion and a crease in each bead;

[0049] Each sidewall layer consists of two axially stacked sublayers. The first sidewall sublayer FE1 is defined by a first axial outermost side and a second axial inner side. The first axial outermost side forms the sidewall of the tire that is in contact with ambient air. The second axial inner side is defined such that the sidewall sublayer FE1 has an average axial thickness E1 and occupies a volume V1.

[0050] Each sidewall layer also includes a second sidewall sublayer FE2, the first side of which overlaps with the second side of the first sidewall sublayer FE1, and the second axial inner side of the second sidewall sublayer FE2 is at least partially in contact with the carcass reinforcement. The sidewall sublayer FE2 has an average thickness E2 and occupies a volume V2.

[0051] The thickness E1 of the first sidewall sublayer FE1 is greater than or equal to 0.7 mm;

[0052] The ratio V1 / (V1+V2) is less than or equal to 0.3;

[0053] The elongation at break of the elastomer compound constituting the first sidewall sublayer FE1, measured at 100°C, is greater than or equal to 200%.

[0054] The viscoelastic loss Tan(δ)max of the second sidewall sublayer FE2 is less than or equal to 0.10.

[0055] The principle of this invention is to reduce the hysteresis of the sidewall layer, thereby reducing the rolling resistance of the tire without compromising other performance levels, particularly industrial performance. To this end, the sidewall layer is a laminate consisting of two superimposed sub-layers arranged in the axial direction, thus separating the functions of the sidewall.

[0056] The average thickness E2 of sublayer FE2 is the average of the thicknesses measured between the first and second points at the intersection of the vertical line perpendicular to the carcass reinforcement and each of the first and second sides of sublayer FE2. The average thickness E1 of sublayer FE1 is defined in the same manner.

[0057] In the two sub-layers, the second sub-layer FE2 occupies the largest volume of the elastomer compound. According to the invention, the volume V1 of sub-layer FE1 is less than or equal to 30% of the total volume of the sidewall. As an example, for a passenger vehicle tire size 245 / 45R18, at the longitudinal coordinate corresponding to the middle of the sidewall layer in the meridional reference frame, E2 is 1.2 mm and E1 is 0.7 mm.

[0058] The viscoelastic loss Tan(δ)max of the FE2 compound in the sidewall sublayer is less than or equal to 0.10. This hysteresis condition applied to the second sublayer is to improve rolling resistance.

[0059] The first sub-ply FE1 is intended to contact the curing mold of the tire during the molding stage. The inventors have established a relationship between the ability of the first sub-ply FE1 to demold without molding defects and the elongation at break of the sub-ply upon heating. According to the invention, the elastomer compound constituting the first sidewall sub-ply FE1 exhibits an elongation at break of greater than or equal to 200% when measured at 100°C.

[0060] The thickness E1 of the first sidewall sub-ply, defined by a value of approximately 0.7 mm (in millimeters), ensures proper operation without causing premature wear of the tire sidewall.

[0061] Choosing a combination of sidewall layers with two sub-layers FE1 and FE2 (where the first sub-layer has a significantly smaller thickness but appropriate mechanical fracture properties, and the second sidewall sub-layer has low hysteresis) provides the tire of the present invention with improved rolling resistance without thereby reducing industrial performance.

[0062] The invention offers additional advantages: the first sublayer FE1, which is in contact with the surrounding environment, is designed to also ensure mechanical and chemical protection, thereby protecting it from environmental damage.

[0063] Chemical attack on the sidewall is understood to refer to the effects of prolonged exposure to sunlight (especially the UV (ultraviolet) portion of the spectrum). Ultraviolet light affects the breakage of the polymer backbone, leading to rapid degradation of the elastomer. This degradation manifests itself as surface cracks (commonly referred to as cracking) and can allow water to penetrate, washing away soluble components and causing the product's bonds to break.

[0064] To address this problem, the inventors have incorporated a UV chemical stabilizer into the formulation of the sidewall sublayer FE1: carbon black is generally considered one of the most effective UV protection systems for elastomers. Similarly, ozone (a strong oxidant) can degrade elastomer components in the same way as UV radiation. The inventors have solved this problem by using antioxidants and by making informed choices of the elastomer (saturated polymer).

[0065] Advantageously, from a process perspective, the two sidewall sub-layers (FE1, FE2) are manufactured via co-extrusion. Co-extrusion technology is now well-established and maintains the same manufacturing cycle time compared to single-layer sidewalls.

[0066] The inventors have proposed various embodiments to ensure, in particular, that the tires of the present invention have a level of lateral slip stiffness sufficient for good handling in vehicles equipped with these tires.

[0067] Advantageously, the elastic shear modulus of the second sidewall FE2 is preferably in the range of 1.5 MPa to 10 MPa, and even more preferably in the range of 2.5 MPa to 10 MPa.

[0068] By allocating an elastomer compound with an elastic shear modulus up to 10 MPa to the second sidewall sublayer FE2 of the tire of the present invention, lateral slip stiffness is improved compared to conventional designs, which is useful for good handling of vehicles equipped with these tires. Conventional sidewall designs aim to achieve an elastic shear modulus of less than or equal to 1.5 MPa.

[0069] Furthermore, the tire bead of the present invention is specifically based on a balance between the shear stiffness and hysteresis of the elastomeric compound constituting the bead. The elastic shear modulus G' of each sidewall sub-ply FE2 is kept less than 10 MPa, such that the hysteresis is maintained at a level measured by a Tan(δ)max value less than or equal to 0.10. The present invention operates based on an elastic shear modulus greater than or equal to 1.5 MPa for the sidewall ply.

[0070] According to a preferred embodiment, each bead includes a filler layer that is at least partially located between the main portion of the carcass reinforcement, the rolled edge of the carcass reinforcement, and the radially outer portion of the annular reinforcement structure, wherein the viscoelastic loss Tan(δ)max of the elastomeric compound constituting the filler layer is less than or equal to 0.1.

[0071] The increased elastic shear modulus of the elastomeric compound in the sidewall sublayer FE2 can reduce the hysteresis of the filler layer. In common bead designs, those skilled in the art choose filler layers with an elastic shear modulus of approximately 40 MPa, thus compromising viscoelastic losses.

[0072] The filler layer of the bead typically occupies a large volume and undergoes intense shear deformation due to tension variations in the main body of the carcass and the reinforcement of its rolled edges. The selection of elastomer blends with low hysteresis helps control the level of viscoelastic dissipation.

[0073] Advantageously, the bead includes a lateral reinforcement layer composed of an elastomeric compound, the volume of which is at least partially located between the second sidewall layer and the rolled edge of the carcass reinforcement.

[0074] According to the inventors, the lateral reinforcement layer of the bead is complementary to the first filler layer to provide lateral stiffness. Depending on these material properties regarding Tan(δ)max and dynamic shear stiffness, the reinforcement enables a performance balance between rolling resistance and tunable handling.

[0075] 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.

[0076] In this variant of the implementation, the two compound layers (i.e., the filler layer and the lateral reinforcement layer) validated the property that the viscoelastic loss Tan(δ)max is less than 0.10. The improvement in rolling resistance is optimal, while the handling of the tire mounted on the vehicle remains as expected.

[0077] In another embodiment of the invention, in each bead, the rim contact curve 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 located at the outermost edge and in contact with the rim, and the second point M2 also contacting the rim and located at the midpoint of 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 section of the pneumatic tire, which is mounted on the rim and pressed against the ground by a vertical load, wherein the load and inflation pressure are determined in a standard specification (e.g., ETRTO (European Tire and Rim Technology Organization)); the first section is located in the ground contact area, and the second section is located on the opposite side of the first section relative to the tire's axis of rotation. In the first section located in the ground contact area, at least in the first bead, the length LADC of the rim contact curve is measured. In the second section opposite to the tire's axis of rotation and the contact area, at least in the second tire bead, the length LCJ of the rim contact curve is measured, and then the ratio of the difference between the lengths of the rim contact curves of the two sections (i.e., 100*(LADC-LCJ) / LCJ) is greater than or equal to 30%.

[0078] In this embodiment, the rate of change of rim contact of the tire of the present invention is significantly greater than the rate of change observed in prior art tires.

[0079] When a pneumatic tire mounted on a rim is compressed by a load, the point of contact between the tire and the rim may vary from one meridian to another. Therefore, the length of the rim contact curve, as defined above, also varies from one meridian to another.

[0080] The tire is designed to have the longest possible rim contact curve in the contact patch region (more precisely, along the meridian at the center of the contact patch region) compared to existing tires. Under these conditions, the inventors believe that the rim contact contributes most to the slip stiffness.

[0081] In the meridional section of an inflatable tire mounted on a rim and compressed by a load, a first section of the tire can be seen passing through the center of the contact patch. The contact patch refers to all points where the tire contacts the compressed ground at a given moment. The point where the contact patch lies on the vertical axis OZ is called the center of the contact patch. On the opposite side of the contact patch relative to the tire's axis of rotation OY, another section of the tire can be seen, which generally defines a deformation state equivalent to an axisymmetric inflation state.

[0082] The rate of change of rim contact corresponds to the maximum change in rim contact length during each wheel rotation.

[0083] According to the inventors, a key step in the tire design of this embodiment includes 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 in the contact area with the same curvature as the rim flange. Another solution involves inserting a compound liner at the rim flange in the area where the sidewall layer and protective layer join. This compound liner can preferably be composed of the same compound as the sidewall layer to maintain industrial manufacturing costs. For such an elastomeric compound liner, it is desirable, for example, that its elastic shear modulus be advantageously equal to, for example, the elastic shear modulus of the sidewall layer.

[0084] Advantageously, the ratio of the difference in length 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 more preferably greater than or equal to 60%.

[0085] The outer contour of the area in contact with the rim can be altered to achieve the rate of change of rim contact. Therefore, it serves as a means of adjusting lateral slip stiffness when seeking a performance trade-off between tire rolling resistance and handling. Lateral slip stiffness is an increasing function of the rate of change of rim contact. For a rim contact rate of change greater than or equal to 60%, altering the outer contour of the sidewall layer makes bead installation easier; however, excessively large rates of change greater than 100% may inhibit installation.

[0086] In addition to the main features of the invention, the inventors have also identified means associated with the geometry of the bead compound layer to further optimize the performance trade-off of a tire with improved rolling resistance and good handling.

[0087] Advantageously, the distance DRB is the radial distance from one end of the radial outer filler layer, said distance DRB being less than or equal to 50% of the radial height H of the tire.

[0088] The tire height H is the vertical distance between a first straight line HH' and a second straight line AA'. The first straight line HH' is parallel to the tire's axis of rotation and is tangent to the innermost radial point of the annular reinforcement structure. The second straight line AA' 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 a tire mounted on a rim and inflated to a reference pressure, according to ETRTO (European Tire and Rim Technology Organization) specifications.

[0089] 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 in the range of 5% to 25% of the radial height H of the tire.

[0090] Furthermore, the distance DRL is the radial distance from the radial outer end of the lateral reinforcement layer to the straight line (HH'), and the radial distance DRL is greater than or equal to 25% of the radial height H of the tire.

[0091] The lateral reinforcement layer between the sidewall and carcass reinforcement layers serves as a reinforcement of the first filler layer, contributing 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-compression stresses of the bead during passage through the contact patch.

[0092] In an advantageous embodiment of the invention, the rolled edge of the carcass reinforcement abuts against the main portion of the carcass reinforcement on its radially outer side over its entire height.

[0093] As described above, the carcass reinforcement is formed by a reinforcement sandwiched between two layers of elastomeric compound. The fact that the crimp of the carcass reinforcement abuts against the main portion of the carcass reinforcement means that the crimp contacts the main portion of the carcass reinforcement. Contact occurs along the surface located between the two coatings of the carcass reinforcement.

[0094] In this configuration, the volume of the first filler layer is limited to a strict minimum around the annular reinforcement structure. This configuration is highly advantageous for reducing the rolling resistance of the tire bead.

[0095] 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.

[0096] The bead reinforcement is formed by parallel reinforcements sandwiched between two layers of elastomeric compound. The addition of this semi-finished component results in additional manufacturing costs that must be compensated for. To limit the cost impact of this solution, the implementation can be combined with the crimping of the carcass reinforcement abutting against the main portion of the carcass reinforcement.

[0097] Advantageously, the elastomer compound constituting at least one of the filler layer and / or lateral reinforcement layer and / or second sidewall layer FE2 has a composition based on a diene elastomer, a crosslinking system, and reinforcing filler (carbon black type 550) in a total content between 50 phr and 75 phr.

[0098] Furthermore, the elastomeric compound constituting the filler layer, the elastomeric compound constituting the lateral reinforcement layer, and the elastomeric compound constituting the sidewall sublayer FE2 have the same composition.

[0099] The term "diene" elastomer (or, more specifically, rubber) is understood in a known manner to mean an elastomer that is at least partially (i.e., a homopolymer or copolymer) derived from a diene monomer (i.e., a monomer 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), butadiene-styrene copolymer (SBR), isoprene-butadiene copolymer (BIR), isoprene-styrene copolymer (SIR), butadiene-styrene-isoprene copolymer (SBIR), and combinations thereof.

[0100] Preferred embodiments include the use of "isoprene" elastomers, i.e., homopolymers or copolymers of isoprene, in other words, diene elastomers selected from natural rubber (NR), synthetic polyisoprene (IR), various isoprene copolymers, and combinations of these elastomers.

[0101] The isoprene elastomer is preferably natural rubber or cis-1,4-type synthetic polyisoprene. In these synthetic polyisoprene, the content (mol%) of cis-1,4- bonds is preferably greater than 90%, and more preferably greater than 98%. According to other preferred embodiments, the diene elastomer may consist entirely or partially of another diene elastomer, for example, an SBR elastomer (E-SBR or S-SBR) used in blend with or without blending with another elastomer (e.g., a BR-type elastomer).

[0102] The rubber composition may also contain all or part of the additives commonly used in rubber matrices intended for the manufacture of tires, such as reinforcing fillers (e.g., carbon black or inorganic fillers (e.g., silica)), inorganic filler coupling agents, anti-aging agents, antioxidants, plasticizers or thickening oils (whether aromatic or non-aromatic) (especially very weakly aromatic or non-aromatic oils, such as naphthenic or paraffinic oils (with high or preferably low viscosity), MES or TDAE oils, plasticizing resins with high Tg greater than 30°C), agents that promote the processing (processability) of the composition in its unprocessed state, tackifying resins, crosslinking systems based on sulfur, sulfur donors and / or peroxides, accelerators, vulcanization activators or vulcanization retardants, anti-reversion agents, methylene acceptors and methylene donors (e.g., HMT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine)), reinforcing resins (e.g., resorcinol or bismaleimide), and known metal salt type adhesive accelerator systems (e.g., especially cobalt or nickel salts). Attached Figure Description

[0103] Other details and advantageous features of the invention will become apparent from the following description of exemplary embodiments, with reference to the accompanying drawings, which show meridional views of a tire graphic according to an embodiment of the invention. For ease of understanding, the drawings are not shown to scale.

[0104] Figure 1-A The cross-section of the tire of the present invention in the meridional plane is shown. Figure 1-B Displayed meridian Figure 1-A An enlarged view of the portion surrounded by dashed lines shows the bead of the tire of the present invention.

[0105] 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 layers (FE1, FE2) is modified to facilitate contact with the rim.

[0106] Figure 3 This figure shows a meridional section of a pneumatic tire mounted on a rim and compressed by the load it bears. The first section in the contact zone and the second section opposite the contact zone relative to the axis (OY) are visible. The figure illustrates the determination of the rate of change of contact with the rim.

[0107] Figure 4-A and Figure 4-B A visualization of the main dimensions of the tire bead is displayed. Detailed Implementation

[0108] According to ETRTO (European Tyre and Rim Technology Organization) standards, this invention is implemented on a passenger vehicle tire with a size of 245 / 45R18. This tire can carry a load of 800 kg and is inflated to a pressure of 250 kPa.

[0109] exist Figure 1-A In the figure, the tire with reference numeral 1 includes a carcass reinforcement 90 and two bead 50s. The carcass reinforcement 90 is composed of a reinforcing body coated with a rubber composition. The bead 50s contact the rim 100. The area 49 defined by the dashed circle defines one of the two bead 50s of the tire. Figure 1-B An enlarged view is shown. The carcass reinforcement 90 is anchored in each bead 50. The tire also includes a crown reinforcement 20 comprising two working layers 21, 22 and a ring layer 23. Each working layer 21 and 22 is reinforced by filamentous reinforcing elements that are parallel in each layer, intersecting from one layer to the other, and forming an angle between 10° and 70° with the circumferential direction. The ring layer 23 is radially arranged on the outside of the crown reinforcement 20 and is formed by circumferentially oriented helically wound reinforcing elements. A tread 10 is radially laid on the ring layer 23; the tread 10 ensures contact between the tire 1 and the ground. The tire 1 shown is a "tubeless" tire: it includes an "inner liner" 95 made of a rubber composition impermeable to inflation gas and covering the inner surface of the tire.

[0110] The sidewall layer 30 includes two sub-layers (FE1, FE2). The first sub-layer FE1 is located axially externally to form the sidewall in contact with the surrounding environment. The second sub-layer FE2 32 is at least partially in contact with the carcass reinforcement 90. Figure 1-A and Figure 1-B In the middle, the first sub-layer FE1 has a dark background, and the second sub-layer FE2 has a shadowed background.

[0111] In the context 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.

[0112] In the meridional plane, the rim 100 includes at least one flange 120 located at an axial end and connected to a base 110, which is designed to receive the radially innermost surface of the tire bead. A straight portion 130, connecting the rim flange 120 to the base 110 by a fillet, is located between the base 110 and the flange 120. The rim flange 120, extending from the straight portion 130, axially restricts the movement of the tire bead during inflation.

[0113] The bead 50 partially includes a carcass reinforcement 90, which includes a main portion 52 and is then rolled up around an annular reinforcement structure 51 to form a rolled edge 53. A filler layer 70 is located between the main portion 52 and the rolled edge 53 of the carcass reinforcement 90. According to an embodiment, the bead 50 may 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 side of the bead 50, a sealing layer 95 forms an inner wall in contact with the internal inflation gas.

[0114] The bead 50 also includes a protective layer 80 that contacts the axially outer portion 130 of the rim to limit axial displacement 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.

[0115] Figure 2-A The outer contour of the bead 50 of a tire according to a specific embodiment of the present invention is shown compared to a conventionally designed tire. The bead 50 is shown in a cross-section opposite the contact patch area. 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 a modification of the contour of the tire of the present invention to facilitate contact with the rim 100.

[0116] exist Figure 2-B In, there exists and Figure 2-A The same view, but showing the outline of the center of the ground contact area. Different from... Figure 2-A The tire contacts the entire rim flange 120. The rate of change of rim contact reflects this change in rim contact.

[0117] exist Figure 2-C In another embodiment shown, an elastomeric compound liner 40 (a change at the radially inner end of the sidewall 30) is present, the elastomeric compound liner 40 being designed to contact the rim flange 120. The radially inner side of the compound liner 40 is defined by a curve that closely follows the contour of the rim flange 120. A first side of the elastomeric compound liner 40 has a suitable geometry intended to contact the curvature of the rim flange to closely follow the shape of the rim flange 120 upon contact; a second side of the elastomeric compound liner extends the outer side of the sidewall that is in contact with ambient air; a third side of the elastomeric compound liner 40 contacts the radially inner end of the sidewall; and finally, a fourth side of the elastomeric compound liner contacts the protective layer 80.

[0118] exist Figure 2-CIn this design, the rim contact curve extends from a first point M1 on the tire and a second point M2 on the tire. The first point M1 is located axially at the outermost point and contacts the rim. The second point M2 also contacts the rim and is located at the midpoint of the straight section connecting the flange 120 of the rim to the base 110. The length of this rim contact curve is the curve distance along the rim contact curve from point M1 to point M2.

[0119] Figure 2-D As a variant of the previous embodiment, it is 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.

[0120] Figure 3 This is a vertical plane view of the tire of the present invention according to a previous embodiment. The tire is inflated, mounted on a rim 100, and pressed against the ground 200 by a load 250. A first meridional section in the contact patch area and a second meridional section opposite the contact patch area can be seen. In the first section located in the contact patch area, the length LADC of the rim contact curve 100 is measured at least in the first bead. At least in the second bead, the length LCJ of the rim contact curve is also measured in the second section. The ratio of the difference between the lengths of the rim contact curves of the two sections (i.e., 100*(LADC-LCJ) / LCJ) is greater than or equal to 30%, and in this case equal to 62%.

[0121] exist Figure 4-A The determination of the tire height H is explained in the text. The tire height H is the vertical 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 is 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. According to ETRTO (European Tire and Rim Technology Organization) specifications, the radial height H is measured on a tire mounted on a rim and inflated to a reference pressure.

[0122] Figure 4-B The geometric parameters of the bead in relation to this invention are shown. The height is defined by a straight line HH', which is tangent to the bead line 51 at its radially innermost point:

[0123] DRI is the radial distance of the inner radial end of the lateral reinforcement layer 60 relative to HH'. The radial distance DRI is less than or equal to 20% of the radial height H of the tire, and in the embodiment shown herein, it is equal to 5 mm;

[0124] DRL is the radial distance of the outermost radial end of the lateral reinforcement layer 60 relative to the straight line HH'. The radial distance DRL is greater than or equal to 25% of the radial height H of the tire, and in the embodiment shown herein, it is equal to 38 mm;

[0125] DRR is the radial distance from the end of the crimp of the carcass reinforcement 90 relative to HH'. The radial distance DRR is greater than or equal to 10% of the radial height H of the tire, and in the embodiment shown herein, it is equal to 20 mm;

[0126] DRB is the radial distance of the outermost end of the filler layer 70 relative to HH', and is 28 mm in the embodiment shown herein.

[0127] Table 1 below shows the composition of the elastomer compound for the tires of the present invention. The main compounds used are listed by indicating each main component (in phr (parts by weight / hundred parts by weight elastomer)).

[0128] [Table 1]

[0129]

[0130] The formulations of the present invention used in this embodiment are based on natural rubber elastomers reinforced with carbon black, or blends of natural rubber and butadiene (for formulations M3 and M4). Plasticizers (reinforcing resins) are introduced into the composition to improve the processability of the formulations. The formulations also contain vulcanizing agents (sulfur), accelerators, and protective agents.

[0131] The compound M4, which constitutes the first sidewall layer FE1, contains 5 phr of antioxidants and 48 phr of carbon black to ensure protection against damage from exposure to light and ozone.

[0132] Table 2 summarizes the relevant mechanical and viscoelastic properties measured at 23°C and 10% deformation amplitude:

[0133] [Table 2]

[0134] G’ G” Tan(δ)max M1 46 7 0.2 M2 48 8 0.2 M3 2.47 0.06 0.03 M4 1.26 0.100 0.08

[0135] The elastomer compound M4 had a breakage elongation of 300% measured at 100°C, while compound M3 had a breakage elongation of 80% measured at 100°C.

[0136] The construction of the tire according to the present invention was tested to clearly highlight the performance provided by the present invention. The results of these tests were compared with those obtained on a control tire.

[0137] according to Figure 1-A and Figure 1-BThe reference T1 corresponds to a conventionally designed tire, which includes a filler layer composed of elastomer compound M1, a lateral bead reinforcement layer composed of elastomer compound M2, and two sidewall sub-layers (FE1, FE2) composed of elastomer compound M4. The profile of the sidewall layers has a conventional design, meaning it is not modified to facilitate contact with the rim.

[0138] The second control, T2, replicated the specifications of T1, but the elastomer blends of the two sidewall sublayers consisted of the same blend M3.

[0139] The first tire P1 according to the invention repeats the specifications of the reference T1, but the first sidewall sublayer FE1 is composed of compound M4 and the second sidewall sublayer FE2 is composed of compound M3.

[0140] In general, all tires according to the present invention have a first sidewall layer FE1 composed of compound M4 and a second sidewall layer FE2 composed of compound M3.

[0141] The second tire P2 according to the invention includes a filler layer composed of compound M3, and also includes a lateral reinforcement layer composed of compound M2.

[0142] The third tire P3 according to the invention has a filler layer and a lateral reinforcement layer composed of the same compound M3.

[0143] Finally, the fourth tire P4 of the present invention differs from P3 in that the profile of the sidewall layer is changed so that the rate of change of rim contact is greater than 30%.

[0144] Figure 1-B The construction of tires P1, P2, and P3 of the present invention is shown. Regarding construction P4, it can be seen that… Figure 2-A , Figure 2-B and Figure 2-D The diagram is shown in the image.

[0145] like Figure 2-A and Figure 2-B As shown, after partially altering the profile of the sidewall layer in the area in contact with the rim, the rate of change in the rim contact of P4 was 62%.

[0146] Industrial performance was measured based on the scrap rate of sidewall molding defects. The tires P1, P2, P3, and P4 of the present invention do not have molding defects that affect marking, and like T1, their industrial performance is satisfactory. On the other hand, the control T2, having a single-layer sidewall composed of compound M3, generated a large number of scraps due to difficulty in demolding.

[0147] Rolling resistance testing is performed according to ISO 28580. For the tires tested, the result is the rolling resistance coefficient, which represents the ratio of the resistance to forward movement of the vehicle caused by tire hysteresis to the load carried.

[0148] Lateral slip stiffness is measured on a dedicated measuring machine (such as a measuring machine sold by MTS).

[0149] Results above (or below) 100% indicate an improvement (or degradation) in the performance under consideration.

[0150] The results are summarized in Table 3 below:

[0151] [Table 3]

[0152] Rolling resistance Lateral slip stiffness T1 100 100 T2 102 101 P1 102 100 P2 104 100 P3 112 98 P4 111 101

[0153] All tires of this invention achieve the desired trade-off between rolling resistance and industrial performance. Depending on the variant tested, rolling resistance is improved by 2% to 12%.

[0154] The lateral slip stiffness of the tires was measured. Tires P1 and P3 have lateral slip stiffnesses of 100% and 98%, respectively, without significantly affecting vehicle handling. Tires P2 and P4 perform better than or equal to the desired performance.

[0155] All variations of the tires according to the invention can be produced without developing processes and at the usual industrial manufacturing costs.

[0156] Furthermore, the present invention can be extended to bead structures other than those described herein, such as bead structures having a first filler layer and a second lateral reinforcement layer, even if the carcass reinforcement does not include a rolled edge.

Claims

1. A tire (1) for a passenger vehicle, said tire (1) comprising, in the meridional plane: Two bead (50), two sidewalls (30), and a crown (20), the bead (50) being designed for mounting on a rim, the sidewalls (30) being connected to the bead (50), and the crown (20) including a tread (10), the crown (20) having a first side and a second side, the first side being connected to the radially outer end of one of the two sidewalls (30), and the second side being connected to the radially outer end of the other of the two sidewalls (30); At least one carcass reinforcement (90) extends from two beads (50) to the crown (20), the carcass reinforcement (90) comprising a plurality of carcass reinforcement elements and anchored in the two beads (50) by a crease around an annular reinforcement structure (51), thereby forming a main portion (52) and a crease (53) in each bead. Each sidewall layer (30) consists of two axially stacked sublayers (FE1, FE2), the first sidewall sublayer (FE1) being defined by a first axial outermost side and a second axial inner side, the first axial outermost side forming the sidewall of the tire in contact with ambient air, and the second axial inner side being defined such that the sidewall sublayer (FE1) has an average axial thickness E1 and occupies a volume V1. Each sidewall also includes a second sidewall sublayer (FE2), the first side of which overlaps with the second side of the first sidewall sublayer (FE1), and the second axial inner side of the second sidewall sublayer (FE2) is at least partially in contact with the carcass reinforcement (90), the sidewall sublayer (FE2) having an average axial thickness E2 and occupying a volume V2; The first sidewall sublayer (FE1) has a thickness E1 greater than or equal to 0.7 mm, a ratio V1 / (V1+V2) less than or equal to 0.3, an elastomer blend constituting the first sidewall sublayer (FE1) has an elongation at break greater than or equal to 200% when measured at 100°C, and a viscoelastic loss Tan(δ)max of the second sidewall sublayer (FE2) less than or equal to 0.

10.

2. Tyre (1) according to claim 1, wherein, The elastic shear modulus of the second sidewall sublayer FE2 is in the range of 1.5 MPa to 10 MPa.

3. Tyre (1) according to any one of the preceding claims, each bead (50) comprising a filler layer (70) at least partially interposed between the main portion (52) of the carcass reinforcement, the turn-up (53) of the carcass reinforcement and the radially external portion of the annular reinforcing structure, wherein, The viscoelastic loss Tan(δ)max of the elastomer compound constituting the filler layer is less than or equal to 0.

1.

4. The tire (1) according to claim 1, wherein, The bead includes a lateral reinforcement layer (60) composed of an elastomeric compound, the volume of which is at least partially located between the second sidewall layer (30) and the rolled edge (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, in each bead (50), the rim contact curve includes the point where the tire (1) contacts the rim (100); the rim contact curve connects a first point M1 of the tire to a second point M2 of the tire, the first point M1 of the tire being located at the outermost point in the axial direction and in contact with the rim, the second point M2 of the tire 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) further includes two sections in the vertical meridional section of the pneumatic tire, the tire being mounted on the rim and pressed against the ground by a vertical load (250), wherein the load and inflation pressure are determined in the specifications of the European Tire and Rim Technology Organization; the first section is located in the grounding region, and the second section is located on the opposite side of the first section relative to the axis of rotation of the tire; In the first cross-section located in the ground contact area, at least in the first tire bead, measure the length of the rim contact curve, LADC. In a second cross-section relative to the tire's axis of rotation and opposite the contact patch, at least in the second bead, the length LCJ of the rim contact curve is measured, where, The ratio of the difference in length of the rim contact curves of the two cross 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 difference in length of the rim contact curves of the two cross 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), wherein, 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 any one of claims 4 to 8, wherein the distance DRI is the radial distance from the radial inner end of the lateral reinforcement layer (60) to the straight line (HH'), wherein, The radial distance DRI is in the range of 5% to 20% of the radial height H of the tire (1).

10. The tire (1) according to any one of claims 4 to 8, wherein the distance DRL is the radial distance from the radially outer end of the lateral reinforcement layer (60) to the 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 rolled edge (53) of the carcass reinforcement (90) abuts against the main part (52) of the carcass reinforcement (90) on its radially outer side over its entire height.

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

13. The tire (1) according to any one of claims 4 to 8, wherein, The elastomeric compound constituting at least one of the filler layer (70) and / or the lateral reinforcement layer (60) and / or the sidewall sublayer (FE2) has a composition based on a diene elastomer, a crosslinking system, and a reinforcing filler in a total content of 50 phr to 75 phr, wherein the reinforcing filler is carbon black type N550.

14. The tire (1) according to claim 13, wherein, The elastomeric compound constituting the filler layer (70), the elastomeric compound constituting the lateral reinforcement layer (60), and the elastomeric compound constituting the sidewall sublayer (FE2) have the same composition.

15. The tire (1) according to claim 1, wherein, The two sidewall sublayers (FE1, FE2) are manufactured by co-extrusion.

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