Tyre with optimized grip

Abstract

The invention relates to a tire (1) comprising a crown (4) having a crown reinforcement (20), a sublayer (7) and a tread (6). The sublayer (7) comprises a base layer (71) radially outside the crown reinforcement (20), a cap layer (72) radially outside the base layer (71) and a groove bottom elastomer compound layer (73) radially inside the tread (6). The dynamic shear modulus G1*, G3* of the base layer (71) and of the groove bottom elastomer compound layer (73) satisfy G3* > 1.25 x G1*; G1*, G3* are measured at 23°C under alternating shear stress at a frequency of 10 Hz and a deformation of 10%.

Description

Technical Field

[0001] This invention relates to a tire whose tread is optimized to achieve a favorable performance trade-off between handling and rolling resistance compared to conventional designs. While not limited to this type of application, the invention will be described more specifically with reference to radial tires intended for mounting on passenger vehicles or trucks.

[0002] definition By convention, a reference frame (O, OX, OY, OZ) is considered, where the center O coincides with the geometric 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.

[0003] Radial inner / radial upper inner and radial outer / radial upper outer refer to being closer to the tire's axis of rotation and farther away from the tire's axis of rotation, respectively.

[0004] Axially inner / axially located inside and axially outer / axially located outside refer to the equatorial plane closer to the tire and the equatorial plane further away from the tire, respectively. The equatorial plane of the tire is a plane that passes through the middle of the tire tread and is perpendicular to the tire's axis of rotation.

[0005] The construction of a tire is typically described by its constituent components as shown in the meridional plane (i.e., the plane containing the tire's axis of rotation). The rationale for this choice is that the geometry of the tire is generally axisymmetric about the tire's axis of rotation.

[0006] 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.

[0007] 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.

[0008] The crown reinforcement of a radial tire comprises stacked crown layers that extend circumferentially and are located radially outside the carcass reinforcement. Each crown layer consists of mutually parallel reinforcements coated with a polymer material of the elastomeric or elastomeric compound type. The assembly consisting of the crown reinforcement and the tread is called the crown.

[0009] The radial tire carcass reinforcement of the present invention typically includes at least one carcass layer comprising metal or fabric reinforcing elements, each of which is coated with an elastomeric coating compound. The at least one carcass layer includes a main portion that joins two beads, the main portion being wound around an annular reinforcing structure (typically a bead cord) in each bead.

[0010] Elastomer blends are understood as elastomeric materials obtained by blending their various components. Elastomer blends typically comprise an elastomeric matrix having at least one diene elastomer of the type of natural or synthetic rubber, at least one reinforcing filler of the type of carbon black and / or silica, a typically sulfur-based crosslinking system, and a protective agent. For some applications, the elastomer may also include thermoplastic materials (TPEs).

[0011] 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.

[0012] Within the meaning of this invention, the expression "parts by weight / 100 parts by weight elastomer" (or phr) should be understood to mean parts by weight / 100 parts of elastomer present in the rubber composition under consideration.

[0013] The mechanical characteristics of elastomer blends, especially after curing, can be attributed to their dynamic properties, such as the dynamic shear modulus G. * =(G'2+G''2)1 / 2 (where G' is the elastic shear stiffness modulus and G” is the viscous shear modulus) and viscoelastic loss Tan(δ)=G'' / G'. The dynamic shear modulus G was measured on a Metravib VA4000 viscosity analyzer according to standard ASTM D5992-96. * And viscoelastic loss Tan(δ). The response of vulcanized elastomer blends subjected to stresses of the form of simple alternating sinusoidal shear stress at a frequency of 10 Hz and a temperature of 100°C was recorded. Strain amplitude scans were 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 For the same outward cycle, the value of the dynamic shear modulus G* is shown. The dynamic shear modulus G* is also called the "complex shear modulus", and the viscoelastic loss Tan(δ) is also called the "dynamic loss". Background Technology

[0014] Technicians in the field of tire design know that tires have at least three expected functions. First, these tires must bear the loads caused by the vehicle's mass and all additional loads associated with the vehicle's dynamic motion, as well as any additional aerodynamic loads that may occur at high speeds. Second, they must be able to steer the vehicle along the path determined by the driver. Finally, the forces of acceleration or braking determined by the driver need to be transmitted to the ground.

[0015] The crown reinforcement is an essential component that makes a decisive contribution to the three functions of load bearing, steering, and force transmission. In a conventional design, the crown reinforcement has at least two intersecting metal layers and surrounds the carcass reinforcement in a belt-like manner to provide the tire with the stability required to perform its load-bearing function.

[0016] The "steering" function is also known as "handling" or "grip." This corresponds to the vehicle / tire assembly's response to various inputs from the driver (steering, acceleration, braking, etc.). Handling is crucial for both vehicle stability and safety in terms of driving performance.

[0017] Tires play a crucial role in handling because they are at the end of the chain, ensuring the transfer of force between the vehicle and the ground to maintain the track defined by the driver.

[0018] 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.

[0019] The deformation of the rubber tread in contact with the ground generates lateral force. The mechanism by which the rubber tread deforms during cornering is called lateral deflection. Lateral deflection is the angle between the wheel's direction and the track the vehicle is traveling on. During cornering, this angle is not zero, causing the rubber tread of the tire to deform, thus generating the necessary lateral force.

[0020] Lateral stiffness is a name given to the variation described below: the lateral force generated in the contact patch of a moving tire under load compression, varying with the slip angle applied to the tire. Lateral stiffness is expressed in Newtons per degree (N / °).

[0021] For small slip angles, i.e., less than 4°, 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 coefficient.

[0022] Lateral stiffness is an important mechanical property that connects the tire to the vehicle and determines the vehicle's handling quality on the road.

[0023] Rolling resistance is another performance factor addressed by this invention. Rolling resistance is one of the forces that impede the forward movement of a vehicle. The rolling resistance coefficient (C) of a tire... RR Rolling resistance is the ratio of rolling resistance to the load carried by the tire. This coefficient is expressed in kg / t.

[0024] Rolling resistance is primarily 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%.

[0025] Reducing greenhouse gas emissions in the transportation sector is one of the major challenges facing vehicle manufacturers today. Tires are a significant source of progress by reducing rolling resistance, as rolling resistance has a direct impact on vehicle fuel consumption. For example, a 20% reduction in rolling resistance of passenger vehicle tires can save approximately 3% of fuel per 100 kilometers in the combined cycle.

[0026] The choice of tread plays a crucial role in establishing a trade-off between handling and rolling resistance. Those skilled in the art are familiar with tire design parameters that treads consist of stacked sub-plyes, each with appropriate dynamic performance and geometry. An example of a sub-ply (i.e., a rubber layer inserted between the crown reinforcement and the tread material) is described in FR 2 954 333.

[0027] Document EP 2 865 543 provides another example, in which the constituent material of the sub-ply is flush with the bottom of the grooves in the tread. Typically, the sub-ply material under the tread is used to improve the rolling resistance of the tire with a low-hysteresis material, or to harden the tread in shear but with moderate stiffness so as not to excessively resist the flattening of the tire tread in the contact patch with the ground.

[0028] However, the lower the stiffness, the worse the tire's drift thrust response when subjected to the stress loads of vehicle steering. Specifically and schematically, the stacked rubber layers located radially outside the crown reinforcement can be considered as a series of continuous springs. For this reason, materials with excessively low dynamic shear moduli are avoided to prevent compromising lateral stiffness. However, this conflicts with the goal of minimizing rolling resistance. Even in variants with maximum stiffness, the dynamic shear modulus G of the sublayer material... * Typically much less than 8 MPa, even when optimal handling performance is expected.

[0029] Document WO 2015 / 170615 also discloses a tire having a base layer (i.e., sublayer) formed by two radially stacked material bodies. The modulus and its Tan(δ) (tangent δ) value of the tread material are lower than the values ​​of the same parameters of the sublayer materials (i.e., the two radially outermost layers) in contact with the tread material. The modulus and its Tan(δ) value of the radially inner layers of the sublayer material are also lower than the values ​​of the same parameters of the sublayer materials in contact with the tread material. However, tires manufactured according to this teaching have not made any progress in balancing performance characteristics.

[0030] Document WO2019 / 145621 discloses a tread configuration located radially outside a sublayer, the sublayer itself resting radially against a crown reinforcement. The sublayer comprises a low-stiffness first layer, i.e., a dynamic shear modulus G* less than or equal to 0.6 MPa, laid radially outside the crown reinforcement. The sublayer also includes a high-stiffness second layer laid radially outside the low-stiffness layer and radially inside the tread. The high-stiffness layer has a dynamic shear modulus greater than 7 MPa, which is greater than the dynamic shear modulus of the tread. This tread configuration results in improved rolling resistance and handling compared to conventionally designed tires.

[0031] Patent EP3031627 discloses a tread including circumferential grooves. These circumferential grooves are reinforced by using a reinforcing compound, thereby improving the lateral stiffness Dz.

[0032] The inventors set their own goal as to find other means to further improve the lateral stiffness of existing tires, preferably to improve the trade-off between lateral stiffness performance and rolling resistance performance. Summary of the Invention

[0033] This objective has been achieved by a tire for a motor vehicle, the tire comprising a crown, the crown comprising a crown reinforcement, sub-layers, and a tread, the tread comprising grooves oriented substantially circumferentially; the sub-layers having a base layer radially outer of the crown reinforcement and a cover layer radially outer of the base layer and radially inner of the tread; the base layer having a dynamic shear modulus G1* less than or equal to 1.5 MPa; the cover layer having a dynamic shear modulus G2* greater than or equal to 5 MPa; the groove bottom layer being radially located inside the outer contour of the tread, and the dynamic shear modulus G3* of the groove bottom elastomer compound layer being strictly greater than 1.25 x G1*; G1*, G2*, and G3* were measured at 23°C under alternating shear stress at a frequency of 10 Hz and a strain of 10%.

[0034] The tire crown is a name given to the area comprising the tread, sublayers, and crown reinforcement, the crown reinforcement comprising a composite layer that tightens the carcass reinforcement. This description is given from the outside of the tire toward the inside.

[0035] A groove that is substantially circumferentially oriented refers to a circumferentially oriented cut in the tread on the wheel rim, wherein the distance between the material walls defining the cut is greater than 2 mm, and the depth of the cut is greater than or equal to 1 mm. In a meridional section, the axial inner wall and axial outer wall of the groove each form an angle with the radial direction and extend toward the inside of the tire. The curves connecting the two radially inner ends of the two walls of the groove form the profile of the groove bottom, which contacts the radially outer surrounding environment. The tread optionally includes NBS grooves, which typically have a value of 3 or 4 depending on the axial width of the tread.

[0036] The tire of the present invention includes a tread having sub-layers, each sub-layer consisting of three layers, two of which are radially stacked. A base layer is laid radially outside the crown reinforcement, and the base layer has a dynamic shear modulus less than or equal to 1.5 MPa. Therefore, the base layer is referred to herein as a "soft" layer. A cover layer is located radially outside the base layer. This second layer has a dynamic shear modulus greater than or equal to 5 MPa and is referred to as "hard". The present invention provides a third layer, namely a groove bottom elastomer blend layer, which is arranged in different configurations depending on the desired performance trade-off. In terms of stiffness, the dynamic shear modulus G3* of this groove bottom elastomer blend layer is strictly greater than 1.25 x G1*, which means that, in the sense of lateral shear stiffness, the groove bottom elastomer blend layer is harder than the base layer, thereby contributing to improved tire lateral stiffness.

[0037] Therefore, a tire comprising a groove bottom elastomer compound layer that is relatively stiff and not limited by the requirement for a composition to perform well in terms of grip and / or wear and / or hysteresis can be designed. Thus, without limiting the invention in any way, a relatively stiff, low-hysteresis groove bottom elastomer compound layer that dissipates less energy than the tread compound can be envisioned, for example, providing improved rolling resistance while maintaining the same handling performance. Without limiting the invention in any way, a relatively stiff groove bottom elastomer compound layer with strong resistance to ozone attack from the surrounding environment, or a groove bottom elastomer compound layer with good resistance to oxidation risks and stone attacks, can also be envisioned. Without limiting the invention in any way, even a relatively stiff groove bottom elastomer compound layer already used in some layers (e.g., sidewall layers) for constructing tires can be envisioned, for example.

[0038] The main features of this invention make up the tire of this invention, which improves lateral stiffness due to the dynamic performance of the tread layer and due to the appropriate radial distribution of the layer, thereby improving, for example, the performance trade-off between handling and rolling resistance.

[0039] Other features associated with different embodiments of the invention contribute to further improving the tire performance trade-off. Typically, these features relate to the geometry and / or dynamic properties of the elastomeric compound layer at the bottom of the grooves.

[0040] In an optional and advantageous embodiment, for a groove or each groove, the tread includes a groove-below volume that extends radially from the bottom surface of the groove to the bottom of the groove-below volume and axially between the various continuations of the walls of the groove or each groove, the groove-below volume or each groove-below volume including a groove-bottom elastomeric compound layer.

[0041] In the meridional section, each groove is defined axially by two sidewalls, for example, in a V-shape, which can form an angle with the radial direction, for example, between 0° and 30°, and extend toward the inside of the tire. The bottom of the groove is defined by the surface connecting the two sidewalls. The bottom of the groove is in contact with the surrounding environment, particularly with the surrounding air. The radial depth of the groove is the distance from the tread surface to the bottom of the groove at its center.

[0042] In a groove, or each groove, the volume below the groove is taken into account, which is defined radially outward by the bottom of the groove and radially inward by a first interface encountered radially inward from the bottom of the groove, such as with the tread, tread sublayer, or crown reinforcement. The volume below the groove is axially defined by the radially inward continuation of the wall that defines the groove or each groove.

[0043] Therefore, in some embodiments, the trench bottom elastomeric compound layer is entirely contained within the trench lower volume. In variations of these embodiments, the trench lower volume contains only the trench bottom elastomeric compound layer. In another variation of these embodiments, the trench lower volume contains the trench bottom elastomeric compound layer and another elastomeric compound layer. In other embodiments, the trench bottom elastomeric compound layer exists both within and outside the trench lower volume, for example, axially outside the continuation of the wall defining the trench.

[0044] The aforementioned features, which are related to the geometry of the groove bottom elastomer compound layer by defining the position, axial width, and maximum radial thickness of the groove bottom elastomer compound layer in the tread, allow the volume of the groove bottom elastomer compound layer to be defined.

[0045] The total volume of the elastomer compound at the bottom of the groove corresponds to the sum of the integrals of the surface areas of each part in the meridional plane over the complete circumference of the wheel.

[0046] Advantageously, the elastomeric compound layer at the bottom of the groove has a viscoelastic loss Tan(δ3) and the tread has a viscoelastic loss Tan(δ4), Tan(δ3) being strictly less than Tan(δ4), preferably, Tan(δ3) being strictly less than 0.75xTan(δ4), and even more preferably, Tan(δ3) being strictly less than 0.5xTan(δ4), Tan(δ3) and Tan(δ4) being measured at 23°C at a frequency of 10 Hz and a strain of 10% under alternating shear stress.

[0047] In addition to improving handling, this feature also allows for maintaining low rolling resistance.

[0048] In an optional and advantageous embodiment that can improve handling, the tread has a dynamic shear modulus G4* measured at 23°C, at a frequency of 10 Hz and a strain of 10% under alternating shear stress, wherein G3* is greater than or equal to G4*, and preferably G3* is strictly greater than G4*.

[0049] In some optional and advantageous implementations, G4* is strictly smaller than G2*.

[0050] In some optional and advantageous implementations, G4* is strictly greater than G1*.

[0051] In some optional and advantageous implementations, G3* is strictly smaller than G2*.

[0052] According to an optional and advantageous embodiment, the elastomeric compound layer at the bottom of the trench is formed by several axially spaced portions, each located below the trench. This embodiment is shown in... Figure 1 In the middle. Located below the trench is understood to mean that the portion is arranged at least partially radially aligned with the trench in question.

[0053] Advantageously, the axial width of at least a portion of the elastomeric compound layer at the bottom of the trench is at least 50% equal to the axial width of the trench in that portion.

[0054] In a variant of this implementation, the cover layer is axially continuous between the two shoulders of the tire.

[0055] In example Figure 2 In the alternative variant shown, the cover layer is formed by several axially spaced portions, and the cover layer is discontinuous below the trench.

[0056] In one variant, the base layer is formed by several axially spaced sections, and the base layer is discontinuous below the trench. This configuration is shown in... Figure 7 In some configurations of this variant, the elastomeric compound layer at the bottom of the trench is located axially between two portions of the base layer.

[0057] In a variant configuration where the cover layer is formed by several axially separated sections, the elastomeric compound layer at the bottom of the trench is located axially between the two sections of the cover layer.

[0058] Advantageously, the tread includes grooves numbered NBS, ESCi is the radial thickness of the elastomeric compound at the bottom of groove i, measured at a first point in the middle of the radial outer contour of the bottom of groove i and at a second point radially inward, flush with the reinforcement of the first composite layer encountered in the tire crown, the first and second points being located on the same radial straight line, ESC being the maximum value of ESCi for i from 1 to NBS, the radial thickness of the elastomeric compound layer at the bottom of the groove, measured at the midpoint of its radial outer contour in the groove, is within the range of [20%; 100%] of ESC, preferably within the range of [50%; 100%] of ESC, the radial thickness being measured between the first point and the point at the intersection of the radial inner contour of the elastomeric compound layer at the bottom of the groove and the radial straight line passing through the first point.

[0059] Taking the radial thickness ESCi into account, it is measured at a first point in the middle of the profile at the bottom of groove i and a second point flush with the reinforcement of the first composite layer encountered in the tire crown, both points lying on the same radial line. The encountered composite layer consists of mutually parallel reinforcements coated with an elastomer compound. Here, the encountered first composite layer should be understood as referring radially from the outer side of the tire towards the inner side. Of course, the ESCi value can vary from one groove to another, but according to the invention, the maximum value of the ESCi value determines the radial thickness of the elastomer compound layer at the bottom of the groove.

[0060] In some embodiments, the first composite layer encountered in the radial direction toward the inside of the tire is a hoop ply with fabric reinforcement, but in other cases, the composite layer may include reinforcement made of steel or nylon coated with an elastomer compound.

[0061] The ESC value indicates the distance between the reinforcement of the first composite layer encountered and the tire's external environment. This thickness of the elastomer compound serves to protect the reinforcement of the first composite layer from the effects of the external environment. Many different types of attacks can occur from the external environment, such as oxidation of metal reinforcements due to oxygen attack, or damage to fabric reinforcements by stones that may enter the grooves.

[0062] The inventors have set a preferred minimum value for the thickness ESC. It is preferably greater than 1.0 mm. Below 1.0 mm, the ESC of the protective layer thickness is at risk of not being able to resist oxidation of the metal reinforcement, while above 3.5 mm, the thickness may impair rolling resistance.

[0063] To improve rolling resistance and simultaneously improve lateral stiffness, wedge-shaped elements can be used in the worn portion of the tread. According to... Figure 3 In one embodiment shown, the tread includes tread pattern blocks separated by substantially circumferentially oriented grooves. An axially oriented overlay facing some of the tread pattern blocks extends radially outward by at least one reinforcing element extending radially from the radially outer surface of the overlay toward the outer side of the tread to a radial height greater than 50% of the radial thickness of the tread. The reinforcing element has a variable axial width that varies from a maximum value and decreases radially upward, the maximum value being less than 50% of the axial width of the tread pattern blocks.

[0064] Preferably, the bottom layer of the groove is based on the same chemical composition as the layer on the sidewall.

[0065] To further optimize tire rolling resistance without adversely affecting industrial costs, a groove bottom elastomer compound layer with the same chemical composition used in the sidewall layer can be used. Since the groove bottom elastomer compound layer is not designed to contact the road surface, its mechanical and viscoelastic properties are suitable for its intended purpose. Furthermore, depending on its chemical composition, the sidewall has the ability to withstand external ozone exposure; these properties are suitable for the bottom of the grooves, which are themselves in contact with the surrounding environment. When using a sidewall elastomer, manufacturing can be better standardized, thus maintaining industrial costs, because the additional groove bottom specification of the elastomer is eliminated.

[0066] Preferably, the elastomeric compound layer at the bottom of the trench has a rubber composition based on at least one blend of polyisoprene (natural rubber) and polybutadiene; a crosslinking system; and a reinforcing filler having a total content of at most 45 phr, and containing carbon black with a content of at most 5 phr and a main silica with a content of at least 20 phr and at most 40 phr.

[0067] The chemical composition defined above is inferred from the chemical composition of the low-hysteresis sidewall layer, whose filler is mainly silica.

[0068] Alternatively, the elastomeric compound layer at the bottom of the trench has a rubber composition based on at least one blend of polyisoprene (natural rubber) and polybutadiene; a crosslinking system; and reinforcing fillers, the total content of which is at most 45 phr, and includes carbon black in a content of at least 20 phr and at most 40 phr.

[0069] In this case, the chemical composition defined above is inferred from the chemical composition of the low-hysteresis sidewall layer, where the filler is mainly carbon black.

[0070] Other features of the invention relate to the dynamic properties of the elastomeric compound of the tread layer.

[0071] Preferably, G3* is greater than or equal to 2 MPa, and more preferably greater than or equal to 4 MPa.

[0072] Preferably, G1* is less than or equal to 0.6 MPa.

[0073] Preferably, the viscoelastic loss Tan(δ1) of the substrate is less than or equal to 0.15, and Tan(δ1) is measured at 23°C with a frequency of 10 Hz and a strain of 10% under alternating shear stress.

[0074] Advantageously, G2* is greater than or equal to 7 MPa, preferably greater than or equal to 12 MPa.

[0075] Preferably, the viscoelastic loss Tan(δ2) of the capping layer is less than or equal to 0.35, and Tan(δ2) is measured at 23°C under alternating shear stress at a frequency of 10 Hz and a strain of 10%. Preferably, Tan(δ2) is greater than or equal to 0.25.

[0076] Advantageously, the dynamic shear modulus G4* of the tread elastomer compound is strictly less than 4.0 MPa, preferably strictly less than 2.5 MPa, and G4* is measured at 23°C under alternating shear stress at a frequency of 10 Hz and a strain of 10%.

[0077] Preferably, Tan(δ3) is greater than or equal to 0.15 and less than or equal to 0.25.

[0078] Preferably, Tan(δ4) is greater than or equal to 0.15 and less than or equal to 0.25.

[0079] According to one embodiment of the present invention, in Figure 4As can be seen, the tread includes at least one tread portion, hereinafter referred to as a tread sidewall, at at least one axial end of the tread, and a central tread portion disposed axially inside the tread sidewall, the tread sidewall having an axial outer contour defined by a first point and a second point, the first point being located at the intersection of the axial and radial outer contours of the sidewall and the axial and radial outer contours of the tread, the second point being located at a curve distance between 5% and 25% of the nominal section width of the tire of this size, the tread sidewall contacting the overlay on its inner side.

[0080] Preferably, the presence of tread sidewalls allows for further improvement in rolling resistance by replacing the end portions of the tread with an elastomer material that exhibits lower hysteresis than the elastomer material in the central portion of the tread. Therefore, the dynamic shear modulus of the tread sidewalls is at most 80% of the dynamic shear modulus of the central portion of the tread, the dynamic shear modulus value being measured at 23°C under alternating shear stress at a frequency of 10 Hz and a strain of 10%.

[0081] Preferably, the viscoelastic loss Tan(δ) of the tread sidewall is at most equal to 80% of the viscoelastic loss of the central tread portion. The viscoelastic loss Tan(δ) and the viscoelastic loss of the central tread portion are measured at 23°C under alternating shear stress at a frequency of 10 Hz and a strain of 10%. Attached Figure Description

[0082] The invention will be better understood by reading the detailed description of the embodiments, which are considered to be completely non-limiting examples and are illustrated with reference to the accompanying drawings, wherein: - Figure 1 A schematic meridional section of a tire according to a first embodiment of the invention is shown, the tire having a discontinuous tread base elastomeric compound layer, the tread base elastomeric compound layer being in the form of multiple portions located below the grooves. The overlay is continuous axially from one shoulder of the tire to the other; - Figure 2 A schematic meridional section of a tire according to a second embodiment of the present invention is shown, the tire still having a discontinuous tread bottom elastomer compound layer in the form of multiple portions located below the grooves, but in this case the overlay is discontinuous and divided into multiple portions; - Figure 3 A schematic meridional section of a tire according to a third embodiment of the invention is shown, the tire having a discontinuous tread bottom elastomer compound layer in the form of multiple portions located below the grooves. The overlay is also divided into multiple portions, but has wedge-shaped reinforcing elements protruding to the tread; - Figure 4A schematic diagram of a tire according to a fourth embodiment of the present invention is shown; - Figure 5 yes Figure 1 An enlarged view of the tread portion of the tire, showing the dimensions of the tread; - Figure 6 and Figure 7 Schematic diagrams of tires according to the fifth and sixth embodiments of the present invention are shown respectively; and - Figure 8 It describes tires using existing technology. Detailed Implementation

[0083] The present invention is studied in more detail in the case of a passenger vehicle tire with the standardized name 245 / 45 R18 XL100W according to ETRTO (European Technical Organization for Tires and Rim).

[0084] In the various figures, the same or similar elements are marked with the same reference numerals. Considering the symmetry of the tread, in order to make the figures easy to read, in principle, elements may be marked only once on one side of the meridional plane.

[0085] Figure 1 A tire 1, an equatorial plane CP, two bead 50s, and two sidewalls 3 each connected to the bead 50s are shown according to a first embodiment of the invention. The tire has a crown 4, which has a crown reinforcement 20, a tread 6, and sub-ply 7. The tread 6 extends axially from one shoulder 60 to the other shoulder 60. The tread 6 includes a tread surface 61 intended to contact the road surface when the tire 1 is in motion. The tread 6 has tread blocks 63 separated by NBS grooves 62, which are oriented substantially circumferentially, in which case NBS=4. Each groove 62 is defined radially inwardly by a groove bottom 620 and axially by two walls 621, 622 extending from the tread surface 61 to the groove bottom 620. For each groove 62, the crown 4 includes a groove-below volume that extends radially from the groove bottom 620 to the bottom of the groove-below volume and axially between the various continuations of the walls 621, 622.

[0086] Bead 50 includes at least one carcass layer (in Figure 1 (Seen in dashed lines). The carcass ply is formed of reinforcements coated with an elastomeric compound. The carcass ply includes a main portion 53 that joins two bead 50 together, the main portion 53 being wound around a circumferential reinforcing element (referred to as bead line 51) typically made of metal from the inside to the outside of the tire in each bead, thereby forming a crimp 52. The reinforcements of the carcass ply are substantially parallel to each other and form an angle between 85° and 95° with respect to the circumferential direction.

[0087] As is known per se, the crown reinforcement 20 has a multi-layer cord or multi-layer monofilament reinforcement, which is typically coated with a thin rubber layer. The crown reinforcement 20 includes two cross layers 22 and 23, each comprising a reinforcement coated with an elastomeric compound. The reinforcements of the cross layers 22 and 23 form an angle between 10° and 45° with respect to the circumferential direction. A third reinforcement layer 21 encircles the first two layers. This layer 21 also comprises a reinforcement coated with an elastomeric compound, forming an angle of approximately ±2.5° with respect to the circumferential direction.

[0088] Sub-layer 7 is arranged radially outward of the crown reinforcement 20 and radially inward of the tread 6. This sub-layer 7 comprises a base layer 71, a cover layer 72, and a final groove bottom elastomer compound layer 73. Here, the bottom of the volume below the groove is formed by the interface between the groove bottom elastomer compound layer 73 and the cover layer 72.

[0089] The base layer 71 is disposed directly on the crown reinforcement 20 in the radial direction. The base layer 71 is continuous in the axial direction between the two shoulders 60. In the embodiment described herein, the base layer 71 is disposed directly on the crown reinforcement 20 in the radial direction, i.e., the base layer 71 contacts the outermost radial layer of the crown reinforcement 20.

[0090] The base layer 71 has a dynamic shear modulus G1* and viscoelastic loss Tan(δ1) measured at 23°C, 10 Hz, and 10% strain under alternating shear stress. G1* is less than or equal to 1.5 MPa, preferably less than or equal to 0.6 MPa. Tan(δ1) is less than or equal to 0.15.

[0091] Table 1 below describes an example formulation for base layer 71 with a dynamic shear modulus G1* equal to 0.2 MPa.

[0092] Table 1 The formula is given by weight (phr means percentage of elastic body weight).

[0093] Cover layer 72 is disposed radially outward of base layer 71. Cover layer 72 is axially continuous between the two shoulders 60. Cover layer 72 is located radially inward of tread 6. In this first embodiment, cover layer 72 is axially continuous between the two shoulders 60.

[0094] The capping layer 72 has a dynamic shear modulus G2* and viscoelastic loss Tan(δ2) measured at 23°C, 10 Hz, and 10% strain under alternating shear stress. G2* is greater than or equal to 5 MPa, preferably greater than or equal to 7 MPa, and even more preferably greater than or equal to 12 MPa. Tan(δ2) is less than or equal to 0.35 and greater than or equal to 0.25.

[0095] Table 2 below describes an example formulation for a capping layer with a dynamic shear modulus G2* equal to 25 MPa.

[0096] Table 2 The formula is given by weight (phr means percentage of elastic body weight).

[0097] The tread 6 has a dynamic shear modulus G4* and viscoelastic loss Tan(δ4) measured at 23°C, 10 Hz, and 10% strain under alternating shear stress. G4* is strictly less than 4.0 MPa, preferably strictly less than 2.5 MPa. Tan(δ4) is less than or equal to 0.25 and greater than or equal to 0.15.

[0098] Table 3 below provides a formulation example for tread layer 6.

[0099] Table 3 The formula is given by weight (phr means percentage of elastic mass), where: (a) SBR, containing 27% styrene; 1,2-butadiene: 5%, cis-1,4-butadiene: 15%, trans-1,4-butadiene: 80%; Tg: -48°C (b) is silica “Zeosil 1165MP” from Solvay, with a BET surface area of ​​160 m². 2 / g (c) is the silane TESPT "SI69" from Evonik. (d) is Shell's TDAE oil "Flexon 630". (e) is the resin "Escorez 2173" from Exxon. (f) is the antioxidant "Santoflex 6PPD" from Solutia. (g) is the promoter "Santocure CBS" from Solutia.

[0100] The volume beneath each trench includes a trench bottom elastomer compound layer 73. The trench bottom elastomer compound layer 73 is formed by several axially spaced portions, each portion located below the trench 62. The width of each portion of the trench bottom elastomer compound layer 73 is at least 50% of the axial width of the trench 62 of that portion. The trench bottom elastomer compound layer 73 has a dynamic shear modulus G3* and viscoelastic loss Tan(δ3) measured at 23°C, at a frequency of 10 Hz, and with a strain of 10%. G3* is greater than or equal to 2 MPa, preferably greater than or equal to 4 MPa. Tan(δ3) is less than or equal to 0.25 and greater than or equal to 0.15.

[0101] For the elastomeric compound layer 73 at the bottom of the trench, use the formulation described in Table 4.

[0102] Table 4 Tan(δ3) and Tan(δ4) satisfy Tan(δ3) < Tan(δ4), preferably Tan(δ3) < 0.75xTan(δ4), and even more preferably Tan(δ3) < 0.5xTan(δ4). G1* and G3* satisfy G3* being strictly greater than 1.25xG1*. G3* is also greater than or equal to G4*, preferably G3* being strictly greater than G4*. It can also be noted that G4* is strictly less than G2*, G4* is strictly greater than G1*, and G3* is strictly less than G2*.

[0103] refer to Figure 5 The ring ply 21 includes a reinforcement 24 coated with an elastomeric matrix. Thicknesses ESC1 and ESC2 can be seen below the groove, which are measured radially from a first point to a second point radially inward at the bottom of the groove 62. The first point is located at the midpoint of the radially outer contour at the bottom of the groove, and the second point is flush with the reinforcement 24 of the first composite layer encountered in the tread of the tire 1. The first and second points lie on the same radial straight line. ESC is the maximum value of ESC1 and ESC2. ESC is greater than 1.0 mm and less than 3.5 mm. Here, ESC = ESC2 = 2.0 mm.

[0104] The radial thicknesses of the layers 71, 72, and 73 of sub-layer 7 are designated as E71, E72, and E73, respectively. The tread 6 has a thickness EKM. The radial thickness E73 of the groove bottom elastomer compound layer 73 is measured between a first point and the point where the radial inner profile of the groove bottom elastomer compound layer 73 intersects with a radial straight line passing through the aforementioned first point. The radial thickness E73 measured at the midpoint of the radial outer profile of each groove 62 falls within the [20%; 100%] range of ESC, preferably within the [50%; 100%] range of ESC. In this case, E73 = 0.8 mm.

[0105] Now refer to Figure 2 Describing a tire according to a second embodiment. In this figure, elements similar to those in the first embodiment are indicated by the same reference numerals. The cover layer 72 is formed by several axially spaced portions. The cover layer 72 is discontinuous below the groove 62. Each portion of the groove bottom elastomer compound layer 73 is axially inserted between two portions of the cover layer 72. In each groove 62, the groove bottom elastomer compound layer 73 extends radially from the groove bottom 620 to the base layer 71, thereby interrupting the cover layer 72. Here, the bottom of the volume below the groove is formed by the interface between the groove bottom elastomer compound layer 73 and the cover layer 72.

[0106] Now refer to Figure 3 Describing a tire according to a third embodiment. In this figure, elements similar to those in the preceding embodiments are indicated by the same reference numerals. Like the cover layer 72, the groove bottom elastomer compound layer 73 includes axially spaced portions. Each portion of the groove bottom elastomer compound layer 73 is radially located below the groove 62. Furthermore, each portion of the groove bottom elastomer compound layer 73 extends axially beyond the continuation of the walls 621, 622, such that the groove bottom elastomer compound layer 73 exists within and reaches the exterior of the groove bottom volume. The portions of the groove bottom elastomer compound layer 73 are axially arranged between the two portions of the cover layer 72. Before and after each groove 62, a reinforcing element 630 extends the cover layer 72 axially toward the tread block 63. The reinforcing element 630 extends from the radially outer surface of the cover layer 72 toward the outer side of the tread 6 to a certain radial height, in this case extending to the tread surface 61, said radial height being greater than 50% of the radial thickness of the tread 6. Each reinforcing element 630 has a variable axial width, which varies from a maximum value less than 50% of the axial width of the tread block. The axial width decreases radially outward.

[0107] Now refer to Figure 4A tire according to a fourth embodiment is described. In this figure, elements similar to those in the preceding embodiments are indicated by the same reference numerals. Unlike the second embodiment, the tire 1 according to the fourth embodiment includes a tread 6, the tread 6 including at least one tread portion 90 at at least one axial end of the tread 6, and a central portion of the tread 6, the tread portion 90 being hereinafter referred to as tread flanks 90 of the tread 6, the central portion being disposed axially inward of each flank 90. ​​Each flank 90 has an axial outer profile defined by a first point and a second point, the first point being located at the intersection of the axial and radial outer profiles of the sidewall 3 and the axial and radial outer profiles of the tread 6, and the second point being located at a curve distance between 5% and 25% of the nominal section width of the tire 1 of this size. Each flank 90 contacts a cover layer 72 radially inward. The dynamic shear modulus of each flank 90 of the tread 6 is at most equal to 80% of the dynamic shear modulus G4* of the central portion of the tread 6. The viscoelastic loss Tan(δ) of each flank 90 is at most equal to 80% of the viscoelastic loss Tan(4) of the central portion of the tread 6.

[0108] Now we will refer to each Figure 6 and Figure 7 The figures depict tires according to the fifth and sixth embodiments. In these figures, elements similar to those in the aforementioned embodiments are indicated by the same reference numerals.

[0109] In the tires according to the fifth and sixth embodiments, the groove bottom elastomer compound layer 73 is based on the same composition as the layer composition of the sidewall 3.

[0110] According to Figure 7 In the tire of the sixth embodiment, the base layer 71 and the cover layer 72 are each formed by several axially spaced portions, and the base layer 71 and the cover layer 72 are discontinuous below the groove 62. Furthermore, the groove bottom elastomer compound layer 73 extends radially from the groove bottom 620 to the crown reinforcement 20, thereby interrupting the base layer 71 and the cover layer 72. Here, the bottom of the volume below the groove is formed by the interface between the groove bottom elastomer compound layer 73 and the crown reinforcement 20. Therefore, the groove bottom elastomer compound layer 73 is axially located between the two portions of the base layer 71 and the cover layer 72.

[0111] Figure 8 The existing tires in the present technology have sub-layers comprising two layers 71 and 72. The elastomeric compound of the bottom groove layer is the elastomeric compound of the tread 6.

[0112] Those skilled in the art, as tire designers, can employ variations of the tread itself, which may include several different materials stacked in the radial direction and / or juxtaposed in the axial direction.

[0113] Comparative Test Tires P1, P2, P3, and P4 of the present invention were tested to clearly highlight the performance aspects provided by the present invention. The results of these evaluation tests were compared with those obtained from control tires T and T'.

[0114] The tires P1, P2, P3, and P4 according to the invention, as well as the control tires T and T', are each tires intended for use in passenger vehicles, with a reference pressure of 290 kPa and a size equal to 245 / 45 R18 XL 100W. The tread comprises a tread reinforcement, sub-layers, and a tread. The sub-layers comprise a base layer radially outer of the tread reinforcement and a cover layer radially outer of the base layer and radially inner of the tread. The sub-layers also include a groove bottom elastomeric compound layer.

[0115] The elastomeric compound layer at the bottom of the grooves of tire T is the elastomeric compound of the tread, while the elastomeric compound layer at the bottom of the grooves of tire T' is the elastomeric compound of the base layer. The elastomeric compound layer at the bottom of the grooves of tire T extends radially from the bottom of the grooves to the base layer, thus interrupting the overlay, while the elastomeric compound layer at the bottom of the grooves of tire T' extends radially from the bottom of the grooves to the crown reinforcement, thus interrupting both the base layer and the overlay.

[0116] Tires P1 and P4 according to the invention include a groove bottom elastomeric compound layer 73 extending radially from the groove bottom 620 to the base layer 71, thereby interrupting the cover layer 72. Tires P2 and P3 according to the invention include a groove bottom elastomeric compound layer 73 extending radially from the groove bottom 620 to the crown reinforcement 20, thereby interrupting the base layer 71 and the cover layer 72.

[0117] The dynamic characteristics of tires P1 to P4 according to the present invention and control tires T and T' are summarized in Table 5.

[0118] The rolling resistance RRT and lateral stiffness Dz of tires P1 to P4 according to the present invention and control tires T and T' were simulated using the finite element method. The results are shown in Table 5, where the performance of control tire T is used as the base number 100.

[0119] In Table 5, values ​​below 100 indicate a deterioration in performance. Conversely, values ​​above 100 indicate an improvement in performance.

[0120] Table 5 These results confirm that tires P1 to P4, with the required dynamic performance in the groove bottom elastomer compound layer, exhibit improved performance in terms of lateral stiffness Dz. Furthermore, compared to the control tire T, the trade-off between lateral stiffness Dz and rolling resistance RRT is improved. This invention is not limited to the embodiments described above.

Claims

1. A tire (1) for a motor vehicle, the tire (1) comprising a crown (4), the crown (4) comprising a crown reinforcement (20), sub-layers (7) and a tread (6), the tread (6) comprising grooves (62) oriented substantially circumferentially; the sub-layers (7) having a base layer (71) radially outer of the crown reinforcement (20) and a cover layer (72) radially outer of the base layer (71) and radially inner of the tread (6); the base layer (71) having a dynamic shear modulus G1* less than or equal to 1.5 MPa; the cover layer (72) having a dynamic shear modulus G2* greater than or equal to 5 MPa; the tire (1) characterized in that a groove bottom elastomer compound layer (73) is radially located inside the outer contour of the tread (6), the dynamic shear modulus G3* of the groove bottom elastomer compound layer (73) being strictly greater than 1.25 x G1*; G1*, G2* and G3* were measured at 23°C with a frequency of 10 Hz and a strain of 10% under alternating shear stress.

2. The tire (1) according to the preceding claim, wherein, The bottom elastomer compound layer (73) of the groove has a viscoelastic loss Tan(δ3) and the tread (6) has a viscoelastic loss Tan(δ4), Tan(δ3) being strictly less than Tan(δ4), preferably, Tan(δ3) being strictly less than 0.75xTan(δ4), and even more preferably, Tan(δ3) being strictly less than 0.5xTan(δ4), Tan(δ3) and Tan(δ4) being measured at 23°C at a frequency of 10 Hz and a strain of 10% under alternating shear stress.

3. The tire (1) according to any one of the preceding claims, wherein, The bottom elastomer compound layer (73) of the trench is formed by several axially spaced portions, each located below the trench (62).

4. The tire (1) according to the preceding claim, wherein, The axial width of at least a portion of the bottom elastomer compound layer (73) of the groove is at least 50% equal to the axial width of the groove (62) of that portion.

5. The tire (1) according to any one of claims 1 to 4, wherein, The cover layer (72) is continuous in the axial direction between the two shoulders (60) of the tire (1).

6. The tire (1) according to any one of claims 1 to 4, wherein, The cover layer (72) is formed by several axially spaced portions, and the cover layer (72) is discontinuous below the trench (62).

7. The tire (1) according to any one of the preceding claims, wherein, The base layer (71) is formed by several axially spaced portions, and the base layer (71) is discontinuous below the trench (62).

8. The tire (1) according to any one of the preceding claims, wherein, The tread includes grooves numbered NBS, ESCi is the radial thickness of the elastomeric compound at the bottom of groove i, the radial thickness being measured at a first point in the middle of the radial outer contour of the bottom of groove i and at a second point on the radial inner side flush with the reinforcement of the first composite layer encountered in the tread of the tire, the first point and the second point being on the same radial straight line, ESC being the maximum value of ESCi for i from 1 to NBS, the radial thickness (E73) of the elastomeric compound layer (73) at the midpoint of its radial outer contour in the groove (62) being within the range of [20%; 100%] of ESC, preferably within the range of [50%; 100%] of ESC, the radial thickness (E73) being measured between the first point and the point at the intersection of the radial inner contour of the elastomeric compound layer (73) at the bottom of the groove and the radial straight line passing through the first point.

9. The tire (1) according to any one of the preceding claims, wherein, The tread (6) comprises tread blocks (63) separated by grooves (62) oriented substantially circumferentially. A cover layer (72) facing some of the tread blocks (63) extends radially outward by at least one reinforcing element (630) extending radially from the radially outer surface of the cover layer (72) toward the outside of the tread (6) to a radial height greater than 50% of the radial thickness of the tread (6). The reinforcing element (630) has a variable axial width that varies from a maximum value and decreases radially outward, the maximum value being less than 50% of the axial width of the tread blocks.

10. The tire (1) according to any one of the preceding claims, wherein, The bottom layer (73) of the groove is based on the same chemical composition as the layer of the sidewall (3).

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