Tyre having optimized rolling resistance performance

Abstract

The proposed invention describes a tyre (1) having a crown (7) comprising a crown reinforcement (17) and a tread (30), the tread (30) comprising elastomeric compounds having a glass transition temperature, the tread (30) comprising a tread layer (29) intended to come into contact with the ground and a base underlayer (21). The material of the tread layer (29) has a glass transition temperature TgCR, and the material of the base underlayer (21) comprises an elastomeric material having a glass transition temperature TgSCB. The elastomeric materials of the tread (30) of the tyre (1) have glass transition temperatures of which the difference TgSCB-TgCR is less than or equal to -10°C.

Description

Tire with optimized rolling resistance performance Scope of the invention

[0001] The invention relates to tires, and more particularly to passenger car tires intended for use in temperate temperature ranges. Previous technique

[0002] A tire is an object with a revolution geometry, essentially toroidal, about an axis of revolution, the axis of revolution coinciding with the tire's axis of rotation. A tire comprises two beads for mounting on a rim, two sidewalls connected to the beads, and a crown. The crown includes a tread for contacting the ground and a crown reinforcement, the tread being arranged radially externally to the crown reinforcement. One axial side of the crown is connected to the radially external end of one of the two sidewalls, and the other axial side of the crown is connected to the radially external end of the other sidewall.

[0003] Documents EP2452834A2, WO2021 / 260335A1 and FR3115498A1 describe state-of-the-art tires.

[0004] The tread comprises at least one layer of polymeric material, that is, a material comprising at least one elastomeric material, at least one reinforcing filler, and a crosslinking system. Typically, the tread is made of a single elastomeric compound. A common characteristic property of an elastomeric compound is its glass transition temperature (Tg), which corresponds to the temperature at which the viscoelastic loss of the material reaches its maximum. The viscoelastic loss of the material, measured according to ASTM D-5992-96, impacts both the tire's grip performance and its rolling resistance performance. Those skilled in the art must necessarily find a balance between these two performance characteristics without being able to improve the compromise itself.

[0005] Document WO2019145621 describes a tire with a tread comprising a tread layer and a sub-layer. The sub-layer is arranged radially externally to the crown reinforcement and radially internally to the tread layer, the tread layer being designed to enter in contact with the ground. The sub-layer and the wearing course each comprise an elastomeric mixture having a distinct dynamic shear modulus G* measured at 23°C in order to shift the performance trade-off between rolling resistance and drift stiffness.

[0006] By minimizing the hysteresis loss of the material measured at 23°C at 10 Hz and under a 10% alternating shear strain, the WO2019145621 tire does not allow for an optimal compromise between grip and rolling resistance. However, for certain applications, particularly passenger car tires, a technical solution is needed to meet the demands of the tire market.

[0007] Thus, the essential goal of the invention is to find a compromise between grip performance and rolling resistance over a wide range of tire operating temperatures. Description of the invention

[0008] This goal was achieved by a tire comprising a crown, the crown comprising a crown reinforcement and a tread, the tread being arranged radially externally to the crown reinforcement, the tread comprising: - a wearing course intended to come into contact with the ground via a tread surface and comprising an elastomeric material having a glass transition temperature TgCR, - a base layer arranged radially externally to the top reinforcement and radially internally to the wearing course, the base layer comprising an elastomeric material having a glass transition temperature TgSCB, each of the glass transition temperatures TgSCB, TgCR corresponding to a maximum viscoelastic loss, the viscoelastic loss being measured according to ASTM D-5992-96 at a frequency of 10Hz and according to a temperature sweep, and the difference of the subtraction of TgCR from TgSCB being less than or equal to -10°C (TgSCB - TgCR<-10°C), preferably at -15°C and very preferably at -20°C.

[0009] By assigning the elastomeric compounds of the tread and base layer a glass transition temperature (Tg) as described previously, the trade-off between rolling resistance and grip can be adjusted remarkably well over a wide range of tire operating temperatures. Indeed, although the base layer is not in contact with the road surface, its physical properties influence tire grip.

[0010] In a specific embodiment, and by amplifying the glass transition temperature difference beyond -10°C, the tire offers an even better compromise between rolling resistance and grip over a correspondingly wider temperature range. This extended temperature range, in addition to being positioned relative to daily temperature variations, allows for full consideration of seasonality. This aspect therefore provides a clear advantage in controlling vehicle fuel consumption over a year of use. Typically, seasonal temperature variations in a temperate climate region are at least 15°C.

[0011] In a particular and optional embodiment, the base sublayer comprises a plurality of elastomers juxtaposed radially and / or axially to form the base sublayer.

[0012] As is well known to those skilled in the art, the viscoelastic loss of the elastomeric compound in the tread is a parameter influencing its grip potential. Specifically, the higher the viscoelastic loss, the better the grip. Conversely, high viscoelastic loss, linked to material hysteresis, increases rolling resistance, thus reducing the product's performance. In other words, the lower the viscoelastic loss, the lower the rolling resistance.

[0013] Regarding adhesion performance, the glass transition represents the operating temperature of the material at which maximum energy dissipation occurs. The closer the surface layer's service temperature is to the glass transition, the stronger the material's adhesion potential. Regarding rolling resistance performance, a shift towards a A lower temperature of the glass transition of the base layer material allows, for a given temperature range of use, to reduce on average the energy losses due to the hysteresis of the material.

[0014] Since the base layer is arranged radially within the tread layer, it is not in direct contact with the ground and therefore has a lesser impact on grip performance. Thus, the properties of the tread base layer can be determined to minimize rolling resistance. According to the invention, by shifting the base layer temperature (TgSCB) to a lower temperature than the tread temperature (TgCR), rolling resistance is improved while maintaining a TgCR temperature that allows for undegraded grip performance. Furthermore, according to the invention, by increasing the TgCR temperature relative to TgSCB, grip performance is improved while limiting the impact on rolling resistance.This improvement in the compromise of said performance is therefore possible thanks to the complementarity and coupling between the base layer and the tread layer, if the temperature difference of the glass transitions respective to each of the tread materials is adapted to the operation and use of the tire.

[0015] The inventors observe that a temperature difference of at least 10°C in the glass transition temperature is necessary for the improvement in the performance compromise to be significant and thus advantageously extend the operating range of the desired performance compromise over real-world tire operating temperatures. In other words, an elastomeric material exhibits a stable region of viscoelastic loss with a lower value compared to the region near the TgSCB temperature. As this stable region shifts towards lower temperatures, the elastomeric material designer can adjust it to match the actual operating temperature range in order to control rolling resistance and grip across the entire extended temperature range.

[0016] "Real-world use" refers to tire usage that takes into account a wide temperature range, which may include both temperature variations throughout the day and the effects of seasonality. For example, it is common in a temperate regions like Europe can observe temperatures varying by more than 10°C in a single day and by more than 20°C over several months.

[0017] To determine the glass transition temperature (Tg) of an elastomer, it is necessary to first determine the viscoelastic loss (TD) of the elastomer over a temperature range, the viscoelastic loss (TD) being deduced from the complex shear modulus (G*). The measurements are made, for example, on one or more test specimens extracted from the tire.

[0018] The complex shear modulus G* is a well-known dynamic property for those skilled in the art and is measured on a Metravib VA4000 viscoanalyzer. The response of specimens subjected to sinusoidal alternating simple shear loading at a frequency of 10 Hz is recorded under specific temperature conditions according to ASTM DI 349-99, until a stress representative of the operating point of the elastomeric material in the tire is reached, in this case 0.7 MPa. A strain amplitude sweep is performed from 0.1% to 100% (forward cycle), then from 100% to 0.1% (reverse cycle). The specimen is preferably of cylindrical cross-section as described in ASTM D 5992-96 (version published in September 2006, originally approved in 1996) in Figure X2.1 (circular embodiment) and has a cross-section diameter of 10 mm [0 to +0.04 mm] and a thickness of 2 mm [1.85-2.

[20] A person skilled in the art will be able to select and adapt the dimensions of the test specimen according to the amount of accessible and available mixture, particularly when taking samples from a finished product such as a tire. The complex dynamic shear modulus G* is defined as the square root of the sum of the squares of G' and G"², where G' represents the elastic modulus and G"² represents the viscous modulus. The complex shear modulus G* is then measured at 10% strain over the forward cycle.

[0019] Viscoelastic loss TD is another well-known dynamic property. Viscoelastic loss represents the tangent of the phase angle between the force exerted on the sample and its displacement; it is equal to the ratio G" / G'. The maximum TD value of the tangent observed over the forward deformation cycle is recorded as the viscoelastic loss. Viscoelastic loss is measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric mixture having the shape of the cylindrical test specimen, subjected to sinusoidal loading in simple alternating shear, at a frequency of 10Hz, at a temperature of 23 °C and for a strain equal to 5%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

[0020] Finally, to determine the glass transition temperature (Tg) of the elastomeric material, a temperature sweep is performed using a ramp increasing by 1.5°C per minute, from a temperature (Tmin) below the glass transition temperature (Tg) of the material, up to a temperature (Tmax) that may correspond to the rubbery plateau of the elastomeric material. Before starting the sweep, the sample is stabilized at temperature Tmin for 20 minutes to ensure a homogeneous temperature within the specimen. For each temperature value, the complex dynamic shear modulus (G*) is recorded, and then the viscoelastic loss (TD) is determined. The glass transition temperature (Tg), in °C, is the value at which the viscoelastic loss (TD) is maximum.

[0021] In general, equivalent means and methods for characterizing the glass transition and the complex shear modulus G* of an elastomeric material can be determined by those skilled in the art. Thus, an equivalent measuring instrument can be used, and the dimensions of the specimen can be adjusted according to the volume of mixture available in the tire being characterized.

[0022] Axial direction means the direction parallel to the tire's rotational angle, that is, the tire's rotational angle.

[0023] Circumferential direction means the direction that is perpendicular to the axial direction and to a radius of the tire.

[0024] By radial direction, we mean the direction along a radius of the tire, that is to say any direction intersecting the rotation axis and perpendicular to this axis.

[0025] By meridian plane, we mean a plane containing the tire rotation tax.

[0026] By median plane of the tire (noted M), we mean the plane perpendicular to the rotation angle of the tire and which passes through the middle of the tread.

[0027] The circumferential equatorial plane of the tire is defined as the theoretical cylindrical surface passing through the tire's equator, perpendicular to the median plane and the radial direction. The tire's equator is, in a meridian-sectional plane... (plane containing the axis of rotation) the axis parallel to the axis of rotation of the tire is located equidistant between the outermost radial point of the tread intended to be in contact with the ground and the innermost radial point of the tire.

[0028] Radially inside and radially outside refer to the area closest to and further from the tire's axis of rotation, respectively. Axially inside and axially outside refer to the area closer to and further from the tire's median plane, respectively.

[0029] In a particular and optional embodiment, the base sub-layer extends axially continuously over at least 80% of the axial width of the wearing surface.

[0030] By increasing the volume occupied by the base layer of the tread, the tire advantageously offers, over a wide temperature range of use, an improvement in rolling resistance performance while maintaining a good compromise with grip performance.

[0031] The tire tread area is the surface of the tread through which the tire mounted on a rim comes into contact with the ground when rolling on that ground at a nominal load and pressure.

[0032] The tread width L is determined on a mounted tire, on a nominal rim, and inflated to the nominal pressure. In the case of a clear boundary between the tread and the rest of the tire, the tread width is trivially determined by a person skilled in the art. If the tread is continuous with the outer sidewall of the tire, the axial boundary of the tread passes through the point where the angle between the tangent to the tread and an axial direction YY' is equal to 30°. When there are several points on a meridian plane where this angle is equal to 30°, the radially outermost point is chosen. The tread width is equal to the axial distance between the two axial boundaries of the tread on either side of the median plane M.

[0033] In a particular and optional embodiment, the outermost radial points of the base sublayer are at a radial distance from the running surface less than the tread depth, preferably the distance between the base sublayer and the running surface is less than the tread depth over at least 50% of the axial width of the base sublayer.

[0034] A groove on a rolling surface has two main characteristic dimensions: a width and a curvilinear length, such that the curvilinear length is at least twice the width. A groove is therefore delimited by at least two main lateral faces that define its curvilinear length, and connected by a bottom face. A groove can be oriented transversely or circumferentially.

[0035] The term "tread depth" refers to the maximum depth of the grooves on a new tire. The depth of a groove is the distance between the bottom of the groove and the tread surface, with the groove forming a gap that meets the tread. The maximum depth of the grooves is the tread depth. Measuring tread depth is well-known to those skilled in the art and is easily done using a tread depth gauge.

[0036] A groove is such that the distance between the main lateral faces is such that these main lateral faces cannot come into contact with each other, especially when the tire is in new condition, during driving at nominal load and pressure.

[0037] In a particular and optional embodiment, the sculpture height is greater than or equal to 7 mm, preferably ranging from 8 mm to 16 mm.

[0038] In a particular and optional embodiment, the elastomeric material of the base layer has a viscoelastic loss less than or equal to 0.15, the viscoelastic loss being measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric mixture from the tire, subjected to sinusoidal loading in alternating simple shear, at a frequency of 10Hz, at a temperature of 23°C and for a strain equal to 10%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

[0039] Choosing to limit viscoelastic loss also improves the rolling resistance performance of the tire.

[0040] In a particular and optional embodiment, the tread comprises an intermediate sublayer extending axially in discontinuous portions, each portion of the intermediate sublayer being arranged radially externally to the base layer and radially internally to the wearing layer, each portion of the intermediate sublayer having a glass transition temperature TgSCI, the difference of the subtraction of TgCR from TgSCI (TgSCI - TgCR < -10°C) is less than or equal to -10°C, preferably -15°C, and very preferably -20°C.

[0041] Because the intermediate layer is discontinuous in portions, the volume occupied by materials with lower glass transition temperatures (TgSCB and TgSCI) relative to the wearing course material (which has a glass transition temperature of TgCR) can be increased. A rib is a raised portion of the tread in the radial direction, as opposed to a groove, which is recessed in the radial direction. Due to their delimitation by at least one circumferential groove, each rib extends substantially circumferentially. A rib can be circumferentially continuous or circumferentially discontinuous, interrupted by transverse grooves or sipes, whether these transverse grooves are blind or open into at least one circumferential groove.

[0042] In a particular and optional embodiment, the distance between the base sub-layer and the tread surface is greater than the tread height over at least 50% of the width of the base sub-layer, and the distance between the intermediate sub-layer and the tread surface is less than the tread height over at least 50%, preferably 80%, of the axial width of the intermediate sub-layer. This further increases the rigidity of the tire's crown.

[0043] Advantageously, this method of implementation maintains controlled grip performance until the regulatory wear level of the tire is reached, while also allowing for optimized road behavior.

[0044] In a particular and optional embodiment, the outermost radial points of each portion of the intermediate sub-layer are at a radial distance from the tread surface less than the radial tread depth.

[0045] In a particular and optional embodiment, the intermediate underlayer has at least one most radially outer point at a radial distance from the running surface that is less than 110% of a useful distance, the useful distance being the radial distance from the most radially outer point of the wear indicator to the running surface.

[0046] Advantageously, this embodiment maintains controlled grip performance until the regulatory wear level of the tire is reached.

[0047] Such regulatory wear indicators are mandated, for example, by United Nations regulations R30 and R54, the United States of America FMVSS139, and China GB97743, and are designed to indicate to the tire user a regulatory wear threshold beyond which driving, particularly on wet surfaces, is risky. These wear indicators are therefore referred to as regulatory wear indicators. Each regulatory wear indicator is formed by a protrusion extending radially outward from the bottom of the circumferential groove, specifically from the bottom of the deepest circumferential groove, to a radial height of approximately 1.6 mm.

[0048] In a particular and optional embodiment, the elastomeric material of the intermediate underlayer has a viscoelastic loss less than or equal to 0.35, the viscoelastic loss being measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric mixture from the tire, subjected to sinusoidal loading in alternating simple shear, at a frequency of 10Hz, at a temperature of 23°C and for a strain equal to 10%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

[0049] Choosing to limit viscoelastic loss in this way improves the tire's rolling resistance performance while minimizing the impact on grip. Since the intermediate layer is closer to the tread surface, its impact on grip is greater than that of the base layer.

[0050] In a particular and optional embodiment, the elastomeric material of the base sub-layer and the elastomeric material of the intermediate sub-layer are identical.

[0051] A performance compromise can be found so that the base sublayer and the intermediate layer can be made of the same elastomer in order to reduce material costs and limit industrial complexity.

[0052] In a particular and optional embodiment, the elastomeric material of the base sublayer has a complex dynamic shear modulus G*M1 of less than 1.5 MPa, and wherein the elastomeric material of the intermediate sublayer has a complex dynamic shear modulus G*M2 of more than 5 MPa, the complex dynamic shear moduli being measured at 10% strain according to ASTM D-5992-96, at a temperature of 23°C and at a frequency of 10Hz for the forward cycle.

[0053] Here, the complex dynamic shear modulus G*M1 of the base layer remains sufficiently low so as not to negatively impact rolling resistance. Similarly, the material of the intermediate layer has a complex dynamic shear modulus G*M2 high enough not to negatively impact the tire's traction stiffness, and may even improve it. Since the intermediate layer is discontinuous in sections, if, for example, each section is aligned with a rib, the proportion of the intermediate layer's volume relative to the tread volume can be maximized while maintaining the necessary base layer thickness. In this way, good traction stiffness is advantageously achieved, while also providing, over a wide operating temperature range, a good compromise between rolling resistance and grip performance.

[0054] In a particular and optional embodiment, the tread comprises two lateral ribs and at least one central rib, and each of the discontinuous lateral portions is positioned entirely in line with each of the two lateral ribs.

[0055] In a particular and optional embodiment, the tread comprises two lateral ribs and at least one central rib, integral to the vertical alignment of each of at least one central rib is positioned one of the central discontinuous portions of the intermediate sublayer.

[0056] The term "fully vertical" means that the entire central discontinuous portion considered is axially contained between the two axial ends of the rib axially with respect to the central discontinuous portion, or that the entire lateral discontinuous portion is axially contained between the axial end of the lateral rib axially with respect to the lateral discontinuous portion and the axial limit of the tread.

[0057] In a particular and optional embodiment, the ratio, as a percentage, of the axial width of at least one central portion of the intermediate sub-layer and the axial width of at least one central rib of the respective tread, is greater than or equal to 70%.

[0058] Each of the last four embodiments mentioned can be combined independently. This advantageously allows for a proportional increase in the volume of the intermediate layer. Thus, the improvement in the compromise between rolling resistance and grip over a wide range of tire operating temperatures is very significant, even optimal if each of the last four embodiments mentioned is implemented; finally, the latitude for adjustment for the tire designer is maximized.

[0059] In a particular and optional embodiment, the elastomeric material of the tread layer has a viscoelastic loss less than or equal to 0.75, the viscoelastic loss being measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric compound from the tire, subjected to sinusoidal loading in alternating simple shear, at a frequency of 10Hz, at a temperature of 23°C and for a strain equal to 10%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

[0060] Advantageously, the viscoelastic loss of the tread layer can be relatively high to improve tire grip. Beyond a certain threshold, the intermediate and sub-base layers can no longer effectively compensate for the viscoelastic losses of the tread layer, and therefore the impact on the tire's rolling resistance becomes significant.

[0061] In a particular and optional embodiment, the tread layer comprises at least a lateral portion comprising a PE elastomer compound and a central portion comprising a PC elastomer compound, the at least one lateral portion extending axially over a distance of 5% to 25% of the Lb bead width of the tire, the complex dynamic shear modulus of the PE elastomer compound is at most equal to 80% of the complex dynamic shear modulus of the PC elastomer compound, the viscoelastic loss of the PE elastomer compound is at most equal to 80% of the viscoelastic loss of the PC elastomer compound.

[0062] The presence of at least one lateral portion of the wearing course further improves rolling resistance.

[0063] In a particular and optional embodiment, the tire is a summer touring tire or an all-season touring tire. Detailed description of the invention

[0064] The invention and its advantages will be readily understood in the light of the detailed, non-limiting description that follows and with reference to [fig. 1] and [fig. 2] and [fig. 3],

[0065] Fig. 1 is a cross-sectional view, in a meridian cutting plane, of a tire 1 in a first configuration of the invention.

[0066] Fig. 2 is a cross-sectional view, in a meridian cutting plane, of a tire 1 according to a second configuration of the invention.

[0067] In the figures relating to the tire, a coordinate system X, Y, Z is shown, corresponding to the usual circumferential (X), axial (Y), and radial (Z) directions of a tire 1. Tire 1 rotates approximately around an axis substantially parallel to the axial direction Y. Tire 1 is intended for a passenger vehicle and has a tire size of 245 / 45R18. Tire 1 is intended to be mounted on a mounting support, for example, a rim.

[0068] The tire 1 comprises a crown 7, two sidewalls 3, two beads 5, each sidewall 3 connecting each bead 5 to the crown 7. The crown 7 of the tire 1 comprises a tread 30 and also a crown reinforcement 17 arranged radially internally to the tread 30 and a carcass reinforcement 11 arranged radially internally to the crown reinforcement 17 in the crown 7 and anchored in each of the two beads 3. The carcass reinforcement 11 wraps around each of the two beads 5 around a bead 9. The tread 30 has a rolling surface 28 intended to come into contact with a road surface. The top reinforcement 17 and the tread 30 are arranged in contact with each other and extend into the top 7 in the circumferential direction X. Here, the tread 30 is present on [fig. 1], [fig. 2] and [fig.3], tread elements, the tread elements comprising several circumferential grooves 19 delimiting two lateral ribs 16A and 16B, and three central ribs 15. Said tread elements extend circumferentially in the apex 7 along the circumferential direction X. The tread 30 has two axial limits E1, E2 passing through the point for which the angle between the tangent to the tread surface 28 and the axial direction is equal to 30° on a mounted inflated tire. The. The width L of the tread 30 is equal to the axial distance between the two axial limits El, E2 of the tread surface on either side of the median plane M. The distance H represents the tread height of the tire 1, H being the maximum radial distance between the bottom of the groove 19 and its projection on the ground during the rolling of the tire, a groove 19 forming a space opening onto the tread surface 28. The distance H here is the maximum value of the depths of each of the grooves 19.

[0069] In a first configuration illustrated in [Fig. 1], the tread 30 comprises a base sublayer 21 and a wearing course 29, each of said layers comprising an elastomeric compound exhibiting a glass transition temperature TgSCB and TgCR, respectively, the glass transition being a temperature at which the viscoelastic loss reaches a maximum during a temperature sweep. The base sublayer 21 is arranged radially externally to the top reinforcement 17 and radially internally to the wearing course 29; here, the base sublayer 21 is in contact with the top reinforcement 17. The base sublayer 21 extends axially over the entire width L of the tread 30. The wearing course 29 is intended to come into contact with the ground via a tread surface 28. The wearing course 29 is here in contact with the base sublayer 21.In this first configuration and according to the invention, the glass transition temperature difference TgSCB-TgCR is less than or equal to -10°C. Here, in [Fig. 1], the base sublayer 21 has its outermost radial points at a radial distance from the tread surface greater than the tread height H of the tread 30.

[0070] We will now describe a second configuration with reference to [Fig. 2] and by contrasting it with tire 1 according to the first configuration described previously. Elements analogous to those described previously are designated by identical reference numerals on [Fig. 2].

[0071] The tread 30 comprises, in addition to a base sublayer 21 and the wear layer 29, an intermediate layer 26. The intermediate layer comprises an elastomeric compound having a TgSCI glass transition. The intermediate sublayer 26 is arranged radially externally to the base sublayer 21 and Radially internal to the wearing course 29, here the intermediate sub-layer 26 is in contact with the base sub-layer 21, comprises an elastomeric material exhibiting a TgSCI glass transition, and extends axially in discontinuous portions between the two axial limits E1, E2 of the tread 30 and extends continuously, in the circumferential direction X, into the apex 7. Here, in [Fig. 3], the discontinuous portions are the two lateral portions 27A, 27B and the central portions 25, which are fully aligned with each of the lateral ribs 16A and 16B and each respective central rib 15. The ratio between the axial width LN of each central rib 15 and the respective central portions 25 is greater than or equal to 70%, here approximately 90%. The ratio between the axial width of each of the lateral portions 27A, 27B and of each of the respective lateral ribs 16A, 16B is also greater than or equal to 70%.According to the invention, the temperature difference TgSCI-TgCR is less than or equal to -10°C and / or the difference TgSCB-TgCR is less than or equal to -10°C.

[0072] In both the first and second configurations, each of the elastomeric compounds in the base layer 21 and the tread 29 has an elastic modulus G' and a viscoelastic loss TD measured at 10% deformation according to ASTM D-5992-96, at a temperature of 23°C and a frequency of 10 Hz. The viscoelastic loss of the base layer 21 of tire 1 is less than or equal to 0.15. The viscoelastic loss of the intermediate layer 26 of tire 1 is less than or equal to 0.35. The elastic modulus of the tread 29 is greater than or equal to 1 MPa.

[0073] We will now describe a third configuration with reference to [Fig. 3] and by contrasting it with tire 1 according to the second configuration described previously. Elements analogous to those described previously are designated by identical reference numerals on [Fig. 3].

[0074] The tread layer 29 of the tread 30 here comprises two lateral portions 40 comprising a PE elastomer compound and a central portion 41 comprising a PC elastomer compound, each of the two lateral portions 40 extending axially over a distance ranging from 5% to 25% of the bead width Lb of the tire 1, the complex dynamic shear modulus of the elastomer compound PE is at most equal to 80% of the complex dynamic shear modulus of the PC elastomer blend, the viscoelastic loss of the PE elastomer blend is more than equal to 80% of the viscoelastic loss of the PC elastomer blend.

[0075] With further reference to [fig. 3] and in a particular and advantageous embodiment, the mass of PE elastomeric compound of each of the lateral portions 40 is extended axially outwardly beyond the axial limit of the tread 1.

[0076] To demonstrate the impact of the invention, a test plan, including the manufacture and testing of tires, is implemented. The test plan compares a control tire T1 with a first tire PI and a second tire P2 according to the first two configurations described previously.

[0077] As such, the reference tire 1 Tl comprises a tread layer 29 made of an elastomeric compound with an elastic modulus of 2.5 MPa, a viscoelastic loss of 0.19, and a glass transition temperature of -30°C. The reference tire 1 Tl is a Michelin ePrimacy 245 / 45R18. The reference tire 1 Tl also comprises a base layer 21 of Tl arranged in contact with the crown reinforcement 17. The base layer 21 of Tl has its outermost radial points at a radial distance from the tread surface 28 greater than the tread depth H of the tread 30. The base layer 21 of Tl comprises an elastomeric compound with an elastic modulus of 1.5 MPa, a glass transition temperature of -20°C, and a viscoelastic loss of 0.09.

[0078] The Tl 29 wearing course has a glass transition temperature TgSCB of -30 °C and the elastomeric compound has the following composition: (1) SBR elastomer with 26% styrene motif and 24% 1,2 motif of the butadiene part (Tg = -48°C), bearing a silanol function and a pendant tertiary amine function, which functions are located for the majority by weight of the elastomer chains (more than 50% by mass of the elastomer mass), outside the ends of the elastomer chain. (2) SBR elastomer with 15% styrene motif and 23% 1,2 motif of the butadiene part (Tg = -65°C), bearing a silanol function and a pendant tertiary amine function, which functions are located for the majority by weight of the elastomer chains (more than 50% by mass of the elastomer mass), outside the ends of the elastomer chain. (3) CTAB silica approximately 160 m2 / g ("Zeosil 1165MP" type "HDS", from the company Solvay). (4) Carbon black grade ASTM N234 (Cabot company). (5) Bis[3-(triethoxysilyl)propyl]polysulfide ("Si 69", from the company Evonik). (6) Diphenylguanidine ("Perkacit DPG", from the company Flexsys). (7) Plasticizing resin with a Tg of approximately 50°C ("Oppera PR383", from ExxonMobil Chemical). (8) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine ("Santoflex 6-PPD", from the company Flexsys). (9) Wax ("CERA SER AO 32", from the company SER S.pa.). (10) Tetrabenzylthiuram disulfide ("Perkacit TBZTD", from Flexsys).

[0079] The second PI tire in the test plan, starting from the control tire T1, includes a base underlayer 21 of PI occupying approximately the same volume than the base sublayer 21 of Tl. The base sublayer 21 of PI comprises an elastomeric blend having an elastic modulus of 0.5 MPa and a glass transition of -40°C, and a viscoelastic loss of 0.06.

[0080] The base layer 21 has a glass transition temperature (TgSCB) of -40 °C and the elastomeric mixture has the following composition: (1) Diene elastomer: natural rubber. (2) Industrial grade zinc oxide from Umicore. (3) Nl,3-dimethylbutyl-N-phenylparaphenylenediamine "Santoflex 6-PPD" from the company Flexsys. (4) N-cyclohexyl-2-benzothiazyl sulfenamide "Santocure CBS" from Flexsys (5) Hardening resin: novolac epoxy resin poly[(o-cresyl glycidylether)-do-formaldehyde] marketed under the name "Araldite ECN1299" by Huntsmann. (6) Amine hardener: Dimethylthiotoluenediamine marketed under the reference "Ethacure 300" by the company Albemarle Louvain. (7) ASTM NI 15 grade carbon black (ASTM D1565-14) marketed by Cabot Company; STSA surface area measured according to ASTM D6556-2016 is 124 m2 / g, COAN index measured according to ASTM D3493-2018 is 97 mL / 100g, iodine adsorption index measured according to ASTM DI 510-2017 is 160 g / kg.

[0081] The second P2 tire in the test plan, starting from the first PI tire, also includes an intermediate sub-layer 26 of P2 arranged in contact with a The volume of rubber occupied by the sum of the intermediate sublayer 26 of P2, the base sublayer 21 of P2, and the wearing course 29 of P2 is substantially the same as the volume occupied by the base sublayer 21 and the wearing course 29 of Tl or PI. Furthermore, the volume of rubber occupied by the base sublayer 21 of P2 is substantially the same as the volume occupied by the base sublayer 21 of Tl or PI. The intermediate sublayer 26 of P2 comprises an elastomeric compound having an elastic modulus of 18 MPa, a glass transition temperature of -50°C, and a viscoelastic loss of 0.3.

[0082] The intermediate sub-layer 26 has a glass transition temperature TgSCI of -50 °C and the elastomeric mixture has the following composition: (1) Carbon black marketed by the Birla company. (2) Diphenylguanidine accelerator (“Perkacit” DPG from Flexsys. (3) Plasticizer. (4) Sunflower oil (plasticizer). (5) Antioxidant “Santoflex 6PPD” from the company Solutia. (6) “Sancure CBS” accelerator from the company Solutia.

[0083] Tl, PI, and P2 tires are tested on a temperature-controlled test device. This allows the ambient temperature to be controlled during The measurements, the ambient temperature range of the test cell thus goes from 25°C to 15°C and finally from 15°C to 5°C.

[0084] Two performance parameters are measured during these tests: the rolling resistance of the tire in question and its drift stiffness. The latter is expressed as a percentage relative to the control tire; a percentage above 100% indicates an increase in drift stiffness, and therefore improved performance. Rolling resistance over the extended temperature range is expressed as a difference relative to the control tire (Tl) and in kg / T / 10°C; a negative value indicates a decrease in rolling resistance and therefore improved performance.

[0085] Following the tests, the results are summarized in the table below and show the benefit of the invention in the case of PI and P2, P2 also showing a benefit in drift stiffness, compared to PI, linked to the increase in the elastic modulus of the intermediate sublayer 26 compared to PI, thus improving the compromise between rolling resistance and drift stiffness of the tire.

Claims

DEMANDS

1. Tire (1) comprising a crown (7), the crown (7) comprising a crown reinforcement (17) and a tread (30), the tread (30) being arranged radially externally to the crown reinforcement (17), the tread (30) comprising: - a wearing course (29) intended to come into contact with the ground via a wearing surface (28) and comprising an elastomeric material having a glass transition temperature TgCR, - a base layer (21) arranged radially externally to the top reinforcement (17) and radially internally to the wear layer (29), the base layer (21) comprising an elastomeric material having a glass transition temperature TgSCB, each of the glass transition temperatures TgSCB, TgCR corresponding to a maximum viscoelastic loss, the viscoelastic loss being measured according to ASTM D-5992-96 at a frequency of 10Hz and according to a temperature sweep, characterized in that the difference of the subtraction of TgCR from TgSCB is less than or equal to -10°C, and in that the outermost radial points of the base layer (21) are at a radial distance from the wear surface (28) less than the tread height (30).

2. Pneumatic (1) according to the preceding claim, wherein the difference in the subtraction of TgCR from TgSCB is less than or equal to -15°C, and preferably -20°C.

3. Pneumatic (1) according to any one of the preceding claims, wherein the base sublayer (21) extends axially continuously over at least 80% of the axial width of the tread surface (28).

4. Pneumatic (1) according to any one of the preceding claims, wherein the elastomeric material of the base sublayer (21) has a viscoelastic loss less than or equal to 0.15, the viscoelastic loss being measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric mixture from tire (1) subjected to sinusoidal stress in simple alternating shear, at a frequency of 10Hz, at a temperature of 23°C and for a deformation equal to 10%, from a deformation amplitude sweep of 0.1% to 50% for the forward cycle.

5. Tire (1) according to any one of the preceding claims, wherein the tread (30) comprises an intermediate sublayer (26) extending axially in discontinuous portions, each portion of the intermediate sublayer (26) being arranged radially externally to the base layer (23) and radially internally to the wearing layer (29), each portion of the intermediate sublayer (26) having a glass transition temperature TgSCI, the difference in the subtraction of TgCR from TgSCI being less than or equal to -10°C.

6. Pneumatic (1) according to the preceding claim, wherein the difference in the subtraction of TgCR from TgSCI is less than or equal to -15°C, and preferably -20°C.

7. Pneumatic (1) according to any one of claims 5 to 6, wherein the outermost radial points of each portion of the intermediate sub-layer (26) are at a radial distance from the tread surface (28) less than the radial tread height of the tread (30).

8. Tire (1) according to any one of claims 5 to 7, wherein the elastomeric material of the intermediate underlayer (26) has a viscoelastic loss less than or equal to 0.35, the viscoelastic loss being measured according to ASTM D 5992-96 by recording the response of a sample of vulcanized elastomeric compound from the tire, subjected to sinusoidal loading in alternating simple shear, at a frequency of 10Hz, at a temperature of 23 °C and for a strain equal to 10%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

9. Pneumatic (1) according to any one of claims 5 to 8, wherein the elastomeric material of the base sublayer (21) and the elastomeric material of the intermediate sublayer (26) are identical.

10. Pneumatic (1) according to any one of claims 5 to 9, wherein the elastomeric material of the base layer (21) has a complex dynamic shear modulus G*M1 of less than 1.5 MPa and wherein the elastomeric material of the intermediate layer (26) has a complex dynamic shear modulus G*M2 of more than 5 MPa, the complex shear moduli being measured at 10% strain according to ASTM D-5992-96, at a temperature of 23°C and at a frequency of 10Hz for the forward cycle.

11. Tire (1) according to any one of claims 5 to 10, wherein the tread (30) comprises two lateral ribs (16A, 16B) and at least one central rib (15), and wherein each of the discontinuous lateral portions (27A, 27B) of the intermediate sublayer (26) is positioned integrally in line with each of the two lateral ribs (16A, 16B).

12. Tire (1) according to any one of claims 5 to 11, wherein the tread (30) comprises at least one central rib (15) and at least one central rib (15), and wherein integrally in line with each of the at least one central rib (15) of the tread (30) is positioned one of the central discontinuous portions (25) of the intermediate sublayer (26).

13. Tire (1) according to any one of claims 5 to 12, wherein the ratio, in percentage, of the axial width of at least one central portion (25) of the intermediate sublayer (26) and the axial width LN of at least one central rib (15) of the respective tread (30), is greater than or equal to 70%.

14. Tire (1) according to any one of the preceding claims, wherein the tread layer (29) of the tread (30) includes at least a lateral portion (40) comprising a PE elastomer blend and a central portion (41) comprising a PC elastomer blend, the at least a lateral portion (40) extending axially over a distance from 5% to 25% of the flange width Lb of the tire (1), the complex dynamic shear modulus of the PE elastomer blend is at most equal to 80% of the complex dynamic shear modulus of the PC elastomer blend, the viscoelastic loss of the PE elastomer blend is at most equal to 80% of the viscoelastic loss of the PC elastomer blend. 25

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