Tire with optimized rolling resistance performance

Abstract

The proposed invention describes a tire (1) having a crown (7) comprising a crown reinforcement (17) and a tread (30), the tread (30) having elastomeric compounds exhibiting a glass transition. The tread (30) comprises a tread layer (29) intended to contact the ground and a base sublayer (21). The tread layer material (29) has a TgCR glass transition, and the base sublayer material (21) is an elastomeric material having a TgSCB glass transition. The elastomeric materials of the tread (30) of the tire (1) have glass transitions having a TgSCB-TgCR temperature difference less than or equal to -10°C. Figure for the abstract: Fig 1

Description

Title of the invention: Tire exhibiting optimized rolling resistance performance. Field of the invention

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

[0002] A tire is an object with a revolution geometry, substantially toric, about an axis of revolution, the axis of revolution coinciding with the axis of rotation of the tire. A tire comprises two beads intended to be mounted on a rim, two sidewalls connected to the beads, and a crown. The crown comprises a tread intended to come into contact with the ground and a crown reinforcement, the tread being arranged radially externally to the crown reinforcement. A first axial side of the crown is connected to the radially external end of one of the two sidewalls, and the second side of the crown is connected to the radially external end of the other sidewall.

[0003] The tread comprises at least one layer of a 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 a 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.

[0004] A tire having a tread comprising a tread layer and a sub-layer is known from document WO2019145621. The sub-layer is arranged radially externally to the crown reinforcement and radially internally to the tread layer, the tread layer being intended to come into contact with the ground. Both the sub-layer and the tread layer comprise an elastomeric compound 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.

[0005] By minimizing the hysteresis loss of the material measured at 23°C at 10 Hz and under an alternating shear strain of 10%, the tire of WO2019145621 does not allow for an optimal improvement in the compromise between grip and rolling resistance. However, for certain applications, particularly for passenger car tires, a technical solution is necessary to meet the needs of the tire market.

[0006] Thus, the compromise between grip performance and rolling resistance over a wide range of tire operating temperatures is the essential goal of the invention. Description of the invention

[0007] This objective 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.

[0008] By assigning the elastomeric compounds of the tread and base layer a glass transition temperature (Tg) as described above, 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.

[0009] In a particular embodiment, and by amplifying the glass transition temperature difference beyond -10°C, the tire advantageously offers, over an even wider temperature range, a further improved compromise between rolling resistance and grip. The extended temperature range also allows it to be positioned with regard to Taking into account daily temperature variations and seasonality is crucial. This aspect offers a significant advantage in managing vehicle fuel consumption over a year of use. Typically, seasonal temperature variations in a temperate climate region are at least 15°C.

[0010] In a particular and optional embodiment, the base sublayer comprises a plurality of elastomers juxtaposed radially and / or axially to form the base sublayer.

[0011] As is known to those skilled in the art, the viscoelastic loss of the elastomeric compound of the tread is a parameter influencing the adhesion potential. In this case, the higher the viscoelastic loss, the better the adhesion. Conversely, a high viscoelastic loss due to material hysteresis increases rolling resistance, thus reducing product performance. In other words, the lower the viscoelastic loss, the lower the rolling resistance.

[0012] Regarding adhesion performance, the glass transition temperature represents the operating temperature of the material under consideration at which maximum energy dissipation occurs. The closer the wearing course's service temperature is to the glass transition temperature, the stronger the material's adhesion potential. Regarding rolling resistance performance, shifting the glass transition temperature of the base layer material towards a lower temperature allows, for a given temperature range, an average reduction in energy losses due to material hysteresis.

[0013] Since the base layer is arranged radially within the tread, the latter 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 temperature of the base layer TgSCB to a temperature lower than TgCR, rolling resistance is improved while maintaining a TgCR temperature that allows for undegraded grip performance. Furthermore, also according to the invention, by increasing the TgCR temperature relative to TgSCB, grip performance is improved while limiting the impact on rolling resistance.This improved compromise between these performance levels is therefore possible thanks to the complementarity and coupling between the base layer and the tread layer, provided that the temperature difference of the glass transitions respective to each of the tread materials is adapted to the operation and use of the tire.

[0014] 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 actual 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 the stable region shifts towards lower temperatures, the elastomeric material designer can adjust it to be consistent with the actual operating temperature range in order to control rolling resistance and grip over the entire extended temperature range.

[0015] "Real-world use" refers to tire use taking into account a wide temperature range, which may include both temperature variations during a day and the effects of seasonality. For example, in a temperate region like Europe, it is common to observe temperatures varying by more than 10°C in a single day and by more than 20°C over several months.

[0016] 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.

[0017] The complex shear modulus G* is a dynamic property well known to those skilled in the art and is measured on a Metravib VA4000 viscoanalyzer. The response of specimens subjected to sinusoidal alternating simple shear loading is recorded at a frequency of 10 Hz under predetermined temperature conditions according to ASTM DI349-99, until a stress representative of the operating point of the elastomeric material in the tire is reached, here 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 know how to choose and adapt the dimensions of the test specimen according to the amount of mixture accessible and available, particularly in the case of specimen sampling 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 square of G' and the square of G" in which G' represents the elastic modulus and G" represents the viscous modulus. The complex shear modulus G* is then measured at 10% strain over the forward cycle.

[0018] Viscoelastic loss TD is another well-known dynamic property to those skilled in the art. 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 value TD 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 vulcanized elastomeric compound sample in the shape of a cylindrical specimen, subjected to sinusoidal loading in alternating simple shear at a frequency of 10 Hz, at a temperature of 23°C, and for a strain of 5%, from a strain amplitude sweep of 0.1% to 50% for the forward cycle.

[0019] Finally, in order to determine the glass transition temperature Tg of the elastomeric material under consideration, a temperature sweep is performed along 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 which 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 value of the glass transition temperature Tg, in °C, is the value at which the viscoelastic loss TD is maximum.

[0020] Generally speaking, 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 to be characterized.

[0021] By axial direction, we mean the direction parallel to the axis of revolution of the tire, that is to say the axis of rotation of the tire.

[0022] By circumferential direction, we mean the direction which is perpendicular to the axial direction and to a radius of the tire.

[0023] By radial direction, we mean the direction along a radius of the tire, that is to say any direction intersecting the axis of rotation and perpendicular to this axis.

[0024] By meridian plane, we mean a plane containing the axis of rotation of the tire.

[0025] By median plane of the tire (denoted M), we mean the plane perpendicular to the axis of rotation of the tire and which passes through the middle of the tread.

[0026] By circumferential equatorial plane of the tire, we mean the theoretical cylindrical surface passing through the equator of the tire, perpendicular to the median plane and to the radial direction. The equator of the tire is, in a meridian cutting plane (plane containing the axis of rotation) the axis parallel to the axis of rotation of the tire is located at an equidistance between the outermost radial point of the tread intended to be in contact with the ground and the innermost radial point of the tire.

[0027] By radially inside, and radially outside respectively, we mean closer to the axis of rotation of the tire, and further from the axis of rotation of the tire respectively. By axially inside, and axially outside respectively, we mean closer to the median plane of the tire, and further from the median plane of the tire respectively.

[0028] In a particular and optional embodiment, the base sublayer extends axially continuously over at least 80% of the axial width of the running surface.

[0029] By thus increasing the volume occupied by the base sublayer of the tread, the tire advantageously presents, over a wide temperature range of use, an improvement in rolling resistance performance while maintaining a good compromise with grip performance.

[0030] 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 it rolls on that ground at a nominal load and pressure.

[0031] The tread width L is determined on a mounted tire, on a nominal rim, and inflated to the nominal pressure. In the case of an obvious boundary between the tread and the rest of the tire, the tread width is trivially determined by a person skilled in the art. In the case where the tread is continuous with the outer lateral surface of the tire, the axial limit of the tread passes through the point for which 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 for which this angle is equal to 30°, the radially outermost point is retained. The tread width is equal to the axial distance between the two axial limits of the tread on either side of the median plane M.

[0032] 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 height, preferably the distance between the base sublayer and the running surface is less than the tread height over at least 50% of the axial width of the base sublayer.

[0033] A groove on the 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 determine its curvilinear length, and connected by a bottom face. A groove can be oriented transversely or circumferentially.

[0034] 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, a groove forming a space opening onto the tread surface. The maximum depth of the grooves is the tread depth. The measurement of tread depth is well known to those skilled in the art and is easily measured using a depth gauge.

[0035] 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, in particular when the tire is in a new condition, during driving at nominal load and pressure.

[0036] 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.

[0037] 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 simple alternating 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.

[0038] The choice to limit viscoelastic loss also improves the rolling resistance performance of the tire.

[0039] In a particular and optional embodiment, the tread comprises an intermediate sub-layer extending axially in discontinuous portions, each portion of the intermediate sub-layer being arranged radially externally to the base layer and radially internally to the wearing layer, each portion of the intermediate sub-layer 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.

[0040] Since the intermediate layer is discontinuous in portions, the volume occupied by the materials with lower glass transition temperatures TgSCB and TgSCI relative to the wearing course material (having a temperature The glass transition temperature (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.

[0041] 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. Thus, the rigidity of the tire crown is further increased.

[0042] Advantageously, this embodiment maintains controlled grip performance until the regulatory wear level of the tire is reached, while allowing for optimized road behavior.

[0043] 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 height of the tread.

[0044] In a particular and optional embodiment, the intermediate sub-layer has at least one most radially outer point at a radial distance from the rolling surface that is radially 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 rolling surface.

[0045] Advantageously, this embodiment maintains controlled grip performance until the regulatory wear level of the tire is reached.

[0046] Such regulatory wear indicators are mandated, for example, by United Nations regulations R30 and R54, United States regulations FMVSS139, or Chinese regulations GB97743, and are intended to indicate to the tire user a regulatory tire wear threshold beyond which driving, particularly on wet surfaces, is risky. These wear indicators are thus 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, over a radial height of approximately 1.6 mm.

[0047] 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 a sinusoidal loading in simple alternating 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.

[0048] Choosing to limit viscoelastic loss in this way improves the tire's rolling resistance performance while limiting 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Here, the complex dynamic shear modulus G*M1 of the base sublayer remains sufficiently low so as not to negatively impact rolling resistance. Also, the material of the intermediate sublayer has a complex dynamic shear modulus G*M2 sufficiently high so as not to negatively impact the tire's drift stiffness, and may even improve it. Since the intermediate sublayer is discontinuous in sections, if, for example, each section is aligned with a rib, the proportion of the intermediate sublayer's volume relative to the tread volume can be maximized while maintaining the necessary base sublayer thickness. In this way, good drift stiffness is advantageously achieved, while also providing, over a wide operating temperature range, a good compromise between rolling resistance and grip performance.

[0053] In a particular and optional embodiment, the tread comprises two lateral ribs and at least one central rib, integral to the plumb line of each of the two lateral ribs is positioned on each of the discontinuous lateral portions.

[0054] In a particular and optional embodiment, the tread comprises two lateral ribs and at least one central rib, fully aligned with each of the at least one central rib is positioned one of the discontinuous central portions of the intermediate sub-layer.

[0055] 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.

[0056] In a particular and optional embodiment, the ratio, in 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%.

[0057] Each of the last four embodiments mentioned can be combined independently. This advantageously allows for a proportional increase in the volume of the intermediate sublayer. 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.

[0058] 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 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 deformation equal to 10%, from a deformation amplitude sweep of 0.1% to 50% for the forward cycle.

[0059] Advantageously, the viscoelastic loss of the tread layer can be relatively high to promote tire grip performance. Beyond a certain threshold, the intermediate layer and the base sublayer no longer effectively compensate for the viscoelastic losses of the tread layer, and therefore the impact on the tire's rolling resistance becomes significant.

[0060] In a particular and optional embodiment, the tread layer comprises at least a lateral portion comprising a PE elastomeric compound and a central portion comprising a PC elastomeric compound, the at less a lateral portion extending axially over a distance of 5% to 25% of the Lb flange width of the tire, 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.

[0061] The presence of at least one lateral portion of the wearing course makes it possible to further improve rolling resistance.

[0062] In a particular and optional embodiment, the tire is a summer passenger tire or an all-season passenger tire. Brief description of the drawings

[0063] 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].

[0064] Fig. 1 is a cross-sectional view, in a meridian cutting plane, of a tire 1 in a first configuration of the invention.

[0065] The [Fig.2] is a cross-sectional view, in a meridian cutting plane, of a tire 1 according to a second configuration of the invention.

[0066] 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. The tire 1 is substantially of revolution about an axis substantially parallel to the axial direction Y. The tire 1 is intended for a passenger vehicle and has a tire size of 245 / 45R18. The tire 1 is intended to be mounted on a mounting support, for example, a rim.

[0067] The tire 1 comprises a crown 7, two sidewalls 3, two bead 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 bead 3. The carcass reinforcement 11 wraps around each of the two bead 5 around a bead 9. The tread 30 has a running surface 28 intended to come into contact with a running 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], sculptural elements, the sculptural elements comprising several circumferential grooves 19 delimiting two lateral ribs 16A and 16B, and three central ribs 15. Said sculptural elements extend circumferentially. in the apex 7 along the circumferential direction X. The tread 30 has two axial limits El, 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 and inflated tire. 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 depth of the tire 1, H being the maximum radial distance between the bottom of the groove 19 and its projection onto the ground during tire rolling, a groove 19 forming a space opening onto the tread surface 28. The distance H here is the maximum depth of each of the grooves 19.

[0068] In a first configuration illustrated by [Fig. 1], the tread 30 comprises a base sublayer 21 and a wearing course 29, each of said layers comprising an elastomeric compound having 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.

[0069] We will now describe a second configuration with reference to [Fig. 2] and by contrast with the tire 1 according to the first configuration described previously. Elements analogous to those described previously are designated by identical reference numerals on [Fig. 2].

[0070] The tread 30 comprises, in addition to a base sublayer 21 and the wearing course 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 internally to the wearing course 29. Here, the intermediate sublayer 26 is in contact with the base sublayer 21, comprises an elastomeric material having a TgSCI glass transition, and extends axially in discontinuous portions between the two axial limits E1, E2 of the The tread 30 extends continuously, along 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 each of the respective lateral ribs 16A, 16B is also greater than or equal to 70%. According to the invention, the temperature difference TgSCLTgCR is less than or equal to -10°C and / or the difference TgSCB-TgCR is less than or equal to -10°C.

[0071] In both the first and second configurations, each of the elastomeric compounds of 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 the tire 1 is less than or equal to 0.15. The viscoelastic loss of the intermediate layer 26 of the 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.

[0072] We will now describe a third configuration with reference to [Fig. 3] and by contrast with the pneumatic 1 according to the second configuration described previously. Elements analogous to those described previously are designated by identical reference numerals on [Fig. 3].

[0073] The tread layer 29 of the tread 30 here comprises two lateral portions 40 comprising a PE elastomer blend and a central portion 41 comprising a PC elastomer blend, each of the two lateral portions 40 extending axially over a distance from 5% to 25% of the bead 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 more than equal to 80% of the viscoelastic loss of the PC elastomer blend.

[0074] Still with 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.

[0075] In order to highlight the impact of the invention, a test plan, including the manufacture and testing of tires, is carried out. 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 above.

[0076] Accordingly, the reference tire 1 Tl comprises a tread 29 comprising an elastomeric compound having 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 sub-layer 21 of Tl arranged in contact with the crown reinforcement 17. The base sub-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 sub-layer 21 of Tl comprises an elastomeric compound having an elastic modulus of 1.5 MPa, a glass transition temperature of -20°C, and a viscoelastic loss of 0.09.

[0077] The Tl wearing course 29 has a glass transition temperature TgSCB of -30 °C and the elastomeric mixture has the following composition: Tl pce Tilt Layer SBR1 (1) 10.0 SBR2 (2) 90.0 Silica (3) 80.0 Carbon Black (4) 3.0 Coupling Agent (5) 8.0 Activator (6) 1.6 Plasticizing Resin (7) 49.0 Antioxidant (8) 4.3 Wax (9) 2.0 Stearic Acid 2.0 ZnO 0.9 Sulfur 0.8 Accelerator (10) 0.7 (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 portion (Tg = -65°C), bearing a silanol function and a pendant function tertiary amine, 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) CT AB silica approximately 160 m2 / g ("Zeosil 1165MP" type "HDS", from the Solvay company). (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).

[0078] The second PI tire in the test plan, starting from the control tire Tl, comprises a PI base layer 21 occupying substantially the same volume as the PI base layer 21. The PI base layer 21 comprises an elastomeric compound having an elastic modulus of 0.5 MPa and a glass transition temperature of -40°C, and a viscoelastic loss of 0.06.

[0079] The base sublayer 21 has a glass transition temperature TgSCB of -40 °C and the elastomeric mixture has the following composition: Base coat 21 (pc) Diene elastomer (1) 100 ZnO (2) 7.5 Antioxidant (3) 2.7 Stearic acid 0.8 CBS (4) 3.2 Sulfur 3.2 Curing resin (5) 16.0 Hardener (6) 7.5 Carbon black (7) 50.0 (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 glycidyl ether)-do-formaldehyde] marketed under the name "Araldite ECN1299" by Huntsmann. (6) Amine hardener: Dimethylthiotoluenediamine marketed under the reference "Ethacure 300" by 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, CO AN index measured according to ASTM D3493-2018 is 97 mL / 100g, iodine adsorption index measured according to ASTM D1510-2017 is 160 g / kg.

[0080] The second tire P2 of the test plan, starting from the first tire PI, further comprises an intermediate sublayer 26 of P2 arranged in contact with a base sublayer 21 of P2. The volume of rubber occupied by the sum of the intermediate sublayer 26 of P2, the base sublayer 21 of P2 and the tread layer 29 of P2 is substantially the same as the volume occupied by the base sublayer 21 and the tread layer 29 of Tl or PL. Moreover, 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 PL. The intermediate sublayer 26 of P2 comprises an elastomeric compound having an elastic modulus of 18 MPa and a glass transition of -50°C and a viscoelastic loss of 0.3.

[0081] The intermediate sub-layer 26 has a glass transition temperature TgSCI of -50 °C and the elastomeric mixture has the following composition: Intermediate undercoat 26 pc NR 100 Birla XT1003 (1) 23.0 DPG (2) 2.0 Ther 8644 Resin (3) 14.6 HTO (4) 11.6 6PPD (5) 2.2 ZnO 3.0 Stearic Acid 2.0 Sulfur Sol 2H 0.8 CBS (6) 3.2 (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.

[0082] The Tl, PI and P2 tires are tested on a temperature-controlled test device. Thus, the ambient temperature can be controlled during measurements, and the ambient temperature range of the test cell is reduced from 25°C to 15°C and finally from 15°C to 5°C.

[0083] Two performance parameters are measured during these tests: the rolling resistance of the tire in question and its drift stiffness. The latter will be expressed as a percentage relative to the control tire; a percentage above 100% indicates an increase in drift stiffness, and therefore an improvement in performance. The rolling resistance over the extended temperature range will be 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 an improvement in performance.

[0084] 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. Extended range gain (kg / T / 10°C) Increased drift stiffness (percentage) Tire adhesion T1 Reference Reference Reference Tire PI -0.05 92% 100% Tire P2 -0.10 100% 100%

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 tread layer (29) intended to come into contact with the ground via a tread surface (28) and comprising an elastomeric material having a glass transition temperature TgCR, - a base layer (21) arranged radially externally to the crown reinforcement (17) and radially internally to the tread 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,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 in the subtraction of TgCR from TgSCB is less than or equal to -10°C.

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 to -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 outermost radially outer points of the base layer (21) are at a radial distance from the tread surface (28) less than the tread height of the tread (30).

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

6. 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 tread layer (29), each portion of the intermediate sublayer (26) having a glass transition temperature TgSCI, the difference in the subtraction of TgCR to TgSCI being less than or equal to -10°C.

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

8. Pneumatic (1) according to any one of claims 6 to 7, 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).

9. Tire (1) according to any one of claims 6 to 8, 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 alternating simple shear stress, 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.

10. Pneumatic (1) according to any one of claims 6 to 9, wherein the elastomeric material of the base sublayer (21) and the elastomeric material of the intermediate sublayer (26) are identical.

11. Pneumatic (1) according to any one of claims 6 to 10, wherein the elastomeric material of the base layer (21) has a dynamic shear complex modulus G*M1 of less than 1.5 MPa and wherein the elastomeric material of the intermediate layer (26) has a dynamic shear complex modulus G*M2 of more than 5 MPa, the shear complex 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.

12. Tire (1) according to any one of claims 6 to 11, 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).

13. Tire (1) according to any one of claims 6 to 12, wherein the tread (30) comprises at least one central rib (15) and at least one central rib (15), and wherein one of the discontinuous central portions (25) of the intermediate sublayer (26) is positioned integrally in line with each of the at least one central rib (15) of the tread (30).

14. Tire (1) according to any one of claims 6 to 13, 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%.

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

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