Pneumatic tires with improved tread

Abstract

The present invention relates to a pneumatic tire for vehicles, comprising a tread (2), the central portion of which comprises at least two rubber compounds (221, 222) and constitutes at least 90% of its volume. The first compound (221) is located radially outside the second compound (222) and constitutes at least 40% and at most 60% of the volume of the central portion. The second rubber compound (222) has a Shore hardness DS2 that is at least 5 greater than the Shore hardness DS1 of the first compound (221). The second rubber compound (222) has a dynamic loss at temperatures of 0°C and 23°C that is at least equal to the dynamic loss of the first rubber compound (221). The axially outer portions of the tread are composed of a third compound (223) that can come into contact with the ground and has a lower stiffness and lower hysteresis than the first compound.

Description

[Technical field]

[0001] The present invention relates to tires for passenger vehicles, and more particularly to the treads for such tires. [Background technology]

[0002] Since tires have a geometry that exhibits rotational symmetry about its axis of rotation, the geometry of the tire is generally depicted in a meridian plane that contains the tire's axis of rotation. For a given meridian plane, the radial, axial and circumferential directions respectively represent the directions perpendicular to the tire's axis of rotation, parallel to the tire's axis of rotation and perpendicular to the meridian plane.

[0003] In the following, the expressions "radially inward of" and "radially outward of" mean "radially closer to the tire's axis of rotation than" and "radially farther from the tire's axis of rotation than", respectively. The expressions "axially inward of" and "axially outward of" mean "axially closer to the equatorial plane than" and "axially farther from the equatorial plane than", respectively. The equatorial plane is the circumferential plane perpendicular to the axis of rotation and passing through the center of the tread.

[0004] "Radial distance" is the distance relative to the tire's axis of rotation and "axial distance" is the distance relative to the tire's equatorial plane. "Radial thickness" is measured in the radial direction and "axial width" is measured in the axial direction.

[0005] The tire comprises a tread intended to come into contact with the ground via a tread surface and a crown including at least one crown reinforcement radially inside the tread. The tire also comprises two beads intended to come into contact with the rim and two sidewalls connecting the crown to the beads. Furthermore, the tire comprises a carcass reinforcement radially inside the crown and including at least one carcass layer connecting the two beads.

[0006] The tread is therefore constituted by one or more rubber compounds radially outside the radially outermost layer of reinforcing elements of the crown reinforcement, excluding the rubber compound covering the reinforcing elements of the crown layer.

[0007] The tread does not include the rubber compound located on each sidewall of the tire, a portion of which may be radially and axially outside the crown reinforcement. The sidewall compound, which has a very specific composition, especially to resist ultraviolet light, is excluded from the surface and volume of the tread. The rubber compound of a tire having more than 30% of its surface on a meridian section radially inside the radially innermost crown layer is not a tread compound, but a sidewall compound.

[0008] The expression "rubber compound" means a composition of rubber comprising at least an elastomer and a filler.

[0009] The tread of the tire considered by the present invention comprises cuts corresponding to the spaces defined by the material walls facing each other and connected at their bottom surface at a non-zero distance from each other. The height of the tread pattern is the maximum radial distance between the radially innermost point of the bottom surface and the tread surface. These cuts are essential for performance in terms of grip on wet ground, and in particular aquaplaning. The overpressure on the ground that the cuts generate at the interface between the tread surface and the material wall in order to bring the rubber compound of the tread into contact with the ground breaks the water film present on the ground on which the tire runs. The cuts also form a void volume, which allows the storage of water present on the ground and displaced by the contact of the tread surface with the ground on which the tire runs. This water storage capacity is crucial for aquaplaning performance.

[0010] The performance of a tire changes with its wear: as the height of the tread pattern decreases with wear, the rolling resistance decreases due to the reduced deformation thickness of the rubber compound, and the stiffness of the tread pattern increases, reducing the water storage capacity and, as a result, the aquaplaning performance decreases.

[0011] To further improve the grip on wet ground, especially with regard to aquaplaning, of worn tires, one solution is to use a rubber compound with high hysteresis at 0° C. in the new tread. However, this solution results in a significant degradation of the rolling resistance, since a rubber compound with such properties at 0° C. also has a high hysteresis at 23° C., which is the property that mainly governs the rolling resistance.

[0012] In the prior art, this objective is achieved by using complex tread patterns that reform the incisions as the tire becomes more worn (EP 2311655(A1), JP 61-160303). These solutions require the manufacture of tire molds that are complex, expensive, cumbersome to demold, and susceptible to rubber chunking.

[0013] Other tires are described in EP 3208110, WO 2015 / 032601, WO 2018 / 002487, and WO 2019 / 145621. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] European Patent No. 2311655(A1) [Patent Document 2] Japanese Patent Application Publication No. 160303 / 1983 [Patent Document 3] European Patent No. 3208110 [Patent Document 4] International Publication No. 2015 / 032601 Brochure [Patent Document 5] International Publication No. 2018 / 002487 Brochure [Patent Document 6] International Publication No. 2019 / 145621 Brochure [Patent Document 7] International Publication No. 2018 / 115722 Brochure [Patent Document 8] International Publication No. 2012 / 069585 Brochure [Patent Document 9] International Publication No. 2012 / 069565 Brochure [Patent Document 10] International Publication No. 2012 / 069567 Brochure Summary of the Invention [Problem to be solved by the invention]

[0015] The object of the invention is to ensure very good grip on wet ground at the end of the tire's life without compromising the rolling resistance. [Means for solving the problem]

[0016] The purpose of this is to This is achieved by a passenger car tire having a tread intended to come into contact with the ground through its tread surface, two beads intended to come into contact with the rim, and two sidewalls connecting the crown to the beads, The tread is radially outward of a crown reinforcement, the crown reinforcement comprising at least one crown layer including reinforcing elements; the tread has a central portion and two axially outer portions, the central portion having an axial width equal to 90% of the axial width L of the tread, the tread comprises at least three rubber compounds, referred to as a first, a second and a third rubber compound; the central portion of the tread comprises at least a first and a second rubber compound, the two rubber compounds constituting at least 90% of the volume of the central portion of the tread; In a central portion of the tread, the first rubber compound is radially outward of the second rubber compound, the first rubber compound constituting at least 40% and at most 60% of the volume of the central portion of the tread; the first and third rubber compounds constitute at least 90% of the volume of an axially outer portion of the tread, the third rubber compound being axially outer of the first rubber compound and constituting at least 40% of the volume of the axially outer portion; the second rubber compound has a Shore hardness DS2 equal to the Shore hardness DS1 of the first rubber compound plus 5, and the third rubber compound has a Shore hardness DS3 equal to the Shore hardness DS1 of the first rubber compound at most, each Shore hardness DS1, DS2, DS3 being measured at 23°C according to ASTM standard 2240-15e1; the second rubber compound has a secant tensile modulus MA300_2 at 300% deformation equal to at least 0.75 times the secant tensile modulus MA300_1 at 300% deformation of the first rubber compound, measured at 23°C according to ASTM standard D 412-16, and equal to at most 1.25 times the secant tensile modulus MA300_1 at 300% deformation of the first rubber compound; and the third rubber compound has a secant modulus MA300_3 at 300% deformation equal to at least 0.9 times the secant tensile modulus MA300_1 at 300% deformation of the first rubber compound, measured at 23°C according to ASTM standard D 412-16, and equal to at most 1.3 times the secant modulus MA300_1 at 300% deformation of the first rubber compound; the second rubber compound has a dynamic loss tan D0_2, measured according to ASTM standard D 5992-96 at 0 ° C and 10 Hz, at least equal to the dynamic loss tan D0_1, measured according to ASTM standard D 5992-96 at 0 ° C and 10 Hz, of the first rubber compound; and the third rubber compound has a dynamic loss tan D0_3, measured according to ASTM standard D 5992-96 at 0 ° C and 10 Hz, at most 70% of the dynamic loss tan D0_1, measured according to ASTM standard D 5992-96 at 0 ° C and 10 Hz, of the first rubber compound; The dynamic loss tangent D23_1 of the first rubber compound, measured at 23°C and 10Hz according to ASTM Standard D 5992-96, is at most equal to the dynamic loss tangent D23_2 of the second rubber compound, measured at 23°C and 10Hz according to ASTM Standard D 5992-96, and the dynamic loss tangent D23_3 of the third rubber compound, measured at 23°C and 10Hz according to ASTM Standard D 5992-96, is at most equal to 70% of the dynamic loss tangent D23_1 of the first rubber compound, measured at 23°C and 10Hz according to ASTM Standard D 5992-96.

[0017] The invention consists essentially of the inventive use of a tread with three rubber compounds: a first and a second rubber compound constitute 90% of the volume of the central part of the tread and are designed from a performance point of view to provide a very good grip in contact with the ground, in a new condition by the first rubber compound and in a worn condition by the second rubber compound after at least a part of the second rubber compound has worn away, according to an embodiment of the invention. In combination with these two rubber compounds in the central part designed for grip performance, a third rubber compound is placed in the outer part of the tread, which can be in contact with the ground and is similar in wear performance to the first and second rubber compounds, but has a reduced hysteresis to compensate for the increased hysteresis of the other two rubber compounds.

[0018] In combination with these three rubber compounds, the tread can, for example, be equipped with any of the following: a thin layer of less than 0.4 mm in radial thickness, located between the rubber compound covering the radially outermost layer of the reinforcing elements of the crown reinforcement and the radially innermost interface of the tread, so as to provide a link between these two elements; -A small axially wide strip of less than 10 mm made of an electrically conductive rubber compound that forms a link between the ground on which the tyre runs and the reinforcing elements of the crown, enabling the tyre to meet electrical conductivity standards.

[0019] The first and second rubber compounds, which occupy 90% of the volume of the central portion, are arranged radially, the first rubber compound being arranged radially outside the second rubber compound. Both rubber compounds have properties, in particular mechanical properties, that are adapted to running on the ground on which the tire runs, so that they have a wear potential similar to each other. The wear potential is in particular expressed by the secant modulus MA300 at 300% deformation, measured at 23°C according to ASTM standard D 412-16-16. Unlike known arrangements for improving rolling resistance, the second rubber compound is not a soft material with very low hysteresis and therefore very low wear potential. The second rubber compound is stiff and hysteretic. Similarly, having the first rubber compound that wears excessively compared to the second rubber compound leads to an excessive shortening of the period of use during which the height of the tread pattern allows good grip on wet ground. The second rubber compound therefore has a secant modulus MA300_2 at 300% deformation equal to at least 0.75 times the secant modulus MA300_1 at 300% deformation of the first rubber compound and equal to at most 1.25 times the secant modulus MA300_1 at 300% deformation of the first rubber compound, measured at 23° C. according to ASTM standard D 412-16.

[0020] The volumes of the various volumes of the rubber compound are evaluated by considering the surface area they occupy on a meridian section of the tire, taking into account the toroidal shape of the tire to evaluate the volumes.

[0021] Having two rubber compounds with similar secant modulus MA300 at 300% deformation allows a more regular and uniform wear and therefore makes it possible to avoid irregular forms of wear.Thus, it is preferred that the second rubber compound has a secant modulus MA300_2 at 300% deformation, measured at 23°C according to ASTM standard D 412-16, equal to at least 0.9 times the secant modulus MA300_1 at 300% deformation of the first rubber compound and equal to at most 1.1 times the secant modulus MA300_1 at 300% deformation of the first rubber compound.

[0022] In order to achieve the desired wet grip performance at the end of the tread wear, preferably without resorting to complex tread patterns, as in winter tires, when it is not necessary to use them, and to compensate for the reduction in tread pattern height, it is necessary for the second rubber compound to have a grip performance superior to that of the first rubber compound. The second rubber compound therefore has a dynamic loss tanD0_2 measured at 0° C. and 10 Hz according to ASTM standard D 5992-96, which is at least equal to the dynamic loss tanD0_1 of the first rubber compound measured at 0° C. and 10 Hz according to ASTM standard D 5992-96. In order to achieve the level of grip targeted by the present invention, the dynamic losses tanD0_1 and tanD0_2 measured at 0° C. and 10 Hz according to ASTM standard D 5992-96 are preferably at least equal to 0.7.

[0023] To achieve such a level of dynamic loss tan D0, measured at 0°C and 10 Hz in accordance with ASTM standard D 5992-96, the first and second rubber compounds comprise a silica filler in a content at least equal to 100 percent of the elastomer.

[0024] In order to avoid disproportionate variations in grip force during the service life of the tire, the second rubber compound has a dynamic loss tanD0_2, measured at 10 Hz and at a temperature of 0° C. in accordance with ASTM standard D 5992-96, equal to at most 1.2 times the dynamic loss tanD0_1, measured at 10 Hz and at a temperature of 0° C. in accordance with ASTM standard D 5992-96, of the first rubber compound.

[0025] For the invention to function, it is also necessary to create a synergy between the location of the rubber compounds in the tread, their stiffness and their hysteresis.To limit the rolling resistance and improve grip, the idea is to increase the stiffness of the material to limit the deformations that generate energy dissipation, but also to combat the blistering phenomenon that occurs with the reduction in tread pattern height associated with wear.

[0026] A phenomenon well known to those skilled in the art at high speeds is that of aquaplaning. With speed, the amount of water evacuated per second in the contact patch increases. As the void ratio of the tread pattern is constant, there is a speed at which this amount of water fills all the voids. With further increases in speed, water can no longer be evacuated and a water surface forms in front of the tire, creating an overpressure in the contact patch. Under the influence of this pressure, the surface area of ​​the contact patch tends to decrease until it is no longer sufficient to ensure grip for the vehicle, and the phenomenon of aquaplaning occurs.

[0027] The study of this phenomenon has revealed that the main parameter of aquaplaning is the porosity of the tread. A closer look shows that the deformation of one or more rubber compounds of the tread also influences this performance. At high water pressure, depending on the stiffness of the rubber compound, the blistering phenomenon may or may not occur due to the loss of contact of the contact area of ​​the tire with the ground on which it is running. This phenomenon is also present at reduced speeds, which makes it possible to link the phenomenon of rubber grip and stiffness and thus rolling resistance. In particular, rolling resistance depends on the hysteresis of the rubber compounds of the tread, but also on their deformations and thus on their stiffness.

[0028] As the tread wears, the void volume decreases, which affects grip. Water withdrawal at the contact patch occurs at higher pressures. The synergy between stiffness and grip is therefore even more effective when the tread pattern height is low. Furthermore, increased stiffness allows for less deformation and therefore less rolling resistance. Surprisingly, this reasoning, based on phenomena of secondary importance to the targeted performance aspects, grip and rolling resistance, is valid as long as the invention is implemented with a tread material that operates over the range of hysteresis and stiffness descriptors according to the invention that effectively creates the synergy.

[0029] With regard to stiffness, it is essential that the second rubber compound has a Shore hardness DS2 at least equal to the Shore hardness DS1 of the first rubber compound plus 5, preferably at most equal to the Shore hardness DS1 of the first rubber compound plus 10, in order to avoid irregular wear problems.

[0030] With regard to the hysteresis of the rubber compound of the tread, it is essential that the dynamic loss tanD23_1 measured at 23°C and 10Hz according to ASTM standard D 5992-96 is at most equal to the dynamic loss tanD23_2 measured at 23°C and 10Hz according to ASTM standard D 5992-96. Preferably, in order to further improve the rolling resistance, it is advantageous that the dynamic loss tanD23_1 measured at 23°C and 10Hz according to ASTM standard D 5992-96 is at most equal to 0.8 times the dynamic loss tanD23_2 measured at 23°C and 10Hz according to ASTM standard D 5992-96. The first rubber compound is radially outermost and therefore has the greatest deformation. For adequate rolling resistance performance, it is required to have the smallest hysteresis at 23°C.

[0031] The synergy obtained in the central part of the tread allows improving grip, wear, behavior and aquaplaning performance, but at the expense of a deterioration in rolling resistance performance.To avoid this deterioration, the idea is to introduce a third material in the tread, at the level of the axially outer part of the tread, taking into account the specific properties of this zone.

[0032] The third material is in contact with the ground only during periods of particularly high stress in terms of load and lateral forces. The axially outer parts of the tread undergo much greater flattening deformations than the central parts, since these parts are doubly curved in the longitudinal and axial directions. The addition of the second rubber material therefore leads to a very significant deterioration of the rolling resistance, and the first rubber compound is of little relevance in terms of the need for grip in this relatively stress-free zone. The idea is to place in these axially outer parts of the tread a material that is stiff enough to come into contact with the ground close to the first rubber compound, but whose hysteresis at 23°C is small enough to compensate in terms of rolling resistance the introduction of the second rubber compound.

[0033] Thus, the first and third rubber compounds must constitute at least 90% by volume of the axially outer portion of the tread, the third rubber compound being present axially outside the first rubber compound, i.e. in the zone of greater deformation, to reduce rolling resistance. The third rubber compound comprises at least 40%, preferentially 75%, preferentially 90% of the volume of the axially outer portion to provide the greatest improvement in rolling resistance.

[0034] Solutions are possible regarding the distribution of the first and third rubber compounds in the axially outer portion of the tread, where there are two rubber compounds at the same axial coordinate. In this case, taking into account the better grip properties of the first rubber compound, the preferred solution is for the third rubber compound of the tread to be radially inside the first rubber compound.

[0035] In order to significantly reduce the rolling resistance, it is essential that the dynamic loss tan D23_3 of the third rubber compound, measured at 10 Hz at 23 ° C. according to ASTM standard D 5992-96, is at most equal to 70% of the dynamic loss tan D23_1 of the first rubber compound, measured at 10 Hz at 23 ° C. according to ASTM standard D 5992-96. Preferably, the dynamic loss tan D23_3 of the third rubber compound, measured at 10 Hz at 23 ° C. according to ASTM standard D 5992-96, is at most equal to 0.3, preferentially at most equal to 0.25, preferentially at most equal to 0.2.

[0036] This reduction in dynamic loss at 23° C. is accompanied by a reduction in dynamic loss at 0° C. It is essential that the dynamic loss tan D0_3 of the third rubber compound, measured at 10 Hz at 0° C. according to ASTM standard D 5992-96, is equal to at most 70% of the dynamic loss tan D0_1 of the first rubber compound, measured at 10 Hz at 0° C. according to ASTM standard D 5992-96. However, it is preferred that the third rubber compound has a sufficiently high grip performance for a good linearity of performance under extreme stress. To that end, it is preferred that the dynamic loss tan D0_3 of the third rubber compound of the tread, measured at 10 Hz at 23° C. according to ASTM standard D 5992-96, is at least equal to 0.22, preferentially at least equal to 0.28.

[0037] Considering the operating mode of the axially outer parts, this reduction in hysteresis must also be accompanied by a reduction in the stiffness of the third material with respect to the second material and also with respect to the first material in order to promote flattening. It is therefore essential that the Shore hardness DS3 of the third rubber compound is at most equal to the Shore hardness DS1 of the first rubber compound and, consequently, is practically less than the Shore hardness DS2 of the second material of the tread, preferably at most equal to the Shore hardness DS1 of the first rubber compound minus 3. However, the difference in Shore hardness between the first and third rubber compounds may make these parts sensitive to the generation of microcracks at their interface, which may result in uneven wear. It is therefore preferable that their Shore hardnesses are close, i.e. the third rubber compound has a Shore hardness DS3 at least equal to the Shore hardness DS1 of the first rubber compound minus 7, and in the range of rubber compounds used for passenger car tyres preferably has a Shore hardness at least equal to 45, preferentially at least equal to 50.

[0038] The axially outer portion, like the central portion, comprises a thin layer of radial thickness less than 0.4 mm located between the rubber compound covering the radially outermost layer of the reinforcing elements of the crown reinforcement and the radially innermost interface of the tread, providing a connection between these two elements.

[0039] The tread is designed so that the third rubber compound comes into contact with the ground when new or before the tire is completely worn down. It is essential that the third material has the ability to come into contact with the ground. Moreover, it must be sufficiently close to the first rubber compound in terms of mechanical properties so that the wear of the axially outer parts of the tread is aligned with that of the central part, especially at the interface between these parts. It is therefore essential that the third rubber compound has a secant modulus MA300_3 at 300% deformation, measured at 23°C according to ASTM standard D 412-16, equal to at least 0.9 times the secant modulus MA300_1 at 300% deformation of the first rubber compound. Likewise, in order to avoid any tendency towards uneven wear, it is preferred that the third rubber compound has a secant modulus MA300_3 at 300% deformation, measured at 23° C. according to ASTM standard D 412-16, of at least equal to 1.5 MPa, preferentially at least equal to 1.7 MPa, at most equal to 2.4 MPa and preferentially at most equal to 2.2 MPa.

[0040] To achieve these performance properties, the preferred solution is for the third rubber compound to comprise a silica filler up to equal 100 weight percent of the elastomer.

[0041] The properties of the rubber compound are measured on adhesive test specimens taken from the tire. The test specimen (circular version) as described in Figure X2.1 in ASTM Standard D 5992-96 (edition published in September 2006, first approved in 1996) is used. The diameter of the test specimen "d" is 10 mm [-0 to +0.04 mm], and the thickness "L" of each part of the rubber compound is 2 mm [1.85 to 2.20].

[0042] These properties are measured on vulcanized test specimens with a Metravib VA4000 type viscoanalyser.

[0043] The terms complex modulus, elastic modulus and viscous modulus refer to dynamic properties well known to those skilled in the art. * is defined by the following relationship: *=√(G'2+G"2), where G' represents the elastic modulus and G" represents the viscous modulus. The phase angle δ between force and displacement is expressed as the dynamic loss tan δ and is equal to the ratio G" / G'.

[0044] The response of vulcanized rubber compound samples subjected to a simple alternating sinusoidal shear stress with a frequency of 10 Hz, imposed symmetrically about the equilibrium position, is recorded. Prior to the temperature sweep measurements, the specimens are conditioned by subjecting them to a sinusoidal shear stress applied at 10 Hz, 100% full scale deformation, and 23°C.

[0045] The temperature sweep measurements are performed on a temperature curve increasing at 1.5°C per minute from a temperature Tmin below the glass transition temperature Tg of the material to a temperature Tmax that may correspond to the rubbery plateau of the material. Before the sweep begins, the sample is stabilized at temperature Tmin for 20 minutes to ensure uniform temperature throughout the sample. The results utilized at a selected temperature and selected stress are generally the dynamic complex shear modulus G, which consists of an elastic part G', a viscous part G", and a phase angle δ between force and displacement expressed as a loss factor tanD equal to the ratio G" / G'. * The glass transition temperature Tg is the temperature at which the dynamic loss tanD reaches a maximum value during the temperature sweep.

[0046] For the invention to function optimally, the first rubber compound preferably constitutes substantially the entire radially outermost portion of the tread, apart from any rubber compound that may be necessary to ensure electrical conductivity of the tire, and thus preferably constitutes at least 90% of the volume of the central portion of the tread radially outer of a point on the wear indicator radially outer of the radially outermost point and spaced from said point by a radial distance equal to 2 mm.

[0047] The preferred solution is that the second rubber compound is present above the wear indicator so that the grip provided is effective at the end of the tire's life, and that the limit of 2 mm above the wear indicator is not exceeded so that the effect of this second rubber compound on the rolling resistance of the hysteresis at 23° C. of the wear indicator remains limited. The preferred solution is therefore that the second rubber compound constitutes at least 20% of the central part of the tread between an axial line passing through the radially outermost point of the wear indicator and a point located radially outside the radially outermost point of the wear indicator and at a radial distance equal to 2 mm from the radially outermost point of the wear indicator.

[0048] An advantageous solution for improving rolling resistance is that the bottom of the tread pattern, the bottom of the circumferential furrows, the bottom of the grooves that do not contribute to the grip or stiffness of the tread pattern elements but contribute to the performance in terms of rolling resistance, are made of the first rubber compound. Thus, an advantageous solution is that for a tire with at least one circumferential furrow, the portion of the tread with a radial thickness of 0.5 mm that vertically coincides with the bottom surface of each furrow is made of the first rubber compound.

[0049] A preferred solution for good resistance of the crown reinforcement to attacks is that between the bottom of the grooves of the tread pattern and the radially outermost reinforcing elements of the crown reinforcement, there is a rubber layer of the tread with a radial thickness at least equal to 1 mm. This layer of rubber compound is mainly made of the first rubber compound of the tread. To optimize the rolling resistance, this layer must be as thin as possible while at the same time allowing protection of the crown reinforcement in the event of an impact, i.e. this layer must be at most equal to 2.5 mm, preferably at most equal to 2 mm. This layer is measured on a meridian section from the radially outermost points of the reinforcing elements of the radially outermost crown layer to a point at the bottom of the circumferential furrow or groove.

[0050] A preferred solution is therefore for the radial distance between the radially innermost point of the groove and the crown reinforcement to be at least equal to 1 mm and at most equal to 2.5 mm, preferentially at most equal to 2 mm. The characteristics and other advantages of the invention will be better understood with the aid of FIGS. 1 and 2, which represent a meridian semi-section of the crown of a tire according to the invention. [Brief description of the drawings]

[0051] [Figure 1] An embodiment of the present invention is shown in which a third rubber compound 223 is axially outward of the first rubber compound across its radial thickness. [Diagram 2] A variation of the invention is shown in which the third rubber compound is axially outboard of the first rubber compound 221, but the two rubber compounds are present in a portion 226 of the axially outer portion of the tread. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] The tire has a tread 2 intended to come into contact with the ground via a tread surface 22. The tread comprises at least three rubber compounds 221, 222, 223. The first and second rubber compounds 221, 222 constitute at least 90% of the volume of a central portion of the tread. The central portion has an axial width equal to 90% of the axial width L of the tread. The first and third rubber compounds 221, 223 constitute at least 90% of the axially outer portions of the tread.

[0053] The tread 2 may also have in its central portion a portion 224 of small axial width forming a link between the crown reinforcement and the tread surface so that the tire meets electrical conductivity standards.

[0054] To ensure the bond between the crown reinforcement 3 and the tread 2, it is also possible for the tread to be provided with a rubber coupling compound 225 having a radial thickness at most equal to 0.4 mm.

[0055] Also shown is the wear indicator, its radially outermost point 11, as well as a point 12 radially outside the outermost point 11 and at a radial distance of 2 mm. The portion of the tread radially outside the point 12 comprises at least 90% by volume of a first rubber compound 221, the remaining volume % being a conductive rubber compound 224 having a small axial width and enabling bonding of the tread surface with the crown reinforcement.

[0056] The portion of the tread between the line passing through point 11 and the line formed by point 12 comprises 40% by volume of the second rubber compound.

[0057] The tire also comprises a crown reinforcement 3 radially inside the tread 2 and comprising reinforcing elements in several layers. The two radially inner layers shown in the figure are the two working layers, whose reinforcing elements parallel to one another in a single layer make an angle with the circumferential direction of between 17 and 50° in absolute value. The reinforcing elements cross from one layer to another. The radially outermost layer is the hooping layer, whose reinforcing elements make an angle with the circumferential direction of between -7 and +7°.

[0058] The figure also shows how to determine the tread width L. The tread width L is determined for a tire mounted on a nominal rim and inflated to a nominal pressure. If there is a clear boundary between the tread surface and the remainder of the tire, the tread width is determined in a manner obvious to a person skilled in the art. If the tread surface 21 is continuous with the outer lateral surface of the tire's sidewall 26, the axial limit of the tread passes through a point where the angle between the tangent to the tread surface 21 and the axial direction YY' is equal to 30°. If there are several points in the meridian plane where the angle is equal to 30°, the radially outermost point is taken. The tread width L is equal to the axial distance between the two axial limits of the tread surface on either side of the equatorial plane.

[0059] Figure 1 shows an embodiment of the invention in which the third rubber compound 223 is axially outside the first rubber compound over its radial thickness. Figure 2 shows a variant of the invention in which the third rubber compound is axially outside the first rubber compound 221, but these two rubber compounds are present in a portion 226 of the axially outer part of the tread. In this configuration, the preferred solution is for the third rubber compound to be radially inside the first rubber compound, as shown in Figure 2.

[0060] The inventors carried out tests according to the invention on tires of size 225 / 45 R17 with a nominal width of 225 mm.

[0061] The control tire T, of conventional design and not according to the invention, comprises two rubber compounds 221 and 222. The first compound is stiffer and more hysteretic, and therefore stickier, but more dissipative than the second compound, which is designed with the conventional aim of reducing rolling resistance, and is therefore not designed to come into contact with the ground on which the tire runs. The two compounds have the following properties, respectively: The Shore hardness DS1 of the first rubber compound is equal to 64 and the Shore hardness DS2 of the first rubber compound is equal to 63.5, each Shore hardness DS1, DS2 being measured at 23°C in accordance with ASTM standard 2240-15e1. The first rubber compound has a secant modulus MA300_1 at 300% deformation equal to 1.77 MPa, measured at 23 °C according to ASTM standard D 412-16. The secant modulus MA300_2 at 300% deformation of the second rubber compound cannot be measured, as it breaks before reaching the MA300 measurement conditions, since this rubber compound has a very small hysteresis and is not designed to be in contact with the ground on which the tire runs. The second rubber compound has a dynamic loss tanD0_2, measured according to ASTM standard D 5992-96 at a temperature of 0°C and 10 Hz, equal to 0.23, and the first rubber compound has a dynamic loss tanD0_1, measured according to ASTM standard D 5992-96 at a temperature of 0°C and 10 Hz, equal to 0.69. The dynamic loss tan D23_1 of the first rubber compound, measured at 10 Hz and 23°C according to ASTM Standard D 5992-96, is equal to 0.38 and the dynamic loss tan D23_2 of the second rubber compound, measured at 10 Hz and 23°C according to ASTM Standard D 5992-96, is equal to 0.15.

[0062] The tread of tire T is composed of 70% by volume of a first rubber compound and 30% by volume of a second rubber compound. The arrangement of the two rubber compounds is optimized according to the prior art of tire T, i.e. the part of the tread below the radially outermost point of the wear indicator is composed of the second rubber compound over the entire width of the tread.

[0063] The present invention consists in reversing this design logic by placing a rubber compound for the tread, which is stiffer, more grippy and therefore more dissipative, and also approaches the wear performance of the first rubber compound, radially inside the first rubber compound, and introducing a third rubber compound in the radially outer portion of the tread. The central portion of the tread is composed of 58% of the first rubber compound and 42% of the second rubber compound. In tire A1, the axially outer portion of the tread is composed of the third rubber compound.

[0064] The three rubber compounds of tire A1 have the following characteristics: The second rubber compound 222 has a Shore hardness DS2 equal to 64, the first rubber compound has a Shore hardness DS1 equal to 57 and the third rubber compound has a Shore hardness DS3 equal to 52, each Shore hardness DS1, DS2, DS3 being measured at 23°C in accordance with ASTM standard 2240-15e1. The second rubber compound 222 has a secant modulus MA300_2 at 300% deformation, measured at 23° C. according to ASTM standard D 412-16, equal to 1.6 MPa, i.e. 1.07 times the secant modulus MA300_1 at 300% deformation of the first rubber compound 221, equal to 1.5 MPa. The third rubber compound 223 has a secant modulus MA300_3 at 300% deformation, measured at 23° C. according to ASTM standard D 412-16, equal to 1.8 MPa, representing a wear reduction of 10 to 15% with respect to the first and second rubber compounds 221, 222. The first and second rubber compounds 221, 222 respectively have dynamic losses tanD0_1 and tanD0_2 measured according to ASTM standard D 5992-96 at a temperature of 0° C. and 10 Hz equal to 0.76, and the third rubber compound 223 has a dynamic loss tanD0_3 measured according to ASTM standard D 5992-96 at a temperature of 0° C. and 10 Hz equal to 0.29, thereby making them suitable for use as rubber compounds in contact with the ground. The first rubber compound 221 has a dynamic loss tan D23_1 equal to 0.39, the second rubber compound 222 has a dynamic loss tan D23_2 equal to 0.51, and the third rubber compound 223 has a dynamic loss tan D23_3 equal to 0.13, all measured at a temperature of 23° C. and 10 Hz according to ASTM standard D 5992-96.

[0065] The compositions of the first, second and third rubber compounds 221, 222, 223 for tire A1 are described with reference to Table 1 below. [Table 1]

[0066] Each of the elastomers 1, 2 and 3 is identical to each of the elastomers C, D and A described in WO 2018 / 115722. The carbon black is of grade N234 and is supplied by Cabot Corporation. The silica is of type HDS and is supplied by Rhodia under the reference Z1165MP. The resin is supplied by ExxonMobil Chemicals under the reference PR-383. The antioxidant is N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine supplied by Flexsys. The liquid silane is supplied by Degussa under the reference TESPT Si69. The DPG is diphenylguanidine supplied by Flexsys under the reference Perkacit. CBS is N-cyclohexyl-2-benzothiazole sulfenamide supplied by Flexsys under the reference Santocure CBS.

[0067] Of course, other compositions may be used having varying contents of the various components thereof to obtain properties suited to a particular application, but without departing from the scope of the invention.

[0068] In particular, inspiration could be gained from the compositions disclosed in WO 2012 / 069585, WO 2012 / 069565 and WO 2012 / 069567, which have a relatively high silica content.

[0069] The tires T and A1 were tested for various performance aspects. Compared to tire T (base 100), tire A1 according to the invention makes it possible to improve the wet braking at new on asphalt concrete at 20° C. by +7% and at the end of life with 2 mm of tread pattern height remaining by +9%. The wet cross grip is also improved (+3.5%), the dry behavior on the circuit is comparable to the reference and the rolling resistance is equal to that of the control.

[0070] If the axially outer portion of a tire of the type of the present invention is constructed from the first rubber compound, the same performance is obtained, but with a penalty of about 5-10% in rolling resistance.

[0071] Thus, the present invention alone makes it possible to obtain improved grip performance both when new and at the end of the tire's life while maintaining rolling resistance performance equivalent to the control.

Claims

1. A tire (1) for a passenger vehicle, comprising: It comprises a tread (2) intended to come into contact with the ground through a tread surface (22), two beads intended to come into contact with the rim, and two sidewalls connecting a crown to said beads, said tread being radially outside a crown reinforcement (3), said crown reinforcement comprising at least one crown layer including reinforcing elements; said tread having a central portion and two axially outer portions, said central portion having an axial width equal to 90% of the axial width L of said tread (2); said tread comprising at least three rubber compounds (221, 222, 223), referred to as first, second and third rubber compounds; said central portion of said tread comprising at least said first and second rubber compounds (221, 222), said two rubber compounds constituting at least 90% of the volume of said central portion of said tread; In the central portion of the tread, the first rubber compound (221) is radially outside the second rubber compound (222), and the first rubber compound (221) constitutes at least 40% and at most 60% of the volume of the central portion of the tread; The first and third rubber compounds (221, 223) constitute at least 90% of the volume of the axially outer portion of the tread, and the third rubber compound is axially outside the first rubber compound and constitutes at least 40% of the volume of the axially outer portion, said second rubber compound (222) has a Shore hardness DS2 at least equal to the Shore hardness DS1 of said first rubber compound (221) plus 5, and said third rubber compound (223) has a Shore hardness DS3 at most equal to the Shore hardness DS1 of said first rubber compound (221), each Shore hardness DS1, DS2, DS3 being measured at 23°C according to ASTM standard 2240-15e1; The second rubber compound (222) has a secant modulus MA300_2 at 300% deformation equal to at least 0.75 times the secant modulus MA300_1 at 300% deformation of the first rubber compound (221) and equal to at most 1.25 times the secant modulus MA300_1 at 300% deformation of the first rubber compound (221), when measured at 23 ° C. according to ASTM standard D 412-16, and the third rubber compound (223) has a secant modulus MA300_2 at 300% deformation equal to at least 0.75 times the secant modulus MA300_1 at 300% deformation of the first rubber compound (221), when measured at 23 ° C. according to ASTM standard D a secant modulus MA300_3 at 300% deformation equal to at least 0.9 times the secant modulus MA300_1 at 300% deformation of said first rubber compound (221) and equal to at most 1.3 times the secant modulus MA300_1 at 300% deformation of said first rubber compound (221), when measured at 23 ° C. in accordance with 412-16; The second rubber compound (222) has a dynamic loss tan D0_2 measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96, which is at least equal to the dynamic loss tan D0_1 of the first rubber compound (221), measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96, and the third rubber compound (223) has a dynamic loss tan D0_3 measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96, which is at most 70% of the dynamic loss tan D0_1 of the first rubber compound (221), measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96, The dynamic loss tan D23_1 of the first rubber compound (221), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, is at most equal to the dynamic loss tan D23_2 of the second rubber compound (222), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, and the dynamic loss tan D23_3 of the third rubber compound (223), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, is at most equal to 70% of the dynamic loss tan D23_1 of the first rubber compound (221), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, A tire (1).

2. said first and second rubber compounds (221, 222) of said tread (2) comprise a silica filler at least equal to 100 weight percent of the elastomer, and the dynamic losses tan D0_1 and tan D0_2 of said first and second rubber compounds (221, 222) of said tread (2) measured at 0° C. and 10 Hz according to ASTM standard D 5992-96 are at least equal to 0.7; said third rubber compound (223) of said tread (2) comprises a silica filler at most equal to 100 weight percent of the elastomer, and the dynamic losses tan D0_3 of said third rubber compound (223) of said tread (2) measured at 0° C. and 10 Hz according to ASTM standard D 5992-96 are at least equal to 0.22; A tire (1) according to claim 1.

3. The second rubber compound (222) has a dynamic loss tan D0_2, measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96, equal to at most 1.2 times the dynamic loss tan D0_1 of the first rubber compound (221), measured at 0 ° C. and 10 Hz according to ASTM standard D 5992-96; A tire (1) according to claim 1 or 2.

4. The dynamic loss tan D23_1 of the first rubber compound (221), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, is at most 0.8 times the dynamic loss tan D23_2 of the second rubber compound (222), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, and the dynamic loss tan D23_3 of the third rubber compound (223), measured at 23 ° C. and 10 Hz according to ASTM standard D 5992-96, is at most 0.3; A tire (1) according to any one of claims 1 to 3.

5. said second rubber compound (222) has a secant modulus MA300_2 at 300% deformation, measured at 23 ° C. according to ASTM standard D 412-16, equal to at least 0.9 times the secant modulus MA300_1 at 300% deformation of said first rubber compound (221) and equal to at most 1.1 times the secant modulus MA300_1 at 300% deformation of said first rubber compound (221); A tire (1) according to any one of the preceding claims.

6. The third rubber compound (223) has a secant modulus MA300_3 at 300% deformation, measured at 23 ° C. according to ASTM standard D 412-16, of at least 1.5 MPa; A tire (1) according to any one of the preceding claims.

7. The second rubber compound (222) has a Shore hardness DS2 equal to the Shore hardness DS1 of the first rubber compound (221) plus up to 10; A tire (1) according to any one of the preceding claims.

8. said third rubber compound (223) has a Shore hardness DS3 at most equal to the Shore hardness DS1 of said first rubber compound (221) minus 3 and at least equal to the Shore hardness DS1 of said first rubber compound (221) minus 7; A tire (1) according to any one of the preceding claims.

9. the third rubber compound (223) of the tread is radially inward of the first rubber compound (221) of the tread over a portion of the tread, A tire (1) according to any one of the preceding claims.

10. said third rubber compound (223) occupies at least 75% of the volume of the axially outer portion of said tread; A tire (1) according to any one of the preceding claims.

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