TIRE HAVING AN IMPROVED TREAD

Abstract

A tire comprises an outer strip (2) having a tread (21). The outer strip (2) has a central part and two axially outer parts and comprises at least two rubber compounds (M1, M2) making up at least 90% of the volume of the outer strip (2). The first compound (M1) is radially outside of the second compound (M2), which makes up at least 60% of the axially outer parts and being disposed in a layer that is substantially continuous from one axially outer part to the other, said layer having a minimum thickness at least equal to 0.3 mm. The compound M1 has a modulus G* that is greater than 1.35 times and less than 3 times that of the compound M2. The compound M1 has a dynamic loss at 0° C. greater than 0.5 and the compound M2 has a dynamic loss at 23° C. less than 0.3.

Claims

1.-15. (canceled)

16. A tire, for a passenger vehicle, bearing a marking on a sidewall that indicates that it is designed to be used on a snow-covered road, comprising: a crown (1) comprising an outer strip (2) having a tread (21) that is intended to come into contact with the ground via a tread surface (SR), two beads that are intended to come into contact with a rim, and two sidewalls (4) that connect the crown to the beads, the outer strip (2) being radially on the outside of a crown reinforcement (3) comprising crown layers (31, 32, 33) comprising reinforcing elements, and the tread being axially on the inside of the part of the sidewalls (4) that is radially on the outside of the crown reinforcement (3), the outer strip (2) being constituted of a central part and two axially outer parts, the central part of the outer strip having an axial width equal to 80% of an axial width (LA) of the tread surface (SR), the outer strip comprising at least two rubber compounds, the two rubber compounds (M1, M2) making up at least 90% of the volume of the outer strip, the first rubber compound (M1) being radially on an outside of the second rubber compound (M2), the second rubber compound (M2) making up at least 60% of a volume of the axially outer parts of the outer strip (2) and being disposed in a layer that is substantially continuous from one axially outer part of the outer strip (2) to the other, the layer having a minimum radial thickness at least equal to 0.3 mm, wherein the first rubber compound (M1) has a dynamic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, at least equal to 1.35 times a dynamic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, of the second rubber compound (M2) and at most equal to 3 times the dynamic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, of the second rubber compound (M2), wherein the first rubber compound (M1) has a dynamic loss tan D-10_1, measured in accordance with standard ASTM D 5992-96, at a temperature of −10° C. and under a stress of 0.7 MPa at 10 Hz, at least equal to 0.5, and wherein the second rubber compound (M2) has a dynamic loss tan D23_2, measured in accordance with standard ASTM D 5992-96, at a temperature of 23° C. and under a deformation of 10% at 10 Hz, at most equal to 0.3.

17. The tire according to claim 16, wherein the second rubber compound (M2) has a dynamic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, at least equal to 0.8 MPa and at most equal to 4 MPa.

18. The tire according to claim 16, wherein the first rubber compound (M1) has a dynamic loss tan D-10_1, measured in accordance with standard ASTM D 5992-96, at a temperature of 0° C. and under a stress of 0.7 MPa at 10 Hz, at least equal to 0.7.

19. The tire according to claim 16, wherein the second rubber compound (M2) has a secant extension modulus MA300 at 300% deformation, measured at 23° C. in accordance with standard ASTM D 412-16, at least equal to 1.4 MPa.

20. The tire according to claim 16, wherein a total volume of the second rubber compound (M2) represents at least 25% and at most 50% of the volume of the outer strip.

21. The tire according to claim 16, wherein the second rubber compound (M2) is disposed in the layer that is substantially continuous from one axially outer part of the outer strip (2) to the other, the layer having a minimum thickness at least equal to 0.6 mm.

22. The tire according to claim 16, wherein the first rubber compound (M1) is axially on an inside of the second rubber compound (M2), and wherein an interface between the first and the second rubber compounds forms an angle with a normal (28) to an external surface of the outer strip (2) at a point of intersection of the interface with the external surface that is at most equal to 60° in terms of absolute value.

23. The tire, the tread (21) of which comprises grooves or circumferential furrows, according to claim 16, wherein the layer of the second rubber compound (M2), which is substantially continuous from one outer part of the outer strip (2) to the other, is radially on an inside, in the central part of the outer strip (2), of bottom surfaces of the grooves or of the circumferential furrows of the tread (21).

24. The tire, the tread (21) of which comprises grooves or circumferential furrows, according to claim 16, wherein the grooves or circumferential furrows are configured such that a surface void ratio of the tread surface increases with wear of the tire.

25. The tire according to claim 16, wherein the first and second rubber compounds have reinforcing fillers made up of at least 80% silica, expressed as a percentage of a total mass of the reinforcing fillers.

26. The tire according to claim 16, wherein volumes of the first and second rubber compounds (M1, M2) of the outer strip (2) are substantially symmetrical with respect to an equatorial plane.

27. The tire according to claim 16, wherein the outer strip is made up of two rubber compounds (M1, M2) and one of the two rubber compounds is an electrical conductor and is configured such that an electrical resistance of the tire, measured in accordance with standard ISO 16392:2017, is at most equal to 10.sup.10 ohms.

28. The tire according to claim 16, wherein the outer strip is made up of three rubber compounds (M1, M2, M3), the third rubber compound (M3) being disposed between a radially outermost layer (33) of reinforcing elements of the crown reinforcement (3) and the tread surface (SR) and configured such that the electrical resistance of the tire, measured in accordance with standard ISO 16392:2017, is at most equal to 10.sup.10 ohms.

29. The tire according to claim 16, wherein the outer strip is made up of three rubber compounds, and wherein the third rubber compound is disposed between a radially outermost layer of reinforcing elements of the crown reinforcement and the second rubber compound (M2), the maximum thickness of the third rubber compound being at most equal to 0.6 mm.

30. The tire according to claim 16, wherein the outer strip is made up of four rubber compounds, wherein a third rubber compound is disposed between a radially outermost layer (33) of reinforcing elements of the crown reinforcement (3) and the second rubber compound (M2), the maximum thickness of the third rubber compound being at most equal to 0.4 mm, and wherein a fourth rubber compound is disposed between the radially outermost layer (33) of reinforcing elements of the crown reinforcement (3) and the tread surface (SR) and configured such that an electrical resistance of the tire, measured in accordance with standard ISO 16392:2017, is at most equal to 10.sup.10 ohms.

Description

[0061] The features and the other advantages of the invention will be understood better with the aid of FIGS. 1 to 3, said figures not being drawn to scale but in a simplified manner so as to make it easier to understand the invention. FIGS. 1 to 3 are parts of a tyre, in particular the crown reinforcement and outer strip and sidewall thereof.

[0062] FIG. 1 schematically depicts the meridian half-section through the crown of the tyre according to the invention. It illustrates in particular the crown 1 comprising an outer strip 2 comprising a tread 21 that is intended to come into contact with the ground via a tread surface SR of width LA. The crown 1 also comprises a crown reinforcement 3, comprising three layers of reinforcing elements 31, 32, 33 radially on the outside of the carcass layer 30. The outer strip 2 is radially on the outside of the radially outermost layer of reinforcing elements 33 of the crown reinforcement 3 and axially on the inside of the part of the sidewalls 4 that is radially on the outside of the crown reinforcement 3.

[0063] The outer strip is made up in this example of three rubber compounds M1, M2 and M3. The first rubber compound M1 is radially on the outside of the second rubber compound M2 and they represent at least 90% of the volume of the outer strip 2—in this case 97%, the remaining 3% consisting of M3. The outer strip has a central part with a width equal to 80% of the tread surface SR and two axially outer parts. The axially outer parts of the outer strip are made up of at least 60% by volume of the second compound M2. The second compound M2 is substantially continuous from one outer part of the outer strip to the other, i.e. it is continuous except if a compound M3 binds the crown layers to the tread surface in order to ensure the compliance of the tyre with the standard on the electrical conductivity of tyres.

[0064] In FIG. 1, the axial borders of the tread surface are determined in a meridian plane, which axial borders make it possible to measure the tread width in this meridian plane. In some cases, the width of the tread surface is trivially determined by those skilled in the art, since the axially outermost rib of the tread on either side of the equatorial plane has a clear discontinuity allowing simple measurement. In FIG. 1, which shows the case of a number of tyres for passenger vehicles in which the tread surface SR is continuous with the outer surface of the sidewall, the tangent 24 to the tread surface SR at any point on said tread surface in the region of transition towards the sidewall is plotted on a meridian section of the tyre, which is in the fitted position and inflated to nominal pressure. On each side of the equatorial plane, the axial border passes through the point for which the angle between said tangent 24 and an axial direction ZZ′ is equal to 60°. When, in a meridian plane, there are several points on one and the same side of the equatorial plane for which the angle between said tangent and an axial direction ZZ″ is equal to 60°, it is the radially outermost point that is adopted. The width of the tread, at the meridian plane, is the axial distance between the two points of the two axial borders of the tread surface. The width of the tread of the tyre is the maximum value of the widths of the tread over all the meridians.

[0065] FIG. 2 gives a variant of the invention with respect to FIG. 1, in which the rubber compound M2 opens onto the tread surface and in which the interface with the rubber compound M1 is radially on the outside of the radially innermost points of the bottom surfaces of the circumferential furrows and the grooves 25. In versions in which rolling resistance would be the most desirable performance aspect, this interface could be radially on the outside of the wear indicator 26. Specifically, M2 is configured to be in contact with the ground on which the tyre is running.

[0066] FIG. 3 shows a detail of the outer strip 2 and the interface 27 between the first rubber compound M1 and the second rubber compound M2 in the axially outer part of the outer strip. The first rubber compound M1 is axially on the inside of the second rubber compound M2, and therefore the second rubber compound M2 opens onto the external surface of the outer strip 2 at the tread surface SR or onto the external surface of the outer strip outside the tread surface. The interface between the first and the second rubber compounds forms an angle with the normal 28 to the tread surface at the point of intersection of the interface with the outer surface of the outer strip that is at most equal to 60° in terms of absolute value.

[0067] A meridian section through the tyre is obtained by cutting the tyre on two meridian planes.

[0068] The invention has been carried out on a tyre of size 225/45 ZR17 intended to be fitted to a passenger vehicle satisfying the conditions for being marked with the symbol 3PMSF authorizing its use on snow-covered roads on European territory. The depths D of the grooves of the tread pattern are between 4 and 8 mm.

[0069] The inventors have a plurality of rubber compounds that originate from the same manufacturing technology and from the same raw materials and that are able to constitute the central part of the outer strip. The materials in question vary in terms of properties between a rather rigid, adherent and hysteretic rubber compound MT1 and a material MT2 that is less rigid, less adherent and less hysteretic than MT1.

[0070] The rubber compound MT1 has an elastic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, equal to 2.65 MPa, a dynamic loss tan D-10_1, measured in accordance with standard ASTM D 5992-96, at a temperature of −10° C. and under a stress of 0.7 MPa at 10 Hz, to 0.73 and a dynamic loss tan D23_2, measured in accordance with the same standard ASTM D 5992-96, at a temperature of 23° C. and under a deformation of 10% at 10 Hz, equal to 0.55.

[0071] The rubber compound MT2 has an elastic shear modulus G*, at 10% deformation at 10 Hz at 23° C. measured in accordance with standard ASTM D 5992-96, equal to 1.45 MPa, a dynamic loss tan D-10_2, measured in accordance with standard ASTM D 5992-96, at a temperature of −10° C. and under a stress of 0.7 MPa at 10 Hz, equal to 0.31 and a dynamic loss tan D23_2 measured in accordance with the same standard ASTM D 5992-96, at a temperature of 23° C. and under a deformation of 10% at 10 Hz, equal to 0.19.

[0072] For tyres according to the prior art, the compound that is able to be in contact with the ground is combined with a rubber compound for the protective strip of an almost constant thickness equal to 2.1 mm on average, representing 20% of the volume of the outer strip, and of which the dynamic loss tan D23_2 measured in accordance with the same standard ASTM D 5992-96, at a temperature of 23° C. and under a deformation of 10% at 10 Hz, is equal to 0.12, with the objective of best optimizing the rolling resistance.

[0073] By varying the properties of the material that is able to be in contact with the ground between the properties of the rubber compounds MT1 and MT2, a person skilled in the art can design tyres according to a certain compromise between rolling resistance and grip.

[0074] The inventors have also produced a tyre according to the invention in which the radially outer compounds are made up of the first rubber compound MT1 and the second rubber compound MT2. The axially outer parts of the outer strip of the tyre comprise at least 85% by volume of the second rubber compound MT2. The rubber compound MT2 is continuous from one axially outer part to the other of the outer strip 2 over an almost constant thickness of 2.1 mm. In total, the volume of the first rubber compound MT1 represents 57% of the total volume of the outer strip.

[0075] Compared to tyres according to the prior art, the invention either, for identical grip, in particular on snow-covered ground, improves the compromise in terms of rolling resistance by approximately 5%, or for the same rolling resistance and the same grip on snow-covered ground, improves wet grip by 3%, the performance being measured on circuits.

[0076] Furthermore, the recycling capacity of the MT1 and MT2 compounds is increased by 100% compared with tyres outside the invention.