TIRE HAVING TREAD SUB-LAYER CONTAINING MULTIPLE MATERIALS - Patent application

Abstract

1. A tire (1) comprising a sublayer (7) consisting essentially of a base layer (71) arranged radially on the apex reinforcement (5) and axially between the central plane (CP) and the shoulders (60), the base layer (71) being made of a rubber compound having a given stiffness A, and a covering layer (72) arranged radially on the base layer (71) and radially inside the tread (6) and axially in at least each portion located between the central plane (CP) and the shoulder edges (721), the covering layer (72) being made of a rubber compound having a given stiffness B, the stiffness A being smaller than the stiffness B and the stiffness B being greater than the stiffness M. [Selected Figure] Figure 1

Description

[Technical field]

[0001] The present invention relates to tires and more particularly to tires having improved performance in terms of rolling resistance and ground contact.

[0002] In general, a tire is an object with a shape that exhibits rotational symmetry about an axis of rotation. It comprises two beads intended to be mounted on a rim, which also comprise two sidewalls connected to the beads, a crown comprising a tread intended to be in contact with the ground, the crown having a first side surface connected to the radially outer end of one of the two sidewalls and a second side surface connected to the radially outer end of the other of the two sidewalls.

[0003] The construction of a tire is usually described by the representation of its components in a meridian plane, i.e. a plane that contains the tire's axis of rotation. Radial, axial and circumferential directions respectively refer to directions perpendicular to the tire's axis of rotation, parallel to the tire's axis of rotation and perpendicular to any meridian plane. In the following text, the expressions "radial", "axial" and "circumferential" mean respectively "radially", "axially" and "circumferentially" of the tire. The expressions "radially inner" and "radially outer" mean respectively "closer" and "further away from the radial tire's axis of rotation". The equatorial plane CP is a plane perpendicular to the tire's axis of rotation, axially positioned so as to intersect the plane of the tread substantially midway between the beads. The expressions "axially inner" and "axially outer" mean respectively "closer" and "further away from the equatorial plane of the tire in the radial direction. [Background technology]

[0004] As is known, tires for road applications, and very specifically tires for passenger cars, contribute essentially to the performance of the vehicle in terms of rolling resistance (and therefore the energy efficiency of the vehicle), grip, dynamic response to guide the vehicle (especially when cornering), and wear (and therefore the overall cost of using the vehicle). Among the tire design parameters, the skilled artisan recognizes the importance of the choice of the material from which the tread is made and the material from which the sublayer is made. An example of a sublayer, i.e. a layer of rubber inserted between the crown reinforcement and the material of the tread, is described in French patent FR 2 954 333. Generally, the sublayer material under the tread is used to improve the rolling resistance of the tire with a material of low hysteresis, or to harden the tread in shear, but with a moderate stiffness so as not to oppose too much the flattening of the tire tread at its contact surface where it contacts the ground.

[0005] However, the lower the stiffness, the worse the tire's drift thrust response when stressed by vehicle turning. Specifically, roughly speaking, the stack of rubber layers radially outward of the crown reinforcement can be considered as a series of springs in series. It is for this reason that the introduction of materials with too low a modulus of elasticity is avoided so as not to impair cornering stiffness. Similarly, the dynamic shear modulus G of the sub-layer material * is generally greater than 1 MPa. However, this may be in conflict with the objective of minimizing rolling resistance. Even at the most rigid deformations, the dynamic shear modulus G of the sublayer material is * is typically much smaller than 8 MPa, even when best performance is desired from a handling point of view. In this document, the dynamic shear modulus G of the problem chosen from other possibilities for characterizing the stiffness * is the dynamic shear modulus G measured under alternating shear stress at 23°C and a frequency of 10 Hz and 10% deformation * Please note that.

[0006] WO 2015 / 170615 also discloses a tire with a base layer, i.e. sub-layer, formed of two radially superimposed materials. The elastic modulus of the material of the tread and its tg δ (tangent delta) value are lower than the values ​​of the same parameters of the sub-layer material in contact with the tread material, i.e. of the two radially outermost layers. The elastic modulus of the material of the radially inner layer of the sub-layer material and its tg δ value are lower than the values ​​of the same parameters of the sub-layer material in contact with the tread material. However, tires made according to this teaching do not achieve any progress in terms of the balance of performance properties.

[0007] FR 2 999 118 A1 also discloses a tire whose tread (but not the sub-layer) is composed of three different rubber compounds with very different purposes, as it is a question of electrical resistance. WO 2014 / 005927 A1 also discloses a tire whose tread (but not the sub-layer) is composed of two different rubber compounds with very different purposes, as it is a question of resistance to attack and wear for tires for construction plant type vehicles. FR 3 007 693 A1 also discloses a tire whose tread (but not the sub-layer) is composed of two different rubber compounds. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] French Patent No. 2954333 [Patent Document 2] International Publication No. 2015 / 170615 [Patent Document 3] French Patent Application Publication No. 2999118A1 [Patent Document 4] International Publication No. 2014 / 005927A1 [Patent Document 5] French Patent Application Publication No. 3007693A1 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to achieve better dynamic drift thrust response under turning stresses without compromising tire rolling resistance. [Means for solving the problem]

[0010] The subject of the invention is a tire having an axis of rotation and a central plane perpendicular to the axis of rotation and comprising a crown reinforcement, a tread radially outside the crown reinforcement, extending axially between two shoulders and including a contact surface intended to be in contact with the road when the tire is driven, said tread being made up of at least one rubber compound of a given stiffness M, and a sublayer arranged radially outside the crown reinforcement and radially inside the tread, on at least one axial side relative to the central plane, the sublayer being radially disposed on the crown reinforcement and A first base layer is arranged axially toward the center plane and between the shoulder ends, said base layer being made of a rubber compound of a given stiffness A, and a cover layer arranged radially on the base layer and radially inside the tread and axially at least in each portion located between the center plane and the shoulder ends, said cover layer being made of a rubber compound of a given stiffness B, wherein stiffness A is smaller than stiffness B, stiffness B is larger than stiffness M, and the dynamic shear modulus G of the material of the base layer measured at 23 ° C and under alternating shear stress at a frequency of 10 Hz and 10% deformation is * is less than 0.6 MPa.

[0011] Here and according to convention, the sublayer is a tire component inserted between the crown reinforcement and the material of the tread, i.e. positioned radially above the cords or equivalent elements and radially inside the wear layer of the tire, generally called "tread", such component being therefore positioned radially inside the radially outermost area of ​​the wear indicator when mounted on the tire. In the present invention, this component comprises several materials of different composition. In an advantageous embodiment, the covering layer is axially continuous from one shoulder of the tire to the other shoulder. In a preferred embodiment, the covering layer is formed by several axially separated parts, the covering layer being interrupted under the grooves and, at some axial points, the covering layer being extended radially outward by at least one reinforcing element extending radially towards the outside of the tread.

[0012] The invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 shows a schematic representation of a meridional section through a tire according to a first embodiment of the invention. [Diagram 2] FIG. 3 shows a schematic meridional section through a tire according to a second embodiment of the invention. [Diagram 3] FIG. 11 is a simplified depiction of a third embodiment of the present invention. [Figure 4] FIG. 11 is a simplified depiction of a fourth embodiment of the present invention. [Diagram 5] FIG. 11 is a simplified depiction of a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 shows a tire 1, an equatorial plane CP, two beads 2 and two sidewalls 3 each connected to a bead 2. The tire has a crown 4 with a crown reinforcement 5 and a tread 6. The tread extends axially from one shoulder 60 to the other. The tread includes a contact surface 61 intended to be in contact with the roadway when the tire is driven. The tread 6 has tread blocks 63 separated by grooves 62 oriented substantially in the circumferential direction. Each groove 62 is bounded radially inwards by a groove bottom 620.

[0015] The crown also has a sublayer 7 arranged radially outside the crown reinforcement 5 and radially inside the tread 6. This sublayer is formed by two parts: a base layer 71 and a covering layer 72.

[0016] The base layer 71 is arranged radially directly on the crown reinforcement 5. As is known per se, the crown reinforcement generally comprises a layer of cord or monofilament reinforcement coated with a thin layer of rubber. In the context of the present invention, the indication that the base layer 71 is arranged radially directly on the crown reinforcement 5 means that it contacts the cord or reinforcement without taking into account its rubber coating.

[0017] Also visible is the covering layer 72 disposed radially on the base layer and axially at least in portions located between the midplane CP and the shoulder end 60. It should be noted that in this embodiment, the material of the tread 6 is visible at the groove bottom 620, the material of the covering layer 72 being thus covered (radially upwards) by a very thin film of the tread material 6.

[0018] FIG. 2 shows a second embodiment of the invention that is very similar to that illustrated in FIG. 1, in which the material of the coating layer 72 is visible at the groove bottom 620.

[0019] The materials used for the sublayer 7 are now discussed below. To characterize them, the dynamic shear modulus G measured at 23° C. and under alternating shear stress at a frequency of 10 Hz and 10% deformation is * is used.

[0020] Preferably, the material of the base layer 71 has a dynamic shear modulus G measured at 23° C. and under alternating shear stress at a frequency of 10 Hz and 10% deformation of less than 1.5 MPa, preferably less than 0.5 MPa. * and very advantageously, the dynamic shear modulus G of this material measured at 23 ° C and under alternating shear stress at a frequency of 10 Hz and 10% deformation is * has a value of 0.3 MPa. These are conventional values ​​for a sub-layer of normal configuration, i.e. made of a single material and extending axially from one shoulder of the tire to the other. Advantageously, the tg δ value measured at 23° C. at 10 Hz and under an alternating shear deformation of 10% of the material of the base layer 71 is less than 0.3 and very advantageously the tg δ value is about 0.05.

[0021] With respect to the covering layer 72, the material preferably has a dynamic shear modulus G measured under alternating shear stress at 23° C. and a frequency of 10 Hz and 10% deformation. * is greater than 7 MPa, preferably greater than 12 MPa, and very advantageously, the dynamic shear modulus G of this material measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation. * has a value greater than 20 MPa. In this way, good cornering stiffness is achieved, resulting in a good performance compromise between drift thrust and good rolling resistance, which can give the tire a good dynamic response. Advantageously, the tg δ value measured at 23° C., 10 Hz and under 10% alternating shear deformation of the material coating layer 72 is less than 0.3.

[0022] Dynamic shear modulus G of 0.2 MPa measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation *An example of a suitable formulation for the base layer 71 material having the formula:

[0023] [Table 1] The formulations are given by weight (phr means percentage by weight of elastomer).

[0024] Dynamic shear modulus G measured under alternating shear stress at 23 °C of 25 MPa and at a frequency of 10 Hz and 10% deformation * An example of a suitable formulation for the material of the coating layer 72 having the formula:

[0025] [Table 2] The formulations are given by weight (phr means percentage by weight of elastomer).

[0026] As regards the material of the tread, according to the invention, its stiffness M is less than the stiffness B of the covering layer. Advantageously, the rubber compound has a dynamic shear modulus G measured at 23° C. and under alternating shear stress at a frequency of 10 Hz and 10% deformation of less than 4.0 MPa, preferably less than 2.5 MPa. * has.

[0027] Table 3 below provides examples of tread formulations.

[0028] [Table 3] The formulations are given by weight (phr means percentage by weight of elastomer) and are as follows: (a) SBR with 27% styrene, 1,2-butadiene: 5%, cis-1,4-butadiene: 15%, trans-1,4-butadiene: 80%, Tg -48°C (b) 160m 2 Solvay's "Zeosil 1165MP" silica with a BET surface area of ​​1.0 g / g (c) "SI69" TESPT silane manufactured by Evonik (d) Shell's "Flexon 630" TDAE oil (e) "Escores 2173" resin manufactured by Exxon (f) Solutia's "Santoflex 6PPD" antioxidant (g) Solutia's "Santocure CBS" accelerator

[0029] It is contemplated that one skilled in the art of tire design may employ embodiment variations in which the tread itself includes several different materials, radially overlapping and / or axially juxtaposed.

[0030] In the embodiment of the invention shown in figures 1 and 2, the covering layer 72 is axially continuous between the two shoulders 60. Figure 3 shows a third embodiment in which the covering layer 721 is formed by several axially separated parts, which are interrupted below the grooves 62. At the interruptions, the material visible at the groove bottom 620 is the same as the material of the tread 6. Overall, this embodiment makes it possible to significantly improve the rolling resistance at the expense of a very moderate deterioration of the cornering stiffness. Advantageously, the material visible at the bottom of the grooves 620 is the same material as the material of which the tread 6 is made (i.e. the main material in the tread).

[0031] Figure 4 shows a fourth embodiment of the invention which is very similar to that shown in Figure 3, in which it can be seen that in the interruptions the material visible at the groove bottom 620 is the same as the material of the base layer (71) located radially below the groove in question, i.e. the material of the base layer 71 is visible at the bottom of grooves 62a and 62b.

[0032] To improve the rolling resistance and at the same time the cornering stiffness, it is possible to use wedge-shaped elements 630 in the wear parts of the tread. Figure 5 shows a fifth embodiment in which the covering layer 722 is extended radially outward (seen in a meridian section) in some tread blocks 63 in the axial direction by a wedge-shaped reinforcing element 630. This reinforcing element 630 extends radially from the radially outer side 722S of the covering layer 722 towards the outside of the tread 6 to a radial height that is greater than 75% of the radial thickness of the tread. This reinforcing element 630 is of variable axial width, decreasing radially upwards from a maximum value that is less than 50% of the axial width of the tread block. The angle formed in the radial section by the two lateral walls of this reinforcing element 630 is preferably between 10° and 50°, in particular for example 40°, as shown in Figure 3. The tread has such a reinforcing element 630 on either side of each groove 62. Each reinforcing element is advantageously made from the same rubber compound as the covering layer 722, thereby making it possible to extrude them in one and the same actuation as the covering layer 722.

[0033] test As a comparison, the dynamic shear modulus G of 3.0 MPa measured at 23° C. and under alternating shear stress at a frequency of 10 Hz and 10% deformation * A tire R is used having a tread made of a compound having the following properties: and a single material sublayer extends axially from one shoulder of the tire to the other and has a thickness that is substantially constant in the radial direction as seen in a radial cross section, the profile of this sublayer being the same as that of the base layer 71 assembly, and this sublayer has a dynamic shear modulus G of 0.2 MPa measured at 23° C. and under alternating shear stress at a frequency of 10 Hz and 10% deformation. *The first test tire T1 is according to the embodiment of the invention shown in FIG. 1 using the materials shown in Tables 1 to 3. The second test tire T2 is according to the embodiment of the invention shown in FIG. 3 using the materials shown in Tables 1 to 3 (interrupted covering layer 721) and the third test tire T3 is according to the embodiment of the invention shown in FIG. 5 using the materials shown in Tables 1 to 3 (this embodiment combines an interrupted covering layer with reinforcing elements 630 on either side of each groove 62, these two embodiments can be used independently of each other). The rolling resistance values ​​(kg / T) and the cornering stiffness values ​​Dz (N / °) are expressed with respect to the base 100 for the control R and as relative values ​​to the base 100 for the tire according to the invention. The measurement of the cornering stiffness of a tire makes it possible to evaluate the road-holding of a vehicle through its ability to react during steering actions or to follow the trajectory of a bend. This cornering stiffness is measured on an apparatus and consists in rolling a tire mounted on a rim and inflated to its nominal pressure on a bonded metal strip using a "flat track" type machine. Measurements are made as the tire rolls at 80 km / h with a series of stresses that vary the load, cornering and camber conditions. Rolling resistance can be measured according to standard ISO 28580.

[0034] [Table 4]

[0035] It will be noted that the present invention makes it possible to move the performance trade-off between rolling resistance and cornering stiffness, which allows a very significant improvement in rolling resistance at the expense of a reduction in cornering stiffness that is quite acceptable for passenger car applications where the desired performance is especially rolling comfort. It will also be noted that by adopting the fifth embodiment, a very large increase in both rolling resistance and cornering stiffness is achieved. [Explanation of symbols]

[0036] 1 Tire 3 side wall 4 Crown 6 Tread 7 sublayers

Claims

1. A tire (1) having an axis of rotation and a central plane (CP) perpendicular to the axis of rotation, A crown reinforcement material (5); A tread (6) radially outside said crown reinforcement (5), extending axially between two shoulders (60) and including a contact surface (61) intended to be in contact with the roadway when the tire is driven, and having a given dynamic shear modulus G * said tread (6) being made up of at least one rubber compound of M; a sublayer (7) arranged radially outward of said crown reinforcement (5) and radially inward of said tread (6); Including, On at least one axial side of said central plane (CP), said sublayer (7) comprises: A radially disposed crown reinforcement (5) and axially disposed between the central plane (CP) and the shoulder (60), the radially disposed crown reinforcement (5) has a given dynamic shear modulus G * A base layer (71) made of rubber compound A; A tire is disposed radially on the base layer (71) and axially at least in each portion located radially inward of the tread (6) and between the central plane (CP) and the shoulder end (711), and has a given dynamic shear modulus G * A coating layer (72) made of rubber compound B; having The dynamic shear modulus G * A is the dynamic shear modulus G * B, and the dynamic shear modulus G * B is the dynamic shear modulus G * Larger than M. The dynamic shear modulus G of the material of the base layer (71) measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation * is smaller than 0.6 MPa; A tire (1).

2. The dynamic shear modulus G of the material of the base layer (71) measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation * Tyre (1) according to claim 1, characterized in that the axial tension is less than 0.5 MPa.

3. 3. Tyre (1) according to claim 1 or 2, characterized in that the tg δ value, measured at 23° C., at a frequency of 10 Hz and under an alternating shear deformation of 10% of the material of the base layer (71), is smaller than 0.

3.

4. The dynamic shear modulus G of the material of the coating layer (72) measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation * Tyre (1) according to any one of claims 1 to 3, characterized in that is strictly greater than 7 MPa.

5. The dynamic shear modulus G of the material of the coating layer (72) measured under alternating shear stress at 23 ° C and a frequency of 10 Hz and 10% deformation * Tyre (1) according to claim 4, characterized in that is strictly greater than 12 MPa.

6. 6. Tyre (1) according to claim 4 or 5, characterized in that the tg δ value, measured at 23°C, at a frequency of 10 Hz and under an alternating shear deformation of 10% of the material of the covering layer (72), is smaller than 0.

3.

7. A tire (1) according to any one of the preceding claims, wherein the tread (6) has substantially circumferentially oriented grooves (62), the coating layer (72) is formed by several axially separated portions, the coating layer (72) being interrupted below the grooves (62); The tire (1), characterized in that

8. Tyre (1) according to claim 7, characterized in that the material visible at the bottom of the groove is the same material from which the tread is made.

9. Tyre (1) according to any one of the preceding claims, characterized in that the covering layer (72) is axially continuous between the two shoulder portions (60).

10. The tread (6) has tread blocks (63) separated by substantially circumferentially oriented grooves (62); the covering layer (722) axially adjacent to some of the tread blocks (63) is extended radially outward by at least one reinforcing element (630) extending radially from a radially outer surface (722S) of the covering layer (722) toward the outside of the tread (6) to a radial height greater than 75% of the radial thickness of the tread, the reinforcing element (630) having a variable axial width, the axial width decreasing radially upward from a maximum value less than 50% of the axial width of the tread block, Tyre (1) according to any one of the preceding claims, characterized in that it is

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