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EP-4134248-B1 - TIRE

EP4134248B1EP 4134248 B1EP4134248 B1EP 4134248B1EP-4134248-B1

Inventors

  • FUJII, Daichi

Dates

Publication Date
20260506
Application Date
20220727

Claims (13)

  1. A tire comprising a tread part (1), the tread part comprising at least a first rubber layer (6) forming a tread surface (10) and a second rubber layer (7) adjacent to an inner side of the first rubber layer (6) in a tire radial direction, wherein the tread part (1) comprises two or more circumferential grooves (11, 12, 13, 14) extending continuously in a tire circumferential direction, a pair of shoulder land parts (16, 17) partitioned by the circumferential grooves (11, 12, 13, 14) and grounding ends, and a center land part (20) located between the pair of the shoulder land parts (16, 17), wherein the first rubber layer (6) and the second rubber layer (7) are formed of a rubber composition comprising a rubber component, wherein a ratio of a distance H 2 , expressed in mm, from an outermost surface of the tread part (1) to an outermost part of the second rubber layer (9) to a groove depth H 1 of deepest parts of the circumferential grooves , H 2 /H 1 , is 0.40 to 0.90, and wherein, when a complex elastic modulus at 30°C of the first rubber layer is defined as E* T and expressed in MPa and a complex elastic modulus at 30°C of the second rubber layer (7) is defined as E* B and expressed in MPa, E* B is greater than E* T , and a ratio of E* T to H 2 /H 1 , E*/(H 2 /H 1 ), is 6.0 or more, wherein the complex elastic modulus is measured under a condition of a temperature at 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain of 1%, and wherein one of options (i) or (ii) is realized: (i) the ratio of the area of the land part (2) in the grounding surface is asymmetric with respect to a tire equatorial plane (C), wherein the ratio of the area of a land part in a grounding surface refers to a ratio of a total area of the shoulder and parts and the center land part of to the total area S of the grounding surface, and wherein, when the tire is mounted to a vehicle, the area S 1 of the land part in a direction from the tire equatorial plane to the inside of the vehicle is less than the area S 2 of the land part in the direction from the tire equatorial plane to the outside of the vehicle, or (ii) the circumferential grooves (11, 12) are not present on the tire equatorial plane (C), wherein, when the tire is mounted to a vehicle, a distance (W 2 ) from the tire equatorial plane (C) to the groove edge of the circumferential groove (11) nearest to an inner direction of the vehicle is different from a distance (W 3 ) from the tire equatorial plane (C) to the groove edge of the circumferential groove (12) nearest to an outer direction of the vehicle, wherein, when the tire is mounted to the vehicle, the distance (W 2 ) from the tire equatorial plane (C) to the groove edge of the circumferential groove (11) located nearest to the inside of the vehicle is larger than the distance (W 3 ) from the tire equatorial plane to the groove edge of the circumferential groove (12) located nearest to the outside of the vehicle.
  2. The tire according to claim 1, the tread part (1) comprising a third rubber layer (8) adjacent to an inner side of the second rubber layer (7) in a tire radial direction.
  3. The tire according to any one of claim 1 or 2, wherein an amount of a polymer in the rubber composition forming the first rubber layer (6) is 40% by mass or less, wherein the amount of the polymer in the rubber composition forming the first rubber layer (6) is greater than an amount of a polymer in the rubber composition forming the second rubber layer (7).
  4. The tire according to any one of claims 1 to 3, wherein a ratio of an area of the land part (2) in a grounding surface is 60 to 80%.
  5. The tire according to any one of claims 1 to 4, wherein a ratio of groove areas in the shoulder land parts (16, 17) is greater than a ratio of a groove area in the center land part (20).
  6. The tire according to any one of claims 1 to 5, wherein a length of at least one land part of the land parts (16, 17) in a width direction increases gradually from an outside toward an inside in a tire radial direction.
  7. The tire according to any one of claims 1 to 6, wherein, when a groove width on the tread surface (10) of the circumferential groove located on the outermost side when mounted on a vehicle is defined as L 0 , and a groove width at 95% of the deepest part of the groove bottom of the circumferential groove located on the outermost side when mounted on the vehicle is defined as L 95 , L 95 /L 0 is 0.20 to 0.80.
  8. The tire according to any one of claims 1 to 7, wherein at least one of the rubber composition forming the first rubber layer and the rubber composition forming the second rubber layer (7) comprises a hydrocarbon resin.
  9. The tire according to any one of claims 1 to 8, wherein the complex elastic modulus E* T of the first rubber layer (6) at 30°C is 4.0 MPa or more.
  10. The tire according to any one of claims 1 to 9, wherein tan δ of the second rubber layer (7) at 30°C is 0.25 or less.
  11. The tire according to any one of claims 1 to 10, wherein a glass transition temperature of the first rubber layer (6) is -25°C or more.
  12. The tire according to any one of claims 1 to 11, wherein Shore hardness (Hs) of the second rubber layer (7) measured at 23°C in accordance with JIS K 6253-3:2012 using a type-A durometer is 50 to 80.
  13. The tire according to any one of claims 1 to 12, wherein a modulus of the second rubber layer (7) at 100% elongation is greater than a modulus of the first rubber layer (6) at 100% elongation.

Description

TECHNICAL FIELD The present invention relates to a tire. BACKGROUND OF THE INVENTION For example, a method of making a two-layer structure of a tread rubber of a pneumatic tire and using a foamed rubber for a rubber layer inside the two-layer structure is known as a method of suppressing a vibrating sound (noise) from a tire during running (JP H06-156016 A). Moreover, recently, steering stability particularly during high-speed running has been strongly demanded in the tire market. EP 3 141 402 A1 discloses a tyre with a reinforcement layer and a tread portion comprising an inner base layer, an outer base layer and a cap layer, so as to improve rolling resistance of the tyre while maintaining ice/snow performance and steering stability of the tyre. SUMMARY OF THE INVENTION An object of the present invention is to provide a tire having improved total performance of steering stability during high-speed running and noise performance. As a result of intensive studies, it has been found that the above-described problem is solved by stacking two or more rubber layers on a tread part of a tire and making complex elastic modulus and groove depths of circumferential grooves of the rubber layers have a predetermined relationship. That is, the present invention relates to a tire according to claim 1. According to the present invention, a tire having improved total performance of steering stability during high-speed running and noise performance is provided. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of one example of a tire that is one embodiment of the present disclosure.FIG. 2 is a schematic view of a grounding surface of a tire when a tread is pressed against a flat surface.FIG. 3 is a schematic view of a grounding surface of a tire that is another embodiment.FIG. 4 is a schematic view of a grounding surface of a tire that is another embodiment.FIG. 5 is an enlarged cross-sectional view illustrating a part of a tread of a tire according to one embodiment of the present invention.FIG. 6 is an enlarged cross-sectional view illustrating a part of a tread of a tire according to one embodiment of the present invention. DETAILED DESCRIPTION The tire according to the present invention is a tire comprising a tread part, the tread part comprising at least a first rubber layer forming a tread surface and a second rubber layer adjacent to an inner side of the first rubber layer in a tire radial direction, wherein the tread part comprises two or more circumferential grooves extending continuously in a tire circumferential direction,a pair of shoulder land parts partitioned by the circumferential grooves and grounding ends, anda center land part located between the pair of the shoulder land parts,wherein the first rubber layer and the second rubber layer are formed of a rubber composition comprising a rubber component,wherein a ratio of a distance H2 (mm) from an outermost surface of the tread part to an outermost part of the second rubber layer to a groove depth H1 of deepest parts of the circumferential grooves (H2/H1) is 0.40 to 0.90, andwherein, when a complex elastic modulus at 30°C of the first rubber layer is defined as E*T (MPa) and a complex elastic modulus at 30°C of the second rubber layer is defined as E*B (MPa), E*B is greater than E*T, and a ratio of E*T to H2/H1 (E*T/(H2/H1)) is 6.0 or more. The tire obtained is improved in total performance of steering stability during high-speed running and noise performance by stacking two or more rubber layers on a tread part of the tire and making complex elastic modulus and groove depths of circumferential grooves of the rubber layers have a predetermined relationship. The reason for that is considered as follows, although the following consideration is not intended to be bound by any theory. In the case that an entire tread land part is soft, the tread land part inevitably collapses at an exit during a cornering motion, transmission of force becomes poor during acceleration, and acceleration does not become smooth when an accelerator is pushed. On the other hand, in the case that the entire tread land part is hard, although a deformation of the tread land returns smoothly, vibrations easily propagate and noise performance deteriorates. The tire has the following features: (1) in order to form interfaces in a land part, the land part is divided into two or more (preferably three or more) rubber layers, the second rubber layer is formed to be harder than the first rubber layer, and a ratio of a distance H2 (mm) from an outermost surface of the tread part to an outermost part of the second rubber layer to a groove depth H1 of deepest parts of the circumferential grooves (H2/H1) is set to be in a predetermined range, thereby making it possible to absorb vibrations inside the first rubber layer and to simultaneously produce a large force from the second rubber layer at an exit of a corner to transmit the force to the land part, so that the deformation of