tire

Abstract

To provide a tire capable of exerting stable and excellent wet performance until a wear terminal period of a tread part.SOLUTION: A tire has a tread part 2, The tread part 2 includes a grounding surface 13, buttress surfaces 14, a first rubber layer 21, and a second rubber layer 22. The pair of buttress surfaces 14 has an inclination with which a tread grounding end Te moves outward in a tire axial direction as the tread part 2 wears. A loss tangent tan δ2 of a second cap rubber 22G is larger than a loss tangent tan δ1 of a first cap rubber 21G. On one of the pair of buttress surfaces 14, an outside lateral groove 25 is provided. The outside lateral groove 25 is located on the outer side in the tire axial direction than the tread grounding end Te, and when the tread grounding Te moves outward in the tire axial direction due to the wear of the tread part 2, at least a part of the outside lateral groove 25 is located on the inner side in the tire axial direction than the tread grounding end Te.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to tires.

Background Art

[0002] In Patent Document 1 below, a pneumatic tire is proposed that expects low rolling resistance and good wet braking performance by specifying the loss tangent and the like of the first cap layer and the second cap layer of the tread.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In conventional tires, the wet performance gradually deteriorates due to the decrease in groove volume accompanying the wear of the tread portion. On the other hand, in recent years, it has been required that tires can exhibit sufficient wet performance even when the wear of the tread portion progresses.

[0005] The present disclosure has been devised in view of the above circumstances, and the main problem is to provide a tire that can exhibit sufficient wet performance even when the tread portion is worn.

Means for Solving the Problems

[0006] This disclosure relates to a tire having a tread portion, the tread portion comprising a pair of tread contact ends, a contact surface between the pair of tread contact ends, a pair of buttress surfaces located axially outward from the tread contact ends, a first rubber layer consisting of at least a first cap rubber constituting the contact surface, and a second rubber layer consisting of a second cap rubber disposed radially inward of the first rubber layer, wherein the pair of buttress surfaces have an inclination such that the tread contact ends move axially outward as the tread portion wears down, the loss tangent tanδ2 of the second cap rubber is greater than the loss tangent tanδ1 of the first cap rubber, and at least one of the pair of buttress surfaces is provided with at least one outer transverse groove extending axially from the tread contact ends, the outer transverse groove being located axially outward from the tread contact ends when the tire is new, and at least a portion of the outer transverse groove being located axially inward from the tread contact ends when the tread contact ends move axially outward due to wear down the tread portion. [Effects of the Invention]

[0007] By adopting the above configuration, the tire disclosed herein can exhibit sufficient wet performance even when the tread is worn. [Brief explanation of the drawing]

[0008] [Figure 1] This is a meridional cross-sectional view of a tire showing one embodiment of the tire of the present disclosure. [Figure 2] Figure 1 is an enlarged cross-sectional view of the tread area. [Figure 3] Figure 1 is an enlarged perspective view showing the buttress surface. [Figure 4] Figure 1 is an enlarged plan view of the buttress surface and the contact surface. [Figure 5] This is a cross-sectional view along line AA in Figure 4. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings. Figure 1 is a meridian cross-sectional view of tire 1 in its normal state, showing one embodiment of the present disclosure. As shown in Figure 1, the present disclosure is preferably applied to, for example, a pneumatic tire for a passenger car. However, it is not limited to this embodiment, and the present disclosure may also be applied to, for example, a heavy-duty tire.

[0010] The aforementioned "normal condition" refers, in the case of pneumatic tires for which various standards are defined, to a state in which the tire is mounted on a standard rim, filled to the standard internal pressure, and under no load. In the case of tires for which various standards are not defined, the aforementioned normal condition means a standard usage condition according to the intended use of the tire, in which it is not mounted on a vehicle and is under no load. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured under the aforementioned normal condition.

[0011] A "standard rim" is the rim defined for each tire within the standards system that the tire is based on. For example, it is the "standard rim" for JATMA, the "Design Rim" for TRA, and the "Measuring Rim" for ETRTO.

[0012] "Regular internal pressure" refers to the air pressure specified for each tire by each standard within the tire standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0013] Inside the tire 1 of this embodiment, tire components such as a carcass 6 and a tread reinforcing cord layer 7 are arranged. Known configurations are appropriately adopted for these tire components.

[0014] The carcass 6 extends from the bead portion 4 on one side, through the sidewall portion 3 and tread portion 2 on one side, and the sidewall portion 3 on the other side, to the bead portion 4 on the other side. In this embodiment, the carcass 6 is composed of, for example, two carcass plies 6A and 6B. The two carcass plies 6A and 6B are composed of carcass cords made of organic fibers arranged at an angle of 75 to 90° with respect to the circumferential direction of the tire, for example.

[0015] The tread reinforcement cord layer 7 is composed of, for example, two reinforcement plies 7A and 7B. The reinforcement plies 7A and 7B are, for example, made of multiple cords covered with topping rubber. The cords are arranged, for example, at an angle of 10 to 45 degrees with respect to the circumferential direction of the tire. For example, organic fiber cords or steel cords may be used as appropriate for the cords.

[0016] The tread portion 2 includes a pair of tread contact edges Te, a contact surface 13 between the pair of tread contact edges Te, and a pair of buttress surfaces 14 located axially outward from the tread contact edges Te. The tread contact edges Te correspond to the edges of the contact surface when the tire 1 in its normal state is loaded with 80% of its normal load and the tread portion 2 is in contact with a plane at a camber angle of 0°.

[0017] "Regular load" refers to the load specified for each tire within the standard system, including the standard on which the tire is based, in the case of pneumatic tires for which various standards are defined. For example, it is the "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO. For tires for which no various standards are defined, "regular load" refers to the maximum load that can be applied when using the tire, in accordance with the above standards.

[0018] The grounding surface 13 is the area that contacts the road surface during normal driving. However, when a large load acts on the tire 1, not only the grounding surface 13 but also a part of the buttress surface 14 may contact the road surface. The grounding surface 13 near the tread grounding end Te and the pair of buttress surfaces 14 have an inclination such that the tread grounding end Te moves outward in the tire axial direction as the tread portion 2 wears. Note that the wear of the tread portion 2 means the normal wear that occurs on the entire grounding surface 13 of the tread portion 2 when the tire 1 is used in a normal manner.

[0019] In the tread portion 2 of the present embodiment, for example, a plurality of circumferential grooves 8 that continuously extend in the tire circumferential direction between two tread grounding ends Te are provided. Thereby, the tread portion 2 includes a first land portion 11 and a second land portion 12 divided by the circumferential groove 8. The second land portion 12 is arranged closer to the tire equator C side than the first land portion 11. The tread portion 2 of the present embodiment is configured to include two second land portions 12 arranged on the tire equator C side and two first land portions 11 arranged so as to sandwich these. Thereby, the tire 1 of the present embodiment is configured as a so-called 4-rib tire. However, the tire 1 of the present disclosure is not limited to such a mode. For example, the tread portion 2 may be configured as a so-called 5-rib tire divided into five land portions by four circumferential grooves 8.

[0020] A plurality of grooves are provided in the tread portion 2. In the present embodiment, in addition to the above-described circumferential grooves 8, a plurality of lateral grooves (not shown) extending in the tire axial direction are provided. It is desirable that wear indicators (not shown) that locally protrude from the groove bottom are provided in the circumferential grooves 8 and the lateral grooves. The wear indicator is a mark indicating the limit of wear of the tread portion 2. For example, when the tread portion 2 wears to the limit, the outer surface in the tire radial direction of the wear indicator is continuous with the grounding surface. Thereby, the user of the tire 1 can know that the limit of the wear has arrived.

[0021] FIG. 2 shows an enlarged cross-sectional view of the tread portion 2. As shown in FIG. 2, the tread portion 2 includes a first rubber layer 21 and a second rubber layer 22. The first rubber layer 21 consists of a first cap rubber 21G and at least constitutes the ground contact surface 13. The second rubber layer 22 consists of a second cap rubber 22G and is disposed on the inner side in the tire radial direction of the first rubber layer 21.

[0022] Generally, it is known that rubber with a large loss tangent can exhibit a large frictional force on a wet road surface. Based on such technical matters, in the present disclosure, the loss tangent tanδ2 of the second cap rubber 22G is larger than the loss tangent tanδ1 of the first cap rubber 21G. In this specification, the loss tangent tanδ is a value measured using a dynamic viscoelasticity measuring device (Implex series) manufactured by GABO under the following conditions in accordance with the provisions of JIS-K6394. Initial strain: 5% Amplitude of dynamic strain: ±1% Frequency: 10 Hz Deformation mode: Extension Measurement temperature: 30°C

[0023] FIG. 3 shows an enlarged perspective view showing the buttress surface 14, and FIG. 4 shows an enlarged plan view of the buttress surface 14 and the ground contact surface 13. In FIG. 4, the ground contact surface 13 from the tread ground contact end Te to the circumferential groove 8 adjacent thereto is shown. In the present embodiment, the first land portion 11 constitutes this ground contact surface 13. As shown in FIGS. 3 and 4, at least one of the pair of buttress surfaces 14 is provided with at least one outer lateral groove 25 extending in the tire axial direction. In a preferred embodiment, a plurality of outer lateral grooves 25 are provided on both of the pair of buttress surfaces 14.

[0024] The outer lateral groove 25 is located axially outward of the tread contact edge Te when the tire is new. Furthermore, when the tread contact edge Te moves axially outward due to wear of the tread portion 2, the outer lateral groove 25 is positioned axially inward of the moved tread contact edge Te. By adopting the above configuration, the tire 1 of this disclosure can exhibit sufficient wet performance even when the tread portion 2 is worn. The mechanism is as follows.

[0025] In the tire 1 of this disclosure, as wear progresses on the tread portion 2, the second rubber layer 22 is exposed. The second cap rubber 22G constituting the second rubber layer 22 has a large loss tangent, and high wet grip can be expected. Therefore, the second rubber layer 22 can compensate for the decrease in wet performance due to wear on the tread portion 2, and sufficient wet performance can be maintained even when the tread portion 2 is worn.

[0026] On the other hand, in the tire 1 of this disclosure, as wear progresses on the tread portion 2, at least a portion of the outer lateral groove 25 is located inward in the tire axial direction from the tread contact edge Te which has moved outward in the tire axial direction. As a result, the outer lateral groove 25 can exert its drainage capacity and maintain wet performance. In this disclosure, sufficient wet performance can be achieved even when the tread portion 2 is worn down due to the above mechanism.

[0027] The configuration of this embodiment will be described in more detail below. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that this disclosure can achieve the above-described effects even without the configurations described below. Furthermore, even if any one of the configurations described below is applied individually to a tire of this disclosure having the above-described features, an improvement in performance corresponding to each configuration can be expected. Moreover, if several of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0028] As shown in Figure 2, the loss tangent tanδ1 of the first cap rubber 21G is preferably 0.13 or higher, more preferably 0.15 or higher, even more preferably 0.18 or higher, preferably 0.29 or lower, more preferably 0.25 or lower, and even more preferably 0.22 or lower. Such a first cap rubber 21G can exhibit a good balance of handling stability on dry surfaces (hereinafter simply referred to as "handling stability") and wet performance when the tire is first used.

[0029] To improve handling stability and wet performance when the tread portion 2 is worn, the loss tangent tanδ2 of the second cap rubber 22G is preferably 0.20 or more, more preferably 0.25 or more, even more preferably 0.28 or more, preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.32 or less.

[0030] In a more desirable embodiment, the tread portion 2 includes a third rubber layer 23 made of base rubber 23G positioned radially inward of the second rubber layer 22. It is desirable that the loss tangent tanδb of the base rubber 23G is smaller than the loss tangent tanδ1. Specifically, the loss tangent tanδb is 0.12 or less. Such a third rubber layer 23 made of base rubber 23G helps suppress excessive heat generation in the tread portion 2 and improves fuel efficiency.

[0031] In this embodiment, the tread rubber 2G is composed of only the first rubber layer 21, the second rubber layer 22, and the third rubber layer 23 described above, at least in the area constituting the contact surface 13, and no other rubber layers are provided. However, the embodiment is not limited to this configuration, and other rubber layers may be provided as appropriate. In this embodiment, the first rubber layer 21, the second rubber layer 22, and the third rubber layer 23 each extend with substantially constant thickness on the radially inward side of the contact surface 13, except around the circumferential groove 8.

[0032] In this embodiment, the maximum thickness t1 of the first rubber layer 21 is 20% to 40% of the effective tread thickness ta. This allows the second cap rubber 22G, which provides high wet grip, to be exposed when the tread portion 2 has worn down to a moderate degree, thereby effectively maintaining wet performance. The effective tread thickness ta refers to the thickness of the tread rubber from the contact surface 13 to the wear limit at which the tire 1 can maintain the minimum necessary performance. In the case of a tire with circumferential grooves 8, it refers to the thickness from the contact surface to the bottom of the circumferential grooves 8.

[0033] In a desirable embodiment, it is desirable that at least a portion of the second rubber layer 22 is exposed to the contact surface 13 when the tread portion 2 is 30% worn. The 30% worn state refers to a state of wear in which the effective tread thickness ta is reduced by 30%. This allows the second rubber layer 22 to be exposed relatively early, effectively maintaining wet performance.

[0034] From the standpoint of reliably maintaining wet performance, it is desirable that the second rubber layer 22 constitutes the contact surface 13 even when the tread rubber 2G is worn to its limit. In other words, it is desirable that the second rubber layer 22 constitutes the contact surface 13 when the above-mentioned wear indicator (not shown) appears on the contact surface. In a more desirable embodiment, it is desirable that the inner surface 22i of the second rubber layer 22 in the tire radial direction is located radially inward from the groove bottom of the circumferential groove 8. This ensures that wet performance is reliably maintained.

[0035] The maximum thickness t2 of the second rubber layer 22 is 50% to 70% of the effective tread thickness ta. This allows the above-mentioned effects to be obtained while maintaining the durability of the tread portion 2.

[0036] The maximum thickness of the third rubber layer 23 is determined in various ways so that the first rubber layer 21 and the second rubber layer 22 can have the above-described configuration. In a preferred embodiment, the thickness t3 of the third rubber layer 23 is 20% to 40% of the effective tread thickness ta. This makes it possible to improve fuel efficiency while achieving the above-described effects.

[0037] As shown in Figures 3 and 4, the tire 1 of this embodiment is provided with a plurality of lateral grooves 27 that extend from a circumferential groove 8 located closest to the tread contact edge Te to a position beyond the tread contact edge Te. Furthermore, the outer lateral grooves 25 are provided alternately with these lateral grooves 27 in the circumferential direction of the tire.

[0038] As shown in Figure 4, the groove width and groove length of the outer lateral groove 25 are determined as appropriate. In this embodiment, the groove width W2 of the outer lateral groove 25 is, for example, 80% to 120% of the groove width W1 of the lateral groove 27. The outer end of the outer lateral groove 25 in the tire axial direction is positioned substantially at the same position as the outer end 27o of the lateral groove 27 in the tire axial direction. However, the outer lateral groove 25 is not limited to this configuration.

[0039] The outer lateral groove 25 in this embodiment extends, for example, along the tire axis. The outer lateral groove 25 may also be inclined with respect to the tire axis. In this case, the angle of the outer lateral groove 25 with respect to the tire axis is preferably 25 to 50°, and more preferably 30 to 45°. Such an outer lateral groove 25 can exhibit excellent drainage performance by utilizing the rotation of the tire.

[0040] At least in the worn state in which the second cap rubber 22G is exposed, it is desirable that the inner end of the outer lateral groove 25 in the tire axial direction is located inward in the tire axial direction from the tread contact edge Te. Furthermore, in a more desirable embodiment, in the 30% worn state, it is desirable that the inner end 25i of the outer lateral groove 25 in the tire axial direction is located inward in the tire axial direction from the tread contact edge Te. This allows sufficient wet performance to be achieved even when the tread portion 2 is worn. In the above configuration, the tread contact edge Te refers to the edge of the contact surface 13 when the tread portion 2 is worn.

[0041] The axial distance L1 from the tread contact edge Te to the inner end 25i of the outer lateral groove 25 in the tire axial direction, when the tire is new, is appropriately determined so that the above-mentioned effects can be achieved. Specifically, the distance L1 is set to, for example, 2.0 to 10.0 mm. This ensures that the above-mentioned effects can be reliably achieved while maintaining handling stability on dry road surfaces when the tire is new.

[0042] Figure 5 shows a cross-sectional view along line AA in Figure 4. Figure 5 shows the cross-sectional shape of the outer lateral groove 25 along its length. As shown in Figure 5, the maximum depth d1 of the outer lateral groove 25 is 2.0 to 4.0 mm. Furthermore, the depth of the outer lateral groove 25 increases from the inner end 25i in the tire axial direction toward the outer side in the tire axial direction, with the maximum depth d1 located in the center of the groove in the longitudinal direction. As a result, the cross-sectional shape of the outer lateral groove 25 is configured as an obtuse triangle with the maximum depth position as the apex of the obtuse angle. This allows the above-mentioned effects to be obtained while maintaining the rubber volume of the buttress surface 14 and maintaining the durability of this region.

[0043] Although a tire according to one embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the specific embodiment described above and can be implemented in various modified forms.

[0044] [Note] This disclosure includes the following aspects.

[0045] [Disclosure 1] A tire having a tread portion, The tread portion includes a pair of tread contact ends, a contact surface between the pair of tread contact ends, a pair of buttress surfaces located axially outward from the tread contact ends, a first rubber layer consisting of at least a first cap rubber constituting the contact surface, and a second rubber layer consisting of a second cap rubber arranged radially inward of the first rubber layer. The pair of buttress surfaces have an inclination such that, as the tread wears down, the tread contact edge moves outward in the tire axial direction. The loss tangent tanδ2 of the second cap rubber is greater than the loss tangent tanδ1 of the first cap rubber. At least one of the pair of buttress surfaces is provided with at least one outer transverse groove extending in the tire axial direction. The aforementioned outer lateral groove is located axially outward from the tread contact edge when the tire is new, and When the tread contact edge moves outward in the tire axial direction due to wear of the tread portion, at least a portion of the outer lateral groove is located inward in the tire axial direction compared to the tread contact edge. tire. [Disclosure 2] The tread portion includes a third rubber layer made of base rubber arranged radially inward of the second rubber layer, The tire according to Disclosure 1, wherein the loss tangent tanδb of the base rubber is smaller than the loss tangent tanδ1. [Disclosure 3] The tire according to disclosure 1 or 2, wherein the angle of the outer lateral groove with respect to the tire axis is 30 to 45°. [Disclosure 4] In a worn state in which the second cap rubber is exposed, the inner end of the outer lateral groove in the tire axial direction is located inward in the tire axial direction from the tread contact edge, as described in any one of disclosures 1 to 3. [Disclosure 5] The tire according to any one of disclosures 1 to 3, wherein, in a state of 30% wear of the tread portion, the inner end of the outer lateral groove in the tire axial direction is located inward in the tire axial direction from the tread contact edge. [Disclosure 6] The tire according to disclosure 5, wherein at least a portion of the second rubber layer is exposed to the contact surface in the 30% wear state. [Disclosure 7] The tread portion is provided with at least one groove, The groove includes at least one wear indicator that protrudes locally from the bottom of the groove, In the wear state in which the wear indicator appears on the contact surface, the second rubber layer constitutes the contact surface, as described in any one of disclosures 1 to 6. [Disclosure 8] The tire according to any one of disclosures 1 to 7, wherein the maximum depth of the outer lateral groove is 2.0 to 4.0 mm. [Disclosure 9] The tire according to any one of disclosures 1 to 7, wherein the outer lateral groove has increasing depth from the inner end in the tire axial direction toward the outer side in the tire axial direction. [Explanation of Symbols]

[0046] 2 Tread section 13 Ground plane 14 Buttress surfaces 21. First rubber layer 21G First cap rubber 22 Second Rubber Layer 22G Second cap rubber 25 Outer transverse groove Te tread contact point

Claims

1. A tire having a tread portion, The tread portion includes a pair of tread contact ends, a contact surface between the pair of tread contact ends, a pair of buttress surfaces located axially outward from the tread contact ends, a first rubber layer consisting of at least a first cap rubber constituting the contact surface, and a second rubber layer consisting of a second cap rubber arranged radially inward of the first rubber layer. The pair of buttress surfaces have an inclination such that, as the tread wears down, the tread contact edge moves outward in the tire axial direction. The loss tangent tanδ2 of the second cap rubber is greater than the loss tangent tanδ1 of the first cap rubber. At least one of the pair of buttress surfaces is provided with a plurality of outer transverse grooves extending in the direction of the tire axis, The aforementioned outer lateral groove is located axially outward from the tread contact edge when the tire is new, and When the tread contact edge moves outward in the tire axial direction due to wear of the tread portion, at least a portion of the outer lateral groove is located inward in the tire axial direction compared to the tread contact edge. The tread portion is provided with a plurality of transverse grooves that extend from the circumferential groove located closest to the tread contact edge to a position beyond the tread contact edge. The aforementioned outer lateral grooves are arranged alternately with these lateral grooves in the circumferential direction of the tire. The groove width of the outer transverse groove is 80% to 120% of the groove width of the transverse groove. When the tire is new, the distance in the axial direction from the tread contact edge to the inner end of the outer lateral groove in the tire axial direction is 2.0 to 10.0 mm. tire.

2. The tread portion includes a third rubber layer made of base rubber arranged radially inward of the second rubber layer, The tire according to claim 1, wherein the loss tangent tanδb of the base rubber is smaller than the loss tangent tanδ1.

3. The tire according to claim 1 or 2, wherein the angle of the outer lateral groove with respect to the tire axis is 30 to 45°.

4. In a worn state in which the second cap rubber is exposed, the inner end of the outer lateral groove in the tire axial direction is located inward in the tire axial direction from the tread contact edge, as described in any one of claims 1 to 3.

5. The tire according to any one of claims 1 to 3, wherein, in a state of 30% wear of the tread portion, the inner end of the outer lateral groove in the tire axial direction is located inward in the tire axial direction from the tread contact edge.

6. The tire according to claim 5, wherein at least a portion of the second rubber layer is exposed to the contact surface in the 30% wear state.

7. The tread portion is provided with at least one groove, The groove includes at least one wear indicator that protrudes locally from the bottom of the groove, The tire according to any one of claims 1 to 6, wherein, in the wear state in which the wear indicator appears on the contact surface, the second rubber layer constitutes the contact surface.

8. The tire according to any one of claims 1 to 7, wherein the maximum depth of the outer lateral groove is 2.0 to 4.0 mm.

9. The tire according to any one of claims 1 to 8, wherein the outer lateral groove has increasing depth from the inner end in the tire axial direction toward the outer side in the tire axial direction.

10. The tire according to any one of claims 1 to 9, wherein the cross-sectional shape of the outer transverse groove is configured as an obtuse triangle with the maximum depth position as the vertex of the obtuse angle.

11. The tire according to any one of claims 1 to 10, wherein the loss tangent tanδ1 of the first cap rubber at 30°C is 0.15 or more.

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