pneumatic tires

Abstract

To provide a pneumatic tire of an outer apex structure, which improves durability performance of a toe of bead.SOLUTION: In a pneumatic tire, a reinforcement rubber layer adjacent to the tire-axial-direction outside of a folded part is arranged on at least one of a pair of toes 4 of bead. The reinforcement rubber layer includes a first rubber layer 11, and a second rubber layer 12 that is arranged on the tire-axial-direction outside of the first rubber layer 11. The loss tangent tanδ1 of the first rubber layer 11 is smaller than the loss tangent tanδ2 of the second rubber layer 12.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to pneumatic tires. [Background technology]

[0002] Patent Document 1 below describes a pneumatic tire that is expected to have improved durability. This pneumatic tire has a bead apex rubber disposed in the bead portion. The bead apex rubber includes a main apex extending from the outer surface of the bead core in the tire radial direction and an outer apex disposed axially outward of the main apex. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-93755 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned pneumatic tire with a so-called outer apex structure has room for improvement in durability of the bead portion under high load conditions.

[0005] The present disclosure has been devised in view of the above circumstances, and has as its main object to improve the durability of the bead portion in a pneumatic tire with an outer apex structure. [Means for solving the problem]

[0006] The present disclosure relates to a pneumatic tire including a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, wherein the carcass includes a carcass ply including a main portion extending between the bead cores and a turned-up portion folded back around each bead core from the inside in the axial direction of the tire to the outside and extending radially outward in the tire, wherein at least one of the pair of bead portions has a reinforcing rubber layer disposed adjacent to the outside of the turned-up portion in the axial direction of the tire, the reinforcing rubber layer including a first rubber layer and a second rubber layer disposed axially outward of the first rubber layer, and wherein a loss tangent tanδ1 of the first rubber layer is smaller than a loss tangent tanδ2 of the second rubber layer. [Effects of the Invention]

[0007] By employing the above-described configuration, the pneumatic tire of the present disclosure can improve the durability of the bead portion, particularly the durability performance under high load conditions. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a tire meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of a bead portion in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a tire meridian cross-sectional view including a tire rotation axis (not shown) of a pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 of this embodiment in a normal state. The present disclosure is used for tires 1 for commercial vehicles and light trucks, for example. However, the present disclosure may also be used for tires 1 for passenger cars and heavy loads.

[0010] The "normal state" refers to a state in which the tire 1 is mounted on a normal rim (not shown), inflated to a normal internal pressure, and no load is applied. Unless otherwise specified, the dimensions of each part of the tire 1 are values ​​measured in this normal state.

[0011] The "genuine rim" is a rim that is defined for each tire by a standard system that includes the standard on which tire 1 is based, such as a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.

[0012] The "normal internal pressure" is the air pressure determined for each tire by each standard in a standard system including the standard on which tire 1 is based, and is the "maximum air pressure" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

[0013] As shown in FIG. 1, a tire 1 of this embodiment includes a pair of bead portions 4, 4 each having a bead core 5 embedded therein, and a carcass 6 extending between the bead cores 5, 5.

[0014] The carcass 6 includes a carcass ply 6A including a main body portion 6a extending between the bead cores 5, 5 and a turned-up portion 6b folded back around each bead core 5 from the inside to the outside in the tire axial direction and extending radially outward in the tire. In this embodiment, the carcass 6 is formed of two carcass plies 6A, 6B arranged on the inside and outside in the tire radial direction. Each carcass ply 6A, 6B includes a main body portion 6a and a turned-up portion 6b. The carcass 6 may be formed of, for example, a single carcass ply 6A (not shown).

[0015] A reinforcing rubber layer 10 is disposed in at least one of the pair of bead portions 4, adjacent to the outer side of the turned-up portion 6b in the tire axial direction. The reinforcing rubber layer 10 increases the rigidity of the bead portion 4 to improve durability. In this embodiment, the reinforcing rubber layer 10 is disposed in each bead portion 4. The reinforcing rubber layer 10 is disposed, for example, adjacent to the outer side of the turned-up portion 6b of the inner carcass ply 6A in the tire axial direction.

[0016] The reinforcing rubber layer 10 includes a first rubber layer 11 and a second rubber layer 12 disposed axially outward of the first rubber layer 11. The loss tangent tanδ1 of the first rubber layer 11 is smaller than the loss tangent tanδ2 of the second rubber layer 12. As described above, the first rubber layer 11 has a small hysteresis loss, so its heat generation is suppressed. This prevents damage to the carcass plies 6A, 6B due to heat. The second rubber layer 12 also exerts a fundamental effect of suppressing distortion occurring in the bead portions 4. This significantly improves durability.

[0017] To effectively exert the above-mentioned effects, the loss tangent tanδ1 is, for example, preferably 0.07 or more, more preferably 0.12 or more, and preferably 0.17 or less, and more preferably 0.14 or less. The loss tangent tanδ1 is, for example, preferably 60% or more of the loss tangent tanδ2, more preferably 70% or more, and preferably 95% or less, and more preferably 90% or less.

[0018] In this specification, the loss tangent tanδ and the complex modulus E* described later are values ​​measured using a viscoelasticity spectrometer under the conditions shown below in accordance with the provisions of JIS K6394 "Vulcanized rubber and thermoplastic rubber - Determination of dynamic properties - General guidelines." Initial distortion: 10% Amplitude: ±2% Frequency: 10Hz Deformation mode: tension Temperature: 70℃ Viscoelasticity spectrometer: GABO "Iplexar (registered trademark)"

[0019] The complex modulus E*2 of the second rubber layer 12 is preferably greater than the complex modulus E*1 of the first rubber layer 11. This increases the rigidity of the second rubber layer 12, which is disposed relatively outward in the tire axial direction, and suppresses distortion under high load conditions, thereby improving durability. If the complex modulus E*2 of the second rubber layer 12 is excessively greater than the complex modulus E*1 of the first rubber layer 11, heat generated in the second rubber layer 12 may be conducted to the carcass plies 6A, 6B via the first rubber layer 11. For this reason, the complex modulus E*2 is preferably 120% or more of the complex modulus E*1, more preferably 130% or more, and more preferably 200% or less, and even more preferably 190% or less. Although not particularly limited, the complex modulus E*1 is preferably 20 MPa or more, more preferably 30 MPa or more, preferably 110 MPa or less, and even more preferably 80 MPa or less.

[0020] It is desirable that the inner end 10i of the reinforcing rubber layer 10 in the tire radial direction be located within 10 mm in the tire radial direction from the outer end 5e of the bead core 5. If the inner end 10i of the reinforcing rubber layer 10 is located more than 10 mm outward in the tire radial direction from the outer end 5e of the bead core 5, it may not be possible to suppress strain occurring in the bead portion 4. If the inner end 10i of the reinforcing rubber layer 10 is located more than 10 mm inward in the tire radial direction from the outer end 5e of the bead core 5, it will not contribute to increasing the rigidity of the bead portion 4, and there is a risk that, for example, the mass of the tire 1 will increase or the ease of mounting on a rim will decrease.

[0021] The height H1 from the bead base line BL to the radially outer end 10e of the reinforcing rubber layer 10 is preferably 25% or more of the tire cross-sectional height H. This ensures that the rigidity of the bead portion 4 at a position where significant distortion occurs can be increased. If the height H1 is excessively large, for example, this may result in an increase in tire mass. From this perspective, the height H1 is more preferably 30% or more of the tire cross-sectional height H, more preferably 50% or less, and even more preferably 45% or less.

[0022] In this specification, the "bead base line BL" is a line in the tire axial direction that passes through the rim diameter position (see JATMA) defined by the standard on which the tire 1 is based. Also, the "tire cross-sectional height H" is the distance in the tire radial direction from the bead base line BL to the outermost position in the tire radial direction.

[0023] Fig. 2 is an enlarged view of the bead portion 4 in Fig. 1. As shown in Fig. 2, the first rubber layer 11 and the second rubber layer 12 are formed, for example, of sheet-shaped rubber members 13. In other words, in this embodiment, the reinforcing rubber layer 10 is formed as a laminate 13R in which sheet-shaped rubber members 13 are stacked in the tire axial direction. Such a reinforcing rubber layer 10 increases the rigidity of the bead portion 4 and prevents a large increase in mass.

[0024] The sheet-like rubber member 13 has a constant thickness T over, for example, 90% or more of its length. The reinforced rubber layer 10 formed with such a rubber member 13 maintains high rigidity, improving durability. In this specification, the "constant thickness" includes a portion where the thickness of the sheet-like rubber member 13 changes by 0.2 mm / mm or less in the direction perpendicular to the thickness thereof.

[0025] The thickness T2 of the second rubber layer 12 is greater than the thickness T1 of the first rubber layer 11. This provides the reinforcing rubber layer 10 with greater rigidity, further improving durability. Although not particularly limited, the thickness T2 of the second rubber layer 12 is preferably 130% or more of the thickness T1 of the first rubber layer 11, more preferably 140% or more, and preferably 170% or less, and more preferably 160% or less. Furthermore, the thickness T2 of the second rubber layer 12 is preferably 1.0 mm or more, more preferably 1.2 mm or more, and preferably 2.5 mm or less, and more preferably 2.0 mm or less.

[0026] In this embodiment, the radially outer end 11e of the first rubber layer 11 is located radially outward of the radially outer end 12e of the second rubber layer 12. Such a first rubber layer 11 effectively prevents heat generated in the second rubber layer 12 from being conducted to the carcass 6. The radially spaced distance Ha between the radially outer end 11e of the first rubber layer 11 and the radially outer end 12e of the second rubber layer 12 is preferably 2% or more of the radially outer length H2 of the first rubber layer 11, more preferably 5% or more, more preferably 20% or less, and even more preferably 10% or less.

[0027] To achieve the same effect, in this embodiment, the radially inner end 11i of the first rubber layer 11 is positioned radially inward of the radially inner end 12i of the second rubber layer 12. The radially spaced distance Hb between the inner end 11i of the first rubber layer 11 and the inner end 12i of the second rubber layer 12 is preferably 2% or more of the length H2 of the first rubber layer 11, more preferably 5% or more, and more preferably 20% or less, and even more preferably 10% or less.

[0028] The bead portion 4 of this embodiment is provided with a bead apex rubber 8 extending radially outward from the bead core 5 and a clinch rubber 4G arranged axially outward of the reinforcing rubber layer 10. Further, for example, a sidewall rubber 3G is adjacent to the clinch rubber 4G radially outward. The sidewall rubber 3G and the clinch rubber 4G form the outer surface of the tire 1.

[0029] The bead apex rubber 8 is formed, for example, in a triangular shape in a tire meridian cross section. Although not particularly limited, a first rubber layer 11 and a second rubber layer 12 are arranged at the height position in the tire radial direction of an outer end 8e of the bead apex rubber 8 in the tire radial direction.

[0030] The complex elastic modulus E*3 of the bead apex rubber 8 is preferably larger than the complex elastic modulus E*1 of the first rubber layer 11. The complex elastic modulus E*3 of the bead apex rubber 8 is preferably smaller than the complex elastic modulus E*2 of the second rubber layer 12, for example.

[0031] The complex modulus E* of the sidewall rubber 3G and the clinch rubber 4G is both smaller than the complex modulus E*1 of the first rubber layer 11. This allows basic ride comfort performance to be exhibited.

[0032] Although one embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the above specific embodiment and can be modified and implemented in various aspects. [Example]

[0033] Pneumatic tires having the basic structure shown in Figure 1 were prototyped based on the specifications in Table 1. The durability performance of each test tire was then tested. The common specifications and test methods for each test tire are as follows:

[0034] <Durability> Each test tire was run on a drum testing machine under the following conditions, and the running distance until damage to the bead portion was measured. The test results were expressed as an index, with Comparative Example 1 being 100. The larger the number, the better. Tire size: 225 / 85R16 Rim: 6.0J Internal pressure: 220kPa Load: 19.84kN tanδ1:0.13 E*1:30MPa The test results are shown in Table 1. "A" in Table 1 is the distance in the tire radial direction between the inner end of the reinforcing rubber layer and the outer end of the bead core, and the outer end of the bead core is located axially outward of the inner end of the reinforcing rubber layer.

[0035] [Table 1]

[0036] As a result of the test, it is understood that the tires of the examples have improved durability performance compared to the tires of the comparative examples.

[0037] [Note] The present disclosure includes the following aspects.

[0038] [Disclosure 1] A pneumatic tire, The tire includes a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, the carcass includes a carcass ply including a main body portion extending between the bead cores and a turned-up portion turned around each bead core from the inside to the outside in the tire axial direction and extending outward in the tire radial direction, a reinforcing rubber layer is disposed on at least one of the pair of bead portions and adjacent to the outer side of the turned-up portion in the tire axial direction, the reinforcing rubber layer includes a first rubber layer and a second rubber layer disposed on the outer side of the first rubber layer in the tire axial direction, a loss tangent tanδ1 of the first rubber layer is smaller than a loss tangent tanδ2 of the second rubber layer; Pneumatic tires. [Disclosure 2] The pneumatic tire according to Disclosure 1, wherein the complex modulus E*2 of the second rubber layer is greater than the complex modulus E*1 of the first rubber layer. [Disclosure 3] The pneumatic tire according to Disclosure 2, wherein the complex modulus E*2 of the second rubber layer is 150% or more of the complex modulus E*1 of the first rubber layer. [Disclosure 4] The pneumatic tire according to any one of Disclosures 1 to 3, wherein an inner end in the tire radial direction of the reinforcing rubber layer is located within 10 mm in the tire radial direction from an outer end in the tire radial direction of the bead core. [Disclosure 5] 5. The pneumatic tire according to any one of Disclosures 1 to 4, wherein the height from a bead base line to an outer end of the reinforcing rubber layer in the tire radial direction is 25% or more of the tire cross-sectional height. [Disclosure 6] The pneumatic tire according to any one of Disclosures 1 to 5, wherein the second rubber layer has a thickness greater than the thickness of the first rubber layer. [Disclosure 7] The pneumatic tire according to any one of Disclosures 1 to 6, wherein the radially outer end of the first rubber layer is positioned radially outward of the radially outer end of the second rubber layer. [Disclosure 8] The pneumatic tire according to any one of Disclosures 1 to 7, wherein the inner end in the tire radial direction of the first rubber layer is located more inward in the tire radial direction than the inner end in the tire radial direction of the second rubber layer. [Explanation of symbols]

[0039] 1 pneumatic tire 6b Folded part 10 Reinforced rubber layer 11 First rubber layer 12 Second rubber layer

Claims

1. A pneumatic tire, The tire includes a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, the carcass includes a carcass ply including a main body portion extending between the bead cores and a turned-up portion turned around each bead core from the inside to the outside in the tire axial direction and extending outward in the tire radial direction, a reinforcing rubber layer is disposed on at least one of the pair of bead portions and adjacent to the outer side of the turned-up portion in the tire axial direction, the reinforcing rubber layer includes a first rubber layer and a second rubber layer disposed on the outer side of the first rubber layer in the tire axial direction, a loss tangent tanδ1 of the first rubber layer is smaller than a loss tangent tanδ2 of the second rubber layer, a complex elastic modulus E*2 of the second rubber layer is greater than a complex elastic modulus E*1 of the first rubber layer, The thickness of the second rubber layer is greater than the thickness of the first rubber layer. Pneumatic tires.

2. A pneumatic tire as described in claim 1, wherein the complex modulus E*2 of the second rubber layer is 150% or more of the complex modulus E*1 of the first rubber layer.

3. A pneumatic tire, The tire includes a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, the carcass includes a carcass ply including a main body portion extending between the bead cores and a turned-up portion turned around each bead core from the inside to the outside in the tire axial direction and extending outward in the tire radial direction, a reinforcing rubber layer is disposed on at least one of the pair of bead portions and adjacent to the outer side of the turned-up portion in the tire axial direction, the reinforcing rubber layer includes a first rubber layer and a second rubber layer disposed on the outer side of the first rubber layer in the tire axial direction, a loss tangent tanδ1 of the first rubber layer is smaller than a loss tangent tanδ2 of the second rubber layer, an inner end of the reinforcing rubber layer in the tire radial direction is located within 10 mm in the tire radial direction from an outer end of the bead core in the tire radial direction, The thickness of the second rubber layer is greater than the thickness of the first rubber layer. Pneumatic tires.

4. A pneumatic tire, The tire includes a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, the carcass includes a carcass ply including a main body portion extending between the bead cores and a turned-up portion turned around each bead core from the inside to the outside in the tire axial direction and extending outward in the tire radial direction, a reinforcing rubber layer is disposed on at least one of the pair of bead portions and adjacent to the outer side of the turned-up portion in the tire axial direction, the reinforcing rubber layer includes a first rubber layer and a second rubber layer disposed on the outer side of the first rubber layer in the tire axial direction, a loss tangent tanδ1 of the first rubber layer is smaller than a loss tangent tanδ2 of the second rubber layer, an inner end of the first rubber layer in the tire radial direction is located more inward in the tire radial direction than an inner end of the second rubber layer in the tire radial direction; Pneumatic tires.

5. 5. The pneumatic tire according to claim 1, wherein a height from a bead base line to an outer end of the reinforcing rubber layer in the tire radial direction is 25% or more of a tire cross-sectional height.

6. A pneumatic tire described in any one of claims 1 to 5, wherein the radially outer end of the first rubber layer is located radially outward of the radially outer end of the second rubber layer.

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