pneumatic tires

Abstract

To provide a pneumatic tire with further improved bead durability.SOLUTION: A pneumatic tire 1 comprises a bead core 5, a carcass 6 and a bead apex rubber. In a rim-unassembled state where a width of a bead part 4 is kept equal to a rim width, an inside surface of the bead core 5 is inclined to outside in a radial direction of the tire, toward outside in a tire axial direction, at angles of 20 degrees ±2 degrees with respect to the tire axial direction. The bead apex rubber includes a first rubber part 10, arranged to surround a circumference of the bead core 5, whose outline has a circular shape or a nearly elliptical shape, and a second rubber part 11 extending in a taper shape from the first rubber part 10 to outside in the radial direction of the tire. The first rubber part 10 is larger in rubber hardness than the second rubber part 11.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Patent Document 1 below describes a heavy-duty tire including a bead core and a carcass folded around the bead core. When the bead core is molded, the inner surface of the bead core is inclined so that the inner diameter increases toward the outside in the tire axial direction and at an angle of 20 degrees relative to the tire axial line. This tire is said to have excellent bead durability because, under standard load conditions, the bead core rotates and the angle between the inner surface and the rim seat surface, which is the outer surface of the rim seat, becomes substantially parallel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-254736 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the invention of Patent Document 1 mentioned above had the risk of causing damage or breakage (hereinafter referred to as CBU) of the carcass cords of the carcass due to friction with the bead core caused by the rotation of the bead core when the standard load is applied.

[0005] The present invention was devised in view of the above circumstances, and its main object is to provide a pneumatic tire that suppresses damage such as CBU and further improves bead durability performance. [Means for solving the problem]

[0006] The present invention is a pneumatic tire comprising a pair of bead portions each having a bead core embedded therein, and a carcass extending between the bead cores, the bead cores having an inner core surface extending in a substantially linear manner on the inner side in the radial direction of the tire, the inner core surface inclining at an angle of 20 degrees ± 2 degrees with respect to the tire axial direction toward the outer side in the axial direction of the tire before assembly with the rim, each of the pair of bead portions having a bead apex rubber extending from the bead core toward the outer side in the radial direction of the tire, the bead apex rubber being arranged to cover the periphery of the bead core in a tire meridian cross section, and including a first rubber portion having a circular or substantially elliptical outline and a second rubber portion extending tapered from the first rubber portion toward the outer side in the radial direction of the tire, the first rubber portion having a higher rubber hardness than the second rubber portion.

[0007] In the pneumatic tire according to the present invention, it is desirable that the radial distance between the radial outer end of the first rubber portion and the bead base line is 10% to 65% of the radial distance between the maximum width position of the tire and the bead base line.

[0008] In the pneumatic tire according to the present invention, it is preferable that the thickness of the first rubber portion in the axial direction of the tire is 1.0 to 2.0 mm at the inner end position in the axial direction of the tire of the bead core.

[0009] In the pneumatic tire according to the present invention, it is preferable that the thickness of the first rubber portion in the tire radial direction at the inner end position of the bead core in the tire radial direction is 1.0 to 2.0 mm.

[0010] In the pneumatic tire according to the present invention, it is desirable that the rubber hardness of the first rubber portion is 1.6 to 2.0 times the rubber hardness of the second rubber portion.

[0011] In the pneumatic tire according to the present invention, it is preferable that a reinforcing layer covering the carcass is provided in the bead portion, and in a tire meridian cross section, the reinforcing layer is U-shaped and both ends thereof are spaced radially outward by 20 mm or more from the radially outer end of the first rubber portion.

[0012] In the pneumatic tire according to the present invention, it is desirable that the periphery of the bead core is covered with a canvas cloth containing organic fiber cords.

[0013] The pneumatic tire according to the present invention is preferably for heavy loads. [Effects of the Invention]

[0014] By employing the above-described configuration, the pneumatic tire of the present invention can further improve the bead durability performance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of one embodiment of a pneumatic tire of the present invention. [Figure 2] 2 is an enlarged view of a bead core of the pneumatic tire of FIG. 1 before being mounted on a rim. [Figure 3] FIG. 2 is an enlarged view of a bead portion in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will now 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. A normal rim (hereinafter sometimes simply referred to as "rim") R is incorporated into the tire 1 of FIG. The present invention is applied to, for example, a tire 1 for heavy loads. However, the present invention may also be applied to tires 1 for passenger cars, light trucks, etc.

[0017] The "normal state" refers to a state in which the tire 1 is mounted on a normal rim R, inflated to a normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire 1 are values ​​measured in this normal state.

[0018] The "regular rim R" is a rim defined for each tire by a standard system including the standard on which the tire 1 is based, for example, "standard rim" for JATMA, "design rim" for TRA, and "measuring rim" for ETRTO. The "regular internal pressure" is an air pressure defined for each tire by a standard system including the standard on which the tire 1 is based, for example, "maximum air pressure" for JATMA, the maximum value listed in the table "TIRELOAD LIMITS SAT VARIOUSCOLD INFLATION PRESSURE" for TRA, and "INFLATION PRESSURE" for ETRTO.

[0019] The tire 1 of this embodiment includes a pair of bead portions 4 each having a bead core 5 embedded therein, and a carcass 6 extending between the bead cores 5. The tire 1 also includes a pair of sidewall portions 3 disposed radially outward of the bead portions 4, and a tread portion 2 connecting the sidewall portions 3 on both sides.

[0020] Fig. 2 is an enlarged view of the bead core 5 of the tire 1 in Fig. 1 in a state before assembly with a rim, in which the width of the bead portion 4 is maintained at the rim width (not shown). As shown in Fig. 2, the bead core 5 has a core inner surface 5a that extends in a substantially straight line on the inner side in the tire radial direction. The core inner surface 5a is a surface that extends along the rim seat surface Ra (shown in Fig. 1) when assembled with a rim.

[0021] Before mounting on the rim, when the width of the bead portion 4 is maintained at the rim width, the core inner surface 5a is inclined axially outward and radially outward at an angle θ1 of 20°±2° with respect to the tire axial direction. As a result, when the tire 1 is in a normal state or a normal load state, the bead core 5 rotates, and the core inner surface 5a and the rim seat surface Ra become substantially parallel, improving bead durability. The angle θ2 (shown in FIG. 1) of the rim seat surface Ra with respect to the tire axial direction is 15°.

[0022] The "normal load condition" refers to a state in which a normal load is applied to the tire 1 in a normal state, with the tire in contact with a flat surface at a camber angle of 0 degrees. The "normal load" is the load determined for each tire by each standard in the standard system including the standard on which the tire is based, and is the "maximum load capacity" 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 "LOAD CAPACITY" in the case of ETRTO.

[0023] As shown in FIG. 1, each of the pair of bead portions 4 is provided with a bead apex rubber 9 extending from a bead core 5 outward in the tire radial direction.

[0024] The bead apex rubber 9 is arranged to cover the periphery of the bead core 5 in the tire meridian cross section, and includes a first rubber portion 10 having a circular or substantially elliptical outline, and a second rubber portion 11 extending tapered from the first rubber portion 10 radially outward from the first rubber portion 10. Even when the bead core 5 rotates, this first rubber portion 10 prevents contact between the carcass 6 arranged around the bead core 5 and the bead core 5, thereby preventing damage to the carcass 6 and suppressing the occurrence of CBU (improving CBU resistance). Furthermore, this first rubber portion 10 equalizes the shear strain of the carcass 6 caused by the bead core 5, thereby preventing damage to the carcass 6. The first rubber portion 10 of this embodiment is formed to cover the entire periphery of the bead core 5.

[0025] The first rubber portion 10 is formed to have a rubber hardness greater than that of the second rubber portion 11. Such a first rubber portion 10 further suppresses contact between the carcass 6 and the bead core 5. Therefore, the tire 1 of this embodiment has excellent bead durability performance.

[0026] The carcass 6 of this embodiment is composed of one carcass ply 6A. The carcass ply 6A includes, for example, a main body portion 6a that reaches both bead cores 5, and a turned-up portion 6b that is continuous with the main body portion 6a and turned up at the bead core 5. The carcass ply 6A is composed of well-known cords and a topping rubber (not shown).

[0027] As shown in Fig. 2, in this embodiment, the bead core 5 is formed in a substantially hexagonal shape including a core inner surface 5a. The bead core 5 further includes, for example, a core outer surface 5b facing the core inner surface 5a, a core outer surface 5c connecting the core inner surface 5a and the core outer surface 5b on the outer side in the tire axial direction, and a core inner surface 5d connecting the core inner surface 5a and the core outer surface 5b on the inner side in the tire axial direction. The core outer surface 5c has, for example, a first bent portion 13a bent outward in the tire axial direction. The core inner surface 5d has, for example, a second bent portion 13b bent inward in the tire axial direction. The core outer surface 5b extends, for example, in a substantially straight line.

[0028] In this embodiment, the inner end position 5i of the bead core 5 in the tire axial direction is formed at the second bend portion 13b of the core inward surface 5d. In this embodiment, the inner end position 5k of the bead core 5 in the tire radial direction is formed at the position where the core inward surface 5a and the core inward surface 5d intersect.

[0029] The bead core 5 of this embodiment is formed by spirally winding the bead wire 14 in the tire circumferential direction. The bead core 5 is formed, for example, by arranging multiple wire layers 15 in the tire radial direction, in which the bead wires 14 are aligned in the tire axial direction. The core inner surface 5a is formed by an innermost wire layer 15A that is arranged on the innermost side in the tire radial direction. However, the bead core 5 is not limited to this form and may be formed, for example, as an integrally molded product.

[0030] The bead wire 14 has, for example, a circular cross section. In this case, the angle θ1 of the core inner surface 5a is the inclination angle of a straight line connecting points c1 and c2 of the bead wires 14a and 14b at both ends of the innermost wire layer 15A in the tire axial direction, which are closest to the rim seat surface Ra. In this embodiment, a steel cord is used as the bead wire 14.

[0031] Fig. 3 is an enlarged view of the bead portion 4 of the tire 1 of Fig. 1. As shown in Fig. 3, in this embodiment, the periphery of the bead core 5 is covered with a canvas cloth 16 containing organic fiber cords. This further suppresses contact between the bead core 5 and the carcass 6. As the organic fiber cords, for example, nylon fiber, rayon fiber, polyester fiber, and aramid fiber are desirable.

[0032] In this embodiment, the first rubber portion 10 is formed in a substantially elliptical shape in the tire meridian cross section. In this specification, the term "substantially elliptical" not only refers to an ellipse in the dictionary sense, but also includes a shape formed by an arc that is convex outward from the centroid (not shown) of the first rubber portion 10 (including the bead core 5). The arc may have a continuously changing radius of curvature r.

[0033] The rubber hardness ha of the first rubber portion 10 is preferably 1.6 to 2.0 times the rubber hardness hb of the second rubber portion 11. Because the rubber hardness ha of the first rubber portion 10 is 1.6 times or more the rubber hardness hb of the second rubber portion 11, the rigidity of the first rubber portion 10 is maintained high, and contact between the bead core 5 and the carcass 6 is suppressed. Because the rubber hardness ha of the first rubber portion 10 is 2.0 times or less the rubber hardness hb of the second rubber portion 11, the rigidity of the second rubber portion 11 is ensured, and deformation of the bead portion 4 is suppressed. In addition, the rigidity of the first rubber portion 10 is prevented from becoming excessively high, and damage to the carcass 6 by the first rubber portion 10 is suppressed. In this specification, the rubber hardness is a durometer A hardness measured using a durometer type A in an environment of 23°C in accordance with JIS-K6253.

[0034] Although not particularly limited, the rubber hardness ha of the first rubber portion 10 is preferably, for example, 75 degrees or more, and more preferably 80 degrees or more. It's nice. The rubber hardness hb of the second rubber portion 11 is, for example, preferably 50 degrees or more, more preferably 55 degrees or more, and is preferably 70 degrees or less, and more preferably 65 degrees or less.

[0035] At the axially inner end position 5i of the bead core 5, the axial thickness t1 of the first rubber portion 10 is preferably 1.0 to 2.0 mm. At the radially inner end position 5k of the bead core 5, the radial thickness t2 of the first rubber portion 10 is preferably 1.0 to 2.0 mm. When the tire 1 is inflated to the normal internal pressure, the rotation of the bead core 5 causes relatively large shear strain at each of the inner end positions 5i and 5k. Therefore, by setting the thicknesses t1 and t2 at each of the inner end positions 5i and 5k to 1.0 mm or more, contact between the bead core 5 and the carcass 6 can be suppressed, thereby preventing damage to the carcass 6. If the thicknesses t1 and t2 are excessively large, the engagement pressure with the rim R may be reduced, potentially reducing bead durability. Therefore, the thicknesses t1 and t2 are preferably 2.0 mm or less.

[0036] In order to ensure the thicknesses t1 and t2 of the first rubber portion 10 at the inner end positions 5i and 5k, it is desirable to form the first rubber portion 10 from a sheet-like rubber material having a thickness of 1.0 mm on the radially inner side of the inner end position 5i in the tire axial direction of the bead core 5. In this embodiment, the portion of the core inward surface 5d from the outer end 5n (shown in FIG. 2) in the tire radial direction to the inner side in the tire radial direction is formed from a sheet-like rubber material.

[0037] As shown in FIG. 1, the distance L2 in the tire radial direction between the outer end 10e of the first rubber portion 10 in the tire radial direction and the bead base line BL is preferably 10% to 65% of the distance L1 in the tire radial direction between the tire maximum width position M and the bead base line BL. The bead base line BL is the tire axial line that defines the rim diameter of the rim R (see JATMA). In this specification, the tire maximum width position M is the position where the outer surface 3a of the sidewall portion 3 protrudes most axially outward. In this specification, the outer surface 3a is a smooth curve that is specified excluding unevenness that is partially formed (for example, decorative serrations, ribs for displaying emblems, side protectors described below, etc.).

[0038] As shown in Fig. 3, the bead portion 4 of this embodiment is provided with a reinforcing layer 20 that covers the carcass 6. In a tire meridian cross section, the reinforcing layer 20 is formed in a U-shape. More specifically, the reinforcing layer 20 of this embodiment includes a first portion 20A that extends along the main body portion 6a and a second portion 20B that is continuous with the first portion 20A and extends along the turned-up portion 6b. The second portion 20B terminates radially inward of the radially outer end 7b of the turned-up portion 6b.

[0039] In this embodiment, the reinforcing layer 20 is made of a large number of parallel cords and a topping rubber (not shown). Each cord is inclined relative to the tire radial direction. The cords are made of steel. The topping rubber is made of a well-known rubber material. The reinforcing layer 20 prevents the bead apex rubber 9 from collapsing too much, thereby improving bead durability.

[0040] The first portion 20A and the second portion 20B each have radially outer ends 21a, 21b. It is desirable that each of the outer ends 21a, 21b be spaced at least 2 mm radially outward from the radially outer end 10e of the first rubber portion 10. This suppresses rotation of the bead core 5 during running. From this perspective, it is more desirable that the radially outer distance LT between the radially outer ends 21a, 21b of the first portion 20A and the second portion 20B and the radially outer end 10e of the first rubber portion 10 be 4 mm or more. If the distance LT is excessively large, a rigidity step may occur in the bead portion 4, potentially reducing bead durability. For this reason, the distance LT is preferably 8 mm or less, and more preferably 6 mm or less.

[0041] In this embodiment, the outer end 21b of the second portion 20B is located radially outward of the outer end 21a of the first portion 20A. This more effectively suppresses rotation of the bead core 5 during running. From the viewpoint of effectively suppressing rotation of the bead core 5 while maintaining the rigidity balance of the bead portion 4, the distance La is preferably 5.0% or more of the length LA of the first rubber portion 10 in the radial direction of the tire, more preferably 6.5% or more, more preferably 12% or less, and even more preferably 10% or less. The distance La is the distance in the radial direction of the tire between the outer end 21b of the second portion 20B and the outer end 21a of the first portion 20A.

[0042] The bead portion 4 of this embodiment further includes a chafer 22 that comes into contact with the rim R (shown in FIG. 1). The chafer 22 is disposed further outward in the tire axial direction than the reinforcing layer 20. The chafer 22 extends, for example, radially inward of the reinforcing layer 20. In this embodiment, the chafer 22 extends radially outward of the radially outer end 7b of the turned-up portion 6b. The chafer 22 is formed, for example, from crosslinked rubber.

[0043] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and implemented in various ways. [Example]

[0044] Heavy-duty pneumatic tires with a size of 275 / 80R22.5 and the basic structure shown in Figure 1 were prototyped based on the specifications shown in Table 1. Each prototype tire was then tested for bead durability. The common specifications and test methods for each prototype tire are as follows: Rim: 22.5 x 7.50 Internal pressure: 900kPa

[0045] <Bead durability> Each test tire mounted on a standard rim was run on a drum test machine of known construction. Water was filled inside each test tire. The time until damage to the bead occurred was measured. The results are expressed as an index, with Example 1 being 100. The higher the index, the better the bead durability performance. Speed: 20km / h Load: 79.50kN

[0046] [Table 1]

[0047] As shown in the table, the tires of the examples are excellent in bead durability performance. [Explanation of symbols]

[0048] 1 pneumatic tire 4 Bead section 5 bead core 6. Carcass 9 Bead apex rubber 10 First rubber part 11 Second rubber part

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 bead core has a core inner surface extending substantially linearly on the inner side in the tire radial direction, In a state before assembly with a rim in which the width of the bead portion is maintained at the rim width, the core inner surface is inclined outward in the tire radial direction toward the tire axially outward at an angle of 20 degrees ± 2 degrees with respect to the tire axial direction, Each of the pair of bead portions is provided with a bead apex rubber extending from the bead core outward in the tire radial direction, the bead apex rubber includes a first rubber portion disposed so as to cover the periphery of the bead core in a tire meridian cross section and having a circular or substantially elliptical outline; a second rubber portion extending tapered from the first rubber portion toward an outer side in the tire radial direction, The first rubber portion has a rubber hardness greater than that of the second rubber portion, A reinforcing layer covering the carcass is provided in the bead portion, In a tire meridian cross section, the reinforcing layer has a U-shape, and both ends thereof are spaced 2 to 6 mm radially outward from the radially outer end of the first rubber portion.

2. 2. The pneumatic tire according to claim 1, wherein a distance in the tire radial direction between an outer end of the first rubber portion in the tire radial direction and a bead base line is 10% to 65% of a distance in the tire radial direction between a maximum tire width position and the bead base line.

3. 3. The pneumatic tire according to claim 1, wherein the axial thickness of the first rubber portion at the inner end position of the bead core is 1.0 to 2.0 mm.

4. 4. The pneumatic tire according to claim 1, wherein the thickness of the first rubber portion in the tire radial direction at an inner end position of the bead core in the tire radial direction is 1.0 to 2.0 mm.

5. 5. The pneumatic tire according to claim 1, wherein the first rubber portion has a rubber hardness that is 1.6 to 2.0 times the rubber hardness of the second rubber portion.

6. The carcass is composed of one carcass ply, The carcass ply includes a main body portion extending to each of the bead cores, and a turn-up portion continuing to the main body portion and turned up at the bead cores, the reinforcing layer includes a first portion extending along the main body portion and a second portion continuing to the first portion and extending along the folded-back portion; 6. The pneumatic tire according to claim 1, wherein a distance in the tire radial direction between an outer end of the second portion in the tire radial direction and an outer end of the first portion in the tire radial direction is 5.0% to 12% of a length in the tire radial direction of the first rubber portion.

7. The pneumatic tire according to claim 1 , wherein the bead core is covered with a canvas cloth containing organic fiber cords.

8. The pneumatic tire according to any one of claims 1 to 7, which is for heavy loads.

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