Pneumatic tires

Abstract

In order to improve the durability of the bead portion, in the pneumatic tire 1, both end portions of the bead core 21 in the tire width direction are formed by vertical lines 25 extending along the tire radial direction, and the length CV of the vertical lines 25 is within a range of 31% to 45% of the core height CH. In the first layer 31a, the second layer 31b, and the third layer 31c of the bead core 21, the number of bead wires 30 in the layer 31 located on the outer side in the tire radial direction between two adjacent layers 31 is two or more than the number of bead wires 30 in the layer 31 located on the inner side in the tire radial direction, and the amount of deviation between the bead wires 30 located at one end in the tire width direction is 0.5 of a bead wire 30. In the first layer 31a and the second layer 31b, and the second layer 31b and the third layer 31c, the sides where the amount of deviation between the bead wires 30 is 0.5 of a bead wire 30 are opposite each other in the tire width direction.

Description

[Technical field]

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

[0002] A pneumatic tire is attached to a rim wheel by fitting a bead portion having a bead core, which is an annular member formed by bundling multiple bead wires, into the rim of the rim wheel. The bead portion is an important part in ensuring the performance of the pneumatic tire because it is the part that is actually attached to the rim wheel when the pneumatic tire is attached to the rim wheel, but some conventional pneumatic tires have been designed with various ideas in mind for the bead portion in order to achieve the desired performance.

[0003] For example, in the pneumatic tire described in Patent Document 1, the bead core has a substantially flat bead surface joined to both rounded ends, thereby reducing wear in the bead region. Also, in the heavy-duty pneumatic tire described in Patent Document 2, the radially inner and radially outer contours of the bead core are formed by a lower base and an upper base extending in the tire axial direction, the axially outer contour is formed by a pair of upper and lower outer oblique sides that extend at an angle from the axially outer ends of the lower base and upper base toward the axially outer side, and the axially inner contour of the bead core is formed by an inner side connecting the axially inner ends of the lower base and upper base, thereby improving the durability of the bead portion.

[0004] In addition, the bead core described in Patent Document 3 has a cross-sectional shape from the cross-sectional center to the inner diameter side formed of a base parallel to the axial direction of the bead core, left and right middle sides perpendicular to the axial direction of the bead core, and an oblique side consisting of two obtuse-angled sides connecting the inner ends of the left and right middle sides to both sides of the base, thereby reducing tire failures due to breakage caused by fretting of the carcass cord and air pockets. In addition, in the pneumatic tire described in Patent Document 4, when manufacturing a bead core having an overall annular shape in which wires are aligned and arranged without gaps in multiple rows and stages, each of the outermost wires in the width direction of each wire row from the innermost side to the maximum width position is positioned widthwise outward relative to each of the outermost wires in the width direction of the wire row on the inner side, and the amount of deviation is gradually reduced from the innermost side toward the maximum width position, thereby preventing breakage of the carcass and preventing waviness at the wound-up end of the carcass during tire manufacturing, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-34784 A [Patent Document 2] Japanese Patent Application Publication No. 9-240223 [Patent Document 3] JP 2005-88793 A [Patent Document 4] Patent No. 4243091 Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, the bead core has a polygonal shape in the tire meridian section, but some extra-large pneumatic tires have a nylon cover wrapped around the bead core to prevent stress concentration on the carcass due to the corners of the bead core. However, with only a nylon cover, the distance between the bead core corners and the carcass is insufficient, so when a large tension acts on the carcass, the vicinity of the bead core corners and the carcass are subject to a large force and are easily rubbed. In this case, there is a risk that the carcass cord will break due to the rubbing between the bead core corners and the carcass. In particular, pneumatic tires mounted on vehicles such as loaders and scrapers that require traction performance often use bead cores that have a relatively flat shape in the tire meridian section, and the corners of the bead core and the carcass are easily rubbed, so the carcass cord is easily broken. For this reason, there is room for improvement in the durability of the bead portion in conventional pneumatic tires.

[0007] The present invention has been made in view of the above, and has an object to provide a pneumatic tire capable of improving the durability of a bead portion. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, a pneumatic tire according to the present invention has a pair of bead portions disposed on both sides of a tire equatorial plane in a tire width direction, a bead core disposed in the bead portions and formed by winding a bead wire in a ring shape and having a polygonal cross section in a tire meridian section, a carcass main body portion disposed between the pair of bead portions, and a turn-up portion formed continuously from the carcass main body portion and folded back from an inner side in the tire width direction of the bead core to an outer side in the tire width direction, and a carcass formed by covering a bead core with a coating rubber, wherein the bead core has a portion located at the innermost side in the tire width direction and a portion located at the outermost side in the tire width direction in a contour in a tire meridian cross section, the portion being formed by a vertical line extending along the tire radial direction, the length of the vertical line being within a range of 31% to 45% of a core height, which is the height of the bead core in the tire radial direction, and the vertical line is a tire diameter from a bead core bottom surface, which is the inner circumferential surface of the bead core, to an inner end of the vertical line in the tire radial direction. a distance in a direction between the first layer and the second layer is within a range of 20% to 35% of the core height, the bead core has a plurality of turns of the bead wire wound in a ring shape aligned in the tire width direction to form one layer, and the plurality of layers are laminated in the tire radial direction, and among the plurality of layers, a first layer which is the layer located at the innermost circumference in the tire radial direction, a second layer which is laminated adjacent to the first layer on the outer side in the tire radial direction, and a third layer which is laminated adjacent to the second layer on the outer side in the tire radial direction are adjacent to each other in the tire radial direction. In the tire width direction, the number of the bead wires in the layer located relatively outside in the tire radial direction is two or more than the number of the bead wires in the layer located inside in the tire radial direction, and the amount of deviation in the tire width direction between the bead wires located at the end on one side in the tire width direction is 0.5 of the bead wire, and the amount of deviation between the bead wires in the first layer and the second layer is 0.5 of the bead wire, and the amount of deviation between the bead wires in the second layer and the third layer is 0.5 of the bead wire.The five-section side is characterized by being on the opposite side in the tire width direction.

[0009] In the pneumatic tire, it is preferable that the width of the bead core bottom surface in the tire meridian section is within a range of 45% to 70% of the maximum width of the bead core.

[0010] Furthermore, in the above pneumatic tire, it is preferable that the distance in the tire width direction between the inner end portion in the tire width direction of the bead core top surface, which is the outer peripheral surface in a tire meridian cross section, and the vertical line on the inner side in the tire width direction is within a range of 10% to 25% of the maximum width of the bead core, the distance in the tire width direction between the inner end portion in the tire width direction of the bead core bottom surface and the vertical line on the inner side in the tire width direction is within a range of 10% to 25% of the maximum width of the bead core, and the maximum width of the bead core is within a range of 0.9 to 1.4 times the core height.

[0011] In the above pneumatic tire, it is preferable that the number of ends of the carcass cord at a position on the inner side of the bead core in the tire width direction is within a range of 10 [pieces / 50 mm] to 20 [pieces / 50 mm]. Effect of the Invention

[0012] The pneumatic tire according to the present invention has an effect of improving the durability of the bead portion. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire according to an embodiment. [Diagram 2] FIG. 2 is a detailed view of part A in FIG. [Diagram 3] FIG. 3 is a detailed view of the bead core shown in FIG. [Figure 4] FIG. 4 is a detailed view of part B in FIG. [Diagram 5] FIG. 5 is a detailed view of a bead core in a modified example of the pneumatic tire according to the embodiment, in which bead wires are laminated in a different manner from the embodiment shown in FIG. [Figure 6A] FIG. 6A is a chart showing the results of a performance evaluation test of a pneumatic tire. [Figure 6B] FIG. 6B is a chart showing the results of a performance evaluation test of a pneumatic tire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0015] [Embodiment] In the following description, the tire radial direction refers to a direction perpendicular to the tire rotation axis (not shown) which is the rotation axis of the pneumatic tire 1, the tire radial inner side refers to the side facing the tire rotation axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to a direction parallel to the tire rotation axis, the tire width inner side refers to the side facing the tire equatorial plane (tire equatorial line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the tire rotation axis and passing through the center of the tire width of the pneumatic tire 1, and the tire equatorial plane CL coincides with the tire width centerline which is the center position in the tire width direction of the pneumatic tire 1. The tire width is the width in the tire width direction between the parts located at the outermost positions in the tire width direction, that is, the distance between the parts farthest from the tire equatorial plane CL in the tire width direction. The tire equatorial line refers to a line that is on the tire equatorial plane CL and extends along the tire circumferential direction of the pneumatic tire 1. In addition, in the following description, the tire meridian section refers to a section obtained by cutting the tire with a plane that includes the tire rotation axis.

[0016] FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire 1 according to an embodiment. The pneumatic tire 1 according to the embodiment is a radial tire for construction vehicles, called an OR tire (Off the Road Tire). When viewed in a tire meridian cross-section, the pneumatic tire 1 shown in FIG. 1 as this embodiment has a tread portion 2 disposed at the outermost part in the tire radial direction, and the tread portion 2 is composed of a tread rubber 2a which is a rubber composition. The surface of the tread portion 2, i.e., the portion that comes into contact with the road surface when a vehicle (not shown) equipped with the pneumatic tire 1 is traveling, is formed as a tread surface 3.

[0017] A plurality of grooves (not shown), such as circumferential grooves 15 extending in the tire circumferential direction and lug grooves extending in the tire width direction, are formed on the tread surface 3 of the tread portion 2, and a plurality of land portions 10 are defined and formed in the tread portion 2 by these grooves.

[0018] Both ends of the tread portion 2 in the tire width direction are formed as shoulder portions 4, and sidewall portions 5 are disposed from the shoulder portions 4 to a predetermined position on the tire radially inward side. That is, the sidewall portions 5 are disposed at two locations on both sides of the pneumatic tire 1 in the tire width direction. The sidewall portions 5 are formed of a sidewall rubber 5a which is a rubber composition. In addition, a rim check line 9 is formed at a position closer to the tire radially inward side of each sidewall portion 5 on both sides in the tire width direction. The rim check line 9 protrudes from the surface of the sidewall portions 5 and is formed around the entire circumference in the tire circumferential direction.

[0019] Furthermore, bead portions 20 are located on the inner side of each sidewall portion 5 in the tire radial direction, and the bead portions 20 are arranged at two locations on both sides of the tire equatorial plane CL, similar to the sidewall portions 5. That is, a pair of bead portions 20 are arranged on both sides of the tire equatorial plane CL in the tire width direction. A bead core 21 is arranged in each of the pair of bead portions 20, and a bead filler 50 is arranged on the outer side of each bead core 21 in the tire radial direction. The bead core 21 is formed by winding a bead wire 30 (see FIG. 3), which is a steel wire, in a ring shape. The bead filler 50 is a rubber material arranged in a space formed by folding back the tire width direction end of the carcass 6, which will be described later, to the outer side in the tire width direction at the position of the bead core 21. The bead filler 50 has a lower filler 51 arranged in contact with the outer peripheral surface of the bead core 21, and an upper filler 52 arranged at a position closer to the outer side in the tire radial direction than the lower filler 51.

[0020] The bead portion 20 is configured so that it can be mounted on a rim wheel having a specified rim radius of 5° taper. That is, the pneumatic tire 1 according to this embodiment can be mounted on a specified rim radius in which the portion that fits with the bead portion 20 is inclined at an inclination angle of 5°±1° with respect to the rotation axis of the rim wheel, inclining from the inner side to the outer side in the tire width direction toward the outer side in the tire radial direction. The specified rim radius refers to the "applicable rim" specified by JATMA, the "Design Rim" specified by TRA, or the "Measuring Rim" specified by ETRTO.

[0021] A belt layer 7 is provided on the tire radial inner side of the tread portion 2. The belt layer 7 has a multi-layer structure in which three or more belt plies are laminated, and in a general OR tire, four to eight belt plies are laminated. In this embodiment, the belt layer 7 is formed by laminating six belt plies 7a, 7b, 7c, 7d, 7e, and 7f. The belt plies 7a, 7b, 7c, 7d, 7e, and 7f constituting the belt layer 7 in this manner are formed by covering a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them. The six belt plies 7a, 7b, 7c, 7d, 7e, and 7f are formed, for example, by cross belt layers 7a, 7b, 7c, and 7d and protective belt layers 7e and 7f. In addition, the belt plies 7a, 7b, 7c, 7d, 7e, and 7f have different inclination angles of the belt cords in the tire width direction relative to the tire circumferential direction, and the cross belt layers and the protective belt layers are laminated with their inclination directions crossing each other within the layers, forming a so-called cross-ply structure.

[0022] A carcass 6 containing the cords of the radial ply is provided continuously on the inner side of the belt layer 7 in the tire radial direction and on the tire equatorial plane CL side of the sidewall portion 5. The carcass 6 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of a plurality of carcass plies stacked together, and is toroidally stretched between the bead cores 21 arranged on both sides in the tire width direction to form the tire framework. In detail, the carcass 6 is stretched between a pair of bead portions 20, and is disposed from one bead portion 20 to the other bead portion 20 of the pair of bead portions 20 located on both sides in the tire width direction. The carcass 6 is also folded back at the bead portion 20 from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction, passing through the inner side of the bead core 21 in the tire radial direction, so as to envelop the bead core 21 and the bead filler 50. That is, the carcass 6 is folded back around the bead core 21 at the bead portion 20 from the inner side of the bead core 21 in the tire width direction to the outer side of the bead core 21 in the tire width direction.

[0023] Therefore, the carcass 6 has a carcass main body 6a disposed between the pair of bead portions 20, and a turn-up portion 6b formed continuously from the carcass main body 6a and folded back from the inner side in the tire width direction of the bead core 21 to the outer side in the tire width direction. The carcass main body 6a here is a portion formed between the inner sides in the tire width direction of the pair of bead cores 21 in the carcass 6, and the turn-up portion 6b is a portion formed continuously from the carcass main body 6a on the inner side in the tire width direction of the bead core 21, and folded back through the inner side in the tire radial direction of the bead core 21 to the outer side in the tire width direction. The bead filler 50 is disposed on the inner side in the tire width direction of the turn-up portion 6b, which is the portion folded back to the outer side in the tire width direction of the bead core 21, and on the outer side in the tire radial direction of the bead core 21.

[0024] The carcass ply of the carcass 6 arranged in this manner is formed by covering a plurality of carcass cords 6c (see FIG. 2), which are cord members made of steel or organic fiber materials such as aramid, nylon, polyester, rayon, etc., with a rubber member, coating rubber 6d (see FIG. 2), and rolling the covered cords. The carcass 6 has a carcass angle, which is the inclination angle of the carcass cords 6c with respect to the tire circumferential direction, of 85° to 95°.

[0025] Further, on the inner side of the carcass 6 , or on the inner side of the carcass 6 in the pneumatic tire 1 , an inner liner 8 is formed along the carcass 6 .

[0026] Fig. 2 is a detailed view of part A in Fig. 1. Fig. 3 is a detailed view of the bead core 21 shown in Fig. 2. The bead core 21 is formed to have a polygonal cross section when viewed in a tire meridian section, and in this embodiment, the bead core 21 is formed to have a cross section close to an octagon. Specifically, the bead core bottom surface 23, which is the inner peripheral surface of the bead core 21 when viewed as a whole, and the bead core top surface 22, which is the outer peripheral surface of the bead core 21, are formed to be approximately parallel. In addition, the bead core 21 is formed such that the part located at the innermost position in the tire width direction and the part located at the outermost position in the tire width direction on the outline in the tire meridian section are formed by vertical lines 25 extending along the tire radial direction.

[0027] In addition, in the contour of the bead core 21 in the tire meridian cross section, a tire radially inner portion of the vertical line 25 on the inner side in the tire width direction and an inner end portion in the tire width direction of the bead core bottom surface 23 are connected in a side shape, and a tire radially outer portion of the vertical line 25 on the inner side in the tire width direction and an inner end portion in the tire width direction of the bead core top surface 22 are connected in a side shape. In addition, in the contour of the bead core 21 in the tire meridian cross section, a tire radially inner portion of the vertical line 25 on the outer side in the tire width direction and an outer end portion in the tire width direction of the bead core bottom surface 23 are connected in a side shape, and a tire radially outer portion of the vertical line 25 on the outer side in the tire width direction and an outer end portion in the tire width direction of the bead core top surface 22 are connected in a side shape. As a result, the bead core 21 is formed in a shape that is approximately octagonal in the tire meridian cross section.

[0028] In this case, the bead core bottom surface 23 of the bead core 21 refers to a surface defined by an imaginary straight line tangent to portions exposed on the surface side of the bead core 21 of the multiple bead wires 30 that are aligned in a row at a position on the inner side of the bead core 21 in the tire radial direction and that constitute the surface of the bead core 21 in the tire meridian cross section. Similarly, the bead core top surface 22 of the bead core 21 refers to a surface defined by an imaginary straight line tangent to portions exposed on the surface side of the bead core 21 of the multiple bead wires 30 that are aligned in a row at a position on the outer side of the bead core 21 in the tire radial direction and that constitute the surface of the bead core 21 in the tire meridian cross section of the pneumatic tire 1 viewed in the tire meridian cross section.

[0029] Moreover, the vertical line 25 of the bead core 21 refers to an imaginary straight line tangent to a portion of the multiple bead wires 30 located on the outermost sides in the width direction of the bead core 21, the portion being exposed to the outer side in the width direction of the bead core 21, in the tire meridian cross section, when the tire width direction is the width direction of the bead core 21. More specifically, the vertical line 25 is formed extending along the tire radial direction in a state in which the distance in the tire width direction between a pair of bead portions 20 located on both sides in the tire width direction with respect to the tire equatorial plane CL is set to the distance when the pneumatic tire 1 is mounted on a specified rim R (see FIG. 1).

[0030] In other words, when the distance in the tire width direction between a pair of bead portions 20 located on both sides of the tire width direction relative to the tire equatorial plane CL is set to the distance when the pneumatic tire 1 is mounted on a specified rim R, the bead wires 30 are arranged in such a manner that an imaginary straight line tangent to the multiple bead wires 30 located on the outermost sides in the width direction of the bead core 21 extends in the tire radial direction.

[0031] In this embodiment, the vertical line 25 on the inner side in the tire width direction of the bead core 21 in the tire meridian cross section is a tangent line that touches three bead wires 30 that are located most inward in the tire width direction and spaced apart from each other and aligned in the tire radial direction in the tire. Also, the vertical line 25 on the outer side in the tire width direction of the bead core 21 in the tire meridian cross section is a tangent line that touches three bead wires 30 that are located most outward in the tire width direction and spaced apart from each other and aligned in the tire radial direction in the tire.

[0032] In the following description, the shape around the bead portion 20 is described assuming that the distance in the tire width direction between the pair of bead portions 20 located on both sides in the tire width direction with respect to the tire equatorial plane CL is the distance when the pneumatic tire 1 is mounted on a specified rim R, similar to the vertical line 25. Also, the vertical line 25 of the bead core 21 does not have to extend strictly in the tire radial direction. It is sufficient that the vertical line 25 is formed within a range of 0° to 15° with respect to the tire radial direction.

[0033] As described above, the vertical lines 25 located on both sides in the width direction of the bead core 21 have a length CV of the vertical line 25 in the range of 31% to 45% of the core height CH, which is the height of the bead core 21 in the tire radial direction. That is, the ratio CV / CH of the length CV of the vertical line 25 to the core height CH of the vertical line 25 is in the range of 31% to 45%. In this case, the length CV of the vertical line 25 is the distance between the outer end of the bead wire 30 located on the outermost side in the tire radial direction and the inner end of the bead wire 30 located on the innermost side in the tire radial direction among the multiple bead wires 30 constituting the vertical line 25. In addition, the core height CH in this case is the distance between the bead core top surface 22 and the bead core bottom surface 23.

[0034] Further, the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 in the tire radial direction is within a range of 20% to 35% of the core height CH. In this case, the inner end 25a of the vertical line 25 in the tire radial direction is the inner end in the tire radial direction of the bead wire 30 that is located most inward in the tire radial direction among the multiple bead wires 30 that constitute the vertical line 25.

[0035] In detail, the bead core 21 has vertical lines 25 on both sides in the width direction of the bead core 21, and for both vertical lines 25 located on both sides in the width direction of the bead core 21, the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 in the tire radial direction is within a range of 20% to 35% of the core height CH. In other words, for both vertical lines 25 on both sides in the width direction of the bead core 21, the ratio Va / CH of the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 to the core height CH is within a range of 20% to 35%.

[0036] In addition, in the tire meridian section, the bead core 21 has a distance Vb in the tire width direction between an end 22in on the inner side in the tire width direction of the bead core upper surface 22 and the inner vertical line 25 in the tire width direction of the vertical lines 25 on both sides of the bead core 21 in the tire width direction, which is within a range of 10% to 25% of the maximum width CW of the bead core 21. That is, the ratio Vb / CW of the distance Vb in the tire width direction between the end 22in on the inner side in the tire width direction of the bead core upper surface 22 and the inner vertical line 25 in the tire width direction to the maximum width CW of the bead core 21 is within a range of 10% to 25%. In this case, the maximum width CW of the bead core 21 is the distance between the vertical lines 25 located on both sides of the bead core 21 in the width direction. In this case, the inner end 22in of the bead core upper surface 22 in the tire width direction is the inner end 22in of the bead wire 30 that is located most inward in the tire width direction among the multiple bead wires 30 that make up the bead core upper surface 22.

[0037] Similarly, in the bead core 21, the distance Vc in the tire width direction between the end 23in on the inner side in the tire width direction of the bead core bottom surface 23 and the vertical line 25 on the inner side in the tire width direction is within a range of 10% to 25% of the maximum width CW of the bead core 21. That is, in the bead core 21, the ratio Vc / CW of the distance Vc in the tire width direction between the end 23in on the inner side in the tire width direction of the bead core bottom surface 23 and the vertical line 25 on the inner side in the tire width direction to the maximum width CW of the bead core 21 is within a range of 10% to 25%. In this case, the end 23in on the inner side in the tire width direction of the bead core bottom surface 23 is the inner end in the tire width direction of the bead wire 30 located most inward in the tire width direction among the multiple bead wires 30 that constitute the bead core bottom surface 23.

[0038] Furthermore, the maximum width CW of the bead core 21 in the tire meridian section is within a range of 0.9 to 1.4 times the core height CH. Also, the width CBW of the bead core bottom surface 23 in the tire meridian section is within a range of 45% to 70% of the maximum width CW of the bead core 21. In other words, the ratio CW / CH of the maximum width CW of the bead core 21 to the core height CH is within a range of 0.9 to 1.4 times, and the ratio CBW / CW of the width CBW of the bead core bottom surface 23 to the maximum width CW of the bead core 21 is within a range of 45% to 70%.

[0039] Fig. 4 is a detailed view of part B in Fig. 3. The bead core 21 is formed by winding the bead wire 30 into a ring shape, and more specifically, a plurality of turns of the bead wire 30 formed by winding into a ring shape are aligned in the tire width direction to form one layer 31, and the plurality of layers 31 are laminated in the tire radial direction. At that time, between layers 31 adjacent in the tire radial direction, the bead wires 30 forming each layer 31 are shifted in the tire width direction by 0.5 of the thickness of the bead wire 30.

[0040] Among the multiple layers 31 of the bead core 21, the first layer 31a, the second layer 31b, and the third layer 31c, counting from the inner side in the tire radial direction, are adjacent to each other in the tire radial direction. The number of bead wires 30 of the layer 31 located relatively on the outer side in the tire radial direction is two or more than the number of bead wires 30 of the layer 31 located on the inner side in the tire radial direction. In this case, the first layer 31a is the layer 31 located on the innermost circumference in the tire radial direction among the multiple layers 31 of the bead core 21. The second layer 31b is the layer 31 stacked adjacent to the first layer 31a on the outer side in the tire radial direction, and the third layer 31c is the layer 31 stacked adjacent to the second layer 31b on the outer side in the tire radial direction. In this embodiment, the second layer 31b has two more bead wires 30 than the first layer 31a, and the third layer 31c has two more bead wires 30 than the second layer 31b.

[0041] In the first layer 31a, the second layer 31b, and the third layer 31c of the bead core 21, between two layers 31 adjacent in the tire radial direction, the amount of deviation in the tire width direction between the bead wires 30 located at one end in the tire width direction is 0.5 of the thickness of the bead wire 30. Furthermore, in the first layer 31a, the second layer 31b, and the third layer 31c, the side where the amount of deviation between the bead wires 30 at the end positions in the tire width direction between the first layer 31a and the second layer 31b is 0.5 of the bead wire 30 and the side where the amount of deviation between the bead wires 30 at the end positions in the tire width direction between the second layer 31b and the third layer 31c is 0.5 of the bead wire 30 are opposite each other in the tire width direction.

[0042] Specifically, between the first layer 31a and the second layer 31b, the amount of deviation in the tire width direction between the bead wires 30 located at the inner ends in the tire width direction is 0.5 of the thickness of the bead wire 30. In contrast, between the second layer 31b and the third layer 31c, the amount of deviation in the tire width direction between the bead wires 30 located at the outer ends in the tire width direction is 0.5 of the thickness of the bead wire 30.

[0043] In addition, in this embodiment, the bead core 21 is made up of multiple layers 31 stacked in the tire radial direction, and the number of bead wires 30 in each layer 31 decreases by one radially outward from the layer 31 including the bead wire 30 that forms the radially outer end of the vertical line 25 (see FIG. 3) located on both sides of the width direction of the bead core 21.

[0044] The carcass 6 is folded around the bead core 21 from the inner side in the tire width direction to the outer side in the tire width direction of the bead core 21 thus formed, and is formed by coating a plurality of carcass cords 6c with a coating rubber 6d and rolling them. The carcass 6 having a plurality of carcass cords 6c has an end number of the carcass cords 6c at the inner position in the tire width direction of the bead core 21 within a range of 10 [cords / 50 mm] to 20 [cords / 50 mm]. In this case, the inner position in the tire width direction of the bead core 21 is a position in which the range in the tire radial direction at the inner position in the tire width direction relative to the bead core 21 is the same as the range in the tire radial direction in which the bead core 21 is arranged. That is, the inner position in the tire width direction of the bead core 21 in this case is a position in which the range in the carcass main body 6a is the same as the range in the tire radial direction in which the bead core 21 is arranged.

[0045] The carcass 6 has a number of ends per 50 mm in the direction in which the carcass cords 6c are arranged at the tire widthwise inner position of the bead core 21 defined in this manner, i.e., the number of carcass cords 6c driven in, in the range of 10 [ends / 50 mm] to 20 [ends / 50 mm].

[0046] The bead filler 50, which has a lower filler 51 and an upper filler 52, is disposed on the tire radially outer side of the bead core 21. Of these, the lower filler 51 is disposed between the carcass main body portion 6a and the turn-up portion 6b of the carcass 6. In addition, the width of the lower filler 51 in the tire width direction in the tire meridian cross section near the bead core 21 is approximately the same as that of the bead core 21, and the width becomes narrower toward the tire radially outer side.

[0047] On the other hand, the upper filler 52 is disposed from the position where the lower filler 51 is disposed in the tire radial direction to a position on the tire radial outer side of the lower filler 51, and the inner end portion of the upper filler 52 in the tire radial direction is located near the bead core 21. In detail, in the range where the lower filler 51 is disposed in the tire radial direction, the upper filler 52 is located on the outer side of the lower filler 51 in the tire width direction and is disposed between the turned-up portion 6b of the carcass 6 and the lower filler 51, and on the tire radial outer side of the lower filler 51, the upper filler 52 is disposed between the carcass main body portion 6a of the carcass 6 and the turned-up portion 6b (see FIG. 1).

[0048] The lower filler 51 and the upper filler 52 of the bead filler 50 are made of rubber compositions having different physical properties.

[0049] The bead portion 20 also has a rim cushion rubber 46 on the radially inner side of the bead core 21. The rim cushion rubber 46 also forms the bead base portion 40, which is the inner peripheral surface of the bead portion 20, and is a rubber composition that comes into contact with the rim hole while elastically deforming when fitted to the rim wheel.

[0050] The bead base portion 40 here refers to the inner circumferential surface of the bead portion 20, and is the portion of the bead portion 20 that comes into contact with and fits onto the rim wheel. The bead base portion 40 has a bead toe 41 at its inner end in the tire width direction and a bead heel 42 at its outer end in the tire width direction, and is formed in a tapered shape with a diameter that increases from the bead toe 41 side toward the bead heel 42 side.

[0051] In the bead portion 20, a reinforcing layer 60 for reinforcing the carcass 6 is disposed in a portion folded around the bead core 21 in the carcass 6. The reinforcing layer 60 is disposed along the carcass 6 at least on the inner side in the tire width direction of the carcass main body portion 6a. In this embodiment, the reinforcing layer 60 is disposed in three layers, and these three reinforcing layers 60 are disposed such that the positions of the ends in the tire radial direction in the tire meridian cross section are different from each other.

[0052] Specifically, when the three reinforcing layers 60 are a first reinforcing layer 61, a second reinforcing layer 62, and a third reinforcing layer 63 arranged from the carcass 6 side toward the direction away from the carcass 6 in the thickness direction of the carcass 6 and the reinforcing layer 60, the first reinforcing layer 61 is arranged by folding back from the inner side in the tire width direction of the bead core 21 to the outer side in the tire width direction along the carcass 6. In contrast, the second reinforcing layer 62 and the third reinforcing layer 63 are not arranged on the outer side in the tire width direction of the bead core 21. That is, the second reinforcing layer 62 and the third reinforcing layer 63 are not arranged on the turn-up portion 6b side, but are arranged along the carcass 6 only in the range where the carcass main body portion 6a is located.

[0053] The second reinforcing layer 62 and the third reinforcing layer 63 thus arranged have their respective radially inner ends in the tire meridian cross section positioned inward in the tire radial direction of the second reinforcing layer 62 than the third reinforcing layer 63. Also, the second reinforcing layer 62 and the third reinforcing layer 63 have their respective radially outer ends in the tire meridian cross section positioned inward in the tire radial direction of the third reinforcing layer 63 than the second reinforcing layer 62.

[0054] The multiple reinforcing layers 60 thus arranged are each formed by coating multiple cords with coating rubber and rolling them. Of these, the first reinforcing layer 61 is made of steel cords. Meanwhile, the second reinforcing layer 62 is made of organic fiber cords. Similarly, the third reinforcing layer 63 has cords 65 made of organic fiber cords.

[0055] The first reinforcing layer 61 is disposed by folding back from the inner side in the tire width direction of the bead core 21 to the outer side in the tire width direction along the carcass 6. In addition, both of the end portion of the first reinforcing layer 61 located on the inner side in the tire width direction of the bead core 21 and the end portion located on the outer side in the tire width direction of the bead core 21 are located on the outer side in the tire radial direction than the bead core upper surface 22 of the bead core 21.

[0056] In addition, among the multiple reinforcing layers 60 arranged in a stacked manner along the carcass 6 in the bead portion 20, the inclination directions of the cords of each reinforcing layer 60 toward the tire circumferential direction relative to the tire radial direction are opposite to each other between adjacent reinforcing layers 60.

[0057] [Manufacturing method of pneumatic tires] Next, a manufacturing method of the pneumatic tire 1 according to the embodiment will be described. When manufacturing the pneumatic tire 1, first, each of the members constituting the pneumatic tire 1 is processed, and the processed members are assembled. That is, each of the rubber members such as the tread rubber 2a, the carcass 6, the belt layer 7, the bead cores 21, and the like is processed, and the processed members are assembled.

[0058] For example, the bead core 21 is formed by winding the bead wire 30 into a ring shape. In this case, the bead core 21 is formed such that the innermost portion in the tire width direction and the outermost portion in the tire width direction of the outline in the tire meridian cross section each form a vertical line 25 extending along the tire radial direction. Furthermore, the bead core 21 is formed such that the length CV of the vertical line 25 is within a range of 31% to 45% of the core height CH of the bead core 21, and the distance Va in the tire radial direction from the bead core bottom surface 23 to an inner end 25a in the tire radial direction of the vertical line 25 is within a range of 20% to 35% of the core height CH.

[0059] In addition, the bead core 21 forms one layer 31 by arranging multiple turns of the bead wire 30 in the tire width direction, and multiple layers 31 are laminated in the tire radial direction. In this case, the three layers 31, i.e., the first layer 31a, the second layer 31b, and the third layer 31c counting from the innermost circumference in the tire radial direction of the bead core 21, are arranged such that, between two layers 31 adjacent in the tire radial direction, the number of bead wires 30 in the layer 31 located relatively outside in the tire radial direction is two or more than the number of bead wires 30 in the layer 31 located inside in the tire radial direction, and the amount of deviation in the tire width direction between the bead wires 30 located at the end on one side in the tire width direction is 0.5 of the thickness of the bead wire 30. Furthermore, the three layers 31 have a side on which the amount of misalignment between the bead wires 30 in the first layer 31a and the second layer 31b is 0.5 of the thickness of the bead wire 30, and a side on which the amount of misalignment between the bead wires 30 in the second layer 31b and the third layer 31c is 0.5 of the thickness of the bead wire 30, which are opposite each other in the tire width direction.

[0060] In this manner, when the bead core 21 is formed during the manufacture of the pneumatic tire 1, the bead wire 30 is wound in a ring shape starting from the outer end of the first layer 31a in the tire width direction. That is, when the bead core 21 is formed by winding the bead wire 30 in a ring shape, the end of the bead wire 30 located at the bead core bottom surface 23 is wound so as to be located at the outer end of the bead core bottom surface 23 in the tire width direction.

[0061] The bead wire 30 starts to be wound from the end of the bead core bottom surface 23 on the outer side in the tire width direction, and is wound spirally a predetermined number of times determined for each layer 31 to arrange the layers 31 in the tire width direction. When the number of times the bead wire 30 is wound reaches the predetermined number of times determined for each layer 31, the bead wire 30 is turned back to the upper side in the tire radial direction, and the layer 31 is formed by winding the bead wire 30 spirally a number of times determined as the number of times of winding the layer 31 adjacent to the outer side in the tire radial direction.

[0062] That is, the bead wire 30 starts to be wound from the end of the first layer 31a on the outer side in the tire width direction, and when the first layer 31a is finished, the second layer 31b adjacent to the first layer 31a on the outer side in the tire radial direction starts to be wound. Therefore, the side where the deviation amount between the bead wire 30 in the first layer 31a and the second layer 31b is set to 0.5 of the thickness of the bead wire 30 is necessarily located on the end side of the first layer 31a and the second layer 31b on the inner side in the tire width direction. By repeating these steps, the bead core 21 is formed such that the layers 31 formed by the multiple turns of the bead wire 30 aligned in the tire d width direction are stacked in the tire radial direction, so that the shape of the tire meridian cross section is a polygonal cross section.

[0063] In the bead portion 20 in which the bead core 21 formed in this manner is disposed, the carcass 6 is disposed by folding back from the inner side in the tire width direction of the bead core 21 to the outer side in the tire width direction. For the carcass 6, a carcass ply is used in which the number of ends of the carcass cord 6c at the inner position in the tire width direction of the bead core 21 is within a range of 10 [pieces / 50 mm] to 20 [pieces / 50 mm]. The pneumatic tire 1 according to this embodiment is manufactured in the manner described above.

[0064] [Actions and Effects] When mounting the pneumatic tire 1 according to this embodiment on a vehicle, first, the bead base portion 40 is fitted to a specified rim R of the rim wheel, thereby mounting the pneumatic tire 1 on the specified rim R, and the pneumatic tire 1 is assembled to the rim wheel. After the pneumatic tire 1 is assembled to the rim, it is inflated, and the rim-assembled and inflated pneumatic tire 1 is mounted on the vehicle. The pneumatic tire 1 according to this embodiment is mounted on vehicles such as loaders and scrapers that require traction performance, and is used under heavy load conditions.

[0065] When a vehicle equipped with a pneumatic tire 1 runs, the pneumatic tire 1 rotates with the lower part of the tread surface 3 in contact with the road surface. The vehicle runs by transmitting driving force and braking force to the road surface and generating turning force due to friction between the tread surface 3 and the road surface.

[0066] When a vehicle equipped with the pneumatic tire 1 is traveling, the frictional force generated between the tread surface 3 of the pneumatic tire 1 and the road surface enables the vehicle to travel, but when the vehicle is traveling, loads act in various directions on each part of the pneumatic tire 1. The load acting on the pneumatic tire 1 is received by the pressure of the air filled inside, the carcass 6 provided as the skeleton of the pneumatic tire 1, etc.

[0067] For example, the load acting in the tire radial direction between the tread portion 2 and the bead portion 20 due to the weight of the vehicle or the unevenness of the road surface is mainly received by the pressure of the air filled inside the pneumatic tire 1, or by the sidewall portion 5 and the like being deflected. In particular, since the pneumatic tire 1 according to this embodiment is mounted on a large vehicle and used under conditions of high load, the sidewall portion 5 and the carcass 6 are subjected to a very large load. Therefore, a large tension acts on the carcass 6.

[0068] The carcass 6 is held by the bead portions 20 by being folded back around the bead cores 21, so that when a large tension acts on the carcass 6, the tension of the carcass 6 is transmitted to the bead cores 21, and a large force acts between the carcass 6 and the bead cores 21. In other words, when tension acts on the carcass 6, a tension acts on the carcass main body portion 6a in a direction from the bead portion 20 side toward the outside in the tire radial direction, because the carcass 6 is held by the bead portions 20 by being folded back around the bead cores 21. Therefore, a large force also acts between the bead cores 21 and the carcass 6.

[0069] Here, the sidewall portion 5 is inclined with respect to the tire radial direction toward the outer side in the tire width direction as it moves toward the tire radial outer side from the position of the bead portion 20. Therefore, when a large tension acts on the carcass main body portion 6a, the carcass main body portion 6a generates a force toward the outer side in the tire width direction near the bead portion 20 while being pulled in the tire radial direction.

[0070] On the other hand, in pneumatic tires mounted on large vehicles and used under high load conditions, the bead core is often formed with a cross-sectional shape in the tire meridian section that is approximately hexagonal, and in this case, the bead core has a corner that is convex on the inner side in the tire width direction. Therefore, when a large tension acts on the carcass and the carcass main body generates a force toward the outer side in the tire width direction near the bead portion and tries to move in the tire radial direction due to the tension, the carcass main body rubs against the corner of the bead core that is convex on the inner side in the tire width direction while applying a large load. As a result, the carcass main body may wear out the coating rubber and directly rub the carcass cord, which may cause a breakdown such as the carcass cord breaking.

[0071] In addition, because the carcass is folded around the bead core, if a large tension is applied to the carcass, the carcass and the bead core will rub against each other at positions other than the corners of the bead core that convexly face inward in the tire width direction, and this rubbing may cause the carcass to malfunction, such as the carcass cord breaking.

[0072] In contrast, in the pneumatic tire 1 according to the present embodiment, the bead core 21 is formed such that the innermost portion in the tire width direction and the outermost portion in the tire width direction in the outline in the tire meridian section are formed by vertical lines 25 extending along the tire radial direction. In other words, the bead core 21 is formed in a shape in which the position of the maximum width in the tire width direction of the bead core 21 forms the vertical line 25 extending along the tire radial direction, and is formed without having a corner that is convex with respect to the tire width direction. As a result, even if a large force acts between the carcass 6 and the bead core 21 due to a large tension acting on the carcass 6, it is possible to suppress the occurrence of stress concentration, and it is possible to disperse the stress acting between the carcass 6 and the bead core 21. Therefore, it is possible to suppress the wear of the coating rubber 6d of the carcass main body 6a due to the stress concentration occurring between the carcass 6 and the bead core 21, and it is possible to suppress the occurrence of a breakdown such as the breakage of the carcass cord 6c caused by the direct rubbing of the carcass cord 6c due to the wear of the coating rubber 6d.

[0073] In addition, the vertical lines 25 located on both sides of the bead core 21 in the tire width direction have a length CV within a range of 31% to 45% of the core height CH, so that the stress generated between the carcass 6 and the bead core 21 can be more reliably dispersed. In other words, if the length CV of the vertical line 25 is less than 31% of the core height CH, the length CV of the vertical line 25 is too short, so even if the vertical lines 25 are formed on both sides of the bead core 21 in the tire width direction, it may be difficult to effectively suppress the stress concentration generated between the carcass 6 and the bead core 21. In addition, if the length CV of the vertical line 25 is greater than 45% of the core height CH, the length CV of the vertical line 25 is too long, so even if the vertical lines 25 are formed on both sides of the bead core 21 in the tire width direction, stress concentration may occur between the carcass 6 and the bead core 21 at both ends in the length direction of the vertical line 25.

[0074] In contrast, when the length CV of the vertical line 25 is within a range of 31% to 45% of the core height CH, the vertical lines 25 formed on both sides of the bead core 21 in the tire width direction can more reliably distribute the stress generated between the carcass 6 and the bead core 21. This makes it possible to more reliably suppress the occurrence of failures such as breakage of the carcass cords 6c caused by the concentration of stress generated between the carcass 6 and the bead core 21.

[0075] Furthermore, the vertical line 25 of the bead core 21 has a distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 in the tire radial direction within a range of 20% to 35% of the core height CH, which more reliably suppresses stress concentration between the carcass 6 and the bead core 21. In other words, if the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 in the tire radial direction is less than 20% of the core height CH, there is a risk that the position of the vertical line 25 will be too close to the inside in the tire radial direction.

[0076] Furthermore, when the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 in the tire radial direction is greater than 35% of the core height CH, the position of the vertical line 25 may be too far outward in the tire radial direction. In such cases, the shape of the bead core 21 on both sides of which the vertical lines 25 are formed in the tire width direction may not easily conform to the shape of the carcass 6 folded back at the bead portion 20, which may cause stress concentration between the carcass 6 and the bead core 21 and may easily lead to breakdowns such as breakage of the carcass cords 6c.

[0077] In contrast, when the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a in the tire radial direction of the vertical line 25 is within a range of 20% to 35% of the core height CH, the shape of the bead core 21 in which the vertical lines 25 are formed on both sides in the tire width direction can be made to approach a shape that follows the shape of the carcass 6 folded back at the bead portion 20. This makes it possible to more reliably prevent stress concentration between the carcass 6 and the bead core 21, and more reliably prevent failures such as breakage of the carcass cords 6c caused by stress concentration occurring between the carcass 6 and the bead core 21.

[0078] In addition, in the bead core 21, among the multiple layers 31 formed by the bead wires 30, the first layer 31a, the second layer 31b, and the third layer 31c, counted from the innermost circumference in the tire radial direction, are such that the number of bead wires 30 in the layer 31 located relatively outside in the tire radial direction is two or more than the number of bead wires 30 in the layer 31 located inside in the tire radial direction between two layers 31 adjacent in the tire radial direction. This allows the contour shape of the bead core 21 from the first layer 31a to the third layer 31c in the tire meridian section to be a shape with a small inclination angle in the tire radial direction with respect to the tire width direction. Therefore, the cross-sectional shape of the bead core 21 at a position close to the bead core bottom surface 23 can be made closer to the shape of the carcass 6 folded back at the bead portion 20.

[0079] Furthermore, among the multiple layers 31 formed by the bead wire 30, the first layer 31a, the second layer 31b, and the third layer 31c are arranged so that, between two layers 31 adjacent in the tire radial direction, the amount of deviation in the tire width direction between the bead wires 30 located at one end in the tire width direction is 0.5 of the thickness of the bead wire 30. This makes it possible to prevent the amount of deviation in the tire width direction from becoming too large at the portion where the bead wire 30 straddles the two layers 31 adjacent in the tire radial direction, and to prevent the shape of the bead core 21 from being distorted due to the amount of deviation becoming too large at the portion where the bead wire 30 straddles the two layers 31 adjacent in the tire radial direction.

[0080] Furthermore, the side where the amount of deviation between the bead wires 30 in the first layer 31a and the second layer 31b is 0.5 of the thickness of the bead wire 30 and the side where the amount of deviation between the bead wires 30 in the second layer 31b and the third layer 31c is 0.5 of the thickness of the bead wire 30 are opposite to each other in the tire width direction. This allows the contour shape of the bead core 21 from the first layer 31a to the third layer 31c in the tire meridian cross section to be close to the shape of the carcass 6 folded back at the bead portion 20 in a well-balanced manner on both sides in the tire width direction. Therefore, the stress generated between the carcass 6 and the bead core 21 can be more reliably dispersed, and the occurrence of failures such as breakage of the carcass cord 6c caused by stress concentration generated between the carcass 6 and the bead core 21 can be more reliably suppressed. As a result, the durability of the bead portion 20 can be improved.

[0081] In addition, since the bead core 21 is formed in a shape in which a vertical line 25 is formed on the outer side in the tire width direction, the contact pressure between the rim wheel and the bead portion outer surface 45 (see FIG. 2), which is the outer surface of the bead portion 20 in the tire width direction, can be made closer to uniform compared to when the bead core has a substantially hexagonal cross-sectional shape. In other words, when the bead core has a substantially hexagonal cross-sectional shape, the bead core is formed with corners whose outer parts in the tire width direction are convex outward in the tire width direction, so the contact pressure between the rim wheel and the bead portion outer surface is high at the corners, but the contact pressure between the rim wheel and the bead portion outer surface is likely to be low in parts other than the corners. In this case, there is a risk that it will be difficult to ensure air sealing between the rim wheel and the bead portion outer surface when the pneumatic tire is assembled to the rim wheel and inflated.

[0082] In contrast, in this embodiment, the bead core 21 is formed in a shape in which the vertical line 25 is formed on the outer side in the tire width direction, so that the change in the distance between the bead core 21 and the bead portion outer surface 45 can be reduced. In other words, the area of ​​the portion where the contact pressure from the bead core 21 to the rim wheel can be increased can be increased. This makes it possible to make the contact pressure between the rim wheel and the bead portion outer surface 45 closer to uniform. As a result, the air sealing performance in the bead portion 20 can be improved.

[0083] In addition, since the width CBW of the bead core bottom surface 23 in the tire meridian section is within a range of 45% to 70% of the maximum width CW of the bead core 21, it is possible to suppress the occurrence of stress concentration between the bead core bottom surface 23 and the carcass 6. In other words, if the width CBW of the bead core bottom surface 23 is less than 45% of the maximum width CW of the bead core 21, the width CBW of the bead core bottom surface 23 is too narrow, so that the shape of the bead core 21 in the tire meridian section may be too convex toward the tire radial downward side. In this case, there is a possibility that stress concentration may easily occur between the carcass 6 and the bead core 21 near the bead core bottom surface 23 of the bead core 21. Furthermore, if the width CBW of the bead core bottom surface 23 is greater than 70% of the maximum width CW of the bead core 21, the width CBW of the bead core bottom surface 23 is too wide, and there is a risk that stress concentration will be more likely to occur between the carcass 6 and the bead core 21 at both ends of the bead core bottom surface 23 in the width direction.

[0084] In contrast, when the width CBW of the bead core bottom surface 23 is within a range of 45% to 70% of the maximum width CW of the bead core 21, it is possible to effectively suppress the occurrence of stress concentration between the bead core bottom surface 23 and the carcass 6. This makes it possible to more reliably suppress the occurrence of failures such as breakage of the carcass cord 6c caused by the stress concentration occurring between the carcass 6 and the bead core 21. As a result, it is possible to more reliably improve the durability of the bead portion 20.

[0085] In addition, the distance Vb in the tire width direction between the inner end 22in of the bead core top surface 22 and the inner vertical line 25 in the tire width direction is within the range of 10% to 25% of the maximum width CW of the bead core 21, and the distance Vc in the tire width direction between the inner end 23in of the bead core bottom surface 23 and the inner vertical line 25 in the tire width direction is within the range of 10% to 25% of the maximum width CW of the bead core 21, so that stress concentration occurring between the carcass 6 and the bead core 21 can be more reliably suppressed. In other words, if the distance Vb between the inner end 22in of the bead core top surface 22 in the tire width direction and the vertical line 25 on the inner side in the tire width direction, or the distance Vc between the inner end 23in of the bead core bottom surface 23 in the tire width direction and the vertical line 25 on the inner side in the tire width direction is less than 10% of the maximum width CW of the bead core 21, the amount of protrusion of the bead core 21 in the tire width direction from the position of the bead core top surface 22 or the bead core bottom surface 23 to the inner side in the tire width direction may become too small. In this case, the shape of the surface located on the inner side in the tire width direction of the bead core 21 in the tire meridian cross section is unlikely to be a shape that follows the curved shape of the portion of the carcass 6 located on the inner side in the tire width direction of the bead core 21, and as a result, stress concentration may easily occur between the carcass 6 and the bead core 21.

[0086] Furthermore, when the distance Vb between the inner end 22in of the bead core top surface 22 in the tire width direction and the vertical line 25 on the inner side in the tire width direction, or the distance Vc between the inner end 23in of the bead core bottom surface 23 in the tire width direction and the vertical line 25 on the inner side in the tire width direction is greater than 25% of the maximum width CW of the bead core 21, there is a concern that the amount of protrusion of the bead core 21 in the tire width direction toward the inner side from the position of the bead core top surface 22 or the bead core bottom surface 23 becomes too large. In this case, too, the shape of the surface located on the inner side in the tire width direction of the bead core 21 in the tire meridian cross section is unlikely to conform to the curved shape of the portion of the carcass 6 located on the inner side in the tire width direction of the bead core 21, and therefore stress concentration may easily occur between the carcass 6 and the bead core 21.

[0087] In contrast, the distance Vb between the inner end 22in of the bead core top surface 22 in the tire width direction and the vertical line 25 on the inner side in the tire width direction, and the distance Vc between the inner end 23in of the bead core bottom surface 23 in the tire width direction and the vertical line 25 on the inner side in the tire width direction are within a range of 10% to 25% of the maximum width CW of the bead core 21, so that the shape of the surface located on the inner side in the tire width direction of the bead core 21 in the tire meridian cross section can be easily made to follow the curved shape of the part of the carcass 6 located on the inner side in the tire width direction of the bead core 21. This makes it possible to more reliably suppress the stress concentration occurring between the carcass 6 and the bead core 21. As a result, the durability of the bead portion 20 can be more reliably improved.

[0088] In addition, the maximum width CW of the bead core 21 is within a range of 0.9 to 1.4 times the core height CH, so that stress concentration occurring between the carcass 6 and the bead core 21 can be more reliably suppressed. In other words, if the maximum width CW of the bead core 21 is less than 0.9 times the core height CH, the maximum width CW of the bead core 21 is too narrow, so that it is difficult to make the shape of the bead core 21 in the tire meridian section conform to the shape of the carcass 6 folded back around the bead core 21, and there is a concern that stress concentration is likely to occur between the carcass 6 and the bead core 21. Specifically, because the maximum width CW of the bead core 21 is too narrow, there is a concern that stress concentration is likely to occur between the bead core 21 and a portion of the carcass 6 folded back around the bead core 21 that is located near the bead core bottom surface 23.

[0089] Furthermore, when the maximum width CW of the bead core 21 is greater than 1.4 times the core height CH, the maximum width CW of the bead core 21 is too wide, so in this case too, it becomes difficult to make the shape of the bead core 21 in the tire meridian section conform to the shape of the carcass 6, and stress concentration may easily occur between the carcass 6 and the bead core 21. Specifically, when the maximum width CW of the bead core 21 is too wide, stress concentration may easily occur between the bead core 21 and portions of the carcass 6 that are folded back around the bead core 21 and located near both sides of the bead core 21 in the tire width direction.

[0090] In contrast, when the maximum width CW of the bead core 21 is within a range of 0.9 to 1.4 times the core height CH, the shape of the bead core 21 in the tire meridian section can be made to approximate a shape that conforms to the shape of the carcass 6 folded around the bead core 21. This makes it possible to more reliably suppress the stress concentration that occurs between the carcass 6 and the bead core 21. As a result, it is possible to more reliably improve the durability of the bead portion 20.

[0091] In addition, the number of ends of the carcass cord 6c at the inner position of the bead core 21 in the tire width direction is within a range of 10 [pieces / 50 mm] to 20 [pieces / 50 mm], so that the breakdown of the carcass 6 at the position of the bead portion 20 can be more reliably suppressed. In other words, if the number of ends of the carcass cord 6c at the inner position of the bead core 21 in the tire width direction is less than 10 [pieces / 50 mm], the number of ends of the carcass cord 6c is too small, so that when a large tension acts on the carcass 6, the tension that each carcass cord 6c bears may be too large. In this case, the stress of each carcass cord 6c may be too large in the portion of the carcass 6 arranged in the bead portion 20, and the carcass cord 6c may be easily broken. Furthermore, if the number of ends of the carcass cord 6c at the inner position in the tire width direction of the bead core 21 is more than 20 [pieces / 50 mm], the number of ends of the carcass cord 6c is too large, so the intervals between the carcass cords 6c become close, and the volume of the coating rubber 6d located between the adjacent carcass cords 6c may become too small. In this case, it becomes difficult to hold the carcass cords 6c by the coating rubber 6d, and the carcass cords 6c become easily peeled off from the coating rubber 6d, so that it may be difficult to produce a carcass 6 having appropriate durability.

[0092] On the other hand, when the number of ends of the carcass cord 6c at the position on the inner side of the bead core 21 in the tire width direction is within a range of 10 [pieces / 50 mm] or more and 20 [pieces / 50 mm] or less, the volume of the coat rubber 6d located between the adjacent carcass cords 6c is prevented from becoming too small, and the force that the carcass cords 6c bear can be distributed to a larger number of carcass cords 6c. This prevents the carcass cords 6c from peeling off the coat rubber 6d, and reduces the tension that each carcass cord 6c bears when a large tension acts on the carcass 6 at the position of the bead portion 20, thereby preventing the carcass cords 6c from easily breaking due to the stress of each carcass cord 6c becoming too large. Therefore, the durability of the carcass 6 can be ensured, and the failure of the carcass 6 at the position of the bead portion 20 can be more reliably prevented. As a result, the durability of the bead portion 20 can be more reliably improved.

[0093] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the bead core 21 is formed such that the part located at the innermost side in the tire width direction of the bead core 21 and the part located at the outermost side in the tire width direction of the bead core 21 form the perpendicular line 25, so that even if a large force acts between the carcass 6 and the bead core 21 due to a large tension acting on the carcass 6, it is possible to suppress the occurrence of stress concentration. Therefore, it is possible to suppress the occurrence of failures such as breakage of the carcass cord 6c caused by the stress concentration occurring between the carcass 6 and the bead core 21.

[0094] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the length CV of the vertical line 25 is set within a range of 31% to 45% of the core height CH, so that the vertical lines 25 formed on both sides of the bead core 21 in the tire width direction can more reliably distribute the stress generated between the carcass 6 and the bead core 21. This makes it possible to more reliably suppress the occurrence of failures such as breakage of the carcass cord 6c caused by the concentration of stress generated between the carcass 6 and the bead core 21.

[0095] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the distance Va in the tire radial direction from the bead core bottom surface 23 to the inner end 25a in the tire radial direction of the vertical line 25 is set within a range of 20% to 35% of the core height CH, so that the shape of the bead core 21 can be made to approximate a shape that follows the shape of the carcass 6 folded back at the bead portion 20. This makes it possible to more reliably suppress the occurrence of stress concentration between the carcass 6 and the bead core 21.

[0096] In the manufacturing method of the pneumatic tire 1 according to the embodiment, among the multiple layers 31 formed by the bead wire 30, the first layer 31a, the second layer 31b, and the third layer 31c, between two adjacent layers 31, the amount of deviation in the tire width direction between the bead wires 30 located at one end in the tire width direction is set to 0.5 of the thickness of the bead wire 30. This makes it possible to prevent the amount of deviation in the tire width direction at the portion where the bead wire 30 straddles two layers 31 adjacent in the tire radial direction from becoming too large, and to prevent the shape of the bead core 21 from being distorted.

[0097] In addition, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the side where the amount of deviation between the bead wires 30 in the first layer 31a and the second layer 31b is set to 0.5 of the thickness of the bead wire 30 and the side where the amount of deviation between the bead wires 30 in the second layer 31b and the third layer 31c is set to 0.5 of the thickness of the bead wire 30 are opposite to each other in the tire width direction. This allows the shape of the bead core 21 in the tire meridian cross section to be close to the shape of the carcass 6 in a well-balanced manner on both sides in the tire width direction, and suppresses stress concentration occurring between the carcass 6 and the bead core 21, thereby more reliably suppressing the occurrence of failures such as breakage of the carcass cord 6c. As a result, the durability of the bead portion 20 can be improved.

[0098] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the bead wire 30 starts to be wound from the end portion on the outer side in the tire width direction of the first layer 31a, so that the durability of the bead core 21 can be ensured. In other words, when the pneumatic tire 1 is inflated, the bead core 21 requires the greatest strength at the end portion 23in on the inner side in the tire width direction of the bead core bottom surface 23. For this reason, if the end portion of the bead wire 30 is located at the end portion 23in on the inner side in the tire width direction of the bead core bottom surface 23, the durability of the bead core 21 may decrease, and the shape of the bead core 21 may easily become deformed.

[0099] In contrast, when the bead wire 30 is wound starting from the end portion on the outer side in the tire width direction of the first layer 31a, it is possible to ensure the strength at the end portion 23in on the inner side in the tire width direction of the bead core bottom surface 23, where the greatest strength is required, and therefore it is possible to prevent the shape of the bead core 21 from easily collapsing. As a result, it is possible to ensure the durability of the bead core 21.

[0100] [Variations] In the pneumatic tire 1 according to the embodiment described above, the number of bead wires 30 in the layer 31 decreases by one each time toward the tire radially outward side from the layer 31 including the bead wire 30 that forms the tire radially outer end of the vertical line 25, but the bead core 21 may be formed in a form other than this.

[0101] Fig. 5 is a detailed view of a bead core 21 in which bead wires 30 are laminated in a form different from that of the above-described embodiment, which is a modified example of the pneumatic tire 1 according to the embodiment. For example, as shown in Fig. 5, the bead core 21 may have a portion in which the number of bead wires 30 in the layer 31 located relatively outward in the tire radial direction is two less than the number of bead wires 30 in the layer 31 located inward in the tire radial direction, between two layers 31 located outward in the tire radial direction and adjacent to each other in the tire radial direction outside the vertical line 25. The bead core 21 is formed in a cross-sectional shape that is close to an octagon when viewed in a tire meridian section, and the first layer 31a, the second layer 31b, and the third layer 31c counted from the innermost circumference in the tire radial direction among the multiple layers 31 formed by the bead wires 30 may be formed as in the above-described embodiment, and the form of the portion outward in the tire radial direction from the vertical line 25 does not matter.

[0102] In addition, in the pneumatic tire 1 according to the embodiment described above, three reinforcing layers 60 are arranged, but the reinforcing layers 60 may be arranged in a number other than three layers. The number of reinforcing layers 60 and the range in which the reinforcing layers 60 are arranged in the tire meridian cross section may be different from the number and range of the embodiment described above.

[0103] [Example] 6A and 6B are diagrams showing the results of a performance evaluation test of a pneumatic tire. Below, a performance evaluation test performed on a conventional pneumatic tire and the pneumatic tire 1 according to the present invention will be described. The performance evaluation test was a durability test to evaluate the durability of the pneumatic tire 1.

[0104] The performance evaluation test was performed under the following conditions: a pneumatic tire 1 having a nominal tire size of 37.25R35 was used as the test tire; this test tire was mounted on a rim wheel conforming to the TRA standard; the air pressure was adjusted to the air pressure specified by the TRA standard; and a load specified by the TRA standard was applied.

[0105] The durability was evaluated using an indoor drum tester, with a running test set at a load of 120% of the maximum load specified by the TRA and a speed of 10 km / h, and the breakage rate of the wires in the carcass cords in the bead portion after the pneumatic tire had been running for 300 hours was evaluated by expressing it as an index with a conventional example described below being 100. The wire breakage rate was determined by sampling 40 carcass cords in the bead portion at random locations at the end of the run, observing all the sampled carcass cords, and taking the average value of (number of broken wires in each carcass cord / total number of wires in each carcass cord) as the breakage rate.

[0106] The performance evaluation test was carried out on 24 types of pneumatic tires, including a conventional pneumatic tire which is an example of a conventional pneumatic tire, and Examples 1 to 23 which are pneumatic tires 1 according to the present invention. Of these, the conventional pneumatic tire has a bead core with a substantially hexagonal cross-sectional shape in the tire meridian section, and the bead core does not have a vertical line on the innermost and outermost sides in the tire width direction.

[0107] In contrast, in Examples 1 to 23, which are examples of the pneumatic tire 1 according to the present invention, the bead core 21 all has vertical lines 25 at the innermost and outermost sides in the tire width direction, the length CV of the vertical line 25 of the bead core 21 is within the range of 31% or more and 45% or less of the core height CH of the bead core 21, and the distance Va from the bead core bottom surface 23 to the inner end 25a of the vertical line 25 is within the range of 20% or more and 35% or less of the core height CH. Furthermore, the pneumatic tires 1 of Examples 1 to 23 are different in the ratio (CBW / CW) of the width CBW of the bead core bottom surface 23 to the maximum width CW of the bead core 21, the ratio (Vb / CW) of the distance Vb between the inner vertical line 25 in the tire width direction and the end 22in of the bead core top surface 22 to the maximum width CW of the bead core 21, the ratio (Vc / CW) of the distance Vc between the inner vertical line 25 in the tire width direction and the end 23in of the bead core bottom surface 23 to the maximum width CW of the bead core 21, the ratio (CW / CH) of the maximum width CW of the bead core to the core height CH, and the number of ends of the carcass cord 6c at the inner position of the bead core 21 in the tire width direction.

[0108] 6A and 6B, a performance evaluation test was conducted using these pneumatic tires 1. As a result, it was found that the pneumatic tires 1 according to Examples 1 to 23 had a better breakage rate of the bare wire of the carcass cord 6c in the bead portion 20 than the conventional tire, and breakage of the carcass cord 6c in the bead portion 20 was less likely to occur, as shown in FIG. [Explanation of symbols]

[0109] 1. Pneumatic tires 2 Tread section 2a Tread rubber 3 Tread surface 4 Shoulder section 5 Sidewall 6. Carcass 6a Carcass body 6b Turnup section 6c Carcass Cord 6d coated rubber 7 Belt layer 10 Land 15 Circumferential groove 20 Bead section 21 Bead core 22 Bead core top surface 23 Bead core bottom 25 Vertical Line 30 Bead wire 31 layers 31a 1st layer 31b 2nd layer 31c 3rd layer 40 Bead base part 41 Bead Toe 42 Bead Heel 45 Bead outer surface 46 Rim cushion rubber 50 Bead Filler 51 Lower Filler 52 Upper Filler 60 Reinforcement layer

Claims

1. A pair of bead portions arranged on both sides of a tire equatorial plane in a tire width direction; a bead core disposed in the bead portion, the bead core being formed by winding a bead wire in a ring shape and having a polygonal cross section in a tire meridian section; a carcass including a carcass body portion disposed between a pair of the bead portions and a turn-up portion formed continuously from the carcass body portion and folded back from an inner side in the tire width direction of the bead core to an outer side in the tire width direction, the carcass being formed by covering a carcass cord with a coating rubber; Equipped with a portion located at the innermost side in the tire width direction and a portion located at the outermost side in the tire width direction in a contour of a tire meridian cross section of the bead core are each formed by a vertical line extending along a tire radial direction, The vertical line has a length in a range of 31% to 45% of a core height, which is a height of the bead core in the tire radial direction, a distance in a radial direction of the tire from a bead core bottom surface, which is an inner circumferential surface of the bead core, to an inner end portion in a radial direction of the vertical line is within a range of 20% to 35% of a core height, The bead core is formed by arranging a plurality of winding portions of the bead wire, which is formed by winding the bead wire in a ring shape, in the tire width direction to form one layer, and the plurality of layers are laminated in the tire radial direction, among the plurality of layers, in a layer located radially outward of a layer including the bead wire forming an end portion on the outer side in the tire radial direction of the vertical line, the number of the bead wires in the layer is reduced by one toward the outer side in the tire radial direction, Among the plurality of layers, in a layer located radially inward of a layer including the bead wire forming the inner end portion of the vertical line, the number of the bead wires in the layer located relatively radially outward of the layer between two layers adjacent in the tire radial direction is two or more than the number of the bead wires in the layer located radially inward of the tire, and the amount of deviation in the tire width direction between the bead wires located at one end portion in the tire width direction is 0.5 of the bead wire, a first layer, which is the layer located at the innermost circumference in the tire radial direction, a second layer, which is stacked adjacent to the first layer on the outer side in the tire radial direction, and a third layer, which is stacked adjacent to the second layer on the outer side in the tire radial direction, are arranged such that a side on which an amount of misalignment between the bead wires in the first layer and the second layer is 0.5 of the bead wire and a side on which an amount of misalignment between the bead wires in the second layer and the third layer is 0.5 of the bead wire are opposite each other in the tire width direction.

2. The pneumatic tire according to claim 1 , wherein the width of the bead core bottom surface in a tire meridian section is within a range of 45% to 70% of the maximum width of the bead core.

3. The bead core is a distance in the tire width direction between an inner end portion in the tire width direction of a bead core upper surface, which is an outer peripheral surface in a tire meridian cross section, and the vertical line on the inner side in the tire width direction is within a range of 10% to 25% of a maximum width of the bead core, a distance in the tire width direction between an end portion on an inner side in the tire width direction of the bottom surface of the bead core and the vertical line on the inner side in the tire width direction is within a range of 10% to 25% of a maximum width of the bead core, 3. The pneumatic tire according to claim 1, wherein a maximum width of the bead core is within a range of 0.9 to 1.4 times the height of the core.

4. 3. The pneumatic tire according to claim 1, wherein the number of ends of the carcass cord at a position on an inner side of the bead core in the tire width direction is within a range of 10 cords / 50 mm or more and 20 cords / 50 mm or less.

5. The pneumatic tire according to claim 3 , wherein the number of ends of the carcass cords at a position on an inner side of the bead core in the tire width direction is within a range of 10 cords / 50 mm or more and 20 cords / 50 mm or less.

6. In the bead portion, a reinforcing layer is arranged along the carcass at least on the inner side in the tire width direction of the carcass main body portion, The reinforcing layer includes a plurality of reinforcing layers each having a plurality of cords, the reinforcing layers being arranged in a layered manner, The pneumatic tire according to claim 1 , wherein adjacent reinforcing layers have cords arranged in such a manner that the cords are inclined in the circumferential direction of the tire with respect to the radial direction of the tire in opposite directions to each other.

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