Pneumatic tire

Abstract

In order to improve the durability of a bead section, in a pneumatic tire (1), both ends of a bead core (21) in the width direction of the tire are each formed by a vertical line (25) extending in the radial direction of the tire, the length CV of the vertical line (25) is 31% or more and 45% or less with respect to the core height CH, and the length CV of a first layer (31a), a second layer (31b), and a third layer (31c) of the bead core (21) are 31% or more and 45% or less with respect to the core height CH of the first layer (31a), the second layer (31b), and the third layer (31c). Among two adjacent layers (31), the number of bead wires (30) in the layer (31) located on the outer side in the tire radial direction is two or more larger than the number of bead wires (30) in the layer (31) located on the inner side in the tire radial direction, the amount of displacement between the bead wires (30) located at the end of one side in the tire width direction is 0.5 of the amount of bead wires (30), and in the first layer (31a), the second layer (31b), the second layer (31b), and the third layer (31c), the number of bead wires (30) in the first layer (31a) and the second layer (31b) is 0.5 of the number of bead wires (30) in the second layer (31c). One side where the amount of displacement between the bead wires (30) is 0.5 of the amount of the bead wires (30) is opposite to each other in the tire width direction.

Description

Pneumatic tires Technical Field

[0001] The present invention relates to pneumatic tires. Background Art

[0002] A pneumatic tire is assembled onto a rim-type wheel by fitting a bead portion, which includes a bead core formed by binding a plurality of bead wires together, onto the rim of the rim-type wheel. The bead portion is the part of the pneumatic tire that is actually mounted on the rim-type wheel during assembly, and therefore plays a crucial role in ensuring the performance of the pneumatic tire. Conventional pneumatic tires have employed various designs on the bead portion to achieve 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 rounded ends on both sides, thereby reducing wear in the bead area. Furthermore, 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 edges extending obliquely from the axially outer ends of the lower and upper bases toward the axially outer sides of the tire, and the axially inner contour of the bead core is formed by the inner side connecting the axially inner ends of the lower and upper bases, thereby improving the durability of the bead portion.

[0004] Furthermore, the bead core described in Patent Document 3 has a cross-sectional shape that is radially inward relative to the bead core's cross-sectional center, formed by a base parallel to the bead core's axial direction, left and right intermediate sides perpendicular to the bead core's axial direction, and obtuse sides formed by connecting the inner ends of the left and right intermediate sides to both sides of the base. This reduces tire failures caused by carcass cord wear and air accumulation. Furthermore, in the pneumatic tire described in Patent Document 4, when manufacturing a bead core having an overall toroidal shape, in which steel wires are arranged in multiple rows and stages without gaps, the outermost wires in the width direction of each row of wires from the innermost circumference to the maximum width position are positioned outward relative to the outermost wires in the width direction of the innermost rows of wires, with the offset decreasing from the innermost circumference toward the maximum width position. This prevents carcass breakage and prevents undulation of the carcass's rolled-up end during tire manufacturing.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-34784

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 9-240223

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2005-88793

[0010] Patent Document 4: Japanese Patent No. 4243091

[0011] Summary of the Invention

[0012] Problems to be solved by the invention

[0013] Generally, the bead core is polygonal in the radial cross-section of the tire. However, in some very large pneumatic tires, a nylon cover is wrapped around the bead core to avoid stress concentration on the carcass caused by the corners of the bead core. However, with only a nylon cover, the distance between the corners of the bead core and the carcass is insufficient. Therefore, when high tension is applied to the carcass, the area near the corners of the bead core and the carcass are susceptible to friction while receiving the high force. In this case, the friction between the corners of the bead core and the carcass can cause the carcass cord to break. In particular, pneumatic tires designed for vehicles such as loaders and scrapers that require high traction often use bead cores with a relatively flat radial cross-section. This makes the corners of the bead core more susceptible to friction with the carcass, which can easily break the carcass cord. Therefore, in conventional pneumatic tires, there is room for improvement in terms of the durability of the bead portion.

[0014] The present invention has been made in view of the above, and an object of the present invention is to provide a pneumatic tire capable of improving the durability of a bead portion.

[0015] Means for solving problems

[0016] In order to solve the above-mentioned problems and achieve the purpose, the pneumatic tire of the present invention is characterized in that it comprises: a pair of bead portions, which are arranged on both sides of the tire equatorial plane in the tire width direction; a bead core, which is arranged on the bead portion and is formed by winding the bead wire into a ring shape, and the shape in the tire meridian section is formed by a polygonal cross section; and a carcass, which has a carcass main body portion arranged between the pair of bead portions and a turn-up portion which is continuously formed from the carcass main body portion and folded from the tire width direction inner side of the bead core toward the tire width direction outer side, The cord is formed by covering with covering rubber, and in the bead core, the innermost part and the outermost part in the tire width direction of the outline at the tire meridian section are respectively formed by vertical lines extending in the tire radial direction, and the length of the vertical line is within the range of 31% or more and 45% or less relative to the height of the bead core in the tire radial direction, that is, the core height, and the distance in the tire radial direction from the inner peripheral surface of the bead core, that is, the bottom surface of the bead core, to the inner end of the vertical line in the tire radial direction is equal to For the range of the core height being greater than 20% and less than 35%, the plurality of surrounding portions of the bead wire formed by winding the bead core into a ring shape are arranged in the tire width direction to form one layer, and the plurality of layers are stacked in the tire radial direction. Regarding the layer located at the innermost circumference in the tire radial direction among the plurality of layers, namely the first layer, the second layer stacked adjacent to and on the outer side of the first layer in the tire radial direction, and the third layer stacked adjacent to and on the outer side of the second layer in the tire radial direction, of the two layers adjacent to each other in the tire radial direction, the layers located relatively on the outer side of the tire radial direction are located. The number of the bead wires of the layer on the side is more than 2 more than the number of the bead wires of the layer located on the radial inner side of the tire, and the bead wires at the end portion on one side in the tire width direction are offset from each other by 0.5 of the bead wire, and the side where the offset between the bead wires in the first layer and the second layer becomes 0.5 of the bead wire and the side where the offset between the bead wires in the second layer and the third layer becomes 0.5 of the bead wire are on the opposite sides of each other in the tire width direction.

[0017] In the above-mentioned pneumatic tire, preferably, regarding the bead core, a width of the bead core bottom surface in a tire meridian cross section is within a range of 45% to 70% of a maximum width of the bead core.

[0018] In addition, in the above-mentioned pneumatic tire, it is preferred that, with respect to the bead core, the distance in the tire width direction between the end portion on the inner side of the tire width direction in the outer peripheral surface in the tire meridian section, i.e., the upper surface of the bead core, and the vertical line on the inner side of the tire width direction is within a range of 10% to 25% relative to the maximum width of the bead core; the distance in the tire width direction between the end portion on the inner side of the tire width direction in the bottom surface of the bead core and the vertical line on the inner side of the tire width direction is within a range of 10% to 25% relative to the maximum width of the bead core; and the maximum width of the bead core is within a range of 0.9 times to 1.4 times relative to the core height.

[0019] In the pneumatic tire, preferably, regarding the carcass, an implantation density of the carcass cords at a position inside 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.

[0020] Effects of the Invention

[0021] The pneumatic tire of the present invention has the effect of improving the durability of the bead portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a meridian cross-sectional view showing a main portion of a pneumatic tire according to an embodiment.

[0023] FIG. 2 is a detailed view of section A of FIG. 1 .

[0024] FIG. 3 is a detailed view of the bead core shown in FIG. 2 .

[0025] FIG. 4 is a detailed view of portion B of FIG. 3 .

[0026] FIG. 5 is a modified example of the pneumatic tire according to the embodiment, and is a detailed view of a bead core in which bead wires are laminated in a manner different from that of the embodiment shown in FIG. 3 .

[0027] FIG6A is a graph showing the results of a performance evaluation test of a pneumatic tire.

[0028] FIG6B is a graph showing the results of a performance evaluation test of a pneumatic tire. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the pneumatic tire of the present invention will be described in detail based on the accompanying drawings. The present invention is not limited to these embodiments. The components of the following embodiments include those that are easily conceivable and replaceable by those skilled in the art, or are substantially the same.

[0030] [Implementation Method]

[0031] In the following description, the tire radial direction refers to the direction perpendicular to the rotation axis of the pneumatic tire 1, i.e., the tire rotation axis (not shown). The tire radial inner side refers to the side radially toward the tire rotation axis, and the tire radial outer side refers to the side radially away from the tire rotation axis. Furthermore, the tire circumferential direction refers to the circumferential direction centered around the tire rotation axis. Furthermore, the tire width direction refers to the direction parallel to the tire rotation axis. The tire width direction inner side refers to the side radially toward the tire equatorial plane (tire equatorial line) CL, and the tire width direction outer side refers to the side radially away from the tire equatorial plane CL. 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. The tire equatorial plane CL's position in the tire width direction coincides with the tire width centerline, i.e., the center position of the pneumatic tire 1 in the tire width direction. The tire width refers to the width of the tire between the outermost portions in the tire width direction, i.e., the distance between the portions furthest away from the tire equatorial plane CL in the tire width direction. The tire equator line is a line located on the tire equatorial plane CL and extending along the tire circumferential direction of the pneumatic tire 1. In the following description, a tire meridian cross section is a cross section obtained by cutting the tire along a plane including the tire rotation axis.

[0032] FIG1 is a meridian cross-sectional view showing the main portion of a pneumatic tire 1 according to an embodiment. The pneumatic tire 1 according to the embodiment is a radial tire for construction vehicles, known as an OR tire (Off the Road Tire). The pneumatic tire 1 shown in FIG1 as this embodiment, when viewed in a meridian cross-section, has a tread portion 2 disposed on the outermost portion in the tire radial direction. 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 contacts the road surface when a vehicle (not shown) equipped with the pneumatic tire 1 is traveling, forms a tread surface 3.

[0033] The tread surface 3 of the tread portion 2 is formed with a plurality of circumferential grooves 15 extending in the tire circumferential direction and grooves (not shown) such as lug grooves extending in the tire width direction. The tread portion 2 is partitioned into a plurality of land portions 10 by these grooves.

[0034] The ends of the tread portion 2 in the tire width direction form shoulder portions 4. Sidewall portions 5 are arranged from the shoulder portions 4 to predetermined positions radially inward of the tire. Specifically, the sidewall portions 5 are arranged at two locations on either side of the pneumatic tire 1 in the tire width direction. The sidewall portions 5 are composed of sidewall rubber 5a, a rubber composition. Furthermore, a rim check line 9 is formed radially inward of each sidewall portion 5 on both sides of the tire width direction. The rim check line 9 protrudes from the surface of the sidewall portion 5 and extends around the circumference of the tire.

[0035] Furthermore, a bead portion 20 is present on the radially inner side of each sidewall portion 5. Like the sidewall portions 5, the bead portions 20 are located at two locations on either side of the tire's equatorial plane CL. That is, a pair of bead portions 20 are located on either side of the tire's equatorial plane CL in the tire's width direction. A bead core 21 is located in each of the pair of bead portions 20, and a bead filler 50 is located radially outward of each bead core 21. The bead core 21 is formed by winding a bead wire 30 (see FIG. 3 ), which is a steel wire, into a ring shape. The bead filler 50 is a rubber member located in a space formed by folding the tire widthwise end portion of the carcass 6 (described later) outward in the tire widthwise direction at the position of the bead core 21. Furthermore, the bead filler 50 includes a lower filler 51 that is located in contact with the outer circumferential surface of the bead core 21, and an upper filler 52 that is located radially outward of the lower filler 51.

[0036] The bead portion 20 is configured to be mounted on a rim-type wheel having a predetermined rim R with a 5° taper. Specifically, the pneumatic tire 1 of this embodiment can be mounted on a predetermined rim R, wherein the portion engaging the bead portion 20 is tilted at an angle of 5°±1° relative to the rotational axis of the rim-type wheel, in a direction that moves outward in the tire radial direction from the inside in the tire width direction. The predetermined rim R refers to the "applicable rim" specified in JATMA, the "design rim" specified in TRA, or the "measuring rim" specified in ETRTO.

[0037] A belt layer 7 is provided radially inward of the tread portion 2. The belt layer 7 has a multilayer structure comprising three or more belt plies stacked together. In typical OR tires, four to eight belt plies are stacked together. In this embodiment, the belt layer 7 comprises six stacked belt plies 7a, 7b, 7c, 7d, 7e, and 7f. The belt plies 7a, 7b, 7c, 7d, 7e, and 7f constituting the belt layer 7 are formed by covering a plurality of belt cords made of steel or an organic fiber material with a covering rubber and then rolling the resulting layers. The six belt plies 7a, 7b, 7c, 7d, 7e, and 7f are comprised, for example, of cross belt layers 7a, 7b, 7c, and 7d and protective belt layers 7e and 7f. In addition, in the belt plies 7a, 7b, 7c, 7d, 7e, and 7f, the inclination angles of the belt cords in the tire width direction relative to the tire circumferential direction are different from each other, and the cross belt layer and the protection belt layer are constructed as a so-called cross ply structure in which the inclination directions are intersected with each other within the layer.

[0038] A carcass 6, containing radial plies of cords, is continuously disposed radially inward of the belt layer 7 and on the tire equatorial plane CL side of the sidewall portion 5. The carcass 6 has a single-layer structure consisting of a single carcass ply or a multi-layer structure consisting of multiple carcass plies. It is annularly arranged between bead cores 21 positioned on both sides of the tire width direction, forming the tire's skeleton. Specifically, the carcass 6 is arranged between a pair of bead portions 20, extending from one bead portion 20 to the other of the pair of bead portions 20 positioned on both sides of the tire width direction. Furthermore, the carcass 6 is folded over at the bead portion 20, from the inner side of the bead core 21 in the tire width direction, through the inner side of the bead core 21 in the tire radial direction, and then outward in the tire width direction, so as to enclose the bead core 21 and the bead filler 50. That is, the carcass 6 is folded 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.

[0039] Thus, the carcass 6 includes a carcass main portion 6a disposed between the pair of bead portions 20, and a turned-up portion 6b formed continuously from the carcass main portion 6a and folded from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction. The carcass main portion 6a herein refers to the portion of the carcass 6 formed between the inner sides of the pair of bead cores 21 in the tire width direction, while the turned-up portion 6b refers to the portion formed continuously from the carcass main portion 6a on the inner side of the bead core 21 in the tire width direction and folded from the inner side of the bead core 21 in the tire radial direction to the outer side in the tire width direction. The bead filler 50 is disposed on the inner side of the turned-up portion 6b, which is folded outward in the tire width direction of the bead core 21, and on the outer side of the bead core 21 in the tire radial direction.

[0040] The carcass ply of the carcass 6 thus arranged is formed by covering a plurality of carcass cords 6c (see FIG. 2 ), which are cord members made of steel or an organic fiber material such as aramid, nylon, polyester, or rayon, with a rubber cover 6d (see FIG. 2 ), which is a rubber member, and rolling the covering rubber. Furthermore, in the carcass 6, the carcass cords 6c have an inclination angle, i.e., a carcass cord angle, with respect to the tire circumferential direction, of 85° or more and 95° or less.

[0041] Furthermore, an inner liner 8 is formed along the carcass 6 on the inner side of the carcass 6 or on the inner side of the pneumatic tire 1 of the carcass 6 .

[0042] FIG2 is a detailed view of section A of FIG1 . FIG3 is a detailed view of the bead core 21 shown in FIG2 . The shape of the bead core 21 when viewed in the tire meridian cross section is formed by a polygonal cross section. In the present embodiment, the bead core 21 is formed with a cross-sectional shape close to an octagon. Specifically, in the bead core 21, the inner circumferential surface of the bead core 21, i.e., the bead core bottom surface 23, and the outer circumferential surface of the bead core 21, i.e., the bead core upper surface 22, when viewed as a whole are formed approximately in parallel. In addition, in the bead core 21, the innermost portion and the outermost portion in the tire width direction of the outline in the tire meridian cross section are respectively formed by vertical lines 25 extending along the tire radial direction.

[0043] Furthermore, in the tire meridian cross-section, the bead core 21 has a radially inner portion of a vertical line 25 located inwardly in the tire width direction and an inner end portion of the bead core bottom surface 23 in the tire width direction connected in a side-like manner. Furthermore, in the tire meridian cross-section, the radially inner portion of a vertical line 25 located inwardly in the tire width direction and an outer end portion of the bead core top surface 22 in the tire width direction are connected in a side-like manner. Furthermore, in the tire meridian cross-section, the radially inner portion of a vertical line 25 located inwardly in the tire width direction and an outer end portion of the bead core bottom surface 23 in the tire width direction are connected in a side-like manner. Furthermore, the radially outer portion of a vertical line 25 located inwardly in the tire width direction and an outer end portion of the bead core top surface 22 in the tire width direction are connected in a side-like manner. Consequently, the bead core 21 is formed in a substantially octagonal shape in the tire meridian cross-section.

[0044] Furthermore, the bead core bottom surface 23 of the bead core 21 in this case refers to a surface represented by an imaginary straight line tangent to the portion of the plurality of bead wires 30 arranged in a row at a position radially inward of the bead core 21 to constitute the surface of the bead core 21, which is exposed toward the surface side of the bead core 21. Similarly, the bead core top surface 22 of the bead core 21 refers to a surface represented by an imaginary straight line tangent to the portion of the plurality of bead wires 30 arranged in a row at a position radially outward of the bead core 21 to constitute the surface of the bead core 21, when the pneumatic tire 1 is viewed in a tire meridian cross section.

[0045] Furthermore, the vertical line 25 of the bead core 21 is an imaginary straight line that is tangent to the portion of the bead wires 30 located on the outermost sides of the bead core 21 in the width direction, which portion is exposed outward in the width direction of the bead core 21, when the tire width direction is set to the width direction of the bead core 21 in the tire meridian cross section. Specifically, the vertical line 25 is formed so as to extend in the tire radial direction while ensuring that the spacing in the tire width direction between the pair of bead portions 20 located on both sides of the tire width direction relative to the tire equatorial plane CL is the spacing when the pneumatic tire 1 is mounted on a predetermined rim R (see FIG. 1 ).

[0046] In other words, in the bead core 21, the bead wire 30 is arranged in such a manner that an imaginary straight line tangent to the multiple bead wires 30 located on the outermost side in the width direction of the bead core 21 extends in the tire radial direction when the interval in the tire width direction of a pair of bead portions 20 located on both sides of the tire width direction relative to the tire equatorial plane CL becomes the interval when the inflated tire 1 is assembled on the specified rim R.

[0047] In this embodiment, a vertical line 25 on the inner side of the bead core 21 in the tire meridian cross section in the tire width direction becomes a tangent line to the three bead lines 30 that are located most inward in the tire width direction and are spaced apart in the tire radial direction among the bead lines 30. Furthermore, a vertical line 25 on the outer side of the bead core 21 in the tire meridian cross section in the tire width direction becomes a tangent line to the three bead lines 30 that are located most outward in the tire width direction and are spaced apart in the tire radial direction among the bead lines 30.

[0048] In the following description, the shape around the bead portion 20 is similar to the description of the vertical line 25, assuming that the distance in the tire width direction between the pair of bead portions 20 located on opposite sides of the tire equatorial plane CL is the same as the distance when the pneumatic tire 1 is assembled on the specified rim R. Furthermore, the vertical line 25 of the bead core 21 does not necessarily need to extend strictly in the tire radial direction. The vertical line 25 can be formed within a range of 0° to 15° relative to the tire radial direction.

[0049] Thus, for each of the vertical lines 25 located on either side of the bead core 21 in the width direction, the length CV of each vertical line 25 is within a range of 31% to 45% of the core height CH, the height of the bead core 21 in the tire radial direction. In other words, the ratio CV / CH of the length CV of each vertical line 25 to the core height CH is within a range of 31% to 45%. In this case, the length CV of each vertical line 25 is the distance between the radially outermost end of the bead wire 30 located closest to the tire radial direction and the radially innermost end of the bead wire 30 located closest to the tire radial direction. Furthermore, the core height CH in this case is the distance between the bead core top surface 22 and the bead core bottom surface 23.

[0050] Furthermore, regarding the vertical line 25, a distance Va in the tire radial direction from the bead core bottom surface 23 to an 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 of the bead wire 30 located most radially inward among the multiple bead wires 30 constituting the vertical line 25.

[0051] Specifically, the bead core 21 has vertical lines 25 on both sides of the bead core 21 in the width direction. For each of the vertical lines 25 on both sides of the bead core 21 in the width direction, a distance Va in the tire radial direction from the bead core bottom surface 23 to an 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 each of the vertical lines 25 on both sides of the bead core 21 in the width direction, a ratio Va / CH of 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 to the core height CH is within a range of 20% to 35%.

[0052] Furthermore, in a tire meridian cross-section, a distance Vb in the tire width direction between an inner end 22in of the bead core upper surface 22 and an inner vertical line 25 of a perpendicular line 25 on either side of the bead core 21 in the tire width direction is within a range of 10% to 25% of the maximum width CW of the bead core 21. In other words, a ratio Vb / CW of the distance Vb in the tire width direction between an inner end 22in of the bead core upper surface 22 and an inner vertical line 25 in the tire width direction relative 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 perpendicular lines 25 on either side of the bead core 21 in the tire width direction. In this case, the tire widthwise inner end 22in of the bead core upper surface 22 becomes the tire widthwise inner end of the bead wire 30 located most inwardly in the tire widthwise direction among the plurality of bead wires 30 constituting the bead core upper surface 22 .

[0053] Similarly, with respect to the bead core 21, a distance Vc in the tire width direction between an inner end 23in of the bead core bottom surface 23 and a perpendicular line 25 extending inwardly in the tire width direction is within a range of 10% to 25% relative to the maximum width CW of the bead core 21. In other words, a ratio Vc / CW of a distance Vc in the tire width direction between an inner end 23in of the bead core bottom surface 23 and a perpendicular line 25 extending inwardly in the tire width direction relative to the maximum width CW of the bead core 21 is within a range of 10% to 25%. In this case, the inner end 23in of the bead core bottom surface 23 is the innermost end of the bead wire 30 located most inwardly in the tire width direction among the multiple bead wires 30 constituting the bead core bottom surface 23.

[0054] Furthermore, the maximum width CW of the bead core 21 in the tire meridian cross section is within a range of 0.9 times or greater and 1.4 times or less of the core height CH. Furthermore, the width CBW of the bead core bottom surface 23 in the tire meridian cross section is within a range of 45% or greater and 70% or less 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 times or greater and 1.4 times or less, 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% or greater and 70% or less.

[0055] Figure 4 is a detailed view of section B of Figure 3 . The bead core 21 is formed by winding a bead wire 30 into a toroidal shape. Specifically, multiple looped portions of the toroidally wound bead wire 30 are arranged in the tire width direction to form a single layer 31, and multiple layers 31 are stacked in the tire radial direction. Within adjacent layers 31 in the tire radial direction, the bead wires 30 forming each layer 31 are staggered in the tire width direction by 0.5 of the bead wire 30's thickness.

[0056] Regarding the first layer 31a, second layer 31b, and third layer 31c, counted from the inner side in the tire radial direction, of the plurality of layers 31 included in the bead core 21, the number of bead wires 30 in the layer 31 located radially outward relative to the tire is two or more greater than the number of bead wires 30 in the layer 31 located radially inward relative to the tire. In this case, the first layer 31a is the innermost layer 31 in the tire radial direction among the plurality of layers 31 included in the bead core 21. Furthermore, the second layer 31b is the layer 31 stacked adjacent to and radially outward of the first layer 31a, and the third layer 31c is the layer 31 stacked adjacent to and radially outward of the second layer 31b. 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.

[0057] Furthermore, with respect to the first layer 31a, the second layer 31b, and the third layer 31c of the bead core 21, the amount of displacement in the tire width direction between the bead wires 30 located at one end portion in the tire width direction of two adjacent layers 31 in the tire radial direction is 0.5 of the thickness of the bead wire 30. Furthermore, with respect to the first layer 31a, the second layer 31b, and the third layer 31c, the side where the bead wires 30 at the ends in the tire width direction of the first and second layers 31a, 31b are displaced by 0.5 of the bead wire 30 and the side where the bead wires 30 at the ends in the tire width direction of the second and third layers 31b, 31c are displaced by 0.5 of the bead wire 30 are on opposite sides in the tire width direction.

[0058] Specifically, the bead wires 30 at the inner ends of the first layer 31a and the second layer 31b in the tire width direction are offset by 0.5 of the thickness of the bead wire 30. In contrast, the bead wires 30 at the outer ends of the second layer 31b and the third layer 31c in the tire width direction are offset by 0.5 of the thickness of the bead wire 30.

[0059] In addition, in the present embodiment, with respect to the bead core 21, in the layer 31 of the bead wires 30 including the end portions on the radially outer side of the tire forming the vertical lines 25 (refer to FIG. 3 ) on both sides of the width direction of the bead core 21 among the multiple layers 31 stacked in the tire radial direction, the number of bead wires 30 in the layer 31 decreases by one each time as it goes toward the radially outer side of the tire.

[0060] The carcass 6 is configured so as to be folded around the bead core 21 formed in this manner, from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction. It is formed by covering a plurality of carcass cords 6c with a covering rubber 6d and then rolling them. In the carcass 6 having a plurality of carcass cords 6c, the implantation density of the carcass cords 6c at a position inward of the bead core 21 in the tire width direction is within a range of 10 [cords / 50 mm] to 20 [cords / 50 mm]. In this case, the position inward of the bead core 21 in the tire width direction is a position where the tire radial range of the position inward of the bead core 21 in the tire width direction is the same as the tire radial range of the bead core 21. In other words, the position inward of the bead core 21 in the tire width direction is a position in the carcass body 6a that is within the same tire radial range as the tire radial range of the bead core 21.

[0061] Regarding the carcass 6, the implantation density per 50 mm in the direction of arrangement of the carcass cords 6c at the position inside the tire width direction of the bead core 21 defined in this way, that is, the number of implanted carcass cords 6c is within the range of 10 [cords / 50 mm] or more and 20 [cords / 50 mm] or less.

[0062] The bead filler 50, comprising a lower filler 51 and an upper filler 52, is arranged radially outward of the bead core 21. The lower filler 51 is positioned between the carcass body portion 6a and the turned-up portion 6b of the carcass 6. The lower filler 51 has a width in the tire width direction in a radial cross section of the tire that is approximately the same as that of the bead core 21 near the bead core 21, and becomes narrower as it moves radially outward.

[0063] On the other hand, the upper filler 52 is arranged in the tire radial direction from the position where the lower filler 51 is arranged to a position radially outward of the lower filler 51, and the inner end of the upper filler 52 in the tire radial direction is located near the bead core 21. Specifically, the upper filler 52 is located radially outward of the lower filler 51 in the tire width direction within the range where the lower filler 51 is arranged, and is arranged between the turned-up portion 6b of the carcass 6 and the lower filler 51. On the tire radial direction outward of the lower filler 51, it is arranged between the carcass main body portion 6a and the turned-up portion 6b of the carcass 6 (see FIG. 1 ).

[0064] The lower filler 51 and the upper filler 52 of the bead filler 50 are rubber compositions having different physical properties from each other.

[0065] The bead portion 20 also includes a rim cushion rubber 46 on the tire radially inner side of the bead core 21. The rim cushion rubber 46 also forms the bead base 40, which is the inner circumferential surface of the bead portion 20, and is a rubber composition that elastically deforms while contacting the rim-type wheel when fitted to the rim-type wheel.

[0066] The bead base 40 referred to herein is the inner circumferential surface of the bead portion 20, and is the portion of the bead portion 20 that contacts and engages with the rim-type wheel. The bead base 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 its diameter increasing as it moves from the bead toe 41 toward the bead heel 42.

[0067] In the bead portion 20, a reinforcing layer 60 is disposed in the portion of the carcass 6 that is folded over around the bead core 21. The reinforcing layer 60 is disposed along the carcass 6 at least on the inner side of the carcass body portion 6a in the tire width direction. In this embodiment, three reinforcing layers 60 are disposed, and the positions of the ends of the three reinforcing layers 60 in the tire radial direction in the tire meridian cross section are different from each other.

[0068] Specifically, when the three reinforcing layers 60 are arranged as a first reinforcing layer 61, a second reinforcing layer 62, and a third reinforcing layer 63, starting from the carcass 6 side and moving away from the carcass 6 in the thickness direction of the carcass 6 and the reinforcing layer 60, the first reinforcing layer 61 is folded over along the carcass 6 from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction. In contrast, the second reinforcing layer 62 and the third reinforcing layer 63 are not arranged on the outer side of the bead core 21 in the tire width direction. In other words, the second reinforcing layer 62 and the third reinforcing layer 63 are not arranged on the side of the turned-up portion 6b, but are arranged along the carcass 6 only in the area where the carcass main body portion 6a is located.

[0069] With respect to the tire radially inner end portions of each of the second reinforcing layer 62 and the third reinforcing layer 63 arranged in this manner in the tire meridian cross section, the second reinforcing layer 62 is located on the tire radially inner side relative to the third reinforcing layer 63. Furthermore, with respect to the tire radially outer end portions of each of the second reinforcing layer 62 and the third reinforcing layer 63 in the tire meridian cross section, the third reinforcing layer 63 is located on the tire radially outer side relative to the second reinforcing layer 62.

[0070] Each of the multiple reinforcing layers 60 arranged in this manner is constructed by coating multiple cords with a covering rubber and then rolling them. The cords of the first reinforcing layer 61 are composed of steel cords. Meanwhile, the cords of the second reinforcing layer 62 are composed of organic fiber cords. Similarly, the cords 65 of the third reinforcing layer 63 are composed of organic fiber cords.

[0071] The first reinforcing layer 61 is folded along the carcass 6 from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction. In addition, regarding the first reinforcing layer 61, the end portion located on the inner side of the bead core 21 in the tire width direction and the end portion located on the outer side of the bead core 21 in the tire width direction are both located on the outer side of the bead core upper surface 22 of the bead core 21 in the tire radial direction.

[0072] Furthermore, regarding the plurality of reinforcing layers 60 stacked and arranged along the carcass 6 at the bead portion 20 , the cords of adjacent reinforcing layers 60 are inclined in opposite directions toward the tire circumferential direction relative to the tire radial direction.

[0073] [Method for Manufacturing Pneumatic Tire]

[0074] Next, a method for manufacturing the pneumatic tire 1 according to the embodiment will be described. When manufacturing the pneumatic tire 1, each component constituting the pneumatic tire 1 is first processed and the processed components are assembled. Specifically, the rubber components such as the tread rubber 2a, the carcass 6, the belt 7, and the bead core 21 are each processed separately, and the processed components are assembled.

[0075] For example, the bead core 21 is formed by winding the bead wire 30 into a toroidal shape. In this case, the bead core 21 is formed so that the innermost and outermost portions of the tire widthwise contour of the tire in a meridian cross-section correspond to a vertical line 25 extending in the tire radial direction. Furthermore, the length CV of the bead core 21 is set to be within a range of 31% to 45% of the core height CH of the bead core 21. Furthermore, 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 set to be within a range of 20% to 35% of the core height CH.

[0076] The bead core 21 is formed by arranging multiple encircling portions of the bead wire 30 in the tire width direction to form a single layer 31, and the multiple layers 31 are stacked in the tire radial direction. In this case, with respect to the three layers 31 (first layer 31a, second layer 31b, and third layer 31c) counted from the innermost circumference of the bead core 21 in the tire radial direction, the number of bead wires 30 in the layer 31 located radially outward is two or more greater than the number of bead wires 30 in the layer 31 located radially inward, and the amount of displacement in the tire width direction between the bead wires 30 located at one end of the bead core 21 is set to be equal to 0.5 of the thickness of the bead wire 30. Moreover, regarding these three layers 31, the side where the offset amount of 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 offset amount of 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.

[0077] Thus, when manufacturing the pneumatic tire 1, the bead wire 30 wound into a ring shape when forming the bead core 21 is wound starting from the end portion of the first layer 31a on the outside in the tire width direction. That is, when the bead wire 30 is wound into a ring shape to form the bead core 21, the bead wire 30 is wound so that the end portion of the bead wire 30 located on the bottom surface 23 of the bead core is located on the outside of the bottom surface 23 of the bead core in the tire width direction.

[0078] The bead wire 30 wound from the end portion on the outside in the tire width direction of the bead core bottom surface 23 is spirally wound for a predetermined number of turns determined for each layer 31 and arranged in the tire width direction to form a layer 31. When the number of times the bead wire 30 is wound reaches the predetermined number of turns determined for each layer 31, the bead wire 30 is folded upward in the tire radial direction and spirally wound for a number of turns determined as the number of turns of the adjacent layer 31 on the outside in the tire radial direction, thereby forming a layer 31.

[0079] Specifically, the bead wire 30 is wound starting from the outer end of the first layer 31a in the tire width direction. Once the first layer 31a is wound, the second layer 31b, adjacent to the first layer 31a and located radially outward, begins winding. Therefore, the side where the bead wires 30 in the first and second layers 31a and 31b are offset by 0.5 of the bead wire 30 thickness is always located on the inner end of the first and second layers 31a and 31b in the tire width direction. By repeating these steps, the bead core 21 is formed by stacking layers 31 in the tire radial direction, each layer consisting of multiple encircled portions of the bead wire 30 arranged in the tire width direction, so that the tire meridian cross-section has a polygonal cross-section.

[0080] In the bead portion 20 in which the bead core 21 is formed, the carcass 6 is folded over from the inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction. In the carcass 6, a carcass ply is used in which the implantation density of the carcass cords 6c at the inner side of the bead core 21 in the tire width direction is within a range of 10 [cords / 50 mm] or more and 20 [cords / 50 mm] or less. The pneumatic tire 1 of this embodiment is manufactured in this manner.

[0081] [Function and Effect]

[0082] When assembling the pneumatic tire 1 of this embodiment on a vehicle, the bead base 40 is first fitted to the predetermined rim R of a rim-type wheel, and the pneumatic tire 1 is then mounted on the predetermined rim R. The pneumatic tire 1 is then rim-assembled onto the rim-type wheel. After the pneumatic tire 1 is rim-assembled and inflated, the pneumatic tire 1 in the rim-assembled and inflated state is then mounted on the vehicle. The pneumatic tire 1 of this embodiment is used, for example, on vehicles such as loaders and scrapers that require high traction performance and are operated under heavy load conditions.

[0083] When a vehicle equipped with a pneumatic tire 1 travels, the pneumatic tire 1 rotates while the lower tread 3 of the tread surface 3 contacts the road surface. The vehicle travels by transmitting driving force or braking force to the road surface or generating cornering force through the friction between the tread 3 and the road surface.

[0084] When a vehicle equipped with a pneumatic tire 1 travels, the friction generated between the tread surface 3 of the pneumatic tire 1 and the road surface enables the vehicle to travel. However, during travel, loads in various directions act on various parts of the pneumatic tire 1. The loads acting on the pneumatic tire 1 are received by the pressure of the air filling the tire, the carcass 6 provided as the framework of the pneumatic tire 1, and other factors.

[0085] 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 and unevenness of the road surface is mainly received by the pressure of the air filling the interior of the pneumatic tire 1 or by the sidewall portion 5 and the like while being flexed. In particular, the pneumatic tire 1 of this embodiment is mounted on a large vehicle and used under heavy load conditions. Therefore, the sidewall portion 5 and the carcass 6 are subjected to extremely heavy loads. Consequently, a large tension acts on the carcass 6.

[0086] The carcass 6 is held by the bead portion 20 by being folded around the bead core 21. Therefore, when a large tension is applied to the carcass 6, the tension of the carcass 6 is transmitted to the bead core 21, causing a large force to act between the carcass 6 and the bead core 21. In other words, the carcass 6 is held by the bead portion 20 by being folded around the bead core 21. Therefore, when a tension is applied to the carcass 6, a tension acts on the carcass main body 6a in a direction from the bead portion 20 toward the outside in the tire radial direction. Consequently, a large force also acts between the bead core 21 and the carcass 6.

[0087] Here, the sidewall portion 5 is inclined relative to the tire radial direction in a direction that moves outward in the tire width direction as it moves outward in the tire radial direction from the position of the bead portion 20. Therefore, when a large tension acts on the carcass main portion 6a, the carcass main portion 6a is pulled in the tire radial direction, while a force is generated in the direction outward in the tire width direction near the bead portion 20.

[0088] On the other hand, in pneumatic tires designed for large vehicles and used under heavy loads, bead cores are often constructed with a roughly hexagonal cross-section in the tire's meridian section. In these cases, the bead core has corners that protrude inward in the tire width direction. Consequently, when high tension is applied to the carcass and the carcass main body near the bead portion generates a force outward in the tire width direction and attempts to move in the tire radial direction due to the tension, the carcass main body applies a high load and rubs against the protruding corners of the bead core in the tire width direction. As a result, the carcass main body wears the cover rubber and directly rubs against the carcass cord, potentially causing problems such as carcass cord breakage.

[0089] In addition, since the carcass is folded around the bead core, when a large tension is applied to the carcass, friction will also occur between the carcass and the bead core at positions other than the corners of the bead core that protrude inward in the tire width direction. The carcass may suffer from faults such as carcass cord breakage due to this friction.

[0090] In contrast, in the pneumatic tire 1 of this embodiment, the innermost and outermost portions of the bead core 21 in the tire meridian cross-section are each formed by a perpendicular line 25 extending in the tire radial direction. Specifically, the bead core 21 is formed so that the position of the bead core 21 with the greatest width in the tire width direction forms a perpendicular line 25 extending in the tire radial direction. Consequently, the bead core 21 is formed without corners protruding in the tire width direction. This prevents stress concentration from occurring between the carcass 6 and the bead core 21 due to high tension acting on the carcass 6, thereby dispersing the stress acting between the carcass 6 and the bead core 21. Consequently, wear of the cover rubber 6d of the carcass body 6a due to stress concentration between the carcass 6 and the bead core 21 can be suppressed, and the carcass cord 6c can be prevented from directly rubbing against the wear of the cover rubber 6d, thereby preventing the carcass cord 6c from breaking.

[0091] Furthermore, since the length CV of the vertical lines 25 located on both sides of the bead core 21 in the tire width direction is within a range of 31% to 45% relative to the core height CH, the stress generated between the carcass 6 and the bead core 21 can be more reliably dispersed. Specifically, if the length CV of the vertical lines 25 relative to the core height CH is less than 31%, the length CV of the vertical lines 25 is too short, and 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. Furthermore, if the length CV of the vertical lines 25 relative to the core height CH is greater than 45%, the length CV of the vertical lines 25 is too long, and 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 of the vertical lines 25 in the longitudinal direction.

[0092] 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 stress generated between the carcass 6 and the bead core 21 can be more reliably dispersed by the vertical lines 25 formed on both sides of the bead core 21 in the tire width direction. This can more reliably suppress 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.

[0093] Furthermore, with respect to the perpendicular line 25 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 perpendicular line 25 in the tire radial direction is within a range of 20% or more and 35% or less of the core height CH. This makes it possible to more reliably suppress the occurrence of 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 perpendicular line 25 in the tire radial direction is less than 20% of the core height CH, the perpendicular line 25 may be positioned too close to the inner side in the tire radial direction.

[0094] Furthermore, 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 greater than 35% of the core height CH, the position of the vertical line 25 may be too close to the outer side in the tire radial direction. In such cases, the shape of the bead core 21 forming the vertical lines 25 on both sides in the tire width direction may not conform to the shape of the carcass 6 folded over at the bead portion 20. This may cause stress concentration between the carcass 6 and the bead core 21, and may easily lead to failures such as breakage of the carcass cord 6c.

[0095] In contrast, 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 within a range of 20% to 35% relative to the core height CH, the shape of the bead core 21 forming the vertical lines 25 on both sides in the tire width direction can be made close to the shape of the carcass 6 folded over at the bead portion 20. This can more reliably suppress the occurrence of stress concentration between the carcass 6 and the bead core 21, and can more reliably suppress 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.

[0096] Furthermore, in the bead core 21, among the multiple layers 31 formed of 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, of the two adjacent layers 31 in the tire radial direction, the number of bead wires 30 in the layer 31 located radially outward is two or more greater than the number of bead wires 30 in the layer 31 located radially inward. This allows the contour of the bead core 21 from the first layer 31a to the third layer 31c in the tire meridian cross-section to have a shape with a small inclination angle in the tire radial direction relative to the tire width direction. Consequently, the cross-sectional shape of the bead core 21 near the bead core bottom surface 23 can be made closer to the shape of the carcass 6 folded over at the bead portion 20.

[0097] Furthermore, with respect to the first layer 31a, the second layer 31b, and the third layer 31c of the plurality of layers 31 formed by the bead wires 30, the amount of displacement in the tire width direction between the bead wires 30 located at one end in the tire width direction of two radially adjacent layers 31 is 0.5 times the thickness of the bead wire 30. This prevents the displacement in the tire width direction of the portion where the bead wire 30 straddles two radially adjacent layers 31 from becoming excessively large, and prevents the shape of the bead core 21 from being distorted due to the excessive displacement of the bead wire 30 straddling two radially adjacent layers 31.

[0098] Furthermore, the bead wires 30 in the first and second layers 31a, 31b are offset by 0.5 of the bead wire 30 thickness, and the bead wires 30 in the second and third layers 31b, 31c are offset by 0.5 of the bead wire 30 thickness, on opposite sides of the tire width direction. This allows the contour of the bead core 21, from the first layer 31a to the third layer 31c in the tire meridian cross-section, to be balanced on both sides in the tire width direction, closely matching the shape of the carcass 6 folded over at the bead portion 20. This allows for more reliable distribution of stress generated between the carcass 6 and the bead core 21, and more reliably suppresses the occurrence of failures such as breakage of the carcass cord 6c caused by stress concentration between the carcass 6 and the bead core 21. Consequently, the durability of the bead portion 20 can be improved.

[0099] Furthermore, the bead core 21 is formed in a shape that forms a vertical line 25 on the outside in the tire width direction. This allows the contact pressure between the bead portion 20, on the outside in the tire width direction, i.e., the bead portion outer surface 45 (see FIG. 2 ), and the rim-type wheel to be nearly uniform, compared to a bead core having a substantially hexagonal cross-section. Specifically, when the bead core has a substantially hexagonal cross-section, the bead core is formed so that the portion on the outside in the tire width direction has corners that protrude outward in the tire width direction. Consequently, the contact pressure between the rim-type wheel and the bead portion outer surface is higher at the corners, but the contact pressure between the rim-type wheel and the bead portion outer surface is likely to be lower at portions other than the corners. In this case, ensuring airtightness between the rim-type wheel and the bead portion outer surface may be difficult when the pneumatic tire is assembled onto the rim of the rim-type wheel and inflated.

[0100] In contrast, in this embodiment, the bead core 21 is formed to form a vertical line 25 on the outside in the tire width direction. This reduces variations in the distance between the bead core 21 and the bead portion outer surface 45. In other words, the area of ​​the portion of the bead core 21 that increases the contact pressure on the rim-mounted wheel can be increased. This allows the contact pressure between the rim-mounted wheel and the bead portion outer surface 45 to be made nearly uniform. Consequently, the airtightness of the bead portion 20 can be improved.

[0101] Furthermore, since the width CBW of the bead core bottom surface 23 in the tire's meridian cross-section is within a range of 45% to 70% of the maximum width CW of the bead core 21, stress concentration between the bead core bottom surface 23 and the carcass 6 can be suppressed. Specifically, 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, and the shape of the bead core 21 in the tire's meridian cross-section may be excessively convex downward in the tire radial direction. In this case, stress concentration may be more likely to occur between the carcass 6 and the bead core 21 near the bead core bottom surface 23 in 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 stress concentration may 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.

[0102] 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, stress concentration between the bead core bottom surface 23 and the carcass 6 can be effectively suppressed. This more reliably prevents the occurrence of failures such as breakage of the carcass cord 6c caused by stress concentration between the carcass 6 and the bead core 21. Consequently, the durability of the bead portion 20 can be more reliably improved.

[0103] In addition, with respect to the bead core 21, the distance Vb in the tire width direction between the end 22in on the inner side of the tire width direction in the upper surface 22 of the bead core and the vertical line 25 on the inner side of the tire width direction is within the range of 10% to 25% relative to the maximum width CW of the bead core 21, and the distance Vc in the tire width direction between the end 23in on the inner side of the tire width direction in the bottom surface 23 of the bead core and the vertical line 25 on the inner side of the tire width direction is within the range of 10% to 25% relative to the maximum width CW of the bead core 21, thereby being able to more reliably suppress the stress concentration generated between the tire body 6 and the bead core 21. Specifically, if the distance Vb between the inner end 22in of the bead core upper surface 22 in the tire width direction and the vertical line 25 inwardly located 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 inwardly located in the tire width direction, relative to the maximum width CW of the bead core 21, the amount of protrusion of the bead core 21 inwardly located in the tire width direction from the positions of the bead core upper surface 22 and the bead core bottom surface 23 may be excessively small. In this case, the shape of the surface of the bead core 21 located inwardly located in the tire width direction in the tire meridian cross section is unlikely to conform to the curved shape of the portion of the carcass 6 located inwardly located in the tire width direction of the bead core 21, and thus stress concentration may be likely to occur between the carcass 6 and the bead core 21.

[0104] Furthermore, if the distance Vb between the inner end 22in of the bead core upper surface 22 in the tire width direction and the vertical line 25 inwardly located 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 inwardly located in the tire width direction, relative to the maximum width CW of the bead core 21, is greater than 25%, the amount of protrusion of the bead core 21 inwardly located in the tire width direction from the positions of the bead core upper surface 22 and the bead core bottom surface 23 may become excessively large. In this case as well, the shape of the surface of the bead core 21 located inwardly located in the tire width direction in the tire meridian cross section is unlikely to conform to the curved shape of the portion of the carcass 6 located inwardly located in the tire width direction of the bead core 21, and stress concentration may be likely to occur between the carcass 6 and the bead core 21.

[0105] In contrast, since the distance Vb between the inner end 22in of the bead core upper surface 22 in the tire width direction and the vertical line 25 inwardly located 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 inwardly located in the tire width direction are within a range of 10% to 25% of the maximum width CW of the bead core 21, the shape of the surface of the bead core 21 located inwardly located in the tire width direction in the tire meridian cross section can be easily adjusted to conform to the curved shape of the portion of the carcass 6 located inwardly located in the tire width direction of the bead core 21. This can more reliably suppress stress concentration between the carcass 6 and the bead core 21. As a result, the durability of the bead portion 20 can be more reliably improved.

[0106] Furthermore, regarding the bead core 21, if the maximum width CW of the bead core 21 is within a range of 0.9 times or greater and 1.4 times or less of the core height CH, stress concentration occurring between the carcass 6 and the bead core 21 can be more reliably suppressed. Specifically, 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, making it difficult to conform the shape of the bead core 21 in the tire meridian cross-section to the shape of the carcass 6 folded around the bead core 21. Consequently, stress concentration may be more 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, stress concentration may be more likely to occur between the bead core 21 and the portion of the carcass 6 folded around the bead core 21 near the bead core bottom surface 23.

[0107] Furthermore, if 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. Therefore, in this case as well, it is difficult to conform the shape of the bead core 21 in the tire meridian cross-section to the shape of the carcass 6, and stress concentration may be 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 wide, stress concentration may be likely to occur between the bead core 21 and the portion of the carcass 6 folded around the bead core 21, which is located near both sides of the bead core 21 in the tire width direction.

[0108] In contrast, when the maximum width CW of the bead core 21 is within a range of 0.9 times or more and 1.4 times or less of the core height CH, the shape of the bead core 21 in the tire meridian cross-section can be made to follow the shape of the carcass 6 folded around the bead core 21. This can more reliably suppress stress concentration between the carcass 6 and the bead core 21. Consequently, the durability of the bead portion 20 can be more reliably improved.

[0109] Furthermore, with respect to the carcass 6, the implantation density of the carcass cords 6c at the inner side of the bead core 21 in the tire width direction is within a range of 10 [cords / 50 mm] or more and 20 [cords / 50 mm] or less. This allows for more reliable suppression of carcass 6 failures at the bead portion 20. Specifically, if the implantation density of the carcass cords 6c at the inner side of the bead core 21 in the tire width direction is less than 10 [cords / 50 mm], the implantation density of the carcass cords 6c is too low. Consequently, when high tension acts on the carcass 6, the tension borne by each carcass cord 6c may become excessively high. In this case, the stress on each carcass cord 6c in the portion of the carcass 6 disposed in the bead portion 20 may become excessively high, and the carcass cords 6c may be susceptible to breakage. Furthermore, if the implantation density of the carcass cords 6c at the inner side of the bead core 21 in the tire width direction exceeds 20 [cords / 50 mm], the implantation density of the carcass cords 6c is too high, and the intervals between the carcass cords 6c become closer, which may result in the volume of the covering rubber 6d between adjacent carcass cords 6c being excessively reduced. In this case, it becomes difficult to retain the carcass cords 6c with the covering rubber 6d, and the carcass cords 6c are easily separated from the covering rubber 6d, making it difficult to produce a carcass 6 with suitable durability.

[0110] In contrast, when the carcass cord 6c implant density at a position inward of the bead core 21 in the tire width direction is within a range of 10 cords / 50 mm or more and 20 cords / 50 mm or less, the volume of the covering rubber 6d between adjacent carcass cords 6c can be prevented from becoming excessively reduced while distributing the force borne by the carcass cords 6c to a greater number of carcass cords 6c. This prevents the carcass cords 6c from peeling off from the covering rubber 6d and reduces the tension borne by each carcass cord 6c when high tension is applied to the carcass 6 at the bead portion 20. This prevents the stress on each carcass cord 6c from becoming excessively high, potentially leading to carcass cord 6c breakage. Consequently, the durability of the carcass 6 can be ensured, and carcass 6 failure at the bead portion 20 can be more reliably prevented. Consequently, the durability of the bead portion 20 can be more reliably improved.

[0111] Furthermore, in the method for manufacturing the pneumatic tire 1 of the embodiment, the bead core 21 is formed so that the innermost portion and the outermost portion of the bead core 21 in the tire width direction are aligned with a perpendicular line 25. Therefore, even when a large force acts between the carcass 6 and the bead core 21 due to a large tension acting on the carcass 6, stress concentration can be suppressed. Consequently, the occurrence of failures such as breakage of the carcass cord 6c due to stress concentration between the carcass 6 and the bead core 21 can be suppressed.

[0112] Furthermore, in the method for manufacturing the pneumatic tire 1 of the embodiment, since the length CV of the vertical line 25 is set within a range of 31% to 45% relative to the core height CH, the stress generated between the carcass 6 and the bead core 21 can be more reliably dispersed by the vertical lines 25 formed on both sides of the bead core 21 in the tire width direction. Consequently, 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.

[0113] Furthermore, in the method for manufacturing the pneumatic tire 1 of the embodiment, since 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 to be within a range of 20% to 35% of the core height CH, the shape of the bead core 21 can be made close to the shape of the carcass 6 folded over at the bead portion 20. As a result, the occurrence of stress concentration between the carcass 6 and the bead core 21 can be more reliably suppressed.

[0114] Furthermore, in the method for manufacturing the pneumatic tire 1 of the embodiment, with respect to the first layer 31a, the second layer 31b, and the third layer 31c among the plurality of layers 31 formed of the bead wires 30, the amount of misalignment in the tire width direction between the bead wires 30 located at one end portion in the tire width direction of two adjacent layers 31 is set to 0.5 of the thickness of the bead wire 30. This prevents the amount of misalignment in the tire width direction at the portion where the bead wire 30 straddles two adjacent layers 31 in the tire radial direction from becoming excessively large, thereby preventing the shape of the bead core 21 from being distorted.

[0115] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the side where the bead wires 30 in the first and second layers 31a, 31b are offset by 0.5 of the bead wire 30 thickness and the side where the bead wires 30 in the second and third layers 31b, 31c are offset by 0.5 of the bead wire 30 thickness are on opposite sides in the tire width direction. This allows the shape of the bead core 21 in the tire meridian cross-section to be balanced and approximate to that of the carcass 6 on both sides in the tire width direction. This reduces stress concentration between the carcass 6 and the bead core 21, thereby more reliably preventing failures such as breakage of the carcass cord 6c. Consequently, the durability of the bead portion 20 can be improved.

[0116] Furthermore, in the manufacturing method of the pneumatic tire 1 of the embodiment, since the bead wire 30 is wound from the end portion of the first layer 31a on the outside in the tire width direction, the durability of the bead core 21 can be ensured. Specifically, when the pneumatic tire 1 is inflated, the bead core 21 is required to have the highest strength at the end portion 23 inches on the inside in the tire width direction of the bead core bottom surface 23. Therefore, if the end portion of the bead wire 30 is located at the end portion 23 inches on the inside in the tire width direction of the bead core bottom surface 23, the durability of the bead core 21 is reduced, and the shape of the bead core 21 may be easily distorted.

[0117] In contrast, when the bead wire 30 is wound starting from the outer end portion in the tire width direction of the first layer 31a, the strength of the bead core bottom surface 23, which is located at the inner end portion 23in in the tire width direction and where the strength is most required, can be ensured, thereby preventing the shape of the bead core 21 from being easily deformed. As a result, the durability of the bead core 21 can be ensured.

[0118] [Modification]

[0119] In addition, in the pneumatic tire 1 of the above-mentioned embodiment, with respect to the bead core 21, the number of bead wires 30 in the layer 31, which is closer to the radial outside of the tire than the layer 31 of the bead wires 30 including the end portion on the radial outside of the tire forming the vertical line 25, decreases by one each time as the layer 31 goes toward the radial outside of the tire, but the bead core 21 may also be formed in a manner other than this.

[0120] FIG5 is a modified example of the pneumatic tire 1 according to the embodiment, and is a detailed view of a bead core 21 having bead wires 30 laminated in a manner different from that of the aforementioned embodiment. For example, as shown in FIG5 , the bead core 21 may include a portion where, between two adjacent layers 31 radially outward from a perpendicular line 25, the number of bead wires 30 in the layer 31 radially outward is two fewer than the number of bead wires 30 in the layer 31 radially inward. As long as the bead core 21 has a cross-sectional shape close to an octagon when viewed in the tire meridian, the first layer 31a, second layer 31b, and third layer 31c of the multiple layers 31 formed of bead wires 30, counted from the innermost circumference in the tire radial direction, may be formed as in the aforementioned embodiment, regardless of the portion radially outward from the perpendicular line 25.

[0121] In the pneumatic tire 1 of the above embodiment, three reinforcing layers 60 are provided. However, the reinforcing layers 60 may be provided in a number other than three. The number of reinforcing layers 60 and the range of the reinforcing layers 60 in the tire meridian cross section may also be different from those in the above embodiment.

[0122] [Example]

[0123] 6A and 6B are graphs showing the results of a performance evaluation test of a pneumatic tire. Hereinafter, a performance evaluation test conducted on a conventional pneumatic tire and the pneumatic tire 1 of the present invention will be described. A durability test was conducted to evaluate the durability of the pneumatic tire 1.

[0124] The performance evaluation test was conducted under the following conditions: a pneumatic tire 1 with a nominal tire size of 37.25R35 was used as a test tire, the test tire was assembled onto a rim-type wheel rim in accordance with 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.

[0125] The durability evaluation method is to conduct a running test using an indoor roller tester with a load set to 120% of the maximum load specified by the TRA and a speed set to 10 km / h. The breakage rate of the bare cords of the carcass cords in the bead portion after the pneumatic tire has been running for 300 hours is evaluated by expressing the rate using an index with the conventional example described below being 100. The bare cord breakage rate is evaluated by sampling 40 carcass cords in the bead portion at random locations at the end of the run. All the sampled carcass cords are observed, and the average value of (the number of broken bare cords in each carcass cord / the total number of bare cords in each carcass cord) is defined as the breakage rate.

[0126] Performance evaluation tests were conducted on 24 pneumatic tires, namely, the conventional pneumatic tire (one example of a conventional pneumatic tire) and the pneumatic tire 1 of the present invention (Examples 1 to 23). In the conventional pneumatic tire, the bead core had a substantially hexagonal cross-sectional shape in the tire meridian, and the bead core had no vertical lines at the innermost and outermost sides in the tire width direction.

[0127] In contrast, with respect to an example of the pneumatic tire 1 of the present invention, namely embodiments 1 to 23, all of the bead cores 21 have vertical lines 25 at the innermost and outermost sides in the tire width direction, and the length CV of the vertical line 25 of the bead core 21 is within the range of greater than 31% and less than 45% relative to the core height CH of the bead core 21, and the distance Va from the bottom surface 23 of the bead core to the inner end 25a of the vertical line 25 is within the range of greater than 20% and less than 35% relative to the core height CH. Moreover, with respect to the pneumatic tires 1 of Examples 1 to 23, the ratio of the width CBW of the bead core bottom surface 23 to the maximum width CW of the bead core 21 (CBW / CW), the ratio of the distance Vb between the inner vertical line 25 in the tire width direction and the end 22in of the bead core upper surface 22 to the maximum width CW of the bead core 21 (Vb / CW), the ratio 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 (Vc / CW), the ratio of the maximum width CW of the bead core to the core height CH (CW / CH), and the implantation density of the carcass cord 6c at the position inside the bead core 21 in the tire width direction are different, respectively.

[0128] The results of performance evaluation tests conducted using these pneumatic tires 1 show that, as shown in Figures 6A and 6B , the pneumatic tires 1 of Examples 1 to 23 have a better breakage rate of the bare wire of the carcass cord 6c in the bead portion 20 than the conventional tires, and the carcass cord 6c is less likely to break in the bead portion 20. In other words, the pneumatic tires 1 of Examples 1 to 23 can improve the durability of the bead portion 20.

[0129] Description of Reference Numerals

[0130] 1 pneumatic tire

[0131] 2 Tread

[0132] 2a Tread rubber

[0133] 3. Tread

[0134] 4. Shoulder

[0135] 5 Sidewall

[0136] 6 Carcass

[0137] 6a Main body of the tire body

[0138] 6b Roll-up

[0139] 6c carcass cord

[0140] 6d covering rubber

[0141] 7 Belt

[0142] 10. Lu Department

[0143] 15 Circumferential groove

[0144] 20 Bead

[0145] 21 Bead core

[0146] 22 Upper surface of tire bead core

[0147] 23 Bead core bottom

[0148] 25 vertical lines

[0149] 30 bead wire

[0150] 31st floor

[0151] 31a Level 1

[0152] 31b Layer 2

[0153] 31c 3rd floor

[0154] 40 Bead base

[0155] 41 fetal toe

[0156] 42 fetal heel

[0157] 45 outer surface of tire bead

[0158] 46 rim buffer rubber

[0159] 50 Bead filler

[0160] 51 Underfill

[0161] 52 Filling

[0162] 60 reinforcement layer

Claims

1. A pneumatic tire, characterized in that: have: a pair of bead portions disposed on both sides of the tire equatorial plane in the tire width direction; a bead core disposed in the bead portion, formed by winding a bead wire into a ring shape, and having a polygonal cross-section in the tire meridian cross-section; and The carcass comprises a carcass main body portion arranged between the pair of bead portions and a turn-up portion formed continuously from the carcass main body portion and folded from the inner side of the bead core in the tire width direction to the outer side in the tire width direction, and is formed by covering the carcass cord with a covering rubber. Regarding the bead core, a portion located innermost and a portion located outermost in the tire width direction of the tire meridian cross section are respectively formed by vertical lines extending in the tire radial direction. Regarding the vertical line, the length of the vertical line is within a range of 31% to 45% of the height of the bead core in the tire radial direction, that is, the core height. Regarding the vertical line, the distance in the tire radial direction from the inner peripheral surface of the bead core, i.e., the bead core bottom surface, to the inner end of the vertical line in the tire radial direction is within a range of 20% to 35% relative to the core height. The bead core is formed by winding the bead wire into a ring shape, and a plurality of surrounding portions of the bead wire are arranged in the tire width direction to form one layer, and the plurality of layers are stacked in the tire radial direction. The first layer, which is the innermost layer in the tire radial direction, of the plurality of layers, the second layer stacked adjacent to and outside the first layer in the tire radial direction, and the third layer stacked adjacent to and outside the second layer in the tire radial direction, In the two layers adjacent to each other in the tire radial direction, the number of the bead wires of the layer located on the outer side of the tire radial direction is more than 2 than the number of the bead wires of the layer located on the inner side of the tire radial direction, and the offset in the tire width direction of the bead wires at the end portions on one side of the tire width direction is 0.5 of the bead wires. The side where the bead wires in the first layer and the second layer are offset by 0.5 of the bead wire and the side where the bead wires in the second layer and the third layer are offset by 0.5 of the bead wire are on opposite sides in the tire width direction.

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

3. The pneumatic tire according to claim 1 or 2, Regarding the bead core, The distance in the tire width direction between the end portion on the inner side of the tire width direction of the outer peripheral surface in the tire meridian cross section, i.e., the upper surface of the bead core, and the vertical line on the inner side of the tire width direction is within a range of 10% to 25% relative to the maximum width of the bead core. The distance in the tire width direction between the inner end of the bead core bottom surface in the tire width direction and the vertical line in the tire width direction is within a range of 10% to 25% of the maximum width of the bead core. The maximum width of the bead core is within a range of 0.9 times or more and 1.4 times or less of the core height.

4. The pneumatic tire according to any one of claims 1 to 3, Regarding the carcass, an implantation density of the carcass cords at a position inside 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.

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