Pneumatic tire

Abstract

In order to improve the durability of a bead portion, in a pneumatic tire (1), with respect to a bead core (21), both end portions in a tire width direction are formed by perpendicular lines (25) extending in a tire radial direction, with respect to the perpendicular lines (25), a length CV of the perpendicular lines (25) is in a range of 31% or more and 45% or less with respect to a core height CH, with respect to a first layer (31a), a second layer (31b), and a third layer (31c) of the bead core (21), among the two adjacent layers (31), the number of bead wires (30) of the layer (31) located on the outside in the tire radial direction is more than the number of bead wires (30) of the layer (31) located on the inside in the tire radial direction by two or more, and the offset amount of the bead wires (30) of the end portions on one side in the tire width direction from each other is 0.5 of the number of the bead wires (30), in the first layer (31a) and the second layer (31b) and the second layer (31b) and the third layer (31c), the side on which the offset amount of the bead wires (30) from each other becomes 0.5 of the number of the bead wires (30) becomes the opposite side in the tire width direction.

Description

Technical Field

[0001] This invention relates to pneumatic tires. Background Technology

[0002] A pneumatic tire is assembled to a rim-type wheel by fitting the bead portion, which has a bead core that serves as a ring-shaped member for bundling multiple bead lines, onto the rim of the rim-type wheel. The bead portion is the part of the pneumatic tire that is actually fitted onto the rim-type wheel during assembly, and therefore becomes a crucial component in ensuring the performance of the pneumatic tire. In conventional pneumatic tires, various designs have been implemented on the bead portion to achieve desired performance.

[0003] For example, in the pneumatic tire described in Patent Document 1, wear in the bead area is reduced by having a substantially flat bead surface that engages with the rounded ends on both sides of the bead core. 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 bottom edge and an upper bottom edge extending axially in the tire 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 bottom edges toward the axially outer side; and the axially inner contour of the bead core is formed by an inner edge connecting the axially inner ends of the lower and upper bottom edges, thereby improving the durability of the bead portion.

[0004] Furthermore, the bead core described in Patent Document 3 utilizes a bottom edge parallel to the bead core's axial direction, middle sides on both sides perpendicular to the bead core's axial direction, and a bevel formed by two obtuse angles connecting the inner ends of the middle sides and the two sides of the bottom edge. This reduces tire failures caused by wear of the tire carcass cords and tire failures caused by air accumulation. Additionally, in the pneumatic tire described in Patent Document 4, when manufacturing a bead core that is a circular ring formed by arranging steel wires in multiple rows and layers without gaps, the outermost steel wires in the width direction of each steel wire row from the innermost circumference to the maximum width position are positioned outside the width direction of the steel wire rows on their inner circumference. The offset is reduced from the innermost circumference towards the maximum width position, thereby preventing tire carcass breakage and preventing undulations towards the rolled-up end of the tire carcass during tire manufacturing.

[0005] Existing technical documents

[0006] Patent documents

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

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

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

[0010] Patent Document 4: Japanese Patent No. 4243091 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Generally, the bead core has a polygonal shape in the tire's meridional section. However, in extra-large pneumatic tires, to avoid stress concentration towards the tire carcass caused by the bead core's corners, a nylon sheath is sometimes wrapped around the bead core. However, with only the nylon sheath, the distance between the bead core's corners and the tire carcass is insufficient. Therefore, when a large tension is applied to the tire carcass, the area near the bead core's corners and the tire carcass easily experience friction under high force. In this case, the tire carcass cords may break due to friction between the bead core's corners and the tire carcass. Especially in pneumatic tires fitted to vehicles requiring traction, such as loaders and scrapers, bead cores with a relatively flat meridional section are often used, making it easy for the bead core's corners to rub against the tire carcass, thus increasing the risk of tire carcass cord breakage. Therefore, there is room for improvement in the durability of the bead portion in conventional pneumatic tires.

[0013] The present invention was made in view of the above and aims to provide a pneumatic tire that can improve the durability of the bead portion.

[0014] Methods for solving problems

[0015] To address the aforementioned problems and achieve the objective, the pneumatic tire of the present invention is characterized by comprising: a pair of bead portions disposed on both sides of the tire equatorial plane in the tire width direction; a bead core disposed on the bead portions, formed by winding bead lines into a loop, and having a shape in the tire meridional section formed by a polygonal cross-section; and a tire carcass having a carcass main body portion disposed throughout the pair of bead portions and a rolled-up portion continuously formed from the carcass main body portion and folded from the inner side of the bead core in the tire width direction toward the outer side in the tire width direction, wherein the tire carcass... The cords are formed by covering with rubber. In the bead core, the innermost portion and the outermost portion of the profile at the tire's meridional section in the tire width direction are each formed by vertical lines extending radially along the tire. The length of these vertical lines is within 31% to 45% of the radial height of the bead core. The radial distance from the inner circumferential surface of the bead core (i.e., the bottom surface of the bead core) to the inner radial end of the vertical line is... For a core height of 20% to 35%, the bead core is formed by arranging multiple loops of the bead cord, which is formed by winding it into a ring, in the tire width direction to form one layer. These multiple layers are stacked radially on the tire. Regarding the innermost layer in the tire radial direction (i.e., the first layer), the second layer stacked adjacent to the outermost layer in the tire radial direction of the first layer, and the third layer stacked adjacent to the outermost layer in the tire radial direction of the second layer, in the case of two adjacent layers in the tire radial direction, the layers are located radially outward from each other. The number of bead lines in the layer on one side is more than two more than the number of bead lines in the layer located radially inside the tire, and the bead lines at the ends of one side in the tire width direction are offset from each other by 0.5 bead lines in the tire width direction. The side where the bead lines in the first and second layers are offset from each other by 0.5 bead lines is opposite to the side where the bead lines in the second and third layers are offset from each other by 0.5 bead lines in the tire width direction.

[0016] Furthermore, in the aforementioned pneumatic tire, it is preferable that, with respect to the bead core, the width of the bottom surface of the bead core in the tire's meridional section is within the range of 45% to 70% of the maximum width of the bead core.

[0017] Furthermore, in the aforementioned pneumatic tire, it is preferable that, regarding the bead core, the distance in the tire width direction between the end of the outer peripheral surface of the tire meridional section (i.e., the upper surface of the bead core) on the inner side of the tire width direction 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 of the bottom surface of the bead core on the inner side of the tire width direction 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 the core height.

[0018] Furthermore, in the aforementioned pneumatic tire, it is preferable that, regarding the tire carcass, the implantation density of the tire carcass cords at the position inside the tire width direction of the bead core is within the range of 10 cords / 50mm or more and 20 cords / 50mm or less.

[0019] Invention Effects

[0020] The pneumatic tire of the present invention has the effect of improving the durability of the bead portion. Attached Figure Description

[0021] Figure 1 This is a meridional sectional view showing the main part of the pneumatic tire according to the embodiment.

[0022] Figure 2 yes Figure 1 Detailed diagram of Part A.

[0023] Figure 3 yes Figure 2 A detailed diagram of the tire bead core is shown.

[0024] Figure 4 yes Figure 3 Detailed diagram of Part B.

[0025] Figure 5 This is a variation of the pneumatic tire implementation method, which is based on... Figure 3 Detailed diagrams of the bead core with different methods of stacking bead lines are shown in the embodiments illustrated.

[0026] Figure 6A It is a graph showing the results of performance evaluation tests on pneumatic tires.

[0027] Figure 6B It is a graph showing the results of performance evaluation tests on pneumatic tires. Detailed Implementation

[0028] Hereinafter, embodiments of the pneumatic tire of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments. Furthermore, the constituent elements in the following embodiments include elements that can be substituted and readily conceived by those skilled in the art, or elements that are substantially the same.

[0029] [Implementation Method]

[0030] In the following description, the tire radial direction refers to the direction orthogonal to the axis of rotation of the pneumatic tire 1, i.e., the tire rotation axis (not shown in the diagram). The inner side of the tire radial direction refers to the side of the tire radial direction that faces the tire rotation axis, and the outer side of the tire radial direction refers to the side of the tire radial direction that moves away from the tire rotation axis. The tire circumferential direction refers to the direction of rotation around the tire rotation axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side of the tire width direction refers to the side of the tire width direction that faces the tire equatorial plane (tire equator) CL, and the outer side of the tire width direction refers to the side of the tire width direction that moves away from the tire equatorial plane CL. The tire equatorial plane CL is a plane orthogonal to the tire rotation axis and passes through the center of the tire width of the pneumatic tire 1. The position of the tire equatorial plane CL in the tire width direction coincides with the center position of the tire width direction of the pneumatic tire 1, i.e., the tire width centerline. The tire width refers to the width of the outermost portions of the tire in the tire width direction relative to each other, that is, the distance between the portions furthest away from the tire equatorial plane CL in the tire width direction. The tire equator is a line located on the tire equatorial plane CL and along the circumference of the pneumatic tire 1. Furthermore, in the following description, the tire meridional section refers to the section of the tire cut along a plane containing the tire's axis of rotation.

[0031] Figure 1 This is a radial cross-sectional view showing the main part of the pneumatic tire 1 in this embodiment. The pneumatic tire 1 in this embodiment is a radial tire for construction vehicles, also known as an OR tire (Off-the-Road Tire). As in this embodiment... Figure 1 The pneumatic tire 1 shown has a tread portion 2 located on the outermost part of the tire's radial direction when viewed in a tire meridional section. The tread portion 2 is composed of tread rubber 2a, which is a rubber composition. The surface of the tread portion 2, which is the part that contacts the road surface when the vehicle equipped with the pneumatic tire 1 (not shown) is in motion, forms the tread tread surface 3.

[0032] The tread surface 3 of the tread portion 2 has multiple circumferential grooves 15 extending in the tire circumferential direction and lateral grooves extending in the tire width direction (not shown in the figure). Multiple land sections 10 are formed on the tread portion 2 by these grooves.

[0033] The two ends of the tread portion 2 in the tire width direction are formed as shoulders 4, and a sidewall portion 5 is disposed from the shoulders 4 to a predetermined position radially inward of the tire. That is, the sidewall portion 5 is disposed on both sides 2 of the pneumatic tire 1 in the tire width direction. The sidewall portion 5 is composed of sidewall rubber 5a, which is a rubber composition. In addition, a rim check line 9 is formed on each sidewall portion 5 on both sides of the tire width direction at a position radially inward of the tire. The rim check line 9 protrudes from the surface of the sidewall portion 5 and is formed around the circumference of the tire.

[0034] Furthermore, a bead portion 20 is present on the radially inner side of each sidewall portion 5, and the bead portions 20, like the sidewall portions 5, are positioned on both sides of the tire equatorial plane CL. That is, a pair of bead portions 20 are positioned on both sides of the tire equatorial plane CL in the tire width direction. A bead core 21 is positioned on each pair of bead portions 20, and a bead filler 50 is positioned on the radially outer side of each bead core 21. The bead core 21 is constructed by using a bead wire 30 (refer to...) as a steel wire. Figure 3 It is formed by winding into a ring. The bead filler 50 is a spatially arranged rubber component formed by folding it outward in the tire width direction at the position of the bead core 21 at the end of the tire carcass 6 described later. In addition, the bead filler 50 has a lower filler 51 disposed in contact with the outer peripheral surface of the bead core 21 and an upper filler 52 disposed at a position further outward in the radial direction of the tire than the lower filler 51.

[0035] The bead portion 20 is configured to be fitted to a rim-type wheel with a specified rim R having a 5° taper. That is, the pneumatic tire 1 of this embodiment can be fitted to a specified rim R with an inclination angle of 5°±1° relative to the axis of rotation of the rim-type wheel, in a direction that moves radially outward from the inner side in the tire width direction to the outer side. Furthermore, the specified rim R refers to "applicable rim" as defined in JATMA, "Design Rim" as defined in TRA, or "Measuring Rim" as defined in ETRTO.

[0036] A belt layer 7 is provided on the radially inner side of the tire tread 2. The belt layer 7 has a multi-layer structure with three or more belt plies stacked on top of each other; in a typical OR tire, four to eight belt plies are stacked. In this embodiment, the belt layer 7 has six belt plies stacked on top of each other: 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 and rolling multiple belt cords made of steel or organic fiber material with a cover rubber. The six belt plies 7a, 7b, 7c, 7d, 7e, and 7f are, for example, composed of cross belt layers 7a, 7b, 7c, and 7d and protective belt layers 7e and 7f. Furthermore, in belt ply layers 7a, 7b, 7c, 7d, 7e, and 7f, the inclination angles of the belt cords relative to the tire circumference in the tire width direction are different from each other, and the cross belt ply layer and the protective belt ply layer are constructed as a so-called cross ply layer structure in which the inclination directions intersect each other within the layer.

[0037] A tire carcass 6, containing radially wrapped ply cords, is continuously provided on the radially inner side of the belt layer 7 and on the equatorial plane CL side of the sidewall 5. This tire carcass 6 has a single-layer structure composed of a single tire carcass ply or a multi-layer structure composed of multiple stacked tire carcass ply layers, and is arranged in a ring between bead cores 21 located on both sides in the tire width direction to form the tire skeleton. Specifically, the tire carcass 6 is arranged between a pair of bead portions 20, from one bead portion 20 on one side of the pair located on both sides in the tire width direction to the other bead portion 20. Furthermore, the tire carcass 6 is folded at the bead portion 20 from the radially inner side of the bead core 21 in the tire width direction to the outer side in the tire width direction, thus enclosing the bead core 21 and bead filler 50. That is, the tire body 6 is folded around the bead core 21 at the bead portion 20 from the inside of the bead core 21 in the tire width direction to the outside of the bead core 21 in the tire width direction.

[0038] Therefore, the tire carcass 6 has a main body portion 6a arranged between a pair of bead portions 20 and a rolled-up portion 6b continuously formed from the main body 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 main body portion 6a, as described here, is the portion of the tire carcass 6 formed between a pair of bead cores 21 in the tire width direction. The rolled-up portion 6b is the portion continuously formed from the main body portion 6a in the tire width direction 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 bead filler 50 is disposed in the portion folded outward in the tire width direction of the bead core 21, i.e., the inner side of the rolled-up portion 6b in the tire width direction and the outer side in the tire width direction of the bead core 21.

[0039] The carcass 6 configured in this way consists of multiple carcass cords 6c (refer to) made of cord components composed of steel or organic fiber materials such as aromatic polyamide, nylon, polyester, and synthetic fibers. Figure 2 ) Using the covering rubber as a rubber component 6d (refer to) Figure 2 It is formed by covering and rolling. In addition, in the tire carcass 6, the inclination angle of the tire carcass cord 6c relative to the tire circumference, i.e., the tire carcass cord angle, is 85° or more and 95° or less.

[0040] Additionally, an inner liner 8 is formed along the inner side of the tire body 6 or the inner side of the pneumatic tire 1 of the tire body 6.

[0041] Figure 2 yes Figure 1 Detailed diagram of Part A. Figure 3 yes Figure 2 A detailed view of the bead core 21 is shown. The shape of the bead core 21, when viewed in the tire's meridional section, is formed by a polygonal cross-section; in this 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 (bottom surface 23) and the outer circumferential surface (upper surface 22) of the bead core 21, when viewed as a whole, are formed approximately parallel. Furthermore, in the bead core 21, the innermost portion and the outermost portion of the profile in the tire's meridional section are each formed by a vertical line 25 extending radially along the tire.

[0042] Furthermore, in the outline of the bead core 21 in the tire's meridional section, the radially inner portion of the vertical line 25 on the inner side of the tire width direction and the inner end of the bead core bottom surface 23 in the tire width direction are connected in a side-like manner, and the radially outer portion of the vertical line 25 on the inner side of the tire width direction and the inner end of the bead core upper surface 22 in the tire width direction are also connected in a side-like manner. Additionally, in the outline of the bead core 21 in the tire's meridional section, the radially inner portion of the vertical line 25 on the outer side of the tire width direction and the outer end of the bead core bottom surface 23 in the tire width direction are also connected in a side-like manner, and the radially outer portion of the vertical line 25 on the outer side of the tire width direction and the outer end of the bead core upper surface 22 in the tire width direction are also connected in a side-like manner. Thus, the bead core 21 is formed in a shape that is approximately octagonal in the tire's meridional section.

[0043] Furthermore, in this case, the bottom surface 23 of the bead core 21 refers to the surface represented by an imaginary straight line tangent to the portion of one of the plurality of bead lines 30 that form the surface of the bead core 21 and are arranged in a row at a position radially inward of the tire. Similarly, the upper surface 22 of the bead core 21 refers to the surface represented by an imaginary straight line tangent to the portion of one of the plurality of bead lines 30 that form the surface of the bead core 21 and are arranged in a row at a position radially outward of the tire.

[0044] Furthermore, the vertical line 25 of the bead core 21 refers to an imaginary straight line tangent to the portion of one of the plurality of bead lines 30 located on the outermost side of the bead core 21 in the width direction, when the tire width direction is set as the width direction of the bead core 21 in the tire's meridional section. Specifically, the vertical line 25 is positioned such that the interval between a pair of bead portions 20 located on either side of the tire equatorial plane CL in the tire width direction is such that it is used to mount the pneumatic tire 1 onto a specified rim R (see reference 1). Figure 1 In the case of a gap, it is formed by extending radially along the tire.

[0045] In other words, in the bead core 21, the bead lines 30 are arranged in a manner that extends radially in the tire, such that the interval between a pair of bead portions 20 located on both sides of the tire width direction relative to the tire equatorial plane CL is the interval when the pneumatic tire 1 is mounted on a specified rim R.

[0046] In this embodiment, the vertical line 25 on the inner side of the bead core 21 in the tire's meridional section in the tire width direction becomes a tangent to the three bead lines 30 that are arranged radially and closest to the inner side of the tire width in the tire width direction. Furthermore, the vertical line 25 on the outer side of the bead core 21 in the tire's meridional section in the tire width direction becomes a tangent to the three bead lines 30 that are arranged radially and closest to the outer side of the tire width in the tire width direction.

[0047] Furthermore, in the following description, the description related to the shape around the bead portion 20, similar to that of the vertical line 25, refers to the situation where the distance between the pair of bead portions 20 located on either side of the tire width direction relative to the tire equatorial plane CL is the distance when the pneumatic tire 1 is mounted on a specified rim R. Additionally, the vertical line 25 of the bead core 21 may not strictly extend 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.

[0048] Thus, for both vertical lines 25 located on either side of the width direction of the bead core 21, regardless of which vertical line 25, the length CV of the vertical line 25 is within the range of 31% to 45% of the radial height CH of the bead core 21. That is, for the vertical line 25, the ratio CV / CH of the length CV of the vertical line 25 to the radial height CH is within the range of 31% to 45%. In this case, the length CV of the vertical line 25 becomes the distance between the radially outer end of the bead line 30 that is furthest from the tire's outermost point and the radially inner end of the bead line 30 that is furthest from the tire's innermost point. Furthermore, in this case, the radial height CH becomes the distance between the upper surface 22 and the bottom surface 23 of the bead core.

[0049] Furthermore, regarding the vertical line 25, the radial distance Va from the bottom surface 23 of the bead core to the inner radial end 25a of the vertical line 25 is within the range of 20% to 35% relative to the core height CH. In this case, the inner radial end 25a of the vertical line 25 becomes the innermost radial end of the bead line 30 among the plurality of bead lines 30 constituting the vertical line 25.

[0050] In detail, the bead core 21 has vertical lines 25 on both sides in the width direction of the bead core 21. Both vertical lines 25 on both sides of the bead core 21 have a tire radial distance Va from the bottom surface 23 of the bead core to the inner end 25a of the vertical line 25 within the tire radial direction, which is within the range of 20% to 35% of the core height CH. That is, both vertical lines 25 on both sides of the bead core 21 have a tire radial distance Va from the bottom surface 23 of the bead core to the inner end 25a of the vertical line 25 within the range of Va / CH, which is within the range of 20% to 35%.

[0051] Furthermore, in the tire's meridional section, the distance Vb between the inner end 22in of the upper surface 22 of the bead core 21 in the tire width direction and the inner vertical line 25 on both sides of the bead core 21 in the tire width direction is within the range of 10% to 25% relative to the maximum width CW of the bead core 21. That is, regarding the bead core 21, the ratio Vb / CW of the distance Vb between the inner end 22in of the upper surface 22 of the bead core 21 in the tire width direction and the inner vertical line 25 in the tire width direction relative to the maximum width CW of the bead core 21 is within the range of 10% to 25%. In this case, the maximum width CW of the bead core 21 becomes the distance between the two vertical lines 25 located on both sides of the bead core 21 in the width direction. In addition, in this case, the end 22in of the upper surface 22 of the bead core in the tire width direction becomes the end of the bead line 30 that is closest to the inner side of the tire width direction among the multiple bead lines 30 constituting the upper surface 22 of the bead core.

[0052] Similarly, regarding the bead core 21, 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 in the tire width direction relative to the maximum width CW of the bead core 21 is within the range of 10% to 25%. That is, regarding the bead core 21, the ratio Vc / CW of 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 in the tire width direction relative to the maximum width CW of the bead core 21 is within the range of 10% to 25%. In this case, the inner end 23in of the bead core bottom surface 23 in the tire width direction becomes the inner end of the bead line 30 closest to the inner side in the tire width direction among the plurality of bead lines 30 constituting the bead core bottom surface 23.

[0053] Furthermore, in the tire's radial section, the maximum width CW of the bead core 21 is within a range of 0.9 to 1.4 times the core height CH. Additionally, regarding the bead core 21, the width CBW of the bead core bottom surface 23 in the tire's radial section is within a range of 45% to 70% of the maximum width CW of the bead core 21. In other words, regarding the bead core 21, 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%.

[0054] Figure 4 yes Figure 3Detailed diagram of Part B. The bead core 21 is formed by winding the bead cord 30 into a loop. Specifically, multiple loop portions of the bead cord 30 formed by winding into a loop are arranged in the tire width direction to form a layer 31, and multiple layers 31 are stacked in the tire radial direction. At this time, in the tire radial direction, the bead cords 30 forming each layer 31 are staggered by 0.5 cords in the tire width direction.

[0055] Regarding the first layer 31a, the second layer 31b, and the third layer 31c, counting from the radially inner side of the tire, among the multiple layers 31 of the bead core 21, the layer 31 located radially outer of the tire has two or more more bead lines 30 than the layer 31 located radially inner. In this case, the first layer 31a is the innermost layer 31 located radially outer of the multiple layers 31 of the bead core 21. Furthermore, the second layer 31b is a layer 31 stacked adjacent to the first layer 31a radially outer, and the third layer 31c is a layer 31 stacked adjacent to the second layer 31b radially outer. In this embodiment, the second layer 31b has two more bead lines 30 than the first layer 31a, and the third layer 31c has two more bead lines 30 than the second layer 31b.

[0056] Furthermore, regarding the first layer 31a, the second layer 31b, and the third layer 31c of the bead core 21, in the radial direction of two adjacent layers 31, the bead lines 30 at one end in the tire width direction are offset by 0.5 bead lines in the tire width direction. Moreover, regarding the first layer 31a, the second layer 31b, and the third layer 31c, the side where the bead lines 30 at the ends of the first layer 31a and the second layer 31b are offset by 0.5 bead lines in the tire width direction is opposite to the side where the bead lines 30 at the ends of the second layer 31b and the third layer 31c are offset by 0.5 bead lines in the tire width direction.

[0057] Specifically, for the first layer 31a and the second layer 31b, the bead lines 30 at the inner ends in the tire width direction are offset from each other by 0.5 bead lines of thickness 30. Conversely, for the second layer 31b and the third layer 31c, the bead lines 30 at the outer ends in the tire width direction are offset from each other by 0.5 bead lines of thickness 30.

[0058] Furthermore, in this embodiment, regarding the bead core 21, among the multiple layers 31 stacked in the radial direction of the tire, there are vertical lines 25 forming on both sides located in the width direction of the bead core 21 (see reference). Figure 3 The number of bead lines 30 in the layer 31 of the tire at the radial outer end of the tire decreases by one each time it moves towards the radial outer end of the tire.

[0059] The tire carcass 6 is configured to fold around the bead core 21 from the inner side of the bead core 21 in the tire width direction to the outer side of the bead core 21, and is constructed by covering and rolling multiple carcass cords 6c with covering rubber 6d. Regarding the tire carcass 6 having multiple carcass cords 6c, the insertion density of the carcass cords 6c at the position inside the bead core 21 in the tire width direction is in the range of 10 cords / 50mm or more and 20 cords / 50mm or less. In this case, the position inside the bead core 21 in the tire width direction is a position where the radial range of the bead core 21 is the same as the radial range of the tire in which the bead core 21 is located. That is, in this case, the position inside the bead core 21 in the tire width direction is a position in the tire carcass body 6a where the radial range of the bead core 21 is located is the same as the radial range of the tire in which the bead core 21 is located.

[0060] Regarding the carcass 6, the implantation density per 50 mm in the direction of the arrangement of the carcass cords 6c at the position inside the tire width direction of the bead core 21 is defined as being between 10 [cords / 50 mm] and 20 [cords / 50 mm].

[0061] The bead filler 50, comprising a lower filler 51 and an upper filler 52, is disposed on the radially outer side of the bead core 21. The lower filler 51 is disposed between the main body portion 6a and the rolled-up portion 6b of the tire carcass 6. Furthermore, regarding the lower filler 51, its width in the tire width direction in the tire's meridional section is the same as that of the bead core 21 near the bead core 21, and its width narrows towards the radially outer side of the tire.

[0062] On the other hand, the upper filler 52 is positioned radially from the location where the lower filler 51 is positioned to the radially outer side of the lower filler 51, with the inner end of the upper filler 52 located near the bead core 21. Specifically, within the radial direction of the lower filler 51, the upper filler 52 is positioned radially outside the lower filler 51, between the rolled-up portion 6b of the tire carcass 6 and the lower filler 51; and radially outside the lower filler 51, it is positioned between the main body portion 6a of the tire carcass 6 and the rolled-up portion 6b (see reference). Figure 1 ).

[0063] The bead filler 50 has lower filler 51 and upper filler 52, which are rubber compositions with different physical properties.

[0064] Additionally, the bead portion 20 has a rim cushioning rubber 46 on the radially inner side of the bead core 21. The rim cushioning 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 wheel during fitting into the rim wheel.

[0065] The bead base 40 mentioned here is the inner circumferential surface of the bead portion 20, which is the part of the bead portion 20 that contacts and engages with the rim-type wheel. The bead base 40 has a toe 41 at its inner end in the tire width direction and a heel 42 at its outer end in the tire width direction, and is formed into a cone shape whose diameter increases as it moves from the toe 41 side to the heel 42 side.

[0066] In the bead portion 20, a reinforcing layer 60 for reinforcing the tire carcass 6 is disposed on the portion of the tire carcass 6 folded around the bead core 21. The reinforcing layer 60 is disposed along the tire carcass 6 at least on the inner side of the tire carcass body portion 6a in the tire width direction. In this embodiment, three reinforcing layers 60 are disposed, and these three reinforcing layers 60 are arranged in such a way that the positions of the radial ends of the tire in the tire meridional section are at different positions.

[0067] In detail, when the three reinforcing layers 60 are designated as a first reinforcing layer 61, a second reinforcing layer 62, and a third reinforcing layer 63, extending from the tire carcass 6 towards the direction away from the tire carcass 6 in the thickness direction, the first reinforcing layer 61 is folded along the tire carcass 6 from the inside of the bead core 21 in the tire width direction to the outside of the tire width direction. In contrast, the second reinforcing layer 62 and the third reinforcing layer 63 are not located on the outside of the bead core 21 in the tire width direction. That is, the second reinforcing layer 62 and the third reinforcing layer 63 are not located on the rolled-up portion 6b side, but are located only along the tire carcass 6 within the area where the main body portion 6a is located.

[0068] Regarding the radially inner ends of the tire in the tire meridional section of each of the second reinforcing layer 62 and the third reinforcing layer 63, the second reinforcing layer 62 is located radially inner compared to the third reinforcing layer 63. Furthermore, regarding the radially outer ends of the tire in the tire meridional section of each of the second reinforcing layer 62 and the third reinforcing layer 63, the third reinforcing layer 63 is located radially outer compared to the second reinforcing layer 62.

[0069] The multiple reinforcing layers 60 configured in this way are each constructed by covering multiple cords with a covering rubber and then rolling them. The cords of the first reinforcing layer 61 are made of steel cords. On the other hand, the cords of the second reinforcing layer 62 are made of organic fiber cords. Similarly, the cords 65 of the third reinforcing layer 63 are also made of organic fiber cords.

[0070] The first reinforcing layer 61 is disposed along the tire carcass 6, folded from the inside of the bead core 21 in the tire width direction to the outside of the tire width direction. Furthermore, regarding the first reinforcing layer 61, both the end of the first reinforcing layer 61 located inside the bead core 21 in the tire width direction and the end located outside the bead core 21 in the tire width direction are located radially outward from the upper surface 22 of the bead core 21.

[0071] Furthermore, regarding the plurality of reinforcing layers 60 that are overlapped along the tire body 6 at the bead portion 20, the inclination direction of the cords of each reinforcing layer 60 relative to the tire radial direction toward the tire circumferential direction is opposite to that of each other.

[0072] [Manufacturing method of pneumatic tires]

[0073] Next, the manufacturing method of the pneumatic tire 1 according to the embodiment will be described. In manufacturing the pneumatic tire 1, firstly, each component constituting the pneumatic tire 1 is processed, and the processed components are assembled. That is, each component, such as the tread rubber 2a, the tire body 6, the belt layer 7, and the bead core 21, is processed separately, and the processed components are assembled.

[0074] For example, the bead core 21 is formed by winding the bead line 30 into a loop. In this case, the bead core 21 is formed such that the innermost portion of the profile in the tire's meridional section in the tire width direction and the outermost portion in the tire width direction are respectively vertical lines 25 extending radially along the tire. Furthermore, regarding the bead core 21, the length CV of the vertical line 25 is within the range of 31% to 45% of the core height CH of the bead core 21, and the radial distance Va from the bottom surface 23 of the bead core to the inner radial end 25a of the vertical line 25 is within the range of 20% to 35% of the core height CH.

[0075] Furthermore, the bead core 21 forms a layer 31 by arranging multiple wrapping portions of the bead lines 30 in the tire width direction, and multiple layers 31 are stacked in the tire radial direction. At this time, regarding the three layers 31, namely 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, in two adjacent layers 31 in the tire radial direction, the number of bead lines 30 in the layer 31 located on the outer side of the tire radial direction is more than two more than the number of bead lines 30 in the layer 31 located on the inner side of the tire radial direction, and the amount of offset in the tire width direction between the bead lines 30 at one end of each other is 0.5 times the thickness of the bead lines 30. Furthermore, regarding these three layers 31, the side where the offset of the bead lines 30 in the first layer 31a and the second layer 31b is 0.5 times the thickness of the bead lines 30 and the side where the offset of the bead lines 30 in the second layer 31b and the third layer 31c is 0.5 times the thickness of the bead lines 30 are opposite to each other in the tire width direction.

[0076] Thus, during the manufacture of the pneumatic tire 1, the bead cord 30, which is wound into a loop when forming the bead core 21, begins to be wound from the end on the outer side of the tire width direction in the first layer 31a. That is, when the bead cord 30 is wound into a loop to form the bead core 21, it is wound in such a way that the end of the bead cord 30 located on the bottom surface 23 of the bead core is located at the end on the outer side of the bottom surface 23 of the bead core in the tire width direction.

[0077] Bead cord 30, starting from the end on the outer side of the bottom surface 23 of the bead core in the tire width direction, is wound into a spiral shape and arranged in the tire width direction to form layer 31. After the number of times the bead cord 30 is wound becomes the predetermined number of turns for each layer 31, the bead cord 30 is folded upwards radially towards the tire and wound into a spiral shape as determined by the number of turns of the adjacent layer 31 on the outer side of the tire in the radial direction, thereby forming layer 31.

[0078] In other words, the bead cord 30 begins to be wound from the outer end of the first layer 31a in the tire width direction. After the first layer 31a is wound, the second layer 31b, which is adjacent to the first layer 31a in the tire radial direction, begins to be wound. Therefore, the side where the bead cords 30 in the first layer 31a and the second layer 31b are offset from each other by an amount equal to 0.5 of the thickness of the bead cord 30, must be located at the inner end side of the first layer 31a and the second layer 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, which are formed by arranging multiple wrapping portions of the bead cord 30 in the tire width direction, so that the shape in the tire meridional section is a polygonal section.

[0079] In the bead portion 20 with the bead core 21 configured in this way, the carcass 6 is arranged such that it is folded from the inside of the bead core 21 in the tire width direction to the outside of the tire width direction. In the carcass 6, the carcass ply with a ply density of 10 cords / 50mm or more and 20 cords / 50mm or less is used at the position of the bead core 21 in the tire width direction. The pneumatic tire 1 of this embodiment is manufactured in this way.

[0080] [Functions and Effects]

[0081] When assembling the pneumatic tire 1 of this embodiment onto a vehicle, firstly, the pneumatic tire 1 is assembled onto the specified rim R by fitting the tire bead base 40 relative to the rim R of the rim-type wheel. The pneumatic tire 1 is then inflated after rim assembly, and the vehicle is equipped with the inflated pneumatic tire 1 in this rim-assembled state. The pneumatic tire 1 of this embodiment can be assembled, for example, onto vehicles requiring traction performance such as loaders and scrapers, and used under heavy load conditions.

[0082] When a vehicle equipped with a pneumatic tire 1 is in motion, the pneumatic tire 1 rotates while the lower tread surface 3 of the tire tread surface 3 is in contact with the road surface. The vehicle moves by transmitting driving force and braking force to the road surface or generating turning force through the friction between the tire tread surface 3 and the road surface.

[0083] When a vehicle equipped with a pneumatic tire 1 is in motion, the vehicle is able to move by the friction generated between the tread surface 3 of the pneumatic tire 1 and the road surface. However, during the movement of the vehicle, various loads in different directions act on different parts of the pneumatic tire 1. The loads acting on the pneumatic tire 1 are received by the pressure of the air filled inside, the tire body 6 which serves as the skeleton of the pneumatic tire 1, and so on.

[0084] For example, the load acting radially on the tire between the tread portion 2 and the bead portion 20 due to the weight of the vehicle and the unevenness of the road surface is mainly borne by the pressure of the air filled inside the pneumatic tire 1 or by the sidewall portion 5 while flexing. In particular, the pneumatic tire 1 of this embodiment is fitted to large vehicles and used under heavy load conditions, so the sidewall portion 5 and the tire body 6 are subjected to very large loads. Therefore, a large tension acts on the tire body 6.

[0085] The tire carcass 6 is held by the bead portion 20 by folding it around the bead core 21 at the bead portion 20. Therefore, when a large tension is applied to the tire carcass 6, the tension of the tire carcass 6 is transmitted to the bead core 21, and a large force acts between the tire carcass 6 and the bead core 21. In other words, because the tire carcass 6 is held by the bead portion 20 by folding it around the bead core 21, when tension is applied to the tire carcass 6, a tension acts on the tire carcass body 6a in a direction from the bead portion 20 toward the radially outward side of the tire. Consequently, a large force also acts between the bead core 21 and the tire carcass 6.

[0086] Here, the sidewall portion 5 is inclined relative to the tire radial direction as it moves from the position of the bead portion 20 toward the outer radial direction of the tire and toward the outer direction of the tire width. Therefore, when a large tension is applied to the tire body portion 6a, the tire body portion 6a is pulled in the tire radial direction while generating a force in the direction toward the outer direction of the tire width near the bead portion 20.

[0087] On the other hand, in pneumatic tires used on large vehicles under heavy loads, the bead core is often formed with a roughly hexagonal cross-sectional shape in the tire's meridional section. In this case, the bead core has a corner protruding inwards in the tire width direction. Therefore, under high tension on the tire carcass, and with the tire carcass body near the bead portion generating a force in the outward direction of the tire width while moving radially due to this tension, the tire carcass body exerts a large load and rubs against the protruding corner in the bead core. Consequently, regarding the tire carcass body, the covering rubber wears and the tire carcass cords rub directly against each other, potentially leading to tire cord breakage and other malfunctions.

[0088] In addition, because the tire carcass folds around the bead core, when a large tension is applied to the tire carcass, friction also occurs between the tire carcass and the bead core at locations other than the corner of the bead core that protrudes inward in the direction of tire width. This friction may cause malfunctions such as tire carcass cord breakage.

[0089] In contrast, in the pneumatic tire 1 of this embodiment, regarding the bead core 21, the innermost portion and the outermost portion of the profile in the tire's meridional section in the tire width direction are each formed by a vertical line 25 extending radially along the tire. That is, the bead core 21 is formed with the vertical line 25 extending radially along the tire at the position where it reaches its maximum width in the tire width direction, thus avoiding any corners protruding relative to the tire width direction. Therefore, even when a large force acts between the tire body 6 and the bead core 21 due to a large tension acting on the tire body 6, stress concentration can be suppressed, and the stress acting between the tire body 6 and the bead core 21 can be dispersed. Thus, wear of the covering rubber 6d of the tire body main body 6a due to stress concentration between the tire body 6 and the bead core 21 can be suppressed, and failures such as tire cord 6c breakage due to direct friction caused by wear of the covering rubber 6d can be suppressed.

[0090] Furthermore, since the length CV of the vertical lines 25 on both sides of the bead core 21 in the tire width direction is within the range of 31% to 45% of the core height CH, the stress generated between the tire carcass 6 and the bead core 21 can be more reliably dispersed. In other words, when 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, and even if 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 stress concentration between the tire carcass 6 and the bead core 21. Conversely, when 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, and even if vertical lines 25 are formed on both sides of the bead core 21 in the tire width direction, stress concentration may occur at the two ends of the length of the vertical lines 25.

[0091] In contrast, when the length CV of the vertical line 25 is within the 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 disperse the stress generated between the tire carcass 6 and the bead core 21. This allows for more reliable suppression of faults such as breakage of the carcass cord 6c caused by stress concentration between the tire carcass 6 and the bead core 21.

[0092] Furthermore, regarding the vertical line 25 of the bead core 21, if the radial distance Va from the bottom surface 23 of the bead core to the inner radial end 25a of the vertical line 25 is within the range of 20% to 35% of the core height CH, stress concentration between the tire carcass 6 and the bead core 21 can be more reliably suppressed. In other words, if the radial distance Va from the bottom surface 23 of the bead core to the inner radial end 25a of the vertical line 25 is less than 20% of the core height CH, the position of the vertical line 25 may be too close to the inner radial side of the tire.

[0093] Furthermore, if the radial distance Va from the bottom surface 23 of the bead core to the inner end 25a of the vertical line 25 is greater than 35% of the core height CH, the position of the vertical line 25 may be too close to the outer radial direction of the tire. In these cases, the shape of the bead core 21 forming the vertical lines 25 on both sides in the tire width direction may be difficult to conform to the shape of the carcass 6 folded at the bead portion 20, thus causing stress concentration between the carcass 6 and the bead core 21, which may easily lead to failures such as breakage of the carcass cords 6c.

[0094] In contrast, when the radial 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 20% to 35% of 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 to approximate the shape of the tire carcass 6 folded at the bead portion 20. This allows for more reliable suppression of stress concentration between the tire carcass 6 and the bead core 21, and more reliable suppression of faults such as breakage of the carcass cord 6c caused by stress concentration between the tire carcass 6 and the bead core 21.

[0095] Furthermore, in the bead core 21, regarding the first layer 31a, the second layer 31b, and the third layer 31c, which are formed by the bead lines 30, counting from the innermost circumference in the tire radial direction, among two adjacent layers 31 in the tire radial direction, the layer 31 located on the outer side of the tire radial direction has at least two more bead lines 30 than the layer 31 located on the inner side of the tire radial direction. This allows the outline shape of the bead core 21 from the first layer 31a to the third layer 31c in the tire's meridional section to be a shape with a small inclination angle towards the tire radial direction relative to the tire width direction. Therefore, the cross-sectional shape of the bead core 21 near the bottom surface 23 of the bead core can be made closer to the shape of the tire carcass 6 folded at the bead portion 20.

[0096] Furthermore, regarding the first layer 31a, the second layer 31b, and the third layer 31c among the multiple layers 31 formed by the bead lines 30, the misalignment of the bead lines 30 at the ends of one side in the tire width direction between two adjacent layers 31 in the tire radial direction is 0.5 times the thickness of the bead lines 30. This prevents the misalignment of the bead lines 30 across the portions of two adjacent layers 31 in the tire radial direction from becoming excessively large, and prevents the shape of the bead core 21 from becoming distorted due to excessive misalignment of the bead lines 30 across the portions of two adjacent layers 31 in the tire radial direction.

[0097] Furthermore, the offset of the bead cords 30 in the first layer 31a and the second layer 31b by 0.5 units of the thickness of the bead cords 30, and the offset of the bead cords 30 in the second layer 31b and the third layer 31c by 0.5 units of the thickness of the bead cords 30, are opposite to each other in the tire width direction. This allows the outline shape of the bead core 21 from the first layer 31a to the third layer 31c in the tire's meridional section to be balanced on both sides in the tire width direction, closely approximating the shape of the carcass 6 folded at the bead portion 20. Therefore, the stress generated between the carcass 6 and the bead core 21 can be more reliably distributed, and the occurrence of failures such as breakage of the carcass cords 6c caused by stress concentration 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.

[0098] Furthermore, the bead core 21 is formed in a shape that creates a vertical line 25 on the outer side in the tire width direction. Therefore, compared to the case where the bead core has a roughly hexagonal cross-sectional shape, the outer surface 45 of the bead portion 20 on the outer side in the tire width direction (see reference) can be made more flexible. Figure 2 The contact pressure between the rim-type wheel and the bead portion is nearly uniform. That is, when the bead core has a roughly hexagonal cross-sectional shape, it is formed such that the portion on the outer side of the tire width direction has corners protruding outwards in the tire width direction. Therefore, at the corner portions, the contact pressure between the rim-type wheel and the outer surface of the bead portion is higher, but outside the corner portions, the contact pressure tends to be lower. In this case, it may be difficult to ensure an airtight seal between the rim-type wheel and the outer surface of the bead portion when assembling and inflating the pneumatic tire to the rim-type wheel rim.

[0099] In contrast, in this embodiment, the bead core 21 is formed with a vertical line 25 extending outward in the tire width direction, thus reducing the variation in the distance between the bead core 21 and the outer surface 45 of the bead portion. In other words, the area of ​​the portion from the bead core 21 that can increase the contact pressure with the rim-type wheel can be increased. As a result, the contact pressure between the rim-type wheel and the outer surface 45 of the bead portion can be made nearly uniform. Consequently, the airtightness at the bead portion 20 can be improved.

[0100] Furthermore, since the width CBW of the bottom surface 23 of the bead core in the tire's radial section is within the range of 45% to 70% of the maximum width CW of the bead core 21, stress concentration between the bottom surface 23 of the bead core and the tire carcass 6 can be suppressed. In other words, when the width CBW of the bottom surface 23 of the bead core is less than 45% of the maximum width CW of the bead core 21, the width CBW of the bottom surface 23 is too narrow, and the shape of the bead core 21 in the tire's radial section may protrude excessively downwards towards the tire's radial direction. In this case, stress concentration may easily occur near the bottom surface 23 of the bead core 21, between the tire carcass 6 and the bead core 21. Conversely, when the width CBW of the bottom surface 23 of the bead core is greater than 70% of the maximum width CW of the bead core 21, the width CBW of the bottom surface 23 is too wide, and stress concentration may easily occur between the tire carcass 6 and the bead core 21 at both ends in the width direction of the bottom surface 23 of the bead core.

[0101] In contrast, when the width CBW of the bead core bottom surface 23 is within the 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 tire carcass 6 can be effectively suppressed. This more reliably suppresses faults such as breakage of the carcass cord 6c caused by stress concentration between the tire carcass 6 and the bead core 21. Consequently, the durability of the bead portion 20 can be more reliably improved.

[0102] Furthermore, regarding the bead core 21, the distance Vb between the inner end 22in of the upper surface 22 in the tire width direction and the vertical line 25 of the inner side of the tire width direction in the tire width direction is within a range of 10% to 25% relative to the maximum width CW of the bead core 21, and the distance Vc between the inner end 23in of the lower surface 23 in the tire width direction and the vertical line 25 of the inner side of the tire width direction in the tire width direction is within a range of 10% to 25% relative to the maximum width CW of the bead core 21, thus more reliably suppressing stress concentration generated between the tire carcass 6 and the bead core 21. In other words, if the distance Vb between the inner end 22in of the upper surface 22 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, and the distance Vc between the inner end 23in of the bottom surface 23 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, are less than 10% of the maximum width CW of the bead core 21, the protrusion of the bead core 21 from the positions of the upper surface 22 and the bottom surface 23 of the bead core towards the inner tire width direction may become too small. In this case, the shape of the surface of the bead core 21 located in the inner tire width direction in the tire meridional section is unlikely to be a curved shape along the portion of the bead core 21 located in the inner tire width direction in the tire carcass 6, and therefore stress concentration may easily occur between the tire carcass 6 and the bead core 21.

[0103] Furthermore, if the distance Vb between the inner end 22in of the upper surface 22 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, and the distance Vc between the inner end 23in of the bottom surface 23 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, are greater than 25% of the maximum width CW of the bead core 21, the protrusion of the bead core 21 from the positions of the upper surface 22 and the bottom surface 23 of the bead core towards the inner tire width direction may become excessively large. In this case, the shape of the surface of the bead core 21 located in the inner tire width direction in the tire's meridional section is also unlikely to be a curved shape along the portion of the tire carcass 6 located in the inner tire width direction of the bead core 21, thus stress concentration may easily occur between the tire carcass 6 and the bead core 21.

[0104] In contrast, since the distance Vb between the inner end 22in of the upper surface 22 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, and the distance Vc between the inner end 23in of the bottom surface 23 of the bead core in the tire width direction and the vertical line 25 in the inner tire width direction, are within a range of 10% to 25% relative to the maximum width CW of the bead core 21, it is easy to make the shape of the surface of the bead core 21 located in the tire width direction in the tire meridional section into a curved shape along the portion of the bead core 21 located in the tire width direction in the tire carcass 6. This allows for more reliable suppression of stress concentration between the tire carcass 6 and the bead core 21. As a result, the durability of the bead portion 20 can be improved more reliably.

[0105] Furthermore, regarding the bead core 21, the maximum width CW of the bead core 21 is within the range of 0.9 times to 1.4 times the core height CH, thus more reliably suppressing stress concentration between the tire carcass 6 and the bead core 21. In other words, when 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 ensure that the shape of the bead core 21 in the tire's meridional section conforms to the shape of the tire carcass 6 folded around the bead core 21, potentially leading to stress concentration between the tire carcass 6 and the bead core 21. Specifically, because the maximum width CW of the bead core 21 is too narrow, stress concentration may easily occur between the portion of the tire carcass 6 folded around the bead core 21 located near the bottom surface 23 of the bead core and the bead core 21.

[0106] 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. Therefore, in this case, it is also difficult to make the shape of the bead core 21 in the tire's meridional section conform to the shape of the tire carcass 6, which may easily lead to stress concentration between the tire carcass 6 and the bead core 21. Specifically, because the maximum width CW of the bead core 21 is too wide, stress concentration may easily occur between the portion of the tire carcass 6 folded around the bead core 21 located near both sides of the bead core 21 in the tire width direction and the bead core 21.

[0107] In contrast, when the maximum width CW of the bead core 21 is within a range of 0.9 times to 1.4 times the core height CH, the shape of the bead core 21 in the tire's meridional section can be made to resemble the shape of the tire carcass 6 folded around the bead core 21. This allows for more reliable suppression of stress concentration between the tire carcass 6 and the bead core 21. Consequently, the durability of the bead portion 20 can be improved more reliably.

[0108] Furthermore, regarding the tire carcass 6, the embedding density of the carcass cords 6c at the inner side of the bead core 21 in the tire width direction is between 10 cords / 50mm and 20 cords / 50mm. This allows for more reliable suppression of tire carcass 6 failures at the bead portion 20. In other words, if the embedding 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 / 50mm, the embedding density is too low. Therefore, when a large tension is applied to the tire carcass 6, the tension borne by each carcass cord 6c may become excessive. In this case, the stress on each carcass cord 6c at the portion of the tire carcass 6 located in the bead portion 20 becomes excessive, and the carcass cords 6c may be prone to breakage. Furthermore, if the implantation density of the carcass cords 6c at the position inside the tire width direction of the bead core 21 is greater than 20 [cords / 50mm], the excessive implantation density of the carcass cords 6c results in the cords 6c being too close together, and the volume of the covering rubber 6d between adjacent carcass cords 6c may become too small. In this case, it is difficult to hold the carcass cords 6c with the covering rubber 6d, and the carcass cords 6c are prone to peeling off from the covering rubber 6d, making it difficult to manufacture a carcass 6 with suitable durability.

[0109] In contrast, when the implantation density of the carcass cords 6c at the position inside the tire width direction of the bead core 21 is within the range of 10 cords / 50mm or more and 20 cords / 50mm or less, it is possible to prevent the volume of the covering rubber 6d between adjacent carcass cords 6c from becoming too small, while distributing the force borne by the carcass cords 6c to more 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 a large tension is applied to the carcass 6 at the bead portion 20, thus preventing excessive stress on each carcass cord 6c and its tendency to break. Therefore, the durability of the carcass 6 can be ensured, and failures of the carcass 6 at the bead portion 20 can be more reliably suppressed. As a result, the durability of the bead portion 20 can be improved more reliably.

[0110] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, since the bead core 21 is formed such that the innermost portion of the bead core 21 in the tire width direction and the outermost portion in the tire width direction are perpendicular to the line 25, stress concentration can be suppressed even when a large force acts between the tire carcass 6 and the bead core 21 due to a large tension acting on the tire carcass 6. Therefore, it is possible to suppress failures such as tire carcass cord 6c breakage caused by stress concentration generated between the tire carcass 6 and the bead core 21.

[0111] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, since the length CV of the vertical line 25 is within the range of 31% or more and 45% or less relative to the core height CH, the stress generated between the tire carcass 6 and the bead core 21 can be more reliably distributed by the vertical lines 25 formed on both sides of the tire width direction of the bead core 21. As a result, the occurrence of faults such as the breakage of the tire carcass cord 6c caused by stress concentration generated between the tire carcass 6 and the bead core 21 can be more reliably suppressed.

[0112] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, since the radial 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 20% to 35% of the core height CH, the shape of the bead core 21 can be made close to the shape of the tire carcass 6 folded at the bead portion 20. This allows for more reliable suppression of stress concentration between the tire carcass 6 and the bead core 21.

[0113] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, regarding the first layer 31a, the second layer 31b, and the third layer 31c of the plurality of layers 31 formed by the bead lines 30, the amount of misalignment in the tire width direction between the bead lines 30 at one end in the tire width direction of two adjacent layers 31 is 0.5 times the thickness of the bead lines 30. Therefore, it is possible to prevent the amount of misalignment in the tire width direction of the bead lines 30 at the portions of two adjacent layers 31 in the tire radial direction from becoming too large, and it is possible to prevent the shape of the bead core 21 from becoming distorted.

[0114] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, the side where the offset of the bead lines 30 in the first layer 31a and the second layer 31b is 0.5 times the thickness of the bead lines 30, and the side where the offset of the bead lines 30 in the second layer 31b and the third layer 31c is 0.5 times the thickness of the bead lines 30, are opposite to each other in the tire width direction. This allows the shape of the bead core 21 in the tire's meridional section to be balanced and approximate along the shape of the tire carcass 6 on both sides in the tire width direction, suppressing stress concentration between the tire carcass 6 and the bead core 21, thus more reliably suppressing failures such as breakage of the carcass cords 6c. As a result, the durability of the bead portion 20 is improved.

[0115] Furthermore, in the manufacturing method of the pneumatic tire 1 according to the embodiment, since the bead cord 30 starts to wrap from the end on the outer side of the tire width direction in the first layer 31a, the durability of the bead core 21 can be ensured. That is, when the pneumatic tire 1 is inflated, the position of the bead core 21 at the end 23in on the inner side of the tire width direction in the bottom surface 23 of the bead core requires the most strength. Therefore, if the end of the bead cord 30 is located at the end 23in on the inner side of the tire width direction in the bottom surface 23 of the bead core, the durability of the bead core 21 decreases, and the shape of the bead core 21 may easily become distorted.

[0116] In contrast, when the bead thread 30 is wound starting from the outer end in the tire width direction of the first layer 31a, the strength of the position at the inner end 23in in the tire width direction of the bottom surface 23 of the bead core, where the most strength is required, can be ensured, thus suppressing the easy distortion of the shape of the bead core 21. As a result, the durability of the bead core 21 can be ensured.

[0117] [Variation Example]

[0118] Furthermore, in the pneumatic tire 1 of the above-described embodiment, regarding the bead core 21, as the layer 31, which includes the bead line 30 at the end that forms the vertical line 25 on the radially outer side of the tire, moves towards the radially outer side of the tire, the number of bead lines 30 in the layer 31 decreases by one each time. However, the bead core 21 can also be formed in a manner other than this.

[0119] Figure 5 This is a variation of the pneumatic tire 1 described in the embodiment, showing a detailed view of the bead core 21 of the bead line 30 layered in a manner different from the embodiment described above. For example, as... Figure 5 As shown, the bead core 21 may also have a portion in which, in the radially outer part of the two adjacent layers 31 located further outward than the vertical line 25, the layer 31 located radially outer of the tire has two fewer bead lines 30 than the layer 31 located radially inner. Regarding the bead core 21, as long as its shape, when viewed in the tire's meridional section, is formed with a cross-sectional shape close to an octagon, the first layer 31a, the second layer 31b, and the third layer 31c, counting from the innermost circumference radially outward of the tire among the multiple layers 31 formed by the bead lines 30, can be formed as described in the embodiment above, regardless of the manner in which the portion located radially outer of the tire than the vertical line 25 is formed.

[0120] Furthermore, in the pneumatic tire 1 of the above embodiment, three reinforcing layers 60 are provided, but the reinforcing layers 60 may also be provided in more than three layers. The number of reinforcing layers 60 and the range of reinforcing layers 60 disposed in the tire meridional section may also be different from the above embodiment.

[0121] [Example]

[0122] Figure 6A , Figure 6B This is a graph showing the results of the performance evaluation test of the pneumatic tire. The performance evaluation test conducted on the conventional pneumatic tire and the pneumatic tire 1 of the present invention will be described below. The performance evaluation test included a durability test to evaluate the durability of the pneumatic tire 1.

[0123] The performance evaluation test was conducted under the following conditions: a pneumatic tire 1 with a nominal size of 37.25R35 was used as the test tire, the test tire was assembled onto a rim of a rim-type wheel in accordance with TRA standards, the air pressure was adjusted to the air pressure specified by TRA standards, and a load specified by TRA standards was applied.

[0124] The durability evaluation method uses an indoor roller testing machine. A driving test is conducted with the load set to 120% of the maximum load specified by TRA and the speed set to 10 km / h. The breakage rate of the bare cords in the bead portion of the tire carcass after 300 hours of tire driving is evaluated using an index of 100 (described later in the previous example). Regarding the bare cord breakage rate, 40 tire carcass cords from the bead portion are collected at random locations at the end of the driving test. All collected tire carcass cords are observed, and the average value of (number of broken bare cords in each tire carcass cord / total number of bare cords in each tire carcass cord) is taken as the breakage rate.

[0125] Performance evaluation tests were conducted on 24 types of pneumatic tires, including conventional pneumatic tires and the pneumatic tire of the present invention, namely Examples 1 to 23. In the conventional pneumatic tires, the cross-sectional shape of the bead core in the tire's meridional section is approximately hexagonal, and the bead core does not have vertical lines at its innermost and outermost points in the tire width direction.

[0126] In contrast, in one example of the pneumatic tire 1 of the present invention, namely Embodiments 1 to 23, all the bead cores 21 have 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 in the range of 31% or more and 45% or less 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 in the range of 20% or more and 35% or less relative to the core height CH. Furthermore, regarding the pneumatic tire 1 of Examples 1 to 23, the ratio of the width CBW of the bottom surface 23 of the bead core 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 upper surface 22 of the bead core 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 bottom surface 23 of the bead core 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 inner position of the bead core 21 in the tire width direction are all different.

[0127] The results of performance evaluation tests conducted using these pneumatic tires 1 show that: Figure 6A , Figure 6B As shown, compared to the conventional example, the pneumatic tires 1 of Examples 1 to 23 exhibit improved breakage rates of the bare cords of the carcass cords 6c in the bead portion 20, making breakage of the carcass cords 6c at the bead portion 20 less likely. In other words, the pneumatic tires 1 of Examples 1 to 23 can improve the durability of the bead portion 20.

[0128] Explanation of reference numerals in the attached figures

[0129] 1. Pneumatic tire

[0130] 2nd pregnancy face

[0131] 2a Tread rubber

[0132] 3. Tread surface

[0133] 4. Tire shoulder

[0134] 5. Sidewall

[0135] 6. Fetal body

[0136] 6a Main body of the fetus

[0137] 6b Roll-up section

[0138] 6c tire cord

[0139] 6d Covered Rubber

[0140] 7. Belt layer

[0141] 10. Land Forces

[0142] 15 Circumferential Grooves

[0143] 20. Bead section

[0144] 21 Tire Bead Core

[0145] 22. Upper surface of the tire bead core

[0146] 23 Bead core bottom surface

[0147] 25 Vertical lines

[0148] 30 Bead Line

[0149] 31st floor

[0150] 31a First Floor

[0151] 31b, Level 2

[0152] 31c, 3rd layer

[0153] 40 Bead base

[0154] 41. Fetal toe

[0155] 42 Fetal heels

[0156] 45 Outer surface of the bead area

[0157] 46 Rim cushioning rubber

[0158] 50 Bead Filler

[0159] 51. Filler glue

[0160] 52 Filler

[0161] 60 Reinforcement Layers

Claims

1. A pneumatic tire, characterized in that, have: A pair of bead portions are positioned on either side of the tire's equatorial plane in the tire's width direction; A bead core, disposed in the bead portion, is formed by winding bead threads into a loop, and its shape in the tire's meridional section is formed by a polygonal cross-section; and The tire carcass has a main body portion disposed between a pair of bead portions and a rolled-up portion continuously formed from the 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, formed by covering the carcass cords with a covering rubber. Regarding the bead core, the innermost portion and the outermost portion of the profile in the tire's meridional section are formed by vertical lines extending radially along the tire. Regarding the vertical line, the length of the vertical line relative to the tire bead core's radial height (i.e., the core height) is within the range of 31% to 45%. Regarding the vertical line, the radial distance from the inner circumferential surface of the bead core (i.e., the bottom surface of the bead core) to the inner end of the vertical line relative to the core height is within a range of 20% to 35%. The bead core, formed by multiple loops of the bead line wound into a ring, is arranged in the tire width direction to form a layer, and the multiple layers are stacked in the tire radial direction. In the plurality of layers, in the layers that are further radially outer than the layers including the bead lines at the ends forming the vertical lines, the number of bead lines in each layer decreases by one as it moves further radially outward. In the plurality of layers, in the layers that are further radially inner than the layers including the bead lines at the inner ends forming the vertical lines, the number of bead lines in the layers that are radially outer of each other in two adjacent layers is more than two more than the number of bead lines in the layers that are radially inner, and the offset of the bead lines at the ends on one side in the tire width direction is 0.5 bead lines. Regarding the innermost layer in the radial direction of the tire, namely the first layer, the second layer stacked adjacent to the outermost layer in the radial direction of the first layer, and the third layer stacked adjacent to the outermost layer in the radial direction of the second layer, the side where the bead lines in the first and second layers are offset from each other by 0.5 bead lines is opposite to the side where the bead lines in the second and third layers are offset from each other by 0.5 bead lines in the tire width direction. Regarding the tire carcass, the implantation density of the tire carcass cords at the position inside the tire width direction of the bead core is within the range of 10 cords / 50mm or more and 20 cords / 50mm or less.

2. The pneumatic tire according to claim 1, Regarding the bead core, the width of the bottom surface of the bead core in the tire's meridional section is within the range of more than 45% and less than 70% of the maximum width of the bead core.

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

4. The pneumatic tire according to claim 1, wherein a reinforcing layer is disposed along the tire carcass at least on the inner side of the tire carcass body in the tire width direction at the bead portion, and a plurality of the reinforcing layers having a plurality of cords are overlapped with respect to the reinforcing layer. Regarding the plurality of reinforcing layers, in adjacent reinforcing layers, the inclination direction of the cords relative to the tire radial direction toward the tire circumferential direction is opposite to that of each other.

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