tire

Abstract

To provide a tire that can exhibit the same level of fracture strength as conventional tires when applied to an automobile. [Solution] The tire 10 comprises a pair of bead portions 12, each of which has a bead core 14. The bead core 14 has a bead wire layer 20 and a bead reinforcing layer 22 positioned radially outward from the bead wire layer 20. The bead wire layer 20 has a bead wire 24 that is spirally wound around the tire rotation axis. The bead reinforcing layer 22 has a plurality of reinforcing layers 26 that are stacked in the radial direction of the tire. Each of the plurality of reinforcing layers 26 contains carbon fibers oriented in a predetermined direction. The bead reinforcing layer 22 includes a crossing reinforcing layer 36, which consists of two adjacent reinforcing layers 26 in the radial direction of the tire, where the fiber directions of the carbon fibers contained in each of the two reinforcing layers 26 intersect when viewed from the radial direction of the tire.

Description

[Technical Field]

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

[0002] From the viewpoint of energy saving, weight reduction of tires is required. Generally, steel used as a member constituting a tire is heavier than rubber, so the tire can be significantly lightened by reducing the amount used. Steel is mainly used for belts and bead cores. For example, Patent Document 1 discloses a tire using a carbon fiber composite material (CFRP: Carbon Fiber Reinforced Plastics) containing resin and carbon fiber for a bead core. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. WO2016 / 143189 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] However, although it is shown that the breaking strength of the tire of Patent Document 1 is equivalent to that of a conventional tire in a single tire, when applied to an actual automobile, there is a problem that the rigidity in the tire lateral direction (lateral spring constant) is insufficient and it cannot be said that the strength is equal to or higher than that of a conventional tire.

[0005] An object of the present invention is to provide a tire that can exhibit a breaking strength equivalent to that of a conventional tire when applied to an automobile. [Means for Solving the Problems]

[0006] A tire according to one aspect of the present invention is The tire comprises a pair of bead portions, each of which has a bead core, the bead core having a bead wire layer and a bead reinforcing layer positioned radially outward from the bead wire layer, the bead wire layer having a bead wire spirally wound around the tire rotation axis, the bead reinforcing layer having a plurality of reinforcing layers stacked in the radial direction of the tire, each of which contains carbon fibers oriented in a predetermined direction, and the bead reinforcing layer includes a cross reinforcing layer, which consists of two adjacent reinforcing layers in the radial direction of the tire, where the fiber directions of the carbon fibers contained in each of the two reinforcing layers intersect when viewed from the radial direction of the tire. [Effects of the Invention]

[0007] According to the present invention, when applied to an automobile, the tire can exhibit the same fracture strength as a conventional tire. [Brief explanation of the drawing]

[0008] [Figure 1] This is a partial end view showing the bead portion in the meridional cross-section of a tire according to the first embodiment. [Figure 2] This is an exploded view from the tire radial direction schematically showing the bead core according to the first embodiment. [Figure 3] This is a partial end view showing the bead portion in the meridional cross-section of a tire according to the second embodiment. [Figure 4] This is an exploded view from the tire radial direction schematically showing the bead core according to the second embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention relate to the following aspects.

[0010] [Aspect 1] Equipped with a pair of bead sections, Each of the pair of bead portions has a bead core, The bead core comprises a bead wire layer and a bead reinforcing layer positioned radially outward from the bead wire layer. The bead wire layer has bead wire that is wound spirally around the tire rotation axis, The bead reinforcement layer has a plurality of reinforcement layers stacked in the radial direction of the tire, Each of the aforementioned multiple reinforcing layers contains carbon fibers oriented in a predetermined direction. The bead reinforcing layer comprises two adjacent reinforcing layers in the tire radial direction, and includes a cross-reinforcing layer in which the fiber directions of the carbon fibers contained in each of the two reinforcing layers intersect when viewed from the tire radial direction. [Aspect 2] The tire according to embodiment 1, wherein at least one of the plurality of reinforcing layers has a carbon fiber direction that is aligned with the tire circumferential direction. [Aspect 3] The tire according to embodiment 1 or 2, wherein the angle between the fiber directions of the carbon fibers contained in each of the cross-reinforcement layers is 5° or more and 45° or less. [Aspect 4] The tire according to any one of embodiments 1 to 3, wherein the bead reinforcing layer has four or more reinforcing layers, and of the reinforcing layers adjacent in the tire radial direction, three or fewer reinforcing layers have the same fiber direction of carbon fibers. [Aspect 5] The bead reinforcement layer comprises, in order from the inside in the radial direction of the tire to the outside in the radial direction of the tire, a first reinforcement layer, a second reinforcement layer, multiple intermediate reinforcement layers, an outer reinforcement layer, and an outermost reinforcement layer. The tire according to any one of embodiments 1 to 4, wherein the fiber directions of the carbon fibers contained in each of the plurality of intermediate reinforcing layers adjacent to each other in the tire radial direction intersect when viewed from the tire radial direction. [Aspect 6] The tire according to any one of embodiments 1 to 5, wherein the thickness of each of the aforementioned multiple reinforcing layers is 0.3 mm or less. [Aspect 7] The tire according to any one of embodiments 1 to 6, wherein the plurality of reinforcing layers include a first reinforcing layer, a second reinforcing layer, a third reinforcing layer, and a fourth reinforcing layer. [Aspect 8] The plurality of reinforcing layers includes a first reinforcing layer, a second reinforcing layer, a third reinforcing layer, a fourth reinforcing layer, a fifth reinforcing layer, a sixth reinforcing layer, a seventh reinforcing layer, and an eighth reinforcing layer, and the tire according to any one of Aspects 1 to 6. [Aspect 9] The tire according to Aspect 7 or 8, wherein the fiber direction of the carbon fiber included in the first reinforcing layer is a direction along the tire circumferential direction.

[0011] (Definition) The tire radial direction refers to the direction orthogonal to the tire rotation axis. The inner side in the tire radial direction refers to the side facing the tire rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the circumferential direction with the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side in the tire width direction refers to the side facing the tire equatorial plane in the tire width direction, and the outer side in the tire width direction refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane refers to a plane that is orthogonal to the tire rotation axis and passes through the center of the tire width of the tire. "Along" with respect to a certain reference includes along a direction within a range of less than ±20°, less than ±10°, or less than ±5° with respect to a certain reference. "Center" includes the midpoint where the distances from two certain points are equal and the range of ±10% of the distance between the two points from the midpoint.

[0012] Similarly, in the following description, the standard rim refers to the "Applicable Rim" defined by JATMA, the "Design Rim" defined by TRA, or the "Measuring Rim" defined by ETRTO.

[0013] Similarly, in the following explanation, "normal internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO. Furthermore, "normal load" refers to the "maximum load capacity" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "LOAD CAPACITY" specified by ETRTO.

[0014] (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a partial end view showing only one side in the tire width direction of a pair of bead portions in the tire meridional cross-section of a tire according to the first embodiment. Figure 1 shows the tire portion in a state where it is mounted on a regular rim and regular internal pressure is applied, and in an unloaded state. The bead portion on one side in the tire width direction and the bead portion on the other side are symmetrical with respect to the tire equatorial plane and have the same basic configuration, so below we will describe one side in the tire width direction and omit the description of the other side.

[0015] The tire 10 of the first embodiment, although not shown in its entirety, has a meridional cross-sectional shape similar to that of a conventional pneumatic tire. That is, in a meridional cross-sectional view of the tire, the tire 10 of the first embodiment has a bead portion 12, a sidewall portion, a shoulder portion, and a tread portion, extending from the inside to the outside in the radial direction of the tire. Furthermore, the tire 10 has, for example, a carcass layer 16 that extends from the tread portion to the bead portions 12 on both sides in a meridional cross-sectional view and is wound around a pair of bead cores 14, and a belt layer and, optionally, a belt cover layer are provided on the radially outer side of the carcass layer 16.

[0016] Each pair of bead portions 12 has a bead core 14 and a bead filler 18. The bead filler 18 is provided on the radially outer side of the bead core 14.

[0017] The bead core 14 has a bead wire layer 20 and a bead reinforcement layer 22. The bead wire layer 20 has a bead wire 24 made of steel. The bead wire 24 is wound multiple times in a spiral shape around the tire rotation axis. While rotating around the tire rotation axis, the bead wire 24 moves parallel to the tire rotation axis by the length of the bead wire diameter and is wound multiple times, five times in the case of Figure 1. The bead wire 24 is a single winding that does not overlap with each other in the radial direction of the tire.

[0018] The length of the bead wire layer 20 in the tire width direction corresponds to the sum of the bead wire diameters according to the number of turns, which in Figure 1 corresponds to bead wire diameter × 5 (mm). The length of the bead wire layer 20 in the tire diameter direction corresponds to the bead wire diameter. The average diameter of the bead wire 24 is preferably 0.8 mm to 1.8 mm, more preferably 1.0 mm to 1.6 mm, and even more preferably 1.1 mm to 1.5 mm. The bead reinforcement layer 22 is positioned radially outward relative to the bead wire layer 20 and is in contact with the bead wire layer 20. The length of the bead reinforcement layer 22 in the tire width direction is the same as the length of the bead wire layer 20 in the width direction. Here, "same" includes a range of plus or minus 15% or less of the length of the bead wire layer 20 in the width direction.

[0019] The bead reinforcement layer 22 has multiple reinforcement layers 26. The reinforcement layers 26 are made of carbon fiber reinforced plastics (CFRP). Each reinforcement layer 26 contains a matrix resin and carbon fibers. The matrix resin is the base resin of the reinforcement layers 26. The matrix resin is not particularly limited, and various thermosetting resins and thermoplastic resins can be used. For example, thermosetting resins include epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, alkyd resins, thermosetting polyimides, cyanate ester resins, bismaleimide resins, vinyl ester resins, and mixtures of these resins may also be used. Furthermore, examples of thermoplastic resins include general-purpose resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile / styrene (AS) resin, acrylonitrile / butadiene / styrene (ABS) resin, methacrylic resin (PMMA, etc.), and thermoplastic epoxy resin; engineering plastics such as polyamide, polyacetal, polyethylene terephthalate, ultra-high molecular weight polyethylene, polycarbonate, and phenoxy resin; and super engineering plastics such as polyphenylene sulfide, polyether ether ketone, polyether ketone ketone, liquid crystal polymer, polytetrafluoroethylene, polyetherimide, polyarylate, and polyimide.

[0020] The carbon fibers are not particularly limited, and PAN-based and pitch-based carbon fibers obtained by calcining organic fibers derived from petroleum, coal, and coal tar, such as polyacrylonitrile, rayon, and pitch, or carbon fibers obtained by calcining organic fibers derived from wood and plant fibers can be used. The diameter and length of the carbon fibers are also not particularly limited. Carbon fibers with a diameter in the range of approximately 5 μm to 20 μm are preferably used, and those in the range of 5 μm to 10 μm are more preferably used. Long carbon fibers are preferably used, and their length is preferably 50 m or more, more preferably in the range of 100 m to 100,000 m, and even more preferably in the range of 100 m to 10,000 m.

[0021] The carbon fibers in the reinforcing layer 26 are aligned in the fiber direction. The fiber direction is the axial direction of the carbon fiber (the longitudinal direction of the fiber). The filling rate of carbon fibers in the reinforcing layer 26 may be, for example, 10% to 40% of the matrix resin, preferably 20% to 30%. The bead reinforcing layer 22 preferably includes one or more reinforcing layers in which the fiber direction of the carbon fibers relative to the tire circumferential direction is ±45° or less, ±30° or less, ±15° or less, ±10° or less, or ±5° or less.

[0022] Each reinforcing layer 26 is preferably 0.2 mm to 0.3 mm thick, and more preferably 0.22 mm to 2.8 mm thick. Generally, the thinner the carbon fiber composite material, the less likely delamination is to occur. By making the reinforcing layer 26 0.3 mm or less thick, the effect of the anisotropy of the carbon fibers can be obtained.

[0023] The bead reinforcement 22 shown in Figure 1 has a four-layer structure including four reinforcement layers 26, which are arranged in order from the inside radially of the tire to the outside radially of the tire: the first reinforcement layer 28, the second reinforcement layer 30, the third reinforcement layer 32, and the fourth reinforcement layer 34. In the following description, when the individual reinforcement layers are not distinguished, the first reinforcement layer 28, the second reinforcement layer 30, the third reinforcement layer 32, and the fourth reinforcement layer 34 are collectively referred to as the reinforcement layer 26.

[0024] The four-layer bead reinforcement layer 22 is configured to exhibit the same strength as a single-wound bead wire layer 20 having the same tire width direction length. In other words, the bead core 14 in Figure 1 can exhibit strength equivalent to that of a configuration with a double-wound bead wire 24 made of steel.

[0025] As shown in Figure 2, the bead reinforcement layer 22 has at least one cross reinforcement layer 36. The cross reinforcement layer 36 consists of two adjacent reinforcement layers 26 in the tire radial direction, where the fiber directions of the carbon fibers contained in each of the two reinforcement layers 26 intersect when viewed from the tire radial direction. That is, the cross reinforcement layer 36 is a combination of two reinforcement layers that are continuous in the thickness direction, where the fiber directions of the carbon fibers intersect when viewed from the tire radial direction. The angle between the fiber directions of the carbon fibers contained in the two reinforcement layers 26 constituting the cross reinforcement layer 36 is preferably 5° to 45°, and more preferably 10° to 40°. In Figure 2, the dashed line schematically shows the fiber direction of the carbon fibers.

[0026] In Figure 2, the bead reinforcement layer 22 has three intersecting reinforcement layers 36. Specifically, the bead reinforcement layer 22 has combinations consisting of a second reinforcement layer 30 and a third reinforcement layer 32, a first reinforcement layer 28 and a second reinforcement layer 30, and a third reinforcement layer 32 and a fourth reinforcement layer 34. In Figure 2, the combination of the second reinforcement layer 30 and the third reinforcement layer 32 is shown as a representative of the three intersecting reinforcement layers 36.

[0027] Preferably, at least one of the four reinforcing layers 26 has carbon fibers whose fiber direction is aligned with the tire circumferential direction. As shown in Figure 2, it is more preferable that the carbon fibers of the first reinforcing layer 28 have a fiber direction aligned with the tire circumferential direction. It is even more preferable that the carbon fibers of the first reinforcing layer 28 have a fiber direction of ±5° or less with respect to the tire circumferential direction, and most preferably that they are parallel to the tire circumferential direction.

[0028] The fiber direction of the carbon fibers in the second reinforcing layer 30 is a first direction, inclined toward one side of the tire width direction with respect to the tire circumferential direction. The fiber direction of the carbon fibers in the third reinforcing layer 32 is a second direction, inclined toward the other side of the tire width direction with respect to the tire circumferential direction. The fiber direction of the carbon fibers in the fourth reinforcing layer 34 is aligned with the tire width direction. The first and second directions differ in their orientation relative to the tire circumferential direction. Although the first and second directions differ in their orientation relative to the tire circumferential direction, their angles relative to the tire circumferential direction are of the same magnitude.

[0029] The tire 10 of this embodiment described above is obtained through the usual manufacturing processes, namely the mixing process of tire materials, the processing process of tire materials, the molding process of green tires, the vulcanization process, and the inspection process after vulcanization.

[0030] When manufacturing the tire 10 of this embodiment, the reinforcing layer 26 is formed using a prepreg. The prepreg is a sheet-like material containing carbon fibers and the uncured matrix resin impregnated into the carbon fibers. Multiple uncured reinforcing layers 26 are formed by shaping the prepreg into predetermined forms. Each of the multiple uncured reinforcing layers 26 is in the shape of a strip with a predetermined width. The carbon fibers of the multiple uncured reinforcing layers 26 have different fiber directions. In the molding process of the green tire, the uncured reinforcing layers 26 are laminated one by one by winding them around predetermined positions on the bead portion 12 using a so-called strip-wind method. In the vulcanization process, the prepreg is cured by heating under pressure, that is, the reinforcing layers 26 are cured, thereby obtaining a tire 10 in which a bead core 14, in which the bead wire layer 20 and the bead reinforcing layer 22 are integrated, is assembled.

[0031] The tire 10 of this embodiment is equipped with a bead core 14 in which a portion of the bead wire 24 is replaced with a bead reinforcement layer 22 made of carbon fiber reinforced material. Therefore, it can be made significantly lighter than conventional tires that are equipped with a bead core made of bead wire 24.

[0032] The bead reinforcement layer 22, by comprising at least one cross reinforcement layer 36, exhibits superior torsional strength, specifically lateral rigidity (lateral spring constant) of the tire. Therefore, when applied to an automobile, the tire 10 equipped with the bead reinforcement layer 22 can exhibit fracture strength equivalent to that of a conventional tire. Because the tire 10 has excellent lateral rigidity, superior handling stability can be obtained.

[0033] The tire 10 has superior fracture strength because at least one of the four reinforcing layers 26 has carbon fibers whose fiber direction is aligned with the tire's circumferential direction. In the bead reinforcing layer 22, the greatest force acts on the innermost part in the tire's radial direction. In the tire 10 according to this embodiment, the fracture strength of the bead reinforcing layer 22 can be more reliably improved because the carbon fibers of the first reinforcing layer 28 have a fiber direction aligned with the tire's circumferential direction.

[0034] The angle between the fiber directions of the carbon fibers contained in the two reinforcing layers 26 that constitute the cross-reinforcement layer 36 is between 5° and 45°. By having the angle between the fiber directions be greater than or equal to the lower limit of the above range, torsional strength is obtained. Furthermore, by having the angle between the fiber directions be less than or equal to the upper limit of the above range, separation of the reinforcing layers 26 in the tire width direction can be suppressed.

[0035] (Second Embodiment) A second embodiment of the present invention will be described with reference to Figures 3 and 4. Figure 3 is a partial end view showing only one side in the tire width direction of a pair of bead portions in the tire meridional cross-section of a tire according to the second embodiment. Figure 3 shows the tire portion in a state where it is mounted on a regular rim and regular internal pressure is applied, and in an unloaded state. In the above embodiment, the bead reinforcement layer was described as having a 4-layer structure, but the present invention is not limited to this, and may have an 8-layer structure as shown in Figure 3.

[0036] The tire 10A of the second embodiment has the same configuration as the first embodiment, except for the bead core. The second embodiment will be described with reference to Figure 3, which uses the same reference numerals as Figure 1 for the same configuration. The same configuration as the first embodiment will not be described.

[0037] The tire 10A shown in Figure 3 comprises a pair of bead portions 12A. Each pair of bead portions 12A has a bead core 14A and a bead filler 18. The bead core 14A comprises a bead wire layer 20 and a bead reinforcement layer 22A. The bead reinforcement layer 22A has an eight-layer structure including eight reinforcement layers 26, and in order from the inside radially of the tire to the outside radially of the tire, it has a first reinforcement layer 38, a second reinforcement layer 40, a third reinforcement layer 42, a fourth reinforcement layer 44, a fifth reinforcement layer 46, a sixth reinforcement layer 48, an outer reinforcement layer which is a seventh reinforcement layer 50, and an outermost reinforcement layer which is an eighth reinforcement layer 52.

[0038] As shown in Figure 4, the bead reinforcement layer 22A has at least one cross reinforcement layer 36. The angle between the respective fiber directions of the carbon fibers contained in the two reinforcement layers 26 constituting the cross reinforcement layer 36 is preferably 5° to 45°, and more preferably 10° to 40°. In Figure 4, the dashed line schematically indicates the fiber direction of the carbon fibers.

[0039] In Figure 4, the bead reinforcement layer 22A has three cross reinforcement layers 36. Specifically, the bead reinforcement layer 22A has a combination consisting of a second reinforcement layer 40 and a third reinforcement layer 42, a combination consisting of a fourth reinforcement layer 44 and a fifth reinforcement layer 46, and a combination consisting of a sixth reinforcement layer 48 and a seventh reinforcement layer 50. In Figure 4, the combination consisting of the fourth reinforcement layer 44 and the fifth reinforcement layer 46 is shown as representative of the three cross reinforcement layers 36. By having the cross reinforcement layers 36, the tire 10A can obtain the same effects as in the first embodiment described above.

[0040] The bead reinforcement layer 22A has an 8-layer structure and is configured to exhibit the same strength as a double-wound bead wire layer 20 having the same tire width direction length. In other words, the bead core 14A in Figure 3 can exhibit strength equivalent to a configuration in which a bead wire 24 made of steel is triple-wound.

[0041] Preferably, at least one of the eight reinforcing layers 26 has carbon fibers whose fiber direction is aligned with the tire circumferential direction. As shown in Figure 4, it is more preferable that the carbon fibers of the first reinforcing layer 38 have a fiber direction aligned with the tire circumferential direction. It is even more preferable that the carbon fibers of the first reinforcing layer 38 have a fiber direction of ±5° or less with respect to the tire circumferential direction, and most preferably that they are parallel to the tire circumferential direction.

[0042] As shown in Figure 4, it is preferable that the carbon fiber direction of the first reinforcing layer 38 and the second reinforcing layer 40, which are the two layers from the innermost in the tire radial direction, and the seventh reinforcing layer 50 and the eighth reinforcing layer 52, which are the two layers from the outermost in the tire radial direction, is aligned with the tire circumferential direction. In this case, it is preferable that the carbon fiber direction of the third reinforcing layer 42, the fourth reinforcing layer 44, the fifth reinforcing layer 46, and the sixth reinforcing layer 48, which are multiple intermediate reinforcing layers sandwiched between the four reinforcing layers 38, 40, 50, and 52, intersects with the first reinforcing layer 38, the second reinforcing layer 40, the seventh reinforcing layer 50, and the eighth reinforcing layer 52 when viewed from the tire radial direction. This provides better fracture strength against torsion.

[0043] In Figure 4, the carbon fiber direction of the third reinforcing layer 42 and the fourth reinforcing layer 44 is the first direction, while the fifth reinforcing layer 46 and the sixth reinforcing layer 48 are in the second direction. Note that if the carbon fiber direction of the third reinforcing layer 42 is the first direction, the carbon fiber direction of the fourth reinforcing layer 44 may be the third direction, which is different from the first direction. If the carbon fiber direction of the fifth reinforcing layer 46 is the second direction, the carbon fiber direction of the sixth reinforcing layer 48 may be the fourth direction, which is different from the second direction. Also, if the carbon fiber direction of the fourth reinforcing layer 44 is the first direction, the carbon fiber direction of the third reinforcing layer 42 may be the third direction, which is different from the first direction. If the carbon fiber direction of the sixth reinforcing layer 48 is the second direction, the carbon fiber direction of the fifth reinforcing layer 46 may be the fourth direction, which is different from the second direction.

[0044] In the thickness direction of the bead reinforcement layer 22A, it is preferable that there are three or fewer combinations of adjacent reinforcement layers 26 in which the carbon fiber direction is the same. In other words, it is preferable that there are three or fewer combinations of reinforcement layers 26 in which the carbon fiber direction is the same and the reinforcement layers are continuous in the thickness direction. In the case of Figure 4, the combinations of adjacent reinforcement layers 26 in the thickness direction in which the carbon fiber direction is the same are the first reinforcement layer 38 and the second reinforcement layer 40, the third reinforcement layer 42 and the fourth reinforcement layer 44, the fifth reinforcement layer 46 and the sixth reinforcement layer 48, and the seventh reinforcement layer 50 and the eighth reinforcement layer 52, each consisting of two layers. As a result, the anisotropy of the carbon fibers in the bead reinforcement layer 22A is suppressed, resulting in superior fracture strength when applied to an automobile.

[0045] (modified version) The present invention is not limited to the embodiments described above and can be modified as appropriate within the scope of the spirit of the invention.

[0046] For example, the bead reinforcement layer is not limited to a 4-layer or 8-layer structure; it may also have a structure with 5 to 7 layers, or even 9 or more layers of reinforcement.

[0047] In the above embodiment, the case in which the fiber direction of the carbon fibers of the first reinforcing layer is aligned with the tire circumferential direction was described, but the present invention is not limited to this. The bead reinforcing layer only needs to have the fiber direction of the carbon fibers of at least one of the multiple reinforcing layers aligned with the tire circumferential direction.

[0048] In the second embodiment described above, the case in which the reinforcing layer 26 includes four layers in which the carbon fibers have the same fiber direction was explained. That is, the bead reinforcing layer 22A has the same fiber direction for the carbon fibers of the first reinforcing layer, the second reinforcing layer, the seventh reinforcing layer, and the eighth reinforcing layer, but the present invention is not limited to this.

[0049] In the above embodiment, the first direction and the second direction have different orientations with respect to the tire circumferential direction, but the angles with respect to the tire circumferential direction are the same. However, the present invention is not limited to this, and the angles with respect to the tire circumferential direction may be different. [Examples]

[0050] This document describes the results of manufacturing a tire corresponding to the invention defined in the claims of this application and evaluating the fracture strength of the bead core.

[0051] (sample) Examples 1 to 14 were manufactured with a tire size of 185 / 65R15 88S (as defined by JATMA) and having the shape shown in Figure 1 when mounted on a rim. The detailed specifications of these tires are shown in Tables 1-1 and 1-2 below. In Tables 1-1 and 1-2, the columns for "First Fiber Layer (°)", "Second Fiber Layer (°)", "Third Fiber Layer (°)", "Fourth Fiber Layer (°)", "Fifth Fiber Layer (°)", "Sixth Fiber Layer (°)", "Seventh Fiber Layer (°)", and "Eighth Fiber Layer (°)" indicate the angle between the fiber direction of the carbon fibers contained in each fiber layer and the tire circumferential direction. The bead wire layer was formed using 1.2 mm diameter steel wire. The bead reinforcement layer used epoxy resin as the matrix resin and PAN-based carbon fibers. The carbon fibers had a diameter of 8 μm. The reinforcement layer contained 3600 to 14400 carbon fibers, had a thickness of 0.3 mm to 0.4 mm, and the carbon fiber weight was 2 g / cm³. 2 That was the case. The tires manufactured in this manner according to Examples 1 to 14 were evaluated by hydrostatic testing, and each test tire was mounted on a front-wheel-drive test vehicle (2000cc engine displacement) with an air pressure (F / R) of 230kPa / 230kPa, and the handling stability was evaluated according to the following procedure.

[0052] (Hydrostatic pressure test) Each test tire was mounted on a hydrostatic testing device, and the pressure inside the tire was increased to determine the fracture strength at which the bead ruptured. The evaluation results are shown as an index with Reference Example 1 set to 100. A higher index value indicates greater fracture strength of the bead. (Handling stability) A test vehicle with two occupants was used on a dry test course, and the handling stability was subjectively evaluated by test drivers at a speed of 100 km / h. The evaluation result was set as "3.0 (baseline)," and was scored on a 5-point scale from 0 to 5 points in 0.25-point increments. The result is shown as the average score of the five participants, excluding the highest and lowest scores. A higher score indicates superior handling stability.

[0053] [Table 1-1]

[0054] [Table 1-2]

[0055] Examples 1-14, with a single steel layer and a cross-reinforcement layer, achieved equivalent or better fracture strength and handling stability compared to Reference Example 1, which had a larger steel layer, while reducing bead mass. Compared to Reference Example 3, which did not have a cross-reinforcement layer, handling stability was improved. Reference Example 2, with three steel layers, achieved excellent fracture strength and handling stability, but the bead mass increased compared to the examples. Example 6, with a reinforcement layer thickness of 0.3 mm, achieved improved fracture strength and handling stability compared to Example 5 while reducing bead mass. Examples 7-14, with eight reinforcement layers, showed improved fracture strength and handling stability compared to Examples 1-6. Example 14, with a reinforcement layer thickness of 0.3 mm, achieved improved fracture strength and handling stability compared to Example 13 while reducing bead mass. [Explanation of symbols]

[0056] 10, 10A tires 12 Bead section 14, 14A bead core 16. Carcass layer 18 Bead Filler 20 Bead wire layers 22, 22A Bead reinforcement layer 24 Bead wire 26 Reinforcement layer 28. First Reinforcement Layer 30. Second Reinforcement Layer 32 Third Reinforcement Layer 34. Fourth reinforcement layer 36 Cross-reinforcement layer 38. First Reinforcement Layer 40. Second Reinforcement Layer 42. Third Reinforcement Layer 44. Fourth reinforcement layer 46. ​​Fifth Reinforcement Layer 48. Sixth Reinforcement Layer 50. Seventh Reinforcement Layer 52. 8th Reinforcement Layer

Claims

1. Equipped with a pair of bead sections, Each of the pair of bead portions has a bead core, The bead core comprises a bead wire layer and a bead reinforcing layer positioned radially outward from the bead wire layer. The bead wire layer has bead wire that is wound spirally around the tire rotation axis, The bead reinforcement layer has a plurality of reinforcement layers stacked in the radial direction of the tire, Each of the aforementioned multiple reinforcing layers contains carbon fibers oriented in a predetermined direction. The bead reinforcing layer comprises two adjacent reinforcing layers in the tire radial direction, and includes a cross-reinforcing layer in which the fiber directions of the carbon fibers contained in each of the two reinforcing layers intersect when viewed from the tire radial direction.

2. The tire according to claim 1, wherein at least one of the plurality of reinforcing layers has a carbon fiber direction that is aligned with the tire circumferential direction.

3. The tire according to claim 1, wherein the angle between the fiber directions of the carbon fibers contained in each of the cross-reinforcement layers is 5° or more and 45° or less.

4. The tire according to claim 1, wherein the bead reinforcing layer has four or more reinforcing layers, and of the reinforcing layers adjacent to each other in the radial direction of the tire, three or fewer reinforcing layers have the same fiber direction of carbon fibers.

5. The bead reinforcement layer comprises, in order from the inside in the radial direction of the tire to the outside in the radial direction of the tire, a first reinforcement layer, a second reinforcement layer, a plurality of intermediate reinforcement layers, an outer reinforcement layer, and an outermost reinforcement layer. The tire according to claim 1, wherein the fiber directions of the carbon fibers contained in each of the plurality of intermediate reinforcing layers adjacent to each other in the tire radial direction intersect when viewed from the tire radial direction.

6. The tire according to claim 1, wherein the thickness of each of the plurality of reinforcing layers is 0.3 mm or less.

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