pneumatic tires

Abstract

Pneumatic tires (1), comprising: a pair of bead cores (11), each formed by repeatedly wrapping a tire bead wire (111) in a ring-shaped form, wherein the bead cores (11) each have a wire arrangement structure in the form of a hexagon, which is formed by winding one or more of the tire bead wires (111) in a tightly packed manner in a cross-sectional view of each of the bead cores (11) in its radial direction, where the hexagon is a protruding hexagon with an obtuse interior angle at each vertex, wherein the vertex of the hexagon on a radially innermost side of each of the bead cores (11) is defined as the first vertex P1, wherein a side of the hexagon extending outwards in a tire transverse direction and enclosing the first vertex P1 is defined as a first side S12, wherein an axis parallel to the first side S12 of the hexagon is defined as an X-axis and an axis perpendicular to the X-axis is defined as a Y-axis, where a number of layers M of wire cross-sections in a Y-axis direction and a maximum value N_max of an arrangement number N of wire cross-sections in an X-axis direction have a ratio that satisfies 0.75 ≤ M / N_max ≤ 1.30, and wherein a distance A in the tire transverse direction from the vertex of the hexagon on the innermost side in the tire transverse direction to the center of gravity of the hexagon and a distance B in the tire transverse direction from the vertex of the hexagon on the outermost side in the tire transverse direction to the center of gravity of the hexagon have a ratio that satisfies 1.05 ≤ B / A.

Description

Technical field

[0001] The present invention relates to a pneumatic tire and in particular to a pneumatic tire which can effectively suppress a bead deformation and ensure the core collapse resistance of a bead core in a suitable manner. State of the art

[0002] Generally, there is a need to suppress bead deformation in heavy-duty tires mounted on trucks or buses. Bead deformation, as described above, is undesirable because it reduces the tire's ease of inflation and also makes the base tire unsuitable for retreading. The known technology described in patent documents JP 5071137 B2, JP H02-37003 A, and JP H02-286408 A involves heavy-duty tires designed with this problem in mind.

[0003] US 4 192 368 A reveals a pneumatic tire with asymmetrical bead cores. Brief description of the invention: Technical problem

[0004] To suppress the bead deformation described above, increasing the number of windings of tire bead wires forming a bead core is effective. Unfortunately, increasing the number of windings of tire bead wires causes a problem in that it increases the material costs of the bead cores and circumferential elements (e.g., a rubber material such as bead filler).

[0005] The present invention is made taking into account the foregoing and one objective thereof is to provide a pneumatic tire which can effectively suppress a bead deformation and ensure the core collapse resistance of a bead core in a suitable manner. Solution to the problem

[0006] To achieve the above-described objective, a pneumatic tire according to an embodiment of the present invention includes a pair of bead cores, each formed by repeatedly winding a tire bead wire in a ring-shaped form, wherein the bead cores each have a wire arrangement structure in the form of a hexagon formed by winding one or more of the tire bead wires in a tightly packed manner in a cross-sectional view of each of the bead cores in its radial direction, wherein the hexagon is a projecting hexagon with an obtuse internal angle at each vertex, wherein the vertex of the hexagon on a radially innermost side of each of the bead cores is defined as the first vertex P1, wherein a side of the hexagon extending outwards in a tire transverse direction and enclosing the first vertex P1 is defined as a first side S12.wherein an axis parallel to the first side S12 of the hexagon is defined as an X-axis, and an axis perpendicular to the X-axis is defined as a Y-axis, wherein a number of layers M of wire cross-sections in a Y-axis direction and a maximum value N_max of an arrangement N of wire cross-sections in an X-axis direction have a ratio that satisfies 0.75 ≤ M / N_max ≤ 1.30, and wherein a distance A in the tire transverse direction from the vertex of the hexagon on the innermost side in the tire transverse direction to the centroid of the hexagon and a distance B in the tire transverse direction from the vertex of the hexagon on the outermost side in the tire transverse direction to the centroid of the hexagon have a ratio that satisfies 1.05 ≤ B / A. Advantageous effects of the invention

[0007] In a pneumatic tire according to one embodiment of the invention, (1) the bead core is formed by winding the tire bead wires in a densely packed manner and has a wire arrangement structure in the form of a protruding hexagon with obtuse internal angles, so that an advantage is that the collapse resistance of the bead core is suitably ensured. In addition, (2) the wire arrangement structure of the bead core is optimized, so that an advantage is that the stroke deformation of the bead core can be effectively suppressed. Brief description of the drawings Fig. Figure 1 is a cross-sectional view in a tire meridional direction, showing a pneumatic tire according to an embodiment of the present invention. Fig. 2 is an enlarged cross-sectional view showing a bead section of the in Fig. 1 represents the pneumatic tire shown. Fig. 3 is an explanatory diagram showing a bead core of the in Fig. 2 represents the depicted bulge section. Fig. 4 is an explanatory diagram showing the bead core of the in Fig. 2 represents the depicted bulge section. Fig. 5 is an explanatory diagram showing a modified example of a wire arrangement structure of the in Fig. 3 represents the bead core shown. Fig. Figure 6 is an explanatory diagram showing a modified example of the wire arrangement structure of the [reference to diagram]. Fig. 3 represents the bead core shown. Fig. Figure 7 is an explanatory diagram showing a modified example of the wire arrangement structure of the [document / model]. Fig. 3 represents the bead core shown. Fig. Figure 8 is an explanatory diagram showing a modified example of the wire arrangement structure of the [reference to figure]. Fig. 3 represents the bead core shown. Fig. Figure 9 is a table showing the results of performance tests of pneumatic tires according to the embodiments of the present invention. Fig. Figure 10 is an explanatory diagram of the state of the art example 1, which is in Fig. 9 is shown. Fig. Figure 11 is an explanatory diagram of the example of the state of the art 2, which is in Fig. 9 is shown. Fig. Figure 12 is an explanatory diagram of comparative example 1, which is in Fig. 9 is shown. Fig. Figure 13 is an explanatory diagram of comparative example 2, which is in Fig. 9 is shown. Fig. Figure 14 is an explanatory diagram of comparative example 3, which is in Fig. 9 is shown. Fig. Figure 15 is an explanatory diagram of comparative example 4, which is in Fig. 9 is shown. Fig. Figure 16 is an explanatory diagram of comparative example 5, which is in Fig. 9 is shown. Fig. Figure 17 is an explanatory diagram of comparative example 6, which is in Fig. 9 is shown. Fig. Figure 18 is an explanatory diagram of comparative example 7, which is in Fig. 9 is shown. Fig. Figure 19 is an explanatory diagram of comparative example 8, which is in Fig. 9 is shown. Fig. Figure 20 is an explanatory diagram of comparative example 9, which is in Fig. 9 is shown. Fig. 21 is an explanatory diagram of comparative example 10, which is in Fig. 9 is shown. Fig. Figure 22 is an explanatory diagram of comparative example 11, which is in Fig. 9 is shown. Fig. Figure 23 is an explanatory diagram of comparative example 12, which is in Fig. 9 is shown. Description of embodiments

[0008] Embodiments of the present invention are described in detail below with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, components of the present embodiments include interchangeable elements that retain conformity with the invention, as well as obviously interchangeable elements. Moreover, the further developments described in the present embodiments can be combined arbitrarily within the scope of protection obvious to a person skilled in the art. pneumatic tires

[0009] Fig. Figure 1 is a cross-sectional view in a tire meridional direction, showing a pneumatic tire according to an embodiment of the present invention. The same drawing is a cross-sectional view showing half a section in a tire radial direction. Furthermore, the same drawing shows a heavy-duty radial tire, mounted on a truck, bus, and the like for long-distance transport, as an example of a pneumatic tire 1.

[0010] In Fig. 1. “Cross-section in a tire meridian direction” refers to a cross-section of the tire along a plane that includes the tire's axis of rotation (not shown). The reference symbol CL denotes the equatorial plane of the tire and refers to a plane perpendicular to the tire's axis of rotation, passing through the tire's center point in the direction of the tire's axis of rotation. “Tire lateral direction” refers to the direction parallel to the tire's axis of rotation. “Tire radial direction” refers to the direction perpendicular to the tire's axis of rotation.

[0011] The pneumatic tire 1 has a ring structure, the center of which is the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16 and a pair of rim pad rubbers 17, 17 (see Fig. 1).

[0012] The pair of bead cores 11, 11 each has an annular structure formed by repeatedly winding a steel tire bead wire in a circumferential direction and forms a core for the corresponding right and left bead sections. Each of the pair of bead fillers 12, 12 is formed from a lower filler 121 and an upper filler 122. Each of the pair of bead fillers 12, 12 is arranged outwards from the corresponding bead core 11, 11 in the radial direction of the tire and forms the corresponding bead section.

[0013] The carcass layer 13 extends in a toroidal shape between the left and right bead cores 11 and 12 and forms the supporting structure of the tire. Furthermore, both end sections of the carcass layer 13 are bent back from the inside out in the transverse direction of the tire so that they are wrapped and fixed around the bead cores 11 and the bead fillers 12. The carcass layer 13 is formed by a rolling process on carcass cord threads made of steel or an organic fiber material (e.g., nylon, polyester, rayon, or the like) that have been coated with coating rubber. The carcass layer 13 has a carcass angle (defined as an angle of inclination in the longitudinal direction of the carcass cord threads with respect to the tire's circumference) ranging from 85 degrees to 95 degrees.

[0014] The belt layer 14 is formed by layers of a large-angle belt 141, a pair of cross belts 142, 143, and a supplementary belt 144, arranged sequentially from the inside in the tire's radial direction, and is wound around the outer circumference of the carcass layer 13. The large-angle belt 141 is formed by rolling a multitude of steel belt cord threads coated with coating rubber. The large-angle belt 141 has a belt angle (defined as an angle of inclination in the longitudinal direction of the belt cord threads with respect to the tire's circumferential direction) ranging from 45 degrees to 70 degrees. The pair of cross belts 142, 143 are formed by rolling a multitude of steel belt cord threads coated with coating rubber.The cross belts 141 and 142 each have a belt angle ranging from 10 to 55 degrees. The pair of cross belts 142 and 143 each have belt angles with opposite signs and are layered, with the belt cord threads overlapping in one longitudinal direction (forming a so-called cross-layer structure). The supplementary belt 144 is formed by rolling a multitude of steel belt cord threads coated with rubber. The supplementary belt 144 has a belt angle ranging from 10 to 55 degrees. The belt angle of the supplementary belt 144 is set to the same sign as that of the belt angle of the cross belt 143 on one side of the outer diameter.

[0015] The tread rubber 15 is arranged radially outwards from the carcass layer 13 and the belt layer 14 and forms a tread section. Each of the pair of sidewall rubbers 16 is arranged transversely outwards from the carcass layer 13 and forms one of the left and right sidewall sections. Each of the pair of rim pad rubbers 17 is arranged radially inwards from the corresponding left and right tire bead cores 11 and a recurved section of the carcass layer 13. Each of the pair of rim pad rubbers 17 forms a contact surface with a rim flange of the corresponding left and right tire bead sections. bead core

[0016] Fig. 2 is an enlarged cross-sectional view showing a bead section of the in Fig. 1 represents the pneumatic tire 1. Fig. 3 and Fig. Figure 4 is each an explanatory diagram showing a bead core 11 of the in Fig. The bulge section shown in section 2 is depicted in these drawings. Fig. 2 shows a cross-sectional view of a bead section in a tire mounted on a rim, in a tire meridional direction, Fig. Figure 3 shows an enlarged view of a single bead core 11 in an unvulcanized state, and Fig. Figure 4 represents an arrangement state of the tire bead wires 111 in the Fig. 3 depicted bead core 11.

[0017] In Fig. 2 The bead core 11 has an annular structure formed by repeatedly wrapping one or more steel tire bead wires 111 around it, and it is embedded in each of the left and right bead sections to form a core therein. The annular structure of the bead core 11 has an axis aligned with a tire rotation axis. The bead core 11 is wrapped and held in the folded-back section of the carcass layer 13. The rim pad rubber 17 is arranged to cover an inner surface of the folded-back section of the carcass layer 13 in the tire radial direction to form a rim-fitting section of the bead section. In the structure of Fig. 2 is an end section of the carcass layer 13 bent back outwards in the tire transverse direction, wrapping around the bead core 11 and the bead filler 12, and extending to a position that exceeds a rim fitting section of the bead section. Additionally, a reinforcing layer 18 made of steel or an organic fiber material is arranged between the carcass layer 13 and the rim pad rubber 17 to surround the entirety of the bead core 11 along an outer circumferential surface of the bent-back section of the carcass layer 13.

[0018] As in Fig. As shown in Figure 2, the pneumatic tire 1 is mounted on a rim 10 by attaching the bead section to the rim 10. More precisely, a bead base section 101 of the rim 10 has a predetermined angle of inclination with respect to a tire rotation axis, and the rim mating surface of the bead section has a shape corresponding to an outer circumferential surface of the bead base section 101. When the tire is mounted on a given rim and inflated to the specified internal pressure without an applied load, a region of the rim mating surface from a bead tip Bt to a bead heel Bh comes into close contact with the outer circumferential surface of the bead base section 101, and a region extending from the bead tip Bt outwards in the tire transverse direction is attached to a rim flange section 102, which is formed on an outer edge section of the bead base section 101.This causes the bead section to be attached to the rim 10 to ensure that the tire is properly airtight.

[0019] "Specified rim" refers to an "applicable rim" as defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a "design rim" as defined by the Tire and Rim Association, Inc. (TRA), or a "measuring rim" as defined by the European Tyre and Rim Technical Organisation (ETRTO). "Specified inflation pressure" refers to a "maximum air pressure" as defined by JATMA, the maximum value in "tire load limits at various cold inflation pressures" as defined by the TRA, and "inflation pressures" as defined by the ETRTO.Furthermore, "specified load" refers to a "maximum load capacity" as defined by JATMA, the maximum value in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "LOAD CAPACITY" as defined by ETRTO. However, in the case of JATMA, the specified internal pressure for a passenger car tire is 180 kPa, and the specified load is 88% of the maximum load capacity.

[0020] Fig. Figure 3 shows a cross-sectional view of the bead core 11 itself in an unvulcanized state in the radial direction. The bead core 11 is formed by repeatedly winding the tire bead wire 111 in a ring-shaped form and has a predetermined wire arrangement structure, which is described below. More precisely, a core forming template (not shown) is used to wind one or more tire bead wires 111 around the core forming template with the predetermined wire arrangement structure to form the bead core 11 in an unvulcanized state. The bead core 11 also includes a bead cover 112 made of rubber material to cover an outer circumference of the wound tire bead wires 111. The formed bead core 11 is then pre-vulcanized prior to a vulcanization forming step of a raw tire.Furthermore, the bead core 11 can be integrated into a raw tire in an unvulcanized state by removing a pre-vulcanization of the bead core 11, and then a vulcanization forming step of the raw tire can be carried out.

[0021] As in Fig. As shown in Figure 4, the tire bead wires 111 each enclose a wire 1111 and an insulating rubber 1112 covering the wire 1111. The wire 1111 is made of steel, as described above. The insulating rubber 1112 preferably consists of a rubber compound with a Mooney viscosity of 70 M or higher. Additionally, a heavy-duty tire for a truck and a bus encloses the tire bead wire 111 with an outer diameter ranging from 1.70 mm to 2.20 mm. The Mooney viscosity is determined according to JIS K6300-1:2013.

[0022] Bead Core Wire Arrangement Structure: In general, heavy-duty tires, each mounted on a truck or bus, have a problem: bead core deformation during vehicle travel must be suppressed. The bead core deformation described above is undesirable because it reduces the tire's ease of inflation and also compromises the suitability of a base tire for retreading. To suppress the bead core deformation described above, increasing the number of windings of tire bead wires forming a bead core is effective. Unfortunately, increasing the number of windings of tire bead wires also causes a problem: it increases the material costs of the bead cores and peripheral elements (e.g., a rubber material such as bead filler).

[0023] Therefore, the pneumatic tire 1 uses the following configuration to effectively suppress bead deformation during lifting and to ensure appropriate core collapse resistance of the bead core 11.

[0024] In other words, as in Fig. As shown in Figure 3, the bead core 11 has a hexagonal wire arrangement structure formed by winding the tire bead wires 111 in a tightly packed state in a cross-sectional view in the radial direction thereof.

[0025] As in Fig. As shown in Figure 4, the densely packed state in a cross-sectional view in the radial direction of the bead core 11 refers to a state in which one wire cross-section is adjacent to six wire cross-sections arranged around that single wire cross-section at intervals of approximately 60 degrees. In the densely packed wire arrangement as described above, the density of wire cross-section placement in the bead core 11 is increased more than in a lattice-like wire arrangement where rows of wire cross-sections are vertically and horizontally perpendicular to each other, thus improving the core collapse resistance of the bead core 11. In the densely packed arrangement described above, each pair of adjacent wire cross-sections need not be in contact with each other, and some pairs may each be arranged with a small gap “g”, as described below.

[0026] As in Fig. As shown in Figure 3, the shape of the wire arrangement structure is defined as a graphic obtained by connecting the midpoint of each of the wire cross-sections that form an outer circumferential surface of the bead core 11. A vertex of the graphic is also defined by the midpoint of one of the wire cross-sections. Each side of the graphic is defined by the midpoints of two or more of the wire cross-sections. However, the midpoints of the wire cross-sections that represent a side of the graphic need not be strictly on a straight line and may be arranged with a small positional displacement due to a manufacturing defect or the like. In the structure of Fig. 3 is the wire arrangement structure in the form of a hexagon with six vertices P1 to P6.

[0027] The hexagon of the wire arrangement structure is a protruding hexagon with vertices that each have an obtuse interior angle. That is, all interior angles of the hexagon lie in the range between 90 degrees and 180 degrees. The wire arrangement structure in the form of a protruding hexagon, as described above, exhibits high dimensional stability of the bead core 11 compared to a wire arrangement structure in the form of a recessed hexagon (see below). Fig. 10) with an inwardly projecting apex, so that the core collapse resistance of the bead core 11 is adequately ensured. The wire arrangement structure in the form of a hexagon with obtuse interior angles also exhibits a higher core collapse resistance of the bead core 11 than a wire arrangement structure in the form of a polygon with an acute interior angle.

[0028] For example, the tire bead wires 111 are used in the structure of Fig. 3. Each is a steel wire with a circular cross-section and constant outer diameter, and the wire cross-sections are arranged in the densely packed manner described above. Therefore, all interior angles of the hexagon are approximately 120 degrees, and especially in the range between 105 degrees and 135 degrees.

[0029] In Fig. 3 is defined as the first vertex P1 of the hexagon on the radially innermost side of the bead core 11. The hexagon has a side S12 that encloses the first vertex P1 and extends outwards in the tire transverse direction, and which is defined as a first side. Furthermore, an axis parallel to the first side S12 of the hexagon is defined as an X-axis, and an axis perpendicular to the X-axis is defined as a Y-axis. The rim mating surface of the bead section is inclined (see Fig. 2), so that the X-axis tilts outwards in the tire radial direction towards the outside in the tire transverse direction.

[0030] At this point, the number of layers M of wire cross-sections in the Y-axis direction and the maximum value N_max of an arrangement N of wire cross-sections preferably have the following ratio: 0.75 ≤ M / N_max ≤ 1.30, and more preferably the following ratio: 0.95 ≤ M / N_max ≤ 1.20. As a result, an aspect ratio of the bead core 11 is optimized. In other words, the lower limit of M / N_max described above prevents the bead core 11 from being excessively enlarged in width, thus reducing the material costs of the bead core 11 and the circumferential elements (in particular the bead filler 12). Furthermore, the upper limit of M / N_max described above prevents the bead core 11 from being vertically enlarged in length in the Y-axis direction, thus ensuring the torsional stiffness of the bead core 11 in a suitable manner.In a heavy-duty lane for a truck and a bus, the maximum value N_max of the number N of wire cross-sections arranged in the X-axis direction lies in the following range: 7 ≤ N_max ≤ 13.

[0031] If a series of wire cross-sections arranged in the X-axis direction along the first side S12 of the hexagon is shown as an innermost layer, the layer number M of wire cross-sections is defined as the number of layers of wire cross-sections stacked on the innermost layer in a densely packed manner in the Y-axis direction.

[0032] The number of wire cross-sections N in arrangement is defined as the number of wire cross-sections that each of the layers of wire cross-sections forms.

[0033] For example, in the structure of Fig. 3. A single tire bead wire 111 is wound spirally in the X-axis direction to form a layer of wire cross-sections. The single tire bead wire 111 is also wound back and forth in the X-axis direction to form a plurality of layers of wire cross-sections. First, a layer of wire cross-sections is formed on the first side S12 of the hexagon to serve as the innermost layer, and a plurality of layers of wire cross-sections are stacked in the Y-axis direction to form the bead core 11. This causes each of three pairs of opposite sides S12 and S45; S23 and S56; and S34 and S61, of the hexagon to be parallel to each other. Additionally, the ratio M / N_max, i.e., the ratio of the number of layers M of wire cross-sections to the maximum value N_max of the number of arrangements N thereof, is as follows: M / N_max = 8 / 8 = 1.00.In the structure described above, the layer of wire cross-section is layered in a direction perpendicular to the bead base section 101 of the rim 10, so that the bead core 11 has increased strength to improve the mounting of the tire on the rim.

[0034] In Fig. 3. A distance A in the tire transverse direction from the vertex P6 of the hexagon on the innermost side in the tire transverse direction to the centroid G of the hexagon, and a distance B in the tire transverse direction from the vertex P3 of the hexagon on the outermost side in the tire transverse direction to the centroid G of the hexagon, preferably in the ratio 1.05 ≤ B / A, and more preferably in the ratio 1.06 ≤ B / A. This results in the centroid G of the hexagon, i.e., the centroid position of the bead core 11, being optimized. In other words, the centroid of the bead core 11 is shifted towards the bead tip due to the lower limit of the ratio B / A (see Fig. 2) As a result, when the tire is inflated, and the tension from the carcass layer 13 acts on the bead core 11, the tension is appropriately held by the bead core 11. This suppresses any lifting deformation of the bead core Bt. For example, in the structure of Fig. 3. The ratio B / A of the distances A and B in the tire transverse direction described above is as follows: B / A = 1.07. While the upper limit of B / A is not particularly restricted, it is subject to limitations due to conditions of the interior angle of the hexagon and the ratio M / N_max, as described above.

[0035] The centroid G of the hexagon is calculated by an arithmetic mean of the coordinates of the respective vertices P1 to P6 of the hexagon.

[0036] Distances A and B are measured when a manufactured tire is mounted on a specific rim and inflated to 5% of its specified internal pressure in an unloaded state. The tire shape at 5% of the specified internal pressure most closely resembles the tire shape in a tire vulcanization mold, i.e., the natural tire shape before inflation.

[0037] As in Fig. As shown in Figure 4, the tire bead wire 111 is wound spirally with a predetermined pitch in the X-axis direction, such that a small gap g may form between adjacent wire cross-sections in the X-axis direction due to a manufacturing defect. A smaller gap g is preferred because it increases the strength of the bead core 11. In particular, the gap g is preferably in the following range: g ≤ 0.08 mm. The gap g and an intercord spacing D1 between wire cross-sections that are adjacent to each other in the X-axis direction preferably have a ratio of 0.020 ≤ g / D1 ≤ 0.045.

[0038] Meanwhile, the tire bead wire 111 is wound under tension, so that the wire cross-sections are compressed in the Y-axis direction to press the insulating rubber 1112 into wire cross-sections that are adjacent to each other in the Y-axis direction. Thus, the intercord spacing D1 between the wire cross-sections that are adjacent to each other in the X-axis direction and the intercord spacing D2 between the wire cross-sections that are adjacent to each other in the Y-axis direction have the ratio D2 < D1. In the bead core 11, one wire cross-section is supported by two wire cross-sections in the Y-axis direction. As a result, the strength of the bead core 11 in the Y-axis direction, i.e., its radial strength, can be improved.

[0039] As in Fig. As shown in Figure 3, the layer of wire cross-sections arranged in the X-axis direction along the first side S12 of the hexagon, i.e., the innermost layer in the Y-axis direction, is inclined at a predetermined angle θ relative to the tire's transverse direction. This causes the inner diameter of the bead core 11 to increase outwards from the first vertex P1 of the hexagon in the tire's transverse direction. The angle θ is set such that the bead core 11 is parallel to the outer circumferential surface of the bead base section 101 (see Figure 3). Fig. 2) of the rim 10 when the tire is mounted on the rim. In a typical heavy-duty tire, the inclination angle θ is set to 15 degrees. When the tire is mounted on the rim, the innermost layer is therefore oriented in the Y-axis direction of the bead core 11 towards the bead base section 101 to efficiently improve the mounting of the bead section on the rim.

[0040] The in Fig. The structure shown in Figure 3 is formed such that one side S23 of the hexagon is parallel to the outer circumferential surface of the rim horn section 102 (see Figure 3). Fig. 2) of the rim 10 when the tire is mounted on the rim. When the tire is mounted on the rim, an end face of the bead core 11 is consequently facing the rim flange section 102 in the transverse direction of the tire in order to efficiently improve the attachment of the bead section to the rim.

[0041] In Fig. 3 It is preferred that the arrangement numbers N12 and N45; N23 and N56; and N34 and N61 of the wire cross-sections in the corresponding three pairs of opposite sides S12 and S45; S23 and S56; and S34 and S61 of the hexagon satisfy the condition as follows: 2 ≤ N12 - N45 = N34 - N61 = N56 - N23 ≤ 3. In other words, the wire arrangement structure in a structure in which wire cross-sections, each having the same diameter, in the form of a protruding hexagon in a densely packed manner (see Fig. 4) are arranged, preferably one of the following conditions: (1) N12 - N45 = N34 - N61 = N56 - N23 = 2; and (2) N12 - N45 = N34 - N61 = N56 - N23 = 3.

[0042] The arrangement numbers N12 to N61 of the wire cross-sections are defined as the number of wire cross-sections including the corresponding vertices P1 to P6 of the hexagon. For example, the structure of Fig. 3 the condition as follows: N12 - N45 = N34 - N61 = N56 - N23 = 2, where N12 = 6, N23 = 3, N34 = 6, N45 = 4, N56 = 5, and N61 = 4.

[0043] In the structure described above, the number of wire cross-sections N12 in the innermost layer in the Y-axis direction (the first side S12 of the hexagon) is greater than the number of wire cross-sections N45 in the outermost layer (the side S45 of the hexagon). As a result, the bead core 11 has a shape with a flared inner circumferential surface. Additionally, the number of wire cross-sections N23 and N61 on the corresponding two sides S23 and S61 adjacent to the innermost layer in the Y-axis direction are each less than the number of wire cross-sections N56 and N34 on the corresponding opposite sides S56 and S34. As a result, the bead core 11 has a shape with flared sides (sides S34 and S56 of the hexagon) on its outer circumferential surface. This increases the strength efficiency of the bead core 11.

[0044] The following condition: N12 - N45 = N34 - N61 = N56 - N23 = 2 is satisfied, so that the center of gravity G of the bead core 11 is shifted in the direction of the bead tip Bt in a suitable manner to ensure a suppression effect against any lifting deformation of the bead tip Bt. Furthermore, the following condition: N12 - N45 = N34 - N61 = N56 - N23 = 3 is satisfied, so that an increase in material costs of the circumferential elements of the bead core 11 is suppressed.

[0045] The number N12 of wire cross-sections arranged on the first side S12 of the hexagon is preferably in the following range: 5 ≤ N12 ≤ 8, and more preferably in the following range: 6 ≤ N12 ≤ 7. As a result, a length of side S12 corresponding to the bead base section 101 (see Fig. 2) opposite, in a suitable manner to ensure the effect of the reinforcement fitting on the rim using the bead core 11 in a suitable manner.

[0046] The number N23 of wire cross-sections arranged on side S23 in the tire transverse direction, adjacent to the first side S12 of the hexagon, is preferably in the following range: 2 ≤ N23 ≤ 5, and more preferably in the following range: 3 ≤ N23 ≤ 4. The side S23 opposite the rim flange section 102 of the rim 10 (see Fig. 2) It absorbs a large reaction force acting from the rim flange section 102, so that the bead core 11 tends to collapse slightly on the rim. Thus, if the number N23 of wire cross-sections at this position is appropriately ensured, the bead core 11 is effectively prevented from collapsing on the rim.

[0047] The number of wire cross-sections N23 arranged on side S23 in the outward direction of the tire, adjacent to the first side S12 of the hexagon, and the number of wire cross-sections N61 arranged on the inward direction of the tire, adjacent to it, preferably have a ratio of 1 ≤ N61 - N23, and more preferably a ratio of 2 ≤ N61 - N23. Thus, in a region radially inward from the bead core 11 in the Y-axis direction, side S23, which corresponds to the rim flange section 102 (see Fig. 2) opposite rim 10, shorter than side S61 on a bead point Bt-side. This allows the center of gravity G of the hexagon to be efficiently shifted towards bead point Bt. While the upper limit of a difference between N61 and N23 is not particularly restricted, it is subject to limitations imposed by the interior angle of the hexagon and the ratio M / N_max, as described above.

[0048] As described above, the number of wire cross-sections arranged on the respective opposite sides of the hexagon fulfills the ratio N34 - N61 = N56 - N23. If the number of wire cross-sections arranged N23 and N61 on the corresponding sides S23 and S61 in the area radially inward from the bead core 11 in the Y-axis direction thus fulfills the condition described above as follows: 1 ≤ N61 - N23, then the number of wire cross-sections arranged N34 on side S34 in the outward direction of the tire, which borders the outermost side S45 in the Y-axis direction of the hexagon, and the number of wire cross-sections arranged N56 on side S56 in the inward direction of the tire, have the ratio 1 ≤ N34 - N56.

[0049] The number of wire cross-sections N12 arranged on the first side S12 of the hexagon and the maximum value N_max of the number of wire cross-sections arranged N in the X-axis direction must, as a further requirement, have the ratio 1 ≤ N_max - N12, and preferably the ratio 2 ≤ N_max - N12. This allows the position of the center of gravity G of the hexagon to be efficiently shifted towards the bulge Bt.

[0050] Furthermore, the difference in the number N of wire cross-sections in all layers adjacent to each other in the Y-axis direction is -1, 0, or 1. In other words, the wire arrangement structure of the bead core 11 is designed such that an increase or decrease in the number of turns of the tire bead wire 111 occurs at most once in the Y-axis direction. This improves the dimensional stability of the wire arrangement structure, thus improving the collapse resistance of the bead core 11 on a rim.

[0051] As in Fig. As shown in Figure 3, the hexagonal center of gravity G is preferably positioned radially inwards in the Y-axis direction from a central position Yc of the bead core 11 in the Y-axis direction. This improves the dimensional stability of the wire arrangement structure, thus improving the collapse resistance of the bead core 11 on a rim.

[0052] The conditions imposed on the wire arrangement structure of the bead core 11, as described above, can be sufficiently fulfilled in an area of ​​50% or more of the bead core 11 in the circumferential direction of the tire, and in particular in a large part of an area with the exception of an outgoing winding end and a terminal winding end of the tire bead wire 11. Modified examples

[0053] Fig. Figures 5 to 8 are each an explanatory diagram of a modified example of the wire arrangement structure of the [reference to be added]. Fig. 3 depicted bead core 11. These drawings each represent an enlarged view of a single bead core 11 in an unvulcanized state.

[0054] The wire arrangement of the bead core 11 is not based on the one in Fig. The structure shown in section 3 is limited and can be modified accordingly within the area that meets the conditions described above.

[0055] For example, in the example of Fig. 5 a wire arrangement structure of a bead core 11 a projecting hexagon with an obtuse interior angle, wherein a ratio M / N_max, i.e. a ratio of a number of layers M of wire cross-sections in the Y-axis direction to a maximum value N_max of an arrangement number N of wire cross-sections in the X-axis direction, is as follows: M / N_max = 1. 14, and a ratio B / A of a distance A in a tire transverse direction from a vertex P6 of the hexagon on the innermost side in the tire transverse direction to the centroid G of the hexagon, and of a distance B in the tire transverse direction from a vertex P3 of the hexagon on the outermost side in the tire transverse direction to the centroid G of the hexagon, is as follows: B / A = 1.09. Additionally, the arrangement numbers N12 to N61 of the wire cross-sections on the corresponding sides S12 to S61 of the hexagon fulfill the following: N12 - N45 = N34 - N61 = N56 - N23 = 2, where N12 = 6, N23 = 2, N34 = 7, N45 = 4, N56 = 4, and N61 = 5.

[0056] In the example of Fig. 6 is a wire arrangement structure of a bead core 11 a projecting hexagon with an obtuse interior angle, wherein a ratio M / N_max is as follows: M / N_max = 1.29, wherein a ratio B / A is as follows: B / A = 1.08, and arrangement numbers N12 to N61 of the wire cross sections satisfy the following: N12 - N45 = N34 - N61 = N56 - N23 = 2, wherein N12 = 5, N23 = 3, N34 = 7, N45 = 3, N56 = 5, and N61 = 5.

[0057] In the example of Fig. 7 is a wire arrangement structure of a bead core 11 a projecting hexagon with an obtuse interior angle, wherein a ratio M / N_max is as follows: M / N_max = 1.13, wherein a ratio B / A is as follows: B / A = 1.12, and arrangement numbers N12 to N61 of the wire cross-sections satisfy the following: N12 - N45 = N34 - N61 = N56 - N23 = 3, where N12 = 6, N23 = 3, N34 = 7, N45 = 3, N56 = 6, and N61 = 4.

[0058] In the example of Fig. Figure 8 is a wire arrangement structure of a bead core 11, a projecting hexagon with an obtuse interior angle, wherein a ratio M / N_max is as follows: M / N_max = 1.00, wherein a ratio B / A is as follows: B / A = 1.13, and arrangement numbers N12 to N61 of the wire cross-sections satisfy the following: N12 - N45 = N34 - N61 = N56 - N23 = 3, where N12 = 6, N23 = 2, N34 = 6, N45 = 3, N56 = 5, and N61 = 3. In the example of Fig. 8. A tire bead wire 111 has a small total number of turns and a suppression effect of a lifting deformation of a bead heel Bt is less than that of the example of Fig. 3. But the example of Fig. 8 exhibits a higher strength efficiency, as described below, than a wire arrangement structure with a total number of turns of the tire bead wire 111 in the same plane, such that a stroke deformation of the bead section Bt can be effectively suppressed. Effects

[0059] As described above, the pneumatic tire 1 encloses the pair of bead cores 11, each formed by repeatedly wrapping the tire bead wire 111 in a ring-shaped form (see Fig. 3) In a cross-sectional view of the bead core 11, the wire arrangement structure in the radial direction has the form of a hexagon, which is formed by winding one or more tire bead wires 111 in a tightly packed manner (see Fig. 4) The hexagon is a projecting hexagon with an obtuse interior angle at each vertex. Furthermore, the number of layers M of wire cross-sections in the Y-axis direction and the maximum value N_max of the number of arrangements N of wire cross-sections in the X-axis direction have a ratio of 0.75 ≤ M / N_max ≤ 1.30. Additionally, the distance A in the tire transverse direction from vertex P6 of the hexagon on the innermost side in the tire transverse direction to the centroid G of the hexagon, and the distance B in the tire transverse direction from vertex P3 of the hexagon on the outermost side in the tire transverse direction to the centroid G of the hexagon, have a ratio of 1.05 ≤ B / A.

[0060] In the structure described above, (1) the bead core 11 has the wire arrangement structure in the form of a protruding hexagon, which is formed by winding the tire bead wire 111 in a tightly packed manner (see Fig. 4) is formed with an obtuse internal angle, so that an advantage is that the dimensional stability of the bead core 11 is high and the core collapse resistance of the bead core 11 is higher compared to a wire arrangement structure in the form of a recessed hexagon (see below described Fig. 10), for example, with an inwardly projecting apex, is ensured in a suitable manner. Furthermore (2) an advantage is that the aspect ratio M / N_max of the bead core 11 is optimized, the material costs of the bead core 11 and the circumferential elements (in particular the bead filler 12) are reduced, and the torsional stiffness of the bead core 11 is ensured in a suitable manner. (3) an advantage is further enhanced by the optimization of the displacement of the center of gravity of the bead core 11 due to the ratio B / A, in order to suppress stroke deformation of the bead stem Bt in a suitable manner.

[0061] The pneumatic tire 1 encloses the pair of bead cores 11, each formed by repeatedly wrapping the tire bead wire 111 in a ring-shaped form (see Fig. 3) In a cross-sectional view, the bead core 11 has a wire arrangement structure in the radial direction in the form of a hexagon, formed by winding one or more tire bead wires 111 in a tightly packed manner. The hexagon is a protruding hexagon with an obtuse interior angle at each vertex. Furthermore, the arrangement numbers N12 and N45; N23 and N56; and N34 and N61 of the wire cross-sections in the corresponding three pairs of opposite sides S12 and S45; S23 and S56; and S34 and S61 of the hexagon satisfy the following condition: 2 ≤ N12 - N45 = N34 - N61 = N56 - N23 ≤ 3.

[0062] In the structure described above, (1) the bead core 11 has the wire arrangement structure in the form of a protruding hexagon, which is formed by winding the tire bead wire 111 in a tightly packed manner (see Fig. 4) is formed with an obtuse internal angle, so that an advantage is that the dimensional stability of the bead core 11 is high and the core collapse resistance of the bead core 11 is higher compared with a wire arrangement structure in the form of a recessed hexagon (see below described Fig. 10), for example, with an inwardly projecting apex, is appropriately ensured. Furthermore, if (2) the three pairs of opposite sides S12 and S45; S23 and S56; and S34 and S61 of the hexagon satisfy the condition as described above, an advantage is that the hexagonal shape of the wire arrangement structure is optimized to increase the strength efficiency of the bead core 11, and the center of gravity G of the bead core 11 is appropriately shifted towards the bead point Bt to ensure the suppression of the stroke deformation of the bead point Bt.

[0063] The pneumatic tire 1 is configured such that the number of layers M of wire cross-sections in the Y-axis direction and the maximum value N_max of the number of arrangements N of wire cross-sections in the X-axis direction have the ratio 0.75 ≤ M / N_max ≤ 1.30 (see Fig. 3) Therefore, an advantage is that the aspect ratio M / N_max of the bead core 11 is optimized, the material costs of the bead core 11 and the circumferential elements (especially the bead filler 12) are reduced, and the torsional stiffness of the bead core 11 is ensured in a suitable manner.

[0064] In pneumatic tire 1, all interior angles of the hexagon lie within the range of 105 degrees to 135 degrees (see Fig. 3) Therefore, an advantage is that the wire cross-sections of the bead core 11 are arranged in a densely packed manner in a suitable way to ensure the core collapse resistance of the bead core 11 in a suitable way.

[0065] The pneumatic tire 1 is configured such that the tire bead wire 11 is wound spirally in the X-axis direction to form a layer of wire cross-sections, and a plurality of the layers of wire cross-sections are stacked in the Y-axis direction on the first side S12 of the hexagon, which serves as an innermost layer, to form the bead core 11 (see Fig. 3) In the structure described above, the layers of the wire cross-section are layered in a direction perpendicular to the bead base section 101 of the rim 10, so that one advantage is that the strength of the bead core 11 is increased to improve the mounting of the tire on the rim.

[0066] The pneumatic tire 1 also includes the bead core 11, which has the wire arrangement structure in the form of a hexagon formed by winding a tire bead wire 11 in a tightly packed manner (see Fig. 3) Therefore, an advantage is that the placement density of the wire cross-sections of the bead core 11 is increased in order to improve the core collapse resistance of the bead core 11.

[0067] The pneumatic tire 1 is also configured such that the number of arrangements N12 of the wire cross-sections on the first side S12 of the hexagon lies in the following range: 5 ≤ N12 (see Fig. 3) Therefore, an advantage is that the length of side S12, which corresponds to the bead base section 101 (see Fig. 2) is opposite, is ensured in a suitable manner and the effect of the reinforcement fitting on the rim is ensured in a suitable manner using the bead core 11.

[0068] The pneumatic tire 1 is also configured such that the number of wire cross-sections N23 arranged on side S23 in the tire transverse direction adjacent to the first side S12 of the hexagon lies in the following range: 2 ≤ N23 (see Fig. 3) Therefore, one advantage is that it effectively prevents the bead core 11 from collapsing on the rim.

[0069] The pneumatic tire 1 is also configured such that the number of wire cross-sections N23 arranged on side S23 in the tire transverse direction outwards, adjacent to the first side S12 of the hexagon, and the number of wire cross-sections N61 arranged on side S61 in the tire transverse direction inwards, adjacent to it, have the ratio 1 ≤ N61 - N23 (see Fig. 3) Therefore, one advantage is that the center of gravity G of the hexagon can be efficiently shifted towards the bulge Bt.

[0070] The pneumatic tire 1 is also configured such that the number of arrangements N12 of the wire cross-sections on the first side S12 of the hexagon and the maximum value N_max of the number of arrangements N of the wire cross-sections in the X-axis direction have the ratio 1 ≤ N_max - N12 (see Fig. 3) Therefore, one advantage is that the center of gravity G of the hexagon can be efficiently shifted towards the bulge Bt.

[0071] The pneumatic tire 1 is also configured such that the difference in the number of arrangements N of the wire cross-sections in all layers adjacent to each other in the Y-axis direction is -1, 0 or 1 (see Fig. 3) Therefore, an advantage is that the dimensional stability of the wire arrangement structure is improved and the collapse resistance of the bead core 11 on a rim is improved.

[0072] The pneumatic tire 1 is also configured such that the center of gravity G of the hexagon is positioned inwards in the Y-axis direction of the layer of the tire bead wire 111, which is positioned in the middle in the Y-axis direction of the bead core 11 (see Fig. 3) Therefore, an advantage is that the dimensional stability of the wire arrangement structure is improved and the collapse resistance of the bead core 11 on a rim is improved.

[0073] The pneumatic tire 1 also includes the carcass layer 13, which extends between the pair of bead cores 11, 11 (see Fig. 2) Furthermore, both end sections of the carcass layer 13 are bent back outwards in the tire transverse direction so that they are wrapped around the corresponding bead cores 11 and fixed (see Fig. 2) In the carcass structure described above, it is less likely that bead core deformation due to stress from the carcass layer 13 will occur. Thus, when a tire with the carcass structure described above is used, an advantage is that the suppression of bead core deformation due to the wire arrangement structure of the bead core 11, as described above, can be efficiently achieved. Examples

[0074] Fig. Figure 9 is a table showing the results of performance tests of pneumatic tires according to the embodiments of the present invention. Fig. Examples 10 to 23 represent examples 1 and 2 of the prior art and comparative examples 1 to 12, which are presented in Fig. 9 will be shown.

[0075] In the performance tests, a variety of test tire types were evaluated for the following characteristics: (1) toe deformation resistance; (2) strength efficiency; and (3) low cost. Pneumatic tires, each with a tire size of 275 / 70R22.5, were then mounted on standard rims specified by JATMA, and 75% of the JATMA-specified inflation pressure and 140% of the JATMA-specified load were applied to each tire. The test tires were mounted on the test vehicle in a 6x2 track for all wheels.

[0076] (1) Toe deformation resistance was assessed by performing a low-pressure resistance test using an internal drum testing machine. Then, the extent of stroke deformation in a bead toe section of each test tire was measured after driving a distance of 40,000 km, and the measurement results are expressed and evaluated as index values, with prior art example 1 assigned as the reference (100). Higher values ​​are to be preferred in this evaluation.

[0077] (2) The strength efficiency was assessed by calculating a ratio of the inverse of the extent of any stroke deformation in the bead toe section, as measured in (1) above, to the total number of wraps of tire bead wire in a bead core, and the calculated values ​​are expressed and evaluated as index values, with prior art example 1 being assigned as the reference (100). Higher values ​​are to be preferred in this evaluation.

[0078] (3) The low costs were assessed by calculating the material costs of the bead core 11 and the circumferential elements (in particular the bead filler 12), and the calculation results are expressed and evaluated as index values, with prior art example 1 being assigned as the reference (100). Higher values ​​are to be preferred in this evaluation.

[0079] The test tires in Example 1 each have the structure of each of the Fig. 1 to 4. The test tires of examples 2 to 5 are each a modified example of example 1 and each includes the wire arrangement structures of the Fig. 5 to 8. In each of the examples 1 to 5, the wire 1111 of the tire bead wire 111 is a steel cord thread with an outer diameter of 1.55 mm and it is covered with the insulating rubber 1112.

[0080] The test tires of examples 1 and 2 of the prior art and of comparative examples 1 to 12 each enclose the wire arrangement structure of the Fig. 10 to 23.

[0081] As can be seen from the test results, the test tires of examples 1 to 5 each achieved (1) toe deformation resistance, (2) strength efficiency and (3) low cost in a compatible manner. List of reference symbols 1 pneumatic tire 11 bead core 111 Tire bead wire 1111 wire 1112 Insulation rubber 12 bead fillers 121 Lower pen 122 Upper fountain pen 13 Carcass layer 14 Belt layer 141 Belts with a large angle 142, 143 Lower belt 144 Additional Belt 15 tread rubber 16 side wall rubber 17 Wheel rim pad rubber 18 Reinforcing layer 10 rim 101 Bead base section 102 Rim section

Claims

Pneumatic tire (1), comprising: a pair of bead cores (11), each formed by repeatedly winding a tire bead wire (111) in an annular shape, wherein the bead cores (11) each have a wire arrangement structure in the form of a hexagon formed by winding one or more of the tire bead wires (111) in a tightly packed manner in a cross-sectional view of each of the bead cores (11) in its radial direction, wherein the hexagon is a projecting hexagon with an obtuse interior angle at each vertex, wherein the vertex of the hexagon on a radially innermost side of each of the bead cores (11) is defined as the first vertex P1, wherein a side of the hexagon extending outwards in a tire transverse direction and enclosing the first vertex P1 is defined as a first side S12,wherein an axis parallel to the first side S12 of the hexagon is defined as an X-axis and an axis perpendicular to the X-axis is defined as a Y-axis, wherein a number of layers M of wire cross-sections in a Y-axis direction and a maximum value N_max of an arrangement N of wire cross-sections in an X-axis direction have a ratio that satisfies 0.75 ≤ M / N_max ≤ 1.30, and wherein a distance A in the tire transverse direction from the vertex of the hexagon on the innermost side in the tire transverse direction to the centroid of the hexagon and a distance B in the tire transverse direction from the vertex of the hexagon on the outermost side in the tire transverse direction to the centroid of the hexagon have a ratio that satisfies 1.05 ≤ B / A. Pneumatic tire (1) according to claim 1, wherein the tire bead wire (111) is wound spirally in the X-axis direction to form a layer of wire cross-sections, and a plurality of the layers of wire cross-sections are stacked in the Y-axis direction on the first side S12 of the hexagon, which serves as an innermost layer to form the bead core (11). Pneumatic tire (1) according to one of claims 1 to 2, wherein the bead core (11) has the wire arrangement structure in the form of a hexagon formed by winding the tire bead wire (111) in a tightly packed manner. Pneumatic tire (1) according to one of claims 1 to 3, wherein the number of arrangements N12 of the wire cross sections on the first side S12 of the hexagon is in the following range: 5 ≤ N12. Pneumatic tire (1) according to one of claims 1 to 4, wherein the number of arrangements N23 of the wire cross sections on side S23 in the tire transverse direction outwards, adjacent to the first side S12 of the hexagon, is in the following range: 2 ≤ N23. Pneumatic tire (1) according to one of claims 1 to 5, wherein the number of arrangements N23 of the wire cross sections on side S23 in the tire transverse direction outwards, adjacent to the first side S12 of the hexagon, and the number of arrangements N61 of the wire cross sections on side S61 in the tire transverse direction inwards, adjacent thereto, have the ratio 1 ≤ N61 - N23. Pneumatic tire (1) according to one of claims 1 to 6, wherein the number of arrangements N12 of the wire cross-sections on the first side S12 of the hexagon and the maximum value N_max of the number of arrangements N of the wire cross-sections in the X-axis direction have the ratio 1 ≤ N_max - N12. Pneumatic tire (1) according to one of claims 1 to 7, wherein a difference in the number of arrangements N of the wire cross sections in all layers adjacent to each other in the Y-axis direction is -1, 0 or 1. Pneumatic tire (1) according to one of claims 1 to 8, wherein the center of gravity G of the hexagon is positioned inwards in the Y-axis direction of the layer of the tire bead wire (111), which is positioned in the middle in the Y-axis direction of the bead core (11). Pneumatic tire (1) according to one of claims 1 to 9, further comprising: a carcass layer (11) extending between the pair of bead cores (11), wherein both end sections of the carcass layer (11) are bent back outwards in the tire transverse direction so that they are wrapped around the corresponding bead cores (11) and are fixed.

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