tire

Abstract

To provide a tire which enables the overall performance of ride comfort performance and durability thereof to be improved.SOLUTION: A tire 1 is provided, comprising a belt layer 7. The belt layer 7 includes at least one belt ply 7A on which belt cords 8 are arrayed. The belt cord 8 has N+M structure constituted of N pieces of cores 10 and M pieces of sheaths 11. The core 10 has a cross section of a flat shape with a major axis d1 and a minor axis d2. A value (d2 / d1 / L1) obtained by dividing an aspect ratio d2 / d1 of the core 10 by the shortest distance L1 (mm) in the tire radial direction from a ground plane 2a of the tread portion 2 to the center of the belt cord 8 at a tire meridian cross section, is 0.07 (1 / mm) or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a tire having a belt layer.

Background Art

[0002] Conventionally, tires having a belt layer are known. For example, Patent Document 1 below describes a heavy-duty pneumatic tire provided with a belt having a ply containing cords of a single-twist structure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, there has been a strong demand for low fuel consumption performance. When aiming for weight reduction that greatly contributes to the improvement of low fuel consumption performance, there is a concern that the riding comfort performance and durability may decrease.

[0005] The present disclosure has been devised in view of the above actual situation, and the main object thereof is to provide a tire capable of improving the overall performance of riding comfort performance and durability.

Means for Solving the Problems

[0006] The present disclosure is a tire having a belt layer, wherein the belt layer includes at least one belt ply in which belt cords are arranged, the belt cords have an N + M structure composed of N cores and M sheaths, the cores have an elliptical cross section having a major diameter d1 and a minor diameter d2, and the flatness ratio d2 / d1 of the cores is 7% or less of the shortest distance L1 (mm) in the tire radial direction from the ground contact surface of the tread portion in the tire meridian cross section to the center of the cores.

Effects of the Invention

[0007] The tire of this disclosure, having the above-described configuration, can improve the overall performance of ride comfort and durability. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the tire of this embodiment. [Figure 2] This is an enlarged cross-sectional view of the tread portion of this embodiment. [Figure 3] This is a schematic cross-sectional view of a belt cord. [Figure 4] This is a magnified view of the core in Figure 3. [Figure 5] This is a schematic cross-sectional view of a belt ply. [Figure 6] This is a schematic cross-sectional view of a belt cord in another embodiment. [Figure 7] This is a schematic cross-sectional view of a belt ply in another embodiment. [Modes for carrying out the invention]

[0009] One form of implementation of this disclosure will be described in detail below with reference to the drawings. Figure 1 shows a meridian cross-sectional view of the tire 1 in its normal state, including the axis of rotation. Here, "normal state" refers to the unloaded state in which, if the tire 1 is a pneumatic tire, the tire 1 is mounted on a normal rim and adjusted to the normal internal pressure. Unless otherwise specified, the dimensions of each part of the tire 1 are values ​​measured in this normal state.

[0010] A "standard rim" is the rim specified for each tire in the standards system that includes the standard on which the tire is based. For example, it is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO.

[0011] "Regular internal pressure" is the air pressure specified for each tire by each standard in the standards system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0012] As shown in Figure 1, tire 1 is suitably used as a heavy-duty tire for trucks, buses, etc. Tire 1 is not limited to heavy-duty tires, and can be applied to various types of tires, such as passenger car tires, motorcycle tires, racing tires, pneumatic tires, and non-pneumatic tires that do not contain pressurized air.

[0013] The tire 1 of this embodiment includes an annularly extending tread portion 2, a pair of sidewall portions 3 extending on both sides of the tread portion 2, and a pair of bead portions 4 extending in conjunction with the sidewall portions 3. The tire 1 has, for example, a toroidal carcass 6 extending across the bead cores 5 of the pair of bead portions 4, and a belt layer 7 disposed on the radially outer side of the carcass 6 and on the radially inner side of the tread portion 2.

[0014] The carcass 6 is composed of, for example, one carcass ply 6A. The carcass ply 6A includes carcass cords and a topping rubber covering the carcass cords. The carcass cords are arranged, for example, at an angle of 75 to 90° with respect to the circumferential direction of the tire. Hereinafter, "A to B" means "greater than or equal to A and less than or equal to B".

[0015] For the carcass cord, organic fiber cords such as nylon, polyester, or rayon, or steel cords are preferably used. Among these, when tire 1 is used as a heavy-duty tire, it is desirable to use steel cord as the carcass cord. The carcass 6 may be composed of, for example, two or more carcass plies 6A.

[0016] The carcass ply 6A has, for example, a main body portion 6a and a folded-back portion 6b. It is desirable that the main body portion 6a extends from the tread portion 2, through the sidewall portion 3, to the bead core 5 of the bead portion 4. The folded-back portion 6b, for example, is continuous with the main body portion 6a and is folded back around the bead core 5 from the inner side to the outer side in the tire axial direction and extends outward in the tire radial direction. The carcass ply 6A may adopt, for example, a so-called ultra-high turn-up structure in which the end of the folded-back portion 6b reaches between the main body portion 6a and the belt layer 7.

[0017] The belt layer 7 includes at least one, and in this embodiment, four belt plies 7A, 7B, 7C, and 7D. It is desirable that the belt layer 7 includes two or more belt plies 7A, 7B, 7C, and 7D that are adjacent to each other in the tire radial direction. Such a belt layer 7 helps improve the rigidity of the tread portion 2 and the durability of the tire 1 as the plurality of belt plies 7A, 7B, 7C, and 7D cooperate with each other.

[0018] The belt plies 7A, 7B, 7C, and 7D preferably have the same configuration. Such belt plies 7A, 7B, 7C, and 7D can be manufactured and managed as one belt ply 7a, and the production cost can be reduced. Note that the belt plies 7A, 7B, 7C, and 7D may have different configurations, for example.

[0019] FIG. 2 is an enlarged cross-sectional view orthogonal to the longitudinal direction of the belt cord 8 of the tread portion 2. As shown in FIG. 2, the belt ply 7a includes, for example, belt cords 8 arranged obliquely with respect to the tire circumferential direction and a covering layer 9 covering the same. Each belt cord 8 is preferably arranged obliquely at an angle of 10 to 45° with respect to the tire circumferential direction.

[0020] When the belt plies 7A, 7B, 7C, and 7D have the same configuration, it is desirable to include the same belt cord 8 and the same covering layer 9. On the other hand, when the belt plies 7A, 7B, 7C, and 7D have different configurations, for example, at least one of the belt cord 8 and the covering layer 9 is different.

[0021] Figure 3 is a schematic cross-sectional view orthogonal to the longitudinal direction of the belt cord 8. As shown in Figure 3, the belt cord 8 of the present embodiment has an N+M structure composed of N cores 10 and M sheaths 11. In Figure 3, a 1+8 structure composed of one core 10 and eight sheaths 11 is illustrated. Such a belt cord 8 can exhibit high rigidity and is helpful for improving the durability of the tire 1.

[0022] The sheath 11 may be, for example, a monofilament cord composed of one filament, or may be a twisted product of a plurality of filaments. Further, for the sheath 11, for example, a product composed of one filament and a twisted product of a plurality of filaments may be combined and used together.

[0023] Figure 4 is an enlarged view of the core 10 in Figure 3. As shown in Figures 3 and 4, the core 10 of the present embodiment has a flat cross-section having a major diameter d1 and a minor diameter d2. The core 10 has, for example, a substantially rectangular cross-section. Such a core 10 can flatten the entire belt cord 8 and moderately relax the rigidity in the minor diameter direction of the belt cord 8, and can improve the riding comfort performance of the tire 1. Note that the cross-sectional shape of the core 10 is not limited to such a mode, and as long as it is a flat shape, for example, it may be an elliptical shape or a polygonal shape such as a hexagonal shape.

[0024] The core 10 may be, for example, a monofilament cord composed of one filament, or may be a twisted product of a plurality of filaments. From the viewpoint of improving the comprehensive performance of riding comfort performance and durability, it is desirable to use a monofilament cord for the core 10.

[0025] The major axis d1 and minor axis d2 of the core 10 are determined by the length of the straight line passing through the center of the cross-section of the core cord and intersecting the contour of the core cord. The longest line is the major axis d1, and the shortest line is the minor axis d2. These can be determined by measuring the length of the core 10 taken from the belt cord 8 using a caliper or similar tool perpendicular to the longitudinal direction.

[0026] As shown in Figures 2 and 3, in this embodiment, the ratio d2 / d1 of the core 10 divided by the shortest radial distance L1 (mm) from the contact surface 2a of the tread portion 2 to the center of the belt cord 8 in the tire meridian cross-section (d2 / d1 / L1) is 0.07 (1 / mm) or less.

[0027] In such a tread section 2, when the shortest distance L1 is small, the aspect ratio d2 / d1 of the core 10 also becomes small, and the rigidity of the belt cord 8 in the short-axis direction can be reduced. As a result, the tread section 2 can improve its ability to follow the road surface, and the ride comfort performance of the tire 1 can be improved. Furthermore, such a tread section 2 can also generate flexible movement in response to the elongation of the sheath 11 arranged around the core 10, thereby improving the overall performance of the tire 1 in terms of ride comfort and durability.

[0028] Here, the shortest distance L1 in the tire radial direction from the contact surface 2a to the center of the belt cord 8 is the shortest distance from the outermost surface in the tire radial direction on the tire equator C to the center of the belt cord 8 of the outermost belt ply 7a in the tire radial direction.

[0029] Furthermore, when a groove is formed on the tire equator C, the outermost surface of the tire in the radial direction on the tire equator C is defined as the intersection of the tire equator C with the straight line connecting the outermost ends of the side walls of the groove on the tire equator C in the radial direction. Also, when no belt cord 8 exists on the tire equator C, the center of the belt cord 8 is defined as the intersection of the tire equator C with the straight line connecting the centers of a pair of belt cords 8 adjacent to the tire equator C.

[0030] As mentioned above, the shortest distance L1 is preferably a value measured under normal conditions, and can be determined, for example, by computed tomography using X-rays. Alternatively, the shortest distance L1 may be simply measured by aligning the bead portion 4 of a cross-section cut from a part of the tire 1 along the tire meridian with the width of the normal rim.

[0031] Such a belt cord 8 can be made more stretchable by increasing the relative length of the sheath 11 to the core 10, and can flexibly follow deformation, thereby improving the durability of the tire 1. For this reason, the tire 1 of this embodiment can improve the overall performance of ride comfort and durability.

[0032] From this viewpoint, the value (d2 / d1 / L1) is more preferably 0.065 (1 / mm) or less, and even more preferably 0.05 (1 / mm) or less. The lower limit of the value (d2 / d1 / L1) is not particularly limited, but is preferably 0.01 (1 / mm) or more, more preferably 0.02 (1 / mm) or more, and even more preferably 0.03 (1 / mm) or more.

[0033] In a more preferred embodiment, the coating layer 9 of the belt ply 7a can be, for example, a rubber composition, a thermoplastic elastomer composition, etc. From the viewpoint of forming a chemical network and firmly bonding the belt cord 8 and the coating layer 9, it is desirable to use a rubber composition for the coating layer 9. Furthermore, from the viewpoint of recyclability, it is desirable to use a thermoplastic elastomer composition for the coating layer 9.

[0034] If the coating layer 9 is a rubber composition, examples of rubber components include isoprene rubber, butadiene rubber, styrene-butadiene rubber, and chloroprene rubber. From the viewpoint of adhesion to the belt cord 8, it is desirable that the coating layer 9 contains isoprene rubber. Examples of isoprene rubber include natural rubber and synthetic isoprene rubber.

[0035] The rubber composition of the coating layer 9 may contain, for example, a reinforcing filler. Examples of fillers include carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, and the like.

[0036] From the viewpoint of durability, the filler content is preferably 30 parts by mass or more per 100 parts by mass of rubber component. On the other hand, from the viewpoint of heat generation, the upper limit of the filler content is preferably 65 parts by mass or less.

[0037] The rubber composition of the coating layer 9 preferably contains carbon black among the fillers. From the viewpoint of durability, the carbon black content is preferably 10 parts by mass or more per 100 parts by mass of rubber components. On the other hand, from the viewpoint of heat generation, the upper limit of the carbon black content is preferably 65 parts by mass or less.

[0038] Carbon black is not particularly limited and can include furnace blacks (furnace carbon blacks) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF, and ECF; acetylene black (acetylene carbon black); thermal blacks (thermal carbon blacks) such as FT and MT; channel blacks (channel carbon blacks) such as EPC, MPC, and CC; and graphite. These may be used individually or in combination of two or more types.

[0039] The rubber composition of the coating layer 9 may contain, for example, a plasticizer. Examples of plasticizers include oils and resin components. The plasticizer content is preferably more than 0.5 parts by mass and less than 10 parts by mass per 100 parts by mass of the rubber component.

[0040] The rubber composition of the coating layer 9 may, for example, contain cobalt in the rubber for better adhesion. Examples of compounds containing cobalt include organic acid cobalt salts such as cobalt stearate, cobalt naphthenate, cobalt neodecanoate, and cobalt boron trineodecanoate.

[0041] The rubber composition of the coating layer 9 may contain, for example, a curable resin component from the viewpoint of adhesion. Examples of curable resin components include modified resorcinol resin and modified phenolic resin. The content of the curable resin component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, the upper limit of the content of the curable resin component is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less.

[0042] If the rubber composition of the coating layer 9 contains a curable resin component, it is desirable that it also contain a resin curing agent. Examples of resin curing agents include methylene donors such as hexamethylenetetramine (HMT), hexamethoxymethylolmelamine (HMMM), and hexamethylenemelamine pentamethyl ether (HMMPME). The content of the resin curing agent is preferably 5 parts by mass or more per 100 parts by mass of the curable resin component.

[0043] The rubber composition of the coating layer 9 may also contain other components, such as antioxidants, zinc oxide, sulfur, vulcanization accelerators, and crosslinking aids.

[0044] From the viewpoint of adhesion with the coating layer 9, it is desirable that the surface of the belt cord 8 be plated. Examples of plating layers include a binary plating layer using copper and zinc, or a ternary plating layer using copper, zinc, and cobalt. By forming a ternary plating layer on the belt cord 8, the adhesion with the coating layer 9 can be further improved.

[0045] In a cross-section perpendicular to the longitudinal direction of the belt cord 8, the distance L2 between the centers of a pair of adjacent belt cords 8 in the width direction of the belt ply 7a is preferably 170% or less of the major axis D1 of the belt cord 8. Such a belt ply 7a can increase in-plane rigidity, suppress the occurrence of belt looseness, and improve the durability of the tire 1.

[0046] Here, the center-to-center distance L2 of the belt cords 8 is calculated as the average of the center-to-center distances L2 of the five belt cords 8 on each side of the tire axial direction of the tire equator C. Furthermore, if a belt cord 8 is located on the tire equator C, it is preferable to calculate the center-to-center distance L2 as the average of the center-to-center distances L2 of the belt cord 8 on the tire equator C and the five belt cords 8 on each side of it, for a total of 11 belt cords 8.

[0047] As mentioned above, the center-to-center distance L2 is preferably a value measured under normal conditions, and can be determined, for example, by computed tomography using X-rays. Alternatively, the center-to-center distance L2 may be simply measured by aligning the bead portion 4 of a cross-section cut from a part of the tire 1 along the tire meridian with the width of the normal rim.

[0048] Figure 5 is a schematic cross-sectional view of the belt ply 7a. As shown in Figure 5, when the belt cords 8 are arranged at an angle θ1 with respect to the circumferential direction of the tire, the distance L2 between the centers of the belt cords 8 can be determined from the distance L2' between the centers of the belt cords 8 in the meridional cross-section of the tire based on the following equation (1). L2 = L2'cosθ1 … (1)

[0049] As shown in Figure 2, the thickness T of the belt ply 7a is preferably 160% to 200% of the minor diameter D2 of the belt cord 8. Since such a belt ply 7a is covered with a sufficient coating layer 9, it can exert a restraining force while allowing the sheath 11 to elongate, thereby improving the ride comfort and durability of the tire 1.

[0050] Here, the thickness T of the belt ply 7a is the thickness T of the belt ply 7a in the radial direction of the tire at the tire equator C in a normal state, and can be determined, for example, by computed tomography using X-rays. Alternatively, the thickness T of the belt ply 7a may be simply measured by aligning the bead portion 4 of a cross-section cut from a part of the tire 1 along the tire meridian with the width of the normal rim.

[0051] In a cross-section perpendicular to the longitudinal direction of the belt cord 8, the cross-sectional area S1 of the belt cord 8 within the belt ply 7a is preferably 30% or less, more preferably 29% or less, and even more preferably 28% or less of the cross-sectional area S2 of the belt ply 7a.

[0052] The lower limit of the cross-sectional area S1 of the belt cord 8 relative to the cross-sectional area S2 of the belt ply 7a is preferably 20% or more, more preferably 22% or more, and even more preferably 23% or more. Such a belt ply 7a can increase in-plane rigidity, suppress the occurrence of belt looseness, improve the durability of the tire 1, and improve ride comfort performance at the same time.

[0053] Here, the cross-sectional area S2 of the belt ply 7a is calculated as the product of the distance L2 between the centers of the belt cords 8 and the thickness T of the belt ply 7a (L2 × T). The cross-sectional area S1 of the belt cord 8 is calculated as the average of the cross-sectional areas S1 of the five belt cords 8 on each side of the tire axial direction of the tire equator C. It is preferable that, when a belt cord 8 is located on the tire equator C, its cross-sectional area S1 be calculated as the average of the cross-sectional areas S1 of the belt cord 8 on the tire equator C and the five belt cords 8 on each side of it, for a total of 11 belt cords 8.

[0054] The major axis D1 of the belt cord 8 is preferably 1.10 mm or more, more preferably 1.12 mm or more, and even more preferably 1.14 mm or more. Furthermore, the major axis D1 of the belt cord 8 is preferably 1.80 mm or less, more preferably 1.70 mm or less, and even more preferably 1.50 mm or less.

[0055] The minor diameter D2 of the belt cord 8 is preferably 0.90 mm or more, more preferably 0.94 mm or more, and even more preferably 0.97 mm or more. Furthermore, the minor diameter D2 of the belt cord 8 is preferably 1.20 mm or less, more preferably 1.10 mm or less, and even more preferably 1.00 mm or less. However, the minor diameter D2 of the belt cord 8 is less than the major diameter D1 of the belt cord 8.

[0056] Such a belt cord 8 can maintain the widthwise rigidity of the belt ply 7a while providing road surface conformity, thus helping to improve the overall performance of the tire 1 in terms of ride comfort and durability.

[0057] It is desirable that the belt cords 8 be arranged on the belt ply 7a such that their major axes form a single plane. Such a belt ply 7a can reduce the rigidity in the thickness direction while maintaining rigidity in the width direction, thereby improving the overall performance of the tire 1 in terms of ride comfort and durability. Here, "forming a single plane in the major axes" means that the relative angle in the major axis direction is within 10°.

[0058] As shown in Figures 3 and 4, the aspect ratio d2 / d1 of the core 10 is preferably 70% or less, more preferably 68% or less, and even more preferably 65% ​​or less. Such a core 10 can reliably form a flattened shape for the belt cord 8, which helps to improve road surface conformability while maintaining the widthwise rigidity of the belt ply 7a. The lower limit of the aspect ratio d2 / d1 of the core 10 is not particularly limited, but is preferably 30% or more, more preferably 45% or more, and even more preferably 55% or more.

[0059] The major axis d1 of the core 10 is preferably 0.30 mm or more, more preferably 0.35 mm or more, and even more preferably 0.38 mm or more. Furthermore, the major axis d1 of the core 10 is preferably 0.50 mm or less, more preferably 0.45 mm or less, and even more preferably 0.43 mm or less.

[0060] The minor diameter d2 of the core 10 is preferably 0.15 mm or more, more preferably 0.20 mm or more, and even more preferably 0.22 mm or more. Furthermore, the minor diameter d2 of the core 10 is preferably 0.42 mm or less, more preferably 0.40 mm or less, and even more preferably 0.38 mm or less. However, the minor diameter d2 of the core 10 is less than the major diameter d1 of the core 10.

[0061] Such a core 10 balances the rigidity in the longitudinal direction and flexibility in the transverse direction of the belt cord 8, helping to improve the overall performance of the tire 1 in terms of ride comfort and durability.

[0062] As shown in Figure 4, the core 10 has, for example, a roughly rectangular cross-section with arc-shaped corners. The radius r of the arc-shaped corners of the core 10 is preferably 0.07 mm or more. Also, the radius r of the arc-shaped corners of the core 10 is preferably 0.15 mm or less. Such a core 10 does not pose a risk of damaging the sheath 11 and can improve the durability of the tire 1.

[0063] Figure 6 is a schematic cross-sectional view of a belt cord 12 in another embodiment. The belt cord 12 in Figure 6 has a 3+12 structure consisting of three cores 10 and twelve sheaths 11. As shown in Figures 3 and 6, it is preferable that the belt cords 8 and 12 include an untwisted core 10 consisting of one to three single steel wires. Figure 3 shows an embodiment including one core 10, and Figure 6 shows an embodiment including three cores 10. Such belt cords 8 and 12 help to improve road surface conformability while maintaining appropriate rigidity.

[0064] The belt cords 8 and 12 preferably include 5 to 12 sheaths 11 with a circular cross-section. Figure 3 shows an embodiment including 8 sheaths 11, and Figure 6 shows an embodiment including 12 sheaths 11. Such belt cords 8 and 12 can generate elongation while maintaining appropriate rigidity, which helps to improve the durability of the tire 1. Here, a circular cross-section means that the cross-sectional shape perpendicular to the longitudinal direction of the sheath 11 is circular, and refers to an aspect ratio of 1.05 or less.

[0065] In this embodiment, the diameter d3 of the sheath 11 is smaller than the major axis d1 of the core 10. Preferably, the diameter d3 of the sheath 11 is equal to or greater than the minor axis d2 of the core 10. Such a sheath 11 helps to balance the rigidity and elongation of the belt cords 8 and 12.

[0066] The diameter d3 of the sheath 11 is preferably 0.30 to 0.37 mm. A diameter d3 of 0.30 mm or more of the sheath 11 allows for good rigidity of the belt cords 8 and 12. A diameter d3 of 0.37 mm or less allows for good elongation of the belt cords 8 and 12.

[0067] The belt cords 8 and 12 preferably have the sheath 11 twisted spirally around the core 10. The twist pitch of the sheath 11 is not particularly limited, but it is preferably greater than or equal to the product of the diameter d3 of the sheath 11 and the number of sheath 11 strands. More preferably, the twist pitch of the sheath 11 is 1.05 to 4.00 times the product of the diameter d3 of the sheath 11 and the number of sheath 11 strands.

[0068] As shown in Figure 6, when there are multiple cores 10, it is desirable that the cores 10 be arranged so that their major axes form a single plane. Such cores 10 can reliably form a flattened shape for the belt cord 8, which helps to reduce weight while maintaining the widthwise rigidity of the belt ply 7a.

[0069] Figure 7 is a schematic cross-sectional view of a belt ply 7b in another embodiment. As shown in Figure 7, in a cross-section perpendicular to the longitudinal direction of the belt cord 8, the belt plies 7b may be arranged such that, for example, the major axis direction of the core 10 has an angle θ2 with respect to the width direction of the belt plies 7b. In this case, it is desirable that the major axis direction of the core 10 is within 30° with respect to the width direction of the belt plies 7b.

[0070] Such belt plies 7b can achieve the same effect as those arranged so that the longitudinal directions of the belt cord 8 form a single plane, and the manufacturing process can be simplified, thereby reducing manufacturing costs.

[0071] While particularly preferred embodiments of this disclosure have been described in detail above, this disclosure can be implemented in various forms without being limited to the embodiments described above. [Examples]

[0072] A prototype tire (11R22.5 14PR) with the basic structure shown in Figure 1 was manufactured based on the specifications in Tables 1 and 2. The prototype tire was tested for ride comfort and durability, and its overall performance was evaluated. The manufacturing and testing methods are as follows.

[0073] <Method for manufacturing prototype tires> First, the following compounding materials were prepared and mixed in a 270L Banbury to obtain a rubber composition for the coating layer.

[0074] (compounding material) (a) Rubber component: Natural rubber :100 parts by mass

[0075] (b) Compounding materials other than rubber components (i) Carbon Black: Show Black N326 manufactured by Cabot Japan Co., Ltd. :40 parts by mass (b) Carbon Black: Show Black N550 manufactured by Cabot Japan Co., Ltd. :15 parts by mass (h) Curable resin component: Sumikanol 620 manufactured by Taoka Chemical Industries, Ltd. :5 parts by mass (ii) Resin hardener: Sumikanol 507 manufactured by Taoka Chemical Industries, Ltd. :1.5 parts by mass (e) Cobalt organic acid: DICNATE NBC-2 manufactured by DIC Corporation :1 part by mass (h) Anti-aging agent: Nocrack 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. :0.5 part by mass (T) Anti-aging agent: Anti-aging agent manufactured by Kawaguchi Chemical Industry Co., Ltd. :1 part by mass (C) Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. :10 parts by mass (R) Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries Co., Ltd. :7 parts by mass (Nu) Vulcanization accelerator: Noxellar DZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd. :1.2 parts by mass (L) Crosslinking agent: Duralink HTS manufactured by Flexis :1.5 parts by mass

[0076] Next, the belt cords shown in Tables 1 and 2 were prepared, and the prepared belt cords were arranged so that the distance between the centers of the belt cords was L2 as shown in Tables 1 and 2. The covering layer was then pressed onto the belt cords from above and below to obtain a belt ply.

[0077] The obtained belt ply was molded together with the inner liner, carcass ply, sidewall rubber, bead apex, bead core, chafer rubber, tread rubber, etc., to obtain an unvulcanized tire. The obtained unvulcanized tire was vulcanized for 40 minutes under conditions of 160°C to obtain a prototype tire. In the prototype tire, the shortest distance L1 between the contact surface of the tread and the center of the belt cord was adjusted by changing the thickness of the tread rubber.

[0078] In addition, a separate verification tire, distinct from the prototype tire used in the test, was manufactured with the same specifications as the prototype tire. The verification tire was subjected to destructive testing, and the dimensions of each part of the prototype tire were confirmed from the tire's meridian cross-section, the cross-section perpendicular to the longitudinal direction of the belt cord, and the arrangement of the belt cord when the tread section was peeled off.

[0079] <Ride comfort performance> The prototype tires were mounted on all wheels of a large truck test vehicle, and the ride comfort performance was evaluated by test drivers on a 5-point scale (out of 5 points) during a test course on paved roads that included straight-line driving, turning, and zigzag maneuvers. Similar tests were conducted by 20 test drivers, and their total scores were calculated. The results are expressed as an index with the total score of Comparative Example 1 set at 100, where a higher number indicates better ride comfort performance.

[0080] <Durability> The prototype tires were mounted on standard rims, adjusted to the standard internal pressure at an oxygen concentration of 90%, and subjected to thermal degradation in a 70°C oven for six weeks. Afterward, the thermally degraded tires were mounted on a drum testing machine and driven until bulging occurred in the tread area, according to the load / speed durability test conditions of the Ministry of Land, Infrastructure, Transport and Tourism's technical inspection standards and conformity inspections. The driving time was then measured. The results are expressed as an index with Comparative Example 1 set to 100, where a higher value indicates a longer driving time and superior durability.

[0081] <Overall Performance> Based on the evaluation results for ride comfort and durability, the overall performance of ride comfort and durability was assessed. The result is expressed as the sum of the ride comfort index and the durability index, with a higher value indicating superior overall performance in ride comfort and durability.

[0082] The test results are shown in Tables 1 and 2. [Table 1]

[0083] [Table 2]

[0084] The test results showed that the tires in the example were superior to the comparative example in terms of ride comfort and durability. Furthermore, the overall performance, judged by the sum of each performance aspect, was also good, confirming an improvement in overall ride comfort and durability.

[0085] [Note] This disclosure is as follows:

[0086] [Disclosure 1] A tire having a belt layer, wherein the belt layer includes at least one belt ply on which belt cords are arranged, the belt cords have an N+M structure composed of N cores and M sheaths, the cores have a flattened cross-section having a major axis d1 and a minor axis d2, and the value obtained by dividing the aspect ratio d2 / d1 of the cores by the shortest radial distance L1 (mm) of the tire from the contact surface of the tread portion in the tire meridian cross-section to the center of the belt cords (d2 / d1 / L1) is 0.07 (1 / mm) or less.

[0087] [Disclosure 2] The tire according to Disclosure 1, wherein the aspect ratio d2 / d1 of the core is 70% or less.

[0088] [Disclosure 3] The tire according to disclosure 1 or 2, wherein the minor diameter d2 of the core is 0.15 to 0.42 mm.

[0089] [Disclosure 4] The tire according to any one of disclosures 1 to 3, wherein the belt cord includes the untwisted core consisting of 1 to 3 single steel wires.

[0090] [Disclosure 5] The tire according to any one of disclosures 1 to 4, wherein the belt cord includes 5 to 12 sheaths with a circular cross-section.

[0091] [Disclosure 6] The tire according to any one of disclosures 1 to 5, wherein the belt layer includes two or more belt plies adjacent to each other in the radial direction of the tire.

[0092] [Disclosure 7] The tire according to any one of claims 1 to 6, wherein the thickness T of the belt ply is 160% to 200% of the short diameter D2 of the belt cord.

[0093] [Disclosure 8] A tire according to any one of disclosures 1 to 7, wherein, in a cross section perpendicular to the longitudinal direction of the belt cord, the distance L2 between the centers of a pair of adjacent belt cords in the width direction of the belt ply is 170% or less of the major axis D1 of the belt cord.

[0094] [Disclosure 9] The tire according to any one of disclosures 1 to 8, wherein in a cross section perpendicular to the longitudinal direction of the belt cord, the sum of the cross-sectional areas of the belt cord is 20% to 30% of the cross-sectional area of ​​the belt ply.

[0095] [Disclosure 10] A tire according to any one of disclosures 1 to 9, wherein, in a cross section perpendicular to the longitudinal direction of the belt cord, the cores are arranged such that the major axis direction is within 30° with respect to the width direction of the belt ply. [Explanation of symbols]

[0096] 1 tire 2 Tread section 2a Ground plane 7 Belt layer 7a Belt ply 8 Belt cord 10 cores 11 Sheath

Claims

1. A tire having a belt layer, The belt layer includes at least one belt ply on which belt cords are arranged, The aforementioned belt cord has an N+M structure composed of N cores and M sheaths. The core has a flattened cross-section with a major axis d1 and a minor axis d2. The ratio d2 / d1 of the core is divided by the shortest radial distance L1 (mm) from the contact surface of the tread portion to the center of the belt cord in the tire meridian cross-section, and the resulting value (d2 / d1 / L1) is 0.07 (1 / mm) or less. The aforementioned belt cords are arranged at an angle of 10 to 45° with respect to the circumferential direction of the tire. In a cross-section perpendicular to the longitudinal direction of the belt cord, the distance L2 between the centers of a pair of adjacent belt cords in the width direction of the belt ply is 170% or less of the major axis D1 of the belt cord. tire.

2. The tire according to claim 1, wherein the aspect ratio d2 / d1 of the core is 70% or less.

3. The tire according to claim 1 or 2, wherein the minor diameter d2 of the core is 0.15 to 0.42 mm.

4. The tire according to any one of claims 1 to 3, wherein the belt cord includes the untwisted core consisting of one to three single steel wires.

5. The tire according to any one of claims 1 to 4, wherein the belt cord includes 5 to 12 sheaths with a circular cross-section.

6. The tire according to any one of claims 1 to 5, wherein the belt layer includes two or more belt pies adjacent to each other in the radial direction of the tire.

7. The tire according to any one of claims 1 to 6, wherein the thickness T of the belt ply is 160% to 200% of the short diameter D2 of the belt cord.

8. The tire according to any one of claims 1 to 7, wherein, in a cross section perpendicular to the longitudinal direction of the belt cord, the cross-sectional area of ​​one of the belt cords is 20% to 30% of the cross-sectional area of ​​the belt ply, which is determined as the product of the distance L2 between the centers of a pair of adjacent belt cords in the width direction of the belt ply and the thickness T of the belt ply (L2 × T).

9. The tire according to any one of claims 1 to 8, wherein in a cross section perpendicular to the longitudinal direction of the belt cord, the cores are arranged such that the major axis direction is within 30° with respect to the width direction of the belt ply.

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