Pneumatic tire

Abstract

To make both high-speed durability and steering stability of a tire compatible at a high dimension, while reducing weight of the tire.SOLUTION: A pneumatic tire 1 comprises a belt layer 20 and a belt reinforcement layer 30. A filament diameter of a steel cord of a belt ply 21 is over 0.10 mm and less than 0.25 mm. When a bending load per unit width of one belt ply 21 is defined as A[N / inch], a product of 2% elongation-time load [N / one] per one organic fiber cord of a belt reinforcement ply 31 and hitting number [number / inch] of the organic fiber cord is defined as B[N / inch], and a product of 5% elongation-time load [N / one] per one organic fiber cord and hitting number [number / inch] of the organic fiber cord is defined as C[N / inch], A, B and C satisfy a relation represented by the following formulae (I) and (II): the formula (I): B / A<400 and the formula (II): 600<C / A<2000.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pneumatic tire.

Background Art

[0002] Conventionally, a pneumatic tire including a carcass, a belt layer disposed on the outer periphery of the crown portion of the carcass, and a belt reinforcing layer disposed on the outer periphery of the belt layer is known (see, for example, Patent Document 1). Further, conventionally, in order to improve the durability of the tire (high-speed durability) during high-speed driving, increasing the strength of the steel cord included in the belt ply constituting the belt layer has been studied. As a method of increasing the strength of the steel cord, for example, increasing the filament diameter of the steel cord can be considered.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when a steel cord having a large filament diameter is used for the belt ply, in addition to an increase in the weight of the tire, the bending rigidity of the belt ply tends to increase. As a result, the contact area of the tire decreases and the handling stability deteriorates. Therefore, it is not easy to achieve both high-speed durability and handling stability of the tire at a high level while reducing the tire weight.

Means for Solving the Problems

[0005] A pneumatic tire according to one aspect of the present invention is a pneumatic tire including a carcass, a belt layer disposed on the outer periphery of the crown portion of the carcass, and a belt reinforcing layer disposed on the outer periphery of the belt layer, wherein the belt layer has a belt ply in which steel cords are arranged obliquely with respect to the tire circumferential direction, the belt reinforcing layer has a belt reinforcing ply in which organic fiber cords are arranged along the tire circumferential direction on the outer periphery of the belt layer, the filament diameter of the steel cord is more than 0.10 mm and less than 0.25 mm, the bending load per unit width of one belt ply is A [N / inch], the product of the load at 2% elongation per organic fiber cord [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply [cords / inch] is B [N / inch], and the product of the load at 5% elongation per organic fiber cord [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply [cords / inch] is C [N / inch], and A, B, and C satisfy the relationships represented by the following formulas (I) and (II). Formula (I): B / A < 400 Formula (II): 600 < C / A < 2000

Advantages of the Invention

[0006] According to the pneumatic tire which is one aspect of the present invention, while reducing the tire weight, it is possible to achieve both high-speed durability and handling stability of the tire at a high level.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0008] Hereinafter, with reference to the drawings, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail. The embodiments described below are merely examples, and the present invention is not limited to the following embodiments.

[0009] FIG. 1 is a cross-sectional view of a pneumatic tire 1 according to the present embodiment, showing a half cross-section in the tire axial direction. As shown in FIG. 1, the pneumatic tire 1 includes a tread 10 which is a portion in contact with the road surface, a pair of sidewalls 11 disposed on both sides of the tread 10, and a pair of beads 12 disposed on the tire radial direction inner side of the sidewalls 11. Further, the pneumatic tire 1 includes a carcass 13 spanned between the pair of beads 12.

[0010] The sidewalls 11 are disposed on both sides of the tread 10 and are provided annularly along the tire circumferential direction. The sidewalls 11 are the portions that protrude most to the outside in the tire axial direction of the pneumatic tire 1, and are gently curved so as to be convex toward the outside in the tire axial direction. The sidewalls 11 have a function of preventing damage to the carcass 13.

[0011] The bead 12 is disposed on the tire radial direction inner side of the sidewall 11 and is a portion fixed to the rim of the wheel. The bead 12 has a bead core 14 and a bead filler 15. The bead core 14 is composed of a steel bead wire and is an annular member extending over the entire circumference in the tire circumferential direction and is embedded in the bead 12. The bead filler 15 has a tip tapered shape extending outward in the tire radial direction and is an annular hard rubber member extending over the entire circumference in the tire circumferential direction.

[0012] The carcass 13 is stretched between a pair of beads 12 and is locked by being folded around the bead core 14. The carcass 13 is composed of at least one carcass ply. The carcass ply is formed by coating a carcass cord made of organic fibers with coating rubber. The carcass cord is arranged substantially perpendicular (for example, 80° or more and 90° or less) to the tire circumferential direction. Examples of the organic fibers used for the carcass cord include polyester fibers, rayon fibers, aramid fibers, and nylon fibers.

[0013] The pneumatic tire 1 further includes a belt layer 20 disposed on the outer periphery of the crown portion of the carcass 13 and a belt reinforcing layer 30 disposed on the outer periphery of the belt layer 20. That is, the belt layer 20 is disposed between the carcass 13 and the tread 10, and the belt reinforcing layer 30 is disposed between the belt layer 20 and the tread 10.

[0014] The belt layer 20 has a belt ply 21 in which steel cords 22 (see FIG. 2) are arranged obliquely with respect to the tire circumferential direction. The belt ply 21 is formed by coating the steel cords 22 (see FIG. 2) with coating rubber. In the present embodiment, the belt ply 21 is composed of two belt plies 21A and 21B. The steel cords 22 are arranged so as to cross each other between the two belt plies 21A and 21B.

[0015] The belt reinforcing layer 30 is a cap ply that covers the belt layer 20 with a belt reinforcing ply 31. The belt reinforcing ply 31 is composed of organic fiber cords 32 (see FIG. 4) arranged along the tire circumferential direction being covered with a coating rubber 33 (see FIG. 4). Although details will be described later, in the present embodiment, the organic fiber cord 32 constituting the belt reinforcing ply 31 is a composite fiber cord obtained by twisting a yarn made of aliphatic polyamide fiber and a yarn made of aromatic polyamide fiber. The belt reinforcing layer 30 can be formed by spirally winding the belt reinforcing ply 31 at an angle of 0° or more and 5° or less with respect to the tire circumferential direction so as to cover the entire width direction of the belt layer 20.

[0016] In the present embodiment, the belt reinforcing layer 30 is a cap ply that covers the entire width direction of the belt layer 20, but the belt reinforcing layer 30 may be an edge ply that covers the belt edge of the belt layer 20.

[0017] Next, with reference to FIGS. 2 and 3, the belt ply 21 constituting the belt layer 20 will be described in detail. FIG. 2 is a diagram schematically showing a cross section of a steel cord 22 constituting the belt ply 21.

[0018] As described above, the belt ply 21 is composed of the steel cord 22 (see FIG. 2) being covered with a coating rubber. Here, in the belt layer 20, the angle of the steel cord 22 with respect to the tire circumferential direction (hereinafter referred to as the belt angle) is, for example, 20° or more and 45° or less. In the present embodiment, the belt layer 20 is composed of two belt plies 21A and 21B. Therefore, the belt angles of the two belt plies 21A and 21B arranged such that the steel cords 22 cross each other are both 20° or more and 45° or less with respect to the tire circumferential direction.

[0019] The structure of the steel cord 22 is not particularly limited. However, as shown in FIG. 2, it is preferably an m + n multi-layer twisted structure (m is 1 or more and 3 or less, n is 2 or more and 15 or less) in which a plurality of filaments 23 are twisted around a core 24 formed by twisting one or more filaments 23, with a sheath portion 25 formed by twisting a plurality of filaments 23. By using the steel cord 22 having the above structure, it becomes easy to achieve both high-speed durability and handling stability of the tire.

[0020] Note that the structure of the steel cord 22 is not limited to the above multi-layer twisted structure, and may be a 1×n single-twisted structure (n is 2 or more and 15 or less) formed by twisting n metal filaments, or an m×n double-twisted structure (m is 3 or more and 5 or less, n is 2 or more and 4 or less) formed by further twisting m strands formed by lower-twisting n metal filaments.

[0021] The twist pitch of the steel cord 22 is not particularly limited. For example, it is 5 mm or more and 13 mm or less, and preferably 7 mm or more and 11 mm or less.

[0022] The cord diameter of the steel cord 22 is not particularly limited, but is preferably 0.90 mm or less, and more preferably 0.3 mm or more and 0.7 mm or less. When the cord diameter of the steel cord 22 is 0.3 mm or more and 0.7 mm or less, it becomes easy to achieve both high-speed durability and handling stability of the tire at a high level.

[0023] The filament diameter of the steel cord 22 is more than 0.10 mm, preferably 0.12 mm or more, and more preferably 0.14 mm or more. By setting the filament diameter to more than 0.10 mm, the high-speed durability of the tire can be ensured. Further, the filament diameter of the steel cord 22 is less than 0.25 mm, preferably 0.23 mm or less, and more preferably 0.21 mm or less. By setting the filament diameter to less than 0.25 mm, while reducing the weight of the tire, the bending rigidity of the belt ply 21 can be reduced. As a result, the contact area of the tire during running can be improved, and the handling stability is further improved. Therefore, the filament diameter of the steel cord 22 is more than 0.10 mm and less than 0.25 mm, preferably 0.12 mm or more and 0.23 mm or less, and more preferably 0.14 mm or more and 0.21 mm or less. Further, the filament diameter of the steel cord 22 may be more than 0.10 mm and 0.23 mm or less, or may be more than 0.10 mm and 0.21 mm or less. Further, the filament diameter of the steel cord 22 may be 0.12 mm or more and less than 0.25 mm, or may be 0.14 mm or more and less than 0.25 mm.

[0024] Further, the number of steel cords 22 driven in is not particularly limited, and for example, it is 15 [pieces / inch] or more and 30 [pieces / inch] or less.

[0025] The wire bending stiffness per single steel wire 22 is preferably 200 cN or less, and more preferably 150 cN or less. By setting the wire bending stiffness per single steel wire 22 to 200 cN or less, it becomes easier to reduce the bending stiffness of the belt ply 21. As a result, the contact area of the tire increases, and the handling stability can be improved. Further, the lower limit of the wire bending stiffness per single steel wire 22 is, for example, 80 cN. When the wire bending stiffness per single steel wire 22 is less than 80 cN, the bending stiffness of the belt ply 21 becomes excessively small, and the handling stability may conversely decrease. Therefore, the wire bending stiffness per single steel wire 22 is preferably 80 cN or more and 200 cN or less, and more preferably 80 cN or more and 150 cN or less.

[0026] In this specification, the wire bending stiffness is a value defined by the maximum load when a single steel wire 22 is bent at its central portion with a fulcrum distance of 25.4 mm. Specifically, it can be measured by performing a three-point bending test using a tensile testing machine including a pair of support bars with a circular cross-section (diameter = 3 mm) arranged at intervals of 25.4 mm and a fixed bar with a circular cross-section (diameter = 3 mm) positioned vertically upward from the midpoint of the pair of support bars. More specifically, at room temperature, a steel wire 22 with a length of 80 mm is placed on a pair of support bars. Then, the pair of support bars is moved upward at a test speed of 500 mm / min, and the maximum load when the steel wire 22 is bent with the fixed bar as the fulcrum is measured. And the average value of the five measured values of the maximum load is taken as the wire bending stiffness per single steel wire 22.

[0027] The tensile strength (strength elongation) per single steel wire 22 is not particularly limited, but is, for example, 400 N or more and 1000 N or less. The tensile strength per single steel wire is the maximum load required for a test piece measured at a tensile speed of 500 m / min in accordance with the tensile test of the cutting load and the total elongation at the time of cutting (section 6.4) in "Steel Tire Cord Test Method" of JIS G3510.

[0028] Here, if the bending load per unit width of one belt ply 21 is A [N / inch], A may be a value that satisfies the following formulas (I) and (II) described later, but is preferably 4.5 or less, and more preferably 4.0 or less. By setting A to 4.5 or less, it becomes easier to improve the contact area of the tire during running, and the handling stability is further improved. Also, A is preferably 1.5 or more, and more preferably 2.0 or more. By setting A to 1.5 or more, it becomes easier to ensure the high-speed durability of the tire. Therefore, the bending load A per unit width of the belt ply 21 is preferably 1.5 or more and 4.5 or less, and more preferably 2.0 or more and 4.0 or less. Note that the bending load per unit width of the belt ply 21 can be adjusted by changing the material and thickness of the filaments 23 of the steel cord 22. For example, by increasing the filament diameter, the bending load per unit width of the belt ply 21 can be increased.

[0029] In this specification, the bending load per unit width of the belt ply 21 is a value defined by the maximum load when one belt ply 21 is bent at its center with a fulcrum distance of 100 mm. Specifically, as shown in FIG. 3, it can be measured using a testing machine including a pair of support rolls 41 with a circular cross-section (diameter = 20 mm) arranged at intervals of 100 mm and a push-in jig 42 with a circular cross-section (diameter = 15 mm) positioned vertically upward from the midpoint between the pair of support rolls 41. More specifically, first, the belt ply 21 is cut into a 1-inch width to produce a measurement sample 50. Then, at room temperature, the measurement sample 50 is placed on the pair of support rolls 41 such that the longitudinal direction of the steel cord 22 of the measurement sample 50 is perpendicular to the axial direction of the support rolls 41. Then, the push-in jig 42 is moved downward (in the direction of the arrow) at a pushing speed of 300 mm / min, and the maximum load when the measurement sample 50 is bent with the push-in jig 42 as a fulcrum is measured. Then, the average value of the five measured values of the maximum load is taken as the bending load per unit width of the belt ply 21.

[0030] Also, the in-plane rigidity of a single belt ply 21 is preferably 9.0 [kN / inch] or more, and more preferably 12 [kN / inch] or more. By setting the in-plane rigidity of the belt ply 21 to 9.0 [kN / inch] or more, the strength of the belt layer 20 can be ensured, and it becomes easier to confirm high-speed durability. Also, the in-plane rigidity of a single belt ply 21 is preferably 25 [kN / inch] or less, and more preferably 20 [kN / inch] or less. By setting the in-plane rigidity of the belt ply 21 to 25 [kN / inch] or less, it becomes easier to improve the contact area of the tire during running, and the handling stability is further improved. Therefore, the in-plane rigidity of a single belt ply 21 is preferably 9.0 [kN / inch] or more and 25 [kN / inch] or less, and more preferably 12 [kN / inch] or more and 20 [kN / inch] or less.

[0031] Here, the in-plane rigidity of the belt ply 21 means the rigidity of the belt ply 21 in the extending direction of the steel cord 22. Specifically, it can be obtained by multiplying the tensile strength (strength at break) of the above-described steel cord 22 by the number of steel cords 22 driven in. The in-plane rigidity of the belt ply 21 can be adjusted by changing the material, number, or thickness of the filaments 23 of the steel cord 22. For example, by increasing the number of filaments 23, the in-plane rigidity of the belt ply 21 can be increased. Also, by increasing the filament diameter, the in-plane rigidity of the belt ply 21 can be increased.

[0032] Next, while referring to FIG. 4, the belt reinforcing ply 31 that constitutes the belt reinforcing layer 30 will be described in detail. FIG. 4 is a diagram schematically showing a part of the cross-section of the belt reinforcing ply 31 that constitutes the belt reinforcing layer 30.

[0033] As shown in FIG. 4, the belt reinforcing ply 31 is composed of organic fiber cords 32 arranged along the tire circumferential direction and coated with a coating rubber 33. Here, the organic fiber cord 32 is preferably a composite fiber cord obtained by twisting a yarn made of aliphatic polyamide fiber and a yarn made of aromatic polyamide fiber. When the organic fiber cord 32 is the above composite fiber cord, it is easy to adjust the load at 2% elongation and the load at 5% elongation of the organic fiber cord 32, which will be described later, within a predetermined range.

[0034] Examples of the resin used as the aliphatic polyamide fiber include aliphatic polyamide-based resins such as nylon 6, nylon 66, nylon 46, nylon 11, nylon 12, nylon 610, nylon 612, nylon 6 / 66 copolymer, nylon 6 / 66 / 610 copolymer, nylon MXD6, nylon 6T, and nylon 6 / 6T copolymer. Among them, from the viewpoint of adjusting the load at 2% elongation and the load at 5% elongation of the organic fiber cord 32, which will be described later, within a predetermined range, nylon 66 is preferable.

[0035] The aromatic polyamide fiber is a polyamide having an aromatic skeleton in the main chain, and may be a para-aramid or a meta-aramid. For example, known aramid fibers used in the present technical field can be appropriately used.

[0036] The fineness of the organic fiber cord 32 is not particularly limited, but for example, it is 700 dtex or more, preferably 800 dtex or more, and more preferably 900 dtex or more. By setting the fineness of the organic fiber cord 32 to 700 dtex or more, the number of organic fiber cords 32 driven in to obtain desired tire performance can be reduced. As a result, adhesive failure between the organic fiber cord 32 and the rubber at the cut end of the belt reinforcing ply 31 is less likely to occur, and it becomes easier to ensure the high-speed durability of the tire. Also, the fineness of the organic fiber cord 32 is, for example, 3000 dtex or less, preferably 2500 dtex or less, and more preferably 2000 dtex or less. By setting the fineness of the organic fiber cord 32 to 3000 dtex or less, the weight of the tire can be reduced. Therefore, the fineness of the organic fiber cord 32 is, for example, 700 dtex or more and 3000 dtex or less, preferably 800 dtex or more and 2500 dtex or less, and more preferably 900 dtex or more and 2000 dtex or less. Note that the fineness is also referred to as the nominal fineness or the indicated fineness.

[0037] The number of organic fiber cords 32 driven in is not particularly limited, but it is preferably 15 [cords / inch] or more and 40 [cords / inch] or less, and more preferably 20 [cords / inch] or more and 35 [cords / inch] or less.

[0038] The number of twists per 10 cm of the organic fiber cord 32 is not particularly limited, but it is preferably 25 [twists / 10 cm] or more and 70 [twists / 10 cm] or less, and more preferably 25 [twists / 10 cm] or more and 60 [twists / 10 cm] or less. When the number of twists of the organic fiber cord 32 is 25 [twists / 10 cm] or more and 70 [twists / 10 cm] or less, it is easy to adjust the load at 2% elongation and the load at 5% elongation of the organic fiber cord 32, which will be described later, within a predetermined range.

[0039] Here, let the product of the load at 2% elongation per organic fiber cord 32 (LASE2%) [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply 31 [cords / inch] be B [N / inch]. Also, let the product of the load at 5% elongation per organic fiber cord 32 (LASE5%) [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply 31 [cords / inch] be C [N / inch]. At this time, the bending load per unit width of the aforementioned single belt ply 21, A [N / inch], the above B [N / inch], and the above C [N / inch] satisfy the relationships expressed by the following formulas (I) and (II). Formula (I): B / A < 400 Formula (II): 600 < C / A < 2000

[0040] By setting (B / A) to less than 400, an appropriate balance can be achieved between the bending rigidity of the belt reinforcing ply 31 and the restraining force by the belt reinforcing layer 30, enabling high - dimensional compatibility between the high - speed durability and the handling stability of the tire. In other words, when (B / A) becomes 400 or more, for example, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in a decrease in the tire's contact area and deterioration of the handling stability. (B / A) only needs to be less than 400, preferably less than 350, and more preferably less than 300. The lower limit of (B / A) is, for example, 50. When (B / A) becomes 50 or less, the bending rigidity of the belt ply 21 tends to increase. As a result, the tire's contact area may decrease and the handling stability may deteriorate. Therefore, it may also be 50 < B / A < 400, preferably 50 < B / A < 350, and more preferably 50 < B / A < 300.

[0041] Also, by setting (C / A) to be greater than 600, the restraining force by the belt reinforcing layer 30 can be ensured, and while ensuring the high-speed durability of the tire, the handling stability can be improved. (C / A) only needs to be greater than 600, but is preferably greater than 700, and more preferably greater than 800. Also, by setting (C / A) to be less than 2000, the bending rigidity of the belt reinforcing ply 31 and the restraining force by the belt reinforcing layer 30 achieve an appropriate balance, and the high-speed durability and handling stability of the tire can be made compatible at a high level. In other words, when (C / A) becomes 2000 or more, for example, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in a decrease in the contact area of the tire and a deterioration in handling stability. (C / A) only needs to be less than 2000, but is preferably less than 1600, and more preferably less than 1200. Therefore, preferably 700 < (C / A) < 1600, and more preferably 800 < (C / A) < 1200. Also, 600 < (C / A) < 1600 may be acceptable, and 600 < (C / A) < 1200 may also be acceptable. Also, 700 < (C / A) < 2000 may be acceptable, and 800 < (C / A) < 2000 may also be acceptable.

[0042] In this specification, the load at 2% elongation [N / strand] per organic fiber cord and the load at 5% elongation [N / strand] per organic fiber cord are the loads at 2% elongation and the loads at 5% elongation when a tensile test conforming to JIS L1017 is carried out in a laboratory under standard conditions of a temperature of 20 ± 2°C and a relative humidity of 65 ± 4% specified in JIS L0105.

[0043] The above B [N / inch] only needs to be within the range that satisfies the above formula (I), but it is preferably 400 or more, and more preferably 500 or more. When B [N / inch] is less than 400, it becomes difficult to maintain the tire shape, and the handling stability may deteriorate. Also, B [N / inch] is preferably 1000 or less, and more preferably 800 or less. When B [N / inch] exceeds 1000, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in a decrease in the tire's contact area with the ground and a possible deterioration in handling stability. Therefore, B [N / inch] is preferably 400 or more and 1000 or less, and more preferably 500 or more and 800 or less.

[0044] Also, the above C [N / inch] only needs to be within the range that satisfies the above formula (II), but it is preferably 1400 or more, and more preferably 1800 or more. By setting C [N / inch] to 1400 or more, it becomes easier to ensure high-speed durability. Also, C [N / inch] is preferably 3000 or less, and more preferably 2600 or less. By setting C [N / inch] to 3000 or less, the tire's contact area with the ground can be ensured, and the handling stability is improved. Therefore, C [N / inch] is preferably 1400 or more and 3000 or less, and more preferably 1800 or more and 2600 or less.

[0045] The load at 2% elongation (N) and the load at 5% elongation (N) of the organic fiber cord 32 can be adjusted, for example, by selecting the fiber type constituting the organic fiber cord 32, adjusting the cord structure, the number of twists, the processing conditions of the cord, etc. For example, by reducing the number of twists, the load at elongation can be increased. Also, examples of the processing conditions of the cord include the conditions of the dip treatment (resin liquid formulation, processing temperature, tension, time, etc.) in which the organic fiber cord 32 is immersed in a resin liquid for adhesion treatment with rubber. For example, when performing dip treatment using a resin liquid such as resorcinol-formalin-latex (RFL) or an aqueous solution of blocked isocyanate, by using a low-temperature bath and setting a high tension applied to the organic fiber cord 32, the load at elongation can be increased.

Example

[0046] Examples are shown below, but the present invention is not limited to these examples.

[0047] A steel cord and an organic fiber cord having the structures shown in Table 1 described later were produced respectively. Then, the produced steel cord was used for the belt ply, and the produced organic fiber cord was used for the belt reinforcing ply. And, as shown in FIG. 1, the belt ply was made into 2 plies, the belt reinforcing ply was made into 1 ply, and a radial tire with a tire size of 205 / 50R16 87V was vulcanized and molded according to a conventional method. For each tire, all the configurations other than the belt layer and the belt reinforcing layer were made common. Also, the two belt plies were arranged so that the belt angles were +25° / -25°.

[0048] For the produced pneumatic tire, the tire weight, high-speed durability, and handling stability were evaluated by the following methods respectively.

[0049] <Tire weight> It is the total weight per tire, and is expressed as an index with the total weight of the tire of Comparative Example 1 being 100. The smaller the number, the smaller the tire weight.

[0050] <High-speed durability> In accordance with FMVSS109 (UTQG), it was measured as follows by a drum tester having a steel rotating drum with a diameter of 1700 mm and a smooth surface. The test tire was inflated to an internal pressure of 220 kPa (2.2 kgf / cm 2) It was assembled onto a standard rim specified by JIS, and the load was set to 88% of the maximum load specified by JATMA. After running-in at a speed of 80 km / h for 60 minutes, it was allowed to cool down once, and after readjusting the air pressure, the main running was carried out. This main running started at 120 km / h, and thereafter, the speed was increased by 8 km / h every 30 minutes and the vehicle was run until a failure occurred. The total running distance of this main running until a failure occurred was expressed as an index with the high-speed durability of the tire of Comparative Example 1 set to 100. A larger index means better high-speed durability.

[0051] <Handling stability> Each tire incorporated at an internal pressure of 200 kPa was mounted on a test vehicle with a displacement of 2000 cc, and three trained test drivers drove on a test course for feeling evaluation. The scoring was evaluated by relative comparison with the tire of Comparative Example 1 set to 6 on a 10-point scale, and the average score of the three was expressed as an index with the tire of Comparative Example 1 set to 100. A larger number means better handling stability.

[0052] The tire weights, high-speed durabilities, and handling stabilities of each pneumatic tire are shown in Table 1 respectively.

[0053]

Table 1

[0054] As shown in Table 1, the pneumatic tires of Examples 1 to 4 can achieve both high-speed durability and handling stability at a high level while reducing the tire weight compared to the pneumatic tire of Comparative Example 1. That is, by setting the filament diameter of the steel cord to be more than 0.10 mm and less than 0.25 mm and satisfying the relationships represented by the above formulas (I) and (II), it can be said that both the high-speed durability and handling stability of the tire can be achieved at a high level.

[0055] On the one hand, the pneumatic tire of Comparative Example 5 with a filament diameter of 0.10 mm has a reduced tire weight, but its high-speed durability is decreased. This is presumably because when the filament diameter is 0.10 mm or less, the strength of the belt layer cannot be ensured.

[0056] Also, the pneumatic tire of Comparative Example 4 with a filament diameter of 0.25 mm has improved high-speed durability, but its tire weight has increased and its handling stability has decreased. This is presumably because when the filament diameter is 0.25 mm or more, in addition to the increase in tire weight, the bending rigidity of the belt ply tends to increase, which reduces the contact area of the tire and deteriorates the handling stability.

[0057] Also, the pneumatic tire of Comparative Example 3 with (B / A) of 400 or more has decreased high-speed durability and handling stability respectively. As described above, (B / A) is an index indicating the balance between the bending rigidity of the belt reinforcing ply 31 and the restraining force by the belt reinforcing layer 30. Therefore, when (B / A) is 400 or more, it is impossible to achieve both high-speed durability and handling stability of the tire at a high level.

[0058] Also, the pneumatic tires of Comparative Examples 2 and 6 with (C / A) of 600 or less have decreased high-speed durability and handling stability respectively. This is presumably because when (C / A) is 600 or less, the restraining force by the belt reinforcing layer 30 is excessively decreased, resulting in a decrease in high-speed durability and an excessive decrease in the contact area, which in turn deteriorates the handling stability.

[0059] Also, the pneumatic tire of Comparative Example 7 with (C / A) of 2000 or more has improved high-speed durability, but its handling stability has decreased. This is presumably because when (C / A) is 2000 or more, the restraining force by the belt reinforcing layer 30 becomes too large, reducing the contact area of the tire and deteriorating the handling stability.

Explanation of Symbols

[0060] 1 Pneumatic tire, 10 Tread, 11 Sidewall, 12 Bead, 13 Carcass, 14 Bead core, 15 Bead filler, 20 Belt layer, 21, 21A, 21B Belt ply, 22 Steel cord, 23 Filament, 24 Core part, 25 Sheath part, 30 Belt reinforcing layer, 31 Belt reinforcing ply, 32 Organic fiber cord (composite fiber cord), 33 Coating rubber, 41 Support roll, 42 Pushing jig, 50 Measurement sample

Claims

1. A pneumatic tire comprising a carcass, a belt layer disposed on the outer periphery of the crown portion of the carcass, and a belt reinforcing layer disposed on the outer periphery of the belt layer, wherein: the belt layer has a belt ply in which steel cords are arranged obliquely with respect to the tire circumferential direction; the belt reinforcing layer has a belt reinforcing ply in which organic fiber cords are arranged along the tire circumferential direction on the outer periphery of the belt layer; the filament diameter of the steel cord is more than 0.10 mm and less than 0.25 mm; let the bending load per unit width of one belt ply be A [N / inch]; let the product of the load at 2% elongation per organic fiber cord [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply [cord / inch] be B [N / inch]; when the product of the load at 5% elongation per organic fiber cord [N / cord] and the number of organic fiber cords driven into the belt reinforcing ply [cord / inch] is C [N / inch], the A, the B, and the C satisfy the relationships represented by the following formulas (I) and (II): a pneumatic tire. Formula (I): B / A < 400 Formula (II): 600 < C / A < 2000

2. The pneumatic tire according to claim 1, wherein the in-plane rigidity of the belt ply is 9 [kN / inch] or more.

3. The pneumatic tire according to claim 1, wherein the organic fiber cord is a composite fiber cord obtained by twisting a yarn made of aliphatic polyamide fiber and a yarn made of aromatic polyamide fiber.

4. The pneumatic tire according to claim 1, wherein the A is 1.5 or more and 4.5 or less.

5. The pneumatic tire according to claim 1, wherein the B is 400 or more and 1000 or less.

6. The pneumatic tire according to claim 1, wherein the C is 1400 or more and 3000 or less.

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