TIRES

Description

TECHNICAL FIELD

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

[0002] Pneumatic tires are conventionally known that include a carcass, a belt layer arranged on an outer circumference of a crown of the carcass, and a belt reinforcing layer arranged on an outer circumference of the belt layer (see, for example, JP 2010-47200 A). In addition, studies have been conventionally conducted on increasing strength of steel cords included in belt ply that forms the belt layer, for an advantage of improving durability of the tire in high-speed driving (high-speed durability). As a method for increasing the strength of the steel cord, for example, the filament diameter of the steel cord may be increased. JP 2020 104773 A discloses a pneumatic tire comprising a carcass, a belt layer arranged at an outer periphery of a crown part of the carcass and a belt reinforcement layer arranged at an outer periphery of the belt layer. The belt layer is formed of belt plies formed by inclining and arranging steel cords with respect to a tire circumferential direction, where filament diameters of the steel cords are 0.20 mm or less, cord flexural rigidity of each of the steel cords is 800 cN or less, cord strength of each of the steel cords is 3600 N / mm2 or more, and cord strength for unit width of each of the belt plies is 16kN / 25.4 mm or more. JP 2013 230744 A discloses a pneumatic tire including a carcass layer and a belt layer having at least two layers each made of a non-metallic material. An under-belt reinforcing layer is disposed between the belt layer and the carcass layer. An inclination angle of a reinforcing cord that constitutes the under-belt reinforcing layer is within a range of 0±10° with respect to a tire circumferential direction, and a width of the under-belt reinforcing layer is from 10% to 110% of a width of an innermost belt layer. JP H08 164704 A discloses a pneumatic tire with a tread part, a pair of side parts, which are connected to both sides of the tread, a carcass ply, which is formed inside the tread part, and a belt layer, which is buried inside the tread part. The belt layer consists of two-layer, steel belt ply layers, which are separated from each other. With regard to the width of the belt layer, the width of the first layer is wider than that of the second layer. The belt ply layers consist of cross layers having a belt angle of 68±2°. In this case, the flexural rigidity of the first belt ply layer is made lower than that of the second belt ply layer. JP 2006 069435 A discloses a radial tire with a radial carcass comprising one sheet or more of carcass ply; and a belt comprising two layers of steel belt layers, arranged on an outer periphery side of a crown part of the radial carcass. A ratio of a steel code amount per unit width of the steel belt layer of first layer and the steel belt layer of second layer (embedding number of steel code×steel code cross section) is 100:85-85:100 and a ratio of volume fraction of the steel code (cross section of steel code / whole cross section of steel code and coating rubber) is 100:85-85:100. Flexural rigidity of any one of the steel belt layer is lower than flexural rigidity of the other steel belt layer. JP 2005 239069 A discloses a radial tire with a band layer composed of a band ply spirally wound by a band cord which is provided outside a belt layer. The band cord is composed of a nylon fiber cord of a single twist yarn structure having a conditioned size of 1,400 to 2,800 dtex and an elongation of a cord of 4.0 to 6.0% at a load of 44 N. The belt layer is composed of a belt ply in which belt cords made of steel are arranged making an angle of 10 to 40° with respect to the peripheral direction of the tire, and the bending stiffness of one of the belt cords is at most 50 gf cm. US 2022 / 161602 A1 discloses a pneumatic radial tire including belt layers disposed on an outer circumferential side of a carcass layer in a tread portion, and a belt cover layer disposed on an outer circumferential side of the belt layers, the belt cover layer including organic fiber cords helically wound along a tire circumferential direction, the belt layers including steel cords arranged at an incline with respect to the tire circumferential direction in such a manner as to intersect one another between the layers, each of the belt layers having a bending rigidity of 16500 N·mm 2< / 50 mm or less per 50 mm width in a direction orthogonal to a longitudinal direction of the steel cords, and the belt cover layer including organic fiber cords having an elongation of 2.0% to 4.0% under a load of 2.0 cN / dtex, the organic fiber cords being helically wound along the tire circumferential direction.SUMMARYTECHNICAL PROBLEM

[0003] When steel cords each with a large filament diameter are used for the belt ply, the tire weight increases and the bending rigidity of the belt ply tends to increase. This reduces the ground contact area of the tire and deteriorates the driving stability. For this reason, it is not easy to achieve both high-speed durability and driving stability of the tire at a high level while reducing the tire weight.SOLUTION TO PROBLEM

[0004] A pneumatic tire according to an aspect of the present invention is a pneumatic tire including: a carcass; a belt layer arranged on an outer circumference of a crown of the carcass; and a belt reinforcing layer arranged on an outer circumference of the belt layer, in which: the belt layer has belt ply in which steel cords are arranged at an angle to a tire circumferential direction; the belt reinforcing layer has a belt reinforcing ply on the outer circumference of the belt layer, the belt reinforcing ply having organic fiber cords arranged in the tire circumferential direction; a filament diameter of each steel cord is more than 0.10 mm and less than 0.25 mm; and A, B, and C satisfy relationships represented by the following Expression (I) and Expression (II), B / A < 400 600 < C / A < 2000 where: A [N / m] ([N / inch]) is a bending load per unit width of a sheet of the belt ply; B [N / m] ([N / inch]) is a product of a load at 2% elongation of each of the organic fiber cords [N / cord] and the number of the organic fiber cords implanted in the belt reinforcing ply [cord / m] ([cord / inch]); and C [N / m] ([N / inch]) is a product of a load at 5% elongation of each of the organic fiber cords [N / cord] and the number of the organic fiber cords implanted in the belt reinforcing ply [cord / m] ([cord / inch]).ADVANTAGEOUS EFFECT OF INVENTION

[0005] The pneumatic tire according to an aspect of the present invention can reduce the tire weight while achieving both high-speed durability and high driving stability of the tire.BRIEF DESCRIPTION OF DRAWINGS

[0006] Embodiment(s) of the present invention will be described based on the following figures, wherein: FIG. 1is a sectional view of a pneumatic tire of an example in an embodiment, showing a half section in a tire axial direction; FIG. 2is a schematic view showing a section of a steel cord forming belt ply of an example in the embodiment; FIG. 3is a view for describing a method for measuring bending rigidity of the belt ply; and FIG. 4is a schematic view showing part of a section of belt reinforcing ply of an example in the embodiment. DESCRIPTION OF EMBODIMENT

[0007] The following describes an example of an embodiment of a pneumatic tire according to the present invention in detail, with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment.

[0008] FIG. 1 is a sectional view of a pneumatic tire 1 according to this embodiment, showing a half section in a tire axial direction. As shown in FIG. 1, the pneumatic tire 1 includes a tread 10 that is a portion that comes into contact with a road surface, a pair of sidewalls 11 arranged on opposite sides of the tread 10, and a pair of beads 12 arranged inside the sidewalls 11 in a tire radial direction. The pneumatic tire 1 also includes a carcass 13 that extends between a pair of beads 12.

[0009] The sidewalls 11 are arranged on opposite sides of the tread 10 and are provided in an annular shape in the tire circumferential direction. The sidewalls 11 are the portions of the pneumatic tire 1 that protrude furthest outward in a tire axial direction, and are gently curved so as to be convex toward the outside in the tire axial direction. The sidewalls 11 function to prevent damage to the carcass 13.

[0010] The beads 12 are portions arranged on the inner side of the sidewall 11 in the tire radial direction and fixed to a rim of a wheel. Each bead 12 includes a bead core 14 and a bead filler 15. The bead core 14 is an annular member that is made of a steel bead wire and extends over the entire circumference in the tire circumferential direction, and is embedded in the bead 12. The bead filler 15 is an annular hard rubber member that has a tapered tip that extends outward in the tire radial direction and that extends over the entire circumference in the tire circumferential direction.

[0011] The carcass 13 extends between the pair of beads 12 and is folded back around each bead core 14 to be engaged with the bead core 14. The carcass 13 is formed of at least one sheet of carcass ply. The carcass ply is formed by covering carcass cords made of organic fiber with coating rubber. The carcass cords are arranged substantially at a right angle (e.g., 80° or more and 90° or less) to the tire circumferential direction. Examples of organic fibers used for the carcass cords include polyester fiber, rayon fiber, aramid fiber, and nylon fiber.

[0012] The pneumatic tire 1 further includes a belt layer 20 arranged on the outer circumference of a crown of the carcass 13, and a belt reinforcing layer 30 arranged on the outer circumference of the belt layer 20. In other words, the belt layer 20 is arranged between the carcass 13 and the tread 10, and the belt reinforcing layer 30 is arranged between the belt layer 20 and the tread 10.

[0013] The belt layer 20 has belt ply 21 in which steel cords 22 (see FIG. 2) are arranged at an angle to the tire circumferential direction. The belt ply 21 is formed by covering steel cords 22 (see FIG. 2) with coating rubber. In this embodiment, the belt ply 21 is formed of two sheets of belt ply 21A and 21B. The steel cords 22 in the sheet of belt ply 21A and the steel cords 22 in the sheet of belt ply 21B are arranged so as to cross each other.

[0014] The belt reinforcing layer 30 is cap ply that covers the belt layer 20 with belt reinforcing ply 31. The belt reinforcing ply 31 is formed by covering organic fiber cords 32 (see FIG. 4) arranged in the tire circumferential direction with coating rubber 33 (see FIG. 4). As will be described in detail later, in this embodiment, each organic fiber cord 32 forming the belt reinforcing ply 31 is a composite fiber cord having yarn made of aliphatic polyamide fibers and yarn made of aromatic polyamide fibers twisted together. 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 belt layer 20 in the width direction.

[0015] In this embodiment, the belt reinforcing layer 30 is cap ply that covers the entire belt layer 20 in the width direction. However, the belt reinforcing layer 30 may be edge ply that covers the belt ends of the belt layer 20.

[0016] Next, the belt ply 21 forming the belt layer 20 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a schematic view showing a cross section of a steel cord 22 forming the belt ply 21.

[0017] As described above, the belt ply 21 is formed by covering the steel cords 22 (see FIG. 2) with a coating rubber. Here, in the belt layer 20, the angle of the steel cords 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 this embodiment, the belt layer 20 is formed of two sheets of belt ply 21A and 21B. Therefore, the belt angles of the two sheets of belt ply 21A and 21B are both 20° or more and 45° or less with respect to the tire circumferential direction, the steel cords 22 in the belt ply 21A being arranged to cross the steel cords 22 in the belt ply 21B.

[0018] The structure of each steel cord 22 is not particularly limited, but as shown in FIG. 2, the structure is preferably a m+n multi-layer twisted structure (m=1 to 3, n=2 to 15) in which a plurality of filaments 23 are twisted together as a sheath 25 around a core 24 having one or more filaments 23 twisted together. Using the steel cords 22 having the above structure makes it easy to achieve both high-speed durability and driving stability of the tire.

[0019] The structure of a steel cord 22 is not limited to the above multi-layer twisted structure, and may include the following: a 1 × n single twisted structure (n = 2 to 15) in which n metal filaments are twisted together; and an m × n multi-twisted structure (m = 3 to 5, n = 2 to 4) formed by forming strands each having n metal filaments preliminarily twisted together and then further subjecting m strands to finish-twisting together.

[0020] The twist pitch of the steel cord 22 is not particularly limited, but is, for example, 5 mm or more and 13 mm or less, and preferably 7 mm or more and 11 mm or less.

[0021] 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. The cord diameter of the steel cord 22 of 0.3 mm or more and 0.7 mm or less makes it easy to achieve both high-speed durability and high driving stability of the tire.

[0022] The filament diameter of each steel cord 22 is more than 0.10 mm, preferably 0.12 mm or more, and more preferably 0.14 mm or more. The filament diameter of more than 0.10 mm can ensure the high-speed durability of the tire. In addition, 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. The filament diameter of less than 0.25 mm can reduce the tire weight while the decreasing bending rigidity of the belt ply 21. This can increase the ground contact area of the tire in running, and further improve driving stability. 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. The filament diameter of the steel cord 22 may be more than 0.10 mm and 0.23 mm or less, or more than 0.10 mm and 0.21 mm or less. The filament diameter of the steel cord 22 may be 0.12 mm or more and less than 0.25 mm, or 0.14 mm or more and less than 0.25 mm.

[0023] The number of steel cords 22 implanted in the belt ply 21 is not particularly limited, and is, for example, 591 [cord / m] (15 [cord / inch]) or more and 1181 [cord / m] (30 [cord / inch]) or less.

[0024] The cord bending rigidity per steel cord 22 is preferably 200 cN or less, and more preferably 150 cN or less. The cord bending rigidity per steel cord 22 of 200 cN or less makes it easy to reduce the bending rigidity of the belt ply 21. This increases the ground contact area of the tire, and can improve the driving stability. The lower limit of the cord bending rigidity per steel cord 22 is, for example, 80 cN. The cord bending rigidity per steel cord 22 of less than 80 cN excessively reduces the bending rigidity of the belt ply 21 and may conversely decrease driving stability. Therefore, the cord bending rigidity per steel cord 22 is preferably 80 cN or more and 200 cN or less, and more preferably 80 cN or more and 150 cN or less.

[0025] In this description, the cord bending rigidity is a value defined as the maximum load when one steel cord 22 is bent at its center with a fulcrum distance of 25.4 mm. Specifically, the value can be measured by conducting a three-point bending test using a tensile testing machine including a pair of support bars with a circular section (diameter = 3 mm) arranged 25.4 mm apart, and a fixed bar with a circular section (diameter = 3 mm) located vertically above the midpoint of the pair of support bars. More specifically, at room temperature, a steel cord 22 with a length of 80 mm is placed on the pair of support bars. The pair of support bars are then moved upward at a test speed of 500 mm / min, and the maximum load is measured when the steel cord 22 is bent with the fixed bars as a fulcrum. The average of the five maximum load measurements is the cord bending rigidity per steel cord 22.

[0026] The tensile strength (strength and elongation) per steel cord 22 is not particularly limited, but is, for example, 400 N or more and 1000 N or less. The tensile strength per steel cord is the maximum load required to break a test piece measured at a tensile speed of 500 m / min in accordance with the tensile test of the breaking load and total elongation at break (section 6.4) in "Testing methods for steel tire cords" of JIS G3510.

[0027] Here, if A [N / m] ([N / inch]) is defined as the bending load per unit width of a sheet of belt ply 21, A just needs to be a value that satisfies the Expression (I) and Expression (II) described later. However, A is preferably 177 [N / m] (4.5 [N / inch]) or less, and more preferably 157 [N / m] (4.0 [N / inch]) or less. A set to 177 [N / m] (4.5 [N / inch]) or less makes it easy to increase the ground contact area of the tire in running, and further improves the driving stability. Furthermore, A is preferably 59 [N / m] (1.5 [N / inch]) or more, and more preferably 79 [N / m] (2.0 [N / inch]) or more. A set to 59 [N / m] (1.5 [N / inch]) or more makes it easy to ensure the high-speed durability of the tire. Therefore, the bending load per unit width A of the belt ply 21 is preferably 59 [N / m] (1.5 [N / inch]) or more and 177 [N / m] (4.5 [N / inch]) or less, and more preferably 79 [N / m] (2.0 [N / inch]) or more and 157 [N / m] (4.0 [N / inch]) or less. 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 each steel cord 22. For example, increasing the filament diameter can increase the bending load per unit width of the belt ply 21.

[0028] In this description, the bending load per unit width of the belt ply 21 is a value defined as the maximum load when a sheet of belt ply 21 is bent at its center with a fulcrum distance of 100 mm. Specifically, as shown in FIG. 3, the measurement can be performed using a tester including a pair of support rolls 41 with a circular section (diameter = 20 mm) arranged 100 mm apart, and a pressing jig 42 with a circular section (diameter = 15 mm) located vertically above the midpoint of the pair of support rolls 41. More specifically, the belt ply 21 is first cut into one-inch widths to produce a measurement sample 50. Then, at room temperature, the measurement sample 50 is placed on the pair of support rolls 41 so that the longitudinal direction of the steel cords 22 of the measurement sample 50 is perpendicular to the axial direction of the support roll 41. Then, the pressing jig 42 is moved downward (in the direction of an arrow) at a pressing speed of 300 mm / min, and the maximum load is measured with the measurement sample 50 being bent with the pressing jig 42 as a fulcrum. The average value of the five measurements of the maximum load is determined as the bending load per unit width of the belt ply 21.

[0029] The in-plane rigidity of a sheet of belt ply 21 is preferably 354 [kN / m] (9.0 [kN / inch]) or more, and more preferably 472 [kN / m] (12 [kN / inch]) or more. The in-plane rigidity of the belt ply 21 set to 354 [kN / m] (9.0 [kN / inch]) or more can ensure strength of the belt layer 20, and makes it easy to ensure high-speed durability. The in-plane rigidity of a sheet of belt ply 21 is preferably 984 [kN / m] (25 [kN / inch]) or less, and more preferably 787 [kN / m] (20 [kN / inch]) or less. The in-plane rigidity of the belt ply 21 set to 984 [kN / m] (25 [kN / inch]) or less makes it easy to increase the ground contact area of the tire in running, and further improve driving stability. Therefore, the in-plane rigidity of a sheet of belt ply 21 is preferably 354 [kN / m] (9.0 [kN / inch]) or more and 984 [kN / m] (25 [kN / inch]) or less, and more preferably 472 [kN / m] (12 [kN / inch]) or more and 787 [kN / m] (20 [kN / inch]) or less.

[0030] 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 cords 22. Specifically, the in-plane rigidity of the belt ply 21 can be determined by multiplying the tensile strength (strength and elongation) of a steel cord 22 by the number of steel cords 22 implanted in the belt ply 21. 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 cords 22. For example, increasing the number of filaments 23 can increase the in-plane rigidity of the belt ply 21. Increasing the filament diameter can increase the in-plane rigidity of the belt ply 21.

[0031] Next, the belt reinforcing ply 31 forming the belt reinforcing layer 30 will be described in detail with reference to FIG. 4. FIG. 4 is a schematic view showing part of a cross section of the belt reinforcing ply 31 forming the belt reinforcing layer 30.

[0032] As shown in FIG. 4, the belt reinforcing ply 31 is formed by covering organic fiber cords 32 arranged in the tire circumferential direction with coating rubber 33. Here, each organic fiber cord 32 is preferably a composite fiber cord formed by twisting yarn made of aliphatic polyamide fibers with yarn made of aromatic polyamide fibers. When the organic fiber cords 32 are the composite fiber cords described above, it is easy to adjust the load at 2% elongation and the load at 5% elongation of the organic fiber cords 32 described later within a predetermined range.

[0033] Examples of resins used as the aliphatic polyamide fibers include aliphatic polyamide 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 these, the resin is preferably nylon 66 from the viewpoint of adjusting the load at 2% elongation and the load at 5% elongation of each organic fiber cord 32 described later within a predetermined range.

[0034] The aromatic polyamide fiber is a polyamide having an aromatic skeleton in the main chain, and may be either para-aramid or meta-aramid. For example, any known aramid fiber used in this technical field may be used as appropriate.

[0035] The fineness of the organic fiber cord 32 is not particularly limited, but is, for example, 700 dtex or more, preferably 800 dtex or more, and more preferably 900 dtex or more. The fineness of the organic fiber cord 32 set to 700 dtex or more allows for reducing the number of organic fiber cords 32 implanted in the belt reinforcing ply 31 required to obtain the desired tire performance. This makes it less likely to cause adhesion failure between the organic fiber cord 32 and the rubber at the cut end of the belt reinforcing ply 31, making it easy to ensure the high-speed durability of the tire. In addition, 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. The fineness of the organic fiber cord 32 set to 3000 dtex or less can reduce the weight of the tire. Thus, 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. The fineness is also referred to as the nominal fineness or the indicated fineness.

[0036] The number of the organic fiber cord 32 implanted in the belt reinforcing ply 31 is not particularly limited, but is preferably 591 [cord / m] (15 [cord / inch]) to 1575 [cord / m] (40 [cord / inch]), and more preferably 787 [cord / m] (20 [cord / inch]) to 1378 [cord / m] (35 [cord / inch]).

[0037] The number of twists per 10 cm of the organic fiber cord 32 is not particularly limited, but is preferably 25 [turns / 10 cm] to 70 [turns / 10 cm], and more preferably 25 [turns / 10 cm] to 60 [turns / 10 cm]. When the number of twists of the organic fiber cord 32 is 25 [turns / 10 cm] to 70 [turns / 10 cm], it is easy to adjust the load at 2% elongation and the load at 5% elongation of the organic fiber cord 32 to be described later within a predetermined range.

[0038] Here, B [N / m] ([N / inch]) is defined as the product of the load at 2% elongation per organic fiber cord 32 (LASE 2%) [N / cord] and the number of organic fiber cords implanted in the belt reinforcing ply 31 [cord / inch]. C [N / m] ([N / inch]) is defined as the product of the load at 5% elongation per organic fiber cord 32 (LASE 5%) [N / cord] and the number of organic fiber cords implanted in the belt reinforcing ply 31 [cord / m] ([cord / inch]). In this case, A [N / m] ([N / inch]), B [N / m] ([N / inch]), and C [N / m] ([N / inch]) described above satisfy the relationships represented by the following Expression (I) and Expression (II), A [N / m] ([N / inch]) being the bending load per unit width of a sheet of belt ply 21. B / A < 400 600 < C / A < 2000

[0039] (B / A) set to less than 400 appropriately balances the bending rigidity of the belt reinforcing ply 31 and the restraining force of the belt reinforcing layer 30, and allows for achieving both high-speed durability and high driving stability of the tire. In other words, (B / A) of 400 or more, for example, causes the restraining force of the belt reinforcing layer 30 to be too large, resulting in reduced ground contact area of the tire and deteriorated driving stability. (B / A) just needs to be less than 400, preferably less than 350, and more preferably less than 300. The lower limit of (B / A) is 50, for example. When (B / A) is 50 or less, the bending rigidity of the belt ply 21 tends to increase. This may reduce the ground contact area of the tire, and deteriorate driving stability. Therefore, the relationship may be 50 < B / A < 400, preferably 50 < B / A < 350, and more preferably 50 < B / A < 300.

[0040] Furthermore, (C / A) exceeding 600 ensures the restraining force of the belt reinforcing layer 30, and can ensure high-speed durability of the tire while improving driving stability. (C / A) just needs to be more than 600, preferably more than 700, and more preferably more than 800. In addition, (C / A) set to less than 2000 appropriately balances the bending rigidity of the belt reinforcing ply 31 and the restraining force of the belt reinforcing layer 30, and allows for achieving both high-speed durability and high driving stability of the tire. In other words, (C / A) of 2000 or more, for example, causes the restraining force of the belt reinforcing layer 30 to be too large, resulting in reduced ground contact area and deteriorated driving stability of the tire. (C / A) just needs to be less than 2,000, but is preferably less than 1,600, and more preferably less than 1,200. Therefore, the relationship is preferably 700 < C / A < 1600, and more preferably 800 < C / A < 1200. In addition, the relationship may be 600 < C / A < 1600, or 600 < C / A < 1200. It may also be 700 < C / A < 2000, or 800 < C / A < 2000.

[0041] In this description, the load at 2% elongation per organic fiber cord [N / cord] and the load at 5% elongation per organic fiber cord [N / cord] respectively mean the load at 2% elongation and the load at 5% elongation when a tensile test is conducted in accordance with JIS L1017 in a test room under standard conditions of a temperature of 20±2°C and a relative humidity of 65±4%, as specified in JIS L0105.

[0042] The above B [N / m] ([N / inch]) just needs to be within a range that satisfies the above Expression (I), but is preferably 15748 [N / m] (400 [N / inch]) or more, and more preferably 19685 [N / m] (500 [N / inch]) or more. B [N / m] ([N / inch]) of less than 15748 [N / m] (400 [N / inch]) may make it difficult to maintain the tire shape and deteriorate driving stability. Furthermore, B [N / m] ([N / inch]) is preferably 39370 [N / m] (1000 [N / inch]) or less, and more preferably 31496 [N / m] (800 [N / inch]) or less. B [N / m] ([N / inch]) exceeding 39370 [N / m] (1000 [N / inch]) may cause the restraining force of the belt reinforcing layer 30 to be too large, resulting in reduced ground contact area of the tire and deteriorated driving stability. Therefore, B [N / m] ([N / inch]) is preferably 15748.0 [N / m] (400 [N / inch]) or more and 39370 [N / m] (1000 [N / inch]) or less, and more preferably 19685 [N / m] (500 [N / inch]) or more and 31496 [N / m] (800 [N / inch]) or less.

[0043] The above C [N / m] ([N / inch]) just needs to be in a range that satisfies the above Expression (II), but is preferably 55118 [N / m] (1400 [N / inch]) or more, and more preferably 70866 [N / m] (1800 [N / inch]) or more. C [N / m] ([N / inch]) set to 55118 [N / m] (1400 [N / inch]) or more makes it easy to ensure high-speed durability. C [N / m] ([N / inch]) is preferably 118110 [N / m] (3000 [N / inch]) or less, and more preferably 102362 [N / m] (2600 [N / inch]) or less. C [N / m] ([N / inch]) set to 118110 [N / m] (3000 [N / inch]) or less allows for ensuring the ground contact area of the tire, thereby improving driving stability. Therefore, C [N / m] ([N / inch]) is preferably 55118 [N / m] (1400 [N / inch]) or more and 118110 [N / m] (3000 [N / inch]) or less, and more preferably 70866 [N / m] (1800 [N / inch]) or more and 102362 [N / m] (2600 [N / inch]) or less.

[0044] The load (N) at 2% elongation and the load (N) at 5% elongation of each organic fiber cord 32 can be adjusted, for example, by selecting the type of fiber forming the organic fiber cord 32, adjusting the cord structure, the number of twists, the cord processing conditions, etc. For example, reducing the number of twists can increase the load at an elongation. Additionally, the cord processing conditions include the conditions of the dip processing in which the organic fiber cord 32 is immersed in a resin liquid for adhesion processing with rubber (resin liquid blend, processing temperature, tension, time, etc.). For example, when dip processing is performed using a resin liquid such as resorcin-formaldehyde-latex (RFL) or a blocked isocyanate aqueous solution, it is possible to increase the load at an elongation if a low-temperature bath is used and the tension applied to the organic fiber cord 32 is set high.[Example]

[0045] The following shows examples, but the present invention is not limited to these examples.

[0046] Steel cords and organic fiber cords are produced, each of which has a structure shown in Table 1 described later. The produced steel cords are used for belt ply, and the produced organic fiber cords are used for the belt reinforcing ply. Then, as shown in FIG. 1, the belt ply is formed of two sheets of ply, the belt reinforcing ply is formed of a sheet of ply, and a radial tire having a tire size of 205 / 50R16 87V is vulcanized and molded in the usual manner. The configuration of each tire is the same except for the belt layer and the belt reinforcing layer. The two sheets of belt ply are arranged so that the belt angles are +25° and -25°.

[0047] The tire weight, high-speed durability, and driving stability of the produced pneumatic tires are evaluated by the following methods.<Tire weight>

[0048] Tire weight is the total weight of one tire, and is expressed as an index with the total weight of the tire of Comparative Example 1 being 100. This means that a smaller number equates to a lower tire weight.<High-speed durability>

[0049] Measurements were made in the following manner using a drum testing machine that conforms to FMVSS109 (UTQG) and has a rotating drum made of steel with a smooth surface and a diameter of 1700 mm. Each test tire is mounted on a standard rim specified by JIS with an internal pressure of 220 kPa (2.2 kgf / cm 2< ), and the load is 88% of the maximum load specified by JATMA. The tire undergoes preliminary run for 60 minutes at a speed of 80 km / h, is left to cool, has its air pressure adjusted again, and then undergoes an actual run. The actual run starts at 120 km / h, increases the speed by 8 km / h every 30 minutes, and keeps running until a failure occurs. The total running distance of the actual run until a failure occurs is expressed as an index with the high-speed durability of the tire of Comparative Example 1 being 100. This means that a higher index equates to a better high-speed durability.<Driving stability>

[0050] Each tire is assembled with an internal pressure of 200 kPa and mounted on a test vehicle with an engine displacement of 2000 cc, and then three trained test drivers each run the vehicle on a test course and evaluate the feel. The tire is scored on a 10-point scale based on a relative comparison with the tire of Comparative Example 1 scored as six, and the average score of the three drivers is expressed as an index, with the tire of Comparative Example 1 scored as 100. This means that a higher number equates to better driving stability.

[0051] Table 1 shows the tire weight, high-speed durability, and driving stability of each pneumatic tire. [Table 1]ItemExample 1Example 2Example 3Example 4Comparative Example 1Comparative Example 2Comparative Example 3Comparative Example 4Comparative Example 5Comparative Example 6Comparative Example 7Belt layerCord materialSteelSteelSteelSteelSteelSteelSteelSteelSteelSteelSteelCord configuration2+7x0.1752+7x0.1752+7x0.2002+7x0.1502+2x0.252+2x0.252+7x0.1752+7x0.2502+7x0.1002+7x0.1752+7x0.175Filament diameter (mm)0.1750.1750.2000.1500.2500.2500.1750.2500.1000.1750.175Cord bending rigidity (cN / cord)1201201559022022012052070120120Strength and elongation (N / cord)6806808905006206206801380225680680Number of cords (cord / inch)2020192621212012352020Belt bending load (N / inch) (A)2.62.63.32.45.75.72.66.42.22.62.6In-plane rigidity (kN / inch)13.613.616.913.013.013.013.616.67.913.613.6Belt reinforcing layerCord materialAramid Nylon 66Aramid Nylon 66Aramid Nylon 66Aramid Nylon 66Nylon 66Nylon 66AramidAramid Nylon 66Aramid Nylon 66Aramid Nylon 66Aramid Nylon 66Cord configuration1100dtex 940dtex1670dtex 1400dtex1100dtex 940dtex1100dtex 940dtex1400dtex / 2900dtex / 21100dtex / 21100dtex 940dtex1100dtex 940dtex550dtex 440dtex2200dtex 1670dtexLoad at 2% elongation (LASE 2%) (N / cord)182518182112581818835Load at 5% elongation (LASE 5%) (N / cord)7310473735024113737330250Number of cords (cord / inch)3520353528341935354022LASE 2% (N / cord) x number of cords [cord / inch] (B)6305006306305884081102630630320770LASE 5% (N / cord) x number of cords [cord / inch] (C)2555208025552555140081621472555255512005500B / A2421921912631037242498286123296C / A983800774106524614382639911614622115Evaluation result (Index)Tire weight949596941009894105939498High-speed durability11011011210510095951069095115Driving stability1181171121201009895951029897

[0052] As shown in Table 1, the pneumatic tires of Examples 1 to 4 all have a lighter tire weight than the pneumatic tire of Comparative Example 1, while achieving both high-speed durability and high driving stability. In other words, it can be said that if the filament diameter of each steel cord is set to more than 0.10 mm and less than 0.25 mm while the relationships represented by the above Expression (I) and Expression (II) are satisfied, it is possible to achieve both high-speed durability and high driving stability of the tire.

[0053] In contrast, the pneumatic tire of Comparative Example 5, which has a filament diameter of 0.10 mm, has a lighter tire weight but decreased high-speed durability. This is presumably because the filament diameter of 0.10 mm or less cannot ensure the strength of the belt layer.

[0054] In addition, the pneumatic tire of Comparative Example 4, which has a filament diameter of 0.25 mm, has improved high-speed durability but an increased tire weight and decreased driving stability. This is presumably because the filament diameter of 0.25 mm or more increases the tire weight while causing a tendency for the bending rigidity of the belt ply to increase, reducing the ground contact area of the tire and deteriorating driving stability.

[0055] The pneumatic tire of Comparative Example 3, in which (B / A) is 400 or more, has both decreased high-speed durability and driving stability. As described above, (B / A) is an index showing the balance between the bending rigidity of the belt reinforcing ply 31 and the restraining force of the belt reinforcing layer 30. Therefore, (B / A) of 400 or more does not allow for achieving both high-speed durability and high driving stability of the tire.

[0056] The pneumatic tires of Comparative Examples 2 and 6, in which (C / A) is 600 or less, have both decreased high-speed durability and driving stability. This is presumably because (C / A) of 600 or less excessively reduces the restraining force of the belt reinforcing layer 30, which not only reduces high-speed durability but also excessively decreases the ground contact area, conversely resulting in decreased driving stability.

[0057] The pneumatic tire of Comparative Example 7, in which (C / A) is 2000 or more, has improved high-speed durability but decreased driving stability. This is presumably because (C / A) of 2000 or more causes the restraining force of the belt reinforcing layer 30 to be too large, reducing the ground contact area of the tire and deteriorating driving stability.REFERENCE SIGNS LIST

[0058] 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, 25 sheath, 30 belt reinforcing layer, 31 belt reinforcing ply, 32 organic fiber cord (composite fiber cord), 33 coating rubber, 41 support roll, 42 pressing jig, 50 measurement sample

Claims

1. A pneumatic tire (1) comprising: a carcass (13); a belt layer (20) arranged on an outer circumference of a crown of the carcass (13); and a belt reinforcing layer (30) arranged on an outer circumference of the belt layer (20), wherein the belt layer (20) has belt ply (21) in which steel cords (22) are arranged at an angle to a tire circumferential direction, the belt reinforcing layer (30) has a belt reinforcing ply (31) on the outer circumference of the belt layer (20), the belt reinforcing ply having organic fiber cords (32) arranged in the tire circumferential direction, characterized in that a filament diameter of each steel cord (22) is more than 0.10 mm and less than 0.25 mm, and A, B, and C satisfy relationships represented by the following Expression (I) and Expression (II), B / A < 400 600 < C / A < 2000 where: the A [N / m] ([N / inch]) is a bending load per unit width of a sheet of the belt ply (21) defined as the maximum load when the sheet of the belt ply (21) is bent at its center with a fulcrum distance of 100 mm, and measured according to the description; B [N / m] ([N / inch]) is a product of a load at 2% elongation of each of the organic fiber cords (32) [N / cord] and the number of the organic fiber cords (32) implanted in the belt reinforcing ply (31) [cord / m] ([cord / inch]); and C [N / m] ([N / inch]) is a product of a load at 5% elongation of each of the organic fiber cords (32) [N / cord] and the number of the organic fiber cords (32) implanted in the belt reinforcing ply (31) [cord / m] ([cord / inch]).

2. The pneumatic tire (1) according to claim 1, wherein in-plane rigidity of the belt ply (21) is 354 [kN / m] (9 [kN / inch]) or more.

3. The pneumatic tire (1) according to claim 1 or 2, wherein each organic fiber cord (32) is a composite fiber cord formed by twisting yarn made of aliphatic polyamide fibers with yarn made of aromatic polyamide fibers.

4. The pneumatic tire (1) according to any one of claims 1 to 3, wherein A is 59 [N / m] (1.5 [N / inch]) or more and 177 [N / m] (4.5 [N / inch]) or less.

5. The pneumatic tire (1) according to any one of claims 1 to 4, wherein B is 15748 [N / m] (400 [N / inch]) or more and 39370 [N / m] (1000 [N / inch]) or less.

6. The pneumatic tire (1) according to any one of claims 1 to 5, wherein C is 55118 [N / m] (1400 [N / inch]) or more and 118110 [N / m] (3000 [N / inch]) or less.

7. The pneumatic tire (1) according to any one of claims 1 to 6, wherein a ratio (B / A) of B to A satisfies 50 < B / A < 300.

8. The pneumatic tire (1) according to any one of claims 1 to 7, wherein a ratio (C / A) of C to A satisfies 800 < C / A < 1200.

9. The pneumatic tire (1) according to any one of claims 1 to 8, wherein a filament diameter of each steel cord (22) is 0.14 mm or more and 0.21 mm or less.