Pneumatic tire

Abstract

To make both high-speed durability and steering stability of a tire compatible at a high dimension.SOLUTION: A pneumatic tire 1 a comprises a belt layer 20 having a belt ply 21 and a belt reinforcement layer 30 having a belt reinforcement ply 31 in which organic fiber cords are arranged along a tire circumferential direction. The in-plane rigidity in the tire width direction of the belt ply 21 is 4.0[kN / inch] or more. When the bending load of the belt ply 21 is defined as A[N / inch], a belt angle is defined as B[deg], a product of 2% elongation-time load of the organic fiber cord and hitting number of the organic fiber cord is defined as C[N / 25 mm], and a product of 5% elongation-time load of the organic fiber cord and hitting number of the organic fiber cord is defined as D[N / 25 mm], A, B, C and D satisfy a relation represented by the following formulae (I) and (II): the formula (I): a formula (I):2.0≤C / (A×(90-B)) and the formula (II):8.0≤D / (A×(90-B))≤30.0.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 (high-speed durability) of the tire during high-speed driving, increasing the strength of the steel cord included in the belt ply constituting the belt layer has been studied.

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 the strength of the steel cord included in the belt ply is increased, the rigidity of the belt layer increases, resulting in deteriorated road surface followability and reduced handling stability in some cases. Therefore, it is not easy to improve the handling stability while ensuring high-speed durability.

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 in-plane rigidity of the belt ply in the tire width direction is 4.0 [kN / inch] or more, the bending load per unit width of one sheet of the belt ply is defined as A [N / inch], in the belt layer, the angle of the steel cord with respect to the tire circumferential direction is defined as B [deg], the product of the load at 2% elongation per one organic fiber cord [N] and the number of organic fiber cords driven into the belt reinforcing ply [number / 25 mm] is defined as C [N / 25 mm], and the product of the load at 5% elongation per one organic fiber cord [N] and the number of organic fiber cords driven into the belt reinforcing ply [number / 25 mm] is defined as D [N / 25 mm], and A, B, C, and D satisfy the relationships represented by the following formula (I) and formula (II). Formula (I): 2.0 ≤ C / (A × (90 - B)) Formula (II): 8.0 ≤ D / (A × (90 - B)) ≤ 30.0

Advantages of the Invention

[0006] According to the pneumatic tire of the present invention, it is possible to improve the handling stability while ensuring high-speed durability.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

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 embodiment described below is merely an example, 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 inner side in the tire radial direction 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 beads 12 are disposed on the inner side in the tire radial direction of the sidewalls 11 and are portions 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 spanned 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 a coating rubber. The carcass cord is arranged substantially at a right angle (for example, 80° or more and 90° or less) with respect 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 with a coating rubber. In the present embodiment, the belt layer 20 is composed of two belt plies 21A and 21B. And 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 formed by coating organic fiber cords 32 (see FIG. 4) arranged along the tire circumferential direction with a coating rubber 33 (see FIG. 4). Although details will be described later, the organic fiber cords 32 constituting the belt reinforcing ply 31 are preferably composite fiber cords 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 addition, 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. Further, the belt reinforcing layer 30 may be composed of a plurality of belt reinforcing plies 31.

[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] The belt ply 21 is formed by coating a steel cord 22 with a coating rubber. The structure of the steel cord 22 is not particularly limited, but as shown in FIG. 2, it is preferably an m + n multi-layer twisted structure (m = 1 or more and 3 or less, n = 2 or more and 15 or less) in which a plurality of filaments 23 are twisted around a core part 24 formed by twisting one or more filaments 23 to form a sheath part 25. By using the steel cord 22 having the above structure, it becomes easy to achieve both high-speed durability and handling stability at a high level while reducing the tire weight.

[0019] 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 formed by twisting n metal filaments (n is 2 or more and 15 or less), or an m×n multi-twisted structure formed by further twisting m strands formed by twisting n metal filaments in a lower twist (m is 3 or more and 5 or less, n is 2 or more and 4 or less), etc.

[0020] 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.

[0021] The cord diameter of the steel cord 22 is not particularly limited, but it 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 while reducing the tire weight.

[0022] The filament diameter of the steel cord 22 is preferably more than 0.10 mm, more preferably 0.12 mm or more, and even more preferably 0.14 mm or more. By setting the filament diameter to more than 0.10 mm, it becomes easy to ensure the high-speed durability of the tire. Also, the filament diameter of the steel cord 22 is preferably less than 0.25 mm, more preferably 0.23 mm or less, and even more preferably 0.21 mm or less. By setting the filament diameter to less than 0.25 mm, it becomes easy to reduce the tire weight. Therefore, the filament diameter of the steel cord 22 is preferably more than 0.10 mm and less than 0.25 mm, more preferably 0.12 mm or more and 0.23 mm or less, and even more preferably 0.14 mm or more and 0.21 mm or less.

[0023] Also, the number of steel cords 22 driven in is not particularly limited. For example, it is 15 [cords / inch] or more and 30 [cords / inch] or less.

[0024] The code bending stiffness per steel cord 22 is preferably 200 cN or less, more preferably 150 cN or less. By setting the code bending stiffness per steel cord 22 to 200 cN or less, it becomes easy 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 code bending stiffness per steel cord 22 is, for example, 80 cN. When the code bending stiffness per steel cord 22 is less than 80 cN, the bending stiffness of the belt ply 21 becomes excessively small, and the handling stability may be deteriorated instead. Therefore, the code bending stiffness per steel cord 22 is preferably 80 cN or more and 200 cN or less, more preferably 80 cN or more and 150 cN or less.

[0025] In this specification, the code bending stiffness is a value defined by the maximum load when a single steel cord 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 circular cross-section support bars (diameter = 3 mm) arranged at intervals of 25.4 mm and a circular cross-section fixing bar (diameter = 3 mm) positioned vertically upward from 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 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 cord 22 is bent with the fixing bar as a fulcrum is measured. Then, the average value of five measured values of the maximum load is defined as the code bending stiffness per steel cord 22.

[0026] The tensile strength (strength 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 for a test piece measured at a tensile speed of 500 m / min in accordance with the tensile test of the cutting load and total elongation at break (section 6.4) in "Steel Tire Cord Test Method" of JIS G3510.

[0027] 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.

[0028] 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 central portion 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 (diameter = 20 mm) with a circular cross-section arranged at intervals of 100 mm and a pressing jig 42 (diameter = 15 mm) with a circular cross-section located vertically upward from the midpoint between the pair of support rolls 41. More specifically, first, the belt ply 21 is cut to a width of 1 inch to prepare 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 pressing jig 42 is moved downward (in the direction of the arrow) at a pressing speed of 300 mm / min, and the maximum load when the measurement sample 50 is bent with the pressing 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.

[0029] Further, assuming that the in-plane rigidity of the steel cord 22 in the extending direction of one belt ply 21 is X [kN / inch], X is preferably 9.0 or more, and more preferably 12.0 or more. By setting X to 9.0 or more, the strength of the belt layer 20 can be ensured, and the high-speed durability can be improved. Also, X is preferably 25.0 or less, and more preferably 20.0 or less. By setting X to 25.0 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 X [kN / inch] of one belt ply 21 is preferably 9.0 or more and 25.0 or less, and more preferably 12.0 or more and 20.0 or less.

[0030] Incidentally, the in-plane rigidity in the extending direction of the steel cord 22 of the belt ply 21 can be obtained by multiplying the above-mentioned tensile strength (strength at break) of the 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.

[0031] As described above, the belt ply 21 is configured by covering the steel cord 22 with a coating rubber. Here, in the belt layer 20, assuming that the angle of the steel cord 22 with respect to the tire circumferential direction (hereinafter referred to as the belt angle) is B [deg], B may be a value that satisfies the following formulas (I) and (II), but is preferably 40 or less, and more preferably 35 or less. By setting B to 40 or less, a decrease in the rigidity in the tire circumferential direction is suppressed, and it becomes easier to improve the handling stability. The lower limit of B is, for example, 20. Therefore, B is preferably 20 or more and 40 or less, and more preferably 20 or more and 35 or less.

[0032] When the in-plane rigidity in the tire width direction of the belt ply 21 is Y [kN / inch], Y is 4.0 or more, preferably 4.5 or more, and more preferably 5.0 or more. By setting Y to 4.0 or more, the strength of the belt layer 20 can be ensured and the high-speed durability can be improved. Also, Y is preferably 10.0 or less, and more preferably 9.0 or less. By setting Y to 10.0 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 Y [kN / inch] in the tire width direction of the belt ply 21 is preferably 4.0 or more, preferably 4.5 or more and 10.0 or less, and more preferably 5.0 or more and 9.0 or less. Note that the in-plane rigidity in the tire width direction of the belt ply 21 can be calculated by multiplying the value of the in-plane rigidity in the extending direction of the steel cord 22 of the belt ply 21 described above by sin(B×π / 180). Here, B represents the belt angle described above.

[0033] Also, the ratio (Y / A) of the in-plane rigidity Y [kN / inch] in the tire width direction of the belt ply 21 to the bending load A [N / inch] per unit width of the single belt ply 21 described above is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.4 or more. By setting (Y / A) to 1.0 or more, it becomes easy to achieve both high-speed durability and handling stability at a high level. The upper limit of (Y / A) is, for example, 5.0.

[0034] Next, with reference 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.

[0035] As shown in FIG. 4, the belt reinforcing ply 31 is constituted by coating organic fiber cords 32 arranged along the tire circumferential direction 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.

[0036] 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.

[0037] 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 this technical field can be appropriately used.

[0038] 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. Further, 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.

[0039] 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.

[0040] 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.

[0041] 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 32 driven into the belt reinforcing ply 31 [cords / inch] be C [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 32 driven into the belt reinforcing ply 31 [cords / inch] be D [N / inch]. At this time, the bending load A [N / inch] per unit width of the single belt ply 21 and the belt angle B [deg] described above, and the above C [N / inch] and D [N / inch] satisfy the relationships represented by the following formulas (I) and (II). Formula (I): 2.0 ≤ C / (A×(90 - B)) Formula (II): 8.0 ≤ D / (A×(90 - B)) ≤ 30.0

[0042] By setting {C / (A×(90 - B))} to be 2.0 or more, 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×(90 - B))} is less than 2.0, the bending rigidity of the belt reinforcing ply 31 cannot be sufficiently ensured, and in particular, during normal driving, the handling stability deteriorates. {C / (A×(90 - B))} only needs to be 2.0 or more, preferably 2.5 or more, and more preferably 3.0 or more. When {C / (A×(90 - B))} is 2.5 or more, the handling stability during normal driving can be further improved.

[0043] Also, {C / (A×(90 - B))} is, for example, 10.0 or less, preferably 9.0 or less, and more preferably 8.0 or less. When {C / (A×(90 - B))} exceeds 10.0, for example, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in an increase in the rigidity of the belt layer 20, deterioration of the road surface following performance, and a possible decrease in handling stability. Therefore, for example, 2.0 ≦ C / (A×(90 - B)) ≦ 10.0, preferably 2.5 ≦ C / (A×(90 - B)) ≦ 9.0, and more preferably 3.0 ≦ C / (A×(90 - B)) ≦ 8.0.

[0044] Also, by setting {D / (A×(90 - B))} to 8.0 or more, it is possible to achieve both high-speed durability and handling stability of the tire at a high level. In other words, when {D / (A×(90 - B))} is less than 8.0, the bending rigidity of the belt ply 21 becomes too large with respect to the bending rigidity of the belt reinforcing ply 31, resulting in a decrease in the contact area of the tire, and particularly during high-speed driving, the handling stability deteriorates. {D / (A×(90 - B))} may be 8.0 or more, preferably 9.0 or more, and more preferably 10.0 or more. When {D / (A×(90 - B))} is 9.0 or more, the handling stability during normal driving can be further improved.

[0045] Also, {D / (A×(90 - B))} is 30.0 or less, preferably 25.0 or less, and more preferably 20.0 or less. When {D / (A×(90 - B))} exceeds 30.0, for example, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in a decrease in the road surface following performance of the tire and a possible deterioration of the handling stability instead. Therefore, 8.0 ≦ D / (A×(90 - B)) ≦ 30.0, preferably 9.0 ≦ D / (A×(90 - B)) ≦ 30.0, and more preferably 10.0 ≦ D / (A×(90 - B)) ≦ 20.0.

[0046] 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 load at 5% elongation when a tensile test is conducted in accordance with JIS L1017 in a laboratory under standard conditions of a temperature of 20 ± 2°C and a relative humidity of 65 ± 4% as defined in JIS L0105.

[0047] The above C [N / inch] may be within the range that satisfies the above formula (I), but is preferably 1100 or less, and more preferably 900 or less. When C [N / inch] exceeds 1100, the restraining force by the belt reinforcing layer 30 becomes too large, resulting in an increase in the rigidity of the belt layer 20, deterioration of the road surface following performance, and a possible decrease in the handling stability. Also, C [N / inch] is preferably 400 or more, and more preferably 500 or more. When C [N / inch] is less than 400, it becomes difficult to maintain the tire shape, and the handling stability may deteriorate. Therefore, C [N / inch] is preferably 400 or more and 1100 or less, and more preferably 500 or more and 900 or less.

[0048] Also, the above D [N / inch] may be within the range that satisfies the above formula (II), but is preferably 2000 or more, and more preferably 2500 or more. By setting D [N / inch] to 2000 or more, it becomes easier to ensure high-speed durability. Also, D [N / inch] is preferably 3500 or less, and more preferably 3000 or less. By setting D [N / inch] to 3500 or less, the contact area of the tire can be ensured, and in particular, the handling stability during high-speed driving is improved. Therefore, D [N / inch] is preferably 2000 or more and 3500 or less, and more preferably 2500 or more and 3000 or less.

[0049] The load (N) at 2% elongation and the load (N) at 5% elongation of the organic fiber cord 32 can be adjusted, for example, by selecting the type of fiber constituting the organic fiber cord 32, the cord structure, the number of twists, the treatment conditions of the cord, and the like. For example, by reducing the number of twists, the load at elongation can be increased. Further, as the treatment conditions of the cord, there are conditions for dip treatment (resin liquid composition, treatment 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 dip treatment is performed 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

[0050] Examples are shown below, but the present invention is not limited to these examples.

[0051] A steel cord and an organic fiber cord having the structure shown in Table 1 described later were each produced. Then, the produced steel cord was used for the belt ply, and the produced organic fiber cord was used for the belt reinforcing ply. A radial tire with a tire size of 205 / 50R16 87V was vulcanized and molded according to a conventional method. In the tire, the number of belt ply components was 2, and the number of belt reinforcing ply components was the number shown in Table 1. Also, the two belt plies were arranged so that the belt angles were +25° / -25°. Further, for each tire, the configurations other than the belt layer and the belt reinforcing layer were all the same.

[0052] The produced pneumatic tire was evaluated for tire weight, high-speed durability, and handling stability by the following methods, respectively.

[0053] <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.

[0054] <High-speed durability> Measured as follows using a drum tester having a rotating drum made of steel with a smooth surface and a diameter of 1700 mm, which complies with FMVSS109 (UTQG). The test tire was assembled on a standard rim specified by JIS at an internal pressure of 220 kPa (2.2 kgf / cm 2 ), and the load was set to 88% of the maximum load specified by JATMA. After a break-in run 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 run was conducted. The main run 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 the main run 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.

[0055] <Handling stability> Each tire assembled 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 a 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.

[0056] The tire weight, high-speed durability, and handling stability of each pneumatic tire are shown in Table 1, respectively.

[0057]

Table 1

[0058] As shown in Table 1, the pneumatic tires of Examples 1 to 6 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 in-plane rigidity in the tire width direction of the belt ply to 4.0 [kN / inch] or more 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.

[0059] On the other hand, in the pneumatic tire of Comparative Example 4 where the in-plane rigidity in the tire width direction of the belt ply is less than 4.0, although the handling stability is improved, the high-speed durability is deteriorated. This is presumably because the strength of the belt layer cannot be sufficiently ensured due to the small in-plane rigidity in the tire width direction of the belt ply.

[0060] Also, the pneumatic tires of Comparative Examples 1, 3, and 5 that do not satisfy the above formula (I), that is, where {C / (A×(90 - B))} is less than 2, have deteriorated handling stability. This is presumably because the bending rigidity of the belt reinforcing ply cannot be sufficiently ensured.

[0061] Also, the pneumatic tire of Comparative Example 2 where {D / (A×(90 - B))} is less than 8 has deteriorated handling stability. This is presumably because the bending rigidity of the belt ply becomes too large with respect to the bending rigidity of the belt reinforcing ply, resulting in an excessive reduction in the tire contact area.

[0062] Also, the pneumatic tire of Comparative Example 6 where {D / (A×(90 - B))} exceeds 30.0 has deteriorated handling stability. This is presumably because the restraining force by the belt reinforcing layer becomes too large, increasing the rigidity of the belt layer and deteriorating the road surface followability.

Explanation of Signs

[0063] 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, 33 Coating rubber, 41 Supporting 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 in-plane rigidity of the belt ply in the tire width direction is 4.0 [kN / inch] or more; let the bending load per unit width of one sheet of the belt ply be A [N / inch]; in the belt layer, let the angle of the steel cord with respect to the tire circumferential direction be B [deg]; let the product of the load at 2% elongation per one organic fiber cord [N] and the number of organic fiber cords driven into the belt reinforcing ply [number / 25 mm] be C [N / 25 mm]; when the product of the load at 5% elongation per one organic fiber cord [N] and the number of organic fiber cords driven into the belt reinforcing ply [number / 25 mm] is D [N / 25 mm], the A, the B, the C, and the D satisfy the relationships represented by the following formulas (I) and (II): a pneumatic tire. Formula (I): 2.0 ≤ C / (A×(90 - B)) Formula (II): 8.0 ≤ D / (A×(90 - B)) ≤ 30.0

2. The pneumatic tire according to claim 1, wherein the C is 1100 or less.

3. The pneumatic tire according to claim 1, wherein the D is 2000 or more.

4. The pneumatic tire according to claim 1, when the in-plane rigidity of the belt ply in the extending direction of the steel cord is X [kN / inch], the X is 9.0 or more and 25.0 or less.

5. When the in-plane rigidity of the belt ply in the tire width direction is Y [kN / inch], the ratio of the Y to the A (Y / A) is 1.0 or more. The pneumatic tire according to claim 1.

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

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