JP4946086B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire that exhibits excellent performance in high-speed durability and high-speed steering stability as a tire for passenger cars.

  In pneumatic radial tires for automobiles, especially passenger cars, by using a high elastic belt cover material using fiber cords with high elastic properties, the crown deformation caused by centrifugal force due to tire rotation is suppressed. It is known that a stable ground contact shape can be obtained, and since the stable ground contact shape is realized, it is known that an effect of improving high-speed durability and high-speed steering stability can be obtained.

  Conventionally, as a fiber material having high elasticity used for such a highly elastic belt cover material, an aramid fiber cord, a polyethylene naphthalate (PEN) fiber cord, an aramid fiber / nylon 66 fiber hybrid cord, or a nylon 66 fiber is used. Codes are known, and various types have been used by taking advantage of their strengths.

  In particular, particularly in the high speed range, the hybrid cord of aramid fiber / nylon 66 fiber is comprehensively superior in terms of rigidity, fatigue resistance, low heat generation characteristics, heat shrinkability, etc., and the aramid fiber / nylon A belt cover material using a 66-fiber hybrid cord is often used.

  Here, the hybrid cord means a cord in which two or three different types of cords are twisted, and the hybrid cord of aramid fiber / nylon 66 fiber is an aramid fiber cord in which each is twisted (under twist) A nylon 66 fiber cord is a cord that is used as a single reinforcing cord by using two or three nylon cords in total and twisting them together (top twist).

  However, there is still room for improvement in the hybrid cord of aramid fiber / nylon 66 fiber. For example, a two-strand cord has a problem in compression fatigue at the tire center because it has poor fatigue resistance during compression. The improvement in durability was not sufficient. In addition, with a three-strand cord, the overall cord diameter is generally thicker and the ply gauge is thicker. As a result, it can be said that the heating element increases, and the shoulder portion tends to store heat, which is a disadvantage in terms of tire durability. It was not enough.

  In the present invention, as described later, the belt cover material is divided into a center portion and a shoulder portion, and different cover cords are used. However, as a background art, such different types of cover cords are used. In the center part and the shoulder part, in particular, a proposal to make the cover residual tension different from each other (Patent Document 1), a proposal to make the cover thermal shrinkage rate and the cover elastic modulus different from each other (Patent Document 2), There are proposals for different cover rigidity (Patent Document 3), and proposals for different modulus (Patent Document 4).

  However, these are all different from the present invention in terms of technical idea and specific configuration, and in particular, focusing on the lower twist and upper twist structure when making a hybrid cord as in the present invention described later. It wasn't.

JP-A-6-297910 Japanese Patent Laid-Open No. 7-215011 JP 2002-356103 A JP 2005-263137 A

  In view of the above-described points, the present invention has been realized with a belt cover material using a conventional aramid fiber / nylon 66 fiber hybrid cord in a pneumatic radial tire for automobiles, particularly passenger cars. Providing pneumatic radial tires that can further improve the high-speed durability and high-speed steering stability that can be obtained based on a stable grounding shape, and achieve higher levels of high-speed durability and high-speed steering stability. It is intended to do.

The pneumatic radial tire of the present invention that achieves the above-described object has the following configuration (1).
In the pneumatic radial tire having an organic fiber reinforced cover layer wound around substantially 0 degrees with respect to the tire circumferential direction on the radially outer side of the belt layer, the organic fiber reinforced cover layer includes the center cover layer of A below: A shoulder cover layer of the following B, the high elastic yarn and the low elastic yarn of A and B are each of the following C, and the ratio of the width of the center cover layer to the total width of the organic fiber reinforced cover layer is A pneumatic radial tire characterized by being 30% or more and less than 90%.
(A) Center cover layer: arranged near the center in the tire axial direction, two high-elastic yarns and one low-elastic yarn are respectively twisted in the same direction and twisted in the direction opposite to the bottom twist direction. A cover layer configured using a three-strand composite cord.
(B) Shoulder cover layer: a two-strand composite cord that is arranged near the edge of the belt layer and is formed by twisting one high-elastic yarn and one low-elastic yarn in the same direction. Cover layer that is constructed using.
(C) The highly elastic yarn is a yarn having an elastic modulus of 200 cN / dtex or more and comprising any one of an aramid fiber, a polyolefin ketone (POK) fiber, and a polybenzoxazole (PBO) fiber. The low elasticity yarn is a yarn having an elastic modulus of 150 cN / dtex or less and made of an aliphatic polyamide fiber.

In the pneumatic radial tire according to the present invention, more specifically, the pneumatic radial tire according to any one of the following (2) to (4) is preferable.
(2) The upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer satisfy the following expressions (a) and (b), respectively. Pneumatic radial tire.
Center cover layer cord upper twist coefficient Kc ≧ 1600 Equation (a)
Upper twist coefficient Ksh ≦ 2250 of the cord of the shoulder cover layer ...... Formula (b)
here,
Center cover layer cord twist coefficient Kc = Tc × √Dc
Upper twist coefficient of the shoulder cover layer cord Ksh = Tsh × √Dsh
Tc: Number of upper twists of the cord of the center cover layer (times / 10 cm)
Dc: Total nominal fineness (dtex) of the cord of the center cover layer
Tsh: Number of upper twists of the cord of the shoulder cover layer (times / 10 cm)
Dsh: Total nominal fineness (dtex) of the cord of the shoulder cover layer

(3) The upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer satisfy the following expressions (c) and (d), respectively (1) or ( 2) The pneumatic radial tire as described.
1600 <= Kc <= 2250 ......... Formula (c) type 1600 <= Ksh <= 2250 ......... Formula (d) type

(4) An auxiliary fiber reinforcing layer using polyester fiber or aliphatic polyamide fiber is further disposed on the outer side in the tire radial direction of the organic fiber reinforcing cover layer and in the vicinity of the center in the tire axial direction. The pneumatic radial tire according to the above (1), (2) or (3) .

  According to the pneumatic radial tire of the present invention according to claim 1, it is realized with a belt cover material using a conventional hybrid cord of aramid fiber / nylon 66 fiber in a pneumatic radial tire for automobiles, particularly for passenger cars. High-speed durability and high-speed driving stability obtained based on the good and stable ground contact shape that has been improved, and a pneumatic radial tire that enables higher-level high-speed durability and high-speed driving stability. Is provided.

Also, according to any one of the present invention of claim 2 to 4, the effect obtained by claim 1 becomes clearer, higher-level high-speed durability, the pneumatic making it possible to obtain a high-speed steering stability Radial tires are provided

  Hereinafter, the pneumatic radial tire of the present invention will be described in more detail.

The pneumatic radial tire according to the present invention is a pneumatic radial tire having an organic fiber reinforced cover layer wound around the belt layer radially outside the belt circumferential direction at approximately 0 degrees with respect to the tire circumferential direction. The layer is composed of a center cover layer of the following A and a shoulder cover layer of the following B, and the high elastic yarn and the low elastic yarn of the A and B are respectively configured as described in C below. is there.
In a pneumatic radial tire having an organic fiber reinforced cover layer wound around substantially zero degrees with respect to the tire circumferential direction on the outer side in the radial direction of the belt layer, the organic fiber reinforced cover layer includes the center cover layer of A below: The shoulder cover layer of the following B is used.
(A) Center cover layer: arranged near the center in the tire axial direction, two high-elastic yarns and one low-elastic yarn are respectively twisted in the same direction and twisted in the direction opposite to the bottom twist direction. A cover layer configured using a three-strand composite cord.
(B) Shoulder cover layer: a two-strand composite cord that is arranged near the edge of the belt layer and is formed by twisting one high-elastic yarn and one low-elastic yarn in the same direction. Cover layer that is constructed using.
(C) The highly elastic yarn is a yarn having an elastic modulus of 200 cN / dtex or more and comprising any one of an aramid fiber, a polyolefin ketone (POK) fiber, and a polybenzoxazole (PBO) fiber. The low elasticity yarn is a yarn having an elastic modulus of 150 cN / dtex or less and made of an aliphatic polyamide fiber.
In the following description of the present invention, unless otherwise specified, the terms “high elasticity yarn” and “low elasticity yarn” refer to the yarns described in C, respectively.

  Furthermore, the ratio of the width of the center cover layer to the entire width of the organic fiber reinforced cover layer is configured to be 30% or more and less than 90%.

  FIG. 1 shows an example of an embodiment of a pneumatic radial tire according to the present invention, and is a schematic cross-sectional view taken in the meridian direction of the pneumatic tire. 1 is a tread portion, 2 is a sidewall portion, It is a bead part. A carcass layer 4 made of organic fiber cords arranged at approximately 90 degrees with respect to the tire circumferential direction is embedded in the tire so as to extend over the entire tread portion 1, left and right sidewall portions 2 and bead portions 3. The both end portions are folded around the bead core 5 from the tire inner side to the outer side.

  For example, two belt layers 6 made of steel cord are provided on the outer peripheral side (radially outer side) of the carcass layer 4, and the belt layer 6 is reinforced on the outer peripheral side (radial outer side) of the belt layer 6. An organic fiber reinforced cover layer 7 is provided. The organic fiber reinforced cover layer 7 has a belt-like structure in which a large number of organic fiber cords arranged in parallel are generally impregnated with rubber, and the organic fiber cords are substantially 0 with respect to the tire circumferential direction. It has a structure wound at an angle of degrees.

  In the present invention, as described above, the organic fiber reinforced cover layer 7 is composed of the center cover layer 71 of A and the shoulder cover layer 72 of B, and in particular, the center cover layer 71 includes: Because it is constituted by using a three-strand composite cord in which two high-elastic yarns and one low-elastic yarn are respectively twisted in the same direction and twisted in the opposite direction to the twisting direction, It has excellent fatigue resistance during compression, which improves the high-speed durability of the tire.

  On the other hand, since the shoulder cover layer 72 is configured by using a two-strand composite cord in which one high-elastic yarn and one low-elastic yarn are respectively twisted in the same direction and twisted together, The ply gauge (ply thickness) can be reduced, and as a result, the amount of heat generation / heat storage material is reduced, and the amount of heat generated during high-speed running is reduced. In this respect, high-speed durability is improved.

  In each of the cover layers, the high elastic yarn and the low elastic yarn are used in combination with the cord characteristics such as rigidity, fatigue resistance during compression, heat generation characteristics, and heat shrinkability. This is because the hybrid twisted cord is provided. Therefore, it is important that the ratio of the width of the center cover layer to the total width of the organic fiber reinforced cover layer is 30% or more and less than 90% as described above, and more preferably 45% or more and less than 75%. It is.

  Also, twisting in the same direction and twisting in the direction opposite to the direction of the lower twist to make one hybrid twisted cord, forming the hybrid twisted cord by applying the upper twist in the direction of untwisting By doing so, each fiber in the cord becomes more parallel (straight state) to the cord axis direction, so that the reinforcing effect, elastic effect, and thus the fiber cord of each fiber This is because the original reinforcing effect and elastic effect can be exhibited.

  Each high-elasticity yarn and each low-elasticity yarn used in the present invention do not have to have the same thickness as a single yarn, in order to exhibit the technical effect of a hybrid structure more. It is practical and preferable to appropriately vary the thickness (fineness). In particular, in order to satisfactorily exhibit the characteristics of the high elastic yarn, it is preferable that the low elastic yarn has a thickness (fineness) of about 75 to 95% of the thickness (fineness) of the high elastic yarn.

  The number of hybrid twisted cords (injection density) in the center cover layer and the shoulder cover layer is within the range of 40-50 / 50 mm width for the center cover layer, and within the range of 35-50 / 50 mm width for the shoulder cover layer. It is good to do.

  The center cover layer and the shoulder cover layer do not need to be formed as being separated from each other, and may be formed as a single body continuous in the tire axial direction as the organic fiber reinforced cover layer. Further, when formed as separate and separate parts, they may be arranged at a distance (separated) from each other.

The high-elasticity yarn and the low-elasticity yarn used in the present invention usually have a relative difference in the value of elastic modulus within the range of various organic fibers used in constituting a hybrid twisted cord. According to the various findings of the present inventors, in order to satisfactorily exert the effect of using the high elastic yarn for the reinforcing cover layer, the elastic modulus of the high elastic yarn is 200 cN / dtex or more. It is more effective and important, and it is important to use a yarn made of aramid fiber, polyolefin ketone (POK) fiber or polybenzoxazole (PBO) fiber in order to obtain a material having such an elastic modulus.

In addition, it is important to use a low elastic yarn used in the present invention having an elastic modulus of 150 cN / dtex or less in that the same effect of the present invention can be more clearly exhibited. Is preferably a yarn made of an aliphatic polyamide fiber. Specifically, it is important to use nylon 66 fiber, nylon 6 fiber, nylon 64 fiber or the like .

In the present invention, the upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer preferably satisfy the following formulas (a) and (b), respectively. The desired effect of the present invention can be clearly obtained.
Center cover layer cord upper twist coefficient Kc ≧ 1600 Equation (a)
Upper twist coefficient Ksh ≦ 2250 of the cord of the shoulder cover layer ...... Formula (b)
here,
Center cover layer cord twist coefficient Kc = Tc × √Dc
Upper twist coefficient of the shoulder cover layer cord Ksh = Tsh × √Dsh
Tc: Number of upper twists of the cord of the center cover layer (times / 10 cm)
Dc: Total nominal fineness (dtex) of the cord of the center cover layer
Tsh: Number of upper twists of the cord of the shoulder cover layer (times / 10 cm)
Dsh: Total nominal fineness (dtex) of the cord of the shoulder cover layer
It is.

Further, preferred ranges of the upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer satisfy the following expressions (c) and (d), respectively. By making it inside, the intended effect of the present invention can be obtained more clearly.
1600 ≦ Kc ≦ 2250 ......... Formula (c)
1600 ≦ Ksh ≦ 2250 ......... Formula (d)

  In addition, the width of the organic fiber reinforced cover layer 7 is preferably in the range of 80% to 110%, and most preferably in the range of 95% to 105% with respect to the entire width of the belt layer 6.

  In the present invention, an auxiliary fiber reinforcement layer using a polyester fiber (such as PEN fiber) or an aliphatic polyamide fiber is further disposed outside the organic fiber reinforcement layer in the tire radial direction and in the vicinity of the center in the tire axial direction. This is also a preferred embodiment. FIG. 2 shows the main part in a model with respect to the embodiment. The belt layer 6, the organic fiber reinforced cover layer 7, and the above-mentioned auxiliary fiber reinforcement in the cross section in the meridian direction of the pneumatic tire as shown in FIG. It is a schematic model diagram showing the arrangement of the layer 8, the organic fiber reinforced cover layer 7 is composed of a center cover layer 71 and a shoulder cover layer 72, and on the outer peripheral side of the center cover layer 7 than the width of the center cover layer. The example of an aspect which has arrange | positioned the auxiliary | assistant fiber reinforcement layer 8 of a small width is shown. As described above, by arranging polyester fiber or aliphatic polyamide fiber having relatively good fatigue resistance in the outermost layer, the compression fatigue resistance of the center portion can be further improved, and high speed durability, high speed resistance can be improved. A pneumatic radial tire excellent in fatigue can be realized. The auxiliary fiber reinforcing layer 8 is not particularly limited, but is preferably a rubberized layer in which organic fiber cords are arranged so as to be parallel to the tire circumferential direction. However, it is good also as a structure arranged in the direction which crosses with a circumferential direction and an angle.

  Examples will be described below, and the specific configuration and effects of the pneumatic radial tire of the present invention will be further described.

The elastic modulus, the number of twists, the width of the organic fiber reinforced fiber cover layer, the width of the center cover layer, and the width of the shoulder cover layer used in the description of the present invention were measured by the following methods.
(1) Elastic modulus of yarn:
Based on JIS L1017-2002 “Chemical Fiber Tire Cord Test Method 8.8 Initial Tensile Resistance”, the initial tensile resistance under the standard condition of the yarn before twisting is calculated, and this is used as the elastic modulus of the yarn.
(2) Number of twists:
Based on JIS L1017-2002 “Testing method for chemical fiber tire cord 8.4”, the number of twists and the number of twists of the twisted cord were determined.
(3) Center cover layer width:
A tire cap tread portion is cut in a radial direction from two locations on the tire circumference, and a cut section having a circumferential length of 15 to 30 mm is collected so that a cross section of the belt portion can be observed.

  The sampling position is an arbitrary point A of the tire cap tread portion and B positioned opposite to the tire center point. The width of the center cover layer was measured on a total of four A and B cut section surfaces, and the average was taken as the width of the center cover layer. The width of each center cover layer is determined by two cords positioned at the outermost ends in the tire width direction, and is a road length measured along another center cover cord positioned therebetween.

(4) Shoulder cover layer width:
The two cut sections A and B collected in the same manner as the center cover layer were each subjected to cross-sectional observation (total of 4 surfaces × 2 each), the width of the shoulder cover layer was measured, and the average was taken as the width of the shoulder cover layer. The width of each shoulder cover layer is determined by two cords positioned at the outermost ends in the tire width direction, and is a road length measured along another shoulder cover cord positioned therebetween.
(5) Width of organic fiber reinforced fiber cover layer:
From the width of the center cover layer and the width of the shoulder cover layer measured in the above (3) and (4), the value calculated by the following formula was used as the width of the organic fiber reinforced fiber cover layer.
Width of organic fiber reinforced fiber cover layer = width of center cover layer + (width of shoulder cover layer × 2)

Moreover, in each Example and the comparative example, the organic fiber reinforcement layer for pneumatic radial tires was manufactured using the following various cords AG. When producing each cord, the lower twist direction was the S direction, and the upper twist direction was the Z direction.
(1) Code A:
Three-stranded hybrid cord of aramid fiber 1670 dtex yarn / aramid fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(2) Code B:
A two-stranded hybrid cord of aramid fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(3) Code C:
Three-stranded hybrid cord of POK fiber 1670 dtex yarn / POK fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(4) Code D:
Two-stranded hybrid cord of POK fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(5) Code E:
Three-stranded hybrid cord of PEN fiber 1670 dtex yarn / PEN fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(6) Code F:
A two-stranded hybrid cord of PEN fiber 1670 dtex yarn / nylon 66 fiber 1400 dtex yarn.
(7) Code G:
Three twisted cords of PEN fiber 1670 dtex yarn / PEN fiber 1670 dtex yarn / PEN fiber 1670 dtex yarn.

Examples 1-16, Comparative Examples 1-10
Tires for passenger cars were manufactured using the organic fiber reinforced cover layer 7 composed of a center cover layer and a shoulder cover layer in various combinations of yarns shown in Tables 1 to 4.

  In the table, the ratio of the width of the shoulder cover layer to the full width of the reinforcing cover layer is indicated by the width of one side of the shoulder cover. The number of cords for the center cover layer and the number of cords for the shoulder cover layer were 45/50 mm width.

  The passenger car tire thus obtained was subjected to a test on the durability of a high-speed running tire and evaluated by the total time until the tire was destroyed.

  The thing of the comparative example 1 is what used the reinforcement layer which consists only of the conventional code | cord | chord A from a center area to a shoulder area (all width 200mm), and set the time until the thing of this comparative example 1 to destruction as 100, Others are shown in the index evaluation, and the larger the value, the longer the time to break, and the higher the durability of the high-speed running tire.

  As shown in Examples 1 to 3 in Table 1, according to the present invention, good high-speed durability can be obtained.

  As in Comparative Examples 1 and 2 in Table 1, when the reinforcing layer is formed of the same cover layer over the entire width (center portion and shoulder portion), it is inferior to the case according to the present invention. Further, as shown in Comparative Example 3, the reverse of the present invention in which a three-strand cord is used for the shoulder and a two-strand cord is used for the center, the high-speed durability is considerably inferior. As shown in Comparative Example 4, even when a three-strand cord is used for the center, if the width is too wide, the improvement effect is hardly obtained and the level is similar to that of Comparative Example 1. Further, as shown in Comparative Example 5, even when a three-strand cord is used for the center, if the width is too narrow, the high-speed durability is considerably inferior.

  Examples 4 to 11 shown in Table 2 are all according to the present invention and have good results. Among them, those having a smaller twist coefficient (Example 4) have a larger twist pitch but a center cord fatigue. Tread peeling occurred from the occurrence of breakage, and although the effect of the present invention was clearly recognized, it was smaller than the other examples (index 105).

  In addition, the one with a larger twist coefficient (Example 11) has a smaller twist pitch but less rigidity, and the shoulder portion (edge portion) cannot be controlled, and the shoulder portion is peeled off. Although it was recognized, it was smaller than other examples (index 105).

  In Examples 12 to 14 shown in Table 3, all of the POK fibers using the hybrid yarn constituting yarn (high elastic side) are according to the present invention and have good results.

  Comparative Examples 6 to 10 shown in Table 3 use POK fibers made of hybrid cord constituent yarns (high elastic side), but use 100% of the reinforcing cover layer as in Comparative Examples 1 to 5 ( When the center portion and the shoulder are the same) or the usage ratio is inappropriate, it indicates that the effect of the present invention cannot be obtained.

  Example 15 in Table 4 uses a PEN fiber yarn as a highly elastic yarn, and the yarn configuration / cord configuration is almost the same as that of Example 13, but the heat generation of the yarn is high, and the effect of the present invention. Was clearly recognized, but was smaller than that of Example 13 (index 110).

  In Example 16, the auxiliary fiber reinforcing layer made of PEN fibers (8 mode in FIG. 2) was further added to that of Example 13 to enhance the durability. , Heat generation due to ground deformation was further suppressed, and high-speed durability was very good (index 130).

FIG. 1 shows an example of an embodiment of the pneumatic radial tire of the present invention, and is a schematic sectional view taken in the meridian direction of the pneumatic tire. FIG. 2 shows another preferred embodiment of the pneumatic radial tire of the present invention. The belt layer, the organic fiber reinforcing layer, and the auxiliary fiber reinforcing layer in the meridional section of the pneumatic tire as shown in FIG. It is the schematic model figure which showed the arrangement | positioning of no.

Explanation of symbols

1: Tread part 2: Side wall part 3: Bead part 4: Carcass layer 5: Bead core 6: Belt layer 7: Organic fiber reinforced cover layer 71: Center cover layer 72: Shoulder cover layer 8: Auxiliary fiber reinforced layer

Claims (4)

In the pneumatic radial tire having an organic fiber reinforced cover layer wound around substantially 0 degrees with respect to the tire circumferential direction on the radially outer side of the belt layer, the organic fiber reinforced cover layer includes the center cover layer of A below: A shoulder cover layer of the following B, the high elastic yarn and the low elastic yarn of A and B are each of the following C, and the ratio of the width of the center cover layer to the total width of the organic fiber reinforced cover layer is A pneumatic radial tire characterized by being 30% or more and less than 90%.
(A) Center cover layer: arranged near the center in the tire axial direction, two high-elastic yarns and one low-elastic yarn are respectively twisted in the same direction and twisted in the direction opposite to the bottom twist direction. A cover layer configured using a three-strand composite cord.
(B) Shoulder cover layer: a two-strand composite cord that is arranged near the edge of the belt layer and is formed by twisting one high-elastic yarn and one low-elastic yarn in the same direction. Cover layer that is constructed using.
(C) The highly elastic yarn is a yarn having an elastic modulus of 200 cN / dtex or more and comprising any one of an aramid fiber, a polyolefin ketone (POK) fiber, and a polybenzoxazole (PBO) fiber. The low elasticity yarn is a yarn having an elastic modulus of 150 cN / dtex or less and made of an aliphatic polyamide fiber. The upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer satisfy the following expressions (a) and (b), respectively: Pneumatic radial tires.
Center cover layer cord upper twist coefficient Kc ≧ 1600 Equation (a)
Upper twist coefficient Ksh ≦ 2250 of the cord of the shoulder cover layer ...... Formula (b)
here,
Center cover layer cord twist coefficient Kc = Tc × √Dc
Upper twist coefficient of the shoulder cover layer cord Ksh = Tsh × √Dsh
Tc: Number of twists of the cord of the center cover layer (times / 10 cm)
Dc: Total nominal fineness (dtex) of the cord of the center cover layer
Tsh: Number of upper twists of the cord of the shoulder cover layer (times / 10 cm)
Dsh: Total nominal fineness (dtex) of the cord of the shoulder cover layer The upper twist coefficient Kc of the cord of the center cover layer and the upper twist coefficient Ksh of the cord of the shoulder cover layer satisfy the following expressions (c) and (d), respectively: 2. A pneumatic radial tire according to 2.
1600 ≦ Kc ≦ 2250 ......... Formula (c)
1600 ≦ Ksh ≦ 2250 ......... Formula (d) In the tire axial direction near the center and a tire radial direction outer side of the organic fiber reinforced cover layer, further, claim 1, characterized by being provided an auxiliary fiber reinforcement layer using a polyester fiber or aliphatic polyamide fibers 2. A pneumatic radial tire according to 2 or 3 .

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