JP2008189274A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire with a thinned belt cover layer, and improved in durability at high-speed operation without deteriorating uniformity. <P>SOLUTION: The pneumatic radial tire provided with belt layers 6a, 6b on an outer periphery side of a carcass layer 4 in a crown portion 1, has 1×N twist structure formed twisting N pieces of (N=2 to 8) wires, and a flat cross sectional shape having a long diameter in width directions of the belt layers 6a, 6b. A steel cord C formed into a zigzag shape which is 1.5 to 3.0 in a ratio of amplitude W to the long diameter D and 20 mm to 50 mm in wave length L, is wound to a tire circumferential direction along the belt layers 6a, 6b at substantially 0° to make the product of a cord cross section area and cord driving density be 2-9 mm<SP>2</SP>/50 mm, thereby providing a belt cover layer 7 on an edge portion outer periphery side of the belt layers 6a, 6b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire provided with a belt cover layer in a crown portion, and more specifically, a pneumatic radial tire capable of thinning a belt cover layer and improving high-speed durability without deteriorating uniformity. About.

  Conventionally, in a pneumatic radial tire for passenger cars, for the purpose of improving high-speed durability, an organic fiber cord is disposed on the outer peripheral side of an edge portion of a cross belt layer (a belt layer in which reinforcing cords cross each other) with respect to the tire circumferential direction. For example, a belt cover layer wound substantially at 0 ° is provided (see, for example, Patent Document 1). However, in order to further improve the high-speed durability by the belt cover layer of the organic fiber cord, it is necessary to wind the belt cover layer in multiple layers. As a result, the gauge of the belt cover layer becomes thick and the tire weight increases. There is a problem of increasing.

On the other hand, in order to reduce the thickness of the belt cover layer and reduce the weight of the tire, it has been proposed to use a steel cord for the belt cover layer (see, for example, Patent Document 2). However, since the steel cord has a high initial elastic modulus before vulcanization, it is difficult to follow the tire lift deformation in the vulcanization process. Therefore, when a steel cord is used for the belt cover layer, there is a problem that the steel cord bites into the belt layer and the tire uniformity deteriorates.
JP 2006-1439 A JP 2000-255214 A

  An object of the present invention is to provide a pneumatic radial tire capable of reducing the thickness of a belt cover layer and improving high-speed durability without deteriorating uniformity.

In order to achieve the above object, a pneumatic radial tire of the present invention is a pneumatic radial tire in which a belt layer is provided on the outer peripheral side of a carcass layer in a crown portion, and N (N = 2 to 8) strands are twisted. While having a combined 1 × N twist structure, the belt layer has a flat cross-sectional shape whose major axis is the width direction of the belt layer, and the ratio of the amplitude to the major axis is 1.5 to 3.0, and the wavelength is 20 mm to 50 mm. The steel cord subjected to zigzag brazing is substantially aligned with respect to the tire circumferential direction along the belt layer so that the product of the cord cross-sectional area and the cord driving density is ² to 9 mm 2/50 mm. The belt cover layer is provided on the outer peripheral side of the edge portion of the belt layer by winding at 0 °.

  In the present invention, a steel cord having a 1 × N twist structure having a flat cross-sectional shape and a zigzag-shaped brazing is used as a cord constituting the belt cover layer. Such a steel cord has a relatively low initial elastic modulus before vulcanization, so it can follow the lift deformation of the tire in the vulcanization process, and has a higher elastic modulus than the organic fiber cord after vulcanization. It is possible to demonstrate. Moreover, when winding the steel cord, the product of the cord cross-sectional area and the cord driving density is defined within the above range in order to achieve both a reduction in the thickness of the belt cover layer and an improvement in high-speed durability. As a result, the belt cover layer can be thinned without deteriorating the uniformity, and further, the high speed durability can be improved. Further, since the amplitude and wavelength of the zigzag steel cord are reduced, it is possible to avoid the inconvenience that the winding accuracy of the steel cord is lowered and the vulcanization failure due to the air pool.

  The ratio of the minor axis to the major axis of the steel cord used for the belt cover layer is preferably 0.60 to less than 1.00. Thereby, the initial elastic modulus of the steel cord before vulcanization can be reduced while maintaining good workability when the zigzag brazing is applied to the steel cord.

  The number N of strands of steel cord used for the belt cover layer is preferably 5-6. Furthermore, the twist pitch of the steel cord used for the belt cover layer is preferably 5 mm to 15 mm. When such a number of strands and a twist pitch are selected, the steel cord which has the said structure can be manufactured efficiently.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a pneumatic radial tire for passenger cars according to an embodiment of the present invention, wherein 1 is a crown portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of left and right bead portions 3, 3, and an end portion of the carcass layer 4 is folded around the bead core 5 from the inside of the tire to the outside.

  A plurality of belt layers 6 a and 6 b including a plurality of reinforcing cords inclined with respect to the tire circumferential direction are embedded on the outer peripheral side of the carcass layer 4 in the crown portion 1. These belt layers 6a and 6b have a cord angle of 15 ° to 60 ° with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other. The number of belt layers is not particularly limited, and can be increased as necessary. A belt cover layer 7 is disposed on the outer peripheral side of the edge portions of the belt layers 6a and 6b. The belt cover layer 7 needs to be disposed so as to cover at least the edge portions of the belt layers 6a and 6b, but may be disposed so as to cover the entire area of the belt layers 6a and 6b.

  FIG. 2 is a plan view showing the belt cover layer. As shown in FIG. 2, the belt cover layer 7 is formed by continuously winding one or a plurality of steel cords C covered with rubber at substantially 0 ° with respect to the tire circumferential direction as necessary. Is formed. The cord winding angle of the belt cover layer 7 may be, for example, 5 ° or less with respect to the tire circumferential direction. Further, the belt cover layer 7 may be wound in multiple layers.

In winding the steel cord C, the product of the cord cross-sectional area and the cord driving density is set to ² to 9 mm 2/50 mm in order to achieve both the thinning of the belt cover layer 7 and the improvement of the high speed durability. The effect of improving the high-speed durability product of the code cross-sectional area and the code driving tool density is less than 2 mm ^2/50 mm is insufficient, more than 9 mm ^2/50 mm on the contrary thinning of the belt cover layer 7 is It becomes insufficient. The cord cross-sectional area referred to here means the sum of the cross-sectional areas of the strands constituting the steel cord C, and the cord driving density means the number of steel cords C driven per 50 mm width of the belt cover layer 7. means.

  FIG. 3 is a plan view of a steel cord constituting the belt cover layer, and FIG. 4 is a cross-sectional view thereof. As shown in FIGS. 3 and 4, the steel cord C has a 1 × N twist structure in which N (N = 2 to 8) strands f are twisted, and the belt layer has a major axis in the width direction. It has a flat cross-sectional shape. This steel cord C is provided with a zigzag brazing. In the steel cord C, the ratio of the amplitude W to the long diameter Dl satisfies the relationship 1.5 ≦ W / Dl ≦ 3.0, and the wavelength L satisfies the relationship 20 mm ≦ L ≦ 50 mm.

  Here, if the ratio of the amplitude W to the long diameter Dl of the steel cord C is less than 1.5, the initial elastic modulus of the steel cord C before vulcanization increases and the uniformity decreases, and conversely exceeds 3.0. As a result, the amount of air entrained in the belt cover layer 7 increases, and vulcanization failure is likely to occur. Also, if the wavelength L of the steel cord C is less than 20 mm, the amount of air trapped in the belt cover layer 7 increases and vulcanization failure is likely to occur. Conversely, if it exceeds 50 mm, the steel cord C before vulcanization The initial elastic modulus increases and the uniformity decreases.

  In the pneumatic radial tire described above, the steel cord C constituting the belt cover layer 7 has a 1 × N twist structure, a flat cross-sectional shape having a long diameter in the width direction of the belt layer, and a zigzag brazing Since the initial elastic modulus before vulcanization is relatively low, it is possible to follow the lift deformation of the tire in the vulcanization process, and after vulcanization, the elastic modulus is higher than that of the organic fiber cord. It is possible to demonstrate. Moreover, when winding the steel cord, the product of the cord cross-sectional area and the cord driving density is regulated within a predetermined range, so that both the thinning of the belt cover layer 7 and the improvement of the high-speed durability are achieved. can do. Therefore, even when the belt cover layer 7 made of the steel cord C is provided, the belt cover layer can be thinned and the high-speed durability can be improved without deteriorating the uniformity. Further, since the amplitude W and the wavelength L of the zigzag steel cord C are reduced, it is possible to avoid the inconvenience that the winding accuracy of the steel cord C is lowered and the vulcanization failure due to the air pool. .

  The ratio of the short diameter Ds to the long diameter Dl of the steel cord C used for the belt cover layer 7 satisfies the relationship of 0.60 ≦ Ds / Dl <1.00. Thereby, the initial elastic modulus of the steel cord C before vulcanization can be reduced while maintaining good workability when the zigzag brazing is applied to the steel cord C. If the ratio of the short diameter Ds to the long diameter Dl is less than 0.60, it becomes difficult to perform the zigzag processing on the steel cord C, and the manufacturing efficiency thereof decreases.

  The number N of strands of the steel cord C used for the belt cover layer 7 can be selected in the range of 2 to 8, preferably 3 to 8, more preferably 5 to 6. When the number of the strands of the steel cord C is one, the production weight per unit time is reduced, and the production efficiency is lowered. When the number of strands of the steel cord C is 9 or more, it becomes difficult to control each strand, and the manufacturing efficiency is lowered.

  The twist pitch of the steel cord C used for the belt cover layer 7 is preferably 5 mm to 15 mm. When the twist pitch of the steel cord C is 5 mm or less, the production efficiency per unit time is lowered. If the twist pitch of the steel cord C is 15 mm or more, zigzag processing becomes difficult, and the production efficiency is lowered.

  In a pneumatic radial tire for passenger cars with a tire size of 175 / 65R14 (rim size: 14 × 5.5JJ) and a belt layer provided on the outer peripheral side of the carcass layer in the crown portion, a steel cord is attached to the outer peripheral side of the edge portion of the belt layer. The belt cover layer is provided by winding at substantially 0 ° with respect to the direction. The twisted structure, twist pitch, major axis Dl, minor axis Ds, amplitude W, wavelength L, and cross-sectional area of the steel cord are shown in Table 1. Examples 1-4 and Comparative Examples 1-7 in which the cord cover density of the belt cover layer, the product of the cord cross-sectional area and the cord drive density, and the gauges were varied as shown in Table 1 Tires were made. For comparison, a tire of Conventional Example 1 using 66 nylon fiber cord for the belt cover layer was prepared.

  Note that a steel cord of 2 + 2 × 0.25HT was used for the belt layer, the cord driving density was 40/50 mm, and the cord angle with respect to the tire circumferential direction was 27 °. The width of the inner belt layer was 145 mm, and the width of the outer belt layer was 135 mm. On the other hand, the belt cover layer had a width of 30 mm and was arranged on the outer peripheral side of the edge portion of the belt layer.

  These test tires were evaluated for high-speed durability and uniformity by the following method, and the results are also shown in Table 1.

High speed durability performance:
After assembling the test tire, after dry heat deterioration at an internal oxygen pressure of 350 kPa and a temperature of 80 ° C. for 5 days, the internal pressure was set to 200 kPa by replacing the charged oxygen with air, and a speed of 120 km / h using a drum tester was applied. Traveling was started at 5 kN, and the speed was increased by 10 km / h every 24 hours, and the travel distance until the tire broke down was measured. The evaluation results are shown as an index with Conventional Example 1 as 100. The larger the index value, the better the high-speed durability performance.

Uniformity:
Under the conditions of an internal test pressure of 230 kPa, a load of 3 kPa, and a tire rotation speed of 60 rpm, the magnitude of force variation in the tire radial direction (N: radial force variation) is measured for each of the ten test tires, and the total value of the measured values Asked. The evaluation results are shown as an index with the conventional example 1 as 100 using the reciprocal of the total value of the measured values. A larger index value means better uniformity.

  As apparent from Table 1, the tires of Examples 1 to 4 were able to improve the high speed durability performance while maintaining good uniformity as compared with Conventional Example 1. However, in Examples 2 to 4, the manufacturing efficiency of the cord was lowered. On the other hand, although the tires of Comparative Examples 1 to 3 have the effect of improving the high-speed durability performance, the uniformity of the steel cord constituting the belt cover layer is higher than that of Conventional Example 1 because the initial elastic modulus before vulcanization is high. It was. Although the tires of Comparative Examples 4 and 5 had good uniformity, the high-speed durability performance was worse than that of Conventional Example 1 because of the large amount of air involved in molding the tire. Although the tire of Comparative Example 6 had good uniformity, the high-speed durability performance was worse than that of Conventional Example 1 because the restraining force by the belt cover layer was low. In the tire of Comparative Example 7, although the improvement effect of the high-speed durability performance was obtained, the uniformity was deteriorated, and the weight of the belt cover layer was increased because the gauge was too thick.

1 is a meridian half sectional view showing a pneumatic radial tire for a passenger car according to an embodiment of the present invention. It is a top view which shows a belt cover layer. It is a top view of the steel cord which comprises a belt cover layer. It is a cross-sectional view of the steel cord which comprises a belt cover layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crown part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6a, 6b Belt layer 7 Belt cover layer C Steel cord f Wire

Claims (4)

In a pneumatic radial tire in which a belt layer is provided on the outer peripheral side of the carcass layer in the crown portion, the pneumatic tire has a 1 × N twist structure in which N (N = 2 to 8) strands are twisted together, and the width of the belt layer A steel cord having a flat cross-sectional shape with a major axis in the direction and a zigzag brazed brazing with a ratio of amplitude to the major axis of 1.5 to 3.0 and a wavelength of 20 mm to 50 mm. And the outer circumference side of the edge of the belt layer by winding the belt layer along the belt layer at substantially 0 ° with respect to the tire circumferential direction so that the product of the cord driving density and the cord driving density is ² to 9 mm 2/50 mm Pneumatic radial tire provided with a belt cover layer.   2. The pneumatic radial tire according to claim 1, wherein a ratio of a minor axis to a major axis of the steel cord used for the belt cover layer is set to less than 0.60 to 1.00.   The pneumatic radial tire according to claim 1 or 2, wherein the number N of strands of steel cord used for the belt cover layer is 5-6.   The pneumatic radial tire according to any one of claims 1 to 3, wherein a twist pitch of a steel cord used for the belt cover layer is 5 mm to 15 mm.

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