JP2009280167A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire capable of enhancing high-speed durability and high-speed turnability without impairing load durability. <P>SOLUTION: A belt cover layer 6 comprises a low-elasticity cover layer 6a for covering at least center areas of belt layers 5a, 5b and a high-elasticity cover layer 6b for covering both end areas thereof. The tensile rigidity R of the belt cover layer which is defined by the product of the sectional area S of a reinforcing cord constituting the belt cover layer 6, the modulus of elasticity M at 2% elongation, and the count Z of cords is set in a predetermined range in the high-elasticity cover layer 6b. The ratio R1/R2 of the tensile rigidity R1 in the high-elasticity cover layer 1b to the tensile rigidity R2 in the low-elasticity cover layer 6a is set to be 1.1 to 1.9. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire with improved high-speed durability and high-speed turning performance without impairing load durability.

  Conventionally, as a technique to ensure high-speed durability of the tire and reduce road noise, a belt cover layer in which a heat-shrinkable organic fiber cord such as nylon is spirally wound in the tire circumferential direction is arranged on the outer peripheral side of the belt layer Has been done. Furthermore, in recent years, with the high performance and quietness of automobiles, there has been a strong demand for further reduction of road noise. As a countermeasure, the use of high elastic fiber cords such as aramid fibers for the belt cover layer. Was attempted.

  However, if fiber cords with a high modulus of elasticity are used for the belt cover layer, compression fatigue is likely to occur in the belt cover cord at the tire center during high load loads or low internal pressure loads, and in addition, high elasticity such as these aramid fibers. Since fiber cords generally have poor adhesion, there has been a problem of reducing tire durability.

  As a countermeasure, an attempt has been made to configure the belt cover layer with a low elastic fiber cord covering the central region of the belt layer and a high elastic fiber cord covering both end regions (see, for example, Patent Document 1). Furthermore, in order to further improve the passing noise and rolling resistance, the stretch resistance value of the belt cover layer expressed by the product of the cross-sectional area of the fiber cord, the 2% modulus value, and the number of cords to be driven is covered at both end regions. In the belt cover layer, the ratio between the stretch resistance value of the belt cover layer covering both end regions and the stretch force value of the belt cover layer covering the central region is set to 2 to 160 to 350 (N · lines / cm). There is a proposal described in 4.125 (see Patent Document 2).

However, in the case of a tire in which the ratio of the stretch resistance value of the belt cover layer in the central area and the both end areas of the belt layer is greatly different as in the tire of Patent Document 2, the ratio of the stretch resistance value is increased. If the method to reduce the elongation drag value in the center of the tire is not enough to suppress the tread lift during high-speed driving, the high-speed durability improvement effect cannot be obtained sufficiently. In the case of increasing the elongation drag value at both ends of the tire, the ground contact shape at the time of cornering decreases, so sudden slip and vibration occur during cornering, resulting in cornering performance, especially at high speeds. There was a problem that the turning performance of the car deteriorated.
Japanese Patent No. 2648652 Japanese Patent No. 3993378

  An object of the present invention is to solve the above-described problems, and to provide a pneumatic radial tire that improves high-speed durability and high-speed turning performance without impairing load durability.

In order to achieve the above object, a pneumatic radial tire according to the present invention includes a plurality of belts in which a carcass layer is mounted between a pair of left and right bead portions, and the outer circumference of the carcass layer in a tread portion intersects the cord direction between the layers. A pneumatic radial tire in which a belt cover layer in which an organic fiber cord is spirally wound in the tire circumferential direction is disposed on an outer periphery of the belt layer, and the belt cover layer is at least a central region of the belt layer A low elastic cover layer covering the belt layer and a high elastic cover layer covering both end regions of the belt layer, and a cross-sectional area S (mm ² ) of the reinforcing cord constituting the belt cover layer and elasticity at 2% elongation The tensile stiffness R = S × M × Z defined by the product of the rate M (N / mm ² ) and the cord driving number Z (lines / 50 mm) is R1 in the high elastic cover layer. = 70,000 to 100,000 (N / piece / 50 mm), and the ratio R1 / R2 of the tensile rigidity R1 in the high elastic cover layer and the tensile rigidity R2 in the low elastic cover layer was set to 1.1 to 1.9. It is characterized by that.

  Furthermore, in the structure mentioned above, it is preferable to comprise as described in the following (1)-(3).

(1) The width of the low elastic cover layer is set to 70 to 100% of the width of the innermost belt layer of the belt layers.
(2) The width of the highly elastic cover layer disposed in one end region of the belt layer is set to 5 to 15% of the width of the innermost belt layer of the belt layer.
(3) The reinforcing cord constituting the high-elasticity cover layer is constituted by a high-elasticity fiber yarn having an elastic modulus at break of 10,000 N / mm ² or more, and the reinforcing cord constituting the low-elasticity cover layer is elastic at breakage. A low elastic fiber yarn having a rate of less than 10000 N / mm ² is used. In this case, the reinforcing cord constituting the high-elasticity cover layer may be constituted by a composite fiber cord obtained by twisting the high-elasticity fiber yarn and the low-elasticity fiber yarn.

  According to the present invention, the belt cover layer is constituted by the low elastic cover layer covering at least the central region of the belt layer and the high elastic cover layer covering both end regions, and the cross-sectional area of the reinforcing cord constituting the belt cover layer. The tensile stiffness of the belt cover layer defined by the product of S and the elastic modulus M at the time of 2% elongation and the cord driving number Z is set to a certain range in the high elastic cover layer. Since the ratio of the tensile stiffness in the low elastic cover layer is 1.1 to 1.9, the balance of the tensile stiffness of the belt cover layer in the tire central area and both shoulder areas is properly secured, High-speed durability and turning performance during high-speed running can be improved without impairing load durability.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example of a pneumatic radial tire according to an embodiment of the present invention, and FIG. 2 is a schematic view showing an arrangement of a belt layer and a belt cover layer in the tire of FIG.

  In FIG. 1, a pneumatic radial tire 1 includes a plurality of carcass layers 3 mounted between a pair of left and right bead portions 2 and 2, and a cord direction intersecting the outer periphery of the carcass layer 3 in a tread portion 4 (see FIG. 1). Then, the belt layers 5a and 5b of 2) are arranged, and the belt cover layer 6 in which the organic fiber cord is spirally wound in the tire circumferential direction is arranged on the outer circumference of the belt layers 5a and 5b. The belt layer 5a, 5b is composed of a low-elasticity cover layer 6a that covers at least the central region (the entire region in the figure) and a high-elasticity cover layer 6b that covers both end regions of the belt layers 5a, 5b.

And in the pneumatic radial tire 1 of this invention, the cross-sectional area S (mm < ² >) of the reinforcement cord which comprises the belt cover layer 6, the elastic modulus M (N / mm < ² >) at the time of 2% expansion | extension, and the number of cord driving | operation Z ( Tensile rigidity R = S × M × Z defined by the product with the product of 50/50 mm), R1 = 70,000 to 100,000 (N / piece / 50 mm), preferably 75,000 to 85,000 (N / piece) in the highly elastic cover layer 6b. / 50 mm), and the ratio R1 / R2 of the tensile rigidity R1 in the high elastic cover layer 6b and the tensile rigidity R2 in the low elastic cover layer 6a is 1.1 to 1.9, preferably 1.5 to 1.8. I have to.

  By comprising in this way, the balance of the tensile rigidity of the belt cover layer 6 in a tire center area and both shoulder areas is ensured appropriately, and high-speed durability and high-speed running can be achieved without impairing load durability. Turning performance can be improved.

  Here, if the tensile rigidity R1 in the high-elasticity cover layer 6b described above is less than 70,000, the effect of improving the high-speed durability cannot be obtained due to insufficient tagging effect at both end regions of the belt layers 5a and 5b during high-speed running, If it exceeds 100,000, the ground contact area at the time of turning cannot be secured, and the steering stability is lowered. Further, if the ratio R1 / R2 of the tensile rigidity R1 in the high elastic cover layer 6b and the tensile rigidity R2 in the low elastic cover layer 6a is less than 1.1, the tensile rigidity R2 of the low elastic cover layer 6a becomes too large and low. Compressive fatigue is likely to occur in the reinforcing cord of the elastic cover layer 6a, and if it exceeds 1.9, the tensile rigidity R1 of the high elastic cover layer 6b becomes too large, and the load durability is lowered. Steering stability will deteriorate rapidly.

  In the present invention, in order to ensure the tensile rigidity of the belt cover layer 6 in the central region of the tire, the width Wa (see FIG. 2) of the low-elasticity cover layer 6a is set to that of the innermost belt layer 5a of the belt layers 5a and 5b. It may be set to 70 to 100% of the width W. Thereby, high-speed durability and high-speed turning ability can be improved with good balance.

  More preferably, the width of the high-elasticity cover layer 6b disposed in one end region of the belt layers 5a and 5b in order to ensure the balance of the tensile rigidity in the tire central region and both shoulder regions of the belt cover layer 6. Wb may be set to 5 to 15% of the width W of the innermost belt layer 5a of the belt layers 5a and 5b. Thereby, high-speed durability and high-speed turning ability can be improved with a better balance.

In the present invention, the reinforcing cord constituting the high-elasticity cover layer 6b described above uses a high-elasticity fiber yarn having an elastic modulus at breakage of 10,000 N / mm ² or more, and the reinforcing cord constituting the low-elasticity cover layer 6a. For this, a low elastic fiber yarn having an elastic modulus at break of less than 10,000 N / mm ² may be used.

  In addition, the elastic modulus at the time of the rupture described above is obtained from a stress-strain curve when a load is applied from 0N to rupture, and is obtained from a slope of a straight line connecting the point at 0N and the rupture point.

  Here, examples of the high elastic fiber yarn include an aramid fiber yarn, a POK fiber yarn, a PEN fiber yarn, and a PBO fiber yarn, and examples of the low elastic fiber yarn include a nylon fiber yarn and a PET fiber yarn.

  More preferably, the reinforcing cord constituting the high-elasticity cover layer 6b may be constituted by a composite fiber cord obtained by twisting the high-elasticity fiber yarn and the low-elasticity fiber yarn described above. This makes it possible to easily and accurately adjust the ratio R1 / R2 between the tensile rigidity R1 of the high elastic cover layer 6b and the tensile rigidity R2 of the low elastic cover layer 6a.

  As described above, the pneumatic radial tire 1 according to the present invention includes the belt cover layer 6 including the low elastic cover layer 6a covering at least the central region of the belt layers 5a and 5b and the high elastic cover layer 6b covering both end regions. After the construction, the tensile rigidity R of the belt cover layer 6 defined by the product of the cross-sectional area S of the reinforcing cord constituting the belt cover layer 6, the elastic modulus M at the time of 2% elongation and the cord driving number Z is made highly elastic. The cover layer has a certain range, and the ratio R1 / R2 between the tensile rigidity R1 of the high elastic cover layer 6b and the tensile rigidity R2 of the low elastic cover layer 6a is 1.1 to 1.9. It has improved high-speed durability and turning performance during high-speed driving without impairing load durability, and can be preferably applied as a tire to be mounted on recent high-performance vehicles. That.

  Comparative tires (Comparative Examples 1 and 2) and tires of the present invention (Examples 1 to 2) in which the tire size is 225 / 45R27, the tire structure is FIG. 1, and the arrangement and specifications of the belt cover layer are different as shown in Table 1. And 3) were prepared.

  These five types of tires were evaluated for high-speed durability, load durability and high-speed turning performance by the following methods, respectively, and the results are also shown in Table 1.

[High-speed durability]
After each tire was mounted on a rim (size: 17 x 7.5 JJ), the air pressure was charged to 180 kPa, and the ambient temperature was adjusted to 38 ± 3 ° C by an indoor drum test (drum diameter: 1707 mm). 120km / h, the load is 120% of the maximum load specified by JATMA, and the vehicle is run for 2 hours, then the speed is accelerated to 150km / h for 30 hours, and then the speed is increased by 10km / h every 30 minutes. While stepping up, the vehicle continued to run until the tire broke down, and the high-speed durability was evaluated based on the distance traveled until the tire broke down. The results are shown in Table 1 using an index with Conventional Example 1 as 100. The larger the value, the better the high-speed durability.

[Load durability]
After each tire was mounted on a rim (size: 17 x 7.5 JJ), the air pressure was charged to 180 kPa, and the ambient temperature was adjusted to 38 ± 3 ° C by an indoor drum test (drum diameter: 1707 mm). Is increased by 81 km / h, and the load is increased by 13% every 2 hours from 88% of the maximum load specified by JATMA, with the distance traveled until the tire breaks, The load durability was evaluated. The results are shown in Table 1 using an index with Conventional Example 1 as 100. It shows that it is excellent in load durability, so that a numerical value is large.

(High speed turning)
After each tire is mounted on (size: 17 x 7.5 JJ), it is filled with air pressure 220 kPa and mounted on the front and rear wheels of a vehicle with a displacement of 3000 cc. Repeated turning, sensory evaluation of steering stability was performed by a skilled test driver. The results are shown in Table 1 by a five-point method using Conventional Example 1 as a reference. The larger the value, the better the high-speed turning performance.

  From Table 1, it can be seen that the tire of the present invention has improved high-speed durability and high-speed turning performance without impairing load durability as compared with Comparative Example 1.

It is sectional drawing which shows an example of the pneumatic radial tire by embodiment of this invention. It is a schematic diagram which shows the arrangement | positioning form of the belt layer and belt cover layer in the tire of FIG. (A) And (b) is a schematic diagram equivalent to FIG. 2 which shows the arrangement | positioning form of the belt layer and belt cover layer in the tire which confirmed the effect in the Example, respectively.

Explanation of symbols

l Pneumatic radial tire 2 Bead part 3 Carcass layer 4 Tread part 5a, 5b Belt layer 6 Belt cover layer 6a Low elastic cover layer 6b High elastic cover layer S Cross-sectional area of the reinforcing cord constituting the belt cover layer M Belt cover Elastic modulus at 2% elongation of the reinforcing cord constituting the layer Z Number of reinforcement cords driven per 50 mm width of the belt cover layer R, R1, R2 Tensile rigidity

Claims (5)

A carcass layer is mounted between a pair of left and right bead portions, and a plurality of belt layers are disposed on the outer periphery of the carcass layer in the tread portion so that the cord directions are crossed between the layers. In a pneumatic radial tire in which a belt cover layer spirally wound in the tire circumferential direction is arranged,
The belt cover layer is composed of a low elastic cover layer that covers at least a central region of the belt layer and a high elastic cover layer that covers both end regions of the belt layer, and the reinforcing cords constituting the belt cover layer are cut off. The tensile stiffness R = S × M × Z defined by the product of the area S (mm ² ), the elastic modulus M (N / mm ² ) at 2% elongation and the number of cords driven (Z / 50 mm) is In the high elastic cover layer, R1 = 70,000 to 100,000 (N / piece / 50 mm), and the ratio R1 / R2 of the tensile rigidity R1 in the high elastic cover layer and the tensile rigidity R2 in the low elastic cover layer is 1.1. Pneumatic radial tire made to 1.9.   2. The pneumatic radial tire according to claim 1, wherein a width of the low-elasticity cover layer is 70 to 100% of a width of an innermost belt layer of the belt layers.   The pneumatic radial according to claim 1 or 2, wherein a width of the high-elasticity cover layer arranged in one end region of the belt layer is 5 to 15% of a width of the innermost belt layer of the belt layer. tire. The reinforcing cord constituting the high elastic cover layer is made of a high elastic fiber yarn having an elastic modulus at break of 10,000 N / mm ² or more, and the reinforcing cord constituting the low elastic cover layer has an elastic modulus at break of 10,000 N / mm the pneumatic radial tire according to claim 1, comprising a low elastic fiber yarn to be less than mm ^2.   The pneumatic radial tire according to claim 4, wherein the reinforcing cord constituting the high-elasticity cover layer is composed of a composite fiber cord obtained by twisting the high-elasticity fiber yarn and the low-elasticity fiber yarn.

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