JPH0930218A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable operational stability and riding comfort to be compatible at a high level by arranging a bead portion reinforcement layer so that the rubber coated fabric of an organic fiber monofilament having an elliptical cross section may have the major axis of the elliptical cross section of the organic fiber filament facing in parallel to a folded back part of a carcass. SOLUTION: An area from a bead portion extending over to a part of a side wall portion is reinforced by arranging a bead portion reinforcement layer 6, which is made of a rubber coated fabric of an organic fiber monofilament having an elliptical cross section, between a carcass folded back part 2b and a stiffener 5. The bead portion reinforcement layer 6 is arranged so that the rubber coated fabric, which has many organic fiber monofilament arranged in nearly the same intervals, is arranged along a folded back part 2b, specially the major axis of the elliptical cross section of an organic monofilament 7 to face in parallel to the folded back part 2b of a carcass. Flexural rigidity of the bead portion reinforcement layer 6 is increased by making the ratio of the major axis 'a' of the elliptical cross section to a minor axis 'b' within the range of 0.2 to 0.8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire for passenger cars which has both steering stability and riding comfort.

[0002]

2. Description of the Related Art Pneumatic radial tires for passenger cars tend to lack steering stability particularly because of their relatively low rigidity at the beads and sidewalls. Therefore, various means have been proposed in order to improve the steering stability, and the reinforcement of the bead part is the most effective means.

This type of tire has a carcass body composed of a radially arranged ply of rubber-coated cords extending over a pair of bead cores, the bead cores from the carcass body, and a stiffener installed on the bead cores, and the inside of the tire. Generally, the carcass consisting of the folded part of the ply that is rolled back from the outside to the outside is used as the skeleton.By arranging the bead reinforcement layer along the folded part of the carcass, steering stability is improved. It is possible to

[0004]

Conventionally, a rubberized cloth in which a large number of steel cords are arranged is applied to this bead portion reinforcing layer, and the reinforcement of the bead portion is strengthened by the high-rigidity steel cords, and steering stability is improved. Sexual improvement has been realized. However, reinforcing the bead portion with the high-rigidity steel cord, on the other hand, reduces the riding comfort of the tire. That is, when the tensile rigidity and bending rigidity of the steel cord are high, the cushioning effect is suppressed by the bending of the sidewall portion of the tire, mainly the side wall portion of the tire, which suppresses the shock when riding over a step on the road surface, and the riding comfort is impaired. .

This riding comfort is regarded as important together with the steering stability in accordance with the recent trend toward higher grade passenger cars, and there is a demand for pneumatic tires for passenger cars that are compatible with each other at a high level. The bead reinforcement layer could not meet this demand. further,
It was also a problem that the addition of a bead reinforcement layer made of steel cord would increase the weight of the tire and reduce the fuel efficiency of the vehicle.

[0006] Therefore, an object of the present invention is to propose a pneumatic radial tire having both a high level of steering stability and a high level of riding comfort.

[0007]

[Means for Solving the Problems] In order to achieve both steering stability and riding comfort, the rigidity of the tread in the circumferential direction should be kept equal to that of a tire having a bead reinforcement layer made of steel cord, and the tire diameter It has been found that it is effective to reduce the rigidity in the width direction and the width direction. Then, in order to impart anisotropic rigidity to the tire, it is advantageous to impart anisotropy to the bending rigidity of the bead portion reinforcing layer.
That is, the bending rigidity of the bead portion reinforcing layer is resistant to the deformation that occurs in the bead portion reinforcing layer schematically shown in FIG. 1 (a) and in the direction orthogonal to the surface of the reinforcing layer shown by the arrow in FIG. 1 (b). The ability to do so (hereinafter referred to as out-of-plane bending rigidity) and the ability to resist deformation that occurs within or along the surface of the reinforcing layer (hereinafter referred to as in-plane bending rigidity), indicated by the arrow in FIG. Therefore, in order to secure the rigidity in the tread circumferential direction, it is required to increase the in-plane bending rigidity, while to reduce the out-of-plane bending rigidity in order to reduce the rigidity in the radial direction and the width direction of the tire.

Next, as a result of extensive studies on a method for imparting anisotropy to the flexural rigidity of the bead reinforcing layer, a monofilament of an organic fiber, particularly a flattened elliptical cross section, was used as a constituent element of the bead reinforcing layer. It was found that applying a monofilament was effective, and completed the present invention. By the way, when the twisted cord of the organic fiber filament is used, the riding comfort is remarkably improved as compared with the tire using the steel cord, but on the other hand, the steering stability is unavoidably deteriorated, so that the bead is ended up. Only the same performance as a tire without a partial reinforcement layer can be obtained.

That is, according to the present invention, there is provided a carcass body composed of a radially arranged ply of rubber-coated cords straddling in a toroidal shape between a pair of bead cores, each bead core from the carcass body, and a stiffener installed on the bead core. A pneumatic radial tire in which a carcass consisting of a folded portion of the ply that extends from the inside to the outside of the tire and has a carcass as a skeleton, and a bead portion reinforcing layer is arranged along the folded portion of the carcass, The bead portion reinforcing layer is formed by arranging a rubberized cloth of an organic fiber monofilament having an elliptical cross section in a direction in which a major axis in the elliptical cross section of the organic fiber monofilament is parallel to the folded portion of the carcass. It is a pneumatic radial tire.

Further, the organic fiber monofilament is made of polyester, and the ratio b / a of the major axis a and the minor axis b in the elliptical cross section of the organic fiber monofilament is 0.2 to 0.
8, in particular, the major axis a is 0.5 to 1.0 mm, and the total length of major axes in the elliptical cross section of the monofilament occupying the widthwise cross section of the bead reinforcing layer is the width length of the bead reinforcing layer. The monofilament of the bead portion reinforcing layer is an imaginary point of intersection between the circumference centering on the rotation axis of the tire and the monofilament, and the angle formed by the tangent to the circumference at this intersection (hereinafter , Indicated as tilt angle)
Is advantageously between 10 and 45 °, respectively.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a cross section of a pneumatic tire according to the present invention. In the figure, 1 is a bead core, 2 is a carcass made of a radial arrangement ply of rubber-coated cords, 3 is a belt, and 4 is a tread.

The carcass 2 has a carcass main body 2a that straddles a pair of bead cores 1 in a toroidal shape, a bead core 1 from the carcass main body 2a, and a stiffener 5 installed on the bead cores 1 to form tires. Folded part 2b of the ply that is rolled up from the inside to the outside.
Consisting of

Between the folded portion 2b and the stiffener 5 of this carcass, a bead portion reinforcing layer 6 made of a rubberized cloth of an organic fiber monofilament having an elliptical cross section is arranged,
The area extending from the bead portion to a part of the sidewall portion is reinforced. As shown in FIGS. 3 and 4, the bead portion reinforcing layer 6 is made of a rubber-lined cloth in which a large number of organic fiber monofilaments 7 are arranged at substantially equal intervals along the folded-back portion 2b, in particular, an elliptical shape of the organic fiber monofilaments 7. It is essential that the long axis in the cross section is arranged in a direction parallel to the folded portion 2b of the carcass. The bead portion reinforcing layer 6 may be located inside or outside the tire with respect to the folded portion 2b as long as it is located along the folded portion 2b of the carcass. Further, as the material of the monofilament, polyester having high bending rigidity and excellent adhesiveness to rubber is advantageously suitable.

Here, the organic fiber monofilament 7 is
Preferably, its cross-section is elliptical, ie elliptical or a shape similar to ellipse, and the contour is curvilinear. In particular, an organic fiber monofilament having an elliptical cross section in which the ratio b / a of the major axis a and the minor axis b is in the range of 0.2 to 0.8 is suitable. This is because when the ratio b / a exceeds 0.8 and the cross section becomes circular, the out-of-plane bending rigidity of the bead reinforcing layer becomes high and the riding comfort deteriorates to the same extent as in the case of steel cords, while the ratio b / a When is less than 0.2, cord breakage easily occurs due to input while the tire is running, and durability is impaired.

The thicker the organic fiber monofilament is, the higher the bending rigidity becomes. However, the tire has a large rigidity difference near the end of the bead reinforcing layer, which impairs the durability. It is preferable to suppress a to 1.0 mm or less. On the other hand, if the filament diameter is too small, the bending rigidity will be insufficient, so the major axis a is preferably 0.5 mm or more.

Further, the total length of the major axes in the elliptical cross section of the monofilament occupying the cross section orthogonal to the axial direction of the filament in the bead reinforcing layer is in the range of 40 to 80% of the width of the bead reinforcing layer. It is advantageous to do
That is, if it is less than 40%, the bending rigidity of the bead portion reinforcing layer is insufficient and the steering stability is deteriorated. On the other hand, if it exceeds 80%, the filament spacing becomes too narrow and the rubber peeling starting from the filament is caused between the filaments. Therefore, it is preferable to limit the content to a range of 40 to 80% because it easily develops into cracks and causes separation in the bead portion reinforcing layer to impair durability.

Further, as shown in FIG. 3, the inclination angle α of the monofilament in the bead reinforcing layer is 10 to 45 °.
Is preferable. That is, in order to enhance the in-plane bending rigidity, it is effective to increase the inclination angle, especially to increase the inclination angle to around 45 °, but the out-of-plane bending rigidity also increases and the tire width-direction rigidity also increases. The inclination angle is set to 45 ° or less because it is increased and the tensile rigidity in the tire radial direction also increases and the riding comfort deteriorates. On the other hand, if the inclination angle is less than 10 ° C., the tire diameter cannot be expanded when the tire is molded on the tire building drum, which makes manufacturing difficult.

The belt 3 is composed of a plurality of layers of rubber-coated steel cords laminated around the outer periphery of the crown portion of the carcass 2 and is embedded in tread rubber to be used for reinforcing the tread 4. Follow conventional conventions for this type of tire.

[0019]

EXAMPLES The filaments or cords having the structure shown in Table 1 were applied to the bead portion reinforcing layers of the tire shown in FIG. 2 to fabricate radial tires for passenger cars of size 205 / 60R15. The carcass of the tire had a two-ply structure different from that shown in FIG. Each of the tires thus obtained was tested for steering stability, riding comfort and durability. The test results are also shown in Table 1.

The steering stability test is carried out by installing each tire in the applicable rim and filling the specified internal pressure, and then mounting the tire in a passenger car, and then running straight at a speed of 60 to 200 km / h, and a stability of turning. Sensory evaluation was performed on a 10-point scale for items such as performance and handling, and the scores of each item were averaged to obtain a steering stability score. The evaluation was carried out by two drivers, and the average of the scores of the two drivers was calculated. The evaluation result is 10 for the steel cord applied tire.
It is shown as an index with 0, and the higher the value, the higher the performance.

Further, in the riding comfort test, similarly to the steering stability test, each tire is mounted on a passenger car, and riding comfort by two drivers, specifically, a seam at a speed of 40 to 80 km / h, A sensory test was carried out for shock feeling and damping when passing various road surfaces such as cracks, and evaluated in the same manner as the steering stability test.

Furthermore, the durability test was conducted with 2.5 kg for each tire.
After filling the internal pressure of / cm, leave it in the room adjusted to the temperature of 25 ° C ± 2 ° C for 24 hours, readjust the air pressure, load the tire with twice the JIS regular load, and measure the diameter. Running on a 3 m drum at a speed of 60 km / h and using the distance traveled until the failure of the conventional tire 1 as a reference, the one that completed the distance is displayed as "○", and the one that did not complete is The mileage with respect to the mileage of the conventional tire 1 is displayed as a percentage.

[0023]

[Table 1]

As is clear from the comparison between the invention tire and the comparative tire 1 in Table 1, the flatness of the filament improves the riding comfort without deteriorating the steering stability. . On the other hand, Comparative Example 1 using the circular filament has almost no performance difference from the conventional tire using the steel cord, and conversely is inferior in riding comfort.

Inventive tire 11 is an example in which the flatness of the filament is excessive, but in this case, durability problems occur. Since the invention tire 13 has a long major axis, separation easily occurs at the end portion of the reinforcing layer, and durability is slightly problematic. On the contrary, since the invention tire 12 has a short major axis, the bending rigidity of the filament itself becomes small, and the steering stability is slightly lowered.

Inventive tire 15 had a relatively large number of impacts, so the rubber between filaments cracked during running, and there was some problem in durability. Conversely, invention tire 14
Since the number of driving is relatively small, the bending rigidity as a reinforcing material is small, and the steering stability is slightly lowered.

Further, the comparative tire 2 is an example using a PET twisted cord, but it can be seen that the steering stability is deteriorated because the bending rigidity of the cord is insufficient. Further, comparing the conventional tire 1 and the conventional tire 2, it can be seen that the steering stability is improved by increasing the number of cords to be driven.
On the other hand, it is also clear that the out-of-plane bending rigidity of the reinforcing layer becomes too high and the riding comfort is extremely deteriorated.

[0028]

According to the present invention, the ride comfort is improved without sacrificing the steering stability which is improved by the installation of the bead reinforcing layer, and at the same time, the weight reduction is achieved. It greatly contributes to fuel efficiency and fuel efficiency.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating bending rigidity in a bead portion reinforcing layer.

FIG. 2 is a diagram showing a tire structure of the present invention.

FIG. 3 is a diagram showing an arrangement of bead portion reinforcing layers.

4 is a sectional view taken along line iv-iv in FIG.

[Explanation of symbols]

 1 bead core 2 carcass 2a carcass body 2b folded part 3 belt 4 tread 5 stiffener 6 bead reinforcement layer 7 organic fiber monofilament

Claims (6)

[Claims] 1. A carcass body composed of a radial array ply of rubber-coated cords that straddle a pair of bead cores in a toroidal shape, and tires around the bead cores and stiffeners mounted on the bead cores. A pneumatic radial tire in which a carcass composed of a folded portion of the ply that winds up from the inside to the outside of the ply has a skeleton, and a bead portion reinforcing layer is arranged along the folded portion of the carcass. The layer is formed by arranging a rubberized cloth of an organic fiber monofilament having an elliptical cross section in a direction in which the major axis of the elliptical cross section of the organic fiber monofilament is parallel to the folded portion of the carcass. Radial tires. 2. The pneumatic radial tire according to claim 1, wherein the organic fiber monofilament is made of polyester. 3. The pneumatic radial tire according to claim 1, wherein the ratio b / a of the major axis a and the minor axis b in the elliptical cross section of the organic fiber monofilament is 0.2 to 0.8. 4. The pneumatic radial tire according to claim 3, wherein the major axis a is 0.5 to 1.0 mm. 5. The width direction cross section of the bead portion reinforcing layer,
The pneumatic radial tire according to any one of claims 1 to 4, wherein a total length of major axes in the elliptical cross section of the organic fiber monofilament is 40 to 80% of a width length of the bead portion reinforcing layer. 6. The monofilament of the bead portion reinforcing layer comprises:
The intersection between the circumference around the rotation axis of the tire and the monofilament is hypothesized, and the included angle with respect to the tangent to the circumference at this intersection is 10 to 45 °. Pneumatic radial tire.