JPH10157410A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire having a load index of 69 or less, reducing weight and improving riding comfort without sacrificing driving stability and wear resistance. SOLUTION: In a pneumatic radial tire with a load index of 69 or less, having a tread, a radial carcass, a main belt, and an auxiliary belt, and vulcanized by use of a mold whose surface facing the tread part of the tire has on its cross-sectional contour a profile consisting of a curve projecting toward its cavity, the main belt 1 comprises two cover rubber cord layers each comprising a plurality of organic fiber cords buried in cover rubber, and laid one on the other in opposite direction across the tire equatorial line E with their cord direction at an acute angle to the circumferential direction of the tire, the organic fiber cords having a tensile elasticity of 800 to 1500kgf/mm<2> . Also, the auxiliary belt 2 comprises cover rubber cord layers each comprising organic fiber cords buried in cover rubber, and arranged in both side areas radially outside the main belt 1, with their cord direction at an angle of 20 to 30 degrees to the circumferential direction, the organic fiber cords having a tensile elasticity of 750kgf/mm<2> or less.

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 having a road index of six.
The present invention relates to a lightweight pneumatic radial tire for a mini vehicle of 9 or less.

Here, the term used in the present specification will be described. The term "ground contact shape" refers to the shape of a portion that comes into contact with the tire when the tire is pressed against a flat plate under a predetermined internal pressure and load. The “rectangular ratio” refers to the ratio of the circumferential contact length L80 at a position 80% of the maximum contact width around the tire equator line and the contact length Le on the tire equator line in the tire contact shape.

[0003]

2. Description of the Related Art One of the important characteristics of a tire for a light vehicle having a road index of 69 or less is to reduce the weight of the tire and to improve the riding comfort. Organic fibers may be used. However, the main belt using organic fibers has a weaker haze effect than the main belt using steel cord, so the diameter growth of the tire crown, especially the shoulder, becomes too large when filled with internal pressure, and it is set as the initial target. There is a problem that it is difficult to obtain a properly grounded shape, and steering stability and wear resistance are reduced.

[0004] For this reason, it has been attempted to arrange a belt layer in which nylon cords substantially arranged in parallel with the tire circumferential direction are embedded in rubber on the outer side in the radial direction of the main belt on both sides of the main belt. I have. However, in this case, the nylon cord angle is substantially parallel to the tire circumferential direction, and the heat shrinkage stress of the nylon is large, so that the rigidity of the tire shoulder portion on both sides of the main belt is high. In this case, there is a problem that the diameter growth of the center portion becomes too large, and the intended ground contact shape cannot be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages of the prior art and reduces weight and improves ride comfort without sacrificing steering stability and wear resistance. Especially, it is an object of the present invention to provide a tire having a road index of 69 or less.

[0006]

In order to achieve the above object, a pneumatic radial tire according to the present invention comprises a tread, a radial carcass, a main belt and an auxiliary belt, and has a mold surface facing a tread portion of the tire. However, in a pneumatic radial tire having a load index of 69 or less, which is vulcanized and molded by a mold having a profile formed by a convex curve toward the cavity in its cross-sectional profile, (1) the main belt includes a plurality of main belts. 800 tensile modulus
Two coated rubber cord layers formed by embedding an organic fiber cord of up to 1500 kgf / mm ^{2 in} a coated rubber are arranged in opposite directions with the cord directions sandwiching the tire equator at an acute angle with respect to the circumferential direction of the tire. It is laminated so that it becomes
(2) The auxiliary belt has a coated rubber cord layer formed by embedding an organic fiber cord having a tensile elastic modulus of 750 kgf / mm ² or less in a coated rubber on both radially outer sides of the main belt. A configuration is adopted in which the directions are arranged at an angle of 20 to 30 degrees with respect to the circumferential direction.

Further, in the present invention, the tire is assembled on a standard rim according to the JATMA standard, the internal pressure is filled at 1.8 kg / cm ^2, and the rectangular ratio in the contact shape when the load is 88% of the maximum load according to the JATMA standard is 90% or more. , Preferably 95
% Is preferable because steering stability and wear resistance can be improved.

In the case of radial tires having a road index of 69 or less, particularly for a mini tire for a light vehicle, it is one of the important characteristics to reduce the weight of the tire and to improve the riding comfort, so that the cord of the main belt is not steel. Organic fibers may be used. In the present invention, the material of the main belt has a tensile modulus of 800 to 1500 kgf.
/ Cm ² of organic fiber such as 1670 D /
3, the weight reduction and ride comfort
It can be easily achieved. However, as described above, in this case, there is a problem that the slack effect of the belt is weakened, the intended ground contact shape cannot be obtained, and steering stability and wear resistance are reduced.

Therefore, in the present invention, even in a main belt structure using organic fibers, the steering stability and abrasion resistance are improved by optimizing the grounding shape by the following method. That is, in the case of the main belt structure using organic fibers, the mold surface of the mold facing the tread portion of the tire in advance has a cross-sectional contour, which is convex toward the cavity, due to the large diameter growth of the tire due to the internal pressure filling. Vulcanization molding is performed with a mold having a profile consisting of a curve. At this time, it is preferable to set d in FIG. 1 which is の of the difference between the maximum outer diameter of the cavity of the mold and the outer shape of the cavity at the center of the mold to 2 to 10 mm.

[0010] In the belt structure using organic fibers, particularly, the belt end portion, that is, the shoulder portion has a large diameter growth, so that an auxiliary belt made of a nylon cord is disposed on both sides of the main belt. At this time, in the case of nylon cords arranged substantially in parallel to the tire circumferential direction, the tagging effect of the shoulder portion is too strong, so that an appropriate ground contact shape cannot be obtained. Therefore, the cord direction is set to 20 to 30 degrees in the present invention. . The cord direction of the auxiliary belt is preferably opposite to the cord direction and the circumferential direction of the cord layer on the radially outer side of the coating rubber cord layer forming the main belt, but may be the same direction.

The relationship between the mold shape, the shape at the time of filling the tire with the internal pressure, and the contact shape is relatively complicated. For example, even when vulcanization molding is performed using the same mold, the type, cord angle, and width of the belt cord are used. And post-cure inflation settings, and it can be said that some trial and error is required to obtain a proper grounding shape.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a pneumatic radial tire according to an embodiment of the present invention and a conventional pneumatic radial tire will be described with reference to the drawings. In each case, the tire size is 145 / 70R12. FIG. 1 is a partial sectional view of a pneumatic radial tire according to an embodiment of the present invention, which includes a tread 4, a radial carcass 3, a main belt 1 and an auxiliary belt 2, and a mold surface facing a tread portion of the tire. Is a pneumatic radial tire having a load index of 69 or less, which is vulcanized and molded by a mold having a profile of a convex curve with a cross section of d being 4 mm toward the cavity. The main belt 1 includes two coated rubber cord layers each formed by embedding a plurality of polyester cords having a tensile modulus of 1003 kgf / mm ^{2 in} a coated rubber, and having a cord direction of 20 degrees with respect to the circumferential direction of the tire. The auxiliary belt 2 has a tensile modulus of elasticity of 500 kg on both sides of the main belt 1 in the radial direction outside of the main belt 1.
A coated rubber cord layer formed by embedding a nylon cord of f / mm ^{2 in} the coated rubber is arranged so that the cord direction is at an angle of 22 degrees to the circumferential direction. In the tire, the central portion of the tread is concave like the shape of the line indicated by M in the mold, and when the internal pressure is filled, the central portion of the tread is substantially straight or convex like the line of S. The tires of the conventional example and the comparative example are vulcanized and molded by a mold in a line indicated by substantially S in FIG.

Next, Table 1 was used to confirm the effects of the present invention.
Based on the specifications, three types of tires were prototyped. These tires have the same structure and materials except for the specifications shown in the table.

The evaluation was performed on the following conditions for steering stability, ride comfort and wear resistance. [Driving stability] The vehicle uses Daihatsu Mira and has an internal pressure of 2.
0kg / cm ² at 12 × 4.00B rim,
Feeling evaluation on the comprehensive test road in the test course with one passenger. The evaluation is 3 ... The response is light and the delay of the rudder is noticeable. 5
--- No major drawbacks. 5 ... Suitable and rigid. [Ride comfort] The test conditions were the same as the driving stability. The evaluation was that the hardness was around 3 ..., the shock was strong, the softness was around 4 ... but the hardness was 5, and the softness was around 5 ... and there was a flat feeling. .

[Abrasion resistance] The vehicle was mounted on a 12 × 4.00B rim with an internal pressure of 2.0 kg / cm ² using Subaru Vivio and traveled 10,000 km in and near Tokyo under the conditions of two passengers. The amount of wear was compared. In the evaluation, the amount of wear of the conventional tire is shown as 100, and the larger the numerical value, the better (the less wear).

[0016]

[Table 1]

[0017]

As can be seen from Table 1, the pneumatic radial tire of the embodiment according to the present invention has improved handling stability, ride comfort and wear resistance as compared with the conventional pneumatic radial tire. .

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view in the tire width direction showing a mold shape and a tire shape after internal pressure filling of a tire of the present invention.

FIG. 2 is a view showing a ground contact shape of the pneumatic radial tire of the present invention.

FIG. 3 is a view showing a grounded shape of a pneumatic radial tire using a normal mold shape and a steel belt.

FIG. 4 is a diagram showing a grounded shape of a pneumatic radial tire using a normal mold shape and organic fibers.

[Explanation of symbols] E Equatorial line M Mold shape S Internal pressure filling shape 1 Main belt 2 Auxiliary belt 3 Carcass 4 Tread

Claims (2)

[Claims] 1. A mold having a tread, a radial carcass, a main belt and an auxiliary belt, wherein a mold surface of a mold facing a tread portion of a tire has a profile having a cross-sectional profile formed by a convex curve toward a cavity. In a pneumatic radial tire having a load index of 69 or less, which is vulcanized and molded by a mold, (1) the main belt is
The tensile modulus of a plurality of pieces is 800 to 1500 kgf / mm ^2.
The two coated rubber cord layers formed by embedding the organic fiber cord in the covered rubber are laminated so that the cord directions are opposite to each other with the tire equator line interposed therebetween at an acute angle with respect to the circumferential direction of the tire. (2) The auxiliary belt has a tensile modulus of elasticity of 750 k
The coated rubber cord layer formed by embedding an organic fiber cord of gf / mm ² or less in the coated rubber is disposed so that the cord direction is at an angle of 20 to 30 degrees with respect to the circumferential direction. Pneumatic radial tires. 2. The tire is assembled on a JATMA standard rim, filled with an internal pressure of 1.8 kg / cm ² , and has a rectangular ratio of 90% or more in a contact shape when 88% of the maximum load of JATMA is applied. The pneumatic radial tire according to claim 1.