JP2003326913A - Pneumatic radial tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for heavy load whose fatigue deterioration of a rubber material around a belt layer edge is improved. <P>SOLUTION: When a distance a from a tire center line CL of a tire meridian cross section to a carcass maximum width position Pa, a distance b from a straight line DL passing the carcass maximum width position Pa in parallel with a tire rotational axis to the carcass maximum outer diameter position Pb and a carcass line from the carcass maximum outer diameter position Pb to the carcass maximum width position Pa is divided into three portions by two dividing lines 1, 2 which divides the distance a into three portions, each of radiuses of curvature R<SB>1</SB>, R<SB>2</SB>and R<SB>3</SB>of each zone is set to relations of b/a=0.45 to 0.75, R<SB>1</SB>=(4.0 to 7.0)b, R<SB>2</SB>=(0.5 to 0.7)a and R<SB>3</SB>=(1.0 to 1.6) R<SB>2</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty pneumatic radial tire, and more particularly to a heavy duty pneumatic radial tire for improving fatigue deterioration of a rubber material around an edge of a belt layer.

[0002]

2. Description of the Related Art Pneumatic radial tires for heavy loads used for trucks, buses, etc., run under a large load, and therefore the rubber material in the tread portion undergoes greater fatigue deterioration than tires for passenger cars. In particular, the fatigue deterioration of the rubber material around the edge of the belt layer appears remarkably.

As a result of a detailed study on the cause of fatigue deterioration of the rubber material in the tread portion as described above, the present inventor has a great influence that the fatigue deterioration is largely influenced by the carcass line shape in the tire meridian section. It was found that strain is unevenly distributed in the rubber material of the tread portion depending on the shape of the line and the deterioration becomes large.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the fatigue deterioration of the rubber material around the edge of the belt layer by specifying the shape of the carcass line, and to improve the durability of the pneumatic tire for heavy loads. To provide radial tires.

[0005]

A pneumatic radial tire for heavy load according to the present invention which achieves the above object, is mounted on a regular rim and has a tire meridian section when filled with 15% of the regular internal pressure. Tire center line CL
To a carcass maximum width position Pa, a, a distance from a straight line DL passing through the carcass maximum width position Pa parallel to the tire rotation axis to the carcass maximum outside diameter position Pb, and a carcass maximum outside diameter position Pb to the carcass maximum width. With respect to the carcass line up to the position Pa, two dividing lines I are drawn in parallel to the tire center line CL so as to divide the distance a into three equal parts.
The intersection points II intersect with P1 and P2, and the tire center line CL.
The radius of curvature of the carcass line from the carcass maximum outer diameter position Pb having the center O1 to the intersection point P1 is R1, and the curvature radius of the carcass line from the intersection point P2 having the center O2 on the straight line DL to the carcass maximum width position Pb is R2, where R3 is the radius of curvature of the carcass line between the intersections P1 and P2, the ratio b / a of the distances a and b and the radius of curvature R1
, R2 and R3 are respectively expressed by b / a = 0.45 to 0.75 R1 = (4.0 to 7.0) b R2 = (0.5 to 0.7) a R3 = (1.0 to 1.6) It is characterized by being set to R2.

In the conventional heavy-duty pneumatic radial tire, the radius of curvature R1 of the carcass line is the distance b.
It was general that the radius of curvature R2 was set to about 8 times, the radius of curvature R2 was set to about twice the distance a, and the radius of curvature R3 was set smaller than the radius of curvature R2. However, according to the present invention, as described above, the radius of curvature R1 is smaller than 7 times the distance b, the radius of curvature R2 is smaller than 0.7 times the distance a, and the radius of curvature R3 is smaller than 1 of the radius of curvature R2. By setting the double or more times, it is possible to disperse the stress in the tread rubber, improve the fatigue deterioration of the rubber material around the edge of the belt layer, and improve the durability.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings.

FIG. 1 illustrates an essential part of a half section of a tire meridian when the pneumatic radial tire for heavy loads according to the present invention is mounted on a regular rim and filled with 15% of a regular internal pressure. Here, the regular rim and the regular internal pressure refer to the rim and the internal pressure defined in “JATMA YEARBOOK 2001”.

In the tire shown in FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and a bead portion extending further from the sidewall portion is omitted. A carcass 3 is provided inside the tire, and a belt layer 4 is provided along the outer periphery of the carcass 3 corresponding to the tread portion 1. The carcass 3 has steel cords or organic fiber cords arranged in a direction of approximately 90 ° with respect to the tire circumferential direction. The belt layer 4 is composed of a plurality of steel cord layers, and the steel cords of the respective layers are inclined at 15 ° to 60 ° with respect to the tire circumferential direction and intersect each other between the layers.

In the carcass line formed by the carcass 3, Pa is the carcass maximum width position and Pb is the carcass maximum outer diameter position. Further, a is the distance from the tire center line CL to the carcass maximum width position Pa, and b
Is a distance from a straight line DL passing through the carcass maximum width position Pa parallel to the tire rotation axis to the carcass maximum outer diameter position Pb.

In the present invention, the carcass line is
Carcass maximum outer diameter position Pb to carcass maximum width position Pa
Up to the above, the center part region, the shoulder part region, and the side part region are respectively formed by the arcs of three radii of curvature R1, R2, and R3.

That is, two dividing lines I and II are drawn in parallel to the tire center line CL so as to divide the distance a into three equal parts.
Where P1 and P2 are intersections that intersect the carcass line from the carcass maximum outer diameter position Pb to the carcass maximum width position Pa.
As the intersection point P from the carcass maximum outer diameter position Pb
1 is divided into a center area, intersections P1 to P2 are divided into shoulder areas, and intersection P2 to the carcass maximum width position Pa is divided into side areas. The center region from the carcass maximum outer diameter position Pb to the intersection P1 has a radius of curvature R1 having a center O1 on the tire center line CL.
The side portion region from the intersection P2 to the carcass maximum width position Pb is formed by an arc of curvature radius R2 having the center O2 on the straight line DL, and the intersections P1 and P
The shoulder area between the two is formed by an arc having a radius of curvature R3.

Further, the ratio b / a of the distances a and b
And the radii of curvature R1, R2 and R3 are set as follows, respectively.

B / a = 0.45 to 0.75 R1 = (4.0 to 7.0) b R2 = (0.5 to 0.7) a R3 = (1.0 to 1.6) R2 By setting the distance ratio b / a and the radii of curvature R1, R2, R3 in the above-described manner, the stress in the tread rubber is dispersed and fatigue deterioration of the rubber material around the edge of the belt layer is suppressed, As compared with a conventional pneumatic radial tire for heavy load, the durability of the tread portion is improved.

When the distance ratio b / a is smaller than 0.45, the carcass line is not formed in shape, and when the distance ratio b / a is larger than 0.75, the fatigue deterioration of the rubber material around the edge of the belt layer is conventionally suppressed. It's harder to improve than a tire.

The radius of curvature R1 is 4.0b
If it is smaller than this, the carcass line is not formed in shape, and if it is larger than 7.0b, it becomes difficult to suppress fatigue deterioration of the rubber material around the edge of the belt layer. If the radius of curvature R2 is smaller than 0.5a, the carcass line will not be formed geometrically, and if it is larger than 0.7a, it will be difficult to suppress fatigue deterioration of the rubber material around the edge of the belt layer. For the radius of curvature R3,
If it is smaller than the radius of curvature R2, it becomes difficult to suppress fatigue deterioration of the rubber material around the edge of the belt layer, and if it is larger than 1.6R2, the carcass line becomes ill-formed.

[0017]

[Example] The tire size is the same for 11R22.5,
The distance ratio b / a and the radius of curvature R1 in the tire meridian section when mounted on the regular rim and filled with 15% of the regular internal pressure,
Eight types of heavy-duty pneumatic radial tires (conventional example, Examples 1 to 3, and Comparative Examples 1 to 4) in which R2 and R3 were different as shown in Table 1 were manufactured.

With respect to these eight types of pneumatic radial tires for heavy load, durability was evaluated by measuring the running distance when the tire was run under the following test conditions, and the results are shown in Table 1. It was The test results are shown as an index when the running distance of the conventional example tire is 100. The larger the index, the better the durability.

[Test conditions] Drum diameter: 1700 mm Air pressure: regular air pressure Load: 140% of specified load Running speed: 120km / h Ambient temperature: 38 ° C

[0020]

[Table 1]

[0021]

As described above, according to the pneumatic radial tire for heavy load of the present invention, by specifying the carcass line shape, fatigue deterioration of the rubber material around the edge of the belt layer is improved as compared with the conventional tire. , Durability can be improved.

[Brief description of drawings]

FIG. 1 is a half section view of a tire meridian illustrating a main part of a heavy duty pneumatic radial tire of the present invention.

[Explanation of symbols]

1 tread portion 2 sidewall portion 3 carcass 4 belt layer CL tire center line DL straight line I, II dividing line Pa carcass maximum width position Pb carcass maximum diameter position P1, P2 intersections R1, R2, R3 radius of curvature O1 center of radius of curvature R1 O2 Center of radius of curvature R2 a Distance from tire center line CL to carcass maximum width position Pa b Distance from straight line DL to carcass maximum outer diameter position Pb

Claims (2)

[Claims] 1. A carcass maximum width position P from the tire center line CL of the tire meridian section in a tire meridian section when the tire is mounted on a regular rim and filled with 15% of the regular internal pressure.
The distance to a is a, and the carcass maximum outer diameter position P from the straight line DL passing through the carcass maximum width position Pa parallel to the tire rotation axis.
The distance to b is b, and the carcass line from the carcass maximum outer diameter position Pb to the carcass maximum width position Pa is drawn in parallel with the tire center line CL so as to divide the distance a into three equal parts. The intersection point of the dividing lines I and II is P1,
P2, the radius of curvature of the carcass line from the carcass maximum outer diameter position Pb having the center O1 on the tire center line CL to the intersection point P1, R1, the intersection point P2 having the center O2 on the straight line DL to the carcass maximum width position Pb Where R2 is the radius of curvature of the carcass line and R3 is the radius of curvature of the carcass line between the intersections P1 and P2, the ratio b / a of the distances a and b and the radii of curvature R1, R2 and R3 are respectively b / a = 0.45 to 0.75 R1 = (4.0 to 7.0) b R2 = (0.5 to 0.7) a R3 = (1.0 to 1.6) R2 Pneumatic radial tire for heavy loads. 2. The heavy-duty pneumatic radial tire according to claim 1, wherein the belt layer is made of steel cord, and the carcass is made of steel cord or organic fiber cord.