JP2879699B2 - Flat pneumatic tire for heavy loads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flat pneumatic radial tire for heavy loads with improved shoulder drop abrasion resistance without impairing steering stability.

[Conventional technology]

Generally, a flat radial tire for heavy load is formed with a single tread radius _R0 as shown by a dotted line in FIG. 3 by molding, and the tire thus vulcanized and formed into a regular rim. When the tire is mounted and filled with the normal internal pressure (hereinafter, referred to as filling the normal internal pressure), as shown by the solid line in FIG. 3, a point P near the point P which is separated from the tread center CL by about 0.6 times the half width TDW / 2 of the tread in the tread width direction. Swell outward in the radial direction.

This phenomenon is particularly noticeable in tires having a small flatness [(tire cross-section height / tire cross-section maximum width) × 100] (flatness is 90% or less), and becomes more pronounced as the flatness is smaller. Therefore, the tread radius Rc of the tread center portion between the points P and the tread radius Rc of the both shoulder portions
and s' form a tread shape defined by two tread radii of different sizes. Such a tread shape has a drawback that when traveling on a road surface, a drag occurs due to a difference in radius from an axle between a tread center portion and a shoulder portion, and the wear of the shoulder portion is accelerated and shoulder wear is easily caused. was there.

Here, the position of the point P usually appears at a position 0.60 times the tread half width TDW / 2 in the tread width direction from the tread center CL, and this position is different from the tread half width TDW due to a difference in tire size and flatness. It fluctuates in the range of ± 0.15 times / 2.

Also, in order to prevent the above-mentioned shoulder drop wear, various studies have been made on changing the tread shape in a heavy load flat radial tire mold so that the tread shape after normal internal pressure filling has a single radius, but this change is unlimited. It was found that the tire performance such as steering stability was impaired if the test was performed.

The present invention provides a tire that does not impair tire performance such as steering stability by regulating the tread radius in a mold within a specific range in relation to a tire tread radius after the normal internal pressure filling of the above change. is there.

[Problems to be solved by the invention]

That is, an object of the present invention is to provide a heavy-load flat radial tire having improved shoulder drop abrasion resistance without impairing tire performance such as steering stability.

[Means for solving the problem]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire having a flattening rate of 90% or less, a tread shape which is attached to a regular rim and filled with a regular internal pressure is formed by a single tread radius R, and is filled with 10% of the regular internal pressure. The tread radius of the tread center from the tread center to the point P separated from the tread center by (0.60 ± 0.15) times the tread half width
It can be achieved by forming a double radius of Rc and the tread radius Rs of both shoulder portions from the point P to the shoulder end, and satisfying 0.50R ≦ Rc ≦ 0.90R and Rs ≧ 1.2R.

In the present invention, the tread shape when 10% of the normal internal pressure is filled means that there is no substantial inflation and the shape corresponds to the mold shape.

As described above, the tread shape at the time of filling 10% of the normal internal pressure is a double radius, but by forming a single tread radius by filling the normal internal pressure, the tire performance such as steering stability is not impaired. In addition, the resistance to abrasion by shoulder drop can be improved.

In the present invention, the normal rim and the normal internal pressure refer to the normal rim and the normal internal pressure specified in the Japan Automobile Tire Association Standard (JATMA).

 Hereinafter, this will be described in detail with reference to the drawings.

FIG. 2 shows a flat radial tire 1 for heavy load according to the present invention.
An example is shown, having a pair of sidewall portions 2 on both left and right sides of the tread 1, and having a carcass layer 3 disposed at an inner side thereof at a cord angle of substantially 90 ° with respect to the tire circumferential direction,
A portion of the carcass layer 3 corresponding to the tread 1 has a belt layer 4 extending in the tire circumferential direction.

In such a structure, the tread shape is formed by a single tread radius R during normal internal pressure filling as shown in FIG. However, the tread shape at the time of filling 10% of the normal internal pressure corresponding to the mold shape is the tread at the tread center portion between the right and left P points specified at the point P separated by (0.60 ± 0.15) times the tread half width from the tread center. The radius Rc and the tread radius Rs of both shoulder portions from the point P to the shoulder end are formed of double radius having different sizes. Moreover,
The tread radius Rc at the tread center is 0.50R ≦ R
The relationship of c ≦ 0.90R is satisfied, and the tread radius Rs of both shoulder portions satisfies the relationship of Rs ≧ 1.2R. Here, Rs is allowed to be infinite, that is, until the tread shape of the shoulder becomes straight. 10% of normal internal pressure
The two tread radius Rc, Rs that specify the tread shape at the time of filling satisfy such a relationship,
When inflated by filling with the normal internal pressure, as shown by the solid line in FIG. 1, the vicinity of the point P does not bulge or conversely sink, so that it is possible to prevent shoulder dropping wear and control. A flat pneumatic tire for heavy load that does not impair tire performance such as stability is provided.

〔Example〕

Example, Conventional Example, Comparative Example A tire having a structure shown in FIG. 2 having the same specifications except that the tread radius was set to the value shown in the table was manufactured and attached to a regular rim (22.5 × 8.25). In the state filled with the regular internal pressure (8.00 kg / cm ² ), the following steering stability and wear resistance against shoulder drop were evaluated. In the table, the evaluation results are shown by an index with the value of the conventional tire being 100.

Note that the position of the point P at which the tread radius changes in the example tire and the comparative example tire is all the tread center.
The position was 0.60 apart from CL in the tread width direction by a half tread width TDW / 1.

Each of these tire sizes was the same 11 / 70R22.5.

Driving stability: Evaluated by cornering force at a load of 2725 Kg and a slip angle of 1 degree using an indoor flat panel tester.

The measurement results are shown as an index with the measured value of the conventional tire being 100. The larger the index value, the better the steering stability.

Shoulder drop abrasion resistance: With the actual vehicle, apply a load of 2725Kg per tire
After running 10,000 km on a 100% paved road, the wear amount of the shoulder portion of the tire was measured and evaluated.

The measurement results are shown as an index with the measured value of the conventional tire being 100. The larger the index value, the better the resistance to shoulder drop abrasion.

As can be seen from the above table, the example tires I, II, III, IV
Compared to the comparative tires I and II, they are excellent in steering stability and resistance to shoulder drop abrasion.

〔The invention's effect〕

As described above, according to the present invention, the normal internal pressure of 10
The tread shape at the time of filling the tread radius Rc at the tread center portion from the tread center to a point P separated by (0.60 ± 0.15) times the tread half width from the tread center, and the tread radius Rs at both shoulder portions from the point P to the shoulder end. Of 0.50R ≦ Rc ≦ 0.90R, Rs at the time of normal internal pressure filling
≧ 1.2R, it is possible to form the tread shape at the time of normal internal pressure filling with a single tread radius R, thereby not impairing tire performance such as steering stability and shoulder drop abrasion resistance Performance can be improved.

[Brief description of the drawings]

1 is a half sectional view showing an example of a tread radius of the tire of the present invention, FIG. 2 is a partial sectional view showing an example of a tire of the present invention, and FIG. 3 is a half sectional view showing a tread radius of a conventional tire. is there. 1 ... tread portion, 2 ... sidewall portion, 3 ... carcass layer, R, Rc, Rs ... tread radius.

Claims (1)

(57) [Claims] 1. A pneumatic radial tire having a flattening rate of 90% or less, a tread shape when attached to a regular rim and filled with a regular internal pressure is formed by a single tread radius R, and when filled with 10% of the regular internal pressure. The point P where the tread shape is separated by (0.60 ± 0.15) times the tread half width from the tread center
The tread radius Rc of the tread center portion up to and the double radius of the tread radius Rs of both shoulder portions from the point P to the shoulder end are formed,
Flat pneumatic radial tire for heavy load with 0.50R ≦ Rc ≦ 0.90R and Rs ≧ 1.2R.