JPH0577609A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To prevent center abrasion by way of keeping a tread radius at the time of inflating from becoming too large by forming a land part in the single tread radius of 0.4-0.45 times as large as the outer diameter of a tire. CONSTITUTION:A land part consisting of a rib or a block having width of 25-35% of tread expansive width is provided on a central part of a tread surface, and simultaneously, a main groove 1 with groove width of 4.5-6% of the tread expansive width is provided in the tire circumferential direction on both sides of the land part. This tread profile before inflation is formed by way of forming the land part in a single tread radius which is 0.4-0.45 times as large as a tire outer diameter Dc and forming both side shoulder parts from the main groove 1 to shoulder edges from combination of the single tread radius with its center on the tire central side or straight and a straight line circumscribing the tread radius, and the size of one half of a tire outer diametrical difference between the tread center and the shoulder edges is to be within a range of 5-7mm.

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 having improved tread surface wear performance.

[0002]

2. Description of the Related Art Recent trends in heavy duty pneumatic radial tires for trucks, buses, etc., have a tread radius on the tread surface of 0.5 times or more the outer diameter of the tire and 25 to 35% of the tread deployment width at the center. It is preferred to provide a tire having a wide block corresponding to No. 1 and a main groove having a considerably wide width corresponding to 4.5 to 6% of the developed tread width on both sides of the block. By providing a block with a large width and high rigidity in the tread center part, good traction performance is demonstrated on snowy roads in winter, while proper placement of the block shape causes conflicting uneven wear resistance required in summer. This is because the heel-and-toe wear between blocks is unlikely to occur.

However, in this heavy duty radial tire, the rigidity of the center portion is too high, while the rigidity of the wide main groove portions on both sides thereof is low, so that the outer diameter change of the center portion and the shoulder portions on both sides after inflation is changed. The difference will be significantly different. That is, before inflation, the whole has a single tread radius as shown by the dotted line in FIG. 4, but after inflation, as shown by the solid line, the center portion has a large tread radius Rc and becomes a straight line. On the other hand, in the shoulders on both sides, the main groove becomes an inflection point and the tread radius Rs becomes too small in the shoulders on both sides. Therefore, center wear occurs at the center, and step wear is remarkable at the shoulders on both sides. there were.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a heavy load radial tire for heavy load, which has both summer and winter characteristics as described above, so as to reduce center wear and shoulder wear at the same time. To provide tires.

[0005]

SUMMARY OF THE INVENTION The present invention which achieves such an object is to provide a land portion composed of ribs or blocks having a width of 25 to 35% of the tread development width in the center portion of the tread surface, and A tire in which a main groove having a groove width of 4.5 to 6% of a tread development width is provided on both sides of a land portion in a tire circumferential direction, and a tread profile before inflating is applied to the land portion of a tire outer diameter. A single tread radius Ra formed by a single tread radius Rc of 0.4 to 0.45 times, and having both shoulder portions from the main groove to the shoulder end in a straight line or on the tire center side and the tread radius. It is characterized in that it is formed by a combination with a straight line circumscribing the radius Ra and that the size of 1/2 of the tire outer diameter difference between the tread center and the shoulder end is in the range of 5 to 7 mm.

As described above, in the heavy load radial tire in which the wide land portion having a large rigidity is provided in the center portion and the wide main grooves are provided on both sides thereof, the tread radius Rc of the land portion is set to be smaller than the conventional one. The center tread radius Rc is prevented from becoming too large when inflated to prevent center wear, and the shoulders on both sides form a linear profile, and the outer diameter difference between the center and shoulder ends is specified. The step wear can be prevented by preventing the tread radius Rs from becoming too small.

In the present invention, the term "inflate" means filling with a normal internal pressure defined by the Japan Automobile Tire Manufacturers Association Standard (JATMA). The present invention will be specifically described below with reference to the drawings. FIG. 2 shows an example of the tread pattern of the heavy duty radial tire of the present invention. Two left and right main grooves 1 having a wide groove width b extending in the tire circumferential direction are arranged in the center portion, and further, a main groove 2 having a narrower groove width than the main groove 1 is arranged in the shoulder portions on both sides. By providing the sub-grooves 3 that intersect with the main grooves 1, 2,
And a block pattern composed of a large number of blocks 4 divided by the sub-grooves 3.

In the above structure, the block 4 located in the center portion has a width a which is considerably wide in the range of 25 to 35% of the tread development width W, and the main grooves 1 on both sides thereof are formed.
Also, the groove width b is configured to be considerably wide in the range of 4.5 to 6% of the developed width of the tread. With such a wide structure, not only great traction performance is exhibited on a snowy road in winter, but also similar performance is exhibited on a road surface in summer.

As shown in FIG. 1, the tread profile has a shape shown by a solid line before inflation and is shown by a dotted line after inflation. The profile of the block 4 in the center portion is formed from a single tread radius Rc that is 0.4 to 0.45 times the tire outer diameter Dc. Since the tread radius Rc is 0.5 times or more the tire outer diameter Dc in the conventional heavy load radial tire, it is relatively small. If this tread radius Rc becomes smaller than 0.4 times the tire outer diameter Dc, the traction performance will deteriorate. If it exceeds 0.45 times, the object of the present invention cannot be achieved. On the other hand, the tread radius R of the shoulders on both sides from the main groove 1 to the shoulder end Q
s is a tire axial outer end P of the main groove 1 and a shoulder end Q
It is formed on a straight line L (Rs = infinity) connecting with. Alternatively, as shown in FIG. 3, a single tread radius Ra centered on the tire center side and a straight line L circumscribing this may be combined.

This tread profile is 1 / the difference between the tire outer diameter Dc at the tread center O and the tire outer diameter Ds at the shoulder end Q (Dc-Ds).
The size β of 2 (difference between both radii) is set to 5 to 7 mm. In this way, the profile of the block 4 in the center portion of the wide width a is set to a single tread radius Rc smaller than the conventional
Since it is formed by the method described above, after the inflation, the radius of curvature can be set to an appropriate size as shown by the dotted line in FIG. 1, so that center wear can be prevented. Further, the profile of the shoulder portion is formed mainly by a straight line, and the difference between the tire outer diameter Dc at the tread center and the tire outer diameter Ds at the shoulder end is defined to be constant, so that it is indicated by the dotted line after inflation. By maintaining a proper tread radius that is not too small, it is possible to prevent step wear.

In the present invention, the tread pattern is not limited to the block pattern shown in FIG. 2 and may be a rib pattern or a pattern in which ribs and blocks are combined. The widths of the main groove 2 and the sub-groove 3 are not particularly limited, but the width of the tread spread W is 2 to 3
It is desirable to set the size to about%.

[0012]

EXAMPLE A tread radius Rc of the center portion before inflating, a tread radius Rs of the shoulder portion, and a half size β of the tire outer diameter difference (Dc-Ds) between the tread center and the shoulder end are shown in the table. Seven types of conventional tires, tires 1 and 2 of the present invention, and comparative tires 1 to 4 having the same tire specifications as described below were manufactured except that the values shown in 1 were used. Tire specifications: Tire size: 1000R20, tire outer diameter Dc = 10
50 mm tread pattern: Fig. 2 tread development width W = 200 mm, main groove 1 groove width b = 10
mm, the groove width of the main groove 2 = 7 mm, these four types of tires are each used for a rim of 20 × 7.00
The rim was assembled to T, a regular internal pressure of 7.25 kg / cm ² was filled, and it was mounted on a vehicle. The center uneven wear amount and shoulder step wear amount were evaluated by the following methods, and the results are shown in Table 1. Center uneven wear amount On the tread surface of the tire after traveling 30,000 km on the paved road,
A radius ruler having a diameter of 1/2 of the tire outer diameter was applied, and a gap generated between the ruler and the tread surface at the tread center and shoulder end was measured. Step wear amount : In the center uneven wear amount, the average value of the left and right wear amounts of the shoulder end was defined as the step wear amount.

[0013] As can be seen from Table 1, in both the tires 1 and 2 of the present invention, the center uneven wear amount and the shoulder step wear amount are smaller than those of the conventional tires. On the other hand, in the comparative tire 1 in which the tread radius Rc of the center portion is smaller than 0.4 times the tire outer diameter D, the ground contact pressure of the center portion is too high, so that uneven wear is likely to occur at the center block end portion. Both the center uneven wear amount and shoulder step wear are large. On the other hand, in the comparative tire 2 in which Rc is larger than 0.45 times the tire outer diameter D, the ground contact pressure at the center portion decreases, so uneven wear is likely to occur at the center of the center block, and the amount of uneven wear on the center increases.

Further, the tread radius Rc is 0.4 times the tire outer diameter D, but in the comparative tire 3 in which β is increased, the shoulder portion is likely to be unevenly worn and the step wear is large. On the other hand, Rc is 0.45 times the tire outer diameter D,
Although the comparative tire 4 having a smaller β is not as thick as the comparative tire 3, step wear is likely to occur, and the ground contact pressure at the shoulder portion is too high, so that there is a surface lacking stability.

[0015]

As described above, according to the present invention,
In addition to providing a wide land with high rigidity in the center,
In a heavy-duty radial tire having wide main grooves on both sides, the tread radius Rc of the land portion is set to be smaller than before, so that the tread radius Rc during inflation is not too large and center wear is prevented. be able to. Also, since the profile is formed mainly in a straight line at the shoulder portions on both sides and the difference in outer diameter between the center and the shoulder end is defined, it is possible to prevent the step wear of the shoulder portion by preventing the tread radius Rs from becoming too small. it can.

[Brief description of drawings]

1 is an example of a tread profile of a tire of the present invention, which is a sectional view taken along line II-II of FIG.

FIG. 2 is a plan view showing an example of a block pattern of the tire of the present invention.

FIG. 3 is a cross-sectional view showing another example of the tread profile of the shoulder portion of the tire of the present invention.

FIG. 4 is a cross-sectional view showing an example of a tread profile of a conventional heavy duty radial tire.

[Explanation of symbols]

1, 2 Main groove 4 Block Rc Center tread radius Rs Shoulder tread radius L Straight line

Claims (1)

[Claims] 1. A land portion composed of ribs or blocks having a width of 25 to 35% of the tread development width is provided in the center portion of the tread surface, and 4.5 to 6% of the tread development width is provided on both sides of the land portion. A tire in which a main groove having a groove width of 4 is provided in a tire circumferential direction, and a tread profile before inflation is provided in which the land portion is 0.4 times to 0.45 times the tire outer diameter.
A single tread radius Ra formed with a double tread radius Rc, and a single tread radius Ra centered on the tire center side on both side shoulder portions from the main groove to the shoulder end and a straight line circumscribing the tread radius Ra. Formed from a combination,
Also, a pneumatic radial tire for heavy load in which the size of 1/2 of the tire outer diameter difference between the tread center and the shoulder end is in the range of 5 to 7 mm.