JPH092026A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE: To reduce dragging generated in the axial direction of a tire on a tread grounding face of a rib pattern, and restrain partial wear without reducing the effective grounding area of the tread. CONSTITUTION: An intermediate rib M12 is provided with a thin groove 5 of which the groove depth direction is slanted from a tread surface to the tread center side, and the intermediate rib M12 is divided into a wide width rib 12a on the tread center side and a narrow width rib 12b on the tread shoulder side each having the same tread height. The ratio W2 :/W1 of the width W2 of the narrow width rib 12b to the width W7 of the wide width rib 12a is set to be 1<=W2 /W1 <0.25, the slant angle α in the groove depth direction of the thin groove 5 against the direction of a tread face normal line and the slant angle,5 of the groove wall on the tread center side of the wide width rib 12a against the direction of a tread face normal line are set in the relation of 0<α<β, and the slant angle θ of the tread face of the wide width rib 12a against the axial direction of a tire satisfies the relation of 3.4θ<=(a+β/2<=6.4θ.

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 a rib pattern, and more particularly to a heavy-duty pneumatic radial tire capable of suppressing uneven wear without reducing the effective ground contact area of the rib pattern. .

[0002]

2. Description of the Related Art Since rib patterns are more excellent in wear resistance than block patterns, they are often used in heavy duty pneumatic tires. However, the problem with heavy-duty pneumatic tires with rib patterns is that the tire outer diameter of the arc-shaped tread surface is smaller toward the tread shoulder, and it is based on the difference in radius between the tread center and the shoulder. There is a difference in peripheral speed, and the shoulder ribs and intermediate ribs with slow peripheral speed are dragged to the road surface,
It was that uneven wear such as rib punches, in which those shoulder side end portions are often worn, was likely to occur.

Among these, as measures against uneven wear of the shoulder ribs, a small groove continuous along the tire circumferential direction is provided slightly inside the tire at the shoulder edge, or a large number of kerfs are arranged at a predetermined pitch along the shoulder edge. By doing so, it is effective to reduce shoulder edge rigidity and avoid uneven wear. On the other hand, as a measure against uneven wear of the shoulder side end portion of the intermediate rib, a narrow groove is formed by providing a narrow groove extending in the tire circumferential direction at the shoulder side end portion of the intermediate rib (JP-A-5-246213). Further, it has been proposed that the narrow rib has a low tread height and is stepped so that the wear is concentrated on the stepped narrow rib (JP-A-2-169305 and JP-A-5-319029). Gazette).

[0006] However, the latter measure for making the stepped narrow rib has a drawback that the wear life of the tire as a whole is shortened because the effective ground contact area of the tire is reduced. In the former measure, even if the tread height of the narrow rib is the same as that of the rib body at the initial stage of wear, the wear concentrates only on the narrow rib, so in the end, the effective ground contact area of the tire is reduced during use. Similarly, it still has the drawback of reducing the wear life of the tire as a whole.

The present inventor has studied in detail the cause of uneven wear occurring in the ribs, and as a result, the uneven wear is compared not only in the drag of the tread based on the difference in circumferential speed in the tire circumferential direction but also in the tire axial direction. It was found that there is a cause of increasing uneven wear due to the occurrence of extremely large drag. That is, when a radial tire having a conventional rib pattern is grounded under load, the grounding shape (footprint) of the tread whose meridian section is curved in an arc shape is broken as shown in FIG. 8 (A). The shape of the rib 52 before contact with the ground changes to the shape shown by the solid line, and also changes in the meridional section as shown in FIG. 8B. That is, the rubber on the shoulder side end having a smaller tire outer diameter moved to the center side as indicated by the arrow, which dragged the road surface to increase uneven wear.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the drag on the tread contact surface in the axial direction of the tire in a heavy-duty pneumatic radial tire having a rib pattern to reduce the effective contact area of the tread. It is intended to provide a heavy-duty pneumatic radial tire capable of suppressing uneven wear without reducing the wear.

[0007]

Means for Solving the Problems The present invention, which achieves the above object, provides a heavy-duty pneumatic radial tire having a rib pattern in which a plurality of ribs extending in the tire circumferential direction are formed on a tread surface, at least a tread center and a tread. The intermediate rib located in the middle of the shoulder is provided with a thin groove extending in the tire circumferential direction and inclined in the groove depth direction from the tread surface to the tread center side, whereby the intermediate rib has the same tread height. It is divided into a wide rib on the center side and a narrow rib on the tread shoulder side, and the width W _{1 of the} wide rib is the width W ₂ of the narrow rib.
The ratio W ₂ / W ₁ to the range of 0.1 ≦ W ₂ / W ₁ ≦ 0.25, the inclination angle α of the narrow groove in the groove depth direction with respect to the normal to the tread surface, and the tread of the wide rib. The inclination angle β of the center side groove wall with respect to the normal to the tread surface is set to 0 <α <β, and the inclination angle θ with respect to the tire axial direction of the tread surface of the wide rib is 3.4θ. It is characterized in that the relationship of ≦ (α + β) /2≦6.4θ is established.

Although the ribs are divided by the narrow grooves as described above, the tread heights of the divided wide ribs and narrow ribs are the same, so that the effective ground contact area of the tread is substantially reduced. There is no. Further, by inclining the groove depth direction of the narrow groove from the tread surface to the tread center side, in order to make the meridian cross-sectional shape of the wide rib divided on the tread center side into a substantially parallelogram inclined to the shoulder side, The wide ribs are likely to bend toward the shoulder side when touching down. The bending action in the shoulder direction and the frictional force in the center direction from the road surface shown in FIG. 8 are canceled each other.

That is, on the tread surface of the rib 12, as shown in FIG. 7B, the bending action of the wide rib 12a and the frictional force from the road surface toward the center cancel each other, so that As shown in FIG. 7 (A), since only the rubber movement in the tire circumferential direction substantially remains, the extra slip is suppressed, and the uneven wear is reduced.

Further, since the narrow rib divided into the tread shoulder side by the narrow groove having the above-mentioned configuration has a substantially trapezoidal cross section of the tire meridian, it supports bending of the wide rib during cornering and high load, Avoid buckling due to excessive bending. In the present invention, the rib width W ₂ of the narrow rib is set such that the ratio W ₂ / W ₁ is within the range of 0.1 ≦ W ₂ / W ₁ ≦ 0.25 with respect to the rib width W ₁ of the wide rib. I have to. When the rib width W ₂ of the narrow rib is smaller than 0.1 of the rib width W ₁ of the wide rib, it becomes difficult to perform the buckling prevention action against excessive bending of the wide rib. If the rib width W ₁ of the wide rib exceeds 0.25, it becomes difficult to fully utilize the bending action of the wide rib.

When the tire is mounted on a regular rim and inflated to a standard air pressure, the inclination angle α of the shoulder side wall surface of the wide rib and the inclination angle β of the center side wall surface are set to be approximately similar to each other. , Α <β. Due to the relationship of α <β, the bending of the wide ribs is prevented from becoming extremely large toward the shoulder side, and an appropriate rigidity can be maintained.

Further, the inclination angles α and β of the wide ribs have a value of 1/2 of the sum, that is, a value of (α + β) / 2 when the tire is mounted on a regular rim and inflated to standard air pressure. The inclination angle θ of the tread surface of the wide rib with respect to the tire axial direction is set to 3.4θ or more and 6.4θ or less. When the value of (α + β) / 2 is smaller than 3.4θ, there is a drawback that the bending action in the shoulder direction at the time of contact is not sufficiently obtained, and when it is larger than 6.4θ, the excessive bending in the shoulder direction is caused. Due to the bending action, a crack occurs on the wide rib side of the narrow groove bottom.

In the present invention, the narrow groove for dividing the wide rib and the narrow rib defined in the present invention may be provided in at least the intermediate rib, and the shoulder rib may be formed by other means known as a measure against uneven wear. You may do it. Also,
In principle, such measures are not necessary because uneven wear does not substantially occur on the center rib. The main groove and the rib provided so as to extend in the tire circumferential direction may be linear or may be bent in a zigzag shape or the like. Further, the narrow groove that divides the rib into a wide rib and a narrow rib may be linear or may be bent in a zigzag shape or the like.

The depth and width of the main groove may be in the range generally used for heavy-duty pneumatic radial tires. For example, the main groove depth is 13 to 16 mm, and the main groove width is 1
The range of 0 to 15 mm is preferable. In addition, the width of each rib such as the center rib, the intermediate rib, and the shoulder rib is not particularly limited, and may be in the range used for a general heavy-duty pneumatic radial tire. Preferably 20 to 3
It is recommended that the range be 5 mm.

The narrow groove that divides the rib into a wide rib and a narrow rib has a groove width of 1/4 to 1 / the main groove width.
The range is 10 and preferably 1.5 to 3.0 mm. The groove depth of the fine groove is 80 to 10 of the main groove depth.
The range of 0% is preferable. The inclination angle α of the fine groove is 1 ° to 1
The range of 4 °, and the inclination angle β of the center side wall surface of the wide rib is preferably in the range of 10 ° to 15 °.

The present invention will be specifically described below with reference to the embodiments shown in the drawings. FIG. 1 shows a half cross section of a heavy duty pneumatic radial tire according to the present invention, and FIG. 2 exemplifies its tread surface. 1 is a tread, 2 is a carcass layer, and 3 is a belt layer. On the outer peripheral surface (tread surface) of the tread 1, a plurality of tires continuous in the tire circumferential direction (four tires in the example in the figure)
Main grooves 4 are provided, and a rib pattern divided into a plurality of (five in the illustrated example) ribs 12 is formed by these main grooves 4. Among these ribs 12, the intermediate rib M12 and the shoulder rib S12 are provided with the narrow grooves 5 continuous in the tire circumferential direction at positions offset to the respective shoulder sides, and the wide ribs 12a are respectively provided on the tread center side.
Further, narrow ribs 12b are formed on the shoulder side.

The narrow groove 5 is provided so that its groove depth direction is inclined from the tread surface to the tread center side, and due to this inclination, the cross section of the wide rib 12a in the tire meridian is inclined to the shoulder side to form a substantially parallelogram. It has a similar shape. Further, the narrow groove 5 is provided at a position offset to the shoulder side with respect to the intermediate rib M12 and the shoulder rib S12, and the rib width W ₂ of the narrow rib 12b becomes the rib width W ₁ of the wide rib 12a. for
The relationship is 0.1 ≦ W ₂ / W ₁ ≦ 0.25 (see FIG. 3).

Further, the inclination angle α of the narrow groove 5, that is, the inclination angle α formed by the groove depth direction with respect to the normal to the tread surface.
Is approximately the same as the inclination angle β formed by the tread center side groove wall of the wide rib 12a with respect to the normal direction to the tread surface, but 0 <α <β (see FIG. 3). Further, the inclination angles α and β are between the inclination angle θ with respect to the tire axial direction of the tread surface of the wide rib 12a,
They are formed to have a relationship of 3.4θ ≦ (α + β) /2≦6.4θ.

Here, the direction of the tread surface of the wide rib 12a means the end portion P of the wide rib 12a on the meridian section side in the meridian section when the tire is mounted on a regular rim and filled with standard air pressure. It is defined as a straight line connecting ₁ and the shoulder side end P ₂ . In the embodiment shown in FIGS. 1 and 2 described above, the specified narrow groove 5 is provided in both the intermediate rib M12 and the shoulder rib S12, but the specified narrow groove 5 includes at least the center rib and the shoulder rib. It suffices to provide it on the intermediate rib located in the middle of the above, and as the uneven wear preventing structure for reducing the rigidity with respect to the shoulder rib, another conventionally known structure may be used.

FIG. 5 shows the shoulder rib S12 as described above.
FIG. 4 shows another embodiment in which the intermediate rib M12 is provided with the narrow groove 5 defined above, but the shoulder rib S12 is provided with a narrow groove 5 ′ different from the above defined. . Fine groove 5'provided on this shoulder rib S12
Since the groove depth direction is not inclined from the tread surface to the tread center side, the meridional cross-sectional shape of the wide rib 12a is not a parallelogram but a trapezoid.

Also according to this embodiment, the same uneven wear suppressing effect as in FIGS. 1 and 2 can be obtained. FIG. 6 shows still another embodiment in which the shoulder rib S12 has another structure as well. In this embodiment as well, the intermediate rib M1
The above-mentioned narrow groove 5 is provided on the shoulder rib S2, but the shoulder rib S12 is provided on the wall surface outside the shoulder end so as to extend obliquely extending narrow groove 5 "in the tire circumferential direction. The non-grounding rib 13 is provided on the outer side of this embodiment.Even in this embodiment, the same uneven wear suppressing effect as in FIGS.

[0022]

【Example】

Example 1 The tire size is 11R22.5 14PR and the tread pattern is shown in FIG. 2. Fine grooves are provided in the intermediate rib and the shoulder rib, and the width of the fine groove of the shoulder rib is 2 mm.
The inclination angle δ is 5 ° in common, and the rib width ratio W ₂ / W ₁ of the wide rib and the narrow rib in the intermediate rib is
(Α + β) / 2 of the inclination angle α of the narrow groove, the inclination angle α of the narrow groove and the inclination angle β of the center side wall surface of the wide rib (however,
The tires 1 to 6 of the present invention and the comparative tires 1 to 5 in which the values of the inclination angle β were kept constant at 15 ° were changed as shown in Table 1 were manufactured.

For comparison, a conventional tire having the same tire size and having no fine groove formed in any rib was manufactured. These 12 types of heavy-duty pneumatic radial tires were respectively mounted on the front shafts of 10-ton trucks (2-2D vehicles), and the condition of uneven wear occurrence on the tread surface after running 40,000 km was visually inspected,
The results shown in Table 1 were obtained.

[0024]

[Table 1]

From the results shown in Table 1, it is understood that the tires 1 to 6 of the present invention satisfying the conditions of the present invention do not substantially cause uneven wear. Example 2 A tire of the present invention 2 of Example 1 and a tire (Comparative Example 6) in which the narrow ribs of the tire of the present invention 2 are subjected to step processing are the same as those of Example 1, and a 10-ton truck (2-2.D) is used. The results are shown in Table 2 when the amount of wear after running for 40,000 km on the front shaft of a vehicle was compared.

[0026]

[Table 2]

From the results shown in Table 2, it can be seen that the wear life of the tire having the narrow rib with a step (Comparative Example 6) is inferior to that of the tire 2 of the present invention. Example 3 A tire of the present invention 2 of Example 1 and a tire (Invention 7) in which the narrow grooves of the embodiments of FIGS. (2
It was mounted on the front shaft of the (-D vehicle) and visually checked for uneven wear on the tread surface after running for 40,000 km, and the results shown in Table 3 were obtained.

[0028]

[Table 3] From the results of Table 3, two types of test tires (Invention 2 and 7)
It can be seen that uneven wear is not substantially generated.

[0029]

As described above, the pneumatic radial tire for heavy load of the present invention has a rib pattern, and when at least the intermediate rib is divided by the fine groove to form the wide rib and the narrow rib. Since the narrow rib has the same tread height as the wide rib, the effective ground contact area of the tread is not reduced, and the tread rubber on the tread ground surface is prevented from moving substantially in the tire axial direction. By doing so, the drag in the axial direction of the tire is reduced, so that the effect of suppressing uneven wear can be improved.

[Brief description of the drawings]

FIG. 1 is a half cross-sectional view showing an example of a heavy duty pneumatic radial tire of the present invention.

FIG. 2 is a plan view showing a main part of a tread surface of the tire shown in FIG.

FIG. 3 is a vertical cross-sectional view showing a main part of a tread portion of the tire shown in FIG.

FIG. 4 is a vertical cross-sectional view showing a main part of a tread portion when the tire of FIG. 1 is inflated.

FIG. 5 is a half sectional view of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 6 is a half sectional view of a heavy duty pneumatic radial tire according to still another embodiment of the present invention.

FIG. 7 shows a tread contact portion of the tire of the present invention,
(A) is a plan view of the tread ground contact shape, and (B) is a sectional view taken along line 7B-7B in (A).

FIG. 8 shows a tread contact portion of a conventional tire,
(A) is a plan view of the tread ground contact shape, and (B) is a sectional view taken along the line 8B-8B in (A).

[Explanation of symbols]

 1 Tread 4 Main groove 5 Narrow groove 12 Rib M12 Intermediate rib S12 Shoulder rib 12a Wide rib 12b Narrow rib

Claims (2)

[Claims] 1. A heavy-duty pneumatic radial tire having a rib pattern in which a plurality of ribs extending in the tire circumferential direction are formed on a tread surface, wherein a tire circumference is provided on at least an intermediate rib located between a tread center and a tread shoulder. And a narrow groove on the tread shoulder side that has the same tread height as the middle rib, by providing a narrow groove that extends in the direction of the groove and is inclined in the groove depth direction from the tread surface to the tread center side. And the ratio W ₂ / W ₁ of the width W ₂ of the narrow rib to the width W ₁ of the wide rib is in the range of 0.1 ≦ W ₂ / W ₁ ≦ 0.25, The inclination angle α in the groove depth direction with respect to the tread surface normal direction and the inclination angle β with respect to the tread surface normal line direction of the tread center side groove wall of the wide rib are 0 <α <β. While the relationship, the relative inclination angle θ which forms with respect to the tire axial direction of the tread surface of the wide rib, the heavy duty pneumatic radial tire was 3.4θ ≦ (α + β) /2≦6.4θ relationship. 2. An intermediate rib and a shoulder rib are sequentially arranged on both sides of the center rib to form a total of five ribs, and the narrow groove is provided in each of the intermediate rib and the shoulder rib to form a wide rib. The heavy-duty pneumatic radial tire according to claim 1, which is divided into narrow ribs.