JPH0796716A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire for heavy load heightened in the discharging effect of a stone bitten into an auxiliary groove even in the case of having a pattern based on blocks formed by main grooves and auxiliary grooves. CONSTITUTION:In a pneumatic tire for heavy load, the tread is provided with plural main grooves 2, and the mutually adjacent main grooves 2 are connected by auxiliary grooves 3 smaller in groove width and shallower in groove depth than the main grooves 2 so as to form numerous blocks 4 divided by the main grooves 2 and auxiliary grooves 3. The groove width of each auxiliary groove 3 is enlarged as it approaches the main groove 2. At least one side groove wall of the auxiliary groove 3 is provided with a ledge part 6, and the height of the ledge part 6 from the groove bottom is lowered as it approaches the main groove 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire for heavy loads such as trucks or buses, and more specifically, in a block-based pattern having sub-grooves having a groove width smaller than the main groove and a shallow groove depth. The present invention relates to a heavy-duty pneumatic tire designed to reduce stone entrainment in the auxiliary groove.

[0002]

2. Description of the Related Art When a block-based pattern is provided on a heavy-duty pneumatic tire such as a truck or a bus, the main groove and the groove width of the main groove are larger than those of the main groove. The wear life can be extended by combining sub-grooves having a small groove depth and a small groove depth to increase the ground contact area ratio. However, on the other hand, there is a disadvantage that the problem of stone biting occurs in the auxiliary groove.

[0003] In this way, the stone once bitten into the sub-groove having a narrow groove width is difficult to separate, which not only causes the block to be chipped, but also the stone that has sunk with the wear of the tire damages the groove bottom,
Further, since the belt is damaged, there is a problem that the tire rehabilitation property is finally deteriorated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty pneumatic tire having a high effect of discharging stones entrapped in the sub-groove even if the block-based pattern formed by the main groove and the sub-groove is provided. To provide.

[0005]

A pneumatic tire for heavy load according to the present invention which achieves the above object, is provided with a plurality of main grooves on a tread surface and has a groove width larger than that of the main grooves adjacent to each other. In a heavy-duty pneumatic tire in which a large number of blocks that are connected to each other by a sub-groove having a small groove depth and a shallow groove depth are formed to divide the main groove into sub-grooves. And a shelf is provided on the groove wall on at least one side of the sub-groove, and the height of the shelf from the groove bottom is lowered as it approaches the main groove.

By thus forming the groove width of the auxiliary groove and the shelf portion provided on the groove wall in the above-described shape, even if a stone bite occurs in the auxiliary groove, the bent stone is received by the shelf portion and the tire is rotated. When contacting with ground and non-contacting are repeated, stones can be pushed out to the main groove side having a large groove width and discharged to the outside of the tire by the action of opening and closing the groove width. Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of a block pattern of a heavy duty pneumatic tire of the present invention. In the figure, 1 is a center rib extending in the tire circumferential direction T at the center of the tread surface, and a plurality of linear main grooves 2 are provided in the tire width direction on the left and right sides of the center rib 1 and between the main grooves 2. A plurality of linear sub-grooves 3 are provided in the above, and a large number of blocks 4 are formed by these main grooves 2 and sub-grooves 3. Further, lug grooves 5 are formed in the center rib 1 at a predetermined pitch, and the lug grooves 5 are opened in the main groove 2 with the opening width thereof being the same as the width of the main groove 2. Here, the sub-groove is defined as a groove having a smaller groove width and a shallower groove depth than the main groove.

According to the present invention, in the block-based pattern as described above, the groove width of the sub-groove 3 is changed from the middle portion thereof to the main groove 2.
It gradually increases as it approaches. In addition, the sub groove 3
A shelf 6 is provided on one of the groove walls, and the height of the shelf 6 from the groove bottom is gradually lowered toward the main groove 2 as shown in FIG. In this way, the width of the sub groove 3 is set to the
Since the height of the shelf portion 6 provided on the groove wall of the sub groove 3 is made smaller as it gets closer to the main groove 2, the sub groove 3 is closed at the time of tire rotation during ground contact and at the time of non-ground contact. By repeating the opening action, even if stones are caught in the sub-grooves 3, the stones are pushed out of the sub-grooves 3 toward the main groove 2 side, and in a cross-sectional view, the force of pushing out obliquely to the main groove 2 side and to the outside of the tire is applied. Since it is received, it can be easily discharged from the sub groove 3.

In the heavy-duty pneumatic tire of the present invention described above, the width of the sub-groove 3 is, as shown in FIG. 2, the narrowest groove width at the center of the sub-groove 3, A, the end opening into the main groove 2. If the groove width of the portion is B and the distance from the central portion to the main groove 2 is C,
It is preferable that the relationship of (B−A) / C is 0.1 to 0.7 (the inclination angle α is about 6 ° to 35 °). If the ratio relationship is smaller than 0.1, the stone discharging effect decreases, and
If it exceeds 7, the auxiliary groove width becomes too wide, and the ground contact area ratio of the tread becomes low, and the wear resistance deteriorates. More preferably, the above ratio is 0.2 to 0.5 (as the inclination angle α,
About 11 ° to 27 °).

As for the height of the shelf 6 from the groove bottom, as shown in FIG. 3, the highest height H at the center is the depth d of the auxiliary groove.
It is preferably 0.3 to 0.9 times. When the maximum height H is smaller than 0.3, the shelf 3 is close to the groove bottom, so that the effect of discharging stones by the shelf 3 cannot be expected when there are many remaining grooves.
Further, if it exceeds 0.9d, since the shelf 3 is located near the tread surface, a part of the shelf 3 is exposed at the initial stage of wear, and the effect of discharging stones by the shelf 3 is reduced. More preferably,
It is good to be 0.4d-0.8d.

The rate at which the height of the shelf 6 decreases toward the main groove is
If the height of the lowest position facing the main groove 2 is h, and the distance from the position of the maximum height H of the central portion to the main groove 2 is E, then (H−
h) / E is 0.1 to 1.5 (inclination angle β is about 6 ° to 56 °), and more preferably 0.2 to 0.7.
(The inclination angle β is preferably about 11 ° to 35 °). If the ratio of (H−h) / E is smaller than 0.1, the stone discharging effect is reduced, and if it exceeds 0.7, the inclination angle β becomes too large and the heights H and h cannot be dimensioned. It will be difficult.

Further, in the present invention, the upper surface 6a of the shelf 6 is
As shown in FIG. 4, it is more preferable to incline toward the groove bottom side from the groove wall of the sub groove 3 toward the groove width center. By providing the slope in this manner, it is possible to prevent the tire from being worn and causing an initiation that causes uneven wear. As this inclination angle θ, θ = 30 ° to 7
It is preferable to set it at 5 °, more preferably 35 ° to 65 °. If the inclination angle θ is less than 30 °, the angle becomes too steep, and the action of discharging stones as a shelf portion decreases. 7
If the angle exceeds 5 °, the tire is worn and the initiation of uneven wear is likely to occur when the shelf 6 approaches the tread surface. 5 and 6 show other examples of block-based patterns provided in the heavy-duty pneumatic tire of the present invention.

In the case of FIG. 5, in the above-mentioned embodiment,
The linear auxiliary groove 3 is formed in a zigzag shape, and the opening end width of the lug groove 5 is narrower than that of the main groove 2. Then, shelves 6 are formed on both side walls of the lug groove 5. Even with such a configuration, the same effect as described above can be obtained. In the case of FIG. 6, the shoulder rib 11 is formed in the shoulder portion, the zigzag-shaped main groove 12 extending in the tire circumferential direction T is formed in the center portion of the tread surface, and the zigzag-shaped auxiliary groove that intersects the main groove 12 in an oblique direction. A groove 13 is provided, and a large number of blocks 14 are formed by the main groove 12 and the sub groove 13. The sub-groove 13 has a groove width gradually increasing in a V-shape as it approaches the main groove 12 from the corner of the intermediate position, and the shelf wall 16 having the same configuration as the above is entirely formed on one side of the groove wall of the sub-groove 13. It is partially provided on the other side. 15 is a lug groove formed in the shoulder rib 11, 18
Is a sipe provided in the block 14. It is clear that even in such a block pattern, the same effect as described above can be obtained.

In the present invention, the shelf portion may be provided on at least one side of the groove wall of the sub groove, and may be provided on a part of the other side or over the entire length as necessary. Also,
The increase rate of the groove width of the auxiliary groove and the decrease rate of the height of the shelf are linear or curved, and are not particularly limited.

[0015]

[Example] Tire size is 11R22.5 14PR
The tread development width is 220 mm, the block pitch length is 56 mm, and the main groove depth D is 20 mm in common, and as shown in Table 1, the conditions such as the sub groove and the shelf portion are different from each other. The tire 1 of the present invention having a block pattern shown in FIG.
2 (Examples 1 and 2), and a comparative tire 1 (Comparative Example 1) in which the groove width of the auxiliary groove shown in FIG.
Comparative tire 2 in which the groove width of the sub groove of the tire is increased toward the main groove
(Comparative Example 2), Comparative tire 3 in which a shelf is provided in one of the sub-grooves of Comparative tire 1 (Comparative Example 3), and Comparative tire 4 in which the height of the shelf of Comparative tire 3 is lowered toward the main groove.
Four (Comparative Example 4) were manufactured. Each of these test tires was mounted on a rim with a rim size of 22.5 x 8.25, and at a pneumatic pressure of 7.0 kg / cm ² , four tires were mounted on each rear wheel of a 2-D car, two on each side, a total of four. Under the measurement conditions shown below, a stone bite resistance evaluation test at the time of new article, a stone bite resistance evaluation test at a time of traveling 20,000 km and a block chipping evaluation test were performed, and the results shown in Table 1 were obtained.

In the table, a is the distance between the tips of the central portions of the blocks 4 and the shelves 6 in the minimum groove width portion of the auxiliary groove shown in FIG. 2, and b is the maximum groove width portion of the auxiliary groove in FIG. The width of the shelf 6 and d are the depths of the sub-grooves 3 shown in FIG. Test for evaluation of stone bite resistance at the time of new article. Vehicles run at 40 h / hr on a riverbed with stones of various sizes.
The number of granites remaining on the four tires after running 500m at a speed of 500km / h forcibly biting stones on each test tire and running 1km at a speed of 60km / h on the paved road in that state, The number of stone bites averaged per tire was evaluated. Stone bite evaluation test and block chipping evaluation test after traveling 20,000 km
Exam 1. Stone bite resistance evaluation test Stone bite that averages the number of granite stones remaining on four test tires when running 20,000 km on a section with gravel roads of about 1% and paved roads of about 99% per tire The number was evaluated. 2. Block chipping evaluation test The occurrence of cracks in the tire block after running 20,000 km was visually observed and evaluated according to the following four grades.

1: No cracks are generated 2: Very few cracks are generated 3: Cracks are generated in the tire block exceeding the minimum amount 4: Many cracks are generated in the tire block

[0018] As is clear from Table 1, the tire of the present invention was
It can be seen that the number of stone bites is extremely small after traveling 10,000 km and there are no cracks, and the stone discharging effect is extremely high.

[0019]

As described above, according to the present invention, in the block-based pattern formed of the main groove and the sub groove, the width of the sub groove is increased toward the main groove side, and the groove wall of the sub groove is further increased. By providing the shelf portion and lowering the height of the shelf portion toward the main groove side, even if stones are caught in the sub groove, they can be easily discharged from the sub groove. Therefore, it is possible to prevent the chipping of the block and prevent the tire rehabilitability from being deteriorated by avoiding the damage caused by the stones that go into the tire as the tire wears.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a block basic pattern provided in a heavy duty pneumatic tire of the present invention.

FIG. 2 is an enlarged view showing a part of the block shown in FIG.

FIG. 3 is a sectional view taken along line XX of FIG.

FIG. 4 is a sectional view taken along the line YY of FIG.

FIG. 5 is a plan view showing another embodiment of the block basic pattern provided in the heavy duty pneumatic tire of the present invention.

FIG. 6 is a plan view showing still another embodiment of the block basic pattern provided in the heavy duty pneumatic tire of the present invention.

7 is a plan view showing a block basic pattern in the heavy duty pneumatic tire of Comparative Example 1. FIG.

[Explanation of symbols]

1 Center rib 2,12 Main groove 3,13 Sub groove 4,14 Block 5,15 Rib groove 6,16 Shelf

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 8408-3D B60C 11/06 B

Claims (2)

[Claims] 1. A plurality of main grooves are provided on a tread surface, and adjacent main grooves are connected to each other by sub-grooves having a groove width smaller and a groove depth smaller than that of the main grooves. In a heavy-duty pneumatic tire having a large number of blocks divided into grooves, the groove width of the sub-groove is increased as it approaches the main groove,
Further, a heavy-duty pneumatic tire in which a shelf is provided on a groove wall on at least one side of the sub-groove, and the height of the shelf from the groove bottom is lowered as the height approaches the main groove. 2. The pneumatic tire for heavy load according to claim 1, wherein the upper surface of the shelf portion is inclined from the groove bottom of the auxiliary groove toward the groove width center toward the groove bottom side.