JP3200506B2 - Pneumatic radial tire for heavy loads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for heavy loads which reduces damage such as edge cracks of closed sipes provided on ribs or blocks.

[0002]

2. Description of the Related Art A tread pattern of a pneumatic radial tire for heavy loads (hereinafter referred to as a "radial tire for heavy loads") often includes a rib pattern or a block pattern. Some ribs and blocks have closed sipes in which both edges stop.

[0003] However, the closed sipes are:
In general, the width is about 0.8 mm or more, easy to bite stone,
There is a disadvantage that cracks are likely to occur at both edges of the closed sipe due to the biting of the stone. In addition, there is a problem that the crack once generated easily grows and eventually causes a tread chipping. In order to solve this problem, narrow the width of closed sipes,
There are proposals such as a method of bending the central portion to form a shape of a letter “H”, or reducing the depth of the central portion (raising the bottom). However, all of these countermeasures have the disadvantage that the stone biting prevention effect and the effect of suppressing the generation of cracks at both edges are insufficient, and the effect of the sipe's original braking and driving performance is reduced, and it is not necessarily the case. It was not satisfactory.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a closed sipe without impairing its inherent braking and driving performance.
It is an object of the present invention to provide a heavy duty radial tire capable of reducing the occurrence of stone biting and edge cracks.

[0005]

A heavy-duty pneumatic radial tire according to the present invention that achieves the above object has a lip pattern or a block pattern, and has ribs or blocks on both ends of a central sipe portion extending in the tire width direction. Bend in the tire circumferential direction from each end to form the longitudinal direction
The closed sipes forming the bent sipes extending to formed provided, the width t of the previous SL central sipe portion from 0.4 to 0.
6 mm, characterized in that the width T of the folded sipe portion was more than twice the width t of the central sipe portion.

As described above, the width of the central sipe portion of the closed sipe is 0.4 to 0.4 mm, which is smaller than the conventional sipe width of 0.8 mm.
By making it 0.6 mm, it is difficult to open and hardly cause biting of stones, and at both ends of this central sipe portion, a wide bent sipe portion having a width of at least twice the width thereof is longitudinally arranged in the tire circumferential direction.
By providing the direction, the stress applied to the edge can be dispersed to suppress the occurrence of cracks and chipping of the tread.

Hereinafter, the present invention will be described in detail with reference to the drawings. 2 and 3 show examples of a rib pattern and a block pattern provided on the heavy duty radial tire of the present invention, respectively. In the former rib pattern, a plurality of ribs 3 are formed by a plurality of main grooves 1 extending in the tire circumferential direction, and the ribs 3 are provided with closed sipes 5. In the latter block pattern, a plurality of blocks 4 are formed by providing the main groove 1 and the horizontal groove 2, and the closed sipe 5 is provided in the block 4.

FIG. 1 shows an example of the closed sipes 5 formed on the above-described ribs or blocks. The closed sipe 5 has a central sipe portion 5c having a width t inclined at an angle α with respect to the tire radial direction FF ′, and a longitudinal direction bent from both ends of the central sipe portion 5c in a tire circumferential direction EE. And a bent sipe portion 5e having a width T inclined at an angle β with respect to '.

In the present invention, the width t of the central sipe portion 5c is
Is narrowed to a range of 0.4 to 0.6 mm, and the width T of the bent sipe portion 5e is set to be twice or more the width t of the central sipe portion 5c. When the width t of the central sipe portion 5c is larger than 0.6 mm, the central sipe portion 5c is easily opened, and the effect of suppressing stone biting is deteriorated. On the other hand, when the thickness is less than 0.4 mm, the sipe formability deteriorates, and the tire productivity decreases. On the other hand, bent sipes 5
If the width T of e is less than twice the width t of the central sipe portion 5c, the effect of dispersing stress at the edge of the bent sipe portion 5e becomes small, and it becomes impossible to reduce edge cracks.

When the width T of the bent sipe portion is set to be twice or more the width t of the central sipe portion, a large radius of curvature R is easily formed on the edge. Can be further increased. The upper limit of the width T of the bent sipe portion is not particularly limited, but if it is too large,
Since the bent sipe portion is likely to bite the stone, the upper limit is preferably about four times the width t of the central sipe portion.

In the present invention, the closed sipe formed on the rib or the block has an angle α of the center sipe portion with respect to the tire radial direction FF ′ in the range of −30 ° to + 30 °, and a tire circumferential portion of the bent sipe portion. It is desirable that the angle β with respect to the direction EE ′ be in the range of −15 ° to + 15 °. Also, the depth of the closed sipe is preferably the same along its length so that the edge effect can be exerted until the end of wear.

[0012]

EXAMPLES Tires 1 and 2 of the present invention and conventional tires 1 to 3 having the same tire size, tread pattern, and number of sipes in the tire and having different shapes and dimensions of the sipe as shown in Table 1 are shown below. And comparative tires.
(Note that the angle α of the central sipe portion and the angle β of the bent sipe portion of the closed sipe in FIGS. 4 and 6 were each set to 0 °, and the length of the bent sipe was set to 3 mm.) Tire size: 11R22.5 14PR tread pattern: FIG. 2 (rib pattern) Number of sipes in tire: about 400 sipe length: 15 mm A road test was performed on these six types of tires by the following method, and the results are shown in Table 1.

Crack generation test : 7.0 for test tires
Filled with air pressure of 0 kg / cm ² , mounted on the front wheels of Vehicle 2 ・ D-4, loaded with a regular load specified by JATMA and completed a 30,000 km tread on 99% paved roads and 1% on rough roads. The occurrence of cracks in the sipe was visually inspected.

[0014] From Table 1, it can be seen that the tires 1 and 2 of the present invention are both conventional tire 1
It can be seen that the occurrence of cracks is greatly reduced as compared with the case of, and the length of the cracks is also short.

On the other hand, the sipe width of the conventional tire 1 is reduced as in the conventional tire 2, the width of the bent sipe is the same as the central sipe portion as in the conventional tire 3, or the comparative tire is Thus, even if the both ends of the conventional tire 2 are made spherical, the occurrence of cracks is significantly reduced and the length cannot be reduced unlike the tire of the present invention.

[0016]

According to the present invention, the width of the central sipe portion of the closed sipe is set to 0.4 to 0.6 mm, which is smaller than the width of the conventional sipe, 0.8 mm, so that the closed sipe is hardly opened, and stone biting occurs. The center sipe has a wide bent sipe at least twice its width at both ends of the tire.
By providing a longitudinal direction in the direction, the stress applied to the edge can be dispersed, and the occurrence of cracks can be suppressed.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a closed sipe provided in a heavy duty radial tire according to the present invention.

FIG. 2 is a plan view showing an example of a rib pattern provided on the heavy duty radial tire of the present invention.

FIG. 3 is a plan view showing an example of a block pattern provided on the heavy duty radial tire of the present invention.

FIG. 4 is a plan view showing another example of the closed sipe.

FIG. 5 is a plan view showing another example of the closed sipe.

FIG. 6 is a plan view showing another example of the closed sipe.

FIG. 7 is a plan view showing still another example of the closed sipe.

[Explanation of symbols]

3 rib 4 block 5 closed sipe 5c central sipe part 5e bent sipe part

Claims (1)

(57) [Claims] 1. A lip pattern or a block pattern having ribs or blocks on both ends of a central sipe portion extending in the tire width direction from the ends in the tire circumferential direction.
Bent to closed sipes forming the bent sipes extending to form a longitudinally arranged, 0.4 to 0.6 mm pre-Symbol central sipe portion width t of the width T of the folded sipe portion center A pneumatic radial tire for heavy loads having a width t of the sipe portion twice or more.