JP3116243B2 - Pneumatic studless tire - 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 studless tire having improved uneven wear resistance without impairing snow and ice performance.

[0002]

2. Description of the Related Art A pneumatic studless tire based on a block pattern has a large number of sipes formed on a block arranged on a tread surface and enhances an edge effect thereof to exhibit good snow and ice performance. .
However, when the sipe is provided, the rigidity of the block is reduced, and there is a disadvantage that uneven wear (cupping) occurs due to running on a dry road surface.

Conventionally, as a measure for reducing the uneven wear of the studless tire as described above, in the case of a groove having a large groove width, the rigidity of the block corner portion is increased by increasing the groove angle with respect to the normal direction of the tread surface. The method of raising is adopted. However, this method has a problem that the performance of the snow and ice road is deteriorated because the groove area and the groove volume on the tread surface decrease as the wear progresses. In the case of a groove having a small groove width, the measures for increasing the groove angle as described above cannot be adopted in order to reduce the groove volume from the beginning.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic studless tire capable of reducing uneven wear without impairing the performance of snow and ice roads.

[0005]

According to the pneumatic studless tire of the present invention, which achieves the above object, a large number of polygonal blocks defined by a circumferential groove and a tire width direction groove are arranged on a tread surface. And at least 3 in a tire provided with a sipe on the surface of the block.
The cross section of the tire circumferential groove and the tire width direction groove where the corners of the block are opposed to each other is shallowly raised so as to satisfy the following expressions (1) and (2). And

0 <a / b ≦ 0.2───────────── (1) 0.2 ≦ h / D ≦ 0.5─────────── (2) where a is the maximum length (mm) of the groove intersection bottom raised portion in the direction along the block side from the block corner, and b is the diagonal line between the corners of each of the at least three blocks. The maximum length (mm) and h are the height (mm) of the groove intersection bottom raised, and D is the groove depth (mm) of the groove not raised.

[0007] As described above, at least three corners of the polygonal block have shallow bottoms at the groove intersections where the corners oppose each other, and the block corners are partially reinforced to effectively reduce the variation in rigidity of the blocks. It can be made smaller and uneven wear can be prevented. In addition, since the groove is partially raised, even if the wear is advanced or the groove is narrow,
Good snow and ice performance can be ensured.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of a block pattern formed on the tread surface of the tire of the present invention. The block pattern includes a large number of polygonal blocks 3 defined by circumferential grooves 1 and width grooves 2 intersecting with the circumferential grooves 1. The two circumferential grooves 1 are wider at the left and right shoulder portions, but are narrower at the center region. In the center area, three block rows composed of hexagonal blocks 3 are arranged so as to be shifted from each other in the tire circumferential direction by a half pitch, and one block row composed of pentagonal blocks 3 is arranged in both shoulder portions. ing. The hexagonal block 3 has a sipe 4 in the tire width direction.
Are formed, and a large number of sipes 4 in the tire circumferential direction are formed in the pentagonal block 3 so as to exhibit good snow and ice road performance.

The block 3 arranged in the center area
Since the three block rows are shifted by half pitch,
Groove intersection A where narrow circumferential groove 1 and width groove 2 intersect
In this example, the corners of the three blocks 3 face each other. In addition, the groove intersection A has a groove bottom that is raised to be shallower than other groove main portions. That is, since the corners of the block 3 are lower in rigidity than the other parts, if three such corners are gathered in one place, the block corners in this region have apparently lower rigidity. This is where cupping wear is likely to occur.
However, by raising the groove bottom of the groove intersection portion A to a shallow level as described above, the rigidity of the corners of each block 3 is improved, the rigidity of the entire block is averaged, and the mutual variation is reduced. Therefore, the above-described cupping wear is prevented.

As shown in FIG. 2, the raised portion of the groove intersection A has a length a along a block side from a corner of each block 3 and a circumferential groove 1 and / or a width direction. The groove 2 is raised by a height h from the groove bottom at a depth D of the groove main body portion. The lengths a for at least three blocks need not necessarily be the same as each other, but may be different. In the tire of the present invention, with respect to at least three blocks in such a configuration, the maximum length a and the raised height h among the lengths along the sides are determined by the above-described formulas (1) and (2). ) Must be satisfied.
The maximum length a is 0.2 to the maximum length b of the diagonal lengths between the corners of at least three blocks.
If it is larger than twice, high snow and ice performance cannot be maintained until the end of wear. The height h of the bottom raised is the groove depth D.
If it is less than 0.2 times, the effect of reducing the variation in rigidity by sufficiently reinforcing the corners of the block 3 cannot be obtained.
If it exceeds five times, the decrease in the groove area becomes too large at the end of wear, so that the performance on snow and ice roads cannot be secured.

Although it is not necessary to raise the bottom of the groove intersection A according to the present invention at all the corners of three or more blocks, it is preferable that the groove width is narrow as in the illustrated embodiment. It may be applied to the block adjacent to the circumferential groove and / or the width groove. The narrow groove width is 7m
In the case of m or less, a remarkable effect is obtained. When the circumferential width of the circumferential groove 1 or the width direction groove 2 is large, the groove angle can be increased. However, as shown in FIG. By raising the bottom, the rigidity of this corner may be increased.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The tread pattern is common in FIG. 1, the tire size is 650R16, and the ground contact width is 148 mm. The maximum length b of the diagonal line between the corners of each block and the groove intersection A are raised at the bottom. The ratio a / b of the length a in the direction along the block side from the corner of the block, and the ratio h / D of the raised height h of the groove intersection and the groove depth D of the groove not raised, respectively, Five kinds of tires changed as shown in Table 1 were prepared.

For comparison, a conventional tire 1 in which the groove bottom A was not raised at all and a conventional tire 2 in which the groove bottom was raised so as to connect the sides of the block 3 as shown in FIG. The following seven types of tires were evaluated for the following snow and ice performance and uneven wear resistance. The results were as shown in Table 1. Snow / Ice Road Performance : When trying to rotate a tire while fixing a car on snow, the traction obtained immediately before the tire starts to spin is measured, and the measured value of the conventional tire 2 is used as a reference (1).
00). The larger the index value, the greater traction is obtained. Uneven wear resistance : The amount of cupping at the time of wear was measured and indicated by an index using the measured value of the conventional tire 2 as a reference (100). The larger the index value, the smaller the amount of cupping.

[0014] Table 1 shows that the performance of the snow and ice roads of the tires 1 and 2 of the present invention and the comparative tires 1 and 3 are all higher than that of the conventional tire 2, but the performance of the comparative tire 2 is lower than that of the conventional tire 1. . On the other hand, the uneven wear resistance of each of the tires 1 and 2 of the present invention and the comparative tire 3 is significantly improved as compared with the conventional tire 2, and the comparative tire 1 is also slightly improved. But,
It turns out that the comparative tire 2 is insufficient in uneven wear resistance.

Next, the tire 1 of the present invention and the comparative tires 1, 3
Of the tread part of the tire in advance, the wear rate is 0
%, 25%, 50%, and 75%, four types of tires were manufactured, and the performance of these tires was evaluated. The results are shown in Table 2. From Table 2, it can be seen that the tire 1 of the present invention retains better snow and ice performance than the new comparative tire 1 even when the wear rate reaches 50%, whereas the comparative tires 1 and 3 and the conventional tire 2 have significantly higher performance. You can see that it is getting worse.

[0016]

According to the present invention, at least three corners of a polygonal block have shallow bottoms at the intersections where the corners face each other, and the corners of the block are partially reinforced. Can be reduced, and uneven wear can be prevented. Further, since the bottom of the groove is partially raised, good snow and ice road performance can be ensured even if the wear is advanced or the groove is narrow.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of a tread pattern of a tire of the present invention.

FIG. 2 is a partially enlarged plan view of FIG.

FIG. 3 is a plan view showing another embodiment of the tread pattern of the tire of the present invention.

FIG. 4 is a plan view showing a tread pattern of a conventional tire.

[Explanation of symbols]

3 Block 4 Sipe A Groove intersection a Maximum length (mm) in the direction along the block side from the block corner of the raised portion of groove intersection A, b The diagonal line between the corners of at least three blocks Maximum length (mm) h Height of bottom of groove intersection A (mm) D Depth of groove not raised (mm)

Claims (1)

(57) [Claims] 1. A tire in which a number of polygonal blocks defined by a tire circumferential groove and a tire width direction groove are arranged on a tread surface, and at least three blocks are provided in a tire provided with a sipe on the surface of the block. A pneumatic studless tire having a groove intersection between the tire circumferential direction groove and the tire width direction groove whose corners face each other shallowly rise so as to satisfy the following formulas (1) and (2). 0 <a / b ≦ 0.2───────────── (1) 0.2 ≦ h / D ≦ 0.5─────────── (2) Here, a is the maximum length (mm) of the groove intersection bottom raised portion in the direction along the block side from the block corner, and b is the maximum of the diagonal lines between the corners of the at least three blocks. The length (mm) and h are the height (mm) of raising the bottom of the groove intersection, and D is the depth (mm) of the groove not raised.