JP3386553B2 - Pneumatic studless tires for heavy loads - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial application] Tires used in vehicles such as trucks and buses that are heavier than ordinary passenger class vehicles, especially snow tires suitable for local use conditions where there is little snowfall or snowfall in the winter. -Improving the pattern performance of the tread portion of the tire.

[0002]

2. Description of the Related Art In studless tires, which are becoming popular as an alternative to spiked tires, generally relatively small blocks are arranged over the entire tire tread portion, and many sipes are cut into the surface of these blocks. Covered pattern
Are used. When such a studless tire is always used especially in a region where there is little snowfall or snowfall, the pattern design of the above-mentioned configuration with emphasis on snowfall, braking on icy road surface and traction performance of the tire, and in cold regions. Because the material design is inclined to the running conditions,
The large frictional force and driving force generated when driving on a dry road surface act on the pattern block for a long time, and the internal stress concentrates on the bottom of the sipe provided in the block, causing fatigue cracks in this part. However, there is a problem that the life of the tire is shortened due to the occurrence of For this reason, in the case of tires that are constantly used in regions where there is little snowfall or snowfall in the winter, increase the block size, reduce the number of tires, reduce the number of sipes, and reduce the depth of snow. There was a tendency to sacrifice performance on wet road surfaces. Further, as one solution of these problems, adopting a sipe is bottom as described was expanded in Japanese Patent Laid-Open No. 4-85111 as sipes of the blocks it has been proposed.

[0003]

In recent years, however, the number of heavy-duty vehicles is increasing, and the number of high-horsepower vehicles is increasing.
Limitations are expected in the improvement plan described in Japanese Patent No. 85111, and tourist buses such as large-sized and long-distance traveling buses enter a deep snow cold region, albeit temporarily, and high-speed high-horsepower traveling is performed on a dry road surface. In vehicles, the need for a high degree of compatibility between snow and snow performance and tire durability has increased, and, in addition, the conventional shallow model that has blocks mainly located on the entire tread surface of the tire has been used. In studless tires for snow regions, there is an increasing need to solve problems such as poor slip resistance on wet road surfaces at the end of wear when the pattern groove becomes shallow.

Therefore, an object of the present invention is to maintain the on-snow performance close to that of a studless tire for deep snow cold regions and to have excellent durability against sipe groove bottom cracks and block root cracks for heavy load pneumatic studless tires. Is to provide.

[0005]

In order to achieve this object, the present invention according to claim 1 has three or more main grooves continuously extending in the circumferential direction of the tire, and the main grooves are A plurality of blocks divided by a plurality of circumferential grooves and a plurality of sub-grooves having a groove depth equal to or less than the main groove facing the width direction of the tire are arranged in the tire circumferential direction, and the sub-grooves are provided in the blocks. At least one sipe that extends in the tire width direction and has an enlarged bottom is provided with a groove depth equal to or less than that, and moreover , between the circumferential grooves.
Separated part sipe of all blocks is divided into
A tire having a pattern block rigidity G represented by these numerical values satisfying the following ranges, where I is the circumferential length, b is the lateral length, and h is the depth of the sipe. The pneumatic studless tire for heavy loads is characterized by having a tread pattern. G = 0.72 × b × (I ³ / h ³ ) × (1 / [1 + 15.6 × (I ² / 4h ² )]) (1) 4.8 <G <7 ... ( 2) The rigidity formula (1) has a length in the circumferential direction divided by the sub-grooves and the sipes and a length in the tire width direction divided by circumferential grooves including the main groove. In a block with a sipe depth of height, when the external force acts parallel to the block surface on the other end of the block with the groove bottom position of the sipe as the fixed end, the block is regarded as a beam and The shear rigidity is obtained by the beam theory. At this time, the material constant of the block and the shape correction value obtained by simplifying the block shape by calculation are experimentally obtained separately and multiplied.

The invention according to claim 2 is characterized in that the tread rubber material of the portion constituting the tire tread pattern is a foamed rubber having a foaming ratio of 1 to 10%. The pneumatic studless tire for heavy load described above was used. Incidentally, it foamed rubber as the tread rubber material, for example, JP 63-90402 and JP 63-9
As described in JP-A No. 0403, the definition of the foaming rate is the volume of the bubbles contained in the rubber with respect to the volume of the rubber containing the bubbles, expressed as a percentage.

[0007]

In the present invention, the relationship between the block rigidity value calculated by experiments in advance, the root of the block and the local stress generation condition at the bottom of the sipe provided inside the block, the block rigidity value, and the snow / frozen road surface The block rigidity was optimized by obtaining the relationship of the friction coefficient above. That is, from the result of this experiment, the block rigidity obtained by the equation (1) is 4.
When it is 8 or less, the deformation of the block during tire running becomes large, and the local stress at the root of the block and the bottom of the sipe exceeds the separately defined allowable limit. On the other hand, when the block rigidity becomes 7.0 or more, the friction required in the shallow snow region Since the coefficient of friction decreased below the coefficient and it became unsuitable for running on snow and ice, each dimension of the block was set so that the block rigidity was between 4.8 and 7, so the durability of the block The road performance on ice and snow is optimally balanced. Further, since the sipe having an enlarged bottom portion extending substantially in the width direction of the tire is provided in the block, the edge component on the surface of the block is increased, and the running performance on the snowy and snowy road surface is further improved. Further, since the enlarged portion formed at the bottom of the sipe relieves the stress concentration on the bottom portion due to the external force received by the tire tread surface while the tire is running, it is combined with the optimization of the shear rigidity by adjusting the dimension of each block. The block durability is greatly improved.

Further, when the foamed rubber is used in the tire tread portion in the range of the foaming ratio of 1 to 10% as described in claim 2, the foamed rubber which has been put into practical use has excellent ice and snow performance. It can be added to the effect of item 1. still,
If the foaming rate is 1% or less, the effect as foamed rubber is not obtained and 10
%, The wear resistance of the tire tends to decrease, so in the present invention, the range is adequately set in consideration of the optimization of block rigidity and the conditions of use in the shallow snow region.

Further, in the present invention, since the number of wide main grooves extending in the circumferential direction is increased to three, even when each groove in the tire pattern becomes shallow at the end of the wear of the tire, it is wet. Good drainage on the road surface and prevent slip resistance from decreasing.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a heavy load radial tire 11R equipped with a tire pattern according to an embodiment of the present invention.
22.5 and 14PR will be described. In this embodiment,
The rubber of the tire tread has a foaming ratio of 7%, which is described in the above-mentioned Japanese Patent Laid-Open No.
3-90402 and JP JP 63-90403
A foam rubber is used based on the description in the publication . In FIG. 1, a straight main groove 2 on the tire equatorial plane SS of the tire tread portion 1 and main grooves 3 and 3 which are symmetric with respect to the equatorial plane and are swayed in a zigzag pattern to the left and right. 3 main grooves 20m deep
It is arranged so as to extend in the circumferential direction of the tire at m. Further, on the left and right of the equatorial plane of the tire, circumferential grooves 4 and 4 which are sandwiched between the main groove 2 and the main groove 3 and which are narrower than the main groove and have a similar shape to the main grooves 3 and 3 are arranged. There is. Further, extremely narrow circumferential grooves 5, 5 are arranged at both ends of the tire tread portion 1. Open in each of these circumferential grooves and have a depth of approximately 14
A plurality of mm sub-grooves 6 are arranged left and right along the circumferential direction of the main groove facing the tire width direction. When the grooves are arranged on the tire tread portion 1 in this manner, the blocks 7 partitioned by these grooves are arranged on the entire surface of the tire tread portion 1. In each of these blocks, a single sipe 8 extending in the width direction and having an enlarged bottom is provided with a groove width of 0.6 on the tire tread surface.
mm, and a groove width of 2.4 mm at the groove bottom is provided in the center of the block. A pair of large blocks 11 and 11 are provided from the buttress portion 9 of the tire to the end of the tire tread portion 1 with a dividing groove 10 in the tire width direction interposed therebetween. Spaces 12 are provided on both sides of the large block in the circumferential direction so as to be used for chain hanging or the like.
Further, the dimension of each part shown in FIG. 2 of the block 7 having the above-mentioned bottom enlarged sipe is such that the circumferential length I = 17.2 mm, the width direction b = 21.4 mm, and the sipe The depth of 8 is h = 11.0 mm. Therefore, when the shear rigidity G of the block is calculated from these numerical values, it is 5.6.
Is within the above setting range. Also, because the dimensions of each block are set in this way, when the tire is loaded with the JIS standard internal pressure and load,
Since there are about 5.4 blocks in each block row, a sufficient edge effect can be obtained.

Next, in order to verify the improvement of the tire performance of the tire of the above-mentioned example, a comparative test with the comparative example tire shown in FIG. 3 was conducted. The tires of the comparative examples have the same tire size as the tires of the examples, but the conventional tread rubber is used for the rubber of the tire tread, and the two main grooves 3 and 20 having a depth of 20 mm and substantially the tire are used. The sub-groove 6 has a depth of 14 mm, which faces the width direction, and a block in which a single sipe with a width of 0.6 mm is cut into the center of the groove in a lightning pattern. Further, the dimension of the block sandwiched between the main groove 3 and the block row in the center of the tire tread is such that the circumferential length I = 11 m at the shortest circumferential distance from the sipe end to the block end.
m, length in the width direction b = 23 mm, depth of sipe 8 h = 1
The block rigidity G is 3.2, which is 1 mm.

First, a durability test of a tire tread block by running an actual vehicle was carried out. The test conditions were such that the tires of Examples and Comparative Examples were mounted on the inside and outside of the left and right of the drive shaft of a 10-ton rear wheel biaxial truck, and the tires were loaded with JIS standard internal pressure and load at a cruise speed of 80 km / h. After traveling 40,000 km on a general dry pavement, the presence of crack damage at the root of the tire tread block and the sipe groove bottom was checked. As a result, in the comparative tires, minute cracks having a length of about 5 mm were scattered at the bottom of the sipe groove, but there was no abnormality in the blocks and sipes of the tires of the examples.

Next, an actual vehicle brake test on an ice and snow road was carried out. The results are shown in Fig. 4. The test conditions and test method are as follows: tire internal pressure 7.0 kg / cm ² , load J per tire J
The same tires were attached to all wheels of a 10-ton truck at 100% of IS standard load, and on the ice-burning road surface with an ice temperature of -5 degrees, at a speed of 20 km / h, the Full Lock Bra.
It measures the distance until the car stops by taking ke. As can be seen from the figure, the example tires obtained about 5% good results.

An actual vehicle running test was carried out on a wet road surface in which the residual groove of the main groove was set to 5 mm and the water depth was adjusted to a predetermined depth by watering (test results are omitted). It was confirmed to be excellent. Furthermore, the tires of Examples and Comparative Examples were mounted on the left and right front wheels of a 10-ton truck, and each tire was loaded with a JIS standard internal pressure and a regular load, and each block of the tire tread after running 10,000 km Heel & toe uneven wear (difference in the amount of wear at the other end relative to one end of the block) was checked. As a result, it was confirmed that the tires of Examples had a small amount of uneven wear of about 35%.

[0015]

According to the present invention, the sipe having the wide bottom portion provided in the block and the block rigidity selected in the optimum range greatly improve the durability of the block on the tire tread portion and the block. It prevents uneven wear and improves the running performance on ice and snow roads. Again,
By increasing the number of wide main grooves that are advantageous for drainage, the effect of slip prevention at the end of wear is added, and tire durability,
It is possible to obtain a heavy-duty pneumatic studless tire for shallow snow regions in which wear performance, wet road running performance, ice and snow running performance, etc. are highly balanced.

[Brief description of drawings]

FIG. 1 is a development view of a tire tread pattern according to an embodiment of the present invention.

FIG. 2 is a diagram showing the size of each part of the block pattern according to the embodiment of the present invention.

FIG. 3 is a development view of a conventional pattern of a comparative example.

FIG. 4 is a diagram showing the results of an actual vehicle brake test on ice and snow roads.

[Explanation of symbols]

1 tire tread 2 Main groove in the center of the tire tread 3, 3 Main groove on the tire tread side 4, 4 narrow circumferential grooves 5, 5 Very narrow circumferential groove 6 Secondary groove 7 blocks 8 sipes 9 Buttress Department 10 division grooves 11, 11 large block 12 spaces

Continuation of the front page (56) Reference JP-A-7-237408 (JP, A) JP-A-4-85111 (JP, A) JP-A-7-172112 (JP, A) JP-A-5-147411 (JP , A) JP 5-131812 (JP, A) JP 4-176707 (JP, A) JP 63-90402 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB) (Name) B60C 11 / 00,11 / 04 B60C 11/11-11/12

Claims (2)

(57) [Claims] 1. A groove depth having three or more main grooves continuously extending in the tire circumferential direction, and having a groove depth equal to or less than a plurality of circumferential grooves including the main grooves and a main groove extending in the tire width direction. A plurality of blocks separated by a plurality of sub-grooves are arranged in the tire circumferential direction, and a sipe that extends in the tire width direction at a groove depth equal to or less than the sub-grooves and has an enlarged bottom is provided in the block. At least one, and all divided between the circumferential grooves
When the circumferential length of the block of the block of Fig. 3 is I, the width is b, and the depth of the sipe is h, the relationship between these numerical values satisfies the following equation: A heavy duty pneumatic studless tire equipped with a surface pattern. 4.8 <0.72 × b × (I ³ / h ³ ) × (1 / [1 + 15.6 × (I ² / 4h ² )]) <7 2. The heavy duty pneumatic studless tire according to claim 1, wherein the tread rubber material of the portion forming the tire tread pattern is a foamed rubber having a foaming rate of 1 to 10%.