JPH07172111A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire for heavy load, a studless tire for heavy load in particular having excellent crack resistance while maintaining excellent on-ice performance over a long period. CONSTITUTION:In a pneumatic tire for heavy load having divided into a plurality of blocks 16a, 16b by a plurality of main grooves and a plurality of lateral grooves 14 and formed sipes 20 in the blocks 16a and 16b, an enlarged portion 22 formed at a bottom portion of the sipe 20 is positioned at lower part than a bottom of the lateral groove.

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 tire, and more particularly to a studless tire.

[0002]

2. Description of the Related Art Conventional studless tires have a block pattern in which a plurality of blocks are arranged on the tread surface, and the area of the groove is reduced to increase the ground contact area, thereby increasing the friction coefficient and improving the performance on ice. Is improving. In addition, sipe extending mainly in the tire width direction is arranged in each block to improve the on-ice performance by the edge effect.

In recent years, studless tires tend to be mainly used for ice and snow road surfaces in the winter from the early to middle stages of wear (the middle of the service life due to wear), and after the middle stage of wear, mainly for normal road surfaces. In addition, there are increasing opportunities to drive on normal roads from the beginning of wear. Therefore,
From the beginning of wear to the end of wear, ensuring good drainage has become important for safety.

Here, if the number of main grooves is increased in order to improve drainage, the width of the block becomes shorter, so that the block rigidity is lowered, and particularly in a heavy load tire, the block is deformed when kicking out. Grows larger. As a result, the strain at the sipe bottom increases, and eventually a sipe bottom crack is generated, which progresses and leads to block chipping. In order to secure the durability of the block, it is performed to provide an enlarged portion at the bottom of the sipe, and it is said that it is better to have a shallow sipe depth. For example,
It was set to about 50% to 75% with respect to the lateral groove.

[0005]

As described above, in the case where the sipes are shallow, the performance on ice cannot be maintained until the middle of the service life of the studless tire, and the depth of the sipes can be reduced. It was found that the sipe becomes more distorted and the uneven wear of the block becomes more severe as it approaches the above range. It is an object of the present invention to provide a heavy duty pneumatic tire, particularly a heavy duty studless tire, which has excellent on-ice performance over a long period of time and is excellent in crack resistance and abrasion resistance.

[0006]

In order to achieve this object, the present invention provides a pneumatic tire in which a large number of blocks are divided by a plurality of main grooves and a plurality of lateral grooves, and the sipes are formed in the blocks. It is characterized in that the enlarged portion formed in is located at a position lower than the groove bottom of the lateral groove. At this time, assuming that the depth of the main groove is a, the depth of the lateral groove is H, and the depth of the enlarged portion is h, a / 2 <H <a and 1.1 × H
It is particularly preferable that <h <1.5 × H is satisfied.

Further, there is a relationship between the radius of curvature of the bottom of the sipe and the radius of curvature of the bottom of the lateral groove, and the radius of curvature R of the enlarged portion is 0.5 mm or more and 3 mm or less, and the radius of curvature r of the bottom of the lateral groove is It has been found that it is preferable to set it to 1.2 mm or more and 5 mm or less.

[0008]

The inventor's study has revealed that the strain at the bottom of the sipe has a great relation with the depth of the lateral groove, and that the strain decreases as the sipe is formed deeper than the lateral groove. FIG. 4 shows the relationship between the expanded portion depth h and the depth of cracks from the sipe generated during traveling when the lateral groove depth H is constant.
An index is displayed with h / H = 0.75 (conventional) as 100. In a region where the expanded portion depth h is smaller than the lateral groove depth H,
The crack depth becomes worse as the expanded portion depth h becomes deeper, but when the expanded portion depth h becomes deeper than the lateral groove depth H, the crack changes in the direction of improvement. Therefore, it is possible to increase the depth h of the enlarged portion so that the performance on ice due to the edge effect can be exerted for a long time, and the deterioration of cracks can be suppressed.

Further, the expanded portion depth h is 1.1 × H <h <
By setting it within the range of 1.5 × H, the depth of cracks can be improved more than when h / H = 0.75, and the performance on ice due to the edge effect can be exerted for a long time. If h / H exceeds 1.5, no further improvement in cracking can be expected, while it is unnecessarily deep with respect to the life of the studless tire (at the time when the lateral grooves disappear), and the block rigidity decreases. This is not preferable because uneven wear occurs in the block. Here, when the depth changes in the extending direction in the same sipe or lateral groove, the average value is taken.

On the other hand, the lateral groove depth H is preferably smaller than the same and larger than 1/2 with respect to the main groove depth a, and 1 /
If it is 2 or less, the lateral groove disappears early and the performance as a studless tire cannot be exhibited. On the other hand, if it is equal or more, the rigidity of the block decreases, the movement of the block becomes large, and a crack from the sipe occurs. Easier to do.

Further, by setting the radius of curvature R of the enlarged portion to 0.5 mm or more and 3 mm or less and the radius of curvature r of the bottom portion of the lateral groove to 1.2 mm or more and less than 5 mm, it is possible to further prevent the sipe bottom crack. The radius of curvature R of the enlarged portion is less than 0.5 mm, and the radius of curvature r of the bottom portion of the lateral groove is 1.2 mm.
If it is less than 100%, stress concentrates on the bottom of the sipe, and cracks are likely to occur. If the radius of curvature R of the enlarged portion exceeds 3 mm, the blade is unlikely to come off and is easily damaged after vulcanization, and the movement of the block becomes large, resulting in poor maneuverability. If the radius of curvature r of the bottom of the lateral groove exceeds 5 mm, the groove width becomes large and the ground contact area decreases.

[0012]

Embodiments of the present invention will be described with reference to FIGS.

FIG. 1 shows a tread pattern 10 of a tire 1 to which the present invention is applied. 4 for tire 1 tread
The main grooves 12a and 12b of the book are formed, and a plurality of lateral grooves 14 are formed to partition a large number of blocks 16. Here, it is desirable that at least four main grooves be formed in consideration of drainage on a wet road surface.
As a result, it has an excellent effect of suppressing skidding on the ice and snow road surface. In order to secure the rigidity of the block 16 in the lateral direction, 5 or less is desirable. The width w1 of the main groove 14 is 6
.About.13 mm and the depth d1 is required to be in the range of 15 to 24 mm in order to secure drainage and block rigidity.

Further, in order to secure drainage, it is preferable that the main groove is in a straight shape or a straight shape.
When the groove has a slight amplitude, it is preferable that there is a portion that is connected in a straight line when the groove is viewed in the circumferential direction (the portions where the blocks do not overlap on both sides when the groove cross section is viewed in the circumferential direction).

At the center of the block 16 in the tire circumferential direction,
A pair of parallel sipes 20 are formed that extend linearly in the tire width direction. Here, the sipes preferably have a width of 1.2 mm or less, and are 0.5 mm in this embodiment.

These sipes reach the side wall on the tire width direction side of the block, and the block has these sipes 2
It is divided into three regions by 0 in the tire circumferential direction. The area sandwiched between the pair of sipes is the narrow area 16
A region which is adjacent to both sides in the tire circumferential direction through the sipe 20 of the narrow region 16a is a wide region 16b. The ratio TS / TL of the width TS of the narrow region 16a and the width TL of the wide region 16b is 0.1 to 0.8, preferably 0.2 to 0.5. In this embodiment, the narrow region 16a has a width TS of 3 mm and the wide region 16b has a width TL.
Is 13 mm and the ratio TS / TL is 0.23.

Therefore, the rigidity of the narrow region 16a is smaller than the rigidity of the wide regions 16b on both sides. For this reason,
The narrow region 16a having low rigidity is deformed by the frictional force from the road surface due to traveling, and the edge is pressed against the ice surface, so that the ice surface is slightly scraped off. Then, the wide area 16b having high rigidity is placed on the freshly appearing fresh ice surface to increase the friction coefficient.

FIG. 2 shows a sectional view of the block as seen from the tire width direction. An enlarged portion 22 is formed at the bottom of the sipe 20, and the enlarged portion 22 is located lower than the lateral groove bottom position. In this embodiment, the lateral groove depth H is 15 mm,
The expanded portion depth h is 18 mm, and h / H is 1.2. The depth a of the main groove is 20 mm, and H / a = 0.75.
Is. The radius of curvature R of the enlarged portion is 0.8 mm, and the radius of curvature r of the bottom portion of the lateral groove is 2.8 mm.

Here, the two sipes 20 forming a pair
The enlarged portions 22 of the two have a shape that enlarges in the opposite directions to each other.
When the distance is too narrow, it is possible to prevent the narrow region from being chipped when the blade comes out after vulcanization.

In this embodiment, the sipe 20 is a pair of parallel sipes 20 extending linearly in the tire width direction. However, as shown in FIG. 3, only one sipe is provided in the block. Although a plurality of sipes may be provided, the distance from the circumferential end of the block to the sipes is preferably at least 10 mm on average. The sipe is not limited to a linear shape, but may be a zigzag shape, a wavy shape, or the like.

(Test Example) Table 1 shows the results of comparison tests of crack resistance, block uneven wear, and on-ice performance at 40% wear for the invention tires 1 and 2 and the comparative tires 1 and 2. Shimesu. Invention tire 1 is the tire of the embodiment shown in FIGS. 1 and 2 (h / H = 1.2), and invention tire 2 is the invention tire 1 with h / H =
1.05, the comparative tire 1 has h / H = 1.6 in the invention tire 1, and the comparative tire 2 has the sipe depth h in the invention tire 1 of 0.
Is 75

With respect to crack resistance, a normal internal pressure was filled and the tire was mounted on the rear wheel of a 10-ton truck, and under a specified load of 120%, an average speed of 120 km / h and an average speed of 20,000 k.
After running for m, the depth of the crack generated from the sipe was measured, and the block uneven wear was measured by the step amount (mm) of the block. Also, the performance on ice is that the normal internal pressure is applied to all wheels of a 10-ton truck and the ice temperature is
A sudden break was applied while running at 5 ° C and 20 km / h, and the distance from the position to the stop position was measured. Comparison tire 2
The result was set to 100, and the smaller the value, the better.

[0023]

[Table 1]

From the results shown in Table 1, the heavy-duty pneumatic tire of the present invention was found to have 4
It was clarified that not only the performance on ice at 0% wear but also the crack resistance was improved.

[0025]

Since the heavy duty pneumatic tire of the present invention has the above construction, it has the effects of maintaining excellent on-ice performance for a long period of time and being excellent in crack resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a tread pattern of a heavy duty pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a view of a block of a heavy duty pneumatic tire according to an embodiment of the present invention, as viewed from the tire width direction.

FIG. 3 is a view of a block of a heavy duty pneumatic tire according to another embodiment of the present invention, as seen from the tire width direction.

FIG. 4 is a diagram showing a relationship between an enlarged portion depth h and a crack depth from a sipe.

[Explanation of symbols]

 1 Pneumatic Tire for Heavy Load 10 Tread Pattern 12a, 12b Main Groove 14 Horizontal Groove 16 Block 16a Narrow Area 16b Wide Area 20 Sipe 22 Expanded Part

Claims (3)

[Claims] 1. A heavy-duty pneumatic tire in which a large number of blocks are divided by a plurality of main grooves and a plurality of lateral grooves, and the sipes are formed in the blocks, wherein an enlarged portion formed at the bottom of the sipes is greater than the groove bottom of the lateral grooves. A heavy duty pneumatic tire characterized by being located in a low place. 2. When the depth of the main groove is a, the depth of the lateral groove is H, and the depth of the enlarged portion of the sipe is h, a / 2
<H <a and 1.1 * H <h <1.5 * H are satisfied, The pneumatic tire for heavy loads of Claim 1 characterized by the above-mentioned. 3. The radius of curvature R of the enlarged portion is 0.5 mm or more and 3 mm or less, and the radius of curvature r of the bottom portion of the lateral groove is 1.2 m.
The pneumatic tire for heavy loads according to claim 1, wherein the pneumatic tire has a thickness of not less than m and not more than 5 mm.