JP2002225512A - Pneumatic tire for icy and snowy road - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for icy and snowy roads, capable of improving its performance with block wear on icy road while avoiding deterioration in the ease in its demolding and increase in production cost. SOLUTION: The pneumatic tire for icy and snowy roads has a tread surface 1 provided with main grooves extending in the tire circumferential direction, with lateral grooves 3 extending in the tire width direction placed with a fixed pitch, with blocks 4 demarcated by the main grooves 2 and the lateral grooves 3 and provided with a plurality of sipes 5 extending in the tire width direction and the tilt angle of the sipes 5 to the normal of the tread surface 1 is gradually increased from the surface side toward the bottom side.

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 snowy roads having a block provided with a sipe extending in the width direction of the tire, and more particularly to a pneumatic tire for snowy roads having improved performance on ice when the tire is worn. For entering tires.

[0002]

2. Description of the Related Art In recent years, with the development of studless tires, a so-called Millerburn phenomenon has occurred, in which frozen roads are polished like a mirror and become slippery in urban areas in snowfall areas. Has become. Therefore, there is a strong demand for pneumatic tires used on icy and snowy roads to further enhance braking / driving performance on ice.

Conventionally, pneumatic tires for icy and snowy roads are provided with a number of blocks on a tread surface, and a plurality of sipes extending in the tire width direction are arranged on the blocks. By adopting such a block pattern and sipes, the edge effect in the tire circumferential direction is enhanced to ensure the performance on ice. In addition, even when a large number of sipes are provided in a block, it is general to raise the bottom of a part of the sipe in the length direction in order to secure the rigidity of the block when new.

However, when a part of the sipe is raised, the sipe length decreases as the wear of the block progresses, so that the rigidity of the block greatly increases as compared with a new one, and the performance on ice deteriorates. was there.

In order to prevent an increase in block rigidity due to the progress of wear, the length of the sipe is made longer at the bottom side than at the surface side, or the sipe molding bone is made thicker at the bottom side. Attempts have been made to increase the width of the sipe on the bottom side than on the front side, but in these cases, the tire is removed from the mold or the tires are made as much as it becomes difficult to manufacture the sipe molding bone. However, there is a problem that the manufacturing cost increases.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the performance on ice when a block is worn while avoiding deterioration in ease of removal from a mold and increase in manufacturing cost. An object of the present invention is to provide a pneumatic tire for use.

[0007]

In order to achieve the above object, a pneumatic tire for snowy and icy roads according to the present invention is provided with a main groove extending in a tire circumferential direction on a tread surface and a lateral groove extending in a tire width direction formed on the tire circumferential surface. Arranged at a predetermined pitch in the direction,
In the pneumatic tire for icy and snowy roads, in which a block is defined by the main groove and the lateral groove, and a plurality of sipes extending in the tire width direction are provided in the block, an inclination angle of the sipe with respect to a normal line of the tread surface is set from a surface side. It is characterized by gradually increasing toward the bottom.

As described above, by gradually increasing the inclination angle of the sipe from the surface side to the bottom side, even when the thickness of the sipe molding bone is kept constant, the sipe is formed with the progress of wear. As the opening width increases, the increase in block rigidity is suppressed, and the drainage of water melted by frictional heat is sufficiently ensured. As a result, excellent performance on ice can be exhibited even when the block is worn. .

Further, as the sipe molding bone to be implanted in the mold, it is only necessary to bend a thin plate having a constant thickness from the surface side to the bottom side of the sipe. It is possible to avoid an increase in cost.

In the present invention, it is preferable that the cross section of the sipe is an arc-shaped curve in order to harmonize the progress of wear with the change in the sipe opening width. In particular, when the cross-sectional shape of the sipe is a function formula y =
It is preferable that a part of an n-th order curve drawn in the range of x> 0 in ax ⁿ (where a> 0, n> 1) is formed.
By configuring the cross-sectional shape of the sipe from an nth-order curve,
By optimizing the relationship between the block wear amount and the block rigidity, it becomes possible to maintain the same performance on ice from the time of new product to the life of the wear.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an example of a pneumatic tire for icy and snowy roads according to an embodiment of the present invention. Tread surface 1
Are provided with a plurality of main grooves 2 along the tire circumferential direction T, and lateral grooves 3 extending in the tire width direction are arranged at a predetermined pitch along the tire circumferential direction T.
And a large number of blocks 4 are defined by the lateral grooves 3. Each block 4 has a plurality of sipes 5 extending straight in the tire width direction. These sipes 5 have an opening width of, for example, 2 mm or less when new, and have a depth smaller than that of the main groove 2 and the lateral groove 3.

As shown in FIG. 2, in the sipe 5, the inclination angle with respect to the normal line of the tread surface 1 gradually increases from the surface side to the bottom side. More specifically, as shown in FIG. 3, in the block cross section obtained by cutting the block 4 along the tire circumferential direction T, the inclination angle θ of the sipe 5 with respect to the normal Y of the tread surface 1 is changed from the surface side to the bottom side. gradually increases toward the cross-sectional shape is variable x of the sipe 5, y and arbitrary constants a, x> 0 in the function equation y = ax ⁿ including n
Constitutes a part of the n-th order curve drawn in the range. However, a> 0 and n> 1. Further, the n-th order curve are those drawn by the y-axis of the function expression y = ax ⁿ match the normal Y.

As described above, if the inclination angle θ of the sipe 5 is increased toward the bottom, the opening width of the sipe 5 can be gradually increased as the block 4 wears. For example, as shown in FIG.
Assuming that the opening width at the time of a new article is L, the opening width increases by 1.1 times when the wear progresses to 50% of the sipe depth, and becomes 1.5 when the wear progresses to 85% of the sipe depth. Increase by a factor of two. Therefore, even if the wear progresses, the block rigidity hardly increases from the time of new product. In the pneumatic tire for snowy and snowy roads, the ice on the road surface is constantly melted by frictional heat, but the sipe 5 whose opening width is increased with the progress of wear is excellent in drainage. Therefore, the pneumatic tire for icy and snowy roads can exhibit good on-ice performance even during block wear. However, in order to surely obtain the effect of improving the performance on ice during wear, it is preferable that the difference between the minimum value and the maximum value of the inclination angle θ of the sipe 5 is 20 ° or more.

The sipe 5 can be formed by implanting a thin plate-shaped sipe molding bone having a constant thickness from the surface side to the bottom side on the inner surface of a mold. Such a sipe-formed bone only needs to be die-cut from a flat plate and bend-processed, so that the production cost of the tire does not increase. In addition, since the sipe-formed bone may have a constant thickness, at least the split mold does not deteriorate the ease of removal from the mold. However, it is preferable that the inclination angle θ of the sipe 5 is 45 ° or less in order to improve the ease of removal from the mold.

[0016] In the present invention, it is preferred cross-sectional shape of the sipe is part of the n-th order curve drawn in the range of x> 0 in as described above function expression y = ax ^n, having a single radius of curvature It may be an arc. Further, the sipe may be formed of a plurality of bent straight portions, and the inclination angles of these straight portions may be gradually increased from the surface side to the bottom side.
Even when the sipe cross-sectional shape is an arc or a combination of a plurality of straight portions, the opening width of the sipe increases with the progress of wear, so that the performance on ice during wear can be improved. it can.

[0017]

EXAMPLES The tire size and 185 / 65R14, the pneumatic tire for ice and snow having a block pattern of Figure 1, the function formula sipe sectional shape y = ax ⁿ (a =
1, n = 2, x = 1 to 10) and the tire 1 of the present invention and a sipe cross-sectional shape are represented by a functional expression y = ax ⁿ (a =
タ イ ヤ, n = 3, x = 1 to 10), and a conventional tire having a sipe inclination angle of 90 ° and a conventional tire 2 were set.

Each of these test tires has a rim size of 14 × 5
Attach to 1 / 2J rim, set the air pressure to 200kPa, and
It was mounted on a 00cc vehicle and evaluated for performance on ice when it was new and when the block was worn by 50% (in a state where it was worn to 85% of the sipe depth) under the following measurement conditions. The result was obtained.

On-ice performance: On an icy road test course at an air temperature of 2 ° C. and an ice temperature of 0 ° C., a distance from a speed of 40 km / h to a stop with lock braking was measured. The evaluation results were expressed as indices using the reciprocal of the measured values assuming that the conventional tire was 100 when new. The larger the index value, the better the performance on ice.

[0020]

[Table 1] As is clear from Table 1, each of the tires 1 and 2 of the present invention was able to maintain the same on-ice performance as the new tire when the block was worn.

[0021]

As described above, according to the present invention, in a pneumatic tire for icy and snowy roads in which a plurality of sipes extending in the tire width direction are provided on a block, the inclination angle of the sipe with respect to the normal line of the tread surface is set from the surface side. By gradually increasing toward the bottom, more preferably, the cross-sectional shape of the sipe is an arc-shaped curve, and more preferably, the cross-sectional shape of the sipe forms a part of an nth-order curve, so that the wear of the block progresses. As the opening width of the sipe becomes wider than when new, the increase in block rigidity can be suppressed, and the performance on ice during wear can be improved. There is no increase.

[Brief description of the drawings]

FIG. 1 is a development view showing a tread surface of a pneumatic tire for icy and snowy roads according to an embodiment of the present invention.

FIG. 2 is an enlarged perspective view showing one of the blocks in FIG. 1;

FIG. 3 is an enlarged sectional view of a main part when the block of FIG. 1 is cut along a tire circumferential direction.

FIG. 4 is an explanatory diagram showing a change in opening width of a sipe provided in the block of FIG. 1;

[Description of Signs] 1 Tread surface 2 Main groove 3 Lateral groove 4 Block 5 Sipe T Tire circumferential direction Y Normal line of tread surface θ Sipe inclination angle

Claims (3)

[Claims] A main groove extending in the tire circumferential direction is provided on a tread surface, and lateral grooves extending in a tire width direction are arranged at a predetermined pitch in a tire peripheral direction, and a block is defined by the main grooves and the lateral grooves. In a pneumatic tire for snowy roads provided with a plurality of sipes extending in the tire width direction on a block, air for snowy and snowy roads in which an inclination angle of the sipes with respect to a normal to the tread surface is gradually increased from a surface side to a bottom side. Containing tires. 2. The pneumatic tire for icy and snowy roads according to claim 1, wherein the cross-sectional shape of the sipe is an arc-shaped curve. 3. A cross-sectional shape of the sipe is a function formula y = ax ⁿ (including a variable x, y and arbitrary constants a, n).
2. The pneumatic tire for icy and snowy roads according to claim 1, wherein a part of an nth-order curve drawn in a range of x> 0 in> 0, n> 1).