JP2000025420A - Pneumatic radial tire for small-sized truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the operating performance on icy road in both areas, i.e. in a low load area and in a high load area while the good braking ability on the dry road surface is maintained. SOLUTION: When the ground contact width-area X of a tread face 1 is quartered respectively on the right and on the left of a tire-center line CL to provide a first area X1, a second area X2, a third area X4 respectively on the right and left of the tire-center line CL side, the ratio of the total extension length of sipes 5 arranged in the first areas X1, X1 and the third areas X3, X3 on the right and left to the total extension length of the whole sipe 5 is increased up to 30 to 45% without changing the total extension length of the whole sipe 5. Further, zigzag main grooves 2B are respectively arranged in the second areas X2, X2 on the right and left.

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 a small truck, and more particularly, to improving performance on ice while maintaining good braking performance on a dry road surface in a low load range and a high load range. The present invention relates to a pneumatic radial tire for a small truck particularly suitable for icy and snowy roads.

[0002]

2. Description of the Related Art In general, a pneumatic radial tire for a small truck used on an icy road has a main groove 12 extending in a tire circumferential direction T and a lateral groove 13 extending in a tire width direction on a tread surface 11, as shown in FIG. And the main grooves 1
A large number of blocks 14 are defined by the grooves 2 and the lateral grooves 13. A plurality of sipes 15 extending in the tire width direction are provided on the ground contact surface 14a of each block 14, respectively. The main groove and the lateral groove secure the groove area to exhibit high on-snow performance, while ensuring the on-ice performance by the edge effect of blocks and sipes.

In recent years, a mirror burn phenomenon in which a frozen road surface in a cold region freezes like a mirror surface and becomes slippery often occurs. Further improvements in performance were required. However,
The pneumatic radial tires for small trucks use a very wide range of loads, and the load range is three times or more the load when the load is full and the fixed load when the load is full. Therefore, it is necessary to deal with both the low load region and the high load region.

Conventionally, as a method of increasing the total length of the sipe, it has been generally practiced to increase the total length of the sipe. However, there is a limit to this. Accordingly, there is a problem that braking performance on dry road surfaces is deteriorated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the performance on ice without impairing the braking performance on a dry road surface in both a low load range and a high load range. An object of the present invention is to provide a suitable pneumatic radial tire for a small truck.

[0006]

In order to achieve the above object, the present invention provides a plurality of main grooves extending in a tire circumferential direction on a tread surface, and lateral grooves extending in a tire width direction are arranged at a predetermined pitch in a tire circumferential direction. In the pneumatic radial tire for a small truck, a large number of blocks defined by the main grooves and the lateral grooves are formed, and a sipe extending in the tire width direction is provided on a ground contact surface of the blocks with a predetermined total extension length. In the state where the total extension length of the sipe is the same and the tread width area of the tread surface is developed, the tread width area is divided into four equal parts on the left and right sides of the tire center line, respectively.
The first area on each side from the tire center line side,
When the second region, the third region, and the fourth region are set, the ratio of the total extension length of the sipe arranged in the first region on the left and right and the third region is set to 30 to 45%, and the second region on the left and right is formed. A zigzag main groove is arranged.

As described above, while the sipes are concentrated in the first and third regions and the zigzag main grooves are provided in the second region, the contact pressure of the tread surface which contacts the ground under a low load and a high load is provided. Therefore, the edge effect of the sipe and the block in the region where the road surface becomes high can be enhanced, so that in both the low load region and the high load region, braking / driving performance on a frozen road surface can be increased, and performance on ice can be improved. Also,
As a result of maintaining the same total extension length of the entire sipe and only changing the distribution ratio, the rigidity of the entire block does not change, so that good braking performance can be obtained on a dry road surface.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be specifically described below with reference to the embodiment shown in the drawings. FIG. 1 shows an example of a main part of a tread surface of a pneumatic radial tire for a small truck according to the present invention. In the tread surface 1, a plurality (three in the figure) of main grooves 2 extending along the tire circumferential direction T are provided. Is provided. A main groove 2A extending straight is arranged on the tire center line CL, and main grooves 2B extending zigzag are arranged on both sides thereof. The zigzag lateral grooves 3 extending in the tire width direction are arranged at a predetermined pitch in the tire circumferential direction, and a large number of blocks 4 are defined by the main grooves 2 and the lateral grooves 3. A plurality of sipes 5 extending in the tire width direction are provided on the ground contact surface 4 a of each block 4. The total extension length of the entire sipe 5 is in a predetermined range that does not impair braking performance on a dry road surface.

In the state of FIG. 1 in which the contact width area X located between the tire contact ends E of the tread surface 1 is developed, the contact width area X is divided into four equal parts on the left and right sides of the tire center line CL, respectively. When the first area X1, the second area X2, the third area X3, and the fourth area X4 are respectively located left and right from the CL side, the first areas X1, X1 on the left and right and the third area
The ratio of the total extension length of the sipe 5 arranged in the regions X3 and X3 is 30 to 45% of the total extension length of the entire sipe, respectively.
Is in the range. The main groove 2 extending in a zigzag shape
B are arranged in the left and right second regions X2 and X2, respectively.

According to the present inventors, as a result of intensive studies on the contact state of the radial tire for small trucks in the low load range and the high load range, the following was found. That is,
In the low load range, the entire contact width area X does not contact the road surface, and the tire contact shape becomes an elliptical shape smaller than the contact width area X as shown in FIG. It was found that the region having a high value was the region surrounded by the solid line Y, that is, the first to third regions X1, X2, and X3. On the other hand, in the high load region, as shown in FIG. 3, a square shape close to a quadrangle is formed, and a region where the contact pressure is high in the contact region is a region surrounded by a solid line Z, that is, the second and third regions X2 , X3. 2 and 3, the same components as those in FIG. 1 are given the same numbers.

Therefore, in a conventional tire having a block pattern used for icy and snowy roads as shown in FIG.
When examining the distribution ratio of sipes, the fourth on the shoulder side
It was found that the total extension length of the sipe in the region X4 was the longest, followed by the first and third regions X1 and X3, and the total extension length of the sipe in the second region X2 was the shortest.

From the above findings, in the present invention, the region X where the contact pressure is high is maintained without changing the total length of the entire sipe 5.
In the second region X2, a zigzag main groove 2B is arranged to block the sipe edge length by increasing the total sipe extension length of the sipe 1 and X3 as in the above-described range. 4 is ensured.

The first and third regions X having a high ground pressure as described above
While the sipe 5 is concentratedly arranged at 1 and X3 to exert a higher sipe edge effect than in the related art, the second region X2 can exert the edge effect of the block 4 partitioned by the zigzag main groove 2B. Therefore, in both the low load region and the high load region, braking / driving performance on a frozen road surface can be improved, and performance on ice can be improved. Moreover,
Since only the distribution ratio is changed without changing the total extension length of the entire sipe 5 and the rigidity of the entire block is not changed, it is possible to suppress a decrease in braking performance on a dry road surface.

If the ratio of the total extension length of the sipe 5 disposed in the first and second regions X1, X1 and the third regions X3, X3 is smaller than 30% of the total extension length of the entire sipe,
It is difficult to improve the performance on ice. Conversely, if it exceeds 45%, a problem of uneven wear occurs in the blocks 4 in the first and third regions X1 and X2. In the present invention, the left and right first regions X
1, X1 is provided with the same amount of sipe as shown in FIG. 1 (for example, if the sipe is provided in the first region on the left and right so that the total extension length is 40%, the sipe is provided on the left and right respectively. 20%) is preferable, but it may be asymmetric as long as uneven wear of the block allows. The same applies to sipes provided in the left and right third regions X3 and X3.

The left and right second regions X2 and X2 and the fourth region X
The ratio of the total extension length of the sipe 5 arranged at 4, X4 can be in the range of 5 to 20% of the total extension length of the entire sipe. These second and fourth regions X2, X
In the case where the sipes 5 are provided on the 4th, the ratio of the left and right
The same can be done as in the case of the third regions X1 and X3.
In the present invention, the above-mentioned ground width region X is defined as JAT
In a radial tire for a small truck described in MA YEAR BOOK (1998), this is a ground contact area of a tread surface which is in contact with a road surface when an air pressure corresponding to a maximum load capacity is filled and the maximum load is applied.

[0016]

EXAMPLE A tire of the present invention having a tread pattern shown in FIG. 1 and a conventional tire having a tread pattern shown in FIG. In each test tire, the ratio of the total length of the sipe in the first to fourth regions is as shown in Table 1.

Each of these test tires was rim size 14 × 5
Mounted on a 1 / 2JJ rim, mounted on a light van type vehicle with an air pressure of 450 kPa, and when the loading weight of the vehicle is 150 kgf and 750 kgf, the performance on ice and the braking performance on dry roads are measured according to the following measurement conditions. When an evaluation test was performed, the results shown in Table 1 were obtained.

On-ice performance On an icy road test course at an ice temperature of -5 ° C. to -8 ° C. and an air temperature of -3 ° C. to -5 ° C., the brake was applied at a speed of 40 km / h, and the braking distance until the vehicle stopped was measured. The result was evaluated by an index value with the conventional tire being 100. The larger the value, the better the performance on ice.

Dry road braking performance A brake was applied at a speed of 60 km / h on our test course dry road, and the braking distance until the vehicle stopped was measured. The result was evaluated by an index value with the conventional tire being 100. The larger the value, the better the dry road braking performance.

[0020]

[Table 1]

As shown in Table 1, the tire of the present invention has a loaded weight of 1
In a low load area of 50 kgf and a high load area of 750 kgf, while maintaining good dry road braking performance,
It turns out that the performance on ice can be improved.

[0022]

As described above, in the pneumatic radial tire for a small truck according to the present invention, the contact width region of the tread surface is divided into four equal parts on the left and right sides of the tire center line, respectively, and the first tires are respectively left and right from the tire center line side. Territory, second
When the region, the third region, and the fourth region are set, the ratio of the total extension length of the sipes arranged in the first region on the left and right and the third region is set to 30 to 45%, respectively, and the second region on the left and right is zigzag. Since the main groove is arranged, the performance on ice can be improved in both the low load region and the high load region without impairing the braking performance on a dry road surface.

[Brief description of the drawings]

FIG. 1 is a development view of a main portion of a tread surface showing an example of a pneumatic radial tire for a small truck of the present invention.

FIG. 2 is an explanatory diagram showing a ground contact state of a tread surface under a low load.

FIG. 3 is an explanatory diagram showing a ground contact state of a tread surface under a high load.

FIG. 4 is a development view of a main portion of a tread surface showing a conventional pneumatic radial tire for a small truck.

[Explanation of symbols]

1 Tread surface 2, 2A, 2B
Main groove 3 Lateral groove 4 Block 4a Contact surface 5 Sipe CL Tire center line E Tire contact end T Tire circumferential direction X Contact width region X1 First region X2 Second region X3 Third region X4 Fourth region

Claims (3)

[Claims] 1. A plurality of main grooves extending in a tire circumferential direction are 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 large number of divided by the main grooves and the lateral grooves. In a pneumatic radial tire for a small truck having blocks formed and a predetermined total extension length of a sipe extending in the tire width direction on the ground contact surface of those blocks, the sipe has the same total extension length, and the tread surface In the state where the contact width area is expanded, the contact width area is divided into four equal parts on the left and right sides of the tire center line, and the first area, the second area, the third area, and the fourth area are respectively provided on the left and right sides from the tire center line side. In this case, the ratio of the total length of the sipes arranged in the first and third regions on the left and right is set to 30 to 45%, respectively, and the zigzag main regions are formed in the second regions on the left and right. Pneumatic radial tire for small trucks arranged respectively. 2. The pneumatic radial tire for a small truck according to claim 1, wherein a main groove is arranged on the tire center line. 3. The pneumatic radial tire for a small truck according to claim 1, wherein the lateral groove extends in a zigzag shape.