JP2824675B2 - Pneumatic tires for icy and snowy roads - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire for snowy and snowy roads, which maintains its kinetic performance on snowy roads and improves its kinetic performance on icy roads.

[Conventional technology]

As regulations on spiked tires in recent years have become stricter and the restricted areas have expanded, studless tires have been in the spotlight as ice and snow road tires having performance that can replace these spiked tires.

However, conventional studless tires have a tread pattern that is a block-based pattern with a kerf, and the groove area ratio of the tread pattern is about 40% to 50%, like snow tires (tires for snowy roads). For this reason, it has a performance similar to that of a spike tire on snowy roads, but its performance on ice is insufficient. Therefore, the kinetic performance on snowy roads for which the groove area ratio is to be reduced in order to enhance the kinetic performance on icy roads is reduced.

[Problems to be solved by the invention]

The present invention has been made to enhance the kinetic performance on icy roads of the above-mentioned studless tires, and has a pneumatic snowy and snowy road in which kinetic performance on icy roads is improved without impairing kinetic performance on snowy roads. The purpose is to provide tires.

[Means for solving the problem]

The pneumatic tire for snowy and snowy roads of the present invention has a groove area ratio of the tread pattern of 30% to 40%, a snow traction index (STI) of 180 to 220 represented by the following equation, and 2202 ρg of the following equation. And 672 ρs satisfy the relationship of the following expression.

STI = −6.8 + 2202 ρg + 672 ρs + 7.6 Dg.....

FIG. 1 (a) shows an example of a tread pattern of a pneumatic tire for icy and snowy roads according to the present invention. In FIG. 1 (a), a tread pattern 1 corresponds to a tire circumferential direction m.
It is composed of a plurality of blocks 4 divided by a plurality of main grooves 2 formed in an annular shape at m 'and a plurality of sub-grooves 3 provided in the tire width direction. Each block 4 has two calfs 5 arranged in the tire width direction. l is the tire equator line.

1 (a) to 1 (e) show different examples of the tread pattern of the pneumatic tire for icy and snowy roads of the present invention. In FIG. 1 (b), three kerfs 5 are arranged in the block 4, in FIG. 1 (c), five kerfs 5 are arranged in the block 4, and in FIG. 8
In FIG. 1 (e), 13 kerfs 5 are arranged in the block 4 respectively.

(1) In the present invention, the groove area ratio of the tread pattern 1 is 30% to 40%, and the snow traction index (STI) represented by the above formula is 180 to 220.

Here, the groove area ratio is the ratio of the groove contact surface to the total contact area (contact width × perimeter) of the tread surface. In the present invention, the groove area ratio is set to 30% to 40%. Groove area ratio is
If it is less than 30%, the tire's kinetic performance on snow decreases, and if it is more than 40%, the land portion of the tread surface decreases, and the edge effect of the block decreases to reduce the kinetic performance on ice. For reference, in the conventional pneumatic tire for ice and snow roads, the groove area ratio is 40% to 50%. According to the present invention, the on-ice performance is improved by reducing the groove area ratio as compared with the related art, and the portion on which the on-snow performance is reduced with this is satisfied by satisfying the relationship of the above expression as described later. This was to keep the drop down.

In the present invention, the value of the snow traction index (STI) is set to 180 to 220. Here, the snow traction index (STI) is SAE Paper 82034.
5 is an index indicating the level of performance on snow calculated by the tire cross-sectional direction (tire width direction) component and the groove depth of the groove and kerf length on the surface of the tread pattern described in 5, and as shown in the above equation. It is expressed as follows.

STE = 6.8 + 2202ρg + 672ρs + 7.6Dg ρg: (total groove length projected in the lateral direction) / (contact width × perimeter) (1 / mm) ρs: (total kerf length projected in the lateral direction) / (contact width × Perimeter) (1 / mm) Dg: Average groove depth (mm) As this STI increases, the on-snow performance of the tire improves, but if it is too large, the rigidity decreases and the dry performance (dry road running performance) Decrease. On the other hand, when the STI becomes smaller, good performance on ice and snow cannot be exhibited. Usually, the value of STI is 180 to 220, and therefore, the range is also set in the present invention.

(2) Further, in the present invention, 2202ρg
And 672ρs satisfy the following relationship shown in the above equation.

0.522 ≧ 2202ρg / (2202ρg + 672ρs) ≧ 0.291 Here, if 2202ρg = a and 672ρs = b, the above relationship is expressed as follows.

If the value of 0.522 ≧ a / (a + b) ≧ 0.291 a / (a + b) is larger than 0.522, the total groove length projected in the lateral direction becomes large, and the groove area becomes small as described above. The distance between each other, i.e., the groove width, is reduced, which reduces the snow column shearing force and reduces the performance on snow. On the other hand, a /
If the value of (a + b) is smaller than 0.291, the distance between the kerfs in the block is too small, the rigidity of the block is insufficient, and the edge effect of the kerf on ice is not sufficiently exerted, and the performance on ice is reduced. Resulting in. Therefore,
The value of a / (a + b) is 0.522 to 0.291, preferably 0.50 to 0.2.
By setting the value to 35, it becomes possible to improve the kinetic performance on ice without impairing the kinetic performance on snow as compared with the conventional pneumatic tire for icy and snowy roads.

 Examples will be described below.

Example For the tires A to J shown in Table 1 (conventional tire 1, comparative tires 1 to 4, present tires 1 to 5), the braking performance on ice, the braking performance on snow, and the climbing performance on snow were evaluated by the following methods. did. The results are shown in Table 1 and FIGS.
It is shown in (c).

Evaluation method of braking performance on ice: The vehicle traveled on an ice plate at an initial speed of 40 km / h, and the braking distance when braking was measured.

Evaluation method of braking performance on snow: The vehicle traveled on a snow-covered snow road at an initial speed of 40 km / h, and the braking distance when braking was measured.

Evaluation method of climbing performance on snow: 5% (2.9 °) on a slick snow-covered road surface where the vehicle was repeatedly braked on a snow-covered snow surface to smooth the road surface
Perform a slope uphill test, measure the 30m section uphill acceleration time using the zero start acceleration method, and compare the measured value of the conventional tire 1
The index was set to 100.

As can be seen from Table 1 and FIGS. 2 (a)-(c),
Comparative tires 1, 2, and 4 have poor braking performance on ice, and comparative tire 3 has poor climbing performance on snow. On the other hand, the tires 1 to 5 of the present invention are excellent in all of the braking performance on ice, the braking performance on snow, and the climbing performance on snow. 2 (a) to 2 (c), the value of a / (a + b) is 0.522 to
It turns out that the range of 0.291 is good.

〔The invention's effect〕

As described above, according to the present invention, the groove area ratio of the tread pattern and the snow traction index (ST
I), and furthermore, the relationship between 2202 pg and 672 ρs in the snow traction index (STI) is determined, so that it is possible to improve the kinetic performance on icy roads without impairing the kinetic performance on snowy roads. .

[Brief description of the drawings]

1 (a) to 1 (e) are explanatory views in plan view showing an example of a tread pattern of a pneumatic tire for icy and snowy roads of the present invention, FIG. 2 (a) shows braking performance on ice, and FIG. FIG. 2B is a graph showing the braking performance on snow and FIG. 2C is a graph showing the climbing performance on snow. 1 ... tread pattern, 2 ... main groove, 3 ... sub groove, 4
... block, 5 ... calf.

Claims (1)

(57) [Claims] 1. The groove area ratio of the tread pattern is 30% to 40%.
A pneumatic tire for icy and snowy roads, wherein the snow traction index (STI) represented by the following equation is 180 to 220, and 2202 pg and 672 ρs in the following equation satisfy the relationship of the following equation. STI = -6.8 + 2202 ρg + 672 ρs + 7.6 Dg ………… 0.522 ≧ 2202 ρg / (2202 ρg + 672 ρs) ≧ 0.291 …………