JP2824680B2 - Pneumatic tires for icy and snowy roads - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic tire for icy and snowy roads (abbreviated as a tire for icy and snowy 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 tyres for icy and snowy roads, which have performance replacing these spiked tires.

As shown in FIG. 4, a conventional studless tire has a plurality of blocks 3 divided by a linear main groove 1 extending in the tire circumferential direction and a sub-groove 2 intersecting the main groove 1. This is a block-like pattern in which the size 4 is formed, and the sipe 4, the sub-groove 2, and the main groove 1 are provided with ice and snow road performance by an edge effect due to radial components. However, these radial component densities (hereinafter referred to as groove edge densities) are generally substantially the same in any region of the tread surface. When trying to improve the performance of ice and snow roads by increasing the groove edge density of the tread surface of such conventional tires for ice and snow roads,
There is a problem that the rigidity of the block is reduced and the exercise performance on a dry road surface is deteriorated.

[Problems to be solved by the invention]

It is an object of the present invention to provide a tire for ice and snow roads in which the movement performance of a studless tire having the above-mentioned block tone pattern on ice and snow roads is improved without impairing the movement performance on dry roads.

[Means for solving the problem]

The tire for icy and snowy roads of the present invention that achieves the object of the present invention has a block pattern in which a block divided by a groove is formed on a tread surface, and the block has a sipe, and is represented by the following formula. In a tire having a snow traction index STI of 190 to 210 as a whole tread surface, the ratio STIs / STIc of the snow traction index STIs of the tread shoulder portion to the snow traction index STIc of the tread center portion is 0.75.
It is characterized in that it is within the range of 0.90.

_{STI = -6.8 + 2202ρ 1 + 672ρ} 2 + 7.6Dg In the above formula, the total groove length projected in the [rho ₁ :( lateral) / (contact width ×
Perimeter) (1 / mm) ρ ₂ : (total kerf length projected in the lateral direction) / (contact width x perimeter) (1 / mm) Dg: Average groove depth (mm).

In the present invention, the snow traction index STI represented by the above equation is an index described in SAE Paper 82345, and is the radial direction (tire width direction) of the length of the groove and the sipe forming the tread pattern.
It is a measure of the performance level on snow calculated by the component and the groove depth. As the STI increases, the kinetic performance of the tire for icy roads, such as drivability and controllability, on icy roads improves.

Further, in the tire of the present invention, the tread center portion refers to a region corresponding to a total width of 2 / 4.W of 1/4 of the tread development width W on the left and right with respect to the tread center line CL. Also, the tread shoulder portion is a width (1 / 4.W) of the tread development width W at each end of the tread, which is 1/4.
Area.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of a tread pattern of an ice road tire according to the present invention. In the figure, the tread pattern includes a plurality of blocks 3 divided by a plurality of main grooves 1 extending in the tire circumferential direction and a plurality of sub-grooves 2 intersecting the main groove 1. In this block 3, a plurality of sipes 4 in the tire width direction are formed. Of these blocks 3, five sipes 4 are formed in two rows of left and right blocks 3 arranged in the tread center part, and three sipes 4 are formed in one row of rows 3 arranged in the left and right tread shoulders. A sipe 4 for each book is formed.

2 and 3 show examples of other tread patterns of the tire of the present invention, respectively. In the example of FIG.
The block in FIG. 1 has a pentagonal shape.
FIG. 3 shows an example in which the number of blocks arranged in the tire circumferential direction is increased to five. In the example of FIG. 3, the second row of blocks arranged from the tread center has a relationship belonging to both the tread center portion and the tread shoulder portion.

The snow traction index STI of the entire tread surface of the tire for ice and snow roads is generally set in the range of 190 to 210, and it is necessary that the tire of the present invention be set in the same range. If the STI exceeds 210, the rigidity of the block is significantly reduced, and the dry performance (dry road running performance) is reduced. On the other hand, if the STI is smaller than 190, the groove edge density becomes insufficient and good ice and snow road performance cannot be exhibited.

In the tire of the present invention, the STI is 190
~ 210, but as shown in Figs.
The groove edge density at the tread center portion is made larger than the groove edge density at the tread shoulder portion, so that the values of STIc and STIs are different.

More specifically, the ratio STIs / STIc is set to 0.75 to 0.90, thereby improving the kinetic performance on ice and snow road surfaces without impairing the dry performance. This ratio STIs / STIc is 0.7
If it is less than 5, the block rigidity of the tread center part is too low, and the initial response of the handle on a dry road surface is deteriorated,
On the other hand, when the ratio STIs / STIc exceeds 0.90, the block rigidity of the tread shoulder decreases, so that the cornering performance on a dry road surface decreases.

In the tire of the present invention, more preferably, the groove area ratio represented by the ratio of the groove area to the total contact area of the tread (contact width × perimeter) is in the range of 30 to 50%. By setting the groove area ratio within the above range, the dry performance and the icy and snowy road performance of the tire of the present invention can be further improved.

〔Example〕

In the tread pattern of FIG. 1, the number of sipes in the tread center portion and the tread shoulder portion was changed, and tires I and II of the present invention and STI, STIc and STIs as shown in the table respectively were prepared. Separately, it has the tread pattern shown in FIG.
Conventional tires with STI, STIc and STIs were made.

All these tires are the same size, 185/70 R
It was set to 13.

For these tires, on the following dry road surface and icy road surface, respectively, steering stability (feeling evaluation),
The climbing performance on snow, braking performance on snow and braking performance on ice were evaluated. The results were as shown in the table and Tables 5 to 7.

Driving stability on dry road (feeling evaluation): Feelings of five test drivers were scored by a 10-point scale, and the average value was shown. Generally, if the score is 7 or more, the steering stability is good.

Steering stability on icy road surface (feeling evaluation): Feelings of five test drivers were scored by a 10-point scale, and the average value was shown. Generally, if the score is 7 or more, the steering stability is good.

Evaluation method of climbing performance on snow: On a snow-covered road where the car was repeatedly braked on a snow-covered road and the road surface was smooth, a 5% (2.9 ゜) slope uphill run was performed, and a 30m section acceleration time was calculated using the zero-start acceleration method. Measured. The reciprocal of the measured value is shown as an index with the measured value of the conventional tire being 100.

Evaluation method of braking performance on snow: The braking distance was measured when the vehicle was braked while traveling at a constant initial speed of 40 km / hr on a compacted snowy road surface. An index with the measured value of the conventional tire being 100 was shown by the reciprocal of the measured value.

Evaluation method of braking performance on ice: The braking distance was measured when the vehicle was braked while traveling on an ice plate at a constant speed of 40 Km / hr. The reciprocal of the measured value is shown as an index with the measured value of the conventional tire being 100.

As can be seen from the above table, the tires I and II of the present invention are superior in both dry performance and on-ice performance to conventional tires. On the other hand, although the on-ice performance of the comparative tire is improved, the dry performance is almost the same as that of the conventional tire.

Further, from FIGS. 5 to 7, the tire according to the present invention is superior to the conventional tires in any of the performance on climbing on snow (FIG. 5), the braking performance on snow (FIG. 6), and the braking performance on ice (FIG. 7). It turns out that it is also excellent.

〔The invention's effect〕

According to the present invention, in a tire for ice and snow roads having a block-like pattern, a snow traction index (STI) in a specific range is provided on the entire tread surface, and a snow traction index (STI) in a tread center portion is provided.
By setting the c) and the snow traction index (STIs) of the tread shoulder to a predetermined ratio STIs / STIc that increases the former, the driving performance on ice and snow roads is greatly improved without impairing the dry performance. be able to.

[Brief description of the drawings]

1 to 3 are plan views each showing an example of a tread pattern of the tire of the present invention, FIG. 4 is a plan view of a tread pattern of a conventional tire, and FIGS. 5 to 7 are tires of the present invention and a comparative tire, respectively. 6 is a graph showing a relationship between a conventional tire and a snow climbing performance index, a snow braking performance index, and an ice braking performance index. 1 ... Main groove, 2 ... Sub groove, 3 ... Block, 4 ... Sipe.

Claims (1)

(57) [Claims] The present invention has a block pattern in which a block is formed on a tread surface by a groove, and a sipe is provided in the block, and a snow traction index STI represented by the following formula is 190 to 210 as a whole tread surface. In the tire, the ratio STIs / STIc of the snow traction index STIs of the tread shoulder portion to the snow traction index STIc of the tread center portion is 0.7.
Pneumatic tires for ice and snow roads in the range of 5 to 0.90. _{STI = -6.8 + 2202ρ 1 + 672ρ} 2 + 7.6Dg In the above formula, the total groove length projected in the [rho ₁ :( lateral) / (contact width ×
Circumferential length) (1 / mm) ρ ₂ : (total sipe length projected in the lateral direction) / (contact width × perimeter) (1 / mm) Dg: Average groove depth (mm).