JPH0740711A - Pneumatic radial tire for passenger car - Google Patents

Abstract

PURPOSE:To improve snowy road traveling performance without deteriorating the operating safety on the dry road and the wet road. CONSTITUTION:At least one main groove 2 extended in the tire circumferential direction and a plurality of lug grooves 4 extended in the tire width direction and sipes 5 are provided on a tread surface 1, thereby the directional pattern wherein a plurality of lug grooves 4 and sipes 5 are so arranged as to be spread like a feather in the opposite direction of the tire rotational direction R is formed. And when the ratio of sum of the tread contact ground width W and the radial direction component length of the lug groove 4 to the product of the tire circumferential length L is taken as rhog, and also when the ratio of sum of the tread contact ground width W and the radial direction component length of the sipes 5 to the product of the tire circumferential length L is taken as rhos, the formulas: STI=120 to 140, and STI'/STI=0.6 to 0.85 are both satisfied, in connection with the snow traction index STI (=36.0+2101rhoq+897rhos) and STI' (=36.0+2101rhog).

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 passenger cars having a directional pattern, and more specifically, to improving on-snow performance without deteriorating steering stability on dry and wet road surfaces. The present invention relates to a pneumatic radial tire for a passenger car that is made possible.

[0002]

2. Description of the Related Art Conventionally, as a flat high-performance tire, at least one main groove extending in the tire circumferential direction and a plurality of lug grooves extending in the tire width direction are provided on a tread surface, and the plurality of lug grooves are formed in the tire. Pneumatic radial tires for passenger vehicles having a directional pattern arranged so as to spread in a counter-rotating direction in the form of arrowheads have been put into practical use. Since such a pneumatic radial tire has a direction of rotation and a high block rigidity, it has excellent steering stability on a dry road surface and a wet road surface.

However, since the pneumatic radial tires having improved performance on dry road surfaces and wet road surfaces as described above have low running performance on snow, their performance was insufficient during winter use. On the other hand, a studless tire has a large number of lug grooves and sipes extending in the tire width direction on the tread surface to reduce the block rigidity, so it is excellent in snow performance, but this snow performance and dry road surface and wet It was not possible to achieve both steering stability on the road surface.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire for a passenger vehicle capable of improving on-snow performance without lowering steering stability on dry and wet road surfaces. It is in.

[0005]

[Means for Solving the Problems] To achieve the above object
The pneumatic radial tire for passenger cars of the present invention is
At least one main groove extending in the tire circumferential direction
And a plurality of lug grooves and sipes extending in the tire width direction
Provide these multiple lug grooves and sipes to the tire anti-rotation
Shape a directional pattern that is arranged so as to spread like a feather
And the product of tread contact width and tire circumference
The ratio of the sum of the radial component lengths of the plurality of lug grooves
_gAnd the product of the tread contact width and tire circumference
Note: The ratio of the sum of the radial component lengths of multiple sipes is ρ_sage
When the snow traction index STI (=
36.0 + 2101ρ_g+897 ρ_s) And STI '(= 36.0 + 21
01ρ _g), STI = 120-140, STI '
/STI=0.6 to 0.85 are both satisfied
It is characterized by that.

In this way, a directional pattern is formed in which a plurality of lug grooves and sipes are arranged so as to spread like a quiver in the tire counter-rotational direction, and the ratio ρ _g of the sum of the radial component lengths of the lug grooves and Ratio of sum of radial component lengths of sipe ρ _s
For the snow traction index STI and STI ′ obtained from STI = 120 to 140, STI ′
By satisfying both /STI=0.6 to 0.85, it is possible to improve the snow performance without lowering the steering stability on the dry road surface and the wet road surface.

That is, the snow traction index S
TI (= 36.0 + 2101 ρ _g +897 ρ _s ) shows the amount of lug grooves and sipes existing on the tread surface, and is an index showing the traction force on snow. In the conventional high-performance tire having directionality, the STI is set to about 80, and in the studless tire, the STI is set to about 150 to 180, whereas in the present invention, the STI is set to both to secure the block rigidity to some extent. 120-140 which is an intermediate value of
Set to the range of.

On the other hand, the snow traction index S
TI ′ (= 36.0 + 2101 ρ _g ) is equivalent to STI when sipe is not taken into consideration, and STI ′ / STI is an index showing the ratio of lug groove and sipe. In a conventional high-performance tire having directionality, STI '/ STI is 0.95 to 1.
It is set to about 0, and STI '/ for studless tires
While STI was set to about 0.5, in the present invention, STI '/ STI is set to an intermediate value of 0.
Set in the range of 6 to 0.85.

By setting STI and STI '/ STI as described above, snow performance can be achieved for studless tires without deteriorating the steering stability on dry roads and wet roads required for high performance tires. It is possible to get closer to each other. Therefore, the pneumatic radial tire for passenger cars of the present invention can exhibit excellent running performance on all road surfaces. Especially when the present invention is applied to a high-performance tire having an aspect ratio of 60% or less, which is generally low in snow performance, remarkable operational effects can be obtained.

In the present invention, the lug groove and sipes extending in the tire width direction are defined as those having a width of 1.5 mm or less and those having a width of more than 1.5 mm as lug grooves. Further, the tread ground contact width is the ground contact width when grounding at 80% of the JATMA maximum load under JATMA standard air pressure. Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a tread pattern of a pneumatic radial tire for passenger cars having an aspect ratio of 55% according to an embodiment of the present invention.

In the figure, on a tread surface 1, two main grooves 2 extending in the tire circumferential direction on both sides of the tire equator E, two quasi-main grooves 3 extending in the tire circumferential direction on the outer sides thereof, and a tire width. A plurality of lug grooves 4 and sipes 5 extending in the direction are provided. The lug groove 4 and the sipe 5 are one lug groove 4
And two sipes 5 as a repeating unit are arranged over the entire circumference of the tire. Also, the tire equator E of the lug groove 4
The portion close to is forming the sipe 5. The plurality of lug grooves 4 and the sipes 5 form a directional pattern so as to spread in a direction opposite to the tire rotation direction R in an arrow shape.

In the present invention, the ratio of the sum G of the radial component lengths of the plurality of lug grooves 4 to the product of the tread ground contact width W and the tire circumferential length L is ρ _g [= G / (W × L)]. , Sipe 5 for the product of tread contact width W and tire circumference L
Ρ _s [= S / (W ×
L)], the snow traction index S
TI (= 36.0 + 2101 ρ _g +897 ρ _s ) and STI '(=
36.0 + 2101 ρ _g ) is set so as to satisfy the following expressions (1) and (2).

120 ≦ STI ≦ 140 (1) 0.6 ≦ STI ′ / STI ≦ 0.85 (2) As described above, the plurality of lug grooves 4 and sipes 5 are spread in a direction opposite to the tire rotation in a wing shape. The STI is set in the range of 120 to 140 and the STI '/ STI is set in the range of 0.6 to 0.85 while forming the directional pattern arranged as described above. It is possible to improve the on-snow performance, which is a drawback thereof, without deteriorating the steering stability on a wet road surface.

In the present invention, if the snow traction index STI is less than 120, the amount of the lug groove 4 and the sipe 5 is small, resulting in insufficient snow performance. Since the block rigidity decreases due to the excessive amount of the sipes 5, the steering stability on dry road surfaces decreases. In addition, the ratio ST of the snow traction index STI and the snow traction index STI 'when sipes are not considered
When I '/ STI is less than 0.6, the dependency of the sipe 5 is too high and the drainage property is deteriorated, so that the steering stability on a wet road surface is deteriorated, and conversely, when it exceeds 0.85, the sipe 5 is decreased. Since the dependency ratio of is too low and the traction force becomes insufficient, snow performance cannot be improved.

In the above-mentioned tire, the angles of the lug groove 4 and the sipe 5 with respect to the tire circumferential direction are the angle θ _{1 at the} center of the tread and the angle θ ₂ at the tread contact end.
The relationship of θ ₁ <θ ₂ is preferable, and more preferably, the angle θ ₁ is set in the range of 45 ° to 50 ° and the angle θ ₂ is set in the range of 80 ° to 90 °. It is desirable to change it so that it smoothly increases from the portion to the tread ground contact end. By setting the angles of the lug groove 4 and the sipe 5 as described above, it is possible to improve steering stability on a dry road surface while maintaining excellent drainage performance.

[0016]

EXAMPLE A tire of the present invention having a tire size of 205 / 55R15 and a tread pattern shown in FIG. 1, a conventional tire 1 having a tire size of 205 / 55R15 and a tread pattern shown in FIG. 2, and a tire size of 205 / 55R15 and the conventional tire 2 having the tread pattern shown in FIG. 3 were manufactured. The conventional tire 1 is a high-performance tire having a conventional directional pattern, and the conventional tire 2 is a studless tire.

These tires of the present invention and conventional tires 1 and 2
For each of the tires, the steering stability on dry roads, snow-packed roads and wet roads was evaluated by the following test methods, and the results were evaluated as ρ _g , ρ _s , STI, ST.
It is shown in Table 1 together with I '/ STI. Steering stability on dry road: 2000 test tires
It was mounted on a passenger car of cc, and slalom-driving on asphalt dry road surface, and a feeling test was conducted by 10 test drivers. The evaluation result is shown by a score of 0-10. The larger this score, the more excellent the steering stability on dry road surfaces, and a score of 6 or above was set to a practical level.

Steering stability on a snow-packed road surface: A test tire was mounted on a 2000 cc passenger car, and slalom running was performed on the snow-packed road surface, and a feeling test was conducted by 10 test drivers. However, the traveling speed was set within the range of grip traveling so that evaluation and vehicle control could be sufficiently performed.
The evaluation result is shown by a score of 0-10. The larger this score is, the better the steering stability on a snow-covered road surface is.
The above points were set to the practical level.

Steering stability on wet road surface: A test tire was mounted on a 2000 cc passenger car and the water depth was 3 mm ±
A slalom running was performed on a wet road surface of 0.5 mm, and a feeling test was conducted by 10 test drivers. The evaluation results are shown by an index with the conventional tire 1 being 100. The larger this index value, the better the steering stability on wet road surfaces, and 97 or more was set as a practical level.

[0020] As is clear from Table 1, the tire of the present invention maintains the driving stability on dry road surfaces and wet road surfaces at a practical level or higher as with the conventional tire 1 made of a high performance tire, The steering stability on the snow-covered road surface was excellent, and it exhibited the same snow performance as the conventional tire 2, which is a studless tire.

Next, in the above-mentioned tire of the present invention, ST
I was varied in the range of 80 to 180, and the steering stability on a dry road surface and a compressed snow road surface was evaluated by the same test method as above, and the results are shown in FIG. Further, in the tire of the present invention, STI was kept constant at 130, and STI '/
The STI was varied in the range of 0.4 to 1.0, the steering stability on a wet road surface was evaluated by the same test method as above, and the results are shown in FIG.

As can be seen from FIG. 4, when the STI is less than 120, the steering stability on the snow-covered road surface becomes lower than the practical level, and when it exceeds 140, the steering stability on the dry road surface becomes lower than the practical level. Was there. Further, as can be seen from FIG. 5, when STI '/ STI was less than 0.6 or more than 0.85, the steering stability on a wet road surface was below the practical level.

[0023]

As described above, according to the present invention, the tread surface is provided with at least one main groove extending in the tire circumferential direction and a plurality of lug grooves and sipes extending in the tire width direction. Of the plurality of lug grooves with respect to the product of the tread contact width and the tire circumferential length, as well as forming a directional pattern in which the lug grooves and sipes of the tire are arranged so as to spread in a tire anti-rotational direction in a quivering manner. the ratio of the sum and [rho _g of the ratio of the plurality of radial component length of the sum of the sipe with respect to the product of the tread width and the tire circumferential length being [rho _s, snow traction index STI
(= 36.0 + 2101 ρ _g +897 ρ _s ) and STI '(= 36.0
+ 2101ρ _g ), STI = 120-140, ST
Since I '/ STI = 0.6 to 0.85 are both satisfied, it is possible to improve snow performance without deteriorating the steering stability on dry road surfaces and wet road surfaces required for high-performance tires. You can

[Brief description of drawings]

FIG. 1 is a development view showing a tread pattern of a pneumatic radial tire for passenger cars according to an embodiment of the present invention.

FIG. 2 is a development view showing a tread pattern of a conventional pneumatic radial tire for passenger cars having a directional pattern.

FIG. 3 is a development view showing a tread pattern of a conventional studless tire.

FIG. 4 is a diagram showing a relationship between STI (snow traction index) and steering stability on a dry road surface and a snow-covered road surface.

FIG. 5 is a diagram showing a relationship between STI ′ / STI and steering stability on a wet road surface.

[Explanation of symbols]

 1 Tread surface 2 Main groove 4 Lag groove 5 Sipe

Claims (1)

[Claims] 1. A tread surface is provided with at least one main groove extending in the tire circumferential direction and a plurality of lug grooves and sipes extending in the tire width direction, and the plurality of lug grooves and sipes are provided in a tire counter-rotating direction. Forming a directional pattern arranged so as to spread like an arrow feather, and the ratio of the sum of the radial component lengths of the plurality of lug grooves to the product of the tread ground contact width and the tire circumference is ρ _g , and the tread ground contact When the ratio of the sum of the radial component lengths of the plurality of sipes to the product of the width and the tire circumference is ρ _s , the snow traction index STI (= 36.0 + 2101 ρ _g +897 ρ _s ) and S
For TI '(= 36.0 + 2101 ρ _g ), STI = 120
~ 140, STI '/ STI = 0.6 to 0.85, both of which are pneumatic radial tires for passenger cars.