JPH079816A - Studless tire - Google Patents

Abstract

PURPOSE:To provide a studless tire which improves the running performance on an icy and showy road face by confining the ratio of the thickness between a tread rubber layer and a cap layer to the hardness below freezing point to a certain range by forming two bass layers on the outside in the radial direction of the tire of a belt buried on a tread. CONSTITUTION:The thickness d1 of a tread rubber layer 21 and the thickness d2 of a cap layer 22 materializes 0.15<d2/d1<0.60, and the hardness CAPHs of the rubber of the cap layer 22 and the hardness BASEHs of the rubber of a base layer 23 are within the range of 50<=CAPHs<=60 and 60<=BASEHs<=75 at 0 deg.C, and the rubber hardness of the cap, the rubber hardness of the base layer, and the average rubber hardness of the tread layer 21 being decided by the mixture rate d2/d1 into the tread rubber 21 of the cap layer 22 and calculated by the formula; Av(Hs)={(CAPHs)Xd1/d2}+{(BASEHs)X(1-d1/d2}; is within the range of 52<Av(HS)<63 at 0 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a studless tire which does not require studs on the tread surface and has good running performance on ice and snow roads.

[0002]

2. Description of the Related Art Conventionally, spiked tires in which studs are embedded in a tread have been often used in automobiles running on ice and snow roads. However, spiked tires have the problem that the road surface is scraped by the stud tip when traveling on a road during snow removal, and in recent years there has been a tendency to prohibit the use of spiked tires. Therefore, studless tires that have improved running performance on icy and snowy roads without providing studs on the tread surface are now widely used, and such studless tires are used to improve running performance on icy and snowy roads. A rubber having a soft composition is used for the part, and a large number of sipings are provided on the surface of the block forming the tread pattern.

[0003]

However, in the above-mentioned conventional studless tire, if excessively soft rubber is used for the tread portion or too much siping is provided, not only the running performance on the ice and snow road surface is deteriorated, but also the running performance is deteriorated. It has been empirically known that abrasion resistance and uneven abrasion resistance are reduced. In addition, the number of sipes provided on the tread pattern and the block surface is set empirically by trial and error and has not been theoretically elucidated.For example, for studless tires with different tire sizes, experience with each individual tire The number of tread patterns and sipings that have been clarified must be determined, and it is difficult to determine an appropriate tread pattern and number of sipings that can obtain sufficient block rigidity to ensure running performance on ice and snow roads. It was In particular, recently, with the prohibition of wearing spiked tires, it is necessary to drive on icy and snowy roads that have been polished by running studless tires, or on icy and snowy roads that have become more slippery due to surface melting during the day (so-called mirror burn). Therefore, the improvement of the running performance of studless tires on the snowy and snowy road surface has been further demanded.

An object of the present invention is to provide a studless tire having improved running performance on a snowy and snowy road surface.

[0005]

In order to achieve the above object, the studless tire of the present invention has a tread rubber layer located on the outer side in the tire radial direction of a belt disposed inside the tread, and an outer cap layer. , The inner base layer, 0.15 <d ₂ / d ₁ <0.60 is established between the thickness d ₁ of the tread rubber layer and the thickness d ₂ of the cap layer, and the cap layer rubber hardness CAP Hs And base layer rubber hardness BASE
Hs is 50 ≤ CAP Hs ≤ 60, 60 ≤ BASE Hs ≤ 75 at 0 ° C
The average rubber hardness Av (Hs) of the tread rubber layer
Is the expression Av (Hs) = {(CAP Hs) × d ₁ / d ₂ } + {(BASEHs)
× (1-d ₁ / d ₂ )}, and a tire having a range of 52 <Av (Hs) <63 at 0 ° C., and the sum of the cross-sectional areas of the sipings provided in the blocks in the entire tire In the total siping cross-sectional area m and the approximate volume W of the block, 0.6 <
It has a siping cross-sectional area density per unit volume of the block in the range of m / W <1.2.

[0006]

[Function] When d ₂ / d ₁ ≤0.15, the thickness d of the cap layer
₂ is too small with respect to the thickness d ₁ of the tread rubber layer, and the effect of providing the cap layer is small. Also, d ₂
When / d ₁ ≧ 0.60, the thickness d ₂ of the cap layer is too large with respect to the thickness d ₁ of the tread rubber layer, that is, the thickness of the base layer is too small and the base layer is provided. The effect is small. Average tread rubber layer rubber hardness Av (Hs) ≤ 52
In this case, the rubber of the tread rubber layer is too soft, which not only deteriorates the running performance on the ice and snowy road surface, but also deteriorates the wear resistance and the uneven wear resistance. When Av (Hs) ≧ 63, the rubber of the tread rubber layer is too hard, and the braking performance and acceleration performance on the ice / snow road surface deteriorate. m / W ≦ 0.6
In, there is little siping provided in the block, the increase in the contact area between the block surface and the snow and snow road surface is insufficient, the effect of providing the above-mentioned siping cannot be obtained, and
When m / W ≧ 1.2, there is too much siping, and the rigidity of the block is insufficient, so it is not possible to obtain sufficient running performance on the snow and snow road surface.

[0007]

EXAMPLES Examples will be described with reference to the drawings. In FIG. 1, a studless tire 1 includes an annular tread 2, a pair of sidewalls 3 extending inward in the tire radial direction from both ends of the tread 2, a bead portion 4 formed at an inner end of the sidewall 3, and a bead portion. 4, a bead core 5 embedded in the carcass 4, a carcass 6 extending through the tread 2 and the sidewall 3 and having both ends wound up around the bead core 5, and disposed inside the tread 2 on the outer side in the tire radial direction of the carcass 6. It is provided with an annular belt 7 provided. In the tread 2, a tread rubber layer 21 on the outer side of the belt 7 in the tire radial direction, that is, on the ground contact surface side, a cap layer 22 on the outer side, that is, the ground contact surface side, and a base layer 23 on the inner side, that is, the belt 7 side.

In FIG. 2, the thickness d ₁ of the tread rubber layer 21 which is the distance from the outer surface of the belt 7 to the ground contact surface of the tread ₂ and the thickness d ₂ of the cap layer 22 in the block are 0.15 <d _2. / D ₁ <0.60 holds, and the cap layer rubber hardness of the cap layer 22 is CAP Hs
And the base layer rubber hardness BASEHs of the base layer 23 are in the range of 50 ≦ CAP Hs ≦ 60 60 ≦ BASEHs ≦ 75 at 0 ° C., the cap layer rubber hardness CAP Hs, the base layer rubber hardness BASEHs, and the cap layer It is determined by the mixing ratio d ₂ / d _{1 of the} layer 22 in the tread rubber layer 21, and the following equation Av (Hs) = {(CAP Hs) × d ₁ / d ₂ } + {(BASEHs)
Average rubber hardness Av (Hs) of the tread rubber layer 21 calculated by × (1-d ₁ / d ₂ )}
Is in the range of 52 <Av (Hs) <63 at 0 ° C.

When d ₂ / d ₁ ≤0.15, the cap layer 22
Has a thickness d ₂ smaller than the thickness d ₁ of the tread rubber layer 21, and the effect of providing the cap layer 21 is small. Further, when d ₂ / d ₁ ≧ 0.60, the thickness d ₂ of the cap layer 22 is excessive with respect to the thickness d ₁ of the tread rubber layer 21, that is, the thickness of the base layer 23 is too small, Base layer 23
The effect of the provision of is small. When the average rubber hardness Av (Hs) of the tread rubber layer 21 ≤ 52, the tread rubber layer 21
Is too soft, which not only deteriorates the running performance on ice and snowy road surfaces, but also deteriorates wear resistance and uneven wear resistance. When Av (Hs) ≧ 63, the rubber of the tread rubber layer 21 is too hard, and the braking performance and the acceleration performance on the snowy and snowy road surface deteriorate.

In FIG. 3, a central vertical groove 8 extending in the tire circumferential direction, an intermediate vertical groove 9 and an outer vertical groove 10 extending in the circumferential direction on both sides of the central vertical groove 8 are provided on the equatorial plane of the tread 2, and one of them is provided. A lateral groove 11 extending in the tire width direction is provided from the tread end 2a to the other tread end 2a, and a central longitudinal groove 8 is provided.
And the intermediate vertical groove 9 and the horizontal groove 11 form a central block 12, the intermediate vertical groove 9, the outer vertical groove 10 and the horizontal groove 11 form an intermediate block 13, and the outer vertical groove 10, the tread end 2a and the horizontal groove 11 form a shoulder block 14.
Is formed. Since the intermediate vertical grooves 9 are formed not in a straight line in the circumferential direction but in the width direction, the blocks 12 and 13 are formed at the intersections of the intermediate vertical grooves 9 and the horizontal grooves 11.
The edges of the are not arranged on the straight line in the circumferential direction but are displaced from each other, and the effect of the edges getting into the snow surface and the ice surface is increased, and the grip performance is improved.

The central block 12 has a central vertical groove 8 and an intermediate vertical groove 9.
Siping 15 having both ends in communication with, and siping 16 having both ends in communication with intermediate vertical groove 9 and outer vertical groove 10 in intermediate block 7.
However, the shoulder block 14 has an outer vertical groove 10 and a tread end 2
3 to 5 pieces (4 pieces in this embodiment) of sipings 17 whose both ends communicate with a are provided, and no other sipings or cuts are provided. By these sipings, the contact area between the block surface and the ice and snow road surface is increased to improve the grip performance on the ice and snow road surface, and the traction performance on the ice and snow road surface is improved due to the effect of digging the ice and snow road surface. Further, if the siping is not in communication with the vertical groove, the effect of the above-mentioned siping is greatly reduced, so that at least one end of each siping is in communication with the vertical groove.

FIG. 4 is a cross-sectional view of the block along the siping, showing the individual siping cross-sectional area m _N as a meshed portion in the peripheral portion, and siping is performed for the entire tire by n.
Assuming that the tire is provided (N = 1 to n), the total siping cross-sectional area m of the entire tire is m = m ₁ + m ₂ + m ₃ + ... + _mn . The approximate volume W of the block is obtained as a product of the tire outer diameter D, the average main groove depth p, the land ratio L of the block on the ground contact surface of the tread, and the ground contact width TW. That is, W = D.p.L.TW. The average main groove depth p is the depth p of each of q (6 in the above embodiment) main grooves formed of vertical grooves and horizontal grooves.
It is an average value of _M (however, M = _{1 to q} ), and is calculated by p = (p ₁ + p ₂ + p ₃ + ... + p _q ) / q. Sum of the above calculated siping cross-sections m
By setting the approximate volume W of the block and the block within the range of 0.6 <m / W <1.2, it is possible to improve the running performance on the ice and snow road surface.

When m / W ≦ 0.6, the siping provided in the block is small, and the contact area between the block surface and the snow and snow road surface is not sufficiently increased, so that the above-mentioned effect of the siping cannot be obtained. , M / W ≧ 1.2, there is too much siping, and the rigidity of the block is insufficient, so it is not possible to obtain sufficient running performance on ice and snow roads. In order to set the total siping cross-sectional area m to an appropriate value, the individual siping cross-sectional area m _N needs to be large, and the siping is made longer than the axial length of the block to improve the above effect. Therefore, as shown in FIG. 3, it is desirable to form the wave shape or the zigzag shape.

Further, in each circumferential block row of the central block 12 and the intermediate block 13, every other block 1
2, 13 are the grooves 8, 9, 1 on the outer side in the tire rotation axis direction.
Via the sub-grooves 12a and 13a formed shallower than 0 and 11,
A sub block 18 having a long side in the circumferential direction and a short side in the rotation axis direction,
The sub-blocks 18 and 19 are provided so as to be offset from each other by one block in the circumferential direction. Sub block 1
By providing 8 and 19, it is possible to improve the running performance on the icy and snowy road surface, and increase the lateral rigidity of the tread pattern to improve the steering stability.

Next, experimental results will be described for an example of a tire to which the present invention is applied and a comparative example of a tire under different conditions. In Example 1, at 0 ° C., the cap layer rubber hardness CAP Hs = 55 and the base layer rubber hardness BASE Hs =
65, average rubber hardness Av (Hs) = 58, distribution ratio of tread rubber layer d ₂ / d ₁ = 0.70, total siping cross-sectional area m = 1300 cm ² , approximate block volume W = 1870 cm ² , m
/W=0.7. Example 2 is the same as Example 1 except that the total siping cross-sectional area m = 2100 cm ² is different, and m / W = 1.1. In Example 3, the cap layer rubber hardness CAP Hs = 5 at 0 ° C.
5, base layer rubber hardness BASEHs = 65, average rubber hardness Av (H
s) = 60 and the distribution ratio of the tread rubber layer is d ₂ /
d ₁ = 0.50, total siping cross-sectional area m = 2100 cm ² , approximate block volume W = 1870 cm ² , m / W = 1.1. In Example 4, the total siping cross-sectional area m = 2600 cm
Only ² is different, other specifications are the same as in Example 3, and m /
W = 1.4.

In Comparative Example 1, the total siping cross sectional area m = 75.
Only 0 cm ² is different, other specifications are the same as in Example 1,
m / W = 0.4. The comparative example 2 is different only in the total siping cross-sectional area m = 2600 cm ² , the other specifications are the same as in the example 1, and m / W = 1.4. The comparative example 3 is different only in the total siping cross-sectional area m = 3000 cm ² , the other specifications are the same as in the example 1, and m / W = 1.6. In Comparative Example 4, at 0 ° C., the cap layer rubber hardness CAP Hs = 63, the base layer rubber hardness BASE Hs = 65,
Average rubber hardness Av (Hs) = 64, distribution ratio of tread rubber layer is d ₂ / d ₁ = 0.52, total siping cross-sectional area m
= 2100cm ² , approximate volume of block W = 1870cm ² , m / W
= 1.1. Comparative Example 5 is different only in the total siping cross-sectional area m = 2600 cm ² , and the other specifications are Comparative Example 4
And m / W = 1.4. Comparative Example 6
At 0 ° C., cap layer rubber hardness CAP Hs = 55, base layer rubber hardness BASE Hs = 65, average rubber hardness Av (Hs) = 57.
And the distribution ratio of the tread rubber layer is d ₂ / d ₁ = 0.
80, total siping cross-sectional area m = 2100 cm ² , approximate block volume W = 1870 cm ² , m / W = 1.1.

The experimental results are shown in Tables 1 and 2. The braking test measures the lock braking distance from 40 km / h, and the acceleration test measures the time required to pass 50 m from the stop position.
In Comparative Example 3 and in Table 2 Comparative Example 6 is 100
Is shown by the index, and the larger the index, the better the performance. [Table 1] Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 CAP Hs (0 ° C.) 55 ← ← ← ← ← BASEHs (0 ° C.) 65 ← ← ← ← ← d ₂ / d ₁ 0.70 ← ← ← ← ← Av (Hs) (0 ℃) 58 ← ← ← ← m (cm ² ) 750 1300 2100 2600 3000 W (cm ² ) 1870 ← ← ← ← m / W 0.4 0.7 1.1 1.4 1.6 [Performance test] Snow braking index 95 107 104 101 100 Braking index on ice 97 105 108 99 100 The results of Table 1 are shown in the graph of FIG. From the above experimental results,
It is found that the optimum region of m / W is 0.6 <m / W <1.2.

[Table 2] Example 3 Comparative Example 4 Example 4 Comparative Example 5 Comparative Example 6 CAP Hs (0 ° C) 55 63 55 63 55 BASEHs (0 ° C) 65 65 65 65 65 d ₂ / d ₁ 0.50 0.52 0.50 0.52 0.80 Av (Hs) (0 ℃) 60 64 60 64 57 m (cm ² ) 2100 2100 2600 2600 2100 W (cm ² ) 1870 ← ← ← ← ← m / W 1.1 1.1 1.4 1.4 1.1 [Performance test] Snow braking Index 108 94 101 91 100 Ice braking index 105 95 106 92 100 Acceleration index on snow 104 95 104 93 100 Acceleration index on ice 104 92 106 94 100 The results of Table 2 are shown in FIGS. 6 and 7.

From the above experimental results, tires in which the average rubber hardness Av (Hs) of the tread rubber layer is excessive (Comparative Examples 4 and 5)
It is clear that the tires (Examples 3 and 4) to which the present invention is applied have better braking performance (see FIG. 6a) and acceleration performance (see FIG. 6b) on the snow and snow road surface. Further, in the tires having an average rubber hardness Av (Hs) within the range of the present invention (Examples 3 and 4) and outside the range (Comparative Examples 4 and 5), when m / W exceeds 1.1, the snow and snow surface It can be seen that the above braking performance and acceleration performance deteriorate. Further, in FIG. 7, in the tire (Example 3 and Comparative Examples 4 and 6) in which m / W = 1.1 (within the range of the present invention), the average rubber hardness Av (Hs) of the tread rubber layer was 60 (Example). 3) has the highest performance, and near the lower limit (Comparative Example 4) and the upper limit (Comparative Example 6) of the range of the present invention, the braking performance on the snow and snow road surface (see FIG. 7a) and the acceleration performance (FIG. 7b). (See) is decreasing.

[0020]

Since the present invention is constructed as described above, it has the following effects. Thickness of tread rubber layer d
0.15 <d ₂ / d ₁ <between ₁ and the thickness d ₂ of the cap layer
With 0.60 established, the cap layer rubber hardness CAP Hs
And the base layer rubber hardness BASEHs and the average rubber hardness Av (Hs) of the tread rubber layer at 0 ° C., 50 ≦ CAP Hs ≦ 60,
By setting the range of 60 ≦ BASEHs ≦ 75 and 52 <Av (Hs) <63, the hardness of the tread rubber is properly maintained and the running performance on the snowy and snowy road surface is secured. Further, in the total siping cross-sectional area m of the siping cross-sectional areas provided in the block in the entire tire and the approximate volume W of the block, 0.6 <
By setting the range of m / W <1.2, the rigidity of the block is maintained properly, the contact area between the block surface and the ice and snow road surface is increased, the grip performance on the ice and snow road surface is improved, and the effect of digging the ice and snow road surface is improved. , Improves traction performance on ice and snow roads.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a development view of a tread according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view along a siping of a block to which the present invention is applied.

5 is a graph showing the results of Table 1. FIG.

FIG. 6 is a graph showing the results of Table 2.

FIG. 7 is a graph showing the results of Table 2.

[Explanation of symbols]

1 studless tire, 2 tread, 7 belt,
21 tread rubber 22 cap layer, 23 base layer, 2a tread edge 8 center vertical groove, 9 middle vertical groove, 10 outer vertical groove, 11 horizontal groove, 12 center block 13 middle block, 14 shoulder block, 15, 16,
17 Siping

Claims (1)

[Claims] 1. A tread rubber layer, which is located on the outer side in the tire radial direction of a belt disposed inside a tread, is formed of an outer cap layer and an inner base layer, and the tread rubber layer has a thickness d ₁ And the thickness d ₂ of the cap layer is 0.15 <
When d ₂ / d ₁ <0.60 is satisfied, the cap layer rubber hardness CAP Hs and the base layer rubber hardness BASE Hs are in the range of 50 ≦ CAP Hs ≦ 60 and 60 ≦ BASE Hs ≦ 75 at 0 ° C., and the tread rubber layer The average rubber hardness Av (Hs) of the formula is Av (Hs) = {(CAP Hs) × d ₁ / d ₂ } + {(BASEHs)
× (1-d ₁ / d ₂ )}, and a tire having a range of 52 <Av (Hs) <63 at 0 ° C., and the sum of the cross-sectional areas of the sipings provided in the blocks in the entire tire In the total siping cross-sectional area m and the approximate volume W of the block, 0.6 <
A studless tire having a sipeping cross-section area density per block unit volume in the range of m / W <1.2.