JP2012035697A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire with further improved braking performance on ice without changing negative rate.SOLUTION: The pneumatic tire allows a plurality of blocks to be partitioned by a plurality of circumferential grooves that extend circumferentially along a tread and a plurality of breadthwise grooves that extend breadthwise along a tread on the tread surface of a tire. When an area between a pair of circumferential grooves in a shoulder that sandwich a tire equatorial plane and are positioned breadthwise at outermost sides along a tread is made to be a tread center part and an area between each of the pair of the circumferential grooves along the shoulder and a tread end is named to be a tread shoulder part, the length Lc of the block of the tread center part circumferentially along the tread is longer than the length Ls of the block of the tread shoulder part circumferentially along the tread, the groove width Wc of the breadthwise groove of the tread center part is shorter than the groove width Ws of the breadthwise groove of the tread shoulder part, and 8 mm≤Ls≤20 mm and 0.3≤Ws/Ls≤0.7 are satisfied.

Description

  The present invention relates to a pneumatic tire having a block pattern and particularly improved on-ice braking performance.

  Conventionally, in winter pneumatic tires, in order to improve braking performance on ice, a plurality of sipes extending in the tread width direction have been added to the block of the tire tread pattern. Since these sipes suck up molten water (water film) generated by the friction between the rubber of the tread and the icy road surface, a reduction in the contact area of the tire is suppressed, and braking performance on ice is ensured (for example, Patent Document 1). ).

JP 2009-029255 A

  In the tread pattern of the conventional pneumatic tire described above, blocks having the same shape are arranged on the entire tread pattern. The inventor has found a way to further improve the on-ice brake performance by changing the tread pattern without changing the negative rate, and has completed the present invention.

The gist of the present invention is as follows.
(1) A pneumatic tire in which a plurality of blocks are defined on a tread surface of the tire by a plurality of circumferential grooves extending in the tread circumferential direction and a plurality of width direction grooves extending in the tread width direction,
A region between a pair of shoulder circumferential grooves located on the outermost side in the tread width direction across the tire equator plane is a tread center portion, and a region between each of the pair of shoulder circumferential grooves and a tread end is a tread shoulder portion. When
A length Lc in the tread circumferential direction of the block of the tread center portion is longer than a length Ls in the tread circumferential direction of the block of the tread shoulder portion,
The groove width Wc of the width direction groove of the tread center portion is shorter than the groove width Ws of the width direction groove of the tread shoulder portion,
8 mm ≦ Ls ≦ 20 mm and 0.3 ≦ Ws / Ls ≦ 0.7 are satisfied.
A pneumatic tire characterized by that.

(2) The lengths Lc and Ls in the tread circumferential direction of the block satisfy 0.4 ≦ Ls / Lc ≦ 0.6,
The groove widths Wc and Ws of the width direction grooves satisfy 2.0 ≦ Ws / Wc ≦ 3.0.
The pneumatic tire according to (1) above, wherein

  According to the present invention, the air braking performance is further improved by adjusting the circumferential length of the block and the groove width of the width direction groove between the tread center portion and the tread shoulder portion without changing the negative rate. An inset tire can be provided.

It is an expanded view of the tread pattern which shows 1st Embodiment of the pneumatic tire of this invention. It is a figure for demonstrating the effect | action of this invention. It is a figure which shows that block length is proportional to the temperature rise of an ice road surface. It is a graph showing the relationship between block length and a friction coefficient on ice. It is a figure which shows that the temperature rise of an ice road surface is reset according to the groove width of the width direction groove | channel. It is a graph showing the relationship between the groove width of a width direction groove | channel, and a friction coefficient on ice. It is an expanded view of the tread pattern which shows 2nd Embodiment of the pneumatic tire of this invention. It is a development view of a tread pattern of a conventional tire. 2 is a development view of a tread pattern of a comparative example tire 1. FIG. 3 is a development view of a tread pattern of a comparative tire 2. FIG. 3 is a development view of a tread pattern of a comparative tire 3. FIG.

Hereinafter, the pneumatic tire of the present invention will be described in detail with reference to the drawings.
In addition, since the internal reinforcement structure of a tire is the same as that of a general radial tire, illustration is abbreviate | omitted.

FIG. 1 is a development view of a tread pattern showing a first embodiment of a pneumatic tire of the present invention.
Two circumferential grooves 2 extending in the circumferential direction of the tread parallel to the tire equatorial plane CL are formed on the tread surface 1 of the tire. Here, a region between the circumferential grooves 2 and 2 is a tread center portion TC, and a region between the circumferential grooves 2 and the tread end TE is a tread shoulder portion TS. A plurality of width direction grooves 5s extending in the tread width direction are formed in the tread shoulder portion TS of the tread surface 1, and a plurality of blocks 20s are defined by the width direction grooves 5s and the circumferential grooves 2. Similarly, a plurality of width direction grooves 5c extending in the tread width direction are formed in the tread center portion TC of the tread surface 1, and a plurality of blocks 20c are defined by the width direction grooves 5c and the circumferential direction grooves 2. Yes.
A plurality of sipes 21 extending in the tread width direction are formed in the illustrated blocks 20c and 20s so as to connect the circumferential grooves 2 to each other. These sipes 21 absorb the melted water generated by the friction between the blocks 20c and 20s and the ice road surface, and ensure the braking performance on ice.
A length Lc in the tread circumferential direction of the block 20c of the tread center portion TC is longer than a length Ls in the tread circumferential direction of the block 20s of the tread shoulder portion TS. Further, the groove width Wc of the width direction groove 5c of the tread center portion TC is shorter than the groove width Ws of the width direction groove 5s of the tread shoulder portion TS. Further, in the tread shoulder portion TS, the length Ls and the groove width Ws satisfy 8 mm ≦ Ls ≦ 20 mm and 0.3 ≦ Ws / Ls ≦ 0.7.

Hereinafter, the operation of the present invention will be described.
Due to the tire diameter difference, on the tread surface 1 of the tire, a driving force is greatly applied to the tread center portion TC, and a braking force is applied to the tread shoulder portion TS.
The driving force is a force that works when the tire is cut along the tire equatorial plane CL and the tread surface (surface that is in contact with the road surface) is shear-deformed forward in the tire traveling direction. On the other hand, the braking force is the reverse of the driving force, and is a force that works by shearing the tread surface backward in the tire traveling direction.
In the tread shoulder portion TS where the braking force works greatly, the amount of water generated by friction between the tread tread surface 1 and the icy road surface is larger than in the tread center portion TC. Therefore, the present inventor has intensively studied this point and designed a tread pattern in consideration of the distribution of frictional force in the tread width direction.

First, consider one block of the tread.
A schematic diagram when one block of the tread is sliding on the ice road surface is shown in FIG. FIG. 2A shows a cross section of the block 20 in the tire circumferential direction. There is no water film on the ice road surface in the first half (position indicated by P1 in the figure) with respect to the direction in which the block 20 slides, whereas the amount of water film increases toward the second half (position indicated by P2 in the figure). . This is because when friction between the icy road surface and one block 20 is considered, friction with the block 20 has not yet occurred at the point P1 on the icy road surface, but the tire of one block 20 at the point P2 on the icy road surface. This is because friction with the rubber in the circumferential direction occurs, and the ice melts due to this friction.
FIG. 2B shows a ground pressure distribution (FEM) of the block 20. The ground pressure of one block 20 is higher in the first half compared to the second half in the direction in which the block 20 slides when viewed for each block piece divided by the sipe 21.
FIG. 2C shows the temperature of the icy road surface when the block 20 slides on the icy road surface. The point P1 on the icy road surface is −2 ° C., but the friction work on the icy road surface is consumed for the temperature rise of the ice, so the temperature increases as the point P2 at the latter half of the icy road surface is approached. The reason why the graph rises to the right with a constriction corresponding to the position of the sipe 21 is that the temperature of the ice does not increase at the position of the sipe 21 because there is no friction with the ice road surface.
From FIG. 2, it can be seen that in one block, the longer the circumferential length of the block, the greater the temperature rise due to friction.

This phenomenon will be specifically described with reference to FIG.
The upper part of FIG. 3 shows the block 20 when sliding on the icy road surface, and the block lengths up to the point P2 and those up to the point P3 are shown in an overlapping manner. The middle part of FIG. 3 shows a water film generated by the block 20 sliding on the ice road surface. The lower part of FIG. 3 shows the temperature of the icy road surface when the block 20 slides on the icy road surface. When the length of the block 20 is up to the point P2, the temperature of the ice road surface is T2, and when the length of the block 20 is up to the point P3, the temperature of the ice road surface is T3. Thus, when the length of the block 20 in the circumferential direction is increased by (P3-P2), it can be seen that the temperature of the ice road surface increases by (T3-T2).
Thus, it can be seen that in one block, the temperature rise due to friction increases as the length of the block in the circumferential direction increases. Therefore, by shortening the length of the block in the circumferential direction, the amount of molten water can be reduced, and as a result, the reduction of the contact area can be suppressed and the on-ice friction performance can be improved.

  Here, the present inventor has intensively studied the block length Ls of the block 20s of the tread shoulder portion TS, and has found that the block length Ls of 8 mm or more and 20 mm or less is effective for the present invention. FIG. 4 is a graph showing the on-ice friction index when the block length Ls of one block 20s is changed. When the block length Ls is increased to some extent (25 mm ≦ Ls), the friction coefficient on ice becomes constant. The coefficient of friction on ice is indexed with this constant value being 100. As described above, it can be seen that when the block length Ls is increased, the friction index on ice decreases. On the other hand, if the block length Ls is too short, the friction index on ice is decreased. This is because the rigidity of the block 20s is not ensured. Therefore, by setting the block length Ls in the range where the friction index on ice is increased by 30% or more, specifically, by making the block length Ls 8 mm or more and 20 mm or less, the friction performance on ice is effectively improved. be able to.

Next, consider a plurality of blocks.
FIG. 5 shows the circumferential section when the two blocks slide on the icy road surface in the upper stage, the amount of water film at that time in the middle stage, and the temperature of the icy road surface at that time in the lower stage.
As shown in the upper part of FIG. 5 (a), consider a case where the interval (groove width of the width direction groove 5) W between the first block 20a and the second block 20b is short. As shown in the lower part of FIG. 5A, the temperature of the ice road surface rises from T0 to T1 by the first block 20a. Next, the temperature of the ice road surface slightly decreases at the width direction groove 5 and becomes T2. Further, the temperature of the ice road surface rises to T3 by the second block 20b. Thus, when the groove width W of the width direction groove 5 is short, the temperature of the ice road surface increases in proportion to the number of blocks 20, and further, as shown in the middle part of FIG. It can be seen that the amount of water film increases.
Next, consider the case where the groove width W of the width direction groove 5 is long as shown in the upper part of FIG. As shown in the lower part of FIG. 5B, the temperature of the ice road surface rises from T0 to T1 by the first block 20a. However, the temperature of the icy road surface decreases to T0 at the widthwise grooves 5. That is, the increased temperature is reset by the width direction groove 5. Next, the temperature of the ice road surface rises from T0 to T1 by the second block 20b. Thus, since the raised temperature is reset when the groove width W of the width direction groove 5 is long, the temperature of the ice road surface does not rise even if the number of blocks 20 increases. Therefore, as shown in the middle part of FIG. 5B, the amount of water film is constant in each block.

  Furthermore, the inventor has studied the block length Ls of the block 20s of the tread shoulder portion TS and the groove width Ws of the width direction groove 5s, and satisfies the relationship of 0.3 ≦ Ws / Ls ≦ 0.7. It was found to be effective for the present invention. FIG. 6 is a graph showing the on-ice friction index when the groove width Ws between two blocks is changed. In this example, the block length Ls is 10 mm. The on-ice friction coefficient when the groove width Ws is 1 mm is taken as 100, and the on-ice friction coefficient is indexed. From the graph, it is understood that the friction index on ice is constant even when the groove width Ws is larger than 7 mm. On the other hand, it can be seen from the graph that when the groove width Ws is less than 3 mm, the increase in friction coefficient on ice is less than 30%, and there is no temperature rise reset effect. Therefore, when the block length Ls is 10 mm, the on-ice friction performance can be effectively improved by setting the groove width Ws to 3 mm to 7 mm. In addition, when the block length Ls was 20 mm, the numbers on the horizontal axis in FIG. Therefore, it can be said that it is effective for the present invention to satisfy the relationship of 0.3 ≦ Ws / Ls ≦ 0.7.

As described above, it can be seen that in order to improve the friction performance on ice, it is only necessary to shorten the circumferential length of the blocks and widen the groove width between the blocks. However, if this knowledge is simply applied to the entire tread pattern, the land area decreases (negative rate increases). As a result, the ground contact area is reduced and the friction performance is deteriorated.
Therefore, in the present invention, the land area of the entire pattern is kept constant, that is, the negative rate is kept constant, and the tread shoulder portion where the braking force contributes greatly is shortened, and the block length is shortened. The width was set wide.
Thereby, it becomes possible to provide a pneumatic tire with improved braking performance on ice.
In the present invention, the negative rate of the entire tread pattern is 20% to 40%, the negative rate of the tread center portion TC is 10% to 25%, and the negative rate of the tread shoulder portion TS is 25 to 55%. It is preferable that

FIG. 7 is a development view of a tread pattern showing a second embodiment of the pneumatic tire of the present invention.
On the tread surface 1 of the tire, five circumferential grooves 2a, 2b, 2c extending in the tread circumferential direction parallel to the tire equatorial plane CL are formed. Here, a region between the pair of circumferential grooves 2a and 2a on the outermost side in the tire width direction is a tread center portion TC, and a region between the circumferential groove 2a and the tread end TE is a tread shoulder portion TS. A plurality of width direction grooves 5s extending in the tread width direction are formed in the tread shoulder portion TS of the tread surface 1, and a plurality of blocks 20s are defined by the width direction grooves 5s and the circumferential direction grooves 2a. In the tread center portion TC, the circumferential grooves 2a and 2b are connected to each other, a plurality of width direction grooves 5c1 extending in the tread width direction are formed, and a plurality of blocks 20c1 are partitioned. In the tread center portion TC, the circumferential grooves 2b and 2c are connected, a plurality of width direction grooves 5c2 extending in the tread width direction are formed, and a plurality of blocks 20c2 are partitioned.
In the illustrated block 20s, 20c1, and 20c2, a plurality of sipes 21 extending in the tread width direction are formed so as to connect the circumferential grooves.
The length Ls in the tread circumferential direction of the block 20s of the tread shoulder portion TS, the length Lc1 in the tread circumferential direction of the block 20c1 of the tread center portion TC, and the length Lc2 in the tread circumferential direction of the block 20c2 are Ls <Lc1. The relationship of <Lc2 is satisfied.
Further, the groove width Ws of the width direction groove 5s of the tread shoulder portion TS, the groove width Wc1 of the width direction groove 5c1 of the tread center portion TC, and the groove width Wc2 of the width direction groove 5c2 are in a relationship of Wc2 <Wc1 <Ws. Meet.
Furthermore, in the tread shoulder portion TS, the length Ls and the groove width Ws satisfy 8 mm ≦ Ls ≦ 20 mm and 0.3 ≦ Ws / Ls ≦ 0.7.
Thus, by adjusting the circumferential length of the block and the groove width of the widthwise groove between the tread center portion and the tread shoulder portion, a pneumatic tire with improved on-ice brake performance can be provided.

In the embodiment described above, the same number of blocks 20 are arranged in the tread width direction across the tire equatorial plane CL, but the number of blocks 20 arranged is not limited to this illustrated example. For example, an asymmetrical arrangement such as two rows on one side in the tread width direction and three rows on the other side across the tire equatorial plane CL is also possible.
In the embodiment described above, the circumferential groove 2 extends linearly in the tread circumferential direction, but the circumferential groove 2 may extend in a zigzag shape or a wave shape in the tread circumferential direction.
In the embodiment described above, the widthwise groove 5 extends linearly in the tread width direction (direction perpendicular to the tread circumferential direction), but the widthwise groove 5 extends in a straight line inclined in the tread circumferential direction. It may be extended in a curved line.
When the block lengths of the blocks 20 arranged in one row in the tread circumferential direction are different for each block, the block length defined in the present invention indicates an average value of all the blocks 20. In addition, when the groove widths of the width direction grooves 5 between the blocks 20 arranged in one row in the tread circumferential direction are different within one groove or different for each groove, the groove width defined in the present invention Denotes the average value of the grooves 5 in the full width direction.

  Further, the inventor of the present invention has the tread circumferential lengths Lc and Ls of the block 20 satisfying 0.4 ≦ Ls / Lc ≦ 0.6, and the groove widths Wc and Ws of the widthwise grooves 5 are 2.0. It was confirmed by an example described later that it was preferable to satisfy ≦ Ws / Wc ≦ 3.0.

Examples of the present invention will be described below, but the present invention is not limited thereto.
Invention example tires, comparative example tires and conventional example tires were prototyped, and the braking performance on an icy road surface was evaluated.
Each test tire has a tire size of 195 / 65R15, and the negative rate of the tread pattern is the same (30%).
Invention example tires 1 to 5 have the tread pattern shown in FIG. 7 and the specifications shown in Table 1.
As other example tires, pneumatic tires having the tread pattern shown in FIG. 7 and the specifications shown in Table 2 were prepared.
Conventional tires have the tread pattern shown in FIG. 8 and the specifications shown in Table 1. That is, the length of the block and the width of the width direction groove are the same in the tread center portion TC and the tread shoulder portion TS (Ls = Lc1 = Lc2, Ws = Wc1 = Wc2).
The comparative tire 1 has the tread pattern shown in FIG. 9 and the specifications shown in Table 1. That is, the closer to the tire equatorial plane CL, the longer the block length and the wider the widthwise groove (Ls <Lc1 <Lc2, Ws <Wc1 <Wc2).
The comparative tire 2 has the tread pattern shown in FIG. 10 and the specifications shown in Table 1. That is, the closer to the tire equatorial plane CL, the shorter the block length and the narrower the width direction groove width (Lc2 <Lc1 <Ls, Wc2 <Wc1 <Ws).
The comparative example tire 3 has the tread pattern shown in FIG. 11 and the specifications shown in Table 1. That is, the closer to the tire equatorial plane CL, the shorter the block length and the wider the widthwise groove (Lc2 <Lc1 <Ls, Ws <Wc1 <Wc2).
The comparative tires 4 to 7 have the tread pattern shown in FIG. 7 and the specifications shown in Table 1.

  Each test tire is filled with an internal pressure of 200 kPa and mounted on a passenger car (vehicle condition: 3000 cc class FR sedan). A brake performance test is performed on an icy road surface under the load condition of 2 passengers or 4.7 kW per tire. went. In the brake performance test, the braking distance from the initial speed of 40 km / h until full braking was applied to the stationary state was measured, and the average deceleration was calculated from the initial speed and the braking distance. The results are shown as indexes in Tables 1 and 2 with the average deceleration of the conventional tire as 100. In addition, it shows that it is excellent in braking performance, so that an index | exponent is large.

From Table 1, the inventive tire satisfying Ls <Lc1 <Lc2, Wc2 <Wc1 <Ws, 8 mm ≦ Ls ≦ 20 mm and 0.3 ≦ Ws / Ls ≦ 0.7 is compared with the conventional tire and the comparative tire. It can be seen that the braking performance on ice is improved.
From Table 2, the invention tires satisfying 0.4 ≦ Ls / Lc2 ≦ 0.6 and 2.0 ≦ Ws / Wc2 ≦ 3.0 have an on-ice brake performance improved by 7% or more compared to the conventional tires. I understand that In addition, the numerical value of a result considers that there is no significant difference below ± 2.

1 tread surface 2 circumferential groove 5 width groove 20 block 21 sipe

Claims (2)

A pneumatic tire in which a plurality of blocks are defined by a plurality of circumferential grooves extending in the tread circumferential direction and a plurality of width direction grooves extending in the tread width direction on the tread surface of the tire,
A region between a pair of shoulder circumferential grooves located on the outermost side in the tread width direction across the tire equator plane is a tread center portion, and a region between each of the pair of shoulder circumferential grooves and a tread end is a tread shoulder portion. When
A length Lc in the tread circumferential direction of the block of the tread center portion is longer than a length Ls in the tread circumferential direction of the block of the tread shoulder portion,
The groove width Wc of the width direction groove of the tread center portion is shorter than the groove width Ws of the width direction groove of the tread shoulder portion,
8 mm ≦ Ls ≦ 20 mm and 0.3 ≦ Ws / Ls ≦ 0.7 are satisfied.
A pneumatic tire characterized by that. The lengths Lc and Ls in the tread circumferential direction of the block satisfy 0.4 ≦ Ls / Lc ≦ 0.6,
The groove widths Wc and Ws of the width direction grooves satisfy 2.0 ≦ Ws / Wc ≦ 3.0.
The pneumatic tire according to claim 1.

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