JP2009262646A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for winter such as a studless tire provided with a sipe on a block, durability of which is improved without spoiling steering stability. <P>SOLUTION: A tread rubber layer 4 arranged on the outer peripheral side of a belt layer 3 of a tread part 1 has an intermediate tread rubber layer 8 between a cap tread rubber layer 6 and an under tread rubber layer 7. The cap tread rubber layer 6 is lower than the under tread rubber layer 7 in rubber hardness at temperature 20°C, and the intermediate tread rubber layer 8 is lower than the under tread rubber layer 7 and higher than the cap tread rubber layer 6 in the rubber hardness at the temperature 20°C. Thickness t1 of the cap tread rubber layer 6 is 35 to 55% of total thickness t0 of the tread rubber layer 4, and thickness t2 of the intermediate tread rubber layer 8 is 5 to 35% of the total thickness t0 of the tread rubber layer 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire for improving durability without impairing steering stability in a winter pneumatic tire such as a studless tire having a sipe provided on a block. .

  Conventionally, in winter pneumatic tires such as studless tires, low-hardness rubber is used for the cap tread rubber layer in contact with the ice / snow road surface, while the snow / snow road performance is improved, while the under-placed inside the cap tread rubber layer. By adopting high hardness rubber for the tread rubber layer, the block rigidity is increased to ensure good steering stability. Further, a sipe having a depth reaching the undertread rubber layer is formed on the block, and the snowy and snowy road performance is enhanced by the edge effect (see, for example, Patent Document 1).

Normally, rubber having a rubber hardness of 10 or more lower than that of the under tread rubber layer is used for the cap tread rubber layer. However, when the hardness difference is large, stress is applied to the interface between the cap tread rubber layer and the under tread rubber layer. Because of the concentration, cracks generated in the sipe are likely to travel along the boundary surface, and the progress of the cracks causes block chipping and the like.
JP 2004-17851 A

  An object of the present invention is to provide a pneumatic tire capable of improving durability without impairing steering stability in a winter pneumatic tire such as a studless tire having a sipe provided on a block.

  In the pneumatic tire of the present invention that achieves the above object, a tread rubber layer is disposed on the outer peripheral side of the belt layer of the tread portion, and the tread rubber layer is disposed on the inner peripheral side of the cap tread rubber layer having a tread on the outer peripheral side. The cap tread rubber layer has a rubber hardness at a temperature of 20 ° C. lower than that of the under tread rubber layer, and forms a block divided by a groove on the tread surface of the cap tread rubber layer. In a pneumatic tire provided with a sipe having a depth reaching the under tread rubber layer, the tread rubber layer is further provided at least in an area where the block is provided and an intermediate tread rubber layer between the under tread rubber layer and the cap tread rubber layer. The intermediate tread rubber layer has an under tread rubber hardness at a temperature of 20 ° C. Lower than the layer and higher than the cap tread rubber layer, and the thickness of the cap tread rubber layer is in the range of 35 to 55% of the total thickness of the tread rubber layer, while the thickness of the intermediate tread rubber layer is It is characterized by being in the range of 5 to 35% of the total thickness of the tread rubber layer.

  According to the present invention described above, since the intermediate tread rubber layer is interposed between the cap tread rubber layer and the under tread rubber layer, the difference in hardness between the adjacent rubber layers can be reduced. It is possible to suppress the occurrence of stress concentration. As a result, the cracks generated in the sipe are prevented from proceeding along the boundary surfaces of the adjacent rubber layers, so that durability can be improved.

  Also, by specifying the upper limit of the thickness of the cap tread rubber layer and the intermediate tread rubber layer as described above, it is possible to secure a block rigidity equal to or higher than the conventional level, thereby avoiding a loss of steering stability. can do.

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

  1 and 2 show an embodiment of a pneumatic tire of the present invention, and show a winter pneumatic tire such as a studless tire used in winter. The carcass layer 2 extends between left and right bead portions (not shown), and both end portions thereof are folded back from the inner side in the tire axial direction around the bead core embedded in the bead portion. A plurality of belt layers 3 are provided on the outer peripheral side of the carcass layer 2 of the tread portion 1.

  A tread rubber layer 4 is disposed on the outer peripheral side of the belt layer 3. The tread rubber layer 4 is exposed on the surface and has a tread rubber layer 6 having a tread surface 5 in contact with the road surface on the outer peripheral side, an under tread rubber layer 7 disposed on the inner peripheral side, the cap tread rubber layer 6 and the under tread. It has an intermediate tread rubber layer 8 disposed between the rubber layer 7 and a wing tip rubber layer 9 disposed on the side. The cap tread rubber layer 6 and the under tread rubber layer 7 extend between the left and right shoulder regions 1S, 1S of the tread portion 1, and the intermediate tread rubber layer 8 is also tread like the cap tread rubber layer 6 and the under tread rubber layer 7. The left and right shoulder regions 1S, 1S of the part 1 extend.

  A plurality of blocks 12 are formed on the tread 5 by a circumferential groove 10 extending in the tire circumferential direction 20 and a lateral groove 11 extending in the tire width direction. In each block 12, sipes 13 extending in a zigzag shape in the tire width direction and reaching the under tread rubber layer 7 are disposed at predetermined intervals in the tire circumferential direction 20 as shown in FIG. 3. .

  The cap tread rubber layer 6 has a rubber hardness at a temperature of 20 ° C. lower than that of the under tread rubber layer 7. As a result, the adhesion force of the cap tread rubber layer 6 to the icy and snowy road surface is increased, thereby improving the icy and snowy road performance. The intermediate tread rubber layer 8 has a rubber hardness at a temperature of 20 ° C. lower than that of the under tread rubber layer 7 and higher than that of the cap tread rubber layer 6. The intermediate hardness between the tread rubber layer 6 is obtained. In the tread rubber layer 4, the rubber hardness at 20 ° C. of the under tread rubber layer 7 is the highest. By adopting a high hardness rubber for the under tread rubber layer, the block rigidity is increased and the steering stability is secured. Like to do.

  The cap tread rubber layer 6 has a thickness t1 in the range of 35 to 55% of the total thickness t0 of the tread rubber layer 4. On the other hand, the thickness t2 of the intermediate tread rubber layer 8 is in the range of 5 to 35% of the total thickness t0 of the tread rubber layer 4. The thickness t3 of the remaining undertread rubber layer 7 is 10 to 60% of the total thickness t0 of the tread rubber layer 4. In addition, the thickness said here is the thickness measured in the area | region of the block 12 except the area | region which provided the sipe 13, and the peripheral part.

  According to the present invention described above, by disposing the above-described intermediate tread rubber layer 8 between the cap tread rubber layer 6 and the under tread rubber layer 7, the hardness difference between the adjacent rubber layers 6, 7, 8. Therefore, the tread rubber layer 4 can prevent stress concentration from occurring between the layers. Therefore, it is possible to suppress the cracks generated in the sipe 13 from proceeding along the boundary surfaces of the adjacent rubber layers 6, 7, and 8, and to improve the durability.

  Further, by defining the upper limit of the thickness of the cap tread rubber layer 6 and the intermediate tread rubber layer 8 as described above, it is possible to secure a block rigidity equal to or higher than the conventional level, thereby impairing steering stability. There is no.

  When the thickness t1 of the cap tread rubber layer 6 is lower than 35% of the total thickness t0 of the tread rubber layer 4, the ratio occupied by the cap tread rubber layer 6 decreases. Is lost early (braking performance on ice during wear deteriorates). On the other hand, if it exceeds 55%, the ratio of the cap tread rubber layer 6 having a low hardness becomes too large, so that the block rigidity is lowered and steering stability is lowered.

  When the thickness t2 of the intermediate tread rubber layer 8 is lower than 5% of the total thickness t0 of the tread rubber layer 4, the intermediate tread rubber layer 8 is too thin and the cap tread rubber layer 6 and the under tread rubber layer have a large hardness difference. It becomes difficult to effectively alleviate the occurrence of stress concentration between the two. On the other hand, if it exceeds 35%, when the thickness of the cap tread rubber layer 6 is ensured, the thickness of the under tread rubber layer 7 becomes thin, which adversely affects steering stability.

  In the present invention, the rubber hardness at a temperature of 20 ° C. of the cap tread rubber layer 6 is preferably in the range of 45-60. When the rubber hardness of the cap tread rubber layer 6 is lower than 45, the block rigidity is lowered and the wear resistance is deteriorated. On the other hand, if it is higher than 60, ice / snowy road performance will deteriorate.

  The rubber hardness of the undertread rubber layer 7 at a temperature of 20 ° C. is preferably in the range of 55 to 70. When the rubber hardness of the under tread rubber layer 7 is lower than 55, the steering stability is adversely affected. On the other hand, when it is higher than 70, the adhesion with the belt layer 3 is deteriorated, and a separation failure with the belt layer 3 is likely to occur.

  The rubber hardness at a temperature of 20 ° C. of the intermediate tread rubber layer 8 is preferably 3 or more lower than that of the under tread rubber layer 7 and 3 or higher than that of the cap tread rubber layer 6. It can be mitigated more effectively.

  The difference in rubber hardness between the cap tread rubber layer 6 and the under tread rubber layer 7 is preferably about 10 to 15 from the viewpoint of ice / snow road performance and steering stability. The rubber hardness referred to in the present invention is a hardness measured according to JISK6253 durometer type A.

  The intermediate tread rubber layer 8 is preferably thicker in the left and right shoulder regions 1S and 1S than in the center region 1C located between the left and right shoulder regions 1S and 1S. In the tread portion 1, a large load acts on the shoulder region 1S during cornering. Therefore, in a pneumatic tire for winter with a wide development width and a deeper groove depth than usual, stress concentration is more likely to occur between the layers in the shoulder region 1S than in the center region 1C. Therefore, by making the thickness of the intermediate tread rubber layer 8 in the shoulder region 1S thicker than that in the center region 1C, the stress relaxation effect by the intermediate tread rubber layer 8 can be enhanced.

  Although the pneumatic tire which provided the block 12 which has the sipe 13 in the whole tread 5 was demonstrated in the said embodiment, the pneumatic tire in which the block 12 which has the sipe 13 and a rib coexist may be sufficient. In that case, the intermediate tread rubber layer 8 described above may be arranged at least in the region where the block 12 is provided.

  The present invention can be preferably used for winter pneumatic tires such as studless tires used for passenger cars, but is not limited thereto.

  The structure shown in FIGS. 1 and 2 in which the tire size is the same for 195 / 65R15, and the thickness and rubber hardness of the cap tread rubber layer, intermediate tread rubber layer and under tread rubber layer are as shown in Table 1 (depth of circumferential groove) Tires 1 to 3 (Examples 1 to 3), Comparative tires 1 to 4 (Comparative Examples 1 to 4), and conventional tires without an intermediate tread rubber layer (Conventional examples) were prepared.

  The tire 3 of the present invention is obtained by increasing the thickness of the intermediate tread rubber layer in the shoulder region. In Table 1, the left side is the thickness of the center region and the right side is the thickness of the shoulder region.

  When each of these test tires was mounted on a rim having a rim size of 15 × 6 J and the air pressure was set to 230 kPa, an evaluation test of durability, handling stability, and braking performance on ice during wear was performed by the following methods. The result shown in 1 was obtained.

Durability After mounting each test tire on a drum testing machine and conducting a load durability test specified in JIS D4230, the load was continuously increased by 15% of the maximum load capacity specified in JIS D4230 every 4 hours. The distance traveled until a block chip failure occurred was measured. The evaluation result is shown as an index value with the conventional tire as 100. The greater this value, the better the durability.

Steering stability Each test tire was mounted on a passenger car (FR car) with a displacement of 2000 cc, and a sensory evaluation test of steering stability was performed by a test driver on a dry road test course. The evaluation result is shown as an index value with the conventional tire as 100. The larger this value, the better the steering stability.

On-ice braking performance at the time of wear Each test tire worn by 4 mm is mounted on a passenger car (FR vehicle) with a displacement of 2000 cc, and full braking is applied at a speed of 40 km / h on an icy road test course until it stops. The distance of was measured. The evaluation result is indicated by an index value where 100 is a value when the conventional tire is new (preliminary running for 100 km). The larger this value, the better the braking performance on ice during wear.

  From Table 1, it can be seen that the tire of the present invention can improve the durability while ensuring the steering stability equal to or higher than the conventional level. It can also be seen that the braking performance on ice during wear does not decrease as in the comparative tire 1.

It is principal part sectional drawing which shows one Embodiment of the pneumatic tire of this invention. FIG. 2 is a main part development view of a tread of the pneumatic tire of FIG. 1. It is a partial expanded sectional view of a block.

Explanation of symbols

1 tread portion 1C center region 1S shoulder region 3 belt layer 4 tread rubber layer 5 tread surface 6 cap tread rubber layer 7 under tread rubber layer 8 intermediate tread rubber layer 10 circumferential groove 11 lateral groove 12 block 13 sipes t0, t1, t2, t3 thickness

Claims (3)

A tread rubber layer is disposed on the belt layer outer peripheral side of the tread portion, and the tread rubber layer has a cap tread rubber layer having a tread on the outer peripheral side and an under tread rubber layer disposed on the inner peripheral side thereof, and the cap tread rubber The layer had a rubber hardness at a temperature of 20 ° C. lower than that of the undertread rubber layer, a block divided by a groove was formed on the tread surface of the cap tread rubber layer, and a sipe having a depth reaching the undertread rubber layer was provided on the block. In pneumatic tires,
The tread rubber layer further has an intermediate tread rubber layer between the under tread rubber layer and the cap tread rubber layer at least in a region where the block is provided, and the intermediate tread rubber layer has a rubber hardness at a temperature of 20 ° C. The tread rubber layer is lower than the under tread rubber layer and higher than the cap tread rubber layer, and the thickness of the cap tread rubber layer is in the range of 35 to 55% of the total thickness of the tread rubber layer. A pneumatic tire having a thickness in the range of 5 to 35% of the total thickness of the tread rubber layer.   2. The pneumatic tire according to claim 1, wherein the intermediate tread rubber layer has a rubber hardness at a temperature of 20 ° C. of 3 or more lower than that of the under tread rubber layer and 3 or more of higher than that of the cap tread rubber layer.   The intermediate tread rubber layer extends between left and right shoulder regions of the tread portion, and the thickness of the intermediate tread rubber layer is thicker in the left and right shoulder regions than the center region located between the left and right shoulder regions. Pneumatic tire described in 2.

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