JP2013199154A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of reducing road noise, without reducing maneuvering stability.SOLUTION: A pneumatic tire includes one circumferential groove 5 formed in a tread part 1 and extended in a tire circumferential direction, and multiple rows of land parts 6 formed by a circumferential directional groove 5. Each of the land parts 6 of the tread part 1 are formed by laminating a base rubber layer 7 positioned inside in the tire radial direction and a tread rubber layer 8 positioned outside in the tire radial direction. The base rubber layer 7 is constituted of a rubber composition relatively high in hardness. The tread rubber layer 8 is constituted of a rubber composition relatively low in the hardness. A thickness of the tread rubber layer 8 is increased toward the center from both ends in the tire width direction of the land parts 6.

Description

  The present invention relates to a pneumatic tire using a plurality of types of rubber compositions having different hardnesses in a tread portion, and more particularly, to a pneumatic tire that can reduce road noise without reducing steering stability. .

  A pneumatic tire usually has at least one circumferential groove extending in the tire circumferential direction in a tread portion, and has a structure in which a plurality of rows of land portions are partitioned by the circumferential groove. For such a cap tread rubber layer of a pneumatic tire, an optimal rubber composition is used in order to exhibit necessary tire characteristics.

  Conventionally, in order to reduce road noise while improving steering stability in pneumatic tires, multiple types of rubber compositions with different hardness are used for the cap tread rubber layer, and it is placed in the area outside the vehicle when mounted on the vehicle The hardness of the rubber composition to be set is higher than the hardness of the rubber composition arranged in the region inside the vehicle, or is arranged in the shoulder region than the hardness of the rubber composition arranged in the center region in the tire width direction. It has been proposed to increase the hardness of the rubber composition (see, for example, Patent Document 1).

  However, as described above, when the hardness of the rubber composition is made different for each region of the tread portion, each land portion is composed of a single type of rubber composition. The land portion having a low hardness is a factor that reduces the steering stability. For this reason, with the above structure, it is not always possible to effectively achieve both steering stability and road noise.

JP 2006-35974 A

  An object of the present invention is to provide a pneumatic tire that can reduce road noise without reducing steering stability.

  In order to achieve the above object, a pneumatic tire according to the present invention is a pneumatic tire in which at least one circumferential groove extending in the tire circumferential direction is provided in a tread portion, and a plurality of rows of land portions are partitioned by the circumferential groove. A rubber composition in which each land portion of the tread portion has a laminated structure of a base rubber layer located on the inner side in the tire radial direction and a tread rubber layer located on the outer side in the tire radial direction, and the base rubber layer has a relatively high hardness And the tread rubber layer is made of a rubber composition having a relatively low hardness, and the thickness of the tread rubber layer is increased from both ends in the tire width direction of each land portion toward the center. It is characterized by.

  In the present invention, each land portion of the tread portion has a laminated structure of a high hardness basic rubber layer and a low hardness tread rubber layer, and the thickness of the tread rubber layer is changed from the both ends in the tire width direction to the center side of each land portion. As the base rubber layer of high hardness is made thicker from the center side in the tire width direction toward both ends of each land part, the land part collapses on the basis of the hard base rubber layer. Can be prevented and excellent steering stability can be exhibited. On the other hand, the thickness of the low-tread tread rubber layer is increased from both ends in the tire width direction toward the center of each land portion, so the input from the road surface is eased and road noise is suppressed. be able to. As a result, road noise can be reduced without deteriorating steering stability.

  In the present invention, the difference between the hardness of the base rubber layer and the hardness of the tread rubber layer is preferably 5 or more. Thereby, the effect of reducing road noise can be sufficiently obtained.

  The maximum thickness of the tread rubber layer in each land portion is preferably set in a range of 40% to 70% of the depth of the circumferential groove adjacent to the land portion. This makes it possible to achieve both steering stability and road noise at a higher level.

  The maximum thickness of the tread rubber layer is preferably decreased from the land portion located on the tread center side toward the land portion located on the shoulder side. In particular, when a region inside the pair of circumferential grooves positioned on the outermost side in the tire width direction is a center region, and a region outside the tire width direction than the center region is a shoulder region, a land portion included in the center region It is preferable that the maximum thickness of the tread rubber layer is 1.2 times to 1.5 times the maximum thickness of the tread rubber layer in the land portion included in the shoulder region. In other words, since the load is more likely to be applied to the shoulder region than the center region when the vehicle is turning, the rigidity of the land portion of the shoulder region is reduced by relatively reducing the maximum thickness of the tread rubber layer in the land portion of the shoulder region. It is possible to improve the steering stability while maintaining the effect of reducing road noise by making it relatively higher than the rigidity of the land portion.

  In the present invention, the hardness means durometer hardness defined in JIS-K6253, and is measured using an A type thurometer.

  In the present invention, the center region and the shoulder region are regions defined in the ground contact region. The contact area is an area on the tire circumference defined by the contact width. The contact width is the maximum linear distance in the tire axial direction at the contact surface with the plane when the tire is placed in a normal rim and the normal internal pressure is filled and the tire is placed perpendicular to the plane and a normal load is applied. It is. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. Then, “Measuring Rim” is set. “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFRATION PRESURES”, “INFLATION PRESURE” for ETRTO, but 180 kPa when the tire is a passenger car. “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFORMATION PRESURES”, “LOAD CAPACITY” if it is ETRTO, and a load corresponding to 88% of the load when the tire is a passenger car.

1 is a meridian cross-sectional view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. It is a perspective sectional view which expands and shows the land part in FIG. It is sectional drawing which expands and shows the land part in FIG. The modification of the basic rubber layer and tread rubber layer which comprise a land part in this invention is shown, (a)-(d) is sectional drawing of each modification.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 to 3 show a pneumatic tire according to an embodiment of the present invention.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and forms an annular shape. The pneumatic tire includes a pair of sidewall portions disposed on both sides of the tread portion 1 and a pair of bead portions disposed on the inner side in the tire radial direction of the sidewall portions, but is omitted here. ing.

  The tread portion 1 includes a carcass layer 2 mounted between a pair of bead portions, a belt layer 3 disposed on the outer peripheral side of the carcass layer 2, and a belt cover disposed on the outer peripheral side of the belt layer 3. Layer 4 is buried. The belt layer 3 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and is disposed so that the reinforcing cords cross each other between the layers. In the belt layer 3, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of 10 ° to 40 °, for example. On the other hand, the belt cover layer 4 has a structure in which reinforcing cords are arranged at an angle of 5 ° or less with respect to the tire circumferential direction. The belt cover layer 4 preferably has a jointless structure in which at least one reinforcing cord is aligned and rubber-coated strip material is continuously wound in the tire circumferential direction. As the reinforcing cord of the belt cover layer 4, an organic fiber cord such as nylon or aramid is preferably used.

  The tread portion 1 is formed with a plurality of circumferential grooves 5 extending in the tire circumferential direction, and a plurality of rows of land portions 6 are partitioned by the circumferential grooves 5. The land portion 6 may be a rib continuous in the tire circumferential direction, or may be composed of a plurality of blocks divided by lateral grooves extending in the tire width direction.

  In the pneumatic tire, two types of rubber compositions having different hardnesses are used for the cap tread rubber layer of the tread portion 1. That is, as shown in FIG. 2, each land portion 6 includes a base rubber layer 7 located on the inner side in the tire radial direction and a tread rubber layer 8 located on the outer side in the tire radial direction. 8 is laminated. The base rubber layer 7 is made of a rubber composition having a relatively high hardness, and the tread rubber layer 8 is made of a rubber composition having a relatively low hardness. And the thickness of the tread rubber layer 8 is increasing from the both ends side of the tire width direction of each land part 6 toward the center side.

  In the pneumatic tire described above, each land portion 6 of the tread portion 1 has a laminated structure of a high hardness base rubber layer 7 and a low hardness tread rubber layer 8, and the thickness of the tread rubber layer 8 is set to each land portion 6. Are gradually increased from both ends in the tire width direction toward the center, and accordingly, the hard rubber base layer 7 is gradually thickened from the center in the tire width direction toward the both ends of each land portion 6. . That is, the high-hardness base rubber layer 7 protrudes outward in the tire radial direction at both ends in the tire width direction of each land portion 6 so as to receive the low-tread tread rubber layer 8. Therefore, it is possible to prevent the land portions 6 from falling on the basis of the high hardness basic rubber layer 7 and to exhibit excellent steering stability.

  On the other hand, since the thickness of the low-tread tread rubber layer 8 is increased from the both ends in the tire width direction toward the center of each land portion 6, the input from the road surface is eased and road noise is generated. Can be suppressed. As a result, road noise can be reduced without deteriorating steering stability.

  In the pneumatic tire, the hardness of the rubber composition constituting the base rubber layer 7 and the tread rubber layer 8 can be selected from the range of 61 to 75. The hardness of the base rubber layer 7 and the tread rubber layer 8 can be selected. The difference from the hardness is set to 5 or more, preferably 5 to 12, more preferably 5 to 10. By setting the difference between the hardness of the base rubber layer 7 and the hardness of the tread rubber layer 8 as described above, the effect of reducing road noise can be sufficiently obtained. If the difference in hardness between the two is less than 5, the effect of reducing road noise is reduced. Further, if the difference in hardness between the two is excessive, uneven wear resistance will be a factor.

  As shown in FIG. 3, the maximum thickness T of the tread rubber layer 8 in each land portion 6 is set in a range of 40% to 70% of the depth GD of the circumferential groove 5 adjacent to the land portion 6. . This makes it possible to achieve both steering stability and road noise at a higher level. If the maximum thickness T of the tread rubber layer 8 is less than 40% of the depth GD of the circumferential groove 5, the effect of reducing road noise is reduced, and conversely if it exceeds 70%, steering stability is reduced. .

  In FIG. 1, the maximum thickness T of the tread rubber layer 8 gradually decreases from the land portion 6 (6A) located on the tread center side toward the land portion 6 (6C) located on the shoulder side. Thus, by making the maximum thickness T of the tread rubber layer 8 in the land portion 6C in the shoulder region relatively small, the rigidity of the land portion 6C in the shoulder region is relatively larger than the rigidity of the land portion 6A in the center region. The steering stability can be improved while maintaining a high road noise reduction effect.

  In particular, when a region inside the pair of circumferential grooves 5 positioned at the outermost side in the tire width direction is a center region Ace and a region outside the tire width direction from the center region Ace is a shoulder region Ash, the center region Ace The maximum thickness T of the tread rubber layer 8 in the land portion 6 (6A, 6B) included in the land portion 6 (6C) is 1.2 times the maximum thickness T of the tread rubber layer 8 in the land portion 6 (6C) included in the shoulder region Ash. It is good that it is 1.5 times. Thereby, the reduction effect of road noise and the improvement effect of steering stability can be enjoyed to the maximum extent. Here, the relationship between the maximum thickness T of the tread rubber layer 8 in the land portion 6 (6A, 6B) of the center region Ace and the maximum thickness T of the tread rubber layer 8 in the land portion 6 (6C) of the shoulder region Ash is as follows. If it is out of the above range, either the road noise reduction effect or the steering stability improvement effect will be reduced.

  FIGS. 4A to 4D show modifications of the basic rubber layer and the tread rubber layer constituting the land portion in the present invention, respectively. That is, in FIG. 3, the cross-sectional shape of the tread rubber layer 8 in the tire meridian cross section is an inverted triangle. For example, as shown in FIGS. 4 (a) to 4 (c), the basic rubber layer 7 and the tread rubber layer It is also possible to make the boundary surface with 8 a curved surface, or to make the cross-sectional shape of the tread rubber layer 8 in the tire meridian cross section into an inverted trapezoidal shape as shown in FIG.

  In a pneumatic tire having a tire size of 195 / 65R15, provided with four circumferential grooves extending in the tire circumferential direction in the tread portion, and partitioning five rows of land portions by these circumferential grooves, each land portion of the tread portion is a tire. A laminated structure consisting of a base rubber layer positioned radially inside and a tread rubber layer positioned radially outside, and the thickness of the tread rubber layer is increased from both ends of the land in the tire width direction toward the center. , The hardness of the tread rubber layer, the hardness of the base rubber layer, the ratio of the maximum thickness Tce of the tread rubber layer in the land portion closest to the tread center and the depth GD of the circumferential groove adjacent to the land portion (Tce / GD × 100%), ratio of the maximum thickness Tce of the tread rubber layer in the land portion closest to the tread center side to the maximum thickness Tsh of the tread rubber layer in the land portion closest to the shoulder (Tc) / Tsh × 100%) was manufactured tire of Comparative Example 1 and Examples 1-5 were set as shown in Table 1.

  For comparison, tires of Conventional Example 1 were prepared in which all land portions were composed of a rubber composition having a high hardness (hardness = 70). Further, the tire of Conventional Example 2 in which the land portion in the center region is composed of a low-hardness rubber composition (hardness = 64) while the land portion in the shoulder region is composed of a high-hardness rubber composition (hardness = 70). Prepared.

  These test tires were evaluated for steering stability and road noise by the following evaluation methods, and the results are also shown in Table 1.

Steering stability:
Each test tire was assembled on a wheel with a rim size of 15 × 6 JJ and mounted on a test vehicle, and sensory evaluation was performed with respect to steering stability by a test driver under the condition of an air pressure of 230 kPa. The evaluation results are shown as an index with Conventional Example 1 as 100. The larger the index value, the better the steering stability.

Road noise:
Each test tire was assembled on a wheel with a rim size of 15 × 6 JJ and mounted on a test vehicle, and sensory evaluation was performed by a test driver for road noise during running under the condition of an air pressure of 230 kPa. The evaluation results are shown as an index with Conventional Example 1 as 100. A larger index value means less road noise.

  As can be seen from Table 1, compared to the tire of Conventional Example 1 in which all the land portions are composed of a high-hardness rubber composition, the land portion in the center region is composed of a low-hardness rubber composition, while the shoulder region In the tire of Conventional Example 2 in which the land portion is made of a rubber composition having a high hardness, although the improvement effect of road noise is recognized, the steering stability is lowered.

  In contrast, the tires of Examples 1 to 5 were able to reduce road noise while maintaining steering stability in comparison with Conventional Example 1. Further, in the tire of Comparative Example 1, since the hardness relationship between the base rubber layer and the tread rubber layer is opposite to that in Examples 1 to 5, the steering stability and the road noise were both deteriorated.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Carcass layer 3 Belt layer 4 Belt cover layer 5 Circumferential groove 6 Land part 7 Base rubber layer 8 Tread rubber layer

Claims (5)

  In a pneumatic tire in which at least one circumferential groove extending in the tire circumferential direction is provided in the tread portion and a plurality of rows of land portions are partitioned by the circumferential groove, each land portion of the tread portion is positioned on the inner side in the tire radial direction. And a tread rubber layer positioned on the outer side in the tire radial direction, the base rubber layer is made of a rubber composition having a relatively high hardness, and the tread rubber layer has a relatively low hardness. A pneumatic tire comprising a rubber composition, wherein the thickness of the tread rubber layer is increased from both ends in the tire width direction toward the center of each land portion.   The pneumatic tire according to claim 1, wherein the difference between the hardness of the base rubber layer and the hardness of the tread rubber layer is 5 or more.   The air according to claim 1 or 2, wherein a maximum thickness of the tread rubber layer in each land portion is set in a range of 40% to 70% of a depth of a circumferential groove adjacent to the land portion. Enter tire.   The pneumatic according to any one of claims 1 to 3, wherein the maximum thickness of the tread rubber layer is decreased from the land portion located on the tread center side toward the land portion located on the shoulder side. tire.   When a region inside the pair of circumferential grooves located on the outermost side in the tire width direction is a center region, and a region outside the tire width direction than the center region is a shoulder region, in the land portion included in the center region The maximum thickness of the tread rubber layer is set to 1.2 to 1.5 times the maximum thickness of the tread rubber layer in the land portion included in the shoulder region. The described pneumatic tire.

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