JP4566788B2 - Pneumatic tires for passenger cars - Google Patents

Description

The present invention relates to a pneumatic tire for a passenger car that has both rolling resistance performance and WET braking performance by providing a divided tread.

  Conventionally, in a pneumatic tire, in order to achieve both rolling resistance performance and WET performance, the tread rubber is divided into a plurality of regions in the tire width direction, and the loss tangent tanδ (loss tangent = loss tangent = The loss elastic modulus / storage elastic modulus (hereinafter abbreviated as tan δ) is appropriately set.

  For example, Patent Document 1 below proposes a pneumatic tire in which a highly elastic rubber is disposed near the tire equator line of a tread rubber and a low elastic rubber is disposed near a shoulder portion, and each tan δ is substantially the same. The above tires reduce distortion near the tire equator line with high elastic rubber and reduce stress near the shoulder with low elastic rubber, thereby reducing tread rubber energy consumption and rolling resistance. It is. Furthermore, by setting tan δ to be substantially the same, it is possible to avoid a decrease in WET performance due to a difference in elastic modulus.

  Patent Document 2 below proposes a pneumatic tire in which the tan δ at 0 ° C. of the tread rubber near the tire equator line is 0.6 or more and the tan δ at 60 ° C. of the tread rubber of the shoulder portion is 0.2 or less. ing. The tire is based on the knowledge that the larger the tan δ at 0 ° C. of the tread rubber, the better the wet drainage, and the smaller the tan δ at 60 ° C., the better the rolling resistance performance. Therefore, it is intended to achieve both wet drainage and rolling resistance performance.

  However, it has been found that the pneumatic tire according to Patent Document 1 has a low tan δ of the tread rubber of the shoulder portion and has insufficient WET braking performance. Moreover, since it is necessary to set the tan δ near the tire equator line and the shoulder portion substantially the same, if the tan δ at the shoulder portion is set high, it is necessary to set the tan δ near the tire equator line as well, and the rolling resistance performance It becomes difficult to achieve both WET braking performance.

  Moreover, since the pneumatic tire according to Patent Document 2 is such that a tread rubber having a large tan δ is disposed in the vicinity of the tire equator line, a tread rubber having an insufficient rolling resistance performance and a small tan δ is disposed in the shoulder portion. Therefore, it was found that the WET braking performance deteriorates.

Furthermore, in the tire behavior of an actual vehicle, particularly when a large load movement and braking force are applied to the front wheels during braking when the ABS is activated, the tire pattern block is likely to buckle, and the actual contact area between the road surface and the block is reduced. Therefore, the viscoelastic properties of rubber may not be utilized. Therefore, it has been found that the setting of the rubber tan δ alone is insufficient to improve the WET braking performance. Then, it was found that the buckling phenomenon of the tire pattern block is caused because the contact pressure at the end in the width direction within the tire contact area rapidly increases compared to the steady rolling state as a result of instantaneous load movement. ing.
Japanese Patent Application Laid-Open No. 7-164821 (second page, FIG. 1) Japanese Patent Laying-Open No. 2003-226114 (second page, FIG. 1)

Therefore, an object of the present invention is to provide a pneumatic tire for a passenger car that can achieve both rolling resistance performance and WET braking performance by providing a divided tread.

The above object can be achieved by the present invention as described below. That is, the pneumatic tire for a passenger car according to the present invention includes a pair of bead portions, sidewall portions extending outward in the tire radial direction from the bead portions, and a tread portion provided between the sidewall portions. In the tire, the tread rubber disposed in the tread portion is divided into at least three parts in the tire width direction, and is disposed on the center rubber disposed in the center portion in the tire width direction and on both sides of the center rubber in the tire width direction. A loss tangent tan δ at 60 ° C. of the center rubber is 0.10 or less, a loss tangent tan δ at 0 ° C. of the shoulder rubber is 0.62 to 0.80 , The ratio of the absolute elastic modulus | E * | at 25 ° C. of the shoulder rubber to the center rubber (shoulder rubber / center rubber) is 1.0 to 1. 2 is a feature. In addition, the physical property values such as tan δ in the present invention are specifically values measured by the measurement methods of the examples.

  According to the pneumatic tire of the present invention, the rolling resistance can be reduced by disposing the center rubber having a small tan δ in the center portion (near the tire equator line) of the tread portion that consumes a large amount of energy during steady running. . Further, by placing a shoulder rubber having a large tan δ on the ground contact end side of the tread portion where the surface pressure during braking is high, the wet braking performance can be enhanced by utilizing the viscoelastic characteristics of the rubber. At that time, by setting the balance of the absolute elastic modulus of the center rubber and the shoulder rubber within a predetermined range, buckling of the pattern block can be suppressed and the WET braking performance can be more reliably improved. Therefore, it is possible to achieve both rolling resistance performance and WET braking performance.

  In the above, the tread rubber is divided into three in the tire width direction, and the boundary between the center rubber and the shoulder rubber is from the tire equator line toward the outer side in the tire width direction, and from the tire equator line to the grounding of the tread portion. Those having a distance of 0.5 to 0.8 times the distance to the end are preferred.

  By adopting the above configuration, a shoulder rubber having relatively high rigidity and a large tan δ can be suitably disposed on the ground contact end side of the tread portion having a high surface pressure during braking. In addition, since the center rubber having a small tan δ is disposed outside the region where the shoulder rubber is disposed in the tread rubber, the rolling resistance of the tire can be effectively reduced. Here, the ground contact edge is the both sides that contact the flat road surface when the tire is mounted on the applicable rim, the internal pressure is 180 kPa, and a mass equivalent to 88% of the maximum load capacity of the displayed tire is loaded. Points to the outermost position.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a half sectional view showing an example of the pneumatic tire of the present invention. As shown in FIG. 1, the pneumatic tire of the present invention includes a pair of bead portions 3, a sidewall portion 2 that extends outward from the bead portion 3 in the tire radial direction, and a tread portion 1 provided between the sidewall portions 2. With. This structure is the same as that of a general tire, and the present invention can be applied to any tire having the structure.

  The carcass layer 6 is disposed between the pair of bead portions 3. The carcass layer 6 is a radial carcass formed from one layer obtained by rubberizing a cord such as polyester, and a rubber layer is formed outside the carcass layer 6 in the tire width direction. In the tubeless tire, the inner liner layer 4 is formed as the innermost layer. A belt layer 5 that reinforces the tire effect is disposed on the outer side in the tire radial direction of the carcass layer 6, and a tread portion 1 is formed on the outer side in the tire radial direction of the belt layer 5. The belt layer 5 is formed by laminating two layers of rubberized steel cords arranged in parallel at an inclination angle of about 20 ° with respect to the tire equator line C so that the steel cords intersect with each other across the tire equator line C. The

  Examples of the raw material of the tread rubber 9 forming the tread portion 1 include natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), butyl rubber (IIR) and the like. These rubbers are reinforced with fillers such as carbon black and silica, and a vulcanizing agent, a vulcanization accelerator, a plasticizer, an antiaging agent, and the like are appropriately blended.

  The tread rubber 9 is divided into three parts, that is, a center rubber 7 disposed in the center portion and shoulder rubbers 8 disposed on both sides of the center rubber 7 in the tire width direction. A boundary 10 between the center rubber 7 and the shoulder rubber 8 is 0.5 to 0.8 of a distance W from the tire equator line C to the ground contact end K of the tread portion 1 from the tire equator line C toward the outer side in the tire width direction. It is preferable that the distance is double. Furthermore, the boundary 10 is preferably arranged on the bottom surface or side surface of the circumferential groove 11 formed in the tread portion 1. This is because if the boundary 10 is present on the surface of the land portion of the tread portion 1, uneven wear may occur at that portion due to a difference in rubber quality or a difference in rigidity.

  The tan δ at 60 ° C. of the center rubber 7 is set to 0.10 or less, and a more preferable range is 0.05 to 0.09. If the tan δ at 60 ° C. of the center rubber 7 is 0.10 or more, the hysteresis loss increases and the rolling resistance increases, which is not preferable.

The tan δ at 0 ° C. of the shoulder rubber 8 is set to 0.60 or more, and the range in the present invention is 0.62 to 0.80. If tan δ at 0 ° C. of the shoulder rubber 8 is less than 0.60, the deformation energy cannot be consumed by the braking force, so that the braking performance is deteriorated.

  Furthermore, the ratio of the absolute elastic modulus | E * | at 25 ° C. of the shoulder rubber 8 to the center rubber 7 (shoulder rubber 8 / center rubber 7) is set to 1.0 to 1.2, and a more preferable range is 1.05-1.20. When this ratio exceeds 1.20, the end portion contact pressure at the time of braking load increases, and the pattern block is likely to buckle, so that the braking performance is deteriorated. Conversely, when this ratio is less than 1.0, the tendency of the center rubber 7 to increase in rigidity and rolling resistance becomes significant.

  The rubber composition for having the above-mentioned physical properties is publicly known, and the formulations shown in the examples can be exemplified. In general, tan δ can be easily adjusted by the type of rubber, the blending amount of carbon, and the like, and the absolute elastic modulus can be easily adjusted by the blending amount of oils and the like.

[Other Embodiments]
(1) In the above-described embodiment, an example in which the tread rubber 9 is not divided in the tire radial direction is shown. However, the tread rubber 9 of the present invention has a base layer disposed between the tread rubber 9 and the belt layer 5. A cap / base structure may be used.

  (2) In the above-described embodiment, an example in which the tread rubber is divided into three in the tire width direction has been shown. It doesn't matter. In the case of the pneumatic tire shown in FIG. 2, an intermediate rubber 12 is disposed between the center rubber 7 and the shoulder rubber 8. The rolling resistance performance and WET braking performance of the intermediate rubber 12 are preferably intermediate performance between the center rubber 7 and the shoulder rubber 8. As a result, problems such as uneven wear of the tread rubber 9 can be avoided.

  (3) The pneumatic tire according to the present invention is not limited to one having a specific tread pattern.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

(1) tan δ, absolute elastic modulus | E * |
Using a spectrometer tester manufactured by Iwamoto Seisakusho, measurement was performed under the conditions of an initial elongation of 10%, an excitation strain of ± 2%, a temperature of 0 to 60 ° C., and a frequency of 10 Hz. A test strip having a strip shape of 5 mm width × 2 mm thickness was prepared, and the grip length was 20 mm.

(2) Rolling resistance performance After assembling a prototype tire, which will be described later, on a rim of size 15 × 5 · 1 / 2JJ, it was filled with an internal pressure of 210 kPa, and rolling resistance was measured according to the American Society of Automotive Engineers test method SAE J1269. . The rolling resistance performance was evaluated by an index with the rolling resistance in Example 1 as 100. The smaller the index, the smaller the rolling resistance.

(3) WET braking performance After assembling a prototype tire, which will be described later, on a rim of size 15 × 5 · 1 / 2JJ, it was filled with an internal pressure of 210 kPa and mounted on an actual vehicle, and traveled on a water resistant road surface with an average water depth of 1 mm at a speed of 100 km / h The braking distance was measured after braking. The WET braking performance was evaluated by an index with the braking distance in Example 1 as 100. The smaller the index, the better the WET braking performance.

Example 1
A prototype tire of size 195 / 65R15 was manufactured according to the structure shown in FIG. 1, and the rolling resistance performance and the WET braking performance were evaluated. The tread rubber provided in the prototype tire is divided into three in the tire width direction, and the boundary between the center rubber and the shoulder rubber is located at a position 0.57 times the distance W from the tire equator line toward the outer side in the tire width direction. Provided. As the tread rubber, a combination of the center rubber embodiment 1 manufactured with the composition shown in Table 1 and the shoulder rubber embodiment 1 was used.

Comparative Examples 1-3
The size and structure of the prototype tire were the same as in the examples, and the tread rubber used was a combination of the center rubber embodiment 1 or comparison 1 manufactured with the formulation shown in Table 1 and the shoulder rubber comparisons 1 and 2 in the same manner. .

  Table 1 shows the composition of the center rubber and shoulder rubber and the measurement results of the item (1), and Table 2 shows the measurement results of the items (2) to (3).

表２の実施例１の結果が示すように、本発明に係る空気入りタイヤによれば、転がり抵抗性能とＷＥＴ制動性能とを好適に両立させることができる。一方、比較例１はショルダーゴムのｔａｎδが低いためにＷＥＴ制動性能が十分でなく、比較例３はセンターゴムのｔａｎδが高いために転がり抵抗が悪化している。また、比較例２は絶対弾性率のショルダーゴム／センターゴムの比率が高いため、制動時にパターンブロックの座屈が抑制できず、ＷＥＴ制動性能が十分でない。

As shown in the results of Example 1 in Table 2, according to the pneumatic tire according to the present invention, it is possible to suitably achieve both the rolling resistance performance and the WET braking performance. On the other hand, the comparative example 1 has a low WET braking performance due to the low tan δ of the shoulder rubber, and the comparative example 3 has a poor rolling resistance due to the high tan δ of the center rubber. Further, in Comparative Example 2, the ratio of the absolute elastic shoulder rubber / center rubber is high, so that the pattern block buckling cannot be suppressed during braking, and the WET braking performance is not sufficient.

Half sectional view showing an example of the pneumatic tire of the present invention Half sectional view showing an example of the pneumatic tire of the present invention according to another embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 7 Center rubber 8 Shoulder rubber 9 Tread rubber C Tire equator line K Grounding edge W Distance from tire equator line C to grounding edge K

Claims (2)

In a pneumatic tire having a pair of bead portions, sidewall portions extending outward in the tire radial direction from the bead portions, and a tread portion provided between the sidewall portions,
The tread rubber disposed in the tread portion is divided into at least three parts in the tire width direction, a center rubber disposed in the center portion in the tire width direction, and shoulders disposed on both sides of the center rubber in the tire width direction. With rubber,
The loss tangent tan δ at 60 ° C. of the center rubber is 0.10 or less, the loss tangent tan δ at 0 ° C. of the shoulder rubber is 0.62 to 0.80 , and the shoulder rubber of the center rubber with respect to the center rubber A pneumatic tire for a passenger car having a ratio of absolute elastic modulus | E * | at 25 ° C. (shoulder rubber / center rubber) of 1.0 to 1.2. The tread rubber is divided into three in the tire width direction, and the boundary between the center rubber and the shoulder rubber extends from the tire equator line to the outer side in the tire width direction, from the tire equator line to the grounding end of the tread portion. The pneumatic tire for a passenger car according to claim 1 , wherein the pneumatic tire is at a distance 0.5 to 0.8 times the distance.

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