JP4812015B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire provided with shoulder rubber disposed on both sides of a center rubber in the tire width direction on the tread surface while communicating below the center rubber.

  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 a loss tangent tan δ (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 high elastic rubber is disposed near the tire equator line of the tread rubber and a low elastic rubber is disposed near the 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 to reduce energy consumption of tread rubber and reduce rolling resistance. It is. Further, 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. It was also found that the tan δ of the tread rubber in the center portion was low and the dry braking performance was not sufficient.

  Moreover, since the pneumatic tire according to Patent Document 2 has a tread rubber having a small tan δ at 60 ° C. disposed on the shoulder portion, the deformation energy cannot be consumed as a braking force in the shoulder portion where the load increases during braking. It was found that WET braking performance deteriorates.

  In other words, 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.

  On the other hand, as in Patent Documents 1 and 2, in the structure in which the tread rubber is divided in the tire width direction (not in the tread thickness direction), the balance of tan δ cannot be changed in the vertical direction. Therefore, there is a limit in achieving both rolling resistance performance and dry braking performance.

  Patent Document 3 discloses a structure in which the tread rubber of the studless tire is divided in the thickness direction and the shoulder rubbers on both sides communicate with each other below the center rubber. It is not intended to achieve both rolling resistance performance and dry braking performance.

Japanese Patent Laid-Open No. 7-164821 JP 2003-226114 A JP-A-60-135309

  Accordingly, an object of the present invention is to provide a pneumatic tire that can satisfy all of the rolling resistance performance, the WET braking performance, and the dry braking performance by providing the divided tread.

The above object can be achieved by the present invention as described below.
That is, the pneumatic tire according to the present invention is 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 portions in the tire width direction on the tread surface, and communicates with a center rubber disposed in the center portion in the tire width direction on the tread surface and below the center rubber. However, the tread surface is provided with shoulder rubber disposed on both sides of the center rubber in the tire width direction , the loss tangent tan δ at 60 ° C. of the center rubber is 0.16 or more, and at 60 ° C. of the shoulder rubber. the loss tangent tanδ of is 0.15 or less, a loss tangent tanδ at 0 ℃ of the shoulder rubber is 0.7 or more, before Absolute modulus at 25 ° C. of the center rubber | E * | is rather greater than the value of the shoulder rubber, the absolute modulus at 25 ° C. of shoulder rubber | E * | is equal to or less than 9 MPa. In addition, the physical property value such as tan δ in the present invention is specifically a value measured by the measurement method of the example.

  According to the pneumatic tire of the present invention, by placing a shoulder rubber having a large tan δ at 60 ° C. on the grounded end side of the tread portion where the surface pressure during braking is high, the wet braking performance utilizing the viscoelastic characteristics of the rubber is provided. Can be increased. At that time, by making the absolute elastic modulus of the shoulder rubber smaller than that of the center rubber, the buckling of the pattern block can be suppressed and the WET braking performance can be improved more reliably. Also, by making the loss tangent tan δ of the center rubber at 60 ° C. larger than the value of the shoulder rubber, it is possible to suppress the loss of the shoulder portion that easily affects the rolling resistance, and the loss of the center portion that easily affects the dry braking performance. By increasing the rolling force, it is possible to achieve both rolling resistance performance and dry braking performance. Furthermore, by adopting a structure in which shoulder rubbers on both sides are communicated below the center rubber, tan δ below the center portion is reduced, so that both rolling resistance performance and dry braking performance can be achieved. As a result, it is possible to satisfy all of the rolling resistance performance, the WET braking performance, and the dry braking performance.

  In the above, the loss tangent tan δ at 0 ° C. of the center rubber is preferably smaller than the value of the shoulder rubber. By increasing the loss tangent tan δ at 0 ° C. of the shoulder rubber that easily affects the WET braking performance, the WET braking performance can be further improved.

  From the above viewpoint, the loss tangent tan δ at 60 ° C. of the center rubber is 0.16 or more, the loss tangent tan δ at 60 ° C. of the shoulder rubber is 0.15 or less, and 0 ° C. of the shoulder rubber. Loss tangent tan δ is 0.7 or more, and the absolute elastic modulus | E * | at 25 ° C. of the shoulder rubber is preferably 9 MPa or less.

  Moreover, it is preferable that the thickness of the shoulder rubber communicated under the center rubber is 1.0 to 3.0 mm on average. Within this thickness range, the effect of changing the physical properties by dividing the tread in the tire width direction can be sufficiently obtained, and both the rolling resistance performance and the dry braking performance can be more reliably achieved.

  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 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 disposed in the tread portion 1 is divided into at least three parts in the tire width direction on the tread surface 9a. The tread rubber 9 communicates with the center rubber 7 disposed in the center in the tire width direction on the tread surface 9a, and is disposed on both sides of the center rubber 7 in the tire width direction on the tread surface 9a while communicating below the center rubber 7. Shoulder rubber 8. In the present embodiment, an example is shown in which a cap base structure including a base rubber 9b at the bottom of the tread rubber 9 is employed.

  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. Further, the boundary 10 is preferably disposed on the bottom surface or side surface of the circumferential groove 11 formed in the tread portion 1. If the boundary 10 is present on the land surface 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 average thickness of the communicating portion 8a of the shoulder rubber 8 disposed below the center rubber 7 is preferably 1.0 to 3.0 mm, and the average value is 2.0 to 2.5 mm. More preferred. When the thickness of the communicating portion 8a of the shoulder rubber 8 is less than 1.0 mm, it tends to be difficult to achieve both rolling resistance performance and dry braking performance. When the thickness of the communicating portion 8a exceeds 3.0 mm The effect of changing the physical properties by dividing the tread in the tire width direction tends to be insufficient.

  In the present invention, the loss tangent tan δ at 60 ° C. of the center rubber 7 is larger than the value of the shoulder rubber 8, and the loss tangent tan δ at 60 ° C. of the center rubber 7 is 1.1 to 1.5 times the value of the shoulder rubber 8. Is preferred.

  Specifically, the loss tangent tan δ at 60 ° C. of the center rubber 7 is preferably 0.16 or more, and more preferably 0.17 or more. If the loss tangent tan δ at 60 ° C. of the center rubber 7 is smaller than 0.16, the dry braking performance tends to be lowered. Further, the loss tangent tan δ at 60 ° C. of the shoulder rubber 8 is preferably 0.15 or less, and more preferably 0.14 or less. If the loss tangent tan δ at 60 ° C. of the shoulder rubber 8 is larger than 0.15, the rolling resistance performance tends to be lowered.

  Also, the absolute elastic modulus | E * | at 25 ° C. of the center rubber 7 is larger than the value of the shoulder rubber 8, and the absolute elastic modulus | E * | 1 to 1.5 times is preferable.

  Specifically, the absolute elastic modulus | E * | at 25 ° C. of the center rubber 7 is preferably 9.5 MPa or more, and more preferably 10.3 MPa or more. Further, the absolute elastic modulus | E * | at 25 ° C. of the shoulder rubber 8 is preferably 9 MPa or less, and more preferably 8 MPa or less. When the absolute elastic modulus | E * | at 25 ° C. of the shoulder rubber 8 is larger than 9 MPa, the WET braking performance tends to be lowered.

  Further, the loss tangent tan δ at 0 ° C. of the center rubber 7 is smaller than the value of the shoulder rubber 8, and the loss tangent tan δ at 0 ° C. of the center rubber 7 is preferably 0.7 to 0.9 times the value of the shoulder rubber 8. .

  Specifically, the loss tangent tan δ at 0 ° C. of the center rubber 7 is preferably 0.6 or less, and more preferably 0.55 or less. The loss tangent tan δ at 0 ° C. of the shoulder rubber 8 is preferably 0.7 or more, and more preferably 0.75 or more. When the loss tangent tan δ at 0 ° C. of the shoulder rubber 8 is smaller than 0.7, the WET braking performance tends to be lowered.

  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 at 60 ° C. can be easily adjusted by the amount of silica blended. Further, tan δ at 0 ° C. can be easily adjusted by the natural rubber ratio or the like.

  In particular, as a method of increasing tan δ at 60 ° C. and decreasing tan δ at 0 ° C., it is effective to increase the amount of silica. The absolute elastic modulus at 25 ° C. can be easily adjusted by the amount of silica blended.

[Other Embodiments]
(1) In the above-described embodiment, an example in which the tread rubber has the cap / base structure has been shown. However, the tread rubber 9 of the present invention may have a structure without the base rubber 9b as shown in FIG. In that case, a two-layer structure of a center rubber 7 and a communicating portion 8 a of a shoulder rubber 8 disposed below the center rubber 7 is provided, and this is disposed on the upper surface of the belt layer 5.

  (2) In the above-described embodiment, an example in which the tread rubber is divided into three in the tire width direction on the tread surface is shown. However, the tread rubber of the present invention is not limited to three, and for example, as shown in FIG. You may divide into 5 parts on the tread surface.

  In the case of the pneumatic tire shown in FIG. 3, an intermediate rubber 12 is disposed between the center rubber 7 and the shoulder rubber 8. The physical properties of the intermediate rubber 12 are preferably intermediate physical properties between the center rubber 7 and the shoulder rubber 8 in order to improve rolling resistance performance, WET braking performance, and dry braking performance. 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 the one having a specific tread pattern, and any conventionally known pattern can be adopted.

  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 * |
For tan δ at 0 ° C. and 60 ° C. and absolute elastic modulus | E * | at 25 ° C., using a spectrometer tester manufactured by Iwamoto Seisakusho, initial elongation rate is 10%, excitation strain rate is ± 2%, temperature is 0 The measurement was performed under conditions of ˜60 ° C. and a frequency of 10 Hz. A test strip having a strip shape of 5 mm width × 1 mm thickness was prepared, and the grip length was 20 mm.

(2) Rolling resistance performance After assembling a prototype tire described later on a rim of size 16 × 6.5JJ, the inner pressure was filled with 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 Comparative Example 1 as 100. The smaller the index, the smaller the rolling resistance.

(3) WET braking performance After mounting a prototype tire, which will be described later, on a rim of size 16 x 6.5 JJ, it was filled with an internal pressure of 210 kPa, mounted on a real vehicle, and braked after running on a water resistant road surface with an average water depth of 1 mm at a speed of 100 km / h. To measure the braking distance. The WET braking performance was evaluated by an index with the braking distance in Comparative Example 1 as 100. The smaller the index, the better the WET braking performance.

(4) Dry braking performance After mounting a prototype tire, which will be described later, on a rim of size 16 x 6.5 JJ, it is filled with an internal pressure of 210 kPa and mounted on an actual vehicle. After driving on a dry road surface at a speed of 100 km / h, braking is applied. The distance was measured. The dry braking performance was evaluated by an index with the braking distance in Comparative Example 1 as 100. The smaller the index, the better the WET braking performance.

Example 1
In accordance with the structure shown in FIG. 1, prototype tires of size 215 / 65R16 98S were manufactured, and snow handling stability and WET braking performance were evaluated. The tread rubber included 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 0.6 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. The shoulder rubber communicating portion was 2.5 mm thick, the base rubber thickness was 2.0 mm, and the base rubber JISA hardness was 56 °.

Example 2
In Example 1, a prototype tire was produced in the same manner as in Example 1 except that the center rubber example 2 was used as the center rubber so that the tan δ at 0 ° C. of the center rubber and the shoulder rubber became substantially equal.

Comparative Example 1
The size and structure of the prototype tire are the same as in Example 1 (however, a two-layer structure of center rubber and base rubber is provided without providing a shoulder rubber communicating portion), and the tread rubber is manufactured with the formulation shown in Table 1. The center rubber run 1 was used as center rubber and shoulder rubber.

Comparative Example 2
The size and structure of the prototype tire are the same as in Example 1 (however, a two-layer structure of center rubber and base rubber is provided without providing a shoulder rubber communicating portion), and the tread rubber is manufactured with the formulation shown in Table 1. The shoulder rubber run 1 was used as the center rubber and shoulder rubber.

Comparative Example 3
A prototype tire was produced in the same manner as in Example 1 except that the shoulder rubber communicating portion was not provided and a two-layer structure of center rubber and base rubber was used.

Comparative Example 4
In Example 1, a prototype tire was produced in the same manner as in Example 1 except that the center rubber example 1 was used as a center rubber and a shoulder rubber.

Comparative Example 5
In Example 1, a prototype tire was produced in the same manner as in Example 1 except that the shoulder rubber example 1 was used as the center rubber and the shoulder rubber.

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 (4).

  As the results of Examples 1 and 2 in Table 2 show, the pneumatic tire according to the present invention can satisfy all of the rolling resistance performance, the WET braking performance, and the dry braking performance.

On the other hand, in Comparative Examples 1 and 4, the tan δ at 60 ° C. of the shoulder rubber is large, so that the rolling resistance performance is deteriorated. The tan δ at 0 ° C. of the shoulder rubber is small, and the WET braking performance is deteriorated. Due to the large | E * | of the rubber, the WET braking performance deteriorated.
In Comparative Examples 2 and 5, dry braking performance deteriorated because | E * | of the center rubber was small. In Comparative Example 3, since the shoulder rubber communication portion was not provided, the rolling resistance performance deteriorated.

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 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 8a Shoulder rubber communication part 9 Tread rubber 9a Tread rubber surface 9b Base rubber C Tire equator line K Ground end W From tire equator line C to ground end K Distance of

Claims (3)

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 portions in the tire width direction on the tread surface, and communicates with a center rubber disposed in the center portion in the tire width direction on the tread surface and below the center rubber. While the tread surface comprises shoulder rubber disposed on both sides of the center rubber in the tire width direction,
The loss tangent tan δ at 60 ° C. of the center rubber is 0.16 or more, and the loss tangent tan δ at 60 ° C. of the shoulder rubber is 0.15 or less.
The loss tangent tan δ at 0 ° C. of the shoulder rubber is 0.7 or more,
Characterized in that is less than 9 MPa | absolute modulus at 25 ° C. of the center rubber | E * | is the rather greater than the value of the shoulder rubber, absolute modulus at 25 ° C. of the shoulder rubber | E * Pneumatic tire.   The pneumatic tire according to claim 1, wherein a loss tangent tan δ of the center rubber at 0 ° C is smaller than a value of the shoulder rubber. The pneumatic tire according to claim 1 or 2 , wherein a thickness of the shoulder rubber communicating below the center rubber is an average value of 1.0 to 3.0 mm .

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