JP4643372B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that can improve ice braking performance without impairing wear performance and rolling resistance performance, and is therefore suitable as a studless tire.

  Conventionally, in a pneumatic tire, as a technique for improving ice braking performance, which is braking performance on an ice road surface, it is common to form a cap rubber layer of a tread rubber portion with a rubber compound having a low rubber hardness. . However, with this method, although the ice braking performance is improved, it is predicted that the wear performance and the rolling resistance performance are greatly deteriorated.

  Incidentally, in Japanese Patent Laid-Open No. 2002-240510 (Patent Document 1), in order to achieve both noise reduction and steering stability, the hardness of the base rubber layer of the tread rubber portion is set to be higher than the hardness of the cap rubber layer. Therefore, it has been proposed to set tan δ of the base rubber layer at 50 ° C. or higher to be larger than tan δ of the cap rubber layer.

  Japanese Patent Application Laid-Open No. 2000-185520 (Patent Document 2) discloses a cap rubber layer and a base rubber layer of a tread rubber portion in order to improve heat generation durability and suppress a decrease in wetness at the end of wear of a tire. Tan δ of the base rubber layer at 0 ° C. is set larger than tan δ of the cap rubber layer, and tan δ of the base rubber layer at 100 ° C. is higher than tan δ of the cap rubber layer. It has been proposed to set a smaller value.

  Japanese Patent Laid-Open No. 8-230212 (Patent Document 3) discloses that a base rubber layer is divided into a center base portion and a side base portion in order to improve noise and steering stability performance without impairing rolling resistance performance. In addition, the tan δ and the hardness between them are defined. In particular, for tan δ, it is proposed that cap rubber layer ≧ side base portion> center base portion.

  In these patent documents, it is disclosed that the base rubber layer of the tread rubber portion or a part thereof is set to be larger than the general loss tangent (tan δ) of the conventional base rubber layer. In addition, there is no disclosure that the placement of rubber having a large tan δ in the base rubber layer contributes to the improvement of braking performance, particularly ice braking performance on the road surface on ice.

On the other hand, Japanese Patent Application Laid-Open No. 2003-127613 (Patent Document 4) discloses that the shoulder portion is set thicker than the tread center portion with respect to the thickness of the base rubber layer in the tread rubber portion. However, Patent Document 4 increases the thickness of the base rubber layer on both sides in the tread width direction as described above in order to suppress heat generated by the movement of the outer end of the belt layer and heat generation in the thick tread shoulder portion. It ’s just that.
JP 2002-240510 A JP 2000-185520 A JP-A-8-230212 JP 2003-127613 A

  In the present invention, by setting tan δ of the base rubber layer of the tread rubber portion within a predetermined range with respect to the cap rubber layer, the thickness of the base rubber layer is set to be thicker at the tread shoulder portion than at the tread center portion. An object of the present invention is to provide a pneumatic tire capable of improving the ice braking performance without lowering the anti-reverse performance such as wear performance and rolling resistance performance.

  The present inventor has considered that the energy required for braking on the road surface on ice, that is, the energy consumed during ice braking, is largely due to the loss energy due to rubber hysteresis. For this reason, a tire with a large difference between the loss energy during braking and the loss energy during steady load loading consumes a large amount of energy and is considered to improve braking performance. As a result of analyzing the loss energy, the portion where the loss energy is large is the base rubber layer of the tread provided on the outer side in the radial direction of the belt layer, and it is confirmed that the contribution of the energy loss rate particularly in the tread shoulder portion is large. I found it. Here, braking on an ice road surface has a smaller friction coefficient on the road surface than braking on a general road surface, and therefore the strain and stress distribution and size are different, so the contribution of the belt layer and the carcass layer inside it is not. The contribution of the base rubber layer of the tread outside the belt layer is greater than the braking performance on a large general road surface. Therefore, if the part is made of rubber with a high tan δ so that the energy loss at this part is increased, the braking performance can be improved without impairing the anti-friction performance such as wear performance and rolling resistance performance. The present invention has been conceived.

  That is, the pneumatic tire according to the present invention is a pneumatic tire having a tread rubber portion including a cap rubber layer and a base rubber layer, and the cap rubber against tan δ (Tb) of the base rubber layer at −5 ° C. The ratio (Tc / Tb) of tan δ (Tc) at −5 ° C. of the layer is in the range of 1.00 to 3.00, and the thickness of the base rubber layer relative to the thickness of the tread rubber portion is larger than that of the tread center portion. Is also set large in the tread shoulder.

  In the pneumatic tire of the present invention, the ratio (Dc / Dt) of the thickness (Dc) of the base rubber layer in the tread center portion to the thickness (Dt) of the tread rubber portion is 0.3 or less, and the tread rubber The ratio (Ds / Dt) of the thickness (Ds) of the base rubber layer in the tread shoulder portion to the thickness (Dt) of the portion is preferably 0.3 to 0.7.

  According to the present invention, by setting the ratio of tan δ between the base rubber layer and the cap rubber layer as described above, the tan δ is higher than that of a conventional general base rubber layer while suppressing deterioration in rolling resistance performance. The base rubber layer is made of rubber. Since the base rubber layer having a high tan δ is disposed so as to be thick at the tread shoulder portion where the contribution of the energy loss rate is large, when the large force acts on the tire in the front-rear direction during braking, the shoulder portion The energy required for braking by increasing the loss energy can be effectively obtained, and the braking performance can be improved.

  In addition, since it is not necessary to change the composition of the cap rubber layer of the tread rubber portion in order to improve the braking performance, it is possible to suppress a decrease in contradiction performance such as wear performance and rolling resistance performance.

  Furthermore, since the loss energy at the tread shoulder is increased by changing the thickness of the base rubber layer in the tread width direction, there is no need to use a different rubber composition in the width direction of the base rubber layer, reducing costs. Can do.

  Hereinafter, a pneumatic tire according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view in the tread width direction of a pneumatic tire 10 according to an embodiment of the present invention. The tire 10 is a studless tire, and includes a pair of left and right bead portions 12 and sidewall portions 14, and a tread portion 16 that extends between the sidewall portions 14.

  A bead core 18 is embedded in the bead portion 12, and a rubber bead filler 20 is disposed on the outer periphery in the radial direction. Further, a carcass 22 is provided between the left and right bead cores 18, and the carcass 22 passes through the sidewall portion 14 from the tread portion 16 and is locked by folding around the bead core 18 at the bead portion 12. Further, a belt 26 is disposed on the outer side in the radial direction of the carcass 22 in the tread portion 16, and the belt 26 overlaps at least two belt layers formed by inclining a belt cord at a shallow angle with respect to the tire circumferential direction. In this embodiment, it is composed of two layers of an inner first belt layer 28 (maximum width belt layer) and an outer second belt layer 30.

  A tread rubber portion 32 is provided outside the belt 26 in the radial direction. The tread rubber portion 32 is composed of two layers of a cap rubber layer 34 on the ground surface side and a base rubber layer 36 on the side adjacent to the belt 26. The cap rubber layer 34 and the base rubber layer 36 are configured as follows.

  When the tan δ at −5 ° C. of the cap rubber layer 34 is Tc and the loss tangent tan δ at −5 ° C. of the base rubber layer 36 is Tb, the ratio Tc / Tb of both is in the range of 1.00 to 3.00. Is set in. If this ratio is smaller than 1.00, the loss energy in the base rubber layer 36 becomes too large, and the rolling resistance performance is greatly deteriorated. Moreover, when this ratio is larger than 3.00, the effect of improving the ice braking performance is small. More preferably, Tc / Tb is in the range of 1.00 to 2.00. Further, the base rubber layer 36 is preferably made of rubber having a tan δ at −5 ° C. of 0.15 to 0.40, and more preferably 0.25 to 0.40. The cap rubber layer 34 is preferably made of rubber having a tan δ at −5 ° C. of 0.30 to 0.50.

  Here, the loss tangent tan δ uses a viscoelastic spectrometer (manufactured by UBM), and for a sample having a width of 5 mm, a thickness of 1 mm, and a length of 20 mm, the initial strain is 10%, the dynamic strain is 3%, the frequency is 15 Hz, and the temperature is −5. It is a value measured under the condition of ° C.

  Note that the base rubber layer 36 is made of a rubber having a higher modulus than the cap rubber layer 34 in order to ensure steering stability.

  The thickness of the base rubber layer 36 is set so that the tread shoulder portion SH is larger than the tread center portion CE. More specifically, as shown in FIG. 2, the thickness of the tread rubber portion 32 is Dt, the thickness of the base rubber layer 36 at the tread center portion CE is Dc, and the base rubber layer 36 at the tread shoulder portion SH. These are set so as to satisfy the following relationship.

Dc / Dt ≦ 0.3 (1)
0.3 ≦ Ds / Dt ≦ 0.7 (2)
Dc <Ds (3)
By increasing the thickness of the base rubber layer 36 at the tread shoulder portion SH as in the above formula (3), the loss energy at the tread shoulder portion SH where the contribution of the energy loss rate is large can be increased efficiently, and braking is performed. The performance can be improved. In the above formula (1), when Dc / Dt is larger than 0.3, the rolling resistance performance is deteriorated. The lower limit of Dc / Dt is not particularly limited, but is preferably 0.1 or more. In the formula (2), when Ds / Dt is smaller than 0.3, the above-described effect margin for effectively increasing the loss energy in the tread shoulder portion SH is reduced. On the contrary, if Ds / Dt exceeds 0.7, the rolling resistance performance is significantly deteriorated. A more preferable range of Ds / Dt is 0.4 to 0.6.

  Here, the tread shoulder portion SH is an outer side area portion when the width W of the first belt layer (maximum width belt layer) 28 is equally divided into four in the tread width direction in the tire 10 after vulcanization molding. That is. The tread center portion CE is a central area portion composed of two central sections when the width W of the first belt layer 28 is equally divided into four in the tread width direction.

  Dt is the total thickness of the tread rubber portion 32, and is an average value obtained by measuring the thickness of the tread rubber portion 32 at intervals of 5 mm within the width W of the first belt layer (maximum width belt layer) 28. Dc is an average value obtained by measuring the thickness of the base rubber layer 36 at intervals of 5 mm in the tread center portion CE. Ds is an average value obtained by measuring the thickness of the base rubber layer 36 at intervals of 5 mm in the tread shoulder portion SH.

  When the thickness of the base rubber layer 36 is changed between the tread center portion CE and the tread shoulder portion SH as described above, the thickness is gradually increased from the tread shoulder portion CE to the tread shoulder portion SH as shown in FIG. Is preferred.

  In the pneumatic tire 10 of the present embodiment configured as described above, the base rubber layer 36 is made of rubber having a tan δ higher than that of a conventional general base rubber layer, and then the base rubber layer 36 is subjected to energy loss. Since the tread shoulder portion SH, which has a large contribution to the rate, is arranged so as to be thicker, the energy loss required for braking can be increased effectively by increasing the loss energy of the portion that contributes greatly to the braking performance, and rolling. The braking performance can be improved without impairing the resistance performance. In addition, since the blending of the cap rubber layer 34 is not changed in order to improve the braking performance, it is possible to suppress a decrease in the contradiction performance such as the wear performance. In addition, since the loss energy in the tread shoulder portion SH is increased by changing the thickness of the base rubber layer 36 in the tread width direction, the above-described braking can be performed without using a different rubber composition in the width direction of the base rubber layer 36. The performance can be improved.

(Examples 1 and 2 and Comparative Examples 1 to 6)
As tires of Examples 1 and 2, studless tires having a cross-sectional structure shown in FIG. 1 were manufactured with a tire size of 205 / 65R15. The tread configuration in each tire is as shown in Table 1 below. The thickness Dt of the tread rubber portion 32 is 11 mm, the thickness Dc of the base rubber layer 36 at the tread center portion CE is 2.2 mm, and the tread shoulder portion SH The thickness Ds of the base rubber layer 36 was set to 5.5 mm.

  For the tires of Examples 1 and 2, the tread configuration was changed as shown in Table 1, and the tires of Comparative Examples 1 to 6 were produced in the same manner. Here, Comparative Example 1 is a control tire, and as shown in FIG. 3, the thickness of the base rubber layer is constant (ie, Dc = Ds) in the tread center portion CE and the tread shoulder portion SH, both of which are tread rubber. The ratio of the portion 32 to the thickness Dt is 0.2. Further, Comparative Example 2 is a tire whose braking performance is improved by a conventional method, and the cap rubber layer is changed to a low modulus compound compared to Comparative Example 1. Comparative Example 3 is obtained by increasing the thickness ratio Ds / Dt at the tread shoulder portion SH as 0.5 in Comparative Example 1. Comparative Example 4 is an example in which, in Example 1, the thickness ratio Dc / Dt at the tread center portion CE is set to 0.5, and the thickness of the base rubber layer having a high tan δ is increased as a whole. In Comparative Examples 5 and 6, the base rubber layer is formed of rubber having different tan δ between the tread center portion CE and the shoulder portion SH. The composition of each rubber is as shown in Table 2 below. Further, the modulus was measured in accordance with the JIS K 6251 vulcanized rubber tensile test method, and was expressed as an index with the modulus of the cap rubber layer of Comparative Example 1 as 100.

  The tires of Examples 1 and 2 and Comparative Examples 1 to 6 were evaluated and measured for ice braking performance, wear performance, and rolling resistance. Evaluation and measurement methods are as follows.

-Ice braking performance: rim used: 15 × 6.5JJ, air pressure: 200 kPa, and each tire is mounted on a 2500 cc passenger car. On an icy road surface with a road surface temperature of -5 ° C, the passenger car is accelerated to 40 km / h in the run-up section and maintained at a test speed of 40 km / h in the initial speed adjustment section. Step on it and keep it until it stops and read the stop distance. The result is an inverse exponential display with the stopping distance of Comparative Example 1 being 100, and the larger the value, the better the braking performance.

Wear performance: Rim used: 15 × 6.5 JJ, air pressure: 200 kPa, each tire is mounted on a 2500 cc passenger car, and runs 10,000 km on a test course (mixed urban area and highway). The amount of wear of the tread center portion CE and the tread shoulder portion SH is measured, and the average of both is calculated. The results are index evaluated with the wear amount of Comparative Example 1 being 100, and the larger the value, the better the wear performance.

Rolling resistance: Measured according to SAE J1269, index evaluation is performed with the rolling resistance of Comparative Example 1 being 100, and the smaller the value, the better the rolling resistance performance.

  As shown in Table 1, in Comparative Example 2 according to the conventional method, although the ice braking performance was improved as compared with Comparative Example 1, the wear performance and the rolling resistance were deteriorated. In contrast, in Examples 1 and 2, the ice braking performance was improved without substantially impairing the wear performance and rolling resistance.

  On the other hand, in Comparative Example 3 in which the base rubber layer having a low tan δ was thickened by the tread shoulder portion SH, the rolling resistance could be reduced, but the ice braking performance was deteriorated. Further, in Comparative Example 4 in which the base rubber layer having a high tan δ was increased not only in the tread shoulder portion SH but also in the center portion CE, the ice braking performance was improved, but the rolling resistance performance was greatly deteriorated. Further, in Comparative Example 5 in which the base rubber layer was divided in the width direction and a rubber having a high tan δ was blended in the tread center portion CE, the effect of improving the ice braking performance was hardly observed. Further, in Comparative Example 6 in which the tan δ of the tread shoulder portion SH was further increased, the ice braking performance was improved, but the rolling resistance performance was greatly deteriorated.

  As described above, according to the present invention, the ice braking performance can be improved without lowering the reverse performance such as the wear performance and the rolling resistance performance, so that it can be suitably used as a studless tire.

It is a tread width direction sectional view of the pneumatic tire concerning an embodiment. It is a cross-sectional schematic diagram of the tread rubber part in an embodiment. 4 is a schematic cross-sectional view of a tread rubber portion in a tire of Comparative Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Pneumatic tire, 32 ... Tread rubber part, 34 ... Cap rubber layer, 36 ... Base rubber layer, CE ... Tread center part, SH ... Tread center part, Dt ... Thickness of tread rubber part, Dc ... Tread center part Base rubber layer thickness, Ds ... thickness of base rubber layer at tread shoulder

Claims (2)

  A pneumatic tire having a tread rubber portion provided with a cap rubber layer and a base rubber layer, wherein the base rubber layer has a tan δ (Tc) at -5 ° C with respect to tan δ (Tb) at -5 ° C. The ratio of Tc / Tb is in the range of 1.00 to 3.00, and the thickness of the base rubber layer with respect to the thickness of the tread rubber portion is set larger in the tread shoulder portion than in the tread center portion. A featured pneumatic tire. The ratio (Dc / Dt) of the thickness (Dc) of the base rubber layer at the tread center portion to the thickness (Dt) of the tread rubber portion is 0.3 or less, and the tread shoulder with respect to the thickness (Dt) of the tread rubber portion 2. The pneumatic tire according to claim 1, wherein the ratio (Ds / Dt) of the thickness (Ds) of the base rubber layer at the portion is 0.3 to 0.7.

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