JP4943779B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire with improved grounding performance with respect to a land portion configuration of a tread portion thereof.

  Pneumatic tires are provided with land parts such as blocks and ribs partitioned by grooves provided on the tread surface. In order to improve braking performance, drive performance, steering stability, etc. Various proposals have been made.

  For example, in Patent Document 1 below, in order to improve the edge effect by suppressing the decrease in rigidity while taking advantage of the water absorption effect by foamed rubber, and to improve the braking performance and drivability on the icy and snowy road surface, It is disclosed that foam rubber is used, and that the side surface of the block is made of non-foamed rubber having a hardness higher than that of the block center.

  Patent Document 2 below discloses that an edge portion made of rubber or synthetic resin having a hardness of 70 or more is provided on a ridge of a block pattern tire made of foamed rubber in order to improve performance on ice. .

  In Patent Document 3 below, in order to improve the handling stability on the dry road surface by making the contact pressure of the block uniform, a recess is provided on the entire circumference of the side wall of the block, thereby reducing the rigidity of the entire block. It is disclosed that only the rigidity of the edge portion is reduced without reducing the contact pressure of the edge portion.

In Patent Document 4 below, in order to improve the braking / driving performance on an icy road, the central part of the block surface is formed in a concave shape, thereby reducing the ground pressure at the central part of the block when grounded. It is disclosed that the ground pressure is made uniform over the entire road surface.
Japanese Patent Laid-Open No. 05-147412 Japanese Patent Laid-Open No. 08-175116 Japanese Patent Laid-Open No. 11-151912 JP 2002-046424 A

  In rubber materials, the coefficient of friction decreases as the load (ground pressure) increases, so to improve tire performance such as braking performance, suppress the local increase in ground pressure in the land such as blocks, It is required to make the ground pressure distribution uniform.

  On the other hand, in Patent Documents 1 and 2 described above, foam rubber is disposed at the center of the block, and hard rubber is disposed at the side surface of the block. Although it can be expected to improve the performance, the grounding performance may be impaired on dry road surfaces with a high friction coefficient.

  On the other hand, in the above-mentioned Patent Document 3, the ground pressure is reduced by reducing the ground pressure at the edge portion while paying attention to the ground pressure at the edge portion of the block. Although it is effective, the contact pressure distribution is impaired on the road surface with a low coefficient of friction such as ice and snow road surface.

  Further, in Patent Document 4 described above, the block surface is formed in a concave shape to reduce the ground pressure at the center of the block to make the ground pressure uniform. It may cause wear and lacks practicality.

  In contrast to the conventional technology as described above, the present invention can improve tire performance such as braking performance by making the contact pressure distribution uniform on the icy and snowy road surface at low temperatures and the dry road surface at high temperatures. An object is to provide a pneumatic tire.

  When the deformation and ground contact property of the rubber block were investigated by experiment and FEM analysis, especially on road surfaces with a low coefficient of friction, such as icy and snowy road surfaces, the higher the vertical load, the more the side surfaces of the block deformed outward. It was found that the contact pressure increased and showed uneven contact pressure distribution. Conversely, on road surfaces with a high coefficient of friction, such as dry road surfaces, the pressure at the edge portion increases, and it has been found that measures to reduce the pressure at the edge portion are important. Along with such knowledge, normally, when traveling on a road surface with a low coefficient of friction such as an icy and snowy road surface, the outside temperature is low, and when traveling on a road surface with a high coefficient of friction such as a dry road surface, the outside temperature is high, Focusing on the temperature dependence of rubber hardness, finding that the above problems can be solved by arranging rubber with a large Young's modulus change with respect to temperature change at the edge part of the land such as a block, to complete the present invention It came.

That is, the pneumatic tire according to the present invention is a pneumatic tire including a land portion partitioned by a groove provided on a tread surface. A rubber part having a large rate change is provided, and the Young's modulus of the rubber part provided at the edge part is 1.2 to 1.8 times the Young's modulus of the central part at −5 ° C., and at 23 ° C. The Young's modulus of the central portion is 0.5 to 0.8 times .

  According to the present invention, the rubber portion having a large Young's modulus change provided at the edge portion hardens the edge portion at a low temperature to increase the pressure at the edge portion, and softens the edge portion at a high temperature to lower the pressure at the edge portion. Thus, the contact pressure distribution can be made uniform from the icy and snowy road surface at low temperatures to the dry road surface at high temperatures, and tire performance such as braking performance can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is a perspective view showing a block of a pneumatic tire according to an embodiment of the present invention, FIG. 2 is a plan view of the block (a diagram showing a grounding surface), and FIG. 3 is a sectional view of the block. 4 is a developed plan view showing an example of a tread pattern to which the block is applied.

  As shown in FIG. 4, the tread portion 10 of the pneumatic tire is provided with a plurality of blocks 16 defined by a main groove 12 extending in the tire circumferential direction and a lateral groove 14 extending in the tire width direction intersecting the main groove 12. ing. In this example, four main grooves 12 are provided in the tire width direction, and thus, the horizontal grooves 14 are provided at predetermined intervals in all of the five regions partitioned in the tire width direction. However, such a tread pattern is merely an example. In addition, various tread patterns having blocks can be employed. For example, the number of the main grooves 12 is not limited to four and may include a region (that is, a rib) where the lateral grooves 14 are not provided. Further, the lateral groove 14 may not be perpendicular to the main groove 12, and the planar shape of the block 16 may be formed in a parallelogram shape, a triangular shape, a trapezoidal shape, or the like by inclining and intersecting.

  On the ground contact surface of the block 16, a plurality (four in this case) of closed sipes 18 each having a cut extending in the tire width direction are arranged in parallel in the tire circumferential direction.

  As shown in FIGS. 1 to 3, the block 16 includes a block center portion 20 and a block side surface portion 22 that surrounds the outer periphery of the block 16 with a substantially constant thickness. The block side surface portion 22 is formed of the block center portion 20. It is made of rubber having a large Young's modulus change with respect to temperature change. That is, the block center portion 20 is formed of a rubber composition having a small Young's modulus change from low temperature to high temperature, whereas the block side surface portion 22 is reduced in temperature so that it is hard at low temperature and soft at high temperature. Along with this, the Young's modulus increases with a change in temperature with respect to the temperature change. Both the block center portion 20 and the block side surface portion 22 are non-foamed rubber.

Examples of such rubbers having different Young's modulus temperature dependence include adjusting the ratio of high cis butadiene rubber (butadiene rubber having a cis-1,4 bond content of 90% or more, hereinafter referred to as high cis BR). Can be obtained. That is, for example, if the ratio of the high cis BR in the rubber component is made large in the block central portion 20 and the ratio of the high cis BR in the rubber component is made smaller in the block side portion 22 than in the block central portion 20, the block side portion The temperature dependence of the Young's modulus at 22 increases. The magnitude of the Young's modulus itself can be adjusted by setting the molecular weight of the polymer and the blending amount of the vulcanizing agent and vulcanization accelerator. Here, the cis-1,4 bond content is a value measured by the infrared absorption spectrum method (Morero's method), cis: 740 cm ^-1, vinyl: calculated microstructure from the absorption intensity ratio of 910 cm ^-1 Is required.

  As described above, rubber having high temperature dependence of Young's modulus is disposed on the block side surface portion 22 constituting the edge portion of the block 16 so that it is uniform with respect to both the ice / snow road surface at a low temperature and the dry road surface at a high temperature. Can maintain a good grounding property.

  An experimental result indicating this will be described. In the block 16 shown in FIG. 1 (however, the sipe 18 is omitted), the Young's modulus of the block center portion 20 is fixed, and the Young's modulus of the block side surface portion 22 is changed to perform FEM analysis. In the analysis, a vertical load corresponding to a pressure of 200 kPa is applied, the Young's modulus of the block central portion 20 is 1.27 MPa, the Young's modulus of the block side surface portion 22 is changed from 0.48 to 3.23 MPa, and the friction coefficient of the road surface Was changed by μ = 0.1 to 0.7. The Young's modulus is a value measured according to JIS K6251.

  The result is as shown in FIG. 5. On the road surface with a low friction coefficient (μ = 0.1), the larger the Young's modulus of the block side surface portion 22, the smaller the dispersion value of the contact pressure, whereas the friction coefficient It can be seen that on a high road surface (μ = 0.7), the smaller the Young's modulus of the block side surface portion 22, the smaller the dispersion value of the contact pressure. Here, in general, the outside air temperature is low when traveling on a road surface with a low friction coefficient such as an icy and snowy road surface, and the outside air temperature is high when traveling on a road surface with a high friction coefficient such as a dry road surface. Therefore, if rubber with a high temperature dependence of the Young's modulus is disposed on the block side surface portion 22, the Young's modulus of the block side surface portion 22 is increased due to the low temperature, and the dispersion value of the ground pressure is reduced for the snowy and snowy road surface. On the dry road surface, the Young's modulus of the block side surface portion 22 is lowered due to the high temperature, and the dispersion value of the ground pressure is lowered. Therefore, uniform grounding can be maintained on both the icy and snowy road surface and the dry road surface as described above.

  In order to ensure more uniform contact on both the icy and snowy road surface at low temperature and the dry road surface at normal temperature, the Young's modulus of the block side surface portion 22 is lower than the Young's modulus of the block center portion 20 at -5 ° C. Larger is preferred. Further, the Young's modulus of the block side surface portion 22 is preferably smaller than the Young's modulus of the block center portion 20 at 23 ° C. Thereby, at the time of low temperature (-5 degreeC), the hardness of the block side surface part 22 becomes higher than the block center part 20, and thereby the pressure of the edge part of the block 16 can be raised and the contact pressure distribution can be made uniform. it can. Moreover, at the time of high temperature (23 degreeC), the hardness of the block side surface part 22 becomes lower than the block center part 20, Therefore The pressure of the edge part of the block 16 can be lowered | hung and the contact pressure distribution can be made uniform. More specifically, as shown in FIG. 5, since there is an appropriate value between the ground pressure dispersion value and the Young's modulus, the Young's modulus of the block side surface portion 22 is −5 ° C. It is preferable that it is 0.5-0.8 times the Young's modulus of the block center part 20 at 23 degreeC.

  Further, the temperature gradient of the Young's modulus of these rubber portions is not particularly limited, but the Young's modulus of the block side surface portion 22 is 0.02 to 0.06 MPa / ° C, and the Young's modulus of the block central portion 20 is Is preferably 0.01 Pa / ° C. or less in order to sufficiently exhibit the above effects.

  As for the ratio of the block side surface portion 22 to the block center portion 20, the area of the block side surface portion 22 is preferably 10 to 50% of the entire block area as an area ratio in the ground contact surface. If the area of the block side surface portion 22 is too small, the above effect will be insufficient. Conversely, if the area is too large, the pressure change at the edge portion may be large and the contact pressure may be uneven.

  The method for manufacturing the pneumatic tire having the block configuration of the present embodiment configured as described above is not particularly limited. For example, a rubber layer that forms the block side surface portion 22 is disposed on a rubber layer that forms the block center portion 20 during green tire molding, and is vulcanized to form a rubber layer that forms the block side surface portion 22. The pneumatic tire of the above embodiment is obtained by forming the tread pattern covered with, and buffing the ground contact surface in the tire after vulcanization molding to expose the block center portion 20.

  FIG. 6 is a perspective view showing a block 30 of a pneumatic tire according to another embodiment, and FIG. 7 is a plan view of the block 30 (a diagram showing a ground contact surface). In the embodiment shown in FIG. 1, the entire block side surface portion 22 including the side surface of the block 16 is made of rubber having a high Young's modulus temperature dependency. In particular, a rubber portion 34 having a high Young's modulus temperature dependency is provided.

  That is, in this example, rubber at a plurality of locations (for example, six locations) on the periphery of the edge portion 32 of the block 30 is made of a rubber having a large Young's modulus change with respect to a temperature change, compared to other portions including the central portion 36 of the block 30 A circular rubber portion 34 is provided. As shown in FIG. 6 and FIG. 8B, the rubber portion 34 is a columnar rubber portion that extends from the base rubber layer 38 and is exposed to the grounding surface. Therefore, in this example, the base rubber layer 38 is a cap. The rubber layer 44 is made of rubber having a higher Young's modulus temperature dependency than the rubber portion including the central portion 36 of the block 30. Other configurations, the Young's modulus of each rubber portion, and the like can be set similarly to the embodiment of FIG.

  In order to manufacture this pneumatic tire, the method described in JP 2000-343916 A can be used. Specifically, as shown in FIG. 8 (a), a vent hole 42 is provided at a predetermined position of a block molding recess in the tread contact surface area of the tire mold 40, and the vent hole 42 is used during vulcanization molding. The base rubber layer 38 is taken inside and the cap rubber layer 44 is sucked up. Then, after the vulcanization molding, the block 30 provided with the rubber portion 34 is obtained by cutting away the protrusion 46 sucked up into the vent hole 42 as shown in FIG. 8B.

  When rubber having a high temperature dependence of Young's modulus is arranged in this way, the rubber portion does not necessarily have to be provided on the entire edge portion of the block (that is, the block side surface portion 22 shown in FIG. 1), as shown in FIG. Alternatively, the edge portions 32 may be scattered. However, more preferably, as shown in FIG. 1, it is arranged on the block side surface portion 22 that surrounds the entire circumference of the block center portion 20, thereby further improving the effect of uniformizing the contact pressure.

  In the above embodiment, the block has been described as an example. However, the present invention can be similarly applied to land portions other than the block, that is, ribs extending continuously in the circumferential direction. A rubber portion having a higher Young's modulus temperature dependency than the central portion of the rib can be provided at the edge portion (side edge portion). Preferably, it is applied to a studless tire provided with a block, and thereby the dry braking performance as well as the ice braking performance of the studless tire can be improved.

  The ground pressure dispersion value was obtained for the block (Example 1) of the embodiment shown in FIGS. Here, the block size was 28 mm long × 28 mm wide × 10 mm high, and the width of the block side surface portion 22 was 2.8 mm (the area of the block side surface portion 22 was 36% of the area of the entire block).

Moreover, in Example 1, the rubber composition of the block center part 20 is set to the blend A of the following Table 1 (rubber with low temperature dependence of Young's modulus), and the rubber composition of the block side part 22 is blended B of the following Table 1 (Rubber with high temperature dependence of Young's modulus). For comparison, Comparative Example 1 in which the entire block was formed by Formulation A and Comparative Example 2 in which block central portion 20 was Formulated B and block side surface portion 22 was Formulated A were also evaluated. Moreover, it replaced with the mixing | blending B and evaluated also the reference example which used the other mixing | blending C with high temperature dependence of Young's modulus for the block side part 22. FIG.

  About each rubber composition of the mixing | blending A, the mixing | blending B, and the mixing | blending C, the Young's modulus in -5 degreeC-23 degreeC was measured based on JISK6251. The results are as shown in FIG. 9, and the temperature gradient of Young's modulus was 0.005 MPa / ° C. for formulation A, 0.044 MPa / ° C. for formulation B, and 0.032 MPa / ° C. for formulation C. The Young's modulus at −5 ° C. is 1.27 MPa for formulation A, 2.05 MPa for formulation B, and 2.25 MPa for formulation C. The Young's modulus at 23 ° C. is 1.13 MPa for formulation A. B was 0.81 MPa, and C was 1.31 MPa.

  The contact pressure dispersion value is measured on a road surface with a friction coefficient μ = 0.1 and a road surface with a friction coefficient μ = 1.0, and a vertical load (154 N) is applied to the block on each road surface. The contact pressure was measured by the treatment, and the contact pressure dispersion value was shown as an index with Comparative Example 1 as 100. The smaller the value, the more uniform the contact pressure and the better the contact performance.

In addition, studless tires (tire size: 205 / 65R15) having the blocks of Example 1 , Reference Example and Comparative Examples 1 and 2 were produced, and the braking performance on ice and the dry braking performance were evaluated. The evaluation method is as follows.

-On-ice braking performance: Each tire is mounted on a domestic 2500cc passenger car (rear wheel drive), and the ABS braking distance from the speed of 40 km / h is measured on the ice board surface (μ = about 0.1) (average road surface temperature = −5 ° C.) and an index with Comparative Example 1 as 100. The larger the value, the better the braking performance.

Dry braking performance: Each tire is mounted on a domestic 2500cc passenger car (rear wheel drive), and the ABS braking distance from a speed of 100 km / h on a dry road surface (μ = about 1.0) is measured (average road surface temperature = 23). ° C.) and an index with Comparative Example 1 as 100. The larger the value, the better the braking performance.

The results are as shown in Table 2 below. In this example, the contact pressure distribution was made uniform on both the on-ice road surface and the dry road surface, and both on-ice performance and dry performance were significantly improved.

  The pneumatic tire of the present invention can be used for various types of pneumatic tires including winter tires such as studless tires.

It is a perspective view showing a block of a pneumatic tire concerning an embodiment. It is a top view of the block. It is sectional drawing of the block. It is a plane development view showing an example of a tread pattern of the pneumatic tire. It is a graph which shows the relationship between the Young's modulus of a block side part, and a ground pressure dispersion value. It is a perspective view which shows the block of the pneumatic tire which concerns on other embodiment. It is a top view of the block. It is an expanded sectional view of the block which shows the manufacturing process of the pneumatic tire. It is a graph which shows the relationship between the temperature of rubber compounding A and B used for the block of an Example, and Young's modulus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Tread part, 12 ... Main groove, 14 ... Side groove, 16 ... Block, 20 ... Block center part, 22 ... Block side part, 30 ... Block, 32 ... Edge part, 34 ... Rubber with high temperature dependence of Young's modulus 34, central part of the block

Claims (3)

In a pneumatic tire including a land portion partitioned by a groove provided on a tread surface,
A rubber part having a large Young's modulus change with respect to a temperature change is provided at the edge part of the land part, compared to the center part of the land part ,
The Young's modulus of the rubber part provided at the edge part is 1.2 to 1.8 times the Young's modulus of the central part at -5 ° C, and 0.5 ~ of the Young's modulus of the central part at 23 ° C. A pneumatic tire characterized by being 0.8 times .   The pneumatic tire according to claim 1, wherein the land portion is a block defined by a groove provided on a tread surface.   The block comprises a block center portion and a block side surface portion surrounding the block center portion, and the block side surface portion is formed of rubber having a larger Young's modulus change with respect to a temperature change than the block center portion. The pneumatic tire according to claim 2.

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