JP2015116838A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pneumatic tire which can improve the fatigue rigidity of a groove bottom wall of a main groove while securing drainage performance and steering stability.SOLUTION: A pneumatic tire comprises a tread part 2 in which a main groove 20 extending to a tire circumferential direction is formed. The tread part 2 includes a tread face, and comprises a cap layer 10 being an outermost layer of the tread part 2, a base layer 11 which is arranged so as to adjoin the inside of the cap layer 10 in a tire radial direction, and a first rubber layer 12 which is arranged so as to oppose a groove bottom wall 21 of the main groove 20 between the cap layer 10 and the base layer 11, and lower than the cap layer 10 in modulus.

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a main groove formed in a circumferential direction of a tread surface.

  In the tread portion of the pneumatic tire, there are a main groove extending in the tire circumferential direction to ensure drainage on a wet road surface when traveling in rainy weather, a block portion and the like partitioned in the tire width direction by the main groove, A plurality are formed. The main groove is defined by a groove bottom wall portion and a pair of groove side wall portions extending from both ends of the groove bottom wall portion in the tire width direction to the tread surface. The groove bottom wall portion includes a cylindrical groove bottom peripheral portion and an R-shaped groove bottom corner continuous from the both ends of the groove bottom peripheral portion in the tire width direction to the groove side wall portion.

  When a load is input to the block portion, the block portion is deformed with the groove bottom side of the main groove as a base point, but the groove bottom portion on the inner side in the tire radial direction of the groove bottom wall portion of the main groove is highly rigid and difficult to deform. The groove bottom wall portion that becomes the boundary between the block portion and the groove bottom portion is likely to be the base point of deformation. As a result, stress concentration due to strain concentration tends to occur on the groove bottom wall. In addition, since stress concentration on the groove bottom wall portion is repeatedly generated as the tire rotates, the groove bottom wall portion is required to have fatigue resistance that can withstand repeated stress concentration.

  In response to this requirement, a method of relaxing stress concentration that occurs repeatedly by enlarging the R shape of the groove bottom corner can be considered. As another method, Patent Document 1 discloses that the thickness of a rubber layer (cap layer) on the tread surface side having excellent wear resistance of a tread portion including a plurality of rubber layers having different viscoelastic properties is controlled. Thus, it is disclosed that the rigidity of the groove bottom wall portion is secured and cracks are suppressed.

JP 2006-62518 A

  However, according to the former method, in order to enlarge the R shape of the groove bottom corner, it is necessary to reduce the depth of the main groove or increase the groove width of the main groove. When the vehicle is made shallower, the drainage performance is deteriorated and the wet performance is lowered, and when the groove width of the main groove is enlarged, the contact area of the tread surface is reduced and the steering stability performance is deteriorated.

  According to the latter method, the rigidity of the cap layer is ensured by controlling the thickness of the cap layer, the stress concentration on the groove bottom wall portion of the main groove cannot be relaxed, and the fatigue strength is reduced. It cannot be improved.

  An object of the present invention is to improve the fatigue strength of the groove bottom wall portion of the main groove while ensuring drainage and steering stability.

  As a means for solving the above-mentioned problems, the present invention is a pneumatic tire, and includes a tread portion in which a main groove extending in the tire circumferential direction is formed, the tread portion including a tread surface, and the tread portion. A cap layer that is the outermost layer of the base layer, a base layer that is provided adjacent to the inner side in the tire radial direction of the cap layer, and a groove bottom wall portion of the main groove between the cap layer and the base layer. And a first rubber layer having a lower modulus than the cap layer.

  According to this configuration, by disposing the first rubber layer having a lower modulus than the cap layer on the groove bottom portion on the inner side in the tire radial direction of the groove bottom wall portion, the rigidity of the groove bottom portion is reduced to reduce the groove bottom portion. Deformation can be allowed, and as a result, stress concentration on the groove bottom wall can be reduced. By disposing the first rubber layer between the cap layer and the base layer, the main groove can be formed of the cap layer as in the conventional case, so that the strength of the groove bottom wall portion can be ensured. That is, according to this configuration, the stress concentration on the groove bottom wall can be relaxed while ensuring the strength of the groove bottom wall, so that the fatigue strength of the groove bottom wall can be improved.

  The tire meridian cross-sectional shape of the first rubber layer preferably extends along the tire meridian cross-sectional shape of the main groove.

  According to this configuration, the rigidity of the groove bottom portion of the main groove can be easily lowered by arranging the first rubber layer along the main groove.

  An end portion in the tire width direction of the first rubber layer is located on the inner side in the tire radial direction from an interface portion between the cap layer and the base layer in a region excluding a region where the main groove is formed. It is preferable.

  According to this configuration, the end portion of the first rubber layer in the tire width direction is located on the inner side in the tire radial direction from the interface portion between the cap layer and the base layer in the region excluding the region where the main groove is formed. Therefore, an excessive decrease in the rigidity of the groove bottom can be suppressed. As a result, excessive deformation of the block portion forming the tread surface is suppressed, and steering stability can be ensured.

  The main groove is defined by the groove bottom wall part and a pair of groove side wall parts extending from both ends of the tire bottom direction of the groove bottom wall part to the tread surface, and the tire width direction of the first rubber layer It is preferable that the edge part of this is located in the tire radial direction outer side rather than the groove bottom corner part which is formed in the both ends of the tire width direction of the said groove bottom wall part, and continues to the said groove side wall part.

  According to this configuration, the first rubber layer is disposed so as to face the entire corner of the groove bottom, and the rigidity of the groove bottom is easily further reduced. As a result, the stress concentration on the groove bottom wall can be further alleviated.

  It is preferable that a second rubber layer provided further on the inner side in the tire radial direction than the first rubber layer is further provided so as to face the first rubber layer in the tire radial direction.

  The second rubber layer preferably has a higher modulus than the base layer.

  According to this configuration, by disposing the second rubber layer having a higher modulus than that of the base layer, it compensates for the deterioration of the cut property due to the disposition of the first rubber layer having a low modulus, and the cut property due to trauma or the like. Can be secured.

  The dimension of the second rubber layer in the tire width direction is preferably substantially the same as or less than the dimension of the first rubber layer in the tire width direction.

  According to this structure, the 2nd rubber layer can be arrange | positioned by the required minimum magnitude | size, compensating the deterioration of the cut property by having arrange | positioned the 1st rubber layer. Thereby, the influence on productivity by having arrange | positioned the 2nd rubber layer can be suppressed to the minimum.

  A belt provided adjacent to the inner side in the tire radial direction of the base layer may further be provided, and the second rubber layer may be disposed between the base layer and the belt.

  According to this configuration, since the second rubber layer having a higher modulus than the base layer is disposed on the innermost side in the tire radial direction in the tread portion, the first rubber layer having a low modulus is disposed. It is possible to compensate for the deterioration of the cutting property due to, and further improve the cutting property due to trauma.

  Alternatively, the second rubber layer may be disposed so as to be in contact with the first rubber layer.

  According to this configuration, the first rubber layer and the second rubber layer can be placed between the cap layer and the base layer in a set state. That is, since the tire material before vulcanization can be easily configured, the productivity of the pneumatic tire having the first rubber layer and the second rubber layer can be improved.

  According to the pneumatic tire of the present invention, it is possible to improve the fatigue strength of the groove bottom wall portion of the main groove while ensuring drainage and steering stability.

The meridian direction sectional drawing of the tread part which shows the pneumatic tire for heavy loads which concerns on embodiment of this invention. The principal part expanded sectional view which expands and shows the main groove vicinity of FIG. The principal part expanded sectional view similar to FIG. 2 which shows the tire which concerns on other embodiment. The principal part expanded sectional view similar to FIG. 2 which shows the tire which concerns on other embodiment. The principal part expanded sectional view similar to FIG. 2 which shows the tire which concerns on a prior art example. The principal part expanded sectional view similar to FIG. 2 which shows the tire which concerns on a comparative example. The principal part expanded sectional view similar to FIG. 2 which shows the tire which concerns on another comparative example.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In addition, the following description is only illustrations essentially and does not intend restrict | limiting this invention, its application thing, or its use.

  FIG. 1 is a half sectional view in the meridian direction of a heavy duty pneumatic tire according to an embodiment of the present invention, and shows only one side with respect to the tire equator line CL. As shown in FIG. 1, a heavy load pneumatic tire 1 includes a tread portion 2 including a tread surface, sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and inner portions of the sidewall portions 3 and 3. And a bead portion (not shown) located at one end. Furthermore, the heavy-duty pneumatic tire 1 includes a carcass 6 that straddles each bead portion, and a belt layer 7 that is disposed on the outer periphery of the carcass 6.

  A plurality of main grooves 20 extending in the tire circumferential direction are formed on the outer periphery of the tread portion 2, and the plurality of block portions 30 are partitioned by the main grooves 20 in the tire width direction. The main groove 20 is defined by a groove bottom wall portion 21 and a pair of groove side wall portions 22 and 22 extending from both ends of the groove bottom wall portion 21 in the tire width direction to the tread surface. The groove bottom wall portion 21 includes a cylindrical groove bottom circumferential portion 21a and a pair of groove bottom corner portions 21b and 21b continuous from both ends in the tire width direction of the groove bottom circumferential portion 21a to the groove side wall portion 22. It is. The region facing the groove bottom wall portion 21 is referred to as the groove bottom portion 25 and will be described below.

  The tread portion 2 includes a cap layer 10 that is the outermost layer, and a base layer 11 that is provided so as to be adjacent to the inner side in the tire radial direction of the cap layer 10. The interface S between the cap layer 10 and the base layer 11 is recessed toward the inner side in the tire radial direction in the tire width direction region corresponding to the main groove 20.

  That is, in the interface portion S, the basic interface portion S1 positioned on the outer side in the tire radial direction from the groove bottom wall portion 21 in the tire width direction region excluding the region where the main groove 20 is formed, and the main groove 20 are formed. In the tire width direction region, a main groove interface portion S2 located on the inner side in the tire radial direction from the groove bottom wall portion 21 is included.

  In the present embodiment, for example, a rubber having a modulus M100 at an elongation of 100% of 1.8 to 2.9 MPa is employed for the cap layer 10. Similarly, the base layer 11 has a modulus M100 of 2.1. A rubber of ˜2.7 MPa is employed.

  Next, the structure of the tread portion 2 will be specifically described with reference to FIG. FIG. 2 is an enlarged cross-sectional view of the main part of the tread portion 2. As shown in FIG. 2, a substantially U-shaped first rubber layer 12 disposed so as to surround the groove bottom wall portion 21 is disposed in the main groove interface portion S <b> 2. The tire radial direction positions of both end portions 12a, 12a in the tire width direction of the first rubber layer 12 are configured to be located between the groove bottom wall portion 21 and the basic interface portion S1.

  The first rubber layer 12 has a modulus lower than that of the cap layer 10. For example, the modulus M100 is 15 to 65% lower than the cap layer 10 (modulus M100: 1.0 to 1.5 MPa).

  The second rubber layer 13 is disposed between the base layer 11 and the belt layer 7 on the inner side in the tire radial direction of the first rubber layer 12. The dimension of the second rubber layer 13 in the tire width direction is substantially the same as or smaller than the dimension of the first rubber layer 12 in the tire width direction.

  The second rubber layer 13 has a modulus higher than that of the base layer 11. For example, the modulus M100 is 25 to 70% higher than the base layer 11 (modulus M100: 3.0 MPa to 4.0 MPa).

  As described above, by arranging the first rubber layer 12 having a lower modulus than the cap layer 10 along the main groove interface S2 so as to surround the groove bottom wall 21, the rigidity of the groove bottom 25 is appropriately set. Can be reduced. Thereby, when a load is applied to the block portion 30, it is possible to moderate the stress at the groove bottom wall portion 21 by appropriately deforming the groove bottom portion 25.

  In addition, the main groove 20 can be configured as the cap layer 10 as in the prior art while reducing the rigidity of the groove bottom 25. That is, while ensuring the strength of the groove bottom wall portion 21, the groove bottom portion 25 can be deformed to reduce the stress concentration on the groove bottom wall portion 21, thereby improving the fatigue strength of the groove bottom wall portion 21. be able to.

  Since both end portions 12a, 12a of the first rubber layer 12 are located on the inner side in the tire radial direction from the basic interface portion S1, an excessive decrease in the rigidity of the groove bottom portion 25 is suppressed. Thereby, the excessive deformation | transformation of the block part 30 can be suppressed and steering stability can be ensured.

  By disposing the first rubber layer 12 having a low modulus by disposing the second rubber layer 13 having a higher modulus than the base layer 11 on the inner side in the tire radial direction so as to face the first rubber layer 12. Cutability due to trauma or the like can be enhanced while compensating for the reduction in cutability.

  In addition, since the size of the second rubber layer 13 in the tire width direction is substantially the same as or less than the size of the first rubber layer 12 in the tire width direction, the second rubber layer 13 is minimized. It is easy to ensure the productivity of the heavy-duty pneumatic tire 1.

  Furthermore, according to this embodiment, since the cut resistance can be improved while improving the fatigue strength, the fatigue strength and the cut resistance can be ensured even if the thickness of the tread portion 2 is reduced. Thereby, since the rubber | gum of the tread part 2 with the largest distortion energy can be reduced, reduction of rolling resistance is attained and it can contribute to a fuel-consumption reduction.

  In the above embodiment, the case where the second rubber layer 13 is disposed between the belt layer 7 and the base layer 11 has been described as an example. However, as shown in FIG. You may arrange | position so that the rubber layer 12 may be contacted. Even with this arrangement, it is possible to improve the cut resistance while improving the crack resistance. Furthermore, by arranging the first rubber layer 12 and the second rubber layer 13 in a set state between the cap layer 10 and the base layer 11, an unvulcanized material of the heavy duty pneumatic tire can be easily configured. Accordingly, the productivity of the heavy duty pneumatic tire 1 having the first rubber layer 12 and the second rubber layer 13 can be improved.

As shown in FIG. 4, the second rubber layer 13 may be arranged at the groove bottom 25 of the main groove 20 without arranging the first rubber layer 12 in the above embodiment. . The cut resistance can be improved by disposing the second rubber layer 13. That is, this summary is
A pneumatic tire, comprising a tread portion formed with a main groove extending in the tire circumferential direction,
The tread portion is
A cap layer that includes a tread surface and is the outermost layer of the tread portion;
A base layer provided so as to be adjacent to the inner side in the tire radial direction of the cap layer;
A second rubber layer provided on the inner side in the tire radial direction than the cap layer so as to face the groove bottom wall portion of the main groove in the tire radial direction and having a higher modulus than the base layer. It is characterized by being.

  The present invention is not limited to the illustrated embodiments, and it goes without saying that various improvements and design variations are possible without departing from the spirit of the present invention.

  Next, the verification test about the effect demonstrated above was implemented. The tire size is common to 295 / 75R22.5 (general TB tire), the width of the second rubber layer relative to the width of the first rubber layer, and the modulus M100 of each rubber layer is configured as shown in Table 1. The tire of the present invention (Examples 1 to 4), the comparative tire (Comparative Examples 1 to 5), and the first and second rubber layers 12 in the present invention having the rubber layer arrangement structure shown in FIGS. A conventional tire (conventional example) without 13 was prepared.

  Example 1 is the heavy-duty pneumatic tire 1 according to the embodiment described above, and the first rubber layer 12 having a modulus M100 of 1.5 MPa and the second rubber layer 13 having a modulus M100 of 3.0 MPa are employed. (See FIG. 2). Example 2 differs from Example 1 in that the dimension of the second rubber layer 13 in the tire width direction is larger than the dimension of the first rubber layer 12 in the tire width direction. In Example 3, compared with Example 1, the first rubber layer 12 has a lower modulus (modulus M100 is 1.0 MPa), and the second rubber layer 13 has a higher modulus (modulus M100 is 4.0 MPa). Is different. Example 4 differs from Example 3 in that the second rubber layer 13 is disposed in contact with the first rubber layer 12 (see FIG. 3).

  Comparative Example 1 is obtained by removing the first rubber layer 12 from Example 1 (see FIG. 4). Comparative Example 2 is obtained by removing the second rubber layer 13 from Example 1 (see FIG. 6). In Comparative Example 3, the first rubber layer 12 has a higher modulus than the cap layer 10 compared to Example 1. In Comparative Example 4, the second rubber layer 13 has a lower modulus than the base layer 11 compared to Example 1. In Comparative Example 5, both end portions 12a and 12a of the first rubber layer 12 are positioned on the outer side in the tire radial direction from the basic interface portion S1 with respect to Example 3 (see FIG. 7).

  When each of these test tires was mounted on a test rim, the air pressure was filled into the normal internal pressure (760 kPa), and the following evaluation test was performed under the standard load (normal load) conditions, the results shown in Table 1 were obtained. Got.

(Groove bottom crack resistance (fatigue strength))
After traveling 100,000 miles (160,000 km) under the above conditions, the presence or absence of occurrence of groove bottom cracks was visually evaluated. The evaluation criteria are as follows.
◎: No cracking even after driving 150,000 miles ○: Allowable cracking after traveling 150,000 miles △: Cracking after traveling 100,000 miles ×: Cracking after traveling 70,000 miles

(Cut-proof, trauma performance)
Prior to the evaluation under the above conditions, an initial cut is made at the bottom of the groove, and the distance until the failure occurs is measured under the above conditions. The evaluation criteria are as follows.
◎: The initial cut growth rate is within 5% after driving 100,000 miles. ○: The growth rate of the initial cut is over 5% and less than 10% after driving 100,000 miles. △: The initial cut reaches the belt layer after driving 70,000 miles. ×: The initial cut reaches the belt layer after running 50,000 miles

(Rolling resistance performance)
Under the following conditions, tire axial force is measured and rolling resistance is calculated according to JSD4234. The values in Table 1 indicate that the lower the value, the better the performance.
Air pressure: Air pressure relative to maximum load Load: 85% of maximum load
Speed: 60km / h

  As shown in Table 1, the heavy-duty pneumatic tire according to the present invention has groove bottom crack resistance (fatigue strength), cut resistance, and trauma performance as compared with the conventional examples and Comparative Examples 1 to 4. It can be seen that the rolling resistance performance can be reduced while increasing the resistance.

  As described above, according to the pneumatic tire according to the present invention, the fatigue strength can be increased while ensuring the drainage performance and the handling stability, so that the pneumatic tire can be suitably implemented in this type of manufacturing technology field. There is sex.

DESCRIPTION OF SYMBOLS 1 Heavy load pneumatic tire 2 Tread part 10 Cap layer 11 Base layer 12 1st rubber 12a End part 13 2nd rubber 20 Main groove 21 Groove bottom wall part 21a Groove bottom peripheral part 21b Groove bottom corner part 22 Groove side wall part 25 Groove Bottom part 30 Block part CL Tire equator S Interface part S1 Basic interface part S2 Main groove interface part

Claims (9)

A pneumatic tire, comprising a tread portion formed with a main groove extending in the tire circumferential direction,
The tread portion is
A cap layer that includes a tread surface and is the outermost layer of the tread portion;
A base layer provided so as to be adjacent to the inner side in the tire radial direction of the cap layer;
A first rubber layer provided between the cap layer and the base layer so as to face the groove bottom wall of the main groove, and having a lower modulus than the cap layer;
Pneumatic tire equipped with.   2. The pneumatic tire according to claim 1, wherein a tire meridian cross-sectional shape of the first rubber layer extends along a tire meridian cross-sectional shape of the main groove.   An end portion in the tire width direction of the first rubber layer is located on the inner side in the tire radial direction from an interface portion between the cap layer and the base layer in a region excluding a region where the main groove is formed. The pneumatic tire according to claim 2. The main groove is defined by the groove bottom wall portion and a pair of groove side wall portions extending from the both ends of the groove bottom wall portion in the tire width direction to the tread surface,
The ends of the first rubber layer in the tire width direction are formed at both ends of the groove bottom wall portion in the tire width direction and are located on the outer side in the tire radial direction than the groove bottom corner portions that are continuous with the groove side wall portions. The pneumatic tire according to claim 3, which is located.   5. The apparatus according to claim 1, further comprising a second rubber layer provided on the inner side in the tire radial direction than the first rubber layer so as to face the first rubber layer in the tire radial direction. Or a pneumatic tire according to claim 1.   The pneumatic tire according to claim 5, wherein the second rubber layer has a higher modulus than the base layer.   The pneumatic tire according to claim 6, wherein a dimension of the second rubber layer in the tire width direction is substantially equal to or less than a dimension of the first rubber layer in the tire width direction.   The belt according to claim 5, further comprising a belt provided adjacent to the inner side in the tire radial direction of the base layer, wherein the second rubber layer is disposed between the base layer and the belt. The pneumatic tire according to one.   The pneumatic tire according to any one of claims 5 to 7, wherein the second rubber layer is disposed so as to contact the first rubber layer.

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