JP5157203B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that can improve the snow braking performance and wet performance of the tire while maintaining the rolling resistance of the tire.

  In recent pneumatic tires, width direction grooves are arranged in the center region and the shoulder region of the tread portion in order to ensure the braking / driving performance of the tire. Such a tread pattern is called a traction pattern. Here, in the pneumatic tire which has a traction pattern, there exists a subject which should improve the snow braking performance and wet performance of a tire. Moreover, since many width direction grooves are arranged, the rolling resistance of the tire tends to increase.

  The technique described in Patent Document 1 is known as a conventional pneumatic tire related to this problem. A conventional pneumatic tire (studless tire) has a tread surface divided into a plurality of blocks by a longitudinal groove extending in the tire circumferential direction and a transverse groove extending in a direction intersecting with the longitudinal groove, and a substantially tire shaft on the surface of the block. A studless tire provided with a plurality of sipings extending in the direction, wherein the joint protrudes from the bottom of the lateral groove and is separated from a block adjacent to the tire circumferential direction by a split groove. And the joint portion has a ratio of the joint height h1 from the groove bottom of the lateral groove to the surface of the joint portion and the block height H from the groove bottom of the transverse groove to the block surface of the block. The height ratio (h1 / H) is 0.4 or more and 0.7 or less, and the width ratio (w1 / W), which is the ratio of the joint width w1 in the axial direction and the block width W, is 0.3. Or more With the 0.6, the sum of the height ratio (h1 / H) and Habahi (w1 / W), and characterized in that 0.8 or more and 1.1 or less.

JP-A-8-67112

  An object of the present invention is to provide a pneumatic tire that can improve the snow braking performance and wet performance of the tire while maintaining the rolling resistance of the tire.

In order to achieve the above object, a pneumatic tire according to the present invention includes at least three circumferential main grooves extending in the tire circumferential direction, a plurality of widthwise grooves extending in the tire width direction, and the circumferential direction. A pneumatic tire having, in a tread portion, a main groove and a plurality of block rows defined by the width direction groove, wherein the width width of the width direction groove is increased at at least one opening of the width direction groove. In addition, the groove depth of the width direction groove in the opening is a first groove bottom portion having the shallowest groove depth h1, and a second groove bottom portion having a groove depth h2 deeper than the first groove bottom portion. And a plurality of groove bottom portions including a third groove bottom portion having a groove depth h3 deeper than the second groove bottom portion and reaching the circumferential main groove , wherein the first groove bottom portion A narrow groove having a narrower groove width than the width direction groove is formed in Is, and, the sum h1 + h4 groove depth h4 of the groove depth h1 and the narrow groove of the first groove bottom, characterized in that the groove depth h2 of the second groove bottom portion are equal.

In this pneumatic tire, (1) the groove width of the width direction groove is enlarged in at least one opening of the width direction groove, and (2) the groove depth of the width direction groove in the opening is first. Since the groove is expanded by a plurality of stages of the groove bottom including the groove bottom, the second groove bottom, and the third groove bottom, the groove volume of the width direction groove increases stepwise at the opening. Thereby, there is an advantage that the edge force of the block row is increased and the snow braking performance of the tire is improved. Further, there is an advantage that the drainage of the width direction groove is improved and the wet performance of the tire is improved. Further, (3) since the narrow groove is formed at the bottom of the first groove of the width direction groove, the drainage of the width direction groove after the progress of wear of the tread portion is ensured. Thereby, there is an advantage that the wet performance of the tire is ensured even after the progress of wear of the tread portion.
In addition, this pneumatic tire has an advantage that generation of cracks at the groove bottom of the narrow groove is suppressed as compared with a configuration in which there is a step between the groove bottom of the narrow groove and the second groove bottom.

  In the pneumatic tire according to the present invention, a chamfering process is performed on a step portion between the first groove bottom and the second groove bottom.

  This pneumatic tire has an advantage that the generation of cracks at the bottom of the narrow groove is effectively suppressed.

  Moreover, in the pneumatic tire according to the present invention, the width direction groove crosses the block row in an S shape or a Z shape in a plan view of the tread portion.

  In this pneumatic tire, the groove wall of the block is partitioned into an S shape or a Z shape by the groove in the width direction, so that the blocks adjacent in the tire circumferential direction mesh firmly with each other during inflation. Then, the amount of displacement of the tread portion (particularly the center region) toward the outer side in the tire radial direction is reduced, and changes in the tire shape at the time of tire contact are suppressed. Thereby, there exists an advantage by which the rolling resistance of a tire is reduced.

  In the pneumatic tire according to the present invention, when the region of 70 [%] of the tire contact width T centered on the center line CL is taken, the four circumferential main grooves are arranged in the region. The

  In this pneumatic tire, the drainage performance is improved by the four circumferential main grooves, and the contact pressure of each block row is made uniform to control the distortion of the tread portion. Thereby, there is an advantage that the wet performance of the tire is maintained and the rolling resistance of the tire is reduced.

  In the pneumatic tire according to the present invention, in the three block rows defined by the four circumferential main grooves, the block width R1 of the central block row and the block width R2 of each block row on both sides are arranged. Have a relationship of 0.95 ≦ R1 / R2 ≦ 1.05.

  In this pneumatic tire, the relationship between the block widths R1 and R2 of each block row in the tread portion center region is optimized, so that the contact pressure of each block row at the time of tire contact is made uniform. Thereby, there is an advantage that uneven wear of the block row is suppressed.

  In the pneumatic tire according to the present invention, the groove wall angle θ of at least one of the circumferential main grooves is in the range of θ ≧ 8 [deg].

  In this pneumatic tire, since the range of the groove wall angle θ of the circumferential main groove is optimized, there is an advantage that the rolling resistance of the tire is reduced.

  In the pneumatic tire according to the present invention, the groove wall angle θ of at least one of the circumferential main grooves changes as it goes in the tire circumferential direction.

  In this pneumatic tire, the rigidity of the land portion (block row) is increased by changing the groove wall angle θ. Thereby, the fall of the land part is suppressed and there exists an advantage which the rolling resistance of a tire increases.

  In the pneumatic tire according to the present invention, a narrow groove extending in the tire circumferential direction is formed at the outer end in the width direction of the tread portion.

  In this pneumatic tire, uneven wear of the shoulder ribs is suppressed by positive wear of the fine ribs formed by the fine grooves when the tire contacts the ground. Thereby, there exists an advantage which the uneven wear-proof performance of a tire improves.

  Moreover, in the pneumatic tire according to the present invention, a narrow groove extending in the tire circumferential direction is formed in the buttress portion.

  In this pneumatic tire, the narrow groove is closed when the tire is in contact with the ground, whereby the contact pressure in the shoulder region (shoulder rib) of the tread portion is reduced, and uneven wear is suppressed. Thereby, there exists an advantage which the uneven wear-proof performance of a tire improves.

  The pneumatic tire according to the present invention is applied to a heavy-duty pneumatic radial tire.

  In a heavy-duty pneumatic radial tire, the rolling resistance of the tire tends to increase. Therefore, there is an advantage that the effect of reducing the rolling resistance can be obtained more remarkably by applying such a pneumatic tire.

  In the pneumatic tire according to the present invention, (1) the groove width of the width direction groove is enlarged at at least one opening of the width direction groove, and (2) the groove depth of the width direction groove at the opening is Since it is enlarged by a plurality of groove bottom portions including the first groove bottom portion, the second groove bottom portion, and the third groove bottom portion, the groove volume of the width direction groove increases stepwise at the opening. Thereby, there is an advantage that the edge force of the block row is increased and the snow braking performance of the tire is improved. Further, there is an advantage that the drainage of the width direction groove is improved and the wet performance of the tire is improved. Further, (3) since the narrow groove is formed at the bottom of the first groove of the width direction groove, the drainage of the width direction groove after the progress of wear of the tread portion is ensured. Thereby, there is an advantage that the wet performance of the tire is ensured even after the progress of wear of the tread portion.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a plan view showing a tread surface of a pneumatic tire according to an embodiment of the present invention. 2 to 5 are a plan view (FIG. 2), an enlarged plan view (FIG. 3), a cross-sectional view taken along line AA (FIG. 4), and a perspective view (FIG. 2) showing the widthwise grooves of the pneumatic tire depicted in FIG. 1. FIG. 5). 6-9 is explanatory drawing which shows the example of the groove width of the width direction groove | channel described in FIG. 10-15 is explanatory drawing which shows the modification of the pneumatic tire described in FIG. FIG. 16 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. 17-20 is explanatory drawing which shows the conventional pneumatic tire.

[Pneumatic tire]
The pneumatic tire 1 includes at least three circumferential main grooves 21 and 22 extending in the tire circumferential direction, a plurality of width direction grooves 31 and 32 extending in the tire width direction, and these circumferential main grooves. 21 and 22 and a plurality of block rows 41 and 42 defined by the width direction grooves 31 and 32 are provided in the tread portion (see FIG. 1). Thereby, a traction pattern based on the block row is formed.

  For example, in this embodiment, four circumferential main grooves 21 and 22 are formed in the tread portion (see FIG. 1). A plurality of width direction grooves 31 (32) that connect adjacent circumferential main grooves 21, 21 (21, 22) are disposed in the tread portion center region. These circumferential main grooves 21 and 22 and width direction grooves 31 and 32 form three block rows 41 and 42 in the tread portion center region. In the tread portion shoulder region, a rib (shoulder rib) 43 defined by the circumferential main groove 22 located on the outer side in the tire width direction and the end portion of the tread portion is formed.

  In this pneumatic tire 1, (1) the groove width w of the width direction groove 31 (32) is enlarged at at least one opening of the width direction groove 31 (32). (2) The groove depth of the width direction groove 31 (32) in the opening is smaller than the first groove bottom 311 (321) having the shallowest groove depth h1 and the first groove bottom 311 (321). A second groove bottom 312 (322) having a deep groove depth h2 and a third groove bottom having a groove depth h3 deeper than the second groove bottom 312 (322) and reaching the circumferential main groove 21 (22) 313 (323) and a plurality of stages of groove bottoms are enlarged step by step (see FIGS. 1 to 5). (3) A narrow groove 314 (324) having a groove width narrower than the groove width w of the width direction groove 31 (32) is formed in the first groove bottom 311 (321) of the width direction groove 31 (32). Is done.

  For example, in this embodiment, the width direction groove 31 (32) is provided so as to connect adjacent circumferential main grooves 21, 21 (21, 22) (see FIGS. 1 and 2). In the opening of the width direction groove 31 (32), the groove width w of the width direction groove 31 (32) increases from the center line l of the block row 41 (42) toward the circumferential main groove 21 (22). (See FIGS. 2, 3 and 5).

  At this time, the groove width w of the width direction groove 31 (32) may be enlarged by two-stage groove widths w1 and w2 from the center line l of the block row 41 (42) toward the opening (FIG. 6). (See FIG. 8), and may be enlarged by three stages of groove widths w1 to w3 (see FIG. 9). Further, the groove width w of the width direction groove 31 (32) may be expanded by a fan-shaped groove wall at the opening (see FIG. 6), or may be linearly expanded from the groove center line l. (See FIG. 7). Also, the opening may be enlarged by a parabolic groove wall (see FIG. 8).

  Further, the groove depth of the width direction groove 31 (32) in the opening is enlarged from the center line l of the block row 41 (42) toward the circumferential main groove 21 (22) (FIGS. 3 to 5). reference). Moreover, the groove depth of the width direction groove | channel 31 (32) is expanded in steps by groove depth h1-h3. Specifically, the groove bottom of the width direction groove 31 (32) has a shallowest groove depth h1, a first groove bottom 311 (321), and a groove depth h2 deeper than the first groove bottom 311 (321). A third groove bottom portion 312 (322) having a groove depth h3 deeper than the second groove bottom portion 312 (322) and reaching the circumferential main groove 21 (22). It is constituted by. The first groove bottom 311 (321), the second groove bottom 312 (322), and the third groove bottom 313 (323) extend from the center line 1 of the block row 41 (42) to the circumferential main groove 21 (22). ) Are arranged in a staircase pattern toward the side. Thereby, the groove depth of the width direction groove | channel 31 (32) is expanded in steps in the opening part.

  Moreover, the groove depth of the width direction groove | channel 31 (32) becomes the deepest in the 3rd groove bottom part 313 (323), and the width direction groove | channel 31 (32) is circumferential direction in this 3rd groove bottom part 313 (323). It opens to the main groove 21 (22) (see FIGS. 4 and 5). Further, the groove depth h3 of the third groove bottom 313 (323) and the groove depth h 'of the circumferential main groove 21 (22) are set equal. Therefore, the third groove bottom 313 (323) and the groove bottom 211 (221) of the circumferential main groove 21 (22) are on the same plane. Thereby, the drainage property from the width direction groove | channel 31 (32) (3rd groove bottom part 313 (323)) to the circumferential direction main groove 21 (22) is improved.

  The first groove bottom 311 (321), the second groove bottom 312 (322), and the third groove bottom 313 (323) all have a groove bottom parallel to the tread surface of the block row 41 (42). These are connected to adjacent groove bottoms by a plane perpendicular to each groove bottom surface (see FIGS. 4 and 5). Further, a groove is further provided between the first groove bottom 311 (321) and the second groove bottom 312 (322) and between the second groove bottom 312 (322) and the third groove bottom 313 (323). A bottom may be added (not shown). Thereby, the opening part of the width direction groove | channel 31 (32) is expanded further in steps.

  A narrow groove 314 (324) is formed in the first groove bottom 311 (321) of the width direction groove 31 (32) (see FIGS. 3 to 5). The narrow groove 314 (324) extends along the groove length direction of the width direction groove 31 (32). The groove width of the narrow groove 314 (324) is set to be narrower than the groove width w of the width direction groove 31 (32). Specifically, when wear of the block row 41 (42) progresses and the first groove bottom 311 (321) reaches the tread surface, the narrow groove 314 (324) serves as a water channel to drain the tread surface. The groove width of the narrow groove 314 (324) is set as much as possible.

[effect]
As described above, in this pneumatic tire 1, (1) the groove width w of the width direction groove 31 (32) is enlarged in at least one opening of the width direction groove 31 (32), and (2 ) The groove depth of the width direction groove 31 (32) in the opening is a plurality of stages including the first groove bottom 311 (321), the second groove bottom 312 (322), and the third groove bottom 313 (323). Since it is enlarged by the bottom part, the groove volume of the width direction groove | channel 31 (32) increases in steps in an opening part. Thereby, the edge force of the block row 41 (42) is increased, and there is an advantage that the snow braking performance of the tire is improved. Further, there is an advantage that the drainage of the width direction groove 31 (32) is improved and the wet performance of the tire is improved.

  Moreover, since the groove depth of the width direction groove 31 (32) gradually changes in multiple steps (at least two steps), the groove depth of the width direction groove changes abruptly (in one step) at the opening. Compared with the structure (refer FIGS. 17-20) to perform, the rigidity of the block row | line | column 41 (42) is ensured appropriately. Accordingly, there is an advantage that the deformation of the block row 41 (42) at the time of tire contact is suppressed and the rolling resistance of the tire is maintained. In particular, in a pneumatic tire having a traction pattern, since a large number of width direction grooves are arranged, the rolling resistance of the tire tends to increase. In this respect, the above configuration is particularly advantageous in that the rolling resistance of the tire is reduced.

  Further, (3) since the narrow groove 314 (324) is formed in the first groove bottom 311 (321) of the width direction groove 31 (32), the drainage of the width direction groove 31 (32) after progress of wear of the tread portion. Sex is secured. Thereby, there is an advantage that the wet performance of the tire is ensured even after the progress of wear of the tread portion.

[Additional matter 1]
In this pneumatic tire 1, the sum h1 + h4 of the groove depth h1 of the first groove bottom 311 (321) and the groove depth h4 of the narrow groove 314 (424), and the groove depth of the second groove bottom 312 (322). The length h2 is preferably equal (see FIG. 4). That is, the groove depth h4 of the narrow groove 314 (424) is set so that the groove bottom of the narrow groove 314 (424) coincides with the second groove bottom portion 312 (322). In such a configuration, there is an advantage that the generation of cracks in the groove bottom of the narrow groove is suppressed as compared with a configuration in which there is a step between the groove bottom and the second groove bottom portion.

  Moreover, in said structure, chamfering is given to the level | step-difference part (edge part of the 1st groove bottom part 311 (321)) of the 1st groove bottom part 311 (321) and the 2nd groove bottom part 312 (322). Preferred (not shown). Thereby, there exists an advantage by which generation | occurrence | production of the crack in the groove bottom of a narrow groove is suppressed effectively.

[Additional matter 2]
Further, in the pneumatic tire 1, it is preferable that the width direction groove 31 (32) crosses the block row 41 (42) in an S shape or a Z shape in a plan view of the tread portion (FIG. 1 and FIG. 2). That is, the width direction groove 31 (32) crosses the block row 41 (42) while meandering in an S shape or a Z shape, and opens in the circumferential main grooves 21, 21 (21, 22).

  In such a configuration, since the groove wall of the block is partitioned into an S shape or a Z shape by the width direction groove 31 (32), the blocks adjacent to each other in the tire circumferential direction mesh firmly with each other during inflation. Then, the amount of displacement of the tread portion (particularly the center region) toward the outer side in the tire radial direction is reduced, and changes in the tire shape at the time of tire contact are suppressed. Thereby, there exists an advantage by which the rolling resistance of a tire is reduced. In such a configuration, when the tire is in contact with the ground, the blocks adjacent to each other in the tire circumferential direction mesh with each other, so that the ground contact pressure of the block is made uniform. Thereby, there is an advantage that the heel and toe wear of the block is suppressed and the uneven wear resistance performance of the tire is improved.

  Further, as described above, in the configuration in which the block row 41 (42) is partitioned by the S-shaped or Z-shaped width direction groove 31 (32), each block of the block row 41 (42) has the following relationship. It is preferable to have (refer FIG. 2). That is, the intersection width (overlap width) in the tire circumferential direction between one block and a pair of blocks adjacent to this block is defined as an intersection width C1 and an intersection width C2, respectively. The length of the block in the tire circumferential direction is referred to as a block length L. At this time, the intersection width C1, the intersection width C2, and the block length L have a relationship of 0.1 ≦ C1 / L, 0.1 ≦ C2 / L, and 0.3 ≦ (C1 + C2) /L≦0.8. Is preferred.

  In such a configuration, the positional relationship between the blocks constituting the block row 41 (42) is optimized, so that the meshing property between adjacent blocks is improved. Thereby, the change of the tire shape at the time of tire contact is suppressed, and there exists an advantage by which the rolling resistance of a tire is reduced. Further, there is an advantage that the uneven wear resistance performance of the tire is improved by suppressing the heel and toe wear of the block.

[Additional matter 3]
Moreover, in this pneumatic tire 1, when taking the area | region of 70 [%] of the contact width T of the tire centering on the centerline CL, the four circumferential direction main grooves 21 and 22 are arrange | positioned in this area | region. (See FIG. 1). In such a configuration, the drainage performance is improved by the four circumferential main grooves 21 and 22, and the ground pressure of each of the block rows 41 to 43 is made uniform to control the distortion of the tread portion. Thereby, there is an advantage that the wet performance of the tire is maintained and the rolling resistance of the tire is reduced.

  For example, in this embodiment, an area of 35 [%] (T / 2 × 0.70) of the tire contact width T is taken in the left-right direction of the tire around the center line CL, and four circumferences are included in this area. Direction main grooves 21 and 22 are arranged (see FIG. 1).

  Note that the tire contact width T means that the tire is attached to the applicable rim and applied with a specified internal pressure and is placed perpendicular to the flat plate in a stationary state and applied with a load corresponding to the specified load. The maximum linear distance in the tire axial direction at the contact surface between the tire and the flat plate.

  Here, the applicable rim means “applied rim” defined in JATMA, “Design Rim” defined in TRA, or “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The specified load means “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO. However, in the case of a tire for a passenger car, the specified internal pressure is an air pressure of 180 [kPa], and the specified load is 88 [%] of the maximum load capacity.

  In the above configuration, in the three block rows 41 and 42 defined by the four circumferential main grooves 21 and 22, the block width R1 of the central block row 41 and the block rows 42 and 42 on both sides are arranged. The block width R2 preferably has a relationship of 0.95 ≦ R1 / R2 ≦ 1.05 (see FIG. 1). In such a configuration, since the relationship between the block widths R1 and R2 of the block rows 41 and 42 in the tread portion center region is optimized, the contact pressure of the block rows 41 and 42 at the time of tire contact is made uniform. Thereby, there is an advantage that uneven wear of the block rows 41 and 42 is suppressed.

  The block widths R1 and R2 of the block rows 41 and 42 are defined by the width dimensions when the tire is mounted on the applicable rim and applied with a specified internal pressure and is in a no-load state.

[Additional matter 4]
Further, in the pneumatic tire 1, the total groove area A of the circumferential main grooves 21 and 22 and the total groove area B of the width direction grooves 31 and 32 on the ground contact surface of the tire are 0.25 ≦ B / (A + B) ≦. It is preferable to have a relationship of 0.45. That is, the ratio S = B / X of the total groove area B of the width direction grooves 31 and 32 on the tire contact surface and the contact area X of the tire. Further, the ratio G + (A + B) / the sum A + B of the total groove area A of the circumferential main grooves 21 and 22 and the total groove area B of the widthwise grooves 31 and 32 on the tire contact surface and the tire contact area X Take X. At this time, the ratio S / G (= B / (A + B)) between the ratio G and the ratio S preferably has a relationship of 0.25 ≦ S / G ≦ 0.45.

  In such a configuration, the ratio B / (A + B) of the total groove area B of the width direction grooves 31 and 32 to the total groove area A + B of the tire ground contact surface is optimized, whereby the block rigidity of the block rows 41 and 42 is optimized. Is done. Thereby, there is an advantage that the rolling resistance of the tire is reduced, and there is an advantage that the uneven wear resistance performance of the tire is improved. For example, when B / (A + B) <0.25, the block rigidity increases and uneven wear tends to occur in the block. In addition, when 0.45 <B / (A + B), the block rigidity is reduced and the rolling resistance of the tire is deteriorated.

  The contact surface of the tire is the contact surface between the tire and the flat plate when the tire is mounted on the applicable rim and applied with the specified internal pressure and is placed perpendicular to the flat plate in a no-load and stationary state. Say. Then, with reference to the tire contact surface, the total groove area A of the circumferential main grooves 21 and 22 and the total groove area B of the width direction grooves 31 and 32 and the tire contact area X are defined on the tire contact surface. The

  Further, in this pneumatic tire 1, the sum A + B of the total groove area A of the circumferential main grooves 21 and 22 and the total groove area B of the width direction grooves 31 and 32 on the ground contact surface of the tire and the ground contact area X of the tire The ratio G = (A + B) / X is preferably in the range of G ≦ 0.25. Furthermore, the ratio G = (A + B) / X is more preferably in the range of 0.21 ≦ G ≦ 0.22.

  In such a configuration, since the ratio of the total groove area A + B to the ground contact area X is optimized, the rigidity of the entire block rows 41 and 42 is ensured. Accordingly, there is an advantage that the distortion of the block rows 41 and 42 at the time of tire contact is suppressed, and the rolling resistance of the tire is reduced.

[Additional matter 5]
Moreover, in this pneumatic tire 1, it is preferable that the groove wall angle θ of at least one circumferential main groove 21, 22 is in a range of θ ≧ 8 [deg] (see FIG. 10). In such a configuration, since the range of the groove wall angle θ of the circumferential main grooves 21 and 22 is optimized, there is an advantage that the rolling resistance of the tire is reduced. For example, when θ <8 [deg], when the distortion of the tread portion increases during rolling of the tire, the block collapses and the rolling resistance of the tire increases. Therefore, by making the cross-sectional shape of the block trapezoidal with θ ≧ 8 [deg], the collapse of the block is suppressed, and the rolling resistance of the tire increases. The groove wall angle θ is defined by the angle of inclination between the perpendicular to the tread of the land portion and the groove wall surface of the circumferential main grooves 21 and 22 in a sectional view of the circumferential main grooves 21 and 22 in the groove depth direction. The

  Moreover, in this pneumatic tire 1, it is preferable that the groove wall angle θ of at least one circumferential main groove 21, 22 changes as it goes in the tire circumferential direction (see FIG. 12). For example, in this embodiment, the groove wall angle θ of the circumferential main grooves 21 and 22 changes to a wave shape or a zigzag shape as it goes in the tire circumferential direction in a plan view of the tread portion. In such a configuration, the rigidity of the land portions (block rows 41 and 42) is increased by the change in the groove wall angle θ. Thereby, the fall of the land part is suppressed and there exists an advantage which the rolling resistance of a tire increases.

[Additional matter 6]
Moreover, in this pneumatic tire 1, it is preferable that the narrow groove extended in the tire circumferential direction is formed in the width direction outer side edge part of a tread part (refer FIG. 13). For example, in this embodiment, a narrow groove 431 is formed in the shoulder rib 43. The narrow groove 431 extends in the tire circumferential direction along the widthwise outer end of the shoulder rib 43. The narrow groove 431 forms a thin rib 432 at the outer end in the width direction of the shoulder rib 43. In such a configuration, the uneven wear of the shoulder ribs 43 is suppressed by the positive wear of the fine ribs 432 formed by the fine grooves 431 at the time of tire contact. Thereby, there exists an advantage which the uneven wear-proof performance of a tire improves.

  In the pneumatic tire 1, it is preferable that a narrow groove 433 extending in the tire circumferential direction is formed in the buttress portion (see FIG. 14). In such a configuration, the narrow groove 433 is closed when the tire is in contact with the ground, so that the contact pressure in the tread shoulder region (shoulder rib 43) is reduced and uneven wear is suppressed. Thereby, there exists an advantage which the uneven wear-proof performance of a tire improves.

[Additional matter 7]
In the pneumatic tire 1, the groove depth h1 of the first groove bottom 311 (321) and the groove depth h ′ of the circumferential main groove 21 (22) are 0.30 ≦ h1 / h ′ ≦ 0. And the groove width w of the circumferential groove 31 (32) and the groove width w ′ of the circumferential main groove 21 (22) have a relationship of 0.20 ≦ w / w ′ ≦ 0.50. It is preferable (see FIG. 10 and FIG. 11).

  In such a configuration, the ratio h1 / h ′ of the groove depth h1 of the first groove bottom 311 (321) and the groove depth h ′ of the circumferential main groove 21 (22), and the grooves of the widthwise grooves 31, 32 Since the ratio w / w ′ between the width w and the groove width w ′ of the circumferential main groove 21 (22) is optimized, the groove volume of the width direction groove 31 (32) is appropriately secured. Thereby, there exists an advantage by which the snow braking performance of a tire is maintained.

[Additional matter 8]
Further, in the pneumatic tire 1, when the belt reinforcing layer 5 is disposed in the tread portion, the thickness of the tread rubber from the groove bottoms of the circumferential main grooves 21 and 22 in the center region of the tread portion to the belt reinforcing layer 5 is increased. The thickness t is preferably in the range of 3.0 [mm] ≦ t ≦ 5.5 [mm] (see FIG. 15). In such a configuration, since the thickness t of the tread rubber under the grooves of the circumferential main grooves 21 and 22 is optimized, there is an advantage that the rolling resistance of the tire is effectively reduced. For example, when 5.5 [mm] <t, the distortion of the tread rubber at the time of tire contact increases, the block collapses, and the tire rolling resistance increases. Further, when t <3.0 [mm], damage due to stone drilling or the like easily reaches the belt reinforcing layer, so that it is likely to cause a failure and cracks are likely to occur.

  In the pneumatic tire 1, tan δ when the tread rubber is heated at 100 [° C.] is preferably in the range of 0.01 ≦ tan δ ≦ 0.10. In such a configuration, since tan δ of the tread rubber is optimized, the hysteresis loss of the tread portion is reduced. Thereby, there exists an advantage by which the rolling resistance of a tire is reduced effectively. For example, when 0.10 <tan δ, the amount of heat generated by the tread rubber during tire rolling increases, and the rolling resistance of the tire increases. Further, when tan δ <0.01, the productivity of the tire is deteriorated.

[Applicable to]
The pneumatic tire 1 is preferably a heavy-duty pneumatic radial tire. In such a pneumatic tire, the rolling resistance of the tire tends to increase. Therefore, there is an advantage that the effect of reducing the rolling resistance can be obtained more remarkably by applying such a pneumatic tire.

[performance test]
In this example, for a plurality of pneumatic tires with different conditions, (1) low rolling resistance performance, (2) snow braking performance, (3) wet performance, (4) uneven wear resistance, and (5) groove bottom A performance test on crack performance was performed (see FIG. 16). In this performance test, a pneumatic tire having a tire size of 275 / 80R22.5 is mounted on an applicable rim specified by JATMA, and a specified internal pressure is applied to the pneumatic tire.

  (1) In a performance test related to low rolling resistance performance, a drum type rolling resistance tester loads a pneumatic tire with a load of 30.89 [kN] and measures rolling resistance. And index evaluation is performed based on this measurement result. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable the rolling resistance tends to decrease.

  (2) In the performance test related to snow braking performance, pneumatic tires are mounted on a heavy load vehicle having a total vehicle weight of 25 [t] (6 × 2), and braking from a running speed of 40 [km / h] on a snow road surface is performed. The distance is evaluated. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  (3) In the performance test relating to wet braking performance, pneumatic tires are mounted on a heavy load vehicle having a total vehicle weight of 25 [t] (6 × 2), and braking from a traveling speed of 40 [km / h] on a wet road surface is performed. The distance is evaluated. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  In the performance test regarding (4) uneven wear resistance and (5) groove bottom crack resistance, a pneumatic tire is mounted on a heavy-duty vehicle having a total vehicle weight of 25 [t] (6 × 2), and a general pavement 3 Drive 10,000 km. Then, after this running, the degree of uneven wear and the occurrence of cracks in the groove bottom of the narrow groove in the width direction groove are observed and index evaluation is performed. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  In the pneumatic tire 100 of Conventional Example 1, the groove width w of the width direction groove 120 is set to be constant (one step) (see FIGS. 17 and 18). Further, a bottom raised portion 121 is provided at the groove bottom of the width direction groove 120, and the groove depth of the width direction groove 120 changes from h1 to h3 (> h1) at the opening. On the other hand, in the pneumatic tire 200 of Conventional Example 2, the groove width w of the width direction groove 220 is set to be constant (one step) (see FIGS. 19 and 20). Also, a bottom raised portion 221 is provided at the groove bottom of the width direction groove 220, and the groove depth of the width direction groove 220 changes from h1 to h3 (> h1) at the opening. The bottom raised portion 221 is provided with a narrow groove 222 having a groove depth h4 from the tread surface.

  In the pneumatic tires 1 of Invention Examples 1 to 3, the groove width w of the width direction groove 31 (32) is enlarged at both openings of the width direction groove 31 (32) (see FIG. 1). Further, the groove depth of the width direction groove 31 (32) in each opening is the first groove bottom 311 (321) having the groove depth h1, the second groove bottom 312 (322) having the groove depth h2, and the groove. The third groove bottom portion 313 (323) having a depth h3 is enlarged stepwise (see FIGS. 3 to 5). A narrow groove 314 (324) having a groove depth h4 is formed in the first groove bottom 311 (321) of the width direction groove 31 (32).

  As shown in the test results, it can be seen that in the inventive examples 1 to 3, the snow braking performance and the wet performance are improved as compared with the conventional example 1 (see FIG. 16). Moreover, it can be seen that the low rolling resistance performance of the tire is maintained at the level of Conventional Example 1 as compared with Conventional Example 2. Further, when Invention Example 1 is compared with Invention Example 2, the relationship (C1 + C2) / L of the intersection width C1, intersection width C2, and block length L of each block constituting the block rows 41 and 42 is optimized. Thus, it can be seen that the low rolling resistance performance of the tire is improved.

  Further, when Invention Example 2 and Invention Example 3 are compared, the number of circumferential main grooves 21 and 22, the ratio of width direction grooves B / (A + B), and the groove area ratio G are optimized, thereby reducing the tire width. It can be seen that the rolling resistance performance is further improved. Further, when Invention Example 3 and Comparative Example 4 are compared, the groove depth h4 of the narrow groove 314 (324) of the first groove bottom portion 311 (321) is optimized, so that the uneven wear resistance and resistance of the tire are improved. It can be seen that the groove bottom crack performance is improved.

  As described above, the pneumatic tire according to the present invention is useful in that the snow braking performance and wet performance of the tire can be improved while maintaining the rolling resistance of the tire.

It is a top view which shows the tread surface of the pneumatic tire concerning the Example of this invention. It is a top view which shows the width direction groove | channel of the pneumatic tire described in FIG. It is an enlarged plan view which shows the width direction groove | channel of the pneumatic tire described in FIG. It is AA sectional view which shows the width direction groove | channel of the pneumatic tire described in FIG. It is a perspective view which shows the width direction groove | channel of the pneumatic tire described in FIG. It is explanatory drawing which shows the example of the groove width of the width direction groove | channel described in FIG. It is explanatory drawing which shows the example of the groove width of the width direction groove | channel described in FIG. It is explanatory drawing which shows the example of the groove width of the width direction groove | channel described in FIG. It is explanatory drawing which shows the example of the groove width of the width direction groove | channel described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is explanatory drawing which shows the modification of the pneumatic tire described in FIG. It is a graph which shows the result of the performance test of the pneumatic tire concerning the Example of this invention. It is explanatory drawing which shows the conventional pneumatic tire. It is explanatory drawing which shows the conventional pneumatic tire. It is explanatory drawing which shows the conventional pneumatic tire. It is explanatory drawing which shows the conventional pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 5 Belt reinforcement layers 21, 22 Circumferential main grooves 211, 221 Groove bottoms 31, 32 Width direction grooves 311, 321 First groove bottom parts 312, 322 Second groove bottom parts 313, 323 Third groove bottom parts 314, 324 Narrow groove 41, 42 Block row 43 Shoulder rib 431 Narrow groove 432 Narrow rib 433 Narrow groove

Claims (10)

A plurality of block rows defined by at least three circumferential main grooves extending in the tire circumferential direction, a plurality of width direction grooves extending in the tire width direction, and the circumferential main grooves and the width direction grooves And a pneumatic tire having a tread portion,
The groove width of the width direction groove is enlarged in at least one opening of the width direction groove, and the groove depth of the width direction groove in the opening has the shallowest groove depth h1. A bottom portion, a second groove bottom portion having a groove depth h2 deeper than the first groove bottom portion, and a third groove bottom portion having a groove depth h3 deeper than the second groove bottom portion and reaching the circumferential main groove. DOO enlarged stepwise by a groove bottom of the plurality of stages including,
A narrow groove having a groove width narrower than the groove width of the widthwise groove is formed at the bottom of the first groove ; and
A pneumatic tire , wherein a sum h1 + h4 of a groove depth h1 of the first groove bottom and a groove depth h4 of the narrow groove is equal to a groove depth h2 of the second groove bottom . The pneumatic tire according to claim 1, chamfering is performed on the stepped portion between the second groove bottom portion and the first groove bottom. The pneumatic tire according to claim 1 or 2 , wherein the widthwise grooves cross the block row in an S shape or a Z shape in a plan view of the tread portion. When taking a region of 70 [%] of the contact width T of the tire around the center line CL, claim 1-3, wherein the circumferential main grooves of the four in the region is located Pneumatic tire described in 2. In the three block rows defined by the four circumferential main grooves, the block width R1 of the central block row and the block width R2 of each block row on both sides are 0.95 ≦ R1 / R2 ≦ 1. The pneumatic tire according to claim 4 , having a relationship of 0.05. At least one pneumatic tire according to any one of claims 1-5, wherein the groove wall angle theta of the circumferential main grooves is in the range of θ ≧ 8 [deg] of. The pneumatic tire according to any one of claims 1 to 6 , wherein a groove wall angle θ of at least one of the circumferential main grooves changes in the tire circumferential direction. The pneumatic tire according to any one of claims 1 to 7 , wherein a narrow groove extending in a tire circumferential direction is formed at an outer end portion in a width direction of the tread portion. The pneumatic tire according to any one of claims 1 to 8 , wherein a narrow groove extending in the tire circumferential direction is formed in the buttress portion. The pneumatic tire according to any one of claims 1 to 9 , which is applied to a heavy-duty pneumatic radial tire.

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