Pneumatic tire

Abstract

To reduce noise during traveling.SOLUTION: A pneumatic tire 1 includes a tread 10 and has a specified rotational direction. The tread 10 includes: a plurality of main grooves 20 and 21 extending from an equator CL side toward ground contact ends E1 and E2 sides; and a first block set 30 and 50 and a second block set 40 and 60 provided along the main grooves 20 and 21 and alternately arranged across the main grooves 20 and 21 along a tire circumferential direction, where the main grooves 20 and 21 have a larger inclination with respect to a tire axial direction on the equator CL side than the inclination on the ground contact ends E1 and E2 sides, the first block set 30 and 50 and the second block set 40 and 60 each include a plurality of blocks, and the number of blocks included in the first block set 30 and 50 is different from the number of blocks included in the second block set 40 and 60.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a specified rotational direction.

Background Art

[0002] Conventionally, directional tires with a specified rotational direction of the tire have been known. For example, Patent Document 1 discloses a pneumatic tire including a main groove extending from the equator side toward the ground contact end side, and blocks formed along the main groove and alternately arranged with the main groove in the tire circumferential direction. In the tread pattern disclosed in Patent Document 1, the blocks include a center block located on the equator side and a shoulder block located on the ground contact end side. And the center block and the shoulder block are continuously arranged along the tire circumferential direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, pneumatic tires with excellent noise performance have been demanded. As the noise during driving, there is the impact sound generated when each block collides with the road surface during driving. As described above, in the pneumatic tire disclosed in Patent Document 1, the center block and the shoulder block are continuously arranged along the tire circumferential direction. Therefore, the impact sound when each block collides with the road surface is likely to occur at a certain period, and the peak value of the impact sound is generated, which causes noise.

Means for Solving the Problems

[0005] The pneumatic tire according to the present invention includes a tread and is a pneumatic tire with a specified rotation direction. The tread extends from the equator side toward the ground contact end side and has a plurality of main grooves arranged at intervals in the tire circumferential direction, and first block groups and second block groups provided along the main grooves and arranged alternately across the main grooves in the tire circumferential direction. The main grooves have a greater inclination with respect to the tire axial direction on the equator side than on the ground contact end side. The first block group and the second block group each include a plurality of blocks, and the number of blocks included in the first block group is different from the number of blocks included in the second block group.

Effects of the Invention

[0006] According to the pneumatic tire of the present invention, the noise during running can be reduced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0008] Hereinafter, with reference to the drawings, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail. The embodiments described below are merely examples, and the present invention is not limited to the following embodiments. Also, forms formed by selectively combining the respective components of the embodiments described below are included in the present invention.

[0009] FIG. 1 is a perspective view showing a part of a pneumatic tire 1 which is an example of an embodiment, and also shows the internal structure of the tire. As shown in FIG. 1, the pneumatic tire 1 includes a tread 10 which is a portion in contact with the road surface, a pair of sidewalls 11 disposed on both sides of the tread 10, and a pair of beads 13 disposed on the inner side in the tire radial direction of the sidewalls 11. Further, the pneumatic tire 1 includes a carcass 14 spanned between the pair of beads 13 and an inner liner 15 disposed on the inner side in the tire radial direction of the carcass 14.

[0010] The pneumatic tire 1 is a directional tire with a specified rotational direction. In this specification, the "rotational direction" of the tire means the rotational direction when the vehicle on which the tire is mounted moves forward. Also, in this specification, the terms "left and right" are used for convenience of explanation, and this left and right means left and right in the traveling direction of the vehicle with the tire mounted on the vehicle. The pneumatic tire 1 preferably has a display for indicating the mounting direction with respect to the vehicle. On the side surface of the pneumatic tire 1, for example, at least one of characters and arrows indicating the rotational direction is provided. FIG. 1 shows an arrow indicating the rotational direction of the tire. Also, in some drawings including FIG. 1, arrows indicating the directions of "front, rear, left, and right" are shown in the direction in which the vehicle moves forward.

[0011] Also, in this specification, the terms "tread-in side" and "kick-out side" are used for the blocks and the like constituting the tread 10. The "tread-in side" of the block or the like means the side that first contacts the road surface (front in the rotational direction) when the pneumatic tire 1 rotates in the direction in which the vehicle moves forward, and the "kick-out side" means the side that contacts the road surface later (rear in the rotational direction).

[0012] The tread 10 has main grooves 20 and 21. The main grooves 20 and 21 extend from the equator CL (see FIG. 2) side toward the ground contact end side, and have a larger inclination angle with respect to the tire axis direction on the equator CL side than on the ground contact end side. More specifically, the main groove 20 extends from the equator CL side toward the ground contact end E1 side (see FIG. 2), and the main groove 21 extends from the equator CL side toward the ground contact end E2 side (see FIG. 2).

[0013] Here, the equator CL means a line along the tire circumferential direction passing through the exact center in the tire axis direction of the tread 10 (a position equidistant from the ground contact ends E1 and E2). Also, in this specification, the ground contact ends E1 and E2 are defined as both ends in the tire axis direction of the region that contacts the flat road surface when a predetermined load is applied in a state where the unused pneumatic tire 1 is mounted on a standard rim and filled with air to reach the standard internal pressure. In the case of a passenger car tire, the predetermined load is a load corresponding to 88% of the standard load.

[0014] Here, the "standard rim" is a rim determined by the tire specifications, which is the "Standard Rim" in JATMA, and the "Measuring Rim" in TRA and ETRTO. The "standard internal pressure" is the "Maximum Air Pressure" in JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and the "INFLATION PRESSURE" in ETRTO. The standard internal pressure is usually 250 kPa for passenger car tires, but 290 kPa for tires marked as Extra Load or Reinforced. The "standard load" is the "Maximum Load Capacity" in JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and the "LOAD CAPACITY" in ETRTO. In the case of a racing kart tire, the standard load is 392 N.

[0015] The tread 10 has a first block group 30 and a second block group 40 that are arranged along the main groove 20 and include a plurality of blocks, and a first block group 50 and a second block group 60 that are arranged along the main groove 21 and include a plurality of blocks. The first block group 30 and the second block group 40 are alternately arranged in the tire circumferential direction via the main groove 20, and the first block group 50 and the second block group 60 are alternately arranged in the tire circumferential direction via the main groove 21. Here, a block is a convex portion that is divided by a main groove or a slit and protrudes toward the outer side in the tire radial direction. That is, a region divided by a sipe is not included in a block. In addition, in this specification, a groove with a width of 1.5 mm or more is defined as a slit, and a groove with a width of less than 1.5 mm is defined as a sipe, respectively.

[0016] As will be described in detail later, the first block group 30 has three blocks, and the second block group 40 has two blocks. Specifically, the first block group 30 has a first center block 31 located on the equator CL side, a first shoulder block 33 located on the ground contact end E1 side, and a first intermediate block 32 disposed between the first center block 31 and the first shoulder block 33. The second block group 40 has a second center block 41 located on the equator CL side and a second shoulder block 42 located on the ground contact end E1 side. By arranging the main grooves 20 and 21 so that the inclination with respect to the tire axial direction is larger on the equator CL side than on the ground contact ends E1 and E2 sides, and changing the number of blocks included in each block group, the period of the impact sound when the tread 10 collides with the road surface can be shifted. As a result, the frequency of the impact sound is dispersed, and the noise during running can be reduced. In this embodiment, the first shoulder block 33 and the second shoulder block 43 have the same shape.

[0017] Further, the first block group 50 has three blocks, similar to the first block group 30, and the second block group 60 has two blocks, similar to the second block group 40. Specifically, the first block group 50 includes a first center block 51 located on the equator CL side, a first shoulder block 53 located on the ground end E2 side, and a first mediate block 52 disposed between the first center block 51 and the first shoulder block 53. Also, the second block group 60 includes a second center block 61 located on the equator CL side and a second shoulder block 62 located on the ground end E2 side. In this embodiment, the first shoulder block 53 and the second shoulder block 63 have the same shape.

[0018] The sidewall 11 is disposed on both sides of the tread 10 and is provided annularly along the tire circumferential direction. The sidewall 11 is the portion that most protrudes outward in the tire axial direction of the pneumatic tire 1 and is gently curved so as to be convex toward the outside in the tire axial direction. The sidewall 11 has a function of preventing damage to the carcass 14. The sidewall 11 is the portion that bends the most when the pneumatic tire 1 performs a cushioning action, and usually, a flexible rubber having fatigue resistance is adopted.

[0019] The pneumatic tire 1 may be provided with side ribs 12 between the ground ends E1, E2 of the tread 10 and the portion that most protrudes outward in the tire axial direction of the sidewall 11. The side ribs 12 protrude outward in the tire axial direction and are provided annularly along the tire circumferential direction. The portion from the ground ends E1, E2 of the pneumatic tire 1 or the vicinity thereof to the left and right side ribs 12 is also called a shoulder or a battless region.

[0020] Also, generally, characters, numbers, symbols, etc. called serials are provided on the sidewall 11. The serial includes information such as, for example, a size code, a manufacturing time (manufacturing year and week), and a manufacturing location (manufacturing factory code).

[0021] The bead 13 is disposed on the inner side in the tire radial direction of the sidewall 11 and is a portion fixed to the rim of the wheel. The bead 13 has a bead core 16 and a bead filler 17. The bead core 16 is composed of a steel bead wire and is an annular member extending over the entire circumference in the tire circumferential direction, and is embedded in the bead 13. The bead filler 17 has a tip-tapering shape extending outward in the tire radial direction and is an annular rigid rubber member extending over the entire circumference in the tire circumferential direction.

[0022] The carcass 14 is spanned between a pair of beads 13 and is locked by being folded around the bead core 16. The carcass 14 includes a carcass cord made of organic fiber and topping rubber. The carcass cord is disposed substantially at a right angle (for example, 80° or more and 90° or less) with respect to the tire circumferential direction. Examples of the organic fiber used for the carcass cord include polyester fiber, rayon fiber, aramid fiber, and nylon fiber.

[0023] The inner liner 15 covers the inner surface of the tire between a pair of beads 13. The inner liner 15 is composed of air-permeability-resistant rubber and has a function of maintaining the air pressure of the pneumatic tire 1.

[0024] The pneumatic tire 1 further includes a belt 18 disposed on the outer side in the tire radial direction of the carcass 14 and a cap ply 19 covering the entire outer side in the tire radial direction of the belt 18. The belt 18 is disposed on the outer peripheral side of the top of the carcass 14 and is provided so as to overlap the outer peripheral surface of the carcass 14. The belt 18 is composed of a belt ply in which cords arranged in a direction inclined with respect to the tire circumferential direction are rubber-coated. The material of the cords of the belt 18 is not particularly limited, and examples thereof include organic fibers such as polyester, rayon, nylon, and aramid, or metals such as steel. Further, the pneumatic tire 1 may further include an edge ply (not shown) disposed on the outer side in the tire radial direction of the cap ply 19 and covering both axial ends in the tire axial direction of the belt 18. The cap ply 19 and the edge ply have a function of reinforcing the belt 18.

[0025] Hereinafter, with reference to FIGS. 2 and 3, the tread pattern of the pneumatic tire 1 will be described in detail. FIG. 2 is a plan view of the pneumatic tire 1 (tread 10).

[0026] As shown in FIG. 2, the tread 10 has main grooves 20 and 21 that extend from the equator CL side toward the ground contact end side and have a larger inclination angle with respect to the tire axial direction on the equator CL side than on the ground contact end side. The main groove 20 extends from the equator CL side toward the ground contact end E1 side, and the main groove 21 extends from the equator CL side toward the ground contact end E2 side. The main grooves 20 and 21 are arranged at arbitrary intervals in the tire circumferential direction.

[0027] The main groove 20 includes two types of main grooves 20A and 20B with different lengths. The main groove 20A is longer than the main groove 20B and is provided with a length that reaches the right region of the tread 10 beyond the equator CL. The main groove 20B is provided with a length that does not exceed the equator CL in the left region of the tread 10. Similarly, the main groove 21 also includes two types of main grooves 21A and 21B with different lengths.

[0028] A first block group 30 is arranged on the indentation side of the main groove 20A, and a second block group 40 is arranged on the indentation side of the main groove 20B. That is, they are repeatedly arranged in the tire circumferential direction in the order of the main groove 20A, the first block group 30, the main groove 20B, and the second block group 40. Also, as described above, the main groove 20A is longer than the main groove 20B and is provided with a length that reaches the right region of the tread 10 beyond the equator CL. Therefore, the first block group 30 is provided with a length that reaches the right region of the tread 10 beyond the equator CL. Also, the second block group 40 is provided with a length that does not exceed the equator CL, similar to the main groove 20B.

[0029] Similarly, regarding the right side region of the tire, the first block group 50 is arranged on the indentation side of the main groove 21A, and the second block group 60 is arranged on the indentation side of the main groove 21B. That is, they are repeatedly arranged in the tire circumferential direction in the order of the main groove 21A, the first block group 50, the main groove 21B, and the second block group 60. And the first block group 50 is provided with a length that reaches the left side region of the tread 10 beyond the equator CL. Also, the second block group 60 is provided with a length that does not exceed the equator CL. Thereby, the first block group 30 and the first block group 50 are arranged in a staggered pattern along the equator CL.

[0030] In the plan view of the tread pattern of the present embodiment, with respect to the equator CL, the first block groups 30, 50 and the second block groups 40, 60 are arranged symmetrically with a predetermined pitch shifted in the tire circumferential direction. That is, the shape of the first block group 30 is the same as the shape when the first block group 50 is inverted with respect to the equator CL, and the shape of the second block group 40 is the same as the shape when the second block group 60 is inverted with respect to the equator CL (the same applies to the main grooves 20, 21). The tread pattern of the present embodiment has good left - right balance and is effective in improving handling stability.

[0031] In the plan view of the tread 10, the main groove 20, the first block group 30, and the second block group 40 have a curved shape that bulges toward the kicking - out side. Similarly, the main groove 21, the first block group 50, and the second block group 60 also have a curved shape that bulges toward the kicking - out side. That is, the main grooves 20, 21, the first block groups 30, 50, and the second block groups 40, 60 are all inclined with respect to the tire axial direction so as to be gradually located on the kicking - out side from the equator CL side toward the grounding ends E1, E2 side.

[0032] As described above, the main grooves 20 and 21 have a larger inclination angle with respect to the tire axis direction on the equator CL side than on the ground contact end E1 and E2 sides. In other words, the main grooves 20 and 21 gradually become along the tire axis direction from the equator CL side toward the ground contact ends E1 and E2, and the inclination with respect to the tire axis direction becomes gentle. The inclination angle of the main grooves 20 and 21 with respect to the tire axis direction is, for example, 30° or more and 60° or less, or 40° or more and 50° or less on the equator CL side. In a tread pattern in which the number of blocks included in the first block groups 30 and 50 and the second block groups 40 and 60 is different as in the present embodiment, by arranging the main grooves 20 and 21 so that the inclination with respect to the tire axis direction is larger on the equator CL side than on the ground contact ends E1 and E2 sides, the period of the impact sound when the tread 10 collides with the road surface can be shifted. As a result, the peak values of the impact sound are dispersed, and the noise during running can be reduced.

[0033] The main groove 20 is connected to the main groove 21 in the vicinity of the equator CL. The main groove 20 extends from the intersection with the main groove 21 toward the ground contact end E1 side and is provided across the left side rib 12 beyond the ground contact end E1. Further, the main groove 21 extends from the intersection with the main groove 20 in the vicinity of the equator CL toward the ground contact end E2 side and is provided across the right side rib 12 beyond the ground contact end E2.

[0034] The widths of the main grooves 20 and 21 may be constant over the entire length, but in this embodiment, they gradually increase from the equator CL side toward the ground contact ends E1 and E2. In this case, in addition to improving the drainage performance, the snow column shear force for grasping and compacting snow is improved, and the braking performance on the snow-covered road surface is improved. The widths of the main grooves 20 and 21 are, for example, 2.0 mm or more and 10.0 mm or less on the equator CL side, and, for example, 3.0 mm or more and 15.0 mm or less on the ground contact ends E1 and E2 side. Further, the main grooves 20 and 21 are configured to have the same depth. The depth of the main grooves 20 and 21 is, for example, 5.0 mm or more and 15.0 mm or less. In this specification, the width of a groove (including a slit and a sipe) means the width on the profile surface along the ground contact surface of the tread 10 unless otherwise specified. Further, the depth of a groove means the length along the tire diameter direction from the profile surface along the ground contact surface of the tread 10 to the bottom of the groove unless otherwise specified.

[0035] Bridges 22 and 23 are provided in the grooves at the tips of the equator CL sides of the main grooves 20 and 21. The bridge 22 includes a bridge 22A provided at the tip of the main groove 20A and a bridge 22B provided at the tip of the main groove 20B. Further, the bridge 23 includes a bridge 23A provided at the tip of the main groove 21A and a bridge 23B provided at the tip of the main groove 21B.

[0036] The bridges 22 and 23 are convex portions protruding radially outward in the tire diameter direction from the bottoms of the main grooves 20 and 21, and connect adjacent center blocks. Specifically, the bridge 22A connects the first center block 31 and the first center block 51, and the bridge 22B connects the first center block 31 and the second center block 41. Further, the bridge 23A connects the second center block 41 and the first center block 51, and the bridge 23B connects the first center block 51 and the second center block 61.

[0037] By providing the bridges 22, 23, each center block is connected in the tire circumferential direction, so that the block rigidity becomes high in the vicinity of the equator CL, and the traction performance during braking can be improved. Further, since the bridges 22, 23 are provided only at the tips of the respective main grooves, good drainage performance can also be ensured. That is, by providing the bridges 22, 23, it is possible to improve the traction performance during braking while ensuring good drainage performance. The length of the bridges 22, 23 along the main grooves 20, 21 may be shorter than, for example, the length along the slits 70, 71 of the bridges 72, 73 described later. The length of the bridges 22, 23 along the main grooves 20, 21 is, for example, 0.5 mm or more and 5.0 mm or less.

[0038] The bridges 22, 23 preferably have a height of 30% or more and 70% or less, or 40% or more and 60% or less of the depth of the main grooves 20, 21. Further, the bridges 22, 23 may have an inclined region in which the height increases toward the tip on the equator CL side of the main grooves 20, 21. By providing the inclined region in the bridges 22, 23, the water in the main grooves 20, 21 easily flows toward the grounding ends E1, E2 side, and the drainage performance of the pneumatic tire 1 is improved.

[0039] The tread 10 has a slit 70 that connects the main grooves 20 to each other in the tire rotation direction and a slit 71 that connects the main grooves 21 to each other in the tire rotation direction. The slits 70, 71 are grooves having a width narrower than the maximum width of the main grooves 20, 21. The width of the slit 70 is, for example, 2.0 mm or more and 6.0 mm or less.

[0040] The slit 70 is inclined with respect to the tire circumferential direction so as to gradually move away from the grounding end E1 from the stepping-in side toward the kicking-out side. Similarly, the slit 71 is also inclined with respect to the tire circumferential direction so as to gradually move away from the grounding end E2 from the stepping-in side toward the kicking-out side. In the present embodiment, the slits 70, 71 are provided at the same depth as the main grooves 20, 21. Note that the depth of the slits 70, 71 may be smaller than the depth of the main grooves 20, 21.

[0041] The slit 70 includes a slit 70A that partitions the first intermediate block 32 and the first shoulder block 33, and a slit 70B that partitions the second center block 41 and the second shoulder block 42. As described above, the first block group 30 and the second block group 40 are alternately arranged in the tire circumferential direction. Therefore, the slit 70A and the slit 70B are alternately arranged in the tire circumferential direction. Note that the slit 70A and the slit 70B have the same shape.

[0042] Similar to the slit 70, the slit 71 includes a slit 71A that partitions the first intermediate block 52 and the first shoulder block 53, and a slit 70B that partitions the second center block 61 and the second shoulder block 62. Also, the slit 71A and the slit 71B are alternately arranged in the tire circumferential direction. Note that the slit 71 has the same shape as the slit 70 when the slit 70 is inverted with respect to the equator CL. That is, the slit 71A and the slit 71B have the same shape.

[0043] Bridges 72 and 73 are provided at the groove bottoms of the depressed ends of the slits 70 and 71, similar to the main grooves 20 and 21. The bridge 72 includes a bridge 72A provided in the slit 70A and a bridge 72B provided in the slit 70B. Also, the bridge 73 includes a bridge 73A provided in the slit 71A and a bridge 73B provided in the slit 71B.

[0044] Similar to the bridges 22 and 23, the bridges 72 and 73 are convex portions protruding radially outward from the groove bottoms of the slits 70 and 71, and connect adjacent center blocks. Specifically, the bridge 72A connects the first intermediate block 32 and the first shoulder block 33, and the bridge 72B connects the second center block 41 and the second shoulder block 42. Also, the bridge 73A connects the first intermediate block 52 and the first shoulder block 53, and the bridge 72B connects the second center block 61 and the second shoulder block 62.

[0045] By providing the bridges 72 and 73, the in-plane shrinkage around the slits 70 and 71 is suppressed. As a result, water can flow more easily through the slits 70 and 71, and the drainage performance of the pneumatic tire 1 is improved. Further, by providing the bridges 72 and 73 at the end portions on the recessed side of the slits 70 and 71, the traction performance during braking is improved.

[0046] The length of the bridges 72 and 73 along the slits 70 and 71 is preferably 60% or less, more preferably 50% or less, of the length of the slits 70 and 71. By setting the length of the bridges 72 and 73 to 60% or less of the length of the slits 70 and 71, the volume of the slits 70 and 71 can be ensured, and the braking performance on a snow-covered road surface can be ensured. Further, the length of the bridges 72 and 73 along the slits 70 and 71 is preferably 10% or more, more preferably 20% or more, of the length of the slits 70 and 71. By setting the length of the bridges 72 and 73 to 10% or more of the length of the slits 70 and 71, the improvement in the above drainage performance and the improvement in the traction performance during braking are remarkable. Therefore, the length of the bridges 72 and 73 along the slits 70 and 71 is preferably 10% or more and 60% or less, more preferably 20% or more and 50% or less, of the length of the slits 70 and 71.

[0047] The bridges 72 and 73 preferably have a height of 30% or more and 70% or less, or 40% or more and 60% or less, of the depth of the slits 70 and 71. Further, in the present embodiment, the bridges 72 and 73 have an inclined region 74 (see FIG. 3) in which the height increases as it goes toward the recessed side of the slits 70 and 71. That is, the slits 70 and 71 have a region in which the depth becomes smaller as it goes toward the recessed side of the slits 70 and 71. By providing the inclined region 74 in the bridges 72 and 73, the water in the slits 70 and 71 can flow more easily toward the main grooves 20 and 21, and the drainage performance of the pneumatic tire 1 is improved.

[0048] In addition to the slits 70 and 71, the tread 10 has a slit 80 that connects the main grooves 20 to each other in the tire rotation direction, and a slit 81 that connects the main grooves 21 to each other in the tire rotation direction. The slit 80 partitions the first center block 31 and the first mediate block 32, and the slit 81 partitions the first center block 51 and the first mediate block 52.

[0049] The slit 80 is provided substantially on the extension of the main groove 21A. The slit 80 is disposed opposite to the main groove 21A with the main groove 20A therebetween, and is disposed opposite to a slit 90 described later with the main groove 20B therebetween. By disposing the slit 80 opposite to the main groove 21A with the main groove 20A therebetween, a large amount of snow can be accumulated inside the slit 80 during driving on snow. As a result, the snow column shearing force for grasping and compacting the snow is improved, and the braking performance on the snow-covered road surface can be improved. Further, the slit 81 is provided substantially on the extension of the main groove 20A. The slit 81 is disposed opposite to the main groove 20A with the main groove 21A therebetween, and is disposed opposite to the slit 90 described later with the main groove 21B therebetween.

[0050] Both the slits 80 and 81 have a bent shape. When the slits 80 and 81 have a bent shape, the frequencies of the noises generated by the slits 80 and 81 are likely to be dispersed. As a result, the noise generated during driving can be reduced.

[0051] On the bottom surfaces of the slits 80 and 81, sipes 85 (see FIG. 3) extending along the first direction are provided. The sipes 85 are provided, for example, over the extending direction of the slits 80 and 81. That is, the sipes 85 connect the main grooves 20 and 21 to each other in the tire rotation direction. By providing the sipes 85 on the bottom surfaces of the slits 80 and 81 having a bent shape, the steering stability performance on a dry road surface can be improved.

[0052] Next, with further reference to FIG. 3, the tread pattern of the pneumatic tire 1 will be described in detail. FIG. 3 is a diagram showing an enlarged part of the tread pattern. As described above, the shape of the first block group 50 is the same as the shape when the first block group 30 is inverted with respect to the equator CL, and the shape of the second block group 60 is the same as the shape when the second block group 40 is inverted with respect to the equator CL. Therefore, hereinafter, the first block group 30 and the second block group 40 will be described, and the description of the first block group 50 and the second block group 60 will be omitted.

[0053] As shown in FIGS. 2 and 3, as described above, the tread 10 is partitioned by the main grooves 20 and has a first block group 30 and a second block group 40 including a plurality of blocks. The first block group 30 and the second block group 40 are alternately arranged in the tire circumferential direction. More specifically, the first block group 30 is arranged on the indentation side of the main groove 20A, and the second block group 40 is arranged on the indentation side of the main groove 20B.

[0054] The first block group 30 has a first center block 31 located on the equator CL side, a first shoulder block 33 located on the ground contact end E1 side, and a first intermediate block 32 arranged between the first center block 31 and the first shoulder block 33. A slit 80 that connects two adjacent main grooves 20 in the tire rotation direction is provided between the first center block 31 and the first intermediate block 32, and a slit 70A that connects two adjacent main grooves 20 in the tire rotation direction is provided between the first intermediate block 32 and the first shoulder block 33. That is, the first center block 31 and the first intermediate block 32 are partitioned by the slit 80, and the first intermediate block 32 and the first shoulder block 33 are partitioned by the slit 70A.

[0055] Further, the second block group 40 includes a second center block 41 located on the equator CL side and a second shoulder block 42 located on the ground end E1 side. Between the second center block 41 and the second shoulder block 42, a slit 70B is provided that connects two adjacent main grooves 20 in the tire rotation direction. That is, the second center block 41 and the second shoulder block 42 are partitioned by the slit 70B.

[0056] As described above, the first block group 30 includes three blocks: a first center block 31, a first intermediate block 32, and a first shoulder block 33. The second block group 40 includes two blocks: a second center block 41 and a second shoulder block 42. Here, the noise during driving is greatly affected by the peak value of the frequency of the impact sound when each block collides with the road surface. When there is no change in the number of blocks over the tire circumferential direction, that is, when the number of blocks included in the first block group 30 is the same as the number of blocks included in the second block group 40, the impact sound generated when the tread 10 collides with the road surface is likely to occur at a constant period, and the peak value of the frequency of the impact sound will occur. As a result, the noise during driving increases. On the other hand, like the tread pattern of the present embodiment, while arranging the main grooves 20, 21 so that the inclination with respect to the tire axial direction is larger on the equator CL side than on the ground end E1, E2 sides, by changing the number of blocks included in each block group, the period of the impact sound generated when the tread 10 collides with the road surface can be shifted. As a result, the frequency of the impact sound is dispersed, and the noise during driving can be reduced.

[0057] In a plan view of the tread 10, the area (S31) of the first center block 31 and the area (S32) of the first intermediate block 32 are each smaller than the area (S41) of the second center block 41, and the sum (S31 + S32) of the area (S31) of the first center block 31 and the area (S32) of the first intermediate block 32 is preferably larger than the area (S41) of the second center block 41. That is, the slit 80 partitioning the first center block 31 and the first intermediate block 32 is preferably arranged so as to satisfy S31 < S41, S32 < S41, and S31 + S32 > S41. When S31 < S41, S32 < S41, and S31 + S32 > S41 are satisfied, the sizes of the respective blocks become closer, and a pneumatic tire excellent in wear resistance can be provided. In other words, when S31 < S41, S32 < S41, and S31 + S32 > S41 are not satisfied, the difference in the sizes of the respective blocks becomes too large, and uneven wear is likely to occur in the blocks with small sizes.

[0058] In a plan view of the tread 10, the area (S31) of the first center block 31 is preferably 75% or more and 125% or less, more preferably 80% or more and 120% or less, of the area (S32) of the first intermediate block 32. When the area (S31) of the first center block 31 is 75% or more and 125% or less of the area (S32) of the first intermediate block 32, a pneumatic tire more excellent in wear resistance can be provided.

[0059] As shown in FIG. 3, in a plan view of the tread 10, the outer end 32A in the tire axial direction of the first intermediate block 32 and the outer end 41A in the tire axial direction of the second center block 41 are provided on the same straight line along the tire circumferential direction.

[0060] Further, it is preferable that the first center block 31 is arranged across the equator CL, and the second center block 41 is arranged without crossing the equator CL. In this case, when the tire described later is rotated one full turn, it becomes easier to keep the variation range of the contact length at the leading edge of contact before contact within a range of ±20% with respect to the central value, and the noise during running can be further reduced.

[0061] The tire axial lengths of the first center block 31 and the first intermediate block 32 are, for example, 10% or more and 30% or less of the contact width D (see FIG. 2), respectively. Also, the tire axial length of the second center block 41 is, for example, 15% or more and 40% or less of the contact width D.

[0062] The second center block 41 is provided with a slit 90 that extends from the main groove 20B toward the inside of the second center block 41 and terminates inside the second center block 41. The slit 90 is provided on a substantially extension of the main groove 21A and is arranged to face the slit 80 with the main groove 20B therebetween. The slit 90 provides a snow column shearing force for grasping and compacting snow during snow travel. That is, the slit 90 contributes to improving the braking performance of the pneumatic tire 1 on a snow-covered road surface.

[0063] By terminating the slit 90 inside the second center block 41, the volume of the second center block 41 can be ensured, and a decrease in block rigidity can be suppressed. As a result, while ensuring the traction performance during braking, the braking performance on a snow-covered road surface can be improved. Also, from the viewpoint of ensuring the wear resistance of the pneumatic tire 1, the slit 90 is preferably provided on the kicking-out side of the second center block 41.

[0064] The slit 90 is inclined with respect to the tire circumferential direction and the tire axial direction. In this case, the edge effect acts in both the tire circumferential direction and the axial direction, and the effect of improving the braking performance on a snow-covered road surface becomes more remarkable. The slit 90 is inclined more greatly with respect to the tire axial direction than the tire circumferential direction, for example. An example of the inclination angle of the slit 90 with respect to the tire axial direction is 60° or more and less than 90°.

[0065] The width of the slit 90 is smaller than the width of the slit 70 at the end on the main groove 20B side, for example. The width of the slit 90 is 1.5 mm or more and 3.0 mm or less at the end on the main groove 20B side, for example. Further, the slit 90 has a width-reducing region 91 in which the width decreases as it goes inside the second center block 41. That is, the slit 90 has a tapered shape in which the width gradually narrows toward the tip. By the slit 90 having the width-reducing region 91, the volume of the second center block 41 can be more ensured, and the decrease in block rigidity can be more suppressed. In the width-reducing region 91, the width of the slit 90 may decrease linearly or non-linearly.

[0066] The depth of the slit 90 may be constant over the extending direction of the slit 90, but in the present embodiment, the depth of the tip side of the slit 90 decreases as it goes inside the second center block 41. The depth of the slit 90 is substantially the same as the depth of the portion where the bridge 22 of the main groove 20 is provided at the end on the main groove 20B side, for example. The depth of the slit 90 is 30% or more and 90% or less of the depth of the main groove 20 at the end on the main groove 20B side, for example, and preferably 40% or more and 80% or less.

[0067] As shown in FIG. 3, a plurality of sipes (corresponding to the first sipes) 92 that cross the first center block 31 are provided in the first center block 31, and a plurality of sipes (corresponding to the second sipes) 93 that cross the first intermediate block 32 are provided in the first intermediate block 32.

[0068] In a plan view of the tread 10, the sipe 92 is provided such that a straight line connecting both longitudinal ends of the sipe 92 extends along the tire axial direction, and the sipe 93 is provided such that a straight line connecting both longitudinal ends of the sipe 93 is inclined with respect to the tire axial direction. That is, the sipe 92 extends along the axial direction of the tire, and the sipe 93 extends along a direction inclined with respect to the tire axial direction. By changing the extending directions of the sipe 92 and the sipe 93, the handling stability on a dry road surface can be improved. The inclination angle of the sipe 93 with respect to the tire axial direction is, for example, 20° or more and 70° or less.

[0069] The sipes 92 and 93 are preferably wavy sipess. In order to improve the braking performance on a snow road surface, it is necessary to increase the number of sipess and increase the edges. However, when the number of sipess is increased, for example, the block rigidity is excessively reduced, and the contact area is likely to decrease due to the collapse of the blocks. If the collapse of the blocks occurs excessively, the handling stability on a dry road surface is reduced. By forming the sipes 92 and 93 as wavy sipess as in this embodiment, the edges can be increased without increasing the number of sipess. As a result, the braking performance on a snow road surface can be improved while ensuring the handling stability on a dry road surface.

[0070] The waves of the sipess 92 and 93 are portions that protrude in a direction orthogonal to the longitudinal direction of the sipess 92 and 93, and are configured to be substantially triangular in plan view. The sipess 92 and 93 have a straight portion formed as a straight line and a wavy portion in which a plurality of waves are repeated. The straight portions are provided at both longitudinal ends of the sipess 92 and 93, and the wavy portion is provided between the straight portions. The wavy portion is configured to be bent in a zigzag shape so as to protrude on both sides of a center line connecting both longitudinal ends of the sipess 92 and 93.

[0071] The amplitudes of cycles 92 and 93 are constant for each wave, for example, and the waveform portions of cycles 92 and 93 are regularly configured at a constant period. An example of the amplitude of cycles 92 and 93 is 0.5 mm or more and 3.0 mm or less. In this specification, the amplitude of the waveform cycle means the distance from the center line connecting both ends in the length direction of cycles 92 and 93 to the apex of the largest wave.

[0072] The depth of cycles 92 and 93 is, for example, 10% or more and 100% or less of the depth of the main groove 20. Also, for cycles 92 and 93, the depth of the waveform portion may be greater than the depth of the straight portion. That is, for cycles 92 and 93, the depth on the central side in the length direction may be greater than the depth on both end sides in the length direction. Also, the depth of cycles 92 and 93 may differ for each cycle.

[0073] Also, a plurality of cycles 94 that cross the second center block 41 are provided in the second center block 41. Cycles 94 are waveform cycles and extend along a direction inclined with respect to the tire axis direction. The inclination angle of cycles 94 with respect to the tire axis direction is, for example, substantially the same as the inclination angle of cycle 93 with respect to the tire axis direction.

[0074] Hereinafter, with reference to FIGS. 4 and 5, the variation range of the contact length at the leading edge before contact during the running of the pneumatic tire 1 will be described. FIG. 4 is a diagram schematically showing the change in the contact line of the tread 10 during the running of the pneumatic tire 1. FIG. 5 is a diagram showing the variation range of the contact length at the leading edge before contact when the pneumatic tire 1 of the present embodiment is rotated one full turn.

[0075] As shown in FIG. 4, the contact line L of the tread 10 has a substantially arc shape and has a shape convex at the center in the tire axis direction. Here, the contact line L is the contour line of the contact surface when a predetermined load (a load corresponding to 70% of the normal load) is applied in a state where the unused pneumatic tire 1 is mounted on a normal rim and filled with air so as to have a normal internal pressure, and is the contour line on the indentation side, which is the portion where the pneumatic tire 1 starts to contact the road surface during running.

[0076] As shown in Fig. 4, as the pneumatic tire 1 travels, the contact line L moves toward the depressed side (rear side). At this time, the contact length of each contact line L gradually changes according to the tread pattern. Note that the contact length of the contact line L means the length of the portion of the contact line L that actually contacts the road surface.

[0077] Here, the amount of change in the contact length of the contact line L greatly affects the noise during running. As shown in Fig. 5, in the tread pattern of the pneumatic tire 1 of the present embodiment, the contact length of the contact line L is within a range of ±20% with respect to the central value over one circumference of the tire 1. More specifically, when the maximum value of the contact length when the contact line L is moved over one circumference of the tire 1 is X, the minimum value of the contact length is Y, and the central value of the contact length is Z ((X + Y) / 2), X ≦ Z × 1.20 and Y ≧ Z × 0.80 are satisfied. By keeping the contact length of the contact line L within a range of ±20% with respect to the central value over one circumference of the tire 1, the noise during running can be reduced.

[0078] It is more preferable that the contact length of the contact line L is within a range of ±18% with respect to the central value over one circumference of the tire 1, and it is even more preferable that it is within a range of ±16%. In this case, the noise during running can be further reduced. Note that the amount of change in the contact length of the contact line L can be adjusted by the arrangement of the tread pattern as described above. In particular, as in the present embodiment, while arranging the main grooves 20 and 21 so that the inclination with respect to the tire axis direction becomes larger on the equator CL side than on the grounding end E1 and E2 sides, by changing the number of blocks included in the first block group 30 and the second block group 40, the amount of change in the contact length of the contact line L can be made smaller.

[0079] As described above, while arranging the main grooves 20 and 21 such that the inclination with respect to the tire axis direction is larger on the equator CL side than on the ground end E1 and E2 sides, by changing the number of blocks included in the first block group 30 and the second block group 40, the period of the impact sound when the tread 10 collides with the road surface can be shifted. As a result, the frequency of the impact sound is dispersed, and the noise during driving can be reduced.

Explanation of Signs

[0080] 1 pneumatic tire, 10 tread, 11 sidewall, 12 side rib, 13 bead, 14 carcass, 15 inner liner, 16 bead core, 17 bead filler, 18 belt, 19 cap ply, 20, 20A, 20B, 21, 21A, 21B main groove, 22, 22A, 22B, 23, 23A, 23B bridge, 30 first block group, 31 first center block, 32 first mediate block, 32A outer end, 33 first shoulder block, 40 second block group, 41 second center block, 41A outer end, 42 second shoulder block, 50 first block group, 51 first center block, 52 first mediate block, 53 first shoulder block, 60 second block group, 61 second center block, 62 second shoulder block, 70, 70A, 70B, 71, 71A, 71B slit, 72, 72A, 72B, 73, 73A, 73B bridge, 74 inclined region, 80, 81 slit, 85 sipe, 90 slit, 91 narrow region, 92 sipe (first sipe), 93 sipe (second sipe)

Claims

1. A pneumatic tire having a tread and a specified rotational direction, wherein the tread includes a plurality of main grooves extending from the equator side toward the ground contact end side and arranged at intervals in the tire circumferential direction, a first block group and a second block group provided along the main grooves and arranged alternately across the main grooves in the tire circumferential direction, and the main grooves have a greater inclination with respect to the tire axial direction on the equator side than on the ground contact end side, the first block group and the second block group each include a plurality of blocks, and the number of blocks included in the first block group is different from the number of blocks included in the second block group. A pneumatic tire.

2. When a predetermined load is applied and the tire is rotated once in a state where the tire is mounted on a standard rim and filled with air to a standard internal pressure, the variation range of the ground contact length of the ground contact line is within ±20% with respect to the central value over one circumference of the tire. The pneumatic tire according to claim 1.

3. The first block group has a first center block located on the equator side, a first shoulder block located on the ground contact end side, and a first mediate block disposed between the first center block and the first shoulder block, and the second block group has a second center block located on the equator side and a second shoulder block located on the ground contact end side. The pneumatic tire according to claim 1 or 2.

4. In a plan view of the tread, the area of the first center block and the area of the first mediate block are each smaller than the area of the second center block, and the sum of the area of the first center block and the area of the first mediate block is larger than the area of the second center block. The pneumatic tire according to claim 3.

5. In the plan view of the tread, the area of the first center block is 75% or more and 125% or less of the area of the first intermediate block. The pneumatic tire according to claim 3.

6. The first center block and the first intermediate block are separated by a slit having a bent shape. The pneumatic tire according to claim 3.

7. In the plan view of the tread, the outer end of the first intermediate block in the tire axial direction and the outer end of the second center block in the tire axial direction are provided on the same straight line along the tire circumferential direction. The pneumatic tire according to claim 3.

8. The first center block is disposed across the equator, and the second center block is disposed without crossing the equator. The pneumatic tire according to claim 3.

9. The inclination angle of the main groove with respect to the tire axial direction is 30° or more and 60° or less on the equator. The pneumatic tire according to claim 1.

10. The second center block is provided with a slit that extends from the main groove toward the inside of the second center block and terminates inside the second center block. The pneumatic tire according to claim 3.

11. The slit has a narrow-width region whose width decreases toward the inside of the second center block. The pneumatic tire according to claim 10.

12. The first center block is provided with a first sipe that crosses the first center block, The first intermediate block is provided with a second sipe that crosses the first intermediate block, In the plan view, a straight line connecting both ends in the length direction of the first sipe is provided along the tire axial direction, The pneumatic tire according to claim 3, wherein in plan view, a straight line connecting both ends in the length direction of the second sipe is inclined with respect to the tire axis direction.

13. The pneumatic tire according to claim 12, wherein the first sipe and the second sipe are arranged in a wave shape in plan view.

Images