Pneumatic tire

Abstract

To provide a pneumatic tire effectively suppressing uneven wear of a block constituting a tread pattern while having excellent traction performance.SOLUTION: In a pneumatic tire 1, a first center block side 20A has a slit side 12A extending from a shoulder main groove side 21A and terminating in the block, and a projection side 21A projecting from a portion adjacent to the slit side 24A. The projecting portion side 24A projects to the outside of the block more than the block end side 21A on the opposite side across the slit side 20Ed. The shoulder main groove side 12A is formed with a groove bottom protruding 21A in which a groove bottom is raised so as to be connected to the protruding portion side 21Ed from a portion adjacent to the opening portion side 24A of the slit side 28A.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Conventionally, pneumatic tires having a tread pattern including circumferential grooves extending in the tire circumferential direction, lateral grooves extending in the tire axial direction, and a plurality of blocks separated by each groove have been widely known (see, for example, Patent Document 1). The tire of Patent Document 1 is a tire having a plurality of protrusions at the bottom of the circumferential grooves, and is designed for the purpose of improving performance on snow. Note that tires having a plurality of blocks separated by circumferential grooves and lateral grooves are used as mud terrain tires (hereinafter referred to as "MT tires") suitable for off-road driving on muddy roads, rocky areas, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-195049 Summary of the Invention [Problem to be solved by the invention]

[0004] Since MT tires need to improve traction performance on muddy roads, rocky areas, etc., for example, parts of the blocks are formed to protrude outward to increase grip on mud, rocks, etc. However, if a protrusion exists on the block, the rigidity of the block is locally reduced at the protruding part, making the block more susceptible to uneven wear. [Means for solving the problem]

[0005] The pneumatic tire of the present invention is a pneumatic tire having a tread pattern including first and second blocks having different shapes and grooves separating the blocks, wherein the first block has a slit extending from the groove and terminating within the block, and a protrusion that protrudes from a portion adjacent to the slit outside the block beyond the end of the block on the opposite side of the slit, and the groove is characterized in that a groove bottom protrusion is formed in the groove, with the bottom of the groove raised from a portion adjacent to the opening of the slit so as to connect to the protrusion. [Effects of the Invention]

[0006] According to the pneumatic tire of the present invention, uneven wear of the blocks constituting the tread pattern can be effectively suppressed. According to the present invention, it is possible to provide a pneumatic tire in which uneven wear of the blocks is effectively suppressed while having excellent traction performance. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of a pneumatic tire as an example of an embodiment. [Figure 2] 1 is a plan view of a pneumatic tire according to an embodiment, showing an enlarged view of a portion of a tread. [Figure 3] FIG. 3 is an enlarged view of part A in FIG. 2. [Figure 4] FIG. 2 is a perspective view of the center region of the tread. [Figure 5] FIG. 2 is a perspective view of a center main groove of a tread and its vicinity. [Figure 6] FIG. 4 is a diagram for explaining the flow of air along the center main groove. [Figure 7] FIG. 2 is a perspective view showing a part of a center region and a part of a shoulder region of the tread. [Figure 8] FIG. 2 is a perspective view of a protrusion of a center block and its vicinity. [Figure 9] FIG. 4 is a cross-sectional view taken along line AA in FIG. [Figure 10] FIG. 4 is a cross-sectional view taken along line BB in FIG. [Figure 11] FIG. 4 is a cross-sectional view taken along line CC in FIG. [Figure 12] FIG. 4 is a cross-sectional view taken along line DD in FIG. 3. [Figure 13] FIG. 2 is a perspective view of a stone ejector and its vicinity. [Figure 14] FIG. 4 is a cross-sectional view taken along line EE in FIG. [Figure 15] FIG. 4 is a cross-sectional view taken along the line FF in FIG. 3. [Figure 16] FIG. 10 is a perspective view of a corner of a shoulder block having a multi-step shape and its vicinity. [Figure 17] FIG. 4 is a cross-sectional view taken along line GG in FIG. 3. [Figure 18] 1 is a side view of a pneumatic tire as an example of an embodiment. [Figure 19] 1 is a side view of a pneumatic tire according to an embodiment, showing an enlarged view of a portion of a buttress region. [Figure 20] FIG. 10 is a perspective view of the buttress region. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes configurations obtained by selectively combining the components of the embodiment described below.

[0009] Fig. 1 is a perspective view of a pneumatic tire 1 as an example of an embodiment. As shown in Fig. 1, the pneumatic tire 1 includes a tread 10, which is the portion that comes into contact with the road surface, a pair of sidewalls 2, a pair of beads 3, which are portions that are fixed to the rim of a wheel, and a pair of buttress regions 4. The buttress regions 4 are portions located between the tread 10 and the sidewalls 2, and are also called shoulder regions. The sidewalls 2, the beads 3, and the buttress regions 4 extend radially inward from both left and right ends of the tread 10, forming the tire side surfaces.

[0010] In this embodiment, the region from the ground contact edges E1, E2 of the pneumatic tire 1 to the side rib 5 is defined as the buttress region 4. That is, the ground contact edges E1, E2 are the boundary positions between the tread 10 and the buttress region 4, and the side rib 5 is the boundary position between the sidewall 2 and the buttress region 4. The side ribs 5 are protrusions formed in a continuous ring shape in the circumferential direction of the tire on the left and right tire side surfaces. For ease of explanation, the right side of the page in FIG. 1 is the right side of the pneumatic tire 1, and the left side of the page in FIG. 1 is the left side of the pneumatic tire 1. Furthermore, the outer side of the tread 10 in the tire radial direction is referred to as the upper side, the inner side in the tire radial direction is referred to as the lower side, and the surface of a block or the like facing outward in the tire radial direction is referred to as the upper side.

[0011] The ground contact edges E1 and E2 of the pneumatic tire 1 are defined as the axial ends of the area (ground contact patch) that comes into contact with a flat road surface when a new tire is mounted on a standard rim, inflated to a standard internal pressure, and a predetermined load is applied. The predetermined load is a load equivalent to 88% of the normal load. In this embodiment, the axially outer ends of the ground contact patches of second shoulder blocks 50A and 50B, which will be described later, are the ground contact edges E1 and E2, respectively.

[0012] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA and a "measuring rim" for TRA and ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0013] The pneumatic tire 1 is suitable for use as a mud terrain tire (MT tire) or a rugged terrain tire (RT tire) suitable for off-road driving on muddy roads, rocky areas, sandy terrain, etc. As will be described in detail later, the pneumatic tire 1 has excellent traction performance and an aggressive appearance, as well as excellent durability, drainage, and quietness. The pneumatic tire 1 is mounted on, for example, light trucks such as pickup trucks and sports utility vehicles (SUVs).

[0014] The pneumatic tire 1 is a point-symmetric tire that does not require a specific mounting direction on a vehicle, and the tread pattern and tire side surface shape remain unchanged regardless of the mounting direction. The tread pattern and tire side surface shape of the pneumatic tire 1 are rotated 180° on either side of the tire equator CL. The equator CL is an imaginary line that runs through the axial center of the tread 10 along the tire circumferential direction.

[0015] The pneumatic tire 1 has a tread pattern including a plurality of blocks and grooves separating the blocks. The tread 10 is formed with a center main groove 11 and shoulder main grooves 12A, 12B (tire circumferential grooves) extending in the tire circumferential direction. The tread 10 also has lateral grooves 13A, 13B, 14, 15A, 15B extending in the tire axial direction. In this embodiment, the region sandwiched between the two shoulder main grooves 12A, 12B is defined as the "center region" of the tread 10. The region from the shoulder main groove 12A to the tread edge E1 and the region from the shoulder main groove 12B to the tread edge E2 are defined as the "shoulder regions" of the tread 10. The blocks of the tread 10 are convex portions that protrude radially outward and are sometimes called "lands" in the tire industry.

[0016] In the center region of the tread 10, a plurality of block groups 16, each group consisting of four first center blocks 20A, 20B and four second center blocks 30A, 30B, are arranged in the tire circumferential direction. Each of the block groups 16 adjacent to each other in the tire circumferential direction is separated by a lateral groove 14 that crosses the center region and extends to the left and right shoulder regions, and the block groups 16 are arranged at a predetermined interval in the tire circumferential direction. While the predetermined interval may be a regular interval, a variable pitch (unequal interval) that varies in the tire circumferential direction is preferable from the viewpoint of improving quietness. The variable pitch is set, for example, in units of half the circumferential length of the block group 16, and has a pitch period of 40 to 50.

[0017] The four center blocks constituting the block group 16 are located closer to the equator CL than the tread edges E1 and E2, and are defined by a center main groove 11 and lateral grooves 13A and 13B (first lateral grooves). As will be described in detail later, the center main groove 11 has a straight region that runs circumferentially through the block group 16 and connects two lateral grooves 14 (second lateral grooves). On the other hand, the two lateral grooves 13A and 13B are positioned slightly offset from each other in the circumferential direction and are not collinear. The lateral groove 13A connects the center main groove 11 to the shoulder main groove 12A, and the lateral groove 13B connects the center main groove 11 to the shoulder main groove 12B.

[0018] The first center block 20A is positioned entirely on the tread edge E1 side of the equator CL, while the first center block 20B is positioned entirely on the tread edge E2 side of the equator CL. The first center block 20A has a protrusion 24A that protrudes toward the tread edge E1, while the first center block 20B has a protrusion 24B that protrudes toward the tread edge E2. The protrusions 24A and 24B protrude in opposite directions, significantly improving traction performance on muddy roads, rocky areas, sandy ground, and the like. The first center blocks 20A and 20B have the same shape but are oriented 180° apart.

[0019] The majority of the second center block 30A is positioned closer to the tread edge E1 than the equator CL, but a portion of it is positioned beyond the equator CL toward the tread edge E2. The majority of the second center block 30B is positioned closer to the tread edge E2 than the equator CL, but a portion of it is positioned beyond the equator CL toward the tread edge E1. That is, the second center blocks 30A and 30B are positioned so that portions of the blocks overlap in the tire circumferential direction. The second center blocks 30A and 30B have the same shape but are oriented 180° apart.

[0020] In the right shoulder region of the tread 10, first shoulder blocks 40A and second shoulder blocks 50A, which have different shapes, are arranged alternately in the tire circumferential direction. The first shoulder blocks 40A and second shoulder blocks 50A are separated by lateral grooves 14, 15A that are arranged alternately in the tire circumferential direction. Similarly, in the left shoulder region of the tread 10, first shoulder blocks 40B and second shoulder blocks 50B are arranged alternately in the tire circumferential direction, and the two types of blocks are separated by lateral grooves 14, 15B.

[0021] The first shoulder block 40A and the second shoulder block 50A have different shapes of sidewalls 43A, 53A facing axially outward. The first sidewall 43A of the first shoulder block 40A is more recessed on the radially outer side than the second sidewall 53A of the second shoulder block 50A, while the radially inner side protrudes more. The difference in the protruding shapes of the sidewalls 43A, 53A of each shoulder block creates unevenness in the buttress region 4 along the circumferential direction of the tire, providing excellent traction performance when driving off-road on muddy, rocky, sandy, and other terrain.

[0022] The sidewalls 43A of the first shoulder blocks 40A and 53A of the second shoulder blocks 50A each have recesses 44A, 54A that open in the same circumferential direction of the tire. The recesses 44A, 54A contribute to further improving traction performance and emphasize an aggressive look. The first shoulder blocks 40A, 40B have the same shape but are oriented 180° apart. The second shoulder blocks 50A, 50B also have the same shape but are oriented 180° apart.

[0023] Conventionally known structures can be applied to the rubber composition and internal structure of the pneumatic tire 1. The pneumatic tire 1 includes, for example, a carcass, a belt, and a cap ply. The carcass is a cord layer coated with rubber and forms the skeleton of the tire, enduring load, impact, air pressure, etc. The carcass is made up of two carcass plies and has a radial structure in which carcass cords are arranged in a direction perpendicular to the circumferential direction of the tire. An inner liner, which is a rubber layer for maintaining air pressure, is provided inside the carcass. The belt is a reinforcing band placed between the carcass and the rubber that constitutes the tread 10.

[0024] The sidewall 2 may be provided with letters, numbers, symbols, etc., called serial numbers. The serial numbers include information such as a size code, manufacturing date (manufacturing year and week), and manufacturing location (manufacturing factory code). The sidewall 2 also has a plurality of side blocks 90, 91, 92, and 94 formed thereon. The provision of these side blocks improves the traction performance and side cut performance of the pneumatic tire 1, while also creating a more aggressive design.

[0025] The tread pattern of the pneumatic tire 1 will be described in detail below with reference to Figures 2 and 3. Figure 2 is a plan view of the pneumatic tire 1, showing an enlarged portion of the tread 10. In Figure 2, curved surfaces such as block side walls are omitted for clarity, and some of the configuration is shown schematically. Figure 3 is an enlarged view of part A in Figure 2, showing the cutting line of the cross-sectional view described later.

[0026] As shown in Figures 2 and 3, the tread 10 has a center region in which a plurality of block groups 16 are arranged in the tire circumferential direction, and shoulder regions in which two types of shoulder blocks are arranged alternately in the tire circumferential direction. As described above, the block group 16 includes a total of four blocks: two first center blocks 20A, 20B and two second center blocks 30A, 30B. That is, the block group 16 has two blocks of each type that are different in shape. The outline of the block group 16 is generally rectangular in plan view, and the first center blocks 20A, 20B are arranged on a first diagonal of the rectangle. The second center blocks 30A, 30B are arranged on a second diagonal of the rectangle.

[0027] The outline of the block group 16 is formed by shoulder main grooves 12A, 12B and two lateral grooves 14. The shoulder main grooves 12A, 12B are inclined relative to the tire circumferential direction, and the lateral grooves 14 are inclined relative to the tire axial direction, so that each side of the rectangle of the block group 16 is inclined relative to the tire circumferential direction and the axial direction. Of the four center blocks constituting the block group 16, of the two blocks located on the side of the tread edge E1, the first center block 20A is positioned closer to the tread edge E1 than the second center block 30A. Furthermore, of the two blocks located on the side of the tread edge E2, the first center block 20B is positioned closer to the tread edge E2 than the second center block 30B.

[0028] The center main groove 11, which runs through the block group 16 and connects the two lateral grooves 14, is inclined relative to the tire circumferential direction, similar to the shoulder main grooves 12A and 12B. The center main groove 11 is bent significantly midway, with two bends 11x and 11y. The bends 11x and 11y give the center block an angular shape. As a result, the blocks are more likely to catch on mud, rocks, etc., improving traction performance on muddy roads, rocky areas, sandy ground, etc. On the other hand, the bends 11x and 11y are detrimental to drainage, but ensuring the straight region ensures good drainage. The center main groove 11 is formed to cross the equator CL at the center of its length.

[0029] The lateral grooves 13A, 13B connect to the center main groove 11 approximately on the equator CL. In this case, good drainage and traction performance are obtained even near the equator CL. The lateral grooves 13A, 13B are inclined in the same direction as the lateral groove 14 relative to the tire axial direction. Like the center main groove 11, the lateral grooves 13A, 13B are significantly bent midway, each having a bend 13Ax, 13Bx at one location. Like the bends 11x, 11y of the center main groove 11, the bends 13Ax, 13Bx give the center block an angular shape, contributing to improved traction performance on muddy roads, rocky areas, sandy ground, etc.

[0030] The tread 10 has a first shoulder block 40A and a second shoulder block 50A at positions axially facing the block group 16 across the shoulder main groove 12A. Also, a first shoulder block 40B and a second shoulder block 50B are provided at positions axially facing the block group 16 across the shoulder main groove 12B. The shoulder main groove 12A connects two lateral grooves 14 and has an intersection with lateral grooves 13A and 15A along its length. Similarly, the shoulder main groove 12B connects two lateral grooves 14 and has an intersection with lateral grooves 13B and 15B along its length.

[0031] In this embodiment, the first shoulder blocks 40A, the first center blocks 20A, the second center blocks 30B, and the second shoulder blocks 50B are arranged in a line, in that order, from the tread edge E1 side, along the extension direction of the lateral grooves 14. The second shoulder blocks 50A, the second center blocks 30A, the first center blocks 20B, and the first shoulder blocks 40B are also arranged in a line, in that order, from the tread edge E1 side, along the extension direction of the lateral grooves 14. The tread pattern of this embodiment can also be said to be a pattern in which two types of block groups arranged in the extension direction of the lateral grooves 14 are alternately arranged in the tire circumferential direction.

[0032] The lateral grooves 14 extend from the ground contact edge E1, past the equator CL, to the ground contact edge E2, and separate the circumferentially aligned block groups 16 in the center region. In the left and right shoulder regions, the lateral grooves 14 separate the first shoulder blocks 40A and the second shoulder blocks 50A, and the first shoulder blocks 40B and the second shoulder blocks 50B, respectively. The lateral grooves 15A, 15B are disposed between the two lateral grooves 14 in the left and right shoulder regions. That is, in the right shoulder region, the lateral grooves 14 and the lateral grooves 15A are disposed alternately in the circumferential direction of the tire, and in the left shoulder region, the lateral grooves 14 and the lateral grooves 15B are disposed alternately in the circumferential direction of the tire.

[0033] The lateral grooves 14, 15A, and 15B are wider than the center main groove 11, the shoulder main grooves 12A and 12B, and the lateral grooves 13A and 13B. Therefore, stones are easily trapped in the lateral grooves 14, 15A, and 15B. Driving with stones trapped in the lateral grooves 14, 15A, and 15B can significantly reduce traction performance. Therefore, stone ejectors, which are protrusions extending along the grooves to prevent stone trapping, are provided at the bottoms of the lateral grooves 14, 15A, and 15B. For ease of explanation, the lateral groove 14 on the lower side of FIG. 2 may be referred to as the "first lateral groove 14," and the lateral groove 14 on the upper side of FIG. 2 may be referred to as the "second lateral groove 14."

[0034] The lateral groove 14 is provided with a stone ejector 60A in the right shoulder region and a stone ejector 60B in the left shoulder region. Furthermore, the lateral groove 15A is provided with stone ejectors 70A and 80A, and the lateral groove 15B is provided with stone ejectors 70B and 80B. The function of each stone ejector allows stones stuck in the groove to be easily ejected, effectively suppressing the deterioration of traction performance caused by stone jamming. As will be described in more detail later, a recessed portion is formed in the middle of each stone ejector's length to reduce its height. The effect of this recess allows stones stuck in the groove to be effectively ejected.

[0035] Each stone ejector is a long, thin protrusion that extends in the direction of the groove, and is formed straight without any bends. The height of the stone ejector is lower than that of the shoulder block, and the upper surface of the stone ejector does not touch the flat road surface. The stone ejectors 70A and 80A are aligned in the direction of the lateral groove 15A and are spaced apart so as not to interfere with each other. Similarly, the stone ejectors 70B and 80B are aligned in the direction of the lateral groove 15B and are spaced apart so as not to interfere with each other.

[0036] The tread 10 further has a stone ejector 17A, which is a protrusion having a generally triangular shape in plan view, at the intersection of the shoulder main groove 12A and the second lateral groove 14, and a stone ejector 17B, which is a protrusion having a generally triangular shape in plan view, at the intersection of the shoulder main groove 12B and the first lateral groove 14. The shoulder main groove 12A bends significantly toward the tread edge E1 along the protrusion 24A of the first center block 20A near the intersection with the second lateral groove 14. The shoulder main groove 12B bends significantly toward the tread edge E2 along the protrusion 24B of the first center block 20B near the intersection with the first lateral groove 14.

[0037] As shown in Figure 2, the uneven shape of the buttress region 4 can be seen in a plan view of the tread 10. Near the contact edges E1, E2, the first shoulder blocks 40A, 40B are recessed axially inward, while the second shoulder blocks 50A, 50B protrude axially outward. Near the side ribs 5, the first shoulder blocks 40A, 40B protrude axially outward more than the second shoulder blocks 50A, 50B. As described above, the difference in the protruding shapes of the side walls 43A, 43B, 53A, 53B of each shoulder block creates unevenness in the buttress region 4 along the tire circumferential direction.

[0038] The configurations of the first center block 20A, the second center block 30A, the first shoulder block 40A, and the second shoulder block 50A will be described in further detail below.

[0039] [First center block 20A] The first center block 20A has a slit 21A extending from the shoulder main groove 12A and terminating within the block, and a protrusion 24A protruding from the portion adjacent to the slit 21A. The slit 21A, also known as a notch in the tire industry, is formed using a mold, similar to the main grooves and lateral grooves. The protrusion 24A protrudes outward beyond the end of the block on the opposite side of the slit 21A. The first center block 20A also has a single sipe 22A.

[0040] In this specification, a groove that terminates within a block and has a width of 1.5 mm or more is defined as a slit, and a narrow groove that is less than 1.5 mm in width is defined as a sipe. The maximum width of a slit is preferably 2.0 mm or more and 4.0 mm or less. The maximum width of a sipe is preferably 0.3 mm or more and 1.0 mm or less.

[0041] The first center block 20A is disposed axially opposite the second center block 30B across the center main groove 11, which has a bent portion 11x between the two blocks. When viewed from the first lateral groove 14 side, the center main groove 11 is bent significantly toward the equator CL at the bent portion 11x. Therefore, the block end of the first center block 20A along the center main groove 11 protrudes closer to the equator CL than the portion closer to the first lateral groove 14. The portion of the center main groove 11 from the first lateral groove 14 to the bent portion 11x and the portion from the bent portion 11x to the equator CL are substantially parallel to each other.

[0042] The first center block 20A is disposed circumferentially opposite the second center block 30A across a lateral groove 13A, and the lateral groove 13A has a bend 13Ax between the two blocks. When viewed from the center main groove 11 side, the lateral groove 13A bends significantly toward the second center block 30A at the bend 13Ax. Therefore, the block end of the first center block 20A along the lateral groove 13A protrudes more toward the second center block 30A at the portion closer to the shoulder main groove 12A than at the portion closer to the center main groove 11. The portion of the lateral groove 13A from the center main groove 11 to the bend 13Ax and the portion from the bend 13Ax to the shoulder main groove 12A are parallel to each other.

[0043] As described above, the first center block 20A has a locally protruding block end, which allows it to catch on mud, rocks, and other debris, contributing to improved traction during off-road driving. In particular, the protrusion 24A protrudes significantly toward the tread edge E1, significantly improving traction. However, the presence of the protrusion 24A locally reduces block rigidity at the protrusion 24A, making the block more susceptible to uneven wear. To prevent this uneven wear, the shoulder main groove 12A is provided with a groove bottom protrusion 28A, which extends from the groove bottom adjacent to the opening 21Ed of the slit 21A (see FIG. 7, etc.). The groove bottom protrusion 28A extends from the groove bottom adjacent to the opening 21Ed of the slit 21A (see FIG. 7, etc.).

[0044] The first center block 20B has a slit 21B, a sipe 22B, and a protrusion 24B, and together with the first center block 20A, contributes to improved traction performance during off-road driving. The protrusion 24B protrudes significantly toward the tread edge E2, and the shoulder main groove 12B has a groove bottom protrusion 28B, which is a raised groove bottom that connects to the protrusion 24B from the portion adjacent to the opening of the slit 21B. Note that although the orientation of the first center block 20B is 180° different from that of the first center block 20A, they have the same shape, so the features common to the two blocks will be explained using the first center block 20A as an example.

[0045] [Second center block 30A] The second center block 30A has a slit 31A extending from the lateral groove 13A and terminating within the block. The slit 31A is formed from the shoulder main groove 12A side of the bend 13Ax of the lateral groove 13A to the center of the second center block 30A. The slit 31A is inclined more circumferentially than the center main groove 11 and the shoulder main grooves 12A and 12B, increasing the block edge area that catches on mud, rocks, etc. The second center block 30A also has a single sipe 32A.

[0046] The second center block 30A is disposed axially opposite the first center block 20B across the center main groove 11, which has a bend 11y between the two blocks. When viewed from the equator CL side, the center main groove 11 bends significantly toward the tread edge E2 at the bend 11y. Therefore, the block end of the second center block 30A along the center main groove 11, at the portion farther from the equator CL (i.e., the portion closer to the second lateral groove 14), protrudes closer to the tread edge E2 than the portion closer to the equator CL. The portion of the center main groove 11 from the equator CL to the bend 11y and the portion from the bend 11y to the second lateral groove 14 are substantially parallel to each other.

[0047] The second center block 30A is disposed opposite the second center block 30B of another block group 16 in the tire circumferential direction, with the lateral groove 14 between them. That is, the second center block 30A of the first block group 16 and the second center block 30A of the second block group 16 are aligned in the tire circumferential direction with the lateral groove 14 interposed therebetween. The lateral groove 14 has a bent portion 14x, which bends between the second center blocks 30A and 30B. The bent portion 14x is located on the equator CL and bends significantly toward the second center block 30B when viewed from the tread edge E2 side. Therefore, the block end of the second center block 30A that is closer to the tread edge E1 than the bent portion 14x protrudes toward the second center block 30B.

[0048] The second center block 30B has slits 31B and sipes 32B, and together with the other center blocks, contributes to improving traction performance during off-road driving. Although the second center block 30B is oriented 180° differently from the second center block 30A, they have the same shape, so the common features of the two blocks will be explained using the second center block 30A as an example.

[0049] [First shoulder block 40A] The first shoulder block 40A is a block that is surrounded on three sides by the shoulder main groove 12A, the first lateral groove 14, and the lateral groove 15A and is longer in the axial direction than in the circumferential direction. The block ends along the shoulder main groove 12A are inclined at an angle of, for example, 10° to 20° relative to the tire axial direction so that they are positioned closer to the equator CL as they approach the lateral groove 15A. Each block end along the lateral grooves 14, 15A extends from the contact edge E along the tire axial direction and then bends in the same direction in the tire circumferential direction. The inclination angle of the bent block ends relative to the tire axial direction is, for example, 15° to 25°.

[0050] As described above, the first shoulder block 40A has a shape in which the portion located on the shoulder main groove 12A side is bent toward the second shoulder block 50A separated by the lateral groove 15A. The first shoulder block 40A protrudes at an acute angle at the intersection of the shoulder main groove 12A and the lateral groove 15A. As will be described in detail later, the corner of the first shoulder block 40A has a multi-step shape with three or more steps. The second step, the second step from the block ground contact surface side, has a slope 45A that is triangular or trapezoidal in plan view and gradually narrows toward the groove bottom. This multi-step shape effectively suppresses uneven wear of the first shoulder block 40A.

[0051] Each first shoulder block 40A is formed with a single sipe 41A extending in the tire axial direction. The sipe 41A improves the ground contact of the first shoulder block 40A, contributing to improvements in, for example, running stability and cornering characteristics. From the perspective of improving the durability of the first shoulder block 40A, the sipe 41A is preferably formed at a position a predetermined distance away from the edge of the block's ground contact surface (the same applies to sipe 51A, described below). The sipe 41A is formed in the circumferential center of the first shoulder block 40A and, like the shape of the block, is bent midway toward the lateral groove 15A.

[0052] As described above, the radially outer portion of the sidewall 43A of the first shoulder block 40A is recessed axially inward compared to the second sidewall 53A of the second shoulder block 50A. Therefore, the ground contact edge (the axially outer edge of the ground contact surface) of the first shoulder block 40A is located axially inward of the ground contact edge E1. The ground contact edge of the first shoulder block 40A is located, for example, approximately 1.0 mm to 6.0 mm inward from the ground contact edge E1 along the tire axial direction. The ground contact area of ​​the first shoulder block 40A is smaller than that of the second shoulder block 50A, for example, 80% to 90% of the ground contact area of ​​the second shoulder block 50A.

[0053] The first shoulder block 40B has a sipe 41B and a slope 45B formed at the corner of the block. Although the orientation of the first shoulder block 40B is 180° different from that of the first shoulder block 40A, the first shoulder block 40B and the first shoulder block 40A have the same shape. Therefore, the common features of the two blocks will be explained using the first shoulder block 40A as an example.

[0054] [Second shoulder block 50A] The second shoulder block 50A is surrounded on three sides by the shoulder main groove 12A, the second lateral groove 14, and the lateral groove 15A. The second shoulder block 50A is longer in the axial direction than in the circumferential direction. The second shoulder block 50A has a tapered shape, with its circumferential length gradually decreasing toward the equator CL. The block ends along the lateral grooves 14 and 15A extend axially from the tread edge E to a predetermined position and then bend toward each other at the predetermined position. The predetermined position is located closer to the equator CL than the position where the first shoulder block 40A bends.

[0055] Each second shoulder block 50A is formed with a single sipe 51A extending in the tire axial direction. The sipe 51A improves the ground contact of the second shoulder block 50A, contributing to improvements in, for example, driving stability and cornering characteristics. The sipe 51A is formed in the circumferential center of the second shoulder block 50A and bends midway toward the lateral groove 15A. The radially outer portion of the sidewall 53B of the second shoulder block 50A is positioned axially outward compared to the sidewall 43A of the first shoulder block 40A, and the ground contact edge of the second shoulder block 50A corresponds to the ground contact edge E1 of the tread 10.

[0056] The second shoulder block 50B is formed with a sipe 51B. Although the second shoulder block 50B is oriented 180° differently from the second shoulder block 50A, they have the same shape, and therefore, the common features of the two blocks will be described using the second shoulder block 50A as an example.

[0057] Here, we will provide additional information about the lateral grooves 14, 15A. Both longitudinal ends of the lateral grooves 14 in the tread 10—specifically, the section from the ground contact edge E1 to the intersection with the shoulder main groove 12A and the section from the ground contact edge E2 to the intersection with the shoulder main groove 12B—extend along the tire axial direction. The middle section connecting the longitudinal ends of the lateral groove 14 is inclined with respect to the tire axial direction and has a bend 14x at the intersection with the equator CL. The center main groove 11 and the shoulder main grooves 12A, 12B are connected to the middle section of the lateral groove 14, meaning that a total of five circumferential grooves are connected to one lateral groove 14.

[0058] Like the lateral grooves 14, the lateral grooves 15A extend in the tire axial direction in the portion located near the ground contact edge E1, and bend in the tire circumferential direction in the middle portion, and are inclined with respect to the tire axial direction. The lateral grooves 15A are bent in a direction intersecting with the lateral grooves 14. The inclination angle of the lateral grooves 15A with respect to the tire axial direction is, for example, 15° to 25°.

[0059] The configuration of the block group 16, particularly the configuration of the center main groove 11 that runs through the block group 16, will be described in more detail below with reference to Figures 4 to 6. Figure 4 is a perspective view of the center region of the tread 10, and Figure 5 is a perspective view of the center main groove 11 and its vicinity. Figure 6 is a diagram for explaining the air flow along the center main groove 11.

[0060] As shown in Figures 4 and 5, the four center blocks that make up the block group 16 have stepped portions along the periphery of their top surfaces, lowering the height of the top surfaces by one step. The stepped portions distribute the ground pressure acting on the block ends, thereby achieving uniformity of the ground pressure. The first center blocks 20A and 20B have stepped portions 23A and 23B that border the periphery of the block top surfaces, including the edges of the slits 21A and 21B. Similarly, the second center blocks 30A and 30B have stepped portions 33A and 33B that border the periphery of the block top surfaces, including the edges of the slits 31A and 31B. The stepped portions can be said to be formed along the grooves, essentially increasing the groove width near the groove openings.

[0061] The step 23A of the first center block 20A is formed with a substantially constant width and depth along the periphery of the block's top surface. The width of the step 23A is, for example, 1.0 mm to 3.0 mm. The depth of the step 23A is, for example, 1.0 mm to 3.0 mm from the ground contact surface of the first center block 20A, and may be substantially the same as the width of the step 23A. The depth of the step 23A is preferably 5% to 20% of the depth of the center main groove 11, and more preferably 10% to 15%. The step 33A of the second center block 30A preferably has substantially the same width and depth as the step 23A of the first center block 20A.

[0062] The first center block 20A has sipes 22A extending from the center main groove 11 and terminating within the block. The sipes 22A improve the ground contact of the first center block 20A, contributing to improvements in, for example, braking performance and running stability. The sipes 22A are formed linearly from the block end recessed inward at the bend 11x of the center main groove 11 to the step 23A along the edge of the slit 21A. The sipes 22A may be connected to the slit 21A. To prevent a decrease in block rigidity, the depth of the sipes 22A is preferably deep in the longitudinal center and shallow at both longitudinal ends. Note that no grooves other than the slits 21A and the sipes 22A are formed in the first center block 20A.

[0063] The second center block 30A has sipes 32A extending from the center main groove 11 and terminating within the block. The sipes 32A improve the ground contact of the second center block 30A, contributing to improvements in, for example, braking performance and running stability. The sipes 32A are formed linearly from the block end recessed inward at the bend 11y of the center main groove 11 to the slits 31A. As with the sipes 22A, the depth of the sipes 32A is preferably deep in the center and shallow at both ends. Note that the second center block 30B does not have any grooves other than the slits 31A and sipes 32A.

[0064] The depth of the center main groove 11 is, for example, 13.5 mm to 16.5 mm and is substantially constant throughout the entire length. In this embodiment, the depths of the center main groove 11, shoulder main grooves 12A, 12B, and lateral grooves 13A, 13B are substantially the same. In this case, stable drainage and mud removal performance is achieved in the center region of the tread 10. Furthermore, the depths of all main grooves and lateral grooves, including lateral grooves 14, 15A, 15B, may be substantially the same. The groove depth refers to the shortest distance from the profile surface P of the tread 10 to the deepest part of the groove (the length along the normal to the profile surface P), and the profile surface P of the tread 10 refers to the surface along the contact surface of the tread 10.

[0065] The width of the center main groove 11 is, for example, 7.0 mm to 17.0 mm and is substantially constant over the entire length. The widths of the lateral grooves 13A, 13B may be the same as the width of the center main groove 11, but in this embodiment, they are slightly larger than the width of the center main groove 11. The widths of the lateral grooves 13A, 13B are, for example, 1.05 to 1.20 times the width of the center main groove 11 and are substantially constant over the entire length. In this specification, the groove width refers to the groove width along the profile surface P, in other words, the groove width at the groove opening. The groove opening refers to the position of the groove on the profile surface P. The width of the step portion is not included in the groove width.

[0066] As described above, the center main groove 11 has bent portions 11x and 11y that are bent in the tire axial direction. The bent portion 11x is located between the first center block 20A and the second center block 30B, and the bent portion 11y is located between the first center block 20B and the second center block 30A. The bent portions 11x and 11y form axial irregularities at the block ends of the four center blocks along the center main groove 11, which increases the traction performance by increasing the grip on mud, rocks, etc.

[0067] The center main groove 11 is formed straight between the bent portions 11x and 11y and has an intersection with the two lateral grooves 13A and 13B. That is, the middle portion of the center main groove 11 located between the bent portions 11x and 11y is formed straight, and the lateral grooves 13A and 13B branch off from this middle portion. Although bending the center main groove 11 may impair drainage, forming the middle portion connecting the lateral grooves 13A and 13B in a straight line effectively improves drainage on wet roads. Furthermore, the middle portion of the center main groove 11 crosses the equator CL, and the longitudinal center of the middle portion is located on the equator CL. This ensures stable drainage near the equator CL.

[0068] In this embodiment, the first center block 20A overlaps with the other three center blocks that make up the block group 16 in the tire axial direction. That is, the four center blocks that make up the block group 16 are arranged in a staggered pattern in the tire circumferential direction so that they overlap in the tire axial direction. Furthermore, the second center block 30A of the first block group 16 and the second center block 30B of the second block group 16 also overlap in the tire axial direction. While this center block arrangement contributes to improved traction performance, it is detrimental to drainage. However, good drainage can be ensured by the effects of the middle portion of the center main groove 11, the straight region, etc.

[0069] The center main groove 11 runs longitudinally through one block group 16 but is separated between each block group 16. The center main grooves 11 are connected in the circumferential direction via the lateral grooves 14, but are not necessarily continuous in the circumferential direction. That is, multiple center main grooves 11 are aligned in the circumferential direction in the center region of the tread 10. Because the center main grooves 11 are inclined relative to the circumferential direction, they abut against center blocks of other block groups 16. Second center blocks 30A, 30B are positioned on the extension of the center main groove 11. Although this configuration of the center main groove 11 also has a disadvantage in terms of drainage, as described above, good drainage can be ensured by the effects of the middle portion and straight region of the center main groove 11.

[0070] The center main groove 11 curves in the same direction at the bends 11x and 11y. The bends 11x and 11y are substantially curved in the same direction. The intermediate portion between the bends 11x and 11y, the portion between the first transverse groove 14 and the bend 11x (hereinafter referred to as the "first end portion"), and the portion between the second transverse groove 14 and the bend 11y (hereinafter referred to as the "second end portion") are parallel to each other. The first and second end portions have, for example, the same length, but are shorter than the length of the intermediate portion. The length of the intermediate portion is, for example, 1.5 to 3.0 times the length of each end portion.

[0071] As described above, the center main groove 11 has a straight region that extends straight over its entire length. In this specification, the straight region of the center main groove 11 is defined as the region where the second intersection with the second lateral groove 14 is visible when the center main groove 11 is viewed in the tire circumferential direction from the side of the first intersection with the first lateral groove 14. The straight region exists on the groove opening side but not on the groove bottom side. In other words, the center main groove 11 is formed so that the straight region exists on the groove opening side but does not exist on the groove bottom side, thereby adjusting the degree of curvature of the center main groove 11 at the bend portions 11x and 11y.

[0072] The sidewalls of the blocks forming the groove walls of the center main groove 11 are gently inclined so that the groove width gradually decreases toward the groove bottom, and are curved near the groove bottom (the same applies to the sidewalls along the lateral grooves 13A, 13B, and 14). The inclination angle of the sidewalls of the center blocks is, for example, 3° to 8° or 4° to 7°. The radius of curvature of the curved surface is, for example, 1.5 mm to 4.5 mm. Therefore, when the center main groove 11 is curved, the overlap between the groove walls is greater at the groove bottom side than at the groove opening side, and no straight region exists. The inclination angle of the sidewalls of the blocks refers to the inclination angle with respect to the normal to the profile plane P passing through the upper end of the sidewall (see Figure 11, etc., described later).

[0073] The ratio of the cross-sectional area of ​​the straight region to the widthwise cross-sectional area of ​​the center main groove 11 is preferably 20% to 80%, more preferably 30% to 70%. Here, the cross-sectional area of ​​the straight region refers to the area of ​​the straight region when the center main groove 11 is viewed from the first lateral groove 14 side, i.e., the area of ​​the second lateral groove 14 visible through the center main groove 11 from the first lateral groove 14 side. The straight region is preferably present only within an area shallower than 85% of the depth of the center main groove 11 from the profile plane P, and particularly preferably only within an area shallower than 75%. In other words, it is preferable that no straight region is present within an area of ​​15% or 25% of the groove bottom side of the center main groove 11.

[0074] In this embodiment, steps 23A, 23B, 33A, and 33B are formed along the center main groove 11, resulting in a larger straight region on the groove opening side compared to when the steps are not present. The width of the steps is not included in the groove width, but the widthwise cross-sectional area of ​​the steps is counted as part of the cross-sectional area of ​​the straight region. Due to the presence of the steps, the cross-sectional area of ​​the straight region is large, for example, in a range shallower than 15% of the depth of the center main groove 11 from the profile plane P, and rapidly decreases beyond the position of the steps. By providing a large straight region on the groove opening side, drainage on wet roads is improved.

[0075] A linearly extending intermediate portion of the center main groove 11 is formed at the center of the four center blocks of the block group 16, and lateral grooves 13A, 13B extend from this intermediate portion. In this embodiment, bends 11x, 11y, 13Ax, 13Ay are formed in each of the shoulder main grooves 12A, 12B formed from the center of the four center blocks to the periphery of the block group 16, and in all grooves connecting two lateral grooves 14. A bend 14x is also formed in the lateral groove 14. By forming the center main groove 11 and lateral grooves 13A, 13B, 14 in a zigzag pattern in the center region of the tread 10, traction performance during off-road driving is significantly improved.

[0076] FIG. 6 is a diagram illustrating the air flow along the center main groove 11. FIG. 6(a) shows the air flow on the tire surface (profile surface P) of the tread 10, and FIG. 6(b) shows the air flow at a position 75% of the depth of the center main groove 11 from the profile surface P. As shown in FIG. 6(a), the center main groove 11 has a straight region on the tire surface side, and part of the air flowing along the center main groove 11 flows straight from the first lateral groove 14 to the second lateral groove 14. On the other hand, as shown in FIG. 6(b), there is no straight region on the groove bottom side of the center main groove 11, and the air does not flow straight.

[0077] As described above, the air flow along the center main groove 11 differs significantly between the tire surface side and the groove bottom side, resulting in a faster flow velocity on the tire surface side and a slower flow velocity on the groove bottom side. This results in turbulence of the airflow, reducing intercolumnar resonance. In other words, because the air flow route and flow velocity differ in the depth direction of the center main groove 11, the curved airflow on the groove bottom side also affects the airflow on the tire surface side, effectively suppressing noise caused by intercolumnar resonance. The center main groove 11, which is curved so that the straight region is present on the tire surface side and not on the groove bottom side, along with the lateral grooves 13A, 13B, 14, etc., significantly contributes to improved traction performance, quietness, and drainage.

[0078] The slits 21A, protrusions 24A, and groove bottom protrusions 28A connected to the protrusions 24A of the first center block 20A will be described in more detail below with reference to Figures 7 to 12. Figure 7 is a perspective view of the first center block 20A, stone ejector 60A, and their vicinity, and Figure 8 is a perspective view of the protrusions 24A of the first center block 20A and their vicinity. Figure 9 is a cross-sectional view taken along line AA in Figure 3, Figure 10 is a cross-sectional view taken along line BB in Figure 3, Figure 11 is a cross-sectional view taken along line CC in Figure 3, and Figure 12 is a cross-sectional view taken along line DD in Figure 3, which will be referenced as appropriate.

[0079] As shown in Figures 7 and 8, the first center block 20A has a tapered protrusion 24A that protrudes axially outward from a portion adjacent to the slit 21A and gradually narrows in width toward its tip. The protrusion 24A protrudes further outward from the block end 20Ed on the opposite side of the slit 21A. The protrusion 24A protrudes axially outward from the block end 20Ed beyond an imaginary line α extending from the block end 20Ed and is triangular in plan view. The slit 21A and the protrusion 24A that protrudes in the direction of the slit 21A increase the block's grip on mud, rocks, and the like, significantly improving traction performance on muddy roads, rocky areas, sandy ground, and the like.

[0080] The slit 21A extends straight to the end inside the block without bending, but the slit width gradually decreases toward the end. The slit width at the opening 21Ed of the slit 21A is, for example, 6.0 mm to 13.0 mm, which is two to three times the slit width at the end. Here, the opening 21Ed of the slit 21A refers to the opening relative to the shoulder main groove 12A and is located on the imaginary line α. The length of the slit 21A is, for example, 15.0 mm to 30.0 mm.

[0081] It is preferable that the depth of the slit 21A gradually becomes shallower from the opening 21Ed side toward the terminal end. As shown in FIG. 9 (a cross-sectional view of the slit 21A along the longitudinal direction), the bottom surface of the slit 21A is inclined at a substantially constant angle along the longitudinal direction of the slit 21A. The inclination angle θ1 of the bottom surface of the slit 21A with respect to the normal N1 is, for example, 60° to 70°, and is larger than the inclination angle of the ridge line 29A of the protrusion 24A described below. The normal N1 is a normal to a profile surface P that passes through the terminal end of the slit 21A. Note that the inclination angle θ1 is the angle between the normal N1 and the bottom surface of the slit 21A inside the block (the same applies to the inclination angles of other slopes).

[0082] The slit 21A is deepest at the opening 21Ed. The depth of the slit 21A at the opening 21Ed is, for example, 85% to 95% of the depth of the shoulder main groove 12A. The slit 21A is shallowest at the end inside the block. The depth of the slit 21A at the end is, for example, 1.5 to 3.0 times the depth of the step portion 23A. The bottom surface of the slit 21A is inclined at an angle of 60° to 70° with respect to the normal N1 along the length direction of the slit 21A from the opening 21Ed to the end. In this case, it is possible to suppress a decrease in block rigidity in the portion adjacent to the slit 21A while ensuring good drainage and mud removal. As will be described in detail later, the bottom surface of the slit 21A at the opening 21Ed is at the same height as the upper surface of the groove bottom protrusion 28A, and the bottom surface of the slit 21A and the upper surface of the groove bottom protrusion 28A are smoothly connected.

[0083] The protrusion 24A protrudes axially outward so as to fit between the first shoulder block 40A and the second shoulder block 50A. The protrusion 24A and the portion adjacent to the slit 21A are block ends that are tapered at an acute angle in plan view, forming a corner of the first center block 20A located at the intersection of the shoulder main groove 12A and the lateral groove 14. One sidewall of the protrusion 24A faces the shoulder main groove 12A. The shoulder main groove 12A is bent at the base of the protrusion 24A, and a groove bottom protrusion 28A is located at the bent portion.

[0084] The axial length of the protrusion 24A (the maximum axial length from the imaginary line α to the tip of the protrusion 24A) is, for example, 11.0 mm to 23.0 mm, which is 70% to 120% of the length of the slit 21A. In this case, it is easy to achieve both improved traction performance and suppressed uneven wear of the blocks. The axial length of the protrusion 24A may be equal to or shorter than the length of the slit 21A, or may be 80% to 100%, or 80% to 95% of the length of the slit 21A.

[0085] The width of the protrusion 24A gradually decreases toward the tip, and the height also gradually decreases. The protrusion 24A has a ridge 29A that is inclined at a substantially constant angle, and the height of the ridge 29A decreases as it approaches the tip of the protrusion 24A. Unless otherwise specified, the tip of the ridge 29A is referred to as the tip of the protrusion 24A. A stone ejector 60A is disposed at a position opposite the tip of the protrusion 24A, with a predetermined distance therebetween. The predetermined distance is, for example, 7.0 mm to 12.0 mm.

[0086] The protrusion 24A is located at the intersection of the shoulder main groove 12A and the lateral groove 14, and can be considered to branch off the groove. Therefore, the sidewalls of the protrusion 24A form the groove walls of the shoulder main groove 12A and the lateral groove 14. The sidewalls of the protrusion 24A are inclined so that the protrusion 24A widens toward the groove bottoms. The sidewalls of the protrusion 24A include a first region 25A, which is a slope with a larger inclination angle with respect to the normal to the profile surface P than other portions of the sidewall of the first center block 20A. The first region 25A is preferably formed on both sides of the protrusion 24A in the width direction, i.e., on the sidewalls along the shoulder main groove 12A and the sidewalls along the lateral groove 14.

[0087] The first region 25A of the protrusion 24A increases the surface area of ​​the protrusion 24A without increasing the contact width of the protrusion 24A with the paved road, significantly contributing to achieving both traction performance during off-road driving and maneuverability during paved road driving. For tires designed for off-road driving, it is preferable to increase the contact width to improve traction performance on muddy roads, sandy terrain, etc. On the other hand, to improve maneuverability on paved roads, the contact width must be set small. However, if the contact width is small, buoyancy cannot be obtained on muddy roads, sandy terrain, etc., increasing the possibility of getting stuck. For this reason, achieving both traction performance during off-road driving and maneuverability during paved road driving is not easy. However, with the pneumatic tire 1, by forming a steeply inclined slope on the protrusion 24A, these performances can be highly compatible.

[0088] The first region 25A is preferably formed beyond the protrusion 24A and into the slit 21A. The first region 25A is more preferably formed on the block sidewall on the shoulder main groove 12A side from the tip of the protrusion 24A to the inside of the slit 21A, and is formed to the end of the slit 21A. The first region 25A is further formed on the block sidewall along the lateral groove 14, beyond the protrusion 24A and over the entire length of the sidewall. By expanding the formation area of ​​the first region 25A, the above-mentioned effect of the first region 25A becomes more pronounced.

[0089] The protrusion 24A has a ridgeline 29A formed by the intersection of two first regions 25A on both sides in the width direction. The ridgeline 29A is the boundary between the two first regions 25A and is inclined so as to approach the groove bottom toward the tip of the protrusion 24A. As shown in FIG. 10 (a cross-sectional view along the ridgeline 29A), the ridgeline 29A is inclined at a substantially constant angle from the step portion 23A toward the tip of the protrusion 24A. The inclination angle θ2 of the ridgeline 29A with respect to the normal line N2 is, for example, 50° to 60°, which is smaller than the inclination angle θ1 of the bottom surface of the slit 21A and larger than the inclination angle θ3 of the first region 25A (see FIG. 11 described later). The normal line N2 is a normal to the profile plane P that passes through the upper end of the ridgeline 29A.

[0090] The first region 25A is formed deeper as it approaches the tip of the protrusion 24A, but because the height of the protrusion 24A gradually decreases toward the tip, the height of the first region 25A is greatest at the upper end of the ridge 29A, i.e., at a position corresponding to the tip of the step 23A. While the first region 25A can be formed over the entire side wall of the protrusion 24A, it is preferable that the side wall of the protrusion 24A include a second region 26A formed approximately perpendicular to the profile surface P and a curved surface 27A connecting the second region 26A to the groove bottom. By forming the first region 25A deeper on the side wall of the protrusion 24A, the protrusion 24A can be effectively reinforced, resulting in improved block rigidity and reduced uneven wear.

[0091] The second region 26A is formed between the first region 25A and the curved surface 27A, but the first region 25A and the curved surface 27A meet at the tip of the ridge 29A. In other words, the second region 26A does not exist at the tip of the ridge 29A. The curved surface 27A is a surface that curves convexly downward and inward of the first center block 20A. Curved surfaces are also formed on other side walls of the first center block 20A and near the groove bottoms of other blocks. However, the curved surface 27A formed on the protruding portion 24A preferably has a larger radius of curvature and a gentler degree of curvature than the other curved surfaces. In this case, stress acting on the base of the protruding portion 24A is more easily dispersed. The radius of curvature of the curved surface 27A is, for example, 3.5 mm to 4.5 mm.

[0092] The first region 25A is formed in a triangular shape on the block sidewall on the shoulder main groove 12A side, with vertices at the upper end of the ridgeline 29A (the tip of the step 23A), the lower end (tip) of the ridgeline 29A, and the end of the slit 21A. The first region 25A is also formed in a triangular shape on the block sidewall on the lateral groove 14 side, with vertices at the upper end of the ridgeline 29A, the lower end of the ridgeline 29A, and the upper end of the corner of the block located at the intersection of the center main groove 11 and the lateral groove 14. In this case, the surface area of ​​the block can be increased at and near the protrusion 24A without increasing the contact-patch width, and the force acting on the protrusion 24A can be dispersed over a wide area.

[0093] The maximum height of the first region 25A is preferably 30% or more, more preferably 50% to 80%, of the depth of the shoulder main groove 12A and the lateral groove 14. In this case, the effect of the first region 25A becomes more pronounced. In this embodiment, the shoulder main groove 12A and the lateral groove 14 have substantially the same depth. As shown in FIG. 11 (a widthwise cross-sectional view of the lateral groove 14), the first region 25A is inclined at a substantially constant angle from the step portion 23A toward the groove bottom. The inclination angle θ3 of the first region 25A with respect to the normal line N3 is, for example, 15° to 50°. The normal line N3 is a normal line to the profile plane P that passes through the upper end of the first region 25A.

[0094] The inclination angle θ3 of the first region 25A is more preferably 20° to 40°, and particularly preferably 20° to 30°. The inclination angle θ3 of the first region 25A is smaller than the inclination angle θ1 of the bottom surface of the slit 21A and the inclination angle θ2 of the ridge line 29A. If the inclination angle θ3 is within this range, traction performance during off-road driving and maneuverability during paved road driving can be more effectively achieved. Note that if the inclination angle θ3 is too small, maneuverability during paved road driving will decrease, and if it is too large, traction performance will decrease. The second region 26A formed between the first region 25A and the curved surface 27A is preferably approximately perpendicular to the profile surface P, and its inclination angle is less than 5°.

[0095] In this embodiment, a step portion 23A is formed on the top surface of the protrusion 24A, and the protrusion 24A does not have a contact surface. In addition, in a plan view of the protrusion 24A, the majority of the protrusion 24A, at least more than 50% of the area, is the first region 25A. In this case, uneven wear of the protrusion 24A is easily suppressed, and it is possible to more effectively achieve both traction performance when driving off-road and maneuverability when driving on paved roads.

[0096] As shown in FIGS. 7 to 9, the shoulder main groove 12A is formed with a groove bottom protrusion 28A, which is a raised groove bottom that connects the portion adjacent to the opening 21Ed of the slit 21A to the protrusion 24A. As described above, the shoulder main groove 12A is bent at the base of the protrusion 24A, and the groove bottom protrusion 28A is formed at this bent portion. The groove bottom protrusion 28A reinforces the base of the protrusion 24A and suppresses movement of the protrusion 24A. As a result, uneven wear of the protrusion 24A is effectively suppressed. In other words, the groove bottom protrusion 28A reinforces the protrusion 24A and suppresses a decrease in block rigidity. The groove bottom protrusion 28A is formed to connect the bottom surface of the slit 21A to the side wall of the protrusion 24A.

[0097] The height of the groove bottom projections 28A is preferably 3% or more, more preferably 5% or more, of the depth of the shoulder main groove 12A. In this case, the effects of the groove bottom projections 28A become more pronounced. The height of the groove bottom projections 28A is not particularly limited from the viewpoint of suppressing uneven wear of the protrusions 24A, but from the viewpoint of improving drainage and mud removal, the height is preferably 50% or less, more preferably 30% or less, and particularly preferably 15% or less, of the depth of the shoulder main groove 12A. Examples of suitable ranges for the height of the groove bottom projections 28A include 5% to 50%, 5% to 30%, 5% to 15%, or 5% to 10% of the depth of the shoulder main groove 12A.

[0098] The groove bottom protrusion 28A may be formed higher than the bottom surface of the slit 21A at the opening 21Ed, but in this embodiment, it is formed at the same height as the bottom surface of the slit 21A. In this case, there is no difference in height between the upper surface of the groove bottom protrusion 28A and the bottom surface of the slit 21A, and no step exists. Furthermore, a flat region of approximately constant height exists on the upper surface of the groove bottom protrusion 28A. The flat upper surface of the groove bottom protrusion 28A is connected to the deepest part of the groove via a curved surface 28Ac, and the base of the protrusion 24A on the shoulder main groove 12A side is formed in a stepped shape with the upper surface of the groove bottom protrusion 28A as the upper step and the deepest part of the groove as the lower step.

[0099] The groove bottom protrusion 28A is preferably formed with a width of 80% or more of the opening width of the slit 21A (the length along the imaginary line α of the opening 21Ed) in the portion adjacent to the opening 21Ed of the slit 21A. In this case, the above-mentioned effect of the groove bottom protrusion 28A becomes more pronounced. In this embodiment, the groove bottom protrusion 28A is formed over the entire opening width of the slit 21A. In this case, the groove bottom protrusion 28A connects the protrusion 24A and the block end 20Ed located on the opposite side of the slit 21A from the protrusion 24A, thereby enhancing the reinforcing effect against reduced rigidity of the protrusion 24A.

[0100] The groove bottom protrusion 28A extends from a portion adjacent to the opening 21Ed of the slit 21A along the protrusion 24A toward the tip of the protrusion 24A. The groove bottom protrusion 28A has a portion adjacent to the opening 21Ed of the slit 21A (hereinafter referred to as the "base portion") and a portion extending from the base along the protrusion 24A (hereinafter referred to as the "extending portion"). The extending portion is connected to the curved surface 27A of the protrusion 24A over its entire length. By forming the extending portion, the area connected to the protrusion 24A is increased, thereby enhancing the reinforcing effect of the protrusion 24A. It is preferable that the extending portion be formed so as to extend toward the tip of the protrusion 24A beyond a position corresponding to the upper end of the ridge line 29A, but not beyond the tip of the protrusion 24A.

[0101] The extension of the groove bottom projection 28A has a tapered shape, with its width gradually decreasing toward the tip of the protrusion 24A. By tapering the extension and gradually widening the width of the shoulder main groove 12A toward the intersection with the lateral groove 14, the protrusion 24A can be reinforced while ensuring good drainage and mud removal. The width of the extension may decrease in stages, but preferably decreases continuously. In this embodiment, the tip of the extension is pointed and connects to the curved surface 27A near the tip of the protrusion 24A.

[0102] The groove bottom protrusion 28A is formed over an area less than half of the shoulder main groove 12A on the first shoulder block 40A side in the width direction. In other words, the groove bottom protrusion 28A is not formed to cross the shoulder main groove 12A. The groove bottom protrusion 28A is formed along the sidewall of the first shoulder block 40A within an area not exceeding the deepest part of the shoulder main groove 12A. In this case, the protrusion 24A can be reinforced without impairing the drainage function of the shoulder main groove 12A.

[0103] As shown in FIG. 12 (a cross-sectional view of the portion extending from the ground contact surface adjacent to the slit 21A through the groove bottom protrusion 28A to the groove bottom), the corners of the first center block 20A, including the protrusion 24A, are acutely angled and tapered to form a multi-step shape extending from the ground contact surface to the groove bottom. This multi-step shape is a three-step shape with a first step S1 (top step) including the step portion 23A, a second step S2 (middle step) including the upper surface of the first region 25A and the groove bottom protrusion 28A, and a third step S3 (bottom step) including the curved surface 28Ac leading to the deepest part of the groove. While a multi-step shape with four or more steps is possible, a three-step shape is preferred. Note that the number of steps in this multi-step shape is counted from the ground contact surface side of the first center block 20A toward the groove bottom.

[0104] The corner of the first center block 20A including the protrusion 24A has a triangular shape in a plan view, and the angle θ 20 (See Figure 3) The angle θ 20 is the angle between the block ends that approach each other toward the tip of the corner, and is, for example, 20° to 65°, preferably 20° to 50°, or 30° to 50°. The corner of the first center block 20A including the protrusion 24A faces the shoulder main groove 12A and is located at the intersection of the shoulder main groove 12A and the lateral groove 14. In such areas, the ground pressure is likely to be high and the block rigidity is locally reduced, making the block particularly susceptible to uneven wear.

[0105] In this embodiment, the reinforcement provided by the groove bottom projections 28A and the multi-step shape ensures excellent traction performance while effectively suppressing uneven wear of the blocks. In the multi-step shape, the height of the first step S1 is greater than the height of the third step S3, and the height of the second step S2, which includes the first region 25A, is the greatest. In this case, the effect of the first region 25A more effectively suppresses a decrease in block rigidity. The second step S2 includes the first region 25A, the second region 26A, the curved surface 27A, and the upper surface of the groove bottom projections 28A. The height of the first region 25A is the greatest of all the steps that make up the multi-step shape.

[0106] The stepped portion 23A that constitutes the multi-stage first stage S1 distributes the ground pressure acting on the corners of the first center block 20A, contributing to uniformity of the ground pressure. The above-mentioned surfaces of the second stage S2 reinforce the corners and prevent a decrease in rigidity. The curved surface 28Ac that constitutes the third stage S3, like the curved surface 27A, is curved so that it is convex toward the inside of the first center block 20A, preventing cracks at the groove bottom. The synergistic effect of each stage ensures excellent traction performance while effectively suppressing uneven block wear.

[0107] Each step constituting the multi-step shape includes a gently sloping surface with an inclination angle of 55° or more relative to the normal to the profile surface P, or a substantially flat surface along the profile surface P. The length of the gently sloping surface or flat surface in the direction in which each step is formed is preferably 0.5 mm or more, and more preferably 1.0 mm or more. The lowest step includes a substantially flat groove bottom surface. In other words, a slope or flat surface that meets this condition is counted as one step, and a shape with three or more steps connected together is defined as a multi-step shape.

[0108] The stone ejectors 60A, 70A, and 80A will be described in further detail below with reference to Figures 7 and 13 to 15. Figure 13 is a perspective view of the stone ejectors 70A and 80A and their vicinity. Figure 14 is a longitudinal cross-sectional view of the stone ejector 60A (cross-sectional view taken along line EE in Figure 3), and Figure 15 is a width-sectional view of the lateral groove 14 in which the stone ejector 60A is disposed (cross-sectional view taken along line FF in Figure 3), and these will be referenced as appropriate.

[0109] As shown in Figures 7 and 13, a stone ejector 60A is formed at the bottom of the lateral groove 14, and stone ejectors 70A and 80A are formed at the bottom of the lateral groove 15A. The stone ejectors 60A, 70A, and 80A are protrusions that extend along the lateral grooves to prevent stone trapping. In the right shoulder region of the tread 10, the lateral groove 14, in which one stone ejector 60A is formed, and the lateral groove 15A, in which two stone ejectors 70A and 80A are formed, are alternately arranged in the tire circumferential direction (see Figure 2, etc.). The stone ejectors 60A and 80A are arranged along the tire axial direction, and the stone ejector 70A is arranged at an angle with respect to the tire axial direction.

[0110] Stone ejectors 60B, 70B, and 80B (see FIG. 2) are disposed in the left shoulder region of the tread 10. The stone ejectors 60B, 70B, and 80B have the same shapes as the stone ejectors 60A, 70A, and 80A, respectively.

[0111] The stone ejectors 60A, 70A, and 80A are all elongated protrusions extending along the lateral grooves and have similar shapes, but the stone ejector 60A or the stone ejector 70A is the longest, and the stone ejector 80A is the shortest. The stone ejectors 60A and 70A may have the same length. The widths of the stone ejectors may differ from one another, but are substantially the same in this embodiment. The stone ejector 60A is formed from the ground contact end E1 to the vicinity of the tip of the protrusion 24A. The stone ejector 80A is formed from the ground contact end E1 to the bent portion 15Ax of the first lateral groove 15A. A portion of the stone ejector 60A or 80A may extend beyond the ground contact end E1 to the buttress region 4.

[0112] As shown in FIG. 7, a recess 63A is formed in the longitudinal middle of the stone ejector 60A, lowering the height of the stone ejector 60A. When the tread contacts the road surface, the shape of the protrusion formed at the groove bottom changes due to the load. However, in the case of a stone ejector whose height is constant along the length, the shape is unlikely to change along the length. In this case, the stone ejector cannot eject stones, and stones stuck in the grooves cannot be effectively removed. In the case of the stone ejector 60A, the recess 63A makes it easy to eject stones stuck in the lateral grooves 14.

[0113] When the surrounding blocks contact the road surface, the stone ejector 60A curves so that both ends in the longitudinal direction are warped upward, and when the blocks leave the road surface, the central portion in the longitudinal direction curves so that it is convex toward the tire radially outward, returning to its original shape. The portion where the recess 63A is formed has reduced rigidity and is easily deformed, so the stone ejector 60A curves from the position of the recess 63A. The stone ejector 60A curves significantly in the longitudinal direction, allowing it to eject stones stuck in the lateral grooves 14 with great force. As a result, a decrease in traction performance due to stone entrapment is suppressed.

[0114] The stone ejector 60A has a length of 24.0 mm to 43.0 mm and a width of 2.5 mm to 3.5 mm, for example. The number of recesses 63A may be two or more, but for a length of this order, one is preferable. When there is one recess 63A, it is preferable to form the recess 63A in the longitudinal center of the stone ejector 60A. In this embodiment, the recess 63A is formed at a position equidistant from both ends of the stone ejector 60A in the longitudinal direction. In this case, the stone ejector 60A can be easily bent or curved in the longitudinal direction around the portion where the recess 63A is formed, and the above-mentioned effect of the recess 63A becomes more pronounced.

[0115] The stone ejector 60A includes a first portion 61A where no recess 63A exists, and a second portion 62A where the recess 63A is formed and the height is reduced. In this embodiment, one recess 63A is formed in the center of the stone ejector 60A in the longitudinal direction, so that first portions 61A of the same length are formed on both sides of the second portion 62A (recess 63A) in the longitudinal direction. In other words, the stone ejector 60A has a structure in which two first portions 61A are connected by the second portion 62A. The second portion 62A serves to improve the elasticity of the stone ejector 60A, increasing the force with which the stone is ejected.

[0116] As shown in FIG. 14, a slope 64A inclined in the longitudinal direction is formed at the boundary between the first portion 61A and the second portion 62A. In this case, the change in height is gradual, which distributes stress acting on the boundary, improving the durability of the stone ejector 60A. The portion including the slope 64A is considered to belong to the second portion 62A. Between the two slopes 64A, a substantially flat upper surface of the second portion 62A is formed along the longitudinal direction. That is, the recess 63A has a substantially trapezoidal shape in a longitudinal cross section (side view) of the stone ejector 60A. The first portion 61A has a substantially constant height except for the longitudinal ends. Furthermore, the heights of the two first portions 61A are substantially the same.

[0117] The stone ejector 60A has a slope 65A inclined in the longitudinal direction at both longitudinal ends. The first portion 61A has the slope 65A and a substantially flat upper surface formed along the longitudinal direction between the slopes 64A and 65A. The slope 65A is connected to the deepest part of the groove via a curved surface 66A. Because the stone ejector 60A undergoes significant shape change along the longitudinal direction, it is preferable to form the curved surface 66A to reduce stress acting on the groove bottom. The inclination angle θ4 of the slope 64A relative to the normal N4 and the inclination angle θ5 of the slope 65A relative to the normal N5 are, for example, substantially the same angle, preferably 40° to 50°, or 45°±3°. The normals N4 and N5 are normals to the profile surface P that pass through the upper ends of the slopes 64A and 65A, respectively.

[0118] The length of each first portion 61A is preferably longer than the length of the second portion 62A, for example, 2 to 6 times the length of the second portion 62A, and more preferably 3.5 to 5 times the length of the second portion 62A. By ensuring that the first portions 61A are sufficiently large, stones can be pushed out with strong force. The second portions 62A (recesses 63A) preferably have a length such that the first portions 61A do not come into contact with each other when the stone ejector 60A is deformed in the longitudinal direction, for example, 3.0 mm to 5.0 mm. In comparing the lengths of the first portions 61A and the second portions 62A, the length of the first portions 61A is the length within a range where the height is constant, and the length of the second portions 62A (recesses 63A) is the distance between the upper ends of the slopes 64.

[0119] As shown in FIG. 15, the maximum height H of the first portion 61A is, for example, 2.5 mm to 3.5 mm, which is preferably 5% to 40%, and more preferably 15% to 25%, of the depth D of the lateral groove 14. In this case, mud, stones, etc. can be captured in the lateral groove 14, ensuring excellent traction performance while also ensuring sufficient force to expel stones. In addition, the maximum depth D of the recess 63A is 63 is preferably 20% to 50% of the height H of the first portion 61A, and more preferably 25% to 40%. In other words, it is preferable that the height of the second portion 62A is 50% to 80%, or 60% to 75% of the height of the first portion 61A. In this case, the longitudinal deformation and elastic force of the stone ejector 60A when the tread 10 is in contact with the tire and when it is not in contact with the tire, and the force to eject stones stuck in the lateral grooves 14 becomes stronger.

[0120] The stone ejector 60A is disposed in the widthwise center of the lateral groove 14, and curved surfaces 66A are formed on both sides in the widthwise direction. The curved surfaces 66 give the stone ejector 60A a shape that gradually widens in width toward the deepest part of the groove.

[0121] As shown in FIG. 13, two stone ejectors 70A, 80A are formed in the lateral groove 15A, lined up in the direction in which the groove extends. The stone ejectors 70A, 80A are separated by a bent portion 15Ax of the lateral groove 15A, and are arranged apart in the longitudinal direction of the lateral groove 15A, sandwiching the bent portion 15Ax. The lateral groove 15A has a bent portion 15Ax in its middle, and is inclined at an angle of 15° to 25° with respect to the tire axial direction. In the lateral groove 15A, the stone ejector 80A is arranged in a portion along the tire axial direction, and the stone ejector 70A is arranged in a portion inclined with respect to the tire axial direction. The stone ejector 70A is inclined at the same angle with respect to the tire axial direction as the lateral groove 15A.

[0122] It is conceivable to connect the stone ejectors 70A, 80A to form a single protrusion, but in that case, when the ejector deforms, the rubber will gather at the bent portion of the ejector, causing cracks. It is also conceivable that the force pushing out the stones will be dissipated in the tire circumferential direction and become smaller. This problem can be prevented by spacing the linear stone ejectors 70A, 80A apart so that they do not interfere with each other. On the other hand, if the stone ejectors 70A, 80A are spaced too far apart, stones may become stuck in the bent portion 15Ax. Therefore, the spacing between each ejector is set, for example, to a linear distance of 1.5 times or less the length of the recesses 73A, 83A, or less than the length of the recesses 73A, 83A.

[0123] Like the stone ejector 60A, the stone ejectors 70A and 80A have recesses 73A and 83A at positions equidistant from both ends in the longitudinal direction. The stone ejectors 70A and 80A also have first portions 71A and 81A, which are portions where the recesses 73A and 83A are not present, and second portions 72A and 82B, which are portions where the recesses 73A and 83A are formed and the height is reduced. The shape of the stone ejectors 70A and 80A, the ratio of the lengths of the first and second portions, the depth of the recesses 73A and 83A, and the dimensions of the height of the first portion are the same as those of the stone ejector 60A.

[0124] The stone ejector 70A extends from the bent portion 15Ax of the lateral groove 15A to the intersection of the shoulder main groove 12A and the lateral groove 15A. Because a large recess is formed at the intersection of the shoulder main groove 12A and the lateral groove 15A, where stones are likely to become clogged, the stone ejector 70A preferably extends to the center of the shoulder main groove 12A in the width direction. Each shoulder block located on both sides of the lateral groove 15A in the width direction has a step 42A, 52A formed along the periphery of the block's top surface with a substantially constant width and depth. The width and depth of the step 42A, 52A are similar to those of the step 23A of the first center block 20A, but the step 42A, 52A differs from the step 23A in that it is not formed on part of the periphery of the block's top surface, specifically, on the axially outer end.

[0125] The corner 40Cd of the first shoulder block 40A, which has a multi-step shape, will be described in further detail below with reference to Figures 16 and 17. Figure 16 is a perspective view of the corner 40Cd and its vicinity. Figure 17 is a cross-sectional view (cross-sectional view taken along line GG in Figure 3) of the multi-step shape formed at the corner 40Cd.

[0126] As shown in Figures 16 and 17, the first shoulder block 40A has a multi-step shape with three or more steps, including a sloped surface 45A, at a corner 40Cd located at the intersection of the shoulder main groove 12A and the lateral groove 15A. The sloped surface 45A is formed in the second step from the ground-contact side of the first shoulder block 40A, and its length extending outward from the block is the longest among the steps constituting the multi-step shape. The first shoulder block 40A bends toward the intersection of the shoulder main groove 12A and the lateral groove 15A, and the corner 40Cd is formed at an acute angle, tapering to a narrow tip. The protruding block end, formed at an acute angle like the corner 40Cd, tends to reduce the block's rigidity. Furthermore, when the shoulder main groove 12A is in contact with the ground, the increased ground pressure increases, increasing the amount of rubber compression, which can easily cause uneven wear.

[0127] As described above, the pneumatic tire 1 is designed for off-road driving. To improve traction on muddy, rocky, and sandy terrain, the blocks are formed with protruding portions on their outer sides to increase traction on mud, rocks, and other surfaces. However, if a block is formed with a sharp angle and protruding, the block rigidity is locally reduced, making the block more susceptible to uneven wear. The corner 40Cd of the first shoulder block 40A faces the shoulder main groove 12A and is located at the intersection of the shoulder main groove 12A and the lateral groove 15A, making it particularly susceptible to uneven wear. However, by adopting a multi-step shape, it is possible to effectively suppress uneven block wear while maintaining excellent traction.

[0128] The corner 40Cd of the first shoulder block 40A has a three-step shape, with a first step S1 including the step portion 42A, a second step S2 including the sloped surface 45A, and a third step S3 including the curved surface 46A. The corner 40Cd can have four or more steps, but a three-step shape is preferred. The step shape of the corner 40Cd is counted from the ground contact surface side of the first shoulder block 40A toward the groove bottom. The corner 40Cd of the first shoulder block 40A has a triangular shape in a plan view, with an angle θ 40 (See Figure 3) The angle θ 40 is, for example, 20° to 65°, and preferably 50° to 60°.

[0129] The first step S1 is the uppermost step of the multi-step shape located on the ground contact surface side of the first shoulder block 40A, forming a step with the ground contact surface as the upper step and the step portion 42A as the lower step. The third step S3 is the lowermost step of the multi-step shape, forming a step with the slope 45A as the upper step and the groove bottom as the lower step. The second step S2 is the middle step of the multi-step shape, forming a step with the step portion 42A as the upper step and the slope 45A as the lower step. In this multi-step shape, the height of the first step S1 is less than the height of the third step S3, and the height of the second step S2 is the greatest.

[0130] The first step S1 has a step 42A that is one step lower than the ground contact surface of the first shoulder block 40A, and a first side surface 47A that connects the ground contact surface and the step 42A. Because the step 42A has a flat surface that is approximately parallel to the ground contact surface, the height difference of the first step S1 is substantially equal to the height of the first side surface 47A. The height of the first side surface 47A is, for example, 1.0 mm to 3.0 mm. Furthermore, the inclination angle of the first side surface 47A is preferably equal to or smaller than the inclination angle θ6 of the second side surface 48A of the second step S2. The first step S1 (step 42A) distributes the ground contact pressure acting on the corner 40Cd, contributing to uniformity of the ground contact pressure.

[0131] The second step S2 has a slope 45A that is one step below the step portion 42A and a second side surface 48A that connects the step portion 42A and the slope 45A. The second side surface 48A is preferably a slope inclined at the same angle as the first side surface 47A or at a slightly larger angle. The second side surface 48A is formed higher than the first side surface 47A and the curved surface 46A, so that the height difference of the second step S2 is the largest. The height of the second side surface 48A is, for example, 4.0 mm to 6.0 mm. The inclination angle θ6 of the second side surface 48A with respect to the normal line N6 is, for example, 4° to 10° or 6° to 8°. The normal line N6 is a normal to the profile surface P that passes through the upper end of the second side surface 48A.

[0132] The inclined surface 45A is a tapered surface having a triangular or trapezoidal shape in a plan view that gradually narrows toward the groove bottom. The inclined surface 45A has a larger inclination angle than the second side surface 48A and protrudes significantly outward from the block. The inclined surface 45A reinforces the base of the corner 40Cd and prevents a decrease in the rigidity of the corner 40Cd. The inclination angle θ7 of the inclined surface 45A with respect to the normal line N7 is preferably 55° to 80°, more preferably 55° to 70°. The normal line N7 is a normal line to the profile surface P that passes through the upper end of the inclined surface 45A. If the inclination angle θ7 of the inclined surface 45A is within this range, the reinforcing effect of the block becomes more pronounced. The inclination angle θ7 of the inclined surface 45A is, for example, 5 to 15 times the inclination angle θ6 of the second side surface 48A.

[0133] The height of the slope 45A may be, for example, 90% to 110% of the height of the second side surface 48A, or may be substantially the same as the height of the second side surface 48A. While the slope 45A has a similar height to the second side surface 48A, its inclination angle is at least five times that of the second side surface 48A, and therefore its area in a plan view is larger than that of the second side surface 48A. By providing a multi-step shape including a large slope 45A at the corner 40Cd of the first shoulder block 40A, uneven wear at the corner 40Cd can be effectively suppressed while increasing buoyancy on muddy roads, sandy ground, and the like, thereby significantly improving off-road driving performance. The length of the slope 45A in the direction in which each step is formed is, for example, 7.0 mm to 14.0 mm.

[0134] The third step S3 has a curved surface 46A connecting the inclined surface 45A to the groove bottom. Like the curved surfaces formed on other portions of the block sidewall, the curved surface 46A is curved so as to be convex toward the inside of the first shoulder block 40A. The inclined surface 45A of the second step S2 is a tapered surface whose width gradually decreases toward the groove bottom. Therefore, if the inclined surface 45A connects to the groove bottom, stress will concentrate at the groove bottom, making it more likely to crack. Forming the curved surface 46A effectively suppresses cracks at the groove bottom. In this embodiment, the inclined surface 45A is trapezoidal in plan view, and the curved surface 46A extends from the base of the trapezoid to the groove bottom. For example, the radius of curvature of the curved surface 46A is 2.0 mm to 4.0 mm, and the height is 1.5 mm to 2.5 mm.

[0135] As described above, by forming the second step S2 including the slope 45A between the step 42A constituting the uppermost step and the curved surface 46A constituting the lowermost step and maximizing the height of the second step S2, it is possible to effectively prevent a decrease in rigidity of the corner 40Cd of the first shoulder block 40A. As a result, uneven wear of the corner 40Cd can be significantly reduced while maintaining excellent traction performance, and the durability of the first shoulder block 40A is greatly improved.

[0136] Additionally, the multi-stepped shape formed at the corner 40Cd of the first shoulder block 40A is positioned to overlap the multi-stepped shape formed at the corner including the protruding portion 24A of the first center block 20A in the tire circumferential direction. That is, the multi-stepped shape of the corner 40Cd of the first shoulder block 40A and the multi-stepped shape of the corner including the protruding portion 24A of the first center block 20A are alternately arranged along the tire circumferential direction. By repeating this structure around the tire circumferential direction, it is possible to achieve both excellent driving performance and durability at a high level.

[0137] The buttress region 4 will be described in further detail below with reference to Figures 18 to 20. Figure 18 is a side view of the pneumatic tire 1, and Figure 19 is a side view of the pneumatic tire 1, showing an enlarged view of the buttress region 4. Figure 20 is a perspective view of the buttress region 4.

[0138] As shown in Figure 18, the side of the pneumatic tire 1 has unevenness formed along the tire circumferential direction. Side blocks 90, 91, 92, and 94 of different shapes and sizes are formed on the sidewall 2, and first shoulder blocks 40A and second shoulder blocks 50A are alternately arranged in the tire circumferential direction to form unevenness in the buttress region 4. The unevenness of the sidewall 2 and buttress region 4 improves the side traction performance of the pneumatic tire 1 and emphasizes its aggressive appearance. The side blocks also effectively suppress side cuts in the pneumatic tire 1.

[0139] In the buttress region 4, the lateral grooves 14, 15A extend up to the side rib 5 and separate the first shoulder block 40A from the second shoulder block 50A. A recess 44A is formed in the sidewall 43A of the first shoulder block 40A, and a recess 54A is formed in the sidewall 53A of the second shoulder block 50A. As will be described in detail later, in a side view of the tire, the edges of the recesses 44A, 54A include a long side extending circumferentially and a short side extending radially inward from one end of the long side, with the angle between these sides set to 55° to 100°. The recess 44A opens in the circumferential direction of the tire to connect with the lateral groove 15A, and the recess 54A opens in the circumferential direction of the tire to connect with the lateral groove 14.

[0140] Side blocks 90 and 91 are arranged on the sidewall 2 so as to be aligned with the first shoulder block 40A in the tire radial direction, and side blocks 92 and 93 are arranged so as to be aligned with the second shoulder block 50A in the tire radial direction. The side blocks 90 and 91 are connected to each other and integrated, but have different protruding heights, forming a step at their boundary. Similarly, the side blocks 92 and 93 are connected to each other and integrated, but have different protruding heights, forming a step at their boundary.

[0141] Side block 90 protrudes further axially outward than side block 91 and has a larger area in a side view of the tire. Side blocks 92, 93 extend further radially inward than side blocks 90, 91. Side block 92 protrudes further axially outward than side block 93 and has a larger area in a side view of the tire. Side block 92 is the largest of the four blocks and extends to a position radially inward of side block 91.

[0142] The side block 91 is formed in a position radially opposite the recess 44A of the first shoulder block 40A, with the side rib 5 interposed therebetween. The side block 93 is formed in a position radially opposite the recess 54A of the second shoulder block 50A, with the side rib 5 interposed therebetween. By lowering the height of the side block aligned radially with the recess 44A, 54A, while raising the side blocks on both sides of the recess 44A, 54A in the tire circumferential direction, for example, mud can be more easily trapped in the recess 44A, 54A, thereby improving traction performance.

[0143] As shown in Figures 18 to 20, the recess 44A formed in the sidewall 43A of the first shoulder block 40A and the recess 54A formed in the sidewall 53A of the second shoulder block 50A are depressions that open in the same direction in the tire circumferential direction. As described above, the sidewalls 43A, 53A of each shoulder block have different shapes, forming recesses and projections in the buttress region 4 along the tire circumferential direction. The recesses 44A, 54A have similar shapes, but the recess 44A is smaller than the recess 54A. In other words, the recesses 44A, 54A of similar shapes but different sizes are arranged alternately in the tire circumferential direction in the buttress region 4.

[0144] Compared with the sidewall 53A of the second shoulder block 50A, the sidewall 43A of the first shoulder block 40A has a radially outer portion that is recessed more axially inward and a radially inner portion that protrudes more axially outward. Compared with the sidewall 53A, the sidewall 43A has a greater difference in radial unevenness, is gradually inclined from the ground contact patch toward the side rib 5 so that it is positioned axially outward, and is significantly curved at a position closer to the side rib 5 than the ground contact patch, protruding significantly axially outward.

[0145] The ground contact surface of the second shoulder block 50A is located axially outboard of the ground contact surface of the first shoulder block 40A. Therefore, the radially outer end of the sidewall 53A is located axially outboard of the radially outer end of the sidewall 43A and is convex in the axial direction. The sidewall 53A has a small curved surface near the ground contact surface, but the area other than the curved surface and the recessed portion 54A forms a slope that slopes at a substantially constant angle from the ground contact edge toward the side rib 5.

[0146] The sidewall 43A of the first shoulder block 40A locally protrudes axially outward more than the sidewall 53A of the second shoulder block 50A, but the sidewall 53A protrudes axially outward overall. Of the two types of shoulder blocks, the volume of the portion protruding axially outward is relatively larger in the second shoulder block 50A. The recess 54A of the sidewall 53A is larger than the recess 44A of the sidewall 43A in a side view of the tire. The recess 54A is longer in the circumferential and radial directions than the recess 44A, and opens more circumferentially.

[0147] As described above, the edge of the recess 44A includes a long side 44x extending long in the tire circumferential direction in a side view of the tire, and a short side 44y extending from one end of the long side 44x toward the tire radially inward. 44 is, for example, 55° to 100°, preferably 60° to 90°, and more preferably 60° to 85°, and the long side 44x and the short side 44y are formed in a substantially L-shape. In addition, the edge of the recess 54A includes a long side 54x extending long in the tire circumferential direction and a short side 54y extending inward in the tire radial direction from one end of the long side 54x in a side view of the tire. The angle θ formed by the long side 54x and the short side 54y is 54 is, for example, 55° to 100°, preferably 70° to 100°, and more preferably 80° to 90°, and the long side 54x and the short side 54y are formed in a substantially L-shape.

[0148] In this embodiment, the angle θ 54 is the angle θ 44The recesses 44A, 54A are formed with edges that are generally L-shaped, which increases the number of block edges that catch on mud, rocks, etc., thereby improving traction performance. In addition, since large forces act on recesses that open in the tire circumferential direction, it is preferable to form slopes or curved surfaces that gradually deepen toward the side rib 5 in the portions of the recesses 44A, 54A adjacent to the long sides 44x, 54x, from the perspective of improving the durability of the blocks.

[0149] The recesses 44A, 54A are both formed in portions adjacent to the side rib 5, and it can be said that the side rib 5 forms the radially inner edges of the recesses 44A, 54A. As described above, the side rib 5 is a protrusion formed in an annular shape along the tire circumferential direction, and forms the boundary between the sidewall 2 and the buttress region 4. The recess 44A is surrounded on three sides by the long side 44x, the short side 44y extending from one end of the long side 44x to the side rib 5, and the side rib 5, and opens into the lateral groove 15A. The recess 54A is surrounded on three sides by the long side 54x, the short side 54y extending from one end of the long side 54x to the side rib 5, and the side rib 5, and opens into the lateral groove 14.

[0150] The long side 44x of the recess 44A is at an angle θ with respect to the block end 40Ed adjacent to the long side 44x. 44x (first angle), and the short side 44y is inclined at an angle θ 44y (Second angle) and the inclination angle θ of the long side 44x 44x is the inclination angle θ of the short side 44y 44y In this embodiment, the block end adjacent to the short side 44y is in contact with the side rib 5, so the angle θ 44y can be said to be the angle formed by the short side 44y and the side rib 5.

[0151] The recess 44A gradually becomes smaller from the opening in the tire circumferential direction (the opening relative to the lateral groove 15A) toward the short side 44y located at the back of the recess 44A on the opposite side from the opening. 44x The angle θ of the short side 44y 44yBy making the recess 44A larger than the width of the recess 44A, the opening width in the tire circumferential direction becomes wider and gradually narrows toward the back. This compresses mud that has entered the recess 44A, resulting in greater grip on the muddy road and improved traction performance.

[0152] The angle θ between the long side 44x and the block end 40Ed 44x is preferably a right angle or an obtuse angle close to a right angle, and the angle θ 44y is preferably an acute angle. 44x The angle θ is preferably 80° to 110°, and more preferably 90° to 100°. 44y The angle is preferably 50° to 75°, and more preferably 60° to 70°. In this case, the above-mentioned effect of the recess 44A becomes more pronounced.

[0153] Similarly, the long side 54x of the recess 54A is at an angle θ 54x The short side 54y is inclined at an angle θ 54y The tilt angle of the long side is 54x. 54x is the inclination angle θ of the short side 54y 54y The angle θ is larger than 54x is preferably an obtuse angle, and the angle θ 54y is preferably an acute angle. 54x The angle θ is preferably 95° to 115°. 54y In this case, the above-described effect of the recess 54A becomes more pronounced. In this embodiment, the angle θ of the recess 54A is 54x is the angle θ of the recess 44A 44x Larger and angle θ 54y is the angle θ 44y Greater than.

[0154] As described above, the recessed portion 54A is longer in the tire circumferential direction and radial direction than the recessed portion 44A, and has a larger opening in the tire circumferential direction. The tire circumferential length of the recessed portion 54A is, for example, 19.0 mm to 40.0 mm, which is 1.4 to 2.0 times the tire circumferential length of the recessed portion 44A. The opening width of the recessed portion 54A relative to the lateral groove 14 is, for example, 8.0 mm to 20.0 mm, which is 1.3 to 1.9 times the opening width of the recessed portion 44A relative to the lateral groove 15A.

[0155] As described above, the pneumatic tire 1 having the above configuration is a high-performance tire that excels in traction performance, drainage, durability, quietness, and steering. The pneumatic tire 1 can effectively suppress uneven wear of the tread pattern blocks while ensuring excellent traction performance when driving off-road on muddy roads, rocky areas, sandy terrain, etc. The pneumatic tire 1 has an aggressive appearance and is suitable for use as a manual transmission tire, a rear tire, etc., but also provides quietness, excellent steering, and a comfortable ride when driving on paved roads.

[0156] The above-described embodiment can be appropriately modified without departing from the scope of the present invention. For example, the pneumatic tire according to the present invention can be applied to a sidewall without side blocks. While omitting the side blocks can improve quietness and reduce air resistance, providing side blocks is preferable when considering off-road driving.

[0157] In the above embodiment, the stone ejectors, which are protrusions extending along the grooves to prevent stone trapping, are formed only in the lateral grooves, but they can also be formed in the circumferential grooves. In this case, too, by forming a recess in the longitudinal middle of the protrusion, stones can be easily ejected, thereby preventing a decrease in traction performance due to stone trapping. [Explanation of symbols]

[0158] 1 pneumatic tire, 2 sidewall, 3 bead, 4 buttress region, 5 side rib, 10 tread, 11 center main groove, 11x, 11y bend, 12A, 12B shoulder main groove, 13A, 13B, 14, 15A, 15B lateral groove, 13Ax, 13Bx, 14x, 15Ax bend, 16 block group, 17A, 17B stone ejector, 20A, 20B first center block, 20Ed block end, 21A, 21B slit, 21Ed opening, 22A, 22B sipe, 23A, 23B step, 24A, 24B protrusion, 25A first region, 26A second region, 27A curved surface, 28A, 28B groove bottom protrusion, 29A ridge, 30A, 30B Second center block, 31A, 31B Slit, 32A, 32B Sipes, 33A, 33B Step, 40A, 40B First shoulder block, 40Ed Block end, 41A, 41B Sipes, 42A Step, 43A, 43B Side wall, 44A Recess, 44x Long side, 44y Short side, 45A, 45B Slope, 46A Curved surface, 47A First side, 48A Second side, 50A, 50B Second shoulder block, 50Ed Block end, 51A, 51B Sipes, 52A Step, 53A, 53B Side wall, 54A Recess, 54x Long side, 54y Short side, 60A, 60B Stone ejector, 61A First part, 62A Second part, 63A Recess, 64A, 65A Slope, 70A, 70B Stone ejector, 71A First part, 72A Second part, 73A Recess, 80A, 80B Stone ejector, 81A First part, 82A Second part, 83A Recess, 90, 91, 92, 93 Side block, CL Equator, E1, E2 Ground edge, α Virtual line, N1, N2, N3, N4, N5, N6, N7 Normal

Claims

1. A pneumatic tire having a tread pattern including first and second blocks having different shapes and grooves separating the blocks, The first block comprises: a slit extending from the groove and terminating within the block; a protruding portion that protrudes from a portion adjacent to the slit toward the outside of the block beyond an end of the block on the opposite side of the slit; and The pneumatic tire has a groove bottom protrusion formed in the groove, the groove bottom protruding from a portion adjacent to the opening of the slit so as to connect to the protruding portion.

2. 2. The pneumatic tire according to claim 1, wherein the height of the groove bottom protrusion is 5% to 50% of the depth of the groove.

3. The pneumatic tire according to claim 1 , wherein the groove bottom protrusion is formed with a width that is 80% or more of the opening width of the slit in a portion adjacent to the opening of the slit.

4. The pneumatic tire according to claim 1 , wherein the protrusion has a tapered shape in which the width gradually decreases toward the tip.

5. The pneumatic tire according to claim 1 , wherein the groove bottom projection extends from a portion adjacent to the opening of the slit along the protruding portion toward a tip end of the protruding portion.

6. The pneumatic tire according to claim 5 , wherein a portion of the groove bottom projection extending along the protruding portion has a tapered shape in which the width gradually decreases toward the tip of the protruding portion.

7. the first block is a center block disposed closer to the equator than the ground contact edge of the tread, The pneumatic tire according to claim 1 , wherein the protrusion protrudes axially outward.

8. The pneumatic tire according to claim 1 , wherein the sidewall of the protrusion includes a slope having a larger inclination angle with respect to a normal to a profile surface of the tread than other portions of the sidewall of the first block.

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