Pneumatic tire

Abstract

To suppress damage such as chipping in a region outside a shoulder block in a tire axial direction while improving grounding property of a tire.SOLUTION: In a pneumatic tire including a tread, the tread includes a shoulder block 21, the shoulder block 21 includes a sipe 40 that terminates inside the shoulder block 21, and a length along a tire axial direction from a tire axial direction outer end 20A of the sipe 40 to a tire axial direction outer end of the shoulder block is equal to or greater than 4mm and is equal to or greater than 8% of a length along the tire axial direction of the shoulder block 21.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Conventionally, off-road tires used on rough terrain, rocky areas, etc. often employ so-called square shoulders, in which shoulder blocks have corners, to ensure a large contact area. As disclosed in Patent Documents 1 and 2, a technique of providing sipes in shoulder blocks to improve tire contact with the ground is widely known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-190432 [Patent Document 2] Japanese Patent Application Publication No. 2023-89763 Summary of the Invention [Problem to be solved by the invention]

[0004] Although providing sipes in the shoulder blocks improves tire ground contact, it also tends to reduce the block rigidity of the shoulder blocks, which can lead to the problem of increased susceptibility to chipping and other damage, particularly in the axially outer regions of the shoulder blocks.

[0005] An object of the present invention is to improve the ground contact of a tire while suppressing damage such as chipping in the axially outer regions of shoulder blocks. [Means for solving the problem]

[0006] One aspect of the present invention is a pneumatic tire having a tread, the tread having shoulder blocks, the shoulder blocks having sipes that terminate inside the shoulder blocks, and the length along the tire axial direction from the axial outer end of the sipe to the axial outer end of the shoulder block is 4 mm or more and is 8% or more of the length along the tire axial direction of the shoulder block. [Effects of the Invention]

[0007] According to the pneumatic tire of the present invention, damage such as chipping in the axially outer regions of the shoulder blocks can be suppressed while improving the ground contact of the tire. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram schematically illustrating a cross section of a pneumatic tire as an example of an embodiment. [Figure 2] 1 is a plan view of a tread included in a pneumatic tire that is an example of an embodiment. [Figure 3] FIG. 3 is an enlarged view of the first shoulder block and its vicinity in FIG. 2. [Figure 4] 4 is a cross-sectional view taken along line AA in FIG. 3, showing the cross-sectional shape of a sipe. [Figure 5] 1 is a cross-sectional view of a pneumatic tire according to an embodiment, showing an enlarged view of the vicinity of a sipe. [Figure 6] FIG. 3 is an enlarged view of the vicinity of the second shoulder block in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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 that are formed by selectively combining the respective components of the multiple embodiments and modified examples described below.

[0010] FIG. 1 is a schematic diagram showing a cross section of a pneumatic tire 1 according to this embodiment. As shown in FIG. 1, the pneumatic tire 1 includes a tread 2, which is the portion that comes into contact with the road surface, a sidewall 3 that forms the tire's side surface, and a bead 4, which is the portion that is fixed to the wheel rim. The pneumatic tire 1 is suitable as a mud terrain tire (MT tire) or a rugged terrain tire (RT tire) that is suitable for off-road driving on muddy roads, rocky areas, etc. The pneumatic tire 1 is mounted on, for example, light trucks such as pickup trucks and sport utility vehicles (SUVs).

[0011] 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. In other words, the tread pattern and tire side surface shape of the pneumatic tire 1 are rotated 180° on either side of the tire equator CL. Here, the tire equator CL is an imaginary line that runs through the axial center of the tread 2 and extends in the tire circumferential direction. As will be described in more detail below, the tread 2 is formed with a plurality of blocks and grooves that separate the blocks.

[0012] The sidewalls 3 are arranged on both sides of the tread 2 in the axial direction of the tire, and are provided in an annular shape along the tire circumferential direction. The sidewalls 3 are the parts of the pneumatic tire 1 that protrude most axially outward, and are gently curved so as to be convex toward the axially outward side of the tire. The tread 2 and the sidewalls 3 are generally made of different types of rubber.

[0013] The bead 4 is disposed on the radially inner side of the sidewall 3 and is fixed to the wheel rim. The bead 4 has a bead core 4A and a bead filler 4B. The bead core 4A is an annular member made of a steel bead wire that extends around the entire circumference of the tire and is embedded in the bead 4. The bead filler 4B is an annular hard rubber member that has a tapered tip that extends outward in the radial direction of the tire and extends around the entire circumference of the tire.

[0014] The pneumatic tire 1 further includes a carcass 5 that is bridged between the pair of beads 4, and an inner liner 6 that is arranged inside the carcass 5 in the tire radial direction.

[0015] The carcass 5 is laid between a pair of beads 4 and is secured by being folded back around the bead core 4A. The carcass 5 is made up of at least one carcass ply. The carcass ply is made up of carcass cords made of organic fibers that are covered with coating rubber.

[0016] The inner liner 6 covers the inner surface of the tire between the pair of beads 4. The inner liner 6 is made of air-permeable resistant rubber and has the function of maintaining the air pressure of the pneumatic tire 1.

[0017] The pneumatic tire 1 further includes a belt 7 disposed radially outward of the carcass 5, and a cap ply 8 covering the radially outward side of the belt 7. The cap ply 8 has a function of reinforcing the belt 7. The number of cap plies 8 may be one, or two or more.

[0018] The belt 7 is disposed on the tire radial outside of the top of the carcass 5 and is provided overlapping the outer peripheral surface of the carcass 5. The belt 7 is formed of a belt ply made of rubber-coated cords arranged in a direction inclined with respect to the tire circumferential direction. There are no particular limitations on the material of the cords of the belt 7, and examples include organic fibers such as polyester, rayon, nylon, and aramid, and metals such as steel. In this embodiment, the belt 7 is made up of two belt plies 7A and 7B. The number of belt plies is not particularly limited and may be one, or three or more.

[0019] Next, the tread pattern of the pneumatic tire 1 will be described with reference to Fig. 2. Fig. 2 is a plan view of the tread 2 of the pneumatic tire 1. For ease of explanation, the right side of the paper in Fig. 2 will be the right side of the pneumatic tire 1, and the left side of the paper in Fig. 2 will be the left side of the pneumatic tire 1.

[0020] The tread 2 is formed with a center main groove 11 and shoulder main grooves 12A, 12B extending in the tire circumferential direction. The tread 2 is further formed with 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 2. Furthermore, the region axially outward of the shoulder main grooves 12A, 12B is defined as the "shoulder region." The tread 2 has a point-symmetric pattern that is point-symmetric with respect to an arbitrary point on the tire equator CL. The blocks of the tread 2 are convex portions that protrude radially outward and are sometimes called "lands" in the tire industry.

[0021] The center main groove 11 and the shoulder main grooves 12A, 12B are formed so as to connect two circumferentially adjacent lateral grooves 14. The center main groove 11 and the shoulder main grooves 12A, 12B are inclined with respect to the circumferential direction of the tire.

[0022] The lateral grooves 13A, 13B are formed to connect the center main groove 11 and the shoulder main grooves 12A, 12B, and are connected to the center main groove 11 approximately on the tire equator CL. In this case, good drainage and traction performance are obtained even near the tire equator CL. The lateral groove 14 is formed from one axial end of the tread 2 to the other axial end. The lateral grooves 15A, 15B are formed to connect to the shoulder main grooves 12A, 12B from the axially outer ends of the tread 2.

[0023] In the center region of the tread 2, a plurality of block groups 20, each group consisting of four first center blocks 21A, 21B and four second center blocks 22A, 22B, are arranged in the tire circumferential direction. Each of the block groups 20 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 20 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 length of the block group 20 in the tire circumferential direction, and has a pitch period of 5 to 60. However, the configuration of the blocks arranged in the center region is not limited to this.

[0024] The first center blocks 21A and 21B have the same shape and size, and the second center blocks 22A and 22B have substantially the same shape and size. The outline of the block group 20 is substantially rectangular in plan view, with the first center blocks 21A and 21B arranged on the first diagonal of the rectangle. The second center blocks 22A and 22B are arranged on the second diagonal of the rectangle.

[0025] The outline of the block group 20 is formed by the shoulder main grooves 12A, 12B and the 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. Therefore, each side of the quadrangle of the block group 20 is inclined relative to the tire circumferential direction and the axial direction.

[0026] A plurality of shoulder blocks 30A, 30B are arranged in the circumferential direction of the tire in the shoulder region of the tread 2. The shoulder block 30A is arranged axially opposite the block group 20 across the shoulder main groove 12A, and the shoulder block 30B is arranged axially opposite the block group 20 across the shoulder main groove 12B. The shoulder blocks 30A, 30B have corners on the axially outer ends of the tire. The radius of curvature of the corners is preferably 15 mm or less from the viewpoint of increasing the contact area and improving the tire's ground contact performance. Furthermore, if the radius of curvature of the corners is 15 mm or less, damage such as chipping is likely to occur in the axially outer regions of the shoulder blocks 30A, 30B, making the effects of the present invention described below more pronounced.

[0027] The shoulder block 30A includes a first shoulder block 31A and a second shoulder block 32A that are different in shape. Similarly to the shoulder block 30A, the shoulder block 30B includes a first shoulder block 31B and a second shoulder block 32B that are different in shape. The first shoulder blocks 31A and 31B have the same shape and size, and the second shoulder blocks 32A and 32B have substantially the same shape and size.

[0028] In this embodiment, the axial length of the first shoulder blocks 31A, 31B at the contact patch of the tread 2 is greater than the axial length of the second shoulder blocks 32A, 32B. The axial length of each block refers to the length along the tire axis from the axially outer end of each block at the contact patch of the tread 2 to the axially inner end of each block.

[0029] In this specification, the contact surface of the tread 2 refers to the contact surface when an unused tire is mounted on a standard rim, inflated to the standard internal pressure, and placed on a flat road surface under a predetermined load. The predetermined load is a load equivalent to 88% of the standard load. The "standard rim" refers to a rim specified by a tire standard, such as a "standard rim" in the case of JATMA, or a "measuring rim" in the cases of TRA and ETRTO. The "standard internal pressure" refers to the "maximum air pressure" in the case of JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in the case of TRA, or the "INFLATION PRESSURE" in the case of ETRTO. The "standard load" refers to the "maximum load capacity" in the case of JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in the case of TRA, or the "LOAD CAPACITY" in the case of ETRTO.

[0030] The axial length of the first shoulder blocks 31A, 31B is, for example, 49 mm or more and 89 mm or less. The axial length of the second shoulder blocks 32A, 32B is, for example, 40 mm or more and 77 mm or less. The axial length of the first shoulder blocks 31A, 31B and the axial length of the second shoulder blocks 32A, 32B may be substantially the same.

[0031] The lateral grooves 14 extend in a direction inclined relative to the tire axial direction from one axial end to the other axial end of the tread 2. In the center region, the lateral grooves 14 divide the circumferentially aligned block groups 20. In the left and right shoulder regions, the lateral grooves 14 also divide the first shoulder block 31A from the second shoulder block 32A, and the first shoulder block 31B from the second shoulder block 32B.

[0032] The lateral grooves 15A, 15B are arranged in the left and right shoulder regions between two lateral grooves 14. That is, in the left shoulder region, the lateral grooves 14 and the lateral grooves 15A are arranged alternately in the tire circumferential direction, and in the right shoulder region, the lateral grooves 14 and the lateral grooves 15B are arranged alternately in the tire circumferential direction.

[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 easily become lodged in the lateral grooves 14, 15A, and 15B. Driving with stones lodged 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 bottom of the lateral grooves 14, 15A, and 15B. Each stone ejector is a long, slender protrusion extending 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 blocks, so the top surface of the stone ejector does not touch the flat road surface.

[0034] A stone ejector 16A is provided in the left shoulder region of the lateral groove 14, and a stone ejector 16B is provided in the right shoulder region. Furthermore, stone ejectors 17A and 18A are provided in the lateral groove 15A, and stone ejectors 17B and 18B are provided in the lateral groove 15B. The function of each stone ejector makes it easy to eject stones stuck in the groove, effectively suppressing the deterioration of traction performance caused by stone jamming.

[0035] The tread 2 further has a stone ejector 19A having a generally triangular shape in plan view at the intersection of the shoulder main groove 12A and the lateral groove 14, and a stone ejector 19B having a generally triangular shape in plan view at the intersection of the shoulder main groove 12B and the lateral groove 14. The stone ejectors 19A and 19B are formed, for example, higher than the stone ejectors 16A and 16B.

[0036] Next, the first shoulder block 31A arranged in the left shoulder region will be described in detail with reference to Figure 3. Figure 3 is an enlarged view of the first shoulder block 31A in Figure 2. As described above, the tread 2 has a point-symmetric pattern that is symmetrical about an arbitrary point on the tire equator CL. Therefore, the first shoulder block 31A arranged in the left shoulder region and the first shoulder block 31B arranged in the right shoulder region have the same shape and size.

[0037] 3, the direction facing axially outward with respect to the first shoulder block 31A may be referred to as the "X1 direction," and the direction facing axially inward with respect to the first shoulder block 31A may be referred to as the "X2 direction." Also, the first direction in the tire circumferential direction may be referred to as the "Y1 direction," and the second direction may be referred to as the "Y2 direction."

[0038] 3, the first shoulder block 31A is defined by the shoulder main groove 12A, the lateral groove 14, and the lateral groove 15A and is formed along the tire axial direction. The first shoulder block 31A has a tapered shape in the region on the X2 direction, with the tire circumferential length decreasing toward the X2 direction.

[0039] The block ends of the first shoulder block 31A on the Y1 and Y2 sides are formed in a generally linear shape in a plan view along the tire axial direction on the X1 side. In other words, the tire circumferential length of the first shoulder block 31A is generally constant on the X1 side. When the first shoulder block 31A has the above-described shape, the block rigidity of the X1 side of the first shoulder block 31A can be increased. As a result, damage such as chipping in the X1 side region of the first shoulder block 31A, as described below, can be further suppressed. In addition, the block ends on the Y1 and Y2 sides of the first shoulder block 31A each have a bending point at the axial middle of the tire.

[0040] The block end of the first shoulder block 31A on the Y1 side is generally linear in plan view, extending in a direction inclined toward the Y2 side with respect to the tire axial direction, toward the X2 side of the bend point. The block end of the first shoulder block 31A on the Y2 side is generally linear in plan view, extending in a direction inclined toward the Y1 side with respect to the tire axial direction, toward the X2 side of the bend point. Therefore, the tire circumferential length of the first shoulder block 31A on the X2 side decreases toward the X2 side. The inclination angle of the block ends of the first shoulder block 31A on the Y1 side and the Y2 side with respect to the tire axial direction may be, for example, 3° to 45°, or 5° to 30°.

[0041] The block end of the first shoulder block 31A on the X2 side is generally linear in plan view, inclined toward the X1 direction with respect to the tire circumferential direction as it extends toward the Y1 direction. The inclination angle of the block end of the first shoulder block 31A on the X2 side with respect to the tire circumferential direction is, for example, 3° to 45°, or may be 5° to 30°.

[0042] The block ends of the first shoulder blocks 31A on the X2, Y1, and Y2 directions are provided with recesses 33 that are recessed radially inward from the profile surface along the contact patch of the tread 2. The recesses 33 are areas that do not form part of the contact patch of the tread 2. By providing the recesses 33 at the block ends of the first shoulder blocks 31A, the contact pressure of the first shoulder blocks 31A can be made uniform, and uneven wear of the first shoulder blocks 31A can be suppressed. The depth of the recesses 33 is, for example, 0.5 mm or more and 3 mm or less. Note that the block ends of the first shoulder blocks 31A do not necessarily have to be provided with the recesses 33.

[0043] The first shoulder blocks 31A are provided at their circumferential center with sipes 40 that terminate inside the first shoulder blocks 31A. Providing the sipes 40 in the first shoulder blocks 31A improves the tire's ground contact, thereby improving, for example, the running stability and cornering characteristics of the pneumatic tire 1. In this specification, a sipe refers to a thin groove having a width of 2 mm or less.

[0044] On the other hand, providing the sipes 40 in the first shoulder blocks 31A improves the tire's ground contact, but tends to reduce the block rigidity of the first shoulder blocks 31A. As a result of studies by the inventors, it was found that as the block rigidity of the first shoulder blocks 31A increases, chipping and other damage tends to occur more easily, particularly in the region of the first shoulder blocks 31A on the X1 direction side.

[0045] After further investigation, the inventors found that chipping and other damage can be suppressed in the axially outer region of the first shoulder block 31A by separating the X1 end 40X of the sipe 40 by a predetermined distance from the X1 end of the first shoulder block 31A. Specifically, they found that chipping and other damage can be suppressed in the axially outer region of the first shoulder block 31A by setting the axial length (D1) from the X1 end 40X of the sipe 40 to the X1 end of the first shoulder block 31A at the contact patch of the tread 2 to 4 mm or more and 8% or more of the axial length (D31A) of the first shoulder block 31A. Note that if D1 is 4 mm or more but less than 8% of D31A, or if D1 is 8% or more of D31A but less than 4 mm, chipping and other damage may occur in the X1 region of the first shoulder block 31A. That is, in order to suppress damage such as chipping in the region of the first shoulder block 31A on the X1 direction side, D1 needs to be 4 mm or more and 8% or more of D31A.

[0046] The axial length (D1) from the X1 end 40X of the sipe 40 to the X1 end of the first shoulder block 31A may be at least 4 mm, preferably at least 4.2 mm, and more preferably at least 4.5 mm. This further reduces chipping and other damage to the X1-side region of the first shoulder block 31A. The upper limit of the axial length (D1) from the X1 end of the sipe 40 to the X1 end of the first shoulder block 31A can be set appropriately depending on the tire size, etc., but is, for example, 10 mm.

[0047] The axial length (D1) from the X1 end 40X of the sipe 40 to the X1 end of the first shoulder block 31A may be at least 8%, preferably at least 9%, and more preferably at least 10% of the axial length (D31A) of the first shoulder block 31A, which further reduces chipping and other damage to the X1-side region of the first shoulder block 31A.

[0048] Furthermore, the axial length (D1) from the X1-direction end 40X of the sipe 40 to the X1-direction end of the first shoulder block 31A is preferably 20% or less, and more preferably 15% or less, of the axial length (D31A) of the first shoulder block 31A. If D1 is more than 20% of D31A, the axial length of the sipe 40 becomes too short, reducing the edge effect of providing the sipe 40 to the first shoulder block 31A and potentially reducing the braking performance of the tire.

[0049] In this embodiment, in a plan view of the tread 2, the sipes 40 have a bending point 41 in a longitudinally intermediate portion. The sipes 40 are formed in a generally linear shape in a plan view along the tire axial direction on the X1 side of the bending point 41. The sipes 40 are also formed in a generally linear shape in a plan view along a direction inclined toward the Y1 side with respect to the tire axial direction on the X2 side of the bending point 41. The inclination angle of the sipes 40 with respect to the tire axial direction on the X2 side of the bending point 41 is, for example, 5° or more and 60° or less, or may be 10° or more and 45° or less. When the sipes 40 have a bent shape in a plan view of the tread 2, the ground contact of the tire can be further improved.

[0050] In addition, in a plan view of the tread 2, the region of the sipes 40 on the X1 side of the bending point 41 is preferably arranged within a length range equivalent to 15% of the circumferential length (L31A) of the first shoulder block 31A, centered on the circumferential center of the first shoulder block 31A. In this case, the sipes 40 are arranged near the circumferential center of the first shoulder block 31A, further improving the ground contact of the tire.

[0051] Next, the configuration of the sipes 40 provided in the first shoulder block 31A will be described in detail with reference to Fig. 4 and Fig. 5. Fig. 4 is a cross-sectional view taken along line AA in Fig. 3, illustrating the cross-sectional shape of the sipes 40. Fig. 5 is a cross-sectional view of the pneumatic tire 1, illustrating an enlarged view of the area where the sipes 40 are provided.

[0052] As shown in FIG. 4 , the sipe 40 has an inclined portion 42 whose wall surface slopes gradually from the X1-direction end 40X of the sipe 40 toward the X2-direction side. That is, the wall surface of the inclined portion 42 is not perpendicular to the profile plane α along the contact patch of the tread 2, but is inclined at a predetermined angle. Providing the inclined portion 42 in the sipe 40 increases the block rigidity of the first shoulder block 31A near the X1-direction end. As a result, damage such as chipping in the X1-direction region of the first shoulder block 31A can be further suppressed.

[0053] The inclination angle of the wall surface of the inclined portion 42 is preferably 50° to 70°, and more preferably 55° to 65°, with respect to the profile plane α along the contact surface of the tread 2. In this case, damage such as chipping in the region of the shoulder block on the X1 direction side can be further suppressed while improving the tire's contact with the ground.

[0054] Furthermore, it is preferable that the sipe 40 has at least one raised portion 43, the bottom surface of which is locally raised toward the outside in the tire radial direction. By providing the raised portion 43 on the sipe 40, the block rigidity of the first shoulder block 31A can be increased while ensuring the ground contact of the tire. As a result, damage such as chipping of the first shoulder block 31A can be further suppressed. The height of the raised portion 43 is, for example, 5.0 mm or more and 9.0 mm or less. In this embodiment, the raised portion 43 includes a first raised portion 44 and a second raised portion 45 provided on the X2 direction side of the first raised portion 44.

[0055] In this embodiment, the depth of the sipe 40 in the region where the first raised portion 44 is formed is substantially the same as the depth of the sipe 40 in the region where the second raised portion 45 is formed. In this case, it is easier to ensure a balance in the block rigidity of the first shoulder block 31A. Note that the depth of the sipe 40 in the region where the first raised portion 44 is formed refers to the length along the tire radial direction from the profile surface α along the contact surface of the tread 2 to the apex of the first raised portion 44. Similarly, the depth of the sipe 40 in the region where the second raised portion 45 is formed refers to the length along the tire radial direction from the profile surface α along the contact surface of the tread 2 to the apex of the second raised portion 45.

[0056] Here, the inclination angle of the wall surface of the inclined portion 42 relative to the profile plane α along the ground contact surface of the tread 2 is preferably smaller than the inclination angle of the wall surface of the raised portion 43. In this case, the block rigidity near the X1-direction end of the first shoulder block 31A can be increased while ensuring the ground contact of the tire. As a result, damage such as chipping in the region of the first shoulder block 31A on the X1 direction side can be further suppressed. The inclination angle of the wall surface of the raised portion 43 relative to the profile plane α along the ground contact surface of the tread 2 is, for example, 60° or more and 90° or less. Note that the inclination angle of the wall surface of the raised portion 43 refers to the inclination angle of the wall surface in the region excluding the curved portions at the top and bottom of the raised portion 43.

[0057] Furthermore, it is preferable that the depth (H1) of the deepest part of the region of the sipe 40 on the X1 side of the first protrusion 44 is smaller than the depth (H2) of the deepest part of the region of the sipe 40 on the X2 side of the first protrusion 44. In this case, the block rigidity of the X1 side of the first shoulder block 31A can be increased. As a result, damage such as chipping in the region of the X1 side of the first shoulder block 31A can be further suppressed.

[0058] As shown in Fig. 5, the pneumatic tire 1 includes a belt 7 disposed radially inward of the tread 2. In this embodiment, the belt 7 includes two belt plies 7A and 7B. The belt ply 7A is disposed radially outward of the belt ply 7B. An axially outer end 7AX of the belt ply 7A is disposed axially inward of an axially outer end 7BX of the belt ply 7B.

[0059] Here, it is preferable that the axially inner end 42Y of the inclined portion 42 is positioned axially more inward than the axially outer ends 7AX, 7BX of the belt plies 7A, 7B. As a result of studies by the present inventors, it has become clear that in the region axially outward of the axially inner end 42Y of the inclined portion 42, the first shoulder block 31A is likely to distort, which may cause cracks to occur at the bottom of the sipe 40. Therefore, by positioning the belt plies 7A, 7B axially outward of the axially inner end 42Y of the inclined portion 42, the binding force of the belt 7 in the region axially outward of the axially inner end 42Y of the inclined portion 42 is increased. This makes it possible to suppress the occurrence of cracks at the bottom of the sipe 40.

[0060] Next, the second shoulder block 32A will be described in detail with reference to Figure 6. Figure 6 is an enlarged view of the second shoulder block 32A in Figure 2. As described above, the tread 2 has a point-symmetric pattern that is symmetrical about an arbitrary point on the tire equator CL. Therefore, the second shoulder block 32A located in the left shoulder region and the second shoulder block 32B located in the right shoulder region have the same shape and size.

[0061] 3, the direction facing axially outward relative to the second shoulder block 32A may be referred to as the "X1 direction," and the direction facing axially inward relative to the second shoulder block 32A may be referred to as the "X2 direction." Also, the first direction in the tire circumferential direction may be referred to as the "Y1 direction," and the second direction may be referred to as the "Y2 direction."

[0062] As shown in Figure 6, the second shoulder block 32A is divided into the shoulder main groove 12A, the lateral groove 14, and the lateral groove 15A. The second shoulder block 32A has a shape in which the X1 region extends along the tire axial direction and the X2 region extends in a direction inclined toward the Y2 direction relative to the tire axial direction. The second shoulder block 32A has a sharp corner near the X2 end, which is located at the intersection of the shoulder main groove 12A and the lateral groove 15A.

[0063] Like the first shoulder blocks 31A, the block ends of the second shoulder blocks 32A on the Y1 and Y2 sides are generally linear in plan view along the tire axial direction on the X1 side. In other words, the tire circumferential length of the second shoulder blocks 32A is generally constant on the X1 side. When the second shoulder blocks 32A have the above-described shape, the block rigidity of the X1 side of the second shoulder blocks 32A can be increased. As a result, chipping and other damage to the X1 side region of the second shoulder blocks 32A can be further suppressed. Furthermore, the block ends on the Y1 and Y2 sides of the second shoulder blocks 32A each have a bending point at the axially middle portion of the tire.

[0064] The block ends of the second shoulder blocks 32A on the Y1 side are generally linear in plan view, extending in a direction inclined toward the Y2 side with respect to the tire axial direction, on the X2 side of the bending point. The block ends of the second shoulder blocks 32A on the Y2 side are generally linear in plan view, extending in a direction inclined toward the Y2 side with respect to the tire axial direction, on the X2 side of the bending point. The inclination angles of the block ends of the second shoulder blocks 32A on the Y1 side and the Y2 side with respect to the tire axial direction may be, for example, 3° to 45°, or 5° to 30°.

[0065] The block end of each second shoulder block 32A on the X2 side is generally linear in plan view, inclining toward the X1 direction with respect to the tire circumferential direction as it extends toward the Y1 direction. The inclination angle of the block end of each second shoulder block 32A on the X2 side with respect to the tire circumferential direction is, for example, 5° to 60°, or may be 10° to 45°. In this embodiment, the inclination angle of the block end of each second shoulder block 32A on the X2 side with respect to the tire circumferential direction is greater than the inclination angle of the block end of each first shoulder block 31A on the X2 side with respect to the tire circumferential direction.

[0066] Similar to the first shoulder blocks 31A, the block ends of the second shoulder blocks 32A on the X2, Y1, and Y2 sides are provided with recesses 34 that are recessed radially inward from the profile surface along the contact patch of the tread 2. The recesses 34 are regions that do not form part of the contact patch of the tread 2. By providing the recesses 34 at the block ends of the second shoulder blocks 32A, the contact pressure of the second shoulder blocks 32A can be made uniform, thereby suppressing uneven wear of the second shoulder blocks 32A. In this embodiment, the depth of the recesses 34 is approximately the same as the depth of the recesses 33 provided in the first shoulder blocks 31A. Note that the block ends of the second shoulder blocks 32A do not necessarily have to be provided with recesses 34.

[0067] The second shoulder block 32A has a slope 35 at a corner near the X2 end, where the block height decreases with increasing distance from the second shoulder block 32A. Similar to the recess 34, the slope 35 is an area that does not form part of the contact patch of the tread 2. By providing the slope 35 at the corner near the X2 end of the second shoulder block 32A, uneven wear of the second shoulder block 32A near the X2 end of the second shoulder block 32A can be suppressed. Note that the slope 35 does not necessarily have to be provided on the second shoulder block 32A.

[0068] Similar to the first shoulder block 31A, the second shoulder block 32A is provided at its circumferential center with sipes 50 that terminate inside the second shoulder block 32A. Providing the sipes 50 in the second shoulder block 32A improves the ground contact of the tire.

[0069] In the contact patch of the tread 2, the axial length (D2) from the X1 end of the sipe 50 to the X1 end of the second shoulder block 32A is 4 mm or more and 8% or more of the axial length (D32A) of the second shoulder block 32A, similar to the sipe 40 described above. This ensures tire ground contact while further reducing damage such as chipping in the region on the X1 side of the second shoulder block 32A. Note that if D2 is 4 mm or more but less than 8% of D32A, or if D2 is 8% or more of D32A but less than 4 mm, chipping or other damage may occur in the region on the X1 side of the second shoulder block 32A. In other words, to reduce damage such as chipping in the region on the X1 side of the second shoulder block 32A, D2 needs to be 4 mm or more and 8% or more of D32A.

[0070] Furthermore, the axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A may be substantially the same as or different from the axial length (D1) of the first shoulder block 31A from the X1 end of the sipe 40 to the X1 end of the first shoulder block 31A. In this embodiment, the axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A is substantially the same as the axial length (D1) from the X1 end of the sipe 40 to the X1 end of the first shoulder block 31A.

[0071] The axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A may be at least 4 mm, but similar to the sipe 40, it is preferably at least 4.2 mm, and more preferably at least 4.5 mm. This further reduces chipping and other damage to the X1-side region of the second shoulder block 32A. The upper limit of the axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A can be set appropriately depending on the tire size, etc., but is, for example, 10 mm.

[0072] Similarly to the sipe 40, the axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A may be at least 8% of the axial length (D32A) of the second shoulder block 32A, but is preferably at least 9%, and more preferably at least 10%. In this case, chipping and other damage to the X1-direction region of the second shoulder block 32A can be further suppressed.

[0073] Similarly to the sipe 40, the axial length (D2) from the X1 end 50X of the sipe 50 to the X1 end of the second shoulder block 32A is preferably 20% or less, and more preferably 15% or less, of the axial length (D32A) of the second shoulder block 32A. If D2 is more than 20% of D32A, the axial length of the sipe 50 becomes too short, reducing the edge effect of providing the sipe 50 to the second shoulder block 32A and potentially reducing the braking performance of the tire.

[0074] In this embodiment, in a plan view of the tread 2, the sipe 50 has a bending point 51 in a longitudinally intermediate portion. The sipe 50 is formed in a substantially linear shape in a plan view along the tire axial direction on the X1 side of the bending point 51. The sipe 50 is formed in a substantially linear shape in a plan view along a direction inclined toward the Y2 side with respect to the tire axial direction on the X2 side of the bending point 51. The inclination angle of the sipe 50 with respect to the tire axial direction on the X2 side of the bending point 51 is, for example, 5° or more and 60° or less, and may be 10° or more and 45° or less. When the sipe 50 has a bent shape in a plan view of the tread 2, the ground contact of the tire can be further improved.

[0075] In addition, in a plan view of the tread 2, the region of the sipes 50 on the X1 direction side of the bend point 51 is preferably arranged within a length range equivalent to 15% of the circumferential length (L32A) of the second shoulder block 32A, centered on the circumferential center of the second shoulder block 32A, similar to the sipes 40. In this case, the sipes 50 are arranged near the circumferential center of the second shoulder block 32A, thereby further improving the ground contact of the tire.

[0076] The cross-sectional shape of the sipe 50 can be the same as the inclined portion 42 of the sipe 40 provided on the first shoulder block 31A. That is, the sipe 50 can be provided with the inclined portion 42 (see FIG. 4) and the raised portion 43 (see FIG. 4) like the sipe 40. In this case, the block rigidity of the X1 direction side of the second shoulder block 32A can be increased. As a result, damage such as chipping in the region of the X1 direction side of the second shoulder block 32A can be further suppressed. [Example]

[0077] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0078] Example 1 A test tire T1 (tire size: LT285 / 70R17 126 / 123Q) was produced having the tread pattern shown in Fig. 2. At this time, the axial length (D1) from the X1-direction end 40X of the sipe 40 to the X1-direction ends of the first shoulder blocks 31A and 31B at the contact surface of the tread 2 was set to 4.0 mm. In addition, the axial length (D2) from the X1-direction end 50X of the sipe 50 to the X1-direction ends of the second shoulder blocks 32A and 32B at the contact surface of the tread 2 was also set to 4.0 mm.

[0079] The sizes of the shoulder blocks 30A, 30B and the sipes 40, 50 of the above tread pattern are as follows: Axial length of first shoulder blocks 31A, 31B: 59.87 mm Axial length of second shoulder blocks 32A, 32B: 49.54 mm Sipe 40 groove width: 0.8 mm Sipe 40 total length: 46.55mm Sipe 50 groove width: 0.8 mm Sipe 50 total length: 38.62mm

[0080] <Examples 2 to 4, Comparative Example 1> Test tires T2 to T5 were produced in the same manner as in Example 1, except that the axial length (D1) from the X1-direction end 40X of the sipe 40 to the X1-direction end 40X of the first shoulder blocks 31A, 31B and the axial length (D2) from the X1-direction end 50X of the sipe 50 to the X1-direction end of the second shoulder blocks 32A, 32B were changed to the values ​​shown in Table 1.

[0081] A general durability test was conducted on each of the test tires T1 to T5. After the test, the appearance of the first shoulder blocks 31A, 31B and second shoulder blocks 32A, 32B of each of the test tires T1 to T5 was visually inspected to evaluate the presence or absence of damage such as chipping.

[0082] In the general durability test, the tire was pressed against a drum with a diameter of 1.7 m and rotated while driving. The time, speed, air pressure, and load at each step were as follows: First step: Time: 4 hours, Speed: 120km / h, Air pressure: 410kPa, Load: 1445kg Second step: Time: 6 hours, Speed: 120km / h, Air pressure: 410kPa, Load: 1530kg Step 3: Time: 24 hours, Speed: 120km / h, Air pressure: 410kPa, Load: 1700kg Step 4: Time: 1.5 hours, Speed: 120km / h, Air pressure: 320kPa, Load: 1700kg Step 5: Time: 6 hours, Speed: 120 km / h, Air pressure: 550 kPa, Load: 1955 kg

[0083] Table 1 shows the presence or absence of chipping or other damage to the first shoulder blocks 31A, 31B and the second shoulder blocks 32A, 32B after testing for each of the test tires T1 to T5. Table 1 also shows the ratio (D1 / D31A) of the axial length (D1) from the X1-direction end 40X of the sipe 40 to the X1-direction end of the first shoulder block 31A to the axial length (D31A) of the first shoulder block 31A. Table 1 also shows the ratio (D2 / D32A) of the axial length (D2) from the X1-direction end 50X of the sipe 50 to the X1-direction end of the second shoulder block 32A to the axial length (D32A) of the second shoulder block 32A.

[0084] [Table 1]

[0085] As shown in Table 1, test tires T1 to T4 did not suffer from damage such as chipping, whereas test tire T5 suffered from damage such as chipping. Therefore, it can be said that damage such as chipping in the shoulder blocks 30A, 30B can be suppressed by setting D1 and D2 to 4.0 mm or more and (D1 / D31A) and (D2 / D32A) to 8% or more. [Explanation of symbols]

[0086] 1 pneumatic tire, 2 tread, 3 sidewall, 3A profile surface, 4 bead, 4A bead core, 4B bead filler, 5 carcass, 6 inner liner, 7 belt, 7A, 7B belt ply, 8 cap ply, 11 center main groove, 12A, 12B shoulder main groove, 13A, 13B, 14, 15A, 15B lateral groove, 16A, 16B, 17A, 17B, 18A, 18B, 19A, 19B stone ejector, 20 block group, 21A, 21B first center block, 22A, 22B second center block, 30A, 30B shoulder block, 31A, 31B first shoulder block, 32A, 32B second shoulder block, 33, 34 recess, 35 slope, 40 sipe, 40A X1 direction end, 41 Inflection point, 42 inclined portion, 42Y inner edge, 43 raised portion, 44 first raised portion, 45 second raised portion, 50 sipe, 51 inflection point, CL tire equator, α profile surface.

Claims

1. A pneumatic tire having a tread, The tread has shoulder blocks, the shoulder block has a sipe terminating inside the shoulder block; a length along the tire axial direction from the axially outer end of the sipe to the axially outer end of the shoulder block at the contact surface of the tread is 4 mm or more and is 8% or more of the axially outer end of the shoulder block.

2. 2. The pneumatic tire according to claim 1, wherein the axial length from the axially outer end of the sipe to the axially outer end of the shoulder block at the contact surface of the tread is 20% or less of the axial length of the shoulder block.

3. The pneumatic tire according to claim 1 , wherein the sipe has an inclined portion whose wall surface is inclined so as to become gradually deeper from an outer end of the sipe in the axial direction of the tire toward an inner end in the axial direction of the tire.

4. The pneumatic tire according to claim 3 , wherein an inclination angle of the wall surface of the inclined portion with respect to a profile surface along the contact surface of the tread is equal to or greater than 50° and is equal to or less than 70°.

5. The pneumatic tire according to claim 1 , wherein the sipe has at least one raised portion whose bottom surface locally rises outward in the tire radial direction.

6. The sipe has an inclined portion whose wall surface is inclined so as to gradually become deeper from an outer end of the sipe in the tire axial direction toward an inner end in the tire axial direction, The pneumatic tire according to claim 5 , wherein an inclination angle of the wall surface of the inclined portion relative to a profile plane along the contact surface of the tread is smaller than an inclination angle of the wall surface of the raised portion.

7. The pneumatic tire according to claim 5 , wherein the depth of the sipe in a region axially outward from the raised portion is smaller than the depth of the sipe in a region axially inward from the raised portion.

8. In a plan view of the tread, the sipe has a bending point, 2. The pneumatic tire according to claim 1, wherein the sipes are arranged in a region axially outward of the bending point on the contact surface of the tread within a length range that is 15% of the circumferential length of the shoulder block, with the region being centered on the circumferential center of the shoulder block.

9. Further, a belt is disposed on the inner side of the tread in the tire radial direction, the belt includes at least one belt ply; The pneumatic tire according to claim 3 , wherein an inner end of the inclined portion in the tire axial direction is disposed axially more inward than an outer end of each of the belt plies in the tire axial direction.

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