Pneumatic tire

Abstract

To provide a pneumatic tire which suppresses block chipping of a shoulder land by blister, and improves steering stability.SOLUTION: In a tire axial direction cross section, a first groove 110 of a lug groove 92 has a region from a position corresponding to a tire axial direction outer end of a shoulder main groove 82 to a position corresponding to a tread ground-contact end 88E at 88% load of the maximum load according to an ESTRO tire standard, the depth of the first groove 110 is gradually reduced toward the tire axial direction outer end, and a crest part 130 of a lug groove 92 has an inclined surface 131 which is gradually reduced toward the tire axial direction outside in the depth of the lug groove 92, by climbing up so as to approach a tread surface 36 toward the tire axial direction outside, up to at least the vicinity of the position corresponding to a tread ground-contact end 120E at 120% load of the maximum load according to the ESTRO tire standard from a start point 130a as the vicinity of the position corresponding to the tread ground-contact end 88E.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire suitable for use on passenger vehicles with a relatively heavy load. [Background technology]

[0002] Conventionally, a pneumatic tire for a vehicle is known that has a reinforcing belt in the tread, and a plurality of lug grooves extending in a direction intersecting the tire circumferential direction are arranged in the tire circumferential direction on shoulder lands at both ends of the tread in the tire axial direction. Patent Document 1 shows a pneumatic tire that is lightweight while maintaining wet performance by providing bottom-up portions in such lug grooves at positions corresponding to the axially outer ends of the belts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 026546 Summary of the Invention [Problem to be solved by the invention]

[0004] In pneumatic tires that are repeatedly subjected to flexural deformation, the distortion near the belt end is relatively large. For this reason, heat is generated near the belt end due to the distortion, and air bubbles called blisters are generated. This may cause a phenomenon called block chipping (also called chunk out) in which rubber peels off on the shoulder land having lug grooves. This phenomenon is likely to occur in heavy-duty vehicles with relatively large vehicle weights, such as EVs (Electric Vehicles) and hybrid vehicles. Block chipping is an issue that must be avoided because it leads to a decrease in driving stability, but the above-mentioned Patent Document 1 does not provide sufficient measures against block chipping on the shoulder land, and there is room for improvement.

[0005] An object of the present invention is to provide a pneumatic tire which suppresses block chipping on the shoulder land due to blisters and improves driving stability even in the case of a heavy-load passenger vehicle. [Means for solving the problem]

[0006] The pneumatic tire of the present invention is a pneumatic tire including a bead, a pair of sidewalls extending radially outward from the bead, a tread disposed between the pair of sidewalls and including a tread surface that comes into contact with a road surface, and a shoulder at a portion transitioning from the tread to the sidewall, the tread surface including a plurality of lands extending in a tire circumferential direction and a plurality of main grooves extending in the tire circumferential direction and dividing the plurality of lands in the tire axial direction, the lands including shoulder lands disposed at ends of the tread surface in the tire axial direction, the main groove including a shoulder main groove adjacent to the shoulder land on the axially inner side, the shoulder land including a plurality of lug grooves extending in a direction intersecting the tire circumferential direction and aligned in the tire circumferential direction, the lug groove including a first groove and a sidewall arranged axially outward from the first groove and adjacent to the sidewall. The shoulder main groove has a second groove that is continuous with the inner periphery of the shoulder main groove, and a ridge portion that separates the first groove from the second groove. In an axial cross section of the tire, the first groove has a region from a position corresponding to the axially outer end of the shoulder main groove to a position corresponding to the tread edge at a load of 88% of the maximum load according to the tire standard ETRTO, and the depth of the first groove gradually decreases toward the outside in the axial direction of the tire. The ridge portion has a slope that starts near a position corresponding to the tread edge at a load of 88% of the maximum load according to the tire standard ETRTO, and rises toward the tread surface toward the outside in the axial direction of the tire from the starting point to at least a position corresponding to the tread edge at a load of 120% of the maximum load according to the tire standard ETRTO, thereby gradually decreasing the depth of the lug groove toward the outside in the axial direction of the tire. Effect of the Invention

[0007] According to the present invention, a pneumatic tire can be provided in which block chipping on the shoulder land due to blisters is suppressed, even in the case of a heavy-load passenger vehicle, thereby improving driving stability. [Brief description of the drawings]

[0008] [Figure 1] 1 is a half cross-sectional view in an axial direction of a pneumatic tire according to an embodiment. FIG. [Diagram 2] FIG. 1 is a diagram showing a tread pattern of a pneumatic tire according to an embodiment, and is a partial plan view of the tire. [Diagram 3] FIG. 2 is a cutaway view of the tread side (the outer side in the tire radial direction) of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiment will be described with reference to the drawings. FIG. 1 is a diagram showing the internal structure of a tire 1, which is a pneumatic tire for vehicles according to the embodiment, and shows a half cross section in the tire axial direction. FIG. 2 is a partially enlarged plan view of the tire 1 seen from above, showing a tread surface 36 of the tire 1 on which a tread pattern 39 is formed. Strictly speaking, the half cross section of FIG. 1 shows a section along the extension direction of the lateral grooves 90, which will be described later, as seen from the tire circumferential direction. The tire 1 according to the embodiment is, for example, a pneumatic tire for passenger cars. The configuration of the tire 1 according to the embodiment can also be applied to tires for various vehicles, such as light trucks, trucks, and buses.

[0010] First, the internal structure of a tire 1 will be described with reference to Fig. 1. The cross-sectional view of Fig. 1 is an axial cross-sectional view of the tire 1 in an unloaded state where the tire 1 is mounted on a standard rim (not shown) and inflated to a standard internal pressure.

[0011] A regular rim is a rim that is determined by the tire standard, and in the case of ETRTO, it is called "Measuring Rim." Regular internal pressure is the air pressure that is determined by the tire standard, and in the case of ETRTO, it is called "INFLATION PRESSURE." Regular internal pressure is usually 180kPa for passenger car tires, but 220kPa for tires that are labeled "Extra Load" or "Reinforced." For ETRTO, regular load is called "LOAD CAPACITY."

[0012] In Fig. 1, the symbol S1 indicates a tire equatorial plane perpendicular to the rotation axis of the tire 1. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis and is located at the center in the tire axial direction. The basic internal structure of the tire 1 is symmetrical with respect to the tire equatorial plane S1. Fig. 1 shows a half cross section of the right half of the tire 1, and the left half (not shown) has the same structure. Note that Fig. 2 shows a tire equator S2 that corresponds to the tire equatorial plane S1 and extends in the tire circumferential direction on the tread surface 36.

[0013] In Fig. 1, the tire axial direction is indicated by arrow X, and the tire radial direction is indicated by arrow Y. The tire axial direction is a direction parallel to the tire rotation axis, and corresponds to the left-right direction on the page in Fig. 1. The tire axially inner side is a direction approaching the tire equatorial plane S1 in the tire axial direction, and corresponds to the left-hand side on the page in Fig. 1. The tire axially outer side is a direction away from the tire equatorial plane S1 in the tire axial direction, and corresponds to the right-hand side on the page in Fig. 1.

[0014] The tire radial direction is a direction perpendicular to the tire rotation axis, and is the up-down direction on the paper in Fig. 1. In Fig. 1, this is illustrated as tire radial direction Y. The outer side in the tire radial direction is a direction away from the tire rotation axis, and is the upper side on the paper in Fig. 1. The inner side in the tire radial direction is a direction approaching the tire rotation axis, and is the lower side on the paper in Fig. 1.

[0015] As shown in FIG. 1, the tire 1 includes a pair of beads 10, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, a shoulder 40 which is a transition portion from the sidewalls 20 to the tread 30, a carcass ply 50 disposed spanning between the pair of beads 10, and an inner liner 60 disposed on the tire cavity side of the carcass ply 50.

[0016] The pair of beads 10 are disposed on both axial sides of the tire and on the inner ends in the radial direction of the tire. Each bead 10 has a bead core 11, a bead filler 12 extending from the bead core 11 to the outer side in the radial direction of the tire, and a rim strip rubber 13.

[0017] The bead core 11 is an annular member in which a rubber-coated metal bead wire is wound multiple times in the tire circumferential direction. The bead core 11 is a member that serves to fix the tire 1 filled with air to the rim. The bead filler 12 has a tapered shape that decreases in thickness as it extends from the tire radial inner side to the tire radial outer side. The bead filler 12 is joined to the tire radial outer surface of the bead core 11. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of, for example, rubber that is harder than the surrounding rubber members.

[0018] The rim strip rubber 13 is provided in a manner that surrounds the outside of the carcass ply 50 which surrounds the bead core 11 and the bead filler 12. The rim strip rubber 13 has a rim line 13c that protrudes axially outward of the tire. The rim strip rubber 13 including the rim line 13c constitutes a rim protector 14 that is positioned to protrude axially outward beyond the rim.

[0019] The sidewall 20 includes a sidewall rubber 21 disposed axially outward of the carcass ply 50. The sidewall rubber 21 constitutes the outer surface of the tire 1. The sidewall rubber 21 is the portion that bends the most when the tire 1 performs its cushioning function, and flexible rubber having fatigue resistance is usually used for the sidewall rubber 21.

[0020] The sidewall rubber 21 is disposed in a region extending in the tire radial direction from the shoulder 40 to the tire radially outer portion of the bead 10. The tire radially outer end 21a of the sidewall rubber 21 covers the tire axially outer end 35a of a tread rubber 35 of the tread 30 described later. The tire radially inner side of the sidewall rubber 21 extends to the rim line 13c.

[0021] The tread 30 includes an endless belt 31 and a tread rubber 35. The belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction. The tread rubber 35 is disposed on the outer side of the belt 31 in the tire radial direction.

[0022] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment is an example of a reinforcing layer according to the present disclosure that the tread 30 includes. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 arranged on the tire radial outer side of the inner liner 60 and an outer belt 33 arranged on the tire radial outer side of the inner belt 32. Both the inner belt 32 and the outer belt 33 have a structure in which a plurality of belt cords such as steel cords are covered with rubber. The inner belt 32 is wider than the outer belt 33. By providing the belt 31, the rigidity of the tire 1 is ensured, and the ground contact of the tread 30 with the road surface is improved. The belt 31 is not limited to a two-layer structure, and may have a single layer structure, or a three-layer structure or more. In addition to the belt 31, the reinforcing layer may include a cap ply arranged on the tire radial outer side of the belt 31.

[0023] The tread rubber 35 is disposed on the outer side of the belt 31 in the tire radial direction. The tread rubber 35 constitutes a tread surface 36 which is the outer surface of the tread 30 and comes into contact with the road surface. An axially outer end 35a of the tread rubber 35 extends axially outward beyond the axially outer end 32a of the belt 31 and curves inward in the tire radial direction. The axially outer end 35a of the tread rubber 35 is covered by an axially outer end 21a of the sidewall rubber 21.

[0024] The tread surface 36 is provided with a tread pattern 39 as shown in FIG. 2. The tread pattern 39 shown in FIG. 2 is an example of a tread pattern formed on the tread of the present disclosure. FIG. 2 shows the tire axial direction X and the tire circumferential direction G. The tread pattern 39 includes a plurality of lands 70, a plurality of main grooves 80 between the lands 70, and a plurality of lateral grooves 90. Each of the lands 70 is a rib-shaped convex portion extending in the tire circumferential direction. Each of the main grooves 80 is a circumferential groove extending in the tire circumferential direction. Each of the lateral grooves 90 is a groove extending in a direction intersecting the tire circumferential direction. The tread pattern 39 of the embodiment is a point-symmetric pattern in which the pattern does not change even when rotated 180 degrees with respect to the center of the total width of the tire 1.

[0025] The multiple lands 70 include a central land 71 arranged in the axial center of the tire, a pair of shoulder lands 72 on both sides in the axial direction of the tire, and a pair of intermediate lands 73 arranged between the central land 71 and each shoulder lands 72.

[0026] The multiple main grooves 80 include a central main groove 83 formed in the widthwise center of the central land 71, a pair of intermediate main grooves 81 between the central land 71 and each intermediate land 73, and a pair of shoulder main grooves 82 between each intermediate land 73 and each shoulder land 72.

[0027] 2, the lateral grooves 90 include a plurality of central lateral grooves 91 formed on both sides of the central main groove 83 of the central land 71, a plurality of lug grooves 92 formed in the shoulder land 72, and a plurality of intermediate lateral grooves 93 formed in the intermediate land 73. The central lateral grooves 91, the lug grooves 92, and the intermediate lateral grooves 93 are each arranged at intervals in the tire circumferential direction.

[0028] The central main groove 83 is disposed on the tire equator S2. The central lateral grooves 91 on both sides of the central main groove 83 are inclined at the same angle and in the same direction with respect to the tire circumferential direction. The central lateral grooves 91 on one side of the central main groove 83 and the central lateral grooves 91 on the other side of the central main groove 83 are disposed so as to be offset from each other in the tire circumferential direction. The left and right intermediate lateral grooves 93 are inclined with respect to the tire circumferential direction in a direction opposite to that of the central lateral groove 91. The left and right intermediate lateral grooves 93 are disposed so as to be offset from each other in the tire circumferential direction.

[0029] The shoulder 40 is a region where the tread 30 transitions to the sidewall 20. The shoulder 40 includes a region where an end 21a of the sidewall rubber 21 on the outer side in the tire radial direction covers an end 35a of the tread rubber 35 on the outer side in the tire axial direction.

[0030] The carcass ply 50 is laid between a pair of beads 10. The carcass ply 50 is embedded inside the tire 1 in a manner that the carcass ply 50 passes between the pair of beads 10, through a pair of sidewalls 20, a pair of shoulders 40, and the tire cavity side of the tread 30. In the tread 30, a belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction.

[0031] The carcass ply 50 includes a plurality of ply cords (not shown) that form the framework of the tire 1. The plurality of ply cords extend, for example, along a plane along the tire axial direction, and are arranged side by side in the tire circumferential direction. The ply cords are made of insulating organic fiber cords such as polyester or polyamide. The carcass ply 50 is formed by covering the plurality of ply cords with rubber.

[0032] The carcass ply 50 includes a ply body 50A and a pair of turned-up portions 50B. The ply body 50A is a portion that extends from the tread 30 through the pair of shoulders 40 and the pair of sidewalls 20 to the axially inner side of each of the pair of beads 10. The pair of turned-up portions 50B are turned back radially outward from the ply body 50A by being wound around each of the pair of bead cores 11, and extend along the sidewalls 20. A tip 50b of the turned-up portion 50B is located slightly radially outward from the maximum width position 20W of the tire 1. A portion of the turned-up portion 50B radially outward from the bead filler 12 overlaps the axially outer side of the ply body 50A.

[0033] The above-mentioned rim strip rubber 13 further surrounds the portion of the carcass ply 50 surrounding the bead core 11 and the bead filler 12 .

[0034] Although the carcass ply 50 in the embodiment has a single layer structure, the carcass ply 50 may have a two-layer or more multi-layer structure.

[0035] The inner liner 60 covers the inner surface of the ply body portion 50A of the carcass ply 50 and the axially inner portion of the rim strip rubber 13 between the pair of beads 10 to form the tire cavity surface. The inner liner 60 may have a single layer structure, or a two-layer or more layer structure. The inner liner 60 is made of air-permeable resistant rubber and prevents air in the tire cavity from leaking to the outside.

[0036] Here, the rubber used for the bead filler 12 has a hardness higher than at least the sidewall rubber 21 and the inner liner 60. The hardness of the rubber is a hardness measured by "JIS K6253-3:2012 durometer hardness type A".

[0037] For example, when the hardness of the sidewall rubber 21 is used as a standard, the hardness of the bead filler 12 is preferably about 1.2 to 2.3 times the hardness of the sidewall rubber 21. By setting the hardness at such a level, it is possible to ensure a balance between the flexibility of the tire and the rigidity in the vicinity of the bead 10. Moreover, the hardness of the tread rubber 35 is preferably relatively low from the viewpoint of good ground contact and low fuel consumption, and is preferably about 50 to 60 in terms of the above-mentioned durometer hardness type A.

[0038] Next, the lug grooves 92, which are a feature of the present disclosure, will be described in further detail with reference to Fig. 3. Fig. 3 is a part of Fig. 1, and shows an axial cross section of a portion extending from the tread 30 through the shoulder 40 to a part of the outer side in the tire radial direction of the sidewall 20. In Fig. 3, hatching of the cross section is omitted in order to clearly show dimension lines, symbols, etc.

[0039] FIG. 3 shows the contact widths of the tread surface 36 in contact with the road surface at 88%, 100%, 120%, and 130% loads, respectively, of the maximum loads in the tire standard ETRTO, as TW88, TW100, TW120, and TW130. Each contact width is the axial length of the tread surface 36 in contact with the road surface. Since FIG. 3 is a half cross-sectional view in the axial direction of the tire, each contact width is half of the actual contact width, but TW88, TW100, TW120, and TW130 indicate the full length of the contact width. Also, in FIG. 3, the tread end, which is the axial end of each contact width, is shown as 88E, 100E, 120E, and 130E. For reference, FIG. 2 shows the contact width TW130 of the tread surface 36.

[0040] The lug groove 92 has a first groove 110 communicating with the shoulder main groove 82, a second groove 120 disposed axially outboard of the first groove 110 and continuing to the sidewall 20, and a ridge portion 130 separating the first groove 110 and the second groove 120. The first groove 110 has an axially inner end communicating with the shoulder main groove 82. That is, the lug groove 92 has an axially inner end communicating with the shoulder main groove 82. Each of the first groove 110 and the second groove 120 has a length of, for example, about 30% to 65% of the periphery length along the curved shape of the lug groove 92 in the axial cross section. The ridge portion 130 has a length of, for example, about 3% to 15% of the periphery length along the curved shape of the lug groove 92 in the axial cross section. The lug groove 92 may have a configuration in which the first groove 110 constituting the axially inner end thereof does not communicate with the shoulder main groove 82 .

[0041] 3, in the tire axial cross section, the first groove 110 is a groove that extends from an axially inner end of the tire that communicates with the shoulder main groove 82 to an axially outer side of the tire to a starting point 130a of the ridge 130, and is the deepest region of the lug groove 92. The starting point 130a of the ridge 130 is disposed near a position corresponding to the tread ground contact edge 88E. The second groove 120 is a groove that is formed so as to continue from the highest peak P of the ridge 130 to the radially outer end 21a of the sidewall 20.

[0042] The depth of the first groove 110 of the lug groove 92 gradually decreases from the vicinity of a position indicated by a depth H1 corresponding to the axially outer end of the shoulder main groove 82 to a position indicated by a depth H2 corresponding to the axially outer end of the first groove 110 and the starting point 130a of the ridge 130 toward the axially outer side of the tire. For example, the depth H2 is preferably about 70% or more and 90% or less of the depth H1.

[0043] The tire 1 is repeatedly subjected to flexural deformation during running, and therefore the distortion is relatively large, particularly near the end of the belt 31, and therefore the distortion of the shoulder land 72 having the lug groove 92 is large. Here, in the tire 1 of the embodiment, the depth of the first groove 110 of the lug groove 92 gradually decreases from the axially outer end of the tire to the vicinity of the starting point 130a of the ridge portion 130 as it moves toward the axially outer side of the tire. Therefore, the rigidity of the shoulder land 72 is ensured. By ensuring the rigidity of the shoulder land 72, the phenomenon that the rubber heats up due to distortion and causes blisters on the shoulder land 72 is unlikely to occur. Therefore, block chipping of the shoulder land 72 is suppressed, and as a result, the steering stability is improved.

[0044] In the tire axial cross section, the ridge portion 130 has a slope 131 on the axially inner side of the tire. The slope 131 is formed from a starting point 130a, which is near a position corresponding to the tread ground contact edge 88E in the tire axial direction, to a peak P of the ridge portion 130. In the tire axial cross section, the slope 131 includes the vicinity of a position corresponding to the tread ground contact edge 120E. The slope 131 rises from the vicinity of the starting point 130a toward the axially outer side so as to approach the tread surface 36. As a result, the depth of the lug groove 92 gradually decreases on the slope 131 toward the axially outer side of the tire.

[0045] When the vehicle is cornering, it is assumed that a load of about 120%, exceeding 100% of the maximum load in the tire standard ETRTO, is applied to the outer side of the cornering of the tread 30. In the tire 1 of the embodiment, as described above, the slope 131 of the ridge portion 130 is located at a position corresponding to the tread ground edge 120E in the tire axial cross section, and the depth of the lug groove 92 gradually decreases toward the tire axial outer side by rising closer to the tread surface 36 toward the tire axial outer side. Therefore, the rigidity of the circumferential component during cornering is improved, and the phenomenon that the rubber heats up due to distortion and causes blisters on the shoulder land 72 is unlikely to occur. Therefore, block chipping of the shoulder land 72 is suppressed, and as a result, the steering stability is improved.

[0046] The axially outer end of the lug groove 92, i.e., the axially outer end 120a of the second groove 120, is located axially outboard of the tread ground contact edge 130E. As a result, the axially outer end 120a of the lug groove 92 is located axially outboard of the tread ground contact edge 130E even under conditions where the maximum load reaches 130% of the ETRTO tire standard, ensuring drainage by the lug groove 92.

[0047] In the second groove 120 of the lug groove 92, the ratio TE / H3 between the depth TE near the axially outer end 120a of the tire and the shortest distance H3 from the axially outer end 32a of the belt 31 to the tire outer surface is 10% or more and 80% or less. This improves the rigidity of the circumferential component during cornering, and the phenomenon of the rubber heating up due to distortion and the occurrence of blisters on the shoulder land 72 is unlikely to occur. Therefore, block chipping of the shoulder land 72 is suppressed, and as a result, the steering stability is improved. In addition, the groove volume near the axially outer end 120a of the lug groove 92 is secured, so that drainage is secured and the occurrence of blisters is suppressed by improving heat dissipation during driving.

[0048] The ratio H4 / TE of the depth H4 of the axially inner end 120b of the second groove 120 of the lug groove 92 to the depth TE of the axially outer end 120a of the second groove 120 of the lug groove 92 is equal to or greater than 1 and equal to or less than 3. This ensures the depth of the axially inner region of the second groove 120 of the lug groove 92, thereby ensuring the drainage performance of the lug groove 92.

[0049] The ratio H5 / H2 of the tire radial direction distance H5 between the tread ground contact edge 120E and the bottom surface 92b of the lug groove 92 to the tire radial direction distance H2 between the tread ground contact edge 88E and the bottom surface 92b of the lug groove 92 is 45% or more and 60% or less.

[0050] In the lug groove 92, the area between the tread ground contact edge 120E and the tread ground contact edge 88E is an area where blisters are likely to occur, so in this area, it is desirable to have as thick a rubber as possible from the viewpoint of suppressing distortion, but on the other hand, if the rubber thickness is too thick, the groove depth becomes small, which may lead to a decrease in drainage. Therefore, by setting H5 / H2 to 45% or more and 60% or less as described above, it is possible to achieve both suppression of blisters and ensuring drainage.

[0051] An apex P of the ridge 130 of the lug groove 92 is disposed axially outboard of a tread ground contact edge 130E.

[0052] Under high loads such as 130% of the maximum load in the tire standard ETRTO, the difference in deformation between the tread 30 side and the sidewall 20 side becomes large near the tread ground edge 130E, and if the crest P of the peak 130 is arranged to overlap there in the tire axial direction, the peak 130 is likely to be distorted. Therefore, if the crest P of the peak 130 of the lug groove 92 is arranged axially outward of the tread ground edge 130E as described above, the peak 130 is less likely to be distorted even under 130% load, and as a result, blisters are suppressed. In addition, a situation in which the distortion of the peak 130 spreads to the surrounding shoulder land 72 and uneven wear of the shoulder land 72 is avoided.

[0053] The tire 1 of the above embodiment provides the following advantages.

[0054] (1) A tire 1 according to an embodiment is a pneumatic tire including a bead 10, a pair of sidewalls 20 extending radially outward from the bead 10, a tread 30 disposed between the pair of sidewalls 20 and including a tread surface 36 that comes into contact with a road surface, and a shoulder 40 at a portion transitioning from the tread 30 to the sidewall 20, the tread surface 36 including a plurality of lands 70 extending in the tire circumferential direction and a plurality of main grooves 80 extending in the tire circumferential direction and dividing the plurality of lands 70 in the tire axial direction, the land 70 having a shoulder land 72 disposed at an end of the tread surface 36 in the tire axial direction, the main groove 80 having a shoulder main groove 82 adjacent to the shoulder land 72 on the axially inner side, the shoulder land 72 having a plurality of lug grooves 92 extending in a direction intersecting the tire circumferential direction and aligned in the tire circumferential direction, the lug groove 92 being disposed axially outward of a first groove 110 and a second groove 110 extending axially outward of the first groove 110 and continuing into the sidewall 20. In the tire axial cross section, the first groove 110 has a region from a position corresponding to the axially outer end of the shoulder main groove 82 to a position corresponding to the tread ground contact edge 88E at a tire standard load of 88% of the maximum load in the ETRTO, and the depth of the first groove 110 gradually decreases toward the outside in the tire axial direction. The ridge portion 130 has a starting point 130a near a position corresponding to the vicinity of the tread ground contact edge 88E at a tire standard load of 88% of the maximum load in the ETRTO, and has a slope 131 that rises from the starting point 130a to at least a position corresponding to the tread ground contact edge 120E at a tire standard load of 120% of the maximum load in the ETRTO so as to approach the tread surface 36 as it moves toward the outside in the tire axial direction, thereby gradually decreasing the depth of the lug groove 92 toward the outside in the tire axial direction.

[0055] This ensures the rigidity of the shoulder land 72 during driving, including cornering, making it less likely that the rubber will heat up due to distortion and cause blisters on the shoulder land 72. As a result, block chipping of the shoulder land 72 is suppressed, improving handling stability.

[0056] (2) In the tire 1 according to the above embodiment (1), it is preferable that the axially outer end 120a of the lug groove 92 is located axially outer than the tread contact end 130E at a load of 130% of the maximum load in the tire standard ETRTO.

[0057] This ensures drainage through the lug grooves 92 even in situations where the load reaches 130% of the maximum load specified by the ETRTO tire standard.

[0058] (3) In the tire 1 according to the above embodiments (1) and (2), the tread 30 further includes a belt 31 as a reinforcing layer, and it is preferable that the ratio TE / H3 between the depth TE of the second groove 120 near the axially outer end of the tire and the shortest distance H3 from the axially outer end 32a of the belt 31 to the outer surface of the tire is 10% or more and 80% or less.

[0059] This improves the circumferential stiffness during cornering, and improves steering stability by suppressing block chipping of the shoulder land 72. In addition, the groove volume near the axially outer end 120a of the lug groove 92 is secured, ensuring drainage and suppressing the occurrence of blisters by improving heat dissipation during driving.

[0060] (4) In the tire 1 according to the above embodiments (1) to (3), the ratio H4 / TE of the depth H4 of the axially inner end 120b of the second groove 120 of the lug groove 92 to the depth TE of the axially outer end 120a of the second groove 120 is preferably 1 or greater and 3 or less.

[0061] This ensures the depth of the region of the second groove 120 of the lug groove 92 on the axially inner side of the tire, thereby ensuring the drainage performance of the lug groove 92.

[0062] (5) In the tire 1 according to the above embodiments (1) to (4), the ratio H5 / H2 of the tire radial distance H5 between the tread ground contact edge 120E and the bottom surface 92b of the lug groove 92 when the tire standard is a load of 120% of the maximum load of the ETRTO to the tire radial distance H2 between the tread ground contact edge 88E and the bottom surface 92b of the lug groove 92 when the tire standard is a load of 88% of the maximum load of the ETRTO is preferably 45% or more and 60% or less.

[0063] This makes it possible to both prevent blisters from occurring and ensure drainage in the shoulder land 72 around the lug groove 92 .

[0064] (6) In the tire 1 according to the above embodiments (1) to (5), it is preferable that the apex P of the ridge portion 130 is positioned axially outboard of the tread edge 130E at a load of 130% of the maximum load in the tire standard ETRTO.

[0065] This makes it difficult for distortion to occur in the ridges 130 even under a load of 130%, resulting in suppression of blisters. In addition, it is possible to prevent the distortion of the ridges 130 from spreading to the surrounding shoulder land 72, causing uneven wear in the shoulder land 72.

[0066] (7) In the tire 1 according to the embodiment described above in (1) to (6), it is preferable that the axially inner end of the lug groove 92 communicates with the shoulder main groove 82.

[0067] This improves the drainage performance of the lug grooves 92.

[0068] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and even if modifications and improvements are made within the scope of the present invention, they will still be included in the scope of the present invention. [Explanation of symbols]

[0069] 1... tire (pneumatic tire), 10... bead, 20... sidewall, 30... tread, 31... belt (reinforcing layer), 32a... axially outer end of belt, 36... tread surface, 40... shoulder, 70... land, 72... shoulder land, 80... main groove, 82... shoulder main groove, 88E, 100E, 120E, 130E... tread ground edge, 92... lug groove, 92b... bottom surface of lug groove, 110... first groove, 120... second groove, 120a... axially outer end of lug groove (axially outer end of second groove), 120b... axially inner end of second groove, 130... ridge, 130a... starting point, 131... slope, P... top of ridge.

Claims

1. Beads and A pair of sidewalls extending from the bead outward in a radial direction of the tire; a tread disposed between the pair of sidewalls and including a tread surface that comes into contact with a road surface; A shoulder at a transition portion from the tread to the sidewall, The tread surface includes a plurality of lands extending in a tire circumferential direction, and a plurality of main grooves extending in the tire circumferential direction and dividing the plurality of lands in the tire axial direction, The land has a shoulder land arranged at an end of the tread surface in the tire axial direction, The main groove includes a shoulder main groove adjacent to the shoulder land on the axially inner side of the tire, The shoulder land has a plurality of lug grooves extending in a direction intersecting the tire circumferential direction and aligned in the tire circumferential direction, The lug groove has a first groove, a second groove disposed axially outward of the first groove and continuing to the sidewall, and a ridge portion separating the first groove and the second groove, In the tire axial cross section, The first groove has a region from a position corresponding to an axially inner end of the lug groove to a position corresponding to a tread edge at a load of 88% of a maximum load in the ETRTO tire standard, and the depth of the first groove gradually decreases toward the axially outer side of the tire, The ridge portion has a slope starting from the vicinity of a position corresponding to the tread ground edge at a load of 88% of the maximum load of the ETRTO tire standard, and rises toward the tread surface as it moves axially outward from the starting point to at least a position corresponding to the tread ground edge at a load of 120% of the maximum load of the ETRTO tire standard, thereby gradually decreasing the depth of the lug groove as it moves axially outward.

2. The pneumatic tire according to claim 1 , wherein an axially outer end of the lug groove is located axially outer than a tread contact end under a load of 130% of a maximum load in accordance with the ETRTO tire standard.

3. The tread further includes a reinforcing layer, 3. The pneumatic tire according to claim 1, wherein a ratio TE / H3 of a depth TE of the second groove near an axially outer end of the tire to a shortest distance H3 from the axially outer end of the reinforcing layer to an outer surface of the tire is 10% or more and 80% or less.

4. 3. The pneumatic tire according to claim 1, wherein a ratio H4 / TE of a depth H4 of the second groove at an axially inner end to a depth TE of the second groove at an axially outer end is 1 or greater and 3 or less.

5. 3. The pneumatic tire according to claim 1, wherein a ratio H5 / H2 of a tire radial direction distance H5 between a tread ground-contact end and a bottom surface of the lug groove when a tire standard is a load of 120% of a maximum load of ETRTO and a tire radial direction distance H2 between a tread ground-contact end and a bottom surface of the lug groove when a tire standard is a load of 88% of a maximum load of ETRTO is 45% or more and 60% or less.

6. 3. The pneumatic tire according to claim 1, wherein the crests of the ridges are disposed axially outward of a tread edge when a load of 130% of a maximum load in accordance with ETRTO tire standards is applied.

7. The pneumatic tire according to claim 1 , wherein an axially inner end of each of the lug grooves communicates with the shoulder main groove.

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