Pneumatic tire

Abstract

To provide a pneumatic tire which suppresses block chipping of a shoulder land accompanied by occurrence of blister due to increase in a load during cornering, even in a case of a high load type passenger vehicle, and thereby improves steering stability.SOLUTION: In a tire axial direction cross section, an apex P of a crest part 130 of a lug groove 92 is positioned in a tire axial direction outside of a tread ground-contact end 120E at 120% load of the maximum load according to an ESTRO tire standard, a rubber thickness 37a in a tire radial direction of a part corresponding to the apex P is larger than the maximum rubber thickness 37b in the tire radial direction of a part corresponding to a first groove 110 of the lug groove 92, a second groove 120 of the lug groove 92 incudes an R-shaped concave curved surface 120c on a tire axial direction outer end, and the curvature radius RA of the concave curved surface 120c is larger than the maximum depth H3 of the second groove 120.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 a relatively large vehicle weight, such as EVs (Electric Vehicles) and hybrid vehicles, and the increase in load during cornering also promotes blisters. Block chipping is an issue that must be avoided because it leads to a decrease in steering 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] The present invention aims to provide a pneumatic tire that suppresses block chipping on the shoulder land due to the generation of blisters caused by increased load, especially when cornering, even in the case of a heavy-load passenger vehicle, thereby improving driving stability. [Means for solving the problem]

[0006] The pneumatic tire of the present invention is a pneumatic tire including a pair of beads, a pair of sidewalls extending radially outward from the pair of beads, a tread including a tread rubber having a tread surface that comes into contact with a road surface and a shoulder at a portion transitioning from the tread to the sidewall, wherein 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 lands having shoulder lands disposed at ends of the tread surface in the tire axial direction, the main groove having a shoulder main groove adjacent to the axially inner side of the shoulder lands, the shoulder The land has a plurality of lug grooves that extend in a direction intersecting the tire circumferential direction and are aligned in the tire circumferential direction, the lug grooves having a first groove, a second groove that is arranged axially outboard of the first groove and continuous with the shoulder, and a ridge portion that separates the first groove and the second groove, and in an axial cross section of the tire, the apex of the ridge portion is located axially outboard of the tread contact edge at a load of 120% of the maximum load in the ETRTO tire standard, and the rubber thickness in the tire radial direction of the portion corresponding to the apex is greater than the maximum rubber thickness in the tire radial direction of the portion corresponding to the first groove, and the second groove includes an R-shaped concave curved surface at the axially outer end of the tire, and the radius of curvature of the concave curved surface is greater than the maximum depth of the second groove. Effect of the Invention

[0007] According to the present invention, a pneumatic tire can be provided in which block chipping on the shoulder land caused by blister formation due to increased load, particularly when cornering, is suppressed even in the case of heavy-load passenger vehicles, 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. [Figure 4A] FIG. 11 is a diagram showing a tread pattern of a first modified example. [Figure 4B] FIG. 2 is a half cross-sectional view of a tire mainly showing the tread of a first modified example. [Figure 5A] FIG. 13 is a diagram showing a tread pattern of a second modified example. [Figure 5B] FIG. 11 is a half cross-sectional view of a tire mainly showing the tread of a second modified example. [Figure 6A] FIG. 13 is a diagram showing a tread pattern of a third modified example. [Figure 6B] FIG. 11 is a half cross-sectional view of a tire mainly showing the tread of a third modified example. 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 reduces 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 features of the present disclosure, including the lug grooves 92, will be described in more detail with reference to Fig. 3. Fig. 3 is a part of Fig. 1, and shows a half cross section in the tire axial direction of a portion extending from the tread 30 through the shoulder 40 to a part of the tire radial outer side of the sidewall 20. In Fig. 3, hatching is omitted from the cross section in order to clearly show dimension lines, symbols, etc.

[0039] FIG. 3 shows the contact widths of the tread surface 36 at 100%, 120%, and 130% loads, which are the maximum loads in the tire standard ETRTO, as TW100, TW120, and TW130. Each contact width is the axial length of the tread surface 36 at which the tread surface 36 contacts 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 TW100, TW120, and TW130 each indicate the full length of the contact width. Also, FIG. 3 shows the tread end, which is the axial end of each contact width, as 100E, 120E, and 130E. Note that 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 the axially inner end of the tire that communicates with the shoulder main groove 82 to the axially outer side to the 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 located axially inner than the tread ground contact edge 120E in the tire axial direction. The second groove 120 is a groove that extends short from the highest peak P of the ridge 130 to the axially outer side.

[0042] An apex P of the ridge 130 of the lug groove 92 is located axially outboard of the tread ground-contact edge 120E. A rubber thickness 37a in the tire radial direction at a portion corresponding to the apex P is greater than a maximum rubber thickness 37b in the tire radial direction at a portion corresponding to the first groove 110.

[0043] If the tread edge 140E is a tread edge under a load of 140% of the maximum load in the tire standard ETRTO, the tread edge 140E is located axially outboard of the tread edge 120E. Here, it is preferable that the apex P of the peak 130 of the lug groove 92 is located between the tread edge 120E and the tread edge 140E in the tire axial direction.

[0044] Rubber thickness 37a is the thickness of tread rubber 35 in the tire radial direction, and is the distance in the tire radial direction between apex P of ridge portion 130 and belt 31. In this case, belt 31 is inner belt 32, and the distance in the tire radial direction between inner belt 32 and apex P is rubber thickness 37a.

[0045] Maximum rubber thickness 37b is the thickness of tread rubber 35, and is the longest distance in the tire radial direction between bottom surface 110a of first groove 110 and belt 31. In this case, belt 31 is outer belt 33, and the longest distance in the tire radial direction between outer belt 33 and bottom surface 110a of first groove 110 is maximum rubber thickness 37b.

[0046] The second groove 120 of the lug groove 92 is arranged so as to be continuous with the shoulder 40. The second groove 120 of the lug groove 92 includes an R-shaped concave curved surface 120c at the axially outer end. In the axial cross section, the radius of curvature RA of this concave curved surface 120c is greater than the depth H3 of the second groove 120. The depth H3 of the second groove 120 is the maximum distance between the bottom surface 120a of the second groove 120 and the tire outer surface. The axially outer end 120d of the concave curved surface 120c is the axially outer end of the lug groove 92. The axially outer end 120d of the concave curved surface 120c does not open to the outer surface of the shoulder 40, but is closed within the outer surface of the shoulder 40.

[0047] 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. Particularly when the vehicle is cornering, a load of about 120% exceeding 100% of the maximum load in the tire standard ETRTO is applied to the cornering outer side of the shoulder land 72, that is, the outer side of the tire axial direction. In the tire 1 of the embodiment, the apex P of the peak portion 130 of the lug groove 92 is located axially outer than the tread ground edge 120E, and the rubber thickness 37a in the tire radial direction of the part corresponding to the apex P is larger than the maximum rubber thickness 37b in the tire radial direction of the tread rubber 35 in the part corresponding to the first groove 110. As a result, the shoulder land 72 including the lug groove 92 has improved rigidity in the circumferential direction during cornering, 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.

[0048] As described above, the tire 1 of the embodiment includes an R-shaped concave curved surface 120c at the axially outer end of the second groove 120 of the lug groove 92, and the curvature radius RA of this concave curved surface 120c is larger than the depth H3 of the second groove 120. As a result, distortion near the axially outer end 120d of the second groove 120 of the lug groove 92 is dispersed and heat generation is suppressed, particularly during cornering. Therefore, the occurrence of cracks at the bottom surface 120a of the second groove 120 is suppressed.

[0049] In FIG. 3, the minimum rubber thickness H1 of the tread rubber 35 is formed between the belt 31 and the bottom surface 110a of the first groove 110 at the tire axially outer end of the first groove 110 of the lug groove 92, i.e., near the starting point 130a of the ridge 130. In this case, the belt 31 is the outer belt 33, and the minimum rubber thickness H1 is the shortest distance between the vicinity of the tire axially outer end 33a of the outer belt 33 and the bottom surface 110a of the first groove 110. In FIG. 3, the minimum rubber thickness H2 of the tread rubber 35 is formed between the belt 31 and the bottom surface 120a near the tire axially outer end of the second groove 120 of the lug groove 92. In this case, the belt 31 is the inner belt 32, and the minimum rubber thickness H2 is the shortest distance between the vicinity of the axially outer end 32a of the inner belt 32 and the bottom surface 120a of the second groove 120. Here, the ratio H1 / H2 of the minimum rubber thickness H1 of the tread rubber 35 in the first groove 110 to the minimum rubber thickness H2 of the tread rubber 35 in the second groove 120 is preferably 40% or more and 80% or less.

[0050] By setting the above H1 / H2 to 40% or more and 80% or less, the rigidity in the tire radial direction of the tread rubber 35 in the portion corresponding to the first groove 110 of the lug groove 92 is ensured, distortion is unlikely to occur, and drainage by the first groove 110 is likely to be ensured. If the above H1 / H2 is below 40%, the thickness in the tire radial direction of the tread rubber 35 in the portion corresponding to the first groove 110 of the lug groove 92 is reduced, so the rigidity is reduced and distortion is likely to occur. On the other hand, if the above H1 / H2 is above 80%, the depth of the first groove 110 is reduced, making it difficult to ensure drainage, and the heat dissipation during driving is reduced, reducing the effect of suppressing the occurrence of blisters. Therefore, the above H1 / H2 is preferably set to 40% or more and 80% or less.

[0051] As shown in Fig. 3, the axially outer end of the lug groove 92, i.e., the axially outer end 120d of the concave curved surface 120c of the second groove 120, is located axially outward of the tread edge 130E. As a result, even under high load conditions such as a maximum load of 130% of the tire standard ETRTO, the axially outer end 120d of the lug groove 92 is located axially outward of the tread edge 130E. Therefore, the lug groove 92 ensures drainage. The lug groove 92 also ensures heat dissipation during driving and a cooling effect within the tire 1.

[0052] As shown in Fig. 3, the axially outer end 120d of the lug groove 92 is located radially inward (lower in Fig. 3) of the apex P of the ridge 130. This allows moisture to be smoothly drained without being accumulated between the axially outer end 120d of the lug groove 92 and the ridge 130, ensuring drainage. Also, heat dissipation during running and a cooling effect within the tire 1 are ensured.

[0053] 3, the axially outer end 120d of the lug groove 92 is located axially outward of the axially outer end 32a of the inner belt 32, which is the axially outer end of the belt 31. That is, the lug groove 92 extends axially outward from the outer end 32a of the belt 31. This ensures drainage by the lug groove 92. In addition, heat dissipation during running and a cooling effect within the tire 1 are also ensured.

[0054] The tire 1 of the above embodiment provides the following advantages.

[0055] (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 including a tread rubber 35 disposed between the pair of sidewalls 20 and having 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 lands 70 having shoulder lands 72 disposed at ends of the tread surface 36 in the tire axial direction, the main groove 80 having shoulder main grooves 82 adjacent to the shoulder lands 72 on the axially inner side, the shoulder lands 72 having shoulder main grooves 82 extending in a direction intersecting the tire circumferential direction, The tire has a plurality of lug grooves 92 extending in the circumferential direction of the tire, the lug grooves 92 having a first groove 110, a second groove 120 arranged axially outboard of the first groove 110 and continuing to the shoulder 40, and a ridge portion 130 separating the first groove 110 and the second groove 120, and in an axial cross section of the tire, an apex P of the ridge portion 130 is located axially outboard of a tread ground contact edge 120E at a load of 120% of the maximum load in the ETRTO tire standard, and a rubber thickness 37a in the radial direction of the tire at a portion corresponding to the apex P of the ridge portion 130 is greater than a maximum rubber thickness 37b in the radial direction of the tire at a portion corresponding to the first groove 110, and the second groove 120 includes an R-shaped concave curved surface 120c at an axially outer end of the tire, and a curvature radius RA of the concave curved surface 120c is greater than a maximum depth H3 of the second groove 120 of the lug groove 92.

[0056] As a result, even in the case of a heavy-load passenger vehicle, the rigidity of the shoulder land 72 is ensured during driving, including cornering, so that the phenomenon of the rubber heating up due to distortion and causing blisters on the shoulder land 72 is less likely to occur. As a result, block chipping of the shoulder land 72 is suppressed, and the handling stability is improved.

[0057] (2) In the tire 1 of the above embodiment (1), the tread 30 further includes a belt 31 as a reinforcing layer arranged radially inward of the tread rubber 35, and it is preferable that the ratio H1 / H2 of the minimum rubber thickness H1 of the tread rubber 35 between the bottom surface 110a near the axially outer end of the first groove 110 of the lug groove 92 and the belt 31 and the minimum rubber thickness H2 of the tread rubber 35 between the bottom surface 120a of the second groove 120 of the lug groove 92 and the belt 31 is 40% or more and 80% or less.

[0058] This ensures the rigidity in the tire radial direction of the tread rubber 35 in the portion corresponding to the first groove 110 of the lug groove 92, suppressing block chipping, and also ensures drainage by the first groove 110.

[0059] (3) In the tire 1 according to the above embodiments (1) and (2), it is preferable that the axially outer end 120d of the lug groove 92 is located axially outboard of the tread contact end 130E at a load of 130% of the maximum load in the tire standard ETRTO.

[0060] As a result, even under high load conditions such as a load reaching 130% of the maximum load specified by the ETRTO tire standard, the axially outer end 120d of the lug groove 92 is located axially outer than the tread contact end 130E, thereby ensuring drainage by the lug groove 92, as well as heat dissipation during driving and a cooling effect within the tire 1.

[0061] (4) In the tire 1 according to the above embodiments (1) to (3), the axially outer end 120d of the lug groove 92 is preferably located inward of the apex P of the ridge 130 in the tire radial direction.

[0062] This allows moisture to be smoothly drained without accumulating between the axially outer end 120d of the lug groove 92 and the ridge portion 130, thereby ensuring drainage as well as heat dissipation during driving and a cooling effect within the tire 1.

[0063] (5) In the tire 1 according to the above embodiments (1) to (4), the axially outer end 120d of the lug groove 92 is preferably positioned axially outer than the axially outer end 32a of the belt 31.

[0064] As a result, the lug grooves 92 extend further axially outward than the outer ends 32a of the belts 31 in the tire axial direction, so that the lug grooves 92 ensure drainage, and also ensure heat dissipation during running and a cooling effect within the tire 1.

[0065] (6) In the tire 1 according to the above embodiments (1) to (5), it is preferable that the lug groove 92 communicates with the shoulder main groove 82 at its axially inner end.

[0066] This improves the drainage performance of the lug grooves 92.

[0067] Hereinafter, first to third modified examples which are partial modifications of the above embodiment will be described. In the drawings referred to in describing these modified examples, the same components as those in the above embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

[0068] (First Modification) Figures 4A and 4B are diagrams showing a first modified example. Figure 4A is a diagram corresponding to Figure 2 and is a partial plan view of the tire 1 showing a tread pattern 39. Figure 4B is a diagram corresponding to Figure 3 and is a half cross-sectional view of the tire 1 mainly including the tread 30. As shown in Figure 4B, the internal structure of the tire 1 of the first modified example has the same structure as that of the tire 1 of the above embodiment.

[0069] In the tire according to the first modification, a shoulder annular groove 45 is formed along the tire circumferential direction on the outer surface of each shoulder 40 on both sides in the tire axial direction. The concave curved surface 120c of the lug groove 92 is open to the shoulder annular groove 45. That is, the lug groove 92 is connected to the shoulder annular groove 45. The cross section of the shoulder annular groove 45 is an arc shape and has approximately the same curvature radius as the concave curved surface 120c of the lug groove 92. Therefore, the concave curved surface 120c is formed integrally with the shoulder annular groove 45. The first modification has the same configuration as the above embodiment, except that the axially outer end 120d of the lug groove 92 is open to the shoulder annular groove 45.

[0070] According to this first modified example, the axially outer end 120d of the lug groove 92 is open and the lug groove 92 is connected to the shoulder annular groove 45, thereby improving the drainage performance of the lug groove 92 and also improving the heat dissipation performance during driving and the cooling effect within the tire 1.

[0071] (Second Modification) Next, a second modified example in which the tread pattern 39 of the above embodiment is modified will be described with reference to Figures 5A and 5B. Figure 5A corresponds to Figure 2 and is a partial plan view of the tire 1 showing the tread pattern 39 of the second modified example. Figure 5B corresponds to Figure 3 and is a half cross-sectional view of the tire mainly including the tread 30. As shown in Figure 5B, the internal structure of the tire 1 of the second modified example has the same structure as that of the tire 1 of the above embodiment.

[0072] As shown in FIG. 5A, the tread pattern 39 of the second modified example is a pattern that is generally symmetrical and has a tire rotation direction that is specified in one direction. In this tread pattern 39, the intermediate lateral grooves 93 that extend from the shoulder main grooves 82 toward the axially inner side of the tire at an angle with respect to the tire circumferential direction cross the intermediate main grooves 81 to a position that straddles the tire equator S2, and the tip portions of the intermediate lateral grooves 93 communicate with each other by merging with the tip portions of the intermediate lateral grooves 93 on the axially opposite side of the tire. This tread pattern 39 does not have the central lateral groove 91 of the above embodiment. The tip portions of the left and right intermediate lateral grooves 93 on the axially inner side that straddle the tire equator S2 communicate with each other and extend in a zigzag shape in the tire circumferential direction so as to alternately intersect with the tire equator S2. In this second modified example, the axially outer end 120d of the concave curved surface 120c of the lug groove 92 is not opened to the outer surface of the shoulder 40, but is closed within the outer surface of the shoulder 40.

[0073] (Third Modification) 6A and 6B are diagrams showing a third modified example. The tire 1 of this third modified example has the same internal structure and tread pattern 39 as the second modified example. The third modified example differs from the second modified example in that, like the first modified example, shoulder annular grooves 45 are formed along the tire circumferential direction on the outer surfaces of the shoulders 40 on both sides in the tire axial direction, and the concave curved surfaces 120c of the lug grooves 92 are open to the shoulder annular grooves 45.

[0074] According to the third variant, as in the first variant, the axially outer end 120d of the lug groove 92 is open and communicates with the shoulder annular groove 45, thereby improving the drainage performance of the lug groove 92 and also improving the heat dissipation performance during driving and the cooling effect within the tire 1.

[0075] 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]

[0076] 1... tire (pneumatic tire), 10... bead, 20... sidewall, 30... tread, 31... belt (reinforcing layer), 32a... tire axial outer end of belt, 35... tread rubber, 36... tread surface, 40... shoulder, 70... land, 72... shoulder land, 80... main groove, 82... shoulder main groove, 92... lug groove, 110... first groove, 120... second groove, 120c... concave curved surface, 120d... tire axial outer end of lug groove, 120E, 130E... tread ground edge, 130... ridge, P... ridge peak.

Claims

1. A pair of beads; a pair of sidewalls extending radially outward from the pair of beads; a tread including a tread rubber disposed between the pair of sidewalls and having 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 shoulder, and a ridge portion separating the first groove and the second groove, In the tire axial cross section, the apex of the ridge portion is located axially outward of the tread edge when a load of 120% of the maximum load in the ETRTO tire standard is applied, and the rubber thickness in the tire radial direction at a portion corresponding to the apex is greater than the maximum rubber thickness in the tire radial direction at a portion corresponding to the first groove, The second groove includes an R-shaped concavely curved surface at an axially outer end of the tire, and a radius of curvature of the concavely curved surface is greater than a maximum depth of the second groove.

2. The tread further includes a reinforcing layer disposed on the inner side in the tire radial direction of the tread rubber, 2. The pneumatic tire according to claim 1, wherein a ratio H1 / H2 of a minimum rubber thickness H1 between a bottom surface of the first groove near an axially outer end of the tire and the reinforcing layer and a minimum rubber thickness H2 of the tread rubber between a bottom surface of the second groove and the reinforcing layer is 40% or more and 80% or less.

3. 3. The pneumatic tire according to claim 1, wherein an axially outer end of the lug groove is located axially outboard of a tread edge at a load of 130% of a maximum load in accordance with the ETRTO tire standard.

4. The pneumatic tire according to claim 1 or 2, wherein an axially outer end of the lug groove is located radially inward of the crest (P) of the ridge portion.

5. The pneumatic tire according to claim 2 , wherein an axially outer end of the lug groove is located axially outer than an axially outer end of the reinforcing layer.

6. 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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