Pneumatic tire

Abstract

To provide a pneumatic tire having sufficient pinch cut resistance and drainage performance even for a high load vehicle.SOLUTION: A pneumatic tire is such that: a tire axial direction outer end 32a of an inner belt 32 is positioned in a tire axial direction cross section on an outer side in a tire axial direction with respect to a tread ground contact end 130E when a tire standard is 130% of the maximum load in ETRTO; a depth of a lug groove 92 gradually reduces toward the outer side in the tire axial direction; and the width of the lug groove 92 gradually increases as it goes toward the outer side in the tire axial direction from the tread ground contact end 130E.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having sufficient pinch cut resistance and drainage properties. [Background technology]

[0002] Conventionally, a pneumatic tire for vehicles has been known in which a component that forms the framework of the tire, called a carcass ply, is embedded between the left and right beads, a reinforcing belt is provided within the tread that comes into contact with the road surface, and a plurality of lug grooves are formed on shoulder land at both ends of the tread in the axial direction of the tire, the shoulder grooves extending in a direction that intersects with the circumferential direction of the tire.

[0003] When a tire receives a strong impact while traveling, for example, when going over a depression called a pothole or a step on the road surface caused by a curbstone, the cord in the carcass ply may break, which is called a pinch cut. Pinch cuts occur when a large distortion occurs near the end of the belt in the width direction, and a large tensile stress is applied to the carcass ply in this vicinity, and are particularly likely to occur in vehicles with high loads. Such pinch cuts may cause the tire to burst, so it is necessary to suppress their occurrence. Patent Document 1 shows a pneumatic tire that is said to have improved pinch cut resistance without a significant increase in tire weight by adjusting the ratio of the developed width of the tread to the maximum width of the tire and the curvature radius of the profile line of the sidewall divided into multiple parts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-108986 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in the potholes, rainwater accumulates during rainy weather, so tires are required to have both pinch cut resistance and drainage. The above-mentioned Patent Document 1 does not describe measures for pinch cut resistance and drainage in heavy-duty vehicles, so there is room for improvement.

[0006] An object of the present invention is to provide a pneumatic tire that has sufficient pinch cut resistance and drainage performance even for a heavy-load vehicle. [Means for solving the problem]

[0007] The pneumatic tire of the present invention is a pneumatic tire including a pair of beads, a pair of sidewalls extending radially outward from each of the pair of beads, a tread disposed between the pair of sidewalls, and a carcass ply embedded inside the tire, the tread including a belt and a tread rubber disposed radially outward from the belt and having a tread surface on its outer surface, the belt including at least an inner belt having a greatest width, and an outer belt disposed radially outward from the inner belt and having a second largest width after the inner belt, the tread surface including a plurality of lands extending in a circumferential direction of the tire and a plurality of lands extending in a circumferential direction of the tire. and a plurality of main grooves dividing the land in the tire axial direction, the land having a shoulder land arranged at the axial end of the tread surface, the main groove having a shoulder main groove adjacent to the axially inner side of the shoulder land, the shoulder land extending in a direction intersecting the tire circumferential direction and having a plurality of lug grooves aligned in the tire circumferential direction, in the tire axial cross section, the axially outer end of the inner belt is located axially outer than the tread ground contact edge A at a load of 130% of the maximum load in the ETRTO tire standard, and the depth of the lug groove gradually decreases toward the outer side in the tire axial direction, and the lug groove gradually increases in width from the tread ground contact edge A toward the outer side in the tire axial direction. Effect of the Invention

[0008] According to the present invention, it is possible to provide a pneumatic tire that has sufficient pinch cut resistance and drainage performance even for a heavy-load vehicle. [Brief description of the drawings]

[0009] [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 4] FIG. 11 is a partial plan view of a tire showing a modified tread pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] 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.

[0012] 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."

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The belt 31 is a member that reinforces the tread 30. 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. The inner belt 32 and the outer belt 33 each 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, and the tire axial outer end 32a of the inner belt 32 is located outside the tire axial outer end 33a of the outer belt 33 in the tire axial direction. That is, the belt 31 of the embodiment includes the inner belt 32 that is the widest, and the outer belt 33 that is arranged on the tire radial outer side of the inner belt 32 and has the second largest width after the inner belt 32. By providing the belt 31, the rigidity of the tire 1 is ensured, and the 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 structure of three or more layers.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 .

[0035] 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.

[0036] 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.

[0037] 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".

[0038] 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.

[0039] Next, the features of the present disclosure, including the lug grooves 92, will be described in more detail with reference to Figures 1 to 3. Figure 3 is a part of Figure 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 Figure 3, hatching of the cross section is omitted in order to clearly show dimension lines, symbols, etc.

[0040] In FIG. 3, TW130 indicates the half contact width, which is the half of the contact width of the tread surface 36 on the right side of the tire equatorial plane S1, at a load of 130% of the maximum load of the tire standard ETRTO. This half tread contact width TW130 is half the length of the tire axial direction where the tread surface 36 contacts the road surface. Also, in FIG. 3, 130E indicates the tread end, which is the end of the half tread contact width TW130 in the tire axial direction. The tread end 130E is the tread end A at a load of 130% of the maximum load of the tire standard ETRTO of the present disclosure. The half tread contact width TW130 is also shown in FIG. 2.

[0041] 2, the lug groove 92 has a gentle arc shape in a plan view. The lug groove 92 is disposed on the extension of the intermediate lateral groove 93 so as to extend axially outward from the intermediate lateral groove 93 adjacent to the axially inner side of the lug groove 92. The axially inner end of the lug groove 92 communicates with the shoulder main groove 82. Meanwhile, the axially outer end of the lug groove 92 communicates with the outer surface of the sidewall 20. The axially inner end of the lug groove 92 may not communicate with the shoulder main groove 82.

[0042] 1 and 3, the lug grooves 92 are formed from the tread 30 through the shoulder 40 to the sidewall 20. The depth of the lug grooves 92 gradually decreases from the axially inner side to the axially outer side of the tire. The depth of the lug grooves 92 on the tread 30 side is greater than the depth on the sidewall 20 side. The depth of the lug grooves 92 on the sidewall 20 side is smaller than the depth on the tread 30 side, for example, by 5% to 10%.

[0043] 2, the width of the lug groove 92 gradually increases from the tread edge 130E toward the axially outer side of the tire, and the lug groove 92 expands in a generally fan-like shape. That is, the lug groove 92 has a widened portion 92w that expands in a fan-like shape from the tread edge 130E toward the axially outer side of the tire.

[0044] As shown in FIG. 3, in the tire axial cross section, the axially outer end 32a of the inner belt 32 of the belt 31 is located axially outer (to the right in FIG. 3) than the tread contact end 130E at a load of 130% of the maximum load in the tire standard ETRTO.

[0045] The tire 1 is repeatedly subjected to flexural deformation during running, and distortion is relatively large, particularly near the axially outer end of the belt 31, which tends to cause large distortion in the shoulder land 72 having the lug groove 92. Here, in the tire 1 of the embodiment, the axially outer end 32a of the inner belt 32 of the belt 31 is located axially outboard of the tread ground edge 130E under high load, such as a load of 130% of the maximum load in the tire standard ETRTO. Therefore, even under such high load, the rigidity of the shoulder land 72 is ensured by the inner belt 32. By ensuring the rigidity of the shoulder land 72 in this way, the expansion of the carcass ply 50 near the axially outer end of the belt 31 is suppressed, and the occurrence of pinch cuts in which the cords of the carcass ply 50 break is suppressed.

[0046] As described above, the lug grooves 92 of the tire 1 of the embodiment have a depth that gradually decreases toward the tire axially outward, and in addition, the lug grooves 92 have a width that gradually increases toward the tire axially outward from the tread edge 130E, and have a widened portion 92w. Since the depth of the lug grooves 92 gradually decreases toward the tire axially outward, the rubber thickness is ensured and the rigidity of the shoulder land 72 is ensured. Since the width of the lug grooves 92 gradually increases toward the tire axially outward from the tread edge 130E, drainage is ensured. Therefore, even under high loads such as 130% of the maximum load of the ETRTO tire standard, durability against pinch cuts, i.e., pinch cut resistance, is ensured, and drainage by the lug grooves 92 is ensured. Therefore, high drainage is exhibited under normal loads, which are 100% load or less.

[0047] As shown in FIG. 3, the tire axial distance L1 between the tire axially outer end 32a of the inner belt 32 of the belt 31 and the tread ground edge 130E is preferably within 15% of the tread ground half width TW130. This improves the vertical rigidity near the tread ground edge 130E and improves pinch cut resistance. If the distance L1 is located axially outwardly of the tire beyond 15% of the tread ground half width TW130, the shoulder 40 becomes too rounded, which makes it easy for block chipping, in which the surface layer of the shoulder land 72 is partially chipped off, and uneven wear to occur. For this reason, the distance L1 is preferably within 15% of the tread ground half width TW130.

[0048] 3, in the tire axial cross section, the rubber thickness forming the shortest distance from the tire axially outer end 33a of the outer belt 33 of the belt 31 to the tire outer surface is shown as H1. Also, in Fig. 3, the rubber thickness forming the distance from the tire axially outer end 33a of the outer belt 33 to the intersection M1 with the bottom surface 92b of the lug groove 92 on a line D1 that is parallel to the line defining the rubber thickness H1, intersects with the bottom surface 92b of the lug groove 92, and passes through the tire axially outer end 33a of the outer belt 33 is shown as H2.

[0049] In the tire 1 of the embodiment, the ratio of H1 to H2: H2 / H1 is preferably 40% or more and 70% or less. H2 in Fig. 3 indicates the rubber thickness when H2 / H1 is about 40%, and (H2) in Fig. 3 indicates the rubber thickness when H2 / H1 is about 70%. (H2) indicates the rubber thickness when the thickness of the tread rubber 35 in the portion corresponding to the lug groove 92 is larger than that in the case of H1, and the bottom surface 92b of the lug groove 92 is indicated by the two-dot chain line. It is preferable that the bottom surface 92b of the lug groove 92 shown in Fig. 3 is between the solid line and the two-dot chain line in H2.

[0050] When the ratio of H1 to H2, H2 / H1, is 40% or more and 70% or less, the vertical rigidity near the tread ground contact edge 130E is maintained and pinch cut resistance is improved, while drainage by the lug grooves 92 is ensured, even under high loads such as 130% of the maximum load in the ETRTO tire standard. From the viewpoint of suppressing distortion, it is desirable for the rubber thickness H2 to be as large as possible, but on the other hand, if the rubber thickness is too large, the depth of the lug grooves 92 may become small, which may lead to a decrease in drainage. Therefore, by making H2 / H1 40% or more and 70% or less as described above, a good balance is achieved between pinch cut resistance due to improved rigidity and drainage.

[0051] In FIG. 3, the rubber thickness forming the shortest distance from the tire axially outer end 32a of the inner belt 32 of the belt 31 to the tire outer surface is shown as H3. This rubber thickness H3 is formed by the sidewall rubber 21 on the tire outer surface side and the tread rubber 35 arranged on the tire cavity side of the sidewall rubber 21, and in the tire 1 of the embodiment, it is preferable that the rubber thickness occupied by the tread rubber 35 is 80% or more of the rubber thickness H3. Since the tread rubber 35 has better bending resistance than the sidewall rubber 21, the rubber thickness occupied by the tread rubber 35 is 80% or more of the rubber thickness H3, so that the bending resistance of the belt 31 near the end in the tire axial direction is improved. As a result, the pinch cut resistance is improved. Note that the rubber thickness occupied by the tread rubber 35 may be 100% of the rubber thickness H3, that is, only the tread rubber 35.

[0052] 3, H4 denotes the rubber thickness that defines the distance from the axially outer end 32a of the inner belt 32 to an intersection M2 with the bottom surface 92b of the lug groove 92 along a line D2 that is parallel to the line defining the rubber thickness H3, intersects the bottom surface 92b of the lug groove 92, and passes through the axially outer end 32a of the inner belt 32. In the tire 1 of the embodiment, it is preferable that H4 and the above H1, H2, and H3 satisfy "1.5≦(H1-H2) / (H3-H4)≦8.0".

[0053] When the above formula is satisfied, the rubber thickness increases from the tread edge 130E to the axially outer side of the tire, improving vertical rigidity and pinch cut resistance. In addition, the volume of the lug grooves 92 is secured, ensuring drainage.

[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 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, and a carcass ply 50 that is bridged between the pair of beads 10 and embedded inside the tire, the tread 30 including a belt 31 and a tread rubber 35 that is disposed radially outward from the belt 31 and has a tread surface 36 on its outer surface, the belt 31 including at least an inner belt 32 that is the widest, and an outer belt 33 that is disposed radially outward from the inner belt 32 and has a width second to that of the inner belt 32, the tread surface 36 including a plurality of lands 70 extending in the tire circumferential direction and a plurality of lands 71 ​​extending in the tire circumferential direction. and a plurality of main grooves 80 dividing a number of lands 70 in the tire axial direction, the lands 70 having shoulder lands 72 arranged at the ends of the tread surface 36 in the tire axial direction, the main groove 80 having shoulder main grooves 82 adjacent to the axially inner sides of the shoulder lands 72, the shoulder lands 72 extending in a direction intersecting the tire circumferential direction and having a plurality of lug grooves 92 arranged in the tire circumferential direction, in the tire axial cross section, the tire axially outer end 32a of the inner belt 32 is located axially outer than a tread ground edge 130E at a load of 130% of the maximum load of the tire standard ETRTO, and the depth of the lug grooves 92 gradually decreases toward the outer side in the tire axial direction, and the lug grooves 92 gradually increase in width from the tread ground edge 130E toward the outer side in the tire axial direction.

[0056] As a result, the tire 1 according to the embodiment exhibits sufficient pinch cut resistance and drainage performance even under a high load that reaches 130% of the maximum load specified by the ETRTO tire standard.

[0057] (2) In the tire 1 of the above embodiment (1), when the half tread contact width at a load of 130% of the maximum load of the tire standard ETRTO is TW130, it is preferable that the axial distance between the axially outer end 32a of the inner belt 32 and the tread contact end 130E is within 15% of the half tread contact width TW130.

[0058] This suppresses block chipping and uneven wear in the shoulder land 72, and improves vertical rigidity in the vicinity of the tread ground contact edge 130E, thereby improving pinch cut resistance.

[0059] (3) In the tire 1 according to the above embodiments (1) and (2), when the rubber thickness forming the shortest distance from the tire axially outer end 33a of the outer belt 33 to the tire outer surface in the tire axial cross section is H1, and the rubber thickness forming the distance from the tire axially outer end 33a of the outer belt 33 to the intersection M1 with the bottom surface 92b of the lug groove 92 on a straight line D1 that is parallel to the straight line defining the rubber thickness H1, intersects the bottom surface 92b of the lug groove 92, and passes through the tire axially outer end 33a of the outer belt 33, is H2, it is preferable that the ratio of H1 to H2: H2 / H1 is 40% or more and 70% or less.

[0060] As a result, the tire 1 according to the embodiment exhibits sufficient pinch cut resistance and drainage performance even under a high load that reaches 130% of the maximum load specified by the ETRTO tire standard.

[0061] (4) In the tire 1 according to the above embodiments (1) to (3), when the rubber thickness forming the shortest distance from the axially outer end 32a of the inner belt 32 to the outer surface of the tire is defined as H3, it is preferable that the rubber thickness accounted for by the tread rubber 35 at the rubber thickness H3 is 80% or more.

[0062] This improves the bending resistance of the belt 31 near the ends in the tire axial direction, and as a result, improves pinch cut resistance.

[0063] (5) In the above embodiments of tire 1 (1) to (4), when the rubber thickness forming the distance from the axially outer end 32a of the inner belt 32 to the intersection point M2 with the bottom surface 92b of the lug groove 92 on a line D2 that is parallel to the line defining the rubber thickness H3, intersects the bottom surface 92b of the lug groove 92, and passes through the axially outer end 32a of the inner belt 32, is H4, it is preferable that H1, H2, H3, and H4 satisfy "1.5≦(H1-H2) / (H3-H4)≦8.0".

[0064] As a result, the rubber thickness increases from the tread ground contact edge 130E to the axially outer side of the tire, improving vertical rigidity and improving pinch cut resistance, while the volume of the lug grooves 92 is secured, improving drainage.

[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] (Modification) Next, a modified example of the tread pattern 39 of the above embodiment will be described with reference to Fig. 4. Fig. 4 is a partial plan view of the tire 1, corresponding to Fig. 2, showing a modified tread pattern 39. In Fig. 4, components common to the tread pattern 39 of the above embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0068] The tread pattern 39 of the 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, intermediate lateral grooves 93 that extend from the shoulder main grooves 82 toward the axially inner side at an angle with respect to the tire circumferential direction cross the intermediate main grooves 81 to a position straddling the tire equator S2, and their leading ends communicate with each other by merging with the leading ends of the intermediate lateral grooves 93 on the axially opposite side. This tread pattern 39 does not have the central lateral groove 91 of the above embodiment. The leading ends of the left and right intermediate lateral grooves 93 on the axially inner side straddling the tire equator S2 communicate with each other and extend in a zigzag shape so as to alternately cross the tire equator S2.

[0069] In the modified tread pattern 39, the lug grooves 92 also gradually increase in width from the tread edge 130E toward the tire axially outward, widening in a generally fan-like shape. That is, the lug grooves 92 have a widened portion 92w that widens in a fan-like shape from the tread edge 130E toward the tire axially outward. By having the widened portion 92w, drainage by the lug grooves 92 is ensured even under high loads such as 130% of the maximum load of the ETRTO tire standard.

[0070] 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.

[0071] (Experimental Example) Next, an experimental example will be described.

[0072] Tires of Experimental Examples 1 to 6 having the same configuration as the above-mentioned embodiment and varying the above-mentioned rubber thicknesses H1, H2, H3, and H4 to vary "(H1-H2) / (H3-H4)" were actually manufactured, and pinch cut resistance and drainage were evaluated. Table 1 shows the data of Experimental Examples 1 to 6, along with their evaluation. The pinch cut resistance was evaluated by performing an extended durability test in accordance with FMVSS 139, and the time until the carcass ply broke was indexed, with the tire of Experimental Example 1 being set at 100. The drainage was evaluated by driving a vehicle into a wet road surface with a water depth of 10 mm at a speed of 50 km / h, which is a speed at which hydroplaning does not occur, and then accelerating the vehicle within the measurement section at a speed of 5 km / h, and the speed at which hydroplaning occurred, causing the test tire to spin, was indexed, with the tire of Experimental Example 1 being set at 100.

[0073] For the pinch cut resistance and drainage in Table 1, each value of Experimental Example 1 is assigned an index of 100, and the other values ​​are evaluated as an index in comparison with Experimental Example 1. For pinch cut resistance, the higher the index evaluation value, the less likely pinch cuts are to occur and the higher the pinch cut resistance. For drainage, the higher the index evaluation value, the higher the drainage.

[0074] [Table 1]

[0075] According to Table 1, when the value of "(H1-H2) / (H3-H4)" is small, such as in Experimental Example 2, which is less than 1.5, the pinch cut resistance is high but the drainage tends to decrease. Experimental Examples 3 to 6, in which the value of "(H1-H2) / (H3-H4)" is 1.5 or more and 8.0 or less, have a stable pinch cut resistance at a higher level than Experimental Example 1. In addition, regarding the drainage, Experimental Examples 3 to 6 maintain a level equivalent to or slightly lower than that of Experimental Example 1, but which is not problematic in practical use. Therefore, by satisfying "1.5≦(H1-H2) / (H3-H4)≦8.0", the pinch cut resistance and drainage are ensured at a balanced level without problems. [Explanation of symbols]

[0076] 1... tire (pneumatic tire), 10... bead, 20... sidewall, 30... tread, 31... belt, 32... inner belt, 32a... axially outer end of inner belt, 33... outer belt, 33a... axially outer end of outer belt, 35... tread rubber, 36... tread surface, 40... shoulder, 50... carcass ply, 70... land, 72... shoulder land, 80... main groove, 82... shoulder main groove, 92... lug groove, 92b... bottom surface of lug groove, 92c... axially outer end of lug groove, 130E... tread ground edge A, TW130... tread ground half width.

Claims

1. A pair of beads; a pair of sidewalls extending radially outward from each of the pair of beads; a tread disposed between the pair of sidewalls; A carcass ply that is bridged between the pair of beads and embedded inside the tire, The tread includes a belt and a tread rubber disposed on the outer side of the belt in the tire radial direction and having a tread surface on its outer surface, The belt includes at least an inner belt having a largest width, and an outer belt arranged radially outward of the inner belt and having a second largest width after the inner belt, 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 extends in a direction intersecting the tire circumferential direction and has a plurality of lug grooves aligned in the tire circumferential direction, In the tire axial cross section, an axially outer end of the inner belt is located axially outward of a tread ground contact end A at a load of 130% of the maximum load in the ETRTO tire standard, and the depth of the lug groove is gradually decreased toward the axially outer side of the tire, The lug grooves have a width that gradually increases from the tread ground contact edge A toward the outside in the tire axial direction.

2. 2. The pneumatic tire according to claim 1, wherein when a half tread contact width is TW130 at a load of 130% of a maximum load in the ETRTO tire standard, a distance in the tire axial direction between an axially outer end of the inner belt and the tread contact end A is within 15% of the half tread contact width TW130.

3. In the tire axial cross section, 3. The pneumatic tire according to claim 1 or 2, wherein a rubber thickness forming the shortest distance from the axially outer end of the outer belt to the outer surface of the tire is defined as H1, and a rubber thickness forming a distance from the axially outer end of the outer belt to an intersection point with the bottom surface of the lug groove on a straight line that is parallel to a straight line defining the rubber thickness H1, intersects the bottom surface of the lug groove, and passes through the axially outer end of the outer belt, a ratio of H1 to H2: H2 / H1 is 40% or more and 70% or less.

4. 3. The pneumatic tire according to claim 1, wherein when a rubber thickness forming the shortest distance from an axially outer end of the inner belt to an outer surface of the tire is H3, a rubber thickness occupied by the tread rubber at the rubber thickness H3 is 80% or more.

5. In the tire axial cross section, 3. The pneumatic tire according to claim 1 or 2, wherein H4 is a rubber thickness that defines a distance from an axially outer end of the inner belt to an intersection point with the bottom surface of the lug groove on a straight line that is parallel to a straight line defining the rubber thickness H3, intersects the bottom surface of the lug groove, and passes through the axially outer end of the inner belt, and H1, H2, H3, and H4 satisfy "1.5≦(H1-H2) / (H3-H4)≦8.0".

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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