pneumatic tires

Abstract

To provide a pneumatic tire which can suppress uneven wear of a shoulder land where a plurality of sipes extending in a tire axial direction are formed on a tread and suppress separation trouble at a belt end.SOLUTION: A pneumatic tire 1 includes a plurality of lateral sipes 60 which are arranged at different positions of a lateral surface 21 in a tire circumferential direction relative to tread sipes 40, depressed to inner side in a tire axial direction, and extending in a tire radial direction. The plurality of lateral sipes 60 with respect to interval between a pair of axial grooves 26 includes: inner lateral face sipes 60a which are positioned in a central side in the tire circumferential direction; and outer lateral face sipes 60b which are positioned in an axial groove 26 side relative to the inner lateral face sipes 60a. Length of the inner lateral face sipe 60a in the tire radial direction is shorter than that of the outer lateral face sipe 60b in the tire radial direction, and a first distance X1 from the outer lateral face sipe 60b to a belt end 19 is 8 mm or more.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a pneumatic tire designed to reduce wear on the shoulder land located at the axially outer end of the tread. This pneumatic tire has a first sipe formed on the side surface located at the axially outer end of the shoulder land, recessed axially inward, extending radially, and terminating at a distance from the tread surface of the shoulder land. Patent Document 1 also discloses a configuration in which a second sipe is formed on the tread surface located at the radially outer end of the shoulder land, between a pair of circumferentially adjacent first sipes, recessed radially inward, extending axially, and opening on the side surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 3-506 Summary of the Invention [Problem to be solved by the invention]

[0004] In a pneumatic tire having multiple axial grooves recessed radially inward from the tread, extending axially and opening at the side, spaced apart in the circumferential direction of the tire on the shoulder land, when the above-mentioned second sipes are provided, uneven wear is likely to occur in the center between a pair of circumferentially adjacent axial grooves. This is because, when a force is applied to the tread, the rigidity of the center between a pair of axial grooves is more likely to decrease and the relative amount of displacement is greater than that of the circumferentially outer grooves. Therefore, the pneumatic tire of Patent Document 1 has room for improvement in terms of measures to prevent uneven wear on the shoulder land.

[0005] Furthermore, for example, if the axial depth of the first sipe is large, the thickness from the belt located radially inward of the tread to the first sipe becomes smaller, which tends to reduce rigidity near the belt end, potentially causing separation failure at the belt end.

[0006] Therefore, the present invention aims to provide a pneumatic tire that suppresses uneven wear on the shoulder land, where multiple sipes extending in the axial direction of the tire are formed on the tread, and also suppresses separation failure at the belt end. [Means for solving the problem]

[0007] First, the present invention provides a tire having a tread located at an outer end in a tire radial direction and extending in a tire circumferential direction, a plurality of belts located radially inward of the tread, extending in a tire circumferential direction, and having belt ends located at outer ends in an axial direction of the tire; a shoulder land located at an outer end of the tread in the tire axial direction, the shoulder land having a tread surface located at an outer end of the tread in the tire radial direction and a side surface located axially outward of the tread surface; a plurality of axial grooves provided at intervals in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread surface, extending in the tire axial direction, and opening at the side surface; a plurality of tread sipes provided at intervals in the tire circumferential direction between a pair of axial grooves adjacent in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread, extending in the tire axial direction and terminating at a position spaced apart from the side surface; a plurality of side sipes provided on the side surface at different positions in the tire circumferential direction relative to the tread sipes, recessed inward in the tire axial direction, and extending in the tire radial direction, the plurality of side sipes including an inner side sipe located closer to the center in the tire circumferential direction within the interval between the pair of axial grooves, and an outer side sipe located closer to the axial groove than the inner side sipe, the length in the tire radial direction of the inner side sipe being shorter than the length in the tire radial direction of the outer side sipe, and the plurality of side sipes being configured such that a first distance from the outer side sipe to the belt end is 8 mm or more; To provide a pneumatic tire comprising:

[0008] According to the present invention, since the inner side sipe and the outer side sipe are provided at different positions in the tire circumferential direction relative to the tread sipe, excessive reduction in stiffness of the shoulder land is suppressed compared to when the tread sipe and the side sipe are provided at the same position in the tire circumferential direction, and therefore the occurrence of cracks originating from the tread sipe and the side sipe is suppressed.

[0009] Furthermore, because the radial length of the inner side sipe is shorter than the radial length of the outer side sipe, the rigidity of the outer circumferential portion of the space between the pair of axial grooves on the shoulder land can be made lower than the rigidity of the central portion in the circumferential direction. This optimizes the circumferential rigidity balance between the pair of axial grooves. This averages out the amount of circumferential displacement when a force is applied to the tread, effectively suppressing uneven wear in the central portion in the circumferential direction.

[0010] Furthermore, since the first distance from the outer side sipe to the belt edge is 8 mm or more, the thickness from the outer side sipe to the belt edge is appropriately set, ensuring rigidity near the belt edge, thereby suppressing separation failure at the belt edge.

[0011] The first distance may be 30% or more and 80% or less of a second distance from the belt end to the tread surface.

[0012] According to this configuration, the first distance is 30% to 80% of the second distance from the belt end to the tread surface, so the thickness from the outer side sipe to the belt end is appropriately set. This ensures rigidity near the belt end, suppresses separation failure at the belt end, and improves heat dissipation at the side. For example, compared to when the first distance is less than 30% of the second distance, the thickness from the outer side sipe to the belt end is greater, ensuring rigidity near the belt end. This suppresses separation failure at the belt end. Furthermore, compared to when the first distance is less than 30% of the second distance, the axial depth of the outer side sipe is smaller, making it less likely for sand, dust, and other particles to become trapped inside the outer side sipe. This ensures that the outer side sipe remains open, ensuring the optimal circumferential rigidity balance of the tire. Furthermore, compared to when the first distance is greater than 80% of the second distance, the thickness from the outer side sipe to the belt end is smaller, ensuring heat dissipation from the outer side sipe. Therefore, the heat dissipation performance of the side surface can be improved.

[0013] Further, the outer side sipe has an inner wall extending from an inner end in the tire radial direction to an inner end in the tire axial direction, The inner wall may have an arc portion whose radius of curvature about the belt end is the first distance.

[0014] According to this configuration, the inner wall formed from the radially inner end of the outer side sipe to the axially inner end has an arc portion with a curvature radius of the first distance centered on the belt end, so that the length of the portion from the outer side sipe to the belt end where the distance is the first distance can be secured widely. Therefore, rigidity near the belt end is secured, and separation failure at the belt end is suppressed.

[0015] Further, the arc portion extends outward in the tire axial direction from a reference line extending in the tire radial direction within a range of 10 degrees to 60 degrees from the reference line, The first distance may be equal to or less than a third distance from the belt end to the side surface.

[0016] According to this configuration, the arc portion having a radius of curvature equal to a first distance, which is equal to or less than a third distance from the belt end to the side, extends from a reference line extending in the tire radial direction outward in the tire axial direction within a range of 10 degrees to 60 degrees. Therefore, the length of the arc portion having a radius of curvature smaller than the third distance is appropriately set, ensuring heat dissipation from the outer side sipe. Therefore, even when the above-described outer side sipe is applied to a pneumatic tire with a large third distance, heat dissipation from the side can be improved. For example, compared to when the arc portion extends from a reference line extending in the tire radial direction outward in the tire axial direction within a range exceeding 60 degrees, rigidity near the belt end is ensured. Therefore, separation failure at the belt end is suppressed.

[0017] The inclination angle of the inner end in the axial direction of the outer side sipe may be equal to or greater than 0 degrees and equal to or less than 15 degrees toward the outer side in the axial direction of the tire with respect to a reference line extending in the radial direction of the tire.

[0018] According to this configuration, the inclination angle of the axially inner end of the outer side sipe is between 0 and 15 degrees outward in the axial direction relative to a reference line extending in the tire radial direction, thereby appropriately setting the length of the arc portion. This ensures the rigidity of the shoulder land, suppressing the occurrence of cracks originating from the tread sipes and side sipes, and improving the heat dissipation performance of the side. For example, compared to when the inclination angle is less than 0 degrees, the thickness from the outer side sipe to the tread sipe is greater, ensuring the rigidity of the shoulder land. This suppresses the occurrence of cracks originating from the tread sipes and side sipes. Furthermore, compared to when the inclination angle is greater than 15 degrees, the length of the arc portion is greater, ensuring the heat dissipation performance of the outer side sipe. This improves the heat dissipation performance of the side.

[0019] The width of the side sipe in the tire circumferential direction may be 1.5 mm or less.

[0020] According to this configuration, the width of the side sipes in the tire circumferential direction is 1.5 mm or less, which prevents excessive reduction in stiffness of the shoulder land compared to when the width of the side sipes in the tire circumferential direction is greater than 1.5 mm, thereby preventing cracks from occurring that originate from the side sipes. [Effects of the Invention]

[0021] Therefore, the pneumatic tire according to the present invention suppresses uneven wear on the shoulder land where a plurality of sipes extending in the tire axial direction are formed on the tread surface, and also suppresses separation failure at the belt end. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a meridian cross-sectional view of a pneumatic tire according to one embodiment of the present invention. [Figure 2] 2 is a development view of the tread of the pneumatic tire of FIG. 1 developed in the tire circumferential direction. [Figure 3] FIG. 3 is an enlarged view of part III in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] 3 is a development view of the outer shoulder block and side surface of the pneumatic tire of FIG. 2 developed in the tire circumferential direction and the tire axial direction. [Figure 6] 5 is a graph showing the relationship between the strain energy density and the first distance in FIG. 4. [Figure 7] FIG. 10 is a meridian cross-sectional view of a pneumatic tire according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0024] Fig. 1 is a meridian cross-sectional view of a pneumatic tire (hereinafter simply referred to as "tire") 1 according to one embodiment of the present invention. The tire 1 of this embodiment is configured as a rubber tire for light trucks or trucks and buses. In this embodiment, the direction toward the tire equator is referred to as the inner side in the tire axial direction, and the direction away from the tire equator is referred to as the outer side in the tire axial direction.

[0025] [Tire structure] The tire 1 includes a tread 11 extending in the tire axial direction, which is shown in the left-right direction in FIG. 1, a pair of sidewalls 12 extending from both ends of the tread 11 inward in the tire radial direction, which is shown in the up-down direction in FIG. 1, and a pair of beads 13 respectively disposed at the inner ends of the pair of sidewalls 12 in the tire radial direction.

[0026] The tread 11 extends in the tire circumferential direction shown in the front-rear direction in FIG. 1 so as to extend cylindrically around the axis of the tire 1.

[0027] Each bead 13 includes a bead core 14 disposed radially inward of the tire, and a bead filler 15 disposed radially outward of the bead core 14. The bead core 14 includes a number of steel wires bundled into a ring shape. The bead filler 15 is ring-shaped and made of rubber that is harder than the rubber that constitutes the tread 11 and sidewall 12. The bead filler 15 extends radially outward from the bead core 14 in a direction inclined outward in the tire axial direction.

[0028] The tire 1 includes an inner liner 16 that extends from the inner end of the tread 11 in the tire radial direction to the inner end of the sidewall 12 in the tire axial direction and the inner end of the bead 13 in the tire axial direction. A carcass 17 is laminated on the outside of the inner liner 16 and is toroidally stretched between the pair of beads 13.

[0029] The carcass 17 is folded back and wound around the bead cores 14 in a direction inclined outward in the tire radial direction toward the outside in the tire axial direction.

[0030] Between the tread 11 and the carcass 17, a belt layer 18 extending in the tire circumferential direction is disposed.

[0031] The belt layer 18 has a plurality of belt plies laminated in the tire radial direction. In this embodiment, the belt layer 18 has two belt plies, that is, a first belt ply 18a on the inner side in the tire radial direction and a second belt ply 18b on the outer side in the tire radial direction.

[0032] The axial length of the first belt ply 18a is longer than the axial length of the second belt ply 18b. In this embodiment, the axially outermost belt end 19 of the belt layer 18 according to the present invention is configured at the axially outer end of the first belt ply 18a.

[0033] [tread] As shown in Fig. 1, the tread 11 is located at the outer edge in the tire's radial direction and has a tread surface 20, which is the contact surface that comes into contact with the ground during rolling, and a side surface 21 that extends from the axial outer edge of the tread surface 20 in a direction that slopes inward in the tire radial direction toward the outer side in the tire axial direction. The tread 11 also has a plurality of main grooves 22 that extend circumferentially at intervals in the tire axial direction. In this embodiment, of the plurality of main grooves 22, one that is located at the tire equator is referred to as a central main groove 22a, and the two that are located axially outward of the central main groove 22a are referred to as outer main grooves 22b.

[0034] Fig. 2 is a circumferentially developed view of the tread 11 of the tire 1 of Fig. 1. A plurality of lands 23 extending in the circumferential direction of the tire are defined in the tread 11 by one central main groove 22a and a pair of outer main grooves 22b. In this embodiment, four rows of lands 23 are defined, but the number of main grooves 22 and the number of lands 23 can be changed as needed.

[0035] Of the multiple lands 23, two located between the center main groove 22a and each of the two outer main grooves 22b are referred to as center lands 23a, and two located axially outboard of each of the two outer main grooves 22b are referred to as shoulder lands 23b.

[0036] 3 is an enlarged view of part III in FIG. 2, showing the area around the shoulder land 23b. The shoulder land 23b has a circumferential groove 24 that passes through the center of the width of the shoulder land 23b and extends in the tire circumferential direction. Each shoulder land 23b is divided by the circumferential groove 24 and has an outer shoulder land row 25a adjacent to the side surface 21 and an inner shoulder land row 25b adjacent to the outer main groove 22b.

[0037] A plurality of axial grooves 26 extending in the tire axial direction are formed in each shoulder land 23b at intervals in the tire circumferential direction.

[0038] Of the multiple axial grooves 26, the axial grooves 26 arranged in the shoulder landward row 25a are each referred to as outer axial grooves 26a, and the axial grooves 26 arranged in the shoulder landward row 25b are each referred to as inner axial grooves 26b.

[0039] Axial inner ends of the outer axial grooves 26a communicate with the circumferential grooves 24. Axial outer ends of the outer axial grooves 26a open at the side surfaces 21 and are open to the outside in the axial direction of the tire.

[0040] The axially inner ends of the inner axial grooves 26b communicate with the outer main grooves 22b, and the axially outer ends of the inner axial grooves 26b communicate with the circumferential grooves 24.

[0041] The groove width W1 of the outer main groove 22b is larger than the groove width W2 of the circumferential groove 24. The groove width W3 of the axial groove 26 is smaller than the groove width W1 of the outer main groove 22b but larger than the groove width W2 of the circumferential groove 24.

[0042] 4 is a cross-sectional view taken along line IV-IV in FIG. 3, and is a meridian cross-sectional view passing through tread sipes 40 and side sipes 60, which will be described later. The depth D1 of the outer main groove 22b is greater than the depth D2 of the circumferential groove 24. The depth D3 of the axial groove 26 is smaller than the depth D1 of the outer main groove 22b but is the same as the depth D2 of the circumferential groove 24. In this embodiment, the depth D2 of the circumferential groove 24 and the depth D3 of the axial groove 26 are the same, but may be different as long as they are smaller than the depth D1 of the outer main groove 22b.

[0043] Each center land 23a has a center rib 27 located radially inward of the center land 23a and a plurality of center blocks 28 located radially outward of the center rib 27. Each shoulder land 23b has a shoulder rib 29 located radially inward of the shoulder land 23b and a plurality of shoulder blocks 30 located radially outward of the shoulder rib 29.

[0044] Of the multiple shoulder blocks 30, the shoulder blocks 30 arranged in the shoulder landward row 25a are each referred to as outer shoulder blocks 30a, and the shoulder blocks 30 arranged in the shoulder landward row 25b are each referred to as inner shoulder blocks 30b.

[0045] In the shoulder land 23b, the shoulder ribs 29 are defined in the axial direction by the side surfaces 21 and the outer main grooves 22b. In the outer row 25a of the shoulder land, the outer shoulder blocks 30a are defined by the side surfaces 21, the circumferential grooves 24, and a pair of circumferentially adjacent outer axial grooves 26a. In the inner row 25b of the shoulder land, the inner shoulder blocks 30b are defined by the circumferential grooves 24, the outer main groove 22b, and a pair of circumferentially adjacent inner axial grooves 26b.

[0046] 3, the positions of the outer axial grooves 26a in the inland shoulder row 25a and the inner axial grooves 26b in the inland shoulder row 25b are different in the tire circumferential direction, and therefore the positions of the outer shoulder blocks 30a and the inner shoulder blocks 30b are also different in the tire circumferential direction.

[0047] In this embodiment, the shape of the shoulder blocks 30 is rectangular when viewed from the outside in the tire radial direction, but this can be modified as needed. For example, the circumferential grooves 24 are formed linearly in the tire circumferential direction, but may also be formed in a zigzag pattern in the tire axial direction along the tire circumferential direction. Furthermore, the axial grooves 26 are formed linearly in the tire axial direction, but may also be inclined with respect to a line extending in the tire axial direction, or may also be formed in a zigzag pattern in the tire circumferential direction along the tire axial direction.

[0048] [Tread sipes] 3, a plurality of tread sipes 40 are formed on the tread surface 20 of each shoulder block 30. These tread sipes 40 are provided at intervals in the tire circumferential direction between pairs of axial grooves 26 adjacent in the tire circumferential direction of the shoulder block 30, are recessed radially inward from the tread surface 20, extend in the tire axial direction, and terminate at a position spaced apart from the side surface 21. In this embodiment, each tread sipe 40 is formed linearly along the tire axial direction, but may be formed so as to be inclined with respect to a straight line extending in the tire axial direction, or may be formed in a zigzag pattern in the tire circumferential direction along the tire axial direction.

[0049] The tread sipes 40 are respectively arranged at intervals in the tire circumferential direction between pairs of axial grooves 26 adjacent in the tire circumferential direction of the shoulder block 30. In this embodiment, four tread sipes 40 are formed on the shoulder block 30 having a circumferential length of 35 mm.

[0050] The spacing between adjacent tread sipes 40 in the tire circumferential direction is preferably 5 mm or more and 8 mm or less. If the spacing between the tread sipes 40 is less than 5 mm, the rigidity of the tread 20 will be excessively reduced, while if the spacing between the tread sipes 40 is greater than 8 mm, it will be difficult to obtain an appropriate grip force. Therefore, the spacing between adjacent tread sipes 40 is preferably 5 mm or more and 8 mm or less.

[0051] Of the four tread sipes 40, the tread sipes 40 arranged on the outer shoulder blocks 30a are referred to as outer tread sipes 40a, and the tread sipes 40 arranged on the inner shoulder blocks 30b are referred to as inner tread sipes 40b.

[0052] The axially inner ends of the outer tread sipes 40a terminate at positions spaced apart from the circumferential grooves 24. The axially outer ends of the outer tread sipes 40a terminate at positions spaced apart from the side surfaces 21.

[0053] The axially inner ends of the inner tread sipes 40b terminate at positions spaced apart from the outer main grooves 22b. The axially outer ends of the inner tread sipes 40b terminate at positions spaced apart from the circumferential grooves 24.

[0054] 4, the depth D4 of the tread sipes 40 is smaller than the depth D1 of the outer main groove 22b, the depth D2 of the circumferential groove 24, and the depth D3 of the axial groove 26. In this embodiment, the depths D4 of the tread sipes 40 are all the same, but the depth of the outer tread sipes 40a may be different from the depth of the inner tread sipes 40b.

[0055] [side] As shown in Figures 1 and 4, the side surface 21 has a chamfer 51 that extends from the axially outer end of the tread surface 20 of the outer shoulder block 30a in a direction that is inclined radially inward toward the outer side in the tire direction, a main portion 52 that extends from the axially outer end of the chamfer 51 in a direction that is further inclined radially inward toward the outer side in the tire direction, and a continuous portion 53 that extends radially inward from the axially outer end of the main portion 52 and connects to the radially outer end of the sidewall 12.

[0056] An inclination angle A1 of the chamfer 51 with respect to a reference line 54 extending in the tire radial direction is larger than an inclination angle A2 of the main portion 52 with respect to the reference line 54.

[0057] The length D5 of the chamfer 51 in the tire radial direction is smaller than the depth D1 of the outer main groove 22b, the depth D2 of the circumferential groove 24, the depth D3 of the axial groove 26, and the depth D4 of the tread sipe 40.

[0058] In the tire axial direction, the distance L1 from the axially outer end of the outer tread sipe 40a to the axially inner end of the main portion 52 is at least 1.5 times the axial length L2 of the chamfer 51. If the distance L1 between the outer tread sipe 40a and the main portion 52 is less than 1.5 times the length L2 of the chamfer 51, cracks may occur that originate from the axially outer end of the outer tread sipe 40a. Therefore, it is preferable that the distance L1 between the outer tread sipe 40a and the main portion 52 be at least 1.5 times the length L2 of the chamfer 51.

[0059] 5 is a development view of the outer shoulder block 30a and the side surface 21 in the tire circumferential direction and the tire axial direction. Of the multiple outer tread sipes 40a in the outer shoulder block 30a, a pair of outer tread sipes 40a located on the inner side in the tire circumferential direction is referred to as first outer tread sipes 40c, and a pair of outer tread sipes 40a located on the outer side in the tire circumferential direction is referred to as second outer tread sipes 40d.

[0060] The tread surface 20 of the outer shoulder block 30a is divided into a central region 41 located between a pair of first outer tread sipes 40c, an intermediate region 42 located between the first outer tread sipe 40c and the second outer tread sipe 40d, and an outer region 43 located circumferentially outside the second outer tread sipe 40d.

[0061] [Side sipes] As shown in Fig. 3, a plurality of side sipes 60 are formed in the chamfer 51 and main portion 52 of the side surface 21. These side sipes 60 are provided at different positions in the tire circumferential direction relative to the outer tread sipes 40a, are recessed axially inward, and extend radially. In this embodiment, four side sipes 60 are formed on the outer shoulder block 30a.

[0062] Of the four side sipes 60, a pair of side sipes 60 located on the inside in the circumferential direction of the tire are referred to as inner side sipes 60a, and a pair of side sipes 60 located on the outside in the circumferential direction of the tire are referred to as outer side sipes 60b.

[0063] The outer ends in the tire radial direction of the inner side surface sipe 60a and the outer side surface sipe 60b are open at the same position in the tire radial direction in the chamfer 51, and are open to the outside in the tire radial direction.

[0064] The inner ends of the inner side surface sipes 60 a and the outer side surface sipes 60 b in the tire radial direction terminate at positions spaced apart from the continuous portion 53 of the side surface 21 .

[0065] 5, the inner side sipe 60a and the outer side sipe 60b are both located at different positions in the tire circumferential direction relative to the outer tread sipe 40a. Specifically, the radially outer end of the inner side sipe 60a is located in a region in the tire circumferential direction corresponding to the intermediate region 42 of the outer shoulder block 30a. The radially outer end of the outer side sipe 60b is located in a region in the tire circumferential direction corresponding to the outer region 43 of the outer shoulder block 30a.

[0066] The radial length L3 of the inner side sipe 60a is shorter than the radial length L4 of the outer side sipe 60b. Therefore, the outer shoulder block 30a is configured such that its rigidity gradually decreases from the central region 41 toward the outer region 43 due to the difference between the length L3 of the inner side sipe 60a and the length L4 of the outer side sipe 60b.

[0067] The tire radial length L3 of the inner side sipe 60a is 0.25 to 0.45 times the tire radial length L4 of the outer side sipe 60b. If the tire radial length L3 of the inner side sipe 60a is less than 0.25 times the tire radial length L4 of the outer side sipe 60b, the rigidity of the intermediate region 42 will not be sufficiently reduced, which may result in uneven wear in the outer region 43. On the other hand, if the tire radial length L3 of the inner side sipe 60a is more than 0.45 times the tire radial length L4 of the outer side sipe 60b, the rigidity of the intermediate region 42 will be excessively reduced, which may result in uneven wear in the central region 41. Therefore, it is preferable that the tire radial length L3 of the inner side sipe 60a be 0.25 to 0.45 times the tire radial length L4 of the outer side sipe 60b.

[0068] In this embodiment, the inner side sipe 60a and the outer side sipe 60b are each inclined radially inward toward the center in the tire circumferential direction between the pair of outer axial grooves 26a, i.e., toward the center line 61 of the outer shoulder block 30a. In this embodiment, the inner side sipe 60a and the outer side sipe 60b each extend linearly in the tire radial direction from the outer end to the inner end in the tire radial direction, but may be curved so as to approach the center line 61 radially inward.

[0069] The inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b are 5 degrees or more and 15 degrees or less with respect to the center line 61. If the inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b are less than 5 degrees with respect to the center line 61, the inner side sipe 60a and the outer side sipe 60b will extend along the center line 61, making it difficult to gradually reduce the rigidity from the central region 41 toward the outer region 43 of the outer shoulder block 30a. If the inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b are greater than 15 degrees with respect to the center line 61, an overlap will occur between the shorter inner side sipe 60a and the longer outer side sipe 60b when viewed from the outside in the tire radial direction, resulting in an excessive reduction in rigidity in the middle region 42. Therefore, it is preferable that the inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b are 5 degrees or more and 15 degrees or less with respect to the center line 61. In this embodiment, the inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b are the same, but they may be different as long as they are within the above range.

[0070] The circumferential width W4 of the inner side sipe 60a and the circumferential width W5 of the outer side sipe 60b are the same and are 1.5 mm or less. Here, the circumferential widths W4 and W5 do not refer to the distance between the sidewalls of the side sipes 60 strictly along the tire circumferential direction, but rather refer to the distance between the sidewalls of the side sipes 60 in a direction perpendicular to the inclination angle A3 of the inner side sipe 60a and the inclination angle A4 of the outer side sipe 60b. If the circumferential width W4 of the inner side sipe 60a and the circumferential width W5 of the outer side sipe 60b are greater than 1.5 mm, the rigidity of the outer shoulder block 30a will be excessively reduced, which may significantly accelerate wear of the entire outer shoulder block 30a. Therefore, the circumferential width W4 of the inner side sipe 60a and the circumferential width W5 of the outer side sipe 60b are preferably 1.5 mm or less, particularly 0.3 mm to 1.5 mm. For example, the width W4 of the inner side sipe 60a in the tire circumferential direction and the width W5 of the outer side sipe 60b in the tire circumferential direction may be 0.6 mm and 0.8 mm, respectively.

[0071] 4, the outer side sipe 60b has an inner wall 62 extending from the inner end in the tire radial direction to the inner end in the tire axial direction. This inner wall 62 has an arc portion 63 that extends from the inner end in the tire radial direction to the inner end in the tire axial direction, with the outer end in the tire radial direction of the belt end 19 as its center, toward the inner side in the tire axial direction and outward in the tire radial direction. The radius of curvature of this arc portion 63, centered on the belt end 19, is a first distance X1 that is 8 mm or more.

[0072] By setting the first distance X1 to 8 mm or more, the thickness from the outer side sipe 60b to the belt end 19 is set appropriately, and rigidity in the vicinity of the belt end 19 is ensured.

[0073] Fig. 6 is a graph showing the relationship between the strain energy density and the first distance X1. The horizontal axis represents the first distance X1, and the vertical axis represents the strain energy density. The graph in Fig. 6 shows the results of a static structural analysis using the finite element method (FEM analysis) to calculate the strain energy density occurring in the structure of tire 1. Specifically, a total of 11 types of tire models were prepared, including tire models without outer side sipes 60b and tire models with outer side sipes 60b having first distances X1 of 2 mm, 3 mm to 11 mm, and the strain energy density applied to belt end 19 was calculated when each tire model was stationary and in contact with the ground under conditions of applying the same air pressure and the same load.

[0074] Research by the applicant of the present invention has revealed that when the strain density energy exceeds 130%, separation failure at the belt end 19 tends to increase. As shown in the figure, when the first distance X1 is 7 mm or less, the strain density energy exceeds 130%, resulting in an increase in separation failure at the belt end 19. Therefore, it is preferable that the first distance X1 be 8 mm or more so that the strain density energy is less than 130%.

[0075] As shown in FIG. 4, the first distance X1 is 30% to 80% of the second distance X2 in the tire radial direction from the belt end 19 to the tread surface 20. Because the first distance X1 is 30% to 80% of the second distance X2, the thickness from the outer side sipe 60b to the belt end 19 is appropriately set, ensuring rigidity near the belt end 19 and heat dissipation properties of the outer side sipe 60b. If the first distance X1 were less than 30% of the second distance X2, the thickness from the outer side sipe 60b to the belt end 19 would be excessively small, significantly reducing rigidity near the belt end 19 and significantly increasing strain energy density. Furthermore, the axial depth of the outer side sipe 60b would be large, making it easier for sand, dust, and the like to become trapped in the outer side sipe 60b. If the first distance X1 is greater than 80% of the second distance X2, the thickness from the outer side sipe 60b to the belt end 19 becomes excessively large, significantly reducing the heat dissipation performance of the outer side sipe 60b. Therefore, it is preferable that the first distance X1 be 30% or more and 80% or less of the second distance X2.

[0076] In this embodiment, the first distance X1 is 30% to 80% of the second distance X2, but may be preferably 40% to 60% of the second distance X2, which further improves the rigidity near the belt end 19 and the heat dissipation of the outer side sipe 60b.

[0077] In this embodiment, the arc portion 63 extends axially outward from the reference line 54 with the belt end 19 as its center within a range of 10 degrees to 60 degrees from the reference line 54 toward the tire axially outward. However, it may preferably extend axially outward from the reference line 54 with the belt end 19 as its center within a range of 10 degrees to 30 degrees from the reference line 54. The continuous portion 53 of the side surface 21 also has an arc portion 64 that extends axially inward and radially outward from the tire radially inner end to the tire radially outer end with the belt end 19 as its center. The radius of curvature of this arc portion 64, centered on the belt end 19, is a third distance X3 that is 10 mm to 20 mm.

[0078] The first distance X1 is equal to or less than the third distance X3. The arc-shaped portion 63 having a curvature radius equal to the first distance X1, which is equal to or less than the third distance X3, extends axially outward from the reference line 54 within a range of 10 degrees to 60 degrees relative to the reference line 54. This appropriately sets the length of the arc-shaped portion 63 having a curvature radius smaller than the third distance X3, thereby ensuring heat dissipation from the outer side sipe 60b. If the dimension of the first distance X1 were greater than the dimension of the third distance X3, the thickness from the outer side sipe 60b to the belt end 19 would be excessively large, significantly reducing the heat dissipation from the outer side sipe 60b. Therefore, it is preferable that the first distance X1 be equal to or less than the third distance X3.

[0079] In this embodiment, the groove bottom of the inner side sipe 60a and the groove bottom of the outer side sipe 60b are each inclined toward the inner side in the tire radial direction and toward the outer side in the tire axial direction.

[0080] The inclination angle A5 of the groove bottom of the inner side sipe 60a relative to the reference line 54 is the same as the inclination angle of the main portion 52 of the side surface 21 relative to the reference line 54. Meanwhile, the inclination angle A6 of the groove bottom of the outer side sipe 60b relative to the reference line 54 is between 0 and 15 degrees. By setting the inclination angle A6 of the groove bottom of the outer side sipe 60b relative to the reference line 54 between 0 and 15 degrees, the length of the arc portion 63 is appropriately set, ensuring the rigidity of the shoulder land 23b and the heat dissipation properties of the outer side sipe 60b. If the inclination angle A6 of the groove bottom of the outer side sipe 60b relative to the reference line 54 is less than 0 degrees, the thickness from the outer side sipe 60b to the outer tread sipe 40a becomes excessively small, significantly reducing the rigidity of the shoulder land 23b and potentially causing cracks to occur originating from the outer tread sipe 40a and the outer side sipe 60b. If the inclination angle A6 of the groove bottom of the outer side sipe 60b with respect to the reference line 54 is greater than 15 degrees, the length of the arc portion 63 of the outer side sipe 60b becomes excessively short, significantly reducing the heat dissipation performance of the outer side sipe 60b. Therefore, it is preferable that the inclination angle A6 of the groove bottom of the outer side sipe 60b with respect to the reference line 54 be greater than or equal to 0 degrees and less than or equal to 15 degrees.

[0081] In this embodiment, the width W4 of the inner side sipe 60a is 0.5 to 1.0 times the axial depth D6 of the inner side sipe 60a. If the width W4 of the inner side sipe 60a is less than 0.5 times the axial depth D6 of the inner side sipe 60a, the stiffness of the outer shoulder block 30a will be insufficient. If the width W4 of the inner side sipe 60a is greater than 1.0 times the axial depth D6 of the inner side sipe 60a, the circumferentially adjacent inner side sipe 60a and outer side sipe 60b will interfere with each other, and the stiffness of the outer shoulder block 30a will be excessively reduced. Therefore, it is preferable that the width W4 of the inner side sipe 60a be 0.5 to 1.0 times the axial depth D6 of the inner side sipe 60a.

[0082] In this embodiment, the axial depth D6 of the inner side sipe 60a is 0.25 to 0.75 times the axial length L2 of the chamfer 51. If the axial depth D6 of the inner side sipe 60a is less than 0.25 times the axial length L2 of the chamfer 51, the rigidity of the outer shoulder block 30a is insufficient. If the axial depth D6 of the inner side sipe 60a is more than 0.75 times the axial length L2 of the chamfer 51, the resistance of the inner side sipe 60a to external damage caused by curbs, bumps, and the like is reduced. Therefore, it is preferable that the axial depth D6 of the inner side sipe 60a be 0.25 to 0.75 times the axial length L2 of the chamfer 51.

[0083] As described above, in this embodiment, the inner side sipe 60a and the outer side sipe 60b, which have different radial lengths L3 and L4, are arranged on the side surface 21 of the outer shoulder block 30a, which includes multiple outer tread sipes 40a. Without these inner side sipes 60a and outer side sipes 60b, the multiple outer tread sipes 40a would cause the rigidity of the side surface 21 of the outer shoulder block 30a to be lowest at the tire circumferential center, resulting in the largest displacement due to forces acting on the tread surface 20, making uneven wear more likely to occur. In contrast, in this embodiment, the arrangement of the inner side sipe 60a and the outer side sipe 60b allows the rigidity of the side surface 21 of the outer shoulder block 30a to gradually decrease from the center line 61 of the outer shoulder block 30a toward the outer side in the tire circumferential direction, thereby optimizing the circumferential rigidity balance of the outer shoulder block 30a. As a result, uneven wear in the central region 41 of the outer shoulder block 30a is suppressed. Furthermore, a decrease in rigidity in the central region 41 of the outer shoulder block 30a can be prevented from occurring from the initial to intermediate stages of wear.

[0084] The pneumatic tire 1 configured in this manner has the following features.

[0085] Since the inner side sipes 60a and the outer side sipes 60b are provided at different positions in the tire circumferential direction relative to the outer tread sipes 40a, excessive reduction in rigidity of the shoulder land 23b is suppressed compared to when the outer tread sipes 40a and the side sipes 60 are provided at the same position in the tire circumferential direction, and therefore, the occurrence of cracks originating from the outer tread sipes 40a and the side sipes 60 is suppressed.

[0086] Furthermore, because the radial length L3 of the inner side sipe 60a is shorter than the radial length L4 of the outer side sipe 60b, the rigidity of the outer region 43 located on the outer side in the tire circumferential direction within the space between the pair of outer axial grooves 26a of the shoulder land 23b can be made lower than the rigidity of the central region 41 located in the tire circumferential center. This optimizes the circumferential rigidity balance between the pair of outer axial grooves 26a. This averages out the amount of circumferential displacement of the tire when a force is applied to the tread 20, effectively suppressing uneven wear in the tire circumferential center.

[0087] Furthermore, since the first distance X1 from the outer side sipe 60b to the belt end 19 is 8 mm or more, the thickness from the outer side sipe 60b to the belt end 19 is appropriately set, ensuring rigidity in the vicinity of the belt end 19. Therefore, separation failure at the belt end 19 is suppressed.

[0088] Because the first distance X1 is 30% or more and 80% or less of the second distance X2 from the belt end 19 to the tread surface 20, the thickness from the outer side sipe 60b to the belt end 19 is appropriately set. This ensures rigidity near the belt end 19, suppresses separation failure at the belt end 19, and improves heat dissipation from the side surface 21. For example, compared to when the first distance X1 is less than 30% of the second distance X2, the thickness from the outer side sipe 60b to the belt end 19 is greater, ensuring rigidity near the belt end 19. This suppresses separation failure at the belt end 19. Furthermore, compared to when the first distance X1 is less than 30% of the second distance X2, the axial depth of the outer side sipe 60b is smaller, making it less likely for sand, dust, and the like to become lodged in the outer side sipe 60b. This ensures that the outer side sipe 60b remains open, ensuring the tire circumferential rigidity balance optimized by the side sipe 60. Furthermore, compared to when the first distance X1 is greater than 80% of the second distance X2, the thickness from the outer side surface sipe 60b to the belt end 19 is smaller, ensuring heat dissipation from the outer side surface sipe 60b. Therefore, the heat dissipation from the side surface 21 can be improved.

[0089] An inner wall 62 formed from the radially inner end of the outer side sipe 60b to the axially inner end thereof has an arc portion 63 whose radius of curvature is the first distance X1 around the belt end 19, so that the length of the portion from the outer side sipe 60b to the belt end 19 that is the first distance X1 can be ensured to be large. Therefore, rigidity in the vicinity of the belt end 19 is ensured, and separation failure of the belt end 19 is suppressed.

[0090] The arc portion 63, whose radius of curvature is the first distance X1, which is equal to or less than the third distance X3, from the belt end 19 to the side surface 21, extends axially outward from the reference line 54 in the tire radial direction within a range of 10 degrees to 60 degrees. Therefore, the length of the arc portion 63, whose radius of curvature is less than the third distance X3, is appropriately set, ensuring heat dissipation from the outer side surface sipe 60b. Therefore, even when the outer side surface sipe 60b is applied to a pneumatic tire 1 having a large third distance X3, the heat dissipation from the side surface 21 can be improved. For example, compared to when the arc portion 63 extends axially outward from the reference line 54 in the tire radial direction within a range exceeding 60 degrees, rigidity near the belt end is ensured. This reduces separation failure at the belt end 19.

[0091] The inclination angle A6 of the axially inner end of the outer side sipe 60b is between 0 and 15 degrees outward in the axial direction relative to the reference line 54 extending in the tire radial direction, thereby appropriately setting the length of the arc portion 63. This ensures the rigidity of the shoulder land 23b, suppressing the occurrence of cracks originating from the outer tread sipe 40a and the outer side sipe 60b, and improving the heat dissipation of the side surface 21. For example, compared to when the inclination angle A6 is less than 0 degrees, the thickness from the outer side sipe 60b to the outer tread sipe 40a is greater, thereby ensuring the rigidity of the shoulder land 23b. This prevents the occurrence of cracks originating from the outer tread sipe 40a and the outer side sipe 60b. Furthermore, compared to when the inclination angle A6 is greater than 15 degrees, the length of the arc portion 63 is greater, thereby ensuring the heat dissipation of the outer side sipe 60b. This improves the heat dissipation of the side surface 21.

[0092] Since the width of the side sipes 60 in the tire circumferential direction is 1.5 mm or less, excessive reduction in rigidity of the shoulder land 23b is suppressed compared to when the width of the side sipes 60 in the tire circumferential direction is greater than 1.5 mm. Therefore, the occurrence of cracks originating from the side sipes 60 is suppressed.

[0093] The present invention is not limited to the configurations of the above-described embodiments, and various modifications are possible.

[0094] For example, in the above embodiment, the belt layer 18 has two belt plies, a first belt ply 18a and a second belt ply 18b, but may have a different number of belt plies.

[0095] 7 is a meridian cross-sectional view of a tire 101 according to another embodiment. The belt layer 118 of the tire 101 includes four belt plies: a first belt ply 118a disposed radially innermost in the tire radial direction; a second belt ply 118b disposed radially outer than the first belt ply 118a; a third belt ply 118c disposed radially outer than the second belt ply 118b; and a fourth belt ply 118d disposed radially outer than the third belt ply 118c. As shown in the figure, the axial length of the second belt ply 118b is longer than the other belt plies: the first belt ply 118a, the third belt ply 118c, and the fourth belt ply 118d. Therefore, the axially outer end of the first belt ply 118a is the belt end 119 located axially outermost of the belt layer 118.

[0096] Furthermore, the pneumatic tire 1 is not limited to a tapered shoulder type in which the side surface 21 is provided with the chamfer 51, but may be a box shoulder type without chamfer.

[0097] A first aspect of the present invention is a tire having a tread located at an outer end in a tire radial direction and extending in a tire circumferential direction, a plurality of belts located radially inward of the tread, extending in a tire circumferential direction, and having belt ends located at outer ends in an axial direction of the tire; a shoulder land located at an outer end of the tread in the tire axial direction, the shoulder land having a tread surface located at an outer end of the tread in the tire radial direction and a side surface located axially outward of the tread surface; a plurality of axial grooves provided at intervals in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread surface, extending in the tire axial direction, and opening at the side surface; a plurality of tread sipes provided at intervals in the tire circumferential direction between a pair of axial grooves adjacent in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread, extending in the tire axial direction and terminating at a position spaced apart from the side surface; a plurality of side sipes provided on the side surface at different positions in the tire circumferential direction relative to the tread sipes, recessed inward in the tire axial direction, and extending in the tire radial direction, the plurality of side sipes including an inner side sipe located closer to the center in the tire circumferential direction within the interval between the pair of axial grooves, and an outer side sipe located closer to the axial groove than the inner side sipe, the length in the tire radial direction of the inner side sipe being shorter than the length in the tire radial direction of the outer side sipe, and the plurality of side sipes being configured such that a first distance from the outer side sipe to the belt end is 8 mm or more; To provide a pneumatic tire comprising:

[0098] A second aspect of the present invention provides the pneumatic tire according to the first aspect, wherein the first distance is 30% to 80% of a second distance from the belt end to the tread surface.

[0099] In a third aspect of the present invention, the outer side sipe has an inner wall extending from an inner end in the tire radial direction to an inner end in the tire axial direction, The pneumatic tire according to the first or second aspect is provided, wherein the inner wall has an arc portion whose radius of curvature around the belt end is the first distance.

[0100] In a fourth aspect of the present invention, the arc portion extends in a range of 10 degrees or more and 60 degrees or less from a reference line extending in the tire radial direction to an outer side in the tire axial direction, There is provided a pneumatic tire according to a third aspect, wherein the first distance is equal to or less than a third distance from the belt end to the side surface.

[0101] A fifth aspect of the present invention provides a pneumatic tire according to any one of the first to fourth aspects, wherein the inclination angle of the inner end of the outer side sipe in the tire axial direction is greater than or equal to 0 degrees and less than or equal to 15 degrees toward the outer side in the tire axial direction relative to a reference line extending in the tire radial direction.

[0102] A sixth aspect of the present invention provides the pneumatic tire according to any one of the first to fifth aspects, wherein the width of the side sipes in the tire circumferential direction is 1.5 mm or less. [Explanation of symbols]

[0103] 1 pneumatic tire 11 Tread 12 Sidewall 13 Bead 14 Bead core 15 Bead filler 16 Inner liner 17 Carcass 18 Belt Layer 18a 1st belt ply 18b Second belt ply 19 Belt end 20 treads 21 Side 22 Main groove 22a Center main groove 22b Outside main groove 23 land 23a Center Land 23b Shoulder Land 24 Circumferential groove 25a Shoulder land outer row 25b Shoulder inland row 26 Axial groove 26a Outer axial groove 26b Inner axial groove 27 Center Rib 28 Center Block 29 Shoulder Rib 30 Shoulder Block 30a outer shoulder block 30b inner shoulder block 40 Tread sipes 40a Outside tread sipe 40b inner tread sipes 40c 1st outer tread sipe 40d 2nd outer tread sipe 40d 41 Central area 42 Intermediate area 43 Outer area 51 Chamfering 52 Main Section 53 Continuous section 54 Reference Line 60 Side sipes 60a inner side sipe 60b Outer side sipe 61 Center line 62 Inner wall 63 Arc section 64 Arc section W1 Groove width W2 groove width W3 Groove width W4 width W5 width D1 Depth D2 Depth D3 Depth D4 depth D5 length D6 Depth A1 Inclination angle A2 Tilt angle A3 Tilt angle A4 tilt angle A5 Tilt angle A6 Tilt angle L1 interval L2 length L3 length L4 length X1 1st distance X2 2nd distance X3 Third distance 101 Tires 118 Belt Layer 118a 1st belt ply 118b Second belt ply 118c 3rd belt ply 118d 4th belt ply 119 Belt End

Claims

1. a tread located at an outer end in a tire radial direction and extending in a tire circumferential direction; a plurality of belts located radially inward of the tread, extending in a tire circumferential direction, and having belt ends located at outer ends in an axial direction of the tire; a shoulder land located at an outer end of the tread in the tire axial direction, the shoulder land having a tread surface located at an outer end of the tread in the tire radial direction and a side surface located axially outward of the tread surface; a plurality of axial grooves provided at intervals in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread surface, extending in the tire axial direction, and opening at the side surface; a plurality of tread sipes provided at intervals in the tire circumferential direction between a pair of axial grooves adjacent in the tire circumferential direction on the shoulder land, recessed inward in the tire radial direction from the tread, extending in the tire axial direction and terminating at a position spaced apart from the side surface; a plurality of side sipes provided on the side surface at different positions in the tire circumferential direction relative to the tread sipes, recessed inward in the tire axial direction, and extending in the tire radial direction, the plurality of side sipes including an inner side sipe located closer to the center in the tire circumferential direction within the interval between the pair of axial grooves, and an outer side sipe located closer to the axial groove than the inner side sipe, the length in the tire radial direction of the inner side sipe being shorter than the length in the tire radial direction of the outer side sipe, and the plurality of side sipes being configured such that a first distance from the outer side sipe to the belt end is 8 mm or more; A pneumatic tire having:

2. The pneumatic tire according to claim 1 , wherein the first distance is equal to or greater than 30% and equal to or less than 80% of a second distance from the belt end to the tread surface.

3. The outer side sipe has an inner wall extending from an inner end in the tire radial direction to an inner end in the tire axial direction, The pneumatic tire according to claim 1 , wherein the inner wall has an arc portion having a radius of curvature of the first distance around the belt end.

4. the arc portion extends from a reference line extending in the tire radial direction to an outer side in the tire axial direction within a range of 10 degrees to 60 degrees from the reference line, The pneumatic tire according to claim 3 , wherein the first distance is equal to or less than a third distance from the belt end to the side surface.

5. The pneumatic tire according to claim 1 , wherein an inclination angle of an inner end in the tire axial direction of the outer side sipe is from 0 degrees to 15 degrees outward in the tire axial direction with respect to a reference line extending in the tire radial direction.

6. The pneumatic tire according to claim 1 , wherein the width of the side sipe in the tire circumferential direction is 1.5 mm or less.

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