Tire

Abstract

The present invention addresses the problem of achieving heat generation resistance, wear resistance, and stone trapping resistance. Provided is a pneumatic tire 1 that, in the tread thereof, comprises: two or more longitudinal grooves 21 and 22 that each continuously extend in the tire circumferential direction; a center transverse groove 41 that extends in the tire width direction and communicates with the longitudinal grooves; a shoulder transverse groove 51 that, in the tire width direction, communicates with the outer side of each longitudinal groove on the outermost side in the tire width direction and that extends in the tire width direction; a center block 31A that is partitioned by the longitudinal grooves and the center transverse groove 41; a shoulder block 32A that is partitioned by the longitudinal grooves and the shoulder transverse groove; and a dimple 61 that is open on the tread surface 15A in the center block, wherein the opening of the dimple is formed to have a polygonal shape, the depth of the dimple is not less than 25 [%] of the groove depth of the shoulder transverse groove, the cross-sectional shape of the dimple in the tire radial direction is formed to become smaller from the opening toward the groove bottom, and the opening area of the dimple relative to the block tread surface area is greater than 6 [%] and smaller than 20 [%].

Description

tire

[0001] The present invention relates to tires.

[0002] For example, US Pat. No. 5,999,649 describes a tire that includes openings along the ground contacting surfaces of the tread blocks.

[0003] Patent No. 6185388

[0004] For example, heavy-duty tires such as off-the-road (OTR) tires are prone to heat separation due to heat generation in the tread area under severe operating conditions of load and running speed. For this reason, a known method for improving heat resistance in these types of tires is to provide openings in the block tread surface to dissipate heat generated inside the tire. However, this method requires larger openings for heat dissipation, which reduces the block tread surface area, degrading wear resistance, and also increases the risk of stone bite in the openings, leading to groove cracks.

[0005] An object of the present invention is to provide a tire that can simultaneously achieve heat resistance, wear resistance, and stone-biting resistance.

[0006] In order to achieve the above object, a tire according to one aspect of the present invention includes, in a tread portion, two or more longitudinal grooves extending continuously in the tire circumferential direction, a plurality of center lateral grooves extending in the tire width direction and communicating with each of the longitudinal grooves and arranged in the tire circumferential direction, a plurality of shoulder lateral grooves extending in the tire width direction outward of each of the two outermost longitudinal grooves in the tire width direction and communicating with each of the longitudinal grooves, a center block defined by the longitudinal grooves and the center lateral groove, shoulder blocks defined by the longitudinal grooves and the shoulder lateral grooves, and dimples opening into the tread surface of the center block, wherein the dimples have polygonal openings and a depth that is 25% or more of the groove depth of the shoulder lateral grooves, and a cross-sectional shape along the tire radial direction that becomes smaller from the opening toward the groove bottom, and the opening area relative to the block tread area is greater than 6% and less than 20%.

[0007] According to this invention, it is possible to achieve both heat resistance, abrasion resistance, and stone trap resistance.

[0008] FIG. 1 is a plan view of the tread of a pneumatic tire according to an embodiment. FIG. 2 is a partially enlarged meridian cross-section view of the pneumatic tire according to an embodiment. FIG. 3 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 4 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 5 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 6 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 7 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 8 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 9 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 10 is a plan view showing example dimples of the pneumatic tire according to an embodiment. FIG. 11 is an explanatory diagram defining the center (center of gravity) of a block. FIG. 12 is a table showing results of a performance test of the pneumatic tire according to an embodiment. FIG. 13 is a table showing results of a performance test of the pneumatic tire according to an embodiment. FIG. 14 is a table showing results of a performance test of the pneumatic tire according to an embodiment.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0010] In the following description, the tire radial direction refers to a direction perpendicular to the tire rotation axis (not shown), which is the rotation axis of the pneumatic tire 1 of this embodiment. The tire radially inner side refers to the side toward the tire rotation axis in the tire radial direction, and the tire radially outer side refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to a direction parallel to the tire rotation axis. The tire widthwise inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the tire rotation axis and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides in position in the tire width direction with the tire widthwise centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line that is on the tire equatorial plane CL and runs along the tire circumferential direction of the pneumatic tire 1. Further, a cross section in the tire meridian direction (meridian cross section) refers to a cross section of the tire cut along a plane including the tire rotation axis.

[0011] 1 is a plan view of a tread of a pneumatic tire according to an embodiment. In this embodiment, a heavy-duty pneumatic radial tire to be mounted on heavy-duty vehicles such as trucks and buses, particularly heavy-duty vehicles for construction or industrial use, will be described as an example.

[0012] The pneumatic tire 1 is formed symmetrically in the tire width direction with respect to the tire equatorial plane CL. Fig. 2 is an enlarged meridian cross-sectional view of the pneumatic tire 1, showing a cross section along a center lateral groove 41 and a shoulder lateral groove 51, which will be described later.

[0013] As shown in FIG. 2 , the pneumatic tire 1 of the embodiment has an annular structure centered on the tire rotation axis, and includes a pair of bead cores (not shown), a pair of bead fillers (not shown), a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers (not shown).

[0014] Although not shown in the figure, the pair of bead cores are made by winding one or more steel bead wires in a circular and multiple manner, and are embedded in the bead portions to form the cores of the bead portions on both sides in the tire width direction.

[0015] Although not shown in the drawings, the pair of bead fillers are made up of a lower filler and an upper filler, and are respectively disposed on the outer periphery of the pair of bead cores in the tire radial direction to reinforce the bead portion.

[0016] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together. In the pneumatic tire 1 of the embodiment, the carcass layer 13 is shown as a single carcass ply. The carcass layer 13 is toroidally laid between the bead cores to form the tire framework. Both ends of the carcass layer 13 are wound back and secured to the outside in the tire width direction so as to enclose the bead cores and bead fillers. The carcass ply of the carcass layer 13 is formed by coating multiple steel carcass cords with coating rubber and rolling them. The carcass ply has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction relative to the tire circumferential direction) of 80 degrees or more and 90 degrees or less in absolute value for a radial tire, or 20 degrees or more and 45 degrees or less in absolute value for a bias tire.

[0017] The belt layer 14, also referred to as a belt member, is formed by laminating multiple belt plies (also referred to as belts) 141-146 and is disposed around the outer periphery of the carcass layer 13. These belt plies 141-146 are combined with belts of various configurations, such as a 0-degree belt or a pair of cross belts. In the pneumatic tire 1 of the embodiment, the belt layer 14 is preferably formed by laminating five or more belt plies so as to be suitable for use in heavy-duty vehicles for construction and industrial use. The belt plies are formed by coating multiple steel belt cords (also referred to as wire rods) with coating rubber and rolling them. The pair of cross belts are formed by coating multiple steel belt cords with coating rubber and rolling them, and have cord angles of opposite signs. The belt cords are laminated so that their longitudinal directions cross each other, forming a so-called cross-ply structure.

[0018] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the pneumatic tire 1. The tread rubber 15 forms a tread surface (also simply referred to as the tread surface) 15A on the outer surface of the tread portion that comes into contact with the road surface during running. The outer ends (corners) of the tread surface 15A in the tire width direction form ground contact edges T. The tread rubber 15 also has buttress portions 15B in the tread portion that do not come into contact with the road surface during running, on side portions on both outer sides in the tire width direction than the ground contact edges T of the tread surface 15A. The buttress portions 15B are provided in the tread rubber 15 from the ground contact edges T to the outer side in the tire width direction and the inner side in the tire radial direction, up to the sidewall rubber 16.

[0019] The pair of sidewall rubbers 16 are respectively arranged on the outer sides of the carcass layer 13 in the tire width direction, and constitute sidewall portions on both sides of the pneumatic tire 1 in the tire width direction, on the inner side of the buttress portion 15B in the tire radial direction.

[0020] Although not shown in the drawings, the pair of rim cushion rubbers extend from the radially inner side of each bead core and the turned-up portion of the carcass layer 13 to the widthwise outer side of the tire, and form the rim fitting surface of the bead portion.

[0021] The pneumatic tire 1 of the embodiment has a tread pattern in the tread portion (tread surface 15A and buttress portion 15B) as shown in Fig. 2. Here, each dimension of the tread pattern is measured in an unloaded state with the tire mounted on a specified rim and inflated to a specified internal pressure.

[0022] "Specified rim" refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. Also, "specified internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. Also, "specified load" refers to the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO.

[0023] The groove width (opening width) is measured as the maximum distance between opposing groove walls of a groove opening on the surface of the tread surface 15A or buttress portion 15B when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width (opening width) is measured using the intersection of an extension of the tread surface and an extension of the groove wall as the endpoint in a cross section parallel to the tire width direction and the tire radial direction.

[0024] The groove depth is measured as the maximum distance from the surface of the tread surface 15A or the buttress portion 15B to the groove bottom when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In addition, if the groove bottom has partial unevenness or sipes, the groove depth is measured excluding these.

[0025] As shown in Fig. 1, the pneumatic tire 1 of the embodiment has, on a tread surface 15A, at least two longitudinal grooves 21, 22 and lateral grooves 41, 51 communicating with the respective longitudinal grooves. Also, as shown in Fig. 1, the pneumatic tire 1 of the embodiment has dimples 61, 62 on the tread surface 15A.

[0026] The longitudinal grooves 21 are grooves that extend continuously along the tire circumferential direction. In the embodiment, the longitudinal grooves 21 are also referred to as circumferential grooves. A pair of longitudinal grooves 21 is arranged on the tread surface 15A, one on each side at the outermost positions in the tire width direction, with the tire equatorial plane CL as the boundary. The space between the pair of longitudinal grooves 21 is referred to as a center region CE, and the outer sides of each longitudinal groove 21 in the tire width direction are referred to as shoulder regions SE. In the embodiment, when there are two longitudinal grooves 21, these longitudinal grooves 21 are included.

[0027] The longitudinal groove 21 has linear inclined portions 21a. The inclined portions 21a are arranged at an angle relative to the tire circumferential direction. The inclined portions 21a have angles with opposite signs relative to the tire circumferential direction, and these are arranged alternately and continuously in the tire circumferential direction and connected by bent portions 21b. Therefore, the longitudinal groove 21 extends continuously along the tire circumferential direction and is formed in a zigzag shape. The longitudinal groove 21 may also be formed in a linear shape that continues along the tire circumferential direction.

[0028] The longitudinal groove 22 is a groove that extends continuously in the tire circumferential direction. In the embodiment, the longitudinal groove 22 is also referred to as a circumferential groove, and is a groove that has a narrower groove width than the longitudinal groove 21 and a groove depth equal to that of the longitudinal groove 21. In the embodiment, one longitudinal groove 22 is disposed along the tire equatorial plane CL.

[0029] The longitudinal grooves 22 have linear inclined portions 22a. The inclined portions 22a are arranged at an angle relative to the tire circumferential direction. The inclined portions 22a have angles with opposite signs relative to the tire circumferential direction, and these are arranged alternately in succession in the tire circumferential direction and connected by bent portions 22b. Therefore, the longitudinal grooves 22 extend continuously along the tire circumferential direction in a zigzag shape. The longitudinal grooves 21 and 22 are arranged such that the bent portion 21b facing inward in the tire width direction of the adjacent longitudinal groove 21 on one side of the tire width direction is located closest to one bent portion 22b facing inward in the tire width direction of the adjacent longitudinal groove 21 on the other side of the tire width direction, and the bent portion 21b facing inward in the tire width direction of the adjacent longitudinal groove 21 on the other side of the tire width direction is located closest to one bent portion 22b facing inward in the tire width direction of the adjacent longitudinal groove 21 on the other side of the tire width direction. The longitudinal grooves 22 may also be formed in a continuous linear shape along the tire circumferential direction.

[0030] In the pneumatic tire 1 of the embodiment, two land portions (hereinafter referred to as center land portions) 31 that are adjacent in the tire width direction along the tire circumferential direction are defined in the center region CE between the pair of longitudinal grooves 21 by two longitudinal grooves 21 and one longitudinal groove 22. In the pneumatic tire 1 of the embodiment, one land portion (hereinafter referred to as shoulder land portion) 32 that is aligned along the tire circumferential direction is defined in each shoulder region SE on the outer side in the tire width direction of each longitudinal groove 21.

[0031] When there are two longitudinal grooves, one center land portion 31 is defined between a pair of adjacent longitudinal grooves 21 in the tire width direction. When there are more than three longitudinal grooves, two or more longitudinal grooves 22 are arranged between the outermost longitudinal grooves 21 in the tire width direction, including a longitudinal groove 22 arranged off the tire equatorial plane CL. When there are more than three longitudinal grooves, three or more center land portions 31 are defined in the center region CE.

[0032] The lateral grooves 41, also referred to as center lateral grooves, are disposed in a center land portion 31 defined in a center region CE between a pair of longitudinal grooves 21. In this embodiment, the lateral grooves 41 extend linearly or curvedly along the tire width direction, with one end communicating with the longitudinal groove 21 and the other end communicating with the longitudinal groove 22. A plurality of lateral grooves 41 are disposed side by side in the tire circumferential direction. One end of each lateral groove 41 communicates with a bent portion 21b of the longitudinal groove 21 facing inward in the tire width direction, and the other end communicates with a bent portion 22b of the longitudinal groove 22 closest to the bent portion 21b. Therefore, the center land portion 31 is defined into a plurality of center blocks 31A arranged side by side in the tire circumferential direction by the longitudinal grooves 21, 22 adjacent in the tire width direction and the plurality of lateral grooves 41. The tread surface 15A of each center block 31A here is formed in a hexagonal shape.

[0033] In addition, when there are two longitudinal grooves, the lateral grooves 41 are arranged in one center land portion 31 between a pair of longitudinal grooves 21 adjacent in the tire width direction, with their ends communicating with the respective longitudinal grooves 21. When there are two longitudinal grooves, the ends of the lateral grooves 41 are connected to the bent portions 21b closest to each of the adjacent longitudinal grooves 21 in the tire width direction. Furthermore, when there are more than three longitudinal grooves, the lateral grooves 41 are also arranged between adjacent longitudinal grooves 22 in the tire width direction, with their ends communicating with the respective longitudinal grooves 22. In this case, the lateral grooves 41 are connected to the bent portions 22b closest to each of the adjacent longitudinal grooves 22 in the tire width direction and to which the lateral grooves 41 of other center land portions 31 do not communicate. Therefore, when there are more than three longitudinal grooves, the center land portion 31 between each of the longitudinal grooves 22 is partitioned into center blocks 31A.

[0034] The lateral grooves 51, also known as shoulder lateral grooves, are arranged in the shoulder land portion 32 defined in the shoulder region SE on the tire widthwise outer side of each longitudinal groove 21. The lateral grooves 51 have a groove depth D1 (see FIG. 2 ) of 30 mm or more when new. The lateral grooves 51 have the same groove width and depth as the lateral grooves 41. The lateral grooves 51 extend linearly or curvedly along the tire width direction, with one end communicating with the longitudinal groove 21 and the other end extending beyond the ground contact edge T and opening onto the surface of the buttress portion 15B. Multiple lateral grooves 51 are arranged side by side in the tire circumferential direction. One end of each lateral groove 51 communicates with the bent portion 21b of the longitudinal groove 21 facing outward in the tire width direction. Therefore, the shoulder land portion 32 is defined by the longitudinal grooves 21 and the multiple lateral grooves 51 into multiple shoulder blocks 32A arranged side by side in the tire circumferential direction. The shoulder block 32A has a tread surface 15A formed in a pentagonal shape.

[0035] The dimples 61 are recesses formed in the tread surface 15A of the center blocks 31A defined in the center region CE, and are hereinafter referred to as center dimples. Preferably, one center dimple 61 is disposed in each center block 31A. The center dimples 61 may be disposed in all center blocks 31A. However, for example, the center dimples 61 may be disposed in all center blocks 31A of a specific center land portion 31, or in specific center blocks 31A of a specific center land portion 31. As shown in FIG. 1 , the center dimple 61 has an opening 61a (see FIG. 2 ) formed in a polygonal shape on the tread surface 15A. The center dimple 61 may have a polygonal shape that continues from the opening 61a to the groove bottom 61b, or may not have a polygonal shape halfway to the groove bottom 61b. Furthermore, as shown in FIG. 2 , the center dimple 61 is formed so that, in a cross section in the tire radial direction, it narrows from the opening 61a that opens to the tread surface 15A toward the groove bottom 61b. The center dimple 61 is formed so that its depth D2 is 25% or more of the groove depth D1 of the lateral groove 51. The center dimple 61 is formed so that the opening area of ​​the opening 61a (total opening area if there are multiple openings) is more than 6% and less than 20% of the block surface area of ​​the tread surface 15A of the single center block 31A in which the center dimple 61 is formed.

[0036] The dimples 62 are recesses formed in the tread surface 15A of the shoulder blocks 32A defined in the shoulder region SE, and are hereinafter referred to as "shoulder dimples." Preferably, one shoulder dimple 62 is disposed in each shoulder block 32A. The shoulder dimples 62 may be disposed in all shoulder blocks 32A. However, for example, the shoulder dimples 62 may be disposed in all shoulder blocks 32A of a specific shoulder land portion 32, or in specific shoulder blocks 32A of a specific shoulder land portion 32. As shown in FIG. 1 , the shoulder dimple 62 has an opening 62a (see FIG. 2 ) formed in a polygonal shape on the tread surface 15A. The shoulder dimple 62 may have a polygonal shape that continues from the opening 62a to the groove bottom 62b, or may cease to have a polygonal shape halfway to the groove bottom 62b. Furthermore, as shown in FIG. 2 , the shoulder dimple 62 is formed so that, in a cross section in the tire radial direction, it narrows from the opening 62a that opens to the tread surface 15A toward the groove bottom 62b. The shoulder dimple 62 is formed so that its depth D3 is 25% or more of the groove depth D1 of the lateral groove 51. The shoulder dimple 62 is formed so that the opening area of ​​the opening 62a (total opening area if there are multiple openings) is more than 6% and less than 20% of the block surface area of ​​the tread surface 15A of the single shoulder block 32A in which the dimple is formed.

[0037] The shapes of the openings 61a, 62a of the center dimple 61 and the shoulder dimples 62 will be described below with reference to FIGS.

[0038] The center dimple 61 and shoulder dimples 62 are collectively referred to as dimples 61, 62, and these dimples 61, 62 are formed in a concave polygonal shape having an outward interior angle 6a and at least one inward interior angle 6b. The outward interior angle 6a has an angle θ of less than 180 degrees, and the inward interior angle 6b has an angle θ of greater than 180 degrees.

[0039] 3 are formed in a concave polygonal shape including three outward interior angles 6a and three inward interior angles 6b. The outward interior angles 6a and the inward interior angles 6b are alternately arranged in the circumferential direction.

[0040] The dimples 61 and 62 shown in Fig. 4 have a shape in which the inward interior angle 6b is formed into a rounded chamfer 6b', as compared to the dimples 61 and 62 shown in Fig. 3. The angle θ in this shape is represented by the angle formed by extending the two sides on either side of the inward interior angle 6b.

[0041] 5 is formed in a concave polygonal shape including five outward interior angles 6a and one inward interior angle 6b. The one inward interior angle 6b is located between two outward interior angles 6a.

[0042] 6 are formed in the shape of a concave polygon including four outward interior angles 6a and four inward interior angles 6b. The outward interior angles 6a and the inward interior angles 6b are alternately arranged in the circumferential direction.

[0043] 7 are formed in the shape of a concave polygon including five outward interior angles 6a and five inward interior angles 6b. The outward interior angles 6a and the inward interior angles 6b are alternately arranged in the circumferential direction.

[0044] 8 are formed in a concave polygonal shape that includes many outward-facing interior angles 6a and many inward-facing interior angles 6b. The outward-facing interior angles 6a and the inward-facing interior angles 6b are alternately arranged in the circumferential direction.

[0045] 9 are formed in a concave polygonal shape including four outward interior angles 6 a and two inward interior angles 6 b. Each inward interior angle 6 b is located between two outward interior angles 6 a and faces each other.

[0046] 10, the dimples 61 and 62 are formed in a polygonal shape with a circular outer diameter and eight outward-facing interior angles 6a and four inward-facing interior angles 6b. Each inward-facing interior angle 6b is located between two outward-facing interior angles 6a.

[0047] The above-described dimples 61, 62 are disposed at the center of the tread surface 15A of the blocks 31A, 32A. The center of the blocks 31A, 32A refers to the center of gravity of the tread surface 15A of the blocks 31A, 32A, calculated using the center of gravity position calculation formulas shown in FIG. 11 and the following Equations 1 and 2.

[0048]

[0049]

[0050] The pneumatic tire 1 of the above-described embodiment is characterized by having, in the tread portion, two or more longitudinal grooves 21, 22 extending continuously along the tire circumferential direction, a plurality of center lateral grooves 41 extending along the tire width direction and communicating between the respective longitudinal grooves 21, 22 and arranged in the tire circumferential direction, a plurality of shoulder lateral grooves 51 extending along the tire width direction and communicating with the respective longitudinal grooves 21 on the outer side in the tire width direction of each of the two outermost longitudinal grooves 21 in the tire width direction, and a plurality of center lateral grooves 51 arranged in the tire circumferential direction, each of which is partitioned by the longitudinal grooves 21, 22 and the center lateral groove 41. The tire includes a center block (31A), a shoulder block (32A) defined by a longitudinal groove (21) and a shoulder lateral groove (51), and a dimple (61) that opens onto the tread (15A) in the center block (31A). The dimple (61) has a polygonal opening (61a), a depth (D2) that is 25% or more of the groove depth (D1) of the shoulder lateral groove (51), a cross-sectional shape along the tire radial direction that becomes smaller from the opening (61a) toward the groove bottom (61b), and an opening area relative to the block tread area that is greater than 6% and less than 20%.

[0051] In this pneumatic tire 1, by arranging dimples 61 with polygonal openings 61a on the tread surface 15A of the center block 31A, the opening area can be increased without increasing the opening range relative to the block tread area, thereby achieving sufficient heat dissipation and improving heat resistance. Furthermore, in this pneumatic tire 1, the opening range of the dimples 61 is reduced relative to the block tread area, ensuring sufficient block tread area, improving wear resistance, and preventing stones from entering the dimples 61, improving stone entrapment resistance. For example, in the case of recesses with circular openings, if the opening range is not increased relative to the block tread area, sufficient heat dissipation cannot be achieved, reducing heat resistance, and the reduced block tread area reduces wear resistance and prevents stones from entering the recesses. Furthermore, in this pneumatic tire 1, if the depth D2 of the dimples 61 is less than 25% of the groove depth D1 of the shoulder lateral grooves 51, it is insufficient to dissipate internal heat. Therefore, the depth D2 is set to 25% or more. However, in this pneumatic tire 1, if the depth D2 of the dimples 61 exceeds 75% of the groove depth D1 of the shoulder lateral grooves 51, block rigidity decreases and wear resistance tends to deteriorate, so a depth D2 of 75% or less is desirable. In order to improve heat resistance and wear resistance, it is more preferable for the pneumatic tire 1 to have the depth D2 of the dimples 61 be 35% or more and 65% or less of the groove depth D1 of the shoulder lateral grooves 51. Furthermore, in this pneumatic tire 1, the cross-sectional shape of the dimples 61 along the tire radial direction is formed to become smaller from the opening 61a to the groove bottom 61b, preventing stones from reaching the groove bottom 61b and improving stone-trapping resistance. Furthermore, in this pneumatic tire 1, by setting the opening area of ​​the dimples 61 relative to the block tread area to be greater than 6% and less than 20%, block rigidity can be ensured, wear resistance deterioration can be suppressed, and stone-trapping resistance can also be ensured. In this pneumatic tire 1, if the opening area of ​​the dimples 61 relative to the block tread area is 6% or less, the heat dissipation effect is insufficient, and if it is 20% or more, the block tread area is reduced, resulting in poor wear resistance and stone-trapping resistance. In this pneumatic tire 1, the opening area of ​​the dimples 61 relative to the block tread area is preferably set to 10% or more and 15% or less, since this effect can be significantly achieved.

[0052] In the pneumatic tire 1 of the embodiment, the dimples 61 are formed in the openings 61a having a concave polygonal shape.

[0053] This pneumatic tire 1 has dimples 61 with concave polygonal openings 61a with at least one interior angle greater than 180 degrees, which makes it possible to increase the opening area of ​​the dimples 61 while limiting the opening area relative to the block tread area, thereby achieving both heat resistance and wear resistance. Furthermore, this pneumatic tire 1 also improves stone-trapping resistance by limiting the opening area of ​​the dimples 61 relative to the block tread area. To significantly achieve the above-mentioned effects, the pneumatic tire 1 preferably has a concave polygonal dimple 61 with three inward-facing interior angles 6b, as shown in FIG. 3 .

[0054] Furthermore, in the pneumatic tire 1 of the embodiment, the shoulder block 32A has a dimple 62 that opens to the tread surface 15A. The dimple 62 has the same configuration as the dimple 61.

[0055] According to this pneumatic tire 1, by providing the dimples 62 not only in the center blocks 31A but also in the shoulder blocks 32A, it is possible to further improve the heat resistance performance.

[0056] In the pneumatic tire 1 of the embodiment, the dimples 61, 62 are formed in the openings of a concave polygonal shape having two or more interior angles greater than 180 degrees.

[0057] According to this pneumatic tire 1, it is possible to increase the opening area of ​​the dimples 61, 62 while suppressing the opening range relative to the block tread area, thereby achieving a better balance between heat resistance and wear resistance.

[0058] In the pneumatic tire 1 of the embodiment, one dimple 61, 62 is disposed at the center of each block 31A, 32A.

[0059] According to this pneumatic tire 1, by providing the dimples 61, 62 in the central portions of the blocks 31A, 32A where heat is most likely to accumulate, a greater heat dissipation effect can be expected.

[0060] In addition, in the pneumatic tire 1 of the embodiment, the groove depth of the shoulder lateral grooves 51 in a new state is 30 mm or more.

[0061] According to this pneumatic tire 1, the longitudinal grooves 21, 22 are relatively deep, and in a tire in which heat accumulates inside the blocks 31A, 32A, the dimples 61, 62 can be expected to have a heat dissipation effect.

[0062] Furthermore, the pneumatic tire 1 of the embodiment has five or more belt plies (141 to 146) arranged on the radially inner side of the tread portion, and is used for heavy-duty construction or industrial vehicles.

[0063] In the present embodiment, as described above, the pneumatic tire 1 has been described as an example of a tire. The pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, or other gases. However, the tread pattern configuration of the pneumatic tire 1 described in the present embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires.

[0064] 12 to 14 are tables showing the results of performance tests of the pneumatic tires according to the embodiment. Performance evaluation tests conducted on a conventional pneumatic tire and an example pneumatic tire according to the embodiment will be described below. The performance evaluation tests were conducted on heat resistance, abrasion resistance, and stone-trapping resistance.

[0065] The heat resistance evaluation test involves mounting a 2400R35 pneumatic tire (test tire) on a specified rim, inflating it to a specified internal pressure, and applying 85% of the specified load. An indoor drum test is then conducted at a test speed of 10 km / h for 24 hours, and the temperature of the tread portion is measured. Based on the measurement results, an index evaluation is performed, with the conventional example being used as the reference (100). The higher the evaluation value, the better.

[0066] The wear resistance evaluation test involves mounting a 2400R35 pneumatic tire (test tire) on a standard rim, inflating it to the standard internal pressure, and mounting it on a dump truck for construction machinery. The tire is then driven off-road at speeds of 10 to 25 km / h for 3,000 hours, and the amount of wear on the tread surface is measured. The reciprocal of these measurement results is then used to evaluate the tire's performance, with a conventional tire being the standard (100). The higher the evaluation value, above 100, the better.

[0067] The stone-trapping resistance evaluation test involves mounting a 2400R35 pneumatic tire (test tire) on a standard rim, inflating it to the standard internal pressure, and mounting it on a dump truck for construction machinery. The tire is then driven off-road at speeds of 10 to 25 km / h for 3,000 hours, and the number of stones trapped in all dimples is counted. The smaller the number, the better.

[0068] The conventional pneumatic tire is based on the tread pattern shown in FIG. 1, but the dimples are circular.

[0069] The pneumatic tires of the examples are based on the tread pattern shown in FIG. 1 and have dimples that are polygonal (rectangular) or concave polygonal as shown in FIGS. 3 to 10 and that satisfy a specified range.

[0070] As shown in the test results, the pneumatic tire of this embodiment has improved heat resistance, wear resistance, and stone-trapping resistance compared to the conventional tire.

[0071] The present disclosure includes the following inventions: [Invention 1] A tire comprising, in a tread portion, two or more longitudinal grooves extending continuously in the tire circumferential direction, a plurality of center lateral grooves extending in the tire width direction and communicating between the longitudinal grooves, lined up in the tire circumferential direction, a plurality of shoulder lateral grooves extending in the tire width direction outward of each of the two outermost longitudinal grooves in the tire width direction and communicating with each of the longitudinal grooves, a center block defined by the longitudinal grooves and the center lateral groove, shoulder blocks defined by the longitudinal grooves and the shoulder lateral grooves, and dimples opening into the tread surface of the center block, wherein the dimples have polygonal openings with a depth of 25% or more of the groove depth of the shoulder lateral grooves, and a cross-sectional shape along the tire radial direction that decreases from the opening toward the groove bottom, and the opening area relative to the block tread area is greater than 6% and less than 20%. [Invention 2] The tire according to Invention 1, wherein the dimples are formed in concave polygonal openings. [Invention 3] The tire according to Invention 1 or 2, wherein the shoulder blocks have dimples that open onto the tread surface. [Invention 4] The tire according to any one of Inventions 1 to 3, wherein the dimples are formed in concave polygonal openings having two or more interior angles greater than 180 degrees. [Invention 5] The tire according to any one of Inventions 1 to 4, wherein one dimple is disposed in the center of the block. [Invention 6] The tire according to any one of Inventions 1 to 5, wherein the shoulder lateral grooves have a groove depth of 30 mm or more when new. [Invention 7] The tire according to any one of Inventions 1 to 6, wherein five or more belt plies are disposed radially inward of the tread portion, and wherein the tire is used for heavy-duty vehicles for construction or industry.

[0072] REFERENCE SIGNS LIST 1 Pneumatic tire (tire) 15A Tread surface (tread surface) 21, 22 Longitudinal groove 31A Center block 32A Shoulder block 41 Center lateral groove 51 Shoulder lateral groove 61 Center dimple (dimple) 61a Opening 61b Groove bottom 62 Shoulder dimple (dimple) 62a Opening 62b Groove bottom

Claims

1. A tire comprising in its tread portion: two or more longitudinal grooves extending continuously in the tire circumferential direction; a plurality of center lateral grooves extending in the tire width direction and connecting between the longitudinal grooves, arranged in the tire circumferential direction; a plurality of shoulder lateral grooves extending in the tire width direction and connecting to each of the two outermost longitudinal grooves in the tire width direction, arranged in the tire circumferential direction; center blocks defined by the longitudinal grooves and the center lateral groove; shoulder blocks defined by the longitudinal grooves and the shoulder lateral grooves; and dimples opening into the tread surface of the center blocks, wherein the openings of the dimples are formed in a polygonal shape and have a depth of 25% or more of the groove depth of the shoulder lateral grooves, and the cross-sectional shape along the tire radial direction is formed to become smaller from the opening toward the groove bottom, and the opening area relative to the block tread area is greater than 6% and less than 20%.

2. The tire according to claim 1, wherein the dimples are formed in the shape of concave polygonal openings.

3. The tire according to claim 1, wherein the dimples are located in the shoulder blocks and open to the tread surface.

4. The tire according to claim 1, wherein the dimple is formed in a concave polygonal opening having two or more interior angles greater than 180 degrees.

5. The tire according to claim 1, wherein one dimple is disposed in the center of the block.

6. The tire according to claim 1, wherein the shoulder lateral grooves have a groove depth of 30 mm or more when new.

7. A tire according to claim 1, wherein five or more belt plies are arranged on the radially inner side of the tread portion, and the tire is used for heavy-duty vehicles for construction or industry.

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