Tire

Abstract

A purpose of the present invention is to improve heat resistance. A center longitudinal groove 21 can be closed when a tire is in contact with the ground, has an average groove width of 50% or less of an average groove width of shoulder longitudinal grooves 22, and has an average groove depth of 80-100% of an average groove depth of the shoulder longitudinal grooves 22. A center lateral groove 41 has an average groove depth that is 90-100% of an average groove depth of shoulder lateral grooves 51. A dimple 61 has a polygonal opening, a depth that is 25% or more of the groove depth of the shoulder lateral grooves 51, a cross-sectional shape along a tire radial direction that becomes smaller from the opening toward a groove bottom, and an opening area relative to a block tread area that is more than 6% and less 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, in heavy-duty tires such as OTR (Off The Road), heat separation is likely to occur due to heat generation in the tread portion under severe operating conditions of load and running speed, so it is desirable to ensure heat resistance.

[0005] An object of the present invention is to provide a tire that can improve heat resistance.

[0006] In order to achieve the above object, a tire according to one aspect of the present invention provides a tire having a tread portion including one center longitudinal groove extending continuously in a zigzag shape along the tire circumferential direction, a pair of shoulder longitudinal grooves extending continuously in a zigzag shape along the tire circumferential direction on both outer sides of the center longitudinal groove in the tire width direction, a center lateral groove connecting the bent portions of the center longitudinal groove and the shoulder lateral groove, shoulder lateral grooves communicating with the bent portions of the shoulder lateral grooves and extending outward in the tire width direction, center blocks defined by the center longitudinal groove, the shoulder longitudinal groove, and the center lateral groove, shoulder blocks defined by the shoulder longitudinal groove and the shoulder lateral groove, and at least front and dimples that open to the tread surface of the center block, wherein the center longitudinal grooves can close when in contact with the ground, have an average groove width of 50% or less of the average groove width of the shoulder longitudinal grooves, and an average groove depth of 80% to 100% of the average groove depth of the shoulder longitudinal grooves, and the center lateral grooves have an average groove depth of 90% to 100% of the average groove depth of the shoulder lateral grooves, and the dimples have polygonal openings and 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 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, heat resistance can be improved.

[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. FIG. 15 is a table showing the results of a performance test of the pneumatic tire according to the 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] 1, the pneumatic tire 1 of the embodiment has, on a tread surface 15A, a center longitudinal groove 21, shoulder longitudinal grooves 22, a center lateral groove 41, and shoulder lateral grooves 51. Also, as shown in FIG. 1, the pneumatic tire 1 of the embodiment has dimples 61, 62 on the tread surface 15A.

[0026] The center longitudinal groove 21 is a groove that extends continuously along the tire equatorial plane CL in the tire circumferential direction.

[0027] The central 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 inclined portions 21a are arranged alternately in the tire circumferential direction and connected by bent portions 21b. Therefore, the central longitudinal groove 21 extends continuously along the tire circumferential direction in a zigzag shape.

[0028] The shoulder longitudinal grooves 22 are grooves that extend continuously in the tire circumferential direction. In the embodiment, the shoulder longitudinal grooves 22 are also referred to as circumferential grooves. The shoulder longitudinal grooves 22 are arranged in pairs on the tread surface 15A, one on each side of the center longitudinal groove 21 in the tire width direction, with the tire equatorial plane CL as the boundary.

[0029] The shoulder 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 respect to the tire circumferential direction of opposite signs, and these inclined portions 22a are arranged alternately in succession in the tire circumferential direction and are connected by bent portions 22b. Therefore, the shoulder longitudinal grooves 22 extend continuously in the tire circumferential direction and are formed in a zigzag shape.

[0030] The center longitudinal groove 21 and the shoulder longitudinal grooves 22 are arranged such that the bent portion 22b facing inward in the tire width direction of the adjacent shoulder longitudinal groove 22 on one side of the tire width direction is located closest to one bent portion 21b facing in one side of the tire width direction in the center longitudinal groove 21, and the bent portion 22b facing inward in the tire width direction of the adjacent shoulder longitudinal groove 22 on the other side of the tire width direction is located closest to one bent portion 21b facing in the other side of the tire width direction in the center longitudinal groove 21.

[0031] Here, at least the opening of the center longitudinal groove 21 can be closed when the tire is mounted on a standard rim, inflated to a standard internal pressure, and in contact with the ground under maximum load. The center longitudinal groove 21 has an average groove width W1 of 50% or less of the average groove width W2 of the shoulder longitudinal grooves 22. The center longitudinal groove 21 has an average groove depth D1 of 80% or more and 100% or less of the average groove depth D2 of the shoulder longitudinal grooves 22.

[0032] 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 by one center longitudinal groove 21 and two shoulder longitudinal grooves 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 on the outer side in the tire width direction of each shoulder longitudinal groove 22.

[0033] A center lateral groove 41 is disposed in each center land portion 31. In this embodiment, the center lateral groove 41 extends linearly or curvedly along the tire width direction, with one end communicating with the shoulder circumferential groove 22 and the other end communicating with the center lateral groove 21. A plurality of center lateral grooves 41 are disposed side by side in the tire circumferential direction. One end of the center lateral groove 41 communicates with the bent portion 22b of the shoulder lateral groove 22 facing inward in the tire width direction, and the other end communicates with the bent portion 21b of the center lateral groove 21 that is closest to the bent portion 22b. The minimum angle θ1 of the center line of the center lateral groove 41 relative to the tire circumferential direction is 45 degrees or greater and 75 degrees or less.

[0034] The center land zone 31 is divided into a plurality of center blocks 31A arranged circumferentially by adjacent longitudinal grooves 21, 22 in the tire width direction and a plurality of center lateral grooves 41. The center blocks 31A have hexagonal tread surfaces 15A. Specifically, each center block 31A is formed in a hexagonal shape by six bends 21b, 22b, and 31Aa, each of which is formed by one bend 21b, one bend 22b, and four bends 31Aa formed by connecting the center lateral groove 41 with the center longitudinal groove 21 and the shoulder longitudinal groove 22.

[0035] The shoulder lateral grooves 51 are disposed in each shoulder land portion 32. The shoulder lateral grooves 51 have the same groove width and depth as the center lateral groove 41. The shoulder lateral grooves 51 extend linearly or curvedly along the tire width direction, with one end communicating with the shoulder circumferential groove 22 and the other end extending beyond the ground contact edge T and opening onto the surface of the buttress portion 15B. Multiple shoulder lateral grooves 51 are disposed side by side in the tire circumferential direction. One end of each shoulder lateral groove 51 communicates with the bent portion 22b of the shoulder lateral groove 22 facing outward in the tire width direction. At one end of the shoulder lateral groove 51 communicating with the shoulder lateral groove 22, the maximum angle θ2 formed by the center lines of the shoulder lateral groove 51 and the shoulder lateral groove 22 is 130 degrees or greater and 180 degrees or less.

[0036] The shoulder land portion 32 is divided into a plurality of shoulder blocks 32A arranged in the tire circumferential direction by the shoulder longitudinal groove 22 and the plurality of shoulder lateral grooves 51.

[0037] Here, the center lateral groove 41 has an average groove depth D3 that is 90% or more and 100% or less of the average groove depth D4 of the shoulder lateral grooves 51.

[0038] The dimple 61 is a recess formed in the tread surface 15A of the center block 31A, and is hereinafter referred to as a center dimple. 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 predetermined center land portion 31, or in a predetermined center block 31A of a predetermined 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 (shown as a triangular shape with arc-shaped corners in FIG. 1 ) 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 tapers 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 D5 is 25% or more of the groove depth D4 of the shoulder 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.

[0039] The dimples 62 are recesses formed in the tread surface 15A of the shoulder blocks 32A, 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 (shown as a square with arcuate corners in FIG. 1 ) 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 it may cease to be polygonal partway to the groove bottom 62b. 2, the shoulder dimple 62 is formed so that its radial cross section tapers from an opening 62a that opens onto the tread surface 15A toward the groove bottom 62b. The shoulder dimple 62 is formed so that its depth D6 is 25% or more of the groove depth D4 of the shoulder lateral groove 51. The shoulder dimple 62 is formed so that the opening area of ​​the opening 62a (or the total opening area if there are multiple shoulder dimples) is greater 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.

[0040] 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.

[0041] The center dimple 61 and shoulder dimples 62 are collectively referred to as dimples 61, 62, and these dimples 61, 62 have a primary shape of a triangle or a square with arcuate corners, as shown in Figure 1, or a pentagon or hexagon, although not explicitly shown. Also, as shown in Figures 3 to 10, the dimples 61, 62 may be formed as a concave polygon 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051]

[0052]

[0053] The pneumatic tire 1 of the above-described embodiment is characterized by having, in the tread portion, one center longitudinal groove 21 extending continuously in a zigzag shape along the tire circumferential direction, a pair of shoulder longitudinal grooves 22 extending continuously in a zigzag shape along the tire circumferential direction on both outer sides of the center longitudinal groove 21 in the tire width direction, a center lateral groove 41 connecting the bent portions 21b, 22b of the center longitudinal groove 21 and the shoulder longitudinal groove 22, a shoulder lateral groove 51 communicating with the bent portion 22b of the shoulder longitudinal groove 22 and extending outward in the tire width direction, a center block 31A defined by the center longitudinal groove 21, the shoulder longitudinal groove 22, and the center lateral groove 41, a shoulder block 32A defined by the shoulder longitudinal groove 22 and the shoulder lateral groove 51, and at least a center block 31B. and a dimple 61 that opens onto the tread 15A at the lock 31A, the center longitudinal groove 21 can be closed when in contact with the ground, has an average groove width W1 that is 50% or less of the average groove width W2 of the shoulder longitudinal grooves 22, and an average groove depth D1 that is 80% or more and 100% or less of the average groove depth D2 of the shoulder longitudinal grooves 22, the center lateral groove 41 has an average groove depth D3 that is 90% or more and 100% or less of the average groove depth D4 of the shoulder lateral grooves 51, the dimple 61 has an opening 61a that is polygonal and has a depth D5 that is 25% or more of the groove depth D4 of the shoulder lateral grooves 51, and the cross-sectional shape along the tire radial direction is formed to become smaller from the opening 61a toward the groove bottom 61b, and the opening area relative to the block tread area is greater than 6% and less than 20%.

[0054] According to this pneumatic tire 1, by making the center longitudinal groove 21 a narrower groove than the shoulder longitudinal grooves 22, when the tire is mounted on a standard rim and inflated to a standard internal pressure and comes into contact with the ground under maximum load, the center blocks 31A that are separated by the center longitudinal groove 21 support each other, thereby maintaining block rigidity and improving heat dissipation in the center portion. Furthermore, according to this pneumatic tire 1, by setting the average groove width W1 of the center longitudinal groove 21 to 50% or less of the average groove width W2 of the shoulder longitudinal grooves 22, a closing effect is achieved when the tire comes into contact with the ground. To achieve this closing effect when the tire comes into contact with the ground, it is preferable that the average groove width W1 of the center longitudinal groove 21 be 30% or more and 45% or less of the average groove width W2 of the shoulder longitudinal grooves 22. Furthermore, according to this pneumatic tire 1, by setting the average groove depth D1 of the center longitudinal groove 21 to 80% or more and 100% or less of the average groove depth D2 of the shoulder longitudinal grooves 22, heat dissipation can be maintained until the middle of wear. Furthermore, with this pneumatic tire 1, by setting the average groove depth D3 of the center lateral groove 41 to 90% to 100% of the average groove depth D4 of the shoulder lateral grooves 51, it is possible to reduce the rubber volume in the center portion, improve heat dissipation, and maintain traction even in the later stages of wear. By arranging dimples 61 with polygonal openings 61a on the tread surface 15A of the center block 31A, it is possible to increase the opening area without increasing the opening range relative to the block tread area, thereby achieving sufficient heat dissipation and improving heat resistance. Furthermore, with this pneumatic tire 1, if the depth D5 of the dimple 61 is less than 25% of the groove depth D4 of the shoulder lateral grooves 51, it is insufficient to dissipate internal heat, so the depth D5 is set to 25% or more. However, with this pneumatic tire 1, if the depth D5 of the dimple 61 exceeds 75% of the groove depth D4 of the shoulder lateral grooves 51, block rigidity decreases and wear resistance tends to deteriorate, so it is preferable that the depth D5 be 75% or less. Furthermore, with this pneumatic tire 1, the cross-sectional shape of the dimple 61 along the tire radial direction is formed to become smaller from the opening 61a toward the groove bottom 61b, so that when the rubber volume of the center block 31A decreases with wear, appropriate block rigidity can be maintained and heat generation can be suppressed.Furthermore, with this pneumatic tire 1, block rigidity can be ensured and deterioration of wear resistance can be suppressed by setting the opening area of ​​the dimples 61 relative to the block tread area to be greater than 6% and less than 20%. With 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, and the impact of heat generation worsens rather than the heat dissipation effect.

[0055] In addition, in the pneumatic tire 1 of the embodiment, the center lateral groove 41 connects the bent portion 22b of the shoulder longitudinal groove 22 facing inward in the tire width direction to the bent portion 21b of the center longitudinal groove 21 that is closest to the bent portion 22b, and the shoulder lateral groove 51 connects the bent portion 22b of the shoulder longitudinal groove 22 facing outward in the tire width direction to the ground contact edge T.

[0056] In this pneumatic tire 1, the blocks 31A, 32A do not have any acute-angled vertices (bends), resulting in a pattern that is less prone to chipping. Moreover, in this pneumatic tire 1, the center lateral groove 41 and the shoulder lateral grooves 51 have a phase relationship with each other in the circumferential direction of the tire, thereby improving traction performance.

[0057] In the pneumatic tire 1 of the embodiment, the maximum angle formed by the shoulder lateral groove 51 and the shoulder longitudinal groove 22 that are in communication with each other is 130 degrees or more and 180 degrees or less.

[0058] According to this pneumatic tire 1, since a portion of the shoulder longitudinal groove 22 is in the above-mentioned angle range with the shoulder lateral groove 51, the shoulder lateral groove 51 is smoothly connected to the shoulder longitudinal groove 22, improving soil discharge and traction.

[0059] In the pneumatic tire 1 of the embodiment, the minimum angle of the center lateral groove 41 with respect to the tire circumferential direction is equal to or greater than 45 degrees and equal to or less than 75 degrees.

[0060] In this pneumatic tire 1, by setting the angle of the center lateral groove 41 with respect to the tire circumferential direction to 75 degrees or less, the center lateral groove 41 can be given a sufficient inclination, which promotes air flow during tire rotation and improves heat dissipation. Furthermore, in this pneumatic tire 1, if the angle of the center lateral groove 41 with respect to the tire circumferential direction is less than 45 degrees, the shape of the center block 31A becomes distorted and the block rigidity decreases, so the angle is set to 45 degrees or more.

[0061] In the pneumatic tire 1 of the embodiment, the center block 31A is surrounded by six bent portions.

[0062] In this pneumatic tire 1, when the zigzag spacing of the center longitudinal groove 21 and the shoulder longitudinal groove 22 is equal and the center lateral groove 41 is straight, the center block has a hexagonal shape surrounded by six bends. With this pneumatic tire 1, traction performance and soil discharge performance are best when this pattern is used.

[0063] Furthermore, in the pneumatic tire 1 of the embodiment, the tire rotation direction is not specified.

[0064] According to this pneumatic tire 1, the tire rotation direction is not specified, which improves the workability of installation, and tire rotation with the inside and outside reversed is possible, which can extend the tire life.

[0065] In the pneumatic tire 1 of the embodiment, the dimples 61, 62 are provided on the center block 31A and the shoulder block 32A.

[0066] According to this pneumatic tire 1, by providing the dimples 62 also in the shoulder blocks 32A, it is possible to uniformly improve the heat resistance of the entire tread portion.

[0067] 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.

[0068] 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.

[0069] 12 to 15 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 to test heat resistance.

[0070] 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.

[0071] The conventional pneumatic tire has zigzag-shaped center longitudinal grooves, shoulder longitudinal grooves, center lateral grooves, and shoulder lateral grooves, but does not satisfy the specified range.

[0072] The pneumatic tire of the example satisfies the specified range based on the tread pattern shown in FIG.

[0073] As shown in the test results, it is understood that the pneumatic tire of this embodiment has improved heat resistance performance compared to the conventional tire.

[0074] The present disclosure includes the following inventions: [Invention 1] A tread portion including: one center longitudinal groove extending continuously in a zigzag shape along the tire circumferential direction; a pair of shoulder longitudinal grooves extending continuously in a zigzag shape along the tire circumferential direction on both outer sides of the center longitudinal groove in the tire width direction; a center lateral groove connecting the bent portions of the center longitudinal groove and the shoulder lateral groove; shoulder lateral grooves communicating with the bent portions of the shoulder lateral grooves and extending outward in the tire width direction; center blocks defined by the center longitudinal groove, the shoulder longitudinal groove, and the center lateral groove; shoulder blocks defined by the shoulder longitudinal groove and the shoulder lateral groove; and dimples opening onto the tread surface in at least the center blocks, wherein the center longitudinal groove can be closed when in contact with the ground, has an average groove width of 50% or less of the average groove width of the shoulder lateral grooves, and an average groove depth of 80% or more and 100% or less of the average groove depth of the shoulder lateral grooves, A tire in which the center lateral groove has an average groove depth of 90% to 100% of the average groove depth of the shoulder lateral grooves, the dimples have polygonal openings with a depth of 25% or more of the groove depth of the shoulder lateral grooves, the cross-sectional shape along the tire radial direction is formed to decrease from the opening to 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, in which the center lateral groove connects a bent portion of the shoulder lateral groove facing inward in the tire width direction to a bent portion of the center lateral groove nearest to the bent portion, and the shoulder lateral groove connects a bent portion of the shoulder lateral groove facing outward in the tire width direction to a ground contact edge. [Invention 3] The tire according to Invention 1 or 2, in which the maximum angle formed by the shoulder lateral groove and the shoulder lateral groove, which are connected to each other, is greater than 130 degrees and less than 180 degrees. [Invention 4] The tire according to any one of Inventions 1 to 3, wherein the minimum angle of the center lateral groove with respect to the tire circumferential direction is 45 degrees or more and 75 degrees or less. [Invention 5] The tire according to any one of Inventions 1 to 4, wherein the center block is surrounded by six bends.[Invention 6] The tire according to any one of Inventions 1 to 5, wherein the tire rotation direction is not specified. [Invention 7] The tire according to any one of Inventions 1 to 6, wherein the dimples are provided on the center blocks and the shoulder blocks. [Invention 8] The tire according to any one of Inventions 1 to 7, 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.

[0075] REFERENCE SIGNS LIST 1 Pneumatic tire (tire) 15A Tread surface (tread surface) 21 Center longitudinal groove 21a Inclined portion 21b Bend portion 22 Shoulder longitudinal groove 22a Inclined portion 22b Bend portion 31A Center block 31Aa Bend portion 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 141 to 146 Belt ply

Claims

1. A tire comprising: a tread portion; one center longitudinal groove extending continuously in a zigzag shape along the tire circumferential direction; a pair of shoulder longitudinal grooves extending continuously in a zigzag shape along the tire circumferential direction on both outer sides of the center longitudinal groove in the tire width direction; a center lateral groove connecting the bent portions of the center longitudinal groove and the shoulder longitudinal groove; shoulder lateral grooves communicating with the bent portions of the shoulder longitudinal grooves and extending outward in the tire width direction; center blocks defined by the center longitudinal groove, the shoulder longitudinal groove, and the center lateral groove; shoulder blocks defined by the shoulder longitudinal groove and the shoulder lateral groove; and dimples opening onto the tread surface in at least the center blocks, wherein the center longitudinal groove is capable of closing when in contact with the ground, has an average groove width of 50% or less of the average groove width of the shoulder longitudinal grooves, and an average groove depth of 80% or more but 100% or less of the average groove depth of the shoulder longitudinal grooves, The center lateral groove has an average groove depth of 90% to 100% of the average groove depth of the shoulder lateral grooves, the dimples have polygonal openings and a depth of 25% or more of the shoulder lateral groove depth, 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 center lateral groove connects a bent portion of the shoulder lateral groove facing inward in the tire width direction to a bent portion of the center lateral groove that is closest to the bent portion, and the shoulder lateral groove connects a bent portion of the shoulder lateral groove facing outward in the tire width direction to the ground contact edge.

3. A tire according to claim 1, wherein the maximum angle formed by the shoulder lateral groove and the shoulder longitudinal groove that are connected to each other is equal to or greater than 130 degrees and equal to or less than 180 degrees.

4. The tire according to claim 1, wherein the minimum angle of the center lateral groove relative to the tire circumferential direction is 45 degrees or more and 75 degrees or less.

5. The tire according to claim 1, wherein the center block is surrounded by six bent portions.

6. The tire according to claim 1, wherein the tire rotation direction is not specified.

7. The tire according to claim 1, wherein the dimples are provided on the center blocks and the shoulder blocks.

8. 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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