tire

Abstract

To improve heat build-up resistance and earth removal performance.SOLUTION: Circumferential narrow grooves 21 and 22 have widened parts 61 formed with a constant depth which include expansion parts 61a with a broad width and connection parts 61b smoothly connecting to the circumferential narrow grooves from the expansion parts. Width-directional narrow grooves 41 and shoulder lug grooves 43 are arranged so that ends 41a and 43a thereof oppose to each other. Groove widths of the narrow grooves 21, 22 and 41 with respect to groove depths thereof are 10[%] or more and 25[%] or less. Center circumferential narrow grooves are formed in a zigzag shape in which long parts 21a and short parts 21b are arranged alternately in the tire circumferential direction. Lengths of the long parts with respect to maximum dimensions in the tire circumferential direction of the center blocks 31A are 65[%] or more and 100[%] or less. The number of shoulder blocks 32A arranged in the tire circumferential direction is 28 or more and 43 or less. In a tread part, a center tread gauge on a tire equatorial plane CL is 40[mm] or more, and a ratio of the center tread gauge with respect to groove depths of shoulder lug grooves is 105[%] or more and 185[%] or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to tires. [Background technology]

[0002] For example, Patent Document 1 describes a tire having, in its tread portion, one central narrow groove extending circumferentially in the tire central region, a pair of lateral narrow grooves extending circumferentially with the central narrow groove between them, lug grooves extending lateral to the tire width direction and passing through the single narrow groove, widthwise narrow grooves communicating with the lug grooves on the inner side in the tire width direction and extending to the central narrow groove, and a plurality of block land portions partitioned by the central narrow groove, the lateral narrow grooves, the lug grooves, and the widthwise narrow grooves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-152836 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in heavy-duty tires such as OTR (Off-The-Road) tires, heat generation in the tread area is likely to cause heat separation under severe operating conditions of high load and high speed, so ensuring heat generation resistance is desirable. Furthermore, in order to increase running costs, it is desirable to ensure wear resistance. Therefore, one approach for this type of tire is to improve heat generation resistance without sacrificing wear resistance by narrowing the heat generation grooves and suppressing block movement. However, this approach raises concerns about the deterioration of traction performance due to mud clogging caused by narrow grooves in the pattern and the occurrence of cracks originating from the narrow grooves. Therefore, in tires based on block patterns, there is a need to improve soil discharge performance while ensuring heat generation resistance.

[0005] An object of the present invention is to provide a tire that can improve heat resistance and soil discharge performance. [Means for solving the problem]

[0006] In order to achieve the above object, a tire according to one aspect of the present invention includes, in a tread portion, a center circumferential narrow groove extending continuously along the tire circumferential direction, a pair of shoulder circumferential narrow grooves extending continuously along the tire circumferential direction and arranged adjacent to each other on the tire widthwise outer side of the center circumferential narrow groove, widthwise narrow grooves extending along the tire width direction so as to divide a center land portion between each of the circumferential narrow grooves into center blocks, and shoulder lug grooves extending along the tire width direction so as to divide each shoulder land portion on both tire widthwise outer sides of each of the shoulder circumferential narrow grooves into shoulder blocks, and having one end communicating with the shoulder circumferential narrow groove and the other end passing through a ground contact edge, wherein the groove width of each of the circumferential narrow grooves is 10% or more and 25% or less of the groove depth of each of the circumferential narrow grooves. At least one of the circumferential narrow grooves has an expanded portion formed to a constant depth including an expanded portion wider than the circumferential narrow groove and a connecting portion smoothly connecting the expanded portion to the circumferential narrow groove, the ends of the widthwise narrow grooves are arranged opposite the ends of the shoulder lug grooves, the center circumferential narrow groove is formed in a zigzag shape with long portions and short portions alternately arranged in the tire circumferential direction, the length of the long side portion is 65% to 100% of the maximum dimension of the center block in the tire circumferential direction, the number of shoulder blocks arranged in the tire circumferential direction is 28 to 43, and the tread portion has a center tread gauge of 40 mm or more at the tire equatorial plane, and the center tread gauge is 105% to 185% of the groove depth of the shoulder lug grooves. [Effects of the Invention]

[0007] According to this invention, heat resistance and soil discharge performance can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view of a tread of a pneumatic tire according to an embodiment. [Figure 2] FIG. 2 is a partially enlarged meridian cross-sectional view of the pneumatic tire according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a plan view of a tread of another example of a pneumatic tire according to the embodiment. [Figure 5] FIG. 5 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 6] FIG. 6 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 7] FIG. 7 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 8] FIG. 8 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 the direction perpendicular to the tire rotational axis (not shown), which is the rotational axis of the pneumatic tire 1 of this embodiment. The tire radial inner side refers to the side toward the tire rotational axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotational axis as the central axis. The tire width direction refers to the direction parallel to the tire rotational axis. The tire width inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire width 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 rotational 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 width 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. Also, a cross section in the tire meridian direction (meridian cross section) refers to a cross section of the tire cut by a plane including the tire rotation axis.

[0011] 1 is a meridian cross section of a pneumatic tire 1 according to an embodiment. In this embodiment, a heavy-duty pneumatic radial tire mounted on heavy-duty vehicles such as trucks and buses will be described as an example. The pneumatic tire 1 according to this embodiment is particularly suitable for use as a tire mounted on the steering axle and drive axle of a heavy-duty vehicle.

[0012] The pneumatic tire 1 is formed symmetrically in the tire width direction with respect to the tire equatorial plane CL. For this reason, Fig. 2 shows a portion of one side in the tire width direction with the tire equatorial plane CL as the boundary. Note that Fig. 2 is an enlarged view of a meridian cross section of the pneumatic tire 1, and shows a cross section along widthwise narrow grooves 41 and shoulder lug grooves 43, which will be described later.

[0013] 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 portion 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 this embodiment, the carcass layer 13 is formed by stacking two carcass plies. The carcass layer 13 is toroidally laid between both 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 covering multiple carcass cords made of steel with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction with respect to the tire circumferential direction) of 80° to 90° in absolute value for radial tires, and 30° to 45° in absolute value for bias tires.

[0017] The belt layer 14 is also referred to as a belt member, and is formed by laminating a plurality of belt plies (also referred to as belts) 141-147, and is disposed by being wound around the outer periphery of the carcass layer 13. These belt plies 141-147 are combinations of belts of various configurations, such as a 0-degree belt and 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 that the tire is suitable for use in heavy-duty vehicles for construction and industrial use. The belt plies are formed by coating a plurality of steel belt cords (also referred to as wire rods) with coating rubber and rolling them. The pair of cross belts are formed by coating a plurality of steel belt cords with coating rubber and rolling them, and have cord angles of opposite signs to each other. 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 called a tread surface) 15A on the outer peripheral surface of the tread portion that comes into contact with the road surface during running. The outer ends of the tread surface 15A in the tire width direction are 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 of 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. The linear distance in the tire width direction when the tread surface 15A is unfolded between each ground contact edge T is defined as the unfolded width TDW.

[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 inner side in the tire radial direction of each bead core and the turned-up portion of the carcass layer 13 to the outer side in the tire width direction, 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. 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. 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 (also called the open groove width) is measured as the maximum distance between opposing groove walls at the groove opening on the tread surface 15A 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 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 tread surface 15A to the groove bottom when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. If the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0025] As shown in FIG. 1, the pneumatic tire 1 of the embodiment has a center circumferential narrow groove 21, shoulder circumferential narrow grooves 22, widthwise narrow grooves 41, shoulder lug grooves 43, and widened portions 61 on a tread surface 15A.

[0026] The center circumferential narrow groove 21 is a groove that extends continuously along the tire circumferential direction. The center circumferential narrow groove 21 is arranged on the tire equatorial plane CL. The shoulder circumferential narrow grooves 22 are grooves that extend continuously along the tire circumferential direction. A pair of shoulder circumferential narrow grooves 22 are arranged adjacent to each other on both outer sides in the tire width direction of the center circumferential narrow groove 21. Therefore, in the pneumatic tire 1, center land portions 31 are defined along the tire circumferential direction between the circumferential narrow grooves 21, 22, and shoulder land portions 32 are defined along the tire circumferential direction on the tire width direction outer sides of the shoulder circumferential narrow grooves 22.

[0027] The widthwise narrow grooves 41 are grooves that extend along the tire width direction. A plurality of widthwise narrow grooves 41 are provided in each center land portion 31, lined up in the tire circumferential direction. Each end 41a of the widthwise narrow groove 41 communicates with the center circumferential narrow groove 21 and the shoulder circumferential narrow groove 22 that are adjacent in the tire width direction. Therefore, in the pneumatic tire 1, the plurality of widthwise narrow grooves 41 divide each center land portion 31 into a plurality of center blocks 31A.

[0028] The shoulder lug grooves 43 are grooves that extend along the tire width direction. A plurality of shoulder lug grooves 43 are provided in each shoulder land portion 32, lined up in the tire circumferential direction. One end 43a of each shoulder lug groove 43 communicates with the shoulder circumferential narrow groove 22. Therefore, in the pneumatic tire 1, the shoulder land portion 32 is divided into a plurality of shoulder blocks 32A by the plurality of shoulder lug grooves 43. The number of shoulder blocks 32A lined up in the tire circumferential direction on one side of the tire width direction is 28 to 43 around the tire (one circumference in the tire circumferential direction). The other end 43a of each shoulder lug groove 43 passes through the ground contact edge T and reaches the buttress portion 15B. Therefore, in the pneumatic tire 1, the buttress portion 15B is divided into a plurality of sections together with the shoulder blocks 32A. Therefore, like the shoulder blocks 32A, the number of sections of the buttress portion 15B lined up in the tire circumferential direction is 28 to 43 around the tire (one circumference in the tire circumferential direction).

[0029] The widened portion 61 is provided in the shoulder circumferential narrow groove 22 and widens a part of the shoulder circumferential narrow groove 22 .

[0030] The above-mentioned grooves and widened portions 61 will be described in detail below.

[0031] As shown in FIG. 1 , the center circumferential narrow groove 21 has linear long portions 21a and short portions 21b. The long portions 21a are longer in the tire circumferential direction than the short portions 21b and are arranged at an incline with respect to the tire circumferential direction. The short portions 21b are shorter in the tire circumferential direction than the long portions 21a and are arranged at an incline with respect to the tire circumferential direction. The long portions 21a and the short portions 21b have angles with respect to the tire circumferential direction that are opposite in sign to each other and are arranged alternately and continuously in the tire circumferential direction. Therefore, the center circumferential narrow groove 21 is formed into a zigzag shape extending continuously along the tire circumferential direction by the long portions 21a and the short portions 21b being arranged alternately in the tire circumferential direction. Here, one end 41a of the widthwise narrow groove 41 is connected to the center circumferential narrow groove 21 and the other end 41a is connected to the shoulder circumferential narrow groove 22. One end 41a of the widthwise narrow groove 41 communicates with a bent portion where the long portion 21a and the short portion 21b of the center circumferential narrow groove 21 communicate with each other. The center circumferential narrow groove 21 has one long portion 21a and one short portion 21b arranged in one center block 31A defined by adjacent widthwise narrow grooves 41 in the tire width direction. The extension length La of one long portion 21a satisfies the relationship 65%≦La / Lmax≦100% with respect to the maximum circumferential dimension Lmax of one center block 31A in the tire circumferential direction.

[0032] The center circumferential narrow groove 21 has a groove width Wa that satisfies the relationship of 10%≦Wa / Da≦25% with respect to its groove depth Da. The center circumferential narrow groove 21 has a groove depth Da that satisfies the relationship of 50%≦Da / De≦100% with respect to the groove depth De of the shoulder lug grooves 43.

[0033] As shown in Fig. 1, the widthwise narrow grooves 41 and the shoulder lug grooves 43 are provided continuously along the tire width direction. The shoulder circumferential narrow grooves 22 communicate with the widthwise narrow grooves 41 and the shoulder lug grooves 43 at positions where the widthwise narrow grooves 41 and the shoulder lug grooves 43 communicate with each other. Therefore, the center blocks 31A and the shoulder blocks 32A are arranged adjacent to each other in the tire width direction with the shoulder circumferential narrow groove 22 between them. Therefore, like the shoulder blocks 32A, the number of center blocks 31A lined up in the tire circumferential direction is 28 to 43 around the tire (one circumferential revolution).

[0034] As shown in FIG. 1, each end 22a of the shoulder circumferential narrow groove 22 extending in the tire circumferential direction communicates with the widthwise narrow groove 41 and the shoulder lug groove 43 between the adjacent center block 31A and shoulder block 32A.

[0035] The groove width Wb of the shoulder circumferential narrow groove 22 and the groove depth Db thereof satisfy the relationship of 10%≦Wb / Db≦25%. The groove depth Db of the shoulder circumferential narrow groove 22 and the groove depth De of the shoulder lug groove 43 satisfy the relationship of 50%≦Db / De≦100%.

[0036] 1, within the tire width direction range of one center block 31A, one end 41a of the widthwise narrow groove 41 communicates with the center circumferential narrow groove 21, and the other end 41a communicates with the shoulder circumferential narrow groove 22. The widthwise narrow groove 41 is formed by bending along the tire width direction with a bent portion 41b between each end 41a.

[0037] Furthermore, the widthwise narrow groove 41 has a larger groove width at its other end 41a, which is connected to the shoulder circumferential narrow groove 22, compared to the other end. The groove width Wc is measured excluding the groove width at this other end 41a. The widthwise narrow groove 41 has a groove width Wc that satisfies the relationship of 10%≦Wc / Dc≦25% with respect to its own groove depth Dc. The widthwise narrow groove 41 has a groove depth Dc that satisfies the relationship of 50%≦Dc / De≦100% with respect to the groove depth De of the shoulder lug groove 43. Furthermore, as shown in FIG. 1, the center block 31A defined by the widthwise narrow groove 41 has a maximum dimension Wmax in the tire width direction that satisfies the relationship of 20%≦Wmax / TDW≦35% with respect to the developed width TDW of the tread surface 15A.

[0038] As shown in FIG. 1 , one or more widened portions 61 are provided in the shoulder circumferential narrow groove 22 between the ends 22a that communicate with the widthwise narrow groove 41 and the shoulder lug groove 43. One or more widened portions 61 are provided for each center block 31A and shoulder block 32A. The widened portions 61 are formed by cutting out portions of the center block 31A and the shoulder block 32A that are separated by the shoulder circumferential narrow groove 22 so that the widened portions 61 are wider than the shoulder circumferential narrow groove 22. The widened portions 61 are configured with an expanded portion 61a and a connecting portion 61b. The expanded portion 61a is a groove with an opening that is wider than the shoulder circumferential narrow groove 22. The expanded portion 61a is formed with a constant width. The connecting portion 61b is a groove with an opening that smoothly connects the expanded portion 61a to the shoulder circumferential narrow groove 22. The connecting portion 61b is formed so that its width narrows in a tapered manner from the expanded portion 61a toward the shoulder circumferential narrow groove 22. The expanded portion 61 also has curved portions 61c at the connecting portions of the openings between the expanded portion 61a and the connecting portion 61b and the openings between the connecting portion 61b and the shoulder circumferential narrow groove 22. The curved portions 61c have a predetermined radius R, which smoothly connects the openings between the expanded portion 61a and the connecting portion 61b and the openings between the connecting portion 61b and the shoulder circumferential narrow groove 22 without any corners.

[0039] As shown in FIG. 2, the widened portion 61 has a width Wh of the expanded portion 61a of 5 mm to 20 mm, and a constant depth Dh along the length Lh of the shoulder circumferential narrow groove 22. The widened portion 61 has a constant width Wh from its opening to its bottom at the depth Dh, and is tapered to smoothly connect to the shoulder circumferential narrow groove 22 at its bottom. The width Wh of the widened portion 61 satisfies the relationship of 200%≦Wh / Wb≦300% with respect to the groove width Wb of the shoulder circumferential narrow groove 22. The length Lh of the widened portion 61 satisfies the relationship of 25%≦Lh / Lb≦50% with respect to the groove length Lb per center block 31A of the shoulder circumferential narrow groove 22 having the widened portion 61.

[0040] The shoulder lug grooves 43 are provided on the surfaces of the tread surface 15A and the buttress portion 15B. The shoulder lug grooves 43 are formed on the tread surface 15A so that their groove widths gradually narrow toward one end 43a that communicates with the shoulder circumferential narrow groove 22. The shoulder lug grooves 43 are formed to have a constant groove width on the buttress portion 15B. The groove width We is measured on the buttress portion 15B. The groove depth De is measured as a maximum value based on the tread surface 15A. As shown in FIG. 2, the groove width We of the shoulder lug grooves 43 satisfies the relationship 10%≦We / P≦35% with respect to the pitch length P of the shoulder blocks 32A.

[0041] Hereinafter, with reference to FIG. 4, a pneumatic tire 1' of another example will be described.

[0042] 1 to 3 in that the shape of the shoulder circumferential narrow grooves 22 and the widened portion 62 are provided in the center circumferential narrow groove 21. The other configuration of the pneumatic tire 1' of the other example is the same as that of the pneumatic tire 1. Therefore, the configuration of the pneumatic tire 1' of the other example will be described with respect to the shape of the shoulder circumferential narrow grooves 22 and the widened portion 62 of the center circumferential narrow groove 21, and the other configuration will be assigned the same reference numerals and description thereof will be omitted.

[0043] 4, each end 22a of the shoulder circumferential narrow groove 22 extending in the tire circumferential direction communicates with the widthwise narrow groove 41 and the shoulder lug groove 43 between the adjacent center block 31A and shoulder block 32A. The shoulder circumferential narrow groove 22 is formed in a zigzag shape along the tire circumferential direction between the adjacent center block 31A and shoulder block 32A, with multiple bends 22b between each end 22a. In the pneumatic tire 1′, the shoulder circumferential narrow groove 22 is formed with two bends 22b between each end 22a.

[0044] As shown in FIG. 4, one or more widened portions 62 are provided in each long portion 21a of the center circumferential narrow groove 21. One or more widened portions 62 are provided for each center block 31A. The widened portions 62 are formed by cutting out a portion of the center block 31A across the center circumferential narrow groove 21 so that the widened portions 62 are wider than the center circumferential narrow groove 21 (long portion 21a). The widened portions 62 are configured to have an expanded portion 62a and a connecting portion 62b. The expanded portion 62a is a groove with an opening that is wider than the center circumferential narrow groove 21. The expanded portion 62a is formed with a constant width. The connecting portion 62b is a groove with an opening that smoothly connects from the expanded portion 62a to the center circumferential narrow groove 21. The connecting portion 62b is formed so that the width narrows in a tapered manner from the expanded portion 62a toward the center circumferential narrow groove 21. Further, the widened portion 62 has curved portions 62c at the connection portions of the openings of the expanded portion 62a and the connecting portion 62b and the openings of the connecting portion 62b and the central circumferential narrow groove 21. The curved portions 62c are formed with a predetermined radius R, similar to the widened portion 61, and smoothly connect the openings of the expanded portion 62a and the connecting portion 62b and the openings of the connecting portion 62b and the central circumferential narrow groove 21 without any corners.

[0045] As shown by the two-dot chain line in FIG. 2 , the width Wi of the expanded portion 62a of the widened portion 62 is 5 mm to 20 mm, and the depth Di is constant along the groove length Li of the widened portion 62, which is the direction in which the center circumferential narrow groove 21 (the elongated portion 21a) extends. The widened portion 62 has a constant width Wi from its opening to its bottom at its depth Di, tapering smoothly and connecting to the center circumferential narrow groove 21 at its bottom. The width Wi of the widened portion 62 satisfies the relationship 200%≦Wi / Wa≦300% with respect to the groove width Wa of the center circumferential narrow groove 21. The length Li of the widened portion 62 satisfies the relationship 25%≦Li / La≦50% with respect to the groove length La (the length of the elongated portion 21a) per center block 31A in the center circumferential narrow groove 21 having the widened portion 62.

[0046] The pneumatic tires 1, 1′ of the above-described embodiment are characterized in that at least one circumferential narrow groove (the shoulder circumferential narrow groove 22 or the center circumferential narrow groove 21) has widened portions 61, 62 formed with constant depths Dh, Di, including expanded portions 61a, 62a whose widths Wh, Wi are wider than those of the circumferential narrow grooves 22, 21 and connecting portions 61b, 62b that smoothly connect the expanded portions 61a, 62a to the circumferential narrow grooves 22, 21, and the widthwise narrow groove 41 has its end 41a disposed opposite to the end 43a of the shoulder lug groove 43, and the center circumferential narrow groove 21, the shoulder circumferential narrow groove 22 and the widthwise narrow groove 41 have their groove widths Wa, Wb, Wc wider than those of the circumferential narrow grooves 22, 21 and their groove depths Dh, Di. a, Db, Dc and is 10% or more and 25% or less, the central circumferential narrow groove 21 is formed in a zigzag shape with long portions 21a and short portions 21b arranged alternately in the circumferential direction of the tire, the length La of the long portions 21a is 65% or more and 100% or less of the maximum circumferential dimension Lmax of the center block 31A, the number of shoulder blocks 32A arranged in the circumferential direction of the tire is 28 or more and 43 or less, the tread portion has a center tread gauge Ga of 40 mm or more at the tire equatorial plane CL, and the center tread gauge Ga is 105% or more and 185% or less of the groove depth De of the shoulder lug grooves 43.

[0047] According to this pneumatic tire 1,1', by configuring it in the above pattern, when the narrow grooves 21, 22, 41 close during contact with the ground, the rigidity of the tread portion increases, strain in the tread portion can be reduced, and heat resistance can be improved. Moreover, in this pneumatic tire 1,1', by satisfying a relationship of 10% to 25% of the groove depths Da, Db, Dc of each narrow groove 21, 22, 41, the groove widths Wa, Wb, Wc of each narrow groove 21, 22, 41 can ensure heat dissipation performance and the function of the grooves closing to increase rigidity during contact with the ground. If the relationship is less than 10%, the heat dissipation effect is reduced, and if the relationship is more than 25%, the narrow grooves 21, 22, 41 have difficulty closing during contact with the ground, resulting in reduced rigidity. Furthermore, in this pneumatic tire 1, 1', the central circumferential narrow groove 21 is formed in a zigzag shape by the long portion 21a and the short portion 21b, and the length La of the long portion 21a is 65% to 100% of the maximum circumferential dimension Lmax of the center block 31A. This ensures the rigidity of the center block 31A and improves heat resistance. If it is less than 65%, the rigidity of the center block 31A in the tire width direction is weakened, and if it exceeds 100%, the rigidity of the center block 31A is reduced. Furthermore, this pneumatic tire 1, 1' ensures heat dissipation and rigidity by specifying the number of shoulder blocks 32A arranged in the tire circumferential direction. If the number of shoulder blocks 32A is less than 28, the number of shoulder lug grooves 43 is reduced, resulting in poor heat dissipation. If the number of shoulder blocks 32A is more than 43, the number of shoulder lug grooves 43 is increased, resulting in poor rigidity and poor heat resistance. Moreover, this pneumatic tire 1,1' can prevent the effects of heat accumulation and ensure heat dissipation by defining the relationship between the center tread gauge Ga and the groove depth De of the shoulder lug grooves 43. Furthermore, this pneumatic tire 1,1' has widened portions 61,62 in at least one circumferential narrow groove 22,21 that smoothly connect to the circumferential narrow groove 22,21 and have constant depths Dh, Di, allowing mud that has entered the circumferential narrow groove 22,21 to be efficiently discharged. Furthermore, this pneumatic tire 1,1' has ends 41a,43a of the widthwise narrow groove 41 and the shoulder lug grooves 43 that are continuously arranged facing each other, thereby improving heat dissipation and mud discharge. As a result, this pneumatic tire 1 can improve heat resistance and soil discharge performance.

[0048] In addition, in the pneumatic tires 1, 1' of the embodiment, the widths Wh, Wi of the expanded portions 61, 62a of the widened portions 61, 62 are 200% or more and 300% or less of the groove widths Wb, Wa of the circumferential narrow grooves 22, 21 that have the widened portions 61, 62.

[0049] According to this pneumatic tire 1, 1', by defining the widths Wh, Wi of the widened portions 61, 62 relative to the groove widths Wb, Wa of the circumferential narrow grooves 22, 21, it is possible to improve soil discharge performance without deteriorating heat resistance. If the widths Wh, Wi are less than twice the groove widths Wb, Wa of the circumferential narrow grooves 22, 21, soil discharge performance tends to be insufficient, while if they exceed three times the groove widths Wb, Wa, rigidity tends to weaken and heat resistance tends to deteriorate. Furthermore, the widths Wh, Wi of the widened portions 61, 62 are preferably 20 mm or less; if they exceed this width, mud tends to accumulate at the groove bottoms of the circumferential narrow grooves 22, 21, making them susceptible to rock cuts.

[0050] In addition, in the pneumatic tires 1, 1' of the embodiment, the lengths Lh, Li of the widened portions 61, 62 are 25% or more and 50% or less of the groove lengths Lb, La per center block 31A in the circumferential narrow grooves 22, 21 having the widened portions 61, 62.

[0051] According to this pneumatic tire 1, 1', soil discharge performance and heat resistance can be ensured by specifying the lengths Lh, Li of the widened portions 61, 62. If the lengths Lh, Li of the widened portions 61, 62 are less than 25% of the groove lengths Lb, La per block of the circumferential narrow grooves 22, 21, soil discharge performance tends to decrease, and if they exceed 50%, the groove lengths Lb, La of the circumferential narrow grooves 22, 21 become too short, causing insufficient meshing of the blocks formed by the circumferential narrow grooves 22, 21, reducing block rigidity and tending to deteriorate heat resistance.

[0052] In the pneumatic tires 1, 1' of the embodiment, the depths Dh, Di of the widened portions 61, 62 themselves are equal to or less than the groove depths Db, Da of the circumferential narrow grooves 22, 21 that include the widened portions 61, 62.

[0053] In this pneumatic tire 1,1', if the depths Dh, Di of the widened portions 61, 62 are shallow, soil discharge performance tends to decrease, and if the depths Dh, Di of the widened portions 61, 62 are deep, the rigidity of the blocks formed by the circumferential narrow grooves 22, 21 tends to decrease, resulting in a decrease in heat resistance. In order to obtain the above effects, it is preferable that the depths Dh, Di of the widened portions 61, 62 be 70[%]≦Dh / Db≦95[%] and 70[%]≦Di / Da≦95[%] with respect to the groove depths Db, Da of the circumferential narrow grooves 22, 21 having the widened portions 61, 62.

[0054] In the pneumatic tires 1, 1' of the embodiment, the widened portions 61, 62 have curved portions 61c, 62c at portions where the connecting portions 61b, 62b and the expanded portions 61a, 62a are connected and at portions where the connecting portions 61b, 62b and the circumferential narrow grooves 22, 21 are connected.

[0055] According to this pneumatic tire 1, 1', by having the curved portions 61c, 62c, there are no corners, and it is possible to prevent mud from clogging in the circumferential narrow grooves 22, 21. Furthermore, in this pneumatic tire 1, 1', it is preferable that the expanded portions 61a, 62a have straight lines of constant widths Wh, Wi that are parallel to the circumferential narrow grooves 22, 21, thereby improving the mud discharge performance of the circumferential narrow grooves 22, 21.

[0056] In the pneumatic tires 1, 1' of the embodiment, one or more widened portions 61, 62 are provided for each block (center block 31A).

[0057] According to this pneumatic tire 1, 1', soil discharge performance can be improved by providing each block with widened portions 61, 62. Furthermore, it is preferable to limit the number of widened portions 61, 62 to four or less per block in order to avoid deterioration of heat resistance due to a decrease in rigidity of the block.

[0058] In the pneumatic tire 1 of the embodiment, the widened portion 61 is provided in the shoulder circumferential narrow groove 22.

[0059] According to this pneumatic tire 1, mud is difficult to discharge in the shoulder circumferential narrow grooves 22 where the ground contact pressure is relatively low, so by providing the widened portions 61 in the shoulder circumferential narrow grooves 22, the soil discharge performance can be improved.

[0060] In the pneumatic tires 1, 1' of the embodiment, the center block 31A has a maximum dimension Wmax in the tire width direction that is 20% to 35% of the developed width TDW of the tread surface 15A.

[0061] In this pneumatic tire 1, 1', by specifying the tire width direction dimension of the center block 31A, excessive movement of the center block 31A can be suppressed, block rigidity can be ensured, and heat resistance performance can be improved. If the ratio is less than 20%, block rigidity tends to be low. If the ratio is more than 35%, the block rigidity of the center block 31A increases, but the shoulder blocks 43 move more, which deteriorates heat resistance performance and tends to shorten the tire life.

[0062] In the pneumatic tires 1, 1' of the embodiment, the groove depths Da, Db, Dc of the circumferential narrow grooves 21, 22 and the widthwise narrow groove 41 are 50% to 100% of the groove depth De of the shoulder lug groove 43.

[0063] According to this pneumatic tire 1, 1', the groove depths Da, Db, and Dc of the circumferential narrow grooves 21, 22 and the widthwise narrow groove 41 are ensured, ensuring heat dissipation and suppressing a decrease in heat resistance. The shallower the groove depths Da, Db, and Dc of the circumferential narrow grooves 21, 22 and the widthwise narrow groove 41, the lower the heat dissipation and the worse the heat resistance. If the depths Da, Db, and Dc are less than 50%, the heat dissipation tends to worsen, and if the depths are more than 100%, the effect of heat dissipation is reduced.

[0064] In the pneumatic tires 1, 1' of the embodiment, the groove width We of the shoulder lug grooves 43 is 10% or more and 35% or less of the pitch length P of the shoulder blocks 32A.

[0065] In the pneumatic tires 1, 1', the relationship between the groove width We of the shoulder lug grooves 43 and the pitch length P of the shoulder blocks 32A ensures heat dissipation and prevents a decrease in heat resistance, while ensuring block rigidity and heat resistance. If the relationship is less than 10%, heat dissipation tends to decrease and heat resistance tends to deteriorate, while if the relationship exceeds 35%, the rigidity of the shoulder blocks 32A decreases, tending to deteriorate heat resistance.

[0066] Furthermore, the pneumatic tires 1, 1' of the embodiment have five or more belt plies arranged therein and are used for heavy-duty construction or industrial vehicles.

[0067] In the present embodiment, as described above, the pneumatic tire 1, 1' has been described as an example of a tire. The pneumatic tire 1, 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, 1' described in the present embodiment can be arbitrarily applied to other tires within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires. [Example]

[0068] 5 to 8 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 and soil discharge performance.

[0069] 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, measuring the temperature of the tread center (tire equatorial plane). Based on the measurement results, an index rating is then calculated, with the conventional tire being used as the benchmark (100). The higher the rating, the better.

[0070] The soil discharge performance evaluation test involves mounting a 2400R35 pneumatic tire (test tire) on a specified rim, inflating it to the specified internal pressure, and mounting it on a construction dump truck. The tire is then driven off-road for 3,000 hours at speeds between 10 and 25 km / h, and the amount of mud clogging the circumferential narrow grooves is measured. Based on the measurement results, an index rating is then calculated, with the conventional tire being assigned a standard value of 100. The higher the rating, the better.

[0071] The conventional pneumatic tire does not have a center circumferential narrow groove, but has shoulder blocks formed by shoulder circumferential narrow grooves and shoulder lug grooves.

[0072] The pneumatic tire of the example mainly has a center circumferential narrow groove, shoulder circumferential narrow grooves, widthwise narrow grooves, shoulder lug grooves, center blocks, shoulder blocks, and widened portions, and satisfies the specified range.

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

[0074] The present disclosure includes the following inventions. [Invention 1] In the tread area, a center circumferential narrow groove extending continuously along the tire circumferential direction; a pair of shoulder circumferential narrow grooves extending continuously along the tire circumferential direction and arranged adjacent to each other on the tire width direction outer sides of the center circumferential narrow groove; widthwise narrow grooves extending along the tire width direction so as to divide a center land portion between each of the circumferential narrow grooves into center blocks, each end of which is connected to each of the adjacent circumferential narrow grooves; shoulder lug grooves, one end of which extends along the tire width direction so as to divide each shoulder land portion on both outer sides in the tire width direction of each shoulder circumferential narrow groove into shoulder blocks and which communicate with the shoulder circumferential narrow groove and the other end of which passes through the ground contact edge; Including, Each of the circumferential narrow grooves has a groove width of 10% to 25% of its own groove depth, At least one of the circumferential narrow grooves has an expanded portion having a width wider than the circumferential narrow groove and a connecting portion smoothly connecting the expanded portion to the circumferential narrow groove, and the expanded portion has a constant depth, The widthwise narrow grooves are arranged such that their ends face the ends of the shoulder lug grooves, The central circumferential narrow groove is formed in a zigzag shape in which long portions and short portions are alternately arranged in the tire circumferential direction, The length of the long side portion is 65% or more and 100% or less of the maximum dimension of the center block in the tire circumferential direction, The number of the shoulder blocks arranged in the tire circumferential direction is 28 or more and 43 or less, The tread portion has a center tread gauge of 40 mm or more at the tire equatorial plane, The center tread gauge is 105% or more and 185% or less of the groove depth of the shoulder lug groove, tire. [Invention 2] The width of the widened portion is 200% or more and 300% or less of the groove width of the circumferential narrow groove having the widened portion. A tire according to claim 1. [Invention 3] The length of the widened portion is 25% or more and 50% or less of the groove length per one of the center blocks in the circumferential narrow groove having the widened portion. The tire according to claim 1 or 2. [Invention 4] The widened portion has a depth equal to or less than the groove depth of the circumferential narrow groove having the widened portion. A tire according to any one of inventions 1 to 3. [Invention 5] The widened portion has a curved portion at a portion where the connecting portion and the expanded portion are connected and at a portion where the connecting portion and the circumferential narrow groove are connected. A tire according to any one of inventions 1 to 4. [Invention 6] One or more widening portions are provided for each block. A tire according to any one of inventions 1 to 5. [Invention 7] The widened portion is provided in the shoulder circumferential narrow groove. A tire according to any one of inventions 1 to 6. [Invention 8] The center block has a maximum dimension in the tire width direction of 20% to 35% of the developed width of the tread surface. A tire according to any one of inventions 1 to 7. [Invention 9] The groove depth of each of the circumferential narrow grooves and the widthwise narrow grooves is 50% or more and 100% or less of the groove depth of the shoulder lug groove. A tire according to any one of inventions 1 to 8. [Invention 10] The shoulder lug groove has a groove width of 10% or more and 35% or less of the pitch length of the shoulder block. A tire according to any one of inventions 1 to 9. [Invention 11] 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. A tire according to any one of inventions 1 to 10. [Explanation of symbols]

[0075] 1. Pneumatic tires (tires) 15A tread surface 21 Center circumferential narrow groove 21a Each long section 21b Short section 22 Shoulder circumferential narrow groove 31 Center Land Section 31A Center Block 32 Shoulder land area 32A Shoulder Block 41 Width direction narrow groove 41a end 43 Shoulder lug groove 43a edge 61 Widening section 61a Extension 61b Connection part 61c curved section 62 Widening section 62a Extension 62b Connection part 62c curved section

Claims

1. In the tread area, a center circumferential narrow groove extending continuously along the tire circumferential direction; a pair of shoulder circumferential narrow grooves extending continuously along the tire circumferential direction and arranged adjacent to each other on the outer sides of the center circumferential narrow groove in the tire width direction; widthwise narrow grooves extending along the tire width direction so as to divide a center land portion between each of the circumferential narrow grooves into center blocks, each end of which is connected to each of the adjacent circumferential narrow grooves; shoulder lug grooves, one end of which extends along the tire width direction so as to divide each shoulder land portion on both outer sides in the tire width direction of each shoulder circumferential narrow groove into shoulder blocks and which communicate with the shoulder circumferential narrow groove and the other end of which passes through the ground contact edge; Including, Each of the circumferential narrow grooves has a groove width of 10% or more and 25% or less of a groove depth of the circumferential narrow groove, At least one of the circumferential narrow grooves has an expanded portion having a width wider than the circumferential narrow groove and a connecting portion smoothly connecting the expanded portion to the circumferential narrow groove, and the expanded portion has a constant depth, The widthwise narrow grooves are arranged such that their ends face the ends of the shoulder lug grooves, The central circumferential narrow groove is formed in a zigzag shape in which long portions and short portions are alternately arranged in the tire circumferential direction, the length of the long portion is 65% or more and 100% or less of the maximum dimension of the center block in the tire circumferential direction, the number of shoulder blocks arranged in the tire circumferential direction is equal to or greater than 28 and is equal to or less than 43, The tread portion has a center tread gauge of 40 mm or more at the tire equatorial plane, The center tread gauge is 105% or more and 185% or less of the groove depth of the shoulder lug groove. tire.

2. The widened portion has a width that is 200% or more and 300% or less of the groove width of the circumferential narrow groove that includes the widened portion.

2. The tire of claim 1.

3. The length of the widened portion is 25% or more and 50% or less of the groove length per one of the center blocks in the circumferential narrow groove having the widened portion.

2. The tire of claim 1.

4. The widened portion has a depth equal to or less than the groove depth of the circumferential narrow groove having the widened portion.

2. The tire of claim 1.

5. The widened portion has a curved portion at a portion where the connecting portion and the expanded portion are connected and at a portion where the connecting portion and the circumferential narrow groove are connected.

2. The tire of claim 1.

6. One or more widening portions are provided for each block.

2. The tire of claim 1.

7. The widened portion is provided in the shoulder circumferential narrow groove.

2. The tire of claim 1.

8. The center block has a maximum dimension in the tire width direction of 20% to 35% of the developed width of the tread surface.

2. The tire of claim 1.

9. The groove depth of each of the circumferential narrow grooves and the widthwise narrow grooves is 50% or more and 100% or less of the groove depth of the shoulder lug groove.

2. The tire of claim 1.

10. The shoulder lug groove has a groove width of 10% or more and 35% or less of the pitch length of the shoulder block.

2. The tire of claim 1.

11. 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.

2. The tire of claim 1.

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