tire

Abstract

The present invention improves the performance for heat generation resistance and wear resistance. In the present invention, circumferential-direction narrow grooves 21, 22 and a width-direction narrow groove 41 each have the width that is 10-25% of the depth of each groove itself. A center block 31A comprises width-direction contoured sections 31Ab that, where mutually adjacent in the tire circumferential direction, mutually overlap in the tire width direction. The center circumferential-direction narrow groove 21 is formed in a zigzag shape, with long sections 21a and short sections 21b being disposed in alternation in the tire circumferential direction. The length of the long sections 21a is 65-100% of the maximum dimension of the center block 31A in the tire circumferential direction. 28-43 shoulder blocks 32A are aligned side-by-side in the tire circumferential direction. The center tread gauge of a tread section at the tire equatorial plane CL is at least 40 mm, and the center tread gauge is 105-185% of the depth of a shoulder lug groove 43.

Description

FIG. 6 is a table showing results of performance tests of the pneumatic tire according to the embodiment. FIG. 7 is a table showing results of performance tests of the pneumatic tire according to the embodiment. FIG. 8 is a table showing results of performance tests of pneumatic tires according to the embodiment. Description of Embodiments

[0009] An embodiment according to the present invention will be described in detail below with reference to the drawings. However, the invention is not limited to the embodiment. Constituent elements of the embodiment include elements that are substitutable while maintaining consistency with the invention and obviously substitutable elements. A plurality of modifications described in the embodiment can be combined as desired within the scope obvious to those skilled in the art.

[0010] In the following description, the term "tire radial direction" refers to a direction orthogonal to a tire rotation axis (not illustrated), which is a rotation axis of a pneumatic tire 1 according to the embodiment, the term "inner side in the tire radial direction" refers to a side toward the tire rotation axis in the tire radial direction, and the term "outer side in the tire radial direction" refers to a side away from the tire rotation axis in the tire radial direction. The term "tire circumferential direction" refers to a circumferential direction with the tire rotation axis as a center axis. The term "tire width direction" refers to a direction parallel with the tire rotation axis, the term "inner side in the tire width direction" refers to a side toward a tire equatorial plane (tire equator line) CL in the tire width direction, and the term "outer side in the tire width direction" refers to a side away from the tire equatorial plane CL in the tire width direction. The term "tire equatorial plane CL" refers to a plane that is orthogonal to the tire rotation axis and that passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL aligns, in position in the tire width direction, with a center line in the tire width direction corresponding to a center position of the pneumatic tire 1 in the tire width direction. The term "tire equator line" refers to a line that lies on the tire equatorial plane CL and extends in the tire circumferential direction of the pneumatic tire 1. The term "cross-section in the tire meridian direction (meridian cross-sectional view)" refers to a cross section of the tire taken along a plane that includes the tire rotation axis.

[0011] FIG. 1 is a meridian cross-sectional view of the pneumatic tire 1 according to the embodiment. In the present embodiment, a heavy duty pneumatic radial tire to be mounted on a heavy load vehicle such as a truck or a bus will be described as an example. The pneumatic tire 1 according to the present embodiment is particularly suitable for use as a tire to be mounted on a steering axle and a drive axle of a heavy load vehicle.

[0012] The pneumatic tire 1 is formed to be symmetrical in the tire width direction with respect to the tire equatorial plane CL. Therefore, FIG. 2 illustrates a part of one side of the tire in the tire width direction with respect to the tire equatorial plane CL. FIG. 2 is a partially enlarged meridian crosssectional view of the pneumatic tire 1, and illustrates a cross section along a width direction narrow groove 41 and a shoulder lug groove 43, which will be described later.

[0013] The pneumatic tire 1 according to the embodiment has an annular structure with the tire rotation axis as its center and includes a pair of bead cores (not illustrated), a pair of bead fillers (not illustrated), 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 illustrated).

[0014] The pair of bead cores are formed by winding one or more bead wires made of steel annularly multiple times, are embedded in bead portions, and constitute cores of the bead portions on both sides in the tire width direction, although not illustrated.

[0015] The pair of bead fillers are each composed of a lower filler and an upper filler, are disposed on an outer circumference in the tire radial direction of the pair of bead cores, and reinforce the bead portions, although not illustrated.

[0016] The carcass layer 13 has a single-layer structure including one carcass ply or a multilayer structure including a plurality of layered carcass plies. In the pneumatic tire 1 according to the embodiment, the carcass layer 13 is formed of two layered carcass plies. The carcass layer 13 extends between the bead cores in a toroidal shape, thereby forming the framework of the tire. Both end portions of the carcass layer 13 are turned back toward the outer side in the tire width direction and fixed to wrap the bead cores and the bead fillers. The carcass plies of the carcass layer 13 are constituted by covering, with coating rubber, a plurality of carcass cords made of steel and performing a rolling process on the carcass cords, and has a cord angle (defined as an inclination angle of a longitudinal direction of the carcass cords with respect to the tire circumferential direction) of 80° or more and 90° or less as an absolute value for a radial tire and 30° or more and 45° or less for a bias tire.

[0017] The belt layer 14, which is also called a belt member, is formed by layering a plurality of belt plies (also called belts) 141 to 147 and is disposed around an outer circumference of the carcass layer 13. These belt plies 141 to 147 are formed by combining belts of various configurations, such as a zerodegree belt and a pair of cross belts. In the pneumatic tire 1 according to the embodiment, the belt layer 14 is preferably formed by layering five or more belt plies so as to be suitably used for heavy load vehicles for construction and industrial use. The belt plies are constituted by covering, with coating rubber, a plurality of belt cords (also called wires) made of steel and performing a rolling process on the belt cords. The pair of cross belts are constituted by covering, with coating rubber, a plurality of belt cords made of steel and performing a rolling process on the belt cords, and have a so-called crossply structure in which respective belt cords have cord angles of opposite signs and are layered such that the longitudinal directions of the belt cords cross each other.

[0018] The tread rubber 15 is disposed on the outer circumference of the carcass layer 13 and the belt layer 14 in the tire radial direction and constitutes a tread portion of the pneumatic tire 1. In the tread portion, the tread rubber 15 constitutes a tread surface 15A (also called a road contact surface) on an outer circumferential surface that comes into contact with a road surface during travel. An end portion of the tread surface 15A on the outer side in the tire width direction is a ground contact edge T. The tread rubber 15 includes, in side portions of the tread portion on both outer sides in the tire width direction from the ground contact edge T on the tread surface 15A, buttress portions 15B that do not contact a road surface during travel. The buttress portions 15B are each provided in the tread rubber 15 on the outer side in the tire width direction and the inner side in the tire radial direction from the ground contact edge T to the sidewall rubber 16. The linear distance in the tire width direction of the tread surface 15A when developed between the ground contact edges T is defined as a development width TDW.

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

[0020] The pair of rim cushion rubbers extend from an inner side in the tire radial direction of the respective bead cores and turned-back portions of the carcass layer 13 toward the outer side in the tire width direction, and constitute rim fitting surfaces of the bead portions, although not illustrated.

[0021] As illustrated in FIG. 2, the pneumatic tire 1 according to the embodiment has a tread pattern on the tread portion (tread surface 15A and buttress portion 15B). Here, dimensions in the tread pattern are measured with the tire mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

[0022] The term "specified rim" refers to a "standard rim" defined by the Japan Automobile Tyre Manufacturers Association, Inc. (JATMA), a "Design Rim" defined by the Tire and Rim Association, Inc. (TRA), or a "Measuring Rim" defined by the European Tyre and Rim Technical Organisation (ETRTO). The term "specified internal pressure" refers to a "maximum air pressure" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES " specified by ETRTO. The term "specified load" refers to a "maximum load capacity" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "LOAD CAPACITY" specified by ETRTO.

[0023] A groove width (also called a groove opening width) is measured as a maximum value of a distance between opposed groove walls of a groove opening portion in the surface of the tread surface 15A or the 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 portion includes a notch portion or a chamfered portion, the groove width is measured by using, as end points, intersection points of an extension line of a tread contact surface and extension lines of the groove walls in a cross section parallel with the tire width direction and the tire radial direction.

[0024] A groove depth is measured as a maximum value of a 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 in an unloaded state. In a configuration in which partial irregular portions or sipes are provided at a groove bottom, the groove depth is measured excluding the partial irregular portions or the sipes.

[0025] As illustrated in FIG. 1, the pneumatic tire 1 according to the embodiment includes: in the tread surface 15A, a center circumferential narrow groove 21; shoulder circumferential narrow grooves 22; width direction narrow grooves 41; one-side opening narrow grooves 42, shoulder lug grooves 43; and shoulder dimples 51. As illustrated in FIG. 1, the pneumatic tire 1 according to the embodiment includes buttress dimples 52 in the surface of the buttress portion 15B.

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

[0027] The width direction narrow grooves 41 are grooves extending in the tire width direction. A plurality of width direction narrow grooves 41 are provided side by side in the tire circumferential direction in each center land portion 31. Each end 41a of the width direction narrow groove 41 communicates with the center circumferential narrow groove 21 and the shoulder circumferential narrow groove 22 adjacent to each other in the tire width direction. Therefore, in the pneumatic tire 1, each center land portion 31 is partitioned into a plurality of center blocks 3 1A by the plurality of width direction narrow grooves 41.

[0028] The one-side opening narrow groove 42 is a groove extending along the tire width direction. One one-side opening narrow groove 42 is provided in each center block 31A.

[0029] The shoulder lug grooves 43 are grooves extending along the tire width direction. A plurality of shoulder lug grooves 43 are provided side by side in the tire circumferential direction in each shoulder land portion 32. One end 43a of the shoulder lug groove 43 communicates with the shoulder circumferential narrow groove 22. Therefore, in the pneumatic tire 1, each shoulder land portion 32 is partitioned into a plurality of shoulder blocks 32A by the plurality of shoulder lug grooves 43. The number of shoulder blocks 32A arranged in the tire circumferential direction on one side in the tire width direction is 28 or more and 43 or less on the tire circumference (per round in the tire circumferential direction). The other end 43a of the shoulder lug groove 43 is provided to penetrate the ground contact edge T and reach the buttress portion 15B. Therefore, in the pneumatic tire 1, a plurality of buttress portions 15B are defined together with the shoulder blocks 32A. Thus, the number of buttress portions 15B arranged in the tire circumferential direction is 28 or more and 43 or less on the tire circumference (per round in the tire circumferential direction), as in the shoulder blocks 32A.

[0030] The shoulder dimples 51 are recessed portions recessed from the tread surface 15A. The shoulder dimples 51 are disposed between the shoulder lug grooves 43 adjacent to each other in the tire circumferential direction, one shoulder dimple 51 in each shoulder block 32A.

[0031] The buttress dimples 52 are recessed portions recessed from the surface of the buttress portions 15B. The buttress dimples 52 are disposed between the shoulder lug grooves 43 adjacent to each other in the tire circumferential direction, one buttress dimple 52 in each buttress portion 15B defined together with the shoulder block 32A.

[0032] Hereinafter, the details of the grooves and the dimples will be described.

[0033] As illustrated in FIG. 1, the center circumferential narrow groove 21 has a long portion 21a and a short portion 21b that are straight. The long portion 21a is a portion that is longer in the tire circumferential direction than the short portion 21b, and is disposed so as to be inclined with respect to the tire circumferential direction. The short portion 21b is a portion that is shorter in the tire circumferential direction than the long portion 21a, and is disposed so as to be inclined with respect to the tire circumferential direction. The long portion 21a and the short portion 21b have angles with respect to the tire circumferential direction with different signs from each other, and are disposed alternately and continuously in the tire circumferential direction. Thus, the center circumferential narrow groove 21 is formed in a zigzag shape continuously extending along the tire circumferential direction by alternately arranging the long portion 21a and the short portion 21b in the tire circumferential direction. Here, the width direction narrow groove 41 has one end 41a communicating with the center circumferential narrow groove 21 and the other end 41a communicating with the shoulder circumferential narrow groove 22. The width direction narrow groove 41 has one end 41a communicating 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. In the center circumferential narrow groove 21, one long portion 21a and one short portion 21b are disposed in one center block 31A defined by the width direction narrow grooves 41 adjacent to each other in the tire width direction. An extension length La of one long portion 21a has a relationship of 65% < La / Lmax < 100% with respect to a maximum dimension Lmax of one center block 31A in the tire circumferential direction.

[0034] The center circumferential narrow groove 21 has a groove width Wa and a groove depth Da that satisfy a relationship of 10% < Wa / Da < 25%. The groove depth Da of the center circumferential narrow groove 21 with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 50% < Da / De < 100%.

[0035] As illustrated in FIG. 1, the width direction narrow groove 41 and the shoulder lug groove 43 are provided continuously along the tire width direction. The shoulder circumferential narrow groove 22 communicates with the width direction narrow groove 41 and the shoulder lug groove 43 at a position where the width direction narrow groove 41 and the shoulder lug groove 43 communicate with each other. Therefore, the center block 31A and the shoulder block 32A are disposed adjacent to each other in the tire width direction with the shoulder circumferential narrow groove 22 interposed therebetween. Thus, the number of center blocks 31A arranged in the tire circumferential direction is 28 or more and 43 or less on the tire circumference (per round in the tire circumferential direction), as in the shoulder blocks 32A.

[0036] As illustrated in FIG. 1, each end 22a of the shoulder circumferential narrow groove 22 extending in the tire circumferential direction communicates with the width direction narrow groove 41 and the shoulder lug groove 43 between the center block 31A and the shoulder block 32A adjacent to each other. The shoulder circumferential narrow groove 22 is formed in a zigzag shape along the tire circumferential direction between the center block 31A and the shoulder block 32A adjacent to each other, and has a plurality of bent portions 22b between the ends 22a. In the pneumatic tire 1 according to the embodiment, the shoulder circumferential narrow groove 22 is formed to have two bent portions 22b between the ends 22a. Therefore, the center block 31A and the shoulder block 32A have circumferential irregular portions 31Aa and 32Aa in which blocks adjacent to each other in the tire width direction mate with each other in the tire circumferential direction. The circumferential irregular portions 31Aa and 32Aa mate with each other at two or more locations (two locations in the pneumatic tire 1 according to the embodiment) between one block 31A and one block 32A adjacent to each other in the tire width direction.

[0037] The shoulder circumferential narrow groove 22 has a groove width Wb and a groove depth Db that satisfy a relationship of 10% < Wb / Db < 25%. The groove depth Db of the shoulder circumferential narrow groove 22 with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 50% < Db / De < 100%.

[0038] As illustrated in FIG. 1, the width direction narrow groove 41 has one end 41A communicating with the center circumferential narrow groove 21 and the other end 41a communicating with the shoulder circumferential narrow groove 22 in a range of one center block 31A in the tire width direction. The width direction narrow groove 41 is formed to have a bent portion 41b between the ends 41a to be bent along the tire width direction. Therefore, the center block 31A has a width direction irregular portion 31Ab in which center blocks adjacent to each other in the tire circumferential direction mate and overlap each other in the tire width direction.

[0039] The width direction narrow groove 41 has a larger groove width at the other end 41a communicating with the shoulder circumferential narrow groove 22 than at the other portions. The groove width Wc is measured excluding the groove width at the other end 41a. The width direction narrow groove 41 has a groove width Wc and a groove depth Dc that satisfy a relationship of 10% < Wc / Dc < 25%. The groove depth Dc of the width direction narrow groove 41 with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 50% < Dc / De < 100%. As illustrated in FIG. 1, a maximum dimension Wmax in the tire width direction of the center block 31A defined by the width direction narrow groove 41 with respect to the development width TDW of the tread surface 15A satisfies a relationship of 20% < Wmax / TDW < 35%.

[0040] As illustrated in FIG. 1, the one-side opening narrow groove 42 has one end 42a communicating with the middle of the shoulder circumferential narrow groove 22 and the other end 42a terminating within the center block 31A in a range of one center block 31A. The one-side opening narrow groove 42 is formed to have a bent portion 42b and be bent along the tire width direction on the side of the terminating other end 42a.

[0041] The one-side opening narrow groove 42 has a groove width Wd and a groove depth Dd that satisfy a relationship of 10% < Wd / Dd < 25%. The groove depth Dd of the one-side opening narrow groove 42 with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 75% < Dd / De < 100% (see FIG. 2).

[0042] The shoulder lug groove 43 is provided in the tread surface 15A and the surface of the buttress portion 15B. The shoulder lug groove 43 is formed in the tread surface 15A so as to gradually narrow toward one end 43a communicating with the shoulder circumferential narrow groove 22. The shoulder lug groove 43 is formed with a constant groove width in the buttress portion 15B. The groove width We is measured at the buttress portion 15B. The maximum value of the groove depth De is measured with reference to the tread surface 15A. As illustrated in FIG. 1, the groove width We of the shoulder lug groove 43 with respect to a pitch length P of the shoulder blocks 32A satisfies a relationship of 10% < We / P < 35%.

[0043] A depth Df of the shoulder dimple 51 with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 10% < Df / De < 50%.

[0044] A depth Dg of the buttress dimple 52 with respect to the development width TDW of the tread surface 15A satisfies a relationship of 1% < Dg / TDW < 2.5%.

[0045] As illustrated in FIG. 2, the tread portion having the grooves and the dimples described above has a center tread gauge Ga of 40 mm < Ga on the tire equatorial plane CL. The center tread gauge Ga is the shortest distance from the tread surface 15A to the belt cord of the outermost belt ply (belt ply 147) in the tire radial direction on the tire equatorial plane CL. The center tread gauge Ga with respect to the groove depth De of the shoulder lug groove 43 satisfies a relationship of 105% < Ga / De < 185%.

[0046] In the pneumatic tire 1 according to the embodiment described above, as a feature thereof, the circumferential narrow grooves 21 and 22 and the width direction narrow grooves 41 each have a groove width Wa, Wb, and Wc of 10% or more and 25% or less of a groove depth Da, Db, and Dc thereof, the center blocks 31A each have a width direction irregular portion 31Ab in which center blocks adjacent to each other in the tire circumferential direction overlap each other in the tire width direction, the center circumferential narrow groove 21 is formed in a zigzag shape in which a long portion 21a and a short portion 21b are alternately disposed in the tire circumferential direction, the long portion 21a has a length of 65% or more and 100% or less of a maximum dimension Lmax of the center blocks 31A in the tire circumferential direction, the number of the shoulder blocks 32A arranged in the tire circumferential direction is 28 or more and 43 or less, the tread portion has a center tread gauge Ga on a tire equatorial plane CL of 40 mm or more, and the center tread gauge Ga is 105% or more and 185% or less of a groove depth De of the shoulder lug grooves 43.

[0047] In the pneumatic tire 1, by configuring the pneumatic tire 1 into the above-described pattern, when the narrow grooves 21, 22, and 41 are closed at the time of grounding, the rigidity of the tread portion is increased, the distortion of the tread portion can be reduced, and the heat build-up resistance performance can be improved. In the pneumatic tire 1, heat dissipation can be improved by disposing the narrow grooves 21, 22, and 41 along the tire circumferential direction or the tire width direction. In the pneumatic tire 1, the groove widths Wa, Wb, and Wc of the narrow grooves 21, 22, and 41 satisfy a relationship of 10% or more and 25% or less of the groove depths Da, Db, Dc of the narrow grooves, and thus heat dissipation and a function of increasing rigidity by closing the grooves at the time of grounding can be ensured. When the ratio is less than 10%, the heat dissipation effect is reduced, and when the ratio is more than 25%, the narrow grooves 21, 22, and 41 are less likely to be closed at the time of grounding, and rigidity is reduced. Moreover, in the pneumatic tire 1, the center blocks 31A adjacent in the tire circumferential direction overlap and mate with each other in the tire width direction at the width direction irregular portions 31Ab, and thus the rigidity against the motion in the tire width direction is increased, and heat build-up resistance performance and wear resistance performance can be improved. Moreover, in the pneumatic tire 1, the center circumferential narrow groove 21 is formed in a zigzag shape with a long portion 21a and a short portion 21b, and the long portion 21a has a length La of 65% or more and 100% or less of a maximum dimension Lmax of the center blocks 31A in the tire circumferential direction, thereby ensuring the rigidity of the center blocks 31A and ensuring the effect of the width direction irregular portions 31Ab of the center blocks 31A. When the ratio is less than 65%, the overlap between the irregular portions 31Ab is small, and the rigidity against the motion in the tire width direction is decreased, and when the ratio is more than 100%, the rigidity of the center blocks 31A is reduced. Moreover, in the pneumatic tire 1, the number of shoulder blocks 32A arranged in the tire circumferential direction is specified, and thus heat dissipation and rigidity can be ensured. When the number of shoulder blocks 32A is less than 28, the number of shoulder lug grooves 43 is reduced and heat dissipation is deteriorated, and when the number of shoulder blocks 32A is more than 43, the number of shoulder lug grooves 43 is increased, rigidity is decreased, and heat build-up resistance performance is deteriorated. Moreover, in the pneumatic tire 1, by defining the relationship between the dimension of the center tread gauge Ga and the groove depth De of the shoulder lug grooves 43, the effect of heat accumulation can be prevented, and heat dissipation can be ensured. As a result, the pneumatic tire 1 can provide improved heat buildup resistance performance and wear resistance performance.

[0048] In the pneumatic tire 1 according to the embodiment, the center blocks 31A and the shoulder blocks 32A have a circumferential irregular portion 31Aa and 32Aa in which blocks adjacent to each other in the tire width direction mate with each other in the tire circumferential direction at two or more locations between one center block 31A and one shoulder block 32A.

[0049] In the pneumatic tire 1, the circumferential irregular portions 31Aa and 32Aa suppress the center block 31A and the shoulder block 32A against the motion in the tire circumferential direction, and thus heat build-up resistance performance and wear resistance performance can be improved.

[0050] In the pneumatic tire 1 according to the embodiment, the center blocks 31A have a maximum dimension Wmax in the tire width direction of 20% or more and 35% or less of a development width TDW of a tread surface 15A.

[0051] In the pneumatic tire 1, by defining the dimension of the center blocks 31A in the tire width direction, excessive motion of the center blocks 31A can be suppressed to ensure block rigidity, and heat build-up resistance performance and wear resistance performance can be improved. When the maximum dimension is less than 20%, the block rigidity tends to be low, and when the maximum dimension is more than 35%, the block rigidity of the center blocks 31A increases, but the motion of the shoulder blocks 43 increases accordingly, and wear resistance performance and heat build-up resistance performance deteriorate, and the tire service life tends to deteriorate.

[0052] In the pneumatic tire 1 according to the embodiment, each of the circumferential narrow grooves 21 and 22 and the width direction narrow grooves 41 has a groove depth Da, Db, and Dc of 50% or more and 100% or less of a groove depth De of the shoulder lug grooves 43.

[0053] In the pneumatic tire 1, the groove depth Da, Db, and Dc of each of the circumferential narrow grooves 21 and 22 and the width direction narrow grooves 41 is ensured, heat dissipation is ensured, and a decrease in heat buildup resistance performance can be suppressed. As the groove depth Da, Db, and Dc of each of the circumferential narrow grooves 21 and 22 and the width direction narrow grooves 41 is smaller, heat dissipation tends to decrease, and heat build-up resistance performance tends to deteriorate. When the ratio is less than 50%, heat dissipation tends to deteriorate, and when the ratio is more than 100%, the effect of the heat dissipation becomes small.

[0054] In the pneumatic tire 1 according to the embodiment, the shoulder lug grooves 43 have a groove width We of 10% or more and 35% or less of a pitch length P of the shoulder blocks 32A.

[0055] In the pneumatic tire 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 suppresses a decrease in heat build-up resistance performance, and ensures block rigidity and ensures wear resistance performance and heat build-up resistance performance. When the ratio is less than 10%, heat dissipation is decreased and heat build-up resistance performance tends to be deteriorated, and when the ratio is more than 35%, the rigidity of the shoulder blocks 32A is decreased and the wear resistance performance and the heat build-up resistance performance tend to be deteriorated.

[0056] In the pneumatic tire 1 according to the embodiment, the one-side opening narrow groove 42 has a groove width Wd of 10% or more and 25% or less of a groove depth Dd of the one-side opening narrow groove 42, and the groove depth Dd of the one-side opening narrow groove 42 is 75% or more and 100% or less of the groove depth De of the shoulder lug grooves 43.

[0057] In the pneumatic tire 1, by disposing the one-side opening narrow groove 42, heat dissipation can be enhanced and heat build-up resistance performance can be improved. By defining the groove width Wd and the groove depth Dd of the one-side opening narrow groove 42, it is possible to suppress a decrease in rigidity and a decrease in heat dissipation of the center blocks 31A, and to ensure wear resistance performance and heat build-up resistance performance. When the groove width Wd is less than 10% of the groove depth Dd, heat dissipation tends to deteriorate, and when the groove width Wd is more than 25% thereof, the one-side opening narrow groove 42 is not closed, and thus rigidity decreases, and wear resistance performance and heat build-up resistance performance tend to deteriorate. Further, when the groove depth Dd is less than 75% of the groove depth De, heat dissipation tends to deteriorate, and when the groove depth Dd is more than 100% thereof, the effect of the heat dissipation becomes small.

[0058] In the pneumatic tire 1 according to the embodiment, the buttress dimples 52 in surfaces of buttress portions 15B have a depth Dg of 1% or more and 2.5% or less of a development width TDW of a tread surface 15A.

[0059] In the pneumatic tire 1, by disposing the buttress dimples 52 in the buttress portions 15B, heat dissipation is improved, the volume of the tread rubber 15 is reduced, and heat build-up resistance performance is improved. In the pneumatic tire 1, by defining the depth Dg of the buttress dimples 52, the above-described effect is significantly obtained while suppressing the deterioration of durability due to the decrease in rigidity of the buttress portions 15B. When the ratio is less than 1%, the effect of the buttress portions 15B cannot be expected, and when the ratio is more than 2.5%, the rigidity of the buttress portions 15B tends to decrease, and the durability tends to decrease.

[0060] In the pneumatic tire 1 according to the embodiment, the shoulder dimples 51 in the shoulder blocks 32A have a depth Df of 10% or more and 50% or less of the groove depth De of the shoulder lug grooves 43.

[0061] In the pneumatic tire 1, by disposing the shoulder dimples 51 in the shoulder blocks 32A, heat dissipation is improved, the volume of the tread rubber 15 is reduced, and heat build-up resistance performance is improved. In the pneumatic tire 1, by defining the depth Df of the shoulder dimples 51, the above-described effect is significantly obtained while suppressing the deterioration of durability due to the decrease in rigidity of the shoulder blocks 32A. When the ratio is less than 10%, the effect of the heat build-up resistance performance tends to be low due to a decrease in the volume of the tread rubber 15, and when the ratio is more than 50%, the wear resistance performance and the heat build-up resistance performance tend to deteriorate due to a decrease in rigidity.

[0062] In the pneumatic tire 1 according to the embodiment, five or more belt plies are disposed, and the pneumatic tire 1 is used for a heavy load vehicle for construction or industrial use.

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

[0064] FIGS. 5 to 8 are tables showing the results of performance tests of the pneumatic tire according to the embodiment. Hereinafter, performance evaluation tests conducted on a pneumatic tire of Conventional Example and pneumatic tires of Examples according to the embodiment will be described. The performance evaluation tests included tests on heat build-up resistance performance and wear resistance performance.

[0065] In the evaluation test of the heat build-up resistance performance, an indoor drum test was performed at a test speed of 10 km / h for 24 hours in a state where a pneumatic tire (test tire) of a tire size of 2400R35 is mounted on a specified rim, inflated to a specified internal pressure, and applied with 85% of a specified load, and the temperature of a tread center portion (tire equatorial plane) was measured. On the basis of the measurement results, the evaluation is expressed as index values determined with reference to the value (100) of Conventional Example. In the evaluation, larger values are more preferable.

[0066] In the evaluation test of the wear resistance performance, a pneumatic tire (test tire) of a tire size of 2400R35 was mounted on a specified rim, inflated to a specified internal pressure, and mounted on a dump truck for construction machinery, off-road travel was performed at 10 km / h to 25 km / h for 3000 hours, and the wear amount of the tread surface was measured. On the basis of the measurement results, the evaluation is expressed as index values determined with reference to the value (100) of Conventional Example. In the evaluation, larger values are more preferable.

[0067] The pneumatic tire of Conventional Example does not have shoulder circumferential narrow grooves, and has shoulder blocks formed by a center circumferential narrow groove and shoulder lug grooves.

[0068] The pneumatic tires of Examples mainly include a center circumferential narrow groove, shoulder circumferential narrow grooves, width direction narrow grooves, shoulder lug grooves, center blocks, and shoulder blocks, and satisfy the specified ranges.

[0069] The test results show that in the pneumatic tires of Examples, heat buildup resistance performance and wear resistance performance are improved with respect to Conventional Example.

[0070] The present disclosure includes the following inventions. Invention 1 A tire including: in a tread portion, a center circumferential narrow groove extending continuously along a tire circumferential direction; a pair of shoulder circumferential narrow grooves extending continuously along the tire circumferential direction and disposed on outer sides in a tire width direction of the center circumferential narrow groove and adjacent thereto; width direction narrow grooves extending along the tire width direction, defining a center land portion between the circumferential narrow grooves into center blocks, and having opposite ends communicating with respective adjacent circumferential narrow grooves; and shoulder lug grooves extending along the tire width direction, defining shoulder land portions on both outer sides in the tire width direction of the shoulder circumferential narrow grooves into shoulder blocks, and having one end communicating with a respective one of the shoulder circumferential narrow grooves and the other end passing through a ground contact edge; the circumferential narrow grooves and the width direction narrow grooves each having a groove width of 10% or more and 25% or less of a groove depth thereof, the center blocks each having a width direction irregular portion in which center blocks adjacent to each other in the tire circumferential direction overlap each other in the tire width direction, the center circumferential narrow groove being formed in a zigzag shape in which a long portion and a short portion are alternately disposed in the tire circumferential direction, the long portion having a length of 65% or more and 100% or less of a maximum dimension of the center blocks in the tire circumferential direction, the number of the shoulder blocks arranged in the tire circumferential direction being 28 or more and 43 or less, the tread portion having a center tread gauge on a tire equatorial plane of 40 mm or more, and the center tread gauge being 105% or more and 185% or less of a groove depth of the shoulder lug grooves. Invention 2 The tire according to invention 1, in which the center blocks and the shoulder blocks each have two or more circumferential irregular portions at which a center block and an adjacent shoulder block in the tire width direction mate with each other in the tire circumferential direction. Invention 3 The tire according to invention 1 or 2, in which the center blocks each have a maximum dimension in the tire width direction of 20% or more and 35% or less of a development width of a tread surface. Invention 4 The tire according to any one of inventions 1 to 3, in which the circumferential narrow grooves and the width direction narrow grooves each have a groove depth of 50% or more and 100% or less of a groove depth of the shoulder lug grooves. Invention 5 The tire according to any one of inventions 1 to 4, in which the shoulder lug grooves each have a groove width of 10% or more and 35% or less of a pitch length of the shoulder blocks. Invention 6 The tire according to any one of inventions 1 to 5, in which the center blocks each have a one-side opening narrow groove extending along the tire width direction and having one end communicating with each of the shoulder circumferential narrow grooves and the other end terminating within the center blocks, the one-side opening narrow groove has a groove width of 10% or more and 25% or less of a groove depth of the one-side opening narrow groove, and the groove depth of the one-side opening narrow groove is 75% or more and 100% or less of the groove depth of the shoulder lug grooves. Invention 7 The tire according to any one of inventions 1 to 6, including buttress dimples recessed from surfaces of buttress portions, in which the buttress dimples each have a depth of 1% or more and 2.5% or less of a development width of a tread surface. Invention 8 The tire according to any one of inventions 1 to 7, including shoulder dimples recessed from surfaces of the shoulder blocks, in which the shoulder dimples each have a depth of 10% or more and 50% or less of the groove depth of the shoulder lug grooves. Invention 9 The tire according to any one of inventions 1 to 8, in which five or more belt plies are disposed on an inner side of the tread portion in a tire radial direction, and the tire is used for a heavy load vehicle for construction or industrial use. Reference Signs List

[0071] 1 Pneumatic tire (tire) 15A Tread surface 15B Buttress portion 21 Center circumferential narrow groove 21a Long portion 21b Short portion 22 Shoulder circumferential narrow groove 31 Center land portion 31A Center block 31Aa Circumferential irregular portion 31Ab Width direction irregular portion 32 Shoulder land portion 32A Shoulder block 32Aa Circumferential irregular portion 41 Width direction narrow groove 41a End 42 One-side opening narrow groove 42a End 5         43 Shoulder lug groove 43a End 51 Shoulder dimple 52 Buttress dimple 141 to 147 Belt ply

Claims

1. A tire, comprising:in a tread portion,a center circumferential narrow groove extending continuously along a tire circumferential direction;a pair of shoulder circumferential narrow grooves extending continuously along the tire circumferential direction and disposed on outer sides in a tire width direction of the center circumferential narrow groove and adjacent thereto;width direction narrow grooves extending along the tire width direction, defining a center land portion between the circumferential narrow grooves into center blocks, and having opposite ends communicating with respective adjacent circumferential narrow grooves; andshoulder lug grooves extending along the tire width direction, defining shoulder land portions on both outer sides in the tire width direction of the shoulder circumferential narrow grooves into shoulder blocks, and having one end communicating with a respective one of the shoulder circumferential narrow grooves and the other end passing through a ground contact edge;the circumferential narrow grooves and the width direction narrow grooves each having a groove width of 10% or more and 25% or less of a groove depth thereof;the center blocks each having a width direction irregular portion in which center blocks adjacent to each other in the tire circumferential direction overlap each other in the tire width direction,the center circumferential narrow groove being formed in a zigzag shape in which a long portion and a short portion are alternately disposed in the tire circumferential direction,the long portion having a length of 65% or more and 100% or less of a maximum dimension of the center blocks in the tire circumferential direction,the number of the shoulder blocks arranged in the tire circumferential direction being 28 or more and 43 or less,the tread portion having a center tread gauge on a tire equatorial plane of 40 mm or more, andthe center tread gauge being 105% or more and 185% or less of a groove depth of the shoulder lug grooves.

2. The tire according to claim 1, wherein the center blocks and the shoulder blocks each have two or more circumferential irregular portions at which a center block and an adjacent shoulder block in the tire width direction mate with each other in the tire circumferential direction.

3. The tire according to claim 1, wherein the center blocks each have a maximum dimension in the tire width direction of 20% or more and 35% or less of a development width of a tread surface.

4. The tire according to claim 1, wherein the circumferential narrow grooves and the width direction narrow grooves each have a groove depth of 50% or more and 100% or less of a groove depth of the shoulder lug grooves.

5. The tire according to claim 1, wherein the shoulder lug grooves each have a groove width of 10% or more and 35% or less of a pitch length of the shoulder blocks.

6. The tire according to claim 1, whereinthe center blocks each have a one-side opening narrow groove extending along the tire width direction and having one end communicating with each of the shoulder circumferential narrow grooves and the other end terminating within the center blocks,the one-side opening narrow groove has a groove width of 10% or more and 25% or less of a groove depth of the one-side opening narrow groove, and the groove depth of the one-side opening narrow groove is 75% or more and 100% or less of the groove depth of the shoulder lug grooves.

7. The tire according to claim 1, comprisingbuttress dimples recessed from surfaces of buttress portions, whereinthe buttress dimples each have a depth of 1% or more and 2.5% or less of a development width of a tread surface.

8. The tire according to claim 1, comprisingshoulder dimples recessed from surfaces of the shoulder blocks, wherein the shoulder dimples each have a depth of 10% or more and 50% or less of the groove depth of the shoulder lug grooves.

9. The tire according to claim 1, whereinfive or more belt plies are disposed on an inner side of the tread portion in a tire radial direction, andthe tire is used for a heavy load vehicle for construction or industrialuse.

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