tire

Abstract

To provide a tire that can make both uneven wear resistance performance and wet performance of the tire compatible.SOLUTION: In a tire 1, at least one middle land part 32 comprises: a plurality of penetrating narrow grooves 321 penetrating, in a tire width direction, through the middle land part 32; a plurality of middle blocks 322 partitioned by the penetrating narrow grooves 321; and non-penetrating lug groove 323 that opens to edge portions at a tire equatorial plane CL side of the middle blocks 322, at one end parts and terminate at central parts of the middle blocks 322, at the other end parts. Central grooves 22 have wave-like shapes having amplitude in a tire width direction. Edge portions at the central groove 22 sides of the middle blocks 322 have circular-arc shapes protruding in a width direction of the middle blocks 322.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire that can achieve both uneven wear resistance and wet performance. [Background technology]

[0002] Tires used in regional operations, where vehicles mainly travel on expressways, have the problem of being prone to uneven wear. On the other hand, there is also a demand for tires to ensure wet traction performance during local driving. The technology described in Patent Document 1 is known as a conventional tire that addresses this problem. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6088483 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can achieve both uneven wear resistance and wet performance. [Means for solving the problem]

[0005] In order to achieve the above object, the tire according to the present invention is a tire comprising a pair of shoulder main grooves and two or more center grooves extending in the tire circumferential direction, a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, at least one of the middle land portions comprises a plurality of thin through grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks defined by the thin through grooves, and a non-penetrating lug groove that opens at one end to an edge portion of the middle block on the tire equatorial plane side and terminates at the center of the middle block at the other end, and the center groove has a wavy shape having an amplitude in the tire width direction. death, The edge portion of the middle block on the side of the center groove has an arc shape that is convex in the width direction of the middle block. and the groove width Wg2 of the center groove is in the range of 0.10≦Wg2 / Wg1≦0.40 with respect to the groove width Wg1 of the shoulder main groove. It is characterized by: The tire according to the present invention has a pair of shoulder main grooves and two or more center grooves extending in the tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, wherein at least one of the middle land portions has a plurality of thin through grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks defined by the thin through grooves, and a non-through lug groove opening at one end to an edge portion of the middle block on the tire equatorial plane side and terminating at the center of the middle block at the other end, wherein the center groove has a wavy shape having an amplitude in the tire width direction, the edge portion of the middle block on the center groove side has an arc shape that is convex in the width direction of the middle block, and the circumferential length La2 of the arc shape of the edge portion of the middle block is in the range of 0.50≦La2 / Le2≦1.00 with respect to the circumferential length Le2 of the edge portion of the middle block. In addition, a tire according to the present invention has a pair of shoulder main grooves and two or more center grooves extending in the tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, wherein at least one of the middle land portions has a plurality of thin through grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks defined by the thin through grooves, and a non-through lug groove opening at one end to an edge portion on the tire equatorial plane side of the middle block and terminating at the center of the middle block at the other end, wherein the center groove has a wavy shape having an amplitude in the tire width direction, the edge portion of the middle block on the center groove side has an arc shape that is convex in the width direction of the middle block, and the non-through lug groove connects to the center groove at a position of maximum amplitude of the wavy shape toward the tire equatorial plane side. Effect of the Invention

[0006] In the tire according to the present invention, (1) the middle blocks in the middle land portion are partitioned by narrow through-grooves, so that the rigidity of the middle blocks in the tire circumferential direction can be increased. This makes it possible to suppress uneven wear of the middle blocks while ensuring the drainage effect of the through-grooves. Also, (2) the edge portion of the middle block on the center groove side has an arc shape that is convex in the width direction of the middle block, so that the rigidity of the middle block in the tire width direction is increased and uneven wear of the middle block is suppressed. Also, (3) the middle block has non-through lug grooves that open only to the edge portion on the tire equatorial plane side, so that the drainage of the center region of the tread portion can be improved while ensuring the rigidity of the middle block. These advantages provide the tire with both uneven wear resistance and wet performance. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Diagram 2]FIG. 2 is a plan view showing a tread surface of the tire shown in FIG. [Diagram 3] FIG. 3 is an enlarged plan view showing the middle land portion and the center land portion of the tire illustrated in FIG. [Figure 4] FIG. 4 is an enlarged plan view showing the middle land portion shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view showing the middle land portion and the center land portion shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing the non-through lug groove of the middle land portion shown in FIG. [Figure 7] FIG. 7 is an enlarged plan view showing the center land portion shown in FIG. [Figure 8] FIG. 8 is an enlarged plan view showing the shoulder main groove shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along line A of the shoulder main groove shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view taken along line B of the shoulder main groove shown in FIG. [Figure 11] FIG. 11 is a plan view showing a modification of the tire shown in FIG. [Figure 12] FIG. 12 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. [Figure 13] FIG. 13 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments. The components of the embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. The multiple modified examples described in the embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[0009] [tire] Fig. 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. In this embodiment, a heavy-duty pneumatic radial tire mounted on the steering wheel of a tractor will be described as an example of a tire.

[0010] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis.

[0011] The tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers 17, 17 (see Figure 1).

[0012] The pair of bead cores 11, 11 are formed by winding one or more steel bead wires in an annular manner in multiple layers, and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are made up of a lower filler 121 and an upper filler 122, and are disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

[0013] 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, and is toroidally stretched between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wrapped around and secured to the outside in the tire width direction so as to envelop the bead cores 11 and the bead fillers 12. 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 relative to the tire circumferential direction) of 80 degrees or more and 90 degrees or less in the case of a radial tire, and 30 degrees or more and 45 degrees or less in the case of a bias tire.

[0014] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is disposed around the outer periphery of the carcass layer 13. These belt plies 141 to 144 include a high-angle belt 141, a pair of cross belts 142 and 143, and a belt cover 144. The high-angle belt 141 is formed by covering a plurality of belt cords made of steel with a coating rubber and rolling the cords, and has an absolute cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 45 degrees or more and 70 degrees or less. The pair of cross belts 142 and 143 are formed by covering a plurality of belt cords made of steel with a coating rubber and rolling the cords, and have an absolute cord angle of 10 degrees or more and 55 degrees or less. The pair of cross belts 142 and 143 have cord angles of opposite signs to each other, and are laminated with the longitudinal directions of the belt cords crossing each other (so-called cross-ply structure). The belt cover 144 is formed by covering a plurality of belt cover cords made of steel or organic fiber material with coating rubber and rolling the covered cords, and has a cord angle of 10 degrees or more and 55 degrees or less in absolute value.

[0015] The tread rubber 15 is disposed on the outer periphery in the tire radial direction of the carcass layer 13 and the belt layer 14 to form a tread portion of the tire 1. A pair of sidewall rubbers 16, 16 are disposed on the outer sides in the tire width direction of the carcass layer 13, respectively, to form left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction of the left and right bead cores 11, 11 and the turned-up portions of the carcass layer 13 to the outer side in the tire width direction, to form a rim fitting surface of the bead portion.

[0016] [Tread surface] FIG. 2 is a plan view showing the tread surface of the tire 1 shown in FIG. 1. The figure shows the tread surface of a tire for regional operation that mainly runs on expressways. In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T indicates the tire ground contact edge, and the dimension symbol TW indicates the tire ground contact width. In the figure, because the tire 1 has a tread surface that is approximately point symmetric, some of the symbols of the components in the right area of ​​the figure are omitted.

[0017] As shown in FIG. 2, the tire 1 has four circumferential grooves 21, 22 and five rows of land portions 31 to 33 on the tread surface.

[0018] The circumferential grooves 21, 22 are composed of a pair of shoulder main grooves 21, 21 and two center grooves 22, 22. These circumferential grooves 21, 22 have an annular structure that extends continuously around the entire circumference of the tire. The shoulder main groove 21 is defined as the outermost main groove in the tire width direction among the multiple circumferential grooves 21, 22. The main groove is defined as a groove that is required to display a wear indicator as specified by JATMA. In addition, the pair of shoulder main grooves 21, 21 are arranged in left and right regions with the tire equatorial plane CL as the boundary. The center groove 22 is defined as the circumferential groove that is closer to the tire equatorial plane CL than the shoulder main groove 21.

[0019] The shoulder main groove 21 has a groove width Wg1 of 5.0 mm or more (see FIG. 2) and a groove depth Hg1 of 10 mm or more (see FIG. 5 described later). The center groove 22 has a groove width Wg2 of more than 1.5 mm (see FIG. 2) and a groove depth Hg2 of 10 mm or more (see FIG. 5 described later). The groove width Wg2 of the center groove 22 is in the range of 0.10≦Wg2 / Wg1≦1.00 with respect to the groove width Wg1 of the shoulder main groove 21, and preferably in the range of 0.10≦Wg2 / Wg1≦0.40. The groove depth Hg2 of the center groove 22 is in the range of 0.70≦Hg2 / Hg1≦1.30 with respect to the groove depth Hg1 of the shoulder main groove 21. In the configuration of Fig. 2, the center groove 22 is a main groove that is required to display a wear indicator as stipulated by JATMA, and has a groove width Wg2 narrower than the groove width Wg1 of the shoulder main groove 21 and the same groove width Wg2 as the shoulder main groove 21. This ensures drainage in the center region of the tread and increases its rigidity.

[0020] The groove width is measured as the maximum distance between the opposing groove walls at the groove opening on the tread surface 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 at the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction.

[0021] The groove depth is measured as the maximum distance from the tread surface to the bottom of the groove when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In the case of a tire having partial unevenness or sipes at the bottom of the groove, the groove depth is measured excluding these.

[0022] The specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The 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. The 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. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

[0023] The land portions 31-33 are composed of a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a row of center land portions 33. These land portions 31-33 are defined by the circumferential grooves 21, 22 and form an annular tread extending around the entire circumference of the tire. The shoulder land portion 31 is defined as a land portion defined by the shoulder main groove 21 on the outer side in the tire width direction. The pair of shoulder land portions 31, 31 are arranged in left and right regions bounded by the tire equatorial plane CL. The middle land portion 32 is defined as a land portion defined by the shoulder main groove 21 on the inner side in the tire width direction. The pair of middle land portions 32, 32 are arranged in left and right regions bounded by the tire equatorial plane CL. The center land portion 33 is defined as a land portion located closer to the tire equatorial plane CL than the middle land portions 32, 32.

[0024] 2, the ground contact width Wb1 of the shoulder land portion 31 is in the range of 0.05≦Wb1 / TW≦0.25 with respect to the tire ground contact width TW, and preferably in the range of 0.15≦Wb1 / TW≦0.25. The ground contact width Wb2 of the middle land portion 32 is in the range of 0.10≦Wb2 / TW≦0.20 with respect to the tire ground contact width TW. The ground contact width Wb1 of the shoulder land portion 31 is in the range of 1.10≦Wb1 / Wb2≦1.60 with respect to the ground contact width Wb2 of the middle land portion 32. In this configuration, the shoulder land portion 31 has a wide structure, so that the rigidity of the shoulder land portion 31 is ensured and uneven wear of the shoulder land portion 31 is effectively suppressed.

[0025] The contact width of the land portion is measured as the maximum straight-line distance in the axial direction of the tire at the contact surface between the land portion and the flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0026] The tire contact width is measured as the maximum straight-line distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0027] The tire contact edge is defined as the widest position in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, placed perpendicular to a flat plate in a stationary state, and subjected to a load corresponding to a specified load.

[0028] Moreover, the ground contact width Wb3 of the center land portion 33 is in the range of 0.10≦Wb3 / TW≦0.20 with respect to the tire ground contact width TW. Moreover, the ground contact width Wb1 of the shoulder land portion 31 is in the range of 1.10≦Wb1 / Wb3≦1.60 with respect to the ground contact width Wb3 of the center land portion 33. In this configuration, since the shoulder land portion 31 has a wide structure, the rigidity of the shoulder land portion 31 is ensured, and uneven wear of the shoulder land portion 31 is effectively suppressed. Moreover, the ground contact width Wb3 of the center land portion 33 is in the range of 1.00≦Wb3 / Wb2≦1.50 with respect to the ground contact width Wb2 of the middle land portion 32, and preferably in the range of 1.00≦Wb3 / Wb2≦1.20. In this configuration, since the center land portion 33 has a wide structure, the rigidity of the center land portion 33 is ensured, and uneven wear of the center land portion 33 is effectively suppressed.

[0029] In the configuration of FIG. 2, as described above, the tire 1 includes a pair of shoulder main grooves 21, 21 and two center grooves 22, 22, thereby defining a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single center land portion 33. However, this is not limited to the above, and the tire 1 may include a single center groove or three or more center grooves (not shown). In the former configuration, the center land portion is omitted, and in the latter configuration, two or more rows of center land portions are defined. In addition, the center land portion 33 may be disposed on the tire equatorial plane CL (see FIG. 2), or may be disposed at a position deviated from the tire equatorial plane CL (not shown).

[0030] 2, the tire 1 has a point-symmetric tread pattern with a center point on the tire equatorial plane CL. However, the tire 1 is not limited to this, and may have a tread pattern that is line-symmetric about the tire equatorial plane CL, a tread pattern that has directionality in the tire rotation direction, or an asymmetric tread pattern (not shown).

[0031] In the configuration of FIG. 2, the shoulder main groove 21 has a straight shape, and the center groove 22 has a wavy shape with amplitude in the tire width direction. The wavy shape of the groove is required to have an arc shape at least at the maximum convex position toward the tire equatorial plane CL side, and includes, for example, a sine wave shape, a zigzag shape formed by connecting multiple straight line portions with short arcs, and a continuous arch shape formed by smoothly connecting multiple arcs that are convex toward the tire equatorial plane CL side. This configuration is preferable in that the rigidity of the shoulder land portion 31 is ensured, uneven wear of the shoulder land portion 31 is reduced, and at the same time, the drainage of the tread center region is improved. However, it is not limited to this, and the shoulder main groove 21 may have a wavy shape, or the center groove 22 may have a straight shape (not shown).

[0032] 2, the center groove 22 has a wavy shape as described above, but also has a see-through structure in the tire circumferential direction. That is, the groove width of the center groove 22 is ensured so that the edges of the left and right land portions 32, 33 defined by the center groove 22 do not overlap each other when viewed in the tire circumferential direction. Specifically, the see-through width Wst of the center groove 22 (see FIG. 3 described later) is in the range of 0.5 mm≦Wst. This effectively ensures the drainage of the center groove 22.

[0033] In the configuration of FIG. 2, the land portions 31-33 have a plurality of multi-sipes 4. The multi-sipes 4 are short sipes that open at one end to the edge portion of the land portion 31-33 and terminate at the other end inside the land portion 31-33, and have a width of 0.3 mm to 1.5 mm, a depth of 2.0 mm to 17 mm, and a length of 2.0 mm to 10 mm (dimension symbols are omitted in the figure). The plurality of multi-sipes are arranged in the tire circumferential direction along the edge portion on the circumferential grooves 21 and 22 side. The pitch length of the multi-sipes 4 is in the range of 0.1% to 0.6% of the tire circumference. In this configuration, the multi-sipes 4 reduce the rigidity of the land portions 31-33, thereby reducing the ground contact pressure of the edge portions of the land portions 31-33 when the tire is in contact with the ground. This suppresses the occurrence of uneven wear (particularly river wear) and improves the uneven wear resistance of the tire.

[0034] [Middle land area] Fig. 3 is an enlarged plan view showing the middle land portion 32 and the center land portion 33 of the tire 1 shown in Fig. 2. Fig. 4 is an enlarged plan view showing the middle land portion 32 shown in Fig. 3. Fig. 5 is a cross-sectional view showing the middle land portion 32 and the center land portion 33 shown in Fig. 3. This figure shows a cross-sectional view of the land portions 32, 33 cut along the thin through-grooves 321, 331. Fig. 6 is a cross-sectional view showing the non-through lug groove 323 of the middle land portion 32 shown in Fig. 3. This figure shows a cross-sectional view perpendicular to the groove length direction of the non-through lug groove 323.

[0035] As shown in FIGS. 2 and 3, the middle land portion 32 includes a plurality of thin through-grooves 321, a plurality of middle blocks 322, and a plurality of non-through-grooves 323.

[0036] As shown in FIG. 3, the thin through groove 321 penetrates the middle land portion 32 in the tire width direction and connects to the left and right circumferential grooves 21, 22. A plurality of thin through grooves 321 are arranged at a predetermined interval in the tire circumferential direction. The inclination angle θ21 (see FIG. 3) of the thin through groove 321 with respect to the tire circumferential direction is in the range of 45 [deg]≦θ21≦90 [deg]. The groove width W21 (see FIG. 4) of the thin through groove 321 is in the range of 0.4 [mm]≦W21≦1.5 [mm]. The groove depth H21 (see FIG. 5) of the thin through groove 321 is in the range of 0.30≦H21 / Hg2≦1.00 with respect to the groove depth Hg2 of the center groove 22, and preferably in the range of 0.40≦H21 / Hg2≦0.70. It is also preferable that the thin through grooves 321 are sipes having a groove width W21 of 1.5 mm or less and a groove depth H21 of more than 2.0 mm, so that they are closed when the tire comes into contact with the ground.

[0037] The inclination angle of the groove is measured as the inclination angle of an imaginary line passing through both ends of the groove with respect to the circumferential direction of the tire when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and under no load.

[0038] In addition, in FIG. 4, the through-thin groove 321 has a wavy shape with a wave number of three or more. In the configuration of FIG. 4, the through-thin groove 321 has a wavy shape consisting of eight curved points, and thus has four wave numbers. In this configuration, compared to a configuration (not shown) having a straight or arc-shaped through-thin groove, the wet traction of the middle land portion 32 can be improved while maintaining the rigidity of the middle block 322. In addition, the wavelength λ21 of the wavy shape of the through-thin groove 321 is in the range of 0.10≦λ21 / Wb2≦0.50 with respect to the contact width Wb2 of the middle land portion 32. In addition, the amplitude A21 of the wavy shape of the through-thin groove 321 is in the range of 0.6 [mm]≦A21≦2.5 [mm].

[0039] The wave shape of the groove and its wave number, wavelength and amplitude are determined by the wave shape of the groove centerline in a plan view of the tread. The groove centerline is defined as an imaginary line connecting the midpoints of the groove widths.

[0040] As shown in FIG. 2 and FIG. 3, the middle block 322 is divided into adjacent through-grooves 321, 321. A plurality of middle blocks 322 are arranged in a row in the tire circumferential direction. The circumferential length Le2 of the edge portion of the middle block 322 on the center groove 22 side is in the range of 0.80≦Le2 / Wb2′≦1.80 with respect to the ground contact width Wb2′ of the middle block 322, and preferably in the range of 1.10≦Le2 / Wb2′≦1.50. Therefore, it is preferable that the aspect ratio of the middle block 322 is set so that the middle block 322 is elongated in the tire circumferential direction. In this configuration, the block rigidity in the tire circumferential direction is ensured, and uneven wear of the middle block 322 is effectively suppressed, compared to a configuration in which the middle block is elongated in the tire width direction (not shown).

[0041] The circumferential length Le2 of the edge portion is measured as the distance in the tire circumferential direction of the edge portion facing the center groove 22 when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and unloaded. In a configuration in which the corners of the middle block 322 have chamfered portions, the circumferential length Le2 is measured with the intersection point of the ridgeline of the edge portion of the middle land portion 32 on the tread surface and the ridgeline of the groove opening of the through-thin groove 321 as the endpoint.

[0042] 4, an edge portion of the middle block 322 on the side of the center groove 22 has an arc shape that protrudes toward the tire equatorial plane CL. That is, an edge portion of the middle block 322 on the side of the center groove 22 protrudes toward the tire equatorial plane CL in a region between adjacent thin through-grooves 321, 321, and has an arc shape having a center within the middle block 322 as a whole. The thin through-groove 321 connects to the center groove 22 at a position of maximum amplitude of the wavy shape of the center groove 22 toward the tire ground contact edge T (see FIG. 2).

[0043] In the above configuration, (1) the middle blocks 322 of the middle land portion 32 are partitioned by narrow through-hole grooves 321, so that the rigidity of the middle blocks 322 in the tire circumferential direction can be increased compared to a configuration (not shown) in which the middle blocks are partitioned by wide through-hole lug grooves. This makes it possible to suppress uneven wear of the middle blocks 322 while ensuring the drainage effect of the through-hole grooves 321. In addition, (2) the edge portion of the middle block 322 on the center groove 22 side has an arc shape that is convex toward the tire equatorial plane CL, so that the rigidity of the middle block 322 in the tire width direction is increased and uneven wear of the middle block 322 is suppressed compared to a configuration (not shown) in which the middle block has a concave edge portion. In addition, (3) the middle block 322 has non-through-hole lug grooves 323 that open only to the edge portion on the tire equatorial plane CL side, so that the drainage of the tread center region can be improved while ensuring the rigidity of the middle block 322. As a result, it is possible to achieve both uneven wear resistance and wet performance of the tire.

[0044] Also, in Figure 4, the maximum convex position of the edge portion of the middle block 322 toward the tire equatorial plane CL (the measurement point of the contact width Wb2' of the middle block 322; symbol omitted in the figure) is in the center of the edge portion, specifically, at a distance of 35% to 65% from one end of the circumferential length Le2 of the edge portion.

[0045] In addition, in FIG. 4, the circumferential length La2 of the arc shape of the edge portion is in the range of 0.50≦La2 / Le2≦1.00 relative to the circumferential length Le2 of the edge portion of the middle block 322, and preferably in the range of 0.90≦La2 / Le2≦1.00.

[0046] The circumferential length La2 of the arc shape is measured as the distance between adjacent inflection points of the wavy shape of the center groove 22, including the maximum convex position of the edge portion of the middle block 322.

[0047] For example, in the configuration of Fig. 2, the wavy shape of the center groove 22 has a continuous arch shape formed by connecting multiple long arcs that are convex toward the tire equatorial plane CL. In addition, the thin through grooves 321 connect to the connecting positions of adjacent arcs, i.e., to both ends of one arc. Therefore, the entire edge portion of the middle block 322 on the center groove 22 side is formed of a single arc, and the above-mentioned ratio La2 / Le2 is 1.00.

[0048] 4, the convexity Pe2 of the edge of the middle block 322 toward the tire equatorial plane CL is in the range of 0.02≦Pe2 / Wb2′≦0.20, preferably 0.05≦Pe2 / Wb2′≦0.12, relative to the ground contact width Wb2′ of the middle block 322. The convexity Pe2 is preferably in the range of 1.0 [mm]≦Pe2. The lower limit ensures the convexity of the edge of the middle block 322, appropriately reinforces the rigidity of the middle block 322, and suppresses uneven wear of the middle block 322. The upper limit suppresses uneven wear of the middle block 322 caused by the convexity of the edge being excessive.

[0049] As shown in FIG. 3, the non-through lug groove 323 opens at one end to an edge portion of the middle block 322 on the tire equatorial plane CL side, and terminates at the other end at the center of the middle block 322. A plurality of non-through lug grooves 323 are arranged at predetermined intervals in the tire circumferential direction. The extension length L23 of the non-through lug groove 323 in the tire width direction is in the range of 0.40≦L23 / Wb2′≦0.90 with respect to the ground contact width Wb2′ of the middle block 322, and preferably in the range of 0.50≦L23 / Wb2′≦0.80. The lower limit ensures the drainage function of the non-through lug groove 323, and the upper limit ensures the rigidity of the middle block 322. For example, in the configuration of FIG. 3, the non-through lug groove 323 is connected to the center groove 22 at the maximum amplitude position of the wave-shaped shape of the center groove 22 toward the tire equatorial plane CL side. This ensures an extension length L23 of the non-through lug groove 323 in the tire width direction.

[0050] 3, the inclination angle θ23 of the non-through lug groove 323 with respect to the tire circumferential direction is in the range of -20[deg]≦θ21-θ23≦20[deg] with respect to the inclination angle θ21 of the through narrow groove 321, and preferably in the range of -10[deg]≦θ21-θ23≦10[deg]. Therefore, the non-through lug groove 323 extends approximately parallel to the through narrow groove 321. Also, in FIG. 4, the groove width W23 of the non-through lug groove 323 is in the range of 1.50≦W23 / W21≦5.50 with respect to the groove width W21 of the through narrow groove 321, and preferably in the range of 2.00≦W23 / W21≦4.00. Also, the groove width W23 of the non-through lug groove 323 is in the range of 1.5[mm]≦W23≦5.0[mm].

[0051] In addition, in FIG. 5, the groove depth H23 of the non-through lug groove 323 is in the range of 0.10≦H23 / Hg2≦0.30 with respect to the groove depth Hg2 of the center groove 22. In addition, the groove depth H23 of the non-through lug groove 323 is shallower than the groove depth H21 of the through narrow groove 321. In addition, in FIG. 6, the groove width W23 and the depth H23 of the non-through lug groove 323 have a relationship of 1.00≦W23 / H23≦1.50, and preferably have a relationship of 1.20≦W23 / H23≦1.50. Therefore, the non-through lug groove 323 has a shallow bottom and a wide structure. This can increase the rigidity of the middle block 322 while ensuring the drainage action of the non-through lug groove 323. In addition, in FIG. 6, the groove wall angle α23 of the non-through lug groove 323 is preferably in the range of 90 [deg]≦α23≦110 [deg].

[0052] In addition, in FIG. 4, the non-through lug grooves 323 have a wavy shape with two or more wave numbers. In addition, in the configuration of FIG. 4, the non-through lug grooves 323 have a wavy shape consisting of five curved points, and thus have two or three wave numbers. In this configuration, compared to a configuration (not shown) having straight or arc-shaped non-through lug grooves, the wet traction of the middle land portion 32 can be improved while maintaining the rigidity of the middle block 322. The wavelength λ23 of the wavy shape of the non-through lug grooves 323 is in the range of 0.70≦λ23 / λ21≦1.30 with respect to the wavelength λ21 of the wavy shape of the through-thin grooves 321, and preferably in the range of 0.90≦λ23 / λ21≦1.20. Furthermore, the amplitude A23 of the wavy shape of the non-through lug grooves 323 is in the range of 0.80≦A23 / A21≦1.50 relative to the amplitude A21 of the wavy shape of the thin through grooves 321, and preferably in the range of 1.20≦A23 / A21≦1.50.

[0053] [Center Land] FIG. 7 is an enlarged plan view showing the center land portion 33 shown in FIG.

[0054] As shown in FIG. 2 and FIG. 3, the central land portion 33 includes a plurality of thin through-grooves 331 and a plurality of central blocks 332. As shown in FIG.

[0055] As shown in FIG. 3, the thin through groove 331 penetrates the center land portion 33 in the tire width direction and connects to the left and right circumferential grooves 22, 22. A plurality of thin through grooves 331 are arranged at a predetermined interval in the tire circumferential direction. The inclination angle θ31 (see FIG. 3) of the thin through groove 331 with respect to the tire circumferential direction is in the range of 45 [deg]≦θ31≦90 [deg]. The groove width W31 (see FIG. 7) of the thin through groove 331 is in the range of 0.4 [mm]≦W31≦1.5 [mm]. The groove depth H31 (see FIG. 5) of the thin through groove 331 is in the range of 0.30≦H31 / Hg2≦1.00 with respect to the groove depth Hg2 of the center groove 22, and preferably in the range of 0.40≦H31 / Hg2≦0.70. It is also preferable that the thin through grooves 331 are sipes having a groove width W31 of 1.5 mm or less and a groove depth H31 of 2.0 mm or more, so that they are closed when the tire comes into contact with the ground.

[0056] 7, the thin through groove 331 has a wavy shape similar to the thin through groove 321 of the middle land portion 32 shown in FIG. 4. Specifically, the thin through groove 331 of the center land portion 33 has a wavy shape with a wave number of 3 or more, and the wavelength λ31 is in the range of 0.10≦λ31 / Wb3≦0.50 with respect to the contact width Wb3 of the center land portion 33. The amplitude A31 of the wavy shape of the thin through groove 331 is in the range of 0.7 [mm]≦A31≦2.5 [mm].

[0057] In the configuration of FIG. 2, the narrow through groove 331 of the center land portion 33 is inclined in the opposite direction to the narrow through groove 321 of the middle land portion 32 in the tire circumferential direction. This increases the rigidity of the center region of the tread portion. Furthermore, the narrow through groove 331 of the center land portion 33 and the narrow through grooves 321, 321 of the left and right middle land portions 32, 32 are inclined in the opposite direction to each other in the tire circumferential direction. In FIG. 3, the distance Dg in the tire circumferential direction between the connection portion of the narrow through groove 331 of the center land portion 33 to the center groove 22 and the connection portion of the narrow through groove 321 of the middle land portion 32 is in the range of 0≦Dg / P21≦0.40 with respect to the pitch length P21 of the narrow through groove 321 of the middle land portion 32. The distance Dg is preferably in the range of 0 [mm]≦Dg≦10 [mm]. Therefore, the communicating grooves consisting of the thin through groove 331 of the center land portion 33 and the thin through grooves 321, 321 of the left and right middle land portions 32, 32 have a zigzag shape with a large wavelength with the center groove 22 as the maximum amplitude position, and cross the tread center region to connect to the left and right shoulder main grooves 21, 21. This improves the drainage in the tread center region.

[0058] As shown in FIG. 2 and FIG. 3, the center block 332 is divided into adjacent through-grooves 331, 331. A plurality of center blocks 332 are arranged in a row in the tire circumferential direction. In FIG. 7, the circumferential length Le3 of the edge portion of the center block 332 is in the range of 0.80≦Le3 / Wb3′≦1.80 with respect to the contact width Wb3′ of the center block 332, and preferably in the range of 1.10≦Le3 / Wb3′≦1.50. Therefore, it is preferable that the aspect ratio of the center block 332 is set so that the center block 332 is long in the tire circumferential direction. In this configuration, the block rigidity in the tire circumferential direction is ensured and uneven wear of the block is suppressed compared to a configuration in which the center block is long in the tire width direction (not shown).

[0059] 7, the edge portion of the center block 332 has an arc shape recessed toward the tire equatorial plane CL. Specifically, the center block 332 is located on the tire equatorial plane CL, and the left and right edge portions of the center block 332 have an arc shape recessed in the width direction of the center block 332 in the region between the adjacent fine through-grooves 331. The fine through-groove 331 connects to the center groove 22 at the position of maximum amplitude of the wavy shape of the center groove 22 toward the tire ground contact edge T (see FIG. 2).

[0060] Also, in Figure 7, the maximum concave position of the edge portion of the center block 332 (the measurement point of the contact width Wb3' of the center block 332; symbol omitted in the figure) is located in the center of the edge portion, specifically, at a distance of 35% to 65% from one end of the circumferential length Le3 of the edge portion.

[0061] In addition, in FIG. 7, the circumferential length La3 of the arc shape of the edge portion is in the range of 0.50≦La3 / Le3≦1.00 relative to the circumferential length Le3 of the edge portion of the center block 332, and preferably in the range of 0.90≦La3 / Le3≦1.00.

[0062] For example, in the configuration of Fig. 2, the wavy shape of the center groove 22 has a continuous arch shape formed by connecting multiple long arcs that are convex toward the tire equatorial plane CL. Also, the thin through grooves 331 connect to the connecting positions of adjacent arcs, i.e., to both ends of one arc. Therefore, the entire edge of the center block 332 on the center groove 22 side is formed of a single arc, and the above-mentioned ratio La3 / Le3 is 1.00.

[0063] 7, the concave amount Pe3 of the edge portion of the center block 332 is in the range of 0.02≦Pe3 / Wb3′≦0.20 with respect to the ground contact width Wb3′ of the center block 332, and preferably in the range of 0.05≦Pe3 / Wb3′≦0.12. It is also preferable that the concave amount Pe3 is in the range of 1.0 [mm]≦Pe3. Therefore, the edge portion of the center block 332 has an arc shape that matches the arc shape of the edge portion of the middle block 322 described above.

[0064] 3, as described above, the connection portion of the thin through groove 331 of the center land portion 33 to the center groove 22 and the connection portion of the thin through groove 321 of the middle land portion 32 are located at approximately the same position in the tire circumferential direction, so that the wavy shape of the edge portion of the center land portion 33 is arranged in approximately the same phase as the wavy shape of the edge portion of the middle land portion 32. As a result, the concave edge portion of the center block 332 matches the convex edge portion of the middle block 322, and the groove width of the center groove 22 having a wavy shape is made uniform.

[0065] [Shoulder land area] As shown in Fig. 2, the shoulder land portion 31 is a rib having a circumferentially continuous tread surface. The shoulder land portion 31 has only the above-mentioned multi-sipes 4, and has no other grooves or sipes. This improves the uneven wear resistance of the shoulder land portion 31, which is prone to uneven wear. However, this is not limiting, and the shoulder land portion 31 may have shallow sipes or shallow grooves with a depth of 15 mm or less (not shown).

[0066] [Shoulder main groove] Fig. 8 is an enlarged plan view showing the shoulder main groove shown in Fig. 2. Figs. 9 and 10 are a cross-sectional view taken along line A (Fig. 9) and line B (Fig. 10) of the shoulder main groove shown in Fig. 8.

[0067] As shown in Figs. 8 to 10, the ridgeline of the connection between the groove bottom of the shoulder main groove 21 and the groove wall on the shoulder land portion 31 side in the plan view of the tread has a wavy or zigzag shape with amplitude in the tire width direction. On the other hand, the ridgeline of the connection between the groove bottom of the shoulder main groove 21 and the groove wall on the middle land portion 32 side has a straight shape. This configuration is preferable in that the rigidity of the shoulder land portion 31 is ensured, uneven wear of the shoulder land portion 31 is reduced, and at the same time, the drainage of the shoulder main groove 21 is ensured. In addition, the groove wall angle φ1 of the shoulder main groove 21 on the shoulder land portion 31 side (defined as the inclination angle of the groove wall surface with respect to the normal line of the tread surface) is in the range of 0 [deg] ≦ φ1 - φ2 with respect to the groove wall angle φ2 on the middle land portion 32 side, and preferably in the range of 1 [deg] ≦ φ1 - φ2. In addition, the groove wall angle φ1 on the shoulder land portion 31 side is in the range of 3 [deg] ≦ φ1 ≦ 20 [deg]. In addition, the radius of curvature (not shown) of the connection part between the groove wall and the groove bottom on the shoulder land portion 31 side of the shoulder main groove 21 is equal to or greater than the radius of curvature of the connection part between the groove wall and the groove bottom on the middle land portion 32 side. This increases the rigidity of the shoulder land portion 31.

[0068] [Variations] Fig. 11 is a plan view showing a modification of the tire 1 shown in Fig. 2. In this figure, the same components as those shown in Fig. 2 are denoted by the same reference numerals, and the description thereof will be omitted.

[0069] 2, as described above, the groove width Wg2 of the center groove 22 is narrower than the groove width Wg1 of the shoulder main groove 21 and is in the range of 0.10≦Wg2 / Wg1≦0.40. This configuration is preferable in that the rigidity of the tread center region is increased, the uneven wear resistance of the tire is improved, and the rolling resistance of the tire is reduced.

[0070] 11, the center groove 22 may have a wide structure so as to have the same groove width as the shoulder main grooves 21. This improves the wet performance of the tire.

[0071] [effect] As described above, the tire 1 includes a pair of shoulder main grooves 21, 21 and two or more center grooves 22, 22 extending in the tire circumferential direction, a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and one or more rows of center land portions 33 defined by the shoulder main grooves 21 and the center groove 22 (see FIG. 2). At least one of the middle land portions 32 includes a plurality of thin through grooves 321 penetrating the middle land portion 32 in the tire width direction, a plurality of middle blocks 322 defined by the thin through grooves 321, and a non-penetrating lug groove 323 that opens at one end to an edge portion of the middle block 322 on the tire equatorial plane CL side and terminates at the center of the middle block 322 at the other end. The center groove 22 has a wavy shape with amplitude in the tire width direction. The edge portion of the middle block 322 on the center groove 22 side has a circular arc shape that is convex in the width direction of the middle block 322.

[0072] In this configuration, (1) the middle blocks 322 of the middle land portion 32 are partitioned by narrow through-hole fine grooves 321, so that the rigidity of the middle blocks 322 in the tire circumferential direction can be increased compared to a configuration (not shown) in which the middle blocks are partitioned by wide through-hole lug grooves. This makes it possible to suppress uneven wear of the middle blocks 322 while ensuring the drainage effect of the through-hole fine grooves 321. In addition, (2) the edge portion of the middle block 322 on the center groove 22 side has an arc shape that is convex in the width direction of the middle block 322, so that the rigidity of the middle block 322 in the tire width direction is increased and uneven wear of the middle block 322 is suppressed compared to a configuration (not shown) in which the middle block has a concave edge portion. In addition, (3) the middle block 322 has non-through-hole lug grooves 323 that open only to the edge portion on the tire equatorial plane CL side, so that the drainage of the tread center region can be improved while ensuring the rigidity of the middle block 322. These advantages provide an advantage of being able to achieve both uneven wear resistance and wet performance of the tire.

[0073] In the tire 1, the most protruding position of the edge portion of the middle block 322 is at a distance of 35% to 65% from one end of the circumferential length Le2 of the edge portion (see FIG. 4). This has the advantage of effectively increasing the rigidity of the middle block 322 in the tire width direction.

[0074] In addition, in this tire 1, the convexity Pe2 of the edge portion of the middle block is in the range of 0.02≦Pe2 / Wb2′≦0.20 with respect to the contact width Wb2′ of the middle block (see FIG. 4). The lower limit ensures the convexity of the edge portion of the middle block 322, appropriately reinforcing the rigidity of the middle block 322 and suppressing uneven wear of the middle block 322. The upper limit suppresses uneven wear of the middle block 322 caused by an excessive convexity of the edge portion.

[0075] Furthermore, the circumferential length Le2 of the edge portion of the middle block 322 is in the range of 0.80≦Le2 / Wb2′≦1.80 relative to the contact width Wb2′ of the middle block 322 (see FIG. 4). This configuration has the advantage that block rigidity in the tire circumferential direction is ensured and uneven wear of the middle block 322 is effectively suppressed compared to a configuration in which the middle block is long in the tire width direction (not shown).

[0076] In addition, in the tire 1, the circumferential length La2 of the arc shape of the edge portions of the middle blocks 322 is in the range of 0.80≦La2 / Le2≦1.00 relative to the circumferential length Le2 of the edge portions of the middle blocks 322 (see FIG. 4). This ensures the circumferential length La2 of the arc shape, and has the advantage that the edge portions of the middle blocks 322 have an arc shape that is convex in the width direction of the middle blocks 322, thereby adequately reinforcing the rigidity of the middle blocks 322.

[0077] In the tire 1, the fine through grooves 321 are sipes that are closed when the tire contacts the ground, which has the advantage of increasing the rigidity of the middle blocks 322 and improving the uneven wear resistance of the tire.

[0078] In the tire 1, the non-through lug grooves 323 connect to the center groove 22 at the maximum amplitude position of the wavy shape toward the tire equatorial plane CL. This makes it possible to lengthen the extension length L23 of the non-through lug grooves 323 in the tire width direction, which has the advantage of improving the wet traction in the tread center region.

[0079] In the tire 1, the fine through grooves 321 have a wavy shape, and the wavelength λ21 of the wavy shape of the fine through grooves 321 is in the range of 0.10≦λ21 / Wb2≦0.50 with respect to the contact width Wb2 of the middle land portion 32 (see FIG. 4). The lower limit ensures the wavelength λ21 of the wavy shape, suppressing uneven wear starting from the bending point of the fine through grooves 321, while the upper limit ensures the number of waves of the wavy shape, ensuring the effect of the fine through grooves 321 in improving drainage.

[0080] In addition, in this tire 1, the inclination angle θ23 of the non-through lug grooves 323 with respect to the tire circumferential direction is in the range of -20 [deg]≦θ21-θ23≦20 [deg] with respect to the inclination angle θ21 of the thin through groove 321 (see FIG. 3). This provides the advantage that the rigidity of the dollar block 322 in the tire circumferential direction in the region between the non-through lug grooves 323 and the thin through groove 321 is uniformized, suppressing uneven wear of the middle block 322.

[0081] In addition, in the tire 1, the groove width W23 of the non-through lug groove 323 is set to the groove width W21 of the through narrow groove 321. 1.50≦W23 / W21≦5.50 (See FIG. 4.) The lower limit ensures that the wide non-penetrating lug grooves 323 improve the wet traction of the middle land portion 32, while the upper limit ensures that the narrow penetrating fine grooves 321 reinforce the rigidity of the middle land portion 32.

[0082] Also, in this tire 1, the non-through lug grooves 323 have a wavy shape, and the wavelength λ23 of the wavy shape of the non-through lug grooves 323 is in the range of 0.70≦λ23 / λ21≦1.30 with respect to the wavelength λ21 of the wavy shape of the thin through groove 321. As a result, the wavelength λ23 of the wavy shape of the non-through lug grooves 323 and the wavelength λ21 of the wavy shape of the thin through groove 321 become approximately the same, and the rigidity of the dollar block 322 in the region between the non-through lug grooves 323 and the thin through groove 321 is made uniform, which has the advantage of suppressing uneven wear of the middle block 322.

[0083] In addition, in the tire 1, the fine through-grooves 331 of the central land portion 33 are inclined in the opposite direction in the tire circumferential direction to the fine through-grooves 321 of the middle land portion 32 (see FIG. 2). This has the advantage of increasing the rigidity of the central region of the tread portion.

[0084] Applies to The tire 1 is a heavy-duty pneumatic radial tire that is mounted on the steering wheel of a tractor. By applying the present invention to such a tire, it is possible to effectively achieve both wet performance and uneven wear resistance of the tire.

[0085] In addition, in this embodiment, as described above, a pneumatic tire has been described as an example of a tire. However, the present invention is not limited to this, and the configuration described in this embodiment can be arbitrarily applied to other tires within the scope of what is obvious to a person skilled in the art. Examples of other tires include airless tires and solid tires. EXAMPLES

[0086] 12 and 13 are tables showing the results of performance tests of the tire according to the embodiment of the present invention.

[0087] In this performance test, several types of test tires were evaluated for (1) wet traction performance and (2) uneven wear resistance. In addition, the test tires with tire size 11R22.5 were mounted on JATMA-specified rims, and the test tires were subjected to the JATMA-specified internal pressure and load. The test tires were also mounted on a 2-D tractor head test vehicle.

[0088] (1) In the evaluation of wet traction performance, the test vehicle runs on an asphalt road that has been watered to a depth of 1 mm, and the running time is measured until the running speed increases from 5 km / h to 20 km / h. Then, based on the measurement results, an index evaluation is performed with the comparative example set as the standard (100). The higher the value, the better the evaluation.

[0089] (2) In the evaluation of uneven wear resistance, after a test vehicle has traveled 150,000 km on a specified pavement, the depth of step wear on the edge of the land is observed and an index evaluation is performed. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the better.

[0090] The test tire of the embodiment has the configuration of FIG. 1 and FIG. 2, the middle land portion 32 has a through-hole fine groove 321, a middle block 322, and a non-through lug groove 323, and the center groove 22 has a wavy shape with amplitude in the tire width direction. In addition, the edge portion of the middle block 322 on the center groove 22 side has a circular arc shape that is convex toward the tire equatorial plane CL side. In addition, the groove width Wg1 of the shoulder main groove 21 is 13.0 [mm], and the groove depth Hg1 is 16.2 [mm]. In addition, the groove width Wg2 of the center groove 22 is 3.6 [mm], and the groove depth Hg2 is 16.7 [mm]. In addition, the tire ground contact width TW is 215 [mm], and the ground contact width Wb1 of the shoulder land portion 31 is 43.5 [mm].

[0091] The test tire of the comparative example is the test tire of Example 1, in which the edge portion of the middle block 322 on the side of the center groove 22 has an arc shape recessed in the width direction of the middle block 322.

[0092] As the test results show, the test tires of the examples have both good wet traction performance and good resistance to uneven wear. [Explanation of symbols]

[0093] 1 Tire; 11 Bead core; 12 Bead filler; 121 Lower filler; 122 Upper filler; 13 Carcass layer; 14 Belt layer; 141 High angle belt; 142, 143 Cross belt; 144 Belt cover; 15 Tread rubber; 16 Sidewall rubber; 17 Rim cushion rubber; 21 Shoulder main groove; 22 Center groove; 31 Shoulder land portion; 32 Middle land portion; 321 Through narrow groove; 322 Middle block; 323 Non-through lug groove; 33 Center land portion; 331 Through narrow groove; 332 Center block; 4 Multi-sipe

Claims

1. A tire comprising a pair of shoulder main grooves and two or more center grooves extending in a tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, At least one of the middle land portions includes a plurality of through-grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks partitioned by the through-grooves, and a non-through lug groove that opens at one end to an edge portion of the middle block on the tire equatorial plane side and terminates at the center of the middle block at the other end, The center groove has a wavy shape having an amplitude in the tire width direction, The edge portion of the middle block on the side of the center groove has an arc shape that is convex in the width direction of the middle block, and A tire characterized in that a groove width Wg2 of the center groove is in a range of 0.10≦Wg2 / Wg1≦0.40 with respect to a groove width Wg1 of the shoulder main groove.

2. 2. The tire according to claim 1, wherein the maximum convex position of the edge portion of the middle block is at a distance of 35% to 65% from one end of a circumferential length Le2 of the edge portion.

3. 3. The tire according to claim 1, wherein a convexity Pe2 of the edge portion of the middle block is in a range of 0.02≦Pe2 / Wb2′≦0.20 with respect to a ground contact width Wb2′ of the middle block.

4. 4. The tire according to claim 1, wherein a circumferential length Le2 of the edge portion of the middle block, relative to a ground contact width Wb2' of the middle block, is in a range of 1.10≦Le2 / Wb2'≦1.

50.

5. 5. The tire according to claim 1, wherein a circumferential length La2 of the arc shape of the edge portion of the middle block is in a range of 0.50≦La2 / Le2≦1.00 relative to a circumferential length Le2 of the edge portion of the middle block.

6. 6. The tire according to claim 1, wherein the fine through-grooves are sipes which are closed when the tire is in contact with the ground.

7. The tire according to any one of claims 1 to 6, wherein the non-through lug groove is connected to the center groove at a position of maximum amplitude of the wavy shape toward the tire equatorial plane side.

8. The tire according to any one of claims 1 to 7, wherein the through-groove has a wavy shape, and the wavelength λ21 of the wavy shape of the through-groove is in the range of 0.10≦λ21 / Wb2≦0.50 with respect to the contact width Wb2 of the middle land portion.

9. The tire according to any one of claims 1 to 8, wherein an inclination angle θ23 of the non-through lug groove with respect to the tire circumferential direction is in a range of -20 [deg]≦θ21-θ23≦20 [deg] with respect to an inclination angle θ21 of the thin through groove.

10. The tire according to any one of claims 1 to 9, wherein a groove width W23 of the non-through lug groove is in a range of 1.50≦W23 / W21≦5.50 with respect to a groove width W21 of the thin through groove.

11. The non-through lug groove has a wavy shape, and the wavelength λ23 of the wavy shape of the non-through lug groove is in the range of 0.70≦λ23 / λ21≦1.30 with respect to the wavelength λ21 of the wavy shape of the through narrow groove. A tire according to any one of claims 1 to 10.

12. The center land portion has a plurality of through-grooves penetrating the center land portion in the tire width direction, and The tire according to any one of claims 1 to 11, wherein the fine through-grooves of the center land portion are inclined in a direction opposite to the tire circumferential direction with respect to the fine through-grooves of the middle land portion.

13. A tire comprising a pair of shoulder main grooves and two or more center grooves extending in a tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, At least one of the middle land portions includes a plurality of through-grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks partitioned by the through-grooves, and a non-through lug groove that opens at one end to an edge portion of the middle block on the tire equatorial plane side and terminates at the center of the middle block at the other end, The center groove has a wavy shape having an amplitude in the tire width direction, The edge portion of the middle block on the side of the center groove has an arc shape that is convex in the width direction of the middle block, and a circumferential length La2 of the arc shape of the edge portion of the middle block, relative to a circumferential length Le2 of the edge portion of the middle block, in the range of 0.50≦La2 / Le2≦1.

00.

14. A tire comprising a pair of shoulder main grooves and two or more center grooves extending in a tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center groove, At least one of the middle land portions includes a plurality of through-grooves penetrating the middle land portion in the tire width direction, a plurality of middle blocks partitioned by the through-grooves, and a non-through lug groove that opens at one end to an edge portion of the middle block on the tire equatorial plane side and terminates at the center of the middle block at the other end, The center groove has a wavy shape having an amplitude in the tire width direction, The edge portion of the middle block on the side of the center groove has an arc shape that is convex in the width direction of the middle block, and The tire is characterized in that the non-through lug groove is connected to the center groove at a position of maximum amplitude of the wave shape toward the tire equatorial plane.

Images