tire

Abstract

To provide a tire that can make both a wet performance and uneven wear resistance of the tire compatible.SOLUTION: Center land parts 32 and 33 respectively comprise circumferential narrow grooves 41 extending in a tire circumferential direction, first lateral grooves 42A whose one ends open to edge parts of either of the center land parts 32 and 33 and whose other end parts are connected to the circumferential narrow grooves 41, and second lateral grooves 42B whose one ends open to edge parts of the other of the center land parts 32 and 33 and whose the other end parts are connected to the circumferential narrow grooves 41. The circumferential narrow groove 41 has a zigzag shape formed by repeatedly connecting first long parts 411, first short parts 412A, second long parts 411B and second short parts 412B. The first lateral grooves 42A are connected to the first long parts 411A in a zigzag shape and the second lateral grooves 42B are connected to the second long parts 411B in a zigzag shape.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 wet performance and uneven wear resistance. [Background technology]

[0002] In recent years, in order to achieve both wet performance and uneven wear resistance of tires, a configuration has been adopted in which the center land portion has circumferential thin grooves and narrow lateral grooves. A conventional tire employing such a configuration is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-326433 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 wet performance and uneven wear resistance. [Means for solving the problem]

[0005] In order to achieve the above object, a tire according to the present invention is a tire comprising a pair of shoulder main grooves and one or more center main grooves, a pair of shoulder land portions defined by the shoulder main grooves and the center main groove, and two or more rows of center land portions, wherein at least one row of the center land portion comprises a circumferential narrow groove extending in the tire circumferential direction, a first lateral groove opening at one end into one edge portion of the center land portion and connecting to the circumferential narrow groove at the other end, and a second lateral groove opening at one end into the other edge portion of the center land portion and connecting to the circumferential narrow groove at the other end, wherein the circumferential narrow groove has a zigzag shape formed by repeatedly connecting a first long portion, a first short portion, a second long portion, and a second short portion, and the first lateral groove is connected to the first long portion of the zigzag shape. death, The second transverse groove is connected to the second long portion of the zigzag shape. and a pitch length Ps of the zigzag shape consisting of the first long portion, the first short portion, the second long portion, and the second short portion is in a range of 0.50≦Ps / Wb2≦1.10 with respect to a contact width Wb2 of the center land portion. It is characterized by: [Effects of the Invention]

[0006] In the tire according to the present invention, (1) the center land portion has circumferential narrow grooves and lateral grooves, thereby improving drainage in the center region of the tread. Also, (2) the circumferential narrow groove has a zigzag shape with long and short portions alternately connected, and the first and second lateral grooves connect to different long portions from the left and right of the circumferential narrow groove. Therefore, the circumferential narrow groove has a zigzag-shaped short portion between the connecting portions of adjacent lateral grooves. This improves drainage in the tread surface of the center land portion and improves the tire's wet performance. Furthermore, compared to a configuration in which both the first and second lateral grooves connect to a single long portion from the left and right, and a configuration in which the first and second lateral grooves connect to the bending points of the zigzag shape, the rigidity of the center land portion is ensured, improving the tire's uneven wear resistance. This provides the advantage of achieving both wet performance and uneven wear resistance. [Brief explanation 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. [Figure 2]FIG. 2 is a plan view showing the tread surface of the tire shown in FIG. [Figure 3] FIG. 3 is an enlarged view showing the center land portion shown in FIG. [Figure 4] FIG. 4 is an enlarged view showing one of the center land portions shown in FIG. [Figure 5] FIG. 5 is an enlarged view showing the circumferential narrow grooves and lateral grooves of the center land portion shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing the center land portion shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing the center land portion shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view showing an edge portion of the shoulder land portion shown in FIG. [Figure 9] FIG. 9 is a plan view showing a modified example of the tire shown in FIG. [Figure 10] FIG. 10 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. [Figure 11] FIG. 11 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. [Figure 12] FIG. 12 is a plan view showing the tread surface of a conventional tire. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] [tire] 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 vehicles for long-distance transportation such as trucks and buses 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 the direction parallel to the tire rotation axis, and the tire radial direction is defined as the 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 and multiple manner 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 respectively disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction 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 laid 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 enclose 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 of the tire) of 80 degrees or more and 90 degrees or less in absolute value for radial tires, and 30 degrees or more and 45 degrees or less in absolute value for bias tires.

[0014] The belt layer 14 is formed by laminating multiple belt plies 141 to 144 and is disposed around 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 multiple steel belt cords with coating rubber and rolling them, and has a 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 in absolute value. The pair of cross belts 142 and 143 are formed by covering multiple steel belt cords with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 10 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 142 and 143 have cord angles of opposite signs to each other, and are laminated with the belt cords' longitudinal directions crossing each other (having a so-called cross-ply structure). The belt cover 144 is made by covering a plurality of belt cover cords made of steel or organic fiber material with coating rubber and rolling them, 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 of the carcass layer 13 and the belt layer 14 in the tire radial direction to form the tread portion of the tire 1. A pair of sidewall rubbers 16, 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction 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 the 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 an all-season tire. In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T indicates the tire contact edge, and the dimension symbol TW indicates the tire contact width.

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

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

[0019] The main groove is defined as a groove that is required to display a wear indicator as specified by JATMA.

[0020] The shoulder main grooves 21 have a groove width Wg1 of 8.0 mm to 13.0 mm (see FIG. 2) and a groove depth Hg1 of 12.0 mm to 16.5 mm (see FIG. 7, described later). The center main groove 22 has a groove width Wg2 of 3.5 mm to 13.0 mm (see FIG. 2) and a groove depth Hg2 of 12.0 mm to 16.5 mm (see FIG. 7, described later). The groove width Wg2 of the center main groove 22, relative to the groove width Wg1 of the shoulder main grooves 21, is in the range of 0.14≦Wg2 / Wg1≦1.00.

[0021] 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 under no load. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured using the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction as the endpoint.

[0022] The groove depth is measured as the maximum distance from the tread surface to the groove bottom when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. If the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0023] A specified rim is a "standard rim" as specified by JATMA, a "design rim" as specified by TRA, or a "measuring rim" as specified by ETRTO. Also, specified internal pressure is the "maximum air pressure" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "inflation pressure" as specified by ETRTO. Also, specified load is the "maximum load capacity" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "load capacity" as 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.

[0024] In addition, in the configuration of FIG. 2, the distance from the tire equatorial plane CL to the groove center lines of the left and right shoulder main grooves 21, 21 (dimension symbols omitted in the figure) is in the range of 26% to 32% of the tire contact width TW.

[0025] The groove centerline is defined as an imaginary line connecting the midpoints of the distance between opposing groove walls.

[0026] The tire contact width TW is measured as the maximum linear 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 ground contact edge T 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, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0028] The land portions 31-33 are composed of a pair of shoulder land portions 31, 31 and three rows of center land portions 32, 33, 32. These land portions 31-33 are defined by the circumferential main grooves 21, 22 and form an annular tread extending around the entire circumference of the tire. The shoulder land portion 31 is defined as the 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 center land portion 32, 33 is defined as the land portion between the pair of shoulder land portions 31, 31.

[0029] 2, the contact width Wb1 of the shoulder land portion 31 is in the range of 0.15≦Wb1 / TW≦0.25, preferably 0.18≦Wb1 / TW≦0.22, relative to the tire contact width TW. The contact widths Wb2 and Wb3 of the center land portions 32 and 33 are in the ranges of 0.13≦Wb2 / TW≦0.16 and 0.13≦Wb3 / TW≦0.16, respectively, relative to the tire contact width TW. The contact widths Wb2 and Wb3 of the center land portions 32 and 33 are in the ranges of 0.70≦Wb2 / Wb1≦0.85 and 0.70≦Wb3 / Wb1≦0.85, respectively, relative to the contact width Wb1 of the shoulder land portion 31. This configuration ensures the shoulder land portion 31's rigidity and effectively suppresses uneven wear of the shoulder land portion 31.

[0030] The contact width of the land portion is measured as the maximum linear 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.

[0031] In the configuration shown in FIG. 2, the tire 1 has a pair of shoulder main grooves 21 and two center main grooves 22, thereby defining a pair of shoulder land portions 31 and three rows of center land portions 32 and 33. However, this is not limiting, and the tire 1 may have a single center main groove or three or more rows of center land portions (not shown). In the former configuration, a pair of center land portions is defined, and in the latter configuration, four or more rows of center land portions are defined. In addition, the center land portion 33 may be positioned on the tire equatorial plane CL (see FIG. 2), or may be positioned at a position deviated from the tire equatorial plane CL (not shown).

[0032] [Zigzag shape of the main groove bottom] In the configuration shown in FIG. 2, the shoulder main grooves 21 and the center main groove 22 have straight edges at their groove openings. Alternatively, the main grooves 21 and 22 may have straight or zigzag edges at their groove bottoms (not shown). For example, it is preferable that the main grooves 21 and 22 have straight edges at their groove openings and zigzag edges at their groove bottoms, with the groove wall surfaces of the main grooves 21 and 22 being curved surfaces connecting the groove openings and groove bottoms (not shown). In this configuration, the inclination angles of the groove walls of the main grooves 21 and 22 relative to the tread surface (the so-called groove wall angle) change in the circumferential direction of the tire due to the curved surfaces. This improves the drainage of the main grooves 21 and 22 and ensures the rigidity of the land portions 31 to 33.

[0033] [Center Land Area] FIG. 3 is an enlarged view showing the center land portions 32, 33 shown in FIG. 2. FIG. 4 is an enlarged view showing one center land portion 32 (33) shown in FIG. 3. FIG. 5 is an enlarged view showing the circumferential narrow groove 41 and the lateral grooves 42A, 42B of the center land portion 32 (33) shown in FIG. 4. FIGS. 6 and 7 are cross-sectional views showing the center land portion 32 (33) shown in FIG. 4. In these figures, FIG. 6 shows a cross-sectional view along the circumferential narrow groove 41, and FIG. 7 shows a cross-sectional view along the lateral grooves 42A, 42B.

[0034] As shown in FIGS. 2 and 3, the center land portions 32, 33 include a single circumferential narrow groove 41 and a plurality of lateral grooves 42A, 42B.

[0035] As shown in Fig. 2, the circumferential narrow groove 41 is a narrow groove that extends in the circumferential direction of the tire and has an annular structure that extends continuously around the entire circumference of the tire. Also, as shown in Fig. 3, the groove center line (not shown) of the circumferential narrow groove 41 is located in the center of the center land portion 32 (33). Specifically, the distance from one edge portion of the center land portion 32 (33) to the groove center line of the circumferential narrow groove 41 is in the range of 30% to 70% of the contact width Wb2 (Wb3) of the center land portion 32 (33).

[0036] 4, the groove width Ws of the circumferential narrow groove 41 is in the range of 0.1 mm≦Ws≦2.0 mm, preferably 0.5 mm≦Ws≦1.5 mm. Also, in FIG. 6, the groove depth Hs of the circumferential narrow groove 41 is in the range of 0.05≦Hs / Hg1≦0.80, preferably 0.10≦Hs / Hg1≦0.65, relative to the groove depth Hg1 of the shoulder main groove 21. The upper limit ensures the drainage of the circumferential narrow groove 41, while the lower limit prevents a decrease in rigidity of the center land portions 32 and 33 due to the arrangement of the circumferential narrow groove 41. The groove width Ws and groove depth Hs of the circumferential narrow groove 41 may increase or decrease in a predetermined region (see FIG. 6), as described below, or may be constant around the entire tire circumference (not shown).

[0037] As shown in Figure 3, the circumferential narrow groove 41 has a zigzag shape formed by alternating long and short sections. The long and short sections are inclined in opposite directions relative to the tire circumferential direction. The maximum amplitude As of the zigzag shape is in the range of 0.05 ≤ As / Wb2 ≤ 0.20, and preferably 0.10 ≤ As / Wb2 ≤ 0.15, relative to the contact width Wb2 of the center land portion 32. The lower limit ensures that the zigzag shape of the circumferential narrow groove 41 improves drainage, while the upper limit ensures the rigidity of the center land portions 32, 33.

[0038] The maximum amplitude As of the zigzag shape is measured as the maximum amplitude of the groove center line of the circumferential groove 41.

[0039] For example, in the configuration of FIG. 4, as shown in FIG. 3, the circumferential groove 41 has a zigzag shape formed by repeatedly connecting a first long portion 411A, a first short portion 412A, a second long portion 411B, and a second short portion 412B. Further, the first and second long portions 411A and 411B are inclined in one direction with respect to the tire circumferential direction, and the first and second short portions 412A and 412B are inclined in the other direction.

[0040] Also, in FIG. 4, the amplitude As1 of the zigzag shape in the first short portion 412A is in the range of 0.10 ≦ As1 / As2 ≦ 0.90 with respect to the amplitude As2 of the zigzag shape in the second short portion 412B, and preferably in the range of 0.40 ≦ As’ / As2 ≦ 0.60. Therefore, the zigzag shape has a small amplitude As1 in the first short portion 412A and a large amplitude As2 in the second short portion 412B (As1 < As2). By the above lower limit, the drainage improvement effect by the first short portion 412A is ensured, and by the above upper limit, the rigidity of the center land portions 32 and 33 is ensured. In the configuration of FIG. 4, the amplitude As2 of the zigzag shape in the second short portion 412B corresponds to the maximum amplitude As of the zigzag shape of the circumferential groove 41.

[0041] Also, in FIG. 4, the pitch length Ps of the zigzag shape composed of the above-described first long portion 411A, first short portion 412A, second long portion 411B, and second short portion 412B is in the range of 0.50 ≦ Ps / Wb2 ≦ 1.10 with respect to the contact width Wb2 (Wb3) of the center land portions 32 (33), and preferably in the range of 0.75 ≦ Ps / Wb2 ≦ 0.95. By the above lower limit, the drainage improvement effect by the zigzag shape of the circumferential groove 41 is ensured, and by the above upper limit, the rigidity of the center land portions 32 and 33 is ensured. Also, the circumferential extension distance Ps’ of a set of adjacent long and short portions 411A, 412A (411B, 412B) is in the range of 0.30 ≦ Ps’ / Ps ≦ 0.70 with respect to the pitch length Ps of the first long portion 411A, and preferably in the range of 0.40 ≦ Ps’ / Ps ≦ 0.60.

[0042] The extension distance Ps' of the first long portion 411A and the first short portion 412A in the tire circumferential direction is measured using the bending points of the zigzag shape as the end points.

[0043] In addition, in FIG. 4, the inclination angle θs1 of the first and second long portions 411A, 411B with respect to the tire circumferential direction is in the range of 3 [deg]≦θs1≦17 [deg], and preferably in the range of 8 [deg]≦θs1≦12 [deg].

[0044] The inclination angle is measured as the angle formed by an imaginary line connecting the end points of the first and second long portions 411A and 411B and the tire equatorial plane CL.

[0045] In addition, the extension length (dimension symbols omitted in the figure) of each of the first and second long portions 411A, 411B in the tire circumferential direction is in the range of 70% to 95% of the tire circumferential extension distance Ps' of the above-mentioned pair of adjacent long and short portions 411A, 412A (411B, 412B), and preferably in the range of 80% to 90%.

[0046] 4, the inclination angle θs2A of the first short portion 412A with respect to the tire circumferential direction is in the range of 20 degrees ≦ θs2A ≦ 50 degrees, and preferably in the range of 35 degrees ≦ θs2A ≦ 45 degrees. The inclination angle θs2B of the second short portion 412B with respect to the tire circumferential direction is in the range of 40 degrees ≦ θs2B ≦ 80 degrees, and preferably in the range of 55 degrees ≦ θs2B ≦ 75 degrees. The inclination angle θs2B of the second short portion 412B with respect to the tire circumferential direction with respect to the inclination angle θs2A of the first short portion 412A is in the range of 10 degrees ≦ θs2B - θs2A ≦ 50 degrees, and preferably in the range of 20 degrees ≦ θs2B - θs2A ≦ 40 degrees. In this configuration, the second short portion 412B having the large amplitude As2 has a large inclination angle θs2B, forming a zigzag shape with different amplitudes As1 and As2, thereby ensuring the effect of improving drainage due to the zigzag shape and increasing the rigidity of the center land portion 32 (33) in the region having the small amplitude As1.

[0047] The groove width Ws and groove depth Hs of the circumferential narrow groove 41 may be constant around the entire tire circumference, as described above, or may periodically increase or decrease at predetermined positions. For example, the circumferential narrow groove 41 may have a wide groove width (symbols omitted in the figure) and a shallow groove depth Hs' (see FIG. 6) in a region including the zigzag-shaped first short portion 412A, more specifically, in a region including the junction of the first and second lateral grooves 42A and 42B (described later). On the other hand, the circumferential narrow groove 41 may have a narrow groove width (symbols omitted in the figure) and a deep groove depth Hs (see FIG. 6) in a region including the zigzag-shaped second short portion 412B. This ensures the groove volume of the circumferential narrow groove 41, thereby ensuring the wet performance of the tire. Furthermore, the rigidity of the center land portions 32 and 33 is ensured, thereby suppressing uneven tire wear. In this case, it is preferable that the ratio of the wide groove width to the narrow groove width be greater than 1.0 and not greater than 2.0. The shallow groove depth Hs' is realized by the bottom upper portion 41' formed at the groove bottom of the circumferential narrow groove 41. The shallow groove depth Hs' is in the range of 0.5 mm≦Hs'≦4.0 mm, and relative to the groove depth Hg1 of the shoulder main groove 21 is in the range of 0.05≦Hs' / Hg1≦0.20.

[0048] As shown in Fig. 3, the multiple lateral grooves 42A, 42B are composed of first and second lateral grooves 42A, 42B. One end of the first lateral groove 42A opens into one edge portion (left side in the figure) of the central land portion 32; 33, and the other end connects to the circumferential narrow groove 41. One end of the second lateral groove 42B opens into the other edge portion (right side in the figure) of the central land portion 32; 33, and the other end connects to the circumferential narrow groove 41. Furthermore, one set of lateral grooves 42A, 42B is disposed at the same position in the tire circumferential direction, and multiple sets of lateral grooves 42A, 42B are arranged at predetermined intervals in the tire circumferential direction.

[0049] 4, the pitch length P1 of the first lateral grooves 42A is in the range of 0.50≦P1 / Wb2≦1.10, preferably 0.75≦P1 / Wb2≦0.95, relative to the contact width Wb2 (Wb3) of the center land portion 32 (33). The lower limit ensures the drainage improvement effect of the lateral grooves 42A, 42B, while the upper limit ensures the rigidity of the center land portions 32, 33. In the configuration of FIG. 4, the pitch length P1 of the first lateral grooves 42A is equal to the pitch length Ps of the zigzag shape of the circumferential narrow grooves 41. Therefore, the wave number of the zigzag shape of the circumferential narrow grooves 41 is twice the pitch number of the first lateral grooves 42A.

[0050] As shown in FIG. 4, the first lateral grooves 42A and the second lateral grooves 42B are alternately connected to the circumferential narrow groove 41 in the tire circumferential direction. The first and second lateral grooves 42A and 42B are connected to the zigzag-shaped long portions 411A and 411B of the circumferential narrow groove 41, respectively. Specifically, as shown in FIG. 4, the first lateral groove 42A is connected to the zigzag-shaped first long portion 411A of the circumferential narrow groove 41 in a T-shape, and the second lateral groove 42B is connected to the second long portion 411B in a T-shape. Adjacent lateral grooves 42A and 42B in the tire width direction are connected to different long portions 411A and 411B. Therefore, one short portion 412A and one short portion 412B and a pair of end points (a pair of bending points of the zigzag shape) are located between the connection points of the adjacent lateral grooves 42A and 42B. In addition, a pair of long portions 411A, 411B and a pair of short portions 412A, 412B are arranged between the connection points of the circumferentially adjacent lateral grooves 42A, 42A and 42B, 42B.

[0051] In the above configuration, (1) the circumferential narrow groove 41 has a zigzag shape in which long portions and short portions are alternately connected, and the first and second lateral grooves 42A, 42B connect to mutually different long portions 411A, 411B from the left and right sides of the circumferential narrow groove 41. Therefore, the circumferential narrow groove 41 has zigzag-shaped short portions 412A, 412B between the connecting portions of adjacent lateral grooves 42A, 42B. This improves drainage on the tread surfaces of the center land portions 32, 33, improving the wet performance of the tire. Furthermore, compared to a configuration (not shown) in which both the first and second lateral grooves connect to one long portion from the left and right, and a configuration (not shown) in which the first and second lateral grooves connect to bending points of a zigzag shape, the rigidity of the center land portions 32, 33 is ensured, strain concentration at the edge portions defined by the lateral grooves 42A, 42B is alleviated, and uneven wear of the center land portions 32, 33 is suppressed. This achieves both wet performance and uneven wear resistance of the tire.

[0052] As shown in FIG. 4, the first and second lateral grooves 42A, 42B are disposed near the first short portion 412A having a small amplitude As1. This ensures the tire widthwise extension length of the first and second lateral grooves 42A, 42B, improving the drainage of the center land portions 32, 33 compared to a configuration (not shown) in which the first and second lateral grooves 42A, 42B are connected near the second short portion 412B having a large amplitude As2. Specifically, in FIG. 5, the tire circumferential distances DL1, DL2 from the end points of the first short portion 412A to the connecting points of the first and second lateral grooves 42A, 42B are in the range of 3% to 20% of the pitch length Ps of the zigzag shape of the circumferential narrow groove 41, more preferably in the range of 5% to 15%. The lower limit ensures the rigidity of the center land portions 32, 33, suppressing uneven wear of the center land portions 32, 33. The upper limit ensures the effect of improving drainage due to the lateral grooves 42A, 42B being disposed in the vicinity of the first short portion 412A.

[0053] The groove widths W1 and W2 (see FIG. 4) of the first and second lateral grooves 42A and 42B are in the range of 0.1 mm to 2.0 mm, preferably 0.5 mm to 1.5 mm. The lower limit ensures the drainage of the lateral grooves 42A and 42B, while the upper limit prevents a decrease in rigidity of the center land portions 32 and 33 due to the arrangement of the lateral grooves 42A and 42B. The groove widths W1 and W2 of the lateral grooves 42A and 42B may be constant throughout the entire lateral grooves 42A and 42B, or may increase or decrease in a predetermined region, as described below.

[0054] 5, each of the first and second transverse grooves 42A, 42B has an inclined portion 421, an axial portion 422, and a connecting portion 423.

[0055] As shown in FIG. 5, the inclined portions 421 are groove portions inclined at predetermined inclination angles φ21A and φ21B with respect to the tire circumferential direction and constitute the longitudinal center portions of the lateral grooves 42A and 42B. The inclined portions 421 of the first and second lateral grooves 42A and 42B are inclined in the opposite direction to the tire circumferential direction of the zigzag-shaped long portions 411A and 411B of the circumferential narrow groove 41. This ensures a balanced rigidity of the center land portion 32 (33). The inclined portions 421 of the first and second lateral grooves 42A and 42B are inclined in the same direction with respect to the tire circumferential direction. Compared to a configuration (not shown) in which the first and second lateral grooves are inclined in opposite directions with respect to the tire circumferential direction, this configuration ensures a balanced rigidity of the center land portion 32 (33), disperses strain energy in the rib-shaped center land portion 32 (33), and improves uneven wear resistance. The inclination angles φ21A and φ21B of the inclined portion 421 are in the range of 40 degrees to 80 degrees, and preferably in the range of 50 degrees to 70 degrees. The inclination angles φ21A and φ21B of the inclined portion 421 are substantially the same, and specifically in the range of -10 degrees≦φ21A-φ21B≦10 degrees.

[0056] The first and second lateral grooves 42A, 42B have maximum groove widths W1, W2 (see FIG. 4) at the inclined portions 421. The groove depth H21 (see FIG. 7) of the inclined portions 421 is in the range of 0.5 mm≦H21≦4.0 mm, and is in the range of 0.05≦H21 / Hg1≦0.15 relative to the groove depth Hg1 of the shoulder main groove 21. In this configuration, the inclined portions 421 are wide and shallow, ensuring the drainage of the lateral grooves 42A, 42B and the rigidity of the center land zone 32 (33).

[0057] 5, the tire widthwise extension length D21 of the inclined portion 421 is in the range of 0.10≦D21 / Wb2≦0.50, preferably 0.20≦D21 / Wb2≦0.45, and more preferably 0.24≦D21 / Wb2≦0.40, relative to the contact width Wb2 (Wb3) of the center land portion 32 (33). The lower limit ensures the improvement of drainage by the inclined portion 421, while the upper limit ensures sufficient space in the tire width direction for the axial portion 422 (described later), thereby suppressing uneven wear at the edge of the center land portion 32 (33). The tire circumferential extension length L21 of the inclined portion 421 is in the range of 0.10≦L21 / Ps≦0.40, preferably 0.20≦L21 / Ps≦0.30, relative to the pitch length Ps of the zigzag shape of the circumferential narrow groove 41. The lower limit ensures that the inclined portion 421 improves drainage, and the upper limit ensures the rigidity of the center land portion 32 (33). In the configuration of Fig. 5, the circumferential extension length L21 of the inclined portion 421 is equal to the circumferential extension length L2 of the lateral grooves 42A, 42B.

[0058] 5, the inclined portion 421 has a straight shape, so that the lateral grooves 42A, 42B have a Z-shape or a step shape. However, this is not limiting, and the inclined portion 421 may have an arc shape or an S-shape, so that the lateral grooves 42A, 42B have a curved shape (not shown).

[0059] The axial portion 422 is a groove portion that connects the inclined portion 421 and the edge portion of the center land portion 32 (33), extends substantially parallel to the tire rotation axis, and is connected to the edge portion of the center land portion 32 (33) in a T-shape. Further, the inclination angle of the axial portion 422 with respect to the tire circumferential direction (dimension symbols in the figure are omitted) is in the range of 80° or more and 110° or less. With such a configuration, since the lateral grooves 42A and 42B are connected perpendicularly to the edge portion of the center land portion 32 (33), failure of the edge portion of the center land portion 32 (33) starting from the openings of the lateral grooves 42A and 42B is suppressed.

[0060] Also, the groove width of the axial portion 422 (dimension symbols in the figure are omitted) is in the range of 0.1 mm or more and 2.0 mm or less, preferably in the range of 0.5 mm or more and 1.5 mm or less. Further, it is preferable that the groove width of the axial portion 422 is narrower than the groove width of the inclined portion 421 and is in the range of 50% or more and less than 100% with respect to the groove width of the inclined portion 421. Also, the groove depth H22 of the axial portion 422 (see FIG. 7) is deeper than the groove depth H21 of the inclined portion 421 (H21 < H22), and is in the range of 0.60 ≦ H21 / Hg1 ≦ 0.80 with respect to the groove depth Hg1 of the shoulder main groove 21. For example, in the configuration of FIG. 5, the multi-sipe 5 described later also serves as the axial portion 422 of the lateral grooves 42A and 42B, so that the axial portion 422 has the same depth as the multi-sipe 5. However, it is not limited to this, and the axial portion 422 may have the same depth H21 as the inclined portion 421, so that the entire lateral grooves 42A and 42B may have a shallow groove structure (not shown).

[0061] In FIG. 5, the extension length D22 of the axial portion 422 in the tire width direction is in the range of 0.05 ≦ D22 / Wb2 ≦ 0.20 with respect to the ground contact width Wb2 (Wb3) of the center land portion 32 (33), preferably in the range of 0.10 ≦ D22 / Wb2 ≦ 0.15. Also, the extension length D22 of the axial portion 422 is in the range of 2.0 mm ≦ D22 ≦ 5.0 mm.

[0062] The connecting portion 423 is a groove portion that connects the inclined portion 421 and the circumferential narrow groove 41, and is connected in a T-shape to the zigzag long portions 411A, 411B of the circumferential narrow groove 41. The inclination angle of the connecting portion 423 with respect to the tire circumferential direction is in the range of 80 degrees to 110 degrees.

[0063] The groove width (dimension symbols omitted in the drawing) of the connecting portion 423 is in the range of 0.1 mm to 2.0 mm, preferably 0.5 mm to 1.5 mm. The groove depth (dimension symbols omitted in the drawing; see FIG. 7) of the connecting portion 423 is the same depth H21 as that of the inclined portion 421. Therefore, the lateral grooves 42A and 42B have a shallow groove depth at the openings relative to the circumferential narrow groove 41.

[0064] 2, a first center land portion 32 adjacent to one of the pair of shoulder land portions 31, 31 (for example, the shoulder land portion 31 on the left side in the figure), a second center land portion 33 adjacent to the first center land portion 32, and a third center land portion 32 adjacent to the other of the pair of shoulder land portions 31, 31 (for example, the shoulder land portion 31 on the right side in the figure) are defined. In the configuration of FIG. 2, the first to third center land portions 32, 33, 32 each include the above-mentioned circumferential narrow groove 41 and first and second lateral grooves 42A, 42B.

[0065] At this time, as shown in Fig. 3, the first and second lateral grooves 42A, 42B of the first center land portion 32 are arranged to overlap each other in the tire circumferential direction. Similarly, the first and second lateral grooves 42A, 42B of the second center land portion 33 are arranged to overlap each other in the tire circumferential direction. Furthermore, as shown in Fig. 2, the first and second lateral grooves 42A, 42B of the third center land portion 32 are arranged to overlap each other in the tire circumferential direction.

[0066] In the above configuration, in each of the first to third center land portions 32, 33, 32, the first lateral groove 42A and the second lateral groove 42B are arranged to overlap each other in the tire circumferential direction. Therefore, compared to a configuration (not shown) in which the lateral grooves are arranged offset in the tire circumferential direction, the concentration of strain in the edge portions defined by the lateral grooves 42A, 42B is alleviated, and uneven wear of the center land portions 32, 33 is suppressed.

[0067] The overlap amount DA (see FIG. 3) of the first and second lateral grooves 42A, 42B in each of the first to third center land portions 32, 33, 32 is in the range of 0.05≦DA / P1≦0.40, preferably 0.10≦DA / P1≦0.30, relative to the pitch length P1 (see FIG. 3) of the first lateral groove 42A. This reduces distortion of the edge portions of the center land portions 32, 33 caused by the lateral grooves 42A, 42B overlapping each other in one center land portion 32, 33.

[0068] The overlap amount DA of the lateral grooves 42A, 42B is measured as the overlap distance between the first and second lateral grooves 42A, 42B in the tire circumferential direction when the first and second lateral grooves 42A, 42B are projected onto the tire equatorial plane CL.

[0069] 3, the first and second lateral grooves 42A, 42B of the first center land portion 32 are arranged to be offset in the tire circumferential direction from the first and second lateral grooves 42A, 42B of the second center land portion 33. Furthermore, as shown in Fig. 2, the first and second lateral grooves 42A, 42B of the first center land portion 32, the first and second lateral grooves 42A, 42B of the second center land portion 33, and the first and second lateral grooves 42A, 42B of the third center land portion 32 are arranged to be offset from each other in the tire circumferential direction.

[0070] In the above configuration, the lateral grooves 42A, 42B of adjacent center land portions 32, 33; 33, 32 are arranged offset from each other in the tire circumferential direction. Therefore, compared to a configuration (not shown) in which the lateral grooves are arranged overlapping in the tire circumferential direction, the periodic resonance sounds caused by the lateral grooves 42A, 42B are canceled out, thereby reducing noise during driving.

[0071] Furthermore, the offset DB (see FIG. 3) between the first and second lateral grooves 42A, 42B of the first center land portion 32 and the first and second lateral grooves 42A, 42B of the second center land portion 33 is in the range of 0.10≦DB / P1, preferably 0.15≦DB / P1, relative to the pitch length P1 (see FIG. 3) of the first lateral groove 42A. This ensures that the offset between the lateral grooves 42A, 42B of the adjacent center land portions 32, 33 reduces noise during driving. While there is no particular upper limit to the ratio DB / L2, it is constrained by the relationship with the pitch length P1 (see FIG. 3) of the lateral grooves 42A, 42B, as long as the adjacent pairs of lateral grooves 42A, 42B do not overlap.

[0072] The offset amount DB between the lateral grooves 42A, 42B is measured as the distance between the first and second lateral grooves 42A, 42B of the adjacent center land portions 32, 33 in the tire circumferential direction when projected onto the tire equatorial plane CL.

[0073] [Shoulder land area] As shown in FIG. 2, the shoulder land portion 31 is a rib with a circumferentially continuous tread surface. The shoulder land portion 31 has only multi-sipes 5 (described later) and no other grooves or sipes. Therefore, the shoulder land portion 31 has a plain tread surface that is not divided in the circumferential direction of the tire by grooves or sipes. This improves the uneven wear resistance of the shoulder land portion 31, which is prone to uneven wear. However, the present invention is not limited to this, and the shoulder land portion 31 may have shallow sipes or shallow grooves with a depth of 15 mm or less (not shown).

[0074] [Multi-sipe] In the configuration of FIG. 2, each land portion 31-33 includes multiple multi-sipes 5. The multi-sipes 5 are short sipes that open at one end to the edge 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 (symbols omitted in the figure), a depth H5 of 2.0 mm to 17 mm (see FIG. 7), and a length of 2.0 mm to 10 mm (symbols omitted in the figure; see FIG. 5). The multiple multi-sipes 5 are arranged in the tire circumferential direction along the edge of the land portions 31-33. The pitch length of the multi-sipes 5 (symbols omitted in the figure) is in the range of 0.1% to 0.6% of the tire circumference. In this configuration, the multi-sipes 5 reduce the rigidity of the land portions 31 to 33, thereby reducing the ground contact pressure at the edges of the land portions 31 to 33 when the tire is in contact with the ground. This suppresses the occurrence of uneven wear (particularly river wear), improving the uneven wear resistance of the tire.

[0075] In the configuration shown in FIG. 2, as shown in FIGS. 5 and 7, some of the multi-sipes 5 also serve as the axial portions 422 of the lateral grooves 42A, 42B of the center land portions 32, 33. In this manner, the lateral grooves 42A, 42B may be connected to the multi-sipes 5 to open to the edge portions of the center land portions 32, 33. In this case, it is preferable that the multi-sipes 5 have a width narrower than the groove widths W1, W2 (see FIG. 4) of the inclined portions 421 of the lateral grooves 42A, 42B and a depth H5 deeper than the groove depth H21 (see FIG. 7) of the inclined portions 421 of the lateral grooves 42A, 42B. This allows for both the drainage effect of the lateral grooves 42A, 42B and the suppression of uneven wear by the multi-sipes 5.

[0076] [Wear-sacrificing rib] FIG. 8 is a cross-sectional view showing an edge portion of the shoulder land portion 31 shown in FIG.

[0077] As shown in Figures 2 and 8, the shoulder land portion 31 includes a narrow groove 61 extending along the edge portion on the tire ground contact edge T side, and a narrow rib 62 defined by the narrow groove 61. The groove width W6 of the narrow groove 61 is in the range of 1.0 mm ≤ W6 ≤ 3.0 mm, and the groove depth H6, relative to the groove depth Hg1 of the shoulder main groove 21 (see Figure 6), is in the range of 0.60 ≤ H6 / Hg1 ≤ 1.00. With this configuration, the narrow rib 62 functions as a so-called wear-sacrificing rib during tire rolling, suppressing uneven wear of the main body of the shoulder land portion 31. This improves the tire's resistance to uneven wear.

[0078] In the configuration shown in FIG. 8, the narrow groove 61 has a circular cross-sectional widened portion (reference numeral omitted in the figure) at the bottom. The diameter of this widened portion is in the range of 1.2 to 5 times the groove width W6 of the narrow groove 61. The top surface of the narrow rib 62 is offset in the tire radial direction from the tread surface of the shoulder land portion 31. The offset amount D6 of the top surface of the narrow rib 62 is in the range of 1.0 mm≦D6≦4.0 mm. The width of the top surface of the narrow rib 62 (dimension symbol omitted in the figure) is in the range of 20% to 40% of the contact width Wb1 (see FIG. 2) of the shoulder land portion 31. These features improve the effect of the wear-sacrificial rib in suppressing uneven wear.

[0079] [Variations] Fig. 9 is a plan view showing a modification of the tire 1 shown in Fig. 2. In this figure, the same components as those in Fig. 2 are given the same reference numerals, and the description thereof will be omitted.

[0080] In the configuration shown in FIG. 2, the groove width Wg2 of the center main groove 22 is set to be the same as or slightly narrower than the groove width Wg1 of the shoulder main grooves 21. Specifically, the groove width Wg2 of the center main groove 22 is set to be 0.70≦Wg2 / Wg1≦1.00 relative to the groove width Wg1 of the shoulder main grooves 21, preferably 0.80≦Wg2 / Wg1≦0.90. Therefore, the groove width Wg2 of the center main groove 22 is set to be the same as or slightly narrower than the groove width Wg1 of the shoulder main grooves 21. This ensures drainage in the tread center region. This configuration is preferable in that it improves drainage in the tread center region and enhances the wet performance of the tire.

[0081] 9, the groove width Wg2 of the center main groove 22 is narrower than the groove width Wg1 of the shoulder main grooves 21, and is in the range of 0.14≦Wg2 / Wg1≦0.45. The groove width Wg2 of the center main groove 22 is also in the range of 3.5 mm≦Wg2≦6.0 mm. This configuration increases the rigidity of the tread center region, improving the tire's resistance to uneven wear and rolling resistance.

[0082] [effect] As described above, the tire 1 includes a pair of shoulder main grooves 21, one or more center main grooves 22, a pair of shoulder land portions 31 defined by the shoulder main grooves 21 and the center main groove 22, and two or more rows of center land portions 32, 33 (see FIG. 2). At least one row of center land portions 32, 33 includes a circumferential narrow groove 41 extending in the tire circumferential direction, a first lateral groove 42A that opens at one end into one edge portion of the center land portions 32, 33 and connects to the circumferential narrow groove 41 at the other end, and a second lateral groove 42B that opens at one end into the other edge portion of the center land portions 32, 33 and connects to the circumferential narrow groove 41 at the other end. The circumferential narrow groove 41 has a zigzag shape formed by repeatedly connecting a first long portion 411A, a first short portion 412A, a second long portion 411B, and a second short portion 412B (see FIG. 4). The first transverse groove 42A is connected to the zigzag-shaped first long portion 411A, and the second transverse groove 42B is connected to the zigzag-shaped second long portion 411B.

[0083] In this configuration, (1) the center land portions 32, 33 have circumferential narrow grooves and lateral grooves 42A, 42B, improving drainage in the tread center region. Also, (2) the circumferential narrow groove 41 has a zigzag shape with long and short portions alternately connected, and the first and second lateral grooves 42A, 42B connect to different long portions 411A, 411B from the left and right sides of the circumferential narrow groove 41. Therefore, the circumferential narrow groove 41 has zigzag-shaped short portions 412A, 412B between the connecting portions of adjacent lateral grooves 42A, 42B. This improves drainage in the tread surfaces of the center land portions 32, 33, improving the wet performance of the tire. Furthermore, compared to a configuration (not shown) in which both the first and second lateral grooves connect to one long portion from the left and right, and a configuration (not shown) in which the first and second lateral grooves connect to a bending point of a zigzag shape, the rigidity of the center land portions 32, 33 is ensured, improving the tire's resistance to uneven wear. This has the advantage of achieving both wet performance and uneven wear resistance of the tire.

[0084] In addition, in the tire 1, the groove width Ws (see FIG. 4) of the circumferential narrow groove 41 is in the range of 0.1 mm≦Ws≦2.0 mm. The lower limit ensures the drainage performance of the circumferential narrow groove 41, while the upper limit has the advantage of suppressing a decrease in rigidity of the center land portions 32, 33 due to the arrangement of the circumferential narrow groove 41.

[0085] In the tire 1, the amplitude As1 of the zigzag shape in the first short portion 412A is in the range of 0.10≦As1 / As2≦0.90 relative to the amplitude As2 of the zigzag shape in the second short portion 412B (see FIG. 4 ). The lower limit ensures the effect of improving drainage by the first short portion 412A, and the upper limit ensures the rigidity of the center land portions 32, 33.

[0086] In addition, in the tire 1, the maximum amplitude As of the zigzag shape is in the range of 0.05≦As / Wb2≦0.20 relative to the contact width Wb2 (Wb3) of the central land portion 32 (33) (see FIG. 4). The lower limit ensures the improvement of drainage due to the zigzag shape of the circumferential narrow groove 41, and the upper limit ensures the rigidity of the central land portions 32, 33.

[0087] In addition, in the tire 1, the pitch length Ps of the zigzag shape formed by the first long portion 411A, the first short portion 412A, the second long portion 411B, and the second short portion 412B is in the range of 0.50≦Ps / Wb2≦1.10 relative to the contact width Wb2 (Wb3) of the center land portion 32 (33) (see FIG. 4 ). The lower limit ensures the improvement of drainage due to the zigzag shape of the circumferential narrow groove 41, while the upper limit ensures the rigidity of the center land portions 32, 33.

[0088] Furthermore, in this tire 1, the inclination angle θs2B of the second short portion 412B relative to the tire circumferential direction is in the range of 10 degrees ≦ θs2B − θs2A ≦ 50 degrees relative to the inclination angle θs2A of the first short portion 412A (see FIG. 4). With this configuration, the inclination angle θs2B of the second short portion 412B, which has a large amplitude As2, is large, so the extension length of the second short portion 412B in the tire circumferential direction is short. This has the advantage of making the extension lengths of the first and second short portions 412A and 412B in the tire circumferential direction uniform.

[0089] In addition, in the tire 1, the groove widths W1, W2 (see FIG. 4) of the first and second lateral grooves 42A, 42B are in the range of 0.1 mm to 2.0 mm. The lower limit ensures the drainage of the lateral grooves 42A, 42B, while the upper limit has the advantage of suppressing a decrease in rigidity of the center land portions 32, 33 due to the arrangement of the lateral grooves 42A, 42B.

[0090] In this tire 1, each of the first and second lateral grooves 42A, 42B has an inclined portion 421 inclined with respect to the tire circumferential direction (see FIG. 5). The inclination angles φ21A, φ21B of the inclined portions 421 are in the range of 40 degrees or more and 80 degrees or less. The inclined portions 421 of the first and second lateral grooves 42A, 42B are inclined in the same direction with respect to the tire circumferential direction. Compared to a configuration (not shown) in which the first and second lateral grooves are inclined in opposite directions with respect to the tire circumferential direction, this configuration ensures a balanced rigidity of the center land portion 32 (33), disperses strain energy in the rib-shaped center land portion 32 (33), and has the advantage of improving uneven wear resistance.

[0091] In addition, in this tire 1, the groove depth H21 of the inclined portion 421 is in the range of 0.05≦H21 / Hg1≦0.15 relative to the groove depth Hg1 of the shoulder main groove 21 (see FIG. 7). The lower limit ensures the drainage of the lateral grooves 42A, 42B, while the upper limit ensures the rigidity of the center land portion 32 (33).

[0092] In addition, in the tire 1, the inclined portions 421 of the first and second lateral grooves 42A and 42B are inclined in the opposite direction to the zigzag-shaped long portions 411A and 411B of the circumferential narrow groove 41 (see FIG. 5). This has the advantage of ensuring a rigidity balance of the center land portion 32 (33).

[0093] In addition, in this tire 1, the extension length D21 of the inclined portion 421 in the tire width direction is in the range of 0.10≦D21 / Wb2≦0.50 relative to the contact width Wb2 of the central land portion 32 (33) (see FIG. 5 ). The lower limit ensures the effect of improving drainage by the inclined portion 421, while the upper limit ensures the arrangement space in the tire width direction of the axial portion 422, which has the advantage of suppressing uneven wear at the edge portion of the central land portion 32 (33).

[0094] In the tire 1, each of the first and second lateral grooves 42A, 42B has an axial portion 422 that connects the inclined portion 421 and the edge portion of the central land portion 32 (33) (see FIG. 5). The inclination angle of the axial portion 422 with respect to the tire circumferential direction (dimension symbols omitted in the drawing) is in the range of 80 degrees to 110 degrees. With this configuration, the lateral grooves 42A, 42B connect perpendicularly to the edge portion of the central land portion, which has the advantage of suppressing failures at the edge portion of the central land portion 32 (33) originating from the opening of the lateral grooves 42A, 42B.

[0095] Applies to The tire 1 is a heavy-duty tire mounted on the steering axle of a vehicle. By applying the present invention to such a tire, the above-described effect of improving tire performance can be effectively obtained.

[0096] 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 applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires. [Example]

[0097] Figures 10 and 11 are tables showing the results of performance tests of the tire according to the embodiment of the present invention, and Figure 12 is a plan view showing the tread surface of a conventional tire.

[0098] In this performance test, several types of test tires were evaluated for (1) wet braking performance and (2) uneven wear resistance. Furthermore, test tires with a tire size of 295 / 75R22.5 were mounted on rims specified by the TRA, and the test tires were subjected to the TRA's specified internal pressure and load. The test tires were also mounted on a 2-D tractor head test vehicle.

[0099] (1) In the evaluation of wet braking performance, a test vehicle is driven on an asphalt road sprayed with 1 mm of water, and the braking distance from an initial speed of 40 km / h is measured. Based on the measurement results, an index rating is then given, with the conventional example being set as the standard (100). The higher the rating, the better.

[0100] (2) In the evaluation of uneven wear resistance, after a test vehicle has traveled 50,000 km on a specified pavement, the depth of step wear on the edge of the land is observed and an index is evaluated. This evaluation is performed using an index evaluation with the conventional example as the standard (100). The higher the evaluation value, the better.

[0101] The test tires of Examples 1 to 15 have the configuration shown in Figures 1 and 2, and include four circumferential main grooves 21, 22, a pair of shoulder land portions 31, and three rows of center land portions 32, 33. Each center land portion 32, 33 includes a circumferential narrow groove 41 formed by connecting long portions 411A, 411B and short portions 412A, 412B, and lateral grooves 42A, 42B connected to the long portions 411A, 411B of the circumferential narrow groove 41. The first and second short portions 412A, 412B of the circumferential narrow groove 41 have different lengths. The lateral grooves 42A, 42B are arranged in a staggered pattern around the tire circumferentially, and alternately connect to the long portions 411A, 411B of the circumferential narrow groove 41, which has a zigzag shape. The shoulder main groove 21 has a groove width Wg1 of 10.5 mm and a groove depth Hg1 of 14.6 mm. The center main groove 22 has a groove width Wg2 of 9.0 mm and a groove depth Hg2 of 12.9 mm. The tire ground contact width TW is 212 mm, the shoulder land portion 31 has a ground contact width Wb1 of 39.5 mm, and the center land portions 32, 33 have ground contact widths Wb2 = 31.0 mm and Wb3 = 32.0 mm. The circumferential narrow groove 41 has a groove width Ws of 0.7 mm and a groove depth Hs of 9.2 mm. In addition, the test tire of Example 16 has the configuration shown in Figure 9 and is the same as the test tire of Example 1 except that the groove width Wg2 of the center main groove 22 is 4.6 [mm], the tire contact width TW is 207 [mm], and the contact width Wb1 of the shoulder land portion 31 is 41.4 [mm].

[0102] In the conventional test tire of Example 1, the number of waves of the zigzag shape of the circumferential narrow groove 41 is equal to the number of pitches of the first lateral groove 42A (see FIG. 12). Therefore, adjacent first lateral grooves 42A, 42A are connected by a pair of long and short portions. The lateral grooves 42A, 42B are arranged in a staggered pattern in the tire circumferential direction and are alternately connected at the bending points of the zigzag circumferential narrow groove 41. Adjacent lateral grooves 42A, 42B are arranged offset from each other in the tire circumferential direction. The lateral grooves 42A, 42B of adjacent center land portions 32, 33 are arranged to overlap each other in the tire circumferential direction.

[0103] As the test results show, the test tires of the examples exhibit both good wet braking performance and good resistance to uneven wear. [Explanation of symbols]

[0104] 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 main groove; 31 shoulder land portion; 32, 33 center land portion; 41 circumferential narrow groove; 41' bottom upper portion; 411A, 411B long portion; 412A, 412B short portion; 42A, 42B lateral groove; 421 inclined portion; 422 axial portion; 423 connection portion; 5 multi-sipe; 61 narrow groove; 62 narrow rib

Claims

1. A tire comprising a pair of shoulder main grooves and one or more center main grooves, and a pair of shoulder land portions and two or more rows of center land portions defined by the shoulder main grooves and the center main groove, At least one row of the center land portion includes a circumferential narrow groove extending in the tire circumferential direction, a first lateral groove having one end opening onto one edge portion of the center land portion and the other end connecting to the circumferential narrow groove, and a second lateral groove having one end opening onto the other edge portion of the center land portion and the other end connecting to the circumferential narrow groove, the circumferential narrow groove has a zigzag shape formed by repeatedly connecting a first long portion, a first short portion, a second long portion, and a second short portion, the first transverse groove is connected to the first long portion of the zigzag shape, The second transverse groove is connected to the second long portion of the zigzag shape, and a pitch length Ps of the zigzag shape consisting of the first long portion, the first short portion, the second long portion, and the second short portion, relative to a contact width Wb2 of the center land portion, in a range of 0.50≦Ps / Wb2≦1.

10.

2. The tire according to claim 1, wherein the groove width Ws of the circumferential narrow groove is in the range of 0.1 mm≦Ws≦2.0 mm.

3. 3. The tire according to claim 1, wherein an amplitude As1 of the zigzag shape in the first short portion and an amplitude As2 of the zigzag shape in the second short portion are in a range of 0.10≦As1 / As2≦0.

90.

4. The tire according to any one of claims 1 to 3, wherein a maximum amplitude As of the zigzag shape is in a range of 0.05≦As / Wb2≦0.20 relative to a contact width Wb2 of the center land portion.

5. The tire according to any one of claims 1 to 4, wherein an inclination angle θs2B of the second short portion with respect to the tire circumferential direction is in a range of 10 [deg]≦θs2B−θs2A≦50 [deg] relative to an inclination angle θs2A of the first short portion.

6. The tire according to any one of claims 1 to 5, wherein the groove width of the first and second lateral grooves is in the range of 0.1 mm to 2.0 mm.

7. The tire according to any one of claims 1 to 6, wherein each of the first and second lateral grooves has an inclined portion inclined with respect to the tire circumferential direction, the inclination angle of the inclined portion is in the range of 40 degrees or more and 80 degrees or less, and the inclined portions of the first and second lateral grooves are inclined in the same direction with respect to the tire circumferential direction.

8. The tire according to claim 7, wherein a groove depth H21 of the inclined portion is in a range of 0.05≦H21 / Hg1≦0.15 relative to a groove depth Hg1 of the shoulder main groove.

9. The tire according to claim 7 or 8, wherein the inclined portions of the first and second lateral grooves are inclined in opposite directions to the long portion of the zigzag shape of the circumferential narrow groove.

10. The tire according to any one of claims 7 to 9, wherein an extension length D21 of the inclined portion in the tire width direction is in the range of 0.10≦D21 / Wb2≦0.50 relative to a contact width Wb2 of the center land portion.

11. The tire according to any one of claims 7 to 10, wherein each of the first and second lateral grooves has an axial portion connecting the inclined portion and an edge portion of the center land portion, and the inclination angle of the axial portion with respect to the tire circumferential direction is in the range of 80 degrees or more and 110 degrees or less.

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