JP7485914B2 - tire - Google Patents

Description

This invention relates to tires, and more specifically to tires that can achieve both snow acceleration performance, uneven wear resistance, and tear resistance.

Conventional heavy-duty tires use zigzag-shaped main grooves to improve the tire's acceleration performance on snow. The technology described in Patent Document 1 is known as a conventional tire that uses such a configuration.

JP 2017-154708 A

On the other hand, heavy-duty tires mounted on vehicle steering axles have the problem that the zigzag shape of the main grooves described above makes them prone to uneven wear (particularly rail wear at the edges of the land areas) and tearing of the land areas.

Therefore, this invention was made in consideration of the above, and aims to provide a tire that can achieve both on-snow acceleration performance, uneven wear resistance, and tear resistance.

In order to achieve the above object, the tire has a pair of shoulder main grooves and one or more center main grooves extending in the tire circumferential direction, and four or more rows of land portions defined by the shoulder main grooves and the center main groove, wherein a groove opening of the shoulder main groove has a straight shape, or a zigzag shape or a wavy shape having an amplitude in the tire width direction, a groove bottom of the shoulder main groove has a zigzag shape or a wavy shape having an amplitude in the tire width direction, an amplitude A1_sh of the groove opening of the shoulder main groove has a relationship A1_sh<A2_sh with respect to an amplitude A2_sh of the groove bottom, and the groove opening of the shoulder main groove has a wavy shape formed by connecting a plurality of circular arcs that are convex toward the tire equatorial plane side . A tire according to the present invention is a tire including a pair of shoulder main grooves and one or more center main grooves extending in the tire circumferential direction, and four or more rows of land portions defined by the shoulder main grooves and the center main groove, wherein a groove opening of the shoulder main groove has a straight shape or a zigzag shape or a wavy shape having an amplitude in the tire width direction, a groove bottom of the shoulder main groove has a zigzag shape or a wavy shape having an amplitude in the tire width direction, and the amplitude A1_s of the groove opening of the shoulder main groove the groove opening of the center main groove has a straight shape or a zigzag shape or a wavy shape having an amplitude in the tire width direction, the groove bottom of the center main groove has a zigzag shape or a wavy shape having an amplitude in the tire width direction, and the amplitude A1_ce of the groove opening of the center main groove has a relationship of A1_ce/A1_sh≦0.95 with the amplitude A1_sh of the groove opening of the shoulder main groove.

In the tire according to the present invention, (1) the amplitude A1_sh of the groove opening of the shoulder main groove is set small, suppressing uneven rail wear of the edge of the land portion, which is likely to occur at the maximum amplitude position toward the shoulder main groove. Also, (2) the amplitude A2_sh of the groove bottom of the shoulder main groove is set large, ensuring the rigidity of the land portion and the tear resistance of the tire. Furthermore, (3) the groove opening of the shoulder main groove has a zigzag or wavy shape with amplitude in the tire width direction, increasing the edge component of the land portion and improving the tire's acceleration performance on snow. This has the advantage of achieving both the tire's acceleration performance on snow, uneven wear resistance, and tear resistance.

FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. FIG. 2 is a plan view showing the tread surface of the tire shown in FIG. FIG. 3 is an enlarged plan view showing the groove wall structure of the shoulder main groove shown in FIG. FIG. 4 is an enlarged plan view showing the groove wall structure of the shoulder main groove shown in FIG. FIG. 5 is a cross-sectional view in the groove depth direction of the shoulder main groove shown in FIG. FIG. 6 is an explanatory diagram showing the groove wall structures of the shoulder main groove and the center main groove shown in FIG. FIG. 7 is a table showing the results of performance tests of the tire according to the embodiment of the present invention.

The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to these 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 combined in any way that is obvious to those skilled in the art.

[tire]
Fig. 1 is a cross-sectional view in the tire meridian direction showing a tire 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 pneumatic radial tire for heavy loads mounted on the steering axle of a truck or tractor will be described as an example of a tire.

In the figure, the cross section in the tire meridian direction refers to a cross section of the tire cut by a plane including the tire rotation axis (not shown). Also, the symbol CL is the tire equatorial plane, which is a plane that passes through the center point of the tire in the tire rotation axis direction and is perpendicular to the tire rotation axis. Also, the tire width direction refers to the direction parallel to the tire rotation axis, and the tire radial direction refers to the direction perpendicular to the tire rotation axis.

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).

The pair of bead cores 11, 11 are made by winding one or more steel bead wires in a circular shape 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 arranged on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

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's framework. In addition, 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. In addition, the carcass ply of the carcass layer 13 is formed by coating multiple carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with coating rubber and rolling them, and has a carcass 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 100 degrees or less in absolute value.

The belt layer 14 is made by laminating four belt plies 141-144, which are arranged around the outer circumference of the carcass layer 13. The belt plies 141-144 are made by covering a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and have a belt angle of 15 degrees or more and 55 degrees or less in absolute value. The belt plies 141-144 have belt angles (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) 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 tread rubber 15 is arranged on the tire radial outer circumference of the carcass layer 13 and the belt layer 14 to form the tread portion of the tire 1. A pair of sidewall rubbers 16, 16 are arranged on the tire widthwise outer sides of the carcass layer 13 to form the left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the tire radial inner side of the left and right bead cores 11, 11 and the turned-up portion of the carcass layer 13 to the tire widthwise outer side to form the rim fitting surface of the bead portion.

[Tread pattern]
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 with the mud and snow mark "M+S". In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T is the tire ground contact edge, and the dimension symbol TW is the tire ground contact width.

As shown in FIG. 2, the tire 1 has a plurality of circumferential main grooves 21, 22 extending in the tire circumferential direction, and a plurality of land portions 31, 32, 33 defined by these circumferential main grooves 21, 22 on the tread surface.

The main groove is a groove that is required to display a wear indicator as specified by JATMA, and has a maximum groove width of 7.0 mm or more and a maximum groove depth of 12 mm or more.

The groove width is measured as the distance between the left and right groove walls at the groove opening when the tire is mounted on a specified rim, inflated to the specified internal pressure, and in an unloaded state. In configurations where the land portion has a notch or chamfered portion at the edge, the groove width is measured at the intersection of the tread surface and the extension of the groove wall in a cross-sectional view normal to the groove length direction.

Groove depth is measured as the distance from the tread surface to the bottom of the groove when the tire is mounted on a specified rim, inflated to the specified internal pressure, and in an unloaded state. In addition, if the groove has partial unevenness or sipes at the bottom of the groove, these are excluded from the measurement of the groove depth.

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.

For example, in the configuration of FIG. 2, the tire 1 has a tread pattern that is approximately point-symmetric with a center point on the tire equatorial plane CL. However, this is not limited to the above, and the tire 1 may have, for example, a tread pattern that is line-symmetric or asymmetric about the tire equatorial plane CL, or a tread pattern that has directionality in the tire rotation direction (not shown).

In the configuration of FIG. 2, the left and right regions bounded by the tire equatorial plane CL each have two circumferential main grooves 21, 22. These circumferential main grooves 21, 22 are arranged symmetrically with the tire equatorial plane CL at the center. These circumferential main grooves 21, 22 define five rows of land portions 31 to 33. One land portion 33 is arranged on the tire equatorial plane CL.

However, this is not limiting, and three or five or more circumferential main grooves may be arranged, and the circumferential main grooves may be arranged asymmetrically about the tire equatorial plane CL (not shown). Also, one circumferential main groove may be arranged on the tire equatorial plane CL, so that the land portion is positioned away from the tire equatorial plane CL (not shown).

Furthermore, of the circumferential main grooves 21, 22 arranged in one region bounded by the tire equatorial plane CL, the circumferential main groove 21 located on the outermost side in the tire width direction is defined as the shoulder main groove, and the circumferential main groove 22 on the tire equatorial plane CL side is defined as the center main groove.

The land portion 31 on the outer side in the tire width direction defined by the shoulder main groove 21 is defined as the shoulder land portion. The shoulder land portion 31 is the outermost land portion in the tire width direction and is located on the tire ground contact edge T. The land portion 32 on the inner side in the tire width direction defined by the shoulder main groove 21 is defined as the middle land portion. The middle land portion 32 is adjacent to the shoulder land portion 31 across the shoulder main groove 21. The land portion 33 on the tire equatorial plane CL side of the middle land portion 32 is defined as the center land portion. The center land portion 33 may be located on the tire equatorial plane CL (see FIG. 2) or may be located at a position off the tire equatorial plane CL (not shown).

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 the specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

The tire ground contact edge T is defined as the maximum axial width position of 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.

In addition, in a configuration having four circumferential main grooves 21, 22 as shown in FIG. 2, a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single center land portion 33 are defined. In addition, for example, in a configuration having five or more circumferential main grooves, two or more rows of center land portions are defined (not shown), and in a configuration having three circumferential main grooves, the middle land portion also serves as the center land portion (not shown).

In the configuration of FIG. 2, the maximum ground contact width Wb1 of the shoulder land portion 31 has a relationship of 0.15≦Wb1/TW≦0.25 with respect to the tire ground contact width TW. In addition, it is preferable that the maximum ground contact width Wb3 of the center land portion 33 closest to the tire equatorial plane CL has a relationship of 0.15≦Wb3/TW≦0.25 with respect to the tire ground contact width TW, and more preferably has a relationship of 0.18≦Wb3/TW≦0.23. In the configuration of FIG. 2, which has four circumferential main grooves 21, 22 and five rows of land portions 31 to 33, the maximum ground contact width Wb2 of the middle land portion 32 is slightly narrower than the maximum ground contact width Wb1 of the shoulder land portion 31, and more preferably is in the range of 0.85≦Wb2/Wb1≦0.95.

In the configuration shown in FIG. 2, the shoulder main groove 21 and the center main groove 22 have a zigzag or wavy shape with amplitude in the tire width direction. However, this is not limited to this, and as described below, the shoulder main groove 21 and the center main groove 22 may have a straight shape at the groove opening (not shown).

The shoulder land portion 31 is a rib with a circumferentially continuous tread surface and does not have lug grooves. The middle land portion 32 and the center land portion 33 each have a plurality of through lug grooves 321, 331. These through lug grooves 321, 331 have an open structure that penetrates the land portions 32, 33 and are arranged at a predetermined interval in the circumferential direction of the tire. As a result, the middle land portion 32 and the center land portion 33 are divided in the circumferential direction of the tire by the through lug grooves 321, 331 to form a block row.

[Shoulder main groove wall structure]
3 to 5 are enlarged plan views (FIGS. 3 and 4) and a cross-sectional view in the groove depth direction (FIG. 5) showing the groove wall structure of the shoulder main groove 21 shown in FIG. 2. In these figures, FIG. 3 particularly shows the groove wall structure on the outer side in the tire width direction of the shoulder main groove 21, and FIG. 4 particularly shows the groove wall structure on the inner side in the tire width direction. Also, FIG. 5 shows a cross-sectional view of the shoulder main groove 21 at the maximum amplitude position on the outer side in the tire width direction.

In the configuration of FIG. 2, as shown in FIG. 3, both the groove opening 211 and the groove bottom 212 of the shoulder main groove 21 have a zigzag or wavy shape with amplitude in the tire width direction. However, this is not limited to this, and the groove opening 211 of the shoulder main groove 21 may have a straight shape (not shown).

Here, an outer edge and an inner edge in the tire width direction are defined at the groove opening and groove bottom of the main groove, respectively. Also, an outer maximum amplitude position that is convex outward in the tire width direction and an inner maximum amplitude position that is convex inward in the tire width direction are defined at each of the outer edge and inner edge.

The edge of the groove opening is defined by a virtual line that connects the intersections of the groove wall and the tread profile in a cross-sectional view in the groove depth direction (see, for example, Figure 5) over the entire circumferential area of the tire. In a configuration in which the edge has a chamfered portion, the virtual line is drawn by connecting the edge of the groove opening at the intersection (not shown) of the extension of the groove wall and the tread profile.

The edge of the groove bottom is defined as a virtual line connecting the end points of the maximum groove depth position in a cross-sectional view in the groove depth direction over the entire tire circumferential direction. When the groove bottom of the main groove is a flat straight line at the maximum groove depth position (see, for example, FIG. 5), the outer edge and inner edge of the groove bottom are defined by both end points of the flat straight line. On the other hand, when the groove bottom of the main groove has an arc shape or a funnel shape (not shown), the maximum groove depth position is one point, and the edge of the groove bottom is defined by one point. Therefore, the outer edge and inner edge of the groove bottom are in the same position. In addition, the maximum groove depth position of the main groove is defined excluding the partial bottom upper part formed at the groove bottom of the main groove.

In the configurations of Figures 3 and 4, the groove opening 211 of the shoulder main groove 21 has a wavy shape with amplitude in the tire width direction at each of the outer edge portion 211o on the shoulder land portion 31 side and the inner edge portion 211i on the middle land portion 32 side. Furthermore, the groove bottom 212 of the shoulder main groove 21 has a zigzag shape with amplitude in the tire width direction at each of the outer edge portion 212o on the shoulder land portion 31 side and the inner edge portion 212i on the middle land portion 32 side.

As shown in Fig. 3, the outer maximum amplitude position P1oo of the outer edge portion 211o of the groove opening 211 of the shoulder main groove 21 is at the same position in the tire circumferential direction as the outer maximum amplitude position P2oo of the outer edge portion 212o of the groove bottom 212. Specifically, in Fig. 3, the offset amount φoo_sh of the outer maximum amplitude positions P1oo, P2oo at the outer edges 211o, 212o of the groove opening 211 and groove bottom 212 of the shoulder main groove 21 has a relationship of 0 < φoo_sh/λ1o_sh < 0.10 with respect to the wavelength λ1o_sh of the outer edge portion 211o of the groove opening 211, and more preferably has a relationship of 0 < φoo_sh/λ1o_sh < 0.05.

The offset of the maximum amplitude position is the circumferential distance of the tire from the maximum amplitude position in a plan view of the tread, and is measured with the tire mounted on a specified rim, with the specified internal pressure applied, and in an unloaded state.

Similarly, as shown in Figure 4, the outer maximum amplitude position P1io of the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 is at the same position in the tire circumferential direction as the outer maximum amplitude position P2io of the inner edge portion 212i of the groove bottom 212. Specifically, in Figure 4, the offset amount φio_sh of the outer maximum amplitude positions P1io, P2io at the inner edge portions 211i, 212i of the groove opening 211 and groove bottom 212 of the shoulder main groove 21 has a relationship of 0 ≦ φio_sh / λ1i_sh ≦ 0.10 with respect to the wavelength λ1i_sh of the inner edge portion 211i of the groove opening 211, and more preferably has a relationship of 0 ≦ φio_sh / λ1i_sh ≦ 0.05.

3, the outer maximum amplitude position P1oo of the outer edge portion 211o at the groove opening 211 of the shoulder main groove 21 and the outer maximum amplitude position P1io of the inner edge portion 211i are at the same position in the tire circumferential direction. Specifically, the offset amount δ_sh between the outer maximum amplitude position P1oo of the outer edge portion 211o at the groove opening 211 of the shoulder main groove 21 and the outer maximum amplitude position P1io of the inner edge portion 211i has a relationship of 0≦δ_sh/λ1o_sh≦0.10 with respect to the wavelength λ1o_sh of the outer edge portion 211o of the groove opening 211, and more preferably has a relationship of 0≦δ_sh/λ1o_sh≦0.05.

In addition, in FIG. 3, the wavelength λ1o_sh of the outer edge 211o of the groove opening 211 of the shoulder main groove 21 is set to be approximately the same as the wavelength λ2o_sh of the outer edge 212o of the groove bottom 212. Specifically, the wavelengths λ1o_sh and λ2o_sh of the groove opening 211 and groove bottom 212 are in the range of 0.90≦λ2o_sh/λ1o_sh≦1.10.

Similarly, in FIG. 4, the wavelength λ1i_sh of the inner edge 211i of the groove opening 211 of the shoulder main groove 21 is set to be approximately the same as the wavelength λ2i_sh of the inner edge 212i of the groove bottom 212. Specifically, the wavelengths λ1i_sh and λ2i_sh of the groove opening 211 and groove bottom 212 are in the range of 0.90≦λ2i_sh/λ1i_sh≦1.10.

In addition, the wavelength λ2_sh (λ2o_sh, λ2i_sh) of the groove bottom 212 of the shoulder main groove 21 has a relationship of 0.10≦λ2_sh/TW≦0.35 with respect to the tire contact width TW.

In addition, in FIG. 3, the maximum distance L1o_sh in the tire circumferential direction between the outer maximum amplitude position P1oo and the inner maximum amplitude position P1oi at the outer edge portion 211o of the groove opening 211 of the shoulder main groove 21 has a relationship of 0.50≦L1o_sh/λ1o_sh≦0.60 with respect to the wavelength λ1o_sh of the outer edge portion 211o, and preferably has a relationship of 0.50≦L1o_sh/λ1o_sh≦0.55. This makes the rigidity of the tread surface uniform in the tire circumferential direction when the tire is new.

The maximum circumferential distance between the outer maximum amplitude position and the inner maximum amplitude position is measured as the greater of the circumferential distances between adjacent outer maximum amplitude positions and the inner maximum amplitude position between these outer maximum amplitude positions.

The wavelength λ1o_sh of the outer edge portion 211o of the groove opening 211 of the shoulder main groove 21 is defined only when the shoulder main groove 21 has a zigzag or wavy shape, and is not defined when the shoulder main groove 21 has a straight shape.

Similarly, in FIG. 4, the maximum distance L1i_sh in the tire circumferential direction between the outer maximum amplitude position P1io and the inner maximum amplitude position P1ii at the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 satisfies the relationship 0.50≦L1i_sh/λ1i_sh≦0.60 with respect to the wavelength λ1i_sh of the inner edge portion 211i, and preferably satisfies the relationship 0.50≦L1i_sh/λ1i_sh≦0.55.

3, the maximum distance L2o_sh in the tire circumferential direction between the outer maximum amplitude position P2oo and the inner maximum amplitude position P2oi at the outer edge portion 212o of the groove bottom 212 of the shoulder main groove 21 has a relationship of 0.50≦L2o_sh/λ2o_sh≦0.60 with respect to the wavelength λ2o_sh of the outer edge portion 212o, and preferably has a relationship of 0.50≦L2o_sh/λ2o_sh≦0.55. Therefore, the outer maximum amplitude position P2oo and the inner maximum amplitude position P2oi at the groove bottom 212 of the shoulder main groove 21 are disposed at approximately equal intervals in the tire circumferential direction.

Similarly, in FIG. 4, the maximum distance L2i_sh in the tire circumferential direction between the outer maximum amplitude position P2io and the inner maximum amplitude position P2ii at the inner edge portion 212i of the groove bottom 212 of the shoulder main groove 21 has a relationship of 0.50≦L2i_sh/λ2i_sh≦0.60 with respect to the wavelength λ2i_sh of the inner edge portion 212i, and preferably has a relationship of 0.50≦L2i_sh/λ2i_sh≦0.55.

3, the amplitude A1o_sh of the outer edge 211o of the groove opening 211 of the shoulder main groove 21 has a relationship of 1.20≦A2o_sh/A1o_sh≦2.00 with respect to the amplitude A2o_sh of the outer edge 212o of the groove bottom 212, and more preferably has a relationship of 1.30≦A2o_sh/A1o_sh≦1.80. Therefore, the amplitude A2o_sh of the zigzag shape of the groove bottom 212 is set to be larger than the amplitude A1o_sh of the wavy shape of the groove opening 211.

Similarly, in FIG. 4, the amplitude A1i_sh of the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 has a relationship of 1.20≦A2i_sh/A1i_sh≦2.00 with respect to the amplitude A2i_sh of the inner edge portion 212i of the groove bottom 212, and more preferably has a relationship of 1.30≦A2i_sh/A1i_sh≦1.80.

In the above configuration, (1) the amplitudes A1o_sh and A1i_sh of the groove opening 211 of the shoulder main groove 21 are set small, so that uneven rail wear of the edge of the land portions 31 and 32, which is likely to occur at the maximum amplitude positions P1io and P1oi toward the shoulder main groove 21, is suppressed. Also, (2) the amplitudes A2o_sh and A2i_sh of the groove bottom 212 of the shoulder main groove 21 are set large, so that the rigidity of the land portions 31 and 32 is ensured, and the tear resistance performance of the tire is ensured. As a result, the uneven wear resistance performance and tear resistance performance of the tire are both achieved. Furthermore, (3) the groove opening 211 of the shoulder main groove 21 has a zigzag or wavy shape with an amplitude in the tire width direction, so that the edge components of the land portions 31 and 32 are increased, and the tire's acceleration performance on snow is improved.

3 and 4, the amplitude A1o_sh of the outer edge portion 211o of the groove opening 211 of the shoulder main groove 21 is set to be substantially the same as the amplitude A1i_sh of the inner edge portion 211i. Specifically, the amplitude A1o_sh of the outer edge portion 211o has a relationship of 0.90≦A1o_sh/A1i_sh≦1.10 with respect to the amplitude A1i_sh of the inner edge portion 211i, and more preferably has a relationship of 0.95≦A1o_sh/A1i_sh≦1.05.

The amplitudes A1o_sh and A1i_sh of the groove opening 211 of the shoulder main groove 21 are preferably in the range of 0 mm to 15.0 mm, and more preferably in the range of 2.0 mm to 10.0 mm. When the amplitudes A1o_sh and A1i_sh are 0 mm, the groove opening 211 of the shoulder main groove 21 has a straight shape.

The amplitudes A2o_sh and A2i_sh of the groove bottom 212 of the shoulder main groove 21 are preferably in the range of 2.5 mm to 15.0 mm, and more preferably in the range of 4.0 mm to 12.0 mm.

Also, as shown in FIG. 5, the groove wall angle α1oo at the outer maximum amplitude position P1oo of the outer edge portion 211o of the groove opening 211 of the shoulder main groove 21 has a relationship of α1oo<α1oi with respect to the groove wall angle α1oi at the inner maximum amplitude position P1oi of the outer edge portion 211o. Similarly, the groove wall angle α1io at the outer maximum amplitude position P1io of the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 has a relationship of α1ii<α1io with respect to the groove wall angle α1ii at the inner maximum amplitude position P1ii of the inner edge portion 211i. Therefore, at the position where the edge portion of the groove opening of the shoulder main groove 21 is convex toward the shoulder main groove 21 (the inner maximum amplitude position P1oi of the outer edge portion 211o and the outer maximum amplitude position P1io of the inner edge portion 211i. See FIG. 3), the groove wall angles α1oi, α1io of the shoulder main groove 21 are set large. This ensures the rigidity of the land portions 31 and 32 at the maximum amplitude positions P1oi and P1io.

Furthermore, as shown in FIG. 3, the entire groove bottom 212 of the shoulder main groove 21 is positioned inward in the tire width direction relative to the entire groove opening 211. Therefore, the average groove wall angle at the inner edge 211i of the shoulder main groove 21 is set to be larger than the average groove wall angle at the outer edge 211o. This ensures the rigidity of the narrow middle land portion 32 (see FIG. 2).

5, the maximum width Wg2_sh of the groove bottom 212 of the shoulder main groove 21 has a relationship of 0<Wg2_sh/Wg1_sh≦0.60 with respect to the maximum width Wg1_sh of the groove opening 211 (i.e., the maximum groove width of the shoulder main groove 21), and more preferably has a relationship of 0.35≦Wg2_sh/Wg1_sh≦0.45. When the groove bottom of the main groove has an arc shape or a funnel shape (not shown), the maximum width Wg2_sh of the groove bottom 212 is approximately 0.

In the configuration of FIG. 3, both the outer edge portion 211o and the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 have a wavy shape formed by connecting multiple arcs that are convex toward the inner side in the tire width direction (i.e., toward the tire equatorial plane CL; see FIG. 2). In addition, the circumferential length of the arcs (dimension symbols omitted in the figure) is 80% or more, and more preferably 85% or more, of the wavelength λ1o_sh of the outer edge portion 211o. In addition, adjacent arcs are connected via short straight lines or arcs. This configuration is preferable in that uneven wear at the maximum protruding position of the edge portion is suppressed compared to a configuration in which the edge portion has a zigzag or sinusoidal shape.

However, this is not limited thereto, and the groove opening 211 of the shoulder main groove 21 may have a straight or zigzag shape as described above, or may have a sinusoidal wave shape (not shown).

3, both the outer edge 212o and the inner edge 212i of the groove bottom 212 of the shoulder main groove 21 have a zigzag shape formed by connecting straight lines of approximately the same length in the tire circumferential direction. It is also preferable that the circumferential length of the straight line of the groove bottom 212 (approximately equal to the maximum distance L2o_sh in the tire circumferential direction of the maximum amplitude positions P2oo and P2oi of the outer edge 212o in FIG. 3; dimensional symbols omitted in the figure) is in the range of 40% to 60% of the wavelength λ2o_sh of the outer edge 212o.

However, this is not limited thereto, and the groove bottom 212 of the shoulder main groove 21 may have a wavy shape as described above (not shown).

[Center main groove wall structure]
FIG. 6 is an explanatory diagram showing the groove wall structures of the shoulder main groove 21 and the center main groove 22 shown in FIG.

As shown in Figures 2 and 6, the groove wall structure of the shoulder main groove 21 is slightly different from the groove wall structure of the center main groove 22. However, this is not limited to the above, and the center main groove 22 may have the same groove wall structure as the shoulder main groove 21. Here, the groove wall structure of the center main groove 22 will be described, focusing on the differences from the groove wall structure of the shoulder main groove 21, and a description of the commonalities will be omitted.

2, as shown in FIG. 6, the groove opening 221 of the center main groove 22 has a wavy shape with amplitude in the tire width direction at each of the outer edge portion 221o on the middle land portion 32 side and the inner edge portion 221i on the center land portion 33 side. Furthermore, the groove bottom 222 of the center main groove 22 has a wavy shape with amplitude in the tire width direction at each of the outer edge portion 222o on the middle land portion 32 side and the inner edge portion 222i on the center land portion 33 side.

Also, as shown in Fig. 6, the outer maximum amplitude position P1oo of the outer edge portion 221o of the groove opening 221 of the center main groove 22 is at the same position in the tire circumferential direction as the outer maximum amplitude position P2oo of the outer edge portion 222o of the groove bottom 222. Specifically, in Fig. 6, the offset amount φoo_ce of the outer maximum amplitude positions P1oo, P2oo at the outer edges 221o, 222o of the groove opening 221 and groove bottom 222 of the center main groove 22 has a relationship of 0 < φoo_ce/λ1o_ce < 0.10 with respect to the wavelength λ1o_ce of the outer edge portion 221o of the groove opening 221, and more preferably has a relationship of 0 < φoo_ce/λ1o_ce < 0.05.

6, the wavelength λ1o_ce of the outer edge 221o of the groove opening 221 of the center main groove 22 is set to be approximately equal to the wavelength λ2o_ce (not shown) of the outer edge 222o of the groove bottom 222. Specifically, the wavelengths λ1o_ce and λ2o_ce of the groove opening 221 and groove bottom 222 are in the range of 0.90≦λ2o_ce/λ1o_ce≦1.10.

The wavelength λ2_ce of the groove bottom 222 of the center main groove 22 (the wavelength λ2o_ce of the outer edge portion 222o and the wavelength λ2i_ce of the inner edge portion 222i; not shown) has a relationship of 0.10≦λ2_ce/TW≦0.35 with respect to the tire contact width TW.

In addition, in FIG. 6, the wavelength λ1_ce of the groove opening 221 of the center main groove 22 (the wavelength λ1o_ce of the outer edge portion 221o and the wavelength λ1i_ce of the inner edge portion 221i (not shown)) is set to be approximately the same as the wavelength λ1_sh of the groove opening 211 of the shoulder main groove 21 (the wavelength λ1o_sh of the outer edge portion 211o and the wavelength λ1i_sh of the inner edge portion 211i (see FIG. 4)), specifically, there is a relationship of 0.90≦λ1_ce/λ1_sh≦1.10.

6, the amplitude A1o_ce of the outer edge 221o of the groove opening 221 of the center main groove 22 has a relationship of 1.05≦A2o_ce/A1o_ce≦1.50 with respect to the amplitude A2o_ce of the outer edge 222o of the groove bottom 222, and more preferably has a relationship of 1.10≦A2o_ce/A1o_ce≦1.20. Therefore, the amplitude A2o_ce of the wavy shape of the groove bottom 222 is set to be larger than the amplitude A1o_ce of the wavy shape of the groove opening 221.

The amplitudes A1o_ce and A1i_ce (not shown) of the groove opening 221 of the center main groove 22 are preferably in the range of 0 mm to 10.0 mm, and more preferably in the range of 2.0 mm to 6.0 mm. When the amplitudes A1o_ce and A1i_ce are 0 mm, the groove opening 221 of the center main groove 22 has a straight shape.

In addition, the amplitudes A2o_ce and A2i_ce of the groove bottom 222 of the center main groove 22 are preferably in the range of 1.5 mm to 13.5 mm, and more preferably in the range of 2.2 mm to 9.0 mm.

6, the amplitude A1_ce (A1o_ce, A1i_ce) of the left and right edge portions 221o, 221i of the groove opening 221 of the center main groove 22 is set to be smaller than the amplitude A1_sh (A1o_sh, A1i_sh) of the left and right edge portions 211o, 211i of the groove opening 211 of the shoulder main groove 21. Specifically, the amplitude A1_ce of the left and right edge portions 221o, 221i of the groove opening 221 of the center main groove 22 has a relationship of A1_ce/A1_sh≦0.95 with respect to the amplitude A1_sh of the left and right edge portions 211o, 211i of the groove opening 211 of the shoulder main groove 21, and more preferably has a relationship of A1_ce/A1_sh≦0.90. There is no particular lower limit for the ratio A1_sh/A1_ce, but it is subject to other conditions.

6, the amplitude A2_ce (A2o_ce, A2i_ce) of the left and right edge portions 222o, 222i of the groove bottom 222 of the center main groove 22 is set to be smaller than the amplitude A2_sh (A2o_sh, A2i_sh) of the left and right edge portions 212o, 212i of the groove bottom 212 of the shoulder main groove 21. Specifically, the amplitude A2_ce of the left and right edge portions 222o, 222i of the groove bottom 222 of the center main groove 22 has a relationship of A2_ce/A2_sh≦0.95 with respect to the amplitude A2_sh of the left and right edge portions 212o, 212i of the groove bottom 212 of the shoulder main groove 21, and more preferably has a relationship of A2_ce/A2_sh≦0.75. There is no particular lower limit for the ratio A2_ce/A2_sh, but it is subject to other conditions.

Furthermore, it is preferable that the maximum width Wg2_ce (dimension symbol omitted in the figure) of the groove bottom 222 of the center main groove 22 has a relationship of 0<Wg2_ce/Wg1_ce≦0.80 with respect to the maximum width Wg1_ce of the groove opening 221 (i.e., the maximum groove width of the center main groove 22; dimension symbol omitted in the figure), and that the relationship is 0.40≦Wg2_ce/Wg1_ce≦0.60. When the groove bottom of the main groove has an arc shape or a funnel shape (not shown), the maximum width Wg2_ce of the groove bottom 222 is approximately 0.

In the configuration of FIG. 6, both the outer edge portion 221o and the inner edge portion 221i of the groove opening 221 of the center main groove 22 have a wavy shape formed by connecting multiple arcs that are convex toward the inside in the tire width direction (i.e., toward the tire equatorial plane CL; see FIG. 2). In addition, the circumferential length of the arcs (dimension symbols omitted in the figure) is 80% or more, and more preferably 85% or more, of the wavelength λ1o_ce of the outer edge portion 221o. In addition, adjacent arcs are connected via short straight lines or arcs.

However, this is not limited thereto, and the groove opening 221 of the center main groove 22 may have a straight or zigzag shape as described above, or may have a sinusoidal wave shape (not shown).

[Shoulder land area]
2, as described above, the shoulder land portion 31 is a rib having a circumferentially continuous tread surface and is not divided in the tire circumferential direction by lug grooves or sipes. Also, as described above, the edge portion of the shoulder land portion 31 on the shoulder main groove 21 side has a wavy shape formed by connecting multiple circular arcs that are convex toward the tire equatorial plane CL.

As shown in FIG. 2, the shoulder land portion 31 has a plurality of narrow shallow grooves 311.

The narrow shallow groove 311 has a U-shape with its opening facing the tire ground contact end T. That is, the U-shape of the narrow shallow groove 311 extends from its apex in two directions outward in the tire width direction and terminates. The narrow shallow groove 311 also has a closed structure that terminates within the ground contact surface of the shoulder land portion 31. For this reason, the narrow shallow groove 311 is not connected to the tire ground contact end T and the shoulder main groove 21, and is positioned away from the edge of the tread surface of the shoulder land portion 31. Furthermore, multiple narrow shallow grooves 311 are arranged at predetermined intervals in the tire circumferential direction.

The edge of the shoulder land portion 31 on the shoulder main groove 21 side may have multiple fine multi-sipes (reference numbers omitted in the figure). These multi-sipes have a width of less than 1.0 mm and an extension length of less than 5.0 mm. These multi-sipes suppress uneven wear of the edge of the shoulder land portion 31.

[Middle and center land sections]
In the configuration of FIG. 2, the middle land portion 32 and the center land portion 33 each include a plurality of through lug grooves 321 and 331 and a plurality of blocks 322 and 332, respectively.

The edge portions of the middle land portion 32 and the center land portion 33 have a wavy shape formed by connecting multiple arcs as described above. The left and right edge portions of the middle land portion 32 also have a wavy shape formed by connecting multiple arcs that are convex toward the tire equatorial plane CL. On the other hand, the center land portion 33 is disposed on the tire equatorial plane CL, and the left and right edge portions of the center land portion 33 have a wavy shape formed by connecting multiple arcs that are convex toward the tire equatorial plane CL, i.e., the widthwise inner side of the center land portion 33. Therefore, the edge portions of the land portions 31 to 33 of the entire tread have a wavy shape formed by connecting multiple arcs that are convex toward the tire equatorial plane CL.

2 and 6, the through lug grooves 321, 331 of the middle land portion 32 and the center land portion 33 open at the maximum amplitude position of the edge portions of the land portions 32, 33. The pitch number of the through lug grooves 321, 331 is set to twice the pitch number of the wavy shapes of the edge portions of the land portions 32, 33. The pitch number of the through lug grooves 321, 331 around the entire circumference of the tire is in the range of 110 to 200. The wavy shapes of the left and right edge portions of the middle land portion 32 and the center land portion 33 are arranged with a phase shift in the tire circumferential direction, so that the through lug grooves 321, 331 extend at an angle with respect to the tire width direction.

As shown in FIG. 6, the through lug grooves 321, 331 have short straight portions parallel to the tire width direction at the opening ends relative to the main grooves 21, 22. It is preferable that the extension length L21 of these straight portions is in the range of 5% to 25% of the ground contact widths Wb2, Wb3 (see FIG. 2) of the land portions 31, 32.

The through lug grooves 321 (331) of the middle land portion 32 (and the center land portion 33) are thin and shallow grooves, and have a maximum groove width W21 (see FIG. 3) of 1.5 mm to 4.0 mm and a maximum groove depth H21 (see FIG. 5) of 1.0 mm to 6.0 mm. In FIG. 5, the maximum groove depth H21 of the through lug grooves 321 (331) has a relationship of 0.05≦H21/Hg1≦0.65 with respect to the maximum groove depth Hg1 of the shoulder main groove 21, and more preferably has a relationship of 0.10≦H21/Hg1≦0.30.

The blocks 322; 332 are divided into a plurality of through lug grooves 321; 331. The blocks 322, 332 have a long shape in the tire width direction. Specifically, the pitch length of the blocks 322; 332 (for the blocks 322 of the middle land portion 32, it is equal to the maximum distance L1i_sh in the tire circumferential direction between the outer maximum amplitude position P1io and the inner maximum amplitude position P1ii at the inner edge portion 211i of the groove opening 211 of the shoulder main groove 21 in FIG. 4. For the blocks 332 of the center land portion 33, the dimensional symbols in the figure are omitted.) is in the range of 40% to 70% of the maximum ground contact width Wb2; Wb3 of the land portions 32; 33, and preferably in the range of 50% to 60%.

In addition, the snow traction index STI (so-called 0 [deg] snow traction index) in the circumferential direction around the entire circumference of the tire is in the range of 130≦STI.

The Snow Traction Index STI is an empirical formula proposed by Uniroyal at the SAE (Society of Automotive Engineers) and is defined by the following formula (1). In this formula, Pg is the groove density [1/mm] and is calculated as the ratio of the groove length [mm] of all grooves (all grooves excluding sipes) projected in the tire circumferential direction on the tire contact surface to the tire contact area (the product of the tire contact width and tire circumference) [mm^2]. Also, ρs is the sipe density [1/mm] and is calculated as the ratio of the sipe length [mm] of all sipes projected in the tire circumferential direction on the tire contact surface to the tire contact area [mm^2]. Also, Dg is the average groove depth [mm] of all grooves projected in the tire circumferential direction on the tire contact surface.

STI = -6.8 + 2202 x Pg + 672 x ρs + 7.6 x Dg ... (1)

[effect]
As described above, the tire 1 includes a pair of shoulder main grooves 21 and one or more center main grooves 22 extending in the tire circumferential direction, and four or more rows of land portions 31 to 33 defined by the shoulder main groove 21 and the center main groove 22 (see FIG. 2). The groove opening 211 of the shoulder main groove 21 has a straight shape or a zigzag or wavy shape having an amplitude in the tire width direction (see FIG. 3). The groove bottom 212 of the shoulder main groove 21 has a zigzag or wavy shape having an amplitude in the tire width direction. The amplitude A1_sh (A1o_sh, A1i_sh) of the groove opening 211 of the shoulder main groove 21 has a relationship of A1_sh<A2_sh with respect to the amplitude A2_sh (A2o_sh, A2i_sh) of the groove bottom 212.

In this configuration, (1) the amplitude A1_sh of the groove opening 211 of the shoulder main groove 21 is set small, so that uneven rail wear of the edge of the land portions 31, 32, which is likely to occur at the maximum amplitude positions P1io, P1oi toward the shoulder main groove 21, is suppressed. In addition, (2) the amplitude A2_sh of the groove bottom 212 of the shoulder main groove 21 is set large, so that the rigidity of the land portions 31, 32 is ensured, and the tear resistance performance of the tire is ensured. Furthermore, (3) the groove opening 211 of the shoulder main groove 21 has a zigzag or wavy shape with an amplitude in the tire width direction, so that the edge components of the land portions 31, 32 are increased, and the acceleration performance on snow of the tire is improved. This has the advantage of achieving both the acceleration performance on snow, uneven wear resistance, and tear resistance of the tire.

In addition, in this tire 1, the amplitude A1_sh (A1o_sh, A1i_sh) of the groove opening 211 of the shoulder main groove 21 has a relationship of 1.20≦A2_sh/A1_sh with respect to the amplitude A2_sh (A2o_sh, A2i_sh) of the groove bottom 212 (see FIG. 3). This has the advantage of ensuring appropriate rigidity of the land portions 31, 32.

In addition, in this tire 1, the wavelength λ2_sh (λ2o_sh, λ2i_sh; see FIG. 3) of the groove bottom 212 of the shoulder main groove 21 has a relationship of 0.10≦λ2_sh/TW≦0.35 with respect to the tire contact width TW (see FIG. 2). This has the advantage of optimizing the amplitude A2_sh of the groove bottom 212.

In addition, in this tire 1, the outer maximum amplitude positions P1oo, P1io of the groove opening 211 of the shoulder main groove 21 are at the same positions in the tire circumferential direction as the outer maximum amplitude positions P2oo, P2io of the groove bottom 212 (see FIG. 3). This has the advantage of increasing the reinforcing effect of the rib and improving the rib tear resistance of the tire.

In addition, in this tire 1, the groove opening 221 of the center main groove 22 has a straight shape or a zigzag or wavy shape with amplitude in the tire width direction, and the groove bottom 222 of the center main groove 22 has a zigzag or wavy shape with amplitude in the tire width direction. This has the advantage of improving the tire's acceleration performance on snow.

In addition, in this tire 1, the amplitude A1_ce (A1o_ce, A1i_ce) of the groove opening 221 of the center main groove 22 has a relationship of 1.05≦A2_ce/A1_ce with respect to the amplitude A2_ce (A2o_ce, A2i_ce) of the groove bottom 222 (see FIG. 6). This has the advantage of improving the uneven wear resistance and tear resistance of the tire.

In addition, in this tire 1, the amplitude A1_ce (A1o_ce, A1i_ce) of the groove opening 221 of the center main groove 22 has a relationship A1_ce/A1_sh≦0.95 with respect to the amplitude A1_sh (A1o_sh, A1i_sh) of the groove opening 211 of the shoulder main groove 21 (see FIG. 6). With this configuration, the shoulder land portion 31 is reinforced, which has the advantage of improving the rib tear resistance of the tire.

In addition, in this tire 1, the amplitude A2_ce (A2o_ce, A2i_ce) of the groove bottom 222 of the center main groove 22 has a relationship of A2_ce/A2_sh≦0.75 with respect to the amplitude A2_sh (A2o_sh, A2i_sh) of the groove bottom 212 of the shoulder main groove 21 (see FIG. 6). In this configuration, (1) the amplitude A2_sh of the groove bottom 212 of the shoulder main groove 21, where tears are likely to occur, is set large, which has the advantage of efficiently improving tear resistance by increasing the amplitude A2_sh of the groove bottom 212. In addition, (2) the amplitude A2_ce of the groove bottom 222 of the center main groove 22 is set small, which has the advantage of ensuring groove volume and improving wet performance of the tire.

In addition, in this tire 1, the wavelength λ1_ce (λ1o_ce, λ1i_ce) of the groove opening 221 of the center main groove 22 has a relationship of 0.90≦λ1_ce/λ1_sh≦1.10 with respect to the wavelength λ1_sh (λ1o_sh, λ1i_sh) of the groove opening 211 of the shoulder main groove 21. This has the advantage of reducing the ground contact pressure at the edge of the shoulder land portion 31 and improving the tire's resistance to uneven wear.

In addition, in this tire 1, the groove opening 211 of the shoulder main groove 21 has a wavy shape formed by connecting multiple arcs that are convex toward the tire equatorial plane CL (see Figure 3). This configuration has the advantage of suppressing uneven wear at the maximum amplitude position compared to an edge portion having a zigzag shape.

In addition, in this tire 1, the circumferential length of the arc (dimension symbols omitted in the figure) is 80% or more of the wavelength λ1_sh (λ1o_sh, λ1i_sh) of the wavy shape of the groove opening 211. This has the advantage of effectively suppressing uneven wear at the maximum amplitude position.

[Applies to]
The tire 1 is a heavy-duty tire that is mounted on the steering axle of a vehicle. By applying the present invention to such a tire, there is an advantage that the uneven wear resistance and tear resistance of the tire can be effectively improved, and also, there is an advantage that the requirement for acceleration performance on snow in an all-season tire can be satisfied.

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 a person skilled in the art. Examples of other tires include airless tires and solid tires.

Figure 7 is a chart showing the results of a performance test of a tire according to an embodiment of the present invention.

In this performance test, several types of test tires were evaluated for (1) acceleration performance on snow, (2) uneven wear resistance, and (3) tear resistance. A test tire with a tire size of 315/70R22.5 was mounted on a rim with a rim size of 22.5 x 9.00", and an internal pressure of 900 kPa and the specified load of JATMA were applied to the test tire. The test tire was also mounted on the steering axle of a 4 x 2 tractor.

(1) Evaluation of acceleration performance on snow is performed under test conditions that comply with ECE (Economic Commission for Europe) R117-2 (Regulation No. 117 Revision 2), by measuring the distance required for acceleration from a specified initial velocity to a terminal velocity. The higher the value, the better.

(2) In the evaluation of resistance to uneven wear, the test vehicle is driven 40,000 km on a paved road, after which the degree of rail wear in the main groove is observed and an index evaluation is performed with the conventional example set as the standard (100). The higher the value, the better.

(3) In the evaluation of tear resistance, the test vehicle runs over a 200 mm high curb 20 times while making a turn, and then the occurrence of tears in the shoulder land area is observed. Then, based on the observation results, an index evaluation is performed with the conventional example set as the standard (100). The higher the value, the more preferable it is.

The test tire of the embodiment has the configuration shown in Fig. 1 and Fig. 2. The groove depth of the shoulder main groove 21 and the center main groove 22 is 14.6 mm, and the groove width is 15.3 mm. The through lug grooves 321 and 331 have a maximum groove width W21 of 2.1 mm and a maximum groove depth H21 of 2.5 mm. The tire ground contact width TW is 268 mm, the maximum ground contact width Wb1 of the shoulder land portion 31 is 49.5 mm, the maximum ground contact width Wb2 of the middle land portion 32 is 36.0 mm, and the maximum ground contact width Wb3 of the center land portion 33 is 36.0 mm.

In the test tire of Conventional Example 1, the groove openings 211, 221 and the edges of the groove bottoms 212, 222 of the main grooves 21, 22 have straight shapes in the test tire of Example 1. In the test tire of Conventional Example 2, the amplitude ratios A2o_sh/A1o_sh and A2i_sh/A1i_sh of the groove openings 211, 221 and the groove bottoms 212, 222 of the main grooves 21, 22 are constant in the test tire of Example 1.

As the test results show, the test tires of the embodiment exhibit a balance between snow acceleration performance, uneven wear resistance, and tear resistance.

1 Tire; 11 Bead core; 12 Bead filler; 13 Carcass layer; 14 Belt layer; 141-144 Belt ply; 15 Tread rubber; 16 Sidewall rubber; 17 Rim cushion rubber; 21 Shoulder main groove; 211 Groove opening; 211o, 211i Edge portion; 212 Groove bottom portion; 212o, 212i Edge portion; 22 Center main groove; 221 Groove opening portion; 221o, 221i Edge portion; 222 Groove bottom portion; 222o, 222i Edge portion; 31 Shoulder land portion; 311 Closed sipe; 32 Middle land portion; 321 Through lug groove; 322 Block; 33 Center land portion; 331 Through lug groove; 332 Block

Claims (11)

A tire having a pair of shoulder main grooves and one or more center main grooves extending in a tire circumferential direction, and four or more rows of land portions defined by the shoulder main grooves and the center main groove,
The groove opening of the shoulder main groove has a straight shape, a zigzag shape having amplitude in the tire width direction, or a wavy shape,
The groove bottom of the shoulder main groove has a zigzag or wavy shape having amplitude in the tire width direction,
The groove opening amplitude A1_sh of the shoulder main groove has a relationship of A1_sh<A2_sh with respect to the groove bottom amplitude A2_sh, and
a groove opening of the shoulder main groove having a wavy shape formed by connecting a plurality of circular arcs that are convex toward the tire equatorial plane side . The tire according to claim 1, wherein the amplitude A1_sh of the groove opening of the shoulder main groove has a relationship of 1.20≦A2_sh/A1_sh with respect to the amplitude A2_sh of the groove bottom. The tire according to claim 1 or 2, wherein the wavelength λ2_sh of the groove bottom of the shoulder main groove has a relationship of 0.10≦λ2_sh/TW≦0.35 with respect to the tire contact width TW. A tire according to any one of claims 1 to 3, wherein the outer maximum amplitude position of the groove opening of the shoulder main groove is at the same position in the tire circumferential direction as the outer maximum amplitude position of the groove bottom. a groove opening of the center main groove has a straight shape, a zigzag shape having amplitude in the tire width direction, or a wavy shape,
5. The tire according to claim 1, wherein the center main groove has a bottom portion that has a zigzag shape or a wavy shape having amplitude in the tire width direction. The tire according to claim 5, wherein the amplitude A1_ce of the groove opening of the center main groove has a relationship of 1.05≦A2_ce/A1_ce with respect to the amplitude A2_ce of the groove bottom. The tire according to claim 5 or 6, wherein the amplitude A1_ce of the groove opening of the center main groove has a relationship with the amplitude A1_sh of the groove opening of the shoulder main groove such that A1_ce/A1_sh≦0.95. The tire according to any one of claims 5 to 7, wherein the amplitude A2_ce of the groove bottom of the center main groove has a relationship with the amplitude A2_sh of the groove bottom of the shoulder main groove such that A2_ce/A2_sh≦0.90. A tire according to any one of claims 5 to 8, wherein the wavelength λ1_ce of the groove opening of the center main groove has a relationship of 0.90≦λ1_ce/λ1_sh≦1.10 with respect to the wavelength λ1_sh of the groove opening of the shoulder main groove. The tire according to any one of claims 1 to 9 , which is a heavy-duty tire mounted on a steering axle of a vehicle. A tire having a pair of shoulder main grooves and one or more center main grooves extending in a tire circumferential direction, and four or more rows of land portions defined by the shoulder main grooves and the center main groove,
The groove opening of the shoulder main groove has a straight shape, a zigzag shape having amplitude in the tire width direction, or a wavy shape,
The groove bottom of the shoulder main groove has a zigzag or wavy shape having amplitude in the tire width direction,
an amplitude A1_sh of the groove opening of the shoulder main groove and an amplitude A2_sh of the groove bottom have a relationship of A1_sh<A2_sh,
The groove opening of the center main groove has a straight shape, or a zigzag shape or a wavy shape having amplitude in the tire width direction, and the groove bottom of the center main groove has a zigzag shape or a wavy shape having amplitude in the tire width direction, and
A tire characterized in that an amplitude A1_ce of the groove opening of the center main groove and an amplitude A1_sh of the groove opening of the shoulder main groove have a relationship of A1_ce/A1_sh≦0.95 .

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