JP7534592B2 - tire - Google Patents

Description

The present invention relates to a tire, and more particularly to a tire that can improve tire noise performance while maintaining the tire's acceleration performance on snow during vehicle travel.

Conventional heavy-duty tires are designed to have a shoulder land portion with sipes in order 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, there is a demand for heavy-duty tires that are mounted on the steering axle of vehicles to improve acceleration performance on snow and noise performance while the vehicle is traveling.

Therefore, the present invention has been made in consideration of the above, and has an object to provide a tire that can improve the tire noise performance while maintaining the tire's acceleration performance on snow when the vehicle is traveling.

In order to achieve the above-mentioned object, the tire of the present invention is a tire having a plurality of main grooves extending in the tire circumferential direction and a plurality of land portions defined by the main grooves, wherein at least one row of the land portions has a U-shape with an opening facing the tire ground contact edge and has a plurality of narrow shallow grooves terminating within the ground contact surface of the land portions, and the widthwise length W11 of the narrow shallow grooves satisfies the relationship of 0.40≦W11/Wb1≦0.90 with respect to the maximum ground contact width Wb1 of the land portions .
The tire according to the present invention is characterized in that it has a plurality of main grooves extending circumferentially of the tire and a plurality of land portions defined by the main grooves, and at least one row of the land portions has a U-shape with an opening facing the tire ground contact edge and has a plurality of narrow shallow grooves terminating within the ground contact surface of the land portions, and the circumferential length L11 of the narrow shallow grooves has a relationship of 0.50≦L11/P11≦0.90 with respect to the pitch length P11 of the narrow shallow grooves.
The tire according to the present invention is characterized in that it has a plurality of main grooves extending in the tire circumferential direction and a plurality of land portions defined by the main grooves, and at least one row of the land portions has a U-shape with an opening facing the tire ground contact edge and has a plurality of narrow shallow grooves terminating within the ground contact surface of the land portions, and the distance D1 between a pair of terminal points of the narrow shallow grooves in the tire circumferential direction satisfies the relationship 0.30≦D1/P11≦0.70 with respect to the pitch length P11 of the narrow shallow groove.
In addition, the tire according to the present invention is a tire having a plurality of main grooves extending in the tire circumferential direction and a plurality of land portions defined by the main grooves, wherein at least one row of the land portions has a U-shape with an opening facing the tire ground contact edge and has a plurality of narrow shallow grooves terminating within the ground contact surface of the land portions, the U-shape of the narrow shallow groove has at least one widthwise extending portion having an inclination angle of 75 degrees or more and 105 degrees or less with respect to the tire circumferential direction, and the sum ΣLa of the widthwise extending portions has a relationship of 1.00≦ΣLa/W11 with respect to the widthwise length W11 of the narrow shallow groove.

In the tire according to the present invention, (1) the narrow shallow groove has a U-shape, and therefore, compared to a configuration having multiple I-shaped widthwise narrow grooves arranged in the tire circumferential direction, the circumferential component of the narrow shallow groove improves the tire's acceleration performance on snow when the vehicle is traveling. Also, (2) the narrow shallow groove has a U-shape with the opening facing the tire ground edge, and therefore, compared to a configuration having narrow shallow grooves with a ring-shaped structure, for example, the circumferential component of the narrow shallow groove in the tire ground edge region can be omitted. This has the advantage of improving the tire's noise performance when the vehicle is traveling. Also, (3) the narrow shallow groove has a closed structure that terminates within the ground contact surface of the land portion, and therefore, compared to a configuration having narrow shallow grooves that penetrate the ground contact surface of the land portion in the tire width direction or tire circumferential direction, the tire's noise performance is improved.

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 view showing a shoulder land portion of the tire shown in FIG. FIG. 4 is an enlarged view showing the narrow shallow grooves in the shoulder land portion shown in FIG. FIG. 5 is a cross-sectional view of the shoulder land portion shown in FIG. FIG. 6 is an enlarged plan view showing the groove wall structure of the shoulder main groove shown in FIG. FIG. 7 is an enlarged plan view showing the groove wall structure of the shoulder main groove shown in FIG. FIG. 8 is a cross-sectional view in the groove depth direction of the shoulder main groove shown in FIG. FIG. 9 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 10 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 11 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 12 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 13 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 14 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 15 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 16 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 17 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 18 is an explanatory diagram showing a modification of the narrow shallow groove shown in FIG. FIG. 19 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. FIG. 20 is an explanatory diagram showing a shoulder land portion of the conventional test tire shown in FIG.

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 land area]
Fig. 3 is an enlarged view showing the shoulder land portion 31 of the tire 1 shown in Fig. 2. Fig. 4 is an enlarged view showing the narrow shallow groove 311 of the shoulder land portion 31 shown in Fig. 3. This figure shows an extracted narrow shallow groove 311 as a single unit. Fig. 5 is a cross-sectional view of the shoulder land portion 31 shown in Fig. 3. This figure shows a cross-sectional view of the shoulder land portion 31 cut along the narrow shallow groove 311.

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

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 (or a V-shape or a C-shape) with an opening facing the tire ground contact end T. In other words, the narrow shallow groove 311 has a closed portion on the tire equatorial plane CL side and a continuous one-sided opening shape with an opening on the tire ground contact end T side. 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 arranged away from the edge portion of the tread surface of the shoulder land portion 31. The multiple narrow shallow grooves 311 are also arranged at a predetermined interval in the tire circumferential direction. Adjacent narrow shallow grooves 311 are also arranged away from each other.

The maximum groove width Wn (see FIG. 4) of the narrow shallow groove 311 is preferably in the range of 0.1 mm≦Wn≦5.0 mm, and more preferably in the range of 0.3 mm≦Wn≦2.0 mm. The maximum groove depth Hn (see FIG. 5) of the narrow shallow groove 311 is preferably in the range of 0.01≦Hn/Hg≦0.30, and more preferably in the range of 0.03≦Hn/Hg≦0.25, relative to the maximum groove depth Hg of the shoulder main groove 21. The narrow shallow groove 311 has the above-mentioned maximum groove width Wn and maximum groove depth Hn, and thus functions as a groove without being blocked when the tire comes into contact with the ground.

In the above configuration, (1) the narrow shallow groove 311 has a U-shape, and therefore the circumferential component of the narrow shallow groove 311 improves the tire's acceleration performance on snow during vehicle travel, compared to a configuration (not shown) with multiple I-shaped widthwise narrow grooves arranged in the tire circumferential direction. Also, (2) the narrow shallow groove 311 has a U-shape with an opening facing the tire ground edge T, and therefore the circumferential component of the narrow shallow groove in the region on the tire ground edge T side can be omitted, compared to a configuration (not shown) with a narrow shallow groove having a ring-shaped structure, for example. This improves the tire's noise performance during vehicle travel, and also suppresses uneven wear starting from the narrow shallow groove 311. Also, (3) the narrow shallow groove 311 has a closed structure that terminates within the ground contact surface of the land portion 31, and therefore the tire's noise performance is improved, compared to a configuration (not shown) with a narrow shallow groove that penetrates the ground contact surface of the land portion in the tire width direction or tire circumferential direction.

In addition, in FIG. 3, the widthwise length W11 of the narrow shallow groove 311 has a relationship of 0.40≦W11/Wb1≦0.90 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31, and preferably has a relationship of 0.50≦W11/Wb1≦0.80.

The widthwise length W11 of the narrow shallow groove 311 is measured as the maximum extension length of the narrow shallow groove 311 in the tire width direction when the tire is mounted on a specified rim, the specified internal pressure is applied, and the tire is in an unloaded state.

In addition, in FIG. 3, the circumferential length L11 of the narrow shallow groove 311 has a relationship of 0.50≦L11/P11≦0.90 with respect to the pitch length P11 of the narrow shallow groove 311, and preferably has a relationship of 0.60≦L11/P11≦0.80.

The circumferential length L11 of the narrow shallow groove 311 is measured as the maximum circumferential extension of the narrow shallow groove 311 when the tire is mounted on a specified rim, the specified internal pressure is applied, and the tire is in an unloaded state.

The pitch number Pn of the narrow shallow grooves 311 is the same as the pitch number of the wavy shape of the edge portion of the shoulder land portion 31, and is in the range of 50 to 100. It is also preferable that the distance (not shown) between adjacent narrow shallow grooves 311, 311 is kept in the range of 10 mm or more.

In addition, in FIG. 3, the distance D1 between the end points A1 and A2 of the narrow shallow groove 311 in the tire circumferential direction has a relationship of 0.30≦D1/P11≦0.70 with respect to the pitch length P11 of the narrow shallow groove 311, and preferably has a relationship of 0.40≦D1/P11≦0.60.

In addition, in FIG. 3, the distance D2 (see FIG. 4) between the end points A1, A2 of the narrow shallow groove 311 in the tire width direction has a relationship of 0≦D2/Wb1≦0.70 with respect to the maximum contact width Wb1 of the shoulder land portion 31, and preferably has a relationship of 0≦D2/Wb1≦0.50.

In addition, in FIG. 3, the distance D3 between the narrow shallow groove 311 and the tire ground edge T has a relationship of 0.05≦D3/Wb1 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31, and preferably has a relationship of 0.10≦D3/Wb1. Similarly, the distance D4 between the narrow shallow groove 311 and the edge portion of the shoulder land portion 31 has a relationship of 0.10≦D4/Wb1 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31, and preferably has a relationship of 0.15≦D4/Wb1. This ensures the rigidity of the edge portion of the shoulder land portion 31. Note that there is no particular limit to the upper limits of the distances D3 and D4, but they are restricted by the relationship with the ratio W11/Wb1 of the width direction length W11 of the narrow shallow groove 311 described above. In addition, in the configuration of FIG. 3, the measurement point of the distance D3 is the terminal point A1, but depending on the shape of the narrow shallow groove 311, the other terminal point A2 may be the measurement point of the distance D3.

In addition, in FIG. 3, the widthwise length W11 and the circumferential length L11 of the narrow shallow groove 311 have a relationship of 0.60≦W11/L11≦1.40, and preferably have a relationship of 0.80≦W11/L11≦1.20.

In addition, in FIG. 3, in a configuration in which the shoulder land portion 31 has a zigzag-shaped or wavy-shaped edge portion having amplitude in the tire width direction as described above, the tire circumferential distance D5 between the innermost point B of the narrow shallow groove 311 in the tire width direction and the maximum amplitude position P1oo of the edge portion of the shoulder land portion 31 toward the outside in the tire width direction is preferably in the range of 0.30≦D5/λ1o_sh≦0.70 with respect to the wavelength λ1o_sh of the edge portion, and in the range of 0.45≦D5/λ1o_sh≦0.65. Therefore, the innermost point B of the narrow shallow groove 311 is disposed away from the maximum amplitude position P1oo of the edge portion of the shoulder land portion 31 toward the outside in the tire width direction. This ensures the rigidity of the edge portion of the shoulder land portion 31.

As shown in FIG. 4, a pair of end points A1, A2 and an innermost point B in the tire width direction of the narrow shallow groove 311 are defined. A virtual line L1 passing through a midpoint M of the end points A1, A2 and the innermost point B is defined. At this time, it is preferable that the angle θ11 between the virtual line L1 and the tire circumferential direction is in the range of 45 [deg]≦θ11≦135 [deg], and in the range of 50 [deg]≦θ11≦70 [deg]. This optimizes the opening direction of the U-shape of the narrow shallow groove 311.

In the configuration of FIG. 4, the U-shape of the narrow shallow groove 311 has continuous widthwise extending portions Ra1 and Ra2 with an inclination angle of 75 degrees or more and 105 degrees or less with respect to the tire circumferential direction. The sum ΣLa of the widthwise extending portions Ra1 and Ra2's widthwise lengths La1 to La4 (dimension symbols omitted in the figure) preferably has a relationship of 1.00≦ΣLa/W11 and 1.30≦ΣLa/W11 with respect to the widthwise length W11 of the narrow shallow groove 311. It is also preferable that each of the widthwise extending portions Ra1 and Ra2's widthwise lengths La1 to La4 is in a range of 25% or more with respect to the widthwise length W11 of the narrow shallow groove 311. This ensures the widthwise extending portions Ra1 and Ra2's widthwise lengths La1 to La4. The upper limit of the above ratio is not particularly limited, but is subject to other conditions.

The inclination angle of the U-shape of the narrow shallow groove 311 is measured as the angle between the tangent to the groove centerline of the narrow shallow groove and the tire circumferential direction.

In the configuration of FIG. 4, the U-shape of the narrow shallow groove 311 has a continuous circumferentially extending portion Rb with an inclination angle of 0 degrees or more and 15 degrees or less with respect to the tire circumferential direction. The circumferential length Lb1 (dimension symbols omitted in the figure) of the circumferentially extending portion Rb has a relationship of 0.50≦Lb/L11 with respect to the circumferential length L11 of the narrow shallow groove 311, and preferably has a relationship of 0.70≦Lb/L11. This ensures the circumferential length Lb1 of the circumferentially extending portion Rb. Note that there is no particular limit to the upper limit of the above ratio, but it is subject to other conditions.

As shown in FIG. 4, it is preferable that the U-shape of the narrow shallow groove 311 has a bent portion (reference numerals omitted in the figure) that is arranged in at least one of the areas between points A1 and B and between points A2 and B and connects adjacent widthwise extending portions Ra1, Ra1; Ra2, Ra2. This bent portion has a crank or S-shape. It is also preferable that the distance D6 from the tire ground contact end T to the center point C of the bent portion has a relationship of 0.30≦D6/Wb1≦0.70 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31, and more preferably has a relationship of 0.40≦D6/Wb1≦0.60. Therefore, the bent portion of the narrow shallow groove 311 is arranged in the widthwise center of the shoulder land portion 31.

For example, in the configuration of FIG. 4, a pair of end points A1, A2 of the narrow shallow groove 311 are arranged at approximately the same position in the tire width direction. The narrow shallow groove 311 also has a single innermost point B. The narrow shallow groove 311 also has a pair of widthwise extending portions Ra1, Ra1; Ra2, Ra2 extending approximately parallel to the tire width direction between points A1, B and points A2, B', respectively. The two sets of widthwise extending portions Ra1, Ra1; Ra2, Ra2 are connected to each other via S-shaped bends. This forms a groove portion extending in a step-like manner in the tire width direction. The bends are inclined or bent in the same direction with respect to the tire circumferential direction. The narrow shallow groove 311 also has a single circumferential extending portion Rb extending approximately parallel to the tire circumferential direction from the innermost point B. The circumferential extension portion Rb has a straight line or a gentle arc shape that is convex toward the tire equatorial plane CL, and is connected to the widthwise extension portions Ra1 and Ra2 in a substantially L-shaped manner at the innermost point B and the other end point B'. The pair of end points A1 and A2 and both end points B and B' of the circumferential extension portion Rb are offset from each other in the tire circumferential direction.

In the configuration of FIG. 4, the U-shape of the narrow shallow groove 311 is made of a single line without a branch. However, this is not limited to this, and the U-shape of the narrow shallow groove 311 may have a branch that branches off from the middle (not shown).

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 edges of the middle land portion 32 and the center land portion 33 have a wavy shape formed by connecting multiple arcs. The left and right edges of the middle land portion 32 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 edges 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 edges 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.

As shown in FIG. 2, 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 to the tire width direction.

The through lug grooves 321 (331) of the middle land portion 32 (and the center land portion 33) are thin and shallow grooves having a maximum groove width W21 of 1.5 mm to 4.0 mm and a maximum groove depth H21 of 1.0 mm to 6.0 mm (not shown). 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 (not shown).

The blocks 322; 332 are partitioned into a plurality of through lug grooves 321; 331. The blocks 322, 332 are elongated in the tire width direction. Specifically, the pitch length of the blocks 322; 332 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×Pg+672×ρs+7.6×Dg...(1)

[Shoulder main groove wall structure]
6 to 8 are enlarged plan views (FIGS. 6 and 7) and a cross-sectional view in the groove depth direction (FIG. 8) showing the groove wall structure of the shoulder main groove 21 shown in FIG. 2. In these figures, FIG. 6 particularly shows the groove wall structure on the outer side in the tire width direction of the shoulder main groove 21, and FIG. 7 particularly shows the groove wall structure on the inner side in the tire width direction. Also, FIG. 8 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. 6, 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, FIG. 8) 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. 8), 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.

6 and 7, 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 211o on the shoulder land portion 31 side and the inner edge 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 212o on the shoulder land portion 31 side and the inner edge 212i on the middle land portion 32 side.

Also, as shown in Fig. 6, 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. 6, 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 7, 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 7, 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.

6, 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.

6, 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. 7, 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. 6, 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. 7, 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.

6, 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. 7, 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 satisfies the relationship 0.50≦L2i_sh/λ2i_sh≦0.60 with respect to the wavelength λ2i_sh of the inner edge portion 212i, and preferably satisfies the relationship 0.50≦L2i_sh/λ2i_sh≦0.55.

6, 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. 7, 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 relative 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.

7, 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 approximately 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.

8, 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. 6), 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. 6, 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 value of the groove wall angle at the inner edge 211i of the shoulder main groove 21 is set to be larger than the average value of the groove wall angle at the outer edge 211o. This ensures the rigidity of the narrow middle land portion 32 (see FIG. 2).

8, 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. 6, 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 arc (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).

6, 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. In addition, it is preferable that the circumferential length of the groove bottom 212 (approximately equal to the maximum distance L2o_sh in the tire circumferential direction of the maximum amplitude positions P2oo, P2oi of the outer edge 212o in FIG. 6) 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).

[Modification]
9 to 18 are explanatory diagrams showing modified examples of the narrow shallow groove 311 shown in Fig. 4. In these drawings, the same components as those shown in Fig. 4 are given the same reference numerals, and the description thereof will be omitted.

In the configuration of FIG. 4, the circumferential extension portion Rb has a straight line or a gentle arc shape that is inclined with respect to the tire circumferential direction, so that the narrow shallow groove 311 has a single innermost point B'. In addition, the innermost point B' is located at the connection between the widthwise extension portion Ra1 of the narrow shallow groove 311 and the circumferential extension portion Rb.

In contrast, in the configuration of FIG. 9, the circumferential extension portion Rb is made up of straight lines parallel to the tire circumferential direction. In this case, the center point of the region of the narrow shallow groove 311 that is on the innermost side in the tire width direction (in FIG. 9, the entire circumferential extension portion Rb) is defined as the innermost point B' of the narrow shallow groove 311. Also, in the configuration of FIG. 10, the left and right widthwise extension portions Ra1 and Ra2 are connected via a groove portion that is convex toward the tire equatorial plane CL. Also, this convex portion of the arc shape has the innermost point B' of the narrow shallow groove 311 and the circumferential extension portion Rb.

In addition, in the configuration of FIG. 4, the narrow shallow groove 311 has a pair of widthwise extending portions Ra1, Ra1; Ra2, Ra2 that extend approximately parallel to the tire width direction between points A1 and B and between points A2 and B, respectively.

In contrast, in the configuration of FIG. 11, the narrow shallow groove 311 has a pair of widthwise extending portions Ra1, Ra1 between points A1 and B, and a single widthwise extending portion Ra2 between points A2 and B. In addition, the widthwise extending portion Ra2 on the point A2 side and the innermost point B are connected via a long arc that includes a short, S-shaped bend and a circumferential extending portion Rb.

In addition, in the configuration of FIG. 4, a pair of end points A1, A2 of the narrow shallow groove 311 are disposed at approximately the same position in the tire width direction. Therefore, the distance D2 between the end points A1, A2 in the tire width direction is approximately zero.

In contrast, in the configuration of FIG. 12, a pair of end points A1, A2 of the narrow shallow groove 311 are offset from each other in the tire width direction. Even in this configuration, the narrow shallow groove 311 has an opening facing the tire ground edge T because the angle θ11 of the narrow shallow groove 311 is within the above-mentioned range.

In the configuration of FIG. 4, the U-shaped opening of the narrow shallow groove 311 is formed by widthwise extending portions Ra1 and Ra2 that are straight or have a gentle arc shape, and these widthwise extending portions Ra1 and Ra2 have end points A1 and A2 of the narrow shallow groove 311.

In contrast, in the configuration of FIG. 13, the U-shaped opening of the narrow shallow groove 311 is curved in a direction narrowing the opening width toward the end points A1, A2. Also, in the configuration of FIG. 14, the S-shaped bends connecting the adjacent widthwise extending portions Ra1, Ra1; Ra2, Ra2 are curved in a direction narrowing the opening width of the U-shape. In this way, the U-shape of the narrow shallow groove 311 may have a shape with a narrow opening width.

In the configuration of FIG. 4, the narrow shallow groove 311 has a pair of widthwise extending portions Ra1, Ra1; Ra2, Ra2 that extend approximately parallel to the tire width direction between points A1 and B and between points A2 and B, and each of the two pairs of widthwise extending portions Ra1, Ra1; Ra2, Ra2 are connected to each other via an S-shaped bend.

In contrast, in the configuration of FIG. 15, the narrow shallow groove 311 has a single widthwise extending portion Ra1 between points A1 and B, and a pair of widthwise extending portions Ra2, Ra2 between points A2 and B. Also, points A1 and B are connected by a long, linear widthwise extending portion Ra1. Also, in the configuration of FIG. 16, a pair of widthwise extending portions Ra1, Ra1 are between points A1 and B, and no widthwise extending portion is between points A2 and B. Also, points A2 and B are connected by a long, arc-shaped groove portion.

In addition, in the configurations of Figures 17 and 18, the narrow shallow groove 311 has a single, long widthwise extending portion Ra1; Ra2 between points A1 and B and between points A2 and B. In particular, in the configuration of Figure 18, points A1 and B and points A2 and B are connected by widthwise extending portions Ra1; Ra2.

[effect]
As described above, the tire 1 includes a plurality of main grooves 21, 22 extending in the tire circumferential direction, and a plurality of land portions 31 to 33 defined by the main grooves 21, 22 (see FIG. 2). At least one row of land portions (left and right shoulder land portions 31, 31 in FIG. 2) includes a plurality of narrow shallow grooves 311 having a U-shape with an opening facing the tire ground contact end T and terminating within the ground contact surface of the land portion 31 (see FIG. 3).

In this configuration, (1) the narrow shallow groove 311 has a U-shape, and therefore, compared to a configuration (not shown) with multiple I-shaped widthwise narrow grooves arranged in the tire circumferential direction, the narrow shallow groove 311 has the advantage of improving the tire's acceleration performance on snow during vehicle travel due to the circumferential component of the narrow shallow groove 311. Also, (2) the narrow shallow groove 311 has a U-shape with an opening facing the tire ground edge T side, and therefore, compared to a configuration (not shown) with narrow shallow grooves having a ring-shaped structure, for example, the circumferential component of the narrow shallow groove in the region on the tire ground edge T side can be omitted. This has the advantage of improving the tire's noise performance during vehicle travel, and also has the advantage of suppressing uneven wear starting from the narrow shallow groove 311. Also, (3) the narrow shallow groove 311 has a closed structure that terminates within the ground contact surface of the land portion 31, and therefore, compared to a configuration (not shown) with narrow shallow grooves that penetrate the ground contact surface of the land portion in the tire width direction or tire circumferential direction, the tire has the advantage of improving the tire's noise performance.

In addition, in this tire 1, the land portion 31 having the narrow shallow grooves 311 is a rib having a tread surface that is continuous in the tire circumferential direction (see FIG. 3). This has the advantage of ensuring the rigidity of the land portion 31 and improving the tire's acceleration performance on snow, and also has the advantage of improving the tire's noise performance compared to a configuration (not shown) with narrow shallow grooves that penetrate the contact surface of the land portion in the tire width direction.

In addition, in this tire 1, the maximum groove width Wn (see FIG. 4) of the narrow shallow groove 311 is in the range of 0.1 mm≦Wn≦5.0 mm, and the maximum groove depth Hn (see FIG. 5) of the narrow shallow groove 311 has a relationship of 0.01≦Hn/Hg1≦0.30 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. This has the advantage that the maximum groove width Wn and maximum groove depth Hg1 of the narrow shallow groove 311 are optimized.

In addition, in this tire 1, the widthwise length W11 of the narrow shallow groove 311 has a relationship of 0.40≦W11/Wb1≦0.90 with respect to the maximum ground contact width Wb1 of the land portion 31 (see FIG. 3). The above lower limit has the advantage of ensuring the edge component of the narrow shallow groove 311 in the tire circumferential direction, thereby ensuring the improvement of the tire's acceleration performance on snow. The above upper limit has the advantage of ensuring the distances D3 and D4 (see FIG. 3) between the narrow shallow groove 311 and the edge portion of the land portion 31, thereby ensuring the rigidity of the land portion 31.

In addition, in this tire 1, the circumferential length L11 of the narrow shallow grooves 311 has a relationship of 0.50≦L11/P11≦0.90 with respect to the pitch length P11 of the narrow shallow grooves 311 (see FIG. 3). The above lower limit ensures the circumferential component of the U-shape of the narrow shallow grooves 311, which has the advantage of ensuring the tire's acceleration performance on snow when the vehicle is traveling. The above upper limit has the advantage of suppressing deterioration in tire noise performance caused by the circumferential component of the narrow shallow grooves 311 becoming excessively large.

In addition, in this tire 1, the distance D1 between the pair of end points A1, A2 of the narrow shallow groove 311 in the tire circumferential direction has a relationship of 0.30≦D1/P11≦0.90 with respect to the pitch length P11 of the narrow shallow groove 311 (see FIG. 3). The above lower limit has the advantage of ensuring the opening width of the U-shape of the narrow shallow groove 311, thereby suppressing deterioration of the tire's noise performance. The above upper limit has the advantage of ensuring the distance between the end points A1, A2 of the adjacent narrow shallow grooves 311, 311.

In addition, in this tire 1, the distance D2 (see FIG. 4) between the pair of end points A1, A2 of the narrow shallow groove 311 in the tire width direction has a relationship of 0≦D2/Wb1≦0.70 with respect to the maximum ground contact width Wb1 (see FIG. 3) of the land portion 31. In this configuration, the pair of end points A1, A2 of the narrow shallow groove 31 are at the same position in the tire width direction, which has the advantage of equalizing the rigidity of the shoulder land portion 31 and suppressing the resistance to uneven wear of the shoulder land portion 31.

In addition, in this tire 1, when a pair of end points A1, A2 and the innermost point B in the tire width direction of the narrow shallow groove 311 are defined, and a virtual line L1 passing through the midpoint M of the end points A1, A2 and the innermost point B is defined, the angle θ11 between the virtual line L1 and the tire circumferential direction is in the range of 45 [deg]≦θ11≦135 [deg] (see FIG. 4). This optimizes the opening direction of the U-shape of the narrow shallow groove 311, which has the advantage of improving the noise performance of the tire when the vehicle is running.

In addition, in this tire 1, the U-shape of the narrow shallow groove 311 has at least one widthwise extending portion Ra1, Ra2 with an inclination angle of 75 degrees or more and 105 degrees or less with respect to the tire circumferential direction (see FIG. 4). In addition, the sum ΣLa of the widthwise extending portions Ra1, Ra2's widthwise lengths La1 to La4 has a relationship of 1.00≦ΣLa/W11 with respect to the widthwise length W11 of the narrow shallow groove 311. With this configuration, the total length ΣLa of the widthwise extending portions Ra1, Ra2 extending approximately perpendicular to the tire circumferential direction is ensured, which has the advantage of efficiently ensuring the narrow shallow groove 311's effect of improving acceleration performance on snow when the vehicle is traveling straight.

In addition, in this tire 1, the U-shape of the narrow shallow groove 311 has a pair of adjacent widthwise extending portions Ra1, Ra1; Ra2, Ra2, and a crank-shaped or S-shaped bent portion (reference numerals omitted in the figure) that connects the pair of widthwise extending portions Ra1, Ra1; Ra2, Ra2 (see FIG. 4). This increases the circumferential component of the narrow shallow groove 311, which has the advantage of improving the noise performance of the tire when the vehicle is running.

In addition, in this tire 1, the U-shape of the narrow shallow groove 311 has a continuous circumferentially extending portion Rb with an inclination angle of 0 degrees or more and 15 degrees or less with respect to the tire circumferential direction (see FIG. 4). The circumferential length Lb of the circumferentially extending portion Rb has a relationship of 0.50≦Lb/L11 with respect to the circumferential length L11 of the narrow shallow groove 311. This configuration has the advantage that the length Lb of the circumferentially extending portion Rb extending approximately parallel to the tire circumferential direction is ensured, so that the narrow shallow groove 311 efficiently improves the acceleration performance on snow when the vehicle is traveling.

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

Figure 19 is a table showing the results of a performance test of a tire according to an embodiment of the present invention. Figure 20 is an explanatory diagram showing the shoulder land portion of the conventional test tire shown in Figure 19.

In this performance test, several types of test tires were evaluated for (1) acceleration performance on snow and (2) pass-by noise performance. 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 evaluation value, the better. A value of 96 or higher can be said to indicate that performance is adequate.

(2) Pass-by noise performance is evaluated by measuring the vehicle's pass-by noise under test conditions that comply with ECE R117-2. Based on the measurement results, the decibel difference is calculated with the conventional example set as the standard (0). The smaller this value, the better.

The test tire of the embodiment has the configuration shown in Figures 1 to 3. 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. The number of pitches of the zigzag shape of the groove openings 211 and 221 of the main grooves 21 and 22 is 50 to 100.

The comparative test tire is the test tire of Example 1, in which the narrow shallow grooves have a straight shape and penetrate the shoulder land portion (see Figure 20).

As the test results show, the test tire of the embodiment can improve the pass-by noise performance when the vehicle is traveling while maintaining the tire's acceleration performance on snow.

1 Tire; 11 Bead core; 12 Bead filler; 13 Carcass layer; 14 Belt layer; 141, 142 Cross belt; 15 Tread rubber; 16 Sidewall rubber; 17 Rim cushion rubber; 21 Shoulder main groove; 211 Groove opening; 212 Groove bottom; 22 Center main groove; 31 Shoulder land portion; 311 Narrow shallow groove; 32 Middle land portion; 321 Through lug groove; 322 Block; 33 Center land portion

Claims (14)

A tire having a plurality of main grooves extending in a tire circumferential direction and a plurality of land portions defined by the main grooves,
At least one row of the land portion has a U-shape with an opening facing the tire ground contact end side and includes a plurality of narrow shallow grooves that terminate within the ground contact surface of the land portion , and
A tire characterized in that a widthwise length W11 of the narrow shallow groove satisfies the relationship of 0.40≦W11/Wb1≦0.90 with respect to a maximum ground contact width Wb1 of the land portion . The tire according to claim 1, wherein the land portion having the narrow shallow groove is a rib having a tread surface that is continuous in the tire circumferential direction. 3. The tire according to claim 1, wherein the narrow shallow groove has a maximum groove width Wn in the range of 0.1 mm≦Wn≦5.0 mm, and the narrow shallow groove has a maximum groove depth Hn with respect to a maximum groove depth Hg1 of a shoulder main groove among the plurality of main grooves, the maximum groove depth Hg/Hg1 being in a relationship of 0.01≦Hn≦0.30. The tire according to any one of claims 1 to 3 , wherein a circumferential length L11 of the narrow shallow groove and a pitch length P11 of the narrow shallow groove satisfy a relationship of 0.50≦L11/P11≦0.90. 5. The tire according to claim 1 , wherein a distance D1 between a pair of end points of the narrow shallow groove in the tire circumferential direction satisfies the relationship 0.30≦D1/P11≦0.70 with respect to a pitch length P11 of the narrow shallow groove. The tire according to any one of claims 1 to 5 , wherein a distance D2 between a pair of end points A1, A2 of the narrow shallow groove in the tire width direction satisfies the relationship of 0≦D2/Wb1≦0.70 with respect to a maximum ground contact width Wb1 of the land portion. A pair of end points A1, A2 and an innermost point B in the tire width direction of the narrow shallow groove are defined, and a virtual line L1 passing through a midpoint M of the end points A1, A2 and the innermost point B is defined,
The tire according to any one of claims 1 to 6 , wherein an angle θ11 between the imaginary line L1 and the tire circumferential direction is in the range of 45 [deg]≦θ11≦135 [deg]. The U-shape of the narrow shallow groove has at least one widthwise extending portion having an inclination angle of 75 degrees or more and 105 degrees or less with respect to the tire circumferential direction, and
The tire according to any one of claims 1 to 7 , wherein a sum ΣLa of widthwise lengths of the widthwise extending portions and a widthwise length W11 of the narrow shallow groove satisfy a relationship of 1.00≦ΣLa/W11. The tire according to claim 8 , wherein the U-shape of the narrow shallow groove has a pair of adjacent widthwise extending portions and a crank-shaped or S-shaped bent portion connecting the pair of widthwise extending portions. The U-shape of the narrow shallow groove has a continuous circumferential extending portion having an inclination angle of 0 degrees or more and 15 degrees or less with respect to the tire circumferential direction, and
The tire according to any one of claims 1 to 8 , wherein a circumferential length Lb of the circumferential extending portion and a circumferential length L11 of the narrow shallow groove satisfy a relationship of 0.50≦Lb/L11. The tire according to any one of claims 1 to 10 , which is a heavy-duty tire mounted on a steering axle of a vehicle. A tire having a plurality of main grooves extending in a tire circumferential direction and a plurality of land portions defined by the main grooves,
At least one row of the land portion has a U-shape with an opening facing the tire ground contact end side and includes a plurality of narrow shallow grooves that terminate within the ground contact surface of the land portion , and
A tire characterized in that a circumferential length L11 of the narrow shallow groove and a pitch length P11 of the narrow shallow groove satisfy a relationship of 0.50≦L11/P11≦0.90 . A tire having a plurality of main grooves extending in a tire circumferential direction and a plurality of land portions defined by the main grooves,
At least one row of the land portion has a U-shape with an opening facing the tire ground contact end side and includes a plurality of narrow shallow grooves that terminate within the ground contact surface of the land portion , and
A tire characterized in that a distance D1 between a pair of end points of the narrow shallow groove in the tire circumferential direction and a pitch length P11 of the narrow shallow groove satisfies the relationship 0.30≦D1/P11≦0.70 . A tire having a plurality of main grooves extending in a tire circumferential direction and a plurality of land portions defined by the main grooves,
At least one row of the land portion has a U-shape with an opening facing the tire ground contact end side and includes a plurality of narrow shallow grooves terminating within the ground contact surface of the land portion ,
The U-shape of the narrow shallow groove has at least one widthwise extending portion having an inclination angle of 75 degrees or more and 105 degrees or less with respect to the tire circumferential direction, and
A tire characterized in that a sum ΣLa of widthwise lengths of the widthwise extending portions and a widthwise length W11 of the narrow shallow groove satisfy a relationship of 1.00≦ΣLa/W11 .

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