tire

Abstract

To provide a tire capable of having both tire snow performance and low rolling resistance performance.SOLUTION: In a tire 1, a middle land part 32 comprises: first middle thin grooves 321 having a linear shape or circular arc shape and penetrating the middle land part 32; and second middle thin grooves 322 having a Z-shape and penetrating the middle land part 32. A center land part 33 comprises: first center thin grooves 331 having one end on an edge of the center land part 33, connected to a center main groove 22, and having the other end in the center land part 33; and second center thin grooves 332 extending in a tire circumferential direction and having both ends in the center land part 33. The first center thin grooves 331 are inclined in one direction in the tire circumferential direction toward the other end from the one end. The first center thin grooves 331 and the second center thin grooves 332 are arrayed in a V-shape with an apex facing the one direction in the tire circumferential direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a tire, and more particularly to a tire that can achieve both snow performance and low rolling resistance. [Background technology]

[0002] In recent heavy-duty tires, in order to reduce the rolling resistance of the tire, lateral grooves that penetrate the middle land portion and the center land portion are narrow grooves with a groove width of 3.0 mm or less. A technology described in Patent Document 1 is known as a conventional tire that employs such a configuration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5498466 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, in recent years, there has been a demand for all-season tires to have good snow performance.

[0005] The present invention has been made in view of the above, and has an object to provide a tire that can achieve both good snow performance and low rolling resistance. [Means for solving the problem]

[0006] In order to achieve the above object, a tire according to the present invention is a tire comprising a pair of shoulder main grooves and two or more center main grooves, a pair of shoulder land portions, a pair of middle land portions, and one or more center land portions defined by the shoulder main grooves and the center main groove, wherein at least one of the middle land portions comprises a first middle narrow groove having a straight or arc shape and penetrating the middle land portion, and a second middle narrow groove having a Z-shape and penetrating the middle land portion, and the first middle narrow groove and the second middle narrow groove are arranged in a circumferential direction of the tire. the center land portion includes a first center narrow groove having one end connected to the center main groove at an edge portion of the center land portion and the other end within the center land portion, and a second center narrow groove extending in the tire circumferential direction and having both ends within the center land portion, the first center narrow groove inclining in one direction in the tire circumferential direction from the one end toward the other end, and the first center narrow groove and the second center narrow groove are arranged in a V shape with their peaks facing in one direction in the tire circumferential direction. [Effects of the Invention]

[0007] In the tire according to the present invention, (1) the middle land portion has a second middle narrow groove with a Z-shape, which increases the edge component of the middle land portion and improves the tire's snow performance compared to a configuration in which all through-thick narrow grooves are linear or arc-shaped. Also, (2) the center land portion has first and second center narrow grooves arranged in a V-shape, which ensures the rigidity of the center land portion and reduces the tire's rolling resistance compared to a configuration in which the center land portion has through-thick narrow grooves. Furthermore, the first and second center narrow grooves arranged in a V-shape ensure edge components in both the tire circumferential direction and the tire width direction, thereby achieving both snow acceleration performance and skid resistance. These advantages result in a tire that achieves both snow performance and low rolling resistance. [Brief explanation of the drawings]

[0008] [Figure 1]FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the tread surface of the tire shown in FIG. [Figure 3] FIG. 3 is an enlarged view showing the middle land portion and the center land portion of the tire shown in FIG. [Figure 4] FIG. 4 is an enlarged plan view showing the center land portion shown in FIG. [Figure 5] FIG. 5 is a cross-sectional view showing the center land portion shown in FIG. [Figure 6] FIG. 6 is an enlarged plan view showing the middle land portion shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing the middle land portion shown in FIG. [Figure 8] FIG. 8 is an enlarged view showing the center main groove shown in FIG. [Figure 9] FIG. 9 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. [Figure 10] FIG. 10 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0010] [tire] 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. In this embodiment, as an example of a tire, a heavy-duty pneumatic radial tire mounted on the steering axle of a vehicle for long-distance transportation such as a truck or bus will be described.

[0011] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as the direction parallel to the tire rotation axis, and the tire radial direction is defined as the direction perpendicular to the tire rotation axis.

[0012] 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).

[0013] The pair of bead cores 11, 11 are formed by winding one or more steel bead wires in an annular and multiple manner and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are made up of a lower filler 121 and an upper filler 122 and are respectively disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction to reinforce the bead portions.

[0014] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally laid between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wrapped around and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction of the tire) of 80 degrees or more and 90 degrees or less in absolute value for radial tires, and 30 degrees or more and 45 degrees or less in absolute value for bias tires.

[0015] The belt layer 14 is formed by laminating multiple belt plies 141 to 144 and is disposed around the carcass layer 13. These belt plies 141 to 144 include a high-angle belt 141, a pair of cross belts 142 and 143, and a belt cover 144. The high-angle belt 141 is formed by covering multiple steel belt cords with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 45 degrees or more and 70 degrees or less in absolute value. The pair of cross belts 142 and 143 are formed by covering multiple steel belt cords with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 10 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 142 and 143 have cord angles of opposite signs to each other, and are laminated with the belt cords' longitudinal directions crossing each other (having a so-called cross-ply structure). The belt cover 144 is made by covering a plurality of belt cover cords made of steel or organic fiber material with coating rubber and rolling them, and has a cord angle of 10 degrees or more and 55 degrees or less in absolute value.

[0016] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form the tread portion of the tire 1. A pair of sidewall rubbers 16, 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction to form left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction of the left and right bead cores 11, 11 and the turned-up portions of the carcass layer 13 to the outer side in the tire width direction to form the rim fitting surface of the bead portion.

[0017] [Tread surface] FIG. 2 is a plan view showing the tread surface of the tire 1 shown in FIG. 1. The figure shows the tread surface of an all-season tire having the mud and snow mark "M+S" and the three-peak mountain snowflake mark "3PMSF." In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T indicates the tire contact edge, and the dimension symbol TW indicates the tire contact width. In the figure, because the tire 1 has a tread surface that is approximately symmetrical with respect to the tire equatorial plane CL as the center line, some of the symbols of the components in the right area of the figure have been omitted.

[0018] The tire 1 also includes a rotation direction indicator (not shown) that indicates the tire rotation direction. The tire rotation direction refers to the rotation direction that is frequently used when the tire is in use, for example, the rotation direction when the vehicle is moving forward. Based on the display of this rotation direction indicator, the first side of the block to contact the ground (the so-called leading side or toe side) and the last side to contact the ground (the so-called trailing side or heel side) are defined (see Figure 2). The leading side is the side that contacts the ground first when the tire rolls in the specified rotation direction, and the trailing side is the side opposite to the leading side. The rotation direction indicator may be configured, for example, by a mark or a concave or convex portion provided on the sidewall of the tire.

[0019] As shown in FIG. 2, the tire 1 has four main grooves 21, 22 extending in the tire circumferential direction, and five rows of land portions 31 to 33 defined by these main grooves on the tread surface.

[0020] The main grooves 21, 22 are composed of a pair of shoulder main grooves 21, 21 and two center main grooves 22, 22. These main grooves 21, 22 have an annular structure that extends continuously around the entire circumference of the tire. The shoulder main grooves 21, 21 are the outermost main grooves in the tire width direction and are defined as left and right regions bounded by the tire equatorial plane CL. The center main grooves 22, 22 are defined as main grooves located closer to the tire equatorial plane CL than the shoulder main grooves 21, 21.

[0021] The main groove is defined as a groove that is required to display a wear indicator as specified by JATMA.

[0022] The shoulder main grooves 21 each have a width Wg1 of 5.0 mm or more (see FIG. 2) and a depth (not shown) of 10 mm or more, and the center main groove 22 has a width Wg2 of 5.0 mm or more (see FIG. 2) and a depth Hg2 of 10 mm or more (see FIG. 5, described later).

[0023] The groove width is measured as the maximum distance between the opposing groove walls at the groove opening on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured using the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction as the endpoint.

[0024] The groove depth is measured as the maximum distance from the tread surface to the groove bottom when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. If the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0025] A specified rim is a "standard rim" as specified by JATMA, a "design rim" as specified by TRA, or a "measuring rim" as specified by ETRTO. Also, specified internal pressure is the "maximum air pressure" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "inflation pressure" as specified by ETRTO. Also, specified load is the "maximum load capacity" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "load capacity" as specified by ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

[0026] In addition, in the configuration of FIG. 2, the distance from the tire equatorial plane CL to the groove center lines of the left and right shoulder main grooves 21, 21 (dimension symbols omitted in the figure) is in the range of 25% to 35% of the tire contact width TW.

[0027] The groove centerline is defined as an imaginary line connecting the midpoints of the distance between opposing groove walls. If the groove centerline of the main groove has a zigzag or wavy shape (not shown), the distance to the groove centerline is defined using the center of the amplitude of the groove centerline as the measurement point.

[0028] The tire contact width TW is measured as the maximum linear distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0029] The tire ground contact edge T is defined as the widest position in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0030] The land portions 31-33 are composed of a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single row of center land portion 33. These land portions 31-33 are defined by the main grooves 21, 22 and form an annular tread extending around the entire circumference of the tire. The shoulder land portions 31, 31 are defined as land portions defined by the shoulder main grooves 21, 21 on the outer side in the tire width direction. The pair of shoulder land portions 31, 31 are arranged in left and right regions bounded by the tire equatorial plane CL. The middle land portions 32, 32 are defined as land portions defined by the shoulder main grooves 21, 21 on the inner side in the tire width direction. The pair of middle land portions 32, 32 are arranged in left and right regions bounded by the tire equatorial plane CL. The center land portion 33 is defined as a land portion located closer to the tire equatorial plane CL than the middle land portions 32, 32.

[0031] 2, the contact width Wb1 of the shoulder land portion 31 is in the range of 0.15≦Wb1 / TW≦0.25, preferably 0.18≦Wb1 / TW≦0.22, relative to the tire contact width TW. The contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33 are in the ranges of 0.13≦Wb2 / TW≦0.17 and 0.13≦Wb3 / TW≦0.17, respectively, relative to the tire contact width TW. The contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33 are in the ranges of 0.70≦Wb2 / Wb1≦0.90 and 0.70≦Wb3 / Wb1≦0.90, respectively, relative to the contact width Wb1 of the shoulder land portion 31. This configuration ensures the shoulder land portion 31's rigidity and effectively suppresses uneven wear of the shoulder land portion 31.

[0032] The contact width of the land portion is measured as the maximum linear distance in the axial direction of the tire at the contact surface between the land portion and the flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0033] In the configuration shown in FIG. 2, the tire 1 has a pair of shoulder main grooves 21 and two center main grooves 22, thereby defining a pair of shoulder land portions 31, a pair of middle land portions 32, and a single center land portion 33. However, this is not limiting, and the tire 1 may have three or more center main grooves (not shown). In such a configuration, two or more rows of center land portions are defined. The center land portion 33 may be located on the tire equatorial plane CL (see FIG. 2) or may be located at a position deviated from the tire equatorial plane CL (not shown).

[0034] 2, the tire 1 has a tread pattern that is symmetrical about the tire equatorial plane CL and has a tread pattern that has directionality in the tire rotation direction, as will be described later.

[0035] 2, the shoulder main grooves 21 and the center main groove 22 have straight shapes, so that the left and right edges of the middle land portion 32 also have straight shapes, and the left and right edges of the center land portion 33 also have straight shapes. However, this is not limiting, and any main groove may have a zigzag or step shape with amplitude in the tire width direction, so that the edges of the land portions also have a zigzag or step shape (not shown).

[0036] [Center Land Area] Fig. 3 is an enlarged view showing the middle land portion 32 and the center land portion 33 of the tire 1 shown in Fig. 2. Fig. 4 and Fig. 5 are an enlarged plan view (Fig. 4) and a cross-sectional view (Fig. 5) of the center land portion 33 shown in Fig. 3. Fig. 5 also shows a cross-sectional view along the first center narrow groove 331 of the center land portion 33.

[0037] In the configuration of Fig. 2, as shown in Fig. 3, the central land portion 33 includes a groove unit consisting of first and second central narrow grooves 331, 332. A plurality of groove units 331, 332 are arranged at predetermined intervals in the tire circumferential direction. For example, in the configuration of Fig. 3, the plurality of groove units 331, 332 are arranged in a staggered pattern in the tire circumferential direction.

[0038] The first and second central narrow grooves 331, 332 are non-through grooves and do not penetrate the central land portion 33 in the tire width direction. The central land portion 33 is a rib with a circumferentially continuous tread surface and does not have other grooves or sipes that penetrate the central land portion 33 in the tire width direction. This ensures the rigidity of the central land portion 33 and reduces the rolling resistance of the tire.

[0039] As shown in FIG. 4, the first center narrow groove 331 is a widthwise groove extending primarily in the tire width direction. One end is connected to the edge of the center land portion 33 and connected to the center main groove 22, and the other end is located within the center land portion 33. The groove width Ws31 of the first center narrow groove 331 is in the range of 1.5 mm ≦ Ws31 ≦ 3.0 mm. The groove depth Hs31 of the first center narrow groove 331 (see FIG. 5) is in the range of 1.5 mm ≦ Hs31 ≦ 3.0 mm. The groove depth Hs31 of the first center narrow groove 331, relative to the groove depth Hg2 of the center main groove 22, is in the range of 0.05 ≦ Hs31 / Hg2 ≦ 0.15. Therefore, the first center narrow groove 331 is a narrow, shallow groove that opens and functions as a groove when the tire is in contact with the ground.

[0040] As shown in FIG. 4 , the first central narrow groove 331 is inclined in one direction in the tire circumferential direction, specifically, in the tire rotation direction, from the end (end point E31a) on the edge side of the center land portion 33 to the end (end point E31b) within the center land portion 33. Therefore, when the tire rolls, the end within the center land portion 33 is the leading side, and the end on the edge side of the center land portion 33 is the trailing side. The inclination angle α of the first central narrow groove 331 with respect to the tire width direction is in the range of 10 degrees ≦ α ≦ 80 degrees, and preferably in the range of 20 degrees ≦ α ≦ 70 degrees. The lower limit ensures an edge component of the first narrow groove 331 with respect to the tire width direction, thereby ensuring skid resistance of the tire, and the upper limit ensures an edge component of the first narrow groove 331 with respect to the tire circumferential direction, thereby ensuring snow traction performance of the tire.

[0041] The inclination angle α of the first central narrow groove 331 is measured as the angle between the tire width direction and an imaginary line passing through the end points E31a and E31b of the first central narrow groove 331. The inclination angle α in the tire rotation direction from the end (end point E31a) on the edge side of the center land portion 33 to the end (end point E31b) within the center land portion 33 is defined as positive.

[0042] The end points E31a and E31b of the first central narrow groove 331 are defined as the intersection points between the groove center line of the first central narrow groove 331 and the end on the edge side of the center land portion 33 and the end within the land portion 33. In addition, when the first central narrow groove 331 has a notch or a chamfer at its end (not shown), the end points E31a and E31b are defined on the main body of the groove excluding these.

[0043] 4, the extension length Ds31 of the first central narrow groove 331 in the tire width direction is in the range of 0.30≦Ds31 / Wb3≦0.70, and preferably 0.40≦Ds31 / Wb3≦0.60, relative to the contact width Wb3 of the center land portion 33. The lower limit ensures the edge component of the first central narrow groove 331, while the upper limit prevents a decrease in the rigidity of the center land portion 33 caused by the first central narrow groove 331 being too long.

[0044] The extension length Ds31 of the first central narrow groove 331 is measured as the distance between the end points E31a and E31b of the first central narrow groove 331 in the tire width direction.

[0045] 4, the first central narrow groove 331 has a straight or arcuate shape as a whole. Specifically, the first central narrow groove 331 has a continuous straight or arcuate portion over a length of 60% or more, preferably 70% or more, of the extension length Ds31 in the tire width direction. The first central narrow groove 331 may also have a partially bent or curved portion near its end (see FIG. 4).

[0046] For example, in the configuration shown in Fig. 4, the first central narrow groove 331 has a short bent portion (indicated by the symbol in the figure) near the opening (end point E31a) to the central main groove 22 so as to connect approximately perpendicularly (90±5 degrees) to the edge of the central land portion 33. The extension length De31 of the bent portion in the tire width direction, relative to the contact width Wb3 of the central land portion 33, is in the range of 0.05≦De31 / Wb3≦0.20, preferably 0.06≦De31 / Wb3≦0.15. The extension length De31 of the bent portion is in the range of 2.0 mm≦De31≦5.0 mm.

[0047] As shown in FIG. 4 , the second center narrow groove 332 is a circumferential groove extending mainly in the tire circumferential direction, with both ends located within the center land portion 33, i.e., in the center of the center land portion 33. The groove width Ws32 of the second center narrow groove 332 is in the range of 1.5 mm ≦ Ws32 ≦ 3.0 mm. The groove depth Hs32 (not shown) of the second center narrow groove 332 is in the range of 1.5 mm ≦ Hs32 ≦ 3.0 mm. The groove depth Hs32 of the second center narrow groove 332, relative to the groove depth Hg2 of the center main groove 22, is in the range of 0.05 ≦ Hs32 / Hg2 ≦ 0.15. Therefore, the second center narrow groove 332 is a narrow, shallow groove that opens and functions as a groove when the tire is in contact with the ground.

[0048] As shown in FIG. 4 , the second central narrow groove 332 extends from near the end (end point E31b) of the first central narrow groove 331 within the center land portion 33 in the direction opposite to the tire rotational direction. The inclination angle β of the second central narrow groove 332 relative to the tire circumferential direction is in the range of 0°≦|β|≦60°, and preferably in the range of 5°≦|β|≦45°. This configuration ensures the rigidity of the center land portion 33 and reduces the rolling resistance of the tire compared to a configuration (not shown) in which both the first and second central narrow grooves 331 and 332 extend primarily in the tire width direction. The edge component of the second central narrow groove 332 also improves the tire's acceleration performance on snow.

[0049] 4, the second central narrow groove 332 is preferably inclined relative to the tire circumferential direction, and more preferably inclined in the same direction as the inclination of the first central narrow groove 331 relative to the tire circumferential direction. Specifically, the second central narrow groove 332 is more preferably inclined toward the first central narrow groove 331 from the leading side to the trailing side in the tire rotation direction. The inclination angle β of the second central narrow groove 332 relative to the tire circumferential direction is preferably in the range of 5 degrees ≦ β ≦ 45 degrees. The inclination of the second central narrow groove 332 toward the first central narrow groove 331 reduces the rolling resistance of the tire.

[0050] The inclination angle β of the second center narrow groove 332 is measured as the angle between an imaginary line passing through the end points E32a and E32b of the second center narrow groove 332 and the tire circumferential direction. The inclination angle β is defined as positive in the same direction as the inclination direction of the first center narrow groove 331 relative to the tire circumferential direction. Specifically, the inclination angle β is defined as positive in the direction inclined toward the first center narrow groove 331 from the leading side to the trailing side in the tire rotational direction.

[0051] End points E32a and E32b of the second central narrow groove 332 are defined as the intersections of the groove center line of the second central narrow groove 332 and both end portions of the second central narrow groove 332. In addition, when the second central narrow groove 332 has a notched portion or a chamfered portion at its end (not shown), the end points E32a and E32b are defined on the main body of the groove excluding these portions.

[0052] 4, the inclination angle θ3 of the second center narrow groove 332 relative to the first center narrow groove 331 is in the range of 5°≦θ3≦140°, and preferably 40°≦θ3≦60°. Therefore, it is preferable that the first center narrow groove 331 and the second center narrow groove 332 are arranged with an acute inclination angle θ3. The lower limit ensures edge components in different directions by the first and second center narrow grooves 331, 332, improving the tire's snow performance, while the upper limit ensures rigidity of the center land zone 33 and reducing the tire's rolling resistance.

[0053] The inclination angle θ3 is defined as the angle formed by an imaginary line passing through the end points E31a and E31b of the first central narrow groove 331 and an imaginary line passing through the end points E32a and E32b of the second central narrow groove 332.

[0054] 4, the extension length Ls32 of the second center narrow groove 332 in the tire circumferential direction, relative to the contact patch width Wb3 of the center land zone 33, is in the range of 0.10≦Ls32 / Wb3≦0.70, preferably 0.20≦Ls32 / Wb3≦0.60. The extension length Ls32 of the second center narrow groove 332 in the tire circumferential direction, relative to the extension length Ds31 of the first center narrow groove 331 in the tire width direction, is in the range of 0.50≦Ls32 / Ds31≦1.10, more preferably 0.60≦Ls32 / Ds31≦1.00. This optimizes the balance between the extension lengths Ls32 and Ds31 of the first and second center narrow grooves 331, 332.

[0055] The extension length Ls32 of the second central narrow groove 332 is measured as the distance between end points E32a and E32b of the second central narrow groove 332 in the tire circumferential direction.

[0056] Furthermore, the extension length Ds31 of the first central narrow groove 331 and the extension length Ls32 of the second central narrow groove 332 are in the range of 0.70≦(Ds31+Ls32) / Wb3≦0.95, preferably 0.80≦(Ds31+Ls32) / Wb3≦0.95, relative to the contact width Wb3 of the center land zone 33. The lower limit ensures edge components of the first and second center narrow grooves 331, 332, ensuring the snow performance of the tire, while the upper limit ensures the rigidity of the center land zone 33, preventing a deterioration in the rolling resistance of the tire.

[0057] As shown in Fig. 4, the second center narrow groove 332 has a straight or arcuate shape as a whole. Specifically, the second center narrow groove 332 has a continuous straight or arcuate portion over 60% or more, preferably 70% or more, of the circumferential extension length Ls32. Therefore, the second center narrow groove 332 may have a partially bent or curved portion near its end (not shown). In the configuration of Fig. 4, the second center narrow groove 332 consists of a single straight line.

[0058] 4, the first central narrow groove 331 and the second central narrow groove 332 are arranged in a V-shape with their peaks facing in one direction in the tire circumferential direction. Specifically, the first central narrow groove 331 is inclined in one direction in the tire circumferential direction from the end (end point E31a) on the edge side of the center land portion 33 toward the end (end point E31b) within the center land portion 33, as described above, and the second central narrow groove 332 extends from near the end (end point E31b) of the first central narrow groove 331 within the center land portion 33 in the direction opposite to the tire rotational direction, thereby forming the V-shape.

[0059] In the above configuration, the center land portion 33 has the first and second center narrow grooves 331, 332 arranged in a V-shape, which increases the edge component of the center land portion 33 and improves the tire's snow performance. Specifically, the first and second center narrow grooves 331, 332 arranged in a V-shape ensure edge components in both the tire circumferential direction and the tire width direction, thereby achieving both the tire's snow acceleration performance and skid resistance. Furthermore, because the first and second center narrow grooves 331, 332 do not penetrate the center land portion 33, the rigidity of the center land portion 33 is ensured and the tire's rolling resistance is reduced.

[0060] As shown in FIG. 4 , the first central narrow groove 331 and the second central narrow groove 332 are spaced apart from each other. Therefore, the second central narrow groove 332 is not connected to the first central narrow groove 331, and both ends of the second central narrow groove 332 terminate inside the center land portion 33. In this configuration, the first and second central narrow grooves 331, 332 are spaced apart from each other, which increases the rigidity of the center land portion 33 and effectively reduces the rolling resistance of the tire compared to a configuration in which the first and second central narrow grooves 331, 332 are connected. The distance Ga between the first central narrow groove 331 and the second central narrow groove 332 is in the range of 1.0 mm≦Ga≦2.5 mm. The lower limit ensures the rigidity of the center land portion 33, while the upper limit ensures the interaction between the first and second central narrow grooves 331, 332.

[0061] The separation distance Ga is measured as the minimum distance of the width of the tread surface of the center land portion 33 existing between the center narrow groove 331 and the second center narrow groove 332.

[0062] 4, the distance Dt in the tire width direction between the end of the first central narrow groove 331 and the end of the second central narrow groove 332 at the apex of the V-shape is in the range of 0≦|Dt| / Ds31≦0.30, more preferably 0≦|Dt| / Ds31≦0.20, relative to the extension length Ds31 of the first central narrow groove 331 in the tire width direction. Therefore, the ends of the first and second central narrow grooves 331, 332 at the apex of the V-shape are located at approximately the same position in the tire width direction. This optimizes the V-shaped arrangement of the first and second central narrow grooves 331, 332.

[0063] 4, the end of the second central narrow groove 332 at the apex of the V-shape is preferably located closer to the first central narrow groove 331 than the end of the first central narrow groove 331. Specifically, in a circumferential projection view, the end of the second central narrow groove 332 preferably overlaps the extension region of the first central narrow groove 331 in the tire width direction (i.e., the range of the extension length Ds31). The distance Dt in the tire width direction between the end of the first central narrow groove 331 at the apex of the V-shape and the end of the second central narrow groove 332 preferably falls within the range of 0≦Dt / Ds31≦0.20.

[0064] The distance Dt is measured as the distance in the tire width direction between the end point E31b of the first central narrow groove 331 at the apex of the V-shape and the end point E32a of the second central narrow groove 332. The distance Dt is defined as positive in the direction from the end point E31b of the first central narrow groove 331 inside the center land portion 33 toward the end point E31a of the first central narrow groove 331 at the edge portion of the center land portion, i.e., in the direction in which the end of the second center narrow groove 332 overlaps with the first center narrow groove 331.

[0065] 4, the circumferential distance Lt between the end of the first central narrow groove 331 and the end of the second central narrow groove 332 at the apex of the V-shape is in the range of 0≦|Lt| / Ls32≦0.50, preferably 0≦|Lt| / Ls32≦0.30, relative to the circumferential extension length Ls32 of the second central narrow groove 332. Therefore, the ends of the first and second central narrow grooves 331, 332 at the apex of the V-shape are at approximately the same position in the circumferential direction of the tire.

[0066] 4, the end of the second central narrow groove 332 at the apex of the V-shape is preferably located further rearward in the tire rotational direction than the end of the first central narrow groove 331. The tire circumferential distance Lt between the end of the first central narrow groove 331 and the end of the second central narrow groove 332 at the apex of the V-shape is preferably in the range of 0.10≦Lt / Ls32≦0.30.

[0067] The distance Lt is measured as the distance in the tire circumferential direction between the end point E31b of the first central narrow groove 331 at the apex of the V-shape and the end point E32a of the second central narrow groove 332. The distance Lt is defined as positive in the direction from the leading side to the trailing side in the tire rotational direction.

[0068] In the configuration shown in Figure 4, multiple groove units each consisting of the first and second central narrow grooves 331, 332 are arranged spaced apart in the tire circumferential direction. Therefore, adjacent groove units 331, 332 (331, 332) are arranged so as not to overlap each other when projected in the tire width direction. This ensures the rigidity of the central land portion 33. Furthermore, the spacing Gb between adjacent groove units 331, 332 (331, 332) is in the range of 1.0 mm or less. There is no particular upper limit to the spacing Gb, but it is subject to other constraints.

[0069] The separation distance Gb is measured as the distance between adjacent groove units 331, 332; 331, 332 when projected in the tire width direction. The separation distance Gb is defined as positive in the direction in which adjacent groove units 331, 332; 331, 332 are spaced apart. Therefore, when adjacent groove units 331, 332; 331, 332 overlap when projected in the tire width direction, the separation distance Gb is Gb<0.

[0070] 3, the center land portion 33 includes the first center narrow groove 331 and the second center narrow groove 332, as well as the multi-sipes 4 described below, but does not include any other lateral grooves that open when the tire is in contact with the ground, specifically, lateral grooves with a groove width exceeding 1.5 mm and a groove length exceeding 10 mm. This ensures a sufficient contact area for the center land portion 33.

[0071] [Middle Land Division] 6 and 7 are an enlarged plan view (FIG. 6) and a cross-sectional view (FIG. 7) of the middle land portion 32 shown in FIG. 3. FIG. 7 shows a cross-sectional view of the middle land portion 32 along the first middle narrow groove 321.

[0072] 2, the middle land portion 32 includes first and second middle narrow grooves 321, 322. The first and second middle narrow grooves 321, 322 are arranged alternately in the tire circumferential direction.

[0073] The first and second middle narrow grooves 321, 322 are through-grooves that penetrate the middle land portion 32 in the tire width direction and connect to the left and right main grooves 21, 22. This allows the middle land portion 32 to be divided into blocks in the tire circumferential direction, improving the snow traction of the middle land portion 32.

[0074] 6, the groove width Ws21 of the first middle narrow groove 321 is in the range of 1.5 mm≦Ws21≦3.0 mm. The groove depth Hs21 (see FIG. 7) of the first middle narrow groove 321 is in the range of 1.5 mm≦Hs21≦3.0 mm. The groove depth Hs21 of the first middle narrow groove 321, relative to the groove depth Hg (Hg1, Hg2) of the main grooves 21, 22, is in the range of 0.05≦Hs21 / Hg≦0.15. Therefore, the first middle narrow groove 321 is a narrow, shallow groove that opens and functions as a groove when the tire contacts the ground.

[0075] 6, the first middle narrow groove 321 is inclined in one direction in the tire circumferential direction, specifically, in the tire rotational direction, toward the tire equatorial plane CL. The inclination angle γ of the first middle narrow groove 321 relative to the tire width direction is in the range of 10 degrees ≦ γ ≦ 45 degrees, and preferably in the range of 15 degrees ≦ γ ≦ 30 degrees.

[0076] The inclination angle γ of the first middle narrow groove 321 is measured as the angle between the tire width direction and an imaginary line passing through the end points E21a and E21b of the first middle narrow groove 321. The inclination angle γ is defined as positive when it is in the same inclination direction as the first center narrow groove 331.

[0077] End points E21a and E21b of the first middle narrow groove 321 are defined as the intersection points between the groove center line of the first middle narrow groove 321 and both end portions of the first middle narrow groove 321. In addition, in a configuration in which the first middle narrow groove 321 has a notched portion or a chamfered portion at the end (not shown), the end points E21a and E21b are defined on the main body of the groove excluding these portions.

[0078] Furthermore, the pitch length Ps21 of the first middle narrow groove 321 is in the range of 0.80≦Ps21 / Wb2≦1.20 relative to the contact width Wb2 of the middle land portion 32. The lower limit ensures the rigidity of the middle land portion 32 and ensures low rolling resistance performance of the tire, while the upper limit ensures the edge component of the first middle narrow groove 321 and ensures snow performance of the tire.

[0079] 6, the first middle narrow groove 321 has a straight or arcuate shape as a whole, and may have a partially bent or curved portion near its end.

[0080] For example, in the configuration shown in Fig. 6, the first middle narrow groove 321 has short bent portions (reference numerals omitted in the figure) near the openings (end points E21a, E21b) to the left and right main grooves 21, 22 to connect approximately perpendicularly (90±5 degrees) to the edges of the middle land portion 32. The extension length De21 (De21a, De21b) of the bent portions in the tire width direction, relative to the contact width Wb2 of the middle land portion 32, is in the range of 0.05≦De21 / Wb2≦0.20, preferably 0.10≦De21 / Wb2≦0.15. The extension length De21 of the bent portions is in the range of 2.0 mm≦De21≦5.0 mm.

[0081] 6, the groove width Ws22 of the second middle narrow groove 322 is in the range of 1.5 mm≦Ws22≦3.0 mm. The groove depth Hs22 (not shown) of the second middle narrow groove 322 is in the range of 1.5 mm≦Hs22≦3.0 mm. The groove depth Hs22 of the second middle narrow groove 322, relative to the groove depth Hg (Hg1, Hg2) of the main grooves 21, 22, is in the range of 0.05≦Hs22 / Hg≦0.15. Therefore, the second middle narrow groove 322 is a narrow, shallow groove that opens and functions as a groove when the tire is in contact with the ground.

[0082] 6, the second middle narrow grooves 322 are bent or curved in a Z-shape in the tire circumferential direction. Therefore, in the middle land portion 32, the first middle narrow grooves 321, which are linear or arc-shaped, and the second middle narrow grooves 322, which are Z-shaped, are alternately arranged in the tire circumferential direction. These second middle narrow grooves 322 increase the edge component of the middle land portion 32, improving the snow performance of the tire.

[0083] In addition, in FIG. 6, the second middle narrow groove 322 is composed of a pair of first groove portions 3221a, 3221b extending mainly in the tire width direction, and a second groove portion 3222 extending mainly in the tire circumferential direction.

[0084] The pair of first groove portions 3221a, 3221b has one end connected to the edge portion of the middle land portion 32 and connected to the shoulder main groove 21 and the center main groove 22, respectively, and the other end inside the middle land portion 32. The pair of first groove portions 3221a, 3221b are inclined in the same direction as the inclination direction of the first middle narrow groove 321, i.e., in one direction in the tire circumferential direction toward the tire equatorial plane CL, specifically in the tire rotational direction.

[0085] 6, the inclination angle δ1 (δ1a, δ1b) of the pair of first groove portions 3221a, 3221b relative to the tire width direction is in the range of 10 degrees ≦ δ1 ≦ 45 degrees, and preferably in the range of 12 degrees ≦ δ1 ≦ 30 degrees. The inclination angle δ1 of the pair of first groove portions 3221a, 3221b relative to the inclination angle γ of the first middle narrow groove 321 is in the range of 0 ≦ |δ1 - γ| ≦ 20 degrees, and preferably in the range of 0 ≦ |δ1 - γ| ≦ 20 degrees. Therefore, the inclination angle δ1 of the pair of first groove portions 3221a, 3221b extends approximately parallel to the inclination angle γ of the first middle narrow groove 321.

[0086] The inclination angle δ1 (δ1a, δ1b) of the first groove portions 3221a, 3221b is measured as the angle formed between an imaginary line passing through the end points E22a, E22b of the first groove portions 3221a, 3221b and the tire width direction.

[0087] The end points E22a and E22b of the first groove portions 3221a and 3221b are defined as the end points and bending points of an imaginary straight line when the entire second middle narrow groove 322 is approximated by the imaginary straight line bent in a Z shape. In addition, in a configuration in which the first groove portions 3221a and 3221b have notched portions or chamfered portions at the ends (not shown), the end points E22a and E22b are defined on the main body of the groove excluding these portions.

[0088] 6, the inclination angles δ1a and δ1b of the pair of first groove portions 3221a and 3221b satisfy the relationship 0≦|δ1a−δ1b|≦20 degrees, and preferably 0≦|δ1a−δ1b|≦15 degrees. Therefore, the pair of first groove portions 3221a and 3221b extend approximately parallel to each other.

[0089] Also, in Figure 6, the extension length Ds22 (Ds22a, Ds22b) of the pair of first groove portions 3221a, 3221b in the tire width direction is in the range of 0.30≦Ds22 / Wb2≦0.70 relative to the contact width Wb2 of the middle land portion 32, and preferably in the range of 0.40≦Ds22 / Wb2≦0.60.

[0090] The extension length Ds22 (Ds22a, Ds22b) of the first groove portions 3221a, 3221b is measured as the distance in the tire width direction between the end points E22a, E22b of the first groove portions 3221a, 3221b.

[0091] 6, the extension lengths Ds22a and Ds22b of the first groove portions 3221a and 3221b are in the range of 0.70≦(Ds22a+Ds22b) / Wb2≦1.30, and preferably 1.00≦(Ds22a+Ds22b) / Wb2≦1.10, relative to the contact width Wb2 of the middle land portion 32. Therefore, it is preferable that the sum of the extension lengths Ds22a and Ds22b of the first groove portions 3221a and 3221b is equal to or greater than the contact width Wb2 of the middle land portion 32, and that the pair of first groove portions 3221a and 3221b overlap in the tire width direction. The lower limit increases the edge component of the middle land portion 32, while the upper limit ensures the rigidity of the middle land portion 32.

[0092] 6, the pair of first grooves 3221a, 3221b have a linear or arcuate shape as a whole. The pair of first grooves 3221a, 3221b may have partially bent or curved portions near their ends.

[0093] For example, in the configuration shown in Fig. 6, the pair of first groove portions 3221a, 3221b have short bent portions (reference numerals omitted in the figure) near the openings (end points E22a, E22a) to the left and right main grooves 21, 22 to connect approximately perpendicularly (90±5 degrees) to the edge portions of the middle land portion 32. The extension length De22 (reference numerals omitted in the figure) of the bent portions in the tire width direction, relative to the contact width Wb2 of the middle land portion 32, is in the range of 0.05≦De22 / Wb2≦0.20, and preferably in the range of 0.06≦De22 / Wb2≦0.15. The extension length De22 of the bent portions is in the range of 2.0 mm≦De22≦5.0 mm.

[0094] 6, the second groove portion 3222 extends mainly in the tire circumferential direction and connects the pair of first groove portions 3221a, 3221b. The inclination angle δ2 of the second groove portion 3222 with respect to the tire circumferential direction is in the range of −30 degrees≦δ2≦30 degrees, and preferably in the range of 0 degrees≦δ2≦15 degrees.

[0095] The inclination angle δ2 of the second groove portion 3222 is measured as the angle between the tire circumferential direction and an imaginary line passing through the end points E22b, E22b of the second groove portion 3222. The inclination angle δ2 is defined as positive in the direction in which the pair of first groove portions 3221a, 3221b overlap each other in the tire width direction.

[0096] As described above, the end points E22b, E22b of the second groove portion 3222 are defined as bending points of an imaginary straight line when the entire second middle narrow groove 322 is approximated by an imaginary straight line bent in a Z shape.

[0097] 6, the inclination angle θ2 (θ2a, θ2b) of the second groove portion 3222 relative to the pair of first groove portions 3221a, 3221b is in the range of 50 degrees ≦ θ2 ≦ 90 degrees, and preferably in the range of 60 degrees ≦ θ2 ≦ 80 degrees. Therefore, it is preferable that the second groove portion 3222 is connected to the pair of first groove portions 3221a, 3221b at an acute inclination angle θ2. It is also preferable that the inclination angles θ2a, θ2b of the second groove portion 3222 are in the range of 0 degrees ≦ |θ2a-θ2b| ≦ 10 degrees, and that the two angles are approximately equal.

[0098] As described above, the inclination angle θ2 (θ2a, θ2b) is defined as the bending angle of an imaginary straight line when the entire second middle thin groove 322 is approximated by the imaginary straight line bent in a Z shape.

[0099] 6, the circumferential extension length Ls22 of the second groove portion 3222 is in the range of 0.10≦Ls22 / Wb2≦0.50, and preferably 0.20≦Ls22 / Wb2≦0.40, relative to the contact patch width Wb2 of the middle land portion 32. The lower limit ensures the circumferential component of the second groove portion 3222 and ensures the snow performance of the tire, while the upper limit ensures the rigidity of the middle land portion 32 and ensures the low rolling resistance of the tire.

[0100] The extension length Ls22 of the second groove portion 3222 is measured as the distance between the end points E22b, E22b of the second groove portion 3222 in the tire circumferential direction.

[0101] 6, the second groove 3222 has a linear or S-shape as a whole. The second groove 3222 is connected to the pair of first grooves 3221a and 3221b by smooth arc-shaped bends.

[0102] Fig. 8 is an enlarged view of the center main groove 22 shown in Fig. 3. The drawing shows the openings of the first and second middle narrow grooves 321, 322 of the middle land portion 32 relative to the center main groove 22, and the opening of the first center narrow groove 331 of the center land portion 33.

[0103] 2, in the middle land zone 32 and the center land zone 33 adjacent to each other with a single center main groove 22 in between, the pitch number N31 of the first center narrow groove 331 opening into the center main groove 22 is equal to the pitch number N21 of the first middle narrow groove 321. In addition, the pitch number N21 of the first middle narrow groove 321 is in the range of 30≦N21≦50.

[0104] As shown in FIG. 3, the first middle narrow groove 321 of the middle land portion 32 and the first center narrow groove 331 of the center land portion 33 are inclined in the same direction with respect to the tire width direction. The first center narrow groove 331 is located on an extension of the groove centerline of the first middle narrow groove 321. Specifically, as shown in FIG. 8, an intersection point R21 between an imaginary line passing through both end points E21a and E21b (see FIG. 6) of the first middle narrow groove 321 and the groove centerline of the center main groove 22 is defined. An intersection point R31 between an imaginary line passing through both end points E31a and E31b (see FIG. 4) of the first center narrow groove 331 and the groove centerline of the center main groove 22 is defined. In this case, the tire circumferential distance DR between the intersection points R21 and R31 is in the range of 0≦|DR| / Ps21≦0.30 with respect to the pitch length Ps21 (see FIG. 3) of the first middle narrow groove 321. This improves the snow removal effect at the opening positions of the first middle narrow groove 321 and the first center narrow groove 331, thereby improving the snow performance of the tire.

[0105] 3, the middle land portion 32 includes the first middle narrow groove 321, the second middle narrow groove 322, and the multi-sipes 4 described below, but does not include any other lateral grooves that open when the tire is in contact with the ground, specifically, lateral grooves with a groove width exceeding 1.5 mm and a groove length exceeding 10 mm. This ensures a sufficient contact area for the middle land portion 32.

[0106] [Shoulder land area] As shown in Figure 2, the shoulder land portion 31 is a rib with a circumferentially continuous tread surface, and does not have any other grooves or sipes that penetrate the shoulder land portion 31 in the widthwise direction of the tire. As described above, the shoulder land portion 31 has a contact width Wb1 that is wider than the contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33. This ensures the rigidity of the shoulder land portion 31 and reduces the rolling resistance of the tire.

[0107] As shown in Fig. 2, the shoulder land portion 31 has a closed decorative groove 311 that terminates within the shoulder land portion 31. The decorative groove 311 has a groove depth of less than 1.0 mm. A plurality of decorative grooves 331 are arranged at predetermined intervals in the tire circumferential direction. In the configuration shown in Fig. 2, the decorative groove 311 has a triangular shape whose groove width increases from the leading side to the trailing side in the tire rotation direction.

[0108] 2, the shoulder land portion 31 has the decorative grooves 331 and the multi-sipes 4 described below, but does not have any other lateral grooves that open when the tire is in contact with the ground, specifically, lateral grooves with a groove width exceeding 1.5 mm and a groove length exceeding 10 mm. This ensures that the shoulder land portion 31 has a sufficient contact area.

[0109] [Multi-sipe] In the configuration of FIG. 2, each of the shoulder land portion 31, the middle land portion 32, and the center land portion 33 includes a plurality of multi-sipes 4 (reference numerals omitted in FIG. 2; see FIGS. 4 and 6).

[0110] The multi-sipes 4 are short sipes that open at one end to the edge of the land portions 31-33 and terminate at the other end inside the land portions 31-33, and are closed when the tire is in contact with the ground. The multi-sipes 4 have a width Wm (symbols omitted in the figures) of 0.3 mm to 1.5 mm, a depth Hm (see Figures 5 and 7) of 2.0 mm to 17 mm, and a length Lm (see Figure 4) of 2.0 mm to 10 mm. A plurality of multi-sipes 4 are arranged in the tire circumferential direction along the edges of the land portions 31-33. The pitch length of the multi-sipes 4 (symbols omitted in the figures) is in the range of 0.1% to 0.6% of the tire circumference. In this configuration, the multi-sipes 4 reduce the ground contact pressure at the edges of the land portions, suppressing uneven wear (particularly river wear) of the land portions.

[0111] The width of the multi-sipe 4 is measured as the opening width of the sipe on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

[0112] The depth of the multi-sipe 4 is measured as the distance from the tread surface to the bottom of the sipe when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In addition, if the sipe has a partial bottom top or an uneven portion at the sipe bottom, the sipe depth is measured excluding these.

[0113] [Bottom sipes] 3, at least a portion of the first and second middle narrow grooves 321, 322 in the middle land portion 32 and at least a portion of the first and second center narrow grooves 331, 332 in the center land portion 33 may have groove bottom sipes (not shown). The groove bottom sipes have a width of 0.3 mm to 1.5 mm and a depth of 6.0 mm to 11 mm, and are closed when the tire is in contact with the ground. This improves snow removal from the land portions 32, 33.

[0114] The width and depth of the groove bottom sipe are measured as the width at the groove bottom of the narrow groove and the depth from the groove bottom of the narrow groove.

[0115] [effect] As described above, the tire 1 includes a pair of shoulder main grooves 21 and two or more center main grooves 22, a pair of shoulder land portions 31 defined by the shoulder main grooves 21 and the center main groove 22, a pair of middle land portions 32, and one or more center land portions 33 (see FIG. 2). At least one of the middle land portions 32 includes a first middle narrow groove 321 having a straight or arc-shaped configuration and penetrating the middle land portion 32, and a second middle narrow groove 322 having a Z-shape and penetrating the middle land portion 32 (see FIG. 3). The first middle narrow grooves 321 and the second middle narrow grooves 322 are arranged alternately in the tire circumferential direction. The center land portion 33 includes a first center narrow groove 331 having one end connected to the edge of the center land portion 33 and connected to the center main groove 22, and the other end within the center land portion 33, and a second center narrow groove 332 extending in the tire circumferential direction and having both ends within the center land portion 33. The first central narrow groove 331 is inclined in one direction in the tire circumferential direction from the one end toward the other end. The first central narrow groove 331 and the second central narrow groove 332 are arranged in a V-shape with their peaks facing in one direction in the tire circumferential direction.

[0116] In this configuration, (1) the middle land portion 32 has the second middle narrow groove 322 with a Z-shape, which increases the edge component of the middle land portion 32 compared to a configuration (not shown) in which all through-thick narrow grooves are linear or arc-shaped, improving the tire's snow performance. Also, (2) the center land portion 33 has the first and second center narrow grooves 331, 332 arranged in a V-shape, which ensures the rigidity of the center land portion 33 and reduces the tire's rolling resistance compared to a configuration in which the center land portion 33 has through-thick narrow grooves. Furthermore, the first and second center narrow grooves 331, 332 arranged in a V-shape ensure edge components in both the tire circumferential direction and the tire width direction, improving both the tire's snow acceleration performance and skid resistance. These advantages result in a tire that combines snow performance with low rolling resistance.

[0117] In the tire 1, the second middle narrow groove 322 is composed of a pair of first groove portions 3221a, 3221b extending in the tire width direction and opening into the shoulder main groove 21 and the center main groove 22, respectively, and a second groove portion 3222 extending in the tire circumferential direction and connecting the pair of first groove portions 3221a, 3221b (see FIG. 6). The circumferential extension length Ls22 of the second groove portion 3222 is in the range of 0.10≦Ls22 / Wb2≦0.50, where Wb2 is the contact width of the middle land portion 32. The lower limit ensures the circumferential component of the second groove portion 3222, thereby ensuring the snow performance of the tire, while the upper limit ensures the rigidity of the middle land portion 32, thereby ensuring low rolling resistance of the tire.

[0118] In the tire 1, the second middle narrow groove 322 is composed of a pair of first groove portions 3221a, 3221b extending in the tire width direction and opening into the shoulder main groove 21 and the center main groove 22, respectively, and a second groove portion 3222 extending in the tire circumferential direction and connecting the pair of first groove portions 3221a, 3221b (see FIG. 6). The extension lengths Ds22a, Ds22b of the pair of first groove portions 3221a, 3221b, relative to the contact width Wb2 of the middle land portion 32, are in the range of 0.70≦(Ds22a+Ds22b) / Wb2≦1.30. The lower limit increases the edge component of the middle land portion 32, while the upper limit ensures the rigidity of the middle land portion 32.

[0119] In addition, in this tire 1, the center land portion 33 is a rib having a circumferentially continuous tread surface (see FIG. 3). This configuration has the advantage of ensuring the rigidity of the center land portion 33 and reducing the rolling resistance of the tire, compared to a configuration (not shown) in which the center land portion is a row of blocks divided in the circumferential direction by through-hole lateral grooves.

[0120] In addition, in the tire 1, the extension length Ds31 of the first central narrow groove 331 in the tire width direction is in the range of 0.30≦Ds31 / Wb3≦0.70 relative to the contact width Wb3 of the center land portion 33 (see FIG. 4). The lower limit ensures the edge component of the first central narrow groove 331, while the upper limit has the advantage of suppressing a decrease in rigidity of the center land portion 33 caused by the first central narrow groove 331 being too long.

[0121] In addition, in this tire 1, in the middle land portion 32 and the center land portion 33 adjacent to each other across the center main groove 22, the number of pitches of the first center narrow grooves 331 opening into the center main groove 22 is equal to the number of pitches of the first middle narrow grooves 321 (see FIG. 2).

[0122] In the tire 1, the groove width Ws21 of the first middle narrow groove 321 (see FIG. 6) and the groove width Ws31 of the first center narrow groove 331 (see FIG. 4) are in the range of 1.5 mm to 3.0 mm. The lower limit ensures the edge action of the narrow grooves 321, 331 on snowy roads, while the upper limit has the advantage of suppressing a decrease in rigidity of the land portions 32, 33 caused by an excessively large groove width.

[0123] In addition, in this tire 1, the first middle narrow groove 321 and the first center narrow groove 331 are inclined in the same direction with respect to the tire width direction (see FIG. 3).

[0124] In addition, in this tire 1, the first central narrow groove 331 is located on an extension of the groove center line of the first middle narrow groove 321 (see FIG. 8 ). This has the advantage of improving the snow removal effect at the opening positions of the first middle narrow groove 321 and the first central narrow groove 331, thereby improving the snow performance of the tire.

[0125] In addition, in this tire 1, the shoulder land portion 31 is a rib having a circumferentially continuous tread surface, which has the advantage of ensuring the rigidity of the shoulder land portion 31 and reducing the rolling resistance of the tire.

[0126] In addition, in the tire 1, the contact width Wb2 of the middle land portion 32 is in the range of 0.70≦Wb2 / Wb1≦0.85 relative to the contact width Wb1 of the shoulder land portion 31. With this configuration, the shoulder land portion 31 has a wide structure, which has the advantage of ensuring the rigidity of the shoulder land portion 31 and effectively suppressing uneven wear of the shoulder land portion 31.

[0127] The tire 1 also includes a display (not shown) that specifies the tire rotation direction (see FIG. 2). The first center narrow groove 331 is inclined in the tire rotation direction from the one end toward the other end (see FIG. 4). This optimizes the inclination direction of the first center narrow groove 331, i.e., the orientation of the V-shapes of the first and second center narrow grooves 331, 332, which has the advantage of optimizing the snow performance improvement effect of the first and second center narrow grooves 331, 332.

[0128] Applies to The tire 1 is a heavy-duty tire mounted on the steering axle of a vehicle. By applying the present invention to such a tire, it is possible to effectively improve the snow performance and low rolling resistance of the tire.

[0129] In addition, in this embodiment, as described above, a pneumatic tire has been described as an example of a tire. However, the present invention is not limited to this, and the configuration described in this embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires. [Example]

[0130] 9 and 10 are tables showing the results of performance tests on the tire 1 according to the embodiment of the present invention.

[0131] In this performance test, several types of test tires were evaluated for (1) snow acceleration performance, (2) skid resistance performance, and (3) low rolling resistance performance. Furthermore, the test tires, measuring 315 / 70R22.5 in size, were mounted on ETRTO-specified rims, and the test tires were subjected to the ETRTO-specified internal pressure and load. The test tires were also mounted on a 2-D tractor head test vehicle.

[0132] (1) Snow acceleration performance is evaluated by measuring the distance required for acceleration from a specified initial velocity to a specified terminal velocity under test conditions in accordance with ECE (Economic Commission for Europe) Regulation R117-2 (Regulation No. 117 Revision 2). Based on these measurement results, an index rating is calculated, with the comparative example being assigned a standard of 100. The higher the rating, the better. A rating of 98 or higher indicates adequate performance.

[0133] (2) In the evaluation of skid resistance, the test vehicle is driven on a snowy road at a speed of 25 km / h, and a sensory evaluation is conducted by the test driver. Based on the measurement results, an index rating is then given, with the comparative example being assigned a standard value of 100. The higher the rating, the better.

[0134] (3) For the evaluation of low rolling resistance performance, a drum testing machine with a drum diameter of 1707 mm is used to measure the resistance force at a load of 33.34 kN and a speed of 80 km / h. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the better.

[0135] The test tire of the example is based on the configuration shown in Figures 1 and 2, with the middle land portion 32 including first and second middle narrow grooves 321, 322, and the center land portion 33 including first and second center narrow grooves 331, 332 arranged in a V-shape. Groove units consisting of the first and second center narrow grooves 331, 332 are arranged in a staggered pattern around the tire circumferential direction. The shoulder main grooves 21 have a groove width Wg1 of 10.1 mm and a groove depth Hg1 of 12.1 mm. The center main groove 22 has a groove width Wg2 of 10.1 mm and a groove depth Hg2 of 12.1 mm. The tire ground contact width TW is 268 mm, the shoulder land portion 31 has a ground contact width Wb1 of 48.7 mm, the middle land portion 32 has a ground contact width Wb2 of 43.4 mm, and the center land portion 33 has a ground contact width Wb3 of 43.4 mm. Each of the first and second middle narrow grooves 321, 322 and the first and second center narrow grooves 331, 332 has a groove width of 2.0 mm and a groove depth of 1.5 mm.

[0136] In the comparative example test tire, in the configuration shown in Figure 2, the center land portion 33 does not have a second center narrow groove 332 extending circumferentially, and all of the first center narrow grooves 331 penetrate the center land portion 33 in the tire width direction, so that the total number of narrow grooves penetrating the center land portion is equal to the total number of the first and second middle narrow grooves 321, 322.

[0137] As the test results show, the test tires of the examples exhibit good snow acceleration performance, skid resistance, and low rolling resistance all at the same time. [Explanation of symbols]

[0138] 1 tire; 11 bead core; 12 bead filler; 121 lower filler; 122 upper filler; 13 carcass layer; 14 belt layer; 141 high angle belt; 142, 143 cross belt; 144 belt cover; 15 tread rubber; 16 sidewall rubber; 17 rim cushion rubber; 21 shoulder main groove; 22 center main groove; 31 shoulder land portion; 32 middle land portion; 321 first middle narrow groove; 322 second middle narrow groove; 3221a, 3221b first groove portion; 3222 second groove portion; 33 center land portion; 331 first center narrow groove; 332 second center narrow groove; 4 multi-sipe

Claims

1. A tire comprising a pair of shoulder main grooves and two or more center main grooves, and a pair of shoulder land portions, a pair of middle land portions, and one or more center land portions defined by the shoulder main grooves and the center main groove, At least one of the middle land portions has a first middle narrow groove having a straight or arcuate shape and penetrating the middle land portion, and a second middle narrow groove having a Z-shape and penetrating the middle land portion, the first middle narrow grooves and the second middle narrow grooves are alternately arranged in the tire circumferential direction, the center land portion includes a first center narrow groove having one end connected to the center main groove at an edge portion of the center land portion and the other end within the center land portion, and a second center narrow groove extending in the tire circumferential direction and having both ends within the center land portion, the first center narrow groove is inclined in one direction in the tire circumferential direction from the one end toward the other end, and The tire is characterized in that the first center narrow groove and the second center narrow groove are arranged in a V-shape with an apex facing in one direction in the tire circumferential direction.

2. the second middle narrow groove comprises a pair of first groove portions extending in the tire width direction and opening into the shoulder main groove and the center main groove, respectively, and a second groove portion extending in the tire circumferential direction and connecting the pair of first groove portions; and 2. The tire according to claim 1, wherein an extension length Ls22 of the second groove portion in the tire circumferential direction, relative to a contact width Wb2 of the middle land portion, is in a range of 0.10≦Ls22 / Wb2≦0.

50.

3. the second middle narrow groove comprises a pair of first groove portions extending in the tire width direction and opening into the shoulder main groove and the center main groove, respectively, and a second groove portion extending in the tire circumferential direction and connecting the pair of first groove portions; and 3. The tire according to claim 1, wherein the extension lengths Ds22a, Ds22b of the pair of first groove portions are in a range of 0.70≦(Ds22a+Ds22b) / Wb2≦1.30 relative to the contact width Wb2 of the middle land portion.

4. The tire according to any one of claims 1 to 3, wherein the center land portion is a rib having a tread surface that is continuous in the tire circumferential direction.

5. The tire according to any one of claims 1 to 4, wherein an extension length Ds31 of the first center narrow groove in the tire width direction, relative to a contact width Wb3 of the center land portion, is in a range of 0.30≦Ds31 / Wb3≦0.

70.

6. 6. The tire according to claim 1, wherein, in the middle land portion and the center land portion adjacent to each other across the center main groove, the number of pitches of the first center narrow groove opening into the center main groove is equal to the number of pitches of the first middle narrow groove.

7. The tire according to any one of claims 1 to 6, wherein the groove width of the first middle narrow groove and the groove width of the first center narrow groove are in the range of 1.5 mm to 3.0 mm.

8. The tire according to any one of claims 1 to 7, wherein the first middle narrow groove and the first center narrow groove are inclined in the same direction with respect to the tire width direction.

9. The tire according to any one of claims 1 to 8, wherein the first center narrow groove is located on an extension of the groove center line of the first middle narrow groove.

10. The tire according to any one of claims 1 to 9, wherein the shoulder land portion is a rib having a tread surface that is continuous in the tire circumferential direction.

11. The tire according to any one of claims 1 to 10, wherein a ground contact width Wb2 of the middle land portion is in a range of 0.70≦Wb2 / Wb1≦0.85 relative to a ground contact width Wb1 of the shoulder land portion.

12. The tire according to any one of claims 1 to 11, further comprising an indicator portion for designating a tire rotation direction, and the first center narrow groove is inclined in the tire rotation direction from the one end portion toward the other end portion.

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