tire

Abstract

To provide a tire that can make both low rolling resistance performance and wet performance of the tire compatible.SOLUTION: The tire comprises a plurality of circumferential grooves 21 and 22 extending in a tire circumferential direction and a plurality of land parts 32 and 33 partitioned by the circumferential grooves 21 and 22. At least the circumferential groove 22 comprises tie-bars 5 formed on groove bottoms of the circumferential groove 22 and connecting the land parts 32 and 33 which are adjacent to each other across the circumferential groove 22 to each other. The tie-bars 5 have slits 51 that penetrate, in the tire circumferential direction, through the tie-bars 5 and block the tie-bars when the tire contacts the ground. The slits 51 have inclining parts inclining with respect to the tire circumferential direction in a planar view of a tread.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 low rolling resistance performance and wet performance. [Background technology]

[0002] In recent years, a configuration in which tie bars are arranged in the circumferential grooves has been adopted to reduce the rolling resistance of tires. On the other hand, there is also the issue of ensuring the wet performance of the tire. As a conventional tire that addresses this issue, the technology described in Patent Document 1 is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6162939 Summary of the Invention [Problem to be solved by the invention]

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

[0005] In order to achieve the above object, a tire according to the present invention includes a plurality of circumferential grooves extending in a tire circumferential direction and a plurality of land portions partitioned by the circumferential grooves, at least one of the circumferential grooves includes a tie bar formed in a groove bottom of the circumferential groove and crossing the circumferential groove to connect adjacent land portions, the tie bar having a slit penetrating the tie bar in the tire circumferential direction and closed when the tire is in contact with the ground. death, The center line of the slit has an inclined portion that is inclined with respect to the tire circumferential direction in a plan view of the tread. and both ends of the slit are offset from each other in the tire width direction. It is characterized by: Effect of the Invention

[0006] In the tire according to the present invention, (1) the circumferential groove is provided with a tie bar connecting adjacent land portions, so that the rigidity of the land portions when the tire is in contact with the ground is reinforced by the tie bar, and the rolling resistance of the tire is reduced. Also, (2) the tie bar has a slit, so that the decrease in drainage performance of the circumferential groove caused by the installation of the tie bar is suppressed. Also, (3) the slit is closed when the tire is in contact with the ground, so that the reinforcing effect of the tie bar on the rigidity of the land portions is ensured. Also, (4) the slit has an inclined portion inclined with respect to the tire circumferential direction, so that when the slit is closed, the wall surface of the slit has an engagement component in both the tire width direction and the tire circumferential direction. This improves the reinforcing effect of the tie bar on the rigidity of the land portions. These have the advantage that the tire has both low rolling resistance performance and wet performance. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing a tread surface of the tire shown in FIG. [Diagram 3] FIG. 3 is an enlarged plan view showing the middle land portion and the center land portion of the tire illustrated in FIG. [Figure 4] FIG. 4 is an enlarged plan view showing the middle land portion shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view showing the middle land portion and the center land portion shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing the non-through lug groove of the middle land portion shown in FIG. [Figure 7] FIG. 7 is an enlarged plan view showing the center land portion shown in FIG. [Figure 8] FIG. 8 is a plan view showing the tie bar of the center groove shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view in the width direction of the tie bar shown in FIG. [Figure 10] FIG. 10 is a circumferential cross-sectional view of the tie bar depicted in FIG. [Figure 11] FIG. 11 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 12] FIG. 12 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 13] FIG. 13 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 14] FIG. 14 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 15] FIG. 15 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 16] FIG. 16 is an enlarged plan view showing the shoulder main groove shown in FIG. [Figure 17] FIG. 17 is a cross-sectional view taken along line A of the shoulder main groove shown in FIG. [Figure 18] FIG. 18 is a cross-sectional view taken along line B of the shoulder main groove shown in FIG. [Figure 19] FIG. 19 is an explanatory diagram showing a test tire of a comparative example. [Figure 20] FIG. 20 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. [Figure 21] FIG. 21 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

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

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

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

[0013] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally stretched between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wrapped around and secured to the outside in the tire width direction so as to envelop the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction relative to the tire circumferential direction) of 80 degrees or more and 90 degrees or less in the case of a radial tire, and 30 degrees or more and 45 degrees or less in the case of a bias tire.

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

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

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

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

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

[0019] The shoulder main groove 21 has a groove width Wg1 of 5.0 mm or more (see FIG. 2) and a groove depth Hg1 of 10 mm or more (see FIG. 5 described later). The center groove 22 has a groove width Wg2 of 5.0 mm or more (see FIG. 2) and a groove depth Hg2 of 10 mm or more (see FIG. 5 described later). The groove width Wg2 of the center groove 22 is in the range of 0.20≦Wg2 / Wg1≦1.00 with respect to the groove width Wg1 of the shoulder main groove 21, and preferably in the range of 0.25≦Wg2 / Wg1≦0.40. The groove depth Hg2 of the center groove 22 is in the range of 0.70≦Hg2 / Hg1≦1.30 with respect to the groove depth Hg1 of the shoulder main groove 21. In the configuration of Fig. 2, the center groove 22 is a main groove that is required to display a wear indicator as stipulated by JATMA, and has a groove width Wg2 narrower than the groove width Wg1 of the shoulder main groove 21 and the same groove width Wg2 as the shoulder main groove 21. This ensures drainage in the center region of the tread and increases its rigidity.

[0020] The groove width is measured as the maximum distance between the opposing groove walls at the groove opening on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured at the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction.

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

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

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

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

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

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

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

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

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

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

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

[0032] In the configuration of FIG. 2, the land portions 31-33 have a plurality of multi-sipes 4. The multi-sipes 4 are short sipes that open at one end to the edge portion of the land portion 31-33 and terminate at the other end inside the land portion 31-33, and have a width of 0.3 mm to 1.5 mm, a depth of 2.0 mm to 17 mm, and a length of 2.0 mm to 10 mm (dimension symbols are omitted in the figure). The plurality of multi-sipes are arranged in the tire circumferential direction along the edge portion on the circumferential grooves 21 and 22 side. The pitch length of the multi-sipes 4 is in the range of 0.1% to 0.6% of the tire circumference. In this configuration, the multi-sipes 4 reduce the rigidity of the land portions 31-33, thereby reducing the ground contact pressure of the edge portions of the land portions 31-33 when the tire is in contact with the ground. This suppresses the occurrence of uneven wear (particularly river wear), improving the uneven wear resistance of the tire.

[0033] [Middle land area] Fig. 3 is an enlarged plan view showing the middle land portion 32 and the center land portion 33 of the tire 1 shown in Fig. 2. Fig. 4 is an enlarged plan view showing the middle land portion 32 shown in Fig. 3. Fig. 5 is a cross-sectional view showing the middle land portion 32 and the center land portion 33 shown in Fig. 3. This figure shows a cross-sectional view of the land portions 32, 33 cut along the thin through-grooves 321, 331. Fig. 6 is a cross-sectional view showing the non-through lug groove 323 of the middle land portion 32 shown in Fig. 3. This figure shows a cross-sectional view perpendicular to the groove length direction of the non-through lug groove 323.

[0034] As shown in FIGS. 2 and 3, the middle land portion 32 includes a plurality of thin through-grooves 321, a plurality of middle blocks 322, and a plurality of non-through-grooves 323.

[0035] As shown in FIG. 3, the thin through groove 321 penetrates the middle land portion 32 in the tire width direction and connects to the left and right circumferential grooves 21, 22. A plurality of thin through grooves 321 are arranged at a predetermined interval in the tire circumferential direction. The inclination angle θ21 (see FIG. 3) of the thin through groove 321 with respect to the tire circumferential direction is in the range of 45 [deg]≦θ21≦90 [deg]. The groove width W21 (see FIG. 4) of the thin through groove 321 is in the range of 0.4 [mm]≦W21≦1.5 [mm]. The groove depth H21 (see FIG. 5) of the thin through groove 321 is in the range of 0.30≦H21 / Hg2≦1.00 with respect to the groove depth Hg2 of the center groove 22, and preferably in the range of 0.40≦H21 / Hg2≦0.70. It is also preferable that the thin through grooves 321 are sipes having a groove width W21 of 1.5 mm or less and a groove depth H21 of more than 2.0 mm, so that they are closed when the tire comes into contact with the ground.

[0036] The inclination angle of the groove is measured as the inclination angle of an imaginary line passing through both ends of the groove with respect to the circumferential direction of the tire when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and under no load.

[0037] In addition, in FIG. 4, the through-thin groove 321 has a wavy shape with a wave number of three or more. In the configuration of FIG. 4, the through-thin groove 321 has a wavy shape consisting of eight curved points, and thus has four wave numbers. In this configuration, compared to a configuration (not shown) having a straight or arc-shaped through-thin groove, the wet traction of the middle land portion 32 can be improved while maintaining the rigidity of the middle block 322. In addition, the wavelength λ21 of the wavy shape of the through-thin groove 321 is in the range of 0.10≦λ21 / Wb2≦0.50 with respect to the contact width Wb2 of the middle land portion 32. In addition, the amplitude A21 of the wavy shape of the through-thin groove 321 is in the range of 0.6 [mm]≦A21≦2.5 [mm].

[0038] The wave shape of the groove and its wave number, wavelength and amplitude are determined by the wave shape of the groove centerline in a plan view of the tread. The groove centerline is defined as an imaginary line connecting the midpoints of the groove widths.

[0039] As shown in FIG. 2 and FIG. 3, the middle block 322 is divided into adjacent through-grooves 321, 321. A plurality of middle blocks 322 are arranged in a row in the tire circumferential direction. The circumferential length Le2 of the edge portion of the middle block 322 on the center groove 22 side is in the range of 0.80≦Le2 / Wb2′≦1.80 with respect to the ground contact width Wb2′ of the middle block 322, and preferably in the range of 1.10≦Le2 / Wb2′≦1.50. Therefore, it is preferable that the aspect ratio of the middle block 322 is set so that the middle block 322 is elongated in the tire circumferential direction. In this configuration, the block rigidity in the tire circumferential direction is ensured, and uneven wear of the middle block 322 is effectively suppressed, compared to a configuration in which the middle block is elongated in the tire width direction (not shown).

[0040] The circumferential length Le2 of the edge portion is measured as the distance in the tire circumferential direction of the edge portion facing the center groove 22 when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and unloaded. In a configuration in which the corners of the middle block 322 have chamfered portions, the circumferential length Le2 is measured with the intersection point of the ridgeline of the edge portion of the middle land portion 32 on the tread surface and the ridgeline of the groove opening of the through-thin groove 321 as the endpoint.

[0041] 4, an edge portion of the middle block 322 on the side of the center groove 22 has an arc shape that protrudes toward the tire equatorial plane CL. That is, an edge portion of the middle block 322 on the side of the center groove 22 protrudes toward the tire equatorial plane CL in a region between adjacent thin through-grooves 321, 321, and has an arc shape having a center within the middle block 322 as a whole. The thin through-groove 321 connects to the center groove 22 at a position of maximum amplitude of the wavy shape of the center groove 22 toward the tire ground contact edge T (see FIG. 2).

[0042] In the above configuration, (1) the middle blocks 322 of the middle land portion 32 are partitioned by narrow through-hole grooves 321, so that the rigidity of the middle blocks 322 in the tire circumferential direction can be increased compared to a configuration (not shown) in which the middle blocks are partitioned by wide through-hole lug grooves. This makes it possible to suppress uneven wear of the middle blocks 322 while ensuring the drainage effect of the through-hole grooves 321. In addition, (2) the edge portion of the middle block 322 on the center groove 22 side has an arc shape that is convex toward the tire equatorial plane CL, so that the rigidity of the middle block 322 in the tire width direction is increased and uneven wear of the middle block 322 is suppressed compared to a configuration (not shown) in which the middle block has a concave edge portion. In addition, (3) the middle block 322 has non-through-hole lug grooves 323 that open only to the edge portion on the tire equatorial plane CL side, so that the drainage of the tread center region can be improved while ensuring the rigidity of the middle block 322. As a result, it is possible to achieve both uneven wear resistance and wet performance of the tire.

[0043] Also, in Figure 4, the maximum convex position of the edge portion of the middle block 322 toward the tire equatorial plane CL (the measurement point of the contact width Wb2' of the middle block 322; symbol omitted in the figure) is in the center of the edge portion, specifically, at a distance of 35% to 65% from one end of the circumferential length Le2 of the edge portion.

[0044] In addition, in FIG. 4, the circumferential length La2 of the arc shape of the edge portion is in the range of 0.50≦La2 / Le2≦1.00 relative to the circumferential length Le2 of the edge portion of the middle block 322, and preferably in the range of 0.90≦La2 / Le2≦1.00.

[0045] The circumferential length La2 of the arc shape is measured as the distance between adjacent inflection points of the wavy shape of the center groove 22, including the maximum convex position of the edge portion of the middle block 322.

[0046] For example, in the configuration of Fig. 2, the wavy shape of the center groove 22 has a continuous arch shape formed by connecting multiple long arcs that are convex toward the tire equatorial plane CL. In addition, the thin through grooves 321 connect to the connecting positions of adjacent arcs, i.e., to both ends of one arc. Therefore, the entire edge portion of the middle block 322 on the center groove 22 side is formed of a single arc, and the above-mentioned ratio La2 / Le2 is 1.00.

[0047] 4, the convexity Pe2 of the edge of the middle block 322 toward the tire equatorial plane CL is in the range of 0.02≦Pe2 / Wb2′≦0.20, preferably 0.05≦Pe2 / Wb2′≦0.12, relative to the ground contact width Wb2′ of the middle block 322. The convexity Pe2 is preferably in the range of 1.0 [mm]≦Pe2. The lower limit ensures the convexity of the edge of the middle block 322, appropriately reinforces the rigidity of the middle block 322, and suppresses uneven wear of the middle block 322. The upper limit suppresses uneven wear of the middle block 322 caused by the convexity of the edge being excessive.

[0048] As shown in FIG. 3, the non-through lug groove 323 opens at one end to an edge portion of the middle block 322 on the tire equatorial plane CL side, and terminates at the other end at the center of the middle block 322. A plurality of non-through lug grooves 323 are arranged at predetermined intervals in the tire circumferential direction. The extension length L23 of the non-through lug groove 323 in the tire width direction is in the range of 0.40≦L23 / Wb2′≦0.90 with respect to the ground contact width Wb2′ of the middle block 322, and preferably in the range of 0.50≦L23 / Wb2′≦0.80. The lower limit ensures the drainage function of the non-through lug groove 323, and the upper limit ensures the rigidity of the middle block 322. For example, in the configuration of FIG. 3, the non-through lug groove 323 is connected to the center groove 22 at the maximum amplitude position of the wave-shaped shape of the center groove 22 toward the tire equatorial plane CL side. This ensures an extension length L23 of the non-through lug groove 323 in the tire width direction.

[0049] 3, the inclination angle θ23 of the non-through lug groove 323 with respect to the tire circumferential direction is in the range of -20[deg]≦θ21-θ23≦20[deg] with respect to the inclination angle θ21 of the through narrow groove 321, and preferably in the range of -10[deg]≦θ21-θ23≦10[deg]. Therefore, the non-through lug groove 323 extends approximately parallel to the through narrow groove 321. Also, in FIG. 4, the groove width W23 of the non-through lug groove 323 is in the range of 1.50≦W23 / W21≦5.50 with respect to the groove width W21 of the through narrow groove 321, and preferably in the range of 2.00≦W23 / W21≦4.00. Also, the groove width W23 of the non-through lug groove 323 is in the range of 1.5[mm]≦W23≦5.0[mm].

[0050] In addition, in FIG. 5, the groove depth H23 of the non-through lug groove 323 is in the range of 0.10≦H23 / Hg2≦0.30 with respect to the groove depth Hg2 of the center groove 22. In addition, the groove depth H23 of the non-through lug groove 323 is shallower than the groove depth H21 of the through narrow groove 321. In addition, in FIG. 6, the groove width W23 and the depth H23 of the non-through lug groove 323 have a relationship of 1.00≦W23 / H23≦1.50, and preferably have a relationship of 1.20≦W23 / H23≦1.50. Therefore, the non-through lug groove 323 has a shallow bottom and a wide structure. This can increase the rigidity of the middle block 322 while ensuring the drainage action of the non-through lug groove 323. In addition, in FIG. 6, the groove wall angle α23 of the non-through lug groove 323 is preferably in the range of 90 [deg]≦α23≦110 [deg].

[0051] In addition, in FIG. 4, the non-through lug grooves 323 have a wavy shape with two or more wave numbers. In addition, in the configuration of FIG. 4, the non-through lug grooves 323 have a wavy shape consisting of five curved points, and thus have two or three wave numbers. In this configuration, compared to a configuration (not shown) having straight or arc-shaped non-through lug grooves, the wet traction of the middle land portion 32 can be improved while maintaining the rigidity of the middle block 322. The wavelength λ23 of the wavy shape of the non-through lug grooves 323 is in the range of 0.70≦λ23 / λ21≦1.30 with respect to the wavelength λ21 of the wavy shape of the through-thin grooves 321, and preferably in the range of 0.90≦λ23 / λ21≦1.20. Furthermore, the amplitude A23 of the wavy shape of the non-through lug grooves 323 is in the range of 0.80≦A23 / A21≦1.50 relative to the amplitude A21 of the wavy shape of the thin through grooves 321, and preferably in the range of 1.20≦A23 / A21≦1.50.

[0052] [Center Land] FIG. 7 is an enlarged plan view showing the center land portion 33 shown in FIG.

[0053] As shown in FIG. 2 and FIG. 3, the central land portion 33 includes a plurality of thin through-grooves 331 and a plurality of central blocks 332. As shown in FIG.

[0054] As shown in FIG. 3, the thin through groove 331 penetrates the center land portion 33 in the tire width direction and connects to the left and right circumferential grooves 22, 22. A plurality of thin through grooves 331 are arranged at a predetermined interval in the tire circumferential direction. The inclination angle θ31 (see FIG. 3) of the thin through groove 331 with respect to the tire circumferential direction is in the range of 45 [deg]≦θ31≦90 [deg]. The groove width W31 (see FIG. 7) of the thin through groove 331 is in the range of 0.4 [mm]≦W31≦1.5 [mm]. The groove depth H31 (see FIG. 5) of the thin through groove 331 is in the range of 0.30≦H31 / Hg2≦1.00 with respect to the groove depth Hg2 of the center groove 22, and preferably in the range of 0.40≦H31 / Hg2≦0.70. It is also preferable that the thin through grooves 331 are sipes having a groove width W31 of 1.5 mm or less and a groove depth H31 of 2.0 mm or more, so that they are closed when the tire comes into contact with the ground.

[0055] 7, the thin through groove 331 has a wavy shape similar to the thin through groove 321 of the middle land portion 32 shown in FIG. 4. Specifically, the thin through groove 331 of the center land portion 33 has a wavy shape with a wave number of 3 or more, and the wavelength λ31 is in the range of 0.10≦λ31 / Wb3≦0.50 with respect to the contact width Wb3 of the center land portion 33. The amplitude A31 of the wavy shape of the thin through groove 331 is in the range of 0.7 [mm]≦A31≦2.5 [mm].

[0056] In the configuration of FIG. 2, the narrow through groove 331 of the center land portion 33 is inclined in the opposite direction to the narrow through groove 321 of the middle land portion 32 in the tire circumferential direction. This increases the rigidity of the center region of the tread portion. Furthermore, the narrow through groove 331 of the center land portion 33 and the narrow through grooves 321, 321 of the left and right middle land portions 32, 32 are inclined in the opposite direction to each other in the tire circumferential direction. In FIG. 3, the distance Dg in the tire circumferential direction between the connection portion of the narrow through groove 331 of the center land portion 33 to the center groove 22 and the connection portion of the narrow through groove 321 of the middle land portion 32 is in the range of 0≦Dg / P21≦0.40 with respect to the pitch length P21 of the narrow through groove 321 of the middle land portion 32. The distance Dg is preferably in the range of 0 [mm]≦Dg≦10 [mm]. Therefore, the communicating grooves consisting of the thin through groove 331 of the center land portion 33 and the thin through grooves 321, 321 of the left and right middle land portions 32, 32 have a zigzag shape with a large wavelength with the center groove 22 as the maximum amplitude position, and cross the tread center region to connect to the left and right shoulder main grooves 21, 21. This improves the drainage in the tread center region.

[0057] As shown in FIG. 2 and FIG. 3, the center block 332 is divided into adjacent through-grooves 331, 331. A plurality of center blocks 332 are arranged in a row in the tire circumferential direction. In FIG. 7, the circumferential length Le3 of the edge portion of the center block 332 is in the range of 0.80≦Le3 / Wb3′≦1.80 with respect to the contact width Wb3′ of the center block 332, and preferably in the range of 1.10≦Le3 / Wb3′≦1.50. Therefore, it is preferable that the aspect ratio of the center block 332 is set so that the center block 332 is long in the tire circumferential direction. In this configuration, the block rigidity in the tire circumferential direction is ensured and uneven wear of the block is suppressed compared to a configuration in which the center block is long in the tire width direction (not shown).

[0058] 7, the edge portion of the center block 332 has an arc shape recessed toward the tire equatorial plane CL. Specifically, the center block 332 is located on the tire equatorial plane CL, and the left and right edge portions of the center block 332 have an arc shape recessed in the width direction of the center block 332 in the region between the adjacent fine through-grooves 331. The fine through-groove 331 connects to the center groove 22 at the position of maximum amplitude of the wavy shape of the center groove 22 toward the tire ground contact edge T (see FIG. 2).

[0059] Also, in Figure 7, the maximum concave position of the edge portion of the center block 332 (the measurement point of the contact width Wb3' of the center block 332; symbol omitted in the figure) is located in the center of the edge portion, specifically, at a distance of 35% to 65% from one end of the circumferential length Le3 of the edge portion.

[0060] In addition, in FIG. 7, the circumferential length La3 of the arc shape of the edge portion is in the range of 0.50≦La3 / Le3≦1.00 relative to the circumferential length Le3 of the edge portion of the center block 332, and preferably in the range of 0.90≦La3 / Le3≦1.00.

[0061] For example, in the configuration of Fig. 2, the wavy shape of the center groove 22 has a continuous arch shape formed by connecting multiple long arcs that are convex toward the tire equatorial plane CL. Also, the thin through grooves 331 connect to the connecting positions of adjacent arcs, i.e., to both ends of one arc. Therefore, the entire edge of the center block 332 on the center groove 22 side is formed of a single arc, and the above-mentioned ratio La3 / Le3 is 1.00.

[0062] 7, the concave amount Pe3 of the edge portion of the center block 332 is in the range of 0.02≦Pe3 / Wb3′≦0.20 with respect to the ground contact width Wb3′ of the center block 332, and preferably in the range of 0.05≦Pe3 / Wb3′≦0.12. The concave amount Pe3 is preferably in the range of 1.0 [mm]≦Pe3. Therefore, the edge portion of the center block 332 has an arc shape that matches the arc shape of the edge portion of the middle block 322 described above.

[0063] 3, as described above, the connection portion of the thin through groove 331 of the center land portion 33 to the center groove 22 and the connection portion of the thin through groove 321 of the middle land portion 32 are located at approximately the same position in the tire circumferential direction, so that the wavy shape of the edge portion of the center land portion 33 is arranged in approximately the same phase as the wavy shape of the edge portion of the middle land portion 32. As a result, the concave edge portion of the center block 332 matches the convex edge portion of the middle block 322, and the groove width of the center groove 22 having a wavy shape is made uniform.

[0064] [Shoulder land area] As shown in Fig. 2, the shoulder land portion 31 is a rib having a circumferentially continuous tread surface. The shoulder land portion 31 has only the above-mentioned multi-sipes 4, and has no other grooves or sipes. This improves the uneven wear resistance of the shoulder land portion 31, which is prone to uneven wear. However, this is not limiting, and the shoulder land portion 31 may have shallow sipes or shallow grooves with a depth of 15 mm or less (not shown).

[0065] [Tie bar slits] Fig. 8 is a plan view showing the tie bar 5 of the center groove 22 shown in Fig. 2. Fig. 9 and Fig. 10 are a widthwise cross-sectional view (Fig. 9) and a circumferential cross-sectional view (Fig. 10) of the tie bar 5 shown in Fig. 8.

[0066] As shown in FIGS. 2 and 3, the center groove 22 includes a plurality of tie bars 5 .

[0067] The tie bar 5 is a rib-like protrusion formed on the bottom of the center groove 22, and connects adjacent land portions 32, 33 across the center groove 22. A plurality of tie bars 5 are arranged at a predetermined interval in the tire circumferential direction. The number of pitches of the tie bars 5 is equal to the number of pitches of the middle blocks 322 defined by the thin through grooves 321. In this configuration, the rigidity of the land portions 32, 33 when the tire is in contact with the ground is reinforced by the tie bars 5. In the configuration of FIG. 2, the center groove 22 has the tie bar 5. However, this is not limited to the above, and the shoulder grooves 5 may have the tie bars 5 (not shown).

[0068] 3, each of the middle land portion 32 and the center land portion 33 includes a plurality of through-thick grooves 321; 331 penetrating the land portions 32; 33, and a plurality of blocks 322; 332 partitioned by the through-thick grooves 321; 331. The tie bar 5 connects the middle block 322 of the middle land portion 32 to the center block 332 of the center land portion 33. The tie bar 5 is disposed between the adjacent through-thick grooves 321, 321; 331, 331 and connects to the blocks 322; 332. Therefore, the tie bar 5 is disposed offset in the tire circumferential direction with respect to the openings of the through-thick grooves 321, 331 of the land portions 32, 33. This ensures the rigidity of the tie bar 5, and also ensures the drainage effect of the through-thick grooves 321, 331.

[0069] As shown in FIG. 8, the tie bar 5 has one slit 51 and a pair of divisions 52A, 52B.

[0070] The slit 51 penetrates the tie bar 5 in the tire circumferential direction and opens into an edge portion of the center groove 22 of the tie bar 5. The slit 51 has a width W51 (see FIG. 8) in the range of 0.5 mm≦W51≦2.0 mm and a depth H51 (see FIG. 9) of 10 mm or more, and is closed when the tire comes into contact with the ground. This ensures that the tie bar 5 reinforces the rigidity of the land portions 32, 33.

[0071] The width W51 of the slit 51 is measured as the maximum distance between the opposing groove walls of the opening of the slit 51 at the top surface of the tie bar 5 when the tire is mounted on a specified rim and inflated to a specified internal pressure in an unloaded state.

[0072] The depth H51 of the slit 51 is measured as the maximum distance from the opening position of the slit 51 on the top surface of the tie bar 5 to the bottom of the slit 51 when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

[0073] Also, the center line of the slit 51 has an inclined portion 511 inclined with respect to the tire circumferential direction in a plan view of the tread. Also, the inclination angle of the inclined portion with respect to the tire circumferential direction (dimension symbol omitted in the figure) is in the range of 2 [deg] to 20 [deg]. Also, in the configuration of FIG. 8, the slit 51 has a straight shape inclined with respect to the tire circumferential direction, so that the entire slit 51 forms the inclined portion 511. Also, both ends of the slit 51 are offset from each other in the tire width direction, so that the entire slit 51 is inclined with respect to the tire circumferential direction. Also, the end of the slit 51 is disposed in the center of the circumferential groove 22. Specifically, the distance from the end of the slit 51 to the groove wall of the circumferential groove 22 (dimension symbol omitted in the figure) is in the range of 20 [%] to 80 [%] with respect to the groove width Wg2 of the circumferential groove 22, and preferably in the range of 30 [%] to 65 [%].

[0074] In the above configuration, (1) the circumferential groove 22 includes the tie bar 5 connecting the adjacent land portions 32, 33, and therefore the rigidity of the land portions 32, 33 is reinforced by the tie bar 5 when the tire is in contact with the ground, thereby reducing the rolling resistance of the tire. Also, (2) the tie bar 5 has the slit 51, and therefore the decrease in drainage performance of the circumferential groove 22 caused by the installation of the tie bar 5 is suppressed. Also, (3) the slit 51 is closed when the tire is in contact with the ground, and therefore the reinforcing effect of the tie bar 5 on the rigidity of the land portions 32, 33 is ensured. Also, (4) the slit 51 has an inclined portion 511 inclined with respect to the tire circumferential direction, and therefore when the slit 51 is closed, the wall surface of the slit 51 has an engagement component in both the tire width direction and the tire circumferential direction. As a result, the reinforcing effect of the rigidity of the land portions 32, 33 by the tie bar 5 is improved compared to a configuration in which the slit does not have an engagement component in the tire circumferential direction (see FIG. 21 described later). As a result, the tire achieves both low rolling resistance performance and wet performance.

[0075] 8, the extension distance Dd of the center line of the slit 51 in the tire width direction is in the range of 0.60≦Dd / W51 with respect to the width W51 of the slit 51, and preferably in the range of 1.50≦Dd / W51. This ensures the engagement component of the slit 51 in the tire circumferential direction when the slit 51 is closed as described above. The extension distance Dd of the slit 51 is in the range of Dd / Wg2≦0.50 with respect to the groove width Wg2 of the circumferential groove 22, and preferably in the range of Dd / Wg2≦0.20.

[0076] The extension distance Dd of the center line of the slit 51 in the tire width direction is measured in an unloaded state in which the tire is mounted on a specified rim and inflated to a specified internal pressure.

[0077] The pair of divided parts 52A, 52B are block-shaped parts divided by a slit 51, connected to the land parts 32, 33 at one end in the width direction of the tie bar 5, respectively, and opposed to each other via the slit 51 at the other end. In addition, in Fig. 8, the circumferential length L52A of the connection part of the first divided part 52A to the middle land part 32 is in the range of 0.30 ≦ L52A / P21 ≦ 0.70 with respect to the pitch length P21 (see Fig. 3) of the thin through-groove 321 of the middle land part 32. Similarly, the circumferential length L52B of the connection part of the second divided part 52B to the center land part 33 is in the range of 0.30 ≦ L52B / P31 ≦ 0.70 with respect to the pitch length P31 (see Fig. 7) of the thin through-groove 331 of the center land part 33. Further, the ratio of the circumferential lengths L52A, L52B of the pair of divided portions 52A, 52B is in the range of 0.80≦L52B / L52A≦1.20.

[0078] 8, the circumferential length L51 of the slit 51 is within the ranges of 0.20≦L51 / L52A≦1.00 and 0.20≦L51 / L52B≦1.00, and preferably within the ranges of 0.70≦L51 / L52A≦1.00 and 0.70≦L51 / L52B≦1.00, relative to the circumferential lengths L52A, L52B of the connecting portions of the first and second divided portions 52A, 52B to the land portions 32, 33. This ensures an engagement allowance for the slit 51.

[0079] In the configuration of FIG. 8, the pair of divided parts 52A, 52B are arranged offset from each other in the tire circumferential direction. This increases the engagement force of the slit 51 in the tire circumferential direction when the slit 51 is closed. Specifically, in a plan view of the tread, a midpoint MA of the connection part of the first divided part 52A to the middle land part 32 and a midpoint MB of the connection part of the second divided part 52B to the center land part 33 are defined. These midpoints MA and MB are defined as the midpoints of the circumferential lengths L52A and L52B of the connection parts of the first and second divided parts 52A and 52B, respectively. As shown in FIG. 8, the midpoints MA and MB of the connection parts of the first and second divided parts 52A and 52B are arranged offset from each other in the tire circumferential direction. The offset amount Ld is in the range of 0.05≦Ld / L52A≦0.40 with respect to the circumferential length L52A of the connection part of the first divided part 52A, and is preferably in the range of 0.10≦Ld / L52A≦0.20.

[0080] 8, an imaginary straight line X passing through midpoints MA, MB of the connection portions of the first and second divided portions 52A, 52B to the land portions 32, 33 is defined. In the configuration of FIG. 8, the pair of divided portions 52A, 52B are arranged offset from each other in the tire circumferential direction as described above, so that the imaginary straight line X is inclined with respect to the tire width direction. At this time, the overall inclination direction of the slit 51, i.e., the imaginary straight lines passing through both ends of the slit 51 (which coincide with the center line of the slit 51 in FIG. 8) are inclined in opposite directions to each other in the tire circumferential direction with respect to the imaginary straight line X of the connection portions of the divided portions 52A, 52B. This increases the engagement force of the slit 51 in the tire circumferential direction when the slit 51 is closed.

[0081] Further, as shown in Fig. 9, in a cross-sectional view in the groove depth direction of the circumferential groove 22, the top surface of the tie bar 5 is located radially inward of the tire diameter with respect to the tread surface. Thereby, the drainage performance of the circumferential groove 22 is ensured. In the configuration of Fig. 9, the distance from the tread surfaces of the land portions 32 and 33 to the top surface of the tie bar 5 (dimension symbols in the figure are omitted) monotonically increases from the connecting portion of the tie bar 5 to the land portions 32 and 33 toward the opening of the slit 51. Specifically, the top surface of the tie bar 5 is inclined in the groove depth direction of the circumferential groove 22 from the tread surfaces of the land portions 32 and 33 toward the opening of the slit 51, thereby having a V-shaped cross-sectional shape with the opening of the slit 51 as the apex. Thereby, the drainage performance of the circumferential groove 22 is enhanced.

[0082] Further, the maximum distance H5t from the tread surfaces of the land portions 32 and 33 to the top surface of the tie bar 5 is in the range of 0 < H5t / Hg2 ≦ 0.50 with respect to the groove depth Hg2 of the circumferential groove 22, preferably in the range of 0.10 ≦ H5t / Hg2 ≦ 0.40. With the above lower limit, the drainage performance of the circumferential groove 22 is ensured, and with the above upper limit, the reinforcing effect of the rigidity of the land portions 32 and 33 by the tie bar 5 is ensured.

[0083] Further, in Fig. 9, the distance (H51 + H5t) from the tread surfaces of the land portions 32 and 33 to the maximum depth position of the slit 51 is in the range of 0.60 ≦ (H51 + H5t) / Hg2 ≦ 1.00, preferably in the range of 0.80 ≦ (H51 + H5t) / Hg2 ≦ 0.98. With the above lower limit, the drainage improvement effect by the slit 51 is ensured, and with the above upper limit, the reinforcing effect of the rigidity of the land portions 32 and 33 by the tie bar 5 is ensured. Also, as shown in Fig. 10, the top surface of the tie bar 5 has a uniform maximum depth H5t, and the slit 51 has a uniform depth H51.

[0084] Further, in the configuration of Fig. 9, the slit 51 has a predetermined width W51 (see Fig. 8) at the top surface of the tie bar 5 and has a substantially constant width in the depth direction. Specifically, the maximum width in the entire depth direction of the slit 51 is 120[%] or less, preferably 100[%] or less, with respect to the width W51 at the top surface of the tie bar 5. Thereby, the reinforcing effect of the rigidity of the land portions 32 and 33 when the slit 51 is blocked is enhanced.

[0085] [Shoulder main groove] Fig. 16 is an enlarged plan view showing the shoulder main groove shown in Fig. 2. Fig. 17 and Fig. 18 are a cross-sectional view taken along line A (Fig. 17) and line B (Fig. 18) of the shoulder main groove shown in Fig. 16.

[0086] As shown in Figs. 16 to 18, the ridgeline of the connection between the groove bottom of the shoulder main groove 21 and the groove wall on the shoulder land portion 31 side in the plan view of the tread has a wavy or zigzag shape with amplitude in the tire width direction. On the other hand, the ridgeline of the connection between the groove bottom of the shoulder main groove 21 and the groove wall on the middle land portion 32 side has a straight shape. This configuration is preferable in that the rigidity of the shoulder land portion 31 is ensured, uneven wear of the shoulder land portion 31 is reduced, and at the same time, the drainage of the shoulder main groove 21 is ensured. In addition, the groove wall angle φ1 of the shoulder main groove 21 on the shoulder land portion 31 side (defined as the inclination angle of the groove wall surface with respect to the normal line of the tread surface) is in the range of 0 [deg] ≦ φ1 - φ2 with respect to the groove wall angle φ2 on the middle land portion 32 side, and preferably in the range of 1 [deg] ≦ φ1 - φ2. In addition, the groove wall angle φ1 on the shoulder land portion 31 side is in the range of 3 [deg] ≦ φ1 ≦ 20 [deg]. In addition, the radius of curvature (not shown) of the connection part between the groove wall and the groove bottom on the shoulder land portion 31 side of the shoulder main groove 21 is equal to or greater than the radius of curvature of the connection part between the groove wall and the groove bottom on the middle land portion 32 side. This increases the rigidity of the shoulder land portion 31.

[0087] [Variations] Figures 11 and 12 are explanatory diagrams showing modified examples of the tie bar 5 shown in Figure 8. In these figures, the same components as those shown in Figure 8 are given the same reference numerals, and the description thereof will be omitted.

[0088] 8, the slit 51 has a straight shape inclined with respect to the tire circumferential direction, so that the entire slit 51 forms an inclined portion 511. In addition, both ends of the slit 51 are offset from each other in the tire width direction, so that the entire slit 51 is inclined with respect to the tire circumferential direction. This forms an engagement component of the wall surface of the slit 51 in the tire circumferential direction when the slit 51 is closed.

[0089] However, the present invention is not limited to this, and the slit 51 may have a bent portion or a curved portion in a plan view of the tread. For example, in the configuration of FIG. 11, the slit 51 has a gently bent shape, has an inclined portion 511 in its center, and extends parallel to the tire circumferential direction at both ends. Even with this configuration, the engagement component of the wall surface of the slit 51 in the tire circumferential direction when the slit 51 is closed is ensured. In addition, in the configuration of FIG. 12, the slit 51 has a zigzag shape having an amplitude in the tire width direction, so that the entire slit 51 becomes the inclined portion 511. This increases the engagement force of the wall surface of the slit 51 when the slit 51 is closed. In addition, the present invention is not limited to the above, and the slit 51 may have a wave-like shape or a step shape having an amplitude in the tire width direction (not shown).

[0090] Figures 13 to 15 are explanatory diagrams showing modified examples of the tie bar 5 shown in Figure 9. In these figures, the same components as those shown in Figure 9 are given the same reference numerals, and the description thereof will be omitted.

[0091] 9, the top surface of the tie bar 5 is inclined in the groove depth direction of the circumferential groove 22 from the tread surfaces of the land portions 32, 33 toward the opening of the slit 51, thereby forming a V-shaped cross-sectional shape with the opening of the slit 51 as the apex. This configuration is preferable in that it can enhance the reinforcing effect of the tie bar 5 on the land portions 32, 33 while maintaining the drainage performance of the circumferential groove 22.

[0092] However, the present invention is not limited to this, and as shown in Fig. 13, the top surface of the tie bar 5 may be connected to the groove wall of the circumferential groove 22, and offset from the tread surface of the land portions 32, 33. This improves the drainage of the circumferential grooves 22, 23. Also, as shown in Fig. 14, the top surface of the tie bar 5 may change in a step shape toward the opening of the slit 51. Also, as shown in Fig. 15, the top surface of the tie bar 5 may have a flat shape.

[0093] [effect] As described above, the tire 1 includes a plurality of circumferential grooves 21, 22 extending in the tire circumferential direction, and a plurality of land portions 31-33 partitioned by these circumferential grooves 21, 22 (see FIG. 2). At least one circumferential groove (center groove 22 in FIG. 2) includes a tie bar 5 formed at the bottom of the circumferential groove 22 and crossing the circumferential groove 22 to connect adjacent land portions 32, 33 (see FIG. 3). The tie bar 5 also has a slit 51 that penetrates the tie bar 5 in the tire circumferential direction and is closed when the tire contacts the ground (see FIG. 8). The slit 51 also has an inclined portion 511 that is inclined with respect to the tire circumferential direction in a tread plan view.

[0094] In this configuration, (1) the circumferential groove 22 includes the tie bar 5 connecting the adjacent land portions 32, 33, and therefore the rigidity of the land portions 32, 33 is reinforced by the tie bar 5 when the tire is in contact with the ground, thereby reducing the rolling resistance of the tire. Also, (2) the tie bar 5 has the slit 51, and therefore the decrease in drainage performance of the circumferential groove 22 caused by the installation of the tie bar 5 is suppressed. Also, (3) the slit 51 is closed when the tire is in contact with the ground, and therefore the reinforcing effect of the tie bar 5 on the rigidity of the land portions 32, 33 is ensured. Also, (4) the slit 51 has an inclined portion 511 inclined with respect to the tire circumferential direction, and therefore when the slit 51 is closed, the wall surface of the slit 51 has an engagement component in both the tire width direction and the tire circumferential direction. As a result, the reinforcing effect of the tie bar 5 on the rigidity of the land portions 32, 33 is improved compared to a configuration in which the slit does not have an engagement component in the tire circumferential direction (see FIG. 21 described later). These have the advantage that the tire has both low rolling resistance and wet performance.

[0095] In addition, in this tire 1, both ends of the slit 51 are disposed offset from each other in the tire width direction (see FIG. 8). This has the advantage that the engaging force of the slit 51 in the tire circumferential direction when the slit 51 is closed is increased.

[0096] In addition, in the tire 1, an extension distance Dd of the center line of the slit 51 in the tire width direction is in the range of 1.50≦Dd / W51 where W51 is the width of the slit (see FIG. 8 ). This has the advantage that an engagement component of the slit 51 in the tire circumferential direction when the slit 51 is closed is secured.

[0097] In addition, in the tire 1, the width W51 of the slit 51 (see FIG. 8) is in the range of 0.5 mm≦W51≦2.0 mm. The lower limit ensures the drainage effect of the slit 51, and the upper limit has the advantage that the slit 51 is properly closed when the tire comes into contact with the ground.

[0098] In the tire 1, the slits 51 have bent or curved portions in a plan view of the tread (see FIGS. 11 and 12). This configuration has an advantage over a configuration in which the slits 51 have a straight shape (see FIG. 8) in that the engaging force of the wall surface of the slits 51 increases when the slits 51 are closed, thereby enhancing the reinforcing effect of the rigidity of the slits 51.

[0099] In the tire 1, the land portions 32; 33 include a plurality of through-slits 321; 331 penetrating the land portions 32; 33, and a plurality of blocks 322; 332 partitioned by the through-slits 321; 331 (see FIG. 2). The tie bar 5 is disposed between the adjacent through-slits 321, 321; 331, 331 and connected to the blocks 322; 332 (see FIG. 8). Therefore, the tie bar 5 is disposed offset in the tire circumferential direction with respect to the openings of the through-slits 321, 331 of the land portions 32, 33. This ensures the rigidity of the tie bar 5, and has the advantage of ensuring the drainage effect of the through-slits 321, 331.

[0100] In the tire 1, the tie bar 5 includes first and second divided portions 52A, 52B partitioned by the slit 51 (see FIG. 8). The circumferential length L51 of the slit 51 is within the ranges of 0.20≦L51 / L52A≦1.00 and 0.20≦L51 / L52B≦1.00, where L52A, L52B are the circumferential lengths of the connecting portions of the first and second divided portions 52A, 52B to the land portions 32, 33. This has the advantage that an engagement allowance of the slit 51 is secured when the slit 51 is closed.

[0101] In addition, in the tire 1, the tie bar 5 includes first and second divided portions 52A, 52B defined by the slit 51 (see FIG. 8). The first and second divided portions 52A, 52B are disposed offset from each other in the tire circumferential direction. This has the advantage that the engaging force of the slit 51 in the tire circumferential direction when the slit 51 is closed is increased.

[0102] In addition, in the tire 1, the tie bar 5 includes first and second divided portions 52A, 52B partitioned by the slit 51 (see FIG. 8). Also, an imaginary straight line X passing through midpoints MA, MB of the connection portions of the first and second divided portions 52A, 52B to the land portions 32, 33 is defined. At this time, an imaginary straight line (not shown) passing through both ends of the slit 51 and the imaginary straight line X of the first and second divided portions 52A, 52B are inclined in opposite directions to each other with respect to the tire circumferential direction. This has the advantage that the engaging force of the slit 51 in the tire circumferential direction when the slit 51 is closed is increased.

[0103] In addition, in this tire 1, the top surface of the tie bar 5 is located radially inward of the tread surface (see FIG. 9). This has the advantage that the drainage performance of the circumferential groove 22 is ensured.

[0104] In addition, in the tire 1, in a cross-sectional view of the circumferential groove 22 in the groove depth direction, the distance H5t from the tread surface of the land portions 32, 33 to the top surface of the tie bar 5 increases monotonically from the connection portion of the tie bar 5 to the land portions 32, 33 toward the opening of the slit 51. This has the advantage of improving the drainage performance of the circumferential groove 22.

[0105] In addition, in this tire 1, the maximum distance H5t from the tread surface of the land portions 32 and 33 to the top surface of the tie bar 5 is in the range of 0 < H5t / Hg2 ≦ 0.50 with respect to the groove depth Hg2 of the circumferential groove 22 (see FIG. 9). By the above lower limit, the drainage performance of the circumferential groove 22 is ensured, and by the above upper limit, there is an advantage that the reinforcing effect of the rigidity of the land portions 32 and 33 by the tie bar 5 is ensured.

[0106] [Applicable Target] In addition, this tire 1 is a heavy-duty pneumatic radial tire to be mounted on the steering wheel of a tractor. By applying such a tire, the effect of achieving both the low rolling resistance performance and the wet performance of the tire can be effectively obtained.

[0107] In addition, in this embodiment, as described above, a pneumatic tire has been described as an example of the tire. However, the present invention is not limited to this, and the configuration described in this embodiment can be arbitrarily applied to other tires within the scope obvious to those skilled in the art. Examples of other tires include, for example, airless tires and solid tires.

Example

[0108] FIG. 19 is an explanatory view showing a test tire of a comparative example. FIGS. 20 and 21 are charts showing the results of the performance test of the tire according to the embodiment of the present invention.

[0109] In this performance test, a plurality of types of test tires were evaluated for (1) low rolling resistance performance and (2) wet traction performance. In addition, a test tire of tire size 11R22.5 was assembled to a JATMA standard rim, and the JATMA standard internal pressure and standard load were applied to this test tire. Further, the test tire was mounted on a 2-D tractor head which is a test vehicle. Also, if the evaluation is 99 or more, it can be said that the performance is properly ensured.

[0110] (1) In the evaluation of low rolling resistance performance, a drum testing machine with a drum diameter of 1707 mm is used, and the reciprocal of the rolling resistance coefficient of the test tire is calculated and evaluated under the conditions of a load of 28.76 kN, an air pressure of 900 kPa, and a speed of 60 km / h in accordance with ISO 28580. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the more preferable it is.

[0111] (2) In the evaluation of wet traction performance, the test vehicle runs on an asphalt road that has been watered to a depth of 1 mm, and the running time is measured until the running speed increases from 5 km / h to 20 km / h. Then, based on the measurement results, an index evaluation is performed with the comparative example as the standard (100). The higher the value, the better the evaluation.

[0112] The test tire of the embodiment has the configuration of FIG. 1 and FIG. 2, and the middle land portion 32 has a through-hole fine groove 321, a middle block 322, and a non-through-hole lug groove 323. The circumferential grooves 21, 22 have a straight shape, and the left and right center grooves 22, 22 have a plurality of tie bars 5. The tie bars 5 have slits 51 (see FIG. 8). The groove width Wg1 of the shoulder main groove 21 is 13.0 [mm], and the groove depth Hg1 is 16.2 [mm]. The groove width Wg2 of the center groove 22 is 12.0 [mm], and the groove depth Hg2 is 16.2 [mm]. The tire ground contact width TW is 220 [mm], the ground contact width Wb1 of the shoulder land portion 31 is 41.5 [mm], the ground contact width Wb2 of the middle land portion 32 is 30.0 [mm], and the ground contact width Wb3 of the center land portion 33 is 31.0 [mm]. The slit 51 has a width W51 of 0.8 mm and a depth H51 of 15.0 mm.

[0113] The test tire of the comparative example is the test tire of Example 1, and the tie bar 5 has the configuration shown in Fig. 21. Specifically, the slit 51 of the tie bar 5 has a straight shape parallel to the tire circumferential direction, and the divided parts 52A and 52B of the tie bar 5 are arranged so that their positions in the tire circumferential direction are aligned.

[0114] As the test results show, the test tires of the examples exhibit both low rolling resistance and wet traction performance. [Explanation of symbols]

[0115] 1 tire; 11 bead core; 12 bead filler; 121 lower filler; 122 upper filler; 13 carcass layer; 14 belt layer; 141 high angle belt; 142, 143 cross belt; 144 belt cover; 15 tread rubber; 16 sidewall rubber; 17 rim cushion rubber; 21 shoulder main groove; 22 center groove; 31 shoulder land portion; 32 middle land portion; 321 through narrow groove; 322 middle block; 323 non-through lug groove; 33 center land portion; 331 through narrow groove; 332 center block; 4 multi-sipe; 5 tie bar; 51 slit; 511 inclined portion; 52A, 52B first and second division portions

Claims

1. The tire has a plurality of circumferential grooves extending in a circumferential direction of the tire, and a plurality of land portions defined by the circumferential grooves. At least one of the circumferential grooves includes a tie bar formed in a groove bottom of the circumferential groove and crossing the circumferential groove to connect adjacent land portions, the tie bar has a slit that penetrates the tie bar in the tire circumferential direction and is closed when the tire is in contact with the ground, The center line of the slit has an inclined portion inclined with respect to the tire circumferential direction in a tread plan view, and A tire characterized in that both ends of the slit are arranged offset from each other in the tire width direction.

2. The tire according to claim 1 , wherein an extension distance Dd of a center line of the slit in the tire width direction is in a range of 1.50≦_Dd / W51, where W51 is a width of the slit.

3. The tire according to claim 1 or 2, wherein a width W51 of the slit is in a range of 0.5 mm≦W51≦2.0 mm.

4. The tire according to any one of claims 1 to 3, wherein the slit has a bent portion or a curved portion in a plan view of the tread.

5. The tire according to any one of claims 1 to 4, wherein the land portion includes a plurality of through-grooves penetrating the land portion and a plurality of blocks partitioned by the through-grooves, and the tie bar is disposed between adjacent through-grooves and connects to the blocks.

6. The tie bar includes first and second divided portions defined by the slit, The tire according to any one of claims 1 to 5, wherein a circumferential length L51 of the slit is in the ranges of 0.20≦L51 / L52A≦1.00 and 0.20≦L51 / L52B≦1.00 with respect to circumferential lengths L52A, L52B of the connection portions of the first and second divided portions to the land portion.

7. The tie bar includes first and second divided portions defined by the slit, and The tire according to any one of claims 1 to 6, wherein the first and second divided portions are disposed offset from each other in the tire circumferential direction.

8. The tie bar includes first and second divided portions defined by the slit, A virtual straight line X passing through a midpoint of a connection portion of the first and second division portions with respect to the land portion is defined; and The tire according to any one of claims 1 to 7, wherein an imaginary line passing through both ends of the slit and an imaginary line X of the first and second divided portions are inclined in mutually opposite directions with respect to the tire circumferential direction.

9. The tire according to any one of claims 1 to 8, wherein a top surface of the tie bar is located radially inward of a tread surface.

10. The tire according to any one of claims 1 to 9, wherein, in a cross-sectional view of the circumferential groove in a groove depth direction, a distance from a tread surface of the land portion to a top surface of the tie bar monotonically increases from a connection portion of the tie bar to the land portion toward an opening of the slit.

11. The tire according to any one of claims 1 to 10, wherein a maximum distance H5t from the tread surface of the land portion to a top surface of the tie bar is in a range of 0 < H5t / Hg2 ≦ 0.50 with respect to a groove depth Hg2 of the circumferential groove.

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