tire

Abstract

To provide a tire that can make both wet performance and low rolling resistance performance compatible.SOLUTION: The tire comprises: a pair of shoulder main grooves 21 and 21 extending in a tire circumferential direction; two or more center thin grooves 22 and 23 arranged between the pair of shoulder main grooves 21 and 21 and extending in the tire circumferential direction; and a pair of shoulder land parts 31 and 31, a pair of middle land parts 32 and 32 and two rows of center land parts 33 partitioned by the shoulder main groove 21 and the center thin grooves 22 and 23. All center lines of the center thin grooves 22 and 23 have zigzag shapes formed by alternately connecting length portions and short portions to each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, heavy-duty tires fitted to vehicles for long-distance transport such as trucks and buses have adopted a configuration in which only a pair of shoulder main grooves are provided on the tread surface, with no other circumferential main grooves or wide circumferential grooves in the center region of the tread, in order to reduce the rolling resistance of the tire while ensuring the wet performance of the tire.

[0003] As a conventional heavy duty tire employing such a configuration, the technology described in Patent Document 1 is known. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 040007 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a tire that can achieve both wet performance and low rolling resistance performance. [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 extending in a tire circumferential direction, two or more center narrow grooves disposed between the pair of shoulder main grooves and extending in the tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions partitioned by the shoulder main grooves and the center narrow groove, wherein at least one of the center narrow grooves has a groove center line having a zigzag shape formed by alternately connecting long portions and short portions, and the center narrow groove has a groove width of 0.5 mm or more and 3.0 mm or less. death, The long portion of the center narrow groove, which is located at the outermost side in the tire width direction, has an arc shape that is convex toward the tire equatorial plane. and the region between the pair of shoulder main grooves does not include another circumferential groove having a maximum groove width exceeding 3.0 [mm] and a maximum groove depth of 10 [mm] or more. It is characterized by do. Effect of the Invention

[0007] In the tire according to the present invention, (1) the land portion in the tread center region is divided into a plurality of center narrow grooves, so the groove area in the tread center region is reduced compared to a configuration in which the tread center region has circumferential main grooves, which has the advantage of reducing the rolling resistance of the tire, while (2) the center narrow groove has a zigzag shape formed by alternatingly connecting long and short portions, so that the tire's wet performance is improved compared to a configuration in which the center narrow groove has a straight shape. [Brief description 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. [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 view showing a center region of the tread portion of the tire shown in FIG. [Figure 4] FIG. 4 is an enlarged view showing the block units of the middle land portion and the center 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 table showing the results of performance tests of the tire according to the embodiment of the present invention. [Figure 7] FIG. 7 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

[0009] 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.

[0010] [tire] Fig. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. The figure also shows, as an example of a tire, a heavy-duty pneumatic radial tire to be mounted on vehicles for long-distance transportation such as trucks and buses.

[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 measurement points specified 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.

[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 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.

[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 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.

[0015] 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.

[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. 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. In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T is the tire ground contact edge, and the dimension symbol TW is the tire ground contact width.

[0018] As shown in FIG. 2, the tire 1 has a pair of shoulder main grooves 21, 21 extending in the tire circumferential direction, two or more center narrow grooves 22, 23 disposed between the shoulder main grooves 21, 21 and extending in the tire circumferential direction, and a pair of shoulder land portions 31, 31 defined by the shoulder main groove 21 and the center narrow groove 22, 23, a pair of middle land portions 32, 32, and one or more rows of center land portions 33 on the tread surface. The middle land portion 32 is defined as a land portion defined by the shoulder main groove 21 and the center narrow groove 22 located closest to the tire ground contact end T. The center land portion 33 is defined as a land portion adjacent to the middle land portion 32. In addition, the region between the pair of shoulder main grooves 21, 21 (defined as the center region of the tread portion) does not have any other circumferential grooves having a maximum groove width exceeding 3.0 [mm] and a maximum groove depth of 10 [mm] or more. Therefore, a single ground contact region having a substantially continuous tread surface is formed in the center region of the tread portion. This ensures rigidity in the central region of the tread and reduces the rolling resistance of the tire.

[0019] The shoulder main groove 21 is a groove that is required to display a wear indicator as specified by JATMA, and has a maximum groove width of 5.0 mm or more and a maximum groove depth of 10 mm or more. The center narrow grooves 22, 23 have a groove width of 0.5 mm to 3.0 mm and a maximum groove depth of 8.0 mm or more. The groove width of the center narrow grooves 22, 23 is in the range of 30% or less of the groove width of the shoulder main groove 21. Details of the center narrow grooves 22, 23 will be described later.

[0020] The groove width is measured as the distance between the opposing groove walls at the groove opening 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 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] 2, the tire 1 has a tread pattern that is substantially point-symmetric 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 or asymmetric about the tire equatorial plane CL, or may have a tread pattern that has directionality in the tire rotation direction (not shown).

[0024] 2, each of the left and right regions bounded by the tire equatorial plane CL has one shoulder main groove 21, 21. Three center narrow grooves 22, 23, 22 are disposed between these shoulder main grooves 21, 21. The center narrow groove 23 is disposed on the tire equatorial plane CL. The shoulder main grooves 21, 21 and center narrow grooves 22, 23, 22 define a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and two rows of center land portions 33, 33.

[0025] However, without being limited thereto, four or more center narrow grooves may be arranged to form a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and two or more rows of center land portions 33 (not shown). Alternatively, two center narrow grooves 22, 22 may be arranged to form a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single center land portion 33 (not shown). Furthermore, the center narrow groove 23 may be arranged at a position deviated from the tire equatorial plane CL, so that the center land portion is arranged on the tire equatorial plane CL (not shown).

[0026] [Tread center area] Fig. 3 is an enlarged view showing the tread center region of the tire 1 shown in Fig. 2. The figure shows one side region of the tread center region bounded by the tire equatorial plane CL. Fig. 4 is an enlarged view showing block units of the middle land portion 32 and the center land portion 33 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.

[0027] In the configuration of Figure 2, as described above, the tire 1 has a pair of shoulder main grooves 21, 21 and three center narrow grooves 22, 23, 22, and a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and two rows of center land portions 33, 33, which are partitioned by these shoulder main grooves 21, 21 and center narrow grooves 22, 23, 22.

[0028] Here, of the center narrow grooves 22, 23, the first center narrow groove 22 adjacent to the shoulder main groove 21 and the second center narrow groove 23 adjacent to the first center narrow groove 22 are defined. In the configuration of Fig. 2, the second center narrow groove 23 is located on the tire equatorial plane CL, so that the middle land portion 32 and the center land portion 33 are located in the left and right regions bounded by the tire equatorial plane CL, respectively. In a configuration (not shown) having only the above-mentioned two center narrow grooves 22, 22 and a single center land portion 33, the second center narrow groove 23 is omitted.

[0029] As shown in FIG. 3, the groove center lines of the first and second central narrow grooves 22, 23 have a zigzag shape formed by alternatingly connecting long portions and short portions (reference numbers omitted in the drawing).

[0030] In this configuration, (1) the land portions 32, 33 in the tread center region are divided into a plurality of center narrow grooves 22, 23, so that the groove area in the tread center region is reduced compared to a configuration (not shown) in which the tread center region has a circumferential main groove. This reduces the rolling resistance of the tire. Meanwhile, (2) the center narrow grooves 22, 23 have a zigzag shape formed by alternatingly connecting long portions and short portions, so that the wet traction performance of the tire is improved compared to a configuration in which the center narrow groove has a straight shape. Also, (3) in a configuration in which only the pair of shoulder main grooves 21, 21 as described above is provided and no circumferential main groove is provided in the tread center region, the rigidity of the tread center region is increased, and the wear resistance of the tire is improved.

[0031] In the configuration of FIG. 3, the long portions of the first and second center narrow grooves 22, 23 are inclined in the same direction (downward to the right in the drawing). As described later, the shoulder main groove 21 has a zigzag shape in which long portions and short portions are alternately connected as a whole (see FIG. 2). The zigzag long portions of the first center narrow groove 22 are inclined in the opposite direction to the zigzag long portions of the shoulder main groove 21 in the tire circumferential direction. The long portions of the first center narrow groove 22 on the tire ground contact edge T side have a circular arc shape that is convex toward the tire equatorial plane CL side. In this configuration, compared to a configuration in which the center narrow groove 22 has a straight shape (not shown), deformation of the blocks 322A to 322C, 332A, 332B in the center region of the tread portion during tire rolling is suppressed, and the rolling resistance of the tire is reduced. On the other hand, the long portion of the second center narrow groove 23 on the tire equatorial plane CL has a straight line shape, which improves the wet performance of the tire.

[0032] In addition, the circumferential lengths L2, L3 of the long parts of the first and second center narrow grooves 22, 23 are in the ranges of 0.85≦L2 / P2≦1.00 and 0.85≦L3 / P3≦1.00, and preferably in the ranges of 0.90≦L2 / P2≦0.96 and 0.90≦L3 / P3≦0.96, relative to the pitch lengths P2, P3 of the zigzag shape. This optimizes the zigzag shape of the center narrow grooves 22, 23. In particular, the lower limit effectively prevents the blocks from collapsing, and increases the edge components to improve the low rolling resistance and wet performance of the tire. In addition, the pitch numbers of the zigzag shapes of the first and second center narrow grooves 22, 23 are equal to each other.

[0033] 3, the pitch length P2 of the zigzag shape of the first center narrow groove 22 on the tire ground contact end T side has a relationship of 1.30≦P2 / Wb2≦2.00 with respect to the maximum ground contact width Wb2 of the middle land portion 32, and preferably has a relationship of 1.50≦P2 / Wb2≦1.85. The pitch length P3 of the zigzag shape of the second center narrow groove 23 on the tire equatorial plane CL side has a relationship of 1.30≦P3 / Wb3≦2.00 with respect to the maximum ground contact width Wb3 of the center land portion 33, and preferably has a relationship of 1.50≦P3 / Wb3≦1.85. This optimizes the zigzag shape of the center narrow grooves 22 and 23. In particular, the above lower limit optimizes the block rigidity, and the tire achieves both low rolling resistance and wet performance.

[0034] In addition, in FIG. 3, the amplitude A2 of the zigzag shape of the first center narrow groove 22 on the tire ground contact edge T side has a relationship of 0.10≦A2 / Wb2≦0.50 and preferably has a relationship of 0.15≦A2 / Wb2≦0.35 with respect to the maximum ground contact width Wb2 of the middle land portion 32. In this configuration, the meshing allowance of the blocks 322A and 332B adjacent in the tire circumferential direction across the short portion of the zigzag shape of the center narrow groove 22 is secured when the tire is in contact with the ground. This ensures the rigidity of the tread center region and reduces the rolling resistance of the tire. Similarly, the amplitude A3 of the zigzag shape of the second center narrow groove 23 on the tire equatorial plane CL side has a relationship of 0.10≦A3 / Wb3≦0.50 and preferably has a relationship of 0.15≦A3 / Wb3≦0.35 with respect to the maximum ground contact width Wb3 of the center land portion 33.

[0035] 5, the maximum groove depths Hg2, Hg3 of the first and second center narrow grooves 22, 23 have the relationships of 0.60≦Hg2 / Hg1≦0.90 and 0.60≦Hg3 / Hg1≦0.90 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. Therefore, the center narrow grooves 22, 23 are shallower than the shoulder main groove 21.

[0036] 2, the maximum distance De2 from the outer edge of the middle land portion 32 in the tire width direction to the tire equatorial plane CL has a relationship of 0.10≦De2 / TW≦0.40 and preferably 0.15≦De2 / TW≦0.35 with respect to the tire contact width TW. The maximum distance De3 from the outer edge of the center land portion 33 in the tire width direction to the tire equatorial plane CL has a relationship of 0.05≦De3 / TW≦0.30 and preferably 0.08≦De3 / TW≦0.20 with respect to the tire contact width TW.

[0037] The tire contact width TW 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.

[0038] 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.

[0039] 3, the maximum ground contact width Wb2 of the middle land portion 32 has a relationship of 0.10≦Wb2 / TW≦0.25 with respect to the tire ground contact width TW (see FIG. 2), and preferably has a relationship of 0.15≦Wb2 / TW≦0.20. The maximum ground contact width Wb3 of the center land portion 33 has a relationship of 0.10≦Wb3 / TW≦0.25 with respect to the tire ground contact width TW, and preferably has a relationship of 0.15≦Wb3 / TW≦0.20. The maximum ground contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33 are substantially the same, and have a relationship of 0.80≦Wb3 / Wb2≦1.20, and preferably have a relationship of 0.90≦Wb3 / Wb2≦1.10.

[0040] The contact widths Wb2 and Wb3 of the land portions are measured as the straight-line distance in the axial direction of the tire at the contact surface between the land portion 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.

[0041] 3, the edge of the central land portion 33 on the tire equatorial plane CL side has a zigzag shape along the central narrow groove 23, and part of the edge intersects with the tire equatorial plane CL, thereby improving the wet traction performance of the tire.

[0042] In addition, in FIG. 3, the middle land portion 32 includes a plurality of middle lateral grooves 321A, 321B and a plurality of middle blocks 322A, 322B, 322C.

[0043] The middle lateral grooves 321A, 321B extend in the tire width direction, penetrate the middle land portion 32, and connect to the shoulder main groove 21 and the first center narrow groove 22. Among these middle lateral grooves 321A, 321B, the first middle lateral groove 321A connects to the first center narrow groove 22 at a maximum amplitude position toward the tire ground contact end T, and the pair of second middle lateral grooves 321B, 321B connect to the first center narrow groove 22 at a position that divides the long portion into three equal parts. The first middle lateral groove 321A extends along an extension line of the groove center line of the short portion of the first center narrow groove 22. The first middle lateral groove 321A and the short portion of the first center narrow groove 22 share a groove center line that is linear or arc-shaped. The inclination angle θ21 of the first middle lateral groove 321A with respect to the tire circumferential direction is in the range of 50 [deg]≦θ21≦80 [deg]. The cross angle (symbols omitted in the drawing) between the center lines of the second middle transverse groove 321B and the long portion of the first center narrow groove 22 is in the range of 80 degrees or more and 100 degrees or less.

[0044] The inclination angle θ21 of the first middle lateral groove 321A is measured as the inclination angle of a virtual line connecting both ends of the first middle lateral groove 321A with respect to the tire circumferential direction.

[0045] In addition, a plurality of (the same number as the number of pitches of the zigzag shape of the first center fine groove 22 in the configuration of FIG. 3) first middle transverse grooves 321A are arranged at predetermined intervals in the tire circumferential direction. Also, at least one (two in the configuration of FIG. 3) second middle transverse groove 321B is disposed between adjacent first middle transverse grooves 321A, 321A. Thereby, the drainage performance of the grounding area partitioned by the long portion of the zigzag shape of the first center fine groove 22 is improved. In the configuration of FIG. 3, the first middle transverse groove 321A has a straight shape or a gentle arc shape, and the second middle transverse groove 321B has a gentle S-shaped.

[0046] In addition, the first and second middle transverse grooves 321A, 321B have a groove width of 0.1 [mm] or more and 3.0 [mm] or less (dimension symbols in the figure are omitted), and also have a maximum groove depth H21 of 7.5 [mm] or more (see FIG. 5). In FIG. 5, the maximum groove depth H21 of the first and second middle transverse grooves 321A, 321B has a relationship of 0.30 ≦ H21 / Hg1 ≦ 0.90 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. Therefore, the middle transverse grooves 321A, 321B are shallower than the shoulder main groove 21. Also, the maximum groove depth H21 of the first and second middle transverse grooves 321A, 321B is shallower than the maximum groove depth Hg2 of the center fine groove 22 (H21 < Hg2). In the configuration of FIG. 5, the first and second middle transverse grooves 321A, 321B do not have a partial bottom upper portion and have a constant groove depth.

[0047] As shown in FIG. 2, the middle blocks 322A, 322B, and 322C are divided into first and second middle lateral grooves 321A and 321B. In the configuration of FIG. 2, three types of middle blocks 322A, 322B, and 322C having different shapes are formed as shown in FIG. 3. The first to third middle blocks 322A, 322B, and 322C are repeatedly arranged in the tire circumferential direction. The first middle block 322A has the largest maximum ground contact width (dimension symbols omitted in the figure) and ground contact area, and the third middle block 322C has the smallest maximum ground contact width and ground contact area. The ratio of the maximum to the minimum ground contact areas of the first to third middle blocks 322A, 322B, and 322C is in the range of 1.30 or less. In addition, the circumferential lengths of the edge portions of the three types of middle blocks 322A, 322B, and 322C relative to the long portion of the zigzag shape of the first central narrow groove 22 are uniform, specifically, the ratio of the maximum value to the minimum value of the circumferential length of the edge portions is in the range of 1.00 to 1.20, thereby suppressing uneven wear of the middle blocks 322A, 322B, and 322C.

[0048] 4, the maximum circumferential length L22 and maximum ground contact width W22 of each of the middle blocks 322A, 322B, and 322C have a relationship of 0.70≦L22 / W22≦1.20, and preferably 0.80≦L22 / W22≦1.15. In the configuration of FIG. 4, each of the middle blocks 322A, 322B, and 322C has a shape that is elongated in the tire width direction and is disposed with its longitudinal direction inclined with respect to the tire width direction, so that the aspect ratio L22 / W22 is set within the above range.

[0049] In addition, in FIG. 3, the central land portion 33 includes a plurality of sets of central lateral grooves 331A, 331B and a plurality of sets of center blocks 332A, 332B.

[0050] The center lateral grooves 331A, 331B extend in the tire width direction, penetrate the center land portion 33, and connect to the adjacent first and second center narrow grooves 22, 23. Among these center lateral grooves 331A, 331B, the first center lateral groove 331A connects the maximum amplitude position of the first center narrow groove 22 toward the tire equatorial plane CL and the maximum amplitude position of the second center narrow groove 23 toward the tire ground contact edge T. The second center lateral groove 331B connects the long portion of the first center narrow groove 22 and the long portion of the second center narrow groove 23.

[0051] The inclination angle θ31 of the first center lateral groove 331A with respect to the tire circumferential direction is in the range of 50 [deg]≦θ31≦80 [deg]. The first center lateral groove 331A of the center land portion 33 and the first middle lateral groove 321A of the middle land portion 32 are inclined in the opposite directions with respect to the tire circumferential direction. Therefore, the long portion of the first center narrow groove 22, the first center lateral groove 331A of the center land portion 33, and the first middle lateral groove 321A of the middle land portion 32 are radially connected at the maximum amplitude position of the first center narrow groove 22 toward the tire equatorial plane CL. The intersection angle (dimension symbols are omitted in the figure) between the second center lateral groove 331B of the center land portion 33 and the long portion of the first center narrow groove 22 is in the range of 70 [deg] to 90 [deg]. In addition, the intersection angle (dimension symbols omitted in the drawing) between the second center lateral groove 331B of the central land portion 33 and the long portion of the second center narrow groove 23 is in the range of 80 degrees or more and 100 degrees or less.

[0052] In addition, a plurality of first center lateral grooves 331A (in the configuration of FIG. 3, the number is the same as the number of pitches of the zigzag shape of the first center narrow groove 22) are arranged at a predetermined interval in the tire circumferential direction. In addition, in the configuration of FIG. 3, one second center lateral groove 331B is arranged between the adjacent first center lateral grooves 331A, 331A. However, this is not limited to this, and two or more second center lateral grooves 331B may be arranged between the adjacent first center lateral grooves 331A, 331A, or the second center lateral groove 331B may be omitted (not shown). In addition, in the configuration of FIG. 3, the first center lateral groove 331A has a straight shape or a gentle arc shape, and the second center lateral groove 331B has a gentle S-shape. In addition, as shown in FIG. 3, the first middle lateral groove 321A of the middle land portion 32 and the first center lateral groove 331A of the center land portion 33 are connected via the short portion of the first center narrow groove 22. This forms a V-shaped or L-shaped bent groove that protrudes in the circumferential direction of the tire.

[0053] The first and second center lateral grooves 331A, 331B have a groove width (dimension symbols omitted in the drawing) of 0.1 mm or more and 3.0 mm or less, and a maximum groove depth H31 (see FIG. 5) of 7.5 mm or more. In FIG. 5, the maximum groove depth H31 of the first and second center lateral grooves 331A, 331B and the maximum groove depth Hg1 of the shoulder main groove 21 have a relationship of 0.50≦H31 / Hg1≦0.90. Therefore, the center lateral grooves 331A, 331B are shallower than the shoulder main groove 21. The maximum groove depth H31 of the first and second center lateral grooves 331A, 331B is shallower (H31) than the maximum groove depth Hg2 of the center narrow groove 22. <Hg2)。

[0054] 5, the first and second center lateral grooves 331A, 331B have a partial bottom upper portion 331' at the connection portion with the second center narrow groove 23 on the tire equatorial plane CL side. The distance H31' from the tread surface to the top surface of the bottom upper portion 331' satisfies the relationships 0.20≦H31' / Hg1 and H31' / H31≦0.70 with respect to the maximum groove depth Hg1 of the shoulder main groove 21 and the maximum groove depth H31 of the center lateral grooves 331A, 331B.

[0055] As shown in FIG. 2, the center blocks 332A and 332B are divided into first and second center lateral grooves 331A and 331B. In the configuration of FIG. 2, two types of center blocks 332A and 332B having different shapes are formed as shown in FIG. 3. These center blocks 332A and 332B are arranged alternately in the tire circumferential direction. The ground contact areas of the center blocks 332A and 332B are uniform, and specifically, the ratio of the maximum and minimum ground contact areas is in the range of 1.00 to 1.20. This suppresses uneven wear of the center blocks 332A and 332B.

[0056] The ground contact area A32 of each of the center blocks 332A, 332B is larger than the maximum ground contact area A22 of the middle blocks 322A-322C of the middle land portion 32, specifically, in the range of 1.20≦A32 / A22≦1.60. This ensures the ground contact areas of the center blocks 332A, 332B on the tire equatorial plane CL side, reducing the rolling resistance of the tire. Also, the groove area of ​​the middle land portion 32 on the tire ground contact edge T side is ensured, improving the wet performance of the tire.

[0057] The circumferential lengths of the edge portions of the two types of center blocks 332A, 332B relative to the long portion of the zigzag shape of the first central narrow groove 22 are uniform, specifically, the ratio of the maximum value to the minimum value of the circumferential length of the edge portions is in the range of 1.00 to 1.20. Similarly, the circumferential lengths of the edge portions of the two types of center blocks 332A, 332B relative to the long portion of the zigzag shape of the second central narrow groove 23 are uniform, specifically, the ratio of the maximum value to the minimum value of the circumferential length of the edge portions is in the range of 1.00 to 1.20.

[0058] Further, in FIG. 4, the maximum circumferential length L32 and the maximum ground contact width W32 of each of the center blocks 332A and 332B have a relationship of 1.05 ≦ L32 / W32 ≦ 1.45, and preferably have a relationship of 1.15 ≦ L32 / W32 ≦ 1.35. In the configuration of FIG. 4, each of the center blocks 332A and 332B has a substantially parallelogram shape.

[0059] Further, in FIG. 3, the number N3 of the center blocks 332A and 332B per unit pitch has a relationship of N3 < N2 with respect to the number N2 of the middle blocks 322A to 322C in the middle land portion 32. Also, the ratio N3 / N2 has a relationship of 0.25 ≦ N3 / N2 ≦ 0.90, and preferably has a relationship of 0.40 ≦ N3 / N2 ≦ 0.80. For example, in the configuration of FIG. 3, the number N2 of the middle blocks 322A to 322C and the number N3 of the center blocks 332A and 332B are N2:N3 = 3:2, but it is not limited thereto, and the ratio N2:N3 may be, for example, 2:1, 3:1, 4:1, 4:3, 5:2, 5:3, 5:4.

[0060] In the above configuration, (1) since the number N3 of the center blocks 332A and 332B on the tire equatorial plane CL side is relatively small, the rigidity near the tire equatorial plane CL is ensured, and the rolling resistance of the tire is reduced. Also, (2) since the number N2 of the middle blocks 322A to 322C on the tire ground contact end T side is relatively large, the groove area of the middle land portion 32 is ensured, and the wet performance of the tire is improved. Thus, the low rolling performance and the wet performance of the tire are made compatible.

[0061] Particularly, when the ratio N2:N3 of the number N2 of the middle blocks 322A to 322C and the number N3 of the center blocks 332A and 332B is 2:1, 3:2, 4:3, 5:4, ···, in each block unit per pitch (the middle blocks 322A to 322C and the center blocks 332A and 332B. See FIG. 4), the second middle transverse groove 321B and the second center transverse groove 332B can be connected in a staggered manner to the long portion of the first center fine groove 22. Thereby, the rigidity balance of the block unit is optimized.

[0062] [Tread shoulder area] 2, as described above, the tire 1 includes a pair of shoulder main grooves 21, 21 and a pair of shoulder land portions 31, 31 defined by these shoulder main grooves 21, 21. Moreover, a groove center line (not shown) of the shoulder main groove 21 has a zigzag shape overall, with long portions and short portions alternately connected.

[0063] 2, the shoulder land portion 31 includes a plurality of shoulder lug grooves 311 and a plurality of shoulder blocks 312. The shoulder lug grooves 311 extend in the tire width direction, penetrate the shoulder land portion 31, and open to the shoulder main groove 21 and the tire ground contact edge T. The groove width of the shoulder lug groove 311 increases from the shoulder main groove 21 toward the tire ground contact edge T.

[0064] [effect] As described above, the tire 1 includes a pair of shoulder main grooves 21, 21 extending in the tire circumferential direction, two or more center narrow grooves 22, 23 disposed between the pair of shoulder main grooves 21, 21 and extending in the tire circumferential direction, and a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and one or more rows (two rows in FIG. 2) of center land portions 33 partitioned by the shoulder main groove 21 and the center narrow groove 22, 23 (see FIG. 2). In addition, the groove center line of at least one (all in FIG. 2) of the center narrow grooves 22, 23 has a zigzag shape formed by alternatingly connecting long portions and short portions (see FIG. 3).

[0065] In this configuration, (1) the land portions 32, 33 in the tread center region (defined as the region between a pair of shoulder main grooves 21, 21) are divided into a plurality of center narrow grooves 22, 23, so that the groove area in the tread center region is reduced compared to a configuration (not shown) in which the tread center region has a circumferential main groove. This has the advantage of reducing the rolling resistance of the tire. On the other hand, (2) the center narrow grooves 22, 23 have a zigzag shape formed by alternately connecting long portions and short portions, so that the wet traction performance of the tire is improved compared to a configuration in which the center narrow groove has a straight shape. Also, (3) in a configuration in which only the pair of shoulder main grooves 21, 21 as described above is provided and no circumferential main groove is provided in the tread center region, the rigidity of the tread center region is increased, so that the wear resistance of the tire is improved.

[0066] In addition, in this tire 1, the center narrow grooves 22, 23 have a groove width of 0.5 mm or more and 3.0 mm or less. The above lower limit ensures the groove width of the center narrow grooves 22, 23, which is advantageous in ensuring the wet performance of the tire. The above upper limit reduces the groove area in the center region of the tread, which is advantageous in reducing the rolling resistance of the tire.

[0067] In addition, in the tire 1, the circumferential length L2;L3 of the long portion of the central narrow groove 22;23 is in the range of 85% to 100% (0.85≦L2 / P2≦1.00 and 0.85≦L3 / P3≦1.00) of the pitch length P2;P3 of the zigzag shape (see FIG. 3). This has the advantage of optimizing the zigzag shape of the central narrow groove 22;23.

[0068] In the tire 1, the long portion of the central narrow groove 22, which is the outermost in the tire width direction among the central narrow grooves 22, 23, has an arc shape that is convex toward the tire equatorial plane CL (see FIG. 3). This configuration has the advantage that, compared to a configuration in which the central narrow groove 22 has a straight shape (not shown), deformation of the blocks 321A-321C, 331A, 331B in the central region of the tread during tire rolling is suppressed, thereby reducing the rolling resistance of the tire.

[0069] In the tire 1, the pitch length P2 of the zigzag shape of the center narrow groove 22, which is the outermost one in the tire width direction among the center narrow grooves 22, 23, satisfies the relationship of 1.30≦P2 / Wb2≦2.00 with respect to the maximum contact width Wb2 of the middle land portion 32 (see FIG. 3). This has the advantage of optimizing the zigzag shape of the center narrow groove 22.

[0070] In addition, in this tire 1, the zigzag amplitude A2 of the center narrow groove 22, which is the outermost in the tire width direction among the center narrow grooves 22, 23, has a relationship of 0.10≦A2 / Wb2≦0.50 with respect to the maximum ground contact width Wb2 of the middle land portion 32. In this configuration, the meshing allowance of the blocks 322A and 332B adjacent in the tire circumferential direction across the short portion of the zigzag shape of the center narrow groove 22 is ensured when the tire is in contact with the ground, and the rigidity of the center region of the tread portion is ensured. This has the advantage of reducing the rolling resistance of the tire.

[0071] In addition, in this tire 1, the maximum distance De2 from the outer edge of the middle land portion 32 in the tire width direction to the tire equatorial plane CL has a relationship of 0.10≦De2 / TW≦0.40 with respect to the tire contact width TW (see FIG. 2). The above lower limit ensures the contact width of the tread center region, which is advantageous in ensuring the reduction of the rolling resistance of the tire due to this tread pattern. The above upper limit also ensures the appropriate contact width Wb1 of the shoulder land portion 31.

[0072] In addition, in this tire 1, the maximum distance De3 from the outer edge of the center land portion 33 in the tire width direction to the tire equatorial plane CL has a relationship of 0.05≦De3 / TW≦0.30 with respect to the tire contact width TW (see FIG. 2). The above lower limit has the advantage of ensuring the width of the center land portion 33 and ensuring the effect of reducing the rolling resistance of the tire by this tread pattern. The above upper limit has the advantage of ensuring the appropriate contact width Wb2 of the middle land portion 32.

[0073] In the tire 1, the maximum ground contact width Wb2 (see FIG. 3) of the middle land portion 32 and the tire ground contact width TW (see FIG. 2) satisfy the relationship 0.10≦Wb2 / TW≦0.25. This has the advantage that the ground contact width Wb2 of the middle land portion 32 is optimized.

[0074] The tire 1 also includes three central narrow grooves 22, 23, 22, and the centrally located central narrow groove 23 is located on the tire equatorial plane CL, which has the advantage of improving the wet performance of the tire.

[0075] In addition, in the tire 1, the middle land portion 32 includes a first middle lateral groove 321A that penetrates the middle land portion 32 and connects to the maximum amplitude position of the center narrow groove 22 toward the tire ground contact end T, and a second middle lateral groove 321B that penetrates the middle land portion 32 and connects to the long portion of the center narrow groove 22 (see FIG. 3). This improves drainage of the ground contact area partitioned by the long portion of the zigzag shape of the first center narrow groove 22, which has the advantage of improving the wet performance of the tire.

[0076] In addition, in the tire 1, the center land portion 33 includes a center lateral groove 331A that penetrates the center land portion 33 and connects to the maximum amplitude position of the first center narrow groove 22 toward the tire equatorial plane CL (see FIG. 3). This provides an advantage that the first middle lateral groove 321A of the middle land portion 32 and the center lateral groove 331A of the center land portion 33 are connected via the short portion of the center narrow groove 22, improving drainage in the center region of the tread portion. EXAMPLES

[0077] 6 and 7 are tables showing the results of performance tests of the tire according to the embodiment of the present invention.

[0078] In this performance test, several types of test tires were evaluated for (1) low rolling resistance performance and (2) wet grip performance. Test tires with a tire size of 275 / 80R22.5 were also manufactured.

[0079] (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 conventional example as the standard (100), and the higher the value, the better.

[0080] (2) In the evaluation of wet grip performance, the test tire is mounted on a JATMA-specified rim, and the JATMA-specified internal pressure and load are applied to the test tire. The test tire is also mounted on a test vehicle for the prescribed μ-S evaluation. The test vehicle then runs on a test course on a wet road surface at a speed of 60 km / h, and the friction coefficient during braking is measured and evaluated. This evaluation is performed using an index evaluation with the conventional example as the standard (100), and the higher the value, the better.

[0081] As shown in Figs. 1 and 2, the test tire of the embodiment includes a pair of shoulder main grooves 21, 21, three center narrow grooves 22, 23, a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and two rows of center land portions 33. The groove center lines of all the center narrow grooves 22, 23 have a zigzag shape formed by alternately connecting long portions and short portions. The tire ground contact width TW is 230 [mm], the maximum distance De2 of the edge portion of the middle land portion 32 is De2 = 70.0 [mm], and the maximum distance De3 of the edge portion of the center land portion 33 is De3 = 38.5 [mm]. The maximum groove width of the shoulder main groove 21 is 10.0 [mm], and the maximum groove depth Hg1 (see Fig. 5) is 14 [mm]. The maximum groove depths Hg2 and Hg3 of the center narrow grooves 22 and 23 are 14 mm, and the maximum groove depths H21 and H31 of the middle lateral grooves 321A and 321B and center lateral grooves 331A and 331B are 12.5 mm. The test tire of Example 1 does not include the second middle lateral groove 321B and the first center lateral groove 331A, and the lateral grooves of the middle land portion 32 and center land portion 33 (the first middle lateral groove 321A and the second center lateral groove 331B) are connected in a staggered manner in the tire circumferential direction along the first center narrow groove 22 (not shown).

[0082] The test tire of the comparative example is the test tire of Example 1, in which the shoulder main grooves 21 and the center narrow grooves 22, 23 have a straight shape.

[0083] As the test results show, the test tires of the examples achieve both low rolling resistance and wet performance. [Explanation of symbols]

[0084] 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, 23 center narrow groove; 31 shoulder land portion; 311 shoulder lug groove; 312 shoulder block; 32 middle land portion; 321A, 321B middle lateral groove; 322A~322C middle block; 33 center land portion; 331A, 331B center lateral groove; 331' bottom upper portion; 332A center block

Claims

1. A tire comprising a pair of shoulder main grooves extending in a tire circumferential direction, two or more center narrow grooves disposed between the pair of shoulder main grooves and extending in the tire circumferential direction, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions defined by the shoulder main grooves and the center narrow groove, At least one of the central narrow grooves has a center line having a zigzag shape formed by alternately connecting long portions and short portions, The central narrow groove has a groove width of 0.5 mm or more and 3.0 mm or less, The long portion of the central narrow groove, which is located at the outermost side in the tire width direction, has an arc shape that is convex toward the tire equatorial plane, and A tire characterized in that the region between the pair of shoulder main grooves does not include any other circumferential groove having a maximum groove width exceeding 3.0 mm and a maximum groove depth of 10 mm or more.

2. 2. The tire according to claim 1, wherein a circumferential length of the long portion of the central narrow groove is in a range of 85% to 100% of a pitch length of the zigzag shape.

3. 3. The tire according to claim 1, wherein a pitch length P2 of the zigzag shape of the central narrow groove located at the outermost side in the tire width direction among the central narrow grooves satisfies a relationship of 1.30≦P2 / Wb2≦2.00 with respect to a maximum ground contact width Wb2 of the middle land portion.

4. 4. The tire according to claim 1, wherein a maximum distance De2 from an outer edge portion in the tire width direction of the middle land portion to the tire equatorial plane satisfies a relationship of 0.10≦De2 / TW≦0.40 with respect to a tire ground contact width TW.

5. The tire according to any one of claims 1 to 4, wherein a maximum distance De3 from an outer edge portion in the tire width direction of the center land portion to the tire equatorial plane satisfies the relationship of 0.05≦De3 / TW≦0.30 with respect to a tire ground contact width TW.

6. 6. The tire according to claim 1, wherein the maximum ground contact width Wb2 of the middle land portion satisfies the relationship of 0.10≦Wb2 / TW≦0.25 with respect to the tire ground contact width TW.

7. 7. The tire according to claim 1, comprising three central narrow grooves, the centrally disposed central narrow groove being located on the tire equatorial plane.

8. A first center narrow groove is defined as being located at the outermost side in the tire width direction among the center narrow grooves, and 8. The tire according to claim 1, wherein the middle land portion includes a first middle lateral groove that penetrates the middle land portion and is connected to a maximum amplitude position of the central narrow groove toward the tire ground contact end side, and a second middle lateral groove that penetrates the middle land portion and is connected to the long portion of the central narrow groove.

9. The tire according to claim 8 , wherein the central land portion includes a central lateral groove that penetrates the central land portion and is connected to a position of maximum amplitude of the first central narrow groove toward the tire equatorial plane side.

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