JP7587115B2 - tire - Google Patents

Description

This invention relates to tires, and more specifically to tires that can improve wet tire performance while maintaining low rolling resistance.

To reduce the rolling resistance of tires while maintaining wet performance, modern heavy-duty tires fitted to trucks, buses and other vehicles used for long-distance transport 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.

A conventional heavy-duty tire that employs such a configuration is known from the technology described in Patent Document 1.

International Publication No. 2017/040007

The objective of this invention is to provide a tire that can improve wet performance while maintaining low rolling resistance.

In order to achieve the above object, the tire according to the present invention is a tire comprising a pair of shoulder main grooves extending in the tire circumferential direction, a pair of shoulder regions bounded by the pair of shoulder main grooves, and a single center region, the center region comprising a middle lug groove having one end opening into the shoulder main grooves and the other end within the ground contact surface of the center region, and a center lug groove having both ends within the ground contact surface of the center region, the middle lug groove and the center lug groove being defined as continuous groove portions having a minimum groove width of 4.0 mm or more. the center region includes 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 middle land portions and one or more rows of center land portions partitioned by the center narrow grooves, the middle lug grooves extending in the middle land portions, the center lug grooves extending in the center land portions, and the center narrow grooves having a zigzag shape formed by alternatingly connecting long portions and short portions .

In the tire according to the present invention, (1) the center region of the tread portion has wide middle lug grooves and center lug grooves, which has the advantage of improving drainage in the center region and improving wet performance of the tire compared to a configuration without wide lug grooves in the center region. Also, (2) at least a portion of the center lug groove extends into a region closer to the tire equatorial plane than the other end of the middle lug groove, which has the advantage of further improving drainage in the center region. Furthermore, (3) the center lug groove has both ends within the ground contact surface of the center region, which has the advantage of ensuring rigidity in the center region and ensuring low rolling resistance performance of the tire compared to a configuration in which the center lug groove opens into the shoulder main groove.

FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. FIG. 2 is a plan view showing the tread surface of the tire shown in FIG. FIG. 3 is an enlarged view showing the center region of the tread portion of the tire shown in FIG. FIG. 4 is an enlarged view showing the block units of the middle land portion and the center land portion shown in FIG. FIG. 5 is a cross-sectional view showing the middle land portion and the center land portion shown in FIG. FIG. 6 is an explanatory diagram showing a modified example of the tire shown in FIG. FIG. 7 is an explanatory diagram showing a modified example of the tire shown in FIG. FIG. 8 is a table showing the results of performance tests of the tire according to the embodiment of the present invention.

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

[tire]
Fig. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. 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.

In the figure, the tire meridian cross section is defined as the cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as the 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 the direction parallel to the tire rotation axis, and the tire radial direction is defined as the direction perpendicular to the tire rotation axis.

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

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

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

The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is arranged around the outer circumference 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 it, and has an absolute cord angle (defined as the inclination angle of the belt cord 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 it, and have an absolute cord angle of 10 degrees or more and 55 degrees or less. In addition, the pair of cross belts 142 and 143 have cord angles of different signs from 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 made by covering multiple belt cover cords made of steel or organic fiber material with coating rubber and rolling them, and has a cord angle of 10 degrees or more and 55 degrees or less in absolute value.

The tread rubber 15 is arranged on the tire radial outer circumference of the carcass layer 13 and the belt layer 14 to form the tread portion of the tire. A pair of sidewall rubbers 16, 16 are arranged on the tire widthwise outer sides of the carcass layer 13 to form the left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the tire radial inner side of the left and right bead cores 11, 11 and the turned-up portion of the carcass layer 13 to the tire widthwise outer side to form the rim fitting surface of the bead portion.

[Tread 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 indicates the tire ground contact end, and the dimension symbol TW indicates the tire ground contact width. In the figure, since 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.

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 arranged between the 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 of center land portions 33, which are partitioned by the shoulder main groove 21 and the center narrow groove 22, 23, on the tread surface. The middle land portion 32 is defined as a land portion partitioned by the shoulder main groove 21 and the center narrow groove 22 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 tread center region) 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 tread center region. This ensures rigidity in the center area of the tread and reduces the rolling resistance of the tire.

The shoulder main groove 21 is a groove that is required to display a wear indicator as stipulated 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 or more and 3.0 mm or less, 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.

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 configurations where 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.

Groove depth is measured as the distance from the tread surface to the bottom of the groove when the tire is mounted on a specified rim, inflated to the specified internal pressure, and in an unloaded state. In addition, for configurations that have partial unevenness or sipes at the bottom of the groove, the groove depth is measured excluding these.

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

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

In the configuration of FIG. 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 arranged between these shoulder main grooves 21, 21. The center narrow groove 23 is arranged on the tire equatorial plane CL. These 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.

[Tread center area]
Fig. 3 is an enlarged view of 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 of the 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 of the middle land portion 32 and the center land portion 33 shown in Fig. 3.

In the configuration of FIG. 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 the shoulder main grooves 21, 21 and the center narrow grooves 22, 23, 22.

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. Note that, for example, in a configuration having only two center narrow grooves 22, 22 and a single center land portion 33 (see FIG. 6 described later), the second center narrow groove 23 is omitted.

As shown in FIG. 3, the groove center lines of the first and second center narrow grooves 22, 23 have a zigzag shape formed by alternating long and short sections (reference numbers omitted in the figure).

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 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. On the other hand, (2) the center narrow grooves 22, 23 have a zigzag shape formed by alternatingly connecting long and short portions, so 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 with only a pair of shoulder main grooves 21, 21 as described above and no circumferential main groove in the tread center region, the rigidity of the tread center region is increased, improving the wear resistance of the tire.

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 figure). As described later, the shoulder main groove 21 has a zigzag shape in which long and short portions are alternately connected as a whole (see FIG. 2). The zigzag long portion of the first center narrow groove 22 is inclined in the opposite direction to the zigzag long portion of the shoulder main groove 21 in the tire circumferential direction. The long portion of the first center narrow groove 22 on the tire ground contact edge T side has an 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-322C, 332A, 332B in the center region of the tread portion during tire rotation 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. This improves the wet performance of the tire.

In addition, the circumferential lengths L2, L3 of the long portions 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 relative to the pitch lengths P2, P3 of the zigzag shape, and preferably in the ranges of 0.90≦L2/P2≦0.96 and 0.90≦L3/P3≦0.96. This optimizes the zigzag shape of the center narrow grooves 22; 23. In particular, the lower limit effectively suppresses the collapse of blocks, and the edge components increase, improving the low rolling resistance and wet performance of the tire. In addition, the number of pitches of the zigzag shape of the first and second center narrow grooves 22, 23 is equal to each other.

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; 23. In particular, the above lower limit optimizes the block rigidity, achieving both low rolling resistance and wet performance of the tire.

3, the zigzag amplitude A2 of the first center narrow groove 22 on the tire ground contact end T side 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, and preferably has a relationship of 0.15≦A2/Wb2≦0.35. 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 center region of the tread portion and reduces the rolling resistance of the tire. Similarly, the zigzag amplitude A3 of the second center narrow groove 23 on the tire equatorial plane CL side has a relationship of 0.10≦A3/Wb3≦0.50 with respect to the maximum ground contact width Wb3 of the center land portion 33, and preferably has a relationship of 0.15≦A3/Wb3≦0.35.

In addition, in FIG. 5, the maximum groove depths Hg2 and Hg3 of the first and second center narrow grooves 22 and 23 have the relationship 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 and 23 are shallower than the shoulder main groove 21.

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 with respect to the tire ground contact width TW, and preferably has a relationship of 0.15≦De2/TW≦0.35. Also, 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 ground contact width TW, and preferably has a relationship of 0.08≦De3/TW≦0.20.

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

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

In addition, in FIG. 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. In addition, 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. In addition, the maximum ground contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33 are approximately 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.

The land contact widths Wb2 and Wb3 are measured as the linear distance in the axial direction of the tire at the contact surface between the land and the flat plate when the tire is mounted on a specified rim, pressurized to the specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to the specified load.

In addition, in the configuration shown in FIG. 3, the edge portion of the center land portion 33 on the tire equatorial plane CL side has a zigzag shape that follows the center narrow groove 23, and part of the edge portion intersects with the tire equatorial plane CL. This improves the wet traction performance of the tire.

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

The middle lug groove 321A is a wide lateral groove and is defined as a continuous groove portion having a minimum groove width described later. The middle lug groove 321A has one end opening into the shoulder main groove 21 and the other end in the ground contact surface of the tread center region. Specifically, as shown in FIG. 3, the middle lug groove 321A extends in the tire width direction, penetrates the middle land portion 32, and connects to the shoulder main groove 21 and the first center narrow groove 22. The middle lug groove 321A also connects to the maximum amplitude position of the first center narrow groove 22 toward the tire ground contact end T. The middle lug groove 321A also extends along an extension line of the groove center line of the short portion of the first center narrow groove 22, and the middle lug groove 321A and the short portion of the first center narrow groove 22 share a groove center line that is linear or arc-shaped. Also, in FIG. 3, the inclination angle θ21 of the middle lug groove 321A with respect to the tire circumferential direction is in the range of 50 [deg] ≦ θ21 ≦ 90 [deg], and preferably in the range of 60 [deg] ≦ θ21 ≦ 80 [deg].

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

In addition, multiple middle lug grooves 321A (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 the configuration of FIG. 3, the middle lug grooves 321A have a straight shape or a gentle arc shape.

The middle lug groove 321A is defined as a continuous groove portion having a minimum groove width of 4.0 mm or more. The middle lug groove 321A has a maximum groove width W21 (see FIG. 3) of 10.0 mm or less, preferably 7.0 mm or less. The middle lug groove 321A has a maximum groove depth H21 (see FIG. 5) of 7.5 mm or more. In FIG. 5, the maximum groove depth H21 of the middle lug groove 321A 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 lug groove 321A is shallower than the shoulder main groove 21. The maximum groove depth H21 of the middle lug groove 321A is shallower than the maximum groove depth Hg2 of the center narrow groove 22 (H21<Hg2). Also, in the configuration of FIG. 5, the middle lug groove 321A does not have a partial bottom top and has a constant groove depth.

3, the extension length of the middle lug groove 321A in the tire width direction (dimension symbols omitted in the figure) is in the range of 70% to 100% of the maximum ground contact width Wb2 of the middle land portion 32. In the configuration of FIG. 3, as described above, the shoulder main groove 21 and the center narrow groove 22 have a zigzag shape, and the middle lug groove 321A connects and terminates the maximum amplitude positions of the zigzag shapes of the shoulder main groove 21 and the center narrow groove 22, so that the extension length of the middle lug groove 321A in the tire width direction is shorter than the maximum ground contact width Wb2 of the middle land portion 32.

The middle lateral groove 321B is a sipe or narrow groove that extends in the tire width direction, penetrates the middle land portion 32, and connects to the shoulder main groove 21 and the first center narrow groove 22. The pair of middle lateral grooves 321B, 321B connects to the first center narrow groove 22 at a position that divides the long portion of the first center narrow groove 22 into approximately three equal parts. The intersection angle (dimension symbol omitted in the figure) of the groove center line between the middle lateral 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.

In addition, at least one (two in the configuration of FIG. 3) middle lateral groove 321B is disposed between adjacent middle lug grooves 321A, 321A. This improves the drainage of the ground contact area partitioned by the long portion of the zigzag shape of the first center narrow groove 22. In the configuration of FIG. 3, the middle lateral groove 321B has a gentle S-shape.

The middle lateral groove 321B has a groove width Ws (see FIG. 3) of 0.1 mm to 3.0 mm, preferably 0.5 mm to 2.2 mm. The middle lateral groove 321B has a maximum groove depth (not shown) of 7.5 mm or more. The ratio of the maximum groove depth of the middle lateral groove 321B to the maximum groove depth Hg1 of the shoulder main groove 21 (see FIG. 5) is in the range of 0.30 to 0.90. Therefore, the middle lateral groove 321B is shallower than the shoulder main groove 21. The maximum groove depth of the middle lateral groove 321B is shallower than the maximum groove depth Hg2 of the center narrow groove 22 (see FIG. 5).

As shown in FIG. 2, the middle blocks 322A, 322B, and 322C are divided into a middle lug groove 321A and a middle lateral groove 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 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 center narrow groove 22 are uniform, and 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. As a result, uneven wear of the middle blocks 322A, 322B, and 322C is suppressed.

In addition, in Fig. 4, the maximum circumferential length L22 and the 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 a relationship of 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 arranged with its longitudinal direction inclined relative to the tire width direction, so that the aspect ratio L22/W22 is set within the above range.

In the configuration of FIG. 2, as described above, the tread center region has a pair of middle lug grooves 321A, 321A that open into a pair of shoulder main grooves 21, 21, respectively. In addition, a plurality of pairs of middle lug grooves 321A, 321A are arranged at a predetermined pitch length Pg2 in the tire circumferential direction. At this time, the pair of middle lug grooves 321A, 321A overlap each other when projected in the tire width direction. In addition, the overlap amount Lg1 of the pair of middle lug grooves 321A, 321A has a relationship of 0.01≦Lg1/Pg2≦0.20 with respect to the pitch length Pg2 of the middle lug groove 321A, and preferably has a relationship of 0.05≦Lg1/Pg2≦0.15.

The overlap amount Lg1 of the middle lug grooves 321A is measured by projecting a pair of left and right middle lug grooves 321A, 321A arranged at one pitch in the tire width direction, with the ends of these middle lug grooves 321A, 321A as measurement points.

In addition, in FIG. 2, the total extension length Lg2 of the pair of middle lug grooves 321A, 321A in the tire circumferential direction has a relationship of 0.30≦Lg2/Pg2≦0.50 with respect to the pitch length Pg2 of the middle lug groove 321A, and preferably has a relationship of 0.35≦Lg2/Pg2≦0.45.

The total extension length Lg2 of the middle lug grooves 321A is measured by projecting the pair of left and right middle lug grooves 321A, 321A arranged at one pitch in the tire width direction, with the ends of these middle lug grooves 321A, 321A as measurement points.

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

The center lug groove 331A is a wide lateral groove and is defined as a continuous groove portion having a minimum groove width described later. The center lug groove 331A has both ends within the ground contact surface of the center region of the tread portion. As shown in FIG. 3, the center lug groove 331A extends in the tire width direction, penetrates the center land portion 33, and connects to the adjacent first and second center narrow grooves 22, 23. The center lug groove 331A also 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 end T.

3, the inclination angle θ31 of the center lug groove 331A with respect to the tire circumferential direction is in the range of 50 [deg] ≦ θ31 ≦ 90 [deg], preferably in the range of 60 [deg] ≦ θ31 ≦ 80 [deg]. The center lug groove 331A of the center land portion 33 and the middle lug groove 321A of the middle land portion 32 are inclined in opposite directions with respect to the tire circumferential direction. The angle φ1 between the middle lug groove 321A and the center lug groove 331A is preferably in the range of 120 [deg] ≦ φ1 ≦ 150 [deg]. Therefore, the long portion of the first center narrow groove 22, the center lug groove 331A of the center land portion 33, and the middle lug 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 side. This improves the drainage of the center region of the tread portion.

However, this is not limited to the above, and the center lug groove 331A of the center land portion 33 and the middle lug groove 321A of the middle land portion 32 may be inclined in the same direction relative to the tire circumferential direction (not shown).

In addition, a plurality of center lug 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 the configuration of FIG. 3, the center lug groove 331A has a straight shape or a gentle arc shape. As shown in FIG. 3, the middle lug groove 321A of the middle land portion 32 and the center lug 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 curved groove that is convex in the tire circumferential direction.

The center lug groove 331A is defined as a continuous groove portion having a minimum groove width of 4.0 mm or more. The center lug groove 331A has a maximum groove width W31 (see FIG. 3) of 10.0 mm or less, preferably 7.0 mm or less. The center lug groove 331A has a maximum groove depth H31 (see FIG. 5) of 7.5 mm or more. In FIG. 5, the maximum groove depth H31 of the center lug groove 331A and the maximum groove depth Hg1 of the shoulder main groove 21 satisfy the relationship of 0.50≦H31/Hg1≦0.90. Therefore, the center lug groove 331A is shallower than the shoulder main groove 21. The maximum groove depth H31 of the center lug groove 331A is shallower than the maximum groove depth Hg2 of the center narrow groove 22 (H31<Hg2).

3, the extension length of the center lug groove 331A in the tire width direction (dimension symbols omitted in the figure) is in the range of 50% to 100% of the maximum ground contact width Wb3 of the center land portion 33. In the configuration of FIG. 3, as described above, the first and second center narrow grooves 22, 22 have a zigzag shape, and the center lug groove 331A connects and terminates the maximum amplitude positions of the zigzag shapes of these center narrow grooves 22, 22, so that the extension length of the center lug groove 331A in the tire width direction is shorter than the maximum ground contact width Wb3 of the center land portion 33.

2, at least a portion of the center lug groove 331A of the center land portion 33 extends further into the region closer to the tire equatorial plane CL than the end of the middle lug groove 321A of the middle land portion 32 on the tire equatorial plane CL side. In the configuration of FIG. 2, as shown in FIG. 3, the end of the center lug groove 331A on the tire ground contact edge T side is closer to the tire equatorial plane CL than the end of the middle lug groove 321A on the tire equatorial plane CL side. Therefore, the center lug groove 331A is positioned at a distance in the tire width direction from the middle lug groove 321A of the middle land portion 32.

In the above configuration, (1) the center region of the tread portion has wide middle lug grooves 321A and center lug grooves 331A, so that the drainage of the center region is improved and the wet performance of the tire is improved compared to a configuration (not shown) that does not have wide lug grooves in the center region. Also, (2) at least a portion of the center lug groove 331A extends into an area closer to the tire equatorial plane CL than the other end of the middle lug groove 321A, so that the drainage of the center region is further improved. Furthermore, (3) since the center lug groove 331A has both ends within the ground contact surface of the center region, the rigidity of the center region is ensured and the low rolling resistance performance of the tire is ensured compared to a configuration in which the center lug groove opens into the shoulder main groove.

3, the distance Dg1 between the center lug groove 331A and the middle lug groove 321A in the tire width direction is preferably 0.03≦Dg1/Wce relative to the maximum ground contact width Wce (see FIG. 2) of the tread center region. There is no upper limit to the ratio Dg1/Wce, but it is restricted by the relationship with the end of the middle lug groove 321A and the lower limit of the extension length of the center lug groove 331A in the tire width direction. In the configuration of FIG. 3, the distance Dg1 between the center lug groove 331A and the middle lug groove 321A is approximately equal to the amplitude A2 of the zigzag shape of the first center narrow groove 22.

The separation distance Dg1 is measured as the distance in the tire width direction from the end of the middle lug groove 321A on the tire equatorial plane CL side to the end of the center lug groove 331A on the tire ground contact edge T side. The separation distance Dg1 is calculated excluding the groove width of the center narrow groove 22 between the middle lug groove 321A and the center lug groove 331A.

The ends of the middle lug groove 321A and the center lug groove 331A are defined as the ends of continuous grooves having a minimum groove width of 4.0 mm or more as described above.

3, the distance Dg2 between adjacent center lug grooves 331A in the tire width direction preferably satisfies the relationship of 0.03≦Dg2/Wce with respect to the maximum ground contact width Wce (see FIG. 2) of the tread center region. There is no particular upper limit to the ratio Dg2/Wce, but it is restricted by the relationship with the end of the center lug groove 331A and the lower limit of the extension length of the center lug groove 331A in the tire width direction. In the configuration of FIG. 3, the distance Dg2 between the center lug grooves 331A is approximately equal to the amplitude A3 of the zigzag shape of the second center narrow groove 23.

The separation distance Dg2 is measured as the distance in the tire width direction between the ends of adjacent center lug grooves 331A, 331A. In addition, the separation distance Dg2 is calculated excluding the groove width of the center narrow groove 23 between the adjacent center lug grooves 331A, 331A.

In the configuration of FIG. 2, as described above, the center lug groove 331A is arranged to be spaced apart in the tire width direction from the middle lug groove 321A of the middle land portion 32. This ensures the rigidity of the tread center region and ensures low rolling resistance performance of the tire. However, this is not limited to this, and the center lug groove 331A may be arranged to overlap the middle lug groove 321A in the tire width direction (not shown).

As shown in FIG. 5, the center lug groove 331A has a partial bottom upper portion 331' at the connection 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 the maximum groove depth Hg1 of the shoulder main groove 21 and the maximum groove depth H31 of the center lug groove 331A.

The center lateral groove 331B extends in the tire width direction, penetrates the center land portion 33, and connects to the adjacent first and second center narrow grooves 22, 23. The center lateral groove 331B also connects the long portion of the first center narrow groove 22 and the long portion of the second center narrow groove 23.

The intersection angle between the center transverse groove 331B and the long portion of the first center narrow groove 22 (dimension symbol omitted in the figure) is in the range of 70 degrees or more and 90 degrees or less. The intersection angle between the center transverse groove 331B and the long portion of the second center narrow groove 23 (dimension symbol omitted in the figure) is in the range of 80 degrees or more and 100 degrees or less.

In the configuration of FIG. 3, one center lateral groove 331B is disposed between adjacent center lug grooves 331A, 331A. However, this is not limited thereto, and two or more center lateral grooves 331B may be disposed between adjacent center lug grooves 331A, 331A, or the center lateral groove 331B may be omitted (not shown). In the configuration of FIG. 3, the center lateral groove 331B has a gentle S-shape.

The center lateral groove 331B has a groove width Ws (see FIG. 3) of 0.1 mm to 3.0 mm, preferably 0.5 mm to 2.2 mm. The center lateral groove 331B has a maximum groove depth (not shown) of 7.5 mm or more. The ratio of the maximum groove depth of the center lateral groove 331B to the maximum groove depth Hg1 of the shoulder main groove 21 (see FIG. 5) is in the range of 0.50 to 0.90. Therefore, the center lateral groove 331B is shallower than the shoulder main groove 21. The maximum groove depth of the center lateral groove 331B is shallower than the maximum groove depth Hg2 of the center narrow groove 22.

As shown in FIG. 2, the center blocks 332A and 332B are partitioned into a center lug groove 331A and a center lateral groove 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. Furthermore, these center blocks 332A and 332B are arranged alternately in the tire circumferential direction. Furthermore, the contact areas of the center blocks 332A and 332B are uniform; specifically, the ratio between the maximum and minimum values of the contact areas is in the range of 1.00 to 1.20. This suppresses uneven wear of the center blocks 332A and 332B.

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. In addition, 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.

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

In addition, 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 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.

In addition, in FIG. 3, the number N3 of center blocks 332A, 332B per unit pitch has a relationship of N3<N2 with respect to the number N2 of middle blocks 322A-322C of the middle land portion 32. 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 middle blocks 322A-322C and the number N3 of center blocks 332A, 332B are N2:N3=3:2, but this 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, or 5:4.

In the above configuration, (1) the number N3 of center blocks 332A, 332B on the tire equatorial plane CL side is relatively small, ensuring rigidity near the tire equatorial plane CL and reducing the rolling resistance of the tire. Also, (2) the number N2 of middle blocks 322A-322C on the tire ground contact end T side is relatively large, ensuring the groove area of the middle land portion 32 and improving the wet performance of the tire. As a result, the tire achieves both low rolling performance and wet performance.

In particular, when the ratio N2:N3 of the number N2 of middle blocks 322A-322C to the number N3 of center blocks 332A, 332B is 2:1, 3:2, 4:3, 5:4, ..., the middle lateral grooves 321B and center lateral grooves 331B can be connected in a staggered manner to the long portion of the first center narrow groove 22 in the block units per pitch (middle blocks 322A-322C and center blocks 332A, 332B; see Figure 4). This optimizes the rigidity balance of the block units.

[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. Also, the groove center line (not shown) of the shoulder main groove 21 has a zigzag shape overall, with long portions and short portions alternately connected.

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

[Modification]
Figures 6 and 7 are explanatory diagrams showing modified examples of the tire shown in Figure 2. In these figures, the same components as those shown in Figure 2 are given the same reference numerals, and the description thereof will be omitted.

In the configuration of FIG. 2, as described above, the left and right regions bounded by the tire equatorial plane CL each have a single shoulder main groove 21, 21. In addition, three center narrow grooves 22, 23, 22 are arranged between these shoulder main grooves 21, 21. In addition, the central center narrow groove 23 is arranged on the tire equatorial plane CL. In addition, these 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.

6, two center narrow grooves 22, 22 are arranged between a pair of shoulder main grooves 21, 21, forming a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single center land portion 33. In this case, the center lug groove 331A of the center land portion 33 crosses the tire equatorial plane CL and connects to the left and right middle lug grooves 321A, 321A via the left and right center narrow grooves 22, 22.

In the modified example of FIG. 7, four or more center narrow grooves 22, 23 are arranged between a pair of shoulder main grooves 21, 21, thereby forming 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. In addition, the center narrow groove 23 is arranged at a position off the tire equatorial plane CL, so that the center land portion 33 is arranged on the tire equatorial plane CL. In the configuration of FIG. 7, the center lug grooves 331A of the three rows of center land portions 33 are inclined in the same direction in the tire circumferential direction.

[effect]
As described above, the tire 1 includes a pair of shoulder main grooves 21, 21 extending in the tire circumferential direction, a pair of shoulder regions bounded by the pair of shoulder main grooves 21, 21, and a single center region (see FIG. 2). The center region includes a middle lug groove 321A having one end opening into the shoulder main groove 21 and the other end in the ground contact surface of the center region, and a center lug groove 331A having both ends in the ground contact surface of the center region. The middle lug groove 321A and the center lug groove 331A have a minimum groove width of 4.0 mm or more. At least a portion of the center lug groove 331A extends into a region closer to the tire equatorial plane CL than the other end of the middle lug groove 321A.

In this configuration, (1) the center region of the tread portion has wide middle lug grooves 321A and center lug grooves 331A, which has the advantage of improving drainage in the center region and improving wet performance of the tire compared to a configuration (not shown) that does not have wide lug grooves in the center region. Also, (2) at least a portion of the center lug groove 331A extends to an area closer to the tire equatorial plane CL than the other end of the middle lug groove 321A, which has the advantage of further improving drainage in the center region. Furthermore, (3) the center lug groove 331A has both ends within the ground contact surface of the center region, which has the advantage of ensuring rigidity in the center region and ensuring low rolling resistance performance of the tire compared to a configuration in which the center lug groove opens into the shoulder main groove.

In addition, in this tire 1, the center region has a substantially continuous tread surface that is not divided in the tire width direction by other circumferential grooves that have a maximum groove width exceeding 3.0 mm (see Figure 2). This has the advantage of ensuring the rigidity of the center region and ensuring low rolling resistance performance of the tire.

In addition, in this tire 1, the inclination angles θ21, θ31 of the middle lug grooves 321A and center lug grooves 331A relative to the tire circumferential direction are in the range of 60 degrees or more and 80 degrees or less. Compared to a configuration (not shown) in which the lug groove inclination angle is approximately 90 degrees, this configuration has the advantage that the collapse of the blocks 322A-322C, 332A, and 332B defined by the lug grooves 321A and 331A is suppressed, ensuring low rolling resistance and wet performance of the tire.

In addition, in this tire 1, the middle lug groove 321A and the center lug groove 331A are inclined in opposite directions relative to the tire circumferential direction (see FIG. 2). Compared to a configuration in which the lug grooves are inclined in the same direction relative to the tire circumferential direction (not shown), this configuration has the advantage that the collapse of the blocks 322A-322C, 332A, and 332B defined by the lug grooves 321A and 331A is suppressed, ensuring low rolling resistance and wet performance of the tire.

In addition, in this tire 1, the angle φ1 between the middle lug groove 321A and the center lug groove 331A is in the range of 120 [deg] ≦ φ1 ≦ 150 [deg] (see FIG. 3). This ensures the rigidity of the center region of the tread, which has the advantage of ensuring low rolling resistance performance of the tire.

In addition, in this tire 1, the center lug groove 331A is arranged to be spaced apart in the tire width direction from the middle lug groove 321A (see FIG. 3). This has the advantage of ensuring rigidity in the center region of the tread and ensuring low rolling resistance performance of the tire, compared to a configuration in which the center lug groove and the middle lug groove overlap each other in the tire width direction.

In addition, in this tire 1, the distance Dg1 (see FIG. 3) between the middle lug groove 321A and the center lug groove 331A in the tire width direction has a relationship of 0.03≦Dg1/Wce with respect to the maximum ground contact width Wce (see FIG. 2) of the center region. This has the advantage that the distance Dg1 between the middle lug groove 321A and the center lug groove 331A is ensured to be optimal.

In addition, in this tire 1, the center region is provided with a pair of middle lug grooves 321A, 321A that open into the pair of shoulder main grooves 21, 21, respectively (see FIG. 2). In addition, the pair of middle lug grooves 321A, 321A overlap each other when projected in the tire width direction (see FIG. 2). This ensures the rigidity of the tread center region, which has the advantage of ensuring low rolling resistance performance of the tire.

In addition, in this tire 1, the total extension length Lg2 of the pair of middle lug grooves 321A, 321A in the tire circumferential direction has a relationship of 0.30≦Lg2/Pg2≦0.50 with respect to the pitch length Pg2 of the middle lug groove 321A (see FIG. 2). This has the advantage that the total extension length Lg2 of the pair of middle lug grooves 321A, 321A in the tire circumferential direction is optimized.

In addition, in this tire 1, the center region has two or more center narrow grooves 22 arranged between a pair of shoulder main grooves 21, 21 and extending in the tire circumferential direction, and a pair of middle land portions 32 and one or more rows of center land portions 33 partitioned by the center narrow grooves 22 (see FIG. 2). Also, the middle lug groove 321A extends in the middle land portion 32, and the center lug groove 331A extends in the center land portion 33. In this configuration, since the center region has the center narrow groove 22, the drainage of the center region is improved. Also, since the middle lug groove 321A and the center lug groove 331A extend in the middle land portion 32 and the center land portion 33, respectively, the drainage of each land portion 32, 33 is properly ensured. This has the advantage of improving the wet performance of the tire.

In addition, in this tire 1, the center narrow grooves 22, 23 have a maximum 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 has the advantage of ensuring the wet performance of the tire. The above upper limit also has the advantage of reducing the groove area in the center region of the tread portion, which has the advantage of reducing the rolling resistance of the tire.

In addition, in this tire 1, the middle lug groove 321A penetrates the middle land portion 32 to connect the shoulder main groove 21 and the center narrow groove 22 (see FIG. 2). This configuration ensures a drainage path from the center narrow groove 22 to the shoulder main groove 21 via the middle lug groove 321A, which has the advantage of ensuring proper drainage in the center region of the tread, which has a wide tread surface.

In addition, in this tire 1, the center lug groove 331A penetrates the center land area and connects adjacent center narrow grooves 22 (see Figure 2). This has the advantage of ensuring proper drainage in the center area of the tread, which has a wide tread surface.

In addition, in this tire 1, the center narrow groove 22 has a zigzag shape formed by alternatingly connecting long and short sections, and the middle lug groove 321A connects to the zigzag shape of the center narrow groove 22 at the maximum amplitude position toward the tire ground contact edge T (see FIG. 2). Also, the center lug groove 331A connects to the zigzag shape of the center narrow groove 22 at the maximum amplitude position toward the tire equatorial plane CL. This has the advantage of ensuring proper drainage in the center region of the tread, which has a wide tread surface.

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

Figure 8 is a chart showing the results of a performance test of a tire according to an embodiment of the present invention.

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

(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 in accordance with ISO 28580 under the conditions of a load of 28.76 kN, an air pressure of 900 kPa, and a speed of 60 km/h. This evaluation is performed using an index evaluation with the conventional example as the standard (100), and the higher the value, the better. Also, if it is 96 or higher, it can be said that the performance is maintained appropriately.

(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 carrying out a prescribed μ-S evaluation. The test vehicle then runs on a test course with a wet road surface, and the deceleration caused by ABS braking is measured from a speed of 60 km/h to 20 km/h. This evaluation is performed using an index evaluation with the conventional example as the standard (100), and the higher the value, the more preferable it is.

As shown in Figures 1 and 2, the test tire of the embodiment has 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. Each of the middle land portions 32 has a plurality of middle lug grooves 321A and middle lateral grooves 321B, and each of the center land portions 33 has a plurality of center lug grooves 331A and center lateral grooves 331B. The tire ground contact width TW is 230 mm, and the maximum ground contact width Wce of the center region is 140 mm. The maximum groove width of the shoulder main grooves 21 (dimension symbols omitted in the figure) is 10.0 mm, and the maximum groove depth Hg1 (see Figure 5) is 14 mm. The maximum groove width of the center narrow grooves 22 and 23 (dimension symbols omitted in the figure) is 2.0 mm, and the maximum groove depths Hg2 and Hg3 are 14 mm. The middle lug groove 321A and the center lug groove 331A are defined as continuous groove portions having a minimum groove width of 4.0 mm or more, and the maximum groove depths H21 and H31 are 12.5 mm.

The comparative test tire is the test tire of Example 1, in which the middle lug groove 321A and the center lug groove 331A are narrow sipes.

As the test results show, the test tire of the embodiment achieves both low rolling resistance and wet performance.

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 Middle lug groove; 321B Middle lateral groove; 322A-322C Middle block; 33 Center land portion; 331A Center lug groove; 331B Center lateral groove; 331' Bottom upper portion; 332A, 332B Center block

Claims (13)

A tire comprising a pair of shoulder main grooves extending in a tire circumferential direction, and a pair of shoulder regions and a single center region bounded by the pair of shoulder main grooves,
the center region includes a middle lug groove having one end that opens into the shoulder main groove and the other end that is in the ground contact surface of the center region, and a center lug groove having both ends that are in the ground contact surface of the center region,
The middle lug groove and the center lug groove are defined as continuous groove portions having a minimum groove width of 4.0 mm or more ,
At least a portion of the center lug groove extends toward the tire equatorial plane side relative to the other end of the middle lug groove,
The center region includes two or more center narrow grooves disposed between the pair of shoulder main grooves and extending in the tire circumferential direction, a pair of middle land portions and one or more rows of center land portions partitioned by the center narrow grooves, the middle lug grooves extend in the middle land portions, and the center lug grooves extend in the center land portions, and
The tire is characterized in that the central narrow groove has a zigzag shape formed by alternatingly connecting long portions and short portions . The tire according to claim 1, wherein the center region has a substantially continuous tread surface that is not interrupted in the tire width direction by other circumferential grooves having a maximum groove width exceeding 3.0 mm. The tire according to claim 1 or 2, wherein the inclination angle of the middle lug groove and the center lug groove with respect to the tire circumferential direction is in the range of 60 degrees or more and 80 degrees or less. A tire according to any one of claims 1 to 3, in which the middle lug groove and the center lug groove are inclined in opposite directions relative to the tire circumferential direction. The tire according to claim 4, wherein the angle φ1 between the middle lug groove and the center lug groove is in the range of 120 [deg] ≦ φ1 ≦ 150 [deg]. A tire according to any one of claims 1 to 5, wherein the center lug groove is spaced apart from the middle lug groove in the tire width direction. The tire according to claim 6, wherein the distance Dg1 between the center lug groove and the middle lug groove in the tire width direction satisfies the relationship 0.03≦Dg1/Wce with respect to the maximum contact width Wce of the center region. the center region includes a pair of middle lug grooves each opening into the pair of shoulder main grooves, and
The tire according to any one of claims 1 to 7, wherein the pair of middle lug grooves overlap each other when projected in the tire width direction. The tire according to claim 8, wherein the total extension length Lg2 of the pair of middle lug grooves in the tire circumferential direction has a relationship of 0.30≦Lg2/Pg2≦0.50 with respect to the pitch length Pg2 of the middle lug grooves. The tire according to any one of claims 1 to 9 , wherein the central narrow groove has a groove width of 0.5 mm or more and 3.0 mm or less. The tire according to any one of claims 1 to 10 , wherein the middle lug groove passes through the middle land portion to connect the shoulder main groove and the center narrow groove. The tire according to any one of claims 1 to 11 , wherein the center lug groove passes through the center land portion and connects adjacent center narrow grooves. The middle lug groove is connected to the center narrow groove at a maximum amplitude position of the zigzag shape toward the tire ground contact end side, and
The tire according to any one of claims 1 to 12 , wherein the center lug groove is connected to a position of maximum amplitude of the zigzag shape of the center narrow groove toward the tire equatorial plane.

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