JP7549201B2 - tire - Google Patents

Description

This invention relates to tires, and more specifically to tires that can achieve both low rolling resistance and wet traction performance.

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 combines low rolling resistance and wet traction performance.

In order to achieve the above object, a tire according to the present invention is a tire comprising a pair of shoulder main grooves, two or more center narrow grooves disposed between the pair of shoulder main grooves and having a groove width of 0.5 mm or more and 3.0 mm or less, 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, wherein an edge portion of the middle land portion on the shoulder main groove side has a main zigzag shape formed by alternately connecting main long portions and main short portions, and the main long portions of the main zigzag shape are connected to sub-long portions and the center narrow groove has a zigzag shape formed by alternately connecting long and short portions, and the main long portions of the main zigzag shape in the middle land portion and the long portions of the center narrow groove incline in opposite directions relative to the circumferential direction of the tire.

In the tire according to the present invention, (1) the land portion in the center region of the tread portion is divided into a center narrow groove, so compared to a configuration with a main groove in the center region of the tread portion, the rigidity of the center region of the tread portion is ensured, and the tire's low rolling resistance performance is improved. Also, (2) the edge portion of the middle land portion on the shoulder main groove side has a zigzag shape that combines a main zigzag shape with a long pitch length and a secondary zigzag shape with a short pitch length, so compared to a configuration in which the land portion has an edge portion with a simple zigzag shape, the edge component of the middle land portion is increased, and the tire's wet traction performance is improved. Furthermore, (3) the circumferential length Ls of the secondary long portion of the secondary zigzag shape is optimized with respect to the circumferential length Lm of the main long portion of the main zigzag shape, so the wet traction performance improvement effect of the secondary zigzag shape is ensured.

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 tread surface of the tire shown in FIG. FIG. 4 is an enlarged view of the middle land portion shown in FIG. FIG. 5 is a cross-sectional view showing the shoulder land portion and the middle land portion shown in FIG. FIG. 6 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. FIG. 7 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 made of a plurality of belt plies 141 to 144 laminated together and arranged 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 made by coating a plurality of belt cords made of steel with coating rubber and rolling them, 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 made by coating a plurality of belt cords made of steel with coating rubber and rolling them, 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 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 tire tread portion. 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 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 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.

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 Wg1 of 5.0 mm or more and a maximum groove depth Hg1 of 10 mm or more (see FIG. 5 described later). The center narrow grooves 22, 23 have a groove width Wg2 of 0.5 mm or more and 3.0 mm or less, and a maximum groove depth Hg2 of 8.0 mm or more (see FIG. 5 described later). The groove width Wg2 of the center narrow grooves 22, 23 is in the range of 30% or less of the groove width Wg1 of the shoulder main groove 21.

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.

In addition, the area between the pair of shoulder main grooves 21, 21 (defined as the tread center area) does not have any other circumferential grooves with a maximum groove width exceeding 3.0 mm and a maximum groove depth of 10 mm or more. As a result, a single ground contact area with a substantially continuous tread surface is formed in the tread center area. This ensures the rigidity of the tread center area and reduces the rolling resistance of the tire.

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.

However, this is not limiting, and two center narrow grooves 22, 22 may be arranged between a pair of shoulder main grooves 21, 21 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).

Figure 3 is an enlarged view of the tread surface of the tire 1 shown in Figure 2. The figure shows one side area of the tread surface bounded by the tire equatorial plane CL. Figure 4 is an enlarged view of the middle land portion 32 shown in Figure 3. Figure 5 is a cross-sectional view of the shoulder land portion 31 and the middle land portion 32 shown in Figure 3.

In the configuration of FIG. 2, the shoulder main groove 21 has a zigzag shape formed by alternating long and short portions. Specifically, as shown in FIG. 3, the shoulder main groove 21 has a zigzag shape that combines a main zigzag shape (see the groove center line in the figure) with a predetermined pitch length P1 and a sub-zigzag shape with a pitch length shorter than the predetermined pitch length P1 (dimension symbols omitted in the figure). In the configuration of FIG. 3, the main zigzag shape of the shoulder main groove 21 is formed by alternating main long portions and main short portions (symbols omitted in the figure). Furthermore, the main long portion of the main zigzag shape has a sub-zigzag shape formed by alternating sub-long portions and sub-short portions (symbols omitted in the figure), and also has two or more sub-long portions. The zigzag shape of the shoulder main groove 21 will be described in detail later as the shape of the edge portion of the middle land portion 32 on the shoulder main groove 21 side.

2, three center narrow grooves 22, 23, 22 are arranged between a pair of shoulder main grooves 21, 21 as described above. In the configuration of FIG. 2, one 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 arranged in the left and right regions bounded by the tire equatorial plane CL, respectively. Also, as shown in FIG. 3, the center narrow grooves 22, 23 have a zigzag shape formed by alternatingly connecting long portions and short portions (reference numbers omitted in the figure). Also, in FIG. 2, the number of pitches of the zigzag shape of the center narrow groove 22 is equal to the number of pitches of the main zigzag shape of the shoulder main groove 21.

In the above 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 adjacent center narrow grooves 22, 23 are inclined in the same direction (downward to the right in the figure). As described above, the shoulder main groove 21 has a zigzag shape in which long and short portions are alternately connected as a whole. The zigzag long portions of the 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 portion of the center narrow groove 22 on the tire ground contact end 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 to 322C, 332A, and 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 center narrow groove 23 on the tire equatorial plane CL has a straight shape. This improves the tire's wet performance.

3, the amplitude A2 of the zigzag shape of the center narrow groove 22 is in the range of 0.10≦A2/Wb2≦0.50 relative to the maximum ground contact width Wb2 of the middle land portion 32, and preferably in the range of 0.15≦A2/Wb2≦0.35. With 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. This ensures the rigidity of the center region of the tread portion and reduces the rolling resistance of the tire.

The contact width of the land portion is measured as the linear distance in the axial direction of the tire at the contact surface between the land portion and the flat plate when the tire is mounted on a specified rim, pressurized to 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 FIG. 4, the circumferential length L2 of the long portion of the center narrow groove 22 is in the range of 0.85≦L2/P2≦1.00 relative to the pitch length P2 of the zigzag shape, and preferably in the range of 0.90≦L2/P2≦0.96. This optimizes the zigzag shape of the center narrow groove 22. In particular, the lower limit effectively prevents the blocks from collapsing, and the edge components increase, improving the low rolling resistance and wet performance of the tire. Also, as shown in FIG. 2, the number of pitches of the zigzag shapes of the center narrow grooves 22 and 23 is equal to each other.

In addition, in FIG. 4, the pitch length P2 of the zigzag shape of the center narrow groove 22 is in the range of 1.30≦P2/Wb2≦2.00 with respect to the maximum ground contact width Wb2 of the middle land portion 32, and preferably in the range of 1.50≦P2/Wb2≦1.85. This optimizes the zigzag shape of the center narrow groove 22. In particular, the above lower limit optimizes the block rigidity, achieving both low rolling resistance and wet performance of the tire. Also, as shown in FIG. 2, the number of pitches of the zigzag shape of the center narrow groove 22 is equal to the number of pitches of the main zigzag shape of the shoulder main groove 21.

In addition, in FIG. 5, the maximum groove depth Hg2 of the center narrow groove 22 is in the range of 0.60≦Hg2/Hg1≦0.90 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. Therefore, the center narrow groove 22 is shallower than the shoulder main groove 21.

In addition, in FIG. 2, the maximum ground contact width Wce of the tread center region partitioned by a pair of shoulder main grooves 21, 21 is in the range of 0.20≦Wce/TW≦0.80 relative to the tire ground contact width TW, and preferably in the range of 0.30≦Wce/TW≦0.70.

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.

[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 center narrow groove 22. The middle lug groove 321A also connects to the maximum amplitude position of the 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 center narrow groove 22, and the middle lug groove 321A and the short portion of the 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 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 is in the range 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.

In addition, in FIG. 2, the maximum ground contact width Wb2 of the middle land portion 32 is in the range of 0.10≦Wb2/TW≦0.25 relative to the tire ground contact width TW (see FIG. 2), and preferably in the range of 0.15≦Wb2/TW≦0.20.

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 center narrow groove 22. The pair of middle lateral grooves 321B, 321B connects to the center narrow groove 22 at a position that divides the long portion of the 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 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 zigzag-shaped long portion of the 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 zigzag-shaped long portion of the 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. This suppresses uneven wear of the middle blocks 322A, 322B, and 322C.

In addition, in FIG. 4, the maximum circumferential length L22 and maximum ground contact width W22 of each of the middle blocks 322A, 322B, and 322C are in the range of 0.70≦L22/W22≦1.20, and preferably in the range of 0.80≦L22/W22≦1.15. In the configuration in FIG. 4, each of the middle blocks 322A, 322B, and 322C has a long shape in the tire width direction, and is arranged with its longitudinal direction inclined with respect to the tire width direction.

In addition, in FIG. 3, the number N3 of center blocks 332A, 332B per unit pitch is in the range of N3<N2 with respect to the number N2 of middle blocks 322A-322C of the middle land portion 32. The ratio N3/N2 is in the range of 0.25≦N3/N2≦0.90, and preferably in the range 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 edge 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 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.

In addition, in FIG. 3, since the shoulder main groove 21 has the zigzag shape described above, the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a zigzag shape that combines a main zigzag shape with a predetermined pitch length Pm (see FIG. 4) and a secondary zigzag shape with a short pitch length (dimension symbol omitted in the figure). Specifically, as shown in FIG. 4, the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a main zigzag shape that is formed by alternatingly connecting main long portions and main short portions (symbol omitted in the figure). In FIG. 4, one main long portion of the main zigzag shape (see the virtual line in the figure) is shown with points X1 and X2, which are the maximum amplitude positions, as its end points.

In addition, in FIG. 4, the pitch length Pm of the main zigzag shape of the middle land portion 32 is in the range of 1.30≦Pm/Wb2≦2.00 with respect to the maximum ground contact width Wb2 of the middle land portion 32, and preferably in the range of 1.50≦Pm/Wb2≦1.85. This optimizes the main zigzag shape of the middle land portion 32. In particular, the above lower limit optimizes the block rigidity, achieving both low rolling resistance performance and wet performance of the tire. Also, as shown in FIG. 2, the number of pitches of the main zigzag shape of the middle land portion 32 is equal to the number of pitches of the main zigzag shape of the shoulder main groove 21.

As shown in FIG. 4, the main long portion of the main zigzag shape has a sub-zigzag shape formed by alternately connecting sub-long portions and sub-short portions (reference numbers omitted in the figure). Each main long portion has a plurality of sub-long portions. In the configuration of FIG. 4, one main long portion X1-X2 is formed by connecting three sub-long portions and two sub-short portions. Each of the sub-long portions has a straight shape or a gentle arc shape that is convex toward the tire equatorial plane CL. Each of the sub-long portions has a circumferential length Ls (Ls1, L2s, Ls3) in the range of 0.25≦Ls/Lm≦0.45 with respect to the circumferential length Lm of the main long portion of the main zigzag shape. Therefore, one main long portion can have 2 to 4 sub-long portions.

The circumferential lengths Lm and Ls of the zigzag shapes are measured by extracting the maximum amplitude positions of the main zigzag shape and the secondary zigzag shape from the ridges of the edges of the middle land portion 32 in a plan view of the tread, and using these maximum amplitude positions as measurement points. At this time, the openings of the middle lug groove 321A and the middle lateral groove 321B are complemented by the extensions of the edges of the middle land portion 32.

In the above configuration, (1) the land portions 32, 33 in the tread center region are divided into center narrow grooves 22, 23, so that the rigidity of the tread center region is ensured, and the tire's low rolling resistance and uneven wear resistance are improved, compared to a configuration (not shown) in which the tread center region has a main groove. Also, (2) the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a zigzag shape that combines a main zigzag shape with a long pitch length Pm (see FIG. 4) and a secondary zigzag shape with a short pitch length, so that the edge component of the middle land portion 32 is increased, and the tire's wet traction performance is improved, compared to a configuration (not shown) in which the land portion has an edge portion with a simple zigzag shape. Furthermore, (3) the circumferential length Ls (Ls1, Ls2, Ls3) of the secondary long portion of the secondary zigzag shape is optimized with respect to the circumferential length Lm of the main long portion of the primary zigzag shape. Specifically, the lower limit of the ratio Ls/Lm suppresses uneven wear on the edge of the middle land portion 32 caused by an excessive number of pitches in the secondary zigzag shape. The upper limit of the ratio Ls/Lm ensures the number of pitches in the secondary zigzag shape, thereby ensuring the effect of improving wet traction performance due to the secondary zigzag shape.

In addition, in FIG. 4, the circumferential length Lm of the main long portion of the main zigzag shape of the middle land portion 32 is in the range of 0.85≦Lm/Pm≦1.00 with respect to the pitch length Pm of the main zigzag shape, and preferably in the range of 0.92≦Lm/Pm≦0.98. Also, the amplitude Am of the main zigzag shape is in the range of 0.05≦Am/Wb2≦0.20 with respect to the maximum ground contact width Wb2 of the middle land portion 32, and preferably in the range of 0.10≦Am/Wb2≦0.15.

In addition, in FIG. 4, the amplitude As of the secondary zigzag shape of the middle land portion 32 is in the range of 0.25≦As/Am≦0.65 relative to the amplitude Am of the main zigzag shape, and preferably in the range of 0.35≦As/Am≦0.60. Also, the amplitude As of the secondary zigzag shape is in the range of 0.03≦As/Ls≦0.20 relative to the circumferential length Ls of the secondary long portion (Ls1, L2s, Ls3), and preferably in the range of 0.05≦As/Ls≦0.15.

In addition, in FIG. 4, the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a main zigzag shape formed by alternating main long portions and main short portions, and the main long portions (portions with points X1 and X2 in FIG. 4 at both ends) are inclined downward in the figure toward the tire ground contact end T. The main long portion of the main zigzag shape has three sub-long portions, and these sub-long portions are inclined downward in the figure toward the tire ground contact end T. One main long portion X1-X2 of the middle land portion 32 is formed by connecting three sub-long portions and two sub-short portions. These sub-long portions are arranged in a curved arc shape so as to be convex from the main long portions X1-X2 toward the tire equatorial plane CL.

In FIG. 4, the secondary zigzag-shaped secondary long portion and secondary short portion of the middle land portion 32 are arranged with their inclination directions with respect to the tire circumferential direction reversed to each other. The secondary long portion is approximately parallel to the main long portion, specifically, inclined in the range of 0 degrees to 10 degrees. The angle between the secondary long portion and the secondary short portion (dimension symbols omitted in the figure) is an obtuse angle, preferably in the range of 100 degrees to 130 degrees.

In FIG. 4, the pitch length Pm of the main zigzag shape of the middle land portion 32 is equal to the pitch length of the middle lug groove 321A. The middle lug groove 321A extends in the tire width direction from the maximum amplitude position X1 of the main zigzag shape toward the tire equatorial plane CL and penetrates the middle land portion 32. The middle lug groove 321A and the main long portion of the main zigzag shape are inclined in the same direction relative to the tire circumferential direction.

In addition, in FIG. 4, the middle lateral groove 321B of the middle land portion 32 extends in the tire width direction from the maximum amplitude position (reference number omitted in the figure) of the secondary zigzag shape toward the tire equatorial plane CL side, penetrating the middle land portion 32. In addition, the middle lateral groove 321B and the main long portion of the primary zigzag shape are mutually inclined in the same direction with respect to the tire circumferential direction.

4, the pitch length Pm of the main zigzag shape of the middle land portion 32 is equal to the pitch length P2 of the zigzag shape on the center narrow groove 22 side. The main long portion of the main zigzag shape of the edge portion on the shoulder main groove 21 side of the middle land portion 32 and the long portion of the zigzag shape on the center narrow groove 22 side are inclined in opposite directions relative to the tire circumferential direction. Therefore, the middle blocks 322A, 322B, and 322C of the middle land portion 32 are arranged so that the maximum contact width increases in one direction (downward in the figure) in the tire circumferential direction.

[Shoulder land area]
In FIG. 2 , the shoulder land portion 31 includes a plurality of shoulder lug grooves 311 and a plurality of shoulder blocks 312 .

The shoulder lug groove 311 extends in the tire width direction, penetrates the shoulder land portion 31, and opens into the shoulder main groove 21 and the tire ground contact end T. Also, as shown in FIG. 3, the groove width W11 of the shoulder lug groove 311 widens in a step-like manner from the shoulder main groove 21 toward the tire ground contact end T. Also, the shoulder lug groove 311 connects to the maximum amplitude position toward the tire ground contact end T of the above-mentioned main zigzag shape of the shoulder main groove 21 (see the groove center line in FIG. 3). Therefore, the opening of the shoulder lug groove 311 of the shoulder land portion 31 relative to the shoulder main groove 21 and the opening of the middle lug groove 321A of the middle land portion 32 are arranged opposite each other with the short portion of the main zigzag shape of the shoulder main groove 21 in between. This improves the drainage from the middle lug groove 321A. Additionally, the shoulder lug groove 311 has a groove width W11 (see FIG. 3) of 9.0 mm or more and 16 mm or less and a groove depth H11 (see FIG. 4) of 10 mm or more and 18 mm or less. Additionally, as shown in FIG. 5, the shoulder lug groove 311 has a bottom upper portion 3111 at the opening on the shoulder main groove 21 side. This increases the rigidity of the edge portion of the shoulder land portion 31 on the shoulder main groove 21 side.

The shoulder block 312 is divided into adjacent shoulder lug grooves 311, 311. In addition, multiple shoulder blocks 312 are arranged at predetermined intervals in the tire circumferential direction.

In addition, in FIG. 3, because the shoulder main groove 21 has the zigzag shape described above, the edge portion of the shoulder land portion 31 on the shoulder main groove 21 side has a zigzag shape that combines a main zigzag shape with a predetermined pitch length and a secondary zigzag shape with a short pitch length. Specifically, as shown in FIG. 4, the edge portion of the shoulder land portion 31 on the shoulder main groove 21 side has a main zigzag shape formed by alternating main long portions and main short portions (reference numbers omitted in the figure). Also, the main long portion of the main zigzag shape has a secondary zigzag shape formed by alternating secondary long portions and secondary short portions (reference numbers omitted in the figure).

[effect]
As described above, the tire 1 includes a pair of shoulder main grooves 21, 21, two or more center narrow grooves 22, 23 arranged between the pair of shoulder main grooves 21, 21 and having a groove width Wg2 of 0.5 mm or more and 3.0 mm or less, 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 (see FIG. 2). In addition, the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a main zigzag shape formed by alternately connecting main long portions and main short portions (see FIG. 3). In addition, the main long portion X1-X2 (see FIG. 4) of the main zigzag shape has a secondary zigzag shape formed by alternately connecting secondary long portions and secondary short portions. In addition, each of the main long portions has a plurality of secondary long portions (see FIG. 4). Further, the circumferential length Ls (Ls1, Ls2, Ls3) of each of the sub long portions of the sub zigzag shape is in the range of 0.25≦Ls/Lm≦0.45 with respect to the circumferential length Lm of the main long portion of the main zigzag shape.

In this configuration, (1) the land portions 32, 33 in the tread center region are divided into center narrow grooves 22, 23, so that the rigidity of the tread center region is ensured, and the tire's low rolling resistance and uneven wear resistance are improved, compared to a configuration (not shown) in which the tread center region has a main groove. Also, (2) the edge portion of the middle land portion 32 on the shoulder main groove 21 side has a zigzag shape that combines a main zigzag shape with a long pitch length Pm (see FIG. 4) and a secondary zigzag shape with a short pitch length, so that the edge component of the middle land portion 32 is increased, and the tire's wet traction performance is improved, compared to a configuration (not shown) in which the land portion has an edge portion with a simple zigzag shape. Furthermore, (3) the circumferential length Ls (Ls1, Ls2, Ls3) of the secondary long portion of the secondary zigzag shape is optimized with respect to the circumferential length Lm of the main long portion of the primary zigzag shape. Specifically, the lower limit of the ratio Ls/Lm suppresses uneven wear on the edge of the middle land portion 32 caused by an excessive number of pitches in the secondary zigzag shape. The upper limit of the ratio Ls/Lm ensures the number of pitches in the secondary zigzag shape, thereby ensuring the effect of improving wet traction performance due to the secondary zigzag shape.

In addition, in this tire 1, the circumferential length Lm of the main long portion of the main zigzag shape at the edge portion of the middle land portion 32 on the shoulder main groove 21 side is in the range of 0.85≦Lm/Pm≦1.00 with respect to the pitch length Pm of the main zigzag shape (see FIG. 4). The above lower limit ensures an area for the secondary zigzag shape, which has the advantage of ensuring the effect of improving wet traction performance by the secondary zigzag shape. The above upper limit also ensures the circumferential length of the short portion of the main zigzag shape, which has the advantage of ensuring the effect of improving wet traction performance by the main zigzag shape.

In addition, in this tire 1, the amplitude Am of the main zigzag shape at the edge of the middle land portion 32 on the shoulder main groove 21 side is in the range of 0.05≦Am/Wb2≦0.20 with respect to the maximum ground contact width Wb2 of the middle land portion 32 (see FIG. 4). The above lower limit has the advantage of ensuring that the main zigzag shape improves the wet traction performance of the tire. The above upper limit has the advantage of suppressing the deterioration of rolling resistance and the occurrence of uneven wear caused by the amplitude Am of the main zigzag shape being too large.

In addition, in this tire 1, the amplitude As of the secondary zigzag shape at the edge portion of the middle land portion 32 on the shoulder main groove 21 side is in the range of 0.25≦As/Am≦0.65 with respect to the amplitude Am of the primary zigzag shape (see FIG. 4). The above lower limit has the advantage of ensuring that the secondary zigzag shape improves the wet traction performance of the tire. The above upper limit has the advantage of suppressing the deterioration of rolling resistance and the occurrence of uneven wear caused by the secondary zigzag shape becoming too large as amplitude As.

In addition, in this tire 1, the amplitude As of the secondary zigzag shape at the edge portion of the middle land portion 32 on the shoulder main groove 21 side is in the range of 0.03≦As/Ls≦0.20 relative to the circumferential length Ls of the secondary long portion (Ls1, Ls2, Ls3) (see FIG. 4). The above lower limit ensures the amplitude As of the secondary zigzag shape, which has the advantage of ensuring the effect of the secondary zigzag shape in improving the wet traction performance of the tire. The above upper limit also has the advantage of suppressing the deterioration of rolling resistance and the occurrence of uneven wear caused by the amplitude As of the secondary zigzag shape being too large.

In addition, in this tire 1, the secondary zigzag shape of the secondary long portion and secondary short portion at the edge portion of the middle land portion 32 on the shoulder main groove 21 side are arranged with mutually inverted inclination directions relative to the tire circumferential direction (see FIG. 4). This configuration has the advantage that the secondary zigzag shape improves the wet traction performance of the tire, compared to a configuration in which the secondary long portion and secondary short portion of the secondary zigzag shape are mutually inclined in the same direction.

In addition, in this tire 1, multiple secondary long portions of the secondary zigzag shape at the edge portion of the middle land portion 32 on the shoulder main groove 21 side are arranged curved in an arc shape that is convex toward the tire equatorial plane CL with respect to the main long portion. This configuration has the advantage of optimizing the rigidity of the middle blocks 322A, 322B, and 322C and suppressing uneven wear.

In addition, in this tire 1, the middle land portion 32 has a plurality of middle lug grooves 321A that extend from the maximum amplitude position X1 of the main zigzag shape toward the tire equatorial plane CL and penetrate the middle land portion 32 (see FIG. 4). This has the advantage of improving the drainage of the middle land portion 32 and improving the wet performance of the tire.

In addition, in this tire 1, the middle land portion 32 has a plurality of middle lateral grooves 321B that extend from the maximum amplitude position (reference number omitted in the figure) toward the tire equatorial plane CL of the secondary zigzag shape and penetrate the middle land portion 32 (see FIG. 4). This has the advantage of improving the drainage of the middle land portion 32 and improving the wet performance of the tire.

In addition, in this tire 1, the center narrow groove 22 has a zigzag shape formed by alternatingly connecting long and short sections (see FIG. 3). The number of pitches of the zigzag shape of the center narrow groove 22 is equal to the number of pitches of the main zigzag shape of the middle land portion 32. This configuration has the advantage of optimizing the rigidity of the middle blocks 322A, 322B, and 322C and suppressing uneven wear.

In addition, in this tire 1, the center narrow groove 22 has a zigzag shape formed by alternatingly connecting long and short sections (see FIG. 3). The main long section of the main zigzag shape of the middle land portion 32 and the long section of the center narrow groove 22 are inclined in opposite directions relative to the tire circumferential direction. This configuration has the advantage that the rigidity of the middle blocks 322A, 322B, and 322C is optimized and uneven wear is suppressed, compared to a configuration in which the main long section of the main zigzag shape of the middle land portion 32 and the long section of the center narrow groove 22 are inclined in the same direction.

In addition, in this tire 1, no other circumferential grooves having a maximum groove width exceeding 3.0 mm are disposed between the pair of shoulder main grooves 21, 21 (see FIG. 2). In this configuration, the tread center region has a substantially continuous tread surface that is not divided in the tire width direction, so the rigidity of the tread center region is ensured, which has the advantage of ensuring low rolling resistance performance of the tire.

Figures 6 and 7 are charts showing the results of performance tests of tires 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, (2) wet traction performance, and (3) uneven wear resistance. 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 ISO28580 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 comparative example as the standard (100), and the higher the value, the more preferable it is.

(2) In the evaluation of wet traction 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. Then, a test vehicle equipped with the test tire runs on a test course with a wet road surface, and acceleration is measured from speeds of 5 km/h to 20 km/h. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the more preferable it is.

(3) In the evaluation of resistance to uneven wear, the test vehicle is driven 30,000 km on a specified paved road, and then the degree of heel-and-toe wear of the middle block is observed and an index evaluation is performed. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the more preferable it is.

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 shoulder land portions 31 has a plurality of shoulder lug grooves 311, 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 130 mm. The maximum groove width Wg1 of the shoulder main groove 21 is 10.0 mm, and the maximum groove depth Hg1 (see Figure 5) is 14 mm. The maximum groove width Wg2 of the center narrow grooves 22, 23 is 2.0 mm, and the maximum groove depth Hg2 is 14 mm. The maximum groove width W11 of the shoulder lug grooves is 13 mm, and the maximum groove depth H11 is 14 mm. The maximum groove width W321 of the middle lug grooves 321A and center lug grooves 331A is 6.0 mm, and the maximum groove depth H21 is 12.5 mm.

The comparative test tire is the test tire of Example 1, in which the zigzag shape of the edge portion of the shoulder land portion 31 and the middle land portion 32 on the shoulder main groove 21 side consists only of a main zigzag shape and does not have a secondary zigzag shape with a short pitch length.

As the test results show, the test tires of the embodiment exhibit low rolling resistance, wet traction performance, and uneven wear resistance.

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; 3111 Bottom upper portion; 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; 332A, 332B Center block

Claims (11)

A tire comprising a pair of shoulder main grooves, two or more center narrow grooves disposed between the pair of shoulder main grooves and having a groove width of 0.5 mm or more and 3.0 mm or less, and a pair of shoulder land portions, a pair of middle land portions, and one or more rows of center land portions, each of which is partitioned by the shoulder main grooves and the center narrow groove,
an edge portion of the middle land portion on the shoulder main groove side has a main zigzag shape formed by alternatingly connecting main long portions and main short portions;
The main long portion of the main zigzag shape has a sub-zigzag shape formed by alternately connecting sub-long portions and sub-short portions,
Each of the main elongated portions has a plurality of the sub-elongated portions,
a circumferential length Ls of each of the plurality of sub-long portions of the sub-zigzag shape is in a range of 0.25≦Ls/Lm≦0.45 with respect to a circumferential length Lm of the main long portion of the main zigzag shape; and
a center narrow groove having a zigzag shape formed by alternatingly connecting long portions and short portions, and a main long portion of the main zigzag shape of the middle land portion and a main long portion of the center narrow groove are inclined in opposite directions to each other with respect to the tire circumferential direction . The tire according to claim 1, wherein the circumferential length Lm of the main long portion of the main zigzag shape is in the range of 0.85≦Lm/Pm≦1.00 with respect to the pitch length Pm of the main zigzag shape. The tire according to claim 1 or 2, wherein the amplitude Am of the main zigzag shape is in the range of 0.05≦Am/Wb2≦0.20 with respect to the maximum contact width Wb2 of the middle land portion. A tire according to any one of claims 1 to 3, wherein the amplitude As of the secondary zigzag shape is in the range of 0.25 ≦ As / Am ≦ 0.65 with respect to the amplitude Am of the primary zigzag shape. A tire according to any one of claims 1 to 4, wherein the amplitude As of the secondary zigzag shape is in the range of 0.03≦As/Ls≦0.20 with respect to the circumferential length Ls of the secondary long portion. A tire according to any one of claims 1 to 5, in which the secondary long section and the secondary short section of the secondary zigzag shape are arranged with their inclination directions with respect to the tire circumferential direction reversed to each other. The tire according to any one of claims 1 to 6, wherein the plurality of secondary long portions of the secondary zigzag shape are arranged curved in an arc shape so as to be convex toward the tire equatorial plane side with respect to the main long portion. A tire according to any one of claims 1 to 7, wherein the middle land portion has a plurality of middle lug grooves that extend from the maximum amplitude position of the main zigzag shape toward the tire equatorial plane and penetrate the middle land portion. A tire according to any one of claims 1 to 8, wherein the middle land portion has a plurality of middle lateral grooves that extend from the maximum amplitude position of the secondary zigzag shape toward the tire equatorial plane and penetrate the middle land portion. A tire according to any one of claims 1 to 9, wherein the center narrow groove has a zigzag shape formed by alternatingly connecting long and short sections, and the number of pitches of the zigzag shape of the center narrow groove is equal to the number of pitches of the main zigzag shape of the middle land portion. The tire according to any one of claims 1 to 10 , wherein no other circumferential groove having a maximum groove width exceeding 3.0 mm is disposed between the pair of shoulder main grooves.

Images