JP2022057908A - tire - Google Patents

Abstract

To provide a tire capable of improving wet performance while maintaining low rolling resistance performance.SOLUTION: A tire comprises: a pair of shoulder main grooves 21, 21 extending in a tire circumferential direction; and a pair of shoulder regions and a single center region having the pair of shoulder main grooves 21, 21 as boundaries. The center region includes: middle lug grooves 321A which are open to the shoulder main groove 21 at one end, whereas the other end falls within a grounding surface of the center region; and center lug grooves 331A whose both ends fall within the grounding 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 part of the center lug groove 331A extends to a region on a tire equator surface CL side beyond the other end of the middle lug groove 321A.SELECTED DRAWING: Figure 2

Description

The present invention relates to a tire, and more particularly to a tire capable of improving the wet performance of the tire while maintaining the low rolling resistance performance of the tire.

In recent years, heavy-duty tires installed in vehicles for long-distance transportation such as trucks and buses have only a pair of shoulder main grooves on the tread surface in order to reduce the rolling resistance of the tire while ensuring the wet performance of the tire. A configuration is adopted in which the center region of the tread portion is not provided with another circumferential main groove or a wide circumferential groove.

As a conventional heavy-duty tire that adopts such a configuration, the technique described in Patent Document 1 is known.

International Publication No. 2017/040007

An object of the present invention is to provide a tire capable of improving the wet performance of the tire while maintaining the low rolling resistance performance of the tire.

In order to achieve the above object, the tire according to the present invention has 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 tire is provided with a middle lug groove in which the center region opens into the shoulder main groove at one end and has the other end in the ground plane of the center region, and both ends of the center region. The middle lug groove and the center lug groove are defined as a continuous groove having a minimum groove width of 4.0 [mm] or more, and the center lug groove is provided with a center lug groove having in the ground plane. It is characterized in that at least a part thereof extends to a region on the equatorial side of the tire with respect to the other end of the middle lug groove.

In this tire according to the present invention, (1) since the center region of the tread portion has a wide middle lug groove and a center lug groove, drainage in the center region is compared with a configuration in which the center region does not have a wide lug groove. There is an advantage that the wet performance of the tire is improved by improving the property. Further, (2) at least a part of the center lug groove extends to the region on the equatorial surface side of the tire from the other end of the middle lug groove, which has an advantage that the drainage property of the center region is further improved. Further, (3) since the center lug groove has both ends thereof in the ground contact surface of the center region, the rigidity of the center region is ensured as compared with the configuration in which the center lug groove opens to the shoulder main groove, and the tire's rigidity is ensured. There is an advantage that low rolling resistance performance 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 a tread portion center region 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 chart showing the results of a tire performance test according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, the components of this embodiment include those that are replaceable and self-explanatory while maintaining the identity of the invention. Further, the plurality of modifications described in this embodiment can be arbitrarily combined within the range of 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 a one-sided region in the tire radial direction. Further, the figure shows, as an example of a tire, a heavy-duty pneumatic radial tire mounted on a vehicle for long-distance transportation such as a truck or a bus.

In the figure, the cross section in the tire meridian direction is defined as the cross section when the tire is cut on a plane including the tire rotation axis (not shown). Further, the tire equatorial plane CL is defined as a plane that passes through the midpoint of the measurement point of the tire cross-sectional width defined by JATTA and is perpendicular to the tire rotation axis. Further, the tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis.

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

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

The carcass layer 13 has a single-layer structure composed of one carcass ply or a multi-layer structure formed by laminating a plurality of carcass plies, and is bridged between the left and right bead cores 11 and 11 in a toroidal shape to form a tire skeleton. To configure. Further, both ends of the carcass layer 13 are wound and locked outward in the tire width direction so as to wrap the bead core 11 and the bead filler 12. Further, the carcass ply of the carcass layer 13 is configured by coating a plurality of carcass cords made of steel with coated rubber and rolling them, and if it is a radial tire, the absolute value is 80 [deg] or more and 90 [deg] or less, bias. A tire has a code angle of 30 [deg] or more and 45 [deg] or less (defined as an inclination angle in the longitudinal direction of the carcass code with respect to the tire circumferential direction).

The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is arranged so as to be hung 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 configured by covering a plurality of belt cords made of steel with coated rubber and rolling them, and has a cord angle of 45 [deg] or more and 70 [deg] or less in absolute value (belt cord with respect to the tire circumferential direction). It has a longitudinal tilt angle). The pair of crossed belts 142 and 143 are formed by coating a plurality of belt cords made of steel with coated rubber and rolling them, and have a cord angle of 10 [deg] or more and 55 [deg] or less in absolute value. Further, the pair of crossed belts 142 and 143 have different code angles and are laminated so that the longitudinal directions of the belt cords cross each other (having a so-called cross-ply structure). The belt cover 144 is formed by coating a plurality of belt cover cords made of steel or an organic fiber material with coated rubber and rolling them, and has a cord angle of 10 [deg] or more and 55 [deg] or less in absolute value.

The tread rubber 15 is arranged on the outer periphery of the carcass layer 13 and the belt layer 14 in the radial direction of the tire to form a tread portion of the tire. The pair of sidewall rubbers 16 and 16 are arranged on the outer sides of the carcass layer 13 in the tire width direction, respectively, to form the left and right sidewall portions. The pair of rim cushion rubbers 17 and 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the rewound portions of the left and right bead cores 11 and 11 and the carcass layer 13 to form a 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. The figure shows the tread surface of an all-season tire. In the figure, the tire circumferential direction means the direction around the tire rotation axis. Further, the reference numeral T is a tire contact end, and the dimension symbol TW is a tire contact width. Further, in the figure, since the tire 1 has a tread surface that is substantially point-symmetrical, a part of the reference numerals of the components in the region on the right side of the figure is omitted.

As shown in FIG. 2, the tire 1 is arranged between a pair of shoulder main grooves 21 and 21 extending in the tire circumferential direction and these shoulder main grooves 21 and 21 and extends in the tire circumferential direction 2. A pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a center of one or more rows, which are divided into the center narrow grooves 22 and 23 and the shoulder main groove 21 and the center narrow grooves 22 and 23. The land portion 33 is provided on the tread surface. The middle land portion 32 is defined as a land portion divided into a shoulder main groove 21 and a center narrow groove 22 closest to the tire contact end T side. The center land portion 33 is defined as a land portion adjacent to the middle land portion 32. Further, the region between the pair of shoulder main grooves 21 and 21 (defined as the tread portion center region) has a maximum groove width of more than 3.0 [mm] and a maximum groove depth of 10 [mm] or more. Does not have other circumferential treads with. For this reason, a single ground contact area with substantially continuous treads is formed in the tread center area. As a result, the rigidity of the tread portion center region is ensured, and the rolling resistance of the tire is reduced.

The shoulder main groove 21 is a groove having an obligation to display a wear indicator specified in JATTA, and has a maximum groove width of 5.0 [mm] or more and a maximum groove depth of 10 [mm] or more. Further, the center fine grooves 22 and 23 have a groove width of 0.5 [mm] or more and 3.0 [mm] or less, and have a maximum groove depth of 8.0 [mm] or more. Further, the groove widths of the center narrow grooves 22 and 23 are in the range of 30 [%] or less with respect to the groove width of the shoulder main groove 21. The details of the center narrow grooves 22 and 23 will be described later.

The groove width is measured as the distance between the opposing groove walls at the groove opening in a no-load state in which the tire is mounted on the specified rim and filled with the specified internal pressure. In a configuration having a notch or a chamfered portion in the groove opening, the groove width is measured at the intersection of the extension line of the tread tread and the extension line of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction. Is measured.

The groove depth is measured as the distance from the tread tread to the bottom of the groove in a no-load state in which the tire is mounted on the specified rim and the specified internal pressure is applied. Further, in a configuration having a partially uneven portion or a sipe at the groove bottom, the groove depth is measured by excluding these.

The specified rim means the "standard rim" specified in JATMA, the "Design Rim" specified in TRA, or the "Measuring Rim" specified in ETRTO. The specified internal pressure means the "maximum air pressure" specified in JATTA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or "INFLATION PRESSURES" specified in ETRTO. The specified load means the "maximum load capacity" specified in JATTA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or the "LOAD CAPACITY" specified in ETRTO. However, in JATTA, in the case of a passenger car tire, the specified internal pressure is an air pressure of 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 substantially point-symmetrical tread pattern having a center point on the tire equatorial plane CL. However, the present invention is not limited to this, and the tire 1 may have, for example, a line-symmetrical tread pattern centered on the tire equatorial plane CL or a left-right asymmetrical tread pattern, or a tread pattern having directionality in the tire rotation direction. May have (not shown).

Further, in the configuration of FIG. 2, the left and right regions with the tire equatorial plane CL as a boundary have one shoulder main groove 21, 21 respectively. Further, three center narrow grooves 22, 23, 22 are arranged between these shoulder main grooves 21, 21. Further, the central narrow groove 23 is arranged on the tire equatorial surface CL. Further, these shoulder main grooves 21, 21 and center narrow grooves 22, 23, 22 divide the pair of shoulder land portions 31, 31, the pair of middle land portions 32, 32, and the two rows of center land portions 33, 33. Has been done.

[Tread section center area]
FIG. 3 is an enlarged view showing a tread portion center region of the tire 1 shown in FIG. The figure shows a one-sided region of the center region of the tread portion with the tire equatorial plane CL as a boundary. FIG. 4 is an enlarged view showing the block units of the middle land portion 32 and the center land portion 33 shown in FIG. FIG. 5 is a cross-sectional view showing the middle land portion 32 and the center land portion 33 shown in FIG.

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 these shoulder main grooves 21, 21 and a center fine groove 22. , 23, 22 with 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.

Here, among the center narrow grooves 22 and 23, the first center fine groove 22 adjacent to the shoulder main groove 21 and the second center fine groove 23 adjacent to the first center fine 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 arranged in the left and right regions with the tire equatorial plane CL as a boundary, respectively. To. Note that, for example, in a configuration including only two center grooves 22, 22 and a single center land portion 33 (see FIG. 6 described later), the second center groove 23 is omitted.

Further, as shown in FIG. 3, the groove center lines of the first and second center narrow grooves 22 and 23 have a zigzag shape formed by alternately connecting long portions and short portions (reference numerals omitted in the figure). Have.

In such a configuration, (1) the land portions 32 and 33 of the tread portion center region are divided into a plurality of center narrow grooves 22 and 23, so that the tread portion center region is provided with a circumferential main groove (not shown). In comparison, the groove area in the center region of the tread portion is reduced. This reduces the rolling resistance of the tire. On the other hand, (2) the center narrow grooves 22 and 23 have a zigzag shape formed by alternately connecting the long portion and the short portion, so that the tire is wet as compared with the configuration in which the center fine groove has a straight shape. Traction performance is improved. Further, (3) in the configuration having only the pair of shoulder main grooves 21 and 21 as described above and not providing the circumferential main groove in the tread portion center region, the rigidity of the tread portion center region is increased and the tire resistance is increased. Abrasion performance is improved.

Further, in the configuration of FIG. 3, the long portions of the first and second center narrow grooves 22 and 23 are inclined in the same direction (downward to the right in the figure). Further, as will be described later, the shoulder main groove 21 has a zigzag shape formed by alternately connecting long portions and short portions as a whole (see FIG. 2). The zigzag-shaped long portion of the first center narrow groove 22 is inclined in the direction opposite to each other in the tire circumferential direction with respect to the zigzag-shaped long portion of the shoulder main groove 21. Further, the long portion of the first center narrow groove 22 on the tire ground contact end T side has an arc shape that is convex toward the tire equatorial surface CL side. In such a configuration, the deformation of the blocks 322A to 322C, 332A, and 332B in the center region of the tread portion during tire rolling is suppressed as compared with the configuration in which the center narrow groove 22 has a straight shape (not shown), and the tire is tired. Rolling resistance is reduced. On the other hand, the long portion of the second center narrow groove 23 on the tire equatorial plane CL has a linear shape. This improves the wet performance of the tire.

Further, the circumferential lengths L2 and L3 of the long portions of the first and second center narrow grooves 22 and 23 are 0.85 ≦ L2 / P2 ≦ 1.00 with respect to the zigzag-shaped pitch lengths P2 and P3. And 0.85 ≦ L3 / P3 ≦ 1.00, preferably 0.90 ≦ L2 / P2 ≦ 0.96 and 0.90 ≦ L3 / P3 ≦ 0.96. As a result, the zigzag shape of the center narrow groove 22; 23 is optimized. In particular, the above lower limit effectively suppresses the collapse of the block, increases the edge component, and improves the low rolling resistance performance and the wet performance of the tire. Further, the numbers of pitches of the zigzag shapes of the first and second center narrow grooves 22 and 23 are equal to each other.

Further, in FIG. 3, the zigzag-shaped pitch length P2 of the first center narrow groove 22 on the tire contact end T side has 1.30 ≦ P2 / Wb2 ≦ 2. with respect to the maximum contact width Wb2 of the middle land portion 32. It has a relationship of 00, preferably 1.50 ≦ P2 / Wb2 ≦ 1.85. Further, the zigzag-shaped pitch length P3 of the second center narrow groove 23 on the CL side of the equatorial surface of the tire has a relationship of 1.30 ≦ P3 / Wb3 ≦ 2.00 with respect to the maximum contact width Wb3 of the center land portion 33. It has a relationship of 1.50 ≦ P3 / Wb3 ≦ 1.85. As a result, the zigzag shape of the center narrow groove 22; 23 is optimized. In particular, the above lower limit optimizes the block rigidity and achieves both low rolling resistance performance and wet performance of the tire.

Further, in FIG. 3, the zigzag-shaped amplitude A2 of the first center narrow groove 22 on the tire contact end T side is 0.10 ≦ A2 / Wb2 ≦ 0.50 with respect to the maximum contact width Wb2 of the middle land portion 32. The relationship is preferably 0.15 ≦ A2 / Wb2 ≦ 0.35. In such a configuration, the meshing allowance of the blocks 322A and 332B adjacent to each other in the tire circumferential direction with the zigzag-shaped short portion of the center narrow groove 22 in contact with the tire is secured. As a result, the rigidity of the tread portion center region is ensured, and the rolling resistance of the tire is reduced. Similarly, the zigzag-shaped amplitude A3 of the second center narrow groove 23 on the CL side of the equatorial plane of the tire has a relationship of 0.10 ≦ A3 / Wb3 ≦ 0.50 with respect to the maximum contact width Wb3 of the center land portion 33. It has a relationship of 0.15 ≦ A3 / Wb3 ≦ 0.35.

Further, in FIG. 5, the maximum groove depths Hg2 and Hg3 of the first and second center narrow grooves 22 and 23 are 0.60 ≦ Hg2 / Hg1 ≦ 0 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. It has a relationship of .90, 0.60 ≦ Hg3 / Hg1 ≦ 0.90. Therefore, the center narrow grooves 22 and 23 are shallower than the shoulder main groove 21.

Further, in FIG. 2, the relationship between the maximum distance De2 from the outer edge portion of the middle land portion 32 in the tire width direction to the tire equatorial plane CL is 0.10 ≦ De2 / TW ≦ 0.40 with respect to the tire contact width TW. , And preferably has a relationship of 0.15 ≦ De2 / TW ≦ 0.35. Further, the maximum distance De3 from the outer edge portion of the center land portion 33 in the tire width direction to the tire equatorial plane CL has a relationship of 0.05 ≦ De3 / TW ≦ 0.30 with respect to the tire contact width TW. Preferably, it has a relationship of 0.08 ≦ De3 / TW ≦ 0.20.

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

The tire ground contact end T is a contact surface between the tire and the flat plate when the tire is mounted on the specified rim to apply a specified internal pressure and the tire is placed perpendicular to the flat plate in a stationary state and a load corresponding to the specified load is applied. It is defined as the maximum width position in the tire axial direction in.

Further, in FIG. 3, the maximum contact width Wb2 of the middle land portion 32 has a relationship of 0.10 ≦ Wb2 / TW ≦ 0.25 with respect to the tire contact width TW (see FIG. 2), and is preferably 0. It has a relationship of 15 ≦ Wb2 / TW ≦ 0.20. Further, the maximum contact width Wb3 of the center land portion 33 has a relationship of 0.10 ≦ Wb3 / TW ≦ 0.25 with respect to the tire contact width TW, preferably 0.15 ≦ Wb3 / TW ≦ 0.20. Have a relationship of. Further, the maximum ground contact widths Wb2 and Wb3 of the middle land portion 32 and the center land portion 33 are substantially the same and have a relationship of 0.80 ≦ Wb3 / Wb2 ≦ 1.20, preferably 0.90 ≦ Wb3 /. It has a relationship of Wb2 ≦ 1.10.

The ground contact widths Wb2 and Wb3 of the land portion are the same as those of the land portion when the tire is mounted on the specified rim to apply the specified internal pressure and the tire is placed perpendicular to the flat plate in a stationary state to apply a load corresponding to the specified load. It is measured as a linear distance in the tire axial direction on the contact surface with the flat plate.

Further, in the configuration of FIG. 3, the edge portion of the center land portion 33 on the tire equatorial surface CL side has a zigzag shape along the center narrow groove 23, and a part of the edge portion intersects the tire equatorial surface CL. ing. This enhances the wet traction performance of the tire.

[Middle land]
Further, 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, and 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. Further, the middle lug groove 321A opens into the shoulder main groove 21 at one end and has the other end in the ground plane of the tread portion 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. Further, the middle lug groove 321A is connected to the maximum amplitude position of the first center narrow groove 22 toward the tire ground contact end T side. Further, the middle lug groove 321A extends along the 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 have a linear shape or Share the arc-shaped groove centerline. Further, 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], preferably 60 [deg] ≤ θ21 ≤ 80 [deg]. It is in the range.

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

Further, a plurality of middle lug grooves 321A (in the configuration of FIG. 3, the same number as the number of zigzag-shaped pitches of the first center narrow groove 22) are arranged at predetermined intervals in the tire circumferential direction. Further, in the configuration of FIG. 3, the middle lug groove 321A has a straight shape or a gentle arc shape.

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

Further, in FIG. 3, the extended length of the middle lug groove 321A in the tire width direction (dimension symbol omitted in the figure) is 70 [%] or more and 100 [%] with respect to the maximum ground contact width Wb2 of the middle land portion 32. It is in the following range. 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 the maximum amplitude positions of the shoulder main groove 21 and the center fine groove 22 in a zigzag shape. The extension length of the middle lug groove 321A in the tire width direction is shorter than the maximum contact width Wb2 of the middle land portion 32.

The middle lateral groove 321B is a sipe or a narrow groove, which extends in the tire width direction, penetrates the middle land portion 32, and connects to the shoulder main groove 21 and the first center fine groove 22. Further, the pair of middle lateral grooves 321B and 321B are connected to positions where the long portion of the first center narrow groove 22 is substantially divided into three equal parts. Further, 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 fine groove 22 is in the range of 80 [deg] or more and 100 [deg] or less.

Further, at least one middle lateral groove 321B (two in the configuration of FIG. 3) is arranged between the adjacent middle lug grooves 321A and 321A. As a result, the drainage property of the ground contact area defined by the zigzag-shaped long portion of the first center narrow groove 22 is improved. Further, in the configuration of FIG. 3, the middle lateral groove 321B has a gentle S-shape.

Further, the middle lateral groove 321B has a groove width Ws (see FIG. 3) of 0.1 [mm] or more and 3.0 [mm] or less, preferably 0.5 [mm] 2.2 [mm] or less. Has a groove width Ws of. Further, the middle lateral groove 321B has a maximum groove depth of 7.5 [mm] or more (not shown). Further, the ratio between the maximum groove depth of the middle lateral groove 321B and the maximum groove depth Hg1 of the shoulder main groove 21 (see FIG. 5) is in the range of 0.30 or more and 0.90 or less. Therefore, the middle lateral groove 321B is shallower than the shoulder main groove 21. Further, 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, as shown in FIG. 3, three types of middle blocks 322A, 322B, and 322C having different shapes are formed. Further, the first to third middle blocks 322A, 322B, and 322C are repeatedly arranged in the tire circumferential direction. Further, the maximum ground contact width (dimension symbol omitted in the figure) and the ground contact area of the first middle block 322A are the largest, and the maximum ground contact width and the ground contact area of the third middle block 322C are the smallest. Further, the ratio of the maximum value and the minimum value of the ground contact area of the first to third middle blocks 322A, 322B, and 322C is in the range of 1.30 or less. Further, the circumferential lengths of the edge portions of the three types of middle blocks 322A, 322B, and 322C with respect to the zigzag-shaped long portion of the first center narrow groove 22 are made uniform, and specifically, the circumferential direction of the edge portion. The ratio of the maximum value to the minimum value of the length is in the range of 1.00 or more and 1.20 or less. As a result, uneven wear of the middle blocks 322A, 322B, and 322C is suppressed.

Further, in FIG. 4, the maximum circumferential length L22 of each of the middle blocks 322A, 322B, and 322C and the maximum ground contact width W22 have a relationship of 0.70 ≦ L22 / W22 ≦ 1.20, and are preferably 0. It has a relationship of .80 ≦ L22 / W22 ≦ 1.15. In the configuration of FIG. 4, each of the middle blocks 322A, 322B, and 322C has a long shape in the tire width direction, and the aspect ratio thereof is arranged so that the longitudinal direction thereof is inclined with respect to the tire width direction. L22 / W22 is set in the above range.

Further, in the configuration of FIG. 2, as described above, the tread portion center region includes a pair of middle lug grooves 321A and 321A which are opened in the pair of shoulder main grooves 21 and 21, respectively. Further, a plurality of sets of middle lug grooves 321A and 321A are arranged with a predetermined pitch length Pg2 in the tire circumferential direction. At this time, the pair of middle lug grooves 321A and 321A overlap each other in the projected view in the tire width direction. Further, the overlap amount Lg1 of the pair of middle lug grooves 321A and 321A has a relationship of 0.01 ≦ Lg1 / Pg2 ≦ 0.20 with respect to the pitch length Pg2 of the middle lug groove 321A, preferably 0.05 ≦ Lg1. It has a relationship of / Pg2 ≦ 0.15.

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

Further, in FIG. 2, the total extending length Lg2 of the pair of middle lug grooves 321A and 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. It has a relationship of 0.35 ≦ Lg2 / Pg2 ≦ 0.45.

The total extended length Lg2 of the middle lug grooves 321A measures the ends of the pair of left and right middle lug grooves 321A and 321A arranged at one pitch in the projection view in the tire width direction. Measured as a point.

[Center land area]
Further, 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 and 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. Further, the center lug groove 331A has both ends in the ground contact surface of the tread portion center region. Further, 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 and 23. Further, the center lug groove 331A connects the maximum amplitude position of the first center narrow groove 22 toward the tire equatorial surface CL side and the maximum amplitude position of the second center narrow groove 23 toward the tire ground contact end T side.

Further, in FIG. 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], and is preferably 60 [deg] ≤ θ31 ≤ 80 [deg]. Is in the range of. Further, 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. Further, it is preferable that the angle φ1 formed by the middle lug groove 321A and the center lug groove 331A is 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 moved to the tire equatorial surface CL side of the first center narrow groove 22. Connect radially at the maximum amplitude position of. As a result, the drainage property of the center area of the tread portion is enhanced.

However, not limited to the above, 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 with respect to the tire circumferential direction (not shown).

Further, a plurality of center lug grooves 331A (in the configuration of FIG. 3, the same number as the number of zigzag-shaped pitches of the first center narrow groove 22) are arranged at predetermined intervals in the tire circumferential direction. Further, in the configuration of FIG. 3, the center lug groove 331A has a straight shape or a gentle arc shape. Further, 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 a short portion of the first center narrow groove 22. As a result, a V-shaped or L-shaped bent groove that is convex in the tire circumferential direction is formed.

Further, the center lug groove 331A is defined as a continuous groove portion having a minimum groove width of 4.0 [mm] or more. Further, the center lug groove 331A has a maximum groove width W31 (see FIG. 3) of 10.0 [mm] or less, and preferably has a maximum groove width W31 of 7.0 [mm] or less. Further, the center lug groove 331A has a maximum groove depth H31 (see FIG. 5) of 7.5 [mm] or more. Further, in FIG. 5, the maximum groove depth H31 of the center lug groove 331A has a relationship of 0.50 ≦ H31 / Hg1 ≦ 0.90 with respect to the maximum groove depth Hg1 of the shoulder main groove 21. Therefore, the center lug groove 331A is shallower than the shoulder main groove 21. Further, 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).

Further, in FIG. 3, the extension length of the center lug groove 331A in the tire width direction (dimension symbol omitted in the figure) is 50 [%] or more and 100 [%] with respect to the maximum contact width Wb3 of the center land portion 33. ] It is in the following range. In the configuration of FIG. 3, as described above, the first and second center narrow grooves 22 and 22 have a zigzag shape, and the center lug groove 331A is the maximum amplitude position of the zigzag shape of these center fine grooves 22 and 22. The extension length of the center lug groove 331A in the tire width direction is shorter than the maximum contact width Wb3 of the center land portion 33 because the center lug groove 331A is connected and terminated.

Further, in FIG. 2, at least a part of the center lug groove 331A of the center land portion 33 extends to the region on the tire equatorial plane CL side from the end portion of the middle lug groove 321A of the middle land portion 32 on the tire equatorial plane CL side. do. In the configuration of FIG. 2, as shown in FIG. 3, the end portion of the center lug groove 331A on the tire ground contact end T side is closer to the tire equatorial plane CL side than the end portion of the middle lug groove 321A on the tire equatorial plane CL side. Therefore, the center lug groove 331A is arranged so as to be separated from the middle lug groove 321A of the middle land portion 32 in the tire width direction.

In the above configuration, (1) the center region of the tread portion includes a wide middle lug groove 321A and a center lug groove 331A, so that the center region is not provided with a wide lug groove (not shown). The drainage of the area is improved and the wet performance of the tire is improved. Further, (2) at least a part of the center lug groove 331A extends to the region on the CL side of the tire equatorial plane from the other end of the middle lug groove 321A, so that the drainage property of the center region is further improved. Further, (3) since the center lug groove 331A has both ends thereof in the ground contact surface of the center region, the rigidity of the center region is ensured as compared with the configuration in which the center lug groove opens to the shoulder main groove, and the tire. Low rolling resistance performance is ensured.

Further, in FIG. 3, the separation distance Dg1 of the center lug groove 331A with respect to the middle lug groove 321A in the tire width direction is 0.03 ≦ Dg1 / Wce with respect to the maximum contact width Wce (see FIG. 2) in the center region of the tread portion. It is preferable to have a relationship. The upper limit of the ratio Dg1 / Wce is not particularly limited, but is limited by the relationship with the lower limit of the extending length of the middle lug groove 321A and the center lug groove 331A in the tire width direction. Further, in the configuration of FIG. 3, the separation distance Dg1 of the center lug groove 331A with respect to the middle lug groove 321A is substantially equal to the zigzag-shaped amplitude A2 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 CL side of the tire equatorial plane to the end of the center lug groove 331A on the tire contact end T side. Further, the separation distance Dg1 is calculated by excluding the groove width of the center narrow groove 22 between the middle lug groove 321A and the center lug groove 331A.

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

Further, in FIG. 3, the separation distance Dg2 of the adjacent center lug grooves 331A and 331A in the tire width direction is 0.03 ≦ Dg2 / Wce with respect to the maximum contact width Wce (see FIG. 2) in the center region of the tread portion. It is preferable to have a relationship. The upper limit of the ratio Dg2 / Wce is not particularly limited, but is restricted by the relationship between the end portion of the center lug groove 331A and the lower limit of the extending length of the center lug groove 331A in the tire width direction. Further, in the configuration of FIG. 3, the separation distance Dg2 of the center lug grooves 331A and 331A is substantially equal to the zigzag-shaped amplitude A3 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 the adjacent center lug grooves 331A and 331A. Further, the separation distance Dg2 is calculated by excluding the groove width of the center narrow groove 23 between the adjacent center lug grooves 331A and 331A.

In the configuration of FIG. 2, as described above, the center lug groove 331A is arranged so as to be separated from the middle lug groove 321A of the middle land portion 32 in the tire width direction. As a result, the rigidity of the tread portion center region is ensured, and the low rolling resistance performance of the tire is ensured. However, the present invention is not limited to this, and the center lug groove 331A may be arranged so as to overlap the middle lug groove 321A in the tire width direction (not shown).

Further, as shown in FIG. 5, the center lug groove 331A has a partial bottom upper portion 331'at a connection portion with the second center narrow groove 23 on the CL side of the tire equatorial plane. Further, the distance H31'from the tread tread to the top surface of the bottom upper portion 331' is 0.20 ≦ H31'/ with respect to the maximum groove depth Hg1 of the shoulder main groove 21 and the maximum groove depth H31 of the center lug groove 331A. It has a relationship of Hg1 and H31'/ H31 ≦ 0.70.

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 and 23. Further, the center lateral groove 331B connects the long portion of the first center narrow groove 22 and the long portion of the second center narrow groove 23.

Further, the intersection angle (dimension symbol omitted in the figure) between the center lateral groove 331B and the long portion of the first center narrow groove 22 is in the range of 70 [deg] or more and 90 [deg] or less. Further, the intersection angle (dimension symbol omitted in the figure) between the center lateral groove 331B and the long portion of the second center narrow groove 23 is in the range of 80 [deg] or more and 100 [deg] or less.

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

Further, the center lateral groove 331B has a groove width Ws (see FIG. 3) of 0.1 [mm] or more and 3.0 [mm] or less, preferably 0.5 [mm] 2.2 [mm] or less. Has a groove width Ws of. Further, the center lateral groove 331B has a maximum groove depth of 7.5 [mm] or more (not shown). Further, the ratio between the maximum groove depth of the center lateral groove 331B and the maximum groove depth Hg1 of the shoulder main groove 21 (see FIG. 5) is in the range of 0.50 or more and 0.90 or less. Therefore, the center lateral groove 331B is shallower than the shoulder main groove 21. Further, 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 divided into a center lug groove 331A and a center lateral groove 331B. In the configuration of FIG. 2, as shown in FIG. 3, two types of center blocks 332A and 332B having different shapes are formed. Further, these center blocks 332A and 332B are arranged alternately in the tire circumferential direction. Further, the ground contact area of the center blocks 332A and 332B is made uniform, and specifically, the ratio of the maximum value and the minimum value of the ground contact area is in the range of 1.00 or more and 1.20 or less. As a result, uneven wear of the center blocks 332A and 332B is suppressed.

Further, the ground contact area A32 of each of the center blocks 332A and 332B is larger than the maximum value A22 of the ground contact area of the middle blocks 322A to 322C of the middle land portion 32, specifically 1.20 ≦ A32 / A22 ≦ 1. It is in the range of 60. As a result, the contact area of the center blocks 332A and 332B on the CL side of the equatorial surface of the tire is secured, and the rolling resistance of the tire is reduced. Further, the groove area of the middle land portion 32 on the tire contact end T side is secured, and the wet performance of the tire is improved.

Further, the circumferential lengths of the edge portions of the two types of center blocks 332A and 332B are made uniform with respect to the zigzag-shaped long portion of the first center narrow groove 22, and specifically, the circumferential length of the edge portion. The ratio of the maximum value to the minimum value of is in the range of 1.00 or more and 1.20 or less. Similarly, the circumferential lengths of the edge portions of the two types of center blocks 332A and 332B with respect to the zigzag-shaped long portion of the second center narrow groove 23 are made uniform, and specifically, the circumferential length of the edge portion. The ratio of the maximum value to the minimum value is in the range of 1.00 or more and 1.20 or less.

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

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

In the above configuration, (1) since the number N3 of the center blocks 332A and 332B on the tire equatorial surface CL side is relatively small, the rigidity in the vicinity of the tire equatorial surface CL is secured and the rolling resistance of the tire is reduced. Further, (2) since the number N2 of the middle blocks 322A to 322C on the tire contact end T side is relatively large, the groove area of the middle land portion 32 is secured, and the wet performance of the tire is improved. As a result, both low rolling performance and wet performance of the tire are compatible.

In particular, when the ratio N2: N3 of the number N2 of the middle blocks 322A to 322C and the number N3 of the center blocks 332A and 332B is 2: 1, 3: 2, 4: 3, 5: 4, ... In the block unit per pitch (middle blocks 322A to 322C and center blocks 332A, 332B; see FIG. 4), the middle lateral groove 321B and the center lateral groove 331B are staggered with respect to the long portion of the first center narrow groove 22. Can be connected to. As a result, the rigidity balance of the block unit is optimized.

[Tread shoulder area]
In the configuration of FIG. 2, as described above, the tire 1 includes a pair of shoulder main grooves 21 and 21 and a pair of shoulder land portions 31 and 31 partitioned by these shoulder main grooves 21 and 21. Further, the groove center line (not shown) of the shoulder main groove 21 has a zigzag shape formed by alternately connecting long portions and short portions as a whole.

Further, 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 to the shoulder main groove 21 and the tire ground contact end T. Further, the groove width of the shoulder lug groove 311 widens from the shoulder main groove 21 toward the tire ground contact end T.

[Modification example]
6 and 7 are explanatory views showing a modified example of the tire shown in FIG. 2. In the figure, the same components as those shown in FIG. 2 are designated by 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 with the tire equatorial plane CL as a boundary have a single shoulder main groove 21 and 21, respectively. Further, three center narrow grooves 22, 23, 22 are arranged between these shoulder main grooves 21, 21. Further, the central narrow groove 23 is arranged on the tire equatorial surface CL. Further, these shoulder main grooves 21, 21 and center narrow grooves 22, 23, 22 divide the pair of shoulder land portions 31, 31, the pair of middle land portions 32, 32, and the two rows of center land portions 33, 33. Has been done.

On the other hand, in the modified example of FIG. 6, the two center narrow grooves 22 and 22 are arranged between the pair of shoulder main grooves 21 and 21, so that the pair of shoulder land portions 31, 31 and the pair Middle land 32, 32 and a single center land 33 are formed. In this case, the center lug groove 331A of the center land portion 33 crosses the tire equatorial plane CL and is connected to the left and right middle lug grooves 321A and 321A via the left and right center narrow grooves 22 and 22.

Further, in the modified example of FIG. 7, four or more center narrow grooves 22 and 23 are arranged between the pair of shoulder main grooves 21 and 21, so that the pair of shoulder land portions 31, 31 and the pair of middle land are arranged. The portions 32, 32 and the center land portion 33 having two or more rows are formed. Further, 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. Further, 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 with each other in the tire circumferential direction.

[effect]
As described above, the tire 1 has a pair of shoulder main grooves 21 and 21 extending in the tire circumferential direction, a pair of shoulder regions and a single center region having the pair of shoulder main grooves 21 and 21 as boundaries. (See FIG. 2). Further, the center region has a middle lug groove 321A that opens into the shoulder main groove 21 at one end and has the other end in the ground plane of the center region, and a center having both ends in the ground plane of the center region. It is provided with a lug groove 331A. Further, the middle lug groove 321A and the center lug groove 331A have a minimum groove width of 4.0 [mm] or more. Further, at least a part of the center lug groove 331A extends to the region on the CL side of the tire equatorial plane from the other end of the middle lug groove 321A.

In such a configuration, (1) the center region of the tread portion includes a wide middle lug groove 321A and a center lug groove 331A, so that the center region is compared with a configuration in which the center region does not have a wide lug groove (not shown). There is an advantage that the drainage property of the tire is improved and the wet performance of the tire is improved. Further, (2) at least a part of the center lug groove 331A extends to the region on the CL side of the tire equatorial plane from the other end of the middle lug groove 321A, which has an advantage that the drainage property of the center region is further improved. There is. Further, (3) since the center lug groove 331A has both ends thereof in the ground contact surface of the center region, the rigidity of the center region is ensured as compared with the configuration in which the center lug groove opens to the shoulder main groove, and the tire. There is an advantage that low rolling resistance performance is ensured.

Further, in this tire 1, the center region has a substantially continuous tread surface that is not divided in the tire width direction by another circumferential groove having a maximum groove width exceeding 3.0 [mm] (see FIG. 2). ). This has the advantage that the rigidity of the center region is ensured and the low rolling resistance performance of the tire is ensured.

Further, in this tire 1, the inclination angles θ21 and θ31 of the middle lug groove 321A and the center lug groove 331A with respect to the tire circumferential direction are in the range of 60 [deg] or more and 80 [deg] or less. In such a configuration, the collapse of the blocks 322A to 322C, 332A, and 332B partitioned in the lug grooves 321A to 331A is suppressed as compared with the configuration in which the inclination angle of the lug groove is approximately 90 [deg] (not shown). Therefore, there is an advantage that low rolling resistance performance and wet performance of the tire are ensured.

Further, in the tire 1, the middle lug groove 321A and the center lug groove 331A are inclined in opposite directions with respect to the tire circumferential direction (see FIG. 2). In such a configuration, the collapse of the blocks 322A to 322C, 332A, and 332B partitioned in the lug grooves 321A to 331A is suppressed as compared with the configuration in which the lug grooves are inclined in the same direction with respect to the tire circumferential direction (not shown). Therefore, there is an advantage that low rolling resistance performance and wet performance of the tire are ensured.

Further, in this tire 1, the angle φ1 formed by 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 has the advantage that the rigidity of the center region of the tread portion is ensured and the low rolling resistance performance of the tire is ensured.

Further, in the tire 1, the center lug groove 331A is arranged so as to be separated from the middle lug groove 321A in the tire width direction (see FIG. 3). This has the advantage that the rigidity of the tread portion center region is ensured and the low rolling resistance performance of the tire is ensured, as compared with the configuration in which the center lug groove and the middle lug groove overlap each other in the tire width direction.

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

Further, in this tire 1, the center region includes a pair of middle lug grooves 321A and 321A which are opened in the pair of shoulder main grooves 21 and 21, respectively (see FIG. 2). Further, the pair of middle lug grooves 321A and 321A overlap each other in the projected view in the tire width direction (see FIG. 2). This has the advantage that the rigidity of the center region of the tread portion is ensured and the low rolling resistance performance of the tire is ensured.

Further, in this tire 1, the total extending length Lg2 of the pair of middle lug grooves 321A and 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 extended length Lg2 of the pair of middle lug grooves 321A and 321A in the tire circumferential direction is optimized.

Further, in the tire 1, the center region is divided into two or more center narrow grooves 22 arranged between the pair of shoulder main grooves 21 and 21 and extending in the tire circumferential direction, and the center fine groove 22. It includes a pair of middle land portions 32 and one or more rows of center land portions 33 (see FIG. 2). Further, 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 such a configuration, since the center region has the center narrow groove 22, the drainage property of the center region is improved. Further, since the middle lug groove 321A and the center lug groove 331A extend in each of the middle land portion 32 and the center land portion 33, the drainage property of each land portion 32 and 33 is appropriately ensured. This has the advantage of improving the wet performance of the tire.

Further, in the tire 1, the center narrow grooves 22 and 23 have a maximum groove width of 0.5 [mm] or more and 3.0 [mm] or less. With the above lower limit, the groove widths of the center narrow grooves 22 and 23 are secured, and there is an advantage that the wet performance of the tire is ensured. Further, the above upper limit has an advantage that the groove area in the center region of the tread portion is reduced and the rolling resistance of the tire is reduced.

Further, in this tire 1, the middle lug groove 321A penetrates the middle land portion 32 and connects the shoulder main groove 21 and the center narrow groove 22 (see FIG. 2). In such a configuration, since the drainage route from the center narrow groove 22 to the shoulder main groove 21 via the middle lug groove 321A is secured, there is an advantage that the drainage property of the tread portion center region having a wide tread is properly secured. ..

Further, in the tire 1, the center lug groove 331A penetrates the center land portion and connects the adjacent center narrow grooves 22 (see FIG. 2). This has the advantage of properly ensuring drainage in the center area of the tread portion having a wide tread surface.

Further, in this tire 1, the center narrow groove 22 has a zigzag shape formed by alternately connecting long portions and short portions, and the middle lug groove 321A has a zigzag shape tire ground contact end T of the center narrow groove 22. Connect to the maximum amplitude position to the side (see FIG. 2). Further, the center lug groove 331A is connected to the center narrow groove 22 at the maximum amplitude position toward the tire equatorial surface CL side in a zigzag shape. This has the advantage of properly ensuring drainage in the center area of the tread portion having a wide tread surface.

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

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

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

(1) In the evaluation of low rolling resistance performance, a drum tester with a drum diameter of 1707 [mm] was used, and the load was 28.76 [kN], the air pressure was 900 [kPa], and the speed was 60 [km / h] in accordance with ISO28580. ], The reciprocal of the rolling resistance coefficient of the test tire is calculated and evaluated. This evaluation is performed by an exponential evaluation based on the conventional example (100), and the larger the value, the more preferable. Further, if it is 96 or more, it can be said that the performance is appropriately maintained.

(2) In the evaluation of wet grip performance, the test tire is assembled to the specified rim of JATTA, and the specified internal pressure and specified load of JATTA are applied to this test tire. Further, the test tire is mounted on the test vehicle for performing a predetermined μ-S evaluation. Then, the test vehicle travels on a test course on a wet road surface, and the deceleration from a speed of 60 [km / h] to 20 [km / h] due to ABS braking is measured. This evaluation is performed by an exponential evaluation based on the conventional example (100), and the larger the value, the more preferable.

As shown in FIGS. 1 and 2, the test tires of the examples include a pair of shoulder main grooves 21, 21 and three center narrow grooves 22, 23, a pair of shoulder land portions 31, 31, and a pair of middle grooves. It includes land 32, 32 and two rows of center land 33. Further, each of the middle land portions 32 is provided with a plurality of middle lug grooves 321A and middle lateral grooves 321B, and each of the center land portions 33 is provided with a plurality of center lug grooves 331A and center lateral grooves 331B. Further, the tire contact width TW is 230 [mm], and the maximum contact width Wce in the center region is 140 [mm]. Further, the maximum groove width (dimension symbol omitted in the drawing) of the shoulder main groove 21 is 10.0 [mm], and the maximum groove depth Hg1 (see FIG. 5) is 14 [mm]. Further, the maximum groove width (dimension symbol omitted in the figure) of the center fine grooves 22 and 23 is 2.0 [mm], and the maximum groove depths Hg2 and Hg3 are 14 [mm]. Further, 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 these maximum groove depths H21 and H31 are 12.5 [mm]. Is.

In the test tire of the comparative example, the middle lug groove 321A and the center lug groove 331A are narrow sipes in the test tire of the first embodiment.

As the test results show, it can be seen that the test tires of the examples have both low rolling resistance performance and wet performance of the tire.

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 area; 311 Shoulder lug groove; 312 Shoulder block; 32 Middle land area; 321A middle lug groove; 321B Middle lateral groove; 322A to 322C middle block; 33 Center land area; 331A center lug groove; 331B center lateral groove; 331'top bottom; 332A, 332B center block

Claims (14)

A tire having 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 has a middle lug groove that opens into the shoulder main groove at one end and has the other end in the ground plane of the center region, and a center having both ends in the ground plane of the center region. With a lug groove,
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, and
A tire characterized in that at least a part of the center lug groove extends to a region on the equatorial surface side of the tire with respect to the other end of the middle lug groove. The tire according to claim 1, wherein the center region has a substantially continuous tread surface that is not divided in the tire width direction by another circumferential groove having a maximum groove width of more than 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 [deg] or more and 80 [deg] or less. The tire according to any one of claims 1 to 3, wherein the middle lug groove and the center lug groove are inclined in opposite directions with respect to the tire circumferential direction. The tire according to claim 4, wherein the angle φ1 formed by the middle lug groove and the center lug groove is in the range of 120 [deg] ≤ φ1 ≤ 150 [deg]. The tire according to any one of claims 1 to 5, wherein the center lug groove is arranged so as to be separated from the middle lug groove in the tire width direction. The tire according to claim 6, wherein the distance Dg1 of the center lug groove with respect to the middle lug groove in the tire width direction has a relationship of 0.03 ≦ Dg1 / Wce with respect to the maximum contact width Wce in the center region. The center region comprises a pair of middle lug grooves that each open into the pair of shoulder main grooves, and the center region comprises a pair of middle lug grooves.
The tire according to any one of claims 1 to 7, wherein the pair of middle lug grooves overlap each other in a projected view in the tire width direction. The tire according to claim 8, wherein the total extending 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 center region is arranged between the pair of shoulder main grooves and extends in the tire circumferential direction, and a pair of middle land portions and a row formed by the center grooves. With the above center land area,
The middle lug groove extends in the middle land area and
The tire according to any one of claims 1 to 9, wherein the center lug groove extends in the land portion of the center. The tire according to claim 10, wherein the center narrow groove has a groove width of 0.5 [mm] or more and 3.0 [mm] or less. The tire according to claim 10 or 11, wherein the middle lug groove penetrates the middle land portion and connects the shoulder main groove and the center narrow groove. The tire according to any one of claims 10 to 12, wherein the center lug groove penetrates the center land portion and connects the adjacent center narrow grooves. The center groove has a zigzag shape formed by alternately connecting long portions and short portions.
The middle lug groove is connected to the center narrow groove at the maximum amplitude position toward the tire contact end side of the zigzag shape, and
The tire according to any one of claims 10 to 13, wherein the center lug groove is connected to the maximum amplitude position of the center narrow groove toward the tire equatorial surface side of the zigzag shape.

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