tire

Abstract

To achieve both low rolling resistance performance and wet traction performance.SOLUTION: A tread surface 15A is provided with a pair of circumferential direction main grooves 21 arranged on the outermost side in a tire width direction zoning a center part 31 in between of four circumferential direction grooves 20, a circumferential direction narrow groove 22 arranged in the center part and formed into a groove width WH of 30% or less of a groove width W1 of the circumferential direction main groove of the circumferential direction grooves, and lug grooves 41 and 42 whose both ends are communicated with the adjacent circumferential direction grooves for zoning each land part into a plurality of blocks 31Aa and 31Ba in three land parts 31A and 31B zoned by the circumferential direction groove in the center part. The center part is provided close to the center in the tire width direction in a range of 45% or more with respect to a development width TW of the tread surface. The blocks which are zoned on the land part closer to the center in the tire width direction are formed longer in a tire circumferential direction. Each block is arranged with the end in the tire circumferential direction deviated in the tire circumferential direction in each land part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to tires. [Background technology]

[0002] For example, Patent Document 1 shows a tire having a pair of shoulder main grooves extending circumferentially of the tire, a pair of shoulder regions bounded by the pair of shoulder main grooves, and a single center region, the center region having middle lug grooves that open into the shoulder main grooves at one end and have the other end within the contact patch of the center region, and center lug grooves that have both ends within the contact patch of the center region. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-057908 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in heavy-duty tires for drive axles, a pattern is increasingly being adopted in which the width of the main groove in the center is narrowed and rows of blocks are concentrated in the center to increase block rigidity and reduce rolling resistance.However, such tires have a reduced groove volume, which can lead to poor drainage performance, and there is a concern that the wet traction performance inherent to the block pattern will be reduced.

[0005] An object of the present invention is to provide a tire that can achieve both low rolling resistance and wet traction performance. [Means for solving the problem]

[0006] In order to achieve the above object, a tire according to one embodiment of the present invention includes, on a tread surface, a pair of circumferential main grooves that are arranged on the outermost sides in the tire width direction of at least four circumferential grooves extending in the tire circumferential direction and that define a center portion therebetween; one or more circumferential narrow grooves that are arranged in the center portion of the four circumferential grooves and that have a groove width that is 30% or less of the groove width of the circumferential main grooves; and lug grooves that extend in the tire width direction and are arranged in a plurality of positions in the tire circumferential direction in the tire, in at least three land portions that are defined by at least two of the circumferential grooves in the center portion, and that have both ends that communicate with adjacent circumferential grooves in the tire width direction, thereby defining each of the land portions into a plurality of blocks, the center portion being located closer to the center in the tire width direction within a range of 45% or more of the developed width of the tread surface, the blocks defined in the land portions that are closer to the center in the tire width direction are formed to be longer in the tire circumferential direction, and the circumferential ends of the blocks in each of the land portions are positioned such that they are offset in the tire circumferential direction. [Effects of the Invention]

[0007] According to this invention, both low rolling resistance and wet traction performance can be achieved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment. [Figure 2] FIG. 2 is a plan view of a tread surface of a pneumatic tire according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 5] FIG. 5 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0010] In the following description, the tire radial direction refers to the direction perpendicular to the tire rotational axis (not shown), which is the rotational axis of the pneumatic tire 1 of this embodiment. The tire radial inner side refers to the side toward the tire rotational axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotational axis as the central axis. The tire width direction refers to the direction parallel to the tire rotational axis. The tire width inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the tire rotational axis and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides in position in the tire width direction with the tire width centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line that is on the tire equatorial plane CL and runs along the tire circumferential direction of the pneumatic tire 1. Also, a cross section in the tire meridian direction (meridian cross section) refers to a cross section of the tire cut by a plane including the tire rotation axis.

[0011] 1 is a meridian cross section of a pneumatic tire 1 according to an embodiment, showing a cross section of one side of the tire rotation axis in the tire radial direction. In this embodiment, a heavy-duty pneumatic radial tire mounted on heavy-duty vehicles such as trucks and buses will be described as an example. The pneumatic tire 1 according to this embodiment is particularly suitable as a tire mounted on the drive axle of a heavy-duty vehicle.

[0012] The pneumatic tire 1 of the embodiment has an annular structure centered on the tire rotation axis, and as shown in Figure 1, includes a pair of bead cores 11, a pair of bead fillers 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers 17.

[0013] The pair of bead cores 11 are formed by winding one or more bead wires made of steel in an annular and multiply fashion, and are embedded in the bead portions to form the cores of the bead portions on both sides in the tire width direction.

[0014] The pair of bead fillers 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 in the tire radial direction to reinforce the bead portion.

[0015] 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. The carcass layer 13 is toroidally laid between the bead cores 11 to form the tire framework. Both ends of the carcass layer 13 are wound back and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction of the tire) of 80 degrees or more and 90 degrees or less in absolute value for a radial tire, or 30 degrees or more and 45 degrees or less in absolute value for a bias tire.

[0016] The belt layer 14 is formed by laminating multiple belt plies 141 to 144 and is disposed around the outer periphery of the carcass layer 13. These belt plies 141 to 144 include a high-angle belt 141, a pair of cross belts 142 and 143, and a belt cover 144. The high-angle belt 141 is formed by covering multiple steel belt cords with coating rubber and rolling them, and has a 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 in absolute value. The pair of cross belts 142 and 143 are formed by covering multiple steel belt cords with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 10 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 142 and 143 have cord angles of opposite signs to each other and are laminated with the belt cords' longitudinal directions crossing each other (having a so-called cross-ply structure). The belt cover 144 is made by covering a plurality of 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.

[0017] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the pneumatic tire 1. In the tread portion, the tread rubber 15 forms a tread surface (tread contact surface) 15A on the outer circumferential surface that comes into contact with the road surface during running.

[0018] The pair of sidewall rubbers 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction, and form sidewall portions on both sides in the tire width direction.

[0019] The pair of rim cushion rubbers 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of each bead core 11 and the turned-up portion of the carcass layer 13, and form the rim fitting surface of the bead portion.

[0020] The pneumatic tire 1 of the embodiment has a tread pattern on a tread surface 15A as shown in Fig. 2. Here, each dimension of the tread pattern is measured in a state where the tire is not mounted on a rim and the width between a pair of bead portions is set to the specified rim width.

[0021] Specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. 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. 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.

[0022] The groove width is measured as the maximum distance between opposing groove walls at a groove opening on the tread surface when the tire is not mounted on a rim and the width between a pair of bead portions is set to the specified rim width. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured using the intersection of an extension of the tread surface and an extension of the groove wall as the endpoint in a cross section parallel to the tire width direction and the tire radial direction.

[0023] The groove depth is measured as the maximum distance from the tread surface to the groove bottom when the tire is not mounted on a rim and the width between a pair of beads is set to the specified rim width. If the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0024] The pneumatic tire 1 has at least four circumferential grooves 20 on the tread surface 15A. The circumferential grooves 20 extend along the tire circumferential direction and have an annular structure that is continuously provided around the entire circumference of the tire. Of the at least four circumferential grooves 20, the pneumatic tire 1 has two circumferential main grooves 21. Of the at least four circumferential grooves 20, the pneumatic tire 1 has at least one circumferential narrow groove 22.

[0025] A pair (two) of circumferential main grooves 21 are provided on the outermost sides in the tire width direction, sandwiching the tire equatorial plane CL therebetween. The circumferential main grooves 21 are defined as grooves that are required to display a treadwear indicator specified by JATMA at their groove bottoms 21b.

[0026] As shown in the meridian cross section of FIG. 3, the pair of circumferential main grooves 21 on the outermost sides in the tire width direction have a pair of first groove walls 21c, a pair of platform portions 21d, and a pair of second groove walls 21e between the opening 21a and the groove bottom 21b. The pair of first groove walls 21c extend from the tread surface 15A toward the groove bottom 21b on both sides of the opening 21a in the tire width direction. The pair of platform portions 21d are connected to the groove bottom 21b sides of the respective first groove walls 21c and form platforms higher than the groove bottom 21b on the tire radially outer side so as to extend along the tread surface 15A. The pair of second groove walls 21e are located closer to the groove center (the center of the circumferential main groove 21 in the tire width direction) than the respective first groove walls 21c and extend from the respective platform portions 21d to the groove bottom 21b. The circumferential main groove 21 is formed in a zigzag shape that extends along the tire circumferential direction and meanders in the tire width direction. 3, the circumferential main groove 21 has a groove width W1 of 10.0 mm to 20.0 mm at the opening 21a, a groove width W2 between the second groove walls 21e (the spacing between the platform portions 21d) of 3.0 mm to 4.5 mm, a groove depth D1 from the tread surface 15A to the groove bottom 21b of 13.5 mm to 23.5 mm, and a groove depth D2 from the tread surface 15A to the platform portion 21d of 7.5 mm to 17.5 mm. Also, as shown in FIG. 3, the circumferential main groove 21 is formed such that the angle θ1 of each first groove wall 21c widens from the groove bottom 21b toward the opening 21a toward the tread surface 15A, and is 10 degrees to 14 degrees with respect to a normal to the profile of the tread surface 15A at the tire width direction end of the opening 21a.

[0027] In the pneumatic tire 1, a pair of circumferential main grooves 21 form three rows of land portions aligned in the tire width direction along the tire circumferential direction on the tread surface 15A. Specifically, the pneumatic tire 1 has a center portion 31 defined between the two circumferential main grooves 21 and shoulder portions 32 defined on the tire widthwise outer sides of each circumferential main groove 21. The center portion 31 is disposed to include the tire equatorial plane CL. Specifically, as shown in FIG. 1 , the center portion 31 is provided toward the center in the tire width direction within a tire widthwise range CW of 45% to 60% of the developed width TW of the tread surface 15A. The shoulder portions 32 are disposed on both outermost sides of the tread surface 15A in the tire width direction.

[0028] Here, the developed width TW is the dimension obtained by developing the tread surface 15A between the ground contact edges T on both sides in the tire width direction. The ground contact edges T are defined as the maximum width position in the tire width direction of the contact surface between the pneumatic tire 1 and a flat plate when the pneumatic tire 1 is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate and subjected to a load corresponding to a specified load. The tire width direction range CW of the center portion 31 is the dimension obtained by developing the tread surface 15A between the inner ends in the tire width direction of the openings 21a of the circumferential main grooves 21 at the outermost positions in the tire width direction.

[0029] Two circumferential narrow grooves 22 are provided adjacent to each other in the tire width direction in the center portion 31, with the tire equatorial plane CL sandwiched between them. The circumferential narrow grooves 22 are formed in a linear shape along the tire circumferential direction. In this embodiment, the circumferential narrow grooves 22 have a groove width of 1.0 mm or more and 5.0 mm or less, and a groove depth of 10.0 mm or more and 23.5 mm or less. The circumferential narrow grooves 22 have a groove width WH that is smaller than that of the circumferential main grooves 21, and are formed to be 30% or less of the groove width W1 of the circumferential main grooves 21 on the outer side in the tire width direction.

[0030] It is sufficient that one or more circumferential narrow grooves 22 are provided in the center portion 31. That is, the pneumatic tire 1 may have, among the at least four circumferential grooves 20, a circumferential main groove 21 in addition to the circumferential narrow grooves 22 in the center portion 31 between the pair of circumferential main grooves 21 arranged on the outermost sides in the tire width direction. Although not explicitly shown in the drawings, the other circumferential main grooves 21 provided in the center portion 31 are formed in a linear shape along the tire circumferential direction, and have a groove width of 5.0 mm to 20.0 mm and a groove depth of 13.5 mm to 23.5 mm.

[0031] When the pneumatic tire 1 has four circumferential grooves 20, the center portion 31 has two rows of middle land portions 31A defined between the circumferential main grooves 21 and the circumferential narrow grooves 22 that are adjacent in the tire width direction. When the pneumatic tire 1 has four circumferential grooves 20, the center portion 31 has one row of center land portions 31B defined between the two rows of middle land portions 31A and the two circumferential narrow grooves 22 (or between the circumferential main groove 21 and the circumferential narrow groove 22). This one row of center land portion 31B includes the tire equatorial plane CL and is positioned closest to the center in the tire width direction.

[0032] In addition, when there are more than four circumferential grooves 20, the center portion 31 has multiple rows of center land portions 31B between two rows of middle land portions 31A, which are separated by other circumferential main grooves 21 and circumferential narrow grooves 22.

[0033] As shown in FIG. 2, the middle land portion 31A is provided with middle lug grooves 41. The middle lug grooves 41 extend in the tire width direction and are arranged in multiple locations in the tire circumferential direction. Both ends 41a of the middle lug grooves 41 communicate with the outermost circumferential main groove 21 in the tire width direction and the circumferential narrow groove 22 (or circumferential main groove 21) adjacent to the circumferential main groove 21 in the tire width direction. The middle lug grooves 41 thus configure the middle land portion 31A as a middle block row that divides the middle land portion 31A into multiple middle blocks 31Aa. The middle lug grooves 41 are formed to curve gently in an S-shape in the direction in which they extend. The middle lug grooves 41 communicate with the outermost circumferential main groove 21 in the tire width direction, at a position that snakes inward in the tire width direction of the zigzag shape. The middle lug groove 41 has a groove width of 1.5 mm or more and 9 mm or less, which is narrower than the circumferential main groove 21, and a groove depth of 13.5 mm or more and 23.5 mm or less.

[0034] The middle lug grooves 41 are inclined with respect to the tire width direction. Specifically, the angle θ of a line connecting the centers of the ends 41a of the middle lug grooves 41 with respect to the tire width direction is 20 degrees or more. All middle lug grooves 41 in one middle land portion 31A are inclined in the same direction with respect to the tire width direction. Furthermore, in the pneumatic tire 1 of the embodiment, the rotation direction when the vehicle is moving forward during use is specified as shown by arrow R in FIG. 2. Specifically, the pneumatic tire 1 has a marking (not shown) for specifying the rotation direction, for example, on the sidewall portion. All middle lug grooves 41 in all middle land portions 31A are inclined with the same direction so that the inner end 41a in the tire width direction faces the front of the rotation direction and the outer end 41a in the tire width direction that communicates with the circumferential main groove 21 comes into contact with the ground later.

[0035] As shown in FIG. 2, the middle land portion 31A is provided with middle sipes 51. The middle sipes 51 extend in the tire width direction and are arranged in multiple locations in the tire circumferential direction. Both ends 51a of the middle sipes 51 communicate with the outermost circumferential main groove 21 in the tire width direction and the circumferential narrow groove 22 (or circumferential main groove 21) adjacent to the circumferential main groove 21 in the tire width direction. The middle sipes 51 and the middle lug grooves 41 are arranged alternately in the tire circumferential direction. As a result, the middle sipes 51 are arranged so as to divide the middle block 31Aa, which is defined by the middle lug grooves 41, into two in the tire circumferential direction. The middle sipes 51 are arranged approximately parallel to the direction in which the middle lug grooves 41 extend. The middle sipes 51 communicate with the outermost circumferential main groove 21 in the tire width direction at a position that snakes outward in the tire width direction from the zigzag shape. The middle sipe 51 has a groove width of 1 mm or less and a groove depth of 10.0 mm or more and 18.0 mm or less.

[0036] The middle blocks 31Aa are formed into a parallelogram shape in plan view when viewed from the tread surface 15A. The middle blocks 31Aa have cutouts 31Ab formed at the corners where the ends 41a of the middle lug grooves 41 communicate with the circumferential main grooves 21 and the circumferential narrow grooves 22. The cutouts 31Ab are formed at acute angles diagonally across the parallelogram shape of the middle blocks 31Aa. The cutouts 31Ab are formed at the corners where the middle blocks 31Aa are first stepped on in the rotational direction and at the corners diagonally where the middle blocks 31Aa are last kicked off.

[0037] As shown in FIG. 2, the center land portion 31B is provided with a center lug groove 42. The center lug grooves 42 extend in the tire width direction and are arranged in the tire circumferential direction, with both ends 42a connecting to adjacent circumferential narrow grooves 22 (or circumferential main grooves 21) in the tire width direction. The center lug grooves 42 thereby form a center block row that divides the center land portion 31B into a plurality of center blocks 31Ba. All of the center lug grooves 42 provided in one center land portion 31B are formed to curve in a gentle arc shape in the direction in which they extend. All of the center lug grooves 42 provided in all center land portions 31B are curved in the same direction so that the center on the inner side in the tire width direction faces further in the rotational direction than each end 42a. One end 42a of the center lug groove 42 is provided in a tire circumferential position that does not face the tire width direction inner end 41a of the middle lug groove 41 in the middle land portion 31A. The center lug groove 42 has a groove width of 1.5 mm or more and 9 mm or less, which is narrower than the circumferential main groove 21, and a groove depth of 13.5 mm or more and 23.5 mm or less.

[0038] The center lug grooves 42 have cutouts 42b formed at their ends 42a that communicate with the circumferential narrow grooves 22 (or circumferential main grooves 21). In other words, the cutouts 42b are formed at the corners of the rectangular center blocks 31Ba. The cutouts 42b are formed on the acute-angle sides of the center blocks 31Ba where the center lug grooves 42 are curved into an arc shape and communicate with the circumferential narrow grooves 22 (or circumferential main grooves 21). The cutouts 42b are formed at both corners in the tire width direction where the center blocks 31Ba are kicked out last in the rotational direction.

[0039] As shown in FIG. 2, the center land portion 31B is provided with a center sublug groove 43. The center sublug grooves 43 extend in the tire width direction and are arranged in multiple locations in the tire circumferential direction. One end 43a of each center sublug groove 43 is connected to the circumferential narrow groove 22 (or circumferential main groove 21) adjacent in the tire width direction, and the other end 43a terminates within the center land portion 31B. One center sublug groove 43 is provided in each center block 31Ba. The center sublug grooves 43 and the center lug grooves 42 are arranged alternately in the tire circumferential direction. The center sublug grooves 43 are arranged alternately in the tire width direction toward the tire circumferential direction, with the center lug grooves 42 interposed therebetween. One end 43a of each center sublug groove 43 is arranged in a tire circumferential position facing in the tire width direction the tire width inner end 41a of the middle lug groove 41 in the middle land portion 31A. The center sub-lug groove 43 has a groove width of 1.5 mm or more and 9 mm or less, narrower than the circumferential main groove 21, and a groove depth of 13.5 mm or more and 23.5 mm or less.

[0040] As shown in FIG. 2, the center land portion 31B is provided with center sipes 52. The center sipes 52 extend in the tire width direction and are arranged in plurality in the tire circumferential direction. One end 52a of each center sipe 52 communicates with the circumferential narrow groove 22 (or circumferential main groove 21) adjacent in the tire width direction, and the other end 52a terminates within the center land portion 31B and communicates with the other end 43a of the center sub-lug groove 43. One center sipe 52 is provided in each center block 31Ba. The center sipes 52 and the center lug grooves 42 are arranged alternately in the tire width direction. The center sipes 52 are arranged alternately in the tire width direction toward the tire circumferential direction, with the center lug grooves 42 interposed therebetween. The center sipes 52 and the center sub-lug grooves 43 that communicate with each other are arranged approximately parallel to the extension direction of the center lug grooves 42. The center sipe 52 is provided at a position in the tire circumferential direction where one end 52a thereof faces in the tire width direction an inner end 51a of the middle sipe 51 of the middle land portion 31A in the tire width direction. The center sipe 52 has a groove width of 1 mm or less and a groove depth of 10.0 mm or more and 18.0 mm or less.

[0041] As shown in FIGS. 2 and 3 , shoulder lug grooves 45 are provided in the shoulder portion 32. The shoulder lug grooves 45 extend in the tire width direction and are arranged at equal intervals in the tire circumferential direction. One end 45a of each shoulder lug groove 45 communicates with the outermost circumferential main groove 21 in the tire width direction, and the other end 45a opens to the ground contact edge T. As a result, the shoulder lug grooves 45 form a shoulder block row that divides the shoulder portion 32 into a plurality of shoulder blocks 32a. All shoulder lug grooves 45 provided in the shoulder portion 32 are formed to curve in a gentle arc shape in the direction in which they extend. The shoulder lug grooves 45 are provided at an incline with respect to the tire width direction. Specifically, all shoulder lug grooves 45 provided in the shoulder portion 32 are provided at an incline in the same direction as the middle lug grooves 41. All shoulder lug grooves 45 provided in the shoulder portion 32 are inclined in the same direction so that one end 45a on the inner side in the tire width direction faces further in the direction of rotation than the other end 45a on the outer side in the tire width direction. The shoulder lug grooves 45 have a groove width of 7.0 mm or more and 15.0 mm or less, and a groove depth of 7.5 mm or more and 17.5 mm or less.

[0042] The shoulder lug grooves 45 have cutouts 45c formed at their ends 45a that communicate with the circumferential main grooves 21. In other words, the cutouts 45c are formed at the corners of the rectangular shoulder blocks 32a. The cutouts 45c are formed on the acute-angle sides of the shoulder blocks 32a where the shoulder lug grooves 45 curve in an arc shape to communicate with the circumferential main grooves 21. The cutouts 45c are formed at the corners on the inner side in the tire width direction where the shoulder blocks 32a are first depressed in the rotational direction. The cutouts 45c are chamfered so as to slope radially inward toward the platform portion 21d of the circumferential main groove 21 on the outermost side in the tire width direction.

[0043] Each shoulder lug groove 45 has an upper bottom portion 45b that protrudes radially outward from the groove bottom. The upper bottom portion 45b has an apex 45ba that protrudes most from the groove bottom, and is positioned along the profile of the tread surface 15A where the shoulder lug groove 45 opens. The shoulder lug groove 45 has a groove depth D3 of 2.0 mm to 8.0 mm, which is shallower than the groove depth D1 from the tread surface 15A to the groove bottom 21b of the outermost circumferential main groove 21 in the tire width direction, and the groove depth D2 from the tread surface 15A to the platform portion 21d of the outermost circumferential main groove 21 in the tire width direction. These groove depths D1, D2, and D3 satisfy the relationships 0.50≦D2 / D1≦0.90 and 0.10≦D3 / D1≦0.40.

[0044] The bottom upper portion 45b has an inclined surface 45bb on the inner side in the tire width direction, which slopes radially inward from the apex 45ba toward the platform portion 21d of the circumferential main groove 21. The angle θ2 of the inclined surface 45bb relative to the normal to the profile of the tread surface 15A where the shoulder lug grooves 45 open is 20 degrees or more and 60 degrees or less. The inclined surface 45bb is smoothly connected to the apex 45ba by a circular arc 45bc. The inclined surface 45bb is smoothly connected to the platform portion 21d of the circumferential main groove 21 on the outermost side in the tire width direction by a circular arc 45bd.

[0045] The bottom upper portion 45b has an inclined surface 45be on the outer side in the tire width direction, which slopes radially inward from the apex 45ba toward the other end 45a of the shoulder lug groove 45. The angle θ3 of the inclined surface 45bb with respect to the normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens is 10 degrees or more and 30 degrees or less. The inclined surface 45be is smoothly connected to the apex 45ba by a circular arc 45bf.

[0046] The tire width direction dimension WS2 of the apex 45ba of the bottom upper portion 45b is the distance in the tire width direction between a normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens at the intersection of the extended lines of the inclined surface 45bb and the apex 45ba and a normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens at the intersection of the extended lines of the inclined surface 45bb and the apex 45ba. The tire width direction dimension WS1 of the shoulder lug groove 45 having the bottom upper portion 45b is the distance in the tire width direction between a normal to the profile of the tread surface 15A at the tire width direction outer end of the opening 21a of the outermost circumferential main groove 21 and a normal to the profile of the tread surface 15A at the contact edge T. The tire width direction dimension WS1 of the shoulder lug groove 45 and the tire width direction dimension WS2 of the apex 45ba satisfy the relationship 0.50≦WS2 / WS1≦0.90. Preferably, the dimension WS1 of the shoulder lug groove 45 in the tire width direction and the dimension WS2 of the apex 45ba in the tire width direction satisfy the relationship 0.60≦WS2 / WS1≦0.80.

[0047] The pneumatic tire 1 of the present embodiment described above is characterized in that, on the tread surface 15A, a pair of circumferential main grooves 21 are arranged on the outermost sides in the tire width direction among at least four circumferential grooves 20 extending in the tire circumferential direction and define a center portion 31 therebetween, one or more circumferential narrow grooves 22 are arranged in the center portion 31 among the four circumferential grooves 20 and are formed with a groove width WH of 30% or less of the groove width W1 of the circumferential main groove 21, and at least three land portions 31A, 31B defined by at least two circumferential grooves 20 in the center portion 31, which extend in the tire width direction and are formed with multiple land portions 31A, 31B in the tire circumferential direction. The center portion 31 is provided closer to the center in the tire width direction within a range of a tire width direction dimension CW of 45% or more of the developed width TW of the tread surface 15A, and the blocks 31Aa, 31Ba defined in the land portion 31B closer to the center in the tire width direction are formed longer in the tire circumferential direction, and the blocks 31Aa, 31Ba are arranged such that the tire circumferential ends of each land portion 31A, 31B are offset in the tire circumferential direction.

[0048] In this pneumatic tire 1, the pair of circumferential main grooves 21 on the outermost side in the tire width direction have a wider groove width than the circumferential main grooves 21 in the center portion 31, which increases the ground contact pressure in the center portion 31. Therefore, the blocks 31Aa and 31Ba are arranged in the center portion 31, suppressing deformation of the entire tread surface 15A. This improves the low rolling resistance performance of this pneumatic tire 1. Furthermore, in this pneumatic tire 1, the blocks 31Ba near the center, which have higher ground contact pressure, are made longer in the tire circumferential direction, thereby further improving the low rolling resistance performance. Meanwhile, in this pneumatic tire 1, the lug grooves 41 open to the pair of circumferential main grooves 21 on the outermost side in the tire width direction, and the blocks 31Aa and 31Ba contact the ground sequentially in a trickle pattern, ensuring efficient drainage. This improves the wet traction performance of this pneumatic tire 1. Furthermore, with this pneumatic tire 1, the blocks 31Aa, 31Ba come into contact with the ground in succession, preventing both the blocks 31Aa, 31Ba from collapsing and deforming in the front and rear directions, thereby suppressing deterioration in low rolling resistance performance caused by the arrangement of the lug grooves 41, 42. As a result, the pneumatic tire 1 of the embodiment can achieve both low rolling resistance performance and wet traction performance.

[0049] In addition, in the pneumatic tire 1 of the embodiment, in the center portion 31, the tire circumferential length L1 of the block 31Ba in the center land portion 31B closest to the center in the tire width direction and the tire circumferential length L2 of the block 31Aa in the middle land portion 31A adjacent to the center land portion 31B in the tire width direction satisfy the relationship 1.2≦L1 / L2≦1.9.

[0050] Increasing the circumferential length of the blocks 31Ba of the central land portion 31B in the tire can further improve low rolling resistance performance of the pneumatic tire 1. In addition, not increasing the circumferential length of the blocks 31Ba of the central land portion 31B in the tire can ensure the total number of lug grooves 42 in the entire tire circumferential direction and maintain wet traction performance.

[0051] In addition, in the pneumatic tire 1 of the embodiment, in the center portion 31, the tire circumferential length L1 of the block 31Ba in the center land portion 31B closest to the center in the tire width direction, and the tire circumferential deviation D between the tire circumferential end of the center land portion 31B and the end of the block 31Aa in the middle land portion 31A adjacent to the center land portion 31B in the tire width direction, satisfy the relationship 0.1≦D / L1≦0.5.

[0052] According to this pneumatic tire 1, by disposing the blocks 31Aa and 31Ba with a circumferential offset in the tire circumferential direction, the horizontally arranged blocks 31Aa and 31Ba are prevented from collapsing simultaneously during rotation, thereby improving low rolling resistance performance.

[0053] In the pneumatic tire 1 of the embodiment, the groove width WH of the circumferential narrow groove 22 is 5 mm or less.

[0054] In this pneumatic tire 1, the blocks 31Aa, 31Ba are closer to each other in the center portion 31 where the ground pressure is high, which increases rigidity and is advantageous for improving low rolling resistance. In this pneumatic tire 1, to further enhance this effect, it is preferable that the groove width WH of the circumferential narrow grooves 22 is 3 mm or less, but in order to ensure drainage performance, it is preferable that the groove width WH of the circumferential narrow grooves 22 is 1.5 mm or more.

[0055] In the pneumatic tire 1 of the embodiment, the groove width WL of the middle lug grooves 41 communicating with the pair of circumferential main grooves 21 arranged on the outermost sides in the tire width direction is 1.5 mm or more and 9 mm or less.

[0056] According to the pneumatic tire 1, by specifying the groove width WL of the middle lug grooves 41, the rigidity of the middle blocks 31Aa is maintained, and the middle blocks 31Aa mutually support each other, which is advantageous for improving low rolling resistance performance. To further enhance this effect, the pneumatic tire 1 preferably has the groove width WL of the middle lug grooves 41 set to 1.5 mm or more and 7 mm or less.

[0057] In the pneumatic tire 1 of the embodiment, the middle lug grooves 41 communicating with the pair of circumferential main grooves 21 arranged on the outermost sides in the tire width direction extend at an angle of 20 degrees or more with respect to the tire width direction.

[0058] According to this pneumatic tire 1, by specifying the angle at which the middle lug grooves 41 extend, drainage into the circumferential main grooves 21 is improved, which is advantageous for improving wet traction performance. Also, in the pneumatic tire 1 of the embodiment, the ends 41a of the middle lug grooves 41 that communicate with the circumferential main grooves 21 are inclined so that they come into contact with the ground later, which further improves drainage into the circumferential main grooves 21 and is advantageous for improving wet traction performance.

[0059] In addition, in the pneumatic tire 1 of the embodiment, the circumferential main groove 21 has a meridian cross-sectional shape comprising a pair of first groove walls 21c extending from the tread surface 15A toward the groove bottom 21b, a pair of terrace portions 21d connecting to the groove bottom 21b sides of each of the first groove walls 21c and forming terraces along the tread surface 15A, and a pair of second groove walls 21e located closer to the groove center than each of the first groove walls 21c and extending from each terrace portion 21d toward the groove bottom 21b. In the shoulder portion 32 defined on the outer side of the circumferential main groove 21 in the tire width direction, shoulder lug grooves 45 are provided which extend in the tire width direction and are arranged in plurality around the tire circumferentially, with one end 45a connected to the circumferential main groove 21 and with an upper bottom portion 45b formed at the groove bottom, and the upper bottom portion 45b of the shoulder lug groove 45 and the terrace portion 21d of the circumferential main groove 21 are smoothly connected by a circular arc 45bd.

[0060] According to this pneumatic tire 1, by forming the groove shape of the circumferential main groove 21 on the outermost side in the tire width direction into a curb groove, the narrow second groove wall 21e on the groove bottom 21b side of the curb portion 21d tends to close when in contact with the ground. Moreover, according to this pneumatic tire 1, by smoothly connecting the bottom upper portion 45b to the curb portion 21d, it is possible to eliminate the stepped space that may occur at the connection portion between the circumferential main groove 21 on the outermost side in the tire width direction and the shoulder lug groove 45. For this reason, this pneumatic tire 1 has a shape that prevents stones that may enter the connection portion between the circumferential main groove 21 and the shoulder lug groove 45 from reaching the groove bottom 21b of the circumferential main groove 21, and the stone chipping resistance performance can be improved. In order to advantageously obtain the said effect, this pneumatic tire 1 preferably has a groove width W2 between the second groove walls 21e of 3.0 [mm] or more and 4.5 [mm] or less, and a radius of the arc 45bd of 2.0 [mm] or more and 15.0 [mm] or less. Moreover, this pneumatic tire 1 is advantageous for reducing the passing noise because the sound is less likely to escape to the outside in the tire width direction by arranging the bottom upper portion 45b.

[0061] Further, in the pneumatic tire 1 of the embodiment, the groove depth D1 of the circumferential main groove 21 on the outermost side in the tire width direction, the groove depth D2 to the curb portion 21d, and the groove depth D3 to the bottom upper portion 45b of the shoulder lug groove 45 satisfy the relationships of 0.50 ≦ D2 / D1 ≦ 0.90 and 0.10 ≦ D3 / D1 ≦ 0.40.

[0062] According to this pneumatic tire 1, by defining the groove depth D2 of the curb portion 21d within an appropriate range, the effect of preventing the bitten stone from reaching the groove bottom 21b of the circumferential main groove 21 and making it easy to escape can be obtained. Also, by defining the groove depth D3 to the bottom upper portion 45b within an appropriate range, the effect of suppressing the escape of sound to the outside in the tire width direction is advantageous. In order to more advantageously obtain these effects, this pneumatic tire 1 preferably satisfies the relationships of 0.60 ≦ D2 / D1 ≦ 0.70 and 0.25 ≦ D3 / D1 ≦ 0.35.

[0063] Further, in the pneumatic tire 1 of the embodiment, the pair of first groove walls 21c of the circumferential main groove 21 on the outermost side in the tire width direction are formed so as to spread toward the tread surface 15A.

[0064] In this pneumatic tire 1, by providing an angle to the pair of first groove walls 21c leading to the tread surface 15A, a difference in groove width occurs between the tread surface 15A side and the platform portion 21d side, improving the ability to remove trapped stones. In this pneumatic tire 1, the groove volume of the circumferential main groove 21 decreases toward the groove bottom 21b, so there is no impact on the effect of reducing passing noise.

[0065] In the pneumatic tire 1 of the embodiment, the tire width direction dimension WS1 of the shoulder lug groove 45 and the tire width direction dimension WS2 of the apex 45ba of the bottom upper portion 45b satisfy the relationship 0.50≦WS2 / WS1≦0.90.

[0066] In this pneumatic tire 1, by setting the tire width direction dimension WS2 of the bottom upper portion 45b within an appropriate range, the stone trapping resistance of the shoulder lug grooves 45 is improved. Moreover, in this pneumatic tire 1, by locating the bottom upper portion 45b in the shoulder lug grooves 45 in the shoulder portions 32, where sound tends to escape, sound escape is reduced and the groove volume is reduced, thereby reducing pass-by noise. To further maximize these effects, it is preferable that this pneumatic tire 1 satisfy the relationship 0.60≦WS2 / WS1≦0.80.

[0067] In addition, in the pneumatic tire 1 of the embodiment, the bottom upper portion 45b has, on the inner side in the tire width direction, an inclined surface (first inclined surface) 45bb that inclines radially inward in the tire from the apex 45ba toward the platform portion 21d of the circumferential main groove 21, and an inclined surface (second inclined surface) 45be that inclines radially inward in the tire on the side from the apex 45ba toward the other end 45a of the shoulder lug groove 45, and the angle θ2 of the inclined surface 45bb with respect to the normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens is 20 degrees or more and 60 degrees or less, and the angle θ3 of the inclined surface 45be with respect to the normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens is 10 degrees or more and 30 degrees or less.

[0068] In this pneumatic tire 1, by specifying within appropriate ranges the angle θ2 of the inclined surface 45bb of the bottom upper portion 45b at the connection between the outermost circumferential main groove 21 in the tire width direction and the bottom upper portion 45b, and the angle θ3 of the inclined surface 45be of the bottom upper portion 45b facing outward in the tire width direction, trapped stones can be smoothly removed, improving stone trapping resistance. Moreover, in this pneumatic tire 1, by specifying the angles θ2 and θ3 within the specified ranges, the effect of reducing pass-by noise is not affected. To further enhance these effects, it is preferable that the angle θ2 be 40 degrees or more and 50 degrees or less, and the angle θ3 be 15 degrees or more and 25 degrees or less.

[0069] In the pneumatic tire 1 of the embodiment, the shoulder lug grooves 45 extend in an arc shape in the tire width direction, and a plurality of shoulder lug grooves 45 are arranged at equal intervals in the tire circumferential direction. Here, the preferable range of the equal intervals is a pitch in the tire circumferential direction of 65 mm to 75 mm.

[0070] In this pneumatic tire 1, the shoulder lug grooves 45 are arranged at equal intervals in the tire circumferential direction, which makes the groove area of ​​the shoulder portion 32 uniform and maintains the effect of reducing passing noise. Moreover, in this pneumatic tire 1, the shoulder lug grooves 45 extend in an arc, allowing trapped stones to be smoothly removed.

[0071] In addition, in the pneumatic tire 1 of the embodiment, in the shoulder block 32a in which the shoulder portion 32 is divided by the shoulder lug groove 45, a chamfered cutout portion 45c is formed at the acute angle where the shoulder lug groove 45 communicates with the circumferential main groove 21, so as to reach the terrace portion 21d in the circumferential main groove 21 and incline radially inward in the tire.

[0072] In this pneumatic tire 1, the generation of impact noise during running is suppressed by chamfering the acute-angled portions of the shoulder blocks 32a. Furthermore, in this pneumatic tire 1, the groove width of the shoulder lug grooves 45 opening to the tread surface 15A is widened by the inclined chamfer, and the groove width narrows toward the platform portion 21d, so that stone-trapping resistance is not adversely affected. To further enhance this effect, the inclination angle of the chamfer of the notch 45c of this pneumatic tire 1 is preferably set to 6 degrees or more and 10 degrees or less.

[0073] In the present embodiment, as described above, a pneumatic tire 1 has been described as an example of a tire. The pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, or other gases. However, the tread pattern configuration of the pneumatic tire 1 described in the present embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires. [Example]

[0074] 4 and 5 are tables showing the results of performance tests of pneumatic tires according to the embodiment. Performance evaluation tests conducted on a conventional pneumatic tire and an example pneumatic tire according to the embodiment will be described below. The performance evaluation tests were conducted on rolling resistance performance and wet grip performance (wet traction performance).

[0075] In the rolling resistance performance evaluation test, a 315 / 70R22.5 size pneumatic tire (test tire) is mounted on a specified rim, inflated to a specified pressure, and mounted on a heavy-duty vehicle. The rolling resistance coefficient (ratio of rolling resistance to load on the test tire) is measured under test conditions in accordance with UN R117-04 (UN Regulation No. 117 Revision 4). Based on the measurement results, an index evaluation is performed, with a conventional example being used as the standard (100). The higher the evaluation value, the better.

[0076] In the wet grip performance evaluation test, a pneumatic tire (test tire) of the above size is mounted on a specified rim, inflated to a specified air pressure, and mounted on a heavy-duty vehicle. The tire is then subjected to testing in accordance with UN R117-04 (UN Regulation No. 117 Revision 4), and the grip index (the ratio of the performance of the test tire to that of a reference tire) is measured on a wet road surface with a water depth of 1 mm. Based on the measurement results, an index evaluation is performed, with a conventional tire being used as the reference (100). The higher the evaluation value, the better.

[0077] The conventional pneumatic tire is based on the tread pattern shown in FIG. 2, but is outside the range of the specifications (1) to (12) shown in FIGS.

[0078] The pneumatic tire of the example is based on the tread pattern shown in FIG. 2 and falls within the specified ranges for the specified contents (1) to (12) shown in FIGS.

[0079] As shown in the test results, it is understood that the pneumatic tire of this example has improved rolling resistance performance and wet traction performance compared to the conventional example.

[0080] The present disclosure includes the following inventions. [Invention 1] On the tread surface A pair of circumferential main grooves that are arranged on the outermost sides in the tire width direction among at least four circumferential grooves extending in the tire circumferential direction and define a center portion therebetween; One or more circumferential narrow grooves among the four circumferential grooves are arranged in the center portion and formed with a groove width of 30% or less of the groove width of the circumferential main groove; In the at least three land portions defined by at least two of the circumferential grooves in the center portion, lug grooves extend in the tire width direction, are arranged in the tire circumferential direction, and both ends of the lug grooves communicate with adjacent circumferential grooves in the tire width direction, thereby defining each of the land portions into a plurality of blocks; Including, The center portion is provided toward the center in the tire width direction within a range of 45% or more of the developed width of the tread surface, The blocks are formed so that the blocks defined in the land portion closer to the center in the tire width direction are longer in the tire circumferential direction, The blocks are arranged such that the ends of the blocks in the land portion in the tire circumferential direction are offset in the tire circumferential direction. tire. [Invention 2] In the center portion, a tire circumferential length L1 of the block in the center land portion closest to the tire width direction center and a tire circumferential length L2 of the block in the middle land portion adjacent to the center land portion in the tire width direction satisfy the relationship 1.2≦L1 / L2≦1.9; A tire according to claim 1. [Invention 3] In the center portion, With respect to the tire circumferential length L1 of the block in the center land portion closest to the center in the tire width direction, the tire circumferential deviation D between the tire circumferential end of the center land portion and the tire width direction end of the block in the middle land portion adjacent to the center land portion satisfies the relationship of 0.1≦D / L1≦0.5. The tire according to claim 1 or 2. [Invention 4] The groove width of the circumferential narrow groove is 5 mm or less. A tire according to any one of inventions 1 to 3. [Invention 5] The groove width of the lug groove communicating with the circumferential main groove is 1.5 mm or more and 9 mm or less. A tire according to any one of inventions 1 to 4. [Invention 6] The lug grooves communicating with the circumferential main grooves extend at an angle of 20 degrees or more with respect to the tire width direction. A tire according to any one of inventions 1 to 5. [Invention 7] The circumferential main groove is a pair of first groove walls each having a meridian cross section extending from the tread surface toward a groove bottom; a pair of platform portions connected to groove bottom sides of the first groove walls and forming platforms along the tread surface; a pair of second groove walls located closer to the groove center than the first groove walls and extending from the platform portions toward the groove bottom; and In a shoulder portion defined on the outer side in the tire width direction of the circumferential main groove, shoulder lug grooves are provided, the shoulder lug grooves extending in the tire width direction and arranged in the tire circumferential direction, the shoulder lug grooves having one end connected to the circumferential main groove and having a bottom upper portion formed at the groove bottom, a bottom upper portion of the shoulder lug groove and the platform portion of the circumferential main groove are smoothly connected by a circular arc; A tire according to any one of inventions 1 to 6. [Explanation of symbols]

[0081] 1. Pneumatic tires (tires) 15A tread surface 20 Circumferential groove 21 Circumferential main groove 21b Groove bottom 21c First groove wall 21d Danbe 21e Second groove wall 22 Circumferential thin groove 31 Center Section 31B Center Land 31Ba Center Block 31A Middle Land Section 31Aa Middle Block 32 Shoulder section 41 Middle lug groove 41a end 42 Center lug groove 42a one end 45 Shoulder lug groove 45a end 45b Bottom top 45bc arc 45bd arc

Claims

1. On the tread surface a pair of circumferential main grooves arranged on the outermost sides in the tire width direction among at least four circumferential grooves extending in the tire circumferential direction, and defining a center portion therebetween; One or more circumferential narrow grooves among the four circumferential grooves are disposed in the center portion and formed with a groove width of 30% or less of the groove width of the circumferential main groove; lug grooves extending in the tire width direction and arranged in the tire circumferential direction, in at least three land portions defined by at least two of the circumferential grooves in the center portion, with both ends communicating with the circumferential grooves adjacent in the tire width direction, and defining each of the land portions into a plurality of blocks; Including, The center portion is provided toward the center in the tire width direction within a range of 45% or more of the developed width of the tread surface, The blocks are formed so that the blocks defined in the land portion closer to the center in the tire width direction are longer in the tire circumferential direction, The blocks are arranged such that the ends of the blocks in the land portion in the tire circumferential direction are offset in the tire circumferential direction. tire.

2. In the center portion, a tire circumferential length L1 of the block in the center land portion closest to the tire width direction center and a tire circumferential length L2 of the block in the middle land portion adjacent to the center land portion in the tire width direction satisfy the relationship 1.2≦L1 / L2≦1.9; 2. The tire of claim 1.

3. In the center portion, a tire circumferential length L1 of the block in the center land portion closest to the center in the tire width direction, and a tire circumferential deviation D between the tire circumferential end of the center land portion and the tire width direction end of the block in the middle land portion adjacent to the center land portion, satisfying the relationship of 0.1≦D / L1≦0.5; 2. The tire of claim 1.

4. The groove width of the circumferential narrow groove is 5 mm or less.

2. The tire of claim 1.

5. The groove width of the lug groove communicating with the circumferential main groove is 1.5 mm or more and 9 mm or less.

2. The tire of claim 1.

6. The lug grooves communicating with the circumferential main grooves extend at an angle of 20 degrees or more with respect to the tire width direction.

2. The tire of claim 1.

7. The circumferential main groove is a pair of first groove walls each having a meridian cross section extending from the tread surface toward a groove bottom; a pair of platform portions connected to groove bottom sides of the first groove walls and forming platforms along the tread surface; a pair of second groove walls located closer to the groove center than the first groove walls and extending from the platform portions toward the groove bottom; and In a shoulder portion defined on the outer side in the tire width direction of the circumferential main groove, shoulder lug grooves are provided, the shoulder lug grooves extending in the tire width direction and arranged in the tire circumferential direction, the shoulder lug grooves having one end connected to the circumferential main groove and having a bottom upper portion formed at the groove bottom, a bottom upper portion of the shoulder lug groove and the platform portion of the circumferential main groove are smoothly connected by a circular arc; 2. The tire of claim 1.

Images