Tire

Abstract

To make both low rolling resistance performance and on-snow traction performance compatible.SOLUTION: Groove walls of one or more circumferential narrow grooves 22 arranged inside in a tire width direction of a circumferential main groove 21 contact each other at least at sides closer to groove bottoms than a center of a groove depth when touching the ground. Groove walls of first penetration middle lug grooves 41 do not contact each other when touching the ground, and ends 41a and 45a communicating with the circumferential main grooves 21 with respect to shoulder lug grooves 45 are arranged to oppose to each other in a tire width direction. Groove walls of second penetration middle lug grooves 42 contact each other at least at a side closer to the groove bottom than a center of a groove depth when touching the ground, and ends 42a and 45a communicating with the circumferential main grooves 21 with respect to the shoulder lug grooves 45 are arranged to be displaced from each other in a tire circumferential direction. A groove width W4 and a groove depth D4 of the first penetration middle lug groove 41, a groove width W5a and a groove depth D5 of an opening part of the second penetration middle lug groove 42 and a groove width W9 and a groove depth D9 of the penetration shoulder lug groove satisfy relational expressions of W4<W5a<W9 and D4<D9<D5 when touching the ground.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] For example, Patent Document 1 discloses a heavy-duty pneumatic tire having a configuration in which a pair of circumferential main grooves extending along the tire circumferential direction are arranged on either side of the tire equatorial plane on the tread surface, dividing the tread surface into a central region and both side regions, and three circumferential narrow grooves extending along the tire circumferential direction are arranged in the central region to define and form four central rib-like land portions, and when the tire comes into contact with the ground, the openings of the circumferential narrow grooves close, causing adjacent central rib-like land portions positioned on either side of the circumferential narrow groove to come into contact and support each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5693069 Summary of the Invention [Problem to be solved by the invention]

[0004] To reduce rolling resistance and increase block rigidity, a trend is being made to adopt a pattern in which the width of the main groove in the center is narrow and the block rows are concentrated in the center. However, with such tires, the narrow grooves close in the center contact area when the tire makes contact with the ground, preventing sufficient groove volume from being secured, raising concerns that traction on snow may deteriorate.

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

[0006] To achieve the above object, a tire according to one aspect of the present invention has, on a tread surface, at least four circumferential grooves extending in the tire circumferential direction, and in a center portion partitioned between each of the circumferential grooves on the outermost side in the tire width direction, a center land portion partitioned by at least two of the circumferential grooves and disposed at the center in the tire width direction, a middle land portion partitioned on the outer side in the tire width direction of the center land portion in the center portion, a shoulder portion partitioned on the outer side in the tire width direction of the circumferential groove on the outermost side in the tire width direction, first through middle lug grooves and second through middle lug grooves in which respective ends extending in the tire width direction communicate with adjacent circumferential grooves so as to partition the middle land portion into a plurality of middle blocks and are alternately arranged in a plurality in the tire circumferential direction, through shoulder lug grooves in which one end communicates with the circumferential groove on the outermost side in the tire width direction so as to partition the shoulder portion into a plurality of shoulder blocks and are arranged in a plurality in the tire circumferential direction, one or more of the circumferential grooves disposed on the inner side in the tire width direction of the circumferential groove on the outermost side in the tire width direction have groove walls contacting each other at least on the groove bottom side from at least the center of the groove depth when in contact with the ground, the first through middle lug groove communicating with the circumferential groove on the outermost side in the tire width direction has groove walls not contacting each other when in contact with the ground, and ends communicating with the circumferential groove are arranged to face each other in the tire width direction with respect to the through shoulder lug groove, the second through middle lug groove communicating with the circumferential groove on the outermost side in the tire width direction has groove walls contacting each other at least on the groove bottom side from at least the center of the groove depth when in contact with the ground, and ends communicating with the circumferential groove are arranged to be offset in the tire circumferential direction with respect to the through shoulder lug groove, and the groove width W4 and groove depth D4 of the first through middle lug groove, the groove width W5a and groove depth D5 of the opening of the second through middle lug groove, and the groove width W9 and groove depth D9 of the through shoulder lug groove satisfy the relationship of W < W5a < W9 and D4 < D9 < D5 when in contact with the ground.

Advantages of the Invention

[0007] According to this invention, it is possible to achieve both low rolling resistance performance and snow traction performance.

Brief Description 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 cross-sectional view taken along line BB in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line CC in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line DD in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along the line E-E in FIG. [Figure 8] FIG. 8 is a cross-sectional view taken along the line FF in FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along line GG in FIG. [Figure 10] FIG. 10 is another example of a cross-sectional view taken along line GG in FIG. [Figure 11] FIG. 11 is a cross-sectional view taken along line HH in FIG. [Figure 12] FIG. 12 is an enlarged plan view of the tread surface of the pneumatic tire according to the embodiment. [Figure 13] FIG. 13 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 14] FIG. 14 is a table showing the results of a performance test of the pneumatic tire according to the embodiment. [Figure 15] FIG. 15 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 disposed 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 an unloaded state with the tire mounted on a specified rim and inflated to a specified internal pressure.

[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 the opposing groove walls at the groove opening on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured 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 mounted on a specified rim, inflated to a specified internal pressure, and under no load. 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 9.0 mm to 16.0 mm, and a groove depth D2 from the tread surface 15A to the platform portion 21d of 5.0 mm to 13.0 mm. Also, as shown in FIG. 3, the circumferential main groove 21 is formed such that the angle θa 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 70% 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 contact edges T on both sides in the tire width direction. The contact edges T are defined as the maximum width position in the tire width direction at 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 maximum width in the tire width direction at the contact surface for defining the contact edges T is called the contact width LT. The range CW in the tire width direction of the center portion 31 is the dimension obtained by developing the area 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, sandwiching the tire equatorial plane CL therebetween. The circumferential narrow grooves 22 are formed in a linear shape along the tire circumferential direction. As shown in FIGS. 2 and 4, the circumferential narrow grooves 22 are provided with notches 31Bb on the tire widthwise inner side of the openings 22a. As shown in FIG. 4, the circumferential narrow grooves 22 have a groove width W3 of 1.0 mm to 5.0 mm and a groove depth D3 of 5.0 mm to 25.0 mm on the groove bottom 22b side. When the circumferential narrow grooves 22 are in contact with each other within the groove width W3 and within a range of at least 20% of the groove depth D3, contact between the groove walls 22c is achieved. When the pneumatic tire 1 is in contact with the ground, the pneumatic tire 1 comes into contact with a flat plate when the pneumatic tire 1 is mounted on a specified rim, a specified internal pressure is applied, and a load corresponding to a specified load is applied. When the tire is in contact with the ground, the circumferential narrow groove 22 opens at the portion of the opening 22a having the notch 31Bb on the tread surface 15A.

[0030] 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 groove 21 and the circumferential narrow groove 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. This row of center land portions 31B includes the tire equatorial plane CL and is positioned closest to the center in the tire width direction. That is, when the pneumatic tire 1 of the embodiment has four circumferential grooves 20, the center of the center land portion 31B can be positioned at the center of the contact width LT when the tire is mounted on a standard rim, pressurized to a standard internal pressure, and subjected to a load corresponding to a standard load.

[0031] When the number of circumferential grooves 20 is more than four, three or more circumferential narrow grooves 22 are provided in the center portion 31. In this case, the center portion 31 has, between one row of middle land portions 31A, multiple rows of center land portions 31B partitioned by the circumferential narrow grooves 22. Alternatively, in this case, the center portion 31 has, between multiple rows of middle land portions 31A, one or multiple rows of center land portions 31B partitioned by the circumferential narrow grooves 22.

[0032] 2, the middle land portion 31A is provided with a first through middle lug groove 41 and a second through middle lug groove 42. The second through middle lug groove 42 may also be simply referred to as a through middle lug groove.

[0033] The first through middle lug grooves 41 extend in the tire width direction and are arranged in plurality in the tire circumferential direction. Their opposite ends 41a communicate with the outermost circumferential main groove 21 in the tire width direction and the circumferential narrow groove 22 adjacent to the circumferential main groove 21 in the tire width direction. The first through middle lug grooves 41 are curved gently in an arc shape in the direction of extension. The first through middle lug grooves 41 are inclined relative to the tire width direction. Specifically, the angle θ1 of a straight line connecting the centers of the ends 41a of the first through middle lug grooves 41 is between 0 and 30 degrees relative to the tire width direction. All of the first through middle lug grooves 41 in one middle land portion 31A are inclined in the same direction relative to the tire width direction. The first through middle lug grooves 41 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. As shown in FIG. 5, the first through middle lug groove 41 has a groove width W4 of 1.5 mm or more and 9.0 mm or less, and a groove depth D4 of 1.5 mm or more and 8.0 mm or less. The groove width W4 and groove depth D4 of the first through middle lug groove 41 satisfy the relationship 1.50≦W4 / D4≦5.0. The groove walls 41e of the first through middle lug grooves 41 do not come into contact with each other when the tire is in contact with the ground. Furthermore, as shown in FIG. 2, the first through middle lug groove 41 has a tire width direction length L1 of 17.0 mm or more and 37.0 mm or less.

[0034] The second through middle lug grooves 42 extend in the tire width direction and are arranged in multiple locations in the tire circumferential direction. Their opposite ends 42a communicate with the outermost circumferential main groove 21 in the tire width direction and the circumferential narrow groove 22 adjacent to the circumferential main groove 21 in the tire width direction. The second through middle lug grooves 42 and the first through middle lug grooves 41 are arranged alternately in the tire circumferential direction. The second through middle lug grooves 42 are curved in a gentle arc shape in the extension direction, similar to the first through middle lug grooves 41. The second through middle lug grooves 42 are arranged at an angle with respect to the tire width direction. Specifically, the angle θ2 of the straight line connecting the centers of the ends 41a of the second through middle lug grooves 42 is between 0 degrees and 30 degrees with respect to the tire width direction. All of the first through middle lug grooves 41 in one middle land portion 31A are inclined in the same direction with respect to the tire width direction, similar to the inclination of the first through middle lug grooves 41. The second through-middle lug grooves 42 communicate with the outermost circumferential main grooves 21 in the tire width direction at a position serpentine toward the tire width direction inward of the zigzag shape. As shown in FIG. 6, the second through-middle lug grooves 42 have chamfered portions 42f where the openings 42c are wider than the groove bottoms 42d. The second through-middle lug grooves 42 have a groove width W5a of 3.0 mm to 10.0 mm at the openings 42c, a groove width W5b between the groove walls 42e extending from the chamfered portions 42f toward the groove bottoms 42d, and a groove depth D5 of 8.0 mm to 22.0 mm. When the second through-middle lug grooves 42 contact each other within a range of at least 20% of the groove depth D5, and the openings 42c are open at the tread surface 15A. The second through-middle lug groove 42 has a groove width W5a of 1.0 mm or more and 8.0 mm or less at an opening 42c when in contact with the ground. Also, as shown in Fig. 2, the second through-middle lug groove 42 has a tire width direction length L2 of 17.0 mm or more and 37.0 mm or less.

[0035] 2, the middle land portion 31A is configured as a middle block row partitioned into a plurality of middle blocks 31Aa by first through middle lug grooves 41 and second through middle lug grooves 42. The second through middle lug grooves 42 have cutouts 42b formed at ends 42a that communicate with the circumferential main groove 21 and the circumferential narrow groove 22. The cutouts 42b are formed at acute-angle corners of the middle blocks 31Aa.

[0036] 2, the center land zone 31B is provided with through-hole center lug grooves 43 and non-through-hole center lug grooves 44. The through-hole center lug grooves 43 may also be simply called "through-hole lug grooves." The non-through-hole center lug grooves 44 may also be simply called "non-through-hole lug grooves."

[0037] The center lug through grooves 43 extend in the tire width direction and are arranged in multiple locations in the tire circumferential direction, with both ends 43a communicating with adjacent circumferential narrow grooves 22 in the tire width direction. The center lug through grooves 43 thereby form a center block row that divides the center land portion 31B into multiple center blocks 31Ba. The center lug through grooves 43 are curved in a gentle S-shape in the direction in which they extend. The center lug through grooves 43 have cutouts 43b at their ends 43a that communicate with the circumferential narrow grooves 22. The cutouts 43b are formed at the acute-angled corners of the center blocks 31Ba. The center lug through grooves 43 are configured to include non-contact groove portions 431 and contact groove portions 432.

[0038] The non-contact groove portions 431 are portions that form each end of the center lug through-groove 43, and are provided with one end communicating with the circumferential narrow groove 22. The non-contact groove portions 431 are provided at an incline with respect to the tire width direction. The non-contact groove portions 431 that form each end of the center lug through-groove 43 are provided at an incline in the same direction with respect to the tire width direction. As shown in FIG. 7 , the non-contact groove portions 431 have chamfered portions 431f where the groove width of the openings 431c is wider than that of the groove bottoms 431d. The non-contact groove portions 431 have a groove width W6 on the groove bottom side that is 3.0 mm or more and 10.0 mm or less, and a groove depth D6 that is 5.0 mm or more and 25.0 mm or less.

[0039] The contact groove portion 432 is a portion forming the center of the through-center lug groove 43, and is provided in communication with each of the non-contact groove portions 431 so as to connect the other ends of the non-contact groove portions 431. The contact groove portion 432 is provided along the tire circumferential direction. The contact groove portion 432 has a groove width W7 of 1.5 mm or more and 4.5 mm or less, and a groove depth D7 of 5.0 mm or more and 25.0 mm or less. At least a portion of the groove walls 432e of the contact groove portions 432 come into contact with each other when the tire comes into contact with the ground. As shown in FIG. 12 , the contact groove portion 432 has a tire circumferential length GL of 13.0 mm or more and 45.0 mm or less. The contact groove portion 432 has a constant groove width W7 in the direction in which it extends, and each end has an inflection point where it widens to connect to the non-contact groove portion 431, and each end forming the tire circumferential length GL can be measured between the inflection points.

[0040] Such center through lug grooves 43 are provided in a tire circumferential position where one end of the center through lug groove 43 at one end faces in the tire width direction an inner end 41a of the first middle through lug groove 41 in one middle land portion 31A in the tire width direction. Also, the center through lug groove 43 is provided in a tire circumferential position where one end of the center through lug groove 43 at the other end faces in the tire width direction an inner end 42a of the second middle through lug groove 42 in the other middle land portion 31A in the tire width direction.

[0041] The non-through center lug grooves 44 are provided in the center blocks 31Ba partitioned by the through center lug grooves 43. The non-through center lug grooves 44 extend in the tire width direction, with one end 44a communicating with the circumferential narrow groove 22 and the other end 44a terminating inside the center block 31Ba. The non-through center lug grooves 44 are provided between the non-contact groove portions 431 of the through center lug grooves 43. That is, within one center block 31Ba, two non-through center lug grooves 44 are provided: one communicating with one circumferential narrow groove 22 in the tire width direction and the other communicating with the other circumferential narrow groove 22 in the tire width direction. The non-through center lug grooves 44 are provided at an incline with respect to the tire width direction. The non-through center lug grooves 44 are provided at an incline with respect to the tire width direction in the same direction as the non-contact groove portions 431 of the through center lug grooves 43. Each non-through center lug groove 44 has a notch 44b formed at an end 44a that communicates with the circumferential narrow groove 22. The notch 44b is formed at an acute-angled corner of the center block 31Ba. As shown in FIG. 9, each non-through center lug groove 44 has a chamfered portion 44f at its opening 44c, where the groove width is wider than the groove bottom 44d. Each non-through center lug groove 44 has a groove width W8a of the opening 44c that is 3.0 mm or greater and 10.0 mm or less, a groove width W8b between the chamfered portion 44f and the groove wall 44e extending from the chamfered portion 44f toward the groove bottom 44d that is 1.5 mm or greater and 9.0 mm or less, and a groove depth D8 of 5.0 mm or greater and 25.0 mm or less. When the non-through center lug grooves 44 are in contact with each other, the groove walls 44e are in contact with each other over a groove width W8b that is at least 20% of the groove depth D8, and the openings 44c are open on the tread surface 15A. When the non-through center lug grooves 44 are in contact with the ground, the groove width W8a of the openings 44c is 1.0 mm or more and 8.0 mm or less. Furthermore, as shown in FIG. 12, the non-through center lug grooves 44 have a groove length GW in the tire width direction that is 7.0 mm or more and 18.0 mm or less.

[0042] As shown in FIG. 10, the non-through center lug groove 44 may have a bulging portion 44g formed with a larger groove width at the groove bottom 44d.

[0043] A cutout portion 31Bb is provided in the center block 31Ba defined by such a through-center lug groove 43. The cutout portion 31Bb is provided at the opening 22a on the inner side in the tire width direction of the circumferential narrow groove 22 between the non-contact groove portion 431 of the through-center lug groove 43 and the cutout portion 44b of the non-through-center lug groove 44 (see FIG. 4).

[0044] As shown in FIG. 12, the center block 31Ba has a tire widthwise length BW, which is the distance between adjacent circumferential narrow grooves 22 in the tire width direction. The center block 31Ba has a tire circumferential length BL, which is the maximum length in the tire circumferential direction that is longer than the tire width direction. The center block 31Ba has a wrap portion adjacent in the tire width direction to another center block 31Ba adjacent in the tire circumferential direction across the center lug through groove 43, because the center lug through groove 43 is curved in an S shape overall. The wrap portion has a wrap length RL, which is the circumferential range of adjacent portions in the tire width direction.

[0045] As shown in FIGS. 2 and 3 , shoulder lug grooves 45 are provided in the shoulder portion 32. The shoulder lug grooves 45 are also referred to as through shoulder lug grooves. 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. The shoulder lug grooves 45 thus form a shoulder block row that divides the shoulder portion 32 into a plurality of shoulder blocks 32a. All of the shoulder lug grooves 45 provided in the shoulder portion 32 are formed to curve gently in the direction in which they extend, forming an arc. The shoulder lug grooves 45 are provided at an angle with respect to the tire width direction. Specifically, the angle θ3 of a line connecting the centers of the ends 45a of each shoulder lug groove 45 is between 0 and 30 degrees with respect to the tire width direction. All shoulder lug grooves 45 provided in one shoulder portion 32 are inclined in the same direction as the middle lug grooves 41, 42. The shoulder lug grooves 45 are arranged such that the ends 45a, 41a that communicate with the circumferential main groove 21 face each other in the tire width direction relative to the first through-middle lug groove 41. The shoulder lug grooves 45 are arranged such that the ends 45a, 42a that communicate with the circumferential main groove 21 are offset in the tire circumferential direction relative to the second through-middle lug groove 42. As shown in FIG. 11 , the shoulder lug grooves 45 have a groove width W9 of 3.0 mm or more and 14.0 mm or less. Furthermore, as shown in FIG. 2 , the shoulder lug grooves 45 have a tire width direction length L3 of 18.0 mm or more and 45.0 mm or less.

[0046] The shoulder lug grooves 45 have cutouts 45c formed at their ends 45a that communicate with the circumferential main grooves 21. The cutouts 45c are formed at the acute-angle corners of the rectangular shoulder blocks 32a. The cutouts 45c are chamfered so as to incline radially inwardly in the tire until they reach the platform portions 21d of the circumferential main grooves 21 that are outermost in the tire width direction.

[0047] 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. As shown in FIGS. 3 and 11 , the shoulder lug groove 45 has a groove depth D9 of 2.0 mm to 12.0 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.

[0048] The bottom upper portion 45b has an inclined surface 45bb that slopes radially inward from the apex 45ba toward the platform portion 21d of the circumferential main groove 21 on the inner side in the tire width direction. The angle θb 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.

[0049] 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 θc 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.

[0050] 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.

[0051] The pneumatic tire 1 of the above-described embodiment is characterized in that on the tread surface 15A, there are at least four circumferential grooves 20 extending in the tire circumferential direction, and in the center portion 31 partitioned between each circumferential groove 20 (circumferential main groove 21) on the outermost side in the tire width direction, there are at least two circumferential grooves 20 (circumferential narrow grooves 22) partitioned to form a center land portion 31B arranged at the center in the tire width direction, and in the center portion 31, there is a middle land portion 31A partitioned outside the center land portion 31B in the tire width direction, and a shoulder portion 32 partitioned outside the circumferential groove 20 on the outermost side in the tire width direction, and adjacent circumferential grooves 20 that partition the middle land portion 31A into a plurality of middle blocks 31Aa have respective ends 41a, 42a extending in the tire width direction communicating with each other, and a plurality of first through middle lug grooves 41 and second through middle lug grooves 42 arranged alternately in the tire circumferential direction, and a through shoulder lug groove (shoulder lug groove 45) having one end communicating with the circumferential groove 20 on the outermost side in the tire width direction and arranged in a plurality in the tire circumferential direction to partition the shoulder portion 32 into a plurality of shoulder blocks 32a, and one or more circumferential grooves 20 arranged inside the circumferential groove 20 on the outermost side in the tire width direction have groove walls 22c contacting each other at least on the groove bottom 22b side from the center of the groove depth D3 when in contact with the ground, and the first through middle lug groove 41 communicating with the circumferential groove 20 on the outermost side in the tire width direction has groove walls 41e not contacting each other when in contact with the ground, and the ends 41a, 45a communicating with the circumferential groove 20 with respect to the shoulder lug groove 45 are arranged opposite to each other in the tire width direction, and the second through middle lug groove 42 communicating with the circumferential groove 20 on the outermost side in the tire width direction has groove walls 42e contacting each other at least on the groove bottom 42d side from the center of the groove depth D8 when in contact with the ground, and the ends 42a, 45a communicating with the circumferential groove 20 with respect to the shoulder lug groove 45 are arranged offset from each other in the tire circumferential direction, and the groove width W4 and groove depth D4 of the first through middle lug groove 41, the groove width W5a of the opening of the second through middle lug groove 42 and groove depth D5, and the groove width W9 and groove depth D9 of the shoulder lug groove 45 satisfy the relationship of W4 < W5a < W9, D4 < D9 < D5 when not in contact with the ground.

[0052] In this pneumatic tire 1, the circumferential groove 20 (circumferential narrow groove 22) located on the tire widthwise inner side of the circumferential groove 20 (circumferential main groove 21) on the outermost side in the tire width direction and the second through-middle lug groove 42 located in the middle land portion 31A are configured as grooves that close when the tire is in contact with the ground, thereby improving the block rigidity of the center portion 31 on the inner side in the tire width direction and improving low rolling resistance. Meanwhile, in this pneumatic tire 1, the first through-middle lug groove 41 located in the middle land portion 31A and the shoulder lug grooves 45 located in the shoulder portions 32 are configured as grooves that do not close when the tire is in contact with the ground, thereby improving traction on snow due to snow column shear force. Moreover, in this pneumatic tire 1, the ends 41 a, 45 a of the first through-middle lug groove 41 located in the middle land portion 31A and the shoulder lug grooves 45 located in the shoulder portions 32 are positioned opposite each other in the tire width direction, thereby increasing the snow column shear effect and further improving traction on snow. Furthermore, with this pneumatic tire 1, the first through-middle lug grooves 41 have a relatively shallow groove depth W4, and the groove walls 42e of the second through-middle lug grooves 42 contact each other when the tire comes into contact with the ground, improving traction on snow without reducing block rigidity. As a result, this pneumatic tire 1 can achieve both low rolling resistance and traction on snow.

[0053] In addition, in the pneumatic tire 1 of the embodiment, the tire width direction length L1 of the first through middle lug groove 41, the tire width direction length L2 of the second through middle lug groove 42, and the tire width direction length L3 of the shoulder lug grooves 45 satisfy the relationships of 0.10≦L1 / LT≦0.20, 0.10≦L2 / LT≦0.20, and 0.12≦L3 / LT≦0.22 relative to the contact width LT of the tread surface 15A when not in contact with the ground.

[0054] With this pneumatic tire 1, by specifying the tire width direction length L1 of the first through-middle lug grooves 41, the tire width direction length L2 of the second through-middle lug grooves 42, and the tire width direction length L3 of the shoulder lug grooves 45 relative to the contact width LT of the tread surface 15A, the snow column shearing effect is increased and traction on snow is improved. Note that, to maximize the above effects, the pneumatic tire 1 preferably satisfies the following conditions: 0.12≦L1 / LT≦0.18, 0.12≦L2 / LT≦0.18, and 0.14≦L3 / LT≦0.20.

[0055] In the pneumatic tire 1 of the embodiment, the groove width W4 and groove depth D4 of the first through-middle lug groove 41 satisfy the relationship 1.50≦W4 / D4≦5.0.

[0056] According to this pneumatic tire 1, by providing grooves with open surfaces without reducing the block rigidity of the middle land portion 31A, traction on snow is improved without deteriorating low rolling resistance performance.

[0057] In addition, in the pneumatic tire 1 of the embodiment, in the second through middle lug groove 42, the groove width W5a of the opening 42c that opens when the tire is in contact with the ground, the groove width W5b of the portion where the groove walls 42e contact each other when the tire is not in contact with the ground, and the groove depth D5 satisfy the relationships 0.10≦W5b / W5a≦0.50 and 0.05≦W5b / D5≦0.30 when the tire is not in contact with the ground.

[0058] According to this pneumatic tire 1, the groove walls 42e of the second through-middle lug grooves 42 do not come into contact with each other when the tire is in contact with the ground, thereby preventing a reduction in the block rigidity of the middle land portion 31A, and the openings 42c of the second through-middle lug grooves 42 open when the tire is in contact with the ground, thereby improving traction on snow without deteriorating low rolling resistance performance.

[0059] In the pneumatic tire 1 of the embodiment, the angle θ1 of the first through-middle lug groove 41 relative to the tire width direction, the angle θ2 of the second through-middle lug groove 42 relative to the tire width direction, and the angle θ3 of the shoulder lug grooves 45 relative to the tire width direction satisfy the relationships 0 [deg]≦θ1≦30 [deg], 0 [deg]≦θ2≦30 [deg], and 0 [deg]≦θ3≦30 [deg]. Note that the angles θ1, θ2, and θ3 are measured when the tread surface 15A is viewed in a plan view from the tire radial direction, with the tire width direction being 0 [deg].

[0060] According to this pneumatic tire 1, by specifying the angle θ1 of the first through-middle lug groove 41 relative to the tire width direction, the angle θ2 of the second through-middle lug groove 42 relative to the tire width direction, and the angle θ3 of the shoulder lug groove 45 relative to the tire width direction, the snow column shearing effect is increased, thereby improving traction on snow.

[0061] In addition, the pneumatic tire 1 of the embodiment has multiple through-hole center lug grooves 43 lined up circumferentially of the tire, one end of which communicates with the circumferential grooves 20 (circumferential narrow grooves 22) to divide the center land portion 31B into multiple center blocks 31Ba, and the through-hole center lug grooves 43 include a pair of non-contact groove portions 431, one end of which communicates with each of the circumferential narrow grooves 22 that divide the center blocks 31Ba, and whose groove walls 431e do not contact each other when the tire is in contact with the ground, and a contact groove portion 432, which connects the other ends of each non-contact groove portion 431 and is arranged along the tire circumferential direction, and whose groove walls 432e at least partially contact each other when the tire is in contact with the ground.

[0062] In this pneumatic tire 1, the center lug through grooves 43 that divide the center land portion 31B into multiple center blocks 31Ba include contact groove portions 432 that close when the tire is in contact with the ground, thereby ensuring block rigidity and preventing deterioration of low rolling resistance. Moreover, in this pneumatic tire 1, the center lug through grooves 43 that divide the center land portion 31B into multiple center blocks 31Ba include non-contact groove portions 431 that do not close when the tire is in contact with the ground, thereby improving traction on snow.

[0063] In the pneumatic tire 1 of this embodiment, the center block 31Ba has a wrap portion that is adjacent to another center block 31Ba in the tire width direction across the through-center lug groove 43, and the tire circumferential length BL of the center block 31Ba, the tire circumferential wrap length RL of the wrap portion, and the tire circumferential groove length GL of the contact groove portion 432 satisfy the relationships 0.20≦RL / BL≦0.45 and 0.35≦GL / RL≦0.65. Note that the tire circumferential length BL, wrap length RL, and groove length GL are measured 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.

[0064] In this pneumatic tire 1, by defining the wrap length RL of the wrap portion relative to the tire circumferential length BL of the center block 31Ba, it is possible to define large blocks in the tire circumferential direction as a whole, ensuring the rigidity of the land portion and contributing to improving low rolling resistance. Furthermore, by defining the groove length GL of the contact groove portion 432, where the groove walls 432e contact each other when the tire is in contact with the ground, relative to the wrap length RL of the wrap portion, the rigidity of the land portion in the wrap portion is ensured while the non-contact groove portion 431 partially ensures snow column shearing effect. Note that, in this pneumatic tire 1, it is preferable that the ratios 0.25≦RL / BL≦0.40 and 0.40≦GL / RL≦0.60 be satisfied to maximize the above effects.

[0065] In addition, in the pneumatic tire 1 of the embodiment, the meridian cross-sectional shape of the circumferential groove 20 (circumferential main groove 21) on the outermost side in the tire width direction has 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 a terrace 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. One end 45a of each shoulder lug groove 45 is connected to the circumferential main groove 21 and has an upper bottom portion 45b formed at the groove bottom. The upper bottom portions 45b of the shoulder lug grooves 45 and the terrace portions 21d of the circumferential main groove 21 are smoothly connected by a circular arc 45bd.

[0066] In this pneumatic tire 1, by forming the groove shape of the outermost circumferential main groove 21 in the tire width direction into a step groove, the narrow second groove wall 21e on the groove bottom 21b side of the step portion 21d tends to close when the tire comes into contact with the ground. Moreover, in this pneumatic tire 1, by smoothly connecting the bottom upper portion 45b to the step portion 21d, it is possible to eliminate a step space that may occur at the connection between the outermost circumferential main groove 21 in the tire width direction and the shoulder lug groove 45. Therefore, this pneumatic tire 1 has a shape that prevents stones that may enter the connection between the circumferential main groove 21 and the shoulder lug groove 45 from reaching the groove bottom 21b of the circumferential main groove 21, thereby improving stone trapping resistance. To maximize this effect, it is preferable that the groove width W2 between the second groove walls 21e be 3.0 mm or more and 4.5 mm or less, and the radius of the arc 45bd be 2.0 mm or more and 15.0 mm or less. Moreover, by providing the bottom upper portion 45b, the pneumatic tire 1 is less likely to lose sound to the outside in the tire width direction, which is advantageous for improving pass-by noise resistance.

[0067] In addition, 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 platform portion 21d, and the groove depth D3 to the bottom upper portion 45b of the shoulder lug groove 45 satisfy the relationships 0.50≦D2 / D1≦0.90 and 0.10≦D3 / D1≦0.40.

[0068] According to this pneumatic tire 1, by setting the groove depth D2 of the platform portion 21d within an appropriate range, it is possible to prevent trapped stones from reaching the groove bottom 21b of the circumferential main groove 21 and make them easier to remove. Also, by setting the groove depth D3 to the bottom upper portion 45b within an appropriate range, it is possible to advantageously suppress sound from escaping to the outside in the tire width direction. To further enhance these effects, it is preferable that this pneumatic tire 1 satisfy the relationships 0.60≦D2 / D1≦0.70 and 0.25≦D3 / D1≦0.35.

[0069] In the pneumatic tire 1 of the embodiment, the pair of first groove walls 21c of the circumferential main groove 21 on the outermost sides in the tire width direction are formed so as to widen toward the tread surface 15A.

[0070] 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 improvement of pass-by noise resistance.

[0071] 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.

[0072] In this pneumatic tire 1, by setting the tire width direction dimension WS2 of the bottom upper portion 45b within an appropriate range, stone trapping resistance in 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 improving pass-by noise resistance. To further maximize these effects, it is preferable that this pneumatic tire 1 satisfy the relationship 0.60≦WS2 / WS1≦0.80.

[0073] 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.

[0074] 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, setting the angles θ2 and θ3 within the specified ranges does not affect the improvement in pass-by noise resistance. To further enhance these effects, the pneumatic tire 1 preferably has the angle θ2 set to 40 degrees or more and the angle θ3 set to 15 degrees or more and 25 degrees or less.

[0075] 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.

[0076] 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 uniform in the shoulder portion 32 and maintains the improved effect of pass-by noise resistance. Moreover, in this pneumatic tire 1, the shoulder lug grooves 45 extend in an arc, allowing trapped stones to be smoothly removed.

[0077] 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.

[0078] 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.

[0079] 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]

[0080] 13 to 15 are tables showing the results of performance tests of the 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 acceleration performance on snow (traction performance on snow).

[0081] The rolling resistance performance evaluation test involves mounting a 205 / 75R17.5 size pneumatic tire (test tire) on a specified rim and applying the specified air pressure. Under test conditions compliant with UN R117-04 (UN Regulation No. 117 Revision 4), the average forward and reverse rolling resistance coefficient (the ratio of rolling resistance to the load on the test tire) is measured at a speed of 80 km / h and a specified load of 85%. Based on these measurement results, an index rating is then given, with the conventional example being assigned a standard value of 100. The higher the rating, the better.

[0082] The snow acceleration performance evaluation test involves mounting a pneumatic tire (test tire) of the above size on a specified rim, applying a specified air pressure, and mounting it on a heavy-duty vehicle. Under test conditions conforming to UN R117-04 (UN Regulation No. 117 Revision 4), the distance required for acceleration from a specified initial velocity to a terminal velocity on a snowy road surface is measured, and the acceleration is calculated. Based on the calculation results, an index rating is then given, with the conventional example being assigned a standard value of 100. The higher the rating, the better.

[0083] The conventional pneumatic tire is based on the tread pattern shown in FIG. 2, but is outside the range of the specifications (1) to (21) shown in FIGS.

[0084] The pneumatic tire of the example is based on the tread pattern shown in FIG. 2 and is within the specified ranges for the specified contents (1) to (21) shown in FIGS.

[0085] As shown in the test results, the pneumatic tire of this embodiment has improved rolling resistance performance and traction performance on snow compared to the conventional tire.

[0086] The present disclosure includes the following inventions. [Invention 1] On the tread surface At least four circumferential grooves extending in the tire circumferential direction; In a center portion defined between the circumferential grooves at the outermost positions in the tire width direction, a center land portion is defined by at least two of the circumferential grooves and is arranged in the center in the tire width direction; a middle land portion defined in the center portion on the outer side of the center land portion in the tire width direction; a shoulder portion defined on the outer side in the tire width direction of the outermost circumferential groove in the tire width direction; The first through middle lug grooves and the second through middle lug grooves, each having ends extending in the tire width direction and communicating with adjacent circumferential grooves so as to partition the middle land portion into a plurality of middle blocks, are arranged alternately in the tire circumferential direction. The through shoulder lug grooves, each having one end communicating with the circumferential groove at the outermost side in the tire width direction so as to partition the shoulder portion into a plurality of shoulder blocks, are arranged in a plurality in the tire circumferential direction. and have One or more of the circumferential grooves arranged on the inner side in the tire width direction of the circumferential groove at the outermost side in the tire width direction are such that the groove walls contact each other at least on the groove bottom side from the center of the groove depth when the tire is in contact with the ground. The first through middle lug grooves communicating with the circumferential groove at the outermost side in the tire width direction are such that the groove walls do not contact each other when the tire is in contact with the ground, and the ends communicating with the circumferential groove are arranged opposite to each other in the tire width direction with respect to the through shoulder lug grooves. The second through middle lug grooves communicating with the circumferential groove at the outermost side in the tire width direction are such that the groove walls contact each other at least on the groove bottom side from the center of the groove depth when the tire is in contact with the ground, and the ends communicating with the circumferential groove are arranged offset from each other in the tire circumferential direction with respect to the through shoulder lug grooves. The groove width W4 and groove depth D4 of the first through middle lug grooves, the groove width W5a and groove depth D5 of the opening of the second through middle lug grooves, and the groove width W9 and groove depth D9 of the through shoulder lug grooves satisfy the relationship of W4 < W5a < W9 and D4 < D9 < D5 when the tire is in contact with the ground. Tire. [Invention 2] The tire width direction lengths L1 of the first through middle lug grooves, L2 of the second through middle lug grooves, and L3 of the through shoulder lug grooves satisfy the relationships of 0.10 ≤ L1 / LT ≤ 0.20, 0.10 ≤ L2 / LT ≤ 0.20, and 0.12 ≤ L3 / LT ≤ 0.22 with respect to the contact width LT of the tread surface when the tire is in contact with the ground. The tire according to Invention 1. [Invention 3] The groove width W4 and groove depth D4 of the first through middle lug grooves satisfy the relationship of 1.50 ≤ W4 / D4 ≤ 5.0. The tire according to Invention 1 or 2. [Invention 4] In the second through middle lug groove, a groove width W5a of an opening that opens when the tire is in contact with the ground, a groove width W5b of a portion where the groove walls contact each other when the tire is in contact with the ground, and a groove depth D5 satisfy the relationships of 0.10≦W5b / W5a≦0.50 and 0.05≦W5b / D5≦0.30 when the tire is not in contact with the ground. A tire according to any one of inventions 1 to 3. [Invention 5] an angle θ1 of the first through-middle lug groove relative to the tire width direction, an angle θ2 of the second through-middle lug groove relative to the tire width direction, and an angle θ3 of the through-shoulder lug groove relative to the tire width direction satisfy the relationships 0 [deg]≦θ1≦30 [deg], 0 [deg]≦θ2≦30 [deg], and 0 [deg]≦θ3≦30 [deg]; A tire according to any one of inventions 1 to 4. [Invention 6] a plurality of through-hole center lug grooves arranged in the tire circumferential direction, each of which communicates with the circumferential groove at one end so as to divide the center land portion into a plurality of center blocks; The through-center lug grooves include a pair of non-contact groove portions, one end of which is connected to each of the circumferential grooves that define the center block, and whose groove walls do not contact each other when the tire is in contact with the ground, and a contact groove portion, which is connected to the other end of each of the non-contact groove portions and is provided along the tire circumferential direction, and whose groove walls at least partially contact each other when the tire is in contact with the ground. A tire according to any one of inventions 1 to 5. [Invention 7] a plurality of through-hole center lug grooves arranged in the tire circumferential direction, each of which communicates with the circumferential groove at one end so as to divide the center land portion into a plurality of center blocks; The through-center lug grooves include a pair of non-contact groove portions, one end of which is connected to each of the circumferential grooves that define the center block, and whose groove walls do not contact each other when the tire is in contact with the ground, and a contact groove portion, which is connected to the other end of each of the non-contact groove portions and is provided along the tire circumferential direction, and whose groove walls at least partially contact each other when the tire is in contact with the ground, The center block has a wrap portion adjacent to another center block in the tire width direction across the through-center lug groove, a tire circumferential length BL of the center block, a tire circumferential length RL of the wrap portion, and a tire circumferential length GL of the contact groove portion satisfy the relationships of 0.20≦RL / BL≦0.45 and 0.35≦GL / RL≦0.65, A tire according to any one of inventions 1 to 6. [Invention 8] The circumferential groove at the outermost side in the tire width direction is A pair of first groove walls whose meridian cross section shape extends from the tread surface to a groove bottom side; 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 a bottom upper portion formed at the groove bottom of the through-shoulder lug groove and the platform portion of the circumferential groove at the outermost side in the tire width direction are smoothly connected by a circular arc; A tire according to any one of inventions 1 to 7. [Explanation of symbols]

[0087] 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 22b Groove bottom 22c groove wall 31 Center Section 31A Middle Land Section 31Aa Middle Block 31B Center Land 31Ba Center Block 32 Shoulder section 32a Shoulder Block 41 First through middle lug groove 41a end 41e Groove wall 42 Second through middle lug groove 42a end 42c opening 42d groove bottom 42e groove wall 43 through center lug groove 43a edge 431 Non-contact groove 431e Groove wall 432 Contact groove 432e groove wall 45 Shoulder lug groove 45a end 45b Bottom top 45bd arc

Claims

1. On the tread surface At least four circumferential grooves extending in the tire circumferential direction; In a center portion defined between the circumferential grooves at the outermost positions in the tire width direction, a center land portion is defined by at least two of the circumferential grooves and is arranged in the center in the tire width direction; a middle land portion defined in the center portion on the outer side of the center land portion in the tire width direction; a shoulder portion defined on the outer side in the tire width direction of the outermost circumferential groove in the tire width direction; a plurality of first through middle lug grooves and second through middle lug grooves arranged alternately in the tire circumferential direction, each end of which extends in the tire width direction and is connected to the adjacent circumferential groove so as to divide the middle land portion into a plurality of middle blocks; a plurality of through-hole shoulder lug grooves arranged in the tire circumferential direction, one end of which communicates with the outermost circumferential groove in the tire width direction so as to divide the shoulder portion into a plurality of shoulder blocks; and In the one or more circumferential grooves arranged on the inner side in the tire width direction of the outermost circumferential groove in the tire width direction, groove walls contact each other at least on the groove bottom side from the center of the groove depth when the tire comes into contact with the ground, the first through-middle lug grooves communicating with the circumferential grooves on the outermost sides in the tire width direction are arranged such that groove walls do not contact each other when the tire is in contact with the ground, and ends communicating with the circumferential grooves face each other in the tire width direction relative to the through-middle lug grooves, the second through-middle lug grooves communicating with the circumferential grooves on the outermost sides in the tire width direction have groove walls that contact each other at least on the groove bottom side from the center of the groove depth when the tire is in contact with the ground, and ends communicating with the circumferential grooves are arranged offset in the tire circumferential direction with respect to the through-middle lug grooves, a groove width W4 and a groove depth D4 of the first through-middle lug groove, a groove width W5a and a groove depth D5 of an opening of the second through-middle lug groove, and a groove width W9 and a groove depth D9 of the through-shoulder lug groove satisfy the relationships W4<W5a<W9 and D4<D9<D5 when the tire is in contact with the ground; tire.

2. a tire width direction length L1 of the first through-middle lug groove, a tire width direction length L2 of the second through-middle lug groove, and a tire width direction length L3 of the through-shoulder lug groove, relative to a contact width LT of the tread surface when in contact with the ground, satisfy the relationships of 0.10≦L1 / LT≦0.20, 0.10≦L2 / LT≦0.20, and 0.12≦L3 / LT≦0.22, 2. The tire of claim 1.

3. a groove width W4 and a groove depth D4 of the first through-middle lug groove satisfy the relationship 1.50≦W4 / D4≦5.0; 2. The tire of claim 1.

4. In the second through-middle lug groove, a groove width W5a of an opening that opens when the tire is in contact with the ground, a groove width W5b of a portion where the groove walls contact each other when the tire is in contact with the ground, and a groove depth D5 satisfy the relationships of 0.10≦W5b / W5a≦0.50 and 0.05≦W5b / D5≦0.30 when the tire is not in contact with the ground.

2. The tire of claim 1.

5. an angle θ1 of the first middle lug groove with respect to the tire width direction, an angle θ2 of the second middle lug groove with respect to the tire width direction, and an angle θ3 of the shoulder lug groove with respect to the tire width direction satisfy the relationships 0 [deg]≦θ1≦30 [deg], 0 [deg]≦θ2≦30 [deg], and 0 [deg]≦θ3≦30 [deg]; 2. The tire of claim 1.

6. a plurality of through-hole center lug grooves arranged in the tire circumferential direction, each of which communicates with the circumferential groove at one end so as to divide the center land portion into a plurality of center blocks; The through-center lug grooves include a pair of non-contact groove portions, one end of which is connected to each of the circumferential grooves that define the center block, and whose groove walls do not contact each other when the tire is in contact with the ground, and a contact groove portion, which is connected to the other end of each of the non-contact groove portions and is provided along the tire circumferential direction, and whose groove walls at least partially contact each other when the tire is in contact with the ground.

2. The tire of claim 1.

7. a plurality of through-hole center lug grooves arranged in the tire circumferential direction, each of which communicates with the circumferential groove at one end so as to divide the center land portion into a plurality of center blocks; The through-center lug grooves include a pair of non-contact groove portions, one end of which is connected to each of the circumferential grooves that define the center block, and whose groove walls do not contact each other when the tire is in contact with the ground, and a contact groove portion, which is connected to the other end of each of the non-contact groove portions and is provided along the tire circumferential direction, and whose groove walls at least partially contact each other when the tire is in contact with the ground, The center block has a wrap portion adjacent to another center block in the tire width direction across the through-center lug groove, a tire circumferential direction length BL of the center block, a tire circumferential direction wrap length RL of the wrap portion, and a tire circumferential direction groove length GL of the contact groove portion satisfy the relationships 0.20≦RL / BL≦0.45 and 0.35≦GL / RL≦0.65, 2. The tire of claim 1.

8. The circumferential groove at the outermost side in the tire width direction is a pair of first groove walls whose meridian cross-sectional shape extends from the tread surface toward the 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 a bottom upper portion formed at the groove bottom of the through-shoulder lug groove and the platform portion of the circumferential groove at the outermost side in the tire width direction are smoothly connected by a circular arc; 2. The tire of claim 1.

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