Tire

Abstract

To improve wet traction performance while reducing passing noise.SOLUTION: Provided is a tire having: a pair of circumferential main grooves 21; a center land part 31 located on an inner side in a tire width direction of the circumferential main grooves; shoulder land parts 32 located on an outer side in the tire width direction of the circumferential main grooves; at least circumferential narrow groove 22, 23, extending in the tire circumferential direction in the center land part; a plurality of shoulder lug grooves 44 formed in the tire circumferential direction with one end communicating with the circumferential main groove and with the other end being open in a ground contact end T in the shoulder land parts; and shoulder sipings 45 each provided between the shoulder lug grooves in the shoulder land parts and formed with one end communicating with the circumferential main groove and with the other being end open in the ground contact end. Each circumferential main groove is formed of: a portion, as a single first arc 21a, which has a groove wall shape being open in a tread surface 15A, and which is on the shoulder land part side, interposed between the shoulder lug grooves and communicates with the shoulder siping; and portions, as a plurality of second arcs 21b, which are on the center land part side and face the first arc.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a tire.

Background Art

[0002] For example, Patent Document 1 describes a tire that achieves both low rolling resistance performance and wet traction performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, for example, in the case of truck tires, in order to reduce rolling resistance, a pattern with a narrow main groove width in the center part is increasingly adopted for the purpose of increasing block rigidity. However, such a tire suffers from deterioration of wet traction performance due to a decrease in groove area and an increase in passing noise due to an increase in block rigidity.

[0005] An object of this invention is to provide a tire capable of improving wet traction performance while reducing passing noise.

Means for Solving the Problems

[0006] To achieve the above object, a tire according to one aspect of the present invention includes a pair of circumferential main grooves extending in the tire circumferential direction, a single center land portion partitioned inside the tire width direction of each of the circumferential main grooves, a pair of shoulder land portions partitioned outside the tire width direction of each of the circumferential main grooves, at least one circumferential fine groove extending in the tire circumferential direction at the center land portion, a plurality of shoulder lug grooves formed at the shoulder land portion with one end communicating with the circumferential main groove and the other end opening to the ground end in the tire circumferential direction, and a shoulder sipe provided between the shoulder lug grooves at the shoulder land portion with one end communicating with the circumferential main groove and the other end opening to the ground end. The circumferential main groove is formed such that, in the shape of the groove wall opening to the tread surface, the portion sandwiched between the shoulder lug grooves on the shoulder land portion side and communicating with the shoulder sipe is formed as a single first arc, and the portion facing the first arc on the center land portion side is formed as a plurality of second arcs.

Advantages of the Invention

[0007] According to this invention, wet traction performance can be improved while reducing passing noise.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by these embodiments. Also, the components of this embodiment include those that are replaceable and self-evidently replaceable while maintaining the identity of the invention. Further, a plurality of modification examples described in this embodiment can be arbitrarily combined within the scope self-evident to those skilled in the art.

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

[0011] In FIG. 1, a meridian cross-section of the pneumatic tire 1 of the embodiment is shown, which is a cross-section of one side region of the tire rotation axis in the tire radial direction. In the present embodiment, as an example, a pneumatic radial tire for heavy loads mounted on a heavy-duty vehicle such as a truck or a bus will be described. The pneumatic tire 1 of the present embodiment is particularly suitable for all-season tires.

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

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

[0014] The pair of bead fillers 12, 12 each consists of a lower filler 121 and an upper filler 122, and is disposed on the outer periphery in the tire radial direction of the pair of bead cores 11, 11 to reinforce the bead portion.

[0015] The carcass layer 13 has a single-layer structure composed of one carcass ply or a multi-layer structure formed by laminating a plurality of carcass plies. The carcass layer 13 is bridged in a toroidal shape between both bead cores 11, 11 to form the skeleton of the tire. Further, both ends of the carcass layer 13 are wound back and locked outward in the tire width direction so as to wrap the bead core 11 and the bead filler 12. Further, the carcass layer 13 is configured such that the carcass ply is formed by covering a plurality of carcass cords made of steel with coating rubber and performing rolling processing, and has a cord angle (defined as the inclination angle of the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of 80° or more and 90° or less in absolute value for a radial tire, and 30° or more and 45° or less for a bias tire.

[0016] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is wound 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 coating a plurality of belt cords made of steel with a coating rubber and performing rolling processing, and has a cord angle (defined as the inclination angle of the longitudinal direction of the belt cord with respect to the tire circumferential direction) of 45° or more and 70° or less in absolute value. The pair of cross belts 142 and 143 are formed by coating a plurality of belt cords made of steel with a coating rubber and performing rolling processing, and have a cord angle of 10° or more and 55° or less in absolute value. Further, the pair of cross belts 142 and 143 have cord angles of opposite signs to each other, and are laminated with the longitudinal directions of the belt cords crossing each other (having a so-called cross-ply structure). The belt cover 144 is formed by coating a plurality of belt cover cords made of steel or an organic fiber material with a coating rubber and performing rolling processing, and has a cord angle of 10° or more and 55° 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 constitute the tread portion of the pneumatic tire 1. The tread rubber 15 has a tread surface (tread tread surface) 15A on the outer peripheral surface that comes into contact with the road surface during running. The outer end of the tread surface 15A in the tire width direction is the grounding end T. Further, the tread rubber 15 has a buttress portion 15B that does not come into contact with the road surface during running on both outer side portions in the tire width direction with respect to the grounding end T of the tread surface 15A. The buttress portion 15B is provided in the tread rubber 15 from the grounding end T outward in the tire width direction and inward in the tire radial direction up to the sidewall rubber 16. In the pneumatic tire 1 of the embodiment, the buttress portion 15B is provided in the range from the grounding end T to the buttress end (index) B that is continuous in the tire circumferential direction outward in the tire width direction and inward in the tire radial direction as shown in FIG. 1.

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

[0019] A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the winding-back portions of the respective bead cores 11, 11 and the carcass layer 13 to form the rim fitting surfaces of the bead portions.

[0020] The pneumatic tire 1 of the embodiment has the above-described form as a basic configuration, and a tread pattern is provided on the tread surface 15A of the tread portion. Hereinafter, the details of the tread pattern will be described.

[0021] As shown in FIG. 2, the pneumatic tire 1 of the embodiment includes a pair (two) of circumferential main grooves 21 provided with the tire equatorial plane CL as a boundary on the tread surface 15A, and three rows of land portions 31, 32, 32 partitioned by the circumferential main grooves 21.

[0022] The circumferential main groove 21 extends along the tire circumferential direction and has an annular structure that continuously extends linearly over the entire tire circumference. The circumferential main groove 21 is defined as a groove having the obligation to display a wear indicator defined by JATMA. The circumferential main groove 21 has a groove width of 5 [mm] or more and 15 [mm] or less, and a groove depth D1 (see FIG. 3) of 9 [mm] or more and 23 [mm] or less.

[0023] The groove width is measured as the maximum value of the distance between the opposing groove walls or edges at the opening edge portion on the tread surface in a non-loaded state where the tire is mounted on a specified rim and filled with a specified internal pressure.

[0024] The groove depth is measured as the maximum value of the distance from the tread surface to the groove bottom in a non-loaded state where the tire is mounted on a specified rim and filled with a specified internal pressure. Also, in a configuration having partial uneven portions or sipes at the groove bottom, the groove depth is measured excluding these.

[0025] The specified rim refers to the "Standard Rim" specified by JATMA, the "Design Rim" specified by TRA, or the "MEASURING RIM" specified by ETRTO. Also, the specified internal pressure refers to the "Maximum Air Pressure" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "INFLATION PRESSURES" specified by ETRTO. Note that the state in which the tire is mounted on the specified rim and filled with the specified internal pressure is called the inflated state.

[0026] In the embodiment, the land portions 31, 32, 32 of the tread are composed of a single row of center land portion 31 and a pair (two rows) of shoulder land portions 32, 32. These land portions 31, 32, 32 extend over the entire circumference of the tire to form an annular tread surface. The shoulder land portions 32, 32 are land portions partitioned on the outer side in the tire width direction of the circumferential main grooves 21, 21, respectively. The shoulder land portions 32, 32 are arranged in regions on both outer sides in the tire width direction with the tire equatorial plane CL as a boundary. The shoulder land portions 32, 32 have a grounding end T at the outer end in the tire width direction of their tread surface 15A, and have a buttress portion 15B on the outer side in the tire width direction than the grounding end T. The center land portion 31 is a land portion between the pair of shoulder land portions 32, 32. The center land portion 31 is partitioned on the tire equatorial plane CL between the two circumferential main grooves 21, 21.

[0027] The grounding end T is defined as the maximum width position in the tire axial direction at the contact surface between the tire and the flat plate when a load corresponding to the specified load is applied perpendicularly to the flat plate in a stationary state in the inflated state. The specified load refers to the "Maximum Load Capacity" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO. In the case of the pneumatic tire 1 of the embodiment, the specified load is 88 [%] of the maximum load capacity at the specified internal pressure.

[0028] The pneumatic tire 1 of the embodiment is configured such that one side and the other side on the outer side in the tire width direction are symmetric with respect to the tire equatorial plane CL as a boundary.

[0029] As shown in FIG. 2, the shoulder land portion 32 is provided with a shoulder lug groove 44 and a shoulder sip 45.

[0030] The shoulder lug grooves 44 extend in the tire width direction and are arranged in a plurality in the tire circumferential direction. One end of the shoulder lug groove 44 communicates with the circumferential main groove 21, and the other end opens at the ground contact end T. The shoulder lug groove 44 is formed in an arc shape that curves in the tire circumferential direction from one end to the other end. The shoulder land portion 32 is divided into shoulder blocks 32a divided in the tire circumferential direction by a plurality of shoulder lug grooves 44. The shoulder lug groove 44 is formed such that, under the same measurement conditions as the circumferential main groove 21, as shown in FIG. 4, the groove width W1 is 4 [mm] or more and 13 [mm] or less, and the groove depth d1 is 2 [mm] or more and 6 [mm] or less.

[0031] The shoulder lug groove 44 has a widened portion 44a at the other end thereof, where the groove width gradually widens toward the ground contact end T. The widened portion 44a is formed to be enlarged by 1.5 times or more with respect to the narrowest groove width W1 of the shoulder lug groove 44. The widened portion 44a is formed to extend in an arc shape from both opening edges of the narrowest groove width W1 of the shoulder lug groove 44.

[0032]

[0033] The shoulder lug groove 44 may extend from the ground contact end T to the outer side in the tire width direction and into the buttress portion 15B. In this case, the shoulder lug groove 44 extends into the buttress portion 15B with the groove width remaining widened in the widened portion 44a.The shoulder sip 45 extends in the tire width direction and is provided in the shoulder block 32a sandwiched between the shoulder lug grooves 44. One end of the shoulder sip 45 communicates with the circumferential main groove 21, and the other end opens at the grounding end T. The shoulder sip 45 is formed in an arc shape that curves in the tire circumferential direction in the same manner as the shoulder lug groove 44 from one end to the other end. The shoulder sip 45 is formed such that the groove width W2 is 0.6 [mm] or more and 1 [mm] or less, and the groove depth d2 is 2 [mm] or more and 6 [mm] or less under the same measurement conditions as the circumferential main groove 21, as shown in FIG. 5. Hereinafter, a groove having a groove width of 1 [mm] or less is defined as a sip.

[0034] The shoulder sip 45 may be formed to extend from the grounding end T outward in the tire width direction and to the buttress portion 15B.

[0035] The circumferential main groove 21 with which one ends of the shoulder lug groove 44 and the shoulder sip 45 communicate has a groove wall shape that opens to the tread surface 15A and is formed in an arc shape. In the circumferential main groove 21, the groove wall of the portion where the shoulder sip 45 communicates in the shoulder block 32a sandwiched between the shoulder lug grooves 44 on the shoulder land portion 32 side is formed as a single first arc 21a. In the circumferential main groove 21, the groove wall of the portion facing the first arc 21a on the center land portion 31 side is formed as a plurality of second arcs 21b arranged in the tire circumferential direction. In the pneumatic tire 1 of the embodiment, three second arcs 21b are arranged in the tire circumferential direction at the portion facing the first arc 21a. The first arc 21a and each second arc 21b are formed as arcs convex toward the tire equatorial plane CL side. Although not shown in the figure, the first arc 21a and each second arc 21b may be formed as arcs concave toward the tire equatorial plane CL side.

[0036] In addition, as shown in FIGS. 2 and 3, in the circumferential main groove 21, the range from the groove bottom 21d to the line DL at 50% or less of the groove depth D1 is formed in a straight shape along the tire circumferential direction. That is, in the circumferential main groove 21, on the groove wall from the line DL toward the opening edge, it is formed as the above-described first arc 21a and second arc 21b, and from the line DL to the groove bottom 21d, it is formed in a straight shape having no first arc 21a and second arc 21b.

[0037] As shown in FIG. 2, the center land portion 31 is provided with circumferential fine grooves 22, 23, 23 and a width-direction sipe 42.

[0038] As shown in FIG. 2, the circumferential fine grooves 22, 23, 23 extend along the tire circumferential direction and have an annular structure that continuously extends over the entire tire circumference. At least one circumferential fine groove 22, 23, 23 may be provided, but in the pneumatic tire 1 of the embodiment, it is composed of a center circumferential fine groove 22 provided along the tire equatorial plane CL and a total of three middle circumferential fine grooves 23, 23 provided one by one on both outer sides in the tire width direction of the center circumferential fine groove 22.

[0039] Due to these circumferential fine grooves 22, 23, 23, as shown in FIG. 2, a center central land portion 311 is formed between the center circumferential fine groove 22 and each middle circumferential fine groove 23 in the center land portion 31. The center central land portion 311 extends over the entire tire circumference along the tire circumferential direction to form an annular tread surface. Also, as shown in FIG. 2, a center intermediate land portion 312 is formed between the middle circumferential fine groove 23 and the circumferential main groove 21 in the center land portion 31. The center intermediate land portion 312 extends over the entire tire circumference along the tire circumferential direction to form an annular tread surface.

[0040] As shown in FIGS. 6 to 10, the center circumferential direction groove 22 is configured such that from the groove bottom 22a to midway of opening to the tread surface 15A is mainly formed as a groove 22b, and a notch 22c is formed at the opening edge portion that opens to the tread surface 15A. As shown in FIG. 2, the groove 22b is formed in a zigzag shape so as to meander in the tire width direction along the tire circumferential direction. The groove 22b is formed continuously in the tire circumferential direction with a constant groove width W3a. The notch 22c is formed in a tapered shape so as to expand in the tire radial direction from the groove 22b toward the tread surface 15A. The notch 22c is provided only on one side in the tire width direction of the groove 22b in accordance with the zigzag shape of the groove 22b at each cross-sectional position in the tire circumferential direction of the center circumferential direction groove 22, as shown in FIGS. 6, 8, and 9, and includes a form provided on both sides in the tire width direction of the groove 22b, as shown in FIGS. 7 and 10. As shown in FIG. 2, the notch 22c is alternately provided on one side and the other side in the tire width direction of the groove 22b in accordance with the zigzag shape of the groove 22b along the tire circumferential direction. For this reason, in the center circumferential direction groove 22, depending on the form of the notch 22c, the groove width W3 including the notch 22c varies in the tire circumferential direction. As shown in FIG. 2, in the center circumferential direction groove 22, the groove width W3 including the notch 22c forms a wide portion 22w (see FIG. 10) at the bent portion of the groove 22b and a narrow portion 22s (see FIG. 7) at the non-bent portion of the groove 22b in accordance with the zigzag shape of the groove 22b along the tire circumferential direction. Under the same measurement conditions as the circumferential main groove 21, as shown in FIGS. 6 to 10, the center circumferential direction groove 22 is formed such that the groove width W3 including the notch 22c is 1 [mm] or more and 8 [mm] or less, the groove width W3a of the groove 22b excluding the notch 22c is 0.5 [mm] or more and 3 [mm] or less, and the groove depth d3 is 9 [mm] or more and 23 [mm] or less. In the notch 22c of the center circumferential direction groove 22, the groove depth is 8 [mm] or less, and as a result of wear of the tread surface 15A by that amount, the notch 22c disappears as shown in FIG. 13 and only the groove 22b remains.

[0041] As shown in Fig. 11, the middle circumferential groove 23 is configured such that from the groove bottom 23a to midway of opening to the tread surface 15A, it is mainly formed as a groove 23b, and a notch 23c is formed at the opening edge portion opening to the tread surface 15A. As shown in Fig. 2, the groove 23b is formed in a zigzag shape so as to meander in the tire width direction along the tire circumferential direction. The groove 23b is formed continuously in the tire circumferential direction with a constant groove width W4a. The notch 23c is formed in a tapered shape so as to spread in the tire radial direction from the groove 23b toward the tread surface 15A. The notch 23c is provided only on one side in the tire width direction of the groove 23b. In the middle circumferential groove 23, the groove width W4 including the notch 23c is formed to vary in the tire circumferential direction. As shown in Fig. 2, in the middle circumferential groove 23, the groove width W4 including the notch 23c is formed to be narrow to wide between the bent portions of the groove 23b in accordance with the zigzag shape of the groove 22b along the tire circumferential direction. Under the same measurement conditions as the circumferential main groove 21, as shown in Fig. 11, in the middle circumferential groove 23, the groove width W4 including the notch 23c is 1 [mm] or more and 8 [mm] or less, the groove width W4a of the groove 23b excluding the notch 23c is 0.5 [mm] or more and 3 [mm] or less, and the groove depth d4 is formed to be 9 [mm] or more and 23 [mm] or less. In the middle circumferential groove 23, the groove depth at the notch 23c is 8 [mm] or less, and due to wear of the tread surface 15A by that amount, as shown in Fig. 13, the notch 23c disappears and only the groove 23b remains.

[0042] The width-direction sipe 42 extends along the tire width direction and is provided in a plurality in the tire circumferential direction as shown in FIG. 2. One end of the width-direction sipe 42 communicates with the bent portion of the middle circumferential-direction fine groove (circumferential-direction fine groove) 23, and the other end communicates with the circumferential-direction main groove 21. As shown in FIG. 12, the width-direction sipe 42 is configured with a main sipe 42b from the groove bottom 42a to midway through the opening to the tread surface 15A, and a notch 42c is formed at the opening edge portion that opens to the tread surface 15A. The width-direction sipe 42 has a cross-sectional spherical shape in which the groove bottom 42a has a wider groove width than the sipe 42b. The width-direction sipe 42 has the sipe 42b communicating with the fine groove 23b of the middle circumferential-direction fine groove 23. As shown in FIG. 2, the sipe 42b is formed in an arc shape that curves in the tire circumferential direction. The sipe 42b is formed continuously in the tire width direction with a constant groove width W5a. The notch 42c is provided on both sides of the sipe 42b in the tire circumferential direction. On one side of the sipe 42b in the tire circumferential direction, the notch 42c is formed in a tapered shape so as to spread in the tire circumferential direction from the sipe 42b toward the tread surface 15A, and on the other side of the sipe 42b in the tire circumferential direction, the notch 42c is formed in a concave groove shape so as to spread in the tire circumferential direction from the sipe 42b toward the tread surface 15A. Under the same measurement conditions as the circumferential-direction main groove 21, as shown in FIG. 12, the width-direction sipe 42 is formed such that the groove width W5 including the notch 42c is 1 [mm] or more and 8 [mm] or less, the groove width W5a of the sipe 42b excluding the notch 42c is 1 [mm] or less, and the groove depth d5 is 4 [mm] or more and 13 [mm] or less. The width-direction sipe 42 has a groove depth in the notch 42c of 8 [mm] or less, and as the tread surface 15A wears by that amount, the notch 42c disappears as shown in FIG. 13 and only the sipe 42b remains.

[0043] As shown in FIG. 2, each center center land portion 311 formed between the center circumferential direction groove 22 and each middle circumferential direction groove 23 has a center siped 41 formed on the tread surface 15A. The center siped 41 includes a first center siped 41a and a second center siped 41b. The first center siped 41a is formed linearly by connecting the bent portion of the groove 22b of the center circumferential direction groove 22 and the bent portion of the groove 23b of the middle circumferential direction groove 23. The second center siped 41b is formed in an S shape by connecting the straight portion of the groove 22b of the center circumferential direction groove 22 and the straight portion of the groove 23b of the middle circumferential direction groove 23. The first center siped 41a and the second center siped 41b are alternately provided in the tire circumferential direction. Each center center land portion 311 is divided into center blocks 311a divided in the tire circumferential direction by a plurality of center sipes 41. The center siped 41 is formed with a groove width of 1 [mm] or less and a groove depth of 4 [mm] or more and 13 [mm] or less under the same measurement conditions as the circumferential main groove 21.

[0044] As shown in FIG. 2, each center intermediate land portion 312 formed between each middle circumferential direction groove 23 and each circumferential main groove 21 has the above-described width direction siped 42 and middle siped 43 formed therein. The middle siped 43 is formed in an S shape by connecting the middle circumferential direction groove 23 and the circumferential main groove 21 between the width direction sipes 42. The middle siped 43 is provided in a plurality (two in the embodiment) in the tire circumferential direction between the width direction sipes 42. Each center intermediate land portion 312 is divided into intermediate blocks 312a divided in the tire circumferential direction by a plurality of width direction sipes 42 and middle sipes 43. The middle siped 43 is formed with a groove width of 1 [mm] or less and a groove depth of 4 [mm] or more and 13 [mm] or less under the same measurement conditions as the circumferential main groove 21.

[0045] Here, as described above, the center central land portion 311 is divided into a plurality of central blocks 311a at each center side 41, and the center intermediate land portion 312 adjacent to the center central land portion 311 in the tire width direction is divided into a plurality of intermediate blocks 312a at each width direction side 42 and each middle side 43. In the pneumatic tire 1 of the embodiment, the number of blocks P1 in the tire circumferential direction of the central block 311a and the number of blocks P2 in the tire circumferential direction of the intermediate block 312a satisfy the relationship of P1 ≤ P2. Specifically, in the pneumatic tire 1 of the embodiment, the number of blocks P1 in the tire circumferential direction of the central block 311a and the number of blocks P2 in the tire circumferential direction of the intermediate block 312a satisfy the relationship of 1.2 ≤ P2 / P1 ≤ 2, and preferably satisfy the relationship of P2 / P1 = 1.5.

[0046] Here, in the pneumatic tire 1 of the embodiment, as shown in FIG. 14, a sipe 47 may be formed in the buttress portion 15B. One end of the sipe 47 communicates with the ground contact end T, and the other end terminates within the buttress portion 15B. A plurality of sipes 47 are arranged side by side in the tire circumferential direction. When the shoulder lug groove 44 extends to the buttress portion 15B, a plurality of sipes 47 are arranged between each shoulder lug groove 44. When the shoulder sipe 45 extends to the buttress portion 15B, one sipe 47 communicates with this shoulder sipe 45. The sipe 47 is formed with a groove width of 1 [mm] or less and a groove depth of 0.5 [mm] or more and 3 [mm] or less under the same measurement conditions as the circumferential main groove 21.

[0047] The pneumatic tire 1 of the present embodiment described above is characterized by a pair of circumferential main grooves 21 extending in the tire circumferential direction, a single center land portion 31 partitioned inside the tire width direction of each circumferential main groove 21, and a pair of shoulder land portions 32 partitioned outside the tire width direction of each circumferential main groove 21. At least one circumferential narrow groove 22, 23 extending in the tire circumferential direction at the center land portion 31, and a plurality of shoulder lug grooves 44 formed at the shoulder land portion 31 with one end communicating with the circumferential main groove 21 and the other end opening to the ground contact end T in the tire circumferential direction. A shoulder sipe 45 is provided between the shoulder lug grooves 44 at the shoulder land portion 32 and is formed with one end communicating with the circumferential main groove 21 and the other end opening to the ground contact end T. The circumferential main groove 21 has a groove wall shape opening to the tread surface 15A, and a portion where the shoulder sipe 45 communicates while being sandwiched between the shoulder lug grooves 44 on the shoulder land portion 32 side is formed as a single first arc 21a, and a portion facing the first arc 21a on the center land portion 31 side is formed as a plurality of second arcs 21b.

[0048] According to this pneumatic tire 1, by combining the groove wall composed of a single first arc 21a and the groove wall composed of a plurality of second arcs 21b facing each other, the groove width continuously changes, so that the reduction of passing noise (PBN: Pass By Noise) becomes possible. However, in the case of the above configuration, the drainage performance deteriorates and the wet traction performance tends to decrease. Therefore, by appropriately arranging the shoulder lug grooves 44 and the shoulder sipe 45, it is possible to achieve both the improvement of wet traction performance and the reduction of passing noise. In addition, it is preferable that the radius of the single first arc 21a is 30% or more and 100% or less of the radius of the plurality of second arcs 21b in order to obtain the above effects.

[0049] Further, in the pneumatic tire 1 of the embodiment, the first arc 21a and the second arc 21b are convex toward the tire equatorial plane CL side.

[0050] According to this pneumatic tire 1, in the case of a configuration that is convex toward the tire equatorial plane CL side, the circumferential ends of the first arc 21a and the second arc 21b have a groove shape that is arranged toward the outer side in the tire width direction, and since the shoulder lug groove 44 that opens to the grounding end T communicates therewith, drainage performance can be improved and wet traction performance can be improved.

[0051] Further, in the pneumatic tire 1 of the embodiment, the first arc 21a and the second arc 21b are concave toward the tire equatorial plane CL side.

[0052] According to this pneumatic tire 1, in the case of a configuration that is concave toward the tire equatorial plane CL side, the central portion in the tire circumferential direction of the first arc 21a has a groove shape that is arranged toward the outer side in the tire width direction, and since the shoulder sip 45 that opens to the grounding end T communicates therewith, drainage performance can be improved and wet traction performance can be improved.

[0053] Further, in the pneumatic tire 1 of the embodiment, in the circumferential main groove 21, a range of 50% or less of the groove depth from the groove bottom 21d has a straight shape along the tire circumferential direction.

[0054] According to this pneumatic tire 1, by making the groove bottom 21d of the circumferential main groove 21 have a straight shape, the passage of water in the tire circumferential direction is improved, drainage performance is improved, and wet traction performance can be improved.

[0055] Further, in the pneumatic tire 1 of the embodiment, the shoulder lug groove 44 has a widened portion 44a whose groove width widens toward the grounding end T.

[0056] According to this pneumatic tire 1, by providing the widened portion 44a at the grounding end T in the shoulder lug groove 44, drainage performance can be improved and wet traction performance can be improved.

[0057] Further, in the pneumatic tire 1 of the embodiment, the groove depth d1 of the shoulder lug groove 44 and the groove depth D1 of the circumferential main groove 21 with which the shoulder lug groove 44 communicates satisfy the relationship of d1 / D1 ≤ 0.3.

[0058] According to this pneumatic tire 1, by setting the groove depth d1 of the shoulder lug groove 44 with respect to the groove depth D1 of the circumferential main groove 21 to the above relationship, it is possible to prevent the volume of the shoulder lug groove 44 with respect to the circumferential main groove 21 from being too large, and to ensure the effect of reducing the passing noise. Note that it is preferable that the groove depth d1 of the shoulder lug groove 44 and the groove depth D1 of the circumferential main groove 21 satisfy the relationship of 0.1 ≦ d1 / D1 ≦ 0.3 in order to reduce the passing noise and improve the wet traction performance.

[0059] Further, in the pneumatic tire 1 of the embodiment, the groove depth d2 of the shoulder sipe 45 and the groove depth D1 of the circumferential main groove 21 with which the shoulder sipe 45 communicates satisfy the relationship of d2 / D1 ≦ 0.4.

[0060] According to this pneumatic tire 1, by setting the groove depth d2 of the shoulder sipe 45 with respect to the groove depth D1 of the circumferential main groove 21 to the above relationship, it is possible to prevent the block rigidity of the shoulder land portion 32 from being too small, and to ensure the effect of reducing the passing noise. Note that in the pneumatic tire 1 of the embodiment, it is preferable that the groove depth d2 of the shoulder sipe 45 and the groove depth D1 of the circumferential main groove 21 satisfy the relationship of 0.2 ≦ d2 / D1 ≦ 0.4 in order to reduce the passing noise and improve the wet traction performance.

[0061] Further, in the pneumatic tire 1 of the embodiment, the groove width W1 of the shoulder lug groove 44 and the groove width W2 of the shoulder sipe 45 satisfy the relationship of 5 ≦ W1 / W2 ≦ 12.

[0062] According to this pneumatic tire 1, since the groove width W2 of the shoulder sipe 45 does not overly expand with respect to the groove width W1 of the shoulder lug groove 44, drainage from the shoulder lug groove 44 is efficiently performed, and the effect of improving wet traction performance is enhanced. Also, according to this pneumatic tire 1, since the groove width W2 of the shoulder sipe 45 does not overly narrow with respect to the groove width W1 of the shoulder lug groove 44, a sufficient edge effect can be obtained, and the effect of improving wet traction performance is enhanced. In the pneumatic tire 1 of the embodiment, the groove width W1 of the shoulder lug groove 44 and the groove width W2 of the shoulder sipe 45 satisfy the relationship of 7 ≦ W1 / W2 ≦ 10, which is preferable for enhancing the effect of improving wet traction performance.

[0063] Incidentally, in the present embodiment, as described above, the pneumatic tire 1 has been described as an example of a tire. This pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, and other gases. However, the configuration of the tread pattern of the pneumatic tire 1 described in the present embodiment can be arbitrarily applied to other tires within the scope obvious to those skilled in the art. Examples of other tires include, for example, airless tires and solid tires.

Example

[0064] FIG. 15 and FIG. 16 are charts showing the results of performance tests of the pneumatic tire according to the embodiment. Hereinafter, performance evaluation tests performed on a conventional pneumatic tire, a comparative example pneumatic tire, and an example pneumatic tire according to the embodiment will be described. The performance evaluation tests were tests on passing noise and wet traction performance.

[0065] For the passing noise evaluation test, an inflated tire of tire size 275 / 80R22.5 was mounted on the test vehicle of tractor head 2-D, and the passing noise from 60 km / h to 80 km / h compliant with ECE R117-02 (ECE Regulation No.117 Revision 2) was measured and indexed. This evaluation was conducted by an index evaluation based on the conventional example as the reference (100), indicating that the smaller the numerical value, the lower the passing noise.

[0066] For the evaluation test of wet traction performance, an inflated tire of the above tire size was mounted on the above test vehicle, and the deceleration from 60 km / h to the final speed of 20 km / h by ABS (Anti-lock Breake System) braking on a wet road surface compliant with ECE R117-02 (ECE Regulation No.117 Revision 2) was measured and indexed. This evaluation was conducted by an index evaluation based on the conventional example as the reference (100), indicating that the larger the numerical value, the higher the wet traction performance.

[0067] In the conventional inflated tire, mainly, the groove walls of two circumferential main grooves are formed in a straight line (straight).

[0068] In the comparative example inflated tire, mainly, the groove walls of two circumferential main grooves are formed in an arc.

[0069] In the inflated tire of the example, mainly, the groove walls of two circumferential main grooves are formed by a single first arc and a plurality of opposing second arcs.

[0070] And, as shown in the test results, it can be seen that the inflated tire of this example has improved passing noise and wet traction performance compared to the conventional example.

[0071] This disclosure includes the following inventions. [Invention 1] A pair of circumferential main grooves extending in the tire circumferential direction, A single center land portion partitioned inside the tire width direction of each of the circumferential main grooves, A pair of shoulder lands partitioned on the outer side in the tire width direction of each of the circumferential main grooves, At least one circumferential narrow groove extending in the tire circumferential direction at the center land, A plurality of shoulder lug grooves formed in the tire circumferential direction, each having one end communicating with the circumferential main groove and the other end opening to the ground contact end at each of the shoulder lands, A shoulder siped formed between each of the shoulder lug grooves at each of the shoulder lands, having one end communicating with the circumferential main groove and the other end opening to the ground contact end, and having In the shape of the groove wall opening to the tread surface, each of the circumferential main grooves is formed such that the portion where the shoulder siped communicates, sandwiched between each of the shoulder lug grooves on the shoulder land side, is formed as a single first arc, and the portion facing the first arc on the center land side is formed as a plurality of second arcs. A tire. [Invention 2] The first arc and the second arc are convex toward the tire equatorial plane side. The tire according to Invention 1. [Invention 3] The first arc and the second arc are concave toward the tire equatorial plane side. The tire according to Invention 1. [Invention 4] In the circumferential main groove, a range of 50% or less of the groove depth from the groove bottom has a straight shape along the tire circumferential direction. The tire according to any one of Inventions 1 to 3. [Invention 5] The shoulder lug groove has a widened portion where the groove width widens toward the ground contact end. The tire according to any one of Inventions 1 to 4. [Invention 6] The groove depth d1 of the shoulder lug groove and the groove depth D1 of the circumferential main groove with which the shoulder lug groove communicates satisfy the relationship of d1 / D1 ≦ 0.3. The tire according to any one of Inventions 1 to 5. [Invention 7] The groove depth d2 of the shoulder side and the groove depth D1 of the circumferential main groove communicating with the shoulder side satisfy the relationship d2 / D1 ≤ 0.4. The tire according to any one of Inventions 1 to 6. [Invention 8] The groove width W1 of the shoulder lug groove and the groove width W2 of the shoulder side satisfy the relationship 5 ≤ W1 / W2 ≤ 12. The tire according to any one of Inventions 1 to 7.

Explanation of Reference Signs

[0072] 1 Pneumatic tire (tire) 15A Tread surface 15B Battless part 21 Circumferential main groove 21a First arc 21b Second arc 22 Center circumferential fine groove (circumferential fine groove) 23 Middle circumferential fine groove (circumferential fine groove) 31 Center land 31 Shoulder land 44 Shoulder lug groove 44a Widening part 45 Shoulder side T Ground contact end

Claims

1. A pair of circumferential main grooves extending in the tire circumferential direction, a single center land portion partitioned inside the tire width direction of each of the circumferential main grooves, a pair of shoulder land portions partitioned outside the tire width direction of each of the circumferential main grooves, at least one circumferential narrow groove extending in the tire circumferential direction at the center land portion, shoulder lug grooves formed in plurality in the tire circumferential direction with one end communicating with the circumferential main groove and the other end opening to the ground contact end at the shoulder land portion, shoulder sipes formed between the shoulder lug grooves at the shoulder land portion with one end communicating with the circumferential main groove and the other end opening to the ground contact end, having, in the shape of the groove wall opening to the tread surface, the circumferential main groove is formed such that the portion where the shoulder sipes communicate, sandwiched between the shoulder lug grooves on the shoulder land portion side, is a single first arc, and the portion facing the first arc on the center land portion side is formed as a plurality of second arcs, a tire.

2. The first arc and the second arc are convex toward the tire equatorial plane side, the tire according to claim 1.

3. The first arc and the second arc are concave toward the tire equatorial plane side, the tire according to claim 1.

4. In the circumferential main groove, the range of 50% or less of the groove depth from the groove bottom is in a straight shape along the tire circumferential direction, the tire according to claim 1.

5. The shoulder lug groove has a widened portion where the groove width widens toward the ground contact end, the tire according to claim 1.

6. The groove depth d1 of the shoulder lug groove and the groove depth D1 of the circumferential main groove with which the shoulder lug groove communicates satisfy the relationship of d1 / D1 ≤ 0.3, the tire according to claim 1.

7. The groove depth d2 of the shoulder sipe and the groove depth D1 of the circumferential main groove with which the shoulder sipe communicates satisfy the relationship of d2 / D1 ≤ 0.4, the tire according to claim 1.

8. The groove width W1 of the shoulder lug groove and the groove width W2 of the shoulder sipe satisfy the relationship of 5 ≤ W1 / W2 ≤ 12, the tire according to claim 1.

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