Heavy-duty tires

Abstract

To provide a heavy-duty tire 2 that achieves improved resistance to uneven wear while ensuring the necessary traction performance. [Solution] The tire 2 is equipped with a tread 4. The tread 4 is equipped with a plurality of land areas 40 separated by a circumferential main groove 26. The plurality of land areas 40 include a crown land area 44. The circumferential main groove 26 includes a first crown circumferential main groove 32 and a second crown circumferential main groove 34. Each of the first crown circumferential main groove 32 and the second crown circumferential main groove 34 is equipped with a first edge 30Ea, a second edge 30Eb, a groove bottom 30T, a first wall surface 30Sa, and a second wall surface 30Eb. Each of the first edge 30Ea and the second edge Eb extends in a zigzag pattern in the circumferential direction. The groove bottom 30T extends in a straight line in the circumferential direction.

Description

Technical Field

[0001] The present invention relates to a heavy-duty tire.

Background Art

[0002] Tires mounted on vehicles such as trucks and buses (hereinafter referred to as heavy-duty tires) are subject to a greater load than tires mounted on passenger cars. Since the tread of heavy-duty tires is prone to wear, wear is suppressed by increasing the rigidity of the tread or the like. For example, in the heavy-duty tire disclosed in Patent Document 1, in order to suppress center wear while ensuring wet performance, the width of the land portion formed in the tread and the width of the circumferential groove are controlled.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a heavy-duty tire that can achieve improved resistance to uneven wear while ensuring necessary traction performance.

Means for Solving the Problems

[0005] The heavy-duty tire according to the present invention comprises a tread having a tread surface that contacts the road surface. The tread comprises a plurality of land portions separated by circumferential main grooves. The plurality of land portions include a crown land portion located on the equatorial plane. The crown land portion is a continuous body extending circumferentially without interruption, comprising closed sipes arranged circumferentially, or an aggregate of a plurality of crown blocks separated by open sipes that traverse the crown land portion. The circumferential main grooves located on either side of the crown land portion are the first crown circumferential main groove and the second crown circumferential main groove. Each of the first crown circumferential main groove and the second crown circumferential main groove comprises a first edge and a second edge, a bottom surface including the groove bottom, a first wall surface bridging the space between the first edge and the bottom surface, and a second wall surface bridging the space between the second edge and the bottom surface. Each of the first edge and the second edge extends in a zigzag pattern in the circumferential direction. The groove bottom extends in a straight line in the circumferential direction. [Effects of the Invention]

[0006] According to the present invention, a heavy-duty tire can be obtained that achieves improved resistance to uneven wear while ensuring the necessary traction performance. [Brief explanation of the drawing]

[0007] [Figure 1] This is an exploded view showing a portion of the tire tread according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line II-II in Figure 1. [Figure 3] This is a cross-sectional view along line III-III in Figure 1. [Figure 4] This is an exploded view showing a portion of the center area of ​​the tread. [Figure 5] This is a cross-sectional view along the VV line in Figure 1. [Figure 6] This is a diagram showing a portion of the Crown's land area. [Figure 7] This is a cross-sectional view along line VII-VII in Figure 6. [Figure 8] This is a diagram showing a portion of the Crown's land area. [Figure 9] This is a cross-sectional view along the line IX-IX in Figure 8. [Figure 10] This is a cross-sectional view along line XX in Figure 8. [Figure 11] This is a diagram illustrating the structure of the reinforcement layer. [Figure 12] This is a cross-sectional view showing a portion of the Crown's land area. [Modes for carrying out the invention]

[0008] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0009] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0010] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state.

[0011] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire's cross-section, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim. The tire's structure, which cannot be confirmed when the tire is mounted on a standard rim, is confirmed at the aforementioned cross-section.

[0012] The standard rim means the rim defined in the standard on which the tire depends. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are standard rims.

[0013] The standard internal pressure means the internal pressure defined in the standard on which the tire depends. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are standard internal pressures.

[0014] The standard load means the load defined in the standard on which the tire depends. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are standard loads.

[0015] In the present invention, the number of cords included per 50 mm width of an element of a tire including parallel cords is represented as cord ends (unit: ends / 50 mm). Cord ends are obtained on the cut surface of the element, which is obtained by cutting the element with a plane perpendicular to the longitudinal direction of the cord, unless otherwise specified. An element including a helically wound cord also apparently has a plurality of parallel cords, so cord ends can be obtained in the same manner as an element of a tire including parallel cords.

[0016] In the present invention, the tread portion of a tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion includes a tread as a component of the tire. The sidewall portion includes a sidewall as a component of the tire. The bead portion includes a bead as a component of the tire.

[0017] [Knowledge on which the present invention is based] In the tread of a tire (hereinafter referred to as a drive tire) mounted on the drive shaft of a truck or a bus, wear is likely to occur in the center region. Since the load during vehicle start-up and braking is large, uneven wear such as heel-and-toe wear is likely to occur.

[0018] Improvement in traction performance is required for drive tires. In order to ensure the necessary traction performance while improving the uneven wear resistance, it has been considered to provide sipes in the center region. In the case of drive tires, the load acting on the center region is larger than that of tires mounted on the steer shaft of a vehicle or tires mounted on a trailer. Therefore, there is a concern that if sipes are provided in the center region, the risk of uneven wear increases. In drive tires, it is difficult to achieve both traction performance and uneven wear resistance.

[0019] Therefore, the present inventor has intensively studied a technique capable of achieving improvement in uneven wear resistance while ensuring the necessary traction performance, and has completed the present invention described below.

[0020] [Outline of embodiments of the present invention] The present invention relates to a heavy-duty tire comprising a tread having a tread surface that contacts the road surface, wherein the tread comprises a plurality of land portions separated by circumferential main grooves, the plurality of land portions include a crown land portion located on the equatorial plane, the crown land portion is a continuous body extending without interruption in the circumferential direction with closed sipes arranged in the circumferential direction, or a collection of a plurality of crown blocks separated by open sipes that traverse the crown land portion, the circumferential main grooves located on both sides of the crown land portion are a first crown circumferential main groove and a second crown circumferential main groove, each of the first crown circumferential main groove and the second crown circumferential main groove comprises a first edge and a second edge, a bottom surface including the groove bottom, a first wall surface bridging the space between the first edge and the bottom surface, and a second wall surface bridging the space between the second edge and the bottom surface, each of the first edge and the second edge extending in a zigzag pattern in the circumferential direction, and the groove bottom extending in a straight line in the circumferential direction.

[0021] The tire of the present invention can achieve improved resistance to uneven wear while ensuring the necessary traction performance. Although the mechanism by which the tire achieves this effect has not been fully elucidated, it is presumed to be as follows.

[0022] This tire's tread has a crown land area located on the equatorial plane. Compared to the center area of ​​a tread with circumferential main grooves on the equatorial plane, this tread's center area has higher rigidity. The crown area is a continuous body extending circumferentially without interruption, comprising multiple closed sipes arranged in the circumferential direction, or an aggregate of multiple crown blocks separated by open sipes that traverse the crown area. Compared to a case where the crown area is composed of an aggregate of blocks separated by lateral grooves that traverse the crown area, the crown area of ​​this tire has higher rigidity. The edges of the crown's circumferential main grooves, located next to the crown's land area, extend in a zigzag pattern in the circumferential direction, while the groove bottoms of these crown's circumferential main grooves extend in a straight line in the circumferential direction. Compared to a case where the crown's circumferential main grooves are configured so that both the edges and groove bottoms extend in a zigzag pattern, the volume of the crown's land area increases. This increase in volume enhances the rigidity of the crown's land area. The crown area effectively increases the rigidity of the center region. Despite the presence of closed or open sipes on the crown area, this tire suppresses uneven wear such as center wear and heel-and-toe wear, which were observed in conventional tires. This tire offers superior resistance to uneven wear. The edges of the main grooves circumferentially on the crown, as well as the closed or open sipes carved into the crown's surface, can function as edge components that contribute to traction. This tire also boasts excellent traction performance. This tire achieves improved resistance to uneven wear while maintaining the necessary traction performance.

[0023] Preferably, the tread further comprises a reinforcing layer located radially inward, the reinforcing layer comprising a belt including a number of parallel belt cords and a band including a helically wound band cord, the belt comprising a plurality of belt plies arranged radially, the plurality of belt plies comprising a reference ply and a sub-reference ply, the reference ply being the belt ply having the widest axial width among the plurality of belt plies, the sub-reference ply being the belt ply having the second widest axial width among the plurality of belt plies, and each of the reference ply and the sub-reference ply includes The heavy-duty tire comprises a full band, the belt cord being a steel cord, the inclination direction of the belt cord included in the reference ply being opposite to the inclination direction of the belt cord included in the sub-reference ply, the band being located between the reference ply and the sub-reference ply, the band cord included in the full band being a steel cord, the plurality of land portions including a shoulder land portion located axially on the outermost side, the circumferential main groove separating the shoulder land portions being a shoulder circumferential main groove, and the end of the full band being located axially outward from the shoulder circumferential main groove. In this case, the reinforcing layer can contribute to suppressing radial growth of the tire. Localized increases in ground pressure in the center region are suppressed. Center wear is suppressed in this tire. This tire can improve resistance to uneven wear.

[0024] More preferably, the plurality of belt plies include a minimum width ply located radially on the outermost side and having the smallest axial width, with the outer end of the minimum width ply located axially outward from the crown circumferential main groove. This effectively suppresses localized increases in ground pressure in the center region. This tire can improve resistance to uneven wear.

[0025] From another perspective, more preferably, the ratio of the axial width at the base of the crown to the axial width of the full band is 0.15 or more and 0.30 or less. This allows the tire to improve resistance to uneven wear.

[0026] Preferably, the first and second wall surfaces are inclined with respect to the normal of the tread surface, and each of the first and second wall surfaces extends circumferentially while changing the inclination angle between a maximum and a minimum value. In each of the first and second wall surfaces, a maximum inclination position defined by the position where the inclination angle shows the maximum value and a minimum inclination position defined by the position where the inclination angle shows the minimum value are alternately arranged in the circumferential direction, and the maximum inclination position of the first wall surface and the minimum inclination position of the second wall surface coincide in the circumferential direction. In this case, even though the crown circumferential main groove is configured such that the inclination angle of the wall surface of the crown circumferential main groove changes in the circumferential direction, the rigidity of the crown land area is well balanced in the circumferential direction. The crown land area can effectively contribute to achieving both traction performance and resistance to uneven wear.

[0027] More preferably, the second edge of the first crown circumferential main groove is the first crown edge of the crown land portion, the first edge of the second crown circumferential main groove is the second crown edge of the crown land portion, and each of the first crown edge and the second crown edge comprises a plurality of edge units arranged in the circumferential direction starting from the position of maximum inclination, each edge unit comprising a first edge element including the starting point, a second edge element connected to the first edge element, a third edge element connected to the second edge element, and a fourth edge element connected to the third edge element, and in the first crown edge, the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the first circumferential side to the second circumferential side. Furthermore, in the second crown edge, the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the second circumferential side to the first circumferential side, the third edge element of the first crown edge and the third edge element of the second crown edge overlap in the axial direction, the crown land is an aggregate of the crown blocks, and the open sipes comprise a first open sipe and a second open sipe, the first open sipe bridging the gap between the first edge element of the first crown edge and the second edge element of the second crown edge, and the second open sipe bridging the gap between the second edge element of the first crown edge and the first edge element of the second crown edge. In this case, even though the crown circumferential main groove is configured such that the inclination angle of the wall surface of the crown circumferential main groove changes in the circumferential direction, the rigidity of the crown land is well balanced in the circumferential direction. The crown land can effectively contribute to achieving both traction performance and resistance to uneven wear.

[0028] More preferably, the assembly of crown blocks comprises a first crown block, a second crown block, and a third crown block arranged in the circumferential direction, wherein the third crown block has a first lateral shallow groove spanning between the first open sipe and the first edge element of the first crown edge, and the second crown block has a second lateral shallow groove spanning between the second open sipe and the first edge element of the second crown edge. In this case, the first lateral shallow groove and the second lateral shallow groove can function as edge components that contribute to traction. This tire can improve traction performance.

[0029] From another perspective, more preferably, the plurality of open sipes further comprises a third open sipe, The third open sipe bridges the gap between the fourth edge element of the first crown edge and the fourth edge element of the second crown edge. In this case, the crown surface can more effectively contribute to achieving both traction performance and resistance to uneven wear.

[0030] Preferably, the crown base is an aggregate of the crown blocks, and the open sipe comprises a first connecting portion connected to the first crown circumferential main groove, a second connecting portion connected to the second crown circumferential main groove, and an inclined portion bridging the gap between the first and second connecting portions, wherein the inclined portion comprises a first inclined portion connected to the first connecting portion and a second inclined portion connected to the second connecting portion, the angle made by the first connecting portion with respect to the axial direction being smaller than the angle made by the first inclined portion with respect to the axial direction, and the angle made by the second connecting portion with respect to the axial direction being smaller than the angle made by the second inclined portion with respect to the axial direction. In this case, the effect of the crown blocks supporting each other in the circumferential direction is enhanced. Lateral forces act on the crown base during turning, but this tire can suppress the amount of movement of the crown blocks when lateral forces act on the crown base. This suppresses the occurrence of heel-and-toe wear. This tire can improve resistance to uneven wear.

[0031] More preferably, the first connecting portion, the second connecting portion, and the first inclined portion, and the second inclined portion each extend in a zigzag pattern in the depth direction. In this case, the effect of the crown blocks supporting each other in the circumferential direction is enhanced. During driving and braking, forces act on the crown land area in the longitudinal direction, i.e., the circumferential direction, but this tire can suppress the amount of movement of the crown blocks when circumferential forces act on the crown land area. This suppresses the occurrence of heel-and-toe wear. This tire can improve resistance to uneven wear.

[0032] From another perspective, more preferably, the inclined portion further comprises an intermediate portion bridging the first inclined portion and the second inclined portion, the intermediate portion extending in the circumferential direction. In this case, the effect of the crown blocks supporting each other is further enhanced. This tire can effectively suppress the amount of movement of the crown blocks when a lateral force is applied to the crown surface. As a result, deformation of the crown surface is effectively suppressed. This tire can improve resistance to uneven wear. During cornering, the intermediate portion can function as an edge component that contributes to the performance of traction. This tire can improve traction performance.

[0033] More preferably, the first connecting portion, the second connecting portion, and the first inclined portion, the second inclined portion each extend in a zigzag pattern in the depth direction, while the intermediate portion extends in a straight line in the depth direction. In this case as well, the effect of the crown blocks supporting each other in the circumferential direction is enhanced, and the occurrence of heel-and-toe wear is suppressed. This tire can achieve improved resistance to uneven wear.

[0034] Thus, according to the present invention, a heavy-duty tire can be obtained that achieves improved resistance to uneven wear while ensuring the necessary traction performance. This will be explained in detail below.

[0035] [Details of the Embodiments of the Invention] [tire] Figure 1 is a plan view showing a portion of the tread 4 of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on vehicles such as trucks and buses. This tire 2 is a heavy-duty tire.

[0036] In Figure 1, the direction indicated by the double-headed arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2 (not shown). The direction indicated by the double-headed arrow CD is the circumferential direction of tire 2. The circumferential direction of tire 2 is also the rotation direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the radial direction of tire 2. In Figure 1, the dashed line EL extending in the circumferential direction represents the equatorial plane of tire 2. In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2. The direction indicated by arrow CD1 is the first circumferential side of tire 2, and the direction indicated by arrow CD2 is the second circumferential side of tire 2.

[0037] Figure 2 shows a portion of the cross-section of tire 2. This cross-section of tire 2 is a meridian cross-section, in other words, a cross-section along the plane containing the axis of rotation of tire 2 (not shown). The line II-II in Figure 1 is included in the meridian cross-section. In Figure 2, the direction indicated by the double arrow RD is the radial direction of tire 2. The direction indicated by arrow RD1 is the radially outward direction of tire 2, and the direction indicated by arrow RD2 is the radially inward direction of tire 2.

[0038] Figure 2 shows the tread portion T of tire 2. The tread portion T comprises a tread 4, a pair of sidewalls 6, a carcass 8, an inner liner 10, a pair of cushioning layers 12, and a reinforcing layer 14. Although not shown in the diagram, tire 2 further comprises elements such as a bead and clincher. While not described in detail, elements other than the tread 4 and reinforcing layer 14 have a configuration typical of heavy-duty tires.

[0039] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 is located axially outward of the carcass 8. The sidewall 6 is made of cross-linked rubber.

[0040] The carcass 8 is located inside the tread 4 and the pair of sidewalls 6. Although not shown, the carcass 8 spans between the pair of beads. The carcass 8 comprises at least one carcass ply 16. The carcass 8 of this tire 2 consists of one carcass ply 16.

[0041] Although not shown, the carcass ply 16 is folded over at each bead. The carcass ply 16 contains numerous parallel carcass cords. These carcass cords intersect the equatorial plane. The carcass 8 of this tire 2 has a radial structure. The carcass cords of this tire 2 are steel cords. Cords made of organic fibers may be used as carcass cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0042] The inner liner 10 is located inside the carcass 8. The inner liner 10 forms the inner surface of the tire 2. The inner liner 10 is made of cross-linked rubber with excellent air-shielding properties. The inner liner 10 maintains the internal pressure of the tire 2.

[0043] Each cushion layer 12 is located at the edge of the reinforcing layer 14, between the reinforcing layer 14 and the carcass 8. The cushion layer 12 is made of soft cross-linked rubber.

[0044] The reinforcing layer 14 is located radially inward of the tread 4. The reinforcing layer 14 is located radially outward of the carcass 8. The reinforcing layer 14 of this tire 2 is laminated on the carcass 8 radially inward of the tread 4. The reinforcing layer 14 comprises a plurality of radially aligned layers 18. Each layer 18 contains a cord. The reinforcing layer 14 is also called a cord reinforcing layer.

[0045] The tread 4 is located on the radially outermost part of the tire 2. The tread 4 extends in the circumferential direction. The tire 2 contacts the road surface at the tread 4. The surface of the tread 4 that contacts the road surface is the tread surface 20. The tread 4 has a tread surface 20 that contacts the road surface. Tread 4 is made of cross-linked rubber. Although not described in detail, tread 4 of this tire 2 is made of cross-linked rubber, which is common for the treads of heavy-duty tires.

[0046] In Figure 1, the solid line TE extending in the circumferential direction represents the edge of the tread surface 20. In the case of a tire where the edge of the tread surface is not identifiable by appearance, the position on the outer surface of the tire corresponding to the axial outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and bringing the tire into contact with a plane, is used as the edge of the tread surface.

[0047] In Figure 1, the length indicated by the double arrow TW represents the width of the tread 4. The width TW of the tread 4 is the axial distance from one end TE to the other end TE of the tread surface 20. The width TW of the tread 4 is measured along the tread surface 20.

[0048] In the tread surface 20 shown in Figure 1, one end TE of the tread surface 20 located to the left of the equatorial plane is called the first end TE1. The other end TE located to the right of the equatorial plane is called the second end TE2. Alternatively, one end TE of the tread surface 20 located to the left of the equatorial plane may be called the second end TE2, and the other end TE located to the right of the equatorial plane may be called the first end TE1.

[0049] Tread 4 has grooves 22 cut into it. This forms the tread pattern. The tread pattern shown in Figure 1 is an example of a tread pattern that makes up the tread 4. This tread pattern is that of a new, unworn tire 2. The portion of the tread surface 20 other than the grooves 22 is also called the land surface 24.

[0050] Figure 3 shows a cross-section of groove 22. The cross-section of groove 22 shown in Figure 3 is the cross-section of the circumferential main groove (more specifically, the crown circumferential main groove), which will be described later. The main structure of groove 22 will be explained based on the cross-section of the circumferential main groove.

[0051] The cross-section of the groove 22 is represented by a cross-section along a plane perpendicular to the longitudinal direction of the groove 22. The longitudinal direction of the groove 22 is represented by the direction in which the groove bottom 22T extends. In Figure 1, the solid line BTL represents the trajectory of the groove bottom 22T of the groove 22, that is, the direction in which the groove bottom 22T extends. Figure 3 is a cross-section of the groove 22 along a plane perpendicular to the direction in which the solid line BTL in Figure 1 extends, that is, a cross-section of the groove 22 along a plane perpendicular to the longitudinal direction of the groove 22. In the present invention, unless otherwise specified, the width and depth of the groove 22 are obtained in the cross-section of the groove 22 along a plane perpendicular to the longitudinal direction of the groove 22.

[0052] The groove 22 comprises a groove opening 22M, a pair of wall surfaces 22S, and a bottom surface 22B. The groove opening 22M is composed of a pair of edges 22E. In other words, the groove opening 22M comprises a pair of edges 22E. Each edge 22E is the boundary between the land surface 24 and the groove 22. The pair of wall surfaces 22S each span between the edges 22E and the bottom surface 22B. The bottom surface 22B includes the groove bottom 22T. Unless otherwise specified, the groove bottom 22T is represented by the position where the distance from the reference plane RP to the bottom surface 22B is maximized, measured along the normal to the reference plane RP, which is the plane containing the groove opening 22M. If the bottom surface 22B is a plane, the groove bottom 22T is represented by the center position of the bottom surface 22B. If the bottom surface 22B has a protrusion, the groove bottom 22T is determined based on a virtual bottom surface obtained by assuming the absence of the protrusion. The normal to the reference plane RP, which connects the reference plane RP and the groove bottom 22T, is the reference normal RN, and the direction of this reference normal RN is in the depth direction of the groove 22. The width of the groove 22 is expressed as the distance between one wall surface 22S and the other wall surface 22S (hereinafter referred to as the inter-wall distance). Unless otherwise specified, the inter-wall distance is measured along a line perpendicular to the reference normal RN. If the profile of the tread surface 20 can be confirmed, the profile of the tread surface 20 may be used as the reference surface RP to determine the groove bottom 22T and width of the groove 22.

[0053] In Figure 3, the length indicated by the double-headed arrow WG is the width of the groove 22 at the groove opening 22M. If the portion of the groove 22 at the groove opening 22M is machined in a tapered manner, the width of the groove 22 at the groove opening 22M is expressed based on a virtual edge obtained assuming that it is not machined in a tapered manner. The length indicated by the double-headed arrow DG is the depth of the groove 22. Unless otherwise specified, the depth DG of the groove 22 is expressed as the distance from the reference surface RP to the groove bottom 22T of the groove 22, measured along the reference normal RN. The position, width WG, and depth DG of the groove 22 are determined as appropriate according to the specifications of the tire 2.

[0054] In the groove 22M, grooves 22 with a width WG of less than 1.0 mm are called sipes. Grooves 22 other than sipes are called ordinary grooves. Ordinary grooves have a width WG of 1.0 mm or more in their groove 22M. Even among ordinary grooves, those with a wide width and a pair of walls that do not come into contact with each other when the tire is in contact with the road surface are also called main grooves. Ordinary grooves with a narrow width and a pair of walls that can come into contact with each other when the tire is in contact with the road surface are also called narrow grooves.

[0055] The tread 4 is provided with circumferential main grooves 26. The circumferential main grooves 26 extend continuously in the circumferential direction. The circumferential main grooves 26 are the main grooves described above. The circumferential main groove 26 comprises a pair of edges 26E that constitute the groove opening 26M, a bottom surface 26B including the groove bottom 26T, and a pair of wall surfaces 26S that bridge the gap between each of the edges 26E and the bottom surface 26B. The circumferential main grooves 26 of this tire 2 have a wide width. The pair of wall surfaces 26S of the circumferential main grooves 26 do not come into contact with each other even when the tire 2 is in contact with the road surface and the tread 4 deforms.

[0056] The depth DGm of the circumferential main groove 26 is, for example, 8 mm or more and 21 mm or less. From the viewpoint of enabling the tire 2 to exhibit good wet performance, it is preferable that the depth DGm of the circumferential main groove 26 is 13 mm or more and 18 mm or less. The width WGm of the circumferential main groove 26 is preferably 4.0% or more and 10% or less of the width TW of the tread 4.

[0057] The tread 4 has multiple circumferential main grooves 26. The tread 4 of this tire 2 has four circumferential main grooves 26. The four circumferential main grooves 26 are arranged in the axial direction. The two circumferential main grooves 26 located on the outermost axial side are the shoulder circumferential main grooves 28. The two circumferential main grooves 26 closest to the equatorial plane are the crown circumferential main grooves 30. The two crown circumferential main grooves 30 are each circumferential main grooves 26 located next to the crown land portion, which will be described later. The multiple circumferential main grooves 26 include two crown circumferential main grooves 30 located next to the crown land portion and two shoulder circumferential main grooves 28 located on the outermost axial side.

[0058] A circumferential main groove 26 may be further provided between the crown circumferential main groove 30 and the shoulder circumferential main groove 28. In this case, the circumferential main groove 26 that is closest to the equatorial plane after the crown circumferential main groove 30 is called the middle circumferential main groove.

[0059] The shoulder circumferential main groove 28 comprises a pair of edges 28E, a bottom surface 28B including the groove bottom 28T, and a pair of wall surfaces 28S that bridge the gap between each edge 28E and the bottom surface 28B. Of the pair of edges 28E, the edge 28E on the TE side of the tread surface 20 is the outer edge 28Es, and the edge 28E on the equatorial side is the inner edge 28Eu. Of the pair of wall surfaces 28S, the wall surface 28S on the TE side of the tread surface 20 is the outer wall surface 28Ss, and the wall surface 28S on the equatorial side is the inner wall surface 28Su.

[0060] As mentioned above, the tread 4 of this tire 2 is equipped with two shoulder circumferential main grooves 28. Of the two shoulder circumferential main grooves 28, the shoulder circumferential main groove 28 located on the first end TE1 side of the tread surface 20 is the first shoulder circumferential main groove 36. The shoulder circumferential main groove 28 located on the second end TE2 side of the tread surface 20 is the second shoulder circumferential main groove 38.

[0061] As shown in Figure 1, the groove bottoms 28T of the first shoulder circumferential main groove 36 and the second shoulder circumferential main groove 38 extend straight in the circumferential direction. The outer edges 28Es of the first shoulder circumferential main groove 36 and the second shoulder circumferential main groove 38 extend straight in the circumferential direction. The inner edges 28Eu of the first shoulder circumferential main groove 36 and the second shoulder circumferential main groove 38 extend in a zigzag pattern in the circumferential direction.

[0062] The crown circumferential main groove 30 comprises a pair of edges 30E, a bottom surface 30B including the groove bottom 30T, and a pair of wall surfaces 30S that bridge the gap between each edge 30E and the bottom surface 30B. Of the pair of edges 30E, the edge 30E on the first end TE1 side of the tread surface 20 is the first edge 30Ea, and the edge 30E on the second end TE2 side of the tread surface 20 is the second edge 30Eb. Of the pair of wall surfaces 30S, the wall surface 30S on the first end TE1 side of the tread surface 20 is the first wall surface 30Sa, and the wall surface 30S on the second end TE2 side of the tread surface 20 is the second wall surface 30Sb.

[0063] As shown in Figure 1, the first edge 30Ea and the second edge 30Eb of the crown circumferential main groove 30 extend in a zigzag pattern in the circumferential direction. The edge 30E of the crown circumferential main groove 30 has a first vertex Ta that protrudes toward the first end TE1 side of the tread surface 20 and a second vertex Tb that protrudes toward the second end TE1 side of the tread surface 20. In each edge 30E, the first vertex Ta and the second vertex Tb are arranged alternately in the circumferential direction.

[0064] In this tire 2, of the two crown circumferential main grooves 30, the crown circumferential main groove 30 located on the first end TE1 side of the tread surface 20 is the first crown circumferential main groove 32. The crown circumferential main groove 30 located on the second end TE2 side of the tread surface 20 is the second crown circumferential main groove 34. The first crown circumferential main groove 32 and the second crown circumferential main groove 34 each include a first edge 30Ea and a second edge 30Eb, a bottom surface 30B including the groove bottom 30T, a first wall surface 30Sa connecting the first edge 30Ea and the bottom surface 30B, and a second wall surface 30Sb connecting the second edge Eb and the bottom surface 30B.

[0065] Multiple circumferential main grooves 26 constitute multiple land areas 40 on the tread 4. The tread 4 comprises multiple land areas 40 separated by the circumferential main grooves 26. The tread 4 shown in Figure 1 has four circumferential main grooves 26, forming five land areas 40. The top surface 40H of each land area 40 forms part of the aforementioned land surface 24. As shown in Figure 3, the edge 26E of the circumferential main groove 26 is the boundary between the wall surface 26S of the circumferential main groove 26 and the top surface 40H of the land area 40.

[0066] The two outermost axially located land sections 40 are shoulder land sections 42. The shoulder land sections 42 include the edge TE of the tread surface 20. The land section 40 located on the equatorial plane is the crown land section 44. The land section 40 located between the crown land section 44 and the shoulder land sections 42 is the middle land section 46. The multiple land sections 40 include the crown land section 44 located on the equatorial plane, the pair of shoulder land sections 42 located on the outermost axially, and the pair of middle land sections 46 located between the crown land section 44 and the shoulder land sections 42.

[0067] The land portion 40 located between the two crown circumferential main grooves 30 is the crown land portion 44. The land portion 40 located between the crown circumferential main groove 30 and the shoulder circumferential main groove 28 is the middle land portion 46. The land portion 40 located axially outward from the shoulder circumferential main groove 28 is the shoulder land portion 42. The shoulder circumferential main groove 28 is the circumferential main groove 26 that separates the shoulder land portion 42.

[0068] For example, two land sections 40 may be provided between the crown land section 44 and the shoulder land section 42. In this case, the land section 40 closer to the equatorial plane is called the inner middle land section, and the land section 40 closer to the edge TE of the tread surface 20 is called the outer middle land section. The configuration of the crown land section 44 is applied to the configuration of the inner middle land section, and the configuration of the middle land section 46 is applied to the configuration of the outer middle land section. A further land section 40 may be provided between the inner middle land section and the outer middle land section. In this case, the configuration of the crown land section 44 is applied to the land section 40 located between the inner middle land section and the outer middle land section.

[0069] In this tire 2, of the two middle sections 46, the middle section 46 located on the first end TE1 side of the tread surface 20 is the first middle section 48. The middle section 46 located on the second end TE2 side of the tread surface 20 is the second middle section 50. Of the two shoulder sections 42, the shoulder section 42 located on the first end TE1 side of the tread surface 20 is the first shoulder section 52. The shoulder section 42 located on the second end TE2 side of the tread surface 20 is the second shoulder section 54.

[0070] Multiple shoulder lateral grooves 94 are engraved on the shoulder land portion 42, traversing it. This creates multiple shoulder blocks 96 arranged in the circumferential direction. The shoulder land portion 42 is an aggregate of multiple shoulder blocks 96 separated by shoulder lateral grooves 94.

[0071] Multiple middle lateral grooves 98 are carved into the middle track section 46, crossing it. This creates multiple middle blocks 100 arranged in the circumferential direction. The middle track section 46 is an aggregate of multiple middle blocks 100 separated by the middle lateral grooves 98. Lateral sipes 102 are further carved into the bottom of the middle lateral grooves 98. The middle block 100 is further engraved with two open sipes 104. This results in the middle block being composed of three sub-middle blocks 106. The middle block 100 is an assembly of three sub-middle blocks 106 separated by open sipes 104.

[0072] Figure 4 shows a portion of the unfolded view of Figure 1. Figure 4 shows a portion of the center area of ​​tread 4. In this tire 2, the center region is the area of ​​the tread 4 where the crown land portion 44 and a pair of middle land portions 46 are located. The shoulder region is the area where the shoulder land portion 42 is located.

[0073] As shown in Figure 4, the crown land portion 44 of this tire 2 is provided with a plurality of transverse sipes 56 that extend in the axial direction. The plurality of transverse sipes 56 are arranged in the circumferential direction. The transverse sipes 56 are the sipes described above. The crown land portion 44 of this tire 2 is not provided with transverse grooves as ordinary grooves that cross the crown land portion 44.

[0074] The crown land portion 44 is located between the first crown circumferential main groove 32 and the second crown circumferential main groove 34. In other words, the circumferential main grooves 26 located on either side of the crown land portion 44 are the first crown circumferential main groove 32 and the second crown circumferential main groove 34.

[0075] The lateral sipe 56 of this tire 2 crosses the crown base 44. The lateral sipe 56 connects to the crown circumferential main groove 30 located next to the crown base 44. The lateral sipe 56 bridges between the first crown circumferential main groove 32 and the second crown circumferential main groove 34. This lateral sipe 56 is an open sipe 58. The open sipe 58 connects to the first crown circumferential main groove 32 at one end and to the second crown circumferential main groove 34 at the other end.

[0076] Multiple open sipes 58 constitute multiple crown blocks 60 on the crown land area 44. The multiple crown blocks 60 are arranged in the circumferential direction. The crown land area 44 is an aggregate of multiple crown blocks 60 separated by open sipes 58 that traverse the crown land area 44.

[0077] Although not shown in the figures, closed sipes terminated at both ends within the crown land portion 44 may be used as the lateral sipes 56. In this case, the portion other than the lateral sipes 56 is composed of a structure that extends continuously in the circumferential direction. Alternatively, closed sipes terminated at both ends within the crown land portion 44 may be used as the lateral sipes 56, and the crown land portion 44 may be constructed as a continuous body that extends without interruption in the circumferential direction, comprising multiple closed sipes arranged in the circumferential direction.

[0078] The tread 4 of this tire 2 has a crown land portion 44 located on the equatorial plane. Compared to the center region of a tread with circumferential main grooves on the equatorial plane, the center region of this tread 4 has higher rigidity. The crown land area 44 of this tire 2 is a continuous body extending circumferentially without interruption, equipped with multiple closed sipes arranged in the circumferential direction, or an aggregate of multiple crown blocks 60 separated by open sipes 58 that traverse the crown land area 44. Compared to a case where the crown land area is composed of an aggregate of blocks separated by lateral grooves that traverse the crown land area, the crown land area 44 of this tire 2 has higher rigidity. As mentioned above, the first edge 30Ea and the second edge 30Eb of the crown circumferential main groove 30 extend in a zigzag pattern in the circumferential direction. As shown in Figure 1, the groove bottom 30T of this crown circumferential main groove 30 extends in a straight line in the circumferential direction. In this tire 2, the volume of the crown land area 44 increases compared to the case where the crown circumferential main groove 30 is configured so that the edges and groove bottoms extend in a zigzag pattern in the circumferential direction. The increase in volume increases the rigidity of the crown land area 44. The crown area 44 of this tire 2 effectively increases the rigidity of the center region. In this tire 2, even though closed or open sipes are engraved on the crown area 44, the occurrence of uneven wear such as center wear and heel-and-toe wear, which have been observed in conventional tires, is suppressed. This tire 2 has excellent resistance to uneven wear. The edges 30E of the crown's circumferential main grooves 30, and the closed or open sipes 58 carved into the crown's land portion 44, can function as edge components that contribute to traction. This tire 2 also boasts excellent traction performance. This tire 2 achieves improved resistance to uneven wear while ensuring the necessary traction performance.

[0079] As mentioned above, the crown land portion 44 of this tire 2 is a continuous body extending circumferentially without interruption, having a plurality of closed sipes arranged in the circumferential direction, or an assembly of a plurality of crown blocks 60 separated by open sipes 58 that cross the crown land portion 44. From the viewpoint of achieving both traction performance and resistance to uneven wear, it is preferable that the crown land portion 44 is an assembly of a plurality of crown blocks 60 separated by open sipes 58 that cross the crown land portion 44.

[0080] Figure 5 shows a cross-section of the crown circumferential main groove 30. In Figure 5, the solid line LN is the normal to the tread surface 20 at the edge 30E of the crown circumferential main groove 30. The first wall surface 30Sa and the second wall surface 30Sb of the crown circumferential main groove 30 are inclined with respect to the normal LN of the tread surface 20, respectively.

[0081] In Figure 5, the angle θt is the angle that the wall surface 30S of the crown circumferential main groove 30 makes with respect to the normal LN of the tread surface 20. In the present invention, the angle θt that the wall surface 30S of the crown circumferential main groove 30 makes with respect to the normal LN of the tread surface 20 is the inclination angle of the wall surface 30S.

[0082] As described above, the first edge 30Ea and the second edge 30Eb of the crown circumferential main groove 30 extend in a zigzag pattern in the circumferential direction, while the groove bottom 30T of this crown circumferential main groove 30 extends in a straight line in the circumferential direction. The inclination angle θt of the first wall surface 30Sa of the first crown circumferential main groove 32 and the second crown circumferential main groove 34 shows a maximum value θx at the first vertex Ta and a minimum value θn at the second vertex Tb. The inclination angle θt of the second wall surface 30Sb of the first crown circumferential main groove 32 and the second crown circumferential main groove 34 shows a minimum value θn at the first vertex Ta and a maximum value θx at the second vertex Tb. Each of the first wall surface 30Sa and the second wall surface 30Sb of the crown circumferential main groove 30 extends in the circumferential direction while changing the inclination angle θt between the maximum value θx and the minimum value θn.

[0083] In this invention, the position where the inclination angle θt of the wall surface 30S of the crown circumferential main groove 30 shows its maximum value θx is the maximum inclination position Tx, and the position where the inclination angle θt shows its minimum value θn is the minimum inclination position Tn. In other words, the maximum inclination position Tx of the wall surface 30S is defined as the position where the inclination angle θt of the wall surface 30S shows its maximum value θx, and the minimum inclination position Tn of the wall surface 30S is defined as the position where the inclination angle θt of the wall surface 30S shows its minimum value θn.

[0084] In the first wall surface 30Sa of the first crown circumferential main groove 32 and the second crown circumferential main groove 34, the first vertex Ta is at the position of maximum inclination Tx, and the second vertex Tb is at the position of minimum inclination Tn. In the second wall surface 30Sa, the first vertex Ta is at the position of minimum inclination Tn, and the second vertex Tb is at the position of maximum inclination Tx.

[0085] As described above, at the first edge 30Ea and the second edge 30Eb of the crown circumferential main groove 30, the first vertex Ta and the second vertex Tb are alternately arranged in the circumferential direction. At the first wall surface 30Sa and the second wall surface 30Sb, the maximum inclination position Tx, defined at the position where the inclination angle θt shows its maximum value θx, and the minimum inclination position Tn, defined at the position where the inclination angle θt shows its minimum value θn, are alternately arranged in the circumferential direction. The maximum inclination position Tx of the first wall surface 30Sa and the minimum inclination position Tn of the second wall surface 30Sb coincide in the circumferential direction. As a result, even though the crown circumferential main groove 30 is configured such that the inclination angle θt of the wall surface 30S of the crown circumferential main groove 30 changes in the circumferential direction, the rigidity of the crown land area 44 is well balanced in the circumferential direction. The crown land area 44 of this tire 2 can effectively contribute to achieving both traction performance and resistance to uneven wear. From this perspective, it is preferable that the first wall surface 30Sa and the second wall surface 30Sb of the crown circumferential main groove 30 each extend in the circumferential direction while changing the inclination angle θt between a maximum value θx and a minimum value θn, and that the maximum inclination position Tx and the minimum inclination position Tn are alternately arranged in the circumferential direction on each of the first wall surface 30Sa and the second wall surface 30Sb, and that the maximum inclination position Tx of the first wall surface 30Sa and the minimum inclination position Tn of the second wall surface 30Sb coincide in the circumferential direction.

[0086] In the present invention, the statement that the maximum inclination position Tx of the first wall surface 30Sa and the minimum inclination position Tn of the second wall surface 30Sb coincide in the circumferential direction means that the circumferential length from the maximum inclination position Tx to the minimum inclination position Tn closest to the maximum inclination position Tx is 2.0 mm or less.

[0087] In this tire 2, it is preferable that the difference (θx-θn) between the maximum value θx and the minimum value θn of the inclination angle θt is between 6 degrees and 18 degrees. This ensures that the rigidity of the crown land area 44 is well-balanced in the circumferential direction. The crown land area 44 of this tire 2 can effectively contribute to achieving both traction performance and resistance to uneven wear. From this viewpoint, it is more preferable that the difference (θx-θn) is between 8 degrees and 16 degrees, and even more preferable that it is between 10 degrees and 14 degrees.

[0088] In this tire 2, the maximum value θx of the inclination angle θt is preferably between 10 degrees and 20 degrees. This ensures that the rigidity of the crown land area 44 is well-balanced in the circumferential direction. The crown land area 44 of this tire 2 can effectively contribute to achieving both traction performance and resistance to uneven wear. From this viewpoint, the maximum value θx of the inclination angle θt is more preferably between 12 degrees and 18 degrees, and even more preferably between 13 degrees and 17 degrees.

[0089] In this tire 2, the minimum value θn of the inclination angle θt is preferably 2 degrees or more and less than 10 degrees. This ensures that the rigidity of the crown land area 44 is well balanced in the circumferential direction. The crown land area 44 of this tire 2 can effectively contribute to achieving both traction performance and resistance to uneven wear. From this viewpoint, the minimum value θn of the inclination angle θt is more preferably 3 degrees or more and 8 degrees or less, and even more preferably 4 degrees or more and 6 degrees or less.

[0090] As described above, the first crown circumferential main groove 32 and the second crown circumferential main groove 34 are located on either side of the crown land portion 44. The second edge 30Eb of the first crown circumferential main groove 32 and the first edge 30Ea of the second crown circumferential main groove 34 constitute the edge of the crown land portion 44 (hereinafter referred to as the crown edge 62). The second edge 30Eb of the first crown circumferential main groove 32 is the first crown edge 62a of the crown land portion 44, and the first edge 30Ea of the second crown circumferential main groove 34 is the second crown edge 62b of the crown land portion 44.

[0091] Figure 6 shows a portion of the central region shown in Figure 4. Figure 6 shows a portion of the crown land area 44.

[0092] The first crown edge 62a and the second crown edge 62b each comprise a plurality of edge units EU arranged in the circumferential direction. Each edge unit EU constitutes a part of the crown edge 62. The edge units EU extend circumferentially, starting at point TB at the position of maximum inclination Tx. One edge unit EU is connected to another edge unit EU located next to it at the starting point TB of the other edge unit EU.

[0093] The edge unit EU comprises four edge elements E. The edge elements E are edges that connect the position of maximum inclination Tx and the position of minimum inclination Tn, which is located next to this position of maximum inclination Tx, and form part of the crown edge 62. Specifically, the edge unit EU comprises a first edge element E1, a second edge element E2, a third edge element E3, and a fourth edge element E4. The first edge element E1, the second edge element E2, the third edge element E3, and the fourth edge element E4 are arranged in this order in the circumferential direction. As mentioned above, the first crown edge 62a and the second crown edge 62b each extend in a zigzag pattern. Each edge element E is inclined with respect to the circumferential direction.

[0094] In this invention, edge elements are defined by their inclination direction, inclination angle, and length. In this tire 2, the inclination direction, inclination angle, and length of the first edge element E1 of the first crown edge 62a are the same as those of the first edge element E1 of the second crown edge 62b. The inclination direction, inclination angle, and length of the second edge element E2 of the first crown edge 62a are the same as those of the second edge element E2 of the second crown edge 62b. The inclination direction, inclination angle, and length of the third edge element E3 of the first crown edge 62a are the same as those of the third edge element E3 of the second crown edge 62b. The inclination direction, inclination angle, and length of the fourth edge element E4 of the first crown edge 62a are the same as those of the fourth edge element E4 of the second crown edge 62b.

[0095] The first edge element E1 includes the starting point TB. The second edge element E2 is connected to the first edge element E1. The second edge element E2 and the first edge element E1 are connected at the minimum incline position Tn, which is adjacent to the maximum incline position Tx that forms the starting point TB. The third edge element E3 is connected to the second edge element E2. The third edge element E3 and the second edge element E2 are connected at the maximum incline position Tx, which is adjacent to the minimum incline position Tn that forms the boundary between the second edge element E2 and the first edge element E1. The fourth edge element E4 is connected to the third edge element E3. The fourth edge element E4 and the third edge element E3 are connected at the minimum incline position Tn, which is adjacent to the maximum incline position Tx that forms the boundary between the third edge element E3 and the second edge element E2. This fourth edge element E4 is connected to the next edge unit EU at the starting point TB of the next edge unit EU.

[0096] At the first crown edge 62a, the first edge element E1, the second edge element E2, the third edge element E3, and the fourth edge element E4 are arranged in this order from the first circumferential side (i.e., the CD1 side) to the second circumferential side (i.e., the CD2 side). At the second crown edge 62b, the first edge element E1, the second edge element E2, the third edge element E3, and the fourth edge element E4 are arranged in this order from the CD2 side to the CD1 side.

[0097] As shown in Figure 6, the edge unit EU of the first crown edge 62a and the edge unit EU of the first crown edge 62a that overlaps with this edge unit EU in the axial direction have the third edge element E3 of the first crown edge 62a and the third edge element E3 of the second crown edge 62b overlapping in the axial direction.

[0098] As mentioned above, the crown land portion 44 shown in Figure 6 is an assembly of multiple crown blocks 60 separated by open sipes 58 that traverse the crown land portion 44. The crown land portion 44 is provided with a plurality of open sipes 58 arranged in the circumferential direction. Each open sipe 58 is connected to an edge element E that constitutes the crown edge 62. The plurality of open sipes 58 that make up the crown land portion 44 of this tire 2 include three types of open sipes 58, specifically a first open sipe 58a, a second open sipe 58b, and a third open sipe 58c, each connected to a different edge element E.

[0099] The open sipes 58 arranged in the circumferential direction constitute the crown land portion 44. The arrangement of the open sipes 58 of this tire 2 comprises multiple sipe groups arranged in the circumferential direction. Each sipe group consists of a first open sipe 58a, a second open sipe 58b, and a third open sipe 58c. The arrangement of open sipes 58 that make up the crown land section 44 consists of a first open sipe 58a, a second open sipe 58b, and a third open sipe 58c, and comprises multiple groups of sipes arranged in the circumferential direction.

[0100] As shown in Figure 6, in the crown land portion 44 of this tire 2, the first open sipe 58a spans between the first edge element E1 of the first crown edge 62a and the second edge element E2 of the second crown edge 62b. The second open sipe 58b spans between the second edge element E2 of the first crown edge 62a and the first edge element E1 of the second crown edge 62b. The third open sipe 58c spans between the fourth edge element E4 of the first crown edge 62a and the fourth edge element E4 of the second crown edge 62b.

[0101] In this tire 2, the open sipe 58 spanning between the first crown edge 62a and the second crown edge 62b is configured in the crown land area 44 as described above. As a result, even though the crown circumferential main groove 30 is configured such that the inclination angle θt of the wall surface 30S of the crown circumferential main groove 30 changes in the circumferential direction, the rigidity of the crown land area 44 is well balanced in the circumferential direction. The crown land area 44 of this tire 2 can effectively contribute to achieving both traction performance and resistance to uneven wear. From this perspective, it is preferable that each of the first crown edge 62a and the second crown edge 62b comprises a plurality of edge units EU arranged in the circumferential direction, each edge unit EU comprising a first edge element E1, a second edge element E2, a third edge element E3, and a fourth edge element E4, and that a plurality of open sipes 58 spanning between the first crown edge 62a and the second crown edge 62b comprises a first open sipe 58a and a second open sipe 58b, with the first open sipe 58a bridging between the first edge element E1 of the first crown edge 62a and the second edge element E2 of the second crown edge 62b, and the second open sipe 58b bridging between the second edge element E2 of the first crown edge 62a and the first edge element E1 of the second crown edge 62b. In this case, from the viewpoint of enabling the crown landing portion 44 to more effectively contribute to achieving both traction performance and resistance to uneven wear, it is more preferable that the multiple open sipes 58 further include a third open sipe 58c, and that this third open sipe 58c bridges the gap between the fourth edge element E4 of the first crown edge 62a and the fourth edge element E4 of the second crown edge 62b.

[0102] In this tire 2, the edge element E that constitutes the crown edge 62 is inclined with respect to the circumferential direction. In Figure 6, angle θc is the angle that the edge element E makes with respect to the circumferential direction. In the present invention, the angle θc that the edge element E makes with respect to the circumferential direction is the inclination angle of the edge element E.

[0103] The crown edge 62 comprises a plurality of edge elements E arranged in the circumferential direction. In this tire 2, it is preferable that each edge element E has an inclination angle θc of 6 degrees or more and 13 degrees or less. In other words, it is preferable that the inclination angle θc of the edge elements E is 6 degrees or more and 13 degrees or less. By setting the inclination angle θc to 6 degrees or more, the edge element E can effectively function as an edge component that contributes to traction. The crown edge 62 can contribute to improved traction performance. From this viewpoint, an inclination angle θc of 8 degrees or more is more preferable. By setting the inclination angle θc to 13 degrees or less, the rigidity of the crown land portion 44 is effectively increased. This contributes to improved resistance to uneven wear of the tire 2. From this viewpoint, an inclination angle θc of 11 degrees or less is more preferable.

[0104] As shown in Figure 6, the crown land section 44 comprises a plurality of crown blocks 60 separated by open sipes 58. This crown land section 44 comprises three types of crown blocks 60, specifically a first crown block 60a, a second crown block 60b, and a third crown block 60c, each separated by different open sipes 58. In this tire 2, the crown block 60 between the first open sipe 58a and the second open sipe 58b is the first crown block 60a. The crown block 60 between the second open sipe 58b and the third open sipe 58c is the second crown block 60b. The crown block 60 between the third open sipe 58c and the next first open sipe 58a is the third crown block 60c.

[0105] The first crown block 60a, the second crown block 60b, and the third crown block 60c are arranged in the circumferential direction, forming a block group. The crown land section 44, which is an assembly of crown blocks 60, comprises multiple block groups arranged in the circumferential direction, and each block group comprises a first crown block 60a, a second crown block 60b, and a third crown block 60c, arranged in the circumferential direction.

[0106] As shown in Figure 6, each block group comprising a first crown block 60a, a second crown block 60b, and a third crown block 60c is provided with a shallow transverse groove 64 on both the first end TE1 side and the second end TE2 side of the tread surface 20. Two shallow transverse grooves 64 are provided in one block group. The shallow transverse groove 64 located on the first end TE1 side of the tread surface 20 is the first shallow transverse groove 64a, and the shallow transverse groove 64 located on the second end TE2 side of the tread surface 20 is the second shallow transverse groove 64b.

[0107] In this tire 2, the first lateral shallow groove 64a is provided on the third crown block 60c, and the second lateral shallow groove 64b is provided on the second crown block 60b. In the crown land portion 44, the first lateral shallow groove 64a and the second lateral shallow groove 64b are arranged alternately in the circumferential direction.

[0108] The first transverse shallow groove 64a spans the gap between the first open sipe 58a and the first edge element E1 of the first crown edge 62a. The second transverse shallow groove 64b spans the gap between the second open sipe 58b and the first edge element E1 of the second crown edge 62b.

[0109] The first lateral shallow groove 64a and the second lateral shallow groove 64b can function as edge components that contribute to the performance of traction. This tire 2 can improve traction performance. From this viewpoint, if the crown land portion 44 is an assembly of crown blocks 60, it is preferable that this assembly of crown blocks 60 comprises a first crown block 60a, a second crown block 60b, and a third crown block 60c arranged in the circumferential direction, wherein the third crown block 60c has a first lateral shallow groove 64a that spans between the first open sipe 58a and the first edge element E1 of the first crown edge 62a, and the second crown block 60b has a second lateral shallow groove 64b that spans between the second open sipe 58b and the first edge element E1 of the second crown edge 62b.

[0110] Figure 7 shows a cross-section of the transverse shallow groove 64. In Figure 7, the length indicated by the double arrow WGh is the groove width at the groove opening 64M of the transverse shallow groove 64. The length indicated by the double arrow DGh is the groove depth of the transverse shallow groove 64.

[0111] In this tire 2, from the viewpoint that the lateral shallow grooves 64 can contribute to improved traction performance while minimizing the impact on resistance to uneven wear, the ratio WGh / WGmc of the width WGh of the lateral shallow grooves 64 to the width WGmc of the crown circumferential main grooves 30 is preferably 0.08 or more and 0.25 or less. From a similar viewpoint, the ratio DGh / DGmc of the groove depth DGh of the lateral shallow grooves 64 to the groove depth DGmc of the crown circumferential main grooves 30 is preferably 0.05 or more and 0.18 or less. In the present invention, the width WGmc of the crown circumferential main grooves 30 is expressed as the axial distance from the maximum inclination position Tx of one wall surface 30S to the minimum inclination position Tn of the other wall surface 30S, as shown in Figure 4.

[0112] Figure 8 shows a portion of the crown land area 44 shown in Figure 6. The open sipe 58 crosses the crown land area 44. As shown in Figure 8, the open sipe 58 is inclined with respect to the axial direction as a whole. The first end of the open sipe 58 on the TE1 side (hereinafter referred to as the first end 58f) and its second end on the TE2 side (hereinafter referred to as the second end 58s) are positioned circumferentially apart. The first end 58f of the open sipe 58 is located on the second circumferential side, i.e., the CD2 side, and the second end 58s is located on the first circumferential side, i.e., the CD1 side. The open sipe 58 connects to the first crown circumferential main groove 32 at the first end 58f and to the second crown circumferential main groove 34 at the second end 58s.

[0113] The open sipe 58 comprises a first connecting portion 66, a second connecting portion 68, and an inclined portion 70. The first connecting portion 66 connects to the first crown circumferential main groove 32. The second connecting portion 68 connects to the second crown circumferential main groove 34. The portions where the first connecting portion 66 and the second connecting portion 68 intersect with the crown circumferential main groove 30 constitute the corners of the crown block 60.

[0114] The inclined section 70 spans between the first connecting section 66 and the second connecting section 68. The inclined section 70 comprises a first inclined section 72, a second inclined section 74, and an intermediate section 76. The first inclined section 72 is connected to the first connecting section 66. The second inclined section 74 is connected to the second connecting section 68. The intermediate section 76 spans between the first inclined section 72 and the second inclined section 74. The first inclined section 72 and the second inclined section 74 may be directly connected without the intermediate section 76.

[0115] In Figure 8, angle θr1 is the inclination angle of the first connecting portion 66. The inclination angle θr1 is represented by the angle that the first connecting portion 66 makes with respect to the axial direction. Angle θr2 is the inclination angle of the second connecting portion 68. The inclination angle θr2 is represented by the angle that the second connecting portion 68 makes with respect to the axial direction. Angle θk1 is the inclination angle of the first inclined portion 72. The inclination angle θk1 is represented by the angle that the first inclined portion 72 makes with respect to the axial direction. Angle θk2 is the inclination angle of the second inclined portion 74. The inclination angle θk2 is represented by the angle that the second inclined portion 74 makes with respect to the axial direction.

[0116] The first connecting portion 66 and the second connecting portion 68, as well as the first inclined portion 72 and the second inclined portion 74, all have the same inclination direction. The difference between the inclination angle θr1 of the first connecting portion 66 and the inclination angle θr2 of the second connecting portion 68 is within 1 degree. The first connecting portion 66 and the second connecting portion 68 have equivalent inclination angles θr. The inclination angles θr1 of the first connecting portion 66 and θr2 of the second connecting portion 68 may be different. The difference between the inclination angle θk1 of the first inclined section 72 and the inclination angle θk2 of the second inclined section 74 is within 1 degree. The first inclined section 72 and the second inclined section 74 have equivalent inclination angles θk. The inclination angles θk1 of the first inclined section 72 and the inclination angle θk2 of the second inclined section 74 may be different.

[0117] As shown in Figure 8, the inclination angle θr1 of the first connecting portion 66 is smaller than the inclination angle θk1 of the first inclined portion 72. The inclination angle θr2 of the second connecting portion 68 is smaller than the inclination angle θk2 of the second inclined portion 74. In this tire 2, the effect of the crown blocks 60, which are arranged in the circumferential direction, supporting each other is enhanced. When turning, a lateral force acts on the crown land portion 44, but this tire 2 can suppress the amount of movement of the crown blocks 60 when a lateral force acts on the crown land portion 44. The volume of the corners of the crown blocks 60 is secured by the fact that the first connecting portion 66 and the second connecting portion 68 each intersect with the crown circumferential main groove 30. In this tire 2, the occurrence of heel-and-toe wear is suppressed. This tire can improve resistance to uneven wear. From this viewpoint, it is preferable that the angle θr1 that the first connecting portion 66 makes with respect to the axial direction is smaller than the angle θk1 that the first inclined portion 72 makes with respect to the axial direction, and that the angle θr2 that the second connecting portion 68 makes with respect to the axial direction is smaller than the angle θk2 that the second inclined portion 74 makes with respect to the axial direction.

[0118] As described above, the inclined portion 70 further comprises an intermediate portion 76 that spans between the first inclined portion 72 and the second inclined portion 74. As shown in Figure 8, the intermediate portion 76 extends in the circumferential direction. In the present invention, the intermediate portion 76 extending in the circumferential direction means that the angle that the length direction of the intermediate portion 76 makes with respect to the circumferential direction is 5 degrees or less.

[0119] In this tire 2, the effect of the crown blocks 60 supporting each other is further enhanced. This tire 2 can effectively suppress the amount of movement of the crown blocks 60 when a lateral force is applied to the crown land portion 44. As a result, deformation of the crown land portion 44 is effectively suppressed. This tire 2 can improve resistance to uneven wear. During cornering, the intermediate portion 76 can function as an edge component that contributes to the performance of traction. This tire 2 can improve traction performance. From this viewpoint, it is preferable that the inclined portion 70 further comprises an intermediate portion 76 that bridges the first inclined portion 72 and the second inclined portion 74, and that the intermediate portion 76 extends in the circumferential direction.

[0120] Figure 9 shows a cross-section of the first inclined portion 72 of the open sipe 58. The cross-sectional shapes of the first connecting portion 66, the second connecting portion 68, and the second inclined portion 74 are the same as those of the first inclined portion 72. A description of the cross-sectional shapes of the first connecting portion 66, the second connecting portion 68, and the second inclined portion 74 is omitted.

[0121] As shown in Figure 8, the first inclined portion 72 extends straight in its longitudinal direction. In contrast, in the depth direction, the first inclined portion 72 extends in a zigzag pattern. The first connecting portion 66 and the second connecting portion 68, as well as the first inclined portion 72 and the second inclined portion 74 of the open sipe 58, each extend in a zigzag pattern in their depth direction. This enhances the effect of the crown blocks 60, which are aligned in the circumferential direction, supporting each other. During driving and braking, forces act on the crown land portion 44 in the longitudinal direction, i.e., the circumferential direction, but this tire 2 can suppress the amount of movement of the crown blocks 60 when circumferential forces act on the crown land portion 44. This suppresses the occurrence of heel-and-toe wear. This tire 2 can improve resistance to uneven wear. From this viewpoint, it is preferable that the first connecting portion 66 and the second connecting portion 68, as well as the first inclined portion 72 and the second inclined portion 74, each extend in a zigzag pattern in their depth direction.

[0122] Figure 10 shows a cross-section of the intermediate portion 76 of the open sipe 58. As shown in Figure 8, the intermediate portion 76 extends straight in its longitudinal direction. As shown in Figure 10, unlike the first connecting portion 66 and the second connecting portion 68, and the first inclined portion 72 and the second inclined portion 74, the intermediate portion 76 extends straight in its depth direction. This enhances the effect of the crown blocks 60, which are aligned in the circumferential direction, supporting each other and suppressing the occurrence of heel-and-toe wear. This tire can be made more resistant to uneven wear. From this viewpoint, if the first connecting portion 66 and the second connecting portion 68, and the first inclined portion 72 and the second inclined portion 74 each extend in a zigzag pattern in their depth direction, it is more preferable for the intermediate portion 76 to extend straight in its depth direction.

[0123] In Figure 9, the length indicated by the double-headed arrow DGs represents the groove depth of the open sipe 58. Considering the impact on traction performance and resistance to uneven wear, it is preferable that the groove depth DGs of the open sipe 58 be set to be slightly shallower than the groove depth DGmc of the crown circumferential main groove 30. Specifically, the ratio DGs / DGmc of the groove depth DGs of the open sipe 58 to the groove depth DGmc of the crown circumferential main groove 30 is preferably 0.70 or more and 0.98 or less. By setting the ratio DGs / DGmc to 0.70 or higher, the open sipe 58 can effectively function as an edge component that contributes to traction. From this perspective, a ratio DGs / DGmc of 0.85 or higher is more preferable. By setting the ratio DGs / DGmc to 0.98 or less, the influence of the open sipes 58 on rigidity is suppressed. Since the rigidity of the crown land area 44 is appropriately maintained, the occurrence of uneven wear is suppressed. From this viewpoint, a ratio DGs / DGmc of 0.95 or less is more preferable.

[0124] As mentioned above, this tire 2 is equipped with a reinforcing layer 14. The reinforcing layer 14 is covered by the tread 4. The reinforcing layer 14 is equipped with a belt 78 and a band 80. Figure 11 shows the structure of the reinforcing layer 14. The front side of the paper is radially outward, and the back side is radially inward.

[0125] The belt 78 comprises a plurality of belt plies 82 arranged radially. The belt plies 82 are elements corresponding to the layer 18 that constitutes the aforementioned reinforcing layer 14. The belt 78 of this tire 2 is provided with three belt plies 82. This belt 78 may be composed of four or more belt plies 82. This belt 78 may be composed of two belt plies 82. From the viewpoint of suppressing the influence on the mass of the tire 2, it is preferable that this belt 78 is composed of two to four belt plies 82.

[0126] The three belt plies 82 are, from radially inward, the first belt ply 82A, the second belt ply 82B, and the third belt ply 82C. The first belt ply 82A is the innermost belt ply 82 in the radial direction. The third belt ply 82C is the outermost belt ply 82 in the radial direction.

[0127] In Figure 11, the length indicated by the double arrow W1 is the axial width of the first belt ply 82A. The length indicated by the double arrow W2 is the axial width of the second belt ply 82B. The length indicated by the double arrow W3 is the axial width of the third belt ply 82C. The axial width of each belt ply 82 is expressed as the axial distance from one end of the belt ply 82 to the other end.

[0128] In this tire 2, the first belt ply 82A has the widest axial width W1. The second belt ply 82B has the next widest axial width W2 after the first belt ply 82A. The third belt ply 82C has the next widest axial width W3 after the second belt ply 82B. In this tire 2, the third belt ply 82C is the belt ply 82 that has the narrowest axial width W3 among the multiple belt plies 82 that make up the belt 78.

[0129] As shown in Figure 2, the ends of the first belt ply 82A and the second belt ply 82B are located in the axial direction between the outer edge 28Es of the shoulder circumferential main groove 28 and the edge TE of the tread surface 20. The end of the third belt ply 82C is located in the axial direction between the edge 30E of the crown circumferential main groove 30 on the edge TE side of the tread surface 20 and the inner edge 28Eu of the shoulder circumferential groove 28.

[0130] From the viewpoint of ensuring the rigidity of the tread portion T, it is preferable that the ratio of the axial width W1 of the first belt ply 82A to the width TW of the tread 4 (W1 / TW) is 0.85 or more and 0.95 or less. It is preferable that the ratio of the axial width W2 of the second belt ply 82B to the width TW of the tread 4 (W2 / TW) is 0.80 or more and 0.90 or less. It is preferable that the ratio of the axial width W3 of the third belt ply 82C to the width TW of the tread 4 (W3 / TW) is 0.25 or more and 0.35 or less.

[0131] As shown in Figure 11, each belt ply 82 constituting the belt 78 contains a number of parallel belt cords 84. The cord ends of each belt ply 82 are between 15 ends / 50 mm and 30 ends / 50 mm. In Figure 11, for ease of explanation, the belt cords 84 are represented by solid lines, but the belt cords 84 are covered with belt topping rubber 86. The belt cord 84 is a steel cord. A cord made of organic fibers may also be used as the belt cord 84. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0132] The belt cords 84 of each belt ply 82 are inclined with respect to the circumferential direction. The direction of inclination of the belt cords 84 included in the second belt ply 82B (hereinafter, second belt cord 84B) is opposite to the direction of inclination of the belt cords 84 included in the first belt ply 82A (hereinafter, first belt cord 84A). The direction of inclination of the belt cords 84 included in the third belt ply 82C (hereinafter, third belt cord 84C) is the same as the direction of inclination of the second belt cord 84B. The direction of inclination of the third belt cord 84C may be opposite to the direction of inclination of the second belt cord 84B.

[0133] In Figure 4, angle α is the angle that the first belt cord 84A makes with respect to the circumferential direction (hereinafter referred to as inclination angle α). Angle β is the angle that the second belt cord 84B makes with respect to the circumferential direction (hereinafter referred to as inclination angle β). Angle γ is the angle that the third belt cord 84C makes with respect to the circumferential direction (hereinafter referred to as inclination angle γ). In this invention, the inclination angle of the belt cord 84 is expressed as the angle that the belt cord 84 makes with respect to the equatorial plane.

[0134] The inclination angle α of the first belt cord 84A, the inclination angle β of the second belt cord 84B, and the inclination angle γ of the third belt cord 84C are preferably between 10 degrees and 60 degrees. From the viewpoint of effectively restraining the tread portion T and obtaining a stable contact surface with minimal shape change, the inclination angle α of the first belt cord 84A is more preferably between 10 degrees and 30 degrees, and even more preferably between 13 degrees and 27 degrees. The inclination angle β of the second belt cord 84B is more preferably between 10 degrees and 30 degrees, and even more preferably between 13 degrees and 27 degrees. The inclination angle γ of the third belt cord 84C is more preferably between 10 degrees and 30 degrees, and even more preferably between 13 degrees and 27 degrees.

[0135] In this invention, among the multiple belt plies that make up the belt, the belt ply having the widest axial width is called the reference ply, and the belt plies having the next widest axial width after the reference ply are called the sub-reference plies.

[0136] As mentioned above, in this tire 2, among the multiple belt plies 82 that make up the belt 78, the first belt ply 82A has the widest axial width W1, and the second belt ply 82B has the next widest axial width W2 after the first belt ply 82A. The first belt ply 82A is the reference ply BP, and the second belt ply 82B is the sub-reference ply SP. For example, if the belt ply 82 with the widest axial width among the multiple belt plies 82 is the second belt ply 82B, and the belt ply 82 with the next widest axial width after the second belt ply 82B is the first belt ply 82A, then the second belt ply 82B is the reference ply BP and the first belt ply 82A is the sub-reference ply SP.

[0137] In this invention, among the multiple belt plies that make up the belt, the belt ply having the narrowest axial width is called the minimum width ply. As mentioned above, in this tire 2, among the multiple belt plies 82 that make up the belt 78, the third belt ply 82C has the narrowest axial width W3. The third belt ply 82C is the ply with the smallest width NP.

[0138] The belt 78 of the reinforcing layer 14 of this tire 2 comprises multiple belt plies 82, each of which comprises a reference ply BP and a sub-reference ply SP. The reference ply BP is the first belt ply 82A, which has the widest axial width W1 among the multiple belt plies 82. The sub-reference ply SP is the second belt ply 82B, which has the second widest axial width W2 among the multiple belt plies 82, after the first belt ply 82A, which is the reference ply BP. As mentioned above, the first belt cord 84A and the second belt cord 84B are steel cords. The belt cords 84 included in the reference ply BP and the sub-reference ply SP are steel cords. And, as mentioned above, the direction of inclination of the first belt cord 84A is opposite to the direction of inclination of the second belt cord 84B. Therefore, the direction of inclination of the belt cord 84 included in the reference ply BP is opposite to the direction of inclination of the belt cord 84 included in the sub-reference ply SP.

[0139] As mentioned above, the reinforcing layer 14 of this tire 2 includes a band 80. The band 80 includes a full band 88. The full band 88 is an element corresponding to the layer 18 that constitutes the aforementioned reinforcing layer 14. The band 80 of this tire 2 is composed of one full band 88. Although not shown, this band 80 may be composed of two or more full bands 88. This band 80 may further include a pair of edge bands that are spaced apart in the axial direction with respect to the equatorial plane. From the viewpoint of suppressing the influence on the mass of the tire 2, it is preferable that the band 80 is composed of one full band 88.

[0140] In Figure 11, the length indicated by the double arrow WF is the axial width of the full band 88. The axial width WF of the full band 88 is represented by the axial distance from one end of the full band 88 to the other end. As mentioned above, the band 80 of this tire 2 is composed of one full band 88. The axial width WF of the full band 88 is also the axial width of the band 80. The axial width WF of the full band 88 is set to be at least 60% or more of the width TW of the tread 4.

[0141] As shown in Figure 2, the end of the full band 88 is located axially between the outer edge 28Es of the shoulder circumferential groove 28 and the end TE of the tread surface 20. The end of the full band 88 is located axially inward of the end of the second belt ply 82B. The full band 88 is narrower than the second belt ply 82B and wider than the third belt ply 82C.

[0142] As shown in Figure 11, the full band 88 includes a band cord 90. In Figure 11, for ease of explanation, the band cord 90 is represented by a solid line, but the band cord 90 is covered with band topping rubber 92. The band cord 90 is a steel cord.

[0143] Although not described in detail, the full band 88 is formed by spirally winding a band strip (not shown) containing a band code 90. The full band 88 constituting the band 80 includes the spirally wound band code 90. The full band 88 has a jointless structure.

[0144] Since the full band 88 is formed by spirally winding a band strip, the band cord 90 is slightly inclined with respect to the circumferential direction. The angle that the band cord 90 makes with respect to the circumferential direction is 5 degrees or less, preferably 2 degrees or less. The band cord 90 extends substantially in the circumferential direction.

[0145] As shown in Figure 2, the full band 88 is located radially between the first belt ply 82A and the second belt ply 82B. As previously mentioned, the first belt ply 82A is the reference ply BP, and the second belt ply 82B is the sub-reference ply SP. The full band 88 is located between the reference ply BP and the sub-reference ply SP. The end of the full band 88 is located axially outward from the shoulder circumferential main groove 28. The reinforcing layer 14 of this tire 2 has a configuration in which a full band 88 is sandwiched between a reference ply BP and a sub-reference ply SP, each having belt cords 84 with different inclination directions. Furthermore, the band cords 90 included in the full band 88 are steel cords, and the ends of the full band 88 are located axially outward from the shoulder circumferential main groove 28. This reinforcing layer 14 can contribute to suppressing radial growth of the tire 2. Local increases in contact pressure in the center region are suppressed. Center wear is suppressed in this tire 2. This tire 2 can improve resistance to uneven wear. From this viewpoint, it is preferable that the full band 88 is located between a reference ply BP and a sub-reference ply SP, each having belt cords 84 with different inclination directions, that the band cords 90 included in the full band 88 are steel cords, and that the ends of the full band 88 are located axially outward from the shoulder circumferential main groove 28.

[0146] The belt 78 comprises multiple belt plies 82, including a reference ply BP and a sub-reference ply SP, as well as a minimum width ply NP. The minimum width ply NP is the belt ply 82 located radially outward among the multiple belt plies 82. The multiple belt plies 82 include the minimum width ply NP, which is located radially outward and has the smallest axial width. The outer end of the minimum width ply NP is located axially outward from the crown circumferential main groove 30. In this tire 2, the increase in localized contact pressure in the center region is effectively suppressed. This tire can improve resistance to uneven wear. From this viewpoint, the multiple belt plies 82 include the minimum width ply NP, which is located radially outward and has the smallest axial width. It is preferable that the outer end of the minimum width ply NP is located axially outward from the crown circumferential main groove 30.

[0147] Figure 12 shows a portion of Figure 2. Figure 12 shows a portion of the Crown Land Area 44. In Figure 12, the solid line TT is a straight line passing through the groove bottoms 30T of the two crown circumferential main grooves 30 located next to the crown land portion 44. The position indicated by the symbol CR is the intersection of the extension of the wall surface 30S of the crown circumferential main groove 30 and the straight line TT. The length indicated by the double arrow WC is the axial distance from one intersection CR to the other intersection CR. The axial distance WC is the axial width at the base of the crown land portion 44.

[0148] In this tire 2, the ratio WC / WF of the axial width WC at the base of the crown land portion 44 to the axial width WF of the full band is preferably 0.15 or more and 0.30 or less. By setting the WC / WF ratio to 0.15 or higher, a crown land portion 44 with appropriate rigidity is formed, and the restraining force of the full band 88 is appropriately maintained. The occurrence of center wear and heel-and-toe wear is suppressed. This tire 2 can improve resistance to uneven wear. From this viewpoint, a WC / WF ratio of 0.21 or higher is more preferable. By setting the WC / WF ratio to 0.30 or less, the full band 88 can effectively perform its function. The full band can effectively contribute to suppressing the radial growth of the tire 2. In this case as well, the tire 2 can improve its resistance to uneven wear. From this viewpoint, a WC / WF ratio of 0.23 or less is more preferable.

[0149] The code ends of the full band 88 are preferably 20 ends / 50 mm or more. This allows the full band 88 to effectively contribute to suppressing changes in the shape of the tire 2 due to driving. The increase in contact pressure in the center region is suppressed. This tire 2 has good resistance to uneven wear. From this viewpoint, the code ends of the full band 88 are preferably 22 ends / 50 mm or more. From the viewpoint of suppressing the influence of the full band 88 on the mass of the tire 2, the code ends of the full band 88 are preferably 30 ends / 50 mm or less, and more preferably 28 ends / 50 mm or less.

[0150] As is clear from the above description, the present invention provides a heavy-duty tire that can achieve improved resistance to uneven wear while ensuring the necessary traction performance. [Industrial applicability]

[0151] The technologies described above, which achieve improved resistance to uneven wear while ensuring the necessary traction performance, can be applied to various types of tires.

[0152] [Note] The present invention includes the following embodiments.

[0153] [1] A heavy-duty tire comprising a tread having a tread surface that contacts the road surface, wherein the tread comprises a plurality of land portions separated by circumferential main grooves, the plurality of land portions include a crown land portion located on the equatorial plane, the crown land portion is a continuous body extending without interruption in the circumferential direction with closed sipes arranged in the circumferential direction, or a collection of a plurality of crown blocks separated by open sipes that traverse the crown land portion, the circumferential main grooves located on both sides of the crown land portion are a first crown circumferential main groove and a second crown circumferential main groove, each of the first crown circumferential main groove and the second crown circumferential main groove comprises a first edge and a second edge, a bottom surface including the groove bottom, a first wall surface bridging the space between the first edge and the bottom surface, and a second wall surface bridging the space between the second edge and the bottom surface, each of the first edge and the second edge extending in a zigzag pattern in the circumferential direction, and the groove bottom extending in a straight line in the circumferential direction. [2] The tread further comprises a reinforcing layer located radially inward, the reinforcing layer comprising a belt including a number of parallel belt cords and a band including a helically wound band cord, the belt comprising a plurality of belt plies arranged radially, the plurality of belt plies comprising a reference ply and a sub-reference ply, the reference ply being the belt ply having the widest axial width among the plurality of belt plies, the sub-reference ply being the belt ply having the second widest axial width among the plurality of belt plies, and the belts included in each of the reference ply and the sub-reference ply The heavy-duty tire according to [1] above, wherein the cord is a steel cord, the direction of inclination of the belt cord included in the reference ply is opposite to the direction of inclination of the belt cord included in the sub-reference ply, the band comprises a full band located between the reference ply and the sub-reference ply, the band cord included in the full band is a steel cord, the plurality of land portions include shoulder land portions located axially outward, the circumferential main grooves separating the shoulder land portions are shoulder circumferential main grooves, and the end of the full band is located axially outward of the shoulder circumferential main grooves. [3] The heavy-duty tire according to [2] above, wherein the plurality of belt plies include a minimum width ply located radially on the outermost side and having the minimum axial width, the outer end of the minimum width ply located axially outward from the crown circumferential main groove. [4] The heavy-duty tire described in [2] or [3] above, wherein the ratio of the axial width at the base of the crown to the axial width of the full band is 0.15 or more and 0.30 or less. [5] The heavy-duty tire according to any of [1] to [4] above, wherein each of the first wall surface and the second wall surface is inclined with respect to the normal of the tread surface, each of the first wall surface and the second wall surface extends in the circumferential direction while changing the inclination angle between a maximum value and a minimum value, and in each of the first wall surface and the second wall surface, a maximum inclination position defined at the position where the inclination angle shows the maximum value and a minimum inclination position defined at the position where the inclination angle shows the minimum value are alternately arranged in the circumferential direction, and the maximum inclination position of the first wall surface and the minimum inclination position of the second wall surface coincide in the circumferential direction. [6] The second edge of the first crown circumferential main groove is the first crown edge of the crown land portion, the first edge of the second crown circumferential main groove is the second crown edge of the crown land portion, and each of the first crown edge and the second crown edge comprises a plurality of edge units arranged in the circumferential direction starting from the position of maximum inclination, each edge unit comprising a first edge element including the starting point, a second edge element connected to the first edge element, a third edge element connected to the second edge element, and a fourth edge element connected to the third edge element, and in the first crown edge, the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the first circumferential side to the second circumferential side, and the second crown edge The heavy-duty tire as described in [5] above, wherein the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the second circumferential side toward the first circumferential side, the third edge element of the first crown edge and the third edge element of the second crown edge overlap in the axial direction, the crown land portion is an aggregate of the crown blocks, and the plurality of open sipes comprises a first open sipe and a second open sipe, the first open sipe spans between the first edge element of the first crown edge and the second edge element of the second crown edge, and the second open sipe spans between the second edge element of the first crown edge and the first edge element of the second crown edge. [7] The heavy-duty tire according to [6] above, wherein the assembly of crown blocks comprises a first crown block, a second crown block, and a third crown block arranged in the circumferential direction, the third crown block having a first transverse shallow groove spanning between the first open sipe and the first edge element of the first crown edge, and the second crown block having a second transverse shallow groove spanning between the second open sipe and the first edge element of the second crown edge. [8] The heavy-duty tire according to [6] or [7] above, wherein the plurality of open sipes further comprises a third open sipe, the third open sipe bridging between the fourth edge element of the first crown edge and the fourth edge element of the second crown edge. [9] The heavy-duty tire according to any one of [1] to [8] above, wherein the crown land portion is an assembly of the crown blocks, and the open sipe comprises a first connecting portion connected to the first crown circumferential main groove, a second connecting portion connected to the second crown circumferential main groove, and an inclined portion spanning between the first connecting portion and the second connecting portion, wherein the inclined portion comprises a first inclined portion connected to the first connecting portion and a second inclined portion connected to the second connecting portion, the angle made by the first connecting portion with respect to the axial direction is smaller than the angle made by the first inclined portion with respect to the axial direction, and the angle made by the second connecting portion with respect to the axial direction is smaller than the angle made by the second inclined portion with respect to the axial direction.

[10] The heavy-duty tire described in [9] above, wherein the first connecting portion and the second connecting portion, and the first inclined portion and the second inclined portion, each extend in a zigzag pattern in the depth direction.

[11] The heavy-duty tire according to [9] or

[10] above, wherein the inclined portion further comprises an intermediate portion bridging the first inclined portion and the second inclined portion, and the intermediate portion extends in the circumferential direction.

[12] The heavy-duty tire described in

[11] above, wherein the intermediate portion extends straight in the direction of its depth. [Explanation of Symbols]

[0154] 2... Tires 4. Tread 14. Reinforcement layer 20...Tread surface 26, 28, 30, 32, 34... Circumferential main groove 40, 42, 44, 46... Rikubu 58, 58a, 58b, 58c... Open sipes 60, 60a, 60b, 60c... Crown block 62, 62a, 62b... Crown edge 64, 64a, 64b...horizontal shallow groove 66...First connection part 68...Second connection part 70, 72, 74...Slope section 76...Middle section 78... belt 80 band 82, 82A, 82B, 82C... Belt ply 84, 84A, 84B, 84C... Belt cord 88... Full Band 90-band code

Claims

1. Equipped with a tread surface that contacts the road surface, The tread comprises a plurality of land portions separated by circumferential main grooves, Multiple of the aforementioned land areas include a crown land area located on the equatorial plane, The crown land portion is a continuous body extending circumferentially without interruption, comprising closed sipes arranged in the circumferential direction, or an aggregate of multiple crown blocks separated by open sipes traversing the crown land portion. The circumferential main grooves located on either side of the crown land portion are the first crown circumferential main groove and the second crown circumferential main groove, Each of the first crown circumferential main groove and the second crown circumferential main groove comprises a first edge and a second edge, a bottom surface including the groove bottom, a first wall surface spanning between the first edge and the bottom surface, and a second wall surface spanning between the second edge and the bottom surface. The first edge and the second edge each extend in a zigzag pattern in the circumferential direction, and the groove bottom extends in a straight line in the circumferential direction. Heavy-duty tires.

2. The tread further comprises a reinforcing layer located radially inward, The reinforcing layer comprises a belt including a number of parallel belt cords and a band including a spirally wound band cord. The belt comprises a plurality of belt plies arranged in the radial direction, Multiple belt plies comprise a reference ply and a sub-reference ply, The reference ply is a belt ply having the widest axial width among the plurality of belt plies. The sub-reference ply is a belt ply having the second widest axial width among the plurality of belt plies, after the reference ply. The belt cord included in each of the reference ply and the sub-reference ply is a steel cord. The direction of inclination of the belt cord included in the reference ply is opposite to the direction of inclination of the belt cord included in the sub-reference ply, The band comprises a full band located between the reference ply and the sub-reference ply, The band code included in the full band is a steel code. Multiple of the aforementioned land portions include a shoulder land portion located at the outermost axial position, The circumferential main groove separating the shoulder land portion is the shoulder circumferential main groove, The end of the full band is located axially outward of the shoulder circumferential main groove. A heavy-duty tire as described in claim 1.

3. Multiple belt plies include a minimum width ply located on the outermost radial side and having the minimum axial width, The outer end of the minimum width ply is located axially outward of the crown circumferential main groove. The heavy-duty tire according to claim 2.

4. The ratio of the axial width at the base of the crown land portion to the axial width of the full band is 0.15 or more and 0.30 or less. The heavy-duty tire according to claim 2.

5. The first wall surface and the second wall surface are inclined with respect to the normal of the tread surface, Each of the first and second wall surfaces extends in the circumferential direction while changing its inclination angle between a maximum value and a minimum value. In each of the first and second wall surfaces, a maximum inclination position, defined as the position where the inclination angle shows the maximum value, and a minimum inclination position, defined as the position where the inclination angle shows the minimum value, are alternately arranged in the circumferential direction. The position of maximum inclination of the first wall surface and the position of minimum inclination of the second wall surface coincide in the circumferential direction. A heavy-duty tire as described in claim 1.

6. The second edge of the first crown circumferential main groove is the first crown edge of the crown land portion. The first edge of the second crown circumferential main groove is the second crown edge of the crown land portion, Each of the first crown edge and the second crown edge comprises a plurality of edge units arranged in the circumferential direction, starting from the position of maximum inclination. Each edge unit comprises a first edge element including the starting point, a second edge element connected to the first edge element, a third edge element connected to the second edge element, and a fourth edge element connected to the third edge element. In the first crown edge, the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the first circumferential side toward the second circumferential side. In the second crown edge, the first edge element, the second edge element, the third edge element, and the fourth edge element are arranged in this order from the second circumferential side toward the first circumferential side. The third edge element of the first crown edge and the third edge element of the second crown edge overlap in the axial direction. The aforementioned crown land portion is an aggregate of the aforementioned crown blocks, The multiple open sipes include a first open sipe and a second open sipe, The first open sipe bridges the gap between the first edge element of the first crown edge and the second edge element of the second crown edge. The second open sipe spans between the second edge element of the first crown edge and the first edge element of the second crown edge. A heavy-duty tire as described in claim 5.

7. The assembly of crown blocks comprises a first crown block, a second crown block, and a third crown block arranged in the circumferential direction. The third crown block is provided with a first transverse shallow groove that spans between the first open sipe and the first edge element of the first crown edge, The second crown block is provided with a second transverse shallow groove that spans between the second open sipe and the first edge element of the second crown edge. A heavy-duty tire according to claim 6.

8. Multiple open sipes further comprise a third open sipe, The third open sipe spans between the fourth edge element of the first crown edge and the fourth edge element of the second crown edge. A heavy-duty tire according to claim 6 or 7.

9. The aforementioned crown land portion is an aggregate of the aforementioned crown blocks, The open sipe comprises a first connecting portion connected to the first crown circumferential main groove, a second connecting portion connected to the second crown circumferential main groove, and an inclined portion spanning between the first connecting portion and the second connecting portion. The inclined portion comprises a first inclined portion connected to the first connecting portion and a second inclined portion connected to the second connecting portion. The angle that the first connecting portion makes with respect to the axial direction is smaller than the angle that the first inclined portion makes with respect to the axial direction. The angle that the second connecting portion makes with respect to the axial direction is smaller than the angle that the second inclined portion makes with respect to the axial direction. A heavy-duty tire as described in claim 1.

10. Each of the first connecting portion and the second connecting portion, and the first inclined portion and the second inclined portion, extends in a zigzag pattern in the depth direction. The heavy-duty tire according to claim 9.

11. The inclined portion further comprises an intermediate portion that spans the first inclined portion and the second inclined portion, The aforementioned intermediate portion extends in the circumferential direction. The heavy-duty tire according to claim 9.

12. Each of the first connecting portion and the second connecting portion, and the first inclined portion and the second inclined portion, extends in a zigzag pattern in the depth direction. The aforementioned intermediate portion extends straight in the direction of its depth, The heavy-duty tire according to claim 11.

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