JP7234692B2 - Heavy duty pneumatic tire - Google Patents

Description

The present invention relates to heavy duty pneumatic tires.

Running may cause uneven wear on the tread of the tire. Uneven wear affects not only the appearance of the tire but also the contact pressure distribution of the tire, thus affecting the running performance and durability.

A large load acts on heavy-duty pneumatic tires mounted on vehicles such as trucks and buses. Therefore, uneven wear is likely to occur in this tire. Therefore, various studies have been made to suppress the occurrence of uneven wear (for example, Patent Document 1 below).

Japanese Patent Publication No. 2002-512575

A tread of a heavy-duty pneumatic tire is provided with a plurality of land portions arranged in parallel in the axial direction. In order to ensure wet performance, this tire is sometimes provided with shallow lateral grooves crossing the land portions. However, in this case, there is a concern that wear originating from the lateral grooves may occur. Therefore, there is a need to establish a technique capable of improving uneven wear resistance while ensuring wet performance without providing lateral grooves in land portions.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heavy-duty pneumatic tire that ensures wet performance and improves resistance to uneven wear.

A heavy-duty pneumatic tire according to the present invention has a tread that contacts a road surface. In this tire, a tread main body and a narrow land portion located axially outside of the tread main body are formed by forming circumferential narrow grooves in the end portions of the tread. At least five land portions arranged in parallel in the axial direction are formed by forming at least four circumferential grooves in the tread body, and among these land portions, the land portion located on or on the equatorial plane side. is the center land portion, the outermost land portion in the axial direction is the shoulder land portion, and the land portion located between the center land portion and the shoulder land portion is the middle land portion. The center land portion, the middle land portion, and the shoulder land portion are each provided with a large number of sipes that are spaced apart in the circumferential direction, and the sipes that are provided in the center land portion and the middle land portion are: The sipe provided in the shoulder land portion is a dead-end sipe having a terminal end within the land portion. A ratio of the actual width of the shoulder land portion to the actual width of the center land portion is 1.15 or more and 1.45 or less. A portion of the outer surface of the tread body other than the circumferential groove and the sipe is flat.

Preferably, in this heavy-duty pneumatic tire, of the at least four circumferential grooves formed on the tread body, the circumferential groove located on or on the equatorial plane side is the center circumferential groove, , the outermost circumferential groove is the shoulder circumferential groove. The actual width of the shoulder circumferential groove is narrower than the actual width of the center circumferential groove.

Preferably, in this heavy duty pneumatic tire, the ratio of the apparent width of the dead end sipe to the actual width of the shoulder land portion is 0.08 or more and 0.10 or less.

Preferably, in this heavy-duty pneumatic tire, the interval between the dead-end sipes in the shoulder land portion is 15 mm or more and 18 mm or less.

Preferably, in this heavy-duty pneumatic tire, the transverse sipe has a deep portion with a deep bottom and a shallow portion with a shallow bottom. A ratio of the depth of the transverse sipe in the deep portion to the depth of the transverse sipe in the shallow portion is 1.7 or more and 3.5 or less.

Preferably, in this heavy-duty pneumatic tire, on the outer surface of the middle land portion, a region axially inner than a center position of the actual width of the middle land portion is a middle land portion inner region, and the middle land portion traverses the middle land portion. The shape of the sipe includes an arc centered on the inner region of the middle land portion, and the ratio of the radius of the arc to the actual width of the middle land portion is 0.75 or more and 1.05 or less.

In the heavy-duty pneumatic tire of the present invention, it is possible to secure wet performance and improve resistance to uneven wear.

FIG. 1 is a cross-sectional view showing a portion of a heavy-duty pneumatic tire according to one embodiment of the present invention. 2 is a developed view showing the tread surface of the tire of FIG. 1. FIG. FIG. 3 is a cross-sectional view taken along line III--III in FIG. 4 is an enlarged cross-sectional view showing a portion of the tire of FIG. 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

In the present invention, a state in which the tire is mounted on a normal rim, the internal pressure of the tire is adjusted to the normal internal pressure, and no load is applied to the tire is referred to as a normal state. In the present invention, the dimensions and angles of each portion of the tire are measured under normal conditions unless otherwise specified.

Regular rim means a rim defined in the standard on which the tire relies. A "standard rim" in the JATMA standard, a "design rim" in the TRA standard, and a "measuring rim" in the ETRTO standard are regular rims.

The normal internal pressure means the internal pressure defined in the standard on which the tire relies. The "maximum air pressure" in JATMA standards, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standards, and the "INFLATION PRESSURE" in ETRTO standards are regular internal pressures.

Normal load means the load specified in the standard on which the tire relies. "Maximum load capacity" in the JATMA standard, "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

FIG. 1 shows part of a heavy-duty pneumatic tire 2 (hereinafter sometimes simply referred to as "tire 2") according to one embodiment of the present invention. This tire 2 is mounted on a vehicle such as a truck or a bus.

FIG. 1 shows part of a cross-section of this tire 2 along a plane containing the axis of rotation of the tire 2 . In FIG. 1 , the horizontal direction is the axial direction of the tire 2 and the vertical direction is the radial direction of the tire 2 . The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2 . In FIG. 1 , the dashed-dotted line CL represents the equatorial plane of the tire 2 . In FIG. 1, the tire 2 is mounted on a rim R (regular rim).

The tire 2 comprises a tread 4 , a pair of sidewalls 6 , a pair of beads 8 , a pair of chafers 10 , a carcass 12 , a belt 14 , a pair of cushion layers 16 , an innerliner 18 and a pair of steel reinforcing layers 20 .

The tread 4 contacts the road surface on its outer surface 22 . Reference character PC in FIG. 1 indicates an intersection point between the outer surface 22 of the tread 4 and the equatorial plane. This point of intersection PC is the equator of tire 2 .

The tread 4 includes a base portion 24 and a cap portion 26 located radially outside the base portion 24 . The base portion 24 is made of low-heat-generating crosslinked rubber in consideration of adhesiveness. The cap portion 26 is made of crosslinked rubber in consideration of abrasion resistance and grip performance. As shown in FIG. 1, cap portion 26 covers the entire base portion 24 .

In this tire 2 , circumferential narrow grooves 28 are cut in the end portion of the tread 4 . Thus, the tread 4 includes a tread body 30 and narrow land portions 32 . The narrow land portion 32 is positioned outside the tread body 30 . The circumferential narrow groove 28 extends continuously in the circumferential direction. In this tire 2 , the portion of the outer surface 22 of the tread 4 that corresponds to the outer surface of the tread body 30 is the tread surface 34 .

In this tire 2 , at least four circumferential grooves 36 are cut in the tread body 30 . Thereby, at least five land portions 38 are formed in the tread body 30 . In the tire 2 shown in FIG. 1, four circumferential grooves 36 are formed in the tread body 30, and five land portions 38 are formed in the tread body 30. As shown in FIG.

Each sidewall 6 continues to the edge of the tread 4 . Sidewalls 6 extend radially inward from the ends of tread 4 . The sidewall 6 is made of crosslinked rubber.

Each bead 8 is located radially inside the sidewall 6 . Bead 8 comprises core 40 and apex 42 .

Core 40 extends in the circumferential direction. The core 40 includes a wound steel wire 44 . Core 40 has a substantially hexagonal cross-sectional shape. In the cross section of this core 40 , the corner indicated by symbol PA is the inner end of the core 40 in the axial direction. The corners of the core 40 are specified based on the outline of the bundle of wires 44 included in the cross section of the core 40 .

The apex 42 is located radially outside the core 40 . The apex 42 includes an inner apex 42u and an outer apex 42s. Inner apex 42u extends radially outward from core 40 . The outer apex 42s is located radially outside the inner apex 42u. The inner apex 42u and the outer apex 42s are made of crosslinked rubber. The outer apex 42s is softer than the inner apex 42u.

Each chafer 10 is positioned axially outside the bead 8 . The chafer 10 is located radially inside the sidewall 6 . The chafer 10 contacts the rim R. The chafer 10 is made of crosslinked rubber.

A carcass 12 is located inside the tread 4 , sidewalls 6 and chafer 10 . Carcass 12 comprises at least one carcass ply 46 . The carcass 12 of this tire 2 consists of one carcass ply 46 . In this tire 2, the carcass ply 46 is folded back around each core 40 from the axial inner side to the outer side.

Although not shown, the carcass ply 46 includes a number of parallel carcass cords. These carcass cords are covered with a topping rubber. Each carcass cord intersects the equatorial plane. In this tire 2, the angle formed by the carcass cords with respect to the equatorial plane is 70° or more and 90° or less. This carcass 12 has a radial structure. In this tire 2, the material of the carcass cords is steel. A cord made of organic fibers may be used as the carcass cord.

The belt 14 is positioned radially inside the tread 4 . This belt 14 is located radially outside the carcass 12 .

The belt 14 is constructed from a plurality of radially laminated layers 48 . The belt 14 of this tire 2 is composed of four layers 48 . In this tire 2, the number of layers 48 forming the belt 14 is not particularly limited. The configuration of the belt 14 is appropriately determined in consideration of the specifications of the tire 2 .

Although not shown, each layer 48 includes a number of belt cords arranged side by side. These belt cords are covered with a topping rubber. The belt cord material is steel.

Although not shown, the belt cords are inclined with respect to the equatorial plane. In this tire 2 , the belt 14 is constructed such that the belt cords of one layer 48 intersect with the belt cords of the other layers 48 laminated on this one layer 48 .

In this tire 2, of the four layers 48, the second layer 48B located between the first layer 48A and the third layer 48C has the largest axial width. The radially outermost fourth layer 48D has the smallest axial width.

As shown in FIG. 1, the ends of the second layer 48B and the third layer 48C are each covered with a rubber layer 50. As shown in FIG. Two more rubber layers 50 are arranged between each end covered with the rubber layer 50 . In this tire 2, an edge member 52 composed of a total of four rubber layers 50 is sandwiched between the end of the second layer 48B and the end of the third layer 48C. As a result, the end portion of the third layer 48C is pushed up radially outward and separated from the end portion of the second layer 48B. This edge member 52 is made of crosslinked rubber.

Each cushioning layer 16 is located between this belt 14 and the carcass 12 at the end portion of the belt 14 , ie at the end of the belt 14 . The cushion layer 16 is made of crosslinked rubber.

An inner liner 18 is positioned inside the carcass 12 . The inner liner 18 constitutes the inner surface of the tire 2 . This inner liner 18 is made of a crosslinked rubber having excellent air shielding properties. The inner liner 18 retains the internal pressure of the tire 2 .

Each steel reinforcing layer 20 is located in the bead 8 portion. The steel reinforcement layer 20 is folded axially inwardly outwardly around the core 40 along the carcass plies 46 . In this tire 2 , at least part of the steel reinforcing layer 20 contacts the carcass ply 46 .

Although not shown, steel reinforcement layer 20 includes a large number of filler cords in parallel. In the steel reinforcing layer 20 the filler cords are covered with a topping rubber. The material of the filler cord is steel.

2 shows an exploded view of the outer surface 22 of the tread 4. FIG. In FIG. 2 , the horizontal direction is the axial direction of the tire 2 and the vertical direction is the circumferential direction of the tire 2 . The direction perpendicular to the paper surface of FIG. 2 is the radial direction of the tire 2 .

In FIG. 2, the symbol PE is the edge of the tread surface 34. As shown in FIG. If the end PE of the tread surface 34 of the tire 2 cannot be identified from the appearance, a normal load is applied to the tire 2 in a normal state, the camber angle is set to 0°, and the tread 4 is brought into contact with a flat surface. The axially outer edge of the resulting contact patch is defined as the edge PE of the tread surface 34 .

As described above, in this tire 2 , four circumferential grooves 36 are cut in the tread body 30 . These circumferential grooves 36 are arranged in parallel in the axial direction and extend continuously in the circumferential direction.

Of the four circumferential grooves 36, the inner circumferential groove 36 in the axial direction, that is, the circumferential groove 36 near the equator PC is the center circumferential groove 36c. The outermost circumferential groove 36 in the axial direction, that is, the circumferential groove 36 near the end PE of the tread surface 34 is the shoulder circumferential groove 36s. If the circumferential grooves 36 formed on the tread body 30 include a circumferential groove positioned on the equator PC, the circumferential groove positioned on the equator PC is defined as the center circumferential groove. Furthermore, when a circumferential groove exists between the center circumferential groove 36c and the shoulder circumferential groove 36s, this circumferential groove is defined as a middle circumferential groove.

In FIG. 2 , a double-headed arrow RT indicates the actual width of the tread body 30 . This actual width RT is represented by the distance from the edge PE of one tread surface 34 to the edge PE of the other tread surface 34 measured along the tread surface 34 . In FIG. 2, a double arrow GC indicates the actual width of the center circumferential groove 36c. A double arrow GS indicates the actual width of the shoulder circumferential groove 36s. Actual width GC and actual width GS are measured along a virtual tread surface obtained by assuming that tread surface 34 has no circumferential grooves 36 . In FIG. 1, a double arrow DC indicates the depth of the center circumferential groove 36c. A double arrow DS indicates the depth of the shoulder circumferential groove 36s. Depth DC and depth DS are represented by the distance from the virtual tread surface to the bottom.

In this tire 2, the actual width GC of the center circumferential groove 36c is preferably about 2 to 10% of the actual width RT of the tread body 30 from the viewpoint of contribution to drainage and traction performance. The depth DC of the center circumferential groove 36c is preferably 13-25 mm.

In this tire 2, the actual width GS of the shoulder circumferential groove 36s is preferably about 1 to 7% of the actual width RT of the tread body 30 from the viewpoint of contribution to drainage and traction performance. The depth DS of the shoulder circumferential groove 36s is preferably 13-25 mm.

As described above, in the tire 2 , the four circumferential grooves 36 are formed in the tread body 30 to form five land portions 38 in the tread body 30 . These land portions 38 are arranged in parallel in the axial direction and extend in the circumferential direction.

Of the five land portions 38, the land portion 38 located on the inner side in the axial direction, that is, the land portion 38 located on the equator PC is the center land portion 38c. The land portion 38 located on the outermost side in the axial direction, that is, the land portion 38 including the edge PE of the tread surface 34 is the shoulder land portion 38s. Further, the land portion 38 positioned between the center land portion 38c and the shoulder land portion 38s is the middle land portion 38m. Note that if the land portion located on the inner side in the axial direction of the land portions formed in the tread body 30 is not on the equator PC but is located near the equator PC, the land portion located near the equator PC may be located near the equator PC. A land portion located on the side of the equator PC is defined as a center land portion.

In FIG. 2, a double arrow RC indicates the actual width of the center land portion 38c. A double arrow RS indicates the actual width of the shoulder land portion 38s. A double arrow RM indicates the actual width of the middle land portion 38m. Actual width RC, actual width RS and actual width RM are measured along tread surface 34 .

In this tire 2, the actual width RC of the center land portion 38c is preferably about 10 to 18% of the actual width RT of the tread body 30 from the viewpoint of steering stability and wet performance. From the same point of view, the actual width RM of the middle land portion 38m is preferably about 10 to 18% of the actual width RT of the tread body 30.

In this tire 2, sipes 54 are provided in each of the center land portion 38c, the middle land portion 38m, and the shoulder land portion 38s. In this tire 2, as shown in FIG. 2, each land portion 38 is provided with a large number of sipes 54. As shown in FIG. These sipes 54 are circumferentially spaced apart.

The sipe 54 is a kind of groove like the circumferential groove 36 described above. In particular, grooves having a width of 1.5 mm or less, expressed as the distance between the walls of the groove, are referred to as sipes 54 . Note that the depth of the sipe 54 is appropriately set according to the specifications of the tire. The gap between the walls is not shown in FIG. 2 due to the narrow width of the sipe 54 .

As shown in FIG. 2, the sipe 54 provided in the center land portion 38c bridges between the center circumferential groove 36c on one side of the center land portion 38c and the center circumferential groove 36c on the other side. This sipe 54 is a transverse sipe 56 that traverses the land portion 38 . A large number of transverse sipes 56c are cut into the center land portion 38c, and these transverse sipes 56c are arranged at intervals in the circumferential direction. In this tire 2, a large number of blocks 58c are formed in the center land portion 38c by forming a large number of transverse sipes 56c in the center land portion 38c. The center land portion 38c of the tire 2 intermittently extends in the circumferential direction. In this center land portion 38c, the interval between the transverse sipes 56c is set within the range of 30 mm or more and 36 mm or less.

In this tire 2, the sipe 54 provided in the middle land portion 38m extends between the center circumferential groove 36c located axially inside the middle land portion 38m and the shoulder circumferential groove 36s located axially outside thereof. bridge over. This sipe 54 is also a transverse sipe 56 that traverses the land portion 38 . A large number of transverse sipes 56m are cut into the middle land portion 38m, and these transverse sipes 56m are arranged at intervals in the circumferential direction. In this tire 2, the middle land portion 38m is formed with a large number of blocks 58m by forming a large number of transverse sipes 56m. A middle land portion 38m of the tire 2 extends intermittently in the circumferential direction. In this middle land portion 38m, the interval between the transverse sipes 56m is set within the range of 30 mm or more and 36 mm or less.

In this tire 2, the sipe 54 provided in the shoulder land portion 38s communicates with the shoulder circumferential groove 36s. The sipe 54 extends outwardly from the shoulder circumferential groove 36s. As shown in FIG. 2, the termination 60 of this sipe 54 is located within this shoulder land portion 38s. This sipe 54 is a dead end sipe 62 having a termination 60 within land portion 38 . A large number of dead end sipes 62 are cut into the shoulder land portion 38s, and these dead end sipes 62 are arranged at intervals in the circumferential direction. In this tire 2, the shoulder land portion 38s intermittently extends in the circumferential direction in its inner portion, and extends continuously in the circumferential direction in the other portions.

In this tire 2, the ratio of the actual width RS of the shoulder land portion 38s to the actual width RC of the center land portion 38c is 1.15 or more and 1.45 or less.

Since the ratio of the actual width RS of the shoulder land portion 38s to the actual width RC of the center land portion 38c is 1.15 or more, the rigidity of the shoulder land portion 38s is sufficiently ensured. Since the movement of the shoulder land portion 38s from contact with the road surface to separation from the road surface is suppressed, in this tire 2, the shoulder land portion 38s is less likely to wear. In this tire 2, the occurrence of uneven wear (for example, uneven wear in which the entire shoulder land portion 38s is worn) is suppressed. From the viewpoint of improving uneven wear resistance, this ratio is more preferably 1.20 or more.

Since the ratio of the actual width RS of the shoulder land portion 38s to the actual width RC of the center land portion 38c is 1.45 or less, the circumferential length difference within the shoulder land portion 38s is appropriately maintained. Since the shoulder land portions 38s are less likely to slip on the road surface differently, in the tire 2, the shoulder land portions 38s are prevented from being worn down. Even in this case, the tire 2 is prevented from uneven wear. From the viewpoint of improving uneven wear resistance, this ratio is more preferably 1.40 or less.

As described above, in this tire 2, the narrow land portion 32 is provided on the axially outer side of the shoulder land portion 38s with the circumferential narrow groove 28 interposed therebetween.

In FIG. 2, a double arrow RL indicates the actual width of the narrow land portion 32. As shown in FIG. The actual width RL is represented by the distance from the edge TE of the outer surface 22 of the tread 4 to the inner edge of the narrow land portion 32, which is measured along the outer surface 22 of the tread 4. In this tire 2, the actual width RL of the narrow land portion 32 is usually set within a range of 3 mm or more and 7 mm or less.

In FIG. 1 , a double-headed arrow DT indicates the depth of the circumferential narrow groove 28 . In FIG. 2, a double-headed arrow GT indicates the actual width of the circumferential narrow groove 28. As shown in FIG. In this tire 2, the actual width GT of the circumferential narrow groove 28 is set to 30% or less of the actual width GS of the shoulder circumferential groove 36s. The depth DT of the circumferential narrow groove 28 is set in the range of 0.6 to 1.0 times the depth DS of the shoulder circumferential groove 36s.

When the tire 2 firmly steps on the road surface, the narrow land portion 32 contacts the shoulder land portion 38s, and the narrow land portion 32 supports the shoulder land portion 38s. In this tire 2, an excessive increase in ground contact pressure at the outer end portion of the shoulder land portion 38s, that is, at the end PE portion of the tread surface 34 is suppressed. This narrow land portion 32 contributes to the improvement of uneven wear resistance.

In this tire 2, a large number of transverse sipes 56 are cut in the center land portion 38c and the middle land portion 38m. These transverse sipes 56 function as edge components. These transverse sipes 56 impart flexibility to the respective land portions 38 and contribute to the discharge of water existing between the road surface and the tire 2 during running on a wet road surface. This tire 2 ensures good wet performance. In this tire 2, unlike conventional tires, it is not necessary to provide shallow grooves in the land portions 38 in order to ensure wet performance.

Grooves other than the circumferential grooves 36 and the sipes 54 are not cut in the tread body 30 of the tire 2 . In other words, the outer surface of the tread body 30, that is, the tread surface 34, is a flat land surface except for the circumferential grooves 36 and the sipes 54. As shown in FIG. In this tire 2, the outer surface of the tread body 30, more specifically, the center land portion 38c, the middle land portion 38m, and the shoulder land portion 38s, are not provided with shallow grooves that may cause uneven wear, for example. . In this tire 2, uneven wear resistance is improved. From this point of view, the tire 2 preferably has a land ratio of 80% or more. On the other hand, from the viewpoint of ensuring wet performance, the land ratio is preferably 83% or less.

The land ratio is expressed by the ratio of the area of the aforementioned land surface to the area of the entire tread surface 34 obtained assuming that the tread body 30 is not cut with grooves including the circumferential grooves 36 and the sipes 54 .

In this tire 2, a large number of blind end sipes 62 are provided in the axially inner portion of the shoulder land portion 38s. These dead end sipes 62 provide flexibility to this axially inner portion. Therefore, in this tire 2, the load acting on this axially inner portion is dispersed, and local increases in ground contact pressure in this axially inner portion are suppressed. In this tire 2, the occurrence of starting wear starting from the axially inner portion of the shoulder land portion 38s is suppressed. In this tire 2, uneven wear resistance is improved.

In this tire 2, the transverse sipes 56 cut into the center land portion 38c and the middle land portion 38m contribute to wet performance. The actual width RS of the shoulder land portion 38s is appropriately controlled, the narrow land portion 32 provided on the outside of the shoulder land portion 38s, and the dead-end sipe 62 carved on the inner portion of the shoulder land portion 38s in the axial direction. However, the excessive sliding of the shoulder land portion 38s on the road surface and the peculiar contact of the shoulder land portion 38s with the road surface are effectively suppressed. In the shoulder land portion 38s of the tire 2, wear such as uneven wear is less likely to occur. In this tire 2, the occurrence of uneven wear is effectively suppressed. In this tire 2, it is possible to secure wet performance and improve resistance to uneven wear.

In this tire 2, the actual width GS of the shoulder circumferential grooves 36s is preferably narrower than the actual width GC of the center circumferential grooves 36c. Thereby, the width RS of the shoulder land portion 38s is sufficiently secured. Since the shoulder land portion 38s has appropriate rigidity, the shoulder land portion 38s is less likely to be worn. In this tire 2, uneven wear (for example, uneven wear in which the entire shoulder land portion 38s is worn) is effectively suppressed. From this point of view, the ratio of the actual width GS of the shoulder circumferential grooves 36s to the actual width GC of the center circumferential grooves 36c is preferably 0.9 or less.

On the other hand, if the actual width GS of the shoulder circumferential groove 36s is excessively narrower than the actual width GC of the center circumferential groove 36c, the difference in circumferential length within the shoulder land portion 38s increases, and the road surface at each portion of the shoulder land portion 38s increases. difference in slip against In this case, there is concern that the shoulder land portion 38s may be worn down. Also, the excessively narrow shoulder circumferential groove 36s affects wet performance. From the viewpoint of securing wet performance and improving resistance to uneven wear, the ratio of the actual width GS of the shoulder circumferential grooves 36s to the actual width GC of the center circumferential grooves 36c is preferably 0.7 or more.

In this tire 2, the ratio of the actual width RM of the middle land portion 38m to the actual width RC of the center land portion 38c is preferably 0.95 or more and preferably 1.05 or less. By setting this ratio to 0.95 or more, the shoulder land portion 38s having an appropriate actual width RS is formed, so that the circumferential length difference in the shoulder land portion 38s is appropriately maintained. Since the shoulder land portions 38s are less likely to slip on the road surface differently, in the tire 2, the shoulder land portions 38s are prevented from being worn down. By setting this ratio to 1.05 or less, the actual width RS of the shoulder land portion 38s is sufficiently ensured, so that the shoulder land portion 38s has sufficient rigidity. Since the movement of the shoulder land portion 38s is suppressed, the shoulder land portion 38s of the tire 2 is less likely to wear. In this tire 2, the occurrence of uneven wear in which the entire shoulder land portion 38s is worn is effectively suppressed.

In FIG. 2, a double arrow C1 indicates the apparent width of the dead-end sipe 62. As shown in FIG. This apparent width C1 is obtained by measuring the axial length along the tread surface 34 from the starting end 64 to the terminal end 60 of the dead end sipe 62 .

In this tire 2, the ratio of the apparent width C1 of the dead-end sipe 62 to the actual width RS of the shoulder land portion 38s is preferably 0.08 or more, and preferably 0.10 or less. As a result, the dead-end sipe 62 effectively contributes to suppressing a local increase in ground contact pressure in the axially inner portion of the shoulder land portion 38s. Wear is suppressed. In this tire 2, uneven wear resistance is improved.

In FIG. 2, the double-headed arrow C2 is the spacing of the dead-end sipes 62. As shown in FIG. This spacing C2 is obtained by measuring the circumferential length along the tread surface 34 from the terminal end 60 of one dead end sipe 62 to the terminal end 60 of the other dead end sipe 62 .

In this tire 2, from the viewpoint of obtaining a uniform ground contact pressure distribution in the axially inner portion of the shoulder land portion 38s, it is preferable that the dead end sipes 62 are arranged at equal intervals in this axially inner portion. The interval C2 between the dead-end sipes 62 is preferably 15 mm or more, and preferably 18 mm or less.

In this tire 2, the depth of the dead end sipe 62 is shallower than the depth DS of the shoulder circumferential groove 36s. Specifically, the depth of the dead end sipe 62 is 95% or less of the depth DS of the shoulder circumferential groove 36s. From the viewpoint that the dead end sipe 62 effectively contributes to suppressing a local increase in ground contact pressure in the axially inner portion of the shoulder land portion 38s, the depth of the dead end sipe 62 is equal to the depth of the shoulder circumferential groove 36s. It is preferably 80% or more, more preferably 90% or more, of the DS.

FIG. 3 shows a cross section of a transverse sipe 56c provided in the center land portion 38c. As shown in FIG. 3 , in this tire 2 , the transverse sipe 56 includes a deep portion 66 with a deep bottom and a shallow portion 68 with a shallow bottom. The transverse sipe 56 has a deep portion 66 and a shallow portion 68 . Although not shown, the transverse sipe 56m provided in the middle land portion 38m also has the same structure as the transverse sipe 56c.

In FIG. 3 , double arrow WR is the width of transverse sipe 56 . The width WR of the transverse sipe 56 is represented by the length of the transverse sipe 56 measured on the outer surface of the land portion 38 . A dashed line ML is a normal line to the outer surface of the land portion 38 passing through the center of the width WR. The dashed-dotted line ML is the centerline of the transverse sipe 56 in the width direction. In this tire 2, the shape of the bottom of the transverse sipe 56 has a symmetrical shape with respect to this centerline ML.

In this tire 2, two shallow bottom portions 68 are provided at the bottom of the transverse sipe 56 across the center line ML. A deep portion 66 is formed between the two shallow portions 68 , that is, the central portion of the land portion 38 and the outer side of the shallow portion 68 , that is, the end portion of the land portion 38 .

In this tire 2 , the deep bottom portion 66 imparts flexibility to the land portion 38 and contributes to securing the volume of the transverse sipe 56 . This tire 2 exhibits good wet performance. In contrast, the shallow bottom portion 68 contributes to securing the rigidity of the land portion 38 . In this tire 2, since the movement of the land portion 38 from contact with the road surface to separation from the road surface is effectively suppressed, good uneven wear resistance is exhibited. In view of this, the bottom of transverse sipe 56 preferably comprises a deep portion 66 and a shallow portion 68 .

In FIG. 3, PB is the boundary between the deep bottom portion 66 and the shallow bottom portion 68 . This boundary PB is specified based on the intersection of the deep portion 66 and the inclined surface of the shallow portion 68 bridging the deep portion 66 and the top surface of the shallow portion 68 . A double arrow WD indicates the width of the deep bottom portion 66 provided in the central portion of the land portion 38 . The width WD of this deep bottom portion 66 is represented by the distance between boundaries PB located on both sides of this deep bottom portion 66 . A double arrow WS is the width of the shallow bottom portion 68 . The width WS of this shallow groove is represented by the distance between boundaries PB located on both sides of this shallow portion 68 .

As described above, in this tire 2 , the deep bottom portion 66 is provided in the central portion of the land portion 38 . The deep bottom portion 66 contributes to imparting flexibility to the land portion 38 and securing the volume of the transverse sipe 56 . This tire 2 exhibits good wet performance. From this point of view, the ratio of the width WD of the deep bottom portion 66 to the width WR of the transverse sipe 56 is preferably 0.1 or more. From the viewpoint of suppressing the influence of the deep bottom portion 66 on the rigidity, this ratio is preferably 0.3 or less.

In this tire 2 , the shallow bottom portion 68 contributes to securing the rigidity of the land portion 38 . In this tire 2, since the movement of the land portion 38 from contact with the road surface to separation from the road surface is effectively suppressed, good uneven wear resistance is exhibited. From this point of view, the ratio of the width WS of the shallow bottom portion 68 to the width WR of the transverse sipe 56 is preferably 0.1 or more. From the viewpoint of suppressing the influence of the shallow bottom portion 68 on the flexibility, this ratio is preferably 0.3 or less.

In this tire 2 , the deep bottom portion 66 is provided at the end portion of the land portion 38 other than the central portion of the land portion 38 . The deep bottom portion 66 also contributes to suppressing local increases in ground pressure at the ends of the land portion 38 . In this tire 2, uneven wear resistance is improved. From this point of view, a deep bottom portion 66 is preferably provided at the end portion of the land portion 38 .

In FIG. 3, double arrow d is the depth of transverse sipe 56 at deep bottom 66 . Double arrow d 1 is the depth of transverse sipe 56 at shallow bottom 68 .

In this tire 2, the ratio of the depth d of the transverse sipe 56 at the deep bottom portion 66 to the depth d1 of the transverse sipe 56 at the shallow bottom portion 68 is preferably 1.7 or more and preferably 3.5 or less. By setting this ratio to 1.7 or more, the volume of the shallow bottom portion 68 is ensured. The shallow bottom portion 68 contributes to the rigidity of the land portion 38 and suppresses movement of the land portion 38 . Good resistance to uneven wear is obtained in this tire 2 . From this point of view, this ratio is more preferably 2.0 or more. By setting this ratio to 3.5 or less, the transverse sipe 56 sufficiently functions as an edge component even in a state where wear progresses. Good wet performance is obtained with this tire. From this point of view, this ratio is more preferably 3.0 or less.

In this tire 2, from the viewpoint that the transverse sipe 56 effectively contributes to ensuring wet performance and improving uneven wear resistance, the depth d of the transverse sipe 56 in the deep bottom portion 66 is d is preferably 0.5 or more and preferably 0.7 or less.

In FIG. 2, a dashed line HL indicates the actual width center position of the middle land portion 38m. This actual width center position HL is specified based on the actual width RM. In this tire 2 , the middle land portion inner region 70 is the region axially inner than the actual width center position HL in the middle land portion 38 m. The area axially outside the actual width center position HL is the middle land portion outside area 72 .

In this tire 2, the shape of the transverse sipe 56 provided in the middle land portion 38m includes an arc having the center AC in the middle land portion inner region 70. As shown in FIG. In FIG. 2, arrow R is the radius of this arc.

In this tire 2, the shape of the transverse sipe 56m of the middle land portion 38m includes an arc having the center AC in the middle land portion inner region 70. Therefore, when the middle land portion 38m slides on the road surface, the middle land portion 38m does not move. The constituting blocks 58m effectively support each other. Since the tilting of the block 58m is suppressed, in the tire 2, heel-and-toe wear caused by the tilting of the block 58m is effectively suppressed. This transverse sipe 56m contributes to the improvement of uneven wear resistance. From this point of view, in this tire 2, the shape of the transverse sipe 56m of the middle land portion 38m preferably includes an arc having the center AC in the middle land portion inner region 70. As shown in FIG.

In this tire 2, the ratio of the aforementioned radius R to the actual width RM of the middle land portion 38m is preferably 0.75 or more, and preferably 1.05 or less. By setting this ratio to 0.75 or more, in the shape of the transverse sipe 56m, the degree of curvature of the portion represented by the arc (hereinafter also referred to as the convex portion) is properly maintained. The occurrence of wear originating from the part can be suppressed. From this point of view, this ratio is more preferably 0.80 or more. By setting this ratio to 1.05 or less, the convex portion contributes to preventing the block 58m from collapsing, so heel-and-toe wear is effectively suppressed. And since this transverse sipe 56m contributes to drainage, good wet performance is ensured. From this point of view, this ratio is more preferably 1.00 or less.

As described above, in this tire 2, the center land portion 38c and the middle land portion 38m each include a large number of blocks 58. As shown in FIG. Each of these blocks 58 has four corners 74 extending radially outward. In this tire 2 , at least two corners 74 s of the four corners 74 are diamond-cut from the viewpoint of preventing the block 58 from chipping. As shown in FIGS. 2 and 3, one corner 74s of opposing corners 74 of two adjacent blocks 58 is diamond-cut.

FIG. 4 shows part of the cross-section of this tire 2 shown in FIG. In FIG. 4 , the horizontal direction is the axial direction of the tire 2 and the vertical direction is the radial direction of the tire 2 . The direction perpendicular to the plane of FIG. 3 is the circumferential direction of the tire 2 .

The belt 14 of this tire 2 is composed of a first layer 48A, a second layer 48B, a third layer 48C and a fourth layer 48D. As shown in FIG. 4, the ends of the first layer 48A, the second layer 48B, the third layer 48C, and the fourth layer 48D, which constitute the belt 14, are located outside the shoulder circumferential groove 36s in the axial direction. To position.

In this tire 2, the layer 48 having the widest width in the axial direction among the multiple layers constituting the belt is also referred to as a first reference layer 76, and the layer 48 laminated on the outside of the first reference layer 76 is the first reference layer 76. Also referred to as double reference layer 78 . In this tire 2, the second layer 48B having the widest axial width is the first reference layer 76, and the third layer 48C laminated outside the second layer 48B in the radial direction is the second reference layer 78. is.

In FIG. 4( a ), an arrow WT indicates the axial width of the tread body 30 . This axial direction WT is represented by the axial distance from one end PE of the tread surface 34 to the other end PE. Arrow W 1 is the axial width of second layer 48 B as first reference layer 76 . This axial width W1 is represented by the axial distance from one end of the second layer 48B to the other end. Arrow W2 is the axial width of the third layer 48C as the second reference layer 78. FIG. This axial width W2 is represented by the axial distance from one end of the third layer 48C to the other end.

In this tire 2, the ratio of the axial width W1 of the first reference layer 76 to the axial width WT of the tread body 30 is preferably 0.85 or more and preferably 1.00 or less.

Since the ratio of the axial width W1 of the first reference layer 76 to the axial width WT of the tread body 30 is 0.85 or more, the belt 14 sufficiently restrains the tread body 30 as a whole. In this tire 2, the outer end portion of the shoulder land portion 38s, that is, the end PE portion of the tread surface 34, is suppressed from peculiar dimensional growth, so that the shoulder land portion 38s is prevented from being worn down. . In this tire 2, the occurrence of uneven wear is suppressed. From this point of view, this ratio is more preferably 0.90 or more, more preferably 0.92 or more.

Since the ratio of the axial width W1 of the first reference layer 76 to the axial width WT of the tread body 30 is 1.00 or less, the binding force of the belt 14 to the shoulder land portion 38s is appropriately maintained. With regard to the tire 2 circumference, the difference in circumference between the equatorial portion and the edge PE portion of the tread body 30 is properly maintained, so that the shoulder land portion 38s is prevented from slipping on the road surface. In this tire 2, the occurrence of uneven wear such as uneven wear is suppressed. From this point of view, this ratio is more preferably 0.97 or less, more preferably 0.95 or less.

In this tire 2, the ratio of the axial width W2 of the second reference layer 78 to the axial width WT of the tread body 30 is preferably 0.80 or more. This second reference layer 78 contributes to the restraint of the tread body 30 . In this tire 2, the belt 14 sufficiently restrains the entire tread body 30, so that the peculiar dimensional growth at the outer end portion of the shoulder land portion 38s is suppressed. In this tire 2, the occurrence of uneven wear such as shoulder drop wear is suppressed. From this point of view, this ratio is more preferably 0.85 or more, more preferably 0.90 or more.

In this tire 2 , the edge of the second reference layer 78 is located inside the edge of the first reference layer 76 in the axial direction. Since the edge of the second reference layer 78 and the edge of the first reference layer 76 do not coincide in the axial direction, the concentration of strain on the edge of the belt 14 is prevented. In this tire 2, damage such as looseness is less likely to occur at the end of the belt 14. As shown in FIG. Moreover, the restraining force of the belt 14 on the shoulder land portion 38s is appropriately maintained, and with respect to the circumference of the tire, the difference in circumference between the circumference of the equator portion and the circumference of the end PE of the tread body 30 is properly maintained. Since the shoulder land portion 38s is prevented from slipping on the road surface, the tire 2 is prevented from uneven wear such as uneven wear.

In FIG. 4( a ), the double arrow D is the axial distance from the edge of the second layer 48 B as the first reference layer 76 to the edge of the third layer 48 C as the second reference layer 78 .

In this tire 2, the axial distance D from the end of the first reference layer 76 to the end of the second reference layer 78 is preferably 3 mm or more, and preferably 8 mm or less.

By setting the distance D to 3 mm or more, the end of the second reference layer 78 and the end of the first reference layer 76 are arranged with an appropriate gap in the axial direction. Since the concentration of strain on the end portion of the belt 14 is suppressed, the tire 2 is prevented from being damaged at the end portion of the belt 14 such as looseness. From this point of view, the distance D is more preferably 4 mm or more.

By setting the distance D to 8 mm or less, the belt 14 sufficiently restrains the entire tread body 30 . Since the peculiar dimensional growth at the outer end portion of the shoulder land portion 38s is suppressed, in this tire 2, the shoulder land portion 38s is suppressed from being worn down. From this point of view, the distance D is more preferably 7 mm or less.

In FIG. 4A, the double arrow Y is the distance from the third layer 48C at the end of the third layer 48C as the second reference layer 78 to the second layer 48B as the first reference layer 76. In FIG. This distance Y is measured along the normal to the outer surface of the second layer 48B. As previously mentioned, the edge member 52 is located between the edge of the second layer 48B and the edge of the third layer 48C. This distance Y is also the thickness of this edge member 52 .

In this tire 2, the distance Y from the second reference layer 78 to the first reference layer 76 at the edge of the second reference layer 78 (or the thickness Y of the edge member 52 at the edge of the second reference layer 78) is 2.5 mm or more is preferable, and 4.0 mm or less is preferable.

By setting the distance Y to 2.5 mm or more, the end of the second reference layer 78 is arranged with a sufficient distance from the end of the first reference layer 76 . In this tire 2 , concentration of strain on the end portion of the belt 14 is sufficiently suppressed while securing the binding force of the belt 14 with respect to the tread body 30 . In this tire 2, the occurrence of uneven wear is suppressed while preventing the occurrence of damage at the ends of the belt 14. FIG. From this point of view, the distance Y is more preferably 3.0 mm or more.

By setting the distance Y to 4.0 mm or less, the end portion of the second reference layer 78 is arranged with an appropriate distance from the tread surface 34 . Since the increase in the contact pressure caused by the proximity of the end portion of the second reference layer 78 to the tread surface 34 is suppressed, the tire 2 prevents the shoulder land portion 38s from being worn such as stepped wear. be. Furthermore, since the end portion of the second reference layer 78 is prevented from sagging, movement of the end portion of the second reference layer 78 is suppressed. Since the heat generation associated with the movement of the end portion is suppressed, the occurrence of damage such as looseness is prevented. From this point of view, the distance Y is more preferably 3.5 mm or less.

As described above, the edge member 52 is positioned between the edge portion of the first reference layer 76 and the edge portion of the second reference layer 78, and the edge member 52 is formed by stacking four rubber layers. 50. In this tire 2, the control of the thickness Y of the edge member 52 is easy and accurate.

In FIG. 4B, reference P1 is the intersection of the tread surface 34 and a straight line passing through the end of the second layer 48B as the first reference layer 76 and extending in the radial direction. This intersection point P1 is the position on the tread surface 34 corresponding to the edge of the first reference layer 76 . Reference P2 is the intersection of the tread surface 34 and a straight line passing through the end of the third layer 48C as the second reference layer 78 and extending in the radial direction. This intersection point P2 is the position on the tread surface 34 corresponding to the edge of the second reference layer 78 .

4(b), the double arrow S1 is measured along the tread surface 34 from the inner end of the shoulder land portion 38s to the position P1 on the tread surface 34 corresponding to the end of the first reference layer 76. length. In the present invention, this length S1 is the actual width of the first reference layer 76 within the shoulder land portion 38s. The double-headed arrow S2 is the length measured along the tread surface 34 from the inner end of the shoulder land portion 38s to the position P2 on the tread surface 34 corresponding to the end of the second reference layer 78 . In the present invention, this length S2 is the actual width of the second reference layer 78 within the shoulder land portion 38s. A double-headed arrow RS in FIG. 4(b) indicates the actual width of the shoulder land portion 38s shown in FIG.

In this tire 2, the ratio of the actual width S1 of the first reference layer 76 in the shoulder land portion 38s to the actual width RS of the shoulder land portion 38s is preferably 0.8 or more. Thereby, in this tire 2 , the belt 14 sufficiently restrains the entire tread body 30 . In this tire 2, since the peculiar dimensional growth at the outer end portion of the shoulder land portion 38s is suppressed, the shoulder land portion 38s is prevented from being worn down. In this tire 2, the occurrence of uneven wear is suppressed. From this point of view, this ratio is more preferably 0.85 or more.

In this tire 2, the ratio of the actual width S1 of the first reference layer 76 in the shoulder land portion 38s to the actual width RS of the shoulder land portion 38s is preferably 1.00 or less. Thereby, in this tire 2, the binding force of the belt 14 to the shoulder land portion 38s is appropriately maintained. With regard to the tire 2 circumference, the difference in circumference between the equatorial portion and the edge PE portion of the tread body 30 is properly maintained, so that the shoulder land portion 38s is prevented from slipping on the road surface. In this tire 2, the occurrence of uneven wear such as uneven wear is suppressed.

In this tire 2, the ratio of the actual width S2 of the second reference layer 78 in the shoulder land portion 38s to the actual width RS of the shoulder land portion 38s is preferably 0.6 or more. Thus, in this tire 2 , the second reference layer 78 contributes to restraining the tread body 30 . In this tire 2, the belt 14 sufficiently restrains the entire tread body 30, so that the peculiar dimensional growth at the outer end portion of the shoulder land portion 38s is suppressed. In this tire 2, the occurrence of uneven wear such as shoulder drop wear is suppressed. From this point of view, this ratio is more preferably 0.70 or more.

In this tire 2, the ratio of the actual width S2 of the second reference layer 78 in the shoulder land portion 38s to the actual width RS of the shoulder land portion 38s is preferably 0.9 or less. Thereby, in this tire 2, the binding force of the belt 14 to the shoulder land portion 38s is appropriately maintained. With regard to the tire 2 circumference, the difference in circumference between the equatorial portion and the edge PE portion of the tread body 30 is properly maintained, so that the shoulder land portion 38s is prevented from slipping on the road surface. In this tire 2, the occurrence of uneven wear such as uneven wear is suppressed. From this point of view, this ratio is more preferably 0.85 or less.

In a conventional tire, the edge of the tread surface is usually axially outboard of the inner edge of the core. On the other hand, in this tire 2, as shown in FIG. End PE is located inside inner end PA of core 40 . In this tire 2, since the axial width WT of the tread body 30 is narrower than that of a conventional tire, there is a concern that the contact pressure increases at the edge PE of the tread surface 34, which promotes uneven wear.

However, in this tire 2, as described above, the narrow land portion 32 is provided on the axially outer side of the shoulder land portion 38s with the circumferential narrow groove 28 sandwiched therebetween, and the dead-end sipe 62 is cut in the axially inner portion thereof. By optimizing the ratio of the actual width RS of the shoulder land portion 38s to the actual width RC of the center land portion 38c, excessive slippage of the shoulder land portion 38s on the road surface and peculiar slippage of the shoulder land portion 38s on the road surface are prevented. contact is effectively prevented, and wear such as stepped wear is less likely to occur in the shoulder land portion 38s. In this tire 2, although the axial width WT of the tread body 30 is narrow, which is disadvantageous in terms of suppressing uneven wear, uneven wear resistance is improved. Moreover, the transverse sipes 56 carved in the center land portion 38c and the middle land portion 38m contribute to ensuring wet performance. In this tire 2, it is possible to secure wet performance and improve resistance to uneven wear.

As is clear from the above description, according to the present invention, a heavy-duty pneumatic tire 2 that ensures wet performance and improves resistance to uneven wear is obtained.

The embodiments disclosed this time are illustrative in all respects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configuration described in the claims.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited only to these Examples.

[Example 1]
A heavy duty pneumatic tire (tire size=295/80R22.5) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

In Example 1, the ratio (RS/RC) of the actual width RS of the shoulder land portion to the actual width RC of the center land portion was 1.40. The ratio (RM/RC) of the actual width RM of the middle land portion to the actual width RC of the center land portion was 1.00. In this Example 1, the actual width RC of the center land portion was set to 29.5 mm.

In Example 1, the ratio (GS/GC) of the actual width GS of the shoulder circumferential grooves to the actual width GC of the center circumferential grooves was 0.85. In Example 1, the actual width GC of the center circumferential groove was set to 9.6 mm. Since Example 1 is provided with thin land portions, this fact is represented by "Y" in the "thin land portion" column of the table.

In Example 1, the ratio (d/d1) of the depth d of the transverse sipe in the deep portion to the depth d1 of the transverse sipe in the shallow portion was 2.2. In this Example 1, the depth d of the transverse sipe at the deep bottom was 9.1 mm.

In Example 1, the ratio (C1/RS) of the apparent width C1 of the blind end sipe to the actual width RS of the shoulder land portion was 0.09. The dead-end sipe interval C2 was 15 mm.

In this Example 1, the shape of the transverse sipe of the middle land portion includes an arc centered in the middle land inner region, and the ratio of the radius R of this arc to the actual width RM of this middle land portion (R/RM). was 0.82.

In this Example 1, the ratio (W1/WT) of the axial width W1 of the first reference layer (that is, the second layer) to the axial width WT of the tread body was 0.96. The ratio of the axial width W2 of the second reference layer (that is, the third layer) to the axial width WT of the tread body (W2/WT) was 0.90. The axial width WT of the tread body was set at 103.45 mm.

In Example 1, the ratio (S1/RS) of the actual width S1 of the first reference layer in the shoulder land portion to the actual width RS of the shoulder land portion was 0.92. The ratio (S2/RS) of the actual width S2 of the second reference layer within the shoulder land portion to the actual width RS of the shoulder land portion was 0.72. The axial distance D from the edge of the first reference layer to the edge of the second reference layer was set to 5.0 mm. The distance Y from this second reference layer to the first reference layer at the edge of the second reference layer, ie the thickness Y of the edge member was set to 3 mm.

[Example 2]
Tires of Example 2 were obtained in the same manner as in Example 1, except that the radius R was changed so that the ratio (R/RM) was as shown in Table 1 below.

[Example 3]
Tires of Example 3 were prepared in the same manner as in Example 1 except that the depth d1 and radius R were varied so that the ratios (d/d1) and ratios (R/RM) were as shown in Table 1 below. Obtained.

[Example 4]
Depth d1, apparent width C1, distance C2 and radius R are varied to provide ratios (d/d1), ratios (C1/RS) and ratios (R/RM) as shown in Table 1 below, and A tire of Example 4 was obtained in the same manner as in Example 1, except that the distance C2 was set as shown in Table 1.

[Comparative Example 1]
The ratio (RS/RC), ratio (d/d1), ratio (C1/RS) and ratio (R/RM) are shown in Table 1 below by changing the actual width RS, depth d1, apparent width C1 and radius R. A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the distance C2 was set as shown in this Table 1, as shown.

[Comparative Examples 2 and 3]
By changing the actual width RS, the actual width GS, the depth d1, the apparent width C1 and the radius R, the ratio (RS/RC), the ratio (GS/GC), the ratio (d/d1), the ratio (C1/RS) and the ratio As in Example 1, except that (R/RM) was as shown in Table 1 below, and distance C2 was as shown in this Table 1, and no detail was provided, Tires of Comparative Examples 2 and 3 were obtained. It should be noted that the absence of the thin land portion is indicated by "N" in the "thin land portion" column of the table.

[Wet performance]
A prototype tire was mounted on a rim (size=22.5×9.00), and the inside of the tire was filled with air. The internal pressure of the tire was adjusted to 900 kPa. This tire was attached to the drive wheels of a truck (2-D vehicle). On an asphalt road surface with a water film of 2 mm, sudden braking was applied from a speed of 65 km/h, and the braking distance from locking of the tires to stopping was measured. The results are shown in Table 1 below. The larger the numerical value, the shorter the braking distance and the better the WET performance.

In this WET performance evaluation test, three types of tires with different wear conditions were prepared. Wear conditions were controlled by running the tires in a bench test machine. The initial stage of wear means that the depth of the circumferential groove has reached 85% of the initial depth. The middle stage of wear means that the depth of the circumferential groove reaches 50% of the initial depth. The final stage of wear means that the depth of the circumferential groove reaches 25% of the initial depth. In Table 1 below, the initial stage of wear is indicated as "early stage," the middle stage of wear as "middle stage," and the final stage of wear as "final stage."

[Uneven wear resistance]
The prototype tire was mounted on a rim (size=22.5×9.00) and filled with air to adjust the internal pressure of the tire to 900 kPa. This tire was attached to the front axle of an express bus, and the express bus was run for six months without rotating the tires. After running, the appearance of the tire was observed to confirm the occurrence of uneven wear (uneven wear or shoulder drop wear, track wear, and heel-and-toe wear). The results are shown in Table 1 below with the following ratings.
A: When the occurrence of uneven wear is suppressed B: When uneven wear occurs but no change in running performance is observed C: Uneven wear occurs and there is no problem with running When a degree of deterioration in performance is observed D: When it is determined that uneven wear has occurred and replacement is necessary

As shown in Table 1, it is confirmed that in the example, the wet performance is ensured and the occurrence of uneven wear is suppressed. In the example, the evaluation is higher than in the comparative example. From this evaluation result, the superiority of the present invention is clear.

The technique for suppressing the occurrence of uneven wear while ensuring the wet performance described above can be applied to various tires.

2 Tire 4 Tread 6 Sidewall 8 Bead 10 Chafer 12 Carcass 14 Belt 28 Circumferential groove 30 Tread Main body 32 Narrow land portion 34 Tread surface 36 Circumferential groove 36c Center circumferential groove 36s Shoulder circumferential groove 38 Land portion 38c Center land portion 38s shoulder land portion 38m middle land portion 54 sipes 56, 56c, 56m transverse sipes 60 ends of sipes 54 (dead end sipes 62) 62 dead end sipes 66 Deep bottom portion 68 Shallow bottom portion 70 Middle land portion inner region 74, 74s Corner portion 76 First reference layer 78 Second reference layer

Claims (5)

Equipped with a tread that contacts the road surface,
A tread main body and a narrow land portion positioned axially outside the tread main body are formed by forming circumferential narrow grooves in the end portion of the tread,
At least five land portions arranged in parallel in the axial direction are formed by forming at least four circumferential grooves in the tread body, and among these land portions, the land portion located on or on the equatorial plane side. is the center land portion, the land portion located on the outermost side in the axial direction is the shoulder land portion, and the land portion located between the center land portion and the shoulder land portion is the middle land portion,
A large number of sipes arranged at intervals in the circumferential direction are provided in each of the center land portion, the middle land portion, and the shoulder land portion,
the sipes provided in the center land portion and the middle land portion are transverse sipes that cross the land portions;
the sipe provided in the shoulder land portion is a dead-end sipe having a terminal end within the land portion;
a ratio of the actual width of the shoulder land portion to the actual width of the center land portion is 1.15 or more and 1.45 or less;
Of the outer surface of the tread body, portions other than the circumferential groove and the sipe are flat,
the transverse sipe has a deep deep portion and a shallow shallow portion;
A heavy-duty pneumatic tire, wherein a ratio of the depth of the transverse sipe in the deep portion to the depth of the transverse sipe in the shallow portion is 1.7 or more and 3.5 or less. Of the at least four circumferential grooves formed on the tread body, the circumferential groove located on or on the equatorial plane side is the center circumferential groove, and the outermost circumferential groove in the axial direction is the shoulder. is a circumferential groove,
The heavy duty pneumatic tire according to claim 1, wherein the actual width of the shoulder circumferential groove is narrower than the actual width of the center circumferential groove. The heavy duty pneumatic tire according to claim 1 or 2, wherein a ratio of the apparent width of the dead-end sipe to the actual width of the shoulder land portion is 0.08 or more and 0.10 or less. The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the interval between the dead-end sipes in the shoulder land portion is 15 mm or more and 18 mm or less. On the outer surface of the middle land portion,
an area axially inward of the center position of the actual width of the middle land portion is a middle land portion inner region;
The shape of the transverse sipe of the middle land portion includes an arc centered on the inner region of the middle land portion, and the ratio of the radius of the arc to the actual width of the middle land portion is 0.75 or more and 1.05 or less. The heavy duty pneumatic tire according to any one of claims 1 to 4 .

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