JP7251161B2 - Heavy duty pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heavy-duty pneumatic tire mounted on vehicles such as trucks and buses.

The tread of heavy duty pneumatic tires has a large volume. Since heat is less likely to be conducted to the tread, the heating state is controlled in tire manufacturing so that members such as sidewalls are not excessively vulcanized (for example, Patent Document 1 below).

JP-A-2000-326706

The present invention has been made in view of such circumstances, and by effectively heating the tread, it is possible to improve productivity and reduce rolling resistance while suppressing the influence on wear resistance. An object of the present invention is to provide a pneumatic tire for heavy loads.

A heavy-duty pneumatic tire according to an aspect of the present invention includes a pair of beads, a carcass that spans one bead and the other bead, a belt positioned radially outside the carcass, and a tread having an outer, road-contacting tread surface. At least three axially parallel circumferential grooves are carved into the tread to form at least four axially parallel land portions, and among these circumferential grooves, the outermost circumferential grooves are positioned axially. The shoulder circumferential groove is the circumferential groove along which the shoulder land is located, and the outermost land portion in the axial direction is the shoulder land portion. The shoulder land portion is provided with a hole extending from its outer surface toward the belt, and the distance from the bottom of the hole to the belt is 1 mm or more and 6 mm or less.

Preferably, in this heavy-duty pneumatic tire, the belt is composed of a plurality of layers laminated in the radial direction, and among these layers, the layer having the widest axial width is the first reference layer. A layer laminated outside one reference layer is a second reference layer. The bottom of the hole is located radially outside the portion of the first reference layer that protrudes from the second reference layer.

Preferably, in this heavy-duty pneumatic tire, the difference between the depth of the hole and the depth of the shoulder circumferential groove is -2 mm or more and 6 mm or less.

Preferably, in this heavy duty pneumatic tire, the holes intersect or contact a normal line of the carcass passing through the edge of the tread surface.

Preferably, in this heavy-duty pneumatic tire, the tread includes a base portion and a cap portion laminated radially outwardly of the base portion and having an outer surface forming the tread surface. The bottom of the hole is located radially outside the boundary between the base portion and the cap portion, and the boundary is recessed inward at the bottom portion of the hole.

Preferably, in this heavy duty pneumatic tire, the mouth width of the hole is wider than the bottom width of the hole.

Preferably, in this heavy-duty pneumatic tire, the opening of the hole is tapered. At the mouth of the hole, the angle formed by the wall of the hole with respect to the imaginary tread surface obtained assuming that the hole is absent is 80° or less.

Preferably, in this heavy-duty pneumatic tire, the center of the mouth of the hole is located outside the center of the shoulder land portion in the axial direction.

In the heavy duty pneumatic tire of the present invention, the tread is effectively heated. In this tire, improvement in productivity and reduction in rolling resistance are achieved while suppressing influence on wear resistance.

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. 3 is an enlarged cross-sectional view showing a portion of the tire of FIG. 1. FIG. FIG. 4 is a diagram for explaining the state of manufacture of the tire of FIG. 5 is an enlarged cross-sectional view showing a hole provided in the shoulder land 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.

As used herein, the term "regular rim" means a rim defined in the standards on which tires rely. 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.

As used herein, the normal internal pressure means the internal pressure defined in the standards 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.

As used herein, the normal load means the load defined 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, for example, on heavy-duty vehicles such as trucks and buses.

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).

In FIG. 1, the axially extending solid line BBL is the bead baseline. This bead baseline is a line that defines the rim diameter of the rim R (see JATMA, etc.).

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 at its outer surface 22 , ie the tread surface 22 . Reference PC is the intersection of the tread plane 22 and the equatorial plane. This intersection point PC is the equator of the 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. The cap portion 26 covers the entire base portion 24 .

In this tire 2 , at least three circumferential grooves 28 are cut into the tread 4 . Thereby, at least four land portions 30 are formed on the tread 4 . In this tire 2 , at least four circumferential grooves 28 may be cut in the tread 4 , thereby forming at least five land portions 30 in this tread 4 . In the tire 2 shown in FIG. 1, four circumferential grooves 28 are formed in the tread 4, and five land portions 30 are formed in the tread 4. 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 32 and apex 34 .

The core 32 extends circumferentially. Core 32 comprises a wound steel wire.

Apex 34 is positioned radially outward of core 32 . Apex 34 extends radially outward from core 32 . The apex 34 includes an inner apex 34u and an outer apex 34s. The inner apex 34u and the outer apex 34s are made of crosslinked rubber. The outer apex 34s is softer than the inner apex 34u.

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 . The carcass 12 spans the one bead 8 and the other bead 8 . Carcass 12 comprises at least one carcass ply 36 . The carcass 12 of this tire 2 consists of one carcass ply 36 .

In this tire 2 , the carcass ply 36 is folded back around each bead 8 from the inner side to the outer side in the axial direction. The carcass ply 36 includes a ply body 36a extending from one bead 8 toward the other bead 8, and a pair of ply bodies 36a connected to the ply body 36a and folded back around each core 32 from the inner side to the outer side in the axial direction. and a folded portion 36b.

Although not shown, the carcass ply 36 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 of a plurality of radially laminated layers 38 . The belt 14 of this tire 2 is composed of four layers 38 . In this tire 2, the number of layers 38 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 38 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. The belt cord of this tire 2 is a steel cord.

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 38 intersect with the belt cords of the other layer 38 laminated on this one layer 38 .

In this tire 2, of the four layers 38, the second layer 38B positioned between the first layer 38A and the third layer 38C has the largest axial width. The radially outermost fourth layer 38D has the smallest axial width.

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. Axially, the steel reinforcement layer 20 lies outside the bead 8 . A steel reinforcement layer 20 is located between the carcass ply 36 and the chafer 10 . The inner end of the steel reinforcement layer 20 is located radially inside the core 32 . The outer edge of the steel reinforcing layer 20 is located radially between the edge of the turn-up portion 36b and the core 32. As shown in FIG.

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.

FIG. 2 shows an exploded view of the tread surface 22. As shown in 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 22 . In the tire 2, if the end PE of the tread surface 22 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 the plane. The axially outer edge of the resulting contact patch is defined as the edge PE of the tread surface 22 .

As described above, in this tire 2 , four circumferential grooves 28 are cut in the tread 4 . These circumferential grooves 28 are arranged in parallel in the axial direction and extend continuously in the circumferential direction.

Of the four circumferential grooves 28, the inner circumferential groove 28c in the axial direction, that is, the circumferential groove 28c near the equator PC is the center circumferential groove. The outermost circumferential groove 28s in the axial direction, that is, the circumferential groove 28s near the end PE of the tread surface 22 is the shoulder circumferential groove. When the circumferential grooves 28 formed on the tread 4 include the circumferential grooves 28 positioned on the equator PC, the circumferential grooves 28 positioned on the equator PC are the center circumferential grooves. Furthermore, when the circumferential groove 28 exists between the center circumferential groove 28c and the shoulder circumferential groove 28s, this circumferential groove 28 is a middle circumferential groove.

Each center circumferential groove 28c continuously extends in a zigzag shape in the circumferential direction. The center circumferential groove 28c has, in the axial direction, a zigzag apex 40a protruding on one side and a zigzag apex 40b protruding on the other side. In the center circumferential groove 28c, the zigzag peaks 40a and the zigzag peaks 40b are alternately arranged in the circumferential direction. In this tire 2, the center circumferential groove 28c may be a groove extending straight in the circumferential direction.

Each shoulder circumferential groove 28s continuously extends in a zigzag shape in the circumferential direction. The shoulder circumferential groove 28s has, in the axial direction, a zigzag apex 40c protruding on one side and a zigzag apex 40d protruding on the other side. In the shoulder circumferential groove 28s, the zigzag peaks 40c and the zigzag peaks 40d are alternately arranged in the circumferential direction. In this tire 2, the shoulder circumferential groove 28s may be formed by a groove extending straight in the circumferential direction.

As shown in FIG. 2, in this tire 2, the zigzag apex 40b of the center circumferential groove 28c (hereinafter also referred to as the first center circumferential groove 28c1) located on the left side of the paper surface and the zigzag apex 40b on the right side of the paper surface. The zigzag apex 40a of the center circumferential groove 28c (hereinafter also referred to as the second center circumferential groove 28c2) is bridged by the axial groove 42c (hereinafter also referred to as the center axial groove 42c). Passed.

As shown in FIG. 2, in this tire 2, a zigzag apex 40d of a shoulder circumferential groove 28s (hereinafter also referred to as a first shoulder circumferential groove 28s1) located on the left side of the paper surface and a first center circumferential groove 28s1. The zigzag vertex 40a of the direction groove 28c1 is bridged by an axial groove 42m (hereinafter also referred to as a first middle axial groove 42m1). The first shoulder circumferential groove 28s1 communicates with an axial groove 42s extending inward from the edge PE of the tread surface 22 (hereinafter also referred to as first shoulder axial groove 42s1) at its zigzag apex 40c.

As shown in FIG. 2, in this tire 2, a zigzag apex 40c of a shoulder circumferential groove 28s (hereinafter also referred to as a second shoulder circumferential groove 28s2) located on the right side of the paper surface and a second center circumferential groove 28s2. The zigzag vertex 40b of the direction groove 28c2 is bridged by an axial groove 42m (hereinafter also referred to as a second middle axial groove 42m2). The second shoulder circumferential groove 28s2 communicates with an axial groove 42s extending inwardly from the edge PE of the tread surface 22 (hereinafter also referred to as a second shoulder axial groove 42s2) at its zigzag apex 40d.

In FIG. 2 , a double arrow RT indicates the actual width of the tread surface 22 . This actual width RT is represented by the distance from the edge PE of one tread surface 22 to the edge PE of the other tread surface 22 . This actual width RT is measured along the tread surface 22 .

In FIG. 2, a double arrow GC indicates the actual width of the center circumferential groove 28c. A double arrow GS indicates the actual width of the shoulder circumferential groove 28s. The actual width GC is represented by the shortest distance from one edge to the other edge of the center circumferential groove 28c. The actual width GS is represented by the shortest distance from one edge to the other edge of the shoulder circumferential groove 28s.

In this tire 2, the actual width GC of the center circumferential groove 28c is preferably 1 to 10% of the actual width RT of the tread surface 22 from the viewpoint of contribution to drainage performance and traction performance. The depth of this center circumferential groove 28c is preferably 13 to 25 mm.

In this tire 2, the actual width GS of the shoulder circumferential grooves 28s is preferably 1 to 10% of the actual width RT of the tread surface 22 from the viewpoint of contribution to drainage and traction performance. The depth of the shoulder circumferential groove 28s is preferably 13 to 25 mm.

In this tire 2, the actual width GS of the shoulder circumferential groove 28s is wider than the actual width GC of the center circumferential groove 28c. The actual width GS of the shoulder circumferential groove 28s may be narrower than the actual width GC of the center circumferential groove 28c, or the actual width GS of the shoulder circumferential groove 28s is equivalent to the actual width GC of the center circumferential groove 28c. may be The actual width of the circumferential groove 28 is appropriately determined according to the specifications of the tire 2 .

In this tire 2, the depth of the shoulder circumferential grooves 28s is the same as the depth of the center circumferential grooves 28c. The shoulder circumferential groove 28s may be deeper than the center circumferential groove 28c, or the shoulder circumferential groove 28s may be shallower than the center circumferential groove 28c. The depth of the circumferential groove 28 is appropriately determined according to the specifications of the tire 2 .

In this tire 2 , the actual width of the axial grooves 42 is appropriately set within a range of 1 to 10% of the actual width RT of the tread surface 22 . The depth of this axial groove 42 is appropriately set within a range of 13 to 25 mm.

In this tire 2 , the actual width of the axial grooves 42 may be equal to the actual width of the circumferential grooves 28 , or the actual width of the axial grooves 42 may be narrower than the actual width of the circumferential grooves 28 . , the actual width of the axial groove 42 may be wider than the actual width of the circumferential groove 28 . The actual width of the axial groove 42 is appropriately determined according to the specifications of the tire 2 .

In this tire 2, the depth of the axial grooves 42 may be equal to the depth of the circumferential grooves 28, the depth of the axial grooves 42 may be deeper than the circumferential grooves 28, or the depth of the axial grooves 42 may be deeper than the circumferential grooves 28. The direction grooves 42 may be shallower than the circumferential grooves 28 . The depth of the axial groove 42 is appropriately determined according to the specifications of the tire 2 .

As described above, in the tire 2 , the tread 4 is formed with the five land portions 30 by forming the four circumferential grooves 28 in the tread 4 . These land portions 30 are arranged in parallel in the axial direction and extend in the circumferential direction.

Of the five land portions 30, the land portion 30c located on the inner side in the axial direction, that is, the land portion 30c located on the equator PC is the center land portion. The land portion 30s located on the outermost side in the axial direction, that is, the land portion 30s including the edge PE of the tread surface 22 is the shoulder land portion. Further, a land portion 30m located between the center land portion 30c and the shoulder land portion 30s is a middle land portion. If the land portion 30 positioned axially inward among the land portions 30 of the tread 4 is positioned near the equator PC instead of on the equator PC, the land portion 30 is positioned near the equator PC. The land portion 30, that is, the land portion 30 located on the equator PC side is the center land portion.

A large number of center axial grooves 42c are formed in the center land portion 30c. Thereby, a large number of center blocks 44c arranged at a predetermined pitch in the circumferential direction are formed. The center land portion 30c of the tire 2 includes a large number of center blocks 44c arranged at a predetermined pitch in the circumferential direction. In addition, this center land portion 30c may be configured by a convex portion that is continuous in the circumferential direction. In this case, the above-described center axial groove 42c is not cut in the center land portion 30c.

A large number of the middle axial grooves 42m are formed in each middle land portion 30m. As a result, a large number of middle blocks 44m arranged at a predetermined pitch in the circumferential direction are formed. A middle land portion 30m of the tire 2 includes a large number of middle blocks 44m arranged at a predetermined pitch in the circumferential direction. It should be noted that the middle land portion 30m may be configured by a convex portion continuous in the circumferential direction. In this case, the middle axial groove 42m is not cut in the middle land portion 30m.

A large number of shoulder axial grooves 42s are formed in each of the shoulder land portions 30s. As a result, a large number of shoulder blocks 44s are arranged circumferentially at a predetermined pitch. A shoulder land portion 30s of the tire 2 includes a large number of shoulder blocks 44s arranged at a predetermined pitch in the circumferential direction. It should be noted that the shoulder land portion 30s may be configured by a convex portion that is continuous in the circumferential direction. In this case, the aforementioned shoulder axial groove 42s is not formed in the shoulder land portion 30s.

FIG. 3 shows a cross-section of this tire 2 along line III--III in FIG. The cross section of the tire 2 shown in FIG. 3 is part of the cross section of the tire 2 shown in FIG. In FIG. 3 , 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 .

In the present invention, the thickness of the tire 2 is measured along the normal to the outer surface of the carcass 12 (specifically, the ply body 36a) in the cross-section of the tire 2 shown in FIG. 1 or 3.

In FIG. 3, the solid line EL is the normal line of the outer surface of the carcass 12 (specifically, the ply body 36a) passing through the edge PE of the tread surface 22. As shown in FIG. Double arrow TE is the thickness of this tire 2 measured along the normal EL of this carcass 12 .

This tire 2 has a maximum thickness TE at the position of the normal EL. In other words, the thickness of the tire 2 measured along the normal of the carcass 12 exhibits a maximum at the normal EL of the carcass 12 passing through the edge PE of the tread surface 22 . As shown in FIG. 3, the normal EL crosses the shoulder land portion 30s of the tire 2. As shown in FIG. In this tire 2, the portion of the shoulder land portion 30s has the maximum thickness TE.

In this tire 2, a hole 46 is provided in the shoulder land portion 30s. 1 or 3, this hole 46 extends toward the belt 14 from the outer surface of the shoulder land portion 30s, specifically the shoulder block 44s, which forms part of the tread surface 22. As shown in FIG. In the radial direction, holes 46 overlap belt 14 . A bottom 48 of this hole 46 is located radially outside the belt 14 . In FIG. 2, symbol HC is the center of the mouth 50 of the hole 46 provided in the shoulder land portion 30s. In FIG. 2, the III-III line is a straight line passing through the center HC of the hole 46 and extending in the axial direction.

As described above, the tread 4 of this tire 2 has the base portion 24 and the cap portion 26 . The tread 4 includes a boundary 52 between the base portion 24 and the cap portion 26 . As shown in FIG. 3, in the tire 2, the bottom 48 of the hole 46 is located radially outside the boundary 52 in the shoulder land portion 30s, and the boundary 52 is located at the bottom 48 of the hole 46. , concave inward.

In FIG. 3, double arrow E is the distance from bottom 48 of hole 46 to belt 14 . This distance E is represented by the shortest distance from the bottom 48 of the hole 46 to the outer surface of the belt 14 overlapping the bottom 48 of this hole 46 in the radial direction. In this tire 2, the distance E is set within a range of 1 mm or more and 6 mm or less.

This tire 2 is manufactured as follows. In manufacturing the tire 2, first, members such as the tread 4 and the sidewall 6 are combined in a molding machine (not shown) to prepare an uncrosslinked tire, that is, a green tire.

In manufacturing the tire 2, the raw tire 2r is vulcanized and molded in the vulcanizer 54 shown in FIG. This vulcanizer 54 comprises a mold 56 and a bladder 58 .

Mold 56 has a cavity surface 60 on its inner surface. This cavity surface 60 abuts on the outer surface of the raw tire 2r and shapes the outer surface of the tire 2. As shown in FIG.

The mold 56 shown in FIG. 4 is a split mold. The mold 56 includes a tread ring 62, a pair of side plates 64, and a pair of bead rings 66 as constituent members. In this mold 56, the aforementioned cavity surface 60 is formed by combining these constituent members. The mold 56 of FIG. 4 is in a state in which these components are combined, in other words, in a closed state.

In this mold 56 a tread ring 62 forms part of the tread 4 of tire 2 . This tread ring 62 is made up of a number of segments 68 . It should be noted that the side plate 64 forms part of the sidewall 6 of the tire 2 and the bead ring 66 forms part of the bead 8 of the tire 2 .

Bladder 58 is located inside mold 56 . Bladder 58 is made of crosslinked rubber. The interior of this bladder 58 is filled with a heating medium such as steam. This inflates the bladder 58 . Bladder 58, shown in FIG. 4, is in an inflated state filled with a heating medium. This bladder 58 abuts against the inner surface of the raw tire 2r and shapes the inner surface of the tire 2. As shown in FIG. In addition, in manufacturing the tire 2, a metallic rigid core may be used in place of the bladder 58. As shown in FIG. The rigid core has a toroidal outer surface. This outer surface approximates the shape of the inner surface of the tire 2 when it is filled with air and the internal pressure is maintained at 5% of the normal internal pressure.

In manufacturing the tire 2, the raw tire 2r is put into a mold 56 set at a predetermined temperature. After injection, the mold 56 is closed. The bladder 58 expanded by filling the heating medium presses the raw tire 2r against the cavity surface 60 from the inside. The green tire 2r is pressurized and heated in the mold 56 for a predetermined time. As a result, the rubber composition of the raw tire 2r is crosslinked, and the tire 2 is obtained.

As is apparent from FIG. 1, the tread 4 portion of the tire 2 has a larger volume than the sidewall 6 portion. As described above, in the tire 2, of the tread 4, the portion of the shoulder land portion 30s has the maximum thickness TE. That is, in this tire 2, the shoulder land portion 30s has a particularly large volume.

In manufacturing the tire 2, heat is transferred to the raw tire 2r by the mold 56 and the bladder 58. As shown in FIG. The raw tire 2r has both a portion with a small volume and a portion with a large volume. Heat is easily transferred to a portion having a small volume, but heat is difficult to be transferred to a portion having a large volume.

If the time for pressurizing and heating the raw tire 2r, that is, the vulcanization time, is set based on the portion where heat is easily conducted, there is concern that the progress of vulcanization will be insufficient in the portion where heat is difficult to be conducted. On the other hand, if the vulcanization time is set based on the portion to which heat is difficult to conduct, there is a concern that vulcanization proceeds excessively in the portion to which heat is easy to conduct.

By the way, in consideration of the environment, regulations regarding fuel consumption of vehicles have been introduced. In order to clear this regulation, tires are strongly required to reduce rolling resistance.

If the vulcanization temperature is set to a temperature lower than normal, it is possible to suppress the progress of excessive vulcanization and reduce the rolling resistance. However, in this case, since a long vulcanization time is set, there is concern that tire productivity may be reduced.

By adopting low-heat-generating rubber, it is possible to reduce rolling resistance while maintaining productivity. However, in this case, there is concern that the wear resistance of the tire will be lower than that of a tire that uses rubber that does not take heat build-up into consideration.

As described above, in this tire 2, the holes 46 are provided in the shoulder land portions 30s. For this reason, as shown in FIG. 4, the mold 56 of the tire 2 is provided with projections 70 for forming the holes 46 . Of the components of mold 56 , segment 68 forms part of tread 4 of tire 2 . For this reason, the protrusion 70 is provided on the portion of the segment 68 that forms the shoulder land portion 30s.

In the manufacture of this tire 2, when the raw tire 2r is pressurized and heated in the mold 56, the portion corresponding to the shoulder land portion 30s (hereinafter referred to as the shoulder land portion corresponding portion 72) of the raw tire 2r is formed with the above-described projections. 70 is inserted.

As described above, in this tire 2, the distance E from the bottom 48 of the hole 46 formed by the protrusion 70 to the belt 14 is 6 mm or less.

In manufacturing the tire 2, the projection 70 is inserted to a deep position of the portion 72 corresponding to the shoulder land portion. As a result, the portion corresponding to the shoulder land portion 72 is also heated from the inside. Therefore, the time required for the portion 72 corresponding to the shoulder land portion to be optimally vulcanized can be shortened. Particularly, in manufacturing the tire 2 , the tip of the protrusion 70 is brought close to the belt 14 . Since the belt 14 contains steel cords, this proximity heats the green tire 2r more effectively. Production of this tire 2 can shorten the vulcanization time. This tire 2 contributes to an improvement in productivity.

With this tire 2, productivity can be improved. From this point of view, the distance E from the bottom 48 of the hole 46 to the belt 14 is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

As described above, in this tire 2, the distance E from the bottom 48 of the hole 46 formed by the projection 70 to the belt 14 is 1 mm or more.

In this tire 2, a sufficient thickness of the rubber positioned between the bottom 48 of the hole 46 and the belt 14 is ensured. In this tire 2, the impact on durability due to the proximity of the bottoms 48 of the holes 46 to the belt 14 is considered. This tire 2 maintains good durability.

In this tire 2, the time required to form the portion of the shoulder land portion 30s is shortened. This shortening of the time limits the progress of excessive vulcanization in areas with small volumes where heat is easily conducted. Since an increase in loss tangent (tan δ) due to overvulcanization is suppressed, the tire 2 can reduce rolling resistance without relying on rubber with low heat build-up and poor wear resistance.

In this tire 2, improvement in productivity and reduction in rolling resistance are achieved while suppressing influence on wear resistance.

As described above, in this tire 2, the belt 14 is composed of the radially laminated first layer 38A, second layer 38B, third layer 38C and fourth layer 38D.

In the present invention, among the plurality of layers 38 constituting the belt 14, the layer 38 having the widest width in the axial direction is the first reference layer 74, and the layer 38 laminated outside the first reference layer 74 is the second reference layer 74. Two reference layers 76 . In this tire 2, the second layer 38B having the widest axial width among the first layer 38A, the second layer 38B, the third layer 38C, and the fourth layer 38D is the first reference layer 74. , the third layer 38C laminated on the outside of the second layer 38B is the second reference layer 76. As shown in FIG.

In this tire 2 , the edge of the first reference layer 74 is located outside the edge of the second reference layer 76 in the axial direction. Accordingly, a portion of first reference layer 74 protrudes from second reference layer 76 .

In this tire 2, of the first reference layer 74, a portion 78 that protrudes from the second reference layer 76 (hereinafter sometimes referred to as a protruding portion of the first reference layer 74) is located deep in the shoulder land portion 30s. placed in As shown in FIG. 3 , in this tire 2 , the bottom 48 of the hole 46 is located radially outside the projecting portion 78 of this first reference layer 74 .

In manufacturing the tire 2, the projection 70 is inserted to a deep position of the portion 72 corresponding to the shoulder land portion. As a result, the portion corresponding to the shoulder land portion 72 is also heated from the inside. Therefore, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanized state is effectively shortened. From this point of view, the belt 14 is composed of a plurality of layers 38 laminated in the radial direction, and the layer 38 having the widest axial width among these layers 38 is designated as the first reference layer 74. When the layer 38 laminated on the outside of 74 is the second reference layer 76 , the bottom 48 of the hole 46 is radially outside the portion 78 of the first reference layer 74 that protrudes from the second reference layer 76 . preferably located.

As shown in FIG. 3, the protruding portion 78 of the first reference layer 74 intersects the aforementioned normal EL. In this tire 2, the bottom 48 of the hole 46 is located radially outside the protruding portion 78 that intersects with the normal EL, and the aforementioned distance E is set to 6 mm or less. In manufacturing the tire 2, the portion 72 corresponding to the shoulder land portion is effectively heated from the inside, so the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanized state is effectively shortened. . From this point of view, in this tire 2 , the projecting portion 78 of the first reference layer 74 on which the bottom 48 of the hole 46 is arranged radially outward intersects the normal EL of the outer surface of the carcass 12 passing through the edge PE of the tread surface 22 . This first reference layer 74 is preferably constructed so as to.

As shown in FIG. 3, in this tire 2, the hole 46 intersects or touches the normal EL. Thereby, in manufacturing the tire 2 , the tip of the projection 70 is effectively arranged at a deep position of the portion 72 corresponding to the shoulder land portion. Since the portion 72 corresponding to the shoulder land portion is effectively heated from the inside, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanization state is effectively shortened. From this point of view, in this tire 2 , the holes 46 provided in the shoulder land portions 30 s preferably cross or contact the normal line EL of the outer surface of the carcass 12 passing through the edge PE of the tread surface 22 . In FIG. 3 this hole 46 intersects the normal EL at its bottom 48 .

In FIG. 3, the double arrow TB is the distance from the boundary 52 at the edge of the second reference layer 76 to the first reference layer 74 .

As described above, in this tire 2, in the shoulder land portion 30s, the bottom 48 of the hole 46 is located radially outside the boundary 52 between the base portion 24 and the cap portion 26, and this boundary 52 is located on the shoulder land portion 30s. At the bottom 48 portion of 46, it is recessed inward. In other words, the distance E from the bottom 48 of the hole 46 to the belt 14 , ie, the distance E from the bottom 48 of the hole 46 to the first reference layer 74 , is the distance E from the boundary 52 at the edge of the second reference layer 76 to the second reference layer 74 . It is shorter than the distance TB to one reference layer 74 .

In this tire 2, the bottom 48 of the hole 46 is located deep in the shoulder land portion 30s. Therefore, in manufacturing the tire 2, the tip of the protrusion 70 is effectively arranged at a deep position of the portion 72 corresponding to the shoulder land portion. Since the portion 72 corresponding to the shoulder land portion is effectively heated from the inside, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanization state is effectively shortened. From this point of view, in this tire 2, the distance E from the bottom 48 of the hole 46 to the belt 14 is from the boundary 52 between the base portion 24 and the cap portion 26 at the end of the second reference layer 76 to the first reference layer 74. is preferably shorter than the distance TB.

In FIG. 3, arrow WT indicates the axial width of tread 4 . This axial direction WT is represented by the axial distance from one end PE of the tread surface 22 to the other end PE. Arrow W 1 is the axial width of second layer 38 B as first reference layer 74 . This axial width W1 is represented by the axial distance from one end of the second layer 38B to the other end. Arrow W2 is the axial width of the third layer 38C as the second reference layer 76. FIG. This axial width W2 is represented by the axial distance from one end of the third layer 38C to the other end. In FIG. 3 , the double arrow HWT represents half the axial width WT of the tread 4 .

In this tire 2, the ratio of the axial width W1 of the first reference layer 74 to the axial width WT of the tread 4 is preferably 0.85 or more and 0.95 or less.

By setting the ratio of the axial width W1 of the first reference layer 74 to the axial width WT of the tread 4 to 0.85 or more, the belt 14 sufficiently restrains the entire tread 4 . In this tire 2, since the peculiar dimensional growth at the edge PE portion of the tread surface 22 is suppressed, the shoulder land portion 30s is suppressed from being worn down. In this tire 2, the occurrence of uneven wear is suppressed. By setting this ratio to 0.95 or less, the influence of the edge of the belt 14 on the durability is suppressed.

In this tire 2, the ratio of the axial width W2 of the second reference layer 76 to the axial width WT of the tread 4 is preferably 0.80 or more. This second reference layer 76 contributes to the restraint of the tread 4 . In this tire 2, since the belt 14 sufficiently restrains the entire tread 4, the peculiar dimensional growth in the edge PE portion of the tread surface 22 is suppressed. In this tire 2, the occurrence of uneven wear such as shoulder drop wear is suppressed.

In this tire 2 , the edge of the second reference layer 76 is located inside the edge of the first reference layer 74 in the axial direction. Since the edges of the second reference layer 76 and the edges of the first reference layer 74 do not coincide in the axial direction, the strain is prevented from concentrating on the edges of the belt 14 . 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 30s is appropriately maintained, and the difference in the circumference between the circumference of the equator portion and the circumference of the edge PE of the tread surface 22 with respect to the circumference of the tire 2 is is properly maintained. Since the shoulder land portion 30s is prevented from slipping on the road surface, the tire 2 is prevented from uneven wear such as uneven wear.

In FIG. 3, the double arrow DP is the axial distance from the edge of the second layer 38B as the first reference layer 74 to the edge of the third layer 38C as the second reference layer 76. In FIG.

In this tire 2, the axial distance DP from the end of the first reference layer 74 to the end of the second reference layer 76 is preferably 3 mm or more, and preferably 8 mm or less. By setting the distance DP to 3 mm or more, the end of the second reference layer 76 and the end of the first reference layer 74 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 DP is more preferably 4 mm or more. By setting the distance DP to 8 mm or less, the belt 14 sufficiently restrains the entire tread surface 22 . Since the peculiar dimensional growth at the edge PE of the tread surface 22 is suppressed, in this tire 2, the shoulder land portion 30s is suppressed from being worn down. From this point of view, the distance DP is more preferably 7 mm or less.

In FIG. 3, double-headed arrow D is the depth of hole 46 . The depth D of this hole 46 is represented by the distance from the tread surface 22 to the bottom 48 of the hole 46 . A double arrow G indicates the depth of the shoulder circumferential groove 28s. The depth of the shoulder circumferential groove 28s is represented by the distance from the tread surface 22 to the bottom 80 of the shoulder circumferential groove 28s.

In this tire 2, the difference (DG) between the depth D of the hole 46 and the depth G of the shoulder circumferential groove 28s is preferably -2 mm or more, and preferably 6 mm or less.

By setting the difference (DG) between the depth D of the hole 46 and the depth G of the shoulder circumferential groove 28s to -2 mm or more, the depth of the shoulder land portion corresponding portion 72 can be reduced in manufacturing the tire 2. , the tip of the projection 70 is effectively arranged. Since the portion 72 corresponding to the shoulder land portion is effectively heated from the inside, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanization state is effectively shortened. From this point of view, this difference is more preferably 0 mm or more. From the viewpoint that the shoulder land portion corresponding portion 72 is heated more effectively from the inside thereof, the bottom 48 of the hole 46 is positioned radially inside the bottom 80 of the shoulder circumferential groove 28s, in other words, the difference ( DG) is more preferably greater than 0 mm, the difference is more preferably 1 mm or more, and particularly preferably 3 mm or more. By setting this difference to 6 mm or less, the thickness of the rubber positioned between the bottom 48 of the hole 46 and the belt 14 is sufficiently secured. In this tire 2, since the impact on durability due to the proximity of the bottoms 48 of the holes 46 to the belt 14 is considered, good durability is maintained. From this point of view, this difference is more preferably 5 mm or less.

FIG. 5 shows a part of the cross-section of the tire 2 shown in FIG. This FIG. 5 shows a hole 46 provided in the shoulder land portion 30s. In FIG. 5, the double arrow A indicates the width of the mouth 50 of the hole 46. As shown in FIG. Double arrow B is the width of the bottom 48 of this hole 46 . The mouth width A and the bottom width B of the hole 46 are defined along the cross section shown in FIG. Identified in the cross section of the tire 2 .

During manufacture of the tire 2 , the projections 70 provided on this mold 56 for forming the holes 46 are pulled out of the tire 2 when the tire 2 is removed from the mold 56 . From the viewpoint of ease of pulling out the tire 2, it is preferable that the opening width A of the hole 46 is wider than the bottom width B thereof.

In the tire 2, the mouth width A is preferably 8 mm or less, more preferably 7 mm or less, from the viewpoint of securing the rigidity of the shoulder land portion 30c. From the viewpoint of securing the rigidity of the protrusions 70 provided on the mold 56 for forming the holes 46, the mouth width A is preferably 1.5 mm or more, more preferably 3 mm or more, and even more preferably 4 mm or more.

In this tire 2, the bottom width B is preferably 6 mm or less, more preferably 5 mm or less, from the viewpoint of securing the rigidity of the shoulder land portion 30c. From the viewpoint of securing the rigidity of the projections 70 provided on the mold 56 for forming the holes 46, the bottom width B is preferably 1 mm or more, more preferably 2 mm or more.

In this tire 2, the cross-sectional shape of the hole 46 is circular. In manufacturing the tire 2 , the cross-sectional shape of the hole 46 can take various shapes such as elliptical and rectangular, as long as the protrusion 70 can be pulled out from the tire 2 . In manufacturing the tire 2 , the cross-sectional shape of the hole 46 is preferably circular or elliptical from the viewpoint of facilitating the extraction of the projection 70 from the tire 2 . When the shape of the mouth 50 of the hole 46 is elliptical, the intersection of the long axis and the short axis of this ellipse is specified as the center HC of the mouth 50 of this hole 46 .

In this tire 2, the hole 46 is cylindrical. In the manufacture of this tire 2, if the protrusion 70 can be pulled out from the tire 2, the hole 46 has a bulging shape in the central portion in the depth direction, a constricted shape in the central portion in the depth direction, and a shape extending from the mouth to the bottom. It can take a variety of shapes, such as a shape that tapers inwards. In manufacturing the tire 2 , the hole 46 is preferably cylindrical or tapered from the viewpoint of facilitating the extraction of the projection 70 from the tire 2 .

As shown in FIG. 5, the hole 46 of the tire 2 is configured such that the mouth portion 50 is tapered. The bore 46 has a tapered mouth 82 and a body 84 positioned inside the mouth 82 and configured to have a cylindrical shape.

In this tire 2 , the tapered mouth portion 50 restrains movement of the tread surface 22 surrounding the mouth 50 . The tapered mouth portion 50, that is, the mouth portion 82, suppresses the occurrence of uneven wear.

5, the angle θ is the angle formed by the wall 86 of the hole 46 with respect to the imaginary tread surface obtained assuming that the hole 46 does not exist at the mouth 50 of the hole 46 (hereinafter referred to as the mouth 50 of the hole 46). is sometimes referred to as the inclination angle of the wall 86 at ).

In this tire 2, the inclination angle θ of the wall 86 at the mouth 50 of the hole 46 is preferably 80° or less. As a result, the movement of the tread surface 22 surrounding the mouth 50 is effectively suppressed, and in this tire 2, uneven wear is effectively suppressed. From this point of view, the angle θ is more preferably 70° or less, more preferably 60° or less. From the same point of view, this angle θ is preferably 20° or more, more preferably 30° or more, and even more preferably 40° or more.

As shown in FIG. 2, a plurality of holes 46 are provided in the shoulder land portion 30s. These holes 46 are circumferentially spaced apart. In FIG. 2, the double arrow DS is the distance between one hole 46 and another hole 46 located next to this one hole 46 in the circumferential direction. This spacing DS is measured along the tread surface 22 .

In this tire 2, the interval DS between the holes 46 provided in the circumferential direction is preferably 20 mm or more, and preferably 80 mm or less. By setting the distance DS to 20 mm or more, the rigidity of the shoulder land portion 30s is appropriately maintained. From this point of view, the distance DS is more preferably 30 mm or more. By setting the distance DS to 80 mm or less, the portion 72 corresponding to the shoulder land portion is effectively heated from the inside by the projection 70 provided on the mold 56 for forming the hole 46 in manufacturing the tire 2. be done. In manufacturing the tire 2, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanized state is effectively shortened. From this point of view, the distance DS is more preferably 70 mm or less.

As shown in FIG. 2, the shoulder block 44s forming the shoulder land portion 30s includes: Two holes 46 are provided. The number of holes 46 provided in the shoulder blocks 44s is appropriately determined in consideration of the rigidity of the shoulder blocks 44s and the vulcanization time of the tire 2 . The number of holes 46 provided in the shoulder block 44s is normally set within a range of two to seven. The number of holes 46 is preferably two or more, and preferably four or less. The number of holes 46 is preferably two or more, and more preferably three or less.

In FIG. 3, a double arrow WS indicates the axial width of the shoulder land portion 30s. The axial width WS is represented by the axial distance from the inner end of the outer surface of the shoulder land portion 30s to the outer end (that is, the end PE of the tread surface 22). A symbol PS indicates a position on the outer surface of the shoulder land portion 30s corresponding to the center of the axial width WS. A double arrow WH is the axial distance from the center HC of the mouth 50 of the hole 46 to the edge PE of the tread surface 22 .

In this tire 2, the ratio of the axial width WS of the shoulder land portion 30s to half the axial width WT of the tread 4 is preferably 0.30 or more and preferably 0.55 or less. By setting this ratio to 0.30 or more, the shoulder land portion 30s has appropriate rigidity. Since the movement of the shoulder land portion 30s from contact with the road surface to separation from the road surface is suppressed, the shoulder land portion 30s of this tire 2 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 30s is worn) is suppressed. By setting this ratio to 0.55 or less, the circumferential length difference in the shoulder land portion 30s is appropriately maintained. Since the shoulder land portions 30s are less likely to slip on the road surface differently, in the tire 2, the shoulder land portions 30s are prevented from being worn down. Even in this case, the tire 2 is prevented from uneven wear.

As shown in FIG. 3, in this tire 2, the center HC of the mouth 50 of the hole 46 is located outside the center PS of the shoulder land portion 30s in the axial direction. Thereby, a sufficient distance from the shoulder circumferential groove 28s to the hole 46 is ensured. In this tire 2, the influence of the hole 46 on the rigidity of the shoulder land portion 30s is suppressed. In the manufacture of the tire 2, the projections 70 provided on the mold 56 for forming the holes 46 cause the edge PE of the tread surface 22 of the tire 2, which is difficult to heat in a conventional tire without the holes 46, to be heated. The portion along the normal line EL of the outer surface of the carcass passing through, that is, the portion corresponding to the shoulder land portion 72 is effectively heated from the inside. In manufacturing the tire 2, the time required for the portion 72 corresponding to the shoulder land portion to reach an optimum vulcanized state is effectively shortened. From this point of view, in the tire 2, it is preferable that the center HC of the mouth 50 of the hole 46 be located outside the center PS of the shoulder land portion 30s in the axial direction.

In this tire 2, the influence of the hole 46 on the rigidity of the shoulder land portion 30s is suppressed, and in the production of the tire 2, the shoulder land portion of the tire 2 is less likely to be heated in a conventional tire without the hole 46. From the viewpoint that the portion 72 is effectively heated by the projection 70 provided on the mold 56 to form the hole 46, the distance from the edge PE of the tread surface 22 to the axial width WS of the shoulder land portion 30s to the center HC of the hole 46 is is preferably 0.30 or more, and preferably 0.45 or less.

As described above, in this tire 2, a plurality of holes 46 are provided in the shoulder land portion 30s. For this reason, the mold 56 for this tire 2, in particular the tread ring 62, is provided with a plurality of protrusions 70 for the formation of these holes 46. FIG.

In the tire 2, the bottom 48 of the hole 46 is located deep in the shoulder land portion 30s. A projection 70 provided on the tread ring 62 for forming the hole 46 has a certain length. Therefore, it is preferable that the tread ring 62 is composed of a large number of segments 68 from the viewpoint that the projections 70 can be easily pulled out from the tire 2 when the tire 2 is removed from the mold 56 in manufacturing the tire 2 . Specifically, the number of segments 68 forming the tread ring 62 is preferably 13 or more.

As is clear from the above description, the tire 2 achieves an improvement in productivity and a reduction in rolling resistance while suppressing the influence on wear resistance. The present invention is particularly remarkable in the tire 2 in which the thickness TE of the portion of the shoulder land portion 30s, which is measured along the normal line EL of the carcass passing through the edge PE of the tread surface 22, is set to 35 mm or more. It works.

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=295/75R22.5) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

In Example 1, the number of holes provided in the shoulder block (hereinafter referred to as the number of holes) was two. The mouth width A of the hole was 6 mm, and the bottom width B of the hole was 4 mm. The inclination angle θ of the wall at the mouth of the hole was 50°. The depth D of the hole was 22 mm. The depth G of the shoulder circumferential groove was 18 mm. The difference (DG) between the depth D of the hole and the depth G of the shoulder circumferential groove was 4 mm. The distance E from the bottom of the hole to the belt was 2 mm. The number of segments (hereinafter referred to as the number of divisions) constituting the tread ring of the mold used to manufacture the tire of Example 1 was 19.

In this Example 1, the tire thickness TE measured along the normal to the carcass passing through the edge of the tread surface was 53 mm. The ratio of the axial width W1 of the first reference layer to the axial width WT of the tread (W1/WT) was 0.88. The ratio (W2/WT) of the axial width W2 of the second reference layer to the axial width WT of the tread was 0.81.

In Example 1, the ratio (WS/HWT) of the axial width WS of the shoulder land portion to the half HWT of the axial width of the tread was 0.31. The ratio of the axial distance WH from the edge of the tread surface to the center of the hole to the axial width WS of the shoulder land portion (WH/WS) was 0.39.

[Comparative Example 1]
Comparative Example 1 is a conventional tire. The shoulder land portion of Comparative Example 1 is not provided with a hole. The depth G of the shoulder circumferential groove was 18 mm. The division number of the tread ring of the mold used to manufacture the tire of Comparative Example 1 was eight.

[Example 2]
The depth D was changed to make the difference (DG) and the distance E as shown in Table 1 below, and the bottom width B, the inclination angle θ and the number of divisions were as shown in this Table 1. A tire of Example 2 was obtained in the same manner as in Example 1.

[Examples 3-5 and Comparative Example 2]
The tires of Examples 3-5 and Comparative Example 2 were prepared in the same manner as in Example 1, except that the depth D was varied so that the difference (DG) and distance E were as shown in Tables 1 and 2 below. Obtained.

[Example 6 and Comparative Example 3]
The same as Example 1 except that the depth D was changed to change the difference (DG) and distance E as shown in Table 2 below, and the number of holes and the number of divisions were as shown in Table 2. As a result, tires of Example 6 and Comparative Example 3 were obtained.

[Example 7]
In the same manner as in Example 1, except that the depth D was changed so that the difference (DG) and the distance E were as shown in Table 2 below, and the number of holes was as shown in this Table 2. A tire of Example 7 was obtained.

[Uneven wear resistance]
The prototype tire was mounted on a rim (size=8.25×22.5) and filled with air to adjust the internal pressure of the tire to 750 kPa. This tire was attached to the first drive shaft of the trailer head. The load on the tire is 60% of the load index (light load condition). An actual vehicle was driven on a general road for 50,000 km, and the step amount at the hole after driving was measured as the wear amount. The results are shown by index in Tables 1 and 2 below. The larger the numerical value, the less uneven wear occurs and the better the wear resistance.

[Rolling resistance]
A rolling resistance tester was used to measure the rolling resistance coefficient (RRC) of each trial tire when running on a drum at a speed of 80 km/h under the following conditions. The results are shown by index in Tables 1 and 2 below. The larger the numerical value, the smaller the rolling resistance and the better.
Rim: 8.25 x 22.5
Internal pressure: 900kPa
Vertical load: 28.76kN

[Productivity]
For each trial tire, the time required for vulcanization of the raw tire (that is, vulcanization time) was measured. The results are shown by index in Tables 1 and 2 below. The larger the numerical value, the shorter the vulcanization time and the better the productivity.

As shown in Tables 1 and 2, it is confirmed that the examples achieve improvement in productivity and reduction in rolling resistance while suppressing the influence on wear resistance. Examples are evaluated higher than Comparative Examples. From this evaluation result, the superiority of the present invention is clear.

The technique for improving productivity and reducing rolling resistance while suppressing the influence on wear resistance described above can be applied to various tires.

2 Tire 2r Raw tire 4 Tread 6 Side wall 8 Bead 12 Carcass 14 Belt 22 Outer surface of tread 4 (tread surface)
24 Base portion 26 Cap portion 28, 28c, 28c1, 28c2, 28s, 28s1, 28s2 Circumferential grooves 30, 30c, 30s, 30m Land portion 36 Carcass ply 36a Ply body 36b Folded portions 38, 38A, 38B, 38C, 38D Layer of belt 14 46 Hole 48 Bottom of hole 50 Mouth of hole 46 52. Boundary between base portion 24 and cap portion 26 54 Vulcanizer 56 Mold 58 Bladder 60 Cavity surface 62 Tread ring 68 Segment 70 Protrusion 72... Portion corresponding to shoulder land portion 74... First reference layer 76... Second reference layer 78... Protruding portion of first reference layer 74 82... Mouth portion of hole 46 84...・Main body of hole 46 86 Wall of hole 46

Claims (9)

A carcass that bridges a pair of beads, one bead and the other bead, a belt positioned radially outwardly of the carcass, and a tread positioned radially outwardly of the belt and having a tread surface in contact with the road surface. with
At least three axially parallel circumferential grooves are carved into the tread to form at least four axially parallel land portions, and among these circumferential grooves, the outermost circumferential grooves are positioned axially. The shoulder circumferential groove is the circumferential groove, and the outermost land portion in the axial direction is the shoulder land portion,
The shoulder land portion is provided with a hole extending from its outer surface toward the belt,
The distance from the bottom of the hole to the belt is 1 mm or more and 6 mm or less,
The belt is composed of a plurality of layers laminated in the radial direction, among these layers, the layer having the widest axial width is the first reference layer, and the layer laminated outside the first reference layer is is the second reference layer,
A heavy-duty pneumatic tire, wherein the bottom of the hole is located radially outside a portion of the first reference layer that protrudes from the second reference layer. The heavy duty pneumatic tire according to claim 1, wherein the difference between the depth of the hole and the depth of the shoulder circumferential groove is -2 mm or more and 6 mm or less. 3. The heavy duty pneumatic tire according to claim 1 or 2, wherein the holes intersect or contact a normal line of the carcass passing through the edge of the tread surface. The tread comprises a base portion and a cap portion laminated radially outwardly of the base portion and having an outer surface forming the tread surface,
the bottom of the hole is located radially outside the boundary between the base portion and the cap portion;
The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the boundary is recessed inwardly at the bottom portion of the hole. The heavy duty pneumatic tire according to any one of claims 1 to 4, wherein the mouth width of the hole is wider than the bottom width of the hole. The mouth portion of the hole exhibits a tapered shape,
6. The heavy load air according to any one of claims 1 to 5, wherein at the mouth of the hole, the angle formed by the wall of the hole with respect to the virtual tread surface obtained assuming that the hole does not exist is 80° or less. entered tire. The heavy duty pneumatic tire according to any one of claims 1 to 6, wherein the center of the mouth of the hole is located outside the center of the shoulder land portion in the axial direction. A carcass that bridges a pair of beads, one bead and the other bead, a belt positioned radially outwardly of the carcass, and a tread positioned radially outwardly of the belt and having a tread surface in contact with the road surface. with
At least three axially parallel circumferential grooves are carved into the tread to form at least four axially parallel land portions, and among these circumferential grooves, the outermost circumferential grooves are positioned axially. The shoulder circumferential groove is the circumferential groove, and the outermost land portion in the axial direction is the shoulder land portion,
The shoulder land portion is provided with a hole extending from its outer surface toward the belt,
The distance from the bottom of the hole to the belt is 1 mm or more and 6 mm or less,
A heavy-duty pneumatic tire in which the holes intersect or contact a normal to the carcass passing through the edge of the tread surface. A carcass that bridges a pair of beads, one bead and the other bead, a belt positioned radially outwardly of the carcass, and a tread positioned radially outwardly of the belt and having a tread surface in contact with the road surface. with
At least three axially parallel circumferential grooves are carved into the tread to form at least four axially parallel land portions, and among these circumferential grooves, the outermost circumferential grooves are positioned axially. The shoulder circumferential groove is the circumferential groove, and the outermost land portion in the axial direction is the shoulder land portion,
The shoulder land portion is provided with a hole extending from its outer surface toward the belt,
The distance from the bottom of the hole to the belt is 1 mm or more and 6 mm or less,
The tread comprises a base portion and a cap portion laminated radially outwardly of the base portion and having an outer surface forming the tread surface,
the bottom of the hole is located radially outside the boundary between the base portion and the cap portion;
A heavy-duty pneumatic tire, wherein the boundary is recessed inwardly at the bottom portion of the hole.

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