Heavy-duty pneumatic tire

Abstract

To provide a pneumatic tire 2 for heavy load of which enhancement of productivity is achieved while influence for abrasion resistance and anti-crack resistance is restrained.SOLUTION: A pneumatic tire is composed of at least four land parts 30 in parallel with each other in an axial direction on a tread 4 of the tire 2 and moreover at least three circumferential grooves 28 in parallel with each other in an axial direction are cut on the tread 4. The land part 30s which situates on outermost side in the axial direction among these land parts 30 is a shoulder land part 30s. There is provided on the shoulder land part 30s a hole 46 which extends from the external surface toward radial direction inside of the tire 2. The hole 46 is provided in position which does not come in contact with a normal line of internal surface of the tire passing through the end of tread surface 22 and a depth D of the hole 46 is equal to or less a depth G of a shoulder circumferential direction groove 28s. The hole 46 comprises an opening side part and a hole bottom side part which comes in communication with the opening side part and is provided from the opening side part to radial direction inside. The pneumatic tire is configured so that the width of a boundary 98 between an outside hole bottom side part 96A and an inside hole bottom side part 96B is 1.5 to 2.5 times of the width of the radial direction inside end part of the opening side part in a hole bottom side part 96.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pneumatic tires for heavy loads mounted on vehicles such as trucks and buses.

Background Art

[0002] The tread of a pneumatic tire for heavy loads has a large volume. In particular, the shoulder part has a large volume and heat is hardly transmitted. Therefore, in a pneumatic tire for heavy loads, the vulcanization time required for forming the shoulder part becomes the rate-determining step of the vulcanization reaction. Thus, it has been proposed to perform vulcanization with a heat conductor inserted into the shoulder part to shorten the vulcanization time (for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, when a hole into which a heat conductor is inserted is formed in the tread during manufacturing, the wear resistance and crack resistance of the tire may decrease. The present invention has been made in view of such a situation, and by effectively heating the tread, while suppressing the influence on wear resistance and crack resistance, an improvement in productivity by shortening the vulcanization time is achieved, and an object is to provide a pneumatic tire for heavy loads.

Means for Solving the Problems

[0005] The pneumatic heavy-duty tire according to one aspect of the present invention includes a pair of beads, a carcass bridging one bead and the other bead, a belt positioned radially outside the carcass, and a tread having a tread surface that is positioned radially outside the belt and contacts the road surface. At least three circumferential grooves arranged in parallel in the axial direction are engraved in the tread, thereby forming at least four land portions arranged in parallel in the axial direction. Among these circumferential grooves, the circumferential groove located most outward in the axial direction is a shoulder circumferential groove. Among these land portions, the land portion located most outward in the axial direction is a shoulder land portion. A hole extending radially inward from the outer surface is provided in the shoulder land portion, and the hole is provided at a position where it does not contact the normal line of the inner surface of the tire passing through the end of the tread surface. The depth of the hole is equal to or less than the depth of the shoulder circumferential groove. The hole includes an opening side portion having at least one of a region where the width decreases radially inward and a region where the width is constant, and a hole bottom side portion that communicates with the opening side portion and is provided radially inward of the opening side portion. The hole bottom side portion includes an outer hole bottom side portion where the width expands radially inward and an inner hole bottom side portion where the width decreases radially inward. The width of the boundary between the outer hole bottom side portion and the inner hole bottom side portion is 1.5 to 2.5 times the width of the radially inner end portion of the opening side portion. Pneumatic heavy-duty tire.

[0006] Preferably, in this pneumatic heavy-duty tire, in the hole, the shape of a cross-section perpendicular to the central axis of the hole is a circle, the width of the radially inner end portion of the opening side portion is 2.0 to 3.5 mm, the shape of the wall surface of the inner hole bottom side portion is a shape composed of only a part of a spherical surface, and the radius R of the spherical surface is 2.0 mm or more.

[0007] Preferably, in this pneumatic heavy-duty tire, in the hole, the shape of a cross-section perpendicular to the central axis of the hole is a circle, the width of the radially inner end portion of the opening side portion is 2.0 to 3.5 mm, and the shape of the wall surface of the inner hole bottom side portion is a shape composed of a combination of a curved surface and a flat surface.

[0008] Preferably, in this pneumatic heavy-duty tire, the distance from the bottom of the boundary between the outer bottom side portion and the inner bottom side portion at the bottom side portion of the hole is 25 to 50% of the width of the boundary between the outer bottom side portion and the inner bottom side portion.

[0009] Preferably, in this pneumatic heavy-duty tire, the depth of the hole is 90 to 100% of the depth of the shoulder circumferential groove.

[0010] Preferably, in this pneumatic heavy-duty tire, at the normal line of the tire inner surface passing through the end of the tread surface, the midpoint between the end of the tread surface and the tire inner surface PM is taken as PM and the normal line of the tread surface passing through [

[0011] Preferably, in this pneumatic heavy-duty tire, the shoulder land portion includes a plurality of shoulder blocks divided by a plurality of axial grooves arranged in parallel in the axial direction, and the mouth of the hole is located in a region where the distance from the one circumferential direction end side in the tread surface of the shoulder block is 30 to 70% of the circumferential length of the shoulder block, and the maximum number of the holes provided in each shoulder block is 3.

[0012] Preferably, in this pneumatic heavy-duty tire, the mouth width of the hole is wider than the width of the radially inner end portion of the opening side portion.

[0013] Preferably, in this pneumatic heavy-duty tire, the cross-sectional shape of at least the portion of the outer bottom side portion connected to the opening side portion has a shape having a curve whose width expands toward the radially inner side.

Advantages of the Invention

[0014] In the pneumatic heavy-duty tire of the present invention, the tread is formed through an effective heating process. In this tire, while the influence on abrasion resistance and crack resistance is suppressed, an improvement in productivity is achieved.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0017] In the present invention, a state where a tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to this tire is referred to as a regular state. In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the regular state.

[0018] As used herein, the regular rim means the rim defined in the standard to which the tire conforms. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

[0019] As used herein, the regular internal pressure means the internal pressure defined in the standard to which the tire conforms. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0020] As used herein, the regular load means the load defined in the standard to which the tire conforms. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0021] FIG. 1 shows a part of a pneumatic tire 2 for heavy loads (hereinafter sometimes simply referred to as "tire 2") according to an embodiment of the present invention. This tire 2 is mounted on a heavy load vehicle such as a truck or a bus, for example.

[0022] Figure 1 shows a partial cross-section of the tire 2 along a plane including the axis of rotation of the tire 2. In this Figure 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of the paper of this Figure 1 is the circumferential direction of the tire 2. In Figure 1, the dashed line CL represents the equatorial plane of the tire 2. In this Figure 1, the tire 2 is incorporated into a rim R (standard rim).

[0023] In Figure 1, the solid line BBL extending in the axial direction is the bead base line. This bead base line is the line that defines the rim diameter of the rim R (refer to JATMA, etc.).

[0024] This tire 2 includes 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 inner liner 18, and a pair of steel reinforcing layers 20.

[0025] The tread 4 contacts the road surface at its outer surface 22, that is, the tread surface 22. The symbol PC is the intersection of the tread surface 22 and the equatorial plane. This intersection PC is the equator of the tire 2.

[0026] This 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 a low heat-generating crosslinked rubber considering adhesiveness. The cap portion 26 is made of a crosslinked rubber considering wear resistance and grip performance. The cap portion 26 covers the entire base portion 24.

[0027] In this tire 2, at least three circumferential grooves 28 are engraved in the tread 4. As a result, at least four land portions 30 are formed in this tread 4. In this tire 2, at least four circumferential grooves 28 may be engraved in the tread 4, and thereby at least five land portions 30 may be formed in this tread 4. In the tire 2 shown in Figure 1, four circumferential grooves 28 are engraved in the tread 4, and five land portions 30 are formed in this tread 4.

[0028] Each sidewall 6 is continuous with the edge of the tread 4. The sidewall 6 extends radially inward from the edge of the tread 4. The sidewall 6 is made of cross-linked rubber.

[0029] Each bead 8 is located radially inside the sidewall 6. The bead 8 includes a core 32 and an apex 34.

[0030] The core 32 extends circumferentially. The core 32 includes a wound steel wire.

[0031] The apex 34 is located radially outside the core 32. The apex 34 extends radially outward from the 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 cross-linked rubber. The outer apex 34s is softer than the inner apex 34u.

[0032] Each chafer 10 is located axially outside the bead 8. This chafer 10 is located radially inside the sidewall 6. The chafer 10 contacts the rim R. The chafer 10 is made of cross-linked rubber.

[0033] The carcass 12 is located inside the tread 4, the sidewall 6 and the chafer 10. The carcass 12 spans between one bead 8 and the other bead 8. The carcass 12 includes at least one carcass ply 36. The carcass 12 of this tire 2 consists of one carcass ply 36.

[0034] In this tire 2, the carcass ply 36 is folded back from the axial inside to the outside around each bead 8. This carcass ply 36 has a ply body 36a extending from one bead 8 toward the other bead 8, and a pair of folded-back portions 36b continuous with this ply body 36a and folded back from the axial inside to the outside around each core 32.

[0035] Although not shown, the carcass ply 36 includes a number of carcass cords arranged in parallel. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane. In this tire 2, the angle formed by the carcass cord 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 cord is steel. A cord made of organic fiber may be used as the carcass cord.

[0036] The belt 14 is located radially inside of the tread 4. This belt 14 is located radially outside of the carcass 12.

[0037] The belt 14 is composed of a plurality of layers 38 laminated in the radial direction. The belt 14 of this tire 2 is composed of four layers 38. In this tire 2, there is no particular limitation on the number of layers 38 constituting the belt 14. The configuration of the belt 14 is determined as appropriate in consideration of the specifications of the tire 2.

[0038] Although not shown, each layer 38 includes a number of belt cords arranged in parallel. These belt cords are covered with topping rubber. The material of the belt cord is steel. The belt cord of this tire 2 is a steel cord.

[0039] Although not shown, the belt cord is inclined with respect to the equatorial plane. In this tire 2, the belt 14 is configured such that the belt cords of one layer 38 intersect the belt cords of another layer 38 laminated on this one layer 38.

[0040] In this tire 2, among the four layers 38, the second layer 38B located between the first layer 38A and the third layer 38C has the largest axial width. The fourth layer 38D located most radially outside has the smallest axial width.

[0041] Each cushion layer 16 is located between the belt 14 and the carcass 12 at the end portion of the belt 14, i.e., at the end of the belt 14. The cushion layer 16 is made of cross-linked rubber.

[0042] The inner liner 18 is located inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. This inner liner 18 is made of cross-linked rubber with excellent air barrier properties. The inner liner 18 retains the internal pressure of the tire 2.

[0043] Each steel reinforcing layer 20 is located at the bead 8 portion. In the axial direction, the steel reinforcing layer 20 is located outside the bead 8. The steel reinforcing layer 20 is located between the carcass ply 36 and the chafer 10. The inner end of the steel reinforcing layer 20 is located radially inside the core 32. The outer end of the steel reinforcing layer 20 is located radially between the end of the folded-back portion 36b and the core 32.

[0044] Although not shown, the steel reinforcing layer 20 includes a number of parallel filler cords. In the steel reinforcing layer 20, the filler cords are covered with topping rubber. The material of the filler cords is steel.

[0045] Figure 2 shows a developed view of the tread surface 22. In this Figure 2, the left-right direction is the axial direction of this tire 2, and the up-down direction is the circumferential direction of this tire 2. The direction perpendicular to the plane of this Figure 2 is the radial direction of this tire 2.

[0046] In Figures 1 and 2, the symbol PE is the end of the tread surface 22. In the tire 2, when the end PE of the tread surface 22 cannot be identified visually, the outer axial end of the contact surface obtained by applying a normal load to the tire 2 in the normal state with the camber angle set to 0° and bringing the tread 4 into contact with a plane is defined as the end PE of the tread surface 22.

[0047] As described above, in this tire 2, four circumferential grooves 28 are formed in the tread 4. These circumferential grooves 28 are arranged in parallel in the axial direction and continuously extend in the circumferential direction.

[0048] Among the four circumferential grooves 28, the circumferential groove 28c located on the inner side in the axial direction, that is, the circumferential groove 28c close to the equator PC, is the center circumferential groove. The circumferential groove 28s located on the outermost side in the axial direction, that is, the circumferential groove 28s close to the edge PE of the tread surface 22, is the shoulder circumferential groove. When the circumferential groove 28 located on the equator PC is included in the circumferential grooves 28 formed in the tread 4, the circumferential groove 28 located on the equator PC is the center circumferential groove. Further, when there is a circumferential groove 28 between the center circumferential groove 28c and the shoulder circumferential groove 28s, this circumferential groove 28 is the middle circumferential groove.

[0049] Each center circumferential groove 28c continuously extends in a zigzag shape in the circumferential direction. The center circumferential groove 28c has a zigzag vertex 40a convex on one side and a zigzag vertex 40b convex on the other side in the axial direction. In this center circumferential groove 28c, the zigzag vertex 40a and the zigzag vertex 40b are alternately arranged in the circumferential direction. In this tire 2, this center circumferential groove 28c may be composed of grooves that extend straight in the circumferential direction.

[0050] Each shoulder circumferential groove 28s continuously extends in a zigzag shape in the circumferential direction. The shoulder circumferential groove 28s has a zigzag vertex 40c convex on one side and a zigzag vertex 40d convex on the other side in the axial direction. In this shoulder circumferential groove 28s, the zigzag vertex 40c and the zigzag vertex 40d are alternately arranged in the circumferential direction. In this tire 2, this shoulder circumferential groove 28s may be composed of grooves that extend straight in the circumferential direction.

[0051] 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 40a of the center circumferential groove 28c (hereinafter also referred to as the second center circumferential groove 28c2) located on the right side of the paper surface are bridged by the axial groove 42c (hereinafter also referred to as the center axial groove 42c).

[0052] As shown in FIG. 2, in this tire 2, the zigzag apex 40d of the shoulder circumferential groove 28s (hereinafter also referred to as the first shoulder circumferential groove 28s1) located on the left side of the paper surface and the zigzag apex 40a of the first center circumferential groove 28c1 are bridged by the axial groove 42m (hereinafter also referred to as the first middle axial groove 42m1). The first shoulder circumferential groove 28s1 communicates with the axial groove 42s (hereinafter also referred to as the first shoulder axial groove 42s1) extending inward from the end PE of the tread surface 22 at its zigzag apex 40c.

[0053] As shown in FIG. 2, in this tire 2, the zigzag apex 40c of the shoulder circumferential groove 28s (hereinafter also referred to as the second shoulder circumferential groove 28s2) located on the right side of the paper surface and the zigzag apex 40b of the second center circumferential groove 28c2 are bridged by the axial groove 42m (hereinafter also referred to as the second middle axial groove 42m2). The second shoulder circumferential groove 28s2 communicates with the axial groove 42s (hereinafter also referred to as the second shoulder axial groove 42s2) extending inward from the end PE of the tread surface 22 at its zigzag apex 40d.

[0054] In FIG. 2, the double arrow RT is the actual width of the tread surface 22. This actual width RT is represented by the distance from the end PE of one tread surface 22 to the end PE of the other tread surface 22. This actual width RT is measured along the tread surface 22.

[0055] In FIG. 2, double arrow GC represents the actual width of the center circumferential groove 28c. Double arrow GS represents 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.

[0056] In this tire 2, from the viewpoint of contribution to drainage performance and traction performance, 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. The depth of this center circumferential groove 28c is preferably 13 to 25 mm.

[0057] In this tire 2, from the viewpoint of contribution to drainage performance and traction performance, the actual width GS of the shoulder circumferential groove 28s is preferably 1 to 10% of the actual width RT of the tread surface 22. The depth of the shoulder circumferential groove 28s is preferably 13 to 25 mm.

[0058] 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 this shoulder circumferential groove 28s may be narrower than the actual width GC of the center circumferential groove 28c, or the actual width GS of this shoulder circumferential groove 28s may be equal to the actual width GC of the center circumferential groove 28c. The actual width of this circumferential groove 28 is appropriately determined according to the specifications of the tire 2.

[0059] In this tire 2, the depth of the shoulder circumferential groove 28s is equal to the depth of the center circumferential groove 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 this circumferential groove 28 is appropriately determined according to the specifications of the tire 2.

[0060] In this tire 2, the actual width of the axial groove 42 is appropriately set within the 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 the range of 13 to 25 mm.

[0061] In this tire 2, the actual width of the axial groove 42 may be equal to the actual width of the circumferential groove 28, the actual width of the axial groove 42 may be narrower than the actual width of the circumferential groove 28, or 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.

[0062] In this tire 2, the depth of the axial groove 42 may be equal to the depth of the circumferential groove 28, the depth of the axial groove 42 may be deeper than the circumferential groove 28, or the depth of the axial groove 42 may be shallower than the circumferential groove 28. The depth of the axial groove 42 is appropriately determined according to the specifications of the tire 2.

[0063] As described above, in this tire 2, four circumferential grooves 28 are engraved in the tread 4, and five land portions 30 are formed in the tread 4. These land portions 30 are arranged in parallel in the axial direction and extend in the circumferential direction.

[0064] Among 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 end PE of the tread surface 22, is the shoulder land portion. Further, the land portion 30m located between the center land portion 30c and the shoulder land portion 30s is the middle land portion. In addition, among the land portions 30 formed in the tread 4, if the land portion 30 located on the inner side in the axial direction is not on the equator PC but is located near the equator PC, the land portion 30 located near the equator PC, that is, the land portion 30 located on the equator PC side, is the center land portion.

[0065] A large number of the aforementioned center axial grooves 42c are engraved 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 this tire 2 includes a large number of center blocks 44c arranged at a predetermined pitch in the circumferential direction. Note that the center land portion 30c may be composed of convex portions continuous in the circumferential direction. In this case, the aforementioned center axial grooves 42c are not engraved in the center land portion 30c.

[0066] In each middle land portion of 30 m, a number of the aforementioned middle axial grooves of 42 m are engraved. As a result, a number of middle blocks of 44 m arranged at a predetermined pitch in the circumferential direction are formed. The middle land portion of 30 m of this tire 2 includes a number of middle blocks of 44 m arranged at a predetermined pitch in the circumferential direction. Note that the middle land portion of 30 m may be composed of convex portions continuous in the circumferential direction. In this case, the aforementioned middle axial grooves of 42 m are not engraved in this middle land portion of 30 m.

[0067] In each shoulder land portion of 30 s, a number of the aforementioned shoulder axial grooves of 42 s are engraved. As a result, a number of shoulder blocks of 44 s arranged at a predetermined pitch in the circumferential direction are formed. The shoulder land portion of 30 s of this tire 2 includes a number of shoulder blocks of 44 s arranged at a predetermined pitch in the circumferential direction. Note that the shoulder land portion of 30 s may be composed of convex portions continuous in the circumferential direction. In this case, the aforementioned shoulder axial grooves of 42 s are not engraved in this shoulder land portion of 30 s.

[0068] FIG. 3 shows a cross-section of this tire 2 along line III-III of FIG. 2. The cross-section of the tire 2 shown in this FIG. 3 is a part of the cross-section of this tire 2 shown in FIG. 1. In this FIG. 3, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of the paper in this FIG. 3 is the circumferential direction of the tire 2.

[0069] In the present invention, the thickness of the tire 2 is measured along the normal line of the inner surface of the tire 2 (specifically, the inner surface of the inner liner 18) in the cross-section of the tire 2 shown in FIG. 1 or 3.

[0070] In FIGS. 1 and 3, the solid line EL is the normal line of the inner surface of the tire 2 (specifically, the inner surface of the inner liner 18) passing through the edge PE of the tread surface 22. The double-headed arrow TE is the thickness of this tire 2 measured along the normal line EL of the inner surface of this tire 2.

[0071] This tire 2 has a maximum thickness TE at the position of the normal line EL. In other words, the thickness of the tire 2 measured along the normal line of the inner surface of the tire 2 shows a maximum at the normal line EL of the inner surface of the tire 2 passing through the edge PE of the tread surface 22. As shown in FIG. 3, this normal line EL crosses the portion of the shoulder land 30s of the tire 2. In this tire 2, the portion of this shoulder land 30s has the maximum thickness TE.

[0072] In this tire 2, a hole 46 is provided in the shoulder land 30s. As shown in FIG. 1 or 3, this hole 46 extends radially inward from the outer surface of the shoulder land 30s, which forms a part of the tread surface 22, specifically, from the outer surface of the shoulder block 44s. In FIG. 2, the line III-III is a straight line extending axially through the center of the hole 46.

[0073] As shown in FIG. 3, this hole 46 is provided at a position where it does not contact the normal line EL of the inner surface of the tire 2 passing through the edge PE of the tread surface 22 (including the case where the normal line EL does not cross the hole 46). That is, the hole 46 is located radially outside the normal line EL. In this case, the bottom 48 of the hole 46 can ensure a sufficient distance from the belt 14. Therefore, compared with the case where the distance between the bottom 48 of the hole 46 and the belt 14 is short, cracks starting from the bottom 48 or the end of the belt 14 are less likely to occur. Also, the hole 46 is provided at a position where it does not contact the normal line EL. Therefore, the hole 46 does not approach the edge PE of the tread surface 22 too closely, and a sufficient distance from the edge PE of the tread surface 22 is ensured. If the hole 46 approaches the edge PE of the tread surface 22 too closely, the hole 46 is likely to be damaged. However, by providing the hole at the above-mentioned position, the damage caused by the hole 46 approaching the edge PE too closely can be avoided.

[0074] In FIG. 3, double arrow D represents the depth of hole 46, and double arrow G represents the depth of the shoulder circumferential groove 28s. In tire 2, the depth D of hole 46 is less than or equal to the depth G of the shoulder circumferential groove 28s. In other words, the depth D of hole 46 is the same as or shallower than the depth G of the shoulder circumferential groove 28s. If the depth D of hole 46 exceeds the depth G of the shoulder circumferential groove 28s, the distance between the bottom 48 of hole 46 and belt 14 becomes closer, and there is concern that cracks starting from the bottom 48 of hole 46 or cracks starting from the end of belt 14 are likely to occur.

[0075] The depth D of hole 46 is preferably 90 - 100% of the depth G of the shoulder circumferential groove 28s. By setting the depth D of hole 46 within such a range, the vulcanization time (heating time) when manufacturing tire 2 is shortened, and efficient manufacturing of tire 2 is achieved. Also, since a sufficient distance from belt 14 is ensured, the occurrence of cracks starting from the bottom 48 of hole 46 and damage at the end of the belt are suppressed, and good abrasion resistance is also ensured. The depth D of hole 46 is preferably set in the range of 12 - 25 mm.

[0076] In FIG. 3, double arrow D represents 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 hole 46. Double arrow G represents the depth of the shoulder circumferential groove 28s. The depth of this shoulder circumferential groove 28s is represented by the distance from the tread surface 22 to the bottom 80 of this shoulder circumferential groove 28s.

[0077] As shown in FIGS. 3 and 5(a), hole 46 is composed of an opening side portion 92 provided in order from the tread surface 22 side toward the radially inner side and a hole bottom side portion 96 communicating with the opening side portion 92. The opening side portion 92 has a region 92A (hereinafter also referred to as a tapered portion 92A) where the width shrinks toward the radially inner side and a region 92B (hereinafter also referred to as an equal width portion 92B) where the width is constant toward the radially inner side. The hole bottom side portion 96 has an outer hole bottom side portion 96A where the width expands toward the radially inner side and an inner hole bottom side portion 96B where the width shrinks toward the radially inner side.

[0078] Figure 5(b) is a cross-sectional view taken along line IV-IV of Figure 5(a). Figure 5(a) shows a cross-sectional view of the hole 46 along a plane including the rotation axis of the tire 2. As shown in Figure 5(b), the shape of the cross-section perpendicular to the central axis HC of the hole 46 is circular. Therefore, the overall shape of the hole 46 is the shape obtained by rotating the cross-sectional shape of Figure 5(a) around the central axis HC of the hole 46. The shape of the hole 46 is like that of a round-bottom flask. In the tire of the embodiment of the present invention, the central axis HC of the hole coincides with the straight line connecting the centroid of the shape of the mouth of the hole on the tread surface and the bottom of the hole (the centroid of the planar shape when the bottom of the hole is a plane).

[0079] In the tire 2 of the present invention, the width of the hole refers to the length of the longest part in the cross-sectional shape perpendicular to the central axis HC of the hole. Therefore, in the hole 46, since the cross-sectional shape perpendicular to the central axis HC of the hole 46 is circular, the diameter of this circle becomes the width of the hole at the cross-sectional position.

[0080] In the bottom side portion 96 of the hole 46, the boundary 98 between the outer bottom side portion 96A and the inner bottom side portion 96B becomes the portion presenting the maximum width Bmax in the bottom side portion 96 of the hole. In the hole 46, the maximum width Bmax of the bottom side portion 96 of the hole is set to be 1.5 to 2.5 times the width A of the radially inner end portion 94 of the opening side portion 92.

[0081] In the hole 46, the width A of the radially inner end portion 94 of the opening side portion 92 is preferably set to 2.0 to 3.5 mm. A more preferable range of the width A is 2.5 to 3.0 mm. When the width A is less than 2.0 mm, the effect of shortening the vulcanization time (heating time) when manufacturing the tire 2 becomes poor. On the other hand, when the width A exceeds 3.5 mm, the rigidity of the shoulder block in the tire 2 becomes low, and the shoulder block may be inferior in wear resistance performance.

[0082] In the tire 2 provided with the hole 46 having such a shape, when the green tire is vulcanized during manufacturing, it is possible to efficiently heat the portion corresponding to the shoulder land portion that has a large volume and poor heat transfer. In addition, in the hole 46, the width of the bottom side portion 96 of the hole is larger than the width of the opening side portion. Therefore, compared with the case where a hole having a constant width along the radial direction is provided, even if the depth of the hole is not so deep, it is possible to efficiently heat the portion corresponding to the shoulder land portion of the green tire.

[0083] This tire 2 is manufactured as follows. In the manufacture of this tire 2, first, in a molding machine (not shown), members such as the tread 4 and the sidewall 6 are combined to prepare an unvulcanized tire, that is, a green tire 2r.

[0084] In the manufacture of this tire 2, the green tire 2r is vulcanized and molded in the vulcanizer 54 shown in FIG. 4. This vulcanizer 54 includes a mold 56 and a bladder 58.

[0085] The mold 56 has a cavity surface 60 on its inner surface. This cavity surface 60 abuts against the outer surface of the green tire 2r and shapes the outer surface of the tire 2.

[0086] The mold 56 shown in FIG. 4 is a split mold. This mold 56 includes, as constituent members, a tread ring 62, a pair of side plates 64, and a pair of bead rings 66. In this mold 56, by combining these constituent members, the aforementioned cavity surface 60 is formed. The mold 56 in FIG. 4 is in a state where these constituent members are combined, in other words, a closed state.

[0087] In this mold 56, the tread ring 62 shapes the tread 4 portion of the tire 2. This tread ring 62 is composed of a large number of segments 68. Note that the side plate 64 shapes the sidewall 6 portion of the tire 2, and the bead ring 66 shapes the bead 8 portion of the tire 2. When manufacturing the tire 2, the number of segments 68 that make up the tread ring 62 is not particularly limited and may be appropriately selected in consideration of the demolding property of the tire 2 after molding. The segment 68 is provided with protrusions 70 having a shape corresponding to the shape of the holes 46 at predetermined positions. The protrusions 70 are formed of a heat-conductive material. Therefore, heat is supplied to the portion corresponding to the shoulder land portion 30s of the green tire 2r in the vulcanization process, and the portion is efficiently heated.

[0088] The bladder 58 is located inside the mold 56. The bladder 58 is made of crosslinked rubber. A heating medium such as steam is filled inside the bladder 58. As a result, the bladder 58 expands. The bladder 58 shown in FIG. 4 is in a state where it is filled with the heating medium and expanded. This bladder 58 abuts against the inner surface of the green tire 2r and shapes the inner surface of the tire 2. In the manufacture of this tire 2, a rigid insert made of metal may be used instead of the bladder 58. The rigid insert has a toroidal outer surface. This outer surface approximates the shape of the inner surface of the tire 2 in a state where air is filled and its internal pressure is maintained at 5% of the normal internal pressure.

[0089] In the manufacture of this tire 2, the green tire 2r is put into the mold 56 set at a predetermined temperature. After the input, the mold 56 is closed. The bladder 58 expanded by filling with the heating medium presses the green 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 green tire 2r is crosslinked, and the tire 2 is obtained.

[0090] As is clear from FIG. 1, the tread 4 portion of the tire 2 has a larger volume than the sidewall 6 portion. As described above, in this tire 2, among the tread 4 portions, 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.

[0091] In the manufacture of this tire 2, heat is transferred to the green tire 2r by the mold 56 and the bladder 58. In the green tire 2r, there are portions with a small volume and portions with a large volume mixed together. Heat is easily transferred to the portions with a small volume, but is difficult to transfer to the portions with a large volume.

[0092] If the pressurization and heating time of the green tire 2r, that is, the vulcanization time, is set based on the portions where heat is easily transferred, there is a concern that the progress of vulcanization in the portions where heat is difficult to transfer will be insufficient. On the other hand, if the vulcanization time is set based on the portions where heat is difficult to transfer, there is a concern that vulcanization will proceed excessively in the portions where heat is easily transferred. And for the portions that are vulcanized excessively, there is a concern that the loss tangent (tanδ) will increase and the abrasion resistance will be inferior.

[0093] To suppress the progress of excessive vulcanization, there is also a method of setting the vulcanization temperature to a lower temperature than usual. However, in this case, since the vulcanization time needs to be set long, there is a concern that the productivity of the tire will decrease.

[0094] As described above, in this tire 2, holes 46 with a predetermined shape are provided in the shoulder land portion 30s. Therefore, as shown in FIG. 4, in the mold 56 of this tire 2, projections 70 are provided for forming these holes 46. Among the constituent members of the mold 56, the segment 68 forms the tread 4 portion of the tire 2. Therefore, the projection 70 is provided in the portion of the segment 68 that forms the shoulder land portion 30s.

[0095] In the manufacture of this tire 2, when the green tire 2r is pressurized and heated in the mold 56, the aforementioned projections 70 are inserted into the portion of the green tire 2r corresponding to the shoulder land portion 30s (hereinafter, the shoulder land portion corresponding portion 72). As a result, this shoulder land portion corresponding portion 72 is heated from the inside as well. Therefore, the time until this shoulder land portion corresponding portion 72 reaches an optimal vulcanization state is shortened. The protrusion 70 has a shape corresponding to the hole 46 of the tire 2. That is, the protrusion 70 is designed such that the width on the tip side is larger than the width on the root side. Therefore, in the manufacture of this tire 2, the inside of the shoulder land corresponding portion 72 is efficiently heated. The manufacture of this tire 2 can shorten the vulcanization time. This tire 2 contributes to the improvement of productivity.

[0096] In this tire 2, from the viewpoint of improving productivity, as shown in FIG. 3, when the midpoint PM between the end PE and the inner surface PI of the tire is defined on the normal line EL of the inner surface of the tire passing through the end PE of the tread surface 22, it is preferable that the hole 46 is provided so as to intersect the normal line FL of the tread surface 22 passing through the point PM. The vicinity of the midpoint PM on the normal line EL is the region where heat is most difficult to transfer when the green tire is heated using a mold without the protrusion 70. Therefore, when the tire 2 is manufactured using a mold provided with the protrusion 70 such that the hole 46 is formed at the above-described position, the tire 2 can be manufactured with high productivity without impairing the wear resistance and crack resistance of the manufactured tire 2.

[0097] In the tire 2, it is particularly preferable that the hole 46 is provided at a position where the central axis HC of the hole 46 overlaps with the normal line FL of the tread surface 22 passing through the point PM. In FIG. 3, the double-headed arrow DL is the distance between the bottom 48 of the hole 46 and the point PM. In the tire 2, the hole 46 is preferably provided such that the distance between the bottom (the deepest part of the hole) 48 of the hole 46 and the point PM becomes small while satisfying the condition that the hole 46 does not contact the normal line EL of the inner surface of the tire passing through the end PE of the tread surface 22.

[0098] In this tire 2, the improvement of productivity is achieved while suppressing the influence on wear resistance and crack resistance.

[0099] The hole 46 provided in this tire 2 has a circular shape in a cross-section perpendicular to the central axis of the hole 46 as described above, and has a shape like a round-bottomed flask. And in the hole 46, the shape of the wall surface of the inner hole bottom side portion 96B is a spherical surface of a hemisphere. In other words, the shape of the wall surface of the inner hole bottom side portion 96B is a shape constituted by a part (half) of a spherical surface. Since the shape of the wall surface of the inner hole bottom side portion 96B has such a shape, good demolding property after vulcanization can be ensured during the manufacture of the tire 2. Further, in the manufactured tire 2, cracks starting from the wall surface of the inner hole bottom side portion 96B are less likely to occur. The shape of the wall surface of the inner hole bottom side portion 96B of the hole 46 provided in the tire 2 is not necessarily limited to such a shape. Other shapes will be described later.

[0100] In the hole 46 provided in this tire 2, the wall surface of the outer hole bottom side portion 96A is constituted by a smooth curved surface whose width continuously expands toward the inner side in the radial direction. Therefore, good demolding property after vulcanization can be ensured. From the viewpoint of ensuring good demolding property after vulcanization, in this tire 2, the cross-sectional shape (the cross-sectional shape along the plane including the rotation axis of the tire 2, see Fig. 5(a)) of at least the portion connected to the opening side portion 92 of the outer hole bottom side portion 96A preferably has a shape having a curve whose width expands toward the inner side in the radial direction.

[0101] In the hole bottom side portion 96 of the hole 46 provided in the tire 2, the shape of the wall surface of the inner hole bottom side portion 96B is a hemisphere. Therefore, in this hole bottom side portion 96, the distance E2 from the bottom 48 of the hole 46 at the boundary 98 between the outer hole bottom side portion 96A and the inner hole bottom side portion 96B is 50% of the width of the boundary between the outer hole bottom side portion 96A and the inner hole bottom side portion 96B. In other words, the distance from the bottom 48 of the hole 46 at the boundary 98 between the outer hole bottom side portion 96A and the inner hole bottom side portion 96B is 50% of the maximum width Bmax of the hole bottom side portion 96.

[0102] In the tire 2, it is preferable to set the distance E2 from the bottom 48 of the hole 46 at the position of the maximum width Bmax of the hole bottom side portion 96 (the position of the boundary 98 between the outer hole bottom side portion 96A and the inner hole bottom side portion 96B) to 25 to 50% of the maximum width of the hole bottom side portion 96. By setting the position of the maximum width of the hole bottom side portion 96 at such a position, the position indicating the maximum width Bmax of the hole bottom side portion 46 will be near the midpoint PM between the tread edge PE and the tire inner surface PI. Therefore, when manufacturing the tire 2 having such a shaped hole, it is more suitable for efficiently heating the shoulder land portion corresponding portion 72 of the green tire 2r.

[0103] On the other hand, when the distance E2 from the bottom 48 of the hole 46 at the position of the maximum width of the hole bottom side portion 96 exceeds 50% of the maximum width of the hole bottom side portion 96, the position of the maximum width of the hole bottom side portion 96 is away from the midpoint PM between the tread edge PE and the tire inner surface PI, which is disadvantageous from the viewpoint of performing efficient heating. Also, when the distance E2 from the bottom 48 of the hole 46 at the position of the maximum width of the hole bottom side portion 96 is less than 25% of the maximum width of the hole bottom side portion 96, it is difficult to make the shape of the wall surface of the inner hole bottom side portion 96B have good demolding property after vulcanization and ensure crack resistance.

[0104] In the hole 46 of the tire 2, the height E1 of the hole bottom side portion 96 is preferably set to 6 to 12 mm. In this case, it is suitable for achieving an improvement in productivity while suppressing the influence on wear resistance.

[0105] In the hole 46 as shown in Fig. 5(a), the radius R1 of the spherical surface constituting the wall surface of the inner hole bottom side portion 96B constituting the hole bottom side portion 96 is preferably 2 mm or more. Thereby, good crack resistance can be ensured. Also, the upper limit of the radius R1 is preferably 4 mm from the viewpoint of being able to ensure good crack resistance.

[0106] Fig. 5(a) shows a part of the cross-section of the tire 2 shown in Fig. 3. In this Fig. 5(a), the hole 46 provided in the shoulder land portion 30s is shown. In this Fig. 5(a), the double-headed arrow F is the width of the mouth 50 of the hole 46 (hereinafter, also referred to as the mouth width F). The mouth width F of this hole 46, the width A of the radially inner end portion 94 of the opening side portion 92, and the maximum width Bmax of the hole bottom side portion 96 are all specified in the cross-section shown in FIG. 5(a), that is, in the cross-section of this tire 2 along the plane including the rotation axis of the tire 2 and the central axis HC of this hole 46.

[0107] In this tire 2, the cross-sectional shape perpendicular to the central axis HC of the hole 46 is a circle. In the manufacture of this tire 2, if the protrusion 70 can be pulled out from the tire 2, the cross-sectional shape of this hole 46 can take various shapes such as an ellipse and a rectangle. From the viewpoint of easy pulling out of the protrusion 70 from the tire 2 in the manufacture of the tire 2 and good crack resistance of the obtained tire 2, the cross-sectional shape of this hole 46 is preferably a circle or an ellipse, and particularly preferably a circle. In the case where the cross-sectional shape of the hole 46 is an ellipse, the intersection of the major axis and the minor axis of this ellipse will be passed through by the central axis HC of this hole 46.

[0108] As described above, the hole 46 of the tire 2 shown in FIG. 5 has a tapered portion 92A in the radially outer portion of the opening side portion 92. In other words, the portion of the mouth 50 is configured to have a tapered shape. In this tire 2, the tapered portion of the mouth 50 suppresses the movement of the tread surface 22 surrounding the mouth 50. This tapered portion of the mouth 50 (tapered portion 92A) suppresses the occurrence of uneven wear. In addition, the tire 2 provided with the hole 46 having the tapered portion 92A is also excellent in demolding property after vulcanization.

[0109] In FIG. 5(a), the angle θ is the angle formed by the wall surface 86 of the tapered portion 92A with respect to the virtual tread surface obtained assuming that this hole 46 does not exist in the tapered portion 92A of the hole 46 (hereinafter, may be referred to as the inclination angle of the wall surface 86 in the tapered portion 92A).

[0110] In this tire 2, the inclination angle θ of the wall surface 86 in the tapered portion 92A is preferably 80° or less. Thereby, the movement of the tread surface 22 surrounding the mouth 50 is effectively suppressed. In this tire 2, the occurrence of uneven wear is effectively suppressed. From this viewpoint, this angle θ is more preferably 70° or less, and even more preferably 60° or less. From the same viewpoint, this angle θ is preferably 20° or more, more preferably 30° or more, and even more preferably 40° or more.

[0111] As shown in FIG. 2, a plurality of holes 46 are provided in the shoulder land portion 30s. These holes 46 are arranged at intervals in the circumferential direction. In FIG. 2, the double-headed arrow DS is the interval between one hole 46 and another hole 46 located adjacent to this one hole 46 in the circumferential direction. This interval DS is measured along the tread surface 22.

[0112] 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 this interval DS to 20 mm or more, the rigidity of the shoulder land portion 30s is appropriately maintained. From this viewpoint, this interval DS is more preferably 30 mm or more. By setting this interval DS to 80 mm or less, in the manufacture of this tire 2, the shoulder land portion corresponding portion 72 is effectively heated from the inside by the protrusion 70 provided in the mold 56 to form the hole 46. In the manufacture of this tire 2, the time until the shoulder land portion corresponding portion 72 reaches an optimal vulcanized state is effectively shortened. From this viewpoint, this interval DS is more preferably 70 mm or less.

[0113] As shown in FIG. 2, two holes 46 are provided in the shoulder block 44s that constitutes the shoulder land portion 30s. The number of holes 46 provided in the shoulder block 44s is appropriately determined in consideration of the rigidity of this shoulder block 44s and the vulcanization time of the tire 2. The number of holes 46 provided in this shoulder block 44s is preferably set to a maximum of 3. If too many holes 46 are provided, there is a concern about a decrease in the rigidity of the shoulder block 44s and a decrease in the designability of the tire 2. The number of the holes 46 is preferably two or three.

[0114] In FIG. 2, reference sign Q indicates a region where the distance from one circumferential end side on the tread surface 22 of the shoulder block 44s is 30 to 70% of the circumferential length TL of the shoulder block 44s. In the tire 2, when the holes 46 are provided in the shoulder land portion 30s, the holes 46 are preferably provided so as to be located within the region Q. In this case, it is avoided that the position where the holes 46 are provided gets too close to the shoulder axial groove 42s provided in the shoulder land portion 30s. Therefore, concerns about a decrease in the rigidity of the shoulder block 44s caused by the position where the holes 46 are provided getting too close to the shoulder axial groove 42s and the occurrence of uneven wear on the tread surface 22 of the shoulder block 44s are avoided. Here, that the hole 46 is located within the region Q means that part or all of the mouth 50 of the hole 46 overlaps with the region Q in the radial direction on the tread surface 22 of the shoulder block 44s.

[0115] In FIG. 3, double-headed arrow WS is the axial width of the shoulder land portion 30s. This axial width WS is represented by the axial distance from the inner end to the outer end of the outer surface of this shoulder land portion 30s (that is, the end PE of the tread surface 22).

[0116] In this tire 2, the ratio of the axial width WS of the shoulder land portion 30s to half HWT of the axial width WT of the tread 4 is preferably 0.30 or more and preferably 0.55 or less. In this case, in the tire 2, wear is less likely to occur in the shoulder land portion 30s. In this case, in the tire 2, the occurrence of uneven wear (for example, one-sided wear where the entire shoulder land portion 30s wears) is further suppressed.

[0117] In the embodiment of the present invention, as described above, the shape of the holes provided in the tire 2 is not limited to the shape of the holes 46. The holes provided in the tire 2 may have a shape like the holes 146 shown in FIG. 6. FIG. 6 is an enlarged cross-sectional view showing a hole provided in a pneumatic heavy load tire according to another embodiment of the present invention.

[0118] As shown in FIG. 6, the hole 146 is composed of an opening side portion 192 provided in order from the tread surface 22 side of the shoulder land portion 30s toward the radially inner side, and a hole bottom side portion 196 communicating with the opening side portion 192. The opening side portion 192 has a region 192B (hereinafter also referred to as an equal width portion 192B) having a constant width toward the radially inner side. The hole bottom side portion 196 has an outer hole bottom side portion 196A whose width expands toward the radially inner side and an inner hole bottom side portion 196B whose width contracts toward the radially inner side. Unlike the hole 46, the hole 146 shown in FIG. 6 does not include a tapered portion having a wall surface that is tapered at the portion of the mouth 150. In the tire 2 according to the embodiment of the present invention, the shape of the hole may be a shape without a tapered portion in this way.

[0119] FIG. 6 shows a cross-sectional view of the hole 146 along a plane including the rotation axis of the tire 2. The shape of the cross-section perpendicular to the central axis HC of the hole 146 is circular, and the overall shape of the hole 146 is a shape obtained by rotating the cross-sectional shape of FIG. 6 around the central axis HC of the hole 146. The shape of the hole 146 is a shape like a triangular flask with a rounded portion connecting the side surface to the bottom surface.

[0120] In the hole bottom side portion 196 of this hole 146, the boundary 198 between the outer hole bottom side portion 196A and the inner hole bottom side portion 196B becomes a portion presenting the maximum width Bmax in the hole bottom side portion 196. In the hole 146, the maximum width Bmax of the hole bottom side portion 196 is set to be 1.5 to 2.5 times the width A of the radially inner end portion 194 of the opening side portion 192.

[0121] In a tire provided with a hole 146 having such a shape, when vulcanizing a green tire during manufacturing, it is possible to efficiently heat the portion corresponding to the shoulder land portion 30s, which has a large volume and is difficult for heat to transfer. Also, since the width of the hole bottom side portion 196 is larger than the width of the opening side portion 192, compared to the case where a hole having a constant width along the radial direction is provided, it is possible to efficiently heat the portion corresponding to the shoulder land portion of the green tire without making the depth of the hole so deep.

[0122] In the hole 146, the width A of the radially inner end portion 194 of the opening side portion 192 is preferably set to 2.0 to 3.5 mm. A more preferable range of the width A is 2.5 to 3.0 mm, similar to the hole 146 shown in FIG. 5. When the width A is less than 2.0 mm, the effect of shortening the vulcanization time (heating time) becomes poor. When the width A exceeds 3.5 mm, the rigidity of the shoulder block in the manufactured tire becomes low, and the shoulder block may be inferior in wear resistance performance.

[0123] As described above, the hole 146 has a circular shape in a cross section perpendicular to the central axis of the hole 146 and has a shape like a triangular flask. And in the hole 146, the shape of the wall surface of the inner hole bottom side portion 196B is a shape formed by combining a curved surface and a flat surface. In other words, the shape of the inner hole bottom side portion 196B is a shape drawn by rotating the outer contour line of the inner hole bottom side portion 196B, which consists of two arcs with a radius R2 connected to the outer hole bottom side portion 196A shown in FIG. 6 and a line segment connecting these two arcs, around the central axis HC of the hole 146. Even when the shape of the wall surface of the inner hole bottom side portion 196B has such a shape, it is possible to efficiently heat the green tire 2r while suppressing the influence on the wear resistance and crack resistance of the manufactured tire.

[0124] At the hole 146, the wall surface of the outer hole bottom side portion 196A has a tapered shape in which the width expands toward the radially inner side. Here, the cross-sectional shape of the outer hole bottom side portion 196A (the shape of the cross-section along the plane including the rotation axis of the tire 2) is composed of a curve in which the portion connected to the opening side portion 192 expands in width toward the radially inner side as shown in FIG. 6, and the portion radially inner than this curve portion is composed of a straight line in which the width expands toward the radially inner side and a curve connected to the inner hole bottom side portion 196B. Even when the mold used in manufacturing has a protrusion 70 having a shape corresponding to the hole 146 of such a shape, after vulcanizing the green tire, it can be demolded from the mold well without breakage or the like.

[0125] In the hole bottom side portion 196 of the hole 146, the distance E2 from the bottom 148 of the hole 146 at the boundary 198 between the outer hole bottom side portion 196A and the inner hole bottom side portion 196B is 25% of the width of the boundary 198 between the outer hole bottom side portion 196A and the inner hole bottom side portion 196B (the maximum width Bmax of the hole bottom side portion 196). The distance E2 is preferably 25 to 50% of the width of the boundary 198 between the outer hole bottom side portion 196A and the inner hole bottom side portion 196B (the maximum width Bmax of the hole bottom side portion 196), and the reason is as described above.

[0126] In the hole 146 of the tire 2, the height E1 of the hole bottom side portion 196 is preferably set to 6 to 12 mm. In this case, while suppressing the influence on abrasion resistance, it is suitable for achieving an improvement in productivity.

[0127] Thus, the shape of the hole provided in the tire according to the embodiment of the present invention may be the hole 146 having the shape shown in FIG. 6. Furthermore, in the hole 146 having the shape shown in FIG. 6, a tapered portion may be provided at the portion of the mouth 150 (the radially outer portion of the opening side portion).

[0128] In the hole 146 as shown in FIG. 6, the curved surface that constitutes the wall surface of the inner hole bottom side portion 196B that constitutes the hole bottom side portion 196 is, as described above, a curved surface drawn by rotating an arc of radius R2 around the central axis HC. Here, from the viewpoint of ensuring good crack resistance, the radius R2 is preferably 1 mm or more and 3 mm or less. Each of the two arcs is, for example, a 1 / 4 arc.

[0129] In the holes 46 and 146 as shown in FIGS. 5(a), (b), and FIG. 6, the opening side portion may be configured by combining a tapered portion and an equal-width portion like the hole 46, or may be configured only by an equal-width portion like the hole 146. Furthermore, it may be configured only by a tapered shape whose width decreases toward the radially inner side. In this case, the mouth width of the hole is preferably smaller than the maximum width of the hole bottom side portion.

[0130] Furthermore, in the embodiment of the present invention, the shape of the wall surface of the inner hole bottom side portion at the hole bottom side portion of the hole is not limited to a part of a spherical surface or a combination of a curved surface and a flat surface, and may be configured by a combination of a part of a spherical surface and a flat surface, a curved surface only, a flat surface only, etc. Also, in the embodiment of the present invention, the outer hole bottom side portion may have a width that expands toward the radially inner side, and the inner hole bottom side portion may have a width that decreases toward the radially inner side. Therefore, the width of the outer hole bottom side portion does not necessarily have to continuously expand, and may expand intermittently. Also, the width of the inner hole bottom side portion does not necessarily have to continuously decrease, and may decrease intermittently.

[0131] As is clear from the above description, in this tire 2, productivity is improved while suppressing the influence on abrasion resistance and crack resistance. The present invention exhibits a more remarkable effect particularly in a tire 2 in which the thickness TE of the portion of the shoulder land portion 30s measured along the normal EL of the carcass passing through the edge PE of the tread surface 22 is set to 35 mm or more.

[0132] The embodiments disclosed this time are illustrative in all respects and not restrictive. The technical scope of the present invention is not limited to the foregoing embodiments, and this technical scope includes all modifications within the scope equivalent to the configurations described in the claims.

Example

[0133] Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the present invention is not limited to such examples only.

[0134] [Example 1] An air-filled heavy-duty tire (tire size = 275 / 80R22.5) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained. In Example 1, a tire 202 was manufactured in which holes 246 having the shape shown in FIG. 7 were provided in the shoulder land portions 230s.

[0135] In this Example 1, the number of holes 246 provided in the shoulder blocks (hereinafter referred to as the number of holes) was two. For the hole 246, the width A of the radially inner end portion on the opening side was 2.5 mm, the maximum width Bmax of the hole bottom side was 6 mm, the mouth width F of the hole 216 was 3.5 mm, and the inclination angle θ of the wall surface in the tapered portion was 50°. Also, the depth D of the hole was 15 mm, and the height E1 of the hole bottom side was 9 mm. The shape of the wall surface of the inner hole bottom side of the hole 246 was a hemisphere (see FIG. 5(a), the radius R1 of the hemisphere was 3 mm), and the distance E2 from the bottom of the hole 246 at the position indicating the maximum width Bmax of the hole bottom side was 50% of the maximum width Bmax of the hole bottom side. The depth G of the shoulder circumferential groove was 16 mm. In this Example 1, the thickness of the tire measured along the normal line EL of the tire inner surface passing through the tread surface end PE was 50 mm. In FIG. 7, PM is the midpoint between the tread surface end PE and the tire inner surface PI (hereinafter, the same applies to FIGS. 8 to 12).

[0136] [Example 2] A tire 302 was obtained in which holes 346 having the shape shown in FIG. 8 were provided in the shoulder land portions 330s. The tire 302 of this Example 2 is the same as the tire of Example 1, except that the shape of the hole 346 is different from the shape of the hole 246 of the tire of Example 1.

[0137] For the hole 346 of the tire 302 of this Example 2, the width A of the radially inner end of the opening side was 2.5 mm, the maximum width Bmax of the hole bottom side was 6 mm, the mouth width F of the hole 346 was 3.5 mm, and the inclination angle θ of the wall surface in the tapered portion was 50°. Also, the depth D of the hole was 15 mm, and the height E1 of the hole bottom side was 10.5 mm. The shape of the wall surface of the inner hole bottom side of the hole 346 is a combination of a curved surface and a flat surface (see Fig. 6, the radius R2 of the arc of the outer contour line in the cross-sectional view is 1.5 mm), and the distance E2 from the bottom of the hole 346 at the position indicating the maximum width Bmax of the hole bottom side was 25% of the maximum width Bmax of the hole bottom side. The depth G of the shoulder circumferential groove was 16 mm.

[0138] [Example 3] A tire 402 was obtained in which a hole 446 having the shape shown in Fig. 9 was provided in the shoulder land portion 430s. The tire 402 of this Example 3 is the same as the tire of Example 2, except that the shape of the hole 446 is different from the hole 346 of the tire of Example 2.

[0139] The hole 446 of the tire 402 of this Example 3 has the same configuration as the hole 346 of the tire 302 of Example 2, except that no tapered portion is provided on the opening side, and the entire opening side is composed of an equal-width portion.

[0140] [Comparative Example 1] Comparative Example 1 is a conventional tire. No hole is provided in the shoulder land portion of this Comparative Example 1. The configuration of this tire is the same as that of the tire 202 of Example 1, except that no hole is provided.

[0141] [Comparative Example 2] A tire 502 was obtained in which a hole 546 having the shape shown in Fig. 10 was provided in the shoulder land portion 530s. The tire 502 of Comparative Example 2 is the same as the tire of Example 1, except that the shape of the hole 546 is different from the shape of the hole 246 of the tire of Example 1.

[0142] The hole 546 of the tire 502 of this Comparative Example 2 had a tapered portion at the end on the opening side, and the portion radially inside this tapered portion had a cylindrical shape with a constant width toward the bottom, and the shape of the bottom surface was hemispherical. The width (diameter of the cylindrical portion) A′ of the hole 546 was 2.5 mm, the mouth width F of the hole 546 was 3.5 mm, and the inclination angle θ of the wall surface in the tapered portion was 50°. Also, the depth D of the hole was 25 mm.

[0143] [Comparative Example 3] A tire 602 was obtained in which a hole 646 having the shape shown in FIG. 11 was provided in the shoulder land portion 630s. The tire 602 of this Comparative Example 3 is the same as the tire of Comparative Example 2, except that the shape of the hole 646 is different from the hole 546 of the tire of Comparative Example 2.

[0144] The hole 646 of the tire 602 of this Comparative Example 3 had the same configuration as the hole 546 of the tire 502 of Comparative Example 2, except that the depth D of the hole was 15 mm.

[0145] [Comparative Example 4] A tire 702 was obtained in which a hole 746 having the shape shown in FIG. 12 was provided in the shoulder land portion 730s. The tire 702 of this Comparative Example 4 is the same as the tire of Example 1, except that the shape of the hole 746 is different from the hole 246 of the tire of Example 1.

[0146] The hole 746 of the tire 702 of this Comparative Example 4 had the same configuration as the hole 246 of the tire 202 of Example 1, except that the depth D of the hole was 25 mm.

[0147] [Evaluation] [Vulcanization Short-Performance] When manufacturing tires in the examples and comparative examples, while inserting a thermocouple into the unvulcanized rubber portion near the midpoint PM between the edge PE and the inner surface PI of the tire on the normal line EL of the inner surface of the tire passing through the edge PE of the tread surface, the green tire r2 was vulcanized, and the change in the internal temperature of the tire during vulcanization was measured and compared. Here, the time until the internal temperature of the tire rose to a predetermined temperature was measured. The results are shown in Table 1 below as relative values with the result of Comparative Example 1 set to 100. The larger the numerical value, the shorter the vulcanization time, which means better productivity.

[0148] [Irregular wear resistance] Separate from the evaluation of the short vulcanization performance described above, tires were manufactured without inserting thermocouples. The prototype tire was mounted on a rim (size = 8.25×22.5), filled with air, and the internal pressure of the tire was adjusted to 750 kPa. This tire was mounted on the first axis of the drive shaft of the trailer head. The load on the tire was 60% of the load index (light load state). The tire was driven on ordinary roads for 50,000 km, and the amount of step at the hole after driving was measured as the wear amount. The results are shown in Table 1 below as relative values with the result of Comparative Example 3 set to 100. The larger the numerical value, the less likely irregular wear occurs, indicating excellent wear resistance.

[0149] [Crack resistance] For the prototype tire manufactured without inserting a thermocouple, the amount of strain applied to the bottom of the hole provided in the shoulder land portion was calculated by simulation using the finite element method (FEM), and the obtained amounts of strain were compared. The results are shown in Table 1 below as relative values with the result of Comparative Example 3 set to 100. The larger the numerical value, the smaller the amount of strain, indicating excellent crack resistance.

[0150]

Table 1

[0151] As shown in Table 1, it was confirmed that in the examples, while suppressing the influence on wear resistance and crack resistance, an improvement in productivity was achieved. The examples have a higher evaluation than the comparative examples. From this evaluation result, the superiority of the present invention is clear.

Industrial Applicability

[0152] The technology for achieving an improvement in productivity while suppressing the influence on wear resistance and crack resistance, as described above, can be applied to various tires.

Explanation of Symbols

[0153] 2···Tire 2r···Green tire 4···Tread 6···Sidewall 8···Bead 12···Carcass 14···Belt 18···Inner liner 22···Outer surface of tread 4 (tread surface) 24···Base part 26···Cap part 28, 28c, 28c1, 28c2, 28s, 28s1, 28s2···Circumferential groove 30, 30c, 30s, 30m···Land part 36···Carcass ply 36a···Ply body 36b···Turn-up part 38, 38A, 38B, 38C, 38D···Layers of belt 14 46, 146, 246, 346, 446, 546, 646, 746···Hole 48, 148···Bottom of hole 50, 150···Mouth of hole 54···Vulcanizer 56···Mold 58···Bladder 60···Cavity surface 62···Tread ring 68···Segment 70 ··· Protrusion 72 ··· Shoulder land corresponding part 86 ··· Wall surface of tapered portion 92A 92, 192 ··· Opening side part 92A, 192A ··· Tapered portion 92B, 192B ··· Equal width portion 94, 194 ··· Radial inner end of opening side part 96, 196 ··· Bottom side part of hole 96A, 196A ··· Outer bottom side part of hole 96B, 196B ··· Inner bottom side part of hole 98, 198 ··· Boundary between outer bottom side part and inner bottom side part of hole

Claims

1. A pair of beads, a carcass spanning one bead and the other bead, a belt positioned radially outside the carcass, and a tread having a tread surface that is positioned radially outside the belt and contacts the road surface, At least three circumferential grooves arranged in parallel in the axial direction are engraved in the tread, thereby forming at least four land portions arranged in parallel in the axial direction. Among these circumferential grooves, the circumferential groove located most outward in the axial direction is a shoulder circumferential groove, and among these land portions, the land portion located most outward in the axial direction is a shoulder land portion, A hole extending radially inward from the outer surface is provided in the shoulder land portion, The hole is provided at a position that does not contact the normal line of the inner surface of the tire passing through the end of the tread surface, The depth of the hole is equal to or less than the depth of the shoulder circumferential groove, The hole includes an opening side portion having at least one of a region where the width decreases radially inward and a region where the width is constant, and a hole bottom side portion that communicates with the opening side portion and is provided radially inward of the opening side portion, The hole bottom side portion consists of an outer hole bottom side portion where the width expands radially inward and an inner hole bottom side portion where the width decreases radially inward, and the width at the boundary between the outer hole bottom side portion and the inner hole bottom side portion is 1.5 to 2.5 times the width of the radially inner end portion of the opening side portion, On the normal line of the inner surface of the tire passing through the end of the tread surface, with the midpoint between the end of the tread surface and the inner surface of the tire being point PM, the normal line of the tread surface passing through point PM intersects the hole, a pneumatic tire for heavy loads.

2. In the hole, the shape of a cross-section perpendicular to the central axis of the hole is a circle, The width of the radially inner end portion of the opening side portion is 2.0 to 3.5 mm, The shape of the wall surface of the inner hole bottom side portion is a shape composed of only a part of a spherical surface, The radius R of the spherical surface is 2.0 mm or more, the pneumatic tire for heavy loads according to Claim 1.

3. In the hole, the shape of a cross-section perpendicular to the central axis of the hole is a circle, The width of the radially inner end portion of the opening side portion is 2.0 to 3.5 mm, The shape of the wall surface of the inner hole bottom side portion is a shape composed of a combination of a curved surface and a flat surface, the pneumatic tire for heavy loads according to Claim 1.

4. The distance from the bottom of the boundary between the outer hole bottom side portion and the inner hole bottom side portion in the hole bottom side portion is 25 to 50% of the width of the boundary between the outer hole bottom side portion and the inner hole bottom side portion. The pneumatic heavy load tire according to any one of claims 1 to 3.

5. The depth of the hole is 90 to 100% of the depth of the shoulder circumferential groove. The pneumatic heavy load tire according to any one of claims 1 to 4.

6. The shoulder land portion includes a plurality of shoulder blocks divided by a plurality of axial grooves arranged in parallel in the axial direction. The mouth of the hole is located in a region where the distance from one circumferential end side of the tread surface of the shoulder block is 30 to 70% of the circumferential length of the shoulder block. The maximum number of the holes provided in each shoulder block is 3. The pneumatic heavy load tire according to any one of claims 1 to 5.

7. The mouth width of the hole is wider than the width of the radially inner end portion of the opening side portion. The pneumatic heavy load tire according to any one of claims 1 to 6.

8. The cross-sectional shape of at least the portion of the outer hole bottom side portion connected to the opening side portion has a shape having a curve whose width expands toward the radially inner side. The pneumatic heavy load tire according to any one of claims 1 to 7.

Images