Pneumatic tire for heavy load

Abstract

Provided is a pneumatic tire for heavy load, which is capable of suppressing shape change caused by running and achieving improvement in cornering wear resistance. The tire (2) has a nominal flat ratio of 65% or less. The tire (2) has a tread (4) and a reinforcement layer (20). The reinforcement layer (20) has a belt layer (38) including a plurality of belt cords (44) arranged side by side, and a crown layer (40) including crown cords (52) wound in a spiral shape. The belt layer (38) has a plurality of belt plies (42) arranged in a radial direction. The crown layer (40) has a full crown layer (48) having two ends (48e) opposite across the equatorial surface, and a pair of edge crown layers (50) located radially outward of the ends (48e) of the full crown layer (48). In the axial direction, the ends (48e) of the full crown layer (48) are located outward of shoulder circumferential grooves (28s) formed on the tread (4).

Description

TECHNICAL FIELD

[0001] The present application relates to a pneumatic tire for heavy load. BACKGROUND

[0002] On a tread of a pneumatic tire for heavy load (hereinafter referred to as a tire), at least three circumferential grooves are engraved from the viewpoint of water drainage. Among the circumferential grooves engraved on the tread, the circumferential groove located on the outer side in the axial direction is a shoulder circumferential groove.

[0003] A belt layer and a crown layer are provided between the tread and the carcass. The belt layer is composed of a plurality of belt plies arranged in the radial direction. Each belt ply contains a plurality of belt cords arranged side by side. The belt cord is usually made of a steel cord. The crown layer contains a crown cord wound in a spiral shape. The crown cord is made of a cord composed of an organic fiber such as nylon fiber, a steel cord. By adjusting the structure of the belt layer or the crown layer, the rigidity of the tread portion is controlled (for example, Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 9-105084

[0005] In a tire in a running state, deformation and restoration are repeated. Due to this, the shape of the tire changes. Since the ground contact shape changes, the cornering power resistance can decrease.

[0006] In a running state of a tire, the tread end portion actively acts. The rigidity of the portion engraved with a circumferential groove is lower than that of the portion not engraved with a circumferential groove. In a low-flat tire having a flat ratio of 65% or less, there is a tire having a tread surface with a wide width. In this tire, the shoulder circumferential groove is located on the outer side in the axial direction compared to a high-flat tire. In this tire, the shape change in the vicinity of the shoulder circumferential groove is large.

[0007] In order to suppress the shape change, the adoption of a full crown layer containing a crown cord wound in a spiral shape is studied. In a low-flat tire, there is a tendency that the shape change during running becomes large, and it can be impossible to sufficiently suppress the shape change by only the full crown layer.

[0008] The crown cord contained in the full crown layer substantially extends in the circumferential direction. On the crown cord of a tire in a running state, a force acts in the direction of stretching the crown cord.

[0009] The tire flexes when in contact with the road surface. As a result, the force acting on the crown belt cord decreases, and thus the tension of the crown belt cord decreases. When the tire recovers away from the road surface, the force acting on the crown belt cord increases, and the tension of the crown belt cord increases. In the crown belt cord of the tire in the running state, the tension repeatedly changes. Depending on the degree of change in the tension, the crown belt cord can be likely to be broken. The change in the tension is greater at the end portion of the full crown belt layer. As described above, in the running state of the tire, the tread end portion actively acts. The more the end portion of the full crown belt layer is disposed on the outer side in the axial direction, the more the breakage of the crown belt cord is likely to occur in the full crown belt layer.

[0010] When the crown belt cord is broken, the restraining force decreases. In this case, the ground contact shape changes, and the cornering wear resistance and the handling stability can decrease. SUMMARY

[0011] The present application has been achieved in view of such circumstances, and aims to provide a heavy load pneumatic tire capable of suppressing shape change caused by running and achieving improvement in cornering wear resistance.

[0012] A heavy load pneumatic tire of one embodiment of the present application has a nominal flat ratio of 65% or less. The heavy load pneumatic tire has a tread that comes into contact with a road surface and a reinforcement layer that is located on the inner side of the tread in the radial direction. At least four land portions that are parallel in the axial direction are formed by carving at least three circumferential grooves on the tread, a circumferential groove that is located on the outer side in the axial direction among the at least three circumferential grooves is a shoulder circumferential groove, and a land portion that is located on the outer side of the shoulder circumferential groove in the axial direction is a shoulder land portion. The reinforcement layer has a belt layer including a plurality of belt cords that are parallel and a crown belt layer including crown belt cords that are wound in a spiral shape. The belt layer has a plurality of belt plies that are arranged in the radial direction. The crown belt layer has a full crown belt layer that has two end portions that face each other across an equatorial plane and a pair of edge crown belt layers that are located on the outer side of the end portions of the full crown belt layer in the radial direction. In the axial direction, the end portions of the full crown belt layer are located on the outer side of the shoulder circumferential groove.

[0013] In the heavy load pneumatic tire, it is preferable that the ratio of the axial distance from the shoulder circumferential groove to the end portion of the full crown belt layer to the axial width of the shoulder land portion be 10% or more and 50% or less.

[0014] In the heavy load pneumatic tire, it is preferable that the axial distance from the end portion of the full crown belt layer to the inner end of the edge crown belt layer be 10 mm or more.

[0015] In the heavy load pneumatic tire, it is preferable that, in the axial direction, the end portions of the full crown belt layer be located on the inner side of the end portions of the belt layer.

[0016] It is preferable that, in the heavy load pneumatic tire, at least one of the plurality of belt plies is located radially inside the full crown ply.

[0017] According to the present application, a heavy load pneumatic tire capable of suppressing shape change caused by running and achieving improvement in resistance to eccentric wear can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a sectional view showing a part of a heavy load pneumatic tire according to one embodiment of the present application.

[0019] Figure 2 is a schematic view for explaining the structure of a reinforcement layer.

[0020] Figure 3 is an enlarged sectional view showing a part of the tire of Figure 1

[0021] REFERENCE NUMERALS

[0022] 2: tire; 4: tread; 20: reinforcement layer; 20e: end portion of the reinforcement layer 20; 22: tread surface; 28, 28s, 28m: circumferential groove; 30, 30s, 30m, 30c: land portion; 38: belt layer; 40: crown layer; 38e: end portion of the belt layer 38; 42: belt ply; 44: belt cord; 48: full crown layer; 48e: end portion of the full crown layer 48; 50: edge crown layer; 50se: outer end of the edge crown layer 50; 50ue: inner end of the edge crown layer 50; 52: crown cord. DETAILED DESCRIPTION

[0023] Hereinafter, the present application will be described in detail based on preferred embodiments, with appropriate reference to the accompanying drawings.

[0024] In the present disclosure, a state in which a tire is assembled to a regular rim, the internal pressure of the tire is adjusted to a regular internal pressure, and no load is applied to the tire is referred to as a regular state. In the present application, unless otherwise specified, the dimensions and angles of each portion of the tire are measured in the regular state.

[0025] A regular rim refers to a rim determined in a specification to which the tire conforms. The "Standard Rim" in the JATMA specification, the "Design Rim" in the TRA specification, and the "Measuring Rim" in the ETRTO specification are regular rims.

[0026] ​The normal internal pressure is the internal pressure determined in the specification to which the tire is based. The "maximum air pressure" in the JATMA specification, the "maximum" in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA specification, and the "INFLATION PRESSURE" in the ETRTO specification are the normal internal pressure.

[0027] The normal load is the load determined in the specification to which the tire is based. The "maximum load capacity" in the JATMA specification, the "maximum" in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA specification, and the "LOAD CAPACITY" in the ETRTO specification are the normal load.

[0028] Figure 1 A portion of a pneumatic tire 2 for heavy load (hereinafter, also simply referred to as "tire 2") according to an embodiment of the present application is shown. The tire 2 is mounted to a vehicle such as a truck, a bus, and the like. The nominal of the flat ratio of the tire 2 is 65% or less. In other words, the tire 2 has a nominal of the flat ratio of 65% or less. The tire 2 is a low flat tire.

[0029] In the present disclosure, the "nominal of the flat ratio" and the "nominal of the cross-sectional width" are the "nominal of the flat ratio" and the "nominal of the cross-sectional width" included in the "nominal of the tire" prescribed in JIS D4202 "Automobile tires - Nomenclature and dimensions".

[0030] Figure 1 A portion of a cross section of the tire 2 along a plane including the axis of rotation of the tire 2 is shown. In 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 in Figure 1 is the circumferential direction of the tire 2. The dotted line CL indicates the equatorial plane of the tire 2.

[0031] The tire 2 has a tread 4, a pair of sidewalls 6, a pair of beads 8, a pair of bead fillers 10, a carcass 12, a pair of breaker layers 14, an inner liner 16, a pair of steel fillers 18, and a reinforcing layer 20.

[0032] The tread 4 contacts a road surface at its outer surface. The outer surface is a tread surface 22. In Figure 1 , the reference sign PC is an intersection of the tread surface 22 and the equatorial plane. The intersection PC is the equator of the tire 2.

[0033] In Figure 1In this diagram, PE represents the end of the tread surface 22. The double arrow WT represents the width of the tread surface 22. The width WT of the tread surface 22 is represented by the axial distance from the end PE of one tread surface 22 to the end PE of another tread surface 22. Furthermore, in tire 2, when the end PE of the tread surface 22 cannot be visually identified, the axially outer end of the contact patch obtained by applying a normal load to the tire 2 in its normal state, setting the camber angle to 0°, and making the tire 2 contact with a plane is defined as the end PE of the tread surface 22.

[0034] The tread 4 has a base 24 and a cap 26 located radially outward of the base 24. The base 24 is made of low-heat-generating cross-linked rubber. The cap 26 is made of cross-linked rubber with consideration for abrasion resistance and grip performance. Figure 1 As shown, the base 24 covers the entire reinforcing layer 20. The cap 26 covers the entire base 24.

[0035] In this tire 2, at least three circumferential grooves 28 are etched on the tread 4. Figure 1 The tire 2 shown has four circumferential grooves 28 engraved on its tread 4. These circumferential grooves 28 are arranged side by side in the axial direction and extend continuously in the circumferential direction.

[0036] Of the four circumferential grooves 28 etched on the tread 4, the outermost circumferential groove 28 in the axial direction is the shoulder circumferential groove 28s. The circumferential groove 28 located axially inside the shoulder circumferential groove 28s is the intermediate circumferential groove 28m. In this tire 2, the four circumferential grooves 28 consist of a pair of intermediate circumferential grooves 28m and a pair of shoulder circumferential grooves 28s.

[0037] In this tire 2, from the viewpoint of contributing to drainage and traction performance, the axial width of the intermediate circumferential groove 28m is preferably about 2% to 10% of the width WT of the tread surface 22. The depth of the intermediate circumferential groove 28m is preferably 13mm to 25mm. The axial width of the shoulder circumferential groove 28s is preferably about 1% to 7% of the width WT of the tread surface 22. The depth of the shoulder circumferential groove 28s is preferably 13mm to 25mm.

[0038] As described above, at least three circumferential grooves 28 are etched on the tread 4. Thus, at least four land sections 30 are formed on the tread 4. Figure 1 The tire 2 shown has four circumferential grooves 28 engraved on its tread 4, forming five land sections 30. These land sections 30 are arranged side by side in the axial direction and extend continuously in the circumferential direction.

[0039] The land portion 30 located on the outer side in the axial direction among the five land portions 30 of the tread 4 is a shoulder land portion 30s. The shoulder land portion 30s is located on the outer side of the shoulder circumferential groove 28s in the axial direction, and contains the end portion PE of the tread surface 22. On the inner side of the shoulder land portion 30s in the axial direction, there is a middle land portion 30m. Between the shoulder land portion 30s and the middle land portion 30m, there is the shoulder circumferential groove 28s. On the inner side of the middle land portion 30m in the axial direction, there is a central land portion 30c. Between the middle land portion 30m and the central land portion 30c, there is the middle circumferential groove 28m. In this tire 2, the five land portions 30 are constituted by the central land portion 30c, a pair of middle land portions 30m, and a pair of shoulder land portions 30s.

[0040] In this tire 2, the axial width of the central land portion 30c is 10% or more and 18% or less of the width WT of the tread surface 22. The axial width of the middle land portion 30m is 10% or more and 18% or less of the width WT of the tread surface 22. The axial width of the shoulder land portion 30s is 15% or more and 25% or less of the width WT of the tread surface 22. The axial width of the land portion 30 is represented by the axial width of the top surface of the land portion 30 that constitutes a part of the tread surface 22.

[0041] In this tire 2, the land portion 30 located in the center in the axial direction among the land portions 30 of the tread 4, that is, the central land portion 30c, is located on the equatorial plane. The circumferential groove 28 engraved on the tread 4 contains the circumferential groove 28 located in the center in the axial direction, and the tread 4 can be constituted in such a manner that the circumferential groove 28 is located on the equatorial plane.

[0042] Each of the side portions 6 is connected to the end portion of the tread 4. The side portion 6 extends toward the radially inner side from the end portion of the tread 4. The side portion 6 is constituted by a crosslinked rubber.

[0043] Each of the beads 8 is located at a position radially inward of the side portion 6. The bead 8 has a core 32 and a bead filler 34.

[0044] The core 32 extends in the circumferential direction. The core 32 contains a steel wire that is wound. The core 32 has a substantially hexagonal cross-sectional shape.

[0045] The bead filler 34 is located radially outward of the core 32. The bead filler 34 has an inner bead filler 34u and an outer bead filler 34s. The inner bead filler 34u extends toward the radially outer side from the core 32. The outer bead filler 34s is located at a position radially outward of the inner bead filler 34u. The inner bead filler 34u is constituted by a hard crosslinked rubber. The outer bead filler 34s is constituted by a crosslinked rubber that is softer than the inner bead filler 34u. The outer bead filler 34s is softer than the inner bead filler 34u.

[0046] Each bead filler 10 is located axially outward of the bead 8. The bead filler 10 is located radially inward of the sidewall 6. The bead filler 10 contacts a rim (not shown). The bead filler 10 is composed of a crosslinked rubber that takes abrasion resistance into consideration.

[0047] The carcass 12 is located inward of the tread 4, the sidewall 6, and the bead filler 10. The carcass 12 has at least one carcass ply 36. The carcass 12 of the tire 2 is composed of one carcass ply 36. The carcass ply 36 is turned up from the axially inner side toward the outer side around each core 32.

[0048] Although not shown, the carcass ply 36 contains a plurality of carcass cords juxtaposed. The carcass cords are covered with a skim rubber. Each carcass cord intersects the equatorial plane. In the tire 2, the angle that the carcass cords make with respect to the equatorial plane is 70° or more and 90° or less. The carcass 12 has a radial structure. In the tire 2, as the carcass cords, steel cords are used.

[0049] Each cushion layer 14 is located between the reinforcement layer 20 and the carcass 12 at the end of the reinforcement layer 20. The cushion layer 14 is composed of a soft crosslinked rubber.

[0050] The inner liner 16 is located inward of the carcass 12. The inner liner 16 constitutes the inner surface of the tire 2. The inner liner 16 is composed of a crosslinked rubber that has excellent air shielding properties. The inner liner 16 maintains the internal pressure of the tire 2.

[0051] Each steel filler 18 is located at a portion of the bead 8. The steel filler 18 is turned up from the axially inner side toward the outer side along the carcass ply 36 around the core 32.

[0052] Although not shown, the steel filler 18 contains a plurality of pad cord juxtaposed. The pad cord is covered with a skim rubber in the steel filler 18. In the tire 2, as the pad cord, a steel cord is used.

[0053] The reinforcement layer 20 is located radially inward of the tread 4. The reinforcement layer 20 is located between the carcass 12 and the tread 4. The reinforcement layer 20 has a belt 38 and a crown 40.

[0054] The structure of the reinforcement layer 20 is shown in Figure 2 In Figure 2 the left-right direction is the axial direction of the tire 2, and the up-down direction is the circumferential direction of the tire 2. The direction perpendicular to the paper surface is the radial direction of the tire 2. The surface side of the paper is the radially outer side, and the back side is the radially inner side.

[0055] The belt layer 38 has a plurality of belt ply layers 42 arranged radially. Each belt ply layer 42 is arranged with its ends facing each other across the equatorial plane. The belt layer 38 of the tire 2 has four belt ply layers 42. The four belt ply layers 42 are composed of a first belt ply layer 42A located radially inside, a second belt ply layer 42B located outside the first belt ply layer 42A, a third belt ply layer 42C located outside the second belt ply layer 42B, and a fourth belt ply layer 42D located outside the third belt ply layer 42C.

[0056] In this tire 2, the second belt ply 42B has the widest axial width, and the fourth belt ply 42D has the narrowest axial width. The first belt ply 42A and the third belt ply 42C have the same axial width, or the axial width of the first belt ply 42A is wider than the axial width of the third belt ply 42C.

[0057] The end 38e of the belt layer 38 of the tire 2 is represented by the end of the belt ply 42 with the widest axial width among the plurality of belt ply 42 constituting the belt layer 38. In the tire 2, as described above, the second belt ply 42B among the four belt ply 42 constituting the belt layer 38 has the widest axial width. The end 38e of the belt layer 38 of the tire 2 is represented by the end 42Be of the second belt ply 42B with the widest axial width. The end 38e of the belt layer 38 is also the end 20e of the reinforcing layer 20.

[0058] like Figure 1 As shown, the end 42Ae of the first belt ply 42A is located axially outside the shoulder circumferential groove 28s. The end 42Be of the second belt ply 42B is located axially outside the shoulder circumferential groove 28s. The end 42Ce of the third belt ply 42C is located axially outside the shoulder circumferential groove 28s. The end 42De of the fourth belt ply 42D is located axially outside the shoulder circumferential groove 28s.

[0059] exist Figure 1 In the diagram, double arrow W1 represents the axial width of the first belted fabric layer 42A. Double arrow W2 represents the axial width of the second belted fabric layer 42B. Double arrow W3 represents the axial width of the third belted fabric layer 42C. Double arrow W4 represents the axial width of the fourth belted fabric layer 42D. The axial width of each belted fabric layer 42 is represented by the axial distance from one end 42e of the belted fabric layer 42 to the other end 42e.

[0060] In this tire 2, from the viewpoint of ensuring the rigidity of the tread 4, the ratio (W1 / WT) of the axial width W1 of the first belt ply 42A to the width WT of the tread surface 22 is preferably 0.80 or more, and preferably 0.90 or less. The ratio (W2 / WT) of the axial width W2 of the second belt ply 42B to the width WT of the tread surface 22 is preferably 0.85 or more, and preferably 0.95 or less. The ratio (W3 / WT) of the axial width W3 of the third belt ply 42C to the width WT of the tread surface 22 is preferably 0.80 or more, and preferably 0.90 or less. The ratio (W4 / WT) ​​of the axial width W4 of the fourth belt ply 42D to the width WT of the tread surface 22 is preferably 0.55 or more, and preferably 0.65 or less.

[0061] like Figure 2 As shown, in this tire 2, each belt ply 42 constituting the belt layer 38 comprises a plurality of belt cords 44 arranged side by side. Figure 2 In the diagram, for ease of explanation, the belt cord 44 is represented by a solid line, but the belt cord 44 is covered by adhesive rubber 46. The belt cord 44 of this tire 2 is a steel cord.

[0062] In this tire 2, the density of belt cords 44 in each belt ply 42 is between 15 cords / 5cm and 30 cords / 5cm. The density of the belt cords 44 is represented by the number of belt cords 44 sections contained in each 5cm width of the belt ply 42 in a cross section along a plane perpendicular to the extension direction of the belt cords 44.

[0063] In each belted fabric layer 42, the belt cords 44 are inclined relative to the circumference. The orientation of the belt cords 44 included in the first belted fabric layer 42A relative to the circumference (hereinafter referred to as the inclination direction of the first belted fabric layer 42A) is the same as the orientation of the belt cords 44 included in the second belted fabric layer 42B relative to the circumference (hereinafter referred to as the inclination direction of the second belted fabric layer 42B). The inclination direction of the second belted fabric layer 42B is opposite to the orientation of the belt cords 44 included in the third belted fabric layer 42C relative to the circumference (hereinafter referred to as the inclination direction of the third belted fabric layer 42C). The inclination direction of the third belted fabric layer 42C is the same as the orientation of the belt cords 44 included in the fourth belted fabric layer 42D relative to the circumference (hereinafter referred to as the inclination direction of the fourth belted fabric layer 42D). Furthermore, the tilt direction of the first belt-girder layer 42A can be opposite to the tilt direction of the second belt-girder layer 42B, and the tilt direction of the fourth belt-girder layer 42D can be opposite to the tilt direction of the third belt-girder layer 42C. From the viewpoint of ensuring a stable grounding shape, it is preferable that the tilt direction of the second belt-girder layer 42B is opposite to the tilt direction of the third belt-girder layer 42C.

[0064] In Figure 2 , the angle θ1 is an inclination angle (hereinafter referred to as a first inclination angle θ1) of the belt cord 44 included in the first belt ply 42A with respect to the equatorial plane. The angle θ2 is an inclination angle (hereinafter referred to as a second inclination angle θ2) of the belt cord 44 included in the second belt ply 42B with respect to the equatorial plane. The angle θ3 is an inclination angle (hereinafter referred to as a third inclination angle θ3) of the belt cord 44 included in the third belt ply 42C with respect to the equatorial plane. The angle θ4 is an inclination angle (hereinafter referred to as a fourth inclination angle θ4) of the belt cord 44 included in the fourth belt ply 42D with respect to the equatorial plane.

[0065] In the tire 2, the first inclination angle θ1, the second inclination angle θ2, the third inclination angle θ3, and the fourth inclination angle θ4 are preferably 10° or more and preferably 60° or less. From the viewpoint of effectively restraining the behavior of the tire 2 and ensuring a stable ground contact shape, the first inclination angle θ1 is preferably 40° or more and preferably 60° or less. The second inclination angle θ2 is preferably 10° or more and preferably 20° or less. The third inclination angle θ3 is preferably 10° or more and preferably 20° or less. The fourth inclination angle θ4 is preferably 10° or more and preferably 60° or less.

[0066] The crown ply 40 has a full crown ply 48 and a pair of edge crown plies 50. As Figure 1 shown, the full crown ply 48 has two ends 48e opposite across the equatorial plane. The pair of edge crown plies 50 are disposed apart in the axial direction across the equatorial plane. In the tire 2, the fourth belt ply 42D forming a part of the belt ply 38 is located between the left and right edge crown plies 50.

[0067] In the tire 2, each of the edge crown plies 50 is located between the tread 4 and the full crown ply 48. The edge crown ply 50 is located radially outward of the end 48e of the full crown ply 48. In the axial direction, the inner end 50ue of the edge crown ply 50 is located inward of the end 48e of the full crown ply 48. The outer end 50se of the edge crown ply 50 is located outward of the end 48e of the full crown ply 48 in the axial direction. The outer end 50se of the edge crown ply 50 can also coincide in the axial direction with the position of the end 48e of the full crown ply 48. The edge crown ply 50 is repeated radially with the end 48e of the full crown ply 48.

[0068] As Figure 2 shown, the full crown ply 48 and the pair of edge crown plies 50 constituting the crown ply 40 include crown cords 52 wound in a spiral shape. In Figure 2 , the crown cords 52 are represented by solid lines for ease of illustration, but the crown cords 52 are covered by the adhesive rubber 54.

[0069] In this tire 2, the crown cord 52 is either steel cord or cord made of organic fibers (hereinafter referred to as organic fiber cord). When using organic fiber cord as the crown cord 52, examples of such organic fibers include nylon fiber, polyester fiber, rayon fiber, and aramid fiber. In this tire 2, the crown cord 52 of the full crown layer 48 and the crown cord 52 of the edge crown layer 50 may use the same cord or different cords. The crown cord 52 used for the full crown layer 48 and the edge crown layer 50 is determined according to the specifications of the tire 2.

[0070] As described above, the full crown band layer 48 includes crown band cords 52 wound in a spiral shape. The full crown band layer 48 has a seamless construction. In the full crown band layer 48, the angle formed by the crown band cords 52 with respect to the circumference is preferably 5° or less, more preferably 2° or less. The crown band cords 52 of the full crown band layer 48 extend substantially circumferentially.

[0071] The density of the coronal cord cords 52 in the full coronal cord layer 48 is more than 20 cords / 5cm and less than 35 cords / 5cm. The density of the coronal cord cords 52 is represented by the number of coronal cord cords 52 sections contained in every 5cm width of the full coronal cord layer 48 in a cross-section along a plane perpendicular to the extension direction of the coronal cord cords 52.

[0072] As described above, the peripheral coronal band layer 50 includes coronal band cords 52 wound in a spiral shape. The peripheral coronal band layer 50 has a seamless construction. In the peripheral coronal band layer 50, the angle formed by the coronal band cords 52 with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less. The coronal band cords 52 of the peripheral coronal band layer 50 extend substantially circumferentially.

[0073] The density of the crown cord filaments 52 in the peripheral crown cord layer 50 is more than 20 cords / 5cm and less than 35 cords / 5cm. The density of the crown cord filaments 52 is represented by the number of cross sections of the crown cord filaments 52 contained in every 5cm width of the peripheral crown cord layer 50 in a cross section along a plane perpendicular to the extension direction of the crown cord filaments 52.

[0074] Figure 3 Show Figure 1 A portion of the cross-section of tire 2 is shown. Figure 3 In the diagram, the left-right direction represents the axial direction of tire 2, and the up-down direction represents the radial direction of tire 2. (And...) Figure 3 The direction perpendicular to the paper is the circumference of tire 2.

[0075] In the tire 2, the end portion 42Be of the second belt ply 42B and the end portion 42Ce of the third belt ply 42C are covered by the rubber layer 56, respectively. Two rubber layers 56 are further arranged between the end portion 42Be of the second belt ply 42B and the end portion 42Ce of the third belt ply 42C. In the tire 2, an edge member 58 composed of a total of four rubber layers 56 is constituted between the end portion 42Be of the second belt ply 42B and the end portion 42Ce of the third belt ply 42C. The edge member 58 is composed of a crosslinked rubber. The edge member 58 contributes to maintaining the interval of the end portion 42Be of the second belt ply 42B and the end portion 42Ce of the third belt ply 42C. In the tire 2, the change in the positional relationship of the end portion 42Be of the second belt ply 42B and the end portion 42Ce of the third belt ply 42C due to running can be suppressed. The edge member 58 is a part of the reinforcement layer 20. The reinforcement layer 20 of the tire 2 has, in addition to the belt layer 38 and the crown layer 40, a pair of edge members 58.

[0076] As described above, the full crown layer 48 has two end portions 48e opposite each other across the equatorial plane. The full crown layer 48 extends in the axial direction from the equatorial plane toward each end portion 48e. Also, the end portion 48e of the full crown layer 48 is located outside in the axial direction of the shoulder circumferential groove 28s. In the radial direction, the full crown layer 48 is located inside of the shoulder circumferential groove 28s.

[0077] The tire 2, although low-flat, the full crown layer 48 can effectively suppress the deformation in the vicinity of the shoulder circumferential groove 28s. Since the change in the shape of the tire 2, such as the profile (hereinafter also referred to as the case line) of the carcass 12, is suppressed, the change in the ground contact shape is suppressed.

[0078] Further, in the tire 2, the edge crown layer 50 is located outside in the radial direction of the end portion 48e of the full crown layer 48. The edge crown layer 50 restrains the end portion 48e of the full crown layer 48. Since the variation in the tension of the crown cord 52 included in the full crown layer 48 is suppressed, the generation of the breakage of the crown cord 52 due to the variation in the tension is suppressed. The full crown layer 48 of the tire 2 can stably exert the function of suppressing the change in the shape. In addition, the edge crown layer 50 is narrower than the full crown layer 48. Therefore, the variation in the tension like that of the full crown layer 48 is not easily generated in the crown cord 52 of the edge crown layer 50. The breakage is not easily generated in the crown cord 52 of the edge crown layer 50.

[0079] In the tire 2, the full crown belt layer 48 and the edge crown belt layer 50 suppress the shape change of the tire 2 caused by running. In particular, the shape change in the vicinity of the shoulder circumferential groove 28s is effectively suppressed. In the tire 2, the generation of the uneven wear feared in the conventional tire is suppressed. The tire 2 can suppress the shape change caused by running, and realize the improvement of the uneven wear resistance.

[0080] In Figure 3 , the double-headed arrow SF is the axial distance from the shoulder circumferential groove 28s (in detail, the outer edge of the shoulder circumferential groove 28s) to the end portion 48e of the full crown belt layer 48. The double-headed arrow WS is the axial width of the shoulder land portion 30s. The axial width WS is indicated by the axial distance from the inner end of the top surface of the shoulder land portion 30s (that is, the outer edge of the shoulder circumferential groove 28s) to the outer end of the top surface (the end portion PE of the tread surface 22 in the tire 2).

[0081] In the tire 2, the ratio (SF / WS) of the axial distance SF from the shoulder circumferential groove 28s to the end portion 48e of the full crown belt layer 48 to the axial width WS of the shoulder land portion 30s is preferably 50% or less. Thereby, since the end portion 48e of the full crown belt layer 48 is disposed apart from the tread 4 end portion portion which actively operates in the running state, the tension variation in the crown belt cord 52 is suppressed. In the tire 2, the generation of the breakage of the crown belt cord 52 is suppressed. The full crown belt layer 48 of the tire 2 contributes to the suppression of the shape change. From this viewpoint, the ratio (SF / WS) is more preferably 35% or less, and further preferably 25% or less.

[0082] By setting the ratio (SF / WS) to 10% or more, the end portion 48e of the full crown belt layer 48 is disposed apart from the shoulder circumferential groove 28s (in detail, the bottom of the shoulder circumferential groove 28s) by an appropriate interval. In the tire 2, the generation of the damage from the bottom of the shoulder circumferential groove 28s is suppressed. Since the width of the full crown belt layer 48 is secured, the full crown belt layer 48 contributes to the suppression of the shape change of the tire 2. From this viewpoint, the ratio (SF / WS) is more preferably 15% or more.

[0083] In Figure 3 , the double-headed arrow We is the axial distance from the end portion 48e of the full crown belt layer 48 to the inner end 50ue of the edge crown belt layer 50.

[0084] In the tire 2, the axial distance We from the end portion 48e of the full crown belt layer 48 to the inner end 50ue of the edge crown belt layer 50 is preferably 10 mm or more. Thereby, the edge crown belt layer 50 effectively restrains the end portion 48e of the full crown belt layer 48. Since the tension variation of the crown belt cord 52 included in the full crown belt layer 48 is suppressed, the generation of the breakage of the crown belt cord 52 caused by the tension variation is suppressed. The full crown belt layer 48 of the tire 2 can more stably exert the function of suppressing the shape change. From this viewpoint, the axial distance We is preferably 20 mm or more.

[0085] In the tire 2, the position of the inner end 50ue of the edge crown belt layer 50 is appropriately determined in consideration of the degree of contribution to the generation of the damage starting from the bottom of the shoulder circumferential groove 28s. Therefore, the upper limit of the axial distance We is not set. From the viewpoint of effectively suppressing the generation of the damage starting from the bottom of the shoulder circumferential groove 28s, in the axial direction, the inner end 50ue of the edge crown belt layer 50 is preferably located at a position outward of the bottom of the shoulder circumferential groove 28s, and more preferably at a position more outward than the shoulder circumferential groove 28s.

[0086] In the tire 2, in the axial direction, the end portion 48e of the full crown belt layer 48 is located inward of the end portion 38e of the belt 38. The belt 38 is wider than the full crown belt layer 48. The belt 38 restrains the end portion 48e of the full crown belt layer 48. The belt 38 contributes to the suppression of the tension variation of the crown belt cord 52 included in the full crown belt layer 48. Since the generation of the breakage of the crown belt cord 52 caused by the tension variation is suppressed, the full crown belt layer 48 can stably exert the function of suppressing the shape change. From this viewpoint, in the axial direction, the end portion 48e of the full crown belt layer 48 is preferably located inward of the end portion 38e of the belt 38.

[0087] On the full crown belt layer 48 of the tire 2, a force acts in a manner expanding in the radial direction from the inner side toward the outer side. By the force, a tension is generated on the crown belt cord 52 of the full crown belt layer 48. In the tire 2, the second belt ply 42B is located radially inward of the full crown belt layer 48.

[0088] In the tire 2, the tension of the crown cords 52 included in the full crown layer 48 is properly maintained due to the second belt ply 42B suppressing the force acting on the full crown layer 48. The second belt ply 42B contributes to the suppression of the variation in the tension of the crown cords 52. Since the second belt ply 42B is wider than the full crown layer 48, the variation in the tension of the crown cords 52 is effectively suppressed. In the tire 2, a break in the crown cords 52 of the full crown layer 48 is less likely to occur. The full crown layer 48 is able to stably function to suppress the change in shape. From this viewpoint, it is preferable that at least one of the plurality of belt plies 42 constituting the belt layer 38 be located radially inward of the full crown layer 48. The at least one of the belt plies 42 located radially inward of the full crown layer 48 is more preferably wider than the full crown layer 48 in width.

[0089] In the tire 2, the first belt ply 42A and the second belt ply 42B are located radially inward of the full crown layer 48. The first belt ply 42A and the second belt ply 42B contribute to the suppression of the variation in the tension of the crown cords 52. Since the first belt ply 42A and the second belt ply 42B are wider than the full crown layer 48, the variation in the tension of the crown cords 52 is more effectively suppressed. In the tire 2, a break in the crown cords 52 of the full crown layer 48 is less likely to occur. The full crown layer 48 is able to stably function to suppress the change in shape. From this viewpoint, it is more preferable that at least two of the plurality of belt plies 42 constituting the belt layer 38 be located radially inward of the full crown layer 48. It is further preferable that the at least two of the belt plies 42 located radially inward of the full crown layer 48 be wider than the full crown layer 48 in width.

[0090] In the tire 2, the second belt ply 42B is located radially inward of the full crown ply 48, and the third belt ply 42C is located radially outward of the full crown ply 48. In the tire 2, the full crown ply 48 is sandwiched between the second belt ply 42B and the third belt ply 42C. As described above, the second belt ply 42B is wider than the full crown ply 48. The third belt ply 42C is also wider than the full crown ply 48. The plurality of belt plies 42 constituting the belt layer 38 of the tire 2 includes two belt plies 42 having a width wider than the width of the full crown ply 48, and the full crown ply 48 is sandwiched by the two belt plies 42 having the wider width. In the tire 2, since the tension variation of the crown cords 52 included in the full crown ply 48 is more effectively suppressed, a breakage of the crown cords 52 of the full crown ply 48 is less likely to occur. The full crown ply 48 of the tire 2 is able to stably exert the function of suppressing a change in shape. From this viewpoint, in the tire 2, it is preferable that the plurality of belt plies 42 constituting the belt layer 38 include two belt plies 42 having a width wider than the width of the full crown ply 48, and the full crown ply 48 be sandwiched by the two belt plies 42 having the wider width.

[0091] In the tire 2, the first belt ply 42A, the second belt ply 42B, and the third belt ply 42C have a width wider than the width of the full crown ply 48. Radially, the first belt ply 42A and the second belt ply 42B are located inward of the full crown ply 48, and the third belt ply 42C is located outward of the full crown ply 48. The pair of edge crown plies 50 are each located radially outward of the third belt ply 42C. As described above, the edge crown ply 50 is located radially outward of the end portion 48e of the full crown ply 48. The edge crown ply 50 radially repeats the end portion 48e of the full crown ply 48 across the third belt ply 42C.

[0092] In the tire 2, the full crown ply 48 is able to stably exert the function of suppressing a change in shape, and an improvement in the cornering power is achieved. From this viewpoint, in the tire 2, the plurality of belt plies 42 constituting the belt layer 38 includes a first belt ply 42A located radially inward, a second belt ply 42B located radially outward of the first belt ply 42A, and a third belt ply 42C located radially outward of the second belt ply 42B, the first belt ply 42A, the second belt ply 42B, and the third belt ply 42C have a width wider than the width of the full crown ply 48, radially, the first belt ply 42A and the second belt ply 42B are located inward of the full crown ply 48, and the third belt ply 42C is located outward of the full crown ply 48, and radially, it is preferable that the edge crown ply 50 located radially outward of the full crown ply 48 radially repeat the end portion 48e of the full crown ply 48 across the third belt ply 42C.

[0093] As is apparent from the foregoing description, according to the present application, a heavy-duty pneumatic tire 2 that can suppress shape changes caused by running and that can achieve an improvement in resistance to eccentric wear can be obtained. The present application exerts a significant effect in a heavy-duty pneumatic tire 2 having a nominal low flatness of 65% or less.

[0094] [EXAMPLE]

[0095] The present application will be described in further detail below by way of examples, but the present application is not limited to the examples.

[0096] [Example 1]

[0097] A heavy-duty pneumatic tire (tire size = 355 / 50R22.5) having the basic structure shown in Fig. 1 and having the specifications shown in Table 1 below was obtained. Figures 1-3

[0098] In Example 1, the end portion of the full crown belt layer was disposed on the outer side of the shoulder circumferential groove in the axial direction. This is indicated by "Y" in the column of "Full Crown Belt Layer End Portion" in Table 1. The axial distance We from the end portion of the full crown belt layer to the inner end of the edge crown belt layer was 25 mm. The ratio (SF / WS) of the axial distance SF from the shoulder circumferential groove to the end portion of the full crown belt layer to the axial width WS of the shoulder land portion was 15%. Two belt plies were provided on the radially inner side of the full crown belt layer. This is indicated by "2" in the column of "Number of Belt Plies" in Table 1.

[0099] [Comparative Example 1]

[0100] The end portion of the full crown belt layer was disposed on the inner side of the shoulder circumferential groove in the axial direction, and the edge crown belt layer was not provided, and otherwise the tire of Comparative Example 1 was obtained similarly to Example 1. The case where the end portion of the full crown belt layer was on the inner side of the shoulder circumferential groove in the axial direction is indicated by "N" in the column of "Full Crown Belt Layer End Portion" in Table 1.

[0101] [Examples 2-4]

[0102] The distance We and the ratio (SF / WS) were as shown in Table 1 below, and otherwise the tires of Examples 2-4 were obtained similarly to Example 1.

[0103] [Examples 5-8]

[0104] The number of belt plies on the radially inner side of the full crown belt layer and the distance We and the ratio (SF / WS) were as shown in Table 2 below, and otherwise the tires of Examples 5-8 were obtained similarly to Example 1.

[0105] [Profile Change]

[0106] ​The test tire was assembled on a rim (11.75 x 22.5), filled with air and the internal pressure of the tire was adjusted to the regular internal pressure. The tire was made to run at a speed of 80 km / h for 1000 km in a drum tester, and the profile of the surface line on the inner side of the circumferential groove of the shoulder was obtained. The profile of the surface line before running was compared with the profile after running, and the change in the profile before and after running was confirmed. The result is indicated by an index according to the following rating in Table 1 and Table 2 below. The larger the value, the more the change in the profile is suppressed. In this running test, the regular load was imparted to the tire.

[0107]

[0108] [Resistance to Uneven Wear]

[0109] The test tire was assembled on a rim (11.75 x 22.5), filled with air and the internal pressure of the tire was adjusted to the regular internal pressure. The tire was installed on the drive shaft of a test vehicle (truck head). The test vehicle was made to tow a trailer loaded with cargo, and the test vehicle was made to run on a general road. At the time point when the wear rate of the tire in terms of mass reached 30%, the difference between the wear amount of the shoulder land portion and the wear amount of the center land portion of the test tire was calculated. The result is indicated by an index with Comparative Example 1 being 100 in Table 1 and Table 2 below. The larger the value, the smaller the difference in the wear amount, and the better the resistance to uneven wear.

[0110] [Resistance to JLB Breakage]

[0111] The tire in which the above evaluation of the resistance to uneven wear was performed was examined by sialography or X-ray, and the presence or absence of internal damage was confirmed. In the case where the internal damage was confirmed, the tire was disassembled, and it was confirmed whether or not the internal damage was the breakage of the crown ply cord of the full crown ply. The result is indicated according to the following rating in Table 1 and Table 2 below.

[0112] No breakage site of the crown ply cord ···· A

[0113] One breakage site of the crown ply cord ···· B

[0114] Two or more breakage sites of the crown ply cord ···· C

[0115] [Table 1]

[0116]

[0117] [Table 2]

[0118]

[0119] As shown in Tables 1 and 2, in the examples, the generation of the break of the crown belt cord was suppressed, and the shape change caused by running was suppressed, achieving an improvement in the resistance to uneven wear. According to this evaluation result, the superiority of the present application is apparent.

[0120] Industrial applicability

[0121] The technology described above for suppressing the shape change caused by running and achieving an improvement in the resistance to uneven wear can be applied to various tires.

Claims

1. A heavy-duty pneumatic tire having a nominal aspect ratio of 65% or less. This heavy-duty pneumatic tire has a tread that contacts the road surface and a reinforcing layer located radially inside the tread. By etching at least three circumferential grooves on the tire tread, at least four land sections are formed side by side along the axial direction. The circumferential groove located on the outer side of the at least three circumferential grooves in the axial direction is the shoulder circumferential groove, and the land section located on the outer side of the shoulder circumferential groove in the axial direction is the shoulder land section. The reinforcing layer has: A belt layer comprising multiple belted cords arranged side-by-side; and The coronal layer comprises coronal cord threads wound into a spiral shape. The belt layer has multiple belt fabric layers arranged radially. The coronal band layer has: The full canopy layer has two opposite ends separated by the equatorial plane; and A pair of marginal coronal layers, which are located radially outside the ends of the full coronal layer. The inner end of the marginal coronal band layer is located axially inside the end of the full coronal band layer. The plurality of belted cord fabric layers include a first belted cord fabric layer, a second belted cord fabric layer located radially outside the first belted cord fabric layer, and a third belted cord fabric layer located radially outside the second belted cord fabric layer, wherein the second belted cord fabric layer has the widest width. The first belted fabric layer, the second belted fabric layer, and the third belted fabric layer have a width greater than that of the full crown belt layer. The first and second belted fabric layers are located radially inside the full crown belt layer, and the full crown belt layer is located between the second and third belted fabric layers. The marginal coronal band layer repeats the end of the full coronal band layer radially, separated by the third bandage fabric layer. The outer end of the edge crown layer is located axially inside the end of the third belt cord fabric layer. The outer end of the marginal coronal band layer is located axially outside the end of the full coronal band layer, or the outer end of the marginal coronal band layer is axially aligned with the end of the full coronal band layer. In the axial direction, the end of the full crown belt layer is located outside the shoulder circumferential groove. The full crown band layer and the pair of marginal crown band layers each comprise crown band cords wound in a spiral shape. The axial distance from the end of the full coronal band to the inner end of the marginal coronal band is more than 10 mm.

2. The heavy-duty pneumatic tire according to claim 1, wherein, The ratio of the axial distance from the shoulder circumferential groove to the end of the full crown layer to the axial width of the shoulder land is more than 10% and less than 50%.

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