JP2019209826A - Heavy duty pneumatic tire - Google Patents

Abstract

To provide a heavy duty pneumatic tire 2 capable of suppressing occurrence of shoulder abrasion in a shoulder part S.SOLUTION: A tire 2 is equipped with a fiber-reinforced layer 22 including a fiber cord 74 comprising a nylon fiber. The fiber-reinforced layer 22 comprises an inner ply 66 covering the outer end 60 of a steel-reinforced layer 20, and an outer ply 68 covering the outer end 70 of the inner ply 66. The inner ply 66 has an inner end 72 located inside the core 40 of a bead 8 in an axial direction. The outer ply 68 is located outside the inner end 72 of the inner ply 66 in the axial direction and has the inner end 78 located inside the core 40 in a radial direction. The ratio of the width of a shoulder rib 28s to that of a center rib 28c is 1.15 or more but 1.45 or less, and the width of a center main groove 26c is wider than that of a shoulder main groove 26s.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heavy duty pneumatic tire.

  Heavy duty pneumatic tires are mounted on large vehicles such as trucks and buses. A large load acts on the tire. Since distortion tends to concentrate on the bead portion, from the viewpoint of preventing damage, the bead portion is made of, for example, a steel reinforcing layer made of a steel cord layer or a fiber reinforcing layer made of an organic fiber cord layer. Reinforced.

  Use in high-temperature areas and areas with frequent braking is increasing. In order to withstand use in a harsh environment, in the tire, a configuration of a fiber reinforcing layer combined with a steel reinforcing layer has been studied (for example, Patent Document 1).

JP 2017-019452 A

  When the tire is filled with air, a force acts on the bead portion so as to tilt the bead portion outward in the axial direction. When the bead portion falls axially outward, the tread shoulder portion moves radially inward with respect to the tread center portion. Thereby, the difference between the circumferential length in the center portion and the circumferential length in the shoulder portion increases. Since this difference in circumferential length causes slippage with respect to the road surface, there is a risk that shoulder wear will occur in the shoulder portion.

  If the volume of the shoulder portion is increased by controlling the profile, there is a possibility that the slip of the shoulder portion based on the above-described difference in circumference can be suppressed. However, in this case, since the shoulder portion has a large volume, heat is accumulated in the shoulder portion, and there is a concern that damage such as looseness may occur in the end portion of the belt. Since the tire mass increases, rolling resistance may increase.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a heavy duty pneumatic tire capable of suppressing the occurrence of shoulder drop wear in the shoulder portion.

  The present inventor has intensively studied the technology for suppressing the occurrence of shoulder drop wear, and controls the rigidity of the bead portion, and the width of the main groove carved in the tread and the width of the rib formed by the main groove. By adjusting, it has been found that it is possible to suppress the fall of the bead portion outward in the axial direction, and to suppress the occurrence of shoulder drop wear without increasing the volume of the shoulder portion, and the present invention has been completed.

A heavy-duty pneumatic tire according to the present invention includes a pair of beads each having a core extending in the circumferential direction, a main body portion that bridges one core and the other core, and the main body portion connected to each other around each core. A carcass having a carcass ply having a pair of folded portions that are folded from the inner side toward the outer side in the axial direction, a tread that is positioned on the outer side in the radial direction of the main body portion, and folded around the core. A steel reinforcing layer including a plurality of parallel steel cords and an inner end located inside the main body portion and an outer end located outside the folded portion in the axial direction, and a plurality of parallel fiber cords A fiber reinforcing layer. The fiber cord is made of nylon fiber. The fiber reinforcing layer includes an inner ply that covers the outer end of the steel reinforcing layer from the outside in the axial direction, and an outer ply that covers the outer end of the inner ply from the outer side in the axial direction. The inner ply has an inner end located inside the core in the axial direction, the outer ply is located outside the inner end of the inner ply in the axial direction, and is located inside the core in the radial direction. Has an inner end. The tread includes at least four ribs formed by cutting at least three main grooves extending continuously in the circumferential direction in the tread.
Of the at least three main grooves, the main groove located on the inner side in the axial direction is the center main groove, and the main groove located on the outer side is the shoulder main groove. Of the at least four ribs, the rib located on the inner side in the axial direction is the center rib, and the rib located on the outer side is the shoulder rib. The ratio of the width of the shoulder rib to the width of the center rib is 1.15 or more and 1.45 or less, and the width of the center main groove is wider than the width of the shoulder main groove.

  Preferably, in the heavy duty pneumatic tire, the number of main grooves cut into the tread is 4 or more and 5 or less.

  Preferably, in the heavy duty pneumatic tire, a rib is located between the center rib and the shoulder rib, the rib is a middle rib, and a ratio of the width of the middle rib to the width of the center rib is 0.95. It is 1.05 or less.

  Preferably, in the heavy duty pneumatic tire, the land ratio in the tread is 80% or more.

  Preferably, in the heavy-duty pneumatic tire, the fiber cord in the inner ply is inclined with respect to the radial direction, and the fiber cord is inclined with respect to the radial direction in the outer ply. The inclination direction of the fiber cord in the inner ply is opposite to the inclination direction of the fiber cord in the outer ply.

  Preferably, in the heavy duty pneumatic tire, the inclination angle of the fiber cord in the inner ply is 55 ° or more and 75 ° or less, and the inclination angle of the fiber cord in the outer ply is 55 ° or more and 75 ° or less. .

  Preferably, in the heavy duty pneumatic tire, the outer end of the inner ply is located outside the end of the folded portion in the radial direction, and the radial direction from the end of the folded portion to the outer end of the inner ply The distance is 8 mm or more and 18 mm or less.

  Preferably, in the heavy duty pneumatic tire, a ratio of a radial distance from a bead base line to an outer end of the outer ply with respect to a reference height of the carcass is 25% or more and 40% or less.

  The heavy duty pneumatic tire of the present invention has a fiber reinforcing layer including a fiber cord made of nylon fiber in a bead portion, and a center main groove having a width wider than a width of the shoulder main groove is engraved. A tread having a shoulder rib having a width of 1.15 to 1.45 times the width is provided.

  In this tire, the bead portion can be prevented from falling outward in the axial direction at the time of air filling. Because the inward movement of the tread edge (shoulder) in the radial direction is suppressed, the difference between the circumference of the center (center) of the tread and the circumference of the shoulder is properly maintained in this tire. Is done. In this tire, since the slip of the shoulder portion is suppressed, occurrence of shoulder drop wear in the shoulder portion is suppressed.

  Further, in this tire, in order to suppress the above-described slip of the shoulder portion, it is not necessary to control the profile and increase the volume of the shoulder portion unlike the conventional tire. In the shoulder portion of the tire, occurrence of damage due to heat is suppressed. Since the tire mass is reduced, this tire can also reduce rolling resistance.

FIG. 1 is a cross-sectional view showing a part of a heavy duty pneumatic tire according to an embodiment of the present invention. FIG. 2 is a development view showing a tread surface of the tire of FIG. 1. FIG. 3 is a diagram for explaining the arrangement of carcass cords, steel cords, and fiber cords in the bead portion of the tire of FIG. FIG. 4 is a cross-sectional view showing a bead portion of the tire of FIG. 1.

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

  FIG. 1 shows a part of a heavy-duty pneumatic tire 2 (hereinafter sometimes simply referred to as “tire 2”) according to an embodiment of the present invention. The tire 2 is attached to a heavy load vehicle such as a truck or a bus.

  FIG. 1 shows a part of a cross section of the tire 2 along a plane including the rotation axis of the tire 2. In FIG. 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 paper surface of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2.

  In FIG. 1, a tire 2 is incorporated in a rim R. This rim R is a regular rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted to a normal internal pressure. No load is applied to the tire 2.

  In the present invention, the state in which the tire 2 is incorporated in the rim R (regular rim), the internal pressure of the tire 2 is adjusted to the normal internal pressure, and no load is applied to the tire 2 is referred to as a normal state. In the present invention, unless otherwise specified, the dimensions and angles of the tire 2 and each member of the tire 2 are measured in a normal state.

  In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims.

  In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in the JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “INFLATION PRESSURE” in the ETRTO standard are normal internal pressures.

  In the present specification, the normal load means a load defined in a standard on which the tire 2 depends. “Maximum value” published in “Maximum load capacity” in the JATMA standard, “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “LOAD CAPACITY” in the ETRTO standard are normal loads.

  In FIG. 1, a solid line BBL extending in the axial direction is a bead base line. This bead base line is a line that defines the rim diameter (refer to JATMA or the like) of the rim R (regular rim).

  The 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 cushion layer 16, an inner liner 18, a pair of steel reinforcing layers 20, and a pair of fiber reinforcements. Layer 22 is provided.

  The tread 4 is made of a crosslinked rubber. The tread 4 comes into contact with the road surface at the outer surface 24 thereof. The outer surface 24 of the tread 4 is a tread surface.

  In the tire 2, at least three main grooves 26 are cut in the tread 4. As a result, at least four ribs 28 are formed on the tread 4.

  FIG. 2 shows a development view of the tread surface 24. In FIG. 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 of FIG. 2 is the radial direction of the tire 2.

  In FIG. 2, the symbol PE is the end of the tread surface 24. When the end PE of the tread surface 24 cannot be identified in appearance, a normal load is applied to the tire 2 in the normal state, the camber angle is set to 0 °, and the tread 4 is brought into contact with the flat surface. The outer end in the axial direction is defined as the end PE of the tread surface 24.

  In the tire 2, four main grooves 26 are cut into the tread 4. These main grooves 26 are arranged in parallel in the axial direction and extend continuously in the circumferential direction. In the tire 2, four ribs 28 are formed in the tread 4 by carving four main grooves 26 in the tread 4. That is, the tread 4 includes five ribs 28 that are formed by carving four main grooves 26 in the tread 4. These ribs 28 are juxtaposed in the axial direction and extend continuously in the circumferential direction.

  In the tire 2, the main groove 26 c located on the inner side in the axial direction among the four main grooves 26 is located near the equator plane. In the tire 2, the main groove 26c close to the equator plane is the center main groove 26c. The main groove 26s located outside in the axial direction, that is, the main groove 26s close to the end PE of the tread surface 24 is the shoulder main groove 26s. When the main groove 26 carved in the tread 4 includes the main groove 26 positioned on the equator plane, the main groove 26 positioned on the equator plane is the center main groove. Further, when the main groove 26 exists between the center main groove 26c and the shoulder main groove 26s, the main groove 26 is a middle main groove.

  In FIG. 2, the double arrow TW is the tread width. The tread width TW is represented by a distance measured along the tread surface 24 from the end PE of one tread surface 24 to the end PE of the other tread surface 24. In FIG. 2, the double arrow GC is the width of the center main groove 26c. A double arrow GS indicates the width of the shoulder main groove 26s. In FIG. 1, the double arrow DC is the depth of the center main groove 26c. A double arrow DS indicates the depth of the shoulder main groove 26s.

  In the tire 2, the width GC of the center main groove 26c is preferably about 2 to 10% of the tread width TW from the viewpoint of contribution to drainage and traction performance. The depth DC of the center main groove 26c is preferably 13 to 25 mm.

  In the tire 2, the width GS of the shoulder main groove 26 s is preferably about 1 to 7% of the tread width TW from the viewpoint of contribution to drainage and traction performance. The depth DS of the shoulder main groove 26s is preferably 13 to 25 mm.

  In the tire 2, the rib 28 c located on the inner side in the axial direction among the five ribs 28 is located on the equator plane. In the tire 2, the rib 28c located on the equator plane is the center rib 28c. The ribs 28s located outside in the axial direction, that is, the ribs 28s including the end PE of the tread surface 24 are shoulder ribs 28s. Furthermore, a rib 28m located between the center rib 28c and the shoulder rib 28s is a middle rib 28m. Of the ribs 28 formed on the tread 4, when the rib 28 located on the inner side in the axial direction is located not on the equator plane but near the equator plane, the rib 28 positioned near the equator plane is used. Is the center rib.

  In FIG. 2, a double arrow RC is the width of the center rib 28c. The double arrow RS is the width of the shoulder rib 28s. A double arrow RM indicates the width of the middle rib 28m.

  In the tire 2, the width RC of the center rib 28c is preferably about 10 to 18% of the tread width TW from the viewpoint of steering stability and wet performance. From the same viewpoint, the width RM of the middle rib 28m is preferably about 10 to 18% of the tread width TW.

  As shown in FIG. 2, the center rib 28c of the tire 2 is provided with a plurality of sipes 30c that cross the center rib 28c. In the center rib 28c, these sipes 30c are arranged at intervals in the circumferential direction. A plurality of sipes 30m crossing the middle rib 28m are also engraved on the middle rib 28m. These sipes 30m are arranged at intervals in the circumferential direction. The sipe 30c of the center rib 28c and the sipe 30m of the middle rib 28m contribute to the improvement of the wet performance. The widths of these sipes 30 are set in the range of 0.5 mm to 1.5 mm. The depth of the sipe 30 is set in a range of 3 mm to 12 mm.

  On the shoulder rib 28s of the tire 2, a narrow vertical groove 32 extending continuously in the circumferential direction is formed. Thus, the shoulder rib 28s includes a rib main body 34 and a thin rib 36 positioned on the outer side in the axial direction of the rib main body 34. The fine ribs 36 suppress an excessive increase in the ground pressure at the end PE of the tread surface 24. Usually, the thin rib 36 is provided in a region where the distance measured along the tread surface 24 in the axially inward direction from the end PE of the tread surface 24 is 5 mm or less.

  In FIG. 1, the double arrow DT is the depth of the narrow vertical groove 32. In FIG. 2, the double-headed arrow GT is the width of the narrow vertical groove 32. In the tire 2, the width GT of the narrow vertical groove 32 is set to 30% or less of the width GS of the shoulder main groove 26s. The depth DT of the narrow vertical groove 32 is set in the range of 0.6 to 1.0 times the depth DS of the shoulder main groove 26s.

  As shown in FIG. 1, each sidewall 6 extends radially inward from the end of the tread 4. The outer surface 38 of the sidewall 6 forms the side surface of the tire 2. The sidewall 6 is made of a crosslinked rubber.

  Each bead 8 is located radially inward of the sidewall 6. The bead 8 includes a core 40 and an apex 42. The core 40 extends in the circumferential direction. The apex 42 is located on the radially outer side of the core 40. The apex 42 extends radially outward from the core 40.

  The core 40 includes a core body 40a and a wrapping layer 40b. The core body 40a includes a wound steel wire 44. The cross section of the core body 40 a includes a cross section of many wires 44. In the cross section of the core body 40a, a plurality of cross-sectional units each including a cross section of a plurality of wires 44 arranged in parallel in the substantially axial direction are stacked in a substantially radial direction. The wrapping layer 40b covers the periphery of the core body 40a. The wrapping layer 40b is made of an organic fiber canvas cloth, and restrains the bundle of wires 44 forming the core body 40a. Nylon fiber is mentioned as an organic fiber which comprises this canvas cloth.

  In the tire 2, the core 40 has a substantially hexagonal cross-sectional shape. The core 40 may be configured such that the core 40 has a substantially rectangular cross-sectional shape.

  The apex 42 includes an inner apex 42u and an outer apex 42s. The inner apex 42u is located on the radially outer side than the core 40. The outer apex 42s is located on the radially outer side than the inner apex 42u. The outer apex 42s contacts the inner apex 42u. The boundary between the inner apex 42u and the outer apex 42s bridges the outer end 46 of the inner apex 42u and the inner end 48 of the outer apex 42s. In the cross section of the tire 2 shown in FIG. 1, this boundary is curved inward in the axial direction.

  The inner apex 42u extends radially outward from the core 40. In the cross section of the tire 2 shown in FIG. 1, the inner apex 42u is tapered outward in the radial direction.

The inner apex 42u is made of a crosslinked rubber. In the tire 2, the complex elastic modulus E ^* u of the inner apex 42u is set in a range of 40 MPa to 65 MPa. The inner apex 42u is hard. The inner apex 42u contributes to the rigidity of the portion of the bead 8 (hereinafter, bead portion B).

In the present invention, the complex elastic modulus E ^* u of the inner apex 42u is measured under the following conditions using a viscoelastic spectrometer in accordance with the provisions of JIS-K6394. In addition, the complex elastic modulus E ^* s of the outer apex 42s and the complex elastic modulus E ^* c of the chafer 10 described later are measured in the same manner.
Initial strain = 10%
Amplitude = ± 1%
Frequency = 10Hz
Deformation mode = Tensile Measurement temperature = 70 ° C

  The outer apex 42s extends radially outward from the inner apex 42u. In the tire 2, the outer apex 42s has a large thickness in the vicinity of the outer end 46 of the inner apex 42u. In the cross section of the tire 2 shown in FIG. 1, the outer apex 42 s tapers radially inward and tapers radially outward.

The outer apex 42s is made of a crosslinked rubber. In the tire 2, the complex elastic modulus E ^* s of the outer apex 42s is set in a range of 3 MPa to 5 MPa. The outer apex 42s contributes to the supple deformation of the bead portion B.

  Each chafer 10 is located outside the bead 8 in the axial direction. The chafer 10 is located radially inward of the sidewall 6. The chafer 10 contacts the seat S and the flange F of the rim R. The chafer 10 covers the fiber reinforcement layer 22 from the outside in the axial direction.

The chafer 10 is made of a crosslinked rubber. In the tire 2, the complex elastic modulus E ^* c of the chafer 10 is set in the range of 7 MPa to 14 MPa. By setting the complex elastic modulus E ^* c of the chafer 10 to 7 MPa or more, occurrence of distortion on the surface of the tire 2 due to the protrusion of the chafer 10 is prevented. From this viewpoint, the complex elastic modulus E ^* c of the chafer 10 is preferably 9 MPa or more. By setting the complex elastic modulus E ^* c of the chafer 10 to 14 MPa or less, occurrence of damage due to hardening of the chafer 10 is prevented. From this viewpoint, the complex elastic modulus E ^* c of the chafer 10 is preferably 13 MPa or less.

  In the tire 2, the minimum thickness of the chafer 10 is set in a range of 2.5 mm or more and 6.0 mm or less between the core 40 and the flange F of the rim R. In the tire 2, the minimum thickness of the chafer 10 is set to 2.5 mm or more, so that damage due to hardening of the chafer 10 is prevented. By setting the minimum thickness of the chafer 10 to 6.0 mm or less, the occurrence of distortion on the surface of the tire 2 due to the protrusion of the chafer 10 is prevented.

  The carcass 12 is located inside the tread 4, the sidewall 6, and the chafer 10. The carcass 12 includes at least one carcass ply 50. The carcass 12 of the tire 2 includes a single carcass ply 50. The carcass ply 50 includes a large number of carcass cords arranged in parallel. These carcass cords are covered with a topping rubber.

  Each carcass cord intersects the equator plane. In the tire 2, the angle formed by the carcass cord with respect to the equator plane is not less than 70 ° and not more than 90 °. The carcass 12 of the tire 2 has a radial structure. In the tire 2, the carcass cord is made of steel. A cord made of organic fiber may be used as the carcass cord.

  FIG. 3 shows an arrangement state of the carcass cords 52 in the side portion of the tire 2. In FIG. 3, a solid line LR is a reference line extending in the radial direction. As shown in FIG. 3, the carcass cord 52 extends in the radial direction in the side surface portion of the tire 2.

  As shown in FIG. 1, in the tire 2, the carcass ply 50 is folded around each core 40 from the inner side toward the outer side in the axial direction. The carcass ply 50 includes a main body portion 50a that bridges one core 40 and the other core 40, and a pair of arms that are connected to the main body portion 50a and are folded from the inner side toward the outer side around each core 40. And a folded portion 50b. In the tire 2, the end 54 of the folded portion 50b is preferably located on the inner side of the outer end 46 of the inner apex 42u in the radial direction.

  In FIG. 1, reference symbol PC is a position where the radial distance from the bead base line to the inner surface of the carcass 12 is maximized. In the tire 2, the position PC is located on the equator plane. In FIG. 1, a double-headed arrow H1 is a radial distance from the bead base line to the position PC. In the present invention, this radial distance H1 is the reference height of the carcass 12.

  The belt 14 is located between the tread 4 and the carcass 12. The belt 14 is located on the radially outer side of the carcass 12. In the tire 2, the tread 4 is laminated on the belt 14.

  In the tire 2, the belt 14 includes four belt plies 56. In the tire 2, the number of belt plies 56 constituting the belt 14 is not particularly limited. The configuration of the belt 14 is appropriately determined in consideration of the specifications of the tire 2.

  Although not shown, each belt ply 56 includes a number of belt cords and topping rubbers arranged in parallel. Each belt cord is inclined with respect to the equator plane. In the tire 2, in the belt ply 56A located on the innermost side in the radial direction, the angle formed by the belt cord with respect to the equator plane is set in a range of 50 ° to 70 °. In the belt ply 56B, the belt ply 56C, and the belt ply 56D that are located on the radially outer side of the belt ply 56A, the angle formed by the belt cord with respect to the equator plane is set in the range of 15 ° to 35 °.

  In the tire 2, of the four belt plies 56, the belt ply 56B located between the belt ply 56A and the belt ply 56C has the maximum axial width. The belt ply 56D located on the outermost side in the radial direction has the smallest axial width. In the tire 2, the material of the belt cord is steel. A cord made of an organic fiber may be used as the belt cord.

  Each cushion layer 16 is located between the belt 14 and the carcass 12 at an end portion of the belt 14. The cushion layer 16 is made of a crosslinked rubber.

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

  FIG. 4 shows the bead portion B of FIG. In FIG. 4, 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 paper surface of FIG. 4 is the circumferential direction of the tire 2.

  Each steel reinforcing layer 20 is located in the bead portion B. The steel reinforcing layer 20 is folded along the carcass ply 50 around the core 40 from the inner side to the outer side in the axial direction. In the tire 2, at least a part of the steel reinforcing layer 20 is in contact with the carcass ply 50.

  The inner end 58 of the steel reinforcing layer 20 is located inside the main body 50a in the axial direction. The inner end 58 is located between the outer end 46 of the inner apex 42u and the core 40 in the radial direction. The outer end 60 of the steel reinforcing layer 20 is located outside the folded portion 50b in the axial direction. The outer end 60 is located between the end 54 of the folded portion 50b and the inner end 48 of the outer apex 42s in the radial direction. From the viewpoint of weight reduction and reinforcing effect, the inner end 58 of the steel reinforcing layer 20 is preferably positioned on the inner side of the outer end 60 of the steel reinforcing layer 20 in the radial direction.

  The steel reinforcing layer 20 includes at least one steel ply 62. In the tire 2, the steel reinforcing layer 20 includes a single steel ply 62. The steel ply 62 includes a number of steel cords arranged in parallel. These steel cords are covered with topping rubber.

  FIG. 3 shows an arrangement state of the steel cords 64 included in the steel ply 62 forming the steel reinforcing layer 20. As shown in FIG. 3, in the tire 2, the steel cord 64 in the steel reinforcing layer 20 is inclined with respect to the radial direction.

  In FIG. 3, the symbol θc is an angle formed by the steel cord 64 with respect to the radial direction. In the tire 2, the inclination angle θc of the steel cord 64 is not less than 30 ° and not more than 70 °. The number of steel cords 64 in the steel ply 62 is 20 or more and 40 or less per 50 mm width of the steel ply 62.

  In the tire 2, the steel reinforcing layer 20 contributes to an improvement in the bending rigidity of the bead portion B. In the tire 2, a large bending deformation of the bead portion B with the core 40 as a fulcrum toward the outside in the axial direction is effectively suppressed.

  Each fiber reinforcing layer 22 is located in the bead portion B. In the tire 2, at least a part of the fiber reinforcement layer 22 extends in the radial direction outside the steel reinforcement layer 20 in the axial direction. The fiber reinforcing layer 22 includes a large number of fiber cords arranged in parallel. These fiber cords are made of nylon fibers.

  The fiber reinforcement layer 22 includes at least an inner ply 66 and an outer ply 68 described later. In the tire 2, the fiber reinforcement layer 22 includes an inner ply 66 and an outer ply 68, that is, two plies.

  The inner ply 66 is in contact with the steel reinforcing layer 20. The inner ply 66 covers the outer end 60 of the steel reinforcing layer 20 from the outer side in the axial direction. In the radial direction, the outer end 70 of the inner ply 66 is located outside the outer end 60 of the steel reinforcing layer 20. The inner end 72 of the inner ply 66 is located outside the core 40 in the axial direction. In the axial direction, the inner end 72 of the inner ply 66 overlaps the core 40.

  As shown in FIG. 3, the inner ply 66 includes a number of fiber cords 74 in parallel. In the tire 2, the number of fiber cords 74 in the inner ply 66 is set in a range of 20 to 40 per 50 mm width of the inner ply 66.

  The outer ply 68 contacts the inner ply 66. The outer ply 68 covers the outer end 70 of the inner ply 66 from the outside in the axial direction. In the radial direction, the outer end 76 of the outer ply 68 is positioned outside the outer end 70 of the inner ply 66. The inner end 78 of the outer ply 68 is located outside the inner end 72 of the inner ply 66 in the axial direction and is located inside the core 40 in the radial direction.

  As shown in FIG. 3, the outer ply 68 includes a number of fiber cords 74 in parallel. In the tire 2, the number of fiber cords 74 in the outer ply 68 is set in a range of 20 to 40 per 50 mm width of the outer ply 68.

  In the tire 2, from the viewpoint of reducing manufacturing costs by sharing parts, the inner ply 66 and the outer ply 68 are measured along the shape of the cross section of the tire 2 shown in FIG. 4, for example. With respect to the length to be made, it is preferred to have the same length.

  In the tire 2, the fiber reinforcement layer 22 contributes to the rigidity of the bead portion B. In particular, since the fiber reinforcing layer 22 includes a fiber cord 74 made of nylon fiber, the bead portion B does not become too hard and has moderate flexibility. The fiber reinforcement layer 22 not only improves the durability of the bead part B but also suppresses the bead part B from falling outward in the axial direction when filled with air. In the tire 2, since the bead portion B is prevented from falling outward in the axial direction, movement of the end portion S (shoulder portion) of the tread 4 in the radial direction is also suppressed.

  In the tire 2, the center main groove 26c has a width GC wider than the width GS of the shoulder main groove 26s. In the tread 4 in which the center main groove 26c and the shoulder main groove 26s are engraved, the rigidity of the shoulder main groove 26s is appropriately maintained, so that the shoulder portion S is effectively moved inward in the radial direction. It is suppressed.

  In the tire 2, the width RS of the shoulder rib 28s is not less than 1.15 times and not more than 1.45 times the width RC of the center rib 28c. Since the shoulder rib 28s has an appropriate rigidity, the movement of the shoulder portion S inward in the radial direction is further effectively suppressed. Since the shoulder rib 28s is in sufficient contact with the road surface, the contact pressure on the shoulder rib 28s is appropriately maintained without being excessively increased.

  The tire 2 has a fiber reinforcement layer 22 including a fiber cord 74 made of nylon fiber in the bead portion B, and a center main groove 26c having a width GC wider than the width GS of the shoulder main groove 26s is engraved, and the center rib. The tread 4 includes a shoulder rib 28s having a width RS of 1.15 to 1.45 times the width RC of 28c.

  In the tire 2, the bead portion B is prevented from falling outward in the axial direction when the air is filled. Since the movement of the shoulder portion S inward in the radial direction is suppressed, in the tire 2, the difference between the circumferential length of the center portion C (center portion) of the tread 4 and the circumferential length of the shoulder portion S is appropriately maintained. . In the tire 2, since the slip of the shoulder portion S is suppressed, occurrence of shoulder drop wear in the shoulder portion S is suppressed.

  Furthermore, in this tire 2, in order to suppress the above-mentioned slip of the shoulder portion S, it is not necessary to increase the volume of the shoulder portion S by controlling the profile as in the conventional tire. In the shoulder portion S of the tire 2, the occurrence of damage due to heat is suppressed. Since the mass of the tire 2 is reduced, the tire 2 can also reduce rolling resistance.

  As described above, in the tire 2, the width GC of the center main groove 26c is wider than the width GS of the shoulder main groove 26s. From the viewpoint of effectively suppressing the occurrence of shoulder drop wear, the width GC of the center main groove 26c is preferably 1.1 times or more and 1.3 times or less than the width GS of the shoulder main groove 26s.

  As described above, in the tire 2, the width RS of the shoulder rib 28s is 1.15 to 1.45 times the width RC of the center rib 28c. From the viewpoint of effectively suppressing the occurrence of shoulder drop wear, the width RS of the shoulder rib 28s is preferably 1.20 times or more and more preferably 1.40 times or less the width RC of the center rib 28c.

  In the tire 2, when the land ratio in the tread 4 is set to 80% or more, the fiber reinforcing layer 22 provided in the bead portion B and the center GC having a width GC wider than the width GS of the shoulder main groove 26s. The tread 4 in which the main groove 26c is carved and the shoulder rib 28s having a width RS of 1.15 times or more and 1.45 times or less with respect to the width RC of the center rib 28c is formed on the shoulder portion S. The generation is more effectively suppressed. From this viewpoint, in the tire 2, the land ratio in the tread 4 is preferably 80% or more.

  In the present invention, the land ratio is the ratio between the surface area S of the tread surface 24 other than the groove, that is, the entire land portion, and the surface area Sa of the entire tread surface 24 obtained on the assumption that the tread surface 24 has no groove. It means a value expressed as a percentage of (S / Sa).

  As described above, in the tire 2, at least three main grooves 26 are formed in the tread 4. In particular, in the tire 2, when the number of main grooves 26 engraved in the tread 4 is 4 or more and 5 or less, in other words, when the tread 4 includes 5 or more and 6 or more ribs 28, The fiber reinforcement layer 22 provided in the bead portion B and the center main groove 26c having a width GC wider than the width GS of the shoulder main groove 26s are engraved, and are 1.15 times or more the width RC of the center rib 28c. The tread 4 in which the shoulder rib 28s having the width RS of 1.45 times or less is configured to more effectively suppress the occurrence of shoulder drop wear in the shoulder portion S. From this viewpoint, in the tire 2, the number of the main grooves 26 carved in the tread 4 is preferably 4 or more, and more preferably 5 or less.

  In the tread 4 of the tire 2, a middle rib 28m is located between the center rib 28c and the shoulder rib 28s. The width RM of the middle rib 28m affects the rigidity of the tread 4. From the viewpoint of effectively suppressing the inward movement of the shoulder portion S in the radial direction during the air filling, the width RM of the middle rib 28m is preferably 0.95 times or more the width RC of the center rib 28c. 1.05 times or less is preferable.

  As described above, the inner ply 66 and the outer ply 68 forming the fiber reinforcing layer 22 of the tire 2 each include a large number of fiber cords 74 arranged in parallel. As shown in FIG. 3, in the inner ply 66, the fiber cord 74 is inclined with respect to the radial direction. In the outer ply 68, the fiber cord 74 is inclined with respect to the radial direction. The inclination direction of the fiber cord 74 in the outer ply 68 is opposite to the inclination direction of the fiber cord 74 in the inner ply 66. The fiber reinforcement layer 22 including the inner ply 66 and the outer ply 68 effectively suppresses the bead portion B from falling outward in the axial direction when filled with air. From this viewpoint, in the tire 2, the fiber cord 74 in the inner ply 66 is inclined with respect to the radial direction, the fiber cord 74 is inclined with respect to the radial direction in the outer ply 68, and the fiber cord 74 in the inner ply 66 is inclined. The direction is preferably opposite to the direction of inclination of the fiber cord 74 in the outer ply 68.

  In FIG. 3, symbol θu is an angle formed by the fiber cord 74 in the inner ply 66 with respect to the radial direction. The symbol θs is an angle formed by the fiber cord 74 in the outer ply 68 with respect to the radial direction.

  In the tire 2, the inclination angle θu of the fiber cord 74 in the inner ply 66 is preferably 55 ° or more from the viewpoint of effectively preventing the bead portion B from falling outward in the axial direction when filled with air. 75 ° or less is preferable. From the same viewpoint, the inclination angle θs of the fiber cord 74 in the outer ply 68 is preferably 55 ° or more, and preferably 75 ° or less. From the viewpoint of more effectively preventing the bead portion B from falling outward in the axial direction during air filling, the inclination angle θu of the fiber cord 74 in the inner ply 66 and the inclination angle of the fiber cord 74 in the outer ply 68 are as follows. It is preferable to be equal to θs. In the present invention, when the absolute value of the difference between the inclination angle θu and the inclination angle θs is 2 ° or less, the inclination angle θu of the fiber cord 74 in the inner ply 66 and the inclination angle of the fiber cord 74 in the outer ply 68 It is determined that it is equal to θs.

  In FIG. 4, a double-headed arrow L1 is a radial distance from the outer end 60 of the steel reinforcing layer 20 to the end 54 of the folded portion 50b. A double-headed arrow L2 is a radial distance from the end 54 of the folded portion 50b to the outer end 70 of the inner ply 66. A double-headed arrow L3 is a radial distance from the outer end 70 of the inner ply 66 to the outer end 76 of the outer ply 68.

  In the tire 2, the outer end 60 of the steel reinforcing layer 20 is disposed away from the end 54 of the folded portion 50b inward in the radial direction by a distance L1. Thereby, the concentration of strain on the outer end 60 of the steel reinforcing layer 20 is suppressed. Since the bead portion B flexes flexibly, the force acting on the bead portion B is effectively relieved so as to be tilted outward in the axial direction. In the tire 2, the bead portion B is prevented from falling outward in the axial direction. From this point of view, the outer end 60 of the steel reinforcing layer 20 is located inside the end 54 of the folded portion 50b in the radial direction, and the radial distance from the end 54 of the folded portion 50b to the outer end 60 of the steel reinforcing layer 20 L1 is preferably 8 mm or more, and preferably 18 mm or less.

  In the tire 2, the outer end 70 of the inner ply 66 is disposed away from the end 54 of the folded portion 50b by a distance L2 outward in the radial direction. Thereby, the concentration of distortion on the end 54 of the folded portion 50b is suppressed. Since the bead portion B flexes flexibly, the force acting on the bead portion B is effectively relieved so as to be tilted outward in the axial direction. In the tire 2, the bead portion B is prevented from falling outward in the axial direction. From this viewpoint, the outer end 70 of the inner ply 66 is positioned outside the end 54 of the folded portion 50b in the radial direction, and the radial distance L2 from the end 54 of the folded portion 50b to the outer end 70 of the inner ply 66 is 8 mm or more is preferable and 18 mm or less is preferable. From the viewpoint of effectively preventing the bead portion B from falling outward in the axial direction, the distance L2 is more preferably equal to the distance L1 described above.

  In the tire 2, the outer end 76 of the outer ply 68 is disposed away from the outer end 70 of the inner ply 66 by a distance L3 outward in the radial direction. Thereby, the concentration of strain on the outer end 70 of the inner ply 66 is suppressed. Since the bead portion B flexes flexibly, the force acting on the bead portion B is effectively relieved so as to be tilted outward in the axial direction. In the tire 2, the bead portion B is prevented from falling outward in the axial direction. From this point of view, the outer end 76 of the outer ply 68 is positioned outside the outer end 70 of the inner ply 66 in the radial direction, and the radial distance from the outer end 70 of the inner ply 66 to the outer end 76 of the outer ply 68. L3 is preferably 8 mm or more, and preferably 18 mm or less. From the viewpoint of effectively preventing the bead portion B from falling outward in the axial direction, the distance L3 is more preferably equal to the distance L2.

  In the tire 2, the core 40 of the bead 8 has an inner side surface 80 that is located on the radially inner side and extends in the substantially axial direction, and an outer side surface 82 that is located on the radially outer side and extends in the substantially axial direction. In a state where the tire 2 is incorporated in the rim R, the inner side surface 80 and the outer side surface 82 extend along the seat S of the rim R. The inner side surface 80 and the outer side surface 82 extending in the substantially axial direction suppress the rotation of the core 40, in other words, the axial fall of the bead portion B. From this point of view, in the tire 2, the core 40 is located on the radially inner side and extends along the sheet S of the rim R, and located on the radially outer side of the rim R along the sheet S of the rim R. It preferably has an outer surface 82 that extends.

  In the tire 2, the tire 2 in a normal state, and the tire 2 in a normal load state in which a normal load is applied to the tire 2 in the normal state and the camber angle is set to 0 ° are brought into contact with the road surface. The angle formed by the inner side surface 80 of the 40 with respect to the sheet S of the rim R (the angle indicated by the symbol θr in FIG. 4) is preferably 0 ° ± 3 °. Thereby, the fall to the axial direction outward of the bead part B is suppressed more effectively.

  When the rim R is a 15 ° taper rim, the core 40 that contributes to the suppression of the bead portion B falling outward in the axial direction described above, for example, the inner side surface 80 when the bead portion B is molded, It is formed by an inclination in the direction of increasing the inner diameter outward in the direction and an angle of 20 ° with respect to the axial direction. The 15 ° taper rim is a rim in which the sheet S of the rim R is inclined at an angle of approximately 15 ° radially outward from the inner side in the axial direction to the outer side.

  In FIG. 4, a double-headed arrow H <b> 2 is a radial distance from the bead base line to the outer end 76 of the outer ply 68.

  In the tire 2, the ratio of the radial distance H2 from the bead base line to the outer end 76 of the outer ply 68 with respect to the reference height H1 of the carcass 12 is preferably 25% or more, and more preferably 40% or less. By setting this ratio to 25% or more, the fiber reinforcement layer 22 effectively contributes to suppression of the bead portion B from falling outward in the axial direction. In the tire 2, shoulder wear is suppressed. By setting this ratio to 40% or less, the influence of the fiber reinforcement layer 22 on the mass of the tire 2 is suppressed. In the tire 2, good rolling resistance is maintained.

  In FIG. 1, a double-headed arrow H3 is a radial distance from the bead base line to the outer end 84 of the outer apex 42s, that is, the outer end of the apex 42. This radial distance H3 is the apex height. A double-headed arrow H4 is a radial distance from the bead base line to the outer end 46 of the inner apex 42u. This radial distance H4 is the inner apex height.

  In the tire 2, from the viewpoint that the apex 42 contributes to the suppression of the fall of the bead portion B in the axially outward direction, the ratio of the apex height H3 to the reference height H1 of the carcass 12 is preferably 35% or more. 45% or less is preferable. From the viewpoint that the inner apex 42u contributes to suppression of the bead portion B from falling outward in the axial direction, the ratio of the inner apex height H4 to the apex height H3 is preferably 55% or more, and 75% or less. preferable.

  In FIG. 4, a double arrow H <b> 5 is a radial distance from the bead base line to the outer end 70 of the inner ply 66.

  In the tire 2, the outer end 46 of the inner apex 42 u is preferably located on the outer side of the outer end 70 of the inner ply 66 in the radial direction. Thereby, the apex 42 including the inner apex 42u and the fiber reinforcing layer 22 including the inner ply 66 contribute to synergistically suppressing the axially outward fall of the bead portion B. In the tire 2, shoulder wear is more effectively suppressed. From this viewpoint, the ratio of the inner apex height H4 to the radial distance H5 from the bead base line to the outer end 70 of the inner ply 66 is preferably 101% or more. From the viewpoint of appropriately maintaining the rigidity of the bead portion B, the ratio is preferably 130% or less, and more preferably 120% or less.

  As is apparent from the above description, according to the present invention, the heavy load pneumatic tire 2 capable of suppressing the occurrence of shoulder drop wear in the shoulder portion S is obtained.

  The embodiments disclosed herein are illustrative and non-restrictive in every respect. The technical scope of the present invention is not limited to the above-described embodiments, and the technical scope includes all modifications within the scope equivalent to the configurations described in the claims.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further in detail, this invention is not limited only to this Example.

[Example 1]
A heavy duty pneumatic tire (tire size = 12R22.5) having the basic configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained.

  This Example 1 includes a fiber reinforcing layer. This is indicated by “Y” in the “fiber reinforcing layer” column of the table. The inner side of the inner ply is located inside the core in the axial direction, the inner end of the outer ply is located axially outside the inner end of the inner ply, and is located radially inward of the core. “RI” is shown in the “end” column.

  In Example 1, the inclination angle θu of the fiber cord in the inner ply was 65 °. The inclination angle θs of the fiber cord in the outer ply was 65 °. The radial distance L2 from the end of the folded portion to the outer end of the inner ply was 10 mm. The ratio (H2 / H1) of the radial distance H2 from the bead base line to the outer end of the outer ply with respect to the carcass reference height H1 was 27%. The ratio of the inner apex height H4 to the radial distance H5 from the bead base line to the outer end of the inner ply (H4 / H5) was 113%. The ratio of the width RS of the shoulder rib to the width RC of the center rib (RS / RC) was 1.30.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as Example 1 except that the fiber reinforcing layer was not provided. The fact that no fiber reinforcing layer is provided is indicated by “N” in the “fiber reinforcing layer” column of the table.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the fiber reinforcement layer was not provided and the ratio (RS / RC) was as shown in Table 1 below.

[Comparative Example 3]
A tire of Comparative Example 3 was obtained in the same manner as in Example 1 except that the inner end of the inner ply was disposed on the radially inner side of the core and the outer end of the outer ply was disposed on the axially outer side of the core. The fact that the inner end of the inner ply is arranged on the inner side in the radial direction of the core and the outer end of the outer ply is arranged on the outer side in the axial direction of the core is indicated by “AO” in the column of “inner end” .

[Example 2]
A tire of Example 2 was obtained in the same manner as Example 1 except that the ratio (RS / RC) was as shown in Table 1 below.

[Example 3-4]
A tire of Example 3-4 was obtained in the same manner as in Example 1 except that the inclination angle θu and the inclination angle θs were set as shown in Table 1 below.

[Example 5]
A tire of Example 5 was obtained in the same manner as Example 1 except that the distance L2 and the ratio (H2 / H1) were as shown in Table 1 below.

[Example 6]
A tire of Example 6 was obtained in the same manner as Example 1 except that the ratio (H4 / H5) was as shown in Table 1 below.

[Uneven wear]
The prototype tire was assembled in a rim (size = 8.25 × 22.5), filled with air, and the internal pressure of the tire was adjusted to 850 kPa. This tire was mounted on the front axle of a high-speed bus, and the distance traveled until shoulder wear occurred was measured. The results are shown in Table 1 below, using an index with Comparative Example 3 as 100. The larger the value, the less likely the shoulder wear will occur and the better the uneven wear resistance.

  As shown in Table 1, in the examples, it is confirmed that occurrence of shoulder drop wear is suppressed. The examples are highly evaluated as compared to the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The above-described technique for suppressing the occurrence of shoulder drop wear can be applied to various tires.

DESCRIPTION OF SYMBOLS 2 ... Tire 4 ... Tread 6 ... Side wall 8 ... Bead 10 ... Chafer 12 ... Carcass 20 ... Steel reinforcement layer 22 ... Fiber reinforcement layer 24 ... External surface (tread surface)
26 ... main groove 26c ... center main groove 26s ... shoulder main groove 28 ... rib 28c ... center rib 28s ... shoulder rib 28m ... middle rib 40 ... core 42 ... · Apex 42u · · · inner apex 42s · · · outer apex 46 · · · outer end of inner apex 42u 48 · · · inner end of outer apex 42s 50 · carcass ply 50a · · · body Numeral 50b ... Folded part 52 ... Carcass cord 54 ... End of folded part 50b 58 ... Inner end of steel reinforcing layer 20 ... Outer end of steel reinforcing layer 20 64 ... Steel cord 66 ... Inner ply 68 ... Outer ply 70 ... Outer end of inner ply 66 72 ... Inner end of inner ply 66 74 ... Fiber cord 6 ... outer surface of the inner surface 82 ... core 40 of the inner end 80 ... core 40 of the outer end 78 ... outer ply 68 of the outer ply 68

Claims (8)

A pair of beads having a circumferentially extending core;
A carcass having a carcass ply having a main body portion that spans one core and the other core, and a pair of folded portions that are connected to the main body portion and are folded from the inside toward the outside in the axial direction around each core. When,
A tread located on the radially outer side of the main body,
A plurality of steel cords that are folded around the core and have an inner end positioned inside the body portion in the axial direction and an outer end positioned outside the folded portion in the axial direction, and arranged in parallel; A steel reinforcement layer,
A fiber reinforcement layer including a large number of parallel fiber cords,
The fiber cord is made of nylon fiber,
The fiber reinforcing layer includes an inner ply that covers the outer end of the steel reinforcing layer from the outside in the axial direction, and an outer ply that covers the outer end of the inner ply from the outer side in the axial direction.
The inner ply has an inner end located inside the core in the axial direction;
The outer ply is located outside the inner end of the inner ply in the axial direction, and has an inner end located inside the core in the radial direction;
The tread includes at least four ribs formed by carving at least three main grooves extending continuously in the circumferential direction in the tread;
Of the at least three main grooves, the main groove located on the inner side in the axial direction is the center main groove, and the main groove located on the outer side is the shoulder main groove,
Of the at least four ribs, the rib located on the inner side in the axial direction is the center rib, and the rib located on the outer side is the shoulder rib,
The ratio of the width of the shoulder rib to the width of the center rib is 1.15 or more and 1.45 or less,
A heavy duty pneumatic tire, wherein the center main groove is wider than the shoulder main groove.   The heavy-duty pneumatic tire according to claim 1, wherein the number of main grooves carved in the tread is 4 or more and 5 or less. A rib is located between the center rib and the shoulder rib, the rib is a middle rib,
The heavy duty pneumatic tire according to claim 2, wherein a ratio of a width of the middle rib to a width of the center rib is 0.95 or more and 1.05 or less.   The heavy duty pneumatic tire according to any one of claims 1 to 3, wherein a land ratio in the tread is 80% or more. In the inner ply, the fiber cord is inclined with respect to the radial direction,
In the outer ply, the fiber cord is inclined with respect to the radial direction,
The heavy duty pneumatic tire according to any one of claims 1 to 4, wherein an inclination direction of the fiber cord in the inner ply is opposite to an inclination direction of the fiber cord in the outer ply. In the inner ply, the inclination angle of the fiber cord is 55 ° or more and 75 ° or less,
The heavy tire for a heavy load according to claim 5, wherein an inclination angle of the fiber cord is 55 ° or more and 75 ° or less in the outer ply. In the radial direction, the outer end of the inner ply is located outside the end of the folded portion,
The heavy duty pneumatic tire according to any one of claims 1 to 6, wherein a radial distance from an end of the folded portion to an outer end of the inner ply is 8 mm or more and 18 mm or less. The heavy load pneumatic according to any one of claims 1 to 7, wherein a ratio of a radial distance from a bead base line to an outer end of the outer ply with respect to a reference height of the carcass is 25% or more and 40% or less. tire.