JP6790845B2 - Pneumatic tires for heavy loads - Google Patents

Description

The present invention relates to a heavy-duty pneumatic tire that can improve the durability of the bead portion.

For example, Patent Document 1 below proposes a heavy-duty pneumatic tire in which a reinforcing layer is provided on a bead portion. The reinforcing layer of Patent Document 1 is a first reinforcing layer composed of a layer of steel cord extending in a substantially U-shaped cross section around the folded portion of the carcass ply, and the reinforcing layer extending in the tire radial direction outside the tire axial direction of the first reinforcing layer. It is composed of a second reinforcing layer composed of a layer of organic fiber cord.

Japanese Unexamined Patent Publication No. 11-02421

By the way, the second reinforcing layer is composed of organic fiber cords arranged substantially in parallel and a topping rubber covering the organic fiber cords. As a result of various experiments, the inventors have found that adjusting the complex elastic modulus of the topping rubber constituting the second reinforcing layer unexpectedly significantly improves the durability of the bead portion.

The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a heavy-duty pneumatic tire capable of improving the durability of a bead portion.

The present invention is from a carcass ply including a main body portion that reaches the bead core of the bead portion from the tread portion through the sidewall portion, and a folded portion that is connected to the main body portion and folds around the bead core from the inside to the outside in the tire axial direction. A heavy-duty pneumatic tire having a carcass, and in the tire meridional cross section, at least a part of the bead portion extends from the inside of the folded portion in the tire radial direction to the outside in the tire radial direction in a substantially U shape. A first reinforcing layer composed of a layer of steel cord and a second reinforcing layer composed of a layer in which at least a part of the first reinforcing layer is covered with a topping rubber of an organic fiber cord extending in the tire radial direction on the outer side in the tire axial direction. The topping rubber of the second reinforcing layer has a complex elastic coefficient of 3 to 8 MPa.

In the heavy-duty pneumatic tire of the present invention, the second reinforcing layer has an inner second ply in contact with the first reinforcing layer and an outer second ply in contact with the inner second ply on the outer side of the inner second ply in the tire axial direction. It is desirable to include 2 plies.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the inner second ply has a topping gauge of 0.2 to 1.0 mm.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the outer second ply has a topping gauge of 0.2 to 1.0 mm.

In the heavy-duty pneumatic tire of the present invention, the bead portion is provided with a bead apex rubber that tapers outward in the tire radial direction from the bead core, and the bead apex rubber is provided on the tire radial outer side from the bead core. The complex elastic modulus of the topping rubber of the second reinforcing layer includes the inner apex extending and the outer apex arranged on the outer side in the tire radial direction of the inner apex, which is larger than the complex elastic modulus of the outer apex. Is desirable.

In the heavy-duty pneumatic tire of the present invention, the bead portion is provided with a chafer rubber covering the second reinforcing layer, and the chafer rubber has a complex elastic modulus larger than that of the topping rubber of the second reinforcing layer. Is desirable.

The bead portion of the heavy-duty pneumatic tire of the present invention includes a first layer of a steel cord extending in a substantially U shape from the inside of the folded portion of the carcass ply in the radial direction of the tire to the outside in the radial direction of the tire. A reinforcing layer and a second reinforcing layer composed of a layer in which at least a part of the first reinforcing layer is coated with a topping rubber on an organic fiber cord extending in the tire radial direction outside the tire axial direction is provided. According to such a reinforcing structure of the bead portion, the distortion of the bead portion during running of the tire is dispersed, and the durability of the bead portion is improved.

Further, since the topping rubber of the second reinforcing layer has a complex elastic modulus of 3 to 8 MPa, the binding force of the bead portion by the second reinforcing layer is optimized, and the durability of the bead portion is further improved.

It is sectional drawing of the heavy load pneumatic tire of one Embodiment of this invention. It is a side view of the bead part of FIG. It is an enlarged sectional view of the bead part of FIG. It is an enlarged perspective view which conceptually shows a part of the 2nd reinforcing layer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a cross-sectional view of a tire meridian including a rotation axis in a normal state of a pneumatic tire for heavy load (hereinafter, may be simply referred to as a “tire”) 1 of the present embodiment.

The "normal state" is a state in which the tire is rim-assembled on the normal rim R and is filled with the normal internal pressure without load. Hereinafter, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in this normal state.

A "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, "standard rim" for JATTA and "Design Rim" for TRA. If it is ETRTO, it is "Measuring Rim".

"Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATTA, "maximum air pressure", for TRA, the table "TIRE LOAD LIMITS AT" The maximum value described in "VARIOUS COLD INFLATION PRESSURES", or "INFLATION PRESSURE" for ETRTO.

As shown in FIG. 1, the tire 1 of the present embodiment has a toroid-shaped carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4. The carcass 6 is formed of at least one carcass ply 6A in this embodiment.

The carcass ply 6A includes a main body portion 6a and a folded portion 6b. The main body portion 6a reaches the bead core 5 of the bead portion 4 from the tread portion 2 through the sidewall portion 3. The folded-back portion 6b is connected to the main body portion 6a, is folded back from the inside to the outside in the tire axial direction around the bead core 5, and has an end portion 9 on the outside in the tire radial direction. The height H1 of the main body 6a of the carcass ply 6A with respect to the bead baseline BL is maximum near the tire equator C. In the present specification, the bead baseline BL is a tire axial line passing through a rim diameter position determined by a standard based on the tire.

FIG. 2 shows a side view of the bead portion 4. As shown in FIG. 2, the carcass ply 6A is preferably configured by arranging steel carcass cords c1 at an angle θ1 of 0 to 20 degrees with respect to the tire radial direction. The tire 1 having such a carcass ply 6A has a small rolling resistance and can contribute to low fuel consumption of the vehicle.

As shown in FIG. 1, it is desirable that the belt layer 7 is arranged outside the carcass 6 in the radial direction and inside the tread portion 2. The belt layer 7 is formed of, for example, a plurality of belt plies using a steel belt cord. The belt layer 7 of the present embodiment has, for example, a four-layer structure formed of the first to fourth belt plies 7A to 7D.

The bead portion 4 of the present embodiment includes a bead apex rubber 8 that tapers outward from the bead core 5 in the radial direction of the tire, and a first reinforcing layer 10 composed of a layer of a steel cord for reinforcing the bead portion 4. A second reinforcing layer 11 made of a layer of an organic fiber cord for reinforcing the bead portion 4 and a chafer rubber 12 in contact with the rim sheet surface R1 of the regular rim R are provided.

FIG. 3 shows an enlarged view of the bead portion 4. As shown in FIG. 3, the bead core 5 has, for example, a polygonal cross-sectional shape in which steel bead wires are wound in multiple rows and multiple stages. The bead core 5 of the present embodiment has, for example, a substantially hexagonal cross-sectional shape. The bead core 5 includes an outer surface 5a located on the outer side in the tire radial direction and extending in the tire axial direction, and an inner side surface 5b located on the inner side in the tire radial direction and extending in the tire axial direction.

The angle θ2 between the inner surface 5b of the bead core 5 and the rim seat surface R1 of the normal rim R in the normal state and the standard load state in which the normal load is applied to the normal state and grounded at a camber angle of 0 degrees (illustrated). (Omitted) is preferably 0 degrees ± 3 degrees. In the tire 1 having such a bead core 5, the rotation of the bead core 5 during traveling is suppressed, the tensile force of the carcass ply 6A at the bead portion 4 is reduced, and as a result, the bead durability can be improved.

Here, the "regular load" is a load defined for each tire in the standard system including the standard on which the tire is based. If it is JATTA, it is "maximum load capacity", and if it is TRA, it is. The maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", or "LOAD CAPACITY" for ETRTO.

In the above-mentioned bead core 5, when the regular rim R is a 15-degree tapered rim, for example, the inner side surface 5b when molding the bead portion 4 is inclined so that the inner diameter becomes larger toward the outer side in the tire axial direction. It is formed by making an angle of, for example, 15 to 20 degrees with respect to the tire axial direction. The 15-degree tapered rim is a rim in which the rim seat surface R1 is inclined from the inside in the tire axial direction to the outside in the radial direction of the tire at an angle of approximately 15 degrees.

The bead core 5 preferably includes, for example, a core body 5A made of bead wires and a wrapping layer 5B that covers the periphery of the core body 5A. The wrapping layer 5B is made of, for example, an organic fiber campus cloth such as nylon, and fixes the bead wire.

The bead apex rubber 8 of the present embodiment includes, for example, an inner apex 8A and an outer apex 8B arranged on the outer side of the inner apex 8A in the radial direction of the tire.

The inner apex 8A has, for example, a substantially triangular cross-sectional shape extending outward from the bead core 5 in the radial direction of the tire between the main body portion 6a and the folded-back portion 6b. The outer end 13 of the inner apex 8A in the tire radial direction is located, for example, on the outer surface of the main body 6a in the tire axial direction. It is desirable that the outer end 13 of the inner apex 8A is located, for example, outside the end portion 9 of the folded-back portion 6b in the radial direction of the tire.

The complex elastic modulus E * 2 of the inner apex 8A is preferably set to, for example, 40 to 65 MPa. Such an inner apex 8A can suppress deformation of the bead portion 4 in the tire axial direction and can exhibit excellent steering stability. Unless otherwise specified in the present specification, the complex elastic modulus E * of rubber is a value measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions in accordance with the provisions of JIS-K6394. Is.
Initial distortion: 10%
Amplitude: ± 2%
Frequency: 10Hz
Deformation mode: Tension measurement temperature: 70 ° C

The outer apex 8B is connected to the inner apex 8A via, for example, the boundary surface 14. The boundary surface 14 extends inward in the radial direction from the outer end 13 of the inner apex 8A toward the folded-back portion 6b, for example. It is desirable that the boundary surface 14 is formed in an arc shape that is convex toward the tire cavity surface side, for example, in the tire meridian cross section.

The complex elastic modulus E * 3 of the outer apex 8B is preferably set to 3 to 5 MPa, which is smaller than the complex elastic modulus E * 2 of the inner apex 8A, for example.

Such a bead apex rubber 8 can relax the shear stress acting on the folded-back portion 6b of the carcass ply 6A in the low elasticity outer apex 8B while ensuring sufficient bending rigidity when the bead portion 4 is deformed, such as separation. Can effectively prevent damage.

The first reinforcing layer 10 is formed of at least one layer of the steel cord ply 10A in this embodiment. In such a first reinforcing layer 10, the steel cord ply 10A enhances the bending rigidity of the bead portion 4, and thus effectively suppresses a large bending deformation of the bead portion 4 with the bead core 5 as a fulcrum in the tire axial direction. can do.

In the tire meridian cross section, at least a part of the steel cord ply 10A extends in a substantially U shape from the inside of the folded-back portion 6b in the radial direction of the tire to the outside in the radial direction of the tire. For example, at least a part of the steel cord ply 10A of the present embodiment is in contact with the main body portion 6a and the folded portion 6b. Such a steel cord ply 10A is effective in improving the riding comfort without excessively increasing the rigidity of the bead portion 4 on the outer side in the tire axial direction. However, the arrangement of the steel cord ply 10A is not limited to such an embodiment.

The outer end 15 of the steel cord ply 10A in the tire axial direction is located inside, for example, the end portion 9 of the folded-back portion 6b by a distance L1 in the tire radial direction. As a result, the concentration of strain near the outer end 15 of the steel cord ply 10A is suppressed. Therefore, damage such as separation starting from the outer end 15 can be suppressed.

The distance L1 is preferably 8 to 18 mm, more preferably 10 to 16 mm. If the distance L1 is smaller than 8 mm, the difference in rigidity at the outer end 15 of the steel cord ply 10A becomes large, and there is a possibility that damage such as separation starting from the outer end 15 may occur. If the distance L1 is larger than 18 mm, the bending rigidity of the bead portion 4 may be reduced.

The inner end 16 of the steel cord ply 10A in the tire axial direction is located, for example, inside the outer end 13 of the inner apex 8A in the tire radial direction. As a more desirable embodiment, the inner end 16 of the steel cord ply 10A is located inside the outer end 15 of the steel cord ply 10A in the tire radial direction. Such a steel cord ply 10A can have a relatively small length measured along its shape, and can achieve both weight reduction and a reinforcing effect.

As shown in FIG. 2, the steel cord ply 10A is configured, for example, by coating the steel cords c2 arranged in parallel with a topping rubber. The steel cord ply 10A preferably has a plurality of steel cords c2 inclined at an angle θ3 of 30 to 70 degrees with respect to the carcass cord c1. The number of arrangements of the steel cord c2 is preferably 20 to 40 per 50 mm of ply width.

It is desirable that the topping rubber of the steel cord ply 10A has, for example, a complex elastic modulus E * 4 of 4 to 10 MPa. Such a steel cord ply 10A has high rigidity and is useful for increasing the durability of the bead portion 4.

As shown in FIG. 3, the second reinforcing layer 11 is composed of at least a part of the first reinforcing layer 10 extending in the tire radial direction outside the tire axial direction. For example, at least a part of the second reinforcing layer 11 of the present embodiment is arranged inside the bead core 5 in the tire radial direction. As a result, the second reinforcing layer 11 of the present embodiment has, for example, a substantially L-shaped cross section.

FIG. 4 is an enlarged perspective view conceptually showing a part of the second reinforcing layer 11. As shown in FIG. 4, the second reinforcing layer 11 is composed of a layer in which the organic fiber cords c3 and c4 are coated with the topping rubber 22. The second reinforcing layer 11 of the present embodiment includes, for example, an inner second ply 11A and an outer second ply 11B in which the organic fiber cords arranged in parallel are coated on the topping rubber 22. The inner second ply 11A is, for example, at least partially in contact with the first reinforcing layer 10 (shown in FIG. 3). The outer second ply 11B is in contact with the inner second ply 11A, for example, on the outer side of the inner second ply 11A in the tire axial direction.

The topping rubber 22 of the second reinforcing layer 11 has a complex elastic modulus E * 1 of 3 to 8 MPa. The complex elastic modulus E * 1 is more preferably 5 to 7 MPa. As a result, the binding force of the bead portion 4 by the second reinforcing layer 11 is optimized, and the durability of the bead portion 4 is further improved. If the complex elastic modulus E * 1 is smaller than 3 MPa, the rigidity of the second reinforcing layer 11 may not be sufficiently secured. When the complex elastic modulus E * 1 is larger than 8 MPa, the difference in rigidity from the outer apex 8B becomes large, so that the second reinforcing layer 11 is easily peeled off, which may impair the durability of the bead portion 4.

Further, such a topping rubber 22 has a small difference in rigidity from the organic fiber cords c3 and c4, and is excellent in adhesion to these. Therefore, even if the bead portion 4 is repeatedly deformed, the organic fiber cords c3 and c4 are difficult to peel off from the topping rubber 22. Therefore, the durability of the bead portion 4 is maintained for a long period of time.

It is desirable that the complex elastic modulus E * 1 of the topping rubber 22 of the second reinforcing layer 11 is larger than, for example, the complex elastic modulus E * 3 of the outer apex 8B (shown in FIG. 3). Specifically, it is desirable that the complex elastic modulus E * 1 of the second reinforcing layer 11 is 1.3 to 2.0 times the complex elastic modulus E * 3 of the outer apex 8B. Such a second reinforcing layer 11 can enhance the durability of the bead portion 4 while maintaining the riding comfort.

The inner second ply 11A preferably has, for example, a topping gauge t1 of 0.2 to 1.0 mm. Similarly, the outer second ply 11B preferably has, for example, a topping gauge t2 of 0.2 to 1.0 mm. Such a second reinforcing layer 11 can sufficiently secure the thickness of the chafer rubber 12 (shown in FIG. 3) inside the bead core 5 in the tire radial direction while increasing the durability of the bead portion 4. This helps prevent heat damage to the chafer rubber 12. In addition, in this specification, a topping gauge means the thickness of each topping rubber before vulcanization molding.

As shown in FIG. 3, the inner second ply 11A and the outer second ply 11B overlap each other and cover the outer end 15 of the steel cord ply 10A from the outside in the tire axial direction. The second reinforcing layer 11 composed of two organic fiber cord plies has better flexibility and adhesion to a rubber member than the steel cord ply 10A. Therefore, the stress at the outer end 15 of the steel cord ply 10A can be relaxed and the separation there can be suppressed for a long period of time.

The outer end 17 of the inner second ply 11A of the present embodiment in the tire radial direction is located outside the tire radial direction by a distance L2 from the end portion 9 of the folded-back portion 6b. As a result, the inner second ply 11A covers the end portion 9 of the folded-back portion 6b. Therefore, the separation starting from the end 9 of the folded-back portion 6b can be effectively suppressed.

The distance L2 is preferably 8 to 18 mm, more preferably 10 to 16 mm. If the distance L2 is smaller than 8 mm, the difference in rigidity at the end portion 9 of the carcass ply 6A becomes large, and damage such as separation starting from the end portion 9 may occur. If the distance L2 is larger than 18 mm, the inner second ply 11A becomes easy to move, and there is a possibility that damage such as separation starting from the outer end 17 of the inner second ply 11A may occur.

It is desirable that the distance L2 between the outer end 17 of the inner second ply 11A and the end portion 9 of the folded-back portion 6b is substantially equal to the distance L1 between the end portion 9 of the folded-back portion 6b and the outer end 15 of the steel cord ply 10A. As a result, the stress of the bead portion 4 is uniformly dispersed, and the bead durability is further improved.

The inner end 18 of the inner second ply 11A in the tire radial direction is located inside the outer end 15 and the inner end 16 of the steel cord ply 10A in the tire radial direction. It is desirable that the inner end 18 of the inner second ply 11A is located inside the inner end 20 of the outer second ply 11B, which will be described later, in the tire axial direction. As a result, the concentration of strain near the inner end 18 of the inner second ply 11A is suppressed. Therefore, damage such as separation starting from the inner end 18 of the inner second ply 11A can be suppressed.

The outer end 19 of the outer second ply 11B in the tire radial direction is located, for example, the outer end 17 of the inner second ply 11A in the tire radial direction by a distance L3. As a result, the outer second ply 11B covers the outer end 17 of the inner second ply 11A, which is easily affected by the tensile force of the carcass ply 6A. Therefore, the separation starting from the outer end 17 of the inner second ply 11A is effectively suppressed.

The distance L3 is preferably 8 to 18 mm, more preferably 10 to 16 mm. If the distance L3 is smaller than 8 mm, the difference in rigidity at the outer end 17 of the inner second ply 11A becomes large, and there is a possibility that damage such as separation starting from the outer end 17 of the inner second ply 11A may occur. If the distance L3 is larger than 18 mm, the outer second ply 11B becomes easy to move, and damage such as separation starting from the outer end 19 of the outer second ply 11B may occur.

The distance L3 between the outer end 19 of the outer second ply 11B and the outer end 17 of the inner second ply 11A is substantially equal to the distance L2 between the outer end 17 of the inner second ply 11A and the end 9 of the folded-back portion 6b. Is desirable. In such a bead portion 4, the stress is uniformly dispersed, and the bead durability is further improved.

The height H2 in the tire radial direction from the bead baseline BL to the outer end 19 of the outer second ply 11B is preferably the maximum height H1 of the carcass ply 6A with respect to the bead baseline BL (shown in FIG. 1). 25% to 40%, more preferably 27% to 37%. Such an outer second ply 11B can enhance the durability of the bead portion 4 while suppressing an excessive increase in the tire weight.

The inner end 20 of the outer second ply 11B of the present embodiment in the tire radial direction is located in the inner region S1 inside the bead core 5 in the tire radial direction. Such an outer second ply 11B can effectively suppress the tensile force of the carcass ply 6A without significantly moving even when a tensile force is generated on the carcass ply 6A. Therefore, the tire 1 is suppressed from being strained due to the tensile force of the carcass ply 6A, and damage such as cracking due to the strain is suppressed. As a result, the bead durability of the bead portion 4 can be further improved.

The distance L4 (not shown) between the inner end 20 of the outer second ply 11B and the inner end 18 of the inner second ply 11A is the distance between the outer end 19 of the outer second ply 11B and the outer end 17 of the inner second ply 11A. It is desirable that it is approximately equal to the distance L3. That is, it is desirable that the outer second ply 11B and the inner second ply 11A have substantially the same length measured along their shapes. As a result, the same ply can be used for the outer second ply 11B and the inner second ply 11A. Therefore, the manufacturing cost can be reduced by sharing the parts.

As shown in FIG. 2, the inner second ply 11A preferably has a plurality of organic fiber cords c3 inclined at an angle θ4 of 40 to 80 degrees with respect to the carcass cord c1. The organic fiber cord c3 of the inner second ply 11A is more preferably inclined in one direction with respect to the carcass cord c1 at an angle θ4 of 50 to 70 degrees. Such an inner second ply 11A can effectively suppress the tensile force of the carcass ply 6A.

The outer second ply 11B preferably has a plurality of organic fiber cords c4 inclined at an angle θ5 of 40 to 80 degrees with respect to the carcass cord c1. The organic fiber cord c4 of the outer second ply 11B is more preferably inclined with respect to the carcass cord c1 at an angle θ5 of 50 to 70 degrees in the direction opposite to that of the inner second ply 11A. Such an outer second ply 11B can effectively suppress the tensile force of the carcass ply 6A.

It is desirable that the angle θ4 of each code c3 of the inner second ply 11A and the angle θ5 of each code c4 of the outer second ply 11B are substantially equal. Such an inner second ply 11A and an outer second ply 11B can complement each other to further suppress the tensile force of the carcass ply 6A.

The angle θ6 between the organic fiber cord c3 of the inner second ply 11A and the organic fiber cord of the outer second ply 11B is preferably, for example, 40 to 80 degrees. As a result, a sufficient tag effect is exhibited by the second plies 11A and 11B, respectively.

The inner second ply 11A and the outer second ply 11B described above can be used, for example, by inverting the front and back of the same ply during manufacturing. As a result, the inner second ply 11A and the outer second ply 11B can share parts, and the manufacturing cost of the tire 1 can be reduced.

As the organic fiber cords c3 and c4 of the second reinforcing layer 11, for example, a nylon cord, a polyester cord, an aromatic polyamide cord, a high-strength vinylon cord, or the like is preferably used. Such organic fiber cord plies c3 and c4 have higher flexibility than steel cord plies and are also excellent in adhesion to rubber members.

The organic fiber cords c3 and c4 are composed of, for example, a single twist. However, the present invention is not limited to such an embodiment, and the organic fiber cords c3 and c4 may be composed of, for example, two twists or three twists. The thickness of the organic fiber cords c3 and c4 is preferably 800 to 1500 dtex, more preferably 940 to 1400 dtex, for example. Such organic fiber cords c3 and c4 can increase the durability of the bead portion 4 while preventing an increase in tire weight.

In order to further enhance the above-mentioned effect, the number of organic fiber cords c3 and c4 arranged in the inner second ply 11A and the outer second ply 11B is preferably 30 to 50 per 50 mm of ply width, respectively.

As shown in FIG. 3, the chafer rubber 12 is located outside the second reinforcing layer 11 in the tire axial direction, and is in contact with the rim seat surface R1 of the regular rim R inside the bead core 5 in the tire radial direction. The outer end 21 of the chafer rubber 12 in the tire radial direction is located, for example, outside the outer end 19 of the outer second ply 11B in the tire radial direction.

The minimum thickness t3 of the bead core 5 of the chafer rubber 12 at the outer position in the tire axial direction is preferably 2.5 to 6.0 mm, more preferably 3.5 to 5.5 mm. If the minimum thickness t3 is smaller than 2.5 mm, the chafer rubber 12 may be hardened and damage such as cracking may occur. If the minimum thickness t1 is larger than 6.0 mm, the chafer rubber 12 may flow on the rim flange of the regular rim R, causing distortion on the tire surface.

It is desirable that the chafer rubber 12 has a complex elastic modulus E * 5, which is larger than that of the topping rubber 22 of the second reinforcing layer 11, for example. Specifically, the complex elastic modulus E * 5 of the chafa rubber 12 is preferably set to 7 to 14 MPa, more preferably 9 to 13 MPa. If the complex elastic modulus E * 5 is smaller than 7 MPa, the chafer rubber 12 may flow on the rim flange of the regular rim R, causing distortion on the tire surface. If the complex elastic modulus E * 5 is larger than 14 MPa, the chafer rubber 12 may be hardened and damage such as cracking may occur.

Although the heavy-duty pneumatic tire according to the embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and may be modified to various embodiments. ..

A size 295 / 80R22.5 heavy-duty pneumatic tire having the basic structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1. As a comparative example, a pneumatic tire for heavy loads, in which the complex elastic modulus E * 1 of the topping rubber of the second reinforcing layer is outside the range of the present invention, was prototyped. Durability was tested on the bead of each test tire. The common specifications and test methods for each test tire are as follows.
Mounting rim: 22.5 x 9.00
Tire internal pressure: 850kPa
<Carcass>
Carcass code angle: 0 degrees (with respect to tire radius direction)
<First reinforcement layer>
Steel cord angle: 60 degrees (relative to carcass cord)
Complex elastic modulus of topping rubber E * 4: 7MPa
<Second reinforcement layer>
Angle of organic fiber cord of inner second ply: 65 degrees (relative to carcass cord)
Angle of organic fiber cord of outer second ply: 65 degrees (relative to carcass cord)
Distance L2: 13mm
Distance L3: 13mm
H2 / H1 = 32.2%

<Bead part durability 1>
The test tire was run on a drum tester at a speed of 20 km / h under the condition of 200% of a standard load, and the mileage until the bead portion was damaged was measured. The result is an index with Comparative Example 1 as 100, and the larger the value, the better the durability of the bead portion.

<Bead part durability 2>
The rim was heated to 140 ° C. and traveled at a speed of 20 km / h under standard load conditions, and the mileage until the bead portion was damaged was measured. The result is an index with Comparative Example 1 as 100, and the larger the value, the better the durability of the bead portion.
The test results are shown in Table 1.

As a result of the test, it was confirmed that the durability of the bead portion of the tire of the example was improved.

2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Main body part 6b Folded part 10 1st reinforcing layer 11 2nd reinforcing layer 11A Inner 2nd ply 11B Outer 2nd ply 22 Topping rubber

Claims (6)

It has a carcass composed of a carcass ply including a main body portion from the tread portion to the bead core of the bead portion via the sidewall portion and a folded portion which is connected to the main body portion and folds around the bead core from the inside to the outside in the tire axial direction. Pneumatic tires for heavy loads
In the tire meridional cross section, the bead portion includes at least a first reinforcing layer composed of a layer of a steel cord extending in a substantially U shape from the inside of the folded portion in the tire radial direction to the outside in the tire radial direction. A second reinforcing layer is provided, which is partially composed of a layer in which an organic fiber cord extending in the radial direction of the tire is covered with a topping rubber on the outer side of the first reinforcing layer in the tire axial direction.
The topping rubber of the second reinforcing layer is a heavy-duty pneumatic tire having a complex elastic modulus of 3 to 8 MPa. The second reinforcing layer according to claim 1, wherein the second reinforcing layer includes an inner second ply in contact with the first reinforcing layer and an outer second ply in contact with the inner second ply on the outer side of the inner second ply in the tire axial direction. Pneumatic tires for heavy loads. The pneumatic tire for heavy loads according to claim 2, wherein the inner second ply has a topping gauge of 0.2 to 1.0 mm. The heavy-duty pneumatic tire according to claim 2 or 3, wherein the outer second ply has a topping gauge of 0.2 to 1.0 mm. The bead portion is provided with a bead apex rubber that tapers from the bead core toward the outside in the radial direction of the tire.
The bead apex rubber includes an inner apex extending outward in the tire radial direction from the bead core and an outer apex arranged on the tire radial outer side of the inner apex.
The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein the complex elastic modulus of the topping rubber of the second reinforcing layer is larger than the complex elastic modulus of the outer apex. A chafer rubber covering the second reinforcing layer is provided on the bead portion.
The pneumatic tire for heavy loads according to any one of claims 1 to 5, wherein the chafer rubber has a complex elastic modulus larger than that of the topping rubber of the second reinforcing layer.

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