JP6790846B2 - Pneumatic tires for heavy loads - Google Patents

Description

The present invention relates to a heavy-duty pneumatic tire with improved 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 includes a first reinforcing layer including a steel cord extending in a substantially U-shaped cross section around the folded portion of the carcass ply, and an organic fiber extending in the tire radial direction outside the tire axial direction of the first reinforcing layer. It is composed of a second reinforcing layer including a cord.

Japanese Unexamined Patent Publication No. 11-02421

However, when the heavy-duty pneumatic tire of Patent Document 1 is used, for example, in a high temperature area or an area where braking frequency is high, the temperature of the bead portion near the rim flange tends to be high, and rubber flows on the rim flange. After that, there was a problem of hardening. The hardened rubber causes damage such as cracks due to the tensile force of the carcass ply, which causes the durability of the bead portion to decrease.

The present invention has been devised in view of the above circumstances, and is based on the fact that the second reinforcing layer provided on the bead portion has an inner second ply and an outer second ply. Its main purpose is to provide pneumatic tires for heavy loads with improved durability.

The present invention is a heavy-duty pneumatic tire including a troid-shaped carcass that extends from the tread portion through the sidewall portion to the bead core of the bead portion, wherein the carcass is the bead portion from the tread portion through the sidewall portion. The bead portion has a carcass ply including a main body portion leading to the bead core 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, and the bead portion has a tire meridional cross section. At least a part of the first reinforcing layer extending from the inside of the folded portion in the tire radial direction toward the outside of the tire radial direction in a substantially U shape, and at least a part of the first reinforcing layer on the outside of the tire axial direction in the tire radial direction. A second reinforcing layer extending is provided, the carcass ply includes a steel carcass cord having an angle of 0 to 20 ° with respect to the tire radial direction, and the first reinforcing layer is relative to the carcass cord. The second reinforcing layer has an inner second ply in contact with the steel cord ply and the inner second ply on the outer side of the inner second ply in the tire axial direction. It has an outer second ply that is in contact with the outer second ply, and the outer end portion of the outer second ply in the tire radial direction is located outside the tire radial outer end of the inner second ply in the tire radial direction. The second ply includes an inner organic fiber cord that inclines in the same direction as the steel cord with respect to the carcass cord, and the outer second ply inclines in the direction opposite to the inner organic fiber cord with respect to the carcass cord. It is characterized by containing an outer organic fiber cord.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the inclination angle of the inner organic fiber cord with respect to the carcass cord is smaller than the inclination angle of the steel cord with respect to the carcass cord.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the inclination angle of the outer organic fiber cord with respect to the carcass cord is substantially equal to the inclination angle of the inner organic fiber cord with respect to the carcass cord.

In the heavy-duty pneumatic tire of the present invention, the inclination angle of the inner organic fiber cord and the outer organic fiber cord with respect to the carcass cord is 20 to 60 °, and the inclination angle of the steel cord with respect to the carcass cord is 50. It is preferably ~ 70 °.

In the heavy load pneumatic tire of the present invention, the distance between the end of the outer second ply and the end of the inner second ply is preferably 8 to 18 mm.

In the heavy-duty pneumatic tire of the present invention, the folded-back portion has an end portion on the outer side in the radial direction of the tire, and the end portion of the inner second ply is outer side in the radial direction of the tire than the end portion of the folded-back portion. It is desirable that the distance between the end portion of the inner second ply and the end portion of the folded-back portion is 8 to 18 mm.

In the heavy-duty pneumatic tire of the present invention, the bead portion is provided with a chafer rubber in contact with the rim seat surface of the regular rim, and the minimum thickness of the chafer rubber at the outer position of the bead core in the tire axial direction is determined. It is preferably 2.5 to 6.0 mm.

In the heavy-duty pneumatic tire of the present invention, the bead portion is provided with a chafer rubber in contact with the rim seat surface of the regular rim, and the complex elastic modulus of the chafer rubber is preferably 7 to 14 MPa.

In the heavy-duty tire of the present invention, the second reinforcing layer includes an inner second ply in contact with the steel cord ply 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. The outer end of the outer second ply is located outside in the tire radial direction with respect to the outer end of the inner second ply. Since such a second reinforcing layer can cover the end portion of the inner second ply, which is easily affected by the tensile force of the carcass ply, with the outer second ply, damage such as cracking or peeling from the outer second ply can be caused. Can be suppressed.

In the heavy-duty tire of the present invention, the inner second ply includes an inner organic fiber cord that is inclined in the same direction as the steel cord with respect to the carcass cord, and the outer second ply is the inner organic fiber with respect to the carcass cord. Contains an outer organic fiber cord that slopes in the opposite direction of the cord. Such an outer second ply and an inner second ply can effectively suppress the tensile force of the carcass ply, and thus can reduce the damage to the bead portion due to the hardening of the rubber. Therefore, the heavy-duty tire of the present invention can improve the durability of the bead portion.

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.

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 1 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 1 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 1 is based. For example, "standard rim" for JATTA and "Design Rim" for TRA. , ETRTO is "Measuring Rim".

"Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which Tire 1 is based. For JATMA, "maximum air pressure", for TRA, the table "TIRE LOAD LIMITS" The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES", or "INFLATION PRESSURE" for ETRTO.

As shown in FIG. 1, the tire 1 of the present embodiment includes 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 has at least one carcass ply 6A, and in this embodiment, one carcass ply 6A.

The carcass ply 6A preferably includes a main body portion 6a and a folded portion 6b. The main body portion 6a of the present embodiment 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 of the present embodiment is connected to the main body portion 6a and is folded back around the bead core 5 from the inside to the outside in the tire axial direction. The folded-back portion 6b has, for example, a first end portion 9 on the outer side in the radial direction of the tire. The height H1 of the main body 6a of the carcass ply 6A of the present embodiment with reference to the bead baseline BL is the maximum near the tire equator C.

FIG. 2 shows a side view of the bead portion 4. As shown in FIG. 2, the carcass ply 6A preferably includes a steel carcass cord c1 having an angle θ1 of 0 to 20 ° with respect to the tire radial direction. In the present specification, the tire radiation direction is a direction along the shape of the ply on a plane including the rotation axis of the tire 1. 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 of the tire and inside the tread portion 2. The belt layer 7 has a plurality of belt plies including, for example, a steel belt cord. The belt layer 7 of the present embodiment has 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 and a second reinforcing layer 11 for reinforcing the bead portion 4. , A chafer rubber 12 in contact with the rim seat surface R1 of the regular rim R is 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 a substantially hexagonal cross-sectional shape. It is desirable that 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.

In the normal state and the standard load load state in which the normal load is applied to the normal state and grounded at a camber angle of 0 °, the angle θ2 formed by the inner surface 5b of the bead core 5 and the rim seat surface R1 of the normal rim R is It is desirable that it is 0 ° ± 3 °. 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 durability of the bead portion 4 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 1 is based, and if it is JATTA, it may be "maximum load capacity" or TRA. For example, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and for ETRTO, "LOAD CAPACITY".

In the above-mentioned bead core 5, when the regular rim R is a 15 ° 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 setting an angle of 20 ° with respect to the tire axial direction. The 15 ° 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 °. In this specification, the dimensions and the like of each part marked with "abbreviation" include those having an error of less than 10%.

The bead core 5 preferably includes 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 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 second end portion 13 on the outer side in the tire radial direction of the inner apex 8A is located, for example, on the outer surface in the tire axial direction of the main body portion 6a. It is desirable that the second end portion 13 of the inner apex 8A is located outside the first end portion 9 of the folded-back portion 6b in the radial direction of the tire.

The complex elastic modulus E * 1 of the inner Apex 8A is preferably 40 to 65 MPa. In the present specification, the complex elastic modulus of the rubber material constituting the tire 1 is a value measured using a viscoelastic spectrometer under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2%. Is.

The outer apex 8B is connected to the inner apex 8A, for example, via a boundary surface 14 extending inward in the radial direction from the second end portion 13 of the inner apex 8A toward the folded-back portion 6b. The complex elastic modulus E * 2 of the outer apex 8B is preferably 3 to 5 MPa, which is smaller than the complex elastic modulus E * 1 of the inner apex 8A.

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

The first reinforcing layer 10 has at least one steel cord ply 10A, and in this embodiment, one steel cord ply 10A. In such a first reinforcing layer 10, the steel cord ply 10A increases the bending rigidity of the bead portion 4 and effectively suppresses a large bending deformation of the bead portion 4 with the bead core 5 as a fulcrum outward in the tire axial direction. be able to.

It is desirable that 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 in the tire meridian cross section. 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-back portion 6b of the carcass ply 6A. Such a steel cord ply 10A does not excessively increase the rigidity of the bead portion 4 on the outer side in the tire axial direction, and improves the riding comfort. The arrangement of the steel cord ply 10A is not limited to such an embodiment.

It is desirable that the third end portion 15 on the outer side of the steel cord ply 10A in the tire axial direction is located on the inner side in the tire radial direction with respect to the first end portion 9 of the folded-back portion 6b. As a result, the third end portion 15 of the steel cord ply 10A can be prevented from concentrating strain in the vicinity thereof. Such a bead portion 4 can suppress damage such as separation starting from the third end portion 15.

The distance L1 between the third end portion 15 of the steel cord ply 10A and the first end portion 9 of the folded-back portion 6b is preferably 8 to 18 mm. If the distance L1 is smaller than 8 mm, the difference in rigidity at the third end portion 15 of the steel cord ply 10A becomes large, and there is a possibility that damage such as separation starting from the third end portion 15 may occur. If the distance L1 is larger than 18 mm, the bending rigidity of the bead portion 4 may not be improved.

It is desirable that the fourth end portion 16 on the inner side of the steel cord ply 10A in the tire axial direction is located on the inner side in the tire radial direction with respect to the second end portion 13 of the inner apex 8A, for example. As a more desirable embodiment, the fourth end portion 16 of the steel cord ply 10A is located inside the third end portion 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. Here, the length measured along the shape is the so-called periferi length.

As shown in FIG. 2, the steel cord ply 10A preferably includes a steel cord c2 that is inclined with respect to the carcass cord c1. The inclination angle θ3 of the steel cord c2 with respect to the carcass cord c1 is preferably 50 to 70 °. The number of arrangements of the steel cord c2 is preferably 20 to 40 per 50 mm of ply width. Such a steel cord ply 10A can increase the bending rigidity of the bead portion 4, and can more effectively suppress a large bending deformation of the bead portion 4 with the bead core 5 as a fulcrum in the tire axial direction.

As shown in FIG. 3, it is desirable that at least a part of the second reinforcing layer 11 extends in the tire radial direction outside the tire axial direction of the first reinforcing layer 10. The second reinforcing layer 11 of the present embodiment has an inner second ply 11A in contact with the steel cord ply 10A and an outer second ply 11B in contact with the inner second ply 11A on the outer side of the inner second ply 11A in the tire axial direction. doing.

In such a second reinforcing layer 11, even if the temperature of the bead portion 4 near the rim flange of the regular rim R becomes high, the chafer rubber 12 in contact with the rim sheet surface R1 softens due to the influence of heat or the like. It can prevent it from flowing over the rim flange and then curing. Therefore, the bead portion 4 can reduce damage caused by hardening of the rubber.

As shown in FIG. 2, the inner second ply 11A of the present embodiment includes an inner organic fiber cord c3 that is inclined in the same direction as the steel cord c2 with respect to the carcass cord c1. Further, the outer second ply 11B of the present embodiment includes an outer organic fiber cord c4 that is inclined in the direction opposite to the inner organic fiber cord c3 with respect to the carcass cord c1. Such an inner second ply 11A and an outer second ply 11B complement each other to effectively suppress the tensile force of the carcass ply 6A, and thus reduce the damage to the bead portion 4 due to the hardening of the rubber. be able to. As a result, the tire 1 of the present embodiment can further improve the durability of the bead portion 4.

As shown in FIG. 3, the inner second ply 11A and the outer second ply 11B overlap each other and cover the third end portion 15 of the steel cord ply 10A from the outside in the tire axial direction. Such a second reinforcing layer 11 has superior flexibility and adhesion to a rubber member as compared with the steel cord ply 10A. Therefore, the stress at the third end portion 15 of the steel cord ply 10A is relaxed, and damage such as separation starting from the third end portion 15 can be suppressed for a long period of time. Further, the second reinforcing layer 11 of the present embodiment can relax the shear stress acting on the folded-back portion 6b of the carcass ply 6A, and can reduce the strain due to the shear stress.

It is desirable that the fifth end portion 17 on the outer side of the inner second ply 11A in the radial direction of the tire is located on the outer side in the radial direction of the tire with respect to the first end portion 9 of the folded-back portion 6b. Such an inner second ply 11A can cover the first end portion 9 of the folded-back portion 6b. Therefore, the bead portion 4 can effectively suppress damage such as separation starting from the first end portion 9 of the folded portion 6b.

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

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

The sixth end portion 18 inside the inner second ply 11A in the tire radial direction is located inside the tire radial direction with respect to the third end portion 15 and the fourth end portion 16 of the steel cord ply 10A. It is desirable that the sixth end 18 of the inner second ply 11A is located inside the eighth end 20 of the outer second ply 11B, which will be described later, in the tire axial direction. As a result, it is possible to suppress the concentration of strain in the vicinity of the sixth end portion 18 of the inner second ply 11A. Such a bead portion 4 can suppress damage such as separation starting from the sixth end portion 18 of the inner second ply 11A.

It is desirable that the seventh end 19 on the outer side of the outer second ply 11B in the radial direction of the tire is located outside the fifth end 17 of the inner second ply 11A in the radial direction of the tire. Such an outer second ply 11B can cover the fifth end 17 of the inner second ply 11A, which is easily affected by the tensile force of the carcass ply 6A. Therefore, the bead portion 4 can effectively suppress damage such as separation starting from the fifth end portion 17 of the inner second ply 11A.

The distance L3 between the seventh end 19 of the outer second ply 11B and the fifth end 17 of the inner second ply 11A is preferably 8 to 18 mm. If the distance L3 is smaller than 8 mm, the difference in rigidity at the fifth end 17 of the inner second ply 11A becomes large, and damage such as separation starting from the fifth end 17 of the inner second ply 11A may occur. There is. 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 seventh end 19 of the outer second ply 11B may occur.

The distance L3 between the 7th end 19 of the outer 2nd ply 11B and the 5th end 17 of the inner 2nd ply 11A is the 5th end 17 of the inner 2nd ply 11A and the 1st end 9 of the folded-back portion 6b. It is desirable that the distance to L2 is approximately equal to. In such a bead portion 4, the stress is uniformly dispersed, and the durability thereof is further improved.

The height H2 in the tire radial direction from the bead baseline BL to the 7th end 19 of the outer second ply 11B is preferably 25% of the maximum height H1 of the carcass ply 6A with respect to the bead baseline BL. It is 40%. When the height H2 of the 7th end 19 is smaller than 25% of the maximum height H1 of the carcass ply 6A, the chafer rubber 12 flows on the rim flange of the regular rim R, and the effect of suppressing hardening is small. There is a risk of becoming. When the height H2 of the 7th end 19 is larger than 40% of the maximum height H1 of the carcass ply 6A, the outer 2nd ply 11B becomes easy to move, and the 7th end 19 of the outer 2nd ply 11B is the starting point. There is a risk of damage such as separation.

The eighth end 20 inside the tire radial direction of the outer second ply 11B of the present embodiment is located in the inner region S1 inside the tire radial direction of the bead core 5. 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 tire 1 of the present embodiment can improve the durability of the bead portion 4.

The distance L4 between the 8th end 20 of the outer 2nd ply 11B and the 6th end 18 of the inner 2nd ply 11A is the 7th end 19 of the outer 2nd ply 11B and the 5th end of the inner 2nd ply 11A. It is desirable that the distance to the portion 17 is substantially equal to 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 inclination angle θ4 of the inner organic fiber cord c3 of the inner second ply 11A with respect to the carcass cord c1 is preferably 20 to 60 °. The inner organic fiber cord c3 is more preferably inclined with respect to the carcass cord c1 in the same direction as the steel cord c2 at an inclination angle θ4 of 30 to 50 °. Such an inner second ply 11A can effectively suppress the tensile force of the carcass ply 6A, and as a result, the durability of the bead portion 4 can be further improved.

It is desirable that the inclination angle θ4 of the inner organic fiber cord c3 is smaller than the inclination angle θ3 of the steel cord c2. Such an inner second ply 11A can more effectively suppress damage such as separation starting from the third end portion 15 of the steel cord ply 10A.

The inclination angle θ5 of the outer organic fiber cord c4 of the outer second ply 11B with respect to the carcass cord c1 is preferably 20 to 60 °. The outer organic fiber cord c4 is more preferably inclined with respect to the carcass cord c1 in the direction opposite to that of the inner organic fiber cord c3 at an inclination angle θ5 of 30 to 50 °. Such an outer second ply 11B can effectively suppress the tensile force of the carcass ply 6A, and as a result, the durability of the bead portion 4 can be further improved.

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

The above-mentioned inner second ply 11A and outer second ply 11B can be easily performed, for example, by inverting the front and back of the same ply at the time of 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.

The number of arrangements of the inner organic fiber cord c3 and the outer organic fiber cord c4 is preferably 20 to 40 per 50 mm of ply width, respectively. As the organic fiber cords c3 and c4, for example, a nylon cord, a polyester cord, an aromatic polyamide cord, a high-strength vinylon cord, or the like is preferably used. Such an inner second ply 11A and an outer second ply 11B have higher flexibility than the steel cord ply 10A and are also excellent in adhesion to the rubber member.

As shown in FIG. 3, the chafer rubber 12 of the present embodiment 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. There is. The ninth end portion 21 on the outer side of the chafer rubber 12 in the tire radial direction is located, for example, on the outer side in the tire radial direction with respect to the seventh end portion 19 of the outer second ply 11B.

The minimum thickness t1 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. If the minimum thickness t1 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.

The complex elastic modulus E * 3 of the chafer rubber 12 is preferably 7 to 14 MPa, more preferably 9 to 13 MPa. If the complex elastic modulus E * 3 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 * 3 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 1 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 is modified to various embodiments. obtain.

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. 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: 850 kPa

<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 a comparative example of 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 the condition of a standard load, and the mileage until the bead portion was damaged was measured. The result is an index with a comparative example of 100, and the larger the value, the better the durability of the bead portion.
The test results are shown in Tables 1 and 2.

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 10A Steel cord ply 11 2nd reinforcing layer 11A Inner 2nd ply 11B Outer 2nd ply

Claims (8)

A heavy-duty pneumatic tire containing a toroid-like carcass that extends from the tread to the bead core of the bead through the sidewall.
The carcass includes a main body portion that extends from the tread portion through the sidewall portion to the bead core of the bead 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. Has a carcass ply
In the tire meridional cross section, at least a part of the bead portion is a first reinforcing layer extending in a substantially U shape from the inside in the tire radial direction to the outside in the tire radial direction of the folded portion, and at least a part is the first A second reinforcing layer extending in the radial direction of the tire is provided on the outside of the reinforcing layer in the tire axial direction.
The carcass ply includes a steel carcass cord having an angle of 0 to 20 ° with respect to the tire radial direction.
The first reinforcing layer has a steel cord ply including a steel cord that is inclined with respect to the carcass cord.
The second reinforcing layer has an inner second ply in contact with the steel cord ply 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.
The outer end portion of the outer second ply in the tire radial direction is located outside the tire radial direction with respect to the outer end portion of the inner second ply in the tire radial direction.
The inner second ply includes an inner organic fiber cord that is inclined in the same direction as the steel cord with respect to the carcass cord.
The outer second ply is a heavy-duty pneumatic tire characterized by including an outer organic fiber cord that is inclined in a direction opposite to that of the inner organic fiber cord with respect to the carcass cord. The pneumatic tire for heavy load according to claim 1, wherein the inclination angle of the inner organic fiber cord with respect to the carcass cord is smaller than the inclination angle of the steel cord with respect to the carcass cord. The heavy-duty pneumatic tire according to claim 1 or 2, wherein the inclination angle of the outer organic fiber cord with respect to the carcass cord is substantially equal to the inclination angle of the inner organic fiber cord with respect to the carcass cord. The inclination angle of the inner organic fiber cord and the outer organic fiber cord with respect to the carcass cord is 20 to 60 °.
The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the inclination angle of the steel cord with respect to the carcass cord is 50 to 70 °. The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein the distance between the end of the outer second ply and the end of the inner second ply is 8 to 18 mm. The folded portion has an end portion on the outer side in the radial direction of the tire.
The end portion of the inner second ply is located outside the end portion of the folded-back portion in the radial direction of the tire.
The heavy-duty pneumatic tire according to any one of claims 1 to 5, wherein the distance between the end portion of the inner second ply and the end portion of the folded-back portion is 8 to 18 mm. The bead portion is provided with a chafer rubber in contact with the rim sheet surface of the regular rim.
The heavy-duty pneumatic tire according to any one of claims 1 to 6, wherein the minimum thickness of the chafer rubber at the outer position of the bead core in the tire axial direction is 2.5 to 6.0 mm. The bead portion is provided with a chafer rubber in contact with the rim sheet surface of the regular rim.
The heavy-duty pneumatic tire according to any one of claims 1 to 7, wherein the complex elastic modulus of the chafer rubber is 7 to 14 MPa.

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