JP7024185B2 - Pneumatic tires for heavy loads - Google Patents

Description

The present invention relates to a heavy-duty pneumatic tire mounted on a heavy-duty vehicle such as a truck or a bus.

Heavy-duty pneumatic tires mounted on heavy vehicles such as trucks and buses need to support a large load, and are therefore prone to damage, especially in the bead portion. Conventionally, in order to improve the durability of the bead portion, various pneumatic tires for heavy loads in which a reinforcing layer is provided on the bead portion have been proposed.

For example, in the bead portion of the heavy load pneumatic tire of Patent Document 1 and Patent Document 2, apart from the carcass ply, a steel cord ply extending around the bead core in a U-shaped cross section and a tire axial direction of the steel cord ply An organic fiber cord ply extending in the radial direction of the tire is provided on the outside. According to such a configuration of the bead portion, it is expected that the strain of the bead portion when the tire is loaded and traveled is dispersed, and that the durability of the bead portion is improved.

Japanese Unexamined Patent Publication No. 11-02421 JP-A-2015-123942

By the way, the organic fiber cord ply 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 the durability of the bead portion is significantly improved by adjusting the arrangement density of the organic fiber cord ply (so-called cord end).

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 comprises a carcass cord including 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. A heavy-duty pneumatic tire having a carcass composed of layers, and in the tire meridional cross section, at least a part of the bead portion has 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 first reinforcing ply consisting of a layer of steel cord extending, and a second reinforcing ply consisting of at least one layer of organic fiber cord extending in the tire radial direction at least partially outside the tire axial direction of the first reinforcing ply. The second reinforcing ply has an end of 30 to 50 (price / 50 mm), which is the number of cords driven per 50 mm ply width.

In another aspect of the present invention, the organic fiber cord of the second reinforcing ply may be a nylon fiber cord of 940/1 to 1400/1 (dtex).

In another aspect of the present invention, the ends of the second reinforcing ply may be set larger than the ends of the first reinforcing ply.

In another aspect of the present invention, the second reinforcing ply has an inner second reinforcing ply adjacent to the first reinforcing ply and an outer second reinforcing ply arranged on the outer side of the inner second reinforcing ply in the tire axial direction. And may be included.

In another aspect of the present invention, the organic fiber cord of the inner second reinforcing ply is inclined at an angle (α1) of 40 to 80 degrees with respect to the carcass cord of the outer second reinforcing ply. The organic fiber cord may be inclined in the direction opposite to the organic fiber cord of the inner second reinforcing ply at an angle (α2) of 40 to 80 degrees with respect to the carcass cord.

In another aspect of the present invention, the crossing angle (θ) between the organic fiber cord of the inner second reinforcing ply and the organic fiber cord of the outer second reinforcing ply may be 80 to 160 degrees.

In another aspect of the present invention, the outer end of the inner second reinforcing ply in the tire radial direction may be located inside the tire radial direction with respect to the outer end of the outer second reinforcing ply in the tire radial direction.

In another aspect of the present invention, the distance in the tire radial direction between the outer end of the inner second reinforcing ply and the outer end of the outer second reinforcing ply may be 8 to 18 mm.

In another aspect of the present invention, the outer end of the inner second reinforcing ply in the tire radial direction may be located outside the tire radial direction of the outer end of the folded portion in the tire radial direction.

In another aspect of the present invention, the distance in the tire radial direction between the outer end of the inner second reinforcing ply and the outer end of the folded portion may be 8 to 18 mm.

The bead portion of the heavy-duty pneumatic tire of the present invention has a first reinforcing ply composed of a layer of steel cord extending in a substantially U shape in the tire meridian cross section, and at least a part thereof in the tire axial direction of the first reinforcing ply. A second reinforcing ply consisting of a layer of at least one organic fiber cord extending in the radial direction of the tire on the outside is provided. According to such a reinforcing structure of the bead portion, the strain of the bead portion during tire running is dispersed, and the durability of the bead portion is improved.

Further, in the second reinforcing ply, the number of cords driven per 50 mm ply width is adjusted to 30 to 50 (lines / 50 mm), so that the binding force of the bead portion by the second reinforcing ply is optimized. As a result, 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 portion of FIG. It is an enlarged view of the main part of the bead part of FIG. It is an enlarged view of the main 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 the pneumatic tire for heavy load (hereinafter, may be simply referred to as “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 to the bead core 5 of the bead portion 4 via the sidewall portion 3. The carcass 6 is formed of at least one carcass ply 6A, or one carcass ply 6A in the present 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 inner side in the tire axial direction to the outer side around the bead core 5, and has an outer end 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 with respect to the bead baseline BL is maximum near the tire equator C.

FIG. 2 shows a side view of the bead portion 4, in which the main rubber portion is peeled off so that the internal structure can be understood. As shown in FIG. 2, in the carcass ply 6A, preferably, the carcass code c1 is tilted at an angle of 0 to 20 degrees with respect to the tire radial direction (radial direction), and is essentially 0 in the present embodiment. It is arranged by degree. In addition, the above-mentioned "essential" is considered to cause some error in view of the fact that the tire 1 is a vulcanized molded product of rubber and the steel cord is not a perfect straight line.

Further, the carcass cord c1 is composed of a steel cord in order to secure the tire strength. Further, in order to obtain the basic strength of the tire, in the carcass ply 6A, the arrangement density of the carcass cord c1, that is, the number of cords driven per 50 mm ply width, is about 26 to 40 (lines / 50 mm). Is desirable. 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, a 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 by stacking a plurality of belt plies using, for example, steel cords. The belt layer 7 of the present embodiment is formed of, for example, the first to fourth belt plies 7A to 7D, but is not limited to such an embodiment.

The bead portion 4 includes a bead apex rubber 8 that tapers from the bead core 5 toward the outside in the radial direction of the tire, a first reinforcing ply 10 composed of a layer of a steel cord for reinforcing the bead portion 4, and a bead portion 4. A second reinforcing ply 11 made of a layer of an organic fiber cord for reinforcing the tire 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 of FIG. 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 extending in the tire axial direction on the outer side in the tire radial direction and an inner surface surface 5b extending in the tire axial direction on the inner side in the tire radial direction.

In the normal state and the standard load load state in which the normal load is applied to the normal state and the ground is grounded at a camber angle of 0 degrees, the angle β between 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 degree ± 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 becomes small, and as a result, the bead durability is 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.

When the tire 1 is a tubeless type mounted on a regular rim R (15-degree tapered rim), the tire 1 as described above can be manufactured by using, for example, a bead core having a specific shape. As such a bead core, for example, in a state before being incorporated into a tire, the inner side surface 5b is inclined in a direction in which the inner diameter becomes larger toward the outside in the tire axial direction, and is about 20 degrees with respect to the tire axial direction. Has an angle of. 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 has, for example, a core body 5A made of bead wires. It is desirable that, for example, a wrapping layer 5B covering the core body 5A is provided around the core body 5A. The wrapping layer 5B is made of, for example, a campus cloth made of organic fibers such as nylon, and bead wires are bundled and fixed.

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 portion 6b of the carcass ply 6A. 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 of the carcass ply 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 outer end 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 set to 40 to 65 MPa.

In the present specification, the complex elastic modulus of the rubber material constituting the tire 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%. be.

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 outer end 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 smaller than the complex elastic modulus E * 1 of the inner apex 8A. In particular, the complex elastic modulus E * 2 of the outer Apex 8B is preferably, for example, 3 to 5 MPa.

The bead apex rubber 8 configured as described above relaxes the shear stress acting on the folded 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. It can effectively prevent damage such as separation.

The first reinforcing ply 10 is formed of at least one, and in the present embodiment, one. The first reinforcing ply 10 can increase the bending rigidity of the bead portion 4, and can effectively suppress a large bending deformation of the bead portion 4 with the bead core 5 as a fulcrum to the outside in the tire axial direction. This helps to reduce the distortion of the bead portion.

In the tire meridian cross section, at least a part of the first reinforcing ply 10 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 first reinforcing ply 10 of the present embodiment is in contact with the main body portion 6a and the folded portion 6b. Such a first reinforcing ply 10 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 first reinforcing ply 10 is not limited to such an embodiment.

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

The above-mentioned distance L1 is preferably, for example, 8 to 18 mm. When the distance L1 is smaller than 8 mm, the difference in rigidity at the outer end 15 of the first reinforcing ply 10 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 not be effectively increased.

The inner end 16 of the first reinforcing ply 10 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 first reinforcing ply 10 is located inside the tire radial direction with respect to the outer end 15 of the first reinforcing ply 10. In such an embodiment, the length measured along the shape of the first reinforcing ply 10 can be made relatively small, and both the weight reduction of the tire and the reinforcing effect of the bead portion 4 can be achieved at the same time.

As shown in FIG. 2, the first reinforcing ply 10 preferably has a plurality of steel cords c2 tilted with respect to the carcass cord c1. When the bead portion 4 is bent and deformed while the tire is running, the first reinforcing ply 10 is elastically deformed so that the angle γ of the steel cord c2 becomes large, and the bending deformation of the bead portion 4 is suppressed. In a preferred embodiment, the steel cord c2 of the first reinforcing ply 10 is tilted with respect to the carcass cord c1 at an angle γ of 30 to 70 degrees.

In a preferred embodiment, the arrangement density of the steel cord c2 of the first reinforcing ply 10, that is, the number of cords driven per 50 mm ply width, is 20 to 40 (lines / 50 mm). Particularly preferably, the ends of the first reinforcing ply 10 are smaller than the ends of the carcass ply 6A. The ply width for specifying the end is measured in a direction orthogonal to the longitudinal direction of the cord.

As shown in FIGS. 2 and 3, the second reinforcing ply 11 extends in the tire radial direction outside the tire axial direction of the first reinforcing ply 10. The second reinforcing ply 11 of the present embodiment is, for example, the inner second reinforcing ply 11A adjacent to the first reinforcing ply 10 and the outer second reinforcing ply 11B arranged on the outer side of the inner second reinforcing ply 11A in the tire axial direction. Includes two sheets. The inner second reinforcing ply 11A and the outer second reinforcing ply 11B are overlapped with each other. In another aspect of the present invention, the second reinforcing ply 11 may be composed of one piece.

As shown in FIG. 2, each of the inner second reinforcing ply 11A and the outer second reinforcing ply 11B is composed of the organic fiber cords c3 and c4 arranged in parallel and the topping rubber g covering them. There is. In the present embodiment, each of the inner second reinforcing ply 11A and the outer second reinforcing ply 11B has an end of 30 to 50 (lines / 50 mm), which is the number of cords driven per 50 mm of ply width.

As a result of various experiments by the inventors, when the ends of the inner second reinforcing ply 11A and the outer second reinforcing ply 11B are set to 30 to 50 (lines / 50 mm), the durability of the bead portion 4 is significantly improved. It has been found to improve. That is, when the end is less than 30 (lines / 50 mm), the binding force of the bead portion 4 by the second reinforcing ply 11 is significantly reduced, so that the strain of the bead portion 4 during tire running is sufficiently dispersed or reduced. It is difficult. On the other hand, when the end exceeds 50 (lines / 50 mm), the binding force of the bead portion by the second reinforcing ply 11 is enhanced. However, when the end of the second reinforcing ply 11 is increased, surprisingly, the outer end of the second reinforcing ply 11 in the tire radial direction when the tire is running (that is, in the present embodiment, the inner second reinforcing ply 11A and the outer second reinforcing ply 11A). 2 The strain tends to be concentrated on the outer ends 17 and 19) of the reinforcing ply 11B, and thus the outer ends 17 or 19 tend to be the starting points of new damage. In a particularly preferred embodiment, the ends are 40 to 50 (lines / 50 mm).

The organic fiber cords c3 and c4 of the second reinforcing ply 11 are not particularly limited, but for example, a nylon fiber cord, a polyester fiber cord, an aromatic polyamide fiber cord, a high tension vinylon fiber cord, or the like is preferable. Used. Such an organic fiber cord ply has higher flexibility than a steel cord ply and is also excellent in adhesion to a rubber member.

In the present embodiment, nylon fiber cords are preferably used as the organic fiber cords c3 and c4 of the second reinforcing ply 11. In particular, when the end of the second reinforcing ply 11 is 30 to 50 (lines / 50 mm), the nylon fiber cord preferably has a fineness of, for example, 940/1 to 1400/1 (dtex). If the nylon fiber cord is thinner than 940/1 (dtex), the effect of dispersing the strain of the bead portion 4 may not be sufficiently obtained. On the contrary, when the nylon fiber cord becomes thicker than 1400/1 (dtex), a new damage starting point may be generated near the outer end of the second reinforcing ply 11.

The second reinforcing ply 11 of the present embodiment configured as described above effectively reduces or disperses the distortion of the bead portion 4 without generating a new starting point of damage in the bead portion 4, and eventually the bead. The durability of the part 4 is greatly improved. In order to further enhance such effects, it is desirable that the ends of the second reinforcing ply 11 are larger than the ends of the first reinforcing ply 10.

Further, in the second reinforcing ply 11, for example, 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 is softened due to the influence of heat or the like. Helps prevent it from flowing over the rim flange and then hardening. Therefore, the bead portion 4 can reduce the damage caused by the hardening of the rubber.

The second reinforcing ply 11 covers the outer end 15 of the first reinforcing ply 10 from the outside in the tire axial direction. As in the present embodiment, the two second reinforcing plies 11A and 11B are more easily stretched than the first reinforcing ply 10 and have excellent adhesive strength to rubber. Therefore, the stress at the outer end 15 of the first reinforcing ply 10 is relaxed, and the separation there can be suppressed for a long period of time.

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

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

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

The inner end 18 of the inner second reinforcing ply 11A in the tire radial direction is located inside the tire radial direction with respect to the outer end 15 and the inner end 16 of the first reinforcing ply 10. It is desirable that the inner end 18 of the inner second reinforcing ply 11A is located inside the tire axial direction with respect to the inner end 20 of the outer second reinforcing ply 11B described later. As a result, it is possible to prevent strain from concentrating near the inner end 18 of the inner second reinforcing ply 11A. Therefore, damage such as separation starting from the inner end 18 of the inner second reinforcing ply 11A can be suppressed.

The outer end 19 of the outer second reinforcing ply 11B in the tire radial direction is located, for example, the outer end 17 of the inner second reinforcing ply 11A in the tire radial direction by a distance L3. As a result, the outer second reinforcing ply 11B covers the outer end 17 of the inner second reinforcing 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 reinforcing ply 11A is effectively suppressed.

The distance L3 is preferably, for example, 8 to 18 mm. When the distance L3 is smaller than 8 mm, the difference in rigidity at the outer end 17 of the inner second reinforcing ply 11A becomes large, and there is a possibility that damage such as separation starting from the outer end 17 of the inner second reinforcing ply 11A may occur. be. When the distance L3 is larger than 18 mm, the outer second reinforcing ply 11B becomes easy to move when the tire is running, and there is a possibility that damage such as separation starting from the outer end 19 of the outer second reinforcing ply 11B may occur.

The distance L3 between the outer end 19 of the outer second reinforcing ply 11B and the outer end 17 of the inner second reinforcing ply 11A is the distance L2 between the outer end 17 of the inner second reinforcing ply 11A and the outer end 9 of the folded-back portion 6b. It is desirable that they are approximately equal. In such a bead portion 4, the stress is uniformly dispersed, and the 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 reinforcing ply 11B is, for example, 25% to 40% of the maximum height H1 of the carcass ply 6A with respect to the bead baseline BL. % Is desirable. When the height H2 of the outer end 19 is smaller than 25% of the maximum height H1 of the carcass ply 6A, the effect of suppressing the chafer rubber 12 from flowing onto the rim flange of the regular rim R and hardening is small. There is a risk of becoming. When the height H2 of the outer end 19 is larger than 40% of the maximum height H1 of the carcass ply 6A, the outer second reinforcing ply 11B becomes easy to move, and the outer end 19 of the outer second reinforcing ply 11B is used as a starting point. There is a risk of damage such as separation.

The inner end 20 of the outer second reinforcing ply 11B of the present embodiment in the tire radial direction is located in the inner region S1 inside the tire radial direction of the bead core 5. Such an outer second reinforcing ply 11B can effectively suppress the tensile force of the carcass ply 6A without significantly moving even when a tensile force is generated in 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 durability of the bead portion 4 is further improved.

The distance L4 between the inner end 20 of the outer second reinforcing ply 11B and the inner end 18 of the inner second reinforcing ply 11A is the distance L4 between the outer end 19 of the outer second reinforcing ply 11B and the outer end 17 of the inner second reinforcing ply 11A. It is desirable that it is approximately equal to the distance L3. That is, it is desirable that the outer second reinforcing ply 11B and the inner second reinforcing ply 11A have substantially the same length measured along their shapes. Thereby, for example, the same ply can be used for the outer second reinforcing ply 11B and the inner second reinforcing ply 11A. This helps to promote the sharing of parts and reduce manufacturing costs.

As shown in FIG. 2, each organic fiber cord c3 of the inner second reinforcing ply 11A is inclined in the first direction at an angle α1 of 40 to 80 degrees, more preferably 50 to 70 degrees with respect to the carcass cord c1. It is desirable to have. Such an inner second reinforcing ply 11A can effectively suppress the tensile force of the carcass ply 6A.

It is desirable that each organic fiber cord c4 of the outer second reinforcing ply 11B is also inclined at an angle α2 of 40 to 80 degrees, more preferably 50 to 70 degrees with respect to the carcass cord c1. In a particularly preferred embodiment, the organic fiber cord c4 of the outer second reinforcing ply 11B is inclined in the direction opposite to the organic fiber cord c3 of the inner second reinforcing ply 11A. Such an outer second reinforcing ply 11B can effectively suppress the tensile force of the carcass ply 6A.

It is desirable that the angle α1 of the organic fiber cord c3 of the inner second reinforcing ply 11A and the angle α2 of the organic fiber cord c4 of the outer second reinforcing ply 11B are substantially equal to each other. Such the inner second reinforcing ply 11A and the outer second reinforcing ply 11B more effectively disperse the strain of the bead portion 4 at the time of bending deformation and improve the durability of the bead portion.

In a particularly preferable embodiment, as shown in an enlarged manner in FIG. 4, the crossing angle θ between the organic fiber cord c3 of the inner second reinforcing ply 11A and the organic fiber cord c4 of the outer second reinforcing ply 11B is 80 to 160. Degree is desirable. When the crossing angle θ exceeds 160 degrees, the bending rigidity of the second reinforcing ply 11 is significantly lower than that of the carcass ply 6A, and as a result, strain tends to concentrate on the outer end 9 of the folded portion 6b of the carcass ply 6A. , Ply turn-up looseness is likely to cause damage.

The above-mentioned inner second reinforcing ply 11A and outer second reinforcing 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 reinforcing ply 11A and the outer second reinforcing ply 11B can share parts, and the manufacturing cost of the tire 1 can be reduced.

The chafer rubber 12 is located on the outer side of the second reinforcing ply 11 in the tire axial direction, and is in contact with the rim seat surface R1 of the regular rim R on the inner side of 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 reinforcing ply 11B in the tire radial direction.

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 set to 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 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. Needless to say.

Pneumatic tires for heavy loads of size 295 / 80R22.5 having the basic structure of FIG. 1 were prototyped based on the specifications in Table 1 and their bead durability was tested. The common specifications and test methods for each test tire are as follows.
<Carcass>
Carcass code specifications: Steel code Carcass code angle: 0 degrees (relative to tire radiation direction)
Carcass code end: 20 (book / 50mm)
<1st reinforcement ply>
Number of plies: 1
Specifications of the first reinforcing ply: Steel cord Angle of the steel cord of the first reinforcing ply: 65 degrees (relative to the carcass cord)
Steel cord end of 1st reinforcement ply: 28 (piece / 50mm)
Distance L1: 13mm
<Second reinforcement ply>
Number of plies: 2
Specifications of the second reinforcing ply: Nylon fiber cord 1400/1 (dtex)
Distance L2: 13mm
Distance L3: 13mm
H2 / H1 = 30%

<Bead durability test>
The above test tire is mounted on a 22.5 x 9.00 rim and run on a drum tester at a speed of 20 km / h under the conditions of an internal pressure of 850 kPa and a standard load of 200%, causing damage to the bead portion. The running time up to was measured. The result is displayed as an index with the value of 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 significantly 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 reinforcement ply 11 2nd reinforcement ply 11A Inner 2nd reinforcement ply 11B Outer 2nd reinforcement ply c1 Carcass code c2 Steel Cord c3, c4 Organic fiber cord

Claims (3)

A carcass consisting of a layer of carcass cord including a main body portion extending 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 with
In the cross section of the tire meridian, the bead portion is
A first reinforcing ply composed of a layer of a steel cord extending in a substantially U-shape from the inside of the folded portion in the radial direction of the tire to the outside in the radial direction of the tire, at least in part.
A second reinforcing ply is provided, which is at least partially composed of a layer of at least one organic fiber cord extending in the radial direction of the tire on the outer side of the tire axial direction of the first reinforcing ply.
The organic fiber cord of the second reinforcing ply is a nylon fiber cord of 940/1 to 1400/1 (dtex).
The second reinforcing ply has 40 to 50 (lines / 50 mm) ends, which is the number of cords driven per 50 mm ply width.
The second reinforcing ply includes an inner second reinforcing ply adjacent to the first reinforcing ply and an outer second reinforcing ply arranged on the outer side of the inner second reinforcing ply in the tire axial direction.
The organic fiber cord of the inner second reinforcing ply is inclined at an angle (α1) of 50 to 65 degrees with respect to the carcass cord.
The organic fiber cord of the outer second reinforcing ply is inclined in the direction opposite to the organic fiber cord of the inner second reinforcing ply at an angle (α2) of 50 to 65 degrees with respect to the carcass cord. ,
The outer end of the inner second reinforcing ply in the tire radial direction is a heavy load pneumatic tire located inside the tire radial direction with respect to the outer end of the outer second reinforcing ply in the tire radial direction. The heavy load pneumatic tire according to claim 1, wherein the end of the second reinforcing ply is larger than the end of the first reinforcing ply. The pneumatic tire for heavy load according to claim 1 or 2, wherein the distance in the tire radial direction between the outer end of the inner second reinforcing ply and the outer end of the outer second reinforcing ply is 8 to 18 mm. ..

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